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排序方式: 共有491条查询结果,搜索用时 515 毫秒
61.
Salim N. Kazi Geoffrey G. Duffy X. Dong Chen 《Chemical Engineering Communications》2002,189(6):742-758
The study of heat exchanger fouling using supersaturated calcium sulphate solutions has been widely reported. In this study fouling was investigated in a larger-scale heat exchange apparatus using stainless-steel pipe, and data were obtained at different flow rates, concentrations and temperature differences. The deposits were examined using a scanning electron microscope, X-ray diffraction and conventional photography. In a novel approach, wood pulp fibers were added to the fouling solution at various concentrations to mitigate fouling. Heat transfer enhancement above the solution-alone was observed initially and the onset of fouling delayed. When fouling eventually developed the final asymptotic level was lower than the fiber-free case for the experimental conditions specified. At a fiber concentration of 0.15% heat transfer augmentation occurred for 11 days. However, at 0.25% fiber concentration, heat transfer augmentation (no fouling) was sustained over the experimental duration of 45 days. It can be concluded that the service-life cycle of a heat exchanger can be prolonged with the addition of asymmetric, flexible, natural fibers. In this work it is argued that fibers modify the onset of deposition by boundary layer scavenging, and interact with turbulent eddies to reduce the rate of mass transfer of the foulant to the heated surface. When scale forms, the crystalline structure of the scale is interrupted by the fibers, which appear to roughen the heat transfer surface initially and increase the heat transfer coefficient. However, the scale deposit continues to build up very slowly, causing the thermal resistance to eventually override the turbulence augmented heat transfer effect of the fibers. 相似文献
62.
Anodic polarization of W has been studied in neutral (Na2SO4, NaCl) and alkaline solutions (ammonium borate, Na2CO3, Na3PO4, and NaOH) by the galvanostatic method under conditions which lead to anode film growth. The rate of oxide growth has been calculated as a function of current density, nature and concentration of electrolyte. Film growth to potentials above 100 V is achieved in alkaline solutions, provided the solution is dilute and the current density is high. The applicability of the high field ionic conduction has been verified from the dependence of both reciprocal capacity and potential on the logarithm of current density. Data are recorded for the coulometric increase of oxide thickness. The constants of the exponential law, and the electric field. 相似文献
63.
Mahshid?DehghanEmail author Nawal?Al Hamad AfzalHussein?Yusufali Fathimunissa?Nusrath Salim?Yusuf Anwar?T?Merchant 《Nutrition journal》2005,4(1):18
Background
The Food Frequency Questionnaire (FFQ) is one of the most commonly used tools in epidemiologic studies to assess long-term nutritional exposure. The purpose of this study is to describe the development of a culture specific FFQ for Arab populations in the United Arab Emirates (UAE) and Kuwait. 相似文献64.
Cement raw materials (clay, limestone and pyrite cinders) were mixed, pressed into pellets, burnt at high temperatures, cooled and the resulting clinkers analysed for free CaO content. The effect of the following parameters and their interactions on the free CaO was studied: top temperature of burning (in three levels: 1300, 1350, 1400°C), soaking time at top temperature (in three levels: 5, 30 and in some cases 60 min), method of heating (in two levels: rapid and normal), method of cooling (in two levels, rapid and slow), lime saturation factor of the mix, LSF (in three levels, 0.95, 0.85, 0.76). Experiments were planned to enable a statistical evaluation (calculation of error variance at various levels of significance). Rapid calcination improves the burnability of cement raw materials, as contrasted to normal calcination. This indicates that rapid calcination enables the use of lower calcination temperatures. A long soaking at top temperature is unnecessary in case of rapid calcination. The free CaO content of the clinker is affected primarily by the LSF of the mix and the top temperature of firing; all other parameters are less effective. 相似文献
65.
Hakim Boudaoud Salim Belouettar El Mostafa Daya Michel Potier-Ferry 《Engineering Structures》2009,31(2):284-291
In this paper, a numerical method is proposed for determining complex vibrations modes of sandwich structures with piezoelectric and viscoelastic layers. Based on homotopy and asymptotic numerical techniques, this method leads to the damping properties calculation (loss factor and natural frequency per mode) of the hybrid sandwich structure. The numerical results of the loss factor and natural frequency are compared to those obtained from analytical beam model and from numerical studies the modal strain energy method. 相似文献
66.
Salim Benaissa Mohamed Hamidouche Mostafa Kolli Gilbert Fantozzi 《International Journal of Applied Ceramic Technology》2019,16(2):638-646
The aim of this work was the analysis of the experimental results of a transparent alumina (BMA15) ceramic which was fabricated by Spark Plasma Sintering (SPS) from nanopowder (BMA15, Baikowski Chimie, France), at different temperatures (1200°C, 1250°C, 1300°C). With the application of a maximum uniaxial pressure of 73 MPa during all the fabrication-cycle (more than 3 hours). We sought an optimal sintering temperature combining better optical and mechanical properties of our pellets. The sintered alumina (BMA15) has a crystalline and dense microstructure. The samples sintered at 1200°C exhibit the best optical properties, in particular: good real inline transmission (RIT) and an optical gap greater than those of the samples sintered at 1250°C and 1300°C. Due to their low density, the Young modulus of alumina sintered at 1200 °C, deduced by ultrasound, has a low value which is about 385 GPa. Similarly, its small grain size gives it a better Vickers hardness ~ 21 GPa. Therefore, the value of the coefficient of friction μ stabilizes around the mean value of 0.21. 相似文献
67.
Specific PCR and sequencing showed that a tet(M) gene was present in two tetracycline-resistant Lactococcus lactis strains isolated from a raw milk, starter-free cheese. Hybridisation experiments using as a probe an internal segment of the gene obtained by PCR associated tet(M) with plasmids of around the same size (30 kbp) in both strains. Molecular analysis of the tetracycline resistance loci, including the upstream and downstream regions of the genes, showed them to be identical to one other and to the tet(M) encoded by the conjugative transposon Tn916. Amplification of Tn916-derived segments suggested the transposon was complete in the two L. lactis strains. Further, curing of the tetracycline resistance was accompanied by a reduction in size of the plasmids comparable to that expected for Tn916. Tetracycline resistance could be transferred by conjugation to plasmid-free Lactococcus and Enterococcus strains. However, no plasmid DNA was detected among the transconjugants while both tet(M) and transposon-related sequences were amplified by PCR. This suggested that only the transposon was mobilized. 相似文献
68.
Insights into the role of quorum sensing in food spoilage 总被引:1,自引:0,他引:1
Food spoilage is a consequence of the degrading enzymatic activity of some food-associated bacteria. Several proteolytic, lipolytic, chitinolytic, and pectinolytic activities associated with the deterioration of goods are regulated by quorum sensing, suggesting a potential role of such cell-to-cell communication in food spoilage. Here we review quorum sensing signaling molecules and methods of their detection and quantification, and we provide insights into the role of quorum sensing in food spoilage and address potential quorum sensing inhibitors that might be used as biopreservatives. 相似文献
69.
Imdad Ali Salim Saifullah Babiker M. El-Haj Heyam Saad Ali Saira Yasmeen Muhammad Imran Jan Nisar Muhammad Raza Shah 《Journal of surfactants and detergents》2020,23(5):973-980
Nonionic surfactants are highly stable and cost-effective and receiving acceptance for applications in many diverse fields including drug delivery, due to their distinctive properties. Here, we report on the synthesis and characterization of sulfanilamide-based nonionic surfactants for nanoscale vesicular drug loading applications. Nonionic surfactants were synthesized through alkylation of sulfanilamide with alkyl halides that possessed diverse degrees of lipophilicity. They were explored for their nanovesicular drug loading with Cefixime as a hydrophobic model drug. Drug-loaded nanovesicles were characterized for surface morphologies, size, size distribution, surface charge, and drug loading efficiency using atomic force microscopy (AFM), dynamic light scattering (DLS), and UV–visible spectrophotometry. All of the synthesized nonionic surfactants revealed their CMC values in 0.055–0.035 mM range depending upon the lipophilic chain length of surfactants. They caused a decreased hemoglobin release and low toxicity against cell culture. They self-assembled and loaded an increased amount of drug in the form of nanorange spherical shape niosomal vesicles. Results of the current study verify these synthesized nonionic surfactants are hemocompatible, nontoxic, and capable of self-assembling into nanorange niosomal vesicles. These niosomal vesicles can be suggested as safe and highly efficient nanocarriers for hydrophobic drug loading and delivery. 相似文献
70.