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161.
J. Boon G. Challa D. W. van Krevelen 《Journal of Polymer Science.Polymer Physics》1968,6(11):1835-1851
The influence of various thermal pretreatments on the nucleation of isotactic polystyrene has been studied quantitatively by dilatometry. A distinction can be made between nuclei still present above the melting point (“resistant” nuclei) and nuclei created by severe supercooling (“induced” nuclei). The number of spherulites formed has been determined for different combinations of supercooling and crystallization temperatures. The results are interpreted in a satisfactory manner by assuming that in severe supercooling induced nuclei are created, which may grow into effective nuclei at higher temperatures. The crystallization of a severely supercooled polymer is completely governed by these induced nuclei, because they outnumber the resistant nuclei by some orders of magnitude. The number of induced nuclei can be decreased by purifying the polymer (removing catalyst residues). When cooled polymer is heated to temperatures just above the melting point, the induced nuclei are destroyed (“reversible melting”), so that only the resistant nuclei, which are few in number, remain. These resistant nuclei govern the crystallization behavior of a polymer which has not previously been cooled. Their number decreases on heating to temperatures far above the melting point. 相似文献
162.
M. R. Boon 《Colloid and polymer science》1974,252(2):182-182
Ohne Zusammenfassung 相似文献
163.
Using photon correlation spectroscopy we have studied the Brownian motion of polystyrene balls. The results of the spectral analysis are consistent with the predicted effect for the long time behaviour of the velocity auto-correlation function. 相似文献
164.
Dong Xue-dong; Soh Cheong Boon; Gunawan Erry 《IMA Journal of Mathematical Control and Information》2002,19(3):229-243
Recently, some multiplicative groups of algebraic integers wereused to obtain quadrature amplitude modulation (QAM) signalspaces and to design error-correcting codes. This paper showsthat one subgroup of the multiplicative group of units in thealgebraic integer ring of each quadratic number field with uniquefactorization property Q(m), modulo the ideal (2n), can be usedto obtain a QAM signal space of 22n2 points with goodgeometrical properties, where n 3, m 1 (mod 8) and m is asquare-free rational integer. These QAM signals can be codedsuch that a differentially coherent method can be applied todemodulate the QAM signals. The multiplicative subgroups canalso be used to construct block codes over Gaussian integerswhich are able to correct some error patterns. 相似文献
165.
We review herein the surface chemical properties of silicon nanowires (SiNWs) and show how SiNWs can be used as platforms in doing chemistry in the nanorealm. In particular, the surfaces of HF-treated SiNWs (which are H-terminated) exhibit interesting chemical reactivities towards reductive deposition of metal ions such as silver, copper, palladium, etc., giving rise to metal particles or aggregates on the SiNW surfaces. By varying the concentration of the metal ions in solution, nanostructures of these metals of different shapes, sizes, and morphologies can be fabricated. The reductive growth of ligated Au–Ag clusters of single size, shape, composition, and structure, on the SiNWs was also investigated. Two interesting phenomena, the sinking cluster and the cluster fusion processes, were observed by TEM. These assemblies of metal nanoparticles on silicon nanowires may be considered as zero-dimensional nanodots, on one-dimensional nanowires. It is hoped that fabrication of these metallic nanodots on silicon nanowires will lead to new and novel composite materials of importance in nanotechnology. 相似文献
166.
Boon JM Shukla R Smith BD Licini G Scrimin P 《Chemical communications (Cambridge, England)》2002,(3):260-261
Two sulfonamide derivatives of tris(aminoethyl)amine selectively facilitate the translocation of a fluorescent phospholipid probe containing the phosphoethanolamine head-group across vesicle membranes. 相似文献
167.
168.
As an extension of earlier work on the crystallization kinetics of isotactic polystyrene, the spherulite growth rate in mixtures of isotactic polystyrene and benzophenone has been measured over a concentration range extending from pure polymer to a mixture containing about 30% benzophenone. The glass transition temperature has been measured over the entire range from pure polymer to pure benzophenone. For the mixtures the dependence of the growth rate on temperature is similar to that of the undiluted polymer. The addition of benzophenone causes a shift of the crystallization range to lower temperatures. For mixtures containing up to about 20% benzophenone, the maximum in the growth rate increases with increasing content of benzophenone. On addition of more benzophenone, the maximum rate is depressed. Taking into account the glass transition temperature of the mixtures, the influence of benzophenone on the melting point of isotactic polystyrene, and the volume fraction of polymer, we can describe the influence of benzophenone on the growth rate in a semiquantitative way. 相似文献
169.
Over recent years the ideas emerging from the discovery of dissipative structures have been applied to the problem of modeling the dynamic evolution of urban systems. A dynamic model of a central place system was developed and tested, as well as a preliminary intraurban model involving six urban actors. Here we present a further development of this latter model, where an initial investigation is made of the evolving structures which characterize the interaction of seven types of urban actor. A transportation network of both public and private modes is introduced explicity into the model, and a combined transportation—land-use model capable of exploring structural urban changes is presented, which will be used to explore the possible effects of changing circumstances and tastes on urban structure and organization. 相似文献
170.
M.R. Boon 《Physics letters. A》1973,42(7):481-482
In this paper the model used to explain the linear negative magnetoresistance of some amorphous semiconductors, in which scattering takes place as a result of interaction between electrons in extended and localised states is used to account for the differences in activation energy between conductivity and thermopower. 相似文献