The Most Turbulent Period in Modern America History Research Paper

The Most Turbulent Period in Modern America History - Research Paper Example In terms of racial inequality, no other time period has come to match the 1960’s in terms of turbulence and instability. This decade saw the uprising of African Americans who were fighting back against the widespread racism and inequality. These series of protestations came to be known as The Civil Rights Movement(Brunner, 2007). Although it began in prior decades, the movement grew in terms of size and effectiveness during this particular time period. Segregation was one of the forefront issues for those seeking equality. Segregation was the separation of African American and Caucasian peoples. This meant that the two races had separate schools, separate restaurants and bathrooms, even separate water fountains. The 1960’s featured the African Americans fighting back and demanding for segregation to be outlawed. Martin Luther King became an important figure and leader throughout this tumultuous time period and often spoke of the importance of peace in regard to the mult itude of riots which occurred as a result of these protests. The American government was compelled to react to the racial inequality as the voices of the African American people—and those who stood with them—grew louder. One such change took place in 1964 when the 24th Amendment was created which abolished the poll tax(Brunner, 2007). The poll tax was originally created in the mid to late 1800’s with the end of the Civil War and the beginning of Reconstruction. The poll tax made it so that people had to pay a specific tax in order to vote. This Jim Crow law made it virtually impossible for African Americans in the south to be able to vote as they often did not have the funds necessary to pay the tax. By abolishing the tax in 1964, one particular road block was removed for the African Americans who had been deterred from exercising their right to vote prior to this(Brunner, 2007). Another important change in terms of how America dealt with race relations also occurred in 1964 when President Johnson signed the Civil Rights Act of 1964. (Trueman, 2010) This important piece of legislature became one of the most significant events in American social policy. The basic premise of the Civil Rights Act prohibited discriminating against anyone based on race, color, religion, or creed(Brunner, 2007). Perhaps President Johnson was convinced to sign the legislature due to the fact that around the same time, the Freedom Summer occurred where both African Americans and Caucasians traveled down to the south in order to convince other African Americans to register for voting(Trueman, 2010). A great deal of violence, threats, and even murder occurred during this short time period which could have been a deciding factor for Johnson since the Civil Rights Act originally was conceived of four years earlier. It also made it possible for the government to end segregation(Brunner,2007). Schools slowly had to integrate African Americans into the student population and often times these instances were met with a great deal o f protest from racist Caucasians and media attention. Not only did America experience many important changes in racial equality, the country also began to experience an important shift in its culture. The cultural changes occurred because of the American youth in the 1960’s. Literature, music, and education were particularly impacted during this time period and reflected the evolving mindset of the decade. Some of the more influential books that were published included â€Å"

Romanticism and Transcendentalism Essay Example for Free

Romanticism and Transcendentalism Essay 1. After reviewing the Romanticism resource page, list three characteristics of Romanticism. Also, identify three authors of the Romantic period. * Three characteristics of Romanticism are appreciation of nature, idealism and nationalism. Three authors of the Romantic Era: Edgar Allan Poe, William Cullen Bryant and Lord Byron. 2. Using the Transcendentalism resource page, list three characteristics of Transcendentalism * Three characteristic of Transcendentalism are nature, intuition and the thought of God being a part of nature. 3. How did Transcendentalists feel about nature? What did Transcendentalists feel about the inherent nature of human beings (were humans inherently good or evil)? * Transcendentalists had much respect for nature and believed in the best and goodness of humans. 4. Describe two specific things Thoreau learned about life by translating the lines below in your own words: I went to the woods because I wished to live deliberately, to front only the essential facts of life, and see if I could not learn what it had to teach, and not, when I came to die, discover that I had not lived. I wanted to live deeply and suck out all the marrow of life. (Walden) * Walden wanted to learn more about life in order to understand it completely by living it. I think Walden got to comprehend that some things aren’t necessary in order to live happy and in the right way. He realized that he didn’t really know what life was, until he was to experience things himself. 5. Which two great passive resistance leaders were influenced by the premise of Transcendentalism through the works of Thoreau and Emerson? *

Relationship Between Piggy And Ralph :: essays research papers

Growing relationship between Piggy and Ralph In order to complete this assignment one must look at too distinct characters. One is Piggy. Piggy represents the law and order of the adult world. He is the superego, the part of man’s personality, which attempts to act according to an absolute set of standards. Throughout the novel, Piggy attempts to condition the island society to mirror the society they all lived in when they were in England. Piggy’s continual references to his auntie demonstrate this philosophy. He tries to pull Ralph towards the reason-oriented side of human nature. The Other Character in the combination is Ralph. Ralph, a tall, blond, twelve-year-old boy, establishes himself as the leader of the boys when he blows the conch shell to call the first assembly. Throughout the story, he struggles to maintain order, forced to compete with Jack for respect. The relationship between Ralph in Piggy is somewhat complicated. Lord of the Flies a novel by William Golding begins with these two characters. One the first several pages the initial interaction between piggy and Ralph is described. At first Piggy is very eager to see that another boy beside himself has survived the plane crash. Piggy is very enthusiastic to introduce himself and get to know Ralph. In fact he is too enthused. This introduction partially alienates Piggy. However Ralph notices that Piggy is a competent individual and may be of value.   Ã‚  Ã‚  Ã‚  Ã‚  Throughout the book Ralph is mean to Piggy. This comes in part from his security with him. Ralph knows that he is Piggy’s only defense. Piggy is described as an outsider on page 21 when the narrator says â€Å"For a moment the boys were a closed circuit of sympathy with Piggy on the outside...† Ralph, nonetheless, does start relying on Piggy’s policies. One of these policies is building shelters so that they would be protected. Ralph also likes Piggy’s idea of using the conch shell to call meetings. Ralph and Piggy are also exposed to the dark side together this brings them closer. This is portrayed on page 152, â€Å"Piggy and Ralph, under the threat of the sky, found themselves eager to take a place in this demented but partly secure society. They were glad to touch the brown backs of the fence that hemmed in the terror and made it governable.

Enron :: GCSE Business Marketing Coursework

Enron Executives at high-flying Enron Corp. (ENE ) never seemed overly concerned with how the rest of the world viewed their business practices. Earlier this year, the California Attorney General had to get a court order to collect documents in an industrywide investigation into energy price fixing. And when an analyst challenged former CEO Jeffrey K. Skilling in a conference call to produce Enron's balance sheet, Skilling called him an "ass----." Still, even some Enron executives worried that the company had gone too far with two complex partnerships set up in 1999 to buy company assets and hedge investments. With Enron's then-chief financial officer acting as general manager of the partnerships and in a position to personally benefit from their investments, the potential for a conflict of interest and backlash from investors seemed overwhelming. "Internally, everybody said this is not a good idea," says a source close to the company. But no one could have predicted such a jaw-dropping outcome for the nation's largest and most innovative energy trader. Since Oct. 16, when Enron revealed a $35 million charge to earnings to reflect losses on those partnerships and was forced to knock $1.2 billion off its shareholders' equity, the company's stock has plunged 60%. The Securities & Exchange Commission is investigating Enron's accounting for its partnerships and whether it properly disclosed them to investors. Suddenly the company, which brought high-tech and complex finance to energy trading, is essentially trying to avoid a run on the bank. Moody's Investors Service has already downgraded the company's debt. Enron says it is meeting with credit agencies to calm their fears, and analysts say Enron is working on a turnaround plan that would likely include accelerating asset sales, issuing shares, and obtaining new credit lines. Enron's board has set up a special committee to look into its controversial partnerships. But analysts also worry that Enron's trading partners could pull the plug if they lose confidence that it can honor its trades. "ON CRACK?" Inside Enron, once-cocky employees are reeling. They were still puzzling over the abrupt Aug. 14 departure of CEO Skilling when the company announced on Oct. 24 that CFO Andrew S. Fastow, architect of the controversial private LJM investments--which got their name from the first initials of his wife and children--was removed from his post and on leave. In a tense meeting held at a Houston hotel after the latest financial disclosures, soft-spoken Chairman and CEO Kenneth L.

Chopper Fed Dc Motor

INTRODUCTION During the nineteenth century, when power supply was dc, dc motors were used extensively to draw power direct from the dc source. The motor speed could be varied by adjusting field current by a rheostat. That was an open loop control. Most of the drives were constant speed and the characteristics could not be matched with a job requirement. A vast development in the dc drives system took place when the ward Leonard Control System was introduced in the 1980s. The system was motor-generator system to deliver power to the drive motor. The supply power available was still dc and dc motor was used to drive the dc generator set at a more or less constant speed. Afterwards when the ac power system came into existence and became popular, ac motors were developed and became attractive owing to their constructional simplicity, ruggedness and lower initial as well as maintenance cost. Machine requiring variable speed drives use the ward Leonard System employing ac motors driving dc motors at a constant speed. In the 1950s electronic came into existence and brought about remarkable improvement in the speed control system. The open- loop manual control system was replaced by close loop feedback control, which resulted in improved response and better accuracy. Initially, gas diodes and ignitrons were developed and ac to dc converters were used to control dc motors. The advent of thyristors capable of handling large current has revolutionized the field of electric power control. Thyratrons, ignitrons, mercury arc rectifiers, magnetic amplifiers and motor generator sets have all been replaced by solid state circuits employing semi-conductor diodes and thyristors. Thyristor controlled drives employing both ac and dc motors find wide applications in industry as variable speed drives. In the 1960s ac power was converted into dc power for direct control of drive motors with solid state devices (high power silicon diodes and silicon controlled rectifiers). Initially saturable reactors were employed in conjunction with power silicon rectifiers for dc drives. Of late solid state circuits using semi- conductor diodes and thyristors are becoming popular for controlling the speed of ac and dc otors and are progressively replacing the traditional electric power control circuit based on thyratrons, ignitrons, mercury arc rectifiers, magnetic amplifiers, motor-generator sets, etc as compared to the electric and electro-mechanical systems of speed control. The electronic system has higher accuracy, greater reliability, and quick response and also has higher efficiency as there is no I2R losses and moving parts. Moreover four-quadrant speed control is possi ble to meet precise high standards. All electronic circuits control the speed of the motor by controlling either, ? The voltage applied to the motor armature or ? The field current or ? Both of the above DC motors can be run from dc supply if available or from ac supply, after it has been converted to dc supply with the help of rectifiers which can be either half wave or full wave and either controlled ( by varying the conduction angle of the thyristors used) or uncontrolled. AC motors can be run on the ac supply or from dc supply, after it has been converted into ac supply with the help of inverters (opposite of rectifiers). As stated above, the average output voltage of a thyristors controlled rectifiers by changing its conduction angle and hence the armature voltage can be adjusted to control its speed. When run on a dc supply, the armature dc voltage can be changed with the help of uncontrolled rectifiers (using only diodes and not thyristors). The dc voltages so obtained can be then chopped with the help of a thyristors chopper circuit. In this method of speed control of a dc motor, available ac supply is first rectified into dc supply using uncontrolled rectifiers. The supply is then filtered and smooth ended dc output is supplied to the thyristors chopper. It allows dc to flow through for the time Ton and then disconnects for the time Toff. This cycle is repeated. During supply-on period (i. e. for the time period Ton) the dc motor gets supply and accelerates. During the supply off period Toff (i. e. for the time period Toff) there is no supply to the motor and the motor decelerates till the next on cycle begins. If the cycles repeated continuously at a definite frequency and the elements of the cycle are maintained in a fixed relationship, the motor will then operate at a constant voltage across the motor will be, V0 = (V*Ton)/(Ton +Toff) = (V*Ton)/T = f*V*Ton The dc voltage across the motor can be control by varying the Time Ratio Control (TRC) which may be accomplished by, ? Varying the duration of the on-time, Ton keeping the total time period, T or frequency, f constant ? Keeping the on- time, Ton constant and varying the frequency, f. ? Varying both. The Variable dc voltage below the supply dc voltage is made available to the dc motor and therefore, the motor speed available is below base speed. For automatic control of speed, both current feedback and speed feedback is used. BRIEF DISCUSSION ON CHOPPER A dc chopper is a static device used to obtain variable dc voltage from a source of constant dc voltage. The dc chopper offers great efficiency, faster response, smooth control, lower maintenance, small size, etc. Solid state chopper due to various advantages are widely used in the battery operated vehicles, traction motor control, control of a large number of dc motors from a common dc bus with a considerable improvement of power factor. PRINCIPLE OF CHOPPER OPERATION: A chopper is a thyristors on/ off switch that connects load to and disconnects it from the supply and produces a chopped load voltage from a constant input voltage. The chopper is represented by a thyristors (SCR). It is triggered periodically and is kept conducting for a period Ton and is blocked for a period Toff. During the period Ton, when the chopper is on, the supply terminals is connected to the load terminals. And during the interval Toff when the chopper is off, load current flows from the freewheeling diode Df. So, the load terminals are short circuited by Df and load voltage is therefore zero during Toff. Hence the chopper dc voltage is produced at the load terminals. Now, the average load voltage, Eo is given by Eo = Edc*? [? =Duty Cycle=(Ton/Toff)] Or, Eo = Edc*(Ton/T) [T=Ton + Toff] So the voltage can be varied by varying the duty cycle, ? of the chopper. CLASSIFICATION OF CHOPPER: Power semiconductor devices are used in chopper circuits are uni-directional device. A chopper can however operate in any of the four quadrants by an appropriate arrangement of semiconductor devices. These characteristics of their operation in any of the four quadrants form the basis of their classification as, 1. Type-A or First Quadrant Chopper 2. Type-B or Second Quadrant Chopper. 3. Type-C or Two Quadrant Type-A Chopper 4. Type-D or Two Quadrant or Type-B Chopper 5. Type-E or Four Quadrant Chopper. PERFORMANCE EQUATION OF DC MOTORS The equivalent circuit and on its basis the performance equation of a separately-excited dc Motor and series dc motor are presented below. ? Separately-excited dc motor: The equivalent circuit of a separately-excited dc motor coupled with a load under steady state condition is shown in the fig 4. 1. The load torque, TL opposes the electro-magnetic torque, Te. For the field circuit, Vf = If*rf For the armature circuit, Vt = Ia + Ia*ra Motor back emf or armature emf, Ea=Ka ? Ia=Km? m ————– (4. 1) Te=ka ? Ia = KmIa Also, Te = D wm + TL where, rf=Field circuit resistance in ohm, Ia=Armature current in A, Vt=Motor terminal voltage in V, ra=Armature circuit resistance in ohm, Km=Ka ?=Torque constant in Nm/A*emf constant in V-sec/rad, m=Angular speed of motor in rad/sec, D=Viscous friction constant in Nm-sec/rad. Electromagnetic power, P=wmTe watts From equation (1), Ea=Kmwm=Vt-Iara Or wm= (Vt – Iara)/Km= (Vt – Iara)/Ka ? ——————– (4. 1) So it is seen from equation (4. 2) that speed can be controlled by varying, ? Armature terminal voltage, Vt : This method is k nown as Armature-voltage control. Speed below base speed is obtained by this method. ? Field flux, ? : This method is known as Field flux control. Speed above base speed is obtained by this method. ? DC Series Motor: In a dc series motor, field winding is in series with the armature circuit. It is designed to carry the rated armature current. The fig. shows the equivalent circuit of a dc series motor driving load with load torque, TL. For the armature circuit, Vt = Ea + Ia ( ra+ rs ) †¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦.. (4. 3) Te = Ka ? Ia For no saturation in the magnetic circuit, ? = CIa Hence, Te = KaCIa2 = KIa2 Also, Ea = Ka ? wm = KaCIawm = KIawm From eqn (4. 3), Vt = KIawm + Ia (ra + rs) = Ia [ Kwm + (ra + rs)] Or, speed wm = (Vt/ KIa) – (ra +rs)/K †¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦. (4. 4) where, rs = Series field resistance in ohm, K = KaC = constant in Nm/A2 or in V-sec/ A- rad. CLOSED LOOP CONTROL OF CHOPPER FED DC MOTOR For practical purposes motors are required to operate at desired speed with low losses to meet the desired load –torque characteristics which depends on the armature current. Suppose a motor is operating at a particular speed an suddenly a load is applied, the speed falls and the motors takes time to come up to the desired speed . but a speed feed back with an inner current loop provides faster response to any disturbance in speed command ,load torque and supply voltage. Another reason for the requirement of feedback loop in dc drives is that, the armature of a large motor represents very small impedance which when supplied with nominal voltage would result in an excessive current of up to 10 times the nominal value. Under normal conditions, this is prevented by the induced armature voltage, E which cancels most of the applied voltage, Va so that only the difference is driving the armature current, Ia. But under transient conditions or steady state over load of the motor, there is always a danger of excessive currents due to sudden torque demand and rapidly changing armature voltage or speed . t is therefore important to provide a fast current or torque limit to protect the motor, the power supply and the load. This is best realized by feedback control establishing an effective safe guard against electrical and mechanical stresses. In it the output of the speed controller, Ec is applied to the current limiter which sets the reference current, Ia (ref erence) for the current loop. the armature current is sensed by a current sensor, after being filtered by an active filter to remove ripples which is then compared with the reference current, Ia (ref. the error current is processed through a current controller whose output, Vc adjusts the firing angle of the chopper and brings the motor speed to the desired value. Any positive speed error caused by an increased in either speed command or load torque demand can produce a high reference current, Ia (ref) the motor accelerates to correct the speed error and finally settles down at any reference current, Ia(ref) which makes the motor torque equal to the load torque resultant in a speed error closed to zero. For any large positive speed error, current limiter saturates and limits the reference currents, Ia (ref) to a maximum value, Ia (max) the speed error is then corrected at the maximum permissible armature current ,Ia(max)until the speed error becomes small and the current limiters comes out of the saturation . normally ,the speed error is corrected with the Ia less than the maximum permissible armature current, Ia max. For speeds below the base speeds, the field error, Ef is large and the field controller saturates thereby applying the maximum ield voltage and current. The speed control from zero to base speed is normally done at the maximum field by armature voltage control. When the speed is closed to the base speed, Va is almost near the rated value and field controller comes out of saturation. The speed control above base speed is generally done by field weakening at the rated armature voltage. In the field control loop, the back emf Eb is compared with a reference voltage , Eb ( ref) the value of which is generally between 0. 85 to 0. 95 of the rated armature voltage. For a speed command above the base speed, the speed error causes a higher value of Va then motor accelerates, back emf , Eb increases and field error, Ef decreases. The field current when decreases and the motor speed continue to increase until it reaches the desired speed. In this mode of operation, the drive responds slowly due to large field time constant. A full converter is generally used in the field because it has the ability to reverse the voltage thereby reducing the field current much faster as compared to the semi converter. MODELING AND OBSERVATIONS ? Modeling using Matlab: ? DC Motor with Load Parameter given: Voltage = 220v Current = 6. 2A Ra = 4 ohm La = 0. 072H Speed = 1470 rpm J = 0. 0607 kg-m2 Kb= 1. 26v/rad/sec Bt =0. 0869N-m/rad/sec Parameters calculated: Ta=La/Ra= 0. 02sec Tm=j/Bt =0. 7sec K1 = Bt/[KB2 + Ra Bt] =0. 0449 -1/T1 – 1/T2 =-1/2[Bt/J +Ra/La] + sqre[1/4(Bi/J + Ra/La)2-{(Kb2 + Ra Bt ) /JLa}] T1 = 0. 1077sec T2 = 0. 0208sec Tm = J/Bt = 0. 7sec DC MotorTransfer function: I(s)/V(s) =[k1(1+sTm)]/ [(1+sT1)(1+sT2)]= [0. 032s+0. 045]/[0. 002s2+0. 4s+1] wm(s)/I(s)= Kb/Bt(1+sTm) =14. 5/(1+0. 75) Converter Transfer function Kr =1. 35V/Vcm =1. 35*230/10 =31. 05V/v Tr = 1/12*Fs = 1/12*50 =0. 00166sec T. F = kr/(1+sTr) =31. 05/(1+0. 00166s) Design of Current Controller Tc=T2=0. 0208sec K = T1/2Tr = 0. 1077/2*0. 00166 = 32. 43 Kc = KTc/k1HCKrTm =32. 43 *0. 0208/0. 0449*1*31. 05*0. 7 =0. 69 Transfer function Gc(s) = Kc(1+sTc)/sTc = 0. 69(1+0. 0208s)/0. 0208s = 0. 69 + 0. 0143s/0. 0208s Current Loop I(s)/I*(s) = Ki/(1+sTi) Ti = T3/1+ kfi Ki = kfi/Hc(1+ kfi) Kfi = KcKrKiTmHc/Tc Kfi = 0. 9*31. 05*0. 0449*0. 7*1/0. 0208 Kfi = 32. 44 Ki = Kfi/HC(1+ Kfi) Kfi = 32. 44/1*(1+32. 44) Kfi = 0. 97 Ti = T3/(1+ Kfi) = T1+Tr/(1+ Kfi) = 0. 1077+0. 00166/1+32. 44 = 0. 0032sec Speed controller Design T4 = Ti + Tw K2 = Ki Kb Hw /Bt Tm K2 = 0. 97*1. 26*1/0. 0869*0. 7 K2 = 20. 092 KS = 1/(2 Kt T4) KS = 1/2*20. 092*0. 0032 KS = 7. 77 Ts = 4T4 =4*0. 0032 Ts = 0. 0128 Transfer function T. F = KS (1+sTS)/sTS = 7. 77(1+0. 0128s)/0. 0128s = (7. 77 + 0. 0994)/0. 0128s ? Modeling using PSIM: Parameters Given: Source (Vdc) = 800V Transistor (npn): Saturation Voltage = 0 Initial Position = 0 Current Flag = 1 Gating Block (G): Frequency = 50Hz Number of Points = 2 Switching Points = [0 180] Diode (D): Diode Voltage Drop = 0 Initial Position = 0 Current Flag = 0 Inductor (L): Inductance = 0. 01 Initial Current = 0A Current Flag = 0 Capacitor (C): Capacitance = 0. 00005F Initial Capacitive Voltage = 0V Current Flag = 0 DC MOTOR (DCM): Ra = 0. 055 ohm La = 0. 01H Rf = 55 ohm Lf = 0. 02H MI = 0. 2 Vt = 440V Ia = 80A If = 4A n = 1500rpm Torque Flag = 0 Master/Slave Flag = 1 Field Source = 400V Speed Sensor (Ws): Gain = 1 Simulation Control: Time Step = 1e-005 Total Time = 0. 02 Print Time = 0 Print Step = 1 Load Flag = 0 Slave Flag = 0 INDUSTRIAL APPLICATIONS DC drives are highly versatile energy conversion devices. It can meet the demand of loads requiring high starting, accelerating and decelerating torques. At the same time dc drives are easily adaptable for wide range of speed control and quick reversal. So, in industrial application where accurate control of speed and / or torque is required chopper controlled dc drives are unrivalled. Therefore, chopper controlled dc motors are universally employed in steel and aluminum mills, power shovels, electric elevators, railway locomotives and large earth moving equipments. Uses o Various Chopper Controlled DC drives with reasons: | | | | |Types of DC drives |Applications |Advantages | | | |Accurate speed control can be done. |Separately Excited dc drives |Used in paper mills, steel rolling |Variation of speed from very high to low value can be| | |mills, diesel-electric propulsion of |done | | |ships, etc. | | | | |Starting torque is very high upto 500%. | | |Maximum momentary operating torque is upto 400%. | | | |Speed regulation is widely variable. It is very high | |Series dc drive |Used in hoists, cranes, conveyors, |at no load. | | |trolley-cars, electric locomotives, |Speed control by series field. | | |etc. | | |Used in lathes, centrifugal pumps, |Starting torque is medium, usually limited to 250% by| |Constant speed dc shunt drive |reciprocating pumps, fans, blo wers, |a starting resistance but may be increased. | | |conveyors, spinning and weaving |Maximum momentary operating torque is usually limited| | |machines, etc. to about 200% by commutation. | | | |Speed regulation is about 5-10 %. | | | |Speed increases about 200% by field control and | | | |decreases by armature voltage control. | | |Starting torque is medium, usually limited to 250% by| | | |a starting resistance but may be increased. | | | |Maximum momentary operating torque is usually limited| |Adjustable speed dc shunt drives |Used for application requiring |to about 200% by commutation. | |adjustable speed control, either | | | |constant torque or constant output. | | SCOPE OF MODIFICATIONS Chopper controlled dc drives are widely used in hoists, cranes, elevators, shears, crushers, conveyor, blending mills, punch presses, air compressors, ice making machines, tractions, etc. So these drives should be modified in the following ways to make them more efficient and accurate, 1. The chopper controlled dc motors should be made with large diameter armatures and large pole size of reduced height. 2. The yoke as well as the main and commutating poles should be well laminated to reduce the eddy current effect and to improve the commutation. 3. Large numbers of commutator bars should be used to reduce the voltage between the commutator segments and to improve the commutation. 4. The commutator should be made larger in order to provide extra insulation to withstand large and rapid voltage fluctuations. 5. Compensating windings should be used in large motors to reduce the armature reactions effects. 6. The current densities used for the armature and Interpol windings should be reduced as compared to the conventional dc motors of the same frame size and rating in order to reduce the effect of heating of armature and Interpol. 7. Low inertia armature should be employed for improving the response. 8. Split brushes of good commutating quality should be used for reducing the effect of transformer voltage in the coil undergoing commutations. 9. Better class of insulation should be used to allow higher temperature rise and dissipation of more losses from a given frame. 10. Now a days chopper controlled dc drives are widely used in the automobile industries. So, it should have high efficiency and accuracy, light weight, low maintenance cost. BIBLIOGRAPHY 1. Electric Drives – Ramakrishnan, Prentice Hall India. 2. Power Electronics – P. S. Bimbhra, Khanna Publishers. 3. Software: MATLAB 6. 5 and PSIM.

Free Essays on Thanks To My Mother

Thanks to My Mother by Schoschana Rabinovici is one of the most moving memoirs I have ever read about the Holocaust. Born Susie Weksler, Rabinovici was only eight when Hitler's forces invaded her Lithuanian city of Vilnius, a great center for Jewish learning and culture. Soon after, her family faced hunger and fear in the Jewish ghetto, but the worse was yet to come. When the ghetto is liquidated, some Jews are selected for forced labor camps and the rest are killed. Susie would live because of her mother's courage and ingenuity. She carries Susie, hidden in a back pack, to the group destined for the labor camps. Susie is disguised as an adult to fool the guards into believing she is 17. Her mother cares for her body and soul through gruesome conditions in three concentration camps and a winter death march. This is a haunting book. It is amazing what the human spirit can endure when there is only a bit of hope. Susie's mother is determined that not only will they both survive, but that she will retain her humanity in the process, often sharing rations and thinking of ways to help other prisoners. Rabinovici is unsparing in her recollections: she describes "selections" when babies abandoned by their mothers are trampled, a bathhouse abortion, and a hellish journey on the cargo deck of a ship where the passengers are sprayed with feces and vomit. The only concession made to younger readers is footnotes that define religious, political and historic terms. Its biggest fault is that the author lacks the redemptive vision of, for example, Livia Bitton-Jackson in I Have Lived a Thousand Years. Readers whose interests include Holocaust testimonies and do not depend on literary polish, and are mentally prepared for the harshness of Rabinovici's experiences, will come away with renewed appreciation of the extraordinary fortitude required to survive those dire times.... Free Essays on Thanks To My Mother Free Essays on Thanks To My Mother Thanks to My Mother by Schoschana Rabinovici is one of the most moving memoirs I have ever read about the Holocaust. Born Susie Weksler, Rabinovici was only eight when Hitler's forces invaded her Lithuanian city of Vilnius, a great center for Jewish learning and culture. Soon after, her family faced hunger and fear in the Jewish ghetto, but the worse was yet to come. When the ghetto is liquidated, some Jews are selected for forced labor camps and the rest are killed. Susie would live because of her mother's courage and ingenuity. She carries Susie, hidden in a back pack, to the group destined for the labor camps. Susie is disguised as an adult to fool the guards into believing she is 17. Her mother cares for her body and soul through gruesome conditions in three concentration camps and a winter death march. This is a haunting book. It is amazing what the human spirit can endure when there is only a bit of hope. Susie's mother is determined that not only will they both survive, but that she will retain her humanity in the process, often sharing rations and thinking of ways to help other prisoners. Rabinovici is unsparing in her recollections: she describes "selections" when babies abandoned by their mothers are trampled, a bathhouse abortion, and a hellish journey on the cargo deck of a ship where the passengers are sprayed with feces and vomit. The only concession made to younger readers is footnotes that define religious, political and historic terms. Its biggest fault is that the author lacks the redemptive vision of, for example, Livia Bitton-Jackson in I Have Lived a Thousand Years. Readers whose interests include Holocaust testimonies and do not depend on literary polish, and are mentally prepared for the harshness of Rabinovici's experiences, will come away with renewed appreciation of the extraordinary fortitude required to survive those dire times....

What are UFOs and what ties them to Extraterrestrial Life essays

What are UFO's and what ties them to Extraterrestrial Life essays The question Are We Alone in the Universe? has been brought up and speculated on for thousands of years. My answer to the above question is I dont know. I will not try to give you answers in this essay, because as of now nobody knows the answer. I will merely speculate on this subject based on the information we obtain at present. The question of UFOs and intelligent life on other planets has become very popular. UFOs stand for Unidentified Flying Objects, which are any object in the sky that the viewer cannot recognize. Many scientists believe that we cannot be alone in the universe. There have been many unreported sightings of UFOs. Many of them however are found to be hoaxed or misperceptions. However among the thousands and thousands of sightings surely some of them have to be genuine. Some researchers believe that there were UFO sightings in ancient times. The evidence however is highly speculative. The next significant reports came into existence during World War I and there were also reports during World War II. Many people point out that UFOs do not and cannot exist and quote Physics and science to back them up. But we have to realize that we can only attempt to describe the universe in terms relative to things that we can measure. Just because UFO has not definitely been measured (as far as we officially know) does not prove they do not exist. John G. Fuller in the book UFOs? Yes! says I would point out that we have always been bombarded by certain wavelengths of radio as universal background noise from the edge of the universe. Until we discovered a way to generate and use radio for our own purposes, we had no way to know of its existence out there...Now that technology exists to listen, we can use that information to add to the description of the universe. Who knows how many other means of describing the univers...