Saturday, January 25, 2020
There are many causes that molded Troy Maxson into the dishonest, cantankerous, hypocritical person that he is in August WilsonÃ¢â¬â¢s play, Ã¢â¬Å"FencesÃ¢â¬ (1985). Troy had an exceptionally unpleasant childhood. He grew up with a very abusive father that beat him on a daily basis. His mother even abandoned him when he was eight years old. In this play, Troy lies habitually and tries to cover himself up by accusing others of lying. He is a very astringent person in general. His dream of becoming a major league baseball player was crushed as a result of his time spent in jail. By the time he was released from jail, he was too old to play baseball efficiently. Troy is a very self-centered individual. He is only concerned with issues regarding him. For instance, he wants to be able to drive the trash trucks at his job like the white men do. In Act One, scene one, Troy tells Bono that he talked to his boss, Mr. Rand, about driving the trucks. Ã¢â¬Å"How come you got all the whites driving and the colored lifting?Ã¢â¬ (1332). If things in TroyÃ¢â¬â¢s life arenÃ¢â¬â¢t going the way he wants them to, he makes himself into the victim and searches for sympathy from others. In addition, if he ever does something erroneous, he never accepts responsibility, never admits his wrongdoing and no matter how much anguish he causes someone, he never apologizes for it. Even though Troy does not physically abuse his children like his father did to him, he verbally abuses them. He treats Cory very callously and unjustly. In a way, Troy is taking out his frustrations of having an unsuccessful baseball career by not allowing Cory to pursue his dream to play football. Troy crushed CoryÃ¢â¬â¢s dream. In Act One, scene four, Cory expresses his misery. Ã¢â¬Å"Why you wanna do that to me? That w... ...oes tell the truth. He talks truthfully about his father and how he is a lot like him. He also admits that the only difference with him and his father is that he does not beat his children. Troy provided for his family. Additionally, even though he was very tough on Cory, he admitted that he was responsible for taking care of him and the rest of the family. In Act One, scene three, Troy explains to Cory why he treats him the way he does. Cory asks, Ã¢â¬Å"How come you ainÃ¢â¬â¢t never liked me?Ã¢â¬ (1346). Troy canÃ¢â¬â¢t admit to like his own son, so points out that he doesnÃ¢â¬â¢t have to like him in order to provide for him. Ã¢â¬Å"[Ã¢â¬ ¦] Ã¢â¬ËCause itÃ¢â¬â¢s my duty to take care of you. I owe a responsibility to you! [Ã¢â¬ ¦] I ainÃ¢â¬â¢t got to like youÃ¢â¬ (1347). Deep down, somewhere in the dark abyss that is TroyÃ¢â¬â¢s heart, he sincerely cares about his family. He just has a very different way of articulating it.
Friday, January 17, 2020
QAM and QPSK: Aim: Review of Quadrature Amplitude Modulator (QAM) in digital communication system, generation of Quadrature Phase Shift Keyed (QPSK or 4-PSK) signal and demodulation. Introduction: The QAM principle: The QAM modulator is of the type shown in Figure 1 below. The two paths to the adder are typically referred to as the Ã¢â¬ËIÃ¢â¬â¢ (inphase), and Ã¢â¬ËQÃ¢â¬â¢ (quadrature), arms. Not shown in Figure 1 is any bandlimiting. In a practical situation this would be implemented either at message level Ã¢â¬â at the input to each multiplier Ã¢â¬â and/or at the output of the adder.Probably both ! The motivation for QAM comes from the fact that a DSBSC signal occupies twice the bandwidth of the message from which it is derived. This is considered wasteful of resources. QAM restores the balance by placing two independent DSBSC, derived from message #1 and message #2, in the same spectrum space as one DSBSC. The bandwidth imbalance is removed. In digital communications this arrangement is popular. It is used because of its bandwidth conserving (and other) properties. It is not used for multiplexing two independent messages.Given an input binary sequence (message) at the rate of n bit/s, two sequences may be obtained by splitting the bit stream into two paths, each of n/2 bit/s. This is akin to a serial-to-parallel conversion. The two streams become the channel 1 and channel 2 messages of Figure 1. Because of the halved rate the bits in the I and Q paths are stretched to twice the input sequence bit clock period. The two messages are recombined at the receiver, which uses a QAM-type demodulator. The two bit streams would typically be band limited and/or pulse shaped before reaching the modulator.A block diagram of such a system is shown in Figure 2 below. QAM becomes QPSK: The QAM modulator is so named because, in analog applications, the messages do in fact vary the amplitude of each of the DSBSC signals. In QPSK the same modulator is used, but wi th binary messages in both the I and Q channels, as describe above. Each message has only two levels, Ã ±V volt. For a non-bandlimited message this does not vary the amplitude of the output DSBSC. As the message changes polarity this is interpreted as a 1800 phase shift, given to the DSBSC.Thus the signal in each arm is said to be undergoing a 1800 phase shift, or phase shift keying Ã¢â¬â or PSK. Because there are two PSK signals combined, in quadrature, the twochannel modulator gives rise to a quadrature phase shift keyed Ã¢â¬â QPSK Ã¢â¬â signal. Constellation: Viewed as a phasor diagram (and for a non-bandlimited message to each channel), the signal is seen to occupy any one of four point locations on the complex plane. These are at the corner of a square (a square lattice), at angles ? /4, 3? /4, 5? /4 and 7? /4 to the real axis.M-PSK and M-QAM: The above has described digital-QAM or QPSK. This signal is also called 4-PSK or 4QAM. More generally signals can be generated which are described as M-QAM or MPSK. Here M = 2L, where L = the number of levels in each of the I and Q arms. For the present experiment L = 2, and so M = 4. The Ã¢â¬ËMÃ¢â¬â¢ defines the number of points in the signal constellation. For the cases M > 4 then M-PSK is not the same as M-QAM. The QAM Receiver: The QAM receiver follows the similar principles to those at the transmitter, and is illustrated in idealised from in the block diagram of Figure 3.It is idealised because it assumes the incoming signal has its two DSBSC precisely in phase quadrature. Thus only one phase adjustment is required. The parallel-to-serial converter block performs the following operations: 1. regenerates the bit clock from the incoming data. 2. regenerates a digital waveform from both the analog outputs of the I and Q arms. 3. re-combines the I and Q signals, and outputs a serial data stream. Not shown is the method of carrier acquisition. This ensures that the oscillator, which supplies the local carrier signal, is synchronized to the received (input) signal in both frequency and phase.In this experiment we will use a stole carrier to ensure that carrier signal in the transmitter and receiver are in synchronism with each other. (Please read about Costas Receiver to understand more about carrier acquisition). In this experiment, two independent data sequences will be used at the input to the modulator, rather than having digital circuitry to split one data stream into two (the serialto-parallel converter). Two such independent data sequences, sharing a common bit clock (2. 083 kHz), are available from a single SEQUENCE GENERATOR module.The data stream from which these two channels are considered to have been derived would have been at a rate of twice this Ã¢â¬â 4. 167 kHz. Lowpass filter bandlimiting and pulse shaping is not a subject of enquiry in this experiment. So a single bandpass filter at the ADDER (summer) output will suffice, providing it is of adequate bandwidth. A 100 kHz CHANNEL FILTERS module is acceptable (filter #3). Experimental Procedure: The QPSK transmitter: A model of the generator of Figure 1 is shown in Figure 4. The QAM modulator involves analog circuitry.Overload must be avoided, to prevent crosstalk between channels when they share a common path Ã¢â¬â the ADDER and output filter. In practice there would probably be a filter in the message path to each multiplier. Although these filters would be included for pulse shaping and/or band limiting, a secondary purpose is to eliminate as many unwanted components at the multiplier (modulator) input as possible. T1 patch up the modulator according to Figure 4. Set the on-board switch SW1 of the PHASE SHIFTER to HI. Select channel #3 of the 100 kHz CHANNEL FILTERS module (this is a bandpass filter of adequate bandwidth).T2 there are no critical adjustments to be made. Set the signals from each input of the ADDER to be, say, 1 volt peak at the ADDER output. T3 for interest predict th e waveforms (amplitude and shape) at all interfaces, then confirm by inspection. Constellation: You can display the four-point constellation for QPSK: T4 set the oscilloscope in X-Y mode. With no input, select equal gains per channel. Locate the Ã¢â¬ËspotÃ¢â¬â¢ in the centre of the screen; then connect the two data streams entering the QAM to the scope X and Y inputs.The Demodulator: Modelling of the demodulator of Figure 3 is straightforward. But it consumes a lot of modules. Consequently only one of the two arms is shown in Figure 5. The PHASE SHIFTER can be used to select either channel from the QAM signal. If both channels required simultaneously, as in practice, then a second, identical demodulator must be provided. T5 patch up the single channel demodulator of Figure 5, including the z-mod facility of the DECISION MAKER. T6 while watching the Ã¢â¬ËIÃ¢â¬â¢ channel at the transmitter, use the PHASE SHIFTER to match the demodulator output with it.T7 while watching the Ã¢â ¬ËQÃ¢â¬â¢ channel at the transmitter, use the PHASE SHIFTER to match the demodulator output with it. Tutorial Questions: 1) Explain how a QAM system conserves bandwidth. 2) The modulator used the quadrature 100 kHz outputs from the MASTER SIGNALS module. Did it matter if these were not precisely in quadrature ? Explain. 3) Name one advantage of making the bit rate a sub-multiple of the carrier frequency. 4) Why is there a need to eliminate as many unwanted components as possible into the modulator ?
Wednesday, January 8, 2020
After a tumultuous century embroiled in world wars and financial crises, the United States economy at the end of the 20th century was experiencing a period of economic calm wherein prices were stable, unemployment fell to its lowest level in 30 years, the stock market boomed and the government posted a budget surplus. Technological innovations and a rapidly globalizing market contributed to the economic boom near the end of the 90s, then again between 2009 and 2017, but many other factors Ã¢â¬â including presidential policy, foreign affairs, and domestic innovations and foreign supply and demand needs Ã¢â¬â affected the rise of the American economy as it entered the 21st century. Long-term challenges like poverty, especially for single mothers and their children, and environmental quality of life still faced the nation as it prepared to enter a new century of technological development and rapid globalization. A Calm Before the Turn of the Century With the presidency of Bill Clinton at the tail end of George Bush Sr.s one-term presidency, the economy of the United States stabilized in the mid-1990s, creating a status in the economy as it prepared to enter a new millennium, finally recovered from two world wars, a 40-year Cold War, a Great Depression and several large recessions, and enormous budget deficits in government in the last half of the century. By 1998, theÃ gross domestic productÃ (GDP) of the U.S. had exceeded $8.5 trillion, achieving the longest uninterrupted period of expansion in American history. With just five percent of the worlds population, the United States was accounting for 25% of the worlds economic output, outproducing its closest rival Japan by nearly double the amount. Innovations in computing, telecommunications, and life sciences opened up new opportunities for Americans to work as well as new goods to consume while the collapse of communism in the Soviet Union and Eastern Europe and the strengthening of Western and Asian economies offered new business ventures for American capitalists. Uncertainty at the Edge of the Millennium While some may have rejoiced in the new expansion in technology and the economy of the United States, others were skeptical of the rapid changes and feared some of the long-term challenges American hadnt resolved yet would be forgotten in the blur of innovation.Ã Although many Americans had achieved economic security by this point, with some even accumulating large sums of earnings, poverty was still a large issue facing the federal government and a substantial number of Americans lacked access to basic health coverage. Industrial jobs in the manufacturing field also took a hit at the end of the millennium, suffering setbacks as automation began to take over jobs and certain markets saw a decrease in demand for their goods. This resulted in a seemingly irreversible deficit in foreign trade. Ever the Market Economy As the United States passed into the early 2000s, one principle remained strong and true in terms of its economy: it was and would always be a market economy wherein the economy works best when decisions about produce and what prices to charge for goods are made through the give-and-take of millions of independent buyers and sellers, not by government or by powerful private interests, according to the State Department website. In thisÃ free market economy, Americans feel that the true value of a good or service is reflected in its price, guiding the production end of the economy to only produce what is needed according to the supply-and-demand model, which leads to peakÃ economic efficiency. As is the tradition in all things concerning American politics, it is essential to limit the governments involvement in determining the economic market of its country in order to prevent an undue concentration of power and promote the pluralist foundation of the United States.