Synthesis of structural geometry using approximation concepts

Some approximation concepts for efficient synthesis of structural geometry are presented. Using the force method of analysis and neglecting temporarily the implicit compatibility conditions, an approximate explicit problem (AEP) is introduced. Solving the AEP, a lower bound of the optimum is efficiently obtained. To evaluate the true optimum of the implicit problem, the compatibility conditions are considered for the final geometry of the AEP.Choosing the geometric variables as the independent ones, multilevel solution procedures are proposed. To improve the solution efficiency, the number of independent variables is reduced by geometric variable linking. Also, the number of trial geometries is reduced by introducing a coarse grid in the independent variables space.Several approximation concepts are proposed for efficient solution of the explicit fixed geometry problem. Linear programming models and approximate treatment of the displacement constraints are presented. The proposed solution procedures do not involve multiple implicit analyses of the structure.Numerical examples show that in a variety of structures, where the optimal geometry is not appreciably affected by the compatibility conditions, a single exact analysis is sufficient to evaluate the final optimum. The efficiency of the solution process and the quality of the approximations used are demonstrated.     

How platinum oxide affects the degradation analysis of PEM fuel cell cathodes

In this work, proton exchange membrane fuel cell cathodes are degraded with accelerated-stress-tests.These PtCo containing cathodes are analyzed at begin-of-life and end-of-test with a dedicated diagnostic procedure. For every individual load point, the oxygen transport resistance and voltage losses due to the formation of platinum oxides were obtained in addition to commonly measured electrochemical surface area, high frequency resistance, as well as cathode ionomer resistance. These data were used to break down the voltage losses into six different contributors. With this break down, performance gains and performance losses were determined at end-of-test. At low current densities, it was found that voltage losses due to degradation are dominated by the loss of specific activity and catalyst surface area - in line with the state-of-the-art knowledge. But by quantifying the losses from platinum oxide formation explicitly, we show that end-of-test an unassigned voltage loss is not only present at highest current densities, but already at low current density. More precisely, the unassigned voltage loss shows a linear increase with decreasing half cell voltage and is independent from the chosen accelerated stress test. As this unassigned loss depends on half cell voltage, it might arise from ionomer adsorption.     

电解磷化膜层的统计试验研究

与传统磷化相比，电解磷化工艺采用电能，具有速度更快，膜层更牢固、覆盖更完整，质量控制更方便等优点。对比了传统工艺与该电解磷化工艺的原理，说明了该工艺无铁淤泥生成的原因。通过统计试验讨论了化学成分对磷化膜质量、表面形貌、组分的影响及膜层质量对其暗度的影响。结果表明，膜层质量与溶液中的锌含量有直接关系，但膜层结构基本不受化学成分的影响，而膜层微观形貌与暗度与其质量有关。由此说明，通过控制磷化液中的锌含量可控制膜层质量，而通过检测膜层外观也可有效监控膜层质量。     

Dissociative identity disorder and the sociocognitive model: Recalling the lessons of the past.

In a recent article in this journal, D. H. Gleaves (1996; see record 1996-01403-003) criticized the sociocognitive model (SCM; N. P. Spanos, 1994) of dissociative identity disorder (DID) and argued in favor of a posttraumatic model (PTM) in which DID is conceptualized as a consequence of childhood abuse and other traumatic events. The present authors demonstrate that (a) many of Gleaves's arguments were predicated on misunderstandings of the SCM, (b) scrutiny of the evidence regarding the psychopathology and assessment of DID raises questions concerning the PIM's conceptual and empirical underpinnings, (c) the treatment literature suggests that iatrogenic factors play an important role in the etiology of DID, and (d) the evidence linking child abuse to DID is more problematic than implied by Gleaves. The present authors conclude that Gleaves's analysis underemphasized the cultural manifestations of multiple role enactments and that the history of DID imparts a valuable lesson to contemporary psychotherapists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simulation of external mass transfer in hollow-fiber membrane contactors

External transverse laminar flow of a viscous incompressible fluid and convective diffusion of a solute in a model membrane contactor with a regular system of monodisperse fibers have been numerically simulated. A row of equally spaced parallel fibers was taken as the simplest model system, for which the dependences of the drag force and the efficiency of solute absorption by the fiber (Sherwood number of fiber) upon the distance between the axes of adjacent fibers, and the Reynolds and Peclet numbers have been calculated. The influence of the flow inertia has been studied, and it has been shown that the flow field and mass transport in the contactor can be described in terms of the linear Stokes approximation up to as high Reynolds numbers as dense is the fiber array.     

Problems of noise in hospitals

Measurements of the bleeding time after the ingestion of small doses of aspirin in patients with aspirin idiosyncrasy demonstrate a marked prolongation compared with control patients. Confirmation of this finding offers a clue to the pathogenesis of this condition. Despite the prolonged bleeding time, gastrointestinal haemorrhage is an uncommon event in patients with aspirin idiosyncrasy.     

Cloning of the late genes in the ergosterol biosynthetic pathway ofSaccharomyces cerevisiae—A review

Research on the ergosterol biosynthetic pathway in fungi has focused on the identification of the specific sterol structure required for normal membrane structure and function and for completion of the cell cycle. The pathway and its end product are also the targets for a number of antifungal drugs. Identification of essential steps in ergo-sterol biosynthesis could provide new targets for the development of novel therapeutic agents. Nine of the eleven genes in the portion of the pathway committed exclusively to ergosterol biosynthesis have been cloned, and their essentiality for aerobic growth has been determined. The first three genes;ERG9 (squalene synthase),ERG1 (squalene epoxidase), andERG7 (lanosterol synthase), have been cloned and found to be essential for aerobic viability since their absence would result in the cell being unable to synthesize a sterol molecule. The remaining eight genes encode enzymes which metabolize the first sterol, lanosterol, to ultimately form ergosterol. The two earliest genes,ERG11 (lanosterol demethylase) andERG24 (C-14 reductase), have been cloned and found to be essential for aerobic growth but are suppressed by mutations in the C-5 desaturase (ERG3) gene andfen1 andfen2 mutations, respectively. The remaining cloned genes,ERG6 (C-24 methylase),ERG2 (D8Æ7 isomerase),ERG3 (C-5 desaturase), andERG4 (C-24(28) reductase), have been found to be nonessential. The remaining genes not yet cloned are the C-4 demethylase and the C-22 desaturase (ERG5).     

Does morphology stick? Tailored particle morphologies by swelling polymerization process

Structured dispersion particles suitable for pressure sensitive adhesives (PSA) were synthesized via swelling polymerization technique (EP 359562). Particles consisting of poly(n‐butyl acrylate) copolymerized with different types of carboxylic acids were used as seeds. The final particles were synthesized by swelling polymerization process, using 6 wt % styrene or 6 wt % methyl methacylate. The resulting particle morphology was analyzed by atomic force microscopy (AFM) and transmission electron microscopy (TEM). From previous works (Coll Surf A 2001, 183–185, 725–737; J Appl Polym Sci 2004, 91, 2610–2623) where two‐step emulsion polymerization was used on similar particles, it is expected that the particle morphology is affected by the polarity of the monomer used for swelling polymerization because of the phase compatibility (thermodynamic parameter). In this work, the seed particles used were always of a glass transition temperature (T_g) below polymerization temperature. The diffusion of the growing polymer chains from the swelling polymerization is therefore mainly affected by their own T_g and the influence of the carboxy groups on the chain length of the entering radicals (kinetic parameter). The different morphologies of the single particles are discussed qualitatively. The effects of reaction parameters are compared with the results given in the previous work. The structure of the corresponding dispersion films was characterized using AFM. Correlations to macroscopic properties such as the cohesive strength and peel adhesion to different substrates are discussed. The results are also compared with the application properties of the corresponding unmodified particles, statistical copolymers, and to blends with small sized PMMA or PS particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1444–1455, 2006