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Search Results: 1 - 10 of 139200 matches for " K. Reuter "
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Exactly Solvable Models: The Road towards a Rigorous Treatment of Phase Transitions in Finite Nuclear Systems
K. A. Bugaev,P. T. Reuter
Physics , 2010,
Abstract: We discuss exact analytical solutions of a variety of statistical models recently obtained for finite systems by a novel powerful mathematical method, the Laplace-Fourier transform. Among them are a constrained version of the statistical multifragmentation model, the Gas of Bags Model and the Hills and Dales Model of surface partition. Thus, the Laplace-Fourier transform allows one to study the nuclear matter equation of state, the equation of state of hadronic and quark gluon matter and surface partitions on the same footing. A complete analysis of the isobaric partition singularities of these models is done for finite systems. The developed formalism allows us, for the first time, to exactly define the finite volume analogs of gaseous, liquid and mixed phases of these models from the first principles of statistical mechanics and demonstrate the pitfalls of earlier works. The found solutions may be used for building up a new theoretical apparatus to rigorously study phase transitions in finite systems. The strategic directions of future research opened by these exact results are also discussed.
kmos: A lattice kinetic Monte Carlo framework
M. J. Hoffmann,S. Matera,K. Reuter
Physics , 2014, DOI: 10.1016/j.cpc.2014.04.003
Abstract: Kinetic Monte Carlo (kMC) simulations have emerged as a key tool for microkinetic modeling in heterogeneous catalysis and other materials applications. Systems, where site-specificity of all elementary reactions allows a mapping onto a lattice of discrete active sites, can be addressed within the particularly efficient lattice kMC approach. To this end we describe the versatile kmos software package, which offers a most user-friendly implementation, execution, and evaluation of lattice kMC models of arbitrary complexity in one- to three-dimensional lattice systems, involving multiple active sites in periodic or aperiodic arrangements, as well as site-resolved pairwise and higher-order lateral interactions. Conceptually, kmos achieves a maximum runtime performance which is essentially independent of lattice size by generating code for the efficiency-determining local update of available events that is optimized for a defined kMC model. For this model definition and the control of all runtime and evaluation aspects kmos offers a high-level application programming interface. Usage proceeds interactively, via scripts, or a graphical user interface, which visualizes the model geometry, the lattice occupations and rates of selected elementary reactions, while allowing on-the-fly changes of simulation parameters. We demonstrate the performance and scaling of kmos with the application to kMC models for surface catalytic processes, where for given operation conditions (temperature and partial pressures of all reactants) central simulation outcomes are catalytic activity and selectivities, surface composition, and mechanistic insight into the occurrence of individual elementary processes in the reaction network.
Critical Exponents of the Statistical Multifragmentation Model
P. T. Reuter,K. A. Bugaev
Physics , 2001, DOI: 10.1016/S0370-2693(01)00996-0
Abstract: For the statistical multifragmentation model the critical indices $\alpha^\prime, \beta, \gamma^\prime, \delta$ are calculated as functions of the Fisher parameter $\tau$. It is found that these indices have different values than in Fisher's droplet model. Some peculiarities of the scaling relations are discussed. The basic model predicts for the index $\tau$ a narrow range of values, $1.799< \tau < 1.846$, which is consistent with two experiments on nuclear multifragmentation.
Therapeutic utility of aspirin in the ApcMin/+ murine model of colon carcinogenesis
Brian K Reuter, Xiao-Jing Zhang, Mark JS Miller
BMC Cancer , 2002, DOI: 10.1186/1471-2407-2-19
Abstract: Min/+ mice with established polyposis were treated orally once daily from 12–16 weeks of age with either drug vehicle or aspirin (25 mg/kg). Upon completion of treatment, the number, location and size of intestinal tumours was determined. Additional variables examined were the number of apoptotic cells within tumours and COX activity.Administration of aspirin for 4 weeks to Min/+ mice produce no effect on tumour number compared to vehicle-treated Min/+ mice (65 ± 8 vs. 63 ± 9, respectively). In addition, aspirin had no effect on tumour size or location. However, aspirin treatment produced a greater than 2-fold (p < 0.05) increase in the number of apoptotic positive cells within tumours and significantly decreased hepatic PGE2 content.Aspirin was found to have no effect on tumour number and size when administered to Min/+ mice with established polyposis. The findings in the present study call in to question the utility of aspirin as a stand-alone treatment for established GI cancer. However, aspirin's ability to significantly promote apoptosis may render it suitable for use in combinatorial chemotherapy.Despite continuing decreases in incidence and mortality rates, cancers of the colon and rectum remain the third leading cause of cancer deaths in the North America [1,2]. The decline in incidence, and hence mortality, from colorectal cancers is most likely attributable to an increase in recommendations to perform routine screening on average risk individuals and to improved screening techniques [2]. In addition, there is ever advancing knowledge into the pathogenic mechanism of cancer and resulting strides in the development of more efficacious therapies.In recent years it has become evident that nonsteroidal anti-inflammatory drugs (NSAIDs) represent a potential class of cancer chemotherapeutic agents. The utility of NSAIDs, in particular aspirin, in the treatment of colon cancer has stemmed from studies conducted both in animals [3-11] and humans [12-15]. Evidence f
Dendritic development of Drosophila high order visual system neurons is independent of sensory experience
Ethan K Scott, John E Reuter, Liqun Luo
BMC Neuroscience , 2003, DOI: 10.1186/1471-2202-4-14
Abstract: We find that the dendrites of VS1 neurons are unchanged in dark-reared flies as compared to control flies raised on a 12 hour light, 12 hour dark cycle. The dendrites of these flies show no differences from control in dendrite complexity, spine number, spine density, or axon complexity. Flies with genetically ablated eyes show a slight but significant reduction in the complexity and overall length of VS1 dendrites, although this effect may be due to a reduction in the overall size of the dendritic field in these flies.Overall, our results indicate no role for visual experience in the development of VS dendrites, while spontaneous activity from photoreceptors may play at most a subtle role in the formation of fully complex dendrites in these high-order visual processing neurons.The mechanisms that underlie the development of the nervous system are numerous and diverse. Over the past several decades, research has begun to give us a sense of the importance of both preprogrammed, invariant mechanisms for neural development, and also programs for development that depend on experience and the electrical activity of the developing neurons themselves. The fact that certain types of neurons develop their basic morphologies even when isolated in culture from other cells provides a simple but powerful argument for the importance of cell autonomous mechanisms in the establishment of neuronal structure [1,2]. These and numerous other experiments have provided overwhelming evidence that neurons possess endogenous, activity independent programs that account for important aspects of their development.On the other hand, neurons deprived of contact with or activity from their normal synaptic partners seldom attain a fully mature structure. For example, Purkinje cells deprived of their efferent projections in Weaver mice have dendritic arborizations that do not extend normally [3]. Additionally, the structures of neurons can be affected by an absence of activity from their efferent pa
Pinning down the Invisible Sneutrino
Kalinowski, J.;Kilian, W.;Reuter, J.;Robens, T.;Rolbiecki, K.
High Energy Physics - Phenomenology , 2008, DOI: 10.1088/1126-6708/2008/10/090
Abstract: For points in SUSY parameter space where the sneutrino is lighter than the lightest chargino and next-to-lightest neutralino, its direct mass determination from sneutrino pair production process at e+e- collider is impossible since it decays invisibly. In such a scenario the sneutrino can be discovered and its mass determined from measurements of two-body decays of charginos produced in pairs at the ILC. Using the event generator WHIZARD we study the prospects of measuring sneutrino properties in a realistic ILC environment. In our analysis we include beamstrahlung, initial state radiation, a complete account of reducible backgrounds from SM and SUSY processes, and a complete matrix-element calculation of the SUSY signal which encompasses all irreducible background and interference contributions. We also simulate photon induced background processes using exact matrix elements. Radiation effects and the cuts to reduce background strongly modify the edges of the lepton energy spectra from which the sneutrino and chargino mass are determined. We discuss possible approaches to measure the sneutrino mass with optimal precision.
MAMAP – a new spectrometer system for column-averaged methane and carbon dioxide observations from aircraft: retrieval algorithm and first inversions for point source emission rates
T. Krings,K. Gerilowski,M. Buchwitz,M. Reuter
Atmospheric Measurement Techniques Discussions , 2011, DOI: 10.5194/amtd-4-2207-2011
Abstract: MAMAP is an airborne passive remote sensing instrument designed for measuring columns of methane (CH4) and carbon dioxide (CO2). The MAMAP instrument consists of two optical grating spectrometers: One in the short wave infrared band (SWIR) at 1590–1690 nm to measure CO2 and CH4 absorptions and another one in the near infrared (NIR) at 757–768 nm to measure O2 absorptions for reference purposes. MAMAP can be operated in both nadir and zenith geometry during the flight. Mounted on an airplane MAMAP can effectively survey areas on regional to local scales with a ground pixel resolution of about 29 m × 33 m for a typical aircraft altitude of 1250 m and a velocity of 200 km h 1. The retrieval precision of the measured column relative to background is typically 1% (1σ). MAMAP can be used to close the gap between satellite data exhibiting global coverage but with a rather coarse resolution on the one hand and highly accurate in situ measurements with sparse coverage on the other hand. In July 2007 test flights were performed over two coal-fired powerplants operated by Vattenfall Europe Generation AG: J nschwalde (27.4 Mt CO2 yr 1) and Schwarze Pumpe (11.9 Mt CO2 yr 1), about 100 km southeast of Berlin, Germany. By using two different inversion approaches, one based on an optimal estimation scheme to fit Gaussian plume models from multiple sources to the data, and another using a simple Gaussian integral method, the emission rates can be determined and compared with emissions as stated by Vattenfall Europe. An extensive error analysis for the retrieval's dry column results (XCO2 and XCH4) and for the two inversion methods has been performed. Both methods – the Gaussian plume model fit and the Gaussian integral method – are capable of delivering reliable estimates for strong point source emission rates, given appropriate flight patterns and detailed knowledge of wind conditions.
A Spherical Plasma Dynamo Experiment
E. J. Spence,K. Reuter,C. B. Forest
Physics , 2009, DOI: 10.1088/0004-637X/700/1/470
Abstract: We propose a plasma experiment to be used to investigate fundamental properties of astrophysical dynamos. The highly conducting, fast-flowing plasma will allow experimenters to explore systems with magnetic Reynolds numbers an order of magnitude larger than those accessible with liquid-metal experiments. The plasma is confined using a ring-cusp strategy and subject to a toroidal differentially rotating outer boundary condition. As proof of principle, we present magnetohydrodynamic simulations of the proposed experiment. When a von K\'arm\'an-type boundary condition is specified, and the magnetic Reynolds number is large enough, dynamo action is observed. At different values of the magnetic Prandtl and Reynolds numbers the simulations demonstrate either laminar or turbulent dynamo action.
Equation of State for the Two-component Van der Waals Gas with Relativistic Excluded Volumes
G. Zeeb,K. A. Bugaev,P. T. Reuter,H. Stocker
Physics , 2002,
Abstract: A canonical partition function for the two-component excluded volume model is derived, leading to two different van der Waals approximations. The one is known as the Lorentz-Berthelot mixture and the other has been proposed recently. Both models are analysed in the canonical and grand canonical ensemble. In comparison with the one-component van der Waals excluded volume model the suppression of particle densities is reduced in these two-component formulations, but in two essentially different ways. Presently used multi-component models have no such reduction. They are shown to be not correct when used for components with different hard-core radii. For high temperatures the excluded volume interaction is refined by accounting for the Lorentz contraction of the spherical excluded volumes, which leads to a distinct enhancement of lighter particles. The resulting effects on pion yield ratios are studied for AGS and SPS data.
Wave-driven dynamo action in spherical MHD systems
K. Reuter,F. Jenko,A. Tilgner,C. B. Forest
Physics , 2009, DOI: 10.1103/PhysRevE.80.056304
Abstract: Hydrodynamic and magnetohydrodynamic numerical studies of a mechanically forced two-vortex flow inside a sphere are reported. The simulations are performed in the intermediate regime between the laminar flow and developed turbulence where a hydrodynamic instability is found to generate internal waves with a characteristic m=2 zonal wave number. It is shown that this time-periodic flow acts as a dynamo although snapshots of the flow as well as the mean flow are not dynamos. The magnetic fields' growth rate exhibits resonance effects depending on the wave frequency. Furthermore, a cyclic self-killing and self-recovering dynamo based on the relative alignment of the velocity and magnetic fields is presented. The phenomena are explained in terms of a mixing of non-orthogonal eigenstates of the time dependent linear operator of the magnetic induction equation. The potential relevance of this mechanism to dynamo experiments is discussed.
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