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The dithionite is the oxyanion with the formula [S 2 O 4 ] 2− . [ 1 ] It is commonly encountered as the salt sodium dithionite . For historical reasons, it is sometimes called hydrosulfite , but it contains no hydrogen and is not a sulfite . [ 2 ] The dianion has a steric number of 4 and trigonal pyramidal geometry.
In its main applications, dithionite is generally prepared in situ by reduction of sulfur dioxide by sodium borohydride , described by the following idealized equation: [ 3 ]
Dithionite is a reducing agent . At pH 7, its reduction potential is −0.66 V vs SHE . Its oxidation occurs with formation of sulfite : [ 4 ]
Dithionite undergoes acid hydrolytic disproportionation to thiosulfate and bisulfite : [ 2 ]
It also undergoes alkaline hydrolytic disproportionation to sulfite and sulfide : [ 2 ]
It is formally derived from dithionous acid (H 2 S 2 O 4 ), but this acid does not exist in any practical sense.
Sodium dithionite finds widespread use in industry as a reducing agent . It is for example used in bleaching of wood pulp and some dyes . [ 3 ]
Dithionite is used in conjunction with complexing agents (for example, citric acid ) to reduce iron (III) oxy-hydroxide into soluble iron(II) compounds and to remove amorphous iron(III)-bearing mineral phases in soil analyses (selective extraction).
The decomposition of dithionite produces reduced species of sulfur that can be very aggressive for the corrosion of steel and stainless steel . Thiosulfate ( S 2 O 2− 3 ) is known to induce pitting corrosion , whereas sulfide (S 2− , HS − ) is responsible for stress corrosion cracking (SCC).
This corrosion -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/S2O42- |
In chemistry, disulfate or pyrosulfate is the anion with the molecular formula S 2 O 2− 7 . Disulfate is the IUPAC name. [ 1 ] It has a dichromate -like structure and can be visualised as two corner-sharing SO 4 tetrahedra , with a bridging oxygen atom. [ 2 ] In this anion, sulfur has an oxidation state of +6. Disulfate is the conjugate base of the hydrogen disulfate (hydrogen pyrosulfate) ion HS 2 O − 7 , which in turn is the conjugate base of disulfuric acid (pyrosulfuric acid).
Industrial production of sulfate ester -based surfactants involves the reaction ( sulfation ) of fatty alcohols with sulfur trioxide . For example, dodecyl alcohol is sulfated using sulfur trioxide . The reaction proceeds by initial formation of the pyrosulfate:
Several million tons are produced annually. [ 3 ] | https://en.wikipedia.org/wiki/S2O7 |
In mathematics, S2S is the monadic second order theory with two successors. It is one of the most expressive natural decidable theories known, with many decidable theories interpretable in S2S. Its decidability was proved by Rabin in 1969. [ 1 ]
The first order objects of S2S are finite binary strings. The second order objects are arbitrary sets (or unary predicates) of finite binary strings. S2S has functions s → s 0 and s → s 1 on strings, and predicate s ∈ S (equivalently, S ( s )) meaning string s belongs to set S .
Some properties and conventions:
Weakenings of S2S: Weak S2S (WS2S) requires all sets to be finite (note that finiteness is expressible in S2S using Kőnig's lemma ). S1S can be obtained by requiring that '1' does not appear in strings, and WS1S also requires finiteness. Even WS1S can interpret Presburger arithmetic with a predicate for powers of 2, as sets can be used to represent unbounded binary numbers with definable addition.
Decision complexity
S2S is decidable, and each of S2S, S1S, WS2S, WS1S has a nonelementary decision complexity corresponding to a linearly growing stack of exponentials. For the lower bound, it suffices to consider Σ 1 1 WS1S sentences. A single second order quantifier can be used to propose an arithmetic (or other) computation, which can be verified using first order quantifiers if we can test which numbers are equal. For this, if we appropriately encode numbers 1.. m , we can encode a number with binary representation i 1 i 2 ... i m as i 1 1 i 2 2 ... i m m , preceded by a guard. By merging testing of guards and reusing variable names, the number of bits is linear in the number of exponentials. For the upper bound, using the decision procedure (below), sentences with k -fold quantifier alternation can decided in time corresponding to k + O (1)-fold exponentiation of the sentence length (with uniform constants).
Axiomatization
WS2S can be axiomatized through certain basic properties plus induction schema. [ 3 ]
S2S can be partially axiomatized by: (1) ∃! s ∀ t ( t 0≠ s ∧ t 1≠ s ) (empty string, denoted by ε; ∃! s means "there is unique s ") (2) ∀ s , t ∀ i ∈{0,1} ∀ j ∈{0,1} ( si = tj ⇒ s = t ∧ i = j ) (the use of i and j is an abbreviation; for i = j , 0 does not equal 1) (3) ∀ S ( S (ε) ∧ ∀ s ( S ( s ) ⇒ S ( s 0) ∧ S ( s 1))⇒ ∀ s S (s)) ( induction ) (4) ∃ S ∀ s ( S ( s ) ⇔ φ( s )) ( S not free in φ)
(4) is the comprehension schema over formulas φ, which always holds for second order logic. As usual, if φ has free variables not shown, we take the universal closure of the axiom. If equality is primitive for predicates, one also adds extensionality S = T ⇔ ∀ s ( S ( s ) ⇔ T ( s )). Since we have comprehension, induction can be a single statement rather than a schema.
The analogous axiomatization of S1S is complete. [ 4 ] However, for S2S, completeness is open (as of 2021). While S1S has uniformization, there is no S2S definable (even allowing parameters) choice function that given a non-empty set S returns an element of S , [ 5 ] and comprehension schemas are commonly augmented with various forms of the axiom of choice . However, (1)-(4) is complete when extended with a determinacy schema for certain parity games . [ 6 ]
S2S can also be axiomatized by Π 1 3 sentences (using the prefix relation on strings as a primitive). However, it is not finitely axiomatizable, nor can it be axiomatized by Σ 1 3 sentences even if we add induction schema and a finite set of other sentences (this follows from its connection to Π 1 2 -CA 0 ).
For every finite k , the monadic second order (MSO) theory of countable graphs with treewidth ≤ k (and a corresponding tree decomposition) is interpretable in S2S (see Courcelle's theorem ). For example, the MSO theory of trees (as graphs) or of series-parallel graphs is decidable. Here (i.e. for bounded tree width), we can also interpret the finiteness quantifier for a set of vertices (or edges), and also count vertices (or edges) in a set modulo a fixed integer. Allowing uncountable graphs does not change the theory. Also, for comparison, S1S can interpret connected graphs of bounded pathwidth .
By contrast, for every set of graphs of unbounded treewidth, its existential (i.e. Σ 1 1 ) MSO theory is undecidable if we allow predicates on both vertices and edges. Thus, in a sense, decidability of S2S is the best possible. Graphs with unbounded treewidth have large grid minors, which can be used to simulate a Turing machine .
By reduction to S2S, the MSO theory of countable orders is decidable, as is the MSO theory of countable trees with their Kleene–Brouwer orders . However, the MSO theory of ( R {\displaystyle \mathbb {R} } , <) is undecidable. [ 7 ] [ 8 ] The MSO theory of ordinals <ω 2 is decidable; decidability for ω 2 is independent of ZFC (assuming Con(ZFC + weakly compact cardinal )). [ 9 ] Also, an ordinal is definable using monadic second order logic on ordinals iff it can be obtained from definable regular cardinals by ordinal addition and multiplication. [ 10 ]
S2S is useful for decidability of certain modal logics, with Kripke semantics naturally leading to trees.
S2S+U (or just S1S+U) is undecidable if U is the unbounding quantifier — U X Φ( X ) iff Φ( X ) holds for some arbitrarily large finite X . [ 11 ] However, WS2S+U, even with quantification over infinite paths, is decidable, even with S2S subformulas that do not contain U. [ 12 ]
A set of binary strings is definable in S2S iff it is regular (i.e. forms a regular language ). In S1S, a (unary) predicate on sets is (parameter-free) definable iff it is an ω-regular language . For S2S, for formulas that use their free variables only on strings not containing a 1, the expressiveness is the same as for S1S.
For every S2S formula φ( S 1 ,..., S k ), (with k free variables) and finite tree of binary strings T , φ( S 1 ∩T,..., S k ∩T) can be computed in time linear in | T | (see Courcelle's theorem ), but as noted above, the overhead can be iterated exponential in the formula size (more precisely, the time is O ( | T | k ) + 2 O ( | ϕ | ) 2 {\displaystyle O(|T|k)+2_{O(|\phi |)}^{2}} ).
For S1S, every formula is equivalent to a Δ 1 1 formula, and to a boolean combination of Π 0 2 arithmetic formulas. Moreover, every S1S formula is equivalent to acceptance by a corresponding ω-automaton of the parameters of the formula. The automaton can be a deterministic parity automaton: A parity automaton has an integer priority for each state, and accepts iff the highest priority seen infinitely often is odd (alternatively, even).
For S2S, using tree automata (below), every formula is equivalent to a Δ 1 2 formula. Moreover, every S2S formula is equivalent to a formula with just four quantifiers, ∃ S ∀ T ∃ s ∀ t ... (assuming that our formalization has both the prefix relation and the successor functions). For S1S, three quantifiers (∃ S ∀ s ∃ t ) suffice, and for WS2S and WS1S, two quantifiers (∃ S ∀ t ) suffice; the prefix relation is not needed here for WS2S and WS1S.
However, with free second order variables, not every S2S formula can be expressed in second order arithmetic through just Π 1 1 transfinite recursion (see reverse mathematics ). RCA 0 + (schema) {τ: τ is a true S2S sentence} is equivalent to (schema) {τ: τ is a Π 1 3 sentence provable in Π 1 2 -CA 0 }. [ 13 ] [ 14 ] Over a base theory, the schemas are equivalent to (schema over k ) ∀ S ⊆ω ∃α 1 <...<α k L α 1 ( S ) ≺ Σ 1 ... ≺ Σ 1 L α k (S) where L is the constructible universe (see also large countable ordinal ). Due to limited induction, Π 1 2 -CA 0 does not prove that all true (under the standard decision procedure) Π 1 3 S2S statements are actually true even though each such sentence is provable Π 1 2 -CA 0 .
Moreover, given sets of binary strings S and T , the following are equivalent: (1) T is S2S definable from some set of binary strings polynomial time computable from S . (2) T can be computed from the set of winning positions for some game whose payoff is a finite boolean combination of Π 0 2 ( S ) sets. (3) T can be defined from S in arithmetic μ-calculus (arithmetic formulas + least fixed-point logic ) (4) T is in the least β-model (i.e. an ω-model whose set-theoretic counterpart is transitive ) containing S and satisfying all Π 1 3 consequences of in Π 1 2 -CA 0 .
For (3)⇒(2), define a game where player 1 attempts to show that the desired element s is inside the least fixed point. Player 1 gradually labels elements including s with rational numbers, intended to correspond to ordinal stages of the monotonic induction (any countable ordinal is embeddable into Q {\displaystyle \mathbb {Q} } ). Player 2 plays elements with strictly descending labels (and he can pass) and wins iff the sequence is infinite or player 2 wins the last auxiliary game. In the auxiliary game, player 1 attempts to show that the last element picked by player 2 is a valid inductive step using elements with smaller labels. Now, if s is not in the least fixed-point, then the set of labels is ill-founded, or an inductive step is wrong, and (using monotonicity) this can be picked up by player 2. (If player 1 plays a smaller label outside the least fixed point, player 2 can use it (abandoning the auxiliary game), otherwise (using monotonicity) player 2 can use an auxiliary game strategy that assumes that the set of smaller labels in the original game will equal the least fixed point.)
For (4)⇒(3), we use monotonic induction to build an initial segment of the constructible hierarchy above a given real number r . This works as long as each ordinal α is identified by some appropriately expressible property of α so that we can encode α by a natural number and continue. Now, suppose that we built L α (r) and the inductive step (which uses L α (r) as a parameter) allows examining L β (r). If a new Σ 1 (L(r),∈,r) fact appears between α and β, we can use it to label α and continue. Otherwise, we get the above Σ 1 elementary chains whose length corresponds to the nesting depth of the monotonic inductive definitions.
For the equivalence of RCA 0 +S2S with {Π 1 3 φ: Π 1 2 -CA 0 ⊢φ}, for each k the positional determinacy with k priorities is provable in Π 1 2 -CA 0 , while the rest (in terms of proving S2S sentences) can be done in a weak base theory. Conversely, RCA 0 +S2S gives us a determinacy schema that gives existence of least fixed points (by a modification of the above (3)⇒(2) and even without requiring positionality; see the reference). In turn, their existence (using (4)⇒(3)) gives the desired Σ 1 elementary chains.
In addition to the standard model (which is the unique MSO model for S1S and S2S), there are other models for S1S and S2S, which use some rather than all subsets of the domain (see Henkin semantics ).
For every S ⊆ω, sets recursive in S form an elementary submodel of the standard S1S model, and same for every non-empty collection of subsets of ω closed under Turing join and Turing reducibility. [ 16 ]
This follows from relative recursiveness of S1S definable sets plus uniformization: - φ( s ) (as a function of s ) can be computed from the parameters of φ and the values of φ( s ′ ) for a finite set of s ′ (with its size bounded by the number of states in a deterministic automaton for φ). - A witness for ∃ S φ( S ) can be obtained by choosing k and a finite fragment of S ′ of S , and repeatedly extending S ′ such that the highest priority during each extension is k and that the extension can be completed into S satisfying φ without hitting priorities above k (these are permitted only for the initial S ′ ). Also, by using lexicographically least shortest choices, there is an S1S formula φ' such that φ'⇒φ and ∃ S φ( S ) ⇔∃! S φ'( S ) (i.e. uniformization; φ may have free variables not shown; φ' depends only on the formula φ).
The minimal model of S2S consists of all regular languages on binary strings. It is an elementary submodel of the standard model, so if an S2S parameter-free definable set of trees is non-empty, then it includes a regular tree. A regular language can also be treated as a regular {0,1}-labeled complete infinite binary tree (identified with predicates on strings). A labeled tree is regular if it can be obtained by unrolling a vertex-labeled finite directed graph with an initial vertex; a (directed) cycle in the graph reachable from the initial vertex gives an infinite tree. With this interpretation and encoding of regular trees, every true S2S sentence may already be provable in elementary function arithmetic . It is non-regular trees that may require nonpredicative comprehension for determinacy (below). There are nonregular (i.e. containing nonregular languages) models of S1S (and presumably S2S) (both with and without standard first order part) with a computable satisfaction relation. However, the set of recursive sets of strings does not form a model of S2S due to failure of comprehension and determinacy.
The proof of decidability is by showing that every formula is equivalent to acceptance by a nondeterministic tree automaton (see tree automaton and infinite-tree automaton ). An infinite tree automaton starts at the root and moves up the tree, and accepts iff every tree branch accepts. A nondeterministic tree automaton accepts iff player 1 has a winning strategy, where player 1 chooses an allowed (for the current state and input) pair of new states ( p 0 , p 1 ), while player 2 chooses the branch, with the transition to p 0 if 0 is chosen and p 1 otherwise. For a co-nondeterministic automaton, all choices are by player 2, while for deterministic, (p 0 ,p 1 ) is fixed by the state and input; and for a game automaton, the two players play a finite game to set the branch and the state. Acceptance on a branch is based on states seen infinitely often on the branch; parity automata are sufficiently general here.
For converting the formulas to automata, the base case is easy, and nondeterminism gives closure under existential quantifiers, so we only need closure under complementation. Using positional determinacy of parity games (which is where we need impredicative comprehension), non-existence of player 1 winning strategy gives a player 2 winning strategy S , with a co-nondeterministic tree automaton verifying its soundness. The automaton can then be made deterministic (which is where we get an exponential increase in the number of states), and thus existence of S corresponds to acceptance by a non-deterministic automaton.
Determinacy: Provably in ZFC , Borel games are determined , and the determinacy proof for boolean combinations of Π 0 2 formulas (with arbitrary real parameters) also gives a strategy here that depends only on the current state and the position in the tree. The proof is by induction on the number of priorities. Assume that there are k priorities, with the highest priority being k , and that k has the right parity for player 2. For each position (tree position + state) assign the least ordinal α (if any) such that player 1 has a winning strategy with all entered (after one or more steps) priority k positions (if any) having labels <α. Player 1 can win if the initial position is labeled: Each time a priority k state is reached, the ordinal is decreased, and moreover in between the decreases, player 1 can use a strategy for k -1 priorities. Player 2 can win if the position is unlabeled: By the determinacy for k -1 priorities, player 2 has a strategy that wins or enters an unlabeled priority k state, in which case player 2 can again use that strategy. To make the strategy positional (by induction on k ), when playing the auxiliary game, if two chosen positional strategies lead to the same position, continue with the strategy with the lower α, or for the same α (or for player 2) lower initial position (so we can switch a strategy finitely many times).
Automata determinization: For determinization of co-nondeterministic tree automata, it suffices to consider ω-automata, treating branch choice as input, determinizing the automaton, and using it for the deterministic tree automaton. Note that this does not work for nondeterministic tree automata as the determinization for going left (i.e. s → s 0) can depend on the contents of the right branch; by contrast to nondeterminism, deterministic tree automata cannot even accept precisely nonempty sets. To determinize a nondeterministic ω-automaton M (for co-nondeterministic, take the complement, noting that deterministic parity automata are closed under complements), we can use a Safra tree with each node storing a set of possible states of M , and node creation and deletion based on reaching high priority states. For details, see [ 17 ] or. [ 18 ]
Decidability of acceptance: Acceptance by a nondeterministic parity automaton of the empty tree corresponds to a parity game on a finite graph G . Using the above positional (also called memoryless) determinacy, this can be simulated by a finite game that ends when we reach a loop, with the winning condition based on the highest priority state in the loop. A clever optimization gives a quasipolynomial time algorithm, [ 19 ] which is polynomial time when the number of priorities is small enough (which occurs commonly in practice).
Theory of trees: For decidability of MSO logic on trees (i.e. graphs that are trees), even with finiteness and modular counting quantifiers for first order objects, we can embed countable trees into the complete binary tree and use the decidability of S2S. For example, for a node s , we can represent its children by s 1, s 01, s 001, and so on. For uncountable trees, we can use Shelah-Stup theorem (below). We can also add a predicate for a set first order objects having cardinality ω 1 , and the predicate for cardinality ω 2 , and so on for infinite regular cardinals. Graphs of bounded tree width are interpretable using trees, and without predicates over edges this also applies to graphs of bounded clique width .
Tree extensions of monadic theories: By Shelah-Stup theorem, [ 20 ] [ 21 ] if a monadic relational model M is decidable, then so is its tree counterpart. For example, (modulo choice of formalization) S2S is the tree counterpart of {0,1}. In the tree counterpart, the first order objects are finite sequences of elements of M ordered by extension, and an M -relation P i is mapped to P i '( vd 1 ,..., vd k ) ⇔ P i ( d 1 ,..., d k ) with P i ' false otherwise ( d j ∈ M , and v is a (possibly empty) sequence of elements of M ). The proof is similar to the S2S decidability proof. At each step, a (nondeterministic) automaton gets a tuple of M objects (possibly second order) as input, and an M formula determines which state transitions are permitted. Player 1 (as above) chooses a mapping child⇒state that is permitted by the formula (given the current state), and player 2 chooses the child (of the node) to continue. To witness rejection by a non-deterministic automaton, for each (node, state) pick a set of (child, state) pairs such that for every choice, at least one of the pairs is hit, and such that all the resulting paths lead to rejection.
Combining a monadic theory with a first order theory: Feferman–Vaught theorem extends/applies as follows. If M is an MSO model and N is a first order model, then M remains decidable relative to a (Theory( M ), Theory( N )) oracle even if M is augmented with all functions M → N where M is identified with its first objects, and for each s ∈ M we use a disjoint copy of N , with the language modified accordingly. For example, if N is ( R {\displaystyle \mathbb {R} } ,0,+,⋅), we can state ∀(function f ) ∀ s ∃ r ∈ N s f ( s ) + N s r = 0 N s . If M is S2S (or more generally, the tree counterpart of some monadic model), the automata can now use N -formulas, and thereby convert f : M → N k into a tuple of M sets. Disjointness is necessary as otherwise for every infinite N with equality, the extended S2S or just WS1S is undecidable. Also, for a (possibly incomplete) theory T , the theory T M of M -products of T is decidable relative to a (Theory( M ), T ) oracle, where a model of T M uses an arbitrary disjoint model N s of T for each s ∈ M (as above, M is an MSO model; Theory( N s ) may depend on s ). The proof is by induction on formula complexity. Let v s be the list of free N s variables, including f ( s ) if function f is free. By induction, one shows that v s is only used through a finite set of N -formulas with | v s | free variables. Thus, we can quantify over all possible outcomes by using N (or T ) to answer what is possible, and given a list possibilities (or constraints), formulate a corresponding sentence in M .
Coding into extensions of S2S: Every decidable predicate on strings can be encoded (with linear time encoding and decoding) for decidability of S2S (even with the extensions above) together with the encoded predicate. Proof: Given a nondeterministic infinite tree automaton, we can partition the set of finite binary labeled trees (having labels over which the automaton can operate) into finitely many classes such that if a complete infinite binary tree can be composed of same-class trees, acceptance depends only on the class and the initial state (i.e. state the automaton enters the tree). (Note a rough similarity with the pumping lemma .) For example (for a parity automaton), assign trees to the same class if they have the same predicate that given initial_state and set Q of (state, highest_priority_reached) pairs returns whether player 1 (i.e. nondeterminism) can simultaneously force all branches to correspond to elements of Q . Now, for each k , pick a finite set of trees (suitable for coding) that belong to the same class for automata 1- k , with the choice of class consistent across k . To encode a predicate, encode some bits using k =1, then more bits using k =2, and so on.
Additional reference: Weyer, Mark (2002). "Decidability of S1S and S2S" . Automata, Logics, and Infinite Games . Lecture Notes in Computer Science. Vol. 2500. Springer. pp. 207– 230. doi : 10.1007/3-540-36387-4_12 . ISBN 978-3-540-00388-5 . | https://en.wikipedia.org/wiki/S2S_(mathematics) |
Silicon disulfide is the inorganic compound with the formula Si S 2 . Like silicon dioxide , this material is polymeric , but it adopts a 1-dimensional structure quite different from the usual forms of SiO 2 .
The material is formed by heating silicon and sulfur or by the exchange reaction between SiO 2 and Al 2 S 3 . The material consists of chains of edge-shared tetrahedra , -Si(μ-S) 2 Si(μ-S) 2 -. [ 2 ]
Like other silicon sulfur-compounds (e.g., bis(trimethylsilyl)sulfide ) SiS 2 hydrolyzes readily to release H 2 S.
In liquid ammonia it is reported to form the imide Si(NH) 2 and NH 4 SH, [ 3 ] but a recent report has identified crystalline (NH 4 ) 2 [SiS 3 (NH 3 )]·2NH 3 as a product which contains the tetrahedral thiosilicate anion, SiS 3 (NH 3 ) 2- . [ 4 ]
Reaction with ethanol gives the alkoxide tetraethyl orthosilicate and H 2 S. [ 3 ] With bulky tert-butanol, alcoholysis gives tris(tert-butoxy)silanethiol : [ 5 ]
Reaction with sodium sulfide , magnesium sulfide and aluminum sulfide give thiosilicates . [ 3 ]
SiS 2 is claimed to occur in certain interstellar objects. [ 6 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/S2Si |
The S 3 molecule , known as trisulfur , sulfur trimer , thiozone , or triatomic sulfur , is a cherry-red allotrope of sulfur . It comprises about 10% of vaporised sulfur at 713 K (440 °C; 824 °F) and 1,333 Pa (10.00 mmHg ; 0.1933 psi ). It has been observed at cryogenic temperatures as a solid. Under ordinary conditions it converts to cyclooctasulfur .
In terms of structure and bonding S 3 and ozone ( O 3 ) are similar. Both adopt bent structures and are diamagnetic . Although represented with S=S double bonds , the bonding situation is more complex. [ 1 ]
The S–S distances are equivalent and are 191.70 ± 0.01 pm , and with an angle at the central atom of 117.36° ± 0.006° . [ 2 ] However, cyclic S 3 , where the sulfur atoms are arranged in an equilateral triangle with three single bonds (similar to cyclic ozone and cyclopropane ), is calculated to be lower in energy than the bent structure experimentally observed. [ 3 ] A similar structure has been predicted for ozone, but has not been observed.
The name thiozone was invented by Hugo Erdmann in 1908 who hypothesized that S 3 comprises a large proportion of liquid sulfur. [ 4 ] However its existence was unproven until the experiments of J. Berkowitz in 1964. [ 5 ] Using mass spectrometry , he showed that sulfur vapour contains the S 3 molecule. Above 1,200 °C (2,190 °F) S 3 is the second most common molecule after S 2 in gaseous sulfur. [ 5 ] In liquid sulfur the molecule is not common until the temperature is high, such as 500 °C (932 °F). However, small molecules like this contribute to most of the reactivity of liquid sulfur. [ 5 ] S 3 has an absorption peak of 425 nm (violet) with a tail extending into blue light. [ 5 ]
S 3 can also be generated by photolysis of S 3 Cl 2 embedded in a glass or matrix of solid noble gas . [ 5 ]
S 3 occurs naturally on Io in volcanic emissions. S 3 is also likely to appear in the atmosphere of Venus at heights of 20 to 30 km, where it is in thermal equilibrium with S 2 and S 4 . [ 6 ] : 546 The reddish colour of Venus' atmosphere at lower levels is likely to be due to S 3 . [ 6 ] : 539
S 3 reacts with carbon monoxide to make carbonyl sulfide and S 2 .
Formation of compounds with a defined number of sulfur atoms is possible:
Although S 3 is elusive under ordinary conditions, the intensely blue radical anion S − 3 is abundant. [ 8 ] The anion is sometimes called thiozonide , [ 9 ] by analogy with the ozonide anion, O − 3 , to which it is valence isoelectronic . The preferred IUPAC name is trisulfanidylo. The gemstone lapis lazuli and the mineral lazurite (from which the pigment ultramarine is derived) contain S − 3 . International Klein Blue , developed by Yves Klein , also contains the S − 3 radical anion. [ 10 ] The blue colour is due to the C 2 A 2 transition to the X 2 B 1 electronic state in the ion, [ 9 ] causing a strong absorption band at 610– 620 nm or 2.07 eV (in the orange region of the visible spectrum). [ 11 ] The Raman frequency is 523 cm −1 and another infrared absorption is at 580 cm −1 . [ 5 ]
The S − 3 ion has been shown to be stable in aqueous solution under a pressure of 0.5 GPa (73,000 psi ), and is expected to occur naturally at depth in the Earth's crust where subduction or high pressure metamorphism occurs. [ 12 ] This ion is probably important in movement of copper and gold in hydrothermal fluids . [ 13 ]
Lithium hexasulfide (which contains S − 6 , another polysulfide radical anion) with tetramethylenediamine solvation dissociates acetone and related donor solvents to S − 3 . [ 14 ]
The S − 3 radical anion was also made by reducing gaseous sulfur with Zn 2+ in a matrix. The material is strongly blue-coloured when dry and changes colour to green and yellow in the presence of trace amounts of water. [ 15 ] Another way to make it is with polysulfide dissolved in hexamethylphosphoramide where it gives a blue colour. [ 16 ]
Other methods of production of S − 3 include reacting sulfur with partially hydroxylated magnesium oxide at 400 °C. [ 17 ]
Raman spectroscopy can be used to identify S − 3 , and it can be used non-destructively in paintings. The bands are 549 cm −1 for symmetric stretch, 585 cm −1 for asymmetric stretch, and 259 cm −1 for bending. [ 18 ] Natural materials can also contain S − 2 which has an optical absorption at 390 nm and Raman band at 590 cm −1 . [ 18 ]
The trisulfide ion, S 2− 3 is part of the polysulfide series. The sulfur chain is bent at an angle of 107.88°. [ 5 ] Strontium trisulfide ( SrS 3 ) has a S–S bond length of 205 pm . [ 5 ] The bonds are single. It is isoelectronic to sulfur dichloride . | https://en.wikipedia.org/wiki/S3- |
Trithiazyl trichloride is the inorganic compound with the formula (NSCl) 3 . A white solid, it is a precursor to other sulfur nitrides , [ 1 ] but has no commercial applications.
The molecule is a 6-membered ring of alternating nitrogen and sulfur atoms, where each sulfur atom is attached to one chlorine atom by a single bond. The molecule contains alternating single and double bonds in the S 3 N 3 core. The molecule has C 3v symmetry . The S 3 N 3 core is slightly ruffled structure with S-N distances of 160.5 pm. The S-Cl distances are 208 pm, and the chlorine atoms are mutually cis . The S centers are tetravalent and pyramidal. In contrast to the NSCl connectivity, nitrosyl chloride has the connectivity ONCl. [ 2 ] [ 3 ]
Trithiazyl trichloride is obtained by chlorination of tetrasulfur tetranitride or thiazyl fluoride monomer: [ 4 ]
At 100 °C in vacuum, thiazyl chloride trimer undergoes cracking to thiazyl chloride monomer, which is a green gas.
In N≡S−Cl, chlorine is bonded to sulfur, in contrast to nitrosyl chloride O=N–Cl, where chlorine is bonded to nitrogen. In contrast, with six fewer electrons, cyanuric chloride is a planar ring.
Alkoxide or silver salts displace the chlorides: [ 5 ]
Treating thiazyl chloride with sulfur in the presence of antimony pentachloride gives dithionitronium hexachloroantimonate : [ 6 ]
It reacts with nitriles to dithiadiazolium chlorides : [ 2 ]
Sulfur trioxide successively oxidizes the compound at the sulfur atoms to (NSOCl) 3 , [ 4 ] which exists as stereoisomers. | https://en.wikipedia.org/wiki/S3N3Cl3 |
Yttrium(III) sulfide ( Y 2 S 3 ) is an inorganic chemical compound . It is a compound of yttrium and sulfur .
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/S3Y2 |
S4000P - International specification for developing and continuously improving preventive maintenance is a specification developed jointly by a multinational team from the AeroSpace and Defence Industries Association of Europe (ASD) and Aerospace Industries Association (AIA). [ 1 ] S4000P is part of the S-Series of ILS specifications and is integrated in the global ILS process defined by SX000i - International guide for the use of the S-Series of Integrated Logistics Support (ILS) specifications . [ 2 ]
The main purpose of this specification is to assist all parties, including regulatory authorities, involved in the analysis process developing and releasing initial PMTR and intervals for new products prior entry into service. S4000P analysis methodologies remain applicable for later optimizations/modifications of the product design and/or of product structure and/or of product zones. Once developed, authorized and packaged into interval clusters in a product OMP, the S4000P In-Service Maintenance Optimization (ISMO) process enables continuously improving product maintenance during its in-service phase.
Every development or improvement of a preventive maintenance task requirement for a product supports at least one of the following aspects:
For a new product or for a new product variant, the maintainability of the intended product design must be assessed by maintainability specialists providing engineering support. Accumulated in-service experience with other products must also be taken into account.
In parallel to the product design process, Preventive Maintenance Task Requirements (PMTR) with intervals and/or redesign requirements must be assessed on an analytical basis and be determined if applicable and effective. Results must be available prior to product development milestones, latest prior to the Critical Design Review (CDR) for the product.
According to the overall ASD scope, the specification S4000P must cover all types of products including any complex technical platform, system, equipment or facility (e.g. on air/sea/land, under the sea-/ground-level, in space).
The S4000P analysis methodologies allow a structured, traceable and complete determination of PMTR with intervals for a product, which become the basis to elaborate and document a product maintenance program/Operators' Maintenance Program (OMP) prior to starting the product in-service phase.
During the product in-service phase, S4000P provides an additional process that allows reviewing the completeness and effectiveness of preventive maintenance tasks from a product OMP, taking into account product in-service experience and the state-of-the-art analysis methodologies. Such a review of the OMP is to be fully traceable and applicable for all products types.
Every S4000P analysis methodology or process must be tailored for the product under analysis in an analysis guideline or handbook to be acceptable to regulatory authorities (if involved), maintainers, operators, manufacturers and suppliers.
S4000P builds on the know-how accumulated over many years on different maintenance analysis techniques such as Reliability-centered maintenance but has simplified and extended to those methodologies:
S4000P development work started in 2013.
European experts from the following international companies and organizations have participated in the developed S4000P:
Issue 1.0 (current issue) was published in May 2014.
S4000P can be downloaded for free from its project website | https://en.wikipedia.org/wiki/S4000P |
Tetrasulfur tetranitride is an inorganic compound with the formula S 4 N 4 . This vivid orange, opaque, crystalline explosive is the most important binary sulfur nitride , which are compounds that contain only the elements sulfur and nitrogen . It is a precursor to many S-N compounds and has attracted wide interest for its unusual structure and bonding. [ 1 ] [ 2 ]
Nitrogen and sulfur have similar electronegativities . When the properties of atoms are so highly similar , they often form extensive families of covalently bonded structures and compounds. Indeed, a large number of S-N and S-NH compounds are known with S 4 N 4 as their parent.
S 4 N 4 adopts an unusual "extreme cradle" structure, with D 2d point group symmetry . It can be viewed as a derivative of a (hypothetical) eight-membered ring (or more simply a 'deformed' eight-membered ring) of alternating sulfur and nitrogen atoms. The pairs of sulfur atoms across the ring are separated by 2.586 Å , resulting in a cage-like structure as determined by single crystal X-ray diffraction. [ 3 ] The nature of the transannular S–S interactions remains a matter of investigation because it is significantly shorter than the sum of the van der Waals radii [ 4 ] but has been explained in the context of molecular orbital theory . [ 1 ] One pair of the transannular S atoms have valence 4, and the other pair of the transannular S atoms have valence 2. [ citation needed ] The bonding in S 4 N 4 is considered to be delocalized , which is indicated by the fact that the bond distances between neighboring sulfur and nitrogen atoms are nearly identical. S 4 N 4 has been shown to co-crystallize with benzene and the C 60 molecule. [ 5 ]
S 4 N 4 is stable to air . It is, however, unstable in the thermodynamic sense with a positive enthalpy of formation of +460 kJ/mol. This endothermic enthalpy of formation originates in the difference in energy of S 4 N 4 compared to its highly stable decomposition products:
S 4 N 4 is shock and friction sensitive and because one of its decomposition products is a gas, it is considered a primary explosive. [ 1 ] [ 6 ] Purer samples tend to be more sensitive. [ 7 ] Small samples can be detonated by striking with a hammer. S 4 N 4 is thermochromic , changing from pale yellow below −30 °C to orange at room temperature to deep red above 100 °C. [ 1 ]
S 4 N 4 was first prepared in 1835 by M. Gregory by the reaction of disulfur dichloride with ammonia , [ 8 ] a process that has been optimized: [ 9 ]
Coproducts of this reaction include heptasulfur imide ( S 7 NH ) and elemental sulfur, and the latter equilibrates with more S 4 N 4 and ammonium sulfide : [ 10 ]
A related synthesis employs [NH 4 ]Cl instead: [ 1 ]
An alternative synthesis entails the use of (((CH 3 ) 3 Si) 2 N) 2 S as a precursor with pre-formed S–N bonds. (((CH 3 ) 3 Si) 2 N) 2 S is prepared by the reaction of lithium bis(trimethylsilyl)amide and SCl 2 .
The (((CH 3 ) 3 Si) 2 N) 2 S reacts with the combination of SCl 2 and SO 2 Cl 2 to form S 4 N 4 , trimethylsilyl chloride , and sulfur dioxide : [ 11 ]
S 4 N 4 is a Lewis base at nitrogen. It binds to strong Lewis acids , such as SbCl 5 and SO 3 , or H[BF 4 ] :
The cage is distorted in these adducts . [ 1 ]
S 4 N 4 reacts with metal complexes, but the bonding situation may be quite complex. The cage remains intact in some cases but in other cases, it is degraded. [ 2 ] [ 12 ] For example, the soft Lewis acid CuCl forms a coordination polymer : [ 1 ]
Reportedly, [Pt 2 Cl 4 (P(CH 3 ) 2 Ph ) 2 ] initially forms a complex with S 4 N 4 at sulfur. This compound, upon standing, isomerizes to additionally bond through a nitrogen atom. S 4 N 4 oxidatively adds to Vaska's complex ( [Ir(Cl)(CO)(P Ph 3 ) 2 ] to form a hexacoordinate iridium complex where the S 4 N 4 binds through two sulfur atoms and one nitrogen atom. [ 2 ]
Dilute NaOH hydrolyzes S 4 N 4 as follows, yielding thiosulfate and trithionate : [ 1 ]
More concentrated base yields sulfite :
Many S-N compounds are prepared from S 4 N 4 . [ 13 ]
In electrophilic substitution or 1,3-dipolar cycloaddition reactions, S 4 N 4 behaves as a combination of the dithionitronium synthon and the sulfide synthon. Thus it adds to arenes and electron-rich alkynes to give 1,2,5‑ thiadiazoles . [ 14 ] Electron-poor alkynes attack S 4 N 4 to give a different cycloadduct of stoichiometry RC(NS) 2 SCR ′ . [ 15 ] [ 14 ] With electron-rich alkenes , S 4 N 4 behaves as a Diels-Alder diene. [ 14 ]
Passing gaseous S 4 N 4 over silver metal yields the low temperature superconductor polythiazyl or polysulfurnitride (transition temperature (0.26±0.03) K [ 16 ] ), often simply called "(SN) x ". In the conversion, the silver first becomes sulfided, and the resulting Ag 2 S catalyzes the conversion of the S 4 N 4 into the four-membered ring S 2 N 2 , which readily polymerizes . [ 1 ]
Oxidation of S 4 N 4 with elemental chlorine gives thiazyl chloride , [ citation needed ] but milder reagents give S 4 N + 3 :
That cation is relatively non- electrophilic and planar, with a delocalized π system . However, it adds triphenylphosphine to give [S(NPPh 3 ) 3 ] 3+ [Cl − ] 3 , a triimide analogue to sulfur trioxide . Conversely, S 4 N + 3 salts react with aluminum azide to recover S 4 N 4 . [ 14 ]
Treatment with tetramethylammonium azide produces the similar 10-π heterocycle [S 3 N 3 ] − :
In a related reaction, the use of the bis(triphenylphosphine)iminium azide gives a salt containing the blue [NS 4 ] − anion: [ 13 ]
[NS 4 ] − has a chain structure approximated by the resonance [S=S=N−S−S − ] ↔ [ − S−S−N=S=S] .
Reaction with piperidine generates [S 4 N 5 ] − :
A related cation is also known, i.e. [S 4 N 5 ] + .
Triphenylphosphine abstracts a sulfur atom, replacing it with another triphenylphosphine moiety: [ 14 ]
S 4 N 4 is a categorized as a primary explosive that is shock and friction sensitive. While comparable to pentaerythritol tetranitrate (PETN) in terms of impact sensitivity, its friction sensitivity is equal to or even lower than lead azide. [ 17 ] Purer samples are more shock-sensitive than those contaminated with elemental sulfur. [ 9 ] [ 7 ] | https://en.wikipedia.org/wiki/S4N4 |
The S9 fraction is the product of an organ tissue homogenate used in biological assays . The S9 fraction is most frequently used in assays that measure the metabolism of drugs and other xenobiotics . It is defined by the U.S. National Library of Medicine 's " IUPAC Glossary of Terms Used in Toxicology" [ 1 ] as the " Supernatant fraction obtained from an organ (usually liver) homogenate by centrifuging at 9000 g for 20 minutes in a suitable medium; this fraction contains cytosol and microsomes ." The microsomes component of the S9 fraction contain cytochrome P450 isoforms ( phase I metabolism ) and other enzyme activities. The cytosolic portion contains the major part of the activities of transferases ( phase II metabolism ). [ 2 ] The S9 fraction is easier to prepare than purified microsomes. [ 3 ]
The S9 fraction has been used in conjunction with the Ames test [ 4 ] to assess the mutagenic potential of chemical compounds. [ 5 ] Chemical substances sometimes require metabolic activation in order to become mutagenic. Furthermore, the metabolic enzymes of bacteria used in the Ames test differ substantially from those in mammals. Therefore, to mimic the metabolism of test substance that would occur in mammals, the S9 fraction is often added to the Ames test.
The S9 fraction has also been used to assess the metabolic stability of candidate drugs. [ 6 ]
This article incorporates text from the United States National Library of Medicine , which is in the public domain .
This cell biology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/S9_fraction |
SABDA or SABDA Bible Software is an Indonesian integrated Bible study platform that's based on the Online Bible engine, [ 1 ] with multilingual Bibles available in the program (including Indonesian , Malay , English , Greek and Hebrew , and many local languages of Indonesia ).
The word sabda is the Indonesian word for Logos (via Sanskrit: shabda ), and also an abbreviation of "Software Alkitab, Biblika Dan Alat-alat" (Bible Software, Biblical Resources, And Tools). It is produced and managed by Yayasan Lembaga SABDA (SABDA Foundation) which translated and made available freely more than 100 Biblical modules [ 2 ] in Indonesian since 1994, besides the default OLB modules.
Since its initial beginning in the 1990s, the SABDA Software has been made available as a free downloadable program with many Indonesian Bible translations [ 1 ] (text and audio [ 3 ] ) and biblical resources [ 1 ] (including pastoral electronic library ), and many more Biblical tools [ 1 ] (including advanced search, footnotes, interlinear , concordances , cross references , maps, lexicons, dictionaries , [ 4 ] etc.), as well as SABDA's web-based versions of online Bible study websites (in English and Indonesian) which are called SABDAweb [ 5 ] and SABDA Alkitab [ 6 ]
One of many things that sets SABDA apart from the rest of the Bible software is its use of the historical Bible translations into the languages of Indonesia and Malaysia as parallel versions to its modern counterpart. The organization have been distributing the software gratis and encouraged others to copy and distribute the software themselves non-commercially.
This software article is a stub . You can help Wikipedia by expanding it .
This article about biblical studies is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SABDA |
SABIO-RK ( S ystem for the A nalysis of Bio chemical Pathways - R eaction K inetics) is a web-accessible database storing information about biochemical reactions and their kinetic properties.
SABIO-RK comprises a reaction-oriented representation of quantitative information on reaction dynamics based on a given selected publication.
This comprises all available kinetic parameters together with their corresponding rate equations ,
as well as kinetic law and parameter types and experimental and environmental conditions under which the kinetic data were determined.
Additionally, SABIO-RK contains information about the underlying biochemical reactions and pathways including their reaction participants , cellular location and detailed information about the enzymes catalysing the reactions. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ]
The data stored in SABIO-RK in a comprehensive manner is mainly extracted manually from literature. This includes reactions, their participants (substrates, products), modifiers ( inhibitors , activators, cofactors ), catalyst details (e.g. EC enzyme classification , protein complex composition , wild type / mutant information), kinetic parameters together with corresponding rate equation, biological sources ( organism , tissue , cellular location), environmental conditions ( pH , temperature, buffer) and reference details. Data are adapted, normalized and annotated to controlled vocabularies, ontologies and external data sources including KEGG , UniProt , ChEBI , PubChem , NCBI , Reactome , BRENDA , MetaCyc , BioModels , and PubMed . As of October 2021 SABIO-RK contains about 71.000 curated single entries extracted from more than 7.300 publications. Several tools, databases and workflows in Systems Biology make use of SABIO-RK biochemical reaction data by integration into their framework including
SYCAMORE, [ 6 ] MeMo-RK, [ 7 ] CellDesigner, [ 8 ] PeroxisomeDB, [ 9 ] Taverna workflows
or tools like KineticsWizard software for data capture and analysis. [ 10 ] Additionally, SABIO-RK is part of MIRIAM registry, a set of guidelines for the annotation and curation of computational models [ 11 ] [ 12 ]
The usage of SABIO-RK is free of charge. Commercial users need a license.
SABIO-RK offers several ways for data access:
Result data sets can be exported in different formats including SBML , BioPAX / SBPAX , and table format. | https://en.wikipedia.org/wiki/SABIO-Reaction_Kinetics_Database |
SAES Getters S.p.A. is an Italian joint stock company, established in 1940. It is the parent company of the SAES industrial group, which focusses its business on the production of components and systems in advanced materials patented by the same company and used in various industrial and medical applications.
In 1940 the company S.A.E.S. (Società Apparecchi Elettrici e Scientifici) was formed in Florence at the initiative of Ernesto Gabbrielli, an engineer from Montecatini Terme and two other shareholders . The impetus for the foundation of the company was the discovery by Gabbrielli of a new method for the production of getters , with nickel lids to protect barium plastics, to prevent the phenomenon of oxidation .
S.A.E.S. initially devoted itself to producing time clocks and a barium- magnesium -aluminium alloy . After a few years, it transferred its headquarters to Milan and began to produce electrical resistance heaters.
In 1946, the Della Porta and Canale families entered the shareholding structure, and in 1949, Paolo della Porta joined the company, subsequently taking over management in 1952. A period began that was distinguished by major innovations, supported by the Research and Development Laboratory, notably the invention of ring-shaped getters in barium-aluminium alloy. The company expanded into Europe, appointing its first agents in France, Germany, and England.
S.A.E.S. continued to invest in scientific research during a period of major change in the electronics sector, characterised by the extensive spread of transistors, to the detriment of vacuum tubes intended for radio and television reception and transmission. In 1957 S.A.E.S. filed a patent for getters for television cathode tubes , first for black and white and then for colour television, launching production on an industrial scale.
This period was characterised by company consolidations, innovations and commercial successes, including at international level. S.A.E.S. also commissioned its first mass production plant.
At the "3rd Symposium on Residual Gases", held in Rome in 1967, S.A.E.S. presented a new configuration of getter, consisting of a metallic tape coated with St 101 alloy, obtained from the combination of zirconium and aluminium. This technological evolution allowed the company to execute new products with Non-Evaporable Getters (NEG) and getter pumps . The non-evaporable getter pumps (NEG pumps) are devices which have the same purpose as barium getters but do not require an evaporation process; they have extremely high absorptive capacity and are still used today, in more advanced forms, in applications requiring a high or ultra-high vacuum.
Exploiting its own technological skills in the field of metallurgy, during these two decades, S.A.E.S. developed new alloys (such as the St 707 alloy in zirconium , vanadium and iron) and was involved in projects on the catalytic module and purifiers of inert gases .
It also pursued its internationalisation with the creation of subsidiaries with commercial responsibilities in the United Kingdom (1966), United States (1969), Canada (1969) and Japan (1973). Other commercial representative offices were opened in France (1978) and in Germany (1979). In 1977, SAES Getters USA Inc. was founded in Colorado Springs , the first foreign subsidiary with a manufacturing mission for satisfying the growing demand for porous non-evaporable getters from the US military industry.
S.A.E.S. continued to grow by virtue of the progressive launch of new products and the expansion of its production structure, both through the construction of new plants and acquisitions of other companies. In 1978, it had grown to 300 employees, redefined its company structure and changed its name, from S.A.E.S. to SAES Getters.
In 1982, a plant was commissioned in Nanjing , in China, for the production of barium getters, the installations for which were supplied directly by SAES Getters.
The objective during this period was the vertical integration of production (or the internal management of all processes), which over the years would become one of the group's strong points. From this perspective, in 1984, SAES Metallurgia was founded in Avezzano (Province of L’Aquila ), for the production of barium and barium-aluminium alloy, SAES Engineering, for the execution of instruments and devices necessary for the metallurgical processing of alloys, and SAES Gemedis dedicated to the production of Gemedis (Getter Mercury Dispenser), i.e. alloys containing mercury . Over the course of the 1990s, the three companies merged into SAES Advanced Technologies S.p.A., adding to their own portfolio numerous other articles and devices used constantly in Hi-Tech applications requiring a vacuum or ultrahigh vacuum.
In the mid-1980s, SAES Getters concluded two important acquisitions in the United States in the field of barium getters for cathode tubes and created Getters Corporation of America.
In 1986, SAES Getters was listed on the stock exchange, [ 1 ] with the financial resources raised allowing it to pursue its acquisitions policy, most notably, towards the end of the decade, the Californian company Cryolab Inc., subsequently renamed SAES Pure Gas Inc., within which it still develops and produces gas purification products, principally for the semiconductor industry.
In 1989, Massimo della Porta, Paolo's son, began to work for SAES Metallurgia. Over the years, Massimo took on increasingly important roles until he was appointed Chairman of SAES Getters in 2009.
At the start of the 1990s, the entire activity of the group was encompassed in three sectors: barium getters for the television industry, non-evaporable getters, NEG pumps and metal dispensers for industrial and scientific applications, gas purifiers and analyzers for the semiconductor industry. Over the decade, production companies were established in South Korea and China and commercial companies in Singapore and Taiwan .
In 1996, to meet the new requirements of the company in the fields of production and research, the new headquarters was inaugurated in Lainate. During the same year, SAES Getters became the first Italian company to be listed on Nasdaq , [ 2 ] the most important equity market in the US for high-tech companies (on which the company remained until 2003, the year in which it requested a delisting). [ 3 ]
During the second half of the 1990s, with the succession of technologies in the field of televisions, SAES Getters, sensing the importance of new market developments, expanded its own field of production and focused on technologies widespread in the flat display sector, in particular, mercury dispensers for backlight lamps for LCD (Liquid Crystal Display) for monitors and televisions.
In 2000, Paolo della Porta was named the Entrepreneur of the year in Italy and in 2001, he was appointed "World Entrepreneur of the Year" in Italy by Ernst & Young - this recognition consolidated the image of the company at an international level. [ 4 ] [ 5 ]
Overall, this decade signalled a notable change for the entire company, with its structure reorganised through new acquisitions and company policy evolving significantly, which, characterised by innovation and diversification, focused increasingly on expanding its technology portfolio in advanced materials. This strategy led SAES Getters to specialise in the execution of components and systems for high-tech industrial and medical applications, allowing the company to survive unscathed after the collapse of a number of key markets, such as barium getters for the television industry or back lights for LCD screens. Furthermore, during this period, the company developed highly innovative technologies and processes for the depositing of getters on silicon wafers for so-called MEMS (Micro Electro-Mechanical Systems), miniaturised devices intended for various applications, such as sensors and gyroscopes .
The company entered the shape memory alloy sector (SMA), becoming a key reference for the sector and the first producer of SMA devices and materials for use in industry. In this way, SAES acquired Memory Metalle GmbH (renamed Memry GmbH in 2010), a German company with metallurgical and application skills relating to SMA in the field of medicine. It also acquired two companies in the United States: Memry Corporation, specialising in the production of SMA devices for medical use and the business division of Special Metal Corporation, dedicated to the production of NiTiNol (renamed SAES Smart Materials). NiTiNol is the commercial name of shape memory alloys used in medicine and the SAES group is one of the major international suppliers of this material. SAES then launched the production of SMA wires and springs for industrial applications at its Italian facilities, with these now concentrated at its headquarters in Lainate .
In this context, in 2011, together with the German company Alfmeier, SAES Getters established the 50-50 joint venture in Germany, Actuator Solutions GmbH, to boost its own competitiveness at international level in the fields of development, production and marketing of SMA-wire-based actuators. [ 6 ] In 2014, the joint venture won the "German Innovation Award" in the medium-sized company category. [ 7 ]
The group is also strengthening its presence in the field of purification, with the acquisition of a division of the company Power & Energy ( Ivyland , Pennsylvania , United States), with the aim of expanding its production of palladium membrane purifiers.
At the same time, the Research and Innovation area of the company is developing innovative hybrid technologies, which integrate getter materials into polymer matrices, initially concentrating on the development of dispensable absorbers for organic electronics applications, in particular OLED (Organic Light Emitting Diodes) light displays and sources. From 2013 onwards, further developments of the polymer technological platform have permitted the group to execute new functional polymer compounds, with the properties of interacting with the gases and optical, mechanical and surface modifying functions, according to the requirements and applications of interest, including implantable medical devices, food packaging and the field of energy storage ( lithium batteries and super condensers).
In 2010, it also established the company ETC, the fruit of a collaboration between CNR and SAES Getters (the majority shareholder). [ 8 ] An innovative research programme was launched within ETC for the development of OLET technology (Organic Light Emitting Transistor).
The group is mainly focused on advanced alloys , advanced inorganic materials, polymer-matrix composites, and thin metal films.
SAES Getters exploits solid-state chemistry to manage multiphase solid-state reactions among one or more solid phases. Evaporable getters, mercury dispensers, alkali metal dispensers are examples of products based on solid-state reactions.
The company has been dealing for decades with vacuum metallurgy ( arc melting and vacuum induction melting ) and powder metallurgy (milling technologies, sieving, powders classification and mixing, screen printing, and sintering). In particular, by the available sintering technologies, processes under high vacuum or inert atmosphere and controlled conditions of temperature, time (traditional sintering), and pressure (hot uniaxial pressing and cold isostatic pressing) can be performed, allowing to obtain either highly porous either full dense sintered bodies.
SMA are materials that can exhibit the property of remembering their original shape even after being severely deformed. Thanks to their intrinsic shape memory and superelastic effects, they represent an enabling technology for implantable medical devices and actuators. SAES Getters deals with designing new materials on a theoretical level, developing new alloys on an industrial scale, and modeling and manufacturing new components.
It is a bundle of technologies grown at SAES to develop advanced polymeric materials that integrate getter properties and rapidly expand towards other functionalities. These materials can be in the form of dispensable polymer composites, functional compounds, and functional coatings for a wide variety of applications, from consumer electronics to implantable medical devices to food packaging and special packaging in general.
The SAES group manages the purification of gases, either under ultra-high vacuum , or at atmospheric pressure . It deals with enabling the generation of ultra-high pure gases, characterized by impurity concentrations below 1 part-per-billion (ppb).
This is the oldest and strongest technology owned by the SAES group, which deals with the design of both ultra-high vacuum pumps and pure metal sources, based on a variety of vacuum gas dynamics codes and on the building of proprietary high-vacuum manufacturing tools, ranging from thin film deposition tools to vacuum reactors.
The company developed a range of technologies enabling the deposition of pure metals and alloys on several kinds of substrates. Sputtering is normally used to deposit high surface area getter alloys onto silicon wafers , used by the vacuum MEMS industry as cap wafers, to create and maintain a well-defined gas composition inside MEMS cavities.
The SAES group's organizational structure is composed of three units dedicated to different technologic solutions: Industrial Applications Business Unit, Shape Memory Alloys (SMA) Business Unit, Business Development Unit.
The SAES group provides advanced technological solutions to the electronic devices of a wide range of markets, including the aeronautical, medical, industrial, security, defence, and basic research sectors. The products developed in this division include getters of different types and formats, alkaline metal dispensers, cathodes , and materials for thermal management. The offered products are employed in various devices such as X-ray tubes, microwave tubes, solid-state lasers, electron sources, photomultiplier, and radiofrequency amplification systems.
SAES Getters produces getters of different types and formats that are employed in various devices such as night vision devices based on infrared sensors, pressure sensors, gyroscopes for navigation systems, and MEMS devices of various natures.
The company supplies getters and metal dispensers for lamps .
The company produces pumps based on non-vaporable getter materials (NEG), which can be applied in both industrial and scientific fields (for example, in analytical instrumentation, vacuum systems for research activities, and particle accelerators).
The solutions for vacuum thermal insulation include NEG products for cryogenic applications, for solar collectors both for home applications and operating at high temperatures and for thermos . Furthermore, SAES is particularly active in the development of innovative getter solutions for vacuum insulating panels for the white goods industry.
In the microelectronics market, SAES Getters develops and sells advanced gas purification systems for the semiconductors industry and other industries that use pure gases. Through the subsidiary SAES Pure Gas, Inc., the group offers a full range of purifiers for bulk gases and special gases.
The SAES group produces semi-finished products, components, and devices in shape memory alloy, and a special alloy made of nickel-titanium (NiTinol), characterized by super-elasticity (a property that allows the material to withstand even large deformations, returning then to its original form) and by the property of assuming predefined forms when subjected to heat treatment.
NiTinol is used in a wide range of medical devices, particularly in the cardiovascular field. In fact, its superelastic properties are ideal for the manufacturing of the devices used in the field of non-invasive surgery, such as catheters to navigate within the cardiovascular system and self-expanding devices (aortic and peripheral stents or heart valves).
The shape memory alloy is used in producing various devices (valves, proportional valves, actuators, release systems, and mini-actuators). The use of SMA devices in the industrial field goes across the board of many application areas such as domotics , the white goods industry, the automotive business, and consumer electronics .
The SAES group has developed the platform of Functional Polymer Composites in the past few years, where getter functionalities, as well as optical and mechanical features, are incorporated into polymer matrices. Originally designed and used for the protection of OLED (Organic Light Emitting Diodes) displays and lamps, these new materials are now being tailored also for new areas such as food packaging and implantable medical devices among others.
Relying on the same FPC platform, the group is also active in the field of new-generation electrochemical devices for energy storage, such as super-capacitors and lithium batteries, primarily intended for the market of hybrid and electric engines.
The main shareholders are: | https://en.wikipedia.org/wiki/SAES_Getters |
The SAE Institute ( SAE ) and SAE University College (in Australia) , formerly the School of Audio Engineering and the SAE Technology College and badged SAE Creative Media Education , is a network of colleges around the world that provides creative media programmes. Founded in 1976 in Sydney , Australia, by Tom Misner, SAE was purchased in 2012 by Navitas Limited , [ 1 ] a private Australian education services company. In 2022 Navitas sold SAE operations in the United Kingdom and mainland Europe to AD Education, part of Ardian a France-based independent private equity investment company. Navitas retained its SAE Creative Media Institute operations in Australia, New Zealand, Canada and the US alongside its network of licensed education partners operating under the SAE brand in other parts of the world. [ 2 ] In 2023, SAE Creative Media Institute in Australia became a University College.
SAE was established by Tom Misnner in 1976 in Sydney, converting a small advertising studio into a classroom. Over the next six years, campuses in Melbourne , Brisbane , Adelaide , and Perth were established. In the mid-1980s, SAE began opening colleges outside of Australia, including locations in London, Munich , Frankfurt, Vienna , Berlin, Auckland , and Glasgow . In the 1990s, SAE opened a European head office in Amsterdam , and locations were opened in Paris, Hamburg, Zürich , Hobart , Cologne , Stockholm, Athens, and Milan . SAE also began expanding into Asia in the 1990s, opening locations in Singapore and Kuala Lumpur . In the late 1990s, SAE formed the SAE Entertainment Company and launched full university degree programs with the co-operation of Southern Cross University and Middlesex University . In 1999, SAE began opening facilities in the United States, and over the following decade opened locations in Nashville , Miami, San Francisco, Atlanta , Los Angeles, and Chicago. In 2000, SAE began licensing franchise schools in India , opening four that year. In 2000s, locations were opened in Liverpool , Madrid, Brussels , Bangkok , Leipzig, Barcelona , Dubai , Amman , Cape Town , Istanbul , and Serbia . Licence agreements were signed for new schools in Qatar, Bogotá Colombia, Mexico, Saudi Arabia and Egypt. The Dubai branch offers degree certification accredited by Middlesex University. In the 2000s SAE also acquired QANTM, an Australian production, media and training company, and relocated its head office to Littlemore Park, Oxford , and its headquarters to Byron Bay , Australia.
In 2010, the SAE Institute was sold to Navitas , a publicly traded educational services company. Over the next few years, new locations were opened in Romania , Jakarta , and Moskhato . Navitas began taking over the US campuses in 2011, and laid off over 40 US employees in 2014. [ citation needed ]
In 2022 Navitas announced the sale of part of its creative media institute, SAE, to AD Education (part of Europe’s leading private investment house, Ardian). Ardian purchased the SAE operations in the United Kingdom and mainland Europe. Navitas retained SAE operations in Australia, New Zealand, Canada and the US alongside its network of licensed education partners operating under the SAE brand in other parts of the world. [ 3 ]
On the 22 December 2023, the Australian operation SAE Creative Media Institute Australia became a University College. [ 4 ]
On 16 July 2024, staff at all six Australian campuses of SAE-Qantm went on strike against pay and conditions. [ 5 ]
SAE Online , formerly SAE Graduate college , was an unaccredited , distance learning , proprietary , for-profit European school that offered post graduate courses from master's degrees to PhDs in Creative Media Industries, as well as several other professional skills courses ( short courses ). SAE Online has since ceased operations.
SAE Creative Media Institute became a University College on the 22 December 2023. The Tertiary Education Quality and Standards Agency’s (TEQSA’s) University College category is reserved for the highest performing Institutes of Higher Education. This decision places SAE in an elite group of just seven University Colleges in Australia – and the only one delivering creative media education nationally. [ 6 ] [ 7 ]
Energy Groove Radio is a digital commercial-style radio network. It is a network of eight Contemporary Hit Radio (CHR)/Top 40 Stations playing a mix of live and pre-recorded programming.
Energy Groove Radio showcases local and international shows, produced by a mix of DJs, presenters, and SAE students.
Freddy El Turk launched Energy Groove Radio in 2009, broadcasting from Sydney, Australia. Since partnering with SAE in 2011, Energy Groove Radio has grown from a single digital radio service - based in Australia at the SAE Sydney campus - to a network of seven stations located across the UK, France, Italy, Germany, US and Spain.
In 2012 Energy Groove and Emirates Airlines entered a collaboration which now sees Emirates Airlines play Energy Groove Radio across its entire fleet. [ 8 ]
SAE is accredited in Australia and South Africa to award its own Bachelor and Masters degrees and awards degrees in Europe and at Licensed campuses via its partnerships with Middlesex University . Since 2013, SAE Germany offers a Master of Arts in Professional Media Creation through a partnership with the Institut für Computermusik und Elektronische Medien (Institute for Computer Music and Electronic Media) of Folkwang University of the Arts .
In the UK, its campuses are [ when? ] in London , Liverpool , Leamington Spa , and Glasgow , providing industry-focused 2-year degrees validated by the University of Hertfordshire across eight subject areas – Audio, Content Creation & Online Marketing, Film, Game Art Animation, Games Programming, Music Business, Visual Effects, and Web Development. [ citation needed ] SAE Institute is a validated partner of Middlesex University in London . Students enrolled in a validated programme will receive a Middlesex award on successful completion of their studies. All BA and BSc programmes are validated by Middlesex University. [ 9 ] SAE Institute has undergone a review for educational oversight by the Quality Assurance Agency for Higher Education (QAA). [ 10 ] SAE Institute became an associate member of GuildHE in July 2013, [ 11 ] one of the two recognised representative bodies for higher education in the UK.
SAE sponsors the national unsigned music competition Top of the Ox , recently won by singer-songwriter Ian Edwards, in association with Oxford based record label Crash Records and other organisations. [ 12 ] | https://en.wikipedia.org/wiki/SAE_Institute |
The SAFE Building System , also known as the SAFE Foundation System , is a way to build in flood zones and coastal areas, developed by architect and inventor Greg Henderson and his team at Arx Pax Labs, Inc. It is designed to float buildings, roadways, and utilities in a few feet of water. [ 1 ] The self-adjusting floating environment draws from existing technologies used to float concrete bridges and runways such as Washington's SR 520 and Japan's Mega-Float . [ 2 ] It also absorbs the shock of earthquakes, allowing buildings and their related communities to remain stable. [ 3 ] Arx Pax is working with Republic of Kiribati and Pacific Rising to solve for sustainable development challenges associated with rising sea levels . [ 4 ]
Arx Pax, the company involved in this technology has proposed building a “floating village” project in north San Jose's Alviso hamlet, deploying a group of pontoons beneath the buildings to protect the development from floods and earthquakes. [ 5 ]
Originally developed for earthquakes as an alternative to Base Isolation the floating foundation decouples the structure from the earth with a simple patented method consisting of three parts. According to the patent, "Three part foundation systems can include a containment vessel, which constrains a buffer medium to an area above the containment vessel, and a construction platform. A building can be built on the construction platform. In a particular embodiment, during operation, the construction platform and structures built on the construction platform can float on the buffer medium. In an earthquake, a construction platform floating on a buffer medium may experience greatly reduced shear forces. In a flood, a construction platform floating on a buffer medium can be configured to rise as water levels rise to limit flood damage." [ 6 ]
This engineering-related article is a stub . You can help Wikipedia by expanding it .
This article about futures studies is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SAFE_Building_System |
SAFIR (or Single Aperture Far-InfraRed ) is a proposed NASA space observatory for far-infrared light. [ 2 ] The plan calls for a single large mirror 5–10 meters (16–33 ft) in diameter, cryogenically cooled to 5 kelvins (−268 °C; −451 °F). [ 2 ] This would feed detector arrays sensitive from 5 to 1000 μm . [ 2 ] The possibility of servicing such a telescope in space has been evaluated. [ 3 ]
The design for SAFIR's primary mirror is large for a space-based telescope; for comparison, SAFIR's predecessor, the 2003 Spitzer Space Telescope , has a primary mirror only 0.85 meters (2.8 ft) in diameter. SAFIR is oriented towards longer wavelengths so the mirror does not have to be as accurate compared to visible and near-infrared telescopes like the Hubble Space Telescope .
SAFIR will study the earliest phases of forming galaxies, stars, and planetary systems at wavelengths where these objects are brightest and which contain a wealth of unique information: from 20 micrometers to one millimeter . Most of this portion of the electromagnetic spectrum is not accessible from the ground because it is absorbed by moisture in Earth's atmosphere . [ 2 ]
The combination of large mirror size and cold temperature would be designed to make SAFIR more than 1000 times more sensitive than Spitzer or even the Herschel Space Observatory ; approaching the ultimate sensitivity limits at far-infrared and submillimeter wavelengths. SAFIR's sensitivity will be limited only by the irreducible noise of photons in the astrophysical background , rather than by infrared radiation from the telescope itself. [ 2 ]
What makes this part of the spectrum so important is that, while far-infrared and submillimeter light can penetrate dust clouds , half or more of the optical and ultraviolet light produced in the universe is absorbed by dust and re-radiated in the far-infrared and submillimeter. Even in our local area of the universe, many galaxies are so dusty that they radiate mainly at those wavelengths .
This has two important consequences. First, to accurately measure the energy output and structure of objects that are obscured by dust, far-infrared continuum emission (emission across a broad band of wavelengths) must be included. Second, spectroscopy at these wavelengths makes the best probe of conditions in the vast clouds of dust and gases that lie between stars, known as the interstellar medium (ISM). These general features apply on all scales from the formation of stars and planetary systems in our corner of the Milky Way to the earliest galaxies that formed when the universe was only 10% to 20% of its current age. [ 2 ]
As a concept, wide ranges of technologies and architectures have been examined. [ 1 ] The use of technology from the James Webb Space Telescope was also explored. [ 1 ] | https://en.wikipedia.org/wiki/SAFIR |
SAFSTOR is a nuclear decommissioning method in which a nuclear power plant or facility governed by the United States Nuclear Regulatory Commission , is "placed and maintained in a condition that allows the facility to be safely stored and subsequently decontaminated (deferred decontamination) to levels that permit release for unrestricted use" . [ 1 ]
During SAFSTOR the de-fuelled plant is monitored before complete decontamination and dismantling of the site, to a condition where nuclear licensing is no longer required. The decommissioning must be completed within 60 years of the plant ceasing operations. [ 2 ]
During the storage interval, some of the radioactive contaminants of the reactor and power plant will decay, which will reduce the quantity of radioactive material to be removed during the final decontamination phase.
Different sub-levels of SAFSTOR are recognized, which vary in the type of activity and monitoring required. [ 3 ]
All varieties of SAFSTOR require positive action to decontaminate the site at the end of the storage period.
The other options set by the NRC are nuclear decommissioning which is immediate dismantling of the plant and remediation of the site, and nuclear entombment which is the enclosure of contaminated parts of the plant in a permanent layer of concrete. [ 4 ] Mixtures of options may be used, for example, immediate removal of steam turbine components and condensers, and SAFSTOR for the more heavily radioactive containment vessel. Since NRC requires decommissioning to be completed within 60 years, ENTOMB is not usually chosen since not all activity will have decayed to an unregulated background level in that time.
Decommissioning options for a retired nuclear plant may be chosen based on availability of decommissioning funds, operation of other reactors at the same site, or availability of waste disposal facilities. In 2004, 11 reactors were planned for DECON and 9 for SAFSTOR. In 2008, 14 shutdown commercial power reactors were planned for or had completed DECON, 11 were in SAFSTOR, 3 were in ENTOMB [ 5 ] and Three Mile Island unit 2 was defuelled and will be decontaminated when Unit 1 ceases operation. | https://en.wikipedia.org/wiki/SAFSTOR |
The SLUGGS ( SAGES Legacy Unifying Globulars and GalaxieS ) survey is an astronomical survey of 25 (and 3 `bonus') nearby early-type ( E and S0 ) galaxies. This survey uses a combination of imaging from Subaru /Suprime-Cam and spectroscopy from Keck /DEIMOS to investigate the chemo-dynamical properties of both the diffuse starlight and the globular cluster systems of the target galaxies.
Pilot data for the survey was obtained in 2006 and data acquisition was completed in 2017. [ 1 ]
The SLUGGS project was so named in honor of the banana slug mascot of the University of California, Santa Cruz .
SAGES (Study of the Astrophysics of Globular Clusters in Extragalactic Systems) is an international network of researchers investigating the formation and evolution of globular clusters and their host galaxies, using observational facilities around the world, particularly the Keck and Subaru telescopes. [ 2 ] It was founded by
Jean Brodie, Duncan Forbes, Aaron Romanowsky and Jay Strader.
Deep wide-field imaging from Subaru/Suprime-Cam is used to identify and measure the positions of candidate globular clusters around each survey galaxy. Several (up to 6) DEIMOS masks are then created which include slits corresponding to the locations of globular clusters, galaxy starlight and random background sky locations in the outer parts of the mask.
The DEIMOS spectrograph, on the Keck telescope, is centred on wavelengths around the Calcium Triplet lines (~850 nm). After a typical 2 hour exposure per mask, spectra of globular clusters and galaxy starlight is obtained.
Using a technique called SKiMS (Stellar Kinematics from Multiple Slits) it is possible to extract the kinematics (and metallicity) of galaxy starlight out to 3 effective radii . Equivalent data for the globular clusters is obtained out to ~10 effective radii. The DEIMOS instrument has the advantages of being a stable, high throughput, wide-field spectrograph coupled with excellent velocity resolution (~12 km/s) on a 10m telescope. This technique effectively uses DEIMOS as a pseudo wide area integral field unit . [ 3 ]
The 25 target galaxies are chosen to be representative (i.e. cover the range of basic galaxy parameters and environments) of nearby (distance < 27 Mpc) early type (E and S0) galaxies. The survey also includes 3 `bonus’ galaxies which have been observed during times that the main sample galaxies are not available. All galaxies are accessible from the northern hemisphere. Although only a small sample, the data reach to large galactocentric radii with excellent velocity resolution and S/N compared to other surveys. [ 4 ]
NGC 720, NGC 821, NGC 1023 , NGC 1400, NGC 1407, NGC 2768, NGC 2974, NGC 3115 , NGC 3377 , NGC 3608, NGC 4111, NGC 4278, NGC 4365, NGC 4374 , NGC 4459, NGC 4473, NGC 4474, NGC 4486 , NGC 4494, NGC 4526 , NGC 4564, NGC 4649 , NGC 4697 , NGC 5846, NGC 7457.
The bonus galaxies are NGC 3607 , NGC 4594 and NGC 5866 .
A complete list of publications using SLUGGS survey data can be found here . | https://en.wikipedia.org/wiki/SAGES_Legacy_Unifying_Globulars_and_GalaxieS_Survey |
The Science of Aging Knowledge Environment ( SAGE KE ) was an online scientific resource provided by the American Association for the Advancement of Science (AAAS).
The American Association for the Advancement of Science established a collaboration with Stanford University Libraries and The Center for Resource Economics/Island Press (Island Press) in 1996 to find means to utilize internet -based technologies to enhance access to scientific information and improve the effectiveness of information transfer. The collaborative coined the term Knowledge Environment (KE) to describe the collection of electronic networking tools they were seeking to develop.
SAGE KE is the third in a series of Knowledge Environments developed by Science and AAAS , after the Signal Transduction Knowledge Environment (STKE) and AIDScience. Funding for SAGE KE comes from The Ellison Medical Foundation , founded and supported by Oracle Corporation CEO Larry Ellison .
SAGE KE published its final issue on 28 June 2006 due to lack of funding. The interactive content was discontinued during the summer of 2006, leaving the SAGE KE site as an archive by August 2006.
The focus of SAGE KE was to provide timely access to information about advances on basic mechanisms of aging and age-related diseases through the internet , to provide searchable databases of information on aging and to provide an active environment in which biogerontologists could share and debate their understandings.
Ouroboros is a WordPress community weblog devoted to research in the biology of aging . It was established in July 2006 in reaction to the termination of the SAGE KE. The primary mission of the site is to provide timely commentary and review of recently published articles in the scholarly literature, either directly or indirectly related to aging. Articles on the site discuss a range of scientific topics, including Alzheimer's disease , bioinformatics , calorie restriction , regulation of gene expression , the role of mitochondria in the aging process, and evolutionary theories of aging. | https://en.wikipedia.org/wiki/SAGE_KE |
SAMPL ( Statistical Assessment of the Modeling of Proteins and Ligands ) is a set of community-wide blind challenges aimed to advance computational techniques as standard predictive tools in rational drug design . [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] A broad range of biologically relevant systems with different sizes and levels of complexities including proteins , host–guest complexes, and drug-like small molecules have been selected to test the latest modeling methods and force fields in SAMPL. New experimental data, such as binding affinity and hydration free energy , are withheld from participants until the prediction submission deadline, so that the true predictive power of methods can be revealed. The most recent SAMPL5 challenge contains two prediction categories: the binding affinity of host–guest systems, and the distribution coefficients of drug-like molecules between water and cyclohexane. [ 6 ] [ 7 ] Since 2008, the SAMPL challenge series has attracte interest from scientists engaged in the field of computer-aided drug design (CADD) [ 8 ] [ 9 ] [ 10 ] The current SAMPL organizers include John Chodera , Michael K. Gilson , David Mobley , and Michael Shirts . [ 11 ]
The SAMPL challenge seeks to accelerate progress in developing quantitative, accurate drug discovery tools by providing prospective validation and rigorous comparisons for computational methodologies and force fields. Computer-aided drug design methods have been considerably improved over time, along with the rapid growth of high-performance computing capabilities. However, their applicability in the pharmaceutical industry are still highly limited, due to the insufficient accuracy. Lacking large-scale prospective validations, methods tend to suffer from over-fitting the pre-existing experimental data. To overcome this, SAMPL challenges have been organized as blind tests: each time new datasets are carefully designed and collected from academic or industrial research laboratories, and measurements are released shortly after the deadline of prediction submission. Researchers then can compare those high-quality, prospective experimental data with the submitted estimates. A key emphasis is on lessons learned, allowing participants in future challenges to benefit from modeling improvements made based on earlier challenges.
SAMPL has historically focused on the properties of host–guest systems and drug-like small molecules. These simply model systems require considerably less computational resources to simulate than protein systems, and thus converge more quickly. Through careful design, these model systems can be used to focus on one particular or a subset of simulation challenges. [ further explanation needed ] [ 12 ] The past several SAMPL host–guest, hydration free energy and log D challenges revealed the limitations in generalized force fields, [ 13 ] [ 14 ] facilitated the development of solvent models, [ 15 ] [ 16 ] and highlighted the importance of properly handling protonation states and salt effects. [ 17 ] [ 18 ]
Registration and participation is free for SAMPL challenges. Beginning with SAMPL7, challenge participation data was posted on the SAMPL website , [ 19 ] as well as the GitHub page for the specific challenge . Instructions, input files and results were then provided through GitHub (earlier challenges provided content primarily through D3R for SAMPL4-5, and via other means for earlier SAMPLs). Participants were allowed to submit multiple predictions through the D3R website, either anonymously or with research affiliation. Since the SAMPL2 challenge, all participants have been invited to attend the SAMPL workshops and submit manuscripts to describe their results. After a peer-review process, the resulting papers, along with the overview papers which summarize all submitting data, were published in the special issues of the Journal of Computer-Aided Molecular Design . [ 20 ]
The SAMPL project was recently funded by the NIH (grant GM124270-01A1), for the period of Sept. 2018 through August 2022, to allow the design of future SAMPL challenges to drive advances in the areas they are most needed for modeling efforts. [ 9 ] [ 10 ] The effort is spearheaded by David L. Mobley (UC Irvine) with co-investigators John D. Chodera (MSKCC), Bruce C. Gibb (Tulane), and Lyle Isaacs (Maryland). Currently challenges and workshops are run in partnership with the NIH-funded Drug Design Data Resource , but this will likely change over time as funding for the two projects is not coupled.
Funding also allowed a broadening of scope of SAMPL; through SAMPL6, its role had been seen as primarily focused on physical properties, with D3R handling protein-ligand challenges. However, the funded effort broadened its focus to include systems which will drive improvements in modeling, including potentially suitable protein-ligand systems. This is still in contrast to D3R, which relies on donated datasets of pharmaceutical interest, whereas SAMPL challenges are specifically designed to focus on specific modeling challenges.
The first SAMPL exercise, SAMPL0 (2008) [ 21 ] focused on the predictions of solvation free energies of 17 small molecules. A research group at Stanford University and scientists at OpenEye Scientific Software carried out the calculations. Despite the informal format, SAMPL0 laid the groundwork for the following SAMPL challenges.
SAMPL1 (2009) [ 22 ] and SAMPL2 challenges (2010) [ 1 ] were organized by OpenEye and continued to focus on predicting solvation free energies of drug-like small molecules. Attempts were also made to predict binding affinities, binding poses and tautomer ratios. Both challenges attracted significant participations from computational scientists and researchers in academia and industry.
The blinded data sets for host–guest binding affinities were introduced for the first time in SAMPL3 (2011-2012), [ 3 ] along with solvation free energies for small molecules and the binding affinity data for 500 fragment-like tyrosine inhibitors. Three host molecules were all from the cucurbituril family. The SAMPL3 challenge received 103 submissions from 23 research groups worldwide. [ 2 ]
Different from the prior three SAMPL events, the SAMPL4 exercise (2013-2014) [ 4 ] [ 5 ] was coordinated by academic researchers, with logistical support from OpenEye. Datasets in SAMPL4 consisted of binding affinities for host–guest systems and HIV integrase inhibitors , as well as hydration free energies of small molecules. Host molecules included cucurbit[7]uril (CB7) and octa-acid . The SAMPL4 hydration challenge involved 49 submissions from 19 groups. The participation of the host–guest challenge also grew significantly compared to SAMPL3. The workshop was held at Stanford University in September, 2013.
The protein-ligand challenges were separated from SAMPL in SAMPL5 (2015-2016) [ 6 ] [ 7 ] and were distributed as the new Grand Challenges of the Drug Design Data Resource (D3R). [ 23 ] SAMPL5 allowed participants to make predictions of the binding affinities of three sets of host–guest systems: an acyclic CB7 derivative and two host from the octa-acid family. Participants were also encouraged to submit predictions for binding enthalpies. A wide array of computational methods were tested, including density functional theory (DFT), molecular dynamics , docking , and metadynamics. The distribution coefficient predictions were introduced for the first time, receiving total of 76 submissions from 18 researcher groups or scientists for a set of 53 small molecules. The workshop was held in March, 2016 at University of California, San Diego as part of the D3R workshop. The top-performing methods in the host–guest challenge yielded encouraging yet imperfect correlations with experimental data, accompanied by large, systematic shifts relative to experiment. [ 24 ] [ 25 ]
The SAMPL6 testing systems include cucurbit[8]uril , octa-acid , tetra-endo-methyl octa-acid, and a series of fragment-like small molecules. The host–guest, conformational sampling and pKa prediction challenges of SAMPL6 are now closed. The SAMPL6 workshop was jointly run with the D3R workshop in February 2018 at the Scripps Institution of Oceanography [ 26 ] and a SAMPL special issue of the Journal of Computer Aided Molecular Design reported many of the results. A SAMPL6 Part II challenge focused on a small octanol-water partition coefficient prediction set and was followed by a virtual workshop on May 16, 2019 and a joint D3R/SAMPL workshop in San Diego in August 2019. A special issue or special section of JCAMD is planned to report the results. [ needs update ] SAMPL6 inputs and results are available via the SAMPL6 GitHub repository .
SAMPL7 again included host-guest challenges and a physical property challenge. A protein-ligand binding challenge on PHIPA fragments was also included. Host-guest binding focused on several small molecules binding to octa-acid and exo-octa-acid; binding of two compounds to a series of cyclodextrin derivatives; and binding of a series of small molecules to a clip-like guest known as TrimerTrip. A SAMPL7 virtual workshop took place and is available online . A SAMPL7 physical properties challenge is currently ongoing . Plans for a EuroSAMPL in-person workshop in Fall 2020 were derailed by COVID-19 and the workshop is being conducted virtually. SAMPL7 inputs and (as challenge components are completed, results) are available via the SAMPL6 GitHub repository .
SAMPL8 included host-guest components on binding of drugs of abuse to CB8, and a series of small molecules to Gibb Deep Cavity Cavitands (GDCCs), as detailed on the SAMPL8 GitHub repository . An additional pKa and logD challenge focused on pK and logD prediction for a series of drug-like molecules.
SAMPL9 is in planning stages, except that a SAMPL9 host-guest challenge on a host from Lyle Isaacs' group is currently underway. Details are available on the SAMPL9 GitHub repository
A relatively complete list of SAMPL-related publications is maintained by the SAMPL organizers; more than 150 related papers have been published.
SAMPL is slated to continue its focus on physical property prediction, including logP and logD values, pKa prediction, host–guest binding, and other properties, as well as broadening to include a protein-ligand component. [ 9 ] Some data is planned to be collected directly by the SAMPL co-investigators (Chodera, Gibb and Isaacs), but industry partnerships and internships are also proposed. [ 9 ] | https://en.wikipedia.org/wiki/SAMPL_Challenge |
SAMSON ( Software for Adaptive Modeling and Simulation Of Nanosystems ) is a computer software platform for molecular design being developed by OneAngstrom and previously by the NANO-D group at the French Institute for Research in Computer Science and Automation (INRIA). [ 2 ]
SAMSON has a modular architecture that makes it suitable for different domains of nanoscience, including material science, [ 3 ] life science, [ 4 ] and drug design. [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ]
SAMSON Elements are modules for SAMSON, developed with the SAMSON software development kit (SDK). SAMSON Elements help users perform tasks in SAMSON, including building new models, performing calculations, running interactive or offline simulations, and visualizing and interpreting results.
SAMSON Elements may contain different class types, including for example:
SAMSON Elements expose their functions to SAMSON and other Elements through an introspection mechanism, and may thus be integrated and pipelined.
SAMSON represents nanosystems using five categories of models:
Simulators (potentially interactive ones) are used to build physically-based models, and predict properties.
All models and simulators are integrated into a hierarchical, layered structure that form the SAMSON data graph. SAMSON Elements interact with each other and with the data graph to perform modeling and simulation tasks. A signals and slots mechanism makes it possible for data graph nodes to send events when they are updated, which makes it possible to develop e.g., adaptive simulation algorithms. [ 12 ] [ 13 ] [ 14 ]
SAMSON has a node specification language (NSL) that users may employ to select data graph nodes based on their properties. Example NSL expressions include:
SAMSON is developed in C++ and implements many features to ease developing SAMSON Elements, including:
SAMSON, SAMSON Elements and the SAMSON Software Development Kit are distributed via the SAMSON Connect website. [ 6 ] The site acts as a repository for the SAMSON Elements being uploaded by developers, and users of SAMSON choose and add Elements from SAMSON Connect. | https://en.wikipedia.org/wiki/SAMSON |
SAMV ( iterative sparse asymptotic minimum variance [ 1 ] [ 2 ] ) is a parameter-free superresolution algorithm for the linear inverse problem in spectral estimation , direction-of-arrival (DOA) estimation and tomographic reconstruction with applications in signal processing , medical imaging and remote sensing . The name was coined in 2013 [ 1 ] to emphasize its basis on the asymptotically minimum variance (AMV) criterion. It is a powerful tool for the recovery of both the amplitude and frequency characteristics of multiple highly correlated sources in challenging environments (e.g., limited number of snapshots and low signal-to-noise ratio ). Applications include synthetic-aperture radar , [ 2 ] [ 3 ] computed tomography scan , and magnetic resonance imaging (MRI) .
The formulation of the SAMV algorithm is given as an inverse problem in the context of DOA estimation. Suppose an M {\displaystyle M} -element uniform linear array (ULA) receive K {\displaystyle K} narrow band signals emitted from sources located at locations θ = { θ a , … , θ K } {\displaystyle \mathbf {\theta } =\{\theta _{a},\ldots ,\theta _{K}\}} , respectively. The sensors in the ULA accumulates N {\displaystyle N} snapshots over a specific time. The M × 1 {\displaystyle M\times 1} dimensional snapshot vectors are
where A = [ a ( θ 1 ) , … , a ( θ K ) ] {\displaystyle \mathbf {A} =[\mathbf {a} (\theta _{1}),\ldots ,\mathbf {a} (\theta _{K})]} is the steering matrix , x ( n ) = [ x 1 ( n ) , … , x K ( n ) ] T {\displaystyle {\bf {x}}(n)=[{\bf {x}}_{1}(n),\ldots ,{\bf {x}}_{K}(n)]^{T}} contains the source waveforms, and e ( n ) {\displaystyle {\bf {e}}(n)} is the noise term. Assume that E ( e ( n ) e H ( n ¯ ) ) = σ I M δ n , n ¯ {\displaystyle \mathbf {E} \left({\bf {e}}(n){\bf {e}}^{H}({\bar {n}})\right)=\sigma {\bf {I}}_{M}\delta _{n,{\bar {n}}}} , where δ n , n ¯ {\displaystyle \delta _{n,{\bar {n}}}} is the Dirac delta and it equals to 1 only if n = n ¯ {\displaystyle n={\bar {n}}} and 0 otherwise. Also assume that e ( n ) {\displaystyle {\bf {e}}(n)} and x ( n ) {\displaystyle {\bf {x}}(n)} are independent, and that E ( x ( n ) x H ( n ¯ ) ) = P δ n , n ¯ {\displaystyle \mathbf {E} \left({\bf {x}}(n){\bf {x}}^{H}({\bar {n}})\right)={\bf {P}}\delta _{n,{\bar {n}}}} , where P = Diag ( p 1 , … , p K ) {\displaystyle {\bf {P}}=\operatorname {Diag} ({p_{1},\ldots ,p_{K}})} . Let p {\displaystyle {\bf {p}}} be a vector containing the unknown signal powers and noise variance, p = [ p 1 , … , p K , σ ] T {\displaystyle {\bf {p}}=[p_{1},\ldots ,p_{K},\sigma ]^{T}} .
The covariance matrix of y ( n ) {\displaystyle {\bf {y}}(n)} that contains all information about p {\displaystyle {\boldsymbol {\bf {p}}}} is
This covariance matrix can be traditionally estimated by the sample covariance matrix R N = Y Y H / N {\displaystyle {\bf {R}}_{N}={\bf {Y}}{\bf {Y}}^{H}/N} where Y = [ y ( 1 ) , … , y ( N ) ] {\displaystyle {\bf {Y}}=[{\bf {y}}(1),\ldots ,{\bf {y}}(N)]} . After applying the vectorization operator to the matrix R {\displaystyle {\bf {R}}} , the obtained vector r ( p ) = vec ( R ) {\displaystyle {\bf {r}}({\boldsymbol {\bf {p}}})=\operatorname {vec} ({\bf {R}})} is linearly related to the unknown parameter p {\displaystyle {\boldsymbol {\bf {p}}}} as
r ( p ) = vec ( R ) = S p {\displaystyle {\bf {r}}({\boldsymbol {\bf {p}}})=\operatorname {vec} ({\bf {R}})={\bf {S}}{\boldsymbol {\bf {p}}}} ,
where S = [ S 1 , a ¯ K + 1 ] {\displaystyle {\bf {S}}=[{\bf {S}}_{1},{\bar {\bf {a}}}_{K+1}]} , S 1 = [ a ¯ 1 , … , a ¯ K ] {\displaystyle {\bf {S}}_{1}=[{\bar {\bf {a}}}_{1},\ldots ,{\bar {\bf {a}}}_{K}]} , a ¯ k = a k ∗ ⊗ a k {\displaystyle {\bar {\bf {a}}}_{k}={\bf {a}}_{k}^{*}\otimes {\bf {a}}_{k}} , k = 1 , … , K {\displaystyle k=1,\ldots ,K} , and let a ¯ K + 1 = vec ( I ) {\displaystyle {\bar {\bf {a}}}_{K+1}=\operatorname {vec} ({\bf {I}})} where ⊗ {\displaystyle \otimes } is the Kronecker product.
To estimate the parameter p {\displaystyle {\boldsymbol {\bf {p}}}} from the statistic r N {\displaystyle {\bf {r}}_{N}} , we develop a series of iterative SAMV approaches based on the asymptotically minimum variance criterion. From, [ 1 ] the covariance matrix Cov p Alg {\displaystyle \operatorname {Cov} _{\boldsymbol {p}}^{\operatorname {Alg} }} of an arbitrary consistent estimator of p {\displaystyle {\boldsymbol {p}}} based on the second-order statistic r N {\displaystyle {\bf {r}}_{N}} is bounded by the real symmetric positive definite matrix
where S d = d r ( p ) / d p {\displaystyle {\bf {S}}_{d}={\rm {d}}{\bf {r}}({\boldsymbol {p}})/{\rm {d}}{\boldsymbol {p}}} . In addition, this lower bound is attained by the covariance matrix of the asymptotic distribution of p ^ {\displaystyle {\hat {\bf {p}}}} obtained by minimizing,
where f ( p ) = [ r N − r ( p ) ] H C r − 1 [ r N − r ( p ) ] . {\displaystyle f({\boldsymbol {p}})=[{\bf {r}}_{N}-{\bf {r}}({\boldsymbol {p}})]^{H}{\bf {C}}_{r}^{-1}[{\bf {r}}_{N}-{\bf {r}}({\boldsymbol {p}})].}
Therefore, the estimate of p {\displaystyle {\boldsymbol {\bf {p}}}} can be obtained iteratively.
The { p ^ k } k = 1 K {\displaystyle \{{\hat {p}}_{k}\}_{k=1}^{K}} and σ ^ {\displaystyle {\hat {\sigma }}} that minimize f ( p ) {\displaystyle f({\boldsymbol {p}})} can be computed as follows. Assume p ^ k ( i ) {\displaystyle {\hat {p}}_{k}^{(i)}} and σ ^ ( i ) {\displaystyle {\hat {\sigma }}^{(i)}} have been approximated to a certain degree in the i {\displaystyle i} th iteration, they can be refined at the ( i + 1 ) {\displaystyle (i+1)} th iteration by,
where the estimate of R {\displaystyle {\bf {R}}} at the i {\displaystyle i} th iteration is given by R ( i ) = A P ( i ) A H + σ ^ ( i ) I {\displaystyle {\bf {R}}^{(i)}={\bf {A}}{\bf {P}}^{(i)}{\bf {A}}^{H}+{\hat {\sigma }}^{(i)}{\bf {I}}} with P ( i ) = Diag ( p ^ 1 ( i ) , … , p ^ K ( i ) ) {\displaystyle {\bf {P}}^{(i)}=\operatorname {Diag} ({\hat {p}}_{1}^{(i)},\ldots ,{\hat {p}}_{K}^{(i)})} .
The resolution of most compressed sensing based source localization techniques is limited by the fineness of the direction grid that covers the location parameter space. [ 4 ] In the sparse signal recovery model, the sparsity of the truth signal x ( n ) {\displaystyle \mathbf {x} (n)} is dependent on the distance between the adjacent element in the overcomplete dictionary A {\displaystyle {\bf {A}}} , therefore, the difficulty of choosing the optimum overcomplete dictionary arises. The computational complexity is directly proportional to the fineness of the direction grid, a highly dense grid is not computational practical. To overcome this resolution limitation imposed by the grid, the grid-free SAMV-SML ( iterative Sparse Asymptotic Minimum Variance - Stochastic Maximum Likelihood ) is proposed, [ 1 ] which refine the location estimates θ = ( θ 1 , … , θ K ) T {\displaystyle {\boldsymbol {\bf {\theta }}}=(\theta _{1},\ldots ,\theta _{K})^{T}} by iteratively minimizing a stochastic maximum likelihood cost function with respect to a single scalar parameter θ k {\displaystyle \theta _{k}} .
A typical application with the SAMV algorithm in SISO radar / sonar range-Doppler imaging problem. This imaging problem is a single-snapshot application, and algorithms compatible with single-snapshot estimation are included, i.e., matched filter (MF, similar to the periodogram or backprojection , which is often efficiently implemented as fast Fourier transform (FFT)), IAA, [ 5 ] and a variant of the SAMV algorithm (SAMV-0). The simulation conditions are identical to: [ 5 ] A 30 {\displaystyle 30} -element polyphase pulse compression P3 code is employed as the transmitted pulse, and a total of nine moving targets are simulated. Of all the moving targets, three are of 5 {\displaystyle 5} dB power and the rest six are of 25 {\displaystyle 25} dB power. The received signals are assumed to be contaminated with uniform white Gaussian noise of 0 {\displaystyle 0} dB power.
The matched filter detection result suffers from severe smearing and leakage effects both in the Doppler and range domain, hence it is impossible to distinguish the 5 {\displaystyle 5} dB targets. On contrary, the IAA algorithm offers enhanced imaging results with observable target range estimates and Doppler frequencies. The SAMV-0 approach provides highly sparse result and eliminates the smearing effects completely, but it misses the weak 5 {\displaystyle 5} dB targets.
An open source MATLAB implementation of SAMV algorithm could be downloaded here . | https://en.wikipedia.org/wiki/SAMV_(algorithm) |
Sequence Alignment Map (SAM) is a text-based format originally for storing biological sequences aligned to a reference sequence developed by Heng Li and Bob Handsaker et al . [ 1 ] It was developed when the 1000 Genomes Project wanted to move away from the MAQ mapper format and decided to design a new format. The overall TAB-delimited flavour of the format came from an earlier format inspired by BLAT ’s PSL. The name of SAM came from Gabor Marth from University of Utah , who originally had a format under the same name but with a different syntax more similar to a BLAST output. [ 2 ] It is widely used for storing data, such as nucleotide sequences, generated by next generation sequencing technologies, and the standard has been broadened to include unmapped sequences. The format supports short and long reads (up to 128 Mbp [ 3 ] ) produced by different sequencing platforms and is used to hold mapped data within the Genome Analysis Toolkit (GATK) and across the Broad Institute , the Wellcome Sanger Institute , and throughout the 1000 Genomes Project .
The SAM format consists of a header and an alignment section. [ 1 ] The binary equivalent of a SAM file is a Binary Alignment Map (BAM) file, which stores the same data in a compressed binary representation. [ 4 ] SAM files can be analysed and edited with the software SAMtools . [ 1 ] The header section must be prior to the alignment section if it is present. Headings begin with the '@' symbol, which distinguishes them from the alignment section. Alignment sections have 11 mandatory fields, as well as a variable number of optional fields. [ 1 ]
From the specification: [ 4 ]
The FLAG field is displayed as a single integer, but is the sum of bitwise flags to denote multiple attributes of a read alignment. [ 4 ] Each attribute denotes one bit in the binary representation of the integer.
The FLAG attributes are summed to get the final value, e.g. a SAM row resulting from an Illumina paired-end FASTQ record having the FLAG value 2145 would indicate:
From the specification for Sequence Alignment/Map Optional Fields Specification (SAMtags): [ 6 ]
The type may be one of A (character), C (integer 0-255), f (real number), H (hexadecimal array), i (integer), or Z (string). It may be a single value or B (general array). | https://en.wikipedia.org/wiki/SAM_(file_format) |
SAMtools is a set of utilities for interacting with and post-processing short DNA sequence read alignments in the SAM (Sequence Alignment/Map), BAM (Binary Alignment/Map) and CRAM formats, written by Heng Li . These files are generated as output by short read aligners like BWA . Both simple and advanced tools are provided, supporting complex tasks like variant calling and alignment viewing as well as sorting, indexing, data extraction and format conversion . [ 3 ] SAM files can be very large (tens of Gigabytes is common), so compression is used to save space. SAM files are human-readable text files, and BAM files are simply their binary equivalent, whilst CRAM files are a restructured column-oriented binary container format. BAM files are typically compressed and more efficient for software to work with than SAM. SAMtools makes it possible to work directly with a compressed BAM file, without having to uncompress the whole file. Additionally, since the format for a SAM/BAM file is somewhat complex - containing reads, references, alignments, quality information, and user-specified annotations - SAMtools reduces the effort needed to use SAM/BAM files by hiding low-level details.
As third-party projects were trying to use code from SAMtools despite it not being designed to be embedded in that way, the decision was taken in August 2014 to split the SAMtools package into a stand-alone software library with a well-defined API (HTSlib), [ 4 ] a project for variant calling and manipulation of variant data (BCFtools), and the stand-alone SAMtools package for working with sequence alignment data. [ 5 ]
Like many Unix commands, SAMtool commands follow a stream model, where data runs through each command as if carried on a conveyor belt . This allows combining multiple commands into a data processing pipeline. Although the final output can be very complex, only a limited number of simple commands are needed to produce it. If not specified, the standard streams (stdin, stdout, and stderr) are assumed. Data sent to stdout are printed to the screen by default but are easily redirected to another file using the normal Unix redirectors (> and >>), or to another command via a pipe (|).
SAMtools provides the following commands, each invoked as samtools <subcommand> :
Convert a bam file into a sam file.
Convert a sam file into a bam file. The -b option compresses or leaves compressed input data.
Extract all the reads aligned to the range specified, which are those that are aligned to the reference element named chr1 and cover its 10th, 11th, 12th or 13th base. The results is saved to a BAM file including the header. An index of the input file is required for extracting reads according to their mapping position in the reference genome, as created by samtools index .
Extract the same reads as above, but instead of displaying them, writes them to a new bam file, tiny_sorted.bam . The -b option makes the output compressed and the -h option causes the SAM headers to be output also. These headers include a description of the reference that the reads in sample_sorted.bam were aligned to and will be needed if the tiny_sorted.bam file is to be used with some of the more advanced SAMtools commands. The order of extracted reads is preserved.
Start an interactive viewer to visualize a small region of the reference, the reads aligned, and mismatches. Within the view, can jump to a new location by typing g: and a location, like g:chr1:10,000,000 . If the reference element name and following colon is replaced with = , the current reference element is used, i.e. if g:=10,000,200 is typed after the previous "goto" command, the viewer jumps to the region 200 base pairs down on chr1 . Typing ? brings up help information for scroll movement, colors, views, ...
Set start position and compare.
Save screen in .txt or .html.
Read the specified unsorted_in.bam as input, sort it by aligned read position, and write it out to sorted_out . Type of output can be either sam, bam, or cram, and will be determined automatically by sorted_out's file-extension.
Read the specified unsorted_in.bam as input, sort it in blocks up to 5 million k (5 Gb) [ units verification needed ] and write output to a series of bam files named sorted_out.0000.bam , sorted_out.0001.bam , etc., where all bam 0 reads come before any bam 1 read, etc. [ verification needed ]
Creates an index file, sorted.bam.bai for the sorted.bam file. | https://en.wikipedia.org/wiki/SAMtools |
SAO 206462 is a young binary star , surrounded by a circumstellar disc of gas and clearly defined spiral arms. It is situated about 440 light-years away from Earth in the constellation Lupus . [ 4 ] The presence of these spiral arms seems to be related to the existence of planets inside the disk of gas surrounding the star. The disk's diameter is about twice the size of the orbit of Pluto . [ 5 ]
The discovery of this object was presented in October 2011 by Carol Grady, astronomer of Eureka Scientific, headquartered in the Goddard Space Flight Center at NASA . It was the first of this class that exhibited a high degree of clarity and was made using several space telescopes ( Hubble , FUSE , Spitzer ) and earth telescopes ( Gemini Observatory and Subaru Telescope , situated in Hawaii ), through an international research program of young stars and of stars with planets. A number of astronomers of different observatories collaborated. [ 6 ]
The pair of spiral arms around SAO 206462 have a rotation rate of −0.85 degrees per year, which are thought to be caused by a dynamically driving protoplanet within the disk, at a distance of 66 ± 3 astronomical units and an orbital period of 424 ± 25 years . This planet should be a challenge to be detected using direct imaging due to the presence of dust particles obscuring it, but could be detected and confirmed via high-resolucion spectroscopic observations. [ 7 ]
Another planet candidate around SAO 206462 has been detected using observations of the JWST's NIRCam imaging instrument, with low signal-to-noise ratio , a mass of 0.8 ± 0.3 M J and a separation of 300 astronomical units. It has been dubbed CC1 (Companion candidate 1). Objects more massive than 2.2 M J at distance of 120 AU have been ruled out by the observations. [ 8 ] | https://en.wikipedia.org/wiki/SAO_206462 |
In computing, the SAP BW Accelerator is a computer appliance - preinstalled software on predefined hardware - which is used to speed up OLAP queries. [ 1 ] The software was initially known as the BI Accelerator .
SAP BW Accelerator includes indexes that are vertically inverted reproductions of all the data included in InfoCubes (i.e., fact and dimension tables as well as master data). [ 2 ] Note that there is no relational or other database management systems in BW Accelerator. There is only a file system, and indexes are essentially held as flat files. The second primary component of SAP BW Accelerator is the engine that processes the queries in memory - it uses the SAP TREX search engine . The software is running on an expandable rack of blade servers. The operating system used for BW Accelerator is 64-bit SUSE Linux Enterprise Server (SLES).
The software is optimized for specific hardware and operating system combinations.
The list of partners which deliver the appliance is:
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SAP_BI_Accelerator |
The SARS conspiracy theory began to emerge during the severe acute respiratory syndrome (SARS) outbreak in China in the spring of 2003, when Sergei Kolesnikov, [ 1 ] a Russian scientist and a member of the Russian Academy of Medical Sciences, first publicized his claim that the SARS coronavirus is a synthesis of measles and mumps . According to Kolesnikov, this combination cannot be formed in the natural world and thus the SARS virus must have been produced under laboratory conditions. Another Russian scientist, Nikolai Filatov, head of Moscow 's epidemiological services, had earlier commented that the SARS virus was probably man-made. [ 2 ] [ 3 ]
Circumstantial evidence suggests that the SARS virus crossed over to humans from Asian palm civets ("civet cats"), a type of animal that is often killed and eaten in Guangdong , where SARS was first discovered. [ 4 ] [ 5 ]
Tong Zeng , an activist with no medical background, authored the book The Last Defense Line: Concerns About the Loss of Chinese Genes , published in 2003. [ 6 ] In the book, Zeng suggested researchers from the United States may have created SARS as an anti-Chinese bioweapon after taking blood samples in China for a longevity study in the 1990s. [ 6 ] The book's hypothesis was a front-page report in the Guangzhou newspaper Southern Metropolis Daily . [ 6 ] | https://en.wikipedia.org/wiki/SARS_conspiracy_theory |
SASTRA-CNR Rao Award is an award instituted by SASTRA University , a private and deemed university in the town of Thirumalaisamudram , Thanjavur district , Tamil Nadu , to honor excellence in chemistry and material science , the two areas in which C N R Rao has made great, important and substantial contributions. The Award was instituted in 2013 and the first award was presented jointly to Suresh Das the then Director of National Institute for Interdisciplinary Science & Technology, Thiruvananthapuram and Sourav Pal , the Director of National Chemical Laboratory , Pune on 28 February 2014. [ 1 ] The award carries a cash prize of Rs. 5 lakh and a citation. | https://en.wikipedia.org/wiki/SASTRA-CNR_Rao_Award |
The Society of Allied Weight Engineers (SAWE) is a professional society of engineers that pertains to the specific field of Mass Properties .
The Society of Allied Weight Engineers is an international organization whose primary purpose is to promote the recognition of “Mass Properties Engineering” as a specialized branch of engineering. The Society is organized into 22 chapters with members from across the United States, Brazil, Europe, United Kingdom, and Canada. [ 1 ]
The Society of Aeronautical Weight Engineers was organized in 1939 in Los Angeles, California, and was incorporated as a nonprofit organization April 2, 1941. As membership grew to include engineers associated with shipbuilding, land transportation, and other allied industries and technologies, the Society name was changed on January 1, 1973 to the Society of Allied Weight Engineers, Inc. [ 1 ]
The Society offers to members and industry a medium for the pooling and exchange of data and experience at local and regional levels, fostering a higher degree of efficiency in Mass Properties Engineering topics. Regular chapter, regional and international meetings provide an opportunity for mass properties engineers to meet and to discuss mutual problems, procedures and specifications, thus broadening their individual horizons and becoming better informed.
The aims of the Society are focused on several key areas, among which are: [ 1 ]
Think for a moment about the latest new milestone in technology in the news today: an innovative new fuel efficient car, the next-generation fighter jet for the US Air Force, the newest nuclear-powered aircraft carrier for the 21st century, a new high resolution imaging satellite, an advanced unmanned underwater vehicle for national defense, the first commercial cargo transportation vehicle to service the International Space Station, or the world's largest commercial airliner... what do they all have in common?
They all rely on Mass Properties Engineering for their success. Mass Properties Engineering refers to the prediction, determination, management, and tracking of weight, centers of gravity, moments of inertia, and products of inertia for any new vehicle; which are critical factors for determination of its performance and capabilities. Mass Properties Engineering, a.k.a. “Weight Engineering”, is the technical discipline that balances the weight and moment of every component of a product to ensure that it functions safely, efficiently, and economically. Behind just about every technological achievement is a successful application of Mass Properties Engineering.
Mass Properties Engineers are creative thinkers who use math and science to solve problems. They come from a variety of backgrounds: aerospace engineering, ocean engineering, automotive engineering, naval architecture, materials engineering, mechanical engineering, math or physics; to name just a few. Still others come from operational backgrounds in the military, or other technical fields like teaching or production. However, they all share a common interest in making things work by successfully integrating the efforts from many diverse technical disciplines and blending them into an effective solution for all. [ 1 ]
As noted, since 1939 the Society of Allied Weight Engineers has been promoting recognition of Mass Properties Engineering as a specialized discipline. One principal method of accomplishing this is to make technical content available to its members. The SAWE publishes technical papers and proceedings from International Conferences through its "Weight Engineering Journal" and on the Internet. The SAWE has produced college level text books covering aircraft and marine mass properties engineering. The SAWE also publishes the "Weight Engineer's Handbook", a collection of engineering formulas and data, used as a reference by engineers of all disciplines. [ 1 ]
The SAWE creates Standards and Recommended Practices for the mass properties design and acquisition communities. The SAWE is the professional society which integrates mass properties best practices across all the transportation sectors: air, sea, space, and ground. The Society Standards effort is international in scope and compliant with modern Open Development of Standards Processes. Recommended Practices will usually, though not always, arise out of the activity of groups within SAWE such as the Standards and Practices Committee. The Recommended Practices will represent the consensus and expertise of the group regarding such topics as design criteria, matters of procedure, etc.; which, when approved by the Board of Directors, are made available as Standard Practices Recommended by SAWE. The present list of Recommended Practices includes: [ 1 ]
Technical papers, textbooks, the handbook, and Recommended Practices are available for purchase from the Society on-line. Recommended Practices and technical papers are available free on-line to the Society members.
The SAWE has developed and offered a number of unique training classes at Regional and International Conferences. These SAWE classes have been offered to further the educational development and broaden the experience of those engaged in the field of Mass Properties Engineering. The goal of the Society has been to offer training classes at a reasonable price so that the greatest number of the Societies membership can experience these opportunities. The SAWE will also present classes on-site through special arrangement, and has embarked on a program of on-line classes. The on-line classes include:
The complete list of classes given by the SAWE is as follows (for details see the SAWE training website referenced at end of this article):
The SAWE sponsors a yearly International Conference which can be domestically (U.S.) hosted or hosted by a foreign chapter. The 2011 70th SAWE International Conference will be held in Houston, Texas on 14–19 May, and the 2012 71st SAWE International Conference will be held in Manching, Germany. Local chapters, of which there are 22 in number, can also sponsor Regional Conferences, such as the 2010 South West Regional to be held in Ventura, California 12–13 November. Such conferences typically involve presentations of technical papers, displays by venders, officer meetings, training classes, awards ceremonies, and various social activities.
Honorary Fellow : Honorary Fellowship is awarded to persons who have achieved eminence in Mass Properties Engineering or who have made outstanding contributions to the advancement of the Society.
Fellow : Fellowship is awarded to persons who have achieved distinction in the field of Mass Properties Engineering or who have materially contributed to the advancement of the Society.
Ed Payne Award : The Ed Payne Award is presented to young engineers, under the age of 35 at time of application, who have made significant contributions to the SAWE or the mass properties engineering profession.
L. R. "Mike" Hackney Award : The L. R. "Mike" Hackney Award is given to the author or authors of the best technical paper presented at the International Conference. Papers are judged for technical content, originality, usefulness, value, clarity, style, and form. Balloting is by each member of the Technical Committee.
Special Merit Award : Occasionally an award is given due to the significance of an achievement or the exceptional merit of a technical paper.
SAWE Scholarship : The SAWE has also established a scholarship fund for engineering students with the principal growing by donations from individuals, chapters, and corporations as well as by sale of our popular Introduction to Weight Engineering textbook. To date, the Society has established endowments at three universities; each provides $1,000 scholarships annually. The first such scholarship was endowed at the University of Texas at Arlington by the Texas Chapter in 1989. The Society has also endowed permanent annual scholarships at West Virginia University in 1999 and at Wichita State University in 2000. In addition, a scholarship award of $1,000 has been given annually since 1994 to an engineering student interested in mass properties engineering at a university within the geographic area of the annual International Conference. The SAWE chapter that hosts the annual International Conference selects the university receiving this annual scholarship money.
The SAWE introduced a scholarship program in 2002 for children and grandchildren of SAWE members who plan to continue their education in college. This program annually distributes scholarships to children of SAWE members. Scholarships are offered for full-time undergraduate course of study at an accredited four-year college or university in a curriculum of the student's choice.
Frank Fong Scholarship : The SAWE/Frank Fong Memorial Scholarship was established by SAWE and the family of SAWE past-President Frank Fong in 2005. The requirements are the same as the SAWE Scholarship, but this scholarship is dedicated to students enrolled in a technical course of study (e.g.: engineering, physics, mathematics, computer sciences, etc.).
Louis B. Popovich (Author of “Weight Engineering, Design Techniques for Weight Reduction”).
Richard Boynton (Founder of Space Electronics INC, namesake of the Richard Boynton Lifetime Achievement Award).
Edward L. Payne (Charter Member of the SAWE who mentored many early young members of the Society, namesake of the Ed Payne Award for young engineers who have made significant contributions).
Lyle R. "Mike" Hackney (Charter Member and co-founder of the SAWE, served as the first president of the Society and chaired the very first conference, namesake of the L. R. Hackney Award for best technical paper presented at International Conference) | https://en.wikipedia.org/wiki/SAWE |
SB-236057 is a compound which is a potent and selective inverse agonist for the serotonin receptor 5-HT 1B , acting especially at 5-HT 1B autoreceptors on nerve terminals. It produces a rapid increase in serotonin levels in the brain, and was originally researched as a potential antidepressant . [ 1 ] [ 2 ] However subsequent research found that SB-236,057 also acts as a potent teratogen , producing severe musculoskeletal birth defects when rodents were exposed to it during pregnancy. This has made it of little use for research into its original applications, yet has made it useful for studying embryonic development instead. [ 3 ] [ 4 ]
This drug article relating to the nervous system is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SB-236057 |
The Systems Biology Markup Language ( SBML ) is a representation format, based on XML , for communicating and storing computational models of biological processes. [ 1 ] It is a free and open standard with widespread software support and a community of users and developers. SBML can represent many different classes of biological phenomena , including metabolic networks , cell signaling pathways, regulatory networks , infectious diseases , and many others. [ 2 ] [ 3 ] [ 4 ] It has been proposed as a standard for representing computational models in systems biology today. [ 4 ]
Late in the year 1999 through early 2000, with funding from the Japan Science and Technology Corporation (JST), Hiroaki Kitano and John C. Doyle assembled a small team of researchers to work on developing better software infrastructure for computational modeling in systems biology . Hamid Bolouri was the leader of the development team, which consisted of Andrew Finney, Herbert Sauro, and Michael Hucka. [ 5 ] Bolouri identified the need for a framework to enable interoperability and sharing between the different simulation software systems for biology in existence during the late 1990s, and he organized an informal workshop in December 1999 at the California Institute of Technology to discuss the matter. In attendance at that workshop were the groups responsible for the development of DBSolve, E-Cell, Gepasi, Jarnac, StochSim, and The Virtual Cell. Separately, earlier in 1999, some members of these groups also had discussed the creation of a portable file format for metabolic network models in the BioThermoKinetics (BTK) group. [ 6 ] [ 7 ] The same groups who attended the first Caltech workshop met again on April 28–29, 2000, at the first of a newly created meeting series called Workshop on Software Platforms for Systems Biology . [ 8 ] It became clear during the second workshop that a common model representation format was needed to enable the exchange of models between software tools as part of any functioning interoperability framework, and the workshop attendees decided the format should be encoded in XML .
The Caltech ERATO team developed a proposal for this XML-based format and circulated the draft definition to the attendees of the 2nd Workshop on Software Platforms for Systems Biology in August 2000. This draft underwent extensive discussion over mailing lists and during the 2nd Workshop on Software Platforms for Systems Biology, [ 9 ] held in Tokyo , Japan, in November 2000 as a satellite workshop of the ICSB 2000 conference. After further revisions, discussions and software implementations, the Caltech team issued a specification for SBML Level 1, Version 1 in March 2001.
SBML Level 2 was conceived at the 5th Workshop on Software Platforms for Systems Biology, held in July 2002, at the University of Hertfordshire , UK. [ 10 ] By this time, far more people were involved than the original group of SBML collaborators and the continued evolution of SBML became a larger community effort, with many new tools having been enhanced to support SBML. The workshop participants in 2002 collectively decided to revise the form of SBML in Level 2. The first draft of the Level 2 Version 1 specification was released in August 2002, and the final set of features was finalized in May 2003 at the 7th Workshop on Software Platforms for Systems Biology in Ft. Lauderdale , Florida.
The next iteration of SBML took two years in part because software developers requested time to absorb and understand the larger and more complex SBML Level 2. The inevitable discovery of limitations and errors led to the development of SBML Level 2 Version 2, issued in September 2006. By this time, the team of SBML Editors (who reconcile proposals for changes and write a coherent final specification document) had changed and now consisted of Andrew Finney, Michael Hucka and Nicolas Le Novère.
SBML Level 2 Version 3 was published in 2007 after countless contributions by and discussions with the SBML community. 2007 also saw the election of two more SBML Editors as part of the introduction of the modern SBML Editor organization in the context of the SBML development process.
SBML Level 2 Version 4 was published in 2008 after certain changes in Level 2 were requested by popular demand. (For example, an electronic vote by the SBML community in late 2007 indicated a majority preferred not to require strict unit consistency before an SBML model is considered valid.) Version 4 was finalized after the SBML Forum meeting held in Gothenburg , Sweden, as a satellite workshop of ICSB 2008 in the fall of 2008. [ 11 ]
SBML Level 3 Version 1 Core was published in final form in 2010, after prolonged discussion and revision by the SBML Editors and the SBML community. It contains numerous significant changes in syntax and constructs from Level 2 Version 4, but also represents a new modular base for continued expansion of SBML's features and capabilities going into the future.
SBML Level 2 Version 5 was published in 2015. This revision included a number of textual (but not structural) changes in response to user feedback, thereby addressing the list of errata collected over many years for the SBML Level 2 Version 4 specification. In addition, Version 5 introduced a facility to use nested annotations within SBML's annotation format (an annotation format that is based on a subset of RDF ).
SBML is sometimes incorrectly assumed to be limited in scope only to biochemical network models because the original publications and early software focused on this domain. In reality, although the central features of SBML are indeed oriented towards representing chemical reaction-like processes that act on entities, this same formalism serves analogously for many other types of processes; moreover, SBML has language features supporting the direct expression of mathematical formulas and discontinuous events separate from reaction processes, allowing SBML to represent much more than solely biochemical reactions. Evidence for SBML's ability to be used for more than merely descriptions of biochemistry can be seen in the variety of models available from BioModels Database .
SBML has three main purposes:
SBML is not an attempt to define a universal language for quantitative models. SBML's purpose is to serve as a lingua franca —an exchange format used by different present-day software tools to communicate the essential aspects of a computational model. [ 12 ]
SBML can encode models consisting of entities (called species in SBML) acted upon by processes (called reactions ). An important principle is that models are decomposed into explicitly-labeled constituent elements, the set of which resembles a verbose rendition of chemical reaction equations (if the model uses reactions) together with optional explicit equations (again, if the model uses these); the SBML representation deliberately does not cast the model directly into a set of differential equations or other specific interpretation of the model. This explicit, modeling-framework-agnostic decomposition makes it easier for a software tool to interpret the model and translate the SBML form into whatever internal form the tool actually uses.
A software package can read an SBML model description and translate it into its own internal format for model analysis. For example, a package might provide the ability to simulate the model by constructing differential equations and then perform numerical time integration on the equations to explore the model's dynamic behavior. Or, alternatively, a package might construct a discrete stochastic representation of the model and use a Monte Carlo simulation method such as the Gillespie algorithm .
SBML allows models of arbitrary complexity to be represented. Each type of component in a model is described using a specific type of data structure that organizes the relevant information. The data structures determine how the resulting model is encoded in XML.
In addition to the elements above, another important feature of SBML is that every entity can have machine-readable annotations attached to it. These annotations can be used to express relationships between the entities in a given model and entities in external resources such as databases. A good example of the value of this is in BioModels Database, where every model is annotated and linked to relevant data resources such as publications, databases of compounds and pathways, controlled vocabularies, and more. With annotations, a model becomes more than simply a rendition of a mathematical construct—it becomes a semantically-enriched framework for communicating knowledge. [ 13 ] [ 14 ]
SBML is defined in Levels : upward-compatible specifications that add features and expressive power. Software tools that do not need or cannot support the complexity of higher Levels can go on using lower Levels; tools that can read higher Levels are assured of also being able to interpret models defined in the lower Levels. Thus new Levels do not supersede previous ones. However, each Level can have multiple Versions within it, and new Versions of a Level do supersede old Versions of that same Level.
There are currently three Levels of SBML defined. The current Versions within those Levels are the following:
Open-source software infrastructure such as libSBML and JSBML allows developers to support all Levels of SBML their software with a minimum amount of effort.
The SBML Team maintains a public issue tracker where readers may report errors or other issues in the SBML specification documents. Reported issues are eventually put on the list of official errata associated with each specification release. The lists of errata are documented on the Specifications page of SBML.org.
Development of SBML Level 3 has been proceeding in a modular fashion. The Core specification is a complete format that can be used alone. Additional Level 3 packages can be layered on to this core to provide additional, optional features.
The Hierarchical Model Composition package, known as " comp ", was released in November 2012. This package provides
the ability to include models as submodels inside another model. The goal is to support the ability
of modelers and software tools to do such things as (1) decompose larger models into smaller ones,
as a way to manage complexity; (2) incorporate multiple instances of a given model within one or more
enclosing models, to avoid literal duplication of repeated elements; and (3) create libraries of reusable,
tested models, much as is done in software development and other engineering fields. The specification was the culmination
of years of discussion by a wide number of people.
The Flux Balance Constraints package (nicknamed " fbc ") was first released
in February, 2013. Import revisions were introduced as part of
Version 2, [ 15 ] released in September, 2015. The
" fbc " package provides support for constraint-based modeling, [ 16 ] frequently used to analyze and study biological networks on
both a small and large scale. [ 17 ] This SBML package makes use of
standard components from the SBML Level 3 core specification, including
species and reactions, and extends them with additional attributes and
structures to allow modelers to define such things as flux bounds and
optimization functions.
The Qualitative Models or " qual " package for SBML Level 3 was
released in May 2013. This package supports the representation of models where an
in-depth knowledge of the biochemical reactions and their kinetics is missing
and a qualitative approach must be used. Examples of phenomena that have
been modeled in this way include gene regulatory networks [ 18 ] and signaling pathways, [ 19 ] basing the model structure on
the definition of regulatory or influence graphs. The definition and use of
some components of this class of models differ from the way that species and
reactions are defined and used in core SBML models. For example,
qualitative models typically associate discrete levels of activities with
entity pools; consequently, the processes involving them cannot be described
as reactions per se, but rather as transitions between states. These systems
can be viewed as reactive systems whose dynamics are represented by means of
state transition graphs (or other Kripke structures [ 20 ] ) in
which the nodes are the reachable states and the edges are the state
transitions.
The SBML layout package originated as a set of annotation conventions
usable in SBML Level 2. It was introduced at the SBML Forum in
St. Louis in 2004. [ 21 ] Ralph Gauges wrote the
specification [ 22 ] and provided an implementation that
was widely used. This original definition was reformulated as an SBML
Level 3 package, and a specification was formally released in August,
2013.
The SBML Level 3 Layout package provides a specification for how to
represent a reaction network in a graphical form. It is thus better tailored
to the task than the use of an arbitrary drawing or graph. The SBML
Level 3 package only deals with the information necessary to define the
position and other aspects of a graph's layout; the additional details
necessary to complete the graph—namely, how the visual aspects are meant
to be rendered— are the purview of the separate SBML Level 3
package called Rendering (nicknamed " render "). As of November 2015, a draft
specification for the " render " package is available, but it has not yet been
officially finalized. [ 23 ]
Development of SBML Level 3 packages is being undertaken such that specifications are reviewed and implementations
attempted during the development process. Once a specification is stable and there are two implementations that support it,
the package is considered accepted. The packages detailed above have all reached the acceptance stage.
The table below gives a brief summary of packages that are currently in the development phase.
A model definition in SBML Levels 2 and 3 consists of lists of one or more of the following components:
SBML is primarily a format for the exchange of systems biology models between software modeling tools or for archiving models in repositories such as BiGG , BioModels , or JWS Online . Since SBML is encoded in XML and in particular uses MathML for representing mathematics, the format is not human-readable. As a result, other groups have developed human-readable formats that can be converted to and from SBML.
SBML shorthand is a specification and associated Python tooling to interconvert SBML and the shorthand notation. The format was developed by the UK Newcastle systems biology group sometime before 2006. [ 24 ] Its aim was to enable modelers to more rapidly create models without having to either write raw XML or use GUI tools. Two Python tools are provided, mod2sbml.py and sbml2mod.py. The libSBML package for Python is required to assist in the conversion. Currently, SBML-shorthand supports SBML Level 3, version 1.
The following code is an example of SBML-shorthand being used to describe the simple enzyme-substrate mechanism.
Antimony is based on an earlier DSL implemented in the Jarnac modeling application. [ 25 ] That, in turn, was based on the SCAMP modeling application [ 26 ] which ultimately drew inspiration from the DSL language developed by David Garfinkel for the BIOSIM simulator. [ 27 ]
Like SBML-shorthand, Antimony provides a simplified text representation of SBML. It uses a minimum of punctuation characters which renders the text easier to read and understand. It also allows users to add comments. Antimony is implemented using C/C++ [ 28 ] and Bison as the grammar parser. However, the distribution also includes Python bindings which can be installed using pip to make it easy to use from Python. It is also available via the Tellurium package. [ 29 ] More recently, a JavaScript/WASM version [ 30 ] has been generated which allows the Antimony language to be used on the web. The website tool makesbml uses the Javascript version. [ 31 ] Antimony supports SBML Level 3, version 2. Antimony also supports the following SBML packages: Hierarchical Model Composition, Flux Balance Constraints, and Distributions.
The following example illustrates Antimony being used to describe a simple enzyme-kinetics model:
As of February 2020, nearly 300 software systems advertise support for SBML. A current list is available in the form of the SBML Software Guide , hosted at SBML.org.
SBML has been and continues to be developed by the community of people making software platforms for systems biology, through active email discussion lists and biannual workshops. The meetings are often held in conjunction with other biology conferences, especially the International Conference on Systems Biology (ICSB). The community effort is coordinated by an elected editorial board made up of five members. Each editor is elected for a 3-year non-renewable term.
Tools such as an online model validator as well as open-source libraries for incorporating SBML into software programmed in the C , C++ , Java , Python , Mathematica , MATLAB and other languages are developed partly by the SBML Team and partly by the broader SBML community. [ 32 ]
SBML is an official IETF MIME type, specified by RFC 3823. [ 33 ] | https://en.wikipedia.org/wiki/SBML |
The Streptavidin-Binding Peptide (SBP)-Tag is a 38- amino acid sequence that may be engineered into recombinant proteins . Recombinant proteins containing the SBP-Tag bind to streptavidin and this property may be utilized in specific purification, detection or immobilization strategies. [ citation needed ]
The sequence of the SBP tag is MDEKTTGWRGGHVVEGLAGELEQLRARLEHHPQGQREP. [ 1 ]
The Streptavidin-Binding Peptide was discovered within a library of seven trillion stochastically generated peptides using the in vitro selection technique of mRNA Display . Selection was performed by incubating with streptavidin-agarose followed by elution with biotin . [ 2 ] The SBP-Tag has been shown to bind streptavidin with an equilibrium dissociation constant of 2.5nM [ 1 ] [ 2 ] and is readily eluted with biotin under native conditions. [ 1 ] [ 2 ]
Because of the mild elution conditions (biotin plus wash buffer) SBP-Tagged proteins can be generated in a relatively pure state with a single purification step. [ 1 ] [ 3 ] [ 4 ] There are several relatively abundant mammalian proteins that inherently associate with the IMAC matrices that bind to the more commonly used Polyhistidine-tag (His-tag). For this reason non-IMAC purification protocols, including with the SBP-Tag, are often preferred for proteins that are expressed in mammalian cells. [ citation needed ]
Complexes of interacting proteins may also be purified using the SBP-Tag because elution with biotin permits recovery under conditions in which desired complexes remain associated. For example, the Condensin Complex was purified by Kim et al. [2010] and complexes with the TAZ transcriptional co-activator were purified by Zhang et al. [2009]. The SBP-Tag has also been incorporated into several Tandem Affinity Purification (TAP) systems in which successive purification steps are utilized with multiple tags, for example GFP fusion proteins and BTK -protein complexes were purified using a TAP protocol with the SBP-Tag and the His-Tag, [ 5 ] [ 6 ] HDGF -protein complexes were purified using a TAP protocol with the SBP-Tag and with the FLAG-tag [ 7 ] and Wnt complexes were purified using a TAP protocol with the SBP-Tag and with the [Calmodulin-Tag]. [ 8 ] TAP is generally used with protein complexes and several studies report significant improvements in purity and yield when the SBP-Tag TAP systems are compared to non-SBP-Tag systems. [ 9 ] [ 10 ] [ 11 ] Commercial TAP systems that use the SBP-Tag include the Interplay® Adenoviral and Mammalian TAP Systems sold by Agilent Technologies , similar products are sold by Sigma-Aldrich . [ 12 ]
Screens for biologically relevant protein-protein interactions have been performed using Tandem Affinity Purification (TAP) with the SBP-Tag and Protein A , [ 10 ] for interaction proteomics and transcription factor complexes with the SBP-Tag and Protein G , [ 10 ] [ 13 ] for proteins that interact with the Dengue Virus protein DENV-2 NS4A with the SBP-Tag and the Calmodulin Tag. [ 14 ] and for proteins that interact with protein phosphatase 2A (PP2A) with the SBP-Tag and the hemagglutinin (HA)-tag. [ 11 ]
The SBP-Tag will also bind to streptavidin or streptavidin reagents in solution. Applications of these engineered associations include the visualization of specific proteins within living cells, [ 15 ] monitoring of the kinetics of the translation of individual proteins in an in vitro translation system, [ 16 ] control of the integration of a multi-spanning membrane protein into the endoplasmic reticulum by fusing the SBP-Tag to the N-terminal translocation sequence and then halting integration with streptavidin and restarting integration with biotin. [ 17 ] [ 18 ] Fluorescent streptavidin reagents (e.g. streptavidin-HRP) can be used to visualize the SBP-tag by immunoblotting of SDS-PAGE. [ 1 ] [ 19 ] [ 20 ] Additionally, antibodies to the SBP-tag are available commercially. [ citation needed ]
The SBP-Tag has been used to reversibly immobilize recombinant proteins onto streptavidin-functionalized surfaces thereby permitting interaction assessment such as by surface plasmon resonance (SPR) techniques with re-use of the functionalized surface. [ 21 ] SPR has also been used to compare the SBP-Tag with other streptavidin-binding peptides such as Strep-tag . [ 22 ] | https://en.wikipedia.org/wiki/SBP-tag |
SB buffer is a buffer solution used in agarose and polyacrylamide gel electrophoresis for the separation of nucleic acids such as DNA and RNA . "SB" is a commercial trademark of Faster Better Media LLC for their sodium boric acid-based conductive medium (US Patent # 7811437), which is based on the publications of Brody and Kern.
It is made up of sodium borate , usually 1–10 mM at pH 8.0. It has a lower conductivity , produces sharper bands, and can be run at higher speeds than can gels made from TBE buffer or TAE buffer (5–35 V /cm as compared to 5–10 V/cm). At a given voltage, heat will be generated and thus the gel will be heated. However, SB buffer has lower conductivity than TBE and TAE, and thus the gel temperature is much lower than with TBE or TAE buffers. Therefore, the voltage can be increased to speed up electrophoresis so that a gel run takes only a fraction of the usual time. Downstream applications, such as isolation of DNA from a gel slice or southern blot analysis, work as expected with sodium borate gels.
LB buffer containing lithium borate is similar to sodium borate and has all of its advantages, but permits use of even higher voltages due to the lower conductivity of lithium ions as compared to sodium ions. [ 1 ] However, lithium borate is somewhat more expensive.
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SB_buffer |
The SCARA is a type of industrial robot . The acronym stands for selective compliance assembly robot arm [ 1 ] or selective compliance articulated robot arm . [ 2 ]
By virtue of the SCARA's parallel-axis joint layout, the arm is slightly compliant in the X-Y direction but rigid in the Z direction, hence the term selective compliance . This is advantageous for many types of assembly operations, for example, inserting a round pin in a round hole without binding.
The second attribute of the SCARA is the jointed two-link arm layout similar to human arms , hence the often-used term, articulated . This feature allows the arm to extend into confined areas and then retract or "fold up" out of the way. This is advantageous for transferring parts from one cell to another or for loading or unloading process stations that are enclosed.
SCARAs are generally faster than comparable Cartesian robot systems. Their single pedestal mount requires a small footprint and provides an easy, unhindered form of mounting. On the other hand, SCARAs can be more expensive than comparable Cartesian systems and the controlling software requires inverse kinematics for linear interpolated moves. However, this software typically comes with the SCARA and is usually transparent to the end-user. [ 3 ]
Sankyo Seiki , Pentel and NEC presented the SCARA robot as a completely new concept for assembly robots in 1981. The robot was developed under the guidance of Hiroshi Makino, [ 4 ] a professor at the University of Yamanashi . [ 2 ] Its arm was rigid in the Z-axis and pliable in the XY-axes, which allowed it to adapt to holes in the XY-axes. [ 5 ] [ 6 ]
The SCARA robot concept was inspired by the presentation of the SIGMA robot for assembly by A. d'Auria at the 7th International Symposium on Robotics in Tokyo , in October 1977. This presentation had a significant impact on engineers in Japan studying assembly automation, prompting Hiroshi Makino to begin working on the SCARA robot design shortly after this event. [ 7 ]
The first SCARA prototype was built in 1978, followed by a second prototype in 1980. Fundamental studies were conducted on the characteristics and usability of these prototypes, which led to the development of SCARA robots by the industry in 1981. [ 7 ]
The development of SCARA robots was the result of a research and development consortium launched by the University of Yamanashi and thirteen Japanese companies. This consortium operated for three years, from April 1978 to March 1981, contributing to the success of SCARA robots in industrial applications. [ 7 ]
As recognition of its importance in the field of robotics , the SCARA robot was included in the Robot Hall of Fame in 2006, becoming the second industrial robot and the third Japanese robot to be included. [ 7 ] | https://en.wikipedia.org/wiki/SCARA |
SCC mec , or staphylococcal cassette chromosome mec , is a mobile genetic element of Staphylococcus bacterial species. This genetic sequence includes the mecA gene coding for resistance to the antibiotic methicillin and is the only known way for Staphylococcus strains to spread the gene in the wild by horizontal gene transfer . [ 1 ] SCC mec is a 21 to 60 kb long genetic element that confers broad-spectrum β-lactam resistance to MRSA. [ 2 ] Moreover, additional genetic elements like Tn 554 , pT181, and pUB110 can be found in SCC mec, which have the capability to render resistance to various non-β-lactam drugs. [ 3 ]
Not all SCC mec elements are identical (in fact, SCC elements without the mecA gene do exist. [ 4 ] ) As of December 2021, SCCmec elements have been classified into fourteen types (I through XIV). [ 5 ] One region is the mec complex including the mecA gene. The other is the ccr gene complex including genes coding for recombinases . [ 6 ]
The mec complex is divided further into five types (I through V) based on the arrangement of regulatory genetic features such as mecR1 , an inducer . [ 7 ] The mec gene complex in SCC mec , comprising mec gene, its regulators ( mecR1 , mecI ), and insertion sequences (IS), is categorized into five classes (A to E). Class A includes mecA , full mecR1 , mecI , and IS 431 . Class B has IS 1272 , mecA , partial mecR1 , and IS 431 . Class C, with two versions (C1, C2), contains mecA , partial mecR1 , IS 431 , differing in IS 431 orientation. Class D includes IS 431 , mecA , partial mecR1 ; Class E consists of blaZ , mecC , mecR1 , mecI . [ 7 ] [ 8 ] [ 9 ]
The ccr and mec gene complexes in SCC mec are connected by joining (J) regions, considered non-essential but capable of carrying extra antimicrobial resistance determinants. [ 10 ] [ 11 ] These are categorized as J1, J2, and J3, based on their SCC mec positions. J1, also known as the L-C region, lies between the right chromosomal junction and upstream of the ccr gene. J2, previously the C-M region, is situated between the ccr and mec gene complexes. J3 (formerly the I-R region) is found downstream of the mec gene complex, extending to the left chromosomal junction. [ 12 ]
The SCC mec found in methicillin-resistant Staphylococcus aureus likely originated in coagulase -negative staphylococcal species and was acquired by S. aureus . [ 13 ]
Staphylococcal strains isolated from pig farms were found to carry several different types of SCC mec , suggesting that they may serve as a reservoir of these elements. [ 14 ]
This genetics article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SCCmec |
SCICEX , standing for Scientific Ice Expeditions , was a five-year (1995–1999) scientific research program involving a collaboration between the U.S. Navy and academic researchers from a variety of different universities. The object of study was geophysical and oceanological conditions in the Arctic Ocean . The Navy made available a nuclear submarine for each research cruise.
Margo Edwards was the chief scientist for the 1999 expedition [ 1 ] and spent thirteen days on the USS Hawkbill , thereby becoming the first women to live aboard a Navy nuclear submarine during under-ice operations. [ 2 ] Edwards' research found evidence of climate change in the Arctic, including thinning sea ice, [ 3 ] volcanoes on the seafloor, [ 4 ] and warm water moving into the Arctic from the Atlantic Ocean. [ 2 ] These data are available for anyone to view. [ 5 ]
This oceanography article is a stub . You can help Wikipedia by expanding it .
This Arctic -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SCICEX |
Mass spectrometry is a scientific technique for measuring the mass-to-charge ratio of ions. It is often coupled to chromatographic techniques such as gas- or liquid chromatography and has found widespread adoption in the fields of analytical chemistry and biochemistry where it can be used to identify and characterize small molecules and proteins ( proteomics ). The large volume of data produced in a typical mass spectrometry experiment requires that computers be used for data storage and processing. Over the years, different manufacturers of mass spectrometers have developed various proprietary data formats for handling such data which makes it difficult for academic scientists to directly manipulate their data. To address this limitation, several open , XML -based data formats have recently been developed by the Trans-Proteomic Pipeline at the Institute for Systems Biology to facilitate data manipulation and innovation in the public sector. [ 1 ] These data formats are described here.
This format was one of the earliest attempts to supply a standardized file format for data exchange in mass spectrometry. JCAMP-DX was initially developed for infrared spectrometry. JCAMP-DX is an ASCII based format and therefore not very compact even though it includes standards for file compression. JCAMP was officially released in 1988. [ 2 ] Together with the American Society for Mass Spectrometry a JCAMP-DX format for mass spectrometry was developed with aim to preserve legacy data. [ 3 ]
The Analytical Data Interchange Format for Mass Spectrometry is a format for exchanging data. Many mass spectrometry software packages can read or write ANDI files. ANDI is specified in the ASTM E1947 Standard. [ 4 ] ANDI is based on netCDF which is a software tool library for writing and reading data files. ANDI was initially developed for chromatography-MS data and therefore was not used in the proteomics gold rush where new formats based on XML were developed. [ 5 ]
AnIML is a joined effort of IUPAC and ASTM International to create an XML based standard that covers a wide variety of analytical techniques including mass spectrometry. [ 6 ]
mzData was the first attempt by the Proteomics Standards Initiative (PSI) from the Human Proteome Organization (HUPO) to create a standardized format for Mass Spectrometry data. [ 7 ] This format is now deprecated, and replaced by mzML. [ 8 ]
mzXML is a XML (eXtensible Markup Language) based common file format for proteomics mass spectrometric data. [ 9 ] [ 10 ] This format was developed at the Seattle Proteome Center/Institute for Systems Biology while the HUPO-PSI was trying to specify the standardized mzData format, and is still in use in the proteomics community.
Y et A nother F ormat for M ass S pectrometry (YAFMS) is a suggestion to save data in four table relational server-less database schema with data extraction and appending being exercised using SQL queries. [ 11 ]
As two formats (mzData and mzXML) for representing the same information is an undesirable state, a joint effort was set by HUPO-PSI, the SPC/ISB and instrument vendors to create a unified standard borrowing the best aspects of both mzData and mzXML, and intended to replace them. Originally called dataXML, it was officially announced as mzML. [ 12 ] The first specification was published in June 2008. [ 13 ] This format was officially released at the 2008 American Society for Mass Spectrometry Meeting, and is since then relatively stable with very few updates.
On 1 June 2009, mzML 1.1.0 was released. There are no planned further changes as of 2013.
Instead of defining new file formats and writing converters for proprietary vendor formats a group of scientists proposed to define a common application program interface to shift the burden of standards compliance to the instrument manufacturers' existing data access libraries. [ 14 ]
The mz5 format addresses the performance problems of the previous XML based formats. It uses the mzML ontology, but saves the data using the HDF5 backend for reduced storage space requirements and improved read/write speed. [ 15 ]
The imzML standard was proposed to exchange data from mass spectrometry imaging in a standardized XML file based on the mzML ontology. It splits experimental data into XML and spectral data in a binary file. Both files are linked by a universally unique identifier . [ 16 ]
mzDB saves data in an SQLite database to save on storage space and improve access times as the data points can be queried from a relational database . [ 17 ]
Toffee is an open lossless file format for data-independent acquisition mass spectrometry. It leverages HDF5 and aims to achieve file sizes similar to those from the proprietary and closed vendor formats. [ 18 ]
mzMLb is another take on using a HDF5 backend for performant raw data saving. It, however, preserves the mzML XML data structure and stays compliant to the existing standard. [ 19 ]
The Allotrope Foundation curates a HDF5 and Triplestore based file format named Allotrope Data Format (ADF) and a flat JSON representation ASM short for Allotrope Simple Model. Both are based on the Allotrope Foundation Ontologies (AFO) and contain schemas for mass spectrometry and chromatography coupled with MS detectors. [ 20 ]
Below is a table of different file format extensions.
(*) Note that the RAW formats of each vendor are not interchangeable; software from one cannot handle the RAW files from another. (**) Micromass was acquired by Waters in 1997 (***) Finnigan is a division of Thermo
There are several viewers for mzXML, mzML and mzData. These viewers are of two types: Free Open Source Software (FOSS) or proprietary.
In the FOSS viewer category, one can find MZmine, [ 22 ] mineXpert2 (mzXML, mzML, native timsTOF, xy, MGF, BafAscii) [ 23 ] MS-Spectre, [ 24 ] TOPPView (mzXML, mzML and mzData), [ 25 ] Spectra Viewer, [ 26 ] SeeMS, [ 27 ] msInspect, [ 28 ] jmzML. [ 29 ]
In the proprietary category, one can find PEAKS, [ 30 ] Insilicos , [ 31 ] Mascot Distiller, [ 32 ] Elsci Peaksel. [ 33 ]
There is a viewer for ITA images. [ 34 ] ITA and ITM images can be parsed with the pySPM python library. [ 35 ]
Known converters for mzData to mzXML:
Known converters for mzXML:
Known converters for mzML:
Converters for proprietary formats:
Currently available converters are : | https://en.wikipedia.org/wiki/SCIEX/ABI_Analyst |
SLP65/SLP76, Csk -interacting membrane protein, termed SCIMP, belongs to family of transmembrane adaptor proteins (TRAP) which do not directly associate with a receptor, such as LAT , NTAL , LIME or LAX . [ 1 ] [ 2 ] [ 3 ] [ 4 ] SCIMP is expressed in antigen-presenting cells (APC), namely B cells , bone marrow-derived dendritic cells and macrophages .
Like other TRAPs, SCIMP has negligible extracellular domain and transmembrane domain followed by intracellular domain, containing several tyrosines and one proline-rich region (PRR). Upon phosphorylation, these tyrosines serve as docking domains for SH2 domains containing proteins. In a contrast to phospho-tyrosines, proline rich regions are generally less susceptible to post-translation modifications and they are rather targets of constitutive interactions with SH3 domains containing proteins. [ 5 ] It has been shown that SCIMP interact via SH2 domains with Csk kinase, negative regulator of Src family kinases , but also with Slp65 /76 and Grb2 adaptors, which are key pro-signalling soluble adaptor proteins in lymphocyte signalling network. SCIMP is constitutively associated with Lyn kinase via SH3 domain.
Some of TRAPs are palmitoylated in a border region between transmembrane and intracellular domain. The aliphatic chain of Palmitic acid is anchored to the membrane bilayer and thus influence protein targeting to membrane microdomains . SCIMP is also palmitoylated and is associated with tetraspanin-enriched mircrodomains (TEMs). TEMs, unlike lipid rafts , are based more on protein-protein interactions than lipid-lipid/lipid-protein interactions. [ 6 ] One of the resident proteins in TEMs is MHC class II molecule . SCIMP is present in the immunological synapse during antigen presentation between a T cell and an antigen-presenting cell (APC).
SCIMP becomes strongly phosphorylated after MHC II stimulation. Studies performed with fusion protein CD25 -SCIMP showed its ability to induce calcium release and Erk phosphorylation upon anti-CD25 antibody treatment. The calcium release was even stronger in CD25-SCIMP mutant protein in binding side for Csk. Indicating negative feedback loop performed by Csk kinase. Fusion proteins are commonly used in order to study signalling ability of proteins with a small extracellular domain hidden for antibody in membrane glycocalix . However knock down of SCIMP didn´t influence calcium release after anti MHC II antibody treatment, but only decrease level of Erk phosphorylation in longer time point (10 min.) [ 7 ] | https://en.wikipedia.org/wiki/SCIMP_protein |
Symbiotic culture of bacteria and yeast (SCOBY) is a culinary symbiotic fermentation culture ( starter ) consisting of lactic acid bacteria (LAB), acetic acid bacteria (AAB), and yeast which arises in the preparation of sour foods and beverages such as kombucha . [ 1 ] Beer and wine also undergo fermentation with yeast, but the lactic acid bacteria and acetic acid bacteria components unique to SCOBY are usually viewed as a source of spoilage rather than a desired addition. [ 2 ] [ 3 ] Both LAB and AAB enter on the surface of barley and malt in beer fermentation and grapes in wine fermentation; LAB lowers the pH of the beer/wine while AAB takes the ethanol produced from the yeast and oxidizes it further into vinegar, resulting in a sour taste and smell. [ 2 ] [ 3 ] AAB are also responsible for the formation of the cellulose SCOBY. [ 1 ]
In its most common form, SCOBY is a gelatinous, cellulose-based biofilm or microbial mat found floating at the container's air-liquid interface. This bacterial cellulose mat is sometimes called a pellicle . [ 4 ] SCOBY pellicles, like sourdough starters , can serve the purpose of continuing the fermentation process into a new vessel and reproducing the desired product. [ 4 ] This can be attributed to SCOBY's ability to house not only the symbiotic growth, but a small amount of the previous media and product due to its ability to absorb water. [ 1 ] SCOBYs can vary greatly in cell density within the biofilm due to fermentation conditions, leading to possible variations in the end product; numerous studies are currently taking place to determine the optimal ratio of SCOBY, if any, to liquid culture to ensure highest product consistency, as there are no standard operating procedures in place. [ 4 ] Further information such as the organisms and culture conditions necessary to ferment and form a SCOBY, biofilm characteristics, and applications in foods and beverages with specific emphasis in kombucha can be found below. [ 5 ]
Based on the desired product of the SCOBY, different species of bacteria and yeast are used. Such cultures generally include aerobic, gram negative AAB species such as Acetobacter , Gluconobacter and Komagataeibacter , aerobic, gram positive LAB such as Lactobacillus , as well as various yeasts such as Saccharomyces and Zygosaccharomyces . [ 1 ] [ 2 ] Strains are pre-screened for viability under compatible conditions, increased yield of desired product, and indisposition to compete; once chosen, various culture conditions are modified for optimal growth and productivity. [ 6 ]
For kombucha SCOBYs, the first step is yeast fermentation of sugars such as glucose from black or green tea into ethanol and carbon dioxide. [ 7 ] Zygosaccharomyces is reported to be involved in 84.1% of all kombucha SCOBY fermentation processes due to its improved stability in high sugar and halophilic conditions, while Saccharomyces is predominantly used for its efficient fermentation rates and resistance to high temperature and alcohol content. [ 1 ] Different variations of yeast can also be added as either a supplemental means to introduce different flavors and aromas or ensure reaction completion by utilizing different niches. [ 1 ] While these niches vary yeast to yeast, certain fermentation conditions remain consistent. Such conditions include but are not limited to high substrate concentration, sufficient oxygen levels, temperatures of 20–30 °C (68–86 °F), and a pH between 4–4.5. [ 8 ]
The second step in the formation of SCOBY is the introduction of different bacteria into the liquid culture to convert the ethanol product of fermentation into organic acids such as lactic acid or acetic acid. These processes are known as lactic acid fermentation and ethanol metabolism respectively. [ 7 ] A possible byproduct of this reaction is cellulose, which serves as the foundation for the SCOBY biofilm. [ 4 ] Like yeasts, the species of bacteria chosen as well as culture conditions directly affect both the characteristics of the liquid kombucha product as well as the composition and morphology of the SCOBY pellicle. While there are many species that have the mechanisms necessary to form cellulose such as Acetobacter and Komagataeibacter , Gluconaceobacter are one of the most populous used, residing in 86–99% of both liquid and biofilm cultures. [ 1 ] The necessary culturing conditions of these bacteria are similar to that of yeasts, but require more oxygen due to their aerobic nature in oxidizing ethanol to form organic acids. [ 9 ]
Once the internal conditions of the co-culture are in place, the symbiotic mixture is left to ferment. Certain studies have claimed optimal fermentation time to be 10 days, but the duration can be modified to change the contents of the yield; greater fermentation times correlate with higher levels of organic acids and other amino acids, which can attribute to the sour undertones of some Kombucha. [ 9 ] Despite controls in place, the species comprising the mixed cultures can still initiate metabolic change preparation to preparation with the slightest change in co-culture conditions and alter product qualities such as sugar concentration, so adequate monitoring is necessary when running in a continuous mode or reusing a starter culture . [ 1 ]
The formation of the cellulose pellicle at the surface of the broth yields a product with unique characteristics that both bacteria and consumers find advantageous. Upon inoculation into the culture, bacteria such as Acetobacter immediately begin pulling glucose molecules together outside of the cell and joining them via β(1-4) linkages to form long, slender structures extending from their cell membranes called fibrils . [ 1 ] The nanocellulose composing these fibrils demonstrates great strength and stability while still allowing hydrophilic interactions and biocompatibility, making it a great resource for the culture to use. [ 10 ] A variety of inter and intramolecular bonding events join numerous fibrils together into the final, much larger structures known as microfibrils; because of the integrity of the microfibrils and the organized, linear nature of cellulose bonds, the resulting biofilm can also be referred to as a matrix or mat. [ 10 ] This biofilm is a natural defense mechanism for the co-culture, and can withstand extreme conditions such as temperature and UV radiation. [ 10 ] Two additional characteristics of the nanofibril cellulose SCOBY—its high purity and crystallinity—are currently a target in biomedical research in the formation of biocompatible tissue scaffolds, cardiovascular components such as blood vessels, bone grafts, and connective tissue replacements. [ 11 ] The nanocellulose fibrils can also be extracted via acid hydrolysis and used in the food packaging , clothing, and wastewater treatment industries. [ 1 ] [ 10 ]
The thickness of a kombucha SCOBY is contingent on all brewing conditions, but one study reported an average a thickness of two to five millimeters. [ 12 ] SCOBYs can be divided to start multiple cultures or dehydrated for storage and later use. Once removed, the culture will begin to regenerate a new pellicle known informally as a "baby SCOBY." This process can be repeated multiple times for months at a time. [ 13 ]
In addition to kombucha, there are a variety of other foods and beverages which require a similar "symbiotic culture" in their production such as:
Queensland University of Technology and the State Library of Queensland have been using kombucha scoby to produce a workable bio-textile, called a " vegan leather ". [ 14 ]
A small international team of material and computer engineers from the UK, Italy and Greece has tested the possibility of using kombucha SCOBY to produce electronic circuit boards . [ 15 ] | https://en.wikipedia.org/wiki/SCOBY |
The SCOPE Alliance was a non-profit and influential Network Equipment provider (NEP) industry group aimed at standardizing "carrier-grade" systems for telecom in the Information Age . The SCOPE Alliance was founded in January 2006 by a group of NEP's, including Alcatel, Ericsson, Motorola, NEC, Nokia, and Siemens. In 2007, it added significantly to its membership. [ 1 ] [ 2 ]
Active between 2006 and 2012, its mission was to enable and promote the availability of open carrier-grade base platforms based on commercial off-the-shelf (COTS) hardware/software and free and open-source software building blocks, and promote interoperability between such components. SCOPE wanted to accelerate the deployment of carrier-grade base platforms (CGBP) for service provider applications so that NEP's could use them to build better solutions for their customers. [ 1 ] [ 2 ] By 2011, SCOPE achieved its aim, having accelerated innovation in carrier-grade communications technology and ATCA , [ 3 ]
NEPs sell integrated hardware/software systems to carriers, with three Computing supply chains (Hardware, Operating system, and Middleware) with well-established industry groups promoting interoperability between products from different vendors. SCOPE published "profiles" aimed at influencing specification groups to focus on the needs of NEP customers (carriers). While SCOPE's focused on open standards like ATCA and Carrier Grade Linux, there is no reason "Proprietary Supplier" could not adopt the SCOPE standards. [ 1 ] [ 2 ]
SCOPE's influence on adapting 'Open Standards' for carrier-grade open-source standards and software is summarized in the table: [ 1 ] [ 2 ]
SCOPE was also interested in advancing Network virtualization ("As a consortium of NEPs, it is important for SCOPE to address the lack of standardization in the area of virtualization"), publishing white papers on hardware virtualization, [ 1 ] [ 4 ] [ 5 ] [ 6 ] and a white paper on Java Virtualization describing " an environment where high availability Java EE and native application can co-exist and be supervised in the same fashion in a clustered environment ". [ 10 ] In 2010 SCOPE organized workshop to discuss the effect of Cloud Computing on traditional Carrier-Grade Platforms and telecom networks, [ 11 ] publishing a Cloud Computing white paper in 2011. [ 10 ] [ 12 ]
SCOPE was placed into "hibernation", effectively retired, by NEPs in January 2012. Telecom carriers (NEP customers) wanted direct involvement in driving transformation, so instead, both groups combined forces on ETSI Network function virtualization standardization, Software-defined networking adoption, and 5G network slicing initiatives. [ 13 ]
SCOPE published various publications, including the following: | https://en.wikipedia.org/wiki/SCOPE_Alliance |
SCO Skunkware , often referred to as simply "Skunkware", is a collection of open-source software projects ported , compiled , and packaged for free redistribution on Santa Cruz Operation (SCO) operating environments. SCO Skunkware packaged components exist for SCO Xenix , SCO UNIX, OpenServer 5–6 , UnixWare 2 and 7, Caldera OpenLinux , and Open UNIX 8. [ 1 ] SCO Skunkware was an early pioneering effort to bring open source software into the realm of business computing and, as such, provided an important initial impetus to the acceptance and adoption of open source software in the small and medium-sized business market . An extensive SCO Skunkware download area [ 2 ] has been maintained since 1993 and SCO Skunkware components were shipped with operating system distributions as far back as 1983, when Xenix for the IBM XT was released by The Santa Cruz Operation . [ 3 ] The annual SCO Forum conference was a venue for the makers and users of SCO Skunkware to meet and discuss its contents and ideas for future additions. [ 4 ]
Later additional open source distributions for operating platforms such as the FreeBSD Ports collection and the Solaris Freeware repository [ 5 ] would lend added momentum to the adoption of open source in the business community.
SCO Skunkware has been released often on CD-ROM and as a downloadable CD ISO image . Individual packages are distributed via FTP . The Skunkware CD release history is: [ 6 ]
SCO Skunkware components are licensed under a variety of terms. Most components are licensed under an Open Source Initiative (OSI) approved open-source license . Many are licensed under the terms of either the GNU General Public License or the GNU Library General Public License .
Licenses used by SCO Skunkware components include or are similar to:
A few of the components are "freeware" with no restrictions on their redistribution. Some components may restrict their use to non-commercial purposes or require a license fee for commercial use (e.g. MBROLA ). Some components may be redistributed with special permission from the author(s) as is the case with KISDN.
SCO Skunkware packages are typically distributed in the native packaging format of the operating system release for which they are intended. Package management systems used by SCO Skunkware include the following: | https://en.wikipedia.org/wiki/SCO_Skunkware |
The SCR-277 was a mobile, trailer mounted radio range set for radio guidance of aircraft . It was standardized by the U.S. Army in June 1941.
The SCR-277 was used as a navigation aid. It included the BC-467 transmitter with an RF output power of 800 watts , the BC-468 Goniometer , and BC-342 receiver . Frequencies utilized were 200-400 kHz for transmission and 1.5-18 MHz for reception. Radio range homing equipment transmitted tone identification signals to aircraft that lacked a radio compass but were equipped with command sets . Range was approximately 300 miles. It was powered by a single PE-90 generator. [ 1 ] [ 2 ] [ 3 ]
In operation the transmitter sends out signals coded "A" or "N" in each of the four quadrants around the beacon. The signals overlap on the range, providing the pilot of the aircraft an indication of his position in relation to location of the beacon. Thus, if he is heading toward the beacon he will receive an aural signal coded "A" or "N" if he is between the beam, and when he is on the beam he will receive "AN" signal. Over land areas the beacon has a range of about 300 miles, while over water areas the range is extended to about 1,000 miles. Charts prepared for air navigation show the position and the orientation of the various beacons. [ 3 ]
This United States military article is a stub . You can help Wikipedia by expanding it .
This United States Air Force article is a stub . You can help Wikipedia by expanding it .
This technology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SCR-277 |
SCRIM (Sideway-force Coefficient Routine Investigation Machine) is a machine, originally developed by TRL Limited in the United Kingdom , used to measure the wet skidding resistance of a road surface . [ 1 ]
W.D.M. Limited and ARRB Systems Pty Ltd ( iSAVe ) manufacture sideways-force coefficient routine investigation apparatus for measuring wet road skid resistance. Newer devices such as the iSAVe (intelligent Safety Assessment Vehicle) incorporate dual-wheel path measurement and collection of ancillary data such as road geometry, texture, IRI and rutting to highlight areas of major safety concern.
The SCRIM machine has a daily survey capacity of 200 to 300 km, depending on road type. A SCRIM survey in the UK can be undertaken at two different target test speeds of 50 and 80 km/h. The permitted speed range covering these target speeds is 25 to 85 km/h. [ 2 ] Skidding resistance data recorded at speeds within this range can be speed-corrected to give equivalent values at 50 km/h.
Besides being the main equipment used for friction testing in the UK, it is also used in many other countries, including Spain , Italy , France , Belgium , New Zealand , Australia , Chile and Argentina .
Currently standards are being prepared by the ASTM for continuous friction measurement devices in the USA, including the development of a conforming tire.
The SKM is a similar device to the SCRIM. It also operates on the sideway-force principle, and is the main equipment used for friction-testing throughout Germany and the Netherlands .
Other friction testing devices include the Pavement Friction Tester, devices by Norsemeter, ViaTech, and the Griptester; all these devices have their own benefits. | https://en.wikipedia.org/wiki/SCRIM |
SCSI Enclosure Services ( SES ) is a protocol for more modern SCSI enclosure products. An initiator can communicate with the enclosure using a specialized set of SCSI commands to access power, cooling, and other non-data characteristics. [ 1 ]
There are two major classes of SES devices:
The SCSI initiator communicates with an SES device using two SCSI commands: Send Diagnostic and Receive Diagnostic Results . Some universal SCSI commands such as Inquiry are also used with standalone enclosure services to perform basic functions such as initial discovery of the devices.
The SCSI Send Diagnostic and Receive Diagnostic Results commands can be addressed to a specific SES element in the enclosure. There are many different element codes defined to cover a wide range of devices. The most common SES elements are power supply, cooling fan, temperature sensor, and UPS . The SCSI command protocols assume that there may be more than one of each device type so they must be each given an 8-bit address.
When an SES controller is interrogated for the status of an SES element, the response includes a 4-bit element status code . The most common element status codes are: 1h=OK, 2h=critical, 3h=warning, 5h=not installed.
Some SES elements, such as voltage sensors, current sensors, and temperature sensors, have a thresholding function. This allows an enclosure to detect and report unacceptable environmental conditions. The SCSI standard allows for two different threshold levels, noncritical (warning) and critical. Also, each threshold has a minimum and maximum value. So for example the threshold values for the 12 volt power-supply could be set as follows:
Threshold values are set by a Send Diagnostic command to the Threshold Out diagnostic page (05h). Threshold values can be interrogated by a Receive Diagnostic Results command to the Threshold In diagnostic page (05h) with the PCV bit set to one.
A larger SCSI storage enclosure may contain multiple subenclosures. The subenclosure with address 00h is designated the primary subenclosure and can return information about the other subenclosures.
SCSI attached enclosure services is a computer protocol used mainly with disk storage enclosures. It allows a host computer to communicate with the enclosure to access its power, cooling, and other non-data characteristics.
The host computer communicates with the disks in the enclosure via a SCSI interface which may be Parallel SCSI , FC-AL , SAS , or SSA . One of the disk devices located in the enclosure is set up to allow SCSI Enclosure Services (SES) communication through a logical unit. The disk-drive then communicates with the SES processor in the enclosure, usually via Enclosure Services Interface (ESI) , or a protocol called DSI for SSA enclosures. The data sent over the ESI or DSI interface is simply the contents of a SCSI command and the response to that command.
Only two SCSI commands are implemented by attached enclosure services devices:
SCSI standalone enclosure services is a computer protocol used mainly with disk storage enclosures. It allows a host computer to communicate with the enclosure to access its power, cooling, and other non-data characteristics.
The host computer communicates with one or more SCSI Enclosure Services (SES) controllers in the enclosure via a SCSI interface which may be Parallel SCSI , FC-AL , SAS , or SSA . Each SES controller has a SCSI identity (address) and so can accept direct SCSI commands .
The following SCSI commands are implemented by standalone enclosure services devices:
Note 1: The initiator needs to send a SCSI inquiry to interrogate the SCCS bit which says whether the SES controller has this command. | https://en.wikipedia.org/wiki/SCSI_Enclosure_Services |
SCTbio is a Czech biotechnology company that offers contract development and manufacturing services ( CDMO ) for Advanced Therapy Medicinal Products (ATMPs), utilizing cGMP standards. [ 2 ] [ 3 ]
Operating in Europe and North America , the company specializes in developing autologous cell-based products, cell banking, and all needle-to-needle good manufacturing practice (GMP) operations. These vary from a validated network of apheresis collection sites to product manufacturing, quality control, GMP storage, Qualified Person (QP), and Quality Assurance (QA) release. SCTbio offers worldwide distribution of drug products for both clinical and commercial sales. [ 4 ]
SCTbio was founded on the 1st of July 2021 and is part of the larger PPF Biotech network. SCTbio was initially part of the Sotio group, and SCTbio's CEO, Luděk Sojka, has been part of the PPF Biotech network and Sotio since 2011. [ 5 ] [ 6 ]
On November 1, 2021, Sotio changed its name to SCTbio. [ 7 ] [ 2 ]
SCTbio conducts global operations in Europe and the USA . The cGMP cell manufacturing facility is based in Prague , Czech Republic . The GMP facility features over 2,000 square meters of total space, including a total clean room area of 420m² (4,520 sq ft). [ 8 ] The company offers the ability to manufacture genetically modified products that require the separation of viral and non-viral components. This physical segregation minimizes any risk of cross-contamination. | https://en.wikipedia.org/wiki/SCTbio |
Sulfur dichloride is the chemical compound with the formula SCl 2 . This cherry-red liquid is the simplest sulfur chloride and one of the most common, and it is used as a precursor to organosulfur compounds. It is a highly corrosive and toxic substance, and it reacts on contact with water to form chlorine-containing acids. [ 1 ]
SCl 2 is produced by the chlorination of either elemental sulfur or disulfur dichloride . The process occurs in a series of steps, some of which are:
The addition of Cl 2 to S 2 Cl 2 has been proposed to proceed via a mixed valence intermediate Cl 3 S−SCl . SCl 2 undergoes even further chlorination to give SCl 4 , but this species is unstable at near room temperature. It is likely that several S n Cl 2 exist where n > 2.
Disulfur dichloride , S 2 Cl 2 , is a common impurity in SCl 2 . [ 1 ] Separation of SCl 2 from S 2 Cl 2 is possible via distillation with PCl 3 to form an azeotrope of 99% purity. Sulfur dichloride loses chlorine slowly at room temperature, converting to disulfur dichloride and eventually higher sulfanes. Pure samples may be stored in sealed glass ampules which develop a slight positive pressure of chlorine, halting the decomposition.
SCl 2 is used in organic synthesis . It adds to alkenes to give chloride-substituted thioethers. Illustrative is its addition to 1,5-cyclooctadiene to give a bicyclic thioether [ 2 ] A well tested method for the production of the mustard gas bis(2-chloroethyl)sulfide , is the addition of ethylene to sulfur dichloride: [ 3 ]
SCl 2 is also a precursor to several inorganic sulfur compounds. Treatment with fluoride salts gives SF 4 via the decomposition of the intermediate sulfur difluoride . With H 2 S , SCl 2 reacts to give "lower" sulfanes such as S 3 H 2 . SO 3 oxidizes SCl 2 to SOCl 2 .
Reaction with ammonia affords sulfur nitrides related to S 4 N 4 . Treatment of SCl 2 with primary amines gives sulfur diimides . One example is di- t -butylsulfurdiimide. [ 4 ]
SCl 2 hydrolyzes with release of HCl . Old samples contain Cl 2 . [ 1 ] | https://en.wikipedia.org/wiki/SCl2 |
Thionyl chloride is an inorganic compound with the chemical formula SOCl 2 . It is a moderately volatile , colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately 45,000 tonnes (50,000 short tons) per year being produced during the early 1990s, [ 5 ] but is occasionally also used as a solvent. [ 6 ] [ 7 ] [ 8 ] It is toxic, reacts with water, and is also listed under the Chemical Weapons Convention as it may be used for the production of chemical weapons .
Thionyl chloride is sometimes confused with sulfuryl chloride , SO 2 Cl 2 , but the properties of these compounds differ significantly. Sulfuryl chloride is a source of chlorine whereas thionyl chloride is a source of chloride ions.
The major industrial synthesis involves the reaction of sulfur trioxide and sulfur dichloride . [ 9 ] This synthesis can be adapted to the laboratory by heating oleum to slowly distill the sulfur trioxide into a cooled flask of sulfur dichloride. [ 10 ]
Other methods include syntheses from:
The second of the above five reactions also affords phosphorus oxychloride (phosphoryl chloride), which resembles thionyl chloride in many of its reactions. They may be separated by distillation, since thionyl chloride boils at a much lower temperature than phosphoryl chloride. [ citation needed ]
SOCl 2 adopts a trigonal pyramidal molecular geometry with C s molecular symmetry . This geometry is attributed to the effects of the lone pair on the central sulfur(IV) center.
In the solid state SOCl 2 forms monoclinic crystals with the space group P2 1 /c. [ 11 ]
Thionyl chloride has a long shelf life, however "aged" samples develop a yellow hue, possibly due to the formation of disulfur dichloride . It slowly decomposes to S 2 Cl 2 , SO 2 and Cl 2 at just above the boiling point. [ 9 ] [ 12 ] Thionyl chloride is susceptible to photolysis , which primarily proceeds via a radical mechanism. [ 13 ] Samples showing signs of ageing can be purified by distillation under reduced pressure, to give a colourless liquid. [ 14 ]
Thionyl chloride is mainly used in the industrial production of organochlorine compounds , which are often intermediates in pharmaceuticals and agrichemicals. It usually is preferred over other reagents, such as phosphorus pentachloride , as its by-products (HCl and SO 2 ) are gaseous, which simplifies purification of the product.
Many of the products of thionyl chloride are themselves highly reactive and as such it is involved in a wide range of reactions.
Thionyl chloride reacts exothermically with water to form sulfur dioxide and hydrochloric acid :
By a similar process it also reacts with alcohols to form alkyl chlorides . If the alcohol is chiral the reaction generally proceeds via an S N i mechanism with retention of stereochemistry; [ 15 ] however, depending on the exact conditions employed, stereo-inversion can also be achieved. Historically the use of SOCl 2 with pyridine was called the Darzens halogenation , but this name is rarely used by modern chemists.
Reactions with an excess of alcohol produce sulfite esters , which can be powerful methylation , alkylation and hydroxyalkylation reagents. [ 16 ]
For example, the addition of SOCl 2 to amino acids in methanol selectively yields the corresponding methyl esters. [ 17 ]
Classically, it converts carboxylic acids to acyl chlorides : [ 18 ] [ 19 ] [ 20 ]
The reaction mechanism has been investigated: [ 21 ]
With primary amines, thionyl chloride gives sulfinylamine derivatives (RNSO), one example being N - sulfinylaniline . Thionyl chloride reacts with primary formamides to form isocyanides [ 22 ] and with secondary formamides to give chloro iminium ions; as such a reaction with dimethylformamide will form the Vilsmeier reagent . [ 23 ]
By an analogous process, primary amides will react with thionyl chloride to form imidoyl chlorides , with secondary amides also giving chloro iminium ions. These species are highly reactive and can be used to catalyse the conversion of carboxylic acids to acyl chlorides; [ 24 ] they are also exploited in the Bischler–Napieralski reaction as a means of forming isoquinolines .
Primary amides will continue on to form nitriles if heated ( Von Braun amide degradation ). [ 25 ]
Thionyl chloride has also been used to promote the Beckmann rearrangement of oximes .
Thionyl chloride converts phosphonic acids and phosphonates into phosphoryl chlorides . It is for this type of reaction that thionyl chloride is listed as a Schedule 3 compound, as it can be used in the "di-di" method of producing G-series nerve agents . For example, thionyl chloride converts dimethyl methylphosphonate into methylphosphonic acid dichloride , which can be used in the production of sarin and soman .
As SOCl 2 reacts with water it can be used to dehydrate various metal chloride hydrates, such magnesium chloride ( MgCl 2 ·6H 2 O ), aluminium chloride ( AlCl 3 ·6H 2 O ), and iron(III) chloride ( FeCl 3 ·6H 2 O ). [ 9 ] This conversion involves treatment with refluxing thionyl chloride and follows the following general equation: [ 31 ]
If an exces SOCl2 is used to dehydrate aluminium trichloride, it will form an adduct (1 molecule of thionyl chloride for each molecule of the aluminium trichloride dimer).
Thionyl chloride is a component of lithium–thionyl chloride batteries , [ 37 ] where it acts as the positive electrode (in batteries: cathode ) with lithium forming the negative electrode ( anode ); the electrolyte is typically lithium tetrachloroaluminate . The overall discharge reaction is as follows:
These non-rechargeable batteries have advantages over other forms of lithium batteries such as a high energy density, a wide operational temperature range, and long storage and operational lifespans. However, their high cost, non-rechargeability, and safety concerns have limited their use. The contents of the batteries are highly toxic and require special disposal procedures; additionally, they may explode if shorted. The technology was used on the 1997 Sojourner Mars rover.
SOCl 2 is highly reactive and can violently release hydrochloric acid upon contact with water and alcohols. It is also a controlled substance under the Chemical Weapons Convention , where it is listed as a Schedule 3 substance, since it is used in the manufacture of G-series nerve agents [ citation needed ] and the Meyer and Meyer–Clarke methods of producing sulfur-based mustard gases . [ 38 ]
In 1849, the French chemists Jean-François Persoz and Bloch, and the German chemist Peter Kremers (1827–?), independently first synthesized thionyl chloride by reacting phosphorus pentachloride with sulfur dioxide . [ 39 ] [ 40 ] However, their products were impure: both Persoz and Kremers claimed that thionyl chloride contained phosphorus, [ 41 ] and Kremers recorded its boiling point as 100 °C (instead of 74.6 °C). In 1857, the German-Italian chemist Hugo Schiff subjected crude thionyl chloride to repeated fractional distillations and obtained a liquid which boiled at 82 °C and which he called Thionylchlorid . [ 42 ] In 1859, the German chemist Georg Ludwig Carius noted that thionyl chloride could be used to make acid anhydrides and acyl chlorides from carboxylic acids and to make alkyl chlorides from alcohols . [ 43 ] | https://en.wikipedia.org/wiki/SCl2O |
Sulfur tetrachloride is an inorganic compound with chemical formula SCl 4 . It has only been obtained as an unstable pale yellow solid. The corresponding SF 4 is a stable, useful reagent.
It is obtained by treating sulfur dichloride with chlorine at 193 K:
It melts with simultaneous decomposition above −20 °C. [ 1 ]
Its solid structure is uncertain. It is probably the salt SCl 3 + Cl − , since related salts are known with noncoordinating anions . [ 2 ] [ 3 ] In contrast to this tetrachloride, SF 4 is a neutral molecule. [ 4 ]
It decomposes above −30 °C (242 K) to sulfur dichloride and chlorine.
It hydrolyzes readily:
Sulfur tetrachloride reacts with water, producing hydrogen chloride and sulfur dioxide through the hydrolysis process. Thionyl chloride is an implied intermediate. [ 5 ]
It can be oxidized by nitric acid : | https://en.wikipedia.org/wiki/SCl4 |
A Software-Defined Wide Area Network ( SD-WAN ) is a wide area network that uses software-defined networking technology, such as communicating over the Internet using overlay tunnels which are encrypted when destined for internal organization locations. [ 1 ]
If standard tunnel setup and configuration messages are supported by all of the network hardware vendors, SD-WAN simplifies the management and operation of a WAN by decoupling the networking hardware from its control mechanism. This concept is similar to how software-defined networking implements virtualization technology to improve data center management and operation. [ 1 ] In practice, proprietary protocols are used to set up and manage an SD-WAN, meaning there is no decoupling of the hardware and its control mechanism.
A key application of SD-WAN is to allow companies to build higher-performance WANs using lower-cost and commercially available Internet access , enabling businesses to partially or wholly replace more expensive private WAN connection technologies such as MPLS . [ 1 ]
Some companies selling SD-WAN devices and SD-WAN software claim that it can replace MPLS or reduce the cost of MPLS, making of it an important selling point. In reality SD-WAN is an overlay on MPLS or other networking technologies: "SD-WAN routers still need MPLS and have a limited impact on overall networking spend." [ 2 ]
When SD-WAN traffic is carried over the Internet, there are no end-to-end performance guarantees. Carrier MPLS VPN WAN services are not carried as Internet traffic, but rather over carefully-controlled carrier capacity, and do come with an end-to-end performance guarantee. [ citation needed ]
WANs were very important for the development of networking in general and for a long time one of the most important applications of networks both for military and enterprise applications. [ 3 ] The ability to communicate data over long distances was one of the main driving factors for the development of data communications, as it made it possible to overcome the distance limitations, as well as shortening the time necessary to exchange messages with other parties.
Legacy WANs allowed communication over circuits connecting two or more endpoints. Earlier networking supported point-to-point communication over a slow speed circuit, usually between two fixed locations. As networking progressed, WAN circuits became faster and more flexible. Innovations like circuit and packet switching (in the form of X.25 , ATM and later Internet Protocol or Multiprotocol Label Switching ) allowed communication to become more dynamic, supporting ever-growing networks. [ 4 ]
The need for strict control, security and quality of service (QOS) meant that multinational corporations were very conservative in leasing and operating their WANs. National regulations restricted the companies that could provide local service in each country, and complex arrangements were necessary to establish truly global networks. All that changed with the growth of the Internet , which permitted entities around the world to connect to each other. However, over the first years, the uncontrolled nature of the Internet was not considered adequate or safe for private corporate use.
Independent of safety concerns, connectivity to the Internet became a necessity to the point where every branch required Internet access. At first, due to safety concerns, private communications were still done via WAN, and communication with other entities (including customers and partners) moved to the Internet.
As the Internet grew in reach and maturity, companies started to evaluate how to leverage it for private corporate communications. During the early 2000s, application delivery over the WAN became an important topic of research and commercial innovation. [ 5 ] Over the next decade, increasing computing power made it possible to create software-based appliances that were able to analyze traffic and make informed decisions without delays, making it possible to create large-scale overlay networks over the public Internet that could replicate all the functionality of legacy WANs, at a fraction of the cost.
SD-WAN combines several networking aspects to create full-fledged private networks, with the ability to dynamically share network bandwidth across the connection points. [ 1 ] Additional enhancements include central controllers, zero-touch provisioning , integrated analytics and on-demand circuit provisioning, with some network intelligence based in the cloud , allowing centralized policy management and security. [ 6 ]
Networking publications started using the term SD-WAN to describe this new networking trend as early as 2014. [ 7 ] With the rapid shift to remote work as a result of lockdowns and stay at home orders during the COVID-19 pandemic, SD-WAN grew in popularity as a way of connecting remote workers. [ 8 ]
WANs allow companies to extend their computer networks over large distances, connecting remote branch offices to data centers and to each other, and delivering applications and services required to perform business functions. Due to the physical constraints imposed by the propagation time over large distances, and the need to integrate multiple service providers to cover global geographies (often crossing nation boundaries), WANs face important operational challenges, including network congestion , packet delay variation , [ 9 ] packet loss , [ 10 ] and even service outages. Modern applications such as VoIP calling, videoconferencing , streaming media , and virtualized applications and desktops require low latency . [ 11 ] Bandwidth requirements are also increasing, especially for applications featuring high-definition video . [ 12 ] It can be expensive and difficult to expand WAN capability, with corresponding difficulties related to network management and troubleshooting. [ 1 ]
SD-WAN products are designed to address these network problems. [ 7 ] By enhancing or even replacing traditional branch routers with virtualization appliances that can control application-level policies and offer a network overlay, less expensive consumer-grade Internet links can act more like a dedicated circuit. This simplifies the setup process for branch personnel. [ 13 ]
SD-WAN products can be physical appliances or software based only. [ 14 ]
The MEF Forum has defined an SD-WAN architecture consisting of an SD-WAN edge, SD-WAN gateway, SD-WAN controller and SD-WAN orchestrator. [ 6 ]
The SD-WAN edge is a physical or virtual network function that is placed at an organization's branch/regional/central office site, data center, and in public or private cloud platforms. [ 6 ] MEF Forum has published the first SD-WAN service standard, MEF 70 [ 15 ] which defines the fundamental characteristics of an SD-WAN service plus service requirements and attributes.
SD-WAN gateways provide access to the SD-WAN service in order to shorten the distance to cloud-based services or the user, and reduce service interruptions. [ 16 ] A distributed network of gateways may be included in an SD-WAN service by the vendor or setup and maintained by the organization using the service. [ 16 ] By sitting outside the headquarters in the cloud, the gateway also reduces headquarters traffic. [ 16 ]
The SD-WAN orchestrator is a cloud hosted or on-premises web management tool that allows configuration, provisioning and other functions when operating an SD-WAN. It simplifies application traffic management by allowing central implementation of an organization's business policies. [ 17 ]
The SD-WAN controller functionality, which can be placed in the orchestrator or in an SD-WAN gateway, is used to make forwarding decisions for application flows. [ 15 ] Application flows are IP packets that have been classified to determine their user application or grouping of applications to which they are associated. The grouping of application flows based on a common type, e.g., conferencing applications, is referred to as an Application Flow Group in MEF 70. Per MEF 70, the SD-WAN Edge classifies incoming IP packets at the SD-WAN UNI (SD-WAN user network interface), [ 15 ] determines, via OSI Layer 2 through Layer 7 classification, which application flow the IP packets belong to, and then applies the policies to block the application flow or allow the application flows to be forwarded based on the availability of a route to the destination SD-WAN UNI on a remote SD-WAN Edge. This helps ensure that application performance meets service level agreements (SLAs). [ 18 ]
Тhe Gartner research firm has defined an SD-WAN as having four required characteristics: [ 1 ]
Features of SD-WANs include resilience, quality of service (QoS), security, and performance, with flexible deployment options; simplified administration and troubleshooting; and online traffic engineering.
A resilient SD-WAN reduces network downtime. To be resilient, the technology must feature real-time detection of outages and automatic switch over (fail over) to working links. [ 19 ]
SD-WAN technology supports quality of service by having application level awareness, giving bandwidth priority to the most critical applications. This may include dynamic path selection, sending an application on a faster link, or even splitting an application between two paths to improve performance by delivering it faster. [ 6 ]
SD-WAN communication is usually secured using IPsec , a staple of WAN security. [ 20 ]
SD-WANs can improve application delivery using caching , storing recently accessed information in memory to speed future access. [ 21 ]
SD-WANs can incorporate artificial intelligence for IT operations (AIOps) for continuous troubleshooting and fixes to network issues. [ 22 ]
Most SD-WAN products are available as pre-configured appliances, placed at the network edge in data centers, branch offices and other remote locations. There are also virtual appliances that can work on existing network hardware, or the appliance can be deployed as a virtual appliance on the cloud in environments such as Amazon Web Services (AWS), Unified Communications as a service (UCaaS) or as Software as a Service (SaaS). [ 23 ] This allows enterprises to benefit from SD-WAN services as they migrate application delivery from corporate servers to cloud based services such as Salesforce.com and Google apps. [ 14 ]
As with network equipment in general, GUIs may be preferred to command line interface (CLI) methods of configuration and control. [ 24 ] Other beneficial administrative features include automatic path selection, the ability to centrally configure each end appliance by pushing configuration changes out, and even a true software defined networking approach that lets all appliances and virtual appliances be configured centrally based on application needs rather than underlying hardware. [ 1 ]
With a global view of network status, a controller that manages SD-WAN can perform careful and adaptive traffic engineering by assigning new transfer requests according to current usage of resources (links). For example, this can be achieved by performing central calculation of transmission rates at the controller and rate-limiting at the senders (end-points) according to such rates. [ 25 ] [ 26 ] [ 27 ] [ 28 ] [ 29 ]
SD-WAN is a core component of secure access service edge solutions (SASE) which incorporate network and security capabilities to more efficiently and securely connect distributed work environments (branch office, headquarters, home office, remote) to distributed applications located in data centers, cloud infrastructure, or delivered by SaaS services. With SASE, SD-WAN is combined with other network and security technologies including cloud access security broker (CASB), Secure Web Gateway , Data Loss Prevention (DLP), Zero Trust Network Access ( ZTNA ), Firewall, and other capabilities to connect and protect users and applications. In December 2021, Gartner research firm estimated that by 2025, 50% of SD-WAN purchases will be part of a single vendor SASE offering. [ 30 ]
There are some similarities between SD-WAN and WAN optimization , the name given to the collection of techniques used to increase data-transfer efficiencies across WANs. The goal of each is to accelerate application delivery between branch offices and data centers, but SD-WAN technology focuses additionally on cost savings and efficiency, specifically by allowing lower cost network links to perform the work of more expensive leased lines, whereas WAN Optimization focuses squarely on improving packet delivery. An SD-WAN utilizing virtualization techniques assisted with WAN Optimization traffic control allows network bandwidth to dynamically grow or shrink as needed. SD-WAN technology and WAN optimization can be used separately or together, [ 31 ] and some SD-WAN vendors are adding WAN optimization features to their products. [ 21 ] [ 32 ]
A WAN edge router is a device that routes data packets between different WAN locations, giving enterprise access to a carrier network. Also called a boundary router, it is unlike a core router, which only sends packets within a single network. [ 33 ] SD-WANs can work as an overlay to simplify the management of existing WAN edge routers, by lowering dependence on routing protocols. [ 7 ] SD-WAN can also potentially be an alternative to WAN Edge routers. [ 13 ]
SD-WANs are similar to hybrid WANs, and sometimes the terms are used interchangeably, but they are not identical. A hybrid WAN consists of different connection types, and may have a software defined network (SDN) component, but doesn't have to. [ 34 ]
Cloud-based SD-WAN offers advanced features, such as enhanced security, seamless cloud, and support for mobile users, that result naturally from the use of cloud infrastructure. As a result, cloud-based SD-WAN can replace MPLS, enabling organizations to release resources once tied to WAN investments and create new capabilities. [ 35 ]
An overview discussing three typical reasons to compare MPLS with SD-WAN. Specifically where IT teams need to retain MPLS due to contract commitments and where the Enterprise migrates from MPLS to an Internet-based SD WAN. [ 36 ]
As there is no standard algorithm for SD-WAN controllers, device manufacturers each use their own proprietary algorithm in the transmission of data. These algorithms determine which traffic to direct over which link and when to switch traffic from one link to another. Given the breadth of options available in relation to both software and hardware SD-WAN control solutions, it's imperative they be tested and validated under real-world conditions within a lab setting prior to deployment. [ citation needed ]
There are multiple solutions available for testing purposes, ranging from purpose-built network emulation appliances which can apply specified network impairments to the network being tested in order to reliably validate performance, to software-based solutions. [ citation needed ]
Network World IT website divides the SD-WAN vendor market into three groups: established networking vendors who are adding SD-WAN products to their offerings, WAN specialists who are starting to integrate SD-WAN functionality into their products, and startups focused specifically on the SD-WAN market. [ 1 ] The global SD-WAN market stood at $ 3.25 billion in 2021 and the market is expected to grow 30% in 2022. According to SD-WAN market Report Datavagyanik, North America accounted for more than 77% of the market. [ 37 ]
Alternatively, a market overview by Nemertes Research groups SD-WAN vendors into categories based on their original technology space, and which are "Pure-play SD-WAN providers", "WAN optimization vendors", "Link-aggregation vendors", and "General network vendors". [ 31 ] While Network World's second category (startups focused specifically on the SD-WAN market), is generally equivalent to Nemertes' "Pure-play SD-WAN providers" category, Nemertes offers a more detailed view of the preexisting WAN and overall networking providers. [ citation needed ]
Additionally, Nemertes Research also describes the in-net side of the SD-WAN market, describing the go-to-market strategy of connectivity providers entering the SD-WAN market. These providers include "Network-as-a-service vendors", "Carriers or telcos", "Content delivery networks" and "Secure WAN providers". [ citation needed ]
MEF 70 standardizes SD-WAN service attributes and uses standard IPv4 and IPv6 routing protocols. SD-WAN services also use standard IPsec encryption protocols. Additional standardization for other SD-WAN functions and related security functionality not covered in MEF 70 are under development at the MEF Forum. There are several opensource SD-WAN solutions and opensource SD-WAN implementations available. For example, the Linux Foundation has three projects that intersect with and help the SD-WAN market: ONAP , OpenDaylight Project , and the Tungsten Fabric (formerly Juniper Networks ' OpenContrail). | https://en.wikipedia.org/wiki/SD-WAN |
SDCH ( Shared Dictionary Compression for HTTP ) is a data compression algorithm created by Google , based on VCDIFF (RFC 3284).
SDCH achieves its effectiveness by using pre-negotiated dictionaries to "warm up" its internal state prior to encoding or decoding. These may either be already stored locally, or uploaded from a source and then cached.
It was supported natively in Google Chrome , Chromium, and Android, as well as on Google websites. [ 1 ] [ 2 ]
SDCH compression was removed from Google Chrome, and other Chromium products, in version 59 (2017-06-05). [ 3 ]
Due to the diffing results and the data being compressed with the same coding, SDCH dictionaries aged relatively quickly and compression density became quickly worse than with the usual non-dictionary compression such as GZip . This created extra effort in production to keep the dictionaries fresh and reduced its applicability. Modern dictionary coding such as Shared Brotli has a more effective solution for this that fixes the dictionary aging problem.
This Internet-related article is a stub . You can help Wikipedia by expanding it .
This algorithms or data structures -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SDCH |
In biochemistry and molecular biology , SDD-AGE is short for S emi- D enaturating D etergent A garose G el E lectrophoresis. This is a method for detecting and characterizing large protein polymers which are stable in 2% SDS at room temperature , unlike most large protein complexes . This method is very useful for studying prions and amyloids , which are characterized by the formation of proteinaceous polymers. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] Agarose is used for the gel since the SDS-resistant polymers are large (in the 200-4000+ kDa range) and cannot enter a conventional polyacrylamide gel , which has small pores. Agarose on the other hand has large pores, which allows for the separation of polymers.
Use of this method allowed researchers to understand that at least some types of prion aggregates existed in a two-level structure - protein molecules grouped into polymers, which are very stable and withstand treatment with 2% SDS at room temperature, and aggregates, which are bundles of polymers, that dissociate under these conditions.
Differences in the size of polymers can indicate the efficiency of polymer fragmentation in vivo .
The method was created in the Molecular Genetics laboratory of the Russian Cardiology Research Institute and was published in 2003 by Kryndushkin et al. [ 1 ] The original method used a TAE buffering system and incorporated a modified vacuum blotting system for the transfer of proteins onto a membrane (originally PVDF ). The modified vacuum blotting system is actually a vacuum-assisted capillary transfer, since the vacuum only helps fluid that has already gone through the gel and membrane to leave the system.
Other modifications have also been used, such as the one described in Bagriantsev et al., [ 7 ] using traditional wet transfer and a TGB buffering system, and others using semi-dry transfer or capillary transfer. [ 8 ]
DD-AGE, a further variation of the method that uses fully denaturing conditions - including reducing agents such as dithiothreitol (DTT) and heat denaturation at 95°C - is suitable for the analysis of heat-stable inclusion bodies of polyglutamine proteins . [ 9 ] | https://en.wikipedia.org/wiki/SDD-AGE |
SDET is a benchmark used in the systems software research community for measuring the throughput of a multi-user computer operating system.
Its name stands for SPEC Software Development Environment Throughput (SDET), and is packaged along with Kenbus in the SPEC SDM91 benchmark.
A more modern benchmark that is related to SDET is the reaim package, which is itself an up-to-date implementation of the venerable AIM Multiuser Benchmark .
This programming-tool -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SDET |
SDI Presence LLC (commonly referred to as SDI ) is an IT consultancy and managed services provider (MSP) that provides technology-based professional services . As of 2024, the firm had more than 350 employees. [ 1 ] SDI is a certified Minority Business Enterprise (MBE) with the City of Chicago , the State of Illinois , the National Minority Supplier Development Council (NMSDC) and the California Public Utilities Commission (CPUC). In 2024 SDI was awarded with the NMSDC Supplier of the Year Award – Class IV, as well as the Chicago MSDC Supplier of the Year Class IV. [ 2 ] SDI is ranked as a Top Workplace by Built In Chicago, [ 3 ] the Chicago Tribune (2018-2024), [ 4 ] and Crain's Chicago Business . [ 5 ] [ 6 ]
David A. Gupta founded the company System Development Integration (SDI) in 1996 in Chicago as a spinout from his father's mechanical engineering company, Environmental Systems Design, Inc.; its business was systems integration . [ 7 ] [ 8 ]
Over the following decades, the firm gained business in its IT systems work in government-run systems, like transportation and public safety, as well as utilities and commercial buildings. The City of Chicago selected SDI for its security technology systems at O'Hare and Midway airports, a paperless permit system in the buildings department, customer service and billing for the water management department, and the City payroll system. [ 9 ] The firm's IT-managed services practice added several clients, including large transportation and transit agencies in the Midwest. [ 10 ] SDI also continued several community initiatives as it grew, including its First Chance Initiative, which provided hands-on technical internships for Chicago Public School and City Colleges of Chicago students. [ 11 ] In 2024 SDI Presence signed a lease as anchor tenant at Xchange Chicago, a first-of-its-kind onshore IT delivery center, in partnership with Chicago's communities, aiming to drive a more inclusive economy through technology. [ 12 ]
SDI took on private equity partners between 2008 and 2016, to further expand. The firm was selected to deploy additional mission-critical systems at airports in the U.S. [ 13 ] [ 14 ] In 2016, Gupta renamed the organization SDI Presence. [ 15 ] The company had about 130 employees at that time. [ 15 ]
In 2017, the firm acquired NexLevel Information Technology Inc., an IT management consulting firm whose clients include over 200 West Coast government agencies and special districts. [ 16 ] The NexLevel consulting team operates under the SDI Presence brand and includes local California senior consultants of municipal/financial leadership in local government and utilities. The team has delivered over 100 IT Assessments/Strategic Plans throughout the West Coast. [ 17 ] It also has a long experience in municipal and utility IT systems selection and program management oversight, with a specialization in ERP systems. [ 18 ]
As of 2019, the firm further positioned itself as “IT Keepers of Chicago’s Aviation, Transit and Utility Industries” and currently holds an 87% customer satisfaction score across its portfolio of clients. [ 19 ] [ 20 ]
In 2019, SDI also expanded its MBE partner network through Chicago United's Five Forward Initiative and spent $11M with its diverse minority/women/veteran-owned partner companies in 2019. [ 21 ] As part of its focus on Diversity, Equity and Inclusion (DE&I), SDI projects spending $100M with its minority, women and veteran-owned business partners by the end of 2026. [ 22 ]
The firm secured a minority investment from Abry Partners, a Boston -based sector-focused private equity firm, in 2021. The investment will fund the firm's continued growth in government, utility and private sector technology markets through acquisitions and organic expansion of its footprint nationally. [ 23 ] In late 2021, SDI acquired California-based Scientia Consulting Group, furthering its presence on the West Coast and building out its cloud and managed services offerings. [ 24 ] | https://en.wikipedia.org/wiki/SDI_Presence |
SDS-PAGE ( sodium dodecyl sulfate–polyacrylamide gel electrophoresis ) is a discontinuous electrophoretic system developed by Ulrich K. Laemmli which is commonly used as a method to separate proteins with molecular masses between 5 and 250 kDa . [ 1 ] [ 2 ] The combined use of sodium dodecyl sulfate (SDS, also known as sodium lauryl sulfate) and polyacrylamide gel eliminates the influence of structure and charge, and proteins are separated by differences in their size. At least up to 2012, the publication describing it was the most frequently cited paper by a single author, and the second most cited overall. [ 3 ]
SDS-PAGE is an electrophoresis method that allows protein separation by mass. The medium (also referred to as ′matrix′) is a polyacrylamide-based discontinuous gel. The polyacrylamide-gel is typically sandwiched between two glass plates in a slab gel . Although tube gels (in glass cylinders) were used historically, they were rapidly made obsolete with the invention of the more convenient slab gels. [ 4 ] In addition, SDS ( sodium dodecyl sulfate ) is used. About 1.4 grams of SDS bind to a gram of protein, [ 5 ] [ 6 ] [ 7 ] corresponding to one SDS molecule charges per two amino acids . [ 8 ] SDS acts as a surfactant , masking the protein's intrinsic charge and conferring them very similar charge-to-mass ratios. The intrinsic charges of the proteins are negligible in comparison to the SDS loading, and the positive charges are also greatly reduced in the basic pH range of a separating gel. Upon application of a constant electric field, the proteins migrate towards the anode, each with a different speed, depending on their mass. This simple procedure allows precise protein separation by mass.
SDS tends to form spherical micelles in aqueous solutions above a certain concentration called the critical micellar concentration (CMC). Above the critical micellar concentration of 7 to 10 millimolar in solutions, the SDS simultaneously occurs as single molecules ( monomer ) and as micelles, below the CMC SDS occurs only as monomers in aqueous solutions. At the critical micellar concentration, a micelle consists of about 62 SDS molecules. [ 9 ] However, only SDS monomers bind to proteins via hydrophobic interactions, whereas the SDS micelles are anionic on the outside and do not adsorb any protein. [ 5 ] SDS is amphipathic in nature, which allows it to unfold both polar and nonpolar sections of protein structure. [ 10 ] In SDS concentrations above 0.1 millimolar, the unfolding of proteins begins, [ 5 ] and above 1 mM, most proteins are denatured. [ 5 ] Due to the strong denaturing effect of SDS and the subsequent dissociation of protein complexes, quaternary structures can generally not be determined with SDS. Exceptions are proteins that are stabilised by covalent cross-linking (e.g. -S-S- linkages) and the SDS-resistant protein complexes, which are stable even in the presence of SDS (the latter, however, only at room temperature). To denature the SDS-resistant complexes a high activation energy is required, which is achieved by heating. SDS resistance is based on a metastability of the protein fold. Although the native, fully folded, SDS-resistant protein does not have sufficient stability in the presence of SDS, the chemical equilibrium of denaturation at room temperature occurs slowly. Stable protein complexes are characterised not only by SDS resistance but also by stability against proteases and an increased biological half-life . [ 11 ]
Alternatively, polyacrylamide gel electrophoresis can also be performed with the cationic surfactants CTAB in a CTAB-PAGE, [ 12 ] [ 13 ] [ 14 ] or 16-BAC in a BAC-PAGE. [ 15 ]
The SDS-PAGE method is composed of gel preparation, sample preparation, electrophoresis, protein staining or western blotting and analysis of the generated banding pattern.
When using different buffers in the gel (discontinuous gel electrophoresis), the gels are made up to one day prior to electrophoresis, so that the diffusion does not lead to a mixing of the buffers. The gel is produced by free radical polymerization in a mold consisting of two sealed glass plates with spacers between the glass plates. In a typical mini-gel setting, the spacers have a thickness of 0.75 mm or 1.5 mm, which determines the loading capacity of the gel. For pouring the gel solution, the plates are usually clamped in a stand which temporarily seals the otherwise open underside of the glass plates with the two spacers. For the gel solution, acrylamide is mixed as gel-former (usually 4% V/V in the stacking gel and 10-12 % in the separating gel), methylenebisacrylamide as a cross-linker, stacking or separating gel buffer, water and SDS. By adding the catalyst TEMED and the radical initiator ammonium persulfate (APS) the polymerisation is started. [ 16 ] The solution is then poured between the glass plates without creating bubbles. Depending on the amount of catalyst and radical starter and depending on the temperature, the polymerisation lasts between a quarter of an hour and several hours. The lower gel (separating gel) is poured first and covered with a few drops of a barely water-soluble alcohol (usually buffer-saturated butanol or isopropanol), which eliminates bubbles from the meniscus and protects the gel solution of the radical scavenger oxygen. After the polymerisation of the separating gel, the alcohol is discarded and the residual alcohol is removed with filter paper . After addition of APS and TEMED to the stacking gel solution, it is poured on top of the solid separation gel. Afterwards, a suitable sample comb is inserted between the glass plates without creating bubbles. The sample comb is carefully pulled out after polymerisation, leaving pockets for the sample application. For later use of proteins for protein sequencing , the gels are often prepared the day before electrophoresis to reduce reactions of unpolymerised acrylamide with cysteines in proteins.
By using a gradient mixer , gradient gels with a gradient of acrylamide (usually from 4 to 12%) can be cast, which have a larger separation range of the molecular masses. [ 17 ] Commercial gel systems (so-called pre-cast gels ) usually use the buffer substance Bis-tris methane with a pH value between 6.4 and 7.2 both in the stacking gel and in the separating gel. [ 18 ] [ 19 ] These gels are delivered cast and ready-to-use. Since they use only one buffer ( continuous gel electrophoresis ) and have a nearly neutral pH, they can be stored for several weeks. The more neutral pH slows the hydrolysis and thus the decomposition of the polyacrylamide. Furthermore, there are fewer acrylamide-modified cysteines in the proteins. [ 18 ] Due to the constant pH in collecting and separating gel there is no stacking effect. Proteins in BisTris gels can not be stained with ruthenium complexes. [ 20 ] This gel system has a comparatively large separation range, which can be varied by using MES or MOPS in the running buffer. [ 18 ]
During sample preparation, the sample buffer, and thus SDS, is added in excess to the proteins, and the sample is then heated to 95 °C for five minutes, or alternatively 70 °C for ten minutes. Heating disrupts the secondary and tertiary structures of the protein by disrupting hydrogen bonds and stretching the molecules. Optionally, disulfide bridges can be cleaved by reduction. For this purpose, reducing thiols such as β-mercaptoethanol (β-ME, 5% by volume), dithiothreitol (DTT, 10–100 millimolar), [ 21 ] dithioerythritol (DTE, 10 millimolar), tris(2-carboxyethyl)phosphine [ 22 ] or tributylphosphine [ 21 ] are added to the sample buffer. After cooling to room temperature, each sample is pipetted into its own well in the gel, which was previously immersed in electrophoresis buffer in the electrophoresis apparatus.
In addition to the samples, a molecular-weight size marker is usually loaded onto the gel. This consists of proteins of known sizes and thereby allows the estimation (with an error of ± 10%) of the sizes of the proteins in the actual samples, which migrate in parallel in different tracks of the gel. [ 23 ] The size marker is often pipetted into the first or last pocket of a gel.
For separation, the denatured samples are loaded onto a gel of polyacrylamide, which is placed in an electrophoresis buffer with suitable electrolytes. Thereafter, a voltage (usually around 100 V, 10-20 V per cm gel length) is applied, which causes a migration of negatively charged molecules through the gel in the direction of the positively charged anode . The gel acts like a sieve. Small proteins migrate relatively easily through the mesh of the gel, while larger proteins are more likely to be retained and thereby migrate more slowly through the gel, thereby allowing proteins to be separated by molecular size. The electrophoresis lasts between half an hour to several hours depending on the voltage and length of gel used.
The fastest-migrating proteins (with a molecular weight of less than 5 kDa) form the buffer front together with the anionic components of the electrophoresis buffer, which also migrate through the gel. The area of the buffer front is made visible by adding the comparatively small, anionic dye bromophenol blue to the sample buffer. Due to the relatively small molecule size of bromophenol blue, it migrates faster than proteins. By optical control of the migrating colored band, the electrophoresis can be stopped before the dye and also the samples have completely migrated through the gel and leave it.
The most commonly used method is the discontinuous SDS-PAGE. [ 24 ] [ 25 ] In this method, the proteins migrate first into a collecting gel with neutral pH, in which they are concentrated and then they migrate into a separating gel with basic pH, in which the actual separation takes place. Stacking and separating gels differ by different pore size (4-6 % T and 10-20 % T), ionic strength and pH values (pH 6.8 or pH 8.8). The electrolyte most frequently used is an SDS-containing Tris - glycine - chloride buffer system. At neutral pH, glycine predominantly forms the zwitterionic form, at high pH the glycines lose positive charges and become predominantly anionic. In the collection gel, the smaller, negatively charged chloride ions migrate in front of the proteins (as leading ions) and the slightly larger, negatively and partially positively charged glycinate ions migrate behind the proteins (as initial trailing ions), whereas in the comparatively basic separating gel both ions migrate in front of the proteins. The pH gradient between the stacking and separation gel buffers leads to a stacking effect at the border of the stacking gel to the separation gel, since the glycinate partially loses its slowing positive charges as the pH increases and then, as the former trailing ion, overtakes the proteins and becomes a leading ion, which causes the bands of the different proteins (visible after a staining) to become narrower and sharper - the stacking effect. For the separation of smaller proteins and peptides, the TRIS- Tricine buffer system of Schägger and von Jagow is used due to the higher spread of the proteins in the range of 0.5 to 50 kDa. [ 26 ]
At the end of the electrophoretic separation, all proteins are sorted by size and can then be analyzed by other methods, e. g. protein staining such as Coomassie staining (most common and easy to use), [ 27 ] [ 28 ] silver staining (highest sensitivity), [ 29 ] [ 30 ] [ 31 ] [ 32 ] [ 33 ] [ 34 ] stains all staining, Amido black 10B staining, [ 28 ] Fast green FCF staining, [ 28 ] fluorescent stains such as epicocconone stain [ 35 ] and SYPRO orange stain, [ 36 ] and immunological detection such as the Western Blot . [ 37 ] [ 38 ] The fluorescent dyes have a comparatively higher linearity between protein quantity and color intensity of about three orders of magnitude above the detection limit (the quantity of protein that can be estimated by color intensity). When using the fluorescent protein dye trichloroethanol , a subsequent protein staining is omitted if it was added to the gel solution and the gel was irradiated with UV light after electrophoresis. [ 39 ] [ 40 ]
In Coomassie staining, gel is fixed in a 50% ethanol 10% glacial acetic acid solution for 1 hr. Then the solution is changed for fresh one and after 1 to 12 hrs gel is changed to a staining solution (50% methanol, 10% glacial acetic acid, 0.1% coomassie brilliant blue) followed by destaining changing several times a destaining solution of 40% methanol, 10% glacial acetic acid.
Protein staining in the gel creates a documentable banding pattern of the various proteins.
The documentation of the banding pattern is usually done by photographing or scanning. For a subsequent recovery of the molecules in individual bands, a gel extraction can be performed.
After protein staining and documentation of the banding pattern, the polyacrylamide gel can be dried for archival storage. [ 43 ] Proteins can be extracted from it at a later date. The gel is either placed in a drying frame (with or without the use of heat) or in a vacuum dryer. The drying frame consists of two parts, one of which serves as a base for a wet cellophane film to which the gel and a one percent glycerol solution are added. Then a second wet cellophane film is applied bubble-free, the second frame part is put on top and the frame is sealed with clips. The removal of the air bubbles avoids a fragmentation of the gel during drying. The water evaporates through the cellophane film. In contrast to the drying frame, a vacuum dryer generates a vacuum and heats the gel to about 50 °C.
For a more accurate determination of the molecular weight, the relative migration distances of the individual protein bands are measured in the separating gel. [ 44 ] [ 45 ] The measurements are usually performed in triplicate for increased accuracy. The relative mobility (called Rf value or Rm value) is defined as the distance migrated by the protein band divided by the distance migrated by the buffer front. The distances are each measured from the beginning of the separation gel. The migration of the buffer front roughly corresponds to the migration of the dye contained in the sample buffer. The Rf's of the size marker are plotted semi-logarithmically against their known molecular weights. By comparison with the linear part of the generated graph or by a regression analysis, the molecular weight of an unknown protein can be determined by its relative mobility. [ 44 ] [ 46 ]
Bands of proteins with glycosylations can be blurred, [ 41 ] as glycosylation is often heterogenous. [ 47 ] Proteins with many basic amino acids (e. g. histones ) [ 48 ] can lead to an overestimation of the molecular weight or even not migrate into the gel at all, because they move slower in the electrophoresis due to the positive charges or even to the opposite direction. On the other hand, many acidic amino acids can lead to accelerated migration of a protein and an underestimation of its molecular mass. [ 49 ]
The SDS-PAGE in combination with a protein stain is widely used in biochemistry for the quick and exact separation and subsequent analysis of proteins. It has comparatively low instrument and reagent costs and is an easy-to-use method. Because of its low scalability , it is mostly used for analytical purposes and less for preparative purposes, especially when larger amounts of a protein are to be isolated.
Additionally, SDS-PAGE is used in combination with the western blot for the determination of the presence of a specific protein in a mixture of proteins - or for the analysis of post-translational modifications . [ 50 ] [ 51 ] Post-translational modifications of proteins can lead to a different relative mobility (i.e. a band shift ) or to a change in the binding of a detection antibody used in the western blot (i.e. a band disappears or appears).
In mass spectrometry of proteins, SDS-PAGE is a widely used method for sample preparation prior to spectrometry, mostly using in-gel digestion . In regards to determining the molecular mass of a protein, the SDS-PAGE is a bit more exact than an analytical ultracentrifugation , but less exact than a mass spectrometry or - ignoring post-translational modifications - a calculation of the protein molecular mass from the DNA sequence .
In medical diagnostics, SDS-PAGE is used as part of the HIV test and to evaluate proteinuria . In the HIV test, HIV proteins are separated by SDS-PAGE and subsequently detected by Western Blot with HIV-specific antibodies of the patient, if they are present in his blood serum . SDS-PAGE for proteinuria evaluates the levels of various serum proteins in the urine, e.g. Albumin , Alpha-2-macroglobulin and IgG .
SDS-PAGE is the most widely used method for gel electrophoretic separation of proteins. Two-dimensional gel electrophoresis sequentially combines isoelectric focusing or BAC-PAGE with a SDS-PAGE. [ 52 ] [ 53 ] Native PAGE is used if native protein folding is to be maintained. For separation of membrane proteins, BAC-PAGE or CTAB-PAGE may be used as an alternative to SDS-PAGE. For electrophoretic separation of larger protein complexes, agarose gel electrophoresis can be used, e.g. the SDD-AGE . Some enzymes can be detected via their enzyme activity by zymography . [ 54 ]
While being one of the more precise and low-cost protein separation and analysis methods, the SDS-PAGE denatures proteins. Where non-denaturing conditions are necessary, proteins are separated by a native PAGE or different chromatographic methods with subsequent photometric quantification , for example affinity chromatography (or even tandem affinity purification ), size exclusion chromatography , ion exchange chromatography . [ 55 ] Proteins can also be separated by size in a tangential flow filtration [ 56 ] or an ultrafiltration . [ 57 ] Single proteins can be isolated from a mixture by affinity chromatography or by a pull-down assay . Some historically early and cost effective but crude separation methods usually based upon a series of extractions and precipitations using kosmotropic molecules, for example the ammonium sulfate precipitation and the polyethyleneglycol precipitation.
In 1948, Arne Tiselius was awarded the Nobel Prize in Chemistry for the discovery of the principle of electrophoresis as the migration of charged and dissolved atoms or molecules in an electric field. [ 58 ] The use of a solid matrix (initially paper discs) in a zone electrophoresis improved the separation. The discontinuous electrophoresis of 1964 by L. Ornstein and B. J. Davis made it possible to improve the separation by the stacking effect. [ 59 ] The use of cross-linked polyacrylamide hydrogels, in contrast to the previously used paper discs or starch gels, provided a higher stability of the gel and no microbial decomposition. The denaturing effect of SDS in continuous polyacrylamide gels and the consequent improvement in resolution was first described in 1965 by David F. Summers in the working group of James E. Darnell to separate poliovirus proteins. [ 60 ] The current variant of the SDS-PAGE was described in 1970 by Ulrich K. Laemmli and initially used to characterise the proteins in the head of bacteriophage T4 . [ 1 ] | https://en.wikipedia.org/wiki/SDS-PAGE |
Smart Distributed System (SDS) protocol was developed by Honeywell and is supported by Holjeron . SDS is an open event-driven protocol used over Controller area network based industrial networks. It is used for a highly reliable Smart device -level network. The SDS Application Layer Protocol is optimized for smart sensors and actuators, where configuration , diagnostic, and process information can be embedded cost-effectively in a very small footprint . | https://en.wikipedia.org/wiki/SDS_Protocol |
Protein chemical synthesis by native peptide ligation of unprotected peptide segments is an interesting complement and potential alternative to the use of living systems for producing proteins. [ 1 ] The synthesis of proteins requires efficient native peptide ligation methods, which enable the chemoselective formation of a native peptide bond in aqueous solution between unprotected peptide segments.
The most frequently used technique for synthesizing proteins is Native chemical ligation (NCL). However, alternatives are emerging,
one of which is SEA Native Peptide Ligation .
The SEA group belongs to the N,S -acyl shift systems because its reactivity is dictated by the intramolecular nucleophilic addition of one SEA thiol group on the C-terminal carbonyl group of the peptide segment. This results in the migration of the peptide chain from the nitrogen to the sulfur. The overall process of SEA native peptide ligation involves first an N,S -acyl shift for in in situ formation of a peptide thioester , and later on, after thiol-thioester exchange, an S,N -acyl shift for formation of the peptide bond.
SEA is an abbreviation of bis (2-sulfanylethyl)amido (Scheme 1). SEA ligation involves the reaction of a peptide featuring a C-terminal bis (2-sulfanylethyl)amido group with a Cys peptide. This reaction proceeds probably through the formation of a transient thioester intermediate, obtained by intramolecular attack of one SEA thiol on the peptide C-terminal carbonyl group as shown in Scheme 1. Then, the thioester undergoes a series of thiol-thioester exchanges, including with exogeneous thiols present in the ligation mixture such as mercaptophenyl acetic acid (MPAA). Exchange with the cysteine thiol group of the second peptide segment results in a transient thioester intermediate, which as for Native Chemical Ligation, rearranges by intramolecular S,N -acyl shift migration into a native peptide bond.
The first peer reviewed publication describing SEA native peptide ligation was published in Organic Letters by Melnyk, O. et al. (Ollivier, N.; Dheur, J.; Mhidia, R.; Blanpain, A.; Melnyk, O., Bis(2-sulfanylethyl)amino native peptide ligation. Org. Lett. 2010, 12, (22), 5238–41; Publication Date (Web): October 21, 2010. [ 2 ] [ 3 ] [ 4 ]
A few weeks later, the same reaction was published in the same journal by Liu, C. F (Hou, W.; Zhang, X.; Li, F.; Liu, C. F., Peptidyl N,N-Bis(2-mercaptoethyl)-amides as Thioester Precursors for Native Chemical Ligation. Org. Lett. 2011, 13, 386–389; Publication Date (Web): December 22, 2010). [ 5 ]
SEA on/off concept exploits the redox properties of SEA group. [ 6 ] Oxidation of SEA on results in a cyclic disulfide called SEA off , which is a self-protected form of SEA on . SEA off and SEA on can be easily interconverted by reduction/oxidation as shown in Scheme 2. | https://en.wikipedia.org/wiki/SEA_Native_Peptide_Ligation |
In biology , the SECIS element (SECIS: se leno c ysteine i nsertion s equence ) is an RNA element around 60 nucleotides in length that adopts a stem-loop structure. [ 1 ] This structural motif (pattern of nucleotides) directs the cell to translate UGA codons as selenocysteines (UGA is normally a stop codon ). SECIS elements are thus a fundamental aspect of messenger RNAs encoding selenoproteins , proteins that include one or more selenocysteine residues.
In bacteria the SECIS element appears soon after the UGA codon it affects. In archaea and eukaryotes , it occurs in the 3' UTR of an mRNA , and can cause multiple UGA codons within the mRNA to code for selenocysteine. One archaeal SECIS element, in Methanococcus , is located in the 5' UTR . [ 2 ] [ 3 ]
The SECIS element appears defined by sequence characteristics, i.e. particular nucleotides tend to be at particular positions in it, and a characteristic secondary structure . The secondary structure is the result of base-pairing of complementary RNA nucleotides, and causes a hairpin-like structure. The eukaryotic SECIS element includes non-canonical A-G base pairs, which are uncommon in nature, but are critically important for correct SECIS element function. Although the eukaryotic, archaeal and bacterial SECIS elements each share a general hairpin structure, they are not alignable, e.g. an alignment-based scheme to recognize eukaryotic SECIS elements will not be able to recognize archaeal SECIS elements. However, in Lokiarcheota , SECIS elements are more similar to eukaryotic elements. [ 4 ]
In bioinformatics , several computer programs have been created that search for SECIS elements within a genome sequence, based on the sequence and secondary structure characteristics of SECIS elements. These programs have been used in searches for novel selenoproteins. [ 5 ]
The SECIS element is found in a wide variety of organisms from all three domains of life (including their viruses). [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ] | https://en.wikipedia.org/wiki/SECIS_element |
The Simulation Experiment Description Markup Language (SED-ML) is a representation format, based on XML , for the encoding and exchange of simulation descriptions on computational models of biological systems. [ 1 ] It is a free and open community development project.
SED-ML Level 1 Version 1, [ 2 ] the first version of SED-ML, enables descriptions of time course simulation experiments.
The SED-ML format is built of five major blocks:
More information on the SED-ML structure is available from the SED-ML home page [ 1 ] and the reference publication. [ 3 ]
The idea of developing a standard format for simulation experiment encoding was born at the European Bioinformatics Institute (EMBL-EBI). In 2007, Dagmar Waltemath and Nicolas Le Novère started to draft such a format during Dagmar's Marie-Curie funded internship in the Computational Neuroscience group at EMBL-EBI. [ 4 ]
The SED-ML project was first discussed publicly at the 12th SBML Forum Meeting in 2007, in Long Beach (US). The first version of SED-ML was then presented at the "Super-hackathon "standards and ontologies for Systems Biology"" in Okinawa in 2008. Back then, the language was called MIASE-ML (in accordance with the MIASE guidelines). In Okinawa, many researchers showed a high interest in the format, and discussions were vital. MIASE became the Minimum Information guideline for simulation experiments. MIASE-ML was renamed into "Simulation Experiment Description Markup Language" (SED-ML).
Level 1 Version 1 of SED-ML officially appeared in March 2011, but SED-ML was presented, discussed and further specified during several community meetings in the years in between, including the combined "CellML-SBGN-SBO-BioPAX-MIASE workshop" in 2009, or the "2010 SBML-BioModels.net Hackathon".
Since then SED-ML has been developed in collaboration with the communities forming the "computational modeling in biology network" COMBINE . Besides dedicated sessions at various meetings, the development of SED-ML benefits from community interactions on the SED-ML-discuss mailing list. [ 5 ]
SED-ML is part of the COmputational Modeling in Biology Network (COMBINE) . Format development is coordinated by an editorial board elected by the community. [ 6 ] Discussions take place at SED-ML-discuss. [ 5 ] | https://en.wikipedia.org/wiki/SED-ML |
SEDAT ("Space Environment DATa System") provides access to near-original satellite data on the space environment in order to perform analyses and queries needed for evaluation of space environment hazards.
The development was performed between 1999 and 2001 by the Rutherford Appleton Laboratory (RAL) and funded by the European Space Agency via its Space Environments and Effects Section.
The aim of the SEDAT project is to develop a new approach to the engineering analysis of the spacecraft charged-particle environments. The project assembled a database containing a large and comprehensive set of data about that environment as measured in-situ by a number of space plasma missions. The user is able to select a set of space environment data appropriate to the engineering problem under study. The project developed a set of software tools, which can operate on the data retrieved from the SEDAT database. These tools allow the user to carry out a wide range of engineering analyses.
This approach differs from traditional space environment engineering studies. In the latter the space environment is characterised by a model that is a synthesis of previous observations. However, in SEDAT the environment is characterised directly by the observations. This approach offers several advantages to the engineering analyst:
The traditional approach would require the production, validation and dissemination of an updated model, which is a far more time-consuming activity.
The SEDAT concept foresees access to distributed datasets, capture of processing methods and openness in analysis tools.
The implementation of SEDAT is divided into three main parts:
Four demonstrations of the SEDAT system were performed in the original study: | https://en.wikipedia.org/wiki/SEDAT |
The SEE-FIM protocol is a pathology dissection protocol for Sectioning and Extensively Examining the Fimbria (SEE-FIM). This protocol is intended to provide for the optimal microscopic examination of the distal fallopian tube (fimbria) to identify either cancerous or precancerous conditions in this organ. [ 1 ] [ 2 ]
Women with either a strong family history of breast and ovarian cancer or a documented inherited (germline) mutation in a BRCA gene are encouraged to consider risk reduction salpingo-oophorectomy (RRSO). The surgery is ideally conducted prior to the time that the risk of developing HGSC became too great to defer the procedure, which was age 35 for women with BRCA1 and 45 for BRCA2 mutations. Removal of both tubes and ovaries has reduced the risk of subsequent HGSC by 85% [see BRCA mutation ]. [ 3 ]
Beginning in 2000, pathologists began to encounter early, often non-invasive HGSCs (serous tubal intraepithelial carcinomas or STICs) in the fallopian tubes of women with germ line BRCA mutation who underwent RRSO. [ 4 ] [ 5 ] [ 6 ] [ 7 ]
The SEE-FIM protocol was introduced in 2005 and required examining all of the fallopian tube, specifically the sectioning and examination of the distal one-third (infundibulum and fimbria). [ 1 ] Early HGSCs of the fallopian tube, once considered rare, were encountered frequently in this portion of the tube once the SEE-FIM protocol was adopted. Based on this information, the distal fallopian tube was cited as an origin for many HGSCs formerly classified as ovarian cancers. The SEE-FIM protocol was adopted by many to identify or exclude these tumors during pathologic examination of the fallopian tubes in risk reduction salpingo-oophorectomies. [ 8 ] [ 9 ]
The SEE-FIM protocol consists of five steps (See Figure):
As of 2018, the SEE-FIM protocol was being used by 85% of academic pathology practices and 65% of private practices in the United States and elsewhere in the World. [ 8 ] [ 10 ] [ 11 ] [ 12 ] [ 13 ] Routine use of the SEE-FIM protocol has been recommended by the College of American Pathologists and the International Society of Gynecologic Pathologists when processing fallopian tubes in risk reduction surgeries, and cases of ovarian and uterine serous cancer. [ 14 ] [ 15 ] It is also recommended in the reporting guidelines for gynecologic cancer sponsored by the British Gynecologic Cancer Society. [ 16 ] It is also part of routine protocols in academic institutions and was employed to ascertain the frequency of STIC in a large population-based study. [ 17 ] [ 18 ]
The primary purpose of the SEE-FIM protocol is to detect small cancers in the fallopian tube that are not visible to the naked eye. It is used most often in the following scenarios.
In RRSO specimens from healthy women at increased risk for HGSC, the protocol is used to confirm or exclude the presence of an early HGSC (STIC). If a malignancy is discovered there is a significant risk of a later recurrence, computed at 10% and 27% at 5 and 10 years. In contrast, if no abnormality is found the risk is less than 1%. [ 19 ]
This procedure has been introduced to remove the fallopian tubes when convenient after the cessation of childbearing. The protocol is used to exclude occult cancer. A recent study of over 25,000 women who underwent this procedure reported no cases of HGSC in follow-up if no cancer was found.[see Prophylactic salpingectomy ]. [ 20 ]
In cases with advanced HGSC, the SEE-FIM protocol provides a detailed assessment of the fallopian tube to determine if the tumor arose in the fallopian tube. If pathologic examination confirmed the presence of HGSC in the tubal epithelium, the tumor would be classified as a primary fallopian tube malignancy. This information is also helpful in ascertaining the extent (or stage) of tumor involvement, which in turn influences choice of therapy.
. [ 21 ]
BRCA – Breast cancer associated tumor suppressor genes, including BRCA1 and BRCA2. Inherited (germline) loss of a BRCA gene imposes an increased risk of breast and ovarian cancer.
TP53 – A tumor suppressor gene that is mutated in High grade serous carcinoma.
RRSO – Risk reduction salpingo-oophorectomy.
RRS – Risk reduction salpingectomy.
HGSC – Extrauterine high grade serous carcinoma.
STIC – Serous tubal intraepithelial carcinoma, a non-invasive precursor to high grade serous carcinoma | https://en.wikipedia.org/wiki/SEE-FIM_Protocol |
Surface-enhanced ellipsometric contrast microscopy (SEEC) uses an upright or inverted optical microscope in a crossed polarization configuration and specific supporting plates called surfs on which the sample is deposited for observation. [ 1 ] It is described as an optical nanoscopy technique.
SEEC relies on precise control of the reflection properties of polarized light on a surface, improving the axial sensitivity of an optical microscope by two orders of magnitude without reducing its lateral resolution. [ 1 ] Applications could include real-time visualization of films as thin as 0.3 micrometers and isolated nano-objects in air and in water.
A 2006 study on polarized light coherence led to the development of new supports (the surfs) having contrast amplification properties for standard optical microscopy in cross-polarizer mode. [ 2 ] Made of optical layers on an opaque or transparent substrate, these supports do not modify the light polarization after reflection even if the numerical aperture of the incident source is significant. This property is modified when a sample is present on a surf; a non-null light component is then detected after it has been analyzed, rendering the sample visible.
The performance of these supports is evaluated by measuring the contrast (C) of the sample defined as: C = (I 1 -I 0 )/(I 0 +I 1 ) where I 0 and I 1 represent the intensities reflected by the bare surf and by the analyzed sample on the surf, respectively. For a one nanometer-film thickness, the surfs display a contrast 200 times higher than on silicon wafer.
This high contrast increase allows the visualization with standard optical microscope of films with thicknesses down to 0.3 nanometers, as well as nano-objects (down to a 2 nanometer diameter) and this, without any kind of sample labeling (neither fluorescence , nor a radioactive marker). An illustration of the contrast enhancement is in the Figure for optical microscopy between cross polarizers of a Langmuir-Blodgett structure on a silicon wafer and on a surf.
Nanolane's Sarfus Mapping Station is based on surface-enhanced ellipsometric contrast microscopy. [ 10 ] | https://en.wikipedia.org/wiki/SEEC_microscopy |
SELF-SCAN is a family of plasma displays introduced by Burroughs Corporation during the 1970s. The most common format was a single-row dot matrix display in sizes from 16 to 40 ASCII characters wide. Other formats were also produced, including the SELF-SCAN II 40 wide by 12 or 6 line high displays, and a variety of custom displays showing gauges or pointers.
The SELF-SCAN displays were an important stepping-stone technology between printer-based teletype-like terminals of the 1960s and the widespread use of cathode ray tube (CRT) displays from the mid-1970s on. They were often used for operator terminals on mainframe and minicomputers , and after that continued to see some use in demanding environments where their thinness, on the order of 1 inch, and resistance to interference from magnetic and electric fields that cause problems for CRTs.
The introduction of low-cost liquid crystal displays (LCD)s replaced plasma displays in these uses by the mid-1990s.
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SELF-SCAN |
SEMAT ( Software Engineering Method and Theory ) is an initiative to reshape software engineering such that software engineering qualifies as a rigorous discipline. The initiative was launched in December 2009 by Ivar Jacobson , Bertrand Meyer , and Richard Soley [ 1 ] with a call for action statement [ 2 ] and a vision statement. [ 3 ] The initiative was envisioned as a multi-year effort for bridging the gap between the developer community and the academic community and for creating a community giving value to the whole software community.
The work is now structured in four different but strongly related areas: Practice, Education, Theory, and Community. [ citation needed ] The Practice area primarily addresses practices. The Education area is concerned with all issues related to training for both the developers and the academics including students. The Theory area is primarily addressing the search for a General Theory in Software Engineering. Finally, the Community area works with setting up legal entities, creating websites and community growth. It was expected that the Practice area, the Education area and the Theory area would at some point in time integrate in a way of value to all of them: the Practice area would be a "customer" of the Theory area, and direct the research to useful results for the developer community. The Theory area would give a solid and practical platform for the Practice area. And, the Education area would communicate the results in proper ways.
The first step was here to develop a common ground or a kernel including the essence of software engineering – things we always have, always do, always produce when developing software. The second step was envisioned to add value on top of this kernel in the form of a library of practices to be composed to become specific methods, specific for all kinds of reasons such as the preferences of the team using it, kind of software being built, etc.
The first step is as of this writing just about to be concluded. The results are a kernel including universal elements for software development – called the Essence Kernel, and a language – called the Essence Language - to describe these elements (and elements built on top of the kernel (practices, methods, and more). Essence, including both the kernel and language, has been published as an OMG standard in beta status in July 2013 [ 4 ] and is expected to become a formally adopted standard in early 2014.
The second step has just started, and the Practice area will be divided into a number of separate but interconnected tracks: the practice (library track), the tool track are so far identified and work has started or is about to get started. [ citation needed ] The practice track is currently working on a Users Guide.
The area focuses on leveraging the work of SEMAT in software engineering education, both within academia and industry. It promotes global education based on a common ground called Essence. The area's target groups are instructors such as university professors and industrial coaches as well as their students and learning practitioners.
The goal of the area is to create educational courses and course materials that are internationally viable, identify pedagogical approaches that are appropriate and effective for specific target groups and disseminate experience and lessons learned.
The area includes members from a number of universities and institutes worldwide. [ citation needed ] Most members have already been involved in leveraging aspects of SEMAT in the context of their software engineering courses. They are gathering their resources and starting a common venture towards defining a new generation of SEMAT-powered software engineering curricula.
As of 2018, some studies of utilizing Essence in educational settings exist. One example of the use of Essence in university education was a software engineering course carried out in Norwegian University of Science and Technology. A study [ 5 ] was conducted by introducing Essence into a project-based software engineering course, with the aim of understanding what difficulties the students faced in using Essence, and whether they considered it to have been useful. The results indicated that Essence could also be useful for novice software engineers by (1) encouraging them to look up and study new practices and methods in order to create their own, (2) encouraging them to adjust their way-of-working reflectively and in a situation-specific manner, (3) helping them structure their way of working. The findings of another study introducing students to Essence through a digital game supported these findings: the students felt that Essence will be useful to them in future, real-world projects, and that they wish to utilize it in them. [ 6 ]
An important part of SEMAT is that a general theory of software engineering is planned to emerge with significant benefits. [ 7 ]
A series of workshops held under the title SEMAT Workshop on a General Theory of Software Engineering (GTSE) are a key component in awareness building around general theories. [ 8 ]
In addition to community awareness building, SEMAT also aims to contribute with a specific general theory of software engineering. This theory should be solidly based on the SEMAT Essence language and kernel, and should support software engineering practitioners' goal-oriented decision making. As argued elsewhere, such support is predicated on the predictive capabilities of the theory. Thus, the SEMAT Essence should be augmented to allow the prediction of critical software engineering phenomena.
The GTSE workshop series assists in the development of the SEMAT general software engineering theory by engaging a larger community in the search for, development of, and evaluation of promising theories, which may be used as a base for the SEMAT theory.
SEMAT is chaired by Sumeet S. Malhotra of Tata Consultancy Services. [ 9 ] The CEO of the organization is Ste Nadin of Fujitsu. The Executive Management Committee of SEMAT are Ivar Jacobson, Ste Nadin, Sumeet S. Malhotra, Paul E. McMahon, Michael Goedicke and Cecile Peraire.
Japan Chapter was established in April 2013, and it has more than 250 members as of November 2013. [ citation needed ] Member activities include carrying out seminars about SEMAT, considering utilization of SEMAT Essence for integrating different requirements engineering techniques and body of knowledges (BoKs), and translating articles into Japanese.
The chapter was inaugurated with about 50 members in October 2013. Member activities include: 2e Consulting started rewriting their IT service engagement methods using the Essence kernel, and uEngine Solutions started developing a tool to orchestrate Essence-kernel based practices into a project method. Korean government supported KAIST to conduct research in Essence.
Semat Latin American Chapter was created in August 2011 in Medellin (Colombia) by Ivar Jacobson during the Latin American Software Engineering Symposium. This Chapter has 9 Executive Committee members from Colombia, Venezuela, Peru, Brazil, Argentina, Chile, and Mexico, chaired by Dr. Carlos Zapata from Colombia. More than 80 people signed the initial declaration of the Chapter and nowadays the Chapter members are in charge of disseminating the Semat ideas in all Latin America. Chapter members have participated in various Latin American conferences, including the Latin American Conference on Informatics (CLEI), [ 10 ] the Ibero American Software Engineering and Knowledge Engineering Journeys (JIISIC), [ 11 ] the Colombian Computing Conference (CCC), [ 12 ] and the Chilean Computing Meeting (ECC). The Chapter contributed in the submission sent in response to the OMG call for proposals and currently studies didactic strategies for teaching the Semat kernel by games, theoretical studies about some kernel elements, and practical representations of several software development and quality methods by using the Semat kernel. Some of the members also translated the Essence book and some other Semat materials and papers into Spanish.
Russian Chapter has about 20 members. A few universities have incorporated SEMAT in their training courses [ citation needed ] , including Moscow State University , Moscow Institute of Physics and Technology , Higher School of Economics , Moscow State University of Economics, Statistics, and Informatics . The chapter and some commercial companies are carrying out seminars about SEMAT. INCOSE Russian Chapter is working on an extension of SEMAT to Systems Engineering . EC-leasing is working on an extension of the Kernel for Software Life Cycle. Russian Chapter attended in two conferences: Actual Problems of System and Software Engineering and SECR with SEMAT section and articles. [ citation needed ] Translation of the Essence book into Russian is in progress.
Ideas developed by the SEMAT community have been applied by both industry and academia. Notable examples include:
The first tool that supported the authoring and development of SEMAT practices based on a kernel was the EssWork Practice Workbench [ 14 ] tool provided by Ivar Jacobson International. The Practice Workbench tool was made available to the SEMAT community in June 2012 and is now publicly available and free to use. The Practice Workbench is an Integrated Practice Development Environment with support for collaborative practice and method development. Key features of the Practice Workbench include:
Other publicly available tools supporting SEMAT's Essence include: | https://en.wikipedia.org/wiki/SEMAT |
SEMATECH (from Semiconductor Manufacturing Technology ) was a not-for-profit consortium that performed research and development to advance chip manufacturing. SEMATECH involved collaboration between various sectors of the R&D community, including chipmakers, equipment and material suppliers, universities, research institutes, and government partners. SEMATECH's mission was to rejuvenate the U.S. semiconductor industry through collective R&D efforts, focused on improving manufacturing processes and introducing cutting-edge technologies.
The group was first funded by the U.S. Department of Defense through the Defense Advanced Research Projects Agency until 1997 and later by member dues. SEMATECH was moved from Austin, Texas to Albany, New York in 2007 after receiving state funding from the state of New York. [ 1 ] The consortium was absorbed by SUNY Polytechnic University in 2015 after a long decline, leaving behind a mixed legacy. [ 2 ]
SEMATECH was conceived in 1986, formed in 1987, and began operating in Austin, Texas in 1988 [ 3 ] [ 4 ] as a partnership between the United States government and 14 U.S.-based semiconductor manufacturers to solve common manufacturing problems and regain competitiveness for the U.S. semiconductor industry that had been surpassed by Japanese industry in the mid-1980s. [ 5 ] SEMATECH was funded over five years by public subsidies coming from the U.S. Department of Defense via the Defense Advanced Research Projects Agency (DARPA) for a total of $500 million. This represents about $1 billion in 2022 dollars or only 2 percent of the CHIPS investment.
Following a determination by SEMATECH Board of Directors to eliminate matching funds from the U.S. government after 1996, [ 4 ] [ 5 ] the organization's focus shifted from the U.S. semiconductor industry to the larger international semiconductor industry, abandoning the initial U.S. government-initiative. Its members represented about half of the worldwide chip market. In late 2015, SEMATECH transferred the Critical Materials Council (CMC), a membership group of semiconductor fabricators, to TECHCET CA LLC, an advisory service firm dedicated to providing supply-chain and market information on electronic materials. This group of procurement and quality managers continues to focus on anticipating and remedying materials supply-chain issues and focusing on best practices. The CMC is now an integral part of TECHCET's business and provides guidance on their work of Critical Materials Reports and CMC Conference activities.
SEMATECH conducted research on the technical challenges and costs associated with developing new materials, processes, and equipment for semiconductor manufacturing. Advanced technology programs focus on EUV lithography including photomask blank and photoresist development, materials and emerging technologies for device structures, metrology, manufacturing, and environment and safety issues.
In 1989, the partnership spent a substantial amount of its resources to help the struggling GCA Corp., an equipment manufacturer being eclipsed by Japanese competitors. The initial investment helped the Massachusetts-based factory stay afloat, and even modernize, but failed to address the larger issue – a lack of demand. [ 6 ]
In early 1993 the parent company of GCA Corp. tried to sell it. The latter closed its steppers factory in early 1993. [ 7 ]
In January 2003 [ 8 ] SEMATECH and the University at Albany – State University of New York – established a major partnership to commercialize advanced semiconductor, nanotechnology and other emerging technologies.
Through its government-university-industry partnership with the State of New York and the College of Nanoscale Science and Engineering (CNSE) of the University at Albany, SEMATECH conducted programs in lithography and metrology at CNSE's Albany NanoTech Complex .
In 2010, [ 9 ] SEMATECH expanded its cooperation with CNSE with the announcement that the ISMI would relocate its headquarters and operations to CNSE's Albany NanoTech Complex beginning in January 2011.
With over $6.5 billion in high-tech investments, CNSE's 800,000-square-foot (74,000 m 2 ) Albany NanoTech Complex features the only fully integrated, 300 mm wafer, computer chip pilot prototyping and demonstration line within 80,000 square feet (7,400 m 2 ) of Class 1 capable cleanrooms. [ 10 ]
SEMATECH had access to laboratories and development fabs in Austin, Texas (1987-2007) and Albany, New York (2007-2015).
SEMATECH hosted a variety of worldwide conferences, symposiums, and workshops (e.g., Litho Forum, Manufacturing Week) and delivered papers, presentations, and joint reports at major industry conferences ( SPIE , IEDM , SEMICON West ). | https://en.wikipedia.org/wiki/SEMATECH |
Sercos III is the third generation of the Sercos interface , a standardized open digital interface for the communication between industrial controls, motion devices, input/output devices (I/O), and Ethernet nodes, such as PCs. Sercos III applies the hard real-time features of the Sercos interface to Ethernet . It is based upon the Ethernet standard ( IEEE 802.3 and ISO/IEC 8802-3). Work began on Sercos III in 2003, [ 1 ] with vendors releasing first products supporting it in 2005. [ 2 ]
To achieve the throughput and jitter requirements in Sercos applications, Sercos III operates primarily in a Master/Slave arrangement exchanging cyclic data between nodes. The master initiates all data transmission during a Sercos real-time cycle. All data transmissions begin and end at the master (circular).
Communication across a Sercos III network occurs in strict cyclic intervals. A cycle time is chosen by the user for a given application, ranging from 31.25 μs to 65 ms. Within each cycle, data is exchanged between Sercos III nodes using two types of telegrams: MDTs and ATs (see Telegram Types ). After all MDTs and ATs are transmitted, Sercos III nodes allow the remaining time in the cycle to be used as an UC (Unified Communication) Channel , which can be used to exchange data using other formats, such as IP.
The network remains available to UCC traffic until the next cycle begins, at which time Sercos III closes the nodes to UCC traffic again. This is an important distinction. Sercos is purposely designed to provide open access at all ports for other protocols between cyclic real-time messages. No tunneling is required. This provides the advantage that any Sercos III node is available, whether Sercos III is in cyclic mode or not, to use other protocols, such as TCP/IP, without any additional hardware to process tunneling. Sercos nodes are specified to provide a store and forward method of buffering non-Sercos messages should they be received at a node while cyclic communication is active.
All Sercos III telegrams conform to the IEEE 802.3 and ISO/IEC 8802-3 MAC ( media access control ) frame format.
Two main types of telegrams are used within the Sercos III Cycle. The Master Data Telegram (MDT) and the Acknowledge Telegram (AT). Both telegram types are issued by the master (control). The MDT contains information provided by the master to other devices. It is filled by the master and read by other devices. The AT is issued by the master but is populated by each other device with appropriate response data (feedback values, input states, etc.). More than one device uses the same AT, filling in its pre-determined area in the AT telegram, updating checksums, and then passing the telegram to the next device. This method reduces the Ethernet frame overhead's impact on the network's performance without compromising IEEE 802.3 and ISO/IEC 8802-3. The amount of data sent from the master to other devices and the sum of the data returned by the other devices may exceed the 802.3-specified maximum 1500-byte data field size. To comply with this limit, Sercos III may use more than one MDT telegram in a cycle and more than one AT telegram (up to 4 in each case).
To achieve true hard real-time characteristics, Sercos III, like Sercos I and II, uses a form of synchronization that depends upon a synchronization “mark” issued by the master control at exact equidistant time intervals. All nodes in a Sercos network use this telegram to synchronize all activities in the node. To account for variations in network components, delays are measured in the node-to-node transmissions during the phase-up (initialization) of a Sercos network, and those values are compensated for during normal operation. Unlike Sercos I and II, where a separate Master Sync Telegram, or MST is used for this purpose, Sercos III includes the MST in the first MDT transmitted. No separate telegram is issued. The time between two MSTs is exactly equal to the designated Sercos cycle time, Stacy.
The synchronization process ensures that cyclical and simultaneous synchronization of all connected devices occurs independently of topology and the number of devices in Sercos networks.
Sercos III supports standard IEEE 802.3 and ISO/IEC 8802-3 100BASE-TX or 100BASE-FX (100 Mbit/s baseband) full duplex physical layer (PHY) entities. 802.3-compliant Media-Access Controller (MAC) sub-layers are used. Auto-negotiation must be enabled on each PHY, but only 100 Mbit full duplex is supported. Auto (MAU [Media Attachment Unit]-Embedded) Crossover is specified between the two Physical Medium Attachment (PMA) units present with a duplex port. These two units are referred to as the Primary Channel and Secondary Channel in the Sercos III specification. Dual interfaces are required (two duplex interfaces per device). Within the Sercos III specification, the dual interfaces are referred to as P1 and P2 (Ports 1 and 2).
Installing a Sercos network does not require infrastructure components such as switches or hubs, and all devices are interconnected by patch or crossover cables The Ethernet ports on the devices are interchangeable and can be used to connect standard Ethernet devices such as notebook computers to network. Every Ethernet and IP protocol on Sercos devices can be accessed without interfering with the real-time protocol and without requiring the real-time operation to be activated.
All of the functionality required to configure a Sercos III interface is contained in a stack that is available in both “hard” and “soft” versions. The hard version is widely used for embedded applications (such as drives, I/O modules, and micro-controller based motion control), where:
The hardware stack is available in several different forms. [ 3 ] These currently include:
The maximum jitter allowed with hard-stack-based masters and slaves is less than 1 μs. Using the above stacks yields a jitter similar to Sercos II (35-70 nanoseconds).
Sercos III also supports an operating system and hardware platform independent “Soft Master”, using a completely software-based stack for the master interface. [ 4 ] Since the maximum jitter in such a configuration is dependent upon the operating system of the Master, the maximum jitter may be set by a variable for the Sercos III network when a Soft Master is employed. A standard Ethernet controller can be used for applications with line topology, bus cycle times greater than 500 us, and microsecond range synchronization. Applications with higher synchronization requirements and lower bus cycle times can be implemented using a TTS-capable Ethernet controller with a suitable real-time operating system.
For basic Slaves, such as I/O devices, EasySlave-IO, a license-free bitstream variant of the EasySlave is available.
A product that uses an Arduino board as a rapid prototype platform for an application, plus a corresponding shield (add-on module) with a Sercos EasySlave FPGA, plus other peripheral components, is available.
A term usually associated with the IT enterprise, data consistency can also apply to real-time control (see for example Peer to Peer Communication ). For this reason, Sercos III specifies that no data be overwritten (destroyed) during a transmission. Every slave on a network may access input and output data for every other slave on the network.
Devices must support Ethernet’s MAC addressing, plus the Sercos III addressing. Other addressing schemes are optional.
The Sercos III specification defines two possible network topologies ; Ring and Line. To those familiar with other networks, both of them may appear to be configured as a ring. All telegrams begin and end at the master. The Full Duplex feature of the physical layer is used to achieve this.
The first slave receives the telegrams on the connected interface’s receive PMA, modifies them as required, and issues them out on the transmit PMA of the second interface. Each cascading Slave does likewise until the last Slave in the Line is reached. That slave, detecting no Sercos III connection on its second port, folds the telegram back on the receiving interface’s transmit port. The telegram then makes its way through each Slave back to the Master. Note the last slave also emits all Sercos III telegrams on its second port, even though no Sercos III connection is detected. This is for snooping, ring closures (see below), and hot-plugging .
Keep in mind that since the Ethernet destination field in all Sercos III telegrams is the broadcast address of 0xFFFF FFFF FFFF (all 1s), all telegrams issued from this open port will be seen by other devices as broadcast telegrams. This behavior is by design, and cannot be disabled. To avoid taxing networks attached to an open Sercos port, an IP-Switch can be used, or alternately a managed Ethernet switch programmed to block broadcast telegrams received from the Sercos port can be used. Starting with Sercos III specification version 1.3.1 the connection of industrial Ethernet devices is supported where devices work with 20 ms cycle time in communication phase 0 (CP 0).
Sercos III is designed in such a way that no additional network infrastructure (standard Ethernet switches , Hubs , etc.) is required to operate. Normal standard Ethernet (non-Sercos III capable) components may be placed within a Sercos III network, as their presence will not adversely affect the timing and synchronization of the network. [ 5 ]
Guarantee synchronization in extended networks using media converters requires Cut-through switching . If ring redundancy shall be achieved, Link Loss Forwarding with appropriate reaction times is necessary.
A variety of products is available that enable the connection of field buses (Profibus and CAN) or sensor/actuator buses (AS-i, SSI, IO-Link) to a Sercos network. Gateways are available to integrate analog axes. Gateways are incorporated into Sercos devices (e.g., modular I/Os) or are connected as separate components in the network.
In addition to the features of the Sercos interface , Sercos III also provides: [ 6 ]
The Sercos III specification defines a broad range of variables developed by a consortium of product suppliers to provide interoperability between components (motion controls, drives, etc.). All traffic across a Sercos III network consists of Idents (parameters) with attributes. The idents define over 700 standardized parameters that describe the interaction between electric, pneumatic, and hydraulic control systems, drives, and other peripheral devices using universal semantics. This method was first defined in Sercos I, as an essentially flat set of idents. They were later grouped into application sets to aid in the selection of pertinent incidents required for a given industry, such as the “Pack Profile” for use with packaging machinery. During the development of the Sercos III specification, this methodology was further refined to group the incidents logically by device class. The definition of the legacy idents has remained largely untouched; rather their grouping has been re-evaluated for a more understandable architecture. This has also enabled the separation of communication idents into a logical subset, simplifying migration from Sercos I/II to Sercos III, and providing a clear overview to users.
When a ring network is employed, Sercos III provides for automatic infrastructure redundancy. If any interconnection point in the ring ceases to function, the associated Sercos III nodes will detect a “ring break” and “loop back” the end nodes, effectively operating as two lines rather than one ring.
The operation is “bump-less”, as the detection and recovery time for such a break is less than 25 μs, which is less than the minimum Sercos III cycle time. Sercos III can also recover from ring breaks and “heal” with no interruption in operation. Since Sercos III telegrams continue to be emitted by transmit PMAs on unconnected ports and receive PMAs on unconnected ports continue to monitor for incoming data, when a Sercos III port recognizes that a ring has by physically re-closed, it will re-activate the counter-rotating telegrams to functionally close the rings again. This operation is also bump-less.
To ensure the determinism required, most real-time Ethernet standards enforce a master-to-slave-only method of communications. This can conflict with the need for a node in the system to exchange data efficiently with a node other than the network master. The conventional method to achieve this in a master-slave network is to pass data from one slave node to the master, where it is reissued to one or more different slaves. For example, if several servo drives on a network are to be synchronized to a signal from another drive on the network, the master must fetch the signal from this drive and reissue it to all other drives on the network. Disadvantages to this method are that delays are induced due to the multiple cycles required, and the master’s processing load is increased as it must actively participate in the function, although it contributes nothing. Since no data is destroyed in a Sercos III telegram, data to and from any slave can be accessed by another node on the network without any additional cycle delay or master intervention. Additionally, as telegrams pass each node twice in a cycle (for both topology types), a node can even have the opportunity to access data supplied by a subsequent node. Two peer communication methods are defined in the Sercos III specification: Controller to Controller (C2C) for multiple masters to communicate with one another, and Cross Communication (CC) for multiple slaves.
Another feature of Sercos III is hot-plugging, which is the ability to add devices to an active network. Using the features described for redundancy, a network can detect when a new device is attached to an active network. Processes exist that configure the new device, and announce its availability to the master control. After that, the master control can select to make use of the new device based on the application currently running.
Oversampling allows more than one nominal/actual value to be transmitted per cycle, increasing the delicate nature of process control in extremely critical applications, such as laser applications.
Time stamping transmits event-controlled results, such as specific measured data, and switches outputs independently from the cycle. This increases the stability of the process in complex processing solutions, such as those in the semiconductor industry.
The time between the end of the transmission of all Sercos III Real Time (RT) cyclic telegrams and the beginning of the next communication cycle is defined as the “Sercos III Unified Communication Channel” (UC Channel). During this period, the Sercos network is opened to allow transmission of Ethernet-compliant frames for other services and protocols. For example:
Every Sercos III-compliant node must support the passing of UC frames through its Sercos III interface. Whether a Sercos III node actively uses the UC feature is determined by the product's feature set. If, for example, the device has an embedded web server, it could make available its IP address for access by other devices.
A Sercos III network will always pass UC frames, even when the cyclic operation has not been initialized. This means that devices always have access to the network for UC messages, as long as the ports are powered.
Sercos III does not define whether a port should operate in cut-through switching or store-and-forward mode when handling UC frames. There are Sercos III products currently on the market that support both modes. Likewise, Sercos III does not define whether a port should intelligently process UC telegrams, such as learning the network topology.
The time allotted for UC traffic is dictated by the amount of data transmitted during the real-time portion of the cycle. In real-world applications, there is a significant amount of bandwidth available for UC frames. For example, in a typical application with 8 axes of motion and a cycle rate of 250 μs, the equivalent of 85 Mbit/s is available for UC use. This amount of time means the UC frames in this example can be as long as the maximum defined for Ethernet ( Maximum Transmission Unit [MTU] =1500). Using the same example of 8 axes but with a cycle time of 62.5 μs, the effective bandwidth available for UC frames would be 40 Mbit/s and the MTU would be reduced to 325. As with any network where time on the bus is shared, MTU values should be configured to ensure reliable communication. Properly configured Sercos networks will set the Sercos parameter “Requested MTU” (S-0-1027.0.1) to the recommended MTU value, which can then be read by other devices to match their MTU settings. Regardless of the value of this parameter, a Sercos node will allow non-Sercos traffic to pass for the entire UC channel period (i.e., telegrams longer than the MTU setting are not discarded by the Sercos stack). Sercos parameter S-0-1027.0.1 is set by default to 576, the minimum value called out in RFC 791.
UC frames may only enter a Sercos III network through a Sercos III-compliant port. This can be achieved in two different ways. One is to employ the unused Sercos III port at the end of a Sercos III network configured in line topology, as shown to the right.
In a network configured in a ring topology, the ring can be temporarily broken at any point to also attach a device. Since the redundancy feature of Sercos III will reconfigure the network in a bump-less manner (responding in less than one cycle), no disruption of network transmission will occur. The ring can again be closed after the access is no longer required.
If access is desired in the middle of a line topology (where no free ports are available), or it is undesirable to break a ring topology for extended periods, the Sercos III specification permits a device called an “IP-Switch” that can be used to provide access to the UC channel anywhere along the network. IP-Switches supply two Sercos III-compliant ports, and one or more ports for UCC access.
Commercially available UCC Switches block the transmission of Sercos III broadcast telegrams out their non-Sercos III port(s), to prevent flooding of non-Sercos III networks with Sercos III cyclic data.
Sercos III is designed so that EtherNet/IP. TC/IP and Sercos devices can operate over the same Ethernet cable. The high-efficiency Sercos telegrams use only a portion of the existing bandwidth, allowing non-Sercos telegrams to be transmitted via the UC channel.
A Sercos master and an EtherNet/IP scanner are required to implement a common network infrastructure. They can be combined into a dual-stack master.
Where redundancy is not necessary, the devices are connected in a line topology, where the last Sercos device in the line transmits and receives non-Sercos telegrams via its free port. A free port is not available when the network is configured in a ring topology for redundant data communication. In such a configuration, an IP switch is required to allow non-Sercos packets into the ring.
"Functional safety" is a general term referring to the design of a system that reduces the risk that a hazardous event harmful to humans can occur with a system. The main definition is contained in the international standard IEC 61508 . Most industrial networks contain some type of features to conform to functional safety requirements. Rather than define a unique specification for this functional safety, Sercos III Safety is based upon the CIP Safety protocol developed by the Open DeviceNet Vendors Association (ODVA). [ 11 ] This provides interoperability at the safety level with all networks based upon the Common Industry Protocol (CIP), including DeviceNet and EtherNet/IP.
CIP Safety on Sercos provides for safe data transmission over Sercos III up to SIL 3 ( Safety Integrity Level ). No additional safety bus is required, as the safety information is sent in addition to the standard data on the Sercos network.
With CIP Safety on Sercos, data is sent on the same medium using the same connections as standard communication. The function of the cross-media CIP Safety protocol is performed by the end units, making it possible to simultaneously operate standard and safety devices in the same network. Reliable communication can take place between all network levels, including peer-to-peer communication and cross-network communication. The master does not necessarily have to be a safety controller. It can also route data without being able to interpret it. This makes it possible to configure the safety network architecture for the implementation of safety programmable controllers or peer-to-peer communication between sensors and actuators.
The Sercos I/O profile is a device profile for decentralized I/O modules, which can be used for block and modular I/Os. It also supports hybrid devices that combine several functionalities in one single device, e.g., a two-axis controller with I/O and master functionality.
An XML-based device and profile description language is specified for I/O device configuration. SDDML (Sercos Device Description Markup Language) describes which profiles are supported by a certain device. SPDML (Sercos Profile Description Markup Language) is used to specify the different profiles based on the Sercos parameter model. Existing standard parameters can be used and manufacturer-specific parameters can also be defined.
Sercos Energy is an application layer profile that defines parameters and commands for the reduction of energy consumption in a uniform vendor-independent manner.
Sercos Energy reduces energy consumption in three areas:
In operation, the control reads out the parameters of each Sercos Energy component via the Sercos III network, receiving status information and detailed consumption values. Depending on the situation (e.g., scheduled or unscheduled breaks, machine components not needed in the current production process) standardized commands can be issued by the control to switch connected components (drives, I/O, sensors) into energy-saving conditions, up to complete shut-down, reducing their energy consumption.
The profile considers energy-saving conditions for predictable breaks such as lunch periods and plant holidays. At pre-defined times, Sercos Energy components are brought into a standstill condition to save energy. Shortly before the end of the interruption, Sercos Energy provides for the re-initialization of components in stand-by condition, to make them available again.
Sercos Energy provides mechanisms for unintended breaks caused by machine errors and missing parts. In these situations, target components can be carefully brought into energy-saving modes while errors are being fixed or during a wait for new parts.
By using intelligent controls, axes, and components that are unneeded in ongoing production processes can be switched off, and/or target completion times can be adjusted, while still achieving full productivity.
The function-specific Encoder Profile ensures that encoders from different manufacturers can be utilized in Sercos applications without compatibility problems. Supported encoder functions are defined, and their use with other devices, e.g., controls, is specified. Both stand-alone encoders and hybrid devices with encoders are supported.
The OPC Foundation and Sercos International developed an OPC UA companion specification [ 12 ] which describes the mapping of Sercos to OPC UA. This makes the functions and parameters of Sercos III devices available to OPC UA, independent of any vendor. This simplifies communication between machine automation devices and higher-level supervisory systems.
The multi-protocol capabilities of Sercos III allow various implementation options. The OPC UA server functionality can be implemented into machine control or directly into a Sercos field device, such as a drive, sensor, or I/O module. An OPC client can also be integrated into a Sercos controller.
An OPC client and OPC UA server can communicate with each other even when Sercos real-time communication is not active, because the Sercos transmission process does not require tunneling.
I/O Link is a digital interface for the connection of sensors and actuators to higher-level automation busses, such as Sercos III. An IO-Link master can be either a stand-alone slave or part of a modular slave device. An IO-Link-to-Sercos mapping guide [ 13 ] is available to assist manufacturers in integrating IO-Link into a Sercos III network. An IO-Link development board with an IO-Link master and a Sercos III slave interface is available.
AS-i ( Actuator Sensor Interface ) is a networking interface for the connection of simple field devices such as actuators and sensors to higher-level busses, such as Sercos III. Several AS-i/Sercos gateways are available for connection of AS-i devices to a Sercos III network.
Standard Ethernet is not deterministic and, therefore not suitable for hard real-time communications. To address that problem, the Time-Sensitive Networking task group of the IEEE 802.1 working group is developing a set of standards that define mechanisms for hard real-time data transmission over Ethernet networks.
A Sercos working group has determined that Sercos is compatible with TSN. A Sercos TSN demonstrator was developed to illustrate the real-time multi-protocol capable Sercos network based on TSN. [ 14 ]
Driver software is used to connect a controller to the device logic. Several basic Sercos drivers are available as open-source software from sourceforge.net. [ 15 ] These include a common Sercos Master API library, Sercos Internet Protocol Services software and a Sercos UCC Ethernet network driver.
An open-source Sercos SoftMaster is also available from sourceforge.net. It emulates the Sercos functions so that a standard Ethernet controller can be used instead of FPGA or ASIC hardware.
A pre-certified CIP Safety on Sercos protocol software is available to equip Sercos and EtherNet/IP devices with the appropriate safe logic up to SIL3.
Conformance testing verifies that both controls and peripheral devices comply with Sercos standards and can operate interoperably in networks with products from multiple vendors. A testing tool, The Sercos Conformizer, can be used to subject a device to a pre-test before the formal conformance procedure.
Sercos International e.V., a Sercos user's group headquartered in Germany, developed and supports Sercos as an open IEC standard, independent of any individual company. Any company can develop and use Sercos. Sercos also has user groups in North America and Asia. [ 16 ]
Membership in a Sercos user's group is voluntary. Experts from both member and non-member companies actively contribute to the further development and support of Sercos via engineering working groups, considering market trends plus input from Sercos vendors regarding practical field applications.
Sercos International is a recognized partner of the Industrial Electrotechnical Commission (IEC) and actively contributes to the IEC standards for machine automation. | https://en.wikipedia.org/wiki/SERCOS_III |
In the field of Industrial Control Systems , the interfacing of various control components must provide means to coordinate the signals and commands sent between control modules. While tight coordination is desirable for discrete inputs and outputs, it is especially important in motion controls , where directing the movement of individual axes of motion must be precisely coordinated so that the motion of the entire system follows a desired path. Types of equipment requiring such coordination include metal cutting machine tools , metal forming equipment, assembly machinery, packaging machinery, robotics, printing machinery and material handling equipment. The Sercos ( se rial r eal-time co mmunication s ystem) interface is a globally standardized open digital interface for the communication between industrial controls, motion devices (drives) and input output devices (I/O). Sercos I and II are standardized in IEC 61491 and EN 61491. Sercos III is specified in standards IEC 61800-7; IEC 61784-1, -2, -3 and IEC 61158. Sercos is designed to provide hard real-time , high performance communications between industrial motion controls and digital servo drives .
Until the early 1980s the majority of servo drive systems used to control motion in industrial machinery were based upon analog electronics . The accepted interface to control such devices was an analog voltage signal, where polarity represented the desired direction of motion, and magnitude represented the desired speed or torque. In the 1980s, drive systems and devices based on digital technology began to emerge. A new method needed to be devised to communicate with, and control such units, as their capabilities could not be exploited with the traditional interface method used with analog drives. The earliest interfaces were either proprietary to one vendor or designed only for a single purpose, making it difficult for users of motion control systems to freely interchange motion control and drives. The membership of the VDW (German Machine Tool Builders' Association) became concerned with the implications of this trend. In response to that, in 1987 the VDW formed a joint working group with the ZVEI (German Electrical and Electronics Industry Association) to develop an open interface specification appropriate for digital-drive systems. [ 1 ] The resulting specification, entitled "Sercos ( se rial r eal-time co mmunication s ystem) interface, was released and later submitted to the IEC , which in 1995 released it as IEC 61491. [ 2 ] After the release of the original standard, original working group member companies including ABB , AEG , AMK, Robert Bosch , Indramat , and Siemens founded the "Interest Group Sercos" to steward the standard. [ 3 ] Over the history of Sercos, its capabilities have been enhanced to the point where today it is not only used for motion control systems, but as a universal automation bus.
Sercos I was released in 1991. The transmission medium used is optical fiber. The data rates supported are 2 and 4 Mbit/s, and cyclic update rates as low as 62.5 microseconds. A ring topology is used. Sercos I also supports a "Service Channel" which allows asynchronous communication with slaves for less time-critical data. [ 4 ]
Sercos II was introduced in 1999. It expanded the data rates supported to 2, 4, 8 and 16 Mbit/s.
Sercos III was introduced in 2003. It merges the hard-real-time aspects of Sercos with the Ethernet standard.
Important features of Sercos include:
Sercos is supported globally by Sercos International e.V. (SI) in Germany. Regional support is provided by Sercos North America (USA), Sercos Japan and Sercos China. These organizations provide a forum for the continued development of the standard, as well as user support.
An important aspect of an open, interoperable communications system is rigorous testing of products for adherence to the standard and their ability to operate in networks of products from multiple vendors. Sercos International e.V. supports a Conformance Laboratory at the University of Stuttgart's Institute for Control Engineering of Machine Tools and Manufacturing Units (ISW). Products successfully passing conformance testing may display a mark indicating they are conformance tested. Conformance-tested Sercos I and II products are publicized in an index of certified products, Sercos I and II . Conformance-tested Sercos III products are publicized in an index of certified products, Sercos III . | https://en.wikipedia.org/wiki/SERCOS_interface |
SERENDIP ( Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations ) is a Search for Extra-Terrestrial Intelligence (SETI) program originated by the Berkeley SETI Research Center at the University of California, Berkeley . [ 1 ]
SERENDIP takes advantage of ongoing "mainstream" radio telescope observations as a " piggy-back " or " commensal " program. Rather than having its own observation program, SERENDIP analyzes deep space radio telescope data that it obtains while other astronomers are using the telescope.
The initial SERENDIP instrument was a 100-channel analog radio spectrometer covering 100 kHz of bandwidth . Subsequent instruments have been significantly more capable, with the number of channels doubling roughly every year. These instruments have been deployed at a large number of telescopes including the NRAO 90m telescope at the Green Bank Observatory and the Arecibo 305m telescope .
SERENDIP observations have been conducted at frequencies between 400 MHz and 5 GHz , with most observations near the so-called Cosmic Water Hole (1.42 GHz (21 cm) neutral hydrogen and 1.66 GHz hydroxyl transitions).
SERENDIP V was installed at the Arecibo Observatory in June 2009. The digital back-end instrument was an FPGA -based 128 million-channel digital spectrometer covering 200 MHz of bandwidth. It took data commensally with the seven-beam Arecibo L-band Feed Array (ALFA). [ 2 ]
The next generation of SERENDIP experiments, SERENDIP VI was deployed in 2014 at both Arecibo and the Green Bank Telescope . [ 3 ] SERENDIP VI will also look for fast radio bursts, in collaboration with scientists from University of Oxford and West Virginia University . [ 4 ]
The program has found around 400 suspicious signals, but there is not enough data to prove that they belong to extraterrestrial intelligence . [ 5 ] In September–October 2004 the media wrote about Radio source SHGb02+14a and its artificial origin, but scrutiny has not been able to confirm its connection with an extraterrestrial civilization. [ 6 ] Currently no confirmed extraterrestrial signals have been found. [ 7 ] | https://en.wikipedia.org/wiki/SERENDIP |
A spin exchange relaxation-free ( SERF ) magnetometer is a type of magnetometer developed at Princeton University in the early 2000s. SERF magnetometers measure magnetic fields by using lasers to detect the interaction between alkali metal atoms in a vapor and the magnetic field.
The name for the technique comes from the fact that spin exchange relaxation , a mechanism which usually scrambles the orientation of atomic spins , is avoided in these magnetometers. This is done by using a high (10 14 cm −3 ) density of potassium atoms and a very low magnetic field. Under these conditions, the atoms exchange spin quickly compared to their magnetic precession frequency so that the average spin interacts with the field and is not destroyed by decoherence. [ 1 ]
A SERF magnetometer achieves very high magnetic field sensitivity by monitoring a high density vapor of alkali metal atoms precessing in a near-zero magnetic field. [ 2 ] The sensitivity of SERF magnetometers improves upon traditional atomic magnetometers by eliminating the dominant cause of atomic spin decoherence caused by spin-exchange collisions among the alkali metal atoms. SERF magnetometers are among the most sensitive magnetic field sensors and in some cases exceed the performance of SQUID detectors of equivalent size. A small 1 cm 3 volume glass cell containing potassium vapor has reported 1 fT/ √ Hz sensitivity and can theoretically become even more sensitive with larger volumes. [ 3 ] They are vector magnetometers capable of measuring all three components of the magnetic field simultaneously. [ citation needed ]
Spin-exchange collisions preserve total angular momentum of a colliding pair of atoms but can scramble the hyperfine state of the atoms. Atoms in different hyperfine states do not precess coherently and thereby limit the coherence lifetime of the atoms. However, decoherence due to spin-exchange collisions can be nearly eliminated if the spin-exchange collisions occur much faster than the precession frequency of the atoms. In this regime of fast spin-exchange, all atoms in an ensemble rapidly change hyperfine states, spending the same amounts of time in each hyperfine state and causing the spin ensemble to precess more slowly but remain coherent. This so-called SERF regime can be reached by operating with sufficiently high alkali metal density (at higher temperature) and in sufficiently low magnetic field. [ 4 ]
The spin-exchange relaxation rate R s e {\displaystyle R_{se}} for atoms with low polarization experiencing slow spin-exchange can be expressed as follows: [ 4 ]
where T s e {\displaystyle T_{se}} is the time between spin-exchange collisions, I {\displaystyle I} is the nuclear spin, ν {\displaystyle \nu } is the magnetic resonance frequency, γ e {\displaystyle \gamma _{e}} is the gyromagnetic ratio for an electron.
In the limit of fast spin-exchange and small magnetic field, the spin-exchange relaxation rate vanishes for sufficiently small magnetic field: [ 2 ]
where Q {\displaystyle Q} is the "slowing-down" constant to account for sharing of angular momentum between the electron and nuclear spins: [ 5 ]
where P {\displaystyle P} is the average polarization of the atoms. The atoms suffering fast spin-exchange precess more slowly when they are not fully polarized because they spend a fraction of the time in different hyperfine states precessing at different frequencies (or in the opposite direction).
The sensitivity δ B {\displaystyle \delta B} of atomic magnetometers are limited by the number of atoms N {\displaystyle N} and their spin coherence lifetime T 2 {\displaystyle T_{2}} according to
where γ {\displaystyle \gamma } is the gyromagnetic ratio of the atom and F z {\displaystyle F_{z}} is the average polarization of total atomic spin F = I + S {\displaystyle F=I+S} . [ 6 ]
In the absence of spin-exchange relaxation, a variety of other relaxation mechanisms contribute to the decoherence of atomic spin: [ 2 ]
where R D {\displaystyle R_{D}} is the relaxation rate due to collisions with the cell walls and R s d , X {\displaystyle R_{sd,X}} are the spin destruction rates for collisions among the alkali metal atoms and collisions between alkali atoms and any other gasses that may be present.
In an optimal configuration, a density of 10 14 cm −3 potassium atoms in a 1 cm 3 vapor cell with ~3 atm helium buffer gas can achieve 10 aT Hz −1/2 (10 −17 T Hz −1/2 ) sensitivity with relaxation rate R t o t {\displaystyle R_{tot}} ≈ 1 Hz. [ 2 ]
Alkali metal vapor of sufficient density is obtained by simply heating solid alkali metal inside the vapor cell. A typical SERF atomic magnetometer can take advantage of low noise diode lasers to polarize and monitor spin precession. Circularly polarized pumping light tuned to the D 1 {\displaystyle D_{1}} spectral resonance line polarizes the atoms. An orthogonal probe beam detects the precession using optical rotation of linearly polarized light. In a typical SERF magnetometer, the spins merely tip by a very small angle because the precession frequency is slow compared to the relaxation rates.
SERF magnetometers compete with SQUID magnetometers for use in a variety of applications. The SERF magnetometer has the following advantages:
Potential disadvantages:
Applications utilizing high sensitivity of SERF magnetometers potentially include:
The SERF magnetometer was developed by Michael V. Romalis at Princeton University in the early 2000s. [ 2 ] The underlying physics governing the suppression spin-exchange relaxation was developed decades earlier by William Happer [ 4 ] but the application to magnetic field measurement was not explored at that time. The name "SERF" was partially motivated by its relationship to SQUID detectors in a marine metaphor. | https://en.wikipedia.org/wiki/SERF |
SERVIR-Mekong project is a joint initiative by the US agency for International Development ( USAID ), NASA and five other countries which are Myanmar, Thailand, Cambodia, Laos and Vietnam. "Servir" is a Spanish word which means "to serve". The project aims to use the latest technologies to help the Mekong river region protect its vital ecosystem. It helps to connect USAID's development network with NASA's technology and satellite data to provide mapping information and satellite imagery. [ 1 ] [ 2 ]
The first such experimental hub was launched in Panama in 2005 to serve the near region. The project was initially undertaken by researchers at NASA's Marshall Space Flight Center in Alabama . [ 3 ] In the Earth Observation Summit, 2007, SERVIR was recognized as a model for the effectuation of the Global Earth Observation System of Systems (GEOSS). In 2010, the organisation had a presence in the Himalayas when a hub, SERVIR-Himalaya, was established at the International Centre for Integrated Mountain Development (ICIMOD) in Kathmandu, Nepal. [ 4 ] The organization has launched similar projects in the past for other regions in Latin America, Africa and Asia.
The project stresses the vital issues associated in the Mekong river basin region which encompasses all the five countries which are also known as the rice bowl of Asia . The project will also allow these countries to better deal with natural disasters and climate studies like green house gas emissions and its effects. It also enables them to use their water resources more efficiently. [ 5 ]
The Mekong basin is covers almost 5,000 kilometres (3,100 mi) from Tibetan plateau up to the South China Sea region. It gives livelihood to almost 40 million people. The environment is considered one of the most volatile ones in the world. The project uses space applications and helps to create geospatial data which is later analyzed to avoid natural disasters like floods and others in the lower Mekong region. [ 1 ]
The implementation of the project is undertaken by the Asian Disaster Preparedness Center (ADPC) in consortium with Stockholm Environment Institute (SEI), Spatial Informatics Group (SIG) and Deltares. The first phase of the project was launched on 31 August 2015. [ 3 ] [ 6 ]
SERVIR-Mekong is an example of the technical collaboration in the region and development of a common analysis. It also aims to see environmental planning agencies leading in technical support and take better development decisions. SERVIR has also served in development of more than 30 countries of Latin America, Africa and Asia which includes providing tools and training to thousands of people of the region. [ 2 ] [ 7 ] | https://en.wikipedia.org/wiki/SERVIR_Mekong_Project |
SETI@home beta , is a hibernating volunteer computing project using the Berkeley Open Infrastructure for Network Computing ( BOINC ) platform, as a test environment for future SETI@home projects:
This astronomy -related article is a stub . You can help Wikipedia by expanding it .
This network -related software article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SETI@home_beta |
SETILive was an online project of Zooniverse that utilized live participants to analyze radio telescope data in real time to recognize patterns to find extraterrestrial intelligences (ETI's). The project ceased live operations on 12 October 2014, but still allows archival analysis. [ 1 ]
The project was launched in February 2012 as part of Jill Tarter 's 2009 TED Prize Wish. [ 2 ] SETILive uses data provided by the Allen Telescope Array and presents it visually so that the public can collectively search for radio signals. [ 3 ] The project focuses on radio frequencies that automated detection systems ignore due to the prevalence of man-made noise. Jill Tarter hopes that human analysts will be able to detect low signal-to-noise transmissions which confuse computers. [ 2 ] The telescope scans the zone between a known star and a known planet where liquid water is possible. This is called the habitable zone . The website displays one to three different scans of an area of space. Its energy is measured and put into a waterfall display . Users must identify the areas of high energy—signals—by making two points through which a line is drawn. [ 4 ] Users classify signals as: broken, continuous, or parallel. Users then must classify the signal as: erratic, wide, or narrow. Many of the signals are just satellites that give off energy.
The makers of SETILive intentionally put some false positives in. Sometimes, when a user clicks "done", a red line would identify the simulated ETI signal. [ 5 ]
Zooniverse projects:
This astrobiology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SETILive |
SEVEN Networks, Inc. is a privately funded American corporation founded in 2000. It had about 265 employees in 2010. [ 1 ] As of 2017, the company has research and development centers in Texas and Finland .
SEVEN mobile messaging products are turnkey multi-device, multi-service computer software for operators and device manufacturers. The company claims its products have a desktop-like experience for core messaging applications like email , instant messaging and social networking .
The company was formerly known as Leap Corporation and changed its name to SEVEN Networks, Inc. in December 2000. [ 2 ] In 2004, the company was selected for FierceWireless' list of 15 promising and innovative wireless startups of the year. [ 3 ] By 2005, CEO Bill Nguyen had left to start another company. [ 4 ] In 2006, the company announced Sprint as a customer. [ 5 ]
Since then, the company expanded its products to support email services, added mobile instant messaging applications, analytics and social networking .
In 2010, the company announced it was selected by Samsung Electronics to provide push technology for Samsung Social Hub, a social networking and integrated messaging service available on several of the company’s handsets. [ 6 ] In January 2010, the company claimed in a press release to have over eight million accounts actively synchronized on mobile devices using its software. [ 1 ] [ 7 ] In early 2011, the company announced Verizon Wireless as a customer [ 8 ] and also announced Open Channel. [ 9 ]
In 2012, the company announced a combined email, instant messaging and social media product, Ping. [ 10 ]
The Open Channel software product line focuses on mobile traffic management and optimization. There are Open Channel products for wireless signaling optimization, carrier network policy enforcement, and mobile data offloading . [ 11 ] Open Channel was launched in February 2011, as a service for carriers to manage the impact of push technology for message notifications on their networks. It works by monitoring requests for data from smartphone applications, such as Facebook , email and Twitter , which make up approximately two hundred of requests per hour, with only a small fraction of them actually returning data. [ 12 ]
The platform acts as a buffer in the network, determining when content for a particular app is available and then allowing the phone access to that content. [ 13 ] Early tests estimated mobile devices might reduce their time on a network by up to 40 percent and mobile traffic by up to 70 percent while boosting battery life by up to 25 percent. These numbers have not been updated since. [ 14 ]
Open Channel is transparent to connected applications and requires no changes or special integration by mobile developers. It does not require changes to the network and can work with new standards for fast network dormancy, smart signaling and other network optimizations. [ 15 ] In February 2011, Open Channel received the GSMA Global Mobile Award for Best Mobile Technology Breakthrough in 2011. [ 16 ]
In February 2013, Open Channel added offerings for policy enforcement and offloading. [ 17 ] Also in early 2013, Toronto-based wireless operator, Public Mobile, selected Open Channel to manage network signaling and reduce service costs stemming from non-optimized mobile applications and unnecessary data traffic, creating excess network congestion. [ 11 ]
In September 2015, Open Channel was made available for individual customers. [ 18 ]
SEVEN's push notification platform, System SEVEN, is deployed as a SaaS (software-as-a-service) solution. [ buzzword ] SEVEN Mobile Email [ 19 ] and SEVEN Mobile IM [ 20 ] are SEVEN's applications built on top of its push platform and its Ping Services [ 21 ] allow operators and device manufacturers to use the SEVEN push notification technology for messaging services and mobile applications. They provide mobile operators and device manufacturers with a service for integrated messaging services.
System SEVEN mobile email is a server-assisted service, where access to a user's email account appears to originate from IP addresses hosted by SEVEN (208.87.200.0 - 208.87.207.255) [ 22 ] or its customers. Although done with the user's permission, email service providers may flag these as potential hacking attempts and have raised security concerns, [ 23 ] most recently with Microsoft Outlook for Android and iOS. [ 24 ]
The firm works with mobile platform providers, device manufacturers, email messaging services, providers of services in the cloud, and infrastructure partners, to sell mobile messaging services.
Its systems use commonly deployed mobile platforms including Android , [ 25 ] Bada , BREW , [ 26 ] J2ME , [ 27 ] Symbian and Windows Mobile . [ 28 ] They work on products from device manufacturers, including HTC, INQ , LG , Motorola , Nokia , Sanyo, Samsung , and Sony Ericsson ; and are embedded in over 550 device types. [ 29 ] The firm has partnered with many of the top Internet service providers including Google , Microsoft (Exchange and Windows Live) and Yahoo !, [ 30 ] and infrastructure providers such as Equinix , [ 31 ] Savvis and Oracle . | https://en.wikipedia.org/wiki/SEVEN_Networks |
1,1,1,2-tetrafluorodisulfane , also known as 1,2-difluorodisulfane 1,1-difluoride or just difluorodisulfanedifluoride ( FSSF 3 ) is an unstable molecular compound of fluorine and sulfur . The molecule has a pair of sulfur atoms, with one fluorine atom on one sulfur, and three fluorine atoms on the other. It has the uncommon property that all the bond lengths are different. [ 3 ] The bond strength is not correlated with bond length but is inversely correlated with the force constant ( Badger's rule ). [ 3 ] The molecule can be considered as sulfur tetrafluoride in which a sulfur atom is inserted into a S-F bond. [ 3 ]
Atoms are labelled with the sulfur atom connected to three fluorine atoms as S hyp (for hypervalent) and S top . The fluorine atoms are labelled F top attached to S top , and on the hypervalent S atom: F cis , the closest F atom to F top , F trans the furthest away F atom from F top , and F eq [ 3 ]
Carlowitz first determined the structure in 1983. [ 3 ]
F eq is 90° from F trans , and 84° from F cis , and the torsion compared to F top is about 95°. [ 4 ]
The dimerization reaction 2SF 2 ⇌ FSSF 3 is reversible. [ 5 ] It also disproportionates: SF 2 + FSSF 3 → FSSF + SF 4 . [ 5 ] A side reaction also produces the intermediate F 3 SSSF 3 . [ 6 ] hydrogen fluoride catalyses disproportionation to sulfur and sulfur tetrafluoride by forming a reactive intermediate HSF molecule. [ 7 ] When FSSF 3 dissociates, the F cis atom forms a new bond to the S top atom, and the S-S bond breaks. [ 3 ] As a gas, at ambient and totally clean conditions, FSSF 3 decomposes with a half life of about 10 hours. Disproportionation to SSF 2 and SF 4 catalysed by metal fluorides can take place in under one second. However it is indefinitely stable at -196 °C. [ 4 ]
A symmetrical molecule F 2 SSF 2 is calculated to be 15.1 kcal/mol higher in energy than FSSF 3 . [ 3 ]
FSSF 3 is easily hydrolysed with water. [ 8 ]
FSSF 3 spontaneously reacts with oxygen gas to make thionyl fluoride , the only sulfur fluoride that does not need any assistance to do this. [ 8 ] FSSF 3 reacts with copper at high temperatures producing copper fluoride and copper sulfide. [ 8 ]
SF 3 SF can be made in the laboratory when low pressure (10 mm Hg) SCl 2 vapour is passed over potassium fluoride or mercuric fluoride heated to 150 °C. Byproducts include FSSF, SSF 2 , SF 4 , SF 3 SCl, and FSSCl. [ 8 ] SF 3 SCl can be removed from this mixture in a reaction with mercury. [ 8 ] Separation of the sulfur fluorides can be achieved by low temperature distillation. SF 3 SF distills just above -50 °C. [ 9 ]
SF 3 SF is also made in small amounts by reacting sulfur with silver fluoride , or photolysis of disulfur difluoride and SSF 2 . [ 8 ] The molecule is formed by the dimerization of sulfur difluoride . [ 3 ]
The nuclear magnetic resonance spectrum of FSSF 3 shows four bands, each of eight lines at -53.2, -5.7, 26.3 and 204.1 ppm. [ 5 ]
FSSF 3 is stable as a solid, as a liquid below -74 °C and dissolved in other sulfur fluoride liquids. [ 8 ] This is in contrast to SF 2 which is only stable as a dilute gas. [ 8 ]
Infrared vibration bands for FSSF 3 are at 810, 678, 530, 725, and 618(S-S) cm −1 . [ 8 ]
The related compound FSSSF 3 has a similar structure, but with an extra sulfur atom in the chain. Thiothionyltetrafluoride, S=SF 4 may exist as a gas. It is less energetically favourable to FSSF 3 by 37 kJ/mol, but has a high energy barrier of 267 kJ/mol. [ 10 ] However it may disproportionate rapidly to sulfur and sulfur tetrafluoride. [ 10 ] The other known sulfur fluorides are sulfur difluoride , sulfur tetrafluoride , sulfur hexafluoride , disulfur decafluoride , disulfur difluoride and thiothionyl fluoride , difluorotrisulfane , and difluorotetrasulfane . [ 10 ] The F top atom can be substituted with Cl to yield ClSSF 3 (2-chloro-1,1,1-trifluorodisulfane). [ 5 ] | https://en.wikipedia.org/wiki/SF3SF |
Sulfur tetrafluoride is a chemical compound with the formula S F 4 . It is a colorless corrosive gas that releases dangerous hydrogen fluoride gas upon exposure to water or moisture. Sulfur tetrafluoride is a useful reagent for the preparation of organofluorine compounds , [ 3 ] some of which are important in the pharmaceutical and specialty chemical industries.
Sulfur in SF 4 is in the +4 oxidation state , with one lone pair of electrons. The atoms in SF 4 are arranged in a see-saw shape , with the sulfur atom at the center. One of the three equatorial positions is occupied by a nonbonding lone pair of electrons. Consequently, the molecule has two distinct types of F ligands, two axial and two equatorial. The relevant bond distances are S–F ax = 164.3 pm and S–F eq = 154.2 pm. It is typical for the axial ligands in hypervalent molecules to be bonded less strongly.
The 19 F NMR spectrum of SF 4 reveals only one signal, which indicates that the axial and equatorial F atom positions rapidly interconvert via pseudorotation . [ 4 ]
At the laboratory scale, sulfur tetrafluoride is prepared from elemental sulfur and cobaltic fluoride [ 5 ]
SF 4 is industrially produced by the reaction of SCl 2 and NaF with acetonitrile as a catalyst [ 6 ]
At higher temperatures (e.g. 225–450 °C), the solvent is superfluous. Moreover, sulfur dichloride may be replaced by elemental sulfur (S) and chlorine (Cl 2 ) . [ 7 ] [ 8 ]
A low-temperature (e.g. 20–86 °C) alternative to the chlorinative process above uses liquid bromine (Br 2 ) as oxidant and solvent: [ 9 ]
In organic synthesis , SF 4 is used to convert COH and C=O groups into CF and CF 2 groups, respectively. [ 10 ] The efficiency of these conversions are highly variable.
In the laboratory, the use of SF 4 has been superseded by the safer and more easily handled diethylaminosulfur trifluoride , (C 2 H 5 ) 2 NSF 3 , "DAST": [ 11 ] This reagent is prepared from SF 4 : [ 12 ]
Sulfur chloride pentafluoride ( SF 5 Cl ), a useful source of the SF 5 group, is prepared from SF 4 . [ 13 ]
Hydrolysis of SF 4 gives sulfur dioxide : [ 14 ]
This reaction proceeds via the intermediacy of thionyl fluoride , which usually does not interfere with the use of SF 4 as a reagent. [ 6 ]
When amines are treated with SF 4 and a base, aminosulfur difluorides result. [ 15 ]
SF 4 reacts inside the lungs with moisture, forming sulfur dioxide and hydrogen fluoride which forms highly toxic and corrosive hydrofluoric acid [ 16 ] | https://en.wikipedia.org/wiki/SF4 |
Sulfur chloride pentafluoride is an inorganic compound with the formula SF 5 Cl . It exists as a colorless gas at room temperature and is highly toxic, like most inorganic compounds containing the pentafluorosulfide (– SF 5 ) functional group. [ 1 ] The compound adopts an octahedral geometry with C 4v symmetry. Sulfur chloride pentafluoride is the only commercially available reagent for adding the – SF 5 group to organic compounds. [ 2 ] [ 3 ]
SF 5 Cl is highly reactive and toxic. In contrast, sulfur hexafluoride ( SF 6 ) is inert and nontoxic despite having a closely related chemical formula. This difference highlights the lability of the S–Cl bond in SF 5 Cl .
Under free-radical conditions, SF 5 Cl adds across double bonds. The following reaction occurs with propene :
The addition reaction is catalyzed by (CH 3 CH 2 ) 3 B at around −30 °C. SF 5 Br is used similarly. [ 2 ]
SF 5 Cl is also a precursor to O(SF 5 ) 2 and F 2 NSF 5 (from tetrafluorohydrazine ).
Sulfur chloropentafluoride can be synthesized by several routes, starting from two lower sulfur fluorides, sulfur tetrafluoride and disulfur decafluoride : [ 1 ]
The corresponding SF 5 Br is prepared similarly from in-situ generated bromine monofluoride . [ 4 ] | https://en.wikipedia.org/wiki/SF5Cl |
Difluoroamino sulfur pentafluoride is a gaseous chemical compound of fluorine, sulfur, and nitrogen. It is unusual in having a hexa-coordinated sulfur atom with a link to nitrogen. Other names for this substance include difluoro(pentafluorosulfur)amine , pentafluorosulfanyldifluoramine , and pentafluorosulfanyl N , N -difluoramine .
Difluoroamino sulfur pentafluoride is a colourless gas at room temperature. [ 3 ] The molecule is shaped as a tetragonal bipyramid around the sulfur atom. [ 3 ]
To within half a degree the boiling point is -17.5 °C. [ 3 ]
Difluoroamino sulfur pentafluoride is stable at room temperature, but decomposes on the timescale of hours at 80 °C. Decomposition results in sulfur tetrafluoride and nitrogen trifluoride . [ 3 ] It is not stable above 220 °C. [ 4 ] It is stable with water or stainless steel. [ 4 ]
When stored in quartz and exposed to ultraviolet light, it decomposes slightly and reacts with silica to make SF 4 , N 2 F 4 , SF 6 , NF 3 , SO 2 F 2 , SOF 4 and N 2 O . [ 3 ]
The bond between sulfur and nitrogen is quite weak with a dissociation energy of 50 kcal/mol. [ 5 ]
The infrared spectrum contains strong absorption bands around 885, 910, and 950 cm −1 due to the bonds with fluorine. If a strong irradiation at 910 cm −1 with a laser takes place the molecules can be disrupted to form S 2 F 10 , SF 4 and N 2 F 4 . By adjusting the frequency of a laser, the break up can be made isotope selective, and also the S 2 F 10 can be broken up by another nearby frequency. [ 5 ]
The fluorine atoms attached to the sulfur are attached at close to 90° from each other, and the four around the equator are also at 90° from the nitrogen sulfur bond. The angle subtended by fluorine atoms on the nitrogen atom is about 98°, and the sulfur-nitrogen-fluorine angle is about 111°. The distance between sulfur and the four equatorial fluorine atoms is 1.545 Å. The axial fluorine to sulfur distance is 1.556 Å. Nitrogen sulfur distance is about 1.696 Å. The fluorine-nitrogen bond is the shortest in the molecule at 1.378 Å. [ 1 ]
Difluoroamino sulfur pentafluoride has been prepared by irradiating a mixture of dinitrogen tetrafluoride and sulfur tetrafluoride with ultraviolet light.
This preparation also works with a mixture of dinitrogen tetrafluoride and sulfur chloride pentafluoride . Formation requires the appearance of the SF 5 radical and chlorine atoms, as well as the nitrogen difluoride radical. [ 3 ]
Another way to make difluoroamino sulfur pentafluoride is by heating dinitrogen tetrafluoride and sulfur. This results in the temporary formation of nitrogen difluoride . However the yield is only around 6%, and mostly sulfur tetrafluoride is formed. [ 3 ] Yet other substrates for dinitrogen tetrafluoride are disulfur decafluoride or sulfur dioxide or thiophosgene in an electric discharge. [ 6 ]
A corona discharge in a sulfur hexafluoride , nitrogen mixture produces a small amount of difluoroamino sulfur pentafluoride. This is important as high voltage equipment is often insulated with this gas combination. [ 7 ]
Pentafluorosulfanylamine reacts with fluorine gas to yield difluoroamino sulfur pentafluoride: [ 8 ]
Difluoroamino sulfur pentafluoride reacts with Lewis acids like KrF + AsF 6 − at -31 °C to yield SF 6 , Kr, NF 3 and solid N 2 F + AsF 6 − . With AsF 5 at -196 °C (as liquid) it produces solid N 2 F + AsF 6 − , SF 6 and trans-N 2 F 2 . Similar products also come from room temperature reactions. [ 9 ]
There is a Russian patent to use a combination of alkenes and difluoroamino sulfur pentafluoride as a rocket fuel. [ 10 ]
Related substances include fluoroimidotetrafluorosulfur F 4 S=NF and (SF 5 ) 2 NF. [ 11 ] A tertiary amine exists with formula (SF 5 ) 3 N.
Other variant substitutions on the nitrogen atom yield SF 5 NFCl, SF 5 NHF, SF 5 NCl 2 and SF 5 NH 2 . | https://en.wikipedia.org/wiki/SF5NF2 |
Esaflon Sulfur(VI) fluoride
Sulfur tetrafluoride
Sulfuryl fluoride Tellurium hexafluoride Polonium hexafluoride
Sulfur hexafluoride or sulphur hexafluoride ( British spelling ) is an inorganic compound with the formula SF 6 . It is a colorless, odorless, non- flammable , and non-toxic gas. SF 6 has an octahedral geometry , consisting of six fluorine atoms attached to a central sulfur atom. It is a hypervalent molecule . [ citation needed ]
Typical for a nonpolar gas, SF 6 is poorly soluble in water but quite soluble in nonpolar organic solvents. It has a density of 6.12 g/L at sea level conditions, considerably higher than the density of air (1.225 g/L). It is generally stored and transported as a liquefied compressed gas . [ 8 ]
SF 6 has 23,500 times greater global warming potential (GWP) than CO 2 as a greenhouse gas (over a 100-year time-frame) but exists in relatively minor concentrations in the atmosphere. Its concentration in Earth's troposphere reached 11.50 parts per trillion (ppt) in October 2023, rising at 0.37 ppt/year. [ 9 ] The increase since 1980 is driven in large part by the expanding electric power sector, including fugitive emissions from banks of SF 6 gas contained in its medium- and high-voltage switchgear . Uses in magnesium, aluminium, and electronics manufacturing also hastened atmospheric growth. [ 10 ] The 1997 Kyoto Protocol , which came into force in 2005, is supposed to limit emissions of this gas. In a somewhat nebulous way it has been included as part of the carbon emission trading scheme. In some countries this has led to the defunction of entire industries. [ 11 ]
Sulfur hexafluoride on Earth exists primarily as a synthetic industrial gas, but has also been found to occur naturally. [ 12 ]
SF 6 can be prepared from the elements through exposure of S 8 to F 2 . This was the method used by the discoverers Henri Moissan and Paul Lebeau in 1901. Some other sulfur fluorides are cogenerated, but these are removed by heating the mixture to disproportionate any S 2 F 10 (which is highly toxic) and then scrubbing the product with NaOH to destroy remaining SF 4 . [ clarification needed ]
Alternatively, using bromine , sulfur hexafluoride can be synthesized from SF 4 and CoF 3 at lower temperatures (e.g. 100 °C), as follows: [ 13 ]
There is virtually no reaction chemistry for SF 6 . A main contribution to the inertness of SF 6 is the steric hindrance of the sulfur atom, whereas its heavier group 16 counterparts, such as SeF 6 are more reactive than SF 6 as a result of less steric hindrance. [ 14 ] It does not react with molten sodium below its boiling point, [ 15 ] but reacts exothermically with lithium . As a result of its inertness, SF 6 has an atmospheric lifetime of around 3200 years, and no significant environmental sinks other than the ocean. [ 16 ]
By 2000, the electrical power industry is estimated to use about 80% of the sulfur hexafluoride produced, mostly as a gaseous dielectric medium . [ 17 ] Other main uses as of 2015 included a silicon etchant for semiconductor manufacturing , and an inert gas for the casting of magnesium . [ 18 ]
SF 6 is used in the electrical industry as a gaseous dielectric medium for high-voltage sulfur hexafluoride circuit breakers , switchgear , and other electrical equipment, often replacing oil-filled circuit breakers (OCBs) that can contain harmful polychlorinated biphenyls (PCBs). SF 6 gas under pressure is used as an insulator in gas insulated switchgear (GIS) because it has a much higher dielectric strength than air or dry nitrogen . The high dielectric strength is a result of the gas's high electronegativity and density . This property makes it possible to significantly reduce the size of electrical gear. This makes GIS more suitable for certain purposes such as indoor placement, as opposed to air-insulated electrical gear, which takes up considerably more room.
Gas-insulated electrical gear is also more resistant to the effects of pollution and climate, as well as being more reliable in long-term operation because of its controlled operating environment. Exposure to an arc chemically breaks down SF 6 though most of the decomposition products tend to quickly re-form SF 6 , a process termed "self-healing". [ 19 ] Arcing or corona can produce disulfur decafluoride ( S 2 F 10 ), a highly toxic gas, with toxicity similar to phosgene . S 2 F 10 was considered a potential chemical warfare agent in World War II because it does not produce lacrimation or skin irritation, thus providing little warning of exposure.
SF 6 is also commonly encountered as a high voltage dielectric in the high voltage supplies of particle accelerators , such as Van de Graaff generators and Pelletrons and high voltage transmission electron microscopes .
Alternatives to SF 6 as a dielectric gas include several fluoroketones. [ 20 ] [ 21 ] Compact GIS technology that combines vacuum switching with clean air insulation has been introduced for a subset of applications up to 420 kV . [ 22 ]
SF 6 is used to provide a tamponade or plug of a retinal hole in retinal detachment repair operations [ 23 ] in the form of a gas bubble. It is inert in the vitreous chamber . [ 24 ] The bubble initially doubles its volume in 36 hours due to oxygen and nitrogen entering it, before being absorbed in the blood in 10–14 days. [ 25 ]
SF 6 is used as a contrast agent for ultrasound imaging. Sulfur hexafluoride microbubbles are administered in solution through injection into a peripheral vein. These microbubbles enhance the visibility of blood vessels to ultrasound. This application has been used to examine the vascularity of tumours. [ 26 ] It remains visible in the blood for 3 to 8 minutes, and is exhaled by the lungs. [ 27 ]
Sulfur hexafluoride was the tracer gas used in the first roadway air dispersion model calibration; this research program was sponsored by the U.S. Environmental Protection Agency and conducted in Sunnyvale, California on U.S. Highway 101 . [ 28 ] Gaseous SF 6 is used as a tracer gas in short-term experiments of ventilation efficiency in buildings and indoor enclosures, and for determining infiltration rates. Two major factors recommend its use: its concentration can be measured with satisfactory accuracy at very low concentrations, and the Earth's atmosphere has a negligible concentration of SF 6 .
Sulfur hexafluoride was used as a non-toxic test gas in an experiment at St John's Wood tube station in London , United Kingdom on 25 March 2007. [ 29 ] The gas was released throughout the station, and monitored as it drifted around. The purpose of the experiment, which had been announced earlier in March by the Secretary of State for Transport Douglas Alexander , was to investigate how toxic gas might spread throughout London Underground stations and buildings during a terrorist attack.
Sulfur hexafluoride is also routinely used as a tracer gas in laboratory fume hood containment testing. The gas is used in the final stage of ASHRAE 110 fume hood qualification. A plume of gas is generated inside of the fume hood and a battery of tests are performed while a gas analyzer arranged outside of the hood samples for SF 6 to verify the containment properties of the fume hood.
It has been used successfully as a transient tracer in oceanography to study diapycnal mixing and air-sea gas exchange. [ 30 ] The concentration of sulfur hexafluoride in seawater (typically on the order of femtomoles per kilogram [ 31 ] ) has been classified by the international oceanography community as a "level one" measurement, denoting the highest priority data for observing ocean changes. [ 32 ]
According to the Intergovernmental Panel on Climate Change , SF 6 is the most potent greenhouse gas . Its global warming potential of 23,900 times that of CO 2 when compared over a 100-year period. [ 45 ] Sulfur hexafluoride is inert in the troposphere and stratosphere and is extremely long-lived, with an estimated atmospheric lifetime of 800–3,200 years. [ 46 ]
Measurements of SF 6 show that its global average mixing ratio has increased from a steady base of about 54 parts per quadrillion [ 12 ] prior to industrialization, to over 11.5 parts per trillion (ppt) as of October 2023, and is increasing by about 0.4 ppt (3.5%) per year. [ 9 ] [ 47 ] Average global SF 6 concentrations increased by about 7% per year during the 1980s and 1990s, mostly as the result of its use in magnesium production, and by electrical utilities and electronics manufacturers. Given the small amounts of SF 6 released compared to carbon dioxide , its overall individual contribution to global warming is estimated to be less than 0.2%, [ 48 ] however the collective contribution of it and similar man-made halogenated gases has reached about 10% as of 2020. [ 49 ] Alternatives are being tested. [ 50 ] [ 51 ]
In Europe, SF 6 falls under the F-Gas directive which ban or control its use for several applications. [ 52 ] Since 1 January 2006, SF 6 is banned as a tracer gas and in all applications except high-voltage switchgear . [ 53 ] It was reported in 2013 that a three-year effort by the United States Department of Energy to identify and fix leaks at its laboratories in the United States such as the Princeton Plasma Physics Laboratory , where the gas is used as a high voltage insulator, had been productive, cutting annual leaks by 1,030 kilograms (2,280 pounds). This was done by comparing purchases with inventory, assuming the difference was leaked, then locating and fixing the leaks. [ 54 ]
Sulfur hexafluoride is a nontoxic gas, but by displacing oxygen in the lungs, it also carries the risk of asphyxia if too much is inhaled. [ 55 ] Since it is more dense than air, a substantial quantity of gas, when released, will settle in low-lying areas and present a significant risk of asphyxiation if the area is entered. That is particularly relevant to its use as an insulator in electrical equipment since workers may be in trenches or pits below equipment containing SF 6 . [ 56 ]
As with all gases, the density of SF 6 affects the resonance frequencies of the vocal tract, thus changing drastically the vocal sound qualities, or timbre , of those who inhale it. It does not affect the vibrations of the vocal folds. The density of sulfur hexafluoride is relatively high at room temperature and pressure due to the gas's large molar mass . Unlike helium , which has a molar mass of about 4 g/mol and pitches the voice up, SF 6 has a molar mass of about 146 g/mol, and the speed of sound through the gas is about 134 m/s at room temperature, pitching the voice down. For comparison, the molar mass of air, which is about 80% nitrogen and 20% oxygen, is approximately 30 g/mol which leads to a speed of sound of 343 m/s. [ 57 ]
Sulfur hexafluoride has an anesthetic potency slightly lower than nitrous oxide ; [ 58 ] it is classified as a mild anesthetic. [ 59 ] | https://en.wikipedia.org/wiki/SF6 |
The SH2 ( S rc H omology 2 ) domain is a structurally conserved protein domain contained within the Src oncoprotein [ 2 ] and in many other intracellular signal-transducing proteins. [ 3 ] SH2 domains bind to phosphorylated tyrosine residues on other proteins, modifying the function or activity of the SH2-containing protein. The SH2 domain may be considered the prototypical modular protein-protein interaction domain, allowing the transmission of signals controlling a variety of cellular functions. [ 4 ] SH2 domains are especially common in adaptor proteins that aid in the signal transduction of receptor tyrosine kinase pathways. [ 5 ]
SH2 domains contain about 100 amino acid residues and exhibit a central antiparallel β-sheet centered between two α-helices . [ 6 ] Binding to phosphotyrosine -containing peptides involves a strictly-conserved Arg residue that pairs with the negatively-charged phosphate on the phosphotyrosine, [ 7 ] and a surrounding pocket that recognizes flanking sequences on the target peptide. [ 6 ] [ 7 ] Compared to other signaling proteins, SH2 domains exhibit only a moderate degree of specificity for their target peptides, due to the relative weakness of the interactions with the flanking sequences. [ 8 ]
Over 100 human proteins are known to contain SH2 domains. [ 9 ] A variety of tyrosine-containing sequences have been found to bind SH2 domains and are conserved across a wide range of organisms, performing similar functions. [ 10 ] Binding of a phosphotyrosine-containing protein to an SH2 domain may lead to either activation or inactivation of the SH2-containing protein, depending on the types of interactions formed between the SH2 domain and other domains of the enzyme. Mutations that disrupt the structural stability of the SH2 domain, or that affect the binding of the phosphotyrosine peptide of the target, are involved in a range of diseases including X-linked agammaglobulinemia and severe combined immunodeficiency . [ 11 ]
SH2 domains are not present in yeast and appear at the boundary between protozoa and animalia in organisms such as the social amoeba Dictyostelium discoideum . [ 12 ]
A detailed bioinformatic examination of SH2 domains of human and mouse reveals 120 SH2 domains contained within 115 proteins encoded by the human genome, [ 13 ] representing a rapid rate of evolutionary expansion among the SH2 domains.
A large number of SH2 domain structures have been solved and many SH2 proteins have been knocked out in mice.
SH2 domains, and other binding domains , have been used in protein engineering to create protein assemblies. Protein assemblies are formed when several proteins bind to one another to create a larger structure (called a supramolecular assembly ). Using molecular biology techniques, fusion proteins of specific enzymes and SH2 domains have been created, which can bind to each other to form protein assemblies.
Since SH2 domains require phosphorylation in order for binding to occur, the use of kinase and phosphatase enzymes gives researchers control over whether protein assemblies will form or not. High affinity engineered SH2 domains have been developed and utilized for protein assembly applications. [ 14 ]
The goal of most protein assembly formation is to increase the efficiency of metabolic pathways via enzymatic co-localization. [ 15 ] Other applications of SH2 domain mediated protein assemblies have been in the formation of high density fractal-like structures, which have extensive molecular trapping properties. [ 16 ]
Human proteins containing this domain include: | https://en.wikipedia.org/wiki/SH2_domain |
SH3BP2 ( SH3 domain -binding protein 2) is a protein that comes from a gene located on Chromosome 4. It is widely expressed in hematopoietic cells, including: Macrophages , B and T lymphocytes , and osteoclast precursors. SH3BP2 has an N-terminal pleckstrin homology domain to bind differentially to the SH3 domains of certain proteins of signal transduction pathways, as well as a proline-rich domain and a C-terminal Src homology domain . [ 1 ] It functions as an adaptor protein involved in signaling pathways, in concert with SRC kinases, SYK, and PLCγ , affecting immune cell activation, inflammatory signaling, and bone metabolism-- it is also associated with cherubism. It binds to phosphatidylinositol, linking the hemopoietic tyrosine kinase fes to the cytoplasmic membrane in a phosphorylation-dependent mechanism.
A gain-of-function mutation in the protein's exon 9 region leads to several common mutations that affect its proline-rich domain, resulting in its hyperactivation. This upregulation of SH3BP2 increases osteoclast formation and activity, causing bone reabsorption and cyst-like lesions in a TNF-α-dependent mechanism. [ 2 ]
Mutated SH3BP2 can lead to upregulation of pro-inflammatory cytokines, including Tumor Necrosis Factor-alpha (TNF-α) , interleukin 1-beta ( IL-1β) , and RANKL , creating a positive feedback loop furthering osteoclast activation. [ 1 ]
SH3BP2 is a key regulator in the growth and survival of gastrointestinal stromal tumors . It supports the expression of two transcriptional factors, ETV1 and MITF, and receptor kinases, KIT and PDGFRA .
There are certain therapies for GISTs that involve silencing SH3BP2 to reduce the expression of the receptor kinases KIT and PDGFRA, which are commonly mutated and drive GISTs development. [ 3 ] The silencing of the adaptor protein, SH3BP2, also indirectly downregulates ETV1 and MITF, through miRNA-mediated post-transcriptional repression. [ 4 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SH3BP2 |
SHAPE.AG (formerly SHAPE Services ) is a cross-platform independent software vendor and web-based services provider. The company develops instant messaging , social networking , productivity, entertainment, games, media and location-based applications for Apple iPhone , [ 1 ] iPod Touch and iPad , [ 2 ] BlackBerry , [ 3 ] Windows Phone / Windows Mobile , Android , Symbian S60 , UIQ , J2ME , and HP / Palm webOS mobile platforms.
SHAPE.AG (with AG standing for Apps&Games [ citation needed ] )is a worldwide operating company headquartered in Stuttgart , Germany and offices in Germany and Ukraine. The company was founded in 2002 and as of 2011 had more than 60 employees. In May 2008 SHAPE acquired Warelex LLC, the US developer of multimedia applications and technologies for mobile devices. [ 4 ] In July 2011 SHAPE has agreed to acquire Crisp App, the Hong Kong–based developer of the fone app for iOS. [ 5 ] In 2011 the company added location-based instant messaging service Neighbors into IM+ application. In 2012 SHAPE raised $10 million from Russian investment firm Finam. [ 6 ] In March 2012 SHAPE officially changed its name from SHAPE Services to SHAPE.AG (AG stands for Apps&Games [ citation needed ] ).
The company's best-known software products include: | https://en.wikipedia.org/wiki/SHAPE_Services |
SHEEP is one of the earliest interactive symbolic computation systems . It is specialized for computations with tensors , and was designed for the needs of researchers working with general relativity and other theories involving extensive tensor calculus computations. [ 1 ] [ 2 ]
SHEEP is a freeware package (copyrighted, but free for educational and research use). [ 3 ]
The name "SHEEP" is pun on the Lisp Algebraic Manipulator or LAM on which SHEEP is based. The package was written by Inge Frick, using earlier work by Ian Cohen and Ray d'Inverno , who had written ALAM - Atlas LISP Algebraic Manipulation in earlier (designed in 1970). [ 4 ] [ 5 ] SHEEP was an interactive computer package whereas LAM and ALAM were batch processing languages. [ 6 ]
Jan E. Åman wrote an important package in SHEEP to carry out the Cartan-Karlhede algorithm . A more recent version of SHEEP, written by Jim Skea, runs under Cambridge Lisp, which is also used for REDUCE .
This relativity -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SHEEP_(symbolic_computation_system) |
SHIFTCOR (Shift Correction) is a freely available web server as well as a stand-alone computer program for protein chemical shift re-referencing . [ 1 ] Chemical shift referencing is a particularly widespread problem in biomolecular NMR with up to 25% of existing NMR chemical shift assignments being improperly referenced. [ 1 ] Some of these referencing problems can lead to systematic errors of between 1.0 and 2.5 ppm (especially in 13C and 15N chemical shifts). Errors of this magnitude can play havoc with any attempt to compare assignments between proteins or to structurally interpret chemical shifts . Identifying which proteins are mis-assigned or improperly referenced can be challenging, as can correcting the errors once they are found. The SHIFTCOR program was designed to assist with identifying and fixing these chemical shift referencing problems. Specifically it compares, identifies, corrects and re-references 1H, 13C and 15N backbone chemical shifts of peptides and proteins by comparing the observed chemical shifts with the predicted chemical shifts derived from the 3D structure (using PDB coordinates) of the protein(s) of interest [ 1 ] [1]. The predicted chemical shifts are calculated using the ShiftX program. [ 2 ] The SHIFTCOR program was originally used to construct a database of properly re-referenced protein chemical shift assignments called RefDB. [ 1 ] RefDB is a web-accessible database of more than 2000 correctly referenced protein chemical shift assignments. While originally available as a stand-alone program only, SHIFTCOR has since been released for general use as a web server.
This biophysics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SHIFTCOR |
SHORTZ! for mobile content , is a mobile portal created [ when? ] for the exhibition of short films and animation series. The portal, although accessible on PC with certain Internet web browsers (such as Mozilla Firefox ), was conceived for viewing on mobile devices and thus only allows the download of short films on portable media players .
SHORTZ! offers currently a programming of over 700 short films (including many animation productions) and more than 20 mini-series from more than 30 European countries and 15 from non-European countries. The vast majority of the short movies are European.
The mobile portal navigation menu is available in 11 European languages. On the home page there are a number of short films that can be downloaded for free, although most of the catalogue can only be accessed through entering a code.
Both the website and the mobile site include information on short film festivals that take place across Europe. On the website there is also a section called "Behind the scenes" that provides an insight into the short film industry.
The mobile portal SHORTZ! has received the support of the European Commission MEDIA Program for the development of the audiovisual sector in the continent. Specifically Video on Demand (VOD) projects. | https://en.wikipedia.org/wiki/SHORTZ! |
SIAM Journal on Discrete Mathematics is a peer-reviewed mathematics journal published quarterly by the Society for Industrial and Applied Mathematics (SIAM). The journal includes articles on pure and applied discrete mathematics . It was established in 1988, along with the SIAM Journal on Matrix Analysis and Applications , to replace the SIAM Journal on Algebraic and Discrete Methods . The journal is indexed by Mathematical Reviews and Zentralblatt MATH . Its 2009 MCQ was 0.57. According to the Journal Citation Reports , the journal has a 2016 impact factor of 0.755. [ 1 ]
Although its official ISO abbreviation is SIAM J. Discrete Math. , its publisher and contributors frequently use the shorter abbreviation SIDMA .
This article about a mathematics journal is a stub . You can help Wikipedia by expanding it .
See tips for writing articles about academic journals . Further suggestions might be found on the article's talk page . | https://en.wikipedia.org/wiki/SIAM_Journal_on_Discrete_Mathematics |
SIA S.p.A. is an Italian company operating in the area of ICT , providing services to the banking and finance sector in addition to platforms for financial markets and e-payment services.
The company was founded in 1977 as Società Interbancaria per l'Automazione by Banca d'Italia , ABI and a pool of Italian banks. During the 1980s, SIA created the Rete Nazionale Interbancaria (RNI – national interbank network) and contributed to developing the interbank payments system in compliance with the white paper on payment systems in Italy, published by Banca d’Italia in 1987.
In 1983 SIA launched Bancomat and in 1987 introduced POS payments.
In 1992, from a branch of SIA's business, SSB - Società per i Servizi Bancari was born, a firm specializing in services in the field of electronic money . The new company worked on further developments in payment cards : Bancomat/Pagobancomat, FASTpay, borsellino elettronico (e-purse with the MINIpay product) and the Microcircuito project for the migration from magnetic stripe cards to microchip cards.
In 1999, SIA merged with Cedborsa, changing its name to "Società Interbancaria per l'Automazione - Cedborsa S.p.A.", working on the automation of the Borsa Italiana markets and the launch of the Italian gross payments markets e-MID and MTS.
In 2003, SIA developed the interbank payments system in Romania, [ 1 ] a condition for the country's entry into the European Union. [ 2 ]
In the early 2000s, SIA created and managed the technology platform for the STEP2 project, the first continental ACH ( automated clearing house ) for retail payments in euros .
In the same period, SIA created RTGS (Real Time Gross Settlement System) platforms for the central banks of Sweden, Norway, Egypt and Palestine. [ 3 ]
In May 2007, the merger between SIA and SSB gave birth to SIA-SSB S.p.A., a name simplified in 2011 to SIA S.p.A. [ 4 ]
In 2012, in partnership with Colt, SIA was awarded the tender announced by the European Central Bank and becomes a licensed Network Service Provider appointed to create the network infrastructure connecting central securities depositaries ( CSD ), central banks in the Eurosystem and major bank groups at European level to TARGET2-Securities (T2S). [ 5 ]
A year later, together with the same partner, SIA won the tender announced by Deutsche Bundesbank (which was also operating on behalf of Banca d’Italia, Banque de France and Banco de España) to create the network infrastructure linking the four central banks charged with managing the single platform of the Eurosystem to settle large payments and securities transactions. [ 6 ]
Over the course of 2013, SIA incorporated its Belgian subsidiary SiNSYS, [ 7 ] a company operating in the processing of payment cards, and acquired Emmecom, [ 8 ] an Italian firm in the sector of fixed, mobile and satellite telecommunications networks.
In the area of mobile payments , during 2014 SIA launched a service called Jiffy for sending and receiving cash in real time to and from a user's contacts by smartphone. [ 9 ]
At the end of 2014, SIA incorporated its subsidiary RA Computer and the payments Gateway business of its TSP subsidiary. [ 10 ] This led to the direct control of payment institution PI4PAY (effective from July 2011).
In January 2016, SIA acquired 69% of UBIQ, a startup born in 2012 from a spin-off of Parma University, specialized in designing and developing innovative technological solutions [ buzzword ] , particularly in the field of promotions, where it operates with the brand Ti Frutta. [ 11 ]
In April 2016, the Reserve Bank of New Zealand (RBNZ), New Zealand's central bank, chose SIA to develop the new Real-Time Gross Settlement (RTGS) system, to create the new domestic interbank payments system, replacing the Exchange Settlement Account System (ESAS). [ 12 ]
On June 2, 2016, SIA and Raphaels Bank, an issuing bank known for enabling innovation in payments, have agreed to a partnership agreement for the development and launch of payment solutions [ buzzword ] in the UK and throughout Europe. [ 13 ]
In August 2016, ČSOB , one of the largest commercial banks in the Czech Republic and part of the Belgian KBC Group, and SIA launched the first mobile wallet for NFC payments in the Czech Republic that supports both the MasterCard and VISA circuits. [ 14 ]
During the same month, Unicredit Business Integrated Solutions (UBIS), a company in the Unicredit Group , and SIA signed an agreement for the sale to the latter – for the sum of €500 million – of the processing activities of around 13.5 million payment cards and the management of 206,000 POS terminals and 12,000 ATMs in Italy, Germany and Austria. UBIS also signed with SIA a ten-year outsourcing contract for the supply of processing services for transactions made using debit, credit and prepaid cards, and for the management of POS and ATM terminals. [ 15 ]
In the final part of 2016, SIA launched a series of partnerships in the e-payments market: American Express Italia has chosen SIA to launch a completely digital and paperless service to support the request for new credit cards. This project uses authentication and digital signature systems to request a card in paperless mode. Moreover, Friday 23 December 2016 saw the completion of the acquisition by SIA of the processing activities of around 13.5 million payment cards and the management of 206,000 POS terminals and 12,000 ATM terminals in Italy, Germany and Austria from Unicredit Business Integrated Solutions (UBIS), a company in the Unicredit Group, for the sum of €500 million. Following this agreement, SIA S.p.A. on January 1, 2017 established two new companies: P4cards S.r.l., based in Verona, and Pforcards GmbH, based in Vienna, to manage the payment cards processing activities.
In the spring of 2017 the Central Bank of Iceland (CBI) has chosen SIA to implement and support the new real-time gross settlement system (RTGS) and the new instant payment platform. These technology infrastructures developed by SIA, planned to go live in 2018, will replace CBI's current mainframe-based real-time solutions [ buzzword ] for high and low-value payment systems, which have been operating since 2001. Central Bank of Iceland manages all interbank payments in the country. Despite the small population, it processes a quite significant daily volume of transactions: up to 1 million payments with a peak of 160,000 per hour. [ 16 ]
In May, Thomson Reuters launched the “SIABookbuilding” application on its flagship desktop platform Eikon, offering sell-side professionals a new fully integrated application for the IPO syndication and distribution process. SIABookbuilding is available through App Studio, Eikon's third-party development platform. [ 17 ]
A couple of weeks later, Poste Italiane and SIA have signed a deal that allows holders of debit cards and Postepay cards to use the Extra Sconti App, which is based on a cash-back mechanism to credit consumers' postal current accounts for supermarket purchases of brands recommended by the Extra Sconti App. [ 18 ]
On July 27, SIA celebrated its first 40 years of existence. [ 19 ]
On May 25, 2018, SIA and First Data Corporation have signed an agreement for SIA to acquire First Data's card processing businesses in parts of Central and Southeastern Europe for €375 million. In 2017, these businesses generated a combined revenue of approximately €100 million for First Data. This acquisition by SIA provides card processing, card production, call center and back-office services, including 13.3 million payment cards, 1.4 billion transactions, in addition to the management of POS terminals and ATMs. These businesses are primarily located in 7 countries: Greece, Croatia, Czech Republic, Hungary, Romania, Serbia and Slovakia. [ 20 ]
On November 29, 2018 the Board of Directors of SIA, meeting under the chairmanship of Giuliano Asperti, appointed Nicola Cordone to the position of Chief Executive Officer of the Company, after having co-opted him as Director. [ 21 ]
On 5 October 2020 it was announced SIA will merge with Nexi , will create one of Europe’s largest fintech groups. [ 22 ]
On December 16, 2021, Nexi signed the merger deed to create one of Europe's largest payment groups. The merger with SIA is effective as of Jan. 1, 2022. [ 23 ]
In 2017, the SIA Group processed overall the clearing of 13.1 billion transactions (+7% compared to 2016), 6.1 billion card transactions (+41.1%) and 3.3 billion payment transactions (+7.1%) relating to credit transfers and collections.
On the financial markets, the number of trading and post-trading transactions rose to 56.2 billion from 47.4 billion in 2016, an increase of 18.8%.
SIA handled a volume of traffic of over 784 terabytes of data, up 19.8% compared to 2016, on the 174,000 km of the SIAnet network, with total infrastructure availability and 100% service levels.
2017 saw a rise in SIA's revenues of €403.4 million, with a growth of €12.6 million (+3.2%). EBITDA is down at €114.6 million from €118.6 million in 2016 (-3.4%) and operating results reached €88.5 million (-12.1%). Net profit is €63.4 million, down by €6.4 million (-9.1%) compared to the previous financial year. These results, as well as SIA's net financial position, were affected by the acquisition of the cards business unit from UBIS for a sum of €500 million. [ 24 ] | https://en.wikipedia.org/wiki/SIA_S.p.A. |
In the context of quantum mechanics and quantum information theory , symmetric, informationally complete, positive operator-valued measures (SIC- POVMs ) are a particular type of generalized measurement (POVM) . SIC-POVMs are particularly notable thanks to their defining features of (1) being informationally complete; (2) having the minimal number of outcomes compatible with informational completeness, and (3) being highly symmetric. In this context, informational completeness is the property of a POVM of allowing to fully reconstruct input states from measurement data.
The properties of SIC-POVMs make them an interesting candidate for a "standard quantum measurement", utilized in the study of foundational quantum mechanics, most notably in QBism [ citation needed ] . SIC-POVMs have several applications in the context of quantum state tomography [ 1 ] and quantum cryptography , [ 2 ] and a possible connection has been discovered with Hilbert's twelfth problem . [ 3 ]
A POVM over a d {\displaystyle d} -dimensional Hilbert space H {\displaystyle {\mathcal {H}}} is a set of m {\displaystyle m} positive-semidefinite operators { F i } i = 1 m {\displaystyle \left\{F_{i}\right\}_{i=1}^{m}} that sum to the identity : ∑ i = 1 m F i = I . {\displaystyle \sum _{i=1}^{m}F_{i}=I.}
If a POVM consists of at least d 2 {\displaystyle d^{2}} operators which span the space of self-adjoint operators L ( H ) {\displaystyle {\mathcal {L}}({\mathcal {H}})} , it is said to be an informationally complete POVM (IC-POVM). IC-POVMs consisting of exactly d 2 {\displaystyle d^{2}} elements are called minimal. A set of d 2 {\displaystyle d^{2}} rank -1 projectors { Π i } i = 1 d 2 {\displaystyle \left\{\Pi _{i}\right\}_{i=1}^{d^{2}}} which have equal pairwise Hilbert–Schmidt inner products , T r ( Π i Π j ) = d δ i j + 1 d + 1 , {\displaystyle \mathrm {Tr} \left(\Pi _{i}\Pi _{j}\right)={\frac {d\delta _{ij}+1}{d+1}},} defines a minimal IC-POVM with elements F i = 1 d Π i {\displaystyle F_{i}={\frac {1}{d}}\Pi _{i}} called a SIC-POVM.
Consider an arbitrary set of rank-1 projectors ( Π i ) i = 1 d 2 {\displaystyle (\Pi _{i})_{i=1}^{d^{2}}} such that F i = Π i / d {\displaystyle F_{i}=\Pi _{i}/d} is a POVM, and thus 1 d ∑ i Π i = I {\displaystyle {\frac {1}{d}}\sum _{i}\Pi _{i}=I} . Asking the projectors to have equal pairwise inner products, T r ( Π i Π j ) = c {\displaystyle \mathrm {Tr} (\Pi _{i}\Pi _{j})=c} for all i ≠ j {\displaystyle i\neq j} , fixes the value of c {\displaystyle c} . To see this, observe that d = T r ( I 2 ) = 1 d 2 ∑ i , j T r ( Π i Π j ) = 1 d 2 ( d 2 + c d 2 ( d 2 − 1 ) ) {\displaystyle {\begin{aligned}d&=\mathrm {Tr} (I^{2})\\&={\frac {1}{d^{2}}}\sum _{i,j}\mathrm {Tr} (\Pi _{i}\Pi _{j})\\&={\frac {1}{d^{2}}}\left(d^{2}+cd^{2}(d^{2}-1)\right)\end{aligned}}} implies that c = 1 d + 1 {\displaystyle c={\frac {1}{d+1}}} . Thus, T r ( Π i Π j ) = d δ i j + 1 d + 1 . {\displaystyle \mathrm {Tr} \left(\Pi _{i}\Pi _{j}\right)={\frac {d\delta _{ij}+1}{d+1}}.} This property is what makes SIC-POVMs symmetric : Any pair of elements has the same Hilbert–Schmidt inner product as any other pair.
In using the SIC-POVM elements, an interesting superoperator can be constructed, the likes of which map L ( H ) → L ( H ) {\displaystyle {\mathcal {L}}({\mathcal {H}})\rightarrow {\mathcal {L}}({\mathcal {H}})} . This operator is most useful in considering the relation of SIC-POVMs with spherical t-designs . Consider the map
This operator acts on a SIC-POVM element in a way very similar to identity, in that
But since elements of a SIC-POVM can completely and uniquely determine any quantum state, this linear operator can be applied to the decomposition of any state, resulting in the ability to write the following:
From here, the left inverse can be calculated [ 4 ] to be G − 1 = 1 d [ ( d + 1 ) I − I ] {\displaystyle G^{-1}={\frac {1}{d}}\left[\left(d+1\right)I-{\mathcal {I}}\right]} , and so with the knowledge that
an expression for a state ρ {\displaystyle \rho } can be created in terms of a quasi-probability distribution , as follows:
where | ρ ) {\displaystyle |\rho )} is the Dirac notation for the density operator viewed in the Hilbert space L ( H ) {\displaystyle {\mathcal {L}}({\mathcal {H}})} . This shows that the appropriate quasi-probability distribution (termed as such because it may yield negative results) representation of the state ρ {\displaystyle \rho } is given by
For d = 2 {\displaystyle d=2} the equations that define the SIC-POVM can be solved by hand, yielding the vectors
which form the vertices of a regular tetrahedron in the Bloch sphere . The projectors that define the SIC-POVM are given by Π i = | ψ i ⟩ ⟨ ψ i | {\displaystyle \Pi _{i}=|\psi _{i}\rangle \langle \psi _{i}|} , and the elements of the SIC-POVM are thus F i = Π i / 2 = | ψ i ⟩ ⟨ ψ i | / 2 {\displaystyle F_{i}=\Pi _{i}/2=|\psi _{i}\rangle \!\langle \psi _{i}|/2} .
For higher dimensions this is not feasible, necessitating the use of a more sophisticated approach.
A SIC-POVM P {\displaystyle P} is said to be group covariant if there exists a group G {\displaystyle G} with a d 2 {\displaystyle d^{2}} -dimensional unitary representation such that
The search for SIC-POVMs can be greatly simplified by exploiting the property of group covariance. Indeed, the problem is reduced to finding a normalized fiducial vector | ϕ ⟩ {\displaystyle |\phi \rangle } such that
The SIC-POVM is then the set generated by the group action of U g {\displaystyle U_{g}} on | ϕ ⟩ {\displaystyle |\phi \rangle } .
So far, most SIC-POVM's have been found by considering group covariance under Z d × Z d {\displaystyle \mathbb {Z} _{d}\times \mathbb {Z} _{d}} . [ 5 ] To construct the unitary representation, we map Z d × Z d {\displaystyle \mathbb {Z} _{d}\times \mathbb {Z} _{d}} to U ( d ) {\displaystyle U(d)} , the group of unitary operators on d-dimensions. Several operators must first be introduced. Let | e i ⟩ {\displaystyle |e_{i}\rangle } be a basis for H {\displaystyle {\mathcal {H}}} , then the phase operator is
and the shift operator as
Combining these two operators yields the Weyl operator W ( p , q ) = S p T q {\displaystyle W(p,q)=S^{p}T^{q}} which generates the Heisenberg-Weyl group. This is a unitary operator since
It can be checked that the mapping ( p , q ) ∈ Z d × Z d → W ( p , q ) {\displaystyle (p,q)\in \mathbb {Z} _{d}\times \mathbb {Z} _{d}\rightarrow W(p,q)} is a projective unitary representation. It also satisfies all of the properties for group covariance, [ 6 ] and is useful for numerical calculation of SIC sets.
Given some of the useful properties of SIC-POVMs, it would be useful if it were positively known whether such sets could be constructed in a Hilbert space of arbitrary dimension. Originally proposed in the dissertation of Zauner, [ 7 ] a conjecture about the existence of a fiducial vector for arbitrary dimensions was hypothesized.
More specifically,
For every dimension d ≥ 2 {\displaystyle d\geq 2} there exists a SIC-POVM whose elements are the orbit of a positive rank-one operator E 0 {\displaystyle E_{0}} under the Weyl–Heisenberg group H d {\displaystyle H_{d}} . What is more, E 0 {\displaystyle E_{0}} commutes with an element T of the Jacobi group J d = H d ⋊ S L ( 2 , Z d ) {\displaystyle J_{d}=H_{d}\rtimes SL(2,\mathbb {Z} _{d})} . The action of T on H d {\displaystyle H_{d}} modulo the center has order three.
Utilizing the notion of group covariance on Z d × Z d {\displaystyle \mathbb {Z} _{d}\times \mathbb {Z} _{d}} , this can be restated as [ 8 ]
For any dimension d ∈ N {\displaystyle d\in \mathbb {N} } , let { k } k = 0 d − 1 {\displaystyle \left\{k\right\}_{k=0}^{d-1}} be an orthonormal basis for C d {\displaystyle \mathbb {C} ^{d}} , and define
Then ∃ | ϕ ⟩ ∈ C d {\displaystyle \exists |\phi \rangle \in \mathbb {C} ^{d}} such that the set { D j , k | ϕ ⟩ } j , k = 1 d {\displaystyle \left\{D_{j,k}|\phi \rangle \right\}_{j,k=1}^{d}} is a SIC-POVM.
The proof for the existence of SIC-POVMs for arbitrary dimensions remains an open question, [ 6 ] but is an ongoing field of research in the quantum information community.
Exact expressions for SIC sets have been found for Hilbert spaces of all dimensions from d = 2 {\displaystyle d=2} through d = 53 {\displaystyle d=53} inclusive, and in some higher dimensions as large as d = 5779 {\displaystyle d=5779} , for 115 values of d {\displaystyle d} in all. [ a ] Furthermore, using the Heisenberg group covariance on Z d × Z d {\displaystyle \mathbb {Z} _{d}\times \mathbb {Z} _{d}} , numerical solutions have been found for all integers up through d = 193 {\displaystyle d=193} , and in some larger dimensions up to d = 2208 {\displaystyle d=2208} . [ b ]
There exists a construction that has been conjectured to work for all prime dimensions of the form n 2 + 3 {\displaystyle n^{2}+3} for integer n {\displaystyle n} , [ 17 ] and another that has been conjectured to work for all dimensions. [ 18 ]
A spherical t-design is a set of vectors S = { | ϕ k ⟩ : | ϕ k ⟩ ∈ S d } {\displaystyle S=\left\{|\phi _{k}\rangle :|\phi _{k}\rangle \in \mathbb {S} ^{d}\right\}} on the d-dimensional generalized hypersphere , such that the average value of any t t h {\displaystyle t^{th}} -order polynomial f t ( ψ ) {\displaystyle f_{t}(\psi )} over S {\displaystyle S} is equal to the average of f t ( ψ ) {\displaystyle f_{t}(\psi )} over all normalized vectors | ψ ⟩ {\displaystyle |\psi \rangle } . Defining H t = ⨂ i = 1 t H {\displaystyle {\mathcal {H}}_{t}=\displaystyle \bigotimes _{i=1}^{t}{\mathcal {H}}} as the t-fold tensor product of the Hilbert spaces, and
as the t-fold tensor product frame operator, it can be shown that [ 8 ] a set of normalized vectors { | ϕ k ⟩ ∈ S d } k = 1 n {\displaystyle \left\{|\phi _{k}\rangle \in \mathbb {S} ^{d}\right\}_{k=1}^{n}} with n ≥ ( t + d − 1 d − 1 ) {\displaystyle n\geq {t+d-1 \choose d-1}} forms a spherical t-design if and only if
It then immediately follows that every SIC-POVM is a 2-design, since
which is precisely the necessary value that satisfies the above theorem.
In a d -dimensional Hilbert space, two distinct bases { | ψ i ⟩ } , { | ϕ j ⟩ } {\displaystyle \left\{|\psi _{i}\rangle \right\},\left\{|\phi _{j}\rangle \right\}} are said to be mutually unbiased if
This seems similar in nature to the symmetric property of SIC-POVMs. Wootters points out that a complete set of d + 1 {\displaystyle d+1} unbiased bases yields a geometric structure known as a finite projective plane , while a SIC-POVM (in any dimension that is a prime power ) yields a finite affine plane , a type of structure whose definition is identical to that of a finite projective plane with the roles of points and lines exchanged. In this sense, the problems of SIC-POVMs and of mutually unbiased bases are dual to one another. [ 19 ]
In dimension d = 3 {\displaystyle d=3} , the analogy can be taken further: a complete set of mutually unbiased bases can be directly constructed from a SIC-POVM. [ 20 ] The 9 vectors of the SIC-POVM, together with the 12 vectors of the mutually unbiased bases, form a set that can be used in a Kochen–Specker proof . [ 21 ] However, in 6-dimensional Hilbert space, a SIC-POVM is known, but no complete set of mutually unbiased bases has yet been discovered, and it is widely believed that no such set exists. [ 22 ] [ 23 ] | https://en.wikipedia.org/wiki/SIC-POVM |
In bioinformatics , SIDD is short for Stress-Induced ( DNA ) Duplex Destabilization. It is the melting of the DNA which is not induced by a promoter, but purely by the superhelical (also called topological) nature of the DNA. [ 1 ] It is based on a statistical mechanics treatment of DNA made by Craig J. Benham and Richard M. Fye. [ 2 ] This stress-induced unwinding was shown to coincide with DNA promoter regions of bacterial plasmids and may direct the global response of cells to changes in their external environments by affecting which genes are transcribed .
The computational model itself calculates the probability profile of a given base-pair sequence of DNA to denature, as well as the energy profile of sequence. It is through this energy profile that the technique derives its name: base pairs at lower energies are less stable (destabilized) than those of higher energies and more likely to denature. Stress related to the linking number (specifically its twist component) of the DNA causes the destabilization of the double helix (duplex); hence, Stress-Induced Duplex Destabilization.
Craig Benham has also developed an online applet that calculates the SIDD profile of input DNA sequences. [ 3 ] It also shows the probability profile for the given base pair sequence to denature, as well as counting the number and location of denaturation runs.
As the full SIDD computational method takes up a large amount of machine processing time (due to its complex nature), an accelerated algorithm proposed by Benham, et al., in their 1999 paper is implemented in the WebSIDD algorithm. This accelerated algorithm truncates the partition function by ignoring contributions of certain conformational states. [ citation needed ]
This chemical reaction article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SIDD |
SIESTA ( Spanish Initiative for Electronic Simulations with Thousands of Atoms ) is an original method and its computer program implementation, to efficiently perform electronic structure calculations and ab initio molecular dynamics simulations of molecules and solids. SIESTA uses strictly localized basis sets and the implementation of linear-scaling algorithms . Accuracy and speed can be set in a wide range, from quick exploratory calculations to highly accurate simulations matching the quality of other approaches, such as the plane-wave and all-electron methods .
SIESTA's backronym is the Spanish Initiative for Electronic Simulations with Thousands of Atoms.
Since 13 May 2016, with the 4.0 version announcement, SIESTA is released under the terms of the GPL open-source license. Source packages and access to the development versions can be obtained from the DevOps platform on GitLab . [ 2 ] The latest version, Siesta 5.2.2, was released on 4 February 2025.
SIESTA has these main characteristics:
SIESTA routinely provides:
And also (though not all options are compatible):
SIESTA's main strengths are:
The use of a linear combination of numerical atomic orbitals makes SIESTA a DFT code. SIESTA can produce very fast calculations with small basis sets, allowing the computation of systems with thousands of atoms. Alternatively, the use of more complete and accurate bases achieves accuracies comparable to those of standard plane wave calculations, with competitive performance.
SIESTA is in continuous development since it was implemented in 1996. The main solutions implemented in the current version are:
Several post-processing tools for SIESTA have been developed. These programs process SIESTA output or provide additional features.
Since its implementation, SIESTA has been used by researchers in geosciences, biology, and engineering (extending beyond materials physics and chemistry) and has been applied to a large variety of systems including surfaces, adsorbates, nanotubes, nanoclusters, biological molecules, amorphous semiconductors, ferroelectric films, low-dimensional metals, etc. [ 3 ] [ 4 ] [ 5 ]
Delphisoftware apps | https://en.wikipedia.org/wiki/SIESTA_(computer_program) |
SIE Neftehim [ a ] ( Russian : НПП Нефтехим ) is a Russian joint stock company based in Krasnodar , undertaking research and development in the petrochemical industry . Its origins lie in the research laboratory attached to Krasnodar Refinery, which first developed the use of aluminium-platinum catalysts in the Soviet Union. Established in its present form in 1996, the company continues to develop catalytic techniques, isomerization processes, and other petroleum refining technologies .
Creation and establishing of the scientific and research enterprise on development and introduction of petrochemical processes in Krasnodar is closely related to solving the issue of introduction of catalytic reforming process for gasoline fractions in Russian oil refining industry. [ 1 ] The main step was construction of catalytic reforming semi-production unit, which allowed testing this process and submitting the necessary data for designing and construction of large scale commercial units. Besides, all new reforming catalysts were tested at the unit beginning with AP-56 (АП-56) and out to KR (КР) catalysts. Since the 1950s, the enterprise has been repeatedly reorganized and renamed:
The modern image, as well as research and activity trends of the enterprise started to form after its corporatization in 1995-1996. The enterprise underwent some structural changes, inefficient researches were reduced and the main efforts were focused on the major trends, i.e. reforming and isomerization of gasoline fractions. The company searches for and develops technologies and catalysts for Russian and foreign refineries. The enterprise is operated in accordance with the ISO 9001:2008 quality management system in the sphere of development and introduction of petrochemical processes.
JSC SIE Neftehim is directed by its major shareholders – Shakun Alexander Nikitovich (General Director) and Fedorova Marina Leonidovna (Technical Director). [ 3 ]
At the present time activity of the enterprise is focused on development of Design Basis or Basic Engineering Design for detailed engineering of isomerization (technology Isomalk-2, [ 7 ] [ 8 ] [ 9 ] [ 10 ] isomerization n-butane Isomalk-3, [ 11 ] isomerization n-heptane Isomalk-4) and reforming units, as well as on isomerization and reforming catalysts supply, [ 12 ] [ 13 ] monitoring of isomerization and reforming units operation, analytical research of hydrocarbon fractions and catalysts, creation of new catalysts. | https://en.wikipedia.org/wiki/SIE_Neftehim |
SIGMOBILE is the Association for Computing Machinery 's Special Interest Group on Mobility of Systems, Users, Data and Computing, which specializes in the field of mobile computing and wireless networks and wearable computing .
Conceived in early 1995, ACM SIGMOBILE started out as an organization that fostered research in the "field of mobility and tetherless ubiquitous connectivity". It was founded as a provisional SIG on June 13, 1996, gaining permanent status on October 12, 2000. On February 8, 2005, the SIGMOBILE Chapter Program was launched. The NTU Singapore chapter became the first Student Chapter, and the Sydney , Australia Chapter became the first Professional Chapter.
SIGMOBILE sponsors four annual international conferences: MobiCom, the International Conference on Mobile Computing and Networking ; MobiHoc, the International Symposium on Mobile Ad Hoc Networking and Computing ; MobiSys, the International Conference on Mobile Systems, Applications, and Services; and SenSys, the ACM Conference on Embedded Networked Sensor Systems . SIGMOBILE publishes a quarterly journal, Mobile Computing and Communications Review ( MC2R ), as well as the annual Proceedings of the conferences and many workshops sponsored by SIGMOBILE such as HotMobile, the International Workshop on Mobile Computing Systems and Applications.
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SIGMOBILE |
SIGRed [ 1 ] ( CVE - 2020-1350 ) is a security vulnerability discovered in Microsoft 's Domain Name System (DNS) implementation of Windows Server versions from 2003 to 2019.
To exploit the vulnerability, an unauthenticated attacker sends malicious requests to a Windows DNS server. [ 2 ] If exploited, the vulnerability could allow an attacker to run arbitrary code on a Domain Controller in the context of the Local System Account.
In Microsoft's advisory of the issue, the vulnerability was classified ' wormable ' and was given a CVSS base score of 10.0. [ 3 ]
It has been the subject of a Department of Homeland Security emergency directive, instructing all government agencies to deploy patches or mitigations for it in 24 hours. [ 4 ]
The vulnerability was discovered by Check Point Software Technologies and publicly disclosed on July 14, 2020. [ 1 ] | https://en.wikipedia.org/wiki/SIGRed |
SIG Group AG is a Swiss multinational corporation and one of the biggest manufacturers in the packaging industry . [ 2 ] [ 3 ] [ 4 ]
Originally founded 1853 as a railway car producer named Schweizerische Waggonfabrik ("Swiss Wagon Factory"), it was renamed SIG ( Schweizerische Industrie Gesellschaft , German for Swiss Industrial Company ; in French, as Société Industrielle Suisse ; and, in Italian, as Societá Industriale Svizzera ) [ 5 ] a decade later, after it had won a contract for the production of firearms by the Swiss government. [ 6 ] [ 7 ]
The SIG Group shares are listed on SIX Swiss Exchange and are a component of the SMI MID index. The industrial site at the headquarters in Neuhausen am Rheinfall is located directly on the Rhine Falls . Built at this location in 1853 for the use of hydroelectric power , [ 8 ] the site was transferred to the SIG Charitable Foundation in 2011. [ 9 ]
In order to address the volatility of the railway vehicle and firearms businesses, SIG started to produce packaging machinery starting from 1906 as a third main business area. [ 10 ] The machines were produced at SIG in Neuhausen [ 11 ] on behalf of the patentee of a "folding box" die-fold system, a co-founder of SAPAL (Société Anonyme des Plieuses Automatiques). Most of SIG's earlier packaging equipment efforts were focused on small dry food items such as chocolates and candy. The first packaging machines were delivered to Swiss chocolate manufacturers. In 1921, SIG started to construct its own packaging machines. [ 12 ]
1956 SIG launched its first continuous flow wrapping machine. 1964 the business unit moved to Beringen where it had built a new factory. By 1981, it was producing 60 models of packaging machines. [ 12 ]
In 1989, through the acquisition of PKL from Linnich , Germany, SIG entered the field of aseptic carton liquid packaging, later known as SIG Combibloc. [ 13 ] [ 14 ]
In 2000, SIG started to focus on food and beverage packaging technology. At that time, SIG already ranked as the second-largest manufacturer in the world, after Tetra Pak , of cardboard composites for fluids packaging. [ 15 ] Motion control specialist SIG Positec, which was mostly successful on the German, Swiss and Italian markets, was sold to Schneider Electric in the same year for €195 million. [ 16 ] With this, SIG divested its automation division. Management directed revenues from the sales of SIG Sauer and Rocktools to acquire global businesses, including Krupp Kunstofftechnik (Corpoplast, Blowtec, and Kautex brands) [ 15 ] and HAMBA in Germany ; [ 17 ] Ryka Blow Molds in Canada ; [ 18 ] [ 19 ] and a substantial portion of the Italian conglomerate SASIB. [ 20 ] The food-related (dry) businesses were organized under the SIG Pack division, [ 12 ] while the beverage-related (wet) businesses formed SIG Beverages. Aseptic liquid packaging remained separate under SIG Combibloc. [ 21 ]
The former SASIB wet businesses Simonazzi , Alfa and Meyer /Mojonnier were sold to Tetra Laval in 2005, [ 22 ] while HAMBA, Kautex and Blowtec were sold separately to private investor groups. [ 23 ] The food packaging businesses were sold to Robert Bosch Verpackungstechnik in 2004. [ 24 ] The former SASIB dry unit Stewart Systems (bakery products) was sold to UCA Group in 2004. [ 25 ] Laser-guided vehicle manufacturer Elettric 80, part of the 1999 SASIB acquisition, was sold back to its original Italian owners in 2004. [ 26 ] [ 27 ]
By 2006, Sigpack Systems had an export ratio of 97% of its products. [ 12 ] The slimmed-down SIG Beverages unit, manufacturer of PET bottle blow-molding machinery, was sold off to the German company Salzgitter AG in March 2008. This sale encompassed the subsidiaries Corpoplast, Asbofill, Plasmax and Moldtec. [ 28 ] [ 29 ]
In 2007, SIG Holding AG was acquired by Rank Group Limited, the private investment company of New Zealand businessman Graeme Hart , and operated under its subsidiary, Reynolds Group Holdings Ltd., which, in March 2015, announced completion of its sale of SIG to ONEX Corporation . [ 30 ] In the early 2010s, SIG started to promote as a world first extra-slim small-format carton packs starting from 80ml tailored for children especially in fast-growing regions as Asia and Middle East. [ 31 ]
Today, SIG Group focuses on aseptic packaging. In 2016, the company introduced Combibloc RS Composite, a composite structural inner layer which increases system stability and reduces the carbon footprint of carton packs. [ 32 ] In 2017, SIG introduced the first individual QR codes with digital sourcing transparency, tailored for dairy product consumers. [ 33 ] In 2018 the company was relisted to the SIX Swiss Exchange. [ 34 ] In 2020 SIG Group fully integrated its Joint Venture SIG Combibloc Obeikan into SIG. The Joint Venture with a manufacturing plant in Riyadh and customers in the Middle East and Africa region had been established in 2001. [ 35 ]
In April 2022, the company was renamed from SIG Combibloc Group AG to SIG Group AG. In the same year, SIG finalised the acquisition of Scholle IPN, [ 36 ] an American producer of flexible food and beverages packaging including spouted pouches and bag-in-box solutions originally developed by William R. Scholle. [ 37 ] Also in 2022, SIG acquired the Asia business of US competitor Pactiv Evergreen [ 38 ] with its production facilities for fresh products, especially fresh milk in the People's Republic of China , Taiwan and South Korea . [ 39 ]
The Schweizerische Waggonfabrik [ 40 ] ("Swiss Wagon Factory") was founded in 1853 by Friedrich Peyer im Hof , Heinrich Moser, and Johann Conrad Neher. [ 7 ] From 1854, it produced railway cars for the emerging Swiss railway companies . Friedrich Peyer was one of the directors of the Swiss Northeastern Railway , also founded in 1853. In 1855 SIG railway carriages were honoured with an award at the World’s Fair in Paris. [ 41 ] Their factory in Neuhausen am Rheinfall was originally powered by the nearby Rhine Falls and employed 150 workers, [ 42 ] [ 7 ] which by the mid-1860s increased to 500 workers. [ 40 ]
One of the signature trains of SIG in the 1960s was the iconic Trans Europe Express (TEE) . [ 41 ] In the late 1970s, SIG was the designer and builder of Toronto 's streetcar , the CLRV L1 . [ 43 ] [ 44 ] [ 45 ] The remaining 190 L2 vehicles, along with 52 articulated variants , were made by Thunder Bay , Ontario-based Urban Transportation Development Corporation (UTDC), now a subsidiary of Bombardier Transportation .
From around 1981, SIG focused in the railway segment on the production of bogies as part of a division of labour with other Swiss railway manufacturers such as the Schindler Group (Schindler Waggon, Schweizerische Wagons- und Aufzügefabrik AG Schlieren-Zürich ) and Flug- und Fahrzeugwerke Altenrhein . These bogies can still be found in many countries today. In the early 1980s, SIG was the designer and builder of the Utrecht sneltram trams. [ 46 ] 27 were ordered and delivered in 1983. Their scheduled replacements ran from 2017 to 2020.
The tilting system of the SBB RABDe 500 was developed by SIG. The railway branch of SIG was sold in 1995 to Fiat Ferroviaria . [ 47 ]
SIG started to produce the Prélaz-Burnand in 1859. It was invented by gunsmith Jean-Louis Joseph Prélaz and forestry inspector Colonel Édouard Burnand (father of Swiss painter Eugène Burnand ). In 1860, the rifle won a competition held by the Swiss Military Department , resulting in a contract to produce 30,000 pieces. [ 48 ] [ 7 ] This rifle was adapted as the M1863.
Upon receiving the contract to produce rifles, the company name was changed to reflect its new emphasis on machined production, becoming Schweizerische Industrie Gesellschaft (SIG) in German, Swiss Industrial Company in English, and Société Industrielle Suisse in French. [ 49 ] [ 50 ] [ 7 ]
SIG produced the Mondragón Rifle between 1908 and 1910. [ 51 ] The SIG P210 pistol was developed in 1937 based on the French Modèle 1935 , and was adopted by the Swiss military in 1949 as the " Pistole 49 ". This pistol's frame design incorporates external rails which fit closely with the slide, thus eliminating play in the mechanism during firing. The P210 was noted for its accuracy. [ 52 ] The Petter-Browning patent was a refinement—and John Moses Browning 's last design—of the Browning Hi-Power (P35). [ 53 ]
In 1975, the Swiss military replaced the P210 with the P220 , dubbed the " Pistole 75 ", which was the first product of a partnership with J.P. Sauer & Sohn. In a 1984 bidding contest to provide more than 300,000 sidearms to the US military, the SIG Sauer P226 was defeated by Beretta 's 92FS which was awarded the contract for the M9 pistol. The SIG SG 510 , or Sturmgewehr 57, battle rifle was produced by SIG from 1957 to 1983. Its appearance was vaguely similar to the German MG34 light machine gun, due to its ventilated barrel jacket. It employed roller-delayed blowback, as used on the CETME / HK rifles. [ 54 ] The only general purpose machine gun produced by SIG was the SIG 710-3 , which is based on the MG42 . [ 55 ]
Due to Swiss restrictions on the export of military weapons, SIG entered into a relationship with the German company J.P. Sauer & Sohn , in order to give SIG access to the global firearms market. During the 1970s, SIG purchased both Hämmerli [ 56 ] [ 57 ] and J.P. Sauer & Sohn , resulting in the formation of SIG Sauer .
In January 1985, SIGARMS was established in Tyson's Corner , Virginia, where its handgun models P220 and P230 were imported into the US from its sister company in Europe. [ 7 ] In 2007, SIGARMS changed its name to SIG Sauer . SIG Arm's division was purchased in 2000 by L & O Holding, [ 58 ] and is now known as SIG SAUER AG .
SIG manufactures aseptic carton packs, bag-in-box packaging and spouted pouches for beverages and food, increasingly based on the world’s first aluminium-layer-free aseptic packs and fully renewable materials. [ 59 ] [ 60 ] [ 61 ] [ 62 ] [ 63 ] [ 64 ] [ 65 ] It also produces, operates and maintains packaging machines. [ 66 ]
The ownership of the SIG site, located directly on the Rhine Falls , was transferred to the SIG Charitable Foundation in 2011. [ 67 ] In addition to the conversion of the site (residential, commercial, retail, gastronomy), it is still home to the company's headquarters and a production facility with 200 employees. The SIG Group has 90 subsidiaries in 41 countries in Europe, Asia, [ 68 ] [ 69 ] Middle East, Africa, North, [ 70 ] Central and South America [ 71 ] [ 72 ] The most important production sites are located in Neuhausen am Rheinfall, Saalfelden, Linnich, Wittenberg, Alsdorf, Eisfeld, Tilburg, Barcelona, Shanghai, Suzhou, [ 73 ] Palghar, [ 74 ] Pune, [ 75 ] Ahsan, Hsinchu, Rayong, Edinburgh North, Riyadh, [ 76 ] Northlake, Peachtree City, Querétaro, [ 77 ] Campo Largo, Vinhedo and Santiago.
The SIG Foundation is active in projects targeted towards civil society and the environment. Its main initiatives are ‘Cartons for Good’ and ‘Recycle for Good’. Cartons for Good intends to save surplus food from being wasted, support farmers’livelihoods, and nourish people in need. The initiative has been piloted in Bangladesh. Winning the project competition by the Save Food Initiative (with involvement of the Food and Agriculture Organization of the United Nations) in 2023 facilitated a locally based study in Egypt. The community recycling program Recycle for Good focuses on encouraging the public to deliver their recyclable waste to a collection point and practice the circular economy. The program in Indonesia (initiated in March 2023) established more than 150 collection points in Jakarta and Greater Jakarta Area in one year. [ 78 ] [ 79 ] | https://en.wikipedia.org/wiki/SIG_Group |
SIMION is an ion optics simulation program that calculates electric fields for electrodes of defined voltages and ion trajectories in those fields. [ 1 ]
The program was developed in the late 1970s by Don C. McGilvery at La Trobe University , Melbourne, Australia as part of his Ph.D. research [ 2 ] working with James Morrison, and was later adapted for personal computers in 1985 by David A. Dahl at the Idaho National Engineering and Environmental Laboratory . [ 3 ] With Richard Morrison at Monash University, McGilvery developed a Macintosh version of SIMION, known as MacSIMION. In recognition of the importance of their work, McGilvery and Dahl shared the Distinguished Contribution Award from the American Society for Mass Spectrometry in 1998. [ 4 ]
SIMION 8.0 was initially released in 2006. The current version is SIMION 8.1, released in August 2011; minor updates are being released continuously.
SIMION 3D is a widely used ion-optics simulation program in many branches of physics. In SIMION, electrostatic fields can be modelled as boundary value problem solutions of an elliptical partial differential equation called the Laplace equation . The specific method used within SIMION to solve this equation is a finite difference method called over-relaxation. This technique is applied to a three-dimensional potential array (PA) of points representing electrode and non-electrode regions. The objective is to obtain a best estimate of the voltages for the points between the electrodes. The three-dimensional array is chosen to have either cylindrical or planar symmetry or no symmetry at all. The Laplace equation has the convenient property that its solution is a sum over the contribution from each electrode. Therefore, after the electric field array has been found once by iteration, the voltages of the individual electrodes can be changed and the new fields are immediately obtained.
When the electric fields have been obtained, the trajectories of charged particles in these fields can be calculated. Particle trajectory calculations are a result of three interdependent computations. First, electrostatic forces must be calculated at the current position of the ion. These forces are then used to compute the current ion acceleration and then by numerical integration techniques to predict the position and velocity of the ion at the next time step. Moreover, the time step itself is continuously adjusted to maximize trajectory accuracy. A standard fourth-order Runge–Kutta method is used for numerical integration of the ion trajectory in three dimensions.
This electromagnetism -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SIMION |
A SIM box (also called a SIM bank ) is device used as part of a VoIP gateway installation. It contains a number of SIM cards , which are linked to the gateway but housed and stored separately from it. A SIM box can have SIM cards of different mobile operators installed, permitting it to operate with several GSM gateways located in different places. [ citation needed ]
The SIM box operator can route calls through the VoIP connection and connect the call as local traffic, allowing the box's operator to bypass high international rates and to reduce prices charged by local mobile network operators (MNO). [ 1 ] [ 2 ] In voice communications, typically a private exchange is used receive traffic from a local area, and the calls are routed over the internet to a SIM box in a remote region. This business model of operation is commonly used to avoid higher tolls for non-mobile long distance calls, particularly those associated with lesser-developed countries.
SIM boxes are often used for lower rate VoIP to MNO termination purposes, including avoidance of high tolls in violation of carriers' acceptable use policies and the sending of mobile text messaging spam.
Some carriers attempt to detect and deny service to SIM boxes through various means, including cancellation or restriction of service to identified SIMs. SIM box operators often swap SIMs to replace restricted ones. They may also rewrite the International Mobile Equipment Identity (IMEI) of the SIM box, often using randomized IMEIs in ranges of or those assigned to common mobile phones to evade detection.
The use of SIM boxes is often legal, but the use may constitute breach of carrier contracts. One example is that of the country of Ghana , where the government has challenged the use of SIM boxes. [ 2 ] [ 3 ]
A lot of Sim Boxes are used by scammers for sending out millions text messages purporting to be from ATO, Centrelink, Medicare, Australia Post, Commonwealth Bank, Transurban, and Linkt. Reporting a Scammer SMS to the DSD in Australia is the best way to get these Bad Actors off line. [ 4 ]
As the normal mobile network are sometimes using a very outdated and low quality sound codecs (such as the GSM HR and FR codecs), a SIM box may provide local connectivity with superior sound quality.
This article related to telecommunications is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SIM_box |
1PO4
25942
20466
ENSG00000169375
ENSMUSG00000042557
Q96ST3
Q60520
NM_001145357 NM_001145358 NM_015477
NM_001110350 NM_001110351 NM_011378 NM_001357754
NP_001138829 NP_001138830 NP_056292
NP_001103820 NP_001103821 NP_035508 NP_001344683
Paired amphipathic helix protein Sin3a is a protein that in humans is encoded by the SIN3A gene . [ 5 ] [ 6 ]
The protein encoded by this gene is a transcriptional regulatory protein. It contains paired amphipathic helix (PAH) domains, which are important for protein-protein interactions and may mediate repression by the Mad-Max complex. [ 7 ]
SIN3A 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/SIN3A |
1E91 , 1PD7 , 2CR7 , 2CZY , 2F05
23309
20467
ENSG00000127511
ENSMUSG00000031622
O75182
Q62141
NM_001297595 NM_001297597 NM_015260
NM_001113248 NM_009188
NP_001284524 NP_001284526 NP_056075
NP_001106719 NP_033214
Paired amphipathic helix protein Sin3b is a protein that in humans is encoded by the SIN3B gene . [ 5 ] [ 6 ]
SIN3B has been shown to interact with HDAC1 , [ 7 ] [ 8 ] Zinc finger and BTB domain-containing protein 16 , [ 9 ] SUDS3 [ 10 ] and IKZF1 . [ 8 ] [ 11 ]
This article incorporates text from the United States National Library of Medicine , which is in the public domain .
This article on a gene on human chromosome 19 is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/SIN3B |
The Session Initiation Protocol ( SIP ) is the signaling protocol selected by the 3rd Generation Partnership Project (3GPP) [ 1 ] [ 2 ] to create and control multimedia sessions with multiple participants in the IP Multimedia Subsystem (IMS). It is therefore a key element in the IMS framework.
SIP was developed by the Internet Engineering Task Force (IETF) as a standard for controlling multimedia communication sessions in Internet Protocol (IP) networks. It is characterized by its position in the application layer of the Internet Protocol Suite . Several SIP extensions published in Request for Comments (RFC) protocol recommendations, have been added to the basic protocol for extending its functionality. [ 3 ] [ 4 ] [ 5 ]
The 3GPP, which is a collaboration between groups of telecommunications associations aimed at developing and maintaining the IMS, stated a series of requirements for SIP [ 1 ] to be successfully used in the IMS. Some of them could be addressed by using existing capabilities and extensions in SIP while, in other cases, the 3GPP had to collaborate with the IETF to standardize new SIP extensions [ 6 ] to meet the new requirements. The IETF develops SIP on a generic basis, so that the use of extensions is not restricted to the IMS framework.
The 3GPP has stated several general requirements for operation of the IMS. These include an efficient use of the radio interface by minimizing the exchange of signaling messages between the mobile terminal and the network, a minimum session setup time by performing tasks prior to session establishment instead of during session establishment, a minimum support required in the terminal, the support for roaming and non-roaming scenarios with terminal mobility management (supported by the access network, not SIP), and support for IPv6 addressing.
Other requirements involve protocol extensions, such as SIP header fields to exchange user or server information, and SIP methods to support new network functionality: requirement for registration, re-registration, de-registration, event notifications, instant messaging or call control primitives with additional capabilities such as call transference.
Other specific requirements are: [ 1 ]
Finally, it is also necessary that other protocols and network services such as DHCP or DNS [ 7 ] are adapted to work with SIP, for instance for outbound proxy (P-CSCF) location and SIP Uniform Resource Identifier (URI) to IP address resolution, respectively.
There is a mechanism [ 2 ] in SIP for extension negotiation between user agents (UA) or servers, consisting of three header fields: supported , require and unsupported , which UAs or servers (i.e. user terminals or call session control function (CSCF) in IMS) may use to specify the extensions they understand. When a client initiates a SIP dialog with a server, it states the extensions it requires to be used and also other extensions that are understood ( supported ), and the server will then send a response with a list of extensions that it requires . If these extensions are not listed in the client's message, the response from the server will be an error response. Likewise, if the server does not support any of the client's required extensions, it will send an error response with a list of its unsupported extensions. This kind of extensions are called option tags , but SIP can also be extended with new methods . In that case, user agents or servers use the Allow header to state which methods they support. To require the use of a particular method in a particular dialog, they must use an option tag associated to that method.
These two extensions allow users to specify their preferences about the service the IMS provides.
With the caller preferences extension, [ 8 ] the calling party is able to indicate the kind of user agent they want to reach (e.g. whether it is fixed or mobile, a voicemail or a human, personal or for business, which services it is capable to provide, or which methods it supports) and how to search for it, with three header fields: Accept-Contact to describe the desired destination user agents, Reject-Contact to state the user agents to avoid, and Request-Disposition to specify how the request should be handled by servers in the network (i.e. whether or not to redirect and how to search for the user: sequentially or in parallel).
By using the user agent capabilities extension, [ 9 ] user agents (terminals) can describe themselves when they register so that others can search for them according to their caller preferences extension headers. For this purpose, they list their capabilities in the Contact header field of the REGISTER message.
The aim of event notification is to obtain the status of a given resource (e.g. a user, one's voicemail service) and to receive updates of that status when it changes.
Event notification is necessary in the IMS framework to inform about the presence of a user (i.e. "online" or "offline") to others that may be waiting to contact them, or to notify a user and its P-CSCF of its own registration state, so that they know if they are reachable and what public identities they have registered. Moreover, event notification can be used to provide additional services such as voicemail (i.e. to notify that they have new voice messages in their inbox ).
To this end, the specific event notification extension [ 10 ] defines a framework for event notification in SIP, with two new methods: SUBSCRIBE and NOTIFY, new header fields and response codes and two roles: the subscriber and the notifier . The entity interested in the state information of a resource (the subscriber ) sends a SUBSCRIBE message with the Uniform Resource Identifier (URI) of the resource in the request initial line, and the type of event in the Event header . Then the entity in charge of keeping track of the state of the resource (the notifier ), receives the SUBSCRIBE request and sends back a NOTIFY message with a subscription-state header as well as the information about the status of the resource in the message body. Whenever the resource state changes, the notifier sends a new NOTIFY message to the subscriber . Each kind of event a subscriber can subscribe to is defined in a new event package . An event package describes a new value for the SUBSCRIBE Event header , as well as a MIME type to carry the event state information in the NOTIFY message.
There is also an allow-events header to indicate event notification capabilities, and the 202 accepted and 489 bad event response codes to indicate if a subscription request has been preliminary accepted or has been turned down because the notifier does not understand the kind of event requested.
In order to make an efficient use of the signaling messages, it is also possible to establish a limited notification rate (not real-time notifications) through a mechanism called event throttling . Moreover, there is also a mechanism for conditional event notification that allows the notifier to decide whether or not to send the complete NOTIFY message depending on if there is something new to notify since last subscription or there is not.
The event notification framework defines how a user agent can subscribe to events about the state of a resource, but it does not specify how that state can be published. The SIP extension for event state publication [ 11 ] was defined to allow user agents to publish the state of an event to the entity ( notifier ) that is responsible for composing the event state and distributing it to the subscribers .
The state publication framework defines a new method: PUBLISH, which is used to request the publication of the state of the resource specified in the request-URI, with reference to the event stated in the Event header , and with the information carried in the message body.
The functionality of sending instant messages to provide a service similar to text messaging is defined in the instant messaging extension. [ 12 ] These messages are unrelated to each other (i.e. they do not originate a SIP dialog) and sent through the SIP signaling network, sharing resources with control messages.
This functionality is supported by the new MESSAGE method, which can be used to send an instant message to the resource stated in the request-URI, with the content carried in the message body. This content is defined as a MIME type, being text/plain the most common one.
In order to have an instant messaging session with related messages, the Message Session Relay Protocol (MSRP) [ 13 ] is available.
The REFER method extension [ 14 ] defines a mechanism to request a user agent to contact a resource which is identified by a URI in the Refer-To header field of the request message. A typical use of this mechanism is call transfer: during a call, the participant who sends the REFER message tells the recipient to contact to the user agent identified by the URI in the corresponding header field. The REFER message also implies an event subscription to the result of the operation, so that the sender will know whether or not the recipient could contact the third person.
However, this mechanism is not restricted to call transfer, since the Refer-To header field can be any kind of URI, for instance, an HTTP URI, to require the recipient to visit a web page .
In the basic SIP specification, [ 15 ] only requests and final responses (i.e. 2XX response codes ) are transmitted reliably, this is, they are retransmitted by the sender until the acknowledge message arrives (i.e. the corresponding response code to a request, or the ACK request corresponding to a 2XX response code). This mechanism is necessary since SIP can run not only over reliable transport protocols ( TCP ) that assure that the message is delivered, but also over unreliable ones ( UDP ) that offer no delivery guarantees, and it is even possible that both kinds of protocols are present in different parts of the transport network.
However, in such an scenario as the IMS framework, it is necessary to extend this reliability to provisional responses to INVITE requests (for session establishment, this is, to start a call). The reliability of provisional responses extension [ 16 ] provides a mechanism to confirm that provisional responses such as the 180 Ringing response code , that lets the caller know that the callee is being alerted, are successfully received. To do so, this extension defines a new method: PRACK, which is the request message used to tell the sender of a provisional response that his or her message has been received. This message includes a RACK header field which is a sequence number that matches the RSeq header field of the provisional response that is being acknowledged, and also contains the CSeq number that identifies the corresponding INVITE request. To indicate that the user agent requests or supports reliable provisional responses, the 100rel option tag will be used.
The aim of the UPDATE method extension [ 17 ] is to allow user agents to provide updated session description information within a dialog, before the final response to the initial INVITE request is generated. This can be used to negotiate and allocate the call resources before the called party is alerted.
In the IMS framework, it is required that once the callee is alerted, the chances of a session failure are minimum. An important source of failure is the inability to reserve network resources to support the session, so these resources should be allocated before the phone rings. However, in the IMS, to reserve resources the network needs to know the callee's IP address, port and session parameters and therefore it is necessary that the initial offer/answer exchange to establish a session has started (INVITE request). In basic SIP, this exchange eventually causes the callee to be alerted. To solve this problem, the concept of preconditions [ 18 ] was introduced. In this concept the caller states a set of constraints about the session (i.e. codecs and QoS requirements) in the offer, and the callee responds to the offer without establishing the session or alerting the user. This establishment will occur if and only if both the caller and the callee agree that the preconditions are met.
The preconditions SIP extension affects both SIP, with a new option tag ( precondition ) and defined offer/answer exchanges, and Session Description Protocol (SDP), which is a format used to describe streaming media initialization parameters, carried in the body of SIP messages. The new SDP attributes are meant to describe the current status of the resource reservation, the desired status of the reservation to proceed with session establishment, and the confirmation status , to indicate when the reservation status should be confirmed.
In the IMS, the initial session parameter negotiation can be done by using the provisional responses and session description updating extensions, along with SDP in the body of the messages.
The first offer, described by means of SDP, can be carried by the INVITE request and will deal with the caller's supported codecs . This request will be answered by the provisional reliable response code 183 Session Progress , that will carry the SDP list of supported codecs by both the caller and the callee. The corresponding PRACK to this provisional answer will be used to select a codec and initiate the QoS negotiation.
The QoS negotiation is supported by the PRACK request, that starts resource reservation in the calling party network, and it is answered by a 2XX response code. Once this response has been sent, the called party has selected the codec too, and starts resource reservation on its side. Subsequent UPDATE requests are sent to inform about the reservation progress, and they are answered by 2XX response codes. In a typical offer/answer exchange, [ 19 ] one UPDATE will be sent by the calling party when its reservation is completed, then the called party will respond and eventually finish allocating the resources. It is then, when all the resources for the call are in place, when the caller is alerted.
In the IMS framework it is fundamental to handle user identities for authentication, authorization and accounting purposes. The IMS is meant to provide multimedia services over IP networks, but also needs a mechanism to charge users for it. All this functionality is supported by new special header fields.
The Private Header Extensions to SIP, [ 6 ] also known as P-Headers, are special header fields whose applicability is limited to private networks with a certain topology and characteristics of lower layers ' protocols. They were designed specifically to meet the 3GPP requirements because a more general solution was not available.
These header fields are used for a variety of purposes including charging and information about the networks a call traverses:
More private headers have been defined for user database accessing:
The private extensions for asserted identity within trusted networks [ 23 ] are designed to enable a network of trusted SIP servers to assert the identity of authenticated users, only within an administrative domain with previously agreed policies for generation, transport and usage of this identification information. These extensions also allow users to request privacy so that their identities are not spread outside the trust domain . To indicate so, they must insert the privacy token id into the Privacy header field. [ 24 ]
The main functionality is supported by the P-Asserted-Identity extension header. When a proxy server receives a request from an untrusted entity and authenticates the user (i.e. verifies that the user is who he or she says that he or she is), it then inserts this header with the identity that has been authenticated, and then forwards the request as usual. This way, other proxy servers that receive this SIP request within the Trust Domain (i.e. the network of trusted entities with previously agreed security policies) can safely rely on the identity information carried in the P-Asserted-Identity header without the necessity of re-authenticating the user.
The P-Preferred-Identity extension header is also defined, so that a user with several public identities is able to tell the proxy which public identity should be included in the P-Asserted-Identity header when the user is authenticated.
Finally, when privacy is requested, proxies must withhold asserted identity information outside the trusted domain by removing P-Asserted-Identity headers before forwarding user requests to untrusted identities (outside the Trust Domain ).
There exist analogous extension headers for handling the identification of services of users, [ 25 ] instead of the users themselves. In this case, Uniform Resource Names are used to identify a service (e.g. a voice call, an instant messaging session, an IPTV streaming ) [ 26 ]
Access security in the IMS consists of first authenticating and authorizing the user, which is done by the S-CSCF, and then establishing secure connections between the P-CSCF and the user. There are several mechanisms to achieve this, such as:
The security mechanisms agreement extension for SIP [ 28 ] was then introduced to provide a secure mechanism for negotiating the security algorithms and parameters to be used by the P-CSCF and the terminal. This extension uses three new header fields to support the negotiation process:
The necessity in the IMS of reserving resources to provide quality of service (QoS) leads to another security issue: admission control and protection against denial-of-service attacks . To obtain transmission resources, the user agent must present an authorization token to the network (i.e. the policy enforcement point, or PEP) . This token will be obtained from its P-CSCF, which may be in charge of QoS policy control or have an interface with the policy control entity in the network (i.e. the policy decision function, or PDF) which originally provides the authorization token.
The private extensions for media authorization [ 29 ] link session signaling to the QoS mechanisms applied to media in the network, by defining the mechanisms for obtaining authorization tokens and the P-Media-Authorization header field to carry these tokens from the P-CSCF to the user agent. This extension is only applicable within administrative domains with trust relationships. It was particularly designed for specialized SIP networks like the IMS, and not for the general Internet .
Source routing is the mechanism that allows the sender of a message to specify partially or completely the route the message traverses. In SIP, the route header field, filled by the sender, supports this functionality by listing a set of proxies the message will visit. In the IMS context, there are certain network entities (i.e. certain CSCFs ) that must be traversed by requests from or to a user, so they are to be listed in the Route header field. To allow the sender to discover such entities and populate the route header field, there are mainly two extension header fields: path and service-route .
The extension header field for registering non-adjacent contacts [ 30 ] provides a Path header field which accumulates and transmits the SIP URIs of the proxies that are situated between a user agent and its registrar as the REGISTER message traverses then. This way, the registrar is able to discover and record the sequence of proxies that must be transited to get back to the user agent.
In the IMS every user agent is served by its P-CSCF, which is discovered by using the Dynamic Host Configuration Protocol or an equivalent mechanism when the user enters the IMS network, and all requests and responses from or to the user agent must traverse this proxy. When the user registers to the home registrar (S-CSCF), the P-CSCF adds its own SIP URI in a Path header field in the REGISTER message, so that the S-CSCF receives and stores this information associated with the contact information of the user. This way, the S-CSCF will forward every request addressed to that user through the corresponding P-CSCF by listing its URI in the route header field.
The extension for service route discovery during registration [ 31 ] consists of a Service-Route header field that is used by the registrar in a 2XX response to a REGISTER request to inform the registering user of the entity that must forward every request originated by him or her.
In the IMS, the registrar is the home network's S-CSCF and it is also required that all requests are handled by this entity, so it will include its own SIP URI in the service-route header field. The user will then include this SIP URI in the Route header field of all his or her requests, so that they are forwarded through the home S-CSCF.
In the IMS it is possible for a user to have multiple terminals (e.g. a mobile phone , a computer ) or application instances (e.g. video telephony , instant messaging , voice mail ) that are identified with the same public identity (i.e. SIP URI). Therefore, a mechanism is needed in order to route requests to the desired device or application. That is what a Globally Routable User Agent URI (GRU) [ 32 ] is: a URI that identifies a specific user agent instance (i.e. terminal or application instance) and it does it globally (i.e. it is valid to route messages to that user agent from any other user agent on the Internet).
These URIs are constructed by adding the gr parameter to a SIP URI, either to the public SIP URI with a value that identifies the user agent instance, or to a specially created URI that does not reveal the relationship between the GRUU and the user's identity, for privacy purposes. They are commonly obtained during the registration process: the registering user agent sends a Uniform Resource Name (URN) that uniquely identifies that SIP instance, and the registrar (i.e. S-CSCF) builds the GRUU, associates it to the registered identity and SIP instance and sends it back to the user agent in the response. When the S-CSCF receives a request for that GRUU, it will be able to route the request to the registered SIP instance.
The efficient use of network resources, which may include a radio interface or other low-bandwidth access, is essential in the IMS in order to provide the user with an acceptable experience in terms of latency . To achieve this goal, SIP messages can be compressed using the mechanism known as SigComp [ 33 ] (signaling compression).
Compression algorithms perform this operation by substituting repeated words in the message by its position in a dictionary where all these words only appear once. In a first approach, this dictionary may be built for each message by the compressor and sent to the decompressor along with the message itself. However, as many words are repeated in different messages, the extended operations for SigComp [ 34 ] define a way to use a shared dictionary among subsequent messages. Moreover, in order to speed up the process of building a dictionary along subsequent messages and provide high compression ratios since the first INVITE message, SIP provides a static SIP/SDP dictionary [ 35 ] which is already built with common SIP and SDP terms.
There is a mechanism [ 36 ] to indicate that a SIP message is desired to be compressed. This mechanism defines the comp=sigcomp parameter for SIP URIs, which signals that the SIP entity identified by the URI supports SigComp and is willing to receive compressed messages. When used in request-URIs, it indicates that the request is to be compressed, while in Via header fields it signals that the subsequent response is to be compressed.
In order to obtain even shorter SIP messages and make a very efficient use of the resources, the content indirection extension [ 37 ] makes it possible to replace a MIME body part of the message with an external reference, typically an HTTP URI. This way the recipient of the message can decide whether or not to follow the reference to fetch the resource, depending on the bandwidth available.
Network address translation (NAT) makes it impossible for a terminal to be reached from outside its private network , since it uses a private address that is mapped to a public one when packets originated by the terminal cross the NAT. Therefore, NAT traversal mechanisms are needed for both the signaling plane and the media plane .
Internet Engineering Task Force 's RFC 6314 [ 38 ] summarizes and unifies different methods to achieve this, such as symmetric response routing and client-initiated connections for SIP signaling, and the use of STUN , TURN and ICE , which combines both previous ones, for media streams
Internet Engineering Task Force 's RFC 6157 [ 39 ] describes the necessary mechanisms to guarantee that SIP works successfully between both Internet Protocol versions during the transition to IPv6 . While SIP signaling messages can be transmitted through heterogeneous IPv4 / IPv6 networks as long as proxy servers and DNS entries are properly configured to relay messages across both networks according to these recommendations, user agents will need to implement extensions so that they can directly exchange media streams . These extensions are related to the Session Description Protocol offer/answer initial exchange, that will be used to gather the IPv4 and IPv6 addresses of both ends so that they can establish a direct communication.
Apart from all the explained extensions to SIP that make it possible for the IMS to work successfully, it is also necessary that the IMS framework interworks and exchanges services with existing network infrastructures, mainly the Public switched telephone network (PSTN).
There are several standards that address this requirements, such as the following two for services interworking between the PSTN and the Internet (i.e. the IMS network):
And also for PSTN-SIP gateways to support calls with one end in each network:
Moreover, the SIP INFO method extension is designed to carry user information between terminals without affecting the signaling dialog and can be used to transport the dual-tone multi-frequency signaling to provide telephone keypad function for users. [ 44 ] | https://en.wikipedia.org/wiki/SIP_extensions_for_the_IP_Multimedia_Subsystem |
SIRIUS is a Java -based open-source software for the identification of small molecules from fragmentation mass spectrometry data without the use of spectral libraries. It combines the analysis of isotope patterns in MS1 spectra with the analysis of fragmentation patterns in MS2 spectra . SIRIUS is the umbrella application comprising CSI:FingerID, CANOPUS, COSMIC and ZODIAC.
SIRIUS, including its web services for structural elucidation , is freely available to use for academic research. Bright Giant GmbH offers subscription-based access to the SIRIUS web services for commercial users.
SIRIUS is not suitable for analyzing proteomics MS data.
The SIRIUS software is developed by the group of Sebastian Böcker at the Friedrich Schiller University Jena , Germany and since 2019 together with Bright Giant GmbH. SIRIUS development started in 2009 as a software for identification of the molecular formula by decomposing high-resolution isotope patterns (also called MS1 data). [ 2 ] The name is an akronym resulting from this original purpose: Sum formula Identification by Ranking Isotope patterns Using mass Spectrometry.
In 2008 the group introduced the concept of fragmentation trees [ 3 ] for identification of the molecular formula based on fragmentation mass spectrometry data, also called tandem MS or MS2 data . Back then, identification of small molecules was approached by searching in a reference spectral library. [ 4 ] Examples of such libraries include MassBank , [ 5 ] METLIN, [ 6 ] or NIST / EPA / NIH EI-MS Library. [ 7 ] However, this is limited to known molecules with available standards that have been measured and put in a reference spectral library. For unknown molecules, identification of the molecular formula is a crucial step. [ 3 ] In 2011/2012, the group conceived fragmentation trees as a means of structural elucidation by automatically comparing these fragmentation trees. [ 8 ] [ 9 ] Fragmentation pattern similarities are strongly correlated with the chemical similarity of molecules. [ 9 ] Thus, aligning the fragmentation tree of an unknown molecule to a set of known molecules helps to elucidate its structure. Fragmentation trees were introduced in SIRIUS 2. [ 8 ]
Also in 2012, the group of Juho Rousu at University of Helsinki , Finland, introduced a machine learning method to predict molecular properties from tandem MS data. [ 10 ] This concept was brought together with the fragmentation tree concept in 2015 resulting in CSI:FingerID, [ 11 ] being introduced in SIRIUS 3. The fragmentation tree is used to predict a molecular fingerprint of the unknown molecule using machine learning , which in turn is used to search a molecular structure database such as PubChem . Molecular structure databases are orders of magnitude larger than reference spectra libraries (PubChem containing ~111 million compounds in 2021 [ 12 ] compared to NIST Tandem Mass Spectral Library containing ~50.000 compounds in 2023 [ 13 ] ). This kind of structure identification refers to the identity and connectivity (with bond multiplicities) of the atoms , but not stereochemistry information. Elucidation of stereochemistry is currently beyond the power of automated search engines.
SIRIUS 3 also introduced the graphical user interface (GUI).
In 2020, in cooperation with the group of Pieter C Dorrestein at UC San Diego , USA, molecular formula identification was improved based on derivative networks from complete biological datasets to rank molecular formula candidates. [ 14 ] This method is called ZODIAC and has been integrated into SIRIUS 4. [ 15 ]
Also in 2020, in cooperation with Rousu's and Dorrestein's groups, CANOPUS for systematic compound class annotation was introduced to SIRIUS 4. [ 16 ]
In 2022, the COSMIC confidence score was added to the CSI:FingerID structure identification workflow in SIRIUS 4, allowing users to determine the trustworthiness of the identification. [ 17 ]
SIRIUS is using data from liquid-chromatography tandem mass spectrometry ( LC-MS /MS). It requires high- resolution , high mass accuracy MS1 and MS2 data as input. LC is not mandatory for SIRIUS, however is often required to separate individual compounds in complex samples.
SIRIUS expects both, MS1 and MS2 spectra, as input. Omitting the MS1 data is possible, but it will make the analysis more time-consuming and can lead to poorer results.
SIRIUS and CSI:FingerID have been trained on a wide variety of data, including data from different instrument types. Certain aspects of the mass spectra are important to successfully process the data:
Different common MS file formats , such as .csv, .ms or .mgf files, can be imported to SIRIUS. SIRIUS can import full LC-MS-runs (.mzML) or single compounds. At present, SIRIUS only handles single-charged compounds. [ 18 ]
SIRIUS identifies small molecules in a two step approach: [ 18 ]
The following algorithms are implemented in SIRIUS:
SIRIUS is the name of the umbrella application, but (for historic reasons) also the name for the identification of the molecular formula. Molecular formula refers to the elemental composition of the molecule. The mere mass of a molecule is not sufficient to determine the correct molecular formula. [ 18 ] Even with very high mass accuracy, many molecular formulas can explain a mass measured in a spectrum, in particular in higher mass regions. In SIRIUS, molecular formula identification is done using isotope pattern analysis on the MS1 data as well as fragmentation tree computation on the MS2 data. The score of a molecular formula candidate is a combination of the isotope pattern score and the fragmentation tree score.
To identify the molecular formula, SIRIUS is considering all possible molecular formulas for a set of elements. The elements most abundant in living beings are hydrogen (H), carbon (C), nitrogen (N), oxygen (O), and phosphor (P). This is the default set of elements in SIRIUS. Some less common elements result in very characteristic isotope pattern changes and can be automatically detected. [ 21 ] Detectable elements are sulfur (S), chlorine (Cl), bromine (Br), boron (B) and selenium (Se). The current version of SIRIUS uses
a deep neural network for auto-detection of elements from the isotope and fragmentation pattern of the query molecule. [ 15 ]
For very large molecules or in case of missing data (e.g., a missing isotope pattern), it is possible to restrict SIRIUS to molecular formulas found in a database, such as PubChem.
In order to quickly generate a manageable number of molecular formula candidates, the monoisotopic mass is decomposed into all possible molecular formulas that would lead to this mass. There are two definitions of the monoisotopic mass: [ 22 ] (1) the sum of the masses of the most abundant naturally occurring stable isotope of each atom (i.e. the highest peak of the isotope pattern) (2) the sum of the masses of the lightest naturally occurring stable isotope of each atom (i.e. the peak of the isotope pattern with the lowest mass). For small molecules, the lightest peak is also mostly the highest peak of the isotope pattern. However, in the computational context of SIRIUS, the second definition is used.
Decomposing the monoisotopic mass into all possible molecular formulas requires a mass interval taking into account the measurement inaccuracy of the instrument. This real-valued decomposition is transformed into a problem instance with integer masses by using a blowup factor. The resulting problem is known as Change-making problem which is well-studied and can be solved in runtime linear in the size of the output. [ 23 ]
Isotope patterns of the candidate molecular formulas are simulated starting with the isotopic distributions of the individual elements, and then combining these distributions by folding. [ 24 ] [ 2 ]
The simulated isotope pattern is compared with the measured pattern by assigning probabilities to the observed masses and intensities. [ 2 ]
A fragmentation tree is a representation of the fragmentation process similar to “fragmentation diagrams” created by experts. The fragmentation tree annotates the MS2 spectrum by providing a molecular formula for each fragment peak. Peaks that do not receive an annotation are considered noise peaks. The fragmentation tree also predicts the fragmentation reactions (called losses) leading to the fragment peaks. Fragmentation trees are a valuable tool for deducing information about the fragmentation but are not a precise depiction of the actual fragmentation process. [ 8 ]
To identify the molecular formula of an unknown molecule, a separate fragmentation tree is computed for every molecular formula candidate. In other words, the method attempts to reconstruct the fragmentation process that led to this MS2 spectrum for each candidate molecular formula. This allows to compare the different hypotheses that a particular candidate is actual the correct molecular formula. The best-scoring fragmentation tree (i.e. the fragmentation process that is best explaining the spectrum) corresponds to the most likely molecular formula explanation.
ZODIAC improves the ranking of the formula candidates provided by SIRIUS. [ 14 ] Organisms produce related metabolites derived from multiple but limited biosynthetic pathways. For a full LC-MS/MS run that is derived from a biological sample or any other set of derivatives the relation of the metabolites is reflected in their similarity. Those similarities are in turn reflected in joint fragments and losses between the fragmentation trees and can be leveraged to improve molecular formula identification of the individual molecules.
ZODIAC uses the top X molecular formula candidates for each molecule from SIRIUS to build a similarity network, and uses Bayesian statistics to re-rank those candidates. Prior probabilities are derived from fragmentation tree similarity. Finding an optimal solution to the resulting computational problem is NP-hard , therefore Gibbs sampling is used.
ZODIAC stands for ZODIAC: Organic compound Determination by Integral Assignment of elemental Compositions .
CSI:FIngerID identifies the structure of a molecule by predicting its molecular fingerprint and using this fingerprint to search in a molecular structure database. [ 11 ]
A molecular fingerprint is a binary vector , where each position corresponds to a specific molecular property . In this representation, a given position X may encode the presence or absence of a particular substructure, with '1' indicating presence and '0' indicating absence. Various types of molecular fingerprints exist, including PubChem CACTVS fingerprints, Klekota-Roth fingerprints, [ 25 ] MACCS fingerprints, and Extended-Connectivity Fingerprints (ECFP). [ 26 ] A molecular fingerprint can be deterministically computed from a given molecular structure. Different molecular structures may yield the same molecular fingerprint.
CSI:FingerID predicts a probabilistic fingerprint with a variety of molecular properties from several fingerprint types. The fingerprint is predicted from the given spectrum and its corresponding fragmentation tree using deep kernel learning, [ 27 ] [ 11 ] which is a combination of kernel methods and deep neural networks . Not only the top scoring molecular formula but multiple high-scoring molecular formula candidates are considered.
To search in a molecular structure database requires a metric to compare and score the molecular fingerprints. Tanimoto similarity (Jaccard index) is a commonly employed metric. A similarity value of 1 signifies identical fingerprints, while a value of 0 indicates structures that do not share any molecular properties. The calculated similarity value depends on the choice of fingerprint type.
CSI:FingerID employs a logarithmic posterior probability to rank the structure candidates, where scores are represented as negative numbers, and zero is the optimum. [ 28 ] This scoring function results in a higher number of correct identifications. [ 11 ] Tanimoto similarities are also given.
The COSMIC confidence score assigns a confidence to CSI:FingerID structure identifications. [ 17 ] The idea is similar to False Discovery Rates : All molecules in a large dataset are analysed using CSI:FingerID, the top-ranked hit for each molecule will be evaluated by COSMIC and the most trustworthy identifications can be selected for further analysis. COSMIC does not re-rank structure candidates of a particular molecule nor does it discard any identifications.
COSMIC employs a confidence score that combines E-value estimation and a linear support vector machine (SVM) with enforced directionality. Calibration of CSI:FingerID scores is achieved using E-value estimates. [ 29 ] Generating decoys for small molecule structures is a non-trivial task, that is why candidates in PubChem serve as a proxy for decoys here.
The score distribution is modeled as a mixture distribution of log-normal distributions , and the P-value and E-value of a hit score are estimated using the kernel density estimate of PubChem candidate scores. The SVM is employed to classify whether a hit is correct, utilizing features such as the calibrated score, score differences to other candidates, the total peak intensity explained by the fragmentation tree, and the cardinality of molecular fingerprints. Learning is constrained to a linear SVM to mitigate the risk of overfitting, and the directionality of features is enforced. This involves making upfront decisions about whether high or low values of a feature should enhance the confidence in an identification. For instance, a high CSI:FingerID score of a hit should increase but never decrease the confidence that the hit is correct. Some features necessitate the existence of at least two candidates for comparison, and separate SVMs are trained for single instances. The decision values of the SVM are mapped to posterior probability estimates using Platt scaling . [ 30 ] This comprehensive approach ensures a robust and nuanced assessment of the confidence in molecule identifications. [ 17 ]
CANOPUS is short for class assignment and ontology prediction using mass spectrometry . [ 16 ] It predicts the compound classes from the molecular fingerprint predicted by CSI:FingerID. This approach is completely database-free, i.e. it is not even limited to molecules that are listed in structure databases.
CANOPUS employs a deep neural network (DNN) [ 31 ] to predict 2,497 compound classes. The DNN was trained on 4.10 million compound structures with compound classes assigned by ClassyFire. [ 32 ] No MS/MS data was used for training, but instead simulated ‘realistic’ probabilistic fingerprints for the training molecular structures were used. The DNN predicts all compound classes simultaneously.
For full biological datasets, CANOPUS provides a comprehensive overview of compound classes present in the sample and allows for comparisons between different cohorts at compound class level.
Small molecules are essential components found throughout nature, playing a significant role in various fields such as drug discovery , diagnostics , food science , environmental monitoring , and more. Effectively addressing many global challenges hinges on the comprehensive identification of small molecules in complex samples. These complex mixtures contain thousands of different molecules measurable in a single mass spectrometry run.
The identification of unknown small molecules is considered a critical bottleneck in metabolomics , natural product research, and related fields, given that widely over 90% of all small molecules remain unknown. [ 33 ] [ 34 ] Commonly, analyses were based on targeted approaches that are limited to the rediscovery of known molecules. In contrast, untargeted analysis is a top-down strategy that avoids the need for a prior specific hypothesis on expected small molecules. The focus shifts from asking, "Is molecule X present in the sample?" to "Which (unknown) molecules are present in the sample and might be relevant for downstream analysis?"
SIRIUS is designed for the untargeted structural elucidation of unknown molecules, addressing various challenges:
Mass spectra alone lack sufficient information to unambiguously identify every molecule. Some molecules produce almost indistinguishable spectra – even more similar than the same molecule measured on two different instruments. [ 22 ] Extensive follow-up experiments are required for unambiguous identification.
Based thereon, it is impossible to always correctly identify a molecular structure merely from a mass spectrum. Thus, CSI:FingerID as well as other methods for structure database search, cannot guarantee finding the correct molecular structure as first hit. That is why it is important to have the correct structure ranked very high from an extensive list of candidates and to assess the confidence in the top hit.
Structure databases are orders of magnitude larger than spectral libraries but still incomplete. [ 41 ] It is understood that not every existing biomolecule is or will be contained in structure databases.
For these instances, SIRIUS offers several solutions:
CASMI (Critical Assessment of Small Molecule Identification) [ 42 ] is an open contest on the identification of small molecules from mass spectrometry data, and was launched in 2012 by Emma Schymanski and Steffen Neumann . [ 43 ]
In CASMI 2016, CSI:FingerID and a derivative of CSI:FingerID, in which the Böcker Group was also involved, won first and second place in the category “Best Automatic Structural Identification - In Silico Fragmentation Only”. Also, CSI:FingerID had the best result for ranking the correct molecule structure at position one (70 out of 127, positive mode). [ 44 ] [ 45 ]
In CASMI 2017, SIRIUS plus CSI:FingerID won in 3 of 4 categories: “Best Structure Identification on Natural Products”, “Best Automatic Structural Identification - In Silico Fragmentation Only”, “Best Automatic Candidate Ranking”. [ 46 ]
In CASMI 2022, six out of 16 contestants used SIRIUS in their workflow to identify the best molecular structure candidates. SIRIUS won in the categories “Correct elemental formulas”, “Correct compound structure classes” and “Correct 2D chemical structures”. CASMI 2022 included compounds that were not even contained in PubChem. [ 47 ]
Sebastian Böcker's group at FSU Jena won the 2022 Thuringian Research Award in the Applied Research category for SIRIUS and the underlying methods. [ 48 ] [ 49 ]
SIRIUS was recognized as a "method to watch" by Nature Methods in 2020. [ 50 ]
SIRIUS is developed by the group of Sebastian Böcker at the FSU Jena in close collaboration with the Bright Giant GmbH. SIRIUS is provided as a software-as-a-service solution. The client software is open-source and installed on the users’ computers. Molecular formula annotation using fragmentation trees and isotope pattern analysis is performed on your local computer without subscription requirement.
The SIRIUS web services for structural elucidation, including molecular fingerprint prediction, structure database search, confidence score assessment and compound class prediction, require a user account. The web services are free for academic/ non-commercial use provided/hosted by the FSU Jena. Academic institutions are identified by their email domain and access will be granted automatically. In some cases, further validation might be required.
Bright Giant GmbH offers subscription-based access to the SIRIUS web services for structural elucidation for commercial users.
Other algorithms and software for searching in structure databases are CFM-ID , [ 51 ] [ 52 ] ICEBERG , [ 53 ] MetFrag , [ 54 ] MS-FINDER , [ 55 ] [ 56 ] MetaboScape® ( Bruker ), MassHunter ( Agilent ) or Compound Discoverer™ ( Thermo Fisher Scientific ). | https://en.wikipedia.org/wiki/SIRIUS_(software) |
Silent Information Regulator ( SIR ) proteins are involved in regulating gene expression. SIR proteins organize heterochromatin near telomeres , [ 1 ] ribosomal DNA (rDNA) , [ 2 ] and at silent loci including hidden mating type loci in yeast. [ 3 ] [ 4 ] The SIR family of genes encodes catalytic and non-catalytic proteins that are involved in de-acetylation of histone tails and the subsequent condensation of chromatin around a SIR protein scaffold. [ 5 ] Some SIR family members are conserved from yeast to humans.
SIR proteins have been identified in many screens , and have historically been known as SIR [ 3 ] ( s ilent i nformation r egulator), MAR [ 6 ] ( ma ting-type r egulator), STE [ 7 ] ( ste rile), CMT [ 8 ] ( c hange of m ating t ype) or SSP [ 9 ] ( s terile s u p pressor) according to which screen led to their identification. Ultimately, the name SIR had the most staying power, because it most accurately describes the function of the encoded proteins. [ citation needed ]
One of the early yeast screens to identify SIR genes was performed by Anita Hopper and Benjamin Hall, who screened with mutagenesis for alleles that allow sporulation in a normally sporulation-deficient heterothallic α/α ( ho/ho MATα/MATα ). Their screen identified a mutation in a novel gene that was not linked to HO that allowed the α/α diploid to sporulate, as if it were an α/a diploid, and inferred that the mutation affected a change in mating type by an HO -independent mechanism. [ 8 ] Later, it was discovered at the CMT allele identified by Hopper & Hall did not cause a mating type conversion at the MAT locus, but rather allowed the expression of cryptic mating type genes that are silenced in wild-type yeast. [ 4 ] In their paper clarifying the mechanism of the CMT mutation, Haber and acknowledge the contribution of Amar Klar , who presented his MAR mutant strains that had similar properties as the CMT mutants at the Cold Spring Harbor Laboratory yeast genetics meeting, which led Haber and to consider the hypothesis that the cmt mutants may act by de-repressing silent information. [ 10 ]
In the same year that Haber & demonstrated that the cmt mutant restores sporulation by de-repressing hidden mating type loci, two other groups published screens for genes involved in the regulation of silent mating type cassettes. [ 6 ] The first study, performed by Amar Klar, Seymour Fogel and Kathy Macleod, identified a mutation in a spontaneous a/a diploid that caused the products of sporulation to be haploids with an apparent diploid phenotype, as assayed by ability to mate. [ 6 ] The authors reasoned that the mutation caused the de-repression of then-recently appreciated silent mating type loci HMa and HMα, which would allow an a/a diploid to sporulate and would cause haploid segregants inheriting the mutant allele to behave as a/α diploids despite being haploid. [ 6 ] The authors named the mutation MAR for its apparent role in mating type regulation, and were able to map the mutation to chromosome IV, and determined that it was located 27.3 cM from a commonly used trp1 marker. [ 6 ]
A few months later, Jasper Rine and Ira Herskowitz published a different screen for genes that affect the ability of yeast to mate , and ultimate discovered the gene family that they called SIR, a name that remains in the modern parlance. [ 3 ] Unlike the Klar et al. screen that identified a mutant by its inability to mate, Rine & Herskowitz took a more directed approach towards discovering factors responsible for mating type silencing. Specifically, Rine & Herskowitz reasoned that a haploid yeast cell with a recessive mutation in matα1 could be complemented if the silent copy of MATα were de-repressed. Starting in a ho matα1 haploid strain, Rine & Herskowitz screened mutants arising from mutagenesis and identified five mutants that restored a MATα phenotype in matα cells, but were not linked to the MAT locus and did not cause a gene conversion between the HMα locus and matα. [ 3 ] These mutants, they reasoned, were specifically defective in silencing the cryptic mating type genes.
Eventually, all of the mutants resulting from the original Hopper & Hall screen as well as the later Rine & Herskowitz screen and the Klar et al. screen were characterized and mapped, and it was shown that the causative genes were the same. [ 11 ] In fact, the genes that are now referred to as SIR1-4 have at one time been referred to as MAR, CMT or STE according to the screen that identified the mutants.
Although Klar, Hartwell and Hopper identified mutations in SIR genes and applied other names to the genes before Rine performed his screen, the SIR name was eventually adopted because Rine eventually identified the most complete set of functionally related genes (SIR1-4), and because the work by Rine and Herskowitz most accurately described the function of the SIR family genes. [ 11 ] Later it would be shown that in yeast and in higher organisms, SIR proteins are important for transcriptional regulation of many chromatin domains.
In budding yeast, SIR proteins are found at the silent mating type loci, telomeres, and at the rDNA locus. At the silent mating type loci and at the telomeres, SIR proteins participate in transcriptional silencing of genes within their domain of localization. At the rDNA locus, SIR proteins are thought to primarily be important for repressing recombination between rDNA repeats rather than for suppressing transcription. [ 12 ]
In transcriptional silencing, SIR2,3,4 are required in stoichiometric amounts to silence specific chromosomal regions. In yeast, SIR proteins bind sites on nucleosome tails and form a multimeric compound of SIR2,3,4 that condenses chromatin and is thought to physically occlude promoters in the silenced interval, preventing their interaction with transcription machinery. [ 12 ] The establishment of SIR-repressed heterochromatin domains is a complicated process that involves different subsets of proteins and regulatory proteins depending on the locus in the genome. [ 12 ] At the silent mating type loci and at yeast telomeres, the transcription factors Abf1 ( A RS b inding f actor) and Rap1 ( r epressor- a ctivator p rotein) associate with specific nucleotide sequences in the silencers that flank heterochromatic regions. [ 13 ] Rap1 contains a Sir3-binding domain that recruits SIR3 to the silencers. [ 14 ] Once at the silencers, Sir3 recruits Sir4-Sir2 dimers to the chromatin nucleation site. Sir2 then deacetylates histone H3 and H4 tails, and free Sir3 binds the now-deacetylated lysine residues H4K16,79, and recruits additional Sir4-Sir2 dimers to promote the further spreading of the heterochromatin domain. [ 12 ]
Once it has spread to cover a genomic locus, the SIR2,3,4 effectively prevents transcription from the region it occupies, in a process that is thought to depend on the physical occlusion of DNA by SIR proteins. Recently, it has been shown that certain promoters are capable of directing transcription inside regions that are otherwise silenced by SIR proteins. [ 15 ] Specifically, if an inducible promoter is induced inside a silent chromatin domain, it can achieve ~200x increase in expression levels with little detectable change in covalent histone modifications . [ 15 ]
SIR2 is an NAD-dependent lysine deacetylase. [ 12 ] It was the first-discovered member of the Sirtuin protein family and it is highly conserved, with homologs found in organisms ranging from humans to bacteria [ 16 ] and archaea. [ 12 ] It interacts with a variety of protein substrates, but does not exhibit strong affinity for DNA, chromatin, or other silencer-binding factors. [ 12 ] Instead, it relies on other SIR proteins to find its appropriate silencing target. [ 12 ]
In the SIR protein complex, SIR2 removes acetyl groups from the lysine on histone tails H3 and H4, [ 17 ] 'priming' the nucleosome for chromatin packaging by the SIR3 component of the complex. [ 18 ]
Beyond its canonical role in the SIR complex, SIR2 also plays a role in rDNA repression. [ 19 ] As part of the cell's regulation mechanism, rDNA repeats are excised from the chromosome so they cannot be expressed. SIR2 forms a complex with NET1 (a nuclear protein) and CDC14 (a phosphatase) to form the re gulator of n ucleolar silencing and t elophase (RENT) complex. [ 19 ] The RENT complex sequesters excised rDNA in 'extrachromosomal circles,' preventing recombination. Accumulation of these circles has been linked to premature aging. [ 12 ] Sirtuin 2 (SIRT2) , SIR2's human analog, has also been linked to age-related disease. [ 16 ]
SIR3 is principally involved in heterochromatin spreading, the silencing activity of the SIR protein complex. [ 12 ] When overexpressed, SIR3 leads to spreading beyond the normal nucleation site. [ 12 ] SIR3 can continue to operate at very low levels of SIR2 and SIR4, but not without them. [ 17 ] [ 18 ] It preferentially binds to unmodified nucleosomes (no acetylation at H4K16 or methylation at H3K79), and relies on SIR2's deacetylation of H4K16 to enhance silencing. [ 18 ] H3K79 methylation by DOT1 methyltransferase inhibits SIR3, resulting in an unsilenced chromatin region. [ 17 ] [ 18 ] SIR3 is recruited to target sequence by the transcription factors RAP1 or ABF1. [ 12 ] [ 17 ]
SIR4 is involved in scaffolding the assembly of silenced chromatin. [ 12 ] [ 19 ] It binds to DNA with high affinity, but low specificity. [ 19 ] It is most stable when co-expressed with SIR2, but neither SIR2 nor SIR3 are required for it to operate at the telomeres. [ 12 ] Each half of the SIR4 protein has distinct responsibilities in heterochromatin spreading. SIR4's N-terminus is required for telomeric silencing, but not for homothallic mating-type (HM) silencing. [ 12 ] Conversely, its C-terminus supports HM but not telomeric repression. [ 12 ] The N-terminus is positively charged and can be recruited to the telomeric repression site by SIR1 and YKU80. [ 12 ] The C-terminus contains the coiled-coil region, which interacts with SIR3 in the heterotrimeric SIR complex and can also interact with RAP1 and YKU70 for recruitment to the telomeric region of the chromosome. [ 17 ] The C-terminus also contains the SIR2-interacting domain (SID), where SIR4 can bind to the extended N-terminus of SIR2. [ 12 ] SIR2 can catalyze reactions without being bound to SIR4, but SIR2's catalytic activity is enhanced when interacting with SIR4. [ 12 ]
SIR proteins are conserved from yeast to humans, and lend their name to a class of mammalian histone deacetylases ( Sirtuins , homologs of Sir2). Sirtuins have been implicated in myriad human traits including Alzheimer's and diabetes, and have been proposed to regulate of lifespan. [ 16 ] | https://en.wikipedia.org/wiki/SIR_proteins |
SISTINE (also known as SISTINE Mission and SISTINE Program ) (acronym for "Suborbital Imaging Spectrograph for Transition region Irradiance from Nearby Exoplanet host stars" ) is a NASA mission designed to study distant stars as a way of finding life on exoplanets . [ 1 ] [ 2 ]
The technology to be employed is up to 100 times the UV spectroscopic ability of the Hubble Space Telescope . [ 3 ] The first test of the mission was launched on a Black Brant 9 rocket , a two-stage sounding rocket , at White Sands Missile Range , New Mexico , on 11 August 2019. [ 4 ] This suborbital rocket can carry a payload of up to 1200 pounds, which, in the case of SISTINE, includes spectrographic equipment capable of covering the far ultra-violet spectral range of 100 to 160 nm, well suited to study strong atomic emission lines associated with the formation temperatures in the atmospheres of low-mass stars , and their effects on the potential atmospheres of exoplanets. [ 4 ]
The second launch of SISTINE occurred on 8 November 2021. This launch focused on observing the spectra of Procyon A . [ 5 ]
A third launch occurred on 6 July 2022 at 13:47 UTC from the Arnhem Space Centre in Nhulunbuy , Australia , reaching an apogee of 243 km (151 mi). This launch focused on the spectra of Alpha Centauri A and B in the Alpha Centauri system which contains three stars and Proxima Centauri b , the closest exoplanet to the Earth. [ 6 ]
The principal investigator of the mission is astronomer Kevin France , Assistant Professor at the Department of Astrophysical and Planetary Sciences , Laboratory for Atmospheric and Space Physics , University of Colorado in Boulder, Colorado . [ 1 ] [ 7 ] [ 8 ] | https://en.wikipedia.org/wiki/SISTINE |
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