Communication Satellites And Computer Networks

Communication Satellites And Computer Networks A communication satellite which is sometimes abbreviated to COMSAT is an artificial satellite to engage in space for the purpose of telecommunications. Modern communication satellites use different orbits including geostationary orbits, Molina orbits, other elliptical orbits and low earth orbits. They are also used for mobile applications such as communications to ships, vehicles, planes and hand held terminals and for TV and radio broadcasting, for which application of other technologies such as cable is impractical or impossible. HISTORY OF COMMUNICATION SATELLTES The first artificial satellite was the soviet sputnik 1, launched on October 4, 1957, and equipped with an onboard radio transmitter that worked on two frequencies, 20.005 and 40.002 MHz The first American satellite to relay communication was project score in 1958, which used a tape recorder to store and forward voice messages. It was used to send messages like greetings etc. After that NASA launched an Echo satellite in 1960. Telstar was the first active, direct relay communications satellite. SATELLITE COMMUNICATION IN COMPUTER NETWORKS. A multi-node, satellite communication system employing a modified broadcast system is disclosed for used with distributed computer networks. The system involves a plurality of network nodes (computer systems) each capable of transmitting to any other node at a single unique frequency, but capable of receiving from all other nodes simultaneously. Each node in the n-node network comprises a single transmitter with up to n-1 receivers, with each node capable of arbitrating a plurality of requests for transmission access. The invention encompasses a method for communicating digital information in a network of geographical distributed computers. GEOSTATIONARY SATELLITES A satellite in a geostationary orbit appears to be in a fixed position to an earth-based observer. In 1945, Arthur C. Clarke describes a complete communication system that used manned geostationary satellites, including the orbits, solar panels, radio frequencies and launch procedures. But it was failed, because these satellites were impractical due to the impossibility of putting power-hungry, fragile, vacuum tube amplifiers into orbit. The first communication satellite, Telstar was launched in July 1962. Then communication Satellites have become a multibillion dollar business and the only aspect of outer space that has become highly portable. These high-flying satellites are called GEO (Geostationary Earth Orbit) satellites. Geostationary satellites space much closer than 2 degrees in the 360-degree equatorial plane, to avoid interference. With a space of 2 degrees, there can only be 360/2 =180 of these satellites in the sky at ones. However, each transponder can use multiple frequ encies and polarization to increase the available bandwidth. Modern satellite was weighing up 4000kg and consuming several kilowatts of electric power produced by the solar panels. ITU has allocated certain frequency bands to satellite users. The main bands are listed as C band was the first to be designated for commercial satellite traffic and the upper case one for uplink traffic. To allow traffic to go both ways at the same time, two channels is required, one going each way. These bands are overcrowded because they are also used by the common carriers for terrestrial microwave links. The L and S bands were added by international agreement in 2000. Band Downlink Uplink Bandwidth Problems L 1.5GHZ 1.6GHZ 15MHZ Low bandwidth; crowded S 1.9GHZ 2.2GHZ 70MHZ Low bandwidth; crowded C 4.0GHZ 6.0GHZ 500MHZ Terrestrial interference Ku 11GHZ 14GHZ 500MHZ Rain Ka 20GHZ 30GHZ 3500MHZ Rain, equipment cost The next highest band available to commercial telecommunication carriers is the Ku band. Bandwidth allocated in the Ka band for commercial traffic, but the equipment needed to use it is still expensive. A modern satellite has around 40 transponders, each with an 80-MHZ band width. The first geostationary satellites had a single beam that illuminated about 1/3 of the earthà ¢Ãƒ ¢Ã¢â‚¬Å¡Ã‚ ¬Ãƒ ¢Ã¢â‚¬Å¾Ã‚ ¢s surface called footprint. MEDIUM-EARTH ORBIT SATELLITES MEO (Medium-Earth Orbit) satellites tracked as move through the sky. These are lower than GEOs; they have smaller footprint on the ground and require less powerful transmitters to reach them. LOW-EARTH ORBIT LEO (LOW EARTH ORBIT) satellite due to their rapid motion, large numbers of them is needed for a complete system. In this section we will examine, two aimed at voice communication and one aimed at internet service. LEO earth satellites are less expensive to launch into orbit than geostationary satellites. A grou8p of satellites working in concert is a Satellite constellation. GLOBAL STAR An iridium alternative design is global star. It based on 48 LEO satellites. But it uses a different switching scheme than that of iridium. Global star uses a traditional bent-pipe design. The call originating at the North Pole is sent back to earth and picked up by the large ground station at Santaà ¢Ãƒ ¢Ã¢â‚¬Å¡Ã‚ ¬Ãƒ ¢Ã¢â‚¬Å¾Ã‚ ¢s Workshop. The call is routed via a terrestrial network to the ground station nearest the cal lee and delivered by a bent-pipe connection. The advantage of global star scheme is that it puts much of the complexity on the ground, where it is easier to manage. MOLNIYA ORBIT The Molniya orbit is designed so that the satellite spends the great majority of its time over the far northern latitudes, during which its ground footprints moves only slightly. Its period is one half day, so that the satellite is available for operation for eight hours every second revolution. The Molniya satellites are typically used for telephony and TV services over Russia. HOW SATELLITE COMMUNICATION WORKS? The concept of satellite based network is to transmit and receive signal from ground stations. The purpose of satellite communication is to use it for video transmission and sharing. In simple words a satellite is a device which revolves around the earth either for collecting useful information or for helping transfer of information. HOW DO SATELLITES COMMUNICATE? Satellites communicate through a complex system of telemetry that connects and transmits signals between satellites and earth-bound stations. This system begins with telemetry, tracking and command (TTC) subsystem which tracks and directs signals. TTC produces signal that are directly commensurable to the quantity that is being measured, encoding and transmitting these signal to distant stations on earth. APPLICATIONS OF COMMUNICATION SATELLITES The applications of communication satellites are, Telephone Satellite Television Fixed Service Satellite Direct Broadcast satellites Satellite radio Mobile satellite technologies Amateur radio Satellite internet Military uses Navigation TELEPHONE The first application for communication satellites was in intercontinental long distance telephony. The public switched telephone network relays telephone calls from landline telephones to an earth station where they are transmitted to geostationary satellite. SATELLITE TELEVISION The satellite television is relatively few signals of large band width to many receivers being a more precise match for the capabilities of geosynchronous comsats. Two satellite types are used for North American Television and radio that are Direct Broadcast Satellite (DBS) and Fixed Service Satellite (FSS). DIRECT BROADCAST SATELLITE It is a communication satellite that transmits to small DBS satellite dishes. It is usually 18 to 24 inches or 45 to 60 cm in a diameter. SATELLITE RADIO A Satellite radio offers audio services in some countries, mostly in United States. Mobile services allow listeners to roam a continent, listening to the same audio programming anywhere. A Satellite radio or subscription radio(SR) is a digital radio signal that is broadcast by a communications satellite, which covers a much wider geographical range than terrestrial radio signals. MOBILE SATELLITE TECHNOLOGIES Initially available for broadcast to stationary TV receivers. Some manufactures have introduced special antennas for mobile reception of DBS television. Such mobile DBS antennas are used by jet-blue Airways for Direct TV, which passengers can view on board on LCD screens mounted in the seats. CONCLUSION Communication satellite has really paved way for many technologies to emerge and its advance in technology radically reduces the cost of deploying a satellite. Users of satellite systems will benefit from new service options and stability in terms current satellites and their replacement. It is very useful to economics of constructing and operating communication satellites. To conclude, I was really benefited by getting more knowledge by doing this assignment by researching on Communication satellite.

Women in Veterinary Medicine Essay -- History Medical Science essays

Women in Veterinary Medicine There is a long history in the sciences of women being subjected to inequality. In almost every area of science, engineering, and technology women are underrepresented. Veterinary medicine is one field where the tide is turning. If one were to look at the admissions profile of any university in the United States it would be evident that women and men comprise an equal share of the entering classes. This of course has not always been the case. The women of the past have had difficulty in entering this field and making it female friendly. Their efforts have been worthwhile - veterinary medicine now has the greatest equality of all the health professions next to nursing. The History The legacy begins in 1910 when the first two women were granted veterinary degrees (AVMA, 1999). By 1930, there were 30 women who had been granted DVMs (Pritchard, 1989). These women were the pioneers for today's female veterinarians. They faced many hardships in their academic and professional careers - hardships began at the admissions level. A book published in 1963 states that "because a number of women have dropped out or fail to continue in veterinary medicine, admissions committees are reluctant to accept more than a few women students." It also claimed that the usual qualifications for a veterinarian are "unusual" in a woman (Riser, 1963). For those women who were lucky enough to be admitted to a veterinary college, it did not get any easier. Early women veterinary students faced resentment from male colleagues and faculty. Women were willing to carry the same academic load as the men did. However, some colleges banned women from certain courses - often times giving no reason for their exclusion (Assoc. ... ... 1997 The Association for Women Veterinarians (AWV-web). 2000. http://www.awv-women-veterinarians.org/ Honsch, J.D. "The New Face of Veterinary Medicine." June 6, 2000. http://www.vetcentric.com/magazine/magazineArticle.cfm?ARTICLEID=873 KPMG LLP Economic Consulting Services. "The Current and Future Market for Veterinarians and Veterinary Medical Services in the United States." JAVMA. Vol. 215 no. 2. July 15, 1999. 161-183 Pritchard, W.R. (ed.). Future Directions for Veterinary Medicine. Pew National Veterinary Education Program (pub.). Durham, NC. 1989. Also found at: http://www.equinevetnet.com/vetcareer/womenvetmed.html Riser, W.H. Your Future in Veterinary Medicine. Richards Rosen Press, Inc. New York. 1963. 141-145 Turner, S. "Women are changing the face of veterinary medicine." Careers in Veterinary Medicine. 2001. http://www.vin.com/Careers/ Women in Veterinary Medicine Essay -- History Medical Science essays Women in Veterinary Medicine There is a long history in the sciences of women being subjected to inequality. In almost every area of science, engineering, and technology women are underrepresented. Veterinary medicine is one field where the tide is turning. If one were to look at the admissions profile of any university in the United States it would be evident that women and men comprise an equal share of the entering classes. This of course has not always been the case. The women of the past have had difficulty in entering this field and making it female friendly. Their efforts have been worthwhile - veterinary medicine now has the greatest equality of all the health professions next to nursing. The History The legacy begins in 1910 when the first two women were granted veterinary degrees (AVMA, 1999). By 1930, there were 30 women who had been granted DVMs (Pritchard, 1989). These women were the pioneers for today's female veterinarians. They faced many hardships in their academic and professional careers - hardships began at the admissions level. A book published in 1963 states that "because a number of women have dropped out or fail to continue in veterinary medicine, admissions committees are reluctant to accept more than a few women students." It also claimed that the usual qualifications for a veterinarian are "unusual" in a woman (Riser, 1963). For those women who were lucky enough to be admitted to a veterinary college, it did not get any easier. Early women veterinary students faced resentment from male colleagues and faculty. Women were willing to carry the same academic load as the men did. However, some colleges banned women from certain courses - often times giving no reason for their exclusion (Assoc. ... ... 1997 The Association for Women Veterinarians (AWV-web). 2000. http://www.awv-women-veterinarians.org/ Honsch, J.D. "The New Face of Veterinary Medicine." June 6, 2000. http://www.vetcentric.com/magazine/magazineArticle.cfm?ARTICLEID=873 KPMG LLP Economic Consulting Services. "The Current and Future Market for Veterinarians and Veterinary Medical Services in the United States." JAVMA. Vol. 215 no. 2. July 15, 1999. 161-183 Pritchard, W.R. (ed.). Future Directions for Veterinary Medicine. Pew National Veterinary Education Program (pub.). Durham, NC. 1989. Also found at: http://www.equinevetnet.com/vetcareer/womenvetmed.html Riser, W.H. Your Future in Veterinary Medicine. Richards Rosen Press, Inc. New York. 1963. 141-145 Turner, S. "Women are changing the face of veterinary medicine." Careers in Veterinary Medicine. 2001. http://www.vin.com/Careers/

Our countries good

After feedback from our mock exam we identified how the whole piece lacked intensity but in other points had too much and became too loud without any real reason for it and at some points felt very scripted and UN-natural, this was having an Impact on the audiences experience and making it difficult to understand the story line as so much was going on.Since our mock we as a group, stripped back and taken a lot of the unnecessary content out of scene two and four as they were too long and came confusing and have been using Clack's card technique to Intensify the piece at points and make the piece calmer In other pieces to show the Intimacy and motherly bond formed between the two hostages In order to highlight our theme to show how the Imprisoned form trust groups and friendships to stay alive'.To reduce the risk of fire in the bungalow we are making sure that there is an adequate evacuation pathway: there will be no tripping hazards in the corridor to enable us to move our audience a nd performers around safely. There is a mirror fire risk from our candles but we will have two buckets of water to hand in case of problems.As performers working under stress we are in danger of straining muscles and vocal chords. We will use physical warm-ups to make sure our muscles are relaxed and diaphragmatic breathing to make sure we don't damage our vocal chords. During the lift we ensure that manual handling principles are followed by bending our knees and lowering centre of gravity.

Monohybrid Cross A Genetics Definition

A monohybrid cross is a breeding experiment between P generation (parental generation) organisms that differ in a single given trait. The P generation organisms are homozygous for the given trait. However, each parent possesses different alleles for that particular trait. A Punnett square may be used to predict the possible genetic outcomes of a monohybrid cross based on probability. This type of genetic analysis can also be performed in a dihybrid cross, a genetic cross between parental generations that differ in two traits. Traits are characteristics that are determined by discrete segments of DNA called genes. Individuals typically inherit two alleles for each gene. An allele is an alternate version of a gene that is inherited (one from each parent) during sexual reproduction. Male and female gametes, produced by meiosis, have a single allele for each trait. These alleles are randomly united at fertilization. Example: Pod Color Dominance In the image above, the single trait being observed is pod color. The organisms in this monohybrid cross are true-breeding for pod color. True-breeding organisms have homozygous alleles for specific traits. In this cross, the allele for green pod color (G) is completely dominant over the recessive allele for yellow pod color (g). The genotype for the green pod plant is (GG), and the genotype for the yellow pod plant is (gg). Cross-pollination between the true-breeding homozygous dominant green pod plant and the true-breeding homozygous recessive yellow pod plant results in offspring with phenotypes of green pod color. All genotypes are (Gg). The offspring or F1 generation are all green because the dominant green pod color obscures the recessive yellow pod color in the heterozygous genotype. Monohybrid Cross: F2 generation Should the F1 generation be allowed to self-pollinate, the potential allele combinations will be different in the next generation (F2 generation). The F2 generation would have genotypes of (GG, Gg, and gg) and a genotypic ratio of 1:2:1. One-fourth of the F2 generation would be homozygous dominant (GG), one-half would be heterozygous (Gg), and one-fourth would be homozygous recessive (gg). The phenotypic ratio would be 3:1, with three-fourths having green pod color (GG and Gg) and one-fourth having yellow pod color (gg). F2Â  Generation G g G GG Gg g Gg gg What Is a Test Cross? How can the genotype of an individual expressing a dominant trait be determined to be either heterozygous or homozygous if it is unknown? The answer is by performing a test cross. In this type of cross, an individual of unknown genotype is crossed with an individual that is homozygous recessive for a specific trait. The unknown genotype can be identified by analyzing the resulting phenotypes in the offspring. The predicted ratios observed in the offspring can be determined by using a Punnett square. If the unknown genotype is heterozygous, performing a cross with a homozygous recessive individual would result in a 1:1 ratio of the phenotypes in the offspring. Test Cross 1 G (g) g Gg gg g Gg gg Using pod color from the earlier example, a genetic cross between a plant with recessive yellow pod color (gg) and a plant heterozygous for green pod color (Gg) produces both green and yellow offspring. Half are yellow (gg), and half are green (Gg). (Test Cross 1) Test Cross 2 G (G) g Gg Gg g Gg Gg A genetic cross between a plant with recessive yellow pod color (gg) and a plant that is homozygous dominant for green pod color (GG) produces all green offspring with heterozygous genotype (Gg). (Test Cross 2)