613 research outputs found
Characterization of the Esp signalosome: Two hybrid histidine kinases utilize a novel signaling mechanism to regulate developmental progression in Myxococcus xanthus.
Histidine-aspartate signaling systems are used by bacteria, archaea and eukarya to integrate stimuli over time and space generating coordinated, fine-tuned cellular responses. A hallmark feature is the high modularity of the signaling protein modules which can form simple âtwo-componentâ systems, and also sophisticated âmulti-componentâ systems. The deltaproteobacterium Myxococcus xanthus contains a large repertoire of signaling proteins, many of which regulate its complex multicellular developmental program. In this respect, one important systems is the Esp signaling system, consisting of the hybrid histidine protein kinase, EspA, two serine/threonine protein kinases (PktA5 and PktB8), and a putative transport protein (EspB).
In the presented study, I assign an orphan hybrid histidine protein kinase, EspC, to the Esp signaling system which negatively regulates progression through the M. xanthus developmental program. The genetic analysis revealed that EspC is an essential component of this system, because ÎespA, ÎespC, and ÎespAÎespC double mutants shared an identical early developmental phenotype. Surprisingly, disruption of EspCâs auto-phosphorylation in vivo did not produce a mutant developmental phenotype, whereas substitution of its phospho-accepting residue within the receiver domain resulted in the null phenotype. Furthermore, it is shown that although the EspC histidine kinase could efficiently autophosphorylate in vitro, it did not act as a phospho-donor to its own receiver domain. Instead, both, in vitro and in vivo analyses elucidated that the phospho-donor instead is EspAâs histidine kinase. Therefore, EspA and EspC participate in a novel hybrid histidine protein kinase signaling mechanism involving both inter- and intraprotein phosphotransfer. This inter- and intraprotein phosphotransfer results in the combined phosphorylation of EspAâs and EspCâs receiver domains which represents the output of the Esp signaling system. Further genetic analyses suggested that this Esp system is regulated on the level of its phosphatase activity, likely involving the sensing domains of EspC for regulation. Finally, I uncovered that the Esp system stimulates the proteolytic turnover of MrpC, a crucial transcription factor of the developmental program, via as yet unidentified serine protease.
Altogether, these data unravel a novel signaling mechanism of His-Asp signaling systems, and thus expand the knowledge about the complexity and plasticity of these crucial signal transduction systems
The Fraunhofer Quantum Computing Portal - www.qc.fraunhofer.de - A web-based Simulator of Quantum Computing Processes
Fraunhofer FIRST develops a computing service and collaborative workspace
providing a convenient tool for simulation and investigation of quantum
algorithms. To broaden the twenty qubit limit of workstation-based simulations
to the next qubit decade we provide a dedicated high memorized Linux cluster
with fast Myrinet interconnection network together with a adapted parallel
simulator engine. This simulation service supplemented by a collaborative
workspace is usable everywhere via web interface and integrates both hardware
and software as collaboration and investigation platform for the quantum
community. The beta test version realizes all common one, two and three qubit
gates, arbitrary one and two bit gates, orthogonal measurements as well as
special gates like Oracle, Modulo function, Quantum Fourier Transformation and
arbitrary Spin-Hamiltonians up to 31 qubits. For a restricted gate set it
feasible to investigate circuits with up to sixty qubits. URL:
http://www.qc.fraunhofer.d
Analyse der NetzrĂŒckwirkungen und Eingangsfilter gepulster leistungselektronischer Umrichter
Die vorliegende Arbeit behandelt die Bauvolumina von Eingangsfiltern
fĂŒr leistungselektronische Umrichter, da diese neben dem KĂŒhlerbauvolumen
ein wesentlicher Faktor fĂŒr das Gesamtbauvolumen sind.Die Untersuchung wird
fĂŒr kleine Ausgangsleistungen (3 kVA) durchgefĂŒhrt, da
dieser Leistungsbereich das gröĂte Marktsegment einnimmt.Aufgrund
neuartiger Halbleitermaterialien werden zukĂŒnftig höhere Pulsfrequenzen
bei gleichzeitig kleiner Verlustleistung möglich sein. Es ist allgemein
bekannt, dass die EingangsfilterbaugröĂe durch die gewĂ€hlte Pulsfrequenz
beeinflusst wird, weshalb ein Untersuchungspunkt dieser Arbeit darin
besteht, Aussagen ĂŒber die Eingangsfilterbauvolumina unter Variation
der Pulsfrequenz abzuleiten. Neben der Variation der Pulsfrequenz besteht die
Möglichkeit, andere Umrichtertopologien als den am Markt etablierten
Spannungszwischenkreisumrichter zu verwenden. Aufgrund des nicht vorhandenen
Zwischenkreiskondensators ist der Matrixumrichter prinzipiell
vollstÀndig in Silizium integrierbar und wird daher ebenfalls hinsichtlich
der Eingangsfilterbauvolumina untersucht.Die Hauptzielsetzung der Arbeit
liegt daher in einer vergleichenden Betrachtung der
Eingangsfilterbauvolumina beider Umrichter unter Variation der Pulsfrequenz
sowie der Filterordnung.Die Untersuchung erfolgt auf einer einheitlichen
Vergleichsbasis, weshalb ein Filterauslegungsalgorithmus, der sowohl fĂŒr
spannungseinprÀgende Stromrichter, zu denen
der Spannungszwischenkreisumrichter zĂ€hlt, als auch fĂŒr stromeinprĂ€gende
Stromrichter, zu denen der Matrixumrichter zÀhlt, herangezogen wird. Der
vorgenannte Filterauslegungsalgorithmus berĂŒcksichtigt auch die
parasitÀren SerienwiderstÀnde der Filterbauelemente.Die Filterauslegung
erfolgt fĂŒr Pseudospektren, welche die maximalen Schwingungsamplituden der
realen Spektren aller Betriebspunkte enthalten. Die realen Spektren
werden mathematisch durch Doppelfourierreihen eindeutig beschrieben. Um auch
bei der Ermittlung der NetzrĂŒckwirkungen eine einheitliche Vergleichsbasis
sicherzustellen, werden allgemeine Modulationsvorschriften angewandt, aus
denen sich die Schaltpulse beider Umrichter ableiten lassen. AbschlieĂend
werden die Eingangsfilterbauvolumina basierend auf
Bauvolumenkennlinien realer Bauelemente fĂŒr beide Umrichter berechnet und
vergleichend diskutiert
Semantically valid integration of development processes and toolchains
As an indispensable component of todayâs world economy and an increasing success factor in production and other processes, as well as products, software needs to handle a growing number of specific requirements and influencing factors that are driven by globalization. Two common success factors in the domain of Software Systems Engineering are standardized software development processes and process-supported toolchains. Development processes should be formally integrated with toolchains. The sequence and the results of toolchains must also be validated with the specifications of the development process on several levels. The outcome of a conceptual deductive analysis is that there is neither a formal general mapping nor a generally accepted validation mechanism for the challenges that such an integrated concept faces. To close this research gap, this paper focuses on the core issue of the integration of development processes and toolchains in order to create benefits for modeling and automatization in the domain of systems engineering. Therefore, it describes a self-developed integration approach related to the recently introduced prototypical technical implementation TOPWATER. A unified metamodel specifies how processes and toolchains are linked by a general mapping mechanism that considers test options for the structural, content, and semantic levels
Configurations with few crossings in topological graphs
AbstractIn this paper we study the problem of computing subgraphs of a certain configuration in a given topological graph G such that the number of crossings in the subgraph is minimum. The configurations that we consider are spanning trees, sât paths, cycles, matchings, and Îș-factors for Îșâ{1,2}. We show that it is NP-hard to approximate the minimum number of crossings for these configurations within a factor of k1âΔ for any Δ>0, where k is the number of crossings in G.We then give a simple fixed-parameter algorithm that tests in Oâ(2k) time whether G has a crossing-free configuration for any of the above, where the Oâ-notation neglects polynomial terms. For some configurations we have faster algorithms. The respective running times are Oâ(1.9999992k) for spanning trees and Oâ((3)k) for s-t paths and cycles. For spanning trees we also have an Oâ(1.968k)-time Monte-Carlo algorithm. Each Oâ(ÎČk)-time decision algorithm can be turned into an Oâ((ÎČ+1)k)-time optimization algorithm that computes a configuration with the minimum number of crossings
Automatische Reduktion chemischer Reaktionsmechanismen am Beispiel der Oxidation von höheren Kohlenwasserstoffen und deren Verwendung in reaktiven Strömungen
Detaillierte Reaktionsmechanismen, die auf Elementarreaktionen beruhen, umfassen fĂŒr Verbrennungssysteme höherer Kohlenwasserstoffe oft mehr als 100 Spezies. Solche komplexen Reaktionssysteme können nicht zur Simulation von technischen Verbrennungssystemen verwendet werden, da der Rechenzeitbedarf fĂŒr eine CFD-Rechnung zu hoch wĂ€re. Eine Möglichkeit zur Reduktion chemischer Reaktionsmechanismen stellt die ILDM-Methode dar. Sie beruht auf einer mathematischen Analyse der lokalen Zeitskalen des chemischen Quellterms und der Annahme, dass das chemische System bereits auf eine niedrig-dimensionale Mannigfaltigkeit relaxiert ist. Die Bestimmung der niedrig-dimensionalen Mannigfaltigkeit ist rechenzeitaufwendig. Daher wird die Mannigfaltigkeit in Tabellen gespeichert, die allerdings sehr groĂ werden können (einige 100 MB). Es wurde eine effiziente Tabellierungsmethode entwickelt, die einen schnellen Zugriff auf die Daten erlaubt. Um die Tabellenerzeugung zu beschleunigen, wurde an Algorithmus entwickelt, der die Erstellung einer ILDM-Tabelle auf einem Parallelrechner ermöglicht. Die erstellten Tabellen wurden zur Simulation rĂ€umlich homogenen Reaktionssysteme und freier laminarer Vormischflammen verwendet
Time to acknowledge the role of consumers in responsible innovation
Innovation is a complex and often uncertain evolutionary process that involves many actors, not just producers, argue Michael P. Schlaile, Matthias Mueller, Michael Schramm, and Andreas Pyk
Imaging correlated wave functions of few-electron quantum dots: Theory and scanning tunneling spectroscopy experiments
We show both theoretically and experimentally that scanning tunneling
spectroscopy (STS) images of semiconductor quantum dots may display clear
signatures of electron-electron correlation. We apply many-body tunneling
theory to a realistic model which fully takes into account correlation effects
and dot anisotropy. Comparing measured STS images of freestanding InAs quantum
dots with those calculated by the full configuration interaction method, we
explain the wave function sequence in terms of images of one- and two-electron
states. The STS map corresponding to double charging is significantly distorted
by electron correlation with respect to the non-interacting case.Comment: RevTeX 4.0, 5 pages, 3 B/W figures, 1 table. This paper is based on
an invited talk presented by the authors at the 28th International Conference
on the Physics of Semiconductors, which was held 24-28 July 2006, in Vienna,
Austri
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