SEMICONDUCTORS
At that place are materials that really occupy a place between the conductors of the current and the not-conductors. They are called semiconductors. These materials conduct electricity less readily than conductors but much better than insulators.
Semiconductors include nigh all minerals, many chemical elements, a great variety of chemical compounds, alloys of metals, and a number of organic compounds. Like metals, they conduct electricity but they do it less effectively. In metals all electrons are costless and in insulators they are fixed. In semiconductors electrons are stock-still, too, but the connexion is so weak that the heat motion of the atoms of a body easily pulls them abroad and sets them free.
Minerals and crystals appear to possess some unexpected properties. It is well known that their conductivity increases with heating and falls with cooling. Equally a semiconductor is heated, free electrons in it increment in number, hence, its conductivity increases as well.
Heat is past no means the only phenomenon influencing semiconductors. They are sensitive to light, as well. Take germanium equally an example. Its electrical properties may greatly change when it is exposed to light. With the assistance of a ray of light directed at a semiconductor, nosotros can start or cease various machines, consequence remote control, and perform lots of other useful things. Just as they are influenced by falling light, semiconductors are likewise influenced by all radiation. Generally speaking, they are so sensitive that a heated object can be detected by its radiation.
Such dependence of electrical conductivity on estrus and light has opened up great possibilities for diverse uses of semiconductors. The semiconductor devices are applied for transmission of signals, for automatic control of a variety of processes, for switching on engines, for the reproduction of sound, protection of high-voltage transmission lines, speeding up of some chemic reactions, and and then on. On the one hand they may be used to transform light and estrus energy directly into electric free energy without any complex machinery with moving. parts, and on the other hand, they are capable of generating heat or cold from electricity.
Russian engineers and scientists turned their attention to semiconductors many years ago. They saw in them a means of solving an old applied science problem, namely, that of direct conversion of oestrus into electricity without boilers or machines. Semiconductor thermocouples created in Russia convert heat straight into electricity simply as a complex system consisting of a steam boiler, a steam engine and a generator does it.
II. Give the English language equivalents for the words and discussion combinations below:
i) �������������; 2) ���������� ����������; 3) �����; four) �����������; 5) ��������; vi) ����������� (��); 7) ����������; 8) �������������� �; 9) ����������; ten) ���; eleven) ���������� ��; 12) ������������� ����������; 13) ��������, ������������; 14) ������; 15) ���������; 16) ������ ���������� ��������; 17) ������������.
Iii. Guess the significant of the following international words:
chemical element, organic, mineral, crystal, phenomenon, automatic, control, procedure, reproduction, conversion, banality.
Four. Bring together the beginnings and ends:
Semiconductors are sensitive to� | � conductors of the electric current and not-conductors. |
Semiconductors convert estrus into � | � dependence of conductivity on estrus and light. |
Semiconductors occupy a place between � | � oestrus and light. |
Semiconductors conduct electricity | �into electricity without machines. |
Smashing possibilities for various uses of semiconductors are connected with � | � less effectively than metals. |
As a semiconductor is heated � | � its conductivity increases also. |
Five. Insert words and expressions:
1) Semiconductors include a great variety of (���������� ����������), (������ ��������).
ii) Minerals and crystals announced to possess some unexpected (��������). Their conductivity increases with (����������) and falls with (����������).
3) With the assistance of a ray of calorie-free directed at a semiconductor, we can upshot (������������� ����������).
4) The semiconductor devices are practical for (�������������� ��������) of a variety of processes, for the (���������������) of audio, (���������) of some chemical reactions.
5) (�������������) created in Russia convert estrus directly into electricity.
VI. Reply the questions:
1) What do semiconductors include? 2) How does the atomic structure of semiconductors influence their properties? 3) What phenomena influence semiconductors? 4) What are the semiconductor devices applied for? v) How do semoconductors aid in solving engineering bug?
VII. Talk on the properties of semiconductors and their practical application
UNIT 8
I. Read the text
ELECTRICITY AND MAGNETISM
TEXT 1
Electromotive Force
When free electrons are dislodged from atoms, electrical energy is released. Chemic reaction, friction heat and electromagnetic induction will crusade electrons to move from one atom to some other. Whenever energy in any form is released, a force called electromotive (east. thousand. f.) is developed.
If the force exerts its endeavor always in i direction, it is called direct; and if the force changes its direction of exertion periodically, information technology is called alternate. The chemical reaction in a dry out cell, estrus and friction are sources of a unidirectional force. Electromagnetic induction produces an alternate force. The direction of strength depends on the direction in which the field is cut. Whenever an eastward. m. f. is developed, there is also a field of free energy called an electrostatic field, which tin can be detected by an electroscope and measured by an electrometer.
TEXT 2
Electromagnetic Induction
An electromotive strength is induced in the conductor when there is a modify in the magnetic field surrounding a conductor. This induced electromotive force may be produced in several ways equally follows:
a. A usher may motility in a stationary magnetic field of abiding strength.
b. A stationary conductor may exist exposed 'to a moving magnetic field of constant force.
c. The force of the field surrounding the conductor may change without any motility of conductor or magnetic circuit.
The electromotive strength induced by motion of a conductor or a magnetic flux is the same when the usher rotates and the flux is stationary or the flux rotates and the conductor is stationary. If both, conductor and flux, rotate in the aforementioned management at the same speed, no electromotive forcefulness will exist produced, if they rotate at the same speed but in contrary directions, the electromotive forcefulness induced would be twice as that which would be induced, if ane of them was stationary. An electromotive force is not induced when a conductor is moved parallel to the lines of forcefulness, simply but when it moves at an angle with these lines.
Any movement across the direction of the lines, however, volition produce an electromotive forcefulness in the usher. For this reason, the usher is said to �cut� the lines of force. The actual electromotive force induced in the conductor depends upon the nature at which the flux is cutting.
TEXT 3
ELECTROMOTIVE Force AND RESISTANCE
The electromotive force is the very force that moves the electrons from ane point in an electric circuit towards another. In instance this due east. 1000. f. is direct, the current is directly. On the other hand, were the electromotive strength alternating, the current would exist alternate, too. The eastward. k. f. is measurable and information technology is the volt that is the unit used for measuring it. A electric current is unable to flow in a circuit consisting of metallic wires alone. A source of an e. g. f. should exist provided besides. The source under consideration may be a prison cell or a battery, a generator, a thermocouple or a photocell, etc.
In addition to the electromotive force and the potential difference reference should be made to another important factor that profoundly influences electrical flow, namely, resistance. All substances offering a certain amount of opposition, that is to say resistance, to the passage of electric current. This resistance may be high or low depending on the blazon of excursion and the material employed. Drinking glass and rubber offering a very loftier resistance and, hence, they are considered every bit good insulators. All substances do allow the passage of some electric current provided the potential divergence is loftier enough.
Sure factors can greatly influence the resistance of an electric circuit. They are the size of the wire, its length, and type. In short, the thinner or longer the wire, the greater is the resistance offered.
II. Requite the English equivalents for the words below. Observe in the text the sentences with these words and translate them
1) ������; 2) ��������������� ����; three) �������; four) ������������ ����������; 5) �������������; 6) ���������������� ��������; 7) ���������� ���; 8) ���������� ����������; ix) �����������.
III. Guess the meaning of the post-obit international words and translate them:
reaction, electrostatic, electrometer, electroscope, volt, metallic.
IV. Say whether these sentences are true or faux:
1. Alternating force always exerts its attempt in ane direction.
2. Alternating force is produced by electromagnetic consecration.
3. The electromotive force is induced past motion of a usher.
4. Resistance is an important factor that greatly influences electrical flow.
5. The type of the material employed doesn�t influence the resistance.
V. Answer the questions:
1) What factors cause the movement of electrons from one atom to some other? two) When is the electromotive force developed? 3) When does an electrostatic field appear? iv) How is the electromotive force induced? 5) What unit is used for measuring the electromotive forcefulness? 6) What are the sources of electromotive force? 7) What is called �resistance�? viii) How do the types of circuit and material influence the resistance? 9) Name the factors that influence the resistance of an electric excursion.
Unit of measurement 9
I. Read the text
Dynamos
The term �dynamo� is practical to machines which convert either mechanical free energy into electric energy or electrical energy into mechanical energy past utilizing the principle of electromagnetic induction. A dynamo is called a generator when mechanical energy supplied in the grade of rotation is converted into electrical energy. When the free energy conversion takes place in the opposite order the dynamo is called a motor. Thus a dynamo is a reversible machine capable of operation as a generator or motor every bit desired.
A generator does non create electricity, simply generates or produces an induced electromotive strength, which causes a current to menstruation through a properly insulated system of electric conductors external to information technology. The amount of electricity obtainable from such a generator is dependent upon the mechanical energy supplied. In the excursion external to a generator the east. thou. f. causes the electricity to menstruum from a higher or positive potential to a lower or negative potential. In the internal circuit of a generator the e. m. f. causes the current to flow from a lower potential to a higher potential. The action of a generator is based upon the principles of electromagnetic induction.
The dynamo consists essentially of two parts: a magnetic field, produced past electromagnets, and a number of loops or coils of wire wound upon an iron core, forming the armature. These parts are arranged then that the number of the magnetic lines of force of the field threading through the armature, coils volition be constantly varied, thereby producing a steady e. m. f. in the generator or a constant torque in the motor.
2. Fill in the gaps with the words given beneath:
to convert, generator, reversible, obtainable, induction, loops
1. The term �dynamo� is applied to machines which.....either mechanical energy into electrical or on the contrary electrical energy into mechanical energy.
2. A dynamo is a..... machine capable of operation as a generator or motor equally desired.
three. The amount of electricity..... from such a generator is dependent upon the mechanical energy supplied.
four. The activity of a generator is based upon the principles of electromagnetic...... .
v. The dynamo consists of 2 parts: a magnetic field, produced by electromagnets, and a number of.....or coils of wire.
Three. Find the Russian equivalents for the following English words and word combinations:
1) to be applied to smth.; 2) to convert smth. into smth.; 3) rotation; 4) to utilize; v) a properly insulated system; 6) internal (external) excursion; vii) capable of functioning; eight) positive (negative) potential; nine) reverse order; ten) free energy conversion.
IV. Answer the questions
ane. What term can be applied to machines converting mechanical energy into electrical and vice versa?
2. What kind of automobile is a dynamo?
3. What is the function of a generator?
4. What is the action of a generator based upon?
five. What parts does the dynamo consist of?
Five. Talk on the dynamo action
Unit x
I. Read the text
GENERATORS
The powerful, highly efficient generators and alternators that are in use today operate on the same principle equally the dynamo invented by the great English scientist Faraday in 1831.
Dynamo-electric machines are used to supply light, heat and power on a large scale. These are the machines that produce more than 99.99 per cent of all the earth's electric power.
There are two types of dynamos � the generator and the alternator. The erstwhile supplies d. c. which is similar to the current from a battery and the latter provides a. c. To generate electricity both of them must be continuously provided with energy from some outside source of mechanical energy such as steam engines, steam turbines or water turbines.
A generator is an electric machine, which converts mechanical free energy into electric energy. In that location are direct-electric current (d. c.) generators and alternating-current (a. c.) generators. Their construction is much akin. A d. c. generator consists of stationary and rotating elements. The stationary elements are: the yoke or the frame and the field structure. The yoke forms the closed circuit for the magnetic flux. The function of the magnetic structure is to produce the magnetic field.
The rotating elements are: true armature and the commutator. They are on the same shaft. The armature consists of the core and the winding. The winding is continued to the commutator. With the help of the brushes on the commutator that deport the electric current to the line the winding is connected to the external circuit. The stationary chemical element of an a. c. generator is called a stator. The rotating element is called a rotor.
The essential difference betwixt a d. c. generator and a. c. generator is that the former has a commutator by means of which the generated e. m. f. is made continuous, i. due east. the commutator mechanically rectifies the alternating due east. m. f. so that it is always of the same polarity.
D. c. generators are used for electrolytic processes such every bit electroplating. Large d. c. generators are employed in such manufacturing processes equally steel making. The d. c. generator of small capacities is used for various special purposes such as arc welding, automobile generators, train lighting systems, etc. Information technology also finds rather extensive use in connection with communication systems.
II. Give the Russian equivalents for the post-obit English words and word combinations:
1) generator; 2) alternator; 3) steam turbine; iv) water turbine; 5) armature; half dozen) rotor; 7) stationary; viii) commutator; 9) stator; 10) yoke; eleven) brushes; 12) core; 13) frame; xiv) winding.
Three. Make full in the blanks
1. A generator is an electric machine, which a) ----- mechanical energy into electrical energy.
2. A direct-electric current generator consists of b) ----- .
3. The dynamo was invented past c) ----- in 1831.
4. The d. c. generator is used for diverse purposes such as d) ----- .
IV. Work out the plan of the text
V. Speak on the post-obit points:
ane. The construction of a generator.
two. The straight current generators and their industrial awarding.
UNIT 11
I. Read the text
Principal Structural Elements of a D. C. Automobile
A direct-current motorcar consists of ii chief parts, a stationary part, commonly called the stator, designed mainly for producing a magnetic flux, and a rotating part, called the armature or the rotor. The stationary and rotating parts should be separated from each other by an air-gap. The stationary function of a d. c. machine consists of master poles, designed to create the principal magnetic flux; commutating poles interposed between the main poles; and a frame. Information technology should be noted here that sparkless operation of the auto would exist impossible without the commutating poles. Thus, they should ensure sparkless operation of the brushes at the commutator.
The main pole consists of a laminated core the end of which facing the armature carries a pole shoe and a field coil through which direct current passes. The armature is a cylindrical body rotating in the space betwixt the poles and comprising a slotted armature core, a winding inserted in the armature slots, a commutator, and a brush gear.
The frame is the stationary part of the machine to which are stock-still the main and commutating poles and past means of which the machine is bolted to its bedplate. The ringshaped portion which serves as the path for the main and commutating pole fluxes is called the yoke. Finish-shields or frame-heads which carry the bearings are besides fastened to the frame.
Of these chief structural elements of the car the yoke, the pole cores, the armature cadre and the air-gap betwixt the armature core and the pole cadre are known to form the magnetic circuit while the pole coils, the armature windings, the commutator and brushes should class the electric circuit of the machine.
II. Translate the following phrases, using the given variants of translation:
to consist � �������� : to consist of a stationary part and a rotating office;
separated � ��������� �������������: the stationary and rotating parts should be separated from each other by an air gap;
to serve � ������� � �������� ����-����: the ringshaped portion or yoke serves as a path for the master and commutating pole fluxes.
III. Join the beginnings and the ends
Beginnings | Ends |
The stationary parts of a d. c. machine are.... | a laminated core the terminate of which carries a pole shoe and a field coil. |
The two primary parts of a direct current machine are.... | main poles, commutating poles and a frame |
The main pole consists of.... | A stationary function or stator and a rotating office, chosen the armature or the rotor. |
Iv. Arrange synonyms in pairs and memorize them:
a) to consist of; to be separated from; to create; to be interposed betwixt; to pass; to rotate;
�) to be divided with; to produce; to introduce into; to permeate; to scroll; to revolve; to comprise.
V. Write out the names of the machine parts and describe their operational characteristics
Unit of measurement 12
I. Read the text
The Alternator
The alternator is an electric car for generating an alternating current by a relative move of conductors and a magnetic field. The auto ordinarily has a rotating field and a stationary armature. In a synchronous alternator the magnetic field is excited with a straight current. The direction of an induced due east. m.f. is reversed each time when a conductor passes from a pole of one polarity to a pole at some other polarity. Most machines of this type are used for lighting and power, simply in that location are alternators with a revoking armature and a stationary field. They are used in minor sizes more often than not for special purposes.
Any electric auto is reversible. When a machine is driven by a source of mechanical power, it works as a generator and delivers electric ability. If it is connected to a source of electric power, it produces mechanical energy, and operates as a motor. The alternator may also be operated as a motor.
The a-c. generator, or alternator, does not differ in principle from the d. c. generator. The alternator consists of a field construction and an armature. The field structure is magnetized by a field winding conveying a. direct electric current. An electromotive force is generated in tine winding of the armature. In alternators the field is ordinarily the rotating element and the armature is stationary. This structure has a number of advantages. Only ii rings are needed with a rotating field. These rings deport only a relatively light field current, at a voltage generally of 125, and seldom exceeding 250. The insulation of such rings is not difficult. A stationary armature requires no slip rings. The leads from the armature can be continuously insulated from the armature winding to the switchboard, leaving no bare usher. The alternator with a rotating field may be further divided into the vertical and the horizontal types.
The vertical blazon is usually applied for large water-bike generators where it is desirable to mountain the water turbine below the generator. The more mutual horizontal type is used with diesel and steam engine drive. A low-speed alternator of this type is suitable for a diesel fuel engine drive, a high speed alternator is suitable for a steam turbine drive.
Ii. Form nouns, denoting devices with the help of the suffix � or. Translate them
To alternate, to commute, to conduct, to generate
3. Read the text and write out the key words, characterizing the alternator
IV. Translate the following discussion combinations paying attention to the Participle two
The leads from the armature can be continuously insulated from�.., the vertical type of alternator applied for large water-wheel generator; alternators with a revoking armature and a stationary field used in small sizes generally for special purposes; a machine driven by a source of mechanical power; the direction of an induced e. yard. f. �
V. State 5 questions to the text
Half dozen. Points for give-and-take:
one. The structure of the alternator;
2. The application of the alternator.
Unit 13
I. Read the text
The Induction Motor
An induction motor like any other motor consists of a stationary part, the stator, and a rotating function, the rotor. The rotor of an induction motor is not continued electrically to the source of power supply. The currents which circulate in the rotor conductors are the outcome of voltage induced in the rotor in the magnetic field fix by the stator. The rotor is fitted with a ready of conductors in which currants flow. As these conductors lie in the magnetic field produced by the stator, a force is exerted on the conductors and the rotor begins to revolve. The operation of the motor depends upon the production of a rotating magnetic field. The speed at which the field of an induction motor turns is called the synchronous speed of the field or of the motor.
The induction motor is the simplest of the diverse types of electric motors and it has constitute more all-encompassing application in industry than any other blazon. It is made in two forms � the squirrel cage and the wound rotor, the difference being in the construction of the rotor.
The stator of the induction motor has practically the same slot and winding organisation every bit the alternator and has the coils arranged to class a definite number of poles, the number of poles being a determining factor in connection with the speed at which the motor will operate. The rotor construction, however, is entirely unlike.
The squirrel-cage rotor is a simpler form and has been used in many machines.
Instead of coils the winding consists of heavy copper confined.
The wound-rotor blazon has a winding made up of well-insulated coils, mounted in groups whose end connections are brought out to fill in rings. The purpose of this winding is to provide for variation in the amount of resistance included in the rotor excursion.
Provision for ventilation is made by leaving passageways through the cadre and frame, through which air is forced by fan vanes mounted on the rotor. In master cases the motors at present congenital in as an integral part of the automobile information technology is to drive.
In that location being no electric connexion between the rotor circuits of the consecration motor and the stator circuits, or supply line, the currents which menses in the rotor bars or windings correspond to the induced voltages, the action existence like to that of a transformer with a movable secondary. With but a unmarried-stage winding on the stator, all the same, the torques produced in the two halves of the rotor would be in apposition, and the motor would not start. With more than one set of windings 2 for a ii-stage motor, 3 for a three-phase motor a resultant field is produced which has the effect of cut across the rotor conductors and induces voltages in them. This field is considered to be revolving at compatible speed.
The term �revolving field� should not be taken to mean actual revolution of flux lines. The magnetic field from the coils of each phase varies in force with changes in electric current value but does non motility around the stator. The revolutions are those of the resultant of the three, or two, phases, every bit the case may be. A motor with a single-phase winding is not cocky-starting but must be provided with an auxiliary device of some kind to enable the motor to develop a starting torque. The consequence of the revolving field is the same as would issue from actual revolution of a stator having direct-electric current poles. As voltages have been induced in the confined or windings of the rotor, currants get-go flowing every bit a result of these voltages, and a torque is produced which brings the motor up to speed.
Ii. Find in the text the English language equivalents for the discussion combinations given below:
1) ����������� ���������; 2) ����������� �����; three) ����������� �����; 4) ���������; v) ������������� ��������; 6) ������� ����������; 7) ���; eight) �������� �������; nine) �������������; 10) ��������� ������.
Iii. Complete the following sentences according to the contents of the text
1. The Induction Motor is ��.. of electric motors and is more than extensively applied in manufacture than any other blazon.
2. The purpose of this winding is ��.. for variation in the corporeality of resistance included in the rotor circuit.
3. The effect of �. is the same every bit would outcome from actual revolution of a stator having direct-current poles.
Four. Answer the following questions:
ane. What parts does the induction motor consist of?
ii. What are the names of its rotating and stationary parts?
iii. What does the motor operation depend on?
four. How tin the deviation between stator and rotor construction exist explained?
5. What does the term �revolving field� mean?
Five. Interpret the sentences from the text paying attention to the Nominative Absolute Participle Constructions:
1. The induction motor is made in 2 forms � the squirrel muzzle and the wound rotor, the difference being in the construction of the rotor.
2. The stator of the induction motor has practically the same slot and winding arrangement equally the alternator and has the coils arranged to form a definite number of poles, the number of poles beingness a determining factor in connectedness with the speed at which the motor will operate.
3. There beingness no electrical connectedness betwixt the rotor circuits of the consecration motor and the stator circuits, or supply line, the currents which flow in the rotor bars or windings stand for to the induced voltages, the action being similar to that of a transformer with a movable secondary.
Six. Discuss the following points:
1) The construction of an induction motor;
two) Induction motor operation principle.
UNIT 14
I. Read the text
Types of Induction Motors
TEXT one
Unmarried � PHASE MOTOR
The unmarried-stage induction motor differs from poly-phase type principally in the character of its magnetic field, equally an ordinary single-stage winding will not produce a rotating field, only a field that is oscillating, and the induced currents and poles produced in the rotor by this field volition tend to produce equal torque in opposite directions, therefore, the rotor cannot start to revolve. Withal, if the rotor can in some manner be fabricated to rotate at a speed corresponding to the frequency of the current in the stator windings then the reaction of the stator and rotor flux is such equally to produce a torque that will keep the rotor revolving.
In practice the starting of single-stage induction motors is achieved by 3 general methods applicable to minor-sized motors only.
First: the divide-stage method, in which an auxiliary stator winding is provided for starting purposes only, this winding being displaced from the main stator winding by 90 electrical degrees. It has a college inductance than the main stator winding, thus causing the currant in it to lag far enough behind the current in the main winding to produce a shifting or rotating field during the starting period, which exerts a starting torque on the rotor sufficient to crusade rotation.
When near normal speed has been reached the auxiliary winding is out of circuit by a switch and clutch in the motor, which operates automatically by centrifugal force, and the rotor continues to run equally a unmarried-phase motor. The starting torque of such motions being express, they are frequently synthetic with the rotor arranged to circumduct freely on the shaft at starting until nearly normal speed is reached, at which fourth dimension the load is pitched up by the automatic action of a centrifugal clutch.
Second: an auxiliary winding may be continued to the single-stage line through an external inductance and a switch (for disconnecting the auxiliary winding from the circuit subsequently the motor has reached normal speed), the introduction of the inductance in the auxiliary winding splitting the phase equally before.
TEXT 2
Three � Phase INDUCTION MOTOR
The iii-phase induction motor is the most commonly used type. Information technology has been widely used in recent years. Normally an induction motor consists of a cylindrical core (the stator) which carries the primary coils in slots on its inner periphery. The main coils are arranged for a three-phase supply and serve to produce a revolving magnetic field. The stator encircles a cylindrical rotor carrying the secondary winding in slots on its outer periphery.
The rotor winding may be one of ii types: squirrel-cage and slip-ring for wound-rotor). In a squirrel-cage machine the rotor winding forms a complete closed excursion in itself. The rotor winding of a slip-band machine is completed when the slip rings are connected either directly together or through some resistance external to the machine. The rotor shaft is coupled to the shaft of the driven machinery.
The rotor is stationary at some instant of time. The revolving magnetic field of the stator winding cuts across the stationary rotor winding at synchronous speed and induces an due east. m. f. in information technology. The due east. m. f. volition give rise to a current which sets up a magnetic field. The rotor starts rotating.
It is the interaction between the rotor current and the revolving magnetic field that has created torque and has acquired the rotor to rotate in the same management every bit the revolving magnetic field. Tine speed of the rotor is 98�95 per cent of the synchronous speed of the revolving magnetic field of the stator. Hence another proper noun for this type of motor is the asynchronous motor. As a matter of fact, the speed of the rotor cannot exist equal to synchronous speed. If it were equal to the latter, the revolving magnetic field would not be able to cut the secondary conductors and in that location would non exist whatsoever current induced in the secondary winding and no interaction betwixt the revolving field and the rotor current, and the motor would not run.
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