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排序方式: 共有210条查询结果,搜索用时 15 毫秒
11.
Sigrid Lædre Ole Edvard Kongstein Anders Oedegaard Frode Seland Håvard Karoliussen 《International Journal of Hydrogen Energy》2012
Stainless steel is attractive as material for bipolar plates in proton exchange membrane fuel cells, due to its high electrical conductivity, high mechanical strength and relatively low material and processing cost. Potentiostatic and potentiodynamic tests were performed in H2SO4 solutions on AISI 316L stainless steel bipolar plates with etched flow fields. The effect of pH and presence of small amounts of fluoride and chloride on the corrosion rate and interfacial contact resistance of the stainless steel bipolar plate were investigated. The tests performed in electrolytes with various pH values revealed that the oxide layer was thinner and more prone to corrosion at pH values significantly lower than the pH one expects the bipolar plate to experience in an operating proton exchange membrane fuel cells. The use of solutions with very low pH in such measurements is thus probably not the best way of accelerating the corrosion rate of stainless steel bipolar plates. By use of strongly acidic solutions the composition and thickness of the oxide layer on the stainless steel is probably altered in a way that might never have happened in an operating proton exchange membrane fuel cell. Additions of fluoride and chloride in the amounts expected in an operating fuel cell (2 ppm F− and 10 ppm Cl−) did not cause significant changes for neither the polarization- nor the contact resistance measurements. However, by increasing the amount of Cl− to 100 ppm, pitting was initiated on the stainless steel surface. 相似文献
12.
Mayrhofer S Paulsen P Smulders FJ Hilbert F 《International journal of food microbiology》2004,97(1):23-29
This study was performed to evaluate the resistance rate against antimicrobials of food isolates of the five major food-borne pathogens to compare these and to possibly distinguish a pattern. A total of 922 samples of the major meat species (pork, beef and poultry) were analysed for thermophilic Campylobacter, Salmonella, Yersinia enterocolitica, pathogenic Escherichia coli and Listeria monocytogenes. Isolates were subjected to antimicrobial resistance testing by the disc diffusion method. Roughly the same overall rate of resistance was identified for thermophilic Campylobacter, Salmonella and pathogenic E. coli. Resistance to quinolones and tetracycline was determined most frequently. In contrast, food isolates of Y. enterocolitica and L. monocytogenes were rarely tested resistant. The significance of our findings is that resistance rates in enteric bacteria seem to be much higher than in pathogens found in a variety of environments, closely associated to the host environment. 相似文献
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Sigrid Seuss Maja Lehmann Aldo R. Boccaccini 《International journal of molecular sciences》2014,15(7):12231-12242
Alternating current (AC) electrophoretic deposition (EPD) was used to produce multifunctional composite coatings combining bioactive glass (BG) particles and chitosan. BG particles of two different sizes were used, i.e., 2 μm and 20–80 nm in average diameter. The parameter optimization and characterization of the coatings was conducted by visual inspection and by adhesion strength tests. The optimized coatings were investigated in terms of their hydroxyapatite (HA) forming ability in simulated body fluid (SBF) for up to 21 days. Fourier transform infrared (FTIR) spectroscopy results showed the successful HA formation on the coatings after 21 days. The first investigations were conducted on planar stainless steel sheets. In addition, scaffolds made from a TiAl4V6 alloy were considered to show the feasibility of coating of three dimensional structures by EPD. Because both BG and chitosan are antibacterial materials, the antibacterial properties of the as-produced coatings were investigated using E. coli bacteria cells. It was shown that the BG particle size has a strong influence on the antibacterial properties of the coatings. 相似文献
16.
Gaseidnes Sigrid; Synstad Bjornar; Jia Xiaohong; Kjellesvik Hege; Vriend Gert; Eijsink Vincent G.H. 《Protein engineering, design & selection : PEDS》2003,16(11):841-846
This paper describes attempts to increase the kinetic stabilityof chitinase B from Serratia marcescens (ChiB) by the introductionof semi-automatically designed rigidifying mutations of theGlyAla and XxxPro type. Of 15 single mutants, several displayedsignificant increases in thermal stability, whereas most mutantsshowed minor effects. All mutations with non-marginal effectson stability clustered in a limited, surface-exposed regionof the enzyme, indicating that this region is involved in apartial unfolding process that triggers irreversible thermalinactivation (aggregation). A double mutant containing two stabilizingmutations in this region (G188A, A234P) displayed a 10-foldincrease in half-life at 57°C and a 4.2°C increase inapparent Tm. These results show that entropic stabilizationworks well for ChiB and they pinpoint a region whose unfoldingmay be crucial for the kinetic stability of this enzyme. Received June 18, 2003; revised September 3, 2003; accepted September 12, 2003. 相似文献
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In NonÅs and Thorstenson [A combined cutting stock and lot sizing problem. European Journal of Operational Research 120(2) (2000) 327–42] a combined cutting-stock and lot-sizing problem is outlined under static and deterministic conditions. In this paper we suggest a new column generating solution procedure for this problem that works well on both small and large-sized problems. The procedure includes characteristics from both the column generating procedure in NonÅs and Thorstenson, which works well on small-sized problems, and from the sequential heuristic due to Haessler [A heuristic programming solution to a nonlinear cutting stock problem, Management Science 17(12) (1971) 793–802], which works well on large-sized problems. Numerical results are presented that show that the new heuristic performs better than both of the earlier procedures. Comparisons with results obtained by other authors indicate that the procedure works well also for the extended cutting-stock problem with only a setup cost for each pattern change. 相似文献
18.
Gas evolution in primary alkaline cells depends on discharge time. This dependence can be so strong that acceptable volumes of gas are evolved in cells when discharged over relatively long periods, whereas shorter times may lead to gassing beyond the limits of the cell design. The dependency of gassing on discharge time was investigated for a number of commercial cells and for different zinc-alloy powders. An indication of a relation between certain alloying elements and the gas evolution at short discharge times was found. The most important result of the investigations, however, was the development of a modified zinc powder production process which leads to zinc powders with reduced gas evolution rates for both short and long discharge times. 相似文献
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A hot‐rolled TRIP steel with a tensile strength level above 800 MPa and an excellent fatigue behaviour has been developed with the purpose of satisfying the increasing demands of the automotive industry. Nb was added to the steel to guarantee a stable process and to make the production of the steel possible in a conventional rolling mill. The formation of red scale and the surface quality problems that arise from it have been studied. Additionally, hot torsion tests have been performed in order to validate a new route that could avoid the formation of this red scale allowing the application of the steel for exposed parts (e.g. wheel sector). 相似文献