Free Essays on Fiber Optics

The Technology of Fiber Optics A fiber optic is a cable that is quickly replacing out-dated copper wires. Fiber optics are based on a concept known as total internal reflection. It can transmit video, sound, or data in either analog or digital form. Compared to copper wires it can transmit thousands of times more data and has many general uses ranging from telecommunications, computing, and medicine. In the summer of 1970, scientists at the Corning Glass Works developed a single mode fiber with a loss of 20 dB/km. This corresponds to over a 99% loss over one km, which may seem useless, but at the time it was a spectacular breakthrough. On October 30, 1986, a fiber across the English Channel became operational. In December 1988, the TAT-8, the first transatlantic fiber cable became fully functional. Currently, the standard losses of fiber are within 0.5 – 0.25 dB/km with a data transfer rate of one trillion bits per second. The basic setup for a fiber optical system is that first, a transmitter receives an electrical signal, usually from a copper wire. The transmitter drives a current on a light source and the light source launches the optical signal into the fiber. Inside the cable, repeaters often amplify the signal due to slight losses in power. Once the signal is through the cable, a light detector receives and converts it back to an electrical signal to send down another copper wire. There are five layers in almost all fiber optic cables. The inner most layer is the optical core. This is the light-carrying element typically made of silica or germania with an index of refraction of 1.48. The layer surrounding the central core is the optical cladding made of pure silica and has an index of refraction of 1.46. It is the boundary between these two layers that the light reflects off of, so the light never actually enters the cladding, it just reflects off the boundary. The next layer is the buffer material that shields the... Free Essays on Fiber Optics Free Essays on Fiber Optics The Technology of Fiber Optics A fiber optic is a cable that is quickly replacing out-dated copper wires. Fiber optics are based on a concept known as total internal reflection. It can transmit video, sound, or data in either analog or digital form. Compared to copper wires it can transmit thousands of times more data and has many general uses ranging from telecommunications, computing, and medicine. In the summer of 1970, scientists at the Corning Glass Works developed a single mode fiber with a loss of 20 dB/km. This corresponds to over a 99% loss over one km, which may seem useless, but at the time it was a spectacular breakthrough. On October 30, 1986, a fiber across the English Channel became operational. In December 1988, the TAT-8, the first transatlantic fiber cable became fully functional. Currently, the standard losses of fiber are within 0.5 – 0.25 dB/km with a data transfer rate of one trillion bits per second. The basic setup for a fiber optical system is that first, a transmitter receives an electrical signal, usually from a copper wire. The transmitter drives a current on a light source and the light source launches the optical signal into the fiber. Inside the cable, repeaters often amplify the signal due to slight losses in power. Once the signal is through the cable, a light detector receives and converts it back to an electrical signal to send down another copper wire. There are five layers in almost all fiber optic cables. The inner most layer is the optical core. This is the light-carrying element typically made of silica or germania with an index of refraction of 1.48. The layer surrounding the central core is the optical cladding made of pure silica and has an index of refraction of 1.46. It is the boundary between these two layers that the light reflects off of, so the light never actually enters the cladding, it just reflects off the boundary. The next layer is the buffer material that shields the...

The History and Archaeology of Vindija Cave

The History and Archaeology of Vindija Cave Vindija Cave is a stratified paleontological and archaeological site in Croatia, which has several occupations associated with both Neanderthals and Anatomically Modern Humans (AMH). Vindija includes a total of 13 levels dated between 150,000 years ago and the present, spanning the upper part of the Lower Paleolithic, Middle Paleolithic, and Upper Paleolithic periods. Although several of the levels are sterile of hominin remains or have been disturbed primarily cryoturbations ice wedging, there are some stratigraphically separated hominin levels at Vindija Cave associated with humans and Neanderthals. Although the earliest recognized hominid occupations date to ca. 45,000 bp, deposits at Vindija include strata that comprise a huge number of animal bones, including tens of thousands of specimens, 90% of which are cave bears, over a period of more than 150,000 years. This record of animals in the region has been used to establish data about the climate and habitat of northwest Croatia during that period. The site was first excavated in the first half of the 20th century, and more extensively excavated between 1974 and 1986 by Mirko Malez of the Croatian Academy of Sciences and Arts. In addition to archaeological and faunal remains, numerous archaeological and faunal remains, with over 100 hominin discoveries have been found at Vindija Cave. Specimens in Level G3 (38,000-45,000 years bp), the lowest hominin-bearing level, are Neanderthals and are associated with exclusively Mousterian artifacts.Specimens in Level G1 (32,000-34,000 years bp) represent the most recent Neanderthals at the site and are associated with both Mousterian and Upper Paleolithic stone tools.Hominins in Level F (31,000-28,000 years bp) are associated with Aurignacian and according to researchers look a little like both AMH and Neanderthal.Hominins in Level D (less than 18,500 years bp, the uppermost hominid-bearing strata in the cave, are associated with Gravettian culture artifacts  and represent only anatomically modern humans. Vindija Cave and mtDNA In 2008, researchers reported that a complete mtDNA sequence had been retrieved from a thigh bone of one of the Neanderthals recovered from Vindija Cave. The bone (called Vi-80) comes from level G3, and it was direct-dated to 38,310  ± 2130 RCYBP. Their research suggests that the two hominins who occupied Vindija Cave at different timesearly modern Homo sapiens and Neanderthalswere clearly separate species. Even more interestingly, Lalueza-Fox and colleagues have discovered similar DNA sequencesfragments of sequences, that isin Neanderthals from Feldhofer Cave (Germany) and El Sidron (northern Spain), suggesting a common demographic history among groups in eastern Europe and the Iberian peninsula. In 2010, the Neanderthal Genome Project announced that it had finished a complete DNA sequence of Neanderthal genes, and discovered that between 1 and 4 percent of the genes that modern humans carry around with them come from Neanderthals, directly contradicting their own conclusions just two years ago. Read more about the latest findings about Neanderthal and Human Interbreeding The Last Glacial Maximum and Vindija Cave A recent study reported in Quaternary International (Miracle et al. listed below) describes the climate data recovered from Vindija Cave, and Veternica, Velika pecina, two other caves in Croatia. Interestingly, the fauna indicate that during the period between 60,000 and 16,000 years ago, the region had a moderate, broadly temperate climate with a range of environments. In particular, there seems to have been no significant evidence for what was thought to be a shift to cooler conditions at the onset of the Last Glacial Maximum, about 27,000 years bp. Sources Each of the links below leads to a free abstract, but payment is needed for the full article unless otherwise noted. Ahern, James C. M., et al. 2004 New discoveries and interpretations of hominid fossils and artifacts from Vindija Cave, Croatia. Journal of Human Evolution 4627-4667. Burbano HA, et al. 2010. Targeted Investigation of the Neandertal Genome by Array-Based Sequence Capture. Science 238:723-725. Free download Green RE, et al. 2010. A Draft Sequence of the Neandertal Genome. Science 328:710-722. Free download Green, Richard E., et al. 2008 A Complete Neandertal Mitochondrial Genome Sequence Determined by High-Throughput Sequencing. Cell 134(3):416-426. Green, Richard E., et al. 2006 Analysis of one million base pairs Neanderthal DNA. Nature 444:330-336. Higham, Tom, et al. 2006 Revised direct radiocarbon dating of the Vindija G1 Upper Paleolithic Neandertals. Proceedings of the National Academy of Sciences 10(1073):553-557. Lalueza-Fox, Carles, et al. 2006 Mitochondrial DNA of an Iberian Neandertal suggests a population affinity with other European Neandertals. Current Biology 16(16):R629-R630. Miracle, Preston T., Jadranka Mauch Lenardic, and Dejana Brajkovic. in press Last glacial climates, Refugia, and faunal change in Southeastern Europe: Mammalian assemblages from Veternica, Velika pecina, and Vindija caves (Croatia). Quaternary International in press Lambert, David M. and Craig D. Millar 2006 Ancient genomics is born. Nature 444:275-276. Noonan, James P., et al. 2006 Sequencing and Analysis of Neanderthal Genomic DNA. Science 314:1113-1118. Smith, Fred. 2004. Flesh and Bone: Analyses of Neandertal Fossils Reveal Diet was High in Meat Content Free press release, Northern Illinois University. Serre, David, et al. 2004 No Evidence of Neandertal mtDNA Contribution to Early Modern Humans. PLoS Biology  2(3):313-317.