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P2000 is a one-way communications network for pagers based on Motorola 's FLEX-protocol in the Netherlands . The network is used by all emergency services and provides nationwide coverage. Several tests have shown the network can cope with the largest disasters when large numbers of emergency personnel need to be reached.
The P2000 network is maintained by the Ministry of the Interior and Kingdom Relations .
Messages are similar to SMS -messages. The FLEX-protocol does not provide encryption , which means any message can be read by everyone with a receiver. Several websites provide a live monitor for all messages on this network. | https://en.wikipedia.org/wiki/P2000_(network) |
Diphosphorus tetrafluoride is a gaseous compound of phosphorus and fluorine with formula P 2 F 4 . Two fluorine atoms are connected to each phosphorus atom, and there is a bond between the two phosphorus atoms. Phosphorus can be considered to have oxidation state +2, as indicated by the name phosphorus difluoride . [ 1 ]
Diphosphorus tetrafluoride was discovered in 1966 by Max Lustig, John K. Ruff and Charles B. Colburn at the Redstone Research Laboratories . The initial synthesis reacted phosphorus iododifluoride with mercury at room temperature: [ 2 ]
The P−P bond in diphosphorus tetrafluoride is much stronger than the corresponding N−N bond in dinitrogen tetrafluoride which easily breaks into nitrogen difluoride . [ 2 ] The infrared spectrum has absorption at 842 cm −1 , 830 cm −1 , 820 cm −1 , and weaker at 408 cm −1 and 356 cm −1 . [ 2 ] The molecule has C 2h symmetry. [ 3 ]
Under ultraviolet light diphosphorus tetrafluoride reacts with alkynes connected to trifluoromethyl groups to add difluorophosphino (- PF 2 ) groups on each side of a double bond. Other kinds of alkynes produced polymers with this treatment. [ 4 ] With alkenes , similarly bis(difluorophosphino) is added across the double bond. [ 5 ]
Diphosphorus tetrafluoride reacts with diborane to yield another gas P 2 F 4 ·BH 3 which does not condense above −85°C. This decomposes to yet another gas PF 3 ·BH 3 and a polymer with formula PF. [ 6 ]
Diphosphorus tetrafluoride reacts with oxygen or water to yield diphosphorus tetrafluoride oxide, which has one oxygen atom inserted between the two phosphorus atoms: [ 2 ] [ 7 ]
The latter compound is a gas with boiling point around −18 °C. | https://en.wikipedia.org/wiki/P2F4 |
Diphosphene is a compound having the formula (PH) 2 . It exists as two geometric isomers , E and Z . [ 1 ] Diphosphene is also the parent member of the entire class of diphosphene compounds with the formula (PR) 2 , where R is an organyl group. [ 2 ]
Visible radiation induces cis-trans isomerization, [ 3 ] although further irradiation can excite the molecule to a triplet diradical state. In triplet trans-HPPH, the P-P bond length is predicted to be 2.291 Å. It is not only longer than the P-P double bond in ground state trans-bis(2,4,6-tri-tert-butylphenyl)diphosphene, but also longer than that of P-P single bond in H 2 P−PH 2 . Calculation of the dihedral angle of trans-HPPH suggests that it is almost 90 degree, which means the formation of π {\displaystyle \pi } and π ∗ {\displaystyle \pi ^{*}} P-P bonds is forbidden and σ bond is enhanced. [ 4 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/P2H2 |
Diphosphane , or diphosphine , is an inorganic compound with the chemical formula P 2 H 4 . This colourless liquid is one of several binary phosphorus hydrides. It is the impurity that typically causes samples of phosphine to ignite in air.
Diphosphane adopts the gauche conformation (like hydrazine , less symmetrical than shown in the image) with a P−P distance of 2.219 angstroms . It is nonbasic, unstable at room temperature, and spontaneously flammable in air . It is only poorly soluble in water but dissolves in organic solvents. Its 1 H NMR spectrum consists of 32 lines resulting from an A 2 XX'A' 2 splitting system. [ 1 ]
Diphosphane is produced by the hydrolysis of calcium monophosphide , which can be described as the Ca 2+ derivative of P 4− 2 . According to an optimized procedure, hydrolysis of 400 g of CaP at −30 °C gives about 20 g of product, slightly contaminated with phosphine .
Reaction of diphosphane with butyllithium affords a variety of condensed polyphosphine compounds.
A variety of organic derivatives of diphosphane are known, but asymmetric diphosphanes are only stable at cryogenic temperatures. Otherwise, the substituents facily redistribute on the phosphorus centers to give a mixture of products. On the other hand, there appears to be a substantial barrier to chiral inversion . [ 2 ]
The central bond is weak, and easily adds substituents. [ 3 ]
The simplest synthesis method heats a phosphorus halide and a phosphane:
Alkali metals can replace the hydrogen in that reaction (i.e., a dialkyl phosphide ), and in some rare cases a dialkylamine can replace the halide. Symmetric diphosphanes are easily prepared by reductive coupling, e.g. tetraphenyldiphosphine from chlorodiphenylphosphine :
Ultraviolet radiation decomposes mercury(II) dialkylphosphides to the metal and a dialkylphosphane. [ 4 ]
The methyl compound P 2 Me 4 is prepared by the reduction of Me 2 P(S)−P(S)Me 2 , which is produced by methylation of thiophosphoryl chloride with methylmagnesium bromide. [ 5 ] | https://en.wikipedia.org/wiki/P2H4 |
Diphosphorus tetraiodide is an orange crystalline solid with the formula P 2 I 4 >. It has been used as a reducing agent in organic chemistry. It is a rare example of a compound with phosphorus in the +2 oxidation state, and can be classified as a subhalide of phosphorus. It is the most stable of the diphosphorus tetrahalides. [ 1 ]
Diphosphorus tetraiodide is easily generated by the disproportionation of phosphorus triiodide in dry ether :
It can also be obtained by treating phosphorus trichloride and potassium iodide in anhydrous conditions. [ 2 ]
Another synthesis route involves combining phosphonium iodide with iodine in a solution of carbon disulfide . An advantage of this route is that the resulting product is virtually free of impurities. [ 3 ]
The compound adopts a centrosymmetric structure with a P-P bond of 2.230 Å. [ 4 ]
Diphosphorus tetraiodide reacts with bromine to form mixtures PI 3−n Br n . With sulfur, it is oxidized to P 2 S 2 I 4 , retaining the P-P bond. [ 1 ] It reacts with elemental phosphorus and water to make phosphonium iodide, which is collected via sublimation at 80 °C. [ 3 ]
Diphosphorus tetraiodide is used in organic synthesis mainly as a deoxygenating agent. [ 5 ] It is used for deprotecting acetals and ketals to aldehydes and ketones , and for converting epoxides into alkenes and aldoximes into nitriles. It can also cyclize 2-aminoalcohols to aziridines [ 6 ] and to convert α,β-unsaturated carboxylic acids to α,β-unsaturated bromides . [ 7 ]
As foreshadowed by the work of Bertholet in 1855, diphosphorus tetraiodide can convert glycols to trans alkenes . [ 5 ] [ 8 ] This reaction is known as the Kuhn–Winterstein reaction, after the chemists who applied it to the production of polyene chromophores . [ 5 ] [ 9 ] | https://en.wikipedia.org/wiki/P2I4 |
Phosphorus trioxide is the chemical compound with the molecular formula P 4 O 6 . Although the molecular formula suggests the name tetraphosphorus hexoxide, the name phosphorus trioxide preceded the knowledge of the compound's molecular structure, and its usage continues today. This colorless solid is structurally related to adamantane . It is formally the anhydride of phosphorous acid , H 3 PO 3 , but cannot be obtained by the dehydration of the acid. A white solid that melts at room temperature, it is waxy, crystalline and highly toxic, with garlic odor. [ 1 ]
It is obtained by the combustion of phosphorus in a limited supply of air at low temperatures.
By-products include red phosphorus suboxide. [ 1 ]
Phosphorus trioxide reacts with water to form phosphorous acid , reflecting the fact that it is the anhydride of that acid. [ 2 ]
It reacts with hydrogen chloride to form H 3 PO 3 and phosphorus trichloride .
With chlorine or bromine it forms the corresponding phosphoryl halide , and it reacts with iodine in a sealed tube to form diphosphorus tetraiodide . [ 1 ]
P 4 O 6 reacts with ozone at 195 K to give the unstable compound P 4 O 18 . [ 3 ]
P 4 O 18 decomposes above 238 K in solution with the release of O 2 gas. Decomposition of dry P 4 O 18 is explosive.
In a disproportionation reaction , P 4 O 6 is converted into the mixed P(III)P(V) species P 4 O 8 when heated in a sealed tube at 710 K, with the side product being red phosphorus. [ 3 ]
P 4 O 6 is a ligand for transition metals, comparable to phosphite . An illustrative complex is P 4 O 6 ·Fe(CO) 4 . [ 4 ] With BH 3 , a dimeric adduct is produced: [ 3 ] | https://en.wikipedia.org/wiki/P2O3 |
Difluorophosphate or difluorodioxophosphate or phosphorodifluoridate is an anion with formula PO 2 F − 2 . It has a single negative charge and resembles perchlorate ( ClO − 4 ) and monofluorosulfonate ( SO 3 F − ) in shape and compounds. [ 2 ] These ions are isoelectronic , along with tetrafluoroaluminate, phosphate , orthosilicate , and sulfate . [ 2 ] [ 3 ] It forms a series of compounds. The ion is toxic to mammals as it causes blockage to iodine uptake in the thyroid. However it is degraded in the body over several hours. [ 2 ]
Compounds containing difluorophosphate may have it as a simple uninegative ion, it may function as a difluorophosphato ligand where it is covalently bound to one or two metal atoms, or go on to form a networked solid. [ 4 ] It may be covalently bound to a non metal or an organic moiety to make an ester or an amide.
Ammonium difluorophosphate ( [NH 4 ]PO 2 F 2 ) is formed from treating phosphorus pentoxide with ammonium fluoride . [ 2 ] This was how the ion was first made by its discoverer, Willy Lange , in 1929. [ 3 ] [ 5 ]
Alkali metal chlorides can react with dry difluorophosphoric acid to form alkali metal salts . [ 6 ]
Fluorination of dichlorophosphates can produce difluorophosphates. [ 7 ] Another method is fluorination of phosphates or polyphosphates . [ 5 ]
Trimethylsilyl difluorophosphate ( (CH 3 ) 3 Si−O−P(=O)F 2 ) reacts with metal chlorides to give difluorophosphates. [ 8 ]
The anhydride of difluorophosphoric acid ( HPO 2 F 2 ), phosphoryl difluoride oxide ( P 2 O 3 F 4 ) reacts with oxides such as UO 3 to yield difuorophosphates. [ 9 ] Phosphoryl difluoride oxide also reacts with alkali metal fluorides to yield difluorophosphates. [ 10 ]
The difluorophosphate ion in ammonium difluorophosphate and potassium difluorophosphate has these interatomic dimensions: [ 11 ]
Hydrogen bonding from ammonium ion to oxygen atoms causes a change to the difluorophosphate ion in the ammonium salt . [ 11 ]
On heating the salts that are not of alkali metals or alkaline earth metals , difluorophosphates decompose firstly by giving off POF 3 forming a monofluorophosphate ( PO 3 F 2− ) compound, and then this in turn decomposes to an orthophosphate PO 3− 4 compound. [ 12 ] [ 13 ]
Difluorophosphate salts are normally soluble and stable in water . However, in acidic or alkaline conditions they can be hydrolyzed to monofluorophosphates and hydrofluoric acid . [ 14 ] The caesium and potassium salts are the least soluble . [ 14 ]
Irradiating potassium difluorophosphate with gamma rays can make the free radicals •PO 2 F − , •PO 3 F − and •PO 2 F 2 . [ 15 ] [ 16 ]
Difluorophosphoric acid ( HPO 2 F 2 ) is one of the fluorophosphoric acids. It is produced when phosphoryl fluoride reacts with water:
This in turn is hydrolysed more to give monofluorophosphoric acid ( H 2 PO 3 F ), and a trace of hexafluorophosphoric acid ( HPF 6 ). HPO 2 F 2 also is produced when HF reacts with phosphorus pentoxide . Yet another method involves making difluorphosphoric acid as a side product of calcium fluoride being heated with damp phosphorus pentoxide. A method to make pure difluorphosphoric acid involves heating phosphoryl fluoride with monofluorophosphoric acid and separating the product by distillation: [ 42 ]
Difluorophosphoric acid can also be produced by fluorinating phosphorus oxychlorides. P 2 O 3 Cl 4 and POCl 3 react with hydrogen fluoride solution to yield HPO 2 Cl 2 and then HPO 2 F 2 . [ 43 ] Yet another way is to treat orthophosphate ( PO 3− 4 ) with fluorosulfuric acid ( HSO 3 F ). [ 44 ]
Difluorphosphoric acid is a colorless liquid. It melts at −96.5 °C (−141.7 °F) and boils at 115.9 °C (240.6 °F). Its density at 25 °C is 1.583 g/cm 3 . [ 14 ]
Difluorophosphoric acid anhydride also known as phosphoryl difluoride oxide or diphosphoryl tetrafluoride ( F 2 (O=)P−O−P(=O)F 2 or P 2 O 3 F 4 ) is an anhydride of difluorphosphoric acid. It crystallises in the orthorhombic system, with space group Pcca and Z = 4. [ 45 ] P 2 O 3 F 4 can be made by refluxing difluorophosphoric acid with phosphorus pentoxide . P 2 O 3 F 4 boils at 71 °C. [ 46 ]
In addition to the isoelectronic series, ions related by substituting fluorine or oxygen by other elements include monofluorophosphate , difluorothiophosphate , dichlorothiophosphate , dichlorophosphate , chlorofluorothiophosphate , chlorofluorophosphate , dibromophosphate , and bromofluorophosphate . [ 47 ]
Difluorophosphate can form adducts with PF 5 and AsF 5 . In these the oxygen atoms form a donor-acceptor link between the P and As (or P) atoms, linking the difluorides to the pentafluorides. Example salts include KPO 2 F 2 ·2AsF 5 , KPO 2 F 2 ·AsF 5 , KPO 2 F 2 ·2PF 5 and KPO 2 F 2 ·PF 5 . [ 48 ]
Amines can react with phosphoryl fluoride to make substances with a formula RR′N−P(=O)F 2 . The amines shown to do this include ethylamine , isopropylamine , n -butylamine , t -butylamine , dimethylamine , and diethylamine . The monoamines can further react to yield an alkyliminophosphoric fluoride ( R−N=P(=O)F ). [ 49 ] | https://en.wikipedia.org/wiki/P2O3F4 |
Diphosphorus tetroxide , or phosphorus tetroxide is an inorganic compound of phosphorus and oxygen . It has the empirical chemical formula P 2 O 4 . Solid phosphorus tetroxide (also referred to as phosphorus(III,V)-oxide) consists of variable mixtures of the mixed-valence oxides P 4 O 7 , P 4 O 8 and P 4 O 9 . [ 1 ] [ 2 ] [ 3 ]
Phosphorus tetroxide can be produced by thermal decomposition of phosphorus trioxide , which disproportionates above 210 °C to form phosphorus tetroxide, with elemental phosphorus as a byproduct:
In addition, phosphorus trioxide can be converted into phosphorus tetroxide by controlled oxidation with oxygen in carbon tetrachloride solution. [ 4 ] [ 5 ] [ 6 ]
Careful reduction of phosphorus pentoxide with red phosphorus at 450-525 °C also produces phosphorus tetroxide. | https://en.wikipedia.org/wiki/P2O4 |
Phosphorus pentoxide is a chemical compound with molecular formula P 4 O 10 (with its common name derived from its empirical formula , P 2 O 5 ). This white crystalline solid is the anhydride of phosphoric acid . It is a powerful desiccant and dehydrating agent .
Phosphorus pentoxide crystallizes in at least four forms or polymorphs . The most familiar one, a metastable form [ 1 ] (shown in the figure), comprises molecules of P 4 O 10 . Weak van der Waals forces hold these molecules together in a hexagonal lattice (However, in spite of the high symmetry of the molecules, the crystal packing is not a close packing [ 2 ] ). The structure of the P 4 O 10 cage is reminiscent of adamantane with T d symmetry point group . [ 3 ] It is closely related to the corresponding anhydride of phosphorous acid , P 4 O 6 . The latter lacks terminal oxo groups. Its density is 2.30 g/cm 3 . It boils at 423 °C under atmospheric pressure; if heated more rapidly it can sublimate. This form can be made by condensing the vapor of phosphorus pentoxide rapidly, and the result is an extremely hygroscopic solid. [ 4 ]
The other polymorphs are polymeric, but in each case the phosphorus atoms are bound by a tetrahedron of oxygen atoms, one of which forms a terminal P=O bond involving the donation of the terminal oxygen p-orbital electrons to the antibonding phosphorus-oxygen single bonds. The macromolecular form can be made by heating the compound in a sealed tube for several hours, and maintaining the melt at a high temperature before cooling the melt to the solid. [ 4 ] The metastable orthorhombic "O"-form (density 2.72 g/cm 3 , melting point 562 °C) adopts a layered structure consisting of interconnected P 6 O 6 rings, not unlike the structure adopted by certain poly silicates . The stable form is a higher density phase, also orthorhombic, the so-called O' form. It consists of a 3-dimensional framework, density 3.5 g/cm 3 . [ 1 ] [ 5 ] The remaining polymorph is a glass or amorphous form; it can be made by fusing any of the others.
P 4 O 10 is prepared by burning white phosphorus with a sufficient supply of oxygen: [ 6 ]
The dehydration of phosphoric acid to give phosphorus pentoxide is not possible, as on heating it forms various polyphosphates but will not dehydrate sufficiently to form P 4 O 10 .
Phosphorus pentoxide is a potent dehydrating agent as indicated by the exothermic nature of its hydrolysis producing phosphoric acid :
However, its utility for drying is limited somewhat by its tendency to form a protective viscous coating that inhibits further dehydration by unspent material. A granular form of P 4 O 10 is used in desiccators .
Consistent with its strong desiccating power, P 4 O 10 is used in organic synthesis for dehydration. The most important application is for the conversion of primary amides into nitriles : [ 7 ]
The indicated coproduct P 4 O 9 (OH) 2 is an idealized formula for undefined products resulting from the hydration of P 4 O 10 .
Alternatively, when combined with a carboxylic acid , the result is the corresponding anhydride : [ 8 ]
The "Onodera reagent", a solution of P 4 O 10 in DMSO , is employed for the oxidation of alcohols . [ 9 ] This reaction is reminiscent of the Swern oxidation .
The desiccating power of P 4 O 10 is strong enough to convert many mineral acids to their anhydrides. Examples: HNO 3 is converted to N 2 O 5 ; H 2 SO 4 is converted to SO 3 ; HClO 4 is converted to Cl 2 O 7 ; CF 3 SO 3 H is converted to (CF 3 ) 2 S 2 O 5 .
P 2 O 5 content is often used by industry as proxy value for all the phosphorus oxides in a material. For example, fertilizer grade phosphoric acid can also contain various related phosphorous compounds which are also of use. All these compounds are described collectively in terms of ' P 2 O 5 content' to allow convenient comparison of the phosphorous content of different products. Despite this, phosphorus pentoxide is not actually present in most samples as it is not stable in aqueous solutions.
Phosphorus pentoxide itself is not flammable. Just like sulfur trioxide , it reacts vigorously with water and water-containing substances like wood or cotton, liberates much heat and may even cause fire due to the highly exothermic nature of such reactions. It is corrosive to metal and is very irritating – it may cause severe burns to the eye, skin, mucous membrane , and respiratory tract even at concentrations as low as 1 mg/m 3 . [ 10 ] | https://en.wikipedia.org/wiki/P2O5 |
In chemistry , pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a P−O−P linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate ( Na 2 H 2 P 2 O 7 ) and tetrasodium pyrophosphate ( Na 4 P 2 O 7 ), among others. Often pyrophosphates are called diphosphates . The parent pyrophosphates are derived from partial or complete neutralization of pyrophosphoric acid . The pyrophosphate bond is also sometimes referred to as a phosphoanhydride bond, a naming convention which emphasizes the loss of water that occurs when two phosphates form a new P−O−P bond, and which mirrors the nomenclature for anhydrides of carboxylic acids . Pyrophosphates are found in ATP and other nucleotide triphosphates, which are important in biochemistry. The term pyrophosphate is also the name of esters formed by the condensation of a phosphorylated biological compound with inorganic phosphate , as for dimethylallyl pyrophosphate . This bond is also referred to as a high-energy phosphate bond.
Pyrophosphoric acid is a tetraprotic acid, with four distinct p K a 's: [ 1 ]
The pKa's occur in two distinct ranges because deprotonations occur on separate phosphate groups. For comparison with the p K a s for phosphoric acid are 2.14, 7.20, and 12.37.
At physiological pHs , pyrophosphate exists as a mixture of doubly and singly protonated forms.
Disodium pyrophosphate is prepared by thermal condensation of sodium dihydrogen phosphate or by partial deprotonation of pyrophosphoric acid. [ 2 ]
Pyrophosphates are generally white or colorless. The alkali metal salts are water-soluble. [ 3 ] They are good complexing agents for metal ions (such as calcium and many transition metals) and have many uses in industrial chemistry. Pyrophosphate is the first member of an entire series of polyphosphates . [ 4 ]
The anion P 2 O 4− 7 is abbreviated PP i , standing for i norganic p yro p hosphate . It is formed by the hydrolysis of ATP into AMP in cells .
For example, when a nucleotide is incorporated into a growing DNA or RNA strand by a polymerase , pyrophosphate (PP i ) is released. Pyrophosphorolysis is the reverse of the polymerization reaction in which pyrophosphate reacts with the 3′-nucleosidemonophosphate ( NMP or dNMP), which is removed from the oligonucleotide to release the corresponding triphosphate ( dNTP from DNA, or NTP from RNA).
The pyrophosphate anion has the structure P 2 O 4− 7 , and is an acid anhydride of phosphate . It is unstable in aqueous solution and hydrolyzes into inorganic phosphate:
or in biologists' shorthand notation:
In the absence of enzymic catalysis, hydrolysis reactions of simple polyphosphates such as pyrophosphate, linear triphosphate, ADP , and ATP normally proceed extremely slowly in all but highly acidic media. [ 5 ]
(The reverse of this reaction is a method of preparing pyrophosphates by heating phosphates.)
This hydrolysis to inorganic phosphate effectively renders the cleavage of ATP to AMP and PP i irreversible , and biochemical reactions coupled to this hydrolysis are irreversible as well.
PP i occurs in synovial fluid , blood plasma , and urine at levels sufficient to block calcification and may be a natural inhibitor of hydroxyapatite formation in extracellular fluid (ECF). [ 6 ] Cells may channel intracellular PP i into ECF. [ 7 ] ANK is a nonenzymatic plasma-membrane PP i channel that supports extracellular PP i levels. [ 7 ] Defective function of the membrane PP i channel ANK is associated with low extracellular PP i and elevated intracellular PP i . [ 6 ] Ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) may function to raise extracellular PP i . [ 7 ]
From the standpoint of high energy phosphate accounting, the hydrolysis of ATP to AMP and PP i requires two high-energy phosphates, as to reconstitute AMP into ATP requires two phosphorylation reactions.
The plasma concentration of inorganic pyrophosphate has a reference range of 0.58–3.78 μM (95% prediction interval). [ 8 ]
Isopentenyl pyrophosphate converts to geranyl pyrophosphate , the precursor to tens of thousands of terpeness and terpenoids . [ 9 ] [ 10 ]
Various diphosphates are used as emulsifiers , stabilisers , acidity regulators , raising agents , sequestrants , and water retention agents in food processing. [ 11 ] They are classified in the E number scheme under E450: [ 12 ]
In particular, various formulations of diphosphates are used to stabilize whipped cream . [ 13 ] | https://en.wikipedia.org/wiki/P2O7 |
Diphosphorus trisulfide (sometimes called phosphorus trisulfide) is a phosphorus sulfide with the formula of P 2 S 3 . The substance is highly unstable and difficult to study. [ 3 ] In contrast, the formal dimer P 4 S 6 is well-known.
Early reports that diphosphorous trisulfide could be formed by heating red phosphorus and sulfur were shown to be incorrect by Helff in 1893. Its existence was again reported by Ralston and Wilkinson in 1928. In 1959, Pitochelli and Audrieth showed that the substance existed by X-ray diffraction but did not succeed in fully isolating it. [ 4 ] In 1997, Lohr and Sundholm published a theoretical analysis of the potential structures of this molecular substance. [ 5 ]
In 2017, Xiao proposed that a 2D crystallisation of P 2 S 3 was possible based on computer simulations. Xiao suggested that nanoribbons and nanotubes of the material may have applications in semiconductor electronics . [ 6 ]
P 2 S 3 is highly flammable . The solid may spontaneously ignite with moist air or in contact with water . Produces phosphoric acid and hydrogen sulfide , a toxic flammable gas in reaction with water. P 2 S 3 is a strong reducing agent . Reacts vigorously with oxidizing agents , including inorganic oxoacids , organic peroxides and epoxides . Produce acidic and corrosive phosphorus pentoxide and sulfur dioxide when burned. [ 7 ] | https://en.wikipedia.org/wiki/P2S3 |
Phosphorus pentasulfide is the inorganic compound with the formula P 2 S 5 ( empirical ) or P 4 S 10 ( molecular ). This yellow solid is the one of two phosphorus sulfides of commercial value. Samples often appear greenish-gray due to impurities. It is soluble in carbon disulfide but reacts with many other solvents such as alcohols , DMSO , and DMF . [ 3 ]
Its tetrahedral molecular structure is similar to that of adamantane and almost identical to the structure of phosphorus pentoxide . [ 4 ]
Phosphorus pentasulfide is obtained by the reaction of liquid white phosphorus ( P 4 ) with sulfur above 300 °C. The first synthesis of P 4 S 10 by Berzelius in 1843 [ 5 ] was by this method. Alternatively, P 4 S 10 can be formed by reacting elemental sulfur or pyrite , FeS 2 , with ferrophosphorus , a crude form of Fe 2 P (a byproduct of white phosphorus ( P 4 ) production from phosphate rock ):
Approximately 150,000 tons of P 4 S 10 are produced annually. The compound is mainly converted to other derivatives for use as lubrication additives such as zinc dithiophosphates .
It is widely used in the production of sodium dithiophosphate for applications as a flotation agent in the concentration of molybdenite minerals. It is also used in the production of pesticides such as Parathion and Malathion . [ 6 ] It is also a component of some amorphous solid electrolytes (e.g. Li 2 S - P 2 S 5 ) for some types of lithium batteries .
Phosphorus pentasulfide is a dual-use material, for the production of early insecticides such as Amiton and also for the manufacture of the related VX nerve agents .
Phosphorus pentasulfide reacts with ethanol to give diethyl dithiophosphoric acid : [ 7 ]
diorganodithiophosphoric acids are used to produce metal dithiophosphates .
Due to hydrolysis by atmospheric moisture, P 4 S 10 evolves hydrogen sulfide H 2 S , thus P 4 S 10 is associated with a rotten egg odour. Aside from H 2 S , hydrolysis of P 4 S 10 eventually gives phosphoric acid :
Other mild nucleophiles react with P 4 S 10 , including alcohols and amines . Reaction with ammonium chloride gives the polymeric (SPN) ∞ . [ 8 ] Aromatic compounds such as anisole , ferrocene and 1-methoxynaphthalene react to form 1,3,2,4-dithiadiphosphetane 2,4-disulfides such as Lawesson's reagent :
P 4 S 10 is used as a thionation reagent. Reactions of this type require refluxing solvents such as benzene , dioxane , or acetonitrile with P 4 S 10 dissociating into P 2 S 5 . Some ketones , esters , and imides are converted to the corresponding thiocarbonyls . Amides give thioamides . With 1,4-diketones the reagent forms thiophenes . It is also used to deoxygenate sulfoxides . The use of P 4 S 10 has been displaced by the aforementioned Lawesson's reagent . [ 9 ]
P 4 S 10 reacts with pyridine to form the complex P 2 S 5 (pyridine) 2 . [ 10 ] | https://en.wikipedia.org/wiki/P2S5 |
Phosphorus selenides are a relatively obscure group of compounds. There have been some studies of the phosphorus - selenium phase diagram and the glassy amorphous phases are reported. The compounds that have been reported are shown below. While some of phosphorus selenides are similar to their sulfide analogues , there are some new forms, molecular P 2 Se 5 and the polymeric catena - [P 4 Se 4 ] x . There is also some doubt about the existence of molecular P 4 Se 10 .
Molecular P 2 Se 5 has a norbornane like structure with two phosphorus atoms with oxidation state +3 bridged by two diselenide units ( −Se−Se− , analogous to disulfide ) and one selenide unit ( −Se− ). [ 1 ] It was isolated by solvent ( CS 2 ) extraction from a P 2 Se 5 amorphous phase made from the elements. [ 2 ]
P 4 Se 3 has been characterised crystallographically and has the same structure as the low temperature form of P 4 S 3 . [ 3 ] It can be prepared from the elements. One preparation is to extract and recrystallise using tetralin .
The P 4 Se 5 molecule has the same structure as P 4 S 5 . [ 4 ] It was prepared by reacting P 4 Se 3 with bromine in CS 2 .
This compound consists of polymeric chains of norbornane -like units joined by Se atoms. [ 5 ] As each P atom in the repeat unit is bonded to another P atom and to two Se atoms, each P atom has a formal oxidation state of +2.
P 4 Se 4 has two crystalline forms α- P 4 Se 4 with the same molecular structure as α- P 4 S 4 and β- P 4 Se 4 with same molecular structure as β- P 4 S 4 . [ 6 ] A fully characterised compound (CuI) 3 P 4 Se 4 contains P 4 Se 4 with a β- P 4 S 4 structure. [ 7 ]
This has been reported to have the same structure as P 4 S 7 . [ 8 ] [ 9 ] One well-known textbook does not mention it at all. [ 10 ]
Molecular P 4 Se 10 has been reported to share the same structure as P 4 S 10 and P 4 O 10 , [ 8 ] [ 9 ] [ 11 ] but one well-known textbook does not mention it at all. [ 10 ] A review (2001) examining P-Se amorphous phases did not confirm the presence of molecular P 4 Se 10 . [ 12 ] The isoelectronic anion [Ge 4 Se 10 ] 4− which has the adamantane like P 4 O 10 structure is known, an example is the sodium salt Na 4 [Ge 4 Se 10 ] . [ 13 ]
P 4 Se 6 , P 14 Se, P 4 Se, P 4 Se 2 , P 2 Se , have been reported. [ 8 ]
Phosphorus - selenium glasses have been examined using 31 P-NMR and Raman spectroscopy. Glasses are formed in P x Se 1− x over the range of compositions 0 < x < 0.8 with a small window around 0.52 – 0.60 centred on 0.57 (corresponding to the compound P 4 Se 3 ) where there is a tendency to crystallise. For x < 0.47 the glasses contain Se n chain fragments, pyramidal P units (P oxidation state +3), quasi-tetrahedral P units (P oxidation state +5, with P=Se double bond ) and P 2 units (P in formal oxidation state +4). There is no evidence for an amorphous phase containing molecular P 4 Se 10 . [ 12 ] | https://en.wikipedia.org/wiki/P2Se5 |
P2 receptor may refer to:
Nucleotides , if released into the extracellular environment, can lead to cell death or other harmful cellular consequences. To avoid cellular damage, nucleotides should be neutralized, which is accomplished by P2 receptors. Almost every cell type expresses P2 receptors. Purinergic signalling also has a pathophysiological role in several immune cells including calcium mobilization, actin polymerization, chemotaxis, the release of mediators, cell maturation, cytotoxicity, and cell death etc. [ 1 ]
Depending on the nature of the receptor they are found to be of two types:
P is for purinergic, P2 refers to ATP receptors, as opposed to P1 adenosine adenosine receptors . P2X receptors are ATP activated channels that allow the passage of ions across cell membranes. P2Y receptors are ATP activated G protein-coupled receptors (GPCRs) that initiate an intracellular chain of reactions.
Extracellular ATP and the related purine and pyrimidine nucleotides exert their functions via signalling through membrane-bound purinergic P2 receptors. These receptors are widely expressed throughout the body on various immune and nonimmune cells. [ 1 ] P2X receptors are ionotropic receptors while P2Y are GPCR type receptors. P2X receptor family encompasses 7 genes. P2Y family has 8 receptors that can be divided into two sub-families depending upon the structural similarity. P2X receptors are activated with ATP while P2Y receptors are activated by diphosphates, triphosphates, purines, pyrimidines, etc. [ 2 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/P2_receptor |
Particle–Particle–Particle–Mesh ( P 3 M ) is a Fourier-based Ewald summation method [ 1 ] [ 2 ] to calculate potentials in N-body simulations . [ 3 ] [ 4 ] [ 5 ]
The potential could be the electrostatic potential among N point charges i.e. molecular dynamics , the gravitational potential among N gas particles in e.g. smoothed particle hydrodynamics , or any other useful function. It is based on the particle mesh method, where particles are interpolated onto a grid, and the potential is solved for this grid (e.g. by solving the discrete Poisson equation ). This interpolation introduces errors in the force calculation, particularly for particles that are close together. Essentially, the particles are forced to have a lower spatial resolution during the force calculation. The P 3 M algorithm attempts to remedy this by calculating the potential through a direct sum for particles that are close, and through the particle mesh method for particles that are separated by some distance.
This computational physics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/P3M |
Triphosphorus pentanitride is an inorganic compound with the chemical formula P 3 N 5 . Containing only phosphorus and nitrogen , this material is classified as a binary nitride . While it has been investigated for various applications this has not led to any significant industrial uses. It is a white solid, although samples often appear colored owing to impurities.
Triphosphorus pentanitride can be produced by reactions between various phosphorus (V) and nitrogen anions (such as ammonia and sodium azide ): [ 1 ]
The reaction of the elements is claimed to produce a related material. [ 2 ] Similar methods are used to prepared boron nitride (BN) and silicon nitride ( Si 3 N 4 ); however the products are generally impure and amorphous . [ 1 ] [ 3 ]
Crystalline samples have been produced by the reaction of ammonium chloride and hexachlorocyclotriphosphazene [ 4 ] or phosphorus pentachloride . [ 1 ]
P 3 N 5 has also been prepared at room temperature, by a reaction between phosphorus trichloride and sodium amide . [ 5 ]
P 3 N 5 is thermally less stable than either BN or Si 3 N 4 , with decomposition to the elements occurring at temperatures above 850 °C: [ 1 ]
It is resistant to weak acids and bases, and insoluble in water at room temperature, however it hydrolyzes upon heating to form the ammonium phosphate salts [NH 4 ] 2 HPO 4 and [NH 4 ]H 2 PO 4 .
Triphosphorus pentanitride reacts with lithium nitride and calcium nitride to form the corresponding salts of PN 7− 4 and PN 4− 3 . Heterogenous ammonolyses of triphosphorus pentanitride gives imides such as HPN 2 and HP 4 N 7 . It has been suggested that these compounds may have applications as solid electrolytes and pigments . [ 6 ]
Several polymorphs are known for triphosphorus pentanitride. The alpha‑form of triphosphorus pentanitride (α‑ P 3 N 5 ) is encountered at atmospheric pressure and exists at pressures up to 11 GPa , at which point it converts to the gamma‑variety (γ‑ P 3 N 5 ) of the compound. [ 7 ] [ 8 ] Upon heating γ‑ P 3 N 5 to temperatures above 2000 K at pressures between 67 and 70 GPa, it transforms into δ- P 3 N 5 . [ 9 ] The release of pressure on the δ- P 3 N 5 polymorph does not revert it back into γ‑ P 3 N 5 or α‑ P 3 N 5 . Instead, at pressures below 7 GPa, δ- P 3 N 5 converts into a fourth form of triphosphorus pentanitride, α′‑ P 3 N 5 . [ 9 ]
The structure of all polymorphs of triphosphorus pentanitride was determined by single crystal X-ray diffraction . α‑ P 3 N 5 and α′‑ P 3 N 5 are formed of a network structure of PN 4 tetrahedra with 2- and 3-coordinated nitrides, [ 7 ] [ 9 ] γ‑ P 3 N 5 is composed of both PN 4 and PN 5 polyhedra [ 8 ] while δ- P 3 N 5 is composed exclusively of corner- and edge-sharing PN 6 octahedra. [ 9 ] δ- P 3 N 5 is the most incompressible triphosphorus pentanitride, having a bulk modulus of 313 GPa. [ 9 ]
Triphosphorus pentanitride has no commercial applications, although it found use as a gettering material for incandescent lamps , replacing various mixtures containing red phosphorus in the late 1960s. The lighting filaments are dipped into a suspension of P 3 N 5 prior to being sealed into the bulb. After bulb closure, but while still on the pump, the lamps are lit, causing the P 3 N 5 to thermally decompose into its constituent elements. Much of this is removed by the pump but enough P 4 vapor remains to react with any residual oxygen inside the bulb. Once the vapor pressure of P 4 is low enough, either filler gas is admitted to the bulb prior to sealing off or, if a vacuum atmosphere is desired, the bulb is sealed off at that point. The high decomposition temperature of P 3 N 5 allows sealing machines to run faster and hotter than was possible using red phosphorus.
Related halogen containing cyclic polymers, trimeric hexabromophosphazene (PNBr 2 ) 3 (melting point 192 °C) and tetrameric octabromophosphazene (PNBr 2 ) 4 (melting point 202 °C) find similar lamp gettering applications for tungsten halogen lamps , where they perform the dual processies of gettering and precise halogen dosing. [ 10 ]
Triphosphorus pentanitride has also been investigated as a semiconductor for applications in microelectronics, particularly as a gate insulator in metal-insulator-semiconductor devices . [ 11 ] [ 12 ]
As a fuel in pyrotechnic obscurant mixtures, it offers some benefits over the more commonly used red phosphorus, owing mainly to its higher chemical stability. Unlike red phosphorus, P 3 N 5 can be safely mixed with strong oxidizers, even potassium chlorate. While these mixtures can burn up to 200 times faster than state-of-the-art red phosphorus mixtures, they are far less sensitive to shock and friction. Additionally, P 3 N 5 is much more resistant to hydrolysis than red phosphorus, giving pyrotechnic mixtures based on it greater stability under long-term storage. [ 13 ]
Patents have been filed for the use of triphosphorus pentanitride in fire fighting measures. [ 14 ] [ 15 ] | https://en.wikipedia.org/wiki/P3N5 |
Phosphorus pentoxide is a chemical compound with molecular formula P 4 O 10 (with its common name derived from its empirical formula , P 2 O 5 ). This white crystalline solid is the anhydride of phosphoric acid . It is a powerful desiccant and dehydrating agent .
Phosphorus pentoxide crystallizes in at least four forms or polymorphs . The most familiar one, a metastable form [ 1 ] (shown in the figure), comprises molecules of P 4 O 10 . Weak van der Waals forces hold these molecules together in a hexagonal lattice (However, in spite of the high symmetry of the molecules, the crystal packing is not a close packing [ 2 ] ). The structure of the P 4 O 10 cage is reminiscent of adamantane with T d symmetry point group . [ 3 ] It is closely related to the corresponding anhydride of phosphorous acid , P 4 O 6 . The latter lacks terminal oxo groups. Its density is 2.30 g/cm 3 . It boils at 423 °C under atmospheric pressure; if heated more rapidly it can sublimate. This form can be made by condensing the vapor of phosphorus pentoxide rapidly, and the result is an extremely hygroscopic solid. [ 4 ]
The other polymorphs are polymeric, but in each case the phosphorus atoms are bound by a tetrahedron of oxygen atoms, one of which forms a terminal P=O bond involving the donation of the terminal oxygen p-orbital electrons to the antibonding phosphorus-oxygen single bonds. The macromolecular form can be made by heating the compound in a sealed tube for several hours, and maintaining the melt at a high temperature before cooling the melt to the solid. [ 4 ] The metastable orthorhombic "O"-form (density 2.72 g/cm 3 , melting point 562 °C) adopts a layered structure consisting of interconnected P 6 O 6 rings, not unlike the structure adopted by certain poly silicates . The stable form is a higher density phase, also orthorhombic, the so-called O' form. It consists of a 3-dimensional framework, density 3.5 g/cm 3 . [ 1 ] [ 5 ] The remaining polymorph is a glass or amorphous form; it can be made by fusing any of the others.
P 4 O 10 is prepared by burning white phosphorus with a sufficient supply of oxygen: [ 6 ]
The dehydration of phosphoric acid to give phosphorus pentoxide is not possible, as on heating it forms various polyphosphates but will not dehydrate sufficiently to form P 4 O 10 .
Phosphorus pentoxide is a potent dehydrating agent as indicated by the exothermic nature of its hydrolysis producing phosphoric acid :
However, its utility for drying is limited somewhat by its tendency to form a protective viscous coating that inhibits further dehydration by unspent material. A granular form of P 4 O 10 is used in desiccators .
Consistent with its strong desiccating power, P 4 O 10 is used in organic synthesis for dehydration. The most important application is for the conversion of primary amides into nitriles : [ 7 ]
The indicated coproduct P 4 O 9 (OH) 2 is an idealized formula for undefined products resulting from the hydration of P 4 O 10 .
Alternatively, when combined with a carboxylic acid , the result is the corresponding anhydride : [ 8 ]
The "Onodera reagent", a solution of P 4 O 10 in DMSO , is employed for the oxidation of alcohols . [ 9 ] This reaction is reminiscent of the Swern oxidation .
The desiccating power of P 4 O 10 is strong enough to convert many mineral acids to their anhydrides. Examples: HNO 3 is converted to N 2 O 5 ; H 2 SO 4 is converted to SO 3 ; HClO 4 is converted to Cl 2 O 7 ; CF 3 SO 3 H is converted to (CF 3 ) 2 S 2 O 5 .
P 2 O 5 content is often used by industry as proxy value for all the phosphorus oxides in a material. For example, fertilizer grade phosphoric acid can also contain various related phosphorous compounds which are also of use. All these compounds are described collectively in terms of ' P 2 O 5 content' to allow convenient comparison of the phosphorous content of different products. Despite this, phosphorus pentoxide is not actually present in most samples as it is not stable in aqueous solutions.
Phosphorus pentoxide itself is not flammable. Just like sulfur trioxide , it reacts vigorously with water and water-containing substances like wood or cotton, liberates much heat and may even cause fire due to the highly exothermic nature of such reactions. It is corrosive to metal and is very irritating – it may cause severe burns to the eye, skin, mucous membrane , and respiratory tract even at concentrations as low as 1 mg/m 3 . [ 10 ] | https://en.wikipedia.org/wiki/P4O10 |
Phosphorus trioxide is the chemical compound with the molecular formula P 4 O 6 . Although the molecular formula suggests the name tetraphosphorus hexoxide, the name phosphorus trioxide preceded the knowledge of the compound's molecular structure, and its usage continues today. This colorless solid is structurally related to adamantane . It is formally the anhydride of phosphorous acid , H 3 PO 3 , but cannot be obtained by the dehydration of the acid. A white solid that melts at room temperature, it is waxy, crystalline and highly toxic, with garlic odor. [ 1 ]
It is obtained by the combustion of phosphorus in a limited supply of air at low temperatures.
By-products include red phosphorus suboxide. [ 1 ]
Phosphorus trioxide reacts with water to form phosphorous acid , reflecting the fact that it is the anhydride of that acid. [ 2 ]
It reacts with hydrogen chloride to form H 3 PO 3 and phosphorus trichloride .
With chlorine or bromine it forms the corresponding phosphoryl halide , and it reacts with iodine in a sealed tube to form diphosphorus tetraiodide . [ 1 ]
P 4 O 6 reacts with ozone at 195 K to give the unstable compound P 4 O 18 . [ 3 ]
P 4 O 18 decomposes above 238 K in solution with the release of O 2 gas. Decomposition of dry P 4 O 18 is explosive.
In a disproportionation reaction , P 4 O 6 is converted into the mixed P(III)P(V) species P 4 O 8 when heated in a sealed tube at 710 K, with the side product being red phosphorus. [ 3 ]
P 4 O 6 is a ligand for transition metals, comparable to phosphite . An illustrative complex is P 4 O 6 ·Fe(CO) 4 . [ 4 ] With BH 3 , a dimeric adduct is produced: [ 3 ] | https://en.wikipedia.org/wiki/P4O6 |
Phosphorus pentasulfide is the inorganic compound with the formula P 2 S 5 ( empirical ) or P 4 S 10 ( molecular ). This yellow solid is the one of two phosphorus sulfides of commercial value. Samples often appear greenish-gray due to impurities. It is soluble in carbon disulfide but reacts with many other solvents such as alcohols , DMSO , and DMF . [ 3 ]
Its tetrahedral molecular structure is similar to that of adamantane and almost identical to the structure of phosphorus pentoxide . [ 4 ]
Phosphorus pentasulfide is obtained by the reaction of liquid white phosphorus ( P 4 ) with sulfur above 300 °C. The first synthesis of P 4 S 10 by Berzelius in 1843 [ 5 ] was by this method. Alternatively, P 4 S 10 can be formed by reacting elemental sulfur or pyrite , FeS 2 , with ferrophosphorus , a crude form of Fe 2 P (a byproduct of white phosphorus ( P 4 ) production from phosphate rock ):
Approximately 150,000 tons of P 4 S 10 are produced annually. The compound is mainly converted to other derivatives for use as lubrication additives such as zinc dithiophosphates .
It is widely used in the production of sodium dithiophosphate for applications as a flotation agent in the concentration of molybdenite minerals. It is also used in the production of pesticides such as Parathion and Malathion . [ 6 ] It is also a component of some amorphous solid electrolytes (e.g. Li 2 S - P 2 S 5 ) for some types of lithium batteries .
Phosphorus pentasulfide is a dual-use material, for the production of early insecticides such as Amiton and also for the manufacture of the related VX nerve agents .
Phosphorus pentasulfide reacts with ethanol to give diethyl dithiophosphoric acid : [ 7 ]
diorganodithiophosphoric acids are used to produce metal dithiophosphates .
Due to hydrolysis by atmospheric moisture, P 4 S 10 evolves hydrogen sulfide H 2 S , thus P 4 S 10 is associated with a rotten egg odour. Aside from H 2 S , hydrolysis of P 4 S 10 eventually gives phosphoric acid :
Other mild nucleophiles react with P 4 S 10 , including alcohols and amines . Reaction with ammonium chloride gives the polymeric (SPN) ∞ . [ 8 ] Aromatic compounds such as anisole , ferrocene and 1-methoxynaphthalene react to form 1,3,2,4-dithiadiphosphetane 2,4-disulfides such as Lawesson's reagent :
P 4 S 10 is used as a thionation reagent. Reactions of this type require refluxing solvents such as benzene , dioxane , or acetonitrile with P 4 S 10 dissociating into P 2 S 5 . Some ketones , esters , and imides are converted to the corresponding thiocarbonyls . Amides give thioamides . With 1,4-diketones the reagent forms thiophenes . It is also used to deoxygenate sulfoxides . The use of P 4 S 10 has been displaced by the aforementioned Lawesson's reagent . [ 9 ]
P 4 S 10 reacts with pyridine to form the complex P 2 S 5 (pyridine) 2 . [ 10 ] | https://en.wikipedia.org/wiki/P4S10 |
Phosphorus sesquisulfide is the inorganic compound with the formula P 4 S 3 . It was developed by Henri Sevene and Emile David Cahen in 1898 as part of their invention of friction matches that did not pose the health hazards of white phosphorus . [ 2 ] [ 3 ] This yellow solid is one of two commercially produced phosphorus sulfides . It is a component of "strike anywhere" matches.
Depending on purity, samples can appear yellow-green to grey. The compound was discovered by G. Lemoine and first produced safely in commercial quantities in 1898 by Albright and Wilson . It dissolves in an equal weight of carbon disulfide ( CS 2 ), and in a 1:50 weight ratio of benzene . Unlike some other phosphorus sulfides, P 4 S 3 is slow to hydrolyze and has a well-defined melting point.
The molecule has C 3v symmetry . It is a derivative of the tetrahedral ( P 4 ) unit from insertion of sulfur into three P-P bonds. The P-S and P-P distances are 2.090 and 2.235 Å, respectively. P 4 Se 3 and P 4 S 3 adopt the same structures. [ 1 ] These compounds can be melted together and form mixed crystals of one dissolved in the other. [ 4 ] Under higher temperatures, mixed chalcogenide molecules P 4 S 2 Se and P 4 SSe 2 will form. [ 5 ]
P 4 S 3 is produced by the reaction of red or white phosphorus with sulfur. Excess sulfur gives phosphorus pentasulfide ( P 4 S 10 ). It is estimated that 150 ton/y were produced in 1989. [ 6 ]
P 4 S 3 and potassium chlorate , together with other materials, composes the heads of "strike-anywhere matches ". [ 7 ]
Its flash point is about 100 °C. [ 8 ]
Exposure to "strike anywhere" matches containing phosphorus sesquisulfide can cause contact dermatitis , usually in the pocket area but also on the face. [ 9 ] Exposure over a long period of time to burning match tips (containing phosphorus
sesquisulfide) can result in a recurring severe primary dermatitis about the eyes and face. Loosening of the teeth has also been reported which may have been due to phosphorus poisoning. [ 10 ]
This article contains public domain text from the NOAA as cited. | https://en.wikipedia.org/wiki/P4S3 |
Phosphorus sulfides comprise a family of inorganic compounds containing only phosphorus and sulfur . These compounds have the formula P 4 S n with n ≤ 10. Two are of commercial significance, phosphorus pentasulfide ( P 4 S 10 ), which is made on a kiloton scale for the production of other organosulfur compounds, and phosphorus sesquisulfide ( P 4 S 3 ), used in the production of "strike anywhere matches" .
There are several other phosphorus sulfides in addition to P 4 S 3 and P 4 S 10 . Six of these phosphorus sulfides exist as isomers : P 4 S 4 , P 4 S 5 , P 4 S 6 , P 4 S 7 , P 4 S 8 , and P 4 S 9 . These isomers are distinguished by Greek letter prefixes. The prefix is based on the order of the discovery of the isomers, not their structure. [ 1 ] All known molecular phosphorus sulfides contain a tetrahedral array of four phosphorus atoms. [ 2 ] P 4 S 2 is also known but is unstable above −30 °C. [ 3 ]
Phosphorus monosulfide monomer, PS, is highly unstable and only exists at elevated temperatures. Its bond, worth about 55 kcal/mol, is about 2.4 angstroms long. [ 4 ]
The main method for preparing these compounds is thermolysis of mixtures of phosphorus and sulfur. The product distributions can be analyzed by 31 P-NMR spectroscopy . More selective syntheses entail:
Phosphorus sesquisulfide is prepared by treating red phosphorus with sulfur above 450 K, [ 7 ] followed by careful recrystallization with carbon disulfide and benzene . An alternative method involves the controlled fusion of white phosphorus with sulfur in an inert, non-flammable solvent. [ 8 ]
The α- and β- forms of P 4 S 4 can be prepared by treating the corresponding isomers of P 4 S 3 I 2 with ((CH 3 ) 3 Sn) 2 S : [ 7 ]
P 4 S 3 I 2 can be synthesized by the reaction of stoichiometric amounts of phosphorus, sulfur, and iodine.
P 4 S 5 can be prepared by treating stoichiometric amounts of P 4 S 3 with sulfur in carbon disulfide solution, in the presence of light and a catalytic amount of iodine . [ 9 ] The respective product distribution is then analyzed by using 31 P-NMR spectroscopy.
In particular, α- P 4 S 5 can be easily made by the photochemical reaction of P 4 S 10 with red phosphorus. [ 7 ] Note that P 4 S 5 is unstable when heated, tending to disproportionate to P 4 S 3 and P 4 S 7 before reaching its melting point. [ 10 ]
P 4 S 6 can be made by abstracting a sulfur atom from P 4 S 7 using triphenylphosphine : [ 7 ]
Treating α- P 4 S 5 with Ph 3 AsS in CS 2 also yields α- P 4 S 6 . [ 5 ] The two new polymorphs δ- P 4 S 6 and ε- P 4 S 6 can be made by treating α- P 4 S 4 with Ph 3 SbS in CS 2 . [ 11 ]
P 4 S 7 is most conveniently made by direct union of the corresponding elements, and is one of the most easily purified binary phosphorus sulfides. [ 12 ]
β- P 4 S 8 can be made by treating α- P 4 S 7 with Ph 3 AsS in CS 2 , which yields a mixture between α- P 4 S 7 and β- P 4 S 8 . [ 5 ]
P 4 S 9 can be made by two methods. One method involves the heating of P 4 S 3 in excess sulfur. [ 7 ] Another
method involves the heating of P 4 S 7 and P 4 S 10 in 1:2 mole ratio, where P 4 S 9 is reversibly formed: [ 11 ]
P 4 S 10 is one of the most stable phosphorus sulfides. It is most easily made by heating white phosphorus with sulfur above 570 K in an evacuated tube. [ 13 ] | https://en.wikipedia.org/wiki/P4S4 |
Phosphorus sulfides comprise a family of inorganic compounds containing only phosphorus and sulfur . These compounds have the formula P 4 S n with n ≤ 10. Two are of commercial significance, phosphorus pentasulfide ( P 4 S 10 ), which is made on a kiloton scale for the production of other organosulfur compounds, and phosphorus sesquisulfide ( P 4 S 3 ), used in the production of "strike anywhere matches" .
There are several other phosphorus sulfides in addition to P 4 S 3 and P 4 S 10 . Six of these phosphorus sulfides exist as isomers : P 4 S 4 , P 4 S 5 , P 4 S 6 , P 4 S 7 , P 4 S 8 , and P 4 S 9 . These isomers are distinguished by Greek letter prefixes. The prefix is based on the order of the discovery of the isomers, not their structure. [ 1 ] All known molecular phosphorus sulfides contain a tetrahedral array of four phosphorus atoms. [ 2 ] P 4 S 2 is also known but is unstable above −30 °C. [ 3 ]
Phosphorus monosulfide monomer, PS, is highly unstable and only exists at elevated temperatures. Its bond, worth about 55 kcal/mol, is about 2.4 angstroms long. [ 4 ]
The main method for preparing these compounds is thermolysis of mixtures of phosphorus and sulfur. The product distributions can be analyzed by 31 P-NMR spectroscopy . More selective syntheses entail:
Phosphorus sesquisulfide is prepared by treating red phosphorus with sulfur above 450 K, [ 7 ] followed by careful recrystallization with carbon disulfide and benzene . An alternative method involves the controlled fusion of white phosphorus with sulfur in an inert, non-flammable solvent. [ 8 ]
The α- and β- forms of P 4 S 4 can be prepared by treating the corresponding isomers of P 4 S 3 I 2 with ((CH 3 ) 3 Sn) 2 S : [ 7 ]
P 4 S 3 I 2 can be synthesized by the reaction of stoichiometric amounts of phosphorus, sulfur, and iodine.
P 4 S 5 can be prepared by treating stoichiometric amounts of P 4 S 3 with sulfur in carbon disulfide solution, in the presence of light and a catalytic amount of iodine . [ 9 ] The respective product distribution is then analyzed by using 31 P-NMR spectroscopy.
In particular, α- P 4 S 5 can be easily made by the photochemical reaction of P 4 S 10 with red phosphorus. [ 7 ] Note that P 4 S 5 is unstable when heated, tending to disproportionate to P 4 S 3 and P 4 S 7 before reaching its melting point. [ 10 ]
P 4 S 6 can be made by abstracting a sulfur atom from P 4 S 7 using triphenylphosphine : [ 7 ]
Treating α- P 4 S 5 with Ph 3 AsS in CS 2 also yields α- P 4 S 6 . [ 5 ] The two new polymorphs δ- P 4 S 6 and ε- P 4 S 6 can be made by treating α- P 4 S 4 with Ph 3 SbS in CS 2 . [ 11 ]
P 4 S 7 is most conveniently made by direct union of the corresponding elements, and is one of the most easily purified binary phosphorus sulfides. [ 12 ]
β- P 4 S 8 can be made by treating α- P 4 S 7 with Ph 3 AsS in CS 2 , which yields a mixture between α- P 4 S 7 and β- P 4 S 8 . [ 5 ]
P 4 S 9 can be made by two methods. One method involves the heating of P 4 S 3 in excess sulfur. [ 7 ] Another
method involves the heating of P 4 S 7 and P 4 S 10 in 1:2 mole ratio, where P 4 S 9 is reversibly formed: [ 11 ]
P 4 S 10 is one of the most stable phosphorus sulfides. It is most easily made by heating white phosphorus with sulfur above 570 K in an evacuated tube. [ 13 ] | https://en.wikipedia.org/wiki/P4S5 |
Phosphorus sulfides comprise a family of inorganic compounds containing only phosphorus and sulfur . These compounds have the formula P 4 S n with n ≤ 10. Two are of commercial significance, phosphorus pentasulfide ( P 4 S 10 ), which is made on a kiloton scale for the production of other organosulfur compounds, and phosphorus sesquisulfide ( P 4 S 3 ), used in the production of "strike anywhere matches" .
There are several other phosphorus sulfides in addition to P 4 S 3 and P 4 S 10 . Six of these phosphorus sulfides exist as isomers : P 4 S 4 , P 4 S 5 , P 4 S 6 , P 4 S 7 , P 4 S 8 , and P 4 S 9 . These isomers are distinguished by Greek letter prefixes. The prefix is based on the order of the discovery of the isomers, not their structure. [ 1 ] All known molecular phosphorus sulfides contain a tetrahedral array of four phosphorus atoms. [ 2 ] P 4 S 2 is also known but is unstable above −30 °C. [ 3 ]
Phosphorus monosulfide monomer, PS, is highly unstable and only exists at elevated temperatures. Its bond, worth about 55 kcal/mol, is about 2.4 angstroms long. [ 4 ]
The main method for preparing these compounds is thermolysis of mixtures of phosphorus and sulfur. The product distributions can be analyzed by 31 P-NMR spectroscopy . More selective syntheses entail:
Phosphorus sesquisulfide is prepared by treating red phosphorus with sulfur above 450 K, [ 7 ] followed by careful recrystallization with carbon disulfide and benzene . An alternative method involves the controlled fusion of white phosphorus with sulfur in an inert, non-flammable solvent. [ 8 ]
The α- and β- forms of P 4 S 4 can be prepared by treating the corresponding isomers of P 4 S 3 I 2 with ((CH 3 ) 3 Sn) 2 S : [ 7 ]
P 4 S 3 I 2 can be synthesized by the reaction of stoichiometric amounts of phosphorus, sulfur, and iodine.
P 4 S 5 can be prepared by treating stoichiometric amounts of P 4 S 3 with sulfur in carbon disulfide solution, in the presence of light and a catalytic amount of iodine . [ 9 ] The respective product distribution is then analyzed by using 31 P-NMR spectroscopy.
In particular, α- P 4 S 5 can be easily made by the photochemical reaction of P 4 S 10 with red phosphorus. [ 7 ] Note that P 4 S 5 is unstable when heated, tending to disproportionate to P 4 S 3 and P 4 S 7 before reaching its melting point. [ 10 ]
P 4 S 6 can be made by abstracting a sulfur atom from P 4 S 7 using triphenylphosphine : [ 7 ]
Treating α- P 4 S 5 with Ph 3 AsS in CS 2 also yields α- P 4 S 6 . [ 5 ] The two new polymorphs δ- P 4 S 6 and ε- P 4 S 6 can be made by treating α- P 4 S 4 with Ph 3 SbS in CS 2 . [ 11 ]
P 4 S 7 is most conveniently made by direct union of the corresponding elements, and is one of the most easily purified binary phosphorus sulfides. [ 12 ]
β- P 4 S 8 can be made by treating α- P 4 S 7 with Ph 3 AsS in CS 2 , which yields a mixture between α- P 4 S 7 and β- P 4 S 8 . [ 5 ]
P 4 S 9 can be made by two methods. One method involves the heating of P 4 S 3 in excess sulfur. [ 7 ] Another
method involves the heating of P 4 S 7 and P 4 S 10 in 1:2 mole ratio, where P 4 S 9 is reversibly formed: [ 11 ]
P 4 S 10 is one of the most stable phosphorus sulfides. It is most easily made by heating white phosphorus with sulfur above 570 K in an evacuated tube. [ 13 ] | https://en.wikipedia.org/wiki/P4S6 |
Phosphorus sulfides comprise a family of inorganic compounds containing only phosphorus and sulfur . These compounds have the formula P 4 S n with n ≤ 10. Two are of commercial significance, phosphorus pentasulfide ( P 4 S 10 ), which is made on a kiloton scale for the production of other organosulfur compounds, and phosphorus sesquisulfide ( P 4 S 3 ), used in the production of "strike anywhere matches" .
There are several other phosphorus sulfides in addition to P 4 S 3 and P 4 S 10 . Six of these phosphorus sulfides exist as isomers : P 4 S 4 , P 4 S 5 , P 4 S 6 , P 4 S 7 , P 4 S 8 , and P 4 S 9 . These isomers are distinguished by Greek letter prefixes. The prefix is based on the order of the discovery of the isomers, not their structure. [ 1 ] All known molecular phosphorus sulfides contain a tetrahedral array of four phosphorus atoms. [ 2 ] P 4 S 2 is also known but is unstable above −30 °C. [ 3 ]
Phosphorus monosulfide monomer, PS, is highly unstable and only exists at elevated temperatures. Its bond, worth about 55 kcal/mol, is about 2.4 angstroms long. [ 4 ]
The main method for preparing these compounds is thermolysis of mixtures of phosphorus and sulfur. The product distributions can be analyzed by 31 P-NMR spectroscopy . More selective syntheses entail:
Phosphorus sesquisulfide is prepared by treating red phosphorus with sulfur above 450 K, [ 7 ] followed by careful recrystallization with carbon disulfide and benzene . An alternative method involves the controlled fusion of white phosphorus with sulfur in an inert, non-flammable solvent. [ 8 ]
The α- and β- forms of P 4 S 4 can be prepared by treating the corresponding isomers of P 4 S 3 I 2 with ((CH 3 ) 3 Sn) 2 S : [ 7 ]
P 4 S 3 I 2 can be synthesized by the reaction of stoichiometric amounts of phosphorus, sulfur, and iodine.
P 4 S 5 can be prepared by treating stoichiometric amounts of P 4 S 3 with sulfur in carbon disulfide solution, in the presence of light and a catalytic amount of iodine . [ 9 ] The respective product distribution is then analyzed by using 31 P-NMR spectroscopy.
In particular, α- P 4 S 5 can be easily made by the photochemical reaction of P 4 S 10 with red phosphorus. [ 7 ] Note that P 4 S 5 is unstable when heated, tending to disproportionate to P 4 S 3 and P 4 S 7 before reaching its melting point. [ 10 ]
P 4 S 6 can be made by abstracting a sulfur atom from P 4 S 7 using triphenylphosphine : [ 7 ]
Treating α- P 4 S 5 with Ph 3 AsS in CS 2 also yields α- P 4 S 6 . [ 5 ] The two new polymorphs δ- P 4 S 6 and ε- P 4 S 6 can be made by treating α- P 4 S 4 with Ph 3 SbS in CS 2 . [ 11 ]
P 4 S 7 is most conveniently made by direct union of the corresponding elements, and is one of the most easily purified binary phosphorus sulfides. [ 12 ]
β- P 4 S 8 can be made by treating α- P 4 S 7 with Ph 3 AsS in CS 2 , which yields a mixture between α- P 4 S 7 and β- P 4 S 8 . [ 5 ]
P 4 S 9 can be made by two methods. One method involves the heating of P 4 S 3 in excess sulfur. [ 7 ] Another
method involves the heating of P 4 S 7 and P 4 S 10 in 1:2 mole ratio, where P 4 S 9 is reversibly formed: [ 11 ]
P 4 S 10 is one of the most stable phosphorus sulfides. It is most easily made by heating white phosphorus with sulfur above 570 K in an evacuated tube. [ 13 ] | https://en.wikipedia.org/wiki/P4S7 |
Phosphorus sulfides comprise a family of inorganic compounds containing only phosphorus and sulfur . These compounds have the formula P 4 S n with n ≤ 10. Two are of commercial significance, phosphorus pentasulfide ( P 4 S 10 ), which is made on a kiloton scale for the production of other organosulfur compounds, and phosphorus sesquisulfide ( P 4 S 3 ), used in the production of "strike anywhere matches" .
There are several other phosphorus sulfides in addition to P 4 S 3 and P 4 S 10 . Six of these phosphorus sulfides exist as isomers : P 4 S 4 , P 4 S 5 , P 4 S 6 , P 4 S 7 , P 4 S 8 , and P 4 S 9 . These isomers are distinguished by Greek letter prefixes. The prefix is based on the order of the discovery of the isomers, not their structure. [ 1 ] All known molecular phosphorus sulfides contain a tetrahedral array of four phosphorus atoms. [ 2 ] P 4 S 2 is also known but is unstable above −30 °C. [ 3 ]
Phosphorus monosulfide monomer, PS, is highly unstable and only exists at elevated temperatures. Its bond, worth about 55 kcal/mol, is about 2.4 angstroms long. [ 4 ]
The main method for preparing these compounds is thermolysis of mixtures of phosphorus and sulfur. The product distributions can be analyzed by 31 P-NMR spectroscopy . More selective syntheses entail:
Phosphorus sesquisulfide is prepared by treating red phosphorus with sulfur above 450 K, [ 7 ] followed by careful recrystallization with carbon disulfide and benzene . An alternative method involves the controlled fusion of white phosphorus with sulfur in an inert, non-flammable solvent. [ 8 ]
The α- and β- forms of P 4 S 4 can be prepared by treating the corresponding isomers of P 4 S 3 I 2 with ((CH 3 ) 3 Sn) 2 S : [ 7 ]
P 4 S 3 I 2 can be synthesized by the reaction of stoichiometric amounts of phosphorus, sulfur, and iodine.
P 4 S 5 can be prepared by treating stoichiometric amounts of P 4 S 3 with sulfur in carbon disulfide solution, in the presence of light and a catalytic amount of iodine . [ 9 ] The respective product distribution is then analyzed by using 31 P-NMR spectroscopy.
In particular, α- P 4 S 5 can be easily made by the photochemical reaction of P 4 S 10 with red phosphorus. [ 7 ] Note that P 4 S 5 is unstable when heated, tending to disproportionate to P 4 S 3 and P 4 S 7 before reaching its melting point. [ 10 ]
P 4 S 6 can be made by abstracting a sulfur atom from P 4 S 7 using triphenylphosphine : [ 7 ]
Treating α- P 4 S 5 with Ph 3 AsS in CS 2 also yields α- P 4 S 6 . [ 5 ] The two new polymorphs δ- P 4 S 6 and ε- P 4 S 6 can be made by treating α- P 4 S 4 with Ph 3 SbS in CS 2 . [ 11 ]
P 4 S 7 is most conveniently made by direct union of the corresponding elements, and is one of the most easily purified binary phosphorus sulfides. [ 12 ]
β- P 4 S 8 can be made by treating α- P 4 S 7 with Ph 3 AsS in CS 2 , which yields a mixture between α- P 4 S 7 and β- P 4 S 8 . [ 5 ]
P 4 S 9 can be made by two methods. One method involves the heating of P 4 S 3 in excess sulfur. [ 7 ] Another
method involves the heating of P 4 S 7 and P 4 S 10 in 1:2 mole ratio, where P 4 S 9 is reversibly formed: [ 11 ]
P 4 S 10 is one of the most stable phosphorus sulfides. It is most easily made by heating white phosphorus with sulfur above 570 K in an evacuated tube. [ 13 ] | https://en.wikipedia.org/wiki/P4S8 |
Phosphorus sulfides comprise a family of inorganic compounds containing only phosphorus and sulfur . These compounds have the formula P 4 S n with n ≤ 10. Two are of commercial significance, phosphorus pentasulfide ( P 4 S 10 ), which is made on a kiloton scale for the production of other organosulfur compounds, and phosphorus sesquisulfide ( P 4 S 3 ), used in the production of "strike anywhere matches" .
There are several other phosphorus sulfides in addition to P 4 S 3 and P 4 S 10 . Six of these phosphorus sulfides exist as isomers : P 4 S 4 , P 4 S 5 , P 4 S 6 , P 4 S 7 , P 4 S 8 , and P 4 S 9 . These isomers are distinguished by Greek letter prefixes. The prefix is based on the order of the discovery of the isomers, not their structure. [ 1 ] All known molecular phosphorus sulfides contain a tetrahedral array of four phosphorus atoms. [ 2 ] P 4 S 2 is also known but is unstable above −30 °C. [ 3 ]
Phosphorus monosulfide monomer, PS, is highly unstable and only exists at elevated temperatures. Its bond, worth about 55 kcal/mol, is about 2.4 angstroms long. [ 4 ]
The main method for preparing these compounds is thermolysis of mixtures of phosphorus and sulfur. The product distributions can be analyzed by 31 P-NMR spectroscopy . More selective syntheses entail:
Phosphorus sesquisulfide is prepared by treating red phosphorus with sulfur above 450 K, [ 7 ] followed by careful recrystallization with carbon disulfide and benzene . An alternative method involves the controlled fusion of white phosphorus with sulfur in an inert, non-flammable solvent. [ 8 ]
The α- and β- forms of P 4 S 4 can be prepared by treating the corresponding isomers of P 4 S 3 I 2 with ((CH 3 ) 3 Sn) 2 S : [ 7 ]
P 4 S 3 I 2 can be synthesized by the reaction of stoichiometric amounts of phosphorus, sulfur, and iodine.
P 4 S 5 can be prepared by treating stoichiometric amounts of P 4 S 3 with sulfur in carbon disulfide solution, in the presence of light and a catalytic amount of iodine . [ 9 ] The respective product distribution is then analyzed by using 31 P-NMR spectroscopy.
In particular, α- P 4 S 5 can be easily made by the photochemical reaction of P 4 S 10 with red phosphorus. [ 7 ] Note that P 4 S 5 is unstable when heated, tending to disproportionate to P 4 S 3 and P 4 S 7 before reaching its melting point. [ 10 ]
P 4 S 6 can be made by abstracting a sulfur atom from P 4 S 7 using triphenylphosphine : [ 7 ]
Treating α- P 4 S 5 with Ph 3 AsS in CS 2 also yields α- P 4 S 6 . [ 5 ] The two new polymorphs δ- P 4 S 6 and ε- P 4 S 6 can be made by treating α- P 4 S 4 with Ph 3 SbS in CS 2 . [ 11 ]
P 4 S 7 is most conveniently made by direct union of the corresponding elements, and is one of the most easily purified binary phosphorus sulfides. [ 12 ]
β- P 4 S 8 can be made by treating α- P 4 S 7 with Ph 3 AsS in CS 2 , which yields a mixture between α- P 4 S 7 and β- P 4 S 8 . [ 5 ]
P 4 S 9 can be made by two methods. One method involves the heating of P 4 S 3 in excess sulfur. [ 7 ] Another
method involves the heating of P 4 S 7 and P 4 S 10 in 1:2 mole ratio, where P 4 S 9 is reversibly formed: [ 11 ]
P 4 S 10 is one of the most stable phosphorus sulfides. It is most easily made by heating white phosphorus with sulfur above 570 K in an evacuated tube. [ 13 ] | https://en.wikipedia.org/wiki/P4S9 |
Phosphorus selenides are a relatively obscure group of compounds. There have been some studies of the phosphorus - selenium phase diagram and the glassy amorphous phases are reported. The compounds that have been reported are shown below. While some of phosphorus selenides are similar to their sulfide analogues , there are some new forms, molecular P 2 Se 5 and the polymeric catena - [P 4 Se 4 ] x . There is also some doubt about the existence of molecular P 4 Se 10 .
Molecular P 2 Se 5 has a norbornane like structure with two phosphorus atoms with oxidation state +3 bridged by two diselenide units ( −Se−Se− , analogous to disulfide ) and one selenide unit ( −Se− ). [ 1 ] It was isolated by solvent ( CS 2 ) extraction from a P 2 Se 5 amorphous phase made from the elements. [ 2 ]
P 4 Se 3 has been characterised crystallographically and has the same structure as the low temperature form of P 4 S 3 . [ 3 ] It can be prepared from the elements. One preparation is to extract and recrystallise using tetralin .
The P 4 Se 5 molecule has the same structure as P 4 S 5 . [ 4 ] It was prepared by reacting P 4 Se 3 with bromine in CS 2 .
This compound consists of polymeric chains of norbornane -like units joined by Se atoms. [ 5 ] As each P atom in the repeat unit is bonded to another P atom and to two Se atoms, each P atom has a formal oxidation state of +2.
P 4 Se 4 has two crystalline forms α- P 4 Se 4 with the same molecular structure as α- P 4 S 4 and β- P 4 Se 4 with same molecular structure as β- P 4 S 4 . [ 6 ] A fully characterised compound (CuI) 3 P 4 Se 4 contains P 4 Se 4 with a β- P 4 S 4 structure. [ 7 ]
This has been reported to have the same structure as P 4 S 7 . [ 8 ] [ 9 ] One well-known textbook does not mention it at all. [ 10 ]
Molecular P 4 Se 10 has been reported to share the same structure as P 4 S 10 and P 4 O 10 , [ 8 ] [ 9 ] [ 11 ] but one well-known textbook does not mention it at all. [ 10 ] A review (2001) examining P-Se amorphous phases did not confirm the presence of molecular P 4 Se 10 . [ 12 ] The isoelectronic anion [Ge 4 Se 10 ] 4− which has the adamantane like P 4 O 10 structure is known, an example is the sodium salt Na 4 [Ge 4 Se 10 ] . [ 13 ]
P 4 Se 6 , P 14 Se, P 4 Se, P 4 Se 2 , P 2 Se , have been reported. [ 8 ]
Phosphorus - selenium glasses have been examined using 31 P-NMR and Raman spectroscopy. Glasses are formed in P x Se 1− x over the range of compositions 0 < x < 0.8 with a small window around 0.52 – 0.60 centred on 0.57 (corresponding to the compound P 4 Se 3 ) where there is a tendency to crystallise. For x < 0.47 the glasses contain Se n chain fragments, pyramidal P units (P oxidation state +3), quasi-tetrahedral P units (P oxidation state +5, with P=Se double bond ) and P 2 units (P in formal oxidation state +4). There is no evidence for an amorphous phase containing molecular P 4 Se 10 . [ 12 ] | https://en.wikipedia.org/wiki/P4Se10 |
Phosphorus selenides are a relatively obscure group of compounds. There have been some studies of the phosphorus - selenium phase diagram and the glassy amorphous phases are reported. The compounds that have been reported are shown below. While some of phosphorus selenides are similar to their sulfide analogues , there are some new forms, molecular P 2 Se 5 and the polymeric catena - [P 4 Se 4 ] x . There is also some doubt about the existence of molecular P 4 Se 10 .
Molecular P 2 Se 5 has a norbornane like structure with two phosphorus atoms with oxidation state +3 bridged by two diselenide units ( −Se−Se− , analogous to disulfide ) and one selenide unit ( −Se− ). [ 1 ] It was isolated by solvent ( CS 2 ) extraction from a P 2 Se 5 amorphous phase made from the elements. [ 2 ]
P 4 Se 3 has been characterised crystallographically and has the same structure as the low temperature form of P 4 S 3 . [ 3 ] It can be prepared from the elements. One preparation is to extract and recrystallise using tetralin .
The P 4 Se 5 molecule has the same structure as P 4 S 5 . [ 4 ] It was prepared by reacting P 4 Se 3 with bromine in CS 2 .
This compound consists of polymeric chains of norbornane -like units joined by Se atoms. [ 5 ] As each P atom in the repeat unit is bonded to another P atom and to two Se atoms, each P atom has a formal oxidation state of +2.
P 4 Se 4 has two crystalline forms α- P 4 Se 4 with the same molecular structure as α- P 4 S 4 and β- P 4 Se 4 with same molecular structure as β- P 4 S 4 . [ 6 ] A fully characterised compound (CuI) 3 P 4 Se 4 contains P 4 Se 4 with a β- P 4 S 4 structure. [ 7 ]
This has been reported to have the same structure as P 4 S 7 . [ 8 ] [ 9 ] One well-known textbook does not mention it at all. [ 10 ]
Molecular P 4 Se 10 has been reported to share the same structure as P 4 S 10 and P 4 O 10 , [ 8 ] [ 9 ] [ 11 ] but one well-known textbook does not mention it at all. [ 10 ] A review (2001) examining P-Se amorphous phases did not confirm the presence of molecular P 4 Se 10 . [ 12 ] The isoelectronic anion [Ge 4 Se 10 ] 4− which has the adamantane like P 4 O 10 structure is known, an example is the sodium salt Na 4 [Ge 4 Se 10 ] . [ 13 ]
P 4 Se 6 , P 14 Se, P 4 Se, P 4 Se 2 , P 2 Se , have been reported. [ 8 ]
Phosphorus - selenium glasses have been examined using 31 P-NMR and Raman spectroscopy. Glasses are formed in P x Se 1− x over the range of compositions 0 < x < 0.8 with a small window around 0.52 – 0.60 centred on 0.57 (corresponding to the compound P 4 Se 3 ) where there is a tendency to crystallise. For x < 0.47 the glasses contain Se n chain fragments, pyramidal P units (P oxidation state +3), quasi-tetrahedral P units (P oxidation state +5, with P=Se double bond ) and P 2 units (P in formal oxidation state +4). There is no evidence for an amorphous phase containing molecular P 4 Se 10 . [ 12 ] | https://en.wikipedia.org/wiki/P4Se3 |
Phosphorus selenides are a relatively obscure group of compounds. There have been some studies of the phosphorus - selenium phase diagram and the glassy amorphous phases are reported. The compounds that have been reported are shown below. While some of phosphorus selenides are similar to their sulfide analogues , there are some new forms, molecular P 2 Se 5 and the polymeric catena - [P 4 Se 4 ] x . There is also some doubt about the existence of molecular P 4 Se 10 .
Molecular P 2 Se 5 has a norbornane like structure with two phosphorus atoms with oxidation state +3 bridged by two diselenide units ( −Se−Se− , analogous to disulfide ) and one selenide unit ( −Se− ). [ 1 ] It was isolated by solvent ( CS 2 ) extraction from a P 2 Se 5 amorphous phase made from the elements. [ 2 ]
P 4 Se 3 has been characterised crystallographically and has the same structure as the low temperature form of P 4 S 3 . [ 3 ] It can be prepared from the elements. One preparation is to extract and recrystallise using tetralin .
The P 4 Se 5 molecule has the same structure as P 4 S 5 . [ 4 ] It was prepared by reacting P 4 Se 3 with bromine in CS 2 .
This compound consists of polymeric chains of norbornane -like units joined by Se atoms. [ 5 ] As each P atom in the repeat unit is bonded to another P atom and to two Se atoms, each P atom has a formal oxidation state of +2.
P 4 Se 4 has two crystalline forms α- P 4 Se 4 with the same molecular structure as α- P 4 S 4 and β- P 4 Se 4 with same molecular structure as β- P 4 S 4 . [ 6 ] A fully characterised compound (CuI) 3 P 4 Se 4 contains P 4 Se 4 with a β- P 4 S 4 structure. [ 7 ]
This has been reported to have the same structure as P 4 S 7 . [ 8 ] [ 9 ] One well-known textbook does not mention it at all. [ 10 ]
Molecular P 4 Se 10 has been reported to share the same structure as P 4 S 10 and P 4 O 10 , [ 8 ] [ 9 ] [ 11 ] but one well-known textbook does not mention it at all. [ 10 ] A review (2001) examining P-Se amorphous phases did not confirm the presence of molecular P 4 Se 10 . [ 12 ] The isoelectronic anion [Ge 4 Se 10 ] 4− which has the adamantane like P 4 O 10 structure is known, an example is the sodium salt Na 4 [Ge 4 Se 10 ] . [ 13 ]
P 4 Se 6 , P 14 Se, P 4 Se, P 4 Se 2 , P 2 Se , have been reported. [ 8 ]
Phosphorus - selenium glasses have been examined using 31 P-NMR and Raman spectroscopy. Glasses are formed in P x Se 1− x over the range of compositions 0 < x < 0.8 with a small window around 0.52 – 0.60 centred on 0.57 (corresponding to the compound P 4 Se 3 ) where there is a tendency to crystallise. For x < 0.47 the glasses contain Se n chain fragments, pyramidal P units (P oxidation state +3), quasi-tetrahedral P units (P oxidation state +5, with P=Se double bond ) and P 2 units (P in formal oxidation state +4). There is no evidence for an amorphous phase containing molecular P 4 Se 10 . [ 12 ] | https://en.wikipedia.org/wiki/P4Se4 |
Phosphorus selenides are a relatively obscure group of compounds. There have been some studies of the phosphorus - selenium phase diagram and the glassy amorphous phases are reported. The compounds that have been reported are shown below. While some of phosphorus selenides are similar to their sulfide analogues , there are some new forms, molecular P 2 Se 5 and the polymeric catena - [P 4 Se 4 ] x . There is also some doubt about the existence of molecular P 4 Se 10 .
Molecular P 2 Se 5 has a norbornane like structure with two phosphorus atoms with oxidation state +3 bridged by two diselenide units ( −Se−Se− , analogous to disulfide ) and one selenide unit ( −Se− ). [ 1 ] It was isolated by solvent ( CS 2 ) extraction from a P 2 Se 5 amorphous phase made from the elements. [ 2 ]
P 4 Se 3 has been characterised crystallographically and has the same structure as the low temperature form of P 4 S 3 . [ 3 ] It can be prepared from the elements. One preparation is to extract and recrystallise using tetralin .
The P 4 Se 5 molecule has the same structure as P 4 S 5 . [ 4 ] It was prepared by reacting P 4 Se 3 with bromine in CS 2 .
This compound consists of polymeric chains of norbornane -like units joined by Se atoms. [ 5 ] As each P atom in the repeat unit is bonded to another P atom and to two Se atoms, each P atom has a formal oxidation state of +2.
P 4 Se 4 has two crystalline forms α- P 4 Se 4 with the same molecular structure as α- P 4 S 4 and β- P 4 Se 4 with same molecular structure as β- P 4 S 4 . [ 6 ] A fully characterised compound (CuI) 3 P 4 Se 4 contains P 4 Se 4 with a β- P 4 S 4 structure. [ 7 ]
This has been reported to have the same structure as P 4 S 7 . [ 8 ] [ 9 ] One well-known textbook does not mention it at all. [ 10 ]
Molecular P 4 Se 10 has been reported to share the same structure as P 4 S 10 and P 4 O 10 , [ 8 ] [ 9 ] [ 11 ] but one well-known textbook does not mention it at all. [ 10 ] A review (2001) examining P-Se amorphous phases did not confirm the presence of molecular P 4 Se 10 . [ 12 ] The isoelectronic anion [Ge 4 Se 10 ] 4− which has the adamantane like P 4 O 10 structure is known, an example is the sodium salt Na 4 [Ge 4 Se 10 ] . [ 13 ]
P 4 Se 6 , P 14 Se, P 4 Se, P 4 Se 2 , P 2 Se , have been reported. [ 8 ]
Phosphorus - selenium glasses have been examined using 31 P-NMR and Raman spectroscopy. Glasses are formed in P x Se 1− x over the range of compositions 0 < x < 0.8 with a small window around 0.52 – 0.60 centred on 0.57 (corresponding to the compound P 4 Se 3 ) where there is a tendency to crystallise. For x < 0.47 the glasses contain Se n chain fragments, pyramidal P units (P oxidation state +3), quasi-tetrahedral P units (P oxidation state +5, with P=Se double bond ) and P 2 units (P in formal oxidation state +4). There is no evidence for an amorphous phase containing molecular P 4 Se 10 . [ 12 ] | https://en.wikipedia.org/wiki/P4Se5 |
Phosphorus selenides are a relatively obscure group of compounds. There have been some studies of the phosphorus - selenium phase diagram and the glassy amorphous phases are reported. The compounds that have been reported are shown below. While some of phosphorus selenides are similar to their sulfide analogues , there are some new forms, molecular P 2 Se 5 and the polymeric catena - [P 4 Se 4 ] x . There is also some doubt about the existence of molecular P 4 Se 10 .
Molecular P 2 Se 5 has a norbornane like structure with two phosphorus atoms with oxidation state +3 bridged by two diselenide units ( −Se−Se− , analogous to disulfide ) and one selenide unit ( −Se− ). [ 1 ] It was isolated by solvent ( CS 2 ) extraction from a P 2 Se 5 amorphous phase made from the elements. [ 2 ]
P 4 Se 3 has been characterised crystallographically and has the same structure as the low temperature form of P 4 S 3 . [ 3 ] It can be prepared from the elements. One preparation is to extract and recrystallise using tetralin .
The P 4 Se 5 molecule has the same structure as P 4 S 5 . [ 4 ] It was prepared by reacting P 4 Se 3 with bromine in CS 2 .
This compound consists of polymeric chains of norbornane -like units joined by Se atoms. [ 5 ] As each P atom in the repeat unit is bonded to another P atom and to two Se atoms, each P atom has a formal oxidation state of +2.
P 4 Se 4 has two crystalline forms α- P 4 Se 4 with the same molecular structure as α- P 4 S 4 and β- P 4 Se 4 with same molecular structure as β- P 4 S 4 . [ 6 ] A fully characterised compound (CuI) 3 P 4 Se 4 contains P 4 Se 4 with a β- P 4 S 4 structure. [ 7 ]
This has been reported to have the same structure as P 4 S 7 . [ 8 ] [ 9 ] One well-known textbook does not mention it at all. [ 10 ]
Molecular P 4 Se 10 has been reported to share the same structure as P 4 S 10 and P 4 O 10 , [ 8 ] [ 9 ] [ 11 ] but one well-known textbook does not mention it at all. [ 10 ] A review (2001) examining P-Se amorphous phases did not confirm the presence of molecular P 4 Se 10 . [ 12 ] The isoelectronic anion [Ge 4 Se 10 ] 4− which has the adamantane like P 4 O 10 structure is known, an example is the sodium salt Na 4 [Ge 4 Se 10 ] . [ 13 ]
P 4 Se 6 , P 14 Se, P 4 Se, P 4 Se 2 , P 2 Se , have been reported. [ 8 ]
Phosphorus - selenium glasses have been examined using 31 P-NMR and Raman spectroscopy. Glasses are formed in P x Se 1− x over the range of compositions 0 < x < 0.8 with a small window around 0.52 – 0.60 centred on 0.57 (corresponding to the compound P 4 Se 3 ) where there is a tendency to crystallise. For x < 0.47 the glasses contain Se n chain fragments, pyramidal P units (P oxidation state +3), quasi-tetrahedral P units (P oxidation state +5, with P=Se double bond ) and P 2 units (P in formal oxidation state +4). There is no evidence for an amorphous phase containing molecular P 4 Se 10 . [ 12 ] | https://en.wikipedia.org/wiki/P4Se7 |
In biochemistry , p 50 represents the partial pressure of a gas required to achieve 50% saturation of a particular protein's binding sites. [ 1 ] [ 2 ] Values of p 50 are negatively correlated with substrate affinity; lower values correspond to higher affinity and vice versa . The term is analogous to the Michaelis–Menten constant ( K M ), which identifies the concentration of substrate required for an enzyme to achieve 50% of its maximum reaction velocity .
The concept of p 50 is derived from considering the fractional saturation of a protein by a gas. Imagine myoglobin , a protein which is able to bind a single molecule of oxygen , as per the reversible reaction below, whose equilibrium constant K (which is also a dissociation constant, since it describes a reversible association-dissociation event) is equal to the product of the concentrations (at equilibrium) of free myoglobin and free oxygen, divided by the concentration of myoglobin-oxygen complex.
The fractional saturation Y O 2 of the myoglobin is what proportion of the total myoglobin concentration is made up of oxygen-bound myoglobin, which can be rearranged as the concentration of free oxygen over the sum of that concentration and the dissociation constant K . Since diatomic oxygen is a gas, its concentration in solution can be thought of as a partial pressure.
From defining the p 50 as the partial pressure at which the fractional saturation is 50%, we can deduce that it is in fact equal to the dissociation constant K .
For example, myoglobin's p 50 for O 2 is 130 pascals while the P 50 for adult hemoglobin is 3.5 kPa. Thus, when O 2 partial pressure is low, hemoglobin-bound O 2 is more readily transferred to myoglobin. Myoglobin, found in high concentrations in muscle tissue, can then transfer the oxygen to muscle tissue muscle fibers , where it will be used in the generation of energy to fuel muscle contraction. [ 3 ] Another example is that of human fetal hemoglobin, which has a higher affinity (lower P 50 ) than adult hemoglobin, and therefore allows uptake of oxygen across the placental diffusion barrier. [ 4 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/P50_(pressure) |
P680 , or photosystem II primary donor , is the reaction-center chlorophyll a molecular dimer associated with photosystem II in plants, algae, and cyanobacteria, and central to oxygenic photosynthesis .
Its name is derived from the word “pigment” (P) and the presence of a major bleaching band centered around 680-685 nm in the flash-induced absorbance difference spectra of P680/ P680+•. [ 1 ]
The structure of P680 consists of a hetero dimer of two distinct chlorophyll molecules,
referred to as P D1 and P D2 . This “special pair” forms an excitonic dimer that functions as a single unit, excited by light energy as if they were a single molecule. [ 2 ]
P680 receives excitation energy either by directly absorbing a photon of suitable frequency or indirectly from other chlorophylls within photosystem II, thereby exciting an electron to a higher energy level . The resulting P680 with a loosened electron is designated as P680*, which is a strong reducing agent .
Following excitation, the loosened electron of P680* is taken up by the primary electron acceptor, a pheophytin molecule located within photosystem II near P680. During this transfer, P680* is ionized and oxidized, producing cationic P680 + .
P680 + is the strongest biological oxidizing agent known, with an estimated redox potential of ~1.3 V. [ 3 ] This makes it possible to oxidize water during oxygenic photosynthesis . P680 + recovers its lost electron by oxidizing water via the oxygen-evolving complex , which regenerates P680.
This photosynthesis article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/P680 |
P700 , or photosystem I primary donor , is a molecular dimer of chlorophyll a associated with the reaction-center of photosystem I in plants, algae, and cyanobacteria. [ 1 ] [ 2 ] [ 3 ] [ 4 ]
Its name is derived from the word “pigment” (P) and the presence of a major bleaching band centered around 695-700 nm in the flash-induced absorbance difference spectra of P700/ P700+•. [ 5 ]
The structure of P700 consists of a heterodimer with two distinct chlorophyll molecules, most notably chlorophyll a and chlorophyll a ’, giving it an additional name of “special pair”. [ 6 ] Inevitably, however, the special pair of P700 behaves as if it were just one unit. This species is vital due to its ability to absorb light energy with a wavelength approximately between 430 nm-700 nm, and transfer high-energy electrons to a series of acceptors that are situated near it, like Fe-S complex, Ferridoxyn( FD) , which have a higher redox potential i.e. greater affinity to electron . [ 7 ]
Photosystem I operates with the functions of producing NADPH , the reduced form of NADP + ( Fd 2- red + NADH + 2 NADP + + H + = Fd ox + NAD + + 2 NADPH.) [1] , at the end of the photosynthetic reaction through electron transfer , and of providing energy to a proton pump and eventually ATP , for instance in cyclic electron transport.
When photosystem I absorbs light, an electron is excited to a higher energy level in the P700 chlorophyll. The resulting P700 with an excited electron is designated as P700*, which is a strong reducing agent due to its very negative redox potential of -1.2V . [ 8 ]
Following the excitation of P700, one of its electrons is passed on to an electron acceptor , A o , triggering charge separation producing an anionic A o − and cationic P700 + . Subsequently, electron transfer continues from A o to a phylloquinone molecule known as A 1 , and then to three iron-sulfur clusters . [ 9 ]
Type I photosystems use iron-sulfur cluster proteins as terminal electron acceptors. Thus, the electron is transferred from F x to another iron sulfur cluster, F A , and then passed on to the last iron-sulfur cluster serving as an electron acceptor, F B . Eventually, the electron is transferred to the protein ferredoxin , causing it to transform into its reduced form, which subsequently finalizes the process by reducing NADP + to NADPH.
The rate of electrons being passed from P700* to the subsequent electron acceptors is high, preventing the electron from being transferred back to P700 + . [ 10 ] Consequently, in most cases, the electrons transferring within photosystem I follow a linear pathway, from the excitation of the P700 special pair to the production of NADPH.
In certain situations, it is vital for the photosynthetic organism to recycle the electrons being transferred, resulting in the electron from the terminal iron-sulfur cluster F B transferring back to the cytochrome b6f complex (adaptor between photosystems II and I). [ 11 ] Utilizing the energy of P700 + , the cyclic pathway creates a proton gradient useful for the production of ATP, while no NADPH is produced, since the protein ferredoxin does not become reduced. [ 12 ]
P700 + recovers its lost electron by oxidizing plastocyanin , which regenerates P700. | https://en.wikipedia.org/wiki/P700 |
PABPII , or polyadenine binding protein II , is a protein involved in the assembly of the polyadenine tail added to newly synthesized pre- messenger RNA (mRNA) molecules during the process of gene transcription . It is a regulatory protein that controls the rate at which polyadenine polymerase (PAP) adds adenine nucleotides to the 3' end of the growing tail within the nucleus of the cell. In the absence of PABPII, PAP adds adenines slowly, typically about 12. PABPII then binds to the short polyadenine tail and induces an acceleration in the rate of addition by PAP until the tail has grown to about 200 adenines long. The mechanism by which PABPII signals the termination of the polymerization reaction once the tail has reached its required length is not clearly understood.
PABPII is distinct from the related protein PABPI in being localized to the cell nucleus rather than the cytoplasm .
This protein -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PABPII |
The PACMAD clade (previously PACCMAD, PACCAD, or PACC [ 2 ] ) is one of two major lineages (or clades ) of the true grasses ( Poaceae ), regrouping six subfamilies and about 5700 species, more than half of all true grasses. Its sister group is the BOP clade . The PACMAD lineage is the only group within the grasses in which the C 4 photosynthesis pathway has evolved; studies have shown that this happened independently multiple times. [ 3 ]
The name of the clade comes from the first initials of the included subfamilies Panicoideae , Arundinoideae , Chloridoideae , Micrairoideae , Aristidoideae , and Danthonioideae . It has no defined taxonomic rank but is used frequently because it refers to a well-defined monophyletic group with a distinct ecology.
Phylogeny of the PACMAD clade, with photosynthetic pathways for each subfamily: [ 3 ]
Anomochlooideae
Pharoideae
Puelioideae
BOP clade
Aristidoideae C 3 & C 4
Panicoideae C 3 & C 4
Chloridoideae C 3 & C 4
Danthonioideae C 3
Arundinoideae C 3
Micrairoideae C 3 & C 4
This Poaceae article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PACMAD_clade |
In interaction design , PACT (an acronym for People, Activities, Contexts, Technologies) is a structure used to analyse with whom, what and where a user interact with a user interface . [ 1 ] Interaction is considered, in this framework, as a relationship between people, activities, contexts, and technologies. [ 2 ]
To analyze a user experience (UX) design using PACT, a designer must scope out the possible variety of people, activities, contexts, and technologies in a domain through brainstorming or envisionment techniques. [ 3 ] PACT also focuses on three categories for mapping people differences: physical differences, psychological differences, and social differences. [ 4 ]
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PACT_(interaction_design) |
The PAH world hypothesis is a speculative hypothesis that proposes that polycyclic aromatic hydrocarbons (PAHs), known to be abundant in the universe , [ 1 ] [ 2 ] [ 3 ] including in comets, [ 4 ] and assumed to be abundant in the primordial soup of the early Earth , played a major role in the origin of life by mediating the synthesis of RNA molecules, leading into the RNA world . However, as yet, the hypothesis is untested. [ 5 ]
The 1952 Miller–Urey experiment demonstrated the synthesis of organic compounds , such as amino acids , formaldehyde and sugars , from the original inorganic precursors the researchers presumed to have been present in the primordial soup (but is no longer considered likely). This experiment inspired many others. In 1961, Joan Oró found that the nucleotide base adenine could be made from hydrogen cyanide (HCN) and ammonia in a water solution. [ 6 ] Experiments conducted later showed that the other RNA and DNA nucleobases could be obtained through simulated prebiotic chemistry with a reducing atmosphere . [ 7 ]
The RNA world hypothesis shows how RNA can become its own catalyst (a ribozyme ). In between there are some missing steps such as how the first RNA molecules could be formed. The PAH world hypothesis was proposed by Simon Nicholas Platts in May 2004 to try to fill in this missing step. [ 8 ] A more thoroughly elaborated idea has been published by Ehrenfreund et al. [ 9 ]
Polycyclic aromatic hydrocarbons are the most common and abundant of the known polyatomic molecules in the visible universe , and are considered a likely constituent of the primordial sea . [ 1 ] [ 2 ] [ 3 ] PAHs, along with fullerenes (or " buckyballs "), have been recently detected in nebulae. [ 10 ] Buckminsterfullerene (C 60 ) has been identified in the interstellar medium spaces . [ 11 ] [ 12 ] ( Fullerenes are also implicated in the origin of life; according to astronomer Letizia Stanghellini, "It's possible that buckyballs from outer space provided seeds for life on Earth." [ 13 ] ) PAHs, subjected to interstellar medium (ISM) conditions, are transformed, through hydrogenation , oxygenation and hydroxylation , to more complex organics — "a step along the path toward amino acids and nucleotides , the raw materials of proteins and DNA , respectively". [ 14 ] [ 15 ] Further, as a result of these transformations, the PAHs lose their spectroscopic signature which could be one of the reasons "for the lack of PAH detection in interstellar ice grains , particularly the outer regions of cold, dense clouds or the upper molecular layers of protoplanetary disks ." [ 14 ] [ 15 ]
In 2013, polycyclic aromatic hydrocarbons were detected in the upper atmosphere of Titan , the largest moon of the planet Saturn . [ 16 ]
Low-temperature chemical pathways from simple organic compounds to complex PAHs have been demonstrated. Such chemical pathways may help explain the presence of PAHs in the low-temperature atmosphere of Saturn 's moon Titan , and may be significant pathways, in terms of the PAH world hypothesis, in producing precursors to biochemicals related to life as we know it. [ 17 ] [ 18 ]
PAHs are not normally very soluble in sea water, but when subject to ionizing radiation such as solar UV light, the outer hydrogen atoms can be stripped off and replaced with a hydroxyl group, rendering the PAHs far more soluble.
These modified PAHs are amphiphilic , which means that they have parts that are both hydrophilic and hydrophobic . When in solution, they assemble in discotic mesogenic ( liquid crystal ) stacks which, like lipids , tend to organize with their hydrophobic parts protected.
In 2014, NASA announced a database [ 19 ] for tracking polycyclic aromatic hydrocarbons (PAHs) in the universe . More than 20% of the carbon in the universe may be associated with PAHs, [ 19 ] [ 20 ] possible starting materials for the formation of life . PAHs seem to have been formed as early as a couple of billion years after the Big Bang , are abundant in the universe, [ 1 ] [ 2 ] [ 3 ] and are associated with new stars and exoplanets . [ 19 ]
In the self-ordering PAH stack, the separation between adjacent rings is 0.34 nm. This is the same separation found between adjacent nucleotides of RNA and DNA . Smaller molecules will naturally attach themselves to the PAH rings. However PAH rings, while forming, tend to swivel around on one another, which will tend to dislodge attached compounds that would collide with those attached to those above and below. Therefore, it encourages preferential attachment of flat molecules such as pyrimidine and purine nucleobases , the key constituents (and information carriers) of RNA and DNA. These bases are similarly amphiphilic and so also tend to line up in similar stacks.
According to the hypothesis, once the nucleobases are attached (via hydrogen bonds ) to the PAH scaffolding, the inter-base distance would select for "linker" molecules of a specific size, such as small formaldehyde ( methanal ) oligomers , also taken from the prebiotic "soup", which will bind (via covalent bonds ) to the nucleobases as well as each other to add a flexible structural backbone. [ 5 ] [ 8 ]
A subsequent transient drop in the ambient pH (increase in acidity), for example as a result of a volcanic discharge of acidic gases such as sulfur dioxide or carbon dioxide , would allow the bases to break off from their PAH scaffolding, forming RNA-like molecules (with the formaldehyde backbone instead of the ribose-phosphate backbone used by "modern" RNA, but the same 0.34 nm pitch). [ 5 ]
The hypothesis further speculates that once long RNA-like single strands are detached from the PAH stacks, and after ambient pH levels became less acidic, they would tend to fold back on themselves, with complementary sequences of nucleobases preferentially seeking out each other and forming hydrogen bonds , creating stable, at least partially double-stranded RNA-like structures, similar to ribozymes . The formaldehyde oligomers would eventually be replaced with more stable ribose-phosphate molecules for the backbone material, resulting in a starting milestone for the RNA world hypothesis , which speculates about further evolutionary developments from that point. [ 5 ] [ 8 ] [ 21 ] | https://en.wikipedia.org/wiki/PAH_world_hypothesis |
PANoptosis is a prominent innate immune, inflammatory, and lytic cell death pathway initiated by innate immune sensors and driven by caspases and receptor-interacting protein kinases (RIPKs) through multiprotein PANoptosome complexes. [ 1 ] [ 2 ] The assembly of the PANoptosome cell death complex occurs in response to germline-encoded pattern-recognition receptors (PRRs) sensing pathogens, including bacterial, viral, and fungal infections, as well as pathogen-associated molecular patterns , damage-associated molecular patterns , and cytokines that are released during infections, inflammatory conditions, and cancer . [ 1 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ] [ 15 ] [ 16 ] Several PANoptosome complexes, such as the ZBP1 -, AIM2 -, RIPK1 -, NLRP3 and NLRC5 - and NLRP12 -PANoptosomes, have been characterized so far. [ 1 ] [ 17 ] [ 18 ] [ 19 ] [ 20 ] [ 21 ] [ 22 ] [ 23 ] [ 24 ]
Emerging genetic, molecular, and biochemical studies have identified extensive crosstalk among the molecular components across various cell death pathways in response to a variety of pathogens and innate immune triggers. [ 3 ] [ 4 ] Historically, inflammatory caspase -mediated pyroptosis and RIPK-driven necroptosis were described as two major inflammatory cell death pathways. While the PANoptosis pathway has some molecular components in common with pyroptosis and necroptosis , as well as with the non-lytic apoptosis pathway, these mechanisms are separate processes that are associated with distinct triggers, protein complexes, and execution pathways. [ 2 ] Inflammasome -dependent pyroptosis involves inflammatory caspases, including caspase-1 and caspase-11 in mice, and caspases-1, - 4 , and - 5 in humans, and is executed by gasdermin D . [ 25 ] [ 26 ] [ 27 ] [ 28 ] [ 29 ] [ 30 ] [ 31 ] In contrast, necroptosis occurs via RIPK1/3-mediated MLKL activation, which is downstream of caspase-8 inhibition. [ 32 ] [ 33 ] [ 34 ] [ 35 ] On the other hand, PANoptosis is [TDK1] driven by caspases and RIPKs and is executed by gasdermins, MLKL, NINJ1 , and potentially other yet to be identified molecules cleaved by caspases. [ 36 ] [ 37 ] [ 38 ] [ 39 ] [ 40 ] [ 41 ] [ 19 ] [ 21 ] Moreover, caspase-8 is essential for cell death in PANoptosis [ 42 ] [ 43 ] but needs to be inactivated or inhibited to induce necroptosis. [ 44 ] [ 45 ]
Summary of the different morphologies, mechanisms and outcomes of apoptosis, pyroptosis, necroptosis, and PANoptosis
PANoptosis has also been implicated in inflammatory diseases, neurological diseases, and cancer. Additionally, activation of PANoptosis can clear infected cells for host defense, and it has shown preclinical promise as an anti-cancer strategy. [ 46 ] [ 47 ] [ 48 ] [ 49 ] [ 50 ] [ 51 ] [ 52 ] [ 53 ] [ 54 ] [ 55 ]
PANoptosis has now been identified in a variety of infections, including influenza A virus , herpes simplex virus 1 (HSV1), and coronavirus . For example, PANoptosis is important for host defense during influenza infection through the ZBP1-PANoptosome and during HSV1 infections through the AIM2-PANoptosome. Studies with beta-coronaviruses have shown that IFN can induce ZBP1 -mediated PANoptosis during SARS-CoV-2 infection, thereby limiting the efficacy of IFN treatment during infection and resulting in morbidity and mortality. This suggests that inhibiting ZBP1 may improve the therapeutic efficacy of IFN therapy during SARS-CoV-2 infection and possibly other inflammatory conditions where IFN-mediated cell death and pathology occur. [ 56 ] [ 57 ]
In Yersinia pseudotuberculosis infections, PANoptosis is induced through the RIPK1-PANoptosome, and the deletion of caspase-8 and RIPK3 prevents cell death. During Francisella novicida infection, PANoptosis occurs through the AIM2-PANoptosome. [ 5 ] [ 7 ] [ 17 ] [ 19 ] PANoptosis has also been observed in Salmonella enterica and Listeria monocytogenes infections, where the combined loss of caspases and RIPK3 significantly protects cells from death. [ 58 ]
PANoptosis also occurs in fungal infections, including those caused by Candida albicans and Aspergillus fumigatus . [ 59 ]
Treatment of cancer cells with the PANoptosis-inducing agents TNF and IFN-γ [ 60 ] [ 6 ] can reduce tumor size in preclinical models. [ 61 ] The combination of the nuclear export inhibitor selinexor and IFN can also cause PANoptosis and regress tumors in preclinical models. [ 3 ] [ 62 ]
More recent evidence suggests that NLRC5 - NLRP12 -mediated PANoptosis is activated by heme , which can be released by red blood cell lysis during infection or inflammatory disease, in combination with specific components of infection or cellular damage. Deletion of NLRP12 protects against pathology in animal models of hemolytic disease, suggesting this could also act as a therapeutic target. Similarly, the NLRC5-PANoptosome, which also contains NLRP12, was identified as a response to NAD + depletion downstream of heme-containing triggers. Deletion of NLRC5 protects against not only hemolytic disease models, but also colitis and HLH models. [ 22 ] [ 23 ]
Additionally, PANoptosis can be induced by heat stress (HS), such as fever, during infection, and NINJ1 is a key executioner in this context. Deletion of NINJ1 in a murine model of HS and infection reduces mortality; furthermore, deleting essential PANoptosis effectors upstream completely rescues the mice from mortality, thereby identifying NINJ1 and PANoptosis effectors as potential therapeutic targets. [ 63 ]
The regulation of PANoptosis involves numerous PANoptosomes, which include multiple sensor molecules such as NLRP3 , ZBP1 , AIM2 , NLRC5 , and NLRP12 , along with complex-forming molecules such as caspases and RIPKs. These components activate various downstream cell death executioners and play a role in disease. Therefore, modulating the components of this pathway has potential for therapy. However, excessive activation of PANoptosis can lead to inflammation , inflammatory disease, and cytokine storm syndromes. [ 6 ] [ 11 ] [ 64 ] [ 21 ] [ 1 ] Treatments that block TNF and IFN-γ to prevent PANoptosis have provided therapeutic benefit in preclinical models of cytokine storm syndromes, including cytokine shock, SARS-CoV-2 infection, sepsis , and hemophagocytic lymphohistiocytosis , suggesting the therapeutic potential of modulating this pathway. [ 6 ] [ 65 ] | https://en.wikipedia.org/wiki/PANoptosis |
PAQ is a series of lossless data compression archivers that have gone through collaborative development to top rankings on several benchmarks measuring compression ratio (although at the expense of speed and memory usage). Specialized versions of PAQ have won the Hutter Prize and the Calgary Challenge . [ 1 ] PAQ is free software distributed under the GNU General Public License . [ 2 ]
PAQ uses a context mixing algorithm. Context mixing is related to prediction by partial matching (PPM) in that the compressor is divided into a predictor and an arithmetic coder , but differs in that the next-symbol prediction is computed using a weighted combination of probability estimates from a large number of models conditioned on different contexts. Unlike PPM, a context doesn't need to be contiguous. Most PAQ versions collect next-symbol statistics for the following contexts:
All PAQ versions predict and compress one bit at a time, but differ in the details of the models and how the predictions are combined and postprocessed. Once the next-bit probability is determined, it is encoded by arithmetic coding . There are three methods for combining predictions, depending on the version:
PAQ1SSE and later versions postprocess the prediction using secondary symbol estimation (SSE). The combined prediction and a small context are used to look up a new prediction in a table. After the bit is encoded, the table entry is adjusted to reduce the prediction error. SSE stages can be pipelined with different contexts or computed in parallel with the outputs averaged.
A string s is compressed to the shortest byte string representing a base-256 big-endian number x in the range [0, 1] such that P( r < s ) ≤ x < P( r ≤ s ), where P( r < s ) is the probability that a random string r with the same length as s will be lexicographically less than s . It is always possible to find an x such that the length of x is at most one byte longer than the Shannon limit , −log 2 P( r = s ) bits. The length of s is stored in the archive header.
The arithmetic coder in PAQ is implemented by maintaining for each prediction a lower and upper bound on x , initially [0, 1]. After each prediction, the current range is split into two parts in proportion to P(0) and P(1), the probability that the next bit of s will be a 0 or 1 respectively, given the previous bits of s . The next bit is then encoded by selecting the corresponding subrange to be the new range.
The number x is decompressed back to string s by making an identical series of bit predictions (since the previous bits of s are known). The range is split as with compression. The portion containing x becomes the new range, and the corresponding bit is appended to s .
In PAQ, the lower and upper bounds of the range are represented in three parts. The most significant base-256 digits are identical, so they can be written as the leading bytes of x . The next 4 bytes are kept in memory, such that the leading byte is different. The trailing bits are assumed to be all zeros for the lower bound and all ones for the upper bound. Compression is terminated by writing one more byte from the lower bound.
In PAQ versions through PAQ6, each model maps a set of distinct contexts to a pair of counts, n 0 {\displaystyle n_{0}} , a count of zero bits, and n 1 {\displaystyle n_{1}} , a count of 1 bits. In order to favor recent history, half of the count over 2 is discarded when the opposite bit is observed. For example, if the current state associated with a context is ( n 0 , n 1 ) = ( 12 , 3 ) {\displaystyle (n_{0},n_{1})=(12,3)} and a 1 is observed, then the counts are updated to (7, 4).
A bit is arithmetically coded with space proportional to its probability, either P(1) or P(0) = 1 − P(1). The probabilities are computed by weighted addition of the 0 and 1 counts:
where w i is the weight of the i -th model. Through PAQ3, the weights were fixed and set in an ad-hoc manner. (Order- n contexts had a weight of n 2 .) Beginning with PAQ4, the weights were adjusted adaptively in the direction that would reduce future errors in the same context set. If the bit to be coded is y , then the weight adjustment is:
Beginning with PAQ7, each model outputs a prediction (instead of a pair of counts). These predictions are averaged in the logistic domain:
where P(1) is the probability that the next bit will be a 1, P i (1) is the probability estimated by the i -th model, and
After each prediction, the model is updated by adjusting the weights to minimize coding cost:
where η is the learning rate (typically 0.002 to 0.01), y is the predicted bit, and ( y − P(1)) is the prediction error. The weight update algorithm differs from backpropagation in that the terms P(1)P(0) are dropped. This is because the goal of the neural network is to minimize coding cost, not root mean square error.
Most versions of PAQ use a small context to select among sets of weights for the neural network. Some versions use multiple networks whose outputs are combined with one more network prior to the SSE stages. Furthermore, for each input prediction there may be several inputs which are nonlinear functions of P i (1) in addition to stretch(P(1)).
Each model partitions the known bits of s into a set of contexts and maps each context to a bit history represented by an 8-bit state. In versions through PAQ6, the state represents a pair of counters ( n 0 , n 1 ). In PAQ7 and later versions under certain conditions, the state also represents the value of the last bit or the entire sequence. The states are mapped to probabilities using a 256-entry table for each model. After a prediction by the model, the table entry is adjusted slightly (typically by 0.4%) to reduce the prediction error.
In all PAQ8 versions, the representable states are as follows:
To keep the number of states to 256, the following limits are placed on the representable counts: (41, 0), (40, 1), (12, 2), (5, 3), (4, 4), (3, 5), (2, 12), (1, 40), (0, 41). If a count exceeds this limit, then the next state is one chosen to have a similar ratio of n 0 to n 1 . Thus, if the current state is ( n 0 = 4, n 1 = 4, last bit = 0) and a 1 is observed, then the new state is not ( n 0 = 4, n 1 = 5, last bit = 1). Rather, it is ( n 0 = 3, n 1 = 4, last bit = 1).
Most context models are implemented as hash tables . Some small contexts are implemented as direct lookup tables .
Some versions of PAQ, in particular PAsQDa, PAQAR (both PAQ6 derivatives), and PAQ8HP1 through PAQ8HP8 (PAQ8 derivatives and Hutter prize recipients) preprocess text files by looking up words in an external dictionary and replacing them with 1- to 3-byte codes. In addition, uppercase letters are encoded with a special character followed by the lowercase letter. In the PAQ8HP series, the dictionary is organized by grouping syntactically and semantically related words together. This allows models to use just the most significant bits of the dictionary codes as context.
The following table is a sample from the Large Text Compression Benchmark by Matt Mahoney that consists of a file consisting of 10 9 bytes (1 GB , or 0.931 GiB ) of English Wikipedia text.
See Lossless compression benchmarks for a list of file compression benchmarks.
The following lists the major enhancements to the PAQ algorithm. In addition, there have been a large number of incremental improvements, which are omitted.
The series PAQ8HP1 through PAQ8HP8 were released by Alexander Ratushnyak from August 21, 2006, through January 18, 2007, as Hutter Prize submissions. The Hutter Prize is a text compression contest using a 100 MB English and XML data set derived from Wikipedia's source. The PAQ8HP series was forked from PAQ8H. The programs include text preprocessing dictionaries and models tuned specifically to the benchmark. All non-text models were removed. The dictionaries were organized to group syntactically and semantically related words and to group words by common suffix. The former strategy improves compression because related words (which are likely to appear in similar context) can be modeled on the high order bits of their dictionary codes. The latter strategy makes the dictionary easier to compress. The size of the decompression program and compressed dictionary is included in the contest ranking.
On October 27, 2006, it was announced [ 5 ] that PAQ8HP5 won a Hutter Prize for Lossless Compression of Human Knowledge of € 3,416.
On June 30, 2007, Ratushnyak's PAQ8HP12 was awarded a second Hutter prize of €1732, [ 6 ] improving upon his previous record by 3.46%.
Being free software , PAQ can be modified and redistributed by anyone who has a copy. This has allowed other authors to fork the PAQ compression engine and add new features such as a graphical user interface or better speed (at the expense of compression ratio). Notable PAQ derivatives include: | https://en.wikipedia.org/wiki/PAQ |
The PAQUID (or Paquid) cohort is a group of 3,777 individuals aged 65 years or older who were studied from 1988 until 2004. [ 1 ] Researchers selected participants for the group from at least 91 different areas of southwestern France to study the effects of different environmental, behavioral, and social vectors of age-related medical conditions and diseases. One of the major research goals was to determine some of the causes of dementia and Alzheimer's disease , such as the correlation between the levels of aluminum in drinking water and the occurrence of dementia. [ 2 ] [ 3 ] [ 1 ]
The studies were conducted by the Université Victor-Segalen, Bordeaux 2 (UB2) in Bordeaux , France.
The source of the term is "Personnes Agées QUID," which can be loosely translated from French and Latin as "What about the elderly?" [ 4 ] | https://en.wikipedia.org/wiki/PAQUID_cohort |
PAR-CLIP [ 1 ] ( photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation ) is a biochemical method for identifying the binding sites of cellular RNA-binding proteins (RBPs) and microRNA -containing ribonucleoprotein complexes (miRNPs). The method relies on the incorporation of ribonucleoside analogs that are photoreactive , such as 4-thiouridine (4-SU) and 6-thioguanosine (6-SG), into nascent RNA transcripts by living cells. Irradiation of the cells by ultraviolet light of 365 nm wavelength induces efficient crosslinking of photoreactive nucleoside– labeled cellular RNAs to interacting RBPs. Immunoprecipitation of the RBP of interest is followed by isolation of the crosslinked and coimmunoprecipitated RNA. The isolated RNA is converted into a cDNA library and is deep sequenced using next-generation sequencing technology. [ 1 ] [ 2 ]
Recently, PAR-CLIP have been applied to determine the transcriptome-wide binding sites of several known RBPs and microRNA-containing ribonucleoprotein complexes at high resolution. [ 1 ] [ 3 ] [ 4 ] [ 5 ] | https://en.wikipedia.org/wiki/PAR-CLIP |
PARSEC is a package designed to perform electronic structure calculations of solids and molecules using density functional theory (DFT). The acronym stands for Pseudopotential Algorithm for Real-Space Electronic Calculations . [ 1 ] It solves the Kohn–Sham equations in real space, without the use of explicit basis sets . [ 2 ]
One of the strengths of this code is that it handles non-periodic boundary conditions in a natural way, without the use of super-cells, but can equally well handle periodic and partially periodic boundary conditions. [ 3 ] [ 4 ] [ 5 ] Another key strength is that it is readily amenable to efficient massive parallelization, making it highly effective for very large systems. [ 6 ]
Its development started in early 1990s with James Chelikowsky (now at the University of Texas ), Yousef Saad and collaborators at the University of Minnesota . The code is freely available under the GNU GPLv 2. Currently, its public version is 1.4.4. Some of the physical/chemical properties calculated by this code are: Kohn–Sham band structure , atomic forces (including molecular dynamics capabilities), static susceptibility , magnetic dipole moment , and many additional molecular and solid state properties. | https://en.wikipedia.org/wiki/PARSEC |
PAST is a large-scale, distributed, persistent storage system based on the Pastry peer-to-peer overlay network.
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PAST_storage_utility |
PAVA spray is an incapacitant spray similar to pepper spray . It is dispensed from a handheld canister, in a liquid stream. It contains a 0.3% solution of pelargonic acid vanillylamide (PAVA), also called nonivamide, a synthetic capsaicinoid (analogue of capsaicin ), in a solvent of aqueous ethanol . The propellant is nitrogen . This solution has been selected because this is the minimum concentration which will fulfill the purpose of the equipment: namely, to minimise a person's capacity for resistance, without unnecessarily prolonging their discomfort.
PAVA is significantly more potent than CS gas . [ 1 ] The liquid stream is a spray pattern and has a maximum effective range of up to four metres (13 ft). Maximum accuracy, however, will be achieved over a distance of 1.25–2 metres (4.1–6.6 ft). The operating distance is the distance between the canister and the subject's eyes, not the distance between the user and the subject. [ 1 ]
PAVA primarily affects the eyes, causing closure and severe pain. The pain to the eyes is reported to be greater than that caused by CS. The effectiveness rate is very high once PAVA gets into the eyes; however, there have been occasions where PAVA and CS have failed to work—especially when the subject is under the influence of alcohol or other drugs. Exposure to fresh moving air will normally result in a significant recovery from the effects of PAVA, within 15–35 minutes. [ 1 ]
Pharmacologically, like other capsaicinoids, PAVA works by direct binding to receptors ( TRPV1 ) that normally produce the pain and sensation of heat, as if exposed to scalding heat.
PAVA is used widely as a less lethal, temporary defence tool around the world including in the United Kingdom , [ 2 ] India , [ 3 ] Switzerland , [ 4 ] and others.
PAVA is approved for police and prison service use in the United Kingdom. [ 5 ] British police forces had traditionally used CS gas spray, but with the more widespread carriage of tasers , PAVA has now entirely replaced its predecessor due to its non-flammable nature. [ 6 ]
There are various treatments to combat the effects of nonivamide. One popular method includes administering a one to one solution of milk of magnesia and water to the eyes. Doctors also recommend not using oils or creams on the skin, and to not wear contact lenses, if one is planning to minimise the effects of nonivamide. [ 8 ] | https://en.wikipedia.org/wiki/PAVA_spray |
PA Server Monitor is a server and network monitoring software from Power Admin LLC. PA Server Monitor focuses primarily on server and network health through numerous resource checks, reports, and alerting options. The agentless , on-premises [ 2 ] software can monitor thousands of devices from a single installation. The monitored devices can be desktop computers , servers , routers and other devices.
The main function of the software is to monitor performance of servers and network devices in Windows and Linux environments. Data is kept on customers servers, not stored in the cloud.
An agentless monitoring software to watch ping , CPU , memory, disk, SNMP + traps, events, with available historical reports. Apps are available for iOS and Android .
Power Admin LLC is a privately held company founded by IT professionals, located in Shawnee, Kansas , outside of downtown Kansas City, Missouri area. Power Admin has been providing professional grade system monitoring products since 1992 for all types of business from SMBs to Fortune 500 companies.
Power Admin also developed two other popular utilities that are used all over the world.
PAExec [ 3 ] allows a user to launch Windows programs [ 4 ] on remote Windows computers without needing to install software on the remote computer first. [ 5 ] This was written as an alternative to Microsoft's PsExec [ 6 ] tool (originally by SysInternals 's Mark Russinovich ), because it could not be redistributed, and sensitive command-line options like username and passwords were sent as clear text. Source code is readily available on GitHub . [ 7 ]
Power Admin also developed SpeedFanHttpAgent. [ 8 ] The SpeedFan HTTP Agent exports and allows you to access SpeedFan 's (utility by Alfredo Milani Comparetti) temperature data from across the network via a simple HTTP request.
PA Server Monitor monitors event logs, disk space, running services, web page content, SNMP object values, log files, processes, ping response time, directory quotas, changed files and directories. [ 9 ] Equipped to monitor thousands of servers/devices from a single installation, and more via satellite monitoring services.
It has extensive reporting to get status reports for servers/devices, group summaries, uptime and historic stats, providing actions and alerts by customizable email, SMS and other types of notifications, and suppression and escalation of certain notifications. It can also automatically restart services and run custom scripts.
Other capabilities include satellite monitoring of remote offices/locations across firewalls and/or across the internet without a VPN , agentless server monitoring and a bulk config feature to speed changes across many servers/devices.
Alerts in PA Server Monitor can use event suppression to cut down on false alerts, event deduplication system to further remove noise, and event escalation [ 10 ] [ 11 ] to give alerts increasing visibility as a problem persists for longer. Alert Reminders can also be used to make sure problems don't get forgotten about.
PA Server Monitor is Windows-based, and many monitors use standard Microsoft Windows APIs (mostly based on Microsoft RPC ). Standard protocols such as SNMP (including Traps), Syslog , IPMI , HTTPS, FTP , various mail protocols, SSH , etc. allows for monitoring non-Windows devices.
PA Server Monitor is made of three main components: [ 12 ] the Central Service, the Console and optional Satellite Monitoring Services. Because the product is agentless, nothing gets installed on monitored devices. In addition, since the software is installed on-premises, all data remains on-premises.
The Central Service is the hub of the software. This is where the database is stored for historical reporting and trend analysis , alerts are sent from, and where all configuration is kept. The Central Service contains a web server from which the web interface and reports are viewed.
The Console application is a native Windows application, and the "single pane of glass" from which all configuration, monitoring and reporting is done. The Console can be installed on multiple workstations, and they all connect to the Central Service through an HTTPS-based API.
The Satellite Monitoring Service enables remote and distributed monitoring . [ 13 ] It is an optional monitoring engine (only available with the Ultra license) that can do all the same monitoring the Central Service can do. This can be installed in the same network as the Central Service to distribute monitoring load, or it can be installed at remote sites for monitoring devices that the Central Service cannot access. Even in the remote site case, all configuration continues to be done through the Console application. The Satellite Monitoring Service also connects to the Central Service through the HTTPS-based API.
An optional second Central Monitoring Server can be installed which will keep track of the status of the main Central Monitoring Server and should it fail, the Failover will automatically take over monitoring duties. Satellite Monitoring Services can automatically switch to the newly active Failover server during this period.
Monitors are the basic function that contains a reference to a resource to be monitored, as well as thresholds to compare against, and a list of actions (alerts) to fire if there are problems. Monitors have several attributes to make them easier to conform to various environments.
Source: [ 14 ] | https://en.wikipedia.org/wiki/PA_Server_Monitor |
PB-28 [ 1 ] is an agonist of the sigma-2 receptor . [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ]
It is derived from cyclohexylpiperazine .
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PB-28 |
P BAD (systematically araBp ) is a promoter found in bacteria and especially as part of plasmids used in laboratory studies. The promoter is a part of the arabinose operon whose name derives from the genes it regulates transcription of: araB , araA , and araD . [ 1 ] [ 2 ] In E. coli , the P BAD promoter is adjacent to the P C promoter (systematically araCp ), which transcribes the araC gene in the opposite direction. araC encodes the AraC protein , which regulates activity of both the P BAD and P C promoters. [ 3 ] [ 4 ] [ 5 ] The cyclic AMP receptor protein CAP binds between the P BAD and P C promoters, stimulating transcription of both when bound by cAMP. [ 6 ]
Transcription initiation at the P BAD promoter occurs in the presence of high arabinose and low glucose concentrations. [ 7 ] Upon arabinose binding to AraC, the N-terminal arm of AraC is released from its DNA binding domain via a “light switch” mechanism. [ 1 ] [ 2 ] This allows AraC to dimerize and bind the I 1 and I 2 operators . [ 3 ] The AraC-arabinose dimer at this site contributes to activation of the P BAD promoter. [ 2 ] Additionally, CAP binds to two CAP binding sites upstream of the I 1 and I 2 operators and helps activate the P BAD promoter. [ 6 ] In the presence of both high arabinose and high glucose concentrations however, low cAMP levels prevent CAP from activating the P BAD promoter. [ 7 ] It is hypothesized that P BAD promoter activation by CAP and AraC is mediated through contacts between the C-terminal domain of the α-subunit of RNA polymerase and the CAP and AraC proteins. [ 8 ]
Without arabinose, and regardless of glucose concentration, the P BAD and P C promoters are repressed by AraC. [ 2 ] [ 7 ] The N-terminal arm of AraC interacts with its DNA binding domain, allowing two AraC proteins to bind to the O 2 and I 1 operator sites. [ 1 ] The O 2 operator is situated within the araC gene. An AraC dimer also binds to the O 1 operator and represses the P C promoter via a negative autoregulatory feedback loop. [ 2 ] The two bound AraC proteins dimerize and cause looping of the DNA. [ 3 ] [ 4 ] The looping prevents binding of CAP and RNA Polymerase, which normally activate the transcription of both P BAD and P C .
Transcription by P BAD
High Arabinose
Low Arabinose
High Glucose
Repressed
Repressed
Low Glucose
Active
Repressed
The spacing between the O 2 and I 1 operator sites is critical. Adding or removing 5 base pairs between the O 2 and I 1 operator sites abrogates AraC mediated repression of the P BAD promoter. [ 1 ] The spacing requirement arises from the double helix nature of DNA , in which a complete turn of the helix is about 10.5 nucleotides . Therefore, adding or removing 5 base pairs between the O 2 and I 1 operator sites rotates the helix roughly 180 degrees. This reverses the direction that the O 2 operator faces when the DNA is looped and prevents dimerization of the O 2 bound AraC with the bound I 1 araC . [ 1 ] [ 2 ]
The P BAD promoter allows for tight regulation and control of a target gene in vivo . [ 7 ] As explained above, P BAD is regulated by the addition and absence of arabinose . As tested, the promoter can be further repressed with reduced levels of cAMP through the addition of glucose. [ 7 ] Plasmid vectors have been constructed and tested with a selectable marker (Cm R in this case), origin of replication , araC and operons, multiple cloning site and P BAD promoter. Studies show that vectors are highly expressed and can be used, in combination with chromosomal null alleles , to study loss of function of essential genes. [ 7 ] | https://en.wikipedia.org/wiki/PBAD_promoter |
pBLU is a commercially produced bacterial plasmid that contains genes for ampicillin resistance ( beta lactamase and beta galactosidase ). It is often used in conjunction with an ampicillin-susceptible E. coli strain to teach students about transformation of eubacteria. [ 1 ] It is 5,437 base pairs long. There is a multiple cloning site in the lacZ gene.
This biotechnology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PBLU |
pBR322 is a plasmid and was one of the first widely used E. coli cloning vectors . Created in 1977 in the laboratory of Herbert Boyer at the University of California, San Francisco , it was named after Francisco Bolivar Zapata , the postdoctoral researcher and Raymond L. Rodriguez . The p stands for "plasmid," and BR for "Bolivar" and "Rodriguez."
pBR322 is 4361 base pairs in length [ 1 ] and has two antibiotic resistance genes – the gene bla encoding the ampicillin resistance (Amp R ) protein , and the gene tetA encoding the tetracycline resistance (Tet R ) protein. It contains the origin of replication of pMB1, and the rop gene, which encodes a restrictor of plasmid copy number . The plasmid has unique restriction sites for more than forty restriction enzymes . Eleven of these forty sites lie within the Tet R gene. There are two sites for restriction enzymes HindIII and ClaI within the promoter of the Tet R gene. There are six key restriction sites inside the Amp R gene.The source of these antibiotic resistance genes are from pSC101 for Tetracycline and RSF2124 for Ampicillin. [ 2 ]
The circular sequence is numbered such that 0 is the middle of the unique EcoRI site and the count increases through the Tet R gene. If we have to remove ampicillin for instance, we must use restriction endonuclease or molecular scissors against PstI and then pBR322 will become anti-resistant to ampicillin. The same process of Insertional Inactivation can be applied to Tetracycline. The Amp R gene is penicillin beta-lactamase . Promoters P1 and P3 are for the beta-lactamase gene. P3 is the natural promoter, and P1 is artificially created by the ligation of two different DNA fragments to create pBR322. P2 is in the same region as P1, but it is on the opposite strand and initiates transcription in the direction of the tetracycline resistance gene. [ 3 ]
Early cloning experiments may be conducted using natural plasmids such the ColE1 and pSC101 . Each of these plasmids may have its advantages and disadvantages. For example, the ColE1 plasmid and its derivatives have the advantage of higher copy number and allow for chloramphenicol amplification of plasmid to produce a high yield of plasmid, however screening for immunity to colicin E1 is not technically simple. [ 4 ] The plasmid pSC101, a natural plasmid from Salmonella panama , [ 5 ] confers tetracycline resistance which allows for simpler screening process with antibiotic selection, but it is a low copy number plasmid which does not give a high yield of plasmid. Another plasmid, RSF 2124, which is a derivative of ColE1, confers ampicillin resistance but is larger.
Many other plasmids were artificially constructed to create one that would be ideal for cloning purpose, and pBR322 was found to be most versatile by many and was therefore the one most popularly used. [ 4 ] It has two antibiotic resistance genes, as selectable markers , and a number of convenient unique restriction sites that made it suitable as a cloning vector . The plasmid was constructed with genetic material from 3 main sources – the tetracycline resistance gene of pSC101, the ampicillin resistance gene of RSF 2124, and the replication elements of pMB1, a close relative of the ColE1 plasmid. [ 6 ] [ 7 ]
A large number of other plasmids based on pBR322 have since been constructed specifically designed for a wide variety of purposes. [ 8 ] [ 9 ] Examples include the pUC series of plasmids. [ 10 ] Most expression vectors for extrachromosomal protein expression and shuttle vectors contain the pBR322 origin of replication, and fragments of pBR322 are very popular in the construction of intraspecies shuttle or binary vectors and vectors for targeted integration and excision of DNA from chromosome. [ 11 ]
The sequence in pBR322 is [ 3 ]
In Michael Crichton's 1990 science fiction novel Jurassic Park “the actual structure of a small fragment of dinosaur DNA“ is shown to visitors to the Jurassic Park Research Insitute. In 1992 NCBI Investigator Mark Boguski used BLAST to compare the Jurassic Park sequence with known DNA sequences, and discovered that the book sequence consisted of three sequences from pBR322, one repeated twice, separated by short random sequences. Boguski wrote up his work as a humorous paper, which was published in the journal BioTechniques . [ 12 ] [ 13 ] | https://en.wikipedia.org/wiki/PBR322 |
Phosphorus tribromide is a colourless liquid with the formula P Br 3 . The liquid fumes in moist air due to hydrolysis and has a penetrating odour. It is used in the laboratory for the conversion of alcohols to alkyl bromides .
PBr 3 is prepared by treating red phosphorus with bromine . An excess of phosphorus is used in order to prevent formation of PBr 5 : [ 1 ] [ 2 ]
Because the reaction is highly exothermic, it is often conducted in the presence of a diluent such as PBr 3 . Phosphorus tribromide is also generated in situ from red phosphorus and bromine. [ 3 ]
Phosphorus tribromide, like PCl 3 and PF 3 , has both properties of a Lewis base and a Lewis acid . For example, with a Lewis acid such as boron tribromide it forms stable 1 :1 adducts such as Br 3 B · PBr 3 . At the same time PBr 3 can react as an electrophile or Lewis acid in many of its reactions, for example with amines .
An important reaction of PBr 3 is with alcohols , where it replaces an OH group with a bromine atom to produce an alkyl bromide . All three bromides can be transferred. [ 4 ]
Several detailed procedures are available. [ 5 ] [ 6 ] In some cases, triphenylphosphine /Br 2 is superior to PBr 3 . [ 7 ]
The mechanism for a primary alcohol involves formation of a phosphorous ester (to form a good leaving group), followed by an S N 2 substitution .
Because of the S N 2 substitution step, the reaction generally works well for primary and secondary alcohols , but fails for tertiary alcohols. If the reacting carbon centre is chiral , the reaction usually occurs with inversion of configuration at the carbon alpha to the alcohol, as is usual with an S N 2 reaction.
In a similar reaction, PBr 3 also converts carboxylic acids to acyl bromides : [ 8 ]
The main use for phosphorus tribromide is for conversion of primary or secondary alcohols to alkyl bromides , [ 9 ] as described above . PBr 3 usually gives higher yields than hydrobromic acid , and it avoids problems of carbocation rearrangement- for example even neopentyl bromide can be made from the alcohol in 60% yield. [ 10 ]
Another use for PBr 3 is as a catalyst for the α-bromination of carboxylic acids . Although acyl bromides are rarely made in comparison with acyl chlorides , they are used as intermediates in Hell-Volhard-Zelinsky halogenation . [ 11 ] Initially PBr 3 reacts with the carboxylic acid to form the acyl bromide, which is more reactive towards bromination. The overall process can be represented as
On a commercial scale, phosphorus tribromide is used in the manufacture of pharmaceuticals such as alprazolam , methohexital and fenoprofen . It is also a potent fire suppression agent marketed under the name PhostrEx .
Phosphorus tribromide is used for doping in microelectronics . [ 12 ]
PBr 3 evolves corrosive HBr , which is toxic, and reacts violently with water and alcohols.
In reactions that produce phosphorous acid as a by-product, when working up by distillation be aware that this can decompose above about 160 °C to give phosphine which can cause explosions in contact with air. [ 9 ] | https://en.wikipedia.org/wiki/PBr3 |
Phosphorus pentabromide is a reactive, yellow solid of formula P Br 5 , which has the structure [PBr 4 ] + Br − (tetrabromophosphonium bromide) in the solid state but in the vapor phase is completely dissociated to PBr 3 and Br 2 . Rapid cooling of this phase to 15 K leads to formation of the ionic species phosphorus heptabromide (tetrabromophosphonium tribromide [PBr 4 ] + [Br 3 ] − ). [ 2 ]
It can be used in organic chemistry to convert carboxylic acids to acyl bromides . It is highly corrosive. It strongly irritates skin and eyes. [ 1 ] It decomposes above 100 °C to give phosphorus tribromide and bromine : [ 3 ]
Reversing this equilibrium to generate PBr 5 by addition of Br 2 to PBr 3 is difficult in practice because the product is susceptible to further addition to yield phosphorus heptabromide [PBr 4 ] + [Br 3 ] − . [ 4 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PBr5 |
Phosphorus heptabromide is an inorganic compound with the chemical formula P Br 7 . It is one of the phosphorus bromides . At normal conditions, it forms red prismatic crystals . PBr 7 can be prepared by the sublimation of a mixture of phosphorus pentabromide and bromine . [ 2 ]
The structure of PBr 7 consists of a tetrabromophosphonium cation [PBr 4 ] + , paired with a tribromide anion [Br 3 ] − , and the tribromide anion is non-symmetric. [ 1 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PBr7 |
The NEC PC-6600 Series were a lineup of personal computers produced by the NEC Corporation in 1985. They were essentially a PC-6001 MK2 with a built-in 3.5" floppy disk drive . Two models in this series were produced: the PC-6601 and the PC-6601 SR .
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PC-6600_series |
PC/TCP Packet Driver is a networking API for MS-DOS , PC DOS , and later x86 DOS implementations such as DR-DOS , FreeDOS , etc. It implements the lowest levels of a TCP/IP stack, where the remainder is typically implemented either by terminate-and-stay-resident drivers or as a library linked into an application program. It was invented in 1983 at MIT 's Lab for Computer Science (CSR/CSC group under Jerry Saltzer and David D. Clark ), and was commercialized in 1986 by FTP Software .
A packet driver uses an x86 interrupt number (INT) between 60h .. 80h. The number used is detected at runtime, it is most commonly 60h but may be changed to avoid application programs which use fixed interrupts for internal communications. The interrupt vector is used as a pointer (4-bytes little endian ) to the address of a possible interrupt handler . If the null-terminated ASCII text string " PKT DRVR " is found within the first 12-bytes -- more specifically in bytes 3 through 11 -- immediately following the entry point then a driver has been located. [ 1 ]
Packet drivers can implement many different network interfaces, including Ethernet , Token Ring , RS-232 , Arcnet , and X.25 . [ 2 ]
WinPKT is a driver that enables use of packet drivers under Microsoft Windows that moves around applications in memory. [ 3 ]
W3C507 is a DLL to packet driver for the Microsoft Windows environment.
Support for Ethernet alike network interface over Serial line IP (using 8250 UART ), CSLIP, Parallel line IP , IPX , Token Ring , LocalTalk , ARCNET . | https://en.wikipedia.org/wiki/PC/TCP_Packet_Driver |
1CM0 , 1JM4 , 1N72 , 1WUG , 1WUM , 1ZS5 , 2RNW , 2RNX , 3GG3 , 4NSQ , 5FE2 , 5FE4 , 5FDZ , 5FE8 , 5FE5 , 5FE1 , 5FE7 , 5FE9 , 5FE3 , 5FE0 , 5FE6
8850
18519
ENSG00000114166
ENSMUSG00000000708
Q92831
Q9JHD1
NM_003884
NM_001190846 NM_020005
NP_003875
NP_001177775 NP_064389
P300/CBP-associated factor ( PCAF ), also known as K(lysine) acetyltransferase 2B ( KAT2B ), is a human gene and transcriptional coactivator associated with p53 .
Several domains of PCAF can act independently or in unison to enable its functions. PCAF has separate acetyltransferase and E3 ubiquitin ligase domains as well as a bromodomain for interaction with other proteins. PCAF also possesses sites for its own acetylation and ubiquitination. [ 5 ]
CBP and p300 are large nuclear proteins that bind to many sequence-specific factors involved in cell growth and/or differentiation, including c-jun and the adenoviral oncoprotein E1A. The protein encoded by the PCAF gene associates with p300/CBP. It has in vitro and in vivo binding activity with CBP and p300, and competes with E1A for binding sites in p300/CBP. It has histone acetyl transferase activity with core histones and nucleosome core particles, indicating that this protein plays a direct role in transcriptional regulation. [ 6 ]
The acetyltransferase activity and cellular location of PCAF are regulated through acetylation of PCAF itself. PCAF may be autoacetylated (acetylated by itself) or by p300 . Acetylation leads to migration to the nucleus and enhances its acetyltransferase activity. [ 7 ] PCAF interacts with and is deacetylated by HDAC3 , leading to a reduction in PCAF acetyltransferase activity and cytoplasmic localisation. [ 8 ]
PCAF forms complexes with numerous proteins that guide its activity. For example PCAF is recruited by ATF [ 9 ] to acetylate histones and promote transcription of ATF4 target genes.
There are various protein targets of PCAF's acetyltransferase activity including transcription factors such as Fli1 , [ 10 ] p53 [ 11 ] and numerous histone residues. Hdm2 , itself a ubiquitin ligase that targets p53, has also been demonstrated to be a target of the ubiquitin-ligase activity of PCAF. [ 5 ]
PCAF has been shown to interact with:
This article incorporates text from the United States National Library of Medicine , which is in the public domain . | https://en.wikipedia.org/wiki/PCAF |
Reverse engineering of printed circuit boards (sometimes called “cloning”, or PCB RE) is the process of generating fabrication and design data for an existing circuit board, either closely or exactly replicating its functionality. [ 1 ]
Obtaining circuit board design data is not by necessity malicious or aimed at intellectual property theft . The data generated in the reverse engineering process can be used for troubleshooting, repair, redesign and re-manufacturing, or even testing the security of a device to be used in a restricted environment. [ 2 ] [ 3 ] [ 4 ] [ 5 ]
Legacy systems need maintenance and replacement parts to operate past their intended life cycle. Demand for parts that are no longer being manufactured can lead to material shortages of parts, called DMS/DMSMS .
There is much demand that entire government divisions have been created to regulate and plan the obsolescence of those systems and parts. Areas commonly affected by technical obsolescence include power station controls, ATC and aviation controls, medical imaging systems, and many aspects of military technology.
There are many legacy systems developed in the 70s, 80s or 90s whose original manufacturer is no longer in business or no longer has the original design data, but whose original equipment is still in use. In many cases exact form, fit and function is required, either that so parts can “handshake” properly with the existing framework, or to avoid requirements of time-consuming and costly testing. [ 1 ]
For industries with highly regulated electronics, (like military or aerospace) this approach can vastly reduce the time required to fabricate replacement parts for system repairs, since the new part's specifications match the original design exactly and therefore do not need to undergo the same level of rigorous re-certification and testing that would be required of a newly designed or revised circuit board.
For example, a power company in Florida was forced to shut down due to the failure of a single, inexpensive PCB, which had no replacement parts and no data available to print them. The failure occurred during peak usage hours, and a power outage at that time can cost a power company thousands of dollars per hour. [ 6 ]
An engineering firm successfully reverse engineered the PCB to generate an exact copy of the PCB using the destructive imaging and milling process, and the power station was subsequently able to resume normal operation. [ 7 ] [ 8 ]
The process can be used to provide important benchmarking information about newly acquired products, prototype PCBs or any circuit board the company does not own. For example, reverse engineering a circuit assembly reveals whether or not the fabricator has exactly matched the design specifications of the board.
The process can be used to inspect for counterfeit or malicious circuits embedded in a PCB, or, if a new product has been purchased by a company, to create schematics or other documentation that may not have been included with the product. [ 9 ] [ 4 ]
Data from the reverse engineering process can be used to immediately repair or reprint a circuit board using additive manufacturing techniques on multi-headed 3-D printers.
In situations where resources are limited like on a ship, submarine, space, or forward deployment, the reverse engineering process can enable a crew to maintain electronics equipment without being required to bring along spare parts. In an ideal scenario, the crew would have access to the design data to use with the 3D printer, but in the event that crew did not have the proper data for the PCBs, they would need to reverse engineer the artifact on hand to create more. [ 10 ]
Data from reverse engineering can be taken with good intentions but mitigating intellectual property theft and maintaining privacy is increasingly important. Obfuscating PCBs, or hiding the intent of processing is one way to help deter theft. [ 11 ] Another is using physical unclonable functions (PUFs) as a digital fingerprint on your PCB that is impossible to recreate. [ 12 ]
Destructive reverse engineering (DRE) is a process where all layers of the board are imaged and subsequently removed by various milling techniques or tools. While it is possible to use nearly any camera or image source for this method, purpose-built RE systems utilize calibrated image sources that allow for extremely accurate reproduction of the design data for the board. This allows an engineer to match the exact form, fit and function of the original PCB. The drawback to this method is that it destroys the PCB. If the data comes from the last remaining circuit card in existence, it cannot be compared to a sample since little or no circuit board remains at the end of the destructive process. Also, care must be taken during the milling process to avoid damaging the copper. If areas of copper are removed before they are imaged, this represents a permanent loss of data which can only be rectified by existing documentation of the PCB, or by reverse engineering a second, identical board. [ 9 ]
There is a growing desire and need for non-destructive reverse engineering technology (NDRE), especially in scenarios like the one mentioned above where there is only a single PCB that can be used. Non-destructive PCB RE (NDRE) mean that the circuit board itself is not destroyed in the process; however, most non-destructive techniques require removing components from the surface of the board.
The primary difference between DRE and NDRE methods are in the way that images for the board are captured before new data is generated - in some cases optical images of the top and bottom of the board are captured, then merged with X-ray images of the boards internal layers. Once all images of all of the layers of the board have been captured the process of generating digital manufacturing data is similar to the destructive process. [ 2 ] [ 4 ]
In recent years, X-ray computed tomography -based imaging processes have advanced to the point that they are able to capture images of the circuit board well enough to isolate individual layers and the features on each of these layers. For simpler boards, X-ray or CT Scans can provide high enough resolution images to reverse engineer a board without requiring the use of destructive milling.
Generally, a high resolution CT scanning machine will capture images of the board in 2-D slices, varying the angle and intensity. The resulting image captures of the board are computationally assembled into a 3-D volumetric model, and images of each layer can then be extracted. Additional research is underway presently to improve the procedure of CT scanning, volumetric data reconstruction, and circuit layer extraction.
In principle this process seems fairly simple, however certain issues such as the non-planarity of circuit layers, resolution and size limitations, and X-ray artifacting greatly complicate the extraction of usable circuit images. [ 4 ] [ 13 ]
X-ray/CT imaging processes suffer many drawbacks, including resolution, equipment costs, and beam hardening and other X-ray artifacts which can distort images or make them harder to use for the reverse engineering process. Additionally, some IC chips can be damaged by exposure to powerful X-rays, so the board must be depopulated before being imaged if components are going to be salvaged for reuse. [ 4 ]
Another drawback is the time involved in creating the images used to generate circuit board design data. In one study, a Versa 510 X-ray machine was used to image a 6 layer board, measuring about 5 in × 8 in (130 mm × 200 mm) - the imaging and processing of the cloud data took over 18 hours to complete. By comparison, destructive reverse engineering can produce high resolution, calibrated optical images of the same 6 layer board in under 2 hours at very low cost by a skilled operator. [ 4 ]
Often, a flying probe test machine (FPT machine) can also be used to generate data from a circuit board. Unlike destructive methods, with this process the PCB can generally be reused. But the only output from this process is a list of connections between surface pads on the board, also known as a netlist .
The netlist is entirely dependent on the electrical connectivity of the PCB. If a PCB has become damaged or delaminated over the course of its life-cycle, it is possible that either via barrels or the copper traces have become broken, and if the damage occurs on the inner layers of the PCB, the FPT operator will have no way to know about the damage. The resulting netlist will reflect the breaks in the track, and should not be used to produce a schematic or additional boards. Additionally, a netlist is a fairly narrow data format that only provides insight into whether different component pins are connected or not. There is no information about the internal geometries of the copper circuits, which are crucial to proper functionality of radio emitting circuits, or circuits with differential signalling . It is impossible to create an identical PCB using this method. These drawbacks mean that this method is generally reserved for the creation of schematics or for troubleshooting and repair purposes. [ 9 ]
Before the digital age of data processing and storage, PCB designers created and stored the designs on Mylar/BoPET drafting films, which were used in the photo-resistive fabrication process for circuit boards . These films were oftentimes the only copy of the design data for the board. While their primary use was in the manufacturing of PCBs they also doubled as their own storage media. Ultimately these films can disintegrate with time and use, so the design must be imaged and converted to vector formatting in order to be used for future fabrication. The reverse engineering of film sets is roughly the same process as reverse engineering a PCB - each layer is imaged, and Gerber /vector data is created for the different circuit layers. [ 1 ]
Whether the board is reverse engineered using a destructive or non-destructive method, the result is that a netlist is obtained. While the netlist itself cannot be used to create an identical replacement, it can be used to generate supporting data for the board like a schematic. Whereas a netlist is a simple ASCII-based text file that simply lists all of the connections of the board, a PCB Schematic relays the same information in a more visual manner.
In addition, a schematic can be merged with the bill of materials (BOM) and component pick and place data to further enhance its usability in troubleshooting scenarios, or can be used as a base for the design of a brand new PCB. If a destructive RE process has been used or images for all PCB layers have been captured using X-ray imaging, the resulting data should include not only a netlist, BOM, and/or Schematic, but also a complete graphical layout of the copper layers of the board. This data can be represented in a vast number of different formats, but the most common data formats created in the reverse engineering process include the following:
The data produced in the reverse engineering process can be immediately sent to a PCB manufacturer for fabrication of replica/"clone" PCBs, or be used for creation of supporting documents. | https://en.wikipedia.org/wiki/PCB_reverse_engineering |
Parsed Character Data ( PCDATA ) is a data definition that originated in Standard Generalized Markup Language (SGML), and is used also in Extensible Markup Language (XML) Document Type Definition (DTD) to designate mixed content XML elements. [ 1 ]
The following sender-element could be part of an XML-document:
The string "Anton Smith" would be considered as parsed character data .
When declaring document elements. An element declaration employing the #PCDATA content model value does not allow for child elements. [ 2 ]
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PCDATA |
PCI Express ( Peripheral Component Interconnect Express ), officially abbreviated as PCIe or PCI-E , [ 2 ] is a high-speed serial computer expansion bus standard, meant to replace the older PCI , PCI-X and AGP bus standards. It is the common motherboard interface for personal computers' graphics cards , capture cards , sound cards , hard disk drive host adapters , SSDs , Wi-Fi , and Ethernet hardware connections. [ 3 ] PCIe has numerous improvements over the older standards, including higher maximum system bus throughput, lower I/O pin count, smaller physical footprint, better performance scaling for bus devices, a more detailed error detection and reporting mechanism (Advanced Error Reporting, AER), [ 4 ] and native hot-swap functionality. More recent revisions of the PCIe standard provide hardware support for I/O virtualization .
The PCI Express electrical interface is measured by the number of simultaneous lanes. [ 5 ] (A lane is a set of send and receive data lines, analogous to a road having one lane of traffic in each direction.) The interface is also used in a variety of other standards — most notably the laptop expansion card interface called ExpressCard . It is also used in the storage interfaces of SATA Express , U.2 (SFF-8639) and M.2 .
Formal specifications are maintained and developed by the PCI-SIG (PCI Special Interest Group ) — a group of more than 900 companies that also maintains the conventional PCI specifications.
Conceptually, the PCI Express bus is a high-speed serial replacement of the older PCI/PCI-X bus. [ 8 ] One of the key differences between the PCI Express bus and the older PCI is the bus topology; PCI uses a shared parallel bus architecture, in which the PCI host and all devices share a common set of address, data, and control lines. In contrast, PCI Express is based on point-to-point topology , with separate serial links connecting every device to the root complex (host). Because of its shared bus topology, access to the older PCI bus is arbitrated (in the case of multiple masters), and limited to one master at a time, in a single direction. Furthermore, the older PCI clocking scheme limits the bus clock to the slowest peripheral on the bus (regardless of the devices involved in the bus transaction). In contrast, a PCI Express bus link supports full-duplex communication between any two endpoints, with no inherent limitation on concurrent access across multiple endpoints.
In terms of bus protocol, PCI Express communication is encapsulated in packets. The work of packetizing and de-packetizing data and status-message traffic is handled by the transaction layer of the PCI Express port (described later). Radical differences in electrical signaling and bus protocol require the use of a different mechanical form factor and expansion connectors (and thus, new motherboards and new adapter boards); PCI slots and PCI Express slots are not interchangeable. At the software level, PCI Express preserves backward compatibility with PCI; legacy PCI system software can detect and configure newer PCI Express devices without explicit support for the PCI Express standard, though new PCI Express features are inaccessible.
The PCI Express link between two devices can vary in size from one to 16 lanes . In a multi-lane link, the packet data is striped across lanes, and peak data throughput scales with the overall link width. The lane count is automatically negotiated during device initialization and can be restricted by either endpoint. For example, a single-lane PCI Express (x1) card can be inserted into a multi-lane slot (x4, x8, etc.), and the initialization cycle auto-negotiates the highest mutually supported lane count. The link can dynamically down-configure itself to use fewer lanes, providing a failure tolerance in case bad or unreliable lanes are present. The PCI Express standard defines link widths of x1, x2, x4, x8, and x16. Up to and including PCIe 5.0, x12, and x32 links were defined as well but virtually [ clarification needed ] never used. [ 9 ] This allows the PCI Express bus to serve both cost-sensitive applications where high throughput is not needed, and performance-critical applications such as 3D graphics, networking ( 10 Gigabit Ethernet or multiport Gigabit Ethernet ), and enterprise storage ( SAS or Fibre Channel ). Slots and connectors are only defined for a subset of these widths, with link widths in between using the next larger physical slot size.
As a point of reference, a PCI-X (133 MHz 64-bit) device and a PCI Express 1.0 device using four lanes (x4) have roughly the same peak single-direction transfer rate of 1064 MB/s. The PCI Express bus has the potential to perform better than the PCI-X bus in cases where multiple devices are transferring data simultaneously, or if communication with the PCI Express peripheral is bidirectional .
PCI Express devices communicate via a logical connection called an interconnect [ 10 ] or link . A link is a point-to-point communication channel between two PCI Express ports allowing both of them to send and receive ordinary PCI requests (configuration, I/O or memory read/write) and interrupts ( INTx , MSI or MSI-X ). At the physical level, a link is composed of one or more lanes . [ 10 ] Low-speed peripherals (such as an 802.11 Wi-Fi card ) use a single-lane (x1) link, while a graphics adapter typically uses a much wider and therefore faster 16-lane (x16) link.
A lane is composed of two differential signaling pairs, with one pair for receiving data and the other for transmitting. Thus, each lane is composed of four wires or signal traces . Conceptually, each lane is used as a full-duplex byte stream , transporting data packets in eight-bit "byte" format simultaneously in both directions between endpoints of a link. [ 11 ] Physical PCI Express links may contain 1, 4, 8 or 16 lanes. [ 12 ] [ 6 ] : 4, 5 [ 10 ] Lane counts are written with an "x" prefix (for example, "x8" represents an eight-lane card or slot), with x16 being the largest size in common use. [ 13 ] Lane sizes are also referred to via the terms "width" or "by" e.g., an eight-lane slot could be referred to as a "by 8" or as "8 lanes wide."
For mechanical card sizes, see below .
The bonded serial bus architecture was chosen over the traditional parallel bus because of the inherent limitations of the latter, including half-duplex operation, excess signal count, and inherently lower bandwidth due to timing skew . Timing skew results from separate electrical signals within a parallel interface traveling through conductors of different lengths, on potentially different printed circuit board (PCB) layers, and at possibly different signal velocities . Despite being transmitted simultaneously as a single word , signals on a parallel interface have different travel duration and arrive at their destinations at different times. When the interface clock period is shorter than the largest time difference between signal arrivals, recovery of the transmitted word is no longer possible. Since timing skew over a parallel bus can amount to a few nanoseconds, the resulting bandwidth limitation is in the range of hundreds of megahertz.
A serial interface does not exhibit timing skew because there is only one differential signal in each direction within each lane, and there is no external clock signal since clocking information is embedded within the serial signal itself. As such, typical bandwidth limitations on serial signals are in the multi-gigahertz range. PCI Express is one example of the general trend toward replacing parallel buses with serial interconnects; other examples include Serial ATA (SATA), USB , Serial Attached SCSI (SAS), FireWire (IEEE 1394), and RapidIO . In digital video, examples in common use are DVI , HDMI , and DisplayPort .
Multichannel serial design increases flexibility with its ability to allocate fewer lanes for slower devices.
A PCI Express card fits into a slot of its physical size or larger (with x16 as the largest used), but may not fit into a smaller PCI Express slot; for example, a x16 card may not fit into a x4 or x8 slot. Some slots use open-ended sockets to permit physically longer cards and negotiate the best available electrical and logical connection.
The number of lanes actually connected to a slot may also be fewer than the number supported by the physical slot size. An example is a x16 slot that runs at x4, which accepts any x1, x2, x4, x8 or x16 card, but provides only four lanes. Its specification may read as "x16 (x4 mode)", while "mechanical @ electrical" notation (e.g. "x16 @ x4") is also common. [ citation needed ] The advantage is that such slots can accommodate a larger range of PCI Express cards without requiring motherboard hardware to support the full transfer rate. Standard mechanical sizes are x1, x4, x8, and x16. Cards using a number of lanes other than the standard mechanical sizes need to physically fit the next larger mechanical size (e.g. an x2 card uses the x4 size, or an x12 card uses the x16 size).
The cards themselves are designed and manufactured in various sizes. For example, solid-state drives (SSDs) that come in the form of PCI Express cards often use HHHL (half height, half length) and FHHL (full height, half length) to describe the physical dimensions of the card. [ 15 ] [ 16 ]
Modern (since c. 2012 [ 17 ] ) gaming video cards usually exceed the height as well as thickness specified in the PCI Express standard, due to the need for more capable and quieter cooling fans , as gaming video cards often emit hundreds of watts of heat. [ 18 ] Modern computer cases are often wider to accommodate these taller cards, but not always. Since full-length cards (312 mm) are uncommon, modern cases sometimes cannot accomodate them. The thickness of these cards also typically occupies the space of 2 to 5 [ 19 ] PCIe slots. In fact, even the methodology of how to measure the cards varies between vendors, with some including the metal bracket size in dimensions and others not.
For instance, comparing three high-end video cards released in 2020: a Sapphire Radeon RX 5700 XT card measures 135 mm in height (excluding the metal bracket), which exceeds the PCIe standard height by 28 mm, [ 20 ] another Radeon RX 5700 XT card by XFX measures 55 mm thick (i.e. 2.7 PCI slots at 20.32 mm), taking up 3 PCIe slots, [ 21 ] while an Asus GeForce RTX 3080 video card takes up two slots and measures 140.1 mm × 318.5 mm × 57.8 mm, exceeding PCI Express's maximum height, length, and thickness respectively. [ 22 ]
The following table identifies the conductors on each side of the edge connector on a PCI Express card. The solder side of the printed circuit board (PCB) is the A-side, and the component side is the B-side. [ 23 ] PRSNT1# and PRSNT2# pins must be slightly shorter than the rest, to ensure that a hot-plugged card is fully inserted. The WAKE# pin uses full voltage to wake the computer, but must be pulled high from the standby power to indicate that the card is wake capable. [ 24 ]
All PCI express cards may consume up to 3 A at +3.3 V ( 9.9 W ). The amount of +12 V and total power they may consume depends on the form factor and the role of the card: [ 29 ] : 35–36 [ 30 ] [ 31 ]
Optional connectors add 75 W (6-pin) or 150 W (8-pin) of +12 V power for up to 300 W total ( 2 @ 75 W + 1 @ 150 W ).
Some cards use two 8-pin connectors, but that has not been standardized as of 2018 [update] . Therefore, such cards must not carry the official PCI Express logo. This configuration allows 375 W total ( 1 @ 75 W + 2 @ 150 W ) and will likely be standardized by PCI-SIG with the PCI Express 4.0 standard. [ needs update ] The 8-pin PCI Express connector should not be confused with the EPS12V connector, which is mainly used for powering SMP and multi-core systems. The power connectors are variants of the Molex Mini-Fit Jr. series connectors. [ 32 ]
The 16-pin 12VHPWR connector is a standard for connecting graphics processing units (GPUs) to computer power supplies for up to 600 W power delivery. It was introduced by Nvidia in 2022 to supersede the previous 6- and 8-pin power connectors for GPUs. The stated aim was to cater to the increasing power requirements of Nvidia GPUs. The connector was formally adopted as part of PCI Express 5. [ 37 ]
In 2023 PCIe CEM 5.1 introduced a connector for 48 Volts with two current-carrying contacts and four sense pins. [ 41 ] The contacts are rated for 15 Amps continuous current. The 48VHPWR connector can carry 720 watts. Later it was removed and an incompatible 48V 1x2 connector was introduced where Sense0 and Sense1 are located farthest from each other.
PCI Express Mini Card (also known as Mini PCI Express , Mini PCIe , Mini PCI-E , mPCIe , and PEM ), based on PCI Express, is a replacement for the Mini PCI form factor. It is developed by the PCI-SIG . The host device supports both PCI Express and USB 2.0 connectivity, and each card may use either standard. Most laptop computers built after 2005 use PCI Express for expansion cards; however, as of 2015 [update] , many vendors are moving toward using the newer M.2 form factor for this purpose. [ 42 ]
Due to different dimensions, PCI Express Mini Cards are not physically compatible with standard full-size PCI Express slots; however, passive adapters exist that let them be used in full-size slots. [ 43 ]
Dimensions of PCI Express Mini Cards are 30 mm × 50.95 mm (width × length) for a Full Mini Card. There is a 52-pin edge connector , consisting of two staggered rows on a 0.8 mm pitch. Each row has eight contacts, a gap equivalent to four contacts, then a further 18 contacts. Boards have a thickness of 1.0 mm, excluding the components. A "Half Mini Card" (sometimes abbreviated as HMC) is also specified, having approximately half the physical length of 26.8 mm. There are also half size mini PCIe cards that are 30 x 31.90 mm which is about half the length of a full size mini PCIe card. [ 44 ] [ 45 ]
PCI Express Mini Card edge connectors provide multiple connections and buses:
Despite sharing the Mini PCI Express form factor, an mSATA slot is not necessarily electrically compatible with Mini PCI Express. For this reason, only certain notebooks are compatible with mSATA drives. Most compatible systems are based on Intel's Sandy Bridge processor architecture, using the Huron River platform. Notebooks such as Lenovo's ThinkPad T, W and X series, released in March–April 2011, have support for an mSATA SSD card in their WWAN card slot. The ThinkPad Edge E220s/E420s, and the Lenovo IdeaPad Y460/Y560/Y570/Y580 also support mSATA. [ 46 ] On the contrary, the L-series among others can only support M.2 cards using the PCIe standard in the WWAN slot.
Some notebooks (notably the Asus Eee PC , the Apple MacBook Air , and the Dell mini9 and mini10) use a variant of the PCI Express Mini Card as an SSD . This variant uses the reserved and several non-reserved pins to implement SATA and IDE interface passthrough, keeping only USB, ground lines, and sometimes the core PCIe x1 bus intact. [ 47 ] This makes the "miniPCIe" flash and solid-state drives sold for netbooks largely incompatible with true PCI Express Mini implementations.
Also, the typical Asus miniPCIe SSD is 71 mm long, causing the Dell 51 mm model to often be (incorrectly) referred to as half length. A true 51 mm Mini PCIe SSD was announced in 2009, with two stacked PCB layers that allow for higher storage capacity. The announced design preserves the PCIe interface, making it compatible with the standard mini PCIe slot. No working product has yet been developed.
Intel has numerous desktop boards with the PCIe x1 Mini-Card slot that typically do not support mSATA SSD. A list of desktop boards that natively support mSATA in the PCIe x1 Mini-Card slot (typically multiplexed with a SATA port) is provided on the Intel Support site. [ 48 ]
M.2 replaces the mSATA standard and Mini PCIe. [ 49 ] Computer bus interfaces provided through the M.2 connector are PCI Express 3.0 or higher (up to four lanes), Serial ATA 3.0, and USB 3.0 (a single logical port for each of the latter two). It is up to the manufacturer of the M.2 host or device to choose which interfaces to support, depending on the desired level of host support and device type.
PCI Express External Cabling (also known as External PCI Express , Cabled PCI Express , or ePCIe ) specifications were released by the PCI-SIG in February 2007. [ 50 ] [ 51 ]
Standard cables and connectors have been defined for x1, x4, x8, and x16 link widths, with a transfer rate of 250 MB/s per lane. The PCI-SIG also expects the norm to evolve to reach 500 MB/s, as in PCI Express 2.0. An example of the uses of Cabled PCI Express is a metal enclosure, containing a number of PCIe slots and PCIe-to-ePCIe adapter circuitry. This device would not be possible had it not been for the ePCIe specification.
OCuLink (standing for "optical-copper link", as Cu is the chemical symbol for copper ) is an extension for the "cable version of PCI Express". Version 1.0 of OCuLink, released in Oct 2015, supports up to 4 PCIe 3.0 lanes (3.9 GB/s) over copper cabling; a fiber optic version may appear in the future.
The most recent version of OCuLink, OCuLink-2, supports up to 16 GB/s (PCIe 4.0 x8) [ 52 ] while the maximum bandwidth of a USB 4 cable is 10GB/s.
While initially intended for use in PCIe interconnections in servers, OCuLink's popularity lies primarily in its use for laptops for the connection of powerful external GPU boxes, a more prevalent application. [ 53 ]
Numerous other form factors use, or are able to use, PCIe. These include:
The PCIe slot connector can also carry protocols other than PCIe. Some 9xx series Intel chipsets support Serial Digital Video Out , a proprietary technology that uses a slot to transmit video signals from the host CPU's integrated graphics instead of PCIe, using a supported add-in.
The PCIe transaction-layer protocol can also be used over some other interconnects, which are not electrically PCIe:
While in early development, PCIe was initially referred to as HSI (for High Speed Interconnect ), and underwent a name change to 3GIO (for 3rd Generation I/O ) before finally settling on its PCI-SIG name PCI Express . A technical working group named the Arapaho Work Group (AWG) drew up the standard. For initial drafts, the AWG consisted only of Intel engineers; subsequently, the AWG expanded to include industry partners.
Since, PCIe has undergone several large and smaller revisions, improving on performance and other features.
In 2003, PCI-SIG introduced PCIe 1.0a, with a per-lane data rate of 250 MB/s and a transfer rate of 2.5 gigatransfers per second (GT/s).
Transfer rate is expressed in transfers per second instead of bits per second because the number of transfers includes the overhead bits, which do not provide additional throughput; [ 59 ] PCIe 1.x uses an 8b/10b encoding scheme, resulting in a 20% (= 2/10) overhead on the raw channel bandwidth. [ 60 ] So in the PCIe terminology, transfer rate refers to the encoded bit rate: 2.5 GT/s is 2.5 Gbit/s on the encoded serial link. This corresponds to 2.0 Gbit/s of pre-coded data or 250 MB/s, which is referred to as throughput in PCIe.
In 2005, PCI-SIG [ 61 ] introduced PCIe 1.1. This updated specification includes clarifications and several improvements, but is fully compatible with PCI Express 1.0a. No changes were made to the data rate.
PCI-SIG announced the availability of the PCI Express Base 2.0 specification on 15 January 2007. [ 62 ] The PCIe 2.0 standard doubles the transfer rate compared with PCIe 1.0 to 5 GT/s and the per-lane throughput rises from 250 MB/s to 500 MB/s. Consequently, a 16-lane PCIe connector (x16) can support an aggregate throughput of up to 8 GB/s.
PCIe 2.0 motherboard slots are fully backward compatible with PCIe v1.x cards. PCIe 2.0 cards are also generally backward compatible with PCIe 1.x motherboards, using the available bandwidth of PCI Express 1.1. Overall, graphic cards or motherboards designed for v2.0 work, with the other being v1.1 or v1.0a.
The PCI-SIG also said that PCIe 2.0 features improvements to the point-to-point data transfer protocol and its software architecture. [ 63 ]
Intel 's first PCIe 2.0 capable chipset was the X38 and boards began to ship from various vendors ( Abit , Asus , Gigabyte ) as of 21 October 2007. [ 64 ] AMD started supporting PCIe 2.0 with its AMD 700 chipset series and nVidia started with the MCP72 . [ 65 ] All of Intel's prior chipsets, including the Intel P35 chipset, supported PCIe 1.1 or 1.0a. [ 66 ]
Like 1.x, PCIe 2.0 uses an 8b/10b encoding scheme, therefore delivering, per-lane, an effective 4 Gbit/s max. transfer rate from its 5 GT/s raw data rate.
PCI Express 2.1 (with its specification dated 4 March 2009) supports a large proportion of the management, support, and troubleshooting systems planned for full implementation in PCI Express 3.0. However, the speed is the same as PCI Express 2.0. The increase in power from the slot breaks backward compatibility between PCI Express 2.1 cards and some older motherboards with 1.0/1.0a, but most motherboards with PCI Express 1.1 connectors are provided with a BIOS update by their manufacturers through utilities to support backward compatibility of cards with PCIe 2.1.
PCI Express 3.0 Base specification revision 3.0 was made available in November 2010, after multiple delays. In August 2007, PCI-SIG announced that PCI Express 3.0 would carry a bit rate of 8 gigatransfers per second (GT/s), and that it would be backward compatible with existing PCI Express implementations. At that time, it was also announced that the final specification for PCI Express 3.0 would be delayed until Q2 2010. [ 67 ] New features for the PCI Express 3.0 specification included a number of optimizations for enhanced signaling and data integrity, including transmitter and receiver equalization, PLL improvements, clock data recovery, and channel enhancements of currently supported topologies. [ 68 ]
Following a six-month technical analysis of the feasibility of scaling the PCI Express interconnect bandwidth, PCI-SIG's analysis found that 8 gigatransfers per second could be manufactured in mainstream silicon process technology, and deployed with existing low-cost materials and infrastructure, while maintaining full compatibility (with negligible impact) with the PCI Express protocol stack.
PCI Express 3.0 upgraded the encoding scheme to 128b/130b from the previous 8b/10b encoding , reducing the bandwidth overhead from 20% of PCI Express 2.0 to approximately 1.54% (= 2/130). PCI Express 3.0's 8 GT/s bit rate effectively delivers 985 MB/s per lane, nearly doubling the lane bandwidth relative to PCI Express 2.0. [ 58 ]
On 18 November 2010, the PCI Special Interest Group officially published the finalized PCI Express 3.0 specification to its members to build devices based on this new version of PCI Express. [ 69 ]
In September 2013, PCI Express 3.1 specification was announced for release in late 2013 or early 2014, consolidating various improvements to the published PCI Express 3.0 specification in three areas: power management, performance and functionality. [ 56 ] [ 70 ] It was released in November 2014. [ 71 ]
On 29 November 2011, PCI-SIG preliminarily announced PCI Express 4.0, [ 72 ] providing a 16 GT/s bit rate that doubles the bandwidth provided by PCI Express 3.0 to 31.5 GB/s in each direction for a 16-lane configuration, while maintaining backward and forward compatibility in both software support and used mechanical interface. [ 73 ] PCI Express 4.0 specs also bring OCuLink-2, an alternative to Thunderbolt . OCuLink version 2 has up to 16 GT/s (16 GB/s total for x8 lanes), [ 52 ] while the maximum bandwidth of a Thunderbolt 3 link is 5 GB/s.
In June 2016 Cadence, PLDA and Synopsys demonstrated PCIe 4.0 physical-layer, controller, switch and other IP blocks at the PCI SIG’s annual developer’s conference. [ 74 ]
Mellanox Technologies announced the first 100 Gbit/s network adapter with PCIe 4.0 on 15 June 2016, [ 75 ] and the first 200 Gbit/s network adapter with PCIe 4.0 on 10 November 2016. [ 76 ]
In August 2016, Synopsys presented a test setup with FPGA clocking a lane to PCIe 4.0 speeds at the Intel Developer Forum . Their IP has been licensed to several firms planning to present their chips and products at the end of 2016. [ 77 ]
On the IEEE Hot Chips Symposium in August 2016 IBM announced the first CPU with PCIe 4.0 support, POWER9 . [ 78 ] [ 79 ]
PCI-SIG officially announced the release of the final PCI Express 4.0 specification on 8 June 2017. [ 80 ] The spec includes improvements in flexibility, scalability, and lower-power.
On 5 December 2017 IBM announced the first system with PCIe 4.0 slots, Power AC922. [ 81 ] [ 82 ]
NETINT Technologies introduced the first NVMe SSD based on PCIe 4.0 on 17 July 2018, ahead of Flash Memory Summit 2018 [ 83 ]
AMD announced on 9 January 2019 its upcoming Zen 2 -based processors and X570 chipset would support PCIe 4.0. [ 84 ] AMD had hoped to enable partial support for older chipsets, but instability caused by motherboard traces not conforming to PCIe 4.0 specifications made that impossible. [ 85 ] [ 86 ]
Intel released their first mobile CPUs with PCI Express 4.0 support in mid-2020, as a part of the Tiger Lake microarchitecture. [ 87 ]
In June 2017, PCI-SIG announced the PCI Express 5.0 preliminary specification. [ 80 ] Bandwidth was expected to increase to 32 GT/s, yielding 63 GB/s in each direction in a 16-lane configuration. The draft spec was expected to be standardized in 2019. [ citation needed ] Initially, 25.0 GT/s was also considered for technical feasibility.
On 7 June 2017 at PCI-SIG DevCon, Synopsys recorded the first demonstration of PCI Express 5.0 at 32 GT/s. [ 88 ]
On 31 May 2018, PLDA announced the availability of their XpressRICH5 PCIe 5.0 Controller IP based on draft 0.7 of the PCIe 5.0 specification on the same day. [ 89 ] [ 90 ]
On 10 December 2018, the PCI SIG released version 0.9 of the PCIe 5.0 specification to its members, [ 91 ] and on 17 January 2019, PCI SIG announced the version 0.9 had been ratified, with version 1.0 targeted for release in the first quarter of 2019. [ 92 ]
On 29 May 2019, PCI-SIG officially announced the release of the final PCI Express 5.0 specification. [ 93 ]
On 20 November 2019, Jiangsu Huacun presented the first PCIe 5.0 Controller HC9001 in a 12 nm manufacturing process [ 94 ] and production started in 2020.
On 17 August 2020, IBM announced the Power10 processor with PCIe 5.0 and up to 32 lanes per single-chip module (SCM) and up to 64 lanes per double-chip module (DCM). [ 95 ]
On 9 September 2021, IBM announced the Power E1080 Enterprise server with planned availability date 17 September. [ 96 ] It can have up to 16 Power10 SCMs with maximum of 32 slots per system which can act as PCIe 5.0 x8 or PCIe 4.0 x16. [ 97 ] Alternatively they can be used as PCIe 5.0 x16 slots for optional optical CXP converter adapters connecting to external PCIe expansion drawers.
On 27 October 2021, Intel announced the 12th Gen Intel Core CPU family, the world's first consumer x86-64 processors with PCIe 5.0 (up to 16 lanes) connectivity. [ 98 ]
On 22 March 2022, Nvidia announced Nvidia Hopper GH100 GPU, the world's first PCIe 5.0 GPU. [ 99 ]
On 23 May 2022, AMD announced its Zen 4 architecture with support for up to 24 lanes of PCIe 5.0 connectivity on consumer platforms and 128 lanes on server platforms. [ 100 ] [ 101 ]
On 18 June 2019, PCI-SIG announced the development of PCI Express 6.0 specification. Bandwidth is expected to increase to 64 GT/s, yielding 128 GB/s in each direction in a 16-lane configuration, with a target release date of 2021. [ 102 ] The new standard uses 4-level pulse-amplitude modulation (PAM-4) with a low-latency forward error correction (FEC) in place of non-return-to-zero (NRZ) modulation. [ 103 ] Unlike previous PCI Express versions, forward error correction is used to increase data integrity and PAM-4 is used as line code so that two bits are transferred per transfer. With 64 GT/s data transfer rate (raw bit rate), up to 121 GB/s in each direction is possible in x16 configuration. [ 102 ]
On 24 February 2020, the PCI Express 6.0 revision 0.5 specification (a "first draft" with all architectural aspects and requirements defined) was released. [ 104 ]
On 5 November 2020, the PCI Express 6.0 revision 0.7 specification (a "complete draft" with electrical specifications validated via test chips) was released. [ 105 ]
On 6 October 2021, the PCI Express 6.0 revision 0.9 specification (a "final draft") was released. [ 106 ]
On 11 January 2022, PCI-SIG officially announced the release of the final PCI Express 6.0 specification. [ 107 ]
PAM-4 coding results in a vastly higher bit error rate (BER) of 10 −6 (vs. 10 −12 previously), so in place of 128b/130b encoding, a 3-way interlaced forward error correction (FEC) is used in addition to cyclic redundancy check (CRC). A fixed 256 byte Flow Control Unit (FLIT) block carries 242 bytes of data, which includes variable-sized transaction level packets (TLP) and data link layer payload (DLLP); remaining 14 bytes are reserved for 8-byte CRC and 6-byte FEC. [ 108 ] [ 109 ] 3-way Gray code is used in PAM-4/FLIT mode to reduce error rate; the interface does not switch to NRZ and 128/130b encoding even when retraining to lower data rates. [ 110 ] [ 111 ]
On 21 June 2022, PCI-SIG announced the development of PCI Express 7.0 specification. [ 112 ] It will deliver 128 GT/s raw bit rate and up to 242 GB/s per direction in x16 configuration, using the same PAM4 signaling as version 6.0. Doubling of the data rate will be achieved by fine-tuning channel parameters to decrease signal losses and improve power efficiency, but signal integrity is expected to be a challenge. The specification is expected to be finalized in 2025.
On 3 April 2024, the PCI Express 7.0 revision 0.5 specification (a "first draft") was released. [ 113 ]
On 17 January 2025, PCI-SIG announced the release of PCIe 7.0 specification version 0.7 (a "complete draft"). [ 114 ]
On 19 March 2025, PCI-SIG announced the release of PCIe 7.0 specification version 0.9 (a "final draft"); planned final release is still in 2025. [ 115 ]
The following main points were formulated as objectives of the new standard:
Some vendors offer PCIe over fiber products, [ 116 ] [ 117 ] [ 118 ] with active optical cables (AOC) for PCIe switching at increased distance in PCIe expansion drawers, [ 119 ] [ 97 ] or in specific cases where transparent PCIe bridging is preferable to using a more mainstream standard (such as InfiniBand or Ethernet ) that may require additional software to support it.
Thunderbolt was co-developed by Intel and Apple as a general-purpose high speed interface combining a logical PCIe link with DisplayPort and was originally intended as an all-fiber interface, but due to early difficulties in creating a consumer-friendly fiber interconnect, nearly all implementations are copper systems. A notable exception, the Sony VAIO Z VPC-Z2, uses a nonstandard USB port with an optical component to connect to an outboard PCIe display adapter. Apple has been the primary driver of Thunderbolt adoption through 2011, though several other vendors [ 120 ] have announced new products and systems featuring Thunderbolt. Thunderbolt 3 forms the basis of the USB4 standard.
Mobile PCIe specification (abbreviated to M-PCIe ) allows PCI Express architecture to operate over the MIPI Alliance 's M-PHY physical layer technology. Building on top of already existing widespread adoption of M-PHY and its low-power design, Mobile PCIe lets mobile devices use PCI Express. [ 121 ]
There are 5 primary releases/checkpoints in a PCI-SIG specification: [ 122 ]
Historically, the earliest adopters of a new PCIe specification generally begin designing with the Draft 0.5 as they can confidently build up their application logic around the new bandwidth definition and often even start developing for any new protocol features. At the Draft 0.5 stage, however, there is still a strong likelihood of changes in the actual PCIe protocol layer implementation, so designers responsible for developing these blocks internally may be more hesitant to begin work than those using interface IP from external sources.
The PCIe link is built around dedicated unidirectional couples of serial (1-bit), point-to-point connections known as lanes . This is in sharp contrast to the earlier PCI connection, which is a bus-based system where all the devices share the same bidirectional, 32-bit or 64-bit parallel bus.
PCI Express is a layered protocol , consisting of a transaction layer , a data link layer , and a physical layer . The Data Link Layer is subdivided to include a media access control (MAC) sublayer. The Physical Layer is subdivided into logical and electrical sublayers. The Physical logical-sublayer contains a physical coding sublayer (PCS). The terms are borrowed from the IEEE 802 networking protocol model.
The PCIe Physical Layer ( PHY , PCIEPHY , PCI Express PHY , or PCIe PHY ) specification is divided into two sub-layers, corresponding to electrical and logical specifications. The logical sublayer is sometimes further divided into a MAC sublayer and a PCS, although this division is not formally part of the PCIe specification. A specification published by Intel, the PHY Interface for PCI Express (PIPE), [ 124 ] defines the MAC/PCS functional partitioning and the interface between these two sub-layers. The PIPE specification also identifies the physical media attachment (PMA) layer, which includes the serializer/deserializer (SerDes) and other analog circuitry; however, since SerDes implementations vary greatly among ASIC vendors, PIPE does not specify an interface between the PCS and PMA.
At the electrical level, each lane consists of two unidirectional differential pairs operating at 2.5, 5, 8, 16 or 32 Gbit /s, depending on the negotiated capabilities. Transmit and receive are separate differential pairs, for a total of four data wires per lane.
A connection between any two PCIe devices is known as a link , and is built up from a collection of one or more lanes . All devices must minimally support single-lane (x1) link. Devices may optionally support wider links composed of up to 32 lanes. [ 125 ] [ 126 ] This allows for very good compatibility in two ways:
In both cases, PCIe negotiates the highest mutually supported number of lanes. Many graphics cards, motherboards and BIOS versions are verified to support x1, x4, x8 and x16 connectivity on the same connection.
The width of a PCIe connector is 8.8 mm, while the height is 11.25 mm, and the length is variable. The fixed section of the connector is 11.65 mm in length and contains two rows of 11 pins each (22 pins total), while the length of the other section is variable depending on the number of lanes. The pins are spaced at 1 mm intervals, and the thickness of the card going into the connector is 1.6 mm. [ 127 ] [ 128 ]
PCIe sends all control messages, including interrupts, over the same links used for data. The serial protocol can never be blocked, so latency is still comparable to conventional PCI, which has dedicated interrupt lines. When the problem of IRQ sharing of pin based interrupts is taken into account and the fact that message signaled interrupts (MSI) can bypass an I/O APIC and be delivered to the CPU directly, MSI performance ends up being substantially better. [ 129 ]
Data transmitted on multiple-lane links is interleaved, meaning that each successive byte is sent down successive lanes. The PCIe specification refers to this interleaving as data striping . While requiring significant hardware complexity to synchronize (or deskew ) the incoming striped data, striping can significantly reduce the latency of the n th byte on a link. While the lanes are not tightly synchronized, there is a limit to the lane to lane skew of 20/8/6 ns for 2.5/5/8 GT/s so the hardware buffers can re-align the striped data. [ 130 ] Due to padding requirements, striping may not necessarily reduce the latency of small data packets on a link.
As with other high data rate serial transmission protocols, the clock is embedded in the signal. At the physical level, PCI Express 2.0 utilizes the 8b/10b encoding scheme [ 58 ] (line code) to ensure that strings of consecutive identical digits (zeros or ones) are limited in length. This coding was used to prevent the receiver from losing track of where the bit edges are. In this coding scheme every eight (uncoded) payload bits of data are replaced with 10 (encoded) bits of transmit data, causing a 20% overhead in the electrical bandwidth. To improve the available bandwidth, PCI Express version 3.0 instead uses 128b/130b encoding (1.54% overhead). Line encoding limits the run length of identical-digit strings in data streams and ensures the receiver stays synchronised to the transmitter via clock recovery .
A desirable balance (and therefore spectral density ) of 0 and 1 bits in the data stream is achieved by XORing a known binary polynomial as a " scrambler " to the data stream in a feedback topology. Because the scrambling polynomial is known, the data can be recovered by applying the XOR a second time. Both the scrambling and descrambling steps are carried out in hardware.
Dual simplex in PCIe means there are two simplex channels on every PCIe lane. Simplex means communication is only possible in one direction. By having two simplex channels, two-way communication is made possible. One differential pair is used for each channel. [ 131 ] [ 1 ] [ 132 ]
The data link layer performs three vital services for the PCIe link:
On the transmit side, the data link layer generates an incrementing sequence number for each outgoing TLP. It serves as a unique identification tag for each transmitted TLP, and is inserted into the header of the outgoing TLP. A 32-bit cyclic redundancy check code (known in this context as Link CRC or LCRC) is also appended to the end of each outgoing TLP.
On the receive side, the received TLP's LCRC and sequence number are both validated in the link layer. If either the LCRC check fails (indicating a data error), or the sequence-number is out of range (non-consecutive from the last valid received TLP), then the bad TLP, as well as any TLPs received after the bad TLP, are considered invalid and discarded. The receiver sends a negative acknowledgement message (NAK) with the sequence-number of the invalid TLP, requesting re-transmission of all TLPs forward of that sequence-number. If the received TLP passes the LCRC check and has the correct sequence number, it is treated as valid. The link receiver increments the sequence-number (which tracks the last received good TLP), and forwards the valid TLP to the receiver's transaction layer. An ACK message is sent to remote transmitter, indicating the TLP was successfully received (and by extension, all TLPs with past sequence-numbers.)
If the transmitter receives a NAK message, or no acknowledgement (NAK or ACK) is received until a timeout period expires, the transmitter must retransmit all TLPs that lack a positive acknowledgement (ACK). Barring a persistent malfunction of the device or transmission medium, the link-layer presents a reliable connection to the transaction layer, since the transmission protocol ensures delivery of TLPs over an unreliable medium.
In addition to sending and receiving TLPs generated by the transaction layer, the data-link layer also generates and consumes data link layer packets (DLLPs). ACK and NAK signals are communicated via DLLPs, as are some power management messages and flow control credit information (on behalf of the transaction layer).
In practice, the number of in-flight, unacknowledged TLPs on the link is limited by two factors: the size of the transmitter's replay buffer (which must store a copy of all transmitted TLPs until the remote receiver ACKs them), and the flow control credits issued by the receiver to a transmitter. PCI Express requires all receivers to issue a minimum number of credits, to guarantee a link allows sending PCIConfig TLPs and message TLPs.
PCI Express implements split transactions (transactions with request and response separated by time), allowing the link to carry other traffic while the target device gathers data for the response.
PCI Express uses credit-based flow control. In this scheme, a device advertises an initial amount of credit for each received buffer in its transaction layer. The device at the
opposite end of the link, when sending transactions to this device, counts the number of credits each TLP consumes from its account. The sending device may only transmit a TLP when doing so does not make its consumed credit count exceed its credit limit. When the receiving device finishes processing the TLP from its buffer, it signals a return of credits to the sending device, which increases the credit limit by the restored amount. The credit counters are modular counters, and the comparison of consumed credits to credit limit requires modular arithmetic . The advantage of this scheme (compared to other methods such as wait states or handshake-based transfer protocols) is that the latency of credit return does not affect performance, provided that the credit limit is not encountered. This assumption is generally met if each device is designed with adequate buffer sizes.
PCIe 1.x is often quoted to support a data rate of 250 MB/s in each direction, per lane. This figure is a calculation from the physical signaling rate (2.5 gigabaud ) divided by the encoding overhead (10 bits per byte). This means a sixteen lane (x16) PCIe card would then be theoretically capable of 16x250 MB/s = 4 GB/s in each direction. While this is correct in terms of data bytes, more meaningful calculations are based on the usable data payload rate, which depends on the profile of the traffic, which is a function of the high-level (software) application and intermediate protocol levels.
Like other high data rate serial interconnect systems, PCIe has a protocol and processing overhead due to the additional transfer robustness (CRC and acknowledgements). Long continuous unidirectional transfers (such as those typical in high-performance storage controllers) can approach >95% of PCIe's raw (lane) data rate. These transfers also benefit the most from increased number of lanes (x2, x4, etc.) But in more typical applications (such as a USB or Ethernet controller), the traffic profile is characterized as short data packets with frequent enforced acknowledgements. [ 133 ] This type of traffic reduces the efficiency of the link, due to overhead from packet parsing and forced interrupts (either in the device's host interface or the PC's CPU). Being a protocol for devices connected to the same printed circuit board , it does not require the same tolerance for transmission errors as a protocol for communication over longer distances, and thus, this loss of efficiency is not particular to PCIe.
As for any network-like communication links, some of the raw bandwidth is consumed by protocol overhead: [ 134 ]
A PCIe 1.x lane for example offers a data rate on top of the physical layer of 250 MB/s (simplex). This is not the payload bandwidth but the physical layer bandwidth – a PCIe lane has to carry additional information for full functionality. [ 134 ]
The Gen2 overhead is then 20, 24, or 28 bytes per transaction. [ clarification needed ] [ citation needed ]
The Gen3 overhead is then 22, 26 or 30 bytes per transaction. [ clarification needed ] [ citation needed ]
The Packet Efficiency = Payload Payload + Overhead {\displaystyle {\text{Packet Efficiency}}={\frac {\text{Payload}}{{\text{Payload}}+{\text{Overhead}}}}} for a 128 byte payload is 86%, and 98% for a 1024 byte payload. For small accesses like register settings (4 bytes), the efficiency drops as low as 16%. [ citation needed ]
The maximum payload size (MPS) is set on all devices based on smallest maximum on any device in the chain. If one device has an MPS of 128 bytes, all devices of the tree must set their MPS to 128 bytes. In this case the bus will have a peak efficiency of 86% for writes. [ 134 ] : 3
PCI Express operates in consumer, server, and industrial applications, as a motherboard-level interconnect (to link motherboard-mounted peripherals), a passive backplane interconnect and as an expansion card interface for add-in boards.
In virtually all modern (as of 2012 [update] ) PCs, from consumer laptops and desktops to enterprise data servers, the PCIe bus serves as the primary motherboard-level interconnect, connecting the host system-processor with both integrated peripherals (surface-mounted ICs) and add-on peripherals (expansion cards). In most of these systems, the PCIe bus co-exists with one or more legacy PCI buses, for backward compatibility with the large body of legacy PCI peripherals.
As of 2013 [update] , PCI Express has replaced AGP as the default interface for graphics cards on new systems. Almost all models of graphics cards released since 2010 by AMD (ATI) and Nvidia use PCI Express. Nvidia used the high-bandwidth data transfer of PCIe for its Scalable Link Interface (SLI) technology, which allowed multiple graphics cards of the same chipset and model number to run in tandem, allowing increased performance. [ citation needed ] This interface has, since, been discontinued. AMD has also developed a multi-GPU system based on PCIe called CrossFire . [ citation needed ] AMD, Nvidia, and Intel have released motherboard chipsets that support as many as four PCIe x16 slots, allowing tri-GPU and quad-GPU card configurations.
Theoretically, external PCIe could give a notebook the graphics power of a desktop, by connecting a notebook with any PCIe desktop video card (enclosed in its own external housing, with a power supply and cooling); this is possible with an ExpressCard or Thunderbolt interface. An ExpressCard interface provides bit rates of 5 Gbit/s (0.5 GB/s throughput), whereas a Thunderbolt interface provides bit rates of up to 40 Gbit/s (5 GB/s throughput).
In 2006, Nvidia developed the Quadro Plex external PCIe family of GPUs that can be used for advanced graphic applications for the professional market. [ 135 ] These video cards require a PCI Express x8 or x16 slot for the host-side card, which connects to the Plex via a VHDCI carrying eight PCIe lanes. [ 136 ]
In 2008, AMD announced the ATI XGP technology, based on a proprietary cabling system that is compatible with PCIe x8 signal transmissions. [ 137 ] This connector is available on the Fujitsu Amilo and the Acer Ferrari One notebooks. Fujitsu launched their AMILO GraphicBooster enclosure for XGP soon thereafter. [ 138 ] Around 2010 Acer launched the Dynavivid graphics dock for XGP. [ 139 ]
In 2010, external card hubs were introduced that can connect to a laptop or desktop through a PCI ExpressCard slot. These hubs can accept full-sized graphics cards. Examples include MSI GUS, [ 140 ] Village Instrument's ViDock, [ 141 ] the Asus XG Station , Bplus PE4H V3.2 adapter, [ 142 ] as well as more improvised DIY devices. [ 143 ] However such solutions are limited by the size (often only x1) and version of the available PCIe slot on a laptop.
The Intel Thunderbolt interface has provided a new option to connect with a PCIe card externally. Magma has released the ExpressBox 3T, which can hold up to three PCIe cards (two at x8 and one at x4). [ 144 ] MSI also released the Thunderbolt GUS II, a PCIe chassis dedicated for video cards. [ 145 ] Other products such as the Sonnet's Echo Express [ 146 ] and mLogic's mLink are Thunderbolt PCIe chassis in a smaller form factor. [ 147 ]
In 2017, more fully featured external card hubs were introduced, such as the Razer Core, which has a full-length PCIe x16 interface. [ 148 ]
The PCI Express protocol can be used as data interface to flash memory devices, such as memory cards and solid-state drives (SSDs).
The XQD card is a memory card format utilizing PCI Express, developed by the CompactFlash Association, with transfer rates of up to 1 GB/s. [ 149 ]
Many high-performance, enterprise-class SSDs are designed as PCI Express RAID controller cards. [ citation needed ] Before NVMe was standardized, many of these cards utilized proprietary interfaces and custom drivers to communicate with the operating system; they had much higher transfer rates (over 1 GB/s) and IOPS (over one million I/O operations per second) when compared to Serial ATA or SAS drives. [ quantify ] [ 150 ] [ 151 ] For example, in 2011 OCZ and Marvell co-developed a native PCI Express solid-state drive controller for a PCI Express 3.0 x16 slot with maximum capacity of 12 TB and a performance of to 7.2 GB/s sequential transfers and up to 2.52 million IOPS in random transfers. [ 152 ] [ relevant? ]
SATA Express was an interface for connecting SSDs through SATA-compatible ports, optionally providing multiple PCI Express lanes as a pure PCI Express connection to the attached storage device. [ 153 ] M.2 is a specification for internally mounted computer expansion cards and associated connectors, which also uses multiple PCI Express lanes. [ 154 ]
PCI Express storage devices can implement both AHCI logical interface for backward compatibility, and NVM Express logical interface for much faster I/O operations provided by utilizing internal parallelism offered by such devices. Enterprise-class SSDs can also implement SCSI over PCI Express . [ 155 ]
Certain data-center applications (such as large computer clusters ) require the use of fiber-optic interconnects due to the distance limitations inherent in copper cabling. Typically, a network-oriented standard such as Ethernet or Fibre Channel suffices for these applications, but in some cases the overhead introduced by routable protocols is undesirable and a lower-level interconnect, such as InfiniBand , RapidIO , or NUMAlink is needed. Local-bus standards such as PCIe and HyperTransport can in principle be used for this purpose, [ 156 ] but as of 2015 [update] , solutions are only available from niche vendors such as Dolphin ICS , and TTTech Auto.
Other communications standards based on high bandwidth serial architectures include InfiniBand , RapidIO , HyperTransport , Intel QuickPath Interconnect , the Mobile Industry Processor Interface (MIPI), and NVLink . Differences are based on the trade-offs between flexibility and extensibility vs latency and overhead. For example, making the system hot-pluggable, as with Infiniband but not PCI Express, requires that software track network topology changes. [ citation needed ]
Another example is making the packets shorter to decrease latency (as is required if a bus must operate as a memory interface). Smaller packets mean packet headers consume a higher percentage of the packet, thus decreasing the effective bandwidth. Examples of bus protocols designed for this purpose are RapidIO and HyperTransport. [ citation needed ]
PCI Express falls somewhere in the middle, [ clarification needed ] targeted by design as a system interconnect ( local bus ) rather than a device interconnect or routed network protocol. Additionally, its design goal of software transparency constrains the protocol and raises its latency somewhat. [ citation needed ]
Delays in PCIe 4.0 implementations led to the Gen-Z consortium, the CCIX effort and an open Coherent Accelerator Processor Interface (CAPI) all being announced by the end of 2016. [ 157 ]
On 11 March 2019, Intel presented Compute Express Link (CXL) , a new interconnect bus, based on the PCI Express 5.0 physical layer infrastructure. The initial promoters of the CXL specification included: Alibaba , Cisco , Dell EMC , Facebook , Google , HPE , Huawei , Intel and Microsoft . [ 158 ]
The PCI-SIG Integrators List lists products made by PCI-SIG member companies that have passed compliance testing. The list include switches, bridges, NICs, SSDs, etc. [ 159 ] | https://en.wikipedia.org/wiki/PCI_Express |
PCKeeper is advertised as an optimization services package featuring a set of software utilities for Windows OS owned by Essentware S.A. (company based in Bratislava, Slovakia ). [ 1 ] [ non-primary source needed ] It includes 2 separate products for Windows: PCKeeper Live and PCKeeper Antivirus . [ 2 ]
PCKeeper was originally developed by Zeobit LLC which was founded in 2009 by Slava Kolomiychuk. PCKeeper was released in September 2010. Kromtech Alliance acquired PCKeeper and MacKeeper from Zeobit in May 2013. In 2015, PCKeeper has changed its legal owners from Kromtech Alliance Corp . to Essentware S.A. Kromtech Alliance has made the decision to focus on the products for Mac users only. [ 3 ] Essentware S.A. office registered in Panama. [ 4 ] The principal officers and developers of the company remain in Ukraine.
Two class action lawsuits have been filed against Kromtech for the Mac OS version of PCKeeper, MacKeeper. The first lawsuit, filed in Illinois, alleges that "Contrary to ZeoBIT's marketing and in-software representations, however, neither the free trial nor the full registered versions of MacKeeper perform any credible diagnostic testing of a user's Mac. Instead, ZeoBIT intentionally designed MacKeeper to invariably and ominously report that the consumer's Mac needs repair and is at-risk due to harmful errors, privacy threats, and other problems, regardless of the computer's actual condition." [ citation needed ] The second complaint, filed by Holly Yencha of Pennsylvania, alleges that the free starter version of MacKeeper identifies harmless programs as "critical" problems. The complaint claims that "under MacKeeper's reporting algorithm , even brand new computers are in 'critical' condition and require repair by purchasing the full version." [ 5 ]
PCKeeper Live is sometimes installed on users' PCs with other partner programs, which can cause unwanted pop-up windows.
PCKeeper Live offers 13 different PC services in 4 categories: Human Assistance (Find & Fix, Geek on Demand, Live Support), Security (Anti-Theft, Data Hider, Shredder, Files Recovery), Cleaning (Disk Cleaner, Disk Explorer, Duplicates Finder, Uninstaller) and Optimization (Context Menu Manager, Startup Manager). [ 6 ] [ 7 ]
PCKeeper is sometimes advertised with pop up ads . Many of their pop up ads occur on pornography websites.
PCKeeper Live is rated "Good" (3.5 out of 5) by the PCMag editor, [ 8 ] stating "improves PC performance", and "great for novice users", "The utility won't clean your PC as well as Iolo System Mechanic, but considering its accessibility and wallet friendliness, it's one to check out" and "Kromtech PCKeeper Live's human specialists and unique price plans make this tune-up utility worthy of consideration, but rival applications offer better PC improvement".
Techradar.pro rates its 3 out of 5 stars and that noted, that "Overall, PCKeeper is a light-weight tool that won't annoy you with pop-up windows", "When you consider the fact most of PCKeeper Live's optimization features are easily found on most free tools, and that some were simply not useful at all, the price for the Kromtech solution seems unreasonably high." and "Kromtech's 24/7 support is what elevates PCKeeper Live from an overpriced utility program to a tool that even a non-geek can use to optimize his/her computer." [ 9 ]
PCKeeper was reviewed by a wide range of tech experts. It was reviewed in Turkish, [ 10 ] French, [ 11 ] Portuguese, [ 12 ] Spanish, [ 13 ] German". [ 14 ] Review at PCMag thus described PCKeeper Live: "Improves PC performance. Multiple price points. Advice from Microsoft -certified computer specialists. Anti-theft technology". It gained 3,5 out of 5 points." [ 15 ]
PCKeeper Antivirus integrates the Avira 's Secure Anti-Virus API (SAVAPI), the official interface for Avira’s anti- malware scanning engine. PCKeeper Antivirus does not block malware-hosting URLs or phishing URLs. [ 16 ] According to Virus Bulletin , PCKeeper Antivirus PRO has scored 96.1% in RAP tests and set a stability level at Stable. PCKeeper Antivirus got a VB100 award. [ 17 ] PCKeeper Antivirus (version 1.x) received 2 OPSWAT Gold Certifications in the Antispyware and Antivirus categories. [ 18 ]
The German organization AV-Test.org tested 25 anti-virus programs. The testers found that AhnLab, Microsoft Windows Defender and PCKeeper Antivirus were the lowest performing anti-virus applications for Windows 8.1 . [ 19 ]
Best Antivirus for Windows Home User
Performance 2.5 (out of 6.0)
Usability (out of 6.0) [ 23 ]
PCMag rated PCKeeper Antivirus Good (3 out of 5), noting that PCKeeper Antivirus has a "Streamlined, attractive interface. Easy to use for non-techies. Good score in our hands-on malware blocking testing". However, it scored poorly in independent lab testing and the chat based support was "soured by the fact that they served me misinformation." PC Mag concluded "you'd be better off with Panda Free Antivirus 2015, an Editors' Choice for free antivirus. It slightly edged PCKeeper in my own tests and swept the field in lab tests, with high marks across the board. For the same price as PCKeeper, you could have Bitdefender Antivirus Plus 2015 or Kaspersky Anti-Virus (2015), both of which we named Editors' Choice for paid antivirus. Any of these is a better choice." [ 16 ]
In May 2013 PCKeeper let its customers decide how much to pay for the software, launching a pay what you want campaign. [ 24 ] | https://en.wikipedia.org/wiki/PCKeeper |
PCLake is a dynamic, mathematical model used to study eutrophication effects in shallow lakes and ponds. PCLake models explicitly the most important biotic groups and their interrelations, within the general framework of nutrient cycles . PCLake is used both by scientist and water managers. PCLake is in 2019 extended to PCLake+, [ 1 ] which can be applied to stratifying lakes.
Typically, shallow lakes are in one of two contrasting alternative stable states : [ 2 ] a clear state with submerged macrophytes and piscivorous fish, or a turbid state dominated by phytoplankton and benthivorous fish. A switch from one state to the other is largely driven by the input of nutrients ( phosphorus and nitrogen ) to the ecosystem. [ 3 ] If the nutrient loading exceeds a critical value, eutrophication causes a switch from the clear to the turbid state. As a result of urban water pollution and/or intensive agriculture in catchment areas , many of the world’s shallow lakes and ponds are in a eutrophic state with turbid waters and poor ecological quality. In this turbid state, the lake also becomes subject to algal blooms of toxic cyanobacteria (also called blue-green algae). Recovery of the clear state however is difficult as the critical nutrient loading for the switch back is often found to be lower than the critical loading towards the turbid state. Lowering the nutrient input thus does not automatically lead to a switch back to the clear water phase. Hence, the system shows hysteresis .
PCLake is designed to study the effects of eutrophication on shallow lakes and ponds. [ 4 ] On one hand, the model is used by scientists to study the general behavior of these ecosystems. For example, PCLake is used to understand the phenomena of alternative stable states and hysteresis, and in that light, the relative importance of lake features such as water depth or fetch length . [ 5 ] Also the potential effects of climate warming for shallow lakes have been studied. [ 6 ] On the other hand, PCLake is applied by lake water resource managers that consider the turbid state as undesirable. They can use the model to define the critical loadings for their specific lakes and evaluate the effectiveness of restoration measures. For this purpose also a meta-model has been developed. [ 7 ] The meta-model can be used by water managers to derive an estimate of the critical loading values for a certain lake based on only a few important parameters, without the need of running the full dynamical model. [ 8 ]
Mathematically, PCLake is composed of a set of coupled differential equations . With a large number of state variables (>100) and parameters (>300), the model may be characterized as relatively complex. The main biotic variables are phytoplankton and submerged aquatic vegetation , describing primary production . A simplified food web is made up of zooplankton , zoo benthos , young and adult whitefish and piscivorous fish. The main abiotic factors are transparency and the nutrients phosphorus (P), nitrogen (N) and silica (Si). At the base of the model are the water and nutrient budgets (in- and outflow). The model describes a completely mixed water body and comprises both the water column and the upper sediment layer. The overall nutrient cycles for N, P and Si are described as completely closed (except for in- and outflow and denitrification ). Inputs to the model are: lake hydrology, nutrient loading, dimensions and sediment characteristics. The model calculates chlorophyll -a, transparency, cyanobacteria, vegetation cover and fish biomass, as well as the concentrations and fluxes of nutrients N, P and Si, and oxygen. Optionally, a wetland zone with marsh vegetation and water exchange with the lake can be included.
PCLake is calibrated against nutrient, transparency, chlorophyll and vegetation data on more than 40 European (but mainly Dutch) lakes, and systematic sensitivity and uncertainty analysis have been performed. [ 13 ] Although PCLake is primarily used for Dutch lakes, it is likely that the model is also applicable to comparable non- stratifying lakes in other regions, if parameters are adjusted or some small changes to the model are made.
The first version of PCLake (by then called PCLoos) was built in the early 1990s at the Netherlands National Institute for Public Health and the Environment (RIVM), within the framework of a research and restoration project on Lake Loosdrecht. It has been extended and improved since then. Parallel to PCLake, PCDitch was created, which is an ecosystem model for ditches and other linear water bodies. The models were further developed by dr. Jan H. Janse and colleagues at the Netherlands Environmental Assessment Agency (PBL), formerly part of the RIVM. Since 2009, the model is jointly owned by PBL and the Netherlands Institute of Ecology, where further development and application of PCLake is taking place, related to aquatic-ecological research. | https://en.wikipedia.org/wiki/PCLake |
PCMark is a computer benchmark tool developed by UL (formerly Futuremark ) to test the performance of a PC at the system and component level. In most cases, the tests in PCMark are designed to represent typical home user workloads. [ citation needed ] Running PCMark produces a score with higher numbers indicating better performance. Several versions of PCMark have been released. Scores cannot be compared across versions since each includes different tests.
In a 2008 Ars Technica article, a VIA Nano gained significant performance after its CPUID changed to Intel . [ 2 ] This was because Intel compilers create conditional code that uses more advanced instructions for CPUs that identify as Intel . [ 3 ] | https://en.wikipedia.org/wiki/PCMark |
p CO 2 , pCO 2 , or P CO 2 {\displaystyle P_{{\ce {CO2}}}} is the partial pressure of carbon dioxide (CO 2 ), often used in reference to blood but also used in meteorology , climate science , oceanography , and limnology to describe the fractional pressure of CO 2 as a function of its concentration in gas or dissolved phases. The units of p CO 2 are mmHg , atm , torr , Pa , or any other standard unit of atmospheric pressure . The p CO 2 of Earth's atmosphere has risen from approximately 280 ppm ( parts-per-million ) to a mean 2019 value of 409.8 ppm as a result of anthropogenic release of carbon dioxide from fossil fuel burning. [ 1 ] This is the highest atmospheric concentration to have existed on Earth for at least the last 800,000 years. [ 2 ]
In medicine, the partial pressure of carbon dioxide in arterial blood is called P a CO 2 {\displaystyle P_{a_{{\ce {CO2}}}}} or PaCO 2 . Measurement of P a CO 2 {\displaystyle P_{a_{{\ce {CO2}}}}} in the systemic circulation indicates the effectiveness of ventilation at the lungs' alveoli , given the diffusing capacity of the gas. It is a good indicator of respiratory function and the closely related factor of acid–base homeostasis , reflecting the amount of acid in the blood (without lactic acid). Normal values for humans are in the range of 35–45 mmHg . Values less than this may indicate hyperventilation and (if blood pH is greater than 7.45) respiratory alkalosis . Values greater than 45 mmHg may indicate hypoventilation , and (if blood pH is less than 7.35) respiratory acidosis . [ 3 ] [ 4 ]
Oceanographers and limnologists use p CO 2 to measure the amount of carbon dioxide dissolved in water, as well as to parameterize its flux into (influx) and out of (efflux) the atmosphere. Carbon dioxide reacts with water to form bicarbonate and carbonate ions, such that the relative solubility of carbon dioxide in water is greater than that of other unreactive gasses (e.g. Helium ). As more carbon dioxide dissolves in water, its p CO 2 rises until it equals the p CO 2 of the overlying atmosphere. Conversely, a body of water with a p CO 2 greater than that of the atmosphere effluxes carbon dioxide. [ 5 ] [ 6 ]
p CO 2 is additionally affected by water temperature and salinity . Carbon dioxide is less soluble in warmer water than cooler water, so hot water will exhibit a larger p CO 2 than cold water with the same concentration of carbon dioxide. p CO 2 can be used to describe the inorganic carbon system of a body of water, together with other parameters such as pH, dissolved inorganic carbon , and alkalinity . Together, these parameters describe the concentration and speciation of inorganic carbon species (CO 2 (aq) , HCO 3 − , CO 3 2- ) in water. [ 6 ]
Biological processes such as respiration and photosynthesis affect and can be affected by aquatic p CO 2 . Respiration degrades organic matter , releasing CO 2 into the water column and increasing p CO 2 . Photosynthesis assimilates inorganic carbon, thereby decreasing aquatic p CO 2 . [ 5 ]
This article incorporates text by Glynda Rees Doyle and Jodie Anita McCutcheon available under the CC BY 4.0 license. | https://en.wikipedia.org/wiki/PCO2 |
In computational complexity theory , the PCP theorem (also known as the PCP characterization theorem ) states that every decision problem in the NP complexity class has probabilistically checkable proofs ( proofs that can be checked by a randomized algorithm ) of constant query complexity and logarithmic randomness complexity (uses a logarithmic number of random bits).
The PCP theorem says that for some universal constant K , for every n , any mathematical proof for a statement of length n can be rewritten as a different proof of length poly( n ) that is formally verifiable with 99% accuracy by a randomized algorithm that inspects only K letters of that proof.
The PCP theorem is the cornerstone of the theory of computational hardness of approximation , which investigates the inherent difficulty in designing efficient approximation algorithms for various optimization problems . It has been described by Ingo Wegener as "the most important result in complexity theory since Cook's theorem " [ 1 ] and by Oded Goldreich as "a culmination of a sequence of impressive works […] rich in innovative ideas". [ 2 ]
The PCP theorem states that
where PCP [ r ( n ), q ( n )] is the class of problems for which a probabilistically checkable proof of a solution can be given, such that the proof can be checked in polynomial time using r ( n ) bits of randomness and by reading q ( n ) bits of the proof, correct proofs are always accepted, and incorrect proofs are rejected with probability at least 1/2. n is the length in bits of the description of a problem instance. Note further that the verification algorithm is non-adaptive : the choice of bits of the proof to check depend only on the random bits and the description of the problem instance, not the actual bits of the proof.
An alternative formulation of the PCP theorem states that the maximum fraction of satisfiable constraints of a constraint satisfaction problem is NP-hard to approximate within some constant factor. [ 3 ]
Formally, for some constants q and α < 1, the following promise problem ( L yes , L no ) is an NP-hard decision problem:
where Φ is a constraint satisfaction problem (CSP) over a Boolean alphabet with at most q variables per constraint.
The connection to the class PCP mentioned above can be seen by noticing that checking a constant number of bits q in a proof can be seen as evaluating a constraint in q Boolean variables on those bits of the proof. Since the verification algorithm uses O (log n ) bits of randomness, it can be represented as a CSP as described above with poly ( n ) constraints. The other characterisation of the PCP theorem then guarantees the promise condition with α = 1/2: if the NP problem's answer is yes, then every constraint (which corresponds to a particular value for the random bits) has a satisfying assignment (an acceptable proof); otherwise, any proof should be rejected with probability at least 1/2, which means any assignment must satisfy fewer than 1/2 of the constraints (which means it will be accepted with probability lower than 1/2). Therefore, an algorithm for the promise problem would be able to solve the underlying NP problem, and hence the promise problem must be NP hard.
As a consequence of this theorem, it can be shown that the solutions to many natural optimization problems including maximum boolean formula satisfiability , maximum independent set in graphs, and the shortest vector problem for lattices cannot be approximated efficiently unless P = NP . This can be done by reducing the problem of approximating a solution to such problems to a promise problem of the above form. These results are sometimes also called PCP theorems because they can be viewed as probabilistically checkable proofs for NP with some additional structure.
A proof of a weaker result, N P ⊆ P C P [ n 3 , 1 ] {\displaystyle {\mathsf {NP}}\subseteq {\mathsf {PCP}}[n^{3},1]} is given in one of the lectures of Dexter Kozen. [ 4 ]
The PCP theorem is the culmination of a long line of work on interactive proofs and probabilistically checkable proofs. The first theorem relating standard proofs and probabilistically checkable proofs is the statement that NEXP ⊆ PCP [poly( n ), poly( n )], proved by Babai, Fortnow & Lund (1990) .
The notation PCP c ( n ), s ( n ) [ r ( n ), q ( n )] is explained at probabilistically checkable proof . The notation is that of a function that returns a certain complexity class. See the explanation mentioned above.
The name of this theorem (the "PCP theorem") probably comes either from "PCP" meaning " probabilistically checkable proof ", or from the notation mentioned above (or both).
Subsequently, the methods used in this work were extended by Babai, Lance Fortnow , Levin, and Szegedy in 1991 ( Babai et al. 1991 ),
Feige, Goldwasser, Lund, Safra, and Szegedy (1991), and Arora and Safra in 1992 ( Arora & Safra 1992 ) to yield a proof of the PCP theorem by Arora, Lund, Motwani, Sudan, and Szegedy in 1998 ( Arora et al. 1998 ).
The 2001 Gödel Prize was awarded to Sanjeev Arora , Uriel Feige , Shafi Goldwasser , Carsten Lund , László Lovász , Rajeev Motwani , Shmuel Safra , Madhu Sudan , and Mario Szegedy for work on the PCP theorem and its connection to hardness of approximation.
In 2005 Irit Dinur discovered a significantly simpler proof of the PCP theorem, using expander graphs . [ 5 ] She received the 2019 Gödel Prize for this. [ 6 ]
In 2012, Thomas Vidick and Tsuyoshi Ito published a result [ 7 ] that showed a "strong limitation on the ability of entangled provers to collude in a multiplayer game". This could be a step toward proving the quantum analogue of the PCP theorem, since when the result [ 7 ] was reported in the media, [ 8 ] [ 9 ] professor Dorit Aharonov called it "the quantum analogue of an earlier paper on multiprover interactive proofs" that "basically led to the PCP theorem". [ 9 ]
In 2018, Thomas Vidick and Anand Natarajan proved [ 10 ] a games variant of quantum PCP theorem under randomized reduction. It states that QMA ⊆ MIP ∗ [log( n ), 1, 1/2] , where MIP ∗ [ f ( n ), c , s ] is a complexity class of multi-prover quantum interactive proofs systems with f ( n )-bit classical communications, and the completeness is c and the soundness is s. They also showed that the Hamiltonian version of a quantum PCP conjecture, namely a local Hamiltonian problem with constant promise gap c − s is QMA -hard, implies the games quantum PCP theorem.
NLTS conjecture was a fundamental unresolved obstacle and precursor to a quantum analog of PCP. [ 11 ] The NLTS conjecture was proven in 2022 by Anurag Anshu , Nikolas Breuckmann , and Chinmay Nirkhe . [ 12 ] | https://en.wikipedia.org/wiki/PCP_theorem |
PCPartPicker is a comparison shopping website that allows users to compare prices and compatibility of computer components on different retailers online. [ 1 ]
PCPartPicker was created by Philip Carmichael in 2011. The website was substantially redesigned in February 2015. [ 2 ] [ 3 ] As of 2023 the site provides localized currencies and links to physical stores in 38 countries. The website is funded through affiliate linking to sites such as Amazon.com . [ 4 ] Additional functionality is available, such as providing building guides, sharing build lists, photos, and instruction, alerts for price drops, forums, and filters for automatically adjusting pre-made lists of components. [ 5 ] They also make PC hardware reviews and custom build tutorials on their YouTube channel. They are currently located in Austin, Texas. [ 6 ]
This website-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PCPartPicker |
PCR food testing is the engagement of polymerase chain reaction (PCR) technologies for the testing of food for the presence or absence of human pathogens , such as E. coli , Salmonella , Listeria , [ 1 ] etc. [ 2 ]
Four sample collection sites for PCR food testing can be:
Each of these sample types can be collected, prepared, and PCR tested within a short time for many sample types. Some sample types may require sample enrichment via shortened culture growth periods prior to PCR testing. [ 3 ] | https://en.wikipedia.org/wiki/PCR_food_testing |
PC Card is a technical standard specifying an expansion card interface for laptops and PDAs . [ 1 ] The PCMCIA originally introduced the 16-bit ISA -based PCMCIA Card in 1990, but renamed it to PC Card in March 1995 to avoid confusion with the name of the organization. [ 2 ] The CardBus PC Card was introduced as a 32-bit version of the original PC Card, based on the PCI specification. CardBus slots are backwards compatible , but older slots are not forward compatible with CardBus cards.
Although originally designed as a standard for memory- expansion cards for computer storage , the existence of a usable general standard for notebook peripherals led to the development of many kinds of devices including network cards , modems , and hard disks .
The PC Card port has been superseded by the ExpressCard interface since 2003, which was also initially developed by the PCMCIA. The organization dissolved in 2009, with its assets merged into the USB Implementers Forum .
Many notebooks in the 1990s had two adjacent type-II slots, which allowed installation of two type-II cards or one, double-thickness, type-III card. The cards were also used in early digital SLR cameras, such as the Kodak DCS 300 series . However, their original use as storage expansion is no longer common.
Some manufacturers such as Dell continued to offer them into 2012 on their ruggedized XFR notebooks. [ 3 ]
Mercedes-Benz used a PCMCIA card reader in the W221 S-Class for model years 2006-2009. It was used for reading media files such as MP3 audio files to play through the COMAND infotainment system. After 2009, it was replaced with a standard SD Card reader.
As of 2013 [update] , some vehicles from Honda equipped with a navigation system still included a PC Card reader integrated into the audio system .
Some Japanese brand consumer entertainment devices such as TV sets include a PC Card slot for playback of media. [ 4 ]
Adapters for PC Cards to Personal Computer ISA slots were available when these technologies were current. Cardbus adapters for PCI slots have been made. These adapters were sometimes used to fit Wireless (802.11) PCMCIA cards into desktop computers with PCI slots. [ 5 ]
The Taito G-NET arcade hardware, based on the original PlayStation , uses PC Card as a software distribution method to allow games to be replaced without total replacement of the arcade board. [ 6 ] Konami also used the PC Card on their System 573 hardware, also based on the original PlayStation, for similar purposes. [ 7 ] [ 8 ] PlayStation 2 models 10000, 15000 and 18000 shipped with a PC Card slot instead of the Expansion Bay ; these models require an external hard disk drive (SCPH-20400) that connects through the PC Card port, instead of an internal IDE port of the Expansion Bay.
Before the introduction of the PCMCIA card, the parallel port was commonly used for portable peripherals. [ 9 ]
The PCMCIA 1.0 card standard was published by the Personal Computer Memory Card International Association in November 1990 and was soon adopted by more than eighty vendors. [ 10 ] [ 11 ] It corresponds with the Japanese JEIDA memory card 4.0 standard. [ 11 ] It was originally developed to support Memory cards . [ 12 ]
Intel authored the Exchangable Card Architecture (ExCA) specification, but later merged this into the PCMCIA. [ 13 ]
SanDisk (operating at the time as "SunDisk") launched its PCMCIA card in October 1992. The company was the first to introduce a writeable Flash RAM card for the HP 95LX (an early MS-DOS pocket computer). These cards conformed to a supplemental PCMCIA-ATA standard that allowed them to appear as more conventional IDE hard drives to the 95LX or a PC. This had the advantage of raising the upper limit on capacity to the full 32 MB available under DOS 3.22 on the 95LX. [ 14 ]
New Media Corporation was one of the first companies established for the express purpose of manufacturing PC Cards; they became a major OEM for laptop manufacturers such as Toshiba and Compaq for PC Card products. [ 15 ]
It soon became clear that the PCMCIA card standard needed expansion to support "smart" I/O cards to address the emerging need for fax, modem, LAN, harddisk and floppy disk cards. [ 10 ] It also needed interrupt facilities and hot plugging , which required the definition of new BIOS and operating system interfaces. [ 10 ] This led to the introduction of release 2.0 of the PCMCIA standard and JEIDA 4.1 in September 1991, [ 10 ] [ 11 ] which saw corrections and expansion with Card Services (CS) in the PCMCIA 2.1 standard in November 1992. [ 10 ] [ 11 ]
To recognize increased scope beyond memory, and to aid in marketing, the association acquired the rights to the simpler term "PC Card" from IBM . This was the name of the standard from version 2 of the specification onwards. These cards were used for wireless networks , modems, and other functions in notebook PCs.
After the release of PCIe -based ExpressCard in 2003, laptop manufacturers started to fit ExpressCard slots to new laptops instead of PC Card slots.
All PC Card devices use a similar sized package which is 85.6 millimetres (3.37 in) long and 54.0 millimetres (2.13 in) wide, the same size as a credit card . [ 16 ]
The original standard was defined for both 5 V and 3.3 volt cards, with 3.3 V cards having a key on the side to prevent them from being inserted fully into a 5 V-only slot. Some cards and some slots operate at both voltages as needed. The original standard was built around an 'enhanced' 16-bit ISA bus platform. A newer version of the PCMCIA standard is CardBus (see below), a 32-bit version of the original standard. In addition to supporting a wider bus of 32 bits (instead of the original 16), CardBus also supports bus mastering and operation speeds up to 33 MHz.
CardBus are PCMCIA 5.0 or later (JEIDA 4.2 or later) 32-bit PCMCIA devices, introduced in 1995 and present in laptops from late 1997 onward. CardBus is effectively a 32-bit, 33 MHz PCI bus in the PC Card design. CardBus supports bus mastering , which allows a controller on the bus to talk to other devices or memory without going through the CPU . Many chipsets, such as those that support Wi-Fi , are available for both PCI and CardBus.
The notch on the left hand front of the device is slightly shallower on a CardBus device so, by design, a 32-bit device cannot be plugged into earlier equipment supporting only 16-bit devices. Most new slots accept both CardBus and the original 16-bit PC Card devices. CardBus cards can be distinguished from older cards by the presence of a gold band with eight small studs on the top of the card next to the pin sockets.
The speed of CardBus interfaces in 32-bit burst mode depends on the transfer type: in byte mode, transfer is 33 MB/s; in word mode it is 66 MB/s; and in dword (double-word) mode 132 MB/s.
CardBay is a variant added to the PCMCIA specification introduced in 2001. It was intended to add some forward compatibility with USB and IEEE 1394 , but was not universally adopted and only some notebooks have PC Card controllers with CardBay features. This is an implementation of Microsoft and Intel's joint Drive Bay initiative.
The card information structure (CIS) is metadata stored on a PC card that contains information about the formatting and organization of the data on the card. [ 21 ] The CIS also contains information such as:
When a card is unrecognized it is frequently because the CIS information is either lost or damaged.
ExpressCard is a later specification from the PCMCIA, intended as a replacement for PC Card, built around the PCI Express and USB 2.0 standards. The PC Card standard is closed to further development and PCMCIA strongly encourages future product designs to utilize the ExpressCard interface. From about 2006, ExpressCard slots replaced PCMCIA slots in laptop computers, with a few laptops having both in the transition period.
ExpressCard and CardBus sockets are physically and electrically incompatible. [ 22 ] ExpressCard-to-CardBus and Cardbus-to-ExpressCard adapters are available that connect a Cardbus card to an Expresscard slot, or vice versa, and carry out the required electrical interfacing. [ 23 ] These adapters do not handle older non-Cardbus PCMCIA cards.
PC Card devices can be plugged into an ExpressCard adaptor, which provides a PCI-to-PCIe Bridge.
Despite being much faster in speed/bandwidth, ExpressCard was not as popular as PC Card, due in part to the ubiquity of USB ports on modern computers. Most functionality provided by PC Card or ExpressCard devices is now available as an external USB device. These USB devices have the advantage of being compatible with desktop computers as well as portable devices. (Desktop computers were rarely fitted with a PC Card or ExpressCard slot.) This reduced the requirement for internal expansion slots ; by 2011, many laptops had none.
Some IBM ThinkPad laptops took their onboard RAM (in sizes ranging from 4 to 16 MB) in the factor of an IC-DRAM Card. While very similar in form-factor, these cards did not go into a standard PC Card Slot, often being installed under the keyboard, for example. They also were not pin-compatible, as they had 88 pins but in two staggered rows, as opposed to even rows like PC Cards. [ 24 ] These correspond to versions 1 and 2 of the JEIDA memory card standard.
The shape is also used by the Common Interface form of conditional-access modules for DVB , and by Panasonic for their professional "P2" video acquisition memory cards.
A CableCARD conditional-access module is a type II PC Card intended to be plugged into a cable set-top box or digital cable-ready television.
The interface has spawned a generation of flash memory cards that set out to improve on the size and features of Type I cards: CompactFlash , MiniCard , P2 Card and SmartMedia . For example, the PC Card electrical specification is also used for CompactFlash, so a PC Card CompactFlash adapter can be a passive physical adapter rather than requiring additional circuitry. CompactFlash is a smaller dimensioned 50 pin subset of the 68 pin PC Card interface. It requires a setting for the interface mode of either "memory" or " ATA storage". [ citation needed ]
The EOMA68 open-source hardware standard uses the same 68-pin PC Card connectors and corresponds to the PC Card form factor in many other ways. [ 25 ] | https://en.wikipedia.org/wiki/PC_Card |
PC Conectado , or Computador para Todos , is a tax-free computer initiative launched by the Brazilian government, since 2003.
PCs available through the project are relatively low-end, but therefore are cheap enough to satisfy most of the population, at R$ 1200 (or about US$ 500). Most PCs available have:
In the initial phases of the project, Microsoft offered the Brazilian government the use of its MS Windows XP Starter Edition , a cut down version of their popular OS for developing countries. The offer was rejected due to the severe limitations of the Starter Edition. Since then, the project has used only free and open source software for general work, like Inkscape , OpenOffice , GIMP and Amarok .
The Brazilian government's decision to reject Microsoft's proprietary and limited (i.e. cut-down) version of MS Windows XP in favor of a full featured and free Linux operating system was widely reported in the US media and IT periodicals. [ 2 ] [ 3 ] [ 4 ] This decision could be interpreted as a severe, humiliating and embarrassing rejection for Microsoft. The president of the Brazilian agency in charge of the governments technology initiatives, Sérgio Amadeu , unequivocally stated that he was against spending Brazilian tax-payers money on furthering Microsoft's monopoly:
We're not going to spend taxpayers' money on a program so that Microsoft can further consolidate its monopoly. It's the government's responsibility to ensure that there is competition, and that means giving alternative software platforms a chance to prosper. [ 2 ]
An option providing cheap dial-up access to the Internet may be available soon, costing R$7 (about US$2.50). Also, a project to offer a popular broadband internet access (512 kbit/s), charging a monthly fee between 15 and 35 reais (between 8.5 and 20 US dollars). [ 5 ]
PC Conectado can be acquired in many major Brazilian department stores. Many Brazilian stores have an independent Linux vendor on site from whom a user can choose the hardware configuration and distro.
This article about government in Brazil is a stub . You can help Wikipedia by expanding it .
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PC_Conectado |
"PC LOAD LETTER? The fuck does that mean!?"
PC LOAD LETTER is a printer error message that has entered popular culture as a technology meme referring to a confusing or inappropriate error message . The message is instructing the user to refill the paper tray on a HP LaserJet with letter-sized paper. The error message's vagueness was mocked in the 1999 comedy film Office Space . [ 2 ]
The message is encountered when printing on older HP LaserJet printers such as the LaserJet II, III, and 4 series. It means that the printer is trying to print a document that needs " Letter size " (8½ × 11 in.) paper when no such paper is available. [ 3 ]
"PC" is an abbreviation for "paper cassette", [ 4 ] the tray which holds blank paper for the printer to use. These two-character codes are a legacy feature carried over from the first LaserJet printers, which could only use a two-character display for all printer status and error messages. "LOAD" is an instruction to refill the paper tray. "LETTER" is the standard paper size used in the United States and Canada . Thus, the message is instructing the user to refill the paper tray with letter-sized paper. Other messages that might be seen include "MP LOAD LEGAL", meaning the "MP" (multi-purpose) tray needs to be filled with legal size (8½ × 14 in.) paper. [ 5 ]
Users confuse "PC" with " personal computer ", "LOAD" with some action someone might do to that computer, and "LETTER" with what is sent in the mail. Outside the United States and Canada, standard paper is A4 size and users may not even know "LETTER" is a paper size. [ citation needed ]
The error can be dismissed (other than by filling the paper tray) by emptying the print queue and printer buffer or pressing "Shift+Continue" [ 6 ] and, in extreme cases, restarting the printer and repeating. The LaserJet 5 introduced a "GO" button to override the warning message.
The LaserJet 5, 4000, and later models added number labels on paper trays and displayed a new message, "TRAY [x] LOAD PLAIN [paper size]" where [x] is the tray number. | https://en.wikipedia.org/wiki/PC_LOAD_LETTER |
PC Perspective (often shortened to PCPer ) is a web site dedicated to news and reviews of personal computing and gaming hardware. [ 1 ] PC Perspective specializes in hardware that is most relevant to home users and enthusiasts. The site also has an active online community, a weekly podcast, and founder Ryan Shrout was the co-host of TWiT.tv 's This Week in Computer Hardware. [ 2 ]
PCPer was founded by Ryan Shrout in 2004. [ 1 ] Shrout previously ran the AMD motherboard centric Amdmb.com, Athlonmb.com, and K7M.com websites. [ 3 ] [ 4 ]
PC Perspective was originally located at pcperspective.com, but quickly moved to pcper.com.
The PCPer website publishes news and reviews of consumer computing and gaming hardware, [ 5 ] [ 6 ] [ 7 ] which has been highlighted in Forbes , [ 8 ] [ 9 ] [ 10 ] PC World , [ 11 ] [ 12 ] Ars Technica , [ 13 ] [ 14 ] [ 15 ] [ 16 ] and Anandtech . [ 17 ] At the editor's discretion, products with exceptional reviews may be given Silver, Gold, or Editor's Choice awards. [ 18 ] PCPer has also been noted for purchasing professional level products in order to infer the performance of consumer products based on the same microarchitecture, [ 19 ] [ 20 ] and livestreaming benchmarking of new products. [ 21 ]
The PCPer website also hosts a leaderboard of suggested components for computers at various price points. [ 22 ]
PCPer also partnered with Polygon in 2016 on the construction and evaluation of computers for virtual reality gaming. [ 23 ]
Due to consulting done by some PCPer staff on products, some PCPer reviews include disclosure statements describing the consulting and review relationship and any potential conflict of interest . [ 24 ] With the departure of PCPer staff involved in private consulting and the transfer of ownership on January 1, 2019 to individuals not involved in any form of private consulting, the PCPer review disclosures statements have remained under the justification of providing readers with relevant information about published reviews. [ 25 ]
PCPer hosts a weekly podcast discussing the weeks technology news and reviews. Video podcasts have been produced since at least 2010, [ 26 ] with a successful Indiegogo fundraising campaign supporting production equipment. [ 27 ] PCPer also began in July 2017 to host a weekly video series answering reader's questions, [ 28 ] after reaching a set support level on Patreon . [ 29 ]
Ryan Shrout was the regular co-host of TWiT.tv's This Week in Computer Hardware with Patrick Norton [ 2 ] with other PCPer editors co-hosting as-well. [ 30 ] Sebastian Peak took over co-hosting duties when Shrout went on to work for Intel. [ 31 ]
Founder Ryan Shrout is also a consultant, [ 32 ] analyst for MarketWatch [ 33 ] [ 34 ] and contributor to EE Times , [ 35 ] [ 36 ] [ 37 ] [ 38 ] and CNBC , [ 39 ] [ 40 ] [ 41 ] and other publications; [ 42 ] often discussing technology related news. Shrout has also co-hosted The Tech Analysts podcast, discussing technology topics, with Patrick Moorehead since 2017. [ 43 ] [ 44 ]
In October 2018, Shrout announced he would leave PCPer and join Intel as the company's Chief Performance Strategist. [ 45 ] [ 46 ] | https://en.wikipedia.org/wiki/PC_Perspective |
The PC System Design Guide (also known as the PC-97 , PC-98 , PC-99 , or PC 2001 specification) is a series of hardware design requirements and recommendations for IBM PC compatible personal computers , compiled by Microsoft and Intel Corporation during 1997–2001. They were aimed at helping manufacturers provide hardware that made the best use of the capabilities of the Microsoft Windows operating system, and to simplify setup and use of such computers.
Every part of a standard computer and the most common kinds of peripheral devices are defined with specific requirements. Systems and devices that meet the specification should be automatically recognized and configured by the operating system .
Four versions of the PC System Design Guide were released. In PC-97, a distinction was made between the requirements of a Basic PC , a Workstation PC and an Entertainment PC . In PC-98, the Mobile PC was added as a category. In PC 2001, the Entertainment PC was dropped.
Required:
Initial version.
(Not to be confused with NEC's incompatible PC-98 series)
Aimed at systems to be used with Windows 98 or Windows 2000 . Required:
It was published as ISBN 1-57231-716-7 .
Required:
Strongly discouraged:
It was published as ISBN 0-7356-0518-1 .
Required:
Final version. First to require IO- APICs to be enabled on all desktop systems. Places a greatly increased emphasis on legacy-reduced and legacy-free systems. Some "legacy" items such as ISA expansion slots and device dependence on MS-DOS are forbidden entirely, while others are merely strongly discouraged. [ 1 ]
PC 2001 removes compatibility for the A20 line : "If A20M# generation logic is still present in the system, this logic must be
terminated such that software writes to I/O port 92, bit 1, do not result in A20M# being asserted to the processor." [ 2 ]
Perhaps the most end-user visible and lasting impact of PC 99 was that it introduced a color code for the various standard types of plugs and connectors used on PCs. [ 3 ] As many of the connectors look very similar, particularly to a novice PC user, this made it far easier for people to connect peripherals to the correct ports on a PC. This color code was gradually adopted by almost all PC and motherboard manufacturers. Some of the color codes have also been widely adopted by peripheral manufacturers.
PDF versions: | https://en.wikipedia.org/wiki/PC_System_Design_Guide |
PCaaS or, Personal Computer as a Service , [ 1 ] is a Personal Computer hardware and optionally software leasing, licensing and delivery model in which personal computer and optionally software (particularly installed on the PC) are leased and licensed on a subscription basis . The subscription often includes services such as staging, imaging, maintenance, fix, logistics services and may also be bundled with help desk services, data backup and recovery.
There are several vendors that have PCaaS offerings including, Bizbang, Dell , HP (they call theirs Device as a Service), and Lenovo (in Australia only for now).
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PCaaS |
Phosphorus trichloride is an inorganic compound with the chemical formula PCl 3 . A colorless liquid when pure, it is an important industrial chemical , being used for the manufacture of phosphites and other organophosphorus compounds . It is toxic and reacts readily with water to release hydrogen chloride .
Phosphorus trichloride was first prepared in 1808 by the French chemists Joseph Louis Gay-Lussac and Louis Jacques Thénard by heating calomel (Hg 2 Cl 2 ) with phosphorus . [ 5 ] Later during the same year, the English chemist Humphry Davy produced phosphorus trichloride by burning phosphorus in chlorine gas. [ 6 ]
World production exceeds one-third of a million tonnes . [ 7 ] Phosphorus trichloride is prepared industrially by the reaction of chlorine with white phosphorus , using phosphorus trichloride as the solvent. In this continuous process PCl 3 is removed as it is formed in order to avoid the formation of PCl 5 .
It has a trigonal pyramidal shape. Its 31 P NMR spectrum exhibits a singlet around +220 ppm with reference to a phosphoric acid standard. [ citation needed ]
The phosphorus in PCl 3 is often considered to have the +3 oxidation state and the chlorine atoms are considered to be in the −1 oxidation state. Most of its reactivity is consistent with this description. [ 8 ]
PCl 3 is a precursor to other phosphorus compounds, undergoing oxidation to phosphorus pentachloride (PCl 5 ), thiophosphoryl chloride (PSCl 3 ), or phosphorus oxychloride (POCl 3 ).
PCl 3 reacts vigorously with water to form phosphorous acid (H 3 PO 3 ) and hydrochloric acid :
Phosphorus trichloride is the precursor to organophosphorus compounds . It reacts with phenol to give triphenyl phosphite :
Alcohols such as ethanol react similarly in the presence of a base such as a tertiary amine: [ 9 ]
With one equivalent of alcohol and in the absence of base, the first product is alkoxyphosphorodichloridite: [ 10 ]
In the absence of base, however, with excess alcohol, phosphorus trichloride converts to diethylphosphite : [ 11 ] [ 12 ]
Secondary amines (R 2 NH) form aminophosphines . For example, bis(diethylamino)chlorophosphine , (Et 2 N) 2 PCl, is obtained from diethylamine and PCl 3 . Thiols (RSH) form P(SR) 3 . An industrially relevant reaction of PCl 3 with amines is phosphonomethylation, which employs formaldehyde :
The herbicide glyphosate is also produced this way.
The reaction of PCl 3 with Grignard reagents and organolithium reagents is a useful method for the preparation of organic phosphines with the formula R 3 P (sometimes called phosphanes) such as triphenylphosphine , Ph 3 P.
Triphenylphosphine is produced industrially by the reaction between phosphorus trichloride, chlorobenzene , and sodium: [ 13 ]
Under controlled conditions or especially with bulky R groups, similar reactions afford less substituted derivatives such as chlorodiisopropylphosphine .
Phosphorus trichloride is commonly used to convert primary and secondary alcohols to the corresponding chlorides. [ 14 ] As discussed above, the reaction of alcohols with phosphorus trichloride is sensitive to conditions. The mechanism for the ROH →RCl conversion involves the reaction of HCl with phosphite esters:
The first step proceeds with nearly ideal stereochemistry but the final step far less so owing to an SN1 pathway.
Phosphorus trichloride undergoes a variety of redox reactions: [ 13 ]
Phosphorus trichloride has a lone pair, and therefore can act as a Lewis base , [ 15 ] e.g., forming a 1:1 adduct Br 3 B-PCl 3 . Metal complexes such as Ni(PCl 3 ) 4 are known, again demonstrating the ligand properties of PCl 3 .
This Lewis basicity is exploited in the Kinnear–Perren reaction to prepare alkylphosphonyl dichlorides (RP(O)Cl 2 ) and alkyl phosphonate esters (RP(O)(OR') 2 ). Alkylation of phosphorus trichloride is effected in the presence of aluminium trichloride give the alkyltrichlorophosphonium salts, which are versatile intermediates: [ 16 ]
The RPCl + 3 product can then be decomposed with water to produce an alkylphosphonic dichloride RP(=O)Cl 2 .
PCl 3 , like the more popular phosphorus trifluoride , is a ligand in coordination chemistry . One example is Mo(CO) 5 PCl 3 . [ 17 ]
PCl 3 is important indirectly as a precursor to PCl 5 , POCl 3 and PSCl 3 , which are used in many applications, including herbicides , insecticides , plasticisers , oil additives , and flame retardants .
For example, oxidation of PCl 3 gives POCl 3 , which is used for the manufacture of triphenyl phosphate and tricresyl phosphate , which find application as flame retardants and plasticisers for PVC . They are also used to make insecticides such as diazinon . Phosphonates include the herbicide glyphosate .
PCl 3 is the precursor to triphenylphosphine for the Wittig reaction , and phosphite esters which may be used as industrial intermediates, or used in the Horner-Wadsworth-Emmons reaction , both important methods for making alkenes . It can be used to make trioctylphosphine oxide (TOPO), used as an extraction agent, although TOPO is usually made via the corresponding phosphine.
PCl 3 is also used directly as a reagent in organic synthesis . It is used to convert primary and secondary alcohols into alkyl chlorides , or carboxylic acids into acyl chlorides , although thionyl chloride generally gives better yields than PCl 3 . [ 18 ]
Industrial production of phosphorus trichloride is controlled under the Chemical Weapons Convention , where it is listed in schedule 3 , as it can be used to produce mustard agents . [ 23 ] | https://en.wikipedia.org/wiki/PCl3 |
Phosphorus pentachloride is the chemical compound with the formula PCl 5 . It is one of the most important phosphorus chlorides/oxychlorides, others being PCl 3 and POCl 3 . PCl 5 finds use as a chlorinating reagent. It is a colourless, water-sensitive solid , although commercial samples can be yellowish and contaminated with hydrogen chloride .
The structures for the phosphorus chlorides are invariably consistent with VSEPR theory . The structure of PCl 5 depends on its environment. Gaseous and molten PCl 5 is a neutral molecule with trigonal bipyramidal geometry and ( D 3h ) symmetry . The hypervalent nature of this species (as well as of [PCl 6 ] − , see below) can be explained with the inclusion of non-bonding molecular orbitals ( molecular orbital theory ) or resonance ( valence bond theory ). This trigonal bipyramidal structure persists in nonpolar solvents, such as CS 2 and CCl 4 . [ 5 ] In the solid state PCl 5 is an ionic compound called tetrachlorophosphonium hexachlorophosphate formulated [PCl 4 ] + [PCl 6 ] − . [ 6 ]
In solutions of polar solvents, PCl 5 undergoes self- ionization . [ 8 ] Dilute solutions dissociate according to the following equilibrium:
At higher concentrations, a second equilibrium becomes more prevalent:
The cation [PCl 4 ] + and the anion [PCl 6 ] − are tetrahedral and octahedral , respectively. At one time, PCl 5 in solution was thought to form a dimeric structure, P 2 Cl 10 , but this suggestion is not supported by Raman spectroscopic measurements.
AsCl 5 and SbCl 5 also adopt trigonal bipyramidal structures. The relevant bond distances are 211 pm (As−Cl eq ), 221 pm (As−Cl ax ), 227 pm (Sb−Cl eq ), and 233.3 pm (Sb−Cl ax ). [ 9 ] At low temperatures, SbCl 5 converts to the dimer, dioctahedral Sb 2 Cl 10 , structurally related to niobium pentachloride .
PCl 5 is prepared by the chlorination of PCl 3 . [ 10 ] This reaction is used to produce around 10,000 tonnes of PCl 5 per year (as of 2000). [ 6 ]
PCl 5 exists in equilibrium with PCl 3 and chlorine , and at 180 °C the degree of dissociation is about 40%. [ 6 ] Because of this equilibrium, samples of PCl 5 often contain chlorine, which imparts a greenish coloration.
In its most characteristic reaction, PCl 5 reacts upon contact with water to release hydrogen chloride and give phosphorus oxides. The first hydrolysis product is phosphorus oxychloride :
In hot water, hydrolysis proceeds completely to orthophosphoric acid :
Phosphorus pentachloride is a Lewis acid. This property underpins many of its characteristic reactions, autoionization, chlorinations, hydrolysis. A well studied adduct is PCl 5 ( pyridine ) . [ 11 ]
In synthetic chemistry, two classes of chlorination are usually of interest: oxidative chlorinations and substitutive chlorinations. Oxidative chlorinations entail the transfer of Cl 2 from the reagent to the substrate. Substitutive chlorinations entail replacement of O or OH groups with chloride. PCl 5 can be used for both processes.
Upon treatment with PCl 5 , carboxylic acids convert to the corresponding acyl chloride . [ 12 ] The following mechanism has been proposed: [ 13 ]
It also converts alcohols to alkyl chlorides . Thionyl chloride is more commonly used in the laboratory because the resultant sulfur dioxide is more easily separated from the organic products than is POCl 3 .
PCl 5 reacts with a tertiary amides, such as dimethylformamide (DMF), to give dimethylchloromethyleneammonium chloride, which is called the Vilsmeier reagent , [(CH 3 ) 2 N=CClH] + Cl − . More typically, a related salt is generated from the reaction of DMF and POCl 3 . Such reagents are useful in the preparation of derivatives of benzaldehyde by formylation and for the conversion of C−OH groups into C−Cl groups. [ 14 ]
It is especially renowned for the conversion of C=O groups to CCl 2 groups. [ 15 ] For example, benzophenone and phosphorus pentachloride react to give the diphenyldichloromethane : [ 16 ]
The electrophilic character of PCl 5 is highlighted by its reaction with styrene to give, after hydrolysis , phosphonic acid derivatives. [ 17 ]
Both PCl 3 and PCl 5 convert R 3 COH groups to the chloride R 3 CCl . The pentachloride is however a source of chlorine in many reactions. It chlorinates allylic and benzylic CH bonds. PCl 5 bears a greater resemblance to SO 2 Cl 2 , also a source of Cl 2 . For oxidative chlorinations on the laboratory scale, sulfuryl chloride is often preferred over PCl 5 since the gaseous SO 2 by-product is readily separated.
As for the reactions with organic compounds, the use of PCl 5 has been superseded by SO 2 Cl 2 . The reaction of phosphorus pentoxide and PCl 5 produces POCl 3 : [ 18 ] [ page needed ]
PCl 5 chlorinates nitrogen dioxide to form unstable nitryl chloride :
PCl 5 is a precursor for lithium hexafluorophosphate , Li[PF 6 ] . Lithium hexafluorophosphate is a commonly employed salt in electrolytes in lithium ion batteries . [ 19 ] Li[PF 6 ] is produced by the reaction of PCl 5 with lithium fluoride , with lithium chloride as a side product:
PCl 5 is a dangerous chemical as it reacts violently with water. It is also corrosive when in contact with skin. It is toxic and can be fatal when inhaled.
Phosphorus pentachloride was first prepared in 1808 by the English chemist Humphry Davy . [ 20 ] Davy's analysis of phosphorus pentachloride was inaccurate; [ 21 ] the first accurate analysis was provided in 1816 by the French chemist Pierre Louis Dulong . [ 22 ] | https://en.wikipedia.org/wiki/PCl5 |
pComb3H , a derivative of pComb3 optimized for expression of human fragments, is a phagemid used to express proteins such as zinc finger proteins and antibody fragments on phage pili for the purpose of phage display selection. [ 1 ]
For the purpose of phage production, it contains the bacterial ampicillin resistance gene (for B-lactamase), allowing the growth of only transformed bacteria. [ citation needed ]
This genetics article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PComb3H |
Protein Data Bank in Europe – Knowledge Base (PDBe-KB) [ 1 ] is a community-driven, open-access, integrated resource whose mission is to place macromolecular structure data in their biological context and to make them accessible to the scientific community in order to support fundamental and translational research and education. It is part of the European Bioinformatics Institute (EMBL-EBI), based at the Wellcome Genome Campus , Hinxton , Cambridgeshire, England. [ 2 ]
This article related to health informatics is a stub . You can help Wikipedia by expanding it .
This database -related article is a stub . You can help Wikipedia by expanding it .
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PDBe-KB |
Peter Garcia ( CFO ) Cary Queen (Founder, former vice-president in charge of research)
PDL BioPharma (known as Protein Design Labs prior to 2006) is a publicly traded American holding company that since 2008 manages patents and other intellectual property that had been generated by the company. [ 2 ] [ 3 ] In 2008 in response to shareholder pressure, PDL spun out its active development programs to a company called Facet Biotech that it capitalized with $400 million. [ 4 ] [ 5 ]
Protein Design Labs, founded in 1986 [ 5 ] by cell biologist Laurence J. Korn and mathematician Cary Queen, [ 6 ] was a pioneer in humanizing monoclonal antibodies . Its humanization technology was used in several monoclonal antibody drugs under licensing and collaboration agreements; such products included trastuzumab (Herceptin), bevacizumab (Avastin), and palivizumab (Synagis). [ 7 ] It held its initial public offering in 1992 [ 8 ] and by 1994 it had 13 compounds in its pipeline, and had partnered its lead product, the humanized monoclonal antibody daclizumab , with Roche under a license that called for a 15% royalty. [ 9 ] Daclizumab became the first humanized monoclonal antibody approved for human use in 1997. [ 10 ] PDL made another public offering in 2000, at the peak of the biotech IPO window that ran from 1998 to 2001. [ 7 ] [ 11 ] In 2003 it settled litigation with Genentech over royalty payments owed to PDL under their license agreement; annual royalties were anticipated at that time to be around $90M per year. [ 12 ] These are the kinds of intellectual property and license agreements that PDL manages on behalf of its shareholders since 2008; [ 3 ] in 2007 those royalty payments were around $220 million. [ 5 ]
One of the development programs that PDL had transferred to Facet was the use of daclizumab in indications it had never licensed to Roche, including multiple sclerosis . Facet partnered that development program with Biogen Idec which attempted a hostile buy out of Facet for $350M in 2009; [ 13 ] Facet rejected that offer and was purchased by Abbvie for $450 million in cash the next year. [ 14 ] The FDA approved daclizumab for multiple sclerosis in 2016 under the trade name Zinbryta. [ 15 ]
PDL Biopharma has filed for a liquidation under Delaware Law that was effective January 7 2021. The liquidation plan was approved by shareholders in October 2020. | https://en.wikipedia.org/wiki/PDL_BioPharma |
The PDP-14 was a specialized computer from Digital Equipment Corporation ’s Industrial Products Group designed to replace industrial level relay controls for machinery and machine tools that performed repetitive tasks. It was specifically designed to function in the harsh electrical environment encountered in facilities where electric motors, solenoids and arc welders were present, a significant adversity for normal computer electronics. The PDP-14 was specifically designed to be the first level of factory automation, functioning as a programmable logic controller (PLC), through its ability to communicate with a standard DEC PDP-8 minicomputer . [ 1 ] [ 2 ]
The first unit was delivered in June 1969 and used to control a gear grinding machine. [ 3 ] Its design as a "programmable machine controller" was patented in 1973. [ 4 ]
The PDP-14 was designed to process Boolean equations , usually expressed as “ ladder diagrams ” and as such had a programmable read-only program ( PROM ) memory. Programs were developed using a PDP-8 then tested using a direct connection to the PDP-14. The PDP-14 was put into a check out mode where instructions were provided by the PDP-8. Following checkout, the PDP-8 provided the instructions to be put into the PROM.
Later versions (for example, the PDP-14/30, whose instruction set was not binary compatible ) [ 5 ] are based on PDP-8 physical packaging technology. There also was a PDP-14/35 [ 6 ] and a lower cost/reduced I/O capability PDP-14/L.
The 12-bit PDP-14 could hold a maximum of 4K words for instructions. The system's configuration included a control unit and a number of external boxes: [ 5 ]
Hence the combined usable output address space of the O-boxes , A-boxes and S-boxes was 255 or fewer.
The PDP-14 has seven 12-bit registers : [ 5 ]
Among the PDP-14 instructions were: [ 5 ]
There were also TEST instructions (Test if something is ON or OFF) and SET instructions (SYN – Set "Y" oN, SYF – Set "Y" ofF).
The original PDP-14 required that programming be done by DEC. [ 7 ]
Subsequently, [ 7 ] software development for the PDP-14 was done on another system, the PDP-8 . A PDP-8
program named SIM-14 allowed for simulating the PDP-14. | https://en.wikipedia.org/wiki/PDP-14 |
PDTV is an abbreviation short for Pure Digital Television . [ 1 ] Often seen as part of the filename of TV shows shared through P2P , The Scene , and FTP servers on the Internet . In this case, PDTV refers not to container, bitrate or dimensions of the video, but the digital nature of the capture source. [ 2 ] [ 3 ] Non Scene European rippers often use the label DVBRip or DVB-rip to specify a purely digital rip of a Digital Video Broadcast (DVB), however all Scene groups use standardized labeling.
PDTV encompasses a broad array of capture methods and sources, but generally it involves the capture of SD or non- HD digital television broadcasts without any analog-to-digital conversion , instead relying on directly ripping MPEG streams. PDTV sources can be captured by a variety of digital TV tuner cards from a digital feed such as ClearQAM unencrypted cable, Digital Terrestrial Television , Digital Video Broadcast or other satellite sources. Just as with Freeview (DVB-T) in the United Kingdom, broadcast television in the United States has no barriers to PDTV capture. Hardware such as the HDHomeRun when connected to an ATSC (Antenna) or unencrypted ClearQAM cable feed allows lossless digital capture of MPEG-2 streams (Pure Digital Television), without monthly fees or other restrictions normally implemented by a Set-top box . Although different from the analog hole , Pure Digital Television capture imposes no technological restriction on what is done with the stream; playback, Mash-Ups and even recompression/pirated distribution are possible without the permission of the rights holder.
A publisher of fan-made DVD releases also uses the name PDTV, but with no connection to the more common usage explained above. The "PD" in this case refers to "planet dust" with an additional connotation of Public Domain, even though the material offered is more often the video equivalent of abandonware as opposed to anything where copyright has actually expired. Whereas PDTV content online (as described above) is indiscriminate in terms of copyright, physical DVD releases from PDTV only exist to supply fans with material not officially published to the DVD format.
As of 2018, the latter PDTV has undergone somewhat of a "rebranding", shifting its focus slightly to further emphasize preservation of VHS, Beta and Laserdisc content. The meaning of the "PD" part of its name thus becoming more associated with "physical disc" rather than anything else. | https://en.wikipedia.org/wiki/PDTV |
PD 5500 is a specification for unfired pressure vessels . It specifies requirements for the design, manufacture, inspection and testing of unfired pressure vessels made from carbon, ferritic alloy, and austenitic steels. It also includes material supplements containing requirements for vessels made from aluminium, copper, nickel, titanium and duplex.
PD 5500 is the UK’s national pressure vessels code, although the code is used outside the UK. A new edition of PD5500 is published every three years. An amendment is usually published every year in September. [ 1 ]
BS5500 was declassified as a full British Standard and reclassified as a 'Publicly Available Specification', which lead to it being renamed to PD5500 . PD5500 was withdrawn from the list of British Standards because it was not harmonized with the European Pressure Equipment Directive (2014/68/EU formerly 97/23/EC) . EN 13445 was introduced as the harmonized standard. Harmonized standards carry presumed conformity with the requirements of the Pressure Equipment Directive, whereas other pressure vessel design codes such as PD5500 or ASME must demonstrate conformity against each of the Essential Safety Requirements of the Pressure Equipment Directive before conformity can be declared. PD5500 is currently published as a "Published Document" (PD) by the British Standards Institution .
In the UK the Pressure Equipment Safety Regulations 2016 enacted the PED into UK law. Since the UK exited the European Union, the PED no longer applies and the Pressure Equipment Safety Regulations 2016 have been amended by the enactment of the UK Product Safety and Metrology Regulations, which update a number of pieces of legislation which required amendments to operate outside of the EU. [ 2 ] Under this new legislation Harmonised Standards are now referred to as Designated Standards, but the practice of demonstrating compliance remains largely the same. EN 13445 is recognised as a Designated Standard, while other codes such as PD5500 must still demonstrate conformity against each Essential Safety Requirement.
This engineering-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PD_5500 |
PEAKS is a proteomics software program for tandem mass spectrometry designed for peptide sequencing, protein identification and quantification.
PEAKS is commonly used for peptide identification (Protein ID) through de novo peptide sequencing assisted search engine database searching. [ 1 ] PEAKS has also integrated PTM and mutation characterization through automatic peptide sequence tag based searching (SPIDER) [ 2 ] and PTM Identification. [ 3 ]
PEAKS provides a complete sequence for each peptide, confidence scores on individual amino acid assignments, simple reporting for high-throughput analysis, amongst other information.
The software has the ability to compare results of multiple search engines. PEAKS inChorus will cross check test results automatically with other protein ID search engines, like Sequest, OMSSA, X!Tandem and Mascot. This approach guards against false positive peptide assignments.
PEAKS Q is an add-on tool for protein quantification, supporting label ( ICAT , iTRAQ , SILAC , TMT , 018 , etc.) and label free techniques.
SPIDER is a sequence tag based search tool within PEAKS, which deals with the possible overlaps between the de novo sequencing errors and the homology mutations. It reconstructs the real peptide sequence by combining both the de novo sequence tag and the homolog, automatically and efficiently. [ 2 ]
A collection of algorithms used within the PEAKS software have been adapted and configured into a specialized project, PEAKS AB, which has proven to be the first method for automatic monoclonal antibody sequencing. [ 4 ] | https://en.wikipedia.org/wiki/PEAKS |
PEARL , or Process and experiment automation realtime language , is a computer programming language designed for multitasking and real-time programming. Being a high-level language , it is fairly cross-platform . Since 1977, the language has undergone several standardization iterations by the Deutsches Institut für Normung . The current version is PEARL-90, which was standardized in 1998 as DIN 66253-2.
PEARL supports both fixed-point and floating-point numeric values, character and character string data as well as bit values. It also provides facilities for structures and multi-dimensional arrays . Both typed and untyped pointers are also supported, along with typecasting .
PEARL is a higher level programming language, which allows comfortable, secure and almost processor independent programming of multitasking and realtime solutions. It has been standardized since 1977 at various stages of its development. The last time was in 1998 as PEARL-90 (DIN 66253-2 1998, Berlin, Beuth-Verlag, 1998).
Besides the simple possibility to map process technical problems, an important principle in the development of PEARL was ease of learning by the programmer.
All basic data types and language structures of other procedural programming languages exist in PEARL. In addition PEARL offers comfortable language elements for the handling of multitasking- and realtime tasks.
Like most other high-level languages, PEARL supports procedures and functions, and passing parameters to these can be done by value or by reference (via pointers ).
OpenPEARL on SourceForge
This programming-language -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PEARL_(programming_language) |
Poly(3,4-ethylenedioxythiophene)-tetramethacrylate or PEDOT-TMA is a p-type conducting polymer based on 3,4-ethylenedioxylthiophene or the EDOT monomer . It is a modification of the PEDOT structure. Advantages of this polymer relative to PEDOT (or PEDOT:PSS ) are that it is dispersible in organic solvents, and it is non-corrosive. PEDOT-TMA was developed under a contract with the National Science Foundation , and it was first announced publicly on April 12, 2004. [ 1 ] The trade name for PEDOT-TMA is Oligotron. PEDOT-TMA was featured in an article entitled "Next Stretch for Plastic Electronics" that appeared in Scientific American in 2004. [ 2 ] [ 3 ] The U.S. Patent office issued a patent protecting PEDOT-TMA on April 22, 2008. [ 4 ]
PEDOT-TMA differs from the parent polymer PEDOT in that it is capped on both ends of the polymer. This limits the chain-length of the polymer, making it more soluble in organic solvents than PEDOT. The methacrylate groups on the two end-caps allow further chemistry to occur such as cross-linking to other polymers or materials.
The bulk conductivity of PEDOT-TMA is 0.1-.5 S/cm, the sheet resistance 1-10 M Ω/sq, and the methacrylate equivalent weight 1360-1600 g/mol. The chemical composition of a film of PEDOT-TMA was measured by energy-dispersive x-ray spectroscopy (EDS). The relative C, O, and S weight percentages were 51.28%, 35.37%, and 10.43%. There was also 2.92% Fe present in the film. [ 5 ]
Several devices and materials have been described in both journals and the patent literature that use PEDOT-TMA as a critical component. In this section, a brief overview of these inventions is given. | https://en.wikipedia.org/wiki/PEDOT-TMA |
Polyethylene glycol–polyvinyl alcohol ( PEG-PVA ) brand name Kollicoat IR ( BASF ) is a multifunctional excipient [ 1 ] used as a pill binder as well as a wet binder. A typical formulation is composed of 25% polyethylene glycol (PEG) and 75% polyvinyl alcohol (PVA); where the vinyl alcohol moieties are grafted on a polyethylene glycol backbone . [ 2 ]
This pharmacology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PEG-PVA |
PEGASE is a design for a space observatory developed by France in the early 2000s. [ 1 ] It combined formation flying with infrared telescopes operating as a double-aperture interferometer . [ 1 ] Three free-flying satellites would operate together;a beam combiner and two siderostats. [ 1 ] The baseline of the interferometer would be adjustable to between 50 and 500 meters. [ 1 ] The goal of the mission is the study of Hot Jupiters ("pegasids"), brown dwarfs and the interior of protoplanetary disks . [ 2 ] The design was developed by Centre National d'Études Spatiales and was studied for a launch as early as 2010–2012. [ 3 ] However, the Phase-0 part of the study in 2005 suggested it would take 8 or 9 years to develop. [ 1 ]
This article about one or more spacecraft of France is a stub . You can help Wikipedia by expanding it .
This astrobiology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PEGASE |
PEGylation (or pegylation ) is the process of both covalent and non-covalent attachment or amalgamation of polyethylene glycol (PEG, in pharmacy called macrogol ) polymer chains to molecules and macrostructures, such as a drug, therapeutic protein or vesicle, which is then described as PEGylated . [ 1 ] [ 2 ] [ 3 ] [ 4 ] PEGylation affects the resulting derivatives or aggregates interactions, which typically slows down their coalescence and degradation as well as elimination in vivo. [ 5 ] [ 6 ]
PEGylation is routinely achieved by the incubation of a reactive derivative of PEG with the target molecule. The covalent attachment of PEG to a drug or therapeutic protein can "mask" the agent from the host's immune system (reducing immunogenicity and antigenicity ), and increase its hydrodynamic size (size in solution), which prolongs its circulatory time by reducing renal clearance. PEGylation can also provide water solubility to hydrophobic drugs and proteins. Having proven its pharmacological advantages and acceptability, PEGylation technology is the foundation of a growing multibillion-dollar industry. [ 7 ]
PEGylation is the process of attaching the strands of the polymer PEG to molecules, most typically peptides , proteins , and antibody fragments, that can improve the safety and efficiency of many therapeutics . [ 9 ] [ 10 ] It produces alterations in the physiochemical properties including changes in conformation , electrostatic binding , hydrophobicity etc. These physical and chemical changes increase systemic retention of the therapeutic agent. Also, it can influence the binding affinity of the therapeutic moiety to the cell receptors and can alter the absorption and distribution patterns.
PEGylation, by increasing the molecular weight of a molecule , can impart several significant pharmacological advantages over the unmodified form, such as improved drug solubility, reduced dosage frequency with potentially reduced toxicity and without diminished efficacy, extended circulating life, increased drug stability, and enhanced protection from proteolytic degradation; PEGylated forms may also be eligible for patent protection. [ 11 ]
The attachment of an inert and hydrophilic polymer was first reported around 1970 to extend blood life and control immunogenicity of proteins . [ 12 ] Polyethylene glycol was chosen as the polymer. [ 13 ] [ 14 ] In 1981 Davis and Abuchowski founded Enzon, Inc., which brought three PEGylated drugs to market. Abuchowski later founded and is CEO of Prolong Pharmaceuticals. [ 15 ]
The clinical value of PEGylation is now well established. ADAGEN (pegademase bovine) manufactured by Enzon Pharmaceuticals, Inc., US was the first PEGylated protein approved by the U.S. Food and Drug Administration (FDA) in March 1990, to enter the market. It is used to treat a form of severe combined immunodeficiency syndrome (ADA-SCID), as an alternative to bone marrow transplantation and enzyme replacement by gene therapy . Since the introduction of ADAGEN, a large number of PEGylated protein and peptide pharmaceuticals have followed and many others are under clinical trial or under development stages. Sales of the two most successful products, Pegasys and Neulasta, exceeded $5 billion in 2011. [ 16 ] [ 17 ] All commercially available PEGylated pharmaceuticals contain methoxypoly(ethylene glycol) or mPEG. PEGylated pharmaceuticals on the market (in reverse chronology by FDA approval year) have included: [ 18 ]
The PEGylated lipid nanoparticle drug delivery (LNP) system of the mRNA vaccine known as mRNA-1273 has been the subject of ongoing patent litigation with Arbutus Biopharma , from whom Moderna had previously licensed LNP technology. [ 25 ] [ 26 ] On 4 September 2020, Nature Biotechnology reported that Moderna had lost a key challenge in the ongoing case. [ 27 ]
PEGylation has practical uses in biotechnology for protein delivery, [ 28 ] cell transfection , and gene editing in non-human cells. [ 29 ]
The first step of the PEGylation is the suitable functionalization of the PEG polymer at one or both ends. PEGs that are activated at each end with the same reactive moiety are known as " homobifunctional ", whereas if the functional groups present are different, then the PEG derivative is referred as " heterobifunctional " or " heterofunctional ". The chemically active or activated derivatives of the PEG polymer are prepared to attach the PEG to the desired molecule. [ 30 ]
The overall PEGylation processes used to date for protein conjugation can be broadly classified into two types, namely a solution phase batch process and an on-column fed-batch process. [ 31 ] The simple and commonly adopted batch process involves the mixing of reagents together in a suitable buffer solution , preferably at a temperature between 4 and 6 °C, followed by the separation and purification of the desired product using a suitable technique based on its physicochemical properties , including size exclusion chromatography (SEC), ion exchange chromatography (IEX), hydrophobic interaction chromatography (HIC) and membranes or aqueous two-phase systems ( ATPS ). [ 32 ] [ 33 ]
The choice of the suitable functional group for the PEG derivative is based on the type of available reactive group on the molecule that will be coupled to the PEG. For proteins, typical reactive amino acids include lysine , cysteine , histidine , arginine , aspartic acid , glutamic acid , serine , threonine and tyrosine . The N-terminal amino group and the C-terminal carboxylic acid can also be used as a site specific site by conjugation with aldehyde functional polymers . [ 34 ]
The techniques used to form first generation PEG derivatives are generally reacting the PEG polymer with a group that is reactive with hydroxyl groups, typically anhydrides , acid chlorides , chloroformates and carbonates . In the second generation PEGylation chemistry more efficient functional groups such as aldehyde, esters , amides etc. are made available for conjugation.
As applications of PEGylation have become more and more advanced and sophisticated, there has been an increase in need for heterobifunctional PEGs for conjugation. These heterobifunctional PEGs are very useful in linking two entities, where a hydrophilic , flexible and biocompatible spacer is needed. Preferred end groups for heterobifunctional PEGs are maleimide , vinyl sulfones , pyridyl disulfide , amine , carboxylic acids and NHS esters. [ 35 ] [ 36 ] [ 37 ]
Third-generation pegylation agents, where the polymer has been branched, Y-shaped or comb-shaped are available and show reduced viscosity and lack of organ accumulation . [ 38 ] Recently also enzymatic approaches of PEGylation have been developed, thus further expanding the conjugation tools. [ 39 ] [ 40 ] PEG-protein conjugates obtained by enzymatic methods are already in clinical use, for example: Lipegfilgrastim , Rebinyn , Esperoct .
Unpredictability in clearance times for PEGylated compounds may lead to the accumulation of large-molecular-weight compounds in the liver leading to inclusion bodies with no known toxicologic consequences. [ 41 ] Furthermore, alteration in the chain length may lead to unexpected clearance times in vivo . [ 42 ] Moreover, the experimental conditions of PEGylation reaction (i.e. pH, temperature, reaction time, overall cost of the process and molar ratio between PEG derivative and peptide) also have an impact on the stability of the final PEGylated products. [ 43 ] To overcome the above-mentioned limitations different strategies such as changing the size (Mw), the number, the location and the type of linkage of PEG molecule were offered by several researchers. [ 44 ] [ 45 ] Conjugation to biodegradable polysaccharides , which is a promising alternative to PEGylation, is another way to solve the biodegradability issue of PEG. [ 46 ] | https://en.wikipedia.org/wiki/PEGylation |
PETREL ( Platform for Extra and Terrestrial Remote Examination with LCTF ) is a technology demonstration satellite being developed by Tokyo Institute of Technology . The microsatellite is equipped with a multispectral camera, which will be used to carry out two distinct missions. One mission is to survey the sky in ultraviolet wavelengths for the field of time-domain astronomy , and the other is to conduct spectroscopic observations of the Earth . [ 2 ] PETREL was originally planned to be launched on a Epsilon rocket flight in 2022 along with the rest of JAXA 's Innovative Satellite Technology Demonstration-3 mission satellites, but was not launched. As of September 2024, PETREL is scheduled to be launched during fiscal year 2025 on the first H3-30 test flight. [ 1 ]
PETREL's role differs depending on its position in orbit: while inside Earth's shadow it will conduct astronomical observations, and while outside it will function as an Earth observation satellite . [ 2 ] [ 3 ]
PETREL will conduct wide field observations in ultraviolet, which will work in tandem with ground-based observatories to study time-domain multi-messenger astronomy . PETREL is a pathfinder for the ULTRASAT mission. [ 4 ]
As an Earth observation satellite, PETREL will perform multispectral observation of both the land and seas to acquire data for use in agriculture and aquaculture . [ 5 ] PETREL's ocean observation will measure the level of plankton and nutrients in the waters, which the aquaculture industry will utilize to help ensure a stable amount of catches. [ 6 ] | https://en.wikipedia.org/wiki/PETREL |
Positron emission tomography for bone imaging, as an in vivo tracer technique, allows the measurement of the regional concentration of radioactivity proportional to the image pixel values averaged over a region of interest (ROI) in bones. Positron emission tomography is a functional imaging technique that uses [ 18 F]NaF radiotracer to visualise and quantify regional bone metabolism and blood flow. [ 18 F]NaF has been used for imaging bones for the last 60 years. This article focuses on the pharmacokinetics of [ 18 F]NaF in bones, and various semi-quantitative and quantitative methods for quantifying regional bone metabolism using [ 18 F]NaF PET images.
The measurement of regional bone metabolism is critical to understand the pathophysiology of metabolic bone diseases.
The chemically stable anion of Fluorine-18-Fluoride is a bone -seeking radiotracer in skeletal imaging. [ 18 F]NaF has an affinity to deposit at areas where the bone is newly mineralizing. [ 5 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] Many studies have [ 18 F]NaF PET to measure bone metabolism at the hip , [ 3 ] lumbar spine , and humerus . [ 11 ] [ 18 F]NaF is taken-up in an exponential manner representing the equilibration of tracer with the extracellular and cellular fluid spaces with a half-life of 0.4 hours, and with kidneys with a half-life of 2.4 hours. [ 12 ] The single passage extraction of [ 18 F]NaF in bone is 100%. [ 13 ] After an hour, only 10% of the injected activity remains in the blood . [ 14 ]
18 F- ions are considered to occupy extracellular fluid spaces because, firstly, they equilibrate with transcellular fluid spaces and secondly, they are not entirely extracellular ions. [ 15 ] [ 16 ] [ 17 ] Fluoride undergoes equilibrium with hydrogen fluoride , which has a high permeability allowing fluoride to cross the plasma blood membrane . [ 18 ] The fluoride circulation in red blood cells accounts for 30%. [ 19 ] However, it is freely available to the bone surface for uptake because the equilibrium between erythrocytes and plasma is much faster than the capillary transit time. This is supported by studies reporting 100% single-passage extraction of whole-blood 18 F- ion by bone [ 13 ] and the rapid release of 18 F- ions from erythrocytes with a rate constant of 0.3 per second. [ 20 ]
[ 18 F]NaF is also taken-up by immature erythrocytes in the bone marrow , [ 21 ] which plays a role in fluoride kinetics. [ 22 ] The plasma protein binding of [ 18 F]NaF is negligible. [ 23 ] [ 18 F]NaF renal clearance is affected by diet [ 24 ] and pH level, [ 25 ] due to its re-absorption in the nephron, which is mediated by hydrogen fluoride. [ 26 ] However, large differences in urine flow rate [ 19 ] are avoided for controlled experiments by keeping patents well hydrated. [ 21 ]
The exchangeable pool and the size of the metabolically active surfaces in bones determines the amount of tracer accumulated or exchanged [ 27 ] with bone extracellular fluid , [ 28 ] chemisorption onto hydroxyapatite crystals to form fluorapatite, [ 14 ] [ 29 ] [ 9 ] as shown in Equation-1: [ 30 ] [ 31 ]
C a 10 ( P O 4 ) 6 ( O H ) 2 + 2 F − => C a 10 ( P O 4 ) 6 F 2 + 2. O H − {\displaystyle Ca_{10}(PO_{4})_{6}(OH)_{2}+2F-=>Ca_{10}(PO_{4})_{6}F_{2}+2.OH-} Equation-1
Fluoride ions from the crystalline matrix of bone are released when the bone is remodelled, thus providing a measure of the rate of bone metabolism. [ 32 ] [ 33 ] [ 34 ]
The standardized uptake value (SUV) is defined as tissue concentration (KBq/ml) divided by activity injected normalized for body weight . [ 35 ]
The SUV measured from the large ROI smooths out the noise and, therefore, more appropriate in [ 18 F]NaF bone studies as the radiotracer is fairly uniformly taken up throughout the bone. The measurement of SUV is easy, [ 36 ] cheap, and quicker to perform, making it more attractive for clinical use. It has been used in diagnosing and assessing the efficacy of therapy. [ 37 ] [ 38 ] SUV can be measured at a single site, or the whole skeleton using a series of static scans and restricted by the small field-of-view of the PET scanner. [ 32 ]
The SUV has emerged as a clinically useful, albeit controversial, semi-quantitative tool in PET analysis. [ 39 ] Standardizing imaging protocols and measuring the SUV at the same time post-injection of the radiotracer, is necessary to obtain a correct SUV [ 40 ] because imaging before the uptake plateau introduces unpredictable errors of up to 50% with SUVs. [ 41 ] Noise, image resolution, and reconstruction do affect the accuracy of SUVs, but correction with phantom can minimize these differences when comparing SUVs for multi-centre clinical trials. [ 42 ] [ 43 ] SUV may lack sensitivity in measuring response to treatment as it is a simple measure of tracer uptake in bone, which is affected by the tracer uptake in other competing tissues and organs in addition to the target ROI. [ 44 ] [ 45 ]
The quantification of dynamic PET studies to measure Ki requires the measurement of the skeletal time-activity curves (TAC) from the region of interest (ROI) and the arterial input function (AIF), which can be measured in various different ways. However, the most common is to correct the image-based blood time-activity curves using several venous blood samples taken at discrete time points while the patient is scanned. The calculation of rate constants or K i requires three steps: [ 3 ]
The method was first described by Cunningham & Jones [ 46 ] in 1993 for the analysis of dynamic PET data obtained in the brain. It assumes that the tissue impulse response function (IRF) can be described as a combination of many exponentials. Since A tissue TAC can be expressed as a convolution of measured arterial input function with IRF, C bone (t) can be expressed as:
C b o n e ( t ) = ∑ k = 1 n α i . ( C p l a s m a ( t ) ⊗ e x p ( − β i . t ) ) {\displaystyle C_{bone}(t)=\sum _{k=1}^{n}\alpha _{i}.{\bigl (}C_{plasma}(t)\otimes exp(-\beta _{i}.t){\bigr )}}
where, ⊗ {\displaystyle \otimes } is a convolution operator, C bone (t) is the bone tissue activity concentration of tracer (in units: MBq/ml) over a period of time t, C plasma (t) is the plasma concentration of tracer (in units: MBq/ml) over a period of time t, IRF(t) is equal to the sum of exponentials, β values are fixed between 0.0001 sec −1 and 0.1 sec −1 in intervals of 0.0001, n is the number of α components that resulted from the analysis and β 1 , β 2 ,..., β n corresponds to the respective α 1 , α 2 ,..., α n components from the resulted spectrum. The values of α are then estimated from the analysis by fitting multi-exponential to the IRF. The intercept of the linear fit to the slow component of this exponential curve is considered the plasma clearance (K i ) to the bone mineral.
The method was first described by Williams et al. in the clinical context. [ 47 ] The method was used by numerous other studies. [ 48 ] [ 49 ] [ 50 ] This is perhaps the simplest of all the mathematical methods for the calculation of K i but the one most sensitive to noise present in the data. A tissue TAC is modelled as a convolution of measured arterial input function with IRF, the estimates for IRF are obtained iteratively to minimise the differences between the left- and right-hand side of the following Equation:
C b o n e ( t ) = C p l a s m a ( t ) ⊗ I R F ( t ) {\displaystyle C_{bone}(t)=C_{plasma}(t)\otimes IRF(t)}
where, ⊗ {\displaystyle \otimes } is a convolution operator, C bone (t) is the bone tissue activity concentration of tracer (in units: MBq/ml) over a period of time t, C plasma (t) is the plasma concentration of tracer (in units: MBq/ml) over a period of time t, and IRF(t) is the impulse response of the system (i.e., a tissue in this case). The K i is obtained from the IRF in a similar fashion to that obtained for the spectral analysis, as shown in the figure.
The measurement of Ki from dynamic PET scans require tracer kinetic modelling to obtain the model parameters describing the biological processes in bone , as described by Hawkins et al. [ 22 ] Since this model has two tissue compartments, it is sometimes called a two-tissue compartmental model. Various different versions of this model exist; however, the most fundamental approach is considered here with two tissue compartments and four tracer-exchange parameters. The whole kinetic modelling process using Hawkins model can be summed up in a single image as seen on the right-hand-side. The following differential equations are solved to obtain the rate constants:
d C e ( t ) d t = K 1 ∗ C p ( t ) − ( k 2 + k 3 ) ∗ C e ( t ) + k 4 ∗ C b ( t ) {\displaystyle {\operatorname {d} \!C_{e}(t) \over \operatorname {d} \!t}=K_{1}*C_{p}(t)-(k_{2}+k_{3})*C_{e}(t)+k_{4}*C_{b}(t)}
d C b ( t ) d t = k 3 ∗ C e ( t ) − k 4 ∗ C b ( t ) {\displaystyle {\operatorname {d} \!C_{b}(t) \over \operatorname {d} \!t}=k_{3}*C_{e}(t)-k_{4}*C_{b}(t)}
The rate constant K 1 (in units: ml/min/ml) describes the unidirectional clearance of fluoride from plasma to the whole of the bone tissue, k 2 (in units: min −1 ) describes the reverse transport of fluoride from the ECF compartment to plasma, k 3 and k 4 (in units min −1 ) describe the forward and backward transportation of fluoride from the bone mineral compartment.
K i represents the net plasma clearance to bone mineral only. K i is a function of both K 1 , reflecting bone blood flow, and the fraction of the tracer that undergoes specific binding to the bone mineral k 3 / ( k 2 + k 3 ). Therefore, K i = ( K 1 ∗ k 3 k 2 + k 3 ) {\displaystyle K_{i}=\left({\frac {K_{1}*k_{3}}{k_{2}+k_{3}}}\right)}
Hawkins et al. found that the inclusion of an additional parameter called fractional blood volume (BV), representing the vascular tissue spaces within the ROI, improved the data fitting problem, although this improvement was not statistically significant. [ 51 ]
Patlak method [ 52 ] is based on the assumption that the backflow of tracer from bone mineral to bone ECF is zero (i.e., k 4 =0). The calculation of K i using Patlak method is simpler than using non-linear regression (NLR) fitting the arterial input function and the tissue time-activity curve data to the Hawkins model. The Patlak method can only measure bone plasma clearance ( K i ), and cannot measure the individual kinetic parameters, K 1 , k 2 , k 3 , or k 4 .
The concentration of tracer in tissue region-of-interest can be represented as a sum of concentration in bone ECF and the bone mineral. It can be mathematically represented as
C b o n e ( T ) C p l a s m a ( T ) = K i ∗ ∫ 0 T C p l a s m a ( t ) d t C p l a s m a ( T ) + V o {\displaystyle {\frac {C_{bone}(T)}{C_{plasma}(T)}}=K_{i}*{\frac {\int \limits _{0}^{T}C_{plasma}(t)dt}{C_{plasma}(T)}}+V_{o}}
where, within the tissue region-of-interest from the PET image, C bone (T) is the bone tissue activity concentration of tracer (in units: MBq/ml) at any time T, C plasma (T) is the plasma concentration of tracer (in units: MBq/ml) at time T, V o is the fraction of the ROI occupied by the ECF compartment, and ∫ 0 T C p l a s m a ( t ) d t {\displaystyle \int \limits _{0}^{T}C_{plasma}(t)dt} is the area under the plasma curve is the net tracer delivery to the tissue region of interest (in units: MBq.Sec/ml) over time T. The Patlak equation is a linear equation of the form Y = m ∗ X + c {\displaystyle Y=m*X+c}
Therefore, linear regression is fitted to the data plotted on Y- and X-axis between 4–60 minutes to obtain m and c values, where m is the slope of the regression line representing K i and c is the Y-intercept of the regression line representing V o . [ 52 ]
The calculation of Ki using arterial input function, time-activity curve, and Hawkins model was limited to a small skeletal region covered by the narrow field-of-view of the PET scanner while acquiring a dynamic scan. However, Siddique et al. [ 53 ] showed in 2012 that it is possible to measure K i values in bones using static [ 18 F]NaF PET scans. Blake et al. [ 32 ] later showed in 2019 that the K i obtained using the Siddique–Blake method has precision errors of less than 10%. The Siddique–Blake approach is based on the combination of the Patlak method, [ 52 ] the semi-population based arterial input function, [ 54 ] and the information that V o does not significantly change post-treatment. This method uses the information that a linear regression line can be plotted using the data from a minimum of two time-points, to obtain m and c as explained in the Patlak method. However, if V o is known or fixed, only one single static PET image is required to obtain the second time-point to measure m , representing the K i value. This method should be applied with great caution to other clinical areas where these assumptions may not hold true.
The most fundamental difference between SUV and K i values is that SUV is a simple measure of uptake, which is normalized to body weight and injected activity. The SUV does not take into consideration the tracer delivery to the local region of interest from where the measurements are obtained, therefore, affected by the physiological process consuming [ 18 F]NaF elsewhere in the body. On the other hand, K i measures the plasma clearance to bone mineral, taking into account the tracer uptake elsewhere in the body affecting the delivery of tracer to the region of interest from where the measurements are obtained. The difference in the measurement of K i and SUV in bone tissue using [ 18 F]NaF are explained in more detail by Blake et al. [ 34 ]
It is critical to note that most of the methods for calculating K i require dynamic PET scanning over an hour, except, the Siddique–Blake methods. Dynamic scanning is complicated and costly. However, the calculation of SUV requires a single static PET scan performed approximately 45–60 minutes post-tracer injection at any region imaged within the skeleton.
Many researchers have shown a high correlation between SUV and K i values at various skeletal sites. [ 55 ] [ 56 ] [ 57 ] However, SUV and K i methods can contradict for measuring response to treatment. [ 45 ] Since SUV has not been validated against the histomorphometry, its usefulness in bone studies measuring response to treatment and disease progression is uncertain. | https://en.wikipedia.org/wiki/PET_for_bone_imaging |
PET radiotracer is a type of radioligand that is used for the diagnostic purposes via positron emission tomography imaging technique. [ 1 ] [ 2 ]
PET is a functional imaging technique that produces a three-dimensional image of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron -emitting radionuclide ( tracer ), which is introduced into the body on a biologically active molecule. [ 3 ]
In in vivo systems it is often used to quantify the binding of a test molecule to the binding site of radioligand. The higher the affinity of the molecule the more radioligand is displaced from the binding site and the increasing radioactive decay can be measured by scintillography . This assay is commonly used to calculate binding constant of molecules to receptors. Due to the probable injuries of PET-radiotracers, they could not be administered in the normal doses of the medications. Therefore, the binding affinity (P KD ) of the PET-tracers must be high. In addition, since via the PET imaging technique is desired to investigate a function accurately, the selectivity of bindings to the specific targets is very important. [ 1 ] | https://en.wikipedia.org/wiki/PET_radiotracer |
Phosphorus trifluoride (formula P F 3 ), is a colorless and odorless gas . It is highly toxic and reacts slowly with water. Its main use is as a ligand in metal complexes . As a ligand, it parallels carbon monoxide in metal carbonyls , [ 1 ] and indeed its toxicity is due to its binding with the iron in blood hemoglobin in a similar way to carbon monoxide.
Phosphorus trifluoride has an F−P−F bond angle of approximately 96.3°. Gaseous PF 3 has a standard enthalpy of formation of −945 kJ/mol (−226 kcal / mol ). The phosphorus atom has a nuclear magnetic resonance chemical shift of 97 ppm (downfield of H 3 PO 4 ).
Phosphorus trifluoride hydrolyzes especially at high pH , but it is less hydrolytically sensitive than phosphorus trichloride . It does not attack glass except at high temperatures, and anhydrous potassium hydroxide may be used to dry it with little loss. With hot metals , phosphides and fluorides are formed. With Lewis bases such as ammonia addition products (adducts) are formed, and PF 3 is oxidized by oxidizing agents such as bromine or potassium permanganate .
As a ligand for transition metals, PF 3 is a strong π-acceptor. [ 2 ] It forms a variety of metal complexes with metals in low oxidation states . PF 3 forms several complexes for which the corresponding CO derivatives (see metal carbonyl ) are unstable or nonexistent. Thus, Pd(PF 3 ) 4 is known, but Pd(CO) 4 is not. [ 3 ] [ 4 ] [ 5 ] Such complexes are usually prepared directly from the related metal carbonyl compound, with loss of CO . However, nickel metal reacts directly with PF 3 at 100 °C under 35 MPa pressure to form Ni(PF 3 ) 4 , which is analogous to Ni(CO) 4 . Cr(PF 3 ) 6 , the analogue of Cr(CO) 6 , may be prepared from dibenzenechromium :
Phosphorus trifluoride is usually prepared from phosphorus trichloride via halogen exchange using various fluorides such as hydrogen fluoride , calcium fluoride , arsenic trifluoride , antimony trifluoride , or zinc fluoride : [ 6 ] [ 7 ] [ 8 ]
Phosphorus trifluoride is similar to carbon monoxide in that it is a gas which strongly binds to iron in hemoglobin , preventing the blood from absorbing oxygen.
PF 3 is highly toxic , comparable to phosgene . [ 9 ] | https://en.wikipedia.org/wiki/PF3 |
Phosphorus pentafluoride is a chemical compound with the chemical formula P F 5 . It is a phosphorus halide . It is a colourless, toxic gas that fumes in air. [ 1 ] [ 2 ]
Phosphorus pentafluoride was first prepared in 1876 by the fluorination of phosphorus pentachloride using arsenic trifluoride , which remains a favored method: [ 1 ]
Phosphorus pentafluoride can be prepared by direct combination of phosphorus and fluorine :
Single-crystal X-ray studies indicate that the PF 5 has trigonal bipyramidal geometry . Thus it has two distinct types of P−F bonds (axial and equatorial): the length of an axial P−F bond is distinct from the equatorial P−F bond in the solid phase, but not the liquid or gas phases due to Berry pseudo rotation .
Fluorine-19 NMR spectroscopy, even at temperatures as low as −100 °C (−148 °F; 173 K), fails to distinguish the axial from the equatorial fluorine environments. The apparent equivalency arises from the low barrier for pseudorotation via the Berry mechanism , by which the axial and equatorial fluorine atoms rapidly exchange positions. The apparent equivalency of the F centers in PF 5 was first noted by Gutowsky. [ 3 ] The explanation was first described by R. Stephen Berry , after whom the Berry mechanism is named. Berry pseudorotation influences the 19 F NMR spectrum of PF 5 since NMR spectroscopy operates on a millisecond timescale. Electron diffraction and X-ray crystallography do not detect this effect as the solid state structures are, relative to a molecule in solution, static and can not undergo the necessary changes in atomic position.
Phosphorus pentafluoride is a Lewis acid . This property is relevant to its ready hydrolysis. A well studied adduct is PF 5 with pyridine . With primary and secondary amines , the adducts convert readily to dimeric amino-bridged derivatives with the formula [PF 4 (NR 2 )] 2 . A variety of complexes are known with bidentate ligands . [ 4 ]
Hexafluorophosphoric acid ( H[PF 6 ] ) is derived from phosphorus pentafluoride and hydrogen fluoride . Its conjugate base, hexafluorophosphate ( [PF 6 ] − ), is a useful non-coordinating anion . It is often used in lithium-ion batteries , where besides providing good ionic conductivity for the liquid electrolyte, it also passivates positive aluminium current collector. | https://en.wikipedia.org/wiki/PF5 |
The PFA-100 ( P latelet F unction A ssay [ 1 ] or P latelet F unction A nalyser [ 2 ] ) is a platelet function analyser that aspirates blood in vitro from a blood specimen into disposable test cartridges through a microscopic aperture cut into a biologically active membrane at the end of a capillary . The membrane of the cartridges are coated with collagen and adenosine diphosphate (ADP) or collagen and epinephrine inducing a platelet plug to form which closes the aperture.
The PFA test result is dependent on platelet function, plasma von Willebrand Factor level, platelet
number, and (to some extent) the hematocrit (that is, the percent composition of red blood cells in the sample).
The PFA test is initially performed with the Collagen/Epinepherine membrane. A normal Col/Epi closure time
(<180 seconds) excludes the presence of a significant platelet function defect.
If the Col/Epi closure time is prolonged (>180 seconds), the Col/ADP test is automatically
performed. If the Col/ADP result is normal (<120 seconds), aspirin-induced platelet dysfunction is
most likely.
Prolongation of both test results (Col/Epi >180 seconds, Col/ADP >120 seconds) may indicate
the following;
Once anemia and thrombocytopenia have been excluded, further evaluation to exclude von
Willebrand disease and inherited/acquired platelet dysfunction can be made. [ 1 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PFA-100 |
Packet Forwarding Control Protocol ( PFCP ) is a 3GPP protocol used on the Sx/N4 interface between the control plane and the user plane function, specified in TS 29.244. [ 1 ] It is one of the main protocols introduced in the 5G Next Generation Mobile Core Network (aka 5GC [ 2 ] ), but also used in the 4G/LTE EPC to implement the Control and User Plane Separation (CUPS). [ 3 ] PFCP and the associated interfaces seek to formalize the interactions between different types of functional elements used in the Mobile Core Networks as deployed by most operators providing 4G, as well as 5G, services to mobile subscribers. These two types of components are:
PFCP's scope is similar to that of OpenFlow , however it was engineered to serve the particular use-case of Mobile Core Networks .
PFCP is also used on the interface between the control plane and user plane functions of a disaggregated BNG , as defined by the BroadBand Forum in TR-459 .
Albeit similar to GTP in concepts and implementation, PFCP is complementary to it. It provides the control means for a signaling component of the Control-Plane to manage packet processing and forwarding performed by a User-Plane component. Typical EPC or 5G Packet Gateways are split by the protocol in two functional parts, allowing for a more natural evolution and scalability.
The PFCP protocol is used on the following 3GPP mobile core interfaces:
Note: Sxa and Sxb can be combined, in case a merged SGW/PGW is implemented.
The Control-Plane functional element (e.g. PGW-C, SMF) controls the packet processing and forwarding in the User-Plane functional elements (e.g. PGW-U, UPF), by establishing, modifying or deleting PFCP Sessions.
User plane packets shall be forwarded between the CP and UP functions by encapsulating the user plane packets using GTP-U encapsulation (see 3GPP TS 29.281 [3]). For forwarding data from the UP function to the CP function, the CP function shall provision Packet Detection Rules (PDR) per PFCP session context, with the Packet Detection Information (PDI) identifying the user plane traffic to forward to the CP function and with a Forwarding Action Rule (FAR) set with the Destination Interface "CP function side" and set to perform GTP-U encapsulation and to forward the packets to a GTP-u F-TEID uniquely assigned in the CP function per PFCP session and PDR. The CP function shall then identify the PDN connection and the bearer to which the forwarded data belongs by the Fully Qualified TEID (F-TEID) in the header of the encapsulating GTP-U packet. For forwarding data from the CP function to the UP function, the CP function shall provision one or more PDR(s) per PFCP session context, with the PDI set with the Source Interface "CP function side" and identifying the GTP-u F-TEID uniquely assigned in the UP function per PDR, and with a FAR set to perform GTP-U decapsulation and to forward the packets to the intended destination. URRs and QERs may also be configured.
Per session multiple PDRs, FARs, QoS Enforcement Rules (QER), Usage Reporting Rules (URR) and/or Buffering Action Rules (BAR) are sent.
Here are the main concepts used, organized in their logical association model:
or 12..15
Priority; else (spare 0s)
or 16..(MsgLen+4)
IEs are defined either as having a proprietary encoding, or as grouped. Grouped IEs are simply a list of other IEs, encoded one after the other like in the PFCP Message Payload.
IE Types 0..32767 are 3GPP specific and do not have an Enterprise-ID set. IE Types 32768..65535 can be used by custom implementation and the Enterprise-ID must be set to the IANA SMI Network Management Private Enterprise Codes [ 4 ] of the issuing party.
No session related messages should be exchanged before this procedure.
While the Association-Release is only triggered by the CP, the UP can request it as part of the Association-Update-Request.
The UP may include Usage Report information in the answer, such that an additional Session-Report message would be avoided.
Very similar to GTP-C , PFCP uses UDP . Port 8805 is reserved. [ 5 ]
For reliability, a similar re-transmission strategy as for GTP-C is employed, lost messages being sent N1-times at T1-intervals. Transactions are identified by the 3-byte long Sequence Number, the IP address and port of the communication peer.
The protocol includes an own Heart-beat Request/Response model, which allows monitoring the availability of communication peers and detecting restarts (by use of a Recovery-Timestamp Information Element).
For User-Plane packet exchanges between the Control and User Plane functional elements, GTP-U for the Sx-u interface, or alternatively a simpler UDP or Ethernet encapsulation for the N4-u interface (to be confirmed, as standards are still incomplete). | https://en.wikipedia.org/wiki/PFCP |
PFD allowance in work systems is the adjustment done to the normal time to obtain the standard time for the purpose of recovering the lost time due to personal needs, fatigue , and unavoidable delays. [ 1 ] By providing a small increase to the normal time in each cycle, a worker can still be able to cover lost time and complete the work assigned to him or her.
There are two types of interruption: (1) interruption related to work (2) interruption not related to work. For example, a machine breakdown, rest break to overcome fatigue, and receiving instruction from the manager are the interruption related to work, but personal needs, lunch breaks , and personal telephone calls are interruptions not related to work. However, the two types of interruption are both essential for the worker because it is almost impossible to work continually during a regular shift.
The standard time is calculated by multiplying the normal time by 1 plus the PFD allowance: [ 2 ]
The personal needs allowance is the time that is associated with workers’ daily personal needs which include going to the restroom , phone calls, going to the water fountain , and similar interruptions of a personal nature. However, it is categorized as 5%, but it also depends on the work environment, e.g. in terms of discomfort and temperature.
The fatigue allowance is intended to cover the time that the worker should be given to overcome fatigue due to work related stress and conditions. There are three factors that cause fatigue: (1) physical factors like standing and use of force, (2) mental and cognitive factors like mental strain and eye strain , and (3) environmental and work factors like poor lighting , noise, and heat.
Unavoidable delays are categorized under unavoidable interruption that occurs at random times during the day in the workplace . They usually refer to work-related events like cleaning up at the end of the shift, and machine breakdowns or malfunctions. Unavoidable delays occur because of many random events at work stations . | https://en.wikipedia.org/wiki/PFD_allowance |
PG5 is the largest stable synthetic molecule ever made. [ 1 ] PG5 is a dendrimer designed by the organic chemistry research group working at the Federal Institute of Technology in Zürich . [ 2 ]
PG5 has a molecular mass of about 200 MDa or 200,000,000 g/mol. It has roughly 17 million atoms and a diameter of roughly 10 nm. Its length is up to a few micrometers. [ 3 ] It is similar in size to a tobacco mosaic virus with comparable length and diameter. PG5 was shown to be resistant against attempts to flatten its structure, and it is one of the heaviest compounds in the world. [ 2 ]
This chemistry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PG5_(molecule) |
Poly-[1-6]--D-glucopyranosyl-[1-3]--D-glucopyranose glucan ( PGG glucan , proprietary name Betafectin ) [ 1 ] is an anti-infective agent and a form or type of beta-glucan .
Betafectin is a PGG-glucan, a novel β-(1,6) branched β-(1,3) glucan, purified from the cell walls of Saccharomyces cerevisiae . [ 2 ]
It is a macrophage -specific immunomodulator .
This pharmacology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PGG-glucan |
The pGLO plasmid is an engineered plasmid used in biotechnology as a vector for creating genetically modified organisms . The plasmid contains several reporter genes , most notably the green fluorescent protein (GFP) and the ampicillin resistance gene. GFP was isolated from the jelly fish Aequorea victoria . Because it shares a bidirectional promoter with a gene for metabolizing arabinose , the GFP gene is expressed in the presence of arabinose, which makes the transgenic organism express its fluorescence under UV light . GFP can be induced in bacteria containing the pGLO plasmid by growing them on +arabinose plates. pGLO is made by Bio-Rad Laboratories .
pGLO is made up of three genes that are joined together using recombinant DNA technology. They are as follows:
Like most other circular plasmids, the pGLO plasmid contains an origin of replication (ori), which is a region of the plasmid where replication will originate.
The pGLO plasmid was made famous by researchers in France who used it to produce a green fluorescent rabbit named Alba .
Other features on pGLO, like most other plasmids, include a selectable marker and an MCS ( multiple cloning site ) located at the end of the GFP gene. The plasmid is 5371 base pairs long. In supercoiled form, it runs on an agarose gel in the 4200–4500 range. [ 1 ] [ 2 ] [ 3 ]
The GFP gene was first observed by Osamu Shimomura [ 4 ] and his team in 1962 while studying the jellyfish Aequorea victoria that have a ring of blue light under their umbrella . Shimomura and his team isolated the protein aequorin from thousands of jellyfish until they gathered enough for a full analysis of the protein. It was through the study of aequorin that Shimomura discovered small amounts of GFP which glows green when aequorin emits blue light. After successfully discovering how GFP works with aequorin in the jellyfish, he set it aside to study bioluminescence in other organisms.
In 1994 Marty Chalfie [ 4 ] and his team were able to successfully create bacteria and round worms that expressed the GFP protein. Soon after, Roger Tsien [ 5 ] and his team were able to create mutant GFP that can emit a range of colors, not just green.
The three scientists hold the Nobel Prize in Chemistry for 2008 [ 6 ] for the discovery and development of the green fluorescent protein, GFP.
This genetics article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PGLO |
The pGreen plasmids are vectors for plant transformation . They were first described in 2000 as components of a novel T-DNA binary system . [ 1 ] The supporting web page [ 2 ] provides supplementary information and ongoing support to researchers to request their plasmid resources. As these plasmids have been taken up by the research community, the plasmids have been developed, expanding the resources available to the community.
Researchers are encouraged to contribute to this research community by submitting their vector sequence to genbank and providing a description of the plasmid on the site.
pGreen is the original pGreen plasmid. [ 3 ] pGreenII features plasmid backbone modification to improve plasmid stability. [ 4 ]
pGreenII 0000: minimal T-DNA with Left and Right border, lacZ gene for blue/white selection during cloning multiple cloning site derived from pBluescript. [ 5 ]
pGreenII 62-SK: derived from pGreenII 0000, the Lac Z blue/white cloning selection has been replaced with a 35S- MCS - CaMV cassette that allows the insertion of a gene of interest into a 35S over-expression cassette. The multiple cloning site (MCS) is derived from pBluescript . [ 6 ] [ 7 ]
pGreenII 0029: derived from pGreenII 0000, a nos-kan cassette has been inserted into the Hpa I site of the Left Border, providing resistance to kanamycin during plant transformation selection. [ 8 ]
pGreenII 0029 62-SK: derived from pGreenII 0029, the Lac Z blue/white cloning selection has been replaced with a 35S-MCS-CaMV cassette that allows the insertion of a gene of interest into a 35S over-expression cassette. The MCS is derived from pBluescript. [ 9 ]
pGreenII 0179: derived from pGreenII 0000, a 35S-hyg cassette has been inserted into the Hpa I site of the Left Border, providing resistance to hygromycin during plant transformation selection. [ 10 ]
pGreenII 0229: derived from pGreenII 0000, a nos-bar cassette has been inserted into the Hpa I site of the Left Border, providing resistance to bialaphos or phosphinothricin during plant transformation selection. [ 11 ] [ 12 ]
pGreenII 0229 62-SK: derived from pGreenII 0229, the Lac Z blue/white cloning selection has been replaced with a 35S-MCS-CaMV cassette that allows the insertion of a gene of interest into a 35S over-expression cassette. The MCS is derived from pBluescript. [ 13 ]
This is the helper plasmid that provides the replicase function for the pSa replication origin of pGreen. pSoup is tetracyclin resistant and a complementary incompatibility group such that it can co-exist with pGreen in the Agrobacterium cell.
pSoup: the original help plasmid for pGreen. pGreen will not replicate in Agrobacterium if it is not present. [ 14 ] | https://en.wikipedia.org/wiki/PGreen |
In chemistry , pH ( / p iː ˈ eɪ tʃ / pee- AYCH ), also referred to as acidity or basicity , historically denotes " potential of hydrogen " (or "power of hydrogen"). [ 1 ] It is a logarithmic scale used to specify the acidity or basicity of aqueous solutions . Acidic solutions (solutions with higher concentrations of hydrogen ( H + ) cations ) are measured to have lower pH values than basic or alkaline solutions.
The pH scale is logarithmic and inversely indicates the activity of hydrogen cations in the solution
where [H + ] is the equilibrium molar concentration of H + (in M = mol / L ) in the solution. At 25 °C (77 °F ), solutions of which the pH is less than 7 are acidic, and solutions of which the pH is greater than 7 are basic. Solutions with a pH of 7 at 25 °C are neutral (i.e. have the same concentration of H + ions as OH − ions, i.e. the same as pure water ). The neutral value of the pH depends on the temperature and is lower than 7 if the temperature increases above 25 °C. The pH range is commonly given as zero to 14, but a pH value can be less than 0 for very concentrated strong acids or greater than 14 for very concentrated strong bases . [ 2 ]
The pH scale is traceable to a set of standard solutions whose pH is established by international agreement. [ 3 ] Primary pH standard values are determined using a concentration cell with transference by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode . The pH of aqueous solutions can be measured with a glass electrode and a pH meter or a color-changing indicator . Measurements of pH are important in chemistry , agronomy , medicine, water treatment, and many other applications.
In 1909, the Danish chemist Søren Peter Lauritz Sørensen introduced the concept of pH at the Carlsberg Laboratory , [ 4 ] originally using the notation "p H• ", with H• as a subscript to the lowercase p. The concept was later revised in 1924 to the modern pH to accommodate definitions and measurements in terms of electrochemical cells .
For the sign p , I propose the name 'hydrogen ion exponent' and the symbol p H• . Then, for the hydrogen ion exponent (p H• ) of a solution, the negative value of the Briggsian logarithm of the related hydrogen ion normality factor is to be understood. [ 4 ]
Sørensen did not explain why he used the letter p, and the exact meaning of the letter is still disputed. [ 5 ] [ 6 ] Sørensen described a way of measuring pH using potential differences, and it represents the negative power of 10 in the concentration of hydrogen ions. The letter p could stand for the French puissance, German Potenz, or Danish potens , all meaning "power", or it could mean "potential". All of these words start with the letter p in French , German , and Danish , which were the languages in which Sørensen published: Carlsberg Laboratory was French-speaking; German was the dominant language of scientific publishing; Sørensen was Danish. He also used the letter q in much the same way elsewhere in the paper, and he might have arbitrarily labelled the test solution "p" and the reference solution "q"; these letters are often paired with e4 then e5. [ 7 ] Some literature sources suggest that "pH" stands for the Latin term pondus hydrogenii (quantity of hydrogen) or potentia hydrogenii (power of hydrogen), although this is not supported by Sørensen's writings. [ 8 ] [ 9 ] [ 10 ]
In modern chemistry , the p stands for "the negative decimal logarithm of", and is used in the term p K a for acid dissociation constants , [ 11 ] so pH is "the negative decimal logarithm of H + ion concentration", while pOH is "the negative decimal logarithm of OH − ion concentration".
American bacteriologist Alice Catherine Evans , who influenced dairying and food safety , credited William Mansfield Clark and colleagues, including herself, with developing pH measuring methods in the 1910s, which had a wide influence on laboratory and industrial use thereafter. In her memoir, she does not mention how much, or how little, Clark and colleagues knew about Sørensen's work a few years prior. [ 12 ] She said:
In these studies [of bacterial metabolism] Dr. Clark's attention was directed to the effect of acid on the growth of bacteria. He found that it is the intensity of the acid in terms of hydrogen-ion concentration that affects their growth. But existing methods of measuring acidity determined the quantity, not the intensity, of the acid. Next, with his collaborators, Dr. Clark developed accurate methods for measuring hydrogen-ion concentration. These methods replaced the inaccurate titration method of determining the acid content in use in biologic laboratories throughout the world. Also they were found to be applicable in many industrial and other processes in which they came into wide usage. [ 12 ]
The first electronic method for measuring pH was invented by Arnold Orville Beckman , a professor at the California Institute of Technology in 1934. [ 13 ] It was in response to a request from the local citrus grower Sunkist , which wanted a better method for quickly testing the pH of lemons they were picking from their nearby orchards. [ 14 ]
The pH of a solution is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity , a H +. [ 3 ] Mathematically, pH is expressed as:
For example, for a solution with a hydrogen ion activity of 5 × 10 −6 mol / L (i.e., the concentration of hydrogen cations), the pH of the solution can be calculated as follows:
The concept of pH was developed because ion-selective electrodes , which are used to measure pH, respond to activity. The electrode potential, E , follows the Nernst equation for the hydrogen ion, which can be expressed as:
where E is a measured potential, E 0 is the standard electrode potential, R is the molar gas constant , T is the thermodynamic temperature, F is the Faraday constant . For H + , the number of electrons transferred is one. The electrode potential is proportional to pH when pH is defined in terms of activity.
The precise measurement of pH is presented in International Standard ISO 31-8 as follows: [ 15 ] A galvanic cell is set up to measure the electromotive force (e.m.f.) between a reference electrode and an electrode sensitive to the hydrogen ion activity when they are both immersed in the same aqueous solution. The reference electrode may be a silver chloride electrode or a calomel electrode , and the hydrogen-ion selective electrode is a standard hydrogen electrode .
Firstly, the cell is filled with a solution of known hydrogen ion activity and the electromotive force, E S , is measured. Then the electromotive force, E X , of the same cell containing the solution of unknown pH is measured.
The difference between the two measured electromotive force values is proportional to pH. This method of calibration avoids the need to know the standard electrode potential . The proportionality constant, 1/ z , is ideally equal to F R T ln 10 {\displaystyle {\frac {F}{RT\ln {10}}}\ } , the "Nernstian slope".
In practice, a glass electrode is used instead of the cumbersome hydrogen electrode. A combined glass electrode has an in-built reference electrode. It is calibrated against Buffer solutions of known hydrogen ion ( H + ) activity proposed by the International Union of Pure and Applied Chemistry ( IUPAC ). [ 3 ] Two or more buffer solutions are used in order to accommodate the fact that the "slope" may differ slightly from ideal. To calibrate the electrode, it is first immersed in a standard solution, and the reading on a pH meter is adjusted to be equal to the standard buffer's value. The reading from a second standard buffer solution is then adjusted using the "slope" control to be equal to the pH for that solution. Further details, are given in the IUPAC recommendations. [ 16 ] When more than two buffer solutions are used the electrode is calibrated by fitting observed pH values to a straight line with respect to standard buffer values. Commercial standard buffer solutions usually come with information on the value at 25 °C and a correction factor to be applied for other temperatures.
The pH scale is logarithmic and therefore pH is a dimensionless quantity . [ 17 ]
This was the original definition of Sørensen in 1909, [ 18 ] which was superseded in favor of pH in 1924. [H] is the concentration of hydrogen ions, denoted [ H + ] in modern chemistry. More correctly, the thermodynamic activity of H + ( a H +) in dilute solution should be replaced by [ H + ]/ c 0 , where the standard state concentration c 0 = 1 mol/L. This ratio is a pure number whose logarithm can be defined.
It is possible to measure the concentration of hydrogen ions directly using an electrode calibrated in terms of hydrogen ion concentrations. One common method is to titrate a solution of known concentration of a strong acid with a solution of known concentration of strong base in the presence of a relatively high concentration of background electrolyte. By knowing the concentrations of the acid and base, the concentration of hydrogen ions can be calculated and the measured potential can be correlated with concentrations. The calibration is usually carried out using a Gran plot . [ 19 ] This procedure makes the activity of hydrogen ions equal to the numerical value of concentration.
The glass electrode (and other Ion selective electrodes ) should be calibrated in a medium similar to the one being investigated. For instance, if one wishes to measure the pH of a seawater sample, the electrode should be calibrated in a solution resembling seawater in its chemical composition.
The difference between p[H] and pH is quite small, and it has been stated that pH = p[H] + 0.04. [ 20 ] However, it is common practice to use the term "pH" for both types of measurement.
pOH is sometimes used as a measure of the concentration of hydroxide ions, OH − . By definition, pOH is the negative logarithm (to the base 10) of the hydroxide ion concentration (mol/L). pOH values can be derived from pH measurements and vice-versa. The concentration of hydroxide ions in water is related to the concentration of hydrogen ions by
where K W is the self-ionization constant of water. Taking Logarithms ,
So, at room temperature, pOH ≈ 14 − pH. However this relationship is not strictly valid in other circumstances, such as in measurements of soil alkalinity .
pH can be measured using indicators, which change color depending on the pH of the solution they are in. By comparing the color of a test solution to a standard color chart, the pH can be estimated to the nearest whole number. For more precise measurements, the color can be measured using a colorimeter or spectrophotometer . A Universal indicator is a mixture of several indicators that can provide a continuous color change over a range of pH values, typically from about pH 2 to pH 10. Universal indicator paper is made from absorbent paper that has been impregnated with a universal indicator. An alternative method of measuring pH is using an electronic pH meter , which directly measures the voltage difference between a pH-sensitive electrode and a reference electrode.
pH values can be measured in non-aqueous solutions, but they are based on a different scale from aqueous pH values because the standard states used for calculating hydrogen ion concentrations ( activities ) are different. The hydrogen ion activity, a H + , is defined [ 21 ] [ 22 ] as:
where μ H + is the chemical potential of the hydrogen ion, μ H + ⊖ {\displaystyle \mu _{{\ce {H+}}}^{\ominus }} is its chemical potential in the chosen standard state, R is the molar gas constant and T is the thermodynamic temperature . Therefore, pH values on the different scales cannot be compared directly because of differences in the solvated proton ions, such as lyonium ions, which require an insolvent scale that involves the transfer activity coefficient of hydronium/lyonium ion .
pH is an example of an acidity function , but others can be defined. For example, the Hammett acidity function , H 0 , has been developed in connection with Superacids .
In 2010, a new approach to measuring pH was proposed, called the unified absolute pH scale . This approach allows for a common reference standard to be used across different solutions, regardless of their pH range. The unified absolute pH scale is based on the absolute chemical potential of the hydrogen ion, as defined by the Lewis acid–base theory. This scale applies to liquids, gases, and even solids. [ 23 ] The advantages of the unified absolute pH scale include consistency, accuracy, and applicability to a wide range of sample types. It is precise and versatile because it serves as a common reference standard for pH measurements. However, implementation efforts, compatibility with existing data, complexity, and potential costs are some challenges.
The measurement of pH can become difficult at extremely acidic or alkaline conditions, such as below pH 2.5 (ca. 0.003 mol /dm 3 acid) or above pH 10.5 (above ca. 0.0003 mol/dm 3 alkaline). This is due to the breakdown of the Nernst equation in such conditions when using a glass electrode. Several factors contribute to this problem. First, liquid junction potentials may not be independent of pH. [ 24 ] Second, the high ionic strength of concentrated solutions can affect the electrode potentials. At high pH the glass electrode may be affected by "alkaline error", because the electrode becomes sensitive to the concentration of cations such as Na + and K + in the solution. [ 25 ] To overcome these problems, specially constructed electrodes are available.
Runoff from mines or mine tailings can produce some extremely low pH values, down to −3.6. [ 26 ]
Pure water has a pH of 7 at 25 °C, meaning it is neutral. When an acid is dissolved in water, the pH will be less than 7, while a base , or alkali , will have a pH greater than 7. A strong acid, such as hydrochloric acid , at concentration 1 mol dm −3 has a pH of 0, while a strong alkali like sodium hydroxide , at the same concentration, has a pH of 14. Since pH is a logarithmic scale, a difference of one in pH is equivalent to a tenfold difference in hydrogen ion concentration.
Neutrality is not exactly 7 at 25 °C, but 7 serves as a good approximation in most cases. Neutrality occurs when the concentration of hydrogen ions ([ H + ]) equals the concentration of hydroxide ions ([ OH − ]), or when their activities are equal. Since self-ionization of water holds the product of these concentration [ H + ] × [ OH − ] = K w , it can be seen that at neutrality [ H + ] = [ OH − ] = √ K w , or pH = p K w /2. p K w is approximately 14 but depends on ionic strength and temperature, and so the pH of neutrality does also. Pure water and a solution of NaCl in pure water are both neutral, since dissociation of water produces equal numbers of both ions. However the pH of the neutral NaCl solution will be slightly different from that of neutral pure water because the hydrogen and hydroxide ions' activity is dependent on ionic strength , so K w varies with ionic strength.
When pure water is exposed to air, it becomes mildly acidic. This is because water absorbs carbon dioxide from the air, which is then slowly converted into bicarbonate and hydrogen ions (essentially creating carbonic acid ).
The United States Department of Agriculture Natural Resources Conservation Service , formerly Soil Conservation Service classifies soil pH ranges as follows: [ 27 ]
Topsoil pH is influenced by soil parent material, erosional effects, climate and vegetation. A recent map [ 28 ] of topsoil pH in Europe shows the alkaline soils in Mediterranean, Hungary, East Romania, North France. Scandinavian countries, Portugal, Poland and North Germany have more acid soils.
Plants contain pH-dependent pigments that can be used as pH indicators , such as those found in hibiscus , red cabbage ( anthocyanin ), and grapes ( red wine ). Citrus fruits have acidic juice primarily due to the presence of citric acid , while other carboxylic acids can be found in various living systems. The protonation state of phosphate derivatives, including ATP , is pH-dependent. Hemoglobin , an oxygen-transport enzyme, is also affected by pH in a phenomenon known as the Root effect .
The pH of seawater plays an important role in the ocean's carbon cycle . There is evidence of ongoing ocean acidification (meaning a drop in pH value): Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. [ 29 ] Carbon dioxide emissions from human activities are the primary cause of ocean acidification, with atmospheric carbon dioxide levels at 430 ppm CO 2 at Mauna Loa observatory in 2025. [ 30 ] In 2024, the annual atmospheric CO 2 increase measured by the NOAA ’s Global Monitoring Laboratory was 3.75 ppm CO 2 /year. [ 31 ] CO 2 from the atmosphere is absorbed by the oceans. This produces carbonic acid (H 2 CO 3 ) which dissociates into a bicarbonate ion ( HCO − 3 ) and a hydrogen ion (H + ). The presence of free hydrogen ions (H + ) lowers the pH of the ocean.
The measurement of pH in seawater is complicated by the chemical properties of seawater, and three distinct pH scales exist in chemical oceanography . [ 32 ] In practical terms, the three seawater pH scales differ in their pH values up to 0.10, differences that are much larger than the accuracy of pH measurements typically required, in particular, in relation to the ocean's carbonate system . [ 32 ] Since it omits consideration of sulfate and fluoride ions, the free scale is significantly different from both the total and seawater scales. Because of the relative unimportance of the fluoride ion, the total and seawater scales differ only very slightly.
As part of its operational definition of the pH scale, the IUPAC defines a series of Buffer solutions across a range of pH values (often denoted with National Bureau of Standards (NBS) or National Institute of Standards and Technology (NIST) designation). These solutions have a relatively low ionic strength (≈ 0.1) compared to that of seawater (≈ 0.7), and, as a consequence, are not recommended for use in characterizing the pH of seawater, since the ionic strength differences cause changes in electrode potential . To resolve this problem, an alternative series of buffers based on artificial seawater was developed. [ 33 ] This new series resolves the problem of ionic strength differences between samples and the buffers, and the new pH scale is referred to as the total scale , often denoted as pH T . The total scale was defined using a medium containing sulfate ions. These ions experience protonation , H + + SO 2− 4 ↔ HSO − 4 , such that the total scale includes the effect of both protons (free hydrogen ions) and hydrogen sulfate ions:
An alternative scale, the free scale , often denoted pH F , omits this consideration and focuses solely on [ H + ] F , in principle making it a simpler representation of hydrogen ion concentration. Only [ H + ] T can be determined, [ 34 ] therefore [ H + ] F must be estimated using the [ SO 2− 4 ] and the stability constant of HSO − 4 , K * S :
However, it is difficult to estimate K * S in seawater, limiting the utility of the otherwise more straightforward free scale.
Another scale, known as the seawater scale , often denoted pH SWS , takes account of a further protonation relationship between hydrogen ions and fluoride ions, H + + F − ⇌ HF. Resulting in the following expression for [ H + ] SWS :
However, the advantage of considering this additional complexity is dependent upon the abundance of fluoride in the medium. In seawater, for instance, sulfate ions occur at much greater concentrations (> 400 times) than those of fluoride. As a consequence, for most practical purposes, the difference between the total and seawater scales is very small.
The following three equations summarize the three scales of pH:
The pH level of food influences its flavor, texture, and shelf life . [ 35 ] Acidic foods, such as citrus fruits , tomatoes, and vinegar , typically have a pH below 4.6 [ 36 ] with sharp and tangy taste, while basic foods taste bitter or soapy. [ 37 ] Maintaining the appropriate pH in foods is essential for preventing the growth of harmful microorganisms . [ 36 ] The alkalinity of vegetables such as spinach and kale can also influence their texture and color during cooking. [ 38 ] The pH also influences the Maillard reaction , which is responsible for the browning of food during cooking, impacting both flavor and appearance. [ 39 ]
In living organisms, the pH of various body fluids , cellular compartments, and organs is tightly regulated to maintain a state of acid–base balance known as acid–base homeostasis . Acidosis , defined by blood pH below 7.35, is the most common disorder of acid–base homeostasis and occurs when there is an excess of acid in the body. In contrast, alkalosis is characterized by excessively high blood pH.
Blood pH is usually slightly alkaline, with a pH of 7.365, referred to as physiological pH in biology and medicine. Plaque formation in teeth can create a local acidic environment that results in tooth decay through demineralization. Enzymes and other Proteins have an optimal pH range for function and can become inactivated or denatured outside this range.
When calculating the pH of a solution containing acids or bases, a chemical speciation calculation is used to determine the concentration of all chemical species present in the solution. The complexity of the procedure depends on the nature of the solution. Strong acids and bases are compounds that are almost completely dissociated in water, which simplifies the calculation. However, for weak acids, a quadratic equation must be solved, and for weak bases, a cubic equation is required. In general, a set of non-linear simultaneous equations must be solved.
Water itself is a weak acid and a weak base, so its dissociation must be taken into account at high pH and low solute concentration (see Amphoterism ). It dissociates according to the equilibrium
with a dissociation constant , K w defined as
where [H + ] stands for the concentration of the aqueous hydronium ion and [OH − ] represents the concentration of the hydroxide ion . This equilibrium needs to be taken into account at high pH and when the solute concentration is extremely low.
Strong acids and bases are compounds that are essentially fully dissociated in water. This means that in an acidic solution, the concentration of hydrogen ions (H + ) can be considered equal to the concentration of the acid. Similarly, in a basic solution, the concentration of hydroxide ions (OH − ) can be considered equal to the concentration of the base. The pH of a solution is defined as the negative logarithm of the concentration of H + , and the pOH is defined as the negative logarithm of the concentration of OH − . For example, the pH of a 0.01 in moles per litreM solution of hydrochloric acid (HCl) is equal to 2 (pH = −log 10 (0.01)), while the pOH of a 0.01 M solution of sodium hydroxide (NaOH) is equal to 2 (pOH = −log 10 (0.01)), which corresponds to a pH of about 12.
However, self-ionization of water must also be considered when concentrations of a strong acid or base is very low or high. For instance, a 5 × 10 −8 M solution of HCl would be expected to have a pH of 7.3 based on the above procedure, which is incorrect as it is acidic and should have a pH of less than 7. In such cases, the system can be treated as a mixture of the acid or base and water, which is an amphoteric substance. By accounting for the self-ionization of water, the true pH of the solution can be calculated. For example, a 5 × 10 −8 M solution of HCl would have a pH of 6.89 when treated as a mixture of HCl and water. The self-ionization equilibrium of solutions of sodium hydroxide at higher concentrations must also be considered. [ 45 ]
A weak acid or the conjugate acid of a weak base can be treated using the same formalism.
First, an acid dissociation constant is defined as follows. Electrical charges are omitted from subsequent equations for the sake of generality
and its value is assumed to have been determined by experiment. This being so, there are three unknown concentrations, [HA], [H + ] and [A − ] to determine by calculation. Two additional equations are needed. One way to provide them is to apply the law of mass conservation in terms of the two "reagents" H and A.
C stands for analytical concentration . In some texts, one mass balance equation is replaced by an equation of charge balance. This is satisfactory for simple cases like this one, but is more difficult to apply to more complicated cases as those below. Together with the equation defining K a , there are now three equations in three unknowns. When an acid is dissolved in water C A = C H = C a , the concentration of the acid, so [A] = [H]. After some further algebraic manipulation an equation in the hydrogen ion concentration may be obtained.
Solution of this quadratic equation gives the hydrogen ion concentration and hence p[H] or, more loosely, pH. This procedure is illustrated in an ICE table which can also be used to calculate the pH when some additional (strong) acid or alkaline has been added to the system, that is, when C A ≠ C H .
For example, what is the pH of a 0.01 M solution of benzoic acid , p K a = 4.19?
For alkaline solutions, an additional term is added to the mass-balance equation for hydrogen. Since the addition of hydroxide reduces the hydrogen ion concentration, and the hydroxide ion concentration is constrained by the self-ionization equilibrium to be equal to K w [ H + ] {\displaystyle {\frac {K_{w}}{{\ce {[H+]}}}}} , the resulting equation is:
Some systems, such as with polyprotic acids, are amenable to spreadsheet calculations. [ 46 ] With three or more reagents or when many complexes are formed with general formulae such as A p B q H r , the following general method can be used to calculate the pH of a solution. For example, with three reagents, each equilibrium is characterized by an equilibrium constant, β .
Next, write down the mass-balance equations for each reagent:
There are no approximations involved in these equations, except that each stability constant is defined as a quotient of concentrations, not activities. Much more complicated expressions are required if activities are to be used.
There are three simultaneous equations in the three unknowns, [A], [B] and [H]. Because the equations are non-linear and their concentrations may range over many powers of 10, the solution of these equations is not straightforward. However, many computer programs are available which can be used to perform these calculations. There may be more than three reagents. The calculation of hydrogen ion concentrations, using this approach, is a key element in the determination of equilibrium constants by potentiometric titration . | https://en.wikipedia.org/wiki/PH |
pH sensitive or pH responsive polymers are materials which will respond to the changes in the pH of the surrounding medium by varying their dimensions. Materials may swell, collapse, or change depending on the pH of their environment. This behavior is exhibited due to the presence of certain functional groups in the polymer chain. pH-sensitive materials can be either acidic or basic, responding to either basic or acidic pH values. These polymers can be designed with many different architectures for different applications. Key uses of pH sensitive polymers are controlled drug delivery systems, biomimetics , micromechanical systems, separation processes, and surface functionalization. [ 1 ]
pH sensitive polymers can be broken into two categories: those with acidic groups (such as -COOH and -SO 3 H) and those with basic groups (-NH 2 ). The mechanism of response is the same for both, only the stimulus varies. The general form of the polymer is a backbone with functional "pendant groups" that hang off of it. When these functional groups become ionized in certain pH levels, they acquire a charge (+/-). Repulsions between like charges cause the polymers to change shape. [ 1 ] [ 2 ]
Polyacids, also known as anionic polymers, are polymers that have acidic groups. [ 2 ] Examples of acidic functional groups include carboxylic acids (-COOH), sulfonic acids (-SO 3 H), phosphonic acids, and boronic acids. Polyacids accept protons at low pH values. At higher pH values, they deprotonate and become negatively charged. [ 1 ] The negative charges create a repulsion that causes the polymer to swell. This swelling behavior is observed when the pH is greater than the pKa of the polymer. [ 2 ] Examples include polymethyl methacrylate polymers (pharmacologyonline 1 (2011)152-164) and cellulose acetate phthalate.
Polybases are the basic equivalent of polyacids and are also known as cationic polymers. They accept protons at low pH like polyacids do, but they then become positively charged. In contrast, at higher pH values they are neutral. Swelling behavior is seen when the pH is less than the pKa of the polymer. [ 1 ]
Although many sources talk about synthetic pH sensitive polymers, natural polymers can also display pH-responsive behavior. Examples include chitosan , hyaluronic acid , alginic acid and dextran . [ 1 ] Chitosan, a frequently used example, is cationic. Since DNA is negatively charged, DNA could be attached to chitosan as a way to deliver genes to cells. [ 3 ] Alginic acid, on the other hand, is anionic. It is often evaluated as a calcium-salt for drug delivery applications(International journal of biological macromolecules 75 (2015) 409-17) . Natural polymers have appeal because they display good biocompatibility, which makes them useful for biomedical applications. However, a disadvantage to natural polymers is that researchers can have more control over the structure of synthetic polymers and so can design those polymers for specific applications. [ 2 ]
Polymers can be designed to respond to more than one external stimulus, such as pH and temperature. Often, these polymers are structured as a copolymer where each polymer displays one type of response. [ 1 ]
pH sensitive polymers have been created with linear block copolymer, star, branched, dendrimer, brush, and comb architectures. Polymers of different architectures will self-assemble into different structures. This self-assembly can occur due to the nature of the polymer and the solvent, or due to a change in pH. pH changes can also cause the larger structure to swell or deswell. For example, block copolymers often form micelles, as will star polymers and branched polymers. However, star and branched polymers can form rod or worm-shaped micelles rather than the typical spheres. Brush polymers are usually used for modifying surfaces since their structure doesn’t allow them to form a larger structure like a micelle. [ 1 ]
Often, the response to different pH values is swelling or deswelling. For example, polyacids release protons to become negatively charged at high pH. Since polymer chains are often in close proximity to other parts of the same chain or to other chains, like-charged parts of the polymer repel each other. This repulsion leads to a swelling of the polymer. [ citation needed ]
Polymers can also form micelles (spheres) in response to a change in pH. This behavior can occur with linear block copolymers. If the different blocks of the copolymer have different properties, they can form micelles with one type of block on the inside and one type on the outside. For example, in water the hydrophobic blocks of a copolymer could end up on the inside of a micelle, with hydrophilic blocks on the outside. [ 4 ] Additionally, a change in pH could cause micelles to swap their inner and outer molecules depending on the properties of the polymers involved. [ 1 ]
Responses other than simply swelling and deswelling with a change in pH are possible as well. Researchers have created polymers that undergo a sol-gel transition (from a solution to a gel) with a change in pH, but which also change from being a stiff gel to a soft gel for certain pH values. [ 5 ]
pH sensitive polymers can be synthesized using several common polymerization methods. Functional groups may need to be protected so that they do not react depending on the type of polymerization. The masking can be removed after polymerization so that they regain their pH-sensitive functionality. Living polymerization is often used for making pH sensitive polymers because molecular weight distribution of the final polymers can be controlled. Examples include group transfer polymerization (GTP), atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer (RAFT). [ 1 ] Graft copolymers are a popular type to synthesize because their structure is a backbone with branches. The composition of the branches can be changed to achieve different properties. [ 2 ] Hydrogels can be produced using emulsion polymerization. [ 1 ]
Several methods can be used to measure the contact angle of a water drop on the surface of a polymer. The contact angle value is used to quantify wettability or hydrophobicity of the polymer. [ 2 ]
Equal to (swollen weight-deswelled weight)/deswelled weight *100% and determined by massing polymers before and after swelling. This indicates how much the polymer swelled upon a change in pH. [ 2 ]
The pH at which a significant structural change in how the molecules are arranged is observed. This structural change does not involve breaking bonds, but rather a change in conformation. For example, a swelling/deswelling transition would constitute a reversible conformational change. The value of the pH critical point can be determined by examining swelling percentage as a function of pH. Researchers aim to design molecules that transition at a pH that matters for the given application. [ 2 ]
Confocal microscopy , scanning electron microscopy , Raman spectroscopy , and atomic force microscopy are all used to determine how the surface of a polymer changes in response to pH. [ 2 ]
pH sensitive polymers have been considered for use in membranes. A change in pH could change the ability of the polymer to let ions through, allowing it to act as a filter. [ 1 ]
pH sensitive polymers have been used to modify the surfaces of materials. For example, they can be used to change the wettability of a surface. [ 1 ]
pH sensitive polymers have been used for drug delivery. For example, they can be used to release insulin in specific quantities. [ 6 ] | https://en.wikipedia.org/wiki/PH-sensitive_polymers |
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