Cap Omega Research Articles

Vortex states in rotating 3He-A in a weak magnetic field.

We study theoretically the phase diagram of vortex states in /sup 3/He-A in a weak magnetic field Happrox.H/sub 0/(30 Oe). We find that the lattice of 2..pi.. analytic vortices proposed by Fujita et al. has the lowest free energy for H H/sub 0/ the lattice of vortex pairs (Seppaelae-Volovik vortices) is more favorable. In the vicinity of the transition temperature (T>0.8T/sub c/) the lattice of dipole-locked vortex pairs appears between the above two configurations in a magnetic field Happrox.0.5H/sub 0/ and for a rotation speed ..cap omega..< or approx. =0.04 rad/sec.

The statistics of gravitational lenses. II - Apparent evolution in the quasars' luminosity function

We study the statistical effects on the luminosity function (LF) of quasars due to gravitational lensing in an inhomogeneous universe. We use a modified version of the approach developed in Vietri and Ostriker, which naturally includes cosmological effects, energy conservation, a realistic mass distribution within galaxies, a realistic mass spectrum for galaxies, amplification bias, lensing by galaxies (equivalentmaxilensing) and by stars (equivalentminilensing); we neglect the influence of galaxy clusters and superclusters. This method is correct for small probabilities of suffering two strongly amplifying scatterings, a condition easily satisfied for ..cap omega../sub baryons/ 2 must have been minilensed. For z>2, m/sub B/<16, we predict the existence of 64 objects over the whole sky, while we only expect 24 if there is no minilensing.« less

Cyclotron Resonance in a Nonneutral Plasma

Single-component plasmas are found to exhibit a reversal in the roles of cyclotron and upper hybrid resonances familiar in neutral plasmas. There is a global resonance at the cyclotron frequency $\ensuremath{\omega}=\ensuremath{\Omega}\ensuremath{\equiv}\frac{\mathrm{qB}}{\mathrm{mc}}$ and a local field cancellation at layers where $\ensuremath{\omega}={\ensuremath{\Omega}}_{1}={({\ensuremath{\Omega}}^{2}\ensuremath{-}{\ensuremath{\omega}}_{p}^{2})}^{\frac{1}{2}}$, ${\ensuremath{\omega}}_{p}$ being the local plasma frequency. Thermal effects limit the amplitude of the global resonance and produce energy absorption at the $\ensuremath{\omega}={\ensuremath{\Omega}}_{1}$ layers.

Evolution of electromagnetic instability in a hot two-component magnetic plasma stream anisotropy: Ion fusion mode.

We derive precisely the results of streaming (V/sub 0/..cap omega../sub e/) and Alfven's (..omega..<..cap omega../sub I/) mode. The electroncyclotron resonance reveals that the phase velocity (..omega../k) is of the order of the velocity of light, and the refractive index is unity for moderate streaming velocity. However, for ion fusion mode, the corresponding ..omega../k approaches 10/sup 2/ in a dense refractive medium for low ion cyclotron frequency. Moreover, with ..cap omega../sub I/ = 10/sup 4/ rad/sec, luminous waves are generated. Early isotropic results are also recovered in our analysis.

Self-similar secondary infall and accretion in an Einstein-de Sitter universe

Similarity solutions have been found for secondary infall and accretion onto an initially overdense perturbation in an Einstein--de Sitter (..cap omega.. = 1) universe. After the initial collapse of a positive density perturbation, bound shells continue to turn around and fall in, with the radius of the shell currently turning around increasing as t/sup 8/9/ and the mass within this radius increasing as t/sup 2/3/. The secondary infall approaches a self-similar form, with the exact behavior depending on the kind of gas and on central boundary conditions. If there is a central black hole, it grows by accretion, with the density having the power-law form rhoproportionalr/sup 01.5/ near the center. If there is no central black hole, a rhoproportionalr/sup 02.25/ density profile results, with infalling matter added to successively larger radii.

Cosmology with decaying particles.

We consider a cosmological model in which an unstable massive relic particle species (denoted by X) has an initial mass density relative to baryons ..beta../sup -1/equivalentrho/sub X//rho/sub B/>>1, and then decays recently (red-shift z< or approx. =1000) into particles which are still relativistic today (denoted by R). We write down and solve the coupled equations for the cosmic scale factor a(t), the energy density in the various components (rho/sub X/,rho/sub R/,rho/sub B/), and the growth of linear density perturbations (deltarho/rho). The solutions form a one-parameter (..beta..) family of solutions; physically ..beta../sup -1/approx. =(..cap omega../sub R//..cap omega../sub NR/)(1+z/sub D/) = (ratio today of energy density of relativistic to nonrelativistic particles) x (1+ red-shift of decay). We discuss the observational implications of such a cosmological model and compare our results to earlier results computed in ''the simultaneous decay approximation.'' In an appendix we briefly consider the case where one of the decay products of the X is massive and becomes nonrelativistic by the present epoch.

Comment on "String-dominated universe"

Theoretical prejudice favors the flat(k=0) cosmology, and the inflationary Universe scenario implements this prejudice in a natural way. For the k=0 model ..cap omega.. (defined as rho total/rho critical; rho total = rho NR + rho vac + rho R + rho S) = 1. However, observational data suggests: ..cap omega../sub OBS/ approx. = 0.2' +- 0.1', where +- 0.1 indicates the range of values reported. This discrepancy is known as the ..cap omega..-problem. A number of solutions have been suggested: ..cap omega../sub OBS/ is determined by assuming that light (i.e., galaxies) traces mass - perhaps this assumption is not valid; ..cap omega../sub OBS/ is not sensitive to a smoothly-distributed component of mass density - perhaps most of the mass density resides in a smooth component. Candidates for the smooth component include: relativistic particles (rho/sub R/), a relic cosmological term (rho/sub vac/), and in a recent letter Vilenkin has suggested fast-moving strings (rho/sub S/).

Proiskhozhdenie deiteriya

Almost described mechanisms described in literature and capable changing the abundance of cosmological nucleosynthesis products any more appreciably have been reviewed. The existing theoretical representations and observational data permit to analyze the problem of the deuterium origin. The main conclusion, following from the analysis, consists, firstly, in the fact that active processes at the subgalactic stage of the Universe evolution, which are connected with the activity of so-called praquasars, are capable of producing deuterium in quantity not more than X approximately 10 /sup -7/, i.e. the initial abundance of deuterium in the Galaxy was equal to its cosmological abundance. Secondly, nonequilibrium phenomena in the Galaxy, such as activity of the galactic nucleus, neutron star explosions and shock waves following explosions of supernovae, produce not more than 1% of the observed quantity of deuterium, that's why during evolution of the Galaxy the deuterium abundance can be reduced only due to its burn-out in stars. Evaluation of destruction degree for this isotope 3-5 times reduction points to the fact that the observed galactic abundance X=(2-3)x10/sup -5/ agrees with the standard Universe model with 0.05(<=)..cap omega..U(<=)0.08, where ..cap omega..U is the relation of mean density of a substance to critical one. Evidently, other cosmological models could be considered satisfactory, if the deuterium yield in them lies within X=(3x15)x10sup(-5).

Galvanic Action Between MnO2 ‐ Metal Couples and Its Effect on the Discharge of Li / MnO2 Cells

not Available.

Resistive vortices and two-dimensional transition in aluminum films

Thermally excited fluxoids are found in the resistive region of the superconducting transition of thin aluminum films with RD'Alembertian = 10 ..cap omega.. by a method using a dc transformer. The R(T) and I--V dependences obtained at T ..-->.. T/sub 2D/ correspond to the universal relations of the theory of a Berezinskii--Kosterlitz--Thouless phase transition. The obeserved effects are related to the presence of a two-dimensional system of Josephson weak links in the films and the dissipative dynamics of the fluxoids in such structures.

Collisionless analogs of riemann ellipsoids: Self-consistent model of an ellipsoid with “oblique” rotation

A new model of an ellipsoidal stellar system in which there is no equatorial plane of symmetry perpendicular to the rotation axis is constructed. In its orientation with respect to the rotation axis, the model recalls some types of Riemann fluid ellipsoids. The motion of a particle is investigated and the condition found for it to touch the boundary surface of the ellipsoid. A feature of the model is the nonvanishing of some of the nondiagonal components of the velocity dispersion tensor. The model has two independent parameters - the semiaxis ratio a/sub 2//a/sub 1/ and the angle of the orientation of the figure of the ellipsoid relative to the rotation axis. Equivalent to the latter is the ratio /eta/ = ..cap omega../sup 2//sub 3//2A/sub 2/. In the (a/sub 2//a/sub 1/, /eta/) plane, the model occupies two isolated regions. In special cases, the model is transformed into four single-parameter figures of equilibrium. Two of them do not have velocity dispersion and are mutually adjoint (in the sense of Dedekind's theorem) analogs of the Riemann ellipsoids of the second kind without pressure. The two other figures have velocity dispersion. One is a Freeman ellipsoid of given shape, and the other ismore » a degenerate model with oblique rotation in which the component of the velocity dispersion is zero in the direction perpendicular to the principal plane (in which the rotation axis lies).« less

Electronic Conductivity Decrease in Porous NiO Cathodes during Operation in Molten Carbonate Fuel Cells

not Available.

Electrical Resistivities of Monocrystalline and Polycrystalline TiB2

The electrical resistivity of monocrystalline and polycrystalline TiB2, was measured under an inert atmosphere by a four‐point ac impedance technique over the range 298 to 1373 K. The results are expressed in the form ρ‐ρ298=m(T‐298). The following values of ρ298 (μω.cm) and m(nω.cm‐K‐1) were determined: for polycrystalline TiB2 (69% dense) 18.2 and 95; for polycrystalline TiB2 (99% dense) 7.4 and 42; and for monocrystalline TiB2, 6.6 and 34.9.

Tests of cosmological models constrained by inflation

The inflationary scenario requires that the universe have negligible curvature along constant-density surfaces. In the Friedmann-Lemaitre cosmology that leaves us with two free parameters, Hubble's constant H/sub 0/ and the density parameter ..cap omega../sub 0/ (or, equivalently, the cosmological constant ..lambda..). I discuss here tests of this set of models from local and high-redshift observations. The data agree reasonably well with ..cap omega../sub 0/approx.0.2.

Remark on allowance for the motion of electrons that interact with photons in astrophysical problems

Attention is drawn to a serious inaccuracy in some studies that are widely used in the interpretation of astrophysical phenomena. Correct determination of the solid angle d..cap omega.. /sub f/ of the direction of the scattered photon results in a correction of the expressions which take into account the motion of the electron in Compton scattering problems. Exact expressions are obtained for the scattering kernel and the energy losses. The results obtained differ significantly from the ones widely used, particularly in the description of an inverse Compton scattering regime.

Localization and electron-interaction contributions to the magnetoresistance in three-dimensional metallic granular aluminum

Magnetoresistance measurements have been made on three-dimensional granular aluminum specimens with room-temperature resistivities rho/sub RT/ between 300 and 6000 ..mu cap omega.. cm. Four contributions, from localization and electron-interaction effects, including superconducting fluctuations, have been separated. This leads to values of the inelastic and spin-orbit scattering times tau/sub in/(T) and tau/sub so/. The dependences of tau/sub in/ on T and rho/sub RT/ are in qualitative agreement with the theory of Schmid based on electron-electron interactions, but there are discrepancies in the quantitative details. The values of tau/sub in/ and tau/sub so/ are of the same order of magnitude as those obtained from measurements on two-dimensional specimens.

The Evolution of Voids in the Expanding Universe

We examine the growth and nonlinear evolution of spherically symmetric, negative density perturbations in an otherwise uniform Friedmann cosmology. In general, the cavity expands and its density relative to the background decreases. In certain cases, the cavity comes to be surrounded by a narrow shell of matter with a density substantially greater than the mean cosmological value; we show that such an overdense shell can form even when no overdense region is present anywhere in the initial density profile. These ''walled-in'' cavities may be identified with recently observed, large-scale holes in the galaxy distribution, and the shells themselves with the superclusters which define the boundaries of such holes. However, we also show that there exist choices for the initial density profile which lead to the formation of deep cavities which are not surrounded by any overdense shells. We examine the behavior of the shell-growth phenomenon under various assumptions about the background universe and the initial density perturbation, and find that shell growth is enhanced for high values of the density parameter ..cap omega.., positive (repulsive) cosmological constant, steep density profile of the initial perturbation, large-amplitude perturbation, and/or early origin of the perturbation. We derive analytic criteria for classifying arbitrary initiallymore » negative density profiles to determine (a) whether shell crossing with formally infinite density will eventually occur for any given comoving mass coordinate, and (b) whether matter at adjacent mass coordinates will form a shell of finite overdensity which persists indefinitely.« less

Bifurcating, chaotic, and intermittent solutions in the rf-biased Josephson junction

Extensive numerical simulations of the rf-biased Josephson junction are presented. It is shown that, as the amplitude is increased for fixed damping and frequency, an apparently endless sequence of bifurcating-chaotic trees separated by periodic solutions exists. The state diagram characterized in the amplitude-damping plane at fixed frequency (..cap omega.. = 0.65) shows a complex set of solutions. A detailed study of the transition in the high-damping limit is presented, indicating the bounds for asymmetric, bifurcating, and chaotic solutions for low ..beta../sub c/. It is shown that strange attractors are common to trapped and free-running chaotic solutions for nearby amplitudes due to intermittency among the various basins of attraction. Return maps at high amplitudes are found to be essentially one dimensional. Experimental consequences of our simulations are presented in terms of equivalent noise temperatures at low frequencies, resulting in maximum noise temperatures of the order of 10/sup 6/--10/sup 7/ K.

Nonstatistical Cooling of the Highly ExcitedDy161Nucleus

Gamma rays following the /sup 162/Dy(/sup 3/He,..cap alpha..) reaction have been studied as a function of excitation energies in /sup 161/Dy. For excitation energies above approx.3 MeV a (2.2 +- 0.2)-MeV pump appears in the ..gamma..-ray spectra. It is suggested that the bump originates from enhanced ..delta cap omega.. = 1 single-quasiparticle transitions.

Proton + nucleus inclusive (p,p′) scattering at 800 MeV

800 MeV inclusive (p,p') data, spanning the momentum range from that of the quasi-elastic peak to outgoing proton momenta of about 350 MeV/c, are reported for the target nuclei /sup 1/H, /sup 2/H, /sup 12/C, /sup 40/Ca, and /sup 208/Pb. The data are consistent with simple ideas concerning quasi-free ..pi.. production, and an angle and momentum integration of d/sup 2/sigma/d..cap omega.. dp across the entire quasi-free region accounts for most of the p+nucleus total reaction cross section.