Soliton Magnetization Dynamics in Spin-Orbit Coupled Bose-Einstein Condensates

Ring-trapped Bose-Einstein condensates subject to spin-orbit coupling support localized dark soliton excitations that show periodic density dynamics in real space. In addition to the density feature, solitons also carry a localized pseudo-spin magnetization that exhibits a rich and tunable dynamics. Analytic results for Rashba-type spin-orbit coupling and spin-invariant interactions predict a conserved magnitude and precessional motion for the soliton magnetization that allows for the simulation of spin-related geometric phases recently seen in electronic transport measurements.Comment: 3 figures, 5 page

Svortices and the fundamental modes of the "snake instability": Possibility of observation in the gaseous Bose-Einstein Condensate

The connection between quantized vortices and dark solitons in a long and thin, waveguide-like trap geometry is explored in the framework of the non-linear Schr\"odinger equation. Variation of the transverse confinement leads from the quasi-1D regime where solitons are stable to 2D (or 3D) confinement where soliton stripes are subject to a transverse modulational instability known as the ``snake instability''. We present numerical evidence of a regime of intermediate confinement where solitons decay into single, deformed vortices with solitonic properties, also called svortices, rather than vortex pairs as associated with the ``snake'' metaphor. Further relaxing the transverse confinement leads to production of 2 and then 3 vortices, which correlates perfectly with a Bogoliubov-de Gennes stability analysis. The decay of a stationary dark soliton (or, planar node) into a single svortex is predicted to be experimentally observable in a 3D harmonically confined dilute gas Bose-Einstein condensate.Comment: 4 pages, 4 figure

First-principles calculations of 2x2 reconstructions of GaN(0001) surfaces involving N, Al, Ga, In, and as atoms

The ab initio studies presented here employed a pseudopotential-plane-wave method in order to obtain the minimum-energy configurations of various 22 GaN0001 surfaces involving N, Al, Ga, In, and As atoms. Comparison of the various possible reconstructions allows predictions to be made regarding the most energetically favorable configurations. Such comparisons depend on the value of the effective chemical potential of each atomic species, which can be related directly to experimental growth conditions. The most stable structure as a function of chemical potentials is determined. Based on these results we have characterized the effect of N in the adlayer surface and the stability dependence with number of substitutions as a function of the model employed and the possible surfactant character of some of the added atoms. Surface phase diagrams as a function of the chemical potential have been calculated to show the phase transition between the different reconstructions

Decay modes of two repulsively interacting bosons

We study the decay of two repulsively interacting bosons tunneling through a delta potential barrier by direct numerical solution of the time-dependent Schr\"odinger equation. The solutions are analyzed according to the regions of particle presence: both particles inside the trap (in-in), one particle in and one particle out (in-out), and both particles outside (out-out). It is shown that the in-in probability is dominated by exponential decay, and its decay rate is predicted very well from outgoing boundary conditions. Up to a certain range of interaction strength the decay of in-out probability is dominated by the single particle decay mode. The decay mechanisms are adequately described by simple models.Comment: 18 pages, 13 figure

Luminescence quenching of the triplet excimer state by air traces in gaseous argon

While developing a liquid argon detector for dark matter searches we investigate the influence of air contamination on the VUV scintillation yield in gaseous argon at atmospheric pressure. We determine with a radioactive alpha-source the photon yield for various partial air pressures and different reflectors and wavelength shifters. We find for the fast scintillation component a time constant tau1= 11.3 +- 2.8 ns, independent of gas purity. However, the decay time of the slow component depends on gas purity and is a good indicator for the total VUV light yield. This dependence is attributed to impurities destroying the long-lived argon excimer states. The population ratio between the slowly and the fast decaying excimer states is determined for alpha-particles to be 5.5 +-0.6 in argon gas at 1100 mbar and room temperature. The measured mean life of the slow component is tau2 = 3.140 +- 0.067 microsec at a partial air pressure of 2 x 10-6 mbar.Comment: 7 pages submitted to NIM

High-Redshift Dust Obscured Galaxies: A Morphology-Spectral Energy Distribution Connection Revealed by Keck Adaptive Optics

A simple optical to mid-IR color selection, R – [24]>14, i.e., f_ν(24 μm)/f_ν(R) ≳ 1000, identifies highly dust obscured galaxies (DOGs) with typical redshifts of z ~ 2 ± 0.5. Extreme mid-IR luminosities (L_(IR) > 10^(12-14)) suggest that DOGs are powered by a combination of active galactic nuclei (AGNs) and star formation, possibly driven by mergers. In an effort to compare their photometric properties with their rest-frame optical morphologies, we obtained high-spatial resolution (0."05-0."1) Keck Adaptive Optics K'-band images of 15 DOGs. The images reveal a wide range of morphologies, including small exponential disks (eight of 15), small ellipticals (four of 15), and unresolved sources (two of 15). One particularly diffuse source could not be classified because of low signal-to-noise ratio. We find a statistically significant correlation between galaxy concentration and mid-IR luminosity, with the most luminous DOGs exhibiting higher concentration and smaller physical size. DOGs with high concentration also tend to have spectral energy distributions (SEDs) suggestive of AGN activity. Thus, central AGN light may be biasing the morphologies of the more luminous DOGs to higher concentration. Conversely, more diffuse DOGs tend to show an SED shape suggestive of star formation. Two of 15 in the sample show multiple resolved components with separations of ~1 kpc, circumstantial evidence for ongoing mergers

Galactic Rotation Parameters from Data on Open Star Clusters

Currently available data on the field of velocities Vr, Vl, Vb for open star clusters are used to perform a kinematic analysis of various samples that differ by heliocentric distance, age, and membership in individual structures (the Orion, Carina--Sagittarius, and Perseus arms). Based on 375 clusters located within 5 kpc of the Sun with ages up to 1 Gyr, we have determined the Galactic rotation parameters Wo =-26.0+-0.3 km/s/kpc, W'o = 4.18+-0.17 km/s/kpc^2, W''o=-0.45+-0.06 km/s/kpc^3, the system contraction parameter K = -2.4+-0.1 km/s/kpc, and the parameters of the kinematic center Ro =7.4+-0.3 kpc and lo = 0+-1 degrees. The Galactocentric distance Ro in the model used has been found to depend significantly on the sample age. Thus, for example, it is 9.5+-0.7 kpc and 5.6+-0.3 kpc for the samples of young (50 Myr) clusters, respectively. Our study of the kinematics of young open star clusters in various spiral arms has shown that the kinematic parameters are similar to the parameters obtained from the entire sample for the Carina-Sagittarius and Perseus arms and differ significantly from them for the Orion arm. The contraction effect is shown to be typical of star clusters with various ages. It is most pronounced for clusters with a mean age of 100 Myr, with the contraction velocity being Kr = -4.3+-1.0 km/s.Comment: 14 pages, 4 figures, 2 table

Comparative analysis of the lambda-interferons IL-28A and IL-29 regarding their transcriptome and their antiviral properties against hepatitis C virus.

Specific differences in signaling and antiviral properties between the different Lambda-interferons, a novel group of interferons composed of IL-28A, IL-28B and IL-29, are currently unknown. This is the first study comparatively investigating the transcriptome and the antiviral properties of the Lambda-interferons IL-28A and IL-29. Expression studies were performed by microarray analysis, quantitative PCR (qPCR), reporter gene assays and immunoluminometric assays. Signaling was analyzed by Western blot. HCV replication was measured in Huh-7 cells expressing subgenomic HCV replicon. All hepatic cell lines investigated as well as primary hepatocytes expressed both IFN-λ receptor subunits IL-10R2 and IFN-λR1. Both, IL-28A and IL-29 activated STAT1 signaling. As revealed by microarray analysis, similar genes were induced by both cytokines in Huh-7 cells (IL-28A: 117 genes; IL-29: 111 genes), many of them playing a role in antiviral immunity. However, only IL-28A was able to significantly down-regulate gene expression (n = 272 down-regulated genes). Both cytokines significantly decreased HCV replication in Huh-7 cells. In comparison to liver biopsies of patients with non-viral liver disease, liver biopsies of patients with HCV showed significantly increased mRNA expression of IL-28A and IL-29. Moreover, IL-28A serum protein levels were elevated in HCV patients. In a murine model of viral hepatitis, IL-28 expression was significantly increased. IL-28A and IL-29 are up-regulated in HCV patients and are similarly effective in inducing antiviral genes and inhibiting HCV replication. In contrast to IL-29, IL-28A is a potent gene repressor. Both IFN-λs may have therapeutic potential in the treatment of chronic HCV

An Observational Limit on the Dwarf Galaxy Population of the Local Group

We present the results of an all-sky, deep optical survey for faint Local Group dwarf galaxies. Candidate objects were selected from the second Palomar survey (POSS-II) and ESO/SRC survey plates and follow-up observations performed to determine whether they were indeed overlooked members of the Local Group. Only two galaxies (Antlia and Cetus) were discovered this way out of 206 candidates. Based on internal and external comparisons, we estimate that our visual survey is more than 77% complete for objects larger than one arc minute in size and with a surface brightness greater than an extremely faint limit over the 72% of the sky not obstructed by the Milky Way. Our limit of sensitivity cannot be calculated exactly, but is certainly fainter than 25 magnitudes per square arc second in R, probably 25.5 and possibly approaching 26. We conclude that there are at most one or two Local Group dwarf galaxies fitting our observational criteria still undiscovered in the clear part of the sky, and a roughly a dozen hidden behind the Milky Way. Our work places the "missing satellite problem" on a firm quantitative observational basis. We present detailed data on all our candidates, including surface brightness measurements.Comment: 58 pages in AJ manuscript format; some figures at slightly reduced quality; accepted by the Astronomical Journa

HST Morphologies of z~2 Dust Obscured Galaxies I: Power-law Sources

We present high spatial resolution optical and near-infrared imaging obtained using the ACS, WFPC2 and NICMOS cameras aboard the Hubble Space Telescope of 31 24um--bright z~2 Dust Obscured Galaxies (DOGs) identified in the Bootes Field of the NOAO Deep Wide-Field Survey. Although this subset of DOGs have mid-IR spectral energy distributions dominated by a power-law component suggestive of an AGN, all but one of the galaxies are spatially extended and not dominated by an unresolved component at rest-frame UV or optical wavelengths. The observed V-H and I-H colors of the extended components are 0.2-3 magnitudes redder than normal star-forming galaxies. All but 1 have axial ratios >0.3, making it unlikely that DOGs are composed of an edge-on star-forming disk. We model the spatially extended component of the surface brightness distributions of the DOGs with a Sersic profile and find effective radii of 1-6 kpc. This sample of DOGs is smaller than most sub-millimeter galaxies (SMGs), but larger than quiescent high-redshift galaxies. Non-parametric measures (Gini and M20) of DOG morphologies suggest that these galaxies are more dynamically relaxed than local ULIRGs. We estimate lower limits to the stellar masses of DOGs based on the rest-frame optical photometry and find that these range from ~10^(9-11) M_sun. If major mergers are the progenitors of DOGs, then these observations suggest that DOGs may represent a post-merger evolutionary stage.Comment: 23 pages, 9 figures, 6 tables, accepted to ApJ; lower limits on stellar mass revised upwards by factor of (1+z