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61.
The anisotropic form factor of polystyrene (PS) chains during tensile and simple shear flows in the melt has been measured by small angle neutron scattering (SANS) on quenched samples containing deuterium labeled chains. For all tensile experiments, carried out in a wide range of strain rates, including linear viscoelastic behaviour, the chain conformation is well predicted by a temporary network model involving the recoverable strain. For binary blends of two PS with different molecular weight, the technique allows to characterize the chain conformation of either species. The scattering patterns of sheared samples show that the principal directions of molecular orientation depend on the magnitude of the scattering vector q: At high q (local level on the chain) the orientation is close to 45° with respect to the shear axis, whereas at low q the chains appear to be almost aligned with the stream lines. 相似文献
62.
Deep level transient spectroscopy has been used to observe the reduced concentrations of vacancy-related defects in γ-irradiated n-type Si containing hydrogen atoms. Data are presented on the efficiency and depth of this damage reduction as a function of the duration and temperature of the exposure to the plasma used to introduce the atomic hydrogen. A 3-hour exposure in an H plasma at 300°C prior to irradiation reduced the concentrations of the O-V, V-V and P-V centres by half or more to a depth of ~20 μm, compared to the control samples. 相似文献
63.
64.
Roger M Guenoun P Muller F Belloni L Delsanti M 《The European physical journal. E, Soft matter》2002,9(4):313-326
The concentration profiles of monomers and counterions in star-branched polyelectrolyte micelles are calculated through Monte
Carlo simulations, using the freely jointed chain model. We have investigated the onset of different regimes corresponding
to the spherical and Manning condensation of counterions as a function of the strength of the Coulomb coupling. The Monte
Carlo results are in fair agreement with the predictions of Self-Consistent-Field analytical models. We have simulated a real
system of diblock copolymer micelles of (sodium-polystyrene-sulfonate)(NaPSS)-(polyethylene-propylene)(PEP) with f = 54 hydrophilic branches of N = 251 monomers at room temperature in salt-free solution. The calculated form factor compares nicely with our neutron scattering
data.
Received 18 July 2002 and Received in final form 11 October 2002
RID="a"
ID="a"e-mail: roger@drecam.saclay.cea.fr 相似文献
65.
Muller T Hulliger J Seichter W Weber E Weber T Wubbenhorst M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(1):54-61
A new type of dumb-bell-shaped host molecule (6-8) has been synthesised, of which 1,8-bis((1)-adamantyl)-1,3,5,7-octatetrayne (8 = BAOT) forms an open porous architecture when cocrystallised with a number of typical solvent molecules. Adamantyl substituents attached to a tetraalkyne spacer build up the walls of parallel channels wherein guest molecules are aligned. Surprisingly, the tetraalkyne unit is significantly bent. Desolvation experiments provide evidence for a reversible inclusion of guests. In the case of the inclusion of 2-butanone, a partial substitution by symmetrical and asymmetrical long-chain chromophores during crystallisation was possible. Stained crystals showed optical frequency doubling. The crystal structure analysis revealed a centric space group, although considerable translational and orientational disorder was present. Application of scanning pyroelectric microscopy revealed that the growth of inclusion compounds with 2-butanone produced polar ordering of guest molecules, which were aligned in two macro-domains of opposing polarity. The resulting orientation of the carbonyl dipoles is in agreement with the theoretical prediction of a Markov model of spontaneous polarity formation based on molecular recognition processes on growing crystal faces. The present case represents a new example of a property-driven supramolecular synthesis. 相似文献
66.
The study of reductive group actions on a normal surface singularityX is facilitated by the fact that the group Aut X of automorphismsof X has a maximal reductive algebraic subgroup G which containsevery reductive algebraic subgroup of Aut X up to conjugation.If X is not weighted homogeneous then this maximal group G isfinite (Scheja, Wiebe). It has been determined for cusp singularitiesby Wall. On the other hand, if X is weighted homogeneous butnot a cyclic quotient singularity then the connected componentG1 of the unit coincides with the C* defining the weighted homogeneousstructure (Scheja, Wiebe, Wahl). Thus the main interest liesin the finite group G/G1. Not much is known about G/G1. Ganterhas given a bound on its order valid for Gorenstein singularitieswhich are not log-canonical. Aumann-Körber has determinedG/G1 for all quotient singularities. We propose to study G/G1 through the action of G on the minimalgood resolution of X. If X is weightedhomogeneous but not a cyclic quotient singularity, let E0 bethe central curve of the exceptional divisor of . We show that the natural homomorphism GAut E0 haskernel C* and finite image. In particular, this re-proves therest of Scheja, Wiebe and Wahl mentioned above. Moreover, itallows us to view G/G1 as a subgroup of Aut E0. For simple ellipticsingularities it equals (ZbxZb)Aut0 E0 where b is theself-intersection number of E0, ZbxZb is the group of b-torsionpoints of the elliptic curve E0 acting by translations, andAut0 E0 is the group of automorphisms fixing the zero elementof E0. If E0 is rational then G/G1 is the group of automorphismsof E0 which permute the intersection points with the branchesof the exceptional divisor while preserving the Seifert invariantsof these branches. When there are exactly three branches weconclude that G/G1 is isomorphic to the group of automorphismsof the weighted resolution graph. This applies to all non-cyclicquotient singularities as well as to triangle singularities.We also investigate whether the maximal reductive automorphismgroup is a direct product GG1xG/G1. This is the case, for instance,if the central curve E0 is rational of even self-intersectionnumber or if X is Gorenstein such that its nowhere-zero 2-form has degree ±1. In the latter case there is a naturalsection G/G1G of GG/G1 given by the group of automorphisms inG which fix . For a simple elliptic singularity one has GG1xG/G1if and only if E0 · E0 = 1. 相似文献
67.
Marie-Paule Muller 《Topology》1980,19(2):199-201
68.
69.
The synthesis of three lipophilic n-dodecyl tetraazacycloalkanes is described. Extraction of Cu(II), Cd(II) and Pb(II) is related. 相似文献
70.
The superconducting transition temperature has been investigated as a function of composition and degree of long-range order in a number of binary and ternary A 15-type phases on Cr and Mo. It is concluded that these compounds are unlike the typical Nb- or V- based phases with the same structure. The maximum Tc does usually not occur at the ideal composition. Nevertheless, a correlation has been found between Tc and the degree of order. 相似文献