Spin drag Hall effect in a rotating Bose mixture

We show that in a rotating two-component Bose mixture, the spin drag between the two different spin species shows a Hall effect. This spin drag Hall effect can be observed experimentally by studying the out-of-phase dipole mode of the mixture. We determine the damping of this mode due to spin drag as a function of temperature. We find that due to Bose stimulation there is a strong enhancement of the damping for temperatures close to the critical temperature for Bose-Einstein condensation.Comment: 1 figur

Nearby Gas-Rich Low Surface Brightness Galaxies

We examine the Fisher-Tully cz<1000 km/s galaxy sample to determine whether it is a complete and representative sample of all galaxy types, including low surface brightness populations, as has been recently claimed. We find that the sample is progressively more incomplete for galaxies with (1) smaller physical diameters at a fixed isophote and (2) lower HI masses. This is likely to lead to a significant undercounting of nearby gas-rich low surface brightness galaxies. However, through comparisons to other samples we can understand how the nearby galaxy counts need to be corrected, and we see some indications of environmental effects that probably result from the local high density of galaxies.Comment: 12 page, 2 figures, to appear in Ap

Current-driven and field-driven domain walls at nonzero temperature

We present a model for the dynamics of current- and field-driven domain-wall lines at nonzero temperature. We compute thermally-averaged drift velocities from the Fokker-Planck equation that describes the nonzero-temperature dynamics of the domain wall. As special limits of this general description, we describe rigid domain walls as well as vortex domain walls. In these limits, we determine also depinning times of the domain wall from an extrinsic pinning potential. We compare our theory with previous theoretical and experimental work

Interaction effects on dynamic correlations in non-condensed Bose gases

We consider dynamic, i.e., frequency-dependent, correlations in non-condensed ultracold atomic Bose gases. In particular, we consider the single-particle correlation function and its power spectrum. We compute this power spectrum for a one-component Bose gas, and show how it depends on the interatomic interactions that lead to a finite single-particle relaxation time. As another example, we consider the power spectrum of spin-current fluctuations for a two-component Bose gas and show how it is determined by the spin-transport relaxation time.Comment: 9 pages, 3 figure

Plasma composition in a sigmoidal anemone active region

Using spectra obtained by the EIS instrument onboard Hinode, we present a detailed spatially resolved abundance map of an active region (AR)-coronal hole (CH) complex that covers an area of 359 arcsec x 485 arcsec. The abundance map provides first ionization potential (FIP) bias levels in various coronal structures within the large EIS field of view. Overall, FIP bias in the small, relatively young AR is 2-3. This modest FIP bias is a consequence of the AR age, its weak heating, and its partial reconnection with the surrounding CH. Plasma with a coronal composition is concentrated at AR loop footpoints, close to where fractionation is believed to take place in the chromosphere. In the AR, we found a moderate positive correlation of FIP bias with nonthermal velocity and magnetic flux density, both of which are also strongest at the AR loop footpoints. Pathways of slightly enhanced FIP bias are traced along some of the loops connecting opposite polarities within the AR. We interpret the traces of enhanced FIP bias along these loops to be the beginning of fractionated plasma mixing in the loops. Low FIP bias in a sigmoidal channel above the AR's main polarity inversion line where ongoing flux cancellation is taking place, provides new evidence of a bald patch magnetic topology of a sigmoid/flux rope configfiuration.Comment: For on-line animation, see http://www.mssl.ucl.ac.uk/~db2/fip_intensity.gif. Accepted by Ap

Tilt effects on moment tensor inversion in the near field of active volcanoes

Dynamic tilts (rotational motion around horizontal axes) change the projection of local gravity onto the horizontal components of seismometers. This causes sensitivity of these components to tilt, especially at low frequencies. We analyse the consequences of this effect onto moment tensor inversion for very long period (vlp) events in the near field of active volcanoes on the basis of synthetic examples using the station distribution of a real deployed seismic network and the topography of Mt. Merapi volcano (Java, Indonesia). The examples show that for periods in the vlp range of 10-30 s tilt can have a strong effect on the moment tensor inversion, although its effect on the horizontal seismograms is significant only for few stations. We show that tilts can be accurately computed using the spectral element method and include them in the Green's functions. The (simulated) tilts might be largely influenced by strain-tilt coupling (stc). However, due to the frequency dependence of the tilt contribution to the horizontal seismograms, only the largest tilt signals affect the source inversion in the vlp frequency range. As these are less sensitive to stc than the weaker signals, the effect of stc can likely be neglected in this application. In the converse argument, this is not necessarily true for longer periods, where the horizontal seismograms are dominated by the tilt signal and rotational sensors would be necessary to account for it. As these are not yet commercially available, this study underlines the necessity for the development of such instrument

Spin Caloritronics in Noncondensed Bose Gases

We consider coupled spin and heat transport in a two-component, atomic Bose gas in the noncon- densed state. We find that the transport coefficients show a temperature dependence reflecting the bosonic enhancement of scattering, and discuss experimental signatures of the spin-heat coupling in spin accumulation and total dissipation. Inside the critical region of Bose-Einstein condensation, we find anomalous behavior of the transport coefficients, and in particular, an enhancement for the spin caloritronics figure of merit that determines the thermodynamic efficiency of spin-heat conversion

THz emission from coherently controlled photocurrents in GaAs

We report broadband terahertz radiation from ballistic photocurrents generated via quantum interference of one- and two-photon absorption in low-temperature-grown and semi-insulating GaAs at 295 K. For 90 fs, 1550 and 775 nm optical pulses, we obtain phase-controllable near-single cycle 4 THz radiation. Higher frequency THz emission should be achievable with shorter pulses. At a 250 kHz repetition rate and average powers of 10 mW (1550 nm) and 400 μμW (775 nm), we measure 3 nW of THz power, limited mainly by phase walkoff of the optical beams within the 1.5-μμm-thick sample and collection efficiency. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70293/2/APPLAB-75-25-3959-1.pd

The Contribution of HI-Rich Galaxies to the Damped Absorber Population at z=0

We present a study of HI-rich galaxies in the local universe selected from blind emission-line surveys. These galaxies represent the emission-line counterparts of local damped Lyman-alpha systems. We find that the HI cross-section of galaxies is drawn from a large range of galaxy masses below M_star, 66% of the area comes from galaxies in the range 8.5 < Log M_star < 9.7. Both because of the low mass galaxy contribution, and because of the range of galaxy types and luminosities at any given HI mass, the galaxies contributing to the HI cross-section are not exclusively L_star spirals, as is often expected. The optical and near infrared counterparts of these galaxies cover a range of types (from spirals to irregulars), luminosities (from L_star to <0.01 L_star), and surface brightnesses. The range of optical and near infrared properties as well as the kinematics for this population are consistent with the properties for the low-z damped Lyman-alpha absorbers. We also show that the number of HI-rich galaxies in the local universe does not preclude evolution of the low-z damped absorber population, but it is consistent with no evolution.Comment: 10 pages, 7 figures. To appear in "Extragalactic Gas at Low Redshift" (ASP Conf. Series, Weymann Conf.