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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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Eucalyptus
Eucalyptus is a paid and open-source computer software for building Amazon Web Services (AWS)-compatible private and hybrid cloud computing environments, originally developed by the company Eucalyptus Systems. Eucalyptus is an acronym for Elastic Utility Computing Architecture for Linking Your Programs To Useful Systems. Eucalyptus enables pooling compute, storage, and network resources that can be dynamically scaled up or down as application workloads change. Mårten Mickos was the CEO of Eucalyptus. In September 2014, Eucalyptus was acquired by Hewlett-Packard and then maintained by DXC Technology. After DXC stopped developing the product in late 2017, AppScale Systems forked the code and started supporting Eucalyptus customers.
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  • 09 Nov 2022
Topic Review
RdRand
RDRAND (previously known as Bull Mountain) is an instruction for returning random numbers from an Intel on-chip hardware random number generator which has been seeded by an on-chip entropy source. RDRAND is available in Ivy Bridge processors[lower-alpha 1] and is part of the Intel 64 and IA-32 instruction set architectures. AMD added support for the instruction in June 2015. The random number generator is compliant with security and cryptographic standards such as NIST SP 800-90A, FIPS 140-2, and ANSI X9.82. Intel also requested Cryptography Research Inc. to review the random number generator in 2012, which resulted in the paper Analysis of Intel's Ivy Bridge Digital Random Number Generator. RDSEED is similar to RDRAND and provides higher level access to the entropy hardware. The RDSEED generator and processor instruction rdseed are available with Intel Broadwell CPUs and AMD Zen CPUs.
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  • 09 Nov 2022
Topic Review
Short Code
Short codes, or short numbers, are short digit sequences, significantly shorter than telephone numbers, that are used to address messages in the Multimedia Messaging System (MMS) and short message service (SMS) systems of mobile network operators. In addition to messaging, they may be used in abbreviated dialing. Short codes are designed to be easier to read and remember than telephone numbers. Short codes are unique to each operator at the technological level. Even so, providers generally have agreements to avoid overlaps. In some countries, such as the United States, some classes of numbers are inter-operator (used by multiple providers or carriers, U.S. inter-operator numbers are called common short codes). Short codes are widely used for value-added services such as charity donations, mobile services, ordering ringtones, and television program voting. Messages sent to a short code can be billed at a higher rate than a standard SMS and may even subscribe a customer to a recurring monthly service that will be added to the customer's mobile phone bill until the user texts, for example, the word "STOP" to terminate the service.
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  • 10 Nov 2022
Topic Review
ATi Radeon R100 Series
The Radeon R100 is the first generation of Radeon graphics chips from ATI Technologies. The line features 3D acceleration based upon Direct3D 7.0 and OpenGL 1.3, and all but the entry-level versions offloading host geometry calculations to a hardware transform and lighting (T&L) engine, a major improvement in features and performance compared to the preceding Rage design. The processors also include 2D GUI acceleration, video acceleration, and multiple display outputs. "R100" refers to the development codename of the initially released GPU of the generation. It is the basis for a variety of other succeeding products.
  • 1.9K
  • 10 Nov 2022
Topic Review
Plasticity
In physics and materials science, plasticity, also known as plastic deformation, is the ability of a solid material to undergo permanent deformation, a non-reversible change of shape in response to applied forces. For example, a solid piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the material itself. In engineering, the transition from elastic behavior to plastic behavior is known as yielding. Plastic deformation is observed in most materials, particularly metals, soils, rocks, concrete, and foams. However, the physical mechanisms that cause plastic deformation can vary widely. At a crystalline scale, plasticity in metals is usually a consequence of dislocations. Such defects are relatively rare in most crystalline materials, but are numerous in some and part of their crystal structure; in such cases, plastic crystallinity can result. In brittle materials such as rock, concrete and bone, plasticity is caused predominantly by slip at microcracks. In cellular materials such as liquid foams or biological tissues, plasticity is mainly a consequence of bubble or cell rearrangements, notably T1 processes. For many ductile metals, tensile loading applied to a sample will cause it to behave in an elastic manner. Each increment of load is accompanied by a proportional increment in extension. When the load is removed, the piece returns to its original size. However, once the load exceeds a threshold – the yield strength – the extension increases more rapidly than in the elastic region; now when the load is removed, some degree of extension will remain. Elastic deformation, however, is an approximation and its quality depends on the time frame considered and loading speed. If, as indicated in the graph opposite, the deformation includes elastic deformation, it is also often referred to as "elasto-plastic deformation" or "elastic-plastic deformation". Perfect plasticity is a property of materials to undergo irreversible deformation without any increase in stresses or loads. Plastic materials that have been hardened by prior deformation, such as cold forming, may need increasingly higher stresses to deform further. Generally, plastic deformation is also dependent on the deformation speed, i.e. higher stresses usually have to be applied to increase the rate of deformation. Such materials are said to deform visco-plastically.
  • 2.8K
  • 10 Nov 2022
Topic Review
Malthusianism
Malthusianism is the idea that population growth is potentially exponential while the growth of the food supply or other resources is linear, which eventually reduces living standards to the point of triggering a population die off. This event, called a Malthusian catastrophe (also known as a Malthusian trap, population trap, Malthusian check, Malthusian crisis, Malthusian spectre, or Malthusian crunch) occurs when population growth outpaces agricultural production, causing famine or war, resulting in poverty and depopulation. Such a catastrophe inevitably has the effect of forcing the population (quite rapidly, due to the potential severity and unpredictable results of the mitigating factors involved, as compared to the relatively slow time scales and well-understood processes governing unchecked growth or growth affected by preventive checks) to "correct" back to a lower, more easily sustainable level. Malthusianism has been linked to a variety of political and social movements, but almost always refers to advocates of population control. These concepts derive from the political and economic thought of the Reverend Thomas Robert Malthus, as laid out in his 1798 writings, An Essay on the Principle of Population. Malthus suggested that while technological advances could increase a society's supply of resources, such as food, and thereby improve the standard of living, the resource abundance would enable population growth, which would eventually bring the per capita supply of resources back to its original level. Some economists contend that since the industrial revolution, mankind has broken out of the trap. Others argue that the continuation of extreme poverty indicates that the Malthusian trap continues to operate. Others further argue that due to lack of food availability coupled with excessive pollution, developing countries show more evidence of the trap. A similar, more modern concept, is that of human overpopulation. Neo-Malthusianism is the advocacy of human population planning to ensure resources and environmental integrities for current and future human populations as well as for other species. In Britain the term 'Malthusian' can also refer more specifically to arguments made in favour of preventive birth control, hence organizations such as the Malthusian League. Neo-Malthusians differ from Malthus's theories mainly in their support for the use of contraception. Malthus, a devout Christian, believed that "self-control" (i.e., abstinence) was preferable to artificial birth control. He also worried that the effect of contraceptive use would be too powerful in curbing growth, conflicting with the common 18th century perspective (to which Malthus himself adhered) that a steadily growing population remained a necessary factor in the continuing "progress of society", generally. Modern neo-Malthusians are generally more concerned than Malthus with environmental degradation and catastrophic famine than with poverty. Malthusianism has attracted criticism from diverse schools of thought, including Marxists and socialists, libertarians and free market enthusiasts, feminists and human rights advocates, characterising it as excessively pessimistic, misanthropic or inhuman. Many critics believe Malthusianism has been discredited since the publication of Principle of Population, often citing advances in agricultural techniques and modern reductions in human fertility. Many modern proponents believe that the basic concept of population growth eventually outstripping resources is still fundamentally valid, and that positive checks are still likely to occur in humanity's future if no action is taken to intentionally curb population growth. In spite of the variety of criticisms against it, the Malthusian argument remains a major discourse based on which national and international environmental regulations are promoted.
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  • 10 Nov 2022
Topic Review
Interference Theory
The interference theory is a theory regarding human memory. Interference occurs in learning. The notion is that memories encoded in long-term memory (LTM) are forgotten and cannot be retrieved into short-term memory (STM) because either memory interferes, or hampers, the other. There is an immense number of encoded memories within the storage of LTM. The challenge for memory retrieval is recalling the specific memory and working in the temporary workspace provided in STM. Retaining information regarding the relevant time of encoding memories into LTM influences interference strength. There are two types of interference effects: proactive and retroactive interference.
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  • 10 Nov 2022
Topic Review
Force Field
In the context of chemistry and molecular modelling, a force field is a computational method that is used to estimate the forces between atoms within molecules and also between molecules. More precisely, the force field refers to the functional form and parameter sets used to calculate the potential energy of a system of atoms or coarse-grained particles in molecular mechanics, molecular dynamics, or Monte Carlo simulations. The parameters for a chosen energy function may be derived from experiments in physics and chemistry, calculations in quantum mechanics, or both. Force fields are interatomic potentials and utilize the same concept as force fields in classical physics, with the difference that the force field parameters in chemistry describe the energy landscape, from which the acting forces on every particle are derived as a gradient of the potential energy with respect to the particle coordinates. All-atom force fields provide parameters for every type of atom in a system, including hydrogen, while united-atom interatomic potentials treat the hydrogen and carbon atoms in methyl groups and methylene bridges as one interaction center. Coarse-grained potentials, which are often used in long-time simulations of macromolecules such as proteins, nucleic acids, and multi-component complexes, sacrifice chemical details for higher computing efficiency.
  • 12.5K
  • 10 Nov 2022
Topic Review
Vichy France
Vichy France (French: Régime de Vichy) is the common name of the French State (État français) headed by Marshal Philippe Pétain during World War II. Evacuated from Paris to Vichy in the unoccupied "Free Zone" (zone libre) in the southern part of metropolitan France which included French Algeria, it remained responsible for the civil administration of all France as well as the French colonial empire. From 1940 to 1942, while the Vichy regime was the nominal government of all of France except for Alsace-Lorraine, the Germans militarily occupied northern France. While Paris remained the de jure capital of France, the government chose to relocate to the town of Vichy, 360 km (220 mi) to the south in the zone libre, which thus became the de facto capital of the French State. Following the Allied landings in French North Africa in November 1942, southern France was also militarily occupied by Germany and Italy to protect the Mediterranean coastline. Petain's government remained in Vichy as the nominal government of France, albeit one that was obliged by circumstances to collaborate with Germany from November 1942 onwards. The government at Vichy remained there until late 1944, when it lost its authority due to the Allied invasion of France. After being appointed Premier by President Albert Lebrun, Marshal Pétain's cabinet agreed to end the war and signed an Armistice with Germany on 22 June 1940. On 10 July, the French Third Republic was dissolved, and Pétain established an authoritarian regime when the National Assembly granted him full powers. The Vichy government reversed many liberal policies and began tight supervision of the economy, calling for "National Regeneration", with central planning a key feature. Labour unions came under tight government control. Conservative Catholics became prominent and clerical input in schools resumed. Paris lost its avant-garde status in European art and culture. The media were tightly controlled and stressed virulent anti-Semitism, and, after June 1941, anti-Bolshevism. The French State maintained nominal sovereignty over the whole of French territory, but had effective full sovereignty only in the unoccupied southern zone libre ("free zone"). It had limited and only civil authority in the northern zones under military occupation. The occupation was to be a provisional state of affairs, pending the conclusion of the war, which at the time (1940) appeared imminent. The occupation also presented certain advantages, such as keeping the French Navy and French colonial empire under French control, and avoiding full occupation of the country by Germany, thus maintaining a degree of French independence and neutrality. The French government at Vichy never joined the Axis alliance. Germany kept two million French soldiers prisoner, carrying out forced labour. They were hostages to ensure that Vichy would reduce its military forces and pay a heavy tribute in gold, food, and supplies to Germany. French police were ordered to round up Jews and other "undesirables" such as communists and political refugees. Much of the French public initially supported the government, despite its undemocratic nature and its difficult position vis-à-vis the Germans, often seeing it as necessary to maintain a degree of French autonomy and territorial integrity. In November 1942, however, the zone libre was also occupied by Axis forces, leading to the disbandment of the remaining army and the sinking of France's remaining fleet and ending any semblance of independence, with Germany now closely supervising all French officials. Most of the overseas French colonies were originally under Vichy control, but with the Allied invasion of North Africa it lost one colony after another to Charles de Gaulle's Allied-oriented Free France. Public opinion in some quarters turned against the French government and the occupying German forces over time, when it became clear that Germany was losing the war, and resistance to them increased. Following the Allied invasion of France in June 1944 and the liberation of France later that year, the Free French Provisional government of the French Republic (GPRF) was installed by the Allies as France's government, led by de Gaulle. Under a "national unanimity" cabinet uniting the many factions of the French Resistance, the GPRF re-established a provisional French Republic, thus apparently restoring continuity with the Third Republic. Most of the legal French government's leaders at Vichy fled or were subject to show trials by the GPRF, and a number were quickly executed for "treason" in a series of purges (épuration légale). Thousands of collaborators were summarily executed by local communists and the Resistance in so-called "savage purges" (épuration sauvage). The last of the French state exiles were captured in the Sigmaringen enclave by de Gaulle's French 1st Armoured Division in April 1945. Pétain, who had voluntarily made his way back to France via Switzerland, was also put on trial for treason by the new Provisional government, and received a death sentence, but this was commuted to life imprisonment by de Gaulle. Only four senior Vichy officials were tried for crimes against humanity, although many more had participated in the deportation of Jews for extermination in Nazi concentration camps, abuses of prisoners, and severe acts against members of the Resistance.
  • 15.3K
  • 09 Nov 2022
Topic Review
Astronomical Interferometer
An astronomical interferometer is an array of separate telescopes, mirror segments, or radio telescope antennas that work together as a single telescope to provide higher resolution images of astronomical objects such as stars, nebulas and galaxies by means of interferometry. The advantage of this technique is that it can theoretically produce images with the angular resolution of a huge telescope with an aperture equal to the separation between the component telescopes. The main drawback is that it does not collect as much light as the complete instrument's mirror. Thus it is mainly useful for fine resolution of more luminous astronomical objects, such as close binary stars. Another drawback is that the maximum angular size of a detectable emission source is limited by the minimum gap between detectors in the collector array. Interferometry is most widely used in radio astronomy, in which signals from separate radio telescopes are combined. A mathematical signal processing technique called aperture synthesis is used to combine the separate signals to create high-resolution images. In Very Long Baseline Interferometry (VLBI) radio telescopes separated by thousands of kilometers are combined to form a radio interferometer with a resolution which would be given by a hypothetical single dish with an aperture thousands of kilometers in diameter. At the shorter wavelengths used in infrared astronomy and optical astronomy it is more difficult to combine the light from separate telescopes, because the light must be kept coherent within a fraction of a wavelength over long optical paths, requiring very precise optics. Practical infrared and optical astronomical interferometers have only recently been developed, and are at the cutting edge of astronomical research. At optical wavelengths, aperture synthesis allows the atmospheric seeing resolution limit to be overcome, allowing the angular resolution to reach the diffraction limit of the optics. Astronomical interferometers can produce higher resolution astronomical images than any other type of telescope. At radio wavelengths, image resolutions of a few micro-arcseconds have been obtained, and image resolutions of a fractional milliarcsecond have been achieved at visible and infrared wavelengths. One simple layout of an astronomical interferometer is a parabolic arrangement of mirror pieces, giving a partially complete reflecting telescope but with a "sparse" or "dilute" aperture. In fact the parabolic arrangement of the mirrors is not important, as long as the optical path lengths from the astronomical object to the beam combiner (focus) are the same as would be given by the complete mirror case. Instead, most existing arrays use a planar geometry, and Labeyrie's hypertelescope will use a spherical geometry.
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  • 09 Nov 2022
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