The effect of pH and halides on the corrosion process of stainless steel bipolar plates for proton exchange membrane fuel cells

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.     

灵活性住宅类型

欧洲受到当今全球性生态和经济的挑战,可持续性和适应性的建筑结构设计概念再次变得愈发重要。此外,个性化的要求、人口结构的变化、民族的多样化以及向灵活工作方式的过渡也激发了对适应性住房需求的日益增长。自20世纪80年代末以来,灵活住宅的范围在欧洲显著扩大,并产生了多种类型：从功能开放的楼层平面、活动墙体的楼层平面以及各种组合类型,到前卫的空间场景、实验性高科技适应结构以及开放功能计划的建筑类型。建立起一种实现灵活性之方法的框架,并介绍了几个具有创新性的案例。     

Stabilization of a chitinase from Serratia marcescens by Gly->Ala and Xxx->Pro mutations

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 T_m. 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.     

Scheduling railway traffic at a construction site

We consider the problem of rescheduling trains in the case where one track of a railway section consisting of two tracks in opposing directions is closed due to construction activities. After presenting an appropriate model for this situation we derive a polynomial algorithm for the subproblem of finding an optimal schedule with minimal latenesss if the subsequences of trains for both directions outside the construction site are fixed. Based on this algorithm we propose a local search procedure for the general problem of finding good schedules and report test results for some real world instances. Received: December 8, 1999 / Accepted: May 2, 2001     

Catalytic role of the active site histidine of porcine pancreatic phospholipase A2 probed by the variants H48Q, H48N and H48K

The catalytic contribution of His48 in the active site of porcinepancreatic phospholipase A2 was examined using site-directedmutagenesis. Replacement of His48 by lysine (H48K) gives riseto a protein having a distorted lipid binding pocket. Activityof this variant drops below the detection limit which is 10⁷-foldlower than that of the wild-type enzyme. On the other hand,the presence of glutamine (H48Q) or asparagine (H48N) at thisposition does not affect the structural integrity of the enzymeas can be derived from the preserved lipid binding propertiesof these variants. However, the substitutions H48Q and H48Nstrongly reduce the turnover number, i.e. by a factor of 10⁵.Residual activity is totally lost after addition of a competitiveinhibitor. We conclude that proper lipid binding on its ownaccelerates ester bond hydrolysis by a factor of 10². With theselected variants, we were also able to dissect the contributionof the hydrogen bond between Asp99 and His48 on conformationalstability, being 5.2 kJ/mol. Another hydrogen bond with His48is formed when the competitive inhibitor (R)-2-dodecanoylamino-hexanol-1-phosphoglycolinteracts with the enzyme. Its contribution to binding of theinhibitor in the presence of an interface was found to be 5.7kJ/mol.     

Alternating Current Electrophoretic Deposition of Antibacterial Bioactive Glass-Chitosan Composite Coatings

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.     

The influence of discharge time on post-partial discharge gassing of zinc powder

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.     

Solving a combined cutting-stock and lot-sizing problem with a column generating procedure

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.