The hydrodynamics of rotating superfluids. II. Finite temperature,dissipative theory

The hydrodynamics of rotating superfluids at finite temperature is formulated, accounting for the elastic properties of the vortex lattice. This theory, which is a generalization of previous work at zero temperature, includes normal fluid motions and dissipation and is used here to investigate the transverse and longitudinal normal modes of the system. Mutual friction, arising microscopically from collisions between the vortex lines and the excitations comprising the normal fluid, leads to a profound change in the nature of the two transverse modes allowed at finite temperatures. One such mode, similar to the Tkachenko mode in zero-temperature theory, is associated with the motion of the total mass current and is damped by first viscosity but unaffected by mutual friction. The other mode, associated with the relative motion of the normal and superfluid-vortex components, is highly damped by mutual friction and cannot propagate at angles greater than a critical angle _c measured from the rotation axis.     

Segregation due to particle shape of a granular mixture in a slowly rotating tumbler

Using DEM particle simulations we consider segregation of a binary granular particle mixture in a slowly rotating cylindrical tumbler where the particles differ only in their shape—spherical versus more cubical particles. We find that the more cubical particles segregate to the inner core of the particle bed while the spherical particles segregate to the curved walls of the tumbler. The main mechanism for this segregation is different energy dissipation rates for the different particle shape types when avalanching down along the free surface. The cubical particles, due to their sharper corners, dissipate energy much faster than the spherical particles. This results in spherical particles reaching the bottom end of the sloped, free surface which are then transported around the cylinder adjacent to the cylinder wall, as rigid body motion. In contrast to size or density segregation, the segregation due to shape is much weaker and takes longer to reach its equilibrium or steady state. In addition, the segregation occurs along the top surface rather than through the top surface (as occurs for size and density segregation). In general, in situations where two particles differ in their ease of flow (viz flowability) the more rapidly flowing particle will segregate to the base of the free surface (which in the case of the tumbler results in spherical particles near the periphery) and the more slowly flowing particle will segregate underneath.     

透平膨胀机转速波动异常分析及处理

介绍了透平膨胀机转速表显示转速大幅度波动的情况,分析了原因并提出了处理方案。     

Boundary effects on sound propagation in superfluids

The equations of strong coupling superconductivity in disordered transition metal alloys have been derived by means of “irreducible” Green's functions and on the basis of the alloy version of the Bari?i?-Labbé-Friedel model for electron-ion interaction. The configurational averaging has been performed by means of the coherent potential approximation. Making some approximations, we have obtained the formulas for the transition temperatureT _c and the electron-phonon coupling constant λ. These depend on the alloy component and total densities of states, the phonon Green's function, and the parameters of the model.     

Liquid-liquid transition without macroscopic phase separation in a water-glycerol mixture

The existence of more than two liquid states in a single-component substance and the ensuing liquid-liquid transitions (LLTs) has attracted considerable attention because of its counterintuitive nature and its importance in the fundamental understanding of the liquid state. Here we report direct experimental evidence for a genuine (isocompositional) LLT without macroscopic phase separation in an aqueous solution of glycerol. We show that liquid I transforms into liquid II by way of two types of kinetics: nucleation and growth, and spinodal decomposition. Although liquid II is metastable against crystallization, we could access both its static and dynamical properties experimentally. We find that liquids I and II differ in density, refractive index, structure, hydrogen bonding state, glass transition temperature and fragility, and that the transition between the two liquids is mainly driven by the local structuring of water rather than of glycerol, suggesting a link to a plausible LLT in pure water.     

Thermodynamic equilibrium of a gas mixture with a solution in the condensed phase

A thermodynamic analysis is made of the equilibrium of a gas mixture (using a nitrogen-hydrogen mixture as an example) with a solid solution of its components. The processes occurring in the surface layer and interphase exchange are taken into account. The equilibrium characteristics are determined in terms of the equilibrium constants of the intermediate stages of the surface reactions.A. M. Gorkii Ural State University. S. M. Kirov Ural Polytechnical Institute, Ekaterinburg. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 62, No. 4, pp. 624–628, April, 1992.     

Gas-liquid two phase flow pattern evolution characteristics based on detrended fluctuation analysis

In this paper, we first extract a nonlinear time series from the Weierestrass function as a toy model and investigate the anti-noise ability of six different fractal scale algorithm. The results indicate that the fractal scales calculated from Detrended Fluctuation Analysis(DFA) are robust with respect to variation in noise level. Based on the conductance fluctuating signals measured from vertical gas-liquid two phase flow experiment, we calculate the fractal scales of five typical flow patterns. The results show that when the water superficial velocity ranging from 0.0453ms⁻¹ to 0.226 ms⁻¹ and the gas superficial velocity ranging from 0.0043ms⁻¹ to 3.43 ms⁻¹, the values of the fractal scale of bubble flow are lowest corresponding to the random complex dynamic behavior, while the values of slug flow are highest corresponding to the alternatively periodic motions between gas slug and liquid slug, and the values of churn flow lies between them indicating the relatively complex dynamic behavior. Our main result is that the fractal scales obtained from conductance fluctuating signals can not only effectively characterize the dynamic characteristics of gas-liquid two phase flow patterns, but also further provide valuable reference for understanding the transitions of different gas-liquid two phase flow patterns.     

Kinetic theory of anisotropic Fermi superfluids

A kinetic theory of anisotropic Fermi superfluids is presented. The kinetic equation for the quasiparticle matrix distribution function is derived from the microscopic theory, supplemented by definitions of the relevant densities and currents. The static spin susceptibility, the normal fluid density, and the specific heat are calculated from the static limit of the kinetic equation. Special attention is given to the collision integral, which is presented explicitly in terms of normal Fermi liquid quantities. The energy dependence of the collision integral makes necessary the introduction of two other distribution function matrices, for which kinetic equations are also derived.     

Full-field optical coherence tomography by achromatic phase shifting with a rotating polarizer

We demonstrate two-dimensional detection optical coherence tomography (OCT) using achromatic phase shifting with a rotating polarizer. This phase shifting, which experiences a light beam with a cyclic change in its polarization state, is, in principle, independent of wavelength. We simulated the wavelength dependence of an achromatic phase shifter using Jones calculus and found that the achromatic region exceeded 145 nm when the deviation of the phase retardation was less than +/- 0.5 degrees. Using the achromatic phase shifter and a conventional phase-shift calculation method, we obtained en face OCT images of an onion at different depths. This method is effective to enhance the quality of OCT with an ultrabroad-spectrum light source.     

Flow of a liquid-gas mixture in a contoured nozzle with constant phase velocity difference

A one-dimensional approximation is used to examine simultaneous flow of a gas and of liquid drops in a shaped nozzle under conditions of constant velocity difference between the phases. The nozzle profile to achieve this flow is determined. The parameters of the gas-liquid mixture are obtained in explicit form as a function of the dimensionless gas velocity.     

Composition measurement of aerosols of submicrometer particles by phase fluctuation absorption spectroscopy

Phase fluctuation optical heterodyne spectroscopy is employed to obtain the first nonextractive data on size-mass distribution of submicrometer ammonium sulfate aerosols. The required theory of aerosol absorption of electromagnetic energy and subsequent thermalization is presented. Based on this theory, the predicted behavior was confirmed by experiments using IR absorption of ammonium sulfate aerosols. The results show good agreement with measurements using conventional methods including condensation nuclei counter, electron micrography, and filtration. In addition, a conversion constant for the photothermal signal of ammonium sulfate aerosols is calculated to be 2.3 microV/(microg/m3). Furthermore, the signal is shown to be linear in excitation energy and modulation frequency and scalable.     

Correlated one-body density matrix of boson superfluids

The correlated density matrix theory is employed and further developed to analyze the one-body density matrix ρ₁(|r ₁-r ₂|) of the normal and superfluid phases of a strongly interacting Bose system at non-zero temperature. The approach continues the formal development described in an earlier article and is based on a suitable trial ansatz for the many-body density matrixW(R, R′)∼Φ(R) Q(R, R′) Φ(R′) with the wave function Φ and incoherence factorQ incorporating the essential statistical and dynamical correlations. Special attention is given to the appearance of off-diagonal long-range order in function ρ₁(|r ₁-r ₂|) and its relation to the condensation strength B_cc characterizing the degree of coherence in the superfluid phase. We derive a number of structural relations that have counterparts in known results on ρ₁ in the Jastrow variational theory of the Bose ground state. We discuss Bose-Einstein condensation and make contact to Landau's phenomenological theory of continuous phase transitions. Numerical estimates are presented on the condensation strength and the condensate fraction of liquid⁴He as functions of the temperature.     

翼型凹变对风轮旋转噪声影响特性分析

针对某分布式小型风力机叶片,为了探究翼型凹变后对风轮旋转噪声的影响效果,利用60通道声阵列系统对凹变叶片和原叶片风轮进行旋转噪声采集,并通过探究翼型凹变对风轮结构动态响应的影响,解析了翼型凹变造成风轮旋转噪声降低的原因.结果表明,翼型凹变可以有效地提高叶片的固有频率和阻尼比,提升了叶片的刚度,有效地减弱了叶片对周围流体...     

Effects of a phase aperture on the fundamental mode of a hard-apertured cavity

This paper shows theoretically that a single-zone diffractive binary optic (step discontinuity) inserted inside an apertured cavity is able to enhance its fundamental mode volume by a factor as high as 12. This allows for a short cavity to have a fundamental mode with a high cross-section.