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Center stable

Even when the a-Si H contains a relatively large concentration of metastable centers, stable solar-cell operation can be achieved by making the i layers thin (= 0.2 /im) (Hanak and Korsun, 1982). The data in Fig. 15 show that no degradation is observed in p-i-n cells with thin i layers, but as the i layer thickness exceeds —0.2 pm, all the photovoltaic parameters (Foe, /sc, FF) exhibit some degradation, with the largest changes occurring in the fill factor. The improved stability of thin cells is related to the observation that the metastable centers are activated by recombination... [Pg.29]

The kinetic curve would then be the result of two curves, one representing the 1st order decay attributed to isospecific polymerization centers, and the other representing a stationary state attributed to the less stereospecific centers. This expression can be credited with taking into consideration a stationary state and, furthermore, it is in agreement with the inverse correlation between productivity and isotacticity of the polymer found experimentally. In fact, assuming Is to be the isotacticity of propylene produced by the isospecific centers, unstable with time, and IA the isotacticity of polypropylene produced by the less specific centers, stable with time, the total isotactic index IIt is given by the expression ... [Pg.32]

Kelley, A. (1967). The stable, center-stable, center, center-unstable and unstable manifolds. J. Diff. Eqs., 3, 546-70. [Pg.235]

Ytterbium has a bright silvery luster, is soft, malleable, and quite ductile. While the element is fairly stable, it should be kept in closed containers to protect it from air and moisture. Ytterbium is readily attacked and dissolved by dilute and concentrated mineral acids and reacts slowly with water. Ytterbium has three allotropic forms with transformation points at -13oC and 795oC. The beta form is a room-temperature, face-centered, cubic modification, while the... [Pg.196]

Research activities in the area of PODs containing aromatic groups have been centered around the production of highly processible, soluble, and thermally stable polymers. In this particular class of PODs, the imide-and phenylene-containing backbones have been widely explored. [Pg.534]

The discussion centers on heat stabilizers for PVC because this polymer is the most important class of halogenated polymers requiring these chemical additives. PVC of ideal chemical stmcture (1) should be a relatively stable compound as predicted from model studies using 2,4,6-trichloroheptane [13049-21-3] (2) (1). [Pg.544]

Replacement of Labile Chlorines. When PVC is manufactured, competing reactions to the normal head-to-tail free-radical polymerization can sometimes take place. These side reactions are few ia number yet their presence ia the finished resin can be devastating. These abnormal stmctures have weakened carbon—chlorine bonds and are more susceptible to certain displacement reactions than are the normal PVC carbon—chlorine bonds. Carboxylate and mercaptide salts of certain metals, particularly organotin, zinc, cadmium, and antimony, attack these labile chlorine sites and replace them with a more thermally stable C—O or C—S bound ligand. These electrophilic metal centers can readily coordinate with the electronegative polarized chlorine atoms found at sites similar to stmctures (3—6). [Pg.546]

When using a cation source in conjunction with a Friedel-Crafts acid the concentration of growing centers is most often difficult to measure and remains unknown. By the use of stable carbocation salts (for instance trityl and tropyhum hexachloroantimonate) the uncertainty of the concentration of initiating cations is eliminated. Due to the highly reproducible rates, stable carbocation salts have been used in kinetic studies. Their use, however, is limited to cationicaHy fairly reactive monomers (eg, A/-vinylcarbazole, -methoxystyrene, alkyl vinyl ethers) since they are too stable and therefore ineffective initiators of less reactive monomers, such as isobutylene, styrene, and dienes. [Pg.245]

A similar effect occurs in highly chiral nematic Hquid crystals. In a narrow temperature range (seldom wider than 1°C) between the chiral nematic phase and the isotropic Hquid phase, up to three phases are stable in which a cubic lattice of defects (where the director is not defined) exist in a compHcated, orientationaHy ordered twisted stmcture (11). Again, the introduction of these defects allows the bulk of the Hquid crystal to adopt a chiral stmcture which is energetically more favorable than both the chiral nematic and isotropic phases. The distance between defects is hundreds of nanometers, so these phases reflect light just as crystals reflect x-rays. They are called the blue phases because the first phases of this type observed reflected light in the blue part of the spectmm. The arrangement of defects possesses body-centered cubic symmetry for one blue phase, simple cubic symmetry for another blue phase, and seems to be amorphous for a third blue phase. [Pg.194]

Iron (qv) exists in three aHotropic modifications, each of which is stable over a certain range of temperatures. When pure iron free2es at 1538°C, the body-centered cubic (bcc) 5-modification forms, and is stable to 1394°C. Between 1394 and 912°C, the face-centered cubic (fee) y-modification exists. At 912°C, bcc a-iron forms and prevails at all lower temperatures. These various aHotropic forms of iron have different capacities for dissolving carbon. y-Iron can contain up to 2% carbon, whereas a-iron can contain a maximum of only about 0.02% C. This difference in solubHity of carbon in iron is responsible for the unique heat-treating capabilities of steel The soHd solutions of carbon and other elements in y-iron and a-iron are caHed austenite and ferrite, respectively. [Pg.236]

The reaction of a mixture of 1,5,9-cyclododecatriene (CDT), nickel acetylacetonate [3264-82-2], and diethylethoxyalurninum in ether gives red, air-sensitive, needle crystals of (CDT)Ni [12126-69-1] (66). Crystallographic studies indicate that the nickel atom is located in the center of the 12-membered ring of (CDT)Ni (104). The latter reacts readily with 1,5-cyclooctadiene (COD) to yield bis(COD) nickel [1295-35-8] which has yellow crystals and is fairly air stable, mp 142°C (dec) (20). Bis(COD)nickel also can be prepared by the reaction of 1,5-COD, triethylaluminum, and nickel acetylacetonate. [Pg.12]

Titanium Trifluoride. The trifluoride (121) is a blue crystalline soHd, density 2980 kg/m, ia which the titanium atoms are six-coordinate at the center of a slightly distorted octahedron, where the mean Ti—F distance is 197 pm. Titanium trifluoride [13470-08-1] is stable ia air at room temperature but decomposes to titanium dioxide when heated to 100°C. It is insoluble ia water, dilute acid, and alkaUes but decomposes ia hot concentrated acids. The compound sublimes under vacuum at ca 900°C but disproportionates to titanium and titanium tetrafluoride [7783-63-3] at higher temperatures. [Pg.129]


See other pages where Center stable is mentioned: [Pg.46]    [Pg.61]    [Pg.120]    [Pg.538]    [Pg.46]    [Pg.61]    [Pg.120]    [Pg.538]    [Pg.121]    [Pg.175]    [Pg.197]    [Pg.203]    [Pg.221]    [Pg.223]    [Pg.223]    [Pg.439]    [Pg.445]    [Pg.109]    [Pg.316]    [Pg.240]    [Pg.44]    [Pg.45]    [Pg.89]    [Pg.13]    [Pg.442]    [Pg.452]    [Pg.452]    [Pg.454]    [Pg.110]    [Pg.179]    [Pg.160]    [Pg.461]    [Pg.524]    [Pg.32]    [Pg.41]    [Pg.41]    [Pg.333]    [Pg.333]    [Pg.344]    [Pg.259]   
See also in sourсe #XX -- [ Pg.282 ]




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