Summary

HandWiki is the world's largest wiki-style encyclopedia dedicated to science, technology and computing. It allows you to create and edit articles as long as you have external citations and login account. In addition, this is a content management environment that can be used for collaborative editing of original scholarly content, such as books, manuals, monographs and tutorials.

Expand All
Entries
Topic Review
Malfatti Circles
In geometry, the Malfatti circles are three circles inside a given triangle such that each circle is tangent to the other two and to two sides of the triangle. They are named after Gian Francesco Malfatti, who made early studies of the problem of constructing these circles in the mistaken belief that they would have the largest possible total area of any three disjoint circles within the triangle. Malfatti's problem has been used to refer both to the problem of constructing the Malfatti circles and to the problem of finding three area-maximizing circles within a triangle. A simple construction of the Malfatti circles was given by (Steiner 1826), and many mathematicians have since studied the problem. Malfatti himself supplied a formula for the radii of the three circles, and they may also be used to define two triangle centers, the Ajima–Malfatti points of a triangle. The problem of maximizing the total area of three circles in a triangle is never solved by the Malfatti circles. Instead, the optimal solution can always be found by a greedy algorithm that finds the largest circle within the given triangle, the largest circle within the three connected subsets of the triangle outside of the first circle, and the largest circle within the five connected subsets of the triangle outside of the first two circles. Although this procedure was first formulated in 1930, its correctness was not proven until 1994.
  • 3.6K
  • 09 Oct 2022
Topic Review
Rigidity Theory
Rigidity theory, or topological constraint theory, is a tool for predicting properties of complex networks (such as glasses) based on their composition. It was introduced by James Charles Phillips in 1979 and 1981, and refined by Michael Thorpe in 1983. Inspired by the study of the stability of mechanical trusses as pioneered by James Clerk Maxwell, and by the seminal work on glass structure done by William Houlder Zachariasen, this theory reduces complex molecular networks to nodes (atoms, molecules, proteins, etc.) constrained by rods (chemical constraints), thus filtering out microscopic details that ultimately don't affect macroscopic properties. An equivalent theory was developed by P.K. Gupta A.R. Cooper in 1990, where rather than nodes representing atoms, they represented unit polytopes. An example of this would be the SiO tetrahedra in pure glassy silica. This style of analysis has applications in biology and chemistry, such as understanding adaptability in protein-protein interaction networks. Rigidity theory applied to the molecular networks arising from phenotypical expression of certain diseases may provide insights regarding their structure and function. In molecular networks, atoms can be constrained by radial 2-body bond-stretching constraints, which keep interatomic distances fixed, and angular 3-body bond-bending constraints, which keep angles fixed around their average values. As stated by Maxwell's criterion, a mechanical truss is isostatic when the number of constraints equals the number of degrees of freedom of the nodes. In this case, the truss is optimally constrained, being rigid but free of stress. This criterion has been applied by Phillips to molecular networks, which are called flexible, stressed-rigid or isostatic when the number of constraints per atoms is respectively lower, higher or equal to 3, the number of degrees of freedom per atom in a three-dimensional system. The same condition applies to random packing of spheres, which are isostatic at the jamming point. Typically, the conditions for glass formation will be optimal if the network is isostatic, which is for example the case for pure silica. Flexible systems show internal degrees of freedom, called floppy modes, whereas stressed-rigid ones are complexity locked by the high number of constraints and tend to crystallize instead of forming glass during a quick quenching.
  • 920
  • 09 Oct 2022
Topic Review
Paleo-Hebrew Leviticus Scroll
Paleo-Hebrew Leviticus scroll, known also as 11QpaleoLev, is an ancient text preserved in one of the Qumran group of caves, and which provides a rare glimpse of the script used formerly by the nation of Israel in writing Torah scrolls during its pre-exilic history. The fragmentary remains of the Torah scroll is written in the Paleo-Hebrew script and was found stashed-away in a cave at Qumran, showing a portion of Leviticus. The scroll is thought to have been penned by the scribe between the late 2nd-century BCE to early 1st-century BCE, while others place its writing in the 1st-century CE. The Paleo-Hebrew Leviticus scroll, although many centuries more recent than the well-known earlier ancient paleo-Hebrew epigraphic materials, such as the Royal Steward inscription from Siloam, Jerusalem (eighth century BCE), now in the Museum of the Ancient Orient, Istanbul, and the Phoenician inscription on the sarcophagus of King Eshmun-Azar at Sidon, dating to the fifth-fourth century BCE, the Lachish ostraca (ca. 6th-century BCE), the Gezer calendar (ca. 950–918 BCE), and the paleo-Hebrew sacerdotal blessing discovered in 1979 near the St Andrew's Church in Jerusalem, is of no less importance to palaeography - even though the manuscript is fragmentary and only partially preserved on leather parchment. Today, the paleo-Hebrew Leviticus scroll (11QpaleoLev) is housed at the Israel Antiquities Authority (IAA), but is not on public display.
  • 3.7K
  • 09 Oct 2022
Topic Review
KH-11 Kennen
The KH-11 KENNEN (later renamed CRYSTAL, then Evolved Enhanced CRYSTAL System, and codenamed 1010 and Key Hole) is a type of reconnaissance satellite first launched by the American National Reconnaissance Office in December 1976. Manufactured by Lockheed in Sunnyvale, California, the KH-11 was the first American spy satellite to use electro-optical digital imaging, and so offer real-time optical observations. Later KH-11 satellites have been referred to by outside observers as KH-11B or KH-12, and by the names "Advanced KENNEN", "Improved Crystal" and "Ikon". Official budget documents refer to the latest generation of electro-optical satellites as Evolved Enhanced CRYSTAL System. The Key Hole series was officially discontinued in favor of a random numbering scheme after repeated public references to KH-7 Gambit, KH-8 Gambit-3, KH-9 Hexagon, and KH-11 satellites. The capabilities of the KH-11 are highly classified, as are images they produce. The satellites are believed to have been the source of some imagery of the Soviet Union and China made public in 1997; images of Sudan and Afghanistan made public in 1998 related to the response to the 1998 U.S. embassy bombings; and a 2019 photo, revealed by President Donald Trump, of a failed Iranian rocket launch.
  • 8.7K
  • 09 Oct 2022
Topic Review
Biblical Sabbath
Biblical Sabbath is a weekly day of rest or time of worship given in the Bible as the seventh day. It is observed differently in Judaism and Christianity and informs a similar occasion in several other faiths. Though many viewpoints and definitions have arisen over the millennia, most originate in the same textual tradition of "Remember the sabbath day, to keep it holy". Observation and remembrance of Sabbath is one of the Ten Commandments (the fourth in the original Jewish, the Eastern Orthodox, and most Protestant traditions, the third in Roman Catholic and Lutheran traditions), sometimes referred to individually as the Sabbath Commandment. Most people who observe Biblical Sabbath regard it as having been made for man (Mark. 2:27) at Creation (Ex. 20:8–11), and instituted as a perpetual covenant for the people of Israel (Ex. 31:13-17, Ex. 23:12, Deut. 5:13-14), a rule that also applies to proselytes, and a sign respecting two events: the seventh day, during which God rested after having completed Creation in six days (Gen. 2:2-3, Ex. 20:8-11), and God's deliverance of the Israelites from Egypt (Deut. 5:12-15).
  • 1.9K
  • 09 Oct 2022
Topic Review
List of Minerals Approved by IMA (T)
This list includes those recognised minerals beginning with the letter T. The International Mineralogical Association is the international group that recognises new minerals and new mineral names, however minerals discovered before 1959 did not go through the official naming procedure, although some minerals published previously have been either confirmed or discredited since that date. This list contains a mixture of mineral names that have been approved since 1959 and those mineral names believed to still refer to valid mineral species (these are called "grandfathered" species). The data was exported from mindat.org on 29 April 2005; updated up to 'IMA2018'. The minerals are sorted by name, followed by the structural group (rruff.info/ima and ima-cnmnc by mineralienatlas.de, mainly) or chemical class (mindat.org and basics), the year of publication (if it's before of an IMA approval procedure), the IMA approval and the Nickel–Strunz code.
  • 3.0K
  • 09 Oct 2022
Topic Review
Corrective Rape
Corrective rape, also called curative or homophobic rape, is a hate crime in which one or more people are raped because of their perceived sexual orientation or gender identity. The common intended consequence of the rape, as seen by the perpetrator, is to turn the person heterosexual or to enforce conformity with gender stereotypes. The term corrective rape was coined in South Africa after well-known cases of corrective rapes of lesbian women such as Eudy Simelane (who was also murdered in the same attack) and Zoliswa Nkonyana became public. Popularisation of the term has raised awareness and encouraged LGBT+ people in countries across the world to come forward with their own stories of being raped as punishment for or in an attempt to change their sexual orientation or gender identity. Although some countries have laws protecting LGBT+ people, corrective rape is often overlooked.
  • 18.8K
  • 09 Oct 2022
Topic Review
Armor-Piercing Ammunition
Armour-piercing ammunition (AP) is a type of projectile designed to penetrate either body armour or vehicle armour. From the 1860s to 1950s, a major application of armour-piercing projectiles was to defeat the thick armour carried on many warships and cause damage to their lightly-armoured interiors. From the 1920s onwards, armour-piercing weapons were required for anti-tank missions. AP rounds smaller than 20 mm are intended for lightly-armoured targets such as body armour, bulletproof glass and lightly-armoured vehicles. As tank armour improved during World War II, anti-vehicle rounds began to use a smaller but dense penetrating body within a larger shell, firing at very high muzzle velocity. Modern penetrators are long rods of dense material like tungsten or depleted uranium (DU) that further improves the terminal ballistics.
  • 10.0K
  • 12 Oct 2022
Topic Review
USRC Washington (1833)
The United States Revenue Cutter Washington was one of the 13 cutters of the Morris-Taney class. These cutters were the backbone of the United States Revenue Cutter Service for more than a decade. Samuel Humphreys designed these cutters for roles as diverse as fighting pirates, privateers, combating smugglers and operating with naval forces. He designed the vessels on a naval schooner concept. They had Baltimore Clipper lines. The vessels built by Webb and Allen, designed by Isaac Webb, resembled Humphreys' but had one less port.
  • 602
  • 09 Oct 2022
Topic Review
Means Test
A means test is a determination of whether an individual or family is eligible for government assistance or welfare, based upon whether the individual or family possesses the means to do without that help.
  • 1.3K
  • 09 Oct 2022
  • Page
  • of
  • 863

Other Entry Collections

>>