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
Cluster Chemistry
In chemistry, a cluster is an ensemble of bound atoms or molecules that is intermediate in size between a molecule and a bulk solid. Clusters exist of diverse stoichiometries and nuclearities. For example, carbon and boron atoms form fullerene and borane clusters, respectively. Transition metals and main group elements form especially robust clusters. Clusters can also consist solely of a certain kind of molecules, such as water clusters. The phrase cluster was coined by F.A. Cotton in the early 1960s to refer to compounds containing metal–metal bonds. In another definition a cluster compound contains a group of two or more metal atoms where direct and substantial metal bonding is present. The prefixed terms "nuclear" and "metallic" are used and imply different meanings. For example, polynuclear refers to a cluster with more than one metal atom, regardless of the elemental identities. Heteronuclear refers to a cluster with at least two different metal elements. The main cluster types are "naked" clusters (without stabilizing ligands) and those with ligands. For transition metal clusters, typical stabilizing ligands include carbon monoxide, halides, isocyanides, alkenes, and hydrides. For main group elements, typical clusters are stabilized by hydride ligands. Transition metal clusters are frequently composed of refractory metal atoms. In general metal centers with extended d-orbitals form stable clusters because of favorable overlap of valence orbitals. Thus, metals with a low oxidation state for the later metals and mid-oxidation states for the early metals tend to form stable clusters. Polynuclear metal carbonyls are generally found in late transition metals with low formal oxidation states. The polyhedral skeletal electron pair theory or Wade's electron counting rules predict trends in the stability and structures of many metal clusters. Jemmis mno rules have provided additional insight into the relative stability of metal clusters.
  • 8.3K
  • 08 Nov 2022
Topic Review
Perovskite Materials
In the development of hydrogen-based technology, a key challenge is the sustainable production of hydrogen in terms of energy consumption and environmental aspects. However, existing methods mainly rely on fossil fuels due to their cost efficiency, and as such, it is difficult to be completely independent of carbon-based technology. Electrochemical hydrogen production is essential, since it has shown the successful generation of hydrogen gas of high purity. Similarly, the photoelectrochemical (PEC) method is also appealing, as this method exhibits highly active and stable water splitting with the help of solar energy. We discuss the exceptional optical and electrical characteristics of perovskite materials which often dictate PEC performance. We further extend our discussion to the material limit of perovskite under a hydrogen production environment, i.e., that PEC reactions often degrade the contact between the electrode and the electrolyte.
  • 8.3K
  • 30 Jul 2021
Topic Review
The Sims 2 Stuff Packs
Stuff packs are minor expansion packs for The Sims 2 that add new items, clothing, and furniture to the game without implementing any significant changes to gameplay.
  • 8.3K
  • 17 Nov 2022
Topic Review
Cyrillic Script
The Cyrillic script (/sɪˈrɪlɪk/ sə-RIL-ik) is a writing system used for various languages across Eurasia and is used as the national script in various Slavic, Turkic, Mongolic, Uralic, Caucasian and Iranic-speaking countries in Southeastern Europe, Eastern Europe, the Caucasus, Central Asia, North Asia and East Asia. (As of 2019), around 250 million people in Eurasia use Cyrillic as the official script for their national languages, with Russia accounting for about half of them. With the accession of Bulgaria to the European Union on 1 January 2007, Cyrillic became the third official script of the European Union, following the Latin and Greek alphabets. In the 9th century AD, the Bulgarian tsar Simeon I the Great – following the cultural and political course of his father Boris I – commissioned a new script, the Early Cyrillic alphabet, to be made at the Preslav Literary School in the First Bulgarian Empire, which would replace the Glagolitic script, produced earlier by Saints Cyril and Methodius and the same disciples that created the new Slavic script in Bulgaria. The usage of the Cyrillic script in Bulgaria was made official in 893. The new script became the basis of alphabets used in various languages, especially those of Orthodox Slavic origin, and non-Slavic languages influenced by Bulgarian. For centuries Cyrillic was used by Catholic and Muslim Slavs too (see Bosnian Cyrillic). Cyrillic is derived from the Greek uncial script, augmented by letters from the older Glagolitic alphabet, including some ligatures. These additional letters were used for Old Church Slavonic sounds not found in Greek. The script is named in honor of the Saint Cyril, one of the two Byzantine brothers, Saints Cyril and Methodius, who created the Glagolitic alphabet earlier on. Modern scholars believe that Cyrillic was developed and formalized by the early disciples of Cyril and Methodius in the Preslav Literary School, the most important early literary and cultural centre of the First Bulgarian Empire and of all Slavs. The school developed the Cyrillic script: The earliest datable Cyrillic inscriptions have been found in the area of Preslav. They have been found in the medieval city itself, and at nearby Patleina Monastery, both in present-day Shumen Province, in the Ravna Monastery and in the Varna Monastery. With the orthographic reform of Saint Evtimiy of Tarnovo and other prominent representatives of the Tarnovo Literary School (14th and 15th centuries) such as Gregory Tsamblak or Constantine of Kostenets the school influenced Russian, Serbian, Wallachian and Moldavian medieval culture. That is famous in Russia as the second South-Slavic influence. In the early 18th century, the Cyrillic script used in Russia was heavily reformed by Peter the Great, who had recently returned from his Grand Embassy in Western Europe. The new letterforms, called the Civil script, became closer to those of the Latin alphabet; several archaic letters were abolished and several letters were designed by Peter himself. Letters became distinguished between upper and lower case. West European typography culture was also adopted. The pre-reform forms of letters called 'Полуустав' were notably kept for use in Church Slavonic and are sometimes used in Russian even today, especially if one wants to give a text a 'Slavic' or 'archaic' feel.
  • 8.3K
  • 22 Nov 2022
Topic Review
Mathematics of Sudoku
The class of Sudoku puzzles consists of a partially completed row-column grid of cells partitioned into N regions each of size N cells, to be filled in ("solved") using a prescribed set of N distinct symbols (typically the numbers {1, ..., N}), so that each row, column and region contains exactly one of each element of the set. The properties of Sudoku puzzles and their solutions can be investigated using mathematics and algorithms.
  • 8.3K
  • 12 Oct 2022
Topic Review
Manufacturing Processes for Ceramic Matrix Composites
Materials such as ceramic matrix composites (CMCs) have been the focus of research and being tested in different conditions for several decades now. They are known as a subgroup of composite materials and ceramics. Ceramic composites were developed to control and address problems that occurred with other commonly used ceramics, such as silicon carbide, alumina, silicon nitride, aluminum nitride, and zirconia. Such ceramics fractured with ease, revealing scratches and cracks while mechanical and thermo-mechanical loads were applied to them. CMCs exhibit mechanical and thermal properties comparable with, and in some cases, even better than, the conventional superalloys used in aero-engines. However, their adoption relies on other variables as well, such as the cost of development, industrialization, manufacturing, and the availability of manufacturing technologies and systems.
  • 8.3K
  • 27 Apr 2023
Topic Review
Fleischmann–Pons Experiment
The Fleischmann–Pons experiment was an investigation conducted in the 1980s by Martin Fleischmann of the University of Southampton and Stanley Pons of the University of Utah into whether electrolysis of heavy water on the surface of a palladium (Pd) electrode produces physical effects that defy chemical explanation. Of particular interest was evidence of "excess" (i.e. non-chemical) heat extracted from the deuterium fraction of common surface water which, if true, could have delivered the largest economic shock to the global energy industry since the Pennsylvania oil rush. On March 23, 1989, Fleischmann (then one of the world's leading electrochemists) and Pons reported their work via a press release from the University of Utah (who asserted ownership of the technology) claiming that the table-top apparatus had produced anomalous heat (understood as "excess" heat) of a magnitude they asserted would defy explanation except in terms of nuclear processes, which later came to be referred to as "cold fusion". In addition to the results from calorimetry, they further reported measuring small amounts of nuclear reaction byproducts, including neutrons and tritium. The reported results received wide media attention, and raised hopes of a cheap and abundant source of energy. Many scientists tried to replicate the experiment with the few details available. Hopes faded due to the large number of negative replications, the withdrawal of many reported positive replications, the discovery of flaws and sources of experimental error in the original experiment, and finally the discovery that Fleischmann and Pons had not actually detected nuclear reaction byproducts. By late 1989, most scientists considered cold fusion claims dead.
  • 8.3K
  • 26 Oct 2022
Topic Review Peer Reviewed
OAM of Light: Origins and Applications
Orbital Angular Momentum (OAM) of light is generating growing interest within the scientific community. This entry reviews the origins and applications of OAM. It is the counterpart of linear momentum for systems in rotation. The general expression of OAM is discussed, followed by its implications in terms of phase distribution and donut-shaped intensity profiles. Applications described include the generation of optical torque, telecommunications enhancement, and the rotational Doppler effect, emphasizing the role and consequences of angular momentum. In particular, its use to manipulate systems or to detect rotations is described. Finally, further developments and technological barriers are considered.
  • 8.3K
  • 17 Sep 2025
Topic Review
Cultural Memory
Historic urban landscapes (HULs) are composed of layers of imbedded tangible and intangible features such as cultural memories. As the collective memories of city inhabitants, cultural memories can affect elements of social sustainability such as health, well-being, community identity, place perception and social engagement. This topic review points to the value of recalling cultural memory features in HULs, which can be used to achieve social sustainability.  In addition, it contributes to sustainable development through the contribution of cultural memory and its influence on the formation of place identity, sense of place, civic pride and quality of life in HULs. 
  • 8.3K
  • 27 Oct 2020
Topic Review
Land Suitability Assessment
Land suitability assessment is a method of land evaluation, which identifies the major limiting factors for planting a particular crop. Land suitability assessment includes qualitative and quantitative evaluation. In the qualitative land suitability evaluations, information about climate, hydrology, topography, vegetation, and soil properties is considered and in quantitative assessment, the results are more detailed and yield is estimated. At present study we prepared land suitability assessment map for rain-fed wheat and barley crops based on FAO "land suitability assessment framework" using parametric method and machine learning algorithms in Kurdistan Province, located in west of Iran. This is a unique study that compared two machine learning-based and traditional-based approaches for mapping current and potential future land suitability classes. Moreover, potential yield of rain-fed wheat and barley crop were computed by FAO model.
  • 8.3K
  • 30 Oct 2020
Topic Review
History of Democratic Socialism
Democratic socialism represents the modernist development of socialism and its outspoken support for democracy. The origins of democratic socialism can be traced back to 19th-century utopian socialist thinkers and the Chartist movement in Great Britain, which somewhat differed in their goals but shared a common demand of democratic decision making and public ownership of the means of production, and viewed these as fundamental characteristics of the society they advocated for. Democratic socialism was also heavily influenced by the gradualist form of socialism promoted by the British Fabian Society and Eduard Bernstein's evolutionary socialism. In the 19th century, the ruling classes were afraid of socialism because it challenged their rule. Socialism has faced opposition since then, and the opposition to it has often been organized and violent. In countries such as Germany and Italy, democratic socialist parties were banned, like with Otto von Bismarck's Anti-Socialist Laws. With the expansion of liberal democracy and universal suffrage during the 20th century, democratic socialism became a mainstream movement which expanded across the world, as centre-left and left-wing parties came to govern, became the main opposition party, or simply a commonality of the democratic process in most of the Western world; one major exception was the United States. Democratic socialist parties greatly contributed to existing liberal democracy.
  • 8.3K
  • 22 Nov 2022
Topic Review
Literacy
Literacy is traditionally defined as the ability to read and write. In the modern world, this is one way of interpreting literacy. A more broad interpretation is literacy as knowledge and competence in a specific area. The concept of literacy has evolved in meaning. The modern term's meaning has been expanded to include the ability to use language, numbers, images, computers, and other basic means to understand, communicate, gain useful knowledge, solve mathematical problems and use the dominant symbol systems of a culture. The concept of literacy is expanding across OECD countries to include skills to access knowledge through technology and ability to assess complex contexts. A person who travels and resides in a foreign country but is unable to read or write in the language of the host country would also be regarded by the locals as illiterate. The key to literacy is reading development, a progression of skills that begins with the ability to understand spoken words and decode written words, and culminates in the deep understanding of text. Reading development involves a range of complex language underpinnings including awareness of speech sounds (phonology), spelling patterns (orthography), word meaning (semantics), grammar (syntax) and patterns of word formation (morphology), all of which provide a necessary platform for reading fluency and comprehension. Once these skills are acquired, the reader can attain full language literacy, which includes the abilities to apply to printed material critical analysis, inference and synthesis; to write with accuracy and coherence; and to use information and insights from text as the basis for informed decisions and creative thought. The inability to do so is called illiteracy or analphabetism. The United Nations Educational, Scientific and Cultural Organization (UNESCO) defines literacy as the "ability to identify, understand, interpret, create, communicate and compute, using printed and written materials associated with varying contexts. Literacy involves a continuum of learning in enabling individuals to achieve their goals, to develop their knowledge and potential, and to participate fully in their community and wider society".
  • 8.3K
  • 05 Dec 2022
Topic Review
Theories of International Trade
Economists have developed theories explaining World Trade, which are called” theories of international trade”. Theories of international trade explain what exactly happens in international trade, such as mercantilist theory. This theory was popular in the sixteenth and eighteenth centuries. During that time, a nation’s wealth consisted only of gold or other types of precious metals, so theorists suggested that nations begin to accumulate more and more gold and other types of metals. 
  • 8.3K
  • 08 Jul 2022
Topic Review
Carbon Emission Efficiency
Carbon emission efficiency is an important concept in environmental science; it refers to the economic benefits generated by production activities that produce carbon emissions at the same time. The less carbon emissions generated per unit of economic output, the more carbon emission efficient it is.
  • 8.3K
  • 26 May 2022
Topic Review
Classical Nucleation Theory
Crystal nucleation determining the formation and assembly pathway of first organic materials is the central science of various scientific disciplines such as chemical, geochemical, biological, and synthetic materials. Classical nucleation theory (CNT)  applies to systems of small organic molecules with an emphasis on the molecular interpretation of nucleation kinetics. CNT holds that density fluctuations are concomitant with the development of crystalline order. In other words, a crystal nucleus has an identical structure to its bulk crystal. 
  • 8.3K
  • 22 Jul 2022
Topic Review
Water-Gas Shift Reaction
The water-gas shift reaction (WGSR) describes the reaction of carbon monoxide and water vapor to form carbon dioxide and hydrogen: The water gas shift reaction was discovered by Italian physicist Felice Fontana in 1780. It was not until much later that the industrial value of this reaction was realized. Before the early 20th century, hydrogen was obtained by reacting steam under high pressure with iron to produce iron, iron oxide and hydrogen. With the development of industrial processes that required hydrogen, such as the Haber–Bosch ammonia synthesis, a less expensive and more efficient method of hydrogen production was needed. As a resolution to this problem, the WGSR was combined with the gasification of coal to produce a pure hydrogen product. As the idea of hydrogen economy gains popularity, the focus on hydrogen as a replacement fuel source for hydrocarbons is increasing.
  • 8.3K
  • 22 Nov 2022
Topic Review
Consanguinity
Consanguinity ("blood relation", from Latin consanguinitas) is the property of being from the same kinship as another person. In that aspect, consanguinity is the quality of being descended from the same ancestor as another person. The laws of many jurisdictions set out the degree of consanguinity in relation to prohibited sexual relations and marriage parties. Such rules are also used to determine heirs of an estate according to statutes that govern intestate succession, which vary from jurisdiction to jurisdiction. In some places and times, cousin marriage is approved and expected; in others, it is taboo as incest. The degree of relative consanguinity can be illustrated with a consanguinity table in which each level of lineal consanguinity (generation or meiosis) appears as a row, and individuals with a collaterally consanguineous relationship share the same row. The Knot System is a numerical notation that defines consanguinity.
  • 8.3K
  • 28 Sep 2022
Topic Review
Design of Block Shear Failure
The block shear failure was reported firstly in 1978 for joints with not optimal geometry from an internal forces point of view. The test results proved the potential failure mode of tearing out in the web of the beam. Several studies concerning block shear failure were published in the last twenty years predicting the block shear capacity as a combination of fracture on the tension and shear plane. Block shear rupture is the potential failure mode for gusset plates, fin plates, coped beams, single/double angles and tee connections, where significant tension/shear forces are present. 
  • 8.3K
  • 21 Jul 2021
Topic Review
Glossolalia
Glossolalia or speaking in tongues is a phenomenon in which people speak words that are apparently in languages unknown to the speaker. One definition used by linguists is the fluid vocalizing of speech-like syllables that lack any readily comprehended meaning, in some cases as part of religious practice in which it is believed to be a divine language unknown to the speaker. Glossolalia is practiced in Pentecostal and charismatic Christianity as well as in other religions. Sometimes a distinction is made between "glossolalia" and "xenolalia" or "xenoglossy", which specifically designates when the language being spoken is a natural language previously unknown to the speaker. This distinction is not universally made, and the New Testament of the Bible mentions the phenomenon in at least one passage in reference to speaking in languages known to others but not to the speakers.
  • 8.2K
  • 01 Dec 2022
Topic Review
Platypus
The platypus (Ornithorhynchus anatinus), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or monotypic taxon of its family (Ornithorhynchidae) and genus (Ornithorhynchus), though a number of related species appear in the fossil record. Together with the four species of echidna, it is one of the five extant species of monotremes, mammals that lay eggs instead of giving birth to live young. Like other monotremes, it senses prey through electrolocation. It is one of the few species of venomous mammals, as the male platypus has a spur on the hind foot that delivers a venom, capable of causing severe pain to humans. The unusual appearance of this egg-laying, duck-billed, beaver-tailed, otter-footed mammal baffled European naturalists when they first encountered it, and the first scientists to examine a preserved platypus body (in 1799) judged it a fake, made of several animals sewn together. The unique features of the platypus make it an important subject in the study of evolutionary biology, and a recognisable and iconic symbol of Australia . It is culturally significant to several Aboriginal peoples of Australia, who also used to hunt the animal for food. It has appeared as a mascot at national events and features on the reverse of the Australian twenty-cent coin, and the platypus is the animal emblem of the state of New South Wales. Until the early 20th century, humans hunted the platypus for its fur, but it is now protected throughout its range. Although captive-breeding programs have had only limited success, and the platypus is vulnerable to the effects of pollution, it is not under any immediate threat. (As of 2020), the platypus is a legally protected species in all states where it occurs. It is listed as an endangered species in South Australia and Victoria and has been recommended for listing in New South Wales. The species is classified as a near-threatened species by the IUCN, but a November 2020 report has recommended that it is upgraded to threatened species under the federal EPBC Act, due to habitat destruction and declining numbers in all states.
  • 8.2K
  • 18 Nov 2022
  • Page
  • of
  • 2786
Featured Entry Collections
>>

Featured Books

>>
Encyclopedia of Digital Society, Industry 5.0 and Smart City
Encyclopedia of Engineering
Encyclopedia of Social Sciences
Encyclopedia of COVID-19
Academic Video Service
Feedback