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Topic Review
Fluid Catalytic Cracking Catalyst Regeneration Intensification Technologies
Fluid catalytic cracking (FCC) is the workhorse of modern crude oil refinery. Its regenerator component plays a critical role in optimizing the overall profitability by efficiently restoring the catalyst activity and enhancing the heat balance in the riser reactor. Improvement in the device metallurgy and process operations have enabled industrial regenerators to operate at high temperatures with a better coke burning rate and longer operating cycle. Today, the carbon content of regenerated catalyst has drastically reduced to less than 0.1 wt.%.
  • 9.6K
  • 15 Mar 2022
Topic Review
Lexical Bundles
The term “lexical bundles” was defined as “recurrent expressions, regardless of their idiomaticity, and regardless of their structural status”. As is well documented, lexical bundles not only contribute to fluent linguistic production but also form essential building blocks of discourse. A good command of lexical bundles could be indicative of a proficient and professional academic writer and is thus considered a pivotal skill for student writers, especially EFL student writers, for achieving sustainable growth of writing competence. Appropriate use of lexical bundles in academic writing helps writers from an academic community demonstrate their research writing ability.
  • 9.6K
  • 17 Jun 2021
Topic Review
Atomic Mass Unit
The dalton or unified atomic mass unit (SI symbols: Da or u) is a unit of mass widely used in physics and chemistry. . It is approximately the mass of one nucleon (either a proton or neutron). A mass of 1 Da is also referred to as the atomic mass constant and denoted by mu. Several definitions of this unit have been used, implying slightly different values. The current IUPAC endorsed definition is the unified atomic mass unit, denoted by the symbol u. As of 2019, the International System of Units (SI) lists the dalton, symbol Da, as a unit acceptable for use with the SI unit system and secondarily notes that the dalton (Da) and the unified atomic mass unit (u) are alternative names (and symbols) for the same unit. The symbol Da is more widely used in most fields. It is defined precisely as 1/12 of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest. Despite being an official abbreviation for a related obsolete unit and not widely used in the scientific literature, the abbreviation "amu" now often refers to the modern unit (Da or u) in many preparatory texts. As of June 2019, the value recommended by the Committee on Data for Science and Technology (CODATA) is 1.66053906660(50)×10−27 kg, or approximately 1.66 yoctograms. This unit is commonly used in physics and chemistry to express the mass of atomic-scale objects, such as atoms, molecules, and elementary particles. For example, an atom of helium has a mass of about 4 Da, and a molecule of acetylsalicylic acid (aspirin), C9H8O4, has a mass of about 180.16 Da. In general, the standard atomic weight of an element is the average weight of its atom as it occurs in nature, expressed in daltons. The molecular masses of proteins, nucleic acids, and other large polymers are often expressed with the units kilodalton (kDa), equal to 1000 daltons, megadalton (MDa), one million daltons, etc. Titin, one of the largest known proteins, has an atomic mass of between 3 and 3.7 megadaltons. The DNA of chromosome 1 in the human genome has about 249 million base pairs, each with an average mass of about 650 Da, or 156 GDa total. The mole is a unit of amount of substance, widely used in chemistry and physics, which was originally defined so that the mass of one mole of a substance, measured in grams, would be numerically equal to the average mass of one of its constituent particles, measured in daltons. That is, the molar mass of a chemical compound was meant to be numerically equal to its average molecular mass. For example, the average mass of one molecule of water is about 18.0153 daltons, and one mole of water is about 18.0153 grams. A protein whose molecule has an average mass of 64 kDa would have a molar mass of 64 kg/mol. However, while this equality can be assumed for almost all practical purposes, it is now only approximate, because of the way the mole was redefined on 20 May 2019. The mass in daltons of an atom is numerically very close to the number of nucleons A in its atomic nucleus. It follows that the molar mass of a compound (grams per mole) is also numerically close to the average number of nucleons per molecule. However, the mass of an atomic-scale object is affected by the binding energy of the nucleons in its atomic nuclei, as well as the mass and binding energy of the electrons. Therefore, this equality holds only for the carbon-12 atom in the stated conditions, and will vary for other substances. For example, the mass of one unbound atom of the common hydrogen isotope (hydrogen-1, protium) is 1.007825032241(94) Da, the mass of one free neutron is 1.008664915823(491) Da, and the mass of one hydrogen-2 (deuterium) atom is 2.014101778114(122) Da. In general, the difference (mass defect) is less than 0.1%; except for hydrogen (about 0.8%), helium-3 (0.5%), lithium (0.25%) and beryllium (0.15%). The atomic mass unit should not be confused with unit of mass in the atomic units systems, which is instead the electron rest mass (me).
  • 9.5K
  • 31 Oct 2022
Topic Review
The Photosynthetic Apparatus of Plants
Chlorophylls together with carotenoids, serve, noncovalently bound to specific apoproteins, as principal light-harvesting and energy-transforming pigments in oxygenic photosynthetic organisms, including plants.
  • 9.5K
  • 10 Jun 2021
Topic Review
Properties of Phase Change Materials
The main drawback of phase change materials (PCMs) is their low thermal conductivity, which limits the possibilities of a wide range of implementations. Therefore, the researchers, as found in the literature, proposed several methods to improve the thermal conductivity of PCMs, including inserting high thermal conductivity materials in nano-, micro-, and macro-scales, as well as encapsulation of PCMs. However, these inserts impact the other properties of PCMs like latent heat, melting temperature, thermal stability, and cycling stability. 
  • 9.5K
  • 18 Sep 2021
Topic Review
History of Geography
This article explores the history of geography.
  • 9.5K
  • 20 Oct 2022
Topic Review
Barrier Layer of Cu Interconnects
The barrier layer in Cu technology is essential to prevent Cu from diffusing into the dielectric layer at high temperatures; therefore, it must have a high stability and good adhesion to both Cu and the dielectric layer. In the past three decades, tantalum/tantalum nitride (Ta/TaN) has been widely used as an inter-layer to separate the dielectric layer and the Cu. However, to fulfill the demand for continuous down-scaling of the Cu technology node, traditional materials and technical processes are being challenged. Direct electrochemical deposition of Cu on top of Ta/TaN is not realistic, due to its high resistivity. Therefore, pre-deposition of a Cu seed layer by physical vapor deposition (PVD) or chemical vapor deposition (CVD) is necessary, but the non-uniformity of the Cu seed layer has a devastating effect on the defect-free fill of modern sub-20 or even sub-10 nm Cu technology nodes. New Cu diffusion barrier materials having ultra-thin size, high resistivity and stability are needed for the successful super-fill of trenches at the nanometer scale. In this review, we briefly summarize recent advances in the development of Cu diffusion-proof materials, including metals, metal alloys, self-assembled molecular layers (SAMs), two-dimensional (2D) materials and high-entropy alloys (HEAs). Also, challenges are highlighted and future research directions are suggested.
  • 9.5K
  • 30 Jul 2021
Topic Review
Methods for Determination of Lipophilicity
Lipophilicity is one of many parameters involved in the biological activity of drugs, as it affects their pharmacokinetic and pharmacodynamic behavior. Generally, lipophilicity is assessed by the partition coefficient of a compound between a nonpolar phase (n-octanol) and an aqueous phase (water), expressed as P (partition coefficient) or as its decimal logarithm (Log P). The gold standard method for the experimental determination of Log P is the shake-flask method.
  • 9.5K
  • 25 Aug 2022
Topic Review
Iron-Containing Oral Contraceptives
Oral contraceptive use has been associated with decreased menstrual blood losses; thus, can independently reduce the risk of anemia and iron deficiency in women. Manufacturers have recently started to include supplemental iron in the non-hormonal placebo tablets of some contraceptives. 
  • 9.5K
  • 15 Jul 2021
Topic Review
Effect of Temperatures on Polyphenols during Extraction
Polyphenols are a set of bioactive compounds commonly found in plants. These compounds are of great interest, as they have shown high antioxidant power and are correlated to many health benefits. Hence, traditional methods of extraction such as solvent extraction, Soxhlet extraction and novel extraction technologies such as ultrasound-assisted extraction and subcritical water extraction (SWE) have been investigated for the extraction of polyphenols.
  • 9.5K
  • 09 Mar 2022
Topic Review
Rudra
Rudra (/ˈrʊdrə/; Sanskrit: रुद्र) is a Rigvedic deity, associated with wind or storm and the hunt. One translation of the name is "the roarer". In the Rigveda, Rudra has been praised as the "mightiest of the mighty". Rudra is the personification of 'terror'. Depending up on the periodic situation, Rudra can be meant as the most severe roarer/howler (could be a hurricane or tempest) or the most frightening one. The Shri Rudram hymn from the Yajurveda is dedicated to Rudra, and is important in the Saivism sect. The Hindu god Shiva shares several features with the Rudra: the theonym Shiva originated as an epithet of Rudra, the adjective shiva ("kind") being used euphemistically of Rudra, who also carries the epithet Aghora, Abhayankar ("extremely calm [sic] non terrifying"). Usage of the epithet came to exceed the original theonym by the post-Vedic period (in the Sanskrit Epics), and the name Rudra has been taken as a synonym for the god Shiva and the two names are used interchangeably.
  • 9.5K
  • 25 Nov 2022
Topic Review
Fiber to the Premises by Country
This article lists the deployment of fiber to the premises, fiber to the home and fiber to the building by country.
  • 9.5K
  • 30 Nov 2022
Topic Review
Overview of Polylactic Acid
Poly(lactic acid) (PLA) is an important polymer that is based on renewable biomass resources. Because of environmental issues, more renewable sources for polymers synthesis have been sought for industrial purposes.
  • 9.5K
  • 20 Jul 2022
Topic Review
Levetiracetam Mechanisms of Action
Epilepsy is a chronic disease that affects millions of people worldwide. Antiepileptic drugs (AEDs) are used to control seizures. Even though parts of their mechanisms of action are known, there are still components that need to be studied. Therefore, the search for novel drugs, new molecular targets, and a better understanding of the mechanisms of action of existing drugs is still crucial. Levetiracetam (LEV) is an AED that has been shown to be effective in seizure control and is well-tolerable, with a novel mechanism of action through an interaction with the synaptic vesicle protein 2A (SV2A). Moreover, LEV has other molecular targets that involve calcium homeostasis, the GABAergic system, and AMPA receptors among others, that might be integrated into a single mechanism of action that could explain the antiepileptogenic, anti-inflammatory, neuroprotective, and antioxidant properties of LEV. This puts it as a possible multitarget drug with clinical applications other than for epilepsy.
  • 9.5K
  • 27 Apr 2022
Topic Review
Architectural Perspective of Ant Nests
Ants are excellent architects in the animal kingdom. The activities of “design”, “material selection” and “construction” of their nests are full of magical secrets. After hundreds of millions of years of survival of the fittest, the nests of each species of ant are generally characterised by reasonable structure and good mechanical performance, and also reflect the law of “obtaining large and solid living space with the least amount of material”. The complex underground ant colony nest system is large in scale, stable in internal environmental characteristics, has excellent ventilation, appropriate humidity and temperature, and makes use of natural barriers, such as thin grasses, trees, sand and stone, around entrances and exits, as well as having good physical structure, resistant to pressure, water, heat and moisture. Ants have very strict requirements on the size, weight, lustre and colour of the building materials for the nest, such as soil particles. As social insects, ants are responsible for the site selection and materials selection of their nests, the design of the whole nest, organising and coordinating the grand construction process, and managing the nest. 
  • 9.5K
  • 26 Dec 2022
Topic Review
Chlorophyll a
Chlorophyll a is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light, and it is a poor absorber of green and near-green portions of the spectrum. Chlorophyll does not reflect light but chlorophyll-containing tissues appear green because green light, diffusively reflected by structures like cell walls, becomes enriched in the reflected light. This photosynthetic pigment is essential for photosynthesis in eukaryotes, cyanobacteria and prochlorophytes because of its role as primary electron donor in the electron transport chain. Chlorophyll a also transfers resonance energy in the antenna complex, ending in the reaction center where specific chlorophylls P680 and P700 are located.
  • 9.5K
  • 10 Oct 2022
Topic Review
Islam and Secularism
Secularism—i.e. the separation of religion from civic affairs and the state—has been a controversial concept in Islamic political thought, owing in part to historical factors and in part to the ambiguity of the concept itself. In the Muslim world, the notion has acquired strong negative connotations due to its association with removal of Islamic influences from the legal and political spheres under foreign colonial domination, as well as attempts to restrict public religious expression by some secularist nation states. Thus, secularism has often been perceived as a foreign ideology imposed by invaders and perpetuated by post-colonial ruling elites, and is frequently understood to be equivalent to irreligion or anti-religion. Especially in the late 19th to mid-20th century, some Muslim thinkers advocated secularism as a way to strengthen the Islamic world in the face of Russian, British and French colonialism. Some have advocated secularism in the sense of political order that does not impose any single interpretation of sharia (Ali Abdel Raziq and Mahmoud Mohammed Taha); argued that such a political order would not/does not violate Islam (Abdullah Saeed); and that combined with constitutionalism and human rights, is more consistent with Islamic history than modern visions of an Islamic state (Abdullahi Ahmed An-Na'im). Strongly opposed to limiting Islam to matters of personal belief, and strongly advocating an Islam encompassing law, politics, economics, culture and every other aspect of the lives of its citizens, are orthodox Islamic scholars and proponents of Islamism (political Islam). Islamist pioneer Abul A'la Maududi claimed that the goal of secularists was not to ameliorate tensions and divisions in multi-religious societies, but to avoid the "restraints of morality and divine guidance", and thus eliminate "all morality, ethics, or human decency from the controlling mechanisms of society." A number of pre-modern polities in the Islamic world demonstrated some level of separation between religious and political authority, even if they did not adhere to the modern concept of a state with no official religion or religion-based laws. Today, some Muslim-majority countries define themselves as or are regarded as secular. Many of them have a dual legal system in which Muslims can bring familial and financial disputes to sharia courts whose jurisdiction varies from country to country but usually includes marriage, divorce, inheritance, and guardianship.
  • 9.5K
  • 26 Oct 2022
Topic Review
Control Techniques in Photovoltaic Systems
Complex control structures are required for the operation of photovoltaic electrical energy systems. In this paper, a general review of the controllers used for photovoltaic systems is presented. This entry is based on the most recent papers presented in the literature. The control architectures considered are complex hybrid systems that combine classical and modern techniques, such as artificial intelligence and statistical models. The main contribution of this paper is the synthesis of a generalized control structure and the identification of the latest trends. The main findings are summarized in the development of increasingly robust controllers for operation with improved efficiency, power quality, stability, safety, and economics.
  • 9.5K
  • 19 Feb 2021
Topic Review
KH-11 Kennen
The KH-11 KENNEN (later renamed CRYSTAL, then Evolved Enhanced CRYSTAL System, and codenamed 1010 and Key Hole) is a type of reconnaissance satellite first launched by the American National Reconnaissance Office in December 1976. Manufactured by Lockheed in Sunnyvale, California, the KH-11 was the first American spy satellite to use electro-optical digital imaging, and so offer real-time optical observations. Later KH-11 satellites have been referred to by outside observers as KH-11B or KH-12, and by the names "Advanced KENNEN", "Improved Crystal" and "Ikon". Official budget documents refer to the latest generation of electro-optical satellites as Evolved Enhanced CRYSTAL System. The Key Hole series was officially discontinued in favor of a random numbering scheme after repeated public references to KH-7 Gambit, KH-8 Gambit-3, KH-9 Hexagon, and KH-11 satellites. The capabilities of the KH-11 are highly classified, as are images they produce. The satellites are believed to have been the source of some imagery of the Soviet Union and China made public in 1997; images of Sudan and Afghanistan made public in 1998 related to the response to the 1998 U.S. embassy bombings; and a 2019 photo, revealed by President Donald Trump, of a failed Iranian rocket launch.
  • 9.5K
  • 09 Oct 2022
Topic Review
CNBC Ticker
The CNBC Ticker is a computer simulation of ticker tapes used by the United States business news-oriented television network CNBC (as well as its international sister channels), that is displayed as a crawl on the lower part of the television screen. The CNBC Ticker shows security and index symbols in the manner of the ticker tapes that received information by telegraph. The security identifiers used on the CNBC Ticker are taken from nomenclatures used by third-party companies like Reuters or from global stock exchanges. The ticker is composed of a faster-scrolling upper band with a white background and a slower-scrolling lower band with a dark blue background for all CNBC channels. In addition for some channels, such as CNBC Europe; CNBC-e; CNBC Arabiya and Class CNBC, a third business news band is displayed in gray with a black background. The ticker is shown throughout the duration of financial news programming on CNBC's domestic and international channels, including national commercial breaks. However, in the United States and Canada , advertisements that are locally inserted by cable television providers may be shown full-screen, omitting the ticker from being displayed during local breaks (as of 2013, all ad inserts by cable television providers, as well as satellite television providers DirecTV and Dish Network are now shown full-screen).
  • 9.5K
  • 18 Oct 2022
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