Gleichrichter mit Ladekondensator und Hochvakuumröhren oder Selengleichrichtern

Übersicht Ausgehend von den Näherungsformeln vonKammerloher für die Kennlinien von Gleichrichtern mit Ladekondensator und Hochvakuumröhren wird die Zulässigkeit der für sie gemachten Annahmen an Hand einer streng durchgeführten Rechnung überprüft. Dann werden die streng gültigen Gleichungen für dieselben Gleichrichter, jedoch wahlweise mit Hochvakuumröhren oder Selengleichrichtern abgeleitet und die daraus hervorgehenden im erweiterten Sinne gültigen Näherungsformeln aufgestellt. Ferner wird eine direkte Ableitung dieser Formeln angegeben. Für die praktische Anwendung werden einige dieser Formeln kurvenmäßig dargestellt.Mit 13 Textabbildungen.Standard Laboratorium der C. Lorenz AG., Werk Berlin.     

The Role of Intuition and Deliberation for Exploration and Exploitation Success

Advances in social and cognitive psychology and related fields have drawn attention to the role of intuition in organizational decision making. In this study we link intuitive and deliberate decision‐making styles to the success of exploration and exploitation activities, which are understood as two qualitatively opposing strategies that organizations can adopt. We provide empirical evidence that the two opposing strategies are linked to two opposing styles of decision making – intuitive and deliberate. In doing so, we draw on data which we received from 140 entrepreneurs and managing partners of Austrian companies and show that exploration is strongly related to intuitive decision making whereas exploitation draws on both intuitive and deliberate decision making. Based on our findings, we stress the complementarity of the two decision‐making styles, and point out that particularly in the light of the fast‐changing premises in which organizations have to manoeuvre today, decision makers are well advised to use both decision‐making styles to their best benefit.     

Polyelectrolyte‐assisted removal of metal ions with ultrafiltration

The water‐soluble polymers poly(styrene sulfonic acid‐co‐maleic acid) and poly(acrylic acid‐co‐maleic acid) were investigated with respect to their metal‐ion‐binding ability with ultrafiltration. The studied metal ions included Ag(I), Cu(II), Ni(II), Co(II), Ca(II), Mg(II), Pb(II), Cd(II), Zn(II), Al(III), and Cr(III) ions. The retention properties of the polyelectrolytes for the metal ions depended strongly on the ligand type. As for the carboxylate ligands, with increasing concentration and pH, the metal‐binding affinity increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1091–1099, 2005     

Effect of combined feeding stimuli on ingestion by the nematodeTrichostrongylus colubriformis

Ingestion by the nematodeTrichostrongylus colubriformis was stimulated by serotonin, histamine, and dopamine. Immune serum inhibited feeding by both sexes while octopamine depressed feeding by only male nematodes. However, the combined influence of these excitatory and inhibitory stimuli is unknown. Feeding in vitro by both sexes of the nematodeT. colubriformis was similar in millimolar ratios of histamine and dopamine or histamine and serotonin, but not dopamine and serotonin. Feeding by nematodes that was stimulated by histamine, dopamine, and serotonin was decreased by subsequent exposure to octopamine. Conversely, elevated concentrations of histamine, dopamine, and serotonin decreased the inhibitory action of octopamine on helminth ingestion in vitro. Doses of immune serum also decreased the stimulated feeding of nematodes that was induced by histamine, dopamine or serotonin. However, the addition of elevated concentrations of these biogenic amines to immune serum reversed the inhibitory effect. The feeding activity of nematodes may represent a summation of the inhibitory and excitatory stimuli that occur in the chemical environment of the helminth.Mention of a trademark or proprietary product does not constitute a guarantee or warranty by USDA and does not imply its approval to the exclusion of other suitable products.     

Interpenetrating polymer networks from polyurethanes and poly(methyl acrylate)

Simultaneous two-component interpenetrating polymer networks (IPNs) of polyurethane (PU)–poly(methyl acrylate) (PMA) were prepared, as well as the corresponding pseudo-IPNs. A comparison was made between the full IPNs, pseudo-IPNs, and the respective homopolymers. Their ultimate mechanical properties were obtained and the dynamic glass transition temperatures (T_g's) were found using a thermomechanical analyzer. At all compositions, a single T_g(except 50–50 wt %) was found.     

Water softening in a crossflow membrane reactor

This paper presents an investigation on the removal of hardness by using a crossflow membrane reactor. Lime soda (LS) and caustic soda (CS) were added to hard water as softening chemical agents. The effect of the LS-CS dosage, specific cake resistances (α) and transmembrane pressure drop (ΔP) on steady-state rejection and flux was investigated. Also, flux declines were evaluated with respect to various flux decline models. It was found that hardness rejections decrease for LS and increase for CS with increasing LS and CS dosage, respectively. As ΔP increases, it was observed that while steady-state fluxes rise for both additives, hardness rejections were decreased for CS and remained constant for LS. A maximum of 97.5% hardness removal was achieved for 100% stochiometric dosages of CS. Obtained steady-state flux values varied between 224 to 881 L/m² h, depending on added chemical dosages and applied ΔP. It was determined that the reason for the flux decline at the beginning of the filtration (i.e., in the rapid flux decline period, RPD) was due to an intermediate pore blocking mechanism. As filtration progressed to the slow flux decline period (SDP), it was concluded that cake filtration occurred for all experiments. If solid matter concentration in the feed solution and applied ΔP are relatively low, the experiments showed that flux decline is due to the intermediate pore blocking mechanism. However, it was determined that if solid matter concentration in the feed solution and applied ΔP are relatively high, the flux decline model fits well with the cake filtration model.     

How does poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) trigger phase separation in aqueous alcohol?

Short chain alcohols, such as methanol and ethanol, are fairly well miscible in water over full mixing ratios. Moreover, when poly(N-isopropylacrylamide) is added in the same mixtures, the solution phase separates at low alcohol concentrations. From the fundamental understanding of phase separation within the mean-field picture, we can expect interaction parameter χ between water and alcohol to be significantly larger than unity. On the contrary, however, χ remains invariant and close to zero over full mixing ratios of aqueous alcohol mixtures. Here, we show how the preferential binding of poly(N-isopropylacrylamide) with alcohols facilitates local phase separation without altering bulk solution χ.     

Controlled Microfabrication of High‐Aspect‐Ratio Structures in Silicon at the Highest Etching Rates: The Role of H2O2 in the Anodic Dissolution of Silicon in Acidic Electrolytes

In this work the authors report on the controlled electrochemical etching of high‐aspect‐ratio (from 5 to 100) structures in silicon at the highest etching rates (from 3 to 10 µm min^?1) at room temperature. This allows silicon microfabrication entering a previously unattainable region where etching of high‐aspect‐ratio structures (beyond 10) at high etching rate (over 3 µm min^?1) was prohibited for both commercial and research technologies. Addition of an oxidant, namely H₂O₂, to a standard aqueous hydrofluoric (HF) acid electrolyte is used to dramatically change the stoichiometry of the silicon dissolution process under anodic biasing without loss of etching control accuracy at the higher depths (up to 200 µm). The authors show that the presence of H₂O₂ reduces the valence of the dissolution process to 1, thus rendering the electrochemical etching more effective, and catalyzes the etching rate by opening a more efficient path for silicon dissolution with respect to the well‐known Gerischer mechanism, thus increasing the etching speed at both shorter and higher depths.     

Biosynthesis and Characterization of Copper Nanoparticles Using Shewanella oneidensis: Application for Click Chemistry

Copper nanoparticles (Cu‐NPs) have a wide range of applications as heterogeneous catalysts. In this study, a novel green biosynthesis route for producing Cu‐NPs using the metal‐reducing bacterium, Shewanella oneidensis is demonstrated. Thin section transmission electron microscopy shows that the Cu‐NPs are predominantly intracellular and present in a typical size range of 20–40 nm. Serial block‐face scanning electron microscopy demonstrates the Cu‐NPs are well‐dispersed across the 3D structure of the cells. X‐ray absorption near‐edge spectroscopy and extended X‐ray absorption fine‐structure spectroscopy analysis show the nanoparticles are Cu(0), however, atomic resolution images and electron energy loss spectroscopy suggest partial oxidation of the surface layer to Cu₂O upon exposure to air. The catalytic activity of the Cu‐NPs is demonstrated in an archetypal “click chemistry” reaction, generating good yields during azide‐alkyne cycloadditions, most likely catalyzed by the Cu(I) surface layer of the nanoparticles. Furthermore, cytochrome deletion mutants suggest a novel metal reduction system is involved in enzymatic Cu(II) reduction and Cu‐NP synthesis, which is not dependent on the Mtr pathway commonly used to reduce other high oxidation state metals in this bacterium. This work demonstrates a novel, simple, green biosynthesis method for producing efficient copper nanoparticle catalysts.