omniomni/omni-engineering huggingface dataset:
Fractionation. Fractionation is a separation process in which a certain quantity of a mixture (of gasses, solids, liquids, enzymes, or isotopes, or a suspension) is divided during a phase transition, into a number of smaller quantities (fractions) in which the composition varies according to a gradient. Fractions are collected based on differences in a specific property of the individual components. A common trait in fractionations is the need to find an optimum between the amount of fractions collected and the desired purity in each fraction. Fractionation makes it possible to isolate more than two components in a mixture in a single run. This property sets it apart from other separation techniques.

Fractionation is widely employed in many branches of science and technology. Mixtures of liquids and gasses are separated by fractional distillation by difference in boiling point. Fractionation of components also takes place in column chromatography by a difference in affinity between stationary phase and the mobile phase. In fractional crystallization and fractional freezing, chemical substances are fractionated based on difference in solubility at a given temperature. In cell fractionation, cell components are separated by difference in mass.

Of natural samples

Bioassay-guided fractionation 
A typical protocol to isolate a pure chemical agent from natural origin is step-by-step separation of extracted components based on differences in their bioassay-guided fractionation physicochemical properties, and assessing the biological activity, followed by next round of separation and assaying. Typically, such work is initiated after a given crude extract is deemed "active" in a particular in vitro assay.

Blood fractionation 

The process of blood fractionation involves separation of blood into its main components.  Blood fractionation refers generally to the process of separation using a centrifuge (centrifugation), after which three major blood components can be visualized: plasma, buffy coat and erythrocytes (blood cells).  These separated components can be analyzed and often further separated.

Of food 

Fractionation is also used for culinary purposes, as coconut oil, palm oil, and palm kernel oil are fractionated to produce oils of different viscosities, that may be used for different purposes. These oils typically use fractional crystallization (separation by solubility at temperatures) for the separation process instead of distillation. Mango oil is an oil fraction obtained during the processing of mango butter.

Milk can also be fractionated to recover the milk protein concentrate or the milk basic proteins fraction.

Isotope fractionation

See also 
 Copurification
 List of purification methods in chemistry
 Transposition cipher#Fractionation

References

Further reading 
 

 
Laboratory techniques
Antonov An-38. The Antonov An-38 is a stretched and upgraded version of Antonov's earlier An-28. It is a twin-engined turboprop transport aircraft, designed by the Antonov Design Bureau in Kyiv, Ukraine. Production is in Novosibirsk, Russia, but some crucial parts are also made in Ukraine and Belarus. It first flew in 1994, and received international flight certification in April 2000. A total of 11 were built and 2 remain in airline service as of August 2019. A recent documentary says that only one remains in service with ALROSA Airlines in 2021.

Development
Impetus for a stretch of the Antonov An-28 design began with a 1989 sales tour in India, where it became clear that a significant market existed for an aircraft similar to the An-28, but with seating in the 25–30 seat range. The design was approved a year later, and was displayed at the 1991 Paris Air Show as a model.

The An-38 is of a similar design to the older An-28, featuring the same wings and tail; but it has a longer fuselage and includes several enhancements, such as higher fuel efficiency, increased comfort (cabin and cockpit), and decreased internal noise, coupled with better sound insulation. Other improvements include an increase in passengers to 27, thanks to an increase in maximum payload to 2,500 kg (5,500 lbs), as well as a maximum speed of 405 km/h (250 mph). Its design also enables it to operate in adverse conditions—it is equipped with weather radar, sophisticated navigational systems, and low pressure tires that allow it to operate from primitive, unpaved and icy airfields. Furthermore, the aircraft is more resistant to stalling at high angles of attack and is stable and maneuverable with ice on the wing and tail assembly.

Civil operators
As of August 2019, 2 Antonov An-38 aircraft remain in airline service with ALROSA. Recent reviews suggest only one remains in service in 2021.

Former operators

 Vostok Aviation Company

Specifications (An-38-100)

See also

References

Further reading 

 

An-038
Antonov An-038
Aircraft first flown in 1994
Twin-turboprop tractor aircraft
Twin-tail aircraft
Aircraft with fixed tricycle landing gear
High-wing aircraft
Cyclohexene. Cyclohexene is a hydrocarbon with the formula . It is an example of a cycloalkene. At room temperature, cyclohexene is a colorless liquid with a sharp odor. Among its uses, it is an intermediate in the commercial synthesis of nylon.

Production and uses
Cyclohexene is produced by the partial hydrogenation of benzene, a process developed by the Asahi Chemical company.  The main product of the process is cyclohexane because cyclohexene is more easily hydrogenated than benzene.

In the laboratory, it can be prepared by dehydration of cyclohexanol.

Reactions and uses
Benzene is converted to cyclohexylbenzene by acid-catalyzed alkylation with cyclohexene. Cyclohexylbenzene is a precursor to both phenol and cyclohexanone.

Hydration of cyclohexene gives cyclohexanol, which can be dehydrogenated to give cyclohexanone, a precursor to caprolactam.

The oxidative cleavage of cyclohexene gives adipic acid. Hydrogen peroxide is used as the oxidant in the presence of a tungsten catalyst. 

1,5-Hexadiene is produced by ethenolysis of cyclohexene. Bromination gives 1,2-dibromocyclohexane.

Structure 
Cyclohexene is most stable in a half-chair conformation, unlike the preference for a chair form of cyclohexane. One basis for the cyclohexane conformational preference for a chair is that it allows each bond of the ring to adopt a staggered conformation. For cyclohexene, however, the alkene is planar, equivalent to an eclipsed conformation at that bond.

See also 
 Diels-Alder reaction
 Cyclohexa-1,3-diene
 Cyclohexa-1,4-diene

References

External links 
 
 
 Material Safety Data Sheet for cyclohexene
 Safety MSDS data
  Reaction of Cyclohexene with Bromine and Potassium Permanganate
 Cyclohexene synthesis
 Data sheet at inchem.org

Cycloalkenes
Hydrocarbon solvents
Cyclohexanol. Cyclohexanol is the organic compound with the formula HOCH(CH2)5. The molecule is related to cyclohexane by replacement of one hydrogen atom by a hydroxyl group. This compound exists as a deliquescent colorless solid with a camphor-like odor, which, when very pure, melts near room temperature.  Millions of tonnes are produced annually, mainly as a precursor to nylon.

Production
Cyclohexanol is produced by the oxidation of cyclohexane in air, typically using cobalt catalysts:
2 C6H12 + O2 → 2 C6H11OH
This process coforms cyclohexanone, and this mixture ("KA oil" for ketone-alcohol oil) is the main feedstock for the production of adipic acid.  The oxidation involves radicals and the intermediacy of the hydroperoxide C6H11O2H.
Alternatively, cyclohexanol can be produced by the hydrogenation of phenol:
C6H5OH + 3 H2 → C6H11OH
This process can also be adjusted to favor the formation of cyclohexanone.

Basic reactions
Cyclohexanol undergoes the main reactions expected for a secondary alcohol. Oxidation gives cyclohexanone, which is converted on a large scale in industry to the oxime, a precursor to caprolactam. As a laboratory exercise, this oxidation can be effected with chromic acid.  Esterification affords the commercially useful derivatives dicyclohexyladipate and dicyclohexylphthalate, which are used as plasticizers. Heating in the presence of acid catalysts converts cyclohexanol to cyclohexene.

Structure
Cyclohexanol has at least two solid phases. One of them is a plastic crystal.

Applications
As indicated above, cyclohexanol is an important feedstock in the polymer industry, firstly as a precursor to nylons, but also to various plasticizers. Small amounts are used as a solvent.

Safety
Cyclohexanol is moderately toxic: the Threshold Limit Value for the vapor for 8 h is 50 ppm. The IDLH concentration is set at 400 ppm, based on studies on the acute oral toxicity in animals. Few studies have been done on its carcinogenicity, but one study on rats found it to have co-carcinogenic effects.

References

Cyclohexyl compounds
Cyclohexanols
Nerve agent precursors
Euler (programming language). Euler is a programming language created by Niklaus Wirth and Helmut Weber, conceived as an extension and generalization of ALGOL 60. The designers' goals were to create a language that is:
 Simpler, yet more flexible, than ALGOL 60
 Useful and processed with reasonable efficiency
 Definable with rigorous formality

Available sources indicate that Euler was operational by 1965.

Overview
Euler employs a general data type concept. In Euler, arrays, procedures, and switches are not quantities which are declared and named by identifiers: in contrast to ALGOL, they are not quantities on the same level as variables. Rather, these quantities are on the level of numeric and boolean constants. Thus, besides the traditional numeric and logical constants, Euler introduces several added types:
 Reference
 Label
 Symbol
 List (array)
 Procedure
 Undefined
All constants can be assigned to variables, which have the same form as in ALGOL, but for which no fixed types are specified: Euler uses dynamic typing. Further, a procedure can produce a value of any type when executed, and this type can vary from one call of the procedure to the next.

Similarly, the elements of a list can have values of any type and these can differ from element to element within a list. So, when the list elements are labels, a switch is obtained. If the elements are procedures, a procedure list is obtained, which is unavailable in ALGOL 60. If the elements are lists themselves, then a general tree structure is obtained.

Euler provides general type-test and type-conversion operators.

See also 
 Wirth–Weber precedence relationship
 Simple precedence parser

References

External links 
  - EULER IV for the Burroughs B5500 from 1965
  - An implementation written in Icon from 2000-2001

Dynamically typed programming languages
Lithe. Lithe is an experimental programming language created in 1982 by David Sandberg at the University of Washington which allows the programmer to freely choose their own syntax. Lithe combines the ideas of syntax-directed translation and classes in a novel manner that results in a remarkably simple yet powerful language.

Overview
The standard class-based programming model does not specify a mechanism by which to manipulate objects: where Smalltalk uses message passing, Lithe uses syntax-directed translation (SDT). SDT is a method of translating a string into a sequence of actions by attaching one such action to each rule of a grammar. Thus, parsing a string of the grammar produces a sequence of rule applications. Lithe merges SDT with the class model by using classes as the non-terminal alphabet of the grammar. Since the grammar class used by Lithe properly contains all context-free grammars, a wide variety of syntax can be described, and SDT provides a simple way to attach semantics to any such syntax.

The package is the unit of program modularity in Lithe. A package is divided into two parts: one that defines classes and another that defines rules. Information hiding is achieved by requiring both export keywords on those rules and classes that are to be seen outside a package and that the source package names be included in the with clause of the consumer package.

Examples
Programming in Lithe consists of defining rule-action pairs and classes. Take the task of computing the absolute value of a number, for example:

 rule "|" <i:int> "|" return int;
   {if i<0 then return -i else return i end}

After this rule-action pair has been defined, it can be freely used within Lithe source code, for example, the following expression will thereafter be valid:

 |x - y| + 3

The equivalent rule in BNF would be:

 <int>  ::=  "|" <int> "|"

Note that the Lithe description swaps the left and right sides of the BNF one, then adds a name to each nonterminal in the BNF right-hand side. These names are used in the action part, which is expressed as a string that is translated into a sequence of actions by using other, previously defined, rule-action pairs (eventually, some of those rule-action pairs will invoke primitive actions).

External links
 "Lithe: a language combining a flexible syntax and classes"

Declarative programming languages
Experimental programming languages
Extensible syntax programming languages
PHM. PHM may refer to:

 Master of Philosophy (M.Phil. or Ph.M.)
 Prognostics and health management
 PulteGroup, NYSE stock symbol
 Penn-Harris-Madison School Corporation, Indiana, US
 A US Navy hull classification symbol: Patrol missile hydrofoil (PHM)
 Pretty Hate Machine, the debut album from Nine Inch Nails
 Proto-Hmong–Mien language
 Pure homopolar motor, is an electric motor not requiring brushes, electronics, or semiconductor parts to convert direct current into torque.
 PHM Racing, a German auto racing team
 Passive hydrogen maser, a type of atomic clock
Johan Håstad. Johan Torkel Håstad (; born 19 November 1960) is a Swedish theoretical computer scientist most known for his work on computational complexity theory. He was the recipient of the Gödel Prize in 1994 and 2011 and the ACM Doctoral Dissertation Award in 1986, among other prizes. He has been a professor in theoretical computer science at KTH Royal Institute of Technology in Stockholm, Sweden since 1988, becoming a full professor in 1992. He is a member of the Royal Swedish Academy of Sciences since 2001.

He received his B.S. in Mathematics at Stockholm University in 1981, his M.S. in Mathematics at Uppsala University in 1984 and his Ph.D. in Mathematics from MIT in 1986.

Håstad's thesis and 1994 Gödel Prize concerned his work on lower bounds on the size of constant-depth Boolean circuits for the parity function.  After Andrew Yao proved that such circuits require exponential size, Håstad proved nearly optimal lower bounds on the necessary size through his switching lemma, which became an important technical tool in circuit complexity with applications to learnability, the IP hierarchy, and proof systems.

He also received the 2011 Gödel Prize for his work on optimal inapproximability results.  In particular, he improved the PCP theorem (which won the same prize in 2001) to give a probabilistic verifier for NP problems which reads only three bits. Further, he used these results to prove results in hardness of approximation.

In 1998 Håstad was an Invited Speaker of the International Congress of Mathematicians in Berlin. In 1999 he was an Erdős Lecturer at the Hebrew University of Jerusalem. In 2012, he became a fellow of the American Mathematical Society. He was elected as an ACM Fellow in 2018 for "contributions in circuit complexity, approximability and inapproximability, and foundations of pseudorandomness".

In 2018 he received the Knuth Prize "for his long and sustained record of milestone
breakthroughs at the foundations of computer science, with huge impact on
many areas including optimization, cryptography, parallel computing, and complexity theory."

References

External links
 Johan Håstad's home page
 

1960 births
Living people
Swedish computer scientists
20th-century Swedish mathematicians
21st-century Swedish mathematicians
Gödel Prize laureates
Knuth Prize laureates
Uppsala University alumni
Stockholm University alumni
Academic staff of the KTH Royal Institute of Technology
Members of the Royal Swedish Academy of Sciences
Massachusetts Institute of Technology School of Science alumni
Fellows of the American Mathematical Society
2018 fellows of the Association for Computing Machinery
International Mathematical Olympiad participants
Theoretical computer scientists
GE U28B. The GE U28B diesel-electric locomotive model replaced the U25B in early 1966, featuring a slightly uprated prime mover (only  more power than the U25B). Early units had the same car body styling as the U25B, while later units had design features (e.g., shortened nose) more in common with later models. After only a year of production, this model was superseded by the U30B.

Trains Magazine editor David P. Morgan wrote about General Electric's decision to go with 2800 horsepower in its 1966 locomotive production. The short article Morgan wrote in the November 1965 issue had line drawings of the proposed short nose U28B.

Original owners

Preservation 
Only two U28B's are in preservation, and one of them has been rebuilt to U30B specs.

Transkentucky Transportation Incorporated 260 is preserved at the Illinois Railway Museum. It was built as Chicago Burlington and Quincy 114 in December 1966.
Vintage Locomotives Inc 5323, originally built as Louisville and Nashville 2504, is preserved at the Southern Appalachia Railway Museum. It was rebuilt to U30B specs late into its career.

References

External links
 Sarberenyi, Robert. GE U28B Original Owners

U28B
B-B locomotives
Diesel–electric locomotives of the United States
Railway locomotives introduced in 1966
Freight locomotives
Standard gauge locomotives of the United States
Shuttle tanker. A shuttle tanker is a ship designed for oil transport from an off-shore oil field as an alternative to constructing oil pipelines. It is equipped with off-loading equipment compatible with the oil field in question. This normally consists of a taut hawser arrangement or dynamic positioning to maintain the position relative to the field, an off-loading arrangement of pipes, and redundant safety systems to ensure that the potentially flammable crude oil is handled safely in a harsh environment.

Shuttle tankers initially started operating in the North Sea. They are now in use also in Brazil and Canada. Trials have been carried out in Gulf Of Mexico. There are plans to take up such operation in the Arctic Sea, north of western Russia.

+Shuttle
Ship types
Conditional quantum entropy. The conditional quantum entropy is an entropy measure used in quantum information theory.  It is a generalization of the conditional entropy of classical information theory.   For a bipartite state , the conditional entropy is written , or , depending on the notation being used for the von Neumann entropy. The quantum conditional entropy was defined in terms of a conditional density operator  by Nicolas Cerf and Chris Adami, who showed that quantum conditional entropies can be negative, something that is forbidden in classical physics. The negativity of quantum conditional entropy is a sufficient criterion for quantum non-separability.

In what follows, we use the notation  for the von Neumann entropy, which will simply be called "entropy".

Definition 

Given a bipartite quantum state , the entropy of the joint system AB is , and the entropies of the subsystems are  and .  The von Neumann entropy measures an observer's uncertainty about the value of the state, that is, how much the state is a mixed state.

By analogy with the classical conditional entropy, one defines the conditional quantum entropy as .

An equivalent operational definition of the quantum conditional entropy (as a measure of the quantum communication cost or surplus when performing quantum state merging) was given by Michał Horodecki, Jonathan Oppenheim, and Andreas Winter.

Properties

Unlike the classical conditional entropy, the conditional quantum entropy can be negative.  This is true even though the (quantum) von Neumann entropy of single variable is never negative. The negative conditional entropy is also known as the coherent information, and gives the additional number of bits above the classical limit that can be transmitted in a quantum dense coding protocol. Positive conditional entropy of a state thus means the state cannot reach even the classical limit, while the negative conditional entropy provides for additional information.

References

 

Quantum mechanical entropy
Ullmannite. Ullmannite or Nickel glance (trivial name) is a nickel antimony sulfide mineral with formula: NiSbS. Considerable substitution occurs with cobalt and iron in the nickel site along with bismuth and arsenic in the antimony site. A solid solution series exists with the high cobalt willyamite.

Physical properties
Ullmannite is steel-gray to tin white in color with a metallic luster, has a Mohs hardness of 5 to 5.5 and a specific gravity of 6.65. Initially thought to be of two species, tetrahedral and cubic, it was later confirmed that both samples conformed to the 23 point group of the isometric crystal class and typically exhibits cubic, octahedral, or pyritohedral forms although euhedral crystals are rare.

Variance in its chemical composition has been shown to be responsible for loss of symmetry and variations in striation patterns.

Ullmannite crystals are usually less than 2 mm, however larger have been identified in especially antimony rich environments.  Ullmannite commonly displays interpenetration twins as well as enantiomorphic twinning along [110].

Occurrence

It is a member of the cobaltite group and forms a series with willyamite (). It occurs with nickeline, gersdorffite, pentlandite, chalcopyrite, pyrrhotite, galena, tetrahedrite and dyscrasite in hydrothermal deposits.

Principal localities are in Germany, it is also found in Austria, Australia, France, England, and Wales.

It was first described in 1843 for an occurrence in the Storch und Schöneberg Mine, North Rhine-Westphalia, Germany.

Specimens of ullmannite were found at Sarrabus, Sardinia, Italy in 1887. The crystals of the specimens from Sarrabus were described as hemihedral with parallel faces, whereas specimens from Lölling in present-day Austria were hemihedral with inclined faces.

Origin of name
Ullmannite was named for German chemist and mineralogist, Johann Christoph Ullmann (1771–1821), one of the fathers of systematic mineralogy.  Ullmann established a mineral collection (now the basis for the internationally renowned  Museum of Mineralogy in Marburg) and authored Ein Systematisch-Tabellarische Übersicht der Mineralogisch einfachen Fossilien, one of the first attempts to provide a structured organization to the observed minerals of the day.

See also
List of minerals
List of minerals named after people

References

 Palache, C., H. Berman, and C. Frondel (1944) Dana’s system of mineralogy, (7th edition), v. I, 301–302.

Nickel minerals
Antimonide minerals
Sulfide minerals
Cubic minerals
Glances
Minerals in space group 198
Minerals described in 1843