5,067 research outputs found
Variational Formulation of Macro-Particle Models for Electromagnetic Plasma Simulations
A variational method is used to derive a self-consistent macro-particle model
for relativistic electromagnetic kinetic plasma simulations. Extending earlier
work [E. G. Evstatiev and B. A. Shadwick, J. Comput. Phys., vol. 245, pp.
376-398, 2013], the discretization of the electromagnetic Low Lagrangian is
performed via a reduction of the phase-space distribution function onto a
collection of finite-sized macro-particles of arbitrary shape and
discretization of field quantities onto a spatial grid. This approach may be
used with both lab frame coordinates or moving window coordinates; the latter
can greatly improve computational efficiency for studying some types of
laser-plasma interactions. The primary advantage of the variational approach is
the preservation of Lagrangian symmetries, which in our case leads to energy
conservation and thus avoids difficulties with grid heating. Additionally, this
approach decouples particle size from grid spacing and relaxes restrictions on
particle shape, leading to low numerical noise. The variational approach also
guarantees consistent approximations in the equations of motion and is amenable
to higher order methods in both space and time. We restrict our attention to
the 1-1/2 dimensional case (one coordinate and two momenta). Simulations are
performed with the new models and demonstrate energy conservation and low
noise.Comment: IEEE Transaction on Plasma Science (TPS) Special Issue: Plenary and
Invited Papers of the Pulsed Power and Plasma Science Conference (PPPS 2013
Kinetic equations for Stark line shapes
The BBGKY formalism is revisited in the framework of plasma spectroscopy. We
address the issue of Stark line shape modeling by using kinetic transport
equations. In the most simplified treatment of these equations, triple
correlations between an emitter and the perturbing charged particles are
neglected and a collisional description of Stark effect is obtained. Here we
relax this assumption and retain triple correlations using a generalization of
the Kirkwood truncature hypothesis to quantum operator. An application to
hydrogen lines is done in the context of plasma diagnostic, and indicates that
the neglect of triple correlations can lead to a significant overestimate of
the line width.Comment: 13 pages, 1 figur
Femtosecond x-ray absorption spectroscopy of spin and orbital angular momentum in photoexcited Ni films during ultrafast demagnetization
We follow for the first time the evolution of the spin and orbital angular
momentum of a thin Ni film during ultrafast demagnetization, by means of x-ray
magnetic circular dichroism. Both components decrease with a 130 +/- 40 fs time
constant upon excitation with a femtosecond laser pulse. Additional x-ray
absorption measurements reveal an increase in the spin-orbit interaction by 6
+/- 2 % during this process. This is the experimental demonstration quantifying
the importance of spin-orbit mediated processes during the demagnetization
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Advances for the topographic characterisation of SMC materials
For a comprehensive study of Sheet Moulding Compound (SMC) surfaces, topographical data obtained by a contact-free optical method (chromatic aberration confocal imaging) were systematically acquired to characterise these surfaces with regard to their statistical, functional and volumetrical properties. Optimal sampling conditions (cut-off length and resolution) were obtained by a topographical-statistical procedure proposed in the present work. By using different length scales specific morphologies due to the influence of moulding conditions, metallic mould topography, glass fibre content and glass fibre orientation can be characterized. The aim of this study is to suggest a systematic topographical characterization procedure for composite materials in order to study and recognize the influence of production conditions on their surface quality. © 2009 by the authors
The Inferred Cardiogenic Gene Regulatory Network in the Mammalian Heart
Cardiac development is a complex, multiscale process encompassing cell fate adoption, differentiation and morphogenesis. To elucidate pathways underlying this process, a recently developed algorithm to reverse engineer gene regulatory networks was applied to time-course microarray data obtained from the developing mouse heart. Approximately 200 genes of interest were input into the algorithm to generate putative network topologies that are capable of explaining the experimental data via model simulation. To cull specious network interactions, thousands of putative networks are merged and filtered to generate scale-free, hierarchical networks that are statistically significant and biologically relevant. The networks are validated with known gene interactions and used to predict regulatory pathways important for the developing mammalian heart. Area under the precision-recall curve and receiver operator characteristic curve are 9% and 58%, respectively. Of the top 10 ranked predicted interactions, 4 have already been validated. The algorithm is further tested using a network enriched with known interactions and another depleted of them. The inferred networks contained more interactions for the enriched network versus the depleted network. In all test cases, maximum performance of the algorithm was achieved when the purely data-driven method of network inference was combined with a data-independent, functional-based association method. Lastly, the network generated from the list of approximately 200 genes of interest was expanded using gene-profile uniqueness metrics to include approximately 900 additional known mouse genes and to form the most likely cardiogenic gene regulatory network. The resultant network supports known regulatory interactions and contains several novel cardiogenic regulatory interactions. The method outlined herein provides an informative approach to network inference and leads to clear testable hypotheses related to gene regulation
Nouveaux Orthoptères (Ensifera, Insecta) du Trias des Vosges (France)
Three new Orthoptera, Ensifera (Hagloidea and Gryllavoidea) from the Grés à Voltzia (Upper Buntsandstein, transition Lower / Middle Triassic) of the Vosges (France) are described based on forewings. Galliagryllavus vogesiacus n.gen., n.sp. (Gryllavidae) shows affinities with Gryllavus madygenicus SHAROV 1968 from the Triassic of Madygen (Kirghizistan). Triassoparacyrtophyllites bifurcatus n.gen., n.sp. (Tuphellidae) displays some similarities with Paracyrtophillites undulatus SHAROV 1968 from the Upper Jurassic of Karatau (Kazakhstan). Voltziahagla pseudoveinosa n.gen., n.sp. (Haglidae) seems close to the genus Archaboilus MARTYNOV 1937 from the Lower Jurassic of Shurab (Tadjikistan). These three Ensifera which belong to distinct families underscore the diversity of the Hagloidea and the Gryllavoidea at the boundary between the Lower and Middle Triassic. A cladistic study would be necessary to determine the phylogenetical relationships between the different families
Optimization of delivery adherence based on capacity planning and bid pricing
Sales revenues of enterprises are often subject to seasonal fluctuation. This leads to high or low utilized resources and this in turn to revenue losses. Hence, the enterprises invest a high effort to improve long and short-term resource utilization. In this context, disregarding future capacity utilization within the process of quotation leads to short-timed capacity adjustments for instance, additional work hours across seasons. This paper presents an approach which focuses on dependencies between costs and capacity by linking cost pricing and production scheduling. A first evaluation at an MTO supplier shows that order delays can be reduced by up to 95% and total costs by 21% compared to using the most appropriate priority rule
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