Your browser does not fully support modern features. Please upgrade for a smoother experience.
Subject:
All Disciplines Arts & Humanities Biology & Life Sciences Business & Economics Chemistry & Materials Science Computer Science & Mathematics Engineering Environmental & Earth Sciences Medicine & Pharmacology Physical Sciences Public Health & Healthcare Social Sciences
Sort by:
Most Viewed Latest Alphabetical (A-Z) Alphabetical (Z-A)
Filter:
All Topic Review Biography Peer Reviewed Entry Video Entry
Topic Review
Heteroscedasticity
In statistics, a vector of random variables is heteroscedastic (or heteroskedastic; from Ancient Greek hetero "different" and skedasis "dispersion") if the variability of the random disturbance is different across elements of the vector. Here, variability could be quantified by the variance or any other measure of statistical dispersion. Thus heteroscedasticity is the absence of homoscedasticity. A typical example is the set of observations of income in different cities. The existence of heteroscedasticity is a major concern in regression analysis and the analysis of variance, as it invalidates statistical tests of significance that assume that the modelling errors all have the same variance. While the ordinary least squares estimator is still unbiased in the presence of heteroscedasticity, it is inefficient and generalized least squares should be used instead. Because heteroscedasticity concerns expectations of the second moment of the errors, its presence is referred to as misspecification of the second order. The econometrician Robert Engle was awarded the 2003 Nobel Memorial Prize for Economics for his studies on regression analysis in the presence of heteroscedasticity, which led to his formulation of the autoregressive conditional heteroscedasticity (ARCH) modeling technique.
  • 5.5K
  • 14 Oct 2022
Topic Review
Solar PV-Hydrogen-PEM Fuel Cell System
The results obtained from the design and analysis of a photovoltaic-hydrogen-PEM fuel cell (PVHPEMFC) hybrid system for Najaf City in Iraq has been presented. The hybrid system consists of photovoltaic arrays coupled with an electrolyzer to produce hydrogen, a PEM fuel cell that converts chemical energy (H2) to electricity, hydrogen storage, a battery storage system, and the load. In this kind of system, all components can be connected electrically in parallel. The voltage of the PV arrays and fuel cell must be high enough to charge the battery, and the voltage of the electrolyzer must be low enough for the battery to power it during periods of low insolation. The designed system model is based on the electrical component models and variable solar radiation data depending on the location.
  • 5.5K
  • 29 Oct 2020
Topic Review
Bacha Bazi
Bacha bāzī (Dari: بچه بازی‎, lit. "boy play"; from بچه bacheh, "boy", and بازی bazi "play, game") is a slang term in some parts of Afghanistan for a wide variety of activities involving sexual relations between younger adolescent men or boys, who are called dancing boys, and older men. The custom is connected to sexual slavery and child prostitution. In the 21st century, Bacha bazi is reportedly practiced in various parts of Afghanistan. Force and coercion are common, and security officials state they are unable to end such practices because many of the men involved in bacha bazi-related activities are powerful and well-armed warlords. During the Afghan Civil War (1996–2001), bacha bazi carried the death penalty under Taliban law. The practice of dancing boys is illegal under Afghan law, but the laws are seldom enforced against powerful offenders and police have reportedly been complicit in related crimes. A controversy arose after allegations surfaced that U.S. government forces in Afghanistan after the invasion of the country deliberately ignored bacha bazi. The U.S. military responded by claiming the abuse was largely the responsibility of the "local Afghan government". As of 2020, despite international concern, the practice continues.
  • 5.5K
  • 18 Oct 2022
Topic Review
Sunday Shopping
Sunday shopping, also called Sunday trading, refers to the ability of retailers to operate stores on Sunday, a day that Christian tradition typically recognises as a day of rest. Rules governing shopping hours, such as Sunday shopping, vary around the world and some countries and subnational jurisdictions ban or restrict Sunday shopping.
  • 5.5K
  • 22 Nov 2022
Topic Review
Thalidomide Scandal
In the late 1950s and early 1960s, the use of thalidomide in pregnant women in 46 countries resulted in the "biggest man‐made medical disaster ever," with over 10,000 children born with a range of severe deformities, such as phocomelia, and thousands of miscarriages. Thalidomide was introduced in 1956 and was aggressively marketed by the German pharmaceutical company Chemie Grünenthal as a medication for anxiety, trouble sleeping, "tension", and morning sickness. It was introduced as a sedative and medication for morning sickness without having been tested on pregnant women. While initially deemed to be safe in pregnancy, concerns regarding birth defects were noted in 1961, and the medication was removed from the market in Europe that year.
  • 5.5K
  • 09 Nov 2022
Topic Review
Trigonometry
Trigonometry (from grc τρίγωνον (trígōnon) 'triangle', and μέτρον (métron) 'measure') is a branch of mathematics that studies relationships between side lengths and angles of triangles. The field emerged in the Hellenistic world during the 3rd century BC from applications of geometry to astronomical studies. The Greeks focused on the calculation of chords, while mathematicians in India created the earliest-known tables of values for trigonometric ratios (also called trigonometric functions) such as sine. Throughout history, trigonometry has been applied in areas such as geodesy, surveying, celestial mechanics, and navigation. Trigonometry is known for its many identities. These trigonometric identities are commonly used for rewriting trigonometrical expressions with the aim to simplify an expression, to find a more useful form of an expression, or to solve an equation.
  • 5.5K
  • 31 Oct 2022
Topic Review
Matrix Metalloproteinases and Their Inhibitors
Matrix metalloproteinases (MMPs) are a family of zinc-dependent extracellular matrix (ECM) remodeling endopeptidases that have the capacity to degrade almost every component of the ECM. The degradation of the ECM is of great importance, since it is related to embryonic development and angiogenesis. It is also involved in cell repair and the remodeling of tissues. When the expression of MMPs is altered, it can generate the abnormal degradation of the ECM. This is the initial cause of the development of chronic degenerative diseases and vascular complications generated by diabetes. In addition, this process has an association with neurodegeneration and cancer progression. Within the ECM, the tissue inhibitors of MMPs (TIMPs) inhibit the proteolytic activity of MMPs. TIMPs are important regulators of ECM turnover, tissue remodeling, and cellular behavior. Therefore, TIMPs (similar to MMPs) modulate angiogenesis, cell proliferation, and apoptosis. An interruption in the balance between MMPs and TIMPs has been implicated in the pathophysiology and progression of several diseases.
  • 5.5K
  • 18 Sep 2021
Topic Review
The Factors That Influence Food Waste
Food conservation is an issue of global importance. In unstable conditions such as pandemics and wars, clean plate campaigns have been developed to limit food waste around the world. The COVID-19 pandemic threatens global food security and has created an urgent need for food conservation
  • 5.5K
  • 31 May 2022
Topic Review
Cyanophyceae
Cyanobacteria (/saɪˌænoʊbækˈtɪəri.ə/), also known as Cyanophyta, are a phylum of Gram-negative bacteria that obtain energy via photosynthesis. The name cyanobacteria refers to their color (from grc κυανός (kuanós) 'blue'), which similarly forms the basis of cyanobacteria's common name, blue-green algae.[note 1] They appear to have originated in a freshwater or terrestrial environment. Sericytochromatia, the proposed name of the paraphyletic and most basal group, is the ancestor of both the non-photosynthetic group Melainabacteria and the photosynthetic cyanobacteria, also called Oxyphotobacteria. Cyanobacteria use photosynthetic pigments, such as carotenoids, phycobilins, and various forms of chlorophyll, which absorb energy from light. Unlike heterotrophic prokaryotes, cyanobacteria have internal membranes. These are flattened sacs called thylakoids where photosynthesis is performed. Phototrophic eukaryotes such as green plants perform photosynthesis in plastids that are thought to have their ancestry in cyanobacteria, acquired long ago via a process called endosymbiosis. These endosymbiotic cyanobacteria in eukaryotes then evolved and differentiated into specialized organelles such as chloroplasts, chromoplasts, etioplasts, and leucoplasts, collectively known as plastids. Cyanobacteria are the first organisms known to have produced oxygen. By producing and releasing oxygen as a byproduct of photosynthesis, cyanobacteria are thought to have converted the early oxygen-poor, reducing atmosphere into an oxidizing one, causing the Great Oxidation Event and the "rusting of the Earth", which dramatically changed the composition of the Earth's life forms. The cyanobacteria Synechocystis and Cyanothece are important model organisms with potential applications in biotechnology for bioethanol production, food colorings, as a source of human and animal food, dietary supplements and raw materials. Cyanobacteria produce a range of toxins known as cyanotoxins that can pose a danger to humans and animals.
  • 5.5K
  • 01 Nov 2022
Topic Review
Adjustable-Speed Drive
Adjustable speed drive (ASD), also known as variable-speed drive (VSD), describes equipment used to control the speed of machinery. Many industrial processes such as assembly lines must operate at different speeds for different products. Where process conditions demand adjustment of flow from a pump or fan, varying the speed of the drive may save energy compared with other techniques for flow control. Where speeds may be selected from several different pre-set ranges, usually the drive is said to be adjustable speed. If the output speed can be changed without steps over a range, the drive is usually referred to as variable speed. Adjustable and variable speed drives may be purely mechanical (termed variators), electromechanical, hydraulic, or electronic.
  • 5.5K
  • 10 Nov 2022
Topic Review Peer Reviewed
The Foundation of Classical Mechanics
Mechanics is the science of the equilibrium and motion of bodies subject to forces. The adjective classical, hence Classical Mechanics , was added in the 20th century to distinguish it from relativistic mechanics which studies motion with speed close to light speed and quantum mechanics which studies motion at a subatomic level.
  • 5.5K
  • 13 Apr 2022
Topic Review
Malaysia’s Housing Policy, Low-Income Households' Housing Affordability
Housing affordability is a long-held issue in Malaysia and housing policies for low-income households have been implemented over years. However, there is a contradiction that housing affordability of low-income households has not been met, while a bulk of affordable housing is still vacant. In 2019, Malaysia enacted the National Affordable Housing Policy (DRMM) which was intended to improve housing affordability for low-income groups. In such circumstances, the questions are, why Malaysia’s long-term implementation of affordable housing policies cannot guarantee housing affordability and whether the DRMM can effectively improve housing affordability as expected.
  • 5.5K
  • 02 Dec 2021
Topic Review
Applications of Nanostructured Materials
In the last few decades, the vast potential of nanomaterials for biomedical and healthcare applications has been extensively investigated. Several case studies demonstrated that nanomaterials can offer solutions to the current challenges of raw materials in the biomedical and healthcare fields. The different nanoparticles and nanostructured material synthesis approaches were described.
  • 5.5K
  • 11 Apr 2022
Topic Review
Law of War
The law of war is the component of international law that regulates the conditions for initiating war (jus ad bellum) and the conduct of warring parties (jus in bello). Laws of war define sovereignty and nationhood, states and territories, occupation, and other critical terms of international law. Among other issues, modern laws of war address the declarations of war, acceptance of surrender and the treatment of prisoners of war; military necessity, along with distinction and proportionality; and the prohibition of certain weapons that may cause unnecessary suffering. The law of war is considered distinct from other bodies of law—such as the domestic law of a particular belligerent to a conflict—which may provide additional legal limits to the conduct or justification of war.
  • 5.5K
  • 08 Oct 2022
Topic Review
Delphi (IDE)
Delphi is an integrated development environment (IDE) for rapid application development of desktop, mobile, web, and console software, developed by Embarcadero Technologies. It is also an event-driven language. Delphi's compilers use their own Object Pascal dialect of Pascal and generate native code for Microsoft Windows, macOS (IA-32 only), iOS, Android and Linux (x64 only). Since 2016, there have been new releases of Delphi every six months, with new platforms being added approximately every second release. Delphi includes a code editor, a visual designer, an integrated debugger, a source code control component, and support for third-party plugins. The code editor features Code Insight (code completion), Error Insight (real-time error-checking), and refactoring. The visual forms designer has traditionally used Visual Component Library (VCL) for native Windows development, but the FireMonkey (FMX) platform was later added for cross-platform development. Database support in Delphi is very strong. A Delphi project of a million lines to compile in a few seconds – one benchmark gave 170,000 lines per second. Delphi was originally developed by Borland as a rapid application development tool for Windows as the successor of Turbo Pascal. Delphi added full object-oriented programming to the existing language, and since then the language has grown to support generics and anonymous methods, and native Component Object Model (COM) support. In 2006, Borland’s developer tools section was transferred from Borland to a wholly owned subsidiary known as CodeGear, which was sold to Embarcadero Technologies in 2008. In 2015, Embarcadero was purchased by Idera Software, but the Embarcadero mark was retained for the developer tools division. Delphi and its C++ counterpart, C++Builder, are interoperable. They share many core components, notably the IDE, VCL, and much of the runtime library. In addition, they can be used jointly in a project. For example, C++Builder 6 and later can consume Delphi source code and C++ in one project, while packages compiled with C++Builder can be used from within Delphi. In 2007, the products were released jointly as RAD Studio, a shared host for Delphi and C++Builder, which can be purchased with either or both.
  • 5.4K
  • 02 Nov 2022
Topic Review
Impact of Automobility on Urban Sprawl
Urban sprawl has become a controversial issue. Lines of thought among academics, practitioners, and local authorities have been diverse. Some academics advocate the compact city as an antidote to urban sprawl, some scholars doubt the ability of conventional notions of containments to create sustainability, and others are fascinated by urban technologies and believe in the feasibility of these technologies, whereas local authorities impose policies, one after the other, without effective results.
  • 5.4K
  • 29 Sep 2022
Topic Review
Cotton Seed
Seed germination is the basis for the proliferation of sexual-reproducing plants, efficient crop production, and a successful crop improvement research program. While seeds are a vital form of dispersal and propagation of plants in the environment, they had to develop mechanisms in unfavorable circumstances to ensure the preservation of the next generation. One of the major survival adaptations of seeds is dormancy. This phenomenon allows the seed to delay and coordinate germination according to environmental conditions and it is essential to the conservation and proliferation of a species. Generally, dormant seeds naturally start or resume the germination process once they detect environmental signals indicating suitable conditions for plant development such as temperature fluctuations, water availability, and even smoke. If unfavorable conditions persist and seeds halt germination for a long period, aging might negatively impact this process. Modifications in the seed structure like the hard seed trait in cotton can also affect germination. Often referred to as physical dormancy, hard seeds are water impermeable and prevent gas exchange and water uptake by the embryo.
  • 5.4K
  • 23 Dec 2021
Topic Review
Taiji
Taiji or Tai chi (simplified Chinese: 太极; traditional Chinese: 太極; pinyin: tàijí; literally: 'great pole') is a Chinese cosmological term for the "Supreme Ultimate" state of undifferentiated absolute and infinite potential, the oneness before duality, from which Yin and Yang originate. It can be compared with the old Wuji (無極, "without pole"). The term Taiji and its other spelling T'ai chi (using Wade–Giles as opposed to Pinyin) are most commonly used in the West to refer to Taijiquan (or T'ai chi ch'uan, 太極拳), an internal martial art, Chinese meditation system and health practice. This article, however, refers only to the use of the term in Chinese philosophy and in Confucianism, Taoism and Buddhism.
  • 5.4K
  • 24 Oct 2022
Topic Review
SCMaglev
The SCMaglev (superconducting maglev, formerly called the MLU) is a magnetic levitation (maglev) railway system developed by Central Japan Railway Company (JR Central) and the Railway Technical Research Institute. On 21 April 2015, a manned seven-car L0 Series SCMaglev train reached a speed of 603 km/h (375 mph), less than a week after the same train clocked 590 km/h (370 mph), breaking the previous land speed record for rail vehicles of 581 km/h (361 mph) set by a JR Central MLX01 maglev train in December 2003.
  • 5.4K
  • 20 Oct 2022
Topic Review
Extensive Sheep and Goat Production
Sheep and goat extensive production systems are conducted in many different parts of the world, and they often use essentially marginal areas unsuitable for crop production, characterized by low productivity per animal and per surface area. They positively impact local socio-economic activities, playing an essential role in the maintenance of rural communities, on ecosystems, and in the production of unique, valued foods such as lamb meat or cheeses. However, such systems are under significant pressure, mainly because there is little labor availability, and they have traditionally low productivity and often poor economic viability.
  • 5.4K
  • 08 Dec 2022
  • Page
  • of
  • 2729
Featured Entry Collections
>>

Featured Reprints

>>
Encyclopedia of Digital Society, Industry 5.0 and Smart City
Encyclopedia of Engineering
Encyclopedia of Social Sciences
Encyclopedia of Medieval Royal Iconography
Academic Video Service
Feedback