Wikisnaps! We find what's interesting on Wikipedia, so you don't have to!

Fluorescence is the emission of visible light by a substance that has absorbed light of a different wavelength. In most cases, absorption of light of a smaller wavelength induces emission of light with a larger wavelength. A smaller wavelength emission is sometimes observed from multiple photon absorption, but this occurs only under conditions of intense radiation such as are just available with laser light. The energy difference between the absorbed and emitted photons is dissipated in the fluorescent material, via internal molecular vibrations and eventually heat. The most striking examples of this phenomenon occur when the absorbed photon is in the ultraviolet region of the spectrum, and is thus invisible, and the emitted light is in the visible region. Practical applications of this effect are found in mineralogy, gemology, chemical sensors, fluorescent labelling, dyes, biological detectors etc. Newer applications of fluorescent compounds are being explored daily. The term 'fluorescence' was coined by George Gabriel Stokes in his 1852 paper; the name was suggested "to denote the general appearance of a solution of sulphate of quinine and similar media". The name itself was derived from the mineral fluorite (calcium difluoride), some examples of which contain traces of divalent europium, which serves as the fluorescent activator to provide a blue fluorescent emission. The fluorite which provoked the observation originally, and which remains one of the most outstanding examples of the phenomenon, originated from the Weardale region, of northern England. In the mid 1990s, white light-emitting diodes (LEDs) became available, which work through a similar process. Typically, the actual light-emitting semiconductor produces light in the blue part of the spectrum, which strikes a phosphor compound deposited on the chip; the phosphor fluoresces from the green to red part of the spectrum. The combination of the blue light that goes through the phosphor and the light emitted by the phosphor produce a net emission of white light. Glow sticks sometimes utilize fluorescent materials to absorb light from the chemiluminescent reaction and emit light of a different color. [READ THE REST OF THIS ARTICLE]



SS America was an ocean liner built in 1940 for the United States Lines and designed by the noted naval architect William Francis Gibbs. She carried many names in the 54 years between her construction and her 1994 wrecking, as she served as the SS America (carrying this name three different times during her career), the USS West Point, the SS Australis, the SS Italis, the SS Noga, the SS Alferdoss, and the SS American Star. America was laid down under the first Maritime Commission contract on August 22, 1938, at Newport News, Virginia, by the Newport News Shipbuilding and Drydock Company. She was one of the few ocean liners, American or otherwise, that had her interiors designed by women. The stodginess and overwrought decor from liners of the past was jettisoned to create a comfortable and friendly ship. Interior design and furniture were installed to provide an atmosphere of cheerfulness and sophisticated charm. America was launched on August 31, 1939 and was sponsored by Eleanor Roosevelt, wife of the President of the United States. America entered service as the flagship of the United States Lines on August 22, 1940, when she commenced her maiden voyage. SS America was moored at Norfolk, Virginia, and acquired by the Navy on June 1, 1941 to be used as a troop transport. The ship was renamed the USS West Point (AP-23). She entered the Norfolk Ship Yards on June 6, 1941 for conversion and on June 15, 1941, she was commissioned for service under the command of Captain Frank H. Kelley, Jr. By the time the conversion was completed, life-rafts covered the promenade deck windows, "standee" bunks could be found everywhere, several anti-aircraft weapons were installed, all of her windows were covered, she was painted in a camouflage gray color, and her troop-carrying capacity was increased to 7,678. In February 1993, the ship was sold yet again, with the intention of being refitted to become a five-star hotel ship off Phuket, in Thailand. Drydocking at that time revealed that despite the years of neglect, her hull was still in remarkably good condition. In August she was renamed American Star, her propellers were removed and placed on the deck, the funnel and bridge were painted red, and ladders were welded to starboard. She left Greece on December 22, 1993 under tow, but the tow proved impossible due to the weather. She then returned to Greece for a few days until the weather calmed down. On New Year's Eve 1993, American Star left Greece for the last time, towed by Ukrainian tugboat Neftegaz 67. The one hundred day tow began; American Star and Neftegaz 67 entered a thunderstorm in the Atlantic. The tow lines broke and six or more men were sent aboard American Star to reattach the emergency tow lines. This proved unsuccessful. Two other towboats were called to assist Neftegaz 67. On January 17, the crew aboard American Star was rescued by helicopter. The ship was left adrift. On January 18, the ship ran aground off the west coast of Fuerteventura in the Canary Islands. In April 2007 the starboard side finally collapsed causing the wreck to break in half and fall into the sea. Throughout 2007 what little remained had been slowly disappearing beneath the waves. As of February 2010, about 15 – 20 feet of the bow remains above the water. [READ THE REST OF THIS ARTICLE]





USS Nautilus (SSN-571) was the world's first operational nuclear-powered submarine and the first vessel to complete a submerged transit across the North Pole. In July 1951 the US Congress authorized the construction of a nuclear-powered submarine for the U.S. Navy, which was planned and personally supervised by Admiral Hyman G. Rickover, known as the "Father of the Nuclear Navy." On 12 December 1951 the U.S. Department of the Navy announced that the submarine would be called Nautilus — the fourth U.S. Navy vessel officially so named — and would carry the hull number SSN-571. Nautilus's keel was laid at General Dynamics' Electric Boat Division in Groton, Connecticut by Harry S. Truman, President of the United States, on 14 June 1952, and the ship was designed by John Burnham. She was christened on 21 January 1954 and launched into the Thames River, sponsored by Mamie Eisenhower, the wife of Truman's successor Dwight D. Eisenhower. Nautilus was commissioned on 30 September 1954, under the command of Commander Eugene P. Wilkinson, USN. Nautilus was powered by the S2W naval reactor, a pressurized water reactor produced for the U.S. Navy by Westinghouse Electric Corporation. She submerged in the Barrow Sea Valley on 1 August and on 3 August 1958, at 2315 (EDST) she became the first watercraft to reach the geographic North Pole. From the North Pole, she continued on and after 96 hours and 2,945 km (1,590 nmi) under the ice, she surfaced northeast of Greenland, having completed the first successful submerged voyage across the North Pole. The technical details of this mission were planned by scientists from the Naval Electronics Laboratory including Dr. Waldo Lyon who accompanied Nautilus as chief scientist and ice pilot. Navigation beneath the arctic ice sheet was difficult. Above 85 degrees both magnetic compasses and normal gyrocompasses become inaccurate. A special gyrocompass built by Sperry Rand was installed shortly before the journey. There was a risk that the submarine would become disoriented beneath the ice and that the crew would have to play "longitude roulette". Cmdr Anderson had considered using torpedoes to blow a hole in the ice if the submarine needed to surface. Nautilus was designated a National Historic Landmark by the United States Secretary of the Interior on 20 May 1982. She was named as the official state ship of Connecticut in 1983. Following an extensive conversion at Mare Island Naval Shipyard, Nautilus was towed back to Groton, Connecticut arriving on 6 July 1985. On April 11, 1986, Nautilus opened to the public as part of the U.S. Navy Submarine Force Museum and Library. Nautilus now serves as a museum of submarine history, after undergoing a five-month preservation in 2002, at the Electric Boat division of General Dynamics, at a cost of approximately $4.7 million. The historic ship Nautilus attracts some 250,000 visitors annually to her present berth near the Naval Submarine Base New London, at the U.S. Navy Submarine Force Museum and Library in Groton. [READ THE REST OF THIS ARTICLE]



The Atari 2600 is a video game console released in September 1977 by Atari, Inc. It is credited with popularizing the use of microprocessor-based hardware and ROM cartridges containing game code, instead of having non-microprocessor dedicated hardware with all games built in. The first game console to use this format was the Fairchild Channel F; however, the Atari 2600 receives credit for making the plug-in concept popular among the game-playing public. The CPU was the MOS Technology 6507, a cut-down version of the 6502, running at 1.19 MHz in the 2600. The 6507 included fewer memory address pins—13 instead of 16—and no external interrupts to fit into a smaller 28-pin package. Smaller packaging was, and still is, an important factor in overall system cost, and since memory was very expensive at the time, the 6507's small 8 kB of maximum external memory space was not going to be used up anyway. In fact, memory was so expensive they could not imagine using up even 4 kB, and when they got a deal on 24-pin connectors for the cartridge socket, they were only too happy to thereby limit the games to 4K. Later games got around this limitation with bank switching. During the console's lifetime, Atari Inc and Atari Corp. published many titles. These games include Adventure (often credited as starting the action-adventure game genre—its creator, Warren Robinett, also introduced the first widely known Easter egg to the gaming world), Breakout, and Yars' Revenge. The console's popularity attracted many third-party developers, which led to popular titles such as Activision's Pitfall! and Imagic's Atlantis. However, two Atari published titles, E.T. the Extra-Terrestrial and Pac-Man, are frequently blamed for contributing to the video game crash of 1983. After 30 years since the launch of the Atari 2600, new homebrew games for the system are still made and sold by hobbyists with several new titles available each year. Most of the development on the platform is still done in 6502 assembly language but a BASIC-like language compiler named batari Basic (or "bB") and visual environment called Visual batari Basic are also available. READ THE REST OF THIS ARTICLE]





wikisnap.com is not affiliated with or endorsed by wikipedia. wikipedia and the wikipedia globe are registered trademarks of wikipedia.org.
article content reproduced in compliance with wikipedia's copyright policy and gnu free documentation license
view our privacy policy and terms of service here