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Base
In chemistry, there are three definitions in common use of the word base, known as Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances which react with acids as originally proposed by G.-F. Rouelle in the mid-18th century. In 1884, Svante Arrhenius proposed that a base is a substance which dissociates in aqueous solution to form Hydroxide ions OH−. These ions can react with hydrogen ions (H+ according to Arrhenius) from the dissociation of acids to form water in an acid–base reaction. A base was therefore a metal hydroxide such as NaOH or Ca(OH)2. Such aqueous hydroxide solutions were also described by certain characteristic properties. They are slippery to the touch, can taste bitter and change the color of pH indicators (e.g., turn red litmus paper blue). In water, by altering the autoionization equilibrium, bases yield solutions in which the hydrogen ion activity is lower than it is in pure water, i.e., the water has a pH higher than 7.0 at standard conditions. A soluble base is called an alkali if it contains and releases OH− ions quantitatively. Metal oxides, hydroxides, and especially alkoxides are basic, and conjugate bases of weak acids are weak bases. Bases and acids are seen as chemical opposites because the effect of an acid is to increase the hydronium (H3O+) concentration in water, whereas bases reduce this concentration. A reaction between aqueous solutions of an acid and a base is called neutralization, producing a solution of water and a salt in which the salt separates into its component ions. If the aqueous solution is saturated with a given salt solute, any additional such salt precipitates out of the solution. In the more general Brønsted–Lowry acid–base theory (1923), a base is a substance that can accept hydrogen cations (H+)—otherwise known as protons. This does include aqueous hydroxides since OH− does react with H+ to form water, so that Arrhenius bases are a subset of Brønsted bases. However, there are also other Brønsted bases which accept protons, such as aqueous solutions of ammonia (NH3) or its organic derivatives (amines). These bases do not contain a hydroxide ion but nevertheless react with water, resulting in an increase in the concentration of hydroxide ion. Also, some non-aqueous solvents contain Brønsted bases which react with solvated protons. For example in liquid ammonia, NH2− is the basic ion species which accepts protons from NH4+, the acidic species in this solvent. G. N. Lewis realized that water, ammonia, and other bases can form a bond with a proton due to the unshared pair of electrons that the bases possess. In the Lewis theory, a base is an electron pair donor which can share a pair of electrons with an electron acceptor which is described as a Lewis acid. The Lewis theory is more general than the Brønsted model because the Lewis acid is not necessarily a proton, but can be another molecule (or ion) with a vacant low-lying orbital which can accept a pair of electrons. One notable example is boron trifluoride (BF3). Some other definitions of both bases and acids have been proposed in the past, but are not commonly used today.
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Topic Review
List of Statistical Packages
Statistical software are specialized computer programs for analysis in statistics and econometrics.
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  • 29 Sep 2022
Topic Review
Upper Mantle (Earth)
The upper mantle of the Earth begins just beneath the crust about 35 km (22 mi) and ends at the top of the lower mantle at 670 km (420 mi). Temperatures range from approximately 200 °C (392 °F) at the upper boundary with the crust to approximately 900 °C (1,650 °F) at the boundary with the lower mantle. Upper mantle material which has come up onto the surface is made up of about 55% olivine, 35% pyroxene and 5 to 10% of calcium oxide and aluminum oxide minerals such as plagioclase, spinel or garnet, depending upon depth.
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Topic Review
Pegasus in Popular Culture
The winged, divine horse Pegasus has been a prominent figure in modern popular culture.
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Topic Review
MINIX
Minix (from "mini-Unix") is a POSIX-compliant (since version 2.0), Unix-like operating system based on a microkernel architecture. Early versions of MINIX were created by Andrew S. Tanenbaum for educational purposes. Starting with MINIX 3, the primary aim of development shifted from education to the creation of a highly reliable and self-healing microkernel OS. MINIX is now developed as open-source software. MINIX was first released in 1987, with its complete source code made available to universities for study in courses and research. It has been free and open-source software since it was re-licensed under the BSD license in April 2000.
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Topic Review
Recovery Model
The recovery model, recovery approach or psychological recovery is an approach to mental disorder or substance dependence that emphasizes and supports a person's potential for recovery. Recovery is generally seen in this model as a personal journey rather than a set outcome, and one that may involve developing hope, a secure base and sense of self, supportive relationships, empowerment, social inclusion, coping skills, and meaning. Recovery sees symptoms as a continuum of the norm rather than an aberration and rejects sane-insane dichotomy. William Anthony, Director of the Boston Centre for Psychiatric Rehabilitation developed a quaint cornerstone definition of mental health recovery in 1993. "Recovery is a deeply personal, unique process of changing one's attitudes, values, feelings, goals, skills and/or roles. It is a way of living a satisfying, hopeful, and contributing life even with limitations caused by the illness. Recovery involves the development of new meaning and purpose in one's life as one grows beyond the catastrophic effects of mental illness." The use of the concept in mental health emerged as deinstitutionalization resulted in more individuals living in the community. It gained impetus as a social movement due to a perceived failure by services or wider society to adequately support social inclusion, and to studies demonstrating that many people do recover. A recovery approach has now been explicitly adopted as the guiding principle of the mental health or substance dependency policies of a number of countries and states. In many cases practical steps are being taken to base services on a recovery model, although a range of obstacles, concerns and criticisms have been raised both by service providers and by recipients of services. A number of standardized measures have been developed to assess aspects of recovery, although there is some variation between professionalized models and those originating in the psychiatric survivors movement.
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Topic Review
History of Research Ships
The research ship had origins in the early voyages of exploration. By the time of James Cook's Endeavour, the essentials of what today we would call a research ship are clearly apparent. In 1766, the Royal Society hired Cook to travel to the Pacific Ocean to observe and record the transit of Venus across the Sun. The Endeavour was a sturdy boat, well designed and equipped for the ordeals she would face, and fitted out with facilities for her research personnel, Joseph Banks. And, as is common with contemporary research vessels, Endeavour carried out more than one kind of research, including comprehensive hydrographic survey work. Some other notable early research vessels were HMS Beagle, RV Calypso, HMS Challenger, and the Endurance and Terra Nova.
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Topic Review
Electronic Data Interchange
Electronic data interchange (EDI) is the concept of businesses electronically communicating information that was traditionally communicated on paper, such as purchase orders and invoices. Technical standards for EDI exist to facilitate parties transacting such instruments without having to make special arrangements. EDI has existed at least since the early 70s, and there are many EDI standards (including X12, EDIFACT, ODETTE, etc.), some of which address the needs of specific industries or regions. It also refers specifically to a family of standards. In 1996, the National Institute of Standards and Technology defined electronic data interchange as "the computer-to-computer interchange of strictly formatted messages that represent documents other than monetary instruments. EDI implies a sequence of messages between two parties, either of whom may serve as originator or recipient. The formatted data representing the documents may be transmitted from originator to recipient via telecommunications or physically transported on electronic storage media." It distinguished mere electronic communication or data exchange, specifying that "in EDI, the usual processing of received messages is by computer only. Human intervention in the processing of a received message is typically intended only for error conditions, for quality review, and for special situations. For example, the transmission of binary or textual data is not EDI as defined here unless the data are treated as one or more data elements of an EDI message and are not normally intended for human interpretation as part of on-line data processing." In short, EDI can be defined as the transfer of structured data, by agreed message standards, from one computer system to another without human intervention.
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Topic Review
Bâton de Commandement
A bâton de commandement, bâton percé or perforated baton is a name given by archaeologists to a particular prehistoric artifact that has been much debated. The name bâtons de commandement was the name first applied to the class of artifacts, but it makes an assumption of function; the name bâton percé, meaning "pierced rod", or "perforated baton" (the term used by the British Museum) is a more recent term, and is descriptive of form rather than any presumed function. Many are decorated with carved or engraved animals, and the most usual explanation of their use is that they were used for straightening spears and arrows, and as spear-throwers.
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Topic Review
Global Energy and Water Cycle Experiment
The Global Energy and Water Cycle Experiment (GEWEX) is a research program of the World Climate Research Programme intended to observe, comprehend and model the Earth's water cycle. The experiment also observes how much energy the Earth receives, studies how much of that energy reaches surfaces of the Earth and how that energy is transformed. Sunlight's energy evaporates water to produce clouds and rain, and dries out land masses after rain. Rain that falls on land becomes the water budget which can be used by people for agricultural and other processes. GEWEX is a collaboration of researchers worldwide to find better ways of studying the water cycle and how it transforms energy through the atmosphere. If the Earth's climates were identical from year to year, then people could predict when, where and what crops to plant. However, instability created by solar variation, weather trends, and chaotic events create weather that is unpredictable on seasonal scales. Through weather patterns such as droughts and higher rainfall these cycles impact ecosystems and human activities. GEWEX is designed to collect a much greater amount of data, and see if better models of that data can forecast weather and climate change into the future. GEWEX is organized into several structures. As GEWEX was conceived projects were organized by participating factions, this task is now done by the International GEWEX Project Office (IGPO). IGPO oversees major initiatives and coordinates between national projects in an effort to bring about communication of researchers. IGPO claims to support communication exchange between 2000 scientist and is the instrument for publication of major reports. The Scientific Steering Group organizes the projects and assigns them to panels, which oversee progress and provide critique. The Coordinated Energy and Water Cycle Observations Project (CEOP) the 'Hydrology Project' is a major instrument in GEWEX. This panel includes geographic study areas such as the Climate Prediction Program for the Americas operated by NOAA, but also examines several types of climate zones (e.g. high altitude and semi-arid). Another panel, the GEWEX Radiation Panel oversees the coordinated use of satellites and ground-based observation to better estimate energy and water fluxes. One recent result GEWEX's Radiation panel has assessed data on rainfall for the last 25 years and determined that global rainfall is 2.61 mm/day with a small statistical variation. While the study period is short, after 25 years of measurement regional trends are beginning to appear. The GEWEX Modeling and Prediction Panel takes current models and analyzes the models when climate forcing phenomena occur (global warming as an example of a 'climate forcing' event). GEWEX is now the core project of WCRP.
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