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11.
James E. Sealey Gamini Samaranayake Jason G. Todd Wolfgang G. Glasser 《Journal of Polymer Science.Polymer Physics》1996,34(9):1613-1620
Cellulose esters with linear aliphatic acyl substituents ranging in size from C12 (lauric acid) to C20 (eicosanoic acid) were prepared in homogeneous solution (DMAc/LiCl) using a novel synthetic method based on the use of a mixed p-toluenesulfonic/carboxylic acid anhydride. The resulting waxy cellulose esters had a high degree of substitution (DS), between 2.8 and 2.9, and showed little degradation. Thermal analysis of these cellulose derivatives by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) revealed a series of transitions that represented motion by both ester substituents and cellulosic main chain. Broad crystallization and melting transitions attributed to side-chain crystallinity were observed in the range between −19 and +55°C; these side-chain Tm and Tc transition temperatures increased by 10°C per carbon atom of the ester substituent. The Tg of these derivatives increased linearly with increasing substituent size from 94°C for C12 (cellulose laurate) to 134°C for C20 (cellulose eicosanoate). Evidence of “main-chain” crystallization was not observed for these samples, except in the case of peracetylated C12 and C14 esters, which had Tm values of 96°C and 107°C, respectively. © 1996 John Wiley & Sons, Inc. 相似文献
12.
Gamini Gunawardena Graham Hills Irene Montenegro Benjamin Scharifker 《Journal of Electroanalytical Chemistry》1982,138(2):255-271
The electrochemical nucleation of mercury on vitreous carbon from solutions of mercurous nitrate in aqueous KNO3 has beenstudied as a function of overpotential and mercurous ion concentration. The nucleation is predominantly progressive and the singlepotential step experiment leads to nuclear number densities and to steady state nucleation rate constants. The double potentialstep experiment is complicated by the progressive nature of the nucleation and largely invalidated by the resultant dispersion ofnuclear sizes. The interpretation of the transients from potentiostatic-galvanostatic and related pulse trains are also complicatedby the similar features and it is suggested that equilibrium steady state and non-steady properties of nucleating systems arebest studied at very small electrodes at which a single nucleus is formed. 相似文献
13.
Members of all known clathrasil families have been synthesized from aqueous silica solutions under hydrothermal conditions in the presence of their characteristic guest molecules and in the absence of atmospheric gases. The small cages of the products, otherwise filled with nitrogen, were found to be empty. In addition to clathrasils, silica-ZSM-48 was obtained as a reaction product in the absence of atmospheric gases and pyrrolidine as the guest. It appears that small “help gas” molecules such as nitrogen play only a minor role in the stability of clathrasil frameworks unlike in the case of some clathrate hydrates. A comparison of rates of formation of clathrasils synthesized in air and in the absence of “help gases” is also presented. 相似文献
14.
C.K.Gamini Piyadasa 《Optics Communications》2012,285(24):4878-4883
The paper shows that the boundary diffraction wave originating at an edge is an omnidirectional cylindrical wave. The experimental set-up used to demonstrate this property employs a He-Ne laser beam. The beam is split into three beams using a glass plate. One of the beams passes straight through, the second beam passes through the glass plate and the third beam is the reflected beam. It is shown that the interference patterns are observed in all three beams. Analysis of these patterns shows that the boundary diffraction wave originating from the edge is an omnidirectional cylindrical wave. This analysis also provides strong evidence that the boundary diffraction wave travels not only within the beam where it originates but also to the neighboring coherent beam. The energy re-distribution was also shown to be dependent on the wavelength of the incident light beam and hence provides further evidence as to why longer wave lengths disperse more compared to shorter wavelengths in white light diffraction by an edge. 相似文献
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Iridium and rhodium are among the platinum group metals. The properties, production processes, and aqueous chemistry of both metals are reviewed. The separation of Ir(IV) and Rh(III) from hydrochloric acid solution is dependent on the characteristics of the solvent extraction systems. In most of the extraction conditions, Ir(IV) is selectively extracted over Rh(III) by either amines or neutral extractants. Rh(I) can be selectively extracted over Ir(III) by neutral extractants after Rh(III) is reduced in the presence of a reducing agent. The separation of these two metals using cationic extractants has also been reported. Although selective extraction of one metal over the other is possible, more efficient solvent extraction systems need to be developed. 相似文献
17.
We consider an extension of the optimal searcher path problem (OSP), where a searcher moving through a discretised environment may now need to spend a non-uniform amount of time travelling from one region to another before being able to search it for the presence of a moving target. In constraining not only where but when the search of each cell can take place, the problem more appropriately models the search of environments which cannot be easily partitioned into equally sized cells. An existing OSP bounding method in literature, the MEAN bound, is generalised to provide bounds for solving the new problem in a branch and bound framework. The main contribution of this paper is an enhancement, discounted MEAN (DMEAN), which greatly tightens the bound for the new and existing problems alike with almost no additional computation. We test the new algorithm against existing OSP bounding methods and show it leads to faster solution times for moving target search problems. 相似文献
18.
Jack E. Baldwin Bulbul Chakravarti Leslie D. Field John A. Murphy Kathy R. Whitten Sir Edward P. Abraham Gamini Jayatilake 《Tetrahedron》1982,38(18):2773-2776
The title peptide () has been synthesized and incubated with an active cell-free extract of , no conversion to active antibiotics was observed; however on co-incubation with the Arnstein tripeptide (ACV) (), strong inhibition of the conversion of ACV to isopenicillin N was observed. 相似文献
19.
Gamini Gunawardena Graham Hills Irene Montenegro 《Journal of Electroanalytical Chemistry》1982,138(2):241-254
A study has been made of the electrochemical nucleation of silver on vitreous carbon from aqueous solutions of silver nitrate.The nucleation is shown to be progressive and mass transferred controlled. The rate of nucleation is somewhat better described bythe atomistic theory than by classical theories. The addition of EDTA reduces the rate of nucleation as the result, it is suggested,of the adsorption of EDTA by the graphite surface. The sensitivity of the rate of the nucleation to the condition of the graphitesurface is also shown by the effects of changing the salvation acidity. 相似文献
20.
Experimental results obtained by membrane equilibria, osmotic pressure, viscosity and circular dichroism measurements on alginate and pectate solutions in the presence of Ca2+ ions are presented. From equilibrium dialysis data both electrostatic and cooperative interactions seem to describe the binding process of Ca2+ ions onto polymer chains. An increase of the number-average molecular weight M̄n for both poly-saccharides with calcium ion concentration is observed. An increase of polymer dimensions can well account for the observed increase of the intrinsic viscosity [η] with bound Ca2+ ion concentration at several ionic strengths. 相似文献