Knowledge N Fact4u

1)The word Christmas originates from the words Christ's Mass. In old English (first recorded in 1038) it was referred to as Cristesmæsse, which literally means 'Christian Mass'. 2)A common figure known throughout the world and associated with Christmas is Santa Claus. Other popular Christmas figures include Christkind, Saint Nicholas, and Father Christmas. 3)Anglo-Saxons referred to the holiday as 'midwinter' or 'nativity'. 4)In order for Santa to visit all the homes on Christmas Eve he would have to visit 822 homes each second. 5)The tradition of hanging stockings comes from a Dutch custom. They would leave shoes full of food for St. Nicolas' donkeys and St. Nicholas would then leave small gifts in return. 6)The world's biggest snowman was 113 feet tall and was built in Maine. 7)The Christmas wreath is symbolic of Jesus. The red berries symbolize his blood and the holly represents the crown of thorns. 8)The best-s...

∆∆Optical fibre links are being increasingly used for both short-distance communications, such as for local area networks (LANs), and long-distance communications. This arises from the fundamental advantages of optical f ibre communications:  • They are low cost.  • They are robust when packaged.  • They can have very wide optical bandwidths (GHz) and long communication links (hundreds of kilometres).  • They are insensitive to electromagnetic interference.  ∆∆This has led to the wide range of intercontinental communication links which are several thousand kilometres long, which distance considerably exceeds the maximum length of optical fibre that can be manufactured. It also exceeds the maximum link length over which an optical signal can be propagated without periodic amplification or regeneration. The environment is also somewhat harsh and remote, requiring high reliability and robust packaging. ∆∆The highest frequency was of the orde...

## Huffman  coding is a statistical data compression technique, which gives a reduction in the average code length, used to represent the symbols of an alphabet. The Huffman code is an example of a code that is optimal in the case where all symbol probabilities are integral powers of 0.5. A Huffman code can be built in the following manner:  1. Rank all symbols in order of probability of occurrence. 2. Successively combine the two symbols of the lowest probability to form a new composite symbol; eventually to build a binary tree where each node is the probability of all nodes beneath it.  3. Trace a path to each leaf, noticing the direction at each node.   ## For  a given probability distribution, there are many possible Huffman codes, but the total compressed length will be the same. This technique is used in most archivers. This is a means of producing a variable length code which has an average length  l close to the average information conta...

££) In  the early nineteenth century, all of the essential components necessary to construct an electrical communication system had been discovered. The most important of these were the battery by Volta, the relationship between electric current and magnetism by Oersted, and the electromagnet by Henry. It now remained for someone to find a practical method to combine these technologies into a working communication system. ££)Some  commercial electrical communications systems existed in Europe as early as the 1830s. A classic example of this is the English ‘Needle Telegraph’. The needle telegraph required two or more lines to form a complete circuit. It was relatively slow and the design of the transmitting and receiving instruments was complex. Something simple and efficient was needed. ££)The  Morse system of telegraphy was invented by Samuel Finley Breese Morse (an American painter and founder of the National Academy of Design in New York) in the 1840s ...

This is of interest in many applications; an example is sending a large document by email. The document may be several hundred kilobytes in size and to send it by email over a telephone line using a modem operating at 28.8 kbps may take a considerable time. If the data are compressed, the file can in certain cases be reduced in size by a factor of over 10, which would reduce the time taken to transmit the file, thus improving the convenience and minimizing cost. If the source information contains redundant information, data compression can shorten the message by removing redundancy. An example would be sending a text file over a communications link where the source device removes redundant characters before transmission. If the file contains sequences that are repeated, such as several space characters in a row, then instead of transmitting each of them the number of spaces could be transmitted. At the receiver the reverse process would allow the original document to be recovered. This...

RECTIFIER CIRCUIT:- Since a diode has the characteristic of having a much greater conductivity in one direction than in the other, it will produce a direct component of current when connected in series with an alternating voltage and a load. This process is known as rectification and is the main use to which diodes are put. There are numerous applications for rectification, e.g. driving a d.c. motor from a.c. mains and the production of direct-voltage supplies for electronic amplifiers . HALF WAVE RECTIFIER:- While alternating currents and voltages play the leading roles in most electrical and electronic equipment, nevertheless many devices can either only operate on unidirectional currents and voltages, or at least they require such a supply as part of their mode of operation. The process of obtaining unidirectional currents and voltages from alternating currents and voltages is termed  rectification. When the applied voltage acts in the forward direction, there is no voltage drop...

The  Mpemba effect  is a process in which hot water  can freeze  faster than cold water. The phenomenon is temperature-dependent. There is disagreement about the parameters required to produce the effect and about its theoretical basis. However, even with this definition it is not clear whether "freezing" refers to the point at which water forms a visible surface layer of ice; the point at which the entire volume of water becomes a solid block of ice; or when the water reaches 0 °C (32 °F). A quantity of water can be at 0 °C (32 °F) and not be ice; after enough heat has been removed to reach 0 °C (32 °F) more heat must be removed before the water changes to solid state (ice), so water can be liquid or solid at 0 °C (32 °F). With the above definition there are simple ways in which the effect might be observed. For example, if the hotter temperature melts the frost on a cooling surface and thus ...