Geodetic Earth Orbiting Satellite /GEOS-C/, Applications Technology Satellite /ATS-F/ tracking experiment

Design analysis of GEOS-C/ATS-F tracking experimen

Dynamic Model and Phase Transitions for Liquid Helium

This article presents a phenomenological dynamic phase transition theory -- modeling and analysis -- for superfluids. As we know, although the time-dependent Ginzburg-Landau model has been successfully used in superconductivity, and the classical Ginzburg-Landau free energy is still poorly applicable to liquid helium in a quantitative sense. The study in this article is based on 1) a new dynamic classification scheme of phase transitions, 2) new time-dependent Ginzburg-Landau models for general equilibrium transitions, and 3) the general dynamic transition theory. The results in this article predict the existence of a unstable region H, where both solid and liquid He II states appear randomly depending on fluctuations and the existence of a switch point M on the lambda-curve, where the transitions changes types

Raman Scattered He II λ\lambda 6545 Line in the Symbiotic Star V1016 Cygni

We present a spectrum of the symbiotic star V1016 Cyg observed with the 3.6 m Canada-France-Hawaii Telescope, in order to illustrate a method to measure the covering factor of the neutral scattering region around the giant component with respect to the hot emission region around the white dwarf component. In the spectrum, we find broad wings around H$\alpha$ and a broad emission feature around 6545${\rm \AA}$ that is blended with the [N II]$\lambda$ 6548 line. These two features are proposed to be formed by Raman scattering by atomic hydrogen, where the incident radiation is proposed to be UV continuum radiation around Ly$\beta$ in the former case and He II $\lambda$ 1025 emission line arising from $n=6\to n=2$ transitions for the latter feature. We remove the H$\alpha$ wings by a template Raman scattering wing profile and subtract the [N II] $\lambda$ 6548 line using the 3 times stronger [N II] $\lambda$ 6583 feature in order to isolate the He II Raman scattered 6545 \AA line. We obtain the flux ratio $F_{6545}/F_{6560}=0.24$ of the He II $\lambda$ 6560 emission line and the 6545 \AA feature for V1016 Cyg. Under the assumption that the He II emission from this object is isotropic, this ratio is converted to the ratio $\Phi_{6545}/\Phi_{1025}=0.17$ of the number of the incident photons and that of the scattered photons. This implies that the scattering region with H I column density $N_{HI}\ge 10^{20}{\rm cm^{-2}}$ covers 17 per cent of the emission region. By combining the presumed binary period $\sim 100$ yrs of this system we infer that a significant fraction of the slow stellar wind from the Mira component is ionized and that the scattering region around the Mira extends a few tens of AU, which is closely associated with the mass loss process of the Mira component.Comment: 12 pages, 6 figures, accepted for publication in Ap

Non-local Control of the Kondo Effect in a Double Quantum Dot-Quantum Wire Coupled System

We have performed low-temperature transport measurements on a double quantum dot-quantum wire coupled device and demonstrated non-local control of the Kondo effect in one dot by manipulating the electronic spin states of the other. We discuss the modulation of the local density of states in the wire region due to the Fano-Kondo antiresonance, and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) exchange interaction as the mechanisms responsible for the observed features.Comment: 4 pages, 4 figure

Spin transitions in a small Si quantum dot

We have studied the magnetic field dependence of the ground state energies in a small Si quantum dot. At low fields the first five electrons are added in a spin-up -- spin-down sequence minimizing the total spin. This sequence does not hold for larger number of electrons in the dot. At high fields the dot undergoes transitions between states with different spins driven entirely by Zeeman energy. We identify some features that can be attributed to transitions between different spin configurations preserving the total spin of the dot. For a few peaks we observed large linear shifts that correspond to the change of the spin of the dot by 3/2. Such a change requires that an electron in the dot flips its spin during every tunneling event.Comment: Revtex, 5 pages, 3 figure

Toward the Evidence of the Accretion Disk Emission in the Symbiotic Star RR Tel

In this paper, we argue that in the symbiotic star RR Tel the existence of an accretion disk around the hot companion is strongly implied by the characteristic features exhibited by the Raman-scattered O VI lines around 6830 \AA and 7088 \AA. High degrees of polarization and double-peaked profiles in the Raman-scattered lines and single-peak profiles for other emission lines are interpreted as line-of-sight effects, where the H I scatterers near the giant see an incident double-peaked profile and an observer with a low inclination sees single-peak profiles. It is predicted that different mass concentrations around the accretion disk formed by a dusty wind may lead to the disparate ratios of the blue peak strength to the red counterpart observed in the 6830 and 7088 features. We discuss the evolutionary links between symbiotic stars and bipolar protoplanetary nebulae and conclude that the Raman scattering processes may play an important role in investigation of the physical properties of these objects.Comment: 11 pages, 3 figures, accepted for publication in the ApJ Letter

Resonant Tunneling through Multi-Level and Double Quantum Dots

We study resonant tunneling through quantum-dot systems in the presence of strong Coulomb repulsion and coupling to the metallic leads. Motivated by recent experiments we concentrate on (i) a single dot with two energy levels and (ii) a double dot with one level in each dot. Each level is twofold spin-degenerate. Depending on the level spacing these systems are physical realizations of different Kondo-type models. Using a real-time diagrammatic formulation we evaluate the spectral density and the non-linear conductance. The latter shows a novel triple-peak resonant structure.Comment: 4 pages, ReVTeX, 4 Postscript figure

Non-ohmic critical fluctuation conductivity of layered superconductors in magnetic field

Thermal fluctuation conductivity for a layered superconductor in perpendicular magnetic field is treated in the frame of the self-consistent Hartree approximation for an arbitrarily strong in-plane electric field. The simultaneous application of the two fields results in a slightly stronger suppression of the superconducting fluctuations, compared to the case when the fields are applied individually.Comment: 4 pages, 1 figure, to be published in Phys. Rev.

Conduction through a quantum dot near a singlet-triplet transition

Kondo effect in the vicinity of a singlet-triplet transition in a vertical quantum dot is considered. This system is shown to map onto a special version of the two-impurity Kondo model. At any value of the control parameter, the system has a Fermi-liquid ground state. Explicit expressions for the linear conductance as a function of the control parameter and temperature $T$ are obtained. At T=0, the conductance reaches the unitary limit $\sim 4e^2/h$ at the triplet side of the transition, and decreases with the increasing distance to the transition at the singlet side. At finite temperature, the conductance exhibits a peak near the transition point