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Alloimmunity	Alloimmunity	Alloimmunity (sometimes called isoimmunity) is an immune response to nonself antigens from members of the same species, which are called alloantigens or isoantigens. Two major types of alloantigens are blood group antigens and histocompatibility antigens. In alloimmunity, the body creates antibodies (called alloantibodies) against the alloantigens, attacking transfused blood, allotransplanted tissue, and even the fetus in some cases. Alloimmune (isoimmune) response results in graft rejection, which is manifested as deterioration or complete loss of graft function. In contrast, autoimmunity is an immune response to the self's own antigens. (The allo- prefix means "other", whereas the auto- prefix means "self".) Alloimmunization (isoimmunization) is the process of becoming alloimmune, that is, developing the relevant antibodies for the first time.
Alloimmunity	Alloimmunity	Alloimmunity is caused by the difference between products of highly polymorphic genes, primarily genes of the major histocompatibility complex, of the donor and graft recipient. These products are recognized by T-lymphocytes and other mononuclear leukocytes which infiltrate the graft and damage it.
Alloimmunity	Types of the rejection	Transfusion reaction Blood transfusion can result in alloantibodies reacting towards the transfused cells, resulting in a transfusion reaction. Even with standard blood compatibility testing, there is a risk of reaction against human blood group systems other than ABO and Rh.
Alloimmunity	Types of the rejection	Hemolytic disease of the fetus and newborn Hemolytic disease of the fetus and newborn is similar to a transfusion reaction in that the mother's antibodies cannot tolerate the fetus's antigens, which happens when the immune tolerance of pregnancy is impaired. In many instances the maternal immune system attacks the fetal blood cells, resulting in fetal anemia. HDN ranges from mild to severe. Severe cases require intrauterine transfusions or early delivery to survive, while mild cases may only require phototherapy at birth.
Alloimmunity	Types of the rejection	Transplant rejection Acute rejection Acute rejection is caused by antigen-specific Th1 and cytotoxic T-lymphocytes. They recognize transplanted tissue because of expression of alloantigens. A transplant is rejected during first several days or weeks after transplantation.
Alloimmunity	Types of the rejection	Hyperacute and accelerated rejection Hyperacute and accelerated rejection is antibody-mediated immune response to the allograft. Recipient's blood already contains circulating antibodies before the transplantation – either IgM or antibodies incurred by previous immunization (e.g. by repeated blood transfusion). In case of hyperacute rejection, antibodies activate complement; moreover, the reaction can be enhanced by neutrophils. This type of rejection is very fast, the graft is rejected in a few minutes or hours after the transplantation. Accelerated rejection leads to phagocyte and NK cell activation (not of the complement) through their Fc receptors that bind Fc parts of antibodies. Graft rejection occurs within 3 to 5 days. This type of rejection is a typical response to xenotransplants.
Alloimmunity	Types of the rejection	Chronic rejection Chronic rejection is not yet fully understood, but it is known that it is associated with alloantibody and cytokine production. Endothelium of the blood vessels is being damaged, therefore the graft is not sufficiently supplied with blood and is replaced with fibrous tissue (fibrosis). It takes two months at least to reject the graft in this way.
Alloimmunity	Mechanisms of rejection	CD4+ and CD8+ T-lymphocytes along with other mononuclear leukocytes (their exact function regarding the topic is not known) participate in the rejection. B-lymphocytes, NK cells and cytokines also play a role in it.
Alloimmunity	Mechanisms of rejection	Cellular rejection – CD4+ and CD8+ T-lymphocytes, NK cells Humoral rejection – B-lymphocytes Cytokines B-lymphocytes Humoral (antibody-mediated) type of rejection is caused by recipient's B-lymphocytes which produce alloantibodies against donor MHC class I and II molecules. These alloantibodies can activate the complement – this leads to target cell lysis. Alternatively, donor cells are coated with alloantibodies that initiate phagocytosis through Fc receptors of mononuclear leukocytes. Mechanism of humoral rejection is relevant for hyperacute, accelerated and chronic rejection.
Alloimmunity	Mechanisms of rejection	Alloimmunity can be also regulated by neonatal B cells. Cytokines Cytokine microenvironment where CD4+ T-lymphocytes recognize alloantigens significantly influences polarization of the immune response. CD4+ T-lymphocytes differentiate into Th1 helper cells in the presence of IL-12 (which is usually secreted by mature dendritic cells). Th1 cells produce proinflammatory cytokine IFN-γ and destroy the allograft tissue. If there is IL-4, CD4+ T-lymphocytes become Th2 cells secreting IL-4 and IL-5. Then allograft tolerance is mostly observed. TGF-β induces expression of Foxp3 gene in the absence of proinflammatory cytokines and thus differentiation of CD4+ T-lymphocytes into regulatory T cells (Treg). Regulatory T cells produce anti-inflammatory cytokines IL-10 and TGF-β which ensures the allograft tolerance. However, in the presence of IL-6 or IL-21 along with TGF-β, CD4+ T-lymphocytes acquire tissue-destructive Th17 phenotype and secrete IL-17.
Alloimmunity	Mechanisms of rejection	NK cells NK cells can also directly target the transplanted tissue. It depends on the balance of activating and inhibitory NK cell receptors and on their ligands expressed by the graft. Receptors of KIR (Killer-cell immunoglobulin-like receptor) family bind concrete MHC class I molecules. If the graft has these ligands on its surface, NK cell cannot be activated (KIR receptors provide inhibitory signal). So if these ligands are missing, there is no inhibitory signal and NK cell becomes activated. It recognizes target cells by "missing-self strategy" and induces their apoptosis by enzymes perforin and granzymes released from its cytotoxic granules. Alloreactive NK cells also secrete proinflammatory cytokines IFN-γ and TNF-α to increase expression of MHC molecules and costimulatory receptors on the surface of APCs (antigen-presenting cells). This promotes APC maturation which leads to amplification of T-cell alloreactivity by means of direct and also indirect pathway of alloantigen recognition (as described below). NK cells are able to kill Foxp3+ regulatory T-lymphocytes as well and shift the immune response from graft tolerance toward its rejection. Besides the ability of NK cells to influence APC maturation and T cell development, they can probably reduce or even prevent alloimmune response to transplanted tissue – either by killing the Donor APCs or by anti-inflammatory cytokine IL-10 and TGF-β secretion. However it is important to note that NK cell sub-populations differ in alloreactivity rate and in their immunomodulatory potential.
Alloimmunity	Mechanisms of rejection	Concerning immunosuppressive drugs, the effects on NK cells are milder in comparison to T cells.
Alloimmunity	Mechanisms of rejection	T-lymphocytes Alloantigen recognition Alloantigen on APC surface can be recognized by recipient's T-lymphocytes through two different pathways: Direct allorecognition – occurs when donor's APCs are presenting graft antigens. Recipient's T-lymphocytes can identify either MHC molecules alone or complex MHC molecule-foreign peptide as alloantigens. Specific T-cell receptors (TCR) of CD8+ T-lymphocytes recognize these peptides when form the complex with MHC class I molecules and TCR of CD4+ T-lymphocytes recognize a complex with MHC class II molecules.
Alloimmunity	Mechanisms of rejection	Indirect allorecognition – recipient's APCs infiltrate transplanted tissue, then they process and present, as any other foreign peptides, donor's MHC glycoproteins by MHC class II molecules. Mechanism of indirect allorecognition and therefore the involvement of CD4+ T-lymphocytes is the main cause of graft rejection. That is why the compatibility between donor and recipient MHC class II molecules is the most important factor concerning transplantation.Activation of T-lymphocytes T-lymphocytes are fully activated under two conditions: T-lymphocytes must recognize complex MHC-alloantigen presented by APC through direct or indirect allorecognition pathway.
Alloimmunity	Mechanisms of rejection	T-lymphocytes must receive costimulatory signal. There are costimulatory molecules on T-cell surface and APCs express their ligands (e.g. molecule CD28, which is on the surface of all naïve CD4+ and CD8+ T-lymphocytes, can bind ligands CD80 and CD86). Receptor-ligand engagement triggers T-cell signaling resulting in IL-2 production, clonal expansion and therefore development of effector and memory T-lymphocytes. In contrast, there are also such receptors on T-lymphocytes that cause inhibition of T-cell activation (for instance CD152/CTLA-4 receptor which binds CD80 and CD86 as well). If T-lymphocyte does not receive costimulatory signal, its activation fails and it becomes anergic.Alloimmune response can be enhanced by proinflammatory cytokines and by CD4+ T-lymphocytes that are responsible for APC maturation and IL-2 production. IL-2 is crucial for memory CD8+ T cell development. These cells may represent a serious problem after the transplantation. As the effect of being exposed to various infections in the past, antigen-specific T-lymphocytes have developed in patient's body. Part of them is kept in organism as memory cells and these cells could be a reason for "cross-reactivity" – immune response against unrelated but similar graft alloantigens. This immune response is called secondary and is faster, more efficient and more robust.
Alloimmunity	Graft tolerance	Transplanted tissue is accepted by immunocompetent recipient if it is functional in the absence of immunosuppressive drugs and without histologic signs of rejection. Host can accept another graft from the same donor but reject graft from different donor. Graft acceptance depends on the balance of proinflammatory Th1, Th17 lymphocytes and anti-inflammatory regulatory T cells. This is influenced by cytokine microenvironment, as mentioned before, where CD4+ T-lymphocytes are activated and also by inflammation level (because pathogens invading organism activate the immune system to various degrees and causing proinflammatory cytokine secretion, therefore they support the rejection). Immunosuppressive drugs are used to suppress the immune response, but the effect is not specific. Therefore, organism can be affected by the infection much more easily. The goal of the future therapies is to suppress the alloimmune response specifically to prevent these risks.
Alloimmunity	Graft tolerance	The tolerance could be achieved by elimination of most or all alloreactive T cells and by influencing alloreactive effector-regulatory T-lymphocytes ratio in favor of regulatory cells which could inhibit alloreactive effector cells. Another method would be based on costimulatory signal blockade during alloreactive T-lymphocytes activation.
Alloimmunity	Literature	Cellular and Molecular Immunology, 7th edition by Abul K. Abbas, Andrew H. Lichtman, Shiv Pillai, Saunders Copyright
Vans challenge	Vans challenge	The Vans challenge is a viral internet challenge that began in March 2019 where people show their Vans shoes landing right-side up after tossing them in the air. The viral sensation reportedly started after a Twitter user shared a video of the occurrence, which was captioned: “Did you know it doesn’t matter how you throw your Vans they will land facing up.” Since then, multiple people on social media posted similar videos of them throwing their Vans in the air and landing right-side up, along with Crocs, UGG boots, and other popular shoes. This theory proved false, as these shoes have not always landed facing up after tossing them.
Nut (climbing)	Nut (climbing)	In rock climbing, a nut (or chock or chockstone) is a metal wedge threaded on a wire that climbers use for protection by wedging it into a crack in the rock. Quickdraws are clipped to the nut wire by the ascending climber and the rope threads through the quickdraw. Nuts come in a variety of sizes and styles, and several different brands are made by competing manufacturers. Most nuts are made of aluminum. Larger nuts may be threaded on Dyneema cord instead of wire, but this has become unusual.The very smallest nuts are known as micronuts and may be made of brass or other metal, and typically have their wires soldered into them, instead of looped through drilled holes. They are mostly used in aid climbing, and their value as protection, arresting a climber's fall, is marginal because of both their low breaking strength and their tiny surface area (the HB 0 measures about 4 x 7 x 2.5 mm) in contact with the rock, though this can be offset if several are placed at a time. Other names used include RPs (the brand name of the first commercially available micronuts) and brassies. They are available from several manufacturers in a variety of styles. British climbers in the 1950s and 1960s were the first to use nuts as climbing protection. In addition to using pitons, they picked up machine nuts from the side of railway tracks, climbed with them in their pockets, and used them as artificial chocks. This developed to the point where they drilled the thread from the middle, threaded them with slings, and used them in cracks.
Nut (climbing)	Nut (climbing)	Nuts or chockstones are named after natural stones occasionally found wedged into cracks. Climbers eventually realized they could insert their own found pebble into a suitable crack. In an article called "Artificial Aids in Mountaineering" dated Oct-Dec 1956, G Sutton wrote about jammed knots for direct aid. He also compared the use of slings, chocks (rocks) and jammed knots to artificial climbing (aid climbing) and that "there should be no illusion that the use of a chockstone is in any way more admirable than that of a piton." By 1967 Royal Robbins saw the need for clean climbing and put up Nutcracker, an all nut protected 6 pitch climb, on the Manure Pile(Ranger Rock),Yosemite. In 1972, when clean climbing became an issue in the US, Yvon Chouinard began manufacturing chocks made specifically for rock climbing, with the familiar wedge shape still in use today. With Tom Frost, Chouinard invented a larger, six-sided nut called a Hexentric or hex. Prominent climbers like Henry Barber and John Stannard helped popularize the use of nuts, especially after it was discovered that a nut was lighter and easier to place and remove while climbing, as well as being at least as secure as a well-placed piton, and less damaging to the rock.
Nut (climbing)	Nut (climbing)	Nuts are available in different shapes to help the climber find the best fit for a given crack. Curved nuts have a concave face on one side and a convex face on the other. Larger nuts can be placed in either of two aspects (hexes in three aspects) to suit different-width cracks, with either the main faces or the sides in contact with the rock.
Nut (climbing)	Nut (climbing)	Nuts may be generically referred to as wires or stoppers, though "Stopper" is a brand name of a nut made by Black Diamond Equipment.
Dental papilla	Dental papilla	In embryology and prenatal development, the dental papilla is a condensation of ectomesenchymal cells called odontoblasts, seen in histologic sections of a developing tooth. It lies below a cellular aggregation known as the enamel organ. The dental papilla appears after 8–10 weeks intra uteral life. The dental papilla gives rise to the dentin and pulp of a tooth. The enamel organ, dental papilla, and dental follicle together forms one unit, called the tooth germ. This is of importance because all the tissues of a tooth and its supporting structures form from these distinct cellular aggregations. Similar to dental follicle, the dental papilla has a very rich blood supply and provides nutrition to the enamel organ.
Dental papilla	Embryology	Formation of dental papilla occurs in the Cap stage of Odontogenesis.
Dental papilla	Embryology	The cap stage The cap stage is the second stage of tooth development and occurs during the ninth or tenth week of prenatal development. Unequal proliferation of the tooth bud forms a three-dimensional cap shape. Overlying this cap structure is the ectomesenchyme, which is attached to the mesodermal tissue known as the dental papilla superiorly, and lies within the epithelial concavity.Various types of differentiation occur at this stage; such as cytodifferentiation, histodifferentiation and morphodifferentation. Histodifferentiation is the differentiation of different tissue types during the development of an embryo/ undifferentiated group of cells. Furthermore, morphogenesis is a predominant physiological process during the cap stage. This is due to formation of primordium of the tooth. The primordium contains each of the primordial tissue types, essential for the development of successive teeth. These primordial tissues together form the enamel organ, dental papilla and dental sac.
Dental papilla	Embryology	Also during the cap stage is the formation of a depression within the deepest part of each tooth bud of the dental lamina. The dental lamina is a band of epithelial tissue which connects the developing tooth bud to the oral epithelium. The dental lamina eventually disintegrates into small clusters of epithelium and is reabsorbed. The dental lamina is first evidence of tooth development and begins at the sixth week in utero.This is responsible for the cap like structure of the enamel organ. It is important to note that enamel is an ectodermal product as it is originally derived from ectoderm which is the outermost of the three germ layers of the forming embryo. The other two are: the mesoderm and the endoderm. It gives rise to the nervous system, sense organs, outer layer of the skin, teeth and the membrane lining the oral cavity (mouth).A section of the ectomesenchyme (a group of tissue made up of neurocrest cells which are present in the initial development of an embryo. This forms the hard and soft tissues of the neck and skull), condenses into a mass within the concavity of the cap of the enamel organ. This mass is now considered the dental papilla. Note that dental papilla is originally derived from ectomesenchyme. Ectomesenchyme (type of mesenchyme) is derived from neural crest cells (NCCs). A basement membrane exists between the enamel organ and dental papilla which will be the site of the future dentinoenamel junction. The dentinoenamel junction is the surface at which the enamel and the dentin of the crown of a tooth are joined.The existing ectomesenchyme around the outside of the cap of the enamel organ then condenses into the dental sac. A basement membrane separate the enamel organ and the dental sac. The dental sac produces the periodontium in future development. The periodontium is the tissue that surrounds and supports the teeth. It includes the connective tissue and overlying keratinised membrane lining the oral cavity that surrounds the teeth, the periodontal ligament, cementum which provides a protective covering for the root surface and supporting alveolar bone The Bell Stage This is the fourth stage of tooth development which occurs between the eleventh and twelfth week of prenatal development. During this stage of Odontogenesis, the epithelial tooth germ forms a bell - shaped structure in the labio - lingual section and is characterised by the formation of the dental sac. The peripheral cells of the dental papilla undergo differentiation, growing larger in size and taking a columnar (uni-layered) form and are now referred to as Odontoblasts (the outer part of the dental pulp). This differentiation begins at the apex of the dental papilla, gradually extending downwards. This differentiation occurs to supplement the development of the dental sac which is responsible for cementum, periodontal ligament and the alveolar process.
Dental papilla	Embryology	Epithelium Layers - Inner is separated from the peripheral cells of the dental papilla by a basement membrane and a cell free zone rich in RNA but do not contain alkaline phosphatase-Outer involved in the maintenance of the shape of the enamel and the environment contain very big nuclei and have small quantities of the intra-cellular organelles involved in protein synthesis. The cells contact each other through desmosomes and gap junctions-Stratum Is concerned with: the synthesis of proteins the transport of materials to and from the enamel- forming cells in the internal enamel epithelium the concentration of materials The Apposition Stage and the Maturation Stage During the apposition stage the enamel, dentin and cementum are secreted in successive layers. The mesenchymal tissue of dental papilla and dental sac and the ectodermal tissue of enamel undergo induction. The outer cells of dental papilla are induced by preameloblasts (cells within the enamel from which a cell that takes part in forming dental enamel develops) to differentiate into odontoblasts (dentin-secreting cells). The odontoblasts undergo differentiation and repolarization and result in formation of the dentin matrix/pre-dentin (the innermost section of the dentin, which is not mineralized and located adjacent to pulp tissues in the crown area and root area). The central cells of dental papilla form the primordium of the pulp during root development. These cells then become surrounded by newly formed dentin..
Dental papilla	Differentiation	Ectomesenchymal cells will multiply continuously in a localized area such that when the bell stage of development is reached, both the epithelial component and the ectomesenchymal component will seem to have been surrounded by something that presents as a fibrous sac. Therefore, among a complicated mass of highly differentiated cells, it would appear to have three major components, which are: 1) The Dental Follicle → The ectomesenchymal cells which are part of the fibrous sac that have been formed 2) The Dental Papilla → The ectomesenchymal cells which are lying deep to the enamel organ 3) The Enamel Organ → purely the epithelial component The tissues which have been derived from each of the three components are: 1) The Dental Follicle → will develop to become the periodontal ligament, the cementum and the alveolar bone 2) The Dental Papilla → will develop to become the dental pulp and the dentine 3) The Enamel Organ → will develop to create the enamel solely It is important to note that till this point, no dental tissues have been created yet.
Dental papilla	Differentiation	When all of the individual components of the tooth germ have become developed, the entire cell mass would have appeared to have migrated deeper into the underlying connective tissues. This phenomenon, which will continue throughout the whole life of the teeth, is most possibly due to the cell mass moving towards a rich blood supply that can be found in the deeper parts of the mandible (lower jaw) and the maxilla (upper jaw) The probable need for a rich blood supply would seem to show that the cell mass will soon be highly productive in the formation of dental tissues. Therefore, when the late bell stage of the tooth germ development has been reached, most of the cells would have been differentiated to an apparent endpoint where the cells will now begin their formative role when the first three stages of the tissue development are almost completed, and the tissues can now start to begin secreting.
Dental papilla	Nerve and Vascular Supply during Early Development	Vascular Supply Clusters of blood vessels are found branching out around the tooth germ in the dental follicle and going into the dental papilla during the cap stage. In the dental papilla the number of blood vessels increase and the matrix deposition will begin once the maximum is reached during the bell stage. Blood vessels going into the dental papilla are formed into groups that coincides with the positions of where the roots will develop in future. As time passes, the viability of the tissue is affected as the blood supply becomes steadily reduced in stages and the volume of pulpal tissue starts decreasing too.
Dental papilla	Nerve and Vascular Supply during Early Development	Nerve Supply During the bud to cap stage of tooth development, the pioneer nerve fibers head towards the developing tooth. The nerve fibers will branch out and create a rich plexus around the tooth germ in that structure as the dental follicle is the clear target of these dental nerve fibers. The dental follicle is a fibrous sac that surrounds the odontogenic organ and developing tooth. The plexus is a system of connections of blood vessels, nerves, or lymphatic vessels. The plexus of Raschkow is a network of nerves immediately beneath the odonblast layer of the dentine, first described by J. Raschkow in 1835. However, the nerve fibers will only begin entering the dental papilla (pulp) when Dentinogenesis starts. The timing is not similar to the establishment of the neural supply and the papillary vascular supply even though a feasible relationship has been assumed between the developing nerve and blood supplies. Furthermore, histo-chemistry studies have shown that in the makeup of pioneer nerve fibers heading towards the tooth germ, automatic nerve fibers are not present. Therefore, the starting innervation of the developing teeth is involved with the sensory innovation of the future periodontal ligament and pulp. Nerve fibers never enters the enamel organ.
Dental papilla	Nerve and Vascular Supply during Early Development	Nerve-related signaling molecules, such as Glial cell line-derived growth factor, Neurotrophin and semaphoring are among the few which have been studied during the tooth development process. Of which, the verve-related signaling molecules seems to show a trend that suggest an early implication of innervation of tooth development. Similar to how many molecules are able to stimulate axonal growth or migration, various molecules are also within the bounds of possibility of being involved in the initial innervation of the tooth germ.
Dental papilla	Odontoblast Differentiation	It is paramount to understand how odontoblast differentiate from ectomesenchymal cells to allow comprehension and explanation of normal development and to be able to affect their recruitment when needed to start repairing the dentin.
Dental papilla	Odontoblast Differentiation	Growth factors in the cells of the inner enamel epithelium and expressions of signaling molecules bring about the differentiation of odontoblast through normal development of the dental papilla. Exhibiting a central nucleus and few organelles, the dental papilla cells are small and undifferentiated. At this stage, the cells are separated by an acellular zone, that consist of some fine collagen fibrils, from the inner enamel epithelium. Changes will also start occurring in the adjacent dental papilla, very quickly after reversed polarity of the cells of the inner enamel epithelium. To contain increasing amounts of protein-synthesizing organelles, odontoblasts as their cytoplasm ( the liquid inside a cell but outside the nucleus) increases in volume after the ectomesenchymal cells beside the acellular zone rapidly enlarge and elongate to become preodontoblasts. When the odontoblasts differentiate and increase in size to occupy the acellular zone between the dental papilla and the inner enamel epithelium, the zone slowly is removed. With their nuclei positioned away from the inner enamel epithelium, these newly differentiated cells are distinguished by being highly polarized.
Behavioral momentum	Behavioral momentum	Behavioral momentum is a theory in quantitative analysis of behavior and is a behavioral metaphor based on physical momentum. It describes the general relation between resistance to change (persistence of behavior) and the rate of reinforcement obtained in a given situation.
Behavioral momentum	Behavioral momentum	B. F. Skinner (1938) proposed that all behavior is based on a fundamental unit of behavior called the discriminated operant. The discriminated operant, also known as the three-term contingency, has three components: an antecedent discriminative stimulus, a response, and a reinforcing or punishing consequence. The organism responds in the presence of the stimulus because past responses in the presence of that stimulus have produced reinforcement.
Behavioral momentum	Resistance to change	According to behavioral momentum theory, there are two separable factors that independently govern the rate with which a discriminated operant occurs and the persistence of that response in the face of disruptions such as punishment, extinction, or the differential reinforcement of alternative behaviors. (see Nevin & Grace, 2000, for a review). First, the positive contingency between the response and a reinforcing consequence controls response rates (i.e., a response–reinforcer relation) by shaping a particular pattern of responding. This is governed by the relative law of effect (i.e., the matching law; Herrnstein, 1970). Secondly, the Pavlovian relation between surrounding, or context, stimuli and the rate or magnitude (but not both) of reinforcement obtained in the context (i.e., a stimulus–reinforcer relation) governs the resistance of the behavior to operations such as extinction. Resistance to change is assessed by measuring responding during operations such as extinction or satiation that tend to disrupt the behavior and comparing these measurements to stable, pre-disruption response rates.
Behavioral momentum	Resistance to change	Resistance to disruption has been considered a better measure of response strength than a simple measure of response rate.(Nevin, 1974). This is because variations in reinforcement contingencies such as differential-reinforcement-of-high- or low-response-rate schedules can yield highly variable response rates even though overall reinforcement rates are equal. Thus it is questionable whether these differences in response rates indicate differences in the underlying strength of a response (see Morse, 1966, for a discussion).
Behavioral momentum	Resistance to change	According to behavioral momentum theory, the relation between response rate and resistance to change is analogous to the relation between velocity and mass of a moving object, according to Newton's second law of motion (Nevin, Mandell & Atak, 1983). Newton's second law states that the change in velocity of an object when a force is applied is directly related to that force and inversely related to the object's mass. Similarly, behavioral momentum theory states that the change in response rate under conditions of disruption (Bx) relative to baseline response rate (Bo) is directly related to the force or magnitude of disruption (f) and inversely related to the rate of reinforcement in a stimulus context (r): log ⁡(BxBo)=−(frb) (1)The free parameter b indicates the sensitivity of resistance to change to the rate of reinforcement in the stimulus context (i.e., the stimulus–reinforcer relation). Resistance to disruption typically is assessed when two distinctive discriminative stimulus contexts alternate and signal different schedules of reinforcement (i.e., a multiple schedule). Equation 1 can be rewritten to account for resistance to change across two stimulus contexts (Nevin, 1992; Nevin, Grace, & McLean, 2001) when a disrupter is uniformly applied across contexts (i.e., f1 = f2): log log ⁡(Bx2/Bo2)=(r2r1)a (2)The subscripts indicate the different stimulus contexts. Thus, Equation 2 states that relative resistance to change is a power function of the relative rate of reinforcement across stimulus contexts, with the a parameter indicating sensitivity to relative reinforcement rate. Consistent with behavioral momentum theory, resistance to disruption often has been found to be greater in stimulus contexts that signal higher rates or magnitudes of reinforcement (see Nevin, 1992, for a review). Studies that add response-independent (i.e., free) reinforcement to one stimulus context strongly support the theory that changes in response strength are determined by stimulus–reinforcer relations and are independent of response–reinforcer relations. For instance, Nevin, Tota, Torquato, and Shull (1990) had pigeons pecking lighted disks on separate variable-interval 60-s schedules of intermittent food reinforcement across two components of a multiple schedule. Additional free reinforcers were presented every 15 or 30 s on average when the disk was red, but not when the disk was green. Thus, the response–reinforcer relation was degraded when the disk was red because each reinforcer was not immediately preceded by a response. Consistent with the matching law, response rates were lower in the red context than in the green context. However, the stimulus–reinforcer relation was enhanced in the red context because the overall rate of food presentation was greater. Consistent with behavioral momentum theory, resistance to presession feeding (satiation) and discontinuing reinforcement in both contexts (extinction) was greater in the red context. Similar results have been found when reinforcers are added to a context by reinforcing an alternative response.
Behavioral momentum	Resistance to change	The findings of Nevin et al. (1990) have been extended across a number of procedures and species including goldfish (Igaki & Sakagami, 2004), rats (Harper, 1999a, 1999b; Shull, Gaynor & Grimes, 2001), pigeons (Podlesnik & Shahan, 2008), and humans (Ahearn, Clark, Gardenier, Chung & Dube, 2003; Cohen, 1996; Mace et al., 1990). The behavioral momentum framework also has been used to account for the partial-reinforcement extinction effect (Nevin & Grace, 1999), to assess the persistence of drug-maintained behavior (Jimenez-Gomez & Shahan, 2007; Shahan & Burke, 2004), to increase task compliance (e.g., Belfiore, Lee, Scheeler & Klein, 2002), and to understand the effects of social policies on global problems (Nevin, 2005).
Behavioral momentum	Resistance to change	Although behavioral momentum theory is a powerful framework for understanding how a context of reinforcement can affect the persistence of discriminated operant behavior, there are a number of findings that are inconsistent with the theory (see Nevin & Grace, 2000, and accompanying commentary). For instance, with equal reinforcement rates across stimulus contexts, resistance to change has been shown to be affected by manipulations to response–reinforcer relations, including schedules that produce different baseline response rates (e.g., Lattal, 1989; Nevin, Grace, Holland & McLean), delays to reinforcement (e.g., Bell, 1999; Grace, Schwendimann & Nevin, 1998; Podlesnik, Jimenez-Gomez, Ward & Shahan, 2006; Podlesnik & Shahan, 2008), and by providing brief stimuli that accompany reinforcement (Reed & Doughty, 2005). Also, it is unclear what factors affect relative resistance to change of responding maintained by conditioned reinforcement (Shahan & Podlesnik, 2005) or two concurrently available responses when different rates of reinforcement are arranged within the same context for those responses (e.g., Bell & Williams, 2002).
Behavioral momentum	Preference and resistance to change	As resistance to disruption across stimulus contexts is analogous to the inertial mass of a moving object, behavioral momentum theory also suggests that preference in concurrent-chains procedures for one stimulus context over another is analogous to the gravitational attraction of two bodies (see Nevin & Grace, 2000). In concurrent-chains procedures, responding on the concurrently available initial links provides access to one of two mutually exclusive stimulus contexts called terminal links. As with multiple schedules, independent schedules of reinforcement can function in each terminal-link context. The relative allocation of responding across the two initial links indicates the extent to which an organism prefers one terminal-link context over the other. Moreover, behavioral momentum theory posits that preference provides a measure of the relative conditioned-reinforcing value of the two terminal-link contexts, as described by the contextual-choice model (Grace, 1994).
Behavioral momentum	Preference and resistance to change	Grace and Nevin (1997) assessed both relative resistance to change in a multiple schedule and preference in a concurrent-chains procedure with pigeons pecking lighted disks for food reinforcement. When the relative rate of reinforcement was manipulated identically and simultaneously across stimulus contexts in the multiple schedule and concurrent-chains procedure, both relative resistance to change and preference was greater with richer contexts of reinforcement. When all the extant resistance to change and preference data were summarized by Grace, Bedell, and Nevin (2002), they found that those measures were related by a structural relation slope of 0.29. Therefore, relative resistance to change and preference both have been conceptualized as expressions of an underlying construct termed response strength, conditioned reinforcement value, or more generally, behavioral mass of discriminated operant behavior (see Nevin & Grace, 2000).
Tropical Storm Greg	Tropical Storm Greg	The name Greg has been used for eleven tropical cyclones worldwide: eight in the Eastern Pacific Ocean, two in the Australian region, and one in the Western Pacific.
Tropical Storm Greg	Tropical Storm Greg	In the Eastern Pacific: Hurricane Greg (1981) – churned in the open ocean Hurricane Greg (1987) – paralleled the Mexican coast while remaining far offshore Hurricane Greg (1993) – formed from the remnants of Atlantic Tropical Storm Bret Hurricane Greg (1999) – made landfall in Baja California Sur Tropical Storm Greg (2005) – short-lived storm that remained well offshore Hurricane Greg (2011) – stayed out to sea Tropical Storm Greg (2017) – churned in the open ocean Tropical Storm Greg (2023) – formed before crossing into the Central PacificIn the Australian region: Cyclone Greg (1990) – developed in the Gulf of Carpentaria Cyclone Greg (2017) (30U) – developed north-east of the Cocos IslandsIn the Western Pacific: Tropical Depression Greg (1996) (43W) – made landfall on northern Borneo in the Malaysian state of Sabah, causing over $280 million in damage (1996 USD) and 238 deaths
PDE8B	PDE8B	High affinity cAMP-specific and IBMX-insensitive 3',5'-cyclic phosphodiesterase 8B is an enzyme that in humans is encoded by the PDE8B gene.
Solvent Yellow 124	Solvent Yellow 124	Solvent Yellow 124 is a yellow azo dye used in European Union as a fuel dye. It is a marker used since August 2002 to distinguish diesel fuel intended for heating from a higher-taxed motor diesel fuel. It is added to fuels not intended for motor vehicles in amounts of 6 mg/L or 7 mg/kg under the name Euromarker.
Solvent Yellow 124	Euromarker	Solvent Yellow 124 is a dye with structure similar to Solvent Yellow 56. This dye can be easily hydrolyzed with acids, splitting off the acetal group responsible for its solubility in nonpolar solvents, and yielding a water-soluble form which is easy to extract to water. Like a similar methyl orange dye, it changes color to red in acidic pH. It can be easily detected in the fuel at levels as low as 0.3 ppm by extraction to a diluted hydrochloric acid, allowing detection of the red diesel added into motor diesel in amounts as low as 2-3%.
Solvent Yellow 124	Euromarker	Solvent Yellow 124 is intended to be difficult to remove from the fuel in an economical way. The Customs, familiar with various tricks including dual fuel systems with hidden fuel tanks, will take samples from the fuel lines to the engine itself if such equipment is suspected in the car. As the amount of Solvent Yellow 124 added to the fuel is known, by measuring its content in the fuel it is possible to calculate how much of the low-taxed fuel was added to the legal one.
Solvent Yellow 124	Concerns	The UK government expressed concerns about the possibility of "laundering" the dye out of "illicit" fuel, hampering the detection. Denmark expressed concerns about the dye's toxicity. Euromarker is intended to be replaced later by newer technology markers, such as biological markers or fuel markers with non-destructive analytical methods. These are all special chemicals tailored for the individual products, and perhaps even for individual refineries, allowing the identification of the source of the material by its content of the molecular markers. In 2014, a new fuel marker more resistant to removal was announced for the United Kingdom.
Swfdec	Swfdec	Swfdec is an outdated free and open-source replacement for Adobe Flash Player. It runs on Linux and FreeBSD and is distributed under the terms of the GNU Lesser General Public License (LGPL). Its last release was 0.8.4, on December 21, 2008 (2008-12-21) and latest in stable 0.9.2 of 2008-11-11. Development of Swfdec has stopped. As of March 2016, the most recent commit to its Git repository was in December 2009.
Swfdec	Technical	Swfdec is a library that can be used to play Flash files. There is a standalone player and a Mozilla plugin that uses the library. Swfdec supports Flash through version 4, and most features of Flash through version 9. The player was routinely updated to support the latest features demanded by video players, resulting in most (including YouTube, Google Video, Lulu.tv, AOL video, and CNN video) working at any given time.
Swfdec	Linux support	Swfdec was chosen in 2007 as the Flash player for Fedora, and it has been ported to DirectFB for embedded use alongside its X11 and GTK+ bindings. It uses the Cairo graphics library for rendering, GStreamer for decoding audio and video, and PulseAudio, OSS, or ALSA for audio playback.
Pullback (category theory)	Pullback (category theory)	In category theory, a branch of mathematics, a pullback (also called a fiber product, fibre product, fibered product or Cartesian square) is the limit of a diagram consisting of two morphisms f : X → Z and g : Y → Z with a common codomain. The pullback is written P = X ×f, Z, g Y.Usually the morphisms f and g are omitted from the notation, and then the pullback is written P = X ×Z Y.The pullback comes equipped with two natural morphisms P → X and P → Y. The pullback of two morphisms f and g need not exist, but if it does, it is essentially uniquely defined by the two morphisms. In many situations, X ×Z Y may intuitively be thought of as consisting of pairs of elements (x, y) with x in X, y in Y, and f(x) = g(y). For the general definition, a universal property is used, which essentially expresses the fact that the pullback is the "most general" way to complete the two given morphisms to a commutative square.
Pullback (category theory)	Pullback (category theory)	The dual concept of the pullback is the pushout.
Pullback (category theory)	Universal property	Explicitly, a pullback of the morphisms f and g consists of an object P and two morphisms p1 : P → X and p2 : P → Y for which the diagram commutes. Moreover, the pullback (P, p1, p2) must be universal with respect to this diagram. That is, for any other such triple (Q, q1, q2) where q1 : Q → X and q2 : Q → Y are morphisms with f q1 = g q2, there must exist a unique u : Q → P such that p1∘u=q1,p2∘u=q2.
Pullback (category theory)	Universal property	This situation is illustrated in the following commutative diagram. As with all universal constructions, a pullback, if it exists, is unique up to isomorphism. In fact, given two pullbacks (A, a1, a2) and (B, b1, b2) of the same cospan X → Z ← Y, there is a unique isomorphism between A and B respecting the pullback structure.
Pullback (category theory)	Pullback and product	The pullback is similar to the product, but not the same. One may obtain the product by "forgetting" that the morphisms f and g exist, and forgetting that the object Z exists. One is then left with a discrete category containing only the two objects X and Y, and no arrows between them. This discrete category may be used as the index set to construct the ordinary binary product. Thus, the pullback can be thought of as the ordinary (Cartesian) product, but with additional structure. Instead of "forgetting" Z, f, and g, one can also "trivialize" them by specializing Z to be the terminal object (assuming it exists). f and g are then uniquely determined and thus carry no information, and the pullback of this cospan can be seen to be the product of X and Y.
Pullback (category theory)	Examples	Commutative rings In the category of commutative rings (with identity), the pullback is called the fibered product. Let A, B, and C be commutative rings (with identity) and α : A → C and β : B → C (identity preserving) ring homomorphisms. Then the pullback of this diagram exists and given by the subring of the product ring A × B defined by A×CB={(a,b)∈A×B\|α(a)=β(b)} along with the morphisms β′:A×CB→A,α′:A×CB→B given by β′(a,b)=a and α′(a,b)=b for all (a,b)∈A×CB . We then have α∘β′=β∘α′.
Pullback (category theory)	Examples	Groups and modules In complete analogy to the example of commutative rings above, one can show that all pullbacks exist in the category of groups and in the category of modules over some fixed ring. Sets In the category of sets, the pullback of functions f : X → Z and g : Y → Z always exists and is given by the set X×ZY={(x,y)∈X×Y\|f(x)=g(y)}=⋃z∈f(X)∩g(Y)f−1[{z}]×g−1[{z}], together with the restrictions of the projection maps π1 and π2 to X ×Z Y. Alternatively one may view the pullback in Set asymmetrically: X×ZY≅∐x∈Xg−1[{f(x)}]≅∐y∈Yf−1[{g(y)}] where ∐ is the disjoint union of sets (the involved sets are not disjoint on their own unless f resp. g is injective). In the first case, the projection π1 extracts the x index while π2 forgets the index, leaving elements of Y.
Pullback (category theory)	Examples	This example motivates another way of characterizing the pullback: as the equalizer of the morphisms f ∘ p1, g ∘ p2 : X × Y → Z where X × Y is the binary product of X and Y and p1 and p2 are the natural projections. This shows that pullbacks exist in any category with binary products and equalizers. In fact, by the existence theorem for limits, all finite limits exist in a category with binary products and equalizers; equivalently, all finite limits exist in a category with terminal object and pullbacks (by the fact that binary product = pullback on the terminal object, and that an equalizer is a pullback involving binary product).
Pullback (category theory)	Examples	Graphs of functions A specific example of a pullback is given by the graph of a function. Suppose that f:X→Y is a function. The graph of f is the set The graph can be reformulated as the pullback of f and the identity function on Y. By definition, this pullback is and this equals Γf Fiber bundles Another example of a pullback comes from the theory of fiber bundles: given a bundle map π : E → B and a continuous map f : X → B, the pullback (formed in the category of topological spaces with continuous maps) X ×B E is a fiber bundle over X called the pullback bundle. The associated commutative diagram is a morphism of fiber bundles. This is also the case in the category of differentiable manifolds. A special case is the pullback of two fiber bundles E1, E2 → B. In this case E1 × E2 is a fiber bundle over B × B, and pulling back along the diagonal map B → B × B gives a space homeomorphic (diffeomorphic) to E1 ×B E2, which is a fiber bundle over B. The pullback of two smooth transverse maps into the same differentiable manifold is also a differentiable manifold, and the tangent space of the pullback is the pullback of the tangent spaces along the differential maps.
Pullback (category theory)	Examples	Preimages and intersections Preimages of sets under functions can be described as pullbacks as follows: Suppose f : A → B, B0 ⊆ B. Let g be the inclusion map B0 ↪ B. Then a pullback of f and g (in Set) is given by the preimage f−1[B0] together with the inclusion of the preimage in A f−1[B0] ↪ Aand the restriction of f to f−1[B0] f−1[B0] → B0.Because of this example, in a general category the pullback of a morphism f and a monomorphism g can be thought of as the "preimage" under f of the subobject specified by g. Similarly, pullbacks of two monomorphisms can be thought of as the "intersection" of the two subobjects.
Pullback (category theory)	Examples	Least common multiple Consider the multiplicative monoid of positive integers Z+ as a category with one object. In this category, the pullback of two positive integers m and n is just the pair (LCM(m, n)/m, LCM(m, n)/n), where the numerators are both the least common multiple of m and n. The same pair is also the pushout.
Pullback (category theory)	Properties	In any category with a terminal object T, the pullback X ×T Y is just the ordinary product X × Y. Monomorphisms are stable under pullback: if the arrow f in the diagram is monic, then so is the arrow p2. Similarly, if g is monic, then so is p1. Isomorphisms are also stable, and hence, for example, X ×X Y ≅ Y for any map Y → X (where the implied map X → X is the identity).
Pullback (category theory)	Properties	In an abelian category all pullbacks exist, and they preserve kernels, in the following sense: if is a pullback diagram, then the induced morphism ker(p2) → ker(f) is an isomorphism, and so is the induced morphism ker(p1) → ker(g). Every pullback diagram thus gives rise to a commutative diagram of the following form, where all rows and columns are exact: Furthermore, in an abelian category, if X → Z is an epimorphism, then so is its pullback P → Y, and symmetrically: if Y → Z is an epimorphism, then so is its pullback P → X. In these situations, the pullback square is also a pushout square.There is a natural isomorphism (A×CB)×B D ≅ A×CD. Explicitly, this means: if maps f : A → C, g : B → C and h : D → B are given and the pullback of f and g is given by r : P → A and s : P → B, and the pullback of s and h is given by t : Q → P and u : Q → D , then the pullback of f and gh is given by rt : Q → A and u : Q → D.Graphically this means that two pullback squares, placed side by side and sharing one morphism, form a larger pullback square when ignoring the inner shared morphism.
Pullback (category theory)	Properties	Any category with pullbacks and products has equalizers.
Pullback (category theory)	Weak pullbacks	A weak pullback of a cospan X → Z ← Y is a cone over the cospan that is only weakly universal, that is, the mediating morphism u : Q → P above is not required to be unique.
Vaginal artery	Vaginal artery	The vaginal artery is an artery in females that supplies blood to the vagina and the base of the bladder.
Vaginal artery	Structure	The vaginal artery is usually a branch of the internal iliac artery. Some sources say that the vaginal artery can arise from the uterine artery, but the phrase vaginal branches of uterine artery is the term for blood supply to the vagina coming from the uterine artery.The vaginal artery is frequently represented by two or three branches. These descend to the vagina, supplying its mucous membrane. They anastomose with branches from the uterine artery. It can send branches to the bulb of the vestibule, the fundus of the bladder, and the contiguous part of the rectum.
Vaginal artery	Function	The vaginal artery supplies oxygenated blood to the muscular wall of the vagina, along with the uterine artery and the internal pudendal artery. It also supplies the cervix, along with the uterine artery.
Vaginal artery	Other animals	In horses, the vaginal artery may haemorrhage after birth, which can cause death.
External intercostal muscles	External intercostal muscles	The external intercostal muscles, or external intercostals (Intercostales externi) are eleven in number on both sides.
External intercostal muscles	Structure	The muscles extend from the tubercles of the ribs behind, to the cartilages of the ribs in front, where they end in thin membranes, the external intercostal membranes, which are continued forward to the sternum. These muscles work in unison when inhalation occurs. The internal intercostal muscles relax while the external muscles contract causing the expansion of the chest cavity and an influx of air into the lungs. Each arises from the lower border of a rib, and is inserted into the upper border of the rib below. In the two lower spaces they extend to the ends of the cartilages, and in the upper two or three spaces they do not quite reach the ends of the ribs. They are thicker than the internal intercostals, and their fibers are directed obliquely downward and laterally on the back of the thorax, and downward, forward, and medially on the front.
External intercostal muscles	Variations	Continuation with the external oblique or serratus anterior: A supracostalis muscle, from the anterior end of the first rib down to the second, third or fourth ribs occasionally occurs.
EMBnet	EMBnet	The European Molecular Biology network (EMBnet) is an international scientific network and interest group that aims to enhance bioinformatics services by bringing together bioinformatics expertises and capacities. On 2011 EMBnet has 37 nodes spread over 32 countries. The nodes include bioinformatics related university departments, research institutes and national service providers.
EMBnet	Operations	The main task of most EMBnet nodes is to provide their national scientific community with access to bioinformatics databanks, specialised software and sufficient computing resources and expertise. EMBnet is also working in the fields of bioinformatics training and software development. Examples of software created by EMBnet members are: EMBOSS, wEMBOSS, UTOPIA. EMBnet represents a wide user group and works closely together with the database producers such as EMBL's European Bioinformatics Institute (EBI), the Swiss Institute of Bioinformatics (Swiss-Prot), the Munich Information Center for Protein Sequences (MIPS), in order to provide a uniform coverage of services throughout Europe. EMBnet is registered in the Netherlands as a public foundation (Stichting).
EMBnet	Operations	Since its creation in 1988, EMBnet has evolved from an informal network of individuals in charge of maintaining biological databases into the only worldwide organization bringing bioinformatics professionals to work together to serve the expanding fields of genetics and molecular biology. Although composed predominantly of academic nodes, EMBnet gains an important added dimension from its industrial members. The success of EMBnet is attracting increasing numbers of organizations outside Europe to join.
EMBnet	Operations	EMBnet has a tried-and-tested infrastructure to organise training courses, give technical help and help its members effectively interact and respond to the rapidly changing needs of biological research in a way no single institute is able to do. In 2005 the organization created additional types of node to allow more than one member per country. The new category denomination is "associated node".
EMBnet	Coordination and organization	EMBnet is governed by the Annual General Meetings (AGM), and is coordinated by an executive board (EB) that oversees the activities of three project committees: Education and Training committee (E&T). Educational support includes a series of courses organised in the member countries and languages, the committee works as well on the continued development of on-line accessible education materials. Publicity and Public Relations committee (P&PR). This committee is responsible for promoting any type of EMBnet activities, for the advertisement of products and services provided by the EMBnet community, as well as for proposing and developing new strategies aiming to enhance EMBnet's visibility, and to take care of public relationships with EMBnet communities and related networks/societies. Technical Manager committee (TM). The TM PC provides assistance and practical help to the participating nodes and their users.
EMBnet	Achievements	EMBnet had the first gopher and World Wide Web servers in biology (CSC BioBox) EMBnet was the first to come up with solutions for daily database updates using Internet (NDT), distributed computing (HASSLE) and efficient database browsing and linking (Sequence Retrieval System, SRS). The Ping project was created as a means to obtain continuous information about network efficiency across the whole of Europe. EMBnet is committed to bringing the latest software algorithms to the user free of charge (Extended GCG or EGCG) and continues to develop state of the art public software (EMBOSS). EMBER: a European Multimedia Bioinformatics Educational Resource. EMBER was a European Union (EU) funded project aiming to develop a suite of multimedia bioinformatics educational tools . EMBER comprises a self-contained, interactive Web tutorial in bioinformatics, & the equivalent stand-alone course on CD-ROM. The EMBnet community was involved in the creation of the peer reviewed journal Briefings in Bioinformatics (BiB). BiB was also supported by an educational grant from EMBnet. The Global Organisation for Bioinformatics Learning, Education and Training (GOBLET) was formed as a nonprofit foundation at the 2012 EMBnet annual meeting.
EMBnet	Journal	Starting from 1994 and up to 2009 EMBnet published EMBnet.news. Its primary goal was to bring information and report on the latest news and developments from the network to the user community.
EMBnet	Journal	Established in 2010 as the successor of the EMBnet.news (with volume numbering continuing uninterrupted), EMBnet.journal is a peer-reviewed open access scientific journal publishing original research and technical papers in bioinformatics. The journal contains two main sections, one for research articles, reviews, and technical notes, and one for non-peer-reviewed commentary, reportage, user-guides, training information, and news. EMBnet.journal publishes also conference proceedings and meeting abstracts as supplements.
Phenomenology (architecture)	Phenomenology (architecture)	Architectural phenomenology is the discursive and realist attempt to understand and embody the philosophical insights of phenomenology within the discipline of architecture. The phenomenology of architecture is the philosophical study of architecture employing the methods of phenomenology.
Phenomenology (architecture)	Phenomenology (architecture)	Architectural phenomenology emphasizes human experience, background, intention and historical reflection, interpretation, and poetic and ethical considerations in contrast to the anti-historicism of postwar modernism and the pastiche of postmodernism. Much like phenomenology itself, architectural phenomenology is better understood as an orientation toward thinking and making rather than a specific aesthetic or movement. Interest in phenomenology within architectural circles began in the 1950s, reached a wide audience in the late 1970s and 1980s, and continues today.
Phenomenology (architecture)	Historical development	Origins Edmund Husserl is credited with founding Phenomenology, as a philosophical approach to understanding experience, in the early 20th Century. The emergence of Phenomenology occurred during a period of extensive transformation referred to as Modernism. During this time, Western society was experiencing rapid technological advances and social change. Concurrently, as the theory and practice of architecture adapted to these changes, Modern architecture emerged. Consistent within the broad context of Modernism which was characterized by the rejection of tradition, systemization, and standardization; both phenomenology and modern architecture were focused on how humans experience their environments. While Phenomenology was focused on how humans can know things and spaces, modern architecture was concerned with how to create the places of human experience aligned to the modernist ethos of the time.
Phenomenology (architecture)	Historical development	Early Architectural Studies (1950's-1960's) Architects first started seriously studying phenomenology at Princeton University in the 1950s under the influence of Jean Labatut. In the 1950's, architect Charles W. Moore conducted some of the first phenomenological studies of architecture during his doctoral studies under Labatut, drawing heavily on the philosopher Gaston Bachelard, which were published in 1958 as Water and Architecture. In Europe, Milanese architect Ernesto Nathan Rogers advanced architectural phenomenology during the 1950's and early 1960's through his influential editorship of the Italian design magazine Casabella Continuità. He collaborated with philosopher Enzo Paci and influenced a generation of young architects including Vittorio Gregotti and Aldo Rossi.
Phenomenology (architecture)	Historical development	The Essex School (1970's-1980's) In the 1970's, the School of Comparative Studies at the University of Essex, under the direction of Dalibor Vesely and Joseph Rykwert, was a breeding ground for a generation of architectural phenomenologists, including David Leatherbarrow, Alberto Pérez-Gómez, and Daniel Libeskind. In the 1980s, Vesely and his colleague Peter Carl continued to develop architectural phenomenology in their research and teaching at the Department of Architecture at the University of Cambridge. As architectural phenomenology became established in academia, professors expanded its considerations through theory seminars beyond Gaston Bachelard and Martin Heidegger, to include Edmund Husserl, Maurice Merleau-Ponty, Hans-Georg Gadamer, Hannah Arendt and theorists whose modes of thinking bordered on phenomenology, including Gilles Deleuze, Henri Bergson, Paul Virilio, Charles Taylor, Hubert Dreyfus and Edward S. Casey. George Baird called the Essex School "the most significant recent mode of phenomenology in current architectural theory" and credits Vesely for architectural phenomenology's historical reliance on Heidegger instead of Merleau-Ponty, who was championed by Rykwert, Moore, and Labatut. During the 1980's, Kenneth Frampton became an influence in architectural phenomenology.In 1979, Norwegian architect, theorist and historian Christian Norberg-Schulz's book Genius Loci: Towards a Phenomenology of Architecture became an important reference for those interested in the topic in the 1980's for its readily accessible explanations for how a such an approach could be translated into design. The book was markedly influenced by Martin Heidegger's hermeneutic ontology. Norberg-Schulz spawned a wide following, including his successor at the Oslo School of Architecture, Thomas Thiis-Evensen.
Phenomenology (architecture)	Historical development	Contemporary Architectural Phenomenology (2010-present) Recent scholarly activity in architectural phenomenology draws on contemporary phenomenology and philosophy of mind authors Gallagher and Zahavi. Some examples include a 2018 issue of Log with the theme "Disorienting phenomenology" as well as Jorge Otero-Pailos' Architecture's Historical Turn, Sara Ahmed's Queer Phenomenology, Dylan Trigg's The Thing, Alexander Weheliye's Habeas Viscus, and Joseph Bedford's dissertation Creativity's Shadow: Dabilor Vesely, Phenomenology and Architectural Education (1968 - 1989). With the expansion of virtual reality as architectural experiences there is new attention to Phenomenology. Heather Renee Barker's Designing Post-Virtual Architectures, Wicked Tactics and World Building addresses the phenomenological method and the life-world within this context. Contemporary scholarship has become more skeptical of Heidegger's influence.
Phenomenology (architecture)	Themes	Dwelling As a phenomenological perspective on being in society and dwelling within a social world took focus, expanded interest in the urban and social experience became central to the thinking of social philosophers like Alfred Schutz. The phenomenon of dwelling, as explicated in Heidegger's essay "Building Dwelling Thinking" (originally published in 1954 as "Bauen Wohnen Denken"), became an important theme in architectural phenomenology. Heidegger links dwelling to the "gathering of the fourfold," namely the regions of being entailed by the phenomena of "the saving of earth, the reception of sky (heavens), the initiation of mortals into their death, and the awaiting/remembering of divinities." The essence of dwelling is not architectural, per se, in the same manner that the essence of technology for him is not technological per se.
Phenomenology (architecture)	Influence in practice	According to Juhani Pallasmaa, contemporary practitioners of the phenomenology of architecture include architects Daniel Libeskind, Steven Holl, and Peter Zumthor.
Phenomenology (architecture)	Notable architects	Notable architects and scholars of architecture associated with architectural phenomenology include:
Histotrophy	Histotrophy	Histotrophy is a form of matrotrophy exhibited by some live-bearing sharks and rays, in which the developing embryo receives additional nutrition from its mother in the form of uterine secretions, known as histotroph (or "uterine milk"). It is one of the three major modes of elasmobranch reproduction encompassed by "aplacental viviparity", and can be contrasted with yolk-sac viviparity (in which the embryo is solely sustained by yolk) and oophagy (in which the embryo feeds on ova).
Histotrophy	Histotrophy	There are two categories of histotrophy: In mucoid or limited histotrophy, the developing embryo ingests uterine mucus or histotroph as a supplement to the energy supplies provided by its yolk sac. This form of histotrophy is known to occur in the dogfish sharks (Squaliformes) and the electric rays (Torpediniformes), and may be more widespread.
Histotrophy	Histotrophy	In lipid histotrophy, the developing embryo is supplied with protein and lipid-enriched histotroph through specialized finger-like structures known as trophonemata. The additional nutrition provided by the enriched histotroph allows the embryo to increase in mass from the egg by several orders of magnitude by the time it is born, much greater than is possible in mucoid histotrophy. This form of histotrophy is found in stingrays and their relatives (Myliobatiformes).
Gbcast	Gbcast	Gbcast (also known as group broadcast) is a reliable multicast protocol that provides ordered, fault-tolerant (all-or-none) message delivery in a group of receivers within a network of machines that experience crash failure. The protocol is capable of solving Consensus in a network of unreliable processors, and can be used to implement state machine replication. Gbcast can be used in a standalone manner, or can support the virtual synchrony execution model, in which case Gbcast is normally used for group membership management while other, faster, protocols are often favored for routine communication tasks.
Gbcast	History	Introduced in 1985, Gbcast was the first widely deployed reliable multicast protocol to implement state machine replication with dynamically reconfigurable membership. Although this problem had been treated theoretically under various models in prior work, Gbcast innovated by showing that the same multicasts used to update replicated data within the state machine can also be used to dynamically reconfigure the group membership, which can then evolve to permit members to join and leave at will, in addition to being removed upon failure. This functionality, together with a state transfer mechanism used to initialize joining members, represents the basis of the virtual synchrony process group execution model.
Gbcast	History	The term state machine replication was first suggested by Leslie Lamport and was widely adopted after publication of a survey paper written by Fred B. Schneider. The model covers any system in which some deterministic object (a state machine) is replicated in such a way that a series of commands can be applied to the replicas fault-tolerantly. A reconfigurable state machine is one that can vary its membership, adding new members or removing old ones. Some state machine protocols can also ride out the temporary unavailability of a subset of the current members without requiring reconfiguration when such situations arise, including Gbcast and also Paxos, Lamport's widely cited protocol for state machine replication.
Gbcast	History	State machine replication is closely related to the distributed Consensus problem, in which a collection of processes must agree upon some decision outcome, such as the winner of an election. In particular, it can be shown that any solution to the state machine replication problem would also be capable of solving distributed consensus. As a consequence, impossibility results for distributed consensus apply to solutions to the state machine replication problem. Implications of this finding are discussed under liveness.

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