RESISTANCE AND CONDUCTANCE SUPERCONDUCTIVITY

Hydrofracturation (Figure) allow to measure directly both the orientation of the horizontal components od stress (S_H et S_h) and the magnitude of this stress (S_H - S_h). This technique is based on the rock fracture in presence of fluids using a fluid pressure larger than the lithostatic pressure.

Figure 6.8. The hydrofracturation technique. A section of the borehole is isolated in-between inflating packers, and a liquid is injected in the isolated portion up to fracture (P_fract). After fracturation, pressure decreases and stabilizes at a Pic value.

Can you represent the different stages of hydrofracturation in a Mohr diagram ?

These techniques give a measurement of the local state of stress. However the local state of stress is perturbated by the borehole itself, or by the pressure induced by the packers. In certains cases, the measured stress values can be corrected, for example by modeling the stress trajectories aroung the borehole.

The fractures are viewed, either directly via their print-marks onto packers placed alon the borehole, or indirectly by imaging them (Figure).

Figure. Printmarks (recorded on a packer) of the microfractures resulting from hydrofrac-turation, and observed after extraction from the borehole.

Figure ; Images obtained through tele-cameras introduced in a borehole (1050 deep) before (left-hand side) and after (righ-hand side) hydraulic fracturation. In-between the white arrows, the imaged fracture has a ESE azimuth.

This technique is the most precise for the determination of the orientations and magnitudes of S_h and S_H.

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Exercice : Traduire cette légende et expliquer la succession des 3 figures suivantes qui illustrent comment la contrainte se concentre autour d’un trou de forage.

RESISTANCE AND CONDUCTANCE SUPERCONDUCTIVITY

Subtechnical vocabulary

load (noun)

the supply of electricity to a particular place

The external energy source includes the wires, loads, switches, etc.

galvanic cell

a cell by zinc producing electricity

A galvanic cell is an elementary electric circuit.

incandescent (adjective)

giving a bright light when heated

An incandescent lamp is a device in which we can observe some forms of energy.

internal ( adjective)

inside something

Internal combustion engine produces power by burning petrol.

external(adjective)

outside surface of something

Electric circuit is divided into internal and external circuits.

vessel (noun)

a tube that carries liquid

Two vessels are filled with liquid.

rheostat ( noun)

a piece of equipment that controls the loudness of a radio or the brightness of an electric

light.

Electric circuit consists of a 2-V battery, rheostat, a voltmeter, etc.

drop ( verb)

to fall to a lower level.

From Ohm’s law, the voltage drop in volts is equal to the current in amperes.

copper (noun)

a reddish-brown metal used for making wires

Copper is the most commonly used metal in electric engineering.

brass (noun)

a very hard bright yellow metal that is a mixture of copper and zinc

Brass is an alloy of 50-70 per cent of copper and 30-50 per cent of zinc.

lead (noun)

a soft easy metal

Lead is a soft-ductile metal grayish in color.

tin (noun)

a soft white metal is used to cover and protect iron and steel

Tin is a silver-white metal, which resists the action of water and air.

tungsten ( noun)

a hard metal that is one of the elements used in making steel

Tungsten is necessary constituent part in making steel.

mercury (noun)

a heavy silver white metal that is liquid at ordinary temperature

Mercury is poisonous, especially its fumes.

A. Learn to recognize the following international words.

potential, difference, terminal, electric, force, free, electrons, kinetic energy, resistant, cycle,

conductor, body, rheostat, resistor, ammeter, material, temperature, factor, section, meter,

machine, apparatus, cable, engineering.

B. Learn the pairs of antonyms and synonyms, translate them.

below – above tiny - huge

useful – useless liquid - solid

easy – difficult unexpected – expected

field – sphere low - high

full – complete conductivity – non-conductivity

to lose – to find advantage - disadvantage

C. Translate the following sentences from English into Russian, paying attention to the new

lexical minimum.

1. The flow of electrons in a conductor is called an electric current.
2. An elementary electric circuit consists of a source of electric energy which may be a galvanic battery, a storage battery, a generator, etc.
3. An electric circuit is divided into internal and external circuits.
4. The internal circuit consists of the energy source, while the external source includes wires, loads, switches, instruments, etc.
5. The temperature of a conductor affects its resistance.
6. The resistance of metals increases with increasing temperature, while that of liquids and carbon decreases.
7. There are several metals, such as manganin, constantan, nickeline, whose resistance remains practically unaffected by temperature rise.
8. The unit of resistance is the ohm, often designated by the Greek letter ‘omega’.
9. A thousand ohms equal one kiloohm.
10. A million ohms make one megaohm.
11. Electric engineering uses chemically pure, refined copper, which goes to make wires, cables and other things.
12. The property of a conductor to pass electric current is called conductance.

D. Read the text, give it the title and explain what electromotive force, voltage, voltmeter

are.

For an electric current to flow continuously around a circuit, the terminals of the

energy source must be maintained at different potentials. A very close analogy is provided by two vessels filled with water to different levels and connected by a tube: water will flow from one vessel into the other as long as the difference in their levels is maintained.

The factor that establishes and maintains the potential difference and causes a current

to flow around a circuit against its internal and external resistance is called electromotive

force (abbreviated EMF and designated by the symbol E).

Electromotive force can be produced in several ways. In chemical sources of electric

energy ( galvanic cells and storage battery), the EMF is set up by the action of certain

chemical solutions on dissimilar metals, in electric generators it is developed by a

combination of magnetic and mechanical means, in thermo cells it is set up by thermal

energy.

The difference of potentials at two points that causes a movement of electricity from

one point to the other is called voltage.

Both emf and voltage are measured in volts by means of voltmeters. The volt has

several multiples and submultiples: the kilovolt, or a thousand volts, and the millivolt,

or one-thousandth of a volt, being the most common ones. Voltages in the millivolt range

are measured with a millivolt meter and in the kilovolt range by a kilovolt meter.

In measuring the emf of a source, a voltmeter should be connected to its terminals

with the external circuit open. For a measurement of the voltage of a partial circuit,

a voltmeter should be connected across that portion of the circuit.

E. Choose the correct response to complete sentences.

electric current electromotive force

resistivity voltage

voltage drop zero

1. The flow of electrons in a conductor is called ……….. ( riccelet rentcur).
2. The resistance in ohms of a conductor 1 meter long and 1 mm² in cross-section is called………. . (sistiretyvi).
3. The factor that establishes and maintains the potential difference and causes a current to

flow around a circuit against its internal and external resistance is called ………..

( vemotitroelec cefor).

1. The difference of potentials at two points that causes a movement of electricity from one point to the other is called ………. ( agevolt).
2. Reduction in voltage across various points down a circuit is called ………( lovtage podr).
3. Kirchhoff’s first law states that the algebraic sum of the currents flowing into a circuit junction is ………. (roze).

F. Read and translate the text, make up 7 questions to it.

Date: 2014-12-28; view: 1257