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71.
Sykes EC Han P Kandel SA Kelly KF McCarty GS Weiss PS 《Accounts of chemical research》2003,36(12):945-953
Adsorbate interactions and reactions on metal surfaces have been investigated using scanning tunneling microscopy. The manners in which adsorbates perturb the surface electronic structure in their vicinity are discussed. The effects these perturbations have on other molecules are shown to be important in overlayer growth. Interactions of molecules with surface steps are addressed, and each molecule's electron affinity is shown to dictate its adsorption sites at step edges. Standing waves emanating from steps are demonstrated to effect transient molecular adsorption up to 40 A away from the step edge. Halobenzene derivatives are used to demonstrate how the surface is important in aligning reactive intermediates. 相似文献
72.
Linear low‐density polyethylene (LLDPE), based on butene‐1 or hexene‐1, was irradiated with γ‐rays under vacuum or in the presence of air. The study focused on the influence of the dose rate and the γ‐dose on the thermal properties of LLDPE. Differential scanning calorimetry, thermogravimetric analysis (TGA), and TGA/FTIR techniques were used to address the thermal behavior as a result of γ‐irradiation. During this irradiation, competition between crosslinking and scission reactions, subsequent to oxidation reactions, occurred in the polymeric material, which strongly depends on the experimental conditions. A decrease of the crystallinity for γ‐irradiated samples was observed in particular for samples irradiated under vacuum. This observation may be explained by increased hindrance of segment mobility due to crosslinking reactions that prevent crystal growth. TGA investigations revealed an enhancement of the thermal stability for samples irradiated under vacuum but not for those irradiated in air. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2790–2795, 2006 相似文献
73.
Adherent and coherent deposits of nickel sponge similar to sintered nickel may be made from sulphate, chloride, fluoborate or sulphamate nickel plating solutions containing nickel powder in suspension, providing the concentration of free acid is maintained sufficiently high to inhibit co-depesition of Ni(OH) In nitrate solution, cathodic reduction of nitrate and deposition of Ni(OH)2 predominates. 相似文献
74.
Claudia Kuster Jean‐Charles Bazin Cengiz Öztireli Teng Deng Tobias Martin Tiberiu Popa Markus Gross 《Computer Graphics Forum》2014,33(2):1-10
Multi‐view reconstruction aims at computing the geometry of a scene observed by a set of cameras. Accurate 3D reconstruction of dynamic scenes is a key component for a large variety of applications, ranging from special effects to telepresence and medical imaging. In this paper we propose a method based on Moving Least Squares surfaces which robustly and efficiently reconstructs dynamic scenes captured by a calibrated set of hybrid color+depth cameras. Our reconstruction provides spatio‐temporal consistency and seamlessly fuses color and geometric information. We illustrate our approach on a variety of real sequences and demonstrate that it favorably compares to state‐of‐the‐art methods. 相似文献
75.
It is well known that a so-called “three-dimensional filler network structure” will be constructed in the polymer/layered silicate nanocomposites when the content of layered clay reaches a threshold value, at which the silicate sheets are incapable of freely rotating, due to physical jamming and connecting of the nanodispersed layered silicate. In this article, the effect of such clay network on the mobility and relaxation of macromolecular chains in isotactic polypropylene(iPP)/organoclay nanocomposites was investigated in detail with a combination of DMTA, DSC, TGA, TEM, rheometry and melt flow index measurements. The main aim is to establish a relationship between the mesoscopic filler network structure and the macroscopic properties of the polymer nanocomposites, particularly to explore the role of the clay network on the mobility and relaxation of macromolecular chains. It was found that the nanodispersed clay tactoids and layers play less important or dominant roles on the mobility of iPP chains depending on the formation of percolating filler network. The turning point of macroscopic properties appeared at 1 wt% organoclay content. Before this point, the effect of organoclay can be negligible, and the increase of chain mobility was ascribed to the decrease of molecular weight of polymer chains, as commonly occurs during dynamic melt processing; after this point, however, a reduced mobility of chains and a retarded chain relaxation were observed and attributed to the formation of a mesoscopic filler network. The essential features of such a mesoscopic organoclay network were estimated and discussed on the basis of stress relaxation and structural reversion measurements. A schematic model was proposed to describe the different relaxation and motion behaviors of macromolecular chains in the unfilled polymer and the filled hybrids with partial and percolated organoclay networks, respectively. 相似文献
76.
Jianding Chen Christian Carrot Yvan Chalamet Jean‐Charles Majeste Mohamed Taha 《应用聚合物科学杂志》2003,88(5):1376-1383
Poly(n‐butyl methacrylate) (PBMA) composites with calcium carbonate (CaCO3) were prepared by in situ radical copolymerization of butyl methacrylate (BMA) and methacrylic acid (MA) with precipitated calcium carbonate. To compare the different rheological behaviors of the monomer mixtures with CaCO3 and the composites, the steady and dynamic viscosities of BMA/MA/CaCO3 and poly(BMA/MA/CaCO3) were measured by means of steady and oscillatory shear flows. The viscosity of the mixture BMA/MA/CaCO3 was found to increase evidently with the increasing of CaCO3%. The influence of MA% on viscosity of BMA/MA/CaCO3 was slight. During the in situ polymerization, the viscosity of the reacting system was measured to be enhanced by a factor of about 104 from the monomer/CaCO3 mixture to composites. The dependency of zero‐shear viscosity on molar mass of PBMA was also investigated. The relation between the zero‐shear viscosity and molar mass is η0 = 10?15 Mw3.5. The evolution of the viscosity with the temperature for both PBMA and its composites was obtained and time–temperature superposition was used to build master curves for the dynamic moduli. The flow activation energies were found to be 115.0, 148.6, and 178.7 kJ/mol for PBMA, composite PBMA/CaCO3 (90/10), and PBMA/MA/CaCO3 (89/1/10), respectively. The viscosity of the composites containing less than 10% CaCO3 was lower than that of pure PBMA with the same molar mass. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1376–1383, 2003 相似文献
77.
The influence of silica support on the α-olefins, internal olefins and branched hydrocarbon selectivities of the gasoline range products of a precipitated iron catalyst in the Fischer-Tropsch synthesis was investigated. Three catalysts with varying silica content and constant promoter content were studied. It was found that there is a linear relationship between the silica content of the catalysts and the internal olefin and branched hydrocarbon product selectivities. The selectivities of the aromatic and alcohol products remain relatively constant, indicating that the production of these two groups of compounds is not affected by the presence of silica support in the catalysts. 相似文献
78.
Laxmidhar Besra Charles Compson Meilin Liu 《Journal of the American Ceramic Society》2006,89(10):3003-3009
This paper reports a method of performing electrophoretic deposition (EPD) on non-conducting substrates overcoming the requirement of a conducting substrate through the use of porous substrates. The conductivity of the substrate is therefore no longer a limiting factor in the application of EPD. This method is applicable to the fabrication of thick or thin layers of ceramic or metal for various applications. As an example, thin and dense yttria-stabilized zirconia (YSZ) layers have been deposited on a non-conducting NiO–YSZ substrate by EPD from a non-aqueous suspension. A solid oxide fuel cell constructed on these sintered bilayers exhibited power densities of 384 and 611 mW/cm2 at 750° and 850°C, respectively. 相似文献
79.
Alkema WB Hensgens CM Snijder HJ Keizer E Dijkstra BW Janssen DB 《Protein engineering, design & selection : PEDS》2004,17(5):473-480
Penicillin acylase catalyses the condensation of Calpha-substituted phenylacetic acids with beta-lactam nucleophiles, producing semi-synthetic beta-lactam antibiotics. For efficient synthesis a low affinity for phenylacetic acid and a high affinity for Calpha-substituted phenylacetic acid derivatives is desirable. We made three active site mutants, alphaF146Y, betaF24A and alphaF146Y/betaF24A, which all had a 2- to 10-fold higher affinity for Calpha-substituted compounds than wild-type enzyme. In addition, betaF24A had a 20-fold reduced affinity for phenylacetic acid. The molecular basis of the improved properties was investigated by X-ray crystallography. These studies showed that the higher affinity of alphaF146Y for (R)-alpha-methylphenylacetic acid can be explained by van der Waals interactions between alphaY146:OH and the Calpha-substituent. The betaF24A mutation causes an opening of the phenylacetic acid binding site. Only (R)-alpha-methylphenylacetic acid, but not phenylacetic acid, induces a conformation with the ligand tightly bound, explaining the weak binding of phenylacetic acid. A comparison of the betaF24A structure with other open conformations of penicillin acylase showed that betaF24 has a fixed position, whereas alphaF146 acts as a flexible lid on the binding site and reorients its position to achieve optimal substrate binding. 相似文献
80.
Igor V. Kovalenko Glen R. Rippke Charles R. Hurburgh 《Journal of the American Oil Chemists' Society》2006,83(5):421-427
A key element of successful development of new soybean cultivars is availability of inexpensive and rapid methods for measurement
of FA in seeds. Published research demonstrated applicability of NIR spectroscopy for FA profiling in oilseeds. The objectives
of this study were to investigate the applicability of NIR spectroscopy for measurement of FA in whole soybeans and compare
performance of calibration methods. Equations were developed using partial least squares (PLS), artificial neural networks
(ANN), and support vector machines (SVM) regression methods. Validation results demonstrated that (i) equations for total
saturates had the highest predictive ability (r
2=0.91–0.94) and were usable for quality assurance applications, (ii) palmitic acid models (r
2=0.80–0.84) were usable for certain research applications, and (iii) equations for stearic (r
2=0.49–0.68), oleic (r
2=0.76–0.81), linoleic (r
2=0.73–0.76), and linolenic (r
2=0.67–0.74) acids could be used for sample screening. The SVM models produced significantly more accurate predictions than
those developed with PLS. ANN calibrations were not different from the other two methods. Reduction in the number of calibration
samples reduced predictive ability of all equations. The rate of performance degradation of SVM models with sample reduction
was the lowest. 相似文献