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
Atomic Radius
The atomic radius of a chemical element is a measure of the size of its atom, usually the mean or typical distance from the center of the nucleus to the outermost isolated electron. Since the boundary is not a well-defined physical entity, there are various non-equivalent definitions of atomic radius. Four widely used definitions of atomic radius are: Van der Waals radius, ionic radius, metallic radius and covalent radius. Typically, because of the difficulty to isolate atoms in order to measure their radii separately, atomic radius is measured in a chemically bonded state; however theoretical calculations are simpler when considering atoms in isolation. The dependencies on environment, probe, and state lead to a multiplicity of definitions. Depending on the definition, the term may apply to atoms in condensed matter, covalently bonding in molecules, or in ionized and excited states; and its value may be obtained through experimental measurements, or computed from theoretical models. The value of the radius may depend on the atom's state and context. Electrons do not have definite orbits nor sharply defined ranges. Rather, their positions must be described as probability distributions that taper off gradually as one moves away from the nucleus, without a sharp cutoff; these are referred to as atomic orbitals or electron clouds. Moreover, in condensed matter and molecules, the electron clouds of the atoms usually overlap to some extent, and some of the electrons may roam over a large region encompassing two or more atoms. Under most definitions the radii of isolated neutral atoms range between 30 and 300 pm (trillionths of a meter), or between 0.3 and 3 ångströms. Therefore, the radius of an atom is more than 10,000 times the radius of its nucleus (1–10 fm), and less than 1/1000 of the wavelength of visible light (400–700 nm). For many purposes, atoms can be modeled as spheres. This is only a crude approximation, but it can provide quantitative explanations and predictions for many phenomena, such as the density of liquids and solids, the diffusion of fluids through molecular sieves, the arrangement of atoms and ions in crystals, and the size and shape of molecules.
  • 3.3K
  • 18 Oct 2022
Topic Review
Sex Differences in Eyewitness Memory
The evidence regarding gender differences in eyewitness memory is contradictory. Studies that have found differences note that women are more capable of remembering details regarding other women at the scene, while men are better able to remember details about other men. Studies maintaining that there is no difference state that accuracy and susceptibility to false information do not vary with gender.
  • 2.4K
  • 14 Oct 2022
Topic Review
Long-term Complications of Standing
The long-term complications of standing are the conditions that may arise after prolonged time in a standing or upright position including standing, walking or running. Many of the complications come from prolonged standing (more the 60% of a work day) that is repeated several times a week. There are many different jobs that require prolonged standing. These included: "retail staff, Baristas, bartenders, assembly line workers, security staff, engineers, catering staff, library assistants, hair stylists and laboratory technicians." Cornell university has calculated that "Standing requires ~20% more energy than sitting".
  • 965
  • 14 Oct 2022
Topic Review
Stoner–Wohlfarth Model
The Stoner–Wohlfarth model is a widely used model for the magnetization of single-domain ferromagnets. It is a simple example of magnetic hysteresis and is useful for modeling small magnetic particles in magnetic storage, biomagnetism, rock magnetism and paleomagnetism.
  • 2.0K
  • 14 Oct 2022
Topic Review
Black Sea Trade and Economy
The Black Sea trade and economy provide an integral part in the connection between Asia and Europe. In addition to sea ports and fishing, key activities include hydrocarbons exploration for oil and natural gas, and tourism. According to NATO, the Black sea is a strategic corridor that provides smuggling channels for moving legal and illegal goods including drugs, radioactive materials, and counterfeit goods that can be used to finance terrorism.
  • 1.7K
  • 14 Oct 2022
Topic Review
Wooden Boats of World War 2
Splinter fleet or Splinter navy was a nickname given to the wooden boats used in World War II. The boats served in many different roles during the war. These boats were built in small boatyards on the West coast and East coast, Great Lakes and the Gulf of Mexico. They could be built quickly, in just 60 to 120 days. Most of the boats were built by boatyards that already had the tools and knowledge from building yachts, sailboats and motor boats. Many were built by craftsmen in family-owned small businesses. Under the Emergency Shipbuilding Program and War Shipping Administration contracts went out to over fifty boatyards across the country. The boats were built for the US Navy, the, United States Army Air Forces , United States Coast Guard, and US Army. Some of the wooden boats went to Allied nations on the Lend-Lease program. In addition to new boat construction, some wooden boats built between 1910 and 1941 were acquired for the war effort, some used as-is and others converted for war use. Wooden boats have lighter weight and are easier to repair than steel hull boats. These wooden boats ranged from 19 to 200 feet in length. Some worked near shore and others working in the open ocean, called the Blue-water navy. The Splinter fleet is in contrast to the more common steel hull war ships and Merchant Marine ships. After the war, many of these boats were deemed not needed. Many were abandoned or destroyed, a few served in the Korean war and a few in the Vietnam War, some sold to private and some donated. During World War I there was a debate as to if wooden boats and ships should be used in war time. William Denman, President of the Emergency Fleet Corporation supported the building of wooden ships for the war and General Goethals disapproved. In the end, both men turned in their resignation over the heated debate. During World War II the situation was different. There was a shortage of steel and steel shipyards, so there was no debate about the need for a vast wooden fleet of boats and ships.
  • 6.9K
  • 14 Oct 2022
Topic Review
Puruṣārtha
Puruṣārtha (Sanskrit: पुरुषार्थ) literally means an "object of human pursuit". It is a key concept in Hinduism, and refers to the four proper goals or aims of a human life. The four puruṣārthas are Dharma (righteousness, moral values), Artha (prosperity, economic values), Kama (pleasure, love, psychological values) and Moksha (liberation, spiritual values). All four Purusarthas are important, but in cases of conflict, Dharma is considered more important than Artha or Kama in Hindu philosophy. Moksha is considered the ultimate ideal of human life. At the same time, this is not a consensus among all Hindus, and many have different interpretations of the hierarchy, and even as to whether one should exist. Historical Indian scholars recognized and debated the inherent tension between active pursuit of wealth (Artha purusartha) and pleasure (Kama), and renunciation of all wealth and pleasure for the sake of spiritual liberation (Moksha). They proposed "action with renunciation" or "craving-free, dharma-driven action", also called Nishkam Karma as a possible solution to the tension.
  • 13.4K
  • 14 Oct 2022
Topic Review
Hamilton Family
The Hamiltons of the United States are a family of Scottish origin, whose most prominent member was Alexander Hamilton (1755/1757–1804), one of the Founding Fathers of the United States. Their ancestors and relations in Scotland included the Lairds of Kerelaw Castle in Stevenston, North Ayrshire, of the Cambuskeith branch of Clan Hamilton.
  • 6.0K
  • 14 Oct 2022
Topic Review
Río Negro Province
Río Negro (Spanish pronunciation: [ˈri.o ˈneɣɾo], Black River) is a province of Argentina , located at the northern edge of Patagonia. Neighboring provinces are from the south clockwise Chubut, Neuquén, Mendoza, La Pampa and Buenos Aires. To the east lies the Atlantic Ocean. Its capital is Viedma, and its largest city is Bariloche. Other important cities include General Roca and Cipolletti.
  • 3.5K
  • 14 Oct 2022
Topic Review
Reanimation Package of Reforms
The Reanimation Package of Reforms Coalition (RPR Coalition) is a voluntary association of non-governmental organizations whose purpose is to support and promote reforms to build an independent, democratic, legal Ukrainian state and a prosperous society with equal opportunities for development and self-realization of all Individuals, as well as promoting civil society consolidation in Ukraine . (As of 2019), the RPR Coalition brings together 25 NGOs, over 300 experts working in 21 profile teams and is partnered with 19 regional coalition.
  • 981
  • 14 Oct 2022
  • Page
  • of
  • 863

Other Entry Collections

>>