You're using an outdated browser. Please upgrade to a modern browser for the best 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
Chemical-based Methodologies for Fresh Fish Shelf-Life Extension
Due to its characteristics, fresh fish is a highly perishable food with a very short shelf-life under refrigeration. Several methods have been introduced to slow down its deterioration, such as by means of oxygen depletion of the food package (vacuum packaging), or by changing the natural atmosphere that is in contact with the fresh fish (modified atmosphere packaging), or by the use of chemicals generally recognized as safe: such compounds can be directly applied (by dipping or spraying) or incorporated into packaging materials and slowly migrate to the product, exerting a hurdle effect against microbial development and lipid oxidation (active packaging).
  • 2.4K
  • 22 Oct 2021
Topic Review
Meta-Wearable Antennas
Wireless Body Area Network (WBAN) has attracted more and more attention in many sectors of society. As a critical component in these systems, wearable antennas suffer from several serious challenges, e.g., electromagnetic coupling between the human body and the antennas, different physical deformations, and widely varying operating environments, and thus, advanced design methods and techniques are urgently needed to alleviate these limitations. Recent developments have focused on the application of metamaterials in wearable antennas, which is a prospective area and has unique advantages.
  • 2.4K
  • 20 Jan 2021
Topic Review
Boron-Silicon Junction
The discovery of the extremely shallow amorphous boron-crystalline silicon heterojunction occurred during the development of highly sensitive, hard and robust detectors for low-penetration-depth ionizing radiation, such as ultraviolet photons and low-energy electrons (below 1 keV). For many years it was believed that the junction created by the chemical vapor deposition of amorphous boron on n-type crystalline silicon was a shallow p-n junction, although experimental results could not provide evidence for such a conclusion. Only recently, quantum-mechanics based modelling revealed the unique nature and the formation mechanism of this new junction. Here, the entry reviews the initiation and the history of understanding the a-B/c-Si interface (henceforth called the “boron-silicon junction”).
  • 2.4K
  • 17 Jun 2021
Topic Review
Iguvine Tablets
The Iguvine Tablets, also known as the Eugubian Tablets or Eugubine Tables, are a series of seven bronze tablets from ancient Iguvium (modern Gubbio), Italy, written in the ancient Italic language Umbrian. The earliest tablets, written in the native Umbrian alphabet, were probably produced in the 3rd century BC, and the latest, written in the Latin alphabet, from the 1st century BC. The tablets contain religious inscriptions that memorialize the acts and rites of the Atiedian Brethren, a group of 12 priests of Jupiter with important municipal functions at Iguvium. The religious structure present in the tablets resembles that of the early stage of Roman religion, reflecting the Roman archaic triad and the group of gods more strictly related to Jupiter. Discovered in a farmer's field near Scheggia in the year 1444, they are currently housed in the Civic Museum of the Palazzo dei Consoli in Gubbio. The tablets are by far the longest and most important document of any of the Osco-Umbrian group of languages, which are closely related to Latin. The tablets shed light on the grammar of this ancient dead language, and also on the religious practices of the ancient peoples of Italy, including the archaic religion of the Romans. Parts of tablets VI and VII appear to be written in an accentual metre, similar to the Saturnian metre that is encountered in the earliest Latin poetry. The complete text, together with a translation into Latin, was published in London in 1863 by Francis Newman and 1931 in a book by Albrecht von Blumenthal. They were translated into English and published by James W. Poultney in 1959. Although the general meaning of the tablets is clear, there are still many obscure and debated points and issues. The main difficulty in understanding the text is the insufficient knowledge of the Umbrian vocabulary. These are the only documents of full details of sacred rituals from the ancient religions of Europe which have come down to us in an almost complete state. Moreover, their content deals with the rituals (sacrifices and prayers) addressed to the highest gods of the local community and to some extent may reflect the common religious beliefs and practices of the Italic peoples. Consequently, a great number of scholars have devoted their efforts to reading and deciphering them since their discovery. The modern Festival of Ceri, celebrated every year in Gubbio on May 15 in honor of Bishop Ubald or Ubaldo of Gubbio (1084–1160), shares certain features with the rites described in the text and so may be a survival of that ancient pre-Christian custom. It is also celebrated in Jessup, Pennsylvania, a town with a large number of immigrants from the Gubbio area, as Saint Ubaldo Day.
  • 2.4K
  • 27 Oct 2022
Topic Review
Modification of Clay Minerals for Carbon Capture
Carbon capture is among the most sustainable strategies to limit carbon dioxide emissions, which account for a large share of human impact on climate change and ecosystem destruction. This growing threat calls for novel solutions to reduce emissions on an industrial level. Carbon capture by amorphous solids is among the most reasonable options as it requires less energy when compared to other techniques and has comparatively lower development and maintenance costs. In this respect, the method of carbon dioxide adsorption by solids can be used in the long-term and on an industrial scale. Furthermore, certain sorbents are reusable, which makes their use for carbon capture economically justified and acquisition of natural resources full and sustainable. Clay minerals, which are a universally available and versatile material, are amidst such sorbents. These materials are capable of interlayer and surface adsorption of carbon dioxide. In addition, their modification allows to improve carbon dioxide adsorption capabilities even more. 
  • 2.4K
  • 13 Apr 2022
Topic Review
GaN-Based LEDs: Modeling and Simulation
Light-emitting diodes (LEDs) based on Gallium Nitride (GaN) have been revolutionizing various applications in lighting, displays, biotechnology, and other fields. Many theoretical models have been developed for GaN-LED simulation, analysis, and design optimization, including carrier transport models, quantum well recombination models, and light extraction models. The overview below is a strongly abbreviated version of Ref. [1].
  • 2.3K
  • 17 Dec 2020
Topic Review
{001} Faceted Anatase TiO2-Based Composites
For anatase TiO2, the {001} crystal facets are the most reactive because they exhibit unique surface characteristics such as visible light responsiveness, dissociative adsorption, efficient charge separation capabilities and photocatalytic selectivity. In this review, a concise survey of the literature in the field of {001} dominated anatase TiO2 crystals and their composites is presented. Even though the design and morphologically controlled synthesis of TiO2-001 is considered to be a hot spot in scientific research, it still has some drawbacks like its wide band gap and high recombination rate. These drawbacks can easily be overcome by coupling them with other materials to form TiO2-001-based composites. This review focusses on the synthesis, properties and applications of TiO2-001-based composites. 
  • 2.3K
  • 12 Nov 2021
Topic Review
Development and Types of High-Entropy Materials
By their unique compositions and microstructures, the high-entropy materials (HEMs) exhibit outstanding properties and performance above the threshold of traditional materials. Wear- and erosion-resistant materials are of significant interest for different applications, such as industrial devices, aerospace materials, and military equipment, related to their capability to tolerate heavy loads during sliding, rolling, or impact events.
  • 2.3K
  • 07 Feb 2023
Topic Review
Unsaturated Fat
An unsaturated fat is a fat or fatty acid in which there is at least one double bond within the fatty acid chain. A fatty acid chain is monounsaturated if it contains one double bond, and polyunsaturated if it contains more than one double bond. Where double bonds are formed, hydrogen atoms are subtracted from the carbon chain. Thus, a saturated fat has no double bonds, has the maximum number of hydrogens bonded to the carbons, and therefore is "saturated" with hydrogen atoms. In cellular metabolism, unsaturated fat molecules contain somewhat less energy (i.e., fewer calories) than an equivalent amount of saturated fat. The greater the degree of unsaturation in a fatty acid (i.e., the more double bonds in the fatty acid) the more vulnerable it is to lipid peroxidation (rancidity). Antioxidants can protect unsaturated fat from lipid peroxidation.
  • 2.3K
  • 28 Sep 2022
Topic Review
CL-20-Based Cocrystal Energetic Materials
Energetic materials (EMs) are widely used in military and civilian applications, such as weaponry, aerospace explorations and fireworks. However, both the power and safety of energetic materials are the most concern in the field of energetic materials application, but there is an essential contradiction between them: the highly energetic materials are often not safe, and, at present, the rareness of pure low-sensitive and highly energetic explosive has been found.  Due to the stringent requirements for both low-sensitivity and high-power simultaneously, the cocrystallization of explosive has attracted great interest since it can alleviate, to a certain extent, the power-safety contradiction. The new energetic cocrystals can potentially exhibit decreased sensitivity, higher performance through increased packing efficiency or oxygen balance, or improve aging due to altered bonds to specific groups on constituent molecules.
  • 2.3K
  • 21 Oct 2020
Topic Review
Benzodiazepine Use Disorder
Benzodiazepine use disorder (BUD), also called misuse or abuse, is the use of benzodiazepines without a prescription, often for recreational purposes, which poses risks of dependence, withdrawal and other long-term effects. Benzodiazepines are one of the more common prescription drugs used recreationally. When used recreationally benzodiazepines are usually administered orally but sometimes they are taken intranasally or intravenously. Recreational use produces effects similar to alcohol intoxication. In tests in pentobarbital trained rhesus monkeys benzodiazepines produced effects similar to barbiturates. In a 1991 study, triazolam had the highest self-administration rate in cocaine trained baboons, among the five benzodiazepines examined: alprazolam, bromazepam, chlordiazepoxide, lorazepam, triazolam. A 1985 study found that triazolam and temazepam maintained higher rates of self-injection in both human and animal subjects compared to a variety of other benzodiazepines (others examined: diazepam, lorazepam, oxazepam, flurazepam, alprazolam, chlordiazepoxide, clonazepam, nitrazepam, flunitrazepam, bromazepam, and clorazepate). A 1991 study indicated that diazepam, in particular, had a greater abuse liability among people who were drug abusers than did many of the other benzodiazepines. Some of the available data also suggested that lorazepam and alprazolam are more diazepam-like in having relatively high abuse liability, while oxazepam, halazepam, and possibly chlordiazepoxide, are relatively low in this regard. A 1991–1993 British study found that the hypnotics flurazepam and temazepam were more toxic than average benzodiazepines in overdose. A 1995 study found that temazepam is more rapidly absorbed and oxazepam is more slowly absorbed than most other benzodiazepines. Benzodiazepines have been abused both orally and intravenously. Different benzodiazepines have different abuse potential; the more rapid the increase in the plasma level following ingestion, the greater the intoxicating effect and the more open to abuse the drug becomes. The speed of onset of action of a particular benzodiazepine correlates well with the 'popularity' of that drug for abuse. The two most common reasons for preference were that a benzodiazepine was 'strong' and that it gave a good 'high'. According to Dr. Chris Ford, former clinical director of Substance Misuse Management in General Practice, among drugs of abuse, benzodiazepines are often seen as the 'bad guys' by drug and alcohol workers. Illicit users of benzodiazepines have been found to take higher methadone doses, as well as showing more HIV/HCV risk-taking behavior, greater poly-drug use, higher levels of psychopathology and social dysfunction. However, there is only limited research into the adverse effects of benzodiazepines in drug misusers and further research is needed to demonstrate whether this is the result of cause or effect.
  • 2.3K
  • 18 Oct 2022
Topic Review
Isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae — that is, same number of atoms of each element — but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural or constitutional isomerism, in which bonds between the atoms differ; and stereoisomerism or spatial isomerism, in which the bonds are the same but the relative positions of the atoms differ. Isomeric relationships form a hierarchy. Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different isotopologues. The depth of analysis depends on the field of study or the chemical and physical properties of interest. The English word "isomer" (/ˈaɪsəmər/) is a back-formation from "isomeric", which was borrowed through German isomerisch from Swedish isomerisk; which in turn was coined from Greek ἰσόμερoς isómeros, with roots isos = "equal", méros = "part".
  • 2.3K
  • 20 Oct 2022
Topic Review
[18F]Difluoromethyl Heteroaryl-Sulfones
The suitability of the 18F radioisotope in positron emission tomography (PET) demanded novel approaches for 18F-fluorination and 18F-fluoroalkylation. The difluoromethyl (CF2H) group has gained increasing attention in medicinal chemistry due to its lipophilic hydrogen-bond donor properties. In non-radioactive chemistry, difluoromethyl heteroaryl-sulfones has been extensively used in difluoromethylation of substrates bearing C=C, C≡C, and C≡N bonds by visible light photoredox catalysis. Herein, we highlight our recent work on the synthesis of [18F]difluoromethyl heteroaryl-sulfones with improved molar activities and their application in photoinduced C-H 18F-difluoromethylation of N-containing heteroarenes via a radical-mediated pathway.
  • 2.3K
  • 25 Aug 2021
Topic Review
The Jahn-Teller Effects
The fundamental property of a polyatomic system to undergo spontaneous symmetry breaking was first formulated by L. Landau in 1934 as follows: the configuration of any nonlinear polyatomic system in a degenerate electronic state undergoes spontaneous distortions that remove the degeneracy. This groundbreaking idea, appended with proof, was published by H. Jahn and E. Teller, resulting in what is presently known as the Jahn-Teller effect (JTE). Since then, many extensions of this groundbreaking idea were revealed and developed. Presently, four types of electronic structures that lead to spontaneous symmetry breaking are revealed: in addition to electronic degeneracy resulting in the proper Jahn-Teller effect, two or more close in energy (pseudodegenerate) electronic states may lead to similar instability and distortions, called the pseudo-JTE (PJTE), and the same spontaneous distortion effects may take place when there is neither degeneracy, nor pseudodegeneracy in the fground state of the high-symmetry configuration, but a strong JTE or pseudo-JTE take place in a low-lying excited state, that penetrates the ground state, distorting the system; these are the hidden -JTE and hidden-PJTE, respectively.
  • 2.2K
  • 26 Oct 2021
Topic Review
Njangsa
The term Njangsa refers to an oily seeds tree, Ricinodendron heudelotii, found in tropical West Africa. It is also known as Munguella (Angola), Essessang (Cameroon), Bofeko (Zaire), Wama (Ghana), Okhuen (Nigeria), Kishongo (Uganda), Akpi (Côte d'Ivoire), Djansang, Essang, Ezezang and Njasang. Two varieties of the tree species are recognized R. heudelotii var. heudelotii in Ghana and R. heudelotii var. africanum in Nigeria and Westwards.
  • 2.2K
  • 01 Nov 2022
Topic Review
Descriptor
A descriptor is in chemical nomenclature a prefix placed before the systematic substance name, which describes the configuration or the stereochemistry of the molecule. Some listed descriptors are only of historical interest and should not be used in publications anymore as they do not correspond with the modern recommendations of the IUPAC. Stereodescriptors are often used in combination with locants to clearly identify a chemical structure unambiguously. The descriptors, usually placed at the beginning of the systematic name, are not taken into account in the alphabetical sorting.
  • 2.2K
  • 25 Nov 2022
Topic Review
Composite Material Recycling Technology
The recycling of fiber reinforced composite materials will therefore play an important role in the future, in particular for the wind energy, but also for aerospace, automotive, construction and marine sectors to reduce environmental impacts and to meet the demand.
  • 2.2K
  • 18 Feb 2021
Topic Review
Amalgam
An amalgam is an alloy of mercury with another metal. It may be a liquid, a soft paste or a solid, depending upon the proportion of mercury. These alloys are formed through metallic bonding, with the electrostatic attractive force of the conduction electrons working to bind all the positively charged metal ions together into a crystal lattice structure. Almost all metals can form amalgams with mercury, the notable exceptions being iron, platinum, tungsten, and tantalum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore. Dentistry has used alloys of mercury with metals such as silver, copper, indium, tin and zinc.
  • 2.2K
  • 31 Oct 2022
Topic Review
Composite Repairs
Composite repairs. Composite materials are used in a wide range of applications in aerospace, marine, automotive, surface transport and sports equipment markets. Damage to composite components is not always visible to the naked eye and the extent of damage is best determined for structural components by suitable Non Destructive Test (NDT) methods. The concept for composite repair of composite or metallic structures is simple. The bonded repair reduces stresses in the damaged region and keeps the cracks from opening and therefore from growing.
  • 2.2K
  • 11 Oct 2022
Topic Review
Tetravalence
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules.
  • 2.2K
  • 27 Oct 2022
  • Page
  • of
  • 22
Featured Entry Collections
>>

Featured Books

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