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91.
Simone Melchionna 《Journal of computational physics》2011,230(10):3966-3976
A method to simulate bodies suspended in a Lattice Boltzmann solvent is proposed. It is based on a generalized reaction force that enforces no-slip boundary conditions at the fluid–body interface as the limiting case of an iterative procedure. A smooth version of the Heaviside function allows to treat spherical particles of arbitrary size and produces smooth hydrodynamic forces as particles move in the continuum. Numerical tests demonstrate the accuracy of the method in reproducing the hydrodynamic field around a single particle and the fluid-mediated forces between pairs of particles. The drag force experienced by a particle moving in a straight channel and at various Reynolds numbers is studied as a non-trivial testcase. 相似文献
92.
We discover that some unstable vacua have long memory. By that we mean that even in the theories containing only massive particles, there are correllators and expectation values which grow with time. We examine the cases of instabilities caused by the constant electric fields, expanding and contracting universes and, most importantly, the global de Sitter space. In the last case the interaction leads to a remarkable UV/IR mixing and to a large back reaction. This gives reasons to believe that the cosmological constant problem could be resolved by the infrared physics. 相似文献
93.
Gravitational sinking in the water column is known to affect size composition of planktonic communities. One important driver toward the reduction of plankton size is the fact that larger cells tend to sink faster below the euphotic layer. In this work, we discuss the role of gravitational sinking in driving cell size selection, showing that the outcome of phytoplankton competition is determined by the dependence of sinking velocity on cell size, shape, and on the temporal variability associated with turbulence. This opens a question on whether regional modulations of the turbulence intensity could affect size distribution of planktonic communities. 相似文献
94.
95.
设计了紧凑型L波段同轴相对论返波振荡器,通过粒子模拟研究了L波段同轴相对论返波振荡器相互作用的物理过程,并对器件的电磁结构进行了优化和改进。分析表明,采用同轴慢波结构可以在较低的外加磁场下实现L波段返波振荡器的微波输出,同时可以大大减小微波器件的径向尺寸。这是因为同轴慢波结构的TM01模式有类似于TEM模的性质,没有截止频率,但纵向电场不为零,电子束能够与它发生强相互作用过程。粒子模拟优化结果表明,在器件半径仅为4.0 cm,电子束能量240 keV,电子束流1.8 kA,导引磁场仅为0.75 T时,返波振荡器可以在频率1.60 GHz处获得较大功率的微波输出, 平均峰值功率达140 MW,平均峰值功率效率约为32%。 相似文献
96.
This paper presents the concept of a Dielectric-lined Multiwave Cerenkov Generator(DMWCG) producing high power millimeter waves, which is investigated with a two and one half dimensional(
) electromagnetic relativistic Particle-in-Cell(PIC) simulation code. It is showed that the DMWCG can operate in a lower diode-voltage regime with much higher radiation efficiency as compared with the usual Multiwave Cerenkov Generator(MWCG). The simulation work indicates both the downshift of the wave frequency in the presence of the dielectric liner and the existence of the optima for the permittivity of the liner as well as for the magnitude of the guiding magnetic field. The required intensity of the guiding field is reduced with the introducing of the liner. The radiation is generated at the dominant frequency of 31.5GHz. The power level of 1.5GW is achieved, with radiation efficiency up to 15%. The features of parameter dependency are presented. And reasonable explanation is put forward. In addition, the enhanced propagation of the electron beam is studied in the presence of the dielectric liner. 相似文献
97.
M. R. Koblischka S. L. Huang K. Fossheim T. H. Johansen H. Bratsberg 《Physica C: Superconductivity and its Applications》1998,300(3-4):207-211
Flux distributions of partial-melting processed Bi2Sr2CaCu2O8+δ ceramics are obtained using magneto-optic imaging. In remanent states (μ0Ha=0 T), large amounts of trapped flux are observed along (Sr,Ca)2CuOy particles embedded in the Bi2Sr2CaCu2O8+δ matrix. Despite the relatively large size of these particles (up to 30 μm), the pinning effect is similar to that of Y2BaCuO5 particles in melt-processed YBa2Cu3O7−δ. Furthermore, we discuss how the pinning capability of non-superconducting particles of different sizes and densities will show up in magneto-optic images. 相似文献
98.
The theorem of Hohenberg and Kohn is extended to subdomains of a bounded quantum system. It is shown that the ground state
particle density of an arbitrary subdomain uniquely determines the ground state properties of this subdomain, of any other
subdomain, and of the total domain of the system. 相似文献
99.
Transverse-energy and charged-particle pseudorapidity densities at midrapidity and their ratio, dET/d|mid/dNch/d|mid, are evaluated in a statistical model with longitudinal and transverse flows for the wide range of colliders, from AGS to RHIC at
= 200 GeV. Evaluations are done at freeze-out parameters obtained from independent fits to observed particle yields and pT spectra. Decays of hadron resonances are treated thoroughly and are included in derivations of dET/d|mid and dNch/d|mid. The predictions of the model agree well with the experimental data. However, some (explicable) overestimation of the ratio has been observed. 相似文献
100.