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971.
We study the existence of solutions u:R3→R2 for the semilinear elliptic systems where W:R2→R is a double well symmetric potential. We use variational methods to show, under generic non-degenerate properties of the set of one dimensional heteroclinic connections between the two minima a± of W, that (0.1) has infinitely many geometrically distinct solutions u∈C2(R3,R2) which satisfy u(x,y,z)→a± as x→±∞ uniformly with respect to (y,z)∈R2 and which exhibit dihedral symmetries with respect to the variables y and z . We also characterize the asymptotic behavior of these solutions as |(y,z)|→+∞. 相似文献
equation(0.1)
−Δu(x,y,z)+∇W(u(x,y,z))=0,
972.
Giovanni Frenza Claudio Fuganti Piero Grasselli Giuseppe Pedrocchi-fantoni 《Journal of carbohydrate chemistry》2013,32(3):225-248
Abstract The erythro and threo chiral C5 methyl ketones (4) and (5), prepared from the (2S, 3R)-methyl diel (1b), were converted into the phenylsulfenimines (6) and (7), which, in turn, on reaction with allyl-magnesiutn bromide, yielded after acid hydrolysis and benzoylation, the diastereoisomeric C8-N-aminodiol derivatives (9) and (11), with threo stereochemistry relative to positions 4 and 5. Ozonolysis of (9) and (11) yielded the l-arabino and l-xylo 3-O-methyl branched aminodeoxysugar derivatives (13) and (15), respectively. Using diallylzinc as the reagent, the diastereoisomeric erythro products (8) and (10) were obtained. The latter materials gave the l-ribo-and l-lyxo-(lL-vancosamine) derivatives (12) and (14) upon oxonolysis. The 1H and 13C NMR spectra of the four isomeric aminodeoxysugar derivatives (12)—(15) were discussed. 相似文献
973.
When a chiral dopant is dissolved in an achiral liquid crystal medium, the whole sample organizes into a helical structure with a characteristic length-scale of the order of microns. The relation between chirality at these quite different length-scales can be rationalized by a relatively simple model, which retains the relevant factors coming into play: the molecular shape of the chiral dopant, which controls the chirality of short range intermolecular interactions, and the elastic properties of the nematic environment, which control the restoring torques opposing distortion of the director. In this tutorial review the relation between molecular and phase chirality will be reviewed and several applications of the chiral doping of nematic LCs will be discussed. These range from the exploitation of the amplified molecular chirality for stereochemical purposes (e.g., the determination of the absolute configuration or the enantiomeric excess), to newer applications in physico-chemical fields. The latter take advantage of the periodicity of the chiral field, with length-scales ranging from hundreds to thousands of nanometres, which characterise the cholesteric phase. 相似文献
974.
Ridi F Fratini E Luciani P Winnefeld F Baglioni P 《Journal of colloid and interface science》2011,364(1):118-124
The kinetics of the cement hydration reaction is a relevant issue in the cement research field, particularly in the presence of additional inorganic and organic components that consistently increase the complexity of the cement paste. In the present study, the hydration reaction of pure tricalcium silicate has been monitored by different calorimetric approaches: the conventional Isothermal Conduction Calorimetry (IC) and a novel Differential Scanning Calorimetry (DSC) protocol. The measured hydration curves have been modeled by using the Boundary Nucleation and Growth Model (BNGM) to extract thermodynamic parameters of the early stages of the hydration reaction. IC and DSC methods provide similar results in terms of rate constants, linear growth, and nucleation rates even though the IC accesses the total evolved heat while DSC discloses the fraction of unreacted water. The validation of the DSC approach as a reliable analytical method to the study of cement hydration kinetic is of particular importance because it allows following very long hydration processes, such as those of pastes containing organic retarders or superplasticizers. The thermodynamic and kinetic parameters for the tricalcium silicate setting has been also evaluated and discussed as a function of the surface area of the powder. 相似文献
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