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Topic Review
Water Quality Index
A critical water quality index (WQI) method has been used to determine the overall water quality status of surface water and groundwater systems globally since the 1960s. WQI follows four steps: parameter selection, sub-indices, establishing weights, and final index aggregation.
  • 10.9K
  • 09 Apr 2021
Topic Review
Cruise Tourism
Cruise tourism is one of the leading industries suffering from covid-19 recently. Cruise tourism uses cruise ships with elegant services and various entertainment facilities as a means of transportation for scenic coastal tourist destinations. In particular, in accordance with the recent trend of increasing the size of ships, cruise lines have expanded the size and facilities of ships, and have continued to increase the maximum number of boarding ships. The cruise travel process and intensive entertainment system turned out to be a tourism structure vulnerable to the covid-19 pandemic. Will cruise tourism be extinguished? Should we prepare for the post-Pandermic cruise tourism era?
  • 10.9K
  • 26 Oct 2020
Topic Review
Single Point Mooring (SPM) Systems with Buoys
The SPM system consists of four main components, namely, the body of the buoy, the anchoring and mooring components, the fluid transfer system and the ancillary elements. Static legs linked to the seabed underneath the surface keep the buoy body in place. Above the water level, the body has a spinning portion that is attached to the offloading/loading tanker. A roller bearing, referred to as the main bearing, connects these two portions. Due to this array, the anchored tanker can easily weather-vane around the buoy and find a steady position. The concept of the buoy is determined by the type of bearing utilized and the divide between the rotating and geostatic sections. The buoy’s size is determined by the amount of counter buoyancy required to keep the anchor chains in place, and the chains are determined by environmental conditions and vessel size.
  • 10.8K
  • 19 Nov 2021
Topic Review
Standard Conditions for Temperature and Pressure
Standard temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST), although these are not universally accepted standards. Other organizations have established a variety of alternative definitions for their standard reference conditions. In chemistry, IUPAC changed the definition of standard temperature and pressure in 1982: STP should not be confused with the standard state commonly used in thermodynamic evaluations of the Gibbs energy of a reaction. NIST uses a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa). This standard is also called normal temperature and pressure (abbreviated as NTP). These stated values of STP used by NIST have not been verified and require a source. However, values cited in Modern Thermodynamics with Statistical Mechanics by Carl S. Helrich and A Guide to the NIST Chemistry WebBook by Peter J. Linstrom suggest a common STP in use by NIST for thermodynamic experiments is 298.15 K (25°C, 77°F) and 1 bar (14.5038 psi, 100 kPa). The International Standard Metric Conditions for natural gas and similar fluids are 288.15 K (15.00 °C; 59.00 °F) and 101.325 kPa. In industry and commerce, standard conditions for temperature and pressure are often necessary to define the standard reference conditions to express the volumes of gases and liquids and related quantities such as the rate of volumetric flow (the volumes of gases vary significantly with temperature and pressure): standard cubic meters per second (Sm3/s), and normal cubic meters per second (Nm3/s). However, many technical publications (books, journals, advertisements for equipment and machinery) simply state "standard conditions" without specifying them; often substituting the term with older "normal conditions", or "NC". In special cases this can lead to confusion and errors. Good practice always incorporates the reference conditions of temperature and pressure. If not stated, some room environment conditions are supposed, close to 1 atm pressure, 293 K (20 °C), and 0% humidity.
  • 10.8K
  • 09 Nov 2022
Topic Review
Vision in Fishes
Vision is an important sensory system for most species of fish. Fish eyes are similar to the eyes of terrestrial vertebrates like birds and mammals, but have a more spherical lens. Birds and mammals (including humans) normally adjust focus by changing the shape of their lens, but fish normally adjust focus by moving the lens closer to or further from the retina. Fish retinas generally have both rod cells and cone cells (for scotopic and photopic vision), and most species have colour vision. Some fish can see ultraviolet and some are sensitive to polarized light. Among jawless fishes, the lamprey has well-developed eyes, while the hagfish has only primitive eyespots. The ancestors of modern hagfish, thought to be the protovertebrate were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. Fish vision shows evolutionary adaptation to their visual environment, for example deep sea fish have eyes suited to the dark environment.
  • 10.8K
  • 10 Nov 2022
Topic Review
List of Anatomy Mnemonics
This is a list of human anatomy mnemonics, categorized and alphabetized. For mnemonics in other medical specialties, see this list of medical mnemonics.
  • 10.8K
  • 24 Nov 2022
Topic Review
Pathophysiology of Obesity
Obesity is a challenging condition of excess body fat, caused by an imbalance in energy consumption and expenditure.
  • 10.8K
  • 18 Mar 2021
Topic Review
Decimation (Signal Processing)
In digital signal processing, decimation is the process of reducing the sampling rate of a signal.  The term downsampling usually refers to one step of the process, but sometimes the terms are used interchangeably.  Complementary to upsampling, which increases sampling rate, decimation is a specific case of sample rate conversion in a multi-rate digital signal processing system. A system component that performs decimation is called a decimator. When decimation is performed on a sequence of samples of a signal or other continuous function, it produces an approximation of the sequence that would have been obtained by sampling the signal at a lower rate (or density, as in the case of a photograph). The decimation factor is usually an integer or a rational fraction greater than one. This factor multiplies the sampling interval or, equivalently, divides the sampling rate. For example, if compact disc audio at 44,100 samples/second is decimated by a factor of 5/4, the resulting sample rate is 35,280.
  • 10.8K
  • 23 Nov 2022
Topic Review
Cretaceous–Paleogene Extinction Event
The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary (K–T) extinction,[lower-alpha 2] was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the exception of some ectothermic species such as the sea turtles and crocodilians, no tetrapods weighing more than 25 kilograms (55 pounds) survived. It marked the end of the Cretaceous period, and with it the end of the entire Mesozoic Era, opening the Cenozoic Era that continues today. In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows high levels of the metal iridium, which is rare in the Earth's crust, but abundant in asteroids. As originally proposed in 1980 by a team of scientists led by Luis Alvarez and his son Walter, it is now generally thought that the K–Pg extinction was caused by the impact of a massive comet or asteroid 10 to 15 km (6 to 9 mi) wide, 66 million years ago, which devastated the global environment, mainly through a lingering impact winter which halted photosynthesis in plants and plankton. The impact hypothesis, also known as the Alvarez hypothesis, was bolstered by the discovery of the 180 km (112 mi) Chicxulub crater in the Gulf of Mexico's Yucatán Peninsula in the early 1990s, which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact. The fact that the extinctions occurred simultaneously provides strong evidence that they were caused by the asteroid. A 2016 drilling project into the Chicxulub peak ring confirmed that the peak ring comprised granite ejected within minutes from deep in the earth, but contained hardly any gypsum, the usual sulfate-containing sea floor rock in the region: The gypsum would have vaporized and dispersed as an aerosol into the atmosphere, causing longer-term effects on the climate and food chain. In October 2019, researchers reported that the event rapidly acidified the oceans producing ecological collapse and, in this way as well, produced long-lasting effects on the climate, and accordingly was a key reason for the end-Cretaceous mass extinction. In January 2020, scientists reported new evidence that the extinction event was mostly a result of the meteorite impact and not volcanism. Other causal or contributing factors to the extinction may have been the Deccan Traps and other volcanic eruptions, climate change, and sea level change. A wide range of species perished in the K–Pg extinction, the best-known being the non-avian dinosaurs. It also destroyed a myriad of other terrestrial organisms, including some mammals, pterosaurs, birds, lizards, insects, and plants. In the oceans, the K–Pg extinction killed off plesiosaurs and mosasaurs and devastated teleost fish, sharks, mollusks (especially ammonites, which became extinct), and many species of plankton. It is estimated that 75% or more of all species on Earth vanished. Yet the extinction also provided evolutionary opportunities: In its wake, many groups underwent remarkable adaptive radiation — sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches. Mammals in particular diversified in the Paleogene, evolving new forms such as horses, whales, bats, and primates. The surviving group of dinosaurs were avians, ground and water fowl who radiated into all modern species of bird. Teleost fish, and perhaps lizards also radiated.
  • 10.8K
  • 03 Nov 2022
Topic Review
Carboniferous Rainforest Collapse
The Carboniferous rainforest collapse (CRC) was a minor extinction event that occurred around 305 million years ago in the Carboniferous period. It altered the vast coal forests that covered the equatorial region of Euramerica (Europe and America). This event may have fragmented the forests into isolated 'islands', which in turn caused dwarfism and, shortly after, extinction of many plant and animal species. Following the event, coal-forming tropical forests continued in large areas of the Earth, but their extent and composition were changed. The event occurred at the end of the Moscovian and continued into the early Kasimovian stages of the Pennsylvanian (Upper Carboniferous).
  • 10.7K
  • 08 Oct 2022
Topic Review
Perceptual Organization
Gestalt theory has provided perceptual science with a conceptual framework relating to brain mechanisms that determine the way we see the visual world. This is referred to as "Perceptual Organization" and has inspired researchers in Psychology, Neuroscience and Computational Design ever since. The major Gestalt principles, such as the principle of Prägnanz, and more importantly the Gestalt laws of perceptual organization, have been critically important to our understanding of visual information processing, how the brain detects order in what we see, and derives likely perceptual representations from statistically significant structural regularities. The perceptual integration of contrast information across co-linear space for the organization of objects in the 2D image plane into figure and ground convey the most elementary basis to our understanding of the visual world. Gestalt theory continues to generate powerful concepts and insights for perceptual science even today, where it is to be placed in the context of image-base decision making by human minds and machines.
  • 10.7K
  • 22 Mar 2021
Topic Review
Ionic Liquid
Ionic Liquids (ILs) are organic salts that melt commonly below 100 °C, constituted entirely by charged species. The tunability and versatility of ILs have given rise to several applications at the academic and industrial levels. Here the following topics are highlighted: chemical structure; ILs classification according to the possibility of proton transfer, and the historical generations of ILs.
  • 10.7K
  • 01 Dec 2020
Topic Review
Subject–object–verb
In linguistic typology, a subject–object–verb (SOV) language is one in which the subject, object, and verb of a sentence always or usually appear in that order. If English were SOV, "Sam oranges ate" would be an ordinary sentence, as opposed to the actual Standard English "Sam ate oranges" which is subject–verb–object (SVO). The term is often loosely used for ergative languages like Adyghe and Basque that really have agents instead of subjects.
  • 10.7K
  • 27 Oct 2022
Topic Review
Hindu Views on Evolution
Hinduism includes a range of viewpoints about the origin of life, creationism and evolution. There is no single story of creation, due to dynamic diversity of Hinduism, and these are derived from various sources like Vedas, some from the Brahmanas, some from Puranas; some are philosophical, based on concepts, and others are narratives. The Rigveda mentions the Hiranyagarbha ("golden embryo") as the source of the creation of the Universe, similar to the world egg motif found in the creation myths of many other civilizations. It also contains a myth of proto-Indo-European origin, in which the creation arises out of the dismemberment of a cosmic being (the Purusha) who is sacrificed by the gods. As for the creation of the primordial gods themselves, the Nasadiya Sukta of Rigveda takes a near-agnostic stand, stating that the Gods came into being after the world's creation, and nobody knows when the world first came into being. In the later Puranic texts, the creator god Brahma is described as performing the act of 'creation', or more specifically of 'propagating life within the universe'. Some texts consider him equivalent to the Hiranyagarbha or the Purusha, while others state that he arose out of these. Brahma is a part of the trinity of gods that also includes Vishnu and Shiva, who are responsible for 'preservation' and 'destruction' (of the universe) respectively. Many Hindu texts mention the cycle of creation and destruction. The Shatapatha Brahmana states that the current human generation descends from Manu, the only man who survived a great deluge after being warned by the God. This legend is comparable to the other flood legends, such as the story of the Noah's Ark mentioned in the Bible and the Quran. Hindus find support for, or foreshadowing of evolutionary ideas in scriptures. For example, the concept of Dashavatara can be seen as having some similarities to Charles Darwin's theory of evolution.The first incarnation of Vishnu in the form of a fish resembles the evolutionary origin of fish in the Silurian Period. In a survey of 909 people, 77% of its respondents in India agreed that enough scientific evidence exists to support Charles Darwin’s Theory of Evolution, and 85% of God-believing people said they agree with evolution as well. According to the survey conducted by Pew Forum in the United States , 80% of Hindus agree that evolution is the best explanation for the origin of human life on earth. However, in India, there were minimal references to Darwinism in the 1800s. Elements of Victorian England opposed the idea of Darwinism. Hindus already had present notion of common ancestry between humans and animals. The Hindu dharma believes that the gods have animal features, showing a theory that humans can be reborn again as animals or with their features.
  • 10.7K
  • 21 Oct 2022
Topic Review
6061 Aluminium Alloy
6061 (Unified Numbering System (UNS) designation A96061) is a precipitation-hardened aluminium alloy, containing magnesium and silicon as its major alloying elements. Originally called "Alloy 61S", it was developed in 1935. It has good mechanical properties, exhibits good weldability, and is very commonly extruded (second in popularity only to 6063). It is one of the most common alloys of aluminum for general-purpose use. It is commonly available in pre-tempered grades such as 6061-O (annealed), tempered grades such as 6061-T6 (solutionized and artificially aged) and 6061-T651 (solutionized, stress-relieved stretched and artificially aged).
  • 10.6K
  • 22 Nov 2022
Topic Review
Guava Leaves
Psidium guajava (L.) belongs to the Myrtaceae family and it is an important fruit in tropical areas like India, Indonesia, Pakistan, Bangladesh, and South America. The leaves of the guava plant have been studied for their health benefits which are attributed to their plethora of phytochemicals, such as quercetin, avicularin, apigenin, guaijaverin, kaempferol, hyperin, myricetin, gallic acid, catechin, epicatechin, chlorogenic acid, epigallocatechin gallate, and caffeic acid. Extracts from guava leaves (GLs) have been studied for their biological activities, including anticancer, antidiabetic, antioxidant, antidiarrheal, antimicrobial, lipid-lowering, and hepatoprotection activities.
  • 10.6K
  • 14 Apr 2021
Topic Review
Dialysis (Biochemistry)
In biochemistry, dialysis is the process of separating molecules in solution by the difference in their rates of diffusion through a semipermeable membrane, such as dialysis tubing. Dialysis is a common laboratory technique that operates on the same principle as medical dialysis. In the context of life science research, the most common application of dialysis is for the removal of unwanted small molecules such as salts, reducing agents, or dyes from larger macromolecules such as proteins, DNA, or polysaccharides. Dialysis is also commonly used for buffer exchange and drug binding studies. The concept of dialysis was introduced in 1861 by the Scottish chemist Thomas Graham. He used this technique to separate sucrose (small molecule) and gum Arabic solutes (large molecule) in aqueous solution. He called the diffusible solutes crystalloids and those that would not pass the membrane colloids. From this concept dialysis can be defined as a spontaneous separation process of suspended colloidal particles from dissolved ions or molecules of small dimensions through a semi permeable membrane. Most common dialysis membrane are made of cellulose, modified cellulose or synthetic polymer (cellulose acetate or nitrocellulose).
  • 10.6K
  • 07 Nov 2022
Topic Review
Physico-Chemical Properties of Sodium Alginate
The macromolecules of natural origin have attracted the attention of many researchers as essential to protect the structures of unstable drug substances. After analyzing the studies carried out by various authors, researchers found that these molecules are used for both investigational and therapeutic purposes. This requires the design of certain drug delivery formulations knowing the nature of the macromolecule, its target organ, the required dose and the route of delivery. Therefore, researchers consider it important to use sodium alginate to optimize the delivery of drug substances for maximum therapeutic performance in the body after administration.
  • 10.6K
  • 19 Oct 2022
Topic Review
Closed Timelike Curves
Closed timelike curves (CTCs) are space-time trajectories that return to their starting point without violating the laws of special relativity. A traveler along a CTC could journey into the future but arrive in its past, creating a possible violation of the principle of causality. Such CTCs occur in Gödel’s rotating universe and many other general relativistic solutions of classical Einstein’s field equations. The chronological protection conjecture suggests that Nature forbids this kind of situation.
  • 10.6K
  • 27 Jan 2021
Topic Review
Malignant Brain Tumors
A discussion of malignant brain tumors including both primary tumors (gliomas, embryonal CNS tumors) and secondary tumors (brain metastasis).
  • 10.6K
  • 18 Jun 2021
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