排序方式: 共有54条查询结果,搜索用时 15 毫秒
31.
Chiaming Wang Tungyou Lin Russel Caflisch Bruce I. Cohen Andris M. Dimits 《Journal of computational physics》2008,227(9):4308-4329
The interactions of charged particles in a plasma are governed by long-range Coulomb collision. We compare two widely used Monte Carlo models for Coulomb collisions. One was developed by Takizuka and Abe in 1977, the other was developed by Nanbu in 1997. We perform deterministic and statistical error analysis with respect to particle number and time step. The two models produce similar stochastic errors, but Nanbu’s model gives smaller time step errors. Error comparisons between these two methods are presented. 相似文献
32.
A multistage stochastic programming approach to airline network revenue management is presented. The objective is to determine
seat protection levels for all itineraries, fare classes, points of sale of the airline network and all dcps of the booking
horizon such that the expected revenue is maximized. While the passenger demand and cancelation rate processes are the stochastic
inputs of the model, the stochastic protection level process represents its output and allows to control the booking process.
The stochastic passenger demand and cancelation rate processes are approximated by a finite number of tree structured scenarios.
The scenario tree is generated from historical data using a stability-based recursive scenario reduction scheme. Numerical
results for a small hub-and-spoke network are reported.
This research is supported by the DFG Research Center Matheon “Mathematics for key technologies” in Berlin. 相似文献
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34.
Kristīne Krūkle-Bērzi?a Andris Acti?? Agris Bērzi?? 《Journal of mathematical chemistry》2012,50(8):2120-2129
A new methodology for the simulation of solid state phase transition kinetics has been developed by combining the influence of nucleation rate, nuclei growth rate and the power p characterizing the contact area between the growing particles. The equations used in this methodology were well known, and have been used previously for creating some of the most popular solid-state kinetic equations. The developed methodology made possible calculations of separate rate constants for two processes affecting the rate of phase transition—nucleation (described with K 1) and nuclei growth (described with K 2). Similar phase transitions were also approximated with the well-known single constant Avrami–Erofeev equation, but we successfully calculated both constants according to the new methodology, which allowed a separate evaluation of these two processes and explained the different induction periods. The effects of empirically adjusted constants on theoretically calculated kinetic curves were thus determined. 相似文献
35.
We look at two possible routes to classical behavior for the discrete quantum random walk on the integers: decoherence in the quantum "coin" which drives the walk, or the use of higher-dimensional (or multiple) coins to dilute the effects of interference. We use the position variance as an indicator of classical behavior and find analytical expressions for this in the long-time limit; we see that the multicoin walk retains the "quantum" quadratic growth of the variance except in the limit of a new coin for every step, while the walk with decoherence exhibits "classical" linear growth of the variance even for weak decoherence. 相似文献
36.
Martin Lindberg Andris Vaivads Savvas Raptis Per-Arne Lindqvist Barbara L. Giles Daniel Jonathan Gershman 《Entropy (Basel, Switzerland)》2022,24(6)
We use Magnetospheric Multiscale (MMS) data to study electron kinetic entropy per particle across Earth’s quasi-perpendicular bow shock. We have selected 22 shock crossings covering a wide range of shock conditions. Measured distribution functions are calibrated and corrected for spacecraft potential, secondary electron contamination, lack of measurements at the lowest energies and electron density measurements based on plasma frequency measurements. All crossings display an increase in electron kinetic entropy across the shock being positive or zero within their error margin. There is a strong dependence of on the change in electron temperature, , and the upstream electron plasma beta, . Shocks with large have large . Shocks with smaller are associated with larger . We use the values of , and density change to determine the effective adiabatic index of electrons for each shock crossing. The average effective adiabatic index is . 相似文献
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38.
Andris M. Dimits Chiaming Wang Russel Caflisch Bruce I. Cohen Yanghong Huang 《Journal of computational physics》2009,228(13):4881-4892
We investigate the accuracy of and assumptions underlying the numerical binary Monte Carlo collision operator due to Nanbu [K. Nanbu, Phys. Rev. E 55 (1997) 4642]. The numerical experiments that resulted in the parameterization of the collision kernel used in Nanbu’s operator are argued to be an approximate realization of the Coulomb–Lorentz pitch-angle scattering process, for which an analytical solution for the collision kernel is available. It is demonstrated empirically that Nanbu’s collision operator quite accurately recovers the effects of Coulomb–Lorentz pitch-angle collisions, or processes that approximate these (such interspecies Coulomb collisions with very small mass ratio) even for very large values of the collisional time step. An investigation of the analytical solution shows that Nanbu’s parameterized kernel is highly accurate for small values of the normalized collision time step, but loses some of its accuracy for larger values of the time step. Careful numerical and analytical investigations are presented, which show that the time dependence of the relaxation of a temperature anisotropy by Coulomb–Lorentz collisions has a richer structure than previously thought, and is not accurately represented by an exponential decay with a single decay rate. Finally, a practical collision algorithm is proposed that for small-mass-ratio interspecies Coulomb collisions improves on the accuracy of Nanbu’s algorithm. 相似文献
39.
Kalnina I Zvagule T Gabruseva N Kirilova J Kurjane N Bruvere R Kesters A Kizane G Kirilovs G Meirovics I 《Journal of fluorescence》2007,17(6):633-638
ABM (3-aminobenzanthrrone derivative) developed at the Riga Technical University, Riga, Latvia) has been previously shown
as a potential probe for determination of the immune state of patients with different pathologies .The fist study (using probe
ABM) of peripheral blood mononuclear cells (PBMC) membranes of 97 Chernobyl clean-up workers from Latvia was conducted in
1997. Now we repeatedly examine the same (n = 54) individuals in dynamics. ABM spectral parameters in PBMC suspension, fluorescence
anisotropy and blood plasma albumin characteristics were recorded. In 1997 screening showed 5 different patterns of fluorescence
spectra, from which in 2007 we obtained only two. These patterns of spectra had never been previously seen in healthy individuals
or patients with tuberculosis, multiple sclerosis, rheumatoid arthritis, etc., examined by us. Patterns of ABM fluorescence
spectra are associated with membrane anisotropy and conformational changes of blood plasma albumin. We observed that in dynamics
1997–2007 the lipid compartment of the membrane became more fluid while the lipid-protein interface became more rigid. The
use of probe ANS and albumin auto-fluorescence allowed show conformational alterations in Chernobyl clean-up workers blood
plasma. It is necessary to note that all investigated parameters significantly differ in observed groups of patients. These
findings reinforce our understanding that that the cell membrane is a significant biological target of radiation. The role
of the membrane in the expression and course of cell damage after radiation exposure must be considered. So ten years dynamic
of PBMC membrane characteristics by ABM (spectral shift and anisotropy indexes) in Chernobyl clean-up workers reveal progressive
trend toward certain resemblance with those of chronic B-cell lymphoid leukemia. 相似文献
40.
A previously published nuclear magnetic resonance (NMR) spectroscopic imaging method for mapping static magnetic fields has been modified, replacing the gradient echo sequence with an asymmetric spin echo sequence. The purpose of the modification is to reinforce the technique and make it useable even in conditions in which the gradient echo sequence cannot be operated. The modification performed was verified by an experiment performed on a low-field NMR scanner. The rough and fine errors due to the long time of measurement were corrected during the processing of the measured images. An optimization procedure was used to correct the fine errors. The map of the static magnetic field acquired using the new technique was compared to the map calculated from the phase images and both were compared to the result measured using a magnetometer. The verification confirmed the legitimacy of the modification and suitability of the novel technique. Some alternatives to the measured data processing have been suggested, shortening the global time of the measurement. 相似文献