PKE-Nefedov — Complex plasma research on the international space station

Complex plasma research is a new and rapidly developing field, with investigations under gravity and microgravity conditions. The complex plasma consists of a common plasma — with electrons, ions and neutrals — and an additional component of small solid particles typically in the range of micrometers. This heavy component in the plasma makes it necessary to perform experiments under microgravity conditions although it is possible to levitate the particles in the laboratory as well. The microparticles in the plasma are charged through the absorption of free electrons and ions to thousands of elementary charges. On Earth, the particles can be levitated in a strong electric field. But this induces stresses to the particle cloud which can only be eliminated under microgravity conditions. It also implies that under gravity conditions only a small part of the parameter phase space of complex plasmas can be investigated. Therefore, to complete the research on complex plasmas, investigations under microgravity conditions are mandatory. This paper overviews the research on complex plasmas on the International Space Station ISS achieved with the first long-term experiment, PKE-Nefedov, used for this research.     

Time-Delayed Positive Velocity Feedback Control Design for Active Control of Structures

In this paper we present and propose a design methodology that uses intentional time delays for the active control of structures. We use here positive velocity-feedback, time-delayed control and show that its performance is, in general, superior to the previously developed methodology of using time delayed, negative velocity-feedback control. A detailed study carried out in this paper of the nonsystem poles and their interaction with the system poles reveals the reasons for this. Analytical results related to performance and stability of the new method are presented. We apply the time delayed positive velocity feedback active control methodology to a multidegree-of-freedom system subjected to the S00E component of ground acceleration recorded during the El Centro 1940 earthquake. The excellent behavior in terms of stability, performance, and control efficiency that is demonstrated by our time-delayed control design as well as its facile implementation makes it attractive for earthquake hazard mitigation in a practical sense.     

Einflu? von Temperatur und mechanischer Behandlung auf die Xanthindehydrase-Aktivit?t der Milch

Zusammenfassung Die Aktivierungsversuche haben gezeigt, daß die Xanthindehydrase in frisch ermolkener Rohmilch nicht quantitativ erfaßbar ist. Erst durch längeres Lagern bei 0° C, durch Rühren; Homogenisieren oder Wolframatzusatz wird das gesamte in der Probe enthaltene Enzym freigesetzt. Da der Aktivierungseffekt dieser Maßnahmen größenordnungsmäßig der gleiche ist, kann angenommen werden, daß die Aktivitätssteigerung in allen diesen Fällen auf ein und demselben Vorgang beruht. Die wahrscheinlichste Erklärung für die Aktivierungserscheinungen ist die Loslösung des Enzyms von der Fettkügelchenmembran.Dagegen können die Ergebnisse aus den Gefrierversuchen nicht in dieser einfachen Weise gedeutet werden. Wie aus der Zusammenstellung der Ergebnisse aus den Aktivierungsversuchen hervorgeht, wird durch Gefrieren der Milch die Aktivität der Probe auf den doppelten bzw. vierfachen Wert gesteigert. Offenbar wird die Xanthindehydrase bei dieser Behandlung in Untereinheiten aufgespalten.Auszug aus der Dissertation vonHubertus Graf zuSolms-Baruth: Über den Einfluß von Effektoren auf die Xanthindehydrase der Milch. Technische Hochschule München 1965.     

Die quantitative Prüfung von Walzgut auf nichtverschweißbare Innenfehler und Sauerstoffgehalt durch Neutronenaktivierungsanalyse

Theoretische und experimentelle Untersuchung zum quantitativen Nachweis von Sauerstoff in Walzgut, insbesondere von nichtver schweißbar en Innenfehlern in Vorbrammen durch Neutronenaktivierungsanalyse. Ableitung eines mathematischen Modells zur Errechnung der γ-Ausbeuten in Abhängigkeit von Sauerstoffgehalt und Diche des Prüfgutes. Beschreibung der Versuchsanordnung für die Messungen an Brammenmodellen und gewalzten Brammen bis 300 mm Dicke. Erörterung der Meßergebnisse und Vergleich mit errechneten Werten. Folgerungen für die betriebliche Anwendung.     

Function of the fully conserved residues Asp99, Tyr52 and Tyr73 in phospholipase A2

In the active centre of pancreatic phospholipase A₂ His48 isat hydrogen-bonding distance to Asp99. This Asp-His couple isassumed to act together with a water molecule as a catalytictriad. Asp99 is also linked via an extended hydrogen bondingsystem to the side chains of Tyr52 and Tyr73. To probe the functionof the fully conserved Asp99, Tyr52 and Tyr73 residues in phospholipaseA₂, the Asp99 residue was replaced by Asn, and each of the twotyrosines was separately replaced by either a Phe or a Gln.The catalytic and binding properties of the Phe52 and Phe73mutants did not change significantly relative to the wild-typeenzyme. This rules out the possibility that either one of thetwo Tyr residues in the wild-type enzyme can function as anacyl acceptor or proton donor in catalysis. The Gln73 mutantcould not be obtained in any significant amounts probably dueto incorrect folding. The Gln52 mutant was isolated in low yield.This mutant showed a large decrease in catalytic activity whileits substrate binding was nearly unchanged. The results suggesta structural role rather than a catalytic function of Tyr52and Tyr73. Substitution of asparagine for aspartate hardly affectsthe binding constants for both monomeric and micellar substrateanalogues. Kinetic characterization revealed that the Asn99mutant has retained no less than 65% of its enzymatic activityon the monomeric substrate rac 1,2-dihexanoyldithio-propyl-3-phosphocholine,probably due to the fact that during hydrolysis of monomericsubstrate by phospholipase A₂ proton transfer is not the rate-limitingstep. The Asp to Asn substitution decreases the catalytic rateon micellar 1,2-dioctanoyl-sn-glycero-3-phosphocholine 25-fold.To explain this remaining activity we suggest that in the mutantthe Asn99 orients His48 in the same way as Asp99 orients His48in native phospholipase A₂ and that the lowered activity iscaused by a reduced stabilization of the transition state.     

Effects of membrane cation transport on pH and microbial fuel cell performance

Due to the excellent proton conductivity of Nafion membranes in polymer electrolyte membrane fuel cells (PEMFCs), Nafion has been applied also in microbial fuel cells (MFCs). In literature, however, application of Nafion in MFCs has been associated with operational problems. Nafion transports cation species other than protons as well, and in MFCs concentrations of other cation species (Na+, K+, NH4+, Ca2+, and Mg2+) are typically 10(5) times higher than the proton concentration. The objective of this study, therefore, was to quantify membrane cation transport in an operating MFC and to evaluate the consequences of this transport for MFC application on wastewaters. We observed that during operation of an MFC mainly cation species other than protons were responsible for the transport of positive charge through the membrane, which resulted in accumulation of these cations and in increased conductivity in the cathode chamber. Furthermore, protons are consumed in the cathode reaction and, consequently, transport of cation species other than protons resulted in an increased pH in the cathode chamber and a decreased MFC performance. Membrane cation transport, therefore, needs to be considered in the development of future MFC systems.     

Influence of size and polarity of residue 31 in porcine pancreatic phospholipase A2 on catalytic properties

Residue 31 of porcine pancreatic phospholipase A₂ (PLA₂) islocated at the entrance to the active site. To study the roleof residue 31 in PLA₂, six mutant enzymes were produced by site-directedmutagenesis, replacing Leu by either Trp, Arg, Ala, Thr, Seror Gly. Direct binding studies indicated a three to six timesgreater affinity of the Trp31 PLA₂ for both monomeric and micellarsubstrate analogs, relative to the wild-type enzyme. The otherfive mutants possess an unchanged affinity for monomers of theproduct analog n-decylphosphocholine and for micelles of thediacyl substrate analog rac-l,2-dioctanoylamino-dideoxy-glycero-3-phosphocholine.The affinities for micelles of the monoacyl product analog n-hexadecylphosphocholinewere decreased 9–20 times for these five mutants. Kineticstudies with monomeric substrates showed that the mutants haveV_max values which range between 15 and 70% relative to the wild-typeenzyme. The V_max values for micelles of the zwitterionic substratel,2-dioctanoyl-sn-glycero-3-phosphocholine were lowered 3–50times. The K_m values for the monomeric substrate and the k_mvalues for the micellar substrate were hardly affected in thecase of five of the six mutants, but were considerably decreasedwhen Trp was present at position 31. The results of these investigationspoint to a versatile role for the residue at position 31: involvementin the binding and orientating of monomeric substrate (analogs),involvement in the binding of the enzyme to micellar substrateanalogs and possibly involvement in shielding the active sitefrom excess water.     

Structural brain changes in early‐onset and late‐onset depression: An update of volumetric MRI findings

Early‐onset (EOD) and late‐onset depression (LOD) are associated with different neuropsychological syndromes and structural brain changes. In this article, neuroimaging studies examining structural brain changes in elderly depressed patients are reviewed. The presented findings support current assumptions that depression in the elderly generally is associated with volume reductions in brain structures, notably in the hippocampus and the orbitofrontal cortex (OFC). Concerning structural cerebral differences between EOD and LOD, the review yielded conflicting results—only for OFC, but not for amygdala or hippocampus, pronounced effects in LOD than in EOD can be assumed. © 2014 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 24, 149–160, 2014