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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.

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Solar Compass
The solar compass, a surveying instrument that makes use of the sun's direction, was first invented and made by William Austin Burt. He patented it on February 25, 1836, in the United States Patent Office as No 9428X. It received a medal at the Great Exhibition of 1851.
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  • 14 Nov 2022
Topic Review
Polar Moment of Inertia
The polar moment (of inertia), also known as second (polar) moment of area, is a quantity used to describe resistance to torsional deformation (deflection), in cylindrical (or non-cylindrical) objects (or segments of an object) with an invariant cross-section and no significant warping or out-of-plane deformation. It is a constituent of the second moment of area, linked through the perpendicular axis theorem. Where the planar second moment of area describes an object's resistance to deflection (bending) when subjected to a force applied to a plane parallel to the central axis, the polar second moment of area describes an object's resistance to deflection when subjected to a moment applied in a plane perpendicular to the object's central axis (i.e. parallel to the cross-section). Similar to planar second moment of area calculations ([math]\displaystyle{ I_x }[/math],[math]\displaystyle{ I_y }[/math], and [math]\displaystyle{ I_{xy} }[/math]), the polar second moment of area is often denoted as [math]\displaystyle{ I_z }[/math]. While several engineering textbooks and academic publications also denote it as [math]\displaystyle{ J }[/math] or [math]\displaystyle{ J_z }[/math], this designation should be given careful attention so that it does not become confused with the torsion constant, [math]\displaystyle{ J_t }[/math], used for non-cylindrical objects. Simply put, the polar moment of inertia is a shaft or beam's resistance to being distorted by torsion, as a function of its shape. The rigidity comes from the object's cross-sectional area only, and does not depend on its material composition or shear modulus. The greater the magnitude of the polar moment of inertia, the greater the torsional resistance of the object.
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Topic Review
Timeline of Computing 2000–09
This article presents a detailed timeline of events in the history of computing from 2000 to 2009. For narratives explaining the overall developments, see the History of computing.
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Topic Review
F9R Dev1
Grasshopper and the Falcon 9 Reusable Development Vehicles (F9R Dev) were experimental flight test reusable rockets that performed vertical takeoffs and landings. The project was privately funded by SpaceX, with no funds provided by any government until later on. Two prototypes were built, and both were launched from the ground. Grasshopper was announced in 2011 and began low-altitude, low-velocity hover/landing testing in 2012. The initial Grasshopper test vehicle was 106 ft (32 m) tall and made eight successful test flights in 2012 and 2013 before being retired. A second Grasshopper-class prototype was the larger and more capable Falcon 9 Reusable Development Vehicle (F9R Dev, also known as F9R Dev1) based on the Falcon 9 v1.1 launch vehicle. It was tested at higher altitudes and was capable of much higher velocity but was never tested at high velocity. The F9R Dev1 vehicle was built in 2013–2014 and made its first low-altitude flight test on 17 April 2014; it was lost during a three-engine test at the McGregor test site on 22 August 2014, which ended the low-velocity test program. Further expansion of the flight test envelope for the reusable rocket was moved to descending Falcon 9 boosters that had been used on orbital flight trajectories on commercial orbital flights of the Falcon 9. The Grasshopper and F9R Dev tests were fundamental to the development of the reusable Falcon 9 and Falcon Heavy rockets, which require vertical landings of the near-empty Falcon 9 and Falcon Heavy first-stage booster tanks and engine assemblies. The Grasshopper and the F9R Dev tests led into a series of high-altitude, high-speed controlled-descent tests of post-mission (spent) Falcon 9 booster stages that accompanied the commercial Falcon 9 missions since September 2013. The latter eventually resulted in the first successful booster landing on 21 December 2015.
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Topic Review
Compounds of Fluorine
Fluorine forms a great variety of chemical compounds, within which it always adopts an oxidation state of −1. With other atoms, fluorine forms either polar covalent bonds or ionic bonds. Most frequently, covalent bonds involving fluorine atoms are single bonds, although at least two examples of a higher order bond exist. Fluoride may act as a bridging ligand between two metals in some complex molecules. Molecules containing fluorine may also exhibit hydrogen bonding (a weaker bridging link to certain nonmetals). Fluorine's chemistry includes inorganic compounds formed with hydrogen, metals, nonmetals, and even noble gases; as well as a diverse set of organic compounds. For many elements (but not all) the highest known oxidation state can be achieved in a fluoride. For some elements this is achieved exclusively in a fluoride, for others exclusively in an oxide; and for still others (elements in certain groups) the highest oxidation states of oxides and fluorides are always equal.
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Biography
George Marshall
General of the Army George Catlett Marshall Jr. (December 31, 1880 – October 16, 1959) was an American soldier and statesman. He rose through the United States Army to become Chief of Staff under presidents Franklin D. Roosevelt and Harry S. Truman, then served as Secretary of State and Secretary of Defense under Truman.[1] Winston Churchill lauded Marshall as the "organizer of victory" for hi
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Topic Review
Italia (Airship)
The Italia was a semi-rigid airship belonging to the Italian Air Force. It was used by Italian engineer and General Umberto Nobile in his second series of flights around the North Pole. It crashed in 1928, with one confirmed fatality from the crash, one fatality from exposure while awaiting rescue, and the death of six crew members who were trapped in the still-airborne envelope. At the end of the rescue operations there were 17 dead (crew and rescuers).
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Topic Review
Features New to Windows 7
Some of the new features included in Windows 7 are advancements in touch, speech and handwriting recognition, support for virtual hard disks, support for additional file formats, improved performance on multi-core processors, improved boot performance, and kernel improvements. Some of the features which are present in versions up to and including Windows Vista were removed or changed.
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Topic Review
NeWS
NeWS (Network extensible Window System) is a discontinued windowing system developed by Sun Microsystems in the mid-1980s. Originally known as "SunDew", its primary authors were James Gosling and David S. H. Rosenthal. The NeWS interpreter was based on PostScript (as was the later Display PostScript, although the two projects were otherwise unrelated) extending it to allow interaction and multiple "contexts" to support windows. Like PostScript, NeWS could be used as a complete programming language, but unlike PostScript, NeWS could be used to make complete interactive programs with mouse support and a GUI.
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Topic Review
History of Purgatory
The idea of purgatory has roots that date back into antiquity. A sort of proto-purgatory called the "celestial Hades" appears in the writings of Plato and Heraclides Ponticus and in many other pagan writers. This concept is distinguished from the Hades of the underworld described in the works of Homer and Hesiod. In contrast, the celestial Hades was understood as an intermediary place where souls spent an undetermined time after death before either moving on to a higher level of existence or being reincarnated back on earth. Its exact location varied from author to author. Heraclides of Pontus thought it was in the Milky Way; the Academicians, the Stoics, Cicero, Virgil, Plutarch, the Hermetical writings situated it between the Moon and the Earth or around the Moon; while Numenius and the Latin Neoplatonists thought it was located between the sphere of the fixed stars and the Earth. Perhaps under the influence of Hellenistic thought, we find another intermediate state entering Jewish religious thought in the last centuries B.C.E. In Maccabees we find the practice of prayer for the dead with a view to their after life purification a practice accepted by some Christians. The same practice appears in other traditions, such as the medieval Chinese Buddhist practice of making offerings on behalf of the dead, who are said to suffer numerous trials. Among other reasons, Catholic belief in purgatory is based on the practice of prayer for the dead. Descriptions and doctrine regarding purgatory developed over the centuries. Those who believe in purgatory interpret extra-biblical passages such as 2 Maccabees 12:41-46 (not accepted as Scripture by Protestants but recognized by Orthodox and Catholics), and biblical passages such as 2 Timothy 1:18, Matthew 12:32, Luke 16:19-16:26, Luke 23:43, 1 Corinthians 3:11-3:15 and Hebrews 12:29 as support for prayer for the dead, an active interim state for the dead prior to the resurrection, and purifying flames after death. The first Christians looked forward to the imminent return of Christ and did not develop detailed beliefs about the interim state. Gradually, Christians, especially in the West, took an interest in circumstances of the interim state between one's death and the future resurrection. Christians both East and West prayed for the dead in this interim state, although theologians in the East refrained from defining it. Augustine of Hippo distinguished between the purifying fire that saves and eternal consuming fire for the unrepentant. Gregory the Great established a connection between earthly penance and purification after death. All Soul's Day, established in the 10th century, turned popular attention to the condition of departed souls. The idea of Purgatory as a physical place (like heaven and hell) was "born" in the late 11th century. Medieval theologians concluded that the purgatorial punishments consisted of material fire. The Western formulation of purgatory proved to be a sticking point in the Great Schism between East and West. The Catholic Church believes that the living can help those whose purification from their sins is not yet completed not only by praying for them but also by gaining indulgences for them as an act of intercession. The later Middle Ages saw the growth of considerable abuses, such as the unrestricted sale of indulgences by professional "pardoners" sent to collect contributions to projects such as the rebuilding of St. Peter's Basilica in Rome. These abuses were one of the factors that led to the Protestant Reformation. Most Protestants rejected the idea of purgatory, as never clearly mentioned in Luther's canon of the Bible, which excludes the Deuterocanonical books. Modern Catholic theologians have softened the punitive aspects of purgatory and stress instead the willingness of the dead to undergo purification as preparation for the happiness of heaven The English Anglican scholar John Henry Newman argued, in a book that he wrote before becoming Catholic, that the essence of the doctrine on purgatory is locatable in ancient tradition, and that the core consistency of such beliefs are evidence that Christianity was "originally given to us from heaven".
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