سد - Dam

Dam

 A barrier or structure across a stream, river, or waterway for the purpose of confining and controlling the flow of water. Dams vary in size from small earth embankments for farm use to high, massive concrete structures for water supply, hydropower, irrigation, navigation, recreation, sedimentation control, and flood control. As such, dams are cornerstones in the water resources development of river basins. Dams are now built to serve several purposes and are therefore known as multipurpose (Fig. 1). The construction of a large dam requires the relocation of existing highways, railroads, and utilities from the river valley to elevations above the reservoir. The two principal types of dams are embankment and concrete. Appurtenant structures of dams include spillways, outlet works, and control facilities; they may also include structures related to hydropower and other project purposes. See also: Electric power generation; Irrigation (agriculture); Water supply engineering

 Fig. 1  John Day Lock and Dam, looking upstream across the Columbia River at Washington shore. In the foreground the navigation lock is seen, then the spillway beyond it, and then the powerhouse. The John Day multiple-purpose project has the highest single-lift navigation lock in the United States. (U.S. Army Corps of Engineers)

 

 

 

 

Dams have been built since ancient times, and improvements were made at varying intervals as engineering technology developed. However, very rapid advances occurred in the twentieth century as a result of developments in the use of concrete, soil mechanics, and construction equipment. In the early 1900s, concrete dams became thinner, and a new era of thin arch dams began. Earth and rock–fill embankment dams became economical during and after World War II. In 1980, an innovative method of using earth-moving and compacting equipment to place dry concrete (roller-compacted concrete) greatly improved the economics of concrete dams. As of December 1997, there was a total of 100,781 dams in the United States. Most of these are small recreational projects and farm ponds. Of this total, 6,389 dams have a height of 50 feet or more and 1,586 dams have a height of 100 feet or more. Numerous dams have been constructed in various countries worldwide (Table 1). Many dams possess considerable height, volume, and reservoir capacity (Table 2).

Purposes

 Dams are built for specific purposes. In ancient times, they were built only for water supply or irrigation. Early in the development of the United States, rivers were a primary means of transportation, and therefore navigation dams with locks (Fig. 2) were constructed on the major rivers. Dams have become more complex to meet large power demands and other needs of modern countries (Figs. 3 and 4). Although recreation is a popular purpose of small private dams, it is planned as a benefit with an assigned monetary value in federal projects in the United States. A typical summary of purposes of nonfederal dams is shown in Table 3.

 Features

In addition to the standard impounded reservoir and the appurtenant structures of a dam (spillway, outlet works, and control facility), a dam with hydropower requires a powerhouse, penstocks, generators, and switchyard. The inflow of water into the reservoir must be monitored continuously, and the outflow must be controlled to obtain maximum benefits. Under normal operating conditions, the reservoir is controlled by the outlet works, consisting of a large tunnel or conduit at stream level with control gates. Under flood conditions, the reservoir is maintained by both the spillway and outlet works.

 Fig. 2  Lock and Dam 1 on the Mississippi River between St. Paul and Minneapolis, Minnesota. Built in 1917 with a single lock to provide barge traffic to Minneapolis, the dam failed in 1929 and was rebuilt with twin locks in 1932. (U.S. Army Corps of Engineers)

 

  

The reservoir level of a flood control dam is maintained as low as possible to create the maximum amount of storage space for use in the flood season. For an irrigation project, the reservoir is filled as high as possible in the winter and early spring, and it is maintained at that level for maximum release of water during the dry season. The reservoir level of a hydropower dam is maintained as constant as feasible to create a uniform head for power generation. Water quality is an important ingredient in sustaining a balance in nature and is taken into account in modern dam design, construction, and operation. The chemical quality and temperature of the water are monitored in the reservoir. Intake ports at various depths allow selective withdrawal and mixing to produce the desired temperature and oxygen content, in order to enhance downstream environmental conditions. Fish ladders, that is, stepped series of elevated pools, are provided at many dams to allow free passage of fish upstream and downstream. Screens are used to keep fish out of the turbines. See also: Reservoir

 

Fig. 3  Guri Dam, Venezuela, showing construction under way on the second stage of the concrete gravity dam. Embankment dams are shown on the left and right abutments. The concrete batch plant is shown at left with a trestle for transporting concrete shown on the downstream face of the dam. The second powerhouse with an excavated outlet channel is shown at the center of the photo. (C.V.G. Electrification del Caroni, C. A. EDELCA, Caracas, Venezuela)

 

 

 

 

 

 

Fig. 4  Itaipu Dam, on the Paraná River between Brazil and Paraguay. An operating spillway with a flip bucket on the Paraguay side of the river is shown at left. The hollow concrete gravity dam with powerhouse construction at the downstream toe is shown at center.(G. S. Sarkaria, International Engineering Company, Inc.)

 

 

 

 

The discharge from modern dams must be managed carefully and continuously. During floods, reservoir inflows may exceed maximum discharges and cause reservoir levels to rise. To prevent dams from overtopping and possibly failing, spillways are provided to pass floodwater safely. They are commonly built at elevations just below dam crests and without gates. These uncontrolled, ungated spillways are designed to allow all of the excess water to pass. In other cases, spillways are constructed at even lower levels and contain gates that are operated from the control facilities. The tops of these gates are lower than the dam crests, thus allowing some control of floodwater.

Penstocks (usually steel pipes or concrete-lined tunnels) are used to convey water from the reservoir through or around the dam to the powerhouse. The penstocks are connected to the turbines, and the water flow is controlled by valves. The number and size of the penstocks vary, depending on the number of generators and amount of water needed.

All the features of a dam are monitored and operated from a control room. The room contains the necessary monitors, controls, computers, emergency equipment, and communications systems to allow project personnel to operate the dam safely under all conditions. Standby generators and backup communications equipment are necessary to operate the gates and other reservoir controls in case of power failure. Weather conditions, inflow, reservoir level, discharge, and downstream river levels are also monitored. In addition, the control room monitors instrumentation located in the dam and appurtenant features that measures their structural behavior and physical condition.

 

 Fig. 5  Aerial view of North Fork Dam, a combination earth-and-rock embankment of the North Fork of Pound River, Virginia. The channel-type spillway (left center) has a simple overflow weir. (U.S. Army Corps of Engineers)

 

 

 

 

 

Requirements

All dams are designed and constructed to meet specific requirements. First, a dam should be built from locally available materials when possible. Second, the dam must remain stable under all conditions, during construction, and ultimately in operation, both at the normal reservoir operating level and under all flood and drought conditions. Third, the dam and foundation must be sufficiently watertight to control seepage and maintain the desired reservoir level. Finally, it must have sufficient spillway and outlet works capacity as well as freeboard to prevent floodwater from overtopping it.

 

Types

 Dams are classified by the type of material from which they are constructed. In early times, the materials were earth, large stones, and timber, but as technology developed, other materials and construction procedures were used. Most modern dams fall into two categories: embankment and concrete. Embankment dams are earth or rock-fill; other gravity dams and arch and buttress dams are concrete.

Earth-fill dam

Earth is the predominant material in this type of embankment dam. Earth dams are further classified by the construction method: hydraulic-fill or rolled-fill. A hydraulic-fill dam is one in which the soil is excavated, transported, and placed by flowing water. A large dredge operating in the river or other borrow area pumps a slurry of earth and water to the damsite. Here the coarse-grained materials settle on the outside portion of the embankment, and the remaining slurry is allowed to pond at the center, where the very fine-grained clay-size particles settle to form the impervious portion of the dam.

 Fig. 6  Plan and sections of North Fork of Pound Dam, Virginia. 1 ft = 0.3 m. (U.S. Army Corps of Engineers)

 

 

 

Advances in earth-moving construction equipment during World War II led to widespread construction of rolled-earth-fill dams. Economic advantages of this type of embankment often include the use of material available from the site excavation as embankment material, and the ready availability of fill material at or near the damsite. Other advantages of earth-fill dams include their adaptability to a wide variety of site configurations and their tolerance of weak foundations.

At various stages during excavation and placement of the fill, the moisture content of the soil may be adjusted by wetting or drying in order to optimize its performance in the finished embankment. The soil is spread on the embankment in uniform layers 8–12 in. (20–30 cm) thick and compacted with sheepsfoot or rubber-tired rollers. The rollers make from four to eight passes, depending on the desired density. Typical dry densities for rolled earth fill range 100–130 lb/ft3 (1602–2083 kg/m3).

Seepage control is an important aspect of earth-dam design. In early times, earth embankments were homogeneous, and seepage would emerge on the downstream slope just above ground level. If uncontrolled, such seepage can move soil particles and cause failure. In 1940, filter criteria were developed after careful scientific tests on all types of soil and on the sands and gravel to be used as filter material. These criteria allow engineers to design internal drains to collect and remove seepage. When an earth dam is built on a site where bedrock is at considerable depth, the foundation must be treated to control seepage. Typical treatment includes one or a combination of several things: upstream impervious blanket, cutoff wall, drainage blanket, gravel drains excavated into the foundation at the downstream toe, and relief wells. See also: Foundations

Earth-fill dams are by far the most popular type in the world. They make up 78%, or 27,260, of all those dams at least 50 ft (15 m) high. The earth dam's spillway is usually located in adjacent terrain rather than in the dam itself. The outlet works are either a conduit in the valley or a tunnel in one of the abutments (Figs. 5 and 6). Excavation for the spillway and outlet works usually produces large quantities of rock. As a result, the use of both earth and rock in an embankment is a common practice.

 

Rock-fill dam

 A rock-fill dam is a rolled fill embankment composed of fragmented rock with an impervious zone or membrane located on the upstream face or incorporated in the center of the embankment. The impervious membrane is typically a concrete slab or asphalt layer on the upstream face. The impervious zone is typically a thin internal core of earth fill. The earth core is separated from the rock shell (the structural mass of the dam) by zones of small rock fragments or gravel, to prevent the earth from washing into the rock fill, and a drain to control seepage. In Europe, it is common to use asphalt for the impervious zone.

Rock-fill dams require solid rock foundations and sites where large quantities of rock are available. Seepage through rock foundations is prevented or minimized by grout curtains. Rock-fill dams are usually more economical than concrete gravity dams at sites having wide valleys and adequate foundations. Spillways and outlet works are at locations similar to those of earth-fill dams. The primary advantage of rock-fill dams is that they require less material. Rock fill has a higher shear strength than earth fill and therefore permits steeper exterior slopes.

Rock for the embankment is normally excavated by drilling and blasting. Hole spacing and powder charges are set to produce a particular gradation of rock fragments for the dam. The rock is placed and spread in the same manner as earth but in thicker layers, 18–36 in. (45–90 cm). The material is normally compacted by weighted or vibratory steel drum rollers. Dry densities of rock fill are normally in the range 110–145 lb/ft3 (1762–2323 kg/m3).

Rock-fill dams became popular in the United States during the California gold rush in the 1860s and 1870s, when many dams were built in remote locations to store water for use in hydraulic sluicing. Of the 34,780 dams in the world that are at least 50 ft (15 m) high, 1590 are rock-fill embankments.

 

Concrete gravity dam

Concrete gravity dams are massive structures, characterized by vertical or near-vertical upstream faces and steep downstream faces (Figs. 7 and 8). They are designed with enough weight to resist being overturned or moved by the force of the water in the reservoirs. They are economical only at sites with shallow, high-strength rock foundations. Because of the large volumes of concrete involved, adequate sources of high-quality aggregates must be available near the sites. Concrete is composed of water, cement, pozzolan, aggregates, and entrained air. These ingredients are proportioned to produce concrete of the desired workability, durability, and strength as economically as possible. The density of concrete in dams typically ranges 140–160 lb/ft3 (2243–2563 kg/m3). An important feature of gravity dams is the simplicity with which safe spillways and outlet works can be provided. See also: Concrete

The design of a concrete gravity dam is controlled by stability considerations and internal stresses. The structure must be able to resist water, sediment, and ice pressures from the reservoir, as well as earthquake forces. Computers permit rapid solutions of complex equations for determining the magnitude and distribution of internal stresses. These dams are built in monolithic units by using the block method of construction (Fig. 9). This promotes dissipation of heat produced by hydration of the cement (chemical combination with the water) and thus helps minimize the volume changes associated with overheating that cause tensile stresses and cracking. The blocks are separated by construction joints. In building a block, the concrete is placed in horizontal layers and vibrated to eliminate voids. The monoliths are cast on top of firm rock foundations that have been cleaned with water and treated by placement of cement and water slurry or grout in the cracks and joints.

A concrete gravity dam usually contains an internal gallery large enough to allow for physical inspection and for collection of drainage from downstream drain holes drilled into the foundation. Grout holes to reduce seepage in the foundation are also drilled from the gallery in the vertical or upstream direction. The grout is injected under pressure to force it into all joints and openings encountered at depth.

 

Arch dam

The arch dam is a thin concrete dam that curves upstream from each abutment (Figs. 10 and 11). Such dams are classified as thin, medium, or thick arch, depending on the ratio of structural height to base thickness. The ratio is 0.2 or less for a thin arch, 0.25 for a medium arch, and 0.3 or greater for a thick arch. The arch transmits the water pressure and other loads directly to the abutments and foundation. It contains significantly less concrete than a concrete gravity dam of the same height and length. Relatively narrow canyons favor the use of arch dams.

 Fig. 7  Green Peter Dam, a concrete gravity type on the Middle Santian River, Willamette River Basin, Oregon. A gate-controlled overflow-type spillway is constructed through the crest of the dam; the powerhouse is at the downstream toe of the dam. (U.S. Army Corps of Engineers)

 

 

 

 

The shape of early arch dams was controlled by construction materials available at the time, and by less sophisticated understanding of structural behavior and the way that loads were transmitted through the curved structures to the foundations. As a result, arches were simple masonry structures with curved alignments and near-vertical upstream faces. This type was popular among water companies supplying domestic and irrigation water.

Beginning in the 1900s, improved structural analysis and actual performance records led to the use of variable-thickness arch dams. Varying the thickness can reduce the volume of concrete required. Measurement of the physical properties of concrete began in the late 1920s. This led to improved design procedures and measurement of actual performance with such instruments as strain gages. The concept of working stresses emerged in the late 1920s. The double-curvature shape (curved top to bottom as well as transversely) emerged in the mid-1950s. Vertical curving and shaping of the arch improves stress distribution. Making the compressive stresses levels throughout the dam as close as possible to the maximum allowable stress results in the minimum volume of concrete. A symmetrical profile is desirable. This may require excavation on one abutment if the canyon is not symmetrical. The economic upper limit of the length-to-height ratio of an arch dam lies between 4:1 and 6:1.

 

 

Fig. 8  Plan and sections of Green Peter Dam. 1 ft = 0.3 m, 1 in. = 2.5 cm. (U.S. Army Corps of Engineers)

 

 

 

 

 

 

Buttress dam

The buttress dam consists of two principal structural elements: a sloping upstream deck that retains the water, and buttress walls that support the deck and transmit the loads to the foundation. Traditionally, buttress dams have been classified into three categories: flat slab, multiple arch, and massive head. The flat-slab type consists of a reinforced concrete flat slab inclined at about 45° and connected to buttresses. The multiple-arch type is a series of concrete arches spanning the buttresses. The massive-head type has a large mass of concrete in the section upstream from the buttresses.

 Fig. 9  Block method of construction on a typical concrete gravity dam. (U.S. Army Corps of Engineers)

 

 

 

 

In 1918, the flat-slab design was patented in the United States. About 200 buttress dams of all three categories have been built in the United States. Many are less than l50 ft (45 m) high. Some landmark buttress dams are the Daniel Johnson in Canada (1986), 702 ft (214 m) high, the world's highest multiple-arch buttress dam; and the José M. Oriol in Spain (1969), 426 ft (130 m), the world's highest flat-slab buttress dam.

 

Site and type selection

The type of dam for a particular site is selected on the basis of technical and economic data and environmental considerations. In the early stages of design, several sites and types are considered. Drill holes and test pits at each site provide soil and rock samples for testing physical properties. In some cases, field pumping tests are performed to evaluate seepage potential. Preliminary designs and cost estimates are prepared and reviewed by hydrologic, hydraulic, geotechnical, and structural engineers, as well as geologists. Environmental quality of the water, ecological systems, and cultural data are also considered in the site-selection process.

Factors that affect the type are topography, geology, foundation conditions, hydrology, earthquakes, and availability of construction materials. The foundation of the dam should be as sound and free of faults as possible. Narrow valleys with shallow sound rock favor concrete dams. Wide valleys with varying rock depths and conditions favor embankment dams. Earth dams are the most common type. See also: Engineering geology; Fault and fault structures

 

Construction process

 

Hydraulic-fill operations over a 4-year period at Fort Peck Dam, on the Missouri River, the largest embankment by volume in the United States (Fig. 12), dredged 156,000,000 yd3 (119,340,000 m3) of material. Of this volume, 122,000,000 yd3 (93,333,000 m3) was retained in the embankment. Large conventional excavation operations can produce hourly volumes of 2000–3000 yd3 (1530–2293 m3). Processing, hauling, placement, and compaction operations for earth or rock result in daily placement rates that vary from as low as 2500 yd3 (1911 m3) on small dams to 6500 yd3 (4969 m3) on larger dams.

The materials and construction procedures for concrete dams evolved gradually from the early dams in Asia and Europe to the modern massive concrete dams. Prior to 1900, portland cement used in the United States was imported from England. Thus, the early concrete dams built in the United States were masonry. Generally, the concrete was mixed and transported in wheelbarrows. In the case of cyclopean masonry, large irregular blocks of rock with mortar, small derricks were erected, and the maximum rate of placement approached a few hundred cubic yards a day. There was no attempt to cure the concrete. Between 1900 and 1930, concrete was placed by towers and chutes. Portland cement had become available in the United States, and placement rates improved. However, little attention was given to the mix design, and wet mixes that could easily flow in chutes were widely used.

 Fig. 10  East Canyon Dam, a thin-arch concrete structure on the East Canyon River, Utah. There is an uncontrolled overflow-type spillway through the crest of the dam at the right. (U.S. Bureau of Reclamation)

 

 

 

 

 

 

Fig. 11  Plan and sections of East Canyon Dam, Utah. 1 ft = 0.3 m. (U.S. Army Corps of Engineers)

 

 

 

 

Hoover Dam, on the Colorado River, was a major turning point in both the design and construction of concrete dams. Its unprecedented size, 4,400,000 yd3 (3,363,800 m3), led to the introduction of mass concrete placement. Average placement rates of 10,000 yd3 (7645 m3) per day were achieved. Advances in design resulting from the Hoover project led to the construction of Grand Coulee, on the Columbia River, 10,585,000 yd3 (8,099,000 m3). Two large concrete plants were used that supported a maximum placement of 20,680 yd3 (15,810 m3) per day and an average rate over the construction period of 6000 yd3 (4587 m3) per day.

Since 1980, the technology of placing dry concrete with paving equipment and compacting it with rollers has gained wide acceptance (Fig. 13). This construction method is known as roller-compacted concrete. By 1997, 30 dams at least 50 ft (15 m) high had been constructed in the United States using the roller-compacted concrete method. As of January 1998, there were 16 RCC dams in the world having a height of 100 m or greater. This method produces the high placement rates usually associated with earth-fill construction and results in economical structures. It was initially used in 1975 in the tunnel repairs at Tarbela Dam, Pakistan, and placement reached a maximum rate of 24,000 yd3 (18,343 m3).

An outstanding example of the rapid construction achieved by using roller-compacted concrete is Copperfield Dam in Australia. This 131-ft-high (40-m) dam contains 183,000 yd3 (140,000 m3) and required only 10 months from initial design to completion. The project was originally designed as an earth- and rock-fill dam, but it was switched to roller-compacted concrete for greater economy.

 

River diversion during construction

The designers of a dam must consider the stream flow around or through the damsite during construction. Stream flow records provide the information for use in determining the largest flood to divert during the selected construction period. One common practice for diversion involves constructing the permanent outlet works, which may be a conduit or a tunnel in the abutment, along with portions of the dam adjacent to the abutments, in the first construction period. In some cases, a temporary channel is built at a preferred diversion location, and levees are built to control the flow of water through the damsite. After the outlet works and main dam are completed to an appropriate level, the stream is diverted into the outlet works by a cofferdam high enough to prevent overtopping during construction. A downstream cofferdam is also required to keep the damsite dry. In the final construction period, the entire dam is brought to full height. See also: Cofferdam

 Fig. 12  Fort Peck Dam, Missouri River, Montana, the largest embankment dam by volume in the United States, 125,628,000 yd3 (95,625,000 m3). A hydraulic-fill dam, it was built between 1935 and 1939 for flood control, hydropower, irrigation, and navigation. (U.S. Army Corps of Engineers)

 

 

 

 

 

 

Fig. 13  Galesville Dam, Oregon, showing roller-compacted concrete construction; completed in 1985, it has a height of 157 ft (48 m) and a volume of 161,000 yd3 (123,100 m3).

 

 

Operation and maintenance

 

Personnel responsible for operation and maintenance of the dam become involved during the final design and construction to become familiar with design details that relate to operation. The operating instructions and maintenance schedule are published in a formal document for each dam. A schedule is established for collection and reporting of data for climatic conditions, rainfall, snow cover, stream flows, and water quality of the reservoir, as well as the downstream reaches. All these data are evaluated for use in reservoir regulation. Another schedule is established for the collection of instrumentation data used to determine the structural behavior and physical condition of the dam. These data are evaluated frequently.

Routine maintenance and inspection of the dam and appurtenant structures are ongoing processes. The scheduled maintenance is important to preserve the integrity of the mechanical equipment.

 

Periodic inspection and evaluation

 Upon completion of construction, the project is inspected in detail by a team made up of the designers, construction managers, operations personnel, and other experts. The purpose is to ensure that the dam has been built as designed and can safely impound water and that all systems are ready for the initial reservoir filling and operation. In addition, the same team conducts an in-depth inspection once a year for about 5 years after completion and at 5-year intervals thereafter. Design criteria and performance of the dam as measured by instruments are reviewed during the life of the dam, and structural reanalyses are made when necessary. Photographs are taken to record rates of deterioration.

The intake structure, trash racks, emergency gates, outlet conduit or tunnel, and stilling basin are normally under water and therefore require special procedures such as dewatering prior to the inspection. At normal velocity, the flowing water can severely erode soil and rock in the approach and discharge channels. High-velocity flow over small irregularities can cause a phenomenon known as cavitation, which can lead to rapid erosion of metal and concrete and can threaten the safety of the outlet works. See also: Cavitation

 Instrumentation

 As the technology of dam design and construction progressed, the need to measure performance and structural behavior became important in order to verify the design. Advances in instruments starting in the 1950s gave the designer a valuable tool. Instrumentation gave the engineer knowledge of how the temperatures from hydration in concrete varied and the effect on strength. Pressure cells were developed that gave information about the interaction between soil backfill and a concrete wall or structure as well as the actual load distribution. Piezometers (devices to measure water level), settlement plates, and slope indicators are used in measuring the performance of embankment dams. Plumb lines, strain gages, and uplift cells are used for the same purpose in concrete dams. In addition, instruments are used to measure vertical and horizontal movement, alignment and plumb, stresses, strains, water pressure, seismic effects, and the quantity and clarity of seepage.

Instrumentation for a dam is installed at first in the design phase to establish baseline data, then during construction and throughout the life of the dam as conditions warrant. The frequency with which instrumentation data are obtained is an extremely important issue and depends on operating conditions. Timely collection and evaluation of data are critical for periods when the loading changes, such as during floods and after earthquakes. Advances in applications of remote sensing to instrumentation have made real-time data collection possible. This is a significant improvement for making dam safety evaluations.

Safety

Throughout history there have been instances of dam failure and discharge of stored water, sometimes causing considerable loss of life and great damage to property. Failures have generally involved dams that were designed and constructed to engineering standards acceptable at the time. Most failures have occurred with new dams, within the first five years of operation.

As dam technology advanced with increasing knowledge of design principles and better understanding of foundation and material properties, dams became safer. There is no question that they can be built and operated safely. The major issue is to monitor deterioration as the structures and equipment get older. In earlier times, the sizes of spillways and outlet pipes had to be determined by judgment. As a result, overtopping was the main cause of dam failure. Little was known about soil mechanics and slope stability, and so slides and slope failures were common. Beginning in the 1930s, statistical methods were used to predict floods. Advances in soil mechanics in the later 1930s and early 1940s produced new methods of stability analysis that revolutionized the slope design for excavations and earth embankment dams. Historical data indicate that the causes of failure (in the order of their significance) are piping, overtopping, slope instability, conduit leakage (outlet works), and foundation failures. See also: Pipeline; Rock mechanics; Soil mechanics

It is estimated that about 150,000 dams around the world present a potential hazard to life or property; there have been 200 failures since 1900. Many of these have involved small dams. Table 4 lists some major failures that resulted in considerable loss of life.

Dam failures cause loss of life and property damage in downstream reaches that are beyond the control of the dam owner or local government. For this reason, and because dam safety practices should apply to all dams, national governments have become involved in order to provide supervision and standardize regulations. The United States government published “Federal Guidelines for Dam Safety” in June 1979. This initiated a coordinated effort in management practices among federal agencies and set an example for private organizations that own dams. The International Commission on Large Dams (ICOLD) was formed in 1928 by 6 countries with the purpose of developing and exchanging dam design experience, and it has grown to 76 member countries. In 1982 ICOLD established a committee on dam safety to define common safety principles, integrate efforts, and develop guidelines, and in 1987 ICOLD published “Dam Safety Guidelines.”

Bibliography

•  Federal Emergency Management Agency, Federal Guidelines for Dam Safety, FEMA 93, June 1979
• Ali Fazeli = egeology.blogfa.com
• International Commission on Large Dams, Dam Safety Guidelines, Bull. 59, ICOLD, 1987
• Ali Fazeli = egeology.blogfa.com
• International Commission on Large Dams, Dam Failures, Statistical Analysis, 1995
• Ali Fazeli = egeology.blogfa.com
• International Commission on Large Dams, World Register of Dams, 1997
• Ali Fazeli = egeology.blogfa.com
• International Commission on Large Dams, Dam Failures, Statistical Analysis, 1995
• Ali Fazeli = egeology.blogfa.com
• R. B. Jansen, Advanced Dam Engineering for Design, Construction, and Rehabilitation, 1988
• Ali Fazeli = egeology.blogfa.com
• R. B. Jansen, Dams and Public Safety, U.S. Department of the Interior, 1980
• Ali Fazeli = egeology.blogfa.com
• E. B. Kollgaard and W. L. Chadwick (eds.), Development of Dam Engineering in the in the United States, 1988
• Ali Fazeli = egeology.blogfa.com
• J. Sherard et al., Earth and Earth-Rock Dams, 1967
• Ali Fazeli = egeology.blogfa.com
• U.S. Bureau of Reclamation, Design of Small Dams, 3d ed., 1987
• Ali Fazeli = egeology.blogfa.com

 

جداول

گاستروپودای آبالون - Abalone

بلبلب

آموزش روش نرماتیو نمودن یک آنالیز شیمیایی

A norm is essentially a set of idealized synthetic minerals that are calculated from a bulk chemical analysis of a rock for comparison purposes. Norms are usually calculated for volcanic rocks which have glass and/or exceedingly small crystals that make it difficult to determine a mode, and for metamorphosed igneous rocks that no longer have the original igneous mineralogy. The normative minerals can be thought of as representing the minerals that could potentially crystallize if the rock were cooled under perfect equilibrium dry conditions. The assemblages of normative minerals are based largely on reality. In real rocks the mineral pairs:

quartz and Mg-rich olivine

quartz and nepheline

Al-silicates and augite

orthopyroxene and nepheline,

are usually mutually exclusive. The mutually exclusive normative mineral pairs are similar:

quartz and olivine

quartz and nepheline

corundum and diopside

orthopyroxene and nepheline.

 

These mutually exclusive mineral pairs result in the four common normative assemblages:

 

Norm assemblages	Meaning
Quartz, corundum, OPX:	Silica-saturated, peraluminous, subalkaline
Quartz, diopside, OPX:	Silica-saturated, subaluminous, subalkaline
Olivine, diopside, OPX:	Silica-undersaturated, subaluminous, subalkaline
Olivine, diopside, nepheline:	Silica-undersaturated, subaluminous, peralkaline

NORM CALCULATION PROCEDURE

The following procedure has been abridged for the most common rocks, omitting many calculations that must be done if the rock is unusual. For example, the procedures to calculate normative leucite in strongly silica-undersaturated rocks, aegirine in alumina-undersaturated alkalic rocks, or hematite in oxidized rocks have been omitted. The procedure below also departs from the original CIPW norm in that the pyroxenes, plagioclase, and olivine are calculated as their solid solutions rather than as end member components. I have included four worked examples so you can see how calculations are done and how to keep track of the numbers. You must do all calculations to at least five decimal places or severe rounding errors will result.

1) Use only the eleven major element oxides, for which the gram formula weights are:

SiO2	60.0843
TiO2	79.8988
Al2O3	101.9613
Fe2O3	159.6922
FeO	71.8464
MnO	70.9374
MgO	40.3044
CaO	56.0794
Na2O	61.9789
K2O	94.1960
P2O5	141.9445

2) Take the oxide weight percents in the chemical analysis and divide them by their respective formula weights to give molar oxide proportions. Use these molar oxide proportions in all subsequent calculations.

3) Add MnO to FeO. MnO is now zero. The combined FeO and MnO will now be called FeO.

4) Apatite (Ap): Multiply P₂O₅ times 3.33 and subtract this number from CaO. P₂O₅ represents 2/3 of an apatite molecule, so multiply P₂O₅ times 2/3, and put this number in Apatite. P₂O₅ is now zero.

5) Ilmenite (Ilm): Subtract TiO₂ from FeO. Put the TiO₂ value in ilmenite. TiO₂ is now zero.

6) Magnetite (Mt): Subtract Fe₂O₃ from FeO. Put the Fe₂O₃ value in magnetite. Fe₂O₃ is now zero.

7) Orthoclase (Or): Subtract K₂O from Al₂O₃. Put the K₂O value in orthoclase. K₂O is now zero.

8) Albite (Ab) [Provisional]: Subtract Na₂O from Al₂O₃. Put the Na₂O value in albite. Retain the Na₂O value for possible normative nepheline.

9) Anorthite (An):

a) If CaO is more than Al₂O₃, then subtract Al₂O₃ from CaO. Put all Al₂O₃ into anorthite. Al₂O₃ is now zero.

b) If Al₂O₃ is more than CaO, then subtract CaO from Al₂O₃. Put all CaO into anorthite. CaO is now zero.

10) Corundum (Cor): If Al₂O₃ is not zero, put the remaining Al₂O₃ into Corundum. Diopside and Al₂O₃ are now zero.

11) Calculate the current ratio of Mg/(Mg+Fe⁺²). This ratio is called Mg' and will be the Mg/(Mg+Fe⁺²) ratio for all normative silicates.

Mg' = MgO/(MgO+FeO)

12) Calculate the mean formula weight of the remaining FeO and MgO. This combined Fe-Mg oxide called FMO will be used in subsequent calculations.

Formula weight of FMO = (Mg'*40.3044)+((1-Mg')*71.8464)

13) Add FeO and MgO to get FMO.

14) Diopside (Di): If CaO is not zero, subtract CaO from FMO. Put all CaO into diopside. CaO is now zero.

15) Hypersthene (Hy) [Provisional]: Put all remaining FMO into hypersthene. Retain the FMO value for the possible calculation of normative olivine.

16) Calculate the amount of SiO₂ needed for all of the normative silicate minerals listed above, allotting SiO₂ as follows:

Orthoclase * 6 = needed SiO₂ for each Orthoclase

Albite * 6 = needed SiO₂ for each Albite

Anorthite * 2 = needed SiO₂ for each Anorthite

Diopside * 2 = needed SiO₂ for each Diopside

Hypersthene * 1 = needed SiO₂ for each Hypersthene

Sum the five SiO2 values just calculated, and call this number pSi for provisional SiO₂.

17) Quartz (Qz): If there is enough silica to make all five minerals then the rock is quartz-normative. Otherwise there is no quartz in the norm and silica to make the rest of the silicates must come from other sources.

a) If pSi calculated in step 16 is less than SiO₂, then there is excess silica. Subtract pSi from SiO₂, and put excess SiO₂ in quartz. SiO₂, Nepheline, and olivine are now zero. Skip to step 20.

b) If pSi calculated in step 16 is more than SiO₂, then the rock is silica deficient. Proceed to step 18.

18) Olivine (Ol), Hypersthene (Hy): If pSi calculated in step 16 is more than SiO₂, then there is an SiO₂ deficit. Quartz is now zero. Calculate a new pSi as in step 16, omitting hypersthene.

Orthoclase * 6 = needed SiO₂ for each Orthoclase

Albite * 6 = needed SiO₂ for each Albite

Anorthite * 2 = needed SiO₂ for each Anorthite

Diopside * 2 = needed SiO₂ for each Diopside

Sum the four SiO₂ values just calculated to get a new value of pSi. Subtract the new pSi from SiO₂ to get the amount of SiO₂ available for olivine and hypersthene, called aSi.

a) If FMO is greater than or equal to 2 times aSi, then put all FMO in olivine. FMO and hypersthene are now zero. Proceed to step 19.

b) If FMO is less than 2 times aSi, then nepheline is zero. Calculate the amount of hypersthene and olivine as follows:

Hypersthene = ((2 * aSi) - FMO)

Olivine = (FMO - Hypersthene)

Skip to step 20.

19) Nepheline (Ne), Albite (Ab): If you reached this step, then turning hypersthene into olivine in step 18a did not yield enough silica to make Or, Ab, An, Di, and Ol. Calculate a new pSi value as in step 16, omitting hypersthene and albite.

Orthoclase * 6 = needed SiO₂ for each Orthoclase

Anorthite * 2 = needed SiO₂ for each Anorthite

Diopside * 2 = needed SiO₂ for each Diopside

Olivine * 0.5 = needed SiO₂ for each Olivine

Sum the three SiO₂ values just calculated to get a new value of pSi. Subtract this pSi from SiO₂ to get a new value of aSi, which is the amount of SiO₂ available for albite and nepheline.

Albite = (aSi-(2*Na₂O))/4

Nepheline = Na₂O-Albite

20) Multiply orthoclase, albite, and nepheline by two. Divide olivine by two.

21) Calculate An', which is the Ca/(Ca+Na) ratio in normative plagioclase:

An' = Anorthite/(Anorthite+Albite)

22) Plagioclase (Plag): Add albite to anorthite to make plagioclase. Retain the albite value.

23) Calculate the formula weight of plagioclase, using the An' value from step 21.

Formula weight Plag = (An'*278.2093)+((1-An')*262.2230)

24) Multiply all of the normative mineral values by their respective formula weights. The formula weight of FMO is from step 12.

Qz	60.0843	SiO2
Or	278.3315	KAlSi3O8
Plag	Calculated in step 23	(Ca,Na)(Al,Si)4O8
Cor	101.9613	Al2O3
Ne	142.0544	NaAlSiO4
Di	176.2480 + formula weight of FMO	Ca(Fe,Mg)Si2O6
Hy	60.0843 + formula weight of FMO	(Fe,Mg)SiO3
Ol	60.0843 + (2 * formula weight of FMO)	(Fe,Mg)2SiO4
Mt	231.5386	Fe3O4
Ilm	151.7452	FeTiO3
Ap	504.3125	Ca5(PO4)3F

25) This is your weight norm. This would usually be published along with four other useful parameters:

Total:	The sum of all mineral weights in the norm, calculated in step 24. Within rounding error the Total should be the same as the original total of the weight % of the oxides from the chemical analysis.
Mg'%:	100*Mg' From step 11.
An'%:	100*An' from step 21.
DI:	The Differentiation Index of Thornton and Tuttle (1960). This is the weight ratio: (Qz+Or+Ab+Ne)/Total. Ab is albite from step 20 times 262.2230.

26) The weight norm is the way norms are usually expressed. If you want to compare norms to modes (which are volume fractions) you should divide each normative mineral by its density and recalculate the Total back to 100%. Mineral densities can be gotten from mineralogy texts, the CRC Handbook of Chemistry and Physics, or elsewhere. The density of plagioclase and the Fe-Mg silicates with intermediate solid solutions can be found in tables or figures in mineralogy texts, or equations derived from them

اطلس میکروسکپی مقاطع صیقلی - مخصوص زمین شناسان اقتصادی

نقره	Auricupride	آمالگام	آلومینیم	کادمیم
کاماسیت	طلا	تائینیت	سرب	Awaruite
مس	آهن	کوهنیت	Carlsbergite	Sinoite

مقطع صیقلی مس - copper

مشخصات فلز مس، شرایط تشکیل، ویژگیهای زمین شناسی

تصویر میکروسکپی مس:

مقطع صیقلی طلا - Gold

مشخصات فلز طلا، شرایط تشکیل، ویژگیهای زمین شناسی اقتصادی:

تصویر میکروسکپی طلا:

مقطع صیقلی نقره - Silver

مشخصات فلز نقره، شرایط تشکیل، ویژگیهای زمین شناسی اقتصادی:

تصویر میکروسکپی نقره:

بررسی تغییرات اقلیم بر اساس مدارک تاریخی چین

Chinese historical documents and climate change

Bibliography          

As late as the nineteenth century, it was commonly believed that climate represented a kind of averaged weather over time at a geographical location and hardly changed, at least for the period comparable to the length of human history. It has been demonstrated that climate changes at millennial, centennial, and even decadal scales, as many studies in the twentieth century have revealed. Such studies were largely done by examining environmental data such as tree rings, pollen assemblages, lake sediment, and ice cores. These data are objective and usually continuous, but they are often difficult to interpret. For example, a narrow tree ring could mean either a dry spell or cold spring, or both. Consequently, conclusions obtained this way are often associated with considerable uncertainties or ambiguities. Furthermore, environmental data usually have low time resolution and hence are not suitable for high-resolution analysis.

Historical climate records

Many historical documents contain records of direct human observations of climatic conditions (cold, warm, wet, and dry) that can be used directly for studying climatic changes. In addition, human activities are influenced by climate, and by carefully scrutinizing the descriptions in historical documents detailing these activities, it is possible to decipher what the climate must have been. These documents, if available, can serve as a very useful source of data for climate studies.

The main advantage of human-recorded climate descriptions, as opposed to those inferred from environmental data, is that the climatic conditions are presumably direct observations, which are easier to interpret, at least qualitatively. For example, it is hard to imagine that an extremely cold winter would be recorded as warm. Of course, missing or discontinuous records may be a serious problem as documents could become lost or destroyed due to dislocation, war, and other causes (such as earthquake and floods). To be useful for climatic studies, it is necessary to have long and continuous records.

China is one of the few countries that has kept a huge amount of historical documents, thanks to its long and continuous history and antiquarian culture. There were governmental offices that were responsible for watching unusual environmental phenomena and recording them in daily logs, and many of these phenomena related to weather and climate. Furthermore, China's main economical activity has been agriculture, which is greatly influenced by climate. As a result, a large amount of agriculture-related records of floods, droughts, famine, harvest, price of grain, damages to fruit trees, and so on have been kept in archives that can be used as a data source for climate studies. Then there are phenological records, such as the freezing and thawing dates of lakes and rivers, blossoming dates of certain flowers, and arrival dates of certain species of migrating birds, which are indicators of climatic conditions. In addition, there are some unusual weather phenomena (for example, thunderstorms in winter), which were considered as bad omens out of superstition and were recorded systematically in official histories that can also serve as sources of climate data. Indeed, all these records have been used successfully for reconstructing past climate conditions in China.

Given that there are so many different kinds of data, one would expect to see many discrepancies among conclusions derived from different data series. Instead, there is a surprising degree of consistency among them, at least in the broad sense. One typical example is shown in the illustration. Here two different series are plotted: a winter temperature series and a winter thunderstorm frequency series. It is obvious that the two series have good correlation, despite the fact that they are of completely different nature.

Winter temperature (dashed curve) and winter thunderstorm frequency (solid curve) of China in historical...

Winter temperature (dashed curve) and winter thunderstorm frequency (solid curve) of China in historical time. The winter temperature series was derived from phenological records (K. C. Chu, 1972), and the winter thunderstorm series was compiled from the Twenty-Four Official Histories of China (P. K. Wang, 1980). The winter temperature series is plotted as the deviation from the modern (1900 to 1960s) mean temperature (the peaks represent cold deviation). Winter thunderstorm frequency represents the number of winter thunderstorm reports in a 30-year interval.

 

Temperature series

In the following, we will focus on discussing the temperature series only. This series, deduced mostly from phenological phenomena as described in historical documents, shows immediately that there had been obvious warm and cold periods in China in the historical time. Several notable broad periods are discussed, for which the ranges are approximate.

A.D. 200–600

This was a cold period (as compared to the current situation) roughly corresponding to the Three-Kingdoms, Wei, Jin and North-South Dynasties in Chinese history. This was a time of relative turmoil when many kingdoms coexisted. Wars within each kingdom and between different kingdoms were frequent. Previous to this period during the Han dynasty, bamboo, a semitropical plant, was still spread widely in northern China. During this colder period, bamboo became less populated, and it is virtually extinct in nature in northern China today. Similarly, the once widespread tangerine orchards became nearly extinct because of the colder climate. One report at the beginning of the third century says that the tangerine trees merely flowered but failed to bear fruit in Henan Province. Cold spells in winter occurred more frequently. In 225, a military exercise at Guangling (33.5°N, 119°E), a town near Huai River, was halted due to a sudden freeze of the river. During the later part of this period, called the South-North Dynasties, China was divided into north and south empires, separated by the Yangtze River. An imperial “icehouse” was established in Nanjing (32N°, 119°E) by the southern empires to store ice obtained during the winter for the imperial family's use. This was the first time in history that the imperial icehouse was built at such a southern latitude. This feat would be impossible today because the winter would not be cold enough to obtain thick chunks of ice there.

600–1000

A relatively warm climate characterized this period and, coincidentally or perhaps consequentially, China enjoyed a relatively stable political climate as well. The Tang Dynasty, often regarded as the golden age of Chinese culture, began at 618 and ended in 907. In 650, 669, and 678, it was reported that there was no snow or ice in winter in the national capital Changan (today's Xian, 34.2°N, 109°E). Orange and tangerine trees were again widely planted in Changan, and “the fruits tasted as good as those tributes from southern China.” Another indication of the warm climate was the wide existence of plum trees at the time, as indicated in many poems.

Near the end of this period, however, the warm climate turned into a colder period. The once stable Tang Empire fragmented into several kingdoms and entered the Five Dynasties and Ten Countries period. This again was a fairly chaotic time, and wars between kingdoms ensued. As a rule in Chinese history, it appears that the cold period usually coincided with more frequent wars between kingdoms. (This coincidence is not explained here.)

After 1000 and until at least the beginning of the twentieth century, it appears that the climate of China fluctuated more rapidly than in previous periods. Cold and warm periods seemed to alternate in intervals of roughly 100–200 years, but in general the mean winter temperature appears to be lower than that in the 600–1000 period and moderately lower than that in the twentieth century. At present it is unclear whether this rapid fluctuation is real or due to artifacts in the data.

1000–1200

This generally cold period culminated around 1150. An initially affluent Song Empire (960–1279) was gradually weakened by the rising nomad rivals in the north—the Liao, Jin, and eventually the Yuan (Mongolian) empires. The Song Empire shrank to become the Southern Song Empire in 1127, occupying only lands to the south of the Yangtze River. Kublai Khan defeated Jin and then the Southern Song Empire in 1279. The Lake Tai [Tai Hu, area 2250 km2 (870 mi2), located at 31.2°N] was reported to freeze for the first time in history in 1111, and the cold spell wiped out all citrus trees in this area. Snowfall records indicated that the average last snow dates in 1131–1260 was the ninth day of the fourth month (roughly corresponding to May in the Gregorian calendar), nearly a full month later than that in 1100–1110, indicating a colder trend. There were also many reports of damage to other fruit plants (notably, Nephelium litchi, commonly known as lichee) in parts of China even farther south because of the cold climate in the twelfth century.

1200–1300

This was a relatively warm period. An indication was the reinstating of government offices overseeing the bamboo production in Shanxi and Henan provinces under the Mongolian rule. These offices were disbanded previously in the twelfth century by Song rulers because the cold climate greatly reduced production.

1300–1400

In this cold period, according to the Mongolian poet Nai-Xian (1309–1352), icing in the Yellow River occurred earlier by as much as a full month as compared to the present. The poet also lamented that swallows “were merely short visitors” due to the colder climate.

1400–1900

The climate became somewhat warmer near 1400, although still colder than the present. In general, this was a colder period but seemed to approach the present warm condition near 1900. Ironically, the records in this period become too numerous to easily decipher the climatic conditions without ambiguities. Many records are probably noise rather than signals, which will take much research effort to sort out. But certain severe climate-caused disasters stand out as clear signals. One such example was the adverse climatic conditions (severe winters and droughts) near the end of Ming Dynasty (1368–1644), which were often attributed to the collapse of the Ming Empire and succession by the Qing (Manchurian) Dynasty (1644–1911).

 See also: Asia; Bamboo; Climate history; Climate modification; Climatic prediction; Global climate change; Lychee; Plant geography

Pao K. Wang

Bibliography

    * K. C. Chu, A preliminary study on the climatic fluctuations during the last 5000 years in China, Scientia Sinica , 16:226–256, 1973

     * Ali Fazeli = egeology.blogfa.com

    * P. K. Wang, On the possible relationship between winter thunder and climatic changes in China over the past 2,200 years. Clim. Change , 3:37–46, 1980 DOI:10.1007/BF00144984

     * Ali Fazeli = egeology.blogfa.com

    * P. K. Wang and D. Zhang, An introduction of some historical governmental weather records in the 18th and 19th centuries of China, Bull. Amer. Meteorol. Soc. , 69:753–758, 1988

     * Ali Fazeli = egeology.blogfa.com

    * P. K. Wang and D. Zhang, Recent studies of the reconstruction of East Asian monsoon climate in the past using historical literature of China, J. Meteorol. Soc. Jap. , 70:423–446, 1992

     * Ali Fazeli = egeology.blogfa.com

    * P. K. Wang and D. Zhang, Reconstruction of the 18th century precipitation of Nanjing, Suzhou, and Hangzhou using the Clear and Rain Records, in Climate Since 1500 AD, ed. by R. S. Bradley and P. D. Jones, pp. 184–209, Routledge, London, 1991

     * Ali Fazeli = egeology.blogfa.com

    * M. Winkler and P. K. Wang, The late Pleistocene and Holocene climate of China: A review of biogeologic evidence and a comparison with GCM climate simulations, in Global Climates since Last Glacial Maximum, ed. by H. E. Wright et al., pp. 221–264, 1994

     * Ali Fazeli = egeology.blogfa.com

مقطع صیقلی Auricupride

مشخصات کانی Auricupride، شرایط تشکیل، ویژگیهای زمین شناسی اقتصادی:

تصویر میکروسکپی Auricupride:

کیمبرلیت ها - Kimberlite

Kimberlite

A variety of peridotite, an igneous rock containing at least 35% olivine. The full definition is unusually complex for an igneous rock, with many qualifications. Briefly, kimberlite is richer in carbon dioxide than most peridotites, and has crystals larger in diameter than 0.5 mm of olivine, garnet, clinopyroxene, phlogopite, and orthopyroxene. All of these silicate minerals have high Mg/Fe ratios in kimberlites. In addition, there can be 0.5 mm or larger crystals of magnesian ilmenite and titanium-poor chromite. The matrix (crystals less than 0.5 mm) contains olivine plus one or more of monticellite, phlogopite, perovskite, spinel, apatite, serpentine, and carbonate minerals. Melilite, leucite, kalsilite, and alkali feldspar do not crystallize from kimberlite magma. In part, the complexity of this definition is caused by the complicated processes of generation and emplacement of kimberlites and, in part, a restrictive definition is imposed as a defense against wishful thinking, because kimberlite was long thought to be the only rock that brought diamonds to the Earth's surface. However, in the 1970s other diamond-bearing rocks (lamproites) were found in western Australia and elsewhere, and in the 1980s R. H. Mitchell distinguished orangeite and kimberlite as separate hosts for diamonds in South Africa. Some eclogites have recently been found to contain diamonds also.  See also: Eclogite; Olivine; Peridotite

Diamonds are the only economically significant mineral extracted from kimberlite. They form deeper than 150 km in the Earth's mantle and are carried upward as “accidental tourists” in kimberlite. Several thousand kimberlite occurrences are known, but less than 10% of these contain any diamonds, and less than 1% can support profitable mines.  See also: Diamond

The magmatic liquid that forms kimberlite is generated by the melting of small amounts of the Earth's upper mantle containing water and carbonate. The liquid moves upward, gathering crystals (including diamond) and rock fragments along the way. The high content of carbon dioxide dissolved in kimberlite magma becomes insoluble at lower pressures as the kimberlite ascends; carbon dioxide begins to form a separate gas phase at a depth of about 120 km, but most of the gas comes out at depths of 30 km and less. By the time the kimberlite breaks through the surface of the Earth, it is a suspension of liquid droplets and solid fragments in rapidly expanding gas. No lava flows representing liquid kimberlite that erupted on the surface have been recognized anywhere. This suggests that whenever kimberlite magma breaches the surface it does so explosively.

Kimberlites usually occur in regions of thick and stable continental crust, in southern Africa (including the Kimberley district), India, Siberia, Canada, Colorado-Wyoming, Venezuela, and Brazil. Most kimberlite outcrops appear on the surface as small, roughly circular areas less than 1 km in diameter; they are usually not well exposed because kimberlite weathers rapidly. In three dimensions, kimberlite bodies are dikes or, more commonly, downward-tapering cylinders (pipes). Those that have not been deeply eroded preserve their eruption craters, flaring out at the top of the pipe like the bell of a trumpet, filled with fragmental rock (kimberlite plus anything encountered on the way).

Because kimberlites usually do not crop out boldly, “indicator minerals” are important in prospecting for them. These are much more abundant than diamonds but occur with them in kimberlites and are stable under conditions of surface weathering, erosion, and deposition. They include pyrope garnet, ilmenite, and clinopyroxene, each with a distinctive composition. Using indicator minerals, one can trace debris from weathered kimberlite back to its source, even if that source has been buried.

During the violent injection of kimberlites into the upper crust, some detached fragments from the crust move downward and others from the lower crust and mantle move upward. Therefore kimberlite bodies are important scientifically because they contain fragments of rocks that were once above the present-day erosion surface as well as fragments of the Earth's mantle from 150 km deep or more.  See also: Igneous rocks

Daniel S. Barker

Bibliography

 

    * A. J. A. Janse and P. A. Sheahan, Catalogue of world wide diamond and kimberlite occurrences: A selective and annotative approach, J. Geochem. Explor., 53:73–111, 1995

    * R. H. Mitchell, Kimberlites: Mineralogy, Geochemistry, and Petrology, Plenum, New York, 1986

     * Ali Fazeli = egeology.blogfa.com

    * R. H. Mitchell, Kimberlites, Orangeites, and Related Rocks, Plenum, New York, 1995

     * Ali Fazeli = egeology.blogfa.com

    * R. H. Mitchell, Kimberlites: Mineralogy, Geochemistry, and Petrology, Plenum, New York, 1986

     * Ali Fazeli = egeology.blogfa.com

    * R. H. Mitchell, Kimberlites, Orangeites, and Related Rocks, Plenum, New York, 1995

. A. Janse and P. A. Sheahan, Catalogue of world wide diamond and kimberlite occurrences: A selective and annotative approach, J. Geochem. Explor., 53:73–111, 1995

     * Ali Fazeli = egeology.blogfa.com

    * R. H. Mitchell, Kimberlites: Mineralogy, Geochemistry, and Petrology, Plenum, New York, 1986

     * Ali Fazeli = egeology.blogfa.com

    * R. H. Mitchell, Kimberlites, Orangeites, and Related Rocks, Plenum, New York, 1995

     * Ali Fazeli = egeology.blogfa.com

سن هسته زمین - Age of the Earth's core

Age of the Earth's core           

Recent research to determine the age of the Earth's core used hafnium–tungsten chronometry. The iron-rich metallic core is the most inaccessible part of the Earth, so determining how it has developed is very difficult. Furthermore, the first 500 million years of Earth history are the most obscure; no indigenous rocks from that period have survived the intense meteorite bombardment of the Earth. The development of a new way of determining the timetable for the growth of the core during the very earliest evolution of the Earth therefore represents a major breakthrough.

 

Hafnium–tungsten chronometry

The technique utilizes the radioactive decay of a now extinct nuclide of hafnium, 182Hf, which decayed to an isotope of tungsten, 182W. The half-life of 182Hf is 9 million years, which is a short period on geological time scales, since the Earth is approximately 4.5 billion years old. Therefore, no 182Hf remains on the Earth. Nevertheless, variations in the isotopic abundance of tungsten in ancient samples provide clues about the timing of processes that fractionated (separated) hafnium from tungsten. Only one process could have produced this major fractionation—the formation of a metallic core. Therefore, this event can be dated by measuring the isotopic composition of tungsten.

 

Refractory elements

Hafnium and tungsten are both present at trace levels (parts per billion or million) in rocks and metals from the inner solar system. Theoretical calculations predict that hafnium and tungsten would have condensed into stable solid phases at very high temperatures when the solar nebula first collapsed to form the solar system. Such elements are described as refractory; because of this characteristic, the proportion of hafnium relative to tungsten in the inner solar system is well established. Any loss of volatile elements (such as the noble gases) during the strong heating of the inner solar system that accompanied the early history of the Sun would have had no effect on the concentrations of refractory elements. As the dust and debris of the inner solar system accreted under the influence of gravity to form planetesimals and planets, the kinetic energy would have been converted to heat. Any such heating from accretional energy that was released as the planets and planetesimals of the early solar system collided with decreasing frequency but increasing impact (as they got bigger) would have caused vaporization of volatile elements, but it would not have affected refractory elements such as hafnium and tungsten.

It is essentially clear exactly how much hafnium and tungsten are in the Earth. Although the absolute concentrations may have increased somewhat because of loss of volatile elements, the Hf/W ratio should be about the same in the Earth as it is in primitive, unprocessed solar-system material. Some very primitive meteorites have been found with textures suggesting that they were never part of a major molten planet, and with chemical compositions remarkably similar to that deduced for the Sun on the basis of spectral measurements (if allowance is made for loss of very light volatile elements, such as hydrogen and helium, from meteorites). These particular primitive meteorites are called chondrites, and they provide a reference sample for the average Hf/W ratio and tungsten isotopic composition of the solar system and the total Earth. Unfortunately, because of analytical difficulties, it had not been possible to measure the tungsten isotopic composition of chondrites in order to discover what the tungsten isotopic composition of the total Earth must be. While the isotopic composition of the tungsten found at the Earth's surface was already known, that value is not necessarily representative of the total Earth, because the core could be different depending on when it formed. Without a knowledge of the tungsten isotopic composition of chondrites—the reference for the total Earth—it was impossible to know whether the tungsten isotopic composition found at the surface of the Earth was the same as that for the total Earth or whether it was affected by core formation.

 

Core formation

Although heating and loss of volatiles would not have affected the ratio of hafnium to tungsten in the Earth as a whole, another important segregation that took place within the planetesimals and planets of the early solar system would have greatly affected this ratio internally. The separation of metal (or metallic liquid) from silicate rock (or magma) appears to have been a very common early process. The two most abundant elements in the Earth are oxygen and iron. From studies of nonprimitive meteorites (silicate achondrites and irons) it is known that segregation of large amounts of iron-rich metallic liquids took place on both a small and large scale. In the latter case the liquid iron, being very dense, would settle toward the center of the planet or protoplanet and form a metallic core. The Earth's core is at a depth of 2900 km (1800 mi), and is still partly molten because of radioactive heating, even 4.5 billion years after the formation of the Earth.

Tungsten is a metal that tends to substitute into iron or iron-rich phases or their liquids; thus, when metal segregated to form the core of the Earth, it incorporated more than 90% of the Earth's tungsten. Hafnium, however, does not fit into iron, iron compounds, or their liquids. Rather, it tends to substitute into silicate rocks and magmas, such as those making up the mantle and crust of the Earth (the outer 2900 km or 1800 mi). For this reason, the ratio of hafnium to tungsten in the silicate Earth is about 20 times higher than its value for the Earth as a whole, whereas the ratio in the core is almost zero. Because the Hf/W ratio of the silicate Earth is so high relative to the starting material from which the Earth was made, it should have generated highly radiogenic tungsten (rich in 182W) if the core formed within the lifetime of 182Hf (effectively about 50 million years), relative to that of the total Earth or that found in primitive solar-system material such as chondrites.

 

Determining age of the core

A comparison between the tungsten isotopic compositions of the silicate Earth (common tungsten metal) and that of chondrites would indicate when the Earth's core formed relative to the start of the solar system. The later the core formed and the Hf/W ratio of the silicate Earth increased, the less would be the tungsten isotopic effect of radioactive decay of hafnium on the tungsten isotopic composition of the residual silicate Earth. This follows because more of the 182Hf would have decayed into tungsten. The amount of 182Hf relative to stable 180Hf and the amount of 182W relative to nonradiogenic 184W are related by the equation below, where CF refers to the time of core formation, BSE to the bulk silicate Earth, and CHOND to chondrites. Because of the phenomenon of radioactive decay, an equation containing ΔT, the amount of time that has elapsed since the start of the solar system, can be obtained, so that ΔT can be determined in terms of known and measurable isotopic ratios.

 

New technique

The potential of hafnium–tungsten chronometry has been recognized for many years. However, until recently there was no way of making the tungsten isotopic measurements. Tungsten has a high work function and a very high first ionization potential (7.98 V). Therefore, it is extremely difficult to generate a sufficient proportion of ions relative to neutral atoms to measure the abundances on a modern mass spectrometer at high precision. However, a new technique for successfully ionizing tungsten has been developed. It uses an inductively coupled plasma source connected to a high-precision multiple-collector mass spectrometer. This technique, known as multiple-collector–inductively coupled plasma mass spectrometry (MC-ICPMS), was immediately applied to the high-precision determination of tungsten isotopic compositions in geological materials. The tungsten isotopic composition of the silicate Earth and chondrites is identical. This is now known to very high precision. Therefore, core formation and the associated increase in the Hf/W ratio have had no effect on the tungsten isotopic composition of the silicate Earth. This being the case, these chemical fractionation effects must have occurred late in Earth history, after all the 182Hf had already decayed. For the first time it is known for certain that the Earth's core formed more than 50 million years after the solar nebula collapsed to form the solar system.

Why the core formed so late is unclear. However, some recent models hypothesize that the core formed as a consequence of a magma ocean in the upper mantle. This magma ocean would have developed as a consequence of bombardment by very large impactors during the late stages of accretion. Perhaps it took such late-stage impacts to produce sufficient melting to result in large-scale metal segregation.

 

Bibliography

    * A. N. Halliday et al., Early evolution of the Earth and Moon: New constraints from Hf-W isotope geochemistry, Earth Planet. Sci. Lett., 142:75–90, 1996 DOI:10.1016/0012-821X(96)00096-9

    * D.-C. Lee and A. N. Halliday, Hafnium–tungsten chronometry and the timing of terrestrial core formation, Nature, 378:771–774, 1995 DOI:10.1038/378771a0

*  [e-mail] = egeology.blogfa.com

تحقیقات اخیر برای تعیین سن هسته زمین با استفاده از گاه شماری هافنیم تنگستن . هسته فلزی غنی از آهنغیر قابل دسترس ترین بخش زمین است ، بنابراین تعیین اینکه چگونه آن را توسعه داده است بسیار دشوار است. علاوه بر این، 500 میلیون سال اول از تاریخ زمین گمنام ترین ؛ هیچ سنگ بومی از آن دورهبمباران شدید شهاب سنگ زمین جان سالم به در برده اند . بنابراین ، توسعه یک راه جدید برای تعیین جدول زمانی برای رشد هسته در نخستین تکامل زمین نشان دهندهدستیابی به موفقیت بزرگ است .

 

گاه شماری هافنیم تنگستن

این تکنیک با بهره گیری از فروپاشی رادیواکتیو از هسته در حال حاضر منقرض شده هافنیم ، 182Hf ، که فرسایش بهایزوتوپ تنگستن، 182W . نیمه عمر 182Hf در 9 میلیون سال است ، که یک دوره کوتاه در مقیاس زمان زمین شناسی است ، از زمین حدود 4.5 میلیارد سال است . در بنابراین، 182Hf بر روی زمین باقی مانده است. با این حال، تفاوت در فراوانی ایزوتوپی از تنگستن در نمونه های باستان ارائه سرنخ در مورد زمان فرآیندهای که تقطیع ( جدا ) هافنیم از تنگستن است . تنها یک فرایند می تواند این جزء به جزء عمده تشکیل یک هسته فلزی تولید می شود. بنابراین ، این رویداد را می توان با اندازه گیری ترکیبات ایزوتوپی تنگستن مورخ .

 

عناصر نسوز

هافنیم و تنگستن هستند هر دو در حال حاضر در سطح ردیابی ( قسمت در هر یک میلیارد یا میلیون ) در سنگها و فلزات از سیستم داخلی خورشیدی است . محاسبات نظری پیش بینی که هافنیم و تنگستن به فاز جامد پایدار در دمای بسیار بالا متراکم که سحابی های خورشیدی برای اولین بار سقوط به تشکیل منظومه شمسی است . این عناصر به عنوان مقاوم ، به دلیل این ویژگی، نسبت در هافنیم نسبت به تنگستن در سیستم داخلی خورشیدی است که به خوبی اثبات شده است . از دست دادن عناصر فرار ( مانند گازهای نجیب ) در حرارت قوی از منظومه شمسی داخلی که همراه با تاریخ اولیه خورشید هیچ تاثیری بر غلظت عناصر مقاوم داشته است. به عنوان گرد و غبار و بقایای داخلی منظومه شمسی تحت تأثیر گرانش به سیارات شکل و سیارات دارای زائده گوشتی ، انرژی جنبشی را به گرما تبدیل می شود. هر گرمایش چنین از انرژی accretional که به عنوان سیارات و سیارات اوایل تشکیل منظومه شمسی از زندان آزاد شد برخورد با کاهش فرکانس اما افزایش تاثیر ( به عنوان آنها به بزرگتر ) که باعث تبخیر از عناصر فرار ، اما آن را عناصر دیر گداز از قبیل را تحت تاثیر قرار نمی هافنیم و تنگستن .

آن است که اساسا روشن است که دقیقا چه مقدار هافنیم و تنگستن در زمین هستند . اگر چه غلظت مطلق ممکن است تا حدودی به دلیل از دست دادن عناصر فرار افزایش یافته است ، نسبت HF / W باید در مورد همان در زمین آن را به عنوان در بدوی، فرآوری نشده مواد سیستم خورشیدی است . برخی از شهاب سنگ ها بسیار ابتدایی شده اند با بافت نشان می دهد که آنها هرگز بخشی از یک سیاره بزرگ مذاب بودند ، و با ترکیبات شیمیایی قابل ملاحظه ای شبیه به استنباط خورشید بر اساس اندازه گیری های طیفی ( اگر کمک هزینه برای از دست دادن فرار بسیار سبک ساخته شده است عناصر، مانند هیدروژن و هلیم ، از شهاب سنگ ) . این شهاب سنگ خاص ابتدایی نمونه شهاب سنگ نامیده می شود، و آنها یک نمونه مرجع برای نسبت HF / W متوسط ​​و تنگستن ترکیب ایزوتوپی از منظومه شمسی و زمینارائه شده است . متاسفانه، به دلیل مشکلات تحلیلی ، آن را به حال ممکن است برای اندازه گیری تنگستن ترکیب ایزوتوپی از نمونه شهاب سنگ به منظور کشف آنچه تنگستن ترکیب ایزوتوپی از کل زمین باید . در حالی که ترکیب ایزوتوپی از تنگستن موجود در سطح زمین در حال حاضر شناخته شده بود، که ارزش لزوما نماینده از کل زمین ، آنجا که این هسته می تواند بسته به زمانی که آن را تشکیل متفاوت باشد . بدون دانش تنگستن ترکیب ایزوتوپی از نمونه شهاب مرجع برای کل زمین ، آن را غیر ممکن می دانم این بود که آیا تنگستن ترکیب ایزوتوپی موجود در سطح زمین همان است که برای کل زمین و یا اینکه آیا آن را تحت تاثیر قرار گرفت تشکیل هسته .

 

تشکیل هسته

اگرچه حرارت و از دست دادن مواد فرار نسبت هافنیم به تنگستن در زمین به عنوان یک کل ، تبعیض نژادی مهم دیگری که در سیارات و سیارات منظومه شمسی اولیه صورت گرفت را تحت تاثیر قرار می توانست تا حد زیادی تحت تاثیر این نسبت در داخل . جدایی از فلز ( یا مایع فلزی ) از سنگ سیلیکات ( یا ماگما ) به نظر می رسد به یک فرایند در اوایل بسیار معمول بوده است . دو عنصر فراوان در زمین اکسیژن و آهن . از مطالعات شهاب سنگ nonprimitive ها ( achondrites سیلیکات و آهن ) شناخته شده است که جدایی از مقادیر زیادی از مایعات غنی از آهن فلزی در هر دو مقیاس کوچک و بزرگ صورت گرفت . در مورد دومی آهن مایع بسیار متراکم ، به سوی مرکز این سیاره یا protoplanet حل و فصل و تشکیل یک هسته فلزی است . هسته زمین در عمق 2900 کیلومتر ( 1800 مایل ) است ، و هنوز هم تا حدودی مذاب به دلیل گرمایش رادیواکتیو ، حتی 4.5 میلیارد سال پس از تشکیل زمین .

تنگستن فلزی است که تمایل به جایگزین به فاز آهن و یا غنی از آهن و یا مایعات خود است ، بنابراین، هنگامی که فلز تفکیک جنسیتی اعمال به تشکیل هسته زمین ، آن گنجانیده شده بیش از 90 ٪ از تنگستن زمین . هافنیم ، با این حال ، به آهن ، ترکیبات آهن، و یا مایعات آنها متناسب نیست . در عوض ، این امر منجر به سنگ سیلیکات و ماگما ، مانند کسانی که به ساخت تا گوشته و پوسته زمین ( بیرونی 2900 کیلومتر یا 1800 مایل ) به جای . به همین دلیل، نسبت هافنیم به تنگستن در زمین سیلیکات است در حدود 20 برابر بیشتر از ارزش خود را برای زمین به عنوان یک کل ، در حالی که نسبت در هسته تقریبا صفر است . از آنجا که نسبت HF / W از زمین سیلیکات بسیار بالا نسبت به ماده اولیه که از آن زمین ساخته شده بود ، باید آن را تولید تنگستن بسیار پرتوزا ( غنی در سال 182W ) اگر هسته در طول عمر 182Hf است تشکیل شده است ( به طور موثر حدود 50 میلیون سال)، نسبت به کل زمین یا که در ابتدایی مواد سیستم خورشیدی مانند نمونه شهاب سنگ است .

 

تعیین سن از هسته

مقایسه بین تنگستن ترکیب ایزوتوپی از زمین سیلیکات (فلز تنگستن مشترک ) و نمونه شهاب سنگ نشان می دهد که هسته زمین نسبت به آغاز منظومه شمسی شکل گرفته است . بعد از هسته شکل گرفته و نسبت HF / W از زمین سیلیکات افزایش یافته است، کمتر خواهد بود تنگستن اثر ایزوتوپی از تجزیه رادیواکتیو از هافنیم در تنگستن ترکیب ایزوتوپی زمین سیلیکات باقی مانده است . این به این خاطر بیش از 182Hf فاسد به تنگستن . مقدار نسبی 182Hf به 180Hf پایدار ومقدار نسبی 182W 184W nonradiogenic است توسط معادله زیر، که در آن CF اشاره به زمان تشکیل هسته ، BSE به زمین سیلیکات فله ، و CHOND نمونه شهاب سنگ مرتبط است. از آنجا که این پدیده از تجزیه رادیواکتیو، یک معادله حاوی ΔT ، مقدار زمانی است که از آغاز منظومه شمسی سپری شده است ، می توان به دست آورد ، به طوری که ΔT را می توان در شرایط شناخته شده و قابل اندازه گیری نسبتهای ایزوتوپی مشخص شده است .

 

روش جدید

پتانسیل گاه شماری هافنیم تنگستن برای سالهای زیادی شده است به رسمیت شناخته شده است. با این حال ، تا همین اواخر هیچ راهی برای اندازه گیری های ایزوتوپی تنگستن وجود دارد . تنگستن دارای یک تابع کار بالا و اولین پتانسیل یونیزاسیون بسیار بالا ( 7.98 V) . بنابراین، بسیار دشوار است برای تولید یک بخش کافی یونهای نسبت به اتم های خنثی برای اندازه گیری فراوانی درطیف سنج جرمی مدرن با دقت بالا است . با این حال ، یک تکنیک جدید برای تنگستن موفقیت یونیزان توسعه داده شده است . این با استفاده از یک منبع پلاسما استقرایی همراه متصل به دقت بالا چند جمع آوری طیف سنج جرمی است . در این روش ، شناخته شده به عنوان چند کلکتور استقرایی همراه پلاسما طیف سنجی جرمی (MC - ICPMS ) ، بلافاصله به تعیین دقت بالا از تنگستن ترکیب ایزوتوپی در مواد زمین شناسی استفاده شود. تنگستن ترکیب ایزوتوپی از زمین سیلیکات و نمونه شهاب سنگ یکسان است . این در حال حاضر به دقت بسیار بالا شناخته شده است. بنابراین ، تشکیل هسته و افزایش در نسبت HF / W هیچ تاثیری بر تنگستن ترکیب ایزوتوپی از زمین سیلیکات بود. این که مورد ، این عوارض جزء به جزء شیمیایی باید در اواخر سال تاریخ زمین رخ داده است ، پس از تمام 182Hf ها تا به حال در حال حاضر فاسد . برای اولین بار آن را برای برخی شناخته شده است که هس

آموزش زبان انگلیسی بصورت آنلاین -فصل سوم

Chapter 3: "This is my home!"

• Teaching aims:
  • Input:
    • "Furniture" vocabulary
    • "Household" vocabulary
  • Recycle:
    • Prepositions: "Where is it?"
  • Free Talking:
    • "Homes"
• Comments:
  • Continuing the theme of exploring the immediate environment of the students, this chapter looks at the home and how to describe it to a friend or to a stranger.
  • The ability to engage in casual conversation of this sort is at the heart of this book, and teachers will want to promote it at all times. For instance, students engage in just this type of communication while waiting for the teacher to enter the classroom. They usually do it in their first language however, so it can be productive to visit the class five minutes early and to get the students saying these things in English. Having set the precedent, they can be encouraged to do this every time, or the first five minutes of each class could be allocated to this. For those who are sufficiently motivated to take on responsibility for their own learning, this could be the catalyst that sets them going!

1) "This is my home!" Title Page Input

Page 37

There are two inputs here:

• 1) presentation of Prepositions, which have already been introduced, and which will be looked at further in this chapter;
• 2) "Home" vocabulary. As before, students can refer to this page in the future, when they want to check on words previously studied.

Vocabulary

• Under, over, above, below, between, next to, beside, far from, opposite (across from), behind (in back of), in front of, inside, outside, on top of, underneath, left of, right of, in, on, in the middle of.
• armchair audio bag basket bed blind bowl brush can opener chair chopsticks closet
• comb computer cup dish door fan fireplace fridge frying pan gas range hair-dryer iron
• jug light mop oven plate radio razor rug saucer saucepan scales sink
• sofa spoon stairs stove table teapot television towel trash vacuum vase wardrobe

2) "In my house" (1) Brainstorming Pairs/Groups (15 minutes)

Page 38

Students will already have a lot of the vocabulary for this chapter, so this exercise helps them to discover that language. It is a useful teaching/ learning technique for students to access the reference material, rather than being "spoon-fed" by the teacher. It is the students who need to develop their conversation skills in English, and who need to develop their learning strategies for all their studies. Asking them to work on the input for this is part of the process of them taking responsibility for their own learning.

Students can work individually or in pairs, subsequently sharing information with others, looking in dictionaries, and finally asking the teacher if there is any unresolved vocabulary. This sequence is again typical of the thinking behind the book, in that the teacher is freed from "teaching" the input, and can move around the class, monitoring progress, and planning future lessons to meet the needs which appear.

3) "In my house" (2) Groups (15 minutes each activity)

Page 39

This group of activities builds upon the previous brainstorming. "Household " cards (Teachers' Resource) are used for various games, all of which are designed to review and reinforce the relevant vocabulary.

In "Step 4", students are asked to add to their "brainstorming" list any new words they might have encountered during the card games, and in "Step 5" they are asked to make a new game with the cards, and to show it to classmates. This is always a useful follow-up with card games, and encourages the students to participate more in the activities. Making and explaining a new game provides opportunities for authentic use of English, though this can be quite difficult!

A sample page from the Teachers' Resource appears on the next page.

3) Teachers' Resource - "In my house" (2)

Teacher's Resource for Page 39

• 039t01.gif - Household Items (1)
• 039t02.gif - Household Items (2)
• 039t03.gif - Household Items (3)
• 039t04.gif - Household Items (4)
• 039t05.gif - Household Items (5)
• 039t06.gif - Household Items (6)
• 039t07.gif - Household Items (7)
• 039t08.gif - Household Items (8)
• 039t09.gif - Household Items (9)
• 039t09.gif - Household Items (10)
• 039t09.gif - Household Items (11)
• 039t09.gif - Household Items (12)
• 039t09.gif - Household Items (13)
• 039t09.gif - Household Items (14)
• 039t09.gif - Household Items (15)

As in other card games, there will be ambiguities about the "correct" terms for the pictures, as well as some "Konglish" terms which will use the English word for a different meaning. These items can soon be identified, and will provide useful opportunities for the students to practise classroom language: "What does it mean?" etc.

4) "Where is it?" Pairs/Groups (10 minutes)

Page 40

This activity continues to look at prepositions of location, asking students to identify the location and relationship of items in a room. This is in preparation for later activities, and ultimately for the one in which they describe their own room and the items in it.

This picture is also used for the next "preposition" activity, so that students can refer to the answers they have written on this page. above, below, left of, right of, in front of, in back of, behind, next to, beside, between, in, on, over, under, on top of, beneath, in the middle of, across from, opposite

5) "Where is my pen?" Groups of four people Students' instructions (20 minutes)

Page 41 - Top

See below for comments on the students' page relating to this activity.

6) "Where shall we put it?" Pairs Students' instructions (20 minutes)

Page 41 - Bottom

See the next page of this book for comments on the students' page relating to this activity.

5) "Where is my pen?" Groups of four people (20 minutes)

Pages 42 & 43

Students (in groups of four) are sharing a dormitory. Each person has lost various items.

Of 16 items in the room, each student (A ,B, C ,D) has 12 items missing, and have to ask other members of the group for the location of them. Each item will be absent from three pictures, so while students can take turns in asking for the location of any one of these, there will only be one who can answer at any given time.

As mentioned above, it will be useful to refer to the previous page for confirmation of the appropriate terms.

6) "Where shall we put it?" Pairs (20 minutes)

Page 44

Students have a plan of a living room, and various furniture to put in it (they have just moved house).

This uses prepositions in an authentic manner, and it's important that students be encouraged to carry out this exercise completely in English, since there are many opportunities for simple but valuable practice in suggesting and agreeing.

• "Over here" "Over there" "In the corner" "Against the wall" "On the balcony" "Next to the door" "Under the window" "In front of the TV" "Opposite the ..." "Left of ...." "Between the ... and the ..."

"Right of the ..."

7) "My house" (plus Teachers' Resource) Whole class (10 minutes)

Page 45 - Top

See the next page of this book for comments on this activity.

8) "My room" "My partner's room" Pairs (20 minutes)

Page 45 - Bottom

See the next page of this book for comments on the students' page relating to this activity.

3) Teachers' Resource - "In my house" (2)

Teacher's Rescue for Page 45

• 045t1.gif - Homes (1)
• 045t2.gif - Homes (2)
• 045t3.gif - Homes (3)
• 045t4.gif - Homes (4)
• 045t5.gif - Homes (5)
• 045t6.gif - Homes (6)

As in other card games, there will be ambiguities about the "correct" terms for these pictures, as well as some "Konglish" terms which will use the English word for a different meaning. These items can soon be identified, and will provide useful opportunities for the students to practise classroom language: "What does it mean?" "How do you spell it?"

4) "Where is it?" Pairs/Groups (10 minutes)

Page 46

This picture is also used for the next "preposition" activity, so that students can refer to the answers they have written on this page.

This activity continues to look at prepositions of location, asking students to identify the location and relationship of items in a room. This is in preparation for later activities, and ultimately for the one in which they describe their own room and the items in it.

9) "Furniture Crossword" Pairs (20 minutes)

Pages 47 & 48

There are a number of "Co-operative Crosswords" in this book. Various formats are used, and in this one each student has a complete crossword, and has to explain every clue to his/her partner.

This can be a valuable means of rehearsing vocabulary and checking comprehension, since both participants will have to agree that the explanation matches the item itself.

Students will usually not be familiar with the terms "Across" and "Down" as used in crosswords.

10) Free Talking: "Homes" Pairs or Groups (20 minutes)

Page 49

Students ask each other about the picture (Montreal, Canada), and the questions gradually take them into talking about their lives and opinions on related topics.

It is important that students spend at least 15 minutes of the time allotted to each chapter in talking to each other in English. If they discuss a topic which has been the subject of various activities, they will have already rehearsed relevant language, and should be able to engage in conversation, adding this material to the non-prescribed language of the discussion. This will encourage them to notice that they are communicating in English, thus improving their perception of their oral abilities, and helping them become more self-confident.

11) Culture page 3 (10 minutes)

Page 50

آموزش زبان انگلیسی بصورت آنلاین -فصل دوم

Chapter 2: "Meet my family"

• Teaching aims:
  • Input:
    • Family members
  • Review:
    • Prepositions, Modals: "Can you ... ?", Comparatives
    • Personal information, "Do you ...?" questions
  • Recycle:
    • "Wh" questions
    Free Talking:
    • "The family"
• Comments:
  • One aim of the first half of "Tell Me More!" is to enable students to talk about themselves, so that when the occasion arises they can introduce themselves and describe their situation. Thus the first 6 chapters contain topics related to their lifestyle: personal information; the family; the home; likes/dislikes; routines; and descriptions.
  • Chapter 2 focuses on the family, but also includes activities dealing with prepositions, modals ("Can you ... ?") and comparatives.

Chapter 2 - "Meet my family" Title Page

Page 25

As noted before, all chapters have input on the title page, which students can refer to. In this case the input is family and occupation lexis (the latter being relevant for giving details about members of the family). It is not necessary to "teach" this vocabulary before beginning the activities however, since the activities will focus on this, and the need to review words will arise naturally and meaningfully.

"The family" Groups (20 minutes)

Page 26

This is one of a number of "Peer Dictation" activities occurring in the book. The aim is to introduce the topic in an interesting way, and in a manner that helps the students to develop their oral skills. In fact this activity has all four language "skills" (reading, speaking, listening, writing) as well as including aspects of Peer Correction and Classroom Language.

The text (Teachers' Resource) is put on a wall, and one member from each group reads it a phrase at a time, and dictates that phrase from memory to the other members of the group. They then use classroom language to arrive at the correct version, which they write on the worksheet.

The second part of this activity asks students to role-play a foreigner and a Korean, the one asking questions, and the other explaining about the the first birthday custom.

Teachers' Resource - Text

Teacher's Rescue for Page 26

• 026t.jpg - The Family - Text

In early times, the typical Korean family was large. Several generations often lived together, and many children were desired for stability and security. It was not unusual for the number of people sharing one house to total a dozen or more. In recent years, the movement to urban areas and the spread of apartment-type housing have meant that newly married couples tend to live in their own quarters instead of living with other family members, giving rise to an increasing number of nuclear families.

Traditionally, in a Korean home the head of the family was regarded as the source of authority. All family members were expected to do what was ordered or desired by the family head. Obedience to the superior was regarded as natural and one of the most admirable virtues. On the other hand, it was understood that the patriarch of the family would be fair in dealing with the family members.

"Who is in my family?" Everyone (20 minutes)

Page 27

This activity reviews language from Chapter 1, as well as introducing new family-related questions. Students are once more asked to take on a role, and to follow it through. In this case, they are given some information (Teachers' Resource), which they have to use (along with information they gather from other people in the class) in order to find out who the other members of their assumed family are. These names are then written on the worksheet.

Students are once more encouraged to interact with members outside their immediate group, setting the scene for later interview and questionnaire-type activities.

Teachers' Resource - "Who is in my family?"

Teacher's Rescue for Page 27

• 027t1.gif - Who is in my family? (1)
• 027t2.gif - Who is in my family? (2)
• 027t3.gif - Who is in my family? (3)

Questions that the students may find useful

• "What is your name?"
• "Where do you live?"
• "Are you married?"
• "Do you have a sister?"
• "Do you have a brother?"
• "Do you have any sisters?"
• "Do you have any brothers?"
• "Do you have a son?"
• "Do you have a daughter?"
• "Do you have any sons?"
• "Do you have any daughters?"
• "What is his name?"
• "What is her name?"
• "What are their names?"

"Myself - My family" (Homework)

Page 28

This activity asks students to write some ideas about themselves in English. There are a number of opportunities for self-study in the book, but the policy regarding the setting of homework is mostly left to individual teachers, who will have their own ways of developing the materials, and their own priorities in terms of student input/output.

The students introduce themselves to the teacher, and attach a photo of themselves. The textbook has many such "workbook" pages that can be very informative to the teacher.

Teacher's Resource - "Myself - My family"

Teacher's Resource for Page 28

• 028t.gif - Myself - My family (Teacher)

The Teachers' Resource is a duplicate of the students' page, but with more space for writing, and with empty places for photos of the teacher and his/her family. In this initial period of the course, when "breaking the ice" is an important factor, such teacher input can be very effective, showing that this course will be worked through together!

In this respect, the teacher might consider taking on the same goal as that prescribed for the students - talking about him/herself in a second language, at the end of the sixth chapter!

5a) "Question - Answer" Two teams (20 minutes)

Page 29

There are two activities on this page. The first one is a "Matching" game. Students get together in two teams, with an additional "Caller". Students in Team A choose two numbers: the first from 1 to 10; the second from 11 to 20. The Caller reads out the sentences corresponding to these numbers on the "Callers' Sheet" (see below). If the two sentences match (Question and Answer), the team gets one point, and has another turn. If not, the next team chooses two sentences.

Students will use various means to remember the sentences. This is fine, since they will be finding ways of dealing with a language problem - how to remember what has been said. In the second version of the game (most students should be able to get to this), they can be encouraged to use only their listening skills!

5a) Teachers' Resource

Teacher's Resource for Page 29

• 029t1.gif - "Question - Answer" Caller's Sheet

The Teachers' Resource is the Callers' Sheet, which has two versions of the game. The first has simple greetings/introductions questions and responses; the second presents Q & As in more of a dialogue format.

"Correct" responses are fairly well defined in the first game, but the second set of questions has a number of possibilities. For instance: "Why didn't you come?" could be answered by "I had to wash my hair." or "We went to a movie."; and "Who did you see?" could be answered by "Jennifer" or "My friend." It is not necessary for the teacher to do more than to be aware of these possibilities, for if the students notice them, it will indicate that they are participating in the activity, using their listening skills, and actively evaluating the text.

5b) Teachers' Resource - "Who is it?" 2 teams (15 minutes)

Teacher's Resource for Page 29

• 029t2.gif - Who is it? (1)
• 029t3.gif - Who is it? (2)
• 029t4.gif - Who is it? (3)
• 029t5.gif - Who is it? (4)

The second activity on this page is another "Team" game, but this time there is no Caller. The teacher gives a set of "Family" cards to each group of two teams (Teachers' Resource). One person from each team then describes the relationship on the card to his/her team (e.g. "This person is my mother's husband." ["Father"]). The first team to guess the correct relationship wins a point. Alternatively both teams could listen to one person (perhaps the previous Caller?!) explaining the term, and could try to guess the word first.

The prevalence of "games" in this chapter will raise for the students the issue of the validity of interactive activities, in terms of "actually learning anything". In their experience of teaching-learning methodology so far, such things will have been relegated to the ends of chapters, after the "real work" has been done. This is an opportunity therefore to bring this matter into the open, and to show the students that the best way to learn to speak is to participate fully in speaking activities.

6) "What do I do?" (plus teachers' resource) Groups (15 minutes)

Page 30

This activity is based on the game "What's my line?". One student performs actions characteristic of an occupation, and the others (in two teams) have to guess what that occupation is. At a basic level the game can continue until the correct answer is guessed, but interest can be added by giving each person a limit of three questions. After that each team must choose what it thinks the occupation is.

A preliminary Matching exercise is provided in order to establish the names of various jobs in English (see the next page of this book for the answer key).

• "Do you work in a post office?"
• "Do you work in a restaurant?"
• "Do you work in a shop?"
• "Do you wear special clothes?"
• "Do you work alone?"
• "Do you use a computer?"
• "Do you use special tools?"

Chapter 2: "Meet my family"; Teachers' Notes.

6) "What do I do?" Answer Key

7) "Can you ... ?" (plus Teachers' Resource) Pairs/Groups (20 minutes)

Page 31

This activity is a simple review of "Can you?", but hopefully the format makes it an interesting one!

The teacher gives each group a set of "Can you?" cards (Teachers' Resource), which is put on the board, face down. Students roll a dice and move a counter around the board, using the verb of the square they land on to answer a "Can you?" question about a card (e.g. "Can you lift a bus?"). If they answer "Yes, I can.", they keep the card, and roll the dice again. If they answer "No, I can't.", the next person rolls. The winner has the most cards at the end of the game.

A number of questions will be strange or funny (e.g. "Can you cook a radio?") but this will add to the interest. If students answer "Yes, I can.", then the others will challenge them to explain (in English!).

7) Teacher's Resource - "Can you ... ?"

Teacher's Resource for Page 31

• 031t1.gif "Can you ... ?" -cards (1)
• 031t2.gif "Can you ... ?" -cards (2)
• 031t3.gif "Can you ... ?" -cards (3)
• 031t4.gif "Can you ... ?" -cards (4)

8) "It's on the pen" Pairs/Groups (20 minutes)

Page 32

Prepositions are a difficult aspect of English, and one which students often see as confusing and important. This book therefore spends some time on these, since they are relevant to the "real-life" situations of giving directions and instructions. By showing the students that there are guidelines, and that they can communicate successfully by following these, it is hoped that their self-confidence will improve.

This activity checks on prepositions of location, and leads on to the next one (next page). It can be done in class, or as a preparatory homework.

9) "Where has it gone?" Pairs/Groups (20 minutes)

Page 33

Further activities on Prepositions of location.

Games 1 & 2 use the "Spot the Difference" format, while game 3 gets the students involved in a memory game, either in teams or pairs. Objects are put on the table (any classroom/personal items will suffice) for the opposing student(s) to look at for 30 seconds. The items are then rearranged, and those students have to put them back in the original locations.

This activity (game 3) can easily proceed without any speaking, so it would be good if (perhaps after the students have become familiar with the game) the teacher mentions that the opposing students are not allowed to touch the items. They must tell the others where to move them (in English!).

10) "What do you think?" Whole class (20 minutes)

Page 34

Questionnaire activity. Use of Comparatives.

Students have to fill in their own choices for the given comparisons, and then to ask at least three people for their opinions, finally reporting their findings to the group or the class as a whole.

This is a chance to look at "Me too", "So do I", "Me neither", and "Neither do I", as well as the responses which occur when participants disagree: "Oh, I do(n't)."

• "Yes, I agree."
• "Yes, maybe."
• "I don't know."
• "No, maybe not."
• "No, I disagree."
• "Me too."
• "So do I."
• "That's just what I think."
• "Me either."
• "Neither do I."

11) Teachers' Resource - "True or false?" Whole Class (15 minutes)

• 02t25.htm - True or False Cards (1)
• 02t30.htm" - True or False Cards (Blank)

This activity is not in the students' book. It only appears as a Teachers' Resource, and therefore can be used at any time.

In more information-gathering, students have to ask everyone in the class about one topic, this time an aspect of their daily routines. Having found out how many people do or do not conform to the statement on the card, students have to decide whether that statement is true or false, and then they have to report that finding to the class.

Blank cards are supplied for students who finish early, and who can be asked to make up their own survey questions.

12) "Free Talking - The family" Pairs/Groups (10 minutes)

Page 35

As with all chapters, the "final" activity is designed to encourage students to discuss the main topic in English. This need not happen solely at the end of the lessons of course, but can occur when appropriate.

10 minutes is suggested for this activity at this time, since while it is important that students develop all the skills necessary for free talking, uncomfortable silences can be counterproductive, and the activity must last only so long as it is effective. The use of simple questions about the picture will hopefully stimulate some response from every student.

13) Culture page 2 (10 minutes)

Page 36

به وبلاگ بزرگ مقالات زمین شناسی خوش آمدید

 

تحقیق دانشجویی

دانلود کتابهای زمین شناسی

دانلود نقشه های جهان

دانلود آهنگ با فرمت Mp3

جدیدترین اخبار ایران و جهان

ماسه های نفتی

 

 

 

انتخاب زبان فارسی	LANGUAGE - BRITISH	جستجوی پیشرفته	دانلود کتابهای زمین شناسی

American Mineralogist	مقالات مجله زمین شناسی نروژ	مقالات نشریه شیکاگو	مقالات نشریه نیوزلند

مقالات ترمومتری سیالات درگیر	نوت بوکهای زمین شناسی	ماسه نفتی	دانلود نقشه های جهان

الزویر	AccessScience	ُُSpringer	Blackwell

ترفندهای موبایل	دانلود فیلمهای سینمایی	ترفنهای رجیستری	تصاویر دیدنی
اطلس رنگی زغال سنگ	زمین شناسی ایران	دانلود کتابهای تافل	دانلود کتابهایIELTS

دانلود نرم افزار	نرم افزارهای زمین شناسی	نشریات زمین شناسی	فلش زمین شناسی
کتابهای زمین شناسی	جدول تناوبی عناصر	کانی ها	سنگها

نشریه دوجا	زمین شناسی خزر	زمین شناسی خلیج فارس	یخچالهای ایران
گسلهای ایران مرکزی	گسل های زاگرس	افیولیتهای زاگرس	سرامیک
سیمان	ساینده ها	شیشه	طبقه بندی سنگهای صنعتی

پترولوژی	چینه شناسی	GPS	براکیوپودها
کارتوگرافی	آنالیز عناصر محدود	مکانیک سیالات	جزایر سدی
آنالیز گاز	ژئومورفولوژی	زمانهای زمین شناسی	سلستیت
مکانیک خاک	فرآیندهای هوازدگی	زمین شناسی زغال سنگ	زمین شناسی پزشکی
آتشفشان	فرآیندهای دگرگونی	دگرگونی	زمین شناسی دریایی
افیولیت ها	نهشت کانسارها	زمین شناسی مهندسی	رخساره های زمین شناسی

یخچالها	تششعات کیهانی	XRF	زمین شناسی عمومی
سنگهای دگرگونی	فسیلهای آثاری	تعیین سن با کربن ۱۴	عناصر Transuranium
رسوب شناسی	زمین لرزه	زمین شناسی باستانی	پوسته زمین
بریوزوآ	طراحی نقشه	تصویر سازی نقشه	کرینوئیدا

سفالوپود	کوهزایی	اکینودرماتا	رادیواکتیو در اردویسین
اثر گلخانه ای	رودخانه ها	بیابان و صحرا	زمین
خواص درونی زمین	جریانهای حرارتی زمین	منابع معدنی	نیروی گرانشی زمین
شبیه ساز زمین	سن زمین	الگوهای منابع زمین	جریانهای کشندی زمین

گوشته زمین	نوسانات زمین	آلودگی آب	نقشه برداری تطابقی
اکسیدها و هیدروکسیدها	کانی های سیلیسی	تسونومی و رسوبات	جزر و مد

رسوبات رودخانه ای	گسل	تحلیل گسل	گسل ترانسفورم
تریلوبیت	مگنزیت	کودهای شیمیایی	دیرگدازها

تحرکات آزاد کربناتها در طبیعت	چینه شناسی کربناتها	تکامل سکانس های کربناته	پتروگرافی سنگهای کربناته
رخساره کربناتها	طبقه بندی کربناتها	دانلود مقاله بافرمت pdf	دانلود مقاله بافرمت pdf
دانلود مقاله بافرمت pdf	دانلود مقاله بافرمت pdf	دانلود مقاله بافرمت pdf	دانلود مقاله بافرمت pdf

گاستروپودها	کمک ذوبها	زلزله شناسی	رسوب شناسی کربناتها

استخراج الکتریکی آبهای زیرزمینی	تونل	میکا	میکا

رسوبات عمیق دریایی	موجودات عمیق دریایی	اطلس رنگی فسیل شناسی	گالری تصاویر زمین شناسی

ماسرال های زغال سنگ	ژئوشیمی آلی	کانی ها و ذخائر معدنی	الکترسیته زمین

 

آخرین مطالب بارگذاری شده در وبلاگ

آموزش زبان انگلیسی بصورت آنلاین - صفحه اصلی - شنبه دوازدهم بهمن 1387
برترین نرم افزارهای آموزش زبان در دنیا - جمعه یازدهم بهمن 1387
الکتریسیته زمین - Geoelectricity - جمعه یازدهم بهمن 1387
تبدیل واحدهای علمی به یکدیگر - پنجشنبه پنجم دی 1387
اخبار ایران و جهان - کورد نیوز - جمعه بیست و نهم آذر 1387
امروز در دنیا چه خبر است - جمعه بیست و نهم آذر 1387
اخبار سایت زمانه - جمعه بیست و نهم آذر 1387
اخبار ایران و جهان - سایت it4u - جمعه بیست و نهم آذر 1387
اخبار و مقالات پزشکی پارسی طب - جمعه بیست و نهم آذر 1387
سرویس خبری هفت خبر - جمعه بیست و نهم آذر 1387
اخبار فن آوری اطلاعات و ارتباطات - سایت newsboy - پنجشنبه بیست و هشتم آذر 1387
اخبار استان قزوین - پنجشنبه بیست و هشتم آذر 1387
اخبار - زمین شناسی - پنجشنبه بیست و هشتم آذر 1387
اخبار - ورزشی - پنجشنبه بیست و هشتم آذر 1387
بررسی مهمترین عناوین روزنامه ها - پنجشنبه بیست و هشتم آذر 1387
اخبار امروز - صفحه دوم - پنجشنبه بیست و هشتم آذر 1387
اخبار - حوادث - پنجشنبه بیست و هشتم آذر 1387
اخبار - اخبار خارجی - پنجشنبه بیست و هشتم آذر 1387
جدیدترین اخبار ایران و جهان - پنجشنبه بیست و هشتم آذر 1387
آخرین خبرها - پنجشنبه بیست و هشتم آذر 1387
اخبار - تکنولوژی - پنجشنبه بیست و هشتم آذر 1387
اخبار - علوم پایه - پنجشنبه بیست و هشتم آذر 1387
اخبار - اخبار داخلی - پنجشنبه بیست و هشتم آذر 1387
اخبار - مسابقات علمی - پنجشنبه بیست و هشتم آذر 1387
اخبار - اختراعات و اکتشافات - پنجشنبه بیست و هشتم آذر 1387
اخبار - دانستنیها - پنجشنبه بیست و هشتم آذر 1387
اخبار - آموزش و پرورش - پنجشنبه بیست و هشتم آذر 1387
اخبار - کنکور - پنجشنبه بیست و هشتم آذر 1387
اخبار - محیط زیست - پنجشنبه بیست و هشتم آذر 1387
اخبار - نجوم - پنجشنبه بیست و هشتم آذر 1387
اخبار - آموزش‌عالی - پنجشنبه بیست و هشتم آذر 1387
اخبار - تحقیق و پژوهش - پنجشنبه بیست و هشتم آذر 1387
اخبار - فناوری‌اطلاعات‌و ارتباطات - پنجشنبه بیست و هشتم آذر 1387
اخبار - علوم پزشکی و بهداشتی - پنجشنبه بیست و هشتم آذر 1387
اخبار - تغذیه و سلامت - پنجشنبه بیست و هشتم آذر 1387
اخبار - کامپیوتر و اینترنت - سه شنبه بیست و ششم آذر 1387
Petroleum geology - زمین شناسی نفت - جمعه بیست و دوم آذر 1387
معرفی نرم افزار 123D Sim&Vis - جمعه بیست و دوم آذر 1387
دانلود نرم افزار زمین شناسی - Oziexplorer - جمعه بیست و دوم آذر 1387
نهشت کانسارها و کانی ها 2 -Ore and mineral deposits - پنجشنبه بیست و یکم آذر 1387
نهشت کانسارها و کانی ها 1-Ore and mineral deposits - پنجشنبه بیست و یکم آذر 1387
زئوشیمی آلی - Organic geochemistry - دوشنبه هجدهم آذر 1387
دانلود کتاب - آب و هوای مربوط به کواترنری - دوشنبه هجدهم آذر 1387
دانلود کتاب- تغییرات آب و هوایی در کواترنری - جمعه پانزدهم آذر 1387
موجودات عمیق دریایی-Deep-sea fauna - جمعه پانزدهم آذر 1387
رسوبات عمیق دریایی-Deep-marine sediments - جمعه پانزدهم آذر 1387
اطلس رنگی فسیل شناسی - جمعه پانزدهم آذر 1387

آموزش زبان انگلیسی بصورت آنلاین - صفحه اصلی

آموزش زبان انگلیسی بصورت آنلاین

جهت استفاده از این منبع، ابتدا فصل اول آن را مطالعه نموده و پس از اتمام درس و حل تمرینات مربوطه، وارد فصل بعدی شوید

Student's Book	Teacher's Book	Page Numbers
فصل اول	Chapter 1 - Teacher's Notes	(5-16)
Study Skills	Study Skills - Teacher's Notes	(18-24)
فصل دوم	Chapter 2 - Teacher's Notes	(25-36)
فصل سوم	Chapter 3 - Teacher's Notes	(37-50)
فصل چهارم	Chapter 4 - Teacher's Notes	(51-62)
فصل پنجم	Chapter 5 - Teacher's Notes	(63-76)
فصل ششم	Chapter 6 - Teacher's Notes	(79-94)
فصل هفتم	Chapter 7 - Teacher's Notes	(95-112)
فصل هشتم	Chapter 8 - Teacher's Notes	(113-128)
فصل نهم	Chapter 9 - Teacher's Notes	(129-144)
فصل دهم	Chapter 10 - Teacher's Notes	(145-162)
فصل یازدهم	Chapter 11 - Teacher's Notes	(163-175)
فصل دوازدهم	Chapter 12 - Teacher's Notes	(177-188)
Extra	Extra - Teacher's Notes	(191-207)

برترین نرم افزارهای آموزش زبان در دنیا

 

امروزه زبان انگليسي به يك پل ارتباطي گفتاري ميان مردم دنيا با يكديگر و به عبارتي زبان بين المللي و اول جهان مبدل گشته است و تمامي افراد براي پيشرفت در هر زمينه اي مستلزم تسلط بر اين زبان زنده و پوياي دنيا هستند . تمامي افراد در كشور عزيزمان براي يادگيري اين زبان در اولين گام پاي به موسسات و مراكز آموزشي مي گذارند تا با شبيه سازي محيطي انگليسي زبان از چندين و چند دانش آموزش يكديگر را در چنين محيطي قرار داده و بر اثر تكرار و تمرين در طول زمان مهارت سخن گفتن را به تدريج فرا گيرند . اين پديده كه در حدود يك يا چند سال و با صرف هزينه و زمان بسيار زيادي به طول مي انجامد كه در قياس با راههاي نوين امروزي ديگر امري مقرون به صرفه در دنياي بسيار پرمشعله امروزي از ديدگاه بسياري افراد به نظر نمي رسد.

بیش از ۸۵۰ ساعت آموزش

كمك گرفتن از پيشرفت هاي علم نرم افزار و بهره گيري از قابليت هاي رايانه يكي از مدرن ترين شيوه هاييست كه براي آموزش زبان مخصوصا زبان انگليسي در بسياري از كشورهاي پيشرفته دنيا مورد استفاده قرار مي گيرد .

Tell Me More Premium 9.0 نرم افزاري فوق حرفه اي و قدرتمند در زمينه آموزش زبان انگليسي كه از سوي اكثر منتقدان نرم افزار دنيا لقب "برترين نرم افزار آموزش زبان انگليسي دنيا " را از آن خود كرده است كه نمونه بارز آن جايگيري در رتبه اول و كسب مدال طلاي برترين نرم افزار آموزش زبان دنيا براي چندمين سال پياپي در وبسايت نقد نرم افزاري دنيا TopTenReviews است . به علاوه استفاده اين نرم افزار در بسياري از مراكز مطرح و علمي دنيا سبب موجب اطمينان اكثر خريداران از منحصر به فرد بودن و خريد آن شده است .

اين نرم افزار فوق العاده با هوش مصنوعي بالايش، درست همانند يك معلم خانگي فوق هوشمند و خستگي ناپذير، تمامي اركان مورد نياز براي آموزش زبان انگليسي و تمامي مهارت هاي لازم يادگيري هر زبان را همچون خواندن، نگارش، قدرت شنيدار، گفتار، دايره لغات و گرامر و حتي فرهنگ مورد نياز يادگيري كشورهاي سخن گوينده آن زبان را به تمرين و تكرار وا مي دارد و داراي سطوح مختلفي از مبتدي تا پيشرفته مي باشد كه براي تمامي افراد در پكيج هاي مختلفي از سوي كمپاني سازنده عرضه شده است .

چرا Tell Me More Premium 9.0 را برترين نرم افزار آموزش زبان دنيا مي ناميم ؟

- به دليل دارا بودن بيش از 5 ميليون كاربر راضي در سرتاسر دنيا كه آماري منحصر به فرد و چشمگير است .

- به دليل استفاده همه روزه در بيش از 10000 آموزشگاه، دانشكده و مراكز علمي آموزش زبان در سراسر دنيا .

قابليت هاي منحصر به فرد Tell Me More Premium 9.0 قدرتمندترين نرم افزار آموزش زبان انگليسي در دنيا :

- ارائه شده در قالب سطوح مجزا و كامل مناسب براي تمامي افراد ، مقدماتي - متوسطه - پيشرفته

- بيش از 2000 ساعت آموزش زبان انگليسي كه بيشترين و سنگين ترين نرم افزار آموزش زبان در دنياست !

- بيش از 5000 تمرين و 37 نوع و زير شاخه از فعاليت هاي تمريني كه در قالب شش طبقه بندي و كارگاه تمريني درسي، فرهنگي، لغات، پرسش و پاسخ شفاهي و نوشتاري .

ارائه شيوه هاي مختلف مراحل يادگيري زبان

- سيستم انتخابي تمريني يا Free-to-Roam كه انتخاب دسته تمرين هاي مورد نياز روز شما را به شما مي دهد .

- سيستم هوشمند Guided Mode كه به شما مسير هاي يادگيري و تمرين را بر طبق فعايلت هاي شما و ميزان استعدادتان پيشنهاد مي كند .

-  سيستم فوق هوشمند Dynamic Mode كه همانند يك معملم خانگي مرحله به مرحله پيشرفت شما را ارزيابي كرده و تمارين مورد نياز بعديتان را پيش رويتان قرار مي دهد .

بهره گيري از جديد ترين فن آوري هاي آموزش زبان در دنيا در زمينه گفتار يا Speaking

- سيستم تشخيص صداي بسيار پيشرفته كه صداي شما را به خوبي آناليز و

 شناسايي مي كند و ايراد تلفظي شما را رفع مي كند .

- بهره گيري از فن آوري نوين S.E.T.S. يا Spoken Error Tracking System كه به يافتن ايرادهاي تلفظي و نمايش دقيقي ايراد هاي شما مي پردازد كه با تمرين بلافاصله مانع تكرار آن در شخص و موجب تصحيح اين ايراد براي هميشه مي شود.

- بهره گيري از انيميشن هاي سه بعدي و شبيه سازي هاي صورت و حركات لب

 كه به يادگيري تلفظ صحيح كلمات بسيار كمك مي كند .

Tell Me More Premium Performance v9.0 نرم افزاری فوق حرفه ای و قدرتمند در زمینه آموزش زبان انگلیسی و نسخه جدید نرم افزار بسیار محبوب Tell Me More Premium 8.0 برای آموزش سطوح مختلف زبان است که از سوی شرکت Auralog برای آموزش الکترونیک و آسان زبان انگلیسی برای تمامی کاربران عرضه شده است و از سوی اکثر منتقدان نرم افزار دنیا لقب "برترین نرم افزار آموزش زبان انگلیسی دنیا " را از آن خود کرده است که نمونه بارز آن جایگیری در رتبه اول و کسب مدال طلای برترین نرم افزار آموزش زبان دنیا برای چندمین سال پیاپی در وبسایت نقد نرم افزاری دنیا TopTenReviews است . منتقدان سایت TopTenReviews این نرم افزار را "بهترین گزینه نرم افزاری در دسترس برای آموزش زبان انگلیسی معرفی کرده اند و آن را به وضوح در صدر نرم افزارهای همرده در زمینه آموزش زبان قرار داده اند". به علاوه استفاده این نرم افزار در بسیاری از مراکز مطرح و علمی دنیا موجب اطمینان اکثر خریداران از منحصر به فرد بودن و خرید آن شده است .

این نرم افزار حرفه ای شامل 2000 ساعت آموزش زبان انگلیسی در 10 سطح مختلف از مقدماتی تا پیشرفته است که با خود 10000 تمرین مختلف برای یادگیری مهارت های مختلف زبان انگلیسی را داراست ! (هم انگلیسی امریکایی American English و هم انگلیسی بریتانیایی British English)

که تمامی مهارت های یادگیری زبان از قبیل Listening یا مهارت گوش دادن، Speaking یا مهارت صحبت کردن، Reading یا مهارت خواندن و Writing یا مهارت نوشتن را در کنار تمرینات متنوع گرامری Grammer ، لغات Vocabulary و حتی تمرینات مرتبط با آشنایی با فرهنگ انگلیسی Culture داراست ! تمامی تمرین ها در محیطی کاملا Interactive و پویا و به صورت چندرسانه ای همراه با نرم افزارهای مختلف درونی دیالوگ و تشخیص صدا همراه است !
- بهره گیری از قدرتمندترین نرم افزار تشخیص صدا در دنیای نرم افزارهای آموزشی

Tell Me More Performance 9.0 از آخرین فن آوری نرم افزاری تشخیص صدا بهره می برد که تاثیر گذار ترین راه برای بهبود تلفظ یک شخص زبان آموز است !

شما به زیبایی هنگام تلفظ به اشتباهات خود پی میبرید و نرم افزار به صورت کاملا هوشمند با هوش مصنوعی بالای خود ایراد های شما را به شما در محیطی انیمیشن و با گراف های نموداری مختلف می گوید تا شما آنها را رفع نمایید!
- بیش از 10 ساعت ویدیو آموزشی
بهره گیری از ویدیو های آموزشی چند رسانه ای که علاوه بر آشنایی با فرهنگ زبان، شما خود را در نقش شخصیت های ویدیو نیز قرار می دهید !

قیمت روی جلد این نرم افزار ۸۵۰۰ تومان بوده که حاوی ۴ دی وی دی و ۲ سی دی است. اما می توانید این نرم افزار ارزشمند را از طریق لینکهای زیر دریافت نمایید.

http://rapidshare.com/files/103838198/Tell_Me_More_Plus.part01.rar

 

http://rapidshare.com/files/103841612/Tell_Me_More_Plus.part02.rar

 

http://rapidshare.com/files/103843444/Tell_Me_More_Plus.part03.rar

 

http://rapidshare.com/files/103845362/Tell_Me_More_Plus.part04.rar

 

http://rapidshare.com/files/103847497/Tell_Me_More_Plus.part05.rar

 

http://rapidshare.com/files/103849816/Tell_Me_More_Plus.part06.rar

 

http://rapidshare.com/files/103851852/Tell_Me_More_Plus.part07.rar

 

http://rapidshare.com/files/103853937/Tell_Me_More_Plus.part08.rar

 

http://rapidshare.com/files/103856268/Tell_Me_More_Plus.part09.rar

 

http://rapidshare.com/files/103858242/Tell_Me_More_Plus.part10.rar

 

http://rapidshare.com/files/103860310/Tell_Me_More_Plus.part11.rar

 

http://rapidshare.com/files/103862263/Tell_Me_More_Plus.part12.rar

 

http://rapidshare.com/files/103862984/Tell_Me_More_Plus.part13.rar

 

الکتریسیته زمین - Geoelectricity

Geoelectricity

  

Electromagnetic phenomena and electric currents, mostly of natural origin, that are associated with the Earth. Geophysical methods utilize natural and artificial electric currents to explore the properties of the Earth's interior and to search for natural resources (for example, petroleum, water, and minerals). Geoelectricity is sometimes known as terrestrial electricity. All electric currents (natural or artificial, local or worldwide) in the solid Earth are characterized as earth currents. The term telluric currents is reserved for the natural, worldwide electric currents whose origins are almost entirely outside the atmosphere. Geoelectromagnetism is a more comprehensive term than geoelectricity. Time variations of any magnetic field are associated with an electric field that induces electric currents in conducting media such as the Earth.

 

 

Fig. 1  Time variations of the horizontal orthogonal components of the natural (a) magnetic and (b) electric fields, simultaneously measured at one site at the surface.

 

 

 

 

Magnetic fields, electric fields, and electric currents are the constituents of electromagnetism, and are related by Maxwell's equations. For instance, Fig. 1 shows the time variations of the natural magnetic and electric fields simultaneously measured at one location at the surface of the Earth. These two traces are related to each other, not only by Maxwell's equations but also by the physical properties of the subsurface rocks in the vicinity of the measuring site. Either one of the two traces may be computed synthetically from the other if the properties of the subsurface rocks are known. Conversely, the two traces together can yield geologic information; this is a form of geophysical exploration or prospecting. Thus, the terms geoelectricity, geomagnetism, and geoelectromagnetism are essentially interchangeable, although each one may have a somewhat different emphasis. For example, the term geomagnetism is sometimes used for the study of the Earth's quasi-stationary main magnetic field. See also: Geomagnetism

Measurements of electric and magnetic fields

 A component of the electric field in a desired direction is measured by planting two electrodes (for example, metal stakes or special nonpolarizable electrodes) aligned in that direction. The electrodes are connected by an insulated wire, and voltage difference between them is measured with a voltmeter of high input impedance (for example, 10 megohms). The average electric field between the electrodes is expressed in units of volts per meter. Since this unit is very cumbersome for measuring the Earth's field, it is customary to use millivolts per kilometer. (Figure 1b and Fig. 2 show the time variations of such components.) To obtain the total horizontal electric field, two orthogonal components, north–south (N–S) and east–west (E–W), are measured by means of an L-shaped electrode array. The trajectory of the head of the electric field vector is traced by feeding the two components into an oscilloscope or a paper X–Y recorder (Fig. 3). The magnetic field is measured by magnetometers. The cryogenic magnetometer has a resolution of better than 1 picotesla, 1 part in 50,000,000 of the Earth's total magnetic field. The nanotesla (nT) or gamma γ is used in practice. Figure 1a shows the time variations of one horizontal component of the Earth's natural magnetic field, measured with a coil-core magnetometer whose output is the time derivative of the magnetic field, with the scale given in terms of nanoteslas times frequency. Worldwide studies of natural electromagnetic phenomena are made by monitoring primarily the magnetic field rather than the electric field, which is much more affected by local geology.

Fig. 2  Two tellurograms (stations 1 and 2, San Joaquin Valley, California) representing the time variations of the natural electric field (micropulsations), N60°E components, simultaneously recorded over a time interval of 30 min. The recording sites are separated by 27 mi (43 km) in the direction of the components. PST = Pacific Standard Time.

 

 جهت مشاهده عکس در اندازه واقعی، بر روی آن کلیک نمایید

 

Fig. 3  A vectogram representing a few minutes of recording of the natural electric field vector. The band-pass filter peaked at the 20-s period (0.05 Hz).

 

 

 Electric earth currents

 These may be local or worldwide.

 Fig. 4  Approximate and schematic frequencies and origins of the natural electromagnetic fields.

 

 

 Local

 Such currents can be natural or caused by human activities. The latter (called stray, industrial, or cultural currents) may be caused by electric trains, rural water pumps, and pipelines. Natural local currents represent the phenomena of spontaneous potentials or self-potentials. Some deposits in the Earth, such as certain metallic sulfides and graphite, constitute buried natural electric cells because of their high electrical conductivity and also because of oxidation and reduction processes associated with ground water. Thus, a hidden ore body, such as a copper ore deposit, can be discovered by measuring the electric field at the surface of the Earth, which may be as large as 1 V over a distance of 300 ft (100 m). Two other sources of spontaneous potentials are ground water movements and topographic elevation changes.

 Worldwide

Telluric currents are of natural origin. There are various types, sources, and frequencies (or periods) of the worldwide natural electromagnetic fields which are associated with electric currents in the Earth (Fig. 4). The time variations of these electromagnetic fields are simply called variations.

 Secular variations

 The Earth's main magnetic field is thought to be caused by motions in the electrically conducting fluid core of the Earth, which acts as a kind of dynamo, creating electric currents which in turn create the magnetic field. This field is not stationary, but has time variations with periods ranging from about 30 to 300 years per cycle, which are the secular variations. Electric currents at the surface of the Earth associated with the main field and its secular variations have not been monitored effectively because of the difficulties involved in separating them from other effects, such as electrode potentials and tidal potentials. See also: Geomagnetic variations

 

Diurnal (daily) variations

 The air layers of the ionosphere, from a height of about 60–200 mi (100–300 km), are ionized by solar radiation, while air below the ionosphere is practically nonconducting. The ionization (electrical conductivity) in the ionosphere is renewed daily. Tidal oscillations of the ionosphere in the presence of the Earth's main magnetic field constitute an atmospheric dynamo, inducing electric currents in the Earth. They are thought to be driven primarily by the thermal effects of the Sun and partially by the attraction of the Moon (Fig. 5). See also: Ionosphere

 

 Fig. 5  Diurnal variations (solar plus lunar) of the horizontal component of the magnetic field, December 21, 1933, Huancayo, Peru. (After S. Chapman and J. Bartels, Geomagnetism. 2 vols., Oxford University Press, 1962)

 

 

 Exospheric-origin variations, or micropulsations

 Shorttime fluctuations of the Earth's magnetic field (micropulsations) that fall within the approximate period range of 0.2–600 s per cycle (5–0.0017 Hz) occur almost continuously as a background noise. Amplitudes depend on latitude, solar activity, frequency, local time, season, and local geology, with worldwide and long-term statistical amplitudes of the order of a few millivolts per kilometer and a few tenths of a nanotesla. While the mechanism of their generation is not completely understood, it appears that micropulsations are generated by the magnetohydrodynamic effect through the interaction of the solar wind with the main magnetic field and atmosphere of the Earth. Study of the exospheric-origin electromagnetic phenomena constitutes a branch of geophysics called aeronomy. Figure 1 is a record of micropulsations measured at stations located in a sedimentary basin. The magnetic field trace (Fig. 1a) is called a magnetogram; the electric field trace (Fig. 1b) a tellurogram. Figure 2 shows two tellurograms simultaneously measured at two stations 27 mi (43 km) apart and in the direction of station separation. These measurements represent normal, usual activity on a quiet day. Figure 6 shows the amplitude spectra of the tellurograms shown in Fig. 2. The differences between the two tellurograms, and consequently between the two spectra, are almost totally due to the differences in the geologic conditions at the two measuring sites (stations). Such measurements can be used for geologic exploration of the subsurface. See also: Magnetohydrodynamics; Seismic stratigraphy; Solar wind; Upper-atmosphere dynamics

 

Fig. 6  Amplitude spectra of the tellurograms shown in Fig. 2.

 

 Magnetic storms are very intense disturbances of long duration that occur about once a month on the average. Caused by large-scale bursts of solar wind associated with sunspots and solar flares, they usually commence suddenly and almost instantaneously (within about 0.5 min) throughout the world. Their amplitudes may reach hundreds of nanoteslas and hundreds of millivolts per kilometer, disrupting radio and telegraph communications. It is interesting to note that they cause fish to migrate into deeper waters. Figure 7 shows the records of a magnetic storm. Magnetic storms are frequently associated with aurorae polares (northern or southern lights), which are seen as spectacular luminous formations at ionospheric heights. See also: Aurora

 

 

Fig. 7  Three components of the magnetic field of a magnetic storm of May 14, 1921, Potsdam, Germany. (After S. Chapman and J. Bartels, Geomagnetism, 2 vols., Oxford University Press, 1962)

 

 Atmospherics

 The major cause of the variations within the frequency range of about 5–10 kHz is the lightning occurring almost continuously in Central Africa and in the Amazon region. While audio-frequency variations are included in atmospherics, lightning itself is a concern of meteorology. See also: Lightning; Sferics

 Stellar variations

 Above the frequency of 30 MHz, these originate predominantly from the direct radiation of electromagnetic waves propagated by the Sun.

 Subsurface  geophysical  exploration

 Electrical methods, more properly called electromagnetic methods, are used to explore the subsurface from depths of a few inches (for example, popular coin detectors or mine detectors) down to depths of hundreds of miles. In general, these methods require an input into the Earth, either an artificial direct or alternating electric current, or a natural electromagnetic field, such as micropulsations or diurnal variations. This input is a source signal coupled with the Earth, which behaves as a filter whose response is measured in terms of electric or magnetic fields. It is analogous to measuring the input and output of an electronic filter to determine its characteristics, which in this case is the geologic information sought. These methods supply only the electrical properties of the subsurface (mainly the electrical conductivity). Different rocks have, in general, different conductivities. For instance, limestones usually have much lower conductivities than clay-rich shales. A knowledge of the conductivity distribution in the subsurface, combined with other geologic information, allows interpretation of the rock-type distribution. Artificial direct-current methods involve feeding a current into the Earth with a pair of electrodes and measuring the resulting electric field with another pair of electrodes. The alternating-current methods use magnetometers to measure the magnetic field created by inducing currents in the Earth. The two most popular methods employing the natural electromagnetic fields are the magnetotelluric and telluric methods. The magnetotelluric method requires simultaneous measurements of the electric and magnetic fields at one site. Figure 1 represents such a data set. The telluric method requires only the measurements of the electric field, made simultaneously at two or more sites (Fig. 2). These electromagnetic (or electrical) methods are unlike the magnetic methods of geophysical exploration, which deal only with the magnetization of rocks due to the main magnetic field of the Earth. See also: Geophysical exploration

 

Bibliography

•  G. V. Keller and F. C. Frischknecht, Electrical Methods in Geophysical Prospecting, 1966
• Ali Fazeli = egeology.blogfa.com
• S. H. Yungul, The telluric methods in the study of sedimentary structures: A survey, Geoexploration, 15:207–238, 1977
• Ali Fazeli = egeology.blogfa.com
• M. S. Zhdanov and G. V. Keller, The Geoelectrical Methods in Geophysical Exploration, 1993
• Ali Fazeli = egeology.blogfa.com