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In Bayesian inference , plate notation is a method of representing variables that repeat in a graphical model . Instead of drawing each repeated variable individually, a plate or rectangle is used to group variables into a subgraph that repeat together, and a number is drawn on the plate to represent the number of repetitions of the subgraph in the plate. [ 1 ] The assumptions are that the subgraph is duplicated that many times, the variables in the subgraph are indexed by the repetition number, and any links that cross a plate boundary are replicated once for each subgraph repetition. [ 2 ]
In this example, we consider Latent Dirichlet allocation , a Bayesian network that models how documents in a corpus are topically related. There are two variables not in any plate; α is the parameter of the uniform Dirichlet prior on the per-document topic distributions, and β is the parameter of the uniform Dirichlet prior on the per-topic word distribution.
The outermost plate represents all the variables related to a specific document, including θ i {\displaystyle \theta _{i}} , the topic distribution for document i . The M in the corner of the plate indicates that the variables inside are repeated M times, once for each document. The inner plate represents the variables associated with each of the N i {\displaystyle N_{i}} words in document i : z i j {\displaystyle z_{ij}} is the topic distribution for the j th word in document i , and w i j {\displaystyle w_{ij}} is the actual word used.
The N in the corner represents the repetition of the variables in the inner plate N j {\displaystyle N_{j}} times, once for each word in document i . The circle representing the individual words is shaded, indicating that each w i j {\displaystyle w_{ij}} is observable , and the other circles are empty, indicating that the other variables are latent variables . The directed edges between variables indicate dependencies between the variables: for example, each w i j {\displaystyle w_{ij}} depends on z i j {\displaystyle z_{ij}} and β .
A number of extensions have been created by various authors to express more information than simply the conditional relationships. However, few of these have become standard. Perhaps the most commonly used extension is to use rectangles in place of circles to indicate non-random variables—either parameters to be computed, hyperparameters given a fixed value (or computed through empirical Bayes ), or variables whose values are computed deterministically from a random variable.
The diagram on the right shows a few more non-standard conventions used in some articles in Wikipedia (e.g. variational Bayes ):
Plate notation has been implemented in various TeX / LaTeX drawing packages, but also as part of graphical user interfaces to Bayesian statistics programs such as BUGS and BayesiaLab and PyMC . | https://en.wikipedia.org/wiki/Plate_notation |
A plate rolling machine is a machine that will roll different kinds of sheet metal into a round or conical shape.
It can be also called a “roll bending machine”, “ plate bending machine ” or “rolling machine”.
There are different kinds of technology to roll the metal plate:
The flat metal plate is placed in the machine on either side and "pre-bent" on the same side.
The side rolls do the work of bending. The pinching roll holds the plate.
The three-roll variable pitch works by having all three rolls able to move and tilt. The top roll moves in the vertical plane and the side rolls move on the horizontal plane .
When rolling, the top roll presses the metal plate between the two side rolls. The advantage of having the variable three roll is the ability to roll many thicknesses and diameters of cylinders.
For example;
The side-rolls are what produce the mechanical advantage. With the side rolls all the way open, one has the maximum mechanical advantage . With the side rolls all the way in, you have the least mechanical advantage.
So, a machine has the capability of rolling 2-inch-thick material with the maximum mechanical advantage, but a job is only 1/2 inch thick. Reduce the mechanical advantage and one has a machine that can roll from 1/2 to 2 inches thick.
Plate rollers can be powered and controlled in multiple ways. Older plate mills are driven by electric motors and newer ones are directed by programs that are loaded into the CNC controller . When thinking about plate roll acquisition, industrial machinery companies like Provetco Technology will ask about the working length of the roller, the maximum thickness of the material, top roll diameter size as well as the minimum thickness of the material. Furthermore, the material yield is another critical component to disclose to machinery companies when looking for a plate roller.
Provetco Technology: www.provetco.com | https://en.wikipedia.org/wiki/Plate_rolling_machine |
In mathematics , Plateau's problem is to show the existence of a minimal surface with a given boundary, a problem raised by Joseph-Louis Lagrange in 1760. However, it is named after Joseph Plateau who experimented with soap films . The problem is considered part of the calculus of variations . The existence and regularity problems are part of geometric measure theory .
Various specialized forms of the problem were solved, but it was only in 1930 that general solutions were found in the context of mappings (immersions) independently by Jesse Douglas and Tibor Radó . Their methods were quite different; Radó's work built on the previous work of René Garnier and held only for rectifiable simple closed curves, whereas Douglas used completely new ideas with his result holding for an arbitrary simple closed curve. Both relied on setting up minimization problems; Douglas minimized the now-named Douglas integral while Radó minimized the "energy". Douglas went on to be awarded the Fields Medal in 1936 for his efforts.
The extension of the problem to higher dimensions (that is, for k {\displaystyle k} -dimensional surfaces in n {\displaystyle n} -dimensional space) turns out to be much more difficult to study. Moreover, while the solutions to the original problem are always regular, it turns out that the solutions to the extended problem may have singularities if k ≤ n − 2 {\displaystyle k\leq n-2} . In the hypersurface case where k = n − 1 {\displaystyle k=n-1} , singularities occur only for n ≥ 8 {\displaystyle n\geq 8} . An example of such singular solution of the Plateau problem is the Simons cone , a cone over S 3 × S 3 {\displaystyle S^{3}\times S^{3}} in R 8 {\displaystyle \mathbb {R} ^{8}} that was first described by Jim Simons and was shown to be an area minimizer by Bombieri , De Giorgi and Giusti . [ 1 ] To solve the extended problem in certain special cases, the theory of perimeters ( De Giorgi ) for codimension 1 and the theory of rectifiable currents ( Federer and Fleming) for higher codimension have been developed. The theory guarantees existence of codimension 1 solutions that are smooth away from a closed set of Hausdorff dimension n − 8 {\displaystyle n-8} . In the case of higher codimension Almgren proved existence of solutions with singular set of dimension at most k − 2 {\displaystyle k-2} in his regularity theorem . S. X. Chang, a
student of Almgren, built upon Almgren’s work to show that the singularities of 2-dimensional area
minimizing integral currents (in arbitrary codimension) form a finite discrete set. [ 2 ] [ 3 ]
The axiomatic approach of Jenny Harrison and Harrison Pugh [ 4 ] treats a wide variety of special cases. In particular, they solve the anisotropic Plateau problem in arbitrary dimension and codimension for any collection of rectifiable sets satisfying a combination of general homological, cohomological or homotopical spanning conditions. A different proof of Harrison-Pugh's results were obtained by Camillo De Lellis , Francesco Ghiraldin and Francesco Maggi . [ 5 ]
Physical soap films are more accurately modeled by the ( M , 0 , Δ ) {\displaystyle (M,0,\Delta )} -minimal sets of Frederick Almgren , but the lack of a compactness theorem makes it difficult to prove the existence of an area minimizer. In this context, a persistent open question has been the existence of a least-area soap film. Ernst Robert Reifenberg solved such a "universal Plateau's problem" for boundaries which are homeomorphic to single embedded spheres.
This article incorporates material from Plateau's Problem on PlanetMath , which is licensed under the Creative Commons Attribution/Share-Alike License . | https://en.wikipedia.org/wiki/Plateau's_problem |
A plateau of a function is a part of its domain where the function has constant value.
More formally, let U , V be topological spaces . A plateau for a function f : U → V is a path-connected set of points P of U such that for some y we have
for all p in P .
Plateaus can be observed in mathematical models as well as natural systems. In nature, plateaus can be observed in physical, chemical and biological systems. An example of an observed plateau in the natural world is in the tabulation of biodiversity of life through time. [ 1 ]
This article incorporates material from plateau on PlanetMath , which is licensed under the Creative Commons Attribution/Share-Alike License .
This topology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Plateau_(mathematics) |
In fluid dynamics , the Plateau–Rayleigh instability , often just called the Rayleigh instability , explains why and how a falling stream of fluid breaks up into smaller packets with the same total volume but less surface area per droplet. It is related to the Rayleigh–Taylor instability and is part of a greater branch of fluid dynamics concerned with fluid thread breakup . This fluid instability is exploited in the design of a particular type of ink jet technology whereby a jet of liquid is perturbed into a steady stream of droplets .
The driving force of the Plateau–Rayleigh instability is that liquids, by virtue of their surface tensions , tend to minimize their surface area. A considerable amount of work has been done recently on the final pinching profile by attacking it with self-similar solutions. [ 1 ] [ 2 ]
The Plateau–Rayleigh instability is named for Joseph Plateau and Lord Rayleigh . In 1873, Plateau found experimentally that a vertically falling stream of water will break up into drops if its length is greater than about 3.13 to 3.18 times its diameter, which he noted is close to π . [ 3 ] [ 4 ] Later, Rayleigh showed theoretically that a vertically falling column of non-viscous liquid with a circular cross-section should break up into drops if its length exceeded its circumference, which is indeed π times its diameter. [ 5 ]
The explanation of this instability begins with the existence of tiny perturbations in the stream. [ 6 ] [ 7 ] These are always present, no matter how smooth the stream is (for example, in the liquid jet nozzle, there is vibration on the liquid stream due to a friction between the nozzle and the liquid stream). If the perturbations are resolved into sinusoidal components, we find that some components grow with time, while others decay with time. Among those that grow with time, some grow at faster rates than others. Whether a component decays or grows, and how fast it grows is entirely a function of its wave number (a measure of how many peaks and troughs per unit length) and the radius of the original cylindrical stream. The diagram to the right shows an exaggeration of a single component.
By assuming that all possible components exist initially in roughly equal (but minuscule) amplitudes, the size of the final drops can be predicted by determining by wave number which component grows the fastest. As time progresses, it is the component with the maximal growth rate that will come to dominate and will eventually be the one that pinches the stream into drops. [ 8 ]
Although a thorough understanding of how this happens requires a mathematical development (see references [ 6 ] [ 8 ] ), the diagram can provide a conceptual understanding. Observe the two bands shown girdling the stream—one at a peak and the other at a trough of the wave. At the trough, the radius of the stream is smaller, hence according to the Young–Laplace equation the pressure due to surface tension is increased. Likewise at the peak the radius of the stream is greater and, by the same reasoning, pressure due to surface tension is reduced. If this were the only effect, we would expect that the higher pressure in the trough would squeeze liquid into the lower-pressure region in the peak. In this way we see how the wave grows in amplitude over time.
But the Young–Laplace equation is influenced by two separate radius components. In this case one is the radius, already discussed, of the stream itself. The other is the radius of curvature of the wave itself. The fitted arcs in the diagram show these at a peak and at a trough. Observe that the radius of curvature at the trough is, in fact, negative, meaning that, according to Young–Laplace, it actually decreases the pressure in the trough. Likewise the radius of curvature at the peak is positive and increases the pressure in that region. The effect of these components is opposite the effects of the radius of the stream itself.
The two effects, in general, do not exactly cancel. One of them will have greater magnitude than the other, depending upon wave number and the initial radius of the stream. When the wave number is such that the radius of curvature of the wave dominates that of the radius of the stream, such components will decay over time. When the effect of the radius of the stream dominates that of the curvature of the wave, such components grow exponentially with time.
When all the maths is done, it is found that unstable components (that is, components that grow over time) are only those where the product of the wave number with the initial radius is less than unity ( k R 0 < 1 {\displaystyle kR_{0}<1} ). The component that grows the fastest is the one whose wave number satisfies the equation [ 8 ]
A special case of this is the formation of small droplets when water is dripping from a faucet/tap. When a segment of water begins to separate from the faucet, a neck is formed and then stretched. If the diameter of the faucet is big enough, the neck does not get sucked back in, and it undergoes a Plateau–Rayleigh instability and collapses into a small droplet.
Another everyday example of Plateau–Rayleigh instability occurs in urination, particularly standing male urination. [ 9 ] [ 10 ] The stream of urine experiences instability after about 15 cm (6 inches), breaking into droplets, which causes significant splash-back on impacting a surface. By contrast, if the stream contacts a surface while still in a stable state – such as by urinating directly against a urinal or wall – splash-back is almost completely eliminated.
Continuous inkjet printers (as opposed to drop-on-demand inkjet printers) generate a cylindrical stream of ink that breaks up into droplets prior to staining printer paper. By adjusting the size of the droplets using tunable temperature or pressure perturbations and imparting electrical charge to the ink, inkjet printers then steer the stream of droplets using electrostatics to form specific patterns on printer paper [ 11 ] | https://en.wikipedia.org/wiki/Plateau–Rayleigh_instability |
Platelets or thrombocytes (from Ancient Greek θρόμβος ( thrómbos ) ' clot ' and κύτος ( kútos ) ' cell ' ) are a part of blood whose function (along with the coagulation factors ) is to react to bleeding from blood vessel injury by clumping to form a blood clot . [ 1 ] Platelets have no cell nucleus ; they are fragments of cytoplasm from megakaryocytes which reside in bone marrow or lung tissue , [ 2 ] and then enter the circulation. Platelets are found only in mammals, whereas in other vertebrates (e.g. birds , amphibians ), thrombocytes circulate as intact mononuclear cells . [ 3 ] : 3
One major function of platelets is to contribute to hemostasis : the process of stopping bleeding at the site where the lining of vessels ( endothelium ) has been interrupted. Platelets gather at the site and, unless the interruption is physically too large, they plug the hole. First, platelets attach to substances outside the interrupted endothelium: adhesion . Second, they change shape, turn on receptors and secrete chemical messengers : activation . Third, they connect to each other through receptor bridges: aggregation . [ 4 ] Formation of this platelet plug (primary hemostasis) is associated with activation of the coagulation cascade , with resultant fibrin deposition and linking (secondary hemostasis). These processes may overlap: the spectrum is from a predominantly platelet plug, or "white clot" to a predominantly fibrin, or "red clot" or the more typical mixture. Berridge adds retraction and platelet inhibition as fourth and fifth steps, [ 5 ] while others would add a sixth step, wound repair . [ citation needed ] Platelets participate in both innate [ 6 ] and adaptive [ 7 ] intravascular immune responses.
In addition to facilitating the clotting process, platelets contain cytokines and growth factors which can promote wound healing and regeneration of damaged tissues. [ 8 ] [ 9 ]
The term thrombocyte (clot cell) came into use in the early 1900s and is sometimes used as a synonym for platelet; but not generally in the scientific literature, except as a root word for other terms related to platelets (e.g. thrombocytopenia meaning low platelets). [ 3 ] : v3 The term thrombocytes are proper for mononuclear cells found in the blood of non-mammalian vertebrates: they are the functional equivalent of platelets, but circulate as intact cells rather than cytoplasmic fragments of bone marrow megakaryocytes. [ 3 ] : 3
In some contexts, the word thrombus is used interchangeably with the word clot , regardless of its composition (white, red, or mixed). In other contexts it is used to contrast a normal from an abnormal clot: thrombus arises from physiologic hemostasis, thrombosis arises from a pathologic and excessive quantity of clot. [ 10 ] In a third context it is used to contrast the result from the process: thrombus is the result, thrombosis is the process.
Structurally the platelet can be divided into four zones, from peripheral to innermost: [ citation needed ]
Circulating inactivated platelets are biconvex discoid (lens-shaped) structures, [ 11 ] [ 3 ] : 117–118 2–3 μm in greatest diameter. [ 12 ] Activated platelets have cell membrane projections covering their surface.
In a first approximation, the shape can be considered similar to oblate spheroids , with a semiaxis ratio of 2 to 8. [ 13 ] This approximation can be used to model the hydrodynamic and optical properties of a population, as well as to restore the geometric parameters of individual measured platelets by flow cytometry . [ 14 ] More accurate biophysical models of platelet surface morphology that model its shape from first principles, make it possible to obtain a more realistic platelet geometry in a calm and activated state. [ 15 ]
The fundamental function of platelets is to clump together to stop acute bleeding. This process is complex, as more than 193 proteins and 301 interactions are involved in platelet dynamics. [ 4 ] Despite much overlap, platelet function can be modeled in three steps:
Thrombus formation on an intact endothelium is prevented by nitric oxide , [ 18 ] prostacyclin , [ 19 ] and CD39 . [ 20 ]
Endothelial cells attach to the subendothelial collagen by von Willebrand factor (VWF), which these cells produce. VWF is also stored in the Weibel-Palade bodies of the endothelial cells and secreted constitutively into the blood. Platelets store vWF in their alpha granules.
When the endothelial layer is disrupted, collagen and VWF anchor platelets to the subendothelium. Platelet GP1b-IX-V receptor binds with VWF; and GPVI receptor and integrin α2β1 bind with collagen. [ 21 ]
Factors from the lining of vessels stop platelets from activating. An intact endothelial lining inhibits platelet activation by producing nitric oxide , endothelial- ADPase , and PGI 2 (prostacyclin). Endothelial-ADPase degrades the platelet activator ADP . [ citation needed ]
Resting platelets maintain active calcium efflux via a cyclic AMP -activated calcium pump. Intracellular calcium concentration determines platelet activation status, as it is the second messenger that drives platelet conformational change and degranulation. Endothelial prostacyclin binds to prostanoid receptors on the surface of resting platelets. This event stimulates the coupled Gs protein to increase adenylate cyclase activity and increases the production of cAMP, further promoting the efflux of calcium and reducing intracellular calcium availability for platelet activation. [ citation needed ]
ADP on the other hand binds to purinergic receptors on the platelet surface. Since the thrombocytic purinergic receptor P2Y12 is coupled to Gi proteins, ADP reduces platelet adenylate cyclase activity and cAMP production, leading to accumulation of calcium inside the platelet by inactivating the cAMP calcium efflux pump. The other ADP-receptor P2Y1 couples to Gq that activates phospholipase C-beta 2 ( PLCB2 ), resulting in inositol 1,4,5-trisphosphate (IP3) generation and intracellular release of more calcium. This together induces platelet activation. Endothelial ADPase degrades ADP and prevents this from happening. Clopidogrel and related antiplatelet medications also work as purinergic receptor P2Y12 antagonists . [ citation needed ] Data suggest that ADP activates the PI3K/Akt pathway during a first wave of aggregation, leading to thrombin generation and PAR‐1 activation, which evokes a second wave of aggregation. [ 22 ]
Platelet activation begins seconds after adhesion occurs. It is triggered when collagen from the subendothelium binds with its receptors ( GPVI receptor and integrin α2β1) on the platelet. GPVI is associated with the Fc receptor gamma chain and leads via the activation of a tyrosine kinase cascade finally to the activation of PLC-gamma2 ( PLCG2 ) and more calcium release. [ citation needed ]
Tissue factor also binds to factor VII in the blood, which initiates the extrinsic coagulation cascade to increase thrombin production. Thrombin is a potent platelet activator, acting through Gq and G12. These are G protein-coupled receptors and they turn on calcium-mediated signaling pathways within the platelet, overcoming the baseline calcium efflux. Families of three G proteins (Gq, Gi, G12) operate together for full activation. Thrombin also promotes secondary fibrin-reinforcement of the platelet plug . Platelet activation in turn degranulates and releases factor V and fibrinogen , potentiating the coagulation cascade. Platelet plugging and coagulation occur simultaneously, with each inducing the other to form the final fibrin-crosslinked thrombus. [ citation needed ]
Collagen-mediated GPVI signalling increases the platelet production of thromboxane A2 (TXA2) and decreases the production of prostacyclin . This occurs by altering the metabolic flux of platelet's eicosanoid synthesis pathway, which involves enzymes phospholipase A2 , cyclo-oxygenase 1 , and thromboxane-A synthase . Platelets secrete thromboxane A2, which acts on the platelet's own thromboxane receptors on the platelet surface (hence the so-called "out-in" mechanism), and those of other platelets. These receptors trigger intraplatelet signaling, which converts GPIIb/IIIa receptors to their active form to initiate aggregation . [ 4 ]
Platelets contain dense granules , lambda granules, and alpha granules . Activated platelets secrete the contents of these granules through their canalicular systems to the exterior. Bound and activated platelets degranulate to release platelet chemotactic agents to attract more platelets to the site of endothelial injury. Granule characteristics:
As shown by flow cytometry and electron microscopy , the most sensitive sign of activation, when exposed to platelets using ADP, are morphological changes. [ 23 ] Mitochondrial hyperpolarization is a key event in initiating morphology changes. [ 24 ] Intraplatelet calcium concentration increases, stimulating the interplay between the microtubule/actin filament complex. The continuous changes in shape from the unactivated to the fully activated platelet are best seen via scanning electron microscopy . The three steps along this path are named early dendritic , early spread, and spread . The surface of the unactivated platelet looks similar to the surface of the brain–a wrinkled appearance from numerous shallow folds that increase the surface area; early dendritic , an octopus with multiple arms and legs; early spread , an uncooked frying egg in a pan, the "yolk" is the central body; and the spread , a cooked fried egg with a denser central body.
These changes are all brought about by the interaction of the microtubule/actin complex with the platelet cell membrane and open canalicular system (OCS), which is an extension and invagination of that membrane. This complex runs just beneath these membranes and is the chemical motor that pulls the invaginated OCS out of the interior of the platelet, like turning pants pockets inside out, creating the dendrites. This process is similar to the mechanism of contraction in a muscle cell . [ 25 ] The entire OCS thus becomes indistinguishable from the initial platelet membrane as it forms the "fried egg". This dramatic increase in surface area comes about with neither stretching nor adding phospholipids to the platelet membrane. [ 26 ]
Platelet activation causes its membrane surface to become negatively charged. One of the signaling pathways turns on scramblase , which moves negatively charged phospholipids from the inner to the outer platelet membrane surface. These phospholipids then bind the tenase and prothrombinase complexes, two of the sites of interplay between platelets and the coagulation cascade. Calcium ions are essential for the binding of these coagulation factors.
In addition to interacting with vWF and fibrin, platelets interact with thrombin, Factors X, Va, VIIa, XI, IX, and prothrombin to complete formation via the coagulation cascade. [ 27 ] [ 28 ] Human platelets do not express tissue factor . [ 27 ] Rat platelets do express tissue factor protein and carry both tissue factor pre-mRNA and mature mRNA. [ 29 ]
Platelet aggregation begins minutes after activation, and occurs as a result of turning on the GPIIb/IIIa receptor, allowing these receptors to bind with vWF or fibrinogen . [ 4 ] Each platelet has around 60,000 of these receptors. [ 30 ] When any one or more of at least nine different platelet surface receptors are turned on during activation, intraplatelet signaling pathways cause existing GpIIb/IIIa receptors to change shape — curled to straight — and thus become capable of binding. [ 4 ]
Since fibrinogen is a rod-like protein with nodules on either end capable of binding GPIIb/IIIa, activated platelets with exposed GPIIb/IIIa can bind fibrinogen to aggregate. GPIIb/IIIa may also further anchor the platelets to subendothelial vWF for additional structural stabilisation.
Classically it was thought that this was the only mechanism involved in aggregation, but three other mechanisms have been identified which can initiate aggregation, depending on the velocity of blood flow (i.e. shear range). [ 31 ]
Platelets have a central role in innate immunity , initiating and participating in multiple inflammatory processes, directly binding and even destroying pathogens. Clinical data show that many patients with serious bacterial or viral infections have thrombocytopenia , thus reducing their contribution to inflammation. Platelet-leukocyte aggregates (PLAs) found in circulation are typical in sepsis or inflammatory bowel disease , showing the connection between thrombocytes and immune cells. [ 32 ]
The platelet cell membrane has receptors for collagen. Following rupture of the blood vessel wall, platelets are exposed and adhere to the collagen in the surrounding tissue.
As hemostasis is a basic function of thrombocytes in mammals, it also has its uses in possible infection confinement. [ 6 ] In case of injury, platelets, together with the coagulation cascade, provide the first line of defense by forming a blood clot. Hemostasis and host defense were thus intertwined in evolution. For example, in the Atlantic horseshoe crab (estimated to be over 400 million years old), the only blood cell type, the amebocyte , facilitates both the hemostatic function and immune functions, including encapsulation, phagocytosis of pathogens , and exocytosis of intracellular granules containing bactericidal defense molecules. Blood clotting supports immune function by trapping the bacteria. [ 33 ]
Thrombosis (blood coagulation in intact blood vessels) is usually viewed as a pathological immune response, leading to obturation of lumen of blood vessel and subsequent hypoxic tissue damage. In some cases, however, directed thrombosis (or immunothrombosis) can locally control the spread of an infection. The thrombosis is directed in concordance with platelets, neutrophils and monocytes . The process is initiated either by immune cells by activating their pattern recognition receptors (PRRs), or by platelet-bacterial binding. Platelets can bind to bacteria either directly through thrombocytic PRRs [ 32 ] and bacterial surface proteins, or via plasma proteins that bind both to platelets and bacteria. [ 34 ] Monocytes respond to bacterial pathogen-associated molecular patterns (PAMPs), or damage-associated molecular patterns (DAMPs) by activating the extrinsic pathway of coagulation. Neutrophils facilitate the blood coagulation by NETosis , while platelets facilitate neutrophils' NETosis. NETs bind tissue factor, binding the coagulation centers to the location of infection. They also activate the intrinsic coagulation pathway by providing a negatively charged surface for factor XII. Other neutrophil secretions, such as proteolytic enzymes which cleave coagulation inhibitors, also bolster the process. [ 6 ]
In case of imbalance in the regulation of immunothrombosis, this process can become aberrant. Regulatory defects in immunothrombosis are suspected to be a major factor in pathological thrombosis in forms such as disseminated intravascular coagulation (DIC) or deep vein thrombosis . DIC in sepsis is a prime example of both the dysregulated coagulation process and an undue systemic inflammatory response. It results in a multitude of microthrombi. These are similar in composition to the thrombi produced in native immunothrombosis — they are made up of fibrin, platelets, neutrophils and NETs. [ 6 ]
Platelets rapidly deploy to sites of injury or infection. There, they are thought to modulate inflammatory processes via interactions with leukocytes and secretion of cytokines , chemokines , and other inflammatory mediators. [ 35 ] [ 36 ] [ 37 ] [ 38 ] [ 39 ] Platelets also secrete platelet-derived growth factor (PDGF).
Platelets modulate neutrophils by forming platelet-leukocyte aggregates (PLAs). These formations induce upregulated production of the complement receptor αmβ2 ( Mac-1 ) integrin in neutrophils. Interaction with PLAs also induces degranulation and increased phagocytosis in neutrophils.
Platelets are the largest source of soluble CD40L (CD154) which induces production of reactive oxygen species (ROS) and upregulates expression of adhesion molecules (such as E-selectin , ICAM-1 , and VCAM-1 ) in neutrophils. CD40L also activates macrophages and activates cytotoxic response in T and B lymphocytes . [ 32 ]
Mammalian platelets lacking nucleus are able to conduct autonomous locomotion. [ 40 ] Platelets are active scavengers, scaling walls of blood vessels and reorganising the thrombus. They are able to recognize and adhere to many surfaces, including bacteria, and can envelop them in their open canalicular system (OCP), leading to a proposal to name the process as covercytosis (OCS) rather than phagocytosis, as OCS is merely an invagination of outer plasma membrane. These platelet-bacteria bundles provide an interaction platform for neutrophils that destroy bacteria using NETs and phagocytosis.
Platelets also participate in chronic inflammatory disease, such as synovitis or rheumatoid arthritis . [ 41 ] Platelets are activated by collagen receptor glycoprotein IV (GPVI). Proinflammatory platelet microvesicles trigger constant cytokine secretion from neighboring fibroblast-like synoviocytes , most prominently Il-6 and Il-8 . Inflammatory damage to the surrounding extracellular matrix continuously reveals more collagen, binding receptors on platelets and maintaining microvesicle production.
Activated platelets are able to participate in adaptive immunity , interacting with antibodies . They are able to specifically bind IgG through FcγRIIA , a receptor for IgG's constant fragment (Fc). When activated and bound to IgG- opsonised bacteria, platelets release reactive oxygen species (ROS), antimicrobial peptides, defensins , kinocidins and proteases , killing the bacteria directly. [ 42 ] Platelets also secrete proinflammatory and procoagulant mediators such as inorganic polyphosphates or platelet factor 4 (PF4), connecting innate and adaptive immune responses. [ 42 ] [ 43 ]
Platelet concentration in the blood (i.e. platelet count), can be measured manually using a hemocytometer , or by placing blood in an automated platelet analyzer using particle counting, such as a Coulter counter or optical methods. [ 44 ] Most common blood testing methods include platelet count in their measurements, usually reported as PLT . [ 45 ]
Platelet concentrations vary between individuals and over time, with the population average between 250,000 and 260,000 cells per mm 3 (equivalent to per microliter), but the typical laboratory accepted normal range is between 150,000 and 400,000 cells per mm 3 or 150–400 × 10 9 per liter. [ 45 ] [ 44 ]
On a stained blood smear , platelets appear as dark purple spots, about 20% of the diameter of red blood cells. The smear reveals size, shape, qualitative number, and clumping . A healthy adult typically has 10 to 20 times more red blood cells than platelets.
Bleeding time was developed as a test of platelet function by Duke in 1910. [ 46 ] Duke's test measured the time taken for bleeding to stop from a standardized wound in the ear lobe that was blotted every 30 seconds, considering less than 3 minutes as normal. [ 47 ] Bleeding time has low sensitivity and specificity for mild to moderate platelet disorders and is no longer recommended for screening. [ 48 ]
In multiple electrode aggregometry , anticoagulated whole blood is mixed with saline and a platelet agonist in a single-use cuvette with two pairs of electrodes. The increase in impedance between the electrodes as platelets aggregate onto them, is measured and visualized as a curve. [ 49 ] [ 50 ]
In light transmission aggregometry (LTA), platelet-rich plasma is placed between a light source and a photocell . Unaggregated plasma allows relatively little light to pass through. After adding an agonist, the platelets aggregate, increasing light transmission, which is detected by a photocell. [ 51 ]
Whole blood impedance aggregometry (WBA) measures the change in electrical impedance between two electrodes when platelet aggregation is induced by an agonist. Whole blood lumiaggregometry may increase the test sensitivity to impairment of platelet granule secretion. [ 52 ]
The PFA-100 (Platelet Function Assay — 100) is a system for analysing platelet function in which citrated whole blood is aspirated through a disposable cartridge containing an aperture within a membrane coated with either collagen and epinephrine or collagen and ADP. These agonists induce platelet adhesion, activation and aggregation, leading to rapid occlusion of the aperture and cessation of blood flow termed the closure time (CT). An elevated CT with EPI and collagen can indicate intrinsic defects such as von Willebrand disease , uremia , or circulating platelet inhibitors. A follow-up test involving collagen and ADP is used to indicate if the abnormal CT with collagen and EPI was caused by the effects of acetyl sulfosalicylic acid (aspirin) or medications containing inhibitors. [ 53 ] The PFA-100 is highly sensitive to von Willebrand disease, but is only moderately sensitive to defects in platelet function. [ 54 ]
Spontaneous and excessive bleeding can occur because of platelet disorders. This bleeding can be caused by deficient numbers of platelets, dysfunctional platelets, or platelet densities over 1 million/microliter. (The excessive numbers create a relative von Willebrand factor deficiency due to sequestration.) [ 55 ] [ 56 ]
Bleeding due to a platelet disorder or a coagulation factor disorder can be distinguished by the characteristics and location of the bleeding. [ 3 ] : 815, Table 39-4 Platelet bleeding involves bleeding from a cut that is prompt and excessive, but can be controlled by pressure; spontaneous bleeding into the skin which causes a purplish stain named by its size: petechiae , purpura , ecchymoses ; bleeding into mucous membranes causing bleeding gums, nose bleed, and gastrointestinal bleeding; menorrhagia; and intraretinal and intracranial bleeding.
Excessive numbers of platelets, and/or normal platelets responding to abnormal vessel walls, can result in venous thrombosis and arterial thrombosis . The symptoms depend on the thrombosis site.
Platelet disorders can occur because there are not enough platelets, too many platelets, or the platelets do not function properly. [ 3 ] : vii
Low platelet concentration is called thrombocytopenia , and is due to either decreased production, increased destruction of platelets, or platelets being sequestered in another part of the body. Elevated platelet concentration is called thrombocytosis , and is either congenital , reactive (to cytokines ), or due to unregulated production: one of the myeloproliferative neoplasms or certain other myeloid neoplasms .
Normal platelets can respond to an abnormality on the vessel wall rather than to hemorrhage, resulting in inappropriate platelet adhesion/activation and thrombosis : the formation of a clot within an intact vessel. This type of thrombosis arises by mechanisms different from those of a normal clot: extending the fibrin of venous thrombosis ; extending an unstable or ruptured arterial plaque, causing arterial thrombosis ; and microcirculatory thrombosis. An arterial thrombus may partially obstruct blood flow, causing downstream ischemia , or may completely obstruct it, causing downstream tissue death .: [ 3 ] : vii
Some drugs used to treat inflammation have the unwanted side effect of suppressing normal platelet function. These are the non-steroidal anti-inflammatory drugs (NSAIDS). Aspirin irreversibly disrupts platelet function by inhibiting cyclooxygenase -1 (COX1), and hence normal hemostasis. The resulting platelets are unable to produce new cyclooxygenase because they have no DNA. Normal platelet function does not return until the use of aspirin has ceased and enough of the affected platelets have been replaced by new ones, which can take over a week. Ibuprofen , another NSAID , does not have such a long duration effect, with platelet function usually returning within 24 hours, [ 65 ] and taking ibuprofen before aspirin prevents the irreversible effects of aspirin. [ 66 ]
These drugs are used to prevent thrombus formation.
Platelet transfusion is most frequently used to correct unusually low platelet counts, either to prevent spontaneous bleeding (typically at counts below 10×10 9 /L) or in anticipation of medical procedures that necessarily involve some bleeding. For example, in patients undergoing surgery , a level below 50×10 9 /L is associated with abnormal surgical bleeding, and regional anaesthetic procedures such as epidurals are avoided for levels below 80×10 9 /L. [ 67 ] Platelets may also be transfused when the platelet count is normal but the platelets are dysfunctional, such as when an individual is taking aspirin or clopidogrel . [ 68 ] Finally, platelets may be transfused as part of a massive transfusion protocol , in which the three major blood components (red blood cells, plasma, and platelets) are transfused to address severe hemorrhage . Platelet transfusion is contraindicated in thrombotic thrombocytopenic purpura (TTP), as it fuels the coagulopathy . Platelet transfusion is generally ineffective, and thus contraindicated, for prophylaxis in immune thrombocytopenia (ITP), because the transfused platelets are immediately cleared; however, it is indicated to treat bleeding. [ 69 ]
Platelets are either isolated from collected units of whole blood and pooled to make a therapeutic dose, or collected by platelet apheresis : blood is taken from the donor, passed through a device which removes the platelets, and the remainder is returned to the donor in a closed loop. The industry standard is for platelets to be tested for bacteria before transfusion to avoid septic reactions, which can be fatal. Recently the AABB Industry Standards for Blood Banks and Transfusion Services (5.1.5.1) has allowed use of pathogen reduction technology as an alternative to bacterial screenings in platelets. [ 70 ]
Pooled whole-blood platelets, sometimes called "random" platelets, are separated by one of two methods. [ 71 ] In the US, a unit of whole blood is placed into a large centrifuge in what is referred to as a "soft spin". At these settings, the platelets remain suspended in the plasma. The platelet-rich plasma (PRP) is removed from the red cells, then centrifuged at a faster setting to harvest the platelets from the plasma. In other regions of the world, the unit of whole blood is centrifuged using settings that cause the platelets to become suspended in the " buffy coat " layer, which includes the platelets and the white blood cells. The "buffy coat" is isolated in a sterile bag, suspended in a small amount of red blood cells and plasma, then centrifuged again to separate the platelets and plasma from the red and white blood cells. Regardless of the initial method of preparation, multiple donations may be combined into one container using a sterile connection device to manufacture a single product with the desired therapeutic dose.
Apheresis platelets are collected using a mechanical device that draws blood from the donor and centrifuges the collected blood to separate out the platelets and other components to be collected. The remaining blood is returned to the donor. The advantage to this method is that a single donation provides at least one therapeutic dose, as opposed to the multiple donations for whole-blood platelets. This means that a recipient is exposed to fewer donors and has less risk of transfusion-transmitted disease and other complications. Sometimes a person such as a cancer patient who requires routine transfusions of platelets receives repeated donations from a specific donor to minimize risk. Pathogen reduction of platelets using for example, riboflavin and UV light treatments can reduce the infectious load of pathogens contained in donated blood products. [ 72 ] [ 73 ] Another photochemical treatment process utilizing amotosalen and UVA light has been developed for the inactivation of viruses, bacteria, parasites, and leukocytes. [ 74 ] In addition, apheresis platelets tend to contain fewer contaminating red blood cells because the collection method is more efficient than "soft spin" centrifugation.
Platelets collected by either method have a typical shelf life of five days. This results in supply shortages, as testing donations often requires up to a full day. No effective preservative solutions have been devised for platelets.
Platelets are stored under constant agitation at 20–24 °C (68–75 °F). Units cannot be refrigerated as this causes platelets to change shape and lose function. Storage at room temperature provides an environment where any introduced bacteria may proliferate and subsequently cause bacteremia . The United States requires products to be tested for the presence of bacterial contamination before transfusion. [ 75 ]
Platelets do not need to belong to the same A-B-O blood group as the recipient or be cross-matched to ensure immune compatibility between donor and recipient unless they contain a significant amount of red blood cells (RBCs). The presence of RBCs imparts a reddish-orange color to the product and is usually associated with whole-blood platelets. Some sites may type platelets, but this is not critical.
Prior to issuing platelets to the recipient, they may be irradiated to prevent transfusion-associated graft versus host disease or they may be washed to remove the plasma.
The change in the recipient's platelet count after transfusion is termed the "increment" and is calculated by subtracting the pre-transfusion platelet count from the post-transfusion count. Many factors affect the increment including body size, the number of platelets transfused, and clinical features that may cause premature destruction of the transfused platelets. When recipients fail to demonstrate an adequate post-transfusion increment, this is termed platelet transfusion refractoriness .
Platelets, either apheresis-derived or random-donor, can be processed through a volume reduction process. In this process, the platelets are spun in a centrifuge and plasma is removed, leaving 10 to 100 mL of platelet concentrate. Such volume-reduced platelets are normally transfused only to neonatal and pediatric patients when a large volume of plasma could overload the child's small circulatory system. The lower volume of plasma also reduces the chances of an adverse transfusion reaction to plasma proteins. [ 76 ] Volume reduced platelets have a shelf life of four hours. [ 77 ]
The blood clot is only a temporary solution to stop bleeding; tissue repair is needed. Small interruptions in the endothelium are handled by physiological mechanisms; large interruptions by a trauma surgeon. [ 78 ] The fibrin is slowly dissolved by the fibrinolytic enzyme, plasmin , and the platelets are cleared by phagocytosis . [ 79 ]
Platelets release platelet-derived growth factor (PDGF), a potent chemotactic agent; and TGF beta , which stimulates the deposition of extracellular matrix ; fibroblast growth factor , insulin-like growth factor 1 , platelet-derived epidermal growth factor , and vascular endothelial growth factor . Local application of these factors in increased concentrations through platelet-rich plasma (PRP) is used as an adjunct in wound healing. [ 80 ]
Instead of platelets, non-mammalian vertebrates have nucleated thrombocytes, which resemble B lymphocytes in morphology. They aggregate in response to thrombin, but not to ADP, serotonin, nor adrenaline, as platelets do. [ 81 ] [ 82 ] | https://en.wikipedia.org/wiki/Platelet |
Platelet-derived growth factor receptors ( PDGF-R ) are cell surface tyrosine kinase receptors for members of the platelet-derived growth factor (PDGF) family. PDGF subunits -A and -B are important factors regulating cell proliferation , cellular differentiation , cell growth , development and many diseases including cancer . [ 2 ] There are two forms of the PDGF-R, alpha and beta each encoded by a different gene. [ 3 ] Depending on which growth factor is bound, PDGF-R homo- or heterodimerizes. [ 4 ]
The PDGF family consists of PDGF-A, -B, -C and -D, which form either homo- or hetero dimers (PDGF-AA, -AB, -BB, -CC, -DD). The four PDGFs are inactive in their monomeric forms. The PDGFs bind to the protein tyrosine kinase receptors PDGF receptor-α and -β. These two receptor isoforms dimerize upon binding the PDGF dimer, leading to three possible receptor combinations, namely -αα, -ββ and -αβ. The extracellular region of the receptor consists of five immunoglobulin -like domains while the intracellular part is a tyrosine kinase domain. The ligand-binding sites of the receptors are located to the three first immunoglobulin-like domains. PDGF-CC specifically interacts with PDGFR-αα and -αβ, but not with -ββ, and thereby resembles PDGF-AB. PDGF-DD binds to PDGFR-ββ with high affinity, and to PDGFR-αβ to a markedly lower extent and is therefore regarded as PDGFR-ββ specific. PDGF-AA binds only to PDGFR-αα, while PDGF-BB is the only PDGF that can bind all three receptor combinations with high affinity. [ 5 ]
Dimerization is a prerequisite for the activation of the kinase . Kinase activation is visualized as tyrosine phosphorylation of the receptor molecules, which occurs between the dimerized receptor molecules ( transphosphorylation ). In conjunction with dimerization and kinase activation, the receptor molecules undergo conformational changes , which allow a basal kinase activity to phosphorylate a critical tyrosine residue, thereby "unlocking" the kinase, leading to full enzymatic activity directed toward other tyrosine residues in the receptor molecules as well as other substrates for the kinase.
Expression of both receptors and each of the four PDGFs is under independent control, giving the PDGF/PDGFR system a high flexibility. Different cell types vary greatly in the ratio of PDGF isoforms and PDGFRs expressed. Different external stimuli such as inflammation , embryonic development or differentiation modulate cellular receptor expression allowing binding of some PDGFs but not others. Additionally, some cells display only one of the PDGFR isoforms while other cells express both isoforms, simultaneously or separately.
Tyrosine phosphorylation sites in growth factor receptors serve two major purposes—to control the state of activity of the kinase and to create binding sites for downstream signal transduction molecules, which in many cases also are substrates for the kinase. The second part of the tyrosine kinase domain in the PDGFβ receptor is phosphorylated at Tyr-857, and mutant receptors carrying phenylalanine at this position have reduced kinase activity. Tyr-857 has therefore been assigned a role in positive regulation of kinase activity. [ 6 ] Sites of tyrosine phosphorylation involved in binding signal transduction molecules have been identified in the juxtamembrane domain, the kinase insert, and in the C-terminal tail in the PDGFβ receptor. The phosphorylated tyrosine residue and in general three adjacent C-terminal amino acid residues form specific binding sites for signal transduction molecules. Binding to these sites involves a common conserved stretches, denoted the Src homology (SH) 2 domain and/or Phosphotyrosine Binding Domains (PTB). The specificity of these interactions appears to be very high, since mutant receptors carrying phenylalanine residues in one or several of the different phosphorylation sites generally lack the capacity to bind the targeted signal transduction molecule. The signal transduction molecules are either equipped with different enzymatic activities, or they are adaptor molecules, which in some but not all cases are found in complexes with subunits that carry a catalytic activity. Upon interaction with the activated receptor, the catalytic activities become up-regulated, through tyrosine phosphorylation or other mechanisms, generating a signal that may be unique for each type of signal transduction molecule.
Examination of the different signaling cascades induced by RTKs established Ras/mitogen-activated protein kinase (MAPK), PI-3 kinase, and phospholipase-γ (PLCγ) pathways as key downstream mediators of PDGFR signaling. [ 7 ] [ 8 ] In addition, reactive oxygen species (ROS)-dependent STAT3 activation has been established to be a key downstream mediator of PDGFR signaling in vascular smooth muscle cells. [ 9 ]
The adaptor protein Grb2 forms a complex with Sos by the Grb2 SH3 domain . Grb2 (or the Grb2/Sos complex) is recruited to the membrane by the Grb2 SH2 domain binding to activated PDGFR-bound SHP2 (also known as PTPN11 , a cytosolic PTP ), thereby allowing interaction with Ras and the exchange of GDP for GTP on Ras . Whereas the interaction between Grb2 and PDGFR occurs through interaction with the SHP2 protein, Grb2 instead binds to activated EGFR through Shc , another adaptor protein that forms a complex with many receptors via its PTB domain . [ 10 ] Once activated, Ras interacts with several proteins, namely Raf. Activated Raf stimulates MAPK-kinase (MAPKK or MEK) by phosphorylating a serine residue in its activation loop . MAPKK then phosphorylates MAPK (ERK1/2) on T and Y residues at the activation-loop leading to its activation. Activated MAPK phosphorylates a variety of cytoplasmic substrates, as well as transcription factors, when translocated into the nucleus. MAPK family members have been found to regulate various biological functions by phosphorylation of particular target molecules (such as transcription factors, other kinases etc.) located in cell membrane, cytoplasm and nucleus, and thus contribute to the regulation of different cellular processes such as cell proliferation, differentiation, apoptosis and immunoresponses .
The class IA phospholipid kinase, PI-3 kinase, is activated by the majority of RTKs. Similarly to other SH2 domain-containing proteins, PI-3 kinase forms a complex with PY sites on activated receptors. The main function of PI3K activation is the generation of PIP3, which functions as a second messenger to activate downstream tyrosine kinases Btk and Itk, the Ser/Thr kinases PDK1 and Akt (PKB). The major biological functions of Akt activation can be classified into three categories – survival, proliferation and cell growth. Akt is also known to be implicated in several cancers, particularly breast. PLCγ is immediately recruited by an activated RTK through the binding of its SH2 domains to phosphotyrosine sites of the receptor. After activation, PLCγ hydrolyses its substrate PtdIns(4,5)P2 and forms two second messengers, diacylglycerol and Ins(1,4,5)P3. Ins(1,4,5)P3 stimulates the release of Ca 2+ from intracellular supplies. Ca 2+ then binds to calmodulin, which subsequently activates a family of calmodulindependent protein kinases (CamKs). In addition, both diacylglycerol and Ca 2+ activate members of the PKC family. The second messengers generated by PtdIns(4,5)P2 hydrolysis stimulate a variety of intracellular processes such as proliferation, angiogenesis, cell motility. | https://en.wikipedia.org/wiki/Platelet-derived_growth_factor_receptor |
A platform-specific model is a model of a software or business system that is linked to a specific technological platform (e.g. a specific programming language , operating system , document file format or database ). Platform-specific models are indispensable for the actual implementation of a system.
For example, if a business needs to implement an online shop, then their software system will need to store different kinds of information: available goods, user info such as credit cards, etc. The designer might decide to use for this purpose an Oracle database . For this to work, the designer will need to express concepts (e.g. the concept of a user) in a relational model using the Oracle 's SQL dialect. This Oracle 's specific relational model is an example of a Platform-specific model .
In Model-driven architecture , a platform-specific model is where the design of the model is constructed with the intended execution-platform driving design choices. [ 1 ] | https://en.wikipedia.org/wiki/Platform-specific_model |
Platform capitalism refers to the activities of companies such as Google , Facebook , Apple , Microsoft , Uber , Airbnb , Amazon and others to operate as platforms. In this business model both hardware and software are used as a foundation (platform) for other actors to conduct their own business. [ 1 ] [ 2 ]
Platform capitalism has been both heralded as beneficial [ 3 ] and denounced as detrimental [ 4 ] by various authors. The trends identified in platform capitalism have similarities with those described under the heading of surveillance capitalism . [ 5 ] Technology companies build platforms that entire industries rely on, and those industries can easily collapse due to the decisions of those technology companies. [ 6 ]
The possible effect of platform capitalism on open science has been discussed. [ 7 ]
Platform capitalism has been contrasted with platform cooperativism . Companies that try to focus on fairness and sharing, instead of just profit motive , are described as cooperatives, whereas more traditional and common companies that focus solely on profit, like Airbnb and Uber, are platform capitalists (or cooperativist platforms vs capitalist platforms). In turn, projects like Wikipedia , which rely on unpaid labor of volunteers, can be classified as commons-based peer-production initiatives. [ 8 ] : 31, 36
This business-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Platform_capitalism |
Platform engineering is a software engineering discipline focused on the development of self-service toolchains , services, and processes to create an internal developer platform (IDP). [ 1 ] [ 2 ] The shared IDP can be utilized by software development teams, enabling them to innovate. [ 3 ] [ 4 ] [ 5 ]
Platform engineering uses components like configuration management , infrastructure orchestration , and role-based access control to improve reliability. The discipline is associated with DevOps and platform as a service practices. [ 4 ] [ 5 ]
Platform engineering aims to improve software engineering productivity by creating streamlined toolchains that can be used by developers. It can be used for digital transformation , or to expand CI/CD setups . [ 6 ]
According to a panel of experts at PlatformCon 2024, [ 7 ] it was stated that building an internal developer platform can improve more than just developer productivity. Platform engineering, which centralizes best practices and components for development teams, is gaining prominence as DevSecOps practices and frameworks become increasingly embedded across organizations. Platform engineering aims to normalize and standardize developer workflows by providing developers with optimized “golden paths” for most of their workloads and flexibility to define exceptions for the rest. Organizations can follow one of two paths when developing a new platform engineering initiative. One option is to build an authentication and visualization layer that sits across multiple point tools — but this does not solve the underlying problems of legacy technology stacks and tooling silos. [ 8 ] Therefore, this would likely not be a long-term solution. Alternatively, the organization could implement an internal developer platform (IDP) [ 9 ] that reduces the cognitive load on developers by bringing multiple technologies and tools into a single self-service experience. [ 10 ] [ 11 ]
Platform engineering’s benefits include faster time to market, reduced security and compliance risk, and improved developer experience. Establishing a product-oriented culture and setting clear business goals are critical for success in platform engineering. Therefore it can be stated that platform engineering has increased importance wherever businesses strive to do more with less.
Despite its benefits, platform engineering faces several criticisms. One major concern is the complexity and overhead associated with building and maintaining such platforms. Additionally, creating a one-size-fits-all platform might not address the unique needs of all development teams, leading to inefficiencies and frustration. Siloed teams and a lack of focus on resolving operational issues can also hinder the effectiveness of the platforms created. | https://en.wikipedia.org/wiki/Platform_engineering |
A platform gap (also known technically as the platform train interface or PTI in some countries) is the space between a train car (or other mass transit vehicle ) and the edge of the station platform , often created by geometric constraints, historic legacies, or use of partially compatible equipment. [ 1 ]
Many high-quality bus rapid transit (BRT) systems also use high platforms at station stops to allow fast and efficient level boarding and alighting, but potentially leaving hazardous gaps between the platforms and the buses. Alignment setups such as Kassel curbs help to reduce platform gaps without requiring time-consuming manual alignment at each BRT station stop.
A platform gap has two component measurements:
The ideal platform would be straight and align perfectly with a train or other large vehicle. Even in this case, a small gap between the conveyances and the platform is necessary to allow the vehicles to move freely without rubbing against the platform edge. In 2007, the Long Island Rail Road regarded an 8-inch (20 cm) platform gap as typical on its non-curved platforms. [ 3 ] : 12
In real-world situations, stations are often constrained by limited space, legacy designs, and track geometry or roadway layout. Stations may have to use a compromise design, with a platform curved in a way that will allow a vehicle or train to arrive and depart without mechanical interference, but which leaves unavoidable horizontal and possibly vertical gaps between the cars and the platform edge. These spaces are caused by the geometric gap between a curve ( circular arc or otherwise) and the straight-line chord or tangent formed by a railcar or bus in proximity to a platform. These types of gaps are geometrically intrinsic, and cannot be eliminated as long as the platform is located on a curved or banked segment of track or guideway.
When passenger car doors are located only at the ends of each car (a common design for commuter rail and long-distance trains), platform access from a concave platform is preferred, since this brings the car ends in closest proximity to the platform edge. By contrast, a convex platform would leave the largest possible gaps between the car ends and the platform edge, making this design undesirable and thus rarely implemented.
An example of platforms designed for access from the concave side is at Lansdowne station in Boston , where side platforms for both the inbound and outbound directions are located to reduce platform gaps to commuter rail trains of the Framingham/Worcester Line . Concave and convex gaps also exist in several MTR stations in Hong Kong, particularly on the East Rail line , which was built on the historic Kowloon–Canton Railway line.
Mechanical platform edge extensions known as platform gap fillers may be used to bridge the gap between platform and vehicle. These stopgaps require careful alignment of the vehicle upon arrival, and careful synchronization to avoid serious damage caused by departure of the vehicle before the extenders are fully retracted. They increase station dwell time , and introduce safety and maintenance concerns of their own.
Alternatively, the gap fillers may be mounted on the train, and linked to the door operating mechanism. They may be found on modern trainsets, like various versions of the Stadler GTW [ failed verification ] and the British Rail Class 555 for the Tyne and Wear Metro . Train-mounted gap fillers eliminate the need for careful alignment and, as the driver only gets the signal that the doors have closed when the fillers have fully retracted, require no special synchronization on departure. Moving all active components of the system to the train instead of the platform allows maintenance to be performed in a shop, rather than in the field.
Many regional trains in Germany come with platform gap fillers, such as the Bombardier Talent 2 . [ 4 ] On subway networks, they have also become more common, as evidenced by the Nuremberg U-Bahn whose 1970s first generation VAG Class DT1 do not have them but whose VAG Class DT3 of the 2000s and 2010s and VAG Class G1 of the 2020s come equipped with automatic gap fillers. [ 5 ]
On the Berlin U-Bahn , which has two different loading gauges ( Kleinprofil on U1-U4 and Großprofil on U5-U9), so-called Blumenbretter ("flower boards") bridging the platform gap were attached to Kleinprofil trains that ran on Großprofil lines at various times of rolling stock shortage. [ 6 ] [ 7 ] [ 8 ]
Platform gap fillers were trialled on the platforms of Lo Wu station on the East Rail line in 2009 due to the difficulty of installing platform screen doors on the curved nature of the platforms . They were planned to be installed at other stations along the line along with signal upgrades. However, during the trial period, MTR found that the time taken for the gap filler to fully extend took 15-20 seconds and so greatly increased dwell times of trains. It was decided unsuitable for service. After the trial period ended in October 2009, the platform gap fillers were not used until it was finally removed during a platform-strengthening maintenance operation. Plans to install it on other stations of the East Rail line were also abandoned.
Some Japanese railway stations have platform gap fillers, which are known as movable steps ( 可動ステップ , kadō steppu ) . [ 9 ] Over 200 fillers are used in the Tokyo subway . [ 9 ] In addition, there is a program to retrofit platform doors for increased safety on Tokyo subway lines. [ 9 ]
Singapore has committed to specifying its newer trains with gap fillers, to reduce the incidence of platform gap accidents in its crowded stations. [ 10 ] Platform gap fillers are used in the Mass Rapid Transit system of Singapore , namely the North South MRT line and the East West MRT line . Platform gap fillers are also planned for installation on trains on the North East MRT line and the Circle MRT line as well, because newer trains can be equipped with gap fillers. [ 11 ]
The Airport Rail Link has installed Platform Gap Fillers at all 8 stations on 12 July 2019 to enhance passenger safety and convenience. These gap fillers bridge the space between the train doors and platforms, providing a safer experience for passengers. The system connects the airport to the city center, with the platform gap fillers made from locally sourced natural rubber, supporting domestic production and ensuring high quality.
With the introduction of the NTfL , Transport for London are hoping to introduce platform gap fillers on the Bakerloo , Central & Piccadilly lines (of which 14 platforms have been identified for installation) at curved platforms such as Bank, where the gap between the train and the platform can exceed 1 foot (30.5 cm). [ 12 ]
The Interborough Rapid Transit Company 's first cars were built with only two doors on each side, at the extreme ends of the car, lining up with the curved platforms so as not to leave a wide gap between the train and the platform. When the IRT modified existing cars and ordered new cars with a middle door, gap fillers were needed because the middle door was not near the platform. After the City of New York bought the IRT in 1940, new car designs (starting with the R12 ) had the end doors away from the extreme ends of the car body, which also required the use of gap fillers at certain stations.
IRT stations with gap fillers are:
The Utah Transit Authority (UTA) has installed platform gap fillers at various stations throughout the Wasatch Front within the states.
In some rail systems, significant platform gaps may also occur (both horizontally and vertically) because of equipment and platforms designed to different and somewhat incompatible height and width standards. This situation may occur especially when previously separate rail systems are consolidated, or start to interoperate , thus allowing equipment to be moved onto tracks where it had not been used before.
In 2007, public testimony by the acting president of the Long Island Rail Road cited the need to interoperate with freight service and other passenger services such as New Jersey Transit and Amtrak , in addition to its own diverse rolling stock, as complicating and slowing efforts to deal with platform gap hazards. [ 3 ] : 6–8
Other variables that can increase platform gaps include rail wear, wheel wear, condition of the railcar suspension, and passenger load. [ 3 ] : 16 A further complication is super-elevation , deliberate tilting of the railbed to allow faster travel around curves. This factor is especially relevant on systems where some express trains (such as long-distance Amtrak trains) operate non-stop through local stations located on curves. [ 3 ] : 15 Higher pass-through speeds also increase railcar sway, requiring even larger physical clearances to avoid platform strikes.
In the US, the Americans with Disabilities Act requires that platforms be “readily accessible to and usable by individuals with disabilities, including individuals who use wheelchairs (49 CFR Part 37, Appendix A, 10.3.1 (9))”. However, this rule only applies to new construction or major renovations of stations. A 2009 report to the New Jersey Department of Transportation (NJDOT) observes that ADA rules specify that "At stations with high level platforms, there may be a gap of no more than 3” horizontal and 5/8" vertical between platform edge and entrance to the rail car. However, currently no passenger rail system in the U.S. has been able to achieve this without the use of manually operated 'bridge plates'.” [ 17 ] : 2
As of 2007 [update] , the US Federal Railway Administration recommended platform gap maximum limits of 7–10 inches (18–25 cm), and 10–13 inches (25–33 cm) on curves. [ 3 ] : 19
Physical measures to reduce platform gaps may include realigning trackbeds, realigning platform slabs, and extending platform edges with wooden boards. [ 3 ] : 22–24 Operational measures may include "zoning off" some railcars (not opening certain doors at problematic stations), relocating where trains stop along a lengthy platform, and temporarily deploying "platform conductor" personnel to assist passengers. [ 3 ] : 25–27
On systems where the floor level of the vehicle and the platform height closely match, an extendible platform can be installed below the doors of the vehicle, to deploy when the doors are opened. This significantly decreases the gap and thus the risks when boarding and alighting vehicles at stations or stops. This method is used by the German BR423 EMU 's and its derivatives, including the Dutch variant SLT .
A public awareness campaign may be used, employing visually distinct platform edge markings, posters, signs, public safety announcements, and web videos to increase safety awareness. [ 3 ] : 28–34 The MTA Long Island Rail Road website lists some precautions passengers should observe regarding platform gaps. [ 18 ]
An article in The Guardian conceded that some passengers who have fallen into platform gaps were drunk at the time, but pointed out other incidents when victims did not have that impairment. The writer complained specifically about gaps that measured from 46 to 51 centimetres (18 to 20 in) which posed safety threats to children and the elderly, and called for modification of dangerous platforms. [ 19 ]
In 1865 the Franklin Institute reported on 'the frequent loss of life that occurred on station platforms' and stated that 'platforms should be built up to the level of the flooring of the carriages, and that a dangerous space between the platform and the carriages ought not to exist'. [ 2 ]
A 2009 American report identified platform gap injury risk factors, including "mobility, being elderly, having disabilities (visual impairment), being accompanied by small children or incidents occurring to small children, behavior of other passengers such as pushing or jostling, carry luggage and other articles, alcohol, degraded platform conditions such as crowding, wet platforms or uneven platforms, and stepping distances". [ 17 ] : 5
In 2023, British transport systems lecturer and co-founder of UK-based Campaign for Level Boarding Gareth Dennis said achieving level boarding "should be a core objective" for any operators and that it is "not acceptable" for passengers to have to worry whether there will be an attendant with a ramp at their destination. [ 2 ] He criticised London's Crossrail project's "poor decision making" which set new inner-city station floor heights on the Elizabeth line at train floor level, while outer suburban platforms remained at their pre-existing height, about 200mm lower: "This brand-new railway has cornered itself into perpetually offering an inaccessible service." [ 2 ]
An incident once occurred involving Robert Todd Lincoln (son of American president Abraham Lincoln ) and a platform gap in Jersey City, New Jersey during the American Civil War . While waiting on a crowded train platform, Robert Lincoln was pushed against the train, and the train started to move, dropping his feet into the gap. He was saved from possible serious injury or death by the prompt actions of well-known actor Edwin Booth , whose brother John Wilkes Booth later assassinated President Lincoln . [ 20 ]
In 2014, a news service in Mumbai , India reported several serious platform gap mutilation incidents and a death within a few months, mostly attributed to crowded conditions. [ 21 ] In 2015, Singapore had at least two platform gap incidents which were eventually resolved, but caused significant disruptions in rush-hour service. [ 10 ]
In 2014 in Perth, Australia , an accident occurred when a man fell between the platform and the train, and could not release his leg because the gap was too small. Other passengers "rocked" the carriage sideways to increase the gap, allowing the victim to escape. [ 22 ]
In 2022 in Duvvada, India , a girl who was standing at the door for alighting was knocked down by the door due to a sudden jerk, and she fell into the gap between coach and the platform, In spite of immediate rescue efforts launched by authorities to free her, it took almost an hour to cut the platform and rush her to the hospital. Injuries to her internal organs led to her death within a day. [ 23 ] | https://en.wikipedia.org/wiki/Platform_gap |
Platform screen doors ( PSDs ), also known as platform edge doors ( PEDs ), are used at some train , rapid transit and people mover stations to separate the platform from train tracks, as well as on some bus rapid transit , tram and light rail systems. Primarily used for passenger safety, [ 1 ] they are a relatively new addition to many metro systems around the world, some having been retrofitted to established systems. They are widely used in newer Asian and European metro systems, and Latin American bus rapid transit systems.
The idea of platform edge doors dates from as early as 1908, when Charles S. Shute of Boston was granted a patent for "Safety fence and gate for railway-platforms". [ 2 ] The invention consisted of "a fence for railway platform edges", composed of a series of pickets bolted to the platform edge, and vertically movable pickets that could retract into a platform edge when there was a train in the station. [ 3 ] In 1917, Carl Albert West was granted a patent for "Gate for subrailways and the like". [ 4 ] The invention provided for spaced guides secured to a tunnel's side wall, with "a gate having its ends guided in the guides, the ends and intermediate portions of the gate having rollers engaging the side wall". Pneumatic cylinders with pistons would be used to raise the gates above the platform when a train was in the station. Unlike Shute's invention, the entire platform gate was movable, and was to retract upward. [ 5 ]
The first stations in the world with platform screen doors were the ten stations of the Saint Petersburg Metro 's Line 2 that opened between 1961 and 1972. The platform "doors" are actually openings in the station wall which supports the ceiling of the platform. The track tunnels adjoining the ten stations' island platforms were built with tunnel boring machines (TBMs), and the island platforms were located in a separate vault between the two track tunnels. Usually, TBMs bore the deep-level tunnels between stations, while the station vaults are dug out manually and contain both the tracks and the platform. However, in the case of the Saint Petersburg Metro, the TBMs bored a pair of continuous tunnels that passed through ten stations, and the stations themselves were built in vaults that only contained the platform, with small openings on the sides of the vault, in order for passengers to access the trains in the tunnels. [ 6 ]
Singapore 's Mass Rapid Transit , opened in 1987, is often described as the first heavy Metro system in the world to incorporate PSDs into its stations for climate control and safety reasons, rather than architectural constraints, [ 6 ] [ 7 ] [ 8 ] though the light Lille Metro , opened in 1983, predates it. [ 9 ]
Although the terms are often used interchangeably, platform screen doors can refer to both full-height and half-height barriers. Full height platform screen doors are total barriers between the station floor and ceiling, while the half-height platform screen doors are referred to as platform edge doors or automatic platform gates , as they do not reach the ceiling and thus do not create a total barrier. Platform gates are usually only half of the height of the full-screen doors, are chest-height sliding doors at the edge of railway platforms to prevent passengers from falling off the platform edge onto the railway tracks . But they sometimes reach to the height of the train. Like full-height platform screen doors, these platform gates slide open or close simultaneously with the train doors. These two types of platform screen doors are presently the main types in the world.
The doors help to:
Their primary disadvantage of PSDs is their cost. When used to retrofit older systems, they can limit the kind of rolling stock that may be used on a line, because the train doors must fit the spacing of the platform doors, which can result in additional costs, due to the otherwise unnecessary purchase of new rolling stock and consequent depot upgrades.
Despite delivering an overwhelming improvement to passenger safety at the platform-train interface, platform screen doors do introduce new hazards which must be carefully managed in design and delivery. The principal hazard is entrapment between closed platform doors and the train carriage which, if undetected, can lead to fatality when the train begins to move (see § Incidents ). Cases of this happening are rare, and the risk can be minimised with careful design, in particular by interlocking the door system with the signalling system, and by minimising the gap between the closed platform doors and the train body. In some cases active monitoring systems are used to monitor this gap.
Half-height platform edge doors, also known as automatic platform gates, are cheaper to install than full-height platform screen doors, which require more metallic framework for support. Some railway operators may therefore prefer such an option to improve safety at railway platforms and, at the same time, keep costs low and non-air-conditioned platforms naturally ventilated. However, these gates are less effective than full platform screen doors in preventing people from intentionally jumping onto the tracks. [ 14 ] These gates were first [ clarify ] in practical use by the Hong Kong MTR on the Disneyland Resort line for the open-air station designs. Most half-height platform edge door designs have taller designs than the ones installed on the Disneyland Resort line.
There are also rope-type platform screen doors at stations where a number of train types, with different lengths and train door spacings, use the same platforms. The barriers move upwards, rather than sideways, to let passengers through.
Some Japanese, Korean, Chinese and Eastern European countries have stations that use rope-type screen doors, to lower the cost of installation and to deal with the problem of different train types and distances between car doors.
The first-ever full-height variable screen doors were installed on the underground platforms of Osaka Station , which opened in March 2023, but a few half-height variants can be found on a set installed at the Shinkansen platforms of Shinagawa Station in Tokyo . Their use is rare since they are a much costlier and more complicated alternative to rope-type screen doors. The only difference from the latter is that they move sideways when letting passengers through.
At Osaka Station, the doors are designed as a single block (equivalent to the length of a train car). It consists of five units: one wall-like "parent door" suspended from the top and two sets of glass "child doors". When the train reaches the station, a special scanner on the platform reads the information on the ID tag placed on the train to identify its type and the number of cars. With the type and the number of cars having been instantly identified, each unit will slide automatically to match the configuration of the stopped train. The parent and child doors then slide into the optimal position to align precisely with the position of each car door. [ 15 ]
Since the technology is still new, such doors are still going through testing phases in several countries around the world. [ 16 ]
Line D of the Buenos Aires Subte is planned to have platform screen doors installed in the future, after the communications-based train control (CBTC) system has been installed. [ 17 ] [ 18 ] [ 19 ]
Sydney Metro , which opened in May 2019, was the first-fully automated rapid transit rail system in Australia. There are full-height screen doors on most underground platforms, with full-height edge doors on at-grade, elevated and some underground platforms. The existing five stations on the Epping to Chatswood railway line were upgraded to rapid transit standard, all being fitted with full-height platform edge doors. [ 20 ]
In Melbourne, the Metro Tunnel , from South Kensington to South Yarra , due to open in 2025, will have platform screen doors on the underground stations. [ 21 ] New rolling stock is being constructed, with doors that will line up with full-height PSDs on the platforms. The fully automated Suburban Rail Loop , which is due to open in 2035, will have platform screen doors at every station.
The Cross River Rail in Brisbane, which is currently under construction and scheduled to open in 2026, will have platform screen doors on the new Boggo Road , Woolloongabba and Albert Street underground stations, and the new underground platforms of Roma Street station . [ 22 ]
Currently, only the Serfaus U-Bahn and Line U2 of the Vienna U-Bahn (from Schottentor station to Karlsplatz station ) use platform screen doors. The section was reopened on 6.12.2024 after 3 years of constructing. [ 23 ]
The Dhaka Metro Rail uses half-height platform screen doors at all of its elevated stations.
Platform screen doors are being installed on Line 3 of the Minsk Metro , which first opened in late 2020, and will be installed at stations on the later sections of the line. [ 24 ]
The Platform Screen Doors have been present in the São Paulo Metro since 2010, when the Sacomã Station was opened. [ 26 ] As of 2019, five of the six lines of the São Paulo Metro have the equipment: Lines 4 - Yellow , 5 - Lilac and 15 - Silver have the equipment installed in all of its stations. The feature is also present in some stations of Line 2 - Green and Line 3 - Red . They are planned to be installed in 41 stations of lines 1, 2 and 3 by the end of
2021, [ 27 ] as well as all stations of line 5 by the end of 2020. [ 28 ] [ needs update ]
PSDs are also found on the tube stations of the RIT BRT and in the Santos Light Rail since 2016. [ 29 ]
Half-height platform screen doors are in use on all stations of the Sofia Metro Line 3. [ 30 ]
In 2020, rope-type screen door (RSD) system was installed in Vasil Levski Stadium Metro Station and Opalchenska Metro Station of the Sofia Metro Line 1 and Line 2. “Standard” platform doors cannot be used on those lines because of the differing door layouts between the 81-717/714 and 81-740/741 models used. In total, such rope-type safety barriers will be installed on more 10 of the busiest stations on the Line 1 and 2 of the Sofia Metro , providing increased safety for passengers and protecting against accidental falls. [ 31 ]
Screen doors are in use at all three LINK Train stations and the Union and Pearson stations along the Union Pearson Express route to Toronto Pearson International Airport in Mississauga, Ontario . Platform screen doors will be installed at all stations on the forthcoming Ontario Line . [ 32 ] In addition, as a part of major renovations and expansions to the Bloor-Yonge interchange, platform screen doors will be installed on both Line 1 platforms. The doors will also be installed on the Line 2 platforms once CBTC signalling upgrades are made to the line. The addition of such doors at Bloor-Yonge has prompted rumours of a broader system wide rollout, including in the forthcoming Scarborough Subway Extension and Yonge North Subway Extension , though no confirmation or funding has been announced by the Toronto Transit Commission or the Government of Ontario . [ 33 ]
Greater Montreal's forthcoming Réseau express métropolitain (REM), the 67-kilometre-long driverless complementary suburban rapid transit network opening in five phases between 2023 and 2027 [ 34 ] will feature screen doors at each of its 26 stations.
With the advent of the REM on the horizon, calls to retrofit platform edge doors in the Montreal Metro to combat delays arising from overcrowding are becoming more common. If full-height doors were to be installed, it may reduce the difficulty in opening station entrance doors at ground level due to the pressure imbalance caused by passing trains. [ citation needed ] Given that there are two different train door layouts on the Montreal Metro, with the older MR-73 trains having 4 doors on each side of the car, and MPM-10 having 3, it is unlikely platform doors will be showing up in the Montreal Metro until the retirement of the MR-73 fleet.
In June 2023, the operator of the Vancouver SkyTrain , TransLink announced a feasibility study into installing platform screen doors on the Expo and Millennium lines. Such installation was previously deemed infeasible, due to SkyTrain's diverse fleet and different door positions. However, with the acquisition of the Alstom Mark V trains , which will replace the ageing Mark I , the door positions allow for a feasibility study to proceed. The results will be released sometime in 2025. [ 35 ]
Platform edge doors are currently in use at Lines 3 and 6 of the Santiago Metro , being a novelty in the system.
All metro systems in China have platform screen doors installed on most of their lines. All stations built after the mid-2000s have some form of platform barrier. Guangzhou Metro Line 2 , which opened in 2002, is the first metro system in mainland China to have installed platform screen doors since its completion. [ 36 ] The older Guangzhou Metro Line 1 also completed the installation of platform screen doors between 2006 and 2009. [ 37 ] [ 38 ] [ 39 ] Only the Dalian Metro lines 3, 12, and 13, Wuhan Metro line 1 and Changchun Metro lines 3, 4, and 8 have stations without the platform screen doors on their early lines (As of 21 September 2019 [update] ). However many are starting the process of retrofitting these lines with platform screen gates.
In addition, many bus rapid transit systems such as the Guangzhou Bus Rapid Transit also have stops that are equipped with platform screen doors. Platform screen doors are also present in some tram and light rail stops such as the Xijiao Light rail , Nanjing tram and Chengdu tram .
Several underground high speed railway stations of the CRH network use platform screen doors set back from the platform edge.
In addition, Fengxian District in Shanghai installed platform gates at a road crossing.
Several stations on Bogota's TransMilenio bus rapid transit system use platform screen doors. The Ayacucho Tram in Medellin also has half-height platform doors at every station.
The Copenhagen Metro uses Westinghouse [ 40 ] and Faiveley platform screen doors on all platforms. Full-height doors are used on underground stations while surface level stations have half-height doors (except from Lufthavnen and Orientkaj ). Underground stations have had platform doors since opening, while above ground stations on lines 1 and 2 did not initially, and were installed later.
The Helsinki Metro had a trial run with Faiveley automatic platform gates installed on a single platform at Vuosaari metro station during phase one of the project. The doors, which are part of the Siemens metro automation project, were built in 2012. Phase 2 of the project has been delayed due to metro automation technical and safety related testings. [ 41 ] The doors were removed in 2015.
All lines of the VAL automated subway system are equipped with platform screen doors at every station, starting with Lille subways in 1983. Those also include Toulouse and Rennes as well as the CDGVAL and Orlyval airport shuttles.
Paris Métro 's line 14 from Saint-Lazare to Bibliothèque François Mitterrand was inaugurated in 1998 with platform screen doors manufactured by Faiveley Transport . The new station Olympiades opened with platform screen doors in June 2007. Lines 1 and 4 have been retrofitted with platform edge doors, for full driverless automation effective in 2012 and 2023, respectively. Some stations on Line 13 have had platform edge doors since 2010 to manage their overcrowding, after tests conducted in 2006.
Since 30 June 2020, a new kind of vertical platform screen doors, called platform curtains , are being tested on the platform 2bis of Vanves–Malakoff station (in Paris region) on the Transilien Line N commuter rail line. The experiment should end in February 2021. [ 42 ] Transilien said that they preferred platform curtains to classical screen doors for this line because the positioning of the doors is not the same across the rolling stock , and that they plan to install them in other Transilien stations if the experiment is successful. [ 43 ]
Paris is now getting a new urban revolution : The Grand Paris Express . As of it, every new stations are getting brand new full platform screen doors, and it begins with the Line 14 extension inaugurated in 2024, from Saint-Denis–Pleyel to Orly Airport.
People movers at Frankfurt International Airport , Munich International Airport and Düsseldorf Airport are equipped with platform screen doors, as well as the suspended monorail in Dortmund , called H-Bahn . Plans are underway to test platform screen doors on the Munich U-Bahn in 2023 and line U5 & U6 will be installed in late 2026. [ 44 ]
All stations on the forthcoming line U5 on the Hamburg U-Bahn will feature full-height platform screen doors.
Platform screen doors are used on the driverless Thessaloniki Metro , [ 45 ] which opened in November 2024. In addition, platform screen doors will be used in the under construction Line 4 of the Athens Metro .
Currently, all heavy rail and medium-capacity railway platforms outside the East Rail line are equipped with either platform screen doors or automatic platform gates. On the East Rail line, PSDs are installed only at Admiralty , Exhibition Centre and Hung Hom stations. Automatic platform gates have also been installed at Racecourse , Lok Ma Chau , Sha Tin , Sheung Shui , Tai Po Market and Tai Wai . Installation is still in progress or are soon to begin at the remaining stations. Automatic platform gates are currently only used in at-grade and elevated stations, while platform screen doors are used in all underground and some at-grade or elevated stations. None of the light rail platforms have platform screen doors or automatic platform gates installed.
The MTR Corporation had since mid-1996, been studying the feasibility of installing PSDs at the older stations to reduce suicides on the MTR and reduce air-conditioning costs. Platforms 2 and 3 of Choi Hung were chosen for the trial due to them being redundant platforms and receiving low numbers of passengers. Platform screen doors of two and a half cars' length were installed on each of the two platforms during the trial in 1996. As the Kwun Tong line trains consisted of eight cars, it was decided that the PSDs were to be removed to allow for smoother train operations. [ citation needed ]
With the opening of the Tung Chung line and Airport Express , Hong Kong had its first full-height PSDs fully operational in 1998.
The MTR decided in 1999 to undertake the PSD Retrofitting Programme at 74 platforms of 30 select underground stations on the Kwun Tong , Island , and Tsuen Wan lines . 2,960 pairs of PSDs were ordered from Gilgen Door Systems. Choi Hung became the first station to receive platform screen doors from this programme in August 2001. The Mass Transit Railway became the first metro system in the world to retrofit PSDs on a transit system already in operation. [ 46 ] The program was completed in March 2006. [ 47 ] All subsequent new stations or platforms installed with PSDs also used those manufactured by Gilgen Door Systems, until the cross-harbour extension of the East Rail Line which used platform screen doors manufactured by Fangda Group. [ 48 ]
The opening of the Sunny Bay and Disneyland Resort stations in 2005 also meant the first platform-edge doors entering operation for the MTR network. These doors are currently the lowest in the entire network of being at around 1.2 m (3 ft 11 in) high, compared to 1.55 m (5 ft 1 in) on the Kwun Tong, Tsuen Wan, Island and Tung Chung lines and 1.7 m (5 ft 7 in) on the Tuen Ma and South Island lines .
In 2006, the MTR began studying ways to introduce barriers at above-ground and at-grade stations, which was considered more complicated as those stations were naturally ventilated and the introduction of full-height platform screen doors would entail the installation of air conditioning systems. In 2008, the corporation decided to install automatic platform gates (APGs) at eight stations (the MTR Corporation Limited and KCR Corporation had been operationally merged since 2007, but KCR stations were not included in this study). [ 47 ] The eight stations were retrofitted with APGs in 2011.
From July 2000 to December 2013, the MTR Corporation collected a surcharge of 10 cents from each Octopus -paying passenger to help pay for the installation of PSDs and APGs. Over HK$1.15 billion was collected in total. [ 49 ]
Platform screen doors were also installed on all platforms of the West Rail line (now part of the Tuen Ma line ), then built by the Kowloon-Canton Railway Corporation (KCRC) before the MTR–KCR merger . The Ma On Shan line did not have gates upon opening even though it was built at the same time as the West Rail; they were eventually added from 2014 to 2017 prior to the opening of the first phase of the Tuen Ma line on 14 February 2020.
The installation of platform screen doors in Hong Kong has been effective in reducing railway injuries and service disruptions. [ 50 ]
The then-longest set of platform screen doors in the world can be found in East Tsim Sha Tsui station , where it first served the East Rail line when 12-car MLR trains were still in service. [ 51 ] Following the completion of the Kowloon Southern Link and handing over of the station to the West Rail line (now part of the Tuen Ma line), the subsequent reduction of train length from 12 to 7 cars caused many of the screen doors to be put out of service, although the trains were lengthened to eight cars in May 2018.
The West Rail line (now part of Tuen Ma line), had all stations installed with APGs, and another constituent line of the Tuen Ma line, the Ma On Shan line, had its final APG installed enter service on 20 December 2017.
The last non-tram/light rail stations in Hong Kong without platform screen doors or gates are all on the East Rail line , a former KCR line not part of the MTR APG retrofitting programmes. The KCR Corporation found it difficult to install APGs because of the wide curves of the platforms and large gaps of their platforms, especially in University , Lo Wu , and Mong Kok East station. However, these remaining thirteen stations are all being retrofitted by Kaba as part of the Sha Tin to Central Link project. The APGs are estimated to be at around 1.8 m (5 ft 11 in) high. [ 52 ] Adding APGs to the East Rail Line platforms requires platform strengthening with rebars and brackets as the gates, combined with heavy winds, can greatly increase structural load on the platform structure. Also extensive waterproofing work is needed as many of these platforms are directly exposed to the elements.
As of May 15, 2022, three stations on the East Rail Line (Hung Hom, Exhibition Centre, Admiralty) are equipped with platform screen doors, while the remaining stations are undergoing retrofitting. The platform screen doors presently in service in the MTR have been supplied by the Swiss manufacturer Kaba Gilgen , the Japanese Nabtesco Corporation (under the Nabco brand), the French Faiveley Transport and Shenzhen Fangda Automatic System.
Apart from the MTR, all stations on the Hong Kong International Airport Automated People Mover are equipped with platform screen doors made from Westinghouse (for Phase 1) [ 53 ] and Panasonic (for Midfield Extension). [ 54 ] The platforms for the shuttle bus service between the North Satellite Concourse and the East Hall of Terminal One at the HKIA, Chek Lap Kok, the New Territories and the bus platforms in Yue Man Square in Kwun Tong, New Kowloon [ 55 ] are also retrofitted with PSDs. After it reopened on 27 August 2022, the Peak Tram was retrofitted with platform edge doors on the boarding side of the terminus stations.
On the Delhi Metro , all stations on the Delhi Airport Metro Express line, which links to Indira Gandhi International Airport have been equipped with full-height platform screen doors since 2011 and the six busiest stations on the Yellow Line have also been equipped with half height platform gates. [ 56 ] [ 57 ] Automatic platform gates on all the stations of the Pink , Magenta Line and Grey Line .
Platform screen doors are also used in all underground stations of the Chennai Metro . [ 58 ]
In Kolkata Metro , all elevated and underground stations of Green Line have platform screen doors. They are planned to be introduced in underground stations of Purple Line , Yellow Line and Orange Line . There are also plans to install platform screen doors in Blue Line . [ 59 ]
All the stations of under-construction Hyderabad Airport Express Metro will have a provision of half-height platform screen doors (PSD) for improved passenger safety. [ 60 ] On the Namma Metro in Bangalore , platform doors will be installed for its phase II operations and is expected to be completed by 2019. [ 61 ] The Electronic City metro station in southern Bengaluru, on the Yellow Line , will be the first Namma Metro station to have platform screen doors installed. [ 62 ]
On the Mumbai Metro , all lines being made by MMRDA will have half-height platform screen doors on all elevated stations and full-height platform screen doors in the underground stations, as the trains used in these lines have a GoA level 4 , and also to reduce risk of passenger deaths by overcrowding. In Line 2A, The Yellow Line , Line 7A, The Red Line and Line 3, the Aqua line , will have full-height platform screen doors, as the line is fully underground, and like the MMRDA lines above, will have GoA level 4 (Unattended train operation). [ 63 ] [ 64 ] [ 65 ] [ 66 ]
All underground stations on the Pune Metro will have platform screen doors. [ 67 ]
The Soekarno–Hatta Airport Skytrain , opened in 2017, has full-height platform screen doors. The Jakarta MRT , opened in 2019, has full-height PSDs in underground stations and half-height PSDs in elevated stations. The Jakarta LRT , opened in 2019, has half-height PSDs. The Greater Jakarta LRT , which opened in 2023, has half-height platform screen doors. [ 68 ] PSDs are used in some TransJakarta bus stops, but they are often broken and have to be turned off. [ 69 ] [ 70 ]
The future Dublin MetroLink will have platform screen doors. [ citation needed ]
The underground stations on the Red Line on the Tel Aviv Light Rail have full height platform screen doors, with the exception of the Elifelet, Shenkar and Kiryat Arye stations which have half-height Platform screen doors.
Platform screen doors are used in most newly built rapid transit lines and systems of new construction in Italy . PSDs are present on Turin Metro , the Venice People Mover , the Perugia Minimetrò , the Brescia Metro , Line 4 and Line 5 of the Milan Metro , Marconi Express Bologna , Pisa Mover (linking Pisa airport and Pisa Centrale station) and Line C of the Rome Metro .
The Tokyo Metro and Toei Subway began using barriers with the 1991 opening of the Namboku Line (which has full-height platform screen doors), [ 71 ] and subsequently installed automatic platform gates on the Mita , Marunouchi , and Fukutoshin lines. Some railway lines, including the subway systems in Sapporo , Sendai , Nagoya , Osaka , Kyoto , and Fukuoka , also utilize barriers to some extent.
In August 2012, the Japanese government announced plans to install barriers at stations used by 100,000 or more people per day, and the Ministry of Land, Infrastructure, Transport and Tourism allotted 36 million yen ($470,800) for research and development of the system the 2011-2012 fiscal year. A difficulty was the fact that some stations are used by different types of trains with different designs, making barrier design a challenge. [ 72 ]
As of November 2012 [update] , only 34 of 235 stations with over 100,000 users per day were able to implement the plan. The ministry stated that 539 of approximately 9,500 train stations across Japan have barriers. Of the Tokyo Metro stations, 78 of 179 have some type of platform barrier. [ 73 ] [ needs update ]
In 2018, automatic platform gates were installed on the Sōbu Rapid Line platforms at Shin-Koiwa . As the line's trains are 300 m (980 ft) long, the set of platform gates broke the world record for the longest platform doors at East Tsim Sha Tsui station in Hong Kong. [ 74 ] [ 75 ]
In March 2023, the underground facilities at Osaka Station (nicknamed Ume-kita during planning and construction) opened. The platforms for the Haruka and Kuroshio limited express services have movable full-screen automated platform doors that cover the entire platform from the edge to the ceiling and such doors are the first of its kind. [ 15 ] [ 76 ]
Platform screen doors (PSD) are installed at all underground Kelana Jaya Line stations, from Ampang Park to Masjid Jamek , Kajang Line , from Muzium Negara to Maluri stations and Putrajaya Line , from Sentul Barat to Chan Sow Lin . The automated announcement message reading "For safety reasons, please stand behind the yellow line" in both English and Malay languages are also heard before the train arrived at all stations.
There are also platform screen doors (PSD) on the KLIA Ekspres at Kuala Lumpur Sentral and KLIA stations. Both stations at KLIA Aerotrain also have platform screen doors.
The automatic platform gates (APG) also have been installed in all elevated and subsurface stations of the Kajang Line , KL Monorail and Putrajaya Line .
Platform screen doors are present at various bus rapid transit systems in Mexico, such as at the stations of the Guadalajara Macrobús and the Ecovía system of Monterrey. Platform screen doors can be seen as well on the Aerotrén , an airport people mover at Mexico City International Airport . No metros in Mexico currently use any type of barrier however.
The Lahore Metro utilises half-height platform edge doors at elevated stations and full-height platform screen doors at underground stations. Many bus rapid transit systems have full-height platform screen doors installed, including the Lahore Metrobus , Rawalpindi-Islamabad Metrobus , Multan Metrobus , TransPeshawar , and Karachi Breeze .
Half-height platform screen doors shall be installed on the North–South Commuter Railway , [ 77 ] while full-height platform screen doors shall be installed on the Metro Manila Subway . [ 78 ] The system is sought to open in stages between 2025 and 2029.
Full-height platform screen doors will be used in underground stations of Line 2 of the Lima Metro , which opened in 2023. [ 79 ] [ needs update ]
Platform screen doors are in use in all stations of the Doha Metro . [ 80 ] They are also found on the Lusail tram .
Platform screen doors shall be used on the future Cluj-Napoca Metro . [ citation needed ]
Park Pobedy (Russian: Парк Победы) is a station of the Saint Petersburg Metro that was the first station in the world with platform doors. The station was opened in 1961. Later, nine more stations of this type were built in Leningrad (nowadays Saint Petersburg ): Petrogradskaya (Russian: Петроградская), Vasileostrovskaya (Russian: Василеостровская), Gostiny Dvor (Russian: Гостиный двор), Mayakovskaya (Russian: Маяковская), Ploshchad Alexandra Nevskogo I (Russian: Площадь Александра Невского-1), Moskovskaya (Russian: Московская), Yelizarovskaya (Russian: Елизаровская), Lomonosovskaya (Russian: Ломоносовская), and Zvyozdnaya (Russian: Звёздная).
There was an electronic device to ensure that the train stopped with its doors adjacent to the platform doors; they were installed so that driverless trains could eventually be used on the lines. [ 81 ] Line 2 uses GoA2 automatic train operation to make this easier, however, Line 3 does not. Unlike other platform screen doors, which are lightweight units with extensive glazing installed on a normal platform edge, the St Petersburg units give the appearance of a solid wall with heavyweight doorways and solid steel sliding doors, similar to a bank of elevators in a large building, and the train cannot be seen entering from the platform; passengers become familiar with the sound alone to indicate a train arrival.
In May 2018, two other similar stations were opened: Novokrestovskaya (now Zenit) and Begovaya . Unlike the first ten stations that were built, these stations utilize glass screen doors, allowing the train to be seen entering from the platform, like most other systems. It is unclear why platform doors were installed here as they are absent in all other metros in Russia, the CIS (except that of Minsk, shown above), or the former Eastern bloc (excluding Sofia, also shown above, albeit on a line with equipment incompatible with that of the typical Eastern bloc metro).
The only other platform doors in Russia are found on the Sheremetyevo International Airport people mover.
The Al Mashaaer Al Mugaddassah Metro line in Mecca uses full platform screen doors. The Riyadh Metro which opened on 1 December 2024 uses full platform screen doors on all stations.
The future Belgrade Metro will have platform screen doors in some stations. [ citation needed ]
The Mass Rapid Transit (MRT) was the first rapid transit system in Asia to incorporate platform screen doors in its stations in 1987. [ 82 ] Full height PSDs mainly manufactured by Westinghouse are installed at all underground MRT and sub-surface stations, while half-height platform screen doors were retrofitted into all elevated stations by March 2012. The LRT stations at Bukit Panjang , Sengkang and Punggol lack physical doors, only barriers with openings where the doors go (excluding the now-closed Ten Mile Junction station , which had full height doors) and vary in size according to their location on the platform. [ citation needed ]
There are two variants of the full-height platform screen doors in use. The first variant, made by Westinghouse, was installed at all underground stations along the North South line and the East West line from 1987 to the completion of the initial system in 1990. The second variant incorporating more glass on the doors has since been used on all lines thereafter. [ citation needed ]
Considered a novelty at the time of its installation, platform screen doors were introduced primarily to minimise hefty air-conditioning costs, especially since elevated stations are not air-conditioned and are much more economical to run in comparison. [ 7 ] The safety aspects of these doors became more important in light of high-profile incidents where individuals were injured or killed by oncoming trains. [ 83 ] In 2008, authorities began the process of retrofitting existing elevated stations with half-height screen doors. [ 84 ] However, Land Transport Authority stated that the retrofit was not motivated by the need to make the stations safe, "but to prevent system-wide delay and service disruption and to reduce the social cost to all commuters caused by track intrusions." [ 85 ] The retrofit was completed in 2012. [ 86 ]
Yongdu station of Seoul Subway Line 2 was the first station on the Seoul Subway to feature platform screen doors; the station opened in October 2005. By the end of 2009, many of the 289 stations operated by Seoul Metro had platform doors by Hyundai Elevator. [ 87 ] Seoul Metro Lined 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 and 9 were equipped with platform screen doors. Most of the stations operated by Korail have completed installation, but some of the stations are not yet equipped with platform screen doors. All stations in South Korea (except for Dorasan Station ) will have platform screen doors by 2023. [ 88 ] [ needs update ] As of 2017, 100% of subway stations are equipped with platform screen doors in Daejeon , Gwangju , Busan , Incheon and Daegu . [ 89 ]
The platform screen doors, installed in Munyang station in Daegu Metro Line 2 by The Korea Transport Institute in 2013, have a unique rope-based platform screen named Rope type Platform Safety Door (RPSD). [ 90 ] A door sets of rope blocks separate the platform from the rails. When the train arrives, the rope screen door sets are vertically opened and allow passenger boarding to and from the train. This RPSD was also used in Nokdong station on Gwangju Metro Line 1 , but was removed in 2012, and a new full-height platform screen door was installed in 2016 instead.
Half platform screens were installed first in Provença FGC station (Barcelona) around 2003. Later doors were tested on Barcelona Metro line 11 before fitting them on all stations for the new lines 9 and 10 , which operate driverless. [ citation needed ] Platform screen doors were also trialed on four stations of line 12 (MetroSur) of the Madrid Metro from November 2009 until January 2010. [ 91 ] Platform doors are also found on the Madrid Barajas Airport People Mover at Adolfo Suárez Madrid–Barajas Airport and the Seville Metro line 1 light metro.
Stockholm commuter rail has platform doors on two underground stations opened in July 2017, as part of the Stockholm City Line . [ 92 ] The Stockholm Metro will test platform doors at Åkeshov metro station in 2015 and Bagarmossen metro station in 2021, the metro stations including Kungsträdgården metro station - Nacka Kungsträdgården metro station - Hagsätra metro station will have platform screen doors when it is completed between 2026 and 2030. [ 93 ] As there are multiple door layouts in use on the Stockholm Metro (a full-length C20 having 21 doors on each side, and the older Cx series and newer C30 having 24), it is unlikely platform doors will be common anytime soon. The underground Liseberg station in Gothenburg has platform doors which were built before its opening 1993. The reason was safety against the freight trains that go in this tunnel. These doors are built one meter from the platform edge and do therefore not restrict the train type.
Zurich International Airport 's Skymetro shuttle between the main building (hosting terminals A and B) and the detached terminal E has glass screen doors separating the tracks from the passenger hall platforms at both ends. Lausanne Metro's Line M2 has glass screen doors at every station, including a rare instance where platform doors are installed on a slanted surface, as the line was previously a funicular.
On Taipei Metro , platform screen doors were first installed on the Wenhu line (then known as Muzha line) in 1996. Older high-capacity MRT lines ( Tamsui Line , Xindian Line , Zhonghe Line , and the Bannan Line ) were initially constructed without platform screen doors but have now been retrofitted with automatic platform gates since 2018. Newer stations, on the Xinyi Line (part of the Tamsui-Xinyi Line) , Luzhou and Xinzhuang Line (part of the Zhonghe-Xinlu Line) , Songshan Line (part of the Songshan-Xindian Line) , Circular line , and part of the Bannan Line's Dingpu Station and Taipei Nangang Exhibition Center Station ) are constructed with platform screen doors. The Circular Line have installed platform screen doors since opening, but Danhai Light Rail did not, as is typical for most street railways to not have platform doors.
On Kaohsiung Metro , all underground stations have installed platform screen doors, while elevated stations did not. Daliao Station installed half-height platform screen doors in 2020.
On Taoyuan Metro and Taichung Metro , all elevated stations installed half-height platform screen doors while underground stations installed full-height platform screen doors.
Platform screen doors were first installed on the BTS Skytrain and Bangkok MRT Systems, followed by the Airport Rail Link System in Makkasan Station (Express Platform) and Suvarnabhumi Station (both City and Express Line platforms). BTS Skytrain system first installed the platform screen doors at Siam Station, later upgrading other busy stations. Today, almost all stations on the Bangkok Electrified Rail System have installed platform screen doors to prevent people from falling onto the tracks. The BTS Skytrain has installed PSDs at 18 out of its 44 stations. PSDs have been installed at all of the stations on the Purple and Blue Lines of the Bangkok MRT system. Airport Rail Link has installed a stainless steel barrier to prevent people from falling, but has not installed full-height doors due to concerns that the high speed of the trains could break the glass [ citation needed ] . All new stations in Bangkok must install platform screen doors.
Platform doors are found on Istanbul Metro lines M5 , M7 , M8 and M11, all fully driverless. Seyrantepe station on line M2 and F1, F3 and F4 also have platform doors.
Platform screen doors are installed on all the platforms in the fully automated Dubai Metro , as well as on the Dubai Airport People Mover , Palm Jumeirah Monorail and Dubai Tram (the world's first tram system to feature platform screen doors).
The Jubilee Line Extension project saw platform edge doors installed on its new stations that were underground, and were produced by Westinghouse. [ 94 ] There are plans to install PEDs in existing London Underground stations along the Bakerloo , Central , Piccadilly , and Waterloo & City lines as part of New Tube for London . [ 95 ] A provision for installing platform edge doors is found on the Northern line extension stations, but no doors were installed in the stations when they opened in 2021. [ 96 ]
PEDs are present on the Gatwick Airport shuttle system , Heathrow Airport Terminal 5 airside people-mover shuttle , Birmingham Airport AirRail Link , Stansted Airport Transit System and the Luton DART .
The Elizabeth line, the new cross-city line for London (delivered as the Crossrail Project) has platform screen doors on each of the sixteen sub-surface platforms of its central section. [ 97 ] Each platform has twenty-seven doors which align with the twenty-seven saloon doors of the new British Rail Class 345 which operates the service. The doors form a 2.5 m (8 ft 2 in) high glass and steel screen the entire length of the platform. The door opening is 2.1 m (6 ft 11 in) wide, and the system includes integrated passenger information and digital advertising screens. The system is unusual in that the trains served are full-sized commuter trains, larger and longer than the trains of metro systems more commonly equipped with platform screen doors. In total, some 4 km of platform screen is provided.
The Glasgow Subway will have half-height screen doors after new rolling stock are introduced in 2023. [ 98 ]
Platform screen doors are rare in the United States, and are nearly exclusively found on small-scale systems. Honolulu's Skyline , which began operations in June 2023, is the first and only large-scale publicly-run metro system in the country to feature platform screen doors, with platform gates at every station manufactured by Stanley Access Technologies . [ 99 ] They are also used by the general-purpose Las Vegas Monorail system.
New York City's Metropolitan Transportation Authority has not committed to installing platform screen doors in its subway system , though it had been considering such an idea since the 1980s. [ 100 ] Their installation presents substantial technical challenges, in part because of different placements of doors on New York City Subway rolling stock . [ 101 ] Additionally, the majority of the system cannot accommodate platform doors regardless of door locations, due to factors such as narrow platforms and structurally insufficient platform slabs (see Technology of the New York City Subway § Platform screen doors ). [ 102 ] [ 103 ] Following a series of incidents during one week in November 2016, in which three people were injured or killed after being pushed into tracks, the MTA started to consider installing platform edge doors for the 42nd Street Shuttle . [ 104 ] In October 2017, the MTA formally announced that platform screen doors would be installed at the Third Avenue station on the L train as part of a pilot program , [ 105 ] [ 106 ] but the pilot was later postponed. [ 107 ] Following several pushing incidents, the MTA announced a PSD pilot program at three stations in February 2022: the 7 and <7> trains' platform at Times Square ; the E train's platform at Sutphin Boulevard–Archer Avenue–JFK Airport ; and the Third Avenue station. [ 108 ] [ 109 ] The MTA started soliciting bids from platform-door manufacturers in mid-2022; [ 110 ] the doors are planned to be installed starting in December 2023 at a cost of $6 million. [ 111 ] Designs for the platform doors were being finalized by June 2023. [ 112 ] [ 113 ]
People movers , systems that ferry passengers across large distances they would otherwise walk, make use of platform screen doors. These systems are common at airports such as Hartsfield–Jackson Atlanta International Airport and Denver International Airport . The Port Authority of New York and New Jersey uses full height platform screen doors at two of its systems: AirTrain JFK and AirTrain Newark (serving John F. Kennedy International Airport and Newark Liberty International Airport respectively). San Francisco International Airport has AirTrain , a 6-mile-long line whose stations are fully enclosed with platform screen doors, allowing access to the fully automated people mover. [ citation needed ] Chicago O'Hare International Airport has a people mover system which operates 24 hours a day and is a 2.5 mile long (4 km) line that operates between the four terminals at the airport and parking areas; each station is fully enclosed with platform screen doors allowing access to the fully automated people mover trains. AeroTrain is a 3.78-mile (6.08 km) people mover system at Washington Dulles International Airport in Dulles, Virginia , with fully enclosed tracks including platform screen doors. The United States Capitol subway system , a train cart people mover system, uses platform gates.
Platform screen doors are in use on the Los Teques Metro . The first station to have screen doors implemented on the system was Guaicaipuro. [ 114 ]
Platform screen doors are currently used on the Ho Chi Minh City Metro , with full-height doors for underground stations and half-height doors for above-ground stations. [ citation needed ]
On the Shanghai Metro in 2007, a man forcing his way onto a crowded train became trapped between the train door and platform door as they closed. He was pulled under the departing train and killed. [ 115 ] In 2010, a woman in Shanghai's Zhongshan Park Station was killed [ 116 ] under the same circumstances when she got trapped between the train and platform doors. An almost identical death occurred on the Beijing Subway in 2014—the third death involving platform doors in China within the several years preceding it. [ 117 ] [ 118 ] In 2018, a woman was similarly trapped between the platform doors and train at Shanghai's Bao'an Highway station . She escaped injury by standing still as the train departed. [ 119 ] On 22 January 2022, an elderly woman was killed when she got trapped between the train doors and platform screen doors at Shanghai's Qi'an Road Station . [ 120 ]
Between 1999 and 2012, London Underground 's platform doors, all on the Jubilee line , were the cause of 75 injuries including strikes to people's heads and arms. [ 121 ] | https://en.wikipedia.org/wiki/Platform_screen_doors |
A platform supply vessel ( PSV ) is a ship specially designed to supply offshore oil and gas platforms and other offshore installations. [ 1 ] They typically range from 50 to 100 metres (160 to 330 ft) in length and are distinguished by the large open deck area used to store supplies and house equipment and to allow for efficient loading and offloading. The primary function for most of these vessels is logistic support and transportation of goods, tools, equipment, and personnel to and from their destination.
They belong to the broad category of offshore vessels (OSVs) which includes Service Operation Vessels (SOVs), Construction Support Vessels (CSVs), well stimulation vessels (WSVs) and anchor handling tug supply vessels (AHTSVs).
A primary function of a platform supply vessel is to transport supplies to the oil platform and return other cargoes to shore. Cargo tanks for drilling mud , pulverized cement, diesel fuel, potable and non-potable water, and chemicals used in the drilling process comprise the bulk of the cargo spaces. Fuel, water, and chemicals are almost always required by oil platforms. Certain other chemicals must be returned to shore for proper recycling or disposal, however, crude oil product from the rig is usually not a supply vessel cargo.
Dynamic positioning (DP) is a computerised system which allows vessels to maintain a certain position or heading by controlling the thrust produced by the vessel's thrusters and propellers. As with most offshore vessels , DP is of critical importance to ensure that the vessel's position is maintained whilst loading or offloading is taking place; this is especially needed for locations with frequent severe weather conditions such as the North Sea.
A typical DP set-up for a PSV is two thrusters located at the bow of the vessel which can be supplemented by two azimuth thrusters or Voith Schneider Propellers located at the stern. All modern PSVs are DP2 rated, meaning that there are two levels of redundancy in the DP system.
Common and specialty tools are carried on the large decks of these vessels. Most carry a combination of deck cargoes and bulk cargo in tanks below deck. Many ships are constructed (or re-fitted) to accomplish a particular job. Some of these vessels are equipped with a firefighting capability and fire monitors for fighting platform fires. Some vessels are equipped with oil containment and recovery equipment to assist in the cleanup of a spill at sea. Equipment for receiving drill cuttings may also be installed on deck.
Crew on these ships can number up to 50 crew members, depending on vessel size and working requirements. One example of a crew size of 13 consists of 4 deck officers (including Captain) working shifts in pairs, 4 Able Seamen working in pairs, 3 Engineers , 1 ETO (Electro-Technical Officer), and 1 Steward. The crew may also include Cadets.
Crews sign on to work and live aboard the ship an extended period of time, this is followed by similar period of time off. Depending on the ship's owner or operator the time aboard varies from 1 to 3 months with 1 month off. Work details on platform supply vessels, like many ships, are organized into shifts of up to 12 hours.
Living aboard the ship, each crew member and worker will have at least a 12-hour shift, lasting some portion of a 24-hour day. Supply vessels are provided with a "bridge" area for navigating and operating the ship, machinery spaces, living quarters, and galley and mess room. Some have built-in work areas and common areas for entertainment. The large main deck area is sometimes utilized for portable housing.
Living quarters consist of cabins, lockers, offices, and spaces for storing personal items. Living areas are provided with wash basins, showers, and toilets.
The galley or cooking and eating areas aboard ship will be stocked with enough grocery items to last for the intended voyage but with the ability also to store provisions for months if required. A walk-in size cooler and freezer, a commercial stove and oven, deep sinks, storage and counter space will be available for the persons doing the cooking. The eating area will have coffee makers, toasters, microwave ovens, cafeteria-style seating, and other amenities needed to feed a hard-working crew. | https://en.wikipedia.org/wiki/Platform_supply_vessel |
Plating is a finishing process in which a metal is deposited on a surface. Plating has been done for hundreds of years; it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solderability, to harden, to improve wearability, to reduce friction, to improve paint adhesion, to alter conductivity, to improve IR reflectivity, for radiation shielding, and for other purposes. Jewelry typically uses plating to give a silver or gold finish.
Thin-film deposition has plated objects as small as an atom, [ 1 ] therefore plating finds uses in nanotechnology .
There are several plating methods, and many variations. In one method, a solid surface is covered with a metal sheet, and then heat and pressure are applied to fuse them (a version of this is Sheffield plate ). Other plating techniques include electroplating , vapor deposition under vacuum and sputter deposition . Recently, plating often refers to using liquids. Metallizing refers to coating metal on non-metallic objects.
In electroplating, an ionic metal is supplied with electrons to form a non-ionic coating on a substrate . A common system involves a chemical solution with the ionic form of the metal, an anode (positively charged) which may consist of the metal being plated (a soluble anode) or an insoluble anode (usually carbon, platinum, titanium, lead, or steel), and finally, a cathode (negatively charged) where electrons are supplied to produce a film of non-ionic metal.
Electroless deposition , also known as chemical or auto- catalytic plating, is a non- galvanic plating method that involves several simultaneous reactions in an aqueous solution , which occur without the use of external electrical power. The reaction is accomplished when hydrogen is released by a reducing agent, normally sodium hypophosphite (Note: the hydrogen leaves as a hydride ion) or thiourea , and oxidized, thus producing a negative charge on the surface of the part. The most common electroless deposition method is electroless nickel plating , although silver, gold and copper layers can also be applied in this manner, as in the technique of angel gilding .
Gold plating is a method of depositing a thin layer of gold on the surface of glass or metal, most often copper or silver.
Gold plating is often used in electronics, to provide a corrosion -resistant electrically conductive layer on copper, typically in electrical connectors and printed circuit boards . With direct gold-on-copper plating, the copper atoms have the tendency to diffuse through the gold layer, causing tarnishing of its surface and formation of an oxide/sulfide layer. Therefore, a layer of a suitable barrier metal , usually nickel, has to be deposited on the copper substrate, forming a copper-nickel-gold sandwich.
Metals and glass may also be coated with gold for ornamental purposes, using a number of different processes usually referred to as gilding .
Sapphires, plastics, and carbon fiber are some other materials that are able to be plated using advance plating techniques. The substrates that can be used are almost limitless. [ 2 ]
Silver plating has been used since the 18th century to provide cheaper versions of household items that would otherwise be made of solid silver, including cutlery , vessels of various kinds, and candlesticks. In the UK the assay offices , and silver dealers and collectors, use the term "silver plate" for items made from solid silver, derived long before silver plating was invented from the Spanish word for silver "plata", seizures of silver from Spanish ships carrying silver from America being a large source of silver at the time. This can cause confusion when talking about silver items; plate or plated. In the UK it is illegal to describe silver-plated items as "silver". It is not illegal to describe silver-plated items as "silver plate", although this is ungrammatical.
The earliest form of silver plating was Sheffield Plate , where thin sheets of silver are fused to a layer or core of base metal, but in the 19th century new methods of production (including electroplating) were introduced. Britannia metal is an alloy of tin, antimony and copper developed as a base metal for plating with silver.
Another method that can be used to apply a thin layer of silver to objects such as glass, is to place Tollens' reagent in a glass, add glucose/dextrose, and shake the bottle to promote the reaction.
For applications in electronics, silver is sometimes used for plating copper, as its electrical resistance is lower (see Resistivity of various materials ); more so at higher frequencies due to the skin effect . Variable capacitors are considered of the highest quality when they have silver-plated plates. Similarly, silver-plated, or even solid silver cables, are prized in audiophile applications; however some experts consider that in practice the plating is often poorly implemented, making the result inferior to similarly priced copper cables. [ 3 ]
Care should be used for parts exposed to high humidity environments because in such environments, when the silver layer is porous or contains cracks, the underlying copper undergoes rapid galvanic corrosion , flaking off the plating and exposing the copper itself; a process known as red plague . Silver plated copper maintained in a moisture-free environment will not undergo this type of corrosion.
Copper plating is the process of electrolytically forming a layer of copper on the surface of an item. It is commonly used as an even cheaper alternative to silver plating as it is much cheaper than silver.
Rhodium plating is occasionally used on white gold, silver or copper and its alloys. A barrier layer of nickel is usually deposited on silver first, though in this case it is not to prevent migration of silver through rhodium, but to prevent contamination of the rhodium bath with silver and copper, which slightly dissolve in the sulfuric acid usually present in the bath composition. [ 4 ]
Chrome plating is a finishing treatment using the electrolytic deposition of chromium . The most common form of chrome plating is the thin, decorative bright chrome , which is typically a 10- μm layer over an underlying nickel plate. When plating on iron or steel, an underlying plating of copper allows the nickel to adhere. The pores (tiny holes) in the nickel and chromium layers work to alleviate stress caused by thermal expansion mismatch but also hurt the corrosion resistance of the coating. Corrosion resistance relies on what is called the passivation layer , which is determined by the chemical composition and processing, and is damaged by cracks and pores. In a special case, micropores can help distribute the electrochemical potential that accelerates galvanic corrosion between the layers of nickel and chromium. Depending on the application, coatings of different thicknesses will require different balances of the aforementioned properties. Thin, bright chrome imparts a mirror -like finish to items such as metal furniture frames and automotive trim. Thicker deposits, up to 1000 μm, are called hard chrome and are used in industrial equipment to reduce friction and wear.
The traditional solution used for industrial hard chrome plating is made up of about 250 g/L of CrO 3 and about 2.5 g/L of SO 4 − . In solution, the chrome exists as chromic acid, known as hexavalent chromium . A high current is used, in part to stabilize a thin layer of chromium(+2) at the surface of the plated work. Acid chrome has poor throwing power, fine details or holes are further away and receive less current resulting in poor plating.
Zinc coatings prevent oxidation of the protected metal by forming a barrier and by acting as a sacrificial anode if this barrier is damaged. Zinc oxide is a fine white dust that (in contrast to iron oxide ) does not cause a breakdown of the substrate's surface integrity as it is formed. Indeed, the zinc oxide, if undisturbed, can act as a barrier to further oxidation, in a way similar to the protection afforded to aluminum and stainless steels by their oxide layers. The majority of hardware parts are zinc-plated, rather than cadmium-plated . [ 5 ]
Zinc-nickel plating is one of the best corrosion resistant finishes available offering over 5 times the protection of conventional zinc plating and up to 1,500 hours of neutral salt spray test performance. This plating is a combination of a high-nickel zinc-nickel alloy (10–15% nickel) and some variation of chromate. The most common mixed chromates include hexavalent iridescent, trivalent or black trivalent chromate. Used to protect steel, cast iron, brass, copper, and other materials, this acidic plating is an environmentally safe option. [ 6 ] Hexavalent chromate has been classified as a human carcinogen by the EPA and OSHA. [ 7 ] [ 8 ]
The tin -plating process is used extensively to protect both ferrous and nonferrous surfaces. Tin is a useful metal for the food processing industry since it is non-toxic, ductile and corrosion resistant. The excellent ductility of tin allows a tin coated base metal sheet to be formed into a variety of shapes without damage to the surface tin layer. It provides sacrificial protection for copper, nickel and other non-ferrous metals, but not for steel .
Tin is also widely used in the electronics industry because of its ability to protect the base metal from oxidation thus preserving its solderability. In electronic applications, 3% to 7% lead may be added to improve solderability and to prevent the growth of metallic "whiskers" in compression stressed deposits, which would otherwise cause electrical shorting. However, RoHS (Restriction of Hazardous Substances) regulations enacted beginning in 2006 require that no lead be added intentionally and that the maximum percentage not exceed 1%. Some exemptions have been issued to RoHS requirements in critical electronics applications due to failures which are known to have occurred as a result of tin whisker formation.
In some cases, it is desirable to co-deposit two or more metals resulting in an electroplated alloy deposit. Depending on the alloy system, an electroplated alloy may be solid solution strengthened or precipitation hardened by heat treatment to improve the plating's physical and chemical properties. Nickel-Cobalt is a common electroplated alloy.
Metal matrix composite plating can be manufactured when a substrate is plated in a bath containing a suspension of ceramic particles. Careful selection of the size and composition of the particles can fine-tune the deposit for wear resistance, high temperature performance, or mechanical strength. Tungsten carbide , silicon carbide , chromium carbide , and aluminum oxide (alumina) are commonly used in composite electroplating.
Cadmium plating is under scrutiny because of the environmental toxicity of the cadmium metal. Cadmium plating is widely used in some applications in the aerospace, military, and aviation fields. However, it is being phased out due to its toxicity. [ 9 ] Military and Aerospace components manufacturers, such as Amphenol Aerospace , have recently been exploring drop-in electroplating replacements for use with currently fielded equipment in order to support the phaseout of the dangerous finish. [ 10 ]
Cadmium plating (or cad. plating ) offers a long list of technical advantages such as excellent corrosion resistance even at relatively low thickness and in salt atmospheres, softness and malleability , freedom from sticky and/or bulky corrosion products, galvanic compatibility with aluminum, freedom from stick-slip thus allowing reliable torquing of plated threads, can be dyed to many colors and clear, has good lubricity and solderability, and works well either as a final finish or as a paint base. [ 5 ] [ 11 ]
If environmental concerns matter, in most aspects cadmium plating can be directly replaced with gold plating as it shares most of the material properties, but gold is more expensive and cannot serve as a paint base.
Nickel is electroplated by using a Watts bath , an electrolytic cell having a nickel anode and electrolyte containing nickel sulfate , nickel chloride , and boric acid . [ 12 ] Other nickel salts such as nickel ammonium sulfate are sometimes used instead of nickel sulfate.
Electroless nickel plating, also known as enickel and NiP , offers many advantages: uniform layer thickness over most complicated surfaces, direct plating of ferrous metals (steel), superior wear and corrosion resistance compared to electroplated nickel or chrome. Much of the chrome plating done in aerospace industry can be replaced with electroless nickel plating, again environmental costs, costs of hexavalent chromium waste disposal and notorious tendency of uneven current distribution favor electroless nickel plating. [ 13 ]
Electroless nickel plating is self-catalyzing process, the resultant nickel layer is NiP compound, with 7–11% phosphorus content. Properties of the resultant layer hardness and wear resistance are greatly altered with bath composition and deposition temperature, which should be regulated with 1 °C precision, typically at 91 °C.
During bath circulation, any particles in it will become also nickel-plated; this effect is used to advantage in processes which deposit plating with particles like silicon carbide (SiC) or polytetrafluoroethylene (PTFE). While superior compared to many other plating processes, it is expensive because the process is complex. Moreover, the process is lengthy even for thin layers. When only corrosion resistance or surface treatment is of concern, very strict bath composition and temperature control is not required and the process is used for plating many tons in one bath at once.
Electroless nickel plating layers are known to provide extreme surface adhesion when plated properly. Electroless nickel plating is non-magnetic and amorphous. Electroless nickel plating layers are not easily solderable, nor do they seize with other metals or another electroless nickel-plated workpiece under pressure. This effect benefits electroless nickel-plated screws made out of malleable materials like titanium. Electrical resistance is higher compared to pure metal plating.
"Aluminum plating" can refer to either plating on aluminum [ 14 ] or the plating of aluminum on other materials. [ 15 ] | https://en.wikipedia.org/wiki/Plating |
Platinum-195 nuclear magnetic resonance spectroscopy ( platinum NMR or 195 Pt NMR ) is a spectroscopic technique which is used for the detection and characterisation of platinum compounds . The sensitivity of the technique and therefore its diagnostic utility have increased significantly starting from the 1970s, with 195 Pt NMR nowadays considered the method of choice for structural elucidation of Pt species in solution. [ 1 ] [ 2 ] [ 3 ]
Examples of compounds routinely characterised with the method include platinum clusters and organoplatinum species such as Pt II -based antitumour agents. [ 2 ] [ 3 ] Additional applications of 195 Pt NMR include kinetic and mechanistic studies or investigations on drug binding . [ 2 ]
Among the naturally occurring isotopes of platinum , 195 Pt is the most abundant (33.8%) and the only one with non-zero spin I =1/2. [ 1 ] [ 2 ] [ 3 ] The magnetic properties of the nucleus are considered favourable; the high natural abundance coupled with a medium gyromagnetic ratio (5.768×10 7 rad T −1 s −1 ) result in good 195 Pt NMR signal receptivity , 19 times that of 13 C (but still only 0.0034 times that of 1 H ). [ 2 ] [ 3 ]
The resonance frequency (relative to a 100 MHz 1 H NMR instrument) is approximately 21.4 MHz, close to the 13 C resonance at 25.1 MHz. [ 1 ] [ 2 ]
The chemical shifts of 195 Pt nuclei span a very large range of over 13000 ppm ( cf . with ~300 ppm range for 13 C). [ 1 ] [ 2 ] [ 3 ] The NMR signals are also very sharp and highly sensitive to the platinum chemical environment ( oxidation state , ligand identity and field strength , coordination number , etc.). [ 1 ] [ 3 ] Therefore, substituting even very similar ligands can result in shift changes in the order of hundreds of ppm which stand out on the spectrum and are easily monitored. [ 2 ] [ 3 ]
The reference compound typically chosen for 195 Pt NMR experiments is 1.2 M sodium hexachloroplatinate(IV) (Na 2 PtCl 6 ) in D 2 O ; this platinum(IV) complex is preferred due to its commercial availability, chemical stability, lower price relative to other platinum compounds, and high solubility which enables spectrum recording within minutes. [ 2 ] [ 3 ] Less soluble ionic platinum complexes have spectrum recording times of about an hour, whereas the borderline insoluble neutral complexes may require overnight measurements. [ 3 ]
The high sensitivity of the experiment means that contributions from different chlorine isotopes in the reference compound or other species can be resolved at high magnetic field strengths, giving a ±5 ppm uncertainty in reported shift values (which is, however, negligible in view of the 13000 ppm overall range). [ 1 ]
L: NR 3 , PR 3 , SR 2 )
Coupling of 195 Pt to 1 H, 13 C, 31 P, 19 F or 15 N has been reported through one up to four bonds ( 1 J to 4 J ) and is commonly studied to provide additional structural information for platinum complexes. [ 2 ] [ 3 ] The ~34% abundance of 195 Pt (with the remaining 66% of natural Pt being NMR-inactive) means that this coupling appears in the respective 1 H/ 31 P/ 15 N/ 13 C NMR spectra as satellite peaks ( cf. 13 C satellites ) which, for example, result in 17:66:17 patterns for singlets. [ 3 ]
The trans influence in 16 e − square planar Pt II complexes has been studied by comparing the magnitude of coupling constants in the cis - and trans - isomers. [ 2 ] [ 3 ]
Complicated homonuclear couplings ranging from 60 to 9000 Hz for 1 J ( 195 Pt– 195 Pt) are of interest in the context of platinum cluster compounds. [ 3 ] | https://en.wikipedia.org/wiki/Platinum-195_nuclear_magnetic_resonance |
Platinum-based antineoplastic drugs (informally called platins ) are chemotherapeutic agents used to treat cancer . Their active moieties are coordination complexes of platinum . These drugs are used to treat almost half of people receiving chemotherapy for cancer. In this form of chemotherapy , commonly used drugs include cisplatin , oxaliplatin , and carboplatin , but several have been proposed or are under development. [ 1 ] Addition of platinum-based chemotherapy drugs to chemoradiation in women with early cervical cancer seems to improve survival and reduce risk of recurrence. [ 2 ]
In total, these drugs can cause a combination of more than 40 specific side effects which include neurotoxicity , which is manifested by peripheral neuropathies including polyneuropathy . [ 3 ]
As studied mainly on cisplatin, but presumably for other members as well, platinum-based antineoplastic agents cause crosslinking of DNA as monoadduct, interstrand crosslinks, intrastrand crosslinks or DNA protein crosslinks. Mostly they act on the adjacent N-7 position of guanine , forming a 1, 2 intrastrand crosslink. [ 4 ] [ 5 ] The resultant crosslinking inhibits DNA repair and/or DNA synthesis . This mechanism leads to specific patterns of damage in DNA, which can kill cancer cells but can also increase the risk of secondary tumors developing. [ 6 ]
Platinum-based antineoplastic agents are sometimes described as "alkylating-like" due to similar effects as alkylating antineoplastic agents , although they do not have an alkyl group. [ 7 ]
Strategies for improving platinum-based anticancer drugs usually involve changes in the neutral spectator ligands , changes in the nature of the anions (halides vs various carboxylates), or changes in the oxidation state of the metal (Pt(II) vs Pt(IV)). Nanotechnology has been explored to deliver platinum more efficiently in the case of lipoplatin , which is introduced into the tumor sites thereby reducing the chance of toxicity. [ 8 ]
Cisplatin was the first to be developed. [ 9 ] Cisplatin is particularly effective against testicular cancer ; the cure rate was improved from 10% to 85%. [ 10 ] Similarly, the addition of cisplatin to adjuvant chemotherapy led to a marked increase in disease-free survival rates for patients with medulloblastoma - again, up to around 85%. [ 11 ] This application of cisplatin was developed by pediatric oncologist Roger Packer in the early 1980s. [ 12 ] | https://en.wikipedia.org/wiki/Platinum-based_antineoplastic |
Platinum silicide , also known as platinum monosilicide, is the inorganic compound with the formula PtSi. It is a semiconductor that turns into a superconductor when cooled to 0.8 K. [ 3 ]
The crystal structure of PtSi is orthorhombic, with each silicon atom having six neighboring platinum atoms. The distances between the silicon and the platinum neighbors are as follows: one at a distance of 2.41 angstroms , two at a distance of 2.43 angstroms, one at a distance of 2.52 angstroms, and the final two at a distance of 2.64 angstroms. Each platinum atom has six silicon neighbors at the same distances, as well as two platinum neighbors, at a distance of 2.87 and 2.90 angstroms. All of the distances over 2.50 angstroms are considered too far to really be involved in bonding interactions of the compound. As a result, it has been shown that two sets of covalent bonds compose the bonds forming the compound. One set is the three center Pt–Si–Pt bond, and the other set the two center Pt–Si bonds. Each silicon atom in the compound has one three center bond and two center bonds. The thinnest film of PtSi would consist of two alternating planes of atoms, a single sheet of orthorhombic structures. Thicker layers are formed by stacking pairs of the alternating sheets. The mechanism of bonding between PtSi is more similar to that of pure silicon than pure platinum or Pt 2 Si , though experimentation has revealed metallic bonding character in PtSi that pure silicon lacks. [ 4 ]
PtSi can be synthesized in several ways. The standard method involves depositing a thin film of pure platinum onto silicon wafers and heating in a conventional furnace at 450–600 °C for a half an hour in inert ambients. The process cannot be carried out in an oxygenated environment, as this results in the formation of an oxide layer on the silicon, preventing PtSi from forming. [ 5 ]
A secondary technique for synthesis requires a sputtered platinum film deposited on a silicon substrate. Due to the ease with which PtSi can become contaminated by oxygen, several variations of the methods have been reported. Rapid thermal processing has been shown to increase the purity of PtSi layers formed. [ 6 ] Lower temperatures (200–450 °C) were also found to be successful, [ 7 ] higher temperatures produce thicker PtSi layers, though temperatures in excess of 950 °C formed PtSi with increased resistivity due to clusters of large PtSi grains. [ 8 ]
Despite the synthesis method employed, PtSi forms in the same way. When pure platinum is first heated with silicon, Pt 2 Si is formed. Once all the available Pt and Si are used and the only available surfaces are Pt 2 Si , the silicide will begin the slower reaction of converting into PtSi. The activation energy for the Pt 2 Si reaction is around 1.38 eV, while it is 1.67 eV for PtSi.
Oxygen is extremely detrimental to the reaction, as it will bind preferably to Pt, limiting the sites available for Pt–Si bonding and preventing the silicide formation. A partial pressure of O 2 as low at 10 −7 has been found to be sufficient to slow the formation of the silicide. To avoid this issue inert ambients are used, as well as small annealing chambers to minimize amount of potential contamination. [ 5 ] The cleanliness of the metal film is also extremely important, and unclean conditions result in poor PtSi synthesis. [ 7 ]
In certain cases an oxide layer can be beneficial. When PtSi is used as a Schottky barrier , an oxide layer prevents wear of the PtSi. [ 5 ]
PtSi is a semiconductor and a Schottky barrier with high stability and good sensitivity, and can be used in infrared detection , thermal imaging , or ohmic and Schottky contacts. [ 9 ] Platinum silicide was most widely studied and used in the 1980s and 90s, but has become less commonly used, due to its low quantum efficiency . PtSi is now most commonly used in infrared detectors , due to the large size of wavelengths it can be used to detect. [ 10 ] It has also been used in detectors for infrared astronomy . It can operate with good stability up to 0.05 °C. Platinum silicide offers high uniformity of arrays imaged. The low cost and stability makes it suited for preventative maintenance and scientific infrared imaging . | https://en.wikipedia.org/wiki/Platinum_silicide |
Platinum-samarium is a binary inorganic compound of platinum and samarium with the chemical formula PtSm. [ 1 ] This intermetallic compound forms crystals.
Fusion of stoichiometric amounts of pure substances:
Platinum-samarium forms crystals of rhombic crystal system , space group P nma , cell parameters a = 0.7148 nm, b = 0.4501 nm, c = 0.5638 nm, Z = 4, structure similar to that of iron boride (FeB).
The compound melts congruently at a temperature of ≈1810 °C. [ 2 ] | https://en.wikipedia.org/wiki/Platinum–samarium |
In organic chemistry , a Platonic hydrocarbon is a hydrocarbon whose structure matches one of the five Platonic solids , with carbon atoms replacing its vertices, carbon–carbon bonds replacing its edges, and hydrogen atoms as needed. [ 1 ] [ page needed ]
Not all Platonic solids have molecular hydrocarbon counterparts; those that do are the tetrahedron ( tetrahedrane ), the cube ( cubane ), and the dodecahedron ( dodecahedrane ). The possibility and existence of each platonic hydrocarbon is affected by the number of bonds to each carbon vertex and the angle strain between the bonds at each vertex.
Tetrahedrane (C 4 H 4 ) is a hypothetical compound . It has not yet been synthesized without substituents , but it is predicted to be kinetically stable in spite of its angle strain. Some stable derivatives , including tetra( tert -butyl )tetrahedrane and tetra( trimethylsilyl )tetrahedrane, have been produced.
Cubane (C 8 H 8 ) has been synthesized. Although it has high angle strain, cubane is kinetically stable , due to a lack of readily available decomposition paths.
Angle strain would make an octahedron highly unstable due to inverted tetrahedral geometry at each vertex. There would also be no hydrogen atoms because four edges meet at each corner; thus, the hypothetical octahedrane molecule, with a molecular formula of C 6 , would be an allotrope of elemental carbon rather than a hydrocarbon. The existence of octahedrane cannot be ruled out completely, although calculations have shown that it is unlikely. [ 2 ]
Dodecahedrane (C 20 H 20 ) was first synthesized in 1982, and has minimal angle strain; the tetrahedral angle is 109.5° and the dodecahedral angle is 108°, only a slight discrepancy. [ 3 ]
The tetravalency (4-connectedness) of carbon excludes an icosahedron because 5 edges meet at each vertex. True pentavalent carbon is unlikely; methanium , nominally CH + 5 , usually exists as CH 3 (H 2 ) + . The hypothetical icosahedral C 12+ 12 lacks hydrogen so it is not a hydrocarbon; it is also an ion.
Both icosahedral and octahedral structures have been observed in boron compounds [ 2 ] such as the dodecaborate ion and some of the carbon-containing carboranes .
Increasing the number of atoms that comprise the carbon skeleton leads to a geometry that increasingly approximates a sphere, and the space enclosed in the carbon "cage" increases. This trend continues with buckyballs or spherical fullerene (C 60 ). Although not a Platonic hydrocarbon, buckminsterfullerene has the shape of a truncated icosahedron , an Archimedean solid .
The concept can also be extended to regular Euclidean tilings, with the hexagonal tiling producing graphane . A square tiling (which would resemble an infinitely large fenestrane ) would suffer from the same problem as octahedrane, and the triangular tiling icosahedrane. No generalisations to hyperbolic tilings seem to be known.
The regular convex 4-polytopes may also have hydrocarbon analogues; hypercubane has been proposed. | https://en.wikipedia.org/wiki/Platonic_hydrocarbon |
Platynereis dumerilii is a species of annelid polychaete worm. [ 3 ] It was originally placed into the genus Nereis [ 1 ] and later reassigned to the genus Platynereis . [ 4 ] Platynereis dumerilii lives in coastal marine waters from temperate to tropical zones. It can be found in a wide range from the Azores , the Mediterranean , in the North Sea , the English Channel , and the Atlantic down to the Cape of Good Hope , in the Black Sea , the Red Sea , the Persian Gulf , the Sea of Japan , the Pacific , and the Kerguelen Islands . [ 4 ] Platynereis dumerilii is today an important lab animal, [ 5 ] it is considered a living fossil , [ 6 ] [ 7 ] [ 8 ] and it is used in many phylogenetic studies as a model organism.
Platynereis dumerilii is a small marine ragworm : Males reach a length of 2 to 3 cm, while females reach a length of 3 to 4 cm. [ 9 ] Like a number of invertebrate phyla, Platynereis dumerilii has an axochord, a paired longitudinal muscle that displays striking similarities to the notochord regarding position, developmental origin, and expression profile. [ 10 ] Its early trochophore larva has a pair of the simplest eyes in the animal kingdom, each eye consists only of a photoreceptor cell and a pigment cell . [ 11 ]
P. dumerilii worms have a ciliated surface which beats synchronously to drive locomotion and fluid flow. Larvae have segmental multiciliated cells that regularly display spontaneous coordinated ciliary arrests, which compose the ciliomotor circuitry in the worms. Whole-body coordination of ciliary locomotion is performed by a "stop-and-go pacemaker system". [ 12 ]
As the worms develop, they use chaetae , and then parapodia , for locomotion. Unlike other polychaetes, in Platynereis larvae, the parapodia are used only for navigation while the cilia are responsible for propulsive force. [ 2 ]
Platynereis dumerilii larvae possess two kinds of photoreceptor cells : Rhabdomeric and ciliary photoreceptor cells.
The ciliary photoreceptor cells are located in the deep brain of the larva. They are not shaded by pigment and thus perceive non-directional light. The ciliary photoreceptor cells resemble molecularly and morphologically the rods and cones of the human eye . Additional, they express an ciliary opsin that is more similar to the visual ciliary opsins of vertebrate rods and cones than to the visual rhabdomeric opsins of invertebrates. Therefore, it is thought that the urbilaterian , the last common ancestor of mollusks , arthropods , and vertebrates already had ciliary photoreceptor cells. [ 13 ] The ciliary opsin is UV -sensitive ( λ max = 383 nm), [ 14 ] and the ciliary photoreceptor cells react on non-directional UV-light by making the larvae swimming down. This forms a ratio-chromatic depth-gauge with phototaxis of the rhabdomeric photoreceptor cells of the eyes. [ 15 ]
A rhabdomeric photoreceptor cell forms with a pigment cell a simple eye. [ 16 ] A pair of these eyes mediate phototaxis in the early Platynereis dumerilii trochophore larva. [ 11 ] In the later nectochaete larva, phototaxis is mediated by the more complex adult eyes. [ 17 ] The adult eyes express at least three opsins: Two rhabdomeric opsins and a Go-opsin. [ 18 ] [ 19 ] The three opsins there mediate phototaxis all the same way via depolarization, [ 19 ] even so a scallop Go-opsin is known to hyperpolarize . [ 20 ] [ 21 ]
P. dumerilii senses chemicals with four types of organs: The antennae , the palps, the nuchal organs , and the tentacular cirri . These organs detect food and chemical cues such as alcohols, esters, amino acids, and sugars. [ 22 ]
Among the four types, the antennae are the primary chemosensory organs and sense a broad range of chemicals, while the palps are specialized on taste, which means they detect food-related chemicals. The cirri are thin thread-like head appendages and are specialized in tactile sensation, but can also give spatial information from were a chemical cue is coming, since a single stimulus can elicit in the left and right cirrus a response at a different times. [ 22 ] The cirri also sense light: When they are shaded, the worm retreats rapidly into its tube to protect them. This behavior is called a shadow reflex. [ 23 ] The nuchal organ is a singular ciliated pit in P. dumerilii . Among annelids, nuchal organs are conserved and seem to have an important chemosensory function. However, what their exact function is, is still unclear. [ 22 ]
The signals from the four chemosensory organs are processed in a lateral region and in the mushroom bodies . [ 22 ] The mushroom bodies in annelids resemble those in insects by anatomy, morphology and gene expression. So probably, annelids and insects inherited mushroom bodies from their last common ancestor. [ 24 ]
Platynereis dumerilii builds tubes on its substrate . The substrate may be algae-covered hard bottoms, [ 25 ] sea grass , [ 26 ] [ 27 ] pelagic Sargassum rafts in the Sargasso Sea , [ 28 ] [ 29 ] or even rotting plant debris. [ 30 ] Platynereis dumerilii commonly lives in depths of 0 to 5 meters, [ 31 ] [ 32 ] [ 26 ] [ 25 ] and so is typical for shallow bright infra- littoral environments. [ 31 ] However, it has been also found on a buoy at 50 meters [ 33 ] and on rotting seaweed at 100 m. [ 34 ] It may also live in less favorable environments, like at thermal vents [ 35 ] [ 36 ] or polluted areas near sewer outfall pipes . [ 37 ] It dominates polluted areas [ 38 ] [ 39 ] and acidic areas with pH values around 6.5 [ 40 ] fitting the preferred pH value of a subpopulation of late Platynereis dumerilii nectochaete larvae. [ 41 ] Larvae feed on plankton, and migrate vertically in the ocean in response to changes in light, causing a daily transport of biomass . [ 42 ]
Platynereis dumerilii is dioecious , that means it has two separate sexes . [ 43 ] Changes in light are importantly linked to reproduction. The bristle worm is originally found in the Bay of Naples , where it displays reproductive synchrony . The adult worms rise en masse to the water surface a few days after the full moon, during a one- to two-hour dark portion of the night between sunset and moonrise. In the worm’s natural environment, it is important to synchronize spawning to increase the potential for gametes to meet and fertilize. By detecting nighttime lighting in accordance with the lunar cycle, the worms synchronize reproductive activity. Worms that make L-Cry protein are better able to detect appropriate light conditions and synchronize the release of gametes. In addition, the molecule r-Opsin is extremely sensitive to light, and appears to help detect moonrise. Some combination of signals from r-Opsin and L-Cry is believed to help the worms to coordinate rising at a common time to spawn. [ 44 ] [ 45 ] [ 46 ]
During mating , the male swims around the female while the female is swimming in small circles. Both release eggs and sperm into the water. This release is triggered by sexual pheromones . The eggs are then fertilized outside of the body in the water. [ 47 ] Like other Nereidids, Platynereis dumerilii has no segmental gonades, the oocytes mature freely swimming in the body cavity ( coelom ), [ 43 ] and stain the body of the mature female epitoke yellow. [ 2 ]
Platynereis dumerilii develops very stereotypically between batches and therefore time can be used to stage Platynereis dumerilii larvae. However, the temperature influences the speed of development greatly. [ 2 ] Therefore, the following developmental times are given with 18 °C as reference temperature:
After 24 hours, a fertilized egg gives rise to a trochophore larva. At 48 hours, the trochophore larva becomes a metatrochophore larva. [ 2 ] Both trochophore and metatrochophore swim with a ring of cilia in the water and are positively phototactic . [ 11 ] The metatrochophore has, beside the larval eyes, already the anlagen for the more complex adult eyes of the adult worm. [ 16 ] [ 18 ] A day later, at 72 hours after fertilization, the metatrochophore larva becomes a nectochaete larva. The nectochaete larva already has three segments, each with a pair of parapodia bearing chaetae , which serve for locomotion. [ 2 ] The nectochaete larva can switch from positive to negative phototaxis. [ 17 ] After five to seven days, the larvae start feeding and develop on their own speed, depending on food supply. After three to four weeks, when six segments have formed, the head is formed. [ 2 ]
Normal development is subdivided into 16 stages. [ 2 ] Platynereis dumerilii lives for 3 up to 18 months [ 5 ] with an average lifespan of seven months. P. dumerilii reproduces only once, [ 42 ] and dies after delivering its gametes. [ 2 ]
The genome of Platynereis dumerilii is diploid (2n chromosomes ) with a haploid set of n = 14 chromosomes. [ 9 ] [ 48 ] It contains approximately 1 Gbp (giga base pairs) or 10 9 base pairs. [ 49 ] This genome size is close to the average observed for other animals. However, compared to many classical invertebrate molecular model organisms , this genome size is rather large and therefore it is a challenge to identify gene regulatory elements that can be far away from the corresponding promoter . But it is intron rich unlike those of Drosophila melanogaster and Caenorhabditis elegans and thus closer to vertebrate genomes including the human genome. [ 50 ]
Bristle worms contain the complex protein haemoglobin , found in vertebrates , annelids (e.g. earthworms ), molluscs (e.g. pond snails ) and crustaceans (e.g. daphnia ). It was once believed that haemoglobin must have evolved multiple times to be a feature of such different species.Comparing bristle worms with other red blooded species suggests that all forms of haemoglobins are derived from a single ancestral gene, cytoglobin . [ 51 ] [ 52 ] | https://en.wikipedia.org/wiki/Platynereis_dumerilii |
Plausible reasoning is a method of deriving new conclusions from given known premises , a method different from the classical syllogistic argumentation methods of Aristotelian two-valued logic . The syllogistic style of argumentation is illustrated by the oft-quoted argument "All men are mortal, Socrates is a man, and therefore, Socrates is mortal." In contrast, consider the statement "if it is raining then it is cloudy." The only logical inference that one can draw from this is that "if it is not cloudy then it is not raining." But ordinary people in their everyday lives would conclude that "if it is not raining then being cloudy is less plausible," or "if it is cloudy then rain is more plausible." The unstated and unconsciously applied reasoning, arguably incorrect, that made people come to their conclusions is typical of plausible reasoning [ citation needed ] .
As another example, [ 1 ] "Suppose some dark night a policeman walks down a street, apparently deserted; but suddenly he hears a burglar alarm, looks across the street, and sees a jewellery store with a broken window. Then a person wearing a mask comes crawling out through the broken window, carrying a bag which turns out to be full of expensive jewellery. The policeman immediately concludes that this person is stealing the jewellery." The question is the reasoning process by which the policeman arrives at this conclusion.
The policeman's conclusion was not a logical deduction from the evidence. There may be a perfectly valid explanation for everything. For example, it might be that this person was the owner of the jewellery store and he was coming home from a fancy dress competition, and he didn't have the key with him. But just as he walked by his store a passing truck threw a stone through the window; and he was only protecting his own property and not stealing the jewellery. Now whatever be the policeman's reasoning process, it has a certain degree of validity. The evidence did not prove that the person was stealing jewellery, but it did make it extremely plausible. This is an example of a kind of reasoning, often referred to as plausible reasoning, in which most people are generally very proficient.
During the fifth century B.C.E., [ 2 ] judicial orators in Greek Sicily developed a method for successfully pleading their cases in such instances in which no eyewitnesses or written documents or other such direct evidence could be produced. They began to base their arguments on the internal or external probability or plausibility of their statements. This new way of arguing was commonly labeled with the Greek term eikós, a term that has been variously rendered as similarity, likelihood, probability or plausibility. The success of the argument depends on the oratorical skills of the speaker, arguments by eikós have often been accused of lack of truthfulness. Here is a classical example of argument by plausible reasoning presented by Aristotle in his Rhetoric:
"If the accused is not open to the charge – for instance if a weakling be tried for violent assault – the defence is that he was not likely ( eikós ) to do such a thing. But if he is open to the charge – that is, if he is a strong man – the defence is still that he was not likely ( eikós ) to do such a thing, since he could be sure that people would think he was likely ( eikós ) to do it."
The sophists, a sort of mendicant academicians were said to have been experts in this type of argumentation and they are said to have taught wealthy young Greeks these methods for a hefty fee. Plato and Aristotle strongly denounced these methods and the method came to acquire a lot of bad repute. Sophistic argumentation styles were equated with fallacious arguments.
George Polya in his two volume book titled Mathematics and Plausible Reasoning [ 3 ] [ 4 ] presents plausible reasoning as a way of generating new mathematical conjectures. To Polya, “a mathematical proof is demonstrative reasoning but the inductive evidence of the physicist, the circumstantial evidence of the lawyer, the documentary evidence of the historian and the statistical evidence of the economist all belong to plausible reasoning”. Polya’s intention is to teach students the art of guessing new results in mathematics for which he marshals such notions as induction and analogy as possible sources for plausible reasoning. The first volume of the book is devoted to an extensive discussion of these ideas with several examples drawn from various field of mathematics.
In the Preface to Volume 1 of the book Polya exhorts all interested students of mathematics thus: "Certainly, let us learn proving, but also let us learn guessing." P. R. Halmos reviewing the book summarized the central thesis of the book thus: ". . . a good guess is as important as a good proof." [ 5 ]
Polya begins Volume I with a discussion on inductive reasoning (not mathematical induction ) as a way of guessing new results. He shows how the chance observations of a few results of the form 4 = 2 + 2, 6 = 3 + 3, 8 = 3 + 5, 10 = 3 + 7, etc., may prompt a sharp mind to formulate the conjecture that every even number greater than 4 can be represented as the sum of two odd prime numbers. This is the well known Goldbach's conjecture . The first problem in the first chapter is to guess the rule according to which the successive terms of the following sequence are chosen: 11, 31, 41, 61, 71, 101, 131, . . . In the next chapter the techniques of generalization, specialization and analogy are presented as possible strategies for plausible reasoning. In the remaining chapters, these ideas are illustrated by discussing the discovery of several results in various fields of mathematics like number theory, geometry, etc. and also in physical sciences.
This volume attempts to formulate certain patterns of plausible reasoning. The relations of these patterns with the calculus of probability are also investigated. Their relation to mathematical invention and instruction are also discussed. The following are some of the patterns of plausible inference discussed by Polya.
After a detailed analysis of several paradigmatic examples drawn from ancient Greek texts, D Walton and others formulated the following eleven properties as the defining characteristics of plausible reasoning. [ 6 ]
Allan M. Collins , a recognized authority on intelligent tutoring systems and plausible reasoning, presenting a core theory of the logic of plausible reasoning identified some of the important problems in the formulation of such a theory. [ 7 ]
1. Representing degree of belief.
This is the problem of representing the differences in the strengths of beliefs indicated by the phrases “entirely certain” and “would guess”.
2. Evaluating the strength of arguments.
We need a computational scheme to calculate and compare different levels and strengths of belief.
3. Applying rules of general but not universal validity.
Standard logic justifies the use of universally quantified rules; rules that are always true without exception. Much commonsense inference relies on applying default rules that hold in general but not always.
4. Avoiding the enumeration of all the conditions on a rule.
It often happens that a plausible commonsense rule, when examined closely, has an almost unlimited number of possible types of exceptions. The problem of dealing with all these potential exceptions is known as the qualification problem .
5. Inference from the absence of information.
It is often reasonable to infer that a statement A is false from the fact that one does not know A to be true, or from the fact that it is not stated to be true in a problem statement.
6. Limiting the extent of inference.
Many intuitively appealing sets of axioms have the property that the first few inferences all seem to be reasonable and to have reasonable conclusions, but that, as the inferences get further and further from the starting axioms, the conclusions seem less and less sensible, and they eventually end up in pure nonsense.
7. Inference using vague concepts.
Inferences that involve reasoning near the boundaries of a vague concept are often uncertain.
8. Finding expected utility.
This is the problem of choosing between actions whose consequences are uncertain. In such a case, a choice may be made based on the likelihoods of the various outcomes with their desirability.
9. Inferring an explanation.
Commonsense reasoners try to explain the reasons underlying their observations. If I observe that the street is wet, I infer that it rained. If I observe that the sidewalk is not wet, I may decide instead that the street-cleaners have been by.
10. Schema-Based Inference.
Many useful commonsense concepts correspond to large systems of relations that are instantiated in many separate instances in the world. Such concepts are called schemas or frames.
11. Inferring a general rule from examples.
People are always on the lookout for general rules that encapsulate their observations. | https://en.wikipedia.org/wiki/Plausible_reasoning |
PlayCanvas is an open-source [ 1 ] 3D game engine/interactive 3D application engine alongside a proprietary cloud-hosted creation platform that allows for simultaneous editing from multiple computers via a browser-based interface. [ 2 ] It runs in modern browsers that support WebGL , including Mozilla Firefox and Google Chrome . The engine is capable of rigid-body physics simulation, handling three-dimensional audio and 3D animations.
PlayCanvas has gained the support of ARM, Activision and Mozilla. [ 3 ]
The PlayCanvas engine was open-sourced on June 4, 2014. [ 4 ] [ 5 ]
In April 2019, BusinessInsider.com reported that the company was acquired by Snap Inc. in 2017. [ 6 ]
The PlayCanvas platform has collaborative real-time Editor that allows editing a project by multiple developers simultaneously. [ 7 ] The engine supports the WebGL 1.0 and 2.0 standard to produce GPU accelerated 3D graphics and allows for scripting via the JavaScript programming language. [ 8 ] Projects can be distributed via a URL web link or packaged in native wrappers, p.g. for Android , using CocoonJS [ 9 ] [ 10 ] [ 11 ] or for Steam using Electron , and many other options and platforms.
Various companies [ 12 ] use PlayCanvas in projects of different disciplines of interactive 3D content in the web.
Disney created an educational game [ 13 ] for Hour of Code based on its Moana film.
King published Shuffle Cats Mini, [ 14 ] as a launch title for Facebook Instant Games .
TANX [ 15 ] – massively multiplayer online game of cartoon styled tanks.
Miniclip published number of games [ 16 ] [ 17 ] on their platform with increase of HTML5 games popularity on the web.
Mozilla collaborated [ 18 ] with PlayCanvas team creating After the Flood [ 19 ] demo for presenting cutting-edge features of WebGL 2.0. | https://en.wikipedia.org/wiki/PlayCanvas |
Play is a range of intrinsically motivated activities done for recreation . [ 1 ] Play is commonly associated with children and juvenile-level activities, but may be engaged in at any life stage, and among other higher-functioning animals as well, most notably mammals and birds .
Play is often interpreted as frivolous; yet the player can be intently focused on their objective, particularly when play is structured and goal-oriented, as in a game . Accordingly, play can range from relaxed, free-spirited, spontaneous, and frivolous to planned or even compulsive. [ 2 ] Play is not just a pastime activity; it has the potential to serve as an important tool in numerous aspects of daily life for adolescents, adults, and cognitively advanced non-human species (such as primates). Not only does play promote and aid in physical development (such as hand-eye coordination ), but it also aids in cognitive development and social skills, and can even act as a stepping stone into the world of integration, which can be a very stressful process. Play is something that most children partake in, but the way play is executed is different between cultures, and the way that children engage with play varies.
The seminal text in the field of play studies is the book Homo Ludens first published in 1944 with several subsequent editions, in which Johan Huizinga defines play as follows: [ 2 ] : 13
Summing up the formal characteristic of play, we might call it a free activity standing quite consciously outside "ordinary" life as being "not serious" but at the same time absorbing the player intensely and utterly. It is an activity connected with no material interest, and no profit can be gained by it. It proceeds within its own proper boundaries of time and space according to fixed rules and in an orderly manner. It promotes the formation of social groupings that tend to surround themselves with secrecy and to stress the difference from the common world by disguise or other means.
This definition of play as constituting a separate and independent sphere of human activity is sometimes referred to as the "magic circle" notion of play, a phrase also attributed to Huizinga. [ 2 ] Many other definitions exist. Jean Piaget stated, "the many theories of play expounded in the past are clear proof that the phenomenon is difficult to understand." [ 3 ]
Another definition of play from the twenty-first century comes from the National Playing Fields Association . The definition reads as follows: "play is freely chosen, personally directed, intrinsically motivated behaviour that actively engages the child." [ 4 ] This definition focuses more on the child's freedom of choice and personal motivation related to an activity.
Play can take the form of improvisation, pretense, interaction, performance, mimicry, games, sports, and thrill-seeking (including extreme or dangerous sports like sky-diving, high-speed racing, etc.).
Philosopher Roger Caillois wrote about play in his 1961 book Man, Play and Games . [ importance? ]
Free-form play gives children the freedom to decide what they want to play and how it will be played. Both the activity and the rules are subject to change in this form, and children can make any changes to the rules or objectives of the play at any time. [ 5 ] Some countries in the twenty-first century have added emphasis of free play into their values for children in early childhood, for example Taiwan and Hungary. [ 5 ]
Structured play has clearly defined goals and rules. Such play is called a " game ". Other play is unstructured or open-ended. Both types of play promote adaptive behaviors and mental states of happiness . [ 6 ] [ 7 ]
Sports with defined rules take place within designated play spaces, such as sports fields—in association football for example, players kick a ball in a certain direction and push opponents out of their way as they do so. While appropriate within the sport's play space, these same behaviors might be inappropriate or even illegal outside the playing field. [ 2 ]
Other designed play spaces can be playgrounds with dedicated equipment and structures to promote active and social play. Some play spaces go even farther in specialization to bring the play indoors, and charge admission, as seen at Children's Museums , Science Centers , or Family Entertainment Centers . Family Entertainment Centers (or Play Zones) are typically for-profit businesses that facilitate play and entertainment, while Children's Museums and Science Centers are typically non-profit organisations for educational entertainment.
The California-based National Institute for Play describes seven play patterns: [ 8 ]
Another classification system uses these categories: [ 9 ]
Some forms overlap, such as a relay race (cooperative and competitive) or building a blanket fort (construction and creative).
Separate from self-initiated play, play therapy is used as a clinical application of play aimed at treating children who suffer from trauma, emotional issues and other problems. [ 10 ]
In young children, play is associated with cognitive development and socialization . Play that promotes learning and recreation often incorporates toys , props , tools , or other playmates . Play can consist of an amusing, pretend, or imaginary activity alone or with another. Some forms of play are rehearsals or trials for later life events, such as "play fighting", pretend social encounters (such as parties with dolls), or flirting. [ 11 ] Findings in neuroscience suggest that play promotes flexibility of mind, including adaptive practices such as discovering multiple ways to achieve a desired result, or creative ways to improve or reorganize a given situation. [ citation needed ]
As children get older, they engage in board games , video games , and computer play, and in this context the word gameplay is used to describe the concept and theory of play and its relationship to rules and game design. In their book, Rules of Play , researchers Katie Salen and Eric Zimmerman outline 18 schemas for games, using them to define "play", "interaction", and "design" formally for behaviorists. [ 12 ] Similarly, in his book Half-Real: Video Games between Real Rules and Fictional Worlds , game researcher and theorist Jesper Juul explores the relationship between real rules and unreal scenarios in play, such as winning or losing a game in the real world when played together with real-world friends, but doing so by slaying a dragon in the fantasy world presented in the shared video game. [ 13 ]
Play is explicitly recognized in Article 31 of the Convention on the Rights of the Child (adopted by the General Assembly of the United Nations , November 29, 1989), which declares:
American historian Howard Chudacoff studied the interplay between parental control of toys and games and children's drive for freedom to play. In the colonial era, toys were makeshift and children taught each other very simple games with little adult supervision. The market economy of the 19th century enabled the modern concept of childhood as a distinct, happy life stage. [ citation needed ] Factory-made dolls and doll houses delighted young girls. Organized sports filtered down from adults and colleges, and boys learned to play with a bat, a ball, and an impromptu playing field.
With the rise of motor vehicle traffic in the 20th century, teenagers were increasingly organized into club sports supervised and coached by adults, with swimming taught at summer camps and through supervised playgrounds. [ 14 ] [ better source needed ]
Under the American New Deal 's Works Progress Administration , thousands of local playgrounds and ball fields opened, promoting softball especially as a sport for all ages and genders. [ citation needed ] By the 21st century, Chudacoff notes, the old tension between parental controls and a child's individual freedom was being played out in cyberspace . [ 15 ]
The act of play time is a cross-cultural phenomenon that is universally accepted and encouraged by most communities; however, it can differ in the ways that is performed. [ 16 ]
Some cultures, such as Euro-American ones, encourage play time in order to stress cognitive benefits and the importance of learning how to care for one's self. Other cultures, such as people of African American or Asian American heritages, stress more group oriented learning and play where kids can learn what they can do with and for others. [ 17 ]
Parent interactions at playtime also differ within communities. Parents in the Mayan culture interact with their children in a playful mindset while parents in the United States tend to set aside time to play and teach their children through games and activities. In the Mayan community, children are supported in their playing but also encouraged to play while watching their parents do household work in order to become familiar with how to follow in their footsteps. [ 16 ]
All around the world, children use natural materials like stones, water, sand, leaves, fruits, sticks, and a variety of resources to play. In addition, there are groups that have access to crafts, industrialized toys, electronics, and video-games. [ 18 ]
In Australia, games and sports are part of play. There, play can be considered as preparation for life and self-expression, like in many other countries. [ 19 ]
Groups of children in Efe of the Democratic Republic of Congo can be seen making ‘food’ from dirt or pretending to shoot bows and arrows much like their elders. These activities are similar to other forms of play worldwide. For instance, children can be seen comforting their toy dolls or animals, anything that they have modeled from adults in their communities. [ 20 ]
In Brazil, children can be found playing with balls, kites, marbles, pretend houses, or mud kitchens, like in many other countries. In smaller communities they use mud balls, little stones or cashews to replace marbles. [ 21 ]
At an indigenous community of Sierra Nevada de Santa Marta in Colombia, children's play is highly valued and encouraged by leaders and parents. They interact with the children of different ages and explore together different environments to let the children express themselves as part of the group. [ 22 ]
Some children in the Sahara use clay figures as their forms of playful toys. Toys in general are a representation of cultural practices. They usually illustrate characters and objects of a community. [ 18 ]
Play time can be a way for children to learn the different ways of their culture. Many communities use play to emulate work. The way in which children mimic work through their play can differ according to the opportunities they have access to, but it is something that tends to be promoted by adults. [ 20 ]
Sport activities are one of the most universal forms of play. Different continents have their own popular/dominant sports. For example, European , South American , and African countries enjoy soccer (also known as ‘football’ in Europe ), while North American countries prefer basketball , ice hockey , baseball , or American football . [ 23 ] [ better source needed ] In Asia , sports such as table tennis and badminton are played professionally; however soccer and basketball are played amongst common folks, [ 23 ] with cricket popular in South Asia . [ 24 ] Events such as The Olympic Games and FIFA World Cup showcase countries competing with each other and are broadcast all over the world. Sports can be played as a leisure activity or within a competition . According to sociologist Norbert Elias it [ ambiguous ] is an important part of "civilization process". [ 25 ] Victory and defeat in sports can influence one's emotions to a point where everything else seems irrelevant. [ 25 ] Sport fans can also imagine what it feels like to play for their preferred team. [ 25 ] The feelings people experience can be so surreal that it affects their emotions and behavior. [ 25 ]
Youth sport can provide a positive outcome for youth development. Research shows adolescents are more motivated and engaged in sports than any other activity, [ 26 ] and these conditions predict a richer personal and interpersonal development. [ 27 ] Anxiety, depression and obesity can stem from lack of activity and social interaction. [ 28 ] There is a high correlation between the amount of time that youth spend playing sports and physical (e.g., better general health), psychological (e.g., subjective well-being), academic (e.g., school grades), and social benefits (e.g., making friends). [ 27 ] Electronics are a form of playtime, but researchers have found that most electronic play leads to lack of motivation, no social interaction, and can lead to obesity. [ 29 ] Play is children using their creativity while developing their imagination, dexterity, and physical, cognitive, and emotional strength. Dramatic play is common in younger children. [ 28 ] For youth to benefit from playtime, the following are recommended: [ by whom? ]
By participating regularly in a variety of sports, children can develop and become more proficient at various skills (such as jumping , kicking , running , throwing , etc.) if they focus on skill mastery and development. [ 30 ] [ 31 ] Young athletes can also develop:
Regular participation in sport and physical activity is associated with a lower risk of diabetes , heart disease , obesity , and other related diseases. According to research by the Australian Early Childhood Mental Health Initiative, children can be assisted in dealing with and managing stress by developing their sense of optimism when playing sports. [ 32 ] Young people also tend to be more nutrition-conscious in their food choices when they participate in sport. [ 30 ] [ 33 ] [ 34 ] Girls involved in sport are less likely to experience teenage pregnancy , begin smoking , or develop breast cancer . [ 35 ] Young athletes have shown lower levels of total cholesterol and other favorable profiles in serum lipid parameters associated with cardiovascular disease . [ 30 ] [ 31 ] [ 33 ] Sport provides an arena for young people to be physically active and so reduces the time spent in sedentary pursuits, such as watching TV and playing video games . [ 31 ]
Although adults who engage in high amounts of play may find themselves described as "childish" or "young at heart" by less playful adults, play is an important activity, regardless of age. Creativity and happiness can result from adult play, where the objective can be more than fun alone, as in adult expression of the arts, or curiosity-driven science. [ 36 ] Some adult " hobbies " are examples of such creative play. In creative professions, such as design, playfulness can dispel more serious attitudes (such as shame or embarrassment) that impede brainstorming or artistic experimentation in design. [ 36 ]
Imaginative play and role play may allow adults to practice useful habits such as learned optimism , which is helpful in managing fear or terrors . Play also offers adults the opportunity to practice concepts that may not have been explicitly or formally taught (e.g. how to manage misinformation or deceit). Thus, even though play is just one of many tools used by effective adults, it remains a necessary one. [ 37 ]
There has been extensive research on the benefits of play among children , youth , and adolescence . Overlooked are the benefits of play for adults—more specifically, adults who spend a lot of time in the workplace. Many adults in North America are in the workforce and spend half of their waking hours in a workplace environment with little to no time for play. [ 38 ] [ full citation needed ] Play in this context refers to leisure-type activities with colleagues during lunch breaks or short breaks throughout the working day. Leisure activities might include physical sport activities, card games , board games , video games , foosball , ping-pong , yoga , and boot-camp sessions.
Playing games may promote a persistent and optimistic motivational style and positive affect . [ 39 ] [ full citation needed ] Positive affect enhances people's experiences, enjoyment , and sense of satisfaction , during their engagement with a task. While people are engaged in work, positive affect increases the satisfaction they feel from the work, and this increases their creativity and improves their performance on problem-solving tasks as well as other tasks. [ 40 ] [ full citation needed ] The development of a persistent motivational style charged with positive affect may lead to lasting work success. [ 39 ] [ full citation needed ]
Work and play are mutually supportive. Employees need to experience the sense of newness, flow , discovery , and liveliness that play provides. This provides the employee with the sense that they are integrated within the organization, and therefore they feel and perform better. [ citation needed ]
Incorporating play at work results in more productivity , creativity and innovation, higher job satisfaction, greater workplace morale , stronger or new social bonds, improved job performance, and a decrease in staff turnover, absenteeism , [ 41 ] and stress. Decreased stress leads to less illness, which results in lower health care costs. [ 42 ] Play at work may help employees function and cope when under stress, refresh body and mind, encourage teamwork, trigger creativity, and increase energy while preventing burnout. [ 41 ]
Companies that encourage play at work, whether short breaks throughout the day or during lunch breaks, are more successful because this leads to positive emotion among employees. Risk taking, confidence in presenting novel ideas, and embracing unusual and fresh perspectives are associated with play at work. Play can increase self-reported job satisfaction and well-being. Employees experiencing positive emotions are more cooperative, more social, and perform better when faced with complex tasks. [ 43 ]
Contests, team-building exercises, fitness programs, mental health breaks, and other social activities make the work environment fun, interactive, and rewarding. [ 44 ] [ better source needed ] Playfighting, i.e. playful fights or fictive disputes, may contribute to organizations and institutions, as in youth care settings. Staff tries to down-key playfight invitations to "treatment" or "learning," but playfighting also offers youth and staff identificatory respite from the institutional regime. [ incomprehensible ] Playfighting is a recurrent pattern in the social life of a youth care institution and sits at the core of what inmates and staff have to deal with [ 45 ]
Older adults represent one of the fastest growing populations around the world. [ 46 ] [ 47 ] [ 48 ] The United Nations predicted an increase of those aged 60 and above from 629 million in 2002 to approximately two billion in 2050 [ 49 ] but increased life expectancy does not necessarily translate to a better quality of life . [ 48 ] For this reason, research has begun to investigate methods to maintain and/or improve quality of life among older adults.
Similar to the data surrounding children and adults, play and activity are associated with improved health and quality of life among seniors. [ 33 ] [ 50 ] [ 48 ] Additionally, play and activity tend to affect [ how? ] successful aging as well as boost well-being throughout the lifespan. [ 46 ] [ 48 ] Although children, adults, and seniors all tend to benefit from play, older adults often perform it in unique ways to account for possible issues, such as health restrictions, limited accessibility, and revised priorities. [ 46 ] [ 33 ] For this reason, elderly people may partake in physical exercise groups, interactive video games , and social forums specifically geared towards their needs and interests. [ 33 ] [ 50 ] [ 51 ] One qualitative research study found older adults often chose to engage in specific games such as dominoes , checkers , and bingo for entertainment. [ 52 ] Another study indicated a common pattern in game preferences among older adults: seniors often favor activities that encourage mental and physical fitness, incorporate past interests, have some level of competition, and foster a sense of belonging. [ 50 ] [ 53 ] Researchers investigating play in older adults are also interested in the benefits of technology and video games as therapeutic tools. These outlets can lower the risk of developing particular diseases, reduce feelings of social isolation and stress, and promote creativity and the maintenance of cognitive skills. [ 47 ] [ 50 ] As a result, play has been integrated into physiotherapy and occupational therapy interventions for seniors. [ 54 ]
The ability to incorporate play into one's routine is important because these activities allow participants to express creativity, [ 50 ] improve verbal and non-verbal intelligence, [ 54 ] and enhance balance. [ 46 ] [ 33 ] These benefits may be especially crucial to seniors because cognitive and physical functioning declines with age. [ 48 ] However, it might not be aging itself that is associated with the decline in cognitive and physical capabilities, but the higher levels of inactivity in older adults. [ 46 ]
Play and activity tend to decline with age [ 48 ] which may result in negative outcomes such as social isolation, depression, and mobility issues. [ 33 ] American studies found that only 24% of seniors took part in regular physical activity [ 33 ] and only 42% use the internet for entertainment purposes. [ 50 ] In comparison to other age groups, the elderly are more likely to experience a variety of barriers, such as difficulty with environmental hazards and accessibility issues, that may hinder their abilities to play. [ 46 ] [ 55 ] Although playing may benefit seniors, it also has the potential to negatively impact their health. For example, those who play may be more susceptible to injury. [ 46 ] [ 55 ] Investigating these barriers may assist in the creation of useful interventions and/or the development of preventative measures, such as establishing safer recreational areas, that promote play throughout elderly life. [ 46 ]
A moderate level of play has numerous positive outcomes in the lives of senior citizens. [ 54 ] [ 46 ] [ 55 ] [ 50 ] To support and promote play within the older population, institutions should set up more diverse equipment, [ 47 ] [ 55 ] improve conditions within recreational areas, [ 46 ] and create more video games or online forums that appeal to the needs of seniors. [ 47 ] [ 50 ]
Evolutionary psychologists believe that there must be an important benefit of play, as there are so many other reasons to avoid it; observations have shown it has arisen independently in such varied groups as mammals, [ 56 ] birds, [ 57 ] reptiles, [ 58 ] [ 59 ] [ 60 ] [ 61 ] amphibians, [ 62 ] fish, [ 63 ] [ 64 ] [ 65 ] [ 66 ] and invertebrates. [ 67 ] [ 68 ] Animals are often injured during play, become distracted from predators, and expend valuable energy. In rare cases, play has even been observed between different species that are natural enemies such as a polar bear and a dog . [ 69 ] Yet play seems to be a normal activity with animals who occupy the higher strata of their own hierarchy of needs . Animals on the lower strata, e.g. stressed and starving animals, generally do not play. [ 37 ] However, in wild Assamese macaques physically active play is performed also during periods of low food availability and even if it is at the expense of growth, which highlights the developmental and evolutionary importance of play. [ 70 ]
The social cognitive complexity of numerous species, including dogs, have been explored in experimental studies. In one such study, conducted by Alexandra Horowitz of the University of California, the communication and attention-getting skills of dogs were investigated. [ 71 ] In a natural setting, dyadic play behavior was observed; head-direction and posture was specifically noted. When one of the two dogs was facing away or otherwise preoccupied, attention-getting behaviors and signals (nudging, barking, growling, pawing, jumping, etc.) were used by the other dog to communicate the intent and/or desire to continue on with the dyadic play. Stronger or more frequent signaling was used if the attention of the other dog was not captured. These observations tell us that these dogs know how play behavior and signaling can be used to capture attention, communicate intent and desire, and manipulate one another. This characteristic and skill, called the "attention-getting skill" has generally only been seen in humans, but is now being researched and seen in many different species.
Observing play behavior in various species can tell much about the player's environment (including the welfare of the animal), personal needs, social rank (if any), immediate relationships, and eligibility for mating. Play activity, often observed through action and signals, serves as a tool for communication and expression. Through mimicry, chasing, biting, and touching, animals act out in ways that send messages to one another; whether it's an alert, initiation of play, or expressing intent. When play behavior was observed for a study in Tonkean macaques , it was discovered that play signals weren't always used to initiate play; rather, these signals were viewed primarily as methods of communication (sharing information and attention-getting).
One theory—"play as preparation"—was inspired by the observation that play often mimics adult themes of survival. Predators such as lions and bears play by chasing, pouncing, pawing, wrestling, and biting, as they learn to stalk and kill prey. Prey animals such as deer and zebras play by running and leaping as they acquire speed and agility. Hoofed mammals also practice kicking their hind legs to learn to ward off attacks. Indeed, time spent in physical play accelerates motor skill acquisition in wild Assamese macaques . [ 70 ] While mimicking adult behavior, attacking actions such as kicking and biting are not completely fulfilled, so playmates do not generally injure each other. In social animals, playing might also help to establish dominance rankings among the young to avoid conflicts as adults. [ 37 ]
John Byers, a zoologist at the University of Idaho , discovered that the amount of time spent at play for many mammals (e.g. rats and cats) peaks around puberty, and then drops off. This corresponds to the development of the cerebellum , suggesting that play is not so much about practicing exact behaviors, as much as building general connections in the brain. Sergio Pellis and colleagues at the University of Lethbridge in Alberta, Canada, discovered that play may shape the brain in other ways, too. Young mammals have an overabundance of brain cells in their cerebrum (the outer areas of the brain—part of what distinguishes mammals). There is evidence that play helps the brain clean up this excess of cells, resulting in a more efficient cerebrum at maturity. [ 37 ]
Marc Bekoff (a University of Colorado evolutionary biologist) proposes a "flexibility" hypothesis that attempts to incorporate these neurological findings. It argues that play helps animals learn to switch and improvise all behaviors more effectively, to be prepared for the unexpected. There may, however, be other ways to acquire even these benefits of play (the concept of equifinality ). The social benefits of play for many animals, for example, could instead be garnered by grooming. Patrick Bateson maintains that equifinality is exactly what play teaches. In accordance with the flexibility hypothesis, play may teach animals to avoid "false endpoints". In other words, they harness the childlike tendency to keep playing with something that works "well enough", eventually allowing them to come up with something that might work better, if only in some situations. This also allows mammals to build up various skills that could come in handy in entirely novel situations. [ 37 ]
A study on two species of monkeys Semnopithecus entellus and Macaca mulatta that came into association with each other during food provisioning by pilgrims at the Ambagarh Forest Reserve, near Jaipur, India, shows the interspecific interaction that developed between the juveniles of the two species when opportunity presented itself. [ 72 ]
Learning through play has been long recognized as a critical aspect of childhood and child development . Some of the earliest studies of play started in the 1890s with G. Stanley Hall , the father of the child study movement that sparked an interest in the developmental, mental, and behavioral world of babies and children. Play promotes healthy development of parent-child bonds, establishing social, emotional, and cognitive developmental milestones that help them relate to others, manage stress, and learn resiliency. [ 73 ]
Modern research in the field of affective neuroscience (the neural mechanisms of emotion) has uncovered important links between role play and neurogenesis in the brain. [ 74 ] [ full citation needed ] For example, [ non sequitur ] researcher Roger Caillois used the word ilinx to describe the momentary disruption of perception that comes from forms of physical play that disorient the senses, especially balance.
Play is positively correlated with coping with daily stressors in children. [ 75 ] [ 76 ] [ full citation needed ] [ 77 ] [ full citation needed ] [ 78 ] By playing, children regulate their emotions. This is important for adaptive functioning because without regulation, emotions could be overwhelming and stressful.
Evolutionary psychologists have begun to explore the phylogenetic relationship between higher intelligence in humans and its relationship to play, i.e., the relationship of play to the progress of whole evolutionary groups as opposed to the psychological implications of play to a specific individual.
Various forms of play, physical or mental, influence cognitive abilities in individuals. As little as ten minutes of exercise (including physical play), can improve cognitive abilities. [ 79 ] An "exergame" is a game that incorporates some physical movement but is not formal exercise. Such games increase one's heart rate to the level of aerobics exercise and result in significant improvements in mental faculties such as math and recall memory. [ 79 ]
Playing video games is one of the most common mediums of play for children and adults today. There have been mixed reviews on the effects of video games. One study found "[playing video games] was positively associated with skills strongly related to academic success, such as time management, attention, executive control, memory, and spatial abilities—when playing video game occurs in moderation". [ 80 ]
Play can also influence one's social development and social interactions. Much of the research focuses on the influence play has on child social development. There are different forms of play that influence child social development. One study [ 81 ] explored the influence of playing styles with mothers versus playing styles with fathers and how it influences child social development. "[I]ntegral to positive development is the child's social competence or, more precisely, the ability to regulate their own emotions and behaviors in the social contexts of early childhood to support the effective accomplishment of relevant developmental tasks." [ 82 ]
Social benefits of play have been measured using basic interpersonal values such as getting along with peers. [ 81 ] Play with parents reduces anxiety in children. Having play time with parents that involves socially acceptable behaviour makes it easier for children to relate to be more socially adjusted to peers at school or at play. [ 81 ] Social development involving child interaction with peers is thus an area of influence for playful interactions with parents and peers.
Anji play ( 安吉游戏 in simplified Chinese, 安吉遊戲 in traditional Chinese) is an educational method based on children's self-directed play in outside spaces, using simple tools made of natural material. The teachers and instructors only observe and document the children's independent play. The method was created by Cheng Xueqin and is organized as two hours of free play during which the children choose the available material they want to use and build structures to play. [ 83 ]
While planning, experimenting, building, and using the structures to play, the children have the opportunity to interact with peers, to think critically about what may work, to discuss the plan, and organize the construction work. The process is observed and recorded by the teachers and instructors without intervention, even in instances of possible risk.
Before and after the two hours of play, the children have the opportunity to express their plans and discuss with their peers. After the play, they get the opportunity to draw, write or explain what they did. Then, they watch the videos recorded the same day and explain how they played and comment on each other's creations.
Anji play is also called "true play" and its guiding principles are love, risk, joy, engagement, and reflection. This method of self-initiated and self-directed play is applied at the pre-schools (children from three to six years old) in Anji county, East China. [ 84 ]
Media related to play at Wikimedia Commons | https://en.wikipedia.org/wiki/Play_(activity) |
Play is a range of intrinsically motivated activities done for recreation . [ 1 ] Play is commonly associated with children and juvenile-level activities, but may be engaged in at any life stage, and among other higher-functioning animals as well, most notably mammals and birds .
Play is often interpreted as frivolous; yet the player can be intently focused on their objective, particularly when play is structured and goal-oriented, as in a game . Accordingly, play can range from relaxed, free-spirited, spontaneous, and frivolous to planned or even compulsive. [ 2 ] Play is not just a pastime activity; it has the potential to serve as an important tool in numerous aspects of daily life for adolescents, adults, and cognitively advanced non-human species (such as primates). Not only does play promote and aid in physical development (such as hand-eye coordination ), but it also aids in cognitive development and social skills, and can even act as a stepping stone into the world of integration, which can be a very stressful process. Play is something that most children partake in, but the way play is executed is different between cultures, and the way that children engage with play varies.
The seminal text in the field of play studies is the book Homo Ludens first published in 1944 with several subsequent editions, in which Johan Huizinga defines play as follows: [ 2 ] : 13
Summing up the formal characteristic of play, we might call it a free activity standing quite consciously outside "ordinary" life as being "not serious" but at the same time absorbing the player intensely and utterly. It is an activity connected with no material interest, and no profit can be gained by it. It proceeds within its own proper boundaries of time and space according to fixed rules and in an orderly manner. It promotes the formation of social groupings that tend to surround themselves with secrecy and to stress the difference from the common world by disguise or other means.
This definition of play as constituting a separate and independent sphere of human activity is sometimes referred to as the "magic circle" notion of play, a phrase also attributed to Huizinga. [ 2 ] Many other definitions exist. Jean Piaget stated, "the many theories of play expounded in the past are clear proof that the phenomenon is difficult to understand." [ 3 ]
Another definition of play from the twenty-first century comes from the National Playing Fields Association . The definition reads as follows: "play is freely chosen, personally directed, intrinsically motivated behaviour that actively engages the child." [ 4 ] This definition focuses more on the child's freedom of choice and personal motivation related to an activity.
Play can take the form of improvisation, pretense, interaction, performance, mimicry, games, sports, and thrill-seeking (including extreme or dangerous sports like sky-diving, high-speed racing, etc.).
Philosopher Roger Caillois wrote about play in his 1961 book Man, Play and Games . [ importance? ]
Free-form play gives children the freedom to decide what they want to play and how it will be played. Both the activity and the rules are subject to change in this form, and children can make any changes to the rules or objectives of the play at any time. [ 5 ] Some countries in the twenty-first century have added emphasis of free play into their values for children in early childhood, for example Taiwan and Hungary. [ 5 ]
Structured play has clearly defined goals and rules. Such play is called a " game ". Other play is unstructured or open-ended. Both types of play promote adaptive behaviors and mental states of happiness . [ 6 ] [ 7 ]
Sports with defined rules take place within designated play spaces, such as sports fields—in association football for example, players kick a ball in a certain direction and push opponents out of their way as they do so. While appropriate within the sport's play space, these same behaviors might be inappropriate or even illegal outside the playing field. [ 2 ]
Other designed play spaces can be playgrounds with dedicated equipment and structures to promote active and social play. Some play spaces go even farther in specialization to bring the play indoors, and charge admission, as seen at Children's Museums , Science Centers , or Family Entertainment Centers . Family Entertainment Centers (or Play Zones) are typically for-profit businesses that facilitate play and entertainment, while Children's Museums and Science Centers are typically non-profit organisations for educational entertainment.
The California-based National Institute for Play describes seven play patterns: [ 8 ]
Another classification system uses these categories: [ 9 ]
Some forms overlap, such as a relay race (cooperative and competitive) or building a blanket fort (construction and creative).
Separate from self-initiated play, play therapy is used as a clinical application of play aimed at treating children who suffer from trauma, emotional issues and other problems. [ 10 ]
In young children, play is associated with cognitive development and socialization . Play that promotes learning and recreation often incorporates toys , props , tools , or other playmates . Play can consist of an amusing, pretend, or imaginary activity alone or with another. Some forms of play are rehearsals or trials for later life events, such as "play fighting", pretend social encounters (such as parties with dolls), or flirting. [ 11 ] Findings in neuroscience suggest that play promotes flexibility of mind, including adaptive practices such as discovering multiple ways to achieve a desired result, or creative ways to improve or reorganize a given situation. [ citation needed ]
As children get older, they engage in board games , video games , and computer play, and in this context the word gameplay is used to describe the concept and theory of play and its relationship to rules and game design. In their book, Rules of Play , researchers Katie Salen and Eric Zimmerman outline 18 schemas for games, using them to define "play", "interaction", and "design" formally for behaviorists. [ 12 ] Similarly, in his book Half-Real: Video Games between Real Rules and Fictional Worlds , game researcher and theorist Jesper Juul explores the relationship between real rules and unreal scenarios in play, such as winning or losing a game in the real world when played together with real-world friends, but doing so by slaying a dragon in the fantasy world presented in the shared video game. [ 13 ]
Play is explicitly recognized in Article 31 of the Convention on the Rights of the Child (adopted by the General Assembly of the United Nations , November 29, 1989), which declares:
American historian Howard Chudacoff studied the interplay between parental control of toys and games and children's drive for freedom to play. In the colonial era, toys were makeshift and children taught each other very simple games with little adult supervision. The market economy of the 19th century enabled the modern concept of childhood as a distinct, happy life stage. [ citation needed ] Factory-made dolls and doll houses delighted young girls. Organized sports filtered down from adults and colleges, and boys learned to play with a bat, a ball, and an impromptu playing field.
With the rise of motor vehicle traffic in the 20th century, teenagers were increasingly organized into club sports supervised and coached by adults, with swimming taught at summer camps and through supervised playgrounds. [ 14 ] [ better source needed ]
Under the American New Deal 's Works Progress Administration , thousands of local playgrounds and ball fields opened, promoting softball especially as a sport for all ages and genders. [ citation needed ] By the 21st century, Chudacoff notes, the old tension between parental controls and a child's individual freedom was being played out in cyberspace . [ 15 ]
The act of play time is a cross-cultural phenomenon that is universally accepted and encouraged by most communities; however, it can differ in the ways that is performed. [ 16 ]
Some cultures, such as Euro-American ones, encourage play time in order to stress cognitive benefits and the importance of learning how to care for one's self. Other cultures, such as people of African American or Asian American heritages, stress more group oriented learning and play where kids can learn what they can do with and for others. [ 17 ]
Parent interactions at playtime also differ within communities. Parents in the Mayan culture interact with their children in a playful mindset while parents in the United States tend to set aside time to play and teach their children through games and activities. In the Mayan community, children are supported in their playing but also encouraged to play while watching their parents do household work in order to become familiar with how to follow in their footsteps. [ 16 ]
All around the world, children use natural materials like stones, water, sand, leaves, fruits, sticks, and a variety of resources to play. In addition, there are groups that have access to crafts, industrialized toys, electronics, and video-games. [ 18 ]
In Australia, games and sports are part of play. There, play can be considered as preparation for life and self-expression, like in many other countries. [ 19 ]
Groups of children in Efe of the Democratic Republic of Congo can be seen making ‘food’ from dirt or pretending to shoot bows and arrows much like their elders. These activities are similar to other forms of play worldwide. For instance, children can be seen comforting their toy dolls or animals, anything that they have modeled from adults in their communities. [ 20 ]
In Brazil, children can be found playing with balls, kites, marbles, pretend houses, or mud kitchens, like in many other countries. In smaller communities they use mud balls, little stones or cashews to replace marbles. [ 21 ]
At an indigenous community of Sierra Nevada de Santa Marta in Colombia, children's play is highly valued and encouraged by leaders and parents. They interact with the children of different ages and explore together different environments to let the children express themselves as part of the group. [ 22 ]
Some children in the Sahara use clay figures as their forms of playful toys. Toys in general are a representation of cultural practices. They usually illustrate characters and objects of a community. [ 18 ]
Play time can be a way for children to learn the different ways of their culture. Many communities use play to emulate work. The way in which children mimic work through their play can differ according to the opportunities they have access to, but it is something that tends to be promoted by adults. [ 20 ]
Sport activities are one of the most universal forms of play. Different continents have their own popular/dominant sports. For example, European , South American , and African countries enjoy soccer (also known as ‘football’ in Europe ), while North American countries prefer basketball , ice hockey , baseball , or American football . [ 23 ] [ better source needed ] In Asia , sports such as table tennis and badminton are played professionally; however soccer and basketball are played amongst common folks, [ 23 ] with cricket popular in South Asia . [ 24 ] Events such as The Olympic Games and FIFA World Cup showcase countries competing with each other and are broadcast all over the world. Sports can be played as a leisure activity or within a competition . According to sociologist Norbert Elias it [ ambiguous ] is an important part of "civilization process". [ 25 ] Victory and defeat in sports can influence one's emotions to a point where everything else seems irrelevant. [ 25 ] Sport fans can also imagine what it feels like to play for their preferred team. [ 25 ] The feelings people experience can be so surreal that it affects their emotions and behavior. [ 25 ]
Youth sport can provide a positive outcome for youth development. Research shows adolescents are more motivated and engaged in sports than any other activity, [ 26 ] and these conditions predict a richer personal and interpersonal development. [ 27 ] Anxiety, depression and obesity can stem from lack of activity and social interaction. [ 28 ] There is a high correlation between the amount of time that youth spend playing sports and physical (e.g., better general health), psychological (e.g., subjective well-being), academic (e.g., school grades), and social benefits (e.g., making friends). [ 27 ] Electronics are a form of playtime, but researchers have found that most electronic play leads to lack of motivation, no social interaction, and can lead to obesity. [ 29 ] Play is children using their creativity while developing their imagination, dexterity, and physical, cognitive, and emotional strength. Dramatic play is common in younger children. [ 28 ] For youth to benefit from playtime, the following are recommended: [ by whom? ]
By participating regularly in a variety of sports, children can develop and become more proficient at various skills (such as jumping , kicking , running , throwing , etc.) if they focus on skill mastery and development. [ 30 ] [ 31 ] Young athletes can also develop:
Regular participation in sport and physical activity is associated with a lower risk of diabetes , heart disease , obesity , and other related diseases. According to research by the Australian Early Childhood Mental Health Initiative, children can be assisted in dealing with and managing stress by developing their sense of optimism when playing sports. [ 32 ] Young people also tend to be more nutrition-conscious in their food choices when they participate in sport. [ 30 ] [ 33 ] [ 34 ] Girls involved in sport are less likely to experience teenage pregnancy , begin smoking , or develop breast cancer . [ 35 ] Young athletes have shown lower levels of total cholesterol and other favorable profiles in serum lipid parameters associated with cardiovascular disease . [ 30 ] [ 31 ] [ 33 ] Sport provides an arena for young people to be physically active and so reduces the time spent in sedentary pursuits, such as watching TV and playing video games . [ 31 ]
Although adults who engage in high amounts of play may find themselves described as "childish" or "young at heart" by less playful adults, play is an important activity, regardless of age. Creativity and happiness can result from adult play, where the objective can be more than fun alone, as in adult expression of the arts, or curiosity-driven science. [ 36 ] Some adult " hobbies " are examples of such creative play. In creative professions, such as design, playfulness can dispel more serious attitudes (such as shame or embarrassment) that impede brainstorming or artistic experimentation in design. [ 36 ]
Imaginative play and role play may allow adults to practice useful habits such as learned optimism , which is helpful in managing fear or terrors . Play also offers adults the opportunity to practice concepts that may not have been explicitly or formally taught (e.g. how to manage misinformation or deceit). Thus, even though play is just one of many tools used by effective adults, it remains a necessary one. [ 37 ]
There has been extensive research on the benefits of play among children , youth , and adolescence . Overlooked are the benefits of play for adults—more specifically, adults who spend a lot of time in the workplace. Many adults in North America are in the workforce and spend half of their waking hours in a workplace environment with little to no time for play. [ 38 ] [ full citation needed ] Play in this context refers to leisure-type activities with colleagues during lunch breaks or short breaks throughout the working day. Leisure activities might include physical sport activities, card games , board games , video games , foosball , ping-pong , yoga , and boot-camp sessions.
Playing games may promote a persistent and optimistic motivational style and positive affect . [ 39 ] [ full citation needed ] Positive affect enhances people's experiences, enjoyment , and sense of satisfaction , during their engagement with a task. While people are engaged in work, positive affect increases the satisfaction they feel from the work, and this increases their creativity and improves their performance on problem-solving tasks as well as other tasks. [ 40 ] [ full citation needed ] The development of a persistent motivational style charged with positive affect may lead to lasting work success. [ 39 ] [ full citation needed ]
Work and play are mutually supportive. Employees need to experience the sense of newness, flow , discovery , and liveliness that play provides. This provides the employee with the sense that they are integrated within the organization, and therefore they feel and perform better. [ citation needed ]
Incorporating play at work results in more productivity , creativity and innovation, higher job satisfaction, greater workplace morale , stronger or new social bonds, improved job performance, and a decrease in staff turnover, absenteeism , [ 41 ] and stress. Decreased stress leads to less illness, which results in lower health care costs. [ 42 ] Play at work may help employees function and cope when under stress, refresh body and mind, encourage teamwork, trigger creativity, and increase energy while preventing burnout. [ 41 ]
Companies that encourage play at work, whether short breaks throughout the day or during lunch breaks, are more successful because this leads to positive emotion among employees. Risk taking, confidence in presenting novel ideas, and embracing unusual and fresh perspectives are associated with play at work. Play can increase self-reported job satisfaction and well-being. Employees experiencing positive emotions are more cooperative, more social, and perform better when faced with complex tasks. [ 43 ]
Contests, team-building exercises, fitness programs, mental health breaks, and other social activities make the work environment fun, interactive, and rewarding. [ 44 ] [ better source needed ] Playfighting, i.e. playful fights or fictive disputes, may contribute to organizations and institutions, as in youth care settings. Staff tries to down-key playfight invitations to "treatment" or "learning," but playfighting also offers youth and staff identificatory respite from the institutional regime. [ incomprehensible ] Playfighting is a recurrent pattern in the social life of a youth care institution and sits at the core of what inmates and staff have to deal with [ 45 ]
Older adults represent one of the fastest growing populations around the world. [ 46 ] [ 47 ] [ 48 ] The United Nations predicted an increase of those aged 60 and above from 629 million in 2002 to approximately two billion in 2050 [ 49 ] but increased life expectancy does not necessarily translate to a better quality of life . [ 48 ] For this reason, research has begun to investigate methods to maintain and/or improve quality of life among older adults.
Similar to the data surrounding children and adults, play and activity are associated with improved health and quality of life among seniors. [ 33 ] [ 50 ] [ 48 ] Additionally, play and activity tend to affect [ how? ] successful aging as well as boost well-being throughout the lifespan. [ 46 ] [ 48 ] Although children, adults, and seniors all tend to benefit from play, older adults often perform it in unique ways to account for possible issues, such as health restrictions, limited accessibility, and revised priorities. [ 46 ] [ 33 ] For this reason, elderly people may partake in physical exercise groups, interactive video games , and social forums specifically geared towards their needs and interests. [ 33 ] [ 50 ] [ 51 ] One qualitative research study found older adults often chose to engage in specific games such as dominoes , checkers , and bingo for entertainment. [ 52 ] Another study indicated a common pattern in game preferences among older adults: seniors often favor activities that encourage mental and physical fitness, incorporate past interests, have some level of competition, and foster a sense of belonging. [ 50 ] [ 53 ] Researchers investigating play in older adults are also interested in the benefits of technology and video games as therapeutic tools. These outlets can lower the risk of developing particular diseases, reduce feelings of social isolation and stress, and promote creativity and the maintenance of cognitive skills. [ 47 ] [ 50 ] As a result, play has been integrated into physiotherapy and occupational therapy interventions for seniors. [ 54 ]
The ability to incorporate play into one's routine is important because these activities allow participants to express creativity, [ 50 ] improve verbal and non-verbal intelligence, [ 54 ] and enhance balance. [ 46 ] [ 33 ] These benefits may be especially crucial to seniors because cognitive and physical functioning declines with age. [ 48 ] However, it might not be aging itself that is associated with the decline in cognitive and physical capabilities, but the higher levels of inactivity in older adults. [ 46 ]
Play and activity tend to decline with age [ 48 ] which may result in negative outcomes such as social isolation, depression, and mobility issues. [ 33 ] American studies found that only 24% of seniors took part in regular physical activity [ 33 ] and only 42% use the internet for entertainment purposes. [ 50 ] In comparison to other age groups, the elderly are more likely to experience a variety of barriers, such as difficulty with environmental hazards and accessibility issues, that may hinder their abilities to play. [ 46 ] [ 55 ] Although playing may benefit seniors, it also has the potential to negatively impact their health. For example, those who play may be more susceptible to injury. [ 46 ] [ 55 ] Investigating these barriers may assist in the creation of useful interventions and/or the development of preventative measures, such as establishing safer recreational areas, that promote play throughout elderly life. [ 46 ]
A moderate level of play has numerous positive outcomes in the lives of senior citizens. [ 54 ] [ 46 ] [ 55 ] [ 50 ] To support and promote play within the older population, institutions should set up more diverse equipment, [ 47 ] [ 55 ] improve conditions within recreational areas, [ 46 ] and create more video games or online forums that appeal to the needs of seniors. [ 47 ] [ 50 ]
Evolutionary psychologists believe that there must be an important benefit of play, as there are so many other reasons to avoid it; observations have shown it has arisen independently in such varied groups as mammals, [ 56 ] birds, [ 57 ] reptiles, [ 58 ] [ 59 ] [ 60 ] [ 61 ] amphibians, [ 62 ] fish, [ 63 ] [ 64 ] [ 65 ] [ 66 ] and invertebrates. [ 67 ] [ 68 ] Animals are often injured during play, become distracted from predators, and expend valuable energy. In rare cases, play has even been observed between different species that are natural enemies such as a polar bear and a dog . [ 69 ] Yet play seems to be a normal activity with animals who occupy the higher strata of their own hierarchy of needs . Animals on the lower strata, e.g. stressed and starving animals, generally do not play. [ 37 ] However, in wild Assamese macaques physically active play is performed also during periods of low food availability and even if it is at the expense of growth, which highlights the developmental and evolutionary importance of play. [ 70 ]
The social cognitive complexity of numerous species, including dogs, have been explored in experimental studies. In one such study, conducted by Alexandra Horowitz of the University of California, the communication and attention-getting skills of dogs were investigated. [ 71 ] In a natural setting, dyadic play behavior was observed; head-direction and posture was specifically noted. When one of the two dogs was facing away or otherwise preoccupied, attention-getting behaviors and signals (nudging, barking, growling, pawing, jumping, etc.) were used by the other dog to communicate the intent and/or desire to continue on with the dyadic play. Stronger or more frequent signaling was used if the attention of the other dog was not captured. These observations tell us that these dogs know how play behavior and signaling can be used to capture attention, communicate intent and desire, and manipulate one another. This characteristic and skill, called the "attention-getting skill" has generally only been seen in humans, but is now being researched and seen in many different species.
Observing play behavior in various species can tell much about the player's environment (including the welfare of the animal), personal needs, social rank (if any), immediate relationships, and eligibility for mating. Play activity, often observed through action and signals, serves as a tool for communication and expression. Through mimicry, chasing, biting, and touching, animals act out in ways that send messages to one another; whether it's an alert, initiation of play, or expressing intent. When play behavior was observed for a study in Tonkean macaques , it was discovered that play signals weren't always used to initiate play; rather, these signals were viewed primarily as methods of communication (sharing information and attention-getting).
One theory—"play as preparation"—was inspired by the observation that play often mimics adult themes of survival. Predators such as lions and bears play by chasing, pouncing, pawing, wrestling, and biting, as they learn to stalk and kill prey. Prey animals such as deer and zebras play by running and leaping as they acquire speed and agility. Hoofed mammals also practice kicking their hind legs to learn to ward off attacks. Indeed, time spent in physical play accelerates motor skill acquisition in wild Assamese macaques . [ 70 ] While mimicking adult behavior, attacking actions such as kicking and biting are not completely fulfilled, so playmates do not generally injure each other. In social animals, playing might also help to establish dominance rankings among the young to avoid conflicts as adults. [ 37 ]
John Byers, a zoologist at the University of Idaho , discovered that the amount of time spent at play for many mammals (e.g. rats and cats) peaks around puberty, and then drops off. This corresponds to the development of the cerebellum , suggesting that play is not so much about practicing exact behaviors, as much as building general connections in the brain. Sergio Pellis and colleagues at the University of Lethbridge in Alberta, Canada, discovered that play may shape the brain in other ways, too. Young mammals have an overabundance of brain cells in their cerebrum (the outer areas of the brain—part of what distinguishes mammals). There is evidence that play helps the brain clean up this excess of cells, resulting in a more efficient cerebrum at maturity. [ 37 ]
Marc Bekoff (a University of Colorado evolutionary biologist) proposes a "flexibility" hypothesis that attempts to incorporate these neurological findings. It argues that play helps animals learn to switch and improvise all behaviors more effectively, to be prepared for the unexpected. There may, however, be other ways to acquire even these benefits of play (the concept of equifinality ). The social benefits of play for many animals, for example, could instead be garnered by grooming. Patrick Bateson maintains that equifinality is exactly what play teaches. In accordance with the flexibility hypothesis, play may teach animals to avoid "false endpoints". In other words, they harness the childlike tendency to keep playing with something that works "well enough", eventually allowing them to come up with something that might work better, if only in some situations. This also allows mammals to build up various skills that could come in handy in entirely novel situations. [ 37 ]
A study on two species of monkeys Semnopithecus entellus and Macaca mulatta that came into association with each other during food provisioning by pilgrims at the Ambagarh Forest Reserve, near Jaipur, India, shows the interspecific interaction that developed between the juveniles of the two species when opportunity presented itself. [ 72 ]
Learning through play has been long recognized as a critical aspect of childhood and child development . Some of the earliest studies of play started in the 1890s with G. Stanley Hall , the father of the child study movement that sparked an interest in the developmental, mental, and behavioral world of babies and children. Play promotes healthy development of parent-child bonds, establishing social, emotional, and cognitive developmental milestones that help them relate to others, manage stress, and learn resiliency. [ 73 ]
Modern research in the field of affective neuroscience (the neural mechanisms of emotion) has uncovered important links between role play and neurogenesis in the brain. [ 74 ] [ full citation needed ] For example, [ non sequitur ] researcher Roger Caillois used the word ilinx to describe the momentary disruption of perception that comes from forms of physical play that disorient the senses, especially balance.
Play is positively correlated with coping with daily stressors in children. [ 75 ] [ 76 ] [ full citation needed ] [ 77 ] [ full citation needed ] [ 78 ] By playing, children regulate their emotions. This is important for adaptive functioning because without regulation, emotions could be overwhelming and stressful.
Evolutionary psychologists have begun to explore the phylogenetic relationship between higher intelligence in humans and its relationship to play, i.e., the relationship of play to the progress of whole evolutionary groups as opposed to the psychological implications of play to a specific individual.
Various forms of play, physical or mental, influence cognitive abilities in individuals. As little as ten minutes of exercise (including physical play), can improve cognitive abilities. [ 79 ] An "exergame" is a game that incorporates some physical movement but is not formal exercise. Such games increase one's heart rate to the level of aerobics exercise and result in significant improvements in mental faculties such as math and recall memory. [ 79 ]
Playing video games is one of the most common mediums of play for children and adults today. There have been mixed reviews on the effects of video games. One study found "[playing video games] was positively associated with skills strongly related to academic success, such as time management, attention, executive control, memory, and spatial abilities—when playing video game occurs in moderation". [ 80 ]
Play can also influence one's social development and social interactions. Much of the research focuses on the influence play has on child social development. There are different forms of play that influence child social development. One study [ 81 ] explored the influence of playing styles with mothers versus playing styles with fathers and how it influences child social development. "[I]ntegral to positive development is the child's social competence or, more precisely, the ability to regulate their own emotions and behaviors in the social contexts of early childhood to support the effective accomplishment of relevant developmental tasks." [ 82 ]
Social benefits of play have been measured using basic interpersonal values such as getting along with peers. [ 81 ] Play with parents reduces anxiety in children. Having play time with parents that involves socially acceptable behaviour makes it easier for children to relate to be more socially adjusted to peers at school or at play. [ 81 ] Social development involving child interaction with peers is thus an area of influence for playful interactions with parents and peers.
Anji play ( 安吉游戏 in simplified Chinese, 安吉遊戲 in traditional Chinese) is an educational method based on children's self-directed play in outside spaces, using simple tools made of natural material. The teachers and instructors only observe and document the children's independent play. The method was created by Cheng Xueqin and is organized as two hours of free play during which the children choose the available material they want to use and build structures to play. [ 83 ]
While planning, experimenting, building, and using the structures to play, the children have the opportunity to interact with peers, to think critically about what may work, to discuss the plan, and organize the construction work. The process is observed and recorded by the teachers and instructors without intervention, even in instances of possible risk.
Before and after the two hours of play, the children have the opportunity to express their plans and discuss with their peers. After the play, they get the opportunity to draw, write or explain what they did. Then, they watch the videos recorded the same day and explain how they played and comment on each other's creations.
Anji play is also called "true play" and its guiding principles are love, risk, joy, engagement, and reflection. This method of self-initiated and self-directed play is applied at the pre-schools (children from three to six years old) in Anji county, East China. [ 84 ]
Media related to play at Wikimedia Commons | https://en.wikipedia.org/wiki/Playful |
Play is a range of intrinsically motivated activities done for recreation . [ 1 ] Play is commonly associated with children and juvenile-level activities, but may be engaged in at any life stage, and among other higher-functioning animals as well, most notably mammals and birds .
Play is often interpreted as frivolous; yet the player can be intently focused on their objective, particularly when play is structured and goal-oriented, as in a game . Accordingly, play can range from relaxed, free-spirited, spontaneous, and frivolous to planned or even compulsive. [ 2 ] Play is not just a pastime activity; it has the potential to serve as an important tool in numerous aspects of daily life for adolescents, adults, and cognitively advanced non-human species (such as primates). Not only does play promote and aid in physical development (such as hand-eye coordination ), but it also aids in cognitive development and social skills, and can even act as a stepping stone into the world of integration, which can be a very stressful process. Play is something that most children partake in, but the way play is executed is different between cultures, and the way that children engage with play varies.
The seminal text in the field of play studies is the book Homo Ludens first published in 1944 with several subsequent editions, in which Johan Huizinga defines play as follows: [ 2 ] : 13
Summing up the formal characteristic of play, we might call it a free activity standing quite consciously outside "ordinary" life as being "not serious" but at the same time absorbing the player intensely and utterly. It is an activity connected with no material interest, and no profit can be gained by it. It proceeds within its own proper boundaries of time and space according to fixed rules and in an orderly manner. It promotes the formation of social groupings that tend to surround themselves with secrecy and to stress the difference from the common world by disguise or other means.
This definition of play as constituting a separate and independent sphere of human activity is sometimes referred to as the "magic circle" notion of play, a phrase also attributed to Huizinga. [ 2 ] Many other definitions exist. Jean Piaget stated, "the many theories of play expounded in the past are clear proof that the phenomenon is difficult to understand." [ 3 ]
Another definition of play from the twenty-first century comes from the National Playing Fields Association . The definition reads as follows: "play is freely chosen, personally directed, intrinsically motivated behaviour that actively engages the child." [ 4 ] This definition focuses more on the child's freedom of choice and personal motivation related to an activity.
Play can take the form of improvisation, pretense, interaction, performance, mimicry, games, sports, and thrill-seeking (including extreme or dangerous sports like sky-diving, high-speed racing, etc.).
Philosopher Roger Caillois wrote about play in his 1961 book Man, Play and Games . [ importance? ]
Free-form play gives children the freedom to decide what they want to play and how it will be played. Both the activity and the rules are subject to change in this form, and children can make any changes to the rules or objectives of the play at any time. [ 5 ] Some countries in the twenty-first century have added emphasis of free play into their values for children in early childhood, for example Taiwan and Hungary. [ 5 ]
Structured play has clearly defined goals and rules. Such play is called a " game ". Other play is unstructured or open-ended. Both types of play promote adaptive behaviors and mental states of happiness . [ 6 ] [ 7 ]
Sports with defined rules take place within designated play spaces, such as sports fields—in association football for example, players kick a ball in a certain direction and push opponents out of their way as they do so. While appropriate within the sport's play space, these same behaviors might be inappropriate or even illegal outside the playing field. [ 2 ]
Other designed play spaces can be playgrounds with dedicated equipment and structures to promote active and social play. Some play spaces go even farther in specialization to bring the play indoors, and charge admission, as seen at Children's Museums , Science Centers , or Family Entertainment Centers . Family Entertainment Centers (or Play Zones) are typically for-profit businesses that facilitate play and entertainment, while Children's Museums and Science Centers are typically non-profit organisations for educational entertainment.
The California-based National Institute for Play describes seven play patterns: [ 8 ]
Another classification system uses these categories: [ 9 ]
Some forms overlap, such as a relay race (cooperative and competitive) or building a blanket fort (construction and creative).
Separate from self-initiated play, play therapy is used as a clinical application of play aimed at treating children who suffer from trauma, emotional issues and other problems. [ 10 ]
In young children, play is associated with cognitive development and socialization . Play that promotes learning and recreation often incorporates toys , props , tools , or other playmates . Play can consist of an amusing, pretend, or imaginary activity alone or with another. Some forms of play are rehearsals or trials for later life events, such as "play fighting", pretend social encounters (such as parties with dolls), or flirting. [ 11 ] Findings in neuroscience suggest that play promotes flexibility of mind, including adaptive practices such as discovering multiple ways to achieve a desired result, or creative ways to improve or reorganize a given situation. [ citation needed ]
As children get older, they engage in board games , video games , and computer play, and in this context the word gameplay is used to describe the concept and theory of play and its relationship to rules and game design. In their book, Rules of Play , researchers Katie Salen and Eric Zimmerman outline 18 schemas for games, using them to define "play", "interaction", and "design" formally for behaviorists. [ 12 ] Similarly, in his book Half-Real: Video Games between Real Rules and Fictional Worlds , game researcher and theorist Jesper Juul explores the relationship between real rules and unreal scenarios in play, such as winning or losing a game in the real world when played together with real-world friends, but doing so by slaying a dragon in the fantasy world presented in the shared video game. [ 13 ]
Play is explicitly recognized in Article 31 of the Convention on the Rights of the Child (adopted by the General Assembly of the United Nations , November 29, 1989), which declares:
American historian Howard Chudacoff studied the interplay between parental control of toys and games and children's drive for freedom to play. In the colonial era, toys were makeshift and children taught each other very simple games with little adult supervision. The market economy of the 19th century enabled the modern concept of childhood as a distinct, happy life stage. [ citation needed ] Factory-made dolls and doll houses delighted young girls. Organized sports filtered down from adults and colleges, and boys learned to play with a bat, a ball, and an impromptu playing field.
With the rise of motor vehicle traffic in the 20th century, teenagers were increasingly organized into club sports supervised and coached by adults, with swimming taught at summer camps and through supervised playgrounds. [ 14 ] [ better source needed ]
Under the American New Deal 's Works Progress Administration , thousands of local playgrounds and ball fields opened, promoting softball especially as a sport for all ages and genders. [ citation needed ] By the 21st century, Chudacoff notes, the old tension between parental controls and a child's individual freedom was being played out in cyberspace . [ 15 ]
The act of play time is a cross-cultural phenomenon that is universally accepted and encouraged by most communities; however, it can differ in the ways that is performed. [ 16 ]
Some cultures, such as Euro-American ones, encourage play time in order to stress cognitive benefits and the importance of learning how to care for one's self. Other cultures, such as people of African American or Asian American heritages, stress more group oriented learning and play where kids can learn what they can do with and for others. [ 17 ]
Parent interactions at playtime also differ within communities. Parents in the Mayan culture interact with their children in a playful mindset while parents in the United States tend to set aside time to play and teach their children through games and activities. In the Mayan community, children are supported in their playing but also encouraged to play while watching their parents do household work in order to become familiar with how to follow in their footsteps. [ 16 ]
All around the world, children use natural materials like stones, water, sand, leaves, fruits, sticks, and a variety of resources to play. In addition, there are groups that have access to crafts, industrialized toys, electronics, and video-games. [ 18 ]
In Australia, games and sports are part of play. There, play can be considered as preparation for life and self-expression, like in many other countries. [ 19 ]
Groups of children in Efe of the Democratic Republic of Congo can be seen making ‘food’ from dirt or pretending to shoot bows and arrows much like their elders. These activities are similar to other forms of play worldwide. For instance, children can be seen comforting their toy dolls or animals, anything that they have modeled from adults in their communities. [ 20 ]
In Brazil, children can be found playing with balls, kites, marbles, pretend houses, or mud kitchens, like in many other countries. In smaller communities they use mud balls, little stones or cashews to replace marbles. [ 21 ]
At an indigenous community of Sierra Nevada de Santa Marta in Colombia, children's play is highly valued and encouraged by leaders and parents. They interact with the children of different ages and explore together different environments to let the children express themselves as part of the group. [ 22 ]
Some children in the Sahara use clay figures as their forms of playful toys. Toys in general are a representation of cultural practices. They usually illustrate characters and objects of a community. [ 18 ]
Play time can be a way for children to learn the different ways of their culture. Many communities use play to emulate work. The way in which children mimic work through their play can differ according to the opportunities they have access to, but it is something that tends to be promoted by adults. [ 20 ]
Sport activities are one of the most universal forms of play. Different continents have their own popular/dominant sports. For example, European , South American , and African countries enjoy soccer (also known as ‘football’ in Europe ), while North American countries prefer basketball , ice hockey , baseball , or American football . [ 23 ] [ better source needed ] In Asia , sports such as table tennis and badminton are played professionally; however soccer and basketball are played amongst common folks, [ 23 ] with cricket popular in South Asia . [ 24 ] Events such as The Olympic Games and FIFA World Cup showcase countries competing with each other and are broadcast all over the world. Sports can be played as a leisure activity or within a competition . According to sociologist Norbert Elias it [ ambiguous ] is an important part of "civilization process". [ 25 ] Victory and defeat in sports can influence one's emotions to a point where everything else seems irrelevant. [ 25 ] Sport fans can also imagine what it feels like to play for their preferred team. [ 25 ] The feelings people experience can be so surreal that it affects their emotions and behavior. [ 25 ]
Youth sport can provide a positive outcome for youth development. Research shows adolescents are more motivated and engaged in sports than any other activity, [ 26 ] and these conditions predict a richer personal and interpersonal development. [ 27 ] Anxiety, depression and obesity can stem from lack of activity and social interaction. [ 28 ] There is a high correlation between the amount of time that youth spend playing sports and physical (e.g., better general health), psychological (e.g., subjective well-being), academic (e.g., school grades), and social benefits (e.g., making friends). [ 27 ] Electronics are a form of playtime, but researchers have found that most electronic play leads to lack of motivation, no social interaction, and can lead to obesity. [ 29 ] Play is children using their creativity while developing their imagination, dexterity, and physical, cognitive, and emotional strength. Dramatic play is common in younger children. [ 28 ] For youth to benefit from playtime, the following are recommended: [ by whom? ]
By participating regularly in a variety of sports, children can develop and become more proficient at various skills (such as jumping , kicking , running , throwing , etc.) if they focus on skill mastery and development. [ 30 ] [ 31 ] Young athletes can also develop:
Regular participation in sport and physical activity is associated with a lower risk of diabetes , heart disease , obesity , and other related diseases. According to research by the Australian Early Childhood Mental Health Initiative, children can be assisted in dealing with and managing stress by developing their sense of optimism when playing sports. [ 32 ] Young people also tend to be more nutrition-conscious in their food choices when they participate in sport. [ 30 ] [ 33 ] [ 34 ] Girls involved in sport are less likely to experience teenage pregnancy , begin smoking , or develop breast cancer . [ 35 ] Young athletes have shown lower levels of total cholesterol and other favorable profiles in serum lipid parameters associated with cardiovascular disease . [ 30 ] [ 31 ] [ 33 ] Sport provides an arena for young people to be physically active and so reduces the time spent in sedentary pursuits, such as watching TV and playing video games . [ 31 ]
Although adults who engage in high amounts of play may find themselves described as "childish" or "young at heart" by less playful adults, play is an important activity, regardless of age. Creativity and happiness can result from adult play, where the objective can be more than fun alone, as in adult expression of the arts, or curiosity-driven science. [ 36 ] Some adult " hobbies " are examples of such creative play. In creative professions, such as design, playfulness can dispel more serious attitudes (such as shame or embarrassment) that impede brainstorming or artistic experimentation in design. [ 36 ]
Imaginative play and role play may allow adults to practice useful habits such as learned optimism , which is helpful in managing fear or terrors . Play also offers adults the opportunity to practice concepts that may not have been explicitly or formally taught (e.g. how to manage misinformation or deceit). Thus, even though play is just one of many tools used by effective adults, it remains a necessary one. [ 37 ]
There has been extensive research on the benefits of play among children , youth , and adolescence . Overlooked are the benefits of play for adults—more specifically, adults who spend a lot of time in the workplace. Many adults in North America are in the workforce and spend half of their waking hours in a workplace environment with little to no time for play. [ 38 ] [ full citation needed ] Play in this context refers to leisure-type activities with colleagues during lunch breaks or short breaks throughout the working day. Leisure activities might include physical sport activities, card games , board games , video games , foosball , ping-pong , yoga , and boot-camp sessions.
Playing games may promote a persistent and optimistic motivational style and positive affect . [ 39 ] [ full citation needed ] Positive affect enhances people's experiences, enjoyment , and sense of satisfaction , during their engagement with a task. While people are engaged in work, positive affect increases the satisfaction they feel from the work, and this increases their creativity and improves their performance on problem-solving tasks as well as other tasks. [ 40 ] [ full citation needed ] The development of a persistent motivational style charged with positive affect may lead to lasting work success. [ 39 ] [ full citation needed ]
Work and play are mutually supportive. Employees need to experience the sense of newness, flow , discovery , and liveliness that play provides. This provides the employee with the sense that they are integrated within the organization, and therefore they feel and perform better. [ citation needed ]
Incorporating play at work results in more productivity , creativity and innovation, higher job satisfaction, greater workplace morale , stronger or new social bonds, improved job performance, and a decrease in staff turnover, absenteeism , [ 41 ] and stress. Decreased stress leads to less illness, which results in lower health care costs. [ 42 ] Play at work may help employees function and cope when under stress, refresh body and mind, encourage teamwork, trigger creativity, and increase energy while preventing burnout. [ 41 ]
Companies that encourage play at work, whether short breaks throughout the day or during lunch breaks, are more successful because this leads to positive emotion among employees. Risk taking, confidence in presenting novel ideas, and embracing unusual and fresh perspectives are associated with play at work. Play can increase self-reported job satisfaction and well-being. Employees experiencing positive emotions are more cooperative, more social, and perform better when faced with complex tasks. [ 43 ]
Contests, team-building exercises, fitness programs, mental health breaks, and other social activities make the work environment fun, interactive, and rewarding. [ 44 ] [ better source needed ] Playfighting, i.e. playful fights or fictive disputes, may contribute to organizations and institutions, as in youth care settings. Staff tries to down-key playfight invitations to "treatment" or "learning," but playfighting also offers youth and staff identificatory respite from the institutional regime. [ incomprehensible ] Playfighting is a recurrent pattern in the social life of a youth care institution and sits at the core of what inmates and staff have to deal with [ 45 ]
Older adults represent one of the fastest growing populations around the world. [ 46 ] [ 47 ] [ 48 ] The United Nations predicted an increase of those aged 60 and above from 629 million in 2002 to approximately two billion in 2050 [ 49 ] but increased life expectancy does not necessarily translate to a better quality of life . [ 48 ] For this reason, research has begun to investigate methods to maintain and/or improve quality of life among older adults.
Similar to the data surrounding children and adults, play and activity are associated with improved health and quality of life among seniors. [ 33 ] [ 50 ] [ 48 ] Additionally, play and activity tend to affect [ how? ] successful aging as well as boost well-being throughout the lifespan. [ 46 ] [ 48 ] Although children, adults, and seniors all tend to benefit from play, older adults often perform it in unique ways to account for possible issues, such as health restrictions, limited accessibility, and revised priorities. [ 46 ] [ 33 ] For this reason, elderly people may partake in physical exercise groups, interactive video games , and social forums specifically geared towards their needs and interests. [ 33 ] [ 50 ] [ 51 ] One qualitative research study found older adults often chose to engage in specific games such as dominoes , checkers , and bingo for entertainment. [ 52 ] Another study indicated a common pattern in game preferences among older adults: seniors often favor activities that encourage mental and physical fitness, incorporate past interests, have some level of competition, and foster a sense of belonging. [ 50 ] [ 53 ] Researchers investigating play in older adults are also interested in the benefits of technology and video games as therapeutic tools. These outlets can lower the risk of developing particular diseases, reduce feelings of social isolation and stress, and promote creativity and the maintenance of cognitive skills. [ 47 ] [ 50 ] As a result, play has been integrated into physiotherapy and occupational therapy interventions for seniors. [ 54 ]
The ability to incorporate play into one's routine is important because these activities allow participants to express creativity, [ 50 ] improve verbal and non-verbal intelligence, [ 54 ] and enhance balance. [ 46 ] [ 33 ] These benefits may be especially crucial to seniors because cognitive and physical functioning declines with age. [ 48 ] However, it might not be aging itself that is associated with the decline in cognitive and physical capabilities, but the higher levels of inactivity in older adults. [ 46 ]
Play and activity tend to decline with age [ 48 ] which may result in negative outcomes such as social isolation, depression, and mobility issues. [ 33 ] American studies found that only 24% of seniors took part in regular physical activity [ 33 ] and only 42% use the internet for entertainment purposes. [ 50 ] In comparison to other age groups, the elderly are more likely to experience a variety of barriers, such as difficulty with environmental hazards and accessibility issues, that may hinder their abilities to play. [ 46 ] [ 55 ] Although playing may benefit seniors, it also has the potential to negatively impact their health. For example, those who play may be more susceptible to injury. [ 46 ] [ 55 ] Investigating these barriers may assist in the creation of useful interventions and/or the development of preventative measures, such as establishing safer recreational areas, that promote play throughout elderly life. [ 46 ]
A moderate level of play has numerous positive outcomes in the lives of senior citizens. [ 54 ] [ 46 ] [ 55 ] [ 50 ] To support and promote play within the older population, institutions should set up more diverse equipment, [ 47 ] [ 55 ] improve conditions within recreational areas, [ 46 ] and create more video games or online forums that appeal to the needs of seniors. [ 47 ] [ 50 ]
Evolutionary psychologists believe that there must be an important benefit of play, as there are so many other reasons to avoid it; observations have shown it has arisen independently in such varied groups as mammals, [ 56 ] birds, [ 57 ] reptiles, [ 58 ] [ 59 ] [ 60 ] [ 61 ] amphibians, [ 62 ] fish, [ 63 ] [ 64 ] [ 65 ] [ 66 ] and invertebrates. [ 67 ] [ 68 ] Animals are often injured during play, become distracted from predators, and expend valuable energy. In rare cases, play has even been observed between different species that are natural enemies such as a polar bear and a dog . [ 69 ] Yet play seems to be a normal activity with animals who occupy the higher strata of their own hierarchy of needs . Animals on the lower strata, e.g. stressed and starving animals, generally do not play. [ 37 ] However, in wild Assamese macaques physically active play is performed also during periods of low food availability and even if it is at the expense of growth, which highlights the developmental and evolutionary importance of play. [ 70 ]
The social cognitive complexity of numerous species, including dogs, have been explored in experimental studies. In one such study, conducted by Alexandra Horowitz of the University of California, the communication and attention-getting skills of dogs were investigated. [ 71 ] In a natural setting, dyadic play behavior was observed; head-direction and posture was specifically noted. When one of the two dogs was facing away or otherwise preoccupied, attention-getting behaviors and signals (nudging, barking, growling, pawing, jumping, etc.) were used by the other dog to communicate the intent and/or desire to continue on with the dyadic play. Stronger or more frequent signaling was used if the attention of the other dog was not captured. These observations tell us that these dogs know how play behavior and signaling can be used to capture attention, communicate intent and desire, and manipulate one another. This characteristic and skill, called the "attention-getting skill" has generally only been seen in humans, but is now being researched and seen in many different species.
Observing play behavior in various species can tell much about the player's environment (including the welfare of the animal), personal needs, social rank (if any), immediate relationships, and eligibility for mating. Play activity, often observed through action and signals, serves as a tool for communication and expression. Through mimicry, chasing, biting, and touching, animals act out in ways that send messages to one another; whether it's an alert, initiation of play, or expressing intent. When play behavior was observed for a study in Tonkean macaques , it was discovered that play signals weren't always used to initiate play; rather, these signals were viewed primarily as methods of communication (sharing information and attention-getting).
One theory—"play as preparation"—was inspired by the observation that play often mimics adult themes of survival. Predators such as lions and bears play by chasing, pouncing, pawing, wrestling, and biting, as they learn to stalk and kill prey. Prey animals such as deer and zebras play by running and leaping as they acquire speed and agility. Hoofed mammals also practice kicking their hind legs to learn to ward off attacks. Indeed, time spent in physical play accelerates motor skill acquisition in wild Assamese macaques . [ 70 ] While mimicking adult behavior, attacking actions such as kicking and biting are not completely fulfilled, so playmates do not generally injure each other. In social animals, playing might also help to establish dominance rankings among the young to avoid conflicts as adults. [ 37 ]
John Byers, a zoologist at the University of Idaho , discovered that the amount of time spent at play for many mammals (e.g. rats and cats) peaks around puberty, and then drops off. This corresponds to the development of the cerebellum , suggesting that play is not so much about practicing exact behaviors, as much as building general connections in the brain. Sergio Pellis and colleagues at the University of Lethbridge in Alberta, Canada, discovered that play may shape the brain in other ways, too. Young mammals have an overabundance of brain cells in their cerebrum (the outer areas of the brain—part of what distinguishes mammals). There is evidence that play helps the brain clean up this excess of cells, resulting in a more efficient cerebrum at maturity. [ 37 ]
Marc Bekoff (a University of Colorado evolutionary biologist) proposes a "flexibility" hypothesis that attempts to incorporate these neurological findings. It argues that play helps animals learn to switch and improvise all behaviors more effectively, to be prepared for the unexpected. There may, however, be other ways to acquire even these benefits of play (the concept of equifinality ). The social benefits of play for many animals, for example, could instead be garnered by grooming. Patrick Bateson maintains that equifinality is exactly what play teaches. In accordance with the flexibility hypothesis, play may teach animals to avoid "false endpoints". In other words, they harness the childlike tendency to keep playing with something that works "well enough", eventually allowing them to come up with something that might work better, if only in some situations. This also allows mammals to build up various skills that could come in handy in entirely novel situations. [ 37 ]
A study on two species of monkeys Semnopithecus entellus and Macaca mulatta that came into association with each other during food provisioning by pilgrims at the Ambagarh Forest Reserve, near Jaipur, India, shows the interspecific interaction that developed between the juveniles of the two species when opportunity presented itself. [ 72 ]
Learning through play has been long recognized as a critical aspect of childhood and child development . Some of the earliest studies of play started in the 1890s with G. Stanley Hall , the father of the child study movement that sparked an interest in the developmental, mental, and behavioral world of babies and children. Play promotes healthy development of parent-child bonds, establishing social, emotional, and cognitive developmental milestones that help them relate to others, manage stress, and learn resiliency. [ 73 ]
Modern research in the field of affective neuroscience (the neural mechanisms of emotion) has uncovered important links between role play and neurogenesis in the brain. [ 74 ] [ full citation needed ] For example, [ non sequitur ] researcher Roger Caillois used the word ilinx to describe the momentary disruption of perception that comes from forms of physical play that disorient the senses, especially balance.
Play is positively correlated with coping with daily stressors in children. [ 75 ] [ 76 ] [ full citation needed ] [ 77 ] [ full citation needed ] [ 78 ] By playing, children regulate their emotions. This is important for adaptive functioning because without regulation, emotions could be overwhelming and stressful.
Evolutionary psychologists have begun to explore the phylogenetic relationship between higher intelligence in humans and its relationship to play, i.e., the relationship of play to the progress of whole evolutionary groups as opposed to the psychological implications of play to a specific individual.
Various forms of play, physical or mental, influence cognitive abilities in individuals. As little as ten minutes of exercise (including physical play), can improve cognitive abilities. [ 79 ] An "exergame" is a game that incorporates some physical movement but is not formal exercise. Such games increase one's heart rate to the level of aerobics exercise and result in significant improvements in mental faculties such as math and recall memory. [ 79 ]
Playing video games is one of the most common mediums of play for children and adults today. There have been mixed reviews on the effects of video games. One study found "[playing video games] was positively associated with skills strongly related to academic success, such as time management, attention, executive control, memory, and spatial abilities—when playing video game occurs in moderation". [ 80 ]
Play can also influence one's social development and social interactions. Much of the research focuses on the influence play has on child social development. There are different forms of play that influence child social development. One study [ 81 ] explored the influence of playing styles with mothers versus playing styles with fathers and how it influences child social development. "[I]ntegral to positive development is the child's social competence or, more precisely, the ability to regulate their own emotions and behaviors in the social contexts of early childhood to support the effective accomplishment of relevant developmental tasks." [ 82 ]
Social benefits of play have been measured using basic interpersonal values such as getting along with peers. [ 81 ] Play with parents reduces anxiety in children. Having play time with parents that involves socially acceptable behaviour makes it easier for children to relate to be more socially adjusted to peers at school or at play. [ 81 ] Social development involving child interaction with peers is thus an area of influence for playful interactions with parents and peers.
Anji play ( 安吉游戏 in simplified Chinese, 安吉遊戲 in traditional Chinese) is an educational method based on children's self-directed play in outside spaces, using simple tools made of natural material. The teachers and instructors only observe and document the children's independent play. The method was created by Cheng Xueqin and is organized as two hours of free play during which the children choose the available material they want to use and build structures to play. [ 83 ]
While planning, experimenting, building, and using the structures to play, the children have the opportunity to interact with peers, to think critically about what may work, to discuss the plan, and organize the construction work. The process is observed and recorded by the teachers and instructors without intervention, even in instances of possible risk.
Before and after the two hours of play, the children have the opportunity to express their plans and discuss with their peers. After the play, they get the opportunity to draw, write or explain what they did. Then, they watch the videos recorded the same day and explain how they played and comment on each other's creations.
Anji play is also called "true play" and its guiding principles are love, risk, joy, engagement, and reflection. This method of self-initiated and self-directed play is applied at the pre-schools (children from three to six years old) in Anji county, East China. [ 84 ]
Media related to play at Wikimedia Commons | https://en.wikipedia.org/wiki/Playfulness |
Playing God was a 2012 BBC documentary in the Horizon series, hosted by Adam Rutherford . The documentary discusses synthetic biology , the potential of science "breaking down nature into spare parts" and then rebuilding it back up as we wish. [ 1 ]
Adam Rutherford has been studying the emerging field of synthetic biology for the past 10 years and believes that this sort of genetic tinkering is the most effective way to pass along traits between different organisms, given that this result cannot be easily obtained through typical mating of certain species. In Playing God , he discusses the creation of the spider-goat by American researchers. It is a part goat, part spider hybrid, whose genetic code has been altered to be able to produce the same proteins found in spider silk. The milk produced by these goats can be used to create an artificial spider's web. [ 2 ] Typically this silk is produced in small quantities by spiders but with the genetic modification of the goats, it may be mass produced. The goats are easier to handle in large groups than spiders and thus this could potentially increase the efficiency of silk production and consumer cost. [ 2 ]
This technology is also being used to make bio-diesel to power cars. Biotech company, Amyris, in Emeryville, California, has applied synthetic biology to yeast. Instead of producing alcohol through the fermentation of sugar, this yeast produces diesel. [ 2 ] The amount of diesel that is produced by this method is substantially greater than that of the conventional method and can exponentially increase the rate of production. This diesel has already been implemented in actual cars, in Brazil. [ 2 ]
Other researchers are looking at how we might, one day, control human emotions by sending 'biological machines' into our brains. [ 1 ] MIT professor Ed Boyden leads a group in synthetic neuroscience. This team utilizes the genetic code for molecules that convert light into electrical energy and inserts it in a virus or cassette that may be installed into various organisms. Because the brain works on electrical impulses, this technology may be applied to neural circuits, in order to treat various neurological disorders. [ 1 ] With this technology, the direct control of various light sensitive and electrical functions in the brain would be enabled.
MIT professor, Ron Weiss, has worked extensively in this field and has been leading a team in incorporating the concepts of computer programming and engineering to biology. [ 2 ] "I decided to take what we understand in computing and apply that to programming biology. To me, that's really the essence of synthetic biology." [ 2 ] Weiss' team published a study that discusses how they combined computer circuit elements with BioBricks parts. The way this works is that the computer circuit is able to distinguish between a healthy and mutated cell by utilizing a set of five criteria. Any cells that satisfy these conditions are deleted, similar to the way code could eliminate certain functions in computer programming. The ability to target individual cells could make this an alternative to treatments that may have harmful effects on healthy cells, such as chemotherapy. [ 2 ]
The area of synthetic biology is extensively discussed in Playing God . This is considered to be a relatively new field that incorporates elements of engineering into biology. [ 3 ] It involves the blending and manipulation of natural molecules and unnatural molecules to obtain a specific outcome. [ 4 ] Through this mean, scientists may use biology as a base for the development of synthetic life and genetic coding. [ 3 ] This area of study has been noted with the potential to increase the efficiency of the production of certain biomolecules and naturally occurring materials, such as enzymes. [ 3 ]
Playing God and presenter, Adam Rutherford, have been subject to criticism following the release of this documentary. As plainly stated by Andrew Marszal of The Telegraph , "Rutherford overcooked it, particularly in his opening gambit – the revelation that scientists have developed a new hybrid breed of 'spider-goats'... we were left a little disappointed as Freckles, Pudding and Sweetie chomped and grazed around the farm looking for all the world like, well, goats." [ 5 ] The portrayal of the applications of synthetic biology in this documentary appeared to be exaggerated and their importance not adequately stressed. The Alliance for Natural Health International (ANHI) wrote a reaction piece in which it expressed concern about the overwhelmingly positive tone the documentary as a whole had towards the development of this technology. "The programme was almost wholly positive about the new technology, even though it has many serious potential consequences for humans and the planet... Dr Rutherford reacts like a kid in a sweetshop at each new technological marvel. Not once does he question whether creating spider-goats is necessary, or whether the 'trickle-down' of genetic engineering into the community is a step too far." [ 6 ] | https://en.wikipedia.org/wiki/Playing_God_(2012_film) |
Playing with Infinity: Mathematical Explorations and Excursions ( German : Das Spiel mit dem Unendlichen ) is a popular mathematics book by Hungarian mathematician Rózsa Péter , published in German in 1955 and in English in 1961.
Playing with Infinity was originally written in 1943 by mathematician Rózsa Péter , [ 1 ] based on a series of letters Péter had written to a non-mathematical friend, Marcell Benedek [ hu ] . [ 2 ] Because of World War II, it was not published until 1955, in German , under the title Das Spiel mit dem Unendlichen , by Teubner. [ 1 ]
An English translation by Zoltán Pál Dienes was published in 1961 by G. Bell & Sons in England, [ 3 ] and by Simon & Schuster in the US. [ 4 ] The English version was reprinted in 1976 by Dover Books . [ 2 ] [ 5 ] [ 6 ] The German version was also reprinted, in 1984, by Verlag Harri Deutsch . [ 7 ] The book has also been translated into Polish in 1962 [ 8 ] and Russian in 1967. [ 9 ] The Basic Library List Committee of the Mathematical Association of America has suggested its inclusion in undergraduate mathematics libraries. [ 2 ]
Playing with Infinity presents a broad panorama of mathematics for a popular audience. It is divided into three parts, the first of which concerns counting, arithmetic, and connections from numbers to geometry both through visual proofs of results in arithmetic like the sum of finite arithmetic series , and in the other direction through counting problems for geometric objects like the diagonals of polygons. These ideas lead to more advanced topics including Pascal's triangle , the Seven Bridges of Königsberg , the prime number theorem and the sieve of Eratosthenes , and the beginnings of algebra and its use in proving the impossibility of certain straightedge and compass constructions . [ 5 ]
The second part begins with the power of inverse operations to construct more powerful systems of numbers: negative numbers from subtraction, and rational numbers from division. Later topics in this part include the countability of the rationals, the irrationality of the square root of 2 , exponentiation and logarithms , graphs of functions, slopes and areas of curves, and complex numbers . [ 5 ] Topics in the third part include non-Euclidean geometry , higher dimensions, mathematical logic , the failings of naive set theory , and Gödel's incompleteness theorems . [ 1 ] [ 5 ]
In keeping with its title, these topics allow Playing with Infinity to introduce many different ways in which ideas of infinity have entered mathematics, in the notions of infinite series and limits in the first part, countability and transcendental numbers in the second, and the introduction of infinite points in projective geometry , higher dimensions, metamathematics , and undecidability in the third. [ 1 ] [ 4 ]
Reviewer Philip Peak writes that the book succeeds in showing readers the joy of mathematics without getting them bogged down in calculations and formulas. [ 6 ] On a similar note, Michael Holt recommends the book to mathematics teachers, as a sample of the more conceptual style of mathematics taught in Hungary at the time in contrast to the orientation towards practical calculation of English pedagogy . [ 5 ] Reuben Goodstein summarizes it more succinctly as "the best book on mathematics for everyman that I have ever seen". [ 3 ]
By the time of Leon Harkleroad's review in 2011, the book had become "an acknowledged classic of mathematical popularization". However, Harkleroad also notes that some idiosyncrasies of the translation, such as its use of pre-decimal British currency , have since become quaint and old-fashioned. [ 2 ] And similarly, although W. W. Sawyer in reviewing the original 1955 publication calls its inclusion of topics from graph theory and topology "truly modern", Harkleroad points out that more recent works in this genre have included other topics in their own quest for modernity such as " fractals , public-key cryptography , and internet search engines ", which for obvious reasons Péter omits. [ 2 ] | https://en.wikipedia.org/wiki/Playing_with_Infinity |
Plazes AG was a Berlin, Germany-based geosocial networking site. Plazes allowed users to post their location and current activities and share this information with other Plazes users via computers or mobile telephones. On 23 June 2008, Nokia Corporation announced plans to acquire Plazes. [ 1 ] Plazes was subsequently integrated to Nokia Maps which itself was integrated to HERE Maps.
Plazes AG introduced the beta version of the Plazes service on 16 August 2004. [ 2 ] The service was continually updated and began to attract attention on technology blogs. [ 3 ] [ 4 ] In October 2004, Plazes introduced two APIs : a Web-based API that advised users of the current location of other Plazes users; and a launcher API that allowed users to create their own Plazes launchers. [ 5 ] In January 2005, Plazes introduced a Movable Type plugin that allowed users to automatically include or add their location to blog postings. [ 6 ] In June 2005, Plazes created an API that allowed users to access photos from their Flickr accounts and to add those photos to their Plazes accounts. [ 7 ] A Flickr group of Plazes users quickly sprang up. [ 8 ] In 2006, Plazes was awarded the LeadAward in Bronze in the Category "WebLeader 2006″. [ 9 ]
The Plazes Web interface allows users to post a location, the time of day they will be at the location and the activity they will be engaged in at the location. This information can be shared with people selected by the user, Plazes contacts or all members of the Plazes community. In addition to the Web interface, users can update their location using Plazer (see below), via text message or via m.plazes.com [ permanent dead link ] , the mobile Plazes Web site. Plazes users are able to publish their Plazes location on Fire Eagle , Twitter, Google Maps , MySpace and on the user's blog.
The Web interface allows users to invite others to join Plazes. Plazes can search a user's Gmail , Yahoo or Hotmail or Microsoft Outlook contacts and send invitations to these contacts.
Plazes allows users to create groups or to join an existing group of Plazes users. Under the Groups tab, Plazes suggests groups that the user may wish to join, as well as offer the user the opportunity to search for existing groups. If the user wants to create a group, the user will need to select a group name and a draft a brief description of the group. The user may add an image to the group to help differentiate it from other groups.
Plazes has a radar function that allows users to discover other Plazes users that are located near the user's current location. The Plazes Radar generates a list of the locations close to the user's current location and lists the number of Plazes users that have previously stated they were at that location. When the user clicks on the location name, information about the user that was at that location is displayed along with a description of the user's activity at the location.
The Plazes Launcher was a client application that allowed Plazes users to update their location and current activities without having to log onto plazes.com. The launcher would detect the MAC address of the user's current router, and query the Plazes database to see if the router already had a "plaze" associated with it. If no existing plaze was found, the user would be prompted to enter details about the plaze, including a name and its physical location. [ 10 ]
In March 2006, the Plazes Launcher was rebranded as Plazer . [ 11 ] Plazer is integrated with Skype; Skype users are able to publish their location on Skype via Plazer. [ 12 ] Plazer is available for Windows, Mac OS X, iPhone and iPod touch, and Symbian. [ 13 ] [ 14 ] There was also a third-party Plazer available for Nokia's Maemo devices. [ 15 ]
In August 2007, Nokia announced that it was moving into the services field with the introduction of Ovi . [ 16 ] Nokia Maps became part of the Ovi service offering. On 23 June 2008, Nokia Corporation announced plans to acquire Plazes. As part of the acquisition, Plazes gained access to the millions of users that own a Nokia device. [ 17 ] At the same time, Nokia gained technology and a research team that was on the cutting edge of the geosocial networking trend. [ 18 ] The acquisition closed on 15 July 2008. [ 19 ] Post acquisition, Plazes became part of Nokia's Services business unit. [ 18 ]
On 4 May 2012 the Plazes team sent an email message for their users informing that on the next week will go out of service. Users could export their Plazes history to Nokia Maps which itself was integrated to HERE Maps. | https://en.wikipedia.org/wiki/Plazes |
The Plebanski tensor is an order 4 tensor in general relativity constructed from the trace-free Ricci tensor . It was first defined by Jerzy Plebański in 1964. [ 1 ]
Let S a b {\displaystyle S_{ab}} be the trace-free Ricci tensor:
Then the Plebanski tensor is defined as
The advantage of the Plebanski tensor is that it shares the same symmetries as the Weyl tensor . It therefore becomes possible to classify different spacetimes based on additional algebraic symmetries of the Plebanski tensor in a manner analogous to the Petrov classification . [ 2 ]
This relativity -related article is a stub . You can help Wikipedia by expanding it .
This mathematical physics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Plebanski_tensor |
A Plectron is a specialized VHF / UHF single-channel, emergency alerting radio receiver , used to activate emergency response personnel, and disaster warning systems. Manufactured from the late 1950s, through the late 1990s, by the now defunct Plectron Corporation in Overton, Nebraska , hundreds of thousands of these radios were placed in homes of first responders across all of North America. This included ambulance crews, full-time and volunteer firefighters , off-duty specialized police response teams, Civil Defense members, and search and rescue teams.
A Plectron's main feature (distinguishing it from a regular squelched radio) was its selective de-squelching. It would only sound when a correct pair of tones were broadcast - allowing many agencies (with different tones) to share the same frequency. Some Plectron Models had a set of "Built-in Re-chargeable Batteries", making the Plectron Portable. The Motorola MINITOR pager also uses this function and has largely replaced the Plectron.
This article related to radio communications is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Plectron |
Pledge and review is a method for facilitating international action against climate change . It involves nations each making a self-determined pledge relating to actions they expect to take in response to global warming, which they submit to the United Nations . Some time after the pledges have been submitted, there is a review process where nations assess each other's progress towards meeting the pledges. Then a further round of enhanced pledges can be made, and the process can further iterate. [ 1 ] [ 2 ] [ 3 ]
Pledge and review is sometimes referred to as a bargaining approach; when nations first announce their pledges they may not be set in stone. A nation might strengthen its pledge in response to pledges by its competitors, which can encourage it to increase its climate ambition if it feels it can do so without losing ground to trading rivals. Additionally, sometimes a nation that feels especially threatened by climate change can make non-climate related concessions to a trading partner, in return for them making a stronger pledge. The main way to increase pledges, however, is when the process iterates after the review phase. Each subsequent round of pledges is supposed to involve an increased level of commitment to combat climate change. Hence the ratcheting up metaphor is often used, as the strengthening of pledges is supposed to be a one-way process. [ 1 ] [ 2 ] [ 3 ]
Pledge-and-review was introduced as a possible way to facilitate global action on climate change in 1991, yet it was little used in the early 1990s. In 1995, it was rejected by the international community, who instead favoured aiming for legally binding emission reduction targets. Due to challenges in securing international agreement to strengthen the only partially successful Kyoto Protocol , pledge-and-review was re-introduced as part of the 2009 Copenhagen Accord . Initially seen as an interim measure, by 2015 it had become the central approach of international efforts to encourage climate mitigation . Though in negotiations leading to the 2015 Paris Agreement , the name pledge-and-review was dropped; pledges are now formally called Nationally Determined Contributions . [ 1 ] [ 2 ] [ 3 ] [ 4 ]
The expected content for pledges depends on the specific implementation of pledge-and-review. Commitments to GHG emissions reduction targets are generally a core feature, though states have full freedom to set where that target lies. States can choose to express their reductions target in different ways. For example, in terms of absolute reductions in the volume of GHG emitted; for the Paris implementation, most developed nations included such a pledge. Yet states can instead commit to reducing GHG emissions in other ways, such as a percentage of GDP growth. As well as emissions reductions targets, the pledges can include intentions to implement climate adaptation measures, as well as specific industry level climate friendly policy, like support for various types of sustainable energy production. States are never legally required to meet the commitments in their pledges, but their progress is subject to review. [ 2 ] [ 4 ] [ 5 ]
The exact mechanism for reviews also varies depending on the specific implementation, and the review concept applies at several levels. Nations periodically review their own pledges, with a view to a one way increase in ambition. Pledges, both the level of commitment they contain, and actual progress in achieving the same, are also reviewed internationally, under the auspices of the UNFCCC . While the formal review processes run by the United Nations aim to be non adversarial, states can also be subject to informal reviews from NGOs , which can take a name and shame approach, though may also choose to "praise and encourage" nations that are doing more than comparable peers to limit climate change. In the implementation of pledge-and-review agreed at Paris in 2015, another level of review is the Global stocktake , where the pledges made by the world's nations are evaluated collectively. [ 5 ] [ 2 ] [ 4 ]
The pledge-and-review system was first proposed by Japan in 1991. In December 1990, in response to the threat of climate change, the United Nations established the Intergovernmental Negotiating Committee for a Framework Convention on Climate Change. It had become apparent that getting nations [ note 1 ] to commit to legally binding emissions targets would be more challenging for greenhouse gas emissions (GHG) than it had been for emissions relating to sulphur pollution and depletion of the ozone layer. With the support of Britain and France, Japan made a proposal for a pledge-and-review system as an alternative. Various nations objected to the idea, however, so only a weakened form of pledge-and-review was included in the United Nations Framework Convention on Climate Change (UNFCCC) by the time it was signed at the 1992 Earth Summit . The pledge-and-review system was formally rejected at the first Conference of the Parties (COP) which took place in Berlin, 1995. The focus switched to negotiations aimed at legally binding emission reduction targets, as embodied by the 1997 Kyoto Protocol . [ 1 ] [ 3 ]
The Kyoto protocol has only aimed to impose emissions reduction targets on Annex parties (largely corresponding to advanced industrialised nations as of the late 20th century, plus some of the economies in transition). The non-Annex countries, including large emitters such as China, did not have targets at all. Even the Annex countries did not all accept the reduction targets, most notably the United States. At the 2009 Copenhagen Summit , the main focus was on strengthening the emission reduction targets. This failed. As a backstop measure, a revival of the voluntary pledge-and-review system was proposed by Australia. While the system was formally rejected for general adoption, 89 countries submitted such a pledge, including the 27 EU member states who issued a combined pledge. 47 of these nations were non-Annex countries. The nations which had made a Copenhagen pledge were collectively responsible for about 80% of global GHG emissions, much more than the 25% covered by Kyoto targets in the first commitment period or the 15% covered by the commitment period later agreed at the 2012 Doha summit . [ 2 ] [ 3 ]
The pledge-and-review system established at Copenhagen was formalised at the 2010 Cancún Summit . The system was further strengthened in the years leading up to the 2015 Paris Conference , though it was no longer called "pledge-and-review", with pledges instead formally labelled Nationally Determined Contributions (NDCs). [ 2 ] [ 3 ] [ 6 ]
There are three broad approaches to coordinating mitigation efforts that nations can attempt to negotiate at international conferences. Setting a carbon price . The acceptance of legally binding emissions reductions targets imposed in a "top down" way by a central body such a United Nations agency. And the "bottom up" pledge-and-review system where each party autonomously decides its own contribution. These approaches can be complementary, though at various periods there have been disagreements as to whether the world's primary method ought to be pledge-and-review or emissions targets. Until about 2010, international negotiations focused largely on emissions targets. Previous environmental successes like the reduction of emissions causing acid rain , and especially the Montreal treaty which led to reduced emissions damaging the ozone layer , suggested that targets could be effective. In practice however, it has been much more challenging to get nations to agree to binding targets relating to GHG. And even when they had signed up to a legally binding target, there is no reliable way to enforce such international law on a powerful nation. So after the relative failure of the Kyoto protocol and attempts to establish a more effective set of targets at Copenhagen, the pledge-and-review system became the dominant approach. As of 2020, international efforts to improve carbon price related mechanisms are still underway. Except at regional level in the EU, actual implementations have so far mostly occurred only at national and sub-national levels (e.g. in China, or in some U.S. states). [ 2 ] [ 3 ] [ 6 ]
Progress towards settling on pledge-and-review can be seen in the light of a decades long attempt to harmonise views between the US led Umbrella Group and the rest of the world, concerning which mitigation method should be central to global agreements on climate change. The other two big climate negotiating groups were the EU and G77+China . During the 1990s, the Umbrella Group was in favour of both pledge-and-review and carbon price. [ note 2 ] But much of the EU and G77+China preferred to focus solely on legally binding emissions reduction targets, and they largely got their way during the nineties. The Kyoto protocol agreed in 1997 was focussed largely on emissions targets, with only a limited role for carbon price and no place for pledge-and-review. US engagement on global climate negotiations have tended to vary depending on who has been president. There was cautious engagement with Bush Sr , leadership with Clinton , dis-engagement with Bush Jr and enthusiastic leadership with Obama . The two years (2009 & 2015) where there was most progress towards pledge-and-review coincided with the two years where there was the highest apparent recognition for US leadership among climate delegates from the rest of the world. In 2009, there was much enthusiasm for President Obama, which may have been a partial reason why it was possible to get pledge-and-review back on the table at the 2009 Copenhagen summit. Overall though, Copenhagen was seen as a failure, denting faith in Obama's climate leadership. After being relatively quiet on climate for two years, major domestic climate initiatives first announced in 2012 and talked up at the 2013 Warsaw and 2014 Lima CoPs, saw faith in Obama's climate leadership reach a new peak just before the 2015 Paris conference, where pledge-and-review became the central method for coordinating climate mitigation efforts. [ 7 ] [ 8 ] [ 9 ] [ 4 ]
In the early 1990s, the pledge-and-review system was heavily criticised by environmental groups; for example, Climate Action Network labelled it "hedge and retreat". It has also been criticised by academics, especially after the system was revived at Copenhagen with some calling it "scientifically inadequate" or "second best". However, other academics described pledge-and-review as an "essential pillar for climate change mitigation ". A survey of participants at the 2011 Durban summit found that the biggest concern over pledge-and-review was the gap between what has been pledged and the level of action needed to meet the 2 degree target (limiting global warming to only 2 °C above pre industrial temperatures.). Participants were least concerned about the voluntary nature of the pledges, suggesting that a system that lacked legally binding commitments could still have international legitimacy. Comparing NGOs with actual negotiators, the study found that in the case of Annex 1 NGOs, they were much more critical of pledge-and-review than negotiators from Annex 1 nations. Whereas with non Annex nations (mostly those in the global south), the opposite pattern emerged. Non annex NGOs were less critical about pledge-and-review compared to non Annex negotiators. [ 1 ] [ 2 ] [ 3 ] [ 6 ] | https://en.wikipedia.org/wiki/Pledge_and_review |
The Pleiades ( / ˈ p l iː ə d iː z , ˈ p l eɪ -, ˈ p l aɪ -/ ; [ 1 ] Ancient Greek : Πλειάδες , Ancient Greek pronunciation: [pleːádes] ), were the seven sister- nymphs , companions of Artemis , the goddess of the hunt. [ 2 ] Together with their sisters, the Hyades , they were sometimes called the Atlantides, Dodonides, or Nysiades , nursemaids and teachers of the infant Dionysus . The Pleiades were thought to have been translated to the night sky as a cluster of stars, the Pleiades , and were associated with rain.
The name Pleiades ostensibly derived from the name of their mother, Pleione , effectively meaning "daughters of Pleione". However, etymologically, the name of the star-cluster likely came first, and Pleione's name indicated that she was the mother of the Pleiades. [ 3 ] According to another suggestion Pleiades derived from πλεῖν ( plein , "to sail") because of the cluster's importance in delimiting the sailing season in the Mediterranean Sea : "the season of navigation began with their heliacal rising ". [ 4 ]
The Pleiades' parents were the Titan Atlas [ 5 ] and the Oceanid Pleione [ 6 ] born on Mount Cyllene . In some accounts, their mother was called Aethra , another Oceanid. [ 7 ] Aside from the above-mentioned sisters (the Hyades), the Pleiades' other siblings were Hyas and the nymph Calypso who was famous in the tale of Odysseus . Sometimes they were related as half-sisters to the Hesperides , nymphs of the morning star.
Several of the most prominent male Olympian gods (including Zeus , Poseidon , and Ares ) engaged in affairs with the seven heavenly sisters. These relationships resulted in the birth of their children.
After Atlas was forced to carry the heavens on his shoulders, Orion began to pursue all of the Pleiades, and Zeus transformed them first into doves, and then into stars to comfort their father. The constellation of Orion is said to still pursue them across the night sky.
One of the most memorable myths involving the Pleiades is the story of how these sisters literally became stars, their catasterism . According to some versions of the tale, all seven sisters killed themselves because they were so saddened by either the fate of their father, Atlas, or the loss of their siblings, the Hyades. In turn, Zeus, the ruler of the Greek gods, immortalized the sisters by placing them in the sky. There these seven stars formed the star cluster known thereafter as the Pleiades.
The Greek poet Hesiod mentions the Pleiades several times in his Works and Days . As the Pleiades are primarily winter stars, they feature prominently in the ancient agricultural calendar. Here is a bit of advice from Hesiod:
And if longing seizes you for sailing the stormy seas, when the Pleiades flee mighty Orion and plunge into the misty deep and all the gusty winds are raging, then do not keep your ship on the wine-dark sea but, as I bid you, remember to work the land.
The Pleiades would "flee mighty Orion and plunge into the misty deep" as they set in the West, which they would begin to do just before dawn during October–November, a good time of the year to lay up your ship after the fine summer weather and "remember to work the land"; in Mediterranean agriculture autumn is the time to plough and sow.
The poet Sappho mentions the Pleiades in one of her poems:
The moon has gone The Pleiades gone In dead of night Time passes on I lie alone
The poet Lord Tennyson mentions the Pleiades in his poem " Locksley Hall ":
Many a night I saw the Pleiads, rising through the mellow shade, Glitter like a swarm of fire-flies tangled in a silver braid.
The loss of one of the sisters, Merope, in some myths may reflect an astronomical event wherein one of the stars in the Pleiades star cluster disappeared from view by the naked eye. [ 22 ] [ 23 ]
Pleiades and Orion are mentioned in the Book of Job :
"Can you bind the beautiful Pleiades? Can you loose the cords of Orion? Can you bring forth the constellations in their seasons or lead out the Bear with its cubs?"
Although most accounts are uniform as to the number, names, and main myths concerning the Pleiades, the mythological information recorded by a scholiast on Theocritus ' Idylls with reference to Callimachus has nothing in common with the traditional version. [ 24 ] According to it, the Pleiades were daughters of an Amazonian queen; their names were Maia, Coccymo, Glaucia, Protis, Parthenia, Stonychia, and Lampado. They were credited with inventing ritual dances and nighttime festivals. | https://en.wikipedia.org/wiki/Pleiades_(Greek_mythology) |
The Pleiades Phenomenon refers to the chance encounter between a star and an interstellar cloud of dust that leads to the appearance of a reflection nebulosity with characteristics similar to those observed in the Pleiades open star cluster. [ 1 ] This contrasts against reflection nebulae surrounding young stars where the dust is the remnant of star formation . The term Pleiades Phenomenon was coined by astronomer Paul Kalas who discovered five nebulosities not related to star forming regions using a coronagraph . [ 2 ] The nebulosities were found to have "linear, filamentary, striated morphological structure" located between 1000 and 100,000 astronomical units from each star. A subsequent study of infrared sources in the Small Magellanic Cloud found evidence for the Pleiades Phenomenon outside of the Milky Way . [ 3 ] | https://en.wikipedia.org/wiki/Pleiades_Phenomenon |
The high visibility of the star cluster Pleiades in the night sky and its position along the ecliptic (which approximates to the Solar System 's common planetary plane) has given it importance in many cultures, ancient and modern. Its heliacal rising , which moves through the seasons over millennia (see precession ) was nonetheless a date of folklore or ritual for various ancestral groups, so too its yearly heliacal setting. [ 2 ]
As noted by scholar Stith Thompson , the constellation was "nearly always imagined" as a group of seven sisters, and their myths explain why there are only six. [ 3 ] Some scientists suggest that these may come from observations back when Pleione was further from Atlas and more visible as a separate star as far back as 100,000 BC. [ 4 ]
Tuareg Berbers of the northern Sahara call the Pleiades Cat iheḍ (or -ahăḍ ). This Berber name means: "daughters of the night". To many other Berbers it is Tagemmunt ("the group"). [ 5 ]
A Tuareg Berber proverb says:
Meaning: When the Pleiades "fall" with the sunset on the west, it still roughly (at J2000) means the hot, dry summer is coming. When they rise from the east with sunrise, the cold somewhat rainy season is coming. Nomads and others need to brace for these. [ 6 ] [ 5 ]
The Mesopotamian cuneiform texts of the MUL.APIN , which were produced from the seventh century BC onwards, describe Pleiades leap rules for the intercalation of months. They refer to a time well before the creation of the surviving clay tablets , which have been copied several times, namely the 26th century BC . This results from the astronomical dates explicitly given in the texts for the visibility of the Pleiades ( Sumerian term MUL.MUL = "stars") and the beginnings of the months. The two surviving Babylonian Pleiades leap rules are recorded in lines eight to eleven of the second clay tablet of the MUL.APIN series. Although the cuneiform characters of the beginnings of lines ten and eleven have not been completely preserved, they can be reconstructed relatively reliably and meaningfully. A normal year has twelve lunar months . A full year requires the intercalation of a thirteenth lunar month. According to this leap rule, seven synodical month have to be intercalated within the duration of a Metonic cycle , which has exactly nineteen solar years . [ 7 ] [ 8 ]
8 When on the first Nisannu Pleiades and moon are in balance, this year is normal. 9 When on the third Nisannu Pleiades and moon are in balance, this year is full. 10 When the Pleiades rise on the first Ajaru, this year is normal. 11 When the Pleiades rise on the first Simanu, this year is full.
In the Old Testament , the Pleiades ( Hebrew : כימה , romanized : Khima ) are mentioned three times. [ 9 ] Each passage also mentions Orion , a nearby, bright, anthropomorphic constellation: Amos 5:8 ; Job 9:9 ; and Job 38:31 . The first two are references about their creation. The third (taken in the context of following verses) stresses their ongoing nature in the night sky; God is speaking directly to Job and challenges him, asking if he can bind the chains of the Pleiades — the implication being that Job cannot, but God can.
The Talmud (Berakhot 58b) suggests understanding ke' me-ah as kimah ( כימה as כמאה ) "about one hundred" stars in the Pleiades star cluster. Like most astronomical figures in rabbinic writing, the Jewish sages pointed to this as having come from Mount Sinai .
Rabbi Shlomo Yitzchaki ("Rashi") suggested even more stars within the cluster when he commented on the Talmud with a question, "What is meant by Kimah?" It is then understood that the Talmud was suggesting hundreds of stars in the Pleiades cluster, and that only the first hundred are mentioned due to them being the most important. [ 10 ]
According to Jewish folklore , when two fallen angels named Azazel and Shemhazai made it to the Earth, they fell strongly in love with the women of humankind. Shemhazai found a maiden named Istehar who swore she would give herself to him if he told her the sacred name which granted him the power to fly to Heaven . He revealed it to her, but she flew up to Heaven, never to fulfill her promise, thus she was placed in the constellation Pleiades, [ 11 ] although she is also associated with the planet Venus. [ 12 ]
In Arabic the Pleiades are known as al-Thurayya ( الثريا ), the first main consonant becoming a morpheme into outlying linguistic zones north and east. Some scholars of Islam suggested that the Pleiades are the "star" mentioned in Sura An-Najm ("The Star") of the Quran . [ 13 ]
The name was borrowed into Persian and Turkish as a female given name, and is in use throughout the Middle East (for example Princess Soraya of Iran and Thoraya Obaid ). It eponymises the Thuraya satellite phone system of the United Arab Emirates .
A Hadith recalled by Imam Bukhari , states:
A companion of The Holy Prophet ( may the peace and blessings of Allah be upon him ) relates: One day we were sitting with The Holy Prophet (may the peace and blessings of Allah be upon him) when this chapter [ a ] [ 14 ] was revealed. I enquired from Muhammad (may the peace and blessings of Allah be upon him). Who are the people to whom the words "and among others of them who have not yet joined them" [ b ] refer? Salman (may Allah be pleased with him), a Persian was sitting among us. The Holy Prophet (may the peace and blessings of Allah be upon him) put his hand on Salman (may Allah be pleased with him) and said. If faith were to go up to the Pleiades, a man from among these would surely find it. ( Bukhari ). [ 16 ]
Notes:
In Turkish the Pleiades are known as Ülker . According to the Middle Turkic lexicographer Kaşgarlı Mahmud , writing in the 11th century, ülker çerig refers to a military ambush ( çerig meaning 'troops in battle formation'): "The army is broken up into detachments posted in various places," and when one detachment falls back the others follow after it, and by this device "(the enemy) is often routed." Thus ülker çerig literally means 'an army made up of a group of detachments', which forms an apt simile for a star cluster. [ 17 ] Ülker is also a unisex given name, a surname and the name of a food company best known for its chocolates.
In Farsi , the Pleiades is primarily known as Parvin ( پروین ) or Parveen . It is a common given name of Iranians , Afghanis and some Pakistanis .
Pleiades has gained, in a few tongues, several creative derivations of its French quite well-known, non-stellar meaning: "multitude".
In Greek mythology , the stars of Pleiades represented the Seven Sisters . The constellation was also described as ἑπτάποροι "heptaporoi", by poet Aratus . [ 18 ]
The astrological Pleiades were described in Three Books of Occult Philosophy by Heinrich Cornelius Agrippa (Köln, 1533, but published manuscript as early as 1510).
In Western astrology they represent coping with sorrow [ 19 ] and were considered a single one of the medieval fixed stars . As such, they are associated with quartz [ citation needed ] and fennel . [ 20 ]
In esoteric astrology the seven planetary systems revolve around Pleiades. [ 21 ]
To the Bronze Age people of Europe, such as the Celts (and probably considerably earlier), the Pleiades were associated with mourning and with funerals, since at that time in history, on the cross-quarter day [ dubious – discuss ] between the autumn equinox and the winter solstice (see Samhain , also Halloween or All Souls Day ), which was a festival devoted to the remembrance of the dead, the cluster rose in the eastern sky as the Sun's light faded in the evening. It was from this acronychal rising that the Pleiades became associated with tears and mourning. As a result of precession over the centuries, the Pleiades no longer marked the festival, but the association has nevertheless persisted, and may account for the significance of the Pleiades astrologically.
In Baltic languages , the name for this constellation is Sietynas in Lithuanian and Sietiņš in Latvian , which is derived from sietas meaning " a sieve ". In Lithuanian folk songs this constellation is often personified as a benevolent brother who helps orphan girls to marry or walks soldiers along the fields. But in Lithuanian folk tales as well as Latvian folk songs this constellation is usually depicted as an inanimate object, a sieve which gets stolen by the devil from the thunder god or is used to conjure light rain by thunder's wife and children. [ 22 ] [ 23 ] [ 24 ]
Ethnographer Svend Grundtvig collected a folkloric account of the myth of the Pleiades in Danish folklore ("The Pleiades, or the Seven Stars"). [ 25 ] In this variant, six brothers travel the world to learn a trade and, with their combined help, rescue a kidnapped princess from a dwarf. Unable to choose which brother she likes best, God allows the seven to pass out in their sleep and turns them into the seven stars of the constellation. [ 26 ]
The old name of the starcluster in Hungarian is Fiastyúk , meaning "a hen with chicks". [ citation needed ]
In historical Russian treatises about astronomy, the constellation was known as semizvedie , as well as vlasozelisci . [ 27 ] Another Russian name to the constellation is Volosozhary or Volosynia , related by some scholars to the word volosy ('wool'), and to the god Volos . [ 28 ] [ 29 ] [ 30 ]
In Ukrainian folklore , the Pleiades are known as Stozhary ( Стожари ), Volosozhary ( Волосожари ), or Baby-Zvizdy ( Баби-Звізди ). [ citation needed ]
Stozhary can be etymologically traced to stozharnya ( стожарня ) meaning a 'granary', 'storehouse for hay and crops', or can also be reduced to the root sto-zhar ( сто-жар ), meaning 'hundredfold glowing' or "a hundred embers". [ 31 ]
Volosozhary ( lit. ' the ones whose hair is glowing ' ) or Baby-Zvizdy ( lit. ' female stars ' ) refer to the female tribal deities. According to the legend, seven maids lived long ago. They used to dance the traditional round dances and sing the glorious songs to honor the gods. After their death the gods turned them into water nymphs, and, having taken them to the Heavens, settled them upon the seven stars, where they dance their round dances (symbolic for moving the time) to this day. [ citation needed ]
In Ukraine , this asterism was considered a female talisman until recent times.
The constellation of the Pleiades is known by several names in Belarusian tradition, such as Sitechko ('a sieve'), and, in a legend from the Horvats, there are seven vil ('spirits of deceased maidens') who dance around in a circle. [ 32 ] Further studies by researcher Tsimafei Avilin show the main names of the constellation in Belarusian : Sieve (Sita or, rarely, Rešata, and variations) and The Hens (Kuročka and variations). [ 33 ]
In Serbian folklore , the Pleiades can be called Vlašići (“children of Vlas"), [ 27 ] a title possibly connected to Slavic deity Veles . [ 34 ] The members of this asterism, considered to be "seven starry brothers", each receive an individual name: in one version, duos Mika and Mioka, Raka and Raoka, Orisav and Borisav, and the last Milisav; in another, Vole and Voleta, Rale and Raleta, Mile and Mileta and Pržožak; in a third, Mile and Mileta, Rade and Radeta, Bore and Boreta and Prigimaz. [ 35 ]
In a version collected by Vuk Karadzic and published in the Archiv für slavische Philologie with the title Die Plejaden , a pair of brothers, Dragoman and Milan, lose their sister to a dragon and try to get her back. The dragon kills them. Years later, their mother gives birth to another son, named Busan. The boy suckles on his mother's breast for 7 years, becomes immensely strong and goes to kill the dragon. He rescues his sister and resurrects his brothers. Milan and Dragoman marry princesses, and the first fathers seven golden-haired children. The children, however, die in their sleep and are elevated to the sky as the Pleiades. [ 36 ]
In another version by Karadzic, translated as Abermals die Plejaden ("Once again, the Pleiades"), a human prince recruits the services of five brothers, sons of a "dragon-woman", to rescue a princess. After the mission, they quarrel about who gets to keep the princess. Their mother solves the quarrel by taking the princess as their sister. The narration then tells that these are the seven stars of the Pleiades, also known in Serbian as Vlašići . [ 36 ]
It was common among the indigenous peoples of the Americas to measure keenness of vision by the number of stars the viewer could see in the Pleiades, a practice which was also used in historical Europe , especially in Greece . [ citation needed ] According to scholarship, some of the themes in their Pleiades stories involve dancing, a punishment inflicted on the characters, or the characters escaping to the sky. [ 37 ]
In the ancient Andes , the Pleiades were associated with abundance, because they return to the Southern Hemisphere sky each year at harvest-time. In Quechua they are called Qullqa (storehouse).
In a tale collected in Belknap, attributed to the Assiniboine , seven youths discuss among themselves what they could change into. They decide to transform into stars by climbing a spiderweb. [ 38 ]
Dutch cartographer Claudius de Goeje reported that the Pleiades constellation among the Arawak is named wīwa yó-koro and marks the beginning of the year. [ 39 ] De Goeje also states that the Pleiades as the beginning of the year occurred "with all the tribes of Guiana". [ 40 ]
According to Anthony Aveni , ancient Aztecs of Mexico and Central America based their calendar upon the Pleiades. Their year began when priests first remarked the asterism heliacal rising in the east, immediately before the Sun's dawn light obliterated the view of the stars. Aztecs called the Pleiades Tiānquiztli ( Nahuatl pronunciation: [tiaːŋˈkistɬi] ; Classical Nahuatl for "marketplace". Compare tianguis ). [ 41 ]
Paul Goble , a British-American author who often depicted Native American stories, tells a Blackfoot legend that he says is told by other tribes as well. In the story, the Pleiades are orphans ("Lost Boys") that were not cared for by the people, so they became stars. Sun Man is angered by the mistreatment of the children and punishes the people with a drought, causing the buffalo to disappear, until the dogs, the only friends of the orphans, intercede on behalf of the people. Because the buffalo are not available while the Lost Boys are in the skies, the cosmic setting of the Pleiades was an assembly signal for Blackfoot hunter to travel to their hunting grounds to conduct the large-scale hunts, culminating in slaughters at buffalo jumps , that characterized their culture.
Another Pleiades story, attributed to the Blackfoot, names the constellation The Bunched Stars . [ 42 ] [ 43 ]
In a Caddo tale, compiled by Frances Jenkins Olcott , a mother has seven boys who did not want to work. One night, their mother sent them to bed without supper and, in the next morning, without breakfast. The boys, who knew magic song, began to dance around their house and slowly make their ascent to the heavens, to become the Seven Stars, which can only be seen in winter. [ 44 ]
A Cherokee myth (similar to that of the Onondaga people ) indicates that seven boys who would not do their ceremonial chores and wanted only to play, ran around and around the ceremonial ball court in a circle, and rose up into the sky. Only six of the boys made it to the sky; the seventh was caught by his mother and fell to the ground with such force that he sank into the ground. A pine tree grew over his resting place. [ 45 ] [ 46 ]
A Cheyenne myth "The Girl Who Married a Dog", states that the group of seven stars known as the Pleiades originated from seven puppies which a Cheyenne chief's daughter gave birth to after mysteriously being visited by a dog in human form to whom she vowed "Wherever you go, I go". [ 47 ] [ 48 ]
The Hopi determined the passage of time for nighttime rituals in the winter by observing the Pleiades ( Tsöötsöqam ) [ 49 ] [ 50 ] and Orion's belt ( Hotòmqam ) through a kiva entrance hatch as they passed overhead. The Pleiades were depicted in a mural on one kiva wall. [ 51 ]
A tale attributed to the Iroquois people tells that the Pleiades were six boys who danced atop a hill to the tune a seventh was singing. On a certain occasion, they danced so fast and so light they began to ascend to the skies, and thus became the constellation. [ 52 ] [ 53 ]
The Kiowa of North America legend of the Seven Star Girls links the origin of the Pleiades to Devils Tower . The seven little girls were chased by bears, and climbed a low rock. They begged the rock to save them, and it grew higher and higher until they were pushed up into the sky. The seven girls became the Pleiades and the grooves on Devils Tower are the marks of the bear's claws. [ 54 ] [ 55 ]
The Lakota Nation of North America had a legend that linked the origin of the Pleiades to Devils Tower .
The Monache people tell of six wives who loved onions more than their husbands and now live happily in "sky country". [ 56 ]
The early Monte Alto Culture , and others in Guatemala such as Ujuxte and Takalik Abaj , made their early observatories using the Pleiades and Eta Draconis as reference; they were called the seven sisters , and thought to be their original land. [ 57 ]
A Nez Perce myth about this constellation mirrors the ancient Greek myths about the Lost Pleiades . In the Nez Perce version the Pleiades is also a group of sisters, however the story itself is somewhat different. One sister falls in love with a man and, following his death, is so absorbed by her own grief that she tells her sisters about him. They mock her and tell her how silly it is of her to feel sad for the human after his death, and she in return keeps her growing sadness to herself, eventually becoming so ashamed and miserable about her own feelings that she pulls the sky over her face like a veil, blocking herself from view. This myth explains why there are only six of the seven stars visible to the naked eye. [ 58 ]
The Pleiades ( dilγéhé ) play a major role in Navajo folklore and ritual. In the Navajo creation story, Upward-reachingway, the Pleiades was the first constellation placed in the sky by Black God. When Black God entered the hogan of creation, the Pleiades were on his ankle; he stamped his foot and they moved to his knee, then to his ankle, then to his shoulder, and finally to his left temple. The seven stars of dilγéhé are depicted on ceremonial masks of Black God, in sand paintings and on ceremonial gourd rattles. [ 59 ]
The Ojibwe language calls the Pleiades Bagone-giizhig (Hole in the Sky) or Madoo'asinik (Sweating Stones). [ 60 ] One myth says that the Ojibwe/Anishinaabe themselves came from the stars through Bagone-giizhig . [ 61 ] [ 62 ] In traditional beliefs it is described as a gateway between the earth and the "star world", through which the star people come to speak to the Jiisakiiwin seers during their ceremonies. [ 63 ]
A story similar to Iroquois and Cherokee stories describes the Pleiades as seven children who danced and played all day rather than helping around the camp, until they danced into the sky and can be seen there to this day, but one fell back to Earth. In summer, when the Pleiades are not in the sky, the children are said to be down on Earth joining in with the ceremonial dances. [ 63 ]
The Onondaga people 's version of the story has lazy children who prefer to dance over their daily chores ignoring the warnings of the Bright Shining Old Man. [ 56 ] [ 64 ]
In a tale attributed to Pacific Coast indigenous populations, the Pleiades are a family of seven sisters who, fed up with their husbands (all brothers) not sharing with them their game, want to be changed into stars. The husband of the youngest sister, the youngest of the seven brothers, accompanies his spouse and transforms into the Taurus constellation. [ 65 ]
The Skidi Pawnee consider the Pleiades to be seven brothers. They observed the seven brothers, as well as Corona Borealis, the Chiefs, through the smoke hole of Pawnee lodges to determine the time of night. [ 66 ]
A second tale tells the Pleiades are six brothers who rescue their sister, who becomes the seventh star of the constellation. [ 67 ]
According to the Seris (of northwestern Mexico), these stars are seven women who are giving birth. The constellation is known as Cmaamc , which is apparently an archaic plural of the noun cmaam "woman". [ 68 ]
The Shasta people tell a story of the children of raccoon killed by coyote avenging their father's death and then rising into the sky to form the Pleiades. The smallest star in the cluster is said to be coyote's youngest who aided the young raccoons. [ 56 ] [ 69 ]
In a tale from the Tachi people, the Pleiades are five sisters who lived in sky and marry a man named Flea. When he is ailed by an itch, they no longer like him and plan to leave him. He follows them to the sky. [ 70 ]
In a tale attributed to the Wyandot people , seven Singing Maidens, daughters of the Sun and the Moon, who live in Sky Land, descend to Earth and dance with human children. Their father, wrathful at their disobedience, banishes them to another part of the sky. [ 71 ] [ 72 ] In another tale, the Pleiades are seven Star Sisters who descend to Earth in a basket. One day, a human hunter captures the youngest by her girdle while their sisters escape in the basket. The maiden promises to become the hunter's wife, but before he must accompany her to the sky. [ 73 ]
To the Ban Raji people, who live semi-nomadically across western Nepal and Uttarakhand , the Pleiades are the "Seven sisters-in-law, and brother-in-law" ( Hatai halyou daa Salla ). [ citation needed ] They hold or held that when they can first make them out annually over the mountains straddling the upper Kali they feel happy to see their ancient kin. [ 74 ] This is about eight hours afternoon by local, traditional time standards. [ citation needed ]
The earliest recorded reference to the Pleiades may be in Chinese astronomical literature dating from 2357 BCE. [ 75 ] For agricultural tribes in the northern hemisphere, the course of the Pleiades indicated the beginning and ending of the growing seasons. In Chinese constellations they are known as mǎo ( 昴 ), the Hairy Head of the white tiger of the West. [ citation needed ]
In Indian astrology the Pleiades were known as the nakshatra Kṛttikā which in Sanskrit is translated as "the cutters". [ 76 ] The Pleiades are called the star of fire, and their ruling deity is the fire god Agni . It is one of the most prominent of the nakshatra and is associated with anger and stubbornness. Karthigai (கார்த்திகை) in Tamil refers to the six wives of the seven rishis (sages) , the seventh being Arundhati the wife of Vasistha which relates to the star Alcor in Ursa Major . The six stars in the Pleiades correspond to six wives, while the faithful wife Arundhati stuck with Sage Vasistha in Ursa Major . [ 77 ] The six wives fell in love with Agni , hence the name Pleiades (star of fire).
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In Japan , the Pleiades are known as Subaru ( 昴 ) which means "coming together" or "cluster" in Japanese and have given their name to the car manufacturer whose logo incorporates six stars to represent the five companies that merged into one. [ 78 ] Subaru Telescope , located in Mauna Kea Observatory on Hawaii, is also named after the Pleiades. [ 79 ]
In Korea , the Pleiades are known as Myoseong ( 묘성 ; 昴星 , with the suffix seong meaning 'star'. It also goes by many other names, directly transliterated from English ( Korean : 플레이아데스 ) and translated literally (일곱으로 된 한 벌 or 7인조 referring to "seven sisters").
The cluster, known as Bintang Tujuh ("seven stars") or Bintang Puyuh (" sparrow stars") in Malay , is a marker in the traditional rice planting season in Kedah for sowing paddy seeds. [ 80 ]
In the island of Java , the asterism is known in Javanese as Lintang Kartika or Gugus Kartika (" Kartika cluster"), a direct influence from the ancient Hindu Javanese . Influenced by Hinduism, the stars represent the seven princesses, which is represented in the court dance of Bedhaya Ketawang of the royal palaces of Surakarta . The dance is performed once per year, on the second day of the Javanese month of Ruwah (during May) and is performed by the nine females, relatives or wives of the Susuhunan (prince) of Surakarta before a private audience in the inner circle of the Sultanate family. [ 81 ] Another name for Pleiades in Java is Wuluh . [ 82 ]
In northern Java, its rising marks the arrival of the mangsa kapitu ("seventh season"), which marks the beginning of rice planting season. [ 82 ]
Pleiades was once of most asterisms that used by Bugis sailors for navigation, called worong-porongngé bintoéng pitu , meaning "cluster of seven stars" [ 83 ]
In the Philippines the Pleiades are known as "Moroporo", meaning either “the boiling lights” or a flock of birds. Its appearance signified a new agricultural season, and thus starts the preparation for the new planting season. [ 84 ]
In Thailand the Pleiades are known as Dao Luk Kai ( Thai : ดาวลูกไก่ ; literally, "Chick Stars") [ 85 ] due to a Thai folk tale . The story tells that a poor elderly couple who lived in a forest had raised a family of chickens : a mother hen and her six (or alternately seven) chicks. One day a monk arrived at the couple's home during his dhutanga journey. Worried that they had no suitable food to offer him, the elderly couple contemplated cooking the mother hen. The hen overheard the conversation and rushed back to the coop to say farewell to her children. She told them to take care of themselves, and that her death would repay the kindness of the elderly couple, who had taken care of all of them for so long. As the mother hen's feathers were being burned over a fire, the chicks threw themselves into the fire to die along with their mother. The deity (in one version, Phya In in Northern Thai and Phra In in Thai , both referring to Indra ), [ 86 ] impressed by and in remembrance of their love, immortalized the seven chickens as the stars of the Pleiades. [ 87 ] In tellings of the story in which there were only six chicks, the mother is included but often includes only the seven chicks. [ 88 ] [ 89 ] [ 90 ] [ 91 ]
The Motif Index of Polynesian Narratives locates stories about the genesis of the Pleiades in New Zealand , Cooks and in Rotuma . [ 92 ] The myth of the Pleiades in South Pacific Islands is related to Matariki , and the stars were originally one. [ 93 ]
Depending on the cultural/language group, there are several stories or songlines , regarding the origins of the Pleiades among Aboriginal Australian peoples, usually referred to as the Seven Sisters.
In the western desert region and cultural bloc , they are said to be seven sisters fleeing from the unwelcome attentions of a man represented by some of the stars in Orion, the hunter. In these stories, the man is called Nyiru [ 94 ] or Nirunja, [ 95 ] and the Seven Sisters songline known as Kungkarangkalpa. [ 96 ] The seven sisters story often features in the artwork of the region. [ 94 ] [ 97 ]
A legend of the Wurundjeri people of south-eastern Australia has it that they are the fire of seven Karatgurk sisters. These women were the first to know fire-making and each carried live coals on the end of their digging sticks . They refused to share these coals with anybody and were ultimately tricked into giving up their secret by Crow , who brought fire to mankind. After this, they were swept into the night sky. Their glowing fire sticks became the bright stars of the Pleiades cluster. [ 98 ] [ 99 ]
The Wirangu people of the west coast of South Australia have a creation story embodied in a songline of great significance based on the Pleiades. In the story, the hunter (the Orion constellation ) is named Tgilby. Tgilby, after falling in love with the seven sisters, known as Yugarilya, chases them out of the sky, onto and across the Earth. He chases them as the Yugarilya chase a snake, Dyunu. [ 100 ]
There is an analogous holiday in Hawaiʻi known as Makahiki . [ 101 ] The makahiki season begins with a new moon following the rising of the pleiades (or makali`i) just after sunset instead of the heliacal rising.
The Hawaiian creation chant known as the Kumulipo also begins with reference to the pleiades (known as the makali`i).
Occurring June 20 – June 22, the winter solstice ( Te Maruaroa o Takurua ) is seen by the New Zealand Māori as the middle of the winter season. It follows directly after the first sighting of Matariki (The Pleiades) and Puanga/Puaka ( Rigel ) [ 102 ] in the dawn sky, an event which marked the beginning of the New Year and was said to be when the Sun turned from his northern journey with his winter-bride Takurua ( Sirius ) and began his journey back to his summer-bride Hine Raumati .
Author Kate Clark retold a Maori tale titled Matariki, or the Little Eyes . [ 103 ]
C. Maxwell Churchward transcribed a tale from the Rotuma about the origin of the Pleiades he dubbed The Two Sisters Who Became Constellations , or in the original language Sianpual'etaf ma Sianpual'ekia' ("Sianpual'etaf and Sianpual'ekia"). In this tale, two sisters, the older Sianpual'etaf, ("Girl Shining In The-Light") and the younger Sianpual'ekia ("Girl Shining In The-Sunset-Glow"), escape from their cruel husbands and become constellations: the older becomes "The Little Eyes" and the younger "The Fan". [ 104 ]
In Samoa , the Pleiades constellation is called Matalii or Mataalii , meaning "Eyes of the Chiefs". [ 105 ] [ 106 ]
Across the Bantu languages of Southern Africa, the Pleiades are associated with agriculture, [ 107 ] [ 108 ] [ 109 ] [ 110 ] from a verb -lima 'cultivate', [ 111 ] e.g., Giryama kirimira , [ 112 ] Kaguru chilimia ; [ 107 ] Xhosa and Zulu isilimela ; Sotho and Tswana selemela ; Tsonga shirimela , Venda tshilimela ; [ 113 ] Karanga chirimera ; Nyabungu kelemera ; Nyasa lemila . [ 114 ]
In Swahili , the cluster is called "kilimia" (from Proto-Bantu "*ki-dimida" in Bantu areas E, F, G, J, L and S), meaning 'The Ploughing Stars'. [ 110 ] The word comes from the verb -lima meaning "dig" or "cultivate", as their visibility was taken as a sign to prepare digging as the onset of the rain was near.
In related Sesotho (of far Southern Africa 's Basotho (people of Sotho)) the Pleiades are called "Seleme se setshehadi" ("the female planter"). Its disappearance in April (the 10th month) and the appearance of the star Achernar signals the beginning of the cold season. Like many neighbours, the Basotho associate its visibility with agriculture and plenty. [ 115 ]
Among the Zulu people , the Pleiades are called in Zulu isi-limela or isiLimela ('the-planting-sign', in Bryant's translation; 'the digging-for (stars)', in James George Frazer 's), [ 116 ] which, according to ethnologue Alfred Thomas Bryant [ de ] , marked the beginning of the rain or planting season. [ 117 ]
The 19th century astronomer Johann Heinrich von Mädler proposed the Central Sun Hypothesis, according to which all stars revolve around the star Alcyone, in the Pleiades. Based on this hypothesis, the Jehovah's Witnesses denomination taught until the 1950s that Alcyone was likely to be the site of the throne of God. [ 118 ]
In Theosophy , it is believed the Seven Stars of the Pleiades focus the spiritual energy of the Seven Rays from the Galactic Logos to the Seven Stars of the Great Bear , then to Sirius , then to the Sun , then to the god of Earth ( Sanat Kumara ) and finally through the seven Masters of the Seven Rays to us. [ 119 ]
In Ufology some believers describe Nordic alien extraterrestrials (called Pleiadeans ) as originating from this system.
The name of the constellation inspired a group of Alexandrian poets, the Alexandrian Pleiad , then the French literary movement La Pléiade .
The "Netted Stars" known as Remmirath in The Fellowship of the Ring by J. R. R. Tolkien are likely a reference to the Pleiades, given their appearance and proximity to a red star called Borgil (identified with Aldebaran) and the constellation Menelvagor of the Shining Belt (Orion). As in real life, Remmirath rise before Borgil and Menelvagor.
Children's book author Edith Ogden Harrison gave the myth of the Pleiades a literary treatment in her book Prince Silverwings , and other fairy tales , as the tale of The Cloud Maidens . [ 120 ] The story tells of the courtship of one of the Seven Sisters by the legendary Man in the Moon . Unfortunately, the Cloud Maiden is banished to Earth and becomes the "Maid of the Mist".
Another etiological tale, from a Slavic source, is The Seven Stars : a princess is kidnapped by a dragon , so the high chamberlain seeks a "Dragon-mother" and her sons, who each possess extraordinary abilities, to rescue her. At the end of the tale, the rescuers and the chamberlain enter a dispute on who should have the princess, but the "Dragon-mother" suggests they should treasure her as a sister, and to keep protecting her. As such, the seven are elevated to the sky as "The Seven Stars" (the Pleiades). [ 121 ]
The Irish writer Lucinda Riley has published a series of books about The seven sisters that is based on the Pleiades of the ancient Greek mythology. [ 122 ]
91 Star-names and their meanings
by Allen, Richard Hinckley, 1838–1908 | https://en.wikipedia.org/wiki/Pleiades_in_folklore_and_literature |
Pleiotropy (from Ancient Greek πλείων ( pleíōn ) ' more ' and τρόπος ( trópos ) ' turn, way, manner, style ' ) is a condition in which a single gene or genetic variant influences multiple phenotypic traits . A gene that has such multiple effects is referred to as a pleiotropic gene . Mutations in pleiotropic genes can impact several traits simultaneously, often because the gene product is used in various cells and affects different biological targets through shared signaling pathways.
Pleiotropy can result from several distinct but potentially overlapping mechanisms, including gene pleiotropy, developmental pleiotropy, and selectional pleiotropy. Gene pleiotropy occurs when a gene product interacts with multiple proteins or catalyzes different reactions. Developmental pleiotropy refers to mutations that produce several phenotypic effects during development. Selectional pleiotropy occurs when a single phenotype influences evolutionary fitness in multiple ways (depending on factors such as age and sex). [ 1 ]
There are also three main types of genetic pleiotropic effects when a variant or gene is associated with more than one trait:
A well- known example of pleiotropy is phenylketonuria (PKU) , a genetic disorder caused by a mutation in a single gene on chromosome 12 that encodes the enzyme phenylalanine hydroxylase . This mutation leads to the accumulation of the amino acid phenylalanine in the body, affecting multiple systems, such as the nervous and integumentary system . [ 3 ]
Pleiotropic gene action can limit the rate of multivariate evolution when natural selection , sexual selection or artificial selection on one trait favors one allele, while selection on other traits favors a different allele. Pleiotropic mutations can sometimes be deleterious, especially when they negatively affect essential traits. Genetic correlations and responses to selection most often exemplify pleiotropy.
Pleiotropy is widespread in the genome, with many genes influencing biological traits and pathways. Understanding pleiotropy is crucial in genome- wide association studies ( GWAS) , where variants are often linked to multiple traits or diseases.
Pleiotropic traits had been previously recognized in the scientific community but had not been experimented on until Gregor Mendel 's 1866 pea plant experiment. Mendel recognized that certain pea plant traits (seed coat color, flower color, and axial spots) seemed to be inherited together; [ 4 ] however, their correlation to a single gene has never been proven.
The term "pleiotropie" was first coined by Ludwig Plate in his Festschrift , which was published in 1910. [ 4 ] He originally defined pleiotropy as occurring when "several characteristics are dependent upon ... [inheritance]; these characteristics will then always appear together and may thus appear correlated". [ 5 ] This definition is still used today.
After Plate's definition, Hans Gruneberg was the first to study the mechanisms of pleiotropy. [ 4 ] In 1938 Gruneberg published an article dividing pleiotropy into two distinct types: "genuine" and "spurious" pleiotropy. "Genuine" pleiotropy is when two distinct primary products arise from one locus . "Spurious" pleiotropy, on the other hand, is either when one primary product is utilized in different ways or when one primary product initiates a cascade of events with different phenotypic consequences. Gruneberg came to these distinctions after experimenting on rats with skeletal mutations . He recognized that "spurious" pleiotropy was present in the mutation, while "genuine" pleiotropy was not, thus partially invalidating his own original theory . [ 6 ] Through subsequent research , it has been established that Gruneberg's definition of "spurious" pleiotropy is what we now identify simply as "pleiotropy". [ 4 ]
In 1941 American geneticists George Beadle and Edward Tatum further invalidated Gruneberg's definition of "genuine" pleiotropy, advocating instead for the "one gene-one enzyme" hypothesis that was originally introduced by French biologist Lucien Cuénot in 1903. [ 4 ] [ 7 ] This hypothesis shifted future research regarding pleiotropy towards how a single gene can produce various phenotypes.
In the mid-1950s Richard Goldschmidt and Ernst Hadorn , through separate individual research, reinforced the faultiness of "genuine" pleiotropy. A few years later, Hadorn partitioned pleiotropy into a "mosaic" model (which states that one locus directly affects two phenotypic traits) and a "relational" model (which is analogous to "spurious" pleiotropy). These terms are no longer in use but have contributed to the current understanding of pleiotropy. [ 4 ]
By accepting the one gene-one enzyme hypothesis, scientists instead focused on how uncoupled phenotypic traits can be affected by genetic recombination and mutations, applying it to populations and evolution . [ 4 ] This view of pleiotropy, "universal pleiotropy", defined as locus mutations being capable of affecting essentially all traits, was first implied by Ronald Fisher 's Geometric Model in 1930. This mathematical model illustrates how evolutionary fitness depends on the independence of phenotypic variation from random changes (that is, mutations). It theorizes that an increasing phenotypic independence corresponds to a decrease in the likelihood that a given mutation will result in an increase in fitness. [ 8 ]
Expanding on Fisher's work, Sewall Wright provided more evidence in his 1968 book Evolution and the Genetics of Populations: Genetic and Biometric Foundations by using molecular genetics to support the idea of "universal pleiotropy". The concepts of these various studies on evolution have seeded numerous other research projects relating to individual fitness. [ 1 ]
In 1957 evolutionary biologist George C. Williams theorized that antagonistic effects will be exhibited during an organism's life cycle if it is closely linked and pleiotropic. Natural selection favors genes that are more beneficial prior to reproduction than after (leading to an increase in reproductive success ). Knowing this, Williams argued that if only close linkage was present, then beneficial traits will occur both before and after reproduction due to natural selection. This, however, is not observed in nature, and thus antagonistic pleiotropy contributes to the slow deterioration with age ( senescence ). [ 9 ]
Pleiotropy describes the genetic effect of a single gene on multiple phenotypic traits. Recent genetic research distinguishes between three forms of pleiotropy:
Biological pleiotropy also known as horizontal pleiotropy is when a causal variant or gene has direct and independent effects on more than one phenotypes. There are two sub- types og biological pleiotropy, single- gene pleiotropy and multigene regulatory pleiotropy.
Causal risk variants can affect several traits by acting on a single gene that has many different effects. There are several ways that this kind of gene pleiotropy can happen, and these possibilities can overlap. For example, a gene might have more than one molecular function, be involved in several separate biological pathways or cellular processes, or be active in different organs, tissues, or times and places in the body, each influencing different traits. Also, one gene can produce different versions of a protein, called isoforms , which vary in strucure and function and contribute to the gene's wide range of effects. [ 10 ]
Pleiotropy also occurs when a causal variant changes the expression of many genes. Every one of these genes may play a role in shaping different phenotypic outcomes. Regulatory pleiotropy can also arise from genetic influences on the 3D structure of chromosomes. [ 10 ]
Also known as vertical pleiotropy and happens when a causal variant effect on one trait which itself causes effect on a different trait. An example of mediated pleiotropy is that gene variants that affect low-density lipoprotein (LDF) also affect coronary artery disease. [ 10 ]
Sometimes, what looks like pleiotropy can be caused by problems in how the study is designed or how risk genes and traits are defined, leading to incorrect conclusions about pleiotropy. Spurious pleiotropy occures when there is a misclassification either at the genomic level or the phenotypic level. At the genomic level, this might happen when a region of the genome linked to a special trait includes causal variants that are related. When this is the case, variants that influence different phenotypes through separate biological mechanisms may wrongly appear as a single pleiotropic locus. [ 10 ]
There has been introduced a fourth type, polygenicity- induced horizontal pleiotropy, where several genetic loci with causal effects could be linked to multiple phenotypic traits. [ 11 ]
Another model that has been proposed is network pleiotropy. In this model, a single causal variant influences several traits through one or more intermediate cell types within the same network. It may be especially useful for explaining multi-dimensional psyciatric disorders such as schizofrenia and bipolar disorder . [ 11 ]
One of the key challenges is to figure out if a gene actually influences more than one trait. One reason is that it's not always clear how traits should be grouped or named when studying them. Another challenge is that many of the methods used to test for pleiotropy, do it in an indirect way. Usually, these methods start by assuming that a gene doesn't affect any traits, and then look for evidence to prove otherwise. To solve this, researchers have developed better ways to test if a gene affects several traits at the same time, using methods that don't rely on these indirect assumptions. [ 11 ]
Early genome- wide association studies (GWAS) that revealed links between many genetic loci and multiple traits were often described in terms of cross- phenotype (CP) associations. When such associations can be traced back to a shared biological mechanism at the causal locus, they can be more precisely defined as pleiotropic effects. [ 11 ]
Genome-wide association studies (GWAS) and machine learning analysis of large- scale genomic data have made it possible to develop SNP- based polygenic predictors for complex human traits. The goal of GWAS was to identify how strongly a specific genetic variant, typically a single- nucleotide polymorphism (SNP ), is associated with a particular human trait. [ 11 ]
One way to quantify pleiotropy is by measuring the proportion of shared genetic variance between two complex traits. Analyses of hundreds of trait pairs have shown that often, the genomic regions involved are largely distinct, with only modest overlap. This suggests that, for the complex traits studied so far, pleiotropy is generally limited. Still, identifying genetic variants through GWAS and linking them to biological pathways offers valuable opportunities to improve diagnosis, develop new therapies, and better prevent diseases.
Polygenic risk scores (PRS), buildt from these findings, holds promise for predicting individual risk for various conditions. However, while PRS has many strengths, their predictive power remains probalistic. The accuracy and reliability of these scores are currently under scrutiny, emphasizing the need for cautious interpretation when applying them to clinical or public health contexts. [ 11 ]
One basic model of pleiotropy's origin describes a single gene locus that influences one trait. At first, this gene only affects the trait by changing how other genes are expressed. Over time, that locus would affect two traits by interacting with a second locus. If both traits are favored by natural selection at the same time, the connection between them becomes stronger. But, if only one trait is selected for, the connection weakens. Eventually, traits that underwent directional selection simultaneously were linked by a single gene, resulting in pleiotropy.
The "pleiotropy-barrier" model proposes a logistic growth pattern for the increase of pleiotropy over time. [ 12 ] This model differentiates between the levels of pleiotropy in evolutionarily younger and older genes subjected to natural selection. It suggests a higher potential for phenotypic innovation in evolutionarily newer genes due to their lower levels of pleiotropy.
Other more complex models compensate for some of the basic model's oversights, such as multiple traits or assumptions about how the loci affect the traits. They also propose the idea that pleiotropy increases the phenotypic variation of both traits since a single mutation on a gene would have twice the effect. [ 13 ]
Pleiotropy can have an effect on the evolutionary rate of genes and allele frequencies . Traditionally, models of pleiotropy have predicted that evolutionary rate of genes is related negatively with pleiotropy – as the number of traits of an organism increases, the evolutionary rates of genes in the organism's population decrease. [ 14 ] This relationship has not been clearly found in empirical studies for a long time. [ 15 ] [ 16 ] However, a study based on human disease genes revealed the evidence of lower evolutionary rate in genes with higher pleiotropy.
In mating, for many animals the signals and receptors of sexual communication may have evolved simultaneously as the expression of a single gene, instead of the result of selection on two independent genes, one that affects the signaling trait and one that affects the receptor trait. [ 17 ] In such a case, pleiotropy would facilitate mating and survival. However, pleiotropy can act negatively as well. A study on seed beetles found that intralocus sexual conflict arises when selection for certain alleles of a gene that are beneficial for one sex causes expression of potentially harmful traits by the same gene in the other sex, especially if the gene is located on an autosomal chromosome . [ 18 ]
Pleiotropic genes act as an arbitrating force in speciation . William R. Rice and Ellen E. Hostert (1993) conclude that the observed prezygotic isolation in their studies is a product of pleiotropy's balancing role in indirect selection. By imitating the traits of all-infertile hybridized species, they noticed that the fertilization of eggs was prevented in all eight of their separate studies, a likely effect of pleiotropic genes on speciation. [ 19 ] Likewise, pleiotropic gene's stabilizing selection allows for the allele frequency to be altered. [ 20 ]
Studies on fungal evolutionary genomics have shown pleiotropic traits that simultaneously affect adaptation and reproductive isolation , converting adaptations directly to speciation . A particularly telling case of this effect is host specificity in pathogenic ascomycetes and specifically, in venturia , the fungus responsible for apple scab . These parasitic fungi each adapts to a host, and are only able to mate within a shared host after obtaining resources. [ 21 ] Since a single toxin gene or virulence allele can grant the ability to colonize the host, adaptation and reproductive isolation are instantly facilitated, and in turn, pleiotropically causes adaptive speciation. The studies on fungal evolutionary genomics will further elucidate the earliest stages of divergence as a result of gene flow, and provide insight into pleiotropically induced adaptive divergence in other eukaryotes . [ 21 ]
Sometimes, a pleiotropic gene may be both harmful and beneficial to an organism, which is referred to as antagonistic pleiotropy . This may occur when the trait is beneficial for the organism's early life, but not its late life. Such "trade-offs" are possible since natural selection affects traits expressed earlier in life, when most organisms are most fertile, more than traits expressed later in life. [ 22 ]
This idea is central to the antagonistic pleiotropy hypothesis , which was first developed by G. C. Williams in 1957. Williams suggested that some genes responsible for increased fitness in the younger, fertile organism contribute to decreased fitness later in life, which may give an evolutionary explanation for senescence . An example is the p53 gene, which suppresses cancer but also suppresses stem cells , which replenish worn-out tissue. [ 17 ]
Unfortunately, the process of antagonistic pleiotropy may result in an altered evolutionary path with delayed adaptation , in addition to effectively cutting the overall benefit of any alleles by roughly half. However, antagonistic pleiotropy also lends greater evolutionary "staying power" to genes controlling beneficial traits, since an organism with a mutation to those genes would have a decreased chance of successfully reproducing, as multiple traits would be affected, potentially for the worse. [ 23 ]
Antagonistic pleiotropy can manifest in many ways, depending on the contexts in which its positive and negative effects occur. These effects may arise in different stages of an life. For example can certain alleles of ORL1 (lectin-like low-density lipoprotein receptor 1) enhance the immune defense in early life but also, increase the risk of cardiovascular disease later. It is also a possibility, that positive and negative effects can occur at the same time, for example some alleles of the androgen receptor (AR), which appears to lower the risk of getting breast cancer at the same time increasing the risk of ovarian cancer . [ 24 ]
Sickle cell anemia is a classic example of the mixed benefit given by the staying power of pleiotropic genes, as the mutation to Hb-S provides the fitness benefit of malaria resistance to heterozygotes as sickle cell trait , while homozygotes have significantly lowered life expectancy—what is known as " heterozygote advantage ". Since both of these states are linked to the same mutated gene, large populations today are susceptible to sickle cell despite it being a fitness-impairing genetic disorder. [ 25 ]
Albinism is the mutation of the TYR gene , also termed tyrosinase. This mutation causes the most common form of albinism. The mutation alters the production of melanin , thereby affecting melanin-related and other dependent traits throughout the organism. Melanin is a substance made by the body that is used to absorb light and provides coloration to the skin. Indications of albinism are the absence of color in an organism's eyes, hair, and skin, due to the lack of melanin. Some forms of albinism are also known to have symptoms that manifest themselves through rapid-eye movement, light sensitivity, and strabismus . [ 26 ]
A common example of pleiotropy is the human disease phenylketonuria (PKU). This disease causes mental retardation and reduced hair and skin pigmentation , and can be caused by any of a large number of mutations in the single gene on chromosome 12 that codes for the enzyme phenylalanine hydroxylase , which converts the amino acid phenylalanine to tyrosine . Depending on the mutation involved, this conversion is reduced or ceases entirely. Unconverted phenylalanine builds up in the bloodstream and can lead to levels that are toxic to the developing nervous system of newborn and infant children. The most dangerous form of this is called classic PKU, which is common in infants. The baby seems normal at first but actually incurs permanent intellectual disability. This can cause symptoms such as mental retardation, abnormal gait and posture, and delayed growth. Because tyrosine is used by the body to make melanin (a component of the pigment found in the hair and skin), failure to convert normal levels of phenylalanine to tyrosine can lead to fair hair and skin. [ 3 ] The frequency of this disease varies greatly. Specifically, in the United States, PKU is found at a rate of nearly 1 in 10,000 births. Due to newborn screening, doctors are able to detect PKU in a baby sooner. This allows them to start treatment early, preventing the baby from suffering from the severe effects of PKU. PKU is caused by a mutation in the PAH gene, whose role is to instruct the body on how to make phenylalanine hydroxylase. Phenylalanine hydroxylase is what converts the phenylalanine, taken in through diet, into other things that the body can use. The mutation often decreases the effectiveness or rate at which the hydroxylase breaks down the phenylalanine. This is what causes the phenylalanine to build up in the body. [ 27 ]
Sickle cell anemia is a genetic disease that causes deformed red blood cells with a rigid, crescent shape instead of the normal flexible, round shape. [ 28 ] It is caused by a change in one nucleotide, a point mutation [ 29 ] in the HBB gene . The HBB gene encodes information to make the beta-globin subunit of hemoglobin , which is the protein red blood cells use to carry oxygen throughout the body. Sickle cell anemia occurs when the HBB gene mutation causes both beta-globin subunits of hemoglobin to change into hemoglobin S (HbS). [ 30 ]
Sickle cell anemia is a pleiotropic disease because the expression of a single mutated HBB gene produces numerous consequences throughout the body. The mutated hemoglobin forms polymers and clumps together causing the deoxygenated sickle red blood cells to assume the disfigured sickle shape. [ 31 ] As a result, the cells are inflexible and cannot easily flow through blood vessels, increasing the risk of blood clots and possibly depriving vital organs of oxygen. [ 30 ] Some complications associated with sickle cell anemia include pain, damaged organs, strokes , high blood pressure , and loss of vision. Sickle red blood cells also have a shortened lifespan and die prematurely. [ 32 ]
Marfan syndrome (MFS) is an autosomal dominant disorder which affects 1 in 5–10,000 people. [ 33 ] MFS arises from a mutation in the FBN1 gene, which encodes for the glycoprotein fibrillin-1, a major constituent of extracellular microfibrils which form connective tissues . [ 33 ] Over 1,000 different mutations in FBN1 have been found to result in abnormal function of fibrillin, which consequently relates to connective tissues elongating progressively and weakening. Because these fibers are found in tissues throughout the body, mutations in this gene can have a widespread effect on certain systems, including the skeletal , cardiovascular , and nervous system , as well as the eyes and lungs. [ 33 ]
Without medical intervention, prognosis of Marfan syndrome can range from moderate to life-threatening, with 90% of known causes of death in diagnosed patients relating to cardiovascular complications and congestive cardiac failure . Other characteristics of MFS include an increased arm span and decreased upper to lower body ratio. [ 33 ]
In the context of pain, pleiotropy refers to the ability of a single gene or genomic region to influence multiple pain-related traits. A study that conducted a genome-wide association joint analysis of 17 pain -related traits revealed that many of the 99 identified risk loci are pleiotropic. [ 34 ] This implies that, rather than these loci being associated with just one type of pain, many genetic loci contribute to susceptibility to various forms of pain, including headaches , muscle pain , and chronic pain .
These pleiotropic loci were classified into four groups: loci associated with nearly all pain traits, loci associated with a specific type of pain, loci associated with multiple forms of musculoskeletal pain , and loci associated with headaches .
Additionally, pleiotropy was not limited to different types of pain but also extended to psychiatric, metabolic, and immunological traits. Genetic correlations were found between pain susceptibility and conditions such as depression , increase of body mass index, asthma , and cardiovascular diseases.
Chickens exhibit various traits affected by pleiotropic genes. Some chickens exhibit frizzle feather trait , where their feathers all curl outward and upward rather than lying flat against the body. Frizzle feather was found to stem from a deletion in the genomic region coding for α-Keratin. This gene seems to pleiotropically lead to other abnormalities like increased metabolism , higher food consumption, accelerated heart rate, and delayed sexual maturity. [ 35 ]
Domesticated chickens underwent a rapid selection process that led to unrelated phenotypes having high correlations, suggesting pleiotropic, or at least close linkage, effects between comb mass and physiological structures related to reproductive abilities. Both males and females with larger combs have higher bone density and strength, which allows females to deposit more calcium into eggshells. This linkage is further evidenced by the fact that two of the genes, HAO1 and BMP2, affecting medullary bone (the part of the bone that transfers calcium into developing eggshells) are located at the same locus as the gene affecting comb mass. HAO1 and BMP2 also display pleiotropic effects with commonly desired domestic chicken behavior; those chickens who express higher levels of these two genes in bone tissue produce more eggs and display less egg incubation behavior. [ 36 ]
Pleiotropy in genes has been linked between certain psychiatric disorders as well. Deletion in the 22q11.2 region of chromosome 22 has been associated with schizophrenia and autism . [ 37 ] Schizophrenia and autism are linked to the same gene deletion but manifest very differently from each other. The resulting phenotype depends on the stage of life at which the individual develops the disorder. Childhood manifestation of the gene deletion is typically associated with autism, while adolescent and later expression of the gene deletion often manifests in schizophrenia or other psychotic disorders. [ 38 ] Though the disorders are linked by genetics, there is no increased risk found for adult schizophrenia in patients who are autistic. [ 37 ]
A 2013 study also genetically linked five psychiatric disorders, including schizophrenia and autism. The link was a single nucleotide polymorphism of two genes involved in calcium channel signaling with neurons . One of these genes, CACNA1C , has been found to influence cognition . It has been associated with autism, as well as linked in studies to schizophrenia and bipolar disorder . [ 39 ] These particular studies show clustering of these diseases within patients themselves or families. [ 40 ] The estimated heritability of schizophrenia is 70% to 90%, [ 41 ] therefore the pleiotropy of genes is crucial since it causes an increased risk for certain psychotic disorders and can aid psychiatric diagnosis.
Through looping in three-dimensional space, distant non-coding regulatory elements, sometimes located several megabases away from gene promoters, can physically interact with and influence the expression of specific genes. For example, there is a genetic variant located upstream of the PCDH gene clusters that play a role in brain development and has been shown to impact the expression of several protocadherin genes. These genes have been linked to schizophrenia (SCZ) and major depressive disorder (MDD). [ 10 ]
A gene recently discovered in laboratory house mice , termed "mini-muscle", causes, when mutated, a 50% reduction in hindlimb muscle mass as its primary effect (the phenotypic effect by which it was originally identified). [ 13 ] In addition to smaller hindlimb muscle mass, the mutant mice exhibit lower heart rates during physical activity, and a higher endurance. Mini Muscle Mice also exhibit larger kidneys and livers. All of these morphological deviations influence the behavior and metabolism of the mouse. For example, mice with the Mini Muscle mutation were observed to have a higher per-gram aerobic capacity. [ 42 ] The mini-muscle allele shows a mendelian recessive behavior. [ 14 ] The mutation is a single nucleotide polymorphism ( SNP ) in an intron of the myosin heavy polypeptide 4 gene. [ 43 ]
DNA repair pathways that repair damage to cellular DNA use many different proteins. These proteins often have other functions in addition to DNA repair. [ 44 ] In humans, defects in some of these multifunctional proteins can cause widely differing clinical phenotypes. [ 44 ] As an example, mutations in the XPB gene that encodes the largest subunit of the basal Transcription factor II H have several pleiotropic effects. XPB mutations are known to be deficient in nucleotide excision repair of DNA and in the quite separate process oDf gene transcription . [ 44 ] In humans, XPB mutations can give rise to the cancer-prone disorder xeroderma pigmentosum or the noncancer-prone multisystem disorder trichothiodystrophy . Another example in humans is the ERCC6 gene, which encodes a protein that mediates DNA repair, transcription , and other cellular processes throughout the body. [ 45 ] Mutations in ERCC6 are associated with disorders of the eye ( retinal dystrophy ), heart (cardiac arrhythmias ), and immune system (lymphocyte immunodeficiency ). [ 46 ] | https://en.wikipedia.org/wiki/Pleiotropy |
In pharmacology , pleiotropy includes all of a drug's actions other than those for which the agent was specifically developed. [ 1 ] It may include adverse effects which are detrimental ones, [ 1 ] but is often used to denote additional beneficial effects. [ 2 ]
For example, statins are HMG-CoA reductase inhibitors that primarily act by decreasing cholesterol synthesis, but which are believed to have other beneficial effects, including acting as antioxidants and stabilizing atherosclerotic plaques . [ 1 ] Steroid drugs, such as prednisone and prednisolone , have pleiotropic effects, including systemic ones, for the same reason that endogenous steroid hormones do: cells throughout the body have receptors that can respond to them, because the endogenous ones are endocrine messengers.
Another example is melatonin, which has a wide range of effects on biological systems on multiple scales, from modulating the circadian rhythm and inducing sleep via the activation of melatoninergic receptors, to recepto-independent antioxydative and anti-inflammatory effects over all organs down to cells. [ 3 ] [ 4 ] | https://en.wikipedia.org/wiki/Pleiotropy_(drugs) |
Pleochroism is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. [ 1 ]
The roots of the word are from Greek (from Ancient Greek πλέων ( pléōn ) ' more ' and and χρῶμα ( khrôma ) ' color ' ). It was first made compound in the German term Pleochroismus by mineralogist Wilhelm Haidinger in 1854, in the journal Annalen der Physik und Chemie . [ 2 ] Its first known English usage is by geologist James Dana in 1854. [ 3 ]
Anisotropic crystals will have optical properties that vary with the direction of light. The direction of the electric field determines the polarization of light, and crystals will respond in different ways if this angle is changed. These kinds of crystals have one or two optical axes. If absorption of light varies with the angle relative to the optical axis in a crystal then pleochroism results. [ 4 ]
Anisotropic crystals have double refraction of light where light of different polarizations is bent different amounts by the crystal , and therefore follows different paths through the crystal. The components of a divided light beam follow different paths within the mineral and travel at different speeds. When the mineral is observed at some angle, light following some combination of paths and polarizations will be present, each of which will have had light of different colors absorbed. At another angle, the light passing through the crystal will be composed of another combination of light paths and polarizations, each with their own color. The light passing through the mineral will therefore have different colors when it is viewed from different angles, making the stone seem to be of different colors.
Tetragonal , trigonal , and hexagonal minerals can only show two colors and are called dichroic . Orthorhombic , monoclinic , and triclinic crystals can show three and are trichroic. For example, hypersthene , which has two optical axes, can have a red, yellow, or blue appearance when oriented in three different ways in three-dimensional space. [ 5 ] Isometric minerals cannot exhibit pleochroism. [ 1 ] [ 6 ] Tourmaline is notable for exhibiting strong pleochroism. Gems are sometimes cut and set either to display pleochroism or to hide it, depending on the colors and their attractiveness.
The pleochroic colors are at their maximum when light is polarized parallel with a principal optical vector. The axes are designated X, Y, and Z for direction, and alpha, beta, and gamma in magnitude of the refractive index. These axes can be determined from the appearance of a crystal in a conoscopic interference pattern . Where there are two optical axes, the acute bisectrix of the axes gives Z for positive minerals and X for negative minerals and the obtuse bisectrix gives the alternative axis (X or Z). Perpendicular to these is the Y axis. The color is measured with the polarization parallel to each direction. An absorption formula records the amount of absorption parallel to each axis in the form of X < Y < Z with the left most having the least absorption and the rightmost the most. [ 7 ]
Pleochroism is an extremely useful tool in mineralogy and gemology for mineral and gem identification, since the number of colors visible from different angles can identify the possible crystalline structure of a gemstone or mineral and therefore help to classify it. Minerals that are otherwise very similar often have very different pleochroic color schemes. In such cases, a thin section of the mineral is used and examined under polarized transmitted light with a petrographic microscope. Another device using this property to identify minerals is the dichroscope . [ 8 ] | https://en.wikipedia.org/wiki/Pleochroism |
In medicine , pleocytosis (or pleiocytosis ) is an increased cell count (from Greek pleion , "more"), particularly an increase in white blood cell count, in a bodily fluid, such as cerebrospinal fluid . [ 1 ] It is often defined specifically as an increased white blood cell count in cerebrospinal fluid. [ 2 ]
Increased white blood cell count in the blood is called leukocytosis . [ 3 ]
This immunology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pleocytosis |
Pleometrosis is a behavior observed in social insects where colony formation is initiated by multiple queens primarily by the same species of insect. This type of behavior has been mainly studied in ants but also occurs in wasps , bees , and termites . This behavior is of significant interest to scientists particularly in ants and termites because nest formation often happens between queens that are unrelated, ruling out the argument of inclusive fitness as the driving force of pleometrosis. [ 1 ] Whereas in other species such as wasps and bees co-founding queens are often related. [ 2 ] The majority of species that engage in pleometrosis after the initial stages of colony formation will reduce their colonies number of queens down to one dominant queen and either kill or push out the supernumerary queens. [ 3 ] However there are some cases where pleometrosis-formed colonies keep multiple queens for longer than the early stages of colony growth. [ 3 ] Multiple queens can help to speed a colony through the early stages of colony growth by producing a larger worker ant population faster which helps to out-compete other colonies in colony-dense areas. [ 3 ] However forming colonies with multiple queens can also cause intra-colony competition between the queens possibly lowering the likelihood of survival of a queen in a pleometrotic colony. [ 2 ]
The driving selection pressure that causes ant species to form colonies through pleometrosis appears to be inter-colony competition in areas with high colony density. When a queen enters an area in which she wants to form a colony, there may be a finite amount of resources to fuel the colony thus necessitating intense competition and territoriality for resources between ant colonies . [ 2 ] If the queen forms a colony on her own then she has a low probability of surviving because other colonies may be able to produce workers faster than her or may already be past the early stages of colony formation. [ 2 ] Forming the colony on her own could also cause her to have to forage for food to out-compete other colonies through number of offspring. This foraging behavior puts her at risk of predators. [ 4 ] However, if she and multiple queens form a colony through pleometrosis they can produce a larger worker force of ants faster and get to a mature reproductive stage of colony growth faster, thus decreasing the chances of death due to inter-colony competition. [ 2 ] It has been observed that ants which form pleometrotic colonies engage in less foraging behavior, thus lowering their chance of predation. [ 4 ] Having multiple queens cuts down on foraging behavior because each queen uses her own stored energy reserves to feed the brood. [ 4 ] By founding the colony pleometrotically ants can form new colonies in high colony density areas and take control of resources in the surrounding area faster. Some genera of ants such as Azteca use the additional worker ants early in the colonies formation to monopolize and take control of resources in close proximity of the colony thus stopping other con-specific colonies from acquiring those resources. [ 2 ] This strategy allows the pleometrotic colonies to monopolize the area and starve out competing colonies. [ 2 ] The additional worker force in pleometrotic colonies also allows for bigger and more effective brood raids on con-specific colonies which additionally helps to out-compete colonies. [ 4 ] A key aspect of founding a colony in a high density colony area is being able to produce a worker force quickly and efficiently so as to not be starved out or robbed of brood from other colonies causing starvation. [ 2 ] By engaging in pleometrosis queens increase their chance of survival past the early stages of colony formation due to the increased worker force produced by multiple reproductive individuals. The colony can better control its surrounding resources and effectively compete with other colonies. [ 2 ]
Pleometrosis is necessary to survive inter-colony competition in high-density and resource-limited areas but the majority of pleometrotic colonies cut back to one queen before the reproductive stages of colony growth. So this suggests that a queen has a better chance of surviving and reproducing offspring if she forms a colony with other queens even though eventually she may be pushed out or killed by intra-colony competition. [ 2 ] The risk of being out-competed by a con-specific queen within one's own colony must be less than the risk of dying out due to other insect colonies. [ 3 ] So in high density colony areas or resource-limited areas where inter-colony competition is high, selection for pleometrosis is higher because the chance of survival in a pleometrotic colony is greater. [ 2 ] As the number of queens in a pleometrotic colony increases, the chances of each queen becoming the dominant queen in the colony lowers, but still selection pressures choose pleometrosis over haplometrosis. [ 2 ] Depending on the species of ant and the selection pressures of the colony there are multiple ways a queen can become the one dominant queen in the colony and gain the full benefit of a pleometrotic colony. The queens that normally come out as dominant in pleometrotic colonies lay more eggs, have well-developed ovaries, and do not engage in foraging behavior. [ 5 ] Worker ants even play a role in deciding whether a queen will become the dominant individual in some species by feeding the queen who is the most fertile more than other queens in the nest. [ 4 ] Queens will also engage in dominance actions to assert dominance over the nest such as brood cannibalism of other queens' brood. [ 2 ] When the most fertile queen in the nest decides to directly challenge another queen, it is usually the initiating queen that wins and takes control of the colony, turning it into a one queen colony. [ 5 ] The benefits of pleometrosis is certain situations outweigh the costs for queens, regardless of the intra-colony competition it causes. Thus it has evolved to occur in high density areas of inter-colony competition. [ 2 ]
Azteca ants form colonies in the internodes of Cecropia trees which are native to Mexico and South America. The tree provides the ants with food and shelter and the ants protect the tree from other insects thus engaging in a mutualistic relationship. Queens form colonies by burrowing into the inter node of the tree and then sealing off the entrance hole with parenchyma cells, after which they begin to lay eggs to produce the first brood. [ 6 ] Any queens which decide to engage in pleometrosis can easily see the filled in hole and will chew through it quickly and join the fellow queen in the inter node. [ 6 ] Colonies that are formed in these trees try to out-compete other colonies by monopolizing the resources of a tree first. By forming a pleometrotic colony in a Cecropia tree the queens can produce workers faster and take control of the resources in the tree first thus out-competing other colonies. However, the social interactions between queens in a pleometrotic colony differ depending on the species of Azteca . [ 2 ] In Azteca xanthochroa which are more aggressive, pleometrotic colonies work together to produce a greater number of workers at the start of colony formation but once the colony breaks out of the inter node of the tree the interactions between the queens change. Once this step occurs queens will try to kill each other to become the dominant queen in the colony and switch the colony to a single queen colony. [ 2 ] However in species of A. constructor which are less aggressive, once the worker ants leave the inter node to take control of the tree's resources, multiple queens remain cooperative with each other for up to a year. [ 2 ] Hypothesizes as to why A. constructor colonies engage in cooperative breeding with multiple queens could be due to similarities in A. constructor queens fighting abilities or the inclusive fitness benefits in some colonies of A. constructor . [ 2 ] In contrast pleometrotic colonies of A. xanthochroa form and change to one queen colonies after the early stages of colony formation. [ 2 ] There are also examples of pleometrotic colonies forming with multiple species of Azteca , however, when these form the more aggressive species will out-compete and kill off the other queens in the colony once the early stages of formation have passed. Mixed species pleometrosis is rare but helps to support the fact that the majority of social insects who form pleometrotic colonies do not do so for kin selection-related benefits, but to be able to out-compete other colonies in the early stages of development. [ 2 ] | https://en.wikipedia.org/wiki/Pleometrosis |
Pleomorphism is a term used in histology and cytopathology to describe variability in the size, shape and staining of cells and/or their nuclei . Several key determinants of cell and nuclear size, like ploidy and the regulation of cellular metabolism , are commonly disrupted in tumors . [ 1 ] Therefore, cellular and nuclear pleomorphism is one of the earliest hallmarks of cancer progression and a feature characteristic of malignant neoplasms and dysplasia. [ 2 ] [ 3 ] Certain benign cell types may also exhibit pleomorphism, e.g. neuroendocrine cells , Arias-Stella reaction .
A rare type of rhabdomyosarcoma that is found in adults is known as pleomorphic rhabdomyosarcoma . [ 4 ]
Despite the prevalence of pleomorphism in human pathology, its role in disease progression is unclear. In epithelial tissue , pleomorphism in cellular size can induce packing defects and disperse aberrant cells. [ 5 ] But the consequence of atypical cell and nuclear morphology in other tissues is unknown.
This article related to pathology is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pleomorphism_(cytology) |
In phylogenetics , a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade , which does not distinguish the clade from other clades.
Plesiomorphy, symplesiomorphy, apomorphy, and synapomorphy all mean a trait shared between species because they share an ancestral species. [ a ]
Apomorphic and synapomorphic characteristics convey much information about evolutionary clades and can be used to define taxa. However, plesiomorphic and symplesiomorphic characteristics cannot.
The term symplesiomorphy was introduced in 1950 by German entomologist Willi Hennig .
A backbone is a plesiomorphic trait shared by birds and mammals, and does not help in placing an animal in one or the other of these two clades. Birds and mammals share this trait because both clades are descended from the same far distant ancestor. Other clades, e.g. snakes, lizards, turtles, fish, frogs, all have backbones and none are either birds nor mammals.
Being a hexapod is plesiomorphic trait shared by ants and beetles , and does not help in placing an animal in one or the other of these two clades. Ants and beetles share this trait because both clades are descended from the same far distant ancestor. Other clades, e.g. bugs, flies, bees, aphids, and many more clades, all are hexapods and none are either ants nor beetles.
Elytra are a synapomorphy for placing any living species into the beetle clade, Elytra are plesiomorphic between clades of beetles, e.g. they do not distinguish the dung beetles from the horned beetles . The metapleural gland is a synapomorphy for placing any living species into the ant clade.
Feathers are a synapomorphy for placing any living species into the bird clade, hair is a synapomorphy for placing any living species into the mammal clade. Note that some mammal species have lost their hair, so the absence of hair does not exclude a species from being a mammal. Another mammalian synapomorphy is milk. All mammals produce milk and no other clade contains animals which produce milk. Feathers and milk are also apomorphies.
All of these terms are by definition relative, in that a trait can be a plesiomorphy in one context and an apomorphy in another, e.g. having a backbone is plesiomorphic between birds and mammals, but is apomorphic between them and insects. That is birds and mammals are vertebrates for which the backbone is a defining synapomorphic characteristic, while insects are invertebrates for which the absence of a backbone is a defining characteristic.
Species should not be grouped purely by morphologic or genetic similarity. Because a plesiomorphic character inherited from a common ancestor can appear anywhere in a phylogenetic tree, its presence does not reveal anything about the relationships within the tree. [ 4 ] Thus grouping species requires distinguishing ancestral from derived character states. [ 5 ]
An example is thermo-regulation in Sauropsida , which is the clade containing the lizards, turtles, crocodiles, and birds. Lizards, turtles, and crocodiles are ectothermic (coldblooded), while birds are endothermic (warmblooded). Being coldblooded is symplesiomorphic for lizards, turtles, and crocodiles, but they do not form a clade, as crocodiles are more closely related to birds than to lizards and turtles. Thus using coldbloodedness as an apomorphic trait to group crocodiles with lizards and turtles would be an error, and thus it is a plesiomorphic trait shared by these three clades due to their distant common ancestry. [ 6 ] | https://en.wikipedia.org/wiki/Plesiomorphy_and_symplesiomorphy |
In algebra, plethysm is an operation on symmetric functions introduced by Dudley E. Littlewood , [ 1 ] who denoted it by { λ } ⊗ { μ }. The word "plethysm" for this operation (after the Greek word πληθυσμός meaning "multiplication") was introduced later by Littlewood ( 1950 , p. 289, 1950b , p.274), who said that the name was suggested by M. L. Clark.
If symmetric functions are identified with operations in lambda rings , then plethysm corresponds to composition of operations.
Let V be a vector space over the complex numbers , considered as a representation of the general linear group GL( V ). Each Young diagram λ corresponds to a Schur functor L λ (-) on the category of GL( V )-representations. Given two Young diagrams λ and μ, consider the decomposition of L λ (L μ ( V )) into a direct sum of irreducible representations of the group. By the representation theory of the general linear group we know that each summand is isomorphic to L ν ( V ) {\displaystyle L_{\nu }(V)} for a Young diagram ν {\displaystyle \nu } . So for some nonnegative multiplicities a λ , μ , ν {\displaystyle a_{\lambda ,\mu ,\nu }} there is an isomorphism
The problem of (outer) plethysm is to find an expression for the multiplicities a λ , μ , ν {\displaystyle a_{\lambda ,\mu ,\nu }} . [ 2 ]
This formulation is closely related to the classical question. The character of the GL( V )-representation L λ ( V ) is a symmetric function in dim( V ) variables, known as the Schur polynomial s λ corresponding to the Young diagram λ. Schur polynomials form a basis in the space of symmetric functions. Hence to understand the plethysm of two symmetric functions it would be enough to know their expressions in that basis and an expression for a plethysm of two arbitrary Schur polynomials { s λ }⊗{ s μ } . The second piece of data is precisely the character of L λ ( L μ ( V )). | https://en.wikipedia.org/wiki/Plethysm |
A plethysmograph is an instrument for measuring changes in volume within an organ or whole body (usually resulting from fluctuations in the amount of blood or air it contains). The word is derived from the Greek "plethysmos" (increasing, enlarging, becoming full), and "graphein" (to write). [ 1 ]
Pulmonary plethysmographs are commonly used to measure the functional residual capacity (FRC) of the lungs —the volume in the lungs when the muscles of respiration are relaxed—and total lung capacity. [ 2 ]
In a traditional plethysmograph (or "body box"), the test subject, or patient, is placed inside a sealed chamber the size of a small telephone booth with a single mouthpiece. At the end of normal expiration, the mouthpiece is closed. The patient is then asked to make an inspiratory effort. As the patient tries to inhale (a maneuver which looks and feels like panting), the lungs expand, decreasing pressure within the lungs and increasing lung volume. This, in turn, increases the pressure within the box since it is a closed system and the volume of the box compartment has decreased to accommodate the new volume of the subject.
With cabinless plethysmography, the patient is seated next to a desktop testing device and inserts the mouthpiece into their mouth. The patient takes a series of normal tidal breaths for approximately one minute. During this tidal breathing, a series of rapid interruptions occurs, with a shutter opening and closing, measuring pressure and volume. [ 3 ] Lung volume measurements taken with cabinless plethysmography are considered equivalent to body plethysmography. [ 4 ]
Boyle's law is used to calculate the unknown volume within the lungs. First, the change in volume of the chest is computed. The initial pressure of the box times its volume is considered equal to the known pressure after expansion times the unknown new volume. Once the new volume is found, the original volume minus the new volume is the change in volume in the box and also the change in volume in the chest. With this information, Boyle's law is used again to determine the original volume of gas in the chest: the initial volume (unknown) times the initial pressure is equal to the final volume times the final pressure. Starting from this principle, it can be shown [ 5 ] that the functional residual capacity is a function of the changes in volume and pressures as follows:
F R C = K V Δ V b o x Δ P m o u t h , K V ≈ P B a r o m e t r i c {\displaystyle FRC=K_{V}{\frac {\Delta V_{box}}{\Delta P_{mouth}}},K_{V}\approx P_{Barometric}}
The difference between full and empty lungs can be used to assess diseases and airway passage restrictions. An obstructive disease will show increased FRC because some airways do not empty normally, while a restrictive disease will show decreased FRC. Body plethysmography is particularly appropriate for patients who have air spaces which do not communicate with the bronchial tree; in such patients helium dilution would give an incorrectly low reading.
Another important parameter, which can be calculated with a body plethysmograph is the airway resistance. During inhalation the chest expands, which increases the pressure within the box. While observing the so-called resistance loop (cabin pressure and flow), diseases can easily be recognized. If the resistance loop becomes planar, this shows a bad compliance of the lung. A COPD , for instance, can easily be discovered because of the unique shape of the corresponding resistance loop. [ 5 ]
Some plethysmograph devices are attached to arms , legs or other extremities and used to determine circulatory capacity.
In water plethysmography an extremity, e.g. an arm, is enclosed in a water-filled chamber where volume changes can be detected. Air plethysmography uses a similar principle but based on an air-filled long cuff, which is more convenient but less accurate.
Another practical device is mercury-filled strain gauges used to continuously measure circumference of the extremity, e.g. at mid calf. Impedance plethysmography is a non-invasive method used to detect venous thrombosis in these areas of the body.
Another common type of plethysmograph is the penile plethysmograph . This device is used to measure changes in blood flow in the penis . Although some researchers use this device to assess sexual arousal and sexual orientation , courts that have considered penile plethysmography generally rule that the technique is not sufficiently reliable for use in court. [ 6 ] An approximate female equivalent to penile plethysmography is vaginal photoplethysmography , which optically measures blood flow in the vagina. [ 7 ]
Plethysmography is a widely used method in basic and preclinical research to study respiration. Several techniques are used:
Whole-body plethysmography is used to measure respiratory parameters in conscious unrestrained subjects, including quantification of bronchoconstriction .
The standard plethysmograph sizes are for the study of mice, rats and guinea pigs. On request, larger plethysmographs can also be manufactured for other animals, such as rabbits, dogs, pigs, or primates.
The plethysmograph has two chambers, each fitted with a pneumotachograph . The subject is placed in one of them (subject chamber) and the other remains empty (reference chamber).
The pressure change is measured by a differential pressure transducer with one port exposed to the subject chamber and the other to the reference chamber. [ 8 ]
The double-chamber plethysmograph (dcp) measures respiratory parameters in a conscious restrained subject, including airway resistance and conductance. Different sizes of plethysmograph exist to study mice, rats or guinea pigs.
The head-out configuration is identical to the standard configuration described above except that there is no head chamber.
Of course the collar seal [ further explanation needed ] is still applied, so that the body chamber remains airtight. With only a thoracic signal, all parameters can be obtained except for specific airway resistance (SRaw) and specific airway conductance (Sgaw).
In anesthetized plethysmography, lung resistance and dynamic compliance are measured directly because the subject is anesthetized.
Depending on the level of sedation, the subject may be spontaneously breathing (SB configuration) or under mechanical ventilation (MV configuration).
A flow signal and a pressure signal are required to calculate compliance and resistance.
Cerebral venous blood flow has been recently studied trying to establish a connection between Chronic cerebrospinal venous insufficiency and multiple sclerosis . The small study is not big enough to establish a conclusion, but some association has been shown. [ 9 ] | https://en.wikipedia.org/wiki/Plethysmograph |
In mathematics , the plethystic exponential is a certain operator defined on (formal) power series which, like the usual exponential function , translates addition into multiplication. This exponential operator appears naturally in the theory of symmetric functions , as a concise relation between the generating series for elementary , complete and power sums homogeneous symmetric polynomials in many variables. Its name comes from the operation called plethysm , defined in the context of so-called lambda rings .
In combinatorics , the plethystic exponential is a generating function for many well studied sequences of integers , polynomials or power series, such as the number of integer partitions . It is also an important technique in the enumerative combinatorics of unlabelled graphs , and many other combinatorial objects. [ 1 ] [ 2 ]
In geometry and topology , the plethystic exponential of a certain geometric/topologic invariant of a space, determines the corresponding invariant of its symmetric products. [ 3 ]
The inverse operator of the plethystic exponential is the plethystic logarithm .
Let R [ [ x ] ] {\displaystyle R[[x]]} be a ring of formal power series in the variable x {\displaystyle x} , with coefficients in a commutative ring R {\displaystyle R} . Denote by
the ideal consisting of power series without constant term. Then, given f ( x ) ∈ R 0 [ [ x ] ] {\displaystyle f(x)\in R^{0}[[x]]} , its plethystic exponential PE [ f ] {\displaystyle {\text{PE}}[f]} is given by
where exp ( ⋅ ) {\displaystyle \exp(\cdot )} is the usual exponential function. It is readily verified that (writing simply PE [ f ] {\displaystyle {\text{PE}}[f]} when the variable is understood):
Some basic examples are:
In this last example, p ( n ) {\displaystyle p(n)} is number of partitions of n ∈ N {\displaystyle n\in \mathbb {N} } .
The plethystic exponential can be also defined for power series rings in many variables.
The plethystic exponential can be used to provide innumerous product-sum identities. This is a consequence of a product formula for plethystic exponentials themselves. If f ( x ) = ∑ k = 1 ∞ a k x k {\displaystyle f(x)=\sum _{k=1}^{\infty }a_{k}x^{k}} denotes a formal power series with real coefficients a k {\displaystyle a_{k}} , then it is not difficult to show that: PE [ f ] ( x ) = ∏ k = 1 ∞ ( 1 − x k ) − a k {\displaystyle {\text{PE}}[f](x)=\prod _{k=1}^{\infty }(1-x^{k})^{-a_{k}}} The analogous product expression also holds in the many variables case. One particularly interesting case is its relation to integer partitions and to the cycle index of the symmetric group . [ 4 ]
Working with variables x 1 , x 2 , … , x n {\displaystyle x_{1},x_{2},\ldots ,x_{n}} , denote by h k {\displaystyle h_{k}} the complete homogeneous symmetric polynomial , that is the sum of all monomials of degree k in the variables x i {\displaystyle x_{i}} , and by e k {\displaystyle e_{k}} the elementary symmetric polynomials . Then, the h k {\displaystyle h_{k}} and the e k {\displaystyle e_{k}} are related to the power sum polynomials: p k = x 1 k + ⋯ + x n k {\displaystyle p_{k}=x_{1}^{k}+\cdots +x_{n}^{k}} by Newton's identities , that can succinctly be written, using plethystic exponentials, as:
Let X be a finite CW complex , of dimension d , with Poincaré polynomial P X ( t ) = ∑ k = 0 d b k ( X ) t k {\displaystyle P_{X}(t)=\sum _{k=0}^{d}b_{k}(X)\,t^{k}} where b k ( X ) {\displaystyle b_{k}(X)} is its k th Betti number . Then the Poincaré polynomial of the n th symmetric product of X , denoted Sym n ( X ) {\displaystyle \operatorname {Sym} ^{n}(X)} , is obtained from the series expansion: PE [ P X ( − t ) x ] = ∏ k = 0 d ( 1 − t k x ) ( − 1 ) k + 1 b k ( X ) = ∑ n ≥ 0 P Sym n ( X ) ( − t ) x n {\displaystyle {\text{PE}}[P_{X}(-t)\,x]=\prod _{k=0}^{d}\left(1-t^{k}x\right)^{(-1)^{k+1}b_{k}(X)}=\sum _{n\geq 0}P_{\operatorname {Sym} ^{n}(X)}(-t)\,x^{n}}
In a series of articles, a group of theoretical physicists, including Bo Feng, Amihay Hanany and Yang-Hui He , proposed a programme for systematically counting single and multi-trace gauge invariant operators of supersymmetric gauge theories . [ 5 ] In the case of quiver gauge theories of D-branes probing Calabi–Yau singularities, this count is codified in the plethystic exponential of the Hilbert series of the singularity. | https://en.wikipedia.org/wiki/Plethystic_exponential |
Plethystic substitution is a shorthand notation for a common kind of substitution in the algebra of symmetric functions and that of symmetric polynomials . It is essentially basic substitution of variables, but allows for a change in the number of variables used.
The formal definition of plethystic substitution relies on the fact that the ring of symmetric functions Λ R ( x 1 , x 2 , … ) {\displaystyle \Lambda _{R}(x_{1},x_{2},\ldots )} is generated as an R -algebra by the power sum symmetric functions
For any symmetric function f {\displaystyle f} and any formal sum of monomials A = a 1 + a 2 + ⋯ {\displaystyle A=a_{1}+a_{2}+\cdots } , the plethystic substitution f[A] is the formal series obtained by making the substitutions
in the decomposition of f {\displaystyle f} as a polynomial in the p k 's.
If X {\displaystyle X} denotes the formal sum X = x 1 + x 2 + ⋯ {\displaystyle X=x_{1}+x_{2}+\cdots } , then f [ X ] = f ( x 1 , x 2 , … ) {\displaystyle f[X]=f(x_{1},x_{2},\ldots )} .
One can write 1 / ( 1 − t ) {\displaystyle 1/(1-t)} to denote the formal sum 1 + t + t 2 + t 3 + ⋯ {\displaystyle 1+t+t^{2}+t^{3}+\cdots } , and so the plethystic substitution f [ 1 / ( 1 − t ) ] {\displaystyle f[1/(1-t)]} is simply the result of setting x i = t i − 1 {\displaystyle x_{i}=t^{i-1}} for each i. That is,
Plethystic substitution can also be used to change the number of variables: if X = x 1 + x 2 + ⋯ , x n {\displaystyle X=x_{1}+x_{2}+\cdots ,x_{n}} , then f [ X ] = f ( x 1 , … , x n ) {\displaystyle f[X]=f(x_{1},\ldots ,x_{n})} is the corresponding symmetric function in the ring Λ R ( x 1 , … , x n ) {\displaystyle \Lambda _{R}(x_{1},\ldots ,x_{n})} of symmetric functions in n variables.
Several other common substitutions are listed below. In all of the following examples, X = x 1 + x 2 + ⋯ {\displaystyle X=x_{1}+x_{2}+\cdots } and Y = y 1 + y 2 + ⋯ {\displaystyle Y=y_{1}+y_{2}+\cdots } are formal sums. | https://en.wikipedia.org/wiki/Plethystic_substitution |
The Pleuger rudder (also known as a Dutch rudder ) is a power assisted ship's rudder . It creates a flow of water in the direction the rudder points powered by an auxiliary electric motor. This aids maneuverability at low speeds greatly, since it operates on a similar principle to a thruster .
A ducted propeller is mounted as an integral part of the rudder and is fixed to it. The duct is a Kort nozzle and enables the propeller to develop more thrust than an unducted propeller.
The Pleuger rudder is necessarily mounted in the flow from the main engine's propeller in a ship with an odd number of propellers. If the Pleuger and the main engine are run at the same time, the Pleuger can often be torn away. [ 1 ] The thrust produced by the Pleuger rudder is sufficient to power the ship in slow speed maneuvers when the force required to move the vessel is relatively small.
The Pleuger rudder is meant to be assisting in the fast maneuverability of ships, in tight harbor operations. Thus, it is only an improvement of rudder by controlling the water flow pattern passing a rudder and thus giving it an artificial flow and thus an extra power to steer even in slow engine r.p.m. It is absolutely not a substitute for a propeller, without which the mammoth energy required to propel a ship through the water is hard to generate. | https://en.wikipedia.org/wiki/Pleuger_rudder |
Pleuran is an insoluble polysaccharide ( β-(1,3/1,6)-D-glucan ), isolated from Pleurotus ostreatus . [ 1 ]
Pleuran belongs to a group of glucose polymers commonly called beta-glucans demonstrating biological response modifier properties. These immunomodulating properties render the host more resistant to infections and neoplasms . [ 2 ]
In a study published in December 2010, pleuran demonstrated to have a protective effect against exercise-induced suppression of immune cell activity ( NK cells ) in subjects taking 100 mg per day. [ 3 ]
In another study published in 2011, pleuran reduced the incidence of upper respiratory tract infections and increased the number of circulating NK cells. [ 4 ]
Pleuran is also being studied as a potential immunologic adjuvant . [ 5 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pleuran |
In cellular biology , plithotaxis (from Greek πλήΘος (plíthos) ' crowd, swarm ' ) is the tendency for each individual cell within a monolayer to migrate along the local orientation of the maximal principal stress , or equivalently, minimal intercellular shear stress . [ 1 ] [ 2 ] [ 3 ] Plithotaxis requires force transmission across many cell-cell junctions and therefore is an emergent property of the cell group.
Plithotaxis is found to hold at the level of both a subcellular grid point and an individual cell of a confluent monolayer, and the stresses must be tensile . [ 4 ]
This cell biology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Plithotaxis |
Ploidy ( / ˈ p l ɔɪ d i / ) is the number of complete sets of chromosomes in a cell , and hence the number of possible alleles for autosomal and pseudoautosomal genes . Here sets of chromosomes refers to the number of maternal and paternal chromosome copies, respectively, in each homologous chromosome pair—the form in which chromosomes naturally exist. Somatic cells , tissues , and individual organisms can be described according to the number of sets of chromosomes present (the "ploidy level"): monoploid (1 set), diploid (2 sets), triploid (3 sets), tetraploid (4 sets), pentaploid (5 sets), hexaploid (6 sets), heptaploid [ 2 ] or septaploid [ 3 ] (7 sets), etc. The generic term polyploid is often used to describe cells with three or more sets of chromosomes. [ 4 ] [ 5 ]
Virtually all sexually reproducing organisms are made up of somatic cells that are diploid or greater, but ploidy level may vary widely between different organisms, between different tissues within the same organism, and at different stages in an organism's life cycle. Half of all known plant genera contain polyploid species, and about two-thirds of all grasses are polyploid. [ 6 ] Many animals are uniformly diploid, though polyploidy is common in invertebrates, reptiles, and amphibians. In some species, ploidy varies between individuals of the same species (as in the social insects ), and in others entire tissues and organ systems may be polyploid despite the rest of the body being diploid (as in the mammalian liver [ citation needed ] ). For many organisms, especially plants and fungi, changes in ploidy level between generations are major drivers of speciation . In mammals and birds, ploidy changes are typically fatal. [ 7 ] There is, however, evidence of polyploidy in organisms now considered to be diploid, suggesting that polyploidy has contributed to evolutionary diversification in plants and animals through successive rounds of polyploidization and rediploidization. [ 8 ] [ 9 ]
Humans are diploid organisms, normally carrying two complete sets of chromosomes in their somatic cells: one copy of paternal and maternal chromosomes, respectively, in each of the 23 homologous pairs of chromosomes that humans normally have. This results in two homologous pairs within each of the 23 homologous pairs, providing a full complement of 46 chromosomes. This total number of individual chromosomes (counting all complete sets) is called the chromosome number or chromosome complement . The number of chromosomes found in a single complete set of chromosomes is called the monoploid number ( x ). The haploid number ( n ) refers to the total number of chromosomes found in a gamete (a sperm or egg cell produced by meiosis in preparation for sexual reproduction). Under normal conditions, the haploid number is exactly half the total number of chromosomes present in the organism's somatic cells, with one paternal and maternal copy in each chromosome pair. For diploid organisms, the monoploid number and haploid number are equal; in humans, both are equal to 23. When a human germ cell undergoes meiosis, the diploid 46 chromosome complement is split in half to form haploid gametes. After fusion of a male and a female gamete (each containing 1 set of 23 chromosomes) during fertilization , the resulting zygote again has the full complement of 46 chromosomes: 2 sets of 23 chromosomes. Euploidy and aneuploidy describe having a number of chromosomes that is an exact multiple of the number of chromosomes in a normal gamete; and having any other number, respectively. For example, a person with Turner syndrome may be missing one sex chromosome (X or Y), resulting in a (45,X) karyotype instead of the usual (46,XX) or (46,XY). This is a type of aneuploidy and cells from the person may be said to be aneuploid with a (diploid) chromosome complement of 45.
The term ploidy is a back-formation from haploidy and diploidy . "Ploid" is a combination of Ancient Greek -πλόος (-plóos, "-fold") and -ειδής (- eidḗs ), from εἶδος ( eîdos , "form, likeness"). [ a ] The principal meaning of the Greek word ᾰ̔πλόος (haplóos) is "single", [ 10 ] from ἁ- (ha-, "one, same"). [ 11 ] διπλόος ( diplóos ) means "duplex" or "two-fold". Diploid therefore means "duplex-shaped" (compare "humanoid", "human-shaped").
Polish-German botanist Eduard Strasburger coined the terms haploid and diploid in 1905. [ b ] Some authors suggest that Strasburger based the terms on August Weismann 's conception of the id (or germ plasm ), [ 14 ] [ 15 ] [ 16 ] hence haplo- id and diplo- id . The two terms were brought into the English language from German through William Henry Lang 's 1908 translation of a 1906 textbook by Strasburger and colleagues. [ 17 ] [ citation needed ]
The term haploid is used with two distinct but related definitions. In the most generic sense, haploid refers to having the number of sets of chromosomes normally found in a gamete . [ 18 ] Because two gametes necessarily combine during sexual reproduction to form a single zygote from which somatic cells are generated, healthy gametes always possess exactly half the number of sets of chromosomes found in the somatic cells, and therefore "haploid" in this sense refers to having exactly half the number of sets of chromosomes found in a somatic cell. By this definition, an organism whose gametic cells contain a single copy of each chromosome (one set of chromosomes) may be considered haploid while the somatic cells, containing two copies of each chromosome (two sets of chromosomes), are diploid. This scheme of diploid somatic cells and haploid gametes is widely used in the animal kingdom and is the simplest to illustrate in diagrams of genetics concepts. But this definition also allows for haploid gametes with more than one set of chromosomes. As given above, gametes are by definition haploid, regardless of the actual number of sets of chromosomes they contain. An organism whose somatic cells are tetraploid (four sets of chromosomes), for example, will produce gametes by meiosis that contain two sets of chromosomes. These gametes might still be called haploid even though they are numerically diploid. [ citation needed ]
An alternative usage defines "haploid" as having a single copy of each chromosome – that is, one and only one set of chromosomes. [ 19 ] In this case, the nucleus of a eukaryotic cell is said to be haploid only if it has a single set of chromosomes , each one not being part of a pair. By extension a cell may be called haploid if its nucleus has one set of chromosomes, and an organism may be called haploid if its body cells (somatic cells) have one set of chromosomes per cell. By this definition haploid therefore would not be used to refer to the gametes produced by the tetraploid organism in the example above, since these gametes are numerically diploid. The term monoploid is often used as a less ambiguous way to describe a single set of chromosomes; by this second definition, haploid and monoploid are identical and can be used interchangeably. [ citation needed ]
Gametes ( sperm and ova ) are haploid cells. The haploid gametes produced by most organisms combine to form a zygote with n pairs of chromosomes, i.e. 2 n chromosomes in total. The chromosomes in each pair, one of which comes from the sperm and one from the egg, are said to be homologous . Cells and organisms with pairs of homologous chromosomes are called diploid. For example, most animals are diploid and produce haploid gametes. During meiosis , sex cell precursors have their number of chromosomes halved by randomly "choosing" one member of each pair of chromosomes, resulting in haploid gametes. Because homologous chromosomes usually differ genetically, gametes usually differ genetically from one another. [ 20 ]
All plants and many fungi and algae switch between a haploid and a diploid state, with one of the stages emphasized over the other. This is called alternation of generations . Most fungi and algae are haploid during the principal stage of their life cycle, as are some primitive plants like mosses . More recently evolved plants, like the gymnosperms and angiosperms , spend the majority of their life cycle in the diploid stage. Most animals are diploid, but male bees , wasps , and ants are haploid organisms because they develop from unfertilized, haploid eggs, while females (workers and queens) are diploid, making their system haplodiploid . [ citation needed ]
In some cases there is evidence that the n chromosomes in a haploid set have resulted from duplications of an originally smaller set of chromosomes. This "base" number – the number of apparently originally unique chromosomes in a haploid set – is called the monoploid number , [ 21 ] also known as basic or cardinal number , [ 22 ] or fundamental number . [ 23 ] [ 24 ] As an example, the chromosomes of common wheat are believed to be derived from three different ancestral species, each of which had 7 chromosomes in its haploid gametes. The monoploid number is thus 7 and the haploid number is 3 × 7 = 21. In general n is a multiple of x . The somatic cells in a wheat plant have six sets of 7 chromosomes: three sets from the egg and three sets from the sperm which fused to form the plant, giving a total of 42 chromosomes. As a formula, for wheat 2 n = 6 x = 42, so that the haploid number n is 21 and the monoploid number x is 7. The gametes of common wheat are considered to be haploid, since they contain half the genetic information of somatic cells, but they are not monoploid, as they still contain three complete sets of chromosomes ( n = 3 x ). [ 25 ]
In the case of wheat, the origin of its haploid number of 21 chromosomes from three sets of 7 chromosomes can be demonstrated. In many other organisms, although the number of chromosomes may have originated in this way, this is no longer clear, and the monoploid number is regarded as the same as the haploid number. Thus in humans, x = n = 23.
Diploid describes a cell or nucleus which contains two copies of genetic material, or a complete set of chromosomes, paired with their homologs (chromosome carrying the same information from the other parent). [ 26 ] Diploid cells have two homologous copies of each chromosome , usually one from the mother and one from the father . All or nearly all mammals are diploid organisms. The suspected tetraploid (possessing four-chromosome sets) plains viscacha rat ( Tympanoctomys barrerae ) and golden viscacha rat ( Pipanacoctomys aureus ) [ 27 ] have been regarded as the only known exceptions (as of 2004). [ 28 ] However, some genetic studies have rejected any polyploidism in mammals as unlikely, and suggest that amplification and dispersion of repetitive sequences best explain the large genome size of these two rodents. [ 29 ] All normal diploid individuals have some small fraction of cells that display polyploidy . Human diploid cells have 46 chromosomes (the somatic number, 2n ) and human haploid gametes (egg and sperm) have 23 chromosomes ( n ). Retroviruses that contain two copies of their RNA genome in each viral particle are also said to be diploid. Examples include human foamy virus , human T-lymphotropic virus , and HIV . [ 30 ]
Polyploidy is the state where all cells have multiple sets of chromosomes beyond the basic set, usually 3 or more. Specific terms are triploid (3 sets), tetraploid (4 sets), pentaploid (5 sets), hexaploid (6 sets), heptaploid [ 2 ] or septaploid [ 3 ] (7 sets), octoploid (8 sets), nonaploid (9 sets), decaploid (10 sets), undecaploid (11 sets), dodecaploid (12 sets), tridecaploid (13 sets), tetradecaploid (14 sets), etc. [ 31 ] [ 32 ] [ 33 ] [ 34 ] Some higher ploidies include hexadecaploid (16 sets), dotriacontaploid (32 sets), and tetrahexacontaploid (64 sets), [ 35 ] though Greek terminology may be set aside for readability in cases of higher ploidy (such as "16-ploid"). [ 33 ] Polytene chromosomes of plants and fruit flies can be 1024-ploid. [ 36 ] [ 37 ] Ploidy of systems such as the salivary gland , elaiosome , endosperm , and trophoblast can exceed this, up to 1048576-ploid in the silk glands of the commercial silkworm Bombyx mori . [ 38 ]
The chromosome sets may be from the same species or from closely related species. In the latter case, these are known as allopolyploids (or amphidiploids, which are allopolyploids that behave as if they were normal diploids). Allopolyploids are formed from the hybridization of two separate species. In plants, this probably most often occurs from the pairing of meiotically unreduced gametes , and not by diploid–diploid hybridization followed by chromosome doubling. [ 39 ] The so-called Brassica triangle is an example of allopolyploidy, where three different parent species have hybridized in all possible pair combinations to produce three new species. [ 40 ]
Polyploidy occurs commonly in plants, but rarely in animals. Even in diploid organisms, many somatic cells are polyploid due to a process called endoreduplication , where duplication of the genome occurs without mitosis (cell division). The extreme in polyploidy occurs in the fern genus Ophioglossum , the adder's-tongues, in which polyploidy results in chromosome counts in the hundreds, or, in at least one case, well over one thousand. [ citation needed ]
It is possible for polyploid organisms to revert to lower ploidy by haploidisation . [ citation needed ]
Polyploidy is a characteristic of the bacterium Deinococcus radiodurans [ 41 ] and of the archaeon Halobacterium salinarum . [ 42 ] These two species are highly resistant to ionizing radiation and desiccation , conditions that induce DNA double-strand breaks. [ 43 ] [ 44 ] This resistance appears to be due to efficient homologous recombinational repair.
Depending on growth conditions, prokaryotes such as bacteria may have a chromosome copy number of 1 to 4, and that number is commonly fractional, counting portions of the chromosome partly replicated at a given time. This is because under exponential growth conditions the cells are able to replicate their DNA faster than they can divide. [ citation needed ]
In ciliates, the macronucleus is called ampliploid , because only part of the genome is amplified. [ 45 ]
Mixoploidy is the case where two cell lines, one diploid and one polyploid, coexist within the same organism . Though polyploidy in humans is not viable, mixoploidy has been found in live adults and children. [ 46 ] There are two types: diploid-triploid mixoploidy, in which some cells have 46 chromosomes and some have 69, [ 47 ] and diploid-tetraploid mixoploidy, in which some cells have 46 and some have 92 chromosomes. It is a major topic of cytology.
Dihaploid and polyhaploid cells are formed by haploidisation of polyploids, i.e., by halving the chromosome constitution. [ citation needed ]
Dihaploids (which are diploid) are important for selective breeding of tetraploid crop plants (notably potatoes), because selection is faster with diploids than with tetraploids. Tetraploids can be reconstituted from the diploids, for example by somatic fusion. [ citation needed ]
The term "dihaploid" was coined by Bender [ 48 ] to combine in one word the number of genome copies (diploid) and their origin (haploid). The term is well established in this original sense, [ 49 ] [ 50 ] but it has also been used for doubled monoploids or doubled haploids , which are homozygous and used for genetic research. [ 51 ]
Euploidy ( Greek eu , "true" or "even") is the state of a cell or organism having one or more than one set of the same set of chromosomes, possibly excluding the sex-determining chromosomes . For example, most human cells have 2 of each of the 23 homologous monoploid chromosomes, for a total of 46 chromosomes. A human cell with one extra set of the 23 normal chromosomes (functionally triploid) would be considered euploid. Euploid karyotypes would consequentially be a multiple of the haploid number , which in humans is 23. [ citation needed ]
Aneuploidy is the state where one or more individual chromosomes of a normal set are absent or present in more than their usual number of copies (excluding the absence or presence of complete sets, which is considered euploidy). Unlike euploidy, aneuploid karyotypes will not be a multiple of the haploid number. In humans, examples of aneuploidy include having a single extra chromosome (as in Down syndrome , where affected individuals have three copies of chromosome 21) or missing a chromosome (as in Turner syndrome , where affected individuals have only one sex chromosome). Aneuploid karyotypes are given names with the suffix -somy (rather than -ploidy , used for euploid karyotypes), such as trisomy and monosomy . [ citation needed ]
Homoploid means "at the same ploidy level", i.e. having the same number of homologous chromosomes . For example, homoploid hybridization is hybridization where the offspring have the same ploidy level as the two parental species. This contrasts with a common situation in plants where chromosome doubling accompanies or occurs soon after hybridization. Similarly, homoploid speciation contrasts with polyploid speciation . [ citation needed ]
Zygoidy is the state in which the chromosomes are paired and can undergo meiosis. The zygoid state of a species may be diploid or polyploid. [ 52 ] [ 53 ] In the azygoid state the chromosomes are unpaired. It may be the natural state of some asexual species or may occur after meiosis. In diploid organisms the azygoid state is monoploid. (See below for dihaploidy.)
In the strictest sense, ploidy refers to the number of sets of chromosomes in a single nucleus rather than in the cell as a whole. Because in most situations there is only one nucleus per cell, it is commonplace to speak of the ploidy of a cell, but in cases in which there is more than one nucleus per cell, more specific definitions are required when ploidy is discussed. Authors may at times report the total combined ploidy of all nuclei present within the cell membrane of a syncytium , [ 38 ] though usually the ploidy of each nucleus is described individually. For example, a fungal dikaryon with two separate haploid nuclei is distinguished from a diploid cell in which the chromosomes share a nucleus and can be shuffled together. [ 54 ]
It is possible on rare occasions for ploidy to increase in the germline , which can result in polyploid offspring and ultimately polyploid species. This is an important evolutionary mechanism in both plants and animals and is known as a primary driver of speciation . [ 8 ] As a result, it may become desirable to distinguish between the ploidy of a species or variety as it presently breeds and that of an ancestor. The number of chromosomes in the ancestral (non-homologous) set is called the monoploid number ( x ), and is distinct from the haploid number ( n ) in the organism as it now reproduces. [ citation needed ]
Common wheat ( Triticum aestivum ) is an organism in which x and n differ. Each plant has a total of six sets of chromosomes (with two sets likely having been obtained from each of three different diploid species that are its distant ancestors). The somatic cells are hexaploid, 2 n = 6 x = 42 (where the monoploid number x = 7 and the haploid number n = 21). The gametes are haploid for their own species, but triploid, with three sets of chromosomes, by comparison to a probable evolutionary ancestor, einkorn wheat . [ citation needed ]
Tetraploidy (four sets of chromosomes, 2 n = 4 x ) is common in many plant species, and also occurs in amphibians , reptiles , and insects . For example, species of Xenopus (African toads) form a ploidy series , featuring diploid ( X. tropicalis , 2n=20), tetraploid ( X. laevis , 4n=36), octaploid ( X. wittei , 8n=72), and dodecaploid ( X. ruwenzoriensis , 12n=108) species. [ 55 ]
Over evolutionary time scales in which chromosomal polymorphisms accumulate, these changes become less apparent by karyotype – for example, humans are generally regarded as diploid, but the 2R hypothesis has confirmed two rounds of whole genome duplication in early vertebrate ancestors. [ citation needed ]
Ploidy can also vary between individuals of the same species or at different stages of the life cycle . [ 56 ] [ 57 ] In some insects it differs by caste . In humans, only the gametes are haploid, but in many of the social insects , including ants , bees , and termites , males develop from unfertilized eggs, making them haploid for their entire lives, even as adults. [ citation needed ]
In the Australian bulldog ant, Myrmecia pilosula , a haplodiploid species, haploid individuals of this species have a single chromosome and diploid individuals have two chromosomes. [ 58 ] In Entamoeba , the ploidy level varies from 4 n to 40 n in a single population. [ 59 ] Alternation of generations occurs in most plants, with individuals "alternating" ploidy level between different stages of their sexual life cycle. [ citation needed ]
In large multicellular organisms, variations in ploidy level between different tissues, organs, or cell lineages are common. Because the chromosome number is generally reduced only by the specialized process of meiosis, the somatic cells of the body inherit and maintain the chromosome number of the zygote by mitosis. However, in many situations somatic cells double their copy number by means of endoreduplication as an aspect of cellular differentiation . For example, the hearts of two-year-old human children contain 85% diploid and 15% tetraploid nuclei, but by 12 years of age the proportions become approximately equal, and adults examined contained 27% diploid, 71% tetraploid and 2% octaploid nuclei. [ 60 ]
There is continued study and debate regarding the fitness advantages or disadvantages conferred by different ploidy levels. A study comparing the karyotypes of endangered or invasive plants with those of their relatives found that being polyploid as opposed to diploid is associated with a 14% lower risk of being endangered, and a 20% greater chance of being invasive. [ 61 ] Polyploidy may be associated with increased vigor and adaptability. [ 62 ] Some studies suggest that selection is more likely to favor diploidy in host species and haploidy in parasite species. [ 63 ] However, polyploidization is associated with an increase in transposable element content [ 64 ] [ 65 ] and relaxed purifying selection on recessive deleterious alleles. [ 66 ] [ 67 ]
When a germ cell with an uneven number of chromosomes undergoes meiosis, the chromosomes cannot be evenly divided between the daughter cells, resulting in aneuploid gametes. Triploid organisms, for instance, are usually sterile. Because of this, triploidy is commonly exploited in agriculture to produce seedless fruit such as bananas and watermelons. If the fertilization of human gametes results in three sets of chromosomes, the condition is called triploid syndrome . [ citation needed ]
In unicellular organisms the ploidy nutrient limitation hypothesis suggests that nutrient limitation should encourage haploidy in preference to higher ploidies. This hypothesis is due to the higher surface-to-volume ratio of haploids, which eases nutrient uptake, thereby increasing the internal nutrient-to-demand ratio. Mable 2001 finds Saccharomyces cerevisiae to be somewhat inconsistent with this hypothesis however, as haploid growth is faster than diploid under high nutrient conditions. The NLH is also tested in haploid, diploid, and polyploid fungi by Gerstein et al. 2017. This result is also more complex: On the one hand, under phosphorus and other nutrient limitation, lower ploidy is selected as expected. However under normal nutrient levels or under limitation of only nitrogen , higher ploidy was selected. Thus the NLH – and more generally, the idea that haploidy is selected by harsher conditions – is cast into doubt by these results. [ 68 ]
Older WGDs have also been investigated. Only as recently as 2015 was the ancient whole genome duplication in Baker's yeast proven to be allopolyploid , by Marcet-Houben and Gabaldón 2015. It still remains to be explained why there are not more polyploid events in fungi, and the place of neopolyploidy and mesopolyploidy in fungal history . [ 68 ]
The concept that those genes of an organism that are expressed exclusively in the diploid stage are under less efficient natural selection than those genes expressed in the haploid stage is referred to as the "masking theory". [ 69 ] Evidence in support of this masking theory has been reported in studies of the single-celled yeast Saccharomyces cerevisiae . [ 70 ] In further support of the masking theory, evidence of strong purifying selection in haploid tissue-specific genes has been reported for the plant Scots Pine . [ 69 ]
The common potato ( Solanum tuberosum ) is an example of a tetraploid organism, carrying four sets of chromosomes. During sexual reproduction, each potato plant inherits two sets of 12 chromosomes from the pollen parent, and two sets of 12 chromosomes from the ovule parent. The four sets combined provide a full complement of 48 chromosomes. The haploid number (half of 48) is 24. The monoploid number equals the total chromosome number divided by the ploidy level of the somatic cells: 48 chromosomes in total divided by a ploidy level of 4 equals a monoploid number of 12. Hence, the monoploid number (12) and haploid number (24) are distinct in this example. [ citation needed ]
However, commercial potato crops (as well as many other crop plants) are commonly propagated vegetatively (by asexual reproduction through mitosis), [ 71 ] in which case new individuals are produced from a single parent, without the involvement of gametes and fertilization, and all the offspring are genetically identical to each other and to the parent, including in chromosome number. The parents of these vegetative clones may still be capable of producing haploid gametes in preparation for sexual reproduction, but these gametes are not used to create the vegetative offspring by this route.
Some eukaryotic genome-scale or genome size databases and other sources which may list the ploidy levels of many organisms: | https://en.wikipedia.org/wiki/Ploidy |
The Plop Boot Manager is a proprietary bootloader written by Elmar Hanlhofer. Plop Boot Manager can make computers boot from media that the original BIOS has no support for, such as USB or IDE CD/DVDs. [ 1 ] [ 2 ] Optionally, Plop can be installed directly onto the hard disk of a computer. [ 3 ]
This software article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Plop_Boot_Manager |
In ecology , plot sampling is a widely used method of abundance estimation in which specific areas, or plots, are selected from within a survey region and sampled. This approach allows scientists to make population estimates using statistical techniques such as the Horvitz–Thompson estimator . Plot sampling is generally effective when it can be assumed that each survey will identify all of the animals in the sampled area, and that the animals will be distributed uniformly and independently. [ 1 ]
Many types of sampling fall under the plot sampling category including quadrant sampling, strip sampling, and many others. Each considers abundance from a statistical standpoint, and only differs in the shape and size of the plot itself. [ 1 ] Plot sampling through area-based counts can also estimate the relative abundance of mobile organisms, like large mammals observed during aerial surveys. However, additional information, like detection probability, may be necessary to estimate absolute population sizes for mobile organisms.
Area-based counts often utilize quadrants, which are sampling areas or volumes of any size or shape. For example, a quadrat could be a 0.25 × 0.25-meter square plot for counting small plants, a 0.1-hectare plot for counting trees, or a soil core of a certain diameter and depth for counting soil organisms. The counts from multiple quadrats are averaged to estimate the number of individuals per unit area or volume, which can then be extrapolated to estimate the total population size. This approach works well if the quadrats accurately represent the population and the counts are accurate within each quadrat. To ensure that quadrats provide a good representation of the population, ecologists often place quadrats at random or evenly spaced intervals along a transect line or grid. The use of multiple quadrats enhances the representativeness of the sample.
The term "covered region" is used to describe the survey region that was sampled for the plot. "Covered area" is used to refer to the surface area that was sampled for the plot. If the entire survey region is covered in this manner, and the survey region equals the covered region rather than a subset of plots that are then used for extrapolation, this is considered a census rather than a plot sampling approach. Plot samples only deal with samples where the covered region is smaller than the survey region. [ 1 ]
To estimate the total number of organisms in a survey region based on the amount of organisms in the covered region, there are two approaches. The first is design-based methods, which examine the randomness in the plots and relate it to the entire survey region. The second approach is model-based methods, which uses statistical models to relate the numbers to the survey region. Depending on the species you are examining, both approaches can be useful. [ 1 ]
In 1905 the first plots were described by Frederic Clements and many variations have developed since. The ability to quantify species abundance and statistically analyze this has been extremely helpful in studying community and population dynamics. Although plot sampling has limitations, it laid the foundation for more intensive sampling methods. [ 2 ]
This ecology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Plot_sampling |
In the mathematics of coding theory , the Plotkin bound , named after Morris Plotkin, is a limit (or bound) on the maximum possible number of codewords in binary codes of given length n and given minimum distance d .
A code is considered "binary" if the codewords use symbols from the binary alphabet { 0 , 1 } {\displaystyle \{0,1\}} . In particular, if all codewords have a fixed length n ,
then the binary code has length n . Equivalently, in this case the codewords can be considered elements of vector space F 2 n {\displaystyle \mathbb {F} _{2}^{n}} over the finite field F 2 {\displaystyle \mathbb {F} _{2}} . Let d {\displaystyle d} be the minimum distance of C {\displaystyle C} , i.e.
where d ( x , y ) {\displaystyle d(x,y)} is the Hamming distance between x {\displaystyle x} and y {\displaystyle y} . The expression A 2 ( n , d ) {\displaystyle A_{2}(n,d)} represents the maximum number of possible codewords in a binary code of length n {\displaystyle n} and minimum distance d {\displaystyle d} . The Plotkin bound places a limit on this expression.
Theorem (Plotkin bound):
i) If d {\displaystyle d} is even and 2 d > n {\displaystyle 2d>n} , then
ii) If d {\displaystyle d} is odd and 2 d + 1 > n {\displaystyle 2d+1>n} , then
iii) If d {\displaystyle d} is even, then
iv) If d {\displaystyle d} is odd, then
where ⌊ ⌋ {\displaystyle \left\lfloor ~\right\rfloor } denotes the floor function .
Let d ( x , y ) {\displaystyle d(x,y)} be the Hamming distance of x {\displaystyle x} and y {\displaystyle y} , and M {\displaystyle M} be the number of elements in C {\displaystyle C} (thus, M {\displaystyle M} is equal to A 2 ( n , d ) {\displaystyle A_{2}(n,d)} ). The bound is proved by bounding the quantity ∑ ( x , y ) ∈ C 2 , x ≠ y d ( x , y ) {\displaystyle \sum _{(x,y)\in C^{2},x\neq y}d(x,y)} in two different ways.
On the one hand, there are M {\displaystyle M} choices for x {\displaystyle x} and for each such choice, there are M − 1 {\displaystyle M-1} choices for y {\displaystyle y} . Since by definition d ( x , y ) ≥ d {\displaystyle d(x,y)\geq d} for all x {\displaystyle x} and y {\displaystyle y} ( x ≠ y {\displaystyle x\neq y} ), it follows that
On the other hand, let A {\displaystyle A} be an M × n {\displaystyle M\times n} matrix whose rows are the elements of C {\displaystyle C} . Let s i {\displaystyle s_{i}} be the number of zeros contained in the i {\displaystyle i} 'th column of A {\displaystyle A} . This means that the i {\displaystyle i} 'th column contains M − s i {\displaystyle M-s_{i}} ones. Each choice of a zero and a one in the same column contributes exactly 2 {\displaystyle 2} (because d ( x , y ) = d ( y , x ) {\displaystyle d(x,y)=d(y,x)} ) to the sum ∑ ( x , y ) ∈ C , x ≠ y d ( x , y ) {\displaystyle \sum _{(x,y)\in C,x\neq y}d(x,y)} and therefore
The quantity on the right is maximized if and only if s i = M / 2 {\displaystyle s_{i}=M/2} holds for all i {\displaystyle i} (at this point of the proof we ignore the fact, that the s i {\displaystyle s_{i}} are integers), then
Combining the upper and lower bounds for ∑ ( x , y ) ∈ C , x ≠ y d ( x , y ) {\displaystyle \sum _{(x,y)\in C,x\neq y}d(x,y)} that we have just derived,
which given that 2 d > n {\displaystyle 2d>n} is equivalent to
Since M {\displaystyle M} is even, it follows that
This completes the proof of the bound. | https://en.wikipedia.org/wiki/Plotkin_bound |
The backstaff is a navigational instrument that was used to measure the altitude of a celestial body , in particular the Sun or Moon . When observing the Sun, users kept the Sun to their back (hence the name) and observed the shadow cast by the upper vane on a horizon vane. It was invented by the English navigator John Davis , who described it in his book Seaman's Secrets in 1594. [ 1 ]
Backstaff is the name given to any instrument that measures the altitude of the sun by the projection of a shadow. It appears that the idea for measuring the sun's altitude using back observations originated with Thomas Harriot . [ 2 ] Many types of instruments evolved from the cross-staff that can be classified as backstaffs. Only the Davis quadrant remains dominant in the history of navigation instruments. Indeed, the Davis quadrant is essentially synonymous with backstaff. However, Davis was neither the first nor the last to design such an instrument and others are considered here as well.
Captain John Davis invented a version of the backstaff in 1594. Davis was a navigator who was quite familiar with the instruments of the day such as the mariner's astrolabe , the quadrant and the cross-staff . He recognized the inherent drawbacks of each and endeavoured to create a new instrument that could reduce those problems and increase the ease and accuracy of obtaining solar elevations .
One early version of the quadrant staff is shown in Figure 1 . [ 3 ] It had an arc affixed to a staff so that it could slide along the staff (the shape is not critical, though the curved shape was chosen). The arc (A) was placed so that it would cast its shadow on the horizon vane (B). The navigator would look along the staff and observe the horizon through a slit in the horizon vane. By sliding the arc so that the shadow aligned with the horizon, the angle of the sun could be read on the graduated staff. This was a simple quadrant, but it was not as accurate as one might like. The accuracy in the instrument is dependent on the length of the staff, but a long staff made the instrument more unwieldy. The maximum altitude that could be measured with this instrument was 45°.
The next version of his quadrant is shown in Figure 2 . [ 3 ] The arc on the top of the instrument in the previous version was replaced with a shadow vane placed on a transom. This transom could be moved along a graduated scale to indicate the angle of the shadow above the staff. Below the staff, a 30° arc was added. The horizon, seen through the horizon vane on the left, is aligned with the shadow. The sighting vane on the arc is moved until it aligns with the view of the horizon. The angle measured is the sum of the angle indicated by the position of the transom and the angle measured on the scale on the arc.
The instrument that is now identified with Davis is shown in Figure 3 . [ 4 ] This form evolved by the mid-17th century. [ 4 ] The quadrant arc has been split into two parts. The smaller radius arc, with a span of 60°, was mounted above the staff. The longer radius arc, with a span of 30° was mounted below. Both arcs have a common centre. At the common centre, a slotted horizon vane was mounted (B). A moveable shadow vane was placed on the upper arc so that its shadow was cast on the horizon vane. A moveable sight vane was mounted on the lower arc (C).
It is easier for a person to place a vane at a specific location than to read the arc at an arbitrary position. This is due to Vernier acuity , the ability of a person to align two line segments accurately. Thus an arc with a small radius, marked with relatively few graduations, can be used to place the shadow vane accurately at a specific angle. On the other hand, moving the sight vane to the location where the line to the horizon meets the shadow requires a large arc. This is because the position may be at a fraction of a degree and a large arc allows one to read smaller graduations with greater accuracy. The large arc of the instrument, in later years, was marked with transversals to allow the arc to be read to greater accuracy than the main graduations allow. [ 5 ]
Thus Davis was able to optimize the construction of the quadrant to have both a small and a large arc, allowing the effective accuracy of a single arc quadrant of large radius without making the entire instrument so large. This form of the instrument became synonymous with the backstaff. It was one of the most widely used forms of the backstaff. Continental European navigators called it the English Quadrant .
A later modification of the Davis quadrant was to use a Flamsteed glass in place of the shadow vane; this was suggested by John Flamsteed . [ 4 ] This placed a lens on the vane that projected an image of the sun on the horizon vane instead of a shadow. It was useful under conditions where the sky was hazy or lightly overcast; the dim image of the sun was shown more brightly on the horizon vane where a shadow could not be seen. [ 5 ]
In order to use the instrument, the navigator would place the shadow vane at a location anticipating the altitude of the sun. Holding the instrument in front of him, with the sun at his back, he holds the instrument so that the shadow cast by the shadow vane falls on the horizon vane at the side of the slit. He then moves the sight vane so that he observes the horizon in a line from the sight vane through the horizon vane's slit while simultaneously maintaining the position of the shadow. This permits him to measure the angle between the horizon and the sun as the sum of the angle read from the two arcs.
Since the shadow's edge represents the limb of the sun, he must correct the value for the semidiameter of the sun.
The Elton's quadrant derived from the Davis quadrant. It added an index arm with spirit levels to provide an artificial horizon.
The demi-cross was an instrument that was contemporary with the Davis quadrant. It was popular outside England. [ 4 ]
The vertical transom was like a half-transom on a cross-staff , hence the name demi-cross . It supported a shadow vane (A in Figure 4 ) that could be set to one of several heights (three according to May, [ 4 ] four according to de Hilster [ 6 ] ). By setting the shadow vane height, the range of angles that could be measured was set. The transom could be slid along the staff and the angle read from one of the graduated scales on the staff.
The sight vane (C) and horizon vane (B) were aligned visually with the horizon. With the shadow vane's shadow cast on the horizon vane and aligned with the horizon, the angle was determined. In practice, the instrument was accurate but more unwieldy than the Davis quadrant. [ 6 ]
The plough was the name given to an unusual instrument that existed for a short time. [ 4 ] It was part cross-staff and part backstaff. In Figure 5 , A is the transom that casts its shadow on the horizon vane at B . It functions in the same manner as the staff in Figure 1 . C is the sighting vane. The navigator uses the sighting vane and the horizon vane to align the instrument horizontally. The sighting vane can be moved left to right along the staff. D is a transom just as one finds on a cross-staff. This transom has two vanes on it that can be moved closer or farther from the staff to emulate different-length transoms. The transom can be moved on the staff and used to measure angles.
The Almucantar staff is a device specifically used for measuring the altitude of the sun at low altitudes.
The cross-staff was normally a direct observation instrument. However, in later years it was modified for use with back observations.
There was a variation of the quadrant – the Back observation quadrant – that was used for measuring the sun's altitude by observing the shadow cast on a horizon vane.
Thomas Hood invented this cross-staff in 1590. [ 4 ] It could be used for surveying, astronomy or other geometric problems.
It consists of two components, a transom and a yard. The transom is the vertical component and is graduated from 0° at the top to 45° at the bottom. At the top of the transom, a vane is mounted to cast a shadow. The yard is horizontal and is graduated from 45° to 90°. The transom and yard are joined by a special fitting (the double socket in Figure 6 ) that permits independent adjustments of the transom vertically and the yard horizontally.
It was possible to construct the instrument with the yard at the top of the transom rather than at the bottom. [ 7 ]
Initially, the transom and yard are set so that the two are joined at their respective 45° settings. The instrument is held so that the yard is horizontal (the navigator can view the horizon along the yard to assist in this). The socket is loosened so that the transom is moved vertically until the shadow of the vane is cast at the yard's 90° setting. If the movement of just the transom can accomplish this, the altitude is given by the transom's graduations. If the sun is too high for this, the yard horizontal opening in the socket is loosened and the yard is moved to allow the shadow to land on the 90° mark. The yard then yields the altitude.
It was a fairly accurate instrument, as the graduations were well spaced compared to a conventional cross-staff . However, it was a bit unwieldy and difficult to handle in wind.
A late addition to the collection of backstaves in the navigation world, this device was invented by Benjamin Cole in 1748. [ 4 ]
The instrument consists of a staff with a pivoting quadrant on one end. The quadrant has a shadow vane , which can optionally take a lens like the Davis quadrant's Flamsteed glass, at the upper end of the graduated scale (A in Figure 7 ). This casts a shadow or projects an image of the sun on the horizon vane (B). The observer views the horizon through a hole in the sight vane (D) and a slit in the horizon vane to ensure the instrument is level. The quadrant component is rotated until the horizon and the sun's image or shadow are aligned. The altitude can then be read from the quadrant's scale. In order to refine the reading, a circular vernier is mounted on the staff (C).
The fact that such an instrument was introduced in the middle of the 18th century shows that the quadrant was still a viable instrument even in the presence of the octant .
English scientist George Adams created a very similar backstaff at the same time. Adam's version ensured that the distance between the Flamsteed glass and horizon vane was the same as the distance from the vane to the sight vane. [ 8 ]
Edmund Gunter invented the cross bow quadrant , also called the mariner's bow , around 1623. [ 4 ] It gets its name from the similarity to the archer's crossbow .
This instrument is interesting in that the arc is 120° but is only graduated as a 90° arc. [ 4 ] As such, the angular spacing of a degree on the arc is slightly greater than one degree. Examples of the instrument can be found with a 0° to 90° graduation or with two mirrored 0° to 45° segments centred on the midpoint of the arc. [ 4 ]
The instrument has three vanes, a horizon vane (A in Figure 8 ) which has an opening in it to observe the horizon, a shadow vane (B) to cast a shadow on the horizon vane and a sighting vane (C) that the navigator uses to view the horizon and shadow at the horizon vane. This serves to ensure the instrument is level while simultaneously measuring the altitude of the sun. The altitude is the difference in the angular positions of the shadow and sighting vanes.
With some versions of this instrument, the sun's declination for each day of the year was marked on the arc. This permitted the navigator to set the shadow vane to the date and the instrument would read the altitude directly.
This article incorporates text from a publication now in the public domain : Chambers, Ephraim , ed. (1728). Cyclopædia, or an Universal Dictionary of Arts and Sciences (1st ed.). James and John Knapton, et al. {{ cite encyclopedia }} : Missing or empty |title= ( help ) | https://en.wikipedia.org/wiki/Plough_(instrument) |
plug.dj was an interactive online social music streaming website based in Los Angeles , owned by Rowl, Inc. [ 1 ] The site was "dedicated to growing positive international communities for sharing and discovering music". It was a free service with microtransactions , and had over 3 million registered accounts. The website was launched on February 29, 2012, by Steven Sacks, Alex Reinlieb, and Jason Grunstra.
Plug.dj consisted of different online chat rooms, called "communities", that users could freely create. [ 2 ] [ 3 ] [ 4 ] Inside each community, users could choose to join a wait list and wait for their turn to be the DJ for everyone else in the community, playing a video or song chosen from either YouTube or SoundCloud , or simply listen passively. [ 5 ] Users could also vote positively or negatively for each song or video played, or add it to their own playlists. [ 6 ] By spending time or being active on the site, they were able to earn experience points (XP) and plug points (PP), which could be used to unlock and purchase various items, such as new avatars and chat badges. Each community on plug.dj was typically focused on a few specific musical genres, usually one of the subgenres of EDM (Electronic Dance Music), such as Trap, Dubstep, Electro, Drum'n'Bass and many others. [ 7 ] Communities dedicated to non-electronic genres, such as rock, jazz, death metal, and classical also existed. [ 8 ] The community creator was able to promote users to moderators to help ensure the community's rules were followed and to keep the environment friendly. [ 9 ] Volunteer global moderators, called "Brand Ambassadors", also existed. [ 10 ] [ 11 ]
In April 2015, a paid subscription service was launched, which provided access to subscriber avatars and badges without the user having to spend PP.
On September 14, 2015, plug.dj announced that the service would be shutting down if it was unable to raise enough money to support the running of the service by a disclosed deadline of September 28 through a donation drive. [ 12 ] It was noted by the administrators of plug.dj that the company was forced to sell their office and developers were to work from home in order to reduce running costs. Other attempts to reduce costs, like another tier in plug.dj subscription system, rewriting some portions of the backend in Go (plug.dj was previously written in Python, a less-efficient and consequently more expensive programming language to operate under) and cutting staff were unsuccessful in keeping the service afloat. [ 13 ] On September 28, 2015, having not met their donation goal in time, the plug.dj service went offline at 3 PM Pacific Standard Time and the closure of its parent company, Plug DJ Inc. followed at an unknown date. [ 14 ] [ 15 ] [ 16 ] [ 17 ]
On December 10, 2015, plug.dj posted a message on their Facebook page, saying "The hype is real". [ 18 ] Later, on February 8, 2016, another post was made explaining that the service will likely return under new management at an unannounced date. [ 19 ] The site was bought by Rowl, Inc [ 1 ] and relaunched on May 31, 2016, with the existing user database restored. This brought all playlists back allowing users to keep all data that they had previously.
On January 28, 2021, plug.dj services went offline without warning. The official Twitter page posted a tweet saying that plug.dj was working to resolve the issue "ASAP". [ 20 ] After 12 days the service was still down, and on February 9, 2021, plug.dj announced that they would be shutting down once again due to financial issues, but with intent to resume service at an unspecified future time. [ 21 ] | https://en.wikipedia.org/wiki/Plug.dj |
A plug in sanitation is an object that is used to close a drainage outlet firmly.
The insertion of a plug into a drainage outlet allows the container to be filled with water or other fluids. In contrast to screw on caps, plugs are pushed into the hole and are not put over the hole.
Plugs are most commonly encountered in the bathroom or kitchen, for use in bathtubs , wash basins or sinks . [ 1 ]
Typically plugs are made from a soft material, such as rubber , or have a soft outer rim, so that they can be fitted to holes slightly smaller than their diameter; this ensures a tight seal. They are often connected by a ball chain which ensures the plug may be pulled from the drain with relative ease.
Some modern plugholes dispense with the need for a separate plug, having instead a built-in 'pop-up plug' operated by a handle on the sink, that can move up or down to open or close the plughole. | https://en.wikipedia.org/wiki/Plug_(sanitation) |
A plug door is a door designed to seal itself by taking advantage of pressure difference on its two sides and is typically used on aircraft with cabin pressurization . The higher pressure on one side forces the usually wedge -shaped door into its socket to create a seal, which prevents it from being opened until the pressure is equalised on both sides. A non-plug door relies on the strength of the locking mechanism to keep the door shut.
Plug doors are often used on aircraft with pressurized cabins because this design of door provides a simple and reliable means of securing the door and preventing leakage of air. [ 1 ] As the air pressure outside becomes increasingly lower than that inside the cabin, the pressure difference causes the door to seal itself closed and prevent leakage. The region of the fuselage around the opening for the door must be reinforced and this adds weight, so for large doors an alternative to the plug design is commonly used.
On some aircraft, a complex hinge design allows half the door to open inward like a plug door, and the other half to open outward. Initially the door can be rotated to fit through the opening for the non-plug half so the whole door then opens outward; this is called a semi-plug door . Alternatively, the door may have locking hinged panels at the top and bottom edges that can make it smaller than the opening, so it may be swung outward.
Plug doors are used on most pressurized airliners, particularly for emergency exits and small passenger doors. However, since plug doors must open inward, the plug design is disadvantageous for large doors. Semi-plug doors are often used for the main passenger doors. For large cargo doors, if the door were to be swung inside the fuselage, it would prevent valuable cargo being loaded into the large space it would occupy. These doors usually open outward using a secure locking mechanism with multiple pins or hatch dogs to prevent opening while in flight with a large outward-facing pressure differential. This design of door can be lighter than a plug door of the same dimensions due to the need for reinforcing the opening around a plug door.
A door plug , not to be confused with a plug door , is used in some of Boeing's 737 -900ER [ 2 ] and MAX 9s instead of an actual emergency exit door. It can be removed outwards for maintenance and requires stop pads on the airframe as well as stop fittings on the door panel to prevent outward movement during operation. This did not prevent the door plug from detaching on Alaska Airlines Flight 1282 on January 5, 2024, which has been attributed to missing bolts in the upper guide fittings and the lower hinge assemblies.
Many passenger trains in the world use sliding plug doors: early examples of passenger trains using plug doors include the MVG Class A of the Munich U-Bahn from 1967, [ 3 ] the first batch of trains for Line 2 of the Milan Metro from 1970, [ 4 ] and the DT1 of the Nuremberg U-Bahn , also from 1970. [ 5 ]
Recent examples of trains with plug doors include the KTX-Eum high-speed train, the Gautrain commuter train, and the E-class tram in Melbourne.
An inward opening plug hatch design was used on the Block I Apollo Command Module , because the explosive-release hatch of Gus Grissom 's Mercury capsule Liberty Bell 7 prematurely blew at the end of the flight, causing the capsule to sink in the Atlantic Ocean and nearly resulting in Grissom's drowning. The Apollo cabin was pressurized at launch to 2 pounds per square inch (14 kPa) above standard sea level pressure, which sealed the hatch. A cabin fire during a 1967 Apollo 1 ground test raised the pressure even higher (29 pounds per square inch (200 kPa)), and made the hatch impossible to remove for the crew to escape. This killed Grissom along with his entire crew, Edward H. White and Roger Chaffee . Because of this, NASA decided to change to a quick-release, outward opening hatch on the Command Module.
Plug hatches were retained for the CM docking hatch and the two hatches on the Apollo Lunar Module , as the risk of fire in the low-pressure (5 pounds per square inch (34 kPa)) in-space atmosphere was much lower. Plug hatches were also used for the inner airlock hatch on the Space Shuttle . Currently, they are used on the International Space Station , as well as on the hatch between the Orbital Module and Descent Module of the Russian Soyuz spacecraft .
Deep-submergence vehicles such as the Alvin use a plug hatch which is sealed inward by the pressure of the ocean water. [ 6 ]
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This spacecraft or satellite related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Plug_door |
In fluid mechanics , plug flow is a simple model of the velocity profile of a fluid flowing in a pipe . In plug flow, the velocity of the fluid is assumed to be constant across any cross-section of the pipe perpendicular to the axis of the pipe. The plug flow model assumes there is no boundary layer adjacent to the inner wall of the pipe.
The plug flow model has many practical applications. One example is in the design of chemical reactors . Essentially no back mixing is assumed with "plugs" of fluid passing through the reactor. This results in differential equations that need to be integrated to find the reactor conversion and outlet temperatures. Other simplifications used are perfect radial mixing and a homogeneous bed structure.
An advantage of the plug flow model is that no part of the solution of the problem can be perpetuated "upstream". This allows one to calculate the exact solution to the differential equation knowing only the initial conditions. No further iteration is required. Each "plug" can be solved independently provided the previous plug's state is known.
The flow model in which the velocity profile consists of the fully developed boundary layer is known as pipe flow . In laminar pipe flow , the velocity profile is parabolic . [ 1 ]
For flows in pipes, if flow is turbulent then the laminar sublayer caused by the pipe wall is so thin that it is negligible. Plug flow will be achieved if the sublayer thickness is much less than the pipe diameter ( δ s {\displaystyle \delta _{s}} << D ).
where f {\displaystyle f} is the Darcy friction factor (from the above equation or the Moody Chart ), δ s {\displaystyle \delta _{s}} is the sublayer thickness, D {\displaystyle D} is the pipe diameter, ρ {\displaystyle \rho } is the density , u ∗ {\displaystyle u^{*}} is the friction velocity (not an actual velocity of the fluid), V {\displaystyle V} is the average velocity of the plug (in the pipe), τ w {\displaystyle \tau _{w}} is the shear on the wall, and Δ P {\displaystyle \Delta P} is the pressure loss down the length L {\displaystyle L} of the pipe. ϵ {\displaystyle \epsilon } is the relative roughness of the pipe.
In this regime the pressure drop is a result of inertia-dominated turbulent shear stress rather than viscosity-dominated laminar shear stress. | https://en.wikipedia.org/wiki/Plug_flow |
The plug flow reactor model ( PFR , sometimes called continuous tubular reactor , CTR , or piston flow reactors ) is a model used to describe chemical reactions in continuous, flowing systems of cylindrical geometry. The PFR model is used to predict the behavior of chemical reactors of such design, so that key reactor variables, such as the dimensions of the reactor, can be estimated.
Fluid going through a PFR may be modeled as flowing through the reactor as a series of infinitely thin coherent "plugs", each with a uniform composition, traveling in the axial direction of the reactor, with each plug having a different composition from the ones before and after it. The key assumption is that as a plug flows through a PFR, the fluid is perfectly mixed in the radial direction but not in the axial direction (forwards or backwards). Each plug of differential volume is considered as a separate entity, effectively an infinitesimally small continuous stirred tank reactor , limiting to zero volume. As it flows down the tubular PFR, the residence time ( τ {\displaystyle \tau } ) of the plug is a function of its position in the reactor. In the ideal PFR, the residence time distribution is therefore a Dirac delta function with a value equal to τ {\displaystyle \tau } .
The stationary PFR is governed by ordinary differential equations , the solution for which can be calculated providing that appropriate boundary conditions are known.
The PFR model works well for many fluids: liquids, gases, and slurries. Although turbulent flow and axial diffusion cause a degree of mixing in the axial direction in real reactors, the PFR model is appropriate when these effects are sufficiently small that they can be ignored.
In the simplest case of a PFR model, several key assumptions must be made in order to simplify the problem, some of which are outlined below. Note that not all of these assumptions are necessary, however the removal of these assumptions does increase the complexity of the problem. The PFR model can be used to model multiple reactions as well as reactions involving changing temperatures, pressures and densities of the flow. Although these complications are ignored in what follows, they are often relevant to industrial processes.
Assumptions:
A material balance on the differential volume of a fluid element, or plug, on species i of axial length dx between x and x + dx gives:
Accumulation is 0 under steady state; therefore, the above mass balance can be re-written as follows:
1. F i ( x ) − F i ( x + d x ) + A t d x ν i r = 0 {\displaystyle F_{i}(x)-F_{i}(x+dx)+A_{t}dx\nu _{i}r=0} . [ 1 ]
where:
The flow linear velocity, u (m/s) and the concentration of species i , C i (mol/m 3 ) can be introduced as:
where v ˙ {\displaystyle {\dot {v}}} is the volumetric flow rate.
On application of the above to Equation 1, the mass balance on i becomes:
2. A t u [ C i ( x ) − C i ( x + d x ) ] + A t d x ν i r = 0 {\displaystyle A_{t}u[C_{i}(x)-C_{i}(x+dx)]+A_{t}dx\nu _{i}r=0\,} . [ 1 ]
When like terms are cancelled and the limit dx → 0 is applied to Equation 2 the mass balance on species i becomes
3. u d C i d x = ν i r {\displaystyle u{\frac {dC_{i}}{dx}}=\nu _{i}r} , [ 1 ]
The temperature dependence of the reaction rate, r , can be estimated using the Arrhenius equation . Generally, as the temperature increases so does the rate at which the reaction occurs. Residence time, τ {\displaystyle \tau } , is the average amount of time a discrete quantity of reagent spends inside the tank.
Assume:
After integration of Equation 3 using the above assumptions, solving for C A (x) we get an explicit equation for the concentration of species A as a function of position:
4. C A ( x ) = C A 0 e − k τ {\displaystyle C_{A}(x)=C_{A0}e^{-k\tau }\,} ,
where C A0 is the concentration of species A at the inlet to the reactor, appearing from the integration boundary condition.
PFRs are used to model the chemical transformation of compounds as they are transported in systems resembling "pipes". The "pipe" can represent a variety of engineered or natural conduits through which liquids or gases flow. (e.g. rivers, pipelines, regions between two mountains, etc.)
An ideal plug flow reactor has a fixed residence time: Any fluid (plug) that enters the reactor at time t {\displaystyle t} will exit the reactor at time t + τ {\displaystyle t+\tau } , where τ {\displaystyle \tau } is the residence time of the reactor. The residence time distribution function is therefore a Dirac delta function at τ {\displaystyle \tau } . A real plug flow reactor has a residence time distribution that is a narrow pulse around the mean residence time distribution.
A typical plug flow reactor could be a tube packed with some solid material (frequently a catalyst ). Typically these types of reactors are called packed bed reactors or PBR's. Sometimes the tube will be a tube in a shell and tube heat exchanger .
When a plug flow model can not be applied, the dispersion model is usually employed. [ 2 ] [ 3 ]
The residence-time distribution (RTD) of a reactor is a characteristic of the mixing that occurs in the chemical reactor. There is no axial mixing in a plug-flow reactor, and this omission is reflected in the RTD which is exhibited by this class of reactors. [ 4 ]
Real plug flow reactors do not satisfy the idealized flow patterns, back mix flow or plug flow deviation from ideal behavior can be due to channeling of fluid through the vessel, recycling of fluid within the vessel or due to the presence of stagnant region or dead zone of fluid in the vessel. [ 5 ] Real plug flow reactors with non-ideal behavior have also been modelled. [ 6 ] To predict the exact behavior of a vessel as a chemical reactor , RTD or stimulus response technique is used. The tracer technique , the most widely used method for the study of axial dispersion, is usually used in the form of: [ 7 ]
The RTD is determined experimentally by injecting an inert chemical, molecule, or atom, called a tracer, into the reactor at some time t = 0 and then measuring the tracer concentration, C, in the effluent stream as a function of time. [ 4 ]
The RTD curve of fluid leaving a vessel is called the E-Curve. This curve is normalized in such a way that the area under it is unity:
The mean age of the exit stream or mean residence time is:
When a tracer is injected into a reactor at a location more than two or three particle diameters downstream from the entrance and measured some distance upstream from the exit, the system can be described by the dispersion model with combinations of open or close boundary conditions. [ 3 ] For such a system where there is no discontinuity in type of flow at the point of tracer injection or at the point of tracer measurement, the variance for open-open system is:
Where,
which represents the ratio of rate of transport by convection to rate of transport by diffusion or dispersion.
Vessel dispersion number is defined as:
The variance of a continuous distribution measured at a finite number of equidistant locations is given by:
Where mean residence time τ is given by:
Thus (σ θ ) 2 can be evaluated from the experimental data on C vs. t and for known values of ( σ θ ) 2 {\displaystyle (\sigma _{\theta })^{2}} , the dispersion number ( 1 / P e ) {\displaystyle (1/P_{e})} can be obtained from eq. (3) as:
Thus axial dispersion coefficient D L can be estimated (L = packed height) [ 5 ]
As mentioned before, there are also other boundary conditions that can be applied to the dispersion model giving different relationships for the dispersion number. [ 8 ] [ 9 ] [ 3 ]
From the safety technical point of view the PFR has the advantages that [ 10 ]
The main problems lies in difficult and sometimes critical start-up and shut down operations. [ 10 ]
Plug flow reactors are used for some of the following applications: | https://en.wikipedia.org/wiki/Plug_flow_reactor_model |
The plum pudding model is an obsolete scientific model of the atom . It was first proposed by J. J. Thomson in 1904 following his discovery of the electron in 1897, and was rendered obsolete by Ernest Rutherford 's discovery of the atomic nucleus in 1911. The model tried to account for two properties of atoms then known: that there are electrons, and that atoms have no net electric charge. Logically there had to be an equal amount of positive charge to balance out the negative charge of the electrons. As Thomson had no idea as to the source of this positive charge, he tentatively proposed that it was everywhere in the atom, and that the atom was spherical. This was the mathematically simplest hypothesis to fit the available evidence, or lack thereof. In such a sphere, the negatively charged electrons would distribute themselves in a more or less even manner throughout the volume, simultaneously repelling each other while being attracted to the positive sphere's center. [ 1 ]
Despite Thomson's efforts, his model couldn't account for emission spectra and valencies . Based on experimental studies of alpha particle scattering (in the gold foil experiment ), Ernest Rutherford developed an alternative model for the atom featuring a compact nucleus where the positive charge is concentrated.
Thomson's model is popularly referred to as the "plum pudding model" with the notion that the electrons are distributed uniformly like raisins in a plum pudding . Neither Thomson nor his colleagues ever used this analogy. [ 2 ] It seems to have been coined by popular science writers to make the model easier to understand for the layman. The analogy is perhaps misleading because Thomson likened the positive sphere to a liquid rather than a solid since he thought the electrons moved around in it. [ 3 ]
Thomson's model was the first atomic model to describe an internal structure. Before this, atoms were simply the basic units of weight by which the chemical elements combined, and their only properties were valency and relative weight to hydrogen. The model had no properties which concerned physicists, such as electric charge , magnetic moment , volume, or absolute mass, and because of this some physicists had doubted atoms even existed.
Thomson hypothesized that the quantity, arrangement, and motions of electrons in the atom could explain its physical and chemical properties, such as emission spectra, valencies, reactivity, and ionization. He was on the right track, though his approach was based on classical mechanics and he did not have the insight to incorporate quantized energy into it.
Throughout the 19th century evidence from chemistry and statistical mechanics accumulated that matter was composed of atoms. The structure of the atom was discussed, and by the end of the century the leading model [ 4 ] : 175 was the vortex theory of the atom , proposed by William Thomson (later Lord Kelvin) in 1867. [ 5 ] By 1890, J.J. Thomson had his own version called the "nebular atom" hypothesis, in which atoms were composed of immaterial vortices and suggested similarities between the arrangement of vortices and periodic regularity found among the chemical elements. [ 6 ]
Thomson's discovery of the electron in 1897 changed his views. Thomson called them "corpuscles" ( particles ), but they were more commonly called "electrons", the name G. J. Stoney had coined for the " fundamental unit quantity of electricity " in 1891. [ 7 ] However even late in 1899, few scientists believed in subatomic particles. [ 8 ] : I:365
Another emerging scientific theme of the 19th century was the discovery and study of radioactivity . Thomson discovered the electron by studying cathode rays , and in 1900 Henri Becquerel determined that the radiation from uranium, now called beta particles , had the same charge/mass ratio as cathode rays. [ 8 ] : II:3 These beta particles were believed to be electrons travelling at high speed. The particles were used by Thomson to probe atoms to find evidence for his atomic theory. The other form of radiation critical to this era of atomic models was alpha particles . Heavier and slower than beta particles, these were the key tool used by Rutherford to find evidence against Thomson's model.
In addition to the emerging atomic theory, the electron, and radiation, the last element of history was the many studies of atomic spectra published in the late 19th century. Part of the attraction of the vortex model was its possible role in describing the spectral data as vibrational responses to electromagnetic radiation. [ 4 ] : 177 Neither Thomson's model nor its successor, Rutherford's model, made progress towards understanding atomic spectra. That would have to wait until Niels Bohr built the first quantum-based atom model.
Thomson's model was the first to assign a specific inner structure to an atom, [ 9 ] : 9 though his earliest descriptions did not include mathematical formulas. [ 2 ] From 1897 through 1913, Thomson proposed a series of increasingly detailed polyelectron models for the atom. [ 4 ] : 178 His first versions were qualitative culminating in his 1906 paper and follow on summaries. Thomson's model changed over the course of its initial publication, finally becoming a model with much more mobility containing electrons revolving in the dense field of positive charge rather than a static structure. Thomson attempted unsuccessfully to reshape his model to account for some of the major spectral lines experimentally known for several elements. [ 10 ]
In a paper titled Cathode Rays , [ 11 ] Thomson demonstrated that cathode rays are not light but made of negatively charged particles which he called corpuscles . He observed that cathode rays can be deflected by electric and magnetic fields, which does not happen with light rays. In a few paragraphs near the end of this long paper Thomson discusses the possibility that atoms were made of these corpuscles , calling them primordial atoms . Thomson believed that the intense electric field around the cathode caused the surrounding gas molecules to split up into their component corpuscles , thereby generating cathode rays. Thomson thus showed evidence that atoms were divisible, though he did not attempt to describe their structure at this point.
Thomson notes that he was not the first scientist to propose that atoms are divisible, making reference to William Prout who in 1815 found that the atomic weights of various elements were multiples of hydrogen's atomic weight and hypothesised that all atoms were made of hydrogen atoms fused together. [ 9 ] Prout's hypothesis was dismissed by chemists when by the 1830s it was found that some elements seemed to have a non-integer atomic weight—e.g. chlorine has an atomic weight of about 35.45. But the idea continued to intrigue scientists. The discrepancies were eventually explained with the discovery of isotopes in 1912.
A few months after Thomson's paper appeared, George FitzGerald suggested that the corpuscle identified by Thomson from cathode rays and proposed as parts of an atom was a "free electron", as described by physicist Joseph Larmor and Hendrik Lorentz . While Thomson did not adopt the terminology, the connection convinced other scientists that cathode rays were particles, an important step in their eventual acceptance of an atomic model based on sub-atomic particles. [ 12 ]
In 1899 Thomson reiterated his atomic model in a paper that showed that negative electricity created by ultraviolet light landing on a metal (known now as the photoelectric effect ) has the same mass-to-charge ratio as cathode rays; then he applied his previous method for determining the charge on ions to the negative electric particles created by ultraviolet light. [ 4 ] : 86 He estimated that the electron's mass was 0.0014 times that of the hydrogen ion (as a fraction: 1 / 714 ). [ 13 ] In the conclusion of this paper he writes: [ 9 ]
I regard the atom as containing a large number of smaller bodies which I shall call corpuscles; these corpuscles are equal to each other; the mass of a corpuscle is the mass of the negative ion in a gas at low pressure, i.e. about 3 × 10 −26 of a gramme. In the normal atom, this assemblage of corpuscles forms a system which is electrically neutral. The negative effect is balanced by something which causes the space through which the corpuscles are spread to act as if it had a charge of positive electricity equal in amount to the sum of the negative charges on the corpuscles.
Thomson provided his first detailed description of the atom in his 1904 paper On the Structure of the Atom . [ 14 ] Thomson starts with a short description of his model
... the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, ... [ 14 ]
Primarily focused on the electrons, Thomson adopted the positive sphere from Kelvin's atom model proposed a year earlier. [ 10 ] [ 15 ] He then gives a detailed mechanical analysis of such a system, distributing the electrons uniformly around a ring. The attraction of the positive electrification is balanced by the mutual repulsion of the electrons. His analysis focuses on stability, looking for cases where small changes in position are countered by restoring forces.
After discussing his many formulae for stability he turned to analysing patterns in the number of electrons in various concentric rings of stable configurations. These regular patterns Thomson argued are analogous to the periodic law of chemistry behind the structure of the periodic table . This concept, that a model based on subatomic particles could account for chemical trends, encouraged interest in Thomson's model and influenced future work even if the details Thomson's electron assignments turned out to be incorrect. [ 16 ] : 135
Thomson at this point believed that all the mass of the atom was carried by the electrons. [ 17 ] This would mean that even a small atom would have to contain thousands of electrons, and the positive electrification that encapsulated them was without mass. [ 18 ]
In a lecture delivered to the Royal Institution of Great Britain in 1905, [ 19 ] Thomson explained that it was too computationally difficult for him to calculate the movements of large numbers of electrons in the positive sphere, so he proposed a practical experiment. This involved magnetised pins pushed into cork discs and set afloat in a basin of water. The pins were oriented such that they repelled each other. Above the centre of the basin was suspended an electromagnet that attracted the pins. The equilibrium arrangement the pins took informed Thomson on what arrangements the electrons in an atom might take.
For instance, he observed that while five pins would arrange themselves in a stable pentagon around the centre, six pins could not form a stable hexagon. Instead, one pin would move to the centre and the other five would form a pentagon around the centre pin, and this arrangement was stable. As he added more pins, they would arrange themselves in concentric rings around the centre.
The experiment functioned in two dimensions instead of three, but Thomson inferred the electrons in the atom arranged themselves in concentric shells and they could move within these shells but did not move from one shell to another them except when electrons were added or subtracted from the atom.
Before 1906 Thomson considered the atomic weight to be due to the mass of the electrons (which he continued to call "corpuscles"). Based on his own estimates of the electron mass, an atom would need tens of thousands electrons to account for the mass. In 1906 he used three different methods, X-ray scattering, beta ray absorption, or optical properties of gases, to estimate that "number of corpuscles is not greatly different from the atomic weight". [ 20 ] [ 21 ] This reduced the number of electrons to tens or at most a couple of hundred and that in turn meant that the positive sphere in Thomson's model contained most of the mass of the atom. This meant that Thomson's mechanical stability work from 1904 and the comparison to the periodic table were no longer valid. [ 4 ] : 186 Moreover, the alpha particle, so important to the next advance in atomic theory by Rutherford, would no longer be viewed as an atom containing thousands of electrons. [ 21 ] : 269
In 1907, Thomson published The Corpuscular Theory of Matter [ 22 ] which reviewed his ideas on the atom's structure and proposed further avenues of research.
In Chapter 6, he further elaborates his experiment using magnetised pins in water, providing an expanded table. For instance, if 59 pins were placed in the pool, they would arrange themselves in concentric rings of the order 20-16-13-8-2 (from outermost to innermost).
In Chapter 7, Thomson summarised his 1906 results on the number of electrons in an atom. He included one important correction: he replaced the beta-particle analysis with one based on the cathode ray experiments of August Becker , giving a result in better agreement with other approaches to the problem. [ 21 ] : 273 Experiments by other scientists in this field had shown that atoms contain far fewer electrons than Thomson previously thought. Thomson now believed the number of electrons in an atom was a small multiple of its atomic weight: "the number of corpuscles in an atom of any element is proportional to the atomic weight of the element — it is a multiple, and not a large one, of the atomic weight of the element." [ 23 ] This meant that almost all of the atom's mass had to be carried by the positive sphere, whatever it was made of.
Thomson in this book estimated that a hydrogen atom is 1,700 times heavier than an electron ( the current measurement is 1,837 ). [ 24 ] Thomson noted that no scientist had yet found a positively charged particle smaller than a hydrogen ion. [ 25 ] He also wrote that the positive charge of an atom is a multiple of a basic unit of positive charge, equal to the negative charge of an electron. [ 26 ] Thomson refused to jump to the conclusion that the basic unit of positive charge has a mass equal to that of the hydrogen ion, arguing that scientists first had to know how many electrons an atom contains. [ 27 ] For all he could tell, a hydrogen ion might still contain a few electrons—perhaps two electrons and three units of positive charge.
Thomson's difficulty with beta scattering in 1906 lead him to renewed interest in the topic. He encouraged J. Arnold Crowther to experiment with beta scattering through thin foils [ 28 ] and, in 1910, Thomson produced a new theory of beta scattering. [ 29 ] The two innovations in this paper was the introduction of scattering from the positive sphere of the atom and analysis that multiple or compound scattering was critical to the final results. [ 21 ] : 273 This theory and Crowther's experimental results would be confronted by Rutherford's theory and Geiger and Mardsen new experiments with alpha particles.
Another innovation in Thomson's 1910 paper was that he modelled how an atom might deflect an incoming beta particle if the positive charge of the atom existed in discrete units of equal but arbitrary size, spread evenly throughout the atom, separated by empty space, with each unit having a positive charge equal to the electron's negative charge. [ 30 ] Thomson therefore came close to deducing the existence of the proton , which was something Rutherford eventually did. In Rutherford's model of the atom, the protons are clustered in a very small nucleus, but in Thomson's alternative model, the positive units were spread throughout the atom.
In his 1910 paper "On the Scattering of rapidly moving Electrified Particles", Thomson presented equations that modelled how beta particles scatter in a collision with an atom. [ 31 ] [ 21 ] : 277 His work was based on beta scattering studies by James Crowther .
Thomson typically assumed the positive charge in the atom was uniformly distributed throughout its volume, encapsulating the electrons. In his 1910 paper, Thomson presented the following equation which isolated the effect of this positive sphere: [ 31 ] [ 21 ] : 278
θ ¯ 2 = π 4 ⋅ k q e q g m v 2 R {\displaystyle {\bar {\theta }}_{2}={\frac {\pi }{4}}\cdot {\frac {kq_{\text{e}}q_{\text{g}}}{mv^{2}R}}}
where k is the Coulomb constant , q e is the charge of the beta particle, q g is the charge of the positive sphere, m is the mass of the beta particle, and R is the radius of the sphere. Because the atom is many thousands of times heavier than the beta particle, no correction for recoil is needed.
Thomson did not explain how this equation was developed, but the historian John L. Heilbron provided an educated guess he called a "straight-line" approximation. [ 32 ] Consider a beta particle passing through the positive sphere with its initial trajectory at a lateral distance b from the centre. The path is assumed to have a very small deflection and therefore is treated here as a straight line.
Inside a sphere of uniformly distributed positive charge the force exerted on the beta particle at any point along its path through the sphere would be directed along the radius r with magnitude: [ 33 ] [ 34 ] : 106
F = k q e q g r 2 ⋅ r 3 R 3 {\displaystyle F={\frac {kq_{\text{e}}q_{\text{g}}}{r^{2}}}\cdot {\frac {r^{3}}{R^{3}}}}
The component of force perpendicular to the trajectory and thus deflecting the path of the particle would be:
F y = k q e q g r 2 ⋅ r 3 R 3 ⋅ cos φ = b k q e q g R 3 {\displaystyle F_{\text{y}}={\frac {kq_{\text{e}}q_{\text{g}}}{r^{2}}}\cdot {\frac {r^{3}}{R^{3}}}\cdot \cos \varphi ={\frac {bkq_{\text{e}}q_{\text{g}}}{R^{3}}}}
The lateral change in momentum p y is therefore
Δ p y = F y t = b k q e q g R 3 ⋅ L v {\displaystyle \Delta p_{\text{y}}=F_{\text{y}}t={\frac {bkq_{\text{e}}q_{\text{g}}}{R^{3}}}\cdot {\frac {L}{v}}}
The resulting angular deflection, θ 2 {\displaystyle \theta _{2}} , is given by
tan θ 2 = Δ p y p x = b k q e q g R 3 ⋅ L v ⋅ 1 m v {\displaystyle \tan \theta _{2}={\frac {\Delta p_{\text{y}}}{p_{\text{x}}}}={\frac {bkq_{\text{e}}q_{\text{g}}}{R^{3}}}\cdot {\frac {L}{v}}\cdot {\frac {1}{mv}}}
where p x is the average horizontal momentum taken to be equal to the incoming momentum. Since we already know the deflection is very small, we can treat tan θ 2 {\displaystyle \tan \theta _{2}} as being equal to θ 2 {\displaystyle \theta _{2}} .
To find the average deflection angle θ ¯ 2 {\displaystyle {\bar {\theta }}_{2}} , the angle for each value of b and the corresponding L are added across the face sphere, then divided by the cross-section area. L = 2 R 2 − b 2 {\displaystyle L=2{\sqrt {R^{2}-b^{2}}}} per Pythagorean theorem . [ 21 ] : 278
θ ¯ 2 = 1 π R 2 ∫ 0 R b k q e q g R 3 ⋅ 2 R 2 − b 2 v ⋅ 1 m v ⋅ 2 π b ⋅ d b {\displaystyle {\bar {\theta }}_{2}={\frac {1}{\pi R^{2}}}\int _{0}^{R}{\frac {bkq_{\text{e}}q_{\text{g}}}{R^{3}}}\cdot {\frac {2{\sqrt {R^{2}-b^{2}}}}{v}}\cdot {\frac {1}{mv}}\cdot 2\pi b\cdot \mathrm {d} b}
= π 4 ⋅ k q e q g m v 2 R {\displaystyle ={\frac {\pi }{4}}\cdot {\frac {kq_{\text{e}}q_{\text{g}}}{mv^{2}R}}}
This matches Thomson's formula in his 1910 paper.
Thomson modelled the collisions between a beta particle and the electrons of an atom by calculating the deflection of one collision then multiplying by a factor for the number of collisions as the particle crosses the atom.
For the electrons within an arbitrary distance s of the beta particle's path, their mean distance will be s / 2 . Therefore, the average deflection per electron will be
2 arctan k q e q e m v 2 s 2 ≈ 4 k q e q e m v 2 s {\displaystyle 2\arctan {\frac {kq_{\text{e}}q_{\text{e}}}{mv^{2}{\tfrac {s}{2}}}}\approx {\frac {4kq_{\text{e}}q_{\text{e}}}{mv^{2}s}}}
where q e is the elementary charge , k is the Coulomb constant , m and v are the mass and velocity of the beta particle.
The factor for the number of collisions was known to be the square root of the number of possible electrons along path. The number of electrons depends upon the density of electrons along the particle path times the path length L .
The net deflection caused by all the electrons within this arbitrary cylinder of effect around the beta particle's path is
θ 1 = 4 k q e q e m v 2 s ⋅ N 0 π s 2 L {\displaystyle \theta _{1}={\frac {4kq_{\text{e}}q_{\text{e}}}{mv^{2}s}}\cdot {\sqrt {N_{0}\pi s^{2}L}}}
where N 0 is the number of electrons per unit volume and π s 2 L {\displaystyle \pi s^{2}L} is the volume of this cylinder.
Since Thomson calculated the deflection would be very small, he treats L as a straight line. Therefore L = 2 R 2 − b 2 {\displaystyle L=2{\sqrt {R^{2}-b^{2}}}} where b is the distance of this chord from the centre. The mean of L {\displaystyle {\sqrt {L}}} is given by the integral
1 π R 2 ∫ 0 R 2 R 2 − b 2 ⋅ 2 π b ⋅ d b = 4 5 2 R {\displaystyle {\frac {1}{\pi R^{2}}}\int _{0}^{R}{\sqrt {2{\sqrt {R^{2}-b^{2}}}}}\cdot 2\pi b\cdot \mathrm {d} b={\frac {4}{5}}{\sqrt {2R}}}
We can now replace L {\displaystyle {\sqrt {L}}} in the equation for θ 1 {\displaystyle \theta _{1}} to obtain the mean deflection θ ¯ 1 {\displaystyle {\bar {\theta }}_{1}} :
θ ¯ 1 = 4 k q e q e m v 2 s ⋅ N 0 π s 2 ⋅ 4 5 2 R {\displaystyle {\bar {\theta }}_{1}={\frac {4kq_{\text{e}}q_{\text{e}}}{mv^{2}s}}\cdot {\sqrt {N_{0}\pi s^{2}}}\cdot {\frac {4}{5}}{\sqrt {2R}}}
= 16 5 ⋅ k q e q e m v 2 ⋅ 1 R ⋅ 3 N 2 {\displaystyle ={\frac {16}{5}}\cdot {\frac {kq_{\text{e}}q_{\text{e}}}{mv^{2}}}\cdot {\frac {1}{R}}\cdot {\sqrt {\frac {3N}{2}}}}
where N is the number of electrons in the atom, equal to N 0 4 3 π R 3 {\displaystyle N_{0}{\tfrac {4}{3}}\pi R^{3}} .
In his 1910 paper, Thomson proposed an alternative model in which the positive charge exists in discrete units separated by empty space, with those units being evenly distributed throughout the atom's volume.
In this concept, the average scattering angle of the beta particle is given by:
θ ¯ 2 = 16 5 ⋅ k q e q e m v 2 ⋅ 1 R ⋅ 3 N 2 1 − ( 1 − π 8 ) σ {\displaystyle {\bar {\theta }}_{2}={\frac {16}{5}}\cdot {\frac {kq_{\text{e}}q_{\text{e}}}{mv^{2}}}\cdot {\frac {1}{R}}\cdot {\sqrt {\frac {3N}{2}}}{\sqrt {1-\left(1-{\frac {\pi }{8}}\right){\sqrt {\sigma }}}}}
where σ is the ratio of the volume occupied by the positive charge to the volume of the whole atom. Thomson did not explain how he arrived at this equation.
To find the combined effect of the positive charge and the electrons on the beta particle's path, Thomson provided the following equation:
θ ¯ = θ ¯ 1 2 + θ ¯ 2 2 {\displaystyle {\bar {\theta }}={\sqrt {{\bar {\theta }}_{1}^{2}+{\bar {\theta }}_{2}^{2}}}}
Thomson probed the structure of atoms through beta particle scattering, whereas his former student Ernest Rutherford was interested in alpha particle scattering. Beta particles are electrons emitted by radioactive decay, whereas alpha particles are essentially helium atoms, also emitted in process of decay. Alpha particles have considerably more momentum than beta particles and Rutherford found that matter scatters alpha particles in ways that Thomson's plum pudding model could not predict.
Between 1908 and 1913, Ernest Rutherford , Hans Geiger , and Ernest Marsden collaborated on a series of experiments in which they bombarded thin metal foils with a beam of alpha particles and measured the intensity versus scattering angle of the particles. They found that the metal foil could scatter alpha particles by more than 90°. [ 35 ] : 4 This should not have been possible according to the Thomson model: the scattering into large angles should have been negligible. The odds of a beta particle being scattered by more than 90° under such circumstances is astronomically small, and since alpha particles typically have much more momentum than beta particles, their deflection should be smaller still. [ 36 ] The Thomson models simply could not produce electrostatic forces of sufficient strength to cause such large deflection. The charges in the Thomson model were too diffuse. This led Rutherford to discard the Thomson for a new model where the positive charge of the atom is concentrated in a tiny nucleus.
Rutherford went on to make more compelling discoveries. In Thomson's model, the positive charge sphere was just an abstract component, but Rutherford found something concrete to attribute the positive charge to: particles he dubbed " protons ". Whereas Thomson believed that the electron count was roughly correlated to the atomic weight, Rutherford showed that (in a neutral atom) it is exactly equal to the atomic number.
Thomson hypothesised that the arrangement of the electrons in the atom somehow determined the spectral lines of a chemical element. He was on the right track, but it had nothing to do with how atoms circulated in a sphere of positive charge. Scientists eventually discovered that it had to do with how electrons absorb and release energy in discrete quantities, moving through energy levels which correspond to emission and absorption spectra. Thomson had not incorporated quantum mechanics into his atomic model, which at the time was a very new field of physics. Niels Bohr and Erwin Schroedinger later incorporated quantum mechanics into the atomic model.
Rutherford's 1911 paper on alpha particle scattering showed that Thomson's scattering model could not explain the large angle scattering and it showed that multiple scattering was not necessary to explain the data. However, in the years immediately following its publication few scientists took note. [ 4 ] The scattering model predictions were not considered definitive evidence against Thomson's plum pudding model. Thomson and Rutherford had pioneered scattering as a technique to probe atoms, its reliability and value were unproven. Before Rutherford's paper the alpha particle was considered an atom, not a compact mass. It was not clear why it should be a good probe. Moreover, Rutherford's paper did not discuss the atomic electrons vital to practical problems like chemistry or atomic spectroscopy. [ 21 ] : 300 Rutherford's nuclear model would only become widely accepted after the work of Niels Bohr .
The Thomson problem in mathematics seeks the optimal distribution of equal point charges on the surface of a sphere. Unlike the original Thomson atomic model, the sphere in this purely mathematical model does not have a charge, and this causes all the point charges to move to the surface of the sphere by their mutual repulsion. There is still no general solution to Thomson's original problem of how electrons arrange themselves within a sphere of positive charge. [ 37 ] [ 38 ]
The first known writer to compare Thomson's model to a plum pudding was an anonymous reporter in an article for the British pharmaceutical magazine The Chemist and Druggist in August 1906.
While the negative electricity is concentrated on the extremely small corpuscle, the positive electricity is distributed throughout a considerable volume. An atom would thus consist of minute specks, the negative corpuscles, swimming about in a sphere of positive electrification, like raisins in a parsimonious plum-pudding, units of negative electricity being attracted toward the centre, while at the same time repelling each other. [ 39 ]
The analogy was never used by Thomson nor his colleagues. It seems to have been coined by popular science writers to make the model easier to understand for the layman. [ 2 ] | https://en.wikipedia.org/wiki/Plum_pudding_model |
A plumb bob , plumb bob level , or plummet , is a weight, usually with a pointed tip on the bottom, suspended from a string and used as a vertical direction as a reference line, or plumb-line . It is a precursor to the spirit level and used to establish a vertical datum . It is typically made of stone, wood, or lead, but can also be made of other metals. If it is used for decoration, it may be made of bone or ivory.
The instrument has been used since at least the time of ancient Egypt [ 1 ] to ensure that constructions are " plumb ", or vertical. It is also used in surveying , to establish the nadir (opposite of zenith ) with respect to gravity of a point in space. It is used with a variety of instruments (including levels , theodolites , and steel tapes ) to set the instrument exactly over a fixed survey marker or to transcribe positions onto the ground for placing a marker. [ 2 ]
The plumb in plumb bob derives from Latin plumbum (' lead '), the material once used for the weighted bob at the end. [ 3 ] The adjective plumb developed by extension, as did the noun aplomb , from the notion of "standing upright".
Until the modern age, plumb bobs were used on most tall structures to provide vertical datum lines for the building measurements. A section of the scaffolding would hold a plumb line, which was centered over a datum mark on the floor. As the building proceeded upward, the plumb line would also be taken higher, still centered on the datum. Many cathedral spires , domes and towers still have brass datum marks inlaid into their floors, which signify the center of the structure above.
A plumb bob and line alone can determine only a vertical reference. However, if they are mounted on a suitable scale the instrument may also be used as an inclinometer to measure angles to the vertical.
Ancient Egyptians used a plumb line attached to the top outer part of a tool resembling a letter E ; when placed against a wall, the plumb line would indicate a vertical line. An archipendulum , an A-frame level with a plumb line hung from the vertex was also used to find horizontal; these were used in Europe until the mid–19th century. A variation of this tool has the plumb line hung from the top of an inverted T shape. [ 3 ]
The early skyscrapers used heavy plumb bobs, hung on wire in their elevator shafts. [ further explanation needed ]
A plumb bob may be in a container of water (when conditions are above freezing temperatures), molasses, very viscous oils or other liquids to dampen any swinging movement, [ 4 ] functioning as a shock absorber .
Students of figure drawing will also make use of a plumb line to find the vertical axis through the center of gravity of their subject and lay it down on paper as a point of reference . The device used may be purpose-made plumb lines, or simply makeshift devices made from a piece of string and a weighted object, such as a metal washer . This plumb line is important for lining up anatomical geometries and visualizing the subject's center of balance . | https://en.wikipedia.org/wiki/Plumb_bob |
In chemistry , a plumbate often refers to compounds that can be viewed as derivatives of the hypothetical PbO 2− 3 anion.
Salts of ([PbI 3 ] − ) n , [Pb 6 I 16 ] 4− , [Pb 18 I 44 ] 8− , etc. are labeled as iodoplumbates. [ 1 ] [ 2 ] Lead perovskite semiconductors are often described as plumbates. [ 3 ]
Plumbates are formed by the reaction of lead(IV) oxide , PbO 2 , with alkali. [ 4 ] [ 5 ] Plumbate salts contain either the hydrated hexahydroxoplumbate(IV) or plumbate anion [Pb(OH) 6 ] 2− , or the anhydrous anions PbO 2− 3 ( metaplumbate ) or PbO 4− 4 ( orthoplumbate ). [ 4 ] For example, dissolving PbO 2 in a hot, concentrated aqueous solution of potassium hydroxide forms the potassium hexahydroxoplumbate(IV) salt K 2 [Pb(OH) 6 ] . The anhydrous salts may be synthesized by heating metal oxides or hydroxides with PbO 2 .
The most widely discussed plumbates are derivatives of barium metaplumbate BaPbO 3 . When doped with some bismuth in place of lead, the material BaPb 0.95 Bi 0.05 O 3 exhibits superconductivity at 13 K. [ 6 ] At the time of this discovery, oxides did not show such properties. The surprise associated with this work was eclipsed by the advent of the cuprate superconductors .
Lead tetroxide ("red lead"), a valence -mixed oxide with formula Pb 3 O 4 (red), may be thought of as lead(II) orthoplumbate(IV), [Pb 2+ ] 2 [PbO 4− 4 ] . Lead sesquioxide , Pb 2 O 3 , is also known (reddish yellow), and has the structure of lead(II) metaplumbate(IV), [Pb 2+ ][PbO 2− 3 ] . [ 4 ] | https://en.wikipedia.org/wiki/Plumbate |
Plumbide is an anion of lead atoms. There are three plumbide anions, written as Pb − , Pb 2− and Pb 4− with 3 oxidation states , −1, −2 and −4, respectively.
A plumbide can refer to one of two things: an intermetallic compound that contains lead , or a Zintl phase compound with lead as the anion.
Plumbides can be formed when lead forms a Zintl phase compound with a more metallic element. One salt that can be formed this way is when cryptand reacts with sodium and lead in ethylenediamine (en) to produce [Na(crypt)] + 2 [Pb 5 ] 2− , which is red in solution. [ 1 ] Lead can also create anions with tin , in a series of anions with the formula [Sn 9− x Pb x ] 4− .
Lead can also form the [Pb 9 ] 4− anion, which is emerald green in solution. [ 2 ]
An example of a plumbide is CeRhPb. The lead atom has a coordination number of 12 in the crystal structure of this compound. It is bound to four rhodiums , six ceriums , and two other lead atoms in the crystal structure of the chemical. [ 3 ]
Several other plumbides are the M 2 Pd 2 Pb plumbides, where M is a rare-earth element , and the intermetallic additionally contains a palladium . These plumbides tend to exhibit antiferromagnetism, and all of them are conductors. [ 4 ]
A third plumbide is Ti 6 Pb 4.8 . Like the above plumbides, it is an intermetallic, but it only contains titanium as the other metal, and not any rare earths. [ 5 ]
Plumbides can also be Zintl phase compounds, such as [K(18-crown-6)] 2 K 2 Pb 9 ·(en) 1.5 . This is not a simple Zintl compound, but rather contains the organic molecules 18-crown-6 and ethylenediamine (en) in order to stabilize the crystal structure. [ 6 ] | https://en.wikipedia.org/wiki/Plumbide |
Plumbosolvency is the ability of a solvent , notably water , to dissolve lead . In the public supply of water this is an undesirable property. In (usually older) consumers' premises plumbosolvent water can attack lead pipes, lead service lines , and any lead in solder used to join copper.
Plumbosolvency of water can be countered by achieving a pH of 7.5 by increasing the pH with lime or sodium hydroxide (lye), or by providing a protective coating to the inside of lead pipes by the addition of phosphate at the water treatment works.
While optimal pH for prevention of plumbosolvency is 7.5, performance remains very good in the range pH 7.2-7.6.
Achieving this pH has been shown to decrease population blood lead concentrations.(3, 4)
Chlorinating water also reduces dissolved lead. It causes the interiors of lead pipes to become coated with lead chloride , which is very insoluble in cold water. However, lead chloride is fairly soluble in hot water. For this reason, water that is to be used for drinking or the preparation of food should never be taken from a hot-water tap, if the water may have been in contact with lead. Water should be taken from a cold-water tap, and heated in a pan or kettle that does not contain lead or lead solder.
This water supply –related article is a stub . You can help Wikipedia by expanding it .
This physical chemistry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Plumbosolvency |
In hydrodynamics , a plume or a column is a vertical body of one fluid moving through another. Several effects control the motion of the fluid, including momentum (inertia), diffusion and buoyancy (density differences). Pure jets and pure plumes define flows that are driven entirely by momentum and buoyancy effects, respectively. Flows between these two limits are usually described as forced plumes or buoyant jets. "Buoyancy is defined as being positive" when, in the absence of other forces or initial motion, the entering fluid would tend to rise. Situations where the density of the plume fluid is greater than its surroundings (i.e. in still conditions, its natural tendency would be to sink), but the flow has sufficient initial momentum to carry it some distance vertically, are described as being negatively buoyant. [ 1 ]
Usually, as a plume moves away from its source, it widens because of entrainment of the surrounding fluid at its edges. Plume shapes can be influenced by flow in the ambient fluid (for example, if local wind blowing in the same direction as the plume results in a co-flowing jet). This usually causes a plume which has initially been 'buoyancy-dominated' to become 'momentum-dominated' (this transition is usually predicted by a dimensionless number called the Richardson number ).
A further phenomenon of importance is whether a plume has laminar flow or turbulent flow . Usually, there is a transition from laminar to turbulent as the plume moves away from its source. This phenomenon can be clearly seen in the rising column of smoke from a cigarette. When high accuracy is required, computational fluid dynamics (CFD) can be employed to simulate plumes, but the results can be sensitive to the turbulence model chosen. CFD is often undertaken for rocket plumes , where condensed phase constituents can be present in addition to gaseous constituents. These types of simulations can become quite complex, including afterburning and thermal radiation , and (for example) ballistic missile launches are often detected by sensing hot rocket plumes.
Spacecraft designers are sometimes concerned with impingement of attitude control system thruster plumes onto sensitive subsystems like solar arrays and star trackers , or with the impingement of rocket engine plumes onto moon or planetary surfaces where they can cause local damage or even mid-term disturbances to planetary atmospheres .
Another phenomenon which can also be seen clearly in the flow of smoke from a cigarette is that the leading-edge of the flow, or the starting-plume, is quite often approximately in the shape of a ring- vortex ( smoke ring ). [ 2 ]
Pollutants released to the ground can work their way down into the groundwater , leading to groundwater pollution . The resulting body of polluted water within an aquifer is called a plume, with its migrating edges called plume fronts. Plumes are used to locate, map, and measure water pollution within the aquifer's total body of water, and plume fronts to determine directions and speed of the contamination's spreading in it. [ 3 ]
Plumes are of considerable importance in the atmospheric dispersion modelling of air pollution . A classic work on the subject of air pollution plumes is that by Gary Briggs. [ 4 ] [ 5 ]
A thermal plume is one which is generated by gas rising above a heat source. The gas rises because thermal expansion makes warm gas less dense than the surrounding cooler gas.
Simple modelling will enable many properties of fully developed, turbulent plumes to be investigated. [ 6 ] Many of the classic scaling arguments were developed in a combined analytic and laboratory study described in an influential paper by Bruce Morton , G.I. Taylor and Stewart Turner [ 7 ] and this and subsequent work is described in the popular monograph of Stewart Turner. [ 8 ]
The value of the entrainment coefficient is the key parameter in simple plume models. Research continues into assessing how the entrainment coefficient is affected by, for example, the geometry of a plume, [ 11 ] suspended particles within a plume, [ 12 ] and background rotation. [ 13 ]
Gaussian plume models can be used in several fluid dynamics scenarios to calculate concentration distribution of solutes, such as a smoke stack release or contaminant released in a river. Gaussian distributions are established by Fickian diffusion , and follow a Gaussian (bell-shaped) distribution. [ 14 ] For calculating the expected concentration of a one dimensional instantaneous point source we consider a mass M {\displaystyle M} released at an instantaneous point in time, in a one dimensional domain along x {\displaystyle x} . This will give the following equation: [ 15 ]
where M {\displaystyle M} is the mass released at time t = t 0 {\displaystyle t=t_{0}} and location x = x 0 {\displaystyle x=x_{0}} , and D {\displaystyle D} is the diffusivity [ m 2 s ] {\displaystyle \left[{\frac {{\text{m}}^{2}}{\text{s}}}\right]} . This equation makes the following four assumptions: [ 16 ] | https://en.wikipedia.org/wiki/Plume_(fluid_dynamics) |
In hydrodynamics , a plume or a column is a vertical body of one fluid moving through another. Several effects control the motion of the fluid, including momentum (inertia), diffusion and buoyancy (density differences). Pure jets and pure plumes define flows that are driven entirely by momentum and buoyancy effects, respectively. Flows between these two limits are usually described as forced plumes or buoyant jets. "Buoyancy is defined as being positive" when, in the absence of other forces or initial motion, the entering fluid would tend to rise. Situations where the density of the plume fluid is greater than its surroundings (i.e. in still conditions, its natural tendency would be to sink), but the flow has sufficient initial momentum to carry it some distance vertically, are described as being negatively buoyant. [ 1 ]
Usually, as a plume moves away from its source, it widens because of entrainment of the surrounding fluid at its edges. Plume shapes can be influenced by flow in the ambient fluid (for example, if local wind blowing in the same direction as the plume results in a co-flowing jet). This usually causes a plume which has initially been 'buoyancy-dominated' to become 'momentum-dominated' (this transition is usually predicted by a dimensionless number called the Richardson number ).
A further phenomenon of importance is whether a plume has laminar flow or turbulent flow . Usually, there is a transition from laminar to turbulent as the plume moves away from its source. This phenomenon can be clearly seen in the rising column of smoke from a cigarette. When high accuracy is required, computational fluid dynamics (CFD) can be employed to simulate plumes, but the results can be sensitive to the turbulence model chosen. CFD is often undertaken for rocket plumes , where condensed phase constituents can be present in addition to gaseous constituents. These types of simulations can become quite complex, including afterburning and thermal radiation , and (for example) ballistic missile launches are often detected by sensing hot rocket plumes.
Spacecraft designers are sometimes concerned with impingement of attitude control system thruster plumes onto sensitive subsystems like solar arrays and star trackers , or with the impingement of rocket engine plumes onto moon or planetary surfaces where they can cause local damage or even mid-term disturbances to planetary atmospheres .
Another phenomenon which can also be seen clearly in the flow of smoke from a cigarette is that the leading-edge of the flow, or the starting-plume, is quite often approximately in the shape of a ring- vortex ( smoke ring ). [ 2 ]
Pollutants released to the ground can work their way down into the groundwater , leading to groundwater pollution . The resulting body of polluted water within an aquifer is called a plume, with its migrating edges called plume fronts. Plumes are used to locate, map, and measure water pollution within the aquifer's total body of water, and plume fronts to determine directions and speed of the contamination's spreading in it. [ 3 ]
Plumes are of considerable importance in the atmospheric dispersion modelling of air pollution . A classic work on the subject of air pollution plumes is that by Gary Briggs. [ 4 ] [ 5 ]
A thermal plume is one which is generated by gas rising above a heat source. The gas rises because thermal expansion makes warm gas less dense than the surrounding cooler gas.
Simple modelling will enable many properties of fully developed, turbulent plumes to be investigated. [ 6 ] Many of the classic scaling arguments were developed in a combined analytic and laboratory study described in an influential paper by Bruce Morton , G.I. Taylor and Stewart Turner [ 7 ] and this and subsequent work is described in the popular monograph of Stewart Turner. [ 8 ]
The value of the entrainment coefficient is the key parameter in simple plume models. Research continues into assessing how the entrainment coefficient is affected by, for example, the geometry of a plume, [ 11 ] suspended particles within a plume, [ 12 ] and background rotation. [ 13 ]
Gaussian plume models can be used in several fluid dynamics scenarios to calculate concentration distribution of solutes, such as a smoke stack release or contaminant released in a river. Gaussian distributions are established by Fickian diffusion , and follow a Gaussian (bell-shaped) distribution. [ 14 ] For calculating the expected concentration of a one dimensional instantaneous point source we consider a mass M {\displaystyle M} released at an instantaneous point in time, in a one dimensional domain along x {\displaystyle x} . This will give the following equation: [ 15 ]
where M {\displaystyle M} is the mass released at time t = t 0 {\displaystyle t=t_{0}} and location x = x 0 {\displaystyle x=x_{0}} , and D {\displaystyle D} is the diffusivity [ m 2 s ] {\displaystyle \left[{\frac {{\text{m}}^{2}}{\text{s}}}\right]} . This equation makes the following four assumptions: [ 16 ] | https://en.wikipedia.org/wiki/Plume_impingement |
The Plummer model or Plummer sphere is a density law that was first used by H. C. Plummer to fit observations of globular clusters . [ 1 ] It is now often used as toy model in N-body simulations of stellar systems.
The Plummer 3-dimensional density profile is given by ρ P ( r ) = 3 M 0 4 π a 3 ( 1 + r 2 a 2 ) − 5 / 2 , {\displaystyle \rho _{P}(r)={\frac {3M_{0}}{4\pi a^{3}}}\left(1+{\frac {r^{2}}{a^{2}}}\right)^{-{5}/{2}},} where M 0 {\displaystyle M_{0}} is the total mass of the cluster, and a is the Plummer radius , a scale parameter that sets the size of the cluster core. The corresponding potential is Φ P ( r ) = − G M 0 r 2 + a 2 , {\displaystyle \Phi _{P}(r)=-{\frac {GM_{0}}{\sqrt {r^{2}+a^{2}}}},} where G is Newton 's gravitational constant . The velocity dispersion is σ P 2 ( r ) = G M 0 6 r 2 + a 2 . {\displaystyle \sigma _{P}^{2}(r)={\frac {GM_{0}}{6{\sqrt {r^{2}+a^{2}}}}}.}
The isotropic distribution function reads f ( x → , v → ) = 24 2 7 π 3 a 2 G 5 M 0 4 ( − E ( x → , v → ) ) 7 / 2 , {\displaystyle f({\vec {x}},{\vec {v}})={\frac {24{\sqrt {2}}}{7\pi ^{3}}}{\frac {a^{2}}{G^{5}M_{0}^{4}}}(-E({\vec {x}},{\vec {v}}))^{7/2},} if E < 0 {\displaystyle E<0} , and f ( x → , v → ) = 0 {\displaystyle f({\vec {x}},{\vec {v}})=0} otherwise, where E ( x → , v → ) = 1 2 v 2 + Φ P ( r ) {\textstyle E({\vec {x}},{\vec {v}})={\frac {1}{2}}v^{2}+\Phi _{P}(r)} is the specific energy .
The mass enclosed within radius r {\displaystyle r} is given by M ( < r ) = 4 π ∫ 0 r r ′ 2 ρ P ( r ′ ) d r ′ = M 0 r 3 ( r 2 + a 2 ) 3 / 2 . {\displaystyle M(<r)=4\pi \int _{0}^{r}r'^{2}\rho _{P}(r')\,dr'=M_{0}{\frac {r^{3}}{(r^{2}+a^{2})^{3/2}}}.}
Many other properties of the Plummer model are described in Herwig Dejonghe 's comprehensive article. [ 2 ]
Core radius r c {\displaystyle r_{c}} , where the surface density drops to half its central value, is at r c = a 2 − 1 ≈ 0.64 a {\textstyle r_{c}=a{\sqrt {{\sqrt {2}}-1}}\approx 0.64a} .
Half-mass radius is r h = ( 1 0.5 2 / 3 − 1 ) − 0.5 a ≈ 1.3 a . {\displaystyle r_{h}=\left({\frac {1}{0.5^{2/3}}}-1\right)^{-0.5}a\approx 1.3a.}
Virial radius is r V = 16 3 π a ≈ 1.7 a {\displaystyle r_{V}={\frac {16}{3\pi }}a\approx 1.7a} .
The 2D surface density is: Σ ( R ) = ∫ − ∞ ∞ ρ ( r ( z ) ) d z = 2 ∫ 0 ∞ 3 a 2 M 0 d z 4 π ( a 2 + z 2 + R 2 ) 5 / 2 = M 0 a 2 π ( a 2 + R 2 ) 2 , {\displaystyle \Sigma (R)=\int _{-\infty }^{\infty }\rho (r(z))dz=2\int _{0}^{\infty }{\frac {3a^{2}M_{0}dz}{4\pi (a^{2}+z^{2}+R^{2})^{5/2}}}={\frac {M_{0}a^{2}}{\pi (a^{2}+R^{2})^{2}}},} and hence the 2D projected mass profile is: M ( R ) = 2 π ∫ 0 R Σ ( R ′ ) R ′ d R ′ = M 0 R 2 a 2 + R 2 . {\displaystyle M(R)=2\pi \int _{0}^{R}\Sigma (R')\,R'dR'=M_{0}{\frac {R^{2}}{a^{2}+R^{2}}}.}
In astronomy, it is convenient to define 2D half-mass radius which is the radius where the 2D projected mass profile is half of the total mass: M ( R 1 / 2 ) = M 0 / 2 {\displaystyle M(R_{1/2})=M_{0}/2} .
For the Plummer profile: R 1 / 2 = a {\displaystyle R_{1/2}=a} .
The escape velocity at any point is v e s c ( r ) = − 2 Φ ( r ) = 12 σ ( r ) , {\displaystyle v_{\rm {esc}}(r)={\sqrt {-2\Phi (r)}}={\sqrt {12}}\,\sigma (r),}
For bound orbits, the radial turning points of the orbit is characterized by specific energy E = 1 2 v 2 + Φ ( r ) {\textstyle E={\frac {1}{2}}v^{2}+\Phi (r)} and specific angular momentum L = | r → × v → | {\displaystyle L=|{\vec {r}}\times {\vec {v}}|} are given by the positive roots of the cubic equation R 3 + G M 0 E R 2 − ( L 2 2 E + a 2 ) R − G M 0 a 2 E = 0 , {\displaystyle R^{3}+{\frac {GM_{0}}{E}}R^{2}-\left({\frac {L^{2}}{2E}}+a^{2}\right)R-{\frac {GM_{0}a^{2}}{E}}=0,} where R = r 2 + a 2 {\displaystyle R={\sqrt {r^{2}+a^{2}}}} , so that r = R 2 − a 2 {\displaystyle r={\sqrt {R^{2}-a^{2}}}} . This equation has three real roots for R {\displaystyle R} : two positive and one negative, given that L < L c ( E ) {\displaystyle L<L_{c}(E)} , where L c ( E ) {\displaystyle L_{c}(E)} is the specific angular momentum for a circular orbit for the same energy. Here L c {\displaystyle L_{c}} can be calculated from single real root of the discriminant of the cubic equation , which is itself another cubic equation E _ L _ c 3 + ( 6 E _ 2 a _ 2 + 1 2 ) L _ c 2 + ( 12 E _ 3 a _ 4 + 20 E _ a _ 2 ) L _ c + ( 8 E _ 4 a _ 6 − 16 E _ 2 a _ 4 + 8 a _ 2 ) = 0 , {\displaystyle {\underline {E}}\,{\underline {L}}_{c}^{3}+\left(6{\underline {E}}^{2}{\underline {a}}^{2}+{\frac {1}{2}}\right){\underline {L}}_{c}^{2}+\left(12{\underline {E}}^{3}{\underline {a}}^{4}+20{\underline {E}}{\underline {a}}^{2}\right){\underline {L}}_{c}+\left(8{\underline {E}}^{4}{\underline {a}}^{6}-16{\underline {E}}^{2}{\underline {a}}^{4}+8{\underline {a}}^{2}\right)=0,} where underlined parameters are dimensionless in Henon units defined as E _ = E r V / ( G M 0 ) {\displaystyle {\underline {E}}=Er_{V}/(GM_{0})} , L _ c = L c / G M r V {\displaystyle {\underline {L}}_{c}=L_{c}/{\sqrt {GMr_{V}}}} , and a _ = a / r V = 3 π / 16 {\displaystyle {\underline {a}}=a/r_{V}=3\pi /16} .
The Plummer model comes closest to representing the observed density profiles of star clusters [ citation needed ] , although the rapid falloff of the density at large radii ( ρ → r − 5 {\displaystyle \rho \rightarrow r^{-5}} ) is not a good description of these systems.
The behavior of the density near the center does not match observations of elliptical galaxies, which typically exhibit a diverging central density.
The ease with which the Plummer sphere can be realized as a Monte-Carlo model has made it a favorite choice of N-body experimenters , in spite of the model's lack of realism. [ 3 ] | https://en.wikipedia.org/wiki/Plummer_model |
A plunge pool (or plunge basin or waterfall lake ) is a deep depression in a stream bed at the base of a waterfall or shut-in . It is created by the erosional forces of cascading water on the rocks at the formation's base where the water impacts. [ 1 ] The term may refer to the water occupying the depression, or the depression itself. [ 2 ]
Plunge pools are formed by the natural force of falling water, such as at a waterfall or cascade; they also result from man-made structures such as some spillway designs. [ 3 ] Plunge pools are often very deep, generally related to the height of the fall, the volume of water, the resistance of the rock below the pool and other factors. [ 4 ] The impacting and swirling water, sometimes carrying rocks within it, abrades the riverbed into a basin, which often features rough and irregular sides. Plunge pools can remain long after the waterfall has ceased flow or the stream has been diverted. Several examples of former plunge pools exist at Dry Falls in the Channeled Scablands of eastern Washington . [ 5 ] They can also be found underwater in areas that were formerly above sea level, for example, Perth Canyon off the coast of Western Australia .
Plunge pools are fluvial features of erosion which occur in the youthful stage of river development, characterized by steeper gradients and faster water flows. Where softer or fractured rock has been eroded back to a knickpoint , water continues to bombard its base. Because this rock is often less resistant than overlying strata, the water from the higher elevation continues eroding downward until an equilibrium is achieved.
A somewhat similar bowl-shaped feature developed by flowing water, as opposed to falling water, is known as a scour hole . These occur both naturally and as a result of bridge building . | https://en.wikipedia.org/wiki/Plunge_pool |
A plunger is a cylindrical rod used to transmit hydraulic compression force . It is characterized by its length being much greater than its diameter , and it is thus distinguished from a regular piston (where the working surface is larger than the thickness of the rod, i.e. more like a disk ). [ 1 ]
They are mainly used as part of certain types of pumps and hydraulic machines. Plungers are used for fluid-mechanical power transmission in pumps ( plunger pumps ), hydraulic gearboxes , high-pressure diesel injection pumps , hydraulic workshop presses and jacks , and other equipment, and are distinguished in fluid mechanics by being a piston without moving seals. The seals are instead located in the wall through which the plunger slides (as opposed to piston rings on a piston).
Plungers are often supplied with a suitable stationary plunger bushing that fits tightly against the plunger (together they are called a plunger pair), and together these form a seal that can withstand high pressures. [ 2 ] Compared to a piston that has to act against a cylinder wall, it is easier to manufacture a plunger to close tolerances against a plunger bushing (since the plunger has a cylindrical shape). Some define a plunger as a type of piston that is also its own piston rod. [ 3 ] Plunger pumps are often used to pump slurries such as sludge or liquid cement .
An advantage compared to classic pistons is the simplicity of manufacture (since the plunger is a simple rod) and the relatively easy use of a plunger bushing for sealing. Another advantage is resistance to dirt. Thanks to the simple shape, dirt has no place to stick, unlike a classic piston.
Unlike a piston (where the seal is on the piston rings), the seal of a plunger is located in the cylinder wall, and when the plunger performs a reciprocating motion, the plunger surface thus moves along the seal. Plungers are mainly used in hydraulic axial piston pumps , radial piston pumps and piston pumps . They have also become widespread in fuel supply systems for diesel engines ( injection pumps ) in pairs of plungers.
Plunger pumps are capable of operating at higher pressures than piston pumps. The reason for this is that plungers require high precision on its outer cylindrical surface, while piston pumps require more precise machining of the inner surface of the cylinder, which is technically more difficult to achieve.
The volume of the displaced medium depends directly on the stroke length of the plunger. By changing the pump stroke length, the flow rate will be adjusted.
The precision achieved on modern plunger and rotary hydraulic plunger machines is so high that the distance between the inner and outer cylindrical surfaces of plunger pairs reaches 2-3 micrometres (0.002-0.003 mm).
The pressure that plunger pairs can withstand is very high. During fuel injection in diesel engines, the pressure in the plunger pair can reach 200 megapascals (MPa).
The term "plunger" is also used in pipelines. Here, the plunger is a movable control element in a control valve whose movement changes the volume flow . [ 4 ] | https://en.wikipedia.org/wiki/Plunger_(hydraulics) |
A plunger lift is an artificial lift method of deliquifying a natural gas well . A plunger is used to remove contaminants from productive natural gas wells, such as water (in liquid, mist, or ice forms), sand, oil and wax.
The basics of the plunger is to open and close the well shutoff valve at the optimum times, to bring up the plunger and the contaminants and maximize natural gas production. A well without a deliquification technique will stop flowing or slow down and become a non-productive well, long before a properly deliquified well. [ 1 ]
The plunger lift has low energy cost, low environmental impact, low capital investment and low maintenance cost. Modern wellhead controllers offer a variety of criteria to control the plunger . The original controllers were just timers, with fixed open and close cycles.
Measuring the various pressures in the system allows intelligent and reactive control. The pressures often measured are casing, tubing, line, and differential (DP). The other items measured are plunger arrival times, flow rates, temperatures and status of various auxiliary equipment: oil tank level, compressor status. | https://en.wikipedia.org/wiki/Plunger_lift |
The Circle of Reason ( TCOR ) is a Twin Cities , Minnesota -based international society of theists , atheists , conservatives , and liberals who espouse the social philosophy of pluralistic rationalism (also plurationalism or methodological rationalism ). [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ]
Pluralistic rationalism is described in cultural media as "commitment to reason[ing], regardless of one's worldview," [ 8 ] and by the society itself as "communal commitment to more consistently practice the basic methodological tenets of a reasoning lifestyle (reality's acceptance, assumption's denial, and emotion's mastery) irrespective of our theological, ethical, cultural or political worldviews." [ 5 ] According to The Circle of Reason, pluralistic rationalism is practiced through encouraging not a particular worldview, but rather factualism, skepticism, and moderationism; and furthermore through discouraging their opposing practices of denialism, dogmatism, and emotionalism – or "denials of reality, unquestioned assumptions (potentially false realities), and emotive arguments or actions (dissociation from reality)." Plurationalist practices include discouraging the verbal, printed or televised use of insults (which the group asserts is immoral because, as ad hominem argumentation, it seeks to "irrationally persuade by evoking emotionality.") Because plurationalists hold that "as a sapient being one's best tool to survive is one's ability to reason," they also claim people's basic universalized moral imperative must then be to likewise "consistently allow, and encourage, others to reason" as well – which, by rationally underpinning social behaviors otherwise considered subjectively emotional (such as compassion, kindness, and nonaggression), they claim represents "the world's first objective moral code." [ 5 ]
Reflecting the plurationalist society's call to "more consistently use everyday reasoning regardless of our worldviews," [ 5 ] its institutional practices have included organizing the United States' first reported "theist + atheist" dialogue group, "Secular Bible Study," for reasoning discussion on the historical context, societal impact and cultural relevance of the Bible and religion, [ 1 ] [ 2 ] [ 9 ] and "Ancient Greek Peripatetic "-style nature walks combined with "transcultural, transbelief reasoning dialogue" on current social issues; [ 1 ] organizing and moderating "Assumptions on the [Minnesota Same-Sex] Marriage Amendment: A Reasoning Forum" for theists, atheists, conservatives & liberals; [ 10 ] [ 11 ] defending a Catholic legislator shunned by his archdiocese for refusing to defund reproductive health clinics; [ 12 ] presenting an address on plurationalism, "Be Sane — Be VERY Sane!" to the "Rally to Restore Sanity Minnesota" at the State Capitol; [ 13 ] [ 14 ] and successfully lobbying the state capital city's Council of Churches to become the first local council of religions in the United States to change the name of its religious " interfaith " dialogue group to "interbelief," to better welcome atheists and secular humanists with no religious faith but with philosophical or ethical beliefs. [ 15 ] [ 16 ] [ 17 ]
The Pluralism Project at Harvard University has described The Circle of Reason as a "promising practice." [ 1 ] [ 2 ] [ 3 ] [ 4 ] | https://en.wikipedia.org/wiki/Pluralistic_Rationalism |
The pluriblast is a pluripotent population of cells in the embryogenesis of marsupials , called the inner cell mass in eutherians . [ 1 ] The pluriblast is distinct from the trophoblast , and gives rise to the germ layers of the embryo , as well as extra embryonic endoderm and extra embryonic mesoderm . Both the pluriblast and trophoblast arise from the totipotent cells of the early conceptus . By definition, the pluriblast does not give rise to trophoblast cells during normal development, although it may retain this potential under experimental conditions.
In metatherians ( marsupials ), the pluriblast forms part of the blastocyst wall and no structure exists that can be described as an inner cell mass. "Inner cell mass" is thus a morphological term peculiar to eutherian mammals, whereas "pluriblast" is a functional term more widely applicable to conserved aspects of mammalian development. | https://en.wikipedia.org/wiki/Pluriblast |
A plurimeter is a hand-held measuring instrument for determining surface area or relative angles between surfaces. The device uses mechanical action for calculating the result, analogous to a slide rule . In modern technology, these results are computed by calculator or computer rather than by mechanical instrument.
This tool article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Plurimeter |
The pluripotency of biological compounds describes the ability of certain substances to produce several distinct biological responses. Pluripotent is also described as something that has no fixed developmental potential, as in being able to differentiate into different cell types in the case of pluripotent stem cells. [ 1 ]
One type of pluripotent cell, called a hematopoietic stem cell, can differentiate into a large variety of cells with different functions. This stem cell can produce red blood cells, platelets, mast cells, dendritic cells, macrophages, lymphocytes, neutrophils, basophils, and eosinophils. Each of these cells have a different function, but they all work together as part of the immune system. Monocytes can differentiate into either dendritic cells or macrophages. Macrophages are covered with chemical receptors and phagocytose foreign particles, but are specific about what immune responses to be involved in. Dendritic cells phagocytose invaders; then they present the antigen on their surface to stimulate the acquired immune system (lymphocytes) as backup. [ 2 ]
Another example are lymphocytes called naïve T-helper cells. These cells can differentiate into many subtypes once activated by antigen presenting cells (APCs) like dendrites. They divide into memory cells, TH1, TH17, and TH2 cells, to name a few. Memory cells are made solely for the purpose of having a template to use in the case of reinfection so the body has a jump start instead of starting over as if never infected. TH17 cells do a variety of tasks including recruiting neutrophils , creating defensins , and mediating inflammation in the intestinal epithelium and skin. TH2 cells produce cytokines that will trigger certain B cells. B cells can differentiate into memory cells or plasma cells. The B plasma cells produce the antibodies that are used to tag invading cells so they can be attacked, among other functions. TH1 cells are created to make cytokines, like interferon gamma, that activate macrophages and cytotoxic T lymphocytes (CTLs). [ 2 ]
Interferon gamma represents an example of pluripotency in itself. Many cytokines are pluripotent, in that each of these compounds can activate specific behavior in some cell types and inhibit other behavior in other cell types. Once activated by T lymphocytes or Natural Killer cells, [ 3 ] interferon gamma upregulates expression of macrophages and both types of Major Histocompatibility Complex (MHC) antigens. In B lymphocytes (B cells), interferon gamma stimulates antibody class switching. All of these cells have different, specialized functions, but they all came from one pluripotent cell. | https://en.wikipedia.org/wiki/Pluripotency_(biological_compounds) |
The plus–minus sign or plus-or-minus sign ( ± ) and the complementary minus-or-plus sign ( ∓ ) are symbols with broadly similar multiple meanings.
Other meanings occur in other fields, including medicine, engineering , chemistry , electronics , linguistics , and philosophy.
A version of the sign, including also the French word ou ("or"), was used in its mathematical meaning by Albert Girard in 1626, and the sign in its modern form was used as early as 1631, in William Oughtred 's Clavis Mathematicae . [ 1 ]
In mathematical formulas , the ± symbol may be used to indicate a symbol that may be replaced by either of the plus and minus signs , + or − , allowing the formula to represent two values or two equations. [ 2 ]
If x 2 = 9 , one may give the solution as x = ±3 . This indicates that the equation has two solutions: x = +3 and x = −3 . A common use of this notation is found in the quadratic formula
which describes the two solutions to the quadratic equation ax 2 + bx + c = 0.
Similarly, the trigonometric identity
can be interpreted as a shorthand for two equations: one with + on both sides of the equation, and one with − on both sides.
The minus–plus sign , ∓ , is generally used in conjunction with the ± sign, in such expressions as x ± y ∓ z , which can be interpreted as meaning x + y − z or x − y + z (but not x + y + z or x − y − z ). The ∓ always has the opposite sign to ± .
The above expression can be rewritten as x ± ( y − z ) to avoid use of ∓ , but cases such as the trigonometric identity are most neatly written using the "∓" sign:
which represents the two equations:
Another example is the conjugate of the perfect squares
which represents the two equations:
A related usage is found in this presentation of the formula for the Taylor series of the sine function:
Here, the plus-or-minus sign indicates that the term may be added or subtracted depending on whether n is odd or even; a rule which can be deduced from the first few terms. A more rigorous presentation would multiply each term by a factor of (−1) n , which gives +1 when n is even, and −1 when n is odd. In older texts one occasionally finds (−) n , which means the same.
When the standard presumption that the plus-or-minus signs all take on the same value of +1 or all −1 is not true, then the line of text that immediately follows the equation must contain a brief description of the actual connection, if any, most often of the form "where the ‘±’ signs are independent" or similar. If a brief, simple description is not possible, the equation must be re-written to provide clarity; e.g. by introducing variables such as s 1 , s 2 , ... and specifying a value of +1 or −1 separately for each, or some appropriate relation, like s 3 = s 1 · ( s 2 ) n or similar.
The use of ± for an approximation is most commonly encountered in presenting the numerical value of a quantity, together with its tolerance or its statistical margin of error . [ 3 ] For example, 5.7 ± 0.2 may be anywhere in the range from 5.5 to 5.9 inclusive. In scientific usage, it sometimes refers to a probability of being within the stated interval, usually corresponding to either 1 or 2 standard deviations (a probability of 68.3% or 95.4% in a normal distribution ).
Operations involving uncertain values should always try to preserve the uncertainty, in order to avoid propagation of error . If n = a ± b , any operation of the form m = f ( n ) must return a value of the form m = c ± d , where c is f ( a ) and d is the range b updated using interval arithmetic .
The symbols ± and ∓ are used in chess annotation to denote a moderate but significant advantage for White and Black, respectively. [ 4 ] Weaker and stronger advantages are denoted by ⩲ and ⩱ for only a slight advantage, and +– and –+ for a strong, potentially winning advantage, again for White and Black respectively. [ 5 ]
The plus–minus sign resembles the Chinese characters 土 ( Radical 32 ) and 士 ( Radical 33 ), whereas the minus–plus sign resembles 干 ( Radical 51 ). | https://en.wikipedia.org/wiki/Plus–minus_sign |
In astronomy , the plutinos are a dynamical group of trans-Neptunian objects that orbit in 2:3 mean-motion resonance with Neptune . This means that for every two orbits a plutino makes, Neptune orbits three times. The dwarf planet Pluto is the largest member as well as the namesake of this group. The next largest members are Orcus , (208996) 2003 AZ 84 , and Ixion . Plutinos are named after mythological creatures associated with the underworld.
Plutinos form the inner part of the Kuiper belt and represent about a quarter of the known Kuiper belt objects . They are also the most populous known class of resonant trans-Neptunian objects (also see adjunct box with hierarchical listing) . The first plutino after Pluto itself, (385185) 1993 RO , was discovered on September 16, 1993.
It is thought that the objects that are currently in mean orbital resonances with Neptune initially followed a variety of independent heliocentric paths. As Neptune migrated outward early in the Solar System's history (see origins of the Kuiper belt ), the bodies it approached would have been scattered; during this process, some of them would have been captured into resonances. [ 1 ] The 3:2 resonance is a low-order resonance and is thus the strongest and most stable among all resonances. [ 2 ] This is the primary reason it has a larger population than the other Neptunian resonances encountered in the Kuiper Belt. The cloud of low-inclination bodies beyond 40 AU is the cubewano family, while bodies with higher eccentricities (0.05 to 0.34) and semimajor axes close to the 3:2 Neptune resonance are primarily plutinos. [ 3 ]
While the majority of plutinos have relatively low orbital inclinations , a significant fraction of these objects follow orbits similar to that of Pluto, with inclinations in the 10–25° range and eccentricities around 0.2–0.25; such orbits result in many of these objects having perihelia close to or even inside Neptune's orbit, while simultaneously having aphelia that bring them close to the main Kuiper belt 's outer edge (where objects in a 1:2 resonance with Neptune, the Twotinos, are found).
The orbital periods of plutinos cluster around 247.3 years (1.5 × Neptune's orbital period), varying by at most a few years from this value.
Unusual plutinos include:
See also the comparison with the distribution of the cubewanos .
Pluto's influence on the other plutinos has historically been neglected due to its relatively small mass. However, the resonance width (the range of semi-axes compatible with the resonance) is very narrow and only a few times larger than Pluto's Hill sphere (gravitational influence). Consequently, depending on the original eccentricity, some plutinos will eventually be driven out of the resonance by interactions with Pluto. [ 5 ] Numerical simulations suggest that the orbits of plutinos with an eccentricity 10%–30% smaller or larger than that of Pluto are not stable over Ga timescales. [ 6 ]
The plutinos brighter than H V =6 include:
(link to all of the orbits of these objects listed above are here )
Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". | https://en.wikipedia.org/wiki/Plutino |
Plutonium-239 ( 239 Pu or Pu-239 ) is an isotope of plutonium . Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons , although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in thermal spectrum nuclear reactors , along with uranium-235 and uranium-233 . Plutonium-239 has a half-life of 24,110 years. [ 1 ]
The nuclear properties of plutonium-239, as well as the ability to produce large amounts of nearly pure 239 Pu more cheaply than highly enriched weapons-grade uranium-235, led to its use in nuclear weapons and nuclear power plants. The fissioning of an atom of uranium-235 in the reactor of a nuclear power plant produces two to three neutrons, and these neutrons can be absorbed by uranium-238 to produce plutonium-239 and other isotopes. Plutonium-239 can also absorb neutrons and fission along with the uranium-235 in a reactor.
Of all the common nuclear fuels, 239 Pu has the smallest critical mass . A spherical untamped critical mass is about 11 kg (24.2 lbs), [ 2 ] 10.2 cm (4") in diameter. Using appropriate triggers, neutron reflectors, implosion geometry and tampers , the critical mass can be less than half of that.
The fission of one atom of 239 Pu generates 207.1 MeV = 3.318 × 10 −11 J, i.e. 19.98 TJ/ mol = 83.61 TJ/kg, [ 3 ] or about 23 gigawatt hours/kg.
Plutonium is made from uranium-238 . 239 Pu is normally created in nuclear reactors by transmutation of individual atoms of one of the isotopes of uranium present in the fuel rods. Occasionally, when an atom of 238 U is exposed to neutron radiation , its nucleus will capture a neutron , changing it to 239 U . This happens more often with lower kinetic energy (as 238 U fission activation is 6.6MeV). The 239 U then rapidly undergoes two β − decays — an emission of an electron and an anti-neutrino ( ν ¯ e {\displaystyle {\bar {\nu }}_{e}} ), leaving a proton in the nucleus — the first β − decay transforming the 239 U into neptunium-239 , and the second β − decay transforming the 239 Np into 239 Pu: [ 4 ] [ 5 ]
Fission activity is relatively rare, so even after significant exposure, the 239 Pu is still mixed with a great deal of 238 U (and possibly other isotopes of uranium), oxygen, other components of the original material, and fission products . Only if the fuel has been exposed for a few days in the reactor, can the 239 Pu be chemically separated from the rest of the material to yield high-purity 239 Pu metal.
239 Pu has a higher probability for fission than 235 U and a larger number of neutrons produced per fission event, so it has a smaller critical mass. [ 6 ] Pure 239 Pu also has a reasonably low rate of neutron emission due to spontaneous fission (10 fission/s·kg), making it feasible to assemble a mass that is highly supercritical before a detonation chain reaction begins.
In practice, however, reactor-bred plutonium will invariably contain a certain amount of 240 Pu due to the tendency of 239 Pu to absorb an additional neutron during production. 240 Pu has a high rate of spontaneous fission events (415,000 fission/s-kg), making it an undesirable contaminant. As a result, plutonium containing a significant fraction of 240 Pu is not well-suited to use in nuclear weapons; it emits neutron radiation, making handling more difficult, and its presence can lead to a " fizzle " in which a small explosion occurs, destroying the weapon but not causing fission of a significant fraction of the fuel. It is because of this limitation that plutonium-based weapons must be implosion-type, rather than gun-type. Moreover, 239 Pu and 240 Pu cannot be chemically distinguished, so expensive and difficult isotope separation would be necessary to separate them. Weapons-grade plutonium is defined as containing no more than 7% 240 Pu; this is achieved by only exposing 238 U to neutron sources for short periods of time to minimize the 240 Pu produced.
Plutonium is classified according to the percentage of the contaminant plutonium-240 that it contains:
A nuclear reactor that is used to produce plutonium for weapons therefore generally has a means for exposing 238 U to neutron radiation and for frequently replacing the irradiated 238 U with new 238 U. A reactor running on unenriched or moderately enriched uranium contains a great deal of 238 U. However, most commercial nuclear power reactor designs require the entire reactor to shut down, often for weeks, in order to change the fuel elements. They therefore produce plutonium in a mix of isotopes that is not well-suited to weapon construction. Such a reactor could have machinery added that would permit 238 U slugs to be placed near the core and changed frequently, or it could be shut down frequently, so proliferation is a concern; for this reason, the International Atomic Energy Agency inspects licensed reactors often. A few commercial power reactor designs, such as the reaktor bolshoy moshchnosti kanalniy ( RBMK ) and pressurized heavy water reactor ( PHWR ), do permit refueling without shutdowns, and they may pose a proliferation risk. By contrast, the Canadian CANDU heavy-water moderated, natural-uranium fueled reactor can also be refueled while operating, but it normally consumes most of the 239 Pu it produces in situ; thus, it is not only inherently less proliferative than most reactors, but can even be operated as an " actinide incinerator ". [ 7 ] The American IFR (Integral Fast Reactor) can also be operated in an incineration mode, having some advantages in not accumulating the plutonium-242 isotope or the long-lived actinides , which cannot be easily burned except in a fast reactor. Also IFR fuel has a high proportion of burnable isotopes, while in CANDU an inert material is needed to dilute the fuel; this means the IFR can burn a higher fraction of its fuel before needing reprocessing. Most plutonium is produced in research reactors or plutonium production reactors called breeder reactors because they produce more plutonium than they consume fuel; in principle, such reactors make extremely efficient use of natural uranium. In practice, their construction and operation is sufficiently difficult that they are generally only used to produce plutonium. Breeder reactors are generally (but not always) fast reactors , since fast neutrons are somewhat more efficient at plutonium production.
Plutonium-239 is more frequently used in nuclear weapons than uranium-235, as it is easier to obtain in a quantity of critical mass. Both plutonium-239 and uranium-235 are obtained from Natural uranium , which primarily consists of uranium-238 but contains traces of other isotopes of uranium such as uranium-235. The process of enriching uranium , i.e. increasing the ratio of 235 U to 238 U to weapons grade, is generally a more lengthy and costly process than the production of plutonium-239 from 238 U and subsequent reprocessing.
The "supergrade" fission fuel, which has less radioactivity, is used in the primary stage of US Navy nuclear weapons in place of the conventional plutonium used in the Air Force's versions. "Supergrade" is industry parlance for plutonium alloy bearing an exceptionally high fraction of 239 Pu (>95%), leaving a very low amount of 240 Pu, which is a high spontaneous fission isotope (see above). Such plutonium is produced from fuel rods that have been irradiated a very short time as measured in MW-day/ton burnup . Such low irradiation times limit the amount of additional neutron capture and therefore buildup of alternate isotope products such as 240 Pu in the rod, and also by consequence is considerably more expensive to produce, needing far more rods irradiated and processed for a given amount of plutonium.
Plutonium-240, in addition to being a neutron emitter after fission, is a gamma emitter, and so is responsible for a large fraction of the radiation from stored nuclear weapons. Whether out on patrol or in port, submarine crew members routinely live and work in very close proximity to nuclear weapons stored in torpedo rooms and missile tubes, unlike Air Force missiles where exposures are relatively brief. The need to reduce radiation exposure justifies the additional costs of the premium supergrade alloy used on many naval nuclear weapons. Supergrade plutonium is used in W80 warheads.
In any operating nuclear reactor containing 238 U, some plutonium-239 will accumulate in the nuclear fuel. [ 8 ] Unlike reactors used to produce weapons-grade plutonium, commercial nuclear power reactors typically operate at a high burnup that allows a significant amount of plutonium to build up in irradiated reactor fuel. Plutonium-239 will be present both in the reactor core during operation and in spent nuclear fuel that has been removed from the reactor at the end of the fuel assembly's service life (typically several years). Spent nuclear fuel commonly contains about 0.8% plutonium-239.
Plutonium-239 present in reactor fuel can absorb neutrons and fission just as uranium-235 can. Since plutonium-239 is constantly being created in the reactor core during operation, the use of plutonium-239 as nuclear fuel in power plants can occur without reprocessing of spent fuel; the plutonium-239 is fissioned in the same fuel rods in which it is produced. Fissioning of plutonium-239 provides more than one-third of the total energy produced in a typical commercial nuclear power plant. [ 9 ] Reactor fuel would accumulate much more than 0.8% plutonium-239 during its service life if some plutonium-239 were not constantly being "burned off" by fissioning.
A small percentage of plutonium-239 can be deliberately added to fresh nuclear fuel. Such fuel is called MOX (mixed oxide) fuel , as it contains a mixture of uranium dioxide (UO 2 ) and plutonium dioxide (PuO 2 ). The addition of plutonium-239 reduces the need to enrich the uranium in the fuel.
Plutonium-239 emits alpha particles to become uranium-235. As an alpha emitter, plutonium-239 is not particularly dangerous as an external radiation source, but if it is ingested or breathed in as dust it is very dangerous and carcinogenic . It has been estimated that a pound (454 grams) of plutonium inhaled as plutonium oxide dust could give cancer to two million people. [ 10 ] However, ingested plutonium is by far less dangerous as only a tiny fraction is absorbed in gastrointestinal tract; [ 11 ] [ 12 ] 800 mg would be unlikely to cause a major health risk as far as radiation is concerned. [ 10 ] As a heavy metal , plutonium is also chemically toxic. See also Nuclear Precautions .
Weapons grade plutonium (with greater than 90% 239 Pu) is used to make nuclear weapons and has many advantages over other fissile material for that purpose. Lower proportions of 239 Pu would make a reliable weapon design difficult or impossible; this is due to the spontaneous fission (and thus neutron production) of the undesirable 240 Pu. | https://en.wikipedia.org/wiki/Plutonium-239 |
Plutonium(II) hydride
Plutonium hydride is a non-stoichiometric chemical compound with the formula PuH 2+x . It is one of two characterized hydrides of plutonium; the other is PuH 3 . [ 1 ] PuH 2+x is non-stoichiometric with a composition range of PuH 2 – PuH 2.7 . Metastable stoichiometries with an excess of hydrogen (PuH 2.7 – PuH 3 ) can also be formed. [ 1 ] PuH 2 has a cubic structure. It is readily formed from the elements at 1 atmosphere at 100–200°C: [ 1 ] When the stoichiometry is close to PuH 2 it has a silver appearance, but gets blacker as the hydrogen content increases, additionally the color change is associated with a reduction in conductivity. [ 2 ]
Studies of the reaction of plutonium metal with moist air at 200–350°C showed the presence of cubic plutonium hydride on the surface along with Pu 2 O 3 , PuO 2 and a higher oxide identified by X-ray diffraction and X-ray photoelectron spectroscopy as the mixed-valence phase Pu IV 3−x Pu VI x O 6+x . [ 3 ] Investigation of the reaction performed without heating suggests that the reaction of Pu metal and moist air the production of PuO 2 and a higher oxide along with adsorbed hydrogen, which catalytically combines with O 2 to form water. [ 4 ]
Like the free metal, plutonium dihydride is pyrophoric . On the surface of hydrided plutonium, it acts as a catalyst for the oxidation of the metal with consumption of both O 2 and N 2 from air. [ 5 ] | https://en.wikipedia.org/wiki/Plutonium_hydride |
Since the mid-20th century, plutonium in the environment has been primarily produced by human activity. The first plants to produce plutonium for use in Cold War atomic bombs were the Hanford nuclear site in Washington, and the Mayak nuclear plant , in Chelyabinsk Oblast , Russia . Over a period of four decades, [ 1 ] "both released more than 200 million curies of radioactive isotopes into the surrounding environment – twice the amount expelled in the Chernobyl disaster in each instance." [ 2 ]
The majority of plutonium isotopes are not short-lived on a geological timescale , [ 3 ] though it has been argued that traces of the long-lived 244 Pu isotope still exist in nature. [ 4 ] This isotope has been found in lunar soil , [ 5 ] meteorites , [ 6 ] and in the Oklo natural reactor. [ 7 ] However, one study on plutonium in marine sediments indicates that the atomic bomb fallout accounts for 66% of the 239 Pu and 59% 240 Pu in the English Channel . In contrast, nuclear reprocessing contributes the majority of the 238 Pu and 241 Pu in the Earth's oceans, whereas nuclear weapons testing is responsible for only 6.5% and 16.5% of these isotopes, respectively. [ 8 ]
Richland, Washington was the first city established to support plutonium production at the nearby Hanford nuclear site , to power the American nuclear weapons arsenals. Ozersk, Russia supported plutonium production to power the Soviet nuclear arsenals at the Mayak nuclear plant. These were the first two cities in the world to produce plutonium for use in cold war atomic bombs . [ 2 ]
In the 2013 book, Plutopia: Nuclear Families, Atomic Cities, and the Great Soviet and American Plutonium Disasters , Kate Brown explores the health of affected citizens in both the United States and Russia, and the "slow-motion disasters" that still threaten the environments where the plants are located. [ 1 ] According to Brown, the plants at Hanford and Mayak released over 200 million curies of radioactive isotopes into the surrounding environment over four decades, which is twice the amount expelled in the Chernobyl disaster in each instance. [ 2 ]
Most of the radioactive contamination over the years from Hanford and Mayak were part of normal operations. Unforeseen accidents did occur, but plant management kept this secret, and the pollution continued unabated. Even today, as pollution threats to health and the environment persist, the government conceals information about the associated risks from the public. [ 2 ]
About 3.5 tons of plutonium have been released into the environment by atomic bomb tests. While this might sound significant, it has only resulted in a very small dose to the majority of the humans on Earth. Overall the health effects of fission products are far greater than the effects of the actinides released by a nuclear bomb detonation. The plutonium from the fuel of the bomb is converted into a high-fired oxide that is carried high into the air. It slowly falls to earth as global fallout and is not soluble , and as a result it is difficult for this plutonium to be incorporated into an organism if ingested. Much of this plutonium is absorbed into sediments of lakes, rivers and oceans. However, about 66% of the plutonium from a bomb explosion is formed by the neutron capture of 238 U ; this plutonium is not converted by the bomb into a high fired oxide , as it is formed more slowly. This formed plutonium is more soluble and more harmful as fallout . [ 9 ]
Some plutonium can be deposited close to the point of detonation. The glassy trinitite formed by the Trinity bomb has been examined to determine what actinides and other radioisotopes it contained. A 2006 paper [ 10 ] reports the levels of long lived radioisotopes in the trinitite. 152 Eu and 154 Eu was mainly formed by the neutron activation of the europium in the soil, and the level of radioactivity for these isotopes is highest where the neutron dose to the soil was larger. Some of the 60 Co was generated by activation of the cobalt in the soil, but some was also generated by the activation of the cobalt in the steel (100 foot) tower on which the bomb stood. This 60 Co from the tower would have been scattered over the site reducing the difference in the soil levels. 133 Ba and 241 Am were created by the neutron activation of barium and plutonium inside the bomb. The barium was present in the form of the nitrate in the chemical explosives used while the plutonium was the fissile fuel used.
As the 239 Pu / 240 Pu ratio only changed slightly during the Trinity detonation, it has been commented [ 11 ] that this isotope ratio for the majority of atomic bombs (in Japan the 239 Pu/ 240 Pu ratio in soil is normally in the range 0.17 to 0.19 [ 12 ] ) is very different than from the bomb dropped upon Nagasaki .
Plutonium has also been released into the environment in safety trials . In these experiments, nuclear bombs have been subjected to simulated accidents or detonated with an abnormal initiation of their chemical explosives. An abnormal implosion will result in a compression of the plutonium pit , which is less uniform and smaller than the designed compression in the device. In these experiments where no or very little nuclear fission occurs, plutonium metal has been scattered around the test sites. While some of these tests have been done underground, other such tests were conducted in open air. A paper on the radioisotopes left on an island by the French nuclear bombs tests of the 20th century has been printed by the International Atomic Energy Agency and a section of this report deals with plutonium contamination resulting from such tests. [ 13 ]
Other related trials were conducted at Maralinga, South Australia where both normal bomb detonations and "safety trials" have been conducted. While the activity from the fission products has decayed away almost totally (as of 2006) the plutonium remains active. [ 14 ] [ 15 ]
Plutonium can also be introduced into the environment via the reentry of artificial satellites containing atomic batteries . There have been several such incidents, the most prominent being the Apollo 13 mission. The Apollo Lunar Surface Experiments Package carried on the Lunar Module re-entered the atmosphere over the South Pacific. Many atomic batteries have been of the Radioisotope thermoelectric generator (RTG) type. The Plutonium-238 used in RTGs has a half-life of 88 years, as opposed to the plutonium-239 used in nuclear weapons and reactors , which has a half-life of 24,100 years. [ full citation needed ] In April 1964 a SNAP-9A failed to achieve orbit and disintegrated, dispersing roughly 1 kilogram (2.2 lb) of plutonium-238 over all continents. Most plutonium fell in the southern hemisphere. An estimated 6300 GBq or 2100 man-Sv of radiation was released [ 16 ] [ 17 ] [ 18 ] [ 19 ] and led to NASA's development of solar photovoltaic energy technology. [ 20 ] [ better source needed ]
Chain reactions do not occur inside RTGs, so a nuclear meltdown is impossible. In fact, some RTGs are designed so that fission does not occur at all; rather, forms of radioactive decay which cannot trigger other radioactive decays are used instead. As a result, the fuel in an RTG is consumed much more slowly and much less power is produced. RTGs are still a potential source of radioactive contamination : if the container holding the fuel leaks, the radioactive material will contaminate the environment. The main concern is that if an accident were to occur during launch or a subsequent passage of a spacecraft close to Earth, harmful material could be released into the atmosphere. However, this event is extremely unlikely with current RTG cask designs. [ full citation needed ]
In order to decrease the risk of the radioactive material being released, the fuel is typically stored in individual modular units with their own heat shielding. They are surrounded by a layer of iridium metal and encased in high-strength graphite blocks. These two materials are corrosion and heat-resistant. Surrounding the graphite blocks is an aeroshell, designed to protect the entire assembly against the heat of reentering the Earth's atmosphere. The plutonium fuel is also stored in a ceramic form that is heat-resistant, decreasing the risk of vaporization and aerosolization. The ceramic is also highly insoluble . [ full citation needed ]
The US Department of Energy has conducted seawater tests and determined that the graphite casing, which was designed to withstand reentry, is stable and no release of plutonium should occur. Subsequent investigations have found no increase in the natural background radiation in the area. The 1970 Apollo 13 crisis represents an extreme scenario due to the high re-entry velocities of the craft returning from cislunar space. This accident has served to validate the design of later-generation RTGs as highly safe.
Plutonium has been released into the environment in aqueous solution from nuclear reprocessing and uranium enrichment plants. The chemistry of this plutonium is different from that of the metal oxides formed from nuclear bomb detonations.
One example of a site where plutonium entered the soil is Rocky Flats where in the recent past XANES ( X-ray spectroscopy ) has been used to determine the chemical nature of the plutonium in the soil . [ 21 ] The XANES was used to determine the oxidation state of the plutonium, while EXAFS was used to investigate the structure of the plutonium compound present in the soil and concrete . [ 22 ]
Because plutonium oxide is involatile, most of the plutonium in the reactor was not released during the fire. However that which was released can be measured. V.I. Yoschenko et al. reported that grass and forest fires can make the caesium , strontium and plutonium become mobile in the air again. [ 23 ]
The ongoing crisis at this site includes Spent Fuel Pools on the upper floors, exposed to the elements with complex MOX and plutonium products. The Japanese Government Taskforce has asked for submissions to the International Research Institute for Nuclear Decommissioning [ 24 ] in regards to the ongoing Contaminated Water Issues. [ 25 ]
There have been 18 incidents concerning theft or loss of highly enriched uranium (HEU) and plutonium confirmed by the IAEA . [ 26 ]
One case exists of a German man who attempted to poison his ex-wife with plutonium stolen from WAK ( Wiederaufbereitungsanlage Karlsruhe ), a small scale reprocessing plant where he worked. He did not steal a large amount of plutonium, just rags used for wiping surfaces and a small amount of liquid waste. The man was sent to prison for his crime. [ 27 ] At least two other people were contaminated by the plutonium. [ citation needed ] Two flats in Rhineland-Palatinate were also contaminated. [ 28 ] These were later cleaned at a cost of two million euros .
Plutonium, like other actinides, readily forms a dioxide plutonyl core (PuO 2 ). In the environment, this plutonyl core readily complexes with carbonate as well as other oxygen moieties (OH − , NO 2 − , NO 3 − , and SO 4 2− ) to form charged complexes which can be readily mobile with low affinities to soil. [ citation needed ]
PuO 2 formed from neutralizing highly acidic nitric acid solutions tends to form polymeric PuO 2 which is resistant to complexation. Plutonium also readily shifts valences between the +3, +4, +5 and +6 states. It is common for some fraction of plutonium in solution to exist in all of these states in equilibrium. [ citation needed ]
Plutonium is known to bind to soil particles very strongly (see above for an X-ray spectroscopic study of plutonium in soil and concrete ). While caesium has very different chemistry to the actinides, it is well known that both caesium and many of the actinides bind strongly to the minerals in soil. Hence it has been possible to use 134 Cs labeled soil to study the migration of Pu and Cs in soils. It has been shown that colloidal transport processes control the migration of Cs (and will control the migration of Pu) in the soil at the Waste Isolation Pilot Plant according to R.D. Whicker and S.A. Ibrahim. [ 29 ] J.D. Chaplin et al. recently reported advances in the Diffusive gradients in thin films technique, which have provided a method to measure labile bioavailable Plutonium in soils, as well as in freshwater and seawater. [ 30 ]
Mary Neu (at Los Alamos in the USA) has done some work which suggests that bacteria can accumulate plutonium because the iron transport systems used by the bacteria also function as plutonium transport systems. [ 31 ] [ 32 ] [ 33 ]
Plutonium ingested by or injected into humans is transported in the transferrin based iron (III) transport system and then is stored in the liver in the iron store ( ferritin ), after an exposure to plutonium it is important to rapidly inject the subject with a chelating agent such as calcium complex [ 34 ] of DTPA . [ 35 ] [ 36 ] This antidote is useful for a single exposure such as that which would occur if a glove box worker were to cut his or her hand with a plutonium-contaminated object. The calcium complex has faster metal binding kinetics than the zinc complex but if the calcium complex is used for a long time it tends to remove important minerals from the person. The zinc complex is less able to cause these effects.
Plutonium that is inhaled by humans lodges in the lungs and is slowly translocated to the lymph nodes . Inhaled plutonium has been shown to lead to lung cancer in experimental animals. [ 37 ] | https://en.wikipedia.org/wiki/Plutonium_in_the_environment |
Plutonium selenide is a binary inorganic compound of plutonium and selenium with the chemical formula PuSe. [ 1 ] [ 2 ] The compound forms black crystals and does not dissolve in water.
Reaction of diplutonium triselenide and plutonium trihydride:
Fusion of stoichiometric amounts of pure substances:
Plutonium selenide forms black crystals of a cubic system, space group Fm 3 m, cell parameters a = 0.57934 nm, Z = 4, structure of the NaCl type. [ 3 ] [ 4 ]
With increasing pressure, two phase transitions occur: at 20 GPa into the trigonal system and at 35 GPa into the cubic system, a structure of the CsCl type.
Its magnetic susceptibility follows the Curie-Weiss law . [ 5 ] | https://en.wikipedia.org/wiki/Plutonium_selenide |
Plutonium silicide is a binary inorganic compound of plutonium and silicon with the chemical formula PuSi. [ 2 ] [ 3 ] [ 4 ] The compound forms gray crystals.
Reaction of plutonium dioxide and silicon carbide :
Reaction of plutonium trifluoride with silicon:
Plutonium silicide forms gray crystals of orthorhombic crystal system , space group Pnma , cell parameters: a = 0.7933 nm, b = 0.3847 nm, c = 0.5727 nm, Z = 4, TiSi type structure.
At a temperature of 72 K, plutonium silicide undergoes a ferromagnetic transition. [ 5 ] | https://en.wikipedia.org/wiki/Plutonium_silicide |
In two-or-more-player sequential games , a ply is one turn taken by one of the players. The word is used to clarify what is meant when one might otherwise say "turn".
The word "turn" can be a problem since it means different things in different traditions. For example, in standard chess terminology, one move consists of a turn by each player; therefore a ply in chess is a half-move . Thus, after 20 moves in a chess game, 40 plies have been completed—20 by white and 20 by black. In the game of Go , by contrast, a ply is the normal unit of counting moves; so for example to say that a game is 250 moves long is to imply 250 plies.
In poker with n players the word "street" is used for a full betting round consisting of n plies; each dealt card may sometimes also be called a "street". For instance, in heads up Texas hold'em , a street consists of 2 plies, with possible plays being check/raise/call/fold: the first by the player at the big blind, and the second by the dealer, who posts the small blind; and there are 4 streets: preflop, flop, turn, river (the latter 3 corresponding to community cards ). The terms "half-street" and "half-street game" are sometimes used to describe, respectively, a single bet in a heads up game, and a simplified heads up poker game where only a single player bets. [ 1 ]
The word "ply" used as a synonym for "layer" goes back to the 15th century. [ 2 ] Arthur Samuel first used the term in its game-theoretic sense in his seminal paper on machine learning in checkers in 1959, [ 3 ] but with a slightly different meaning: the "ply", in Samuel's terminology, is actually the depth of analysis ("Certain expressions were introduced which we will find useful. These are: Ply, defined as the number of moves ahead, where a ply of two consists of one proposed move by the machine and one anticipated reply by the opponent" [ 4 ] ).
In computing, the concept of a ply is important because one ply corresponds to one level of the game tree . The Deep Blue chess computer which defeated Kasparov in 1997 would typically search to a depth of between six and sixteen plies to a maximum of forty plies in some situations. [ 5 ] | https://en.wikipedia.org/wiki/Ply_(game_theory) |
A ply is a layer of material which has been combined with other layers in order to provide strength. The number of layers is indicated by prefixing a number, for example 4-ply, indicating material composed of 4 layers.
The word "ply" derives from the French verb plier , [ 1 ] "to fold", from the Latin verb plico , from the ancient Greek verb πλέκω . [ 2 ] | https://en.wikipedia.org/wiki/Ply_(layer) |
In geometry , Plücker's conoid is a ruled surface named after the German mathematician Julius Plücker . It is also called a conical wedge or cylindroid ; however, the latter name is ambiguous, as "cylindroid" may also refer to an elliptic cylinder .
Plücker's conoid is the surface defined by the function of two variables:
This function has an essential singularity at the origin .
By using cylindrical coordinates in space, we can write the above function into parametric equations
Thus Plücker's conoid is a right conoid , which can be obtained by rotating a horizontal line about the z -axis with the oscillatory motion (with period 2 π ) along the segment [–1, 1] of the axis (Figure 4).
A generalization of Plücker's conoid is given by the parametric equations
where n denotes the number of folds in the surface. The difference is that the period of the oscillatory motion along the z -axis is 2π / n . (Figure 5 for n = 3 )
This algebraic geometry –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Plücker's_conoid |
In geometry , Plücker coordinates , introduced by Julius Plücker in the 19th century, are a way to assign six homogeneous coordinates to each line in projective 3-space , P 3 {\displaystyle \mathbb {P} ^{3}} . Because they satisfy a quadratic constraint, they establish a one-to-one correspondence between the 4-dimensional space of lines in P 3 {\displaystyle \mathbb {P} ^{3}} and points on a quadric in P 5 {\displaystyle \mathbb {P} ^{5}} (projective 5-space). A predecessor and special case of Grassmann coordinates (which describe k -dimensional linear subspaces, or flats , in an n -dimensional Euclidean space ), Plücker coordinates arise naturally in geometric algebra . They have proved useful for computer graphics , and also can be extended to coordinates for the screws and wrenches in the theory of kinematics used for robot control .
A line L in 3-dimensional Euclidean space is determined by two distinct points that it contains, or by two distinct planes that contain it (a plane-plane intersection ). Consider the first case, with points x = ( x 1 , x 2 , x 3 ) {\displaystyle x=(x_{1},x_{2},x_{3})} and y = ( y 1 , y 2 , y 3 ) . {\displaystyle y=(y_{1},y_{2},y_{3}).} The vector displacement from x to y is nonzero because the points are distinct, and represents the direction of the line. That is, every displacement between points on the line L is a scalar multiple of d = y − x . If a physical particle of unit mass were to move from x to y , it would have a moment about the origin of the coordinate system. The geometric equivalent to this moment is a vector whose direction is perpendicular to the plane containing the line L and the origin, and whose length equals twice the area of the triangle formed by the displacement and the origin. Treating the points as displacements from the origin, the moment is m = x × y , where "×" denotes the vector cross product . For a fixed line, L , the area of the triangle is proportional to the length of the segment between x and y , considered as the base of the triangle; it is not changed by sliding the base along the line, parallel to itself. By definition the moment vector is perpendicular to every displacement along the line, so d ⋅ m = 0 , where "⋅" denotes the vector dot product .
Although neither direction d nor moment m alone is sufficient to determine the line L , together the pair does so uniquely, up to a common (nonzero) scalar multiple which depends on the distance between x and y . That is, the coordinates
may be considered homogeneous coordinates for L , in the sense that all pairs (λ d : λ m ) , for λ ≠ 0 , can be produced by points on L and only L , and any such pair determines a unique line so long as d is not zero and d ⋅ m = 0 . Furthermore, this approach extends to include points , lines , and a plane "at infinity" , in the sense of projective geometry . In addition a point x {\displaystyle x} lies on the line L if and only if x × d = m {\displaystyle x\times d=m} .
Alternatively, let the equations for points x of two distinct planes containing L be
Then their respective planes are perpendicular to vectors a and b , and the direction of L must be perpendicular to both. Hence we may set d = a × b , which is nonzero because a , b are neither zero nor parallel (the planes being distinct and intersecting). If point x satisfies both plane equations, then it also satisfies the linear combination
That is,
is a vector perpendicular to displacements to points on L from the origin; it is, in fact, a moment consistent with the d previously defined from a and b .
Proof 1 : Need to show that
Without loss of generality , let
Point B is the origin. Line L passes through point D and is orthogonal to the plane of the picture. The two planes pass through CD and DE and are both orthogonal to the plane of the picture. Points C and E are the closest points on those planes to the origin B , therefore angles ∠ BCD and ∠ BED are right angles and so the points B, C, D, E lie on a circle (due to a corollary of Thales's theorem ). BD is the diameter of that circle.
Angle ∠ BHF is a right angle due to the following argument. Let ε := ∠ BEC . Since △ BEC ≅ △ BFG (by side-angle-side congruence), then ∠ BFG = ε . Since ∠ BEC + ∠ CED = 90° , let ε' := 90° − ε = ∠ CED . By the inscribed angle theorem , ∠ DEC = ∠ DBC , so ∠ DBC = ε' . ∠ HBF + ∠ BFH + ∠ FHB = 180° ; ε' + ε + ∠ FHB = 180° , ε + ε' = 90° ; therefore, ∠ FHB = 90° . Then ∠ DHF must be a right angle as well.
Angles ∠ DCF , ∠ DHF are right angles, so the four points C, D, H, F lie on a circle, and (by the intersecting secants theorem )
that is,
Proof 2 :
Let
This implies that
According to the vector triple product formula,
Then
When | | r | | = 0 , {\displaystyle ||\mathbf {r} ||=0,} the line L passes the origin with direction d . If | | r | | > 0 , {\displaystyle ||\mathbf {r} ||>0,} the line has direction d ; the plane that includes the origin and the line L has normal vector m ; the line is tangent to a circle on that plane (normal to m and perpendicular to the plane of the picture) centered at the origin and with radius | | r | | . {\displaystyle ||\mathbf {r} ||.}
Although the usual algebraic definition tends to obscure the relationship, ( d : m ) are the Plücker coordinates of L .
In a 3-dimensional projective space P 3 {\displaystyle \mathbb {P} ^{3}} , let L be a line through distinct points x and y with homogeneous coordinates ( x 0 : x 1 : x 2 : x 3 ) and ( y 0 : y 1 : y 2 : y 3 ) .
The Plücker coordinates p ij are defined as follows:
(the skew symmetric matrix whose elements are p ij is also called the Plücker matrix ) This implies p ii = 0 and p ij = − p ji , reducing the possibilities to only six (4 choose 2) independent quantities. The sextuple
is uniquely determined by L up to a common nonzero scale factor. Furthermore, not all six components can be zero.
Thus the Plücker coordinates of L may be considered as homogeneous coordinates of a point in a 5-dimensional projective space, as suggested by the colon notation.
To see these facts, let M be the 4×2 matrix with the point coordinates as columns.
The Plücker coordinate p ij is the determinant of rows i and j of M .
Because x and y are distinct points, the columns of M are linearly independent ; M has rank 2. Let M′ be a second matrix, with columns x′ , y′ a different pair of distinct points on L . Then the columns of M′ are linear combinations of the columns of M ; so for some 2×2 nonsingular matrix Λ ,
In particular, rows i and j of M′ and M are related by
Therefore, the determinant of the left side 2×2 matrix equals the product of the determinants of the right side 2×2 matrices, the latter of which is a fixed scalar, det Λ . Furthermore, all six 2×2 subdeterminants in M cannot be zero because the rank of M is 2.
Denote the set of all lines (linear images of P 1 {\displaystyle \mathbb {P} ^{1}} ) in P 3 {\displaystyle \mathbb {P} ^{3}} by G 1,3 . We thus have a map:
where
Alternatively, a line can be described as the intersection of two planes. Let L be a line contained in distinct planes a and b with homogeneous coefficients ( a 0 : a 1 : a 2 : a 3 ) and ( b 0 : b 1 : b 2 : b 3 ) , respectively. (The first plane equation is ∑ k a k x k = 0 , {\textstyle \sum _{k}a^{k}x_{k}=0,} for example.) The dual Plücker coordinate p ij is
Dual coordinates are convenient in some computations, and they are equivalent to primary coordinates:
Here, equality between the two vectors in homogeneous coordinates means that the numbers on the right side are equal to the numbers on the left side up to some common scaling factor λ . Specifically, let ( i , j , k , ℓ ) be an even permutation of (0, 1, 2, 3) ; then
To relate back to the geometric intuition, take x 0 = 0 as the plane at infinity; thus the coordinates of points not at infinity can be normalized so that x 0 = 1 . Then M becomes
and setting x = ( x 1 , x 2 , x 3 ) {\displaystyle x=(x_{1},x_{2},x_{3})} and y = ( y 1 , y 2 , y 3 ) {\displaystyle y=(y_{1},y_{2},y_{3})} , we have d = ( p 01 , p 02 , p 03 ) {\displaystyle d=(p_{01},p_{02},p_{03})} and m = ( p 23 , p 31 , p 12 ) {\displaystyle m=(p_{23},p_{31},p_{12})} .
Dually, we have d = ( p 23 , p 31 , p 12 ) {\displaystyle d=(p^{23},p^{31},p^{12})} and m = ( p 01 , p 02 , p 03 ) . {\displaystyle m=(p^{01},p^{02},p^{03}).}
If the point z = ( z 0 : z 1 : z 2 : z 3 ) {\displaystyle \mathbf {z} =(z_{0}:z_{1}:z_{2}:z_{3})} lies on L , then the columns of
are linearly dependent , so that the rank of this larger matrix is still 2. This implies that all 3×3 submatrices have determinant zero, generating four (4 choose 3) plane equations, such as
The four possible planes obtained are as follows.
Using dual coordinates, and letting ( a 0 : a 1 : a 2 : a 3 ) be the line coefficients, each of these is simply a i = p ij , or
Each Plücker coordinate appears in two of the four equations, each time multiplying a different variable; and as at least one of the coordinates is nonzero, we are guaranteed non-vacuous equations for two distinct planes intersecting in L . Thus the Plücker coordinates of a line determine that line uniquely, and the map α is an injection .
The image of α is not the complete set of points in P 5 {\displaystyle \mathbb {P} ^{5}} ; the Plücker coordinates of a line L satisfy the quadratic Plücker relation
For proof, write this homogeneous polynomial as determinants and use Laplace expansion (in reverse).
Since both 3×3 determinants have duplicate columns, the right hand side is identically zero.
Another proof may be done like this:
Since vector
is perpendicular to vector
(see above), the scalar product of d and m must be zero. q.e.d.
Letting ( x 0 : x 1 : x 2 : x 3 ) be the point coordinates, four possible points on a line each have coordinates x i = p ij , for j = 0, 1, 2, 3 . Some of these possible points may be inadmissible because all coordinates are zero, but since at least one Plücker coordinate is nonzero, at least two distinct points are guaranteed.
If ( q 01 : q 02 : q 03 : q 23 : q 31 : q 12 ) {\displaystyle (q_{01}:q_{02}:q_{03}:q_{23}:q_{31}:q_{12})} are the homogeneous coordinates of a point in P 5 {\displaystyle \mathbb {P} ^{5}} , without loss of generality assume that q 01 is nonzero. Then the matrix
has rank 2, and so its columns are distinct points defining a line L . When the P 5 {\displaystyle \mathbb {P} ^{5}} coordinates, q ij , satisfy the quadratic Plücker relation, they are the Plücker coordinates of L . To see this, first normalize q 01 to 1. Then we immediately have that for the Plücker coordinates computed from M , p ij = q ij , except for
But if the q ij satisfy the Plücker relation
then p 23 = q 23 ,
completing the set of identities.
Consequently, α is a surjection onto the algebraic variety consisting of the set of zeros of the quadratic polynomial
And since α is also an injection, the lines in P 3 {\displaystyle \mathbb {P} ^{3}} are thus in bijective correspondence with the points of this quadric in P 5 {\displaystyle \mathbb {P} ^{5}} , called the Plücker quadric or Klein quadric .
Plücker coordinates allow concise solutions to problems of line geometry in 3-dimensional space, especially those involving incidence .
Two lines in P 3 {\displaystyle \mathbb {P} ^{3}} are either skew or coplanar , and in the latter case they are either coincident or intersect in a unique point. If p ij and p′ ij are the Plücker coordinates of two lines, then they are coplanar precisely when
as shown by
When the lines are skew, the sign of the result indicates the sense of crossing: positive if a right-handed screw takes L into L′ , else negative.
The quadratic Plücker relation essentially states that a line is coplanar with itself.
In the event that two lines are coplanar but not parallel, their common plane has equation
where x = ( x 1 , x 2 , x 3 ) . {\displaystyle x=(x_{1},x_{2},x_{3}).}
The slightest perturbation will destroy the existence of a common plane, and near-parallelism of the lines will cause numeric difficulties in finding such a plane even if it does exist.
Dually, two coplanar lines, neither of which contains the origin, have common point
To handle lines not meeting this restriction, see the references.
Given a plane with equation
or more concisely,
and given a line not in it with Plücker coordinates ( d : m ) , then their point of intersection is
The point coordinates, ( x 0 : x 1 : x 2 : x 3 ) , can also be expressed in terms of Plücker coordinates as
Dually, given a point ( y 0 : y ) and a line not containing it, their common plane has equation
The plane coordinates, ( a 0 : a 1 : a 2 : a 3 ) , can also be expressed in terms of dual Plücker coordinates as
Because the Klein quadric is in P 5 {\displaystyle \mathbb {P} ^{5}} , it contains linear subspaces of dimensions one and two (but no higher). These correspond to one- and two-parameter families of lines in P 3 {\displaystyle \mathbb {P} ^{3}} .
For example, suppose L, L′ are distinct lines in P 3 {\displaystyle \mathbb {P} ^{3}} determined by points x , y and x ′, y ′ , respectively. Linear combinations of their determining points give linear combinations of their Plücker coordinates, generating a one-parameter family of lines containing L and L ′ . This corresponds to a one-dimensional linear subspace belonging to the Klein quadric.
If three distinct and non-parallel lines are coplanar; their linear combinations generate a two-parameter family of lines, all the lines in the plane. This corresponds to a two-dimensional linear subspace belonging to the Klein quadric.
If three distinct and non-coplanar lines intersect in a point, their linear combinations generate a two-parameter family of lines, all the lines through the point. This also corresponds to a two-dimensional linear subspace belonging to the Klein quadric.
A ruled surface is a family of lines that is not necessarily linear. It corresponds to a curve on the Klein quadric. For example, a hyperboloid of one sheet is a quadric surface in P 3 {\displaystyle \mathbb {P} ^{3}} ruled by two different families of lines, one line of each passing through each point of the surface; each family corresponds under the Plücker map to a conic section within the Klein quadric in P 5 {\displaystyle \mathbb {P} ^{5}} .
During the nineteenth century, line geometry was studied intensively. In terms of the bijection given above, this is a description of the intrinsic geometry of the Klein quadric.
Line geometry is extensively used in ray tracing application where the geometry and intersections of rays need to be calculated in 3D. An implementation is described in Introduction to Plücker Coordinates written for the Ray Tracing forum by Thouis Jones. | https://en.wikipedia.org/wiki/Plücker_coordinates |
Promethium(III) oxide is a compound with the formula Pm 2 O 3 . It is the most common form of promethium .
Promethium oxide exists in three major crystalline forms: [ 1 ]
*a, b and c are lattice parameters, Z is the number of formula units per unit cell, density is calculated from X-ray data.
The low-temperature cubic form converts to the monoclinic structure upon heating to 750–800 °C, and this transition can only be reversed by melting the oxide. The transition from the monoclinic to hexagonal form occurs at 1740 °C.
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pm2O3 |
Promethium(III) chloride is a chemical compound of promethium and chlorine with the formula PmCl 3 . It is an ionic, water soluble, crystalline salt that glows in the dark with a pale blue or green light due to promethium's intense radioactivity.
Promethium(III) chloride is obtained from promethium(III) oxide by heating it in a stream of dry HCl at 580 °C. [ 5 ]
Promethium(III) chloride is a purple solid with a melting point of 655 °C. [ 1 ] It crystallizes in the hexagonal crystal system (NdCl 3 type) with the lattice parameters a = 739 pm and c = 421 pm with two formula units per unit cell and thus a calculated density of 4.19 g·cm −3 . [ 6 ] [ 7 ] When PmCl 3 is heated in the presence of H 2 O, the pale pink colored promethium(III) oxychloride (PmOCl) is obtained. [ 6 ] [ 8 ]
Promethium(III) chloride (with 147 Pm ) has been used to generate long-lasting glow in signal lights and buttons. This application relied on the unstable nature of promethium, which emitted beta radiation (electrons) with a half-life of several years. The electrons were absorbed by a phosphor , generating visible glow. [ 9 ] Unlike many other radioactive nuclides , promethium-147 does not emit alpha particles that would degrade the phosphor. [ 10 ] | https://en.wikipedia.org/wiki/PmCl3 |
Promethium(III) fluoride or promethium trifluoride is a salt of promethium and fluorine with the formula PmF 3 .
Promethium(III) fluoride is sparingly soluble in water. It reacts with metallic lithium to yield lithium fluoride and metallic promethium: [ 3 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PmF3 |
A pneumatic barrier is a method to contain oil spills . It is also called a bubble curtain . Air bubbling through a perforated pipe causes an upward water flow that slows the spread of oil. It can also be used to stop fish from entering polluted water . A further application of the pneumatic barrier is to decrease the salt-water exchange in navigation locks and prevent salt intrusion in rivers.
. [ 1 ] Pneumatic barriers are also known as air curtains.
The pneumatic barrier is a (non-patented) invention of the Dutch engineer Johan van Veen from around 1940
. [ 2 ]
A pneumatic barrier is an active (as opposed to passive ) method of waterway oil spill control. (An example of a passive method would be a containment boom .)
The pneumatic barrier consists of a perforated pipe and a compressed air source. Air escaping from the pipe provides a "hump" of rising water and air which contains the oil spill. Anchors to keep the pipe in a particular spot are helpful. In case of a density current due to salinity differences the barrier mixes the salt water, but also slows down the speed of the density current.
At water-current speeds exceeding one foot per second, the pneumatic barrier no longer functions effectively, limiting deployable sites.
The release of compressed air in the water adds oxygen to the local environment. This may be particularly useful in areas that have become a dead zone due to eutrophication .
Air curtains may have another application. Dolphin and whale beaching has increased with the rise in ocean temperatures. On Thursday February 12th, 2017, a group of nearly 400 whales beached near Golden Bay on the tip of New Zealand’s South Island, following a similar incident earlier that week. The simplicity of an air curtain system, requiring only air compressors and perforated hoses, could allow for rapid deployment and create aerated zones of oxygenated seawater during a marine emergency.
Air curtains are also used to control the release of smoke particles into the environment. After a natural disaster, or during brush clearing activities, debris is disposed of by incineration in either a ceramic or earth pit containment. Similar to an air curtain to separate indoor air from outdoor air, for instance in restaurants and walk-in refrigerators, a powerful air curtain can defeat the chimney effect of the incineration process to eliminate any smoke from a brush incinerator. The air curtain acts as a lid on the process, and forces the smoke back into the fuel bed for a cleaner burn.
Like all active systems of any type, a mechanical failure can result in total failure of protection.
Development of an air bubble curtain to reduce underwater noise of percussive piling Marine Environmental Research 49(2000)79-93, Elsevier Retrieved 2/16/2017
Bubble Curtains: Can They Dampen Offshore Energy Sound for Whales? National Geographic Retrieved 2/16/2017
You Tube: How an Air Curtain Works by Berner International Retrieved 2/16/2017 | https://en.wikipedia.org/wiki/Pneumatic_barrier |
A pneumatic bladder is an inflatable ( pneumatic ) bag technology with many applications.
Pneumatic bladders are used to seal drains and ducts to contain chemical spills or gases. Pneumatic bladders are often used for the containment of chemical spills, oil spills or fire water on water to prevent them from entering the environment, usually in the form of booms . [ 1 ]
The Reef Ball Foundation uses a pneumatic bladder technology to float an artificial coral reef ("reef ball") into location, then deflate the bladder to sink the reef to the bottom.
Pneumatic bladders, known as dunnage bags , are used to stabilize cargo within a container.
Pneumatic bladders are used in medical research. [ 2 ]
Leading edge inflatable kites use pneumatic bladders restrained by a fabric case; the bladder is selected slightly larger than the case, so that at operational inflation the bladder is not stressed while the case defines the final shape of the leading edge. Many of the wing's airfoil ribs are similarly bladdered.
This industry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pneumatic_bladder |
In the history of science , pneumatic chemistry is an area of scientific research of the seventeenth, eighteenth, and early nineteenth centuries. Important goals of this work were the understanding of the physical properties of gases and how they relate to chemical reactions and, ultimately, the composition of matter . The rise of phlogiston theory , and its replacement by a new theory after the discovery of oxygen as a gaseous component of the Earth atmosphere and a chemical reagent participating in the combustion reactions, were addressed in the era of pneumatic chemistry.
In the eighteenth century, as the field of chemistry was evolving from alchemy , a field of the natural philosophy was created around the idea of air as a reagent . Before this, air was primarily considered a static substance that would not react and simply existed. However, as Lavoisier and several other pneumatic chemists would insist, the air was indeed dynamic, and would not only be influenced by combusted material, but would also influence the properties of different substances.
The initial concern of pneumatic chemistry was combustion reactions, beginning with Stephen Hales . These reactions would give off different "airs" as chemists would call them, and these different airs contained more simple substances. Until Lavoisier, these airs were considered separate entities with different properties; Lavoisier was responsible largely for changing the idea of air as being constituted by these different airs that his contemporaries and earlier chemists had discovered. [ 1 ]
This study of gases was brought about by Hales with the invention of the pneumatic trough, an instrument capable of collecting the gas given off by reactions with reproducible results. The term gas was coined by J. B. van Helmont , in the early seventeenth century. This term was derived from the Ancient Greek word χάος, chaos , as a result of his inability to collect properly the substances given off by reactions, as he was the first natural philosopher to make an attempt at carefully studying the third type of matter. However, it was not until Lavoisier performed his research in the eighteenth century that the word was used universally by scientists as a replacement for airs . [ 2 ]
Van Helmont (1579 – 1644) is sometimes considered the founder of pneumatic chemistry, as he was the first natural philosopher to take an interest in air as a reagent. [ 3 ] Alessandro Volta began investigating pneumatic chemistry in 1776 and argued that there were different types of inflammable air based on experiments on marsh gases. [ 4 ] Pneumatic chemists credited with discovering chemical elements include Joseph Priestley , Henry Cavendish , Joseph Black , Daniel Rutherford , and Carl Scheele . Other individuals who investigated gases during this period include Robert Boyle , Stephen Hales , William Brownrigg , Antoine Lavoisier , Joseph Louis Gay-Lussac , and John Dalton . [ 5 ] [ 6 ] [ 7 ]
"In the years between 1770 and 1785, chemists all over Europe started catching, isolating, and weighing different gasses." [ 8 ] : 40
The pneumatic trough was integral to the work with gases (or, as contemporary chemists called them, airs). Work done by Joseph Black, Joseph Priestley, Herman Boerhaave, and Henry Cavendish revolved largely around the use of the instrument, allowing them to collect airs given off by different chemical reactions and combustion analyses. Their work led to the discovery of many types of airs, such as dephlogisticated air (discovered by Joseph Priestley).
Moreover, the chemistry of airs was not limited to combustion analyses. During the eighteenth century, many chymists used the discovery of airs as a new path for exploring old problems, with one example being the field of medicinal chemistry. One particular Englishman, James Watt, began to take the idea of airs and use them in what was referred to as pneumatic therapy , or the use of airs to make laboratories more workable with fresh airs and also aid patients with different illnesses, with varying degrees of success. Most human experimentation done was performed on the chymists themselves, as they believed that self-experimentation was a necessary part or progressing the field.
James Watt 's research in pneumatic chemistry involved the use of inflammable ( H 2 ) and dephlogisticated ( O 2 ) airs to create water . In 1783, James Watt showed that water was composed of inflammable and dephlogisticated airs, and that the masses of gases before combustion were exactly equal to the mass of water after combustion. [ 9 ] Until this point, water was viewed as a fundamental element rather than a compound. James Watt also sought to explore the use of different " factitious airs " such as hydrocarbonate in medicinal treatments as "pneumatic therapy" by collaborating with Dr. Thomas Beddoes and Erasmus Darwin to treat Jessie Watt, his daughter suffering from tuberculosis , using fixed air. [ 10 ]
Joseph Black was a chemist who took interest in the pneumatic field after studying under William Cullen . He was first interested in the topic of magnesia alba, or magnesium carbonate (MgCO 3 ), and limestone , or calcium carbonate (CaCO 3 ) , and wrote a dissertation called " De humore acido a cibis orto, et magnesia alba " on the properties of both. [ 11 ] His experiments on magnesium carbonate led him to discover that fixed air, or carbon dioxide (CO 2 ), was being given off during reactions with various chemicals, including breathing . Despite him never using the pneumatic trough or other instrumentation invented to collect and analyze the airs, his inferences led to more research into fixed air instead of common air, with the trough actually being used. [ 2 ]
Gaseous ammonia was first isolated by Joseph Black in 1756 by reacting sal ammoniac ( ammonium chloride ) with calcined magnesia ( magnesium oxide ). [ 12 ] [ 13 ] It was isolated again by Peter Woulfe in 1767, [ 14 ] [ 15 ] by Carl Wilhelm Scheele in 1770 [ 16 ]
Joseph Priestley , in Observations on different kinds of air, was one of the first people to describe air as being composed of different states of matter, and not as one element. [ 17 ] Priestley elaborated on the notions of fixed air (CO 2 ), mephitic air and inflammable air to include "inflammable nitrous air," " vitriolic acid air ," " alkaline air " and " dephlogisticated air ". [ 17 ] Priestley also described the process of respiration in terms of phlogiston theory . [ 17 ] Priestley also established a process for treating scurvy and other ailments using fixed air in his Directions for impregnating water with fixed air. Priestley's work on pneumatic chemistry had an influence on his natural world views. His belief in an "aerial economy" stemmed from his belief in "dephlogisticated air" being the purest type of air and that phlogiston and combustion were at the heart of nature. [ 18 ] Joseph Priestley chiefly researched with the pneumatic trough, but he was responsible for collecting several new water-soluble airs. This was achieved primarily by his substitution of mercury for water, and implementing a shelf under the head for increased stability, capitalizing on the idea Cavendish proposed and popularizing the mercury pneumatic trough. [ 2 ]
While not credited for direct research into the field of pneumatic chemistry, Boerhaave (teacher, researcher, and scholar) did publish the Elementa Chimiae in 1727. This treatise included support for Hales' work and also elaborated upon the idea of airs. Despite not publishing his own research, this section on airs in the Elementa Chimiae was cited by many other contemporaries and contained much of the current knowledge of the properties of airs. [ 19 ] Boerhaave is also credited with adding to the world of chemical thermometry through his work with Daniel Fahrenheit , also discussed in Elementa Chimiae. [ 20 ]
Henry Cavendish , despite not being the first to replace water in the trough with mercury , was among the first to observe that fixed air was insoluble over mercury and therefore could be collected more efficiently using the adapted instrument. He also characterized fixed air ( CO 2 ) and inflammable air ( H 2 ). Inflammable air was one of the first gases isolated and discovered using the pneumatic trough. However, he did not exploit his own idea to its limit, and therefore did not use the mercury pneumatic trough to its full extent. [ 2 ] Cavendish is credited with nearly correctly analyzing the content of gases in the atmosphere. [ 21 ] Cavendish also showed that inflammable air and atmospheric air could be combined and heated to produce water in 1784. [ 21 ]
In the eighteenth century, with the rise of combustion analysis in chemistry, Stephen Hales invented the pneumatic trough in order to collect gases from the samples of matter he used; while uninterested in the properties of the gases he collected, he wanted to explore how much gas was given off from the materials he burned or let ferment . Hales was successful in preventing the air from losing its "elasticity," i.e. preventing it from experiencing a loss in volume, by bubbling the gas through water, and therefore dissolving the soluble gases.
After the invention of the pneumatic trough, Stephen Hales continued his research into the different airs, and performed many Newtonian analyses of the various properties of them. He published his book Vegetable Staticks in 1727, which had a profound impact on the field of pneumatic chemistry, as many researchers cited this in their academic papers. In Vegetable Staticks , Hales not only introduced his trough, but also published the results he obtained from the collected air, such as the elasticity and composition of airs along with their ability to mix with others. [ 22 ]
Stephen Hales , called the creator of pneumatic chemistry, created the pneumatic trough in 1727. [ 23 ] This instrument was widely used by many chemists to explore the properties of different airs, such as what was called inflammable air (what is modernly called hydrogen). Lavoisier used this in addition to his gasometer to collect gases and analyze them, aiding him in creating his list of simple substances.
The pneumatic trough, while integral throughout the eighteenth century, was modified several times to collect gases more efficiently or just to collect more gas. For example, Cavendish noted that the amount of fixed air that was given off by a reaction was not entirely present above the water; this meant that fixed water was absorbing some of this air, and could not be used quantitatively to collect that particular air. So, he replaced the water in the trough with mercury instead, in which most airs were not soluble. By doing so, he could not only collect all airs given off by a reaction, but he could also determine the solubility of airs in water, beginning a new area of research for pneumatic chemists. While this was the major adaptation of the trough in the eighteenth century, several minor changes were made before and after this substitution of mercury for water, such as adding a shelf to rest the head on while gas collection occurred. This shelf would also allow for less conventional heads to be used, such as Brownrigg 's animal bladder . [ 2 ]
A practical application of a pneumatic trough was the eudiometer , which was used by Jan Ingenhousz to show that plants produced dephlogisticated air when exposed to sunlight , a process now called photosynthesis . [ 8 ]
During his chemical revolution, Lavoisier created a new instrument for precisely measuring out gases. He called this instrument the gazomètre . He had two different versions; the one he used in demonstrations to the Académie and to the public, which was a large expensive version meant to make people believe that it had a large precision, and the smaller, more lab practical, version with a similar precision. This more practical version was cheaper to construct, allowing more chemists to use Lavoisier's instrument. [ 17 ] | https://en.wikipedia.org/wiki/Pneumatic_chemistry |
Pneumatic cylinder , also known as air cylinder , is a mechanical device which uses the power of compressed gas to produce a force in a reciprocating linear motion. [ 1 ] : 85
Like in a hydraulic cylinder , something forces a piston to move in the desired direction. The piston is a disc or cylinder, and the piston rod transfers the force it develops to the object to be moved. [ 1 ] : 85 Engineers sometimes prefer to use pneumatics because they are quieter, cleaner, and do not require large amounts of space for fluid storage.
Because the operating fluid is a gas, leakage from a pneumatic cylinder will not drip out and contaminate the surroundings, making pneumatics more desirable where cleanliness is a requirement. For example, in the mechanical puppets of the Disney Tiki Room , pneumatics are used to prevent fluid from dripping onto people below the puppets.
Once actuated, compressed air enters into the tube at one end of the piston and imparts force on the piston. Consequently, the piston becomes displaced.
One major issue engineers come across working with pneumatic cylinders has to do with the compressibility of a gas. Many studies have been completed on how the precision of a pneumatic cylinder can be affected as the load acting on the cylinder tries to further compress the gas used. Under a vertical load, a case where the cylinder takes on the full load, the precision of the cylinder is affected the most. A study at the National Cheng Kung University in Taiwan, concluded that the accuracy is about ± 30 nm, which is still within a satisfactory range but shows that the compressibility of air has an effect on the system. [ 2 ]
Pneumatic systems are often found in settings where even rare and brief system failure is unacceptable. In such situations, locks can sometimes serve as a safety mechanism in case of loss of air supply (or its pressure falling) and, thus remedy or abate any damage arising in such a situation.
Leakage of air from the input or output reduces the output pressure.
Although pneumatic cylinders will vary in appearance, size and function, they generally fall into one of the specific categories shown below. However, there are also numerous other types of pneumatic cylinder available, many of which are designed to fulfill specific and specialized functions.
A single-acting cylinder (SAC) has one port, which allows compressed air to enter and for the rod to move in one direction only. The high pressure of the compressed air causes the rod to extend as the cylinder chamber continues to fill. When the compressed air leaves the cylinder through the same port the rod is returned to its original position.
Double-acting cylinders (DAC) use the force of air to move in both extend and retract strokes. They have two ports to allow air in, one for outstroke and one for instroke. Stroke length for this design is not limited, however, the piston rod is more vulnerable to buckling and bending. Additional calculations should be performed as well. [ 1 ] : 89
Telescoping cylinders, also known as telescopic cylinders can be either single or double-acting. The telescoping cylinder incorporates a piston rod nested within a series of hollow stages of increasing diameter. Upon actuation, the piston rod and each succeeding stage "telescopes" out as a segmented piston. The main benefit of this design is the allowance for a notably longer stroke than would be achieved with a single-stage cylinder of the same collapsed (retracted) length. One cited drawback to telescoping cylinders is the increased potential for piston flexion due to the segmented piston design. Consequently, telescoping cylinders are primarily utilized in applications where the piston bears minimal side loading. [ 3 ]
Although SACs and DACs are the most common types of pneumatic cylinder, the following types are not particularly rare: [ 1 ] : 89
Rodless cylinders have no rod, only a relatively long piston. Cable cylinders retain openings at one or both ends, but pass a flexible cable rather than a rod. This cable has a smooth plastic jacket for sealing purposes. Of course, a single cable has to be kept in tension. [ 4 ] Other rodless cylinders close off both ends, coupling the piston either magnetically or mechanically to an actuator that runs along the outside of the cylinder. In the magnetic type, the cylinder is thin-walled and of a non-magnetic material, the cylinder is a powerful magnet, and pulls along a magnetic traveller on the outside.
In the mechanical type, part of the cylinder extends to the outside through a slot cut down the length of the cylinder. The slot is then sealed by flexible metal sealing bands on the inside (to prevent gas escape) and outside (to prevent contamination). The piston itself has two end seals, and between them, camming surfaces to "peel off" the seals ahead of the projecting linkage and to replace them behind. The interior of the piston, then, is at atmospheric pressure. [ 5 ]
One well-known application of the mechanical type (albeit steam-powered) are the catapults used on many modern aircraft carriers .
Depending on the job specification, there are multiple forms of body constructions available: [ 1 ] : 91
Upon job specification, the material may be chosen. Material range from nickel-plated brass to aluminum, and even steel and stainless steel. Depending on the level of loads, humidity, temperature, and stroke lengths specified, the appropriate material may be selected. [ 6 ]
Depending on the location of the application and machinability, there exist different kinds of mounts for attaching pneumatic cylinders: [ 1 ] : 95
Air cylinders are available in a variety of sizes and can typically range from a small 2.5 mm ( 1 ⁄ 10 in) air cylinder, which might be used for picking up a small transistor or other electronic component, to 400 mm (16 in) diameter air cylinders which would impart enough force to lift a car. Some pneumatic cylinders reach 1,000 mm (39 in) in diameter, and are used in place of hydraulic cylinders for special circumstances where leaking hydraulic oil could impose an extreme hazard.
Due to the forces acting on the cylinder, the piston rod is the most stressed component and has to be designed to withstand high amounts of bending, tensile and compressive forces. Depending on how long the piston rod is, stresses can be calculated differently. If the rods length is less than 10 times the diameter, then it may be treated as a rigid body which has compressive or tensile forces acting on it. In which case the relationship is:
Where:
However, if the length of the rod exceeds the 10 times the value of the diameter, then the rod needs to be treated as a column and buckling needs to be calculated as well. [ 1 ] : 92
Although the diameter of the piston and the force exerted by a cylinder are related , they are not directly proportional to one another. Additionally, the typical mathematical relationship between the two assumes that the air supply does not become saturated . Due to the effective cross sectional area reduced by the area of the piston rod, the instroke force is less than the outstroke force when both are powered pneumatically and by same supply of compressed gas.
The relationship between the force, radius, and pressure can derived from simple distributed load equation: [ 7 ]
Where:
Using the distributed load equation provided the A e {\displaystyle A_{e}} can be replaced with area of the piston surface where the pressure is acting on.
Where:
On instroke, the same relationship between force exerted, pressure and effective cross sectional area applies as discussed above for outstroke. However, since the cross sectional area is less than the piston area the relationship between force, pressure and radius is different. The calculation isn't more complicated though, since the effective cross sectional area is merely that of the piston surface minus the cross sectional area of the piston rod.
For instroke, therefore, the relationship between force exerted, pressure, radius of the piston, and radius of the piston rod, is as follows:
Where: | https://en.wikipedia.org/wiki/Pneumatic_cylinder |
Pneumatic fracturing is a method that has become very popular in the last ten years used to remediate contaminated sites . The method consists of injecting gas into a contaminated subsurface at a pressure higher than that of the gases that are present. By doing this fractures "spider-web" throughout the subsurface so that pumps may be placed in the ground to suck out the contaminated water through these cracks. Substrates may also be injected into the soil through the cracks to further the remediation of the soil and ground water . The clean-up technique was developed and patented through the research of various professors at the New Jersey Institute of Technology in 1996 with hopes of cleaning up various United States Environmental Protection Agency (EPA) Superfund sites which are some of the most heavily contaminated sites in the country. The patent is held by John R. Schuring, PhD and PE, professor of civil and environmental engineering at the New Jersey Institute of Technology , developed in conjunction with Thomas M. Boland, Trevor C. King, Sean T. McGonigal, David S. Kosson, Conan D. Fitzgerald, and Sankar Venkatraman. This method has been adopted by environmental contractors all over the country since it has been patented. [ 1 ] [ 2 ] | https://en.wikipedia.org/wiki/Pneumatic_fracturing |
A pneumatic gripper is a specific type of pneumatic actuator that typically involves either parallel or angular motion of surfaces, A.K.A. “tooling jaws or fingers” that will grip an object. The gripper makes use of compressed air which powers a piston rod inside the tool.Grippers exist both internal with and external bore grip with the same equipment because of an increased quantity of cross rollers in the parallel slide part.
This article about a mechanical engineering topic is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Pneumatic_gripper |
A pneumatic motor ( air motor ), or compressed-air engine , is a type of motor which does mechanical work by expanding compressed air . Pneumatic motors generally convert the compressed-air energy to mechanical work through either linear or rotary motion. Linear motion can come from either a diaphragm or piston actuator, while rotary motion is supplied by either a vane type air motor, piston air motor, air turbine or gear type motor.
Pneumatic motors have existed in many forms over the past two centuries, ranging in size from hand-held motors to engines of up to several hundred horsepower. Some types rely on pistons and cylinders; others on slotted rotors with vanes (vane motors) and others use turbines. Many compressed-air engines improve their performance by heating the incoming air or the engine itself. Pneumatic motors have found widespread success in the hand-held tool industry, [ 1 ] but are also used stationary in a wide range of industrial applications. Continual attempts are being made to expand their use to the transportation industry. However, pneumatic motors must overcome inefficiencies before being seen as a viable option in the transportation industry.
In order to achieve linear motion from compressed air, a system of pistons is most commonly used. The compressed air is fed into an air-tight chamber that houses the shaft of the piston. Also inside this chamber a spring is coiled around the shaft of the piston in order to hold the chamber completely open when air is not being pumped into the chamber. As air is fed into the chamber the force on the piston shaft begins to overcome the force being exerted on the spring. [ 2 ] As more air is fed into the chamber, the pressure increases and the piston begins to move down the chamber. When it reaches its maximum length the air pressure is released from the chamber and the spring completes the cycle by closing off the chamber to return to its original position.
Piston motors are the most commonly used in hydraulic systems. Essentially, piston motors are the same as hydraulic motors except they are used to convert hydraulic energy into mechanical [ 3 ] energy. [ 4 ]
Piston motors are often used in series of two, three, four, five, or six cylinders that are enclosed in a housing. This allows for more power to be delivered by the pistons because several motors are in sync with each other at certain times of their cycle.
The practical mechanical efficiencies attained by a piston air motor are between 40–50%. [ 5 ]
A type of pneumatic motor, known as a rotary vane motor, uses air to produce rotational motion to a shaft. The rotating element is a slotted rotor which is mounted on a drive shaft. Each slot of the rotor is fitted with a freely sliding rectangular vane. [ 4 ] The vanes are extended to the housing walls using springs, cam action, or air pressure, depending on the motor design. Air is pumped through the motor input which pushes on the vanes creating the rotational motion of the central shaft. Rotation speeds can vary between 100 and 25,000 rpm depending on several factors which include the amount of air pressure at the motor inlet and the diameter of the housing. [ 2 ]
One application for vane-type air motors is to start large industrial diesel or natural gas engines. Stored energy in the form of compressed air, nitrogen or natural gas enters the sealed motor chamber and exerts pressure against the vanes of a rotor. This causes the rotor to turn at high speed. Because the engine flywheel requires a great deal of torque to start the engine, reduction gears are used. Reduction gears create high torque levels with the lower amounts of energy input. These reduction gears allow for sufficient torque to be generated by the engine flywheel while it is engaged by the pinion gear of the air motor or air starter.
Air turbines spin the burr in high-speed dental handpieces , at speeds over 180,000 rpm, but with limited torque . A turbine is small enough to fit in the tip of a handpiece without adding to the weight.
A widespread application of pneumatic motors is in hand-held tools, impact wrenches, pulse tools, screwdrivers, nut runners, drills, grinders, sanders and so on. Pneumatic motors are also used stationary in a wide range of industrial applications. Though overall energy efficiency of pneumatics tools is low and they require access to a compressed-air source, there are several advantages over electric tools. They offer greater power density (a smaller pneumatic motor can provide the same amount of power as a larger electric motor), do not require an auxiliary speed controller (adding to its compactness), generate less heat, and can be used in more volatile atmospheres as they do not require electric power [ 6 ] and do not create sparks. They can be loaded to stop with full torque without damage. [ 7 ] The efficiency of a rotary piston engine is highly dependent on mechanical energy losses. The value of mechanical losses, according to various estimates, can be 20% of the energy supplied to the engine. [ 8 ] At the same time it was experimentally shown that efficiency of a motor can be increased by the usage of anti-friction additives to the lubricating oil. [ 9 ]
Historically, many individuals have tried to apply pneumatic motors to the transportation industry. Guy Negre, CEO and founder of Zero Pollution Motors, has pioneered this field since the late 1980s. [ 10 ] Recently Engineair has also developed a rotary motor for use in automobiles. Engineair places the motor immediately beside the wheel of the vehicle and uses no intermediate parts to transmit motion which means almost all of the motor's energy is used to rotate the wheel. [ 11 ]
The pneumatic motor was first applied to the field of transportation in the mid-19th century. Though little is known about the first recorded compressed-air vehicle, it is said that the Frenchmen Andraud and Tessie of Motay ran a car powered by a pneumatic motor on a test track in Chaillot, France, on 9 July 1840. Although the car test was reported to have been successful, the pair did not explore further expansion of the design. [ 12 ]
The first successful application of the pneumatic motor in transportation was the Mekarski system air engine used in locomotives. Mekarski's innovative engine overcame cooling that accompanies air expansion by heating air in a small boiler prior to use. The Tramway de Nantes , located in Nantes, France, was noted for being the first to use Mekarski engines to power their fleet of locomotives. The tramway began operation on December 13, 1879, and continues to operate today, although the pneumatic trams were replaced in 1917 by more efficient and modern electrical trams.
American Charles Hodges also found success with pneumatic motors in the locomotive industry. In 1911 he designed a pneumatic locomotive and sold the patent to the H.K. Porter Company in Pittsburgh for use in coal mines. [ 13 ] Because pneumatic motors do not use combustion they were a much safer option in the coal industry. [ 12 ]
Many companies [ who? ] claim to be developing compressed-air cars , but none are actually available for purchase or even independent testing.
Impact wrenches , pulse tools, torque wrenches , screwdrivers , drills , grinders , die grinders , sanders , dental drills , tire changers and other pneumatic tools use a variety of air motors . These include vane type motors, turbines and piston motors.
Most successful early forms of self-propelled torpedoes used high-pressure compressed air , although this was superseded by internal or external combustion engines, steam engines (driven by the catalytic decomposition of hydrogen peroxide), or electric motors.
Compressed-air engines were used in trams and shunters, and eventually found a successful niche in mining locomotives, although in the end they were replaced by electric trains, underground. [ 14 ] Over the years designs increased in complexity, resulting in a triple expansion engine with air-to-air reheaters between each stage. [ 15 ] For more information see Fireless locomotive and Mekarski system .
Water rockets use compressed air to power their water jet and generate thrust; they are used as toys.
Air Hogs , a toy brand, also uses compressed air to power piston engines in toy airplanes (and some other toy vehicles).
There is currently some interest in developing air cars . Several engines have been proposed for these, although none have demonstrated the performance and long life needed for personal transport.
The Energine Corporation was a South Korean company that claimed to deliver fully assembled cars running on a hybrid compressed air and electric engine. The compressed-air engine is used to activate an alternator , which extends the autonomous operating capacity of the car. The CEO was arrested for fraudulently promoting air motors with false claims. [ 17 ]
EngineAir, an Australian company, is making a rotary engine powered by compressed air, called The Di Pietro motor .
The Di Pietro motor concept is based on a rotary piston. Different from existing rotary engines, the Di Pietro motor uses a simple cylindrical rotary piston (shaft driver) which rolls, with little friction, inside the cylindrical stator. [ 18 ]
It can be used in boats, cars, burden carriers and other vehicles. Only 1 psi (≈ 6,8 kPa ) of pressure is needed to overcome the friction. [ 19 ] [ 20 ] The engine was also featured on the ABC's New Inventors programme in Australia on 24 March 2004. [ 21 ]
K'Airmobiles vehicles were intended to be commercialized from a project developed in France in 2006–2007 by a small group of researchers. However, the project has not been able to gather the necessary funds.
People should note that, meantime, the team has recognized the physical impossibility to use on-board stored compressed air due to its poor energy capacity and the thermal losses resulting from the expansion of the gas.
These days, using the patent pending 'K'Air Generator', converted to work as a compressed-gas motor, the project should be launched in 2010, thanks to a North American group of investors, but for the purpose of developing first a green energy power system. [ 22 ]
In the original Nègre air engine, one piston compresses air from the atmosphere to mix with the stored compressed air (which will cool drastically as it expands). This mixture drives the second piston, providing the actual engine power. MDI's engine works with constant torque, and the only way to change the torque to the wheels is to use a pulley transmission of constant variation, losing some efficiency. When vehicle is stopped, MDI's engine had to be on and working, losing energy. In 2001–2004 MDI switched to a design similar to that described in Regusci's patents (see below), which date back to 1990.
It has been reported in 2008 that Indian car manufacturer Tata was looking at an MDI compressed-air engine as an option on its low priced Nano automobiles. [ 23 ] Tata announced in 2009 that the compressed-air car was proving difficult to develop due to its low range and problems with low engine temperatures.
The Pneumatic Quasiturbine engine is a compressed-air pistonless rotary engine using a rhomboidal-shaped rotor whose sides are hinged at the vertices.
The Quasiturbine has been demonstrated as a pneumatic engine using stored compressed air. [ 24 ]
It can also take advantage of the energy amplification possible from using available external heat, such as solar energy . [ 25 ]
The Quasiturbine rotates from pressure as low as 0.1 atm (1.47psi).
Since the Quasiturbine is a pure expansion engine, while the Wankel and most other rotary engines are not, it is well-suited as a compressed fluid engine, air engine or air motor. [ 25 ]
Armando Regusci's version of the air engine couples the transmission system directly to the wheel, and has variable torque from zero to the maximum, enhancing efficiency. Regusci's patents date from 1990. [ 26 ]
Psycho-Active is developing a multi-fuel/air-hybrid chassis which is intended to serve as the foundation for a line of automobiles. Claimed performance is 50 hp/litre. The compressed air motor they use is called the DBRE or Ducted Blade Rotary Engine. [ 27 ] [ 28 ]
Milton M. Conger in 1881 patented and supposedly built a motor that ran on compressed air or steam using a flexible tubing which will form a wedge-shaped or inclined wall or abutment in the rear of the tangential bearing of the wheel, and propel it with greater or less speed according to the pressure of the propelling medium. [ 29 ] | https://en.wikipedia.org/wiki/Pneumatic_motor |
A Pneumatic stabilized platform (PSP) is a technology used to float a very large floating structure (VLFS).
PSP utilizes indirect displacement, in which a platform rests on trapped air that displaces the water. The primary buoyancy force is provided by air pressure acting on the underside of the deck. The PSP is a distinct type of pneumatic platform, one in which the platform is composed of a number of cylindrical shaped components packed together in a rectangular pattern to form a module.
The Pneumatically Stabilized Platform was originally proposed for constructing a new floating airport for San Diego in the Pacific Ocean, at least three miles off the tip of Point Loma . However, this proposed design was rejected in October, 2003 due to high cost, the difficulty in accessing such an airport, the difficulty in transporting jet fuel , electricity, water, and gas to the structure, failure to address security concerns such as a bomb blast, inadequate room for high-speed exits and taxiways, and environmental concerns. [1] Archived 2007-09-28 at the Wayback Machine | https://en.wikipedia.org/wiki/Pneumatic_stabilized_platform |
Legend
The pnictogens [ 1 ] ( / ˈ p n ɪ k t ə dʒ ə n / or / ˈ n ɪ k t ə dʒ ə n / ; from Ancient Greek πνῑ́γω (pnígo) ' to choke ' and -gen ' generator ' ) are the chemical elements in group 15 of the periodic table . This group is also known as the nitrogen group or nitrogen family . Group 15 consists of the elements nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and moscovium (Mc).
Since 1988, it has been called Group 15 by the IUPAC . Before that, in America it was called Group V A , owing to a text by H. C. Deming and the Sargent-Welch Scientific Company , while in Europe it was called Group V B , which the IUPAC had recommended in 1970. [ 2 ] (Pronounced "group five A" and "group five B"; "V" is the Roman numeral 5). In semiconductor physics, it is still usually called Group V. [ 3 ] The "five" ("V") in the historical names comes from the " pentavalency " of nitrogen, reflected by the stoichiometry of compounds such as N 2 O 5 . They have also been called the pentels .
Like other groups, the members of this family manifest similar patterns in electron configuration , notably in their valence shells , resulting in trends in chemical behavior.
This group has a defining characteristic whereby each component element has 5 electrons in its valence shell, that is, 2 electrons in the s sub-shell and 3 unpaired electrons in the p sub-shell. They are therefore 3 electrons shy of filling their valence shell in their non- ionized state. The Russell-Saunders term symbol of the ground state in all elements in the group is 4 S 3 ⁄ 2 .
The most important elements of this group to life on Earth are nitrogen (N), which in its diatomic form is the principal component of air, and phosphorus (P), which, like nitrogen, is essential to all known forms of life.
Binary compounds of the group can be referred to collectively as pnictides . Magnetic properties of pnictide compounds span the cases of diamagnetic systems (such as BN or GaN) and magnetically ordered systems (MnSb is paramagnetic at elevated temperatures and ferromagnetic at room temperature); the former compounds are usually transparent and the latter metallic. Other pnictides include the ternary rare-earth (RE) main-group variety of pnictides. These are in the form of RE a M b Pn c , where M is a carbon group or boron group element and Pn is any pnictogen except nitrogen. These compounds are between ionic and covalent compounds and thus have unusual bonding properties. [ 4 ]
These elements are also noted for their stability in compounds due to their tendency to form covalent double bonds and triple bonds . This property of these elements leads to their potential toxicity , most evident in phosphorus, arsenic, and antimony. When these substances react with various chemicals of the body, they create strong free radicals that are not easily processed by the liver, where they accumulate. Paradoxically, this same strong bonding causes nitrogen's and bismuth's reduced toxicity (when in molecules), because these strong bonds with other atoms are difficult to split, creating very unreactive molecules. For example, N 2 , the diatomic form of nitrogen, is used as an inert gas in situations where using argon or another noble gas would be too expensive.
Formation of multiple bonds is facilitated by their five valence electrons , as the octet rule permits a pnictogen to accept three electrons on covalent bonding. As 5 > 3, it leaves two unused electrons in a lone pair unless there is a positive charge around (like in [NH 4 ] + ). When a pnictogen forms only three single bonds , effects of the lone pair typically results in trigonal pyramidal molecular geometry .
The light pnictogens (nitrogen, phosphorus, and arsenic) tend to form −3 charges when reduced, completing their octet. When oxidized or ionized, pnictogens typically take an oxidation state of +3 (by losing all three p-shell electrons in the valence shell) or +5 (by losing all three p-shell and both s-shell electrons in the valence shell). However heavier pnictogens are more likely to form the +3 oxidation state than lighter ones due to the s-shell electrons becoming more stabilized. [ 5 ]
Pnictogens can react with hydrogen to form pnictogen hydrides such as ammonia . Going down the group to phosphane (phosphine), arsane (arsine), stibane (stibine), and finally bismuthane (bismuthine), each pnictogen hydride becomes progressively less stable (more unstable), more toxic, and has a smaller hydrogen-hydrogen angle (from 107.8° in ammonia [ 6 ] to 90.48° in bismuthane). [ 7 ] (Also, technically, only ammonia and phosphane have the pnictogen in the −3 oxidation state because, for the rest, the pnictogen is less electronegative than hydrogen.)
Crystal solids featuring pnictogens fully reduced include yttrium nitride , calcium phosphide , sodium arsenide , indium antimonide , and even double salts like aluminum gallium indium phosphide . These include III-V semiconductors , including gallium arsenide , the second-most widely used semiconductor after silicon.
Nitrogen forms a limited number of stable III compounds. Nitrogen(III) oxide can only be isolated at low temperatures, and nitrous acid is unstable. Nitrogen trifluoride is the only stable nitrogen trihalide, with nitrogen trichloride , nitrogen tribromide , and nitrogen triiodide being explosive—nitrogen triiodide being so shock-sensitive that the touch of a feather detonates it (the last three actually feature nitrogen in the −3 oxidation state). Phosphorus forms a +III oxide which is stable at room temperature, phosphorous acid , and several trihalides , although the triiodide is unstable. Arsenic forms +III compounds with oxygen as arsenites , arsenous acid , and arsenic(III) oxide , and it forms all four trihalides. Antimony forms antimony(III) oxide and antimonite but not oxyacids. Its trihalides, antimony trifluoride , antimony trichloride , antimony tribromide , and antimony triiodide , like all pnictogen trihalides, each have trigonal pyramidal molecular geometry .
The +3 oxidation state is bismuth's most common oxidation state because its ability to form the +5 oxidation state is hindered by relativistic properties on heavier elements , effects that are even more pronounced concerning moscovium. Bismuth(III) forms an oxide , an oxychloride , an oxynitrate , and a sulfide . Moscovium(III) is predicted to behave similarly to bismuth(III). Moscovium is predicted to form all four trihalides, of which all but the trifluoride are predicted to be soluble in water. [ 8 ] It is also predicted to form an oxychloride and oxybromide in the +III oxidation state.
For nitrogen, the +5 state typically serves only as a formal explanation of molecules like N 2 O 5 , as the high electronegativity of nitrogen causes the electrons to be shared almost evenly. [ clarification needed ] Pnictogen compounds with coordination number 5 are hypervalent . Nitrogen(V) fluoride is only theoretical and has not been synthesized. The "true" +5 state is more common for the essentially non-relativistic typical pnictogens phosphorus , arsenic , and antimony , as shown in their oxides, phosphorus(V) oxide , arsenic(V) oxide , and antimony(V) oxide , and their fluorides, phosphorus(V) fluoride , arsenic(V) fluoride , antimony(V) fluoride . They also form related fluoride-anions, hexafluorophosphate , hexafluoroarsenate , hexafluoroantimonate , that function as non-coordinating anions . Phosphorus even forms mixed oxide-halides, known as oxyhalides , like phosphorus oxychloride , and mixed pentahalides, like phosphorus trifluorodichloride . Pentamethylpnictogen(V) compounds exist for arsenic , antimony , and bismuth . However, for bismuth, the +5 oxidation state becomes rare due to the relativistic stabilization of the 6s orbitals known as the inert-pair effect , so that the 6s electrons are reluctant to bond chemically. This causes bismuth(V) oxide to be unstable [ 9 ] and bismuth(V) fluoride to be more reactive than the other pnictogen pentafluorides, making it an extremely powerful fluorinating agent . [ 10 ] This effect is even more pronounced for moscovium, prohibiting it from attaining a +5 oxidation state.
The pnictogens exemplify the transition from nonmetal to metal going down the periodic table: a gaseous diatomic nonmetal (N), two elements displaying many allotropes of varying conductivities and structures (P and As), and then at least two elements that only form metallic structures in bulk (Sb and Bi; probably Mc as well). All the elements in the group are solids at room temperature , except for nitrogen which is gaseous at room temperature. Nitrogen and bismuth, despite both being pnictogens, are very different in their physical properties. For instance, at STP nitrogen is a transparent non-metallic gas, while bismuth is a silvery-white metal. [ 12 ]
The densities of the pnictogens increase towards the heavier pnictogens. Nitrogen's density is 0.001251 g/cm 3 at STP. [ 12 ] Phosphorus's density is 1.82 g/cm 3 at STP, arsenic's is 5.72 g/cm 3 , antimony's is 6.68 g/cm 3 , and bismuth's is 9.79 g/cm 3 . [ 13 ]
Nitrogen's melting point is −210 °C and its boiling point is −196 °C. Phosphorus has a melting point of 44 °C and a boiling point of 280 °C. Arsenic is one of only two elements to sublimate at standard pressure; it does this at 603 °C. Antimony's melting point is 631 °C and its boiling point is 1587 °C. Bismuth's melting point is 271 °C and its boiling point is 1564 °C. [ 13 ]
Nitrogen's crystal structure is hexagonal . Phosphorus's crystal structure is cubic . Arsenic, antimony, and bismuth all have rhombohedral crystal structures. [ 13 ]
All pnictogens up to antimony have at least one stable isotope ; bismuth has no stable isotopes, but has a primordial radioisotope with a half-life much longer than the age of the universe ( 209 Bi ); and all known isotopes of moscovium are synthetic and highly radioactive. In addition to these isotopes, traces of 13 N , 32 P , and 33 P occur in nature, along with various bismuth isotopes (other than 209 Bi) in the decay chains of thorium and uranium.
The nitrogen compound sal ammoniac (ammonium chloride) has been known since the time of the Ancient Egyptians. In the 1760s two scientists, Henry Cavendish and Joseph Priestley , isolated nitrogen from air, but neither realized the presence of an undiscovered element. It was not until several years later, in 1772, that Daniel Rutherford realized that the gas was indeed nitrogen. [ 14 ]
The alchemist Hennig Brandt first discovered phosphorus in Hamburg in 1669. Brandt produced the element by heating evaporated urine and condensing the resulting phosphorus vapor in water. Brandt initially thought that he had discovered the Philosopher's Stone , but eventually realized that this was not the case. [ 14 ]
Arsenic compounds have been known for at least 5000 years, and the ancient Greek Theophrastus recognized the arsenic minerals called realgar and orpiment . Elemental arsenic was discovered in the 13th century by Albertus Magnus . [ 14 ]
Antimony was well known to the ancients. A 5000-year-old vase made of nearly pure antimony exists in the Louvre . Antimony compounds were used in dyes in the Babylonian times. The antimony mineral stibnite may have been a component of Greek fire . [ 14 ]
Bismuth was first discovered by an alchemist in 1400. Within 80 years of bismuth's discovery, it had applications in printing and decorated caskets . The Incas were also using bismuth in knives by 1500. Bismuth was originally thought to be the same as lead, but in 1753, Claude François Geoffroy proved that bismuth was different from lead. [ 14 ]
Moscovium was successfully produced in 2003 by bombarding americium-243 atoms with calcium-48 atoms. [ 14 ]
The term "pnictogen" (or "pnigogen") is derived from the ancient Greek word πνίγειν ( pnígein ) meaning "to choke", referring to the choking or stifling property of nitrogen gas. [ 15 ] It can also be used as a mnemonic for the two most common members, P and N. The term "pnictogen" was suggested by the Dutch chemist Anton Eduard van Arkel in the early 1950s. It is also spelled "pnicogen" or "pnigogen". The term "pnicogen" is rarer than the term "pnictogen", and the ratio of academic research papers using "pnictogen" to those using "pnicogen" is 2.5 to 1. [ 4 ] It comes from the Greek root πνιγ- (choke, strangle), and thus the word "pnictogen" is also a reference to the Dutch and German names for nitrogen ( stikstof and Stickstoff , respectively, "suffocating substance": i.e., substance in air, unsupportive of breathing). Hence, "pnictogen" could be translated as "suffocation maker". The word "pnictide" also comes from the same root. [ 15 ]
Previously, the name pentels (from Greek πέντε , pénte , five) was also used for this group. [ 16 ]
Nitrogen makes up 25 parts per million of the Earth's crust , 5 parts per million of soil on average, 100 to 500 parts per trillion of seawater, and 78% of dry air. Most nitrogen on Earth is in nitrogen gas, but some nitrate minerals exist. Nitrogen makes up 2.5% of a typical human by weight. [ citation needed ]
Phosphorus is 0.1% of the earth's crust, making it the 11th most abundant element . Phosphorus comprises 0.65 parts per million of soil and 15 to 60 parts per billion of seawater. There are 200 Mt of accessible phosphates on earth. Phosphorus makes up 1.1% of a typical human by weight. [ 14 ] Phosphorus occurs in minerals of the apatite family, which are the main components of the phosphate rocks.
Arsenic constitutes 1.5 parts per million of the Earth's crust, making it the 53rd most abundant element. The soils hold 1 to 10 parts per million of arsenic, and seawater carries 1.6 parts per billion of arsenic. Arsenic comprises 100 parts per billion of a typical human by weight. Some arsenic exists in elemental form, but most arsenic is found in the arsenic minerals orpiment , realgar , arsenopyrite , and enargite . [ 14 ]
Antimony makes up 0.2 parts per million of the earth's crust, making it the 63rd most abundant element. The soils contain 1 part per million of antimony on average, and seawater contains 300 parts per trillion on average. A typical human has 28 parts per billion of antimony by weight. Some elemental antimony occurs in silver deposits. [ 14 ]
Bismuth makes up 48 parts per billion of the earth's crust, making it the 70th most abundant element. The soils contain approximately 0.25 parts per million of bismuth, and seawater contains 400 parts per trillion of bismuth. Bismuth most commonly occurs as the mineral bismuthinite , but bismuth also occurs in elemental form or sulfide ores. [ 14 ]
Moscovium is a synthetic element which does not occur naturally.
Nitrogen can be produced by fractional distillation of air. [ 17 ]
The principal method for producing phosphorus is to reduce phosphates with carbon in an electric arc furnace . [ 18 ]
Most arsenic is prepared by heating the mineral arsenopyrite in the presence of air. This forms As 4 O 6 , from which arsenic can be extracted via carbon reduction. However, it is also possible to make metallic arsenic by heating arsenopyrite at 650 to 700 °C without oxygen. [ 19 ]
With sulfide ores, the method by which antimony is produced depends on the amount of antimony in the raw ore. If the ore contains 25% to 45% antimony by weight, then crude antimony is produced by smelting the ore in a blast furnace . If the ore contains 45% to 60% antimony by weight, antimony is obtained by heating the ore, also known as liquidation. Ores with more than 60% antimony by weight are chemically displaced with iron shavings from the molten ore, resulting in impure metal.
If an oxide ore of antimony contains less than 30% antimony by weight, the ore is reduced in a blast furnace. If the ore contains closer to 50% antimony by weight, the ore is instead reduced in a reverberatory furnace .
Antimony ores with mixed sulfides and oxides are smelted in a blast furnace. [ 20 ]
Bismuth minerals do occur, in particular in the form of sulfides and oxides, but it is more economic to produce bismuth as a by-product of the smelting of lead ores or, as in China, of tungsten and zinc ores. [ 21 ]
Moscovium is produced a few atoms at a time in particle accelerators by firing a beam of calcium-48 ions at americium-243 until the nuclei fuse. [ 22 ]
Nitrogen is a component of molecules critical to life on earth, such as DNA and amino acids . Nitrates occur in some plants, due to bacteria present in the nodes of the plant. This is seen in leguminous plants such as peas [ clarification needed ] or spinach and lettuce. [ citation needed ] A typical 70 kg human contains 1.8 kg of nitrogen. [ 14 ]
Phosphorus in the form of phosphates occur in compounds important to life, such as DNA and ATP . Humans consume approximately 1 g of phosphorus per day. [ 25 ] Phosphorus is found in foods such as fish, liver, turkey, chicken, and eggs. Phosphate deficiency is a problem known as hypophosphatemia . A typical 70 kg human contains 480 g of phosphorus. [ 14 ]
Arsenic promotes growth in chickens and rats, and may be essential for humans in small quantities . Arsenic has been shown to be helpful in metabolizing the amino acid arginine . There are 7 mg of arsenic in a typical 70 kg human. [ 14 ]
Antimony is not known to have a biological role. Plants take up only trace amounts of antimony. There are approximately 2 mg of antimony in a typical 70 kg human. [ 14 ]
Bismuth is not known to have a biological role. Humans ingest on average less than 20 μg of bismuth per day. There is less than 500 μg of bismuth in a typical 70 kg human. [ 14 ]
Moscovium is too unstable to occur in nature or have a known biological role. Moscovium does not typically occur in organisms in any meaningful amount.
Nitrogen gas is completely non-toxic , but breathing in pure nitrogen gas is deadly, because it causes nitrogen asphyxiation . [ 23 ] The build-up of nitrogen bubbles in the blood, such as those that may occur during scuba diving , can cause a condition known as the "bends" ( decompression sickness ). Many nitrogen compounds such as hydrogen cyanide and nitrogen-based explosives are also highly dangerous. [ 14 ]
White phosphorus , an allotrope of phosphorus, is toxic, with 1 mg per kg bodyweight being a lethal dose. [ 12 ] White phosphorus usually kills humans within a week of ingestion by attacking the liver . Breathing in phosphorus in its gaseous form can cause an industrial disease called " phossy jaw ", which eats away the jawbone. White phosphorus is also highly flammable. Some organophosphorus compounds can fatally block certain enzymes in the human body. [ 14 ]
Elemental arsenic is toxic, as are many of its inorganic compounds ; however some of its organic compounds can promote growth in chickens. [ 12 ] The lethal dose of arsenic for a typical adult is 200 mg and can cause diarrhea, vomiting, colic, dehydration, and coma. Death from arsenic poisoning typically occurs within a day. [ 14 ]
Antimony is mildly toxic. [ 23 ] Additionally, wine steeped in antimony containers can induce vomiting . [ 12 ] When taken in large doses, antimony causes vomiting in a victim, who then appears to recover before dying several days later. Antimony attaches itself to certain enzymes and is difficult to dislodge. Stibine , or SbH 3 , is far more toxic than pure antimony. [ 14 ]
Bismuth itself is largely non-toxic , although consuming too much of it can damage the liver. Only one person has ever been reported to have died from bismuth poisoning. [ 14 ] However, consumption of soluble bismuth salts can turn a person's gums black. [ 12 ]
Moscovium is too unstable to conduct any toxicity chemistry.
Nitrogen N Atomic Number: 7 Atomic Weight: 14.0067 Melting Point: 63.29 K Boiling Point: 77.36 K Specific mass: 0.0012506 g/cm 3 Electronegativity: 2.55
Phosphorus P Atomic Number: 15 Atomic Weight: 30.973762 Melting Point: 317.25 K Boiling Point: 553 K Specific mass: 1.82 g/cm 3 Electronegativity: 2.19
Arsenic As Atomic Number: 33 Atomic Weight: 74.92160 Melting Point: 1090.15 K Boiling Point: 887 K Specific mass: 5.776 g/cm 3 Electronegativity: 2.18
Antimony Sb Atomic Number: 51 Atomic Weight: 121.760 Melting Point: 904.05 K Boiling Point: 1860 K Specific mass: 6.685 g/cm 3 Electronegativity: 2.05
Bismuth Bi Atomic Number: 83 Atomic Weight: 208.98040 Melting Point: 544.67 K Boiling Point: 1837 K Specific mass: 9.807 g/cm 3 Electronegativity: 2.02
Moscovium Mc Atomic Number: 115 Atomic Weight: [289] Melting Point: ? 700 K Boiling Point: ? 1400 K Specific mass: ? 11 g/cm 3 Electronegativity: ? | https://en.wikipedia.org/wiki/Pnictogen |
In chemistry , a pnictogen bond ( PnB ) is a non-covalent interaction , occurring where there is a net attractive force between an electrophilic region on a 'donor' pnictogen atom (Pn) in a molecule, and a nucleophilic region on an 'acceptor' atom, which may be in the same or another molecule. [ 1 ] Closely related to halogen and chalcogen bonding , pnictogen bonds are a form of non-covalent interaction which can be considered in terms of charge-transfer and electrostatic interactions. [ 2 ]
Pnictogen bonds typically demonstrate directionality, with the interaction forming either on a linear projection to the R–Pn bond (a σ-hole ) or in a plane perpendicular to the three coplanar R–Pn bonds (a π-hole). [ 3 ] In such cases, polarisation of the pnictogen atom by an electron-withdrawing substituent, results in an anisotropic electron distribution in the Pn atom affording a directional electropositive region, resulting in an attractive electrostatic interaction. As the polarisability of an atom increases upon descending the periodic table, pnictogen bond strengths typically increase upon descending pnictogen group, both as a result of increased poliarisation resulting in a greater electrostatic contribution to bonding, but also through increased dispersion interactions between the heavier PnB donor and the PnB acceptor atom. [ 4 ]
Contributions to pnictogen bonding interactions can also arise through charge transfer interactions, in which a lone pair on the pnictogen bond acceptor are donated into a σ*-orbital on the pnictogen atom. Despite the charge transfer interaction, pnictogen bond interactions are non-covalent interactions , with X···Y bond lengths shorter than the sum of the van der Waals radii , but significantly longer than the sum of the covalent radii . [ 5 ]
The directionality of σ-hole interactions , including PnB interactions, has resulted in their exploitation within the field of supramolecular chemistry , incorporating PnB donor systems into a range of systems exploiting the formation of weak intermolecular interactions for a range of applications.
PnB donors have been demonstrated to be capable of functioning as Lewis acidic catalysts . [ 6 ] PnB catalysis was first reported in 2018 when PnB interactions were demonstrated to be potent catalysts for the Reissert reaction . [ 7 ] Given their intermediate position in the main group of the periodic table, PnB catalysis may be appealing due to a balance between steric repulsion and polarisability factors.
As for halogen and chalocogen bonding interactions, the σ-hole interactions in PnB hosts have been exploited for anion binding and recognition, with a report in 2022 exploiting a series of triaryl antinomy and bismuth receptors for binding of halide anions. [ 8 ] The reported systems demonstrated selectivity for chloride from other halies and over the binding of oxoanions , in contrast to trends observed for hydrogen bonding systems, suggesting PnB interactions may have advantages in selective halide anion sensing over hydrogen bonding systems.
PnB systems have also been shown to be capable of transmembrane anion transport, in which lipophilic organopnictogen compounds bind an anion through PnB interactions, enabling transport. [ 9 ] The redox activity of main group systems enables the tuning of transport, in which 'on/off' switchable behaviour is enabled between an inactive carrier and an reduced carrier. Park and Gabbaï have demonstrated such a system, in which reduction of an adjacent sulfonium enables the transmembrane transport of anions by an antimony transporter. [ 10 ] | https://en.wikipedia.org/wiki/Pnictogen_bond |
Phosphates are the naturally occurring form of the element phosphorus . [ 2 ]
In chemistry , a phosphate is an anion , salt , functional group or ester derived from a phosphoric acid . It most commonly means orthophosphate , a derivative of orthophosphoric acid, a.k.a. phosphoric acid H 3 PO 4 .
The phosphate or orthophosphate ion [PO 4 ] 3− is derived from phosphoric acid by the removal of three protons H + . Removal of one proton gives the dihydrogen phosphate ion [H 2 PO 4 ] − while removal of two protons gives the hydrogen phosphate ion [HPO 4 ] 2− . These names are also used for salts of those anions, such as ammonium dihydrogen phosphate and trisodium phosphate .
In organic chemistry , phosphate or orthophosphate is an organophosphate , an ester of orthophosphoric acid of the form PO 4 RR′R″ where one or more hydrogen atoms are replaced by organic groups. An example is trimethyl phosphate , (CH 3 ) 3 PO 4 . The term also refers to the trivalent functional group OP(O − ) 3 in such esters. Phosphates may contain sulfur in place of one or more oxygen atoms ( thiophosphates and organothiophosphates ).
Orthophosphates are especially important among the various phosphates because of their key roles in biochemistry , biogeochemistry , and ecology , and their economic importance for agriculture and industry. [ 2 ] The addition and removal of phosphate groups ( phosphorylation and dephosphorylation ) are key steps in cell metabolism .
Orthophosphates can condense to form pyrophosphates .
The phosphate ion has a molar mass of 94.97 g/mol, and consists of a central phosphorus atom surrounded by four oxygen atoms in a tetrahedral arrangement. It is the conjugate base of the hydrogen phosphate ion [HPO 4 ] 2− , which in turn is the conjugate base of the dihydrogen phosphate ion [H 2 PO 4 ] − , which in turn is the conjugate base of orthophosphoric acid , H 3 PO 4 .
Many phosphates are soluble in water at standard temperature and pressure . The sodium, potassium, rubidium , caesium , and ammonium phosphates are all water-soluble. Most other phosphates are only slightly soluble or are insoluble in water. As a rule, the hydrogen and dihydrogen phosphates are slightly more soluble than the corresponding phosphates.
In water solution, orthophosphoric acid and its three derived anions coexist according to the dissociation and recombination equilibria below [ 3 ]
Values are at 25 °C and 0 ionic strength.
The p K a values are the pH values where the concentration of each species is equal to that of its conjugate bases . At pH 1 or lower, the phosphoric acid is practically undissociated. Around pH 4.7 (mid-way between the first two p K a values) the dihydrogen phosphate ion, [H 2 PO 4 ] − , is practically the only species present. Around pH 9.8 (mid-way between the second and third p K a values) the monohydrogen phosphate ion, [HPO 4 ] 2− , is the only species present. At pH 13 or higher, the acid is completely dissociated as the phosphate ion, [PO 4 ] 3− .
This means that salts of the mono- and di-phosphate ions can be selectively crystallised from aqueous solution by setting the pH value to either 4.7 or 9.8.
In effect, H 3 PO 4 , [H 2 PO 4 ] − and [HPO 4 ] 2− behave as separate weak acids because the successive p K a differ by more than 4.
Phosphate can form many polymeric ions such as pyrophosphate , [P 2 O 7 ] 4− , and triphosphate , [P 3 O 10 ] 5− . The various metaphosphate ions (which are usually long linear polymers) have an empirical formula of [PO 3 ] − and are found in many compounds.
In biological systems , phosphorus can be found as free phosphate anions in solution ( inorganic phosphate ) or bound to organic molecules as various organophosphates . [ 5 ]
Inorganic phosphate is generally denoted P i and at physiological ( homeostatic ) pH primarily consists of a mixture of [HPO 4 ] 2− and [H 2 PO 4 ] − ions. At a neutral pH, as in the cytosol (pH = 7.0), the concentrations of the orthophoshoric acid and its three anions have the ratios [ H 2 PO 4 − ] [ H 3 PO 4 ] ≈ 7.5 × 10 4 [ HPO 4 2 − ] [ H 2 PO 4 − ] ≈ 0.62 [ PO 4 3 − ] [ HPO 4 2 − ] ≈ 2.14 × 10 − 6 {\displaystyle {\begin{aligned}{\frac {[{\ce {H2PO4-}}]}{[{\ce {H3PO4}}]}}&\approx 7.5\times 10^{4}\\[4pt]{\frac {[{\ce {HPO4^2-}}]}{[{\ce {H2PO4-}}]}}&\approx 0.62\\[4pt]{\frac {[{\ce {PO4^3-}}]}{[{\ce {HPO4^2-}}]}}&\approx 2.14\times 10^{-6}\end{aligned}}}
Thus, only the [H 2 PO 4 ] − and [HPO 4 ] 2− ions are present in significant amounts in the cytosol (62% [H 2 PO 4 ] − , 38% [HPO 4 ] 2− ). In extracellular fluid (pH = 7.4), this proportion is inverted (61% [HPO 4 ] 2− , 39% [H 2 PO 4 ] − ).
Inorganic phosphate can also be present as pyrophosphate anions [P 2 O 7 ] 4− , which give orthophosphate by hydrolysis :
Organic phosphates are commonly found in the form of esters as nucleotides (e.g. AMP , ADP , and ATP ) and in DNA and RNA . Free orthophosphate anions can be released by the hydrolysis of the phosphoanhydride bonds in ATP or ADP. These phosphorylation and dephosphorylation reactions are the immediate storage and source of energy for many metabolic processes. ATP and ADP are often referred to as high-energy phosphates , as are the phosphagens in muscle tissue. Similar reactions exist for the other nucleoside diphosphates and triphosphates .
An important occurrence of phosphates in biological systems is as the structural material of bone and teeth. These structures are made of crystalline calcium phosphate in the form of hydroxyapatite . The hard dense enamel of mammalian teeth may contain fluoroapatite , a hydroxy calcium phosphate where some of the hydroxyl groups have been replaced by fluoride ions.
Phosphates are medicinal salts of phosphorus. Some phosphates, which help cure many urinary tract infections , are used to make urine more acidic. To avoid the development of calcium stones in the urinary tract, some phosphates are used. [ 6 ] For patients who are unable to get enough phosphorus in their daily diet, phosphates are used as dietary supplements, usually because of certain disorders or diseases. [ 6 ] Injectable phosphates can only be handled by qualified health care providers. [ 6 ]
Plants take up phosphorus through several pathways: the arbuscular mycorrhizal pathway and the direct uptake pathway.
Hyperphosphatemia , or a high blood level of phosphates, is associated with elevated mortality in the general population. The most common cause of hyperphosphatemia in people, dogs, and cats is kidney failure. In cases of hyperphosphatemia, limiting consumption of phosphate-rich foods, such as some meats and dairy items and foods with a high phosphate-to-protein ratio, such as soft drinks, fast food, processed foods, condiments, and other products containing phosphate-salt additives is advised. [ 7 ]
Phosphates induce vascular calcification , and a high concentration of phosphates in blood was found to be a predictor of cardiovascular events . [ 8 ]
Phosphates are the naturally occurring form of the element phosphorus , found in many phosphate minerals . In mineralogy and geology, phosphate refers to a rock or ore containing phosphate ions. Inorganic phosphates are mined to obtain phosphorus for use in agriculture and industry. [ 2 ]
The largest global producer and exporter of phosphates is Morocco . Within North America, the largest deposits lie in the Bone Valley region of central Florida , the Soda Springs region of southeastern Idaho , and the coast of North Carolina . Smaller deposits are located in Montana , Tennessee , Georgia , and South Carolina . The small island nation of Nauru and its neighbor Banaba Island , which used to have massive phosphate deposits of the best quality, have been mined excessively. Rock phosphate can also be found in Egypt, Israel, Palestine, Western Sahara, Navassa Island , Tunisia, Togo, and Jordan, countries that have large phosphate-mining industries.
Phosphorite mines are primarily found in:
In 2007, at the current rate of consumption, the supply of phosphorus was estimated to run out in 345 years. [ 9 ] However, some scientists thought that a " peak phosphorus " would occur in 30 years and Dana Cordell from Institute for Sustainable Futures said that at "current rates, reserves will be depleted in the next 50 to 100 years". [ 10 ] Reserves refer to the amount assumed recoverable at current market prices. In 2012 the USGS estimated world reserves at 71 billion tons, while 0.19 billion tons were mined globally in 2011. [ 11 ] Phosphorus comprises 0.1% by mass of the average rock [ 12 ] (while, for perspective, its typical concentration in vegetation is 0.03% to 0.2%), [ 13 ] and consequently there are quadrillions of tons of phosphorus in Earth's 3×10 19 -ton crust, [ 14 ] albeit at predominantly lower concentration than the deposits counted as reserves, which are inventoried and cheaper to extract. If it is assumed that the phosphate minerals in phosphate rock are mainly hydroxyapatite and fluoroapatite, phosphate minerals contain roughly 18.5% phosphorus by weight. If phosphate rock contains around 20% of these minerals, the average phosphate rock has roughly 3.7% phosphorus by weight.
Some phosphate rock deposits, such as Mulberry in Florida, [ 15 ] are notable for their inclusion of significant quantities of radioactive uranium isotopes. This is a concern because radioactivity can be released into surface waters [ 16 ] from application of the resulting phosphate fertilizer .
In December 2012, Cominco Resources announced an updated JORC compliant resource of their Hinda project in Congo-Brazzaville of 531 million tons, making it the largest measured and indicated phosphate deposit in the world. [ 17 ]
Around 2018, Norway discovered phosphate deposits almost equal to those in the rest of Earth combined. [ 18 ] [ 19 ]
In July 2022 China announced quotas on phosphate exportation. [ 20 ]
The largest importers in millions of metric tons of phosphate are Brazil 3.2, India 2.9 and the USA 1.6. [ 21 ]
The three principal phosphate producer countries (China, Morocco and the United States) account for about 70% of world production.
In ecological terms, because of its important role in biological systems, phosphate is a highly sought after resource. Once used, it is often a limiting nutrient in environments , and its availability may govern the rate of growth of organisms. This is generally true of freshwater environments, whereas nitrogen is more often the limiting nutrient in marine (seawater) environments. Addition of high levels of phosphate to environments and to micro-environments in which it is typically rare can have significant ecological consequences. For example, blooms in the populations of some organisms at the expense of others, and the collapse of populations deprived of resources such as oxygen (see eutrophication ) can occur. In the context of pollution, phosphates are one component of total dissolved solids , a major indicator of water quality, but not all phosphorus is in a molecular form that algae can break down and consume. [ 23 ]
Calcium hydroxyapatite and calcite precipitates can be found around bacteria in alluvial topsoil. [ 24 ] As clay minerals promote biomineralization, the presence of bacteria and clay minerals resulted in calcium hydroxyapatite and calcite precipitates. [ 24 ]
Phosphate deposits can contain significant amounts of naturally occurring heavy metals. Mining operations processing phosphate rock can leave tailings piles containing elevated levels of cadmium , lead , nickel , copper , chromium , and uranium . Unless carefully managed, these waste products can leach heavy metals into groundwater or nearby estuaries. Uptake of these substances by plants and marine life can lead to concentration of toxic heavy metals in food products. [ 25 ] | https://en.wikipedia.org/wiki/Po4 |
Polonium dichloride is a chemical compound of the radioactive metalloid , polonium and chlorine . Its chemical formula is PoCl 2 . It is an ionic salt.
Polonium dichloride appears to crystallise with an orthorhombic unit cell in either the P 222, P mm2 or Pmmm space group , although this is likely a pseudo-cell. Alternatively, the true space group may be monoclinic or triclinic, with one or more cell angles close to 90°. [ 2 ] Assuming the space group is P 222, the structure exhibits distorted cubic coordination of Po as {PoCl 8 } and distorted square planar coordination of Cl as {ClPo 4 } .
PoCl 2 can be obtained either by halogenation of polonium metal or by dehalogenation of polonium tetrachloride , PoCl 4 . [ 1 ] Methods for dehalogenating PoCl 4 include thermal decomposition at 300 °C, reduction of cold, slightly moist PoCl 4 by sulfur dioxide ; and heating PoCl 4 in a stream of carbon monoxide or hydrogen sulfide at 150 °C. [ 2 ]
PoCl 2 dissolves in dilute hydrochloric acid to give a pink solution, which autoxidises to Po(IV). PoCl 2 is rapidly oxidised by hydrogen peroxide or chlorine water. Addition of potassium hydroxide to the pink solution results in a dark brown precipitate – possibly hydrated PoO or Po(OH) 2 – which is rapidly oxidised to Po(IV). With dilute nitric acid , PoCl 2 forms a dark red solution followed by a flaky white precipitate of unknown composition. [ 2 ] | https://en.wikipedia.org/wiki/PoCl2 |
Polonium hexafluoride ( PoF 6 ) is a possible chemical compound of polonium and fluorine and one of the seventeen known binary hexafluorides . [ 1 ]
The synthesis of PoF 6 via the reaction
was attempted in 1945, but the attempt was unsuccessful. The boiling point was predicted to be about −40 °C. [ 2 ]
208 PoF 6 was probably successfully synthesised via the same reaction in 1960 with the more stable isotope 208 Po , [ 1 ] : 594 where a volatile polonium fluoride was produced, [ 3 ] but it was not fully characterized before it underwent radiolysis and decomposed to polonium tetrafluoride . [ 4 ] [ 5 ] | https://en.wikipedia.org/wiki/PoF6 |
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