Asymmetric laminate

In the symmetric case, three inner layers B-A-B of equal thickness are surrounded by two layers A of half thickness, yielding an overall layer sequence A-B-A-B-A [140], In the asymmetric case, all layers A and B have equal thickness, but the outer layers belong to two different fluids. Thus, the sequence refers to A-B-A-B. The time required to achieve a homogeneous concentration profile, i.e. the mixing time, is much longer for the asymmetric lamination. 

Ply orientations in a laminate are taken with reference to a particular loading direction, usually taken to be the direction of the maximum applied load, which, more often than not, coincides with the fibre direction to sustain the maximum load, and this is defined as the 0° direction. It is usual to choose balanced, symmetric laminates in design. A balanced laminate is one in which there are equal numbers of-1-0 and - 0 plies a symmetric laminate is one in which the plies are symmetric in terms of geometry and properties with respect to the laminate mid-plane. Hence, a laminate with a stacking sequence 0/90/-I-45/-45/-45/-I-45/90/0, which is written (0/90/ 45), is both balanced and symmetric. Balanced, symmetric laminates have a simplicity of response. In contrast, an unbalanced, asymmetric laminate will, in general, shear, bend, and twist under a simple axial loading. 

However, a simple cascade of two-input two-output mixers results in an asymmetric lamination. Symmetric lamination can be obtained with a modification of the first mixer into a three-input two-output mixer which builds up a (7//4, Hjl, HjA) type of laminate. This initial mixer can be followed by as many regular two-input two-output mixers as desired for the particular application. 

Reaction of 266a with suitable methyl alkyl amines having an asymmetric center at the neighboring carbon atom provided optically active amides 302, which after reduction with LAH gave optically active py razolylmethy-lamines 303 (92CB701). 

In order to gain some understanding of the behavior of an asymmetric membrane, let s consider a composite membrane consisting of two homogeneous membranes laminated together as shown in Figure 3. The same model has been studied recently by Henkens et al. (10). The first layer solution is ... 

Jun, W.J, and Hong C.S. (1990). Effects of residual shear strain on the cured shape of asymmetric cross-ply thin laminates. Composites Sci. Technoi. 38, 55-67. 

The ultrathin dense barrier layer and the thick porous underlayer can be separately fabricated from various materials and laminated together to give an asymmetric membrane. Thus a thin barrier membrane can be formed on the porous matrix by casting from a polymer solution, in-situ polymerization, or in-situ-interfacial condensation polymerization. 

Membranes classified under (c) in the introductory section are of considerable importance. Most natural membranes are macroscopically non-homogeneous. In artificial membranes non-homogeneity may be introduced either deliberately (laminates, asymmetric membranes) or spuriously (e.g. skin layers on films made by extrusion). Variation of S and Dx across the membrane, i.e. in the X direction, is of particular interest non-homogeneity along the plane of the membrane is important in certain special cases, e.g. charged mosaic membranes, which are not of immediate interest here. Also asymmetric membranes prepared for the sole purpose of producing an ultrathin active layer to maximize permeation flux are outside the scope of the present discussion. 

Olefinic double-bond isomerization is probably one of the most commonly observed and well-studied reactions that uses transition metals as catalysts [1]. However, prior to our first achievement of asymmetric isomerization of allylamine by optically active Co(I) complex catalysts [2], there were only a few examples of catalytic asymmetric isomerization, and these were characterized by very low asymmetric induction (<4% ee) [3], In 1978 we reported that an enantioselective hydrogen migration of a prochiral allylamine such as AVV-diethylgerany-lamine, (1) or N V-diethylnerylamine (2) gave optically active citronellal ( )-enamine 3 with about 32% ee utilizing Co(I)-DIOP [DIOP = 2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis(diphenylphosphino)butane] complexes as the catalyst (eq 3.1). 

When using an asymmetric flow ratio (5 1) for still better flow visualization, the regularity of the multi-laminated pattern is the most striking feature (see Figure 1.92) [39]. 

Theoretical analysis of mixing via symmetric and asymmetric multi-lamination... 

Delorme D, Berthelette C, Lavoie R, Roberts E (1998) Asymmetric synthesis of diarylmethy-lamines preparation of selective opioid delta receptor ligands. Tetrahedron Asymmetry 9 3963-3966... 

Jessop and co-workers have pointed out that homogeneous catalysis in supercritical fluids can offer high rates, improved selectivity, and elimination of mass-transfer problems.169 They have used a ruthenium phosphine catalyst to reduce supercritical carbon dioxide to formic acid using hydrogen.170 The reaction might be used to recycle waste carbon dioxide from combustion. It also avoids the use of poisonous carbon monoxide to make formic acid and its derivatives. There is no need for the usual solvent for such a reaction, because the excess carbon dioxide is the solvent. If the reaction is run in the presence of dimethy-lamine, dimethylformamide is obtained with 100% selectivity at 92-94% conversion.171 In this example, the ruthenium phosphine catalyst was supported on silica. Asymmetric catalytic hydrogenation of dehydroaminoacid derivatives (8.16) can be performed in carbon dioxide using ruthenium chiral phosphine catalysts.172... 

The hydrosilylation of nitrones provides a route to N,N-disubstituted hydroxy-lamines. The use of an Ru/ToIBINAP complex was reported to give the best results in the asymmetric hydrosilylation of nitrones. Nitrone (3.198) was converted into hydroxylamine (3.199) in reasonable yield and good enantioselectivity. 

Worsley and coworkers utilized an SVET to investigate the corrosion at cut edges of coil-coated steel [143]. Samples were hot-dip galvanized steel, chromate treated and coated on both sides by a 5-pm epoxy-based polymer. A 140-p.m PVC laminate coating was applied to one or both sides of the sheet to produce asymmetrically and symmetrically coated samples. Measurements were done in 0.86 M NaCl solution. Interestingly, the measurements of Kne... 

Prombut et al. [77] used carbon fibre epoxy (T7(X)/M21) laminates in asymmetric double cantilever beam (ADCB) and asymmetric mixed-mode flexure (AMMF) specimens besides standard mode I, mode II and mixed mode I/II flexure specimens in their investigation, and they complemented the experiments with numerical simulations. Although they succeeded in preventing jumps in the delamination plane and achieved reasonable crack front profiles, they concluded that more work would be needed to establish a crack propagation criterion for the 0°/45° interface. 

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