Asymmetric tracking

Phelan, P. L. (1992). Evolution of sex pheromones and the role of asymmetric tracking. In Insect Chemical Ecology An Evolutionary Approach, eds. B. D. Roitberg and M. B. Isman, pp. 265-314. New York Chapman Hall. 

Evolution of mate-signaling in moths phylogenetic consideration and predictions from the asymmetric tracking hypothesis. In Evolution of Insect Mating Systems in Insects and Arachnids, eds. J. C. Choe and B. J. Crespi, pp. 240-256. Cambridge Cambridge University Press. 

Kravets, L.I., Dmitriev, S.N., Sleptsov, V.V. and Elinson, V.M. 2002. Production of asymmetric track membranes with a high permeability and separation selectivity. DesglinMj 144 27-34. 

Becker25 improved the biaxial extension apparatus of Blatz and Ko in such a way that pairs of different values of Xj and X2, i.e., general biaxial extensions, can be obtained. Here, pairs of two rectangular tracks are connected to the pulling rods in asymmetric fashion, as shown in Fig. 7. With the use of this apparatus he obtained valuable information about the behavior of dW/d/j and dW/d/2 for natural rubber vulcanizate. His principal results are presented in Section V. 

Articles dealing with the epimerization reaction are not easy to find. The term epimerization is often not mentioned in the abstract or title of an article and hence the discovery of a specific publication is sometimes pure coincidence. Furthermore, some authors use the term isomerization instead of epimerization, which naturally makes the search even more complicated. By definition, epimerization is the alteration of one asymmetric centre (the given compound has more than one asymmetric centre) but isomerization is the process whereby a compound is converted into an isomer [9]. Isomerization is therefore a more general term, resulting in an abundance of references and making it virtually impossible to track down all the publications of interest. We therefore apologize if we have omitted any crucial publications from this review. 

Cross-section structure. An anisotropic membrane (also called asymmetric ) has a thin porous or nonporous selective barrier, supported mechanically by a much thicker porous substructure. This type of morphology reduces the effective thickness of the selective barrier, and the permeate flux can be enhanced without changes in selectivity. Isotropic ( symmetric ) membrane cross-sections can be found for self-supported nonporous membranes (mainly ion-exchange) and macroporous microfiltration (MF) membranes (also often used in membrane contactors [1]). The only example for an established isotropic porous membrane for molecular separations is the case of track-etched polymer films with pore diameters down to about 10 run. All the above-mentioned membranes can in principle be made from one material. In contrast to such an integrally anisotropic membrane (homogeneous with respect to composition), a thin-film composite (TFC) membrane consists of different materials for the thin selective barrier layer and the support structure. In composite membranes in general, a combination of two (or more) materials with different characteristics is used with the aim to achieve synergetic properties. Other examples besides thin-film are pore-filled or pore surface-coated composite membranes or mixed-matrix membranes [3]. 

Symmetric membranes and asymmetric membranes are two basic types of membrane based on their structure. Symmetric membranes include non-porous (dense) symmetric membranes and porous symmetric membranes, while asymmetric membranes include integrally skinned asymmetric membranes, coated asymmetric membranes, and composite membranes. A number of different methods are used to prepare these membranes. The most important techniques are sintering, stretching, track-etching, template leaching, phase inversion, and coating (13,33). 

Our efforts were amply rewarded and a real breakthrough was achieved when, very unexpectedly, finding that the addition of a base had a tremendous impact on the transformation to the desired sulfoxide enantiomer [24]. We now knew that our sulfide could in fact be oxidized in an asymmetric fashion so we were on the right track Some facts for this crucial progress will be described in more detail below. 

Fitzgerald PG, Stump E (1997) Cretaceous tmd Cenozoic episodic denudation of the Transantarctic Mountains, Antarctica New constraints from apatite fission track thermochronology in the Scott Glacier region. J Geophys Res 102 7747-7765 Fitzgerald PG, Sandiford M, Barrett PJ, Gleadow AJ (1986) Asymmetric extension associated with uplift and subsidence in the Transantarctic Mountains and Ross Embayment. Earth Planet Sci Lett 81(l) 67-78... 

For PET track membranes treated in air plasma, a decrease in their thickness and an increase in the effective pore diameter were observed. Additionally, the pores became asymmetric. The permeability increased and depended on the pH of the filtered solution. The membrane surface was no longer smooth, because of the faster etching of the amorphous areas than of the crystalline areas (Dmitriev et al. 2002). The surface of the PET membrane becomes hydrophilic and, in properly chosen conditions, the surface properties are stable (Dmitriev et al. 1995). In polypropylene hollow fiber microporous membranes (PPHFMMs), both the O and the N functionalities were found and numerous cracks could be seen on the surface. Generally, a decrease in the flow rate was observed as a result of faster cake formation and its compaction. The main positive result of the plasma treatment was a significant improvement in the membrane regeneration characteristics (Yu et al. 2008b). 

Both the etching and deposition of thin diamond-like films were observed for PET track membranes treated with a mixture of N2 and cyclohexane plasma. The effective pore diameter increases and the membrane remains asymmetric. Such a modification improves the hydrodynamic characteristics of the track membranes— an increase in the filtration rate constant was observed however, this did not cause a drastic change in the value of the water permeability (Kravets et al. 2002). The plasma polymerization of the allylamine and AAc deposited a nonconsistent layer that decreased and partially blocked the pores of the PET track membranes (Toufik et al. 2002). Polymerization of lH,lH,2H-perfluoro-l-octene on the track PET membranes was aimed at protecting one side of the membrane against etching by the alkali (Trofimov et al. 2009) and in that way to change the pore shape... 

Membranes composed of the PET track membrane and a layer of pp-pyrrole showed asymmetric conductivity. Such membranes can be used to create chemical and biochemical sensors (Kravets et al. 2010). 

Flat-sheet asymmetric-skinned membranes made from synthetic polymers (also copolymers and blends), track-etched polymer membranes, inorganic membranes with inorganic porous supports and inorganic colloids such as Zr02 or alumina with appropriate binders, and melt-spun thermal inversion membranes (e.g., hollow-fiber membranes) are in current use. The great majority of analytically important UF membranes belong to the first type. They are usually made of polycarbonate, cellulose (esters), polyamide, polysulfone, poly(ethylene terephtha-late), etc. 

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