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排序方式: 共有219条查询结果,搜索用时 45 毫秒
211.
Hemant K. Jain 《Information Systems》1984,9(3-4):217-230
The performance of a database system depends, to a large extent, on the storage structure selected to represent the logical schema of the database. A comprehensive model for the physical design of network model databases is presented. It evaluates the retrieval time for each user query, database updating cost, storage requirements and total cost of the system in terms of design parameters. A linear 0–1 goal programming model, because of its multicriteria nature, has been selected here as a solution procedure. It finds the optimal location mode of each database record type based on the priority and weights assigned to the conflicting design objectives; short retrieval time for a user query, low database updating cost, small storage requirements and low total cost of the system. The designer can interactively change value of design parameters, priority and weights to perform tradeoff analysis. The model has been tested in the design of a department store database. 相似文献
212.
R.M. Mehra Surinder Koul Hemant Kumar P.C. Mathur 《Materials Chemistry and Physics》1985,12(2):129-144
D. C. conductivity measurements have been made as a function of temperature and electric field on bulk amorphous GexTe10Se90?x (10? x ?40) samples, in order to identify the conduction mechanism and to study the effect of the electric field on the conductivity. In the entire range of temperature (80–300 K) the conduction in all the samples is found to take place thermally assisted tunnelling of the charge carriers in the localized states of the band tails. The addition of germanium results in an increase in the localized state density and hence an increase in conductivity. An increase in the electric field decreases the activation energy, thereby increasing the conductivity of the samples. The conductivity shows an exponential dependence on the electric field. 相似文献
213.
Hemant V. Borgaonkar Sampatraj B. Chandalia 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1984,34(3):107-112
Liquid phase oxidation of several substituted methyl aromatic compounds by air in an acetic acid medium, using cobalt acetate as a catalyst and sodium bromide or paraldehyde as a promoter, has been investigated with a view to developing manufacturing processes for the production of various pharmaceutical intermediates. In most cases carboxylic acids and aldehydes were the major products of oxidation. The process parameters such as temperature, period of reaction, and concentrations of the substrate, catalyst and promoter were chosen to obtain a high proportion of the desired oxidation product. 相似文献
214.
This paper reports on the effects of the great Sumatra earthquake and tsunami of December 26, 2004, in and around Port Blair, the capital city of the Andaman and Nicobar Islands, India. The earthquake shaking and subsequent tsunami caused substantial damage to structures that include buildings, harbors, overhead water tanks, seaport control towers, and so on. Other important structures, for example, dams, bridges, hangars, and so on, also suffered minor damage without disrupting their functioning. Reinforced concrete structures on the islands were the worst performers, while traditionally constructed timber and masonry structures performed well in response to ground shaking. The mandatory Indian Standards were not complied within the design of many recent structures on the islands located in the most severe seismic zone in India. 相似文献
215.
In this study, microcellular Acrylonitrile–Butadiene–Styrene foams with high cell density and expansion ratio has been manufactured using ultrasound‐induced nucleation technique in solid‐state batch foaming process. Influence of sonication time, sonication frequency, and ultrasound power were found very crucial in designing of cellular morphology. The initial 10 s of ultrasound exposure was found to influence the foam morphology critically. Longer periods of ultrasound exposure developed foams with lower average cell size as compared to foams developed with lesser ultrasound exposure time. Higher sonication power resulted in foams with uniform morphology and higher cell densities as compared to foams developed with lower sonication intensities. Finally, the ultrasonic frequency was also found to influence the morphology intensely. Low frequency sonication resulted in foams with uniform cell distribution, whereas high frequency sonication developed bimodal microcellular type of microstructure. The results coherently demonstrate that with the advent of ultrasonic waves, the energy barrier for cell nucleation swiftly decreases which enhances the cell density in the final foamed product. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40742. 相似文献
216.
This study explores the synthesis and characterization of polyurethanes (PUs) derived from hexamethylene diisocyanate (HDI) and 1,n-alkane diols with varying chain lengths (n = 4, 6, and 10). Additionally, pentaerythritol (PE) is introduced as a dopant in PU6 at different weight percentages (25%, 50%, 75%, and 1:1%w/w). The research encompasses a comprehensive analysis of PU properties, including morphology, crystallinity, surface area, porosity, thermal behavior, rheological properties, and electrical conductivity. Of particular interest is the evaluation of protein adsorption capabilities employing bovine serum albumin (BSA) and fibrinogen proteins in in vitro tests. The study emphasizes the crucial role played by the chain length between isocyanate and diol groups and the nature and strength of hydrogen bonds among chains in shaping the polymer's properties, especially crystallinity and biocompatibility. Among the synthesized PUs, PU6 emerges as the top performer in terms of crystallinity and biocompatibility. Furthermore, the addition of PE is found to act as a plasticizer, reducing the glass transition temperature (Tg) from 75°C to 31°C. Electrochemical Impedance Spectroscopy shows that doping influences charge transfer processes, rendering the material semi-conducting, as evidenced by decreased conductance when adding silver nanoparticles to PU6. Notably, protein adsorption studies reveal that undoped PU6 displays superior protein resistance compared to its doped counterpart, with fibrinogen exhibiting a higher adsorption affinity than BSA. The study discusses a plausible mechanism underlying protein adsorption. 相似文献
217.
Prosanta Gope Hemant Ghayvat Yongqiang Cheng Sohag Kabir 《International Journal of Communication Systems》2023,36(12):e4199
Rapid development of wireless networks brings about many security problems in portable communication systems (PCSs), which can provide mobile users with an opportunity to enjoy global roaming services. In this regard, designing a secure user authentication scheme, especially for recognizing legal roaming users, is indeed a challenging task. It is noticed that there is no delegation-based protocol for PCSs, which can guarantee anonymity, untraceability, perfect forward secrecy, and resistance of denial-of-service (DoS) attack. Therefore, in this article, we put forward a novel delegation-based anonymous and untraceable authentication protocol, which can guarantee to resolve all the abovementioned security issues and hence offer a solution for secure communications for PCSs. 相似文献
218.
219.
Hemant Gawande Sumit Arora Vivek Sharma Ganga Sahay Meena Ashish Kumar Singh 《International Journal of Dairy Technology》2023,76(3):650-658
Buffalo milk was utilised for preparing paneer samples after standardisation of protein:fat ratio to 0.68 with the addition of buffalo milk protein co-precipitates (BMPC). These paneer samples along with control paneer (from buffalo milk) were analysed for yield, composition, microstructure, sensory, texture profile and protein loss in whey during manufacture. Paneer prepared using BMPC was considerably higher in yield and recovery of total solids, protein and calcium content than control paneer and could withstand the frying conditions in terms of retention of shape and integrity. Texture profile analysis and microstructure evaluation revealed the differences in textural properties of paneer samples prepared using BMPC with control paneer. 相似文献