Density increase of turbulently flowing He II

A density increase of He II up toΔρ/ρ=3·10^?4 due to turbulent flow caused by a heat current in a wide tube has been observed by pycnometric measurements and by measuring the dielectric constant of He II. The state of increased density appears to be metastable against mechanical disturbances.     

3He spin diffusion measurements in 3He- 4He mixture films

3He spin diffusion measurements for 3He-4He mixture films on Nuclepore are reported as a function of 3He coverage for 0. 030相似文献   

Bound state for 3He quasiparticles in dilute 3He-He II mixtures

We argue that a weak bound state might exist for two ³He quasiparticles in dilute ³He-He II mixtures. This should manifest itself below ? 8 mdeg K as a negative bump in the otherwise linear-in-temperature specific heat.     

Magnetokinetic effects in 3HeHe II solutions

Magnetokinetic effects in ³He-⁴He solutions at arbitrary temperatures, impurity concentrations and magnetic fields are discussed. In strong fields kinetic coefficients increase exponentially with the field. The phonon contribution is significant only at extremely low concentrations.     

Imaging of a mixture of hyperpolarized 3He and 129Xe

With the use of hyperpolarized gases, a great number of experiments have been carried out in order to improve the diagnostics of the lung, both from a structural and a functional point of view. 3He is best suited for structural studies, whereas 129Xe gives more detailed information about the functionality of the lung because it enters the bloodstream. In this work, we propose the use of a gas mixture to perform consecutive analysis of lung structure and functionality upon the delivery of a single bolus of gas. We show images of a helium-xenon gas mixture in the presence of a small amount of liquid toluene in order to demonstrate how both nuclei can be detected independently, extracting the spectroscopic information provided by the 129Xe spectra and obtaining an image with high sensitivity for 3He. A second experiment performed on a dissected mouse lung was used to demonstrate how the mixture of gases can enhance sensitivity in the larger airways of the lung.     

Density functional for a model colloid-polymer mixture

Elliptic shear applied to a homeotropically oriented nematic above the electric bend Freedericks transition (FT) generates slow precession of the director. The character of the accompanying nonlinear waves changes from diffusive phase waves to dispersive ones exhibiting spirals and spatiotemporal chaos as the FT is approached from above. An exact solution of the flow alignment equations captures the observed precession and predicts its reversal for non-flow-aligning materials. The FT transforms into a Hopf bifurcation opening the way to understand the wave phenomena.     

Bipolar atmospheric-pressure corona discharge in a He/H2 mixture

Results are presented from a study of the characteristics of a steady-state plasma in a He/H₂ mixture at high pressures. The plasma is formed in the outer region of a multielectrode corona discharge. It is shown that molecules of helium hydride form in such a medium, and their decomposition is accompanied by continuum emission in the 350–650 nm region. The corona discharge is distributed over the length and can be used in systems for the transverse electric circulation of the working medium of atmospheric-pressure plasma radiation sources. The reference spectra of the plasma emission and the dependence of the relative intensity of the lines and the brightness of the bands of He ₂ ^* on the value of the discharge current, pressure, and composition of the working mixture are investigated. Zh. Tekh. Fiz. 69, 33–37 (July 1999)     

Density matrix formalism for anelastic relaxation

A density matrix formalism is developed for anelastic (mechanical) relaxation in crystalline materials with point defects characterized by elastic dipoles. The time-dependent approach to equilibrium of the strain response under the action of a constant applied stress is deduced. The formalism parallels the one used in nuclear magnetic relaxation. The anelastic relaxation time is determined as a function of the parameters occurring in the defect hopping term in the Hamiltonian. This term is responsible for the dissipation of the anelastic ‘potential’ energy into the host lattice. In a lengthy concluding section, the following aspects are discussed point by point: the advantages of the formalism presented, its scope and special cases; the physical implications of the expression obtained for the relaxation time; the similarities and differences between magnetic relaxation and anelastic relaxation, etc.     

Momentum distribution and one-body density matrix in liquid3He.

Summary The momentum distributionn(k) and the one-body density matrix ρ₁(r,r' have been calculated in normal liquid³He atT=0. A variational wave function containing two-, three-body and backflow correlations has been used. The Fermi hypernetted chain technique has been employed and the elementary diagrams have been evaluated by the scaling approximation. The present estimate ofn(k) is in good agreement with the Monte Carlo data obtained with similar wave functions.n(k) and the discontinuityZ ofn(k) at the Fermi surface have been computed at several values of the density. The density dependence of the effective massm ^* has been found to be mainly due to that ofZ.     

Temperature dependent specular reflection of 3He quasiparticles from a wall in He II

Measurements of the transverse acoustic impedance of dilute solutions of ³He in superfluid ⁴He show that the fraction of ³He quasiparticles which are specularly reflected at a plane wall is temperature dependent between 0.1 and 1 K. Values of the ³He relaxation time are also obtained.     

The characteristics of a negative corona discharge in He/Xe/SF6 mixture

The results of investigation of the electrical and optical characteristics of a negative corona discharge in the electrode system of the type needle-grid lit in a He/Xe/SF₆ mixture under the pressure of 100–300 kPa are presented in this paper. The given medium is working for a pulse-periodic excimer lamp on = 351 nm XeF(B–X). Distributed on the length of a lamp active media a bipolar corona discharge is intended for using in the electric circulation of the XeF-lamp working medium. It is shown that the given discharge is ignited steadily in the He/Xe/SF₆ mixture, containing 0, 5kPa SF₆ molecules and is characterised by a low power consumption; the current of the discharge is limited to the development of instability by increasing the voltage on the needles; in hot zones of corona discharge SF₆ molecules cause the effective population 6s of XeI state.     

Density matrix formalism for coupled dynamical systems

A density matrix first principles formalism is extended for use in coupled dynamical systems within the framework of the Zwanzig projection operator technique. Coupled linear integro-differential equations for the reduced density operators of two (or more) dynamical subsystems interacting with one (or more) dissipative subsystem(s) and weak driving fields are obtained. These coupled equations, which are highly problem independent and rendered in a form simple for applications, are applied to the well-known s-d exchange model in metals where the coupled Bloch-like equations obtained by others using many-body techniques are recovered. The problem of the instantaneous destination vector is discussed within the framework of our formalism using superoperator resolvent techniques.