Statische und dynamische Eigenschaften komplexer Flüssigkeiten aus Molekulardynamiksimulationen

Diese Arbeit mit dem Titel "Statische und dynamische Eigenschaften komplexer Flüssigkeiten aus Molekulardynamiksimulationen" behandelt einige Aspekte des Ableitens von Flüssigkeitseigenschaften aus Molekulardynamiksimulationen. Kapitel 1 ist eine Einleitung in die Methode der Molekulardynamiksimulation. Es beschreibt die theoretische Grundlage für diese Simulationsmethode. Kapitel 2 erklärt die statistischen Methoden, die benutzt werden, um Struktur und Dynamik von Flüssigkeiten zu beschreiben, während Kapitel 3 die Strukturbeschreibung von Flüssigkristallen einführt. Kapitel 4 ist das erste Kapitel, das Ergebnisse der Doktorarbeit enthält und ist eine Erweiterung der Diplomarbeit des Authors: Durch die sehr gute Übereinstimmung von Messungen an Salzschmelzen mit Molekulardynamiksimulationen, die ein einfaches Paarpotential nutzen, werden zusätzliche Konsequenzen für die Auswertung der Experimentaldaten beschrieben. Anisotrope Diffusion von Flüssigkristallen wird in Kapitel 5 beschrieben; insbesondere single-file Diffusion in kolumnaren Diskotenphasen wird erforscht. Kapitel 6 behandelt die isotrope-nematische Phasengrenze. Einige Verfahren, die Position der Phasengrenze in Simulationen zu erfassen, werden diskutiert. Abschließend wird eine Methode diskutiert, die die Oberflächenspannung aus der Simulation erfassen kann, ohne die Phasengrenze direkt zu bestimmen. Die jüngeren Entwicklungen im Bereich der Zellenlistenalgorithmen werden in Kapitel 7 diskutiert. Durch einen zusätzlichen Sortierschritt kann die Anzahl der ausgewerteten Paarabstände reduziert werden und verbessert so das Skalierungsverhalten für Dichte und Wechselwirkungsreichweite des Systems. Ein Weg, wie der optimale Algorithmus während der Laufzeit der Simulation ausgewählt werden kann, wird vorgeschlagen

Dendritic flux avalanches and nonlocal electrodynamics in thin superconducting films

We present numerical and analytical studies of coupled nonlinear Maxwell and thermal diffusion equations which describe nonisothermal dendritic flux penetration in superconducting films. We show that spontaneous branching of propagating flux filaments occurs due to nonlocal magnetic flux diffusion and positive feedback between flux motion and Joule heat generation. The branching is triggered by a thermomagnetic edge instability which causes stratification of the critical state. The resulting distribution of magnetic microavalanches depends on a spatial distribution of defects. Our results are in good agreement with experiments performed on Nb films.Comment: 4 pages, 3 figures, see http://mti.msd.anl.gov/aran_h1.htm for extensive collection of movies of dendritic flux and temperature pattern

Efficiency of linked cell algorithms

The linked cell list algorithm is an essential part of molecular simulation software, both molecular dynamics and Monte Carlo. Though it scales linearly with the number of particles, there has been a constant interest in increasing its efficiency, because a large part of CPU time is spent to identify the interacting particles. Several recent publications proposed improvements to the algorithm and investigated their efficiency by applying them to particular setups. In this publication we develop a general method to evaluate the efficiency of these algorithms, which is mostly independent of the parameters of the simulation, and test it for a number of linked cell list algorithms. We also propose a combination of linked cell reordering and interaction sorting that shows a good efficiency for a broad range of simulation setups.Comment: Submitted to Computer Physics Communications on 22 December 2009, still awaiting a referee repor

Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO

Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principle calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI. Supplemental material in the ancillary file

The Pierre Auger Observatory: Contributions to the 34th International Cosmic Ray Conference (ICRC 2015)

Contributions of the Pierre Auger Collaboration to the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The NetherlandsComment: 24 proceedings, the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands; will appear in PoS(ICRC2015