共查询到20条相似文献,搜索用时 0 毫秒
1.
P. Entel 《Zeitschrift für Physik B Condensed Matter》1976,24(3):263-271
The influence of Fermi surface anisotropy on the specific heat jumps,C, at the phase transition for superconductors containing magnetic and nonmagnetic impurities is discussed. In the framework of a simple two-band or two-zone model we find for small interband electron-phonon coupling constants characteristic maxima in theC(T
c
)-curve.These departures from the correspondingC-curve of a single-band isotropic superconductor are mostly pronounced forweak andstrong interband Coulomb scattering of conduction electrons on nonmagnetic ions. There is only a small range of intermediate scattering rates for which the maxima are smeared out.Work performed within the research program of the Sonderforschungsbereich 125 — Aachen/Jülich/Köln 相似文献
2.
P. Entel 《Solid State Communications》1976,19(12):1233-1235
The upper critical field Hc2(T) and the specific heat jump ΔC(Tc) are calculated for Cs0.1WO2.9F0.1 using a two-band model. The model parameters are obtained by adjusting the theoretical Hc2(T) values to experimental results. The model calculation predicts an anomalous specific heat jump ΔC as a function of the inverse relation Tc(H). 相似文献
3.
M. Pinho B. Brouard J.M. Génevaux N. Dauchez O. Volkova H. Mézière P. Collas 《Journal of magnetism and magnetic materials》2011,323(18-19):2386-2390
The use of ferrofluid seals in mechanical systems can lead to viscous damping that affects their dynamic behavior. This paper describes an investigation into local viscous properties in the case of an axial harmonic force. The influence of magnetic field level, shear stress amplitude and frequency are studied. Even for ferrofluid particles in a highly saturated magnetic field, it is shown that viscosity increases with magnetic intensity, decreases with the frequency of harmonic excitation and is not sensitive to shear rate amplitude. Viscosity is lower for oscillatory flows than for steady flows. 相似文献
4.
Melissa K. Santala 《Surface science》2006,600(4):782-792
Arrays of controlled-geometry, semi-infinite pore channels of systematically varied crystallographic orientation were introduced into undoped m-plane sapphire substrates using microfabrication techniques and ion-beam etching and subsequently internalized by solid-state diffusion bonding. A series of anneals at 1700 °C caused the breakup of these channels into discrete pores via Rayleigh instabilities. In all cases, channels broke up with a characteristic wavelength larger than that expected for a material with isotropic surface energy, reflecting stabilization effects due to surface-energy anisotropy. The breakup wavelength and the time required for complete breakup varied significantly with channel orientation. For most orientations, the instability wavelength for channels of radius R was in the range of 13.2R-25R, and complete breakup occurred within 2-10 h. To first order, the anneal times for complete breakup scale with the square of the breakup wavelength. Channels oriented along a direction had a wavelength of ≈139R, and required 468 h for complete breakup. Cross-sectional analysis of channels oriented along a direction showed the channel to be completely bounded by stable c(0 0 0 1), , and facets. 相似文献
5.
Parametric instabilities induced by the nonlinear interaction between high frequency quantum Langmuir waves and low frequency quantum ion-acoustic waves in quantum plasmas with the electron exchange-correlation effects are presented.By using the quantum hydrodynamic equations with the electron exchange-correlation correction,we obtain an effective quantum Zaharov model,which is then used to derive the modified dispersion relations and the growth rates of the decay and four-wave instabilities.The influences of the electron exchange-correlation effects and the quantum effects on the existence of quantum Langmuir waves and the parametric instabilities are discussed in detail.It is shown that the electron exchange-correlation effects and quantum effects are strongly coupled.The quantum Langmuir wave can propagate in quantum plasmas only when the electron exchange-correlation effects and the quantum effects satisfy a certain condition.The electron exchange-correlation effects tend to enhance the parametric instabilities,while quantum effects suppress the instabilities. 相似文献
6.
P. Entel 《Zeitschrift für Physik B Condensed Matter》1976,23(4):321-330
The influence of Fermi surface anisotropy on the superconducting transition temperature of strong coupling superconductors containing magnetic and nonmagnetic impurities is investigated. It is found that the concentration dependent transition temperature shows typical departures from the corresponding curve of a single-band isotropic superconductor. These departures occur either for very small (
ij) or for very large (
ij0) interband scattering of conduction electrons on nonmagnetic impurities (i, j label the states in different bands or in different zones of the Fermi surface). In the case of unequal cut-off frequencies for different zones on the Fermi surface it is shown that all effects of unequal cut-offs can be eliminated by introducing effective electron-phonon pairing interactions. In the presence of impurities these effective pairing interactions become weakly impurity dependent giving rise to a new pair-weakening mechanism. Quantitative results on the basis of a simple two-band or two-zone model are presented. 相似文献
7.
T. Prokopyeva V. DanilovA. Dobroserdova S. Kantorovich C. Holm 《Journal of magnetism and magnetic materials》2011,323(10):1298-1301
Computer and theoretical investigation of particle arrangements in a thin film of a magnetic fluid at low temperatures is presented. The approach developed by us combines the simplicity of simulations and accuracy of the analytical model and allows studying particle aggregates and their properties. The systems under investigation were: a monodisperse and a bidisperse model in the absence of an external magnetic field, and a monodisperse model under the influence of an external field. Careful analysis of the most probable microstructures in a ferrofluid thin layer has been carried out at 0 K. The analysis of the stability of structures under thermal fluctuations allows making a conclusion about the microstructure of investigated system at low temperatures. 相似文献
8.
The growth of magnetic energy density is considered in a collapsing ferrofluid with infinite electrical conductivity whose magnetic permeability is not a constant. It is shown that the variation of the magnetic permeability affects the growth of magnetic energy. The case of isotropic collapse and a specific case of anisotropic collapse are examined. 相似文献
9.
《Physica A》2006,371(1):46-49
In this work we report theoretical and numerical results on convection for a binary magnetic mixture under rotation. We obtain explicit expressions of convective thresholds in terms of the control parameters of the system for stationary convection. Finally, we analyze the stabilizing effect of rotation on instability thresholds for aqueous suspensions. 相似文献
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12.
Microstructure evolution is largely dominated by the internal stress fields that appear upon the appearance of inhomogeneous structures in a material. The hardening behaviour of metals physically originates from such a complex microstructure evolution. As deformation proceeds, statistically homogeneous distributions of dislocations in grains become unstable, which constitutes the driving force for the development of a pronounced dislocation substructure. The dislocation structure already appears at early stages of deformation due to the statistical trapping of dislocations. Cell walls contain dislocation dipoles and multipoles with high dislocation densities and enclose cell-interior regions with a considerably smaller dislocation density. The presence and evolution of such a dislocation arrangement in the material influence the mechanical response of the material and is commonly associated with the transient hardening after strain path changes. This contribution introduces a micromechanical continuum model of the dislocation cell structure based on the physics of the dislocation interactions. The approximation of the internal stress field in such a microstructure and the impact on the macroscopic mechanical response are the main items investigated here. 相似文献
13.
On the basis of a nuclear matter model calculation at finite temperature it is shown that at densities of about 1/15 of normal nuclear mattor density a new metastable phase exists which is determined by cluster formation effects. The existence of a low density isomer might be related to the recently observed anomalous short reaction mean free paths from 2 GeV/N heavy ion collisions. 相似文献
14.
When a ferrofluid drop is trapped in a horizontal Hele-Shaw cell and subjected to a vertical magnetic field, a fingering instability
results in the droplet evolving into a complex branched structure. This fingering instability depends on the magnetic field
ramp rate but also depends critically on the initial state of the droplet. Small perturbations in the initial droplet can
have a large influence on the resulting final pattern. By simultaneously applying a stabilizing (horizontal) azimuthal magnetic
field, we gain more control over the mode selection mechanism. We perform a linear stability analysis that shows that any
single mode can be selected by appropriately adjusting the strengths of the applied fields. This offers a unique and accurate
mode selection mechanism for this confined magnetic fluid system. We present the results of numerical simulations that demonstrate
that this mode selection mechanism is quite robust and “overpowers” any initial perturbations on the droplet. This provides
a predictable way to obtain patterns with any desired number of fingers. 相似文献
15.
Nanoparticles of Cr2O3 are prepared through hydrothermal synthesis process using CrO3/PVA in aqueous solution using sucrose as a reducing agent. The calcination temperature is taken 300 and 350 °C. XRD and SEM of the powdered Cr2O3 particles are done for the characterization. The average particle size is found 30–80 nm. It is found that average particle size increases with calcination temperature. The UV–visible absorption spectra are taken for the study of photo-physical properties of ferrofluids. Ultrasonic velocity and absorption measurements are performed in Cr2O3 ferrofluid using variable path interferometer and pulse-echo techniques, respectively. The achieved results are discussed in correlation with the magnetic and other physical properties of Cr2O3. 相似文献
16.
D. Laroze J. Martinez-Mardones R.G. Rojas 《Journal of magnetism and magnetic materials》2010,322(21):3576-3583
We report theoretical and numerical results on convection for a magnetic fluid in a viscoelastic carrier liquid. We focus in the stationary convection for idealized boundary conditions. We obtain explicit expressions of convective thresholds in terms of the control parameters of the system. Close to bifurcation, the coefficients of the corresponding amplitude equation are determined analytically. Finally, the secondary instabilities are performed. 相似文献
17.
Wah-Keat Lee 《Journal of magnetism and magnetic materials》2010,322(17):2525-2528
X-ray microtomography is used to visualize, in-situ, the three-dimensional nature of the magnetic field induced macro-structures (>1 μm) inside a bulk (∼1 mm diameter) magnetite-particle-mineral oil ferrofluid sample. Columnar structures of ∼10 μm diameter were seen under a 0.35 kG applied magnetic field, while labyrinth type structures ∼4 μm in width were seen at 0.55 kG. The structures have height/width aspect ratios >100. The results show that the magnetite volume fraction is not constant within the structures and on average is considerably less than a random sphere packing model. 相似文献
18.
R. Mortezazadeh H. Aminfar M. Mohammadpourfard 《Journal of Engineering Thermophysics》2017,26(4):580-597
The nucleate pool boiling heat transfer of ferrofluid on a horizontal plate in the presence of a non-uniform magnetic field has been studied numerically using Eulerian–Eulerian approach. Also, the wall partitioning model was extended to consider the boiling surface modification by the nanoparticles deposition on the heated surface. Adding nanoparticles causes deterioration in the boiling heat transfer coefficient and void fraction. Moreover, applying the magnetic field intensifies these reductions. 相似文献
19.
A ferrofluid torsion pendulum in an oscillating magnetic field exhibits a rich variety of nonlinear self-oscillatory regimes. The dynamics is governed by the system of coupled differential equations for the in- and off-axis components of the fluid magnetization and the pendulum angular deflection. In the limiting case of high driving frequency, the system reduces to the sole Rayleigh-type equation. Much more complicated temporal patterns arise when the field frequency and the pendulum eigen frequency are of the same order. 相似文献
20.
The present experimental investigation was focused on the study of the simultaneous influence of the water-based ferrofluid and static magnetic field exposure on young cereal plants. Water-based ferrofluid, stabilized with citric acid was added daily in various concentrations, ranging between 10 and 250 μL/L, in the culture medium of maize (Zea mays) plants in their early ontogenetic stages. The used static magnetic field was about 50 mT. In order to investigate the biochemical changes of chlorophylls and total carotenoids, spectrophotometric measurements were carried out, that revealed stimulatory effects of ferrofluid and magnetic exposure upon the studied plant species. 相似文献