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Onium Compound
In chemistry, an onium ion is a cation formally obtained by the protonation of mononuclear parent hydride of a pnictogen (group 15 of the periodic table), chalcogen (group 16), or halogen (group 17). The oldest-known onium ion, and the namesake for the class, is ammonium, NH+4, the protonated derivative of ammonia, NH3. The name onium is also used for cations that would result from the substitution of hydrogen atoms in those ions by other groups, such as organic radicals, or halogens; such as tetraphenylphosphonium, (C6H5)4P+. The substituent groups may be divalent or trivalent, yielding ions such as iminium and nitrilium. A simple onium ion has a charge of +1. A larger ion that has two onium ion subgroups is called a double onium ion, and has a charge of +2. A triple onium ion has a charge of +3, and so on. Compounds of an onium cation and some other negative ion are known as onium compounds or onium salts. Onium ions and onium compounds are inversely analogous to -ate ions and ate complexes:
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  • 16 Nov 2022
Topic Review
Overhead Camshaft
Overhead camshaft, commonly abbreviated to OHC, is a valvetrain configuration which places the camshaft of an internal combustion engine of the reciprocating type within the cylinder heads ("above" the pistons and combustion chambers) and drives the valves or lifters in a more direct manner compared with overhead valves (OHV) and pushrods.
  • 16.5K
  • 21 Nov 2022
Topic Review
Sanguinones
Mycena sanguinolenta, commonly known as the bleeding bonnet, the smaller bleeding Mycena, or the terrestrial bleeding Mycena, is a species of mushroom in the family Mycenaceae. It is a common and widely distributed species, and has been found in North America, Europe, Australia, and Asia. The fungus produces reddish-brown to reddish-purple fruit bodies with conic to bell-shaped caps up to 1.5 cm (0.6 in) wide held by slender stipes up to 6 cm (2.4 in) high. When fresh, the fruit bodies will "bleed" a dark reddish-purple sap. The similar Mycena haematopus is larger, and grows on decaying wood, usually in clumps. M. sanguinolenta contains alkaloid pigments that are unique to the species, may produce an antifungal compound, and is bioluminescent. The edibility of the mushroom has not been determined.
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  • 16 Nov 2022
Topic Review
Educator Effectiveness
Educator effectiveness is a K-12 school system education policy initiative that measures the quality of an educator performance in terms of improving student learning. It describes a variety of methods, such as observations, student assessments, student work samples and examples of teacher work, that education leaders use to determine the effectiveness of a K-12 educator. The drive for educator effectiveness programs stem from Race to the top where states were awarded points for meeting educational policies based on the teacher's effectiveness. This policy was the basis of the emergence of statewide educator effectiveness programs. Educator effectiveness programs vary from state to state. Typically, an educator effectiveness program describes a cycle of observations and assessments that apply to different groups of teachers during an academic year. New teachers are evaluated more frequently, and veteran teachers are evaluated across multiple year cycles. Evaluated teachers have multiple scheduled classroom observations and conferences with the evaluator in addition to unannounced classroom observations. A controversial aspect of The purpose of evaluations is to help educators determine what is effective in their practices and provides them a medium to reflect upon and change their practice to help teachers become more effective.
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  • 16 Nov 2022
Topic Review
Acute Necrotizing Ulcerative Gingivostomatitis
Acute necrotizing ulcerative gingivitis (ANUG) is a common, non-contagious infection of the gums with sudden onset. The main features are painful, bleeding gums, and ulceration of inter-dental papillae (the sections of gum between adjacent teeth). This disease, along with necrotizing (ulcerative) periodontitis (NP or NUP) is classified as a necrotizing periodontal disease, one of the seven general types of gum disease caused by inflammation of the gums (periodontitis). The often severe gum pain that characterizes ANUG distinguishes it from the more common chronic periodontitis which is rarely painful. If ANUG is improperly treated or neglected, it may become chronic and/or recurrent. The causative organisms are mostly anaerobic bacteria, particularly Fusobacteriota and spirochete species. Predisposing factors include poor oral hygiene, smoking, poor nutrition, psychological stress, and a weakened immune system. When the attachments of the teeth to the bone are involved, the term NUP is used. Treatment of ANUG is by removal of dead gum tissue and antibiotics (usually metronidazole) in the acute phase, and improving oral hygiene to prevent recurrence. Although the condition has a rapid onset and is debilitating, it usually resolves quickly and does no serious harm. The informal name trench mouth arose during World War I as many soldiers developed the disease, probably because of the poor conditions and extreme psychological stress.
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  • 16 Nov 2022
Topic Review
Apparitional Experience
In parapsychology, an apparitional experience is an anomalous experience characterized by the apparent perception of either a living being or an inanimate object without there being any material stimulus for such a perception. The person experiencing the apparition is awake, excluding dream visions from consideration. In academic discussion, the term "apparitional experience" is to be preferred to the term "ghost" in respect of the following points:
  • 699
  • 16 Nov 2022
Topic Review
Infinity
In philosophy and theology, infinity is explored in articles under headings such as the Absolute, God, and Zeno's paradoxes. In Greek philosophy, for example in Anaximander, 'the Boundless' is the origin of all that is. He took the beginning or first principle to be an endless, unlimited primordial mass (ἄπειρον, apeiron). The Jain metaphysics and mathematics were the first to define and delineate different "types" of infinities. The work of the mathematician Georg Cantor first placed infinity into a coherent mathematical framework. Keenly aware of his departure from traditional wisdom, Cantor also presented a comprehensive historical and philosophical discussion of infinity. In Christian theology, for example in the work of Duns Scotus, the infinite nature of God invokes a sense of being without constraint, rather than a sense of being unlimited in quantity.
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  • 16 Nov 2022
Topic Review
Proto-Norse
Proto-Norse (also called Ancient Nordic, Ancient Scandinavian, Primitive Norse, Proto-Nordic, Proto-Scandinavian, Proto-North Germanic and North Proto-Germanic) was an Indo-European language spoken in Scandinavia and a reconstructed proto-language of Old Norse that is thought to have evolved as a northern dialect of Proto-Germanic in the first centuries CE. It is the earliest stage of a characteristically North Germanic language, and the language attested in the oldest Scandinavian Elder Futhark inscriptions, spoken from around the 2nd to the 8th centuries CE (corresponding to the late Roman Iron Age and the Germanic Iron Age). It evolved into the dialects of Old Norse at the beginning of the Viking Age around 800 CE, which later themselves evolved into the modern North Germanic languages (Faroese, Icelandic, the three Continental Scandinavian languages, and their dialects).
  • 2.0K
  • 17 Nov 2022
Topic Review
Coherence
In physics, two wave sources are coherent if their frequency and waveform are identical. Coherence is an ideal property of waves that enables stationary (i.e. temporally or spatially constant) interference. It contains several distinct concepts, which are limiting cases that never quite occur in reality but allow an understanding of the physics of waves, and has become a very important concept in quantum physics. More generally, coherence describes all properties of the correlation between physical quantities of a single wave, or between several waves or wave packets. Interference is the addition, in the mathematical sense, of wave functions. A single wave can interfere with itself, but this is still an addition of two waves (see Young's slits experiment). Constructive or destructive interference are limit cases, and two waves always interfere, even if the result of the addition is complicated or not remarkable. When interfering, two waves can add together to create a wave of greater amplitude than either one (constructive interference) or subtract from each other to create a wave of lesser amplitude than either one (destructive interference), depending on their relative phase. Two waves are said to be coherent if they have a constant relative phase. The amount of coherence can readily be measured by the interference visibility, which looks at the size of the interference fringes relative to the input waves (as the phase offset is varied); a precise mathematical definition of the degree of coherence is given by means of correlation functions. Spatial coherence describes the correlation (or predictable relationship) between waves at different points in space, either lateral or longitudinal. Temporal coherence describes the correlation between waves observed at different moments in time. Both are observed in the Michelson–Morley experiment and Young's interference experiment. Once the fringes are obtained in the Michelson interferometer, when one of the mirrors is moved away gradually from the beam-splitter, the time for the beam to travel increases and the fringes become dull and finally disappear, showing temporal coherence. Similarly, in a double-slit experiment, if the space between the two slits is increased, the coherence dies gradually and finally the fringes disappear, showing spatial coherence. In both cases, the fringe amplitude slowly disappears, as the path difference increases past the coherence length.
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  • 16 Nov 2022
Topic Review
IntelliStar
The IntelliStar was the fifth-generation successor to the WeatherStar systems used by the United States cable and satellite television channel The Weather Channel (TWC), that is used to insert local forecasts and current weather information (such as the "Local on the 8s" segments within its program schedule) into TWC's programming. Like the WeatherStar, it is installed at the cable provider's headend. The IntelliStar has many enhanced features over its predecessor, the Weather Star XL. Like all other WeatherStar systems, the IntelliStar receives its data over a satellite connection and over the Internet. However, unlike the rest of the systems, it has the capability to receive more complex information in a more efficient manner. It also has a DualFeed feature, which allows a selection of two different video feeds. In the event of inclement weather, the DualFeed option would switch from the first (network) feed, to a second (localized) feed, providing weather information to a specific STAR or network of STARs. By doing this, the specified network of STARs could be addressed with weather updates, versus the entire national network of STARs (where such information would be irrelevant). It also has an improved graphics display and dynamic radar capabilities. HiRAD (High Resolution Aggregated Data) technology – which was added to the IntelliStar in 2006 – allows The Weather Channel to choose any city, town or landmark as an observation or forecast site and provide data. Occasionally, the HiRAD function will fail, in which case the National Weather Service sites are used (only the current conditions – and previously, the eight-city product and regional/metro products – are affected significantly). In May 2015, it was announced that all IntelliStar units would be replaced with either the IntelliStar 2 or the IntelliStar 2 Jr. by October 1, 2015. The IntelliStar was discontinued on November 16, 2015.
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  • 16 Nov 2022
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