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51.
A series of chain-extended PET samples were obtained by the use of different amounts of a diepoxide as chain extender, which
was prepared for this purpose. These samples exhibited different intrinsic viscosities and degrees of branching or cross-linking.
The effects of this differentiation on the thermal properties were studied by differential scanning calorimetry. The thermal
parameters studied were the glass transition temperature (Tg), the cold-crystallization temperature (Tcc), the melting temperature (Tm), the enthalpy (ΔHm) and the degree of crystallinity. The data revealed that, the higher the quantity of chain extender or the chain extension
time, the higher Tgand Tcc, but the lower Tmand ΔHm, i.e. the more amorphous the chain-extended samples, as also shown by density measurements.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
52.
Klaus Ziegler 《Journal of multivariate analysis》1997,62(2):233-272
Functional central limit theorems for triangular arrays of rowwise independent stochastic processes are established by a method replacing tail probabilities by expectations throughout. The main tool is a maximal inequality based on a preliminary version proved by P. Gaenssler and Th. Schlumprecht. Its essential refinement used here is achieved by an additional inequality due to M. Ledoux and M. Talagrand. The entropy condition emerging in our theorems was introduced by K. S. Alexander, whose functional central limit theorem for so-calledmeasure-like processeswill be also regained. Applications concern, in particular, so-calledrandom measure processeswhich include function-indexed empirical processes and partial-sum processes (with random or fixed locations). In this context, we obtain generalizations of results due to K. S. Alexander, M. A. Arcones, P. Gaenssler, and K. Ziegler. Further examples include nonparametric regression and intensity estimation for spatial Poisson processes. 相似文献
53.
We introduce a new class of experiments which provide graphic insights into the propagation of acoustic waves in anisotropic media. Simply stated, we have devised a means of observing the expanding acoustic wavefront from a point disturbance in a solid. The data may be viewed as a movie or a series of snapshots. The observed wavefronts represent the group-velocity surfaces of acoustic waves, which reflect the basic elastic anisotropy of the solid. The technique has been applied to coherent acoustic waves with frequencies in the megahertz range (at ambient temperatures) and to incoherent heat pulses in the hundred-gigahertz range (at liquid-helium temperatures). In this article, we first provide a pedagogical introduction to wave propagation in elastically anisotropic media, reviewing some early methods for visualizing acoustic waves. Next, we describe the “acoustic wavefront imaging” method and give representative results in crystals and composite materials. Finally, we show how this method relates to recent advances in phonon imaging and internal diffraction of ultrasound. 相似文献
54.
In this note, we characterize the regular probability measures satisfying the Choquet-Deny convolution equation =* on Abelian topological semigroups for a given probability measure . 相似文献
55.
Let (
t
)
t0 be a -semistable convolution semigroup of probability measures on a Lie groupG whose idempotent
0 is the Haar measure on some compact subgroupK. Then all the measures
1
are supported by theK-contraction groupC
K() of the topological automorphism ofG. We prove here the structure theoremC
K()=C()K, whereC() is the contraction group of . Then it turns out that it is sufficient to study semistable convolution semigroups on simply connected nilpotent Lie groups that have Lie algebras with a positive graduation. 相似文献
56.
57.
秦俊法 《广东微量元素科学》2007,14(10):11-19
根据全国人口普查资料,用指数函数拟合法计算了中国百岁老人的死亡率和生存率,得出中国人口的最高自然寿限为120岁,并预测到2010年中国百岁老人绝对数将达4万多人,届时每百万人口中将有30位百岁老人,比2000年增加1倍以上。 相似文献
58.
The natural products cis-p-menthane-1,7-diol (cis-IV), cis-p-menth-8-ene-1,7-diol (cis-I) and cis-p-menthane-1,7,8-triol (cis-II) are obtained starting from the corresponding cis-cyanohydrins, cis-2 and cis-7, respectively, by chemical transformation of the cyano into the hydroxymethyl group. The key step of the synthesis is the very high cis-selectivity (> or = 96 %) of the MeHNL-catalyzed HCN addition to 4-alkylcyclohexanones. From 4-isopropylcyclohexanone (1) the cyanohydrin cis-2 and from 4-(1-methylvinyl)cyclohexanone (6) the cyanohydrin cis-7 result almost quantitatively. Regioselective hydroxylation of cis-I affords the triol cis-II. X-ray crystal structure determinations of the final products confirm their cis-configuration. 相似文献
59.
60.
Simultaneous isolation and determination of esculin and rutin in natural materials using SPE and HPLC 总被引:1,自引:0,他引:1
Summary Esculin (ESC) and rutin (RUT) have been simultaneously isolated from pharmaceutical natural materials by solid phase extraction (SPE). Determination of both substances was performed by reversed phase high performance liquid chromatography (RPHPLC) with UV detection. Optimization of the separation conditions showed that simultaneous isolation and determination of rutin and esculin from pharmaceutical material was possible. The recovery obtained was not lower than 95±2%. 相似文献