Chemistry chapter
QMRIn a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos−1(−1/3) =109.4712206...° ≈ 109.5° when all four substituents are the same, as in methane (CH4).[1] [2] The perfectly symmetrical tetrahedron belongs to point group Td, but most tetrahedral molecules are have lower symmetry. Tetrahedral molecules can be chiral.
Main group chemistry[edit]
The tetrahedral molecule methane (CH4)
Aside from virtually all saturated organic compounds, most compounds of Si, Ge, and Sn are tetrahedral. Often tetrahedral molecules feature multiple bonding to the outer ligands, as in xenon tetroxide (XeO4), the perchlorate ion (ClO4−), the sulfate ion (SO42−), the phosphate ion (PO43−). Thiazyl trifluoride (SNF3) is tetrahedral, featuring a sulfur-to-nitrogen triple bond.[3]
Ammonia (NH3) can be classified as tetrahedral, if one considers the lone pair as a ligand as in the language of VSEPR theory. The H-N-H angles are 107°, being contracted from 109.4°, a difference attributed to the influence of the lone pair. Ammonia is actually classified as pyramidal, as nonbonding electron pairs have a greater repulsive influence.
Transition metal chemistry[edit]
Again the geometry is widespread, particularly so for complexes where the metal has d0 or d10 configuration. Illustrative examples include tetrakis(triphenylphosphine)palladium(0) (Pd[P(C6H5)3]4), nickel carbonyl (Ni(CO)4), and titanium tetrachloride (TiCl4). Many complexes with incompletely filled d-shells are often tetrahedral, e.g. the tetrahalides of iron(II), cobalt(II), and nickel(II).
Water structure[edit]
The most common arrangement of liquid water (H2O) molecules is tetrahedral with two hydrogen atoms covalently attached to oxygen and two attached by hydrogen bonds. Since the hydrogen bonds vary in length many of these water molecules are not symmetrical and form transient irregular tetrahedra between their four associated hydrogen atoms.[4]
Exceptions and distortions[edit]
Inversion of tetrahedral occurs widely in organic and main group chemistry. The so-called Walden inversion illustrates the stereochemical consequences of inversion at carbon. Nitrogen inversion in ammonia also entails transient formation of planar NH3.
Inverted tetrahedral geometry[edit]
Geometrical constraints in a molecule can cause a severe distortion of idealized tetrahedral geometry. In compounds featuring "inverted carbon" for instance, the carbon is pyramidal.[5]
Inverted carbon
The simplest examples of organic molecules displaying inverted carbon are the smallest propellanes, such as [1.1.1]propellane; or more generally paddlanes,[6] and pyramidane (or [3.3.3.3]fenestrane).[7][8] Such molecules are typically strained, resulting in increased reactivity.
A tetrahedron can also be distorted by increasing the angle between two of the bonds. In the extreme case, flattening results. For carbon this phenomenon can be observed in a class of compounds called the fenestranes.
Tetrahedral molecules with no central atom[edit]
A few molecules have a tetrahedral geometry with no central atom. An inorganic example is tetraphosphorus (P4) which has four phosphorus atoms at the vertices of a tetrahedron and each bonded to the other three. An organic example is tetrahedrane (C4H4) with four carbon atoms each bonded to one hydrogen and the other three carbons.
QMRTetrahedrane is a platonic hydrocarbon with chemical formula C4H4 and a tetrahedral structure. Extreme angle strain (carbon bond angles deviate considerably from the tetrahedral bond angle of 109.5°) prevents this molecule from forming naturally.
QMrIn silico (literally Latin for "in silicon", alluding to the mass use of silicon for semiconductor computer chips) is an expression used to mean "performed on computer or via computer simulation." The phrase was coined in 1989 as an allusion to the Latin phrases in vivo, in vitro, and in situ, which are commonly used in biology (see also systems biology) and refer to experiments done in living organisms, outside of living organisms, and where they are found in nature, respectively.
Tetra-tert-butyltetrahedrane[edit]
The tert-butyl derivative was first synthesised starting from a cycloaddition of an alkyne with t-Bu substituted maleic anhydride,[4] followed by rearrangement with carbon dioxide expulsion to a cyclopentadienone and its bromination, followed by addition of the fourth t-Bu group and a photochemical rearrangement with expulsion of carbon monoxide.
Tetra(trimethylsilyl)tetrahedrane[edit]
Tetra(trimethylsilyl)tetrahedrane is relatively stable
In tetra(trimethylsilyl)tetrahedrane (I) the tert-butyl groups have been replaced by trimethylsilyl groups.[5] This compound (prepared from the corresponding cyclobutadiene) is far more stable than the tert-butyl analogue. The silicon-carbon bond is longer than a carbon-carbon bond, and therefore the corset effect is reduced. On the other hand, the trimethylsilyl group is a sigma donor which explains the increased stabilization of the tetrahedrane. Whereas the tert-butyl tetrahedrane melts at 135 °C, at which temperature decomposition to the cyclobutadiene starts, the trimethylsilyl tetrahedrane melts at a much higher temperature of 202 °C, and is stable up to 300 °C, at which point it reverts to the acetylene starting material. The tetrahedrane skeleton is made up of banana bonds, and hence the carbon atoms are high in s-orbital character. From NMR, sp hybridization can be deduced, normally reserved for triple bonds. As a consequence the bond lengths are unusually short with 152 picometers.
An improved synthesis of tetra(trimethylsilyl)tetrahedrane has been reported, by one-electron reduction of the cyclobutadiene precursor with tris(pentafluorophenyl)borane.[6] Reaction with methyllithium has yielded the stable tetrahedranyllithium derivative.[7] Coupling reactions with this lithium compound have given access to more derivatives.[8][9][10]
The tetrahedrane dimer (II) has also been reported.[11] The connecting bond is even shorter with 143.6 pm. An ordinary carbon-carbon bond has a length of 154 pm.
Tetrasilatetrahedrane[edit]
In tetrasilatetrahedrane, the carbon atoms in the tetrahedrane cage are replaced by silicon. The standard silicon silicon bond is much longer (235 pm) and the cage is again enveloped by a total of 16 trimethylsilyl groups. This makes the compound thermally stable. The silatetrahedrane can be reduced with potassium graphite to the tetrasilatetrahedranide potassium salt. In this compound one of the silicon atoms of the cage has lost a silyl substituent and carries a negative charge. The potassium cation can be captured by a crown ether and in the resulting complex potassium and the silyl anion are separated by a distance of 885 pm. One of the Si− - Si bonds is now 272 pm and its silicon atom has an inverted tetrahedral geometry. Furthermore the four cage silicon atoms are equivalent on the NMR timescale due to migrations of the silyl substituents over the cage.[12]
The dimerization reaction observed for the carbon tetrahedrane compound is also attempted for a tetrasilatetrahedrane.[13] In this tetrahedrane the cage is protected by 4 so-called super silyl groups in which a silicon atom has 3 tert-butyl substituents. The dimer does not materialize but a reaction with iodine in benzene followed by reaction with the tri-tert-butyl sila anion results in the formation of an eight membered silicon cluster compound which can be described as a Si2 dumbbell (length 229 picometer and with inversion of tetrahedral geometry) sandwiched between two almost parallel Si3 rings.
In known eight-membered clusters of in the same carbon group, tin Sn8R6 and germanium Ge8R6 the cluster atoms are located on the corners of a cube.
Tetranitrotetrahedrane[edit]
Due to its bond strain and perfect oxygen balance, tetranitrotetrahedrane, an analogue of tetrahedrane with four nitro group substituents, has potential as a high-performance energetic material. The addition of these nitro groups is likely to reduce tetranitrohedrane's stability.[14]
Inorganic and organometallic tetrahedranes[edit]
Metal clusters that have tetrahedral cores are often called tetrahedranes.
The tetrahedrane motif occurs broadly in chemistry. White phosphorus (P4) and yellow arsenic (As4) are examples. Several types of metal carbonyl clusters are referred to as tetrahedranes.
QMR Carbon has four valence electrons and thus looks like a quadrant
QMR Carbon has four valence electrons and thus looks like a quadrant
A Platonic hydrocarbon is a hydrocarbon (molecule) whose structure matches one of the five Platonic solids, with carbon atoms replacing its vertices, carbon–carbon bonds replacing its edges, and hydrogen atoms as needed.[1]
Not all Platonic solids have molecular hydrocarbon counterparts.
Tetrahedrane[edit]
Tetrahedrane (C4H4) is a hypothetical compound. It has not yet been synthesized without substituents, but it is predicted to be kinetically stable in spite of its acute bond angle and angle strain. Some stable derivatives, including tetra-tert-butyltetrahedrane (a hydrocarbon) and tetra(trimethylsilyl)tetrahedrane, have been produced.
(carbon molecules are shaped like quadrants)
Cubane[edit]
Cubane (C8H8) has been synthesized.
Octahedrane[edit]
Angle strain prevents formation of an octahedron,[2] and since 4 edges meet at each corner, there would be no hydrogen atoms; thus, the hypothetical octahedrane molecule would be an allotrope of elemental carbon, C6, and not a hydrocarbon. The existence of octahedrane cannot be ruled out completely, although calculations have shown that it is unlikely.[3]
The fifth is always questionable
Icosahedrane[edit]
The tetravalency (4-connectedness) of carbon excludes an icosahedron since 5 edges meet at each vertex; pentacoordinate carbon, such as CH5+, is unlikely, although both icosahedrane and octahedrane have been observed in boron compounds. The fourth is always different
Dodecahedrane[edit]
Dodecahedrane (C20H20) has been synthesized.
QMRA fullerene is a molecule of carbon in the form of a hollow sphere, ellipsoid, tube, and many other shapes. Spherical fullerenes are also called Buckminsterfullerene (buckyballs), and they resemble the balls used in football (soccer). Cylindrical ones are called carbon nanotubes or buckytubes. Fullerenes are similar in structure to graphite, which is composed of stacked graphene sheets of linked hexagonal rings; but they may also contain pentagonal (or sometimes heptagonal) rings.[1]
The first fullerene molecule to be discovered, and the family's namesake, buckminsterfullerene (C60), was prepared in 1985 by Richard Smalley, Robert Curl, James Heath, Sean O'Brien, and Harold Kroto at Rice University. The name was a homage to Buckminster Fuller, whose geodesic domes it resembles. The structure was also identified some five years earlier by Sumio Iijima, from an electron microscope image, where it formed the core of a "bucky onion".[2] Fullerenes have since been found to occur in nature.[3] More recently, fullerenes have been detected in outer space.[4] According to astronomer Letizia Stanghellini, "It’s possible that buckyballs from outer space provided seeds for life on Earth."[5]
The discovery of fullerenes greatly expanded the number of known carbon allotropes, which until recently were limited to graphite, diamond, and amorphous carbon such as soot and charcoal. Buckyballs and buckytubes have been the subject of intense research, both for their unique chemistry and for their technological applications, especially in materials science, electronics, and nanotechnology.
The icosahedral C60H60 cage was mentioned in 1965 as a possible topological structure.[6] Eiji Osawa of Toyohashi University of Technology predicted the existence of C60 in 1970.[7][8] He noticed that the structure of a corannulene molecule was a subset of a Association football shape, and he hypothesised that a full ball shape could also exist. Japanese scientific journals reported his idea, but it did not reach Europe or the Americas.
Also in 1970, R. W. Henson (then of the Atomic Energy Research Establishment) proposed the structure and made a model of C60. Unfortunately, the evidence for this new form of carbon was very weak and was not accepted, even by his colleagues. The results were never published but were acknowledged in Carbon in 1999.[9][10]
QMRCarbon is a scientific journal published by Elsevier. According to the journal's website, "Carbon publishes papers that deal with original research on carbonaceous solids with an emphasis on graphene-based materials. These materials include, but are not limited to, carbon nanotubes, carbon fibers and filaments, graphites, activated carbons, pyrolytic carbons, glass-like carbons, carbon blacks, and chars."
Independently from Henson, in 1973 a group of scientists from the USSR, directed by Prof. Bochvar, made a quantum-chemical analysis of the stability of C60 and calculated its electronic structure. As in the previous cases, the scientific community did not accept the theoretical prediction. The paper was published in 1973 in Proceedings of the USSR Academy of Sciences (in Russian).[11]
In mass spectrometry, discrete peaks appeared corresponding to molecules with the exact mass of sixty or seventy or more carbon atoms. In 1985, Harold Kroto (then of the University of Sussex), James R. Heath, Sean O'Brien, Robert Curl and Richard Smalley, from Rice University, discovered C60, and shortly thereafter came to discover the fullerenes.[12] Kroto, Curl, and Smalley were awarded the 1996 Nobel Prize in Chemistry[13] for their roles in the discovery of this class of molecules. C60 and other fullerenes were later noticed occurring outside the laboratory (for example, in normal candle-soot). By 1991, it was relatively easy to produce gram-sized samples of fullerene powder using the techniques of Donald Huffman, Wolfgang Krätschmer and Konstantinos Fostiropoulos. Fullerene purification remains a challenge to chemists and to a large extent determines fullerene prices. So-called endohedral fullerenes have ions or small molecules incorporated inside the cage atoms. Fullerene is an unusual reactant in many organic reactions such as the Bingel reaction discovered in 1993. Carbon nanotubes were first discovered and synthesized in 1991.[14][15]
Minute quantities of the fullerenes, in the form of C60, C70, C76, C82 and C84 molecules, are produced in nature, hidden in soot and formed by lightning discharges in the atmosphere.[16] In 1992, fullerenes were found in a family of minerals known as Shungites in Karelia, Russia.[3]
In 2010, fullerenes (C60) have been discovered in a cloud of cosmic dust surrounding a distant star 6500 light years away. Using NASA's Spitzer infrared telescope the scientists spotted the molecules' unmistakable infrared signature. Sir Harry Kroto, who shared the 1996 Nobel Prize in Chemistry for the discovery of buckyballs commented: "This most exciting breakthrough provides convincing evidence that the buckyball has, as I long suspected, existed since time immemorial in the dark recesses of our galaxy."[17]
Naming[edit]
The discoverers of Buckminsterfullerene (C60) named it after Richard Buckminster Fuller, a noted architectural modeler who popularized the geodesic dome. Since buckminsterfullerenes have a shape similar to that sort of dome, they thought the name appropriate.[18] As the discovery of the fullerene family came after buckminsterfullerene, the shortened name 'fullerene' is used to refer to the family of fullerenes. The suffix "-ene" indicates that each C atom is covalently bonded to three others (instead of the maximum of four), a situation that classically would correspond to the existence of bonds involving two pairs of electrons ("double bonds")
Types of fullerene[edit]
Since the discovery of fullerenes in 1985, structural variations on fullerenes have evolved well beyond the individual clusters themselves. Examples include:[19]
Buckyball clusters: smallest member is C
20 (unsaturated version of dodecahedrane) and the most common is C
60;
Nanotubes: hollow tubes of very small dimensions, having single or multiple walls; potential applications in electronics industry;
Megatubes: larger in diameter than nanotubes and prepared with walls of different thickness; potentially used for the transport of a variety of molecules of different sizes;[20]
polymers: chain, two-dimensional and three-dimensional polymers are formed under high-pressure high-temperature conditions; single-strand polymers are formed using the Atom Transfer Radical Addition Polymerization (ATRAP) route;[21]
nano"onions": spherical particles based on multiple carbon layers surrounding a buckyball core;[22] proposed for lubricants;[23]
linked "ball-and-chain" dimers: two buckyballs linked by a carbon chain;[24]
fullerene rings.[25]
Buckminsterfullerene[edit]
Main article: Buckminsterfullerene
Buckminsterfullerene is the smallest fullerene molecule containing pentagonal and hexagonal rings in which no two pentagons share an edge (which can be destabilizing, as in pentalene). It is also most common in terms of natural occurrence, as it can often be found in soot.
The structure of C60 is a truncated icosahedron, which resembles an association football ball of the type made of twenty hexagons and twelve pentagons, with a carbon atom at the vertices of each polygon and a bond along each polygon edge.
The van der Waals diameter of a C60 molecule is about 1.1 nanometers (nm).[26] The nucleus to nucleus diameter of a C60 molecule is about 0.71 nm.
The C60 molecule has two bond lengths. The 6:6 ring bonds (between two hexagons) can be considered "double bonds" and are shorter than the 6:5 bonds (between a hexagon and a pentagon). Its average bond length is 1.4 angstroms.
Silicon buckyballs have been created around metal ions.
Other buckyballs[edit]
Another fairly common fullerene is C70,[31] but fullerenes with 72, 76, 84 and even up to 100 carbon atoms are commonly obtained.
In mathematical terms, the structure of a fullerene is a trivalent convex polyhedron with pentagonal and hexagonal faces. In graph theory, the term fullerene refers to any 3-regular, planar graph with all faces of size 5 or 6 (including the external face). It follows from Euler's polyhedron formula, V − E + F = 2 (where V, E, F are the numbers of vertices, edges, and faces), that there are exactly 12 pentagons in a fullerene and V/2 − 10 hexagons.
The smallest fullerene is the dodecahedral C20. There are no fullerenes with 22 vertices.[32] The number of fullerenes C2n grows with increasing n = 12, 13, 14, ..., roughly in proportion to n9 (sequence A007894 in OEIS). For instance, there are 1812 non-isomorphic fullerenes C60. Note that only one form of C60, the buckminsterfullerene alias truncated icosahedron, has no pair of adjacent pentagons (the smallest such fullerene). To further illustrate the growth, there are 214,127,713 non-isomorphic fullerenes C200, 15,655,672 of which have no adjacent pentagons. Optimized structures of many fullerene isomers are published and listed on the web.[33]
Trimetasphere carbon nanomaterials were discovered by researchers at Virginia Tech and licensed exclusively to Luna Innovations. This class of novel molecules comprises 80 carbon atoms (C
80) forming a sphere which encloses a complex of three metal atoms and one nitrogen atom. These fullerenes encapsulate metals which puts them in the subset referred to as metallofullerenes. Trimetaspheres have the potential for use in diagnostics (as safe imaging agents), therapeutics[34] and in organic solar cells.[35]
Carbon nanotubes[edit]
This rotating model of a carbon nanotube shows its 3D structure.
Main article: Carbon nanotube
Nanotubes are cylindrical fullerenes. These tubes of carbon are usually only a few nanometres wide, but they can range from less than a micrometer to several millimeters in length. They often have closed ends, but can be open-ended as well. There are also cases in which the tube reduces in diameter before closing off. Their unique molecular structure results in extraordinary macroscopic properties, including high tensile strength, high electrical conductivity, high ductility, high heat conductivity, and relative chemical inactivity (as it is cylindrical and "planar" — that is, it has no "exposed" atoms that can be easily displaced). One proposed use of carbon nanotubes is in paper batteries, developed in 2007 by researchers at Rensselaer Polytechnic Institute.[36] Another highly speculative proposed use in the field of space technologies is to produce high-tensile carbon cables required by a space elevator.
QMRGang run printing is a method in which multiple printing projects are placed on a common paper sheet in an effort to reduce printing costs and paper waste. Gang runs are generally used with sheet-fed printing presses and CMYK process color jobs, which require four separate plates that are hung on the plate cylinder of the press. Printers use the term "gang run" or "gang" to describe the practice of placing many print projects on the same oversized sheet. Basically, instead of running one postcard that is 4 x 6 as an individual job the printer would place 15 different postcards on 20 x 18 sheet therefore using the same amount of press time the printer will get 15 jobs done in the roughly the same amount of time as one job.
Conventional printing has four types of process:
Planographics, in which the printing and non-printing areas are on the same plane surface and the difference between them is maintained chemically or by physical properties, the examples are: offset lithography, collotype, and screenless printing.
Relief, in which the printing areas are on a plane surface and the non printing areas are below the surface, examples: flexography and letterpress.
Intaglio, in which the non-printing areas are on a plane surface and the printing area are etched or engraved below the surface, examples: steel die engraving, gravure
Porous, in which the printing areas are on fine mesh screens through which ink can penetrate, and the non-printing areas are a stencil over the screen to block the flow of ink in those areas, examples: screen printing, stencil duplicator.
QMRA diode's I–V characteristic can be approximated by four regions of operation:
At very large reverse bias, beyond the peak inverse voltage or PIV, a process called reverse breakdown occurs that causes a large increase in current (i.e., a large number of electrons and holes are created at, and move away from the p–n junction) that usually damages the device permanently. The avalanche diode is deliberately designed for use in that manner. In the Zener diode, the concept of PIV is not applicable. A Zener diode contains a heavily doped p–n junction allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material, such that the reverse voltage is "clamped" to a known value (called the Zener voltage), and avalanche does not occur. Both devices, however, do have a limit to the maximum current and power they can withstand in the clamped reverse-voltage region. Also, following the end of forward conduction in any diode, there is reverse current for a short time. The device does not attain its full blocking capability until the reverse current ceases.
For a bias less than the PIV, the reverse current is very small. For a normal P–N rectifier diode, the reverse current through the device in the micro-ampere (µA) range. However, this is temperature dependent, and at sufficiently high temperatures, a substantial amount of reverse current can be observed (mA or more).
With a small forward bias, where only a small forward current is conducted, the current–voltage curve is exponential in accordance with the ideal diode equation. There is a definite forward voltage at which the diode starts to conduct significantly. This is called the knee voltage or cut-in voltage and is equal to the barrier potential of the p-n junction. This is a feature of the exponential curve, and appears sharper on a current scale more compressed than in the diagram shown here.
At larger forward currents the current-voltage curve starts to be dominated by the ohmic resistance of the bulk semiconductor. The curve is no longer exponential, it is asymptotic to a straight line whose slope is the bulk resistance. This region is particularly important for power diodes. The diode can be modeled as an ideal diode in series with a fixed resistor.
QMRAccording to the original 1971 definition, the memristor was the fourth fundamental circuit element, forming a non-linear relationship between electric charge and magnetic flux linkage. In 2011 Chua argued for a broader definition that included all 2-terminal non-volatile memory devices based on resistance switching.[3] Williams argued that MRAM, phase change memory and RRAM were memristor technologies.[15] Some researchers argued that biological structures such as blood[16] and skin[17] fit the definition. Others argued that the memory device under development by HP Labs and other forms of RRAM were not memristors but rather part of a broader class of variable resistance systems[18] and that a broader definition of memristor is a scientifically unjustifiable land grab that favored HP's memristor patents.[19
1971[edit]
Leon Chua postulated a new two-terminal circuit element characterized by a relationship between charge and flux linkage as a fourth fundamental circuit element.[1]- the fourth is always different
On June 1 Mouttet argued that the interpretation of the memristor as a fourth fundamental was incorrect and that the HP Labs device was part of a broader class of memristive systems.[101
QMRToday, most diodes are made of silicon, but other semiconductors such as selenium or germanium are sometimes used.[6]
Germanium like silicon and carbon has four valence electrons and thus looks like a quadrant
Indian scientist Jagadish Chandra Bose was the first to use a crystal for detecting radio waves in 1894.[14] The crystal detector was developed into a practical device for wireless telegraphy by Greenleaf Whittier Pickard, who invented a silicon crystal detector in 1903 and received a patent for it on November 20, 1906.
A p–n junction diode is made of a crystal of semiconductor, usually silicon, but germanium and gallium arsenide are also used. Impurities are added to it to create a region on one side that contains negative charge carriers (electrons), called an n-type semiconductor, and a region on the other side that contains positive charge carriers (holes), called a p-type semiconductor. When the two materials i.e. n-type and p-type are attached together, a momentary flow of electrons occur from the n to the p side resulting in a third region between the two where no charge carriers are present. This region is called the depletion region due to the absence of charge carriers (electrons and holes in this case). The diode's terminals are attached to the n-type and p-type regions. The boundary between these two regions, called a p–n junction, is where the action of the diode takes place. When a higher electrical potential is applied to the P side (the anode) than to the N side (the cathode), it allows electrons to flow from the N-type side to the P-type side. The junction does not allow the flow of electrons in the opposite direction when the potential is applied in reverse, creating, in a sense, an electrical check valve.
Normal (p–n) diodes, which operate as described above, are usually made of doped silicon or, more rarely, germanium. Before the development of silicon power rectifier diodes, cuprous oxide and later selenium was used. Their low efficiency required a much higher forward voltage to be applied (typically 1.4 to 1.7 V per "cell", with multiple cells stacked so as to increase the peak inverse voltage rating for application in high voltage rectifiers), and required a large heat sink (often an extension of the diode's metal substrate), much larger than the later silicon diode of the same current ratings would require. The vast majority of all diodes are the p–n diodes found in CMOS integrated circuits, which include two diodes per pin and many other internal diodes.
in cuprous oxide the solid is diamagnetic. In terms of their coordination spheres, copper centres are 2-coordinated and the oxides are tetrahedral. The structure thus resembles in some sense the main polymorphs of SiO2, and both structures feature interpenetrated lattices.
QMRA thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. It acts exclusively as a bistable switch, conducting when the gate receives a current trigger, and continuing to conduct while the voltage across the device is not reversed (forward-biased). A three-lead thyristor is designed to control the larger current of its two leads by combining that current with the smaller current of its other lead, known as its control lead. In contrast, a two-lead thyristor is designed to switch on if the potential difference between its leads is sufficiently large (breakdown voltage).
Some sources define silicon-controlled rectifier (SCR) and thyristor as synonymous.[1] Other sources define thyristors as a larger set of devices with at least four layers of alternating N and P-type material.
The thyristor is a four-layered, three terminal semiconductor device, with each layer consisting of alternately N-type or P-type material, for example P-N-P-N. The main terminals, labelled anode and cathode, are across all four layers. The control terminal, called the gate, is attached to p-type material near the cathode. (A variant called an SCS—Silicon Controlled Switch—brings all four layers out to terminals.) The operation of a thyristor can be understood in terms of a pair of tightly coupled bipolar junction transistors, arranged to cause a self-latching action:
For applications with frequencies higher than the domestic AC mains supply (e.g. 50 Hz or 60 Hz), thyristors with lower values of tQ are required. Such fast thyristors can be made by diffusing heavy metal ions such as gold or platinum which act as charge combination centers into the silicon. Today, fast thyristors are more usually made by electron or proton irradiation of the silicon, or by ion implantation. Irradiation is more versatile than heavy metal doping because it permits the dosage to be adjusted in fine steps, even at quite a late stage in the processing of the silicon.
History[edit]
The silicon controlled rectifier (SCR) or thyristor proposed by William Shockley in 1950 and championed by Moll and others at Bell Labs was developed in 1956 by power engineers at General Electric (G.E.), led by Gordon Hall and commercialized by G.E.'s Frank W. "Bill" Gutzwiller.
Silicon carbide thyristors[edit]
In recent years, some manufacturers[8] have developed thyristors using silicon carbide (SiC) as the semiconductor material. These have applications in high temperature environments, being capable of operating at temperatures up to 350 °C.
QMRQuadracs are a special type of thyristor which combines a "diac" and a "triac" in a single package. The diac is the triggering device for the triac. Thyristors are four-layer (PNPN) semiconductor devices that act as switches, rectifiers or voltage regulators in a variety of applications. When triggered, thyristors turn on and become low-resistance current paths. They remain so even after the trigger is removed, and until the current is reduced to a certain level (or until they are triggered off). Diacs are bi-directional diodes that switch AC voltages and trigger triacs or silicon-controlled rectifiers (SCRs). Except for a small leakage current, diacs do not conduct until the breakover voltage is reached. Triacs are three-terminal, silicon devices that function as two SCRs configured in an inverse, parallel arrangement. They provide load current during both halves of the AC supply voltage. By combining the functions of diacs and triacs, quadracs eliminate the need to buy and assemble discrete parts.
Quadracs are used in lighting control, speed control, and temperature modulation control applications. They carry performance specifications such as peak repetitive off voltage, peak repetitive reverse voltage, root mean square (RMS) on-state current, and temperature junction. Peak repetitive off voltage is the maximum, instantaneous value of the off-state voltage that occurs across a thyristor, including all repetitive transient voltages and excluding all non-transient voltages. Peak repetitive reverse voltage is the maximum peak reverse voltage that may be applied continuously to the main terminals (anode and cathode) of quadracs. RMS on-state current is the maximum RMS current allowed for the specified use-case temperature. Temperature junction for quadracs is expressed as a full-required range.
Quadracs are available in a variety of integrated circuit (IC) package types with different numbers of pins. Basic IC packages types for quadracs include discrete packaging (DPAK), power packaging (PPAK), and in-line packaging (IPAK). Other IC package types include diode outline (DO), transistor outline (TO), and small outline transistor (SOT). Quadracs that use metal electrode leadless face (MELF) packaging have metallized terminals at each end of a cylindrical body. Other available package types for quadracs include thin small outline package (TSOP), thin shrink small outline L-leaded package (TSSOP), and thin small outline J-lead (TSOJ) package.
QMRFull-wave rectification[edit]
A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to pulsating DC (direct current), and yields a higher average output voltage. Two diodes and a center tapped transformer, or four diodes in a bridge configuration and any AC source (including a transformer without center tap), are needed.[3] Single semiconductor diodes, double diodes with common cathode or common anode, and four-diode bridges, are manufactured as single components.
QMREarly transistors were made from germanium but most modern BJTs are made from silicon. A significant minority are also now made from gallium arsenide, especially for very high speed applications (see HBT, below).
QMRThe silicon bandgap temperature sensor is an extremely common form of temperature sensor (thermometer) used in electronic equipment. Its main advantage is that it can be included in a silicon integrated circuit at very low cost. The principle of the sensor is that the forward voltage of a silicon diode, which may be the base-emitter junction of a bipolar junction transistor (BJT), is temperature-dependent,
QMRMost integrated circuits large enough to include identifying information include four common sections: the manufacturer's name or logo, the part number, a part production batch number and serial number, and a four-digit code that identifies when the chip was manufactured. Extremely small surface mount technology parts often bear only a number used in a manufacturer's lookup table to find the chip characteristics.
The manufacturing date is commonly represented as a two-digit year followed by a two-digit week code, such that a part bearing the code 8341 was manufactured in week 41 of 1983, or approximately in October 1983.
QMRAn integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small plate ("chip") of semiconductor material, normally silicon.
Wafer-scale integration (WSI) is a means of building very large integrated circuits that uses an entire silicon wafer to produce a single "super-chip". Through a combination of large size and reduced packaging, WSI could lead to dramatically reduced costs for some systems, notably massively parallel supercomputers. The name is taken from the term Very-Large-Scale Integration, the current state of the art when WSI was being developed.[28]
A system-on-a-chip (SoC or SOC) is an integrated circuit in which all the components needed for a computer or other system are included on a single chip. The design of such a device can be complex and costly, and building disparate components on a single piece of silicon may compromise the efficiency of some elements. However, these drawbacks are offset by lower manufacturing and assembly costs and by a greatly reduced power budget: because signals among the components are kept on-die, much less power is required (see Packaging).[
Mono-crystal silicon wafers (or for special applications, silicon on sapphire or gallium arsenide wafers) are used as the substrate. Photolithography is used to mark different areas of the substrate to be doped or to have polysilicon, insulators or metal (typically aluminium) tracks deposited on them.
As of 2005, a fabrication facility (commonly known as a semiconductor fab) costs over US$1 billion to construct.[36] The cost of a fabrication facility rises over time (Rock's law) because much of the operation is automated. Today, the most advanced processes employ the following techniques:
The wafers are up to 300 mm in diameter (wider than a common dinner plate).
Use of 32 nanometer or smaller chip manufacturing process. Intel, IBM, NEC, and AMD are using ~32 nanometers for their CPU chips. IBM and AMD introduced immersion lithography for their 45 nm processes[37]
Copper interconnects where copper wiring replaces aluminium for interconnects.
Low-K dielectric insulators.
Silicon on insulator (SOI)
Strained silicon in a process used by IBM known as strained silicon directly on insulator (SSDOI)
Multigate devices such as tri-gate transistors being manufactured by Intel from 2011 in their 22 nm process.
Silicon labelling and graffiti[edit]
To allow identification during production most silicon chips will have a serial number in one corner. It is also common to add the manufacturer's logo. Ever since ICs were created, some chip designers have used the silicon surface area for surreptitious, non-functional images or words. These are sometimes referred to as chip art, silicon art, silicon graffiti or silicon doodling.
QMRChip art, also known as silicon art, chip graffiti or silicon doodling, refers to microscopic artwork built into integrated circuits, also called chips or ICs. Since ICs are printed by photolithography
QMRMicroelectronics This application, mainly applied to silicon wafers/silicon integrated circuits is the most developed of the technologies and the most specialized in the field.
QMRLevels of biohazard[edit]
Main article: Biosafety level
Immediate disposal of used needles into a sharps container is standard procedure.
NHS medics practise using protective equipment used to treat Ebola patients
The United States Centers for Disease Control and Prevention (CDC) categorizes various diseases in levels of biohazard, Level 1 being minimum risk and Level 4 being extreme risk. Laboratories and other facilities are categorized as BSL (Biosafety Level) 1-4 or as P1 through P4 for short (Pathogen or Protection Level).
Biohazard Level 1: Bacteria and viruses including Bacillus subtilis, canine hepatitis, Escherichia coli, varicella (chicken pox), as well as some cell cultures and non-infectious bacteria. At this level precautions against the biohazardous materials in question are minimal, most likely involving gloves and some sort of facial protection.
Biohazard Level 2: Bacteria and viruses that cause only mild disease to humans, or are difficult to contract via aerosol in a lab setting, such as hepatitis A, B, and C, some influenza A strains, Lyme disease, salmonella, mumps, measles, scrapie, dengue fever, HIV. "Routine diagnostic work with clinical specimens can be done safely at Biosafety Level 2, using Biosafety Level 2 practices and procedures. Research work (including co-cultivation, virus replication studies, or manipulations involving concentrated virus) can be done in a BSL-2 (P2) facility, using BSL-3 practices and procedures.
Biohazard Level 3: Bacteria and viruses that can cause severe to fatal disease in humans, but for which vaccines or other treatments exist, such as anthrax, West Nile virus, Venezuelan equine encephalitis, SARS virus, MERS coronavirus, hantaviruses, tuberculosis, typhus, Rift Valley fever, Rocky Mountain spotted fever, yellow fever, and malaria. Among parasites Plasmodium falciparum, which causes Malaria, and Trypanosoma cruzi, which causes trypanosomiasis, also come under this level.
Biohazard Level 4: Viruses and bacteria that cause severe to fatal disease in humans, and for which vaccines or other treatments are not available, such as Bolivian and Argentine hemorrhagic fevers, Marburg virus, Ebola virus, Lassa fever virus, Crimean–Congo hemorrhagic fever, and other hemorrhagic diseases and rishibola. Variola virus (smallpox) is an agent that is worked with at BSL-4 despite the existence of a vaccine, as it has been eradicated. When dealing with biological hazards at this level the use of a positive pressure personnel suit, with a segregated air supply, is mandatory. The entrance and exit of a Level Four biolab will contain multiple showers, a vacuum room, an ultraviolet light room, autonomous detection system, and other safety precautions designed to destroy all traces of the biohazard. Multiple airlocks are employed and are electronically secured to prevent both doors opening at the same time. All air and water service going to and coming from a Biosafety Level 4 (P4) lab will undergo similar decontamination procedures to eliminate the possibility of an accidental release.
QMRWith the exception of the four-toed African hunting dog (Lycaon pictus), there are five toes on the forefeet but the pollex (thumb) is reduced and does not reach the ground. On the hind feet, there are four toes, but in some domestic dogs, a fifth vestigial toe, known as a dewclaw, is sometimes present but has no anatomical connection to the rest of the foot. The slightly curved nails are non-retractile and more or less blunt
QMRThe Acheson process is a process to synthesize graphite and silicon carbide, named after its inventor Edward Goodrich Acheson. Again, graphite is composed of carbon, which is shaped as a quadrant, and silicon is shaped as a quadrant.
The process consists of heating a mixture of silica or quartz sand[1] and powdered coke (carbon) in an iron bowl. Acheson, in 1890, originally attempted to synthesize artificial diamond, but ended up creating blue crystals of silicon carbide, which he called carborundum.[2] When heated to 4150 °C, the silicon is removed, leaving graphite. The process was patented by Acheson in 1896.[3] After discovering this process, Acheson developed an efficient electric furnace based on resistive heating, the design of which is the basis of most silicon carbide manufacturing today. Silicon carbide was a useful material in jewelry making due to its abrasive properties, and this was the first commercial application of the Acheson process.[4]
In the furnace, an electric current was passed through a graphite core, surrounded by sand, salt, and carbon. The electric current heated the graphite and other materials, allowing them to react, producing a layer of silicon carbide around the graphite core. The process gives off carbon monoxide. There are four chemical reactions in the process that produces silicon carbide (SiC):[4]
C + SiO2 → SiO + CO
SiO2 + CO → SiO + CO2
C + CO2 → 2CO
2C + SiO → SiC + CO
The first light emitting diodes were produced using silicon carbide from the Acheson process. The potential use of silicon carbide as a semiconductor led to the development of the Lely process, which was based on the Acheson process, but allowed control over the purity of the silicon carbide crystals.[5]
The first commercial plant using the Acheson process was built by Acheson in Niagara Falls, New York, where hydroelectric plants nearby could cheaply produce the necessary power for the energy intensive process. By 1896, The Carborundum Company was producing 1 million pounds of "carborundum".[6] Many current silicon carbide plants use the same basic design as the first Acheson plant. In the first plant, sawdust and salt were added to the sand to control purity. The addition of salt was stopped in the 1960s, as the advantages of greater purity were outweighed by the disadvantages of the corrosion of steel structures, which the salt caused. The addition of sawdust was stopped in some plants to reduce emissions.[4]
In the manufacture of synthetic graphite, the Acheson process is run for approximately 20 hours, with currents of 200 A, and voltages of 40,000–50,000 V (8–10 MW). The purity of graphite achievable using the process is 99.5%.
Biology Chapter
QMRWith the exception of the four-toed African hunting dog (Lycaon pictus), there are five toes on the forefeet but the pollex (thumb) is reduced and does not reach the ground. On the hind feet, there are four toes, but in some domestic dogs, a fifth vestigial toe, known as a dewclaw, is sometimes present but has no anatomical connection to the rest of the foot. The slightly curved nails are non-retractile and more or less blunt
QMRAll mammals except the monotremes, the xenarthrans, the pangolins, and the cetaceans[citation needed] have up to four distinct types of teeth, with a maximum number for each. These are the incisor (cutting), the canine, the premolar, and the molar (grinding). The incisors occupy the front of the tooth row in both upper and lower jaws. They are normally flat, chisel-shaped teeth that meet in an edge-to-edge bite. Their function is cutting, slicing, or gnawing food into manageable pieces that fit into the mouth for further chewing. The canines are immediately behind the incisors. In many mammals, the canines are pointed, tusk-shaped teeth, projecting beyond the level of the other teeth. In carnivores, they are primarily offensive weapons for bringing down prey. In other mammals such as some primates, they are used to split open hard surfaced food. The premolars and molars are at the back of the mouth. Depending on the particular mammal and its diet, these two kinds of teeth prepare pieces of food to be swallowed by grinding, shearing, or crushing. The specialised teeth—incisors, canines, premolars, and molars—are found in the same order in every mammal.[4] In many mammals the infants have a set of teeth that fall out and are replaced by adult teeth. These are called deciduous teeth, primary teeth, baby teeth or milk teeth.[5][6] Animals that have two sets of teeth, one followed by the other, are said to be diphyodont. Normally the dental formula for milk teeth is the same as for adult teeth except that the molars are missing.
QMRMonotremes are mammals that lay eggs (Prototheria) instead of giving birth to live young like marsupials (Metatheria) and placental mammals (Eutheria). The only surviving examples of monotremes are all indigenous to Australia and New Guinea, although there is evidence that they were once more widespread. The existing monotreme species are the platypus and four species of echidnas (or spiny anteaters).
QMRMale echidnas have a four-headed penis.
QMRThe ancestors of marsupials, part of a larger group called metatherians, probably split from those of placental mammals (eutherians) during the mid-Jurassic period, though no fossil evidence of metatherians themselves are known from this time.[38] Fossil metatherians are distinguished from eutherians by the form of their teeth; metatherians possess four pairs of molar teeth in each jaw, whereas eutherian mammals (including true placentals) never have more than three pairs.[39] Using this criterion, the earliest known metatherian is Sinodelphys szalayi, which lived in China around 125 million years ago (mya).[40] This makes it a contemporary to some early eutherian species which have been found in the same area.[41]
QMRThe ancestors of marsupials, part of a larger group called metatherians, probably split from those of placental mammals (eutherians) during the mid-Jurassic period, though no fossil evidence of metatherians themselves are known from this time.[38] Fossil metatherians are distinguished from eutherians by the form of their teeth; metatherians possess four pairs of molar teeth in each jaw, whereas eutherian mammals (including true placentals) never have more than three pairs.[39] Using this criterion, the earliest known metatherian is Sinodelphys szalayi, which lived in China around 125 million years ago (mya).[40] This makes it a contemporary to some early eutherian species which have been found in the same area.[41]
Timing of childbirth
Further information: Preterm birth and Postterm pregnancy
Stages of pregnancy term
stage starts ends
Preterm[47]
-
at 37 weeks
Early term[48] 37 weeks 39 weeks
Full term[48] 39 weeks 41 weeks
Late term[48] 41 weeks 42 weeks
Postterm[48] 42 weeks
-
In the ideal childbirth labor begins on its own when a woman is "at term".[49] Pregnancy is considered at term when gestation has lasted between 37 and 42 weeks.[48]
Events before completion of 37 weeks are considered preterm.[47] Preterm birth is associated with a range of complications and should be avoided if possible.[50]
Sometimes if a woman's water breaks or she has contractions before 39 weeks, birth is unavoidable.[48] However, spontaneous birth after 37 weeks is considered term and is not associated with the same risks of a pre-term birth.[51] Planned birth before 39 weeks by Caesarean section or labor induction, although "at term", results in an increased risk of complications.[52] This is from factors including underdeveloped lungs of newborns, infection due to underdeveloped immune system, feeding problems due to underdeveloped brain, and jaundice from underdeveloped liver.[53]
Babies born between 39 and 41 weeks gestation have better outcomes than babies born either before or after this range.[48] This special time period is called "full term".[48] Whenever possible, waiting for labor to begin on its own in this time period is best for the health of the mother and baby.[49] The decision to perform an induction must be made after weighing the risks and benefits, but is safer after 39 weeks.[49]
Events after 42 weeks are considered postterm.[48] When a pregnancy exceeds 42 weeks, the risk of complications for both the woman and the fetus increases significantly.[54][55] Therefore, in an otherwise uncomplicated pregnancy, obstetricians usually prefer to induce labour at some stage between 41 and 42 weeks.[56]
Psychology chapter
QMRErikson was a student of Anna Freud,[29] the daughter of Sigmund Freud, whose psychoanalytic theory and psychosexual stages contributed to the basic outline of the eight stages, at least those concerned with childhood. Namely, the first four of Erikson's life stages correspond to Freud's oral, anal, phallic, and latency phases, respectively. Also, the fifth stage of adolescence is said to parallel the genital stage in psychosexual development:
Although the first three phases are linked to those of the Freudian theory, it can be seen that they are conceived along very different lines. Emphasis is not so much on sexual modes and their consequences as on the ego qualities which emerge from each stages. There is an attempt also to link the sequence of individual development to the broader context of society.[13]
QMRMarcia defines four identity statuses which combines the presence or absence of the processes of exploration and commitment: Identity diffusion (not engaged in exploration or commitment), identity foreclosure (a lack of exploration, yet committed), moratorium (process of exploration without having made a commitment), and identity achievement (exploration and commitment of identity).
QMRAttachments between infants and caregivers form even if this caregiver is not sensitive and responsive in social interactions with them.[6] This has important implications. Infants cannot exit unpredictable or insensitive caregiving relationships. Instead they must manage themselves as best they can within such relationships. Based on her established Strange Situation Protocol, research by developmental psychologist Mary Ainsworth in the 1960s and 70s found that children will have different patterns of attachment depending primarily on how they experienced their early caregiving environment. Early patterns of attachment, in turn, shape — but do not determine — the individual's expectations in later relationships.[7] Four different attachment classifications have been identified in children: secure attachment, anxious-ambivalent attachment, anxious-avoidant attachment, and disorganized attachment. Attachment theory has become the dominant theory used today in the study of infant and toddler behavior and in the fields of infant mental health, treatment of children, and related fields. Secure attachment is when children feel they can rely on their caregivers to attend to their needs of proximity, emotional support and protection. It is considered to be the best attachment style. Separation anxiety is what infants feel when they are separated from their caregivers. Anxious-ambivalent attachment is when the infant feels separation anxiety when separated from his caregiver and does not feel reassured when the caregiver returns to the infant. Anxious-avoidant attachment is when the infant avoids their parents. Disorganized attachment is when there is a lack of attachment behavior. In the 1980s, the theory was extended to attachment in adults. Attachment applies to adults when adults feel close attachment to their parents and their romantic partners.
QMRMainly on the basis of their reunion behaviours (although other behaviors are taken into account) in the Strange Situation Paradigm (Ainsworth et al., 1978; see below), infants can be categorized into three 'organized' attachment categories: Secure (Group B); Avoidant (Group A); and Anxious/Resistant (Group C). There are subclassifications for each group (see below). A fourth category, termed Disorganized (D), can also be assigned to an infant assessed in the Strange Situation although a primary 'organized' classification is always given for an infant judged to be disorganized. Each of these groups reflects a different kind of attachment relationship with the mother. A child may have a different type of attachment to each parent as well as to unrelated caregivers. Attachment style is thus not so much a part of the child's thinking, but is characteristic of a specific relationship. However, after about age five children tend to exhibit one primary consistent pattern of attachment in relationships.[30]
The pattern the child develops after age five demonstrates the specific parenting styles used during the developmental stages within the child. These attachment patterns are associated with behavioral patterns and can help further predict a child's future personality.[31]
QMRAinsworth herself was the first to find difficulties in fitting all infant behaviour into the three classifications used in her Baltimore study. Ainsworth and colleagues sometimes observed "tense movements such as hunching the shoulders, putting the hands behind the neck and tensely cocking the head, and so on. It was our clear impression that such tension movements signified stress, both because they tended to occur chiefly in the separation episodes and because they tended to be prodromal to crying. Indeed, our hypothesis is that they occur when a child is attempting to control crying, for they tend to vanish if and when crying breaks through."[43] Such observations also appeared in the doctoral theses of Ainsworth's students. Crittenden, for example, noted that one abused infant in her doctoral sample was classed as secure (B) by her undergraduate coders because her strange situation behavior was "without either avoidance or ambivalence, she did show stress-related stereotypic headcocking throughout the strange situation. This pervasive behavior, however, was the only clue to the extent of her stress."[44]
Drawing on records of behaviours discrepant with the A, B and C classifications, a fourth classification was added by Ainsworth's colleague Mary Main.[45] In the Strange Situation, the attachment system is expected to be activated by the departure and return of the caregiver. If the behaviour of the infant does not appear to the observer to be coordinated in a smooth way across episodes to achieve either proximity or some relative proximity with the caregiver, then it is considered 'disorganised' as it indicates a disruption or flooding of the attachment system (e.g. by fear). Infant behaviours in the Strange Situation Protocol coded as disorganised/disoriented include overt displays of fear; contradictory behaviours or affects occurring simultaneously or sequentially; stereotypic, asymmetric, misdirected or jerky movements; or freezing and apparent dissociation. Lyons-Ruth has urged, however, that it should be more widely "recognized that 52% of disorganized infants continue to approach the caregiver, seek comfort, and cease their distress without clear ambivalent or avoidant behavior."[46]
There is rapidly growing interest in disorganized attachment from clinicians and policy-makers as well as researchers.[47] However, the disorganized/disoriented attachment (D) classification has been criticised by some for being too encompassing, including Ainsworth herself.[48] In 1990, Ainsworth put in print her blessing for the new 'D' classification, though she urged that the addition be regarded as "open-ended, in the sense that subcategories may be distinguished", as she worried that too many different forms of behaviour might be treated as if they were the same thing.[49] Indeed, the D classification puts together infants who use a somewhat disrupted secure (B) strategy with those who seem hopeless and show little attachment behaviour; it also puts together infants who run to hide when they see their caregiver in the same classification as those who show an avoidant (A) strategy on the first reunion and then an ambivalent-resistant (C) strategy on the second reunion. Perhaps responding to such concerns, George and Solomon have divided among indices of disorganized/disoriented attachment (D) in the Strange Situation, treating some of the behaviours as a 'strategy of desperation' and others as evidence that the attachment system has been flooded (e.g. by fear, or anger).[50] Moreover, Crittenden argues that some behaviour classified as Disorganized/disoriented can be regarded as more 'emergency' versions of the avoidant and/or ambivalent/resistant strategies, and function to maintain the protective availability of the caregiver to some degree. Sroufe et al. have agreed that "even disorganised attachment behaviour (simultaneous approach-avoidance; freezing, etc.) enables a degree of proximity in the face of a frightening or unfathomable parent."[51] However, "the presumption that many indices of 'disorganisation' are aspects of organised patterns does not preclude acceptance of the notion of disorganisation, especially in cases where the complexity and dangerousness of the threat are beyond children's capacity for response."[52] For example, "Children placed in care, especially more than once, often have intrusions. In videos of the Strange Situation Procedure, they tend to occur when a rejected/neglected child approaches the stranger in an intrusion of desire for comfort, then loses muscular control and falls to the floor, overwhelmed by the intruding fear of the unknown, potentially dangerous, strange person."[53
QMRAttachment theory was extended to adult romantic relationships in the late 1980s by Cindy Hazan and Phillip Shaver. Four styles of attachment have been identified in adults: secure, anxious-preoccupied, dismissive-avoidant and fearful-avoidant. These roughly correspond to infant classifications: secure, insecure-ambivalent, insecure-avoidant and disorganized/disoriented.
Securely attached adults tend to have positive views of themselves, their partners and their relationships. They feel comfortable with intimacy and independence, balancing the two. Anxious-preoccupied adults seek high levels of intimacy, approval and responsiveness from partners, becoming overly dependent. They tend to be less trusting, have less positive views about themselves and their partners, and may exhibit high levels of emotional expressiveness, worry and impulsiveness in their relationships. Dismissive-avoidant adults desire a high level of independence, often appearing to avoid attachment altogether. They view themselves as self-sufficient, invulnerable to attachment feelings and not needing close relationships. They tend to suppress their feelings, dealing with rejection by distancing themselves from partners of whom they often have a poor opinion. Fearful-avoidant adults have mixed feelings about close relationships, both desiring and feeling uncomfortable with emotional closeness. They tend to mistrust their partners and view themselves as unworthy. Like dismissive-avoidant adults, fearful-avoidant adults tend to seek less intimacy, suppressing their feelings.[77][78][79][80]
A young couple relax under a tree. The man lies on his back looking up at the woman. The woman, with striking long blond hair and sunglasses, is seated by his head, looking down at him and with her hand placed round his head. Both are laughing
Attachment styles in adult romantic relationships roughly correspond to attachment styles in infants but adults can hold different internal working models for different relationships.
Two main aspects of adult attachment have been studied. The organization and stability of the mental working models that underlie the attachment styles is explored by social psychologists interested in romantic attachment.[81][82] Developmental psychologists interested in the individual's state of mind with respect to attachment generally explore how attachment functions in relationship dynamics and impacts relationship outcomes. The organisation of mental working models is more stable while the individual's state of mind with respect to attachment fluctuates more. Some authors have suggested that adults do not hold a single set of working models. Instead, on one level they have a set of rules and assumptions about attachment relationships in general. On another level they hold information about specific relationships or relationship events. Information at different levels need not be consistent. Individuals can therefore hold different internal working models for different relationships.[82][83]
There are a number of different measures of adult attachment, the most common being self-report questionnaires and coded interviews based on the Adult Attachment Interview. The various measures were developed primarily as research tools, for different purposes and addressing different domains, for example romantic relationships, parental relationships or peer relationships. Some classify an adult's state of mind with respect to attachment and attachment patterns by reference to childhood experiences, while others assess relationship behaviours and security regarding parents and peers.[84]
QMRBoszormenyi-Nagy is best known for developing the Contextual approach to family therapy and individual psychotherapy. It is a comprehensive model which integrates individual psychological, interpersonal, existential, systemic, and intergenerational dimensions of individual and family life and development.
The contextual model, in its most well-known formulation, proposes four dimensions of relational reality, both as a guide for conducting therapy and for conceptualizing relational reality in general:
(1) Facts (e.g., genetic input, physical health, ethnic-cultural background, socioeconomic status, basic historical facts, events in a person's life cycle, etc)
(2) Individual psychology (the domain of most individual psychotherapies)
(3) Systemic transactions (the domain covered by classical systemic family therapy: e.g., rules, power, alignments, triangles, feedback, etc)
(4) Relational ethics.
These dimensions are taken to be inter-linked, but not equatable or reducible to one another.[1][2]
The contextual model proposes relational ethics—the ethical or "justice" dimension of close relationships—as an overarching integrative conceptual and methodological principle. Relational ethics focuses in particular on the nature and roles of connectedness, caring, reciprocity, loyalty, legacy, guilt, fairness, accountability, and trustworthiness - within and between generations. It is taken to represent not just a set of prescriptive norms, nor simply psychological phenomena, perspectives, or constructions. Rather, relational ethics is seen as (1) having some objective ontological and experiential basis by virtue of being derived from basic needs and from real relationships that have concrete consequences (i.e., as distinct from abstract or "value" ethics[3]); and (2) as being significant explanatory and motivational dynamics operating - in both beneficial and destructive ways - in individuals, families, social groups, and broader society. The construct validity and significance of relational ethics in clinical and educational contexts have been supported by a number of studies.[4][5][6] (See also Relational ethics.)
In a later formulation of the contextual model, Boszormenyi-Nagy proposed a fifth dimension - the ontic dimension - which was implicit in the earlier formulations, but which considers more explicitly the nature of the interconnection between people that allows an individual to exist decisively as a person, and not just a self.[7] (See also Intersubjectivity and Philosophy of dialogue.)
QMREmotion response types[edit]
Although EFT posits that each person's emotions are organized into idiosyncratic emotion schemes that are highly variable both between people and within the same person over time,[14] nevertheless emotional responses can be classified into four broad types: primary adaptive, primary maladaptive, secondary reactive, and instrumental.[15]
Primary adaptive[edit]
Primary adaptive emotion responses are initial emotional responses to a given stimulus that have a clear beneficial value—for example, sadness at loss, anger at violation, and fear at threat. Sadness is an adaptive response when it motivates us to reconnect with someone or something important that is missing. Anger is an adaptive response when it motivates us to take assertive action to end the violation. Fear is an adaptive response when it motivates us to avoid or escape an overwhelming threat. In addition to emotions that indicate action tendencies (such as the three just mentioned), primary adaptive emotion responses include the feeling of being certain and in control or uncertain and out of control, and/or a general felt sense of emotional pain—these feelings and emotional pain do not provide immediate action tendencies but do provide adaptive information that can be symbolized and worked through in therapy. Primary adaptive emotion responses "are attended to and expressed in therapy in order to access the adaptive information and action tendency to guide problem solving."[16]
Primary maladaptive[edit]
Primary maladaptive emotion responses are also initial emotional responses to a given stimulus; however, they are generally dysfunctional responses based on emotion schemes that are no longer useful (and that may or may not have been useful in the past) and that were often formed through previous traumatic experiences. Examples include sadness at the joy of others, anger at the genuine caring or concern of others, fear at harmless situations, and chronic feelings of insecurity (fear) or worthlessness (shame). For example, a person may respond with anger at the genuine caring or concern of others because as a child he or she was offered caring or concern that was usually followed by a violation; as a result, he or she learned to respond to caring or concern with anger even when there is no violation. The person's angry response is understandable, and needs to be met with empathy and compassion even though his or her angry response is not helpful.[17] Secondary maladaptive emotion responses are accessed in therapy with the aim of transforming the emotion scheme through new experiences.[18]
Secondary reactive[edit]
Secondary reactive emotion responses are complex chain reactions where a person reacts to his or her primary adaptive or maladaptive emotional response and then replaces it with another, secondary emotional response. In other words, they are emotional responses to prior emotional responses. ("Secondary" means that a different emotion response occurred first.) They can include secondary reactions of hopelessness, helplessness, rage, or despair that occur in response to primary emotion responses that are experienced (secondarily) as painful, uncontrollable, or violating. They may be escalations of a primary emotion response, as when people are angry about being angry, afraid of their fear, or sad about their sadness. They may be defenses against a primary emotion response, such as feeling anger to avoid sadness or fear to avoid anger; this can include gender role-stereotypical responses such as expressing anger when feeling primarily afraid (stereotypical of men's gender role), or expressing sadness when primarily angry (stereotypical of women's gender role).[18] "These are all complex, self-reflexive processes of reacting to one's emotions and transforming one emotion into another. Crying, for example, is not always true grieving that leads to relief, but rather can be the crying of secondary helplessness or frustration that results in feeling worse."[19] Secondary reactive emotion responses are accessed and explored in therapy in order to increase awareness of them and to arrive at more primary and adaptive emotion responses.[20]
Instrumental[edit]
Instrumental emotion responses are experienced and expressed by a person because the person has learned that the response has an effect on others, "such as getting them to pay attention to us, to go along with something we want them to do for us, to approve of us, or perhaps most often just not to disapprove of us."[17] Instrumental emotion responses can be consciously intended or unconsciously learned (i.e., through operant conditioning). Examples include crocodile tears (instrumental sadness), bullying (instrumental anger), crying wolf (instrumental fear), and feigned embarrassment (instrumental shame). When a client responds in therapy with instrumental emotion responses, it may feel manipulative or superficial to the therapist. Instrumental emotion responses are explored in therapy in order to increase awareness of their interpersonal function and/or the associated primary and secondary gain.[21]
QMRStyles of attachment[edit]
Johnson & Sims (2000) describe four attachment styles:
People who are secure and trusting perceive themselves as lovable, able to trust others and themselves within a relationship. They give clear emotional signals, and are engaged, resourceful and flexible in unclear relationships. Secure partners express feelings, articulate needs, and allow their own vulnerability to show.
People who have a diminished ability to articulate feelings, tend not to acknowledge their need for attachment, and struggle to name their needs in a relationship. They tend to adopt a safe position and solve problems dispassionately without understanding the effect that their safe distance has on their partners.
People who are psychologically reactive and who exhibit anxious attachment. They tend to demand reassurance in an aggressive way, demand their partner's attachment and tend to use blame strategies (including emotional blackmail) in order to engage their partner.
People who have been traumatized and have experienced little to no recovery from it vacillate between attachment and hostility.
QMRResults of a study on male patients at a maximum-security forensic hospital suggested four potential subtypes of psychopathy: narcissistic, borderline, sadistic, and antisocial. The researchers have stated that additional data are needed to understand the observed variations
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