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Ordovician–Silurian Extinction Events

The Ordovician–Silurian extinction events, when combined, are the second-largest of the five major extinction events in Earth's history in terms of percentage of genera that became extinct. This event greatly affected marine communities, which caused the disappearance of one third of all brachiopod and bryozoan families, and further numerous groups of conodonts, trilobites, and graptolites. The Ordovician–Silurian extinction occurred during the Hirnantian stage of the Ordovician Period and the subsequent Rhuddanian stage of the Silurian Period. The last event, the Late Ordovician mass extinction (LOME), is dated in the interval of 455 to 430 million years ago, lasting from the Middle Ordovician to Early Silurian, thus including the extinction period. This event was the first of the big five Phanerozoic events and was the first to significantly affect animal-based communities. In May 2020, geologists reported that this mass extinction, the Late Ordovician mass extinction, 445 million years ago, may have been the result of global warming. Almost all major taxonomic groups were affected during this extinction event. Extinction was global during this period, eliminating 49–60% of marine genera and nearly 85% of marine species. Brachiopods, bivalves, echinoderms, bryozoans and corals were particularly affected. Before the late Ordovician cooling, temperatures were relatively warm and it is the suddenness of the climate changes and the elimination of habitats due to sea-level fall that are believed to have precipitated the extinctions. The falling sea level disrupted or eliminated habitats along the continental shelves. Evidence for the glaciation was found through deposits in the Sahara Desert. A combination of lowering of sea level and glacially driven cooling were likely driving agents for the Ordovician mass extinction.

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23 Oct 2022

Topic Review

Obiter dictum (usually used in the plural, obiter dicta) is Latin phrase meaning "by the way", that is, a remark in a judgment that is "said in passing". It is a concept derived from English common law, whereby a judgment comprises only two elements: ratio decidendi and obiter dicta. For the purposes of judicial precedent, ratio decidendi is binding, whereas obiter dicta are persuasive only.

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18 Oct 2022

Topic Review

Friction Stir Processing

Friction stir processing (FSP) is a material processing technique developed in 1999 derived from friction stir welding (FSW). Developed by Mishra et al., this process utilizes localized plastic deformation by rotating a specialized pin through the working piece.

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22 Sep 2021

Topic Review

Orgasm (from Greek ὀργασμός, orgasmos; "excitement, swelling") or sexual climax is the sudden discharge of accumulated sexual excitement during the sexual response cycle, resulting in rhythmic, involuntary muscular contractions in the pelvic region characterized by sexual pleasure. Experienced by males and females, orgasms are controlled by the involuntary or autonomic nervous system. They are usually associated with involuntary actions, including muscular spasms in multiple areas of the body, a general euphoric sensation and, frequently, body movements and vocalizations. The period after orgasm (known as the refractory period) is typically a relaxing experience, attributed to the release of the neurohormones oxytocin and prolactin as well as endorphins (or "endogenous morphine"). Human orgasms usually result from physical sexual stimulation of the penis in males (typically accompanying ejaculation) and of the clitoris in females. Sexual stimulation can be by self-practice (masturbation) or with a sex partner (penetrative sex, non-penetrative sex, or other sexual activity). The health effects surrounding the human orgasm are diverse. There are many physiological responses during sexual activity, including a relaxed state created by prolactin, as well as changes in the central nervous system such as a temporary decrease in the metabolic activity of large parts of the cerebral cortex while there is no change or increased metabolic activity in the limbic (i.e., "bordering") areas of the brain. There is also a wide range of sexual dysfunctions, such as anorgasmia. These effects affect cultural views of orgasm, such as the beliefs that orgasm and the frequency or consistency of it are either important or irrelevant for satisfaction in a sexual relationship, and theories about the biological and evolutionary functions of orgasm.

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30 Nov 2022

Topic Review

2010 Flash Crash

The May 6, 2010, Flash Crash, also known as the Crash of 2:45, the 2010 Flash Crash or simply the Flash Crash, was a United States trillion-dollar stock market crash, which started at 2:32 p.m. EDT and lasted for approximately 36 minutes.:1 Stock indexes, such as the S&P 500, Dow Jones Industrial Average and Nasdaq Composite, collapsed and rebounded very rapidly. The Dow Jones Industrial Average had its second biggest intraday point drop (from the opening) up to that point, plunging 998.5 points (about 9%), most within minutes, only to recover a large part of the loss. It was also the second-largest intraday point swing (difference between intraday high and intraday low) up to that point, at 1,010.14 points. The prices of stocks, stock index futures, options and exchange-traded funds (ETFs) were volatile, thus trading volume spiked.:3 A CFTC 2014 report described it as one of the most turbulent periods in the history of financial markets.:1 When new regulations put in place following the 2010 Flash Crash proved to be inadequate to protect investors in the August 24, 2015 flash crash—"when the price of many ETFs appeared to come unhinged from their underlying value"—ETFs were put under greater scrutiny by regulators and investors. On April 21, 2015, nearly five years after the incident, the U.S. Department of Justice laid "22 criminal counts, including fraud and market manipulation" against Navinder Singh Sarao, a trader. Among the charges included was the use of spoofing algorithms; just prior to the Flash Crash, he placed thousands of E-mini S&P 500 stock index futures contracts which he planned on canceling later. These orders amounting to about "$200 million worth of bets that the market would fall" were "replaced or modified 19,000 times" before they were canceled. Spoofing, layering, and front running are now banned. The Commodity Futures Trading Commission (CFTC) investigation concluded that Sarao "was at least significantly responsible for the order imbalances" in the derivatives market which affected stock markets and exacerbated the flash crash. Sarao began his alleged market manipulation in 2009 with commercially available trading software whose code he modified "so he could rapidly place and cancel orders automatically." Traders Magazine journalist, John Bates, argued that blaming a 36-year-old small-time trader who worked from his parents' modest stucco house in suburban west London for sparking a trillion-dollar stock market crash is a little bit like blaming lightning for starting a fire" and that the investigation was lengthened because regulators used "bicycles to try and catch Ferraris." Furthermore, he concluded that by April 2015, traders can still manipulate and impact markets in spite of regulators and banks' new, improved monitoring of automated trade systems. As recently as May 2014, a CFTC report concluded that high-frequency traders "did not cause the Flash Crash, but contributed to it by demanding immediacy ahead of other market participants.":1 Some recent peer-reviewed research shows that flash crashes are not isolated occurrences, but have occurred quite often. Gao and Mizrach studied US equities over the period of 1993–2011. They show that breakdowns in market quality (such as flash crashes) have occurred in every year they examined and that, apart from the financial crisis, such problems have declined since the introduction of Reg NMS. They also show that 2010, while infamous for the Flash Crash, was not a year with an inordinate number of breakdowns in market quality.

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30 Nov 2022

Topic Review

Causes of Egg Spoilage and Preventing Egg Spoilage

Eggs are a rich source of protein, minerals, lipids, and vitamins. Eggs are an essential source of bacterial microflora. Controlling antimicrobial resistance and reducing food loss and waste are essential for a sustainable future. To prevent spoilage and to preserve eggs, a variety of techniques, including thermal and non-thermal, are often used. The decontamination methods for egg preservation that have been applied are discussed. In previous studies, the initial contamination of the eggs varied from 2 to 9 log CFU per egg. Either thermal or non-thermal techniques resulted in reduced concentrations of Salmonella enteritidis, Salmonella typhimurium, and Escherichia coli, respectively, on the surface of the egg that ranged 0.62–5.9 log, 1.27–4.9 log, and 0.06–6.39 log, respectively, for the former, and being 1.2–7.8 log, 5.0–7.8 log, and 6.5–6.6 log, respectively, for the latter. Thermal approaches were more effective than the non-thermal approaches. Some of these methods had negative consequences on the egg’s functionality, while combination methods, such as thermoultrasonifcation (ozone-UV radiation or heat-ozone), mitigated these effects.

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12 Jan 2023

Topic Review

Isosceles Triangle

In geometry, an isosceles triangle (/aɪˈsɒsəliːz/) is a triangle that has at least two sides of equal length. Sometimes it is specified as having exactly two sides of equal length, and sometimes as having at least two sides of equal length, the latter version thus including the equilateral triangle as a special case. Examples of isosceles triangles include the isosceles right triangle, the golden triangle, and the faces of bipyramids and certain Catalan solids. The mathematical study of isosceles triangles dates back to ancient Egyptian mathematics and Babylonian mathematics. Isosceles triangles have been used as decoration from even earlier times, and appear frequently in architecture and design, for instance in the pediments and gables of buildings. The two equal sides are called the legs and the third side is called the base of the triangle. The other dimensions of the triangle, such as its height, area, and perimeter, can be calculated by simple formulas from the lengths of the legs and base. Every isosceles triangle has an axis of symmetry along the perpendicular bisector of its base. The two angles opposite the legs are equal and are always acute, so the classification of the triangle as acute, right, or obtuse depends only on the angle between its two legs.

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07 Nov 2022

Topic Review

Dysgraphia is a learning disability of written expression, that affects the ability to write, primarily handwriting, but also coherence. It is a specific learning disability (SLD) as well as a transcription disability, meaning that it is a writing disorder associated with impaired handwriting, orthographic coding and finger sequencing (the movement of muscles required to write). It often overlaps with other learning disabilities and neurodevelopmental disorders such as speech impairment, attention deficit hyperactivity disorder (ADHD) or developmental coordination disorder (DCD). In the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), dysgraphia is characterized as a learning disability in the category of written expression, when one's writing skills are below those expected given a person's age measured through intelligence and age-appropriate education. The DSM is unclear in whether writing refers only to the motor skills involved in writing, or if it also includes orthographic skills and spelling. Dysgraphia should be distinguished from agraphia (sometimes called acquired dysgraphia), which is an acquired loss of the ability to write resulting from brain injury, progressive illness, or a stroke. The prevalence of dysgraphia throughout the world is not known, due to difficulties in diagnosis and lack of research.

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10 Nov 2022

Topic Review

Control rods are used in nuclear reactors to control the rate of fission of the nuclear fuel – uranium or plutonium. Their compositions include chemical elements such as boron, cadmium, silver, hafnium, or indium, that are capable of absorbing many neutrons without themselves fissioning. These elements have different neutron capture cross sections for neutrons of various energies. Boiling water reactors (BWR), pressurized water reactors (PWR), and heavy-water reactors (HWR) operate with thermal neutrons, while breeder reactors operate with fast neutrons. Each reactor design can use different control rod materials based on the energy spectrum of its neutrons.

3.0K
11 Nov 2022

Topic Review

In biology, the electric organ is an organ common to all electric fish used for the purposes of creating an electric field. The electric organ is derived from modified nerve or muscle tissue. The electric discharge from this organ is used for navigation, communication, mating, defense and also sometimes for the incapacitation of prey.

3.0K
29 Sep 2022

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