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101.
The Tikhonov regularization is applied to convert specific molar volume data of binary solutions of dimethyl sulfoxide with
a number of acrylates and with styrene into their second- and first-partial derivatives with respect to mole fraction under
constant temperature and pressure. Generalized Cross Validation is used to guide the selection of the regularization parameter
that keeps noise amplification under control. The resulting first derivative is then used to compute the partial molar volumes.
These are compared against that obtained by the traditional method of least-squares fitting of excess molar volumes. Some
of the advantages of the current approach and possible extension to other partial molar quantities are briefly discussed. 相似文献
102.
Hongqian Bao Jinhua Hu Leong Huat Gan Lin Li 《Journal of polymer science. Part A, Polymer chemistry》2009,47(23):6682-6692
Herein, we report the synthesis of a comb‐like pH‐sensitive graft copolymer, poly[(2‐dimethylamino)ethyl methacrylate]‐graft‐chitosan, using atom transfer radical polymerization (ATRP) and active ester conjugation methods. The utilization of ATRP guaranteed the narrow molecular weight distribution of the side chains, which further led to the low polydispersity of the copolymer aggregates. The active ester reaction took place in the mild and homogeneous solutions, and the graft ratio reached 58%. The pH‐responsive association behavior of the graft copolymer in aqueous solution was examined by potentiometric titration, laser light scattering, surface tensiometry, and transmission electron microscopy. Because of the difference in proton dissociation between the amine groups of chitosan and DMAEMA segments, the copolymer exhibited the different conformations with pH variation: random coils at pH ∼ 4, core‐shell structured micelles at pH 5–6, double‐layered hard spheres at pH ∼ 7, and larger aggregates at pH ∼ 8. The beneath mechanism cause the microstructure changes as a function of pH was discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6682–6692, 2009 相似文献
103.
Leong YK 《Journal of colloid and interface science》2005,292(2):557-566
The effects of hydrolysable Cu2+, Al3+ and Th4+ ions on the zeta potential and yield stress behaviour of silica dispersions were evaluated as a function of pH and metal ions concentration. Silica dispersion remained dispersed at its point of zero charge (pzc) of pH approximately 2.0 (CR1). Adsorbed hydrolysis products of Cu2+ and Al3+ caused the dispersion to display two further points of charge reversal (CR2 and CR3) at moderate ions concentration. CR2 occurred near the pH for the formation of the first hydrolysis product. This pH is about 2.8 for Al3+ and 5.0 for Cu2+. For all three metal ions, CR3 approached the pzc of the metal hydroxides at complete surface coverage. At CR3, the dispersions displayed a maximum yield stress. As many as three type of attractive forces; bridging, charged patch and van der Waals, may account for the maximum yield stress at low surface coverage. At complete coverage, only the van der Waals force is in play--the adsorbed hydrolysis products must have increased significantly the effective Hamaker constant of silica. With Al3+ the yield stress was absent at CR2 because particle bridging and charged patch attraction are unimportant as the silica surface charge is near zero. Adsorption of strongly hydrolysed Th4+ ions at pH<2.0 caused the dispersion to display only one pzc (CR3). 相似文献
104.
105.
A computational model of auditory localization resulting in performance similar to humans is reported. The model incorporates both the monaural and binaural cues available to a human for sound localization. Essential elements used in the simulation of the processes of auditory cue generation and encoding by the nervous system include measured head-related transfer functions (HRTFs), minimum audible field (MAF), and the Patterson-Holdsworth cochlear model. A two-layer feed-forward back-propagation artificial neural network (ANN) was trained to transform the localization cues to a two-dimensional map that gives the direction of the sound source. The model results were compared with (i) the localization performance of the human listener who provided the HRTFs for the model and (ii) the localization performance of a group of 19 other human listeners. The localization accuracy and front-back confusion error rates exhibited by the model were similar to both the single listener and the group results. This suggests that the simulation of the cue generation and extraction processes as well as the model parameters were reasonable approximations to the overall biological processes. The amplitude resolution of the monaural spectral cues was varied and the influence on the model's performance was determined. The model with 128 cochlear channels required an amplitude resolution of approximately 20 discrete levels for encoding the spectral cue to deliver similar localization performance to the group of human listeners. 相似文献
106.
Loudon AY Hiskett PA Buller GS Carline RT Herbert DC Leong WY Rarity JG 《Optics letters》2002,27(4):219-221
An enhancement of the infrared detection efficiency of Si photon-counting detectors by inclusion of SiGe absorbing layers has been demonstrated for what is believed to be the first time. An improvement of 30 times in detection efficiency at a wavelength of 1210 nm compared with that of an all-Si structure operated under identical conditions has been measured. The Si/Si(0.7)Ge(0.3) device is capable of room-temperature operation and has a response time of less than 300 ps. 相似文献
107.
Extensive ring cleavage in the mercaptobenzothiazole chromium complex CpCr(CO)2(SCSN(C6H4)) (2), initiated by cyclopentadienyl chromium tricarbonyl, produced novel polynuclear complexes 3-5. 相似文献
108.
A novel biodegradable gene carrier based on polyphosphoester 总被引:11,自引:0,他引:11
109.
Y. K. Leong Prof. David V. Boger G. B. Christie D. E. Mainwaring 《Rheologica Acta》1993,32(3):277-285
The paper describes how the theology of low concentration brown coal suspensions can be exploited to produce high concentration, low viscosity suspensions which are attractive as a potential coal-water fuel. Brown coal suspensions with solid concentrations approaching those of bituminous black coal have been prepared. The high inherent water content ( 60 wt %) and macroporosity of the brown coal have been reduced by thermal and chemical means. The hydrophobicity of the coal surface has been increased sufficiently to reduce the tendency for swelling and water uptake. This, together with densification, has allowed the solids content to be progressively improved from 30 wt % solids with raw coal to 65 wt% solids with modified coals while maintaining the viscosity of the suspension at a low level. The high solid concentration was achieved without additives. 相似文献
110.
Eunice S. P. Leong J. Deng Y. J. Liu J. H. Teng 《Applied Physics A: Materials Science & Processing》2014,116(3):907-912
The flexibility to deposit metallic structures on any substrates without the need of lift-off or etching process are the main reasons for the recent popularity of using stencil lithography for plasmonic applications. In this work, we fabricate nanoholes on a Si3N4 membrane and deposit metal–dielectric layers and such approach allows us to have a perforated fishnet metamaterial structure on the membrane as well as its complementary pillar structure on a quartz substrate. We then studied and compared their optical properties from both experiment and simulation results. 相似文献