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Thermoplasmatota is phylum of Archaea . [ 1 ] It is among six other phyla validly published according to the Bacteriological Code . These Archaea can live in acidic environments [ 2 ] and have also been found in the South China Sea and Mediterranean grassland soil . [ 3 ]
"Izemarchaea" (MBG-D, E2)
"Poseidoniia" (MGII & MGIII)
" Thermoplasmatia " | https://en.wikipedia.org/wiki/Thermoplasmatota |
Thermoplastic elastomers ( TPE ), sometimes referred to as thermoplastic rubbers ( TPR ), are a class of copolymers or a physical mix of polymers (usually a plastic and a rubber) that consist of materials with both thermoplastic and elastomeric properties.
While most elastomers are thermosets , thermoplastic elastomers are not, in contrast making them relatively easy to use in manufacturing, for example, by injection moulding . Thermoplastic elastomers show advantages typical of both rubbery materials and plastic materials. The benefit of using thermoplastic elastomers is the ability to stretch to moderate elongations and return to its near original shape creating a longer life and better physical range than other materials. [ 1 ]
The principal difference between thermoset elastomers and thermoplastic elastomers is the type of cross-linking bond in their structures. In fact, crosslinking is a critical structural factor which imparts high elastic properties.
Thermoplastic elastomer: Elastomer comprising a thermoreversible network. [ 2 ]
There are six generic classes of commercial TPEs (designations according to ISO 18064) together with one unclassified category:
In order to qualify as a thermoplastic elastomer, a material must have these three essential characteristics:
TPE became a commercial reality when thermoplastic polyurethane polymers became available in the 1950s. During the 1960s styrene block copolymer became available, and in the 1970s a wide range of TPEs came on the scene. The worldwide usage of TPEs (680,000 tons/year in 1990) is growing at about nine percent per year.
The styrene-butadiene materials possess a two-phase microstructure due to incompatibility between the polystyrene and polybutadiene blocks, the former separating into spheres or rods depending on the exact composition. With low polystyrene content, the material is elastomeric with the properties of the polybutadiene predominating. Generally they offer a much wider range of properties than conventional cross-linked rubbers because the composition can vary to suit final construction goals.
Block copolymers can "microphase separate" to form periodic nanostructures, as in the styrene-butadiene-styrene (SBS) block copolymer (shown at right). The polymer is known as Kraton and is used for shoe soles and adhesives . Owing to the microfine structure, a transmission electron microscope (TEM) was needed to examine the structure. The butadiene matrix was stained with osmium tetroxide to provide contrast in the image.
The material was made by living polymerization so that the blocks are almost monodisperse , so helping to create a very regular microstructure. The molecular weight of the polystyrene blocks in the main picture is 102,000; the inset picture has a molecular weight of 91,000, producing slightly smaller domains. The spacing between domains has been confirmed by small-angle X-ray scattering , a technique which gives information about microstructure .
Since most polymers are incompatible with one another, forming a block polymer will usually result in phase separation, and the principle has been widely exploited since the introduction of the SBS block polymers, especially where one of the block is highly crystalline. One exception to the rule of incompatibility is the material Noryl , where polystyrene and polyphenylene oxide or PPO form a continuous blend with one another.
Other TPEs have crystalline domains where one kind of block co-crystallizes with other block in adjacent chains, such as in copolyester rubbers, achieving the same effect as in the SBS block polymers. Depending on the block length, the domains are generally more stable than the latter owing to the higher crystal melting point . That point determines the processing temperatures needed to shape the material, as well as the ultimate service use temperatures of the product. Such materials include Hytrel, a polyester-polyether copolymer and Pebax , a nylon or polyamide-polyether copolymer.
Depending on the environment, TPEs have outstanding thermal properties and material stability when exposed to a broad range of temperatures and non-polar materials. [ 1 ] TPEs consume less energy to produce, can be colored easily by most dyes, and allow economical quality control. TPE requires little or no compounding, with no need to add reinforcing agents, stabilizers or cure systems. Hence, batch-to-batch variations in weighting and metering components are absent, leading to improved consistency in both raw materials and fabricated articles. TPE materials have the potential to be recyclable since they can be molded, extruded and reused like plastics, but they have typical elastic properties of rubbers which are not recyclable owing to their thermosetting characteristics. They can also be ground up and turned into 3D printing filament with a recyclebot .
The two most important manufacturing methods with TPEs are extrusion and injection molding. TPEs can now be 3D printed and have been shown to be economically advantageous to make products using distributed manufacturing . [ 5 ] [ 6 ] Compression molding is seldom, if ever, used. Fabrication via injection molding is extremely rapid and highly economical. Both the equipment and methods normally used for the extrusion or injection molding of a conventional thermoplastic are generally suitable for TPEs. TPEs can also be processed by blow molding , melt calendaring, [ 7 ] thermoforming , and heat welding .
TPEs are used where conventional elastomers cannot provide the range of physical properties needed in the product. These materials find large application in the automotive sector and in household appliances sector. For instance, copolyester TPEs are used in snowmobile tracks where stiffness and abrasion resistance are at a premium. Thermoplastic olefins (TPO) are increasingly used as a roofing material. [ 8 ] TPEs are also widely used for catheters where nylon block copolymers offer a range of softness ideal for patients. Thermoplastic silicone and olefin blends are used for extrusion of glass run and dynamic weatherstripping car profiles. Styrene block copolymers are used in shoe soles for their ease of processing, and widely as adhesives.
Owing to their unrivaled abilities in two-component injection molding to various thermoplastic substrates, engineered TPS materials also cover a broad range of technical applications ranging from automotive market to consumer and medical products. Examples of those are soft grip surfaces, design elements, back-lit switches and surfaces, as well as sealings, gaskets, or damping elements. TPE is commonly used to make suspension bushings for automotive performance applications because of its greater resistance to deformation when compared to regular rubber bushings. Thermoplastics have experienced growth in the heating, ventilation, and air conditioning ( HVAC ) industry due to the function, cost effectiveness and adaptability to modify plastic resins into a variety of covers, fans and housings. | https://en.wikipedia.org/wiki/Thermoplastic_elastomer |
Thermoplastic olefin , thermoplastic polyolefin (TPO), or olefinic thermoplastic elastomers refer to polymer /filler blends usually consisting of some fraction of a thermoplastic , an elastomer or rubber, and usually a filler . [ 1 ]
Outdoor applications such as roofing frequently contain TPO because it does not degrade under solar UV radiation, a common problem with nylons . [ 2 ] TPO is used extensively in the automotive industry .
Thermoplastics may include polypropylene (PP), polyethylene (PE), block copolymer polypropylene (BCPP), and others.
Common fillers include, though are not restricted to talc , fiberglass , carbon fiber , wollastonite , and MOS (Metal Oxy Sulfate).
Common elastomers include ethylene propylene rubber (EPR), EPDM (EP-diene rubber), ethylene-octene (EO), ethylbenzene (EB), and styrene ethylene butadiene styrene (SEBS). Currently there are a great variety of commercially available rubbers and BCPP's. They are produced using regioselective and stereoselective catalysts known as metallocenes . The metallocene catalyst becomes embedded in the polymer and cannot be recovered.
Components for TPO are blended together at 210 - 270 °C under high shear . A twin screw extruder or a continuous mixer may be employed to achieve a continuous stream, or a Banbury compounder may be employed for batch production. A higher degree of mixing and dispersion is achieved in the batch process, but the superheat batch must immediately be processed through an extruder to be pelletized into a transportable intermediate. Thus batch production essentially adds an additional cost step.
The geometry of the metallocene catalyst will determine the sequence of chirality in the chain, as in, atactic , syndiotactic , isotactic , as well as average block length, molecular weight and distribution. These characteristics will in turn govern the microstructure of the blend.
As in metal alloys the properties of a TPO product depend greatly upon controlling the size and distribution of the microstructure . PP and PE form lamellar crystallites separated by amorphous regions that can grow into a variety of microstructures ranging from single crystals from dilute solution crystallization to fiberous crystals and shish-kabob structures. Thin films from quiescent melts can form spherulitic impinging structures that display cylindrically symmetric birefringence. The PP and PE components of a blend constitute the "crystalline phase", and the rubber and branched PE chains and PE/PP end groups gives the "amorphous phase".
If PP and PE are the dominant component of a TPO blend then the rubber fraction will be dispersed into a continuous matrix of "crystalline" polypropylene. If the fraction of rubber is greater than 40% phase inversion may be possible when the blend cools, resulting in an amorphous continuous phase, and a crystalline dispersed phase. This type of material is non-rigid, and is sometimes called TPR for ThermoPlastic Rubber.
To increase the rigidity of a TPO blend, fillers exploit a surface tension phenomena. By selecting a filler with a higher surface area per weight, a higher flexural modulus can be achieved. Specific density of TPO blends range from 0.92 to 1.1.
TPO is easily processed by injection molding, profile extrusion, and thermoforming. However, TPO cannot be blown, or sustain a film thickness less than 1/4 mil (about 6 micrometers). | https://en.wikipedia.org/wiki/Thermoplastic_olefin |
Thermoplastic vulcanizates ( TPVs ) are a type of thermoplastic elastomers (TPE) that undergo vulcanization processes during manufacturing , giving elastomeric properties to the final product. Vulcanization involves the cross-linking of polymer chains, leading to increased strength, durability, and flexibility. Their thermoplastic nature allows TPVs, unlike traditional vulcanized rubbers, to be melted and reprocessed multiple times. Across the automotive, household appliance, electrical, construction, and healthcare sectors, nearly 100 TPV grades are used globally.
Monsanto trademarked the name Santoprene for these materials in 1977. [ 1 ] The trademark is now owned by the Celanese Corporation . Similar material is available from Elastron, [ 2 ] and others. [ 3 ]
Thermoplastic vulcanizates were first reported in 1962 by A.M. Gessler and W.H. Haslett. [ 4 ] In 1973, W.K. Fisher reported the dynamic vulcanization process through his prior work on polypropylene and EPDM rubber-based TPVs with peroxides as a cross-linking agent. This resulted in the commercialization of "Uniroyal TPR" thermoplastic rubber. [ 5 ] [ 6 ] TPVs are a blend between a thermoplastic matrix and vulcanized rubber - combining the properties of both. A combination of elastomeric properties, including compressibility, tension sets, aging performance, and chemical resistance, characterizes TPVs. Although TPVs are part of the TPE family of polymers, they behave closer to EPDM thermoset rubbers in terms of their elastomeric properties.
The first sales of developmental products began in 1977, the same year TPV was registered as Santoprene by Monsanto, [ 1 ] and it was fully commercialized in 1981. [ 7 ]
Santoprene TPV had early application successes in the automotive sector, including rack and pinion boots. This was motivated by its flex life, fluid resistance, and sealability. In the appliance sector, a dishwasher sump boot was developed where Santoprene TPV provided sealing and resistance to heat and fluids. Santoprene TPV was also successful in the domestic and high-rise construction sectors in applications such as window seals, caster wheels , tubing, small hose parts, electrical connectors, and coatings for wires and cables. It was also used in the medical industry for gaskets on syringe plungers.
Santoprene TPV is a dynamically vulcanized polymer alloy consisting mostly of fully cured EPDM rubber particles encapsulated in a polypropylene (PP) matrix.
Photographs made using atomic force microscopy and scanning electron microscopy show a multitude of very small particles, typically no bigger than a few microns in diameter. These particles are fully vulcanized rubber (typically EPDM rubber for most Santoprene TPV grades) in a thermoplastic phase (most often PP in the case of Santoprene TPV grades). Fully cross-linked or vulcanized means 98% or above, and because the morphology is "locked-in," it provides stable physical properties.
The properties of thermoplastic vulcanizates include:
Commercial TPV grades can be designed for a broad range of specific engineering applications, with grades ranging from hardness of 35 Shore A to 50 Shore D.
Thermoplastic vulcanization is used commercially for weather seals as a lightweight alternative to thermoset rubber materials in semi-dynamic and static parts. In under-hood and under-vehicle applications, it is well-suited for air ducts, tubing, molded seals, grommets, suspension bellows, cable jacketing, plugs, bumpers, and many other parts, thanks to its sealing performance and resistance to extreme temperatures, chemical exposure, and harsh environments.
In commercial glazing seals, TPV can be used for curtain walls, storefronts, architectural windows, and skylight weather-seal applications. It is also commonly used for residential glazing seals because of its low air- and water-infiltration ratings for the life of window and door systems.
Other applications include bridge decks, parking decks, water stops, rail pads, road construction projects and rail construction projects. TPV can be used to make durable seals, gaskets, and grommets that are resistant to flex fatigue, harsh temperatures, and chemicals, as well as for a variety of sealing applications, including pipe seals, bridge expansion joints and curtain walls, parts for potable water, and pipe seals for sewer and drainage.
Some TPV is used commercially in washing machines, dryers, dishwashers, refrigerators, small appliances, and floor care. Other uses include parts such as pump seals, hoses, couplings, vibration dampeners, drum rollers, knobs, and controls.
Commercial TPV is used in wiring connectors to make watertight seals with electrical and thermal resistance, insulation for high voltage applications, and parts requiring the use of temperatures down to −60 °C. For applications requiring watertight seals, TPV enables connectors to be insert-molded to cable jacketing, producing a single integral part.
It is also used for industrial wire and cable connectors and low-voltage industrial cable applications that include insulation and jackets, in addition to consumer wire and cable use.
After a short drying period, TPV pellets are automatically transferred to the molding machine or extrusion line. Cycle times can be significantly faster compared with rubber (2 to 3 minutes) because the parts do not have to cure in the mold. Once the TPV parts are allowed to cool (about 30 seconds), they can be removed from the mold.
Some commercial TPVs can be processed using conventional thermoplastic processes, such as injection molding, blow molding , and extrusion . The manufacture of TPV parts is less complex in contrast to rubber. Some commercial TPVs are ready to use and do not need to be compounded with other ingredients, such as reinforcing fillers (carbon black, mineral fillers), stabilizers, plasticizing oils, and curing systems. [ 9 ] [ 10 ]
Compared to processing rubber, thermoplastic processing of TPV can deliver shorter cycle times, higher parts output per hour, and the reuse of scrap produced during processing. These attributes can result in cost reduction, less tooling/machinery, lower scrap costs, and optimization of material logistic costs compared to rubber.
Injection molding : TPV can be processed using conventional thermoplastics injection-molding equipment at reduced cycle times compared to thermoset rubber. This flexibility allows for greater freedom of mold design where undercuts are employed.
Insert molding : This method consists of placing a preformed substrate into the mold and injecting TPV around or over it. If the insert and the TPV are compatible materials, a melt bond occurs at the interface between the two materials. The strength of this bond is affected by several factors, including interface temperature, cleanliness of the insert, and the TPV's melt temperature.
Two-shot injection molding : TPV can be combined with other polymers through several multi-shot injection molding processes. By combining multiple materials, a wide variety of parts applications, such as a hard/soft combination, can be achieved. The process produces both a finished part and a substrate during each cycle. Two-shot molding is more efficient than insert molding because no substrate handling is required
Blow molding : Santoprene TPV can be blow molded in a single-layer, multi-layer, exchange blow, sequential 3D, suction blow, flashless extrusion blow, injection blow, and press-blow molding process.
Extrusion: TPV easily extrudes into single and complex profiles. These materials can also be coextruded to yield a part with both rigid and soft components.
Thermoforming : The thermoforming properties of TPV are similar to those of acrylonitrile butadiene styrene (ABS) rubber and exhibit good melt strength, which provides uniform and predictable sag characteristics during heating. When producing a sheet for thermoformed parts, key attributes of some commercial TPV can be maintained, including colorability, impact resistance, weather ability, chemical resistance, and non-skid, and matte surface in appearance and feel.
The use of some commercial TPV can contribute to a reduction in overall waste in the manufacturing process, as scrap produced during processing can be recycled. Material that has been recycled – even from old parts – exhibits properties almost as good as virgin material, according to a 2013 publication. [ 11 ]
One of the most significant benefits of TPVs is their potential for recycling. Unlike traditional thermoset rubbers, thermoplastic vulcanizates can be:
According to the article: | https://en.wikipedia.org/wiki/Thermoplastic_vulcanizates |
Thermoporometry and cryoporometry are methods for measuring porosity and pore-size distributions. A small region of solid melts at a lower temperature than the bulk solid, as given by the Gibbs–Thomson equation . Thus, if a liquid is imbibed into a porous material, and then frozen, the melting temperature will provide information on the pore-size distribution. The detection of the melting can be done by sensing the transient heat flows during phase transitions using differential scanning calorimetry – DSC thermoporometry , [ 1 ] measuring the quantity of mobile liquid using nuclear magnetic resonance – NMR cryoporometry (NMRC) [ 2 ] [ 3 ] or measuring the amplitude of neutron scattering from the imbibed crystalline or liquid phases – ND cryoporometry (NDC). [ 4 ]
To make a thermoporometry / cryoporometry measurement, a liquid is imbibed into the porous sample, the sample cooled until all the liquid is frozen, and then warmed until all the liquid is again melted. Measurements are made of the phase changes or of the quantity of the liquid that is crystalline / liquid (depending on the measurement technique used).
The techniques make use of the Gibbs–Thomson effect : small crystals of a liquid in the pores melt at a lower temperature than the bulk liquid : The melting point depression is inversely proportional to the pore size. The technique is closely related to that of use of gas adsorption to measure pore sizes but uses the Gibbs–Thomson equation rather than the Kelvin equation . They are both particular cases of the Gibbs Equations ( Josiah Willard Gibbs ): the Kelvin equation is the constant temperature case, and the Gibbs–Thomson equation is the constant pressure case. [ 2 ]
This technique uses differential scanning calorimetry (DSC) to detect the phase changes. The signal detection relies on transient heat flows of latent heat of fusion at the phase changes, and thus the measurement can not be made arbitrarily slowly, limiting the resolution in pore size. There are also difficulties in obtaining measurements of pore volume. [ 1 ]
NMRC is a recent technique (originated in 1993) for measuring total porosity and pore size distributions. It makes use of the Gibbs–Thomson effect: small crystals of a liquid in the pores melt at a lower temperature than the bulk liquid : The melting point depression is inversely proportional to the pore size. The technique is closely related to that of use of gas adsorption to measure pore sizes but uses the Gibbs–Thomson equation rather than the Kelvin equation . They are both particular cases of the Gibbs Equations ( Josiah Willard Gibbs ): the Kelvin equation is the constant temperature case, and the Gibbs–Thomson equation is the constant pressure case. [ 2 ] [ 3 ]
Nuclear magnetic resonance (NMR) may be used as a convenient method of measuring the quantity of liquid that has melted, as a function of temperature, making use of the fact that the T 2 {\displaystyle T_{2}} relaxation time in a frozen material is usually much shorter than that in a mobile liquid. To make the measurement it is common to just measure the amplitude of an NMR echo at a few milliseconds delay, to ensure that all the signal from the solid has decayed. The technique was developed at the University of Kent in the UK, by Prof. John H. Strange. [ 5 ]
NMRC is based on two equations, the Gibbs–Thomson equation, that maps the melting point depression to pore size, and the Strange–Rahman–Smith equation [ 5 ] that maps the melted signal amplitude at a particular temperature to pore volume.
To make an NMR cryoporometry measurement, a liquid is imbibed into the porous sample, the sample cooled until all the liquid is frozen, and then warmed slowly, while measuring the quantity of the liquid that is liquid.
Thus NMRC cryoporometry is similar to DSC thermoporosimetry, but has higher resolution, as the signal detection does not rely on transient heat flows, and the measurement can be made arbitrarily slowly. Volume calibration of the total porosity and pore-size can be good, just involving ratioing the NMR signal amplitude at a particular pore diameter to the amplitude when all the liquid (of known mass) is melted. NMRC is suitable for measuring pore diameters in the range 1 nm to about 2 μm. Instrumentation to make NMR Cryoporometric measurements is commercially available. [ 6 ]
Note: the Gibbs-Thomson equation contains a geometric term relating to the curvature of the ice-liquid interface. This curvature may be different in different pore geometries; thus using a sol-gel calibration (~spheres) gives about a factor of two error when used with SBA-15 (cylindrical pores). Similarly the freezing and melting curvatures (typically spherical on ice intrusion, and cylindrical on ice melting), result in a difference in freezing and melting temperature even in cylindrical pores where there is no "ink-bottle" effect. [ 7 ]
It is also possible to adapt the basic NMRC experiment to provide structural resolution in spatially dependent pore size distributions, by combining NMRC with standard Magnetic resonance imaging protocols, [ 8 ] or to provide behavioural information about the confined liquid. [ 9 ]
Modern neutron diffractometers have the capability to measure complete scattering spectra in a couple of minutes, as the temperature is ramped, enabling cryoporometry experiments to be performed. [ 4 ]
ND cryoporometry has the unique distinction of being able to monitor as a function of temperature the quantity of different crystalline phases (such as hexagonal ice and cubic ice) as well as the liquid phase, and thus can give pore-phase structural information as a function of temperature. [ 4 ]
The Gibbs–Thomson effect acts to lower both melting and freezing point, and also to raise boiling point. However, simple cooling of an all-liquid sample usually leads to a state of non-equilibrium super cooling and only eventual non-equilibrium freezing – to obtain a measurement of the equilibrium freezing event, it is necessary to first cool enough to freeze a sample with excess liquid outside the pores, then warm the sample until the liquid in the pores is all melted, but the bulk material is still frozen. Then on re-cooling the equilibrium freezing event can be measured, as the external ice will then grow into the pores. [ 10 ] [ 11 ] This is in effect an "ice intrusion" measurement (cf. Mercury Intrusion Porosimetry ), and as such in part may provide information on pore throat properties. The melting event was then previously expected to provide more accurate information on the pore body. However, a new melting mechanism has been proposed which means the melting event does not provide accurate information on the pore body. [ 12 ] The melting mechanism has been termed advanced melting and is described below.
The melting process for the frozen phase is initiated from existing molten phase, such as the liquid-like layer that is retained at the pore wall. This is shown in Figure 1 for a through ink bottle pore model (position A); the arrows show how the liquid-like layer initiates the melting process and this melting mechanism is said to occur via sleeve shaped menisci. For such a melting mechanism, the smaller necks will melt first and as the temperature is raised the large pore will then melt. Therefore, the melting event would give an accurate description of the necks and body.
However, in cylindrical pores, melting would occur at a lower temperature via a hemispherical meniscus (between solid and molten phases), than it would via a sleeve-shaped meniscus. Scanning curves and loops have been used to show that cryoporometry melting curves are prone to pore-pore cooperative effects [ 12 ] and this is demonstrated by position B in Figure 1. For the through ink bottle pore, melting is initiated in the outer necks from the thin cylindrical sleeve of permanently unfrozen liquid-like fluid that exists at the pore wall. Once the necks have become molten via the cylindrical sleeve meniscus mechanism, a hemispherical meniscus will be formed at both ends of the larger pore body. The hemispherical menisci can then initiate the melting process in the large pore. Moreover, if the larger pore radius is smaller than the critical size for melting via a hemispherical meniscus at the current temperature, then the larger pore will melt at the same temperature as the smaller pore. Therefore, the melting event will not give accurate information on the pore body. If the incorrect melting mechanism is assumed when deriving a PSD (pore size distribution) there will be at least a 100% error in the PSD. Moreover, it has been shown that advanced melting effects can lead to a dramatic skew towards smaller pores in PSDs for mesoporous sol-gel silicas, determined from cryoporometry melting curves. [ 12 ]
NMR cryoporometry ( external cryoporometry website ) is a very useful nano- through meso- to micro-metrology technique ( nanometrology , nano-science.co.uk/nano-metrology ) that has been used to study many materials, and has particularly been used to study porous rocks (i.e. sandstone , shale and chalk / carbonate rocks), with a view to improving oil extraction , shale gas extraction and water abstraction . Also very useful for studying porous building materials such as wood , cement and concrete . A currently exciting application for NMR Cryoporometry is the measurement of porosity and pore-size distributions, in the study of carbon , charcoal and biochar . Biochar is regarded as an important soil enhancer (used since pre-history), and offers great possibilities for carbon dioxide removal from the biosphere .
Materials studied by NMR cryoporometry include:
Possible future application include measuring porosity and pore-size distributions in porous medical implants. [ citation needed ] | https://en.wikipedia.org/wiki/Thermoporometry_and_cryoporometry |
Thermoresponsive polymers can be used as stationary phase in liquid chromatography . [ 1 ] Here, the polarity of the stationary phase can be varied by temperature changes, altering the power of separation without changing the column or solvent composition. Thermally related benefits of gas chromatography can now be applied to classes of compounds that are restricted to liquid chromatography due to their thermolability. In place of solvent gradient elution, thermoresponsive polymers allow the use of temperature gradients under purely aqueous isocratic conditions. [ 2 ] The versatility of the system is controlled not only through changing temperature, but through the addition of modifying moieties that allow for a choice of enhanced hydrophobic interaction, or by introducing the prospect of electrostatic interaction. [ 3 ] These developments have already introduced major improvements to the fields of hydrophobic interaction chromatography, size exclusion chromatography, ion exchange chromatography, and affinity chromatography separations as well as pseudo-solid phase extractions ("pseudo" because of phase transitions).
The research that appeared to spark an onslaught of modified applications was a gel permeation chromatography technique of fixing poly( isopropyl acrylate ) (PIPA) strands to glass beads and separating a mixture of dextrans , which was developed by Gewehr et al. [ 4 ] They found that between the temperatures of 25–32 °C, the elution time of dextrans at different molecular weights exhibited a dependence on the temperature. Dextrans of the highest molecular weight eluted first since the PIPA chains exhibit hydrophilicity at temperatures below the LCST. As the temperature of the elution increased, when the chains behave in a more hydrophobic manner, the elution times increased for each of the analytes for the given range. The trend generally applies over the entire temperature range, but there is a flattening of the curve before 25 °C and after 32 °C (the approximate LCST for this experiment). It is important to note that above the LCST, the PIPA acts as a typical nonpolar stationary phase that would be used in reverse-phased chromatography. There are also instances of the elution times increasing below 15 °C, which most likely can be attributed to the lower temperatures’ effects on mass transfer playing a more significant role on retention than the stationary phase behavior. This study showed that the resolution could essentially be tuned by adjusting the operating temperature . The scope of this study was limited to isothermal conditions and attaching polymer chains to glass beads. The results, however, were satisfying enough to inspire other investigations and modifications to create a more versatile stationary phase for the advancement of chromatography.
Okano’s group expanded on their success by using different modifiers to enhance hydrophobicity through the attachment of butyl methacrylate (BMA), a hydrophobic comonomer. [ 5 ] For simplification the resultant polymer has been labeled as IBc (isopropylacrylamide butyl methacrylate copolymer). The polymers were synthesized using radical telomerization with varying BMA content. Where pure PNIPAAm was unable to resolve hydrophobic steroids at any temperature, IBc-grafted silica stationary phases were able to resolve steroid peaks with increasingly retarded retention times in correlation to both increased BMA content and increased temperature. They went on to develop a method to separate phenylthiohydantoin(PTH)-amino acids using their IBc stationary phase with a stronger emphasis of implementing environmentally friendly conditions using a purely aqueous phase in HPLC. [ 6 ] Another group separated catechins using PNIPAAm. [ 7 ]
Since the separation of biological molecules such as proteins would be better served by isocratic elution with an aqueous solvent, resolution of HPLC analysis should be tweaked in the area of stationary phases to elute such analytes that may be sensitive to organic solvents. Kanazawa et al. recognized the possibility of changing the LCST parameter through the addition of different moieties. [ 8 ] Kanazawa’s group investigated the reversible changes of PNIPAAm once modifying it with a carboxyl end. It was suggested that the modification leads to faster changes in conformation due to the restrictions introduced by the carboxyl group. They attached the carboxyl-terminated PNIPAAm chains to (aminopropyl)silica and used it as packing material for HPLC analysis of steroids. The separation took place under isocratic conditions using pure water as the mobile phase, and controlled the temperature using a water bath. They were able to shift the LCST from 32 °C to 20 °C by making the solution 1M in NaCl concentration. Of the 5 steroids and benzene, only testosterone could be resolved from the other peaks below the LCST (5 °C, LCST=20 °C in 1M NaCl). Above the LCST (25 °C, LCST=20 °C in 1M NaCl), all of the peaks are well resolved, and there is an increasing trend of retention time versus temperature up to 50 °C.
Prior to these studies, HPLC analyses were tuned by modifying the mobile and stationary phases only. Gradient elution for HPLC merely meant changing the ratio of solvents to improve column efficiency, and this requires the use of sophisticated solvent pumping mechanisms along with extra steps and precautions in the chromatographic analysis. Enlightened by the prospect of using temperature gradient elutions for HPLC analyses, Hosoya et al. sought to make surface modification of HPLC stationary phases more accessible. Their study utilizes graft-type copolymerization of PNIPAAm onto macroporous polymeric materials. [ 9 ] The in-situ preparation compared the use of cyclohexanol and toluene as porogens in the preparation of the modified polystyrene seeds. Reverse-phased size-exclusion chromatography (SEC) revealed pore size and pore size distribution of the particles and its dependence on temperature. Cyclohexanol acted as a successful porogen showing a dependent relationship of pore size to temperature. The use of toluene as a porogen gave results that were similar to unmodified macroporous particles. This indicates that PNIPAAm can be successfully grafted onto the surface and within the pores of macroporous materials. The application of this preparatory technique gives rise to tunable pore sizes. Temperature gradient elutions can be used to improve column efficiency through the changing of pore size in SEC. The mechanism of the change in pore size is simple, the pores are smaller under LCST due to the elongated chains of PNIPAAm within the pores, as temperature increases to and above LCST, the chains retract into a globular formation increasing the pore size.
Modification had also been extended past hydrophobic and hydrophilic attachments, charged compounds have also been introduced to TRPs. Kobayashi et al. had previously performed successful modifications to separate bioactive ionic compounds, and continued on that success to improve separation efficiency of bioactive compounds. [ 10 ] Common methods of separating angiotensin peptides had involved reverse-phased high-performance liquid chromatography (RP-HPLC) and cation-exchange chromatography . RP-HPLC requires the use of organic solvents, which is not favored and current trends are moving away from that. Hydrophobic interaction chromatography requires high concentration salt elutions and eluent cleaning to remove the salt. To address the shortcomings of the previous methods, Kobayashi’s group grafted acrylic acid (anionic acrylate under neutral conditions) and tert-butylacrylamide (hydrophobic) monomers onto PNIPAAm, resulting in PNIPAAm-co-AAc-co-tBAAm (IAtB) onto silica beads as a stationary phase medium. The reason for incorporating both ionic and hydrophobic compounds is multifaceted. The ionic compound improves interactivity with the ionic species, but raises the LCST significantly. The hydrophobic addition counteracts against the raise in LCST and lowers it to a more standard value, but also interacts with the hydrophobic surfaces of biological compounds. This resulted in successful and resolved elution of angiotensin peptides. Additionally, they were able to tune the retention factor for the analytes through isocratic temperature gradient elution. Ideal elutions occurred at 35 °C, but decreasing the temperature to 10 °C or raising it to 50 °C caused faster elutions either way. This is a strong indication that electrostatic and hydrophobic interactions can be similarly affected by changes in temperature. The major advantages from applying these success of this study include stationary phase versatility and maintaining bioactivity of the analytes.
Ayano et al. modified PNIPAAm with cationic N,N-dimethylaminopropylacrylamide (DMAPAAm) and hydrophobic BMA and grafted it onto silica beads to form IDB. [ 11 ] They used pH changes to adjust the LCST. The effect of pH on the LCST is as follows, from a plateau value between pH 4.5 and pH 6.0, the LCST decreased up to pH 9 and below pH 4.5. This can be interpreted as requiring slightly basic or moderately acidic conditions, as the 4.5–6.0 pH region holds a maximum value of the LCST, an unfavorable condition. They used these properties to separate several non-steroidal anti-inflammatory drugs (NSAIDs). The analysis of acidic drugs ( salicylic acid : BA; SA; MS; and As) was performed below pH 4.5. MS is hydrophobic only its retention time was affected by an increase in temperature on the column without a terminally modified anion-exchanger (IB column). However, with an anion-exchanger present, dissociated acidic drugs were retained longer at temperatures below LCST, and shorter at temperatures above LCST. When the IBD column compared to recently established PNIPAAm columns, electrostatic forces show remarkably higher retention ability of charged compounds than its hydrophilic predecessor. A single stationary phase can accomplish pharmaceutical separations based on hydrophobic interactions, hydrophilic interactions, and electrostatic interactions merely by adjusting the temperature (while adjusting pH to tweak the LCST).
Selective enzyme and antibody separation can be achieved with the use of specific end groups that conjugate with the specific compounds. This results in a formation of a polymer-enzyme conjugate which can be reversibly precipitated and dissolved by changing the temperature. Chen and Hoffman used N-Hydroxysuccinimide (NHS) ester functional end group on NIPAAm to conjugate selectively with β-D-glucosidase . [ 12 ] They found that the conjugated enzyme could be repeatedly precipitated and dissolved in solution and still maintain sufficient enzymatic activity.
In a study that was published in 1998, Hoshino et al. prepared a TRP with a maltose ligand , evaluated it with concanavalin A (Con A), and attempted to separate and purify α-glucosidase , a thermolabile compound. [ 13 ] Since the goal is to selectively isolate a thermolabile enzyme, a TRP with a small LCST value is desired. To fit this condition, the selected TRP was poly(N-acryloylpiperidine)-cysteamine (pAP), which has an LCST of 4 °C. The terminally bound maltose moiety maintains affinity for both analytes, thus the modified TRP, pAPM, met critical conditions of external temperature requirements and affinity for both target analytes. The solubility properties changed from 4 °C (soluble) to 8 °C (insoluble). Several reagents were tested for the recovery of Con A by desorption which had higher binding affinities to Con A than maltose. These reagents were α-D-glucopyranoside , D- mannose , methyl α-D-mannopyranoside, and glucose. α-D-mannopyranoside was the most effective for desorbing Con A from pAPM at virtually 100% after 1 hour. As a control, pAPM was used to bind Con A from a crude extract, which found the pickup of several impurities but still managed to recover 80% of Con A. This exemplifies the need for selective moieties, maltose not residing among them. Finally, the application of pAPM was tested by attempting to separate α-glucosidase from yeast extract under low temperature conditions. In conclusion, the pAPM was found to recover 68% of α-glucosidase activity tested against, maltose being the selected desorption reagent.
Another interesting development for AC was involved with antibody separation using another TRP-ligand combination. Anastase-Ravion et al. attached a dextran derivative to the classic PNIPAAm to result in a poly(NIPAAm)-DD, and used this stationary phase to separate polyclonal antibodies from subcutaneous rabbit serum . [ 14 ] From the study, the dextran derivative of choice was carboxymethyl dextran benzylamide sulfonate / sulfate , and when bound to the TRP was labeled poly(NIPAAm)-CMDBS. The LCST for the poly(NIPAAm)-CMDBS was raised from 32 °C to 33 °C. To test the success of the affinity binding, the antibodies were eluted with glycine buffer (adjusted to pH 2.6 with HCl ).
Promising results were obtained in 2003 in a study that merged the newer developments in affinity chromatography with microfluidic devices. Upon the development of microfluidic technology, coupling it with affinity chromatography meant modifying channel surfaces, packing coated beads, or packing with coated porous material, neither of which allow for replenishing the columns. [ 15 ] This produces limitations that prevent the packing material from being changed or the column being regenerated. The approach they took to address those challenges meant incorporating TRP particles as a reversibly immobilized stationary phase. What separates this development from other AC methods is that the beads on which the modified TRP are attached can reversibly adhere to the inner surfaces of the microfluidic channels. The formulation of the smart bead matrix is a little complex, but in general PNIPAAm is modified two times, first with NHS, then with polyethylene glycol -biotin (PEG-b) resulting in PEG-b/pNIPAAm beads. The inner surface of the microfluidic channels is composed of polyethylene terephthalate , to which the PEG-b/pNIPAAm beads reversibly bind above the LCST. When the sample solution is passed through the channels, the target analyte binds to the biotin ligand. The temperature can then be brought below the LCST to dissociate and become removed from the inner channels. This allows for a system adept to being reloaded with stationary phase under mild conditions. They successfully separated and eluted Streptavidin. Further application of these procedures allow for portable AC columns which can be packed on site and used for local or clinical analytical separations of complex biological fluids. | https://en.wikipedia.org/wiki/Thermoresponsive_polymers_in_chromatography |
The Thermosalinograph or TSG is an measuring instrument mounted near the water intake of ships to continuously measure sea surface temperature and conductivity while the ship is in motion. [ 1 ] Various programs have been developed to assist in the collection and analysis of data from a TSG . The data can be used to calculate salinity , density , sound velocity within the water, and other parameters. There are various types of thermosalinographs available on the market today.
NOAA fleet Ship of Opportunity Program (SOOP) Global Ocean Observing System (GOOS) GOSUD Global Ocean Surface Underway Data ( http://www.gosud.org )
The thermosalinograph uses a conductivity cell to measure conductivity , which can then be translated into a value of salinity . Also a thermistor cell measures the temperature of the surface water, which when combined with the conductivity can be used calculate the density of the water and the sound velocity within it.
Water is measured in the engine room, which can cause biases from heat in the room. [ 2 ]
This standards - or measurement -related article is a stub . You can help Wikipedia by expanding it .
This article related to water transport is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thermosalinograph |
A thermoset polymer matrix is a synthetic polymer reinforcement where polymers act as binder or matrix to secure in place incorporated particulates, fibres or other reinforcements. They were first developed for structural applications, [ 1 ] such as glass-reinforced plastic radar domes on aircraft and graphite - epoxy payload bay doors on the Space Shuttle .
They were first used after World War II , and continuing research has led to an increased range of thermoset resins , polymers or plastics, [ 2 ] as well as engineering grade thermoplastics. [ 3 ] They were all developed for use in the manufacture of polymer composites with enhanced and longer-term service capabilities. Thermoset polymer matrix technologies also find use in a wide diversity of non-structural industrial applications. [ 4 ]
The foremost types of thermosetting polymers used in structural composites are benzoxazine resins , bis-maleimide resins (BMI), cyanate ester resins, epoxy (epoxide) resins, phenolic (PF) resins, unsaturated polyester (UP) resins, polyimides, polyurethane (PUR) resins, silicones, and vinyl esters .
These are made by the reaction of phenols, formaldehyde and primary amines which at elevated temperatures (400 °F (204 °C)) undergo ring–opening polymerisation forming polybenzoxazine thermoset networks; when hybridised with epoxy and phenolic resins the resulting ternary systems have glass transition temperatures in excess of 490 °F (254 °C). [ 5 ]
Cure is characterised by expansion rather than shrinkage and uses include structural prepregs , liquid molding and film adhesives for composite construction, bonding and repair. The high aromatic content of the high molecular weight polymers provides enhanced mechanical and flammability performance compared to epoxy and phenolic resins.
Formed by the condensation reaction of a diamine with maleic anhydride , and processed basically like epoxy resins (350 °F (177 °C) cure). [ 6 ] After an elevated post-cure (450 °F (232 °C)), they will exhibit superior properties. These properties are influenced by a 400–450 °F (204–232 °C) continuous use temperature and a glass transition of 500 °F (260 °C).
This thermoset polymer type is merged into composites as a prepreg matrix used in electrical printed circuit boards , and for large scale structural aircraft – aerospace composite structures, etc. It is also used as a coating material and as the matrix of glass reinforced pipes, particularly in high temperature and chemical environments.
The reaction of bisphenols or multifunctional phenol novolac resins with cyanogen bromide or chloride leads to cyanate functional monomers which can be converted in a controlled manner into cyanate ester functional prepolymer resins by chain extension or copolymerization. [ 7 ] When postcured, all residual cyanate ester functionality polymerises by cyclotrimerisation leading to tightly crosslinked polycyanurate networks with high thermal stability and glass transition temperatures up to 752 °F (400 °C) and wet heat stability up to around 400 °F (204 °C).
Cyanate ester resin prepregs combine the high temperature stability of polyimides with the flame and fire resistance of phenolics and are used in the manufacture of aerospace structural composite components which meet fire protection regulations concerning flammability, smoke density and toxicity. Other uses include film adhesives, surfacing films and 3D printing .
Epoxy resins are thermosetting prepolymers made either by the reaction of epichlorohydrin with hydroxyl functional aromatics, cycloaliphatics and aliphatics or amine functional aromatics, or by the oxidation of unsaturated cycloaliphatics. [ 8 ] The diglycidyl ethers of bisphenol-A (DGEBA) and bisphenol-F (DGEBF) are the most widely used due to their characteristic high adhesion, mechanical strength, heat and corrosion resistance. [ 9 ] Epoxide functional resins and prepolymers cure by polyaddition/copolymerisation or homopolymerisation depending on the selection of crosslinker, hardener, curing agent or catalyst as well as by the temperature. [ 10 ]
Epoxy resin is used widely in numerous formulations and forms in the aircraft-aerospace industry. It is regarded as "the work-horse of modern day composites". In recent years, the epoxy formulations used in composite prepregs have been fine-tuned to improve their toughness, impact strength and moisture absorption resistance. Maximum properties have been realized for this polymer.
This is not only used in aircraft-aerospace demand. It is used in military and commercial applications and is also used in construction. Epoxy-reinforced concrete and glass-reinforced and carbon-reinforced epoxy structures are used in building and bridge structures.
Epoxy composites have the following properties:
Epoxy Phenol Novolac (EPN) and Epoxy Cresol Novolac (ECN) resins made by reacting epichlorohydrin with multifunctional phenol novolac or cresol novolac resins have more reactive sites compared to DGEBF epoxy resins and on cure result in higher crosslink density thermosets. They are used in printed wire/circuit board laminating and also for electrical encapsulation, adhesive and coatings for metal where there is a need to provide protection from corrosion, erosion or chemical attack at high continuous operating temperatures.
There are two types of phenolic resins [ 11 ] - novolacs and resoles. Novolacs are made with acid catalysts and a molar ratio of formaldehyde to phenol of less than one to give methylene linked phenolic oligomers; resoles are made with alkali catalysts and a molar ratio of formaldehyde to phenol of greater than one to give phenolic oligomers with methylene and benzylic ether-linked phenol units.
Phenolic resins, originally developed in the late 19th century and, regarded as the first truly synthetic polymer types, are often referred to as the “work-horse of thermosetting resins”. They are characterised by high bonding strength, dimensional stability and creep resistance at elevated temperatures, and frequently combined with co-curing resins such as epoxies.
General purpose molding compounds, engineering molding compounds and sheet molding compounds are the primary forms of phenolic composites. Phenolics are also used as the matrix binder with Honeycomb core. Phenolics find use in many electrical applications such as breaker boxes, brake lining materials and most recently in combination with various reinforcements in the molding of an engine block-head assembly, called the polimotor . Phenolics may be processed by the various common techniques, including compression, transfer and injection molding .
Properties of phenolic composites have the following properties:
Unsaturated polyester resins are an extremely versatile, [ 12 ] [ 13 ] and fairly inexpensive class of thermosetting polymer formed by the polycondensation of glycol mixtures often containing propylene glycol , with a dibasic acid and anhydrides usually maleic anhydride to provide backbone unsaturation needed for crosslinking, and phthalic anhydride , isophthalic acid or terephthalic acid where superior structural and corrosion resistance properties are required. Polyester resins are routinely diluted/dissolved in a vinyl functional monomer such as styrene and include an inhibitor to stabilize the resin for storage purposes. Polymerisation in service is initiated by free radicals generated from ionizing radiation or by the photolytic or thermal decomposition of a radical initiator. Organic peroxides , such as methyl ethyl ketone peroxide and auxiliary accelerators which promote decomposition to form radicals are combined with the resin to initiate a room temperature cure.
In the liquid state, unsaturated polyester resins may be processed by numerous methods, including Hand Layup, vacuum bag molding, and spray-up and compression molded Sheet Molding Compound (SMC). They can also be B-staged after application to chopped reinforcement and continuous reinforcement, to form pre-pregs. Solid molding compounds in the form of pellets or granules are also used in processes such as compression and transfer molding.
There are two types of commercial polyimides : thermosetting cross-linkable polyimides made by the condensation of aromatic diamines with aromatic dianhydride derivatives and anhydrides with unsaturated sites that facilitate addition polymerisation between preformed imide monomers and oligomers, [ 14 ] [ 15 ] and thermoplastic polyimides formed by the condensation reaction between aromatic diamines and aromatic dianhydrides. Thermoset polyimides are the most advanced of all thermoset polymer matrices with characteristics of high temperature physical and mechanical properties and are available commercially as resin, prepreg, stock shapes, thin sheets/films, laminates, and machined parts. Along with the high temperature properties, this thermoset polymer type must be processed at very high temperatures and relative pressure to produce optimum characteristics. With prepreg materials, 600 °F (316 °C) to 650 °F (343 °C) temperatures and 200 psi (1,379 kPa ) pressures are required. The entire cure profiles are inherently long as there are a number of intermediate temperatures dwells, duration of which are dependent on part size and thickness.
The cut of polyimides is 450 °F (232 °C), highest of all thermosets, with short term exposure capabilities of 900 °F (482 °C). Normal operating temperatures range from cryogenic to 500 °F (260 °C).
Polyimide composites have the following properties:
Polyimide film possesses a unique combination of properties that make it ideal for a variety of applications in many different industries especially as excellent physical, electrical, and mechanical properties are maintained over a wide temperature range. [ 16 ] [ 17 ] [ 18 ] [ 19 ] [ 20 ]
High-performance polyimide resin is used in electrical, wear resistant and as structural materials when combined with reinforcement for aircraft-aerospace applications, which are replacing heavier more expensive metals. High temperature processing causes some technical problems as well as higher costs compared to other polymers. Hysols [ 21 ] PMR series is an example of this polymer.
Thermoset polyurethane prepolymers with carbamate (-NH-CO-O-) links are linear and elastomeric if formed by combining diisocyanates (OCN-R1-NCO) with long chain diols (HO-R2-OH), or crosslinked and rigid if formed from combinations of polyisocyanates and, polyols . They can be solid or have an open cellular structure if foamed, and are widely used for their characteristic [ 22 ] high adhesion and resistance to fatigue. Polyurethane foam structural cores combined with glass-reinforced or graphite-reinforced composite laminates are used to make lightweight, strong, sandwich structures. [ 23 ] [ 24 ] [ 25 ] All forms of the material, inclusive of flexible and rigid foams, foam moldings, solid elastomeric moldings and extrudates, when combined with various reinforcement–fillers have found commercial applications in thermoset polymer matrix composites. [ 26 ]
They differ from polyureas which are thermoset elastomeric polymers with carbamide (-NH-CO-NH-) links made by combining diisocyanate monomers or prepolymers (OCN-R-NCO) with blends of long-chain amine-terminated polyether or polyester resins (H2N-RL-NH2) and short-chain diamine extenders (H2N-RS-NH2). Polyureas are characterised by near instantaneous cure, high mechanical strength and resistance to corrosion so are widely used for 1:1 volume mix ratio spray applied, abrasion resistant waterproofing protective coating and lining. [ 27 ]
Silicone resins are partly organic in nature with a backbone polymer structure made of alternating silicon and oxygen atoms rather than the familiar carbon -to-carbon backbone characteristics of organic polymers. In addition to having at least one oxygen atom bonded to each silicon atom, silicone resins have direct bonds to carbon and therefore also known as polyorganosiloxanes. They have the general formula (R2SiO)n and the physical form (liquid, gel, elastomer or solid) and use varies with molecular weight, structure (linear, branched, caged) and nature of substituent groups (R = alkyl, aryl, H, OH, alkoxy). Aryl substituted silicone resins have greater thermal stability than alkyl substituted silicone resins when polymerised (condensation cure mechanism) at temperatures between ~300 °F (~150 °C) and ~400 °F (~200 °C). Heating above ~600 °F (~ 300 °C) converts all silicone polymers into ceramics [ 28 ] since all organic constituents pyrolytically decompose leaving crystalline silicate polymers with the general formula (-SiO2-)n. In addition to applications as ceramic matrix composite precursors, silicone resins in the form of polysiloxane polymers made from silicone resins with pendant acrylate, vinyl ether or epoxy functionality find application as UV, electron beam and thermoset polymer matrix composites where they are characterised by their resistance to oxidation, heat and ultraviolet degradation.
Assorted other uses in the general area of composites for silicones include sealants, coating materials, and as a reusable bag material for vacuum-bag curing of composite parts.
Vinyl ester resins made by addition reactions between an epoxy resin with acrylic acid derivatives, when diluted/dissolved in a vinyl functional monomer such as styrene , polymerise. The resulting thermosets are notable for their high adhesion, heat resistance and corrosion resistance. They are stronger than polyesters and more resistant to impact than epoxies. [ 29 ] Vinyl ester resins are used for wet lay-up laminating, SMC and BMC in the manufacture and repair of corrosion and heat resistant components ranging from pipelines, vessels and buildings to transportation, marine, military and aerospace applications.
Amino resins are another class of thermoset prepolymers formed by copolymerisation of amines or amides with an aldehyde. Urea-formaldehyde and melamine-formaldehyde resins, although not widely used in high performance structural composite applications, are characteristically used as the polymer matrix in molding and extrusion compounds where some use of fillers and reinforcements occurs. Urea-formaldehyde resins are widely used as the matrix binder in construction utility products such as particle board , wafer board , and plywood , which are true particulate and laminar composite structures. Melamine-formaldehyde resins are used for plastic laminating.
Furan resin prepolymers made from furfuryl alcohol , or by modification of furfural with phenol , formaldehyde ( methanal ), urea or other extenders, are similar to amino and phenolic thermosetting resins in that cure involves polycondensation and release of water as well as heat. While they are generally cured under the influence of heat, catalysts and pressure, furan resins can also be formulated as dual-component no-bake acid-hardened systems which are characterised by high resistance to heat, acids and alkalies. Furan resins are of increasing interest for the manufacture of sustainable composites - biocomposites made from a bio-derived matrix (in this case furan resin), or biofibre reinforcement, or both. [ 30 ] | https://en.wikipedia.org/wiki/Thermoset_polymer_matrix |
In materials science , a thermosetting polymer , often called a thermoset , is a polymer that is obtained by irreversibly hardening (" curing ") a soft solid or viscous liquid prepolymer ( resin ). [ 1 ] Curing is induced by heat or suitable radiation and may be promoted by high pressure or mixing with a catalyst . Heat is not necessarily applied externally, and is often generated by the reaction of the resin with a curing agent ( catalyst , hardener ). Curing results in chemical reactions that create extensive cross-linking between polymer chains to produce an infusible and insoluble polymer network.
The starting material for making thermosets is usually malleable or liquid prior to curing, and is often designed to be molded into the final shape. It may also be used as an adhesive . Once hardened, a thermoset cannot be melted for reshaping, in contrast to thermoplastic polymers which are commonly produced and distributed in the form of pellets, and shaped into the final product form by melting, pressing, or injection molding .
Curing a thermosetting resin transforms it into a plastic , or elastomer ( rubber ) by crosslinking or chain extension through the formation of covalent bonds between individual chains of the polymer . Crosslink density varies depending on the monomer or prepolymer mix, and the mechanism of crosslinking:
Acrylic resins, polyesters and vinyl esters with unsaturated sites at the ends or on the backbone are generally linked by copolymerisation with unsaturated monomer diluents, with cure initiated by free radicals generated from ionizing radiation or by the photolytic or thermal decomposition of a radical initiator – the intensity of crosslinking is influenced by the degree of backbone unsaturation in the prepolymer; [ 2 ]
Epoxy functional resins can be homo-polymerized with anionic or cationic catalysts and heat, or copolymerised through nucleophilic addition reactions with multifunctional crosslinking agents which are also known as curing agents or hardeners. As reaction proceeds, larger and larger molecules are formed and highly branched crosslinked structures develop, the rate of cure being influenced by the physical form and functionality of epoxy resins and curing agents [ 3 ] – elevated temperature postcuring induces secondary crosslinking of backbone hydroxyl functionality which condense to form ether bonds;
Polyurethanes form when isocyanate resins and prepolymers are combined with low- or high-molecular weight polyols, with strict stoichiometric ratios being essential to control nucleophilic addition polymerisation – the degree of crosslinking and resulting physical type (elastomer or plastic) is adjusted from the molecular weight and functionality of isocyanate resins, prepolymers, and the exact combinations of diols, triols and polyols selected, with the rate of reaction being strongly influenced by catalysts and inhibitors; polyureas form virtually instantaneously when isocyanate resins are combined with long-chain amine functional polyether or polyester resins and short-chain diamine extenders – the amine-isocyanate nucleophilic addition reaction does not require catalysts. Polyureas also form when isocyanate resins come into contact with moisture; [ 4 ]
Phenolic , amino , and furan resins all cured by polycondensation involving the release of water and heat, with cure initiation and polymerisation exotherm control influenced by curing temperature, catalyst selection or loading and processing method or pressure – the degree of pre-polymerisation and level of residual hydroxymethyl content in the resins determine the crosslink density. [ 5 ]
Polybenzoxazines are cured by an exothermal ring-opening polymerisation without releasing any chemical, which translates in near zero shrinkage upon polymerisation. [ 6 ]
Thermosetting polymer mixtures based on thermosetting resin monomers and pre-polymers can be formulated and applied and processed in a variety of ways to create distinctive cured properties that cannot be achieved with thermoplastic polymers or inorganic materials. [ 7 ] [ 8 ]
Thermosetting plastics are generally stronger than thermoplastic materials due to the three-dimensional network of bonds (crosslinking), and are also better suited to high- temperature applications up to the decomposition temperature since they keep their shape as strong covalent bonds between polymer chains cannot be broken easily. The higher the crosslink density and aromatic content of a thermoset polymer, the higher the resistance to heat degradation and chemical attack. Mechanical strength and hardness also improve with crosslink density, although at the expense of brittleness. [ 9 ] They normally decompose before melting.
Hard, plastic thermosets may undergo permanent or plastic deformation under load. Elastomers, which are soft and springy or rubbery and can be deformed and revert to their original shape on loading release.
Conventional thermoset plastics or elastomers cannot be melted and re-shaped after they are cured. This usually prevents recycling for the same purpose, except as filler material. [ 10 ] New developments involving thermoset epoxy resins which on controlled and contained heating form crosslinked networks permit repeatedly reshaping, like silica glass by reversible covalent bond exchange reactions on reheating above the glass transition temperature. [ 11 ] There are also thermoset polyurethanes shown to have transient properties and which can thus be reprocessed or recycled. [ 12 ]
When compounded with fibers, thermosetting resins form fiber-reinforced polymer composites, which are used in the fabrication of factory-finished structural composite OEM or replacement parts, [ 13 ] and as site-applied, cured and finished composite repair [ 14 ] [ 15 ] and protection materials. When used as the binder for aggregates and other solid fillers, they form particulate-reinforced polymer composites, which are used for factory-applied protective coating or component manufacture, and for site-applied and cured construction, or maintenance purposes.
Application/process uses and methods for thermosets include protective coating , seamless flooring , civil engineering construction grouts for jointing and injection, mortars , foundry sands, adhesives , sealants , castings , potting , electrical insulation , encapsulation , solid foams , wet lay-up laminating, pultrusion , gelcoats , filament winding , pre-pregs , and molding.
Specific methods of molding thermosets are: | https://en.wikipedia.org/wiki/Thermosetting_polymer |
A thermosome is a group II chaperonin protein complex that functions in archaea . It is the homolog of eukaryotic CCT . [ 1 ] This group II chaperonin is an ATP-dependent chaperonin that is responsible for folding or refolding of incipient or denatured proteins . [ 2 ] A thermosome has two rings, each consisting of eight subunits , stacked together to form a cylindrical shape with a large cavity at the center. [ 2 ] The thermosome is also defined by its heterooligomeric nature. The complex consists of two subunits [ dubious – discuss ] that alternate location within its two rings. [ 2 ]
Being a Group II chaperonin , the thermosome has a similar structure to group I chaperonins . The main difference, however, lies in the existence of a helical protrusion in the thermosome which composes of a built-in lid of the hydrophilic cavity. [ 2 ] Not only is thermosome ATP-dependent , but the mechanism in which thermosome shifts from open to close conformation is also temperature-dependent. The open conformation of the ATP-thermosome exists mainly at low temperatures. [ 3 ] Whereas, the closed conformation of the thermosome occurs when heating to physiological temperature. [ 3 ]
Similar to the GroEL chaperonins in bacteria, the thermosome shows negative cooperativity since the two rings of the thermosome show different affinities for the binding of ATP. However, unlike the GroEL system, the thermosome is less affected by the concentration of ATP. In the absence of ATP, the thermosome does not have a preference for the T-state over the R-state. There is, however, an inhibition for the loading of the second ring when ADP is bound to the first ring. [ 4 ]
The N-terminus and C-terminus of thermosomes are arranged in an anti-parallel fashion and their interactions form part of the intra-ring interactions. Both the N-terminus and C-terminus of the thermosome have charged residues which interact with each other to contribute to the thermal stability of the thermosome. The cpn-α and cpn-β thermosomes specifically show maximum thermal stability in the pH range of 7.0 to 8.0 because this is the range where the charged N- and C-termini residues have net charges close to zero. Under lower or high pH conditions, these residues are charged and repelled each other which negatively affect thermal stability. This shows one possible way in which pH affects the stability of the thermosome. [ 5 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thermosome |
In materials science and molecular biology , thermostability is the ability of a substance to resist irreversible change in its chemical or physical structure, often by resisting decomposition or polymerization , at a high relative temperature .
Thermostable materials may be used industrially as fire retardants . A thermostable plastic , an uncommon and unconventional term, is likely to refer to a thermosetting plastic that cannot be reshaped when heated, than to a thermoplastic that can be remelted and recast.
Thermostability is also a property of some proteins . To be a thermostable protein means to be resistant to changes in protein structure due to applied heat.
Most life-forms on Earth live at temperatures of less than 50 °C, commonly from 15 to 50 °C. Within these organisms are macromolecules (proteins and nucleic acids) which form the three-dimensional structures essential to their enzymatic activity. [ 2 ] Above the native temperature of the organism, thermal energy may cause the unfolding and denaturation , as the heat can disrupt the intramolecular bonds in the tertiary and quaternary structure. This unfolding will result in loss in enzymatic activity, which is understandably deleterious to continuing life-functions. An example of such is the denaturing of proteins in albumen from a clear, nearly colourless liquid to an opaque white, insoluble gel.
Proteins capable of withstanding such high temperatures compared to proteins that cannot, are generally from microorganisms that are hyperthermophiles. Such organisms can withstand above 50 °C temperatures as they usually live within environments of 85 °C and above. [ 3 ] Certain thermophilic life-forms exist which can withstand temperatures above this, and have corresponding adaptations to preserve protein function at these temperatures. [ 4 ] These can include altered bulk properties of the cell to stabilize all proteins, [ 5 ] and specific changes to individual proteins. Comparing homologous proteins present in these thermophiles and other organisms reveal some differences in the protein structure. One notable difference is the presence of extra hydrogen bonds in the thermophile's proteins—meaning that the protein structure is more resistant to unfolding. Similarly, thermostable proteins are rich in salt bridges or/and extra disulfide bridges stabilizing the structure. [ 6 ] [ 7 ] Other factors of protein thermostability are compactness of protein structure, [ 8 ] oligomerization, [ 9 ] and strength interaction between subunits.
Thermostable DNA polymerases such as Taq polymerase and Pfu DNA polymerase are used in polymerase chain reactions (PCR) where temperatures of 94 °C or over are used to melt DNA strands in the denaturation step of PCR. [ 10 ] This resistance to high temperature allows for DNA polymerase to elongate DNA with a desired sequence of interest with the presence of dNTPs.
Enzymes are often added to animal feed to improve the health and growth of farmed animals, particularly chickens and pigs. The feed is typically treated with high pressure steam to kill bacteria such as Salmonella . Therefore the added enzymes (e.g. phytase and xylanase ) must be able to withstand this thermal challenge without being irreversibly inactivated. [ 11 ]
Knowledge of an enzyme's resistance to high temperatures is especially beneficial in protein purification . In the procedure of heat denaturation, one can subject a mixture of proteins to high temperatures, which will result in the denaturation of proteins that are not thermostable, and the isolation of the protein that is thermodynamically stable. One notable example of this is found in the purification of alkaline phosphatase from the hyperthermophile Pyrococcus abyssi . This enzyme is known for being heat stable at temperatures greater than 95 °C, and therefore can be partially purified by heating when heterologously expressed in E. coli . [ 12 ] The increase in temperature causes the E. coli proteins to precipitate, while the P. abyssi alkaline phosphatase remains stably in solution.
Another important group of thermostable enzymes are glycoside hydrolases . These enzymes are responsible of the degradation of the major fraction of biomass, the polysaccharides present in starch and lignocellulose. Thus, glycoside hydrolases are gaining great interest in biorefining applications in the future bioeconomy. [ 13 ] Some examples are the production of monosaccharides for food applications as well as use as carbon source for microbial conversion in fuels (ethanol) and chemical intermediates, production of oligosaccharides for prebiotic applications and production of surfactants alkyl glycoside type. All of these processes often involve thermal treatments to facilitate the polysaccharide hydrolysis, hence give thermostable variants of glycoside hydrolases an important role in this context.
Protein engineering can be used to enhance the thermostability of proteins. A number of site-directed and random mutagenesis techniques, [ 14 ] [ 15 ] in addition to directed evolution , [ 16 ] have been used to increase the thermostability of target proteins. Comparative methods have been used to increase the stability of mesophilic proteins based on comparison to thermophilic homologs. [ 17 ] [ 18 ] [ 19 ] [ 20 ] Additionally, analysis of the protein unfolding by molecular dynamics can be used to understand the process of unfolding and then design stabilizing mutations. [ 21 ] Rational protein engineering for increasing protein thermostability includes mutations which truncate loops, increase salt bridges [ 22 ] or hydrogen bonds, introduced disulfide bonds . [ 23 ] In addition, ligand binding can increase the stability of the protein, particularly when purified. [ 24 ] There are various different forces that allow for the thermostability of a particular protein. These forces include hydrophobic interactions, electrostatic interactions, and the presence of disulfide bonds. The overall amount of hydrophobicity present in a particular protein is responsible for its thermostability. Another type of force that is responsible for thermostability of a protein is the electrostatic interactions between molecules. These interactions include salt bridges and hydrogen bonds. Salt bridges are unaffected by high temperatures, therefore, are necessary for protein and enzyme stability. A third force used to increase thermostability in proteins and enzymes is the presence of disulfide bonds. They present covalent cross-linkages between the polypeptide chains. These bonds are the strongest because they're covalent bonds, making them stronger than intermolecular forces. [ 25 ] Glycosylation is another way to improve the thermostability of proteins. Stereoelectronic effects in stabilizing interactions between carbohydrate and protein can lead to the thermostabilization of the glycosylated protein. [ 26 ] Cyclizing enzymes by covalently linking the N-terminus to the C-terminus has been applied to increase the thermostability of many enzymes. Intein cyclization and SpyTag/SpyCatcher cyclization have often been employed. [ 27 ] [ 28 ]
Certain poisonous fungi contain thermostable toxins , such as amatoxin found in the death cap and autumn skullcap mushrooms and patulin from molds. Therefore, applying heat to these will not remove the toxicity and is of particular concern for food safety. [ 29 ] | https://en.wikipedia.org/wiki/Thermostability |
Thermostable DNA polymerases are DNA polymerases that originate from thermophiles , usually bacterial or archaeal species, and are therefore thermostable . They are used for the polymerase chain reaction and related methods for the amplification and modification of DNA .
Several DNA polymerases have been described with distinct properties that define their specific utilisation in a PCR, in real-time PCR or in an isothermal amplification . Being DNA polymerases, the thermostable DNA polymerases all have a 5'→3' polymerase activity, and either a 5'→3' or a 3'→5' exonuclease activity.
DNA polymerases are roughly shaped like a hand with a thumb, palm and fingers. [ 12 ] [ 13 ] The thumb is involved in binding and moving double-stranded DNA . [ 12 ] The palm carries the polymerase active site , whereas the fingers bind substrates (template DNA and nucleoside triphosphates ). [ 12 ] [ 14 ] The exonuclease activity is in a separate protein domain . [ 12 ] Mg 2+ is a cofactor .
The polymerase active site in the palm catalyses the prolongation of DNA, starting from a primer bound to a template DNA single strand:
Thermostable DNA polymerases of natural origin are found in thermophilic bacteria , archaea and their pathogens. Among the bacterial thermostable DNA polymerases, Taq polymerase , Tfl polymerase, Tma polymerase, Tne polymerase, Tth and Bst polymerase are used. [ 4 ] [ 15 ] [ 16 ] [ 2 ]
In addition to 5'→3' polymerase activity, the bacterial thermostable DNA polymerases (belonging to the A-type DNA polymerases) have 5'→3' exonuclease activity and generate an adenosine overhang ( sticky ends ) at the 3' end of the newly generated strand. The Klenow fragment of Bst (BF) has a strand displacement activity which allows for use in isothermal amplification without the necessity of denaturation of the DNA in a thermocycler , and its 5'→3' exonuclease activity is deleted for higher yield. [ 2 ]
Frequently used B-type DNA polymerases are the Pfu polymerase , [ 4 ] the Pwo polymerase, [ 17 ] the KOD polymerase, [ 3 ] the Tli polymerase (also called Vent), which originates from various archaea, [ 18 ] the Tag polymerase, [ 19 ] the Tce polymerase, [ 20 ] the Tgo polymerase, [ 8 ] the TNA1 polymerase, [ 21 ] the Tpe polymerase, [ 22 ] the Tthi polymerase, [ 23 ] the Neq polymerase [ 24 ] and the Pab polymerase. [ 25 ]
The archaeal variants (belonging to the B-type) produce blunt ends (the Tli polymerase produces an overhang in about 30% of the products) and instead of the 5'→3' exonuclease activity have an activity for correcting synthesis errors (proof-reading), the 3'→5' exonuclease activity. [ 26 ] [ 27 ] In archaeal polymerases, the error rate suffers when a Klenow fragment analogue is generated, as the correcting exonuclease activity is removed in the process. [ 4 ] Some archaeal DNA polymerases are characterised less by their suitability for standard PCR than by their reduced inhibition in the amplification of A-DNA [ 28 ] or DNA with modified bases. [ 29 ] [ 30 ]
Various fusion proteins with the low error rate of archaeal and the high synthesis rate of bacterial thermostable DNA polymerases ( Q5 polymerase ) were generated from various thermostable polymerases and the DNA clamp of the thermostable DNA-binding protein SSo7d by protein design . [ 31 ] A fusion protein of the PCNA homologue from Archaeoglobus fulgidus was also generated with archaeal thermostable DNA polymerases. [ 32 ] Similarly, fusion proteins of thermostable DNA polymerases with the thermostable DNA-binding protein domain of a topoisomerase (type V, with helix-hairpin-helix motif , HhH) from Methanopyrus kandleri were generated ( TopoTaq and PfuC2 ). [ 33 ] [ 34 ] A modified Pfu polymerase was also generated by protein design ( Pfu Ultra ). [ 35 ] Similar effects are also achieved with mixtures of thermostable DNA polymerases of both types with a mixing ratio of the enzyme activities of type A and B polymerases of 30 to 1, [ 22 ] [ 36 ] e.g. Herculase [ 8 ] and TaqPlus [ 10 ] as a commercial mixture of Taq and Pfu polymerase, Expand as a commercial mixture of Taq and Pwo, [ 37 ] Expand High Fidelity as a commercial mixture of Taq and Tgo, [ 10 ] Platinum Taq High Fidelity as a commercial mixture of Taq and Tli (Vent), [ 10 ] and Advantage HF 2 as a commercial mixture of Titanium Taq and an unnamed proof-reading polymerase. [ 10 ] These mixtures can be used for long-range PCR to synthesize products of up to 35kb length. [ 36 ] [ 38 ] Other additives are used to help against difficult G C -rich sequences, avoid or neutralise the negative effects of PCR inhibitors (like blood components or detergents [ 39 ] or dUTP [ 40 ] ), or alter the reaction kinetics . [ 41 ]
The baseline synthesis rates (speed, productivity) of various polymerases have been compared. [ 8 ] The synthesis rate of Taq polymerase is around 60 base pairs per second. Among the unmodified thermostable DNA polymerases, only the synthesis rate of KOD polymerase is above 100 base pairs per second (approx. 120 bp/s). [ 11 ] Among the modified thermostable DNA polymerases, various mutations have been described that increase the synthesis rate. [ 42 ] [ 43 ] [ 44 ] KOD polymerase and some modified thermostable DNA polymerases ( iProof / Phusion , Pfu Ultra , Velocity or Z-Taq ) are used as a PCR variant with shorter amplification cycles (fast PCR, high-speed PCR) due to their high synthesis rate. Processivity describes the average number of base pairs before a polymerase falls off the DNA template. The processivity of the polymerase limits the maximum distance between the primer and the probe in some forms of real-time quantitative PCR (qPCR).
The error rates of various polymerases (fidelity) have been described. The error rate of Taq polymerase is 8 × 10 −6 errors per base, that of Advantage HF 6.1 × 10 −6 errors per base, that of Platinum Taq High Fidelity 5.8 × 10 −6 errors per base and doubling, that of TaqPlus 4 × 10 −6 errors per base and doubling, that of KOD polymerase 3.5 × 10 −6 errors per base and doubling, that of Tli polymerase and Herculase 2.8 × 10 −6 errors per base and doubling, that of Deep Vent 2.8 × 10 −6 errors per base and doubling, that of Pfu, Phusion DNA Polymerase (identical with iProof DNA Polymerase ) and Herculase II Fusion 1.3 × 10 −6 errors per base and doubling and that of Pfu Ultra and Pfu Ultra II 4.3 × 10 −7 errors per base and doubling. [ 4 ] [ 8 ] [ 10 ] A newer analysis found slightly different error rates: Deep Vent (exo-) polymerase (5.0 × 10 −4 errors per base and doubling), Taq polymerase (1.5 × 10 −4 errors per base and doubling), Kapa HiFi HotStart ReadyMix (1.6 × 10 −5 errors per base and doubling), KOD (1.2 × 10 −5 errors per base and doubling), PrimeSTAR GXL (8.4 × 10 −6 errors per base and doubling), Pfu (5.1 × 10 −6 errors per base and doubling), Deep Vent DNA polymerase (4.0 × 10 −6 ) errors per base and doubling, Phusion (3.9 × 10 −6 errors per base and doubling), and Q5 DNA polymerase (5.3 × 10 −7 errors per base and doubling). [ 5 ] Yet another found error rates of 3–5.6 × 10 −6 for Taq, 7.6 × 10 −6 for KOD, 2.8 × 10 −6 for Pfu, 2.6 × 10 −6 for Phusion , and 2.4 × 10 −6 for Pwo. [ 6 ] To reduce the number of mutations in the PCR product (e.g. for molecular cloning ), more template DNA and less cycles can be used in the PCR. [ 10 ]
Bacterial thermostable DNA polymerases generally produce higher product concentrations than archaeal, but with more copy errors. In the bacterial thermostable DNA polymerases, a Klenow fragment ( Klen-Taq ) or a Stoffel fragment can be generated by deleting the exonuclease domain in the course of protein design, analogous to the DNA polymerase from E. coli , which results in a higher product concentration. [ 45 ] [ 15 ] Two amino acids required for the exonuclease function of Taq polymerase were identified by mutagenesis as arginines at positions 25 and 74 (R25 and R74). [ 46 ] A histidine to glutamic acid mutation at position 147 (short: H147E) in KOD polymerase lowers the relatively high exonuclease activity of KOD. [ 27 ]
The favouring of individual nucleotides by a thermostable DNA polymerase is referred to as nucleotide specificity (bias). In PCR-based DNA sequencing with chain termination substrates (dideoxy method), their uniform incorporation and thus unbiased generation of all chain termination products is often desired in order to enable higher sensitivity and easier analysis. For this purpose, a KlenTaq polymerase was generated by deletion and a phenylalanine at position 667 was exchanged for tyrosine by site-directed mutagenesis (short: F667Y) and named Thermo Sequenase . [ 47 ] [ 48 ] This polymerase can also be used for the incorporation of fluorescence-labelled dideoxynucleotides. [ 49 ]
The template specificity of the polymerases is increased by using hot-start polymerases, to avoid binding of primers to unwanted DNA templates or to each other at low temperatures before the beginning of the PCR. [ 50 ] Examples are the antibody -inhibited Pfu polymerase Pfu Turbo , the Platinum Pfx as a commercial KOD polymerase with an inhibiting antibody and the Platinum Taq as an antibody-inhibited Taq polymerase. [ 8 ] Hot-start polymerases are either inhibited by inactivation with formaldehyde [ 51 ] [ 52 ] (or maleic anhydride , exo-cis-3,6-endoxo-Δ4-tetrahydropthalic anhydride, citraconic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, cis-aconitic anhydride, or 2,3-dimethylmaleic anhydride), [ 53 ] by complexing the magnesium with phosphates [ 54 ] or by binding an antibody to their active site. [ 55 ] [ 56 ] Upon heating to 95 °C, the formaldehyde dissociates from proteins, [ 57 ] [ 58 ] [ 59 ] or the magnesium ions are released, [ 54 ] or the antibody is denatured and released in the process. [ 60 ] [ 61 ] Furthermore, polymerases can be inhibited with aptamers that denature upon heating. [ 62 ] [ 63 ] A fifth variant is a polymerase adsorbed on latex beads via hydrophobic effects , which dissolves with increasing temperature. In the sixth and oldest variant, the reaction mixture without polymerase is coated with wax and the polymerase is added on top of the cooled wax. When heated, the wax layer melts and the polymerase mixes with the reaction mixture. [ 64 ]
Some DNA polymerases used in isothermal DNA amplification, e.g. in loop-mediated isothermal amplification , multidisplacement amplification , recombinase polymerase amplification or isothermal assembly , for the amplification of entire genomes (e.g. the φ29 DNA polymerase from the bacteriophage phi29 , B35DNAP from the phage Bam35 ) are not thermostable, while others like the Bst Klenow fragment are thermostable. [ 65 ] The T4, T6 and T7 DNA polymerases are also not thermostable.
The standard reverse transcriptases (RNA-dependent DNA polymerases) of retroviral origin used for RT-PCR , like the AMV - and the MoMuLV -Reverse-Transcriptase, are not thermostable at 95 °C. At the lower temperatures of a reverse transcription unspecific hybridisation of primers to wrong sequences can occur, as well as unwanted secondary structures in the DNA template, which can lead to unwanted PCR products and less desired PCR products. The AMV reverse transcriptase may be used up to 70 °C. [ 66 ] Also, some thermostable DNA-dependent DNA polymerases can be used as RNA-dependent DNA polymerases by exchanging Mg 2+ as cofactors with Mn 2+ , so that they may be used for an RT-PCR. [ 67 ] But since the synthesis rate of Taq with Mn 2+ is relatively low, Tth was increasingly used for this approach. [ 68 ] The use of Mn 2+ also increases the error rate and the necessary amount of template, so that this method is rarely used. These problems can be avoided with the thermostable 3173 -Polymerase from a thermophilic bacteriophage , which can withstand the high temperatures of a PCR and prefers RNA as a template. [ 69 ]
In addition to the choice of thermostable DNA polymerase, other parameters of a PCR are specifically changed in the course of PCR optimisation.
In addition to PCR, thermostable DNA polymerases are also used for RT-PCR variants, qPCR in different variants, site-specific mutagenesis and DNA sequencing. They are also used to produce hybridisation probes for Southern blot and Northern blot by random priming. The 5'→3' exonuclease activity is used for nick translation and TaqMan , among other things, without DNA replication (amplification).
Alice Chien and colleagues were the first to characterise the thermostable Taq polymerase in 1976. [ 70 ] The first use of a thermostable DNA polymerase was by Randall K. Saiki and colleagues in 1988, introducing Taq polymerase for PCR. [ 71 ] [ 72 ] The thermostability of Taq polymerase obliviated the need to add a non-thermostable DNA polymerase to the reaction after every melting phase of the PCR, because the Taq polymerase is not denatured by heating to 95 °C during the melting phase of each cyle. In 1989, the Taq polymerase gene was cloned and the Taq polymerase was produced in Escherichia coli as a recombinant protein . [ 73 ] [ 72 ] DNA of up to 35,000 basepairs was synthesized by Wayne M. Barnes by using different mixtures of A and B type polymerases, [ 36 ] [ 72 ] thereby creating the long-range PCR. The high synthesis rate of KOD polymerase was published in 1997 by Masahiro Takagi and colleagues, [ 3 ] [ 72 ] [ 14 ] thereby creating the fundamentals of high speed PCR. Other optimisations to the PCR were developed in the following years, e.g. circumventing PCR inhibitors and amplifying difficult GC-rich DNA sequences, [ 41 ] as well as modifying thermostable DNA polymerases by protein design. In 1998 the loop-mediated isothermal amplification was developed by Tsugunori Notomi and colleagues at Eiken Chemical Company , using Bst polymerase at 65 °C. [ 74 ] [ 75 ] | https://en.wikipedia.org/wiki/Thermostable_DNA_polymerase |
Thermosynthesis is a theoretical mechanism proposed by Anthonie Muller for biological use of the free energy in a temperature gradient to drive energetically uphill anabolic reactions. [ 1 ] [ 2 ] It makes use of this thermal gradient, or the dissipative structure of convection in this gradient, to drive a microscopic heat engine that performs condensation reactions . Thus negative entropy is generated. The components of the biological thermosynthesis machinery concern progenitors of today's ATP synthase , which functions according to the binding change mechanism , driven by chemiosmosis . Resembling primitive free energy generating physico-chemical processes based on temperature-dependent adsorption to inorganic materials such as clay , [ 3 ] this simple type of energy conversion is proposed to have sustained the origin of life , [ 4 ] [ 5 ] [ 6 ] [ 7 ] including the emergence of the RNA World . [ 8 ] For this RNA World it gives a model that describes the stepwise acquisition of the set of transfer RNAs that sustains the Genetic code . The phylogenetic tree of extant transfer RNAs is consistent with the idea. [ 9 ]
Thermosynthesis may still occur in some terrestrial [ 10 ] and extraterrestrial [ 11 ] [ 12 ] [ 13 ] environments. However, no organisms are known at present that use thermosynthesis as a source of energy, although it is possible that it might occur in extraterrestrial environments where no light is available, such as on the subsurface ocean that may exist on the moon Europa . [ 14 ] Thermosynthesis also permits a simple model for the origin of photosynthesis . [ 15 ] It has moreover been used to explain the origin of animals by symbiogenesis of benthic sessile thermosynthesizers at hydrothermal vents during the Snowball Earths of the Precambrian . [ 16 ] [ 17 ] [ 18 ] Preliminary experiments have started to attempt to isolate thermosynthetic organisms. [ 19 ]
A Dutch biochemist and physicist Anthonie Muller [ 1 ] wrote many papers on thermosynthesis since 1983.
He defined thermosynthesis as:
"Biological heat engines working on thermal cycling."
also as:
"Theoretical biological mechanism for free energy gain from thermal cycling, tentatively stated as the energy source for origin of life."
The thermosynthesis concept, biological free energy gain from thermal cycling, is combined with the concept of the RNA World. The resulting overall origin of life model suggests new explanations for the emergence of the genetic code and the ribosome. It is proposed that the first protein named pF(1) obtained the energy to support the RNA World by a thermal variation of F(1) ATP synthase's binding change mechanism. It is further proposed that this pF(1) was the single translation product during the emergence of the genetic machinery. During thermal cycling pF(1) condensed many substrates with broad specificity, yielding NTPs and randomly constituted protein and RNA libraries that contained self-replicating RNA. The smallness of pF(1) permitted the emergence of the genetic machinery by selection of RNA that increased the fraction of pF(1)s in the protein library: (1) an amino acids concatenating progenitor of rRNA bound to (2) a chain of 'positional tRNAs' linked by mutual recognition, and yielded a pF(1) (or its main motif); this positional tRNA set gradually evolved to a set of regular tRNAs functioning according to the genetic code, with concomitant emergence of (3) an mRNA coding for pF(1). | https://en.wikipedia.org/wiki/Thermosynthesis |
Thermotolerance is the ability of an organism to survive high temperatures. An organism's natural tolerance of heat is their basal thermotolerance . [ 1 ] Meanwhile, acquired thermotolerance is defined as an enhanced level of thermotolerance after exposure to a heat stress. [ 2 ]
Multiple factors contribute to thermotolerance including signaling molecules like abscisic acid , salicylic acid , and pathways like the ethylene signaling pathway and heat stress response pathway . [ 3 ]
The various heat stress response pathways enhance thermotolerance. [ 4 ] The heat stress response in plants is mediated by heat shock transcription factors ( HSF ) and is well conserved across eukaryotes. HSFs are essential in plants’ ability to both sense and respond to stress. [ 5 ] The HSFs, which are divided into three families (A, B, and C), encode the expression of heat shock proteins ( HSP ). Past studies have found that transcriptional activators HsfA1 and HsfB1 are the main positive regulators of heat stress response genes in Arabidopsis thaliana . [ 6 ] The general pathway to thermotolerance is characterized by sensing of heat stress, activation of HSFs, upregulation of heat response, and return to the non-stressed state. [ 7 ]
In 2011, while studying heat stress A. thaliana , Ikeda et al. concluded that the early response is regulated by HsfA1 and the extended response is regulated by HsfA2. They used RT-PCR to analyze the expression of HS-inducible genes of mutant (ectopic and nonfunctional HsfB1) and wild type plants. Plants with mutant HsfB1 had lower acquired thermotolerance, based on both lower expression of heat stress genes and visibly altered phenotypes. With these results they concluded that class A HSFs positively regulated the heat stress response while class B HSFs repressed the expression of HSF genes. Therefore, both were necessary for plants to return to non-stressed conditions and acquired thermotolerance. [ 8 ]
In bacteria, thermotolerance is the resistance of cells to the lethal effects of higher temperatures. Escherichia coli bacteria can be induced to undergo thermotolerance by exposure to a brief period of heat shock, i.e. 15 minutes at 42 degrees. [ 9 ] As a result of such exposure the E. coli cells become resistant to the lethal effects of higher temperatures, such as 50 degrees. Thermotolerance in E. coli depends on the expression of the gene dnaK (that encodes a heat shock protein) so that thermotolerance does not develop in dnaK mutant cells. [ 9 ] | https://en.wikipedia.org/wiki/Thermotolerance |
Thermotomaculum hydrothermale is a species of Acidobacteriota . [ 1 ]
This Acidobacteriota -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thermotomaculum_hydrothermale |
Thermus aquaticus is a species of bacteria that can tolerate high temperatures, one of several thermophilic bacteria that belong to the Deinococcota phylum. It is the source of the heat-resistant enzyme Taq DNA polymerase , one of the most important enzymes in molecular biology because of its use in the polymerase chain reaction (PCR) DNA amplification technique.
When studies of biological organisms in hot springs began in the 1960s, scientists thought that the life of thermophilic bacteria could not be sustained in temperatures above about 55 °C (131 °F). [ 1 ] Soon, however, it was discovered that many bacteria in different springs not only survived, but also thrived in higher temperatures. In 1969, Thomas D. Brock and Hudson Freeze of Indiana University reported a new species of thermophilic bacteria which they named Thermus aquaticus . [ 2 ] The bacterium was first isolated from Mushroom Spring in the Lower Geyser Basin of Yellowstone National Park , which is near the major Great Fountain Geyser and White Dome Geyser , [ 3 ] and has since been found in similar thermal habitats around the world.
Decades later, this discovery had profound implications, including the invention of Polymerase Chain Reaction (PCR) by biochemist Kary Mullis , which revolutionized DNA research and earned Mullis a Nobel Prize in Chemistry in 1993. PCR facilitated advancements in medical diagnostics, genetics, and other fields. After Kary Mullis' discovery of PCR, Cetus awarded him $10,000. However, Cetus later sold the PCR patent to F. Hoffmann-La Roche (Roche) for $300 million. This transaction left Mullis feeling cheated throughout his life. Roche has since profited immensely from the PCR patent, with annual PCR-related sales reaching $5.4 billion in 2022. Despite these profits, neither the National Park Service, Yellowstone National Park, nor the state of Wyoming have received any share of these revenues. Recognizing the scientific and financial potential of Yellowstone's extremophiles, biotechnology companies like Diversa signed agreements with the National Park Service for bioprospecting. This led to further scientific exploration and potential commercial applications, despite some environmental concerns. Overall, Brock's initial discovery in Yellowstone's hot springs paved the way for significant scientific breakthroughs, demonstrating the importance of basic research in driving innovation and technological advancements. [ 4 ]
T. aquaticus shows best growth at 65–70 °C (149–158 °F), but can survive at temperatures of 50–80 °C (122–176 °F). It primarily scavenges for protein from its environment as is evidenced by the large number of extracellular and intracellular proteases and peptidases as well as transport proteins for amino acids and oligopeptides across its cell membrane. This bacterium is a chemotroph —it performs chemosynthesis to obtain food. However, since its range of temperature overlaps somewhat with that of the photosynthetic cyanobacteria that share its ideal environment, it is sometimes found living jointly with its neighbors, obtaining energy for growth from their photosynthesis . T. aquaticus normally respires aerobically but one of its strains, Thermus aquaticus Y51MC23, is able to be grown anaerobically. [ 5 ]
The genetic material of T. aquaticus consists of one chromosome and four plasmids , and its complete genome sequencing revealed that it contains two full and two partial prophages , as well as numerous CRISPR loci. [ 6 ]
Thermus aquaticus is generally of cylindrical shape with a diameter of 0.5 μm to 0.8 μm. The shorter rod shape has a length of 5 μm to 10 μm. The longer filament shape has a length that varies greatly and in some cases exceeds 200 μm. T. aquaticus has shown multiple possible morphologies in different cultures, rod-shaped or as short filaments. The rod-shaped bacteria have a tendency to aggregate. Associations of several individuals can lead to the formation of spherical bodies 10 μm to 20 μm in diameter, also called rotund bodies. [ 2 ] [ 7 ] These bodies are not composed of cell envelope or outer membrane components as previously thought, but are instead made from remodelled peptidoglycan cell wall. Their exact function in the survival of T. aquaticus remains unknown but has been theorised to include temporary food and nucleotide storage, or they may play a role in the attachment and organisation of colonies. [ 6 ] Thermus aquaticus is a typical gram-negative bacterium, which indicates that its cell walls have considerably less peptidoglycan compared to gram-positive counterparts. In the presence of sunlight, Thermus can display hues ranging from yellow to pink or red, which are visible in hot springs. Additionally, Thermus aquaticus may possess flagella for motility or remain immotile.
T. aquaticus has become famous as a source of thermostable enzymes, particularly the Taq DNA polymerase, as described below.
Studies of this extreme thermophilic bacterium that could be grown in cell culture was initially centered on attempts to understand how enzymes , which are normally inactive at high temperature, can function at high temperature in thermophiles . In 1970, Freeze and Brock published an article describing a thermostable aldolase enzyme from T. aquaticus . [ 8 ]
The first polymerase enzyme isolated from T. aquaticus in 1974 was a DNA-dependent RNA polymerase , [ 9 ] used in the process of transcription .
Most molecular biologists probably became aware of T. aquaticus in the late 1970s or early 1980s because of the isolation of useful restriction endonucleases from this organism. [ 10 ] Use of the term Taq to refer to T hermus aq uaticus arose at this time from the convention of giving restriction enzymes short names, such as Sal and Hin, derived from the genus and species of the source organisms.
DNA polymerase was first isolated from T. aquaticus in 1976. [ 11 ] The first advantage found for this thermostable (temperature optimum 72°C, does not denature even in 95 °C) DNA polymerase was that it could be isolated in a purer form (free of other enzyme contaminants) than could the DNA polymerase from other sources. Later, Kary Mullis and other investigators at Cetus Corporation discovered this enzyme could be used in the polymerase chain reaction (PCR) process for amplifying short segments of DNA , [ 12 ] eliminating the need to add E. coli polymerase enzymes after every cycle of thermal denaturation of the DNA. The enzyme was also cloned , sequenced , modified (to produce the shorter 'Stoffel fragment'), and produced in large quantities for commercial sale. [ 13 ] In 1989 Science magazine named Taq polymerase as its first "Molecule of the Year". [ 14 ] In 1993, Mullis was awarded the Nobel Prize in Chemistry for his work with PCR. [ 15 ]
The high optimum temperature for T. aquaticus allows researchers to study reactions under conditions for which other enzymes lose activity. Other enzymes isolated from this organism include DNA ligase , alkaline phosphatase , NADH oxidase , isocitrate dehydrogenase , amylomaltase , and fructose 1,6-disphosphate-dependent L-lactate dehydrogenase .
The commercial use of enzymes from T. aquaticus has not been without controversy. After Brock's studies, samples of the organism were deposited in the American Type Culture Collection , a public repository. Other scientists, including those at Cetus, obtained it from there. As the commercial potential of Taq polymerase became apparent in the 1990s, [ 16 ] the National Park Service labeled its use as the "Great Taq Rip-off". [ 17 ] Researchers working in National Parks are now required to sign "benefits sharing" agreements that would send a portion of later profits back to the Park Service. | https://en.wikipedia.org/wiki/Thermus_aquaticus |
Thermus thermophilus is a Gram-negative bacterium used in a range of biotechnological applications, including as a model organism for genetic manipulation , structural genomics , and systems biology . The bacterium is extremely thermophilic , with an optimal growth temperature of about 65 °C (149 °F). Thermus thermophilus was originally isolated from a thermal vent within a hot spring in Izu , Japan by Tairo Oshima and Kazutomo Imahori. [ 1 ] The organism has also been found to be important in the degradation of organic materials in the thermogenic phase of composting . [ 2 ] T. thermophilus is classified into several strains, of which HB8 and HB27 are the most commonly used in laboratory environments. Genome analyses of these strains were independently completed in 2004. [ 3 ] Thermus also displays the highest frequencies of natural transformation known to date. [ 4 ]
Thermus thermophilus is a Gram-negative bacterium with an outer membrane that is composed of phospholipids and lipopolysaccharides . This bacterium also has a thin peptidoglycan (also known as murein ) layer, in this layer there are 29 muropeptides which account for more than 85% of the total murein layer. The presence of Ala, Glu, Gly, Orn, N -acetyl glucosamine and N -acetylmuramic were found in the murein layer of this bacterium. Another unique feature of this murein layer is that the N-terminal Gly is substituted with phenylacetic acid . This is the first instance of phenylacetic acid found in the murein of bacterial cells. The composition and peptide cross-bridges found in this murein layer are typical of Gram-positive bacterium , but the amount, the degree of the cross-linkage and length of the glycan chain gives this bacterium its Gram-negative properties. [ 5 ]
Thermus thermophilus was originally found within a thermal vent in Japan. These bacteria can be found in a variety of geothermal environments. These Thermophiles require a more stringent DNA repair system, as DNA becomes unstable at high temperatures. The GC-content of this bacterium is about 69%, this contributes to the thermostability of this bacterium's genome. [ 6 ]
The two most widely used strains in laboratory settings are HB27 and HB8. The strain HB27 is capable of living in an aerobic or anaerobic environment . It has a genome that consists of a main chromosome (1.89Mb long), as well as a megaplasmid , known as pTT27 (0.23Mb long). [ 7 ] The chromosome of HB27 contains 1,968 protein coding genes, with 20% of these genes having no known function. While the megaplasmid contains 230 protein coding genes, about 39% of these genes have no known function. [ 8 ]
The strain HB8 is also an aerobic organism and is a model organism for systems biology. It has a genome consisting of a plasmid, known as pTT8 (9.3kb long), that is coupled with a chromosome (1.85Mb), as well as a megaplasmid, also known as pTT27 (0.26Mb). This strain was found to be a polyploid organism, with a chromosome and megaplasmid copy number of about four to five. [ 7 ]
This organism has been advantageous for industrial biotechnological fields as it is an excellent source of enzymes, more specifically thermozymes. One of these enzymes being the Tth DNA polymerase (rTth to emphasize it being recombinant).
rTth DNA polymerase is a recombinant thermostable DNA polymerase derived from Thermus thermophilus HB8, with optimal activity at 70-80 °C, used in some PCR applications. The enzyme possesses efficient reverse transcriptase activity in the presence of manganese . [ 9 ] This enzyme is beneficial for amplification of GC-rich targets and for crude samples. It can be used in applications of PCR, RT-PCR and also primer extension. [ 10 ] This polymerase has been shown to be resistant to DNA polymerase inhibitors present in clinical samples, it also has the capacity to detect RNA in the presence of inhibitors. Under the presence of inhibitors, it was shown to detect this RNA at a comparable level with its capacity to detect DNA . [ 9 ] | https://en.wikipedia.org/wiki/Thermus_thermophilus |
These Waves of Girls is a hypermedia novella by Caitlin Fisher that won the Electronic Literature Organization 's Award for Fiction in 2001. [ 1 ] [ 2 ] The work is frequently taught in undergraduate literature courses [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] and is referenced in the field of electronic literature as a significant example of early multimodal web-based hypertext fiction, [ 9 ] [ 1 ] placing Fisher "at the forefront of digital writing". [ 10 ]
The plot of These Waves of Girls is described by Andreas Kitzmann as concerning "a young girl struggling with her sexual identity", [ 11 ] while Raine Koskimaa describes the work as "a confessional autobiography about a girl coming to terms with her lesbian identity". [ 9 ]
The "waves" of girls are "supposed to be about different moments in girlhood, different kinds of girls, different ways of discursively producing the girl. There are so many layers of stories of girls as victims, as victimisers, as cruel, as strong, as just so many different things at once", Fisher explained in a television interview in 2001. [ 12 ]
In an interview with TechTV immediately after receiving the ELO Award for These Waves of Girls , Fisher said the experience of writing with links and multiple modalities was exciting: "Writing in a hypertext environment, and working on the links as you're working on the writing, that becomes another way of writing - I think there is a new grammar to hypermedia." However, she also noted that "what I love best about traditional writing, I could keep." [ 12 ]
In 2001, publishing a story on the web was still fairly unusual. Koskimaa notes that this affects the experience of reading the work itself: "it situates itself in the huge docuverse of the Internet –even though there are no links from the work reaching outside of its self-contained whole, through the web browser functionality it is always just one click away from other documents in the Web". [ 9 ]
George Landow in his 2006 textbook, Hypertext 3.0. explains that this work is link intensive and provides navigational links as well as semantic links within the text. [ 13 ]
The hypertextual structure is what Koskimaa calls a textbook example of "associative hypertext". [ 9 ] Larry McCaffery described the linking as working in "often surprising ways that establish hidden connections that often seem to be operating on the basis of emotional, associational logic". [ 14 ]
These Waves of Girls "effectively integrates visual and audio material into a nonlinear hypertext where the reader actively determines the process of the reading experience". [ 11 ] The integration of sound and visuals through a combination of HTML and Adobe Flash was new in 2001. Colours, images and sounds (like the laughter of girls at the beginning of the piece) are integral to the narrative. Koskimaa also notes that "[s]ome of the images are mildly interactive in a way that moving the cursor over them distorts the picture like it was 'squeezed'." [ 9 ] Vertical and horizontal scrolling beyond the immediately visible part of the page in the browser are also utilised. [ 9 ]
Kitzmann writes that These Waves of Girls is "structured as a confessional autobiography that parallels, to some extent, the experience of someone reminiscing about childhood experiences while flipping through old photographs." [ 11 ] This is a common way of structuring hypertext fictions, Kitzmann writes, because it is a familiar mode of storytelling that is often characterised by the storyteller's memories being triggered by "a variety of cues, such as old photographs, comments by listeners, and random daily events". [ 11 ] Koskimaa also notes that the work uses an unreliable narrator , a familiar literary technique in fictional autobiographies. [ 9 ]
The autobiographical framing is also visible in the slightly unpolished feel of the web design. Anja Rau has criticised this in her "beta-test" of the work, where she argues that the use of frames, Flash and the embedding of sound is done in a way that "does not meet the technological standards of current internet or CD-ROM productions." [ 15 ] In an analysis of how people read electronic literature based on teaching the works in undergraduate and Masters level classes, James Pope noted that all students reading These Waves of Girls commented "that the interface design was messy and confusing, with cluttered layout, awkward navigation and nested frames creating very distracting pages". [ 16 ]
Raine Koskimaa counters this argument, saying that the unpolished style "has to be taken as a conscious choice by the author". [ 9 ] While nested frames would be unacceptable if following web design guidelines, they might "be a successful device in a hyperfictional context (..) We can interpret the instance of nested frames as a meaningful element in the work". [ 9 ]
Larry McCaffery 's description of the work in his role as judge of the fiction contest supports Koskimaa's interpretation that the unpolished web design is a meaningful narrative element. McCaffrey writes, "There is a raw energy and garish intensity to these visual features that perfectly captures the feel of childhood and adolescence." [ 14 ]
In Digital Fiction and the Unnatural , Astrid Ensslin and Alice Bell note that another aspect making These Waves of Girls difficult to read is the way links are used: "words used as hyperlinks are not always immediately indicative of the destination lexias to which they lead, so that they can inhibit rather than empower readers in their role as link chooser." [ 17 ]
Writing for the Bloomsbury Handbook of Electronic Literature , Daniel Punday argues that These Waves of Girls "locates narrativity within individual stages and sections, but eschew(s) narrative progression through these stages." [ 18 ] Like Koskimaa, Sunday sees the structure of These Waves of Girls as strongly connected to the aesthetic and culture of the web at the turn of the century. He writes, "Fisher's narrative exemplifies the way that early Web-based hypertext could tell a series of interrelated stories using a menu system that allows the reader to enter (and reenter) sections in any order. (..) [N]arrativity exists entirely within the stories narrated and alluded to within individual alexia; the overall menu structure of the text is unconnected to narrative progression." [ 18 ]
The Electronic Literature Organization awarded These Waves of Girls its fiction award in 2001. [ 19 ] The judge, Larry McCaffery , wrote: "I found myself hooked on Waves from the moment I first logged on and watched Caitlin's gorgeous graphic interface assemble itself out of images of moving clouds drifting across the screen, mingling with the sounds of girls laughing." [ 14 ] Despite this excitement, writing in 2006, James Pope notes the apparent paradox that a work so highly thought of in the field of electronic literature, and about as popular a topic as teen sexuality, "remains 'stuck' in a sort of twilight zone, apparently known only to a few insiders". [ 16 ]
The work is frequently taught in undergraduate literature courses and is referenced in the scholarship as a highly influential example of early multimodal web-based hypertext fiction. [ 20 ] Fisher is described as having "established herself at the forefront of digital writing" with These Waves of Girls and the augmented reality poem Andromeda (2008). [ 10 ] | https://en.wikipedia.org/wiki/These_Waves_of_Girls |
The theta nigrum ( lit. ' black theta ' ) or theta infelix ( lit. ' unlucky theta ' ) is a symbol of death in Greek and Latin epigraphy . [ 1 ] Isidore of Seville notes the letter was appended after the name of a deceased soldier and finds of papyri containing military records have confirmed this use. [ 1 ] Additionally it can be seen in the Gladiator Mosaic .
The term theta nigrum was coined by Theodor Mommsen . It consists of a circle with a horizontal line. The theta signified Thanatos , the Greek deity of death. [ 2 ]
This death -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Theta_nigrum |
In a polymer solution, a theta solvent (or θ solvent ) is a solvent in which polymer coils act like ideal chains , assuming exactly their random walk coil dimensions. [ clarification needed ] Therefore, the Mark–Houwink equation exponent is 1 / 2 {\displaystyle 1/2} in a theta solvent. Thermodynamically, the excess chemical potential of mixing between a polymer and a theta solvent is zero. [ 1 ] [ 2 ] [ 3 ] [ 4 ]
The conformation assumed by a polymer chain in dilute solution can be modeled as a random walk of monomer subunits using a freely jointed chain model. However, this model does not account for steric effects . Real polymer coils are more closely represented by a self-avoiding walk because conformations in which different chain segments occupy the same space are not physically possible. This excluded volume effect causes the polymer to expand.
Chain conformation is also affected by solvent quality. The intermolecular interactions between polymer chain segments and coordinated solvent molecules have an associated energy of interaction which can be positive or negative. For a good solvent , interactions between polymer segments and solvent molecules are energetically favorable, and will cause polymer coils to expand. For a poor solvent , polymer-polymer self-interactions are preferred, and the polymer coils will contract. The quality of the solvent depends on both the chemical compositions of the polymer and solvent molecules and the solution temperature.
If a solvent is precisely poor enough to cancel the effects of excluded volume expansion, the theta (θ) condition is satisfied. For a given polymer-solvent pair, the theta condition is satisfied at a certain temperature, called the theta (θ) temperature or theta point . A solvent at this temperature is called a theta solvent.
In general, measurements of the properties of polymer solutions depend on the solvent. However, when a theta solvent is used, the measured characteristics are independent of the solvent. They depend only on short-range properties of the polymer such as the bond length, bond angles, and sterically favorable rotations. The polymer chain will behave exactly as predicted by the random walk or ideal chain model. This makes experimental determination of important quantities such as the root mean square end-to-end distance or the radius of gyration much simpler.
Additionally, the theta condition is also satisfied in the bulk amorphous polymer phase . Thus, the conformations adopted by polymers dissolved in theta solvents are identical to those adopted in bulk polymer polymerization .
Thermodynamically, the excess chemical potential of mixing between a theta solvent and a polymer is zero. [ vague ] Equivalently, the enthalpy of mixing is zero, making the solution ideal . [ vague ]
One cannot measure the chemical potential by any direct means, but one can correlate it to the solution's osmotic pressure ( Π {\displaystyle \Pi } ) and the solvent's partial specific volume ( v s {\displaystyle v_{s}} ):
One can use a virial expansion to express how osmotic pressure depends on concentration:
This relationship with osmotic pressure is one way to determine the theta condition or theta temperature for a solvent.
The change in the chemical potential when the two are mixed has two terms: ideal and excess:
The second virial coefficient, B, is proportional to the excess chemical potential of mixing:
B reflects the energy of binary interactions between solvent molecules and segments of polymer chain. When B > 0, the solvent is "good," and when B < 0, the solvent is "poor". For a theta solvent, the second virial coefficient is zero because the excess chemical potential is zero; otherwise it would fall outside the definition of a theta solvent. A solvent at its theta temperature is, in this way, analogous to a real gas at its Boyle temperature .
Similar relationships exist for other experimental techniques , including light scattering , intrinsic viscosity measurement, sedimentation equilibrium , and cloud point titration . | https://en.wikipedia.org/wiki/Theta_solvent |
Thevetins are a group of poisonous cardiac glycosides . They are obtained especially from the seeds of a West Indian shrub or small tree ( Cascabela thevetia syn. Thevetia nereifolia ) of the dogbane family ( Apocynaceae ). [ 1 ] Hydrolysis products include glucose , digitalose , and a sterol . [ 1 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thevetin |
In chemistry, thiadiazoles are a sub-family of azole compounds, with the name thiadiazole originating from the Hantzsch–Widman nomenclature . Structurally, they are five-membered heterocyclic compounds containing one sulfur and two nitrogen atoms. The ring is aromatic by virtue of the two double bonds and one of the lone pairs of electrons of sulfur. Four constitutional isomers are possible, differing by the relative positions of the sulfur and nitrogen atoms. The nomenclature thus includes the locations of each of those three atoms, with the first of the three numbers referring to the sulfur.
The parent compounds are rarely synthesized and possess no particular application, however, compounds bearing them as a structural motif are fairly common in pharmacology . Of them, 1,3,4-thiadiazole is the most common, appearing in such medications as cephazolin and acetazolamide . [ 1 ] [ 2 ] [ 3 ]
3,4-Dichloro-1,2,5-thiadiazole arises readily from cyanogen .
In the Hurd–Mori reaction , an acyl hydrazone reacts with thionyl chloride to give a 1,2,3-thiadiazole. [ 4 ] | https://en.wikipedia.org/wiki/Thiadiazoles |
In organic chemistry , a thial or thioaldehyde is a functional group which is similar to an aldehyde , RC(O)H , in which a sulfur (S) atom replaces the oxygen (O) atom of the aldehyde (R represents an alkyl or aryl group). Thioaldehydes are even more reactive than thioketones . Unhindered thioaldehydes are generally too reactive to be isolated — for example, thioformaldehyde , H 2 C=S , condenses to the cyclic trimer 1,3,5-trithiane . Thioacrolein, H 2 C=CHCH=S , formed by decomposition of allicin from garlic , undergoes a self Diels-Alder reaction giving isomeric vinyldithiins . [ 1 ] [ 2 ] While thioformaldehyde is highly reactive, it is found in interstellar space along with its mono- and di-deuterated isotopologues . [ 3 ] With sufficient steric bulk, however, stable thioaldehydes can be isolated. [ 4 ]
In early work, the existence of thioaldehydes was inferred by trapping processes. For instance the reaction of Fc 2 P 2 S 4 with benzaldehyde was proposed to form thiobenzaldehyde, which forms a cycloadduct with the dithiophosphine ylides to form a C 2 PS 3 ring. [ 5 ] | https://en.wikipedia.org/wiki/Thial |
Thiamine triphosphate (ThTP) is a biomolecule found in most organisms including bacteria , fungi , plants and animals . [ 1 ] Chemically, it is the triphosphate derivative of the vitamin thiamine .
It has been proposed that ThTP has a specific role in nerve excitability, [ 2 ] but this has never been confirmed and recent results suggest that ThTP probably plays a role in cell energy metabolism. [ 1 ] [ 3 ] Low or absent levels of thiamine triphosphate have been found in Leigh's disease . [ 4 ] [ 5 ]
In E. coli , ThTP is accumulated in the presence of glucose during amino acid starvation. [ 1 ] [ 3 ] On the other hand, suppression of the carbon source leads to the accumulation, of adenosine thiamine triphosphate (AThTP).
It has been shown that in brain ThTP is synthesized in mitochondria by a chemiosmotic mechanism , perhaps similar to ATP synthase . [ 6 ] In mammals , ThTP is hydrolyzed to thiamine pyrophosphate (ThDP) by a specific thiamine-triphosphatase . [ 3 ] [ 7 ] It can also be converted into ThDP by thiamine-diphosphate kinase .
Thiamine triphosphate (ThTP) was chemically synthesized in 1948 at a time when the only organic triphosphate known was ATP. [ 8 ] The first claim of the existence of ThTP in living organisms was made in rat liver, [ 9 ] followed by baker’s yeast. [ 10 ] Its presence was later confirmed in rat tissues [ 11 ] and in plants germs, but not in seeds, where thiamine was essentially unphosphorylated . [ 12 ] In all those studies, ThTP was separated from other thiamine derivatives using a paper chromatographic method, followed by oxidation in fluorescent thiochrome compounds with ferricyanide in alkaline solution. This method is at best semi-quantitative, and the development of liquid chromatographic methods suggested that ThTP represents far less than 10% of total thiamine in animal tissues. [ 13 ] | https://en.wikipedia.org/wiki/Thiamine_triphosphate |
Electroluminescence ( EL ) is an optical and electrical phenomenon , in which a material emits light in response to the passage of an electric current or to a strong electric field . This is distinct from black body light emission resulting from heat ( incandescence ), chemical reactions ( chemiluminescence ), reactions in a liquid ( electrochemiluminescence ), sound ( sonoluminescence ), or other mechanical action ( mechanoluminescence ), or
organic electroluminescence.
Electroluminescence is the result of radiative recombination of electrons and holes in a material, usually a semiconductor . The excited electrons release their energy as photons – light. Prior to recombination, electrons and holes may be separated either by doping the material to form a p-n junction (in semiconductor electroluminescent devices such as light-emitting diodes ) or through excitation by impact of high-energy electrons accelerated by a strong electric field (as with the phosphors in electroluminescent displays ).
It has been recently shown that as a solar cell improves its light-to-electricity efficiency (improved open-circuit voltage), it will also improve its electricity-to-light (EL) efficiency. [ 1 ]
Electroluminescent technologies have low power consumption compared to competing lighting technologies, such as neon or fluorescent lamps. This, together with the thinness of the material, has made EL technology valuable to the advertising industry. Relevant advertising applications include electroluminescent billboards and signs. EL manufacturers can control precisely which areas of an electroluminescent sheet illuminate, and when. This has given advertisers the ability to create more dynamic advertising that is still compatible with traditional advertising spaces.
An EL film is a so-called Lambertian radiator : unlike with neon lamps, filament lamps, or LEDs, the brightness of the surface appears the same from all angles of view; electroluminescent light is not directional. The light emitted from the surface is perfectly homogeneous and is well-perceived by the eye. EL film produces single-frequency (monochromatic) light that has a very narrow bandwidth, is uniform and visible from a great distance.
In principle, EL lamps can be made in any color. However, the commonly used greenish color closely matches the peak sensitivity of human vision, producing the greatest apparent light output for the least electrical power input. Unlike neon and fluorescent lamps, EL lamps are not negative resistance devices so no extra circuitry is needed to regulate the amount of current flowing through them. A new technology now being used is based on multispectral phosphors that emit light from 600 to 400 nm depending on the drive frequency; this is similar to the color-changing effect seen with aqua EL sheet but on a larger scale.
Electroluminescent devices are fabricated using either organic or inorganic electroluminescent materials. The active materials are generally semiconductors of wide enough bandwidth to allow the exit of the light.
The most typical inorganic thin-film EL (TFEL) is ZnS:Mn with yellow-orange emission. Examples of the range of EL material include:
The most common electroluminescent (EL) devices are composed of either powder (primarily used in lighting applications) or thin films (for information displays.)
Light-emitting capacitor , or LEC , is a term used since at least 1961 [ 3 ] to describe electroluminescent panels. General Electric has patents dating to 1938 on flat electroluminescent panels that are still made as night lights and backlights for instrument panel displays. Electroluminescent panels are a capacitor where the dielectric between the outside plates is a phosphor that gives off photons when the capacitor is charged. By making one of the contacts transparent, the large area exposed emits light. [ 4 ]
Electroluminescent automotive instrument panel backlighting, with each gauge pointer also an individual light source, entered production on 1960 Chrysler and Imperial passenger cars, and was continued successfully on several Chrysler vehicles through 1967 and marketed as "Panelescent Lighting".
The Sylvania Lighting Division in Salem and Danvers, Massachusetts , produced and marketed an EL night light, under the trade name Panelescent at roughly the same time that the Chrysler instrument panels entered production. These lamps have proven extremely reliable, with some samples known to be still functional after nearly 50 years of continuous operation. [ when? ]
Later in the 1960s, Sylvania's Electronic Systems Division in Needham, Massachusetts developed and manufactured several instruments for the Apollo Lunar Module and Command Module using electroluminescent display panels manufactured by the Electronic Tube Division of Sylvania at Emporium, Pennsylvania . Raytheon in Sudbury, Massachusetts manufactured the Apollo Guidance Computer , which used a Sylvania electroluminescent display panel as part of its display-keyboard interface ( DSKY ).
Powder phosphor-based electroluminescent panels are frequently used as backlights for liquid crystal displays . They readily provide gentle, even illumination for the entire display while consuming relatively little electric power. This makes them convenient for battery-operated devices such as pagers, wristwatches, and computer-controlled thermostats, and their gentle green-cyan glow is common in the technological world.
EL backlights require relatively high voltage (between 60 and 600 volts). [ 5 ] For battery-operated devices, this voltage must be generated by a boost converter circuit within the device. This converter often makes a faintly audible whine or siren sound while the backlight is activated. Line-voltage-operated devices may be activated directly from the power line; some electroluminescent nightlights operate in this fashion. Brightness per unit area increases with increased voltage and frequency. [ 5 ]
Thin-film phosphor electroluminescence was first commercialized during the 1980s by Sharp Corporation in Japan, Finlux (Oy Lohja Ab) in Finland, and Planar Systems in the US. In these devices, bright, long-life light emission is achieved in thin-film yellow-emitting manganese-doped zinc sulfide material. Displays using this technology were manufactured for medical and vehicle applications where ruggedness and wide viewing angles were crucial, and liquid crystal displays were not well developed. In 1992, Timex introduced its Indiglo EL display on some watches.
Recently, [ when? ] blue-, red-, and green-emitting thin film electroluminescent materials that offer the potential for long life and full-color electroluminescent displays have been developed.
The EL material must be enclosed between two electrodes and at least one electrode must be transparent to allow the escape of the produced light. Glass coated with indium tin oxide is commonly used as the front (transparent) electrode, while the back electrode is coated with reflective metal. Additionally, other transparent conducting materials, such as carbon nanotube coatings or PEDOT can be used as the front electrode.
The display applications are primarily passive (i.e., voltages are driven from the edge of the display cf. driven from a transistor on the display). Similar to LCD trends, there have also been Active Matrix EL (AMEL) displays demonstrated, where the circuitry is added to prolong voltages at each pixel. The solid-state nature of TFEL allows for a very rugged and high-resolution display fabricated even on silicon substrates. AMEL displays of 1280×1024 at over 1000 lines per inch (LPI) have been demonstrated by a consortium including Planar Systems. [ 6 ] [ 7 ]
Thick-film dielectric electroluminescent technology ( TDEL ) is a phosphor -based flat panel display technology developed by Canadian company iFire Technology Corp. TDEL is based on inorganic electroluminescent (IEL) technology that combines both thick-and thin-film processes. [ 8 ] The TDEL structure is made with glass or other substrates, consisting of a thick-film dielectric layer and a thin-film phosphor layer sandwiched between two sets of electrodes to create a matrix of pixels. Inorganic phosphors within this matrix emit light in the presence of an alternating electric field.
Color By Blue (CBB) was developed in 2003. [ 9 ] The Color By Blue process achieves higher luminance and better performance than the previous triple pattern process, with increased contrast, grayscale rendition, and color uniformity across the panel. Color By Blue is based on the physics of photoluminescence . High luminance inorganic blue phosphor is used in combination with specialized color conversion materials, which absorb the blue light and re-emit red or green light, to generate the other colors.
Electroluminescent lighting is now used as an application for public safety identification involving alphanumeric characters on the roof of vehicles for clear visibility from an aerial perspective. [ 10 ]
Electroluminescent lighting, especially electroluminescent wire (EL wire), has also made its way into clothing as many designers have brought this technology to the entertainment and nightlife industry. [ 11 ] From 2006, t-shirts with an electroluminescent panel stylized as an audio equalizer , the T-Qualizer, saw a brief period of popularity. [ 12 ]
Engineers have developed an electroluminescent "skin" that can stretch more than six times its original size while still emitting light. This hyper-elastic light-emitting capacitor (HLEC) can endure more than twice the strain of previously tested stretchable displays. It consists of layers of transparent hydrogel electrodes sandwiching an insulating elastomer sheet. The elastomer changes luminance and capacitance when stretched, rolled, and otherwise deformed. In addition to its ability to emit light under a strain of greater than 480% of its original size, the group's HLEC was shown to be capable of being integrated into a soft robotic system. Three six-layer HLEC panels were bound together to form a crawling soft robot, with the top four layers making up the light-up skin and the bottom two the pneumatic actuators. The discovery could lead to significant advances in health care, transportation, electronic communication and other areas. [ 13 ] | https://en.wikipedia.org/wiki/Thick-film_dielectric_electroluminescent_technology |
Thick-skinned deformation is a geological term which refers to crustal shortening that involves basement rocks and deep-seated faults as opposed to only the upper units of cover rocks above the basement which is known as thin-skinned deformation. While thin-skinned deformation is common in many different localities, thick-skinned deformation requires much more strain to occur and is a rarer type of deformation.
Different processes can deform rocks, the deformation is almost always the result of stress . This stress leads to the formation of fault and fold structures, both can either extend or shorten of the Earth's crust. Thick-skinned deformation specifically affects deep crystalline rock of the basement and may extend deeper into the lower crust. Thin-skinned deformation affects the upper crustal layers and does not deform the deeper basement. [ 1 ]
Thick-skinned deformation is most commonly a result of crustal shortening and occurs when the region is undergoing horizontal compression. This frequently occurs in at the sites of continental collisions where orogenesis , or mountain building, is taking place and during which the crust is shortened horizontally and thickened vertically. [ 2 ] The massive compressional forces involved in such a collision cause the basement rock and all of the units above it to deform. Deformation occurs in the form of both folds and thrust faults and may form a fold and thrust belt along the collisional zone or as crustal flow. [ 1 ]
At convergent plate boundaries two plates move towards each other as one is subducted downwards beneath the other but when the crust of two continents meet at a convergent zone neither one of them will be subducted due to their low density. As the two continents are pushed together by tectonic processes a large amount of stress is put on the rock. Eventually deformation will occur in one or multiple ways in order to relieve the stress.
Folding usually occurs in areas with a very slow strain rate or when the rock being deformed is relatively weak and ductile. As folding occurs the units of rock bend forming anticlines, ridges, and synclines, valleys. While the true thickness of the underlying crust may not be equal to the elevation changes of the resulting mountains and hills, the average crustal thickness is greater than before the deformation occurred. One way in which folding can occur in such a formation is by a small amount of subduction of one plate. One continent may be partially overridden by the other but since the plate is far too light to sink it will uplift the overriding plate creating very large folds that deform the entire crust.
Thrust faults are another common form of deformation to occur in these areas. Faulting is generally the result of greater strain rates and stronger or more brittle rocks. These faults have a high angle and cause thickening by uplifting the rock onto itself. These types of faults are identified by the vertically repeating stratigraphy that they produce. During a collision when the strain reaches the breaking point of the rock a fracture will form in the rock. This fracture cuts across layers of rock to form a ramp which will allow movement to dissipate the accumulated strain. Under compression the upper hanging wall rises and overrides the lower foot wall.
The final type of deformation is crustal flow. This type of deformation is only able to occur when the crustal material is heated to a very high temperature, approximately 2/3 of its melting temperature. When this occurs in a collisional zone then the rock can be deformed by creep and will behave similarly to a fluid over the long periods of geologic time. [ 3 ] | https://en.wikipedia.org/wiki/Thick-skinned_deformation |
Thiele/Small parameters (commonly abbreviated T/S parameters, or TSP) are a set of electromechanical parameters that define the specified low frequency performance of a loudspeaker driver . These parameters are published in specification sheets by driver manufacturers so that designers have a guide in selecting off-the-shelf drivers for loudspeaker designs. Using these parameters, a loudspeaker designer may simulate the position, velocity and acceleration of the diaphragm, the input impedance and the sound output of a system comprising a loudspeaker and enclosure. Many of the parameters are strictly defined only at the resonant frequency, but the approach is generally applicable in the frequency range where the diaphragm motion is largely pistonic, i.e., when the entire cone moves in and out as a unit without cone breakup.
Rather than purchase off-the-shelf components, loudspeaker design engineers often define desired performance and work backwards to a set of parameters and manufacture a driver with said characteristics or order it from a driver manufacturer. This process of generating parameters from a target response is known as synthesis. Thiele/Small parameters are named after A. Neville Thiele of the Australian Broadcasting Commission , and Richard H. Small of the University of Sydney , who pioneered this line of analysis for loudspeakers. A common use of Thiele/Small parameters is in designing PA system and hi-fi speaker enclosures ; the TSP calculations indicate to the speaker design professionals how large a speaker cabinet will need to be and how large and long the bass reflex port (if it is used) should be.
The 1925 paper [ 1 ] of Chester W. Rice and Edward W. Kellogg , fueled by advances in radio and electronics, increased interest in direct radiator loudspeakers. In 1930, A. J. Thuras of Bell Labs patented (US Patent No. 1869178) his "Sound Translating Device" (essentially a vented box) which was evidence of the interest in many types of enclosure design at the time.
Progress on loudspeaker enclosure design and analysis using acoustic analogous circuits by academic acousticians like Harry F. Olson continued in the 1940s. In 1952, Bart N. Locanthi developed equivalent electrical models of common loudspeaker configurations. [ 2 ] In 1954 when Leo L. Beranek of the Massachusetts Institute of Technology published Acoustics , [ 3 ] a book summarizing and extending the electroacoustics of the era. J. F. Novak used novel simplifying assumptions in an analysis in a 1959 paper [ 4 ] [ 5 ] which led to a practical solution for the response of a given loudspeaker in sealed and vented boxes, and also established their applicability by empirical measurement. In 1961, leaning heavily on Novak's work, A. N. Thiele described a series of sealed and vented box "alignments" (i.e., enclosure designs based on electrical filter theory with well-characterized behavior, including frequency response, power handling, cone excursion, etc.) in a publication in an Australian journal. [ 6 ] This paper remained relatively unknown outside Australia until it was re-published in the Journal of the Audio Engineering Society in 1971. [ 7 ] [ 8 ] It is important to note that Thiele's work neglected enclosure losses and, although the application of filter theory is still important, his alignment tables now have little real-world utility due to neglecting enclosure losses.
Many others continued to develop various aspects of loudspeaker enclosure design in the 1960s and early 1970s. From 1968 to 1972, J. E. Benson published three articles [ 9 ] in an Australian journal that thoroughly analyzed sealed , vented and passive radiator designs, all using the same basic model, which included the effects of enclosure, leakage and port losses. Beginning in June 1972, Richard H. Small published a series of very influential articles on direct radiator loudspeaker system analysis, [ 10 ] including closed-box, [ 11 ] [ 12 ] vented-box, [ 13 ] [ 14 ] [ 15 ] [ 16 ] and passive-radiator [ 17 ] [ 18 ] loudspeaker systems, in the Journal of the Audio Engineering Society , restating and extending Thiele's work. These articles were also originally published in Australia, where he had attended graduate school, and where his thesis supervisor was J. E. Benson. The work of Benson and Small overlapped considerably, but differed in that Benson performed his work using computer programs and Small used analog simulators . Small also analyzed the systems including enclosure losses. Richard H. Small and Garry Margolis, the latter of JBL , published an article in the Journal of the Audio Engineering Society (June 1981), [ 19 ] which recast much of the work that had been published up till then into forms suited to the programmable calculators of the time.
These are the physical parameters of a loudspeaker driver, as measured at small signal levels, used in the equivalent electrical circuit models. Some of these values are neither easy nor convenient to measure in a finished loudspeaker driver, so when designing speakers using existing drive units (which is almost always the case), the more easily measured parameters listed under Small Signal Parameters are more practical:
These values can be determined by measuring the input impedance of the driver, near the resonance frequency, at small input levels for which the mechanical behavior of the driver is effectively linear (i.e., proportional to its input). These values are more easily measured than the fundamental ones above. The small signal parameters are:
These parameters are useful for predicting the approximate output of a driver at high input levels, though they are harder, sometimes extremely hard or impossible, to accurately measure. In addition, power compression , thermal, and mechanical effects due to high signal levels (e.g., high electric current and voltage, extended mechanical motion, and so on) all change driver behavior, often increasing distortion of several kinds:
Some caution is required when using and interpreting T/S parameters. Individual units may not match manufacturer specifications. Parameters values are almost never individually taken, but are at best averages across a production run, due to inevitable manufacturing variations. Driver characteristics will generally lie within a (sometimes specified) tolerance range. C m s {\displaystyle C_{\rm {ms}}} is the least controllable parameter, but typical variations in C m s {\displaystyle C_{\rm {ms}}} do not have large effects on the final response. [ 25 ]
It is also important to understand that most T/S parameters are linearized small signal values. An analysis based on them is an idealized view of driver behavior, since the actual values of these parameters vary in all drivers according to drive level, voice coil temperature, over the life of the driver, etc. C m s {\displaystyle C_{\rm {ms}}} decreases the farther the coil moves from rest. B l {\displaystyle Bl} is generally maximum at rest, and drops as the voice coil approaches X m a x {\displaystyle X_{\rm {max}}} . R e {\displaystyle R_{\rm {e}}} increases as the coil heats and the value will typically double by 270 °C (exactly 266 °C for Cu and 254 °C for Al), at which point many voice coils are approaching (or have already reached) thermal failure.
As an example, f s {\displaystyle f_{\rm {s}}} and V a s {\displaystyle V_{\rm {as}}} may vary considerably with input level, due to nonlinear changes in C m s {\displaystyle C_{\rm {ms}}} . A typical 110-mm diameter full-range driver with an f s {\displaystyle f_{\rm {s}}} of 95 Hz at 0.5 V signal level, might drop to 64 Hz when fed a 5 V input. A driver with a measured V a s {\displaystyle V_{\rm {as}}} of 7 L at 0.5 V, may show a V a s {\displaystyle V_{\rm {as}}} increase to 13 L when tested at 4 V. Q m s {\displaystyle Q_{\rm {ms}}} is typically stable within a few percent, regardless of drive level. Q e s {\displaystyle Q_{\rm {es}}} and Q t s {\displaystyle Q_{\rm {ts}}} decrease <13% as the drive level rises from 0.5 V to 4 V, due to the changes in B l {\displaystyle Bl} . Because V a s {\displaystyle V_{\rm {as}}} can rise significantly and f s {\displaystyle f_{\rm {s}}} can drop considerably, with a trivial change in measured M m s {\displaystyle M_{\rm {ms}}} , the calculated sensitivity value ( η 0 {\displaystyle \eta _{0}} ) can appear to drop by >30% as the level changes from 0.5 V to 4 V. Of course, the driver's actual sensitivity has not changed at all, but the calculated sensitivity is correct only under some specific conditions. From this example, it is seen that the measurements to be preferred while designing an enclosure or system are those likely to represent typical operating conditions. Unfortunately, this level must be arbitrary, since the operating conditions are continually changing when reproducing music. Level-dependent nonlinearities typically cause lower than predicted output, or small variations in frequency response.
Level shifts caused by resistive heating of the voice coil are termed power compression . Design techniques which reduce nonlinearities may also reduce power compression, and possibly distortions not caused by power compression. There have been several commercial designs that have included cooling arrangements for driver magnetic structures, which are intended to mitigate voice coil temperature rise, and the attendant rise in resistance that is the cause of the power compression. Elegant magnet and coil designs have been used to linearize B l {\displaystyle Bl} and reduce the value and modulation of L e {\displaystyle L_{\rm {e}}} . Large, linear spiders can increase the linear range of C m s {\displaystyle C_{\rm {ms}}} , but the large signal values of B l {\displaystyle Bl} and C m s {\displaystyle C_{\rm {ms}}} must be balanced to avoid dynamic offset.
The mechanical components in typical speaker drivers may change over time. Paper, a popular material in cone fabrication, absorbs moisture easily and unless treated may lose some structural rigidity over time. This may be reduced by coating with water-impregnable material such as various plastic resins. Cracks compromise structural rigidity and if large enough are generally non-repairable. Temperature has a strong, generally reversible effect; typical suspension materials become stiffer at lower temperatures. The suspension experiences fatigue , and also undergoes changes from chemical and environmental effects associated with aging such as exposure to ultraviolet light, and oxidation which affect foam and natural rubber components badly, though butyl, nitrile, SBR rubber, and rubber-plastic alloys (such as Santoprene ) are more stable. The polyester type of polyurethane foam is highly prone to disintegration after 10 to 15 years. The changes in behavior from aging may often be positive, though since the environment that they are used in is a major factor the effects are not easily predicted. Gilbert Briggs, founder of Wharfedale Loudspeakers in the UK, undertook several studies of aging effects in speaker drivers in the 1950s and 1960s, publishing some of the data in his books, notably Loudspeakers: The Why and How of Good Reproduction . [ 26 ]
There are also mechanical changes which occur in the moving components during use. [ 27 ] [ 28 ] In this case, however, most of the changes seem to occur early in the life of the driver, and are almost certainly due to relaxation in flexing mechanical parts of the driver (e.g., surround, spider, etc.). Several studies have been published documenting substantial changes in the T/S parameters over the first few hours of use, some parameters changing by as much as 15% or more over these initial periods. The proprietor of the firm GR Research has publicly reported several such investigations of several manufacturers' drivers. Other studies suggest little change, or reversible changes after only the first few minutes. This variability is largely related to the particular characteristics of specific materials, and reputable manufacturers attempt to take them into account. While there are a great many anecdotal reports of the audible effects of such changes in published speaker reviews, the relationship of such early changes to subjective sound quality reports is not completely clear. Some changes early in driver life are complementary (such as a reduction in f s {\displaystyle f_{\rm {s}}} accompanied by a rise in V a s {\displaystyle V_{\rm {as}}} ) and result in minimal net changes (small fractions of a dB) in frequency response. If the performance of speaker system is critical, as with high order (complex) or heavily equalized systems, it is sensible to measure T/S parameters after a period of run-in (some hours, typically, using program material), and to model the effects of normal parameter changes on driver performance.
There are numerous methods to measure Thiele-Small parameters, but the simplest use the input impedance of the driver, measured near resonance. The impedance may be measured in free air (with the driver unhoused and either clamped to a fixture or hanging from a wire, or sometimes resting on the magnet on a surface) and/or in test baffles, sealed or vented boxes or with varying amounts of mass added to the diaphragm. Noise in the measurement environment can have an effect on the measurement, so one should measure parameters in a quiet acoustic environment.
The most common ( DIY -friendly) method before the advent of computer-controlled measurement techniques is the classic free air constant current method, described by Thiele in 1961. This method uses a large resistance (e.g., R t e s t {\displaystyle R_{\rm {test}}} = 500 to 1000 ohms ) in series with the driver and a signal generator is used to vary the excitation frequency. The voltage across the loudspeaker terminals is measured and considered proportional to the impedance. It is assumed that variations in loudspeaker impedance will have little effect on the current through the loudspeaker. This is an approximation, and the method results in Q {\displaystyle Q} measurement errors for drivers with a high Z m a x {\displaystyle Z_{\rm {max}}} – the measured value of Z m a x {\displaystyle Z_{\rm {max}}} will always be somewhat low. This measurement can be corrected by measuring the total voltage across the calibration resistor and the driver (call this V {\displaystyle V} ) at resonance and calculating the actual test current I = V / ( R t e s t + Z m a x ) {\displaystyle I=V/(R_{\rm {test}}+Z_{\rm {max}})} . You may then obtain a corrected Z m a x {\displaystyle Z_{\rm {max}}} = Z m a x ( u n c o r r e c t e d ) × R t e s t / I {\displaystyle Z_{\rm {max(uncorrected)}}\times R_{\rm {test}}/I} .
A second method is the constant voltage measurement, where the driver is excited by a constant voltage, and the current passing through the coil is measured. The excitation voltage divided by the measured current equals the impedance.
A common source of error using these first two methods is the use of inexpensive AC voltage meters. Most inexpensive meters are designed to measure residential power frequencies (50–60 Hz) and are increasingly inaccurate at other frequencies (e.g., below 40 Hz or above a few hundred hertz). In addition, distorted or non–sine wave signals can cause measurement inaccuracies. Inexpensive voltmeters are also not very accurate or precise at measuring current and can introduce appreciable series resistance, which causes measurement errors.
A third method is a response to the deficiencies of the first two methods. It uses a smaller (e.g., 10 ohm) series resistor and measurements are made of the voltage across the driver, the signal generator, and/or series resistor for frequencies around resonance. Although tedious, and not often used in manual measurements, simple calculations exist which allow the true impedance magnitude and phase to be determined. This is the method used by many computer loudspeaker measurement systems. When this method is used manually, the result of taking the three measurements is that their ratios are more important than their actual value, removing the effect of poor meter frequency response. | https://en.wikipedia.org/wiki/Thiele/Small_parameters |
The Thiele modulus was developed by Ernest Thiele in his paper 'Relation between catalytic activity and size of particle' in 1939. [ 1 ] Thiele reasoned that a large enough particle has a reaction rate so rapid that diffusion forces can only carry the product away from the surface of the catalyst particle . Therefore, only the surface of the catalyst would experience any reaction.
The Thiele Modulus was developed to describe the relationship between diffusion and reaction rates in porous catalyst pellets with no mass transfer limitations. This value is generally used to measure the effectiveness factor of pellets.
The Thiele modulus is represented by different symbols in different texts, but is defined in Hill [ 2 ] as h T .
The derivation of the Thiele Modulus (from Hill) begins with a material balance on the catalyst pore . For a first-order irreversible reaction in a straight cylindrical pore at steady state:
π r 2 ( − D c d C d x ) x = π r 2 ( − D c d C d x ) x + Δ x + ( 2 π r Δ x ) ( k 1 C ) {\displaystyle {\pi }r^{2}\left(-D_{c}{\frac {dC}{dx}}\right)_{x}={\pi }r^{2}\left(-D_{c}{\frac {dC}{dx}}\right)_{x+{\Delta }x}+\left(2{\pi }r{\Delta }x\right)\left(k_{1}C\right)}
where D c {\displaystyle D_{c}} is a diffusivity constant , and k 1 {\displaystyle k_{1}} is the rate constant .
Then, turning the equation into a differential by dividing by Δ x {\displaystyle {\Delta }x} and taking the limit as Δ x {\displaystyle {\Delta }x} approaches 0,
D c ( d 2 C d x 2 ) = 2 k 1 C r {\displaystyle D_{c}\left({\frac {d^{2}C}{dx^{2}}}\right)={\frac {2k_{1}C}{r}}}
This differential equation with the following boundary conditions :
C = C o at x = 0 {\displaystyle C=C_{o}{\text{ at }}x=0}
and
d C d x = 0 at x = L {\displaystyle {\frac {dC}{dx}}=0{\text{ at }}x=L}
where the first boundary condition indicates a constant external concentration on one end of the pore and the second boundary condition indicates that there is no flow out of the other end of the pore.
Plugging in these boundary conditions, we have
d 2 C d ( x / L ) 2 = ( 2 k 1 L 2 r D c ) C {\displaystyle {\frac {d^{2}C}{d(x/L)^{2}}}=\left({\frac {2k_{1}L^{2}}{rD_{c}}}\right)C}
The term on the right side multiplied by C represents the square of the Thiele Modulus, which we now see rises naturally out of the material balance. Then the Thiele modulus for a first order reaction is:
h T 2 = 2 k 1 L 2 r D c {\displaystyle h_{T}^{2}={\frac {2k_{1}L^{2}}{rD_{c}}}}
From this relation it is evident that with large values of h T {\displaystyle h_{T}} , the rate term dominates and the reaction is fast, while slow diffusion limits the overall rate. Smaller values of the Thiele modulus represent slow reactions with fast diffusion.
Other order reactions may be solved in a similar manner as above. The results are listed below for irreversible reactions in straight cylindrical pores.
h 2 2 = 2 L 2 k 2 C o r D c {\displaystyle h_{2}^{2}={\frac {2L^{2}k_{2}C_{o}}{rD_{c}}}}
h o 2 = 2 L 2 k o r D c C o {\displaystyle h_{o}^{2}={\frac {2L^{2}k_{o}}{rD_{c}C_{o}}}}
The effectiveness factor η relates the diffusive reaction rate with the rate of reaction in the bulk stream.
For a first order reaction in a slab geometry, [ 1 ] [ 3 ] this is:
η = tanh h T h T {\displaystyle {\eta }={\frac {\tanh h_{T}}{h_{T}}}} | https://en.wikipedia.org/wiki/Thiele_modulus |
1,4-Benzoquinone , commonly known as para -quinone , is a chemical compound with the formula C 6 H 4 O 2 . In a pure state, it forms bright-yellow crystals with a characteristic irritating odor, resembling that of chlorine , bleach , and hot plastic or formaldehyde. This six-membered ring compound is the oxidized derivative of 1,4- hydroquinone . [ 4 ] The molecule is multifunctional: it exhibits properties of a ketone , being able to form oximes ; an oxidant, forming the dihydroxy derivative; and an alkene, undergoing addition reactions, especially those typical for α,β-unsaturated ketones . 1,4-Benzoquinone is sensitive toward both strong mineral acids and alkali, which cause condensation and decomposition of the compound. [ 5 ] [ 6 ]
1,4-Benzoquinone is prepared industrially by oxidation of hydroquinone , which can be obtained by several routes. One route involves oxidation of diisopropylbenzene and the Hock rearrangement . The net reaction can be represented as follows:
The reaction proceeds via the bis( hydroperoxide ) and the hydroquinone. Acetone is a coproduct. [ 7 ]
Another major process involves the direct hydroxylation of phenol by acidic hydrogen peroxide :
C 6 H 5 OH + H 2 O 2 → C 6 H 4 (OH) 2 + H 2 O
Both hydroquinone and catechol are produced. Subsequent oxidation of the hydroquinone gives the quinone. [ 8 ]
Quinone was originally prepared industrially by oxidation of aniline , for example by manganese dioxide . [ 9 ] This method is mainly practiced in PRC where environmental regulations are more relaxed.
Oxidation of hydroquinone is facile. [ 4 ] [ 10 ] One such method makes use of hydrogen peroxide as the oxidizer and iodine or an iodine salt as a catalyst for the oxidation occurring in a polar solvent ; e.g. isopropyl alcohol . [ 11 ]
When heated to near its melting point, 1,4-benzoquinone sublimes , even at atmospheric pressure, allowing for an effective purification. Impure samples are often dark-colored due to the presence of quinhydrone, a dark green 1:1 charge-transfer complex of quinone with hydroquinone . [ 12 ]
Benzoquinone is a planar molecule with localized, alternating C=C, C=O, and C–C bonds. Reduction gives the semiquinone anion C 6 H 4 O 2 − }, which adopts a more delocalized structure. Further reduction coupled to protonation gives the hydroquinone, wherein the C6 ring is fully delocalized. [ 13 ]
Quinone is mainly used as a precursor to hydroquinone, which is used in photography and rubber manufacture as a reducing agent and antioxidant. [ 8 ] Benzoquinonium is a skeletal muscle relaxant, ganglion blocking agent that is made from benzoquinone. [ 14 ]
It is used as a hydrogen acceptor and oxidant in organic synthesis . [ 15 ] 1,4-Benzoquinone serves as a dehydrogenation reagent. It is also used as a dienophile in Diels Alder reactions. [ 16 ]
Benzoquinone reacts with acetic anhydride and sulfuric acid to give the triacetate of hydroxyquinol . [ 17 ] [ 18 ] This reaction is called the Thiele reaction or Thiele–Winter reaction [ 19 ] [ 20 ] after Johannes Thiele , who first described it in 1898, and after Ernst Winter, who further described its reaction mechanism in 1900. An application is found in this step of the total synthesis of Metachromin A: [ 21 ]
Benzoquinone is also used to suppress double-bond migration during olefin metathesis reactions.
An acidic potassium iodide solution reduces a solution of benzoquinone to hydroquinone, which can be reoxidized back to the quinone with a solution of silver nitrate .
Due to its ability to function as an oxidizer, 1,4-benzoquinone can be found in methods using the Wacker-Tsuji oxidation , wherein a palladium salt catalyzes the conversion of an alkene to a ketone. This reaction is typically carried out using pressurized oxygen as the oxidizer, but benzoquinone can sometimes preferred. It is also used as a reagent in some variants on Wacker oxidations .
1,4-Benzoquinone is used in the synthesis of Bromadol and related analogs.
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) is a stronger oxidant and dehydrogenation agent than 1,4-benzoquinone. [ 23 ] Chloranil 1,4-C 6 Cl 4 O 2 is another potent oxidant and dehydrogenation agent. Monochloro-p-benzoquinone is yet another but milder oxidant. [ 24 ]
1,4-Benzoquinone is a toxic metabolite found in human blood and can be used to track exposure to benzene or mixtures containing benzene and benzene compounds, such as petrol. [ 25 ] The compound can interfere with cellular respiration, and kidney damage has been found in animals receiving severe exposure. It is excreted in its original form and also as variations of its own metabolite, hydroquinone. [ 9 ]
1,4-Benzoquinone is able to stain skin dark brown, cause erythema (redness, rashes on skin) and lead on to localized tissue necrosis . It is particularly irritating to the eyes and respiratory system. Its ability to sublime at commonly encountered temperatures allows for a greater airborne exposure risk than might be expected for a room-temperature solid. IARC has found insufficient evidence to comment on the compound's carcinogenicity, but has noted that it can easily pass into the bloodstream and that it showed activity in depressing bone marrow production in mice and can inhibit protease enzymes involved in cellular apoptosis . [ 9 ] | https://en.wikipedia.org/wiki/Thiele_reaction |
Thienamycin (also known as thienpenem ) is one of the most potent naturally produced antibiotics known thus far, discovered in Streptomyces cattleya in 1976. Thienamycin has excellent activity against both Gram-positive and Gram-negative bacteria and is resistant to bacterial β-lactamase enzymes . Thienamycin is a zwitterion at pH 7. [ 1 ]
In 1976, fermentation broths obtained from the soil bacterium Streptomyces cattleya were found to be active in a screen for inhibitors of peptidoglycan biosynthesis. [ 2 ] [ 3 ] Initial attempts to isolate the active compound proved difficult due to its chemical instability. After many attempts and extensive purification, the material was finally isolated in >90% purity, allowing for the structural elucidation of thienamycin in 1979. [ 4 ]
Thienamycin was the first among the naturally occurring class of carbapenem antibiotics to be discovered and isolated. [ 3 ] Carbapenems are similar in structure to their antibiotic “cousins” the penicillins . Like penicillins, carbapenems contain a β-lactam ring (cyclic amide) fused to a five-membered ring. Carbapenems differ in structure from penicillins in that within the five-membered ring a sulfur is replaced by a carbon atom (C1) and an unsaturation is present between C2 and C3 in the five-membered ring. [ citation needed ]
In vitro , thienamycin employs a similar mode of action as penicillins through disrupting the cell wall synthesis (peptidoglycan biosynthesis) of various Gram-positive and Gram-negative bacteria ( Staphylococcus aureus , Staphylococcus epidermidis , Pseudomonas aeruginosa to name a few). [ 5 ] Although thienamycin binds to all of the penicillin-binding proteins (PBPs) in Escherichia coli , it preferentially binds to PBP-1 and PBP-2, which are both associated with the elongation of the cell wall. [ 6 ]
Unlike penicillins, which are rendered ineffective through rapid hydrolysis by the β-lactamase enzyme present in some strains of bacteria, thienamycin remains antimicrobially active. Thienamycin displayed high activity against bacteria that were resistant to other β-lactamase-stable compounds ( cephalosporins ), highlighting the superiority of thienamycin as an antibiotic among β-lactams . [ 7 ]
The formation of thienamycin is thought to occur through a different pathway from classic β-lactams (penicillins, cephalosporins). Production of classic β-lactams in both fungi and bacteria occur through two steps: First, the condensation of l - cysteine , l - valine , and l -α-aminoadipic acid by ACV synthetase (ACVS, a nonribosomal peptide synthetase ) and then cyclization of this formed tripeptide by isopenicillin N synthetase (IPNS). [ citation needed ]
The gene cluster ( thn ) for the biosynthesis of thienamycin of S. cattleya was identified and sequenced in 2003, lending insight into the biosynthetic mechanism for thienamycin formation. [ 8 ] The biosynthesis is thought to share features with the biosynthesis of the simple carbapenems , beginning with the condensation of malonyl-CoA with glutamate-5-semialdehyde to form the pyrroline ring. The β-lactam is then formed by a β-lactam synthetase, which makes use of ATP , providing a carbapenam . At some later point, oxidation to the carbapenem and ring inversions must occur. [ citation needed ]
The hydroxyethyl side chain of thienamycin is thought to be a result of two separate methyl transfers from S-adenosyl methionine . [ 9 ] According to the proposed gene functions, ThnK, ThnL, and ThnP could catalyze these methyl-transfer steps. A β-lactam synthetase (ThnM) is thought to catalyze the formation of the β-lactam ring fused to the five-membered ring. How the cysteaminyl side-chain is incorporated is largely unknown, although ThnT, ThnR, and ThnH are involved in the processing of CoA to cysteamine for use in the pathway. [ 10 ] Various oxidations complete the biosynthesis. [ citation needed ]
Due to low titre and to difficulties in isolating and purifying thienamycin produced by fermentation, total synthesis is the preferred method for commercial production. Numerous methods are available in the literature for the total synthesis of thienamycin. One synthetic route [ 11 ] is given in Figure 3.
The starting β-lactam for the pathway given above can be synthesized using the following method (Figure 4): [ 12 ]
Since thienamycin decomposes in the presence of water , it is impractical for the clinical treatment of bacterial infections, so stable derivatives were created for medicinal consumption. One such derivative, imipenem , was formulated in 1985. Imipenem, an N -formimidoyl derivative of thienamycin, is rapidly metabolized by a renal dipeptidase enzyme found in the human body. To prevent its rapid degradation, imipenem is normally coadministered with cilastatin , an inhibitor of this enzyme. [ 13 ] | https://en.wikipedia.org/wiki/Thienamycin |
Thin-filament pyrometry ( TFP ) is an optical method used to measure temperatures. It involves the placement of a thin filament in a hot gas stream. Radiative emissions from the filament can be correlated with filament temperature. Filaments are typically silicon carbide ( SiC ) fibers with a diameter of 15 micrometres. Temperatures of about 800–2500 K can be measured.
TFP in flames was first used by Vilimpoc et al. (1988). [ 1 ] More recently, this was demonstrated by Pitts (1996), [ 2 ] Blevins et al. (1999), [ 3 ] and Maun et al. (2007). [ 4 ]
The typical TFP apparatus consists of a flame or other hot gas stream, a filament, and a camera.
TFP has several advantages, including the ability to simultaneously measure temperatures along a line and minimal intrusiveness. Most other forms of pyrometry are not capable of providing gas-phase temperatures.
Calibration is required. Calibration typically is performed with a thermocouple . Both thermocouples and filaments require corrections in estimating gas temperatures from probe temperatures. Also, filaments are fragile and typically break after about an hour in a flame.
The primary application is to combustion and fire research. | https://en.wikipedia.org/wiki/Thin-filament_pyrometry |
Thin-film composite membranes ( TFC or TFM ) are semipermeable membranes manufactured to provide selectivity with high permeability. Most TFC's are used in water purification or water desalination systems. They also have use in chemical applications such as gas separations , dehumidification , batteries and fuel cells . A TFC membrane can be considered a molecular sieve constructed in the form of a film from two or more layered materials. The additional layers provide structural strength and a low-defect surface to support a selective layer that is thin enough to be selective but not so thick that it causes low permeability.
TFC membranes for water treatment are commonly classified as nanofiltration (NF) and reverse osmosis (RO) membranes. Both types are typically made out of a thin polyamide layer (<200 nm) deposited on top of a polyethersulfone or polysulfone porous layer (about 50 microns) on top of a non-woven fabric support sheet. The three layer configuration gives the desired properties of high rejection of undesired materials (like salts), high filtration rate, and good mechanical strength. The polyamide top layer is responsible for the high rejection and is chosen primarily for its permeability to water and relative impermeability to various dissolved impurities including salt ions and other small, unfilterable molecules . [ 1 ] Although not fully commercialized yet, TFC's are also used in other water treatment technologies, including Forward osmosis , [ 2 ] membrane distillation , [ 3 ] and electrodialysis . [ 4 ] [ 5 ]
The first viable reverse osmosis membrane was made from cellulose acetate as an integrally skinned asymmetric semi-permeable membrane. This membrane was made by Loeb and Sourirajan at UCLA in 1959 and patented in 1960. In 1972, John Cadotte of North Star Technologies (later FilmTec Corporation ) developed the first interfacial polyamide (IP) thin-film-composite (TFC) membrane. [ 6 ] The current generation of reverse osmosis (RO) membrane materials are based on a composite material patented by FilmTec Corporation in 1970 (now part of DuPont ). Today, most such membranes for reverse osmosis and nanofiltration use a Polyamide active layer.
As is suggested by the name, TFC membranes are composed of multiple layers. Membranes designed for desalination use an active thin-film layer of polyamide layered with polysulfone as a porous support layer. The active layers tend to be extremely thin and relatively nonporous. The chemistry of these layers often imparts selectivity. Meanwhile the support layers tend to need to be both extremely porous and robust to higher pressures. [ 7 ]
Other materials, usually zeolites , are also used in the manufacture of TFC membranes.
Thin film composite membranes are used in
Thin film composites membranes typically suffer from compaction effects under pressure. As the water pressure increases, the polymers are slightly reorganized into a tighter fitting structure that results in a lower porosity, ultimately limiting the efficiency of the system designed to use them. In general, the higher the pressure, the greater the compaction.
Surface fouling: Colloidal particulates, bacteria infestation ( biofouling ). [ 8 ]
Chemical decomposition and oxidation.
A filtration membrane's performance is rated by selectivity, chemical resistance, operational pressure differential and the pure water flow rate per unit area.
Due to the importance of throughput, a membrane is manufactured as thinly as possible. These thin layers introduce defects that may affect selectivity, so system design usually trades off the desired throughput against both selectivity and operational pressure.
In applications other than filtration, parameters such as mechanical strength, temperature stability, and electrical conductivity may dominate.
Nano-composite membranes (TFN). Key points: multiple layers, multiple materials. [ 9 ]
Mitigation of membrane fouling [ 10 ]
New materials, synthetic zeolites, [ 11 ] etc. to obtain higher performance.
NanoH2O Inc. commercialized a membrane in which zeolite nanoparticles were synthesized and embedded within an RO membrane to form a thin-film nanocomposite, or TFN, which has proven to be more than 50-100% more permeable compared to conventional RO membranes while maintaining the same level of salt rejection. [ 12 ]
Fuel-cells.
Batteries. | https://en.wikipedia.org/wiki/Thin-film_composite_membrane |
Thin-film drug delivery uses a dissolving film or oral drug strip to administer drugs via absorption in the mouth ( buccally or sublingually ) and/or via the small intestines ( enterically ). A film is prepared using hydrophilic polymers that rapidly dissolves on the tongue or buccal cavity, delivering the drug to the systemic circulation via dissolution when contact with liquid is made.
Thin-film drug delivery has emerged as an advanced alternative to the traditional tablets , capsules and liquids often associated with prescription and OTC medications. Similar in size, shape and thickness to a postage stamp , thin-film strips are typically designed for oral administration , with the user placing the strip on or under the tongue (sublingual) or along the inside of the cheek (buccal). These drug delivery options allow the medication to bypass the first pass metabolism thereby making the medication more bioavailable. [ citation needed ] As the strip dissolves, the drug can enter the blood stream enterically, buccally or sublingually. Evaluating the systemic transmucosal drug delivery, the buccal mucosa is the preferred region as compared to the sublingual mucosa. Oral Thin Films (Oral Dissolvable Strips) address several of the disadvantages of tablets or capsules such as dysphagia or the inability to adjust dosing to patient parameters, often resulting to a lack of treatment adherence, especially in low-resource settings. [ 1 ] [ 2 ]
Different buccal delivery products have been marketed or are proposed for certain diseases like trigeminal neuralgia , Ménière's disease , diabetes , and addiction . [ citation needed ] There are many commercial non-drug product to use thin films like Mr. Mint and Listerine PocketPaks breath freshening strips . Since then, thin-film products for other breath fresheners, as well as a number of cold, flu, anti-snoring and gastrointestinal medications, have entered the marketplace. There are currently [ when? ] several projects in development that will deliver prescription drugs using the thin-film dosage form . [ 3 ]
Formulation of oral drug strips involves the application of both aesthetic and performance characteristics such as strip-forming polymers, plasticizers , active pharmaceutical ingredient, sweetening agents, saliva stimulating agent, flavoring agents, coloring agents, stabilizing and thickening agents. From the regulatory perspectives, all excipients used in the formulation of oral drug strips should be approved for use in oral pharmaceutical dosage forms.
The polymer employed should be non-toxic, non-irritant and devoid of leachable impurities. It should have good wetting and spreadability property. The polymer should exhibit sufficient peel, shear and tensile strengths. The polymer should be readily available and should not be very expensive. Film obtained should be tough enough so that there won't be any damage while handling or during transportation. Combination of microcrystalline cellulose and maltodextrin has been used to formulate Oral Strips of piroxicam made by hot melt extrusion technique. Pullulan has been the most widely used film former (used in Listerine PocketPak, Benadryl, etc.)
Plasticizer is a vital ingredient of the OS formulation. It helps to improve the flexibility and reduces the brittleness of the strip. Plasticizer significantly improves the strip properties by reducing the glass transition temperature of the polymer. Glycerol , Propylene glycol , low molecular weight polyethylene glycols , phthalate derivatives like dimethyl , diethyl and dibutyl phthalate , Citrate derivatives such as tributyl, triethyl, acetyl citrate, triacetin and castor oil are some of the commonly used plasticizer excipients.
Since the size of the dosage form has limitation, high-dose molecules are difficult to be incorporated in OS. Generally 5%w/w to 30%w/w of active pharmaceutical ingredients can be incorporated in the oral strip. [ 4 ]
An important aspect of thin film drug technology is its taste and color. The sweet taste in formulation is more important in case of pediatric population. Natural sweeteners as well as artificial sweeteners are used to improve the flavor of the mouth dissolving formulations for the flavors changes from individual to individual. Pigments such as titanium dioxide is incorporated for coloring.
The stabilizing and thickening agents are employed to improve the viscosity and consistency of dispersion or solution of the strip preparation solution or suspension before casting. Drug content uniformity is a requirement for all dosage forms, particularly those containing low dose highly potent drugs. To uniquely meet this requirement, thin film formulations contain uniform dispersions of drug throughout the whole manufacturing process. [ 5 ] Since this criterion is essential for the quality of the thin film and final pharmaceutical dosage form, the use of Laser Scanning Confocal Microscopy (LSCM) was recommended to follow the manufacturing process. [ 6 ]
An increasing number of film-based therapeutics are in development, including: | https://en.wikipedia.org/wiki/Thin-film_drug_delivery |
The thin-film lithium-ion battery is a form of solid-state battery . [ 1 ] Its development is motivated by the prospect of combining the advantages of solid-state batteries with the advantages of thin-film manufacturing processes.
Thin-film construction could lead to improvements in specific energy , energy density , and power density on top of the gains from using a solid electrolyte . It allows for flexible cells only a few microns thick. [ 2 ] It may also reduce manufacturing costs from scalable roll-to-roll processing and even allow for the use of cheap materials. [ 3 ]
Lithium-ion batteries store chemical energy in reactive chemicals at the anodes and cathodes of a cell. Typically, anodes and cathodes exchange lithium (Li+) ions through a fluid electrolyte that passes through a porous separator which prevents direct contact between the anode and cathode. Such contact would lead to an internal short circuit and a potentially hazardous uncontrolled reaction. Electric current is usually carried by conductive collectors at the anodes and cathodes to and from the negative and positive terminals of the cell (respectively).
In a thin-film lithium battery the electrolyte is solid and the other components are deposited in layers on a substrate . In some designs, the solid electrolyte also serves as a separator.
Cathode materials in thin-film lithium-ion batteries are the same as in classical lithium-ion batteries. They are normally metal oxides that are deposited as a film by various methods.
Metal oxide materials are shown below as well as their relative specific capacities ( Λ ), open circuit voltages ( V oc ), and energy densities ( D E ).
There are various methods being used to deposit thin film cathode materials onto the current collector.
In pulsed laser deposition , materials are fabricated by controlling parameters such as laser energy and fluence, substrate temperature, background pressure, and target-substrate distance.
In magnetron sputtering the substrate is cooled for deposition.
In chemical vapor deposition , volatile precursor materials are deposited onto a substrate material.
Sol-gel processing allows for homogeneous mixing of precursor materials at the atomic level.
The greatest difference between classical lithium-ion batteries and thin, flexible, lithium-ion batteries is in the electrolyte material used. Progress in lithium-ion batteries relies as much on improvements in the electrolyte as it does in the electrode materials, as the electrolyte plays a major role in safe battery operation.
The concept of thin-film lithium-ion batteries was increasingly motivated by manufacturing advantages presented by the polymer technology for their use as electrolytes. LiPON, lithium phosphorus oxynitride, is an amorphous glassy material used as an electrolyte material in thin film flexible batteries. Layers of LiPON are deposited over the cathode material at ambient temperatures by RF magnetron sputtering. This forms the solid electrolyte used for ion conduction between anode and cathode. [ 4 ] [ 5 ] LiBON, lithium boron oxynitride, is another amorphous glassy material used as a solid electrolyte material in thin film flexible batteries. [ 6 ] Solid polymer electrolytes offer several advantages in comparison to a classical liquid lithium-ion battery. Rather than having separate components of electrolyte, binder, and separator, these solid electrolytes can act as all three. This increases the overall energy density of the assembled battery because the constituents of the entire cell are more tightly packed.
Separator materials in lithium-ion batteries must not block the transport of lithium ions while preventing the physical contact of the anode and cathode materials, e.g. short-circuiting. In a liquid cell, this separator would be a porous glass or polymer mesh that allows ion transport via the liquid electrolyte through the pores, but keeps the electrodes from contacting and shorting. However, in a thin film battery the electrolyte is a solid, which conveniently satisfies both the ion transportation and the physical separation requirements without the need for a dedicated separator.
Current collectors in thin film batteries must be flexible, have high surface area, and be cost-effective. Silver nanowires with improved surface area and loading weight have been shown to work as a current collector in these battery systems, but still are not as cost-effective as desired. Extending graphite technology to lithium-ion batteries, solution processed carbon nanotubes (CNT) films are being looked into for use as both the current collector and anode material. CNTs have the ability to intercalate lithium and maintain high operating voltages, all with low mass loading and flexibility.
Thin-film lithium-ion batteries offer improved performance by having a higher average output voltage, lighter weights thus higher energy density (3x), and longer cycling life (1200 cycles without degradation) and can work in a wider range of temperatures (between -20 and 60 °C)than typical rechargeable lithium-ion batteries.
Li-ion transfer cells are the most promising systems for satisfying the demand of high specific energy and high power and would be cheaper to manufacture.
In the thin-film lithium-ion battery, both electrodes are capable of reversible lithium insertion, thus forming a Li-ion transfer cell. In order to construct a thin film battery it is necessary to fabricate all the battery components, as an anode , a solid electrolyte , a cathode and current leads into multi-layered thin films by suitable technologies.
In a thin film based system, the electrolyte is normally a solid electrolyte, capable of conforming to the shape of the battery. This is in contrast to classical lithium-ion batteries, which normally have liquid electrolyte material. Liquid electrolytes can be challenging to utilize if they are not compatible with the separator. Also liquid electrolytes in general call for an increase in the overall volume of the battery, which is not ideal for designing a system that has high energy density. Additionally, in a thin film flexible Li-ion battery, the electrolyte, which is normally polymer -based, can act as the electrolyte, separator, and binder material. This provides the ability to have flexible systems since the issue of electrolyte leakage is circumvented. Finally, solid systems can be packed together tightly which affords an increase in energy density when compared to classical liquid lithium-ion batteries.
Separator materials in lithium-ion batteries must have the ability to transport ions through their porous membranes while maintaining a physical separation between the anode and cathode materials in order to prevent short-circuiting. Furthermore, the separator must be resistant to degradation during the battery’s operation. In a thin film Li-ion battery, the separator must be a thin and flexible solid. Typically today, this material is a polymer-based material. Since thin film batteries are made of all solid materials, allows one to use simpler separator materials in these systems such as Xerox paper rather than in liquid based Li-ion batteries.
Development of thin solid state batteries allows for roll to roll type production of batteries to decrease production costs. Solid-state batteries can also afford increased energy density due to decrease in overall device weight, while the flexible nature allows for novel battery design and easier incorporation into electronics. Development is still required in cathode materials which will resist capacity reduction due to cycling.
The advancements made to the thin-film lithium-ion battery have allowed for many potential applications. The majority of these applications are aimed at improving the currently available consumer and medical products. Thin-film lithium-ion batteries can be used to make thinner portable electronics, because the thickness of the battery required to operate the device can be reduced greatly. These batteries have the ability to be an integral part of implantable medical devices, such as defibrillators and neural stimulators, “smart” cards, [ 8 ] radio frequency identification tags [ 3 ] and wireless sensors. [ 9 ] They can also serve as a way to store energy collected from solar cells or other harvesting devices. [ 9 ] Each of these applications is possible because of the flexibility in the size and shape of the batteries. The size of these devices does not have to revolve around the size of the space needed for the battery anymore. The thin film batteries can be attached to the inside of the casing or in some other convenient way. There are many opportunities in which to use this type of batteries.
The thin-film lithium-ion battery can serve as a storage device for the energy collected from renewable sources with a variable generation rate, such as a solar cell or wind turbine . These batteries can be made to have a low self discharge rate, which means that these batteries can be stored for long periods of time without a major loss of the energy that was used to charge it. These fully charged batteries could then be used to power some or all of the other potential applications listed below, or provide more reliable power to an electric grid for general use.
Smart cards have the same size as a credit card, but they contain a microchip that can be used to access information, give authorization, or process an application. These cards can go through harsh production conditions, with temperatures in the range of 130 to 150 °C, in order to complete the high temperature, high pressure lamination processes. [ 10 ] These conditions can cause other batteries to fail because of degassing or degradation of organic components within the battery. Thin-film lithium-ion batteries have been shown to withstand temperatures of -40 to 150 °C. [ 9 ] This use of thin-film lithium-ion batteries is hopeful for other extreme temperature applications.
Radio-frequency identification tags can be used in many different applications. These tags can be used in packaging, inventory control, used to verify authenticity and even allow or deny access to something. These ID tags can even have other integrated sensors to allow for the physical environment to be monitored, such as temperature or shock during travel or shipping. Also, the distance required to read the information in the tag depends on the strength of the battery. The farther away you want to be able to read the information, the stronger the output will have to be and thus the greater the power supply to accomplish this output. As these tags get more and more complex, the battery requirements will need to keep up. Thin-film lithium-ion batteries have shown that they can fit into the designs of the tags because of the flexibility of the battery in size and shape and are sufficiently powerful enough to accomplish the goals of the tag. Low cost production methods, like roll to roll lamination, of these batteries may even allow for this kind of radio frequency identification technology to be implemented in disposable applications. [ 3 ]
Thin films of LiCoO 2 have been synthesized in which the strongest X-ray reflection is either weak or missing, indicating a high degree of preferred orientation. Thin film solid state batteries with these textured cathode films can deliver practical capacities at high current densities. For example, for one of the cells 70% of the maximum capacity between 4.2 V and 3 V (approximately 0.2 mAh/cm 2 ) was delivered at a current of 2 mA /cm 2 . When cycled at rates of 0.1 mA/cm 2 , the capacity loss was 0.001%/cycle or less. The reliability and performance of Li LiCoO 2 thin-film batteries make them attractive for application in implantable devices such as neural stimulators, pacemakers , and defibrillators .
Implantable medical devices require batteries that can deliver a steady, reliable power source for as long as possible. These applications call for a battery that has a low self-discharge rate, for when it’s not in use, and a high power rate, for when it needs to be used, especially in the case of an implantable defibrillator . Also, users of the product will want a battery that can go through many cycles, so these devices will not have to be replaced or serviced often. Thin-film lithium-ion batteries have the ability to meet these requirements. The advancement from a liquid to a solid electrolyte has allowed these batteries to take almost any shape without the worry of leaking, and it has been shown that certain types of thin film rechargeable lithium batteries can last for around 50,000 cycles. [ 11 ] Another advantage to these thin film batteries is that they can be arranged in series to give a larger voltage equal to the sum of the individual battery voltages. This fact can be used in reducing the “footprint” of the battery, or the size of the space needed for the battery, in the design of a device.
Wireless sensors need to be in use for the duration of their application, whether that may be in package shipping or in the detection of some unwanted compound, or controlling inventory in a warehouse. If the wireless sensor cannot transmit its data due to low or no battery power, the consequences could potentially be severe based on the application. Also, the wireless sensor must be adaptable to each application. Therefore the battery must be able to fit within the designed sensor. This means that the desired battery for these devices must be long-lasting, size specific, low cost, if they are going to be used in disposable technologies, and must meet the requirements of the data collection and transmission processes. Once again, thin-film lithium-ion batteries have shown the ability to meet all of these requirements. | https://en.wikipedia.org/wiki/Thin-film_lithium-ion_battery |
Thin-film memory is a high-speed alternative to magnetic-core memory developed by Sperry Rand in a government-funded research project.
Instead of threading individual ferrite cores on wires, thin-film memory consisted of 4-micrometer thick dots of permalloy , an iron – nickel alloy, deposited on small glass plates by vacuum evaporation techniques and a mask. The drive and sense lines were then added using printed circuit wiring over the alloy dots. This provided very fast access times in the range of 670 nanoseconds, but was very expensive to produce.
In 1962, the UNIVAC 1107 , intended for the civilian marketplace, used thin-film memory only for its 128-word general register stack. Military computers , where cost was less of a concern, used larger amounts of thin-film memory. Thin film was also used in a number of high-speed computer projects, including the high-end of the IBM System/360 line, but general advances in core tended to keep pace.
This computer hardware article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thin-film_memory |
Thin-film thickness monitors , deposition rate controllers , and so on, are a family of instruments used in high and ultra-high vacuum systems. They can measure the thickness of a thin film , not only after it has been made, but while it is still being deposited , and some can control either the final thickness of the film, the rate at which it is deposited, or both. Not surprisingly, the devices which control some aspect of the process tend to be called controllers, and those that simply monitor the process tend to be called monitors.
Most such instruments use a quartz crystal microbalance as the sensor. Optical measurements are sometimes used; this may be especially appropriate if the film being deposited is part of a thin film optical device .
A thickness monitor measures how much material is deposited on its sensor. Most deposition processes are at least somewhat directional. The sensor and the sample generally cannot be in the same direction from the deposition source (if they were, the one closer to the source would shadow the other), and may not even be at the same distance from it. Therefore, the rate at which the material is deposited on the sensor may not equal the rate at which it is deposited on the sample. The ratio of the two rates is sometimes called the "tooling factor". For careful work, the tooling factor should be checked by measuring the amount of material deposited on some samples after the fact and comparing it to what the thickness monitor measured. Fizeau interferometers are often used to do this. Many other techniques might be used, depending on the thickness and characteristics of the thin film, including surface profilers , ellipsometry , dual polarisation interferometry and scanning electron microscopy of cross-sections of the sample. Many thickness monitors and controllers allow tooling factors to be entered into the device before deposition begins.
The correct tooling factor can be calculated as follows:
F m = F i T m T i {\displaystyle F_{m}=F_{i}\,{\frac {T_{m}}{T_{i}}}}
where F i is the initial tooling factor, T i is the film thickness indicated by the instrument, and T m is the actual, independently measured thickness of the deposited film. If no tooling factor has been preset or used before, F i equals 1. | https://en.wikipedia.org/wiki/Thin-film_thickness_monitor |
A thin-film transistor ( TFT ) is a special type of field-effect transistor (FET) where the transistor is made by thin film deposition . TFTs are grown on a supporting (but non-conducting) substrate , such as glass . This differs from the conventional bulk metal-oxide-semiconductor field-effect transistor ( MOSFET ), where the semiconductor material typically is the substrate, such as a silicon wafer . [ 1 ] The traditional application of TFTs is in TFT liquid-crystal displays .
TFTs can be fabricated with a wide variety of semiconductor materials. Because it is naturally abundant and well understood, amorphous or polycrystalline silicon were (and still are) used as the semiconductor layer. However, because of the low mobility of amorphous silicon [ 2 ] and the large device-to-device variations found in polycrystalline silicon, [ 3 ] [ 4 ] [ 5 ] other materials have been studied for use in TFTs. These include cadmium selenide , [ 6 ] [ 7 ] metal oxides such as indium gallium zinc oxide (IGZO) or zinc oxide , [ 8 ] organic semiconductors , [ 9 ] carbon nanotubes , [ 10 ] or metal halide perovskites . [ 11 ]
Because TFTs are grown on inert substrates, rather than on wafers, the semiconductor must be deposited in a dedicated process. A variety of techniques are used to deposit semiconductors in TFTs. These include chemical vapor deposition (CVD), atomic layer deposition (ALD), and sputtering . The semiconductor can also be deposited from solution, [ 12 ] via techniques such as printing [ 13 ] or spray coating. [ 14 ] Solution-based techniques are hoped to lead to low-cost, mechanically flexible electronics. [ 15 ] Because typical substrates will deform or melt at high temperatures, the deposition process must be carried out under relatively low temperatures compared to traditional electronic material processing. [ 16 ]
Some wide band gap semiconductors, most notable metal oxides, are optically transparent. [ 17 ] By also employing transparent substrates, such as glass, and transparent electrodes , such as indium tin oxide (ITO), some TFT devices can be designed to be completely optically transparent. [ 18 ] Such transparent TFTs (TTFTs) could be used to enable head-up displays (such as on a car windshield).The first solution-processed TTFTs, based on zinc oxide , were reported in 2003 by researchers at Oregon State University . [ 19 ] The Portuguese laboratory CENIMAT at the Universidade Nova de Lisboa has produced the world's first completely transparent TFT at room temperature. [ 20 ] CENIMAT also developed the first paper transistor, [ 21 ] which may lead to applications such as magazines and journal pages with moving images.
Many AMOLED displays use LTPO ( Low-temperature Poly-Crystalline Silicon and Oxide ) TFT transistors. These transistors offer stability at low refresh rates, and variable refresh rates, which allows for power saving displays that do not show visual artifacts. [ 22 ] [ 23 ] [ 24 ] Large OLED displays usually use AOS (amporphous oxide semiconductor) TFT transistors instead, also called oxide TFTs [ 25 ] and these are usually based on IGZO. [ 26 ]
The best known application of thin-film transistors is in TFT LCDs , an implementation of liquid-crystal display technology. Transistors are embedded within the panel itself, reducing crosstalk between pixels and improving image stability.
As of 2008 [update] , many color LCD TVs and monitors use this technology. TFT panels are frequently used in digital radiography applications in general radiography. A TFT is used in both direct and indirect capture [ jargon ] as a base for the image receptor in medical radiography .
As of 2013 [update] , all modern high-resolution and high-quality electronic visual display devices use TFT-based active matrix displays. [ 27 ]
AMOLED displays also contain a TFT layer for active-matrix pixel addressing of individual organic light-emitting diodes .
The most beneficial aspect of TFT technology is its use of a separate transistor for each pixel on the display. Because each transistor is small, the amount of charge needed to control it is also small. This allows for very fast re-drawing of the display.
This picture does not include the actual light-source (usually cold-cathode fluorescent lamps or white LEDs ), just the TFT-display matrix.
In February 1957, John Wallmark of RCA filed a patent for a thin film MOSFET in which germanium monoxide was used as a gate dielectric. Paul K. Weimer , also of RCA implemented Wallmark's ideas and developed the thin-film transistor (TFT) in 1962, a type of MOSFET distinct from the standard bulk MOSFET. It was made with thin films of cadmium selenide and cadmium sulfide . In 1966, T.P. Brody and H.E. Kunig at Westinghouse Electric fabricated indium arsenide (InAs) MOS TFTs in both depletion and enhancement modes . [ 28 ] [ 29 ] [ 30 ] [ 31 ] [ 32 ] [ 33 ]
The idea of a TFT-based liquid-crystal display (LCD) was conceived by Bernard J. Lechner of RCA Laboratories in 1968. [ 34 ] Lechner, F.J. Marlowe, E.O. Nester and J. Tults demonstrated the concept in 1968 with an 18x2 matrix dynamic scattering LCD that used standard discrete MOSFETs, as TFT performance was not adequate at the time. [ 35 ] In 1973, T. Peter Brody , J. A. Asars and G. D. Dixon at Westinghouse Research Laboratories developed a CdSe (cadmium selenide) TFT, which they used to demonstrate the first CdSe thin-film-transistor liquid-crystal display (TFT LCD). [ 31 ] [ 36 ] The Westinghouse group also reported on operational TFT electroluminescence (EL) in 1973, using CdSe. [ 37 ] Brody and Fang-Chen Luo demonstrated the first flat active-matrix liquid-crystal display (AM LCD) using CdSe in 1974, and then Brody coined the term "active matrix" in 1975. [ 34 ] However, mass production of this device was never realized, due to complications in controlling the compound semiconductor thin film material properties, and device reliability over large areas. [ 31 ]
A breakthrough in TFT research came with the development of the amorphous silicon (a-Si) TFT by P.G. le Comber, W.E. Spear and A. Ghaith at the University of Dundee in 1979. They reported the first functional TFT made from hydrogenated a-Si with a silicon nitride gate dielectric layer. [ 31 ] [ 38 ] The a-Si TFT was soon recognized as being more suitable for a large-area AM LCD. [ 31 ] This led to commercial research and development (R&D) of AM LCD panels based on a-Si TFTs in Japan. [ 39 ]
By 1982, pocket TVs based on AM LCD technology were developed in Japan. [ 40 ] In 1982, Fujitsu 's S. Kawai fabricated an a-Si dot-matrix display , and Canon 's Y. Okubo fabricated a-Si twisted nematic (TN) and guest-host LCD panels. In 1983, Toshiba 's K. Suzuki produced a-Si TFT arrays compatible with CMOS (complementary metal–oxide–semiconductor) integrated circuits (ICs), Canon's M. Sugata fabricated an a-Si color LCD panel, and a joint Sanyo and Sanritsu team including Mitsuhiro Yamasaki, S. Suhibuchi and Y. Sasaki fabricated a 3-inch a-SI color LCD TV. [ 39 ]
The first commercial TFT-based AM LCD product was the 2.1-inch Epson [ 41 ] [ 42 ] [ 43 ] ET-10 [ 37 ] (Epson Elf), the first color LCD pocket TV, released in 1984. [ 44 ] In 1986, a Hitachi research team led by Akio Mimura demonstrated a low-temperature polycrystalline silicon (LTPS) process for fabricating n-channel TFTs on a silicon-on-insulator (SOI), at a relatively low temperature of 200 °C. [ 45 ] A Hosiden research team led by T. Sunata in 1986 used a-Si TFTs to develop a 7-inch color AM LCD panel, [ 46 ] and a 9-inch AM LCD panel. [ 47 ] In the late 1980s, Hosiden supplied monochrome TFT LCD panels to Apple Computer . [ 31 ] In 1988, a Sharp research team led by engineer T. Nagayasu used hydrogenated a-Si TFTs to demonstrate a 14-inch full-color LCD display, [ 34 ] [ 48 ] which convinced the electronics industry that LCD would eventually replace cathode-ray tube (CRT) as the standard television display technology . [ 34 ] The same year, Sharp launched TFT LCD panels for notebook PCs . [ 37 ] In 1992, Toshiba and IBM Japan introduced a 12.1-inch color SVGA panel for the first commercial color laptop by IBM . [ 37 ]
TFTs can also be made out of indium gallium zinc oxide ( IGZO ). TFT-LCDs with IGZO transistors first showed up in 2012, and were first manufactured by Sharp Corporation. IGZO allows for higher refresh rates and lower power consumption. [ 49 ] [ 50 ] In 2021, the first flexible 32-bit microprocessor was manufactured using IGZO TFT technology on a polyimide substrate. [ 51 ] | https://en.wikipedia.org/wiki/Thin-film_transistor |
Thin-layer chromatography ( TLC ) is a chromatography technique that separates components in non-volatile mixtures. [ 1 ]
It is performed on a TLC plate made up of a non-reactive solid coated with a thin layer of adsorbent material. [ 2 ] This is called the stationary phase. [ 2 ] The sample is deposited on the plate, which is eluted with a solvent or solvent mixture known as the mobile phase (or eluent ). [ 3 ] This solvent then moves up the plate via capillary action . [ 4 ] As with all chromatography , some compounds are more attracted to the mobile phase, while others are more attracted to the stationary phase. [ 5 ] Therefore, different compounds move up the TLC plate at different speeds and become separated. [ 6 ] To visualize colourless compounds, the plate is viewed under UV light or is stained. [ 7 ] Testing different stationary and mobile phases is often necessary to obtain well-defined and separated spots. [ citation needed ]
TLC is quick, simple, and gives high sensitivity for a relatively low cost. [ 5 ] It can monitor reaction progress, identify compounds in a mixture, determine purity, or purify small amounts of compound. [ 5 ]
The process for TLC is similar to paper chromatography but provides faster runs, better separations, and the choice between different stationary phases. [ 5 ] Plates can be labelled before or after the chromatography process with a pencil or other implement that will not interfere with the process. [ 8 ]
There are four main stages to running a thin-layer chromatography plate: [ 3 ] [ 8 ]
Plate preparation: Using a capillary tube, a small amount of a concentrated solution of the sample is deposited near the bottom edge of a TLC plate. The solvent is allowed to completely evaporate before the next step. A vacuum chamber may be necessary for non-volatile solvents. To make sure there is sufficient compound to obtain a visible result, the spotting procedure can be repeated. Depending on the application, multiple different samples may be placed in a row the same distance from the bottom edge; each sample will move up the plate in its own "lane."
Development chamber preparation: The development solvent or solvent mixture is placed into a transparent container (separation/development chamber) to a depth of less than 1 centimetre. A strip of filter paper (aka "wick") is also placed along the container wall. This filter paper should touch the solvent and almost reach the top of the container. The container is covered with a lid and the solvent vapors are allowed to saturate the atmosphere of the container. Failure to do so results in poor separation and non-reproducible results.
Development: The TLC plate is placed in the container such that the sample spot(s) are not submerged into the mobile phase. The container is covered to prevent solvent evaporation. The solvent migrates up the plate by capillary action , meets the sample mixture, and carries it up the plate (elutes the sample). The plate is removed from the container before the solvent reaches the top of the plate; otherwise, the results will be misleading. The solvent front , the highest mark the solvent has travelled along the plate, is marked.
Visualization: The solvent evaporates from the plate. Visualization methods include UV light, staining, and many more.
The separation of compounds is due to the differences in their attraction to the stationary phase and because of differences in solubility in the solvent. [ 9 ] As a result, the compounds and the mobile phase compete for binding sites on the stationary phase. [ 9 ] Different compounds in the sample mixture travel at different rates due to the differences in their partition coefficients . [ 10 ] Different solvents, or different solvent mixtures, gives different separation. [ 5 ] The retardation factor ( R f ), or retention factor , quantifies the results. It is the distance traveled by a given substance divided by the distance traveled by the mobile phase. [ citation needed ]
In normal-phase TLC, the stationary phase is polar . Silica gel is very common in normal-phase TLC. More polar compounds in a sample mixture interact more strongly with the polar stationary phase. [ citation needed ] As a result, more-polar compounds move less (resulting in smaller R f ) while less-polar compounds move higher up the plate (higher R f ). [ 10 ] A more-polar mobile phase also binds more strongly to the plate, competing more with the compound for binding sites; a more-polar mobile phase also dissolves polar compounds more. [ 10 ] As such, all compounds on the TLC plate move higher up the plate in polar solvent mixtures. [ citation needed ] "Strong" solvents move compounds higher up the plate, whereas "weak" solvents move them less. [ 11 ]
If the stationary phase is non-polar, like C18 -functionalized silica plates, it is called reverse-phase TLC. In this case, non-polar compounds move less and polar compounds move more. [ citation needed ] The solvent mixture will also be much more polar than in normal-phase TLC. [ 11 ]
An eluotropic series , which orders solvents by how much they move compounds, can help in selecting a mobile phase. [ 5 ] Solvents are also divided into solvent selectivity groups. [ 5 ] [ 12 ] Using solvents with different elution strengths or different selectivity groups can often give very different results. [ 5 ] [ 12 ] While single-solvent mobile phases can sometimes give good separation, some cases may require solvent mixtures. [ 13 ]
In normal-phase TLC, the most common solvent mixtures include ethyl acetate/hexanes ( EtOAc / Hex ) for less-polar compounds and methanol/dichloromethane ( MeOH / DCM ) for more polar compounds. [ 14 ] Different solvent mixtures and solvent ratios can help give better separation. [ 15 ] In reverse-phase TLC, solvent mixtures are typically water with a less-polar solvent: Typical choices are water with tetrahydrofuran ( THF ), acetonitrile ( ACN ), or methanol. [ 14 ]
As the chemicals being separated may be colourless, several methods exist to visualise the spots:
TLC plates are usually commercially available, with standard particle size ranges to improve reproducibility . [ 4 ] They are prepared by mixing the adsorbent, such as silica gel , with a small amount of inert binder like calcium sulfate (gypsum) and water. [ 18 ] This mixture is spread as a thick slurry on an unreactive carrier sheet, usually glass , thick aluminum foil, or plastic. The resultant plate is dried and activated by heating in an oven for thirty minutes at 110 °C. [ 18 ] The thickness of the absorbent layer is typically around 0.1–0.25 mm for analytical purposes and around 0.5–2.0 mm for preparative TLC. [ 19 ] Other adsorbent coatings include aluminium oxide (alumina), or cellulose . [ 18 ]
TLC is a useful tool for reaction monitoring. [ 15 ] For this, the plate normally contains a spot of starting material, a spot from the reaction mixture, and a co-spot (or cross-spot) containing both. [ 4 ] [ 14 ] The analysis will show if the starting material disappeared and if any new products appeared. [ 14 ] This provides a quick and easy way to estimate how far a reaction has proceeded. In one study, TLC has been applied in the screening of organic reactions . [ 20 ] The researchers react an alcohol and a catalyst directly in the co-spot of a TLC plate before developing it. This provides quick and easy small-scale testing of different reagents .
Compound characterization with TLC is also possible [ citation needed ] and is similar to reaction monitoring. However, rather than spotting with starting material and reaction mixture, it is with an unknown and a known compound. They may be the same compound if both spots have the same R f and look the same under the chosen visualization method. [ citation needed ] However, co-elution complicates both reaction monitoring and characterization. This is because different compounds will move to the same spot on the plate. In such cases, different solvent mixtures may provide better separation. [ 21 ]
TLC helps show the purity of a sample. [ citation needed ] A pure sample should only contain one spot by TLC. TLC is also useful for small-scale purification. [ 22 ] Because the separated compounds will be on different areas of the plate, a scientist can scrape off the stationary phase particles containing the desired compound and dissolve them into an appropriate solvent. [ 22 ] Once all the compound dissolves in the solvent, they filter out the silica particles, then evaporate the solvent to isolate the product. Big preparative TLC plates with thick silica gel coatings can separate more than 100 mg of material. [ 22 ]
For larger-scale purification and isolation, TLC is useful to quickly test solvent mixtures before running flash column chromatography on a large batch of impure material. [ 13 ] [ 23 ] A compound elutes from a column when the amount of solvent collected is equal to 1/ R f . [ 24 ] The eluent from flash column chromatography gets collected across several containers (for example, test tubes) called fractions. TLC helps show which fractions contain impurities and which contain pure compound. [ citation needed ]
Furthermore, two-dimensional TLC [ 4 ] can help check if a compound is stable on a particular stationary phase. This test requires two runs on a square-shaped TLC plate. The plate is rotated by 90º before the second run. If the target compound appears on the diagonal of the square, it is stable on the chosen stationary phase. Otherwise, it is decomposing on the plate. If this is the case, an alternative stationary phase may prevent this decomposition. [ 25 ]
TLC is also an analytical method for the direct separation of enantiomers and the control of enantiomeric purity, e.g. active pharmaceutical ingredients ( APIs ) that are chiral. [ 26 ] | https://en.wikipedia.org/wiki/Thin-layer_chromatography |
A shell is a three-dimensional solid structural element whose thickness is very small compared to its other dimensions. It is characterized in structural terms by mid-plane stress which is both coplanar and normal to the surface. A shell can be derived from a plate in two steps: by initially forming the middle surface as a singly or doubly curved surface, [ 1 ] then by applying loads which are coplanar to the plate's plane thus generating significant stresses.
Materials range from concrete (a concrete shell ) to fabric (as in fabric structures ).
Thin-shell structures (also called plate and shell structures ) are lightweight constructions using shell elements . These elements, typically curved, are assembled to make large structures. Typical applications include aircraft fuselages , boat hulls, and the roofs of large buildings.
A thin shell is defined as a shell with a thickness which is small compared to its other dimensions and in which deformations are not large compared to thickness. A primary difference between a shell structure and a plate structure is that, in the unstressed state, the shell structure has curvature as opposed to the plates structure which is flat. Membrane action in a shell is primarily caused by in-plane forces ( plane stress ), but there may be secondary forces resulting from flexural deformations. Where a flat plate acts similar to a beam with bending and shear stresses , shells are analogous to a cable which resists loads through tensile stresses. The ideal thin shell must be capable of developing both tension and compression. [ 2 ]
The most popular types of thin-shell structures are:
Persons related:
This article about a civil engineering topic is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thin-shell_structure |
Thin Solid Films is a peer-reviewed scientific journal published 24 times per year by Elsevier . It was established in July 1967. The current editor-in-chief is J. E. Greene ( University of Illinois at Urbana–Champaign ).
The journal covers research on thin-film synthesis , characterization, and applications, including synthesis, surfaces, interfaces , colloidal behavior , metallurgical topics, mechanics (including nanomechanics), electronics , optics , optoelectronics , magnetics, magneto-optics , and superconductivity .
The journal is indexed and abstracted in:
According to the Journal Citation Reports , the journal has a 2020 impact factor of 2.183. [ 1 ] | https://en.wikipedia.org/wiki/Thin_Solid_Films |
A thin film is a layer of materials ranging from fractions of a nanometer ( monolayer ) to several micrometers in thickness. [ 1 ] The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many applications. A familiar example is the household mirror , which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as sputtering . Advances in thin film deposition techniques during the 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media , electronic semiconductor devices , integrated passive devices , light-emitting diodes , optical coatings (such as antireflective coatings), hard coatings on cutting tools, and for both energy generation (e.g. thin-film solar cells ) and storage ( thin-film batteries ). It is also being applied to pharmaceuticals, via thin-film drug delivery . A stack of thin films is called a multilayer .
In addition to their applied interest, thin films play an important role in the development and study of materials with new and unique properties. Examples include multiferroic materials , and superlattices that allow the study of quantum phenomena.
Nucleation is an important step in growth that helps determine the final structure of a thin film. Many growth methods rely on nucleation control such as atomic-layer epitaxy (atomic layer deposition). Nucleation can be modeled by characterizing surface process of adsorption , desorption , and surface diffusion . [ 2 ]
Adsorption is the interaction of a vapor atom or molecule with a substrate surface. The interaction is characterized the sticking coefficient , the fraction of incoming species thermally equilibrated with the surface. Desorption reverses adsorption where a previously adsorbed molecule overcomes the bounding energy and leaves the substrate surface.
The two types of adsorptions, physisorption and chemisorption , are distinguished by the strength of atomic interactions. Physisorption describes the van der Waals bonding between a stretched or bent molecule and the surface characterized by adsorption energy E p {\displaystyle E_{p}} . Evaporated molecules rapidly lose kinetic energy and reduces its free energy by bonding with surface atoms. Chemisorption describes the strong electron transfer (ionic or covalent bond) of molecule with substrate atoms characterized by adsorption energy E c {\displaystyle E_{c}} . The process of physic- and chemisorption can be visualized by the potential energy as a function of distance. The equilibrium distance for physisorption is further from the surface than chemisorption. The transition from physisorbed to chemisorbed states are governed by the effective energy barrier E a {\displaystyle E_{a}} . [ 2 ]
Crystal surfaces have specific bonding sites with larger E a {\displaystyle E_{a}} values that would preferentially be populated by vapor molecules to reduce the overall free energy. These stable sites are often found on step edges, vacancies and screw dislocations. After the most stable sites become filled, the adatom-adatom (vapor molecule) interaction becomes important. [ 3 ]
Nucleation kinetics can be modeled considering only adsorption and desorption. First consider case where there are no mutual adatom interactions, no clustering or interaction with step edges.
The rate of change of adatom surface density n {\displaystyle n} , where J {\displaystyle J} is the net flux, τ a {\displaystyle \tau _{a}} is the mean surface lifetime prior to desorption and σ {\displaystyle \sigma } is the sticking coefficient:
d n d t = J σ − n τ a {\displaystyle {dn \over dt}=J\sigma -{n \over \tau _{a}}}
n = J σ τ a [ 1 − exp ( − t τ a ) ] n = J σ τ a [ exp ( − t τ a ) ] {\displaystyle n=J\sigma \tau _{a}\left[1-\exp \left({-t \over \tau _{a}}\right)\right]n=J\sigma \tau _{a}\left[\exp \left({-t \over \tau _{a}}\right)\right]}
Adsorption can also be modeled by different isotherms such as Langmuir model and BET model . The Langmuir model derives an equilibrium constant b {\displaystyle b} based on the adsorption reaction of vapor adatom with vacancy on the substrate surface. The BET model expands further and allows adatoms deposition on previously adsorbed adatoms without interaction between adjacent piles of atoms. The resulting derived surface coverage is in terms of the equilibrium vapor pressure and applied pressure.
Langmuir model where P A {\displaystyle P_{A}} is the vapor pressure of adsorbed adatoms:
θ = b P A ( 1 + b P A ) {\displaystyle \theta ={bP_{A} \over (1+bP_{A})}}
BET model where p e {\displaystyle p_{e}} is the equilibrium vapor pressure of adsorbed adatoms and p {\displaystyle p} is the applied vapor pressure of adsorbed adatoms:
θ = X p ( p e − p ) [ 1 + ( X − 1 ) p p e ] {\displaystyle \theta ={Xp \over (p_{e}-p)\left[1+(X-1){p \over p_{e}}\right]}}
As an important note, surface crystallography and differ from the bulk to minimize the overall free electronic and bond energies due to the broken bonds at the surface. This can result in a new equilibrium position known as “selvedge”, where the parallel bulk lattice symmetry is preserved. This phenomenon can cause deviations from theoretical calculations of nucleation. [ 2 ]
Surface diffusion describes the lateral motion of adsorbed atoms moving between energy minima on the substrate surface. Diffusion most readily occurs between positions with lowest intervening potential barriers. Surface diffusion can be measured using glancing-angle ion scattering. The average time between events can be describes by: [ 2 ]
τ d = ( 1 / v 1 ) exp ( E d / k T s ) {\displaystyle \tau _{d}=(1/v_{1})\exp(E_{d}/kT_{s})}
In addition to adatom migration, clusters of adatom can coalesce or deplete. Cluster coalescence through processes, such as Ostwald ripening and sintering, occur in response to reduce the total surface energy of the system. Ostwald repining describes the process in which islands of adatoms with various sizes grow into larger ones at the expense of smaller ones. Sintering is the coalescence mechanism when the islands contact and join. [ 2 ]
The act of applying a thin film to a surface is thin-film deposition – any technique for depositing a thin film of material onto a substrate or onto previously deposited layers. "Thin" is a relative term, but most deposition techniques control layer thickness within a few tens of nanometres . Molecular beam epitaxy , the Langmuir–Blodgett method , atomic layer deposition and molecular layer deposition allow a single layer of atoms or molecules to be deposited at a time.
It is useful in the manufacture of optics (for reflective , anti-reflective coatings or self-cleaning glass , for instance), electronics (layers of insulators , semiconductors , and conductors form integrated circuits ), packaging (i.e., aluminium-coated PET film ), and in contemporary art (see the work of Larry Bell ). Similar processes are sometimes used where thickness is not important: for instance, the purification of copper by electroplating , and the deposition of silicon and enriched uranium by a chemical vapor deposition -like process after gas-phase processing.
Deposition techniques fall into two broad categories, depending on whether the process is primarily chemical or physical . [ 4 ]
Here, a fluid precursor undergoes a chemical change at a solid surface, leaving a solid layer. An everyday example is the formation of soot on a cool object when it is placed inside a flame. Since the fluid surrounds the solid object, deposition happens on every surface, with little regard to direction; thin films from chemical deposition techniques tend to be conformal , rather than directional .
Chemical deposition is further categorized by the phase of the precursor:
Plating relies on liquid precursors, often a solution of water with a salt of the metal to be deposited. Some plating processes are driven entirely by reagents in the solution (usually for noble metals ), but by far the most commercially important process is electroplating . In semiconductor manufacturing, an advanced form of electroplating known as electrochemical deposition is now used to create the copper conductive wires in advanced chips, replacing the chemical and physical deposition processes used to previous chip generations for aluminum wires [ 5 ]
Chemical solution deposition or chemical bath deposition uses a liquid precursor, usually a solution of organometallic powders dissolved in an organic solvent. This is a relatively inexpensive, simple thin-film process that produces stoichiometrically accurate crystalline phases. This technique is also known as the sol-gel method because the 'sol' (or solution) gradually evolves towards the formation of a gel-like diphasic system.
The Langmuir–Blodgett method uses molecules floating on top of an aqueous subphase. The packing density of molecules is controlled, and the packed monolayer is transferred on a solid substrate by controlled withdrawal of the solid substrate from the subphase. This allows creating thin films of various molecules such as nanoparticles , polymers and lipids with controlled particle packing density and layer thickness. [ 6 ]
Spin coating or spin casting, uses a liquid precursor, or sol-gel precursor deposited onto a smooth, flat substrate which is subsequently spun at a high velocity to centrifugally spread the solution over the substrate. The speed at which the solution is spun and the viscosity of the sol determine the ultimate thickness of the deposited film. Repeated depositions can be carried out to increase the thickness of films as desired. Thermal treatment is often carried out in order to crystallize the amorphous spin coated film. Such crystalline films can exhibit certain preferred orientations after crystallization on single crystal substrates. [ 7 ]
Dip coating is similar to spin coating in that a liquid precursor or sol-gel precursor is deposited on a substrate, but in this case the substrate is completely submerged in the solution and then withdrawn under controlled conditions. By controlling the withdrawal speed, the evaporation conditions (principally the humidity, temperature) and the volatility/viscosity of the solvent, the film thickness, homogeneity and nanoscopic morphology are controlled. There are two evaporation regimes: the capillary zone at very low withdrawal speeds, and the draining zone at faster evaporation speeds. [ 8 ]
Chemical vapor deposition generally uses a gas-phase precursor, often a halide or hydride of the element to be deposited. In the case of metalorganic vapour phase epitaxy , an organometallic gas is used. Commercial techniques often use very low pressures of precursor gas.
Plasma Enhanced Chemical Vapor Deposition uses an ionized vapor, or plasma , as a precursor. Unlike the soot example above, this method relies on electromagnetic means (electric current, microwave excitation), rather than a chemical-reaction, to produce a plasma.
Atomic layer deposition and its sister technique molecular layer deposition , uses gaseous precursor to deposit conformal thin film's one layer at a time. The process is split up into two half reactions, run in sequence and repeated for each layer, in order to ensure total layer saturation before beginning the next layer. Therefore, one reactant is deposited first, and then the second reactant is deposited, during which a chemical reaction occurs on the substrate, forming the desired composition. As a result of the stepwise, the process is slower than chemical vapor deposition; however, it can be run at low temperatures. When performed on polymeric substrates, atomic layer deposition can become sequential infiltration synthesis , where the reactants diffuse into the polymer and interact with functional groups on the polymer chains.
Physical deposition uses mechanical, electromechanical or thermodynamic means to produce a thin film of solid. An everyday example is the formation of frost . Since most engineering materials are held together by relatively high energies, and chemical reactions are not used to store these energies, commercial physical deposition systems tend to require a low-pressure vapor environment to function properly; most can be classified as physical vapor deposition .
The material to be deposited is placed in an energetic , entropic environment, so that particles of material escape its surface. Facing this source is a cooler surface which draws energy from these particles as they arrive, allowing them to form a solid layer. The whole system is kept in a vacuum deposition chamber, to allow the particles to travel as freely as possible. Since particles tend to follow a straight path, films deposited by physical means are commonly directional , rather than conformal .
Examples of physical deposition include:
A thermal evaporator that uses an electric resistance heater to melt the material and raise its vapor pressure to a useful range. This is done in a high vacuum, both to allow the vapor to reach the substrate without reacting with or scattering against other gas-phase atoms in the chamber, and reduce the incorporation of impurities from the residual gas in the vacuum chamber. Only materials with a much higher vapor pressure than the heating element can be deposited without contamination of the film. Molecular beam epitaxy is a particularly sophisticated form of thermal evaporation.
An electron beam evaporator fires a high-energy beam from an electron gun to boil a small spot of material; since the heating is not uniform, lower vapor pressure materials can be deposited. The beam is usually bent through an angle of 270° in order to ensure that the gun filament is not directly exposed to the evaporant flux. Typical deposition rates for electron beam evaporation range from 1 to 10 nanometres per second.
In molecular beam epitaxy , slow streams of an element can be directed at the substrate, so that material deposits one atomic layer at a time. Compounds such as gallium arsenide are usually deposited by repeatedly applying a layer of one element (i.e., gallium ), then a layer of the other (i.e., arsenic ), so that the process is chemical, as well as physical; this is known also as atomic layer deposition . If the precursors in use are organic, then the technique is called molecular layer deposition . The beam of material can be generated by either physical means (that is, by a furnace ) or by a chemical reaction ( chemical beam epitaxy ).
Sputtering relies on a plasma (usually a noble gas , such as argon ) to knock material from a "target" a few atoms at a time. The target can be kept at a relatively low temperature, since the process is not one of evaporation, making this one of the most flexible deposition techniques. It is especially useful for compounds or mixtures, where different components would otherwise tend to evaporate at different rates. Note, sputtering's step coverage is more or less conformal. It is also widely used in optical media. The manufacturing of all formats of CD, DVD, and BD are done with the help of this technique. It is a fast technique and also it provides a good thickness control. Presently, nitrogen and oxygen gases are also being used in sputtering.
Pulsed laser deposition systems work by an ablation process. Pulses of focused laser light vaporize the surface of the target material and convert it to plasma; this plasma usually reverts to a gas before it reaches the substrate. [ 10 ]
Thermal laser epitaxy uses focused light from a continuous-wave laser to thermally evaporate sources of material. [ 11 ] By adjusting the power density of the laser beam, the evaporation of any solid, non-radioactive element is possible. [ 12 ] The resulting atomic vapor is then deposited upon a substrate, which is also heated via a laser beam. [ 13 ] [ 14 ] The vast range of substrate and deposition temperatures allows of the epitaxial growth of various elements considered challenging by other thin film growth techniques. [ 15 ] [ 16 ]
Cathodic arc deposition (arc-physical vapor deposition), which is a kind of ion beam deposition where an electrical arc is created that blasts ions from the cathode. The arc has an extremely high power density resulting in a high level of ionization (30–100%), multiply charged ions, neutral particles, clusters and macro-particles (droplets). If a reactive gas is introduced during the evaporation process, dissociation , ionization and excitation can occur during interaction with the ion flux and a compound film will be deposited.
Electrohydrodynamic deposition (electrospray deposition) is a relatively new process of thin-film deposition. The liquid to be deposited, either in the form of nanoparticle solution or simply a solution, is fed to a small capillary nozzle (usually metallic) which is connected to a high voltage. The substrate on which the film has to be deposited is connected to ground. Through the influence of electric field, the liquid coming out of the nozzle takes a conical shape ( Taylor cone ) and at the apex of the cone a thin jet emanates which disintegrates into very fine and small positively charged droplets under the influence of Rayleigh charge limit. The droplets keep getting smaller and smaller and ultimately get deposited on the substrate as a uniform thin layer.
Frank–van der Merwe growth [ 17 ] [ 18 ] [ 19 ] ("layer-by-layer"). In this growth mode the adsorbate-surface and adsorbate-adsorbate interactions are balanced. This type of growth requires lattice matching, and hence considered an "ideal" growth mechanism.
Stranski–Krastanov growth [ 20 ] ("joint islands" or "layer-plus-island"). In this growth mode the adsorbate-surface interactions are stronger than adsorbate-adsorbate interactions.
Volmer–Weber [ 21 ] ("isolated islands"). In this growth mode the adsorbate-adsorbate interactions are stronger than adsorbate-surface interactions, hence "islands" are formed right away.
There are three distinct stages of stress evolution that arise during Volmer-Weber film deposition. [ 22 ] The first stage consists of the nucleation of individual atomic islands. During this first stage, the overall observed stress is very low. The second stage commences as these individual islands coalesce and begin to impinge on each other, resulting in an increase in the overall tensile stress in the film. [ 23 ] This increase in overall tensile stress can be attributed to the formation of grain boundaries upon island coalescence that results in interatomic forces acting over the newly formed grain boundaries. The magnitude of this generated tensile stress depends on the density of the formed grain boundaries, as well as their grain-boundary energies. [ 24 ] During this stage, the thickness of the film is not uniform because of the random nature of the island coalescence but is measured as the average thickness. The third and final stage of the Volmer-Weber film growth begins when the morphology of the film’s surface is unchanging with film thickness. During this stage, the overall stress in the film can remain tensile, or become compressive.
On a stress-thickness vs. thickness plot, an overall compressive stress is represented by a negative slope, and an overall tensile stress is represented by a positive slope. The overall shape of the stress-thickness vs. thickness curve depends on various processing conditions (such as temperature, growth rate, and material). Koch [ 25 ] states that there are three different modes of Volmer-Weber growth. Zone I behavior is characterized by low grain growth in subsequent film layers and is associated with low atomic mobility. Koch suggests that Zone I behavior can be observed at lower temperatures. The zone I mode typically has small columnar grains in the final film. The second mode of Volmer-Weber growth is classified as Zone T, where the grain size at the surface of the film deposition increases with film thickness, but the grain size in the deposited layers below the surface does not change. Zone T-type films are associated with higher atomic mobilities, higher deposition temperatures, and V-shaped final grains. The final mode of proposed Volmer-Weber growth is Zone II type growth, where the grain boundaries in the bulk of the film at the surface are mobile, resulting in large yet columnar grains. This growth mode is associated with the highest atomic mobility and deposition temperature. There is also a possibility of developing a mixed Zone T/Zone II type structure, where the grains are mostly wide and columnar, but do experience slight growth as their thickness approaches the surface of the film. Although Koch focuses mostly on temperature to suggest a potential zone mode, factors such as deposition rate can also influence the final film microstructure. [ 23 ]
A subset of thin-film deposition processes and applications is focused on the so-called epitaxial growth of materials,
the deposition of crystalline thin films that grow following the crystalline structure of the substrate. The term epitaxy comes from the Greek roots epi (ἐπί), meaning "above", and taxis (τάξις), meaning "an ordered manner". It can be translated as "arranging upon".
The term homoepitaxy refers to the specific case in which a film of the same material is grown on a crystalline
substrate. This technology is used, for instance, to grow a film which is more pure than the substrate, has a lower density
of defects, and to fabricate layers having different doping levels. Heteroepitaxy refers to the case in which the film being deposited is different from the substrate.
Techniques used for epitaxial growth of thin films include molecular beam epitaxy , chemical vapor deposition ,
and pulsed laser deposition . [ 26 ]
Thin films may be biaxially loaded via stresses originated from their interface with a substrate. Epitaxial thin films may experience stresses from misfit strains between the coherent lattices of the film and substrate, and from the restructuring of the surface triple junction. [ 27 ] Thermal stress is common in thin films grown at elevated temperatures due to differences in thermal expansion coefficients with the substrate. [ 28 ] Differences in interfacial energy and the growth and coalescence of grains contribute to intrinsic stress in thin films. These intrinsic stresses can be a function of film thickness. [ 29 ] [ 30 ] These stresses may be tensile or compressive and can cause cracking , buckling , or delamination along the surface. In epitaxial films, initially deposited atomic layers may have coherent lattice planes with the substrate. However, past a critical thickness misfit dislocations will form leading to relaxation of stresses in the film. [ 28 ] [ 31 ]
Films may experience a dilatational transformation strain e T {\displaystyle e_{T}} relative to its substrate due to a volume change in the film. Volume changes that cause dilatational strain may come from changes in temperature, defects, or phase transformations. A temperature change will induce a volume change if the film and substrate thermal expansion coefficients are different. The creation or annihilation of defects such as vacancies, dislocations , and grain boundaries will cause a volume change through densification. Phase transformations and concentration changes will cause volume changes via lattice distortions. [ 32 ] [ 33 ]
A mismatch of thermal expansion coefficients between the film and substrate will cause thermal strain during a temperature change. The elastic strain of the film relative to the substrate is given by:
ε = − ( α f − α s ) ( T − T 0 ) {\displaystyle \varepsilon =-(\alpha _{f}-\alpha _{s})(T-T_{0})}
where ε {\displaystyle \varepsilon } is the elastic strain, α f {\displaystyle \alpha _{f}} is the thermal expansion coefficient of the film, α s {\displaystyle \alpha _{s}} is the thermal expansion coefficient of the substrate, T {\displaystyle T} is the temperature, and T 0 {\displaystyle T_{0}} is the initial temperature of the film and substrate when it is in a stress-free state. For example, if a film is deposited onto a substrate with a lower thermal expansion coefficient at high temperatures, then cooled to room temperature, a positive elastic strain will be created. In this case, the film will develop tensile stresses. [ 32 ]
A change in density due to the creation or destruction of defects, phase changes, or compositional changes after the film is grown on the substrate will generate a growth strain. Such as in the Stranski–Krastanov mode, where the layer of film is strained to fit the substrate due to an increase in supersaturation and interfacial energy which shifts from island to island. [ 34 ] The elastic strain to accommodate these changes is related to the dilatational strain e T {\displaystyle e_{T}} by:
ε = − e T / 3 {\displaystyle \varepsilon =-e_{T}/3}
A film experiencing growth strains will be under biaxial tensile strain conditions, generating tensile stresses in biaxial directions in order to match the substrate dimensions. [ 32 ] [ 35 ]
An epitaxially grown film on a thick substrate will have an inherent elastic strain given by:
ε ≈ a s − a f a f {\displaystyle \varepsilon \approx {a_{s}-a_{f} \over a_{f}}}
where a s {\displaystyle a_{s}} and a f {\displaystyle a_{f}} are the lattice parameters of the substrate and film, respectively. It is assumed that the substrate is rigid due to its relative thickness. Therefore, all of the elastic strain occurs in the film to match the substrate. [ 32 ]
The stresses in Films deposited on flat substrates such as wafers can be calculated by measuring the curvature of the wafer due to the strain by the film. Using optical setups, such as those with lasers, [ 36 ] allow for whole wafer characterization pre and post deposition. Lasers are reflected off the wafer in a grid pattern and distortions in the grid are used to calculate the curvature as well as measure the optical constants . Strain in thin films can also be measured by x-ray diffraction or by milling a section of the film using a focused ion beam and monitoring the relaxation via scanning electron microscopy . [ 30 ]
A common method for determining the stress evolution of a film is to measure the wafer curvature during its deposition. Stoney [ 37 ] relates a film’s average stress to its curvature through the following expression:
κ = 6 ⟨ σ ⟩ h f M s h s 2 {\displaystyle \kappa ={\frac {6\langle \sigma \rangle h_{f}}{M_{s}h_{s}^{2}}}}
where M s = E 1 − υ {\displaystyle M_{s}={\frac {\mathrm {E} }{1-\upsilon }}} , where E {\displaystyle \mathrm {E} } is the bulk elastic modulus of the material comprising the film, and υ {\displaystyle \upsilon } is the Poisson’s ratio of the material comprising the film, h s {\displaystyle h_{s}} is the thickness of the substrate, h f {\displaystyle h_{f}} is the height of the film, and ⟨ σ ⟩ {\displaystyle \langle \sigma \rangle } is the average stress in the film. The assumptions made regarding the Stoney formula assume that the film and substrate are smaller than the lateral size of the wafer and that the stress is uniform across the surface. [ 38 ] Therefore the average stress thickness of a given film can be determined by integrating the stress over a given film thickness:
⟨ σ ⟩ = 1 h f ∫ 0 h f σ ( z ) d z {\displaystyle \langle \sigma \rangle ={\frac {1}{h_{f}}}\int _{0}^{h_{f}}\sigma (z)dz}
where z {\displaystyle z} is the direction normal to the substrate and σ ( z ) {\displaystyle \sigma (z)} represents the in-place stress at a particular height of the film. The stress thickness (or force per unit width) is represented by ⟨ σ ⟩ h f {\displaystyle \langle \sigma \rangle h_{f}} is an important quantity as it is directionally proportional to the curvature by 6 M s h s 2 {\displaystyle {\frac {6}{M_{s}h_{s}^{2}}}} . Because of this proportionality, measuring the curvature of a film at a given film thickness can directly determine the stress in the film at that thickness. The curvature of a wafer is determined by the average stress of in the film. However, if stress is not uniformly distributed in a film (as it would be for epitaxially grown film layers that have not relaxed so that the intrinsic stress is due to the lattice mismatch of the substrate and the film), it is impossible to determine the stress at a specific film height without continuous curvature measurements. If continuous curvature measurements are taken, the time derivative of the curvature data: [ 39 ] d κ d t ∝ σ ( h f ) ∂ h f ∂ t + ∫ 0 h f ∂ σ ( z , t ) ∂ t d z {\displaystyle {\frac {d\kappa }{dt}}\propto \sigma (h_{f}){\frac {\partial h_{f}}{\partial t}}+\int _{0}^{h_{f}}{\frac {\partial \sigma (z,t)}{\partial t}}dz}
can show how the intrinsic stress is changing at any given point. Assuming that stress in the underlying layers of a deposited film remains constant during further deposition, we can represent the incremental stress σ ( h f ) {\displaystyle \sigma (h_{f})} as: [ 39 ]
σ ( h f ) ∝ ∂ κ ∂ t ∂ h f ∂ t = d κ d h {\displaystyle \sigma (h_{f})\propto {\frac {\frac {\partial \kappa }{\partial t}}{\frac {\partial h_{f}}{\partial t}}}={\frac {d\kappa }{dh}}}
Nanoindentation is a popular method of measuring the mechanical properties of films. Measurements can be used to compare coated and uncoated films to reveal the effects of surface treatment on both elastic and plastic responses of the film. Load-displacement curves may reveal information about cracking, delamination, and plasticity in both the film and substrate. [ 40 ]
The Oliver and Pharr method [ 41 ] can be used to evaluate nanoindentation results for hardness and elastic modulus evaluation by the use of axisymmetric indenter geometries like a spherical indenter. This method assumes that during unloading, only elastic deformations are recovered (where reverse plastic deformation is negligible). The parameter P {\displaystyle P} designates the load, h {\displaystyle h} is the displacement relative to the undeformed coating surface and h f {\displaystyle h_{f}} is the final penetration depth after unloading. These are used to approximate the power law relation for unloading curves:
P = α ( h − h f ) m {\displaystyle P=\alpha (h-h_{f})^{m}}
After the contact area A {\displaystyle A} is calculated, the hardness is estimated by:
H = P m a x A {\displaystyle H={\frac {P_{max}}{A}}}
From the relationship of contact area, the unloading stiffness can be expressed by the relation: [ 42 ]
S = β 2 √ π E e f f √ A {\displaystyle S=\beta {\frac {2}{\surd \pi }}E_{eff}\surd A}
Where E e f f {\displaystyle E_{eff}} is the effective elastic modulus and takes into account elastic displacements in the specimen and indenter. This relation can also be applied to elastic-plastic contact, which is not affected by pile-up and sink-in during indentation.
1 E e f f = 1 − ν 2 E + 1 − ν 2 E i {\displaystyle {\frac {1}{E_{eff}}}={\frac {1-\nu ^{2}}{E}}+{\frac {1-\nu ^{2}}{E_{i}}}}
Due to the low thickness of the films, accidental probing of the substrate is a concern. To avoid indenting beyond the film and into the substrate, penetration depths are often kept to less than 10% of the film thickness. [ 43 ] For a conical or pyramidal indenters, the indentation depth scales as a / t {\displaystyle a/t} where a {\displaystyle a} is the radius of the contact circle and t {\displaystyle t} is the film thickness. The ratio of penetration depth h {\displaystyle h} and film thickness can be used as a scale parameter for soft films. [ 40 ]
Stress and relaxation of stresses in films can influence the materials properties of the film, such as mass transport in microelectronics applications. Therefore precautions are taken to either mitigate or produce such stresses; for example a buffer layer may be deposited between the substrate and film. [ 30 ] Strain engineering is also used to produce various phase and domain structures in thin films such as in the domain structure of the ferroelectric Lead Zirconate Titanate (PZT). [ 44 ]
In the physical sciences, a multilayer or stratified medium is a stack of different thin films. Typically, a multilayer medium is made for a specific purpose. Since layers are thin with respect to some relevant length scale, interface effects are much more important than in bulk materials, giving rise to novel physical properties. [ 45 ]
The term "multilayer" is not an extension of " monolayer " and " bilayer ", which describe a single layer that is one or two molecules thick. A multilayer medium rather consists of several thin films.
The usage of thin films for decorative coatings probably represents their oldest application. This encompasses ca. 100 nm thin gold leaves that were already used in ancient India more than 5000 years ago. It may also be understood as any form of painting, although this kind of work is generally considered as an arts craft rather than an engineering or scientific discipline. Today, thin-film materials of variable thickness and high refractive index like titanium dioxide are often applied for decorative coatings on glass for instance, causing a rainbow-color appearance like oil on water. In addition, intransparent gold-colored surfaces may either be prepared by sputtering of gold or titanium nitride .
These layers serve in both reflective and refractive systems. Large-area (reflective) mirrors became available during the 19th century and were produced by sputtering of metallic silver or aluminum on glass. Refractive lenses for optical instruments like cameras and microscopes typically exhibit aberrations , i.e. non-ideal refractive behavior. While large sets of lenses had to be lined up along the optical path previously, nowadays, the coating of optical lenses with transparent multilayers of titanium dioxide, silicon nitride or silicon oxide etc. may correct [ dubious – discuss ] these aberrations. A well-known example for the progress in optical systems by thin-film technology is represented by the only a few mm wide lens in smart phone cameras . Other examples are given by anti-reflection coatings on eyeglasses or solar panels .
Thin films are often deposited to protect an underlying work piece from external influences. The protection may operate by minimizing the contact with the exterior medium in order to reduce the diffusion from the medium to the work piece or vice versa. For instance, plastic lemonade bottles are frequently coated by anti-diffusion layers to avoid the out-diffusion of CO 2 , into which carbonic acid decomposes that was introduced into the beverage under high pressure. Another example is represented by thin TiN films in microelectronic chips separating electrically conducting aluminum lines from the embedding insulator SiO 2 in order to suppress the formation of Al 2 O 3 . Often, thin films serve as protection against abrasion between mechanically moving parts. Examples for the latter application are diamond-like carbon layers used in car engines or thin films made of nanocomposites .
Thin layers from elemental metals like copper, aluminum, gold or silver etc. and alloys have found numerous applications in electrical devices. Due to their high electrical conductivity they are able to transport electrical currents or supply voltages. Thin metal layers serve in conventional electrical system, for instance, as Cu layers on printed circuit boards , as the outer ground conductor in coaxial cables and various other forms like sensors etc. [ 47 ] A major field of application became their use in integrated passive devices and integrated circuits , [ 48 ] where the electrical network among active and passive devices like transistors and capacitors etc. is built up from thin Al or Cu layers. These layers dispose of thicknesses in the range of a few 100 nm up to a few μm, and they are often embedded into a few nm thin titanium nitride layers in order to block a chemical reaction with the surrounding dielectric like SiO 2 . The figure shows a micrograph of a laterally structured TiN/Al/TiN metal stack in a microelectronic chip. [ 46 ]
Heterostructures of gallium nitride and similar semiconductors can lead to electrons being bound to a sub-nanometric layer, effectively behaving as a two-dimensional electron gas . Quantum effects in such thin films can significantly enhance electron mobility as compared to that of a bulk crystal, which is employed in high-electron-mobility transistors .
Noble metal thin films are used in plasmonic structures such as surface plasmon resonance (SPR) sensors. Surface plasmon polaritons are surface waves in the optical regime that propagate in between metal-dielectric interfaces; in Kretschmann-Raether configuration for the SPR sensors, a prism is coated with a metallic film through evaporation. Due to the poor adhesive characteristics of metallic films, germanium , titanium or chromium films are used as intermediate layers to promote stronger adhesion. [ 49 ] [ 50 ] [ 51 ] Metallic thin films are also used in plasmonic waveguide designs. [ 52 ] [ 53 ]
Thin-film technologies are also being developed as a means of substantially reducing the cost of solar cells . The rationale for this is thin-film solar cells are cheaper to manufacture owing to their reduced material costs, energy costs, handling costs and capital costs. This is especially represented in the use of printed electronics ( roll-to-roll ) processes. Other thin-film technologies, that are still in an early stage of ongoing research or with limited commercial availability, are often classified as emerging or third generation photovoltaic cells and include, organic , dye-sensitized , and polymer solar cells , as well as quantum dot , [ 54 ] copper zinc tin sulfide , nanocrystal and perovskite solar cells . [ 55 ] [ 56 ]
Thin-film printing technology is being used to apply solid-state lithium polymers to a variety of substrates to create unique batteries for specialized applications. Thin-film batteries can be deposited directly onto chips or chip packages in any shape or size. Flexible batteries can be made by printing onto plastic, thin metal foil, or paper. [ 57 ]
For miniaturising and more precise control of resonance frequency of piezoelectric crystals thin-film bulk acoustic resonators TFBARs/FBARs are developed for oscillators, telecommunication filters and duplexers, and sensor applications. | https://en.wikipedia.org/wiki/Thin_film |
Thin layer extraction is a time-periodic reactive liquid extraction process that provides excellent mass transfer while maintaining phase separation. [ 1 ] It is performed via a periodic batch production process that controls the time of each chemical reaction .
A small amount of a liquid organic extract is spread, as a thin layer, onto a matrix made of a thin microporous material whose surfaces are freely accessible from and to the outside. The extract is held by capillary forces or other forces. This layer is alternately and repeatedly brought into brief contact with thin layers of the donor and the strip aqueous liquid. In the extraction step, selected species that are present in the donor solution are transported from the donor aqueous solution to the organic phase where a reaction ensues. In the stripping step the reaction reverses and the extracted species are stripped into the strip aqueous solution. Thus, two alternate product batches are generated: a raffinate and a strip product. As each of the species to be separated associates differently with the host, the composition of the raffinate and strip product is differentiated.
With a typical liquid mass diffusivity in the order of 10 −9 m 2 /s, [ 2 ] the characteristic time for diffusion through a 20 micron thick liquid layer is 0.4 s. Therefore, the thinness of both phases (organic and aqueous) causes a relatively "immediate" mass transfer of guest species from one phase to the other, which means that this process has a low mass transfer resistance. The low mass transfer resistance permits the uncoupling of effects attributed to mass transfer from the effects attributed to the reaction rates; it also allows relatively frequent cycling that helps mitigate the limited capacity that is due to the small batches of aqueous feed processed within each cycle.
A secondary characteristic of thin layer extraction arises from the batch periodic mode of operation. It permits precise control in time and space over small processed elements in the course of the process, a degree of control that is not possible in any other liquid-liquid extraction method. This control is instrumental in enabling the exploitation of differences in reaction rates of the different species (see Thermodynamic versus kinetic reaction control ) and the "harvesting" of separated species early on the reaction trajectories where the relative differences in concentration are largest. This forms the basis for kinetic, reactive, thin layer extraction. [ 3 ]
The extractant, including the host, must be substantially insoluble in the processed aqueous solutions to avoid being washed away. However, the difference in density between the immiscible phases, which plays an important role in conventional liquid-liquid extraction, is irrelevant in thin layer extraction.
When the separation of two closely related compounds by liquid-liquid extraction is necessary, conventional wisdom indicates that a selective extractant must be found that will discern between the two by associating each to different equilibrium compositions.
Thin layer extraction is recommended for the separation of high-value products that are produced in moderate volumes (for example the separation of chiral molecules [ 4 ] [ 5 ] ).
Thin layer extraction is used in specialized equipment operated as robots consisting of:
A thin layer extraction cell consists of a section of the matrix that takes turns at being alternately exposed to the donor and then the strip solutions. Each cell accepts two alternating aqueous feed batches and generates two corresponding alternating batches of the products.
In multistage operation, a train of cells is operated synchronously with the products from one cell directed as feeds to a next upstream or downstream cell.
The multistage thin layer extraction equipment is linearly scalable, permitting results obtained on table-top laboratory devices to be directly scaled up to full-scale production plants. | https://en.wikipedia.org/wiki/Thin_layer_extraction |
A thin walled beam is a type of beam that does not have a solid cross sectional area. The cross section of a thin walled beam is made up from thin panels connected together. Typical closed sections include round, square, and rectangular tubes. Open sections include I-beams, T-beams, L-beams, and so on.
The advantages of thin walled beams are their lighter weight and their bending stiffness per unit cross sectional area, which is much higher than for solid cross sections such as a rod or bar. Thin-walled beams are found almost everywhere, in civil and naval engineering, as well as aeronautics and aerospace designs. Apart from lightweight construction, strong rigidity, and load resistance, there are also lower manufacturing costs, and lower transport and maintenance costs. They also give the designer more flexibility in the choice of material and shape to meet any specific requirements. [ 1 ]
Thin walled beams are particularly useful when the material is a composite laminate. Pioneer work in this regard was done by Librescu .
This material -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thin_walled_beam |
Thinkfree Office is a web-based commercial office productivity suite developed by Thinkfree Inc. It includes Word (a word processor ), Spreadsheet (a spreadsheet ) and Presentation (a presentation program ). [ 1 ] [ 2 ] [ 3 ]
They are compatible with Microsoft Office 's Word , PowerPoint , and Excel . It also features collaborative editing . [ 4 ] [ 5 ] The product is hosted on the client’s server.
Thinkfree Office supports ISO/IEC international standard ISO/IEC 26300 Open Document Format for Office Applications (odf, odt, odp, ods, odg). [ 6 ] It also supports Microsoft's XML formats ( docx , pptx, xlsx) and Microsoft's legacy binary formats (doc, ppt, xls).
The software was previously marketed under different names, such as Thinkfree Server, Thinkfree Online, Hancom Office Online, and Hancom Office Web. [ 7 ] Eventually, the brand was consolidated under the name Thinkfree Office. | https://en.wikipedia.org/wiki/Thinkfree_Office |
Thinking, Fast and Slow is a 2011 popular science book by psychologist Daniel Kahneman .
The book's main thesis is a differentiation between two modes of thought : "System 1" is fast, instinctive and emotional ; "System 2" is slower, more deliberative , and more logical .
The book delineates rational and non-rational motivations or triggers associated with each type of thinking process, and how they complement each other, starting with Kahneman's own research on loss aversion . From framing choices to people's tendency to replace a difficult question with one that is easy to answer, the book summarizes several decades of research to suggest that people have too much confidence in human judgment. [ 1 ] Kahneman performed his own research, often in collaboration with Amos Tversky , which enriched his experience to write the book. [ 2 ] [ 3 ] It covers different phases of his career: his early work concerning cognitive biases , his work on prospect theory and happiness , and with the Israel Defense Forces .
The book was a New York Times bestseller [ 4 ] and was the 2012 winner of the National Academies Communication Award for best creative work that helps the public understanding of topics in behavioral science , engineering and medicine. [ 5 ] The integrity of some priming studies cited in the book has been called into question in the midst of the psychological replication crisis . [ 6 ]
In the book's first section, Kahneman describes two different ways the brain forms thoughts:
Kahneman describes a number of experiments which purport to examine the differences between these two thought systems and how they arrive at different results even given the same inputs. Terms and concepts include coherence, attention, laziness, association, jumping to conclusions, WYSIATI (What you see is all there is), and how one forms judgments. The System 1 vs. System 2 debate includes the reasoning or lack thereof for human decision making, with big implications for many areas including law and market research. [ 7 ]
The second section offers explanations for why humans struggle to think statistically. It begins by documenting a variety of situations in which we either arrive at binary decisions or fail to associate precisely reasonable probabilities with outcomes. Kahneman explains this phenomenon using the theory of heuristics . Kahneman and Tversky originally discussed this topic in their 1974 article titled Judgment Under Uncertainty: Heuristics and Biases. [ 8 ]
Kahneman uses heuristics to assert that System 1 thinking involves associating new information with existing patterns, or thoughts, rather than creating new patterns for each new experience. For example, a child who has only seen shapes with straight edges might perceive an octagon when first viewing a circle. As a legal metaphor, a judge limited to heuristic thinking would only be able to think of similar historical cases when presented with a new dispute, rather than considering the unique aspects of that case. In addition to offering an explanation for the statistical problem, the theory also offers an explanation for human biases.
The "anchoring effect" names a tendency to be influenced by irrelevant numbers. Shown greater/lesser numbers, experimental subjects gave greater/lesser responses. [ 2 ] As an example, most people, when asked whether Gandhi was more than 114 years old when he died, will provide a much greater estimate of his age at death than others who were asked whether Gandhi was more or less than 35 years old. Experiments show that people's behavior is influenced, much more than they are aware, by irrelevant information.
The availability heuristic is a mental shortcut that occurs when people make judgments about the probability of events on the basis of how easy it is to think of examples. The availability heuristic operates on the notion that, "if you can think of it, it must be important". The availability of consequences associated with an action is related positively to perceptions of the magnitude of the consequences of that action. In other words, the easier it is to recall the consequences of something, the greater we perceive these consequences to be. Sometimes, this heuristic is beneficial, but the frequencies at which events come to mind are usually not accurate representations of the probabilities of such events in real life. [ 9 ] [ 10 ]
System 1 is prone to substituting a simpler question for a difficult one. In what Kahneman terms their "best-known and most controversial" experiment, "the Linda problem ", subjects were told about an imaginary Linda, young, single, outspoken, and intelligent, who, as a student, was very concerned with discrimination and social justice. They asked whether it was more probable that Linda is a bank teller or that she is a bank teller and an active feminist. The overwhelming response was that "feminist bank teller" was more likely than "bank teller", violating the laws of probability . (All feminist bank tellers are bank tellers, so the former can't be more likely). In this case System 1 substituted the easier question, "Is Linda a feminist?", neglecting the occupation qualifier. An alternative interpretation is that the subjects added an unstated cultural implicature to the effect that the other answer implied an exclusive or , that Linda was not a feminist. [ 2 ]
Kahneman writes of a "pervasive optimistic bias ", which "may well be the most significant of the cognitive biases." This bias generates the illusion of control : the illusion that we have substantial control of our lives.
A natural experiment reveals the prevalence of one kind of unwarranted optimism. The planning fallacy is the tendency to overestimate benefits and underestimate costs, impelling people to begin risky projects. In 2002, American kitchen remodeling was expected on average to cost $18,658, but actually cost $38,769. [ 2 ]
To explain overconfidence , Kahneman introduces the concept he terms What You See Is All There Is (WYSIATI). This theory states that when the mind makes decisions, it deals primarily with Known Knowns , phenomena it has observed already. It rarely considers Known Unknowns , phenomena that it knows to be relevant but about which it does not have information. Finally it appears oblivious to the possibility of Unknown Unknowns , unknown phenomena of unknown relevance.
He explains that humans fail to take into account complexity and that their understanding of the world consists of a small and necessarily un-representative set of observations. Furthermore, the mind generally does not account for the role of chance and therefore falsely assumes that a future event will be similar to a past event.
Framing is the context in which choices are presented. Experiment: subjects were asked whether they would opt for surgery if the "survival" rate is 90 percent, while others were told that the mortality rate is 10 percent. The first framing increased acceptance, even though the situation was no different. [ 11 ]
Rather than consider the odds that an incremental investment would produce a positive return, people tend to "throw good money after bad" and continue investing in projects with poor prospects that have already consumed significant resources. In part this is to avoid feelings of regret. [ 11 ]
This part (part III, sections 19–24) of the book is dedicated to the undue confidence in what the mind believes it knows. It suggests that people often overestimate how much they understand about the world and underestimate the role of chance in particular. This is related to the excessive certainty of hindsight, when an event seems to be understood after it has occurred or developed. Kahneman's opinions concerning overconfidence are influenced by Nassim Nicholas Taleb . [ 12 ]
In this section Kahneman returns to economics and expands his seminal work on Prospect Theory. He discusses the tendency for problems to be addressed in isolation and how, when other reference points are considered, the choice of that reference point (called a frame) has a disproportionate effect on the outcome. This section also offers advice on how some of the shortcomings of System 1 thinking can be avoided.
Kahneman developed prospect theory, the basis for his Nobel prize, to account for experimental errors he noticed in Daniel Bernoulli 's traditional utility theory . [ 13 ] According to Kahneman, Utility Theory makes logical assumptions of economic rationality that do not represent people's actual choices, and does not take into account cognitive biases .
One example is that people are loss-averse: they are more likely to act to avert a loss than to achieve a gain. Another example is that the value people place on a change in probability (e.g., of winning something) depends on the reference point: people seem to place greater value on a change from 0% to 10% (going from impossibility to possibility) than from, say, 45% to 55%, and they place the greatest value of all on a change from 90% to 100% (going from possibility to certainty). This occurs despite the fact that by traditional utility theory all three changes give the same increase in utility. Consistent with loss-aversion, the order of the first and third of those is reversed when the event is presented as losing rather than winning something: there, the greatest value is placed on eliminating the probability of a loss to 0.
After the book's publication, the Journal of Economic Literature published a discussion of its parts concerning prospect theory, [ 14 ] as well as an analysis of the four fundamental factors on which it is based. [ 15 ]
The fifth part of the book describes recent evidence which introduces a distinction between two selves, the 'experiencing self' and 'remembering self'. [ 16 ] Kahneman proposed an alternative measure that assessed pleasure or pain sampled from moment to moment, and then summed over time. Kahneman termed this "experienced" well-being and attached it to a separate "self". He distinguished this from the "remembered" well-being that the polls had attempted to measure. He found that these two measures of happiness diverged. [ 17 ]
The author's significant discovery was that the remembering self does not care about the duration of a pleasant or unpleasant experience. Instead, it retrospectively rates an experience by the maximum or minimum of the experience, and by the way it ends. The remembering self dominated the patient's ultimate conclusion.
"Odd as it may seem," Kahneman writes, "I am my remembering self, and the experiencing self, who does my living, is like a stranger to me." [ 3 ]
Kahneman first began the study of well-being in the 1990s. At the time most happiness research relied on polls about life satisfaction . Having previously studied unreliable memories, the author was doubtful that life satisfaction was a good indicator of happiness. He designed a question that emphasized instead the well-being of the experiencing self. The author proposed that "Helen was happy in the month of March" if she spent most of her time engaged in activities that she would rather continue than stop, little time in situations that she wished to escape, and not too much time in a neutral state that wouldn't prefer continuing or stopping the activity either way.
Kahneman suggests that emphasizing a life event such as a marriage or a new car can provide a distorted illusion of its true value. This " focusing illusion " revisits earlier ideas of substituting difficult questions and WYSIATI.
As of 2012 the book had sold over one million copies. [ 23 ] On the year of its publication, it was on the New York Times Bestseller List . [ 4 ] The book was reviewed in media including the Huffington Post , [ 24 ] The Guardian , [ 25 ] The New York Times , [ 2 ] The Financial Times , [ 26 ] The Independent , [ 27 ] Bloomberg [ 11 ] and The New York Review of Books . [ 28 ] [ further explanation needed ] On Book Marks , the book received a "rave" consensus, based on eight critic reviews: six "rave" and two "positive". [ 29 ] Prosenotes gave it a "C" (72%) based on critic reviews with a consensus saying, "On the whole it is an important, readable, and interesting book about judgment and decision making, but even some of the author's diehard fans found small portions of this book hard to work through". [ 30 ] In March/April 2012 issue of Bookmarks , the book received a (4.00 out of 5) with the critical summary stating, "Either way, it's an enlightening tome on how--fast or slow--we make decisions". [ 31 ]
The book was also widely reviewed in academic journals, including the Journal of Economic Literature , [ 14 ] American Journal of Education , [ 32 ] The American Journal of Psychology , [ 33 ] Planning Theory , [ 34 ] The American Economist , [ 35 ] The Journal of Risk and Insurance , [ 36 ] The Michigan Law Review , [ 37 ] American Scientist , [ 38 ] Contemporary Sociology , [ 39 ] Science , [ 40 ] Contexts , [ 41 ] The Wilson Quarterly , [ 42 ] Technical Communication , [ 43 ] The University of Toronto Law Journal , [ 44 ] A Review of General Semantics [ 45 ] and Scientific American Mind . [ 46 ] The book was also reviewed in a monthly magazine Observer , published by the Association for Psychological Science . [ 47 ] [ further explanation needed ]
The book has achieved a large following among baseball scouts and baseball executives. The ways of thinking described in the book are believed to help scouts, who have to make major judgements off little information and can easily fall into prescriptive yet inaccurate patterns of analysis. [ 48 ]
The last chapter of Paul Bloom 's Against Empathy discusses concepts also touched in Daniel Kahneman's book, Thinking, Fast and Slow, that suggest people make a series of rational and irrational decisions. [ 49 ] [ 49 ] : 214 He criticizes the argument that "regardless of reason's virtues, we just aren't any good at it." His point is that people are not as "stupid as scholars think they are." [ 49 ] : 216 He explains that people are rational because they make thoughtful decisions in their everyday lives. For example, when someone has to make a big life decision they critically assess the outcomes, consequences, and alternative options. [ 49 ] : 230
Author Nicholas Taleb has equated the book's importance to that of Adam Smith's The Wealth of Nations and Sigmund Freud's The Interpretation of Dreams . [ 50 ]
Part of the book has been swept up in the replication crisis facing psychology and the social sciences. It was discovered many prominent research findings were difficult or impossible for others to replicate, and thus the original findings were called into question. An analysis [ 51 ] of the studies cited in chapter 4, "The Associative Machine", found that their replicability index (R-index) [ 52 ] is 14, indicating essentially low to no reliability. Kahneman himself responded to the study in blog comments and acknowledged the chapter's shortcomings: "I placed too much faith in underpowered studies." [ 53 ] Others have noted the irony in the fact that Kahneman made a mistake in judgment similar to the ones he studied. [ 54 ]
A later analysis [ 55 ] made a bolder claim that, despite Kahneman's previous contributions to the field of decision making, most of the book's ideas are based on 'scientific literature with shaky foundations'. A general lack of replication in the empirical studies cited in the book was given as a justification. | https://en.wikipedia.org/wiki/Thinking,_Fast_and_Slow |
Thinking Strategically: The Competitive Edge in Business, Politics, and Everyday Life is a non-fiction book by Indian-American economist Avinash Dixit and Barry Nalebuff , a professor of economics and management at Yale School of Management . The text was initially published by W. W. Norton & Company on February 1, 1991. [ 1 ]
The book discusses issues of strategic behaviour, decision making, and game theory . The authors present the main concepts, such as backward induction , auction theory , Nash equilibrium , noncooperative bargaining, to a general audience. Each concept is illustrated by examples from common life, business, sports, politics, etc.—as applying game theory to real life may be the best way of crystallizing the best options available. [ 2 ]
Today our writers and critics nominate the books they have enjoyed reading most over the last twelve months. No rules were imposed but, as you will see, all have been encouraged to be adventurous and broaden their interests away from their usual subjects Thinking Strategically by Avinash Dixit & Barry Nalebuff (W W Norton) offers essential training in making choices and weighing possibilities not only in business but in daily life. Reading it is a trip to the gym for the reasoning faculties. It presents game theory and business strategy as understandable, usable and everyday tools for living with others. Its examples of tactics in action range from King Lear to Maradonna. And the case studies make great bit-reading in queues or waiting-rooms. I also much enjoyed Howard Rheingold's Virtual Reality (Secker & Warburg), which describes the computer-created world waiting around the corner of the century, and Simon Schama's Dead Certainties (Granta), which sent a bright spark between history and fiction: illuminating.
—Review by Financial Times [ 3 ] | https://en.wikipedia.org/wiki/Thinking_Strategically |
Thinking like a mountain is a term coined by Aldo Leopold in his book A Sand County Almanac . [ 1 ] In the section entitled "Sketches Here and There" Leopold discusses the thought process as a holistic view on where one stands in the entire ecosystem . [ 2 ] To think like a mountain means to have a complete appreciation for the profound interconnectedness of the elements in the ecosystems. [ 3 ] It is an ecological exercise using the intricate web of the natural environment rather than thinking as an isolated individual.
Aldo Leopold first came up with this term as a result of watching the death of wolf that had been shot and was dying slowly. In those days of Leopold's adventures, no one would ever pass up killing a wolf because fewer wolves meant more deer, which meant great hunting experiences. However, when Leopold saw the “fierce green fire dying in her eyes” he knew that neither the mountain nor the wolf deserved this. Leopold stated in his book, A Sand County Almanac :
Since then I have lived to see state after state extirpate its wolves. I have watched the face of many a newly wolfless mountain, and seen the south-facing slopes wrinkle with a maze of new deer trails. I have seen every edible bush and seedling browsed, first to anaemic desuetude, and then to death. I have seen every edible tree defoliated to the height of a saddlehorn … In the end the starved bones of the hoped-for deer herd, dead of its own too-much, bleach with the bones of the dead sage, or molder under the high-lined junipers … So also with cows. The cowman who cleans his range of wolves does not realize that he is taking over the wolf’s job of trimming the herd to fit the change. He has not learned to think like a mountain. Hence we have dustbowls, and rivers washing the future into the sea. [ 4 ]
In this example Leopold shows that the removal of a single species can result in serious negative consequences in an ecosystem. While avoiding trophic cascades is one way to think like a mountain, there are countless other environmental actions that can be categorized under this broad and interconnected concept.
Although the term was not coined until 1949, several philosophers of the ancient times had viewpoints similar to those who “think like a mountain”. Epicurus was one of the first ancient philosophers to view the role man plays in nature. His philosophy, Epicureanism , is a materialistic viewpoint that sought to explain the universe solely by natural causes.
Lucretius was a later philosopher who had Epicurean ideals. He wrote a six book collection, De Rerum Natura , categorizing the natural word. In Book 5 of De Rerum Natura he writes:
They [Roman gods] did not create the world for us [man], why should they? They did not create man, how could they? They had no conception of man until nature and natural causes (the union of atoms) showed them the way. Besides the gods were absolutely happy as they were, and the creating of man could not increase their happiness. After numberless attempts and numberless failures the concourse of atoms gradually formed the world. [ 5 ]
In this passage, Lucretius is defining man's place in the creation of the world. Lucretius is an Epicurean supporter, believing that living modestly and gaining knowledge of the working world were the keys to a more pleasurable life. [ 6 ]
Aristotle also philosophized about man's place in the ecosystem. In his Politics , he discusses the role of community as used when referring to cities, neighborhoods, and households. The idea of thinking like a mountain is primarily ecological, but it can be applied to politics as well. Aristotle provides resources for citizens on how they as individuals fit into their community. [ 7 ]
Other ancient philosophers approach the idea of viewing one's place in the ecosystem as well. They include Sophocles , a Greek philosopher , and Columella , a Roman philosopher. Sophocles writes in Antigone about natural law and legal institutions. In his eyes, the laws of the gods outweigh those of man and man must understand his place in the order of natural law. [ 8 ] Columella, similar to the Epicureans, believed that in order to make the most efficient use of the land, humans should not rely on the gods, but should become more educated and learn to use resources more efficiently.
In much the same way that Rachel Carson ’s bellwether manuscript Silent Spring changed the realm of how and which chemicals are used in nature, Aldo Leopold forever changed the way we view our ecological impact on the environment around us with the introduction of the term “Thinking Like a Mountain” in his book A Sand County Almanac [ 1 ] in 1949. Since then, the phrase and the particular mindset it generates has greatly influenced people in all walks of life.
Philip Connors has attempted to further Leopold's elucidation with respect to matters of the environment through literature. In many of his books, most notably Fire Season , [ 9 ] Connors alludes to thinking like a mountain when he urges the reader to think about more than just the costs and benefits an action has on their person. He believes that everyone who witnesses the environment should have the goal of achieving what Leopold spoke of when he describes living in harmony with nature. Connors said,
We touch the ancient mysteries of life in the wild. We may even learn to see in new ways — more closely, perhaps, and deeper into geologic time. If we’re lucky we get close to learning how to ‘think like a mountain,’ in Aldo Leopold’s great phrase.
Another author, Leslie Thiele refers to thinking like a mountain in multiple chapters in his book Indra's Net and the Midas Touch. [ 3 ] Within one chapter, Thiele explains how thinking like a mountain is, first and foremost, an ecological principle for a sustainable existence. Later, he also cites this sort of living as a basis for environmental ethics . Thiele summarizes his view of thinking like a mountain as
a full appreciation of the vast and intricate web of interdependent relationships that constitute a mountain oikos. [ 3 ]
The idea of thinking like a mountain has also permeated its way into the world of full-length movies and documentaries. Green Fire , released in 2011, is a documentary about Aldo Leopold's influence on modern environmentalism and revolves around the concept of thinking like a mountain. [ 10 ] The name Green Fire was meant to capture the image of Leopold's dying she wolf and the passion with which he pursued environmental justice and ecological balance throughout his life.
Filmmaker Alexander Hick spent several months in 2017 among the Arhuaco community in the Sierra Nevada de Santa Marta , Colombia, filming a feature documentary titled "Thinking Like A Mountain" with his brother Immanuel Hick as Director of Photography. The film was released at the International Film Festival Nyon " visions du reel " on April 15, 2018, and screened at other festivals around the world. The Film won the Human Rights Film Award Deutscher Menschenrechts Filmpreis " in one of the categories. [ 11 ] [ 12 ]
Mission Wolf: Experiment in Living (2018) documents a group of volunteers near the southern edge of the Rocky Mountains who seek to nurture themselves just as they nurture the wolves they care deeply about. Leopold's thoughts on wolves and nature are reflected and reference in the film.
The mindset of thinking like a mountain has been infused into music as well. Folk artist Libby Roderick has used the idea of thinking like a mountain as a foundation for her album Thinking Like a Mountain . [ 13 ] In one song in particular, Roderick equates thinking like a mountain to being safe, home, or complete. Also, she ends each stanza with “Thinking like a mountain, honey, we will make it home” as if to say that eventually we will all think with a long-term perspective and get our lives back on a safe and sustainable track. Furthermore, Roderick ends the song with an ultimatum for each of our lives.
Find the mountain deep within your heart, it's calling you back home! | https://en.wikipedia.org/wiki/Thinking_like_a_mountain |
The prefix thio- , when applied to a chemical, such as an ion , means that an oxygen atom in the compound has been replaced by a sulfur atom. This term is often used in organic chemistry . For example, from the word ether , referring to an oxygen-containing compound having the general chemical structure R−O−R′ , where R and R′ are organic functional groups and O is an oxygen atom, comes the word thioether , which refers to an analogous compound with the general structure R−S−R′ , where S is a sulfur atom covalently bonded to two organic groups. [ 1 ] A chemical reaction involving the replacement of oxygen to sulfur is called thionation or thiation .
Thio- can be prefixed with di- and tri- in chemical nomenclature.
The word derives from Ancient Greek θεῖον (theîon) ' sulfur ' (which occurs in Greek epic poetry as θέ(ϝ)ειον , théweion and may come from the same root as Latin fumus ( Indo-European dh-w ) and may have originally meant " fumigation substance".) | https://en.wikipedia.org/wiki/Thio- |
In organosulfur chemistry , thioacetals are the sulfur ( thio- ) analogues of acetals ( R−CH(−OR) 2 ). There are two classes: the less-common monothioacetals , with the formula R−CH(−OR')−SR" , and the dithioacetals , with the formula R−CH(−SR') 2 (symmetric dithioacetals) or R−CH(−SR')−SR" (asymmetric dithioacetals). [ 1 ]
The symmetric dithioacetals are relatively common. They are prepared by condensation of thiols ( −SH ) or dithiols (two −SH groups) with aldehydes ( −CH=O ). These reactions proceed via the intermediacy of hemithioacetals ( R−CH(−OH)−SR' ):
Such reactions typically employ either a Lewis acid or Brønsted acid as catalyst .
Dithioacetals generated from aldehydes and either 1,2-ethanedithiol or 1,3-propanedithiol are especially common among this class of molecules for use in organic synthesis . [ 2 ]
The carbonyl carbon of an aldehyde is electrophilic and therefore susceptible to attack by nucleophiles , whereas the analogous central carbon of a dithioacetal is not electrophilic. As a result, dithioacetals can serve as protective groups for aldehydes.
Far from being unreactive, and in a reaction unlike that of aldehydes, that carbon can be deprotonated to render it nucleophilic:
The inversion of polarity between R'(H)C δ+ =O δ− and R'CLi(SR) 2 is referred to as umpolung . The reaction is commonly performed using the 1,3-dithiane . The lithiated intermediate can be used for various nucleophilic bond-forming reactions, and then the dithioketal hydrolyzed back to its carbonyl form. This overall process, the Corey–Seebach reaction , gives the synthetic equivalent of an acyl anion. | https://en.wikipedia.org/wiki/Thioacetal |
Thioacetic acid is an organosulfur compound with the molecular formula CH 3 C(O)SH . It is a thioic acid : the sulfur analogue of acetic acid ( CH 3 C(O)OH ), as implied by the thio- prefix. It is a yellow liquid with a strong thiol -like odor. It is used in organic synthesis for the introduction of thiol groups ( −SH ) in molecules. [ 4 ]
Thioacetic acid is prepared by the reaction of acetic anhydride with hydrogen sulfide : [ 5 ]
It has also been produced by the action of phosphorus pentasulfide on glacial acetic acid , followed by distillation. [ 6 ]
Thioacetic acid is typically contaminated by acetic acid.
The compound exists exclusively as the thiol tautomer , consistent with the strength of the C=O double bond. Reflecting the influence of hydrogen-bonding , the boiling point (93 °C) and melting points are 20 and 75 K lower than those for acetic acid .
With a p K a near 3.4, thioacetic acid is about 15 times more acidic than acetic acid. [ 7 ] The conjugate base is thioacetate :
In neutral water, thioacetic acid is fully ionized.
Most of the reactivity of thioacetic acid arises from the conjugate base, thioacetate. Salts of this anion, e.g. potassium thioacetate , are used to generate thioacetate esters. [ 8 ] Thioacetate esters undergo hydrolysis to give thiols. A typical method for preparing a thiol from an alkyl halide using thioacetic acid proceeds in four discrete steps, some of which can be conducted sequentially in the same flask:
In an application that illustrates the use of its radical behavior, thioacetic acid is used with AIBN in a free radical mediated nucleophilic addition to an exocyclic alkene forming a thioester : [ 9 ]
Potassium thioacetate can be used convert nitroarenes to aryl acetamides in one step. This is particularly useful in the preparation of pharmaceuticals, e.g., paracetamol from 4-nitrophenol or 4-nitro anisole . [ 10 ] | https://en.wikipedia.org/wiki/Thioacetic_acid |
In organic chemistry , a thioacyl chloride is an organic compound containing the functional group −C(=S)Cl . Their formula is usually written R−C(S)Cl , where R is a side chain . Thioacyl chlorides are analogous to acyl chlorides , but much rarer and less robust. The best studied is thiobenzoyl chloride, a purple oil first prepared by chlorination of dithiobenzoic acid with a combination of chlorine and thionyl chloride . [ 1 ] [ 2 ]
A more modern preparation employs phosgene as the chlorinating agent; [ 3 ] this also generates carbonyl sulfide as a by-product:
The most common thioacyl chloride is thiophosgene . | https://en.wikipedia.org/wiki/Thioacyl_chloride |
A thioamide (rarely, thionamide , but also known as thiourylenes ) is a functional group with the general structure R 1 −C(=S)−NR 2 R 3 , where R 1 , R 2 and R 3 are any groups (typically organyl groups or hydrogen ). Analogous to amides , thioamides exhibit greater multiple bond character along the C-N bond, resulting in a larger rotational barrier. [ 1 ]
Thioamides are typically prepared by treating amides with phosphorus sulfides such as phosphorus pentasulfide , a reaction first described in the 1870s. [ 2 ] [ 3 ] An alternative to P 2 S 5 is its more soluble analogue Lawesson's reagent . [ 4 ] The Willgerodt-Kindler reaction can give benzylthioamides via an analogous process. [ 5 ] These transformations can be seen in the synthesis of tolrestat .
The reaction of nitriles with hydrogen sulfide also affords thioamides:
Imidoyl chlorides react with hydrogen sulfide to produce thioamides.
A well-known thioamide is thioacetamide , which is used as a source of the sulfide ion.
Thioamides are precursors to heterocycles . [ 6 ] Such approaches often exploit the nucleophilicity of the thione -like sulfur. [ 7 ]
The C(R)(N)(S) core of thioamides is planar. Using thioacetamide as representative: the C-S, C-N, and C-C distances are 1.68, 1.31, and 1.50 Å, respectively. The short C-S and C-N distances indicate multiple bonding. [ 8 ]
Some thioamides exhibit the phenomenon of atropisomerism , reflecting the partial double bond character of their C-N bonds. [ 9 ]
Thioamides or anti-thyroid drugs are also a class of drugs that are used to control thyrotoxicosis .
Thioamides have been incorporated into peptides as isosteres for the amide bond. [ 10 ] Peptide modifications are analogues of the native peptide, which can reveal the structure-activity relationship ( SAR ). Analogues of peptides can also be used as drugs with an improved oral bioavailability .
Thioamides inhibit the enzyme thyroid peroxidase in the thyroid , reducing the synthesis of triiodothyronine (T 3 ) and thyroxine (T 4 ), thereby blocking uptake of iodotyrosines from the colloid . They also block iodine release from peripheral hormone. Maximum effects occur only after a month, since hormone depletion is caused by reduced synthesis, which is a slow process. | https://en.wikipedia.org/wiki/Thioamide |
In organic chemistry , thiocarbamates ( thiourethanes ) are a family of organosulfur compounds . As the prefix thio- suggests, they are sulfur analogues of carbamates . There are two isomeric forms of thiocarbamates: O -thiocarbamates, ROC(=S)NR 2 ( esters ), and S -thiocarbamates, RSC(=O)NR 2 ( thioesters ).
Thiocarbamates can be synthesised by the reaction of water or alcohols upon thiocyanates ( Riemschneider thiocarbamate synthesis ): [ 1 ] [ 2 ]
Similar reactions are seen between alcohols and thiocarbamoyl chlorides such as dimethylthiocarbamoyl chloride ; as well as between thiols and cyanates . [ 2 ] The herbicide Cycloate is produced in this way:
Other related thiocarbamate herbicides include vernolate (C 3 H 7 ) 2 NCOSC 3 H 7 and triallate ( (i−C 3 H 7 ) 2 NCOSCH 2 CCl=CCl 2 . [ 3 ]
Salts of thiocarbamate arise by the reaction of amines with carbonyl sulfide :
In the Newman-Kwart rearrangement O -thiocarbamates can isomerise to S -thiocarbamates. [ 4 ] This reaction, which generally requires high temperatures, is an important method for the synthesis of thiophenols .
Goitrin is a cyclic thiocarbamate found in some vegetables. [ 5 ]
Thiocarbamate based herbicides (e.g. prosulfocarb ) were introduced in 1957 and in 2017 was a $200,000,000 market. [ 6 ] Other thiocarbamate herbicides are pebulate , molinate , EPTC , butylate , triallate , vernolate and cycloate . [ 7 ] | https://en.wikipedia.org/wiki/Thiocarbamate |
In organic chemistry , thiocarboxylic acids or carbothioic acids are organosulfur compounds related to carboxylic acids by replacement of one of the oxygen atoms with a sulfur atom. Two tautomers are possible: a thione form ( RC(S)OH ) and a thiol form ( RC(O)SH ). [ 1 ] [ 2 ] These are sometimes also referred to as "carbothioic O -acid" and "carbothioic S -acid" respectively. Of these the thiol form is most common (e.g. thioacetic acid ).
Thiocarboxylic acids are rare in nature, however the biosynthetic components for producing them appear widespread in bacteria . [ 3 ] Examples include pyridine-2,6-dicarbothioic acid , [ 4 ] and thioquinolobactin. [ 3 ]
Thiocarboxylic acids are typically prepared by salt metathesis from the acid chloride , as in the following conversion of benzoyl chloride to thiobenzoic acid using potassium hydrosulfide according to the following idealized equation: [ 5 ]
Covalent sulfides, such as P 2 S 5 , generally give poor yields unless catalyzed with triphenylstibine oxide . [ 6 ]
2,6-Pyridinedicarbothioic acid is synthesized by treating the diacid dichloride with a solution of H 2 S in pyridine :
This reaction produces the orange pyridinium salt of pyridinium-2,6-dicarbothioate. Treatment of this salt with sulfuric acid gives colorless the bis(thiocarboxylic acid), which can then be extracted with dichloromethane . [ 7 ]
At neutral pH, thiocarboxylic acids are fully ionized. Thiocarboxylic acids are about 100 times more acidic than the analogous carboxylic acids. Thiobenzoic acid has a p K a of 2.48 compared with 4.20 for benzoic acid, and thioacetic acid has a p K a near 3.4 compared with 4.72 for acetic acid . [ 8 ] Alkylation of the corresponding thioate ion gives a thioester . [ 9 ]
The conjugate base of thioacetic acid, thioacetate , is a reagent used for installing thiol groups via the displacement of alkyl halides by a two-step process. The halide is displaced to give a thioester intermediate, which is then hydrolyzed :
Thiocarboxylic acids react with various nitrogen functional groups, such as organic azide , nitro , and isocyanate compounds, to give amides under mild conditions. [ 10 ] [ 11 ] This method avoids needing the amine to initiate an amide-forming acyl substitution but does requires synthesis and handling of the unstable thiocarboxylic acid. [ 11 ] Unlike the Schmidt reaction or other nucleophilic-attack pathways, reaction with an aryl or alkyl azide begins with a [3+2] cycloaddition . The resulting heterocycle expels N 2 and the sulfur atom to give the monosubstituted amide. [ 10 ] [ 12 ]
Halogens or their equivalents (e.g. sulfuryl chloride ) oxidize thiocarboxylic acids to acylsulfenyl halides. The latter are unstable, and decay over the course of several hours to the free halogen and the diacyl disulfide. [ 13 ] | https://en.wikipedia.org/wiki/Thiocarboxylic_acid |
In organic chemistry , thioenols (also known as alkenethiols ) are alkenes with a thiol group ( −SH ) affixed to one of the carbon atoms composing the double bond (i.e. C=C−SH ). They are the sulfur analogs of enols (hence the thio- prefix). Alkenes with a thiol group on both atoms of the double bond are called enedithiols . Deprotonated anions of thioenols are called thioenolates .
These structures exhibit tautomerism to give thioketones or thioaldehydes , analogous to keto–enol tautomerism of carbonyl structures. [ 1 ]
This organic chemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thioenol |
In organic chemistry , thioesters are organosulfur compounds with the molecular structure R−C(=O)−S−R’ . They are analogous to carboxylate esters ( R−C(=O)−O−R’ ) with the sulfur in the thioester replacing oxygen in the carboxylate ester, as implied by the thio- prefix. They are the product of esterification of a carboxylic acid ( R−C(=O)−O−H ) with a thiol ( R'−S−H ). In biochemistry , the best-known thioesters are derivatives of coenzyme A , e.g., acetyl-CoA . [ 1 ] The R and R' represent organyl groups, or H in the case of R.
One route to thioesters involves the reaction of an acid chloride with an alkali metal salt of a thiol: [ 1 ]
Another common route entails the displacement of halides by the alkali metal salt of a thiocarboxylic acid . For example, thioacetate esters are commonly prepared by alkylation of potassium thioacetate : [ 1 ]
The analogous alkylation of an acetate salt is rarely practiced. The alkylation can be conducted using Mannich bases and the thiocarboxylic acid:
Thioesters can be prepared by condensation of thiols and carboxylic acids in the presence of dehydrating agents : [ 2 ] [ 3 ]
A typical dehydration agent is DCC . [ 4 ] Efforts to improve the sustainability of thioester synthesis have also been reported utilising safer coupling reagent T3P and greener solvent cyclopentanone . [ 5 ] Acid anhydrides and some lactones also give thioesters upon treatment with thiols in the presence of a base.
Thioesters can be conveniently prepared from alcohols by the Mitsunobu reaction , using thioacetic acid . [ 6 ]
They also arise via carbonylation of alkynes and alkenes in the presence of thiols. [ 7 ]
Thioesters hydrolyze to thiols and the carboxylic acid:
The carbonyl center in thioesters is more reactive toward amine than oxygen nucleophiles, giving amides :
This reaction is exploited in native chemical ligation , a protocol for peptide synthesis . [ 8 ]
In a related reaction, thioesters can be converted into esters. [ 9 ] Thioacetate esters can also be cleaved with methanethiol in the presence of stoichiometric base, as illustrated in the preparation of pent-4-yne-1-thiol: [ 10 ]
A reaction unique to thioesters is the Fukuyama coupling , in which the thioester is coupled with an organozinc halide by a palladium catalyst to give a ketone.
Thioesters are common intermediates in many biosynthetic reactions, including the formation and degradation of fatty acids and mevalonate , precursor to steroids. Examples include malonyl-CoA , acetoacetyl-CoA , propionyl-CoA , cinnamoyl-CoA , and acyl carrier protein (ACP) thioesters. Acetogenesis proceeds via the formation of acetyl-CoA . The biosynthesis of lignin , which comprises a large fraction of the Earth's land biomass, proceeds via a thioester derivative of caffeic acid . [ 11 ] These thioesters arise analogously to those prepared synthetically, the difference being that the dehydration agent is ATP. In addition, thioesters play an important role in the tagging of proteins with ubiquitin , which tags the protein for degradation.
Oxidation of the sulfur atom in thioesters ( thiolactones ) is postulated in the bioactivation of the antithrombotic prodrugs ticlopidine , clopidogrel , and prasugrel . [ 12 ] [ 13 ]
As posited in a "Thioester World", thioesters are possible precursors to life. [ 14 ] As Christian de Duve explains:
It is revealing that thioesters are obligatory intermediates in several key processes in which ATP is either used or regenerated. Thioesters are involved in the synthesis of all esters , including those found in complex lipids . They also participate in the synthesis of a number of other cellular components, including peptides , fatty acids , sterols , terpenes , porphyrins , and others. In addition, thioesters are formed as key intermediates in several particularly ancient processes that result in the assembly of ATP. In both these instances, the thioester is closer than ATP to the process that uses or yields energy. In other words, thioesters could have actually played the role of ATP in a "thioester world" initially devoid of ATP. Eventually, [these] thioesters could have served to usher in ATP through its ability to support the formation of bonds between phosphate groups .
However, due to the high free energy change of thioester's hydrolysis and correspondingly their low equilibrium constants, it is unlikely that these compounds could have accumulated abiotically to any significant extent especially in hydrothermal vent conditions. [ 15 ]
Thionoesters are isomeric with thioesters. In a thionoester, sulfur replaces the carbonyl oxygen in an ester. Methyl thionobenzoate is C 6 H 5 C(S)OCH 3 . Such compounds are typically prepared by the reaction of the thioacyl chloride with an alcohol. [ 16 ]
They can also be made by the reaction of Lawesson's reagent with esters or by treating pinner salts with hydrogen sulfide .
Various thionoesters may be prepared through the transesterification of an existing methyl thionoester with an alcohol under base-catalyzed conditions. [ 17 ]
Xanthates [ 18 ] and thioamides [ 19 ] can be transformed to thionoesters under metal-catalyzed cross-coupling conditions. | https://en.wikipedia.org/wiki/Thioester |
Thioester containing protein 1 , often called TEP1 is a key component of the arthropod innate immune system. TEP1 was first identified as a key immunity gene in 2001 through functional studies on Anopheles gambiae mosquitoes. [ 1 ]
TEP1 is an antimicrobial protein which acts in a system reminiscent of the human complement pathway, which damages the cell membranes of pathogens. Studies have shown that TEP1 is structurally and functionally homologous to the human complement protein C3 . [ 2 ] TEP1 is now known to be important in the resistance of Anopheles mosquitoes to Plasmodium infection, targeting the malaria parasite during its invasion into the mosquitoes body cavity. Following this discovery insect thioester containing proteins have come under increased scrutiny from the scientific community as possible targets for disease control.
TEP1 is coded for by two different alleles TEP1-S and TEP-R which are specific to susceptible and resistant mosquito populations respectively. [ 3 ]
Several crystallography studies have been used to determine the structure of TEP1. TEP1 contains a highly reactive thioester motif, which can undergo spontaneous hydrolysis. [ 4 ] The thioester group is functionally essential for TEP1 to covalently bind to the surface of invading pathogens. [ 4 ] Tep1 is a multimeric protein, meaning it is formed of multiple associated polypeptide chains . TEP1 is composed of a series of 6 macroglobulin domains, a β sheet CUB domain and an essential thioester domain, which protects the thioester motif from premature activation and hydrolysis by shielding it in the core of the molecule. [ 5 ]
Comparisons of the TEP1-S and TEP1-R gene products show that the two allelic variants encode structural differences which are particularly prevalent in the thioester domain. These differences alter both the stability of the thioester bond and the ability of TEP1 to interact with other factors in the hemolymph of the mosquito. [ 3 ] [ 6 ]
The structure of TEP1 and its vertebrate homologue - complement protein C3- is mostly conserved. However, there are some differences between the two molecules, for example unlike C3, TEP1 lacks an anaphylatoxin domain. The absence of this domain means that the exposed thioester bond of active TEP1 is unstable. [ 2 ] [ 4 ]
The TEP1 protein is glycosylated and secreted into the body cavity by mosquito immune cells as a 165 kDa zymogen - this inactivated form is known as TEP1-F. Upon parasite infection TEP1-F is cleaved. A protease processes the full length molecule into two fragments which remain closely associated: a ~75 kDa N-terminal and an ~85 kDa C-terminal fragment which contains the thioester bond. [ 7 ] The cleaved protein is known as TEP1-cut and represents the activated form. This mechanism is equivalent to the maturation of vertebrate pro-C3 to active C3 which occurs in the endoplasmic reticulum . [ 3 ]
Recent work has suggested the two forms of TEP1, the full TEP1-F and TEP1-cut, have separate roles. [ 2 ]
TEP1 is a central component in the mosquito's immune response against invading parasites such as Plasmodium . Similar to the complement protein C3 in function, TEP1 acts as an opsonin which facilitates extensive parasite killing. [ 8 ] TEP1 covalently binds to the surface of invading pathogens, promoting phagocytosis , lysis and melanisation . [ 8 ] Through this activity TEP1 is considered an important determinant of Anopheles vector capacity. [ 9 ] TEP1 is an antimicrobial peptide which associates with APL1C/LRIM1 heterodimers to act as a pattern recognition receptor (PRR) which identifies and responds to specific patterns on pathogen cell surfaces. [ 2 ]
Studies have shown TEP1 to be a key molecule in limiting parasite numbers in mosquitoes. RNA interference (RNAi) experiments have illustrated the importance of TEP1 in clearing malaria infections in mosquitoes. RNAi knockdown of TEP1 using dsRNA resulted in a five-fold increase of Plasmodium oocysts in TEP1-S silenced mosquitoes. Knock down of TEP1-R stops parasite melanisation. [ 1 ]
TEP1-F is secreted into the hemolymph where it is processed by a currently unknown protease into its active form – the two chained molecule TEP1-Cut. Cleavage into the cut form is followed by a change in protein structure which exposes the thioester bond. This conformational change enables TEP1 to react and covalently bind to molecules on the surface of invading pathogens. [ 7 ]
The expression of TEP1 and other genes involved in the mosquito's anti-parasitic response is a highly regulated process. The base level of TEP1 expression is regulated by insect Toll and IMD pathways. These immune pathways limit the expression of TEP1 coding genes through NF-kB / REL transcription factors . [ 10 ] TEP1 interacts with a heterodimeric protein complex made up of two leucine-rich repeat (LRR) domain containing proteins: leucine-rich immune molecule 1 (LRIM1) and Anopheles Plasmodium -responsive leucine-rich repeat protein 1 (APL1C). The LRR molecules have two main roles: firstly acting as control proteins which prevent the inactivation of TEP1 through hydrolysis of the thioester bond or binding to self -tissues and secondly mediate the binding of TEP1 to pathogen surfaces. [ 11 ]
The LRIM1/APL1C heterodimer has three domains, combining the elements of a N-terminal LRR region, a pattern of cysteine residues and a C-terminal coiled-coil domain. These features determine how the complex interacts with TEP1. [ 11 ]
The complement system was previously thought to be an exclusive feature of the immune defense of vertebrates until complement-like molecules were cloned in non-vertebrate species such as the horseshoe crab and mosquitoes. [ 1 ] The discovery of C3 like molecules in a diverse range of species suggests that the complement pathway in particular the alternative complement pathway is evolutionary ancient. [ 7 ] The TEP1 cascade most closely resembles the alternative pathway as insects do not possess adaptive immunity . [ 11 ] Therefore, unlike the classical complement pathway the TEP1 pathway is antibody independent and instead relies on the presence of factors permanently present at low levels in the hemolymph. Furthermore, both the TEP1 pathway and the alternative pathway utilise convertase mediated amplification loops to increase pathogen opsonisation.
Thioester containing protein (TEPs) appeared early in animal evolution: members of this family have been identified in diverse organisms as nematodes , insects, molluscs, fish, birds and mammals. TEP1 in Anopheles gambiae is one of the best studied of these molecules. [ 12 ] Despite close structural and functional similarities, phylogenic analysis has shown that TEP1 and other arthropod thioester proteins actually form a separate clade from vertebrate complement factors. [ 4 ] This data suggests that their complement-like activity is a likely example of parallel evolution . Further research is needed into this area. [ 2 ]
The characterization of TEP1 and other similar insect immune factors in insects represent new opportunities to prevent the transmission of insect vector borne diseases. Research is currently focusing on vector/parasite interactions, specifically those between Plasmodium and Anopheles mosquitoes, in order to discover novel, improved malaria prevention methods. [ 13 ] TEP1 is being explored as a possible target for genetic manipulation . A significant aim of this research is to create mosquito populations resistant to Plasmodium parasites therefore reducing the spread of malaria. [ 14 ] | https://en.wikipedia.org/wiki/Thioester-containing_protein_1 |
In organosulfur chemistry , a thioketal is the sulfur analogue of a ketal ( R 2 C(OR) 2 ), with one of the oxygen replaced by sulfur (as implied by the thio- prefix), giving the structure R 2 C(SR)OR . A dithioketal has both oxygens replaced by sulfur ( R 2 C(SR) 2 ).
Thioketals can be obtained by reacting ketones ( >C=O ) or aldehydes ( −CH=O ) with thiols ( −SH ).
An oxidative cleavage mechanism has been proposed for dithioketals, which involves thioether oxidation, the formation of thionoiums, and hydrolysis , resulting in the formation of aldehyde and ketone products. [ 1 ]
Thioketal moieties are found to be responsive to reactive oxygen species (ROS). [ 1 ] In the presence of ROS, thioketals can be selectively cleaved. [ 2 ] ROS successfully cleave heterobifunctional thioketal linkers, which have been found to have therapeutic potential, as they can produce ROS-responsive agents with two different functionalities. [ 2 ]
Ketones can be reduced at neutral pH via conversion to thioketals; the thioketal prepared from the ketone can be easily reduced by catalytic hydrogenation using Raney nickel in a reaction known as the Mozingo reduction .
This organic chemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thioketal |
In organic chemistry , thioketenes are organosulfur compounds analogous to ketenes with the general formula R 2 C=C=S , where R is alkyl or aryl . The parent thioketene (ethenthione) has the formula CH 2 =C=S . It is the simplest thioketene. [ 1 ] Ethenthione is stable as a gas, but like most thioketenes, it polymerizes upon condensation.
Some thioketenes are produced as transient species upon pyrolysis of 1,2,3-thiadiazoles . [ 2 ] It has been suggested that thioketenes could be involved in cell damage processes. [ 3 ]
Thioketenes can be stabilized by either steric protection or by electronic effects. Thus, di-tert-butylthioketene is easily isolated and air-stable. [ 4 ] Several examples have been characterized by X-ray crystallography . The C=S distance is 157 pm and the C=C distance is 124 pm, both bonds being suitable for the C=C=S assignment. The violet color characteristic of thioketenes indicates the small HOMO-LUMO gap . [ 5 ] These compound are prepared by treatment of the acid chloride with phosphorus pentasulfide as described by the following idealized equation:
Bis(trifluoromethyl)thioketene ( (CF 3 ) 2 C=C=S ) is an example of an electronically stabilized thioketene. [ 6 ]
Thioketenes are electrophilic. They add amines to give thioamides: [ 4 ]
With peroxyacids, they produce thioketene-S-oxides: [ 5 ]
Thioketenes bind to metal carbonyls giving adducts. [ 7 ] | https://en.wikipedia.org/wiki/Thioketene |
In organic chemistry , thioketones (from Ancient Greek θεῖον (theion) ' sulfur ' ; [ 1 ] also known as thiones or thiocarbonyls ) are organosulfur compounds related to conventional ketones in which the oxygen has been replaced by a sulfur. [ 2 ] Instead of a structure of R 2 C=O , thioketones have the structure R 2 C=S , which is reflected by the prefix " thio- " in the name of the functional group. Thus the simplest thioketone is thioacetone , the sulfur analog of acetone . Unhindered alkylthioketones typically tend to form polymers or rings . [ 3 ] [ 4 ]
The C=S bond length of thiobenzophenone is 1.63 Å, which is comparable to 1.64 Å, the C=S bond length of thioformaldehyde, measured in the gas phase. Due to steric interactions, the phenyl groups are not coplanar and the dihedral angle SC-CC is 36°. [ 5 ] Unhindered dialkylthiones polymerize or oligomerize but thio camphor is well characterized red solid. [ 6 ]
Consistent with the double bond rule , most alkyl thioketones are unstable with respect to dimerization. [ 7 ] The energy difference between the p orbitals of sulfur and carbon is greater than that between oxygen and carbon in ketones. [ 8 ] The relative difference in energy and diffusity of the atomic orbitals of sulfur compared with carbon results in poor overlap of the atomic orbitals and the energy gap between the HOMO and LUMO is thus reduced for C=S molecular orbitals relative to C=O. [ 5 ] The striking blue appearance of thiobenzophenone is attributed to π→ π* transitions upon the absorption of red light. [ 8 ] Thiocamphor is red.
Thiones are usually prepared from ketones using reagents that exchange S and O atoms. A common reagent is phosphorus pentasulfide , [ 9 ] although that reagent also tends to induce side-reactions. [ 10 ] : 928 Lawesson's reagent is related. Other methods uses a mixture of hydrogen chloride combined with hydrogen sulfide . Bis(trimethylsilyl)sulfide has also been employed. [ 3 ] [ 11 ] Thiones can also be prepared from geminal dichlorides, [ 10 ] : 927 but geminal dichlorides are typically prepared from ketones as well.
There are no general methods to oxidize methylene groups to thioketones, [ 10 ] : 929–930 reflecting sulfur 's comparable electronegativity to carbon .
Thiobenzophenone [(C 6 H 5 ) 2 CS] is a stable deep blue compound that dissolves readily in organic solvents. It photooxidizes in air to benzophenone and sulfur. Since its discovery, a variety of related thiones have been prepared. [ 12 ]
Thiosulfines, also called thiocarbonyl S -sulfides, are compounds with the formula R 2 CSS. Although superficially appearing to be cumulenes , with the linkage R 2 C=S=S, they are more usefully classified as 1,3-dipoles and indeed participate in 1,3-dipolar cycloadditions . Thiosulfines are proposed to exist in equilibrium with dithiiranes , three-membered CS 2 rings. Thiosulfines are often invoked as intermediates in mechanistic discussions of the chemistry of thiones. For example, thiobenzophenone decomposes upon oxidation to the 1,2,4- trithiolane (Ph 2 C) 2 S 3 , which arises via the cycloaddition of Ph 2 CSS to its parent Ph 2 CS. [ 13 ] | https://en.wikipedia.org/wiki/Thioketone |
In organic chemistry , a thiol ( / ˈ θ aɪ ɒ l / ; [ 1 ] from Ancient Greek θεῖον (theion) ' sulfur ' [ 2 ] ), or thiol derivative , is any organosulfur compound of the form R−SH , where R represents an alkyl or other organic substituent . The −SH functional group itself is referred to as either a thiol group or a sulfhydryl group , or a sulfanyl group . Thiols are the sulfur analogue of alcohols (that is, sulfur takes the place of oxygen in the hydroxyl ( −OH ) group of an alcohol), and the word is a blend of " thio- " with "alcohol".
Many thiols have strong odors resembling that of garlic , cabbage or rotten eggs. Thiols are used as odorants to assist in the detection of natural gas (which in pure form is odorless), and the smell of natural gas is due to the smell of the thiol used as the odorant.
Thiols are sometimes referred to as mercaptans ( / m ər ˈ k æ p t æ n / ) [ 3 ] or mercapto compounds , [ 4 ] [ 5 ] [ 6 ] a term introduced in 1832 by William Christopher Zeise and is derived from the Latin mercurio captāns ('capturing mercury') [ 7 ] because the thiolate group ( RS − ) bonds very strongly with mercury compounds. [ 8 ]
Thiols having the structure R−SH, in which an alkyl group (R) is attached to a sulfhydryl group (SH), are referred to as alkanethiols or alkyl thiols . [ 9 ] Thiols and alcohols have similar connectivity. Because sulfur atoms are larger than oxygen atoms, C−S bond lengths —typically around 180 picometres —are about 40 picometers longer than typical C−O bonds. The C−S−H angles approach 90° whereas the angle for the C−O−H group is more obtuse. In solids and liquids, the hydrogen-bonding between individual thiol groups is weak, the main cohesive force being Van der Waals interactions between the highly polarizable divalent sulfur centers.
The S−H bond is much weaker than the O−H bond as reflected in their respective bond dissociation energies (BDE). For CH 3 S−H, the BDE is 366 kJ/mol (87 kcal/mol), while for CH 3 O−H, the BDE is 440 kJ/mol (110 kcal/mol). [ 10 ]
An S−H bond is moderately polar because of the small difference in the electronegativity of sulfur and hydrogen. In contrast, O−H bonds in hydroxyl groups are more polar. Thiols have a lower dipole moment relative to their corresponding alcohols.
There are several ways to name the alkylthiols:
Many thiols have strong odors resembling that of garlic . The odors of thiols, particularly those of low molecular weight, are often strong and repulsive. The spray of skunks consists mainly of low-molecular-weight thiols and derivatives. [ 11 ] [ 12 ] [ 13 ] [ 14 ] [ 15 ] These compounds are detectable by the human nose at concentrations of only 10 parts per billion. [ 16 ] Human sweat contains ( R )/( S )-3-methyl-3-sulfanylhexan-1-ol (3M3SH), detectable at 2 parts per billion and having an onion-like (S enantiomer) and fruity, grapefruit-like odor (R enantiomer). [ 17 ] (Methylthio)methanethiol (MeSCH 2 SH; MTMT) is a strong-smelling volatile thiol, also detectable at parts per billion levels, found in male mouse urine. Lawrence C. Katz and co-workers showed that MTMT functioned as a semiochemical , activating certain mouse olfactory sensory neurons, and attracting female mice . [ 18 ] Copper has been shown to be required by a specific mouse olfactory receptor, MOR244-3, which is highly responsive to MTMT as well as to various other thiols and related compounds. [ 19 ] A human olfactory receptor, OR2T11 , has been identified which, in the presence of copper, is highly responsive to the gas odorants (see below) ethanethiol and t -butyl mercaptan as well as other low molecular weight thiols, including allyl mercaptan found in human garlic breath, and the strong-smelling cyclic sulfide thietane . [ 20 ]
Thiols are also responsible for a class of wine faults caused by an unintended reaction between sulfur and yeast and the "skunky" odor of beer that has been exposed to ultraviolet light.
Not all thiols have unpleasant odors. For example, furan-2-ylmethanethiol contributes to the aroma of roasted coffee , whereas grapefruit mercaptan , a monoterpenoid thiol, is responsible for the characteristic scent of grapefruit . The effect of the latter compound is present only at low concentrations. The pure mercaptan has an unpleasant odor.
In the United States, natural gas distributors were required to add thiols, originally ethanethiol , to natural gas (which is naturally odorless) after the deadly New London School explosion in New London, Texas , in 1937. Many gas distributors were odorizing gas prior to this event. Most currently-used gas odorants contain mixtures of mercaptans and sulfides, with t -butyl mercaptan as the main odor constituent in natural gas and ethanethiol in liquefied petroleum gas (LPG, propane). [ 21 ] In situations where thiols are used in commercial industry, such as liquid petroleum gas tankers and bulk handling systems, an oxidizing catalyst is used to destroy the odor. A copper-based oxidation catalyst neutralizes the volatile thiols and transforms them into inert products.
Thiols show little association by hydrogen bonding , both with water molecules and among themselves. Hence, they have lower boiling points and are less soluble in water and other polar solvents than alcohols of similar molecular weight. For this reason also, thiols and their corresponding sulfide functional group isomers have similar solubility characteristics and boiling points, whereas the same is not true of alcohols and their corresponding isomeric ethers.
The S−H bond in thiols is weak compared to the O−H bond in alcohols. For CH 3 X−H, the bond enthalpies are 365.07 ± 2.1 kcal/mol for X = S and 440.2 ± 3.0 kcal/mol for X = O. [ 22 ] Hydrogen-atom abstraction from a thiol gives a thiyl radical with the formula RS • , where R = alkyl or aryl.
Volatile thiols are easily and almost unerringly detected by their distinctive odor. Sulfur-specific analyzers for gas chromatographs are useful. Spectroscopic indicators are the D 2 O -exchangeable S H signal in the 1 H NMR spectrum ( 33 S is NMR -active but signals for divalent sulfur are very broad and of little utility [ 23 ] ). The ν SH band appears near 2400 cm −1 in the IR spectrum . [ 4 ] In the nitroprusside reaction , free thiol groups react with sodium nitroprusside and ammonium hydroxide to give a red colour.
In industry, methanethiol is prepared by the reaction of hydrogen sulfide with methanol . This method is employed for the industrial synthesis of methanethiol :
Such reactions are conducted in the presence of acidic catalysts. The other principal route to thiols involves the addition of hydrogen sulfide to alkenes . Such reactions are usually conducted in the presence of an acid catalyst or UV light. Halide displacement, using the suitable organic halide and sodium hydrogen sulfide has also been used. [ 24 ]
Another method entails the alkylation of sodium hydrosulfide .
This method is used for the production of thioglycolic acid from chloroacetic acid .
In general, on the typical laboratory scale, the direct reaction of a haloalkane with sodium hydrosulfide is in efficient owing to the competing formation of sulfides. Instead, alkyl halides are converted to thiols via an S -alkylation of thiourea . This multistep, one-pot process proceeds via the intermediacy of the isothiouronium salt , which is hydrolyzed in a separate step: [ 25 ] [ 26 ]
The thiourea route works well with primary halides, especially activated ones. Secondary and tertiary thiols are less easily prepared. Secondary thiols can be prepared from the ketone via the corresponding dithioketals . [ 27 ] A related two-step process involves alkylation of thiosulfate to give the thiosulfonate (" Bunte salt "), followed by hydrolysis. The method is illustrated by one synthesis of thioglycolic acid :
Organolithium compounds and Grignard reagents react with sulfur to give the thiolates, which are readily hydrolyzed: [ 28 ]
Phenols can be converted to the thiophenols via rearrangement of their O -aryl dialkylthiocarbamates. [ 29 ]
Thiols are prepared by reductive dealkylation of sulfides, especially benzyl derivatives and thioacetals. [ 30 ]
Thiophenols are produced by S -arylation or the replacement of diazonium leaving group with sulfhydryl anion (SH − ): [ 31 ] [ 32 ]
Akin to the chemistry of alcohols, thiols form sulfides , thioacetals , and thioesters , which are analogous to ethers , acetals , and esters respectively. Thiols and alcohols are also very different in their reactivity, thiols being more easily oxidized than alcohols. Thiolates are more potent nucleophiles than the corresponding alkoxides .
Thiols, or more specific their conjugate bases, are readily alkylated to give sulfides:
Thiols are easily deprotonated. [ 33 ] Relative to the alcohols, thiols are more acidic. The conjugate base of a thiol is called a thiolate . Butanethiol has a p K a of 10.5 vs 15 for butanol. Thiophenol has a p K a of 6, versus 10 for phenol . A highly acidic thiol is pentafluorothiophenol (C 6 F 5 SH) with a p K a of 2.68. Thus, thiolates can be obtained from thiols by treatment with alkali metal hydroxides.
Thiols, especially in the presence of base, are readily oxidized by reagents such as bromine and iodine to give an organic disulfide (R−S−S−R).
Oxidation by more powerful reagents such as sodium hypochlorite or hydrogen peroxide can also yield sulfonic acids (RSO 3 H).
Oxidation can also be effected by oxygen in the presence of catalysts: [ 34 ]
Thiols participate in thiol-disulfide exchange:
This reaction is important in nature.
With metal ions, thiolates behave as ligands to form transition metal thiolate complexes . The term mercaptan is derived from the Latin mercurium captans (capturing mercury) [ 7 ] because the thiolate group bonds so strongly with mercury compounds. According to hard/soft acid/base (HSAB) theory , sulfur is a relatively soft (polarizable) atom. This explains the tendency of thiols to bind to soft elements and ions such as mercury, lead, or cadmium. The stability of metal thiolates parallels that of the corresponding sulfide minerals.
Thiolates react with carbon disulfide to give thioxanthate ( RSCS − 2 ).
Free radicals derived from mercaptans, called thiyl radicals , are commonly invoked to explain reactions in organic chemistry and biochemistry . They have the formula RS • where R is an organic substituent such as alkyl or aryl . [ 6 ] They arise from or can be generated by a number of routes, but the principal method is H-atom abstraction from thiols. Another method involves homolysis of organic disulfides. [ 35 ] In biology thiyl radicals are responsible for the formation of the deoxyribonucleic acids, building blocks for DNA . This conversion is catalysed by ribonucleotide reductase (see figure). [ 36 ] Thiyl intermediates also are produced by the oxidation of glutathione , an antioxidant in biology. Thiyl radicals (sulfur-centred) can transform to carbon-centred radicals via hydrogen atom exchange equilibria . The formation of carbon -centred radicals could lead to protein damage via the formation of C −C bonds or backbone fragmentation. [ 37 ]
Because of the weakness of the S−H bond, thiols can function as scavengers of free radicals . [ 38 ]
As the functional group of the proteinogenic amino acid cysteine , the thiol group plays a very important role in biology. When the thiol groups of two cysteine residues (as in monomers or constituent units) are brought near each other in the course of protein folding, an oxidation reaction can generate a cystine unit with a disulfide bond (−S−S−). Disulfide bonds can contribute to a protein's tertiary structure if the cysteines are part of the same peptide chain, or contribute to the quaternary structure of multi-unit proteins by forming fairly strong covalent bonds between different peptide chains. A physical manifestation of cysteine-cystine equilibrium is provided by hair straightening technologies. [ 39 ]
Sulfhydryl groups in the active site of an enzyme can form noncovalent bonds with the enzyme's substrate as well, contributing to covalent catalytic activity in catalytic triads . Active site cysteine residues are the functional unit in cysteine protease catalytic triads . Cysteine residues may also react with heavy metal ions (Zn 2+ , Cd 2+ , Pb 2+ , Hg 2+ , Ag + ) because of the high affinity between the soft sulfide and the soft metal (see hard and soft acids and bases ). This can deform and inactivate the protein, and is one mechanism of heavy metal poisoning .
Many cofactors (non-protein-based helper molecules) feature thiols. The biosynthesis and degradation of fatty acids and related long-chain hydrocarbons is conducted on a scaffold that anchors the growing chain through a thioester derived from the thiol coenzyme A . Dihydrolipoic acid , a dithiol , is the reduced form of lipoic acid , a cofactor in several metabolic processes in mammals.
The biosynthesis of methane , the principal hydrocarbon on Earth, arises from the reaction mediated by coenzyme M (2-mercaptoethyl sulfonic acid) and coenzyme B (7-mercaptoheptanoylthreoninephosphate). Thiolates, the conjugate bases derived from thiols, form strong complexes with many metal ions, especially those classified as soft. The stability of metal thiolates parallels that of the corresponding sulfide minerals.
Drugs containing thiol group:
The defensive spray of skunks consists mainly of low-molecular-weight thiols and derivatives with a foul odor, which protects the skunk from predators. Owls are able to prey on skunks, as they lack a sense of smell. [ 41 ] | https://en.wikipedia.org/wiki/Thiol |
In organosulfur chemistry , the thiol-ene reaction (also alkene hydrothiolation ) is an organic reaction between a thiol ( R−SH ) and an alkene ( R 2 C=CR 2 ) to form a thioether ( R−S−R' ). This reaction was first reported in 1905, [ 1 ] but it gained prominence in the late 1990s and early 2000s for its feasibility and wide range of applications. [ 2 ] [ 3 ] This reaction is accepted as a click chemistry reaction given the reactions' high yield , stereoselectivity , high rate , and thermodynamic driving force.
The reaction results in an anti-Markovnikov addition of a thiol compound to an alkene. Given the stereoselectivity, high rate and yields, this synthetically useful reaction may underpin future applications in material and biomedical sciences. [ 2 ] [ 4 ]
Thiol-ene additions are known to proceed through two mechanisms: free-radical additions and catalyzed Michael additions . Free-radical additions can be initiated by light, heat or radical initiators, which form a thiyl radical species. The radical then propagates with an ene functional group via an anti-Markovnikov addition to form a carbon-centered radical. A chain-transfer step removes a hydrogen radical from a thiol, which can subsequently participate in multiple propagation steps. [ 4 ]
Thiol-ene radical additions are advantageous for chemical synthesis because the step growth (propagation and chain-transfer steps) and chain growth (homopolymerization) processes can be effectively used to form homogeneous polymer networks. Photopolymerization is a useful radical-based reaction for applications within the nanotechnology, biomaterial, and material sciences, but these reactions are hindered by the inhibitory capabilities of oxygen . The thiol-ene radical addition combines the benefits of photopolymerization reactions with the aforementioned advantages of click chemistry reactions. This reaction is useful to the field of radical-based photopolymerization because it quantitatively and rapidly proceeds through a simple mechanism under ambient atmospheric conditions. [ 4 ] The carbon-centered radical can undergo chain-growth polymerization depending on the thiol and ene functional groups. This free-radical polymerization can be useful in the synthesis of uniform polymer networks. [ 5 ]
Thiol-ene reactions are known to proceed through a Michael addition pathway. These reactions are catalyzed by either a base or a nucleophile, resulting in a similar anti-Markovnikov addition product as the thiol-ene radical addition. [ 6 ]
Click chemistry reactions are known to be high efficiency and have fast reaction rates, yet there is considerable variability in the overall reaction rate depending on the functionality of the alkene. To better understand the kinetics of thiol-ene reactions, calculations and experiments of transition-state and reaction enthalpies were conducted for a number of alkenes and their radical intermediates. [ 5 ] [ 7 ] It was shown that the reactivity and structure of the alkene determines whether the reaction will follow a step-growth or chain-growth pathway. [ 5 ] It was also shown that the thiol-ene polymerization can be tuned by enhancing intermolecular interactions between the thiol and alkene functional groups. [ 7 ] A currently accepted trend is that electron-rich alkenes (such as vinyl ether or allyl ether) and norbornene are highly reactive compared to conjugated and electron-poor alkenes ( butadiene and methoxyethene ). In the case of norbornene and vinyl ether only step-growth is observed, no homopolymerization occurs after the formation of the carbon centered radical. [ 4 ]
Due to the complex kinetics of this two-step cyclic reaction, the rate-determining step was difficult to delineate. Given that the rates of both steps must be equal, the concentration of the radical species is determined by the rate constant of the slower of the reaction steps. Thus the overall reaction rate ( R P ) can be modeled by the ratio of the propagation rate ( k P ) to the chain-transfer rate ( k CT ).The behavior of the reaction rate is outlined by the relationship below. In all cases the reaction is first order , when k P ≫ k CT [Eq. 1] the reaction rate is determined by the thiol concentration and the rate limiting step is chain-transfer, when k P ≪ k CT [Eq. 2] the reaction rate is determined by the alkene concentration and the rate limiting step is the propagation, and finally when k P ≈ k CT [Eq. 3] the reaction is half order with respect to both the alkene and thiol concentrations.
The functional groups on the thiol and alkene compounds can affect the reactivity of the radical species and their respective rate constants. The structure of the alkene determines whether the reaction will be propagation or chain-transfer limited, and therefore first order with respect to alkene or thiol concentration respectively. In the case of reactive alkenes, such as allyl ether, chain-transfer is the rate-limiting step, while in the case of less reactive alkenes, such as vinyl silazanes, propagation is the rate-limiting step. The thiol's hydrogen affinity also affects the rate-limiting step. Alkyl thiols have less abstractable protons and therefore the chain-transfer step has a lower reaction rate than the propagation step. [ 4 ]
Most time the quasi-first-order reaction yields a kinetic rate equation following the exponential decay function for the reactants and products.
where k is an effective rate constant and t is time.
However, when the radical generation becomes the rate-limiting step, an induction period is often observed at the early stage of the reaction, for example, for photoinitiated reaction under weak light condition. The kinetic curve deviates from the exponential decay function for a common first-order reaction by having a slow growth period. The kinetic model has to include the radical generation step to explain this induction period (right figure). The final expression has a Gaussian-like shape . [ 8 ]
where k is an effective rate constant and t is time.
The thiol-ene reaction (and analogous thiol-yne reaction) have extensively been used in generating reactive intermediates for the cyclization of unsaturated substrates . Radical hydrothiolation of an unsaturated functional group indirectly generates a carbon-centered radical, which can then cyclize intramolecularly onto alkenes, oxime ethers, isocyanides , cyano groups, and aromatic rings. [ 9 ] The use of thiyl radicals as initiators of cyclization has been employed in the synthesis of a number of natural products, including aplysins, [ 10 ] α- kainic acid , [ 11 ] asperparalines, [ 12 ] and alkaloids such as narciclasine and lycoricidine. [ 13 ]
Intramolecular thiol-ene reactions provide a means to create sulphur-containing heterocycles . The radical-initiated thiol-ene reaction has enabled the synthesis of four- to eight-membered rings, as well as macrocycles. While the radical thiol-ene reaction favors the anti-Markovnikov product, the regiochemistry of the cycloaddition depends on substituent effects and reaction conditions, which serve to direct the cyclization towards the thermodynamically or kinetically favored product respectively. This section examines intramolecular thiol-ene cyclization reactions, which yields a mixture of 5- exo and 6- endo products in order to facilitate a discussion of the factors, which may affect the regioselectivity of the intramolecular addition. This reaction has relevance for the synthesis of C -linked thiosugars. [ 14 ] Both the furanose and pyranose thiosugars can be prepared from the same thiyl radical precursor; 5- exo and 6- endo cyclizations of this precursor form the respective desired compound. The conditions under which these cyclization reactions occur follow Baldwin's rules for ring closure.
Intramolecular cyclization of thiyl and acyl thiyl radicals has been used to access alicyclic and heteorcyclic compounds, via anti-Markovnikov thiol-ene reactions on 1,6-dienes, under photochemical conditions. [ 15 ]
Given the reversibility of the thiol-ene radical addition, the reaction can be used to facilitate cis – trans isomerizations . The thiyl radical propagates with the alkene to form a carbon-centered radical, the previous double bond now allows free rotation around the single sigma bond . When the reverse reaction occurs, the orientation of the hydrogen addition on the carbon radical determines whether the isomerization product will be cis or trans . Therefore, composition of the products depends on the conformational stability of the carbon-centered radical intermediate. [ 16 ]
Dendrimers are promising in medicine, biomaterials, and nanoengineering . These polymers can functions as targeting components, detecting agents, and pharmaceutically-active compounds. Thiol-ene additions are useful in the divergent synthesis of dendrimers due to the characteristics of click chemistry such as the mild reaction conditions (benign solvents), regioselectivity , high efficiency, high conversion and quantitative yield . [ 17 ] Because this reaction is photo-initiated , it does not require copper catalysis , unlike other common reactions used in dendrimer preparation; this is advantageous for the synthesis of functional biomaterials given the inhibitory characteristic of copper on biological systems. [ 18 ] Thiol-ene reactions have been used alongside anhydride, esterification , Grignard , and Michael reactions to functionalize chain ends and build polymer backbones in the synthesis of branched molecules such as glycodendrons, polythioether dendrimers and organosilicon thioether dendrimers. [ 3 ] [ 4 ] [ 19 ]
A general strategy for the divergent synthesis of a dendrimer begins with a core; commonly-used cores include 2,4,6-triallyloxy-1,3,5-triazine, triallyl isocyanurate and tetravinylsilane. [ 17 ] [ 18 ] [ 20 ] In a well cited report, 2,4,6-triallyloxy-1,3,5-triazine was mixed with 1-thioglycerol in the absence of solvent, the thiol-ene reaction was initiated by the radical initiator 2,2-dimethoxy-2-phenylacetophenone and UV irradiation. Terminal alkene functional groups were added to the dendrimer via esterification by pent-4-enoic anhydride in the presence of DMAP and pyridine . The fourth generation product prepared in a stepwise fashion contains 48 terminal hydroxyl groups [ 17 ]
Multifunctional thiols such as pentaerythritol tetrakis(3-mercaptopropionate) can react with multifunctional enes such as norbornene -functionalized monomers, by photopolymerization to form cross-linked polymer networks. These thiol-ene networks are advantageous over traditional networks in that they form rapidly and quantitatively under atmospheric conditions (no oxygen inhibition) to form homogeneous polymer networks. [ 4 ]
The thiol-ene functionalization of surface has been widely investigated in material science and biotechnology. The attachment of a molecule with a sterically accessible alkene or thiol group to a solid surface enables the construction of polymers on the surface through subsequent thiol-ene reactions. [ 2 ] Given that in aqueous solutions thiol-ene reactions can be initiated by UV light (wavelength 365–405 nm) or sunlight, the attachment of a given functional group to the exposed thiol or alkene can be controlled spatially through photomasking. [ 21 ] More specifically, a photomask , enables the selective exposure of a surface to a UV light source, controlling the location of a given thiol-ene reaction, whereas the identity of the attached molecule is determined by the composition of the aqueous phase placed above the surface at the time of UV exposure. Thus, the manipulation of the shape of the photomask and the composition of the aqueous layer results in the creation of heterogeneous surface, whose properties depend on identity of the attached molecule at a given location. [ 2 ]
Thiol-ene functionalization of a surface can be achieved with a high level of spatial specificity, allowing the production of photomasks. [ 21 ]
Organo-triethoxysilane molecules, either thiol or vinyl tailed, have been introduced in surface functionalization. Ethoxysilane and methoxysilane functional groups are commonly used to anchor organic molecules on a variety of oxides surfaces. The thiol-ene coupling can be achieved either in the bulk solution before molecular anchoring [ 8 ] or step-wise onto a substrate that enables photolithography. [ 22 ] The reaction can be done in five minutes under sunlight that has ~4% UV light that is useful for the thiol-ene reaction. [ 8 ]
Thiol-ene can also be used as an electron beam resist, [ clarification needed ] resulting in nanostructures that allow direct protein functionalization. [ 23 ] | https://en.wikipedia.org/wiki/Thiol-ene_reaction |
In organic chemistry , the thiol-yne reaction (also known as alkyne hydrothiolation ) is an organic reaction between a thiol ( −SH ) and an alkyne ( −C≡CH ). The reaction product is an alkenyl sulfide ( −CH=CH−S− ). [ 1 ] [ 2 ]
The reaction was first reported in 1949 with thioacetic acid as reagent [ 3 ] [ 4 ] and rediscovered in 2009. [ 5 ] It is used in click chemistry [ 6 ] [ 7 ] [ 8 ] and in polymerization , especially with dendrimers .
This addition reaction is typically facilitated by a radical initiator or UV irradiation and proceeds through a sulfanyl radical species. With monoaddition a mixture of ( E / Z )-alkenes form. The mode of addition is anti-Markovnikov . The radical intermediate can engage in secondary reactions such as cyclisation. [ 9 ] [ 10 ] With diaddition the 1,2-disulfide or the 1,1- dithioacetal forms. Reported catalysts for radical additions are triethylborane , [ 11 ] indium(III) bromide [ 12 ] and AIBN . [ 13 ] The reaction is also reported to be catalysed by cationic rhodium and iridium complexes, [ 14 ] by thorium and uranium complexes, [ 15 ] by rhodium complexes, [ 16 ] [ 17 ] [ 18 ] by caesium carbonate [ 19 ] and by gold . [ 20 ]
Diphenyl disulfide reacts with alkynes to a 1,2-bis(phenylthio)ethylene. [ 21 ] Reported alkynes are ynamides. [ 22 ] A photoredox thiol-yne reaction has been reported. [ 23 ]
In polymer chemistry , systems have been described based on addition polymerization with 1,4-benzenedithiol and 1,4-diethynylbenzene, [ 24 ] [ 25 ] in the synthesis of other addition polymer systems [ 26 ] in the synthesis of dendrimers , [ 27 ] [ 28 ] [ 29 ] [ 30 ] in star polymers , [ 31 ] [ 32 ] [ 33 ] [ 34 ] in graft polymerization , [ 35 ] block copolymers , [ 36 ] and in polymer networks . [ 5 ] [ 37 ] Another reported application is the synthesis of macrocycles via dithiol coupling. [ 38 ] | https://en.wikipedia.org/wiki/Thiol-yne_reaction |
Thiolactones are a class of heterocyclic compounds in organic chemistry . They are analogs of the more common lactones in which an oxygen atom is replaced with a sulfur atom. The sulfur atom is within the ring system and adjacent to a carbonyl group .
Thiolactones can be prepared by dehydration of thiol-containing carboxylic acids. Thiolactones can be hydrolyzed back to the thiol acids under basic conditions. [ 1 ] β-Thiolactones can be opened by reaction at the 4-position via S N 2 nucleophilic reactions . [ 2 ]
Thiolactones are intermediates in the activation of some drugs. [ 4 ]
In nature, the most common thiolactone is homocysteine thiolactone . It is produced from homocysteine . It may play a role in protein damage. [ 5 ] The drugs citiolone and erdosteine are modified versions of homocysteine thiolactone.
Thiolactones have been found in peptides synthesized by bacteria such as Staphylococcus aureus in order to regulate their quorum-sensing system. [ 6 ] | https://en.wikipedia.org/wiki/Thiolactone |
Thiolate-protected gold clusters are a type of ligand-protected metal cluster , synthesized from gold ions and thin layer compounds that play a special role in cluster physics because of their unique stability and electronic properties. They are considered to be stable compounds. [ 1 ]
These clusters can range in size up to hundreds of gold atoms, above which they are classified as passivated gold nanoparticles.
The wet chemical synthesis of thiolate-protected gold clusters is achieved by the reduction of gold(III) salt solutions, using a mild reducing agent in the presence of thiol compounds. This method starts with gold ions and synthesizes larger particles from them, therefore this type of synthesis can be regarded as a "bottom-up approach" in nanotechnology to the synthesis of nanoparticles.
The reduction process depends on the equilibrium between different oxidation states of the gold and the oxidized or reduced forms of the reducing agent, or thiols. Gold(I)-thiolate polymers have been identified as important in the initial steps of the reaction. [ 2 ] Several synthesis recipes exist that are similar to the Brust synthesis of colloidal gold , however the mechanism is not yet fully understood. The synthesis produces a mixture of dissolved, thiolate-protected gold clusters of different sizes. These particles can then be separated by gel electrophoresis ( PAGE ). [ 3 ] If the synthesis is performed in a kinetically controlled manner, particularly stable representatives can be obtained with particles of uniform size ( monodispersely ), avoiding further separation steps. [ 4 ] [ 5 ]
Rather than starting from "naked" gold ions in solution, template reactions can be used for directed synthesis of clusters. The high affinity of the gold ions to electronegative and (partially) charged atoms of functional groups yields potential seeds for cluster formation. The interface between the metal and the template can act as a stabilizer and steer the final size of the cluster. Some potential templates are dendrimers , oligonucleotides , proteins , polyelectrolytes and polymers .
Top-down synthesis of the clusters can be achieved by the "etching" of larger metallic nanoparticles with redox-active, thiol -containing biomolecules. [ 6 ] In this process, gold atoms on the nanoparticles' surface react with the thiol, dissolving as gold-thiolate complexes until the dissolution reaction stops; this leaves behind a residual species of thiolate-protected gold clusters that is particularly stable. This type of synthesis is also possible using other non thiol-based ligands.
The electronic structure of the thiolate-protected gold clusters is characterized by strongly pronounced quantum effects. These result in discrete electronic states, and a nonzero HOMO/LUMO gap. This existence of discrete electronic states was first indicated by the discrepancy between their optical absorption and the predictions of classical Mie scattering . [ 7 ] The discrete optical transitions and occurrence of photoluminescence in these species are areas where they behave like molecular, rather than metallic, substances. This molecular optical behavior sharply distinguishes thiolate-protected clusters from gold nanoparticles, whose optical characteristics are driven by Plasmon resonance . Some of thiolate-protected clusters' properties can be described using a model in which the clusters are treated like " superatoms ". [ 8 ] According to this model they exhibit atomic-like electronic states , that are labeled S, P, D, F according to their respective angular momentum on the atomic level. Those clusters that have a " closed superatomic shell " configuration have indeed been identified as the most stable ones. This electronic shell closure and the resulting gain in stability is responsible for the discrete distribution of a few stable cluster sizes (magic numbers) observed in their synthesis, rather than a quasi-continuous distribution of sizes.
Magic numbers are connected with the number of metal atoms in those thiolate-protected clusters which display an outstanding stability. Such clusters can be synthesized monodispersely and are end products of the etching procedure after an addition of excess thiols does not lead to further metal dissolution. Some important clusters with magic numbers are (SG: Glutathione ): Au 10 (SG) 10 , Au 15 (SG) 13 , Au 18 (SG) 14 , Au 22 (SG) 16 , Au 22 (SG) 17 , Au 25 (SG) 18 , Au 29 (SG) 20 , Au 33 (SG) 22 , and Au 39 (SG) 24 . [ 2 ]
Au 20 (SCH 2 Ph) 16 is also well-known. [ 9 ] It was greater than representatives Au 102 (p-MBA) 44 with the para-mercaptobenzoice (para-mercapto-benzoic acid, p-MBA) produced ligand. [ 10 ]
Worthy of note is that in 2013, a structural prediction of the Au 130 (SCH 3 ) 50 cluster, based on Density Functional Theory (DFT) was confirmed in 2015. [ 11 ] This result represents the maturity of this field where calculations are able to guide the experimental work. [ 12 ] The following table features some sizes.
In bionanotechnology , intrinsic properties of the clusters (for example, fluorescence ) can be made available for bionanotechnological applications by linking them with biomolecules through the process of bioconjugation . [ 13 ] The protected gold particles' stability and fluorescence makes them efficient emitters of electromagnetic radiation that can be tuned by varying the cluster size and the type of ligand used for protection. The protective shell can function (have functional groups added) in a way that selective binding (for example, as a complementary protein receptor of DNA-DNA-interaction) qualifies them for the use as biosensors . [ 14 ] | https://en.wikipedia.org/wiki/Thiolate-protected_gold_cluster |
Thiolysis is a reaction with a thiol (R-SH) that cleaves one compound into two. [ 1 ] Thiolysis involves the addition of coenzyme A to one of the products. This reaction is similar to hydrolysis , which involves water instead of a thiol . [ 2 ] This reaction is seen in β-oxidation of fatty acids . [ 3 ] The depolymerisation of condensed tannins with the use of benzyl mercaptan as nucleophile is also called thiolysis. [ 4 ]
This chemical reaction article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thiolysis |
Thiolated polymers – designated thiomers – are functional polymers used in biotechnology product development with the intention to prolong mucosal drug residence time and to enhance absorption of drugs . The name thiomer was coined by Andreas Bernkop-Schnürch in 2000. [ 1 ] Thiomers have thiol bearing side chains . [ 2 ] [ 3 ] Sulfhydryl ligands of low molecular mass are covalently bound to a polymeric backbone consisting of mainly biodegradable polymers, such as chitosan , [ 4 ] [ 5 ] hyaluronic acid , [ 6 ] cellulose derivatives, [ 7 ] pullulan , [ 8 ] [ 9 ] starch , [ 10 ] gelatin , [ 11 ] polyacrylates , [ 12 ] cyclodextrins , [ 13 ] [ 14 ] or silicones . [ 15 ]
Thiomers exhibit properties potentially useful for non-invasive drug delivery via oral, ocular, nasal, vesical, buccal and vaginal routes. Thiomers show also potential in the field of tissue engineering and regenerative medicine . Various thiomers such as thiolated chitosan [ 16 ] and thiolated hyaluronic acid [ 17 ] are commercialy available as scaffold materials. Thiomers can be directly compressed to tablets or given as solutions. [ 18 ] [ 19 ] In 2012, a second generation of thiomers – called "preactivated" or "S-protected" thiomers – were introduced. [ 20 ]
In contrast to thiomers of the first generation, preactivated thiomers are stable towards oxidation and display comparatively higher mucoadhesive and permeation enhancing properties. [ 21 ] Approved thiomer products for human use are for example eyedrops for treatment of dry eye syndrome or adhesive gels for treatment of nickel allergy. [ 22 ]
Thiomers are capable of forming disulfide bonds with cysteine substructures of the mucus gel layer covering mucosal membranes. Because of this property they exhibit up to 100-fold higher mucoadhesive properties in comparison to the corresponding unthiolated polymers. [ 23 ] [ 24 ] [ 25 ] Because of their mucoadhesive properties, thiolated polymers are an effective tool in the treatment of diseases such as dry eye, dry mouth, and dry vagina syndrome where dry mucosal surfaces are involved. [ 26 ] [ 27 ] [ 28 ]
Various polymers such as poloxamers exhibit in situ gelling properties. Because of these properties they can be administered as liquid formulations forming stable gels once having reached their site of application. An unintended rapid elimination or outflow of the formulation from mucosal membranes such as the ocular, nasal or vaginal mucosa can therefore be avoided. Thiolated polymers are capable of providing a comparatively more pronounced increase in viscosity after application, as an extensive crosslinking process by the formation of disulfide bonds between the polymer chains due to oxidation takes place. This effect was first described in 1999 by Bernkop-Schnürch et al. [ 29 ] for polymeric excipients. In case of thiolated chitosan, for instance, a more than 10,000-fold increase in viscosity within a few minutes was shown. [ 30 ] These high in situ gelling properties can also be used for numerous further reasons such as for parenteral formulations, [ 31 ] as coating material [ 32 ] or for food additives [ 33 ]
Due to a sustained drug release, a prolonged therapeutic level of drugs exhibiting a short elimination half-life can be maintained. Consequently the frequency of dosing can be reduced contributing to an improved compliance. The release of drugs out of polymeric carrier systems can be controlled by a simple diffusion process. So far the efficacy of such delivery systems, however, was limited by a too rapid disintegration and/or erosion of the polymeric network. [ 34 ] By using thiolated polymers this essential shortcoming can be overcome. Because of the formation of inter- and intrachain disulfide bonds during the swelling process, the stability of the polymeric drug carrier matrix is strongly improved. Hence, a controlled drug release for numerous hours is guaranteed. There are numerous drug delivery systems making use of this technology. [ 35 ] [ 36 ] [ 37 ] [ 38 ] [ 39 ] [ 40 ]
Due to the binding of metal ions being essential for various enzymes to maintain their enzymatic activity, thiomers are potent reversible enzyme inhibitors. Many non-invasively administered drugs such as therapeutic peptides or nucleic acids are degraded on the mucosa by membrane bound enzymes, strongly reducing their bioavailability. In case of oral administration, this ‘enzymatic barrier’ is even more pronounced as an additional degradation caused by luminally secreted enzymes takes place. Because of their capability to bind zinc ions via thiol groups, thiomers are potent inhibitors of most membrane bound and secreted zinc-dependent enzymes. Due to this enzyme inhibitory effect, thiolated polymers can significantly improve the bioavailability of non-invasively administered drugs [ 41 ] [ 42 ] [ 43 ]
In vitro , thiomers were shown to have antimicrobial activity towards Gram-positive bacteria. [ 44 ] [ 45 ] In particular, N-acyl thiolated chitosans show great potential as highly efficient, biocompatible and cost-effective antimicrobial compounds. [ 46 ] Metabolism and mechanistic studies are under way to optimize these thiomers for clinical applications. Because of their antimicrobial activity, thiolated polymers are also used as coatings that avoid bacterial adhesion. [ 47 ]
Thiomers are able to reversibly open tight junctions. The responsible mechanism seems to be based on the inhibition of protein tyrosine phosphatase being involved in the closing process of tight junctions. [ 48 ] Due to thiolation the permeation enhancing effect of polymers such as polyacrylic acid or chitosan can be up to 10-fold improved. [ 49 ] [ 50 ] [ 51 ] In comparison to most low molecular weight permeation enhancers, thiolated polymers offer the advantage of not being absorbed from the mucosal membrane. Hence, their permeation enhancing effect can be maintained for a comparatively longer period of time and systemic toxic side effects of the auxiliary agent can be excluded.
Thiomers are able to reversibly inhibit efflux pumps. Because of this property the mucosal uptake of various efflux pump substrates such as anticancer drugs, antimycotic drugs and antiinflammatory drugs can be tremendously improved. [ 52 ] [ 53 ] [ 54 ] The postulated mechanism of efflux pump inhibition is based on an interaction of thiolated polymers with the channel forming transmembrane domain of various efflux pumps such as P-gp and multidrug resistance proteins (MRPs). P-gp, for instance, exhibits 12 transmembrane regions forming a channel through which substrates are transported outside of the cell. Two of these transmembrane domains – namely 2 and 11 – exhibit on position 137 and 956, respectively, a cysteine subunit. Thiomers seem to enter in the channel of P-gp and likely form subsequently one or two disulfide bonds with one or both cysteine subunits located within the channel. Due to this covalent interaction the allosteric change of the transporter being essential to move drugs outside of the cell might be blocked. [ 55 ] [ 56 ]
Thiomers have the ability to form complexes with different metal ions, especially divalent metal ions, due to their thiol groups. Thiolated chitosans, for instance, were shown to effectively absorb nickel ions. [ 57 ] [ 58 ]
As thiolated polymers exhibit biocompatibility, cellular mimicking properties and efficiently support proliferation and differentiation of various cell types, they are used as scaffolds for tissue engineering. [ 59 ] [ 60 ] [ 61 ] [ 62 ] Furthermore thiolated polymers such as thiolated hyaluronic acid [ 63 ] and thiolated chitosan [ 64 ] were shown to exhibit wound healing properties. | https://en.wikipedia.org/wiki/Thiomer |
Thionyl chloride is an inorganic compound with the chemical formula SOCl 2 . It is a moderately volatile , colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately 45,000 tonnes (50,000 short tons) per year being produced during the early 1990s, [ 5 ] but is occasionally also used as a solvent. [ 6 ] [ 7 ] [ 8 ] It is toxic, reacts with water, and is also listed under the Chemical Weapons Convention as it may be used for the production of chemical weapons .
Thionyl chloride is sometimes confused with sulfuryl chloride , SO 2 Cl 2 , but the properties of these compounds differ significantly. Sulfuryl chloride is a source of chlorine whereas thionyl chloride is a source of chloride ions.
The major industrial synthesis involves the reaction of sulfur trioxide and sulfur dichloride . [ 9 ] This synthesis can be adapted to the laboratory by heating oleum to slowly distill the sulfur trioxide into a cooled flask of sulfur dichloride. [ 10 ]
Other methods include syntheses from:
The second of the above five reactions also affords phosphorus oxychloride (phosphoryl chloride), which resembles thionyl chloride in many of its reactions. They may be separated by distillation, since thionyl chloride boils at a much lower temperature than phosphoryl chloride. [ citation needed ]
SOCl 2 adopts a trigonal pyramidal molecular geometry with C s molecular symmetry . This geometry is attributed to the effects of the lone pair on the central sulfur(IV) center.
In the solid state SOCl 2 forms monoclinic crystals with the space group P2 1 /c. [ 11 ]
Thionyl chloride has a long shelf life, however "aged" samples develop a yellow hue, possibly due to the formation of disulfur dichloride . It slowly decomposes to S 2 Cl 2 , SO 2 and Cl 2 at just above the boiling point. [ 9 ] [ 12 ] Thionyl chloride is susceptible to photolysis , which primarily proceeds via a radical mechanism. [ 13 ] Samples showing signs of ageing can be purified by distillation under reduced pressure, to give a colourless liquid. [ 14 ]
Thionyl chloride is mainly used in the industrial production of organochlorine compounds , which are often intermediates in pharmaceuticals and agrichemicals. It usually is preferred over other reagents, such as phosphorus pentachloride , as its by-products (HCl and SO 2 ) are gaseous, which simplifies purification of the product.
Many of the products of thionyl chloride are themselves highly reactive and as such it is involved in a wide range of reactions.
Thionyl chloride reacts exothermically with water to form sulfur dioxide and hydrochloric acid :
By a similar process it also reacts with alcohols to form alkyl chlorides . If the alcohol is chiral the reaction generally proceeds via an S N i mechanism with retention of stereochemistry; [ 15 ] however, depending on the exact conditions employed, stereo-inversion can also be achieved. Historically the use of SOCl 2 with pyridine was called the Darzens halogenation , but this name is rarely used by modern chemists.
Reactions with an excess of alcohol produce sulfite esters , which can be powerful methylation , alkylation and hydroxyalkylation reagents. [ 16 ]
For example, the addition of SOCl 2 to amino acids in methanol selectively yields the corresponding methyl esters. [ 17 ]
Classically, it converts carboxylic acids to acyl chlorides : [ 18 ] [ 19 ] [ 20 ]
The reaction mechanism has been investigated: [ 21 ]
With primary amines, thionyl chloride gives sulfinylamine derivatives (RNSO), one example being N - sulfinylaniline . Thionyl chloride reacts with primary formamides to form isocyanides [ 22 ] and with secondary formamides to give chloro iminium ions; as such a reaction with dimethylformamide will form the Vilsmeier reagent . [ 23 ]
By an analogous process, primary amides will react with thionyl chloride to form imidoyl chlorides , with secondary amides also giving chloro iminium ions. These species are highly reactive and can be used to catalyse the conversion of carboxylic acids to acyl chlorides; [ 24 ] they are also exploited in the Bischler–Napieralski reaction as a means of forming isoquinolines .
Primary amides will continue on to form nitriles if heated ( Von Braun amide degradation ). [ 25 ]
Thionyl chloride has also been used to promote the Beckmann rearrangement of oximes .
Thionyl chloride converts phosphonic acids and phosphonates into phosphoryl chlorides . It is for this type of reaction that thionyl chloride is listed as a Schedule 3 compound, as it can be used in the "di-di" method of producing G-series nerve agents . For example, thionyl chloride converts dimethyl methylphosphonate into methylphosphonic acid dichloride , which can be used in the production of sarin and soman .
As SOCl 2 reacts with water it can be used to dehydrate various metal chloride hydrates, such magnesium chloride ( MgCl 2 ·6H 2 O ), aluminium chloride ( AlCl 3 ·6H 2 O ), and iron(III) chloride ( FeCl 3 ·6H 2 O ). [ 9 ] This conversion involves treatment with refluxing thionyl chloride and follows the following general equation: [ 31 ]
If an exces SOCl2 is used to dehydrate aluminium trichloride, it will form an adduct (1 molecule of thionyl chloride for each molecule of the aluminium trichloride dimer).
Thionyl chloride is a component of lithium–thionyl chloride batteries , [ 37 ] where it acts as the positive electrode (in batteries: cathode ) with lithium forming the negative electrode ( anode ); the electrolyte is typically lithium tetrachloroaluminate . The overall discharge reaction is as follows:
These non-rechargeable batteries have advantages over other forms of lithium batteries such as a high energy density, a wide operational temperature range, and long storage and operational lifespans. However, their high cost, non-rechargeability, and safety concerns have limited their use. The contents of the batteries are highly toxic and require special disposal procedures; additionally, they may explode if shorted. The technology was used on the 1997 Sojourner Mars rover.
SOCl 2 is highly reactive and can violently release hydrochloric acid upon contact with water and alcohols. It is also a controlled substance under the Chemical Weapons Convention , where it is listed as a Schedule 3 substance, since it is used in the manufacture of G-series nerve agents [ citation needed ] and the Meyer and Meyer–Clarke methods of producing sulfur-based mustard gases . [ 38 ]
In 1849, the French chemists Jean-François Persoz and Bloch, and the German chemist Peter Kremers (1827–?), independently first synthesized thionyl chloride by reacting phosphorus pentachloride with sulfur dioxide . [ 39 ] [ 40 ] However, their products were impure: both Persoz and Kremers claimed that thionyl chloride contained phosphorus, [ 41 ] and Kremers recorded its boiling point as 100 °C (instead of 74.6 °C). In 1857, the German-Italian chemist Hugo Schiff subjected crude thionyl chloride to repeated fractional distillations and obtained a liquid which boiled at 82 °C and which he called Thionylchlorid . [ 42 ] In 1859, the German chemist Georg Ludwig Carius noted that thionyl chloride could be used to make acid anhydrides and acyl chlorides from carboxylic acids and to make alkyl chlorides from alcohols . [ 43 ] | https://en.wikipedia.org/wiki/Thionyl_chloride |
The thionyl group is SO, a sulfur atom plus an oxygen atom.
It occurs in compounds such as thionyl fluoride , SOF 2 .
Thionyl chloride , SOCl 2 , is a common reagent used in organic synthesis to convert carboxylic acids to acyl chlorides .
In organic chemistry , the thionyl group is known as a sulfoxide group or sulfinyl group, and has the general structure RS(=O)R'. In the context of acid-base reactions, it may also be referred to as a sulfinyl group (i.e. sulfinylamines ).
Greenwood, Norman N. ; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann . ISBN 978-0-08-037941-8 .
This article about chemical compounds is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thionyl_group |
Thiophosphates (or phosphorothioates , PS ) are chemical compounds and anions with the general chemical formula PS 4− x O 3− x ( x = 0, 1, 2, or 3) and related derivatives where organic groups are attached to one or more O or S. Thiophosphates feature tetrahedral phosphorus(V) centers. [ 1 ]
Organothiophosphates are a subclass of organophosphorus compounds that are structurally related to the inorganic thiophosphates. Common members have formulas of the type (RO) 3− x (RS) x PS and related compounds where RO is replaced by RS. Many of these compounds are used as insecticides , some have medical applications, and some have been used as oil additives . [ 1 ]
Oligonucleotide phosphorothioates (OPS) are modified oligonucleotides where one of the oxygen atoms in the phosphate moiety is replaced by sulfur. They are the basis of antisense therapy , e.g., the drugs fomivirsen (Vitravene), oblimersen , alicaforsen , and mipomersen (Kynamro). [ 3 ]
The simplest thiophosphates have the formula [PS 4− x O x ] 3− . These trianions are only observed at very high pH, instead they exist in protonated form with the formula [H n PS 4− x O x ] (3− n )− (x = 0, 1, 2, or 3 and (n = 1, 2, or 3).
Monothiophosphate is the anion [PO 3 S] 3− , which has C 3v symmetry . A common salt is sodium monothiophosphate (Na 3 PO 3 S). Monothiophosphate is used in research as an analogue of phosphate in biochemistry . Monothiophosphate esters are biochemical reagents used in the study of transcription , [ 4 ] substitution interference assays. Sometimes, "monothiophosphate" refers to esters such as (CH 3 O) 2 POS − . [ 5 ]
Dithiophosphate has the formula [PO 2 S 2 ] 3− , which has C 2v symmetry . Sodium dithiophosphate , which is colorless, is the major product from the reaction of phosphorus pentasulfide with NaOH : [ 6 ]
Dithiophosphoric acid is obtained by treatment of barium dithiophosphate with sulfuric acid :
Both Na 3 PO 2 S 2 and especially H 3 PO 2 S 2 are prone toward hydrolysis to their monothio derivatives.
Trithiophosphate is the anion [POS 3 ] 3− , which has C 3v symmetry. Tetrathiophosphate is the anion [PS 4 ] 3− , which has T d symmetry.
A number of these anions known. Some have attracted interest as components in fast ion conductors for use in solid state batteries. The binary thiophosphates do not exhibit the extensive diversity of the analogous oxyanions but contain similar structural features, for example P is 4 coordinate, P−S−P links form and there are P−P bonds. One difference is that ions may include polysulfide fragments of 2 or more S atoms whereas in the P−O anions there is only the reactive −O−O−, peroxo, unit. | https://en.wikipedia.org/wiki/Thiophosphate |
Thioquinanthrene , also known as thiochinathren , is an aromatic organic chemical compound. It has the chemical formula C 18 H 10 N 2 S 2 and reacts with alcoholates or alkoxides . [ 1 ] One of the key uses is to act as a catalyst poison in the Rosenmund reduction . [ 2 ] [ 3 ] It has the IUPAC name of 2,13-dithia-10,21-diazapentacyclo[12.8.0.0 3,12 .0 4,9 .0 15,20 ]docosa-1(14),3(12),4,6,8,10,15,17,19,21-decaene. [ 4 ]
In the Rosenmeund reaction, an acid chloride is reduced to an aldehyde . Continuing the reduction produces an alcohol . This further reaction is undesirable as the alcohol will now react with the acyl chloride to produce the unwanted ester product. For this reaction (over reduction) to be prevented, the catalyst needs to be poisoned. Thioquinanthrene was used initially, although other materials have been used since. [ 5 ] [ 6 ] [ 7 ] [ 8 ] | https://en.wikipedia.org/wiki/Thioquinanthrene |
Thioreductor is a Gram-negative , mesophilic , hydrogen-oxidizing, sulfur-reducing and motile genus of bacteria from the phylum Campylobacterota with one known species ( Thioreductor micantisoli ). [ 2 ] [ 1 ] [ 3 ] [ 4 ] Thioreductor micantisoli has been isolated from hydrothermal sediments from the Iheya North from the Mid-Okinawa Trough in Japan . [ 4 ] [ 5 ]
This bacteria -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thioreductor |
Thiosemicarbazide is the chemical compound with the formula H 2 NC(S)NHNH 2 . A white, odorless solid, it is related to thiourea (H 2 NC(S)NH 2 ) by the insertion of an NH center. They are commonly used as ligands for transition metals. [ 2 ] Many thiosemicarbazides are known. These feature an organic substituent in place of one or more H's of the parent molecule. 4-Methyl-3-thiosemicarbazide is a simple example.
According to X-ray crystallography , the CSN 3 core of the molecule is almost planar as are the three H atoms nearest the thiocarbonyl group. [ 3 ] This can be explained by models of electron delocalisation.
Thiosemicarbazides are precursors to thiosemicarbazones . They are precursors to heterocycles . [ 4 ] Formylation of thiosemicarbazide provides access to triazole. [ 5 ] | https://en.wikipedia.org/wiki/Thiosemicarbazide |
A thiosemicarbazone is an organosulfur compound with the formula H 2 NC(S)NHN=CR 2 . Many variations exist, including those where some or all of the N H centers are substituted by organic groups. Thiosemicarbazones are usually produced by condensation of a thiosemicarbazide with an aldehyde or ketone :
In terms of their chemical structures, the CSN3 core atoms are coplanar. [ 1 ]
Some thiosemicarbazones have medicinal properties, e.g. the antiviral metisazone and the antibiotic thioacetazone . Thiosemicarbazones are also widely used as ligands in coordination chemistry . [ 2 ] The affinity of thiosemicarbazones for metal ions is exploited in controlling iron overload. [ 3 ] | https://en.wikipedia.org/wiki/Thiosemicarbazone |
Thiosulfate ( IUPAC-recommended spelling ; sometimes thiosulphate in British English) is an oxyanion of sulfur with the chemical formula S 2 O 2− 3 . Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid , such as sodium thiosulfate Na 2 S 2 O 3 and ammonium thiosulfate (NH 4 ) 2 S 2 O 3 . Thiosulfate salts occur naturally. Thiosulfate rapidly dechlorinates water, and is used to halt bleaching in the paper-making industry. Thiosulfate salts are mainly used for dyeing in textiles, and bleaching of natural substances. [ 2 ]
The thiosulfate ion is tetrahedral at the central S atom. The thiosulfate ion has C 3v symmetry. The external sulfur atom has a valence of 2 while the central sulfur atom has a valence of 6. The oxygen atoms have a valence of 2. The S-S distance of about 201 pm in sodium thiosulphate is appropriate for a single bond. The S-O distances are slightly shorter than the S-O distances in sulfate.
For many years, the oxidation states of the sulfur atoms in the thiosulfate ion were considered to be +6 as in sulfate and −2 as in sulfide for the central and terminal atoms, respectively. This view precluded the disproportionation reaction of thiosulfate into sulfate and sulfide as a redox mechanism for providing energy to bacteria under anaerobic conditions in sediments because there is no change in oxidation state for either S atom. However, XANES spectroscopy measurements have revealed that the charge densities of the sulfur atoms point towards +5 and −1 oxidation states for the central and terminal S atoms, respectively. This observation is consistent with the disproportionation of thiosulfate into sulfate and sulfide as a redox mechanism freeing up energy from microbial fermentation . [ 3 ] Yet another interpretation suggests an oxidation state of +4 for the central S atom and 0 for the terminal atom and an unusually long 'full' S=S double bond between the two.
Thiosulfate ion is produced by the reaction of sulfite ion with elemental sulfur, and by incomplete oxidation of sulfides (e.g. pyrite oxidation). Sodium thiosulfate can be formed by disproportionation of sulfur dissolving in sodium hydroxide (similar to phosphorus ).
Thiosulfate ions reacts with acids to give sulfur dioxide and various sulfur rings: [ 4 ]
This reaction may be used to generate sulfur colloids and demonstrate the Rayleigh scattering of light in physics . If white light is shone from below, blue light is seen from sideways and orange light from above, due to the same mechanisms that color the sky at midday and dusk . [ citation needed ]
Thiosulfate ions react with iodine to give tetrathionate ions:
This reaction is key for iodometry .
With bromine (X = Br) and chlorine (X = Cl), thiosulfate ions are oxidized to sulfate ions:
Thiosulfate ion extensively forms diverse complexes with transition metals . This reactivity is related to its role in of silver-based photography .
Also reflecting its affinity for metals , thiosulfate ion rapidly corrodes metals in acidic conditions. Steel and stainless steel are particularly sensitive to pitting corrosion induced by thiosulfate ions. Molybdenum improves the resistance of stainless steel toward pitting (AISI 316L hMo). In alkaline aqueous conditions and medium temperature (60 °C), carbon steel and stainless steel (AISI 304L, 316L) are not attacked, even at high concentration of base (30%w KOH ), thiosulfate ion (10%w) and in presence of fluoride ion (5%w KF ). [ citation needed ]
In the era of silver-based photography , thiosulfate salts were consumed on a large scale as a "fixer" reagent. This application exploits thiosulfate ion's ability to dissolve silver halides . Sodium thiosulfate , commonly called hypo (from "hyposulfite"), was widely used in photography to fix black and white negatives and prints after the developing stage; modern "rapid" fixers use ammonium thiosulfate as a fixing salt because it acts three to four times faster. [ 5 ]
Thiosulfate salts have been used to extract or leach gold and silver from their ores as a less toxic alternative to cyanide ion. [ 2 ]
The enzyme rhodanase (thiosulfate sulfurtransferase) catalyzes the detoxification of cyanide ion by thiosulfate ion by transforming them into thiocyanate ion and sulfite ion:
Sodium thiosulfate has been considered as an empirical treatment for cyanide poisoning, along with hydroxocobalamin . It is most effective in a pre-hospital setting, since immediate administration by emergency personnel is necessary to reverse rapid intracellular hypoxia caused by the inhibition of cellular respiration , at complex IV . [ 6 ] [ 7 ] [ 8 ] [ 9 ]
It activates thiosulfate sulfurtransferase ( TST ) in mitochondria. TST is associated with protection against obesity and type II (insulin resistant) diabetes . [ 10 ] [ 11 ]
Thiosulfate can also work as electron donor for growth of bacteria oxidizing sulfur , such as Chlorobium limicola forma thiosulfatophilum . These bacteria use electrons from thiosulfate (and other sources) and carbon from carbon dioxide to synthesize carbon compounds through reverse Krebs cycle . [ 12 ]
Some bacteria can metabolise thiosulfates. [ 13 ]
Thiosulfate ion is a component of the very rare mineral sidpietersite Pb 4 (S 2 O 3 )O 2 (OH) 2 . [ 14 ] The presence of this anion in the mineral bazhenovite was disputed. [ 15 ]
Thiosulfate is an acceptable common name and used almost always.
The functional replacement IUPAC name is sulfurothioate ; the systematic additive IUPAC name is trioxidosulfidosulfate(2−) or trioxido-1 κ 3 O -disulfate( S — S )(2−) . [ 1 ]
Thiosulfate also refers to the esters of thiosulfuric acid , e.g. O , S -dimethyl thiosulfate CH 3 −O−S(=O) 2 −S−CH 3 . Such species are rare. | https://en.wikipedia.org/wiki/Thiosulfate |
Thiosulfonate esters are organosulfur compounds with the formula R−SO 2 −S−R' . The parent member S -methyl methanethiosulfonate CH 3 −SO 2 −S−CH 3 is a colorless liquid.
Thiosulfonate esters are usually produced by oxidation of disulfides or the nucleophilic attack of thiolates on organosulfonyl halides. [ 1 ] The simplest thiosulfonate, CH 3 SO 2 SCH 3 can however be prepared from dimethyl sulfoxide by treatment with oxalyl chloride . [ 2 ]
Thiosulfonate also refers to the thiosulfonate anion R−S 2 O − 2 and its salts . Alkali metal organylthiosulfonates are the salts of organylthiosulfonic acids (e.g., sodium methanethiosulfonate CH 3 −S 2 O − 2 Na + ). They are prepared by the reaction of organo sulfonyl chlorides with sources of sulfide. [ 1 ] [ 3 ]
Oxidation with mCPBA gives disulfones . [ 1 ]
This organic chemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thiosulfonate |
Thiourea ( / ˌ θ aɪ . oʊ j ʊəˈr iː . ə , - ˈ jʊər i -/ ) [ 2 ] [ 3 ] is an organosulfur compound with the formula SC(NH 2 ) 2 and the structure H 2 N−C(=S)−NH 2 . It is structurally similar to urea ( H 2 N−C(=O)−NH 2 ), with the oxygen atom replaced by sulfur atom (as implied by the thio- prefix). The properties of urea and thiourea differ significantly. Thiourea is a reagent in organic synthesis . Thioureas are a broad class of compounds with the formula SC(NHR)(NH 2 ), SC(NHR) 2 , etc
Thiourea is a planar molecule. The C=S bond distance is 1.71 Å. The C-N distances average 1.33 Å. [ 4 ] The weakening of the C-S bond by C-N pi-bonding is indicated by the short C=S bond in thiobenzophenone , which is 1.63 Å.
Thiourea occurs in two tautomeric forms, of which the thione form predominates in aqueous solutions. The equilibrium constant has been calculated as K eq is 1.04 × 10 −3 . [ 5 ] The thiol form, which is also known as an isothiourea, can be encountered in substituted compounds such as isothiouronium salts.
The global annual production of thiourea is around 8,000 tonnes, mostly in China. Thiourea is manufactured by the reaction of hydrogen sulfide with calcium cyanamide in the presence of carbon dioxide . [ 6 ]
Thiourea is a precursor to thiourea dioxide , which is achieved using hydrogen peroxide :
Thiourea dioxideis a common reducing agent in textile processing. [ 6 ]
Thiourea has utility in practical heterocyclic chemistry . It is a precursor to sulfathiazoles , tetramisole , and cephalosporins .
Other industrial uses of thiourea include production of flame retardant resins, and vulcanization accelerators.
Thiourea is building blocks to pyrimidine derivatives. Thus, thioureas condense with β-dicarbonyl compounds. [ 7 ] The amino group on the thiourea initially condenses with a carbonyl, followed by cyclization and tautomerization. Desulfurization delivers the pyrimidine. The pharmaceuticals thiobarbituric acid and sulfathiazole are prepared using thiourea. [ 6 ] 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea and hydrazine .
Thiourea is used as an auxiliary agent in diazo paper, light-sensitive photocopy paper and almost all other types of copy paper.
It is also used to tone silver-gelatin photographic prints (see Sepia Toning ).
Thiourea is used in the Clifton-Phillips and Beaver bright and semi-bright electroplating processes. [ 8 ] It is also used in a solution with tin(II) chloride as an electroless tin plating solution for copper printed circuit boards .
Thiourea has been proposed as a fertilizer especially under conditions of environmental stress. [ 9 ]
Thiourea exists in dynamic equilibrium with ammonium thiocyanate at 150 °C. This equilibrium was once exploited as a route to thiourea, but the separation of the mixture is problematic. [ 6 ] Thiourea is basic, sustaining protonation at sulfur. According to X-ray crystallography , the product is [HSC(NH 2 ) 2 ] + , a planar cation. Protonation does not substantially perturb the bond distances. [ 10 ]
When treated with a variety of oxidants, thiourea forms a cationic disulfide. Oxidation with iodine proceeds as follows: [ 11 ]
Oxidized with hydrogen peroxide gives thiourea dioxide . [ 12 ]
Thiourea reduces peroxides to the corresponding diols . [ 13 ]
Thiourea is also used in the reductive workup of ozonolysis to give carbonyl compounds. [ 14 ] Dimethyl sulfide is also an effective reagent for this reaction, but it is highly volatile (boiling point 37 °C ) and has an obnoxious odor whereas thiourea is odorless and conveniently non-volatile (reflecting its polarity).
Thiourea is employed as a source of sulfide, such as for converting alkyl halides to thiols. The reaction capitalizes on the nucleophilicity of the sulfur center and is reminiscent of the protonation of thiourea. S-alkylation gives a isothiouronium salt :
Isothiouronium cations are prone to base hydrolysis to give the thiolate, which can undergo protonation to give the thiol.
In one example, ethane-1,2-dithiol is prepared from 1,2-dibromoethane : [ 15 ]
Like other thioamides , thiourea can serve as a source of sulfide upon reaction with metal ions. For example, mercury sulfide forms when mercuric salts in aqueous solution are treated with thiourea:
These sulfiding reactions have been applied to the synthesis of many metal sulfides.. [ 16 ] [ 17 ]
Thiourea is a building block for many heterocycles. It is a precursor to pyrimidine derivatives via condensation with β-dicarbonyl compounds. [ 18 ]
Similarly, aminothiazoles can be synthesized by the reaction of α-halo ketones and thiourea. [ 19 ]
The pharmaceuticals thiobarbituric acid and sulfathiazole are prepared using thiourea. [ 6 ] 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea and hydrazine .
Being a soft nucleophile, thiourea has an affinity for metal ions, forming coordination complexes . Representative is [Tc(SC(NH 2 ) 2 ] 6 ]Cl 3 . [ 20 ] One practical consequence of its affinity for metals, thiourea is used as a silver polish . [ 6 ] Another potential application is the use of thiourea as a lixiviant for gold and silver leaching, bypassing the steps of cyanide use and smelting. [ 21 ]
Thiourea is a reagent in the Kurnakov test used to differentiate cis- and trans- isomers of certain square planar platinum complexes. The reaction was discovered in 1893 by Russian chemist Nikolai Kurnakov and is still performed as an assay for compounds of this type. [ 22 ]
The LD 50 for thiourea is 125 mg/kg for rats (oral). [ 23 ]
A goitrogenic effect (enlargement of the thyroid gland) has been reported for chronic exposure, reflecting the ability of thiourea to interfere with iodide uptake. [ 6 ] | https://en.wikipedia.org/wiki/Thiourea |
Thiourea dioxide or thiox is an organosulfur compound that is used in the textile industry. [ 1 ] It functions as a reducing agent . [ 2 ] It is a white solid, and exhibits tautomerism in solution. [ 3 ]
Crystalline and gaseous thiourea dioxide adopts a C 2v - symmetric structure. Selected bond lengths : S-C = 186, C-N = 130, and S-O = 149 pm. The sulfur center is pyramidal. The C-S bond length is close to that of a single bond. For comparison, the C=S bond in thiourea is 171 pm. [ 4 ] [ 5 ] Instead the bonding is described with a significant contribution from a dipolar resonance structure with multiple bonding between C and N. One consequence of this bonding is the planarity of the nitrogen centers. [ 6 ] In the presence of water or DMSO , thiourea dioxide converts to the tautomer , a sulfinic acid , (H 2 N)HN=CS(O)(OH), named formamidine sulfinic acid. [ 6 ]
Thiourea dioxide was first prepared in 1910 by the English chemist Edward de Barry Barnett. [ 7 ]
Thiourea dioxide is prepared by the oxidation of thiourea with hydrogen peroxide . [ 8 ]
The mechanism of the oxidation has been examined. [ 9 ] An aqueous solution of thiourea dioxide has a pH about 6.5 at which thiourea dioxide is hydrolyzed to urea and sulfoxylic acid . It has been found that at pH values of less than 2, thiourea and hydrogen peroxide react to form a disulfide species. It is therefore convenient to keep the pH between 3 and 5 and the temperature below 10 °C . [ 10 ] It can also be prepared by oxidation of thiourea with chlorine dioxide . [ 11 ] The quality of the product can be assessed by titration with indigo . [ 8 ]
Thiourea dioxide is used in reductive bleaching in textiles . [ 12 ] Thiourea dioxide has also been used for the reduction of aromatic nitroaldehydes and nitro ketones to nitroalcohols. [ 13 ] | https://en.wikipedia.org/wiki/Thiourea_dioxide |
Within the area of organocatalysis , (thio)urea organocatalysis describes the use of ureas and thioureas to accelerate and stereochemically alter organic transformations. The effects arise through hydrogen-bonding interactions between the substrate and the (thio)urea. Unlike classical catalysts, these organocatalysts interact by non-covalent interactions, especially hydrogen bonding ("partial protonation "). The scope of these small-molecule H-bond donors termed (thio)urea organocatalysis covers both non-stereoselective and stereoselective reactions. [ 1 ]
Hydrogen-bonding between thiourea derivatives and carbonyl substrates involve two hydrogen bonds provided by coplanar amino substituents in the (thio)urea. [ 2 ] [ 3 ] [ 4 ] [ 5 ] Squaramide catalysts engage in double H-bonding interactions and are often superior to thioureas. [ 6 ]
Thioureas are often found to be stronger hydrogen-bond donors ( i.e., more acidic) than ureas [ 7 ] because their amino groups are more positively charged. Quantum chemical analyses revealed that this counterintuitive phenomenon, which is not explainable by the relative electronegativities of O and S, results from the effective steric size of the chalcogen atoms. [ 8 ]
（Thio) ureas are green and sustainable catalysts. When effective, they can offer these advantages:
H-bond accepting substrates include carbonyl compounds, imines , nitroalkenes . The Diels-Alder reaction is one process that can benefit from (thio)urea catalysts.
Early contributions were made by Kelly, Etter, Jorgensen, Hine, Curran, Göbel, and De Mendoza (see review articles cited below) on hydrogen bonding interactions of small, metal-free compounds with electron-rich binding sites. Peter R. Schreiner and co-workers identified and introduced electron-poor thiourea derivatives as hydrogen-bonding organocatalysts. Schreiner's thiourea, N,N' -bis 3,5-bis(trifluormethyl)phenyl thiourea , combines all structural features for double H-bonding mediated organocatalysis:
A broad variety of monofunctional and bifunctional (concept of bifunctionality) chiral double hydrogen-bonding (thio)urea organocatalysts have been developed. | https://en.wikipedia.org/wiki/Thiourea_organocatalysis |
In organic chemistry , thioureas are members of a family of organosulfur compounds with the formula S=C(NR 2 ) 2 and structure R 2 N−C(=S)−NR 2 . The parent member of this class of compounds is thiourea ( S=C(NH 2 ) 2 ). Substituted thioureas are found in several commercial chemicals.
Thioureas have a trigonal planar molecular geometry of the N 2 C=S core. The C=S bond distance is near 1.71 Å , which is 0.1 Å longer than in normal ketones ( R 2 C=O ). The C–N bond distances are short. [ 1 ] Thioureas occurs in two tautomeric forms.
On the other hand, some compounds depicted as isothioureas and in fact thioureas, one example being mercaptobenzimidazole . [ 2 ]
N , N ′-unsubstituted thioureas can be prepared by treating the corresponding cyanamide with hydrogen sulfide or similar sulfide sources. [ 3 ] Organic ammonium salts react with potassium thiocyanate as the source of the thiocarbonyl ( C=S ). [ 4 ]
Alternatively, N , N ′-disubstituted thioureas can be prepared by coupling two amines with thiophosgene : [ 5 ]
Amines also condense with organic thiocyanates to give thioureas: [ 6 ]
Cyclic thioureas are prepared by transamidation of thiourea with diamines. Ethylene thiourea is synthesized by treating ethylenediamine with carbon disulfide . [ 7 ] In some cases, thioureas can be prepared by thiation of ureas using phosphorus pentasulfide .
Thioureas are susceptible to tautomerization. For the parent thiourea, the thione tautomer predominates in aqueous solutions. [ 8 ] The thiol form, known as an isothiourea, can be encountered in substituted compounds such as isothiouronium salts.
Thioureas are nucleophilic at sulfur. When they contain a pair of N-H substituents, thioureas engage in hydrogen bonding . This interaction is the basis of a research theme called thiourea organocatalysis . [ 9 ] Thioureas are often found to be stronger hydrogen-bond donors ( i.e., more acidic) than ureas . [ 10 ] [ 11 ]
Agrichemicals that feature the thiourea functional group include diafenthiuron , methimazole , carbimazole (converted in vivo to methimazole), and propylthiouracil . [ 12 ] α-Naphthylthiourea is a commercial rodenticide .
Some thioureas are vulcanization accelerators.
Ergothioneine , which is derived from histidine , is a rare example of a thiourea found in nature.
The cyclic of thiourea called thiamazole is used to treat overactive thyroid | https://en.wikipedia.org/wiki/Thioureas |
In chemistry , a thioxanthate is an organosulfur compound with the formula RSCS 2 X. When X is an alkali metal, the thioxanthate is a salt. When X is a transition metal, the thioxanthate is a ligand , and when X is an organic group, the compounds are called thioxanthate esters. They are usually yellow colored compounds that often dissolve in organic solvents. They are used as precursors to some catalysts, froth flotation agents, and additives for lubricants.
The alkali metal thioxanthates are produced by treating a thiol with a base in the presence of carbon disulfide , as illustrated by the preparation of sodium ethyl thioxanthate:. [ 1 ]
Sodium ethyl thioxanthate is similar structurally to sodium ethyl xanthate .
Alkylation of such thioxanthate anions gives thioxanthate esters, as illustrated by the preparation of ethyl methyl thioxanthate:
Thioxanthate esters are also called esters of trithiocarbonate . | https://en.wikipedia.org/wiki/Thioxanthate |
Third-generation sequencing (also known as long-read sequencing ) is a class of DNA sequencing methods which produce longer sequence reads , under active development since 2008. [ 1 ]
Third generation sequencing technologies have the capability to produce substantially longer reads than second generation sequencing , also known as next-generation sequencing. [ 1 ] Such an advantage has critical implications for both genome science and the study of biology in general. However, third generation sequencing data have much higher error rates than previous technologies, which can complicate downstream genome assembly and analysis of the resulting data. [ 2 ] These technologies are undergoing active development and it is expected that there will be improvements to the high error rates. For applications that are more tolerant to error rates, such as structural variant calling, third generation sequencing has been found to outperform existing methods, even at a low depth of sequencing coverage. [ 3 ]
Sequencing technologies with a different approach than second-generation platforms were first described as "third-generation" in 2008–2009. [ 4 ]
There are several companies currently at the heart of third generation sequencing technology development, namely, Pacific Biosciences , Oxford Nanopore Technology , Quantapore (CA-USA), and Stratos (WA-USA). These companies are taking fundamentally different approaches to sequencing single DNA molecules.
PacBio developed the sequencing platform of single molecule real time sequencing (SMRT) , based on the properties of zero-mode waveguides . Signals are in the form of fluorescent light emission from each nucleotide incorporated by a DNA polymerase bound to the bottom of the zL well.
Oxford Nanopore’s technology involves passing a DNA molecule through a nanoscale pore structure and then measuring changes in electrical field surrounding the pore; while Quantapore has a different proprietary nanopore approach. Stratos Genomics spaces out the DNA bases with polymeric inserts, " Xpandomers ", to circumvent the signal to noise challenge of nanopore ssDNA reading.
Also notable is Helicos 's single molecule fluorescence approach, but the company entered bankruptcy in the fall of 2015 .
In comparison to the current generation of sequencing technologies, third generation sequencing has the obvious advantage of producing much longer reads. It is expected that these longer read lengths will alleviate numerous computational challenges surrounding genome assembly, transcript reconstruction, and metagenomics among other important areas of modern biology and medicine. [ 1 ]
It is well known that eukaryotic genomes including primates and humans are complex and have large numbers of long repeated regions. Short reads from second generation sequencing must resort to approximative strategies in order to infer sequences over long ranges for assembly and genetic variant calling. Pair end reads have been leveraged by second generation sequencing to combat these limitations. However, exact fragment lengths of pair ends are often unknown and must also be approximated as well. By making long reads lengths possible, third generation sequencing technologies have clear advantages.
Epigenetic markers are stable and potentially heritable modifications to the DNA molecule that are not in its sequence. An example is DNA methylation at CpG sites, which has been found to influence gene expression. Histone modifications are another example. The current generation of sequencing technologies rely on laboratory techniques such as ChIP-sequencing for the detection of epigenetic markers. These techniques involve tagging the DNA strand, breaking and filtering fragments that contain markers, followed by sequencing. Third generation sequencing may enable direct detection of these markers due to their distinctive signal from the other four nucleotide bases. [ 5 ]
Other important advantages of third generation sequencing technologies include portability and sequencing speed. [ 6 ] Since minimal sample preprocessing is required in comparison to second generation sequencing, smaller equipments could be designed. Oxford Nanopore Technology has recently commercialized the MinION sequencer . This sequencing machine is roughly the size of a regular USB flash drive and can be used readily by connecting to a laptop. In addition, since the sequencing process is not parallelized across regions of the genome, data could be collected and analyzed in real time. These advantages of third generation sequencing may be well-suited in hospital settings where quick and on-site data collection and analysis is demanded.
Third generation sequencing, as of 2008, faced important challenges mainly surrounding accurate identification of nucleotide bases; error rates were still much higher compared to second generation sequencing. [ 2 ] This is generally due to instability of the molecular machinery involved. For example, in PacBio’s single molecular and real time sequencing technology, the DNA polymerase molecule becomes increasingly damaged as the sequencing process occurs. [ 2 ] Additionally, since the process happens quickly, the signals given off by individual bases may be blurred by signals from neighbouring bases. This poses a new computational challenge for deciphering the signals and consequently inferring the sequence. Methods such as Hidden Markov Models , for example, have been leveraged for this purpose with some success. [ 5 ]
On average, different individuals of the human population share about 99.9% of their genes. In other words, approximately only one out of every thousand bases would differ between any two person. The high error rates involved with third generation sequencing are inevitably problematic for the purpose of characterizing individual differences that exist between members of the same species. [ citation needed ]
Genome assembly is the reconstruction of whole genome DNA sequences. This is generally done with two fundamentally different approaches.
When a reference genome is available, as one is in the case of human, newly sequenced reads could simply be aligned to the reference genome in order to characterize its properties. Such reference based assembly is quick and easy but has the disadvantage of “hiding" novel sequences and large copy number variants. In addition, reference genomes do not yet exist for most organisms.
De novo assembly is the alternative genome assembly approach to reference alignment. It refers to the reconstruction of whole genome sequences entirely from raw sequence reads. This method would be chosen when there is no reference genome, when the species of the given organism is unknown as in metagenomics , or when there exist genetic variants of interest that may not be detected by reference genome alignment.
Given the short reads produced by the current generation of sequencing technologies, de novo assembly is a major computational problem. It is normally approached by an iterative process of finding and connecting sequence reads with sensible overlaps. Various computational and statistical techniques, such as de bruijn graphs and overlap layout consensus graphs, have been leveraged to solve this problem. Nonetheless, due to the highly repetitive nature of eukaryotic genomes, accurate and complete reconstruction of genome sequences in de novo assembly remains challenging. Pair end reads have been posed as a possible solution, though exact fragment lengths are often unknown and must be approximated. [ 7 ]
Long read lengths offered by third generation sequencing may alleviate many of the challenges currently faced by de novo genome assemblies. For example, if an entire repetitive region can be sequenced unambiguously in a single read, no computation inference would be required. Computational methods have been proposed to alleviate the issue of high error rates. For example, in one study, it was demonstrated that de novo assembly of a microbial genome using PacBio sequencing alone performed superior to that of second generation sequencing. [ 8 ]
Third generation sequencing may also be used in conjunction with second generation sequencing. This approach is often referred to as hybrid sequencing. For example, long reads from third generation sequencing may be used to resolve ambiguities that exist in genomes previously assembled using second generation sequencing. On the other hand, short second generation reads have been used to correct errors in that exist in the long third generation reads. In general, this hybrid approach has been shown to improve de novo genome assemblies significantly. [ 9 ]
DNA methylation (DNAm) – the covalent modification of DNA at CpG sites resulting in attached methyl groups – is the best understood component of epigenetic machinery. DNA modifications and resulting gene expression can vary across cell types, temporal development, with genetic ancestry, can change due to environmental stimuli and are heritable. After the discovery of DNAm, researchers have also found its correlation to diseases like cancer and autism . [ 10 ] In this disease etiology context DNAm is an important avenue of further research.
The current most common methods for examining methylation state require an assay that fragments DNA before standard second generation sequencing on the Illumina platform. As a result of short read length, information regarding the longer patterns of methylation are lost. [ 5 ] Third generation sequencing technologies offer the capability for single molecule real-time sequencing of longer reads, and detection of DNA modification without the aforementioned assay. [ 11 ]
Oxford Nanopore Technologies ’ MinION has been used to detect DNAm. As each DNA strand passes through a pore, it produces electrical signals which have been found to be sensitive to epigenetic changes in the nucleotides, and a hidden Markov model (HMM) was used to analyze MinION data to detect 5-methylcytosine (5mC) DNA modification. [ 5 ] The model was trained using synthetically methylated E. coli DNA and the resulting signals measured by the nanopore technology. Then the trained model was used to detect 5mC in MinION genomic reads from a human cell line which already had a reference methylome. The classifier has 82% accuracy in randomly sampled singleton sites, which increases to 95% when more stringent thresholds are applied. [ 5 ]
Other methods address different types of DNA modifications using the MinION platform. Stoiber et al. examined 4-methylcytosine (4mC) and 6-methyladenine (6mA), along with 5mC, and also created software to directly visualize the raw MinION data in a human-friendly way. [ 12 ] Here they found that in E. coli , which has a known methylome , event windows of 5 base pairs long can be used to divide and statistically analyze the raw MinION electrical signals. A straightforward Mann-Whitney U test can detect modified portions of the E. coli sequence, as well as further split the modifications into 4mC, 6mA or 5mC regions. [ 12 ]
It seems likely that in the future, MinION raw data will be used to detect many different epigenetic marks in DNA.
PacBio sequencing has also been used to detect DNA methylation. In this platform, the pulse width – the width of a fluorescent light pulse – corresponds to a specific base. In 2010 it was shown that the interpulse distance in control and methylated samples are different, and there is a "signature" pulse width for each methylation type. [ 11 ] In 2012 using the PacBio platform the binding sites of DNA methyltransferases were characterized. [ 13 ] The detection of N6-methylation in C Elegans was shown in 2015. [ 14 ] DNA methylation on N 6 -adenine using the PacBio platform in mouse embryonic stem cells was shown in 2016. [ 15 ]
Other forms of DNA modifications – from heavy metals, oxidation, or UV damage – are also possible avenues of research using Oxford Nanopore and PacBio third generation sequencing.
Processing of the raw data – such as normalization to the median signal – was needed on MinION raw data, reducing real-time capability of the technology. [ 12 ] Consistency of the electrical signals is still an issue, making it difficult to accurately call a nucleotide. MinION has low throughput; since multiple overlapping reads are hard to obtain, this further leads to accuracy problems of downstream DNA modification detection. Both the hidden Markov model and statistical methods used with MinION raw data require repeated observations of DNA modifications for detection, meaning that individual modified nucleotides need to be consistently present in multiple copies of the genome, e.g. in multiple cells or plasmids in the sample.
For the PacBio platform, too, depending on what methylation you expect to find, coverage needs can vary. As of March 2017, other epigenetic factors like histone modifications have not been discoverable using third-generation technologies. Longer patterns of methylation are often lost because smaller contigs still need to be assembled.
Transcriptomics is the study of the transcriptome , usually by characterizing the relative abundances of messenger RNA molecules in the tissue under study. According to the central dogma of molecular biology , genetic information flows from double stranded DNA molecules to single stranded mRNA molecules where they can be readily translated into functional protein molecules. By studying the transcriptome, one can gain valuable insight into the regulation of gene expression.
While expression levels can be more or less accurately depicted by second generation sequencing (we can assume that actual abundances of the population of transcripts are randomly sampled), transcript-level information still remains an important challenge. [ 16 ] As a consequence, the role of alternative splicing in molecular biology remains largely elusive. Third generation sequencing technologies hold promising prospects in resolving this issue by enabling sequencing of mRNA molecules at their full lengths.
Alternative splicing (AS) is the process by which a single gene may give rise to multiple distinct mRNA transcripts and consequently different protein translations. [ 17 ] Some evidence suggests that AS is a ubiquitous phenomenon and may play a key role in determining the phenotypes of organisms, especially in complex eukaryotes; all eukaryotes contain genes consisting of introns that may undergo AS. In particular, it has been estimated that AS occurs in 95% of all human multi-exon genes. [ 18 ] AS has undeniable potential to influence myriad biological processes. Advancing knowledge in this area has critical implications for the study of biology in general.
The current generation of sequencing technologies produce only short reads, putting tremendous limitation on the ability to detect distinct transcripts; short reads must be reverse engineered into original transcripts that could have given rise to the resulting read observations. [ 19 ] This task is further complicated by the highly variable expression levels across transcripts, and consequently variable read coverages across the sequence of the gene. [ 19 ] In addition, exons may be shared among individual transcripts, rendering unambiguous inferences essentially impossible. [ 17 ] Existing computational methods make inferences based on the accumulation of short reads at various sequence locations often by making simplifying assumptions. [ 19 ] Cufflinks takes a parsimonious approach, seeking to explain all the reads with the fewest possible number of transcripts. [ 20 ] On the other hand, StringTie attempts to simultaneously estimate transcript abundances while assembling the reads. [ 19 ] These methods, while reasonable, may not always identify real transcripts.
A study published in 2008 surveyed 25 different existing transcript reconstruction protocols. [ 16 ] Its evidence suggested that existing methods are generally weak in assembling transcripts, though the ability to detect individual exons are relatively intact. [ 16 ] According to the estimates, average sensitivity to detect exons across the 25 protocols is 80% for Caenorhabditis elegans genes. [ 16 ] In comparison, transcript identification sensitivity decreases to 65%. For human, the study reported an exon detection sensitivity averaging to 69% and transcript detection sensitivity had an average of a mere 33%. [ 16 ] In other words, for human, existing methods are able to identify less than half of all existing transcript.
Third generation sequencing technologies have demonstrated promising prospects in solving the problem of transcript detection as well as mRNA abundance estimation at the level of transcripts. While error rates remain high, third generation sequencing technologies have the capability to produce much longer read lengths. [ 21 ] Pacific Bioscience has introduced the iso-seq platform, proposing to sequence mRNA molecules at their full lengths. [ 21 ] It is anticipated that Oxford Nanopore will put forth similar technologies. The trouble with higher error rates may be alleviated by supplementary high quality short reads. This approach has been previously tested and reported to reduce the error rate by more than 3 folds. [ 22 ]
Metagenomics is the analysis of genetic material recovered directly from environmental samples.
The main advantage for third-generation sequencing technologies in metagenomics is their speed of sequencing in comparison to second generation techniques. Speed of sequencing is important for example in the clinical setting (i.e. pathogen identification), to allow for efficient diagnosis and timely clinical actions.
Oxford Nanopore's MinION was used in 2015 for real-time metagenomic detection of pathogens in complex, high-background clinical samples. The first Ebola virus (EBOV) read was sequenced 44 seconds after data acquisition. [ 23 ] There was uniform mapping of reads to genome; at least one read mapped to >88% of the genome. The relatively long reads allowed for sequencing of a near-complete viral genome to high accuracy (97–99% identity) directly from a primary clinical sample. [ 23 ]
A common phylogenetic marker for microbial community diversity studies is the 16S ribosomal RNA gene. Both MinION and PacBio's SMRT platform have been used to sequence this gene. [ 24 ] [ 25 ] In this context the PacBio error rate was comparable to that of shorter reads from 454 and Illumina's MiSeq sequencing platforms. [ citation needed ]
MinION's high error rate (~10-40%) prevented identification of antimicrobial resistance markers, for which single nucleotide resolution is necessary. For the same reason, eukaryotic pathogens were not identified. [ 23 ] Ease of carryover contamination when re-using the same flow cell (standard wash protocols don’t work) is also a concern. Unique barcodes may allow for more multiplexing. Furthermore, performing accurate species identification for bacteria , fungi and parasites is very difficult, as they share a larger portion of the genome, and some only differ by <5%.
The per base sequencing cost is still significantly more than that of MiSeq. However, the prospect of supplementing reference databases with full-length sequences from organisms below the limit of detection from the Sanger approach; [ 24 ] this could possibly greatly help the identification of organisms in metagenomics. | https://en.wikipedia.org/wiki/Third-generation_sequencing |
Third-party reproduction or donor-assisted reproduction is any human reproduction in which DNA or gestation is provided by a third party or donor other than the one or two parents who will raise the resulting child . [ 1 ] This goes beyond the traditional father – mother model, and the third party's involvement is limited to the reproductive process and does not extend into the raising of the child. Third-party reproduction is used by couples unable to reproduce by traditional means, by same-sex couples , and by men and women without a partner. Where donor gametes are provided by a donor, the donor will be a biological parent of the resulting child, but in third party reproduction, he or she will not be the caring parent.
One can distinguish several categories, some of which may be combined:
Gestation is typically initiated by artificial insemination in the case of sperm donation and by embryo transfer after in vitro fertilisation (IVF) in the case of egg donation, embryo donation, and surrogacy. Thus a child can have a genetic and social (non-genetic, non-biological) father, and a genetic, gestational, and social (non-biological) mother, and any combinations thereof. Theoretically a child thus could have 5 parents. [ citation needed ]
A donor treatment is where gametes, i.e. sperm, ova or embryos are provided, or 'donated' by a third party for the purpose of third-party reproduction.
Surrogacy includes, in its wider sense, all situations where a surrogate carries a pregnancy for another person. Recently, there has been a tendency to separate the gestational carrier situation from the "true" surrogate restricting the term for a woman who provides a combination of ovum donation and gestational carrier services.
In a 'conventional surrogacy', a surrogate agrees to be inseminated with the sperm of the male partner of the 'commissioning' couple, or with the sperm of one of the male partners in a same-sex relationship, or with sperm provided by a sperm donor . The surrogate is inseminated, conceives, and hands over the baby at the completion of the pregnancy. In conventional surrogacy, the egg which is fertilized is therefore that of the surrogate. A famous case involving paternity rights and surrogacy is the Baby M case.
In a 'gestational surrogacy', a surrogate agrees to the implantation in her of an embryo which may be created either by using an egg provided by another woman who may be part of a 'commissioning' couple, or she may be a single woman. Alternatively, an egg provided by a donor may be used to create the embryo. The embryo implanted in the surrogate may be fertilised using sperm from the male partner of the 'commissioning couple', or by using sperm provided by a sperm donor .
Embryo donation is where extra embryos from a successful IVF of a couple are given to other couples or women for transfer with the goal of producing a successful pregnancy. Embryos for embryo donation may also be created specifically for embryo transfer using donor eggs and sperm, or in some cases donor eggs and donor sperm. It may thus be seen as a combination of sperm donation and egg donation, since what is donated is a combination of these. Such embryos may also be donated to a 'commissioning' woman or a 'commissioning' couple and gestated by a surrogate where, for example, the 'commissioning' woman or the woman of the 'commissioning' couple is infertile and is unable to bring a pregnancy to full term on medical grounds, or is unwilling for social, medical or other reasons, to do so. | https://en.wikipedia.org/wiki/Third-party_reproduction |
In calculus , a branch of mathematics , the third derivative or third-order derivative is the rate at which the second derivative , or the rate of change of the rate of change, is changing. The third derivative of a function y = f ( x ) {\displaystyle y=f(x)} can be denoted by
Other notations for differentiation can be used, but the above are the most common.
Let f ( x ) = x 4 {\displaystyle f(x)=x^{4}} . Then f ′ ( x ) = 4 x 3 {\displaystyle f'(x)=4x^{3}} and f ″ ( x ) = 12 x 2 {\displaystyle f''(x)=12x^{2}} . Therefore, the third derivative of f is, in this case,
or, using Leibniz notation ,
Now for a more general definition. Let f be any function of x such that f ′′ is differentiable . Then the third derivative of f is given by
The third derivative is the rate at which the second derivative ( f ′′( x )) is changing.
In differential geometry , the torsion of a curve — a fundamental property of curves in three dimensions — is computed using third derivatives of coordinate functions (or the position vector) describing the curve. [ 1 ]
In physics , particularly kinematics , jerk is defined as the third derivative of the position function of an object. It is, essentially, the rate at which acceleration changes. In mathematical terms:
where j ( t ) is the jerk function with respect to time, and r ( t ) is the position function of the object with respect to time.
When campaigning for a second term in office, U.S. President Richard Nixon announced that the rate of increase of inflation was decreasing, which has been noted as "the first time a sitting president used the third derivative to advance his case for reelection." [ 2 ] Since inflation is itself a derivative—the rate at which the purchasing power of money decreases—then the rate of increase of inflation is the derivative of inflation, opposite in sign to the second time derivative of the purchasing power of money. Stating that a function is decreasing is equivalent to stating that its derivative is negative, so Nixon's statement is that the second derivative of inflation is negative, and so the third derivative of purchasing power is positive.
Since Nixon's statement allowed for the rate of inflation to increase, his statement did not necessarily indicate immediate price stability but proposed a trend of more stability in the future. | https://en.wikipedia.org/wiki/Third_derivative |
The third medium contact (TMC) is an implicit formulation used in contact mechanics . Contacting bodies are embedded in a highly compliant medium (the third medium), which becomes increasingly stiff under compression. The stiffening of the third medium allows tractions to be transferred between the contacting bodies when the third medium between the bodies is compressed. In itself, the method is inexact; however, in contrast to most other contact methods, the third medium approach is continuous and differentiable, which makes it applicable to applications such as topology optimization . [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ]
The method was first proposed in 2013 by Peter Wriggers [ de ] , Jörg Schröder, and Alexander Schwarz, where a St. Venant-Kirchhoff material was used to model the third medium. [ 7 ] This approach required explicit treatment of surface normals and continued to be used [ 10 ] [ 11 ] [ 12 ] until 2017, when Bog et al. simplified the method by applying a Hencky material with the inherent property of becoming rigid under ultimate compression. [ 8 ] This property made the explicit treatment of surface normals redundant, transforming the third medium contact method into a fully implicit method, contrasting with the more widely used Mortar methods or Penalty methods . However, at this stage, the third medium contact method could only handle very small degrees of sliding, and a friction model for TMC had yet to be developed. The rising popularity of Mortar methods, which emerged in the same period with a rigorous mathematical foundation and rapid development and adoption, overshadowed the TMC method. [ 11 ] [ 12 ] Consequently, TMC was abandoned at an early stage and remained largely unknown in contact mechanics.
In 2021, the method was revived when Gore Lukas Bluhm, Ole Sigmund , and Konstantinos Poulios worked on nonlinear buckling problems and realized that a highly compliant void material could transfer forces in a topology optimization setting. Bluhm et al. added a new regularization to stabilize the third medium, enabling the method to contact problems involving moderate sliding and thus making it practically applicable. [ 1 ] This novel regularization, known as HuHu regularization, is a general regularization technique for finite elements which has also been used outside TMC. [ 13 ] The use of TMC in topology optimization was refined in subsequent work and applied to more complex problems. [ 14 ] [ 6 ] [ 4 ]
In 2024, Frederiksen et al. [ 3 ] proposed a crystal plasticity-inspired scheme to include friction. This involved adding a term to the material model to contribute to high shear stresses in the contact interface, along with a plastic slip scheme to release shear stresses and accommodate sliding. During the same period, new regularization methods were proposed, [ 4 ] [ 9 ] [ 15 ] and the method was extended to thermal contact by Dalklint et al. [ 5 ] and utilized for pneumatic actuation by Faltus et al. [ 9 ] who also introduced Gauss-Lobatto integration to TMC, improving upon numerical stability and thus allowing for stable solution with lower stiffness values for the third medium.
TMC relies on a material model for the third medium, which stiffens under compression. The most commonly applied material models are of a neo-Hookean type, characterized by a strain energy density function:
W ( u ) = K 2 ( ln | F | ) 2 + G 2 ( | F | − 2 / 3 | | F | | 2 − 3 ) {\displaystyle W({\mathbf {u}})={\frac {K}{2}}({\text{ln}}|{\mathbf {F}}|)^{2}+{\frac {G}{2}}\left(|{\mathbf {F}}|^{-2/3}||{\mathbf {F}}||^{2}-3\right)} ,
where K {\displaystyle K} is the bulk modulus , G {\displaystyle G} is the shear modulus , and F = ∇ u + I {\displaystyle {\mathbf {F}}=\nabla {\mathbf {u}}+{\mathbf {I}}} is the deformation gradient tensor of the displacement field u {\displaystyle {\mathbf {u}}} .
As the current material volume | F | {\displaystyle |{\mathbf {F}}|} approaches zero, this material model exhibits the characteristic of becoming infinitely stiff. Consequently, when the third medium is compressed, its volume remains positive and finite. This ensures that if two solids are embedded in a third medium with significantly lower bulk and shear moduli, the third medium can still transfer substantial forces to deform the solids when sufficiently compressed, as its stiffness becomes comparable to that of the embedded solids.
While the neo-Hookean material model can be stable for contact without sliding, sliding often leads to instability. To address this, regularization techniques are applied to the strain energy density function.
Regularization is typically achieved by adding a regularization term to the strain energy density function of the material model. A common approach is the HuHu regularization, [ 1 ] expressed as:
Ψ ( u ) = W ( u ) + H u ⋮ H u {\displaystyle \Psi ({\mathbf {u}})=W({\mathbf {u}})+\mathbb {H} {\mathbf {u}}\,{\boldsymbol {\scriptstyle {\vdots }}}\,\mathbb {H} {\mathbf {u}}} ,
where Ψ ( u ) {\textstyle \Psi ({\mathbf {u}})} represents the augmented strain energy density of the third medium, H u ⋮ H u {\textstyle \mathbb {H} {\mathbf {u}}\,{\boldsymbol {\scriptstyle {\vdots }}}\,\mathbb {H} {\mathbf {u}}} is the regularization term representing the inner product of the spatial Hessian of u {\displaystyle {\mathbf {u}}} by itself, and W ( u ) {\textstyle W({\mathbf {u}})} is the underlying strain energy density of the third medium, e.g. a neo-Hookean solid or another hyperelastic material .
The HuHu regularization was the first regularization method specifically developed for TMC. A subsequent refinement is known as the HuHu-LuLu regularization, [ 4 ] expressed as:
Ψ ( u ) = W ( u ) + H u ⋮ H u − 1 T r ( I ) L u ⋅ L u {\displaystyle \Psi ({\mathbf {u}})=W({\mathbf {u}})+\mathbb {H} {\mathbf {u}}\,{\boldsymbol {\scriptstyle {\vdots }}}\,\mathbb {H} {\mathbf {u}}-{\dfrac {1}{\mathrm {Tr} ({\mathbf {I}})}}\mathbb {L} {\mathbf {u}}\cdot \mathbb {L} {\mathbf {u}}} ,
where L u {\displaystyle \mathbb {L} {\mathbf {u}}} is the Laplacian of the displacement field u {\displaystyle {\mathbf {u}}} , and Tr ( I ) {\displaystyle {\text{Tr}}({\mathbf {I}})} is the trace of the identity matrix corresponding to the problem's dimension (2D or 3D). [ 4 ] The LuLu term is designed to mitigate the penalization of bending and quadratic compression deformations while maintaining the penalization of excessive skew deformations, thus preserving the stabilizing properties of the HuHu regularization. This reduced penalization on bending deformations enhances the accuracy of modelling curved contacts, particularly beneficial when using coarse finite element meshes. Similarly, the reduced penalization on quadratic compression is advantageous in topology optimization applications, where finite elements with varying material densities undergo non-uniform compression.
An alternative and more complex regularization approach involves penalizing volume change and rotations, initially proposed by Faltus et al. [ 9 ] This approach requires further extension to 3D applications. A later improvement by Wriggers et al. [ 15 ] directly utilizes the rotation tensor R {\displaystyle {\mathbf {R}}} instead of the approximation used in. [ 9 ]
The integration of friction into the TMC method represents a significant advancement in simulating realistic contact conditions, addressing the previous limitations in replicating real-world scenarios. Currently, there is only one approach available for adding friction. This approach introduces shear stress to the contact and releases it through plastic slip if the contact is sliding.
When a neo-Hookean material model is used to represent the third medium, it exhibits much greater stiffness in compression compared to shear during contact. To address this and provide shear resistance, an anisotropic term is incorporated into the neo-Hookean material model. This modification rapidly builds up shear stress in compressed regions of the third medium, which is crucial for accurately modelling frictional contact.
In this formulation, the extended strain energy density expression with the added shear term is:
W e x t ( u ) = W ( u ) + β 2 ( C e : ( s 0 ⊗ n 0 ) ) 2 {\displaystyle W_{ext}({\mathbf {u}})=W({\mathbf {u}})+{\dfrac {\beta }{2}}\left({\mathbf {C}}_{e}:({\mathbf {s}}_{0}\otimes {\mathbf {n}}_{0})\right)^{2}} ,
where:
The shear extension works by penalising the contribution in C e {\displaystyle {\mathbf {C}}_{e}} associated with shear in the slip direction s 0 {\displaystyle {\mathbf {s}}_{0}} .
To release the shear stresses at the onset of sliding, a framework inspired by crystal plasticity is employed. This includes a yield criterion specifically designed to replicate the effects of Coulomb friction. This framework allows the model to simulate the onset of sliding when the shear stress, provided by the added anisotropic term, exceeds a certain threshold, effectively mimicking real-world frictional behaviour. The yield criterion, based on the Coulomb friction model, determines when sliding occurs, initiating once the shear stress surpasses a critical value.
The C-shape contact problem used in [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 9 ] [ 15 ] has established itself as a benchmark problem for third medium contact models. It involves two solid beams, upper and lower, clamped at their left end. The region between the beams is considered "void" and is modelled as a third medium to allow for contact between the beams.
A vertical displacement or load is added to a small region on the upper right edge of the C-shape. The vertical displacement is prescribed such that the upper beam of the C-shape contacts the lower beam of the C-shape. When contact is established, a corner of the upper beam will slide along the lower beam, resulting in severe shear within the third medium. Additionally, the free edge on the right boundary of the third medium is not bounded, leading to severe distortions in the third medium, which are handled by the third medium material model and the applied regularization.
The C-shape problem has also been solved using the frictional TMC model. [ 3 ]
TMC is widely used in computational mechanics and topology optimization due to its ability to model contact mechanics in a differentiable and fully implicit manner. One of the key advantages of TMC is that it eliminates the need to explicitly define surfaces and contact pairs, thereby simplifying the modelling process.
In topology optimization, TMC ensures that sensitivities are properly handled, enabling gradient-based optimization approaches to converge effectively and produce designs with internal contact. Notable designs achieved through this approach include compliant mechanisms such as hooks, bending mechanisms, and self-contacting springs. [ 1 ] [ 2 ] [ 4 ] [ 14 ] The design of metamaterials is a common application for topology optimization, where TMC has expanded the range of possible designs. [ 6 ] Additionally, soft springs and pneumatically activated systems, which are useful in the design of soft robots, have been modelled using TMC. [ 14 ] [ 9 ]
TMC has also been extended to applications involving frictional contact and thermo-mechanical coupling. [ 3 ] [ 5 ] These advancements enhance the method’s utility in modelling real-world mechanical interfaces. | https://en.wikipedia.org/wiki/Third_medium_contact_method |
The third platform [ 1 ] [ 2 ] is a term coined by marketing firm International Data Corporation (IDC) for a model of a computing platform . It was promoted as inter-dependencies between mobile computing , social media , cloud computing , and information / analytics ( big data ), [ 3 ] [ 4 ] [ 5 ] and possibly the Internet of things . [ 6 ] The term was in use in 2013, and possibly earlier. Gartner claimed that these interdependent trends were "transforming the way people and businesses relate to technology" and have since provided a number of reports on the topic. [ 7 ]
The paradigm of numbered platforms sees several platforms evolving, the first platform as the mainframe computer system.
First Platform ( Mainframe ) - late 1950s to present
The first platform is the mainframe computer system, which began in the late 1950s and continues today.
Second Platform ( Client/Server ) - mid 1980s to present
The second platform is the client/server system, which began in the mid-1980s with PCs tapping into mainframe databases and applications. [ 8 ]
Third Platform (Social, Mobile , Cloud & Analytics , possibly IoT ) - early 2010s to present
The Open Platform 3.0 initiative of The Open Group aims to produce a consensus definition of the third platform, and to identify open standards for it, in order to help enterprises gain business benefit from these technologies. This has produced an analysis of requirements . [ 9 ]
In January 2016 The Economist offered the following analysis: "The third platform is based on the online computing "cloud" and its interaction with all manner of devices, including wirelessly connected ones such as smartphones, machinery and sensors (known collectively as the "internet of things"). [ 10 ]
Fourth Platform -- despite the term being used by some consultants and IT companies, there is no clear consensus on a definition. Discussions around the fourth platform are currently mostly predictions about what it might include - such as AI , IoT , Quantum Computing and massively distributed Grid computing approaches.
No single "third platform" product has emerged, but there are a number of proprietary and free software products that enterprises can use to create, deploy and operate solutions that use third platform technologies. Within an enterprise, a combination of these products that meet enterprise needs is a "third platform" for that enterprise. Its design can be considered part of Enterprise Architecture .
Suitable products include:
Enterprise third platforms can use web APIs to access social media websites and cloud services giving access to third platform technologies.
Gartner defined a social technology as, “Any technology that facilitates social interactions and is enabled by a communications capability, such as the Internet or a mobile device.” This extends not only to social media but also to all social technologies that make social interaction possible. A VoIP service, for example, would be considered a social technology.
In a trend that has been described as ‘social everything’, companies both big and small, will continue to inject a social element into every product and service. The cloud provides the infrastructure that makes the information accessible, the social technology helps to organise the data and facilitate access, and the mobile devices will provide the means by which most people receive the data. [ 11 ]
The third platform is designed to give everybody access to big data via mobile devices; it is this mobility that really defines the third platform. A company representative on the road or working from home will have instant access to data through his or her mobile device with this third platform whenever and wherever they need it.
An example of the use of mobile devices in the third platform would be a school that gives every student a tablet. The tablet would take the place of textbooks and paper used in assignments, but more importantly, the student will have access to a virtual classroom at additional times. [ 11 ]
The concept behind big data is to maximize the utility of all data. An executive at a company that streamlines its business functions with the third platform would have easy access to all of the data, including sales figures, personnel information, accounting data, financials and so on. This data can then be used to inform more areas of the business.
Big data can be further differentiated once we analyze its three distinguishing features: variety, volume, and velocity.
Variety means that many forms of data are collected, with formats ranging from audio and video to client log files and Tweets. Volume represents the fact that big data must come in massive quantities, often over a petabyte . Finally, Velocity signifies that big data must be constantly collected for maximum effectiveness; even data that is a few days old is not ideal.
In summary, big data utilizes and collects all forms of data, gathered from both traditional and digital sources, in order to complement a company's decision-making processes. [ 11 ]
Cloud services are at the heart of the third platform. Having big data and mobile devices is one thing, but without the cloud, there will be no way to access this data from outside of the office.
This differs greatly from the first platform, where computer networks consisted of large mainframes. All of a company's employees had access to the data in the mainframe but they could only access it through their desktop computers. In the second platform, a company's employees could access the data in the mainframe as well as outside data, via an Internet connection.
The third platform will allow all of a company's IT solutions to be available through the cloud, accessible via a variety of mobile devices. Data storage, servers and many IT solutions, which are on-site, can now be cloud-based. [ 11 ]
The Internet of Things is the network of connected devices that enable computer systems to monitor and control aspects of the physical environment. It has applications in personal and home environments, smart cities, factory automation, transport, and many other areas. The incorporation of the Internet of Things in the third platform gives enterprises the ability to interact with these systems and use these applications.
Sensors and actuators have been used in computer systems for many years. It is the ability to connect to such devices anywhere in the world through the Internet that characterizes the Internet of things. | https://en.wikipedia.org/wiki/Third_platform |
This is My Earth ( TiME ) is a non-profit organization dedicated to preserving biodiversity by using crowdsourcing to purchase lands in biodiversity hotspots .
TiME was established in 2015 by Prof. Uri Shanas [ 1 ] of the University of Haifa at Oranim , who continues to act as TiME's CEO. The organization is advised by an international team of scientists and environmental activists.
TiME functions as a democracy in which every member, regardless of the amount of their donation, has an equal vote to determine which of the scientifically vetted conservation projects proposed each year is allocated the annual crowdfunded grant.
The organization's goal is to preserve biodiversity hotspots and to curb the Sixth Extinction , which is mainly caused by human activity. [ 2 ]
TiME was founded in 2015 by Professor Uri Shanas, [ 3 ] who was soon thereafter joined by Professor Alon Tal of Tel Aviv University to co-lead the organization. Both are noted scholars and environmental activists. TiME capitalized on the rise in popularity of crowdfunding and the increasing internet access worldwide to found an organization in which even small donors can take an active role to protect biodiversity. TiME raised US$35,515 on Indiegogo by August 13, 2015; 819 people from over 40 countries donated. [ 4 ] This initial seed money was used to establish a basic organizational infrastructure, register as a non-profit, expand the Scientific Advisory Committee, [ 5 ] set up an active Facebook page, and build a website. [ 6 ] In its first year, TiME had over one thousand members.
Over its first seven years, with the support of its generous members, This is My Earth successfully purchased eight plots of land in biodiversity hotspots for conservation. Its first land purchase, in 2016, was in the El Toro forest, Peru , which lies at the heart of the Tropical Andes Biodiversity Hotspot. [ 7 ] [ 8 ]
TiME transferred it to Mr. Isidoro Lozano, a community member of Yambrasbamba Campesino Community in La Esperanza, who works in conjunction with the local Asociación Neotropical Primate Conservation Peru [ 9 ] to protect the land. The El Toro forest campaign, designed to purchase land in the Peruvian Amazon to protect the habitat of the Critically Endangered yellow-tailed woolly monkey ( Oreonax flavicauda ), managed to raise US$30,000.
In 2017, TiME bought land to expand the Sun Angel's Gardens reserve in Peru. The reserve's biodiversity, including the Near Threatened royal sunangel hummingbird ( Heliangelus regalis ) [ 10 ] and the Endangered white-bellied spider monkey ( Ateles belzebuth ), [ 11 ] was particularly vulnerable to illegal loggers, hunters and squatters because of its horseshoe shape. TiME's purchase of 700 hectares for US$17,000 inside the U-shape of the reserve was transferred to the local indigenous community of La Primavera and the local NGO, Asociación Neotropical Primate Conservation Peru, [ 12 ] to ensure the conservation of the land.
TiME's purchase of a 5-acre plot in Turneffe Atoll , Belize , in 2018 protected part of a global ecological hotspot for marine biodiversity. Turneffe Atoll faces numerous threats because of its close proximity to Belize City, especially unsustainable fishing practices, development and dredging, and the extraction of non-timber products. Some of the threatened species now protected in this habitat are the Critically Endangered hawksbill sea turtle ( Eretmochelys imbricate ) [ 13 ] and the Vulnerable goliath grouper ( Epinephelus itajara ). [ 14 ] TiME's local partner to protect this area is Turneffe Atoll Trust. [ 15 ]
The threatened Tumbes–Chocó–Magdalena biodiversity hotspot in Colombia was the site of TiME's 2019 land purchase. [ 16 ] The 58-hectare plot of land bought for US$70,000, expanded the El Silencio reserve, managed by TiME's local partner, Fundación Biodiversa Colombia. [ 17 ] An expanded reserve offers more habitat to protect threatened species, like the Critically Endangered blue-billed curassow ( Crax alberti ) [ 18 ] and the Critically Endangered brown spider monkey ( Ateles hybridus ), [ 19 ] and increases the reserve's financial sustainability by making it more attractive to tourists and researchers.
2020 was a milestone for This is My Earth because it raised sufficient funds (nearly US$200,000) to purchase two plots of land in two vastly different biodiversity hotspots. [ 20 ] [ 21 ] TiME's 300-acre purchase in the Dakatcha Woodland of Kenya , in the East African Coastal Forests hotspot, protected—among other threatened species—the Endangered Clarke's weaver ( Ploceus golandi ), [ 22 ] which nests only in this particular area of the world. TiME's local partner for this project is Nature Kenya—the East Africa Natural History Society (EANHS). [ 23 ] TiME also purchased 84 acres in the Atlantic Forest in Brazil , allowing its local partner, Instituto Uiraçu, [ 24 ] to expand the Serra Bonita Reserve. Among the threatened species now protected in Serra Bonita are the Critically Endangered buff-headed capuchin ( Sapajus xanthosternos ) [ 25 ] and the Critically Endangered banded cotinga ( Cotinga maculata ), [ 26 ] as well as predators that require larger territories, like the puma ( Puma concolor ) and the Vulnerable harpy eagle ( Harpia harpyja ). [ 27 ]
In 2021, TiME protected land in the iconic Maasai Mara ecosystem, which has the highest density of wildlife in Kenya , purchasing 20 acres in partnership with the Wildlife Clubs of Kenya. [ 28 ] The acquisition of this land creates a migratory corridor and habitat for wildlife, including the Critically Endangered Black Rhinoceros ( Diceros bicorn ) [ 29 ] and the Endangered Masai giraffe ( Giraffa tippelskirchi ). [ 30 ]
The Chocó Forest in Ecuador is the site of This is My Earth's eighth land purchase in 2022. Partnering with Fundación Jocotoco, [ 31 ] TiME purchased 65 hectares of rainforest, helping to protect the Critically Endangered great green macaw ( Ara ambiguus ) [ 32 ] and the Endangered brown-headed spider monkey ( Ateles fusciceps ), [ 33 ] among other threatened species.
TiME raises funds on two different platforms for two purposes:
TiME uses crowdfunding to buy land for conservation. All funds raised through its website goes towards a land purchase and long-term conservation. Funds are allocated based on an annual voting system, in which every donor receives one vote to cast for their preferred conservation project.
Grants are used to offset institutional costs, such as professional communications via social media and newsletters. TiME collects grants from agencies and institutional donors, not from crowdfunding.
TiME allocates its funds democratically, according to which of the scientifically vetted conservation projects in different biodiversity hotspots receives the most votes by TiME members. If, by December, the board determines that none of the projects is likely to reach its minimum goal, it may decide to pool all funds donated that year to support a single project, if that sum will allow one project to achieve its goal. Projects that are selected again for the subsequent annual campaign may or may not carry with them the previous year’s allocated donations, depending on the Board's decision.
Projects, or plots of land to be purchased and protected, may be suggested to TiME by any organization worldwide. TiME's Scientific Advisory Committee evaluates proposed projects, approves those best able to protect species and habitats, and determines the minimum necessary funds needed to realize the project. The project is then posted on TiME's website and has one calendar year (January 1 to December 31) to garner as many votes as possible. If a project does not attract enough support to receive the minimum funds from TiME (see Voting below), it may be resubmitted for consideration in the subsequent year by either the Scientific Advisory Committee or the organization that initially proposed it. A project that is resubmitted must be reapproved by the Scientific Advisory Committee. Once reapproved, the votes are reset as if it had just been submitted for the first time unless the Board of Directors decides to extend the voting period.
Each member receives one vote per year. To become a member for a given calendar year, a donation of at least one US dollar must be made through TiME's website. Once a donation has been made, the member is given a vote to choose their preferred project. Memberships for a group of people, such as a family or class, may be purchased through one donation, the number of votes being contingent on the size of the group and the amount donated.
On December 31 votes are tallied. Each project is given a portion of that year's donation equivalent to the percentage of votes it received. A project will receive its allotment of TiME donations only if the total exceeds the minimum necessary funds determined at the outset. If a project does not obtain enough votes to reach the minimum, the project is given an additional four months to match TiME's funds with an external funding source. If the project is unable to raise the necessary funds in the given timeframe, the money it would have received from TiME rolls over into the subsequent year's total fund allocation.
When a project achieves its fundraising goal, TiME works with the local conservation organization that proposed the conservation project to purchase the land, ensuring that the deed remains in local/Indigenous hands and that the natural habitat is protected.
TiME signs a legal agreement that will ensure the protection of the land, for at least 100 years. Once the land is purchased, TiME regularly receives updates from its local conservation partner.
TiME is led by an international team of scientists and environmental leaders representing every continent, all working to save biodiversity through the conservation of critical habitats around the world.
Dr. Dianne Brunton
Dr. Gerardo Ceballos
Dr. Paul R. Ehrlich
Dr. Nick Haddad
Dr. David Mutekanga
Dr. Simone Oigman-Pszczol
Dr. William (Bill) Ripple
Dr. Uri Shanas
Dr. Jian Wu
Mr. Guy Milhalter [ 34 ]
Mr. David Baldock
Dr. Dror Ben-Ami
Ms. Hadas Dabas
Mr. Darrell Erb Jr.
Dr. Deborah Goldberg
Dr. Clive G. Jones
Ms. Josephine Kishapoi
Dr. Konstantinos C. Makris
Ms. Wanjira Mathai
Mr. Tom Murtha
Ms. Kirsten Oates
Dr. Uri Shanas
Ms. Ondine Sherman
Mr. Jack Platt
Ms. Tauni Sauvage | https://en.wikipedia.org/wiki/This_Is_My_Earth |
Thixotropy is a time-dependent shear thinning property. Certain gels or fluids that are thick or viscous under static conditions will flow (become thinner, less viscous) over time when shaken, agitated, shear-stressed , or otherwise stressed ( time-dependent viscosity ). They then take a fixed time to return to a more viscous state. [ 1 ] Some non-Newtonian pseudoplastic fluids show a time-dependent change in viscosity ; the longer the fluid undergoes shear stress , the lower its viscosity. A thixotropic fluid is a fluid which takes a finite time to attain equilibrium viscosity when introduced to a steep change in shear rate. Some thixotropic fluids return to a gel state almost instantly, such as ketchup , and are called pseudoplastic fluids. Others such as yogurt take much longer and can become nearly solid. Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated. Thixotropy arises because particles or structured solutes require time to organize. [ 2 ]
Some fluids are anti-thixotropic: constant shear stress for a time causes an increase in viscosity or even solidification. Fluids which exhibit this property are sometimes called rheopectic . Anti-thixotropic fluids are less well documented than thixotropic fluids. [ 2 ]
Many sources of thixotropy comes from the studies of Bauer and Collins as the earliest source of origin. Later in 1923, other researchers began experimenting with thixotropy and then began reporting that many gels consist of aqueous Fe 2 O 3 dispersions.
These researchers, Mewis and Barnes, Schalek and Szegvari, and H. Freundlich, then learned that they could make the gel turn into a liquid simply by shaking the contents. The more that was learned of this material has been found in numerous other products without the realization of the people making said products. [ 3 ]
Some clays are thixotropic, influenced by thermochemical treatment, and their behaviour is of great importance in structural and geotechnical engineering . [ 4 ] [ 5 ] Landslides , such as those common in the cliffs around Lyme Regis , Dorset and in the Aberfan spoil tip disaster in Wales are evidence of this phenomenon. Similarly, a lahar is a mass of earth liquefied by a volcanic event, which rapidly solidifies once coming to rest.
Drilling muds used in geotechnical applications can be thixotropic. Honey from honey bees may also exhibit this property under certain conditions (such as heather honey or mānuka honey ).
Both cytoplasm and the ground substance in the human body are thixotropic, as is semen . [ 6 ]
Some clay deposits found in the process of exploring caves exhibit thixotropism: an initially solid-seeming mudbank will turn soupy and yield up moisture when dug into or otherwise disturbed. These clays were deposited in the past by low-velocity streams which tend to deposit fine-grained sediment.
A thixotropic fluid is best visualised by an oar blade embedded in mud. Pressure on the oar often results in a highly viscous (more solid) thixotropic mud on the high pressure side of the blade, and low viscosity (very fluid) thixotropic mud on the low pressure side of the oar blade. Flow from the high pressure side to the low pressure side of the oar blade is non-Newtonian. (i.e., fluid velocity is not linearly proportional to the square root of the pressure differential over the oar blade).
Many kinds of paints and inks—e.g., plastisols used in silkscreen textile printing —exhibit thixotropic qualities. [ 7 ] In many cases it is desirable for the fluid to flow sufficiently to form a uniform layer, then to resist further flow, thereby preventing sagging on a vertical surface. Some other inks, such as those used in CMYK -type process printing, are designed to regain viscosity even faster, once they are applied, in order to protect the structure of the dots for accurate color reproduction.
There are several methods to using thixotropy; one method, the most popular way, is to use a two-phase mixture to model to allow the mixture to continue without added equations entering when thixotropy is working through its process on the different materials. [ 8 ]
Thixotropic ink (along with a gas pressurized cartridge and special shearing ball design) is a key feature of the Fisher Space Pen , used for writing during zero gravity space flights by the US and Russian space programs.
Solder pastes used in electronics manufacturing printing processes are thixotropic.
Thread-locking fluid is a thixotropic adhesive that cures anaerobically.
Thixotropy has been proposed as a scientific explanation of blood liquefaction miracles such as that of Saint Januarius in Naples . [ 9 ]
Semi-solid casting processes such as thixomoulding use the thixotropic property of some alloys (mostly light metals like magnesium). Within certain temperature ranges and with appropriate preparation, an alloy can be put into a semi-solid state, which can be injected with less shrinkage and better overall properties than by normal injection molding .
Fumed silica is commonly used as a rheology agent to make otherwise low-viscous fluids thixotropic. Examples range from foods to epoxy resin in structural bonding applications like fillet joints .
Thixotropy has shown to be useful in many ways concerning cement paste. The thixotropy allows the cement to be broken down in a way that allows the user to slowly put down the paste in a controlled manner so it can then be set and dry. [ 10 ]
Thixotropy is also used in drilling fluids due to their rheological makeup. This however is connected to drilling hydraulics and how thixotropy affects the process of hydraulics. [ 11 ]
While thixotropy has been seen to benefit in areas pertaining to clay and cement, the material also comes with many harmful effects. To try and prevent thixotropy from fracturing the sustainability of the concrete, catatonic polymer began to be used in order to counteract the thixotropy, however this agent is needed in order to allow the mixing of the clay and cementitious material. [ 12 ] There is now no true way to counteract the effect of thixotropy while also allowing it to break down the materials in the cement and clay.
The word comes from Ancient Greek θίξις thixis 'touch' (from thinganein 'to touch') and -tropy , -tropous , from Ancient Greek -τρόπος -tropos 'of turning', from τρόπος tropos 'a turn', from τρέπειν trepein , 'to turn, change'. [ 13 ] [ 14 ] Hence, it can be translated as something that turns (or changes) when touched. It was invented by Herbert Freundlich originally for a sol-gel transformation. [ 15 ] | https://en.wikipedia.org/wiki/Thixotropy |
In chemistry , a thiyl radical has the formula RS, sometimes written RS • to emphasize that they are free radicals . R is typically an alkyl or aryl substituent. Because S–H bonds are about 20% weaker than C–H bonds, thiyl radicals are relatively easily generated from thiols RSH. [ 1 ] Thiyl radicals are intermediates in the thiol-ene reaction , which is the basis of some polymeric coatings and adhesives . They are generated by hydrogen-atom abstraction from thiols using initiators such as AIBN : [ 2 ]
Thiyl radicals are also invoked as intermediates in some biochemical reactions.
The formation of thiyl radicals in vivo primarily occurs through the action of various radicals on the amino acid cysteine incorporated into proteins. The rate of radical formation is highest with the OH · radical (k = 6.8 x 10 9 M −1 s −1 ) [ 3 ] and decreases through the H · radical (k = 6.8 x 10 9 M −1 s −1 ) [ 3 ] down to peroxyl radicals R-CHOO · (k = 4.2 x 10 3 M −1 s −1 ). One of the most important substrates of thiyl radicals in biological systems is lipids , where thiyl radicals play a crucial role in lipid peroxidation. [ 4 ] In this process, thiyl radicals act as chain transfer catalysts by transferring the unpaired electron to a new lipid, thereby accelerating lipid peroxidation. [ 4 ] Other substrates of thiyl radicals include other proteins (k = 1.4 x 10 5 M −1 s −1 ), [ 5 ] monounsaturated fatty acids ( MUFAs ) (k = 1.6 x 10 5 M −1 s −1 ), [ 6 ] and ubiquinone (k = 2.5 x 10 3 M −1 s −1 ). Interestingly, the addition of lipophilic thiols in cell culture or administration to C. elegans accelerated lipid peroxidation, caused damage to membrane proteins and was associated with a decline in polyunsaturated fatty acids ( PUFAs ) and a shortened lifespan. [ 7 ] [ 8 ]
The most important phenolic antioxidants , such as ubiquinone or α-tocopherol , are inefficient scavengers of thiyl radicals. [ 4 ] Both substances are not sufficiently reactive, [ 9 ] [ 10 ] [ 3 ] and α-tocopherol is also not present in sufficient quantities to scavenge thiyl radicals. Nonetheless, both compounds have high rate constants for their reaction with peroxyl radicals, highlighting their evolutionary importance as scavengers. [ 11 ] [ 12 ] [ 13 ] Isoprenoid polyenes, such as carotenoids like lycopene , exhibit very high rate constants regarding thiyl radicals (up to 10 9 M −1 s −1 ). [ 14 ] However, even with supplementation, the effect of lycopene is not sufficient to adequately counteract lipid peroxidation. [ 4 ] The situation is significantly more promising in aqueous media: ascorbic acid and glutathione also have high rate constants (>10 8 M −1 s −1 ) and are present in sufficiently high concentrations, so in aqueous environments, thiyl radicals can be effectively neutralized by the aforementioned antioxidants. | https://en.wikipedia.org/wiki/Thiyl_radical |
Tho-Radia was a French pharmaceutical company making cosmetics between 1932 and 1968. Tho-Radia-branded creams, toothpastes and soaps were notable for containing radium and thorium until 1937, as a scheme to exploit popular interest for radium after it was discovered by Pierre and Marie Curie , in a fad of radioactive quackery .
In the early 1910s, French pharmacist Alexandre Jaboin postulated the principles of "microcurietherapy", inspired by the success of curietherapy in treating certain cancers : he assumed that very small doses of radium would stimulate living cells and increase their energy. These notions were not scientifically demonstrated, but they triggered a fad for radium-laden medicine and cosmetics. Several brands started exploiting the market in the course of the 1910s, notably Activa and Radior. [ 1 ]
In the early 1920s, pharmacist Alexis Moussalli joined the Millot pharmaceutical laboratories in Paris. Leveraging his expertise of rare-earth elements , he invented a beauty cream laden with thorium chloride and radium bromide . [ 2 ] In order to start his own brand and as a marketing device, he associated with Alfred Curie, a medical doctor, homonymous to Pierre and Marie Curie but with no connection to them. [ 3 ] Pierre and Marie Curie apparently considered legal action against the company. [ 3 ] Alfred Curie was to register the Tho-Radia brand on 29 November 1932 and approved the mention "after Dr Alfred Curie's formula" on the packaging and publicities. [ 2 ]
In order to launch his company, Alexis Moussalli also associated with Secor (Société d'exportation, commission, représentation), a French-American corporation, which was to field Tho-Radia products on the market. The brand was officially launched in 1932 for Paris and in 1933 for the rest of France. [ 2 ] Tho-Radia creams got noticed through their recognisable advertising , designed by publicist Tony Burnand, depicting a young, blond woman lit from below by visible rays. This image, which became associated with the brand in the public consciousness, would serve into the 1950s. [ 1 ] The success of Tho-Radia creams allowed Alexis Moussalli to start selling powder, toothpaste and soap, although the two later were sold as containing only thorium. [ 2 ]
The first products by Tho-Radia did actually contain radium, as a July 1932 analysis by Colombes scientific research laboratory certified that 100 grams of cream contained "0,223 microgram of radium bromide". [ 2 ]
From 1937, regulation on radioactive materials changed, limiting their usage to medical prescription and mandating a red label with the mentions "Poison", or "Toxic" for products with internal use. Tho-Radia then changed its marketing, and on 23 April 1937, SECOR registered the Tho-Radia brand again, but leaving out any mention of radium and of Alfred Curie, only to keep the name of the now successful line of products. [ 2 ]
The Second World War forced the company to relocate from Paris to Vichy , where several other pharmaceutical companies were already installed. The Vichy Regime took an interest in the company, and attempted to despoil Jewish stakeholders . However, two of the main stakeholders were from Switzerland, and Swiss ambassador Walter Stucki managed to first delay the ploy, and eventually to derail it entirely. [ 4 ]
Business slowed down for Tho-Radia during the war, but from 1948 it gathered momentum again, as Alexis Moussalli and chemist Pierre Corniou developed further products such as skincare beauty milk, perfume and lipstick. [ 2 ] At its zenith, the company had between 80 and 90 employees. [ 4 ]
After Alexis Moussalli died in 1955, his heirs dismissed SECOR administrators, but the company faced increasing competition and lost market shares. [ 2 ]
In 1962, the company was sold to Lafarge laboratories, which were in turn purchased by Sanofi in 1976. Lafarge closed the Vichy factory in 1965 and relocated to Châteauroux . With declining sales, the Tho-Radia brand was finally abandoned in 1968. [ 4 ] | https://en.wikipedia.org/wiki/Tho-Radia |
Tholins (after the Greek θολός ( tholós ) "hazy" or "muddy"; [ 1 ] from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon dioxide ( CO 2 ), methane ( CH 4 ) or ethane ( C 2 H 6 ), often in combination with nitrogen ( N 2 ) or water ( H 2 O ). [ 2 ] [ 3 ] Tholins are disordered polymer-like materials made of repeating chains of linked subunits and complex combinations of functional groups, typically nitriles and hydrocarbons , and their degraded forms such as amines and phenyls . Tholins do not form naturally on modern-day Earth , but they are found in great abundance on the surfaces of icy bodies in the outer Solar System , and as reddish aerosols in the atmospheres of outer Solar System planets and moons.
In the presence of water, tholins could be raw materials for prebiotic chemistry (i.e., the non-living chemistry that forms the basic chemicals of which life is made). Their existence has implications for the origins of life on Earth and possibly on other planets. As particles in an atmosphere, tholins scatter light, and can affect habitability .
Tholins may be produced in a laboratory, and are usually studied as a heterogeneous mixture of many chemicals with many different structures and properties. Using techniques like thermogravimetric analysis , astrochemists analyze the composition of these tholin mixtures, and the exact character of the individual chemicals within them. [ 4 ]
The term "tholin" was coined by astronomer Carl Sagan and his colleague Bishun Khare to describe the difficult-to-characterize substances they obtained in his Miller–Urey-type experiments on the methane-containing gas mixtures such as those found in Titan 's atmosphere. [ 1 ] Their paper proposing the name "tholin" said:
For the past decade we have been producing in our laboratory a variety of complex organic solids from mixtures of the cosmically abundant gases CH 4 , C 2 H 6 , NH 3 , H 2 O , HCHO, and H 2 S . The product, synthesized by ultraviolet (UV) light or spark discharge, is a brown, sometimes sticky, residue, which has been called, because of its resistance to conventional analytical chemistry, "intractable polymer". [...] We propose, as a model-free descriptive term, 'tholins' (Greek Θολός, muddy; but also Θόλος, vault or dome), although we were tempted by the phrase 'star-tar'. [ 3 ] [ 1 ]
Tholins are not one specific compound but rather are descriptive of a spectrum of molecules, including heteropolymers , [ 5 ] [ 6 ] that give a reddish, organic surface covering on certain planetary surfaces. Tholins are disordered polymer-like materials made of repeating chains of linked subunits and complex combinations of functional groups. [ 7 ] Sagan and Khare note "The properties of tholins will depend on the energy source used and the initial abundances of precursors, but a general physical and chemical similarity among the various tholins is evident." [ 1 ]
Some researchers in the field prefer a narrowed definition of tholins, for example S. Hörst wrote: "Personally, I try to use the word 'tholins' only when describing the laboratory-produced samples, in part because we do not really know yet how similar the material we produce in the lab is to the material found on places like Titan or Triton (or Pluto!)." [ 3 ] French researchers also use the term tholins only when describing the laboratory-produced samples as analogues. [ 8 ] NASA scientists also prefer the word 'tholin' for the products of laboratory simulations, and use the term 'refractory residues' for actual observations on astronomical bodies. [ 7 ]
The key elements of tholins are carbon, nitrogen, and hydrogen. Laboratory infrared spectroscopy analysis of experimentally synthesized tholins has confirmed earlier identifications of chemical groups present, including primary amines , nitriles , and alkyl portions such as CH 2 / CH 3 forming complex disordered macromolecular solids. Laboratory tests generated complex solids formed from exposure of N 2 : CH 4 gaseous mixtures to electrical discharge in cold plasma conditions, reminiscent of the famous Miller–Urey experiment conducted in 1952. [ 9 ]
As illustrated to the right, tholins are thought to form in nature through a chain of chemical reactions known as pyrolysis and radiolysis . This begins with the dissociation and ionization of molecular nitrogen ( N 2 ) and methane ( CH 4 ) by energetic particles and solar radiation. This is followed by the formation of ethylene , ethane , acetylene , hydrogen cyanide , and other small simple molecules and small positive ions. Further reactions form benzene and other organic molecules, and their polymerization leads to the formation of an aerosol of heavier molecules, which then condense and precipitate on the planetary surface below. [ 10 ]
Tholins formed at low pressure tend to contain nitrogen atoms in the interior of their molecules, while tholins formed at high pressure are more likely to have nitrogen atoms located in terminal positions. [ 11 ] [ 12 ]
Tholins may be a major constituent of the interstellar medium . [ 1 ] On Titan, their chemistry is initiated at high altitudes and participates in the formation of solid organic particles. [ 8 ]
These atmospherically-derived substances are distinct from ice tholin II , which are formed instead by irradiation ( radiolysis ) of clathrates of water and organic compounds such as methane ( CH 4 ) or ethane ( C 2 H 6 ). [ 2 ] [ 13 ] The radiation-induced synthesis on ice are independent of temperature. [ 2 ]
Models show that, even when far from UV radiation of a star, cosmic ray doses may be fully sufficient to convert carbon-containing ice grains entirely to complex organics in less than the lifetime of the typical interstellar cloud . [ 2 ]
Some researchers have speculated that Earth may have been seeded by organic compounds early in its development by tholin-rich comets, providing the raw material necessary for life to develop. [ 1 ] [ 2 ] (See Miller–Urey experiment for discussion.) Tholins do not exist naturally on present-day Earth due to the oxidizing properties of the free oxygen component of its atmosphere ever since the Great Oxygenation Event around 2.4 billion years ago. [ 14 ]
Laboratory experiments [ 15 ] suggest that tholins near large pools of liquid water that might persist for thousands of years could facilitate the formation of prebiotic chemistry to take place, [ 16 ] [ 3 ] and has implications for the origins of life on Earth and possibly other planets. [ 3 ] [ 14 ] Also, as particles in the atmosphere of an exoplanet , tholins affect the light scatter and act as a screen for protecting planetary surfaces from ultraviolet radiation, affecting habitability . [ 3 ] [ 17 ] Laboratory simulations found derived residues related to amino acids as well as urea , with important astrobiological implications. [ 14 ] [ 15 ] [ 18 ]
On Earth, a wide variety of soil bacteria are able to use laboratory-produced tholins as their sole source of carbon. Tholins could have been the first microbial food for heterotrophic microorganisms before autotrophy evolved. [ 19 ] [ 20 ]
Sagan and Khare note the presence of tholins through multiple locations: "as a constituent of the Earth's primitive oceans and therefore relevant to the origin of life ; as a component of red aerosols in the atmospheres of the outer planets and Titan; present in comets , carbonaceous chondrites asteroids, and pre-planetary solar nebulae; and as a major constituent of the interstellar medium ." [ 1 ] The surfaces of comets, centaurs , and many icy moons and Kuiper-belt objects in the outer Solar System are rich in deposits of tholins. [ 21 ]
Titan tholins are nitrogen-rich [ 22 ] [ 23 ] organic substances produced by the irradiation of the gaseous mixtures of nitrogen and methane found in the atmosphere and surface of Titan. Titan's atmosphere is about 97% nitrogen, 2.7±0.1% methane and the remaining trace amounts of other gases. [ 24 ] In the case of Titan, the haze and orange-red color of its atmosphere are both thought to be caused by the presence of tholins. [ 10 ] [ 25 ]
Colored regions on Jupiter's satellite Europa are thought to be tholins. [ 16 ] [ 26 ] [ 27 ] [ 28 ] The morphology of Europa's impact craters and ridges is suggestive of fluidized material welling up from the fractures where pyrolysis and radiolysis take place. In order to generate colored tholins on Europa there must be a source of materials (carbon, nitrogen, and water), and a source of energy to drive the reactions. Impurities in the water ice crust of Europa are presumed both to emerge from the interior as cryovolcanic events that resurface the body, and to accumulate from space as interplanetary dust. [ 16 ]
The extensive dark areas on the trailing hemisphere of Saturn's moon Rhea are thought to be deposited tholins. [ 13 ]
Neptune's moon Triton is observed to have the reddish color characteristic of tholins. [ 22 ] Triton's atmosphere is mostly nitrogen, with trace amounts of methane and carbon monoxide. [ 29 ] [ 30 ]
Tholins occur on the dwarf planet Pluto [ 31 ] and are responsible for red colors [ 32 ] as well as the blue tint of the atmosphere of Pluto . [ 33 ] The reddish-brown cap of the north pole of Charon , [ 3 ] the largest of five moons of Pluto , is thought to be composed of tholins, produced from methane, nitrogen and related gases released from the atmosphere of Pluto and transferred over about 19,000 km (12,000 mi) distance to the orbiting moon. [ 34 ] [ 35 ] [ 36 ]
Tholins were detected on the dwarf planet Ceres by the Dawn mission . [ 37 ] [ 38 ] Most of the planet's surface is extremely rich in carbon, with approximately 20% carbon by mass in its near surface. [ 39 ] [ 40 ] The carbon content is more than five times higher than in carbonaceous chondrite meteorites analyzed on Earth. [ 40 ]
Makemake exhibits methane , large amounts of ethane and tholins, as well as smaller amounts of ethylene , acetylene and high-mass alkanes may be present, most likely created by photolysis of methane by solar radiation. [ 41 ] [ 42 ] [ 43 ]
The reddish color typical of tholins is characteristic of many Trans-Neptunian objects , including plutinos in the outer Solar System such as 28978 Ixion . [ 44 ] Spectral reflectances of Centaurs also suggest the presence of tholins on their surfaces. [ 45 ] [ 46 ] [ 47 ] The New Horizons exploration of the classical Kuiper belt object 486958 Arrokoth revealed reddish color at its surface, suggestive of tholins. [ 7 ] [ 48 ]
Tholins were detected in situ by the Rosetta mission to comet 67P/Churyumov–Gerasimenko . [ 49 ] [ 50 ] Tholins are not typically characteristic of main-belt asteroids, but have been detected on the asteroid 24 Themis . [ 51 ] [ 52 ]
Tholins might have also been detected in the stellar system of the young star HR 4796A using the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) aboard the Hubble Space Telescope. [ 53 ] The HR 4796 system is approximately 220 light years from Earth. [ 54 ] | https://en.wikipedia.org/wiki/Tholin |
In mathematics, especially in differential topology , Thom's first isotopy lemma states: given a smooth map f : M → N {\displaystyle f:M\to N} between smooth manifolds and S ⊂ M {\displaystyle S\subset M} a closed Whitney stratified subset , if f | S {\displaystyle f|_{S}} is proper and f | A {\displaystyle f|_{A}} is a submersion for each stratum A {\displaystyle A} of S {\displaystyle S} , then f | S {\displaystyle f|_{S}} is a locally trivial fibration . [ 1 ] The lemma was originally introduced by René Thom who considered the case when N = R {\displaystyle N=\mathbb {R} } . [ 2 ] In that case, the lemma constructs an isotopy from the fiber f − 1 ( a ) {\displaystyle f^{-1}(a)} to f − 1 ( b ) {\displaystyle f^{-1}(b)} ; whence the name "isotopy lemma".
The local trivializations that the lemma provide preserve the strata. However, they are generally not smooth (not even C 1 {\displaystyle C^{1}} ). On the other hand, it is possible that local trivializations are semialgebraic if the input data is semialgebraic. [ 3 ] [ 4 ]
The lemma is also valid for a more general stratified space such as a stratified space in the sense of Mather but still with the Whitney conditions (or some other conditions). The lemma is also valid for the stratification that satisfies Bekka's condition (C) , which is weaker than Whitney's condition (B). [ 5 ] (The significance of this is that the consequences of the first isotopy lemma cannot imply Whitney’s condition (B).)
Thom's second isotopy lemma is a family version of the first isotopy lemma.
The proof [ 1 ] is based on the notion of a controlled vector field . [ 6 ] Let { ( T A , π A , ρ A ) ∣ A } {\displaystyle \{(T_{A},\pi _{A},\rho _{A})\mid A\}} be a system of tubular neighborhoods T A {\displaystyle T_{A}} in M {\displaystyle M} of strata A {\displaystyle A} in S {\displaystyle S} where π A : T A → A {\displaystyle \pi _{A}:T_{A}\to A} is the associated projection and ρ A : T A → [ 0 , ∞ ) {\displaystyle \rho _{A}:T_{A}\to [0,\infty )} given by the square norm on each fiber of π A {\displaystyle \pi _{A}} . (The construction of such a system relies on the Whitney conditions or something weaker.) By definition, a controlled vector field is a family of vector fields (smooth of some class) η A {\displaystyle \eta _{A}} on the strata A {\displaystyle A} such that: for each stratum A , there exists a neighborhood T A ′ {\displaystyle T'_{A}} of A {\displaystyle A} in T A {\displaystyle T_{A}} such that for any B > A {\displaystyle B>A} ,
on T A ′ ∩ B {\displaystyle T_{A}'\cap B} .
Assume the system T A {\displaystyle T_{A}} is compatible with the map f : M → N {\displaystyle f:M\to N} (such a system exists). Then there are two key results due to Thom:
The lemma now follows in a straightforward fashion. Since the statement is local, assume N = R n {\displaystyle N=\mathbb {R} ^{n}} and ∂ i {\displaystyle \partial _{i}} the coordinate vector fields on R n {\displaystyle \mathbb {R} ^{n}} . Then, by the lifting result, we find controlled vector fields ∂ i ~ {\displaystyle {\widetilde {\partial _{i}}}} on S {\displaystyle S} such that f ∗ ( ∂ i ~ ) = ∂ i ∘ f {\displaystyle f_{*}({\widetilde {\partial _{i}}})=\partial _{i}\circ f} . Let φ i : R × S → S {\displaystyle \varphi _{i}:\mathbb {R} \times S\to S} be the flows associated to them. Then define
by
It is a map over R n {\displaystyle \mathbb {R} ^{n}} and is a homeomorphism since G ( x ) = ( φ 1 ( − t 1 , ⋯ , φ n ( − t n , x ) ⋯ ) , t ) , t = f ( x ) {\displaystyle G(x)=(\varphi _{1}(-t_{1},\cdots ,\varphi _{n}(-t_{n},x)\cdots ),t),t=f(x)} is the inverse. Since the flows φ i {\displaystyle \varphi _{i}} preserve the strata, H {\displaystyle H} also preserves the strata. ◻ {\displaystyle \square }
This topology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thom's_first_isotopy_lemma |
In mathematics, especially in differential topology , Thom's second isotopy lemma is a family version of Thom's first isotopy lemma ; i.e., it states a family of maps between Whitney stratified spaces is locally trivial when it is a Thom mapping . [ 1 ] Like the first isotopy lemma, the lemma was introduced by René Thom .
( Mather 2012 , § 11) gives a sketch of the proof. ( Verona 1984 ) gives a simplified proof. Like the first isotopy lemma, the lemma also holds for the stratification with Bekka's condition (C) , which is weaker than Whitney's condition (B). [ 2 ]
Let f : M → N {\displaystyle f:M\to N} be a smooth map between smooth manifolds and X , Y ⊂ M {\displaystyle X,Y\subset M} submanifolds such that f | X , f | Y {\displaystyle f|_{X},f|_{Y}} both have differential of constant rank. Then Thom's condition ( a f ) {\displaystyle (a_{f})} is said to hold if for each sequence x i {\displaystyle x_{i}} in X converging to a point y in Y and such that ker ( d ( f | X ) x i ) {\displaystyle \operatorname {ker} (d(f|_{X})_{x_{i}})} converging to a plane τ {\displaystyle \tau } in the Grassmannian, we have ker ( d ( f | Y ) y ) ⊂ τ . {\displaystyle \operatorname {ker} (d(f|_{Y})_{y})\subset \tau .} [ 3 ]
Let S ⊂ M , S ′ ⊂ N {\displaystyle S\subset M,S'\subset N} be Whitney stratified closed subsets and p : S → Z , q : S ′ → Z {\displaystyle p:S\to Z,q:S'\to Z} maps to some smooth manifold Z such that f : S → S ′ {\displaystyle f:S\to S'} is a map over Z ; i.e., f ( S ) ⊂ S ′ {\displaystyle f(S)\subset S'} and q ∘ f | S = p {\displaystyle q\circ f|_{S}=p} . Then f {\displaystyle f} is called a Thom mapping if the following conditions hold: [ 3 ]
Then Thom's second isotopy lemma says that a Thom mapping is locally trivial over Z ; i.e., each point z of Z has a neighborhood U with homeomorphisms h 1 : p − 1 ( z ) × U → p − 1 ( U ) , h 2 : q − 1 ( z ) × U → q − 1 ( U ) {\displaystyle h_{1}:p^{-1}(z)\times U\to p^{-1}(U),h_{2}:q^{-1}(z)\times U\to q^{-1}(U)} over U such that f ∘ h 1 = h 2 ∘ ( f | p − 1 ( z ) × id ) {\displaystyle f\circ h_{1}=h_{2}\circ (f|_{p^{-1}(z)}\times \operatorname {id} )} . [ 3 ]
This topology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thom's_second_isotopy_lemma |
In mathematics , a smooth algebraic curve C {\displaystyle C} in the complex projective plane , of degree d {\displaystyle d} , has genus given by the genus–degree formula
The Thom conjecture , named after French mathematician René Thom , states that if Σ {\displaystyle \Sigma } is any smoothly embedded connected curve representing the same class in homology as C {\displaystyle C} , then the genus g {\displaystyle g} of Σ {\displaystyle \Sigma } satisfies the inequality
In particular, C is known as a genus minimizing representative of its homology class. It was first proved by Peter Kronheimer and Tomasz Mrowka in October 1994, [ 1 ] using the then-new Seiberg–Witten invariants .
Assuming that Σ {\displaystyle \Sigma } has nonnegative self intersection number this was generalized to Kähler manifolds (an example being the complex projective plane) by John Morgan , Zoltán Szabó , and Clifford Taubes , [ 2 ] also using the Seiberg–Witten invariants.
There is at least one generalization of this conjecture, known as the symplectic Thom conjecture (which is now a theorem, as proved for example by Peter Ozsváth and Szabó in 2000 [ 3 ] ). It states that a symplectic surface of a symplectic 4-manifold is genus minimizing within its homology class. This would imply the previous result because algebraic curves (complex dimension 1, real dimension 2) are symplectic surfaces within the complex projective plane, which is a symplectic 4-manifold. | https://en.wikipedia.org/wiki/Thom_conjecture |
In mathematics , Thomae's formula is a formula introduced by Carl Johannes Thomae ( 1870 ) relating theta constants to the branch points of a hyperelliptic curve ( Mumford 1984 , section 8).
In 1824, the Abel–Ruffini theorem established that polynomial equations of a degree of five or higher could have no solutions in radicals . It became clear to mathematicians since then that one needed to go beyond radicals in order to express the solutions to equations of the fifth and higher degrees. In 1858, Charles Hermite , Leopold Kronecker , and Francesco Brioschi independently discovered that the quintic equation could be solved with elliptic transcendents . This proved to be a generalization of the radical, which can be written as: x n = exp ( 1 n ln x ) = exp ( 1 n ∫ 1 x d t t ) . {\displaystyle {\sqrt[{n}]{x}}=\exp \left({{\frac {1}{n}}\ln x}\right)=\exp \left({\frac {1}{n}}\int _{1}^{x}{\frac {dt}{t}}\right).} With the restriction to only this exponential, as shown by Galois theory , only compositions of Abelian extensions may be constructed, which suffices only for equations of the fourth degree and below. Something more general is required for equations of higher degree, so to solve the quintic, Hermite, et al. replaced the exponential by an elliptic modular function and the integral (logarithm) by an elliptic integral . Kronecker believed that this was a special case of a still more general method. [ 1 ] Camille Jordan showed [ 2 ] that any algebraic equation may be solved by use of modular functions. This was accomplished by Thomae in 1870. [ 3 ] Thomae generalized Hermite's approach by replacing the elliptic modular function with even more general Siegel modular forms and the elliptic integral by a hyperelliptic integral . Hiroshi Umemura [ 4 ] expressed these modular functions in terms of higher genus theta functions .
If we have a polynomial function : f ( x ) = a 0 x n + a 1 x n − 1 + ⋯ + a n {\displaystyle f(x)=a_{0}x^{n}+a_{1}x^{n-1}+\cdots +a_{n}} with a 0 ≠ 0 {\displaystyle a_{0}\neq 0} irreducible over a certain subfield of the complex numbers, then its roots x k {\displaystyle x_{k}} may be expressed by the following equation involving theta functions of zero argument ( theta constants ): x k = [ θ ( 1 0 ⋯ 0 0 ⋯ 0 0 ) ( Ω ) ] 4 [ θ ( 1 1 0 ⋯ 0 0 ⋯ 0 0 0 ) ( Ω ) ] 4 + [ θ ( 0 ⋯ 0 0 ⋯ 0 ) ( Ω ) ] 4 [ θ ( 0 1 0 ⋯ 0 0 0 0 ⋯ 0 ) ( Ω ) ] 4 − [ θ ( 0 0 ⋯ 0 1 0 ⋯ 0 ) ( Ω ) ] 4 [ θ ( 0 1 0 ⋯ 0 1 0 ⋯ 0 0 ) ( Ω ) ] 4 2 [ θ ( 1 0 ⋯ 0 0 ⋯ 0 0 ) ( Ω ) ] 4 [ θ ( 1 1 0 ⋯ 0 0 0 ⋯ 0 0 ) ( Ω ) ] 4 {\displaystyle {\begin{aligned}x_{k}={}&\left[\theta \left({\begin{matrix}1&0&\cdots &0\\0&\cdots &0&0\end{matrix}}\right)(\Omega )\right]^{4}\left[\theta \left({\begin{matrix}1&1&0&\cdots &0\\0&\cdots &0&0&0\end{matrix}}\right)(\Omega )\right]^{4}\\[6pt]&{}+\left[\theta \left({\begin{matrix}0&\cdots &0\\0&\cdots &0\end{matrix}}\right)(\Omega )\right]^{4}\left[\theta \left({\begin{matrix}0&1&0&\cdots &0\\0&0&0&\cdots &0\end{matrix}}\right)(\Omega )\right]^{4}\\[6pt]&{}-{\frac {\left[\theta \left({\begin{matrix}0&0&\cdots &0\\1&0&\cdots &0\end{matrix}}\right)(\Omega )\right]^{4}\left[\theta \left({\begin{matrix}0&1&0&\cdots &0\\1&0&\cdots &0&0\end{matrix}}\right)(\Omega )\right]^{4}}{2\left[\theta \left({\begin{matrix}1&0&\cdots &0\\0&\cdots &0&0\end{matrix}}\right)(\Omega )\right]^{4}\left[\theta \left({\begin{matrix}1&1&0&\cdots &0\\0&0&\cdots &0&0\end{matrix}}\right)(\Omega )\right]^{4}}}\end{aligned}}} where Ω {\displaystyle \Omega } is the period matrix derived from one of the following hyperelliptic integrals. If f ( x ) {\displaystyle f(x)} is of odd degree, then, u ( a ) = ∫ 1 a d x x ( x − 1 ) f ( x ) {\displaystyle u(a)=\int _{1}^{a}{\frac {dx}{\sqrt {x(x-1)f(x)}}}} Or if f ( x ) {\displaystyle f(x)} is of even degree, then, u ( a ) = ∫ 1 a d x x ( x − 1 ) ( x − 2 ) f ( x ) {\displaystyle u(a)=\int _{1}^{a}{\frac {dx}{\sqrt {x(x-1)(x-2)f(x)}}}}
This formula applies to any algebraic equation of any degree without need for a Tschirnhaus transformation or any other manipulation to bring the equation into a specific normal form, such as the Bring–Jerrard form for the quintic. However, application of this formula in practice is difficult because the relevant hyperelliptic integrals and higher-genus theta functions are very complex. | https://en.wikipedia.org/wiki/Thomae's_formula |
Thomae's function is a real -valued function of a real variable that can be defined as: [ 1 ] : 531 f ( x ) = { 1 q if x = p q ( x is rational), with p ∈ Z and q ∈ N coprime 0 if x is irrational. {\displaystyle f(x)={\begin{cases}{\frac {1}{q}}&{\text{if }}x={\tfrac {p}{q}}\quad (x{\text{ is rational), with }}p\in \mathbb {Z} {\text{ and }}q\in \mathbb {N} {\text{ coprime}}\\0&{\text{if }}x{\text{ is irrational.}}\end{cases}}}
It is named after Carl Johannes Thomae , but has many other names: the popcorn function , the raindrop function , the countable cloud function , the modified Dirichlet function , the ruler function (not to be confused with the integer ruler function ), [ 2 ] the Riemann function , or the Stars over Babylon ( John Horton Conway 's name). [ 3 ] Thomae mentioned it as an example for an integrable function with infinitely many discontinuities in an early textbook on Riemann's notion of integration. [ 4 ]
Since every rational number has a unique representation with coprime (also termed relatively prime) p ∈ Z {\displaystyle p\in \mathbb {Z} } and q ∈ N {\displaystyle q\in \mathbb {N} } , the function is well-defined . Note that q = + 1 {\displaystyle q=+1} is the only number in N {\displaystyle \mathbb {N} } that is coprime to p = 0. {\displaystyle p=0.}
It is a modification of the Dirichlet function , which is 1 at rational numbers and 0 elsewhere.
For all x ∈ R ∖ Q , {\displaystyle x\in \mathbb {R} \setminus \mathbb {Q} ,} we also have x + n ∈ R ∖ Q {\displaystyle x+n\in \mathbb {R} \setminus \mathbb {Q} } and hence f ( x + n ) = f ( x ) = 0 , {\displaystyle f(x+n)=f(x)=0,}
For all x ∈ Q , {\displaystyle x\in \mathbb {Q} ,\;} there exist p ∈ Z {\displaystyle p\in \mathbb {Z} } and q ∈ N {\displaystyle q\in \mathbb {N} } such that x = p / q , {\displaystyle \;x=p/q,\;} and gcd ( p , q ) = 1. {\displaystyle \gcd(p,\;q)=1.} Consider x + n = ( p + n q ) / q {\displaystyle x+n=(p+nq)/q} . If d {\displaystyle d} divides p {\displaystyle p} and q {\displaystyle q} , it divides p + n q {\displaystyle p+nq} and q {\displaystyle q} . Conversely, if d {\displaystyle d} divides p + n q {\displaystyle p+nq} and q {\displaystyle q} , it divides ( p + n q ) − n q = p {\displaystyle (p+nq)-nq=p} and q {\displaystyle q} . So gcd ( p + n q , q ) = gcd ( p , q ) = 1 {\displaystyle \gcd(p+nq,q)=\gcd(p,q)=1} , and f ( x + n ) = 1 / q = f ( x ) {\displaystyle f(x+n)=1/q=f(x)} .
Let x 0 = p / q {\displaystyle x_{0}=p/q} be an arbitrary rational number, with p ∈ Z , q ∈ N , {\displaystyle \;p\in \mathbb {Z} ,\;q\in \mathbb {N} ,} and p {\displaystyle p} and q {\displaystyle q} coprime.
This establishes f ( x 0 ) = 1 / q . {\displaystyle f(x_{0})=1/q.}
Let α ∈ R ∖ Q {\displaystyle \;\alpha \in \mathbb {R} \setminus \mathbb {Q} \;} be any irrational number and define x n = x 0 + α n {\displaystyle x_{n}=x_{0}+{\frac {\alpha }{n}}} for all n ∈ N . {\displaystyle n\in \mathbb {N} .}
These x n {\displaystyle x_{n}} are all irrational, and so f ( x n ) = 0 {\displaystyle f(x_{n})=0} for all n ∈ N . {\displaystyle n\in \mathbb {N} .}
This implies | x 0 − x n | = α n , {\displaystyle |x_{0}-x_{n}|={\frac {\alpha }{n}},} and | f ( x 0 ) − f ( x n ) | = 1 q . {\displaystyle |f(x_{0})-f(x_{n})|={\frac {1}{q}}.}
Let ε = 1 / q {\displaystyle \;\varepsilon =1/q\;} , and given δ > 0 {\displaystyle \delta >0} let n = 1 + ⌈ α δ ⌉ . {\displaystyle n=1+\left\lceil {\frac {\alpha }{\delta }}\right\rceil .} For the corresponding x n {\displaystyle \;x_{n}} we have | f ( x 0 ) − f ( x n ) | = 1 / q ≥ ε {\displaystyle |f(x_{0})-f(x_{n})|=1/q\geq \varepsilon } and | x 0 − x n | = α n = α 1 + ⌈ α δ ⌉ < α ⌈ α δ ⌉ ≤ δ , {\displaystyle |x_{0}-x_{n}|={\frac {\alpha }{n}}={\frac {\alpha }{1+\left\lceil {\frac {\alpha }{\delta }}\right\rceil }}<{\frac {\alpha }{\left\lceil {\frac {\alpha }{\delta }}\right\rceil }}\leq \delta ,}
which is exactly the definition of discontinuity of f {\displaystyle f} at x 0 {\displaystyle x_{0}} .
Since f {\displaystyle f} is periodic with period 1 {\displaystyle 1} and 0 ∈ Q , {\displaystyle 0\in \mathbb {Q} ,} it suffices to check all irrational points in I = ( 0 , 1 ) . {\displaystyle I=(0,1).\;} Assume now ε > 0 , i ∈ N {\displaystyle \varepsilon >0,\;i\in \mathbb {N} } and x 0 ∈ I ∖ Q . {\displaystyle x_{0}\in I\setminus \mathbb {Q} .} According to the Archimedean property of the reals, there exists r ∈ N {\displaystyle r\in \mathbb {N} } with 1 / r < ε , {\displaystyle 1/r<\varepsilon ,} and there exist k i ∈ N , {\displaystyle \;k_{i}\in \mathbb {N} ,} such that
for i = 1 , … , r {\displaystyle i=1,\ldots ,r} we have 0 < k i i < x 0 < k i + 1 i . {\displaystyle 0<{\frac {k_{i}}{i}}<x_{0}<{\frac {k_{i}+1}{i}}.}
The minimal distance of x 0 {\displaystyle x_{0}} to its i -th lower and upper bounds equals d i := min { | x 0 − k i i | , | x 0 − k i + 1 i | } . {\displaystyle d_{i}:=\min \left\{\left|x_{0}-{\frac {k_{i}}{i}}\right|,\;\left|x_{0}-{\frac {k_{i}+1}{i}}\right|\right\}.}
We define δ {\displaystyle \delta } as the minimum of all the finitely many d i . {\displaystyle d_{i}.} δ := min 1 ≤ i ≤ r { d i } , {\displaystyle \delta :=\min _{1\leq i\leq r}\{d_{i}\},\;} so that
for all i = 1 , … , r , {\displaystyle i=1,\dots ,r,} | x 0 − k i / i | ≥ δ {\displaystyle |x_{0}-k_{i}/i|\geq \delta } and | x 0 − ( k i + 1 ) / i | ≥ δ . {\displaystyle |x_{0}-(k_{i}+1)/i|\geq \delta .}
This is to say, all these rational numbers k i / i , ( k i + 1 ) / i , {\displaystyle k_{i}/i,\;(k_{i}+1)/i,\;} are outside the δ {\displaystyle \delta } -neighborhood of x 0 . {\displaystyle x_{0}.}
Now let x ∈ Q ∩ ( x 0 − δ , x 0 + δ ) {\displaystyle x\in \mathbb {Q} \cap (x_{0}-\delta ,x_{0}+\delta )} with the unique representation x = p / q {\displaystyle x=p/q} where p , q ∈ N {\displaystyle p,q\in \mathbb {N} } are coprime. Then, necessarily, q > r , {\displaystyle q>r,\;} and therefore, f ( x ) = 1 / q < 1 / r < ε . {\displaystyle f(x)=1/q<1/r<\varepsilon .}
Likewise, for all irrational x ∈ I , f ( x ) = 0 = f ( x 0 ) , {\displaystyle x\in I,\;f(x)=0=f(x_{0}),\;} and thus, if ε > 0 {\displaystyle \varepsilon >0} then any choice of (sufficiently small) δ > 0 {\displaystyle \delta >0} gives | x − x 0 | < δ ⟹ | f ( x 0 ) − f ( x ) | = f ( x ) < ε . {\displaystyle |x-x_{0}|<\delta \implies |f(x_{0})-f(x)|=f(x)<\varepsilon .}
Therefore, f {\displaystyle f} is continuous on R ∖ Q . {\displaystyle \mathbb {R} \setminus \mathbb {Q} .}
Empirical probability distributions related to Thomae's function appear in DNA sequencing . [ 7 ] The human genome is diploid , having two strands per chromosome. When sequenced, small pieces ("reads") are generated: for each spot on the genome, an integer number of reads overlap with it. Their ratio is a rational number, and typically distributed similarly to Thomae's function.
If pairs of positive integers m , n {\displaystyle m,n} are sampled from a distribution f ( n , m ) {\displaystyle f(n,m)} and used to generate ratios q = n / ( n + m ) {\displaystyle q=n/(n+m)} , this gives rise to a distribution g ( q ) {\displaystyle g(q)} on the rational numbers. If the integers are independent the distribution can be viewed as a convolution over the rational numbers, g ( a / ( a + b ) ) = ∑ t = 1 ∞ f ( t a ) f ( t b ) {\textstyle g(a/(a+b))=\sum _{t=1}^{\infty }f(ta)f(tb)} . Closed form solutions exist for power-law distributions with a cut-off. If f ( k ) = k − α e − β k / L i α ( e − β ) {\displaystyle f(k)=k^{-\alpha }e^{-\beta k}/\mathrm {Li} _{\alpha }(e^{-\beta })} (where L i α {\displaystyle \mathrm {Li} _{\alpha }} is the polylogarithm function) then g ( a / ( a + b ) ) = ( a b ) − α L i 2 α ( e − ( a + b ) β ) / L i α 2 ( e − β ) {\displaystyle g(a/(a+b))=(ab)^{-\alpha }\mathrm {Li} _{2\alpha }(e^{-(a+b)\beta })/\mathrm {Li} _{\alpha }^{2}(e^{-\beta })} . In the case of uniform distributions on the set { 1 , 2 , … , L } {\displaystyle \{1,2,\ldots ,L\}} g ( a / ( a + b ) ) = ( 1 / L 2 ) ⌊ L / max ( a , b ) ⌋ {\displaystyle g(a/(a+b))=(1/L^{2})\lfloor L/\max(a,b)\rfloor } , which is very similar to Thomae's function. [ 7 ]
For integers, the exponent of the highest power of 2 dividing n {\displaystyle n} gives 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0, ... (sequence A007814 in the OEIS ). If 1 is added, or if the 0s are removed, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, ... (sequence A001511 in the OEIS ). The values resemble tick-marks on a 1/16th graduated ruler , hence the name. These values correspond to the restriction of the Thomae function to the dyadic rationals : those rational numbers whose denominators are powers of 2.
A natural follow-up question one might ask is if there is a function which is continuous on the rational numbers and discontinuous on the irrational numbers. This turns out to be impossible. The set of discontinuities of any function must be an F σ set . If such a function existed, then the irrationals would be an F σ set. The irrationals would then be the countable union of closed sets ⋃ i = 0 ∞ C i {\textstyle \bigcup _{i=0}^{\infty }C_{i}} , but since the irrationals do not contain an interval, neither can any of the C i {\displaystyle C_{i}} . Therefore, each of the C i {\displaystyle C_{i}} would be nowhere dense, and the irrationals would be a meager set . It would follow that the real numbers, being the union of the irrationals and the rationals (which, as a countable set, is evidently meager), would also be a meager set. This would contradict the Baire category theorem : because the reals form a complete metric space , they form a Baire space , which cannot be meager in itself.
A variant of Thomae's function can be used to show that any F σ subset of the real numbers can be the set of discontinuities of a function. If A = ⋃ n = 1 ∞ F n {\textstyle A=\bigcup _{n=1}^{\infty }F_{n}} is a countable union of closed sets F n {\displaystyle F_{n}} , define f A ( x ) = { 1 n if x is rational and n is minimal so that x ∈ F n − 1 n if x is irrational and n is minimal so that x ∈ F n 0 if x ∉ A {\displaystyle f_{A}(x)={\begin{cases}{\frac {1}{n}}&{\text{if }}x{\text{ is rational and }}n{\text{ is minimal so that }}x\in F_{n}\\-{\frac {1}{n}}&{\text{if }}x{\text{ is irrational and }}n{\text{ is minimal so that }}x\in F_{n}\\0&{\text{if }}x\notin A\end{cases}}}
Then a similar argument as for Thomae's function shows that f A {\displaystyle f_{A}} has A as its set of discontinuities. | https://en.wikipedia.org/wiki/Thomae's_function |
In the dynamical systems theory , Thomas' cyclically symmetric attractor is a 3D strange attractor originally proposed by René Thomas . [ 1 ] It has a simple form which is cyclically symmetric in the x, y, and z variables and can be viewed as the trajectory of a frictionally dampened particle moving in a 3D lattice of forces. [ 2 ] The simple form has made it a popular example.
It is described by the differential equations
where b {\displaystyle b} is a constant.
b {\displaystyle b} corresponds to how dissipative the system is, and acts as a bifurcation parameter. For b > 1 {\displaystyle b>1} the origin is the single stable equilibrium. At b = 1 {\displaystyle b=1} it undergoes a pitchfork bifurcation , splitting into two attractive fixed points. As the parameter is decreased further they undergo a Hopf bifurcation at b ≈ 0.32899 {\displaystyle b\approx 0.32899} , creating a stable limit cycle. The limit cycle then undergoes a period doubling cascade and becomes chaotic at b ≈ 0.208186 {\displaystyle b\approx 0.208186} . Beyond this the attractor expands, undergoing a series of crises (up to six separate attractors can coexist for certain values). The fractal dimension of the attractor increases towards 3. [ 2 ]
In the limit b = 0 {\displaystyle b=0} the system lacks dissipation and the trajectory ergodically wanders the entire space (with an exception for 1.67%, where it drifts parallel to one of the coordinate axes: this corresponds to quasiperiodic torii). The dynamics has been described as deterministic fractional Brownian motion , and exhibits anomalous diffusion . [ 2 ] [ 3 ] | https://en.wikipedia.org/wiki/Thomas'_cyclically_symmetric_attractor |
The Thomas A. Scott Fellowship in Hygiene was a competitive academic grant made at the University of Pennsylvania for the study of scientific hygiene and sanitary science , the precursors of the modern science of pathology . It was established in 1892 [ 1 ] in the name of late railroad executive and financier Thomas Alexander Scott by his widow. [ 2 ]
This article about a university or college in Pennsylvania is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Thomas_A._Scott_Fellowship_in_Hygiene |
Thomas Albrecht is an American radiochemist specializing in the chemistry and physics of transuranium elements. He is jointly appointed as a University Distinguished Professor at the Colorado School of Mines in Golden, Colorado, and Director of the Nuclear Science & Engineering Center and as a scientist at Idaho National Laboratory.
Thomas Albrecht received his undergraduate education in chemistry at Southwest Minnesota State University , during which time he also performed research at Texas A&M with J. P. Fackler on gold chemistry and Ron Caple on organometallic chemistry at the University of Minnesota-Duluth via REU-NSF programs. [ 1 ] He received his doctorate in inorganic chemistry in 1997 from Northwestern University under James Ibers where he studied the synthesis, structures, and reactivity of transition metal polychalcogenides. Following a postdoctoral position at the University of Illinois in 1998 with J. R. Shapley on metal-fullerene chemistry, he became an assistant professor at Auburn University later that year, transitioning to associate professor in 2002 and full professor in 2007. While at Auburn, he built a large program dedicated to understanding the chemistry and physics of f-block compounds. He opened the first new transuranium laboratory in decades in the U.S. while at Auburn, and continued this theme as the Frank M. Freimann Chair at the University of Notre Dame from 2009 to 2012. He moved to Florida State University in 2012 to become the first Gregory R. Choppin Chair in Chemistry. [ 1 ] In 2022 he joined the faculty at the Colorado School of Mines in Golden, Colorado, and was a part of the inaugural group of University Distinguished Professors.
Prof. Albrecht directs a research group at the Colorado School of Mines in radio- and nuclear chemistry as well as the chemistry and physics of critical materials. In 2016 he received federal funding from the U.S. Department of Energy through the Office of Basic Energy Sciences as part of the Energy Frontier Research Center program to establish the Center for Actinide Science & Technology (CAST), a multi-institution research center dedicated to advancing our understanding of how electronic structure and bonding control the properties of radioactive materials, with focus on alleviating the environmental impacts of nuclear power and the Cold War. [ 2 ] [ 3 ]
His research focuses on the use of synthetic, crystallographic, and spectroscopic techniques and quantum chemical simulation to better understand the nature of bonding and physical properties in lanthanides and actinides complexes . Prof. Albrecht is particularly known for his research on the chemistry of highly radioactive and scarce heavy actinides such as berkelium and californium . [ 4 ] [ 5 ]
In 2019 Prof. Albrecht was awarded the Glenn T. Seaborg Award in Nuclear Chemistry for outstanding contributions to nuclear and radiochemistry at the American Chemical Society meeting in Orlando, Florida. [ 6 ] The focus of this award was his group's discovery of a fundamental break in the chemistry of actinides that begins at californium. His group is responsible for the majority of transuranium single crystal structures and was the first to apply the use of microdiffraction techniques to compounds of these elements. His team was also the first to report the single crystal structure of a berkelium compound. He was in 2015 elected as a fellow of the Royal Society of Chemistry for contributions including his pioneering work on californium. [ 7 ] In 2018, Prof. Albrecht was elected a fellow of the American Association for the Advancement of Science [ 8 ] and was the preceptor for the ACS Nobel Signature Prize for Graduate Education in Chemistry. He has delivered a number of important endowed lectures throughout the world including the Gerhard and Lisolette Closs Memorial Lecture at the University of Chicago and the George Fischer Baker Lecture at Cornell University. In 2024, he was awarded the M. J. Buerger Award for contributions of exceptional distinction in areas of interest to the American Crystallographic Association. | https://en.wikipedia.org/wiki/Thomas_Albrecht |
Thomas Anderson (2 July 1819 – 2 November 1874) was a 19th-century Scottish chemist. In 1853 his work on alkaloids led him to discover the correct formula/composition for codeine . [ 1 ] In 1868 he discovered pyridine and related organic compounds such as picoline through studies on the distillation of bone oil and other animal matter. [ 2 ]
As well as his work on organic chemistry , Anderson made important contributions to agricultural chemistry , writing over 130 reports on soils, fertilisers and plant diseases. He kept abreast of all areas of science, and was able to advise his colleague Joseph Lister on Pasteur's germ theory and the use of carbolic acid as an antiseptic .
Born in Leith , [ 3 ] Thomas Anderson graduated from the University of Edinburgh with a medical doctorate in 1841. Having developed an interest in chemistry during his medical studies, he then spent several years studying chemistry in Europe, including spells under Jöns Jakob Berzelius in Sweden and Justus von Liebig in Germany. Returning to Edinburgh, he worked at the University of Edinburgh and at the Highland and Agricultural Society of Scotland . In 1852, he was appointed Regius Professor of Chemistry at the University of Glasgow and remained in that post for the remainder of his career. In 1854, he became one of the editors of the Edinburgh New Philosophical Journal . [ 4 ] In 1872, Anderson was awarded a Royal Medal from the Royal Society "for his investigations on the organic bases of Dippells animal oil; on codeine; on the crystallized constituents of opium; on piperin and on papaverin; and for his researches in physiological and animal chemistry."
His later years were marred by a progressive neurological disease which may have been syphilis . [ 5 ] He resigned his chair in early 1874, and died later that year in Chiswick .
He was succeeded by John Ferguson . [ 6 ] | https://en.wikipedia.org/wiki/Thomas_Anderson_(chemist) |
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