As the personal computer became feasible in the early 1970s, the idea of a portable personal computer followed. A "personal, portable information manipulator" was imagined by Alan Kay at Xerox PARC in 1968[2] and described in his 1972 paper as the "Dynabook".[3]
The IBM SCAMP project (Special Computer APL Machine Portable), was demonstrated in 1973. This prototype was based on the PALM processor (Put All Logic In Microcode).
The IBM 5100, the first commercially available portable computer, appeared in September 1975, and was based on the SCAMP prototype.[4]
As 8-bit CPU machines became widely accepted, the number of portables increased rapidly. The Osborne 1, released in 1981, used the Zilog Z80 and weighed 23.5 pounds (10.7 kg). It had no battery, a 5" CRT screen and dual 5¼" single-density floppy drives. In the same year the first laptop-sized portable computer, the Epson HX-20, was announced.[5] The Epson had a LCD screen, a rechargeable battery and a calculator-size printer in a 1.6 kg (3.5 lb) chassis. Both Tandy/RadioShack and HP also produced portable computers of varying designs during this period.[6][7]
The first laptop using the flip form factor appeared in 1982. The $8150 GRiD Compass 1100 was used at NASA and by the military among others. The Gavilan SC, released in 1983, was the first notebook marketed using the term "laptop".[8] From 1983 onwards, several new input techniques were developed and included in laptops, including the touchpad (Gavilan SC, 1983), the pointing stick (IBM ThinkPad 700, 1992) and handwriting recognition (Linus Write-Top,[9] 1987). Some CPUs were designed specifically for low power use including laptops (Intel i386SL, 1990), and were supported by dynamic power management features (Intel SpeedStep and AMD PowerNow!) in some designs. Displays reached VGA resolution by 1988 (Compaq SLT/286) and 256-color screens by 1993 (PowerBook 165c), progressing quickly to millions of colors and high resolutions. High-capacity hard drives and optical storage (CD-ROM followed by CD-R and CD-RW and eventually by DVD-ROM and the writable varieties) became available in laptops soon after their introduction to the desktops.
http://en.wikipedia.org/wiki/Laptop#Advantages
Wednesday, October 28, 2009
Origins of Nuclear power
As the father of nuclear physics, Ernest Rutherford is credited with splitting the atom in 1917.[11] His team in England bombarded nitrogen with naturally occurring alpha particles from radioactive material and observed a proton emitted with energy higher than the alpha particle. In 1932 two of his students John Cockcroft and Ernest Walton, working under Rutherford's direction, attempted to split the atomic nucleus by entirely artificial means, using a particle accelerator to bombard lithium with protons, thereby producing two helium nuclei.[12]
After James Chadwick discovered the neutron in 1932, nuclear fission was first experimentally achieved by Enrico Fermi in 1934 in Rome, when his team bombarded uranium with neutrons.[13] In 1938, German chemists Otto Hahn[14] and Fritz Strassmann, along with Austrian physicists Lise Meitner[15] and Meitner's nephew, Otto Robert Frisch,[16] conducted experiments with the products of neutron-bombarded uranium. They determined that the relatively tiny neutron split the nucleus of the massive uranium atoms into two roughly equal pieces, which was a surprising result. Numerous scientists, including Leo Szilard who was one of the first, recognized that if fission reactions released additional neutrons, a self-sustaining nuclear chain reaction could result. This spurred scientists in many countries (including the United States, the United Kingdom, France, Germany, and the Soviet Union) to petition their government for support of nuclear fission research.
In the United States, where Fermi and Szilard had both emigrated, this led to the creation of the first man-made reactor, known as Chicago Pile-1, which achieved criticality on December 2, 1942. This work became part of the Manhattan Project, which built large reactors at the Hanford Site (formerly the town of Hanford, Washington) to breed plutonium for use in the first nuclear weapons, which were used on the cities of Hiroshima and Nagasaki. A parallel uranium enrichment effort also was pursued.
After World War II, the fear that reactor research would encourage the rapid spread of nuclear weapons and technology, combined with what many scientists thought would be a long road of development, created a situation in which the government attempted to keep reactor research under strict government control and classification. In addition, most reactor research centered on purely military purposes. There was an immediate arms and development race when the United States military refused to follow the advice of its own scientific community to form an international cooperative to share information and control nuclear materials. By 2006, things have come full circle with the Global Nuclear Energy Partnership (see below.)
Electricity was generated for the first time by a nuclear reactor on December 20, 1951 at the EBR-I experimental station near Arco, Idaho, which initially produced about 100 kW (the Arco Reactor was also the first to experience partial meltdown, in 1955). In 1952, a report by the Paley Commission (The President's Materials Policy Commission) for President Harry Truman made a "relatively pessimistic" assessment of nuclear power, and called for "aggressive research in the whole field of solar energy."[17] A December 1953 speech by President Dwight Eisenhower, "Atoms for Peace," emphasized the useful harnessing of the atom and set the U.S. on a course of strong government support for international use of nuclear power.
http://en.wikipedia.org/wiki/Nuclear_power
Friday, October 23, 2009
network topology
Topology in Network Design
Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there.
Bus Topology
Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.
Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.
Ring Topology
In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.
To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Ring topologies are found in some office buildings or school campuses.
Star Topology
Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.
Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)
Tree Topology
Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.
Mesh Topology
Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.
A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.
source from:About.com
Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there.
Bus Topology
Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.
Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.
Ring Topology
In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.
To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Ring topologies are found in some office buildings or school campuses.
Star Topology
Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.
Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)
Tree Topology
Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.
Mesh Topology
Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.
A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.
source from:About.com
Tg
Glass transition or vitrification refer to the transformation of a glass-forming liquid into a glass, which usually occurs upon rapid cooling. It is a dynamic phenomenon occurring between two distinct states of matter (liquid and glass), each with different physical properties. Upon cooling through the temperature range of glass transition (a "glass transformation range"), without forming any long-range order or significant symmetry of atomic arrangement, the liquid contracts more continuously at about the same rate as above the melting point until there is a decrease in the thermal expansion coefficient (TEC). [1]
The glass transition temperature Tg is lower than melting temperature, Tm, due to supercooling. It depends on the time scale of observation which must be defined by convention. One approach is to agree on a standard cooling rate of 10 K/min. Another approach is by requiring a viscosity of 1013 poise. Otherwise, one can only talk about a glass transformation range.
sorce from www.wikipedia.com
The glass transition temperature Tg is lower than melting temperature, Tm, due to supercooling. It depends on the time scale of observation which must be defined by convention. One approach is to agree on a standard cooling rate of 10 K/min. Another approach is by requiring a viscosity of 1013 poise. Otherwise, one can only talk about a glass transformation range.
sorce from www.wikipedia.com
Wednesday, July 29, 2009
Watt Steam Engine
The Watt steam engine, a major driver in the industrial revolution, underscores the importance of engineering in modern history. This model is on display at the main building of the ETSIIM in Madrid, Spain
The concept of engineering has existed since ancient times as humans devised fundamental inventions such as the pulley, lever, and wheel. Each of these inventions is consistent with the modern definition of engineering, exploiting basic mechanical principles to develop useful tools and objects.
The term engineering itself has a much more recent etymology, deriving from the word engineer, which itself dates back to 1325, when an engine’er (literally, one who operates an engine) originally referred to “a constructor of military engines.” In this context, now obsolete, an “engine” referred to a military machine, i. e., a mechanical contraption used in war (for example, a catapult). The word “engine” itself is of even older origin, ultimately deriving from the Latin ingenium (c. 1250), meaning “innate quality, especially mental power, hence a clever invention.”
Later, as the design of civilian structures such as bridges and buildings matured as a technical discipline, the term civil engineering entered the lexicon as a way to distinguish between those specializing in the construction of such non-military projects and those involved in the older discipline of military engineering (the original meaning of the word “engineering,” now largely obsolete, with notable exceptions that have survived to the present day such as military engineering corps, e.g., the U.S. Army Corps of Engineers.
source from (www.wikipedia.com)
The concept of engineering has existed since ancient times as humans devised fundamental inventions such as the pulley, lever, and wheel. Each of these inventions is consistent with the modern definition of engineering, exploiting basic mechanical principles to develop useful tools and objects.
The term engineering itself has a much more recent etymology, deriving from the word engineer, which itself dates back to 1325, when an engine’er (literally, one who operates an engine) originally referred to “a constructor of military engines.” In this context, now obsolete, an “engine” referred to a military machine, i. e., a mechanical contraption used in war (for example, a catapult). The word “engine” itself is of even older origin, ultimately deriving from the Latin ingenium (c. 1250), meaning “innate quality, especially mental power, hence a clever invention.”
Later, as the design of civilian structures such as bridges and buildings matured as a technical discipline, the term civil engineering entered the lexicon as a way to distinguish between those specializing in the construction of such non-military projects and those involved in the older discipline of military engineering (the original meaning of the word “engineering,” now largely obsolete, with notable exceptions that have survived to the present day such as military engineering corps, e.g., the U.S. Army Corps of Engineers.
source from (www.wikipedia.com)
Friday, July 24, 2009
Robotics in the Middle Ages
Main article: Inventions in medieval Islam
Al-Jazari's programmable humanoid robots
In the 8th century, the Muslim alchemist, Jabir ibn Hayyan (Geber), included recipes for constructing artificial snakes, scorpions, and humans which would be subject to their creator's control in his coded Book of Stones. In 827, Caliph al-Mamun had a silver and golden tree in his palace in Baghdad, which had the features of an automatic machine. There were metal birds that sang automatically on the swinging branches of this tree built by Muslim inventors and engineers at the time. The Abbasid Caliph al-Muktadir also had a golden tree in his palace in Baghdad in 915, with birds on it flapping their wings and singing. In the 9th century, the Banū Mūsā brothers invented an automatic flute player which appears to have been the first programmable machine, and which they described in their Book of Ingenious Devices.
Al-Jazari is credited with creating the earliest forms of a programmable humanoid robot in 1206. Al-Jazari's automaton was originally a boat with four automatic musicians that floated on a lake to entertain guests at royal drinking parties. His mechanism had a programmable drum machine with pegs (cams) that bump into little levers that operated the percussion. The drummer could be made to play different rhythms and different drum patterns if the pegs were moved around. According to Charles B. Fowler, the automata were a "robot band" which performed "more than fifty facial and body actions during each musical selection."
Al-Jazari also invented a hand washing automaton first employing the flush mechanism now used in modern flush toilets. It features a female automaton standing by a basin filled with water. When the user pulls the lever, the water drains and the female automaton refills the basin. His "peacock fountain" was another more sophisticated hand washing device featuring humanoid automata as servants which offer soap and towels. Mark E. Rosheim describes it as follows: "Pulling a plug on the peacock's tail releases water out of the beak; as the dirty water from the basin fills the hollow base a float rises and actuates a linkage which makes a servant figure appear from behind a door under the peacock and offer soap. When more water is used, a second float at a higher level trips and causes the appearance of a second servant figure — with a towel!" Al-Jazari thus appears to have been the first inventor to display an interest in creating human-like machines for practical purposes such as manipulating the environment for human comfort.
Main article: Inventions in medieval Islam
Al-Jazari's programmable humanoid robots
In the 8th century, the Muslim alchemist, Jabir ibn Hayyan (Geber), included recipes for constructing artificial snakes, scorpions, and humans which would be subject to their creator's control in his coded Book of Stones. In 827, Caliph al-Mamun had a silver and golden tree in his palace in Baghdad, which had the features of an automatic machine. There were metal birds that sang automatically on the swinging branches of this tree built by Muslim inventors and engineers at the time. The Abbasid Caliph al-Muktadir also had a golden tree in his palace in Baghdad in 915, with birds on it flapping their wings and singing. In the 9th century, the Banū Mūsā brothers invented an automatic flute player which appears to have been the first programmable machine, and which they described in their Book of Ingenious Devices.
Al-Jazari is credited with creating the earliest forms of a programmable humanoid robot in 1206. Al-Jazari's automaton was originally a boat with four automatic musicians that floated on a lake to entertain guests at royal drinking parties. His mechanism had a programmable drum machine with pegs (cams) that bump into little levers that operated the percussion. The drummer could be made to play different rhythms and different drum patterns if the pegs were moved around. According to Charles B. Fowler, the automata were a "robot band" which performed "more than fifty facial and body actions during each musical selection."
Al-Jazari also invented a hand washing automaton first employing the flush mechanism now used in modern flush toilets. It features a female automaton standing by a basin filled with water. When the user pulls the lever, the water drains and the female automaton refills the basin. His "peacock fountain" was another more sophisticated hand washing device featuring humanoid automata as servants which offer soap and towels. Mark E. Rosheim describes it as follows: "Pulling a plug on the peacock's tail releases water out of the beak; as the dirty water from the basin fills the hollow base a float rises and actuates a linkage which makes a servant figure appear from behind a door under the peacock and offer soap. When more water is used, a second float at a higher level trips and causes the appearance of a second servant figure — with a towel!" Al-Jazari thus appears to have been the first inventor to display an interest in creating human-like machines for practical purposes such as manipulating the environment for human comfort.
source by www.wikipedia .com
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