Multispace and multilevel BDDC

The Balancing Domain Decomposition by Constraints (BDDC) method is the most advanced method from the Balancing family of iterative substructuring methods for the solution of large systems of linear algebraic equations arising from discretization of elliptic boundary value problems. In the case of many substructures, solving the coarse problem exactly becomes a bottleneck. Since the coarse problem in BDDC has the same structure as the original problem, it is straightforward to apply the BDDC method recursively to solve the coarse problem only approximately. In this paper, we formulate a new family of abstract Multispace BDDC methods and give condition number bounds from the abstract additive Schwarz preconditioning theory. The Multilevel BDDC is then treated as a special case of the Multispace BDDC and abstract multilevel condition number bounds are given. The abstract bounds yield polylogarithmic condition number bounds for an arbitrary fixed number of levels and scalar elliptic problems discretized by finite elements in two and three spatial dimensions. Numerical experiments confirm the theory.     

G-protein signaling: fine-tuning signaling kinetics

Mammalian 'regulators of G protein signaling' (RGS proteins) help shut off G-protein-mediated signaling by GTPase activation. But new evidence shows that RGS proteins can also speed up the activation of signaling. The combined effect is a change in signaling kinetics without a decrease in signaling intensity.     

Identification and characterization of epitopes on the 120-kilodalton surface protein antigen of Rickettsia prowazekii with synthetic peptides

The 120-kDa surface protein antigens (SPAs) of typhus rickettsiae are highly immunogenic and have been shown to be responsible for the species-specific serological reactions of the typhus group rickettsiae. To study the immunochemistry of these proteins, overlapping decapeptides encompassing the whole protein were synthesized on derivatized polyethylene pins. A modified enzyme-linked immunosorbent assay was used to identify epitopes recognized by rabbit hyperimmune antisera to Rickettsia prowazekii SPA. Eight distinct epitopes were mapped by this method in three regions. Four of the epitopes, which were located in the carboxyterminus of mature processed SPA, were strongly competitively inhibited by native folded SPA but not by intact rickettsiae, suggesting that they were on the SPA surface but not exposed on the rickettsial surface. Three of these epitopes were present on both R. prowazekii and Rickettsia typhi SPAs. The immunoreactivities of five epitopes were further characterized by synthesizing modified peptides. Glycine substitution experiments determined the critical residues in the epitopes. The dependence of binding of the peptide epitopes to the polyclonal antisera was mapped to single residues. The limited number and weak reactivity of linear peptide epitopes observed with human and rabbit sera, possibly due to a lack of the methylated amino acids which are present in rickettsia-derived SPA, suggest that the present approach will not provide useful synthetic antigens for diagnosis of typhus infections.     

更大温度范围的钽电容器

汽车电子应用不断增多,从驾驶室娱乐、安全气囊、ABS到发动机.它们各自由于在车内位置不同而要求不同,由此对工作温度、过程电压和可靠性提出了多种要求.     

Polyaniline nanotubes: conditions of formation

The courses of aniline oxidation with ammonium peroxydisulfate in aqueous solutions of strong (sulfuric) and in weak (acetic) acids, followed by temperature and acidity changes, are different. In solutions of sulfuric acid, granular polyaniline (PANI) was produced; in solutions of acetic acid, PANI nanotubes were obtained. The external diameter of the nanotubes was 100–300 nm, the internal cavity 20–100 nm, and the length extended to several micrometres. The morphology of PANI, granular or tubular, depends on the acidity conditions during the reaction rather than on the chemical nature of the acid. PANI nanotubes were also produced when aniline was oxidized in the absence of any acid. The bulk conductivity of PANI prepared in solutions of acetic acid was 0.08–0.27 S cm^?1, depending on the acid concentration. Protonated PANI prepared in sulfuric and acetic acids were deprotonated with ammonium hydroxide to obtain PANI bases and the ammonium salt of the protonating acid. FTIR spectroscopy showed the differences in the molecular structure of the PANI bases. Irrespective of whether the polymerization was performed in solutions of sulfuric or acetic acid, PANI had hydrogen sulfate counter‐ions only. The PANI morphology is thus not controlled by the nature of counter‐ions. The acidity of the reaction medium determines the protonation of monomer, oligomer and polymer species. The chemistry of aniline oxidation is likely to be affected especially by the protonation of an intermediate in the pernigraniline form. It is proposed that, in the course of aniline oxidation, pH‐dependent self‐assembly of aniline oligomers predetermines the final PANI morphology. Copyright © 2005 Society of Chemical Industry     

Overview: Signal production and detection.

Studies of signal production and detection are complicated by the diverse modalities used by animals, constraints of human signal perception, and limitations of a controlled laboratory environment. These complications can be addressed by creative approaches to studying anatomical adaptations for signal production and detection, innovative technology, and careful studies of signal production and detection in the field. These solutions should overcome the perceptual limitations of researchers as they explore Umwelten in other species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Safety-relevant mode confusions—modelling and reducing them

Mode confusions are a significant safety concern in safety-critical systems, for example in aircraft. A mode confusion occurs when the observed behaviour of a technical system is out of sync with the user's mental model of its behaviour. But the notion is described only informally in the literature. We present a rigorous way of modelling the user and the machine in a shared-control system. This enables us to propose precise definitions of ‘mode’ and ‘mode confusion’ for safety-critical systems. We then validate these definitions against the informal notions in the literature. A new classification of mode confusions by cause leads to a number of design recommendations for shared-control systems. These help in avoiding mode confusion problems. Our approach supports the automated detection of remaining mode confusion problems. We apply our approach practically to a wheelchair robot.     

Stress singularities in a periodically layered composite near interface crack tips

The paper deals with the asymptotic analysis of stresses near interface crack tips in the periodically two-layered elastic composites. The problem is investigated for the plane state of strain within the framework of the homogenized model with microlocal parameters. The angular dependence of stresses at the crack tip is presented for different mechanical and geometrical properties of the composite.