Thermal generation

When the temperature of a solar cell rises, cell conversion efficiency decreases because the additional thermal energy increases the thermally generated minority (dark-drift) current. This increase in dark-drift current is balanced in the cell by lowering the built-in barrier potential, lU, to boost the majority diffusion current. The drop in F causes a decrease in and F. Therefore, a cell s output, ie, the product of F and decreases with increasing cell temperature. is less sensitive to temperature changes than F and actually increases with temperature. 

The isotope plutonium-238 [13981 -16-3] Pu, is of technical importance because of the high heat that accompanies its radioactive decay. This isotope has been and is being used as fuel in small terrestrial and space nuclear-powered sources (3,4). Tu-based radioisotope thermal generator systems dehvered 7 W/kg and cost 120,000/W in 1991 (3). For some time, %Pu was considered to be the most promising power source for the radioisotope-powered artificial heart and for cardiovascular pacemakers. Usage of plutonium was discontinued, however, after it was determined that adequate elimination of penetrating radiation was uncertain (5) (see PROSTHETIC AND BIOMEDICAL devices). 

Instead of depending on the thermally generated carriers just described (intrinsic conduction), it is also possible to deUberately incorporate various impurity atoms into the sihcon lattice that ionize at relatively low temperatures and provide either free holes or electrons. In particular. Group 13 (IIIA) elements n-type dopants) supply electrons and Group 15 (VA) elements (p-type dopants) supply holes. Over the normal doping range, one impurity atom supphes one hole or one electron. Of these elements, boron (p-type), and phosphoms, arsenic, and antimony (n-type) are most commonly used. When... 

Another type of smoke mixture, a volatile hygroscopic chloride for thermal generation, has the U.S. Army designation HC, type C. It is composed of ca 6.7 wt % grained aluminum, 46.7 wt % zinc oxide ZnO, and 46.7 wt % hexachloroethane [67-72-17, The ratio of zinc oxide to... 

A solution of sulfur trioxide [7446-11-9] dissolved in chlorosulfonic acid [7990-94-5] CISO H, has been used as a smoke (U.S. designation FS) but it is not a U.S. standard agent (see Chlorosulfuric acid Sulfuric acid and sulfur trioxide). When FS is atomized in air, the sulfur trioxide evaporates from the small droplets and reacts with atmospheric moisture to form sulfuric acid vapor. This vapor condenses into minute droplets that form a dense white cloud. FS produces its effect almost instantaneously upon mechanical atomization into the atmosphere, except at very low temperatures. At such temperatures, the small amount of moisture normally present in the atmosphere, requires that FS be thermally generated with the addition of steam to be effective. FS can be used as a fill for artillery and mortar shells and bombs and can be effectively dispersed from low performance aircraft spray tanks. FS is both corrosive and toxic in the presence of moisture, which imposes limitations on its storage, handling, and use. 

Air filter A device that removes particulate matter from a gas flowing through it. These are classified as Absolute A high-efficiency particulate air filter that is at least 99.79% efficient in the removal of thermally generated mOnodisperse dioctylphthalate smoke particles with a diameter of 0.3 pm, also known as a HEPA filter. 

The reaction fails with the thermally generated nitrene on account of the thermal instability of the paracyclophane under the reaction conditions. 

Only a few diacvl peroxides see widespread use as initiators of polymerization. The reactions of the diaroyl peroxides (36, R=aryl) will be discussed in terms of the chemistry of BPO (Scheme 3.25). The rate of p-scission of thermally generated benzoyloxy radicals is slow relative to cage escape, consequently, both benzoyloxy and phenyl radicals are important as initiating species. In solution, the only significant cage process is reformation of BPO (ca 4% at 80 °C in isooctane) II"l only minute amounts of phenyl benzoate or biphenyl are formed within the cage. Therefore, in the presence of a reactive substrate (e.g. monomer), tire production of radicals can be almost quantitative (see 3.3.2.1.3). 

Sulfonyl nitrenes react with benzene to produce appreciable yields of aromatic substitution products. The nitrene thermally generated in benzene from 229 gives a monosubstitution product. When the reaction is carried out in mesitylene as a solvent, the two sulfonylnitrenes react with mesitylene to afford 230 (equation 140)135. 

Dark current comes from the thermal excitation of electrons in the detector material - thermally generated electrons can not be distinguished from photoelectrons. 

N-Alkoxylamines 88 are a class of initiators in "living" radical polymerization (Scheme 14). A new methodology for their synthesis mediated by (TMSlsSiH has been developed. The method consists of the trapping of alkyl radicals generated in situ by stable nitroxide radicals. To accomplish this simple reaction sequence, an alkyl bromide or iodide 87 was treated with (TMSlsSiH in the presence of thermally generated f-BuO radicals. The reaction is not a radical chain process and stoichiometric quantities of the radical initiator are required. This method allows the generation of a variety of carbon-centered radicals such as primary, secondary, tertiary, benzylic, allylic, and a-carbonyl, which can be trapped with various nitroxides. 

Silane radical atom transfer (SRAA) was demonstrated as an efficient, metal-free method to generate polystyrene of controllable molecular weight and low polydispersity index values. (TMSlsSi radicals were generated in situ by reaction of (TMSlsSiH with thermally generated f-BuO radicals as depicted in Scheme 14. (TMSlsSi radicals in the presence of polystyrene bromide (PS -Br), effectively abstract the bromine from the chain terminus and generate macroradicals that undergo coupling reactions (Reaction 70). 

Metal-vapor synthesis also prepares metallaboranes and metallacarboranes with oxidation of the metal. Thermally generated Ni, Co and Fe atoms react with the nido-carborane 2,6-C2B7H, and either cyclopentadiene, toluene, mesitylene, or... 

The Suzuki cross coupling reaction features in a synthesis of 4-arylcoumarins from the 4-halogeno derivatives c96JCS(Pl)2591> and in a route to the thieno[3,4-c]coumarin (8) from which coumarin 3,4-quinodimethane (9) can be thermally generated <96T3117>. 

Entries 10 and 11 are examples of reactions involving thermal generation of quinodimethanes. In Entry 12 a quinodimethane is generated by photoenolization and used in conjunction with an IMDA reaction to create the carbon skeleton found in the hamigerans, which are marine natural products having antiviral activity. 

Another elegant example of the thermal generation and subsequent intramolecular cycloaddition of an o-QM can be found in Snider s biomimetic synthesis of the tetracyclic core of bisabosquals.2 Treatment of the starting material with acid causes the MOM ethers to cleave from the phenol core (Fig. 4.3). Under thermal conditions, a proton transfer ensues from one of the phenols to its neighboring benzylic alcohol residue. Upon expulsion of water, an o-QM forms. The E or Z geometry of the o-QM intermediate and its propensity toward interception by formaldehyde, water, or itself, again prove inconsequential as the outcome is decided by the relative thermodynamic stabilities among accessible products. 

ELCD, HECD Electrolytic conductivity (Hall) detector Thermal generation of inorganic ions... 

Holscher, W., Steinhart, H., Formation pathways for primary roasted coffee aroma compounds, in ACS Symposium Series 543, Thermally Generated Flavors, 1994, 206. (CA120 105189t)... 

---