Copyright © Philip M. Parker, INSEAD. Terms of Use.

AA

Specialty Definition: AA

Top     

Specialty Definition: Aa

(From Wikipedia, the free Encyclopedia)

• A type of lava; see Aa (lava).
• Several rivers in Europe; see Aa River.
• A village in Estonia; see Aa, Estonia.
• An alternative version, or transcription, of the letter Å in the Danish and Norwegian alphabets.
• A plant genus; see Aa (plant)

See also AA for usage as an initialism.

Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Aa."

Top     

AA

(From Wikipedia, the free Encyclopedia)

The initialism AA is an abbreviation for:

• Alcoholics Anonymous
• American Airlines
• Automobile Association
• Anti-aircraft
• Argentinum Astrum

AA is also a standard size dry cell battery.

See also: Aa

Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "AA."

Top     

Aa (lava)

(From Wikipedia, the free Encyclopedia)

Aa (from Hawaiian ‘a‘a, rough lava, ) is one of three types of flow lava. The other two types of flow lava are pillow lava characterized by smooth rounded pillows formed where lava contacts water, and pahoehoe characterized by ropy surface.

Glowing aa flow front advancing over pahoehoe on the coastal plain of Kilauea Volcano, Hawaii.

Aa is characterized by a rough rubbly surface composed of broken lava blocks called clinkers. The incredibly spiny surface of a solidified aa flow makes walking very difficult and slow. The clinkery surface actually covers a massive dense core, which is the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an aa flow, however, these cooled fragments tumble down the steep front and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an aa flow. Accretionary lava balls as large as 3 m are common on aa flows. Aa is usually higher viscosity than pahoehoe. Pahoehoe can turn into aa if it becomes turbulent due to meeting impediments or steep slopes.

External link

• http://volcanoes.usgs.gov/Products/Pglossary/aa.html

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Aa (lava)."

Top     

Aa (plant)

(From Wikipedia, the free Encyclopedia)

Aa, is a genus in the Orchidaceae family, commonly known as orchids. The name apparently was rendered by the author to always appear first in alphabetical listings.

There are 25 known species endemic to the Andes.

Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Aa (plant)."

Top     

Aa River

(From Wikipedia, the free Encyclopedia)

Aa is the name of a large number of small European rivers. The word is derived from the Old German aha, cognate to the Latin aqua, water (cf. German -ach). In German also Au and Aue exists with the same meaning, similar to å in North Germanic languages.

The following are the more important streams of this name:

• two rivers in Latvia, Lielupe (in German Kurländische Aa) and Gauja (in German Livländische Aa), both falling into the Gulf of Riga, near Riga, which is situated between them
• a river in the north of France, falling into the sea below Gravelines, and navigable as far as Saint-Omer
• a river of Switzerland, in German Aabach, in the cantons of Lucerne and Aargau, which carries the waters of Lakes Baldegg and Hallwil into the Aar.
• in Germany there are the Westphalian Aa, rising in the Teutoburg Forest, and joining the Werre at Herford, the Münster Aa, a tributary of the Ems, and others.
• in the Netherlands, a river in Groningen province that flows through Groningen city.
• in the Netherlands, a river in Noord-Brabant.

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Aa River."

Top     

Anti-aircraft

(From Wikipedia, the free Encyclopedia)

Anti-aircraft, or air defense, is any method of combating military aircraft from the ground. Various guns and cannons have been used in this role since the first military aircraft were used in World War I, growing in power and accuracy over the years. Starting in the post-World War II era the guns were joined by the guided missile, and today both are used in combination in most roles.

Nicknames for anti-aircraft guns include AAA or triple-A for anti-aircraft artillery, ack-ack (from the World War I phonetic alphabet for AA), archie, a WWI British term, and flak (from the German fliegerabwehrkanonen, aircraft defense guns). An anti-aircraft missile is a ground-based missile used to destroy aircraft.

History

Earliest use

The earliest known use of weapons specifically for the anti-aircraft role appears to have occurred during the Franco-Prussian War of 1870. After the disaster at Sedan, Paris was besieged and French troops outside the city started at attempt at resupply via balloon. Krupps quickly modified a 1-pounder (20mm) gun to be mounted on top of a horse-drawn carriage for the purposes of shooting down these balloons. Very little information on this weapon is published.

World War I

Given this early history, it is perhaps not surprising that it was only in Germany that development of anti-aircraft guns continued. In 1909 a number of Krupp's designs were shown, including adaptations of their 65mm 9-pounder, a 75mm 12-pounder, and even a 105mm gun. By the start of World War I the 75mm had become the standard German weapon, and came mounted on a large traverse that could be easily picked up on a wagon for movement.

Other countries involved seem to have largely ignored the possibility of aircraft being an important part of the hostilities, but this soon changed when German spotter aircraft started calling down increasingly accurate artillery fire. All armies soon deployed a number of guns based on their smaller field pieces, notably the French 75mm and Russian 76.2, typically simply propped up on some sort of embankment to get the muzzle pointed skyward. The British Army decided on an entirely new weapon, and deployed a 3-inch gun that was perhaps the best of the bunch.

In general these ad-hoc solutions proved largely useless. With little experience in the role, and no ability to spot the "fall" of their rounds with accuracy, gunners proved unable to get the altitude correct and most fire fell well below their targets. The exceptioin to this rule were the guns protecting spotting balloons, in which case the altitude could be accurately measured from the length of the cable holding the balloon. The Krupp guns were later supplied with an optical sighting system and soon improved their capabilities, but these sorts of systems were not deployed by other forces.

As the aircraft started to be used in tactical roles against ground targets, these larger weapons proved too ponderous to aim at the quickly moving targets. Soon the forces were adding various machine gun based weapons mounted on poles, and the British also introduced another new weapon based on their 1-pounder "pom-pom" (a 20mm belt-fed gun). These short-range weapons proved more deadly, and the Red Baron arguably fell victim to an anti-aircraft Vickers gun.

When the war closed it was clear that the increasing capabilities of aircraft would require a much more serious attempt at downing them. Nevertheless the die was cast: anti-aircraft weapons would be based around heavy weapons attacking high-altitude targets, and on lighter weapons for use when they came to lower altitudes.

World War II

World War I had proven that the aircraft was an important part of the battlefield, even if used solely in the reconnaissance role. As the capabilities of aircraft improved, and more specificially their engines, it was clear that their role in future combat would be even more critical as their warload grew.

Oddly enough, it was once again only the Germans that considered what to do about this. They developed a number of new anti-aircraft weapons in the early 1930s, including a new rapid-fire 20mm gun for low-altitude work, and a 37mm gun for low and medium altitudes. By the mid-1930s the 20mm was considered to be too low power against the increasingly fast planes, but instead of introducing a new gun, Krupps managed to squeeze four of the existing 20mm guns onto a single carriage of about the same weight. By the end of the war the Germans had essentially given up on the 20mm as lacking punch. It was never cleanly replaced however; the 37mm was available in limited numbers, and a new dual-30mm system based on the MK 103 aircraft gun was never put into widespread use.

Their high-altitude needs were originally going to be filled by an updated 75mm Krupps design, but the specifications were later ammended to require much higher performance. In response Krupps engineers collaborated on a new 88mm design, the Flak 18.

The eighty-eight would go on to become one of the most famous artillery pieces in history. First used in Spain during the Spanish Civil War, the gun proved to be one of the best anti-aircraft guns in the world, as well as particularily deadly against tanks. It is in this later role that it became most widely known, the bane of allied tank crews everywhere.

After the Dambusters raid in 1943 an entirely new system was developed that was required to knock down any low-flying aircraft with a single hit. The first attempt to produce such a system used a 50mm gun, but this proved inaccurate and a new 55mm gun replaced it. The system used a centralized control system including both search and targeting radar, which calculated the aim point for the guns after considering windage and ballisitics, the commands were then sent to the guns which used hydraulics to point themselves at high speeds. Operators simply fed the guns and selected the targets. This system, modern even by today's standards, was in late development when the war ended.

At the start of the war England had started a slow upgrade to their own systems, including a new 90mm gun in addition to their existing WWI-era 3" guns. Both were delivered with optical sighting systems for ranging. At the small-end of the scale a number of 20mm designs were used, but testing showed, as the Germans had discovered, that these weapons were of little use against modern aircraft.

Their solution was the introduction into service of 40mm guns based on the Bofors design. These had the power to knock down aircraft of any size, yet were light enough to be mobile and easily swung. The gun became so important to the British war effort that they even produced a movie, The Gun, in order to make workers on the assembly line work harder.

Service trials demonstrated another problem however, that the problem of ranging and tracking the new high-speed targets was almost impossible – at shorter ranges the "lead" required (aiming in front of the target because it is moving) is so small that it can be done manually, and at very long ranges the apparent speed is so slow that existing manual calculators were good enough. For the ranges and speeds that the Bofors worked at neither solution was good enough.

The solution was automation, in the form of a mechanical computer, the Kerrison Director. Operators kept it pointed at the target, and the Director then calculated the proper aim point automatically and displayed it as a pointer mounted on the gun. The gun operators simply followed the pointer and loaded the shells. The Kerrison was fairly simple, but it pointed the way to future generations which incorporated radar for ranging, and then tracking.

Although they receive little attention, US Army anti-aircraft systems were actually quite good. Their smaller tactical needs were filled with quad-mounted 50-calibre machine guns, which were often mounted on the back of a half-track to form the Half Track M16, Anti-Aircraft. Although of even less power than the German 20mm systems, they were at least widely available. Their larger 90mm heavy guns would prove, as did the eighty-eight, to make an excellent anti-tank gun as well, and was widely used late in the war in this role. Finally just as the war was ending a new 120mm gun with an impressive 48,000ft altitude capability was introduced, the so-called stratosphere gun, which would continue in use after the war into the 1950s.

Post-war

Post-war analysis demonstrated that even with newer anti-aircraft systems employed by both sides, the vast majority of bombers reached their targets successfully, on the order of 90%. This was bad enough during the war, but the introduction of the nuclear bomb into the equasion upset things considerably. Now even a single bomber reaching the target would be generally unacceptable.

The developments during WWII continued for a short time into the post-war period as well. In particular the US Army set up a huge air defense network around its larger cities based on radar-guided 90mm and 120mm guns. But given the general lack of success of guns against even propeller bombers, it was clear that any defense was going to have to rely almost entirely on interceptor aircraft.

Things changed with the introduction of the guided missile. Although the Germans had been desperate to introduce them during the war, none were ready for service, and British countermeasures were likely to defeat them even if they were. With a few years of development however, these system started to mature into practical weapons. The US started an upgrade of their defenses using the Nike Ajax missile, and soon the larger anti-aircraft guns disappeared.

The evolution since this time has been a slow change from guns to missiles for the shorter range roles. Originally missiles were useful only as a replacement for the very largest of anti-aircraft guns, but by the 1960s they had been scaled down to the point where they were also replacing smaller weapons previously serviced by guns in the 40 to 57mm range. Today man-portable missiles are generally replacing even the very smallest of gun systems.

List of Anti-Aircraft Weapons

Germany

• 2cm Gebirgsflak 38

Russia

• ZSU-24

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Anti-aircraft."

Top     

List of people by name: Aa

(From Wikipedia, the free Encyclopedia)

List of people by name: A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z Aa - Ab - Ac - Ad - Ae - Af - Ag - Ah - Ai - Aj - Ak - Al - Am - An - Ao - Ap - Aq - Ar - As - At - Au - Av - Aw - Ax - Ay - Az

• Aagesen, Andrew, (1826-1879), Danish jurist
• Aali, Mehemet, (1815-1871), Turkish statesman
• Aaliyah, (1979-August 25, 2001), American rhythm and blues singer
• Aalto, Alvar, (1898-1976), Finnish architect
• Aaron, (ca. 1300 BC), Biblical figure
• Aaron, Hank, (born 1934), baseball player
• Aaronsohn, Sarah, (1890-1917), head of Nili, a Jewish spy-ring
• Aaronson, Marc, (USA, 1950-1987), astronomer
• Aasen, Ivar, (1813-1896), linguist

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "List of people by name: Aa."

Top     

Abbreviations & Acronyms: AA

Top     

Top     

Top     

Modern Usage: AA

Top     

Commercial Usage: AA

Top     

Image Slideshow: AA

Computer Images: AA More pictures...

Top     

Photo Album: AA

Thumbnail	Description & Credit	Thumbnail	Description & Credit
	A view of snow-capped Mauna Kea as seen over an aa lava flow from Mauna Loa. Credit: Paths Less Taken - NOAA at the Ends of the Earth.		AA Membership Survey. Credit: National Library of Medicine.
	First Jap torpedo bomber, "Jill," flying through hail of AA fire toward the USS Yorktown (CV-20) to attack, during the raid on Truk, Caroline Is. / Official U.S. Navy photo. Credit: Library of Congress.
Source: pictures compiled by the editor from various references; see picture credits.

Top     

Digital Photo Gallery: AA
 

"Battery Power 2" by Paige Foster Commentary: "AA batteries."

Source: photographs selected by the editor, with permission from the photographers.

Top     

Non-Fiction Usage: AA

Top     

Usage Frequency: AA

Source: compiled by the editor from several corpora; see credits.

Top     

Expressions: AA

Top     

Frequency of Internet Keywords: AA

Top     

Modern Translation: AA

Top     

Derivations: AA

Top     

Anagrams: AA

Top