Fast Algorithms for the Simulation of Electromagnetic Metal Forming

Despite the comprehensive understanding of the modelling and numerical simulation of electromagnetic metal forming that has recently been gained, the simulation of real forming situations is still a challenging task due to the large computational resources required. A bottleneck is the computation of the electromagnetic fields, since 100 000 up to several million unknowns are required to represent the geometry of a typical forming device. The purpose of this article is to present new techniques to speed up the simulation of electromagnetic metal forming with particular emphasis on the computation of the electromagnetic fields. An acceleration of the electromagnetic field computation is a significant step towards a virtual design of electromagnetic forming processes.     

Zur ethischen Beurteilung der Präimplantationsdiagnostik

Ethik in der Medizin -     

Influence of Pretreatment Stresses on Inhibitory Effects of Ferulic Acid, an Allelopathic Phenolic Acid

Experiments were conducted to determine the potential for acclimation (i.e., increased tolerance) to allelopathic phenolic acids resulting from pretreatment of seedlings with allelochemical (ferulic acid), drought, or nutrient stress. Cucumber seedlings were exposed to pretreatment stresses in a nutrient culture system for nine days, starting with day 3. Seedlings were subsequently treated for 5 hr with 0, 0.25, 0.5, or 0.75 mM ferulic acid. Acclimation (tolerance) was quantified by percentage inhibition of net phosphorus uptake. Seedlings grown with ferulic acid or drought pretreatment stresses were more tolerant to subsequent ferulic acid treatments (i.e., inhibition of net phosphorus uptake by ferulic acid was reduced). Nutrient pretreatment stress eliminated the inhibitory activity of ferulic acid on net phosphorus uptake. The results suggest that a general acclimation response to a variety of pretreatment stresses can confer an increased tolerance of plants to allelopathic phenolic acids such as ferulic acid.     

Analysis of STAP algorithms for cases with mismatched steering andclutter statistics

In the majority of adaptive radar detection algorithms, the covariance matrix for the clutter-plus-noise is estimated using samples taken from range cells surrounding the test cell. In a nonhomogeneous environment, this can lead to a mismatch between the mean of the estimated covariance matrix and the true covariance matrix for the test cell. Further, an inaccurate target steering vector may also be employed. Closed-form expressions are provided, which give the performance for such cases when any of a set of popular space-time adaptive processing (STAP) algorithms are used. The expressions are exact for some interesting cases. For some other cases, it is demonstrated that the expressions provide good approximations to the exact performance. To simplify the analysis, the samples from the surrounding range cells are assumed to be independent and identically distributed, and these samples are assumed to be independent from the sample taken from the test cell. A small number of important parameters describe which types of mismatches are important and which are not. Monte Carlo simulations, which closely match the predictions of our equations, are included     

Do domain interactions of glycosyl hydrolases from Clostridium thermocellum contribute to protein thermostability?

Cellulolytic and hemicellulolytic enzymes usually have a domaincomposition. The mutual influence of a cellulose-binding domainand a catalytic domain was investigated with cellobiohydrolaseCelK and xylanase XynZ from Clostridium thermocellum. CelK iscomposed of an N-terminal family IV cellulose-binding domain(CBDIV_CelK), a family 9 glycosyl hydrolase domain (Gh9_CelK)and a dockerin domain (DD). CelK without the DD, (CBDIV–Gh9)_CelKand CBDIV_CelK bound cellulose. The thermostability of (CBDIV–Gh9)_CelKwas significantly higher than that of CBDIV_CelK and Gh9_CelK.The temperature optima of (CBDIV–Gh9)_CelK and Gh9_CelKwere 65 and 45°C, respectively. XynZ consists of an N-terminalferuloyl esterase domain (FAE_XynZ), a linker (L), a family VICBD (CBDVI_XynZ), a DD and a xylanase domain. FAE_XynZ and (FAE–L–CBDVI)_XynZ,used in the present study did not bind cellulose, but both werehighly thermostable. Replacement of CBDVI_XynZ with CBDIV_CelKresulted in chimeras with feruloyl esterase activity and theability to bind cellulose. CBDIV_CelK–FAE_XynZ bound cellulosewith parameters similar to that of (CBDIV–Gh9)_CelK. (FAE–L)_XynZ–CBDIV_CelKand FAE_XynZ–CBDIV_CelK had lower relative affinities andbinding capacities than those of (CBDIV–Gh9)_CelK. Thethree chimeras were much less thermostable than FAE_XynZ and(FAE–L–CBDVI)_XynZ. The results indicate that domainsof glycosyl hydrolases are not randomly combined and that domaininteractions affect properties of these domain-structured enzymes.     

A simple dislocation model of deformation resistance of ultrafine-grained materials explaining Hall–Petch strengthening and enhanced strain rate sensitivity

A model is presented where the properties of ultrafine-grained (UFG) materials are explained in terms of the influence of high-angle boundaries on the rates at which dislocations are stored and recovered at the boundaries. The model reproduces the experimental observations that UFG materials reach a steady state where the deformation resistance is independent of strain, that the strain rate sensitivity of flow stress is relatively high and that the steady-state flow stress increases inversely with the square root of grain size. The model results are compared to experimental data for UFG Cu and nanostructured Ni.     

On the microstructural development of the tempered martensitic Cr-steel P 91 during long-term creep—a comparison of data

Microstructural data for creep of the tempered martensitic 9 wt.%CrMoV steel P 91 at 873 K were analyzed. It was found that the variation of the subgrain size with strain conforms to an exponential change from the initial to the stress dependent steady-state value. Analysis of the size distributions of precipitated particles confirmed the previous result that in P 91 there is a superposition of growth of particles with the dynamic precipitation of new particles mostly of type MX. From the distributions the numerical fractions of two types of particles, a predominating population of M₂₃C₆ carbides and a population of fine particles representing mostly carbonitrides of type MX, and their sizes could be deduced. The variation of the creep rate with strain is in qualitative agreement with these microstructural changes.     

Worldwide SOFC Technology Overview and Benchmark

Solid oxide fuel cells (SOFC) are generally considered to be a promising future electricity-generation technology due to their high electrical efficiency. They also display a multi-fuel capability (hydrogen, carbon monoxide, methane, etc.), may play a role in carbon sequestration strategies, and may render the highest electricity generation efficiency in power station design if coupled with a gas turbine. Nevertheless, their development still faces various problems with high-temperature materials, design of cost-effective materials and manufacturing processes, and efficient plant design. This article summarizes world wide efforts in the field of SOFC, presenting an overview of the main SOFC designs and the main developers active in this field. Based on data published in proceedings of international conferences during the last few years, a comparison is made of the results achieved in cell, stack, and system development.     

Improved space-time coding for MIMO-OFDM wireless communications

Improved space-time coding for multiple-input multiple-output orthogonal frequency division multiplexing is studied for wireless systems using QPSK modulation for four transmit and four receive antennas. A 256-state code is shown to perform within 3 dB of outage capacity (and within 2 dB with perfect channel estimation), which is better than any other published result without using iterative decoding     

Use of the unique properties of fluoropolymers in the design of new,highly effective,ecologically friendly technologies for the fine purification of hydrogen halides and their aqueous solutions

A number of properties of fluoropolymers in aqueous solutions of hydrogen halides were investigated. The results enable fluoropolymers to be used in the purification of hydrogen halides and their aqueous solutions. The hydrophobicity of fluoropolymers and their diffusion permeability enable production of hydrogen halides of low moisture content. A second unit for hydroionic convection is based on hydroionic repulsion (determined by the hydrophobic properties of the fluoropolymer) and ionic elimination. The two units enable the highly effective, ecologically safe manufacture of highly pure hydrogen halides and their aqueous solutions to be carried out with minimum feedstock, cooling water, and power consumption. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1383–1387, 2001