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排序方式: 共有379条查询结果,搜索用时 15 毫秒
1.
Cypriano G da Trindade Neto Ana LP Fernandes Ana IB Santos Waldenice A Morais Marcos VM Navarro Tereza NC Dantas Mrcia R Pereira Jos LC Fonseca 《Polymer International》2005,54(4):659-666
Complexation of chitosan in aqueous solutions by low molecular weight electrolytes is one of the simplest methods for the preparation of aqueous chitosan dispersions. In this work, the influence of storage time, sulfate concentration, method of preparation and surfactant content on some properties of the resultant chitosan dispersions (turbidity, viscosity and zeta potential) was analyzed. Turbidimetry was adequate to monitor the formation of particles, while viscometry was suitable to monitor changes in the dispersing phase. An analysis of the properties of these systems, mainly in terms of particle–particle and macromolecule–macromolecule interactions was carried out. Copyright © 2004 Society of Chemical Industry 相似文献
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RGS proteins (regulators of G protein signaling) are GTPase activating proteins (GAPs) for Gi and Gq families of heterotrimeric G proteins but have not been found to interact with Gs alpha. The Gs alpha residue Asp229 has been suggested to be responsible for the inability of RGS proteins to interact with Gs alpha [Natochin, M., and Artemyev, N. O. (1998) J. Biol. Chem. 273, 4300-4303]. To test this hypothesis, we have investigated the possibility of generating an interaction between Gs alpha and RGS proteins by substituting Gs alpha Asp229 with Ser and replacing the potential Gs alpha Asp229 contact residues in RGS16, Glu129 and Asn131, by Ala and Ser, respectively. RGS16 and its mutants failed to interact with Gs alpha. A single mutation of Gs alpha, Asp229Ser, rendered the Gs alpha subunit with the ability to interact with RGS16 and RGS4. Like RGS protein binding to Gi and Gq alpha-subunits, RGS16 preferentially recognized the AlF4--bound conformation of Gs alpha Asp229Ser. In a single-turnover assay, RGS16 maximally stimulated GTPase activity of Gs alpha Asp229Ser by approximately 5-fold with an EC50 value of 7.5 microM. Our findings demonstrate that Asp229 of Gs alpha represents a major barrier for Gs alpha interaction with known RGS proteins. 相似文献
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Agostinho de Medeiros Brito Junior Adri?o Duarte Dória Neto Jorge Dantas de Melo Luiz Marcos Garcia Goncalves 《Neural Networks, IEEE Transactions on》2008,19(6):1130-1140
In this paper, we propose a multiresolution approach for surface reconstruction from clouds of unorganized points representing an object surface in 3-D space. The proposed method uses a set of mesh operators and simple rules for selective mesh refinement, with a strategy based on Kohonen's self-organizing map (SOM). Basically, a self-adaptive scheme is used for iteratively moving vertices of an initial simple mesh in the direction of the set of points, ideally the object boundary. Successive refinement and motion of vertices are applied leading to a more detailed surface, in a multiresolution, iterative scheme. Reconstruction was experimented on with several point sets, including different shapes and sizes. Results show generated meshes very close to object final shapes. We include measures of performance and discuss robustness. 相似文献
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Marcella Feitosa De Figueiredo Karoline Dantas Brito Wagner Brandão Ramos Luís Gonzaga Sales Vasconcelos 《Chemical Engineering Communications》2013,200(9):1191-1199
This article sets out to evaluate the effect of solvent content in the extractive section on the separation efficiency and energy consumption of extractive distillation columns. Contrary to the classical approach, the proposed approach enables a simultaneous evaluation of the effect of the major decision variables (reflux ratio, solvent flow rate, and the number of stages of the extractive section [NSE]). The procedure allows calculating the minimum solvent flow rate for the separation and the minimum specific energy consumption. The results show that the minimum specific energy consumption is obtained for the minimum reflux ratio and not for the minimum solvent flow rate. Moreover, the results show that it is not always the case that a larger NSE results in lower energy consumption. Due to its industrial importance, the dehydration of aqueous mixtures of ethanol using ethylene glycol as solvent has been chosen as a case study. 相似文献
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Juliana Starling Cleiton Moreira da Silva Maria Sylvia Silva Dantas Ângelo de Fátima Rodrigo L. Oréfice 《International Journal of Adhesion and Adhesives》2011,31(7):767-774
In an attempt to enrich the world of dentistry through the development of new materials, this study proposes to synthesize and incorporate a monomer containing the N-hydroxysuccinimide (NHS) ester reactive group to a dental adhesive. As such, this study developed a simple method to obtain NHS esters by employing acrylic acid (AA) and NHS in the presence of EDC (N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide), from an aprotic medium. The experimental N-acryloxysuccinimide (NSA) monomer was analyzed by infrared spectroscopy (FTIR) and nuclear magnetic resonance of hydrogen (1H NMR). This monomer was then incorporated within a prepared dental adhesive, in a 5% proportion. The modified adhesive, containing NSA, was applied to the dental surface of bovine teeth to obtain an adhesive/dentin interface in vitro. The characterization of this interface by Raman spectroscopy presented the formation of new amide bonds. Moreover, through scanning electron microscopy (SEM), it became possible to observe an intense penetration of this modified adhesive on the dental surface. Considering the outcome, it can be concluded that the synthesized NSA monomer provided a favorable condition for the dental adhesives to interact chemically with the dentin collagen fibers. 相似文献
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安徽省第一建筑工程公司技术质量处 《建筑施工》2006,28(1):44-45
为降低建筑采暖和空调制冷的能耗,贵都花园外墙采用外保温,介绍了墙体外保温用材、施工程序及操作工艺,竣工后通过热工性能检测,取得了明显的节能效果,并获安徽省“省级科技示范工程”称号。 相似文献
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E. V. Faria S. T. Dantas V. C. A. Junqueira A. E. Garcia 《Packaging Technology and Science》1996,9(4):187-202
Microseaming is a significant technological development in the can manufacturing process that has been employed in the packaging of tomato processed products in Brazil. It was developed by the Brazilian company Grupo Kramer in 1990. Due to its reduced dimensions in relation to the traditional can closing system, i.e. the conventional double seam, microseam mechanical resistance as well as its capability to guarantee package integrity when submitted to processing and distribution remain questionable. In this study microseam resistance was compared to conventional double seam resistance when submitted to mechanical abuse through a standardized impact on the seam region positioned at angles of 45 and 67°. As evaluation parameters of closing integrity loss after impact swelling resulting from the cans external contact with a bacterial suspension, internal vacuum loss and can centre depth changes were used. The microseam presented a performance comparable to the conventional double seam for the impact at 45°, whereas at 67° its performance was found to be superior. This superior microseam performance can be credited to its being more malleable, i.e., to its greater capability of deforming itself when submitted to a puncture-type impact, to its more compact structure and to the type of deformation resulting from this type of impact. 相似文献