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Telecommunications in South Africa

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Suburban communication towers in Pretoria Telecommunications infrastructure in South Africa provides modern and efficient service to urban areas, including cellular and internet services. In 1997, Telkom , the South African telecommunications parastatal , was partly privatised and entered into a strategic equity partnership with a consortium of two companies, including SBC, a U.S. telecommunications company. In exchange for exclusivity (a monopoly ) to provide certain services for 5 years, Telkom assumed an obligation to facilitate network modernisation and expansion into the unserved areas. A Second Network Operator was to be licensed to compete with Telkom across its spectrum of services in 2002, although this license was only officially handed over in late 2005 and has recently begun operating under the name, Neotel . Four cellular companies provide service to over 30 million subscribers, with South Africa considered to have the 4th most advanced mobile telecommunications network worldwide. The four cellul ...more...



P1 phage

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P1 is a temperate bacteriophage that infects Escherichia coli and some other bacteria. When undergoing a lysogenic cycle the phage genome exists as a plasmid in the bacterium unlike other phages (e.g. the lambda phage ) that integrate into the host DNA. P1 has an icosahedral head containing the DNA attached to a contractile tail with six tail fibers. The P1 phage has gained research interest because it can be used to transfer DNA from one bacterial cell to another in a process known as transduction . As it replicates during its lytic cycle it captures fragments of the host chromosome. If the resulting viral particles are used to infect a different host the captured DNA fragments can be integrated into the new host's genome. This method of in vivo genetic engineering was widely used for many years and is still used today, though to a lesser extent. P1 can also be used to create the P1-derived artificial chromosome cloning vector which can carry relatively large fragments of DNA. P1 encodes a site-specific rec ...more...



Human body

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The human body is the entire structure of a human being . It is composed of many different types of cells that together create tissues and subsequently organ systems . They ensure homeostasis and the viability of the human body. It comprises a head, neck , trunk (which includes the thorax and abdomen ), arms and hands, legs and feet. The study of the human body involves anatomy , physiology , histology and embryology . The body varies anatomically in known ways. Physiology focuses on the systems and organs of the human body and their functions. Many systems and mechanisms interact in order to maintain homeostasis , with safe levels of substances such as sugar and oxygen in the blood. The body is studied by health professionals , physiologists, anatomists, and by artists to assist them in their work. Composition Elements of the human body by mass. Trace elements are less than 1% combined (and each less than 0.1%). The human body is composed of elements including hydrogen , oxygen , carbon , calcium and phospho ...more...



Bone

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A bone is a rigid organ that constitutes part of the vertebrate skeleton . Bones support and protect the various organs of the body, produce red and white blood cells , store minerals , provide structure and support for the body, and enable mobility . Bones come in a variety of shapes and sizes and have a complex internal and external structure. They are lightweight yet strong and hard, and serve multiple functions . Bone tissue (osseous tissue) is a hard tissue , a type of dense connective tissue . It has a honeycomb-like matrix internally, which helps to give the bone rigidity. Bone tissue is made up of different types of bone cells . Osteoblasts and osteocytes are involved in the formation and mineralization of bone; osteoclasts are involved in the resorption of bone tissue. Modified (flattened) osteoblasts become the lining cells that form a protective layer on the bone surface. The mineralised matrix of bone tissue has an organic component of mainly collagen called ossein and an inorganic component of bo ...more...



Wallerian degeneration

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Wallerian degeneration is a process that results when a nerve fiber is cut or crushed and the part of the axon distal to the injury (i.e. farther from the neuron 's cell body) degenerates. This is also known as anterograde or orthograde degeneration . A related process known as 'Wallerian-like degeneration' occurs in many neurodegenerative diseases, especially those where axonal transport is impaired. Primary culture studies suggest that a failure to deliver sufficient quantities of the essential axonal protein NMNAT2 is a key initiating event. Wallerian degeneration occurs after axonal injury in both the peripheral nervous system (PNS) and central nervous system (CNS). It occurs in the axon stump distal to a site of injury and usually begins within 24–36 hours of a lesion. Prior to degeneration, distal axon stumps tend to remain electrically excitable. After injury, the axonal skeleton disintegrates, and the axonal membrane breaks apart. The axonal degeneration is followed by degradation of the myelin sheat ...more...



IBM BladeCenter

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The IBM BladeCenter was IBM 's blade server architecture, until it was replaced by Flex System . The x86 division was later sold to Lenovo in 2014. BladeCenter E front side: 8 blade servers (HS20) followed by 6 empty slots BladeCenter E back side, showing on the left two FC switches and two Ethernet switches . On the right side a management module with console cables. Magerit supercomputer ( CeSViMa ) has 86 Blade Centers (6 Blade Center E on each computing rack) History Introduced in 2002, based on engineering work started in 1999, the IBM BladeCenter was relatively late to the blade server market. It differed from prior offerings in that it offered a range of x86 Intel server processors and input/output (I/O) options. In February 2006, IBM introduced the BladeCenter H with switch capabilities for 10 Gigabit Ethernet and InfiniBand 4X. A web site called Blade.org was available for the blade computing community through about 2009. In 2012 the replacement Flex System was introduced. Versions IBM BladeCenter (E ...more...



Histology

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A typical histologic specimen, mounted between a glass microscope slide and a glass coverslip , positioned on the stage of a light microscope. Typical histologic specimen: glass microscope slide glass coverslip stained tissue section, mounted between 1. and 2. Light micrograph of a histologic specimen of human lung tissue stained with hematoxylin and eosin . Histology is the study of the microscopic anatomy ( microanatomy ) of cells and tissues of plants and animals . It is commonly performed by examining cells and tissues under a light microscope or electron microscope , the specimen having been sectioned (cut into a thin cross section with a microtome ), stained , and mounted on a microscope slide . Histological studies may be conducted using tissue culture , where live human or animal cells are isolated and maintained in an artificial environment for various research projects. The ability to visualize or differentially identify microscopic structures is frequently enhanced through the use of histological s ...more...



Microtrauma

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Microtrauma is the general term given to small injuries to the body. Muscle fibres may be "microtorn" during microtrauma Microtrauma can include the microtearing of muscle fibres, the sheath around the muscle and the connective tissue . It can also include stress to the tendons , and to the bones (see Wolff's law ). It is unknown whether or not the ligaments adapt like this. Microtrauma to the skin (compression, impact, abrasion) can also cause increases in a skin's thickness, as seen from the calluses formed from running barefoot or the hand calluses that result from rock climbing. This might be due to increased skin cell replication at sites under stress where cells rapidly slough off or undergo compression or abrasion. Most microtrauma cause a low level of inflammation that cannot be seen or felt. These injuries can arise in muscle, ligament, vertebrae, and discs, either singly or in combination. Repetitive microtrauma which are not allowed time to heal can result in the development of more serious conditi ...more...



Candex

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Candex is a dietary supplement manufactured by Pure Essence Laboratories . It is marketed as an enzymatic remedy to treat the yeast infection candida . Having the status of a dietary supplement , its efficiency has not been proven in scientifically controlled and peer-reviewed trials. Similar formulas exist, such as Candigest . Way of function Candex contains the fibre digesting enzymes , cellulase and hemicellulase. The manufacturer claims because yeast cell walls are built mainly of fibre, which is mostly made of the complex carbohydrate, cellulose , cellulase and hemicellulase are capable of killing yeast. However, a review of the scientific literature suggests that this mechanism of action is unlikely to be true. For while plant cell walls are made predominantly of cellulose , yeast cell walls are not ( yeast are classified as fungi). For example, in the article, "Synthesis of the yeast cell wall and its regulation" in the Annual Review of Biochemistry, there is mention of many other complex carbohydrates ...more...



Eye

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Eyes are organs of the visual system . They provide organisms with vision , the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and convert it into electro-chemical impulses in neurons . In higher organisms, the eye is a complex optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm , focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. Image-resolving eyes are present in molluscs , chordates and arthropods . The simplest "eyes", such as those in microorganisms , do nothing but detect whe ...more...



Comet assay

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The single cell gel electrophoresis assay ( SCGE , also known as comet assay ) is an uncomplicated and sensitive technique for the detection of DNA damage at the level of the individual eukaryotic cell . It was first developed by Östling & Johansson in 1984 and later modified by Singh et al. in 1988. It has since increased in popularity as a standard technique for evaluation of DNA damage/repair, biomonitoring and genotoxicity testing. It involves the encapsulation of cells in a low-melting-point agarose suspension, lysis of the cells in neutral or alkaline (pH>13) conditions, and electrophoresis of the suspended lysed cells. The term "comet" refers to the pattern of DNA migration through the electrophoresis gel, which often resembles a comet. The comet assay (single-cell gel electrophoresis) is a simple method for measuring deoxyribonucleic acid (DNA) strand breaks in eukaryotic cells. Cells embedded in agarose on a microscope slide are lysed with detergent and high salt to form nucleoids containing sup ...more...



Organ of Zuckerkandl

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The organ of Zuckerkandl is a chromaffin body derived from neural crest located at the bifurcation of the aorta or at the origin of the inferior mesenteric artery . It can be the source of paraganglioma . The term para-aortic body is also sometimes used to describe it, as it usually arises near the abdominal aorta , but this term can be the source of confusion, because the term "corpora paraaortica" is also used to describe the aortic body , which arises near the thoracic aorta . This diffuse group of neuroendocrine sympathetic fibres was first described by Emil Zuckerkandl , a professor of anatomy at the University of Vienna , in 1901. Some sources equate the " aortic bodies " and "paraaortic bodies", while other sources explicitly distinguish between the two. When a distinction is made, the "aortic bodies" are chemoreceptors which regulate circulation , while the "paraaortic bodies" are the chromaffin cells which manufacture catecholamines . Structure Function Its physiological role is thought to be of g ...more...



Cytoskeleton

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The eukaryotic cytoskeleton. Actin filaments are shown in red, and microtubules composed of beta tubulin are in green. A cytoskeleton is present in all cells of all domains of life ( archaea , bacteria , eukaryotes ). It is a complex network of interlinking filaments and tubules that extend throughout the cytoplasm , from the nucleus to the plasma membrane. The cytoskeletal systems of different organisms are composed of similar proteins. In eukaryotes, the cytoskeletal matrix is a dynamic structure composed of three main proteins, which are capable of rapid growth or disassembly dependent on the cell's requirements at a certain period of time. The structure, function and dynamic behavior of the cytoskeleton can be very different, depending on organism and cell type. Even within one cell the cytoskeleton can change through association with other proteins and the previous history of the network. A multitude of functions can be performed by the cytoskeleton. Its primary function would arguably be to give the ...more...

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Zone

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Look up Zone , zone , or zones in Wiktionary, the free dictionary. Zone or The Zone or In the Zone may refer to: Places Places Zone, Lombardy , a comune in the province of Brescia Zone (colony) (Ζώνη), an ancient Greek city Zones Any of the divisions of France during the World War II German occupation Any of the divisions of Germany during the post-World War II Allied occupation The Zone (die Zone in German), a derogatory term for the German Democratic Republic The Korean Demilitarized Zone Zone of alienation , the exclusion zone around the site of the Chernobyl disaster Zones of Nepal , administrative divisions Administrative divisions of India Exclusion zone , a geographic area in which certain activities are prohibited Frigid zone , a geographical zone on Earth The Green Zone in Baghdad, Iraq Hardiness zone , a geographically-defined zone in which a specific category of plant life is capable of growing International zone , an extraterritorial political zone Temperate zone , a geographical zone on Earth Tor ...more...



Glass wool

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Fiberglass insulation from a ceiling tile Glass wool batt insulation Fiberglass pipe insulation with ASJ (All Service Jacket) penetrating concrete slab opening about to be firestopped . Intumescent wrap strip is used to seal off where the fiberglass will be consumed by fire. Glass wool is an insulating material made from fibres of glass arranged using a binder into a texture similar to wool . The process traps many small pockets of air between the glass, and these small air pockets result in high thermal insulation properties. Glass wool is produced in rolls or in slabs, with different thermal and mechanical properties. It may also be produced as a material that can be sprayed or applied in place, on the surface to be insulated. The modern method for producing glass wool is the invention of Games Slayter working at the Owens-Illinois Glass Co. ( Toledo, Ohio ). He first applied for a patent for a new process to make glass wool in 1933. Principles of function Gases possess bad thermal conduction properties com ...more...



Floating island

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Uros island in Lake Titicaca A floating island is a mass of floating aquatic plants, mud, and peat ranging in thickness from several centimetres to a few metres. Floating islands are a common natural phenomenon that are found in many parts of the world. They exist less commonly as a man-made phenomenon . Floating islands are generally found on marshlands , lakes , and similar wetland locations, and can be many hectares in size. Natural occurrences Sometimes referred to as tussocks, floatons, or suds, natural floating islands are composed of vegetation growing on a buoyant mat of plant roots or other organic detritus. Some cenotes in northern Mexico have natural floating islands. They typically occur when growths of cattails , bulrush , sedge , and reeds extend outward from the shoreline of a wetland area. As the water gets deeper the roots no longer reach the bottom, so they use the oxygen in their root mass for buoyancy , and the surrounding vegetation for support to retain their top-side-up orientation. The ...more...



Radio masts and towers

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The Tokyo Skytree , the tallest freestanding tower in the world, in 2012 Radio masts and towers are, typically, tall structures designed to support antennas (also known as aerials) for telecommunications and broadcasting , including television . There are two main types: guyed and self-supporting structures. They are among the tallest man-made structures. Masts are often named after the broadcasting organizations that originally built them or currently use them. In the case of a mast radiator or radiating tower, the whole mast or tower is itself the transmitting antenna. Mast or tower? A radio mast base showing how virtually all lateral support is provided by the guy-wires The terms "mast" and "tower" are often used interchangeably. However, in structural engineering terms, a tower is a self-supporting or cantilevered structure, while a mast is held up by stays or guys . Broadcast engineers in the UK use the same terminology. A mast is a ground-based or rooftop structure that supports antennas at a height whe ...more...



Nucleosome

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A nucleosome is a basic unit of DNA packaging in eukaryotes , consisting of a segment of DNA wound in sequence around eight histone protein cores. This structure is often compared to thread wrapped around a spool. Nucleosomes form the fundamental repeating units of eukaryotic chromatin , which is used to pack the large eukaryotic genomes into the nucleus while still ensuring appropriate access to it (in mammalian cells approximately 2 m of linear DNA have to be packed into a nucleus of roughly 10 µm diameter). Nucleosomes are folded through a series of successively higher order structures to eventually form a chromosome ; this both compacts DNA and creates an added layer of regulatory control, which ensures correct gene expression. Nucleosomes are thought to carry epigenetically inherited information in the form of covalent modifications of their core histones . Nucleosomes were observed as particles in the electron microscope by Don and Ada Olins in 1974, and their existence and structure (as histone octa ...more...



Telomere

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Human chromosomes (grey) capped by telomeres (white) A telomere is a region of repetitive nucleotide sequences at each end of a chromosome , which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. Its name is derived from the Greek nouns telos (τέλος) "end" and merοs (μέρος, root: μερ-) "part". For vertebrates , the sequence of nucleotides in telomeres is TT A GGG , with the complementary DNA strand being AATCCC, with a single-stranded TTAGGG overhang . This sequence of TTAGGG is repeated approximately 2,500 times in humans. In humans, average telomere length declines from about 11 kilobases at birth to less than 4 kilobases in old age, with the average rate of decline being greater in men than in women. During chromosome replication , the enzymes that duplicate DNA cannot continue their duplication all the way to the end of a chromosome, so in each duplication the end of the chromosome is shortened (this is because the synthesis of Okazaki fragments requ ...more...



Coxsackie virus and adenovirus receptor

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Coxsackievirus and adenovirus receptor (CAR) is a protein that in humans is encoded by the CXADR gene . The protein encoded by this gene is a type I membrane receptor for group B coxsackie viruses and subgroup C adenoviruses . CAR protein is expressed in several tissues, including heart , brain , and, more generally, epithelial and endothelial cells . In cardiac muscle , CAR is localized to intercalated disc structures, which electrically and mechanically couple adjacent cardiomyocytes . CAR plays an important role in the pathogenesis of myocarditis , dilated cardiomyopathy , and in arrhythmia susceptibility following myocardial infarction or myocardial ischemia . Structure Human CAR protein has a theoretical molecular weight of 40.0 kDa and is composed of 365 amino acids . The human CAR gene (CXADR) is found on chromosome 21. Alternative splicing is known to produce at least 2 splice variants known as hCAR1 and hCAR2 and are each composed of at least 7 exons. Pseudogenes of this gene are found on chromos ...more...



Wood drying

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Wood drying (also seasoning lumber or wood seasoning ) reduces the moisture content of wood before its use. When the drying is done in a kiln , the product is known as kiln-dried timber or lumber , whereas air drying is the more traditional method. There are two main reasons for drying wood: Woodworking: when wood is used as a construction material, whether as a structural support in a building or in woodworking objects, it will absorb or desorb moisture until it is in equilibrium with its surroundings. Equilibration (usually drying) causes unequal shrinkage in the wood, and can cause damage to the wood if equilibration occurs too rapidly. The equilibration must be controlled to prevent damage to the wood. Wood burning: when wood is burned, it is usually best to dry it first. Damage from shrinkage is not a problem here, and the drying may proceed more rapidly than in the case of drying for woodworking purposes. Moisture affects the burning process, with unburnt hydrocarbons going up the chimney. If a 50% wet ...more...



Ainsworth Mill, Breightmet

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Ainsworth Mill, Breightmet is a mercerising mill near Breightmet , Bolton , Greater Manchester . It was bought by the Lancashire Cotton Corporation in the 1940s as an attempt to develop a cotton finishing presence. Location Breightmet is a small town 3 km to the east on Bolton town centre and 6 km west of Bury. The Ainsworth estate though physically attached to Breightment is for administrative purposes in the Metropolitan Borough of Bury . The early name Bolton le Moors described the position of the town amid the low hills on the edge of the West Pennine Moors south east of Rivington Pike (456 m). Breightmet lies on relatively flat land on west of the clough or steep-banked valley through which the Bradshaw Brook flows in a southerly direction towards the River Tonge and then the River Irwell . The geological formation around Breightmet consists of sandstones of the Carboniferous series and coal measures, to the north of Bolton Bury road the lower coal measures are mixed with underlying Millstone Grit . His ...more...



Electrospinning

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Photograph of a meniscus of polyvinyl alcohol in aqueous solution showing a fibre being electrospun from a Taylor cone . Electrospinning is a fiber production method which uses electric force to draw charged threads of polymer solutions or polymer melts up to fiber diameters in the order of some hundred nanometers. Electrospinning shares characteristics of both electrospraying and conventional solution dry spinning of fibers. The process does not require the use of coagulation chemistry or high temperatures to produce solid threads from solution. This makes the process particularly suited to the production of fibers using large and complex molecules. Electrospinning from molten precursors is also practiced; this method ensures that no solvent can be carried over into the final product. Process When a sufficiently high voltage is applied to a liquid droplet, the body of the liquid becomes charged, and electrostatic repulsion counteracts the surface tension and the droplet is stretched; at a critical point a s ...more...



NMDA receptor

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Stylized depiction of an activated NMDAR. Glutamate is in the glutamate-binding site and glycine is in the glycine-binding site. The allosteric site , which modulates receptor function when bound to a ligand, is not occupied. NMDARs require the binding of two molecules of glutamate or aspartate and two of glycine. The N-methyl-D-aspartate receptor (also known as the NMDA receptor or NMDAR ), is a glutamate receptor and ion channel protein found in nerve cells . The NMDA receptor is one of three types of ionotropic glutamate receptors , the others being the AMPA and kainate receptors . It is activated when glutamate and glycine (or D-serine ) bind to it, and when activated it allows positively charged ions to flow through the cell membrane . The NMDA receptor is very important for controlling synaptic plasticity and memory function. The NMDAR is a specific type of ionotropic glutamate receptor . The NMDA receptor is so named because the agonist molecule N -methyl-D-aspartate (NMDA) binds selectively to it, a ...more...



Hypothalamus

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The hypothalamus (from Greek ὑπό, "under" and θάλαμος, thalamus ) is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland (hypophysis). The hypothalamus is located below the thalamus and is part of the limbic system . In the terminology of neuroanatomy , it forms the ventral part of the diencephalon . All vertebrate brains contain a hypothalamus. In humans, it is the size of an almond . The hypothalamus is responsible for the regulation of certain metabolic processes and other activities of the autonomic nervous system . It synthesizes and secretes certain neurohormones , called releasing hormones or hypothalamic hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones . The hypothalamus controls body temperature , hunger , important aspects of parenting and attachment behaviours , thirst , fatigue , sleep , and ...more...



Itch

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Itch (also known as pruritus ) is a sensation that causes the desire or reflex to scratch. Itch has resisted many attempts to classify it as any one type of sensory experience. Modern science has shown that itch has many similarities to pain , and while both are unpleasant sensory experiences, their behavioral response patterns are different. Pain creates a withdrawal reflex, whereas itch leads to a scratch reflex . Unmyelinated nerve fibers for itch and pain both originate in the skin ; however, information for them is conveyed centrally in two distinct systems that both use the same nerve bundle and spinothalamic tract . Signs and symptoms Pain and itch have very different behavioral response patterns. Pain evokes a withdrawal reflex , which leads to retraction and therefore a reaction trying to protect an endangered part of the body. Itch in contrast creates a scratch reflex , which draws one to the affected skin site. Itch generates stimulus of a foreign object underneath or upon the skin and also the ur ...more...



Chrysotile

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Chrysotile or white asbestos is the most commonly encountered form of asbestos , accounting for approximately 95% of the asbestos in the United States and a similar proportion in other countries. It is a soft, fibrous silicate mineral in the serpentine subgroup of phyllosilicates ; as such, it is distinct from other asbestiform minerals in the amphibole group . Its idealized chemical formula is Mg ( Si O )( OH ). The material has physical properties which make it desirable for inclusion in building materials, but poses serious health risks when dispersed into air and inhaled. Polytypes Three polytypes of chrysotile are known. These are very difficult to distinguish in hand specimens, and polarized light microscopy must normally be used. Some older publications refer to chrysotile as a group of minerals—the three polytypes listed below, and sometimes pecoraite as well—but the 2006 recommendations of the International Mineralogical Association prefer to treat it as a single mineral with a certain variation ...more...



Reissner's fiber

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Reissner's fiber (named after Ernst Reissner ) is a fibrous aggregation of secreted molecules extending from the subcommissural organ (SCO) through the ventricular system and central canal to the terminal ventricle , a small ventricle-like structure near the end of the spinal cord . In vertebrates, Reissner's fiber is formed by secretions of SCO-spondin from the subcommissural organ into the ventricular cerebrospinal fluid . Reissner's fiber is highly conserved, and present in the central canal of all chordates . In cephalochordates , Reissner's fiber is produced by the ventral infundibular organ , as opposed to the dorsal SCO. Structure Reissner’s fiber (RF) is a complex and dynamic structure present in the third and fourth ventricles and in the central canal of the spinal cord, observed in almost all vertebrates. It is formed by the assembly of complex and variable high weight molecular glycoproteins secreted by the SCO that are released to the cerebrospinal fluid. At least five different proteins were f ...more...



Eyeblink conditioning

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Eyeblink conditioning ( EBC ) is a form of classical conditioning that has been used extensively to study neural structures and mechanisms that underlie learning and memory . The procedure is relatively simple and usually consists of pairing an auditory or visual stimulus (the conditioned stimulus (CS)) with an eye blink -eliciting unconditioned stimulus (US) (e.g. a mild puff of air to the cornea or a mild shock). Naïve organisms initially produce a reflexive, unconditioned response (UR) (e.g. blink or extension of nictitating membrane) that follows US onset. After many CS-US pairings, an association is formed such that a learned blink, or conditioned response (CR), occurs and precedes US onset. The magnitude of learning is generally gauged by the percentage of all paired CS-US trials that result in a CR. Under optimal conditions, well-trained animals produce a high percentage of CRs (> 90%). The conditions necessary for, and the physiological mechanisms that govern, eyeblink CR learning have been studied ac ...more...



Sympathetic nervous system

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The sympathetic nervous system ( SNS ) is one of the two main divisions of the autonomic nervous system , the other being the parasympathetic nervous system . The autonomic nervous system functions to regulate the body's unconscious actions. The sympathetic nervous system's primary process is to stimulate the body's fight-or-flight response . It is, however, constantly active at a basic level to maintain homeostasis . The sympathetic nervous system is described as being complementary to the parasympathetic nervous system which stimulates the body to "feed and breed" and to (then) "rest-and-digest". Structure There are two kinds of neurons involved in the transmission of any signal through the sympathetic system: pre-ganglionic and post-ganglionic. The shorter preganglionic neurons originate from the thoracolumbar region of the spinal cord specifically at T1 to L2~L3 , and travel to a ganglion , often one of the paravertebral ganglia , where they synapse with a postganglionic neuron. From there, the long post ...more...



Micrograph

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100x light micrograph of Meissner's corpuscle at the tip of a dermal papillus. 40x micrograph of a canine rectum cross section. A photomicrograph of a thin section of a limestone with ooids . The largest is approximately 1.2 mm in diameter. The red object in the lower left is a scale bar indicating relative size. Approximately 10x micrograph of a doubled die on a coin, where the date was struck twice. A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an item. This is opposed to a macrographic image, which is at a scale that is visible to the naked eye. Micrography is the practice or art of using microscopes to make photographs. A micrograph contains extensive details that form the features of a microstructure. A wealth of information can be obtained from a simple micrograph like behavior of the material under different conditions, the phases found in the system, failure analysis, grain size estimation, elemental analysis ...more...



Actin

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Actin is a family of globular multi-functional proteins that form microfilaments . It is found in essentially all eukaryotic cells (the only known exception being nematode sperm), where it may be present at a concentration of over 100 μM . An actin protein's mass is roughly 42- kDa , with a diameter of 4 to 7 nm, and it is the monomeric subunit of two types of filaments in cells: microfilaments , one of the three major components of the cytoskeleton , and thin filaments, part of the contractile apparatus in muscle cells. It can be present as either a free monomer called G-actin (globular) or as part of a linear polymer microfilament called F-actin (filamentous), both of which are essential for such important cellular functions as the mobility and contraction of cells during cell division . Actin participates in many important cellular processes, including muscle contraction , cell motility , cell division and cytokinesis , vesicle and organelle movement, cell signaling , and the establishment and maintenance ...more...



St. Francis Institute of Technology

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St. Francis Institute of Technology ( SFIT ) in Mumbai , India is an engineering college named after Francis of Assisi , the 12th-century Italian saint. The college is accredited by the National Board of Accreditation , approved by the AICTE and is affiliated to University of Mumbai . The college is run by the Society of Franciscan brothers, with a special consideration to Roman Catholic students. It offers undergraduate, post-graduate and doctoral courses in Engineering. It is the first Catholic technical institute in India to acquire Minority Status. Invocation Francis of Assisi , the namesake of the college “ Lord, make me an instrument of your peace, Where there is hatred, let me sow love; Where there is injury, pardon; Where there is doubt, faith; Where there is despair, hope; Where there is darkness, light; Where there is sadness, joy. O Divine Master, grant that I may not so much seek to be consoled, as to console; to be understood, as to understand; to be loved, as to love. For it is in giving that w ...more...



Muscle

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Muscle is a soft tissue found in most animals. Muscle cells contain protein filaments of actin and myosin that slide past one another, producing a contraction that changes both the length and the shape of the cell. Muscles function to produce force and motion . They are primarily responsible for maintaining and changing posture , locomotion , as well as movement of internal organs , such as the contraction of the heart and the movement of food through the digestive system via peristalsis . Muscle tissues are derived from the mesodermal layer of embryonic germ cells in a process known as myogenesis . There are three types of muscle, skeletal or striated, cardiac , and smooth . Muscle action can be classified as being either voluntary or involuntary. Cardiac and smooth muscles contract without conscious thought and are termed involuntary, whereas the skeletal muscles contract upon command. Skeletal muscles in turn can be divided into fast and slow twitch fibers. Muscles are predominantly powered by the oxidati ...more...



Insulin

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Insulin (from Latin insula, island) is a peptide hormone produced by beta cells of the pancreatic islets , and it is considered to be the main anabolic hormone of the body. It regulates the metabolism of carbohydrates , fats and protein by promoting the absorption of, especially, glucose from the blood into fat , liver and skeletal muscle cells. In these tissues the absorbed glucose is converted into either glycogen via glycogenesis or fats ( triglycerides ) via lipogenesis , or, in the case of the liver, into both. Glucose production and secretion by the liver is strongly inhibited by high concentrations of insulin in the blood. Circulating insulin also affects the synthesis of proteins in a wide variety of tissues. It is therefore an anabolic hormone, promoting the conversion of small molecules in the blood into large molecules inside the cells. Low insulin levels in the blood have the opposite effect by promoting widespread catabolism , especially of reserve body fat . Beta cells are sensitive to glucos ...more...



Killala

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Killala ( Irish : Cill Ala ) is a village in County Mayo in Ireland , north of Ballina . The railway line from Dublin to Ballina once extended to Killala. To the west of Killala is a Townsplots West (known locally as Enagh Beg), which contains a number of ancient forts. History Killala was the site of the first battle of the French force of General Humbert in the 1798 Rebellion , which landed at nearby Kilcummin Harbour and quickly seized the town. The town was also the site of the last land battle of the rebellion on 23 September 1798 when the British army defeated a rebel Irish force in Killala. Killala was used as the major location for the 1981 multi-million-pound television series The Year of the French (based on the novel by Thomas Flanagan ). In 1989 sculptor Carmel Gallagher unveiled a bust of General Humbert in the area to mark the then upcoming bicentennial of the 1798 Rebellion. In 1998 Killala celebrated the bicentenary of this event by twinning with the commune of Chauvé in France and Killala ha ...more...



Motility

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Cell division. All cells can be considered motile for having the ability to divide into two new daughter cells. '> Eukaryotic cytoskeletons induce cells to move through liquid and over surfaces, divide into new cells, and the cytoskeleton guides the transport of organelles within the cell. This video captures stained cytoskeletons from the cross section of a leaf of Arabidopsis thaliana . In biology , motility is the ability to move spontaneously and actively, consuming energy in the process. It is not to be confused with mobility , which describes the ability of an object to be moved. Motility is genetically determined (see genetic determinism ) but may be affected by environmental factors. For instance, muscles give animals motility but the consumption of hydrogen cyanide (the environmental factor in this case) would adversely affect muscle physiology causing them to stiffen leading to rigor mortis . Most animals are motile but the term applies to unicellular and simple multicellular organisms , as wel ...more...



List of examples of lengths

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Planets of the Solar System to scale This is a list of examples of lengths , in metres in order to give an understanding of lengths . Shorter than 1 ym 1.62 × 10 metres = the Planck length 1 ym to 1 zm 1 × 10 metres = 1 ym = 1 yoctometre , the smallest named subdivision of the metre in the SI base unit of length. 1 × 10 metres = 10 ym 2 × 10 metres = 20 ym, the effective cross-section radius of 1 MeV neutrinos as measured by Clyde Cowan and Frederick Reines 1 zm to 1 am 1 × 10 metres = 1 zm = 1 zeptometre = 1000 yoctometres 2 × 10 metres = radius of effective cross section for a 20 GeV neutrino scattering off a nucleon 7 × 10 metres = radius of effective cross section for a 250 GeV neutrino scattering off a nucleon 1 × 10 metres = 10 zm 1 × 10 metres = 100 zm 310 zm — de Broglie wavelength of protons at the Large Hadron Collider (4 TeV as of 2012) 1 am to 1 fm 1 × 10 metres = 1 am = 1 attometre = 1000 zeptometres 1 am — sensitivity of the LIGO detector for gravitational waves 1 × 10 metres = 10 am 1 × 10 metr ...more...



Development of the nervous system

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Neural development refers to the processes that generate, shape, and reshape the nervous system of animals, from the earliest stages of embryogenesis to adulthood. The field of neural development draws on both neuroscience and developmental biology to describe and provide insight into the cellular and molecular mechanisms by which complex nervous systems develop, from the nematode and fruit fly to mammals . Defects in neural development can lead to malformations and a wide variety of sensory, motor, and cognitive impairments, including holoprosencephaly and other neurological disorders such as Rett syndrome , Down syndrome and intellectual disability . Overview of brain development The mammalian central nervous system (CNS) is derived from the ectoderm —the outermost tissue layer—of the embryo. In the third week of human development the neuroectoderm appears and forms the neural plate along the dorsal side of the embryo. The neural plate is the source of the majority of neurons and glial cells of the CNS. A g ...more...



Collagen

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Tropocollagen molecule: three left-handed procollagens (red, green, blue) join to form a right-handed triple helical tropocollagen. Collagen is the main structural protein in the extracellular space in the various connective tissues in animal bodies. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole-body protein content. Collagen consists of amino acids wound together to form triple- helices to form of elongated fibrils . It is mostly found in fibrous tissues such as tendons , ligaments and skin . Depending upon the degree of mineralization, collagen tissues may be rigid (bone), compliant (tendon), or have a gradient from rigid to compliant (cartilage). It is also abundant in corneas , cartilage , bones , blood vessels , the gut , intervertebral discs , and the dentin in teeth. In muscle tissue , it serves as a major component of the endomysium . Collagen constitutes one to two percent of muscle tissue, and accounts for 6% of the ...more...



Adenoviridae

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Adenoviruses (members of the family Adenoviridae ) are medium-sized (90–100 nm ), nonenveloped (without an outer lipid bilayer) viruses with an icosahedral nucleocapsid containing a double stranded DNA genome. Their name derives from their initial isolation from human adenoids in 1953. They have a broad range of vertebrate hosts; in humans, more than 50 distinct adenoviral serotypes have been found to cause a wide range of illnesses , from mild respiratory infections in young children (known as the common cold ) to life-threatening multi-organ disease in people with a weakened immune system . Virology Taxonomy Group: dsDNA Order: Unassigned Family: Adenoviridae Genus: Atadenovirus   Bovine atadenovirus D Duck atadenovirus A Ovine atadenovirus D Possum atadenovirus A Snake atadenovirus A Genus: Aviadenovirus   Falcon aviadenovirus A Fowl aviadenovirus A Fowl aviadenovirus B Fowl aviadenovirus C Fowl aviadenovirus D Fowl aviadenovirus E Goose aviadenovirus A Turkey aviadenovirus B Genus: Ichtadenovirus   Sturge ...more...



Microtubule

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Microtubules are one of the cytoskeletal filament systems in eukaryotic cells. The microtubule cytoskeleton is involved in the transport of material within cells, carried out by motor proteins that move on the surface of the microtubule. Microtubules ( micro- + tube + -ule ) are a component of the cytoskeleton , found throughout the cytoplasm . These tubular polymers of tubulin can grow as long as 50  micrometres and are highly dynamic. The outer diameter of a microtubule is about 24  nm while the inner diameter is about 12 nm. They are found in eukaryotic cells , as well as some bacteria , and are formed by the polymerization of a dimer of two globular proteins , alpha and beta tubulin . Microtubules are very important in a number of cellular processes . They are involved in maintaining the structure of the cell and, together with microfilaments and intermediate filaments , they form the cytoskeleton . They also make up the internal structure of cilia and flagella .They provide platforms for intracellular t ...more...



Endometriosis

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Endometriosis is a condition in which the layer of tissue that normally covers the inside of the uterus grows outside of it. Most often this is on the ovaries , fallopian tubes , and tissue around the uterus and ovaries; however, in rare cases it may also occur in other parts of the body. The main symptoms are pelvic pain and infertility . Nearly half of those affected have chronic pelvic pain , while in 70% pain occurs during menstruation . Pain during sex is also common. Infertility occurs in up to half of women affected. Less common symptoms include urinary or bowel symptoms. About 25% of women have no symptoms. Endometriosis can have both social and psychological effects. The cause is not entirely clear. Risk factors include having a family history of the condition. The areas of endometriosis bleed each month, resulting in inflammation and scarring. The growths due to endometriosis are not cancer . Diagnosis is usually based on symptoms in combination with medical imaging . Biopsy is the mos ...more...



Tolonium chloride

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Tolonium chloride ( INN , also known as toluidine blue or TBO ) is a blue cationic (basic) dye used in histology and sometimes clinically. Test for lignin Toluidine blue solution is used in testing for lignin , a complex organic molecule that bonds to cellulose fibres and strengthens and hardens the cell walls in plants . A positive toluidine blue test causes the solution to turn from blue to pink . A similar test can be performed with phloroglucinol - HCl solution, which turns red. Other histological uses Toluidine Blue is often used to identify mast cells , by virtue of the heparin in their cytoplasmic granules . It is also used to stain proteoglycans and glycosaminoglycans in tissues such as cartilage. The strongly acidic macromolecular carbohydrates of mast cells and cartilage are coloured red by the blue dye, a phenomenon called metachromasia . Alkaline solutions of toluidine blue are commonly used for staining semi-thin (0.5 to 1 μm) sections of resin-embedded tissue. At high pH (about 10) the dye bind ...more...



Calcification

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Calcification is the accumulation of calcium salts in a body tissue . It normally occurs in the formation of bone , but calcium can be deposited abnormally in soft tissue , causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification. Calcification may also refer to the processes of normal mineral deposition in biological systems, such as the formation of stromatolites or mollusc shells (see Mineralization (biology) or Biomineralization ). Density-Dependent Colour Scanning Electron Micrograph SEM (DDC-SEM) of cardiovascular calcification, showing in orange calcium phosphate spherical particles (denser material) and, in green, the extracellular matrix (less dense material). Causes of soft tissue calcification Calcification of soft tissue (arteries, cartilage, heart valves , etc.) can be caused by vitamin K deficiency or by poor calcium absorption due to a high calcium/vitamin D ratio. This can occur with or without a mineral imbal ...more...



Pulpitis

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Pulpitis is inflammation of dental pulp tissue. The pulp contains the blood vessels the nerves and connective tissue inside a tooth and provides the tooth’s blood and nutrients. Pulpitis is mainly caused by bacteria infection which itself is a secondary development of caries (tooth decay). It manifests itself in the form of a toothache . Symptoms Increased sensitivity to stimuli , specifically hot and cold, is a common symptom of pulpitis. A prolonged throbbing pain may be associated with the disease. However, pulpitis can also occur without any pain. Causes Pulpitis may be caused by dental caries that penetrate through the enamel and dentin to reach the pulp, or it may be a result of trauma, such as physical abuse of the tooth or thermal insults, including overheating from insufficiently cooled dental drills and use of dental curing lights . More often it is from physical trauma rather than dental treatments. Inflammation is commonly associated with a bacterial infection but can also be due to other insults ...more...



Digestion

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Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma . In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream . Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes . In chemical digestion , enzymes break down food into the small molecules the body can use. In the human digestive system , food enters the mouth and mechanical digestion of the food starts by the action of mastication (chewing), a form of mechanical digestion, and the wetting contact of saliva . Saliva, a liquid secreted by the salivary glands , contains salivary amylase , an enzyme which starts the digestion of starch in the food; the sa ...more...



Sponge

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Sponges , the members of the phylum Porifera ( ; meaning "pore bearer"), are a basal Metazoa clade as sister of the Diploblasts .  They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells . Sponges have unspecialized cells that can transform into other types and that often migrate between the main cell layers and the mesohyl in the process. Sponges do not have nervous , digestive or circulatory systems . Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes. Sponges were first to branch off the evolutionary tree from the common ancestor of all animals, making them the sister group of all other animals. Etymology Sponge; from the Greek σπόγγος (spoggos). Overview Sponge biodiversity and morphotypes at the lip of a wall site in 60 feet (20 m) of water. Included are the yellow tube sponge, Aplysina fist ...more...



Peterstar

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PeterStar is a competitive local exchange carrier (CLEC) in St. Petersburg , Russia . It was founded in 1992 as the first non-state owned cell phone operator in St. Petersburg. In 1992 - 1995 the company was headed by Anatoly Afanasyev . Initially St. Petersburg City Telephone Network had 45% stake in PeterStar. Valery Yashin , the Director General of the St. Petersburg City Telephone Network, was a member of the Managing Committee, Leonid Reiman , First Deputy Director General of the St. Petersburg City Telephone Network, was a member of the Board of Directors. The remaining 55% stake belonged to the Tiller company of the British businessman Anthony Georgiou . PeterStar offers a wide range of fixed telecommunication services including voice, data (ISDN, Frame Relay, ATM, Ethernet), calling cards, PBX sales (Avaya and Ericsson). PeterStar maintains the entire 32x-xxxx St. Petersburg numbering range and has over 2,000 kilometers of fibre optic cables under the city streets. Competitors include Golden Telecom , ...more...



DNA vaccination

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DNA vaccination is a technique for protecting against disease by injection with genetically engineered DNA so cells directly produce an antigen , producing a protective immunological response . DNA vaccines have potential advantages over conventional vaccines, including the ability to induce a wider range of immune response types. Several DNA vaccines are available for veterinary use. Currently no DNA vaccines have been approved for human use. Research is investigating the approach for viral , bacterial and parasitic diseases in humans, as well as for several cancers. History Vaccines have eliminated naturally occurring smallpox , and nearly eliminated polio , while other diseases, such as typhus , rotavirus , hepatitis A and B and others are well controlled. Conventional vaccines cover a small number of diseases, while other infections kill millions of people every year. Whole organism First generation vaccines are whole-organism vaccines – either live and weakened , or killed forms. Live, attenuated vaccin ...more...

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