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排序方式: 共有163条查询结果,搜索用时 15 毫秒
81.
Dmitriy M. Markovich Sergey S. Abdurakipov Leonid A. Kozinkin Mikhail P. Tokarev Kemal Hanjalić 《Journal of Turbulence》2016,17(7):678-698
We report on a parallel study on properties of large-scale vortical structures in low- and high-swirl turbulent jets by means of the time-resolved tomographic particle image velocimetry technique. The high-swirl jet flow is featured by a well-established bubble-type vortex breakdown with a central recirculation zone. In the low-swirl flow, the mean axial velocity, while intermittently acquiring negative values, remains positive in the mean but with a local velocity defect immediately downstream from the nozzle exit, followed by a spiralling vortex core system and its eventual breakdown. Measurements of the 3D velocity fields allowed direct analysis of the azimuthal/helical modes via Fourier transform over the azimuthal angle and proper orthogonal decomposition (POD) analysis in the Fourier space. A precessing vortex core is detected for both swirl cases, whereas the POD analysis showed that the one originating in the bubble-type vortex breakdown is much more energetic and easier to detect. 相似文献
82.
S. V. Savilov V. N. Khrustalev A. N. Kuznetsov B. A. Popovkin M. Yu. Antipin 《Russian Chemical Bulletin》2005,54(1):87-92
Two new subvalent bismuth telluroiodides, Bi2TeI and Bi4TeI1.25, were prepared by the gas-phase synthesis. The compositions of these phases were determined by energy-dispersive X-ray spectroscopy. X-ray diffraction study of melt grown Bi2TeI single crystals demonstrated that the compound crystallizes in the monoclinic system (space group C/2m) with the unit cell parameters a = 7.586(1) Å, b = 4.380(1) Å, c = 17.741(3) Å, β = 98.20°. The layered crystal structure of Bi2TeI consists of weakly bonded two dimensional blocks with a stoichiometry of the title compound. The blocks are stacked along the c axis. Each block consists of eight atomic layers alternating in the Te-Bi-I-Bi-Bi-I-Bi-Te order and includes a double layer of bismuth atoms. Based on the results of ab initio quantum-chemical calculations, the title compound is expected to possess a pronounced anisotropy of conductivity.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 86–91, January, 2005. 相似文献
83.
s 《Superlattices and Microstructures》2001,29(6):385
A variational formalism for calculating the binding and the transition energies between 1 s - and 2 p ± -like states of a shallow donor in cylindrical pills of GaAs low-dimensional systems, under the action of the electric and magnetic fields applied in the axial direction, is presented. Results were obtained for several values of the magnetic field as a function of the system geometry and the applied electric field. Within the two-dimensional limits, the theoretical results for the 1 s– 2 p + transition energies are in good agreement with infrared-magnetospectroscopy measurements on donor doped quantum-wells. 相似文献
84.
V. G. Zubkov G. V. Bazuev A. P. Tyutyunnik I. F. Berger 《Journal of solid state chemistry》2001,160(2):293
Synthesis conditions, crystal structures, and magnetic properties of quasi-one-dimensional complex oxides Ca3CuMnO6 (space group P-1, z=4, triclinic cell) and Ca3Co1+xMn1−xO6 with x=0, 0.25, 1.0 (structural type K4CdCl6, space group R-3c, z=6) are presented. The crystal structures of Ca3CoMnO6 and Ca3CuMnO6 were refined using neutron and combined X-ray and neutron diffraction analysis, respectively. The interatomic distances in oxygen polyhedra were found. In contrast to ferromagnetic Ca3Co2O6 (Tc=24 K), manganese-containing phases Ca3Co1+xMn1−xO6 are characterized by antiferromagnetic interactions with Neel temperatures 18 K (x=0.25) and 13 K (x=0). For Ca3CuMnO6TN was established to be 6 K. 相似文献
85.
The brownmillerite-type layered compound Ca2.375La0.125Sr0.5GaMn2O8 has been synthesized. The crystal and magnetic structures have been refined by the Rietveld analysis of the neutron powder diffraction patterns at 300 and 20 K. This compound crystallizes in the orthorhombic symmetry under the space group Pcm21 (a = 5.447(2), b = 11.359(4) and c = 5.322(2) Å). The compound is found to be antiferromagnetic at 20 K. The ordered Mn magnetic moment, aligned along the crystallographic b-direction, is derived to be 2.53(5) µB per Mn ion at 20 K. 相似文献
86.
Francesco Laviano Gianluca Ghigo Enrica Mezzetti Eugen Hollmann Roger Wördenweber 《Physica C: Superconductivity and its Applications》2010,470(19):844-847
High-energy heavy-ion lithography is a powerful tool for tuning both structural and electromagnetic properties of high temperature superconductors by inducing nanometer scale defects confined in micron scale patterns. We show how the vortex dynamics in YBCO thin films patterned by heavy-ion lithography can be controlled and potentially exploited for device applications. Both local critical temperature and local critical currents are effectively tailored by the imposed irradiation geometry. The direct visualization of the real-time dynamics of the magnetic pattern is achieved by the magneto-optical imaging technique, while confined vortex flow is revealed by the simultaneous measurement of the electrical resistance both along and perpendicular (Hall resistance) to the direction of the applied current. It is shown that, for microchannel arrays inclined with respect to the transport current flow, the direction of vortex motion is solely determined by the imposed irradiation pattern geometry, in a well-defined temperature range, for a given applied current. 相似文献
87.
低维无机功能材料电学行为的调控主要依赖于本征异质原子掺杂,但是该方法在性质调控的同时,由于异质原子的嵌入常导致原有晶体结构对称性发生改变,产生变形扭曲甚至破坏.目前,基于清晰结构调控无机材料功能性依然是极具挑战性的难题.氢作为一种小半径轻原子,对低维无机功能材料的修饰或嵌入为调控无极功能材料物性带来了新思路,特别是通过氢的嵌入可以在结构不发生大变化的前提下调制材料载流子浓度并提升导电率,这已逐渐成为低维无机材料电学行为调控的重要途径.本文概述了近年来发展的系列氢化调控方法,以及通过对电子结构调制实现对电学行为的调控,并基于此广泛应用于能源领域、电子器件及催化等方面. 相似文献
88.
C. M.J. Wijers J.-H. Chu O. Voskoboynikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):225-241
The influence of the surrounding semiconducting matrix upon the
optical response of embedded nano-objects (quantum dots) has been
investigated. This system can be described by means of a hybrid model, where the full response is a combination of a macroscopic
electrostatic response term and a dynamic response term, obtained quantum mechanically. The result is a modified discrete
dipole model, where excess discrete dipoles having an excess polarizability with respect to a uniform background identical
to the dielectric host material represent the response. In this model all electrodynamic interactions are screened by the
host material. The electrostatic response is obtained by approximating the quantum dots by embedded dielectric oblate ellipsoids.
Closed expressions for the electrostatic response of these ellipsoids have been derived. The electrodynamic nature of the
dynamic quantum mechanical polarizability term however is unclear. It is not certain whether this polarizability is dressed
or bare. Therefore we have investigated in detail the consequences of both options. Although there is no real qualitative
difference between them, the difference is so large that experiment can easily discriminate between both. Results should be
easily measurable anyhow. 相似文献
89.
G. Iadonisi F. Trani G. Cantele D. Ninno 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(2):143-154
In this work we show that the polaron effects in cylindrical quantum
wires are function of the cylinder radius R0 through the boundary conditions
for both the ionic and the electronic motion and through the size dependence of the static
and high frequency dielectric constants. We find that the dielectric constants
are increasing functions of R0. This fact and the different boundary conditions
for the ions and the electrons have the final consequence that polaron self-energy can
either be an increasing or a decreasing function of R0. 相似文献
90.
T. M. Mishonov M. V. Stoev 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(4):419-421
A simple electronic experiment using a field-effect-transistor–type
microstructure is suggested. The thin superconductor layer forms the
source-drain channel of a layered structure across which an AC current is
applied. It is found necessary to measure the second harmonic of the
source-gate voltage, and the third harmonic of the source-drain voltage;
these electronic measurements then give the logarithmic derivative of
the density of states, which is an important consideration when fitting
parameters of the band structure. 相似文献