1,208 research outputs found

    The Parallel Implementation of the Waveform Relaxation Method for Transient Stability Simulations

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    In this paper, the authors extend the results of their earlier paper on waveform relamtion (WR), which is a parallel algorithm for transient stability analysis. The WR algorithm is extended to a structure-preserving power system model in which the loads are retained. This results in a system of differential/ algebraic equations (DAEs). Power systems exhibit several unique dynamic properties which may be exploited in an advantageous manner by the WR algorithm. This leads to a greater computational efficiency than most other direct methods of simulation. This paper presents several theoretical results as well as computational results on parallel implementation

    Technical Design Report for PANDA Electromagnetic Calorimeter (EMC)

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    This document presents the technical layout and the envisaged performance of the Electromagnetic Calorimeter (EMC) for the PANDA target spectrometer. The EMC has been designed to meet the physics goals of the PANDA experiment. The performance figures are based on extensive prototype tests and radiation hardness studies. The document shows that the EMC is ready for construction up to the front-end electronics interface

    Bayesian analysis of variable-order, reversible Markov chains

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    We define a conjugate prior for the reversible Markov chain of order rr. The prior arises from a partially exchangeable reinforced random walk, in the same way that the Beta distribution arises from the exchangeable Poly\'{a} urn. An extension to variable-order Markov chains is also derived. We show the utility of this prior in testing the order and estimating the parameters of a reversible Markov model.Comment: Published in at http://dx.doi.org/10.1214/10-AOS857 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

    Quality-of-service provisioning in high speed networks : routing perspectives

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    The continuous growth in both commercial and public network traffic with various quality-of-service (QoS) requirements is calling for better service than the current Internet\u27s best effort mechanism. One of the challenging issues is to select feasible paths that satisfy the different requirements of various applications. This problem is known as QoS routing. In general, two issues are related to QoS routing: state distribution and routing strategy. Routing strategy is used to find a feasible path that meets the QoS requirements. State distribution addresses the issue of exchanging the state information throughout the network, and can be further divided into two sub-problems: when to update and how to disseminate the state information. In this dissertation, the issue of when to update link state information from the perspective of information theory is addressed. Based on the rate-distortion analysis, an efficient scheme, which outperforms the state of the art in terms of both protocol overhead and accuracy of link state information, is presented. Second, a reliable scheme is proposed so that, when a link is broken, link state information is still reachable to all network nodes as long as the network is connected. Meanwhile, the protocol overhead is low enough to be implemented in real networks. Third, QoS routing is NP-complete. Hence, tackling this problem requires heuristics. A common approach is to convert this problem into a shortest path or k-shortest path problem and solve it by using existing algorithms such as Bellman-Ford and Dijkstra algorithms. However, this approach suffers from either high computational complexity or low success ratio in finding the feasible paths. Hence, a new problem, All Hops k-shortest Path (AHKP), is introduced and investigated. Based on the solution to AHKP, an efficient self-adaptive routing algorithm is presented, which can guarantee in finding feasible paths with fairly low average computational complexity. One of its most distinguished properties is its progressive property, which is very useful in practice: it can self-adaptively minimize its computational complexity without sacrificing its performance. In addition, routing without considering the staleness of link state information may generate a significant percentage of false routing. Our proposed routing algorithm is capable of minimizing the impact of stale link state information without stochastic link state knowledge. Fourth, the computational complexities of existing s-approximation algorithms are linearly proportional to the adopted linear scaling factors. Therefore, two efficient algorithms are proposed for finding the optimal (the smallest) linear scaling factor such that the computational complexities are reduced. Finally, an efficient algorithm is proposed for finding the least hop(s) multiple additive constrained path for the purpose of saving network resources

    Team MIT Urban Challenge Technical Report

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    This technical report describes Team MITs approach to theDARPA Urban Challenge. We have developed a novel strategy forusing many inexpensive sensors, mounted on the vehicle periphery,and calibrated with a new cross-­modal calibrationtechnique. Lidar, camera, and radar data streams are processedusing an innovative, locally smooth state representation thatprovides robust perception for real­ time autonomous control. Aresilient planning and control architecture has been developedfor driving in traffic, comprised of an innovative combination ofwell­proven algorithms for mission planning, situationalplanning, situational interpretation, and trajectory control. These innovations are being incorporated in two new roboticvehicles equipped for autonomous driving in urban environments,with extensive testing on a DARPA site visit course. Experimentalresults demonstrate all basic navigation and some basic trafficbehaviors, including unoccupied autonomous driving, lanefollowing using pure-­pursuit control and our local frameperception strategy, obstacle avoidance using kino-­dynamic RRTpath planning, U-­turns, and precedence evaluation amongst othercars at intersections using our situational interpreter. We areworking to extend these approaches to advanced navigation andtraffic scenarios

    Characterization and optimization of the prototype DEPFET modules for the Belle II Pixel Vertex Detector

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    Der Elektron-Positron-Speicherring KEKB wurde von 1999 bis 2010 am Hochenergie- und Beschleunigerforschungszentrum KEK in Tsukuba (Japan) betrieben, wobei die Schwerpunktsenergie hauptsächlich dem Anregungszustand des Y(4S)-Teilchens (10.58 GeV) entsprach. KEKB erreichte während seiner Betriebszeit eine integrierte Luminosität von 1041 fb^-1. Mit dem Belle-Detektor wurden die Zerfälle von B-Mesonen untersucht, die die Theorie über den Ursprung der CP-Verletzung im Standardmodell von Kobayashi und Maskawa bestätigten; dafür erhielten beide im Jahr 2008 den Nobelpreis. Der Speicherring KEKB wird zu SuperKEKB erneuert, um Antworten auf die vielen offenen Fragen des Standardmodells und möglicherweise „Neue Physik“ jenseits des Standardmodells zu finden. Die Teilchenstrahlen werden auf etwa 50 Nanometer am Wechselwirkungspunkt kollimiert (“nano-beam scheme“), damit die weltweit höchste instantane Luminosität von KEKB um einen weiteren Faktor 40 auf 8x10^35 cm^-2 s^-1 gesteigert werden kann. Die (physikalischen) Ziele des Projekts sind die präzise Vermessung der CP-Verletzung und die Suche nach seltenen oder sogar „verbotenen“ Zerfällen von B-Mesonen, um mögliche Abweichungen vom Standardmodell zu finden. Verschiedene Komponenten müssen von Belle erneuert werden (Belle II), um die hohe instantane Luminosität von SuperKEKB zu bewältigen. Nicht nur die Anzahl der Ereignisse nimmt zu, sondern auch der Untergrund, insbesondere der unvermeidbare Zwei-Photonen-Untergrundprozess. Mit einem Siliziumvertexdetektor werden im Experiment die Zerfallsvertices der B-Mesonen analysiert. Der Vertexdetektor soll so nah wie möglich um das Strahlrohr platziert werden, damit Extrapolationsfehler der Zerfallsvertices minimiert werden. Da ein Siliziumstreifendetektor, wie er in Belle benutzt wurde, den hohen Untergrund im geringen Abstand zum Strahlrohr nicht bewältigen kann, wird ein neuartiger Pixel-Detektor (PXD) installiert, der aus monolitischen DEPFET (DEPletierter p-Kanal Feld Effekt Transistor) Pixel-Sensoren besteht. Der DEPFET-Sensor kann bis zu 75 um gedünnt werden, um die Mehrfachstreuung zu minimieren, besitzt ein hohes Signal-Rausch-Verhältnis, verfügt über eine intrinsische Positionsausflösung von 15 um, unterstützt schnelle Auslesezeiten von weniger als 20 us und hat einen geringen Stromverbrauch. Der PXD besteht insgesamt aus 40 Sensor-Modulen, wobei jedes mit 14 ASICs für die Steuerung und Auslese bestückt ist. Die Module werden in zwei Lagen um das Strahlrohr montiert. Die vorliegende Arbeit fokussiert sich auf die Charakterisierung und Optimierung der ersten Prototypen der finalen PXD-Module. Die kombinierte Kontroll- und Ausleseelektronik wurde auf Prototyp-Modulen untersucht, verbessert und optimiert: Sechs Switcher pro Modul schalten die Pixelzeilen nacheinander ein (rolling-shutter Modus / zeilenweiser Auslesemodus), um die signalverstärkten Drainströme der DEPFET-Pixel zu messen und die Pixelzelle zurückzusetzen. Insgesamt messen 1000 ADCs auf jedem Modul die Drainströme mit einer PXD-Auslesefrequenz von 50 kHz. Damit die Pixel korrekt angesteuert werden, wurden Steuerungssequenzen für die Switcher simuliert und auf den Prototyp-Modulen getestet. Die systemrelevanten Aspekte, wie die inter-ASIC Kommunikation, Kontrollsequenzen und Synchronisationsprobleme wurden eingehend untersucht und optimiert. Zusätzlich wurden Messungen mit radioaktiven Quellen und Lasern durchgeführt, um die optimalen Operationsspannungen für verschiedene Betriebsmodi zu bestimmen. Der zeilenweise Auslesemodus von 20 us erscheint problematisch, wenn ein kurzzeitiger, periodischer Untergrund auftritt, beispielsweise während der Aufstockungsinjektion der Teilchenpakete in SuperKEKB. Um dieses Problem zu lösen, wurde ein neuer Arbeitsmodus vorgeschlagen und untersucht, welcher einen „gated“ Betriebsmodus des Detektors ermöglicht. Dies schaltet den Pixel-Vertex-Detektor für eine kurze Zeitspanne 1-2 us blind, während der hohe Untergrund erwartet wird. Ein Prototyp-Modul wurde im „Gated Mode“ betrieben; Ursachen von auftretenden Problemen wurden ausfindig gemacht. Die daraus resultierenden Verbesserungen trugen dem finalen Modul-Layout bei. Außerdem wurden zwei verschiedene Arten von Prototyp-Modulen erfolgreich in einer Strahltest-Kampagne betrieben. Die Ladungs-Cluster-Verteilungen, Positionsauflösung und Effizienzen wurden studiert, wobei deutlich wird, dass sich die Sensoren gut für den Betrieb in Belle II eignen.The Belle detector was located at the electron-positron collider KEKB in Tsukuba, Japan. It operated from 1999 to 2010, running mostly at the Y(4S) resonance, and achieved an integrated luminosity of 1041 fb^-1. The main research topic was the CP violation in the B meson system. The measured results on B meson decays confirmed the theory of Kobayashi and Maskawa (Nobel Prize 2008) on the origin of CP violation within the Standard Model. Since the Standard Model nevertheless leaves many open questions, the upgrade of KEKB to SuperKEKB has the potential to find New Physics beyond the Standard Model. SuperKEKB will increase the world-record instantaneous luminosity of KEKB by a factor of 40 to 8x10^35 cm^-2 s^-1 using the nano-beam scheme. The physics goals are the precise measurement of CP violation, searching for rare or even "forbidden" decays of B mesons and finding small deviations from the Standard Model with larger statistics and more precise measurements than ever before. To cope with the large luminosity of SuperKEKB various components of Belle need to be upgraded to the Belle II detector. Given the high luminosity, not only the number of events increases but also the background, in particular, the inevitable two-photon process. To minimize the extrapolation errors of the decay vertices of the B mesons the vertex detector should be situated as close as possible to the beam pipe. A silicon strip detector, as used in Belle, is not able to cope with the high background at SuperKEKB. Therefore, a novel pixel vertex detector (PXD) will be installed, featuring monolithic sensors using the DEPFET (DEPleted p-channel Field Effect Transistor) technology. The sensors can be thinned down to only 75 um to minimize multiple scattering, offer high signal-to-noise ratio, provide high intrinsic position resolution of ~15 um, support fast readout within 20 us and have low power consumption. The PXD consists of 40 sensors, each equipped with 14 custom-made ASICs for control and readout, which are mounted in two layers around the beam pipe. This thesis focuses on the characterization and optimization of the first full-size prototypes of the final sensor modules for the PXD. The combined control and readout electronics was investigated, improved and optimized on prototype modules equipped with the complete set of ASICs: six Switchers per module enable the pixel rows subsequently (rolling shutter mode) to measure the signal-amplified Drain currents from the DEPFETs and reset the device. A total of 1000 ADCs on each module sample the Drain currents resulting in a readout frequency of 50 kHz for the PXD. Switcher control sequences were simulated and applied for the prototypes to control the pixels properly. The system-related aspects like the inter-ASIC communication, control sequences and synchronization issues were studied and optimized. Measurements with radioactive sources and lasers were performed to determine optimal voltages for the different operation modes. The rolling shutter readout mode is problematic when transient intermittent high background is present, for instance during the top-up injection of SuperKEKB. To address this issue a new readout mode is proposed and investigated, which allows a "gated" or shutter-controlled operation of the detector. This makes the detector blind for a certain time interval in which high background is expected. A prototype module was operated in the Gated Mode; causes of encountered problems were identified and improvements were proposed and applied to the module layout. Two different kinds of prototype modules were operated successfully in a beam test campaign. The cluster charge distributions, position resolutions and efficiencies were studied and prove that the sensor is well suited for the operation at Belle II
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