The NIRSPEC Brown Dwarf Spectroscopic Survey II: High-Resolution J-Band Spectra of M, L and T Dwarfs

We present a sequence of high resolution (R~20,000 or 15 km/s) infrared spectra of stars and brown dwarfs spanning spectral types M2.5 to T6. Observations of 16 objects were obtained using eight echelle orders to cover part of the J-band from 1.165-1.323 micron with NIRSPEC on the Keck II telescope. By comparing opacity plots and line lists, over 200 weak features in the J-band are identified with either FeH or H2O transitions. Absorption by FeH attains maximum strength in the mid-L dwarfs, while H2O absorption becomes systematically stronger towards later spectral types. Narrow resolved features broaden markedly after the M to L transition. Our high resolution spectra also reveal that the disappearance of neutral Al lines at the boundary between M and L dwarfs is remarkably abrupt, presumably because of the formation of grains. Neutral Fe lines can be traced to mid-L dwarfs before Fe is removed by condensation. The neutral potassium (K I) doublets that dominate the J-band have pressure broadened wings that continue to broaden from ~50 km/s (FWHM) at mid-M to ~500 km/s at mid-T. In contrast however, the measured pseudo-equivalent widths of these same lines reach a maximum in the mid-L dwarfs. The young L2 dwarf, G196-3B, exhibits narrow potassium lines without extensive pressure-broadened wings, indicative of a lower gravity atmosphere. Kelu-1AB, another L2, has exceptionally broad infrared lines, including FeH and H2O features, confirming its status as a rapid rotator. In contrast to other late T objects, the peculiar T6 dwarf 2MASS 0937+29 displays a complete absence of potassium even at high resolution, which may be a metallicity effect or a result of a cooler, higher-gravity atmosphere.Comment: 53 pages, 21 figures, data will be available at http://www.astro.ucla.edu/~mclean/BDSSarchive

Transcriptional regulation of the human ALDH1A1 promoter by the oncogenic homeoprotein TLX1/HOX11

The homeoprotein TLX1, which is essential to spleen organogenesis and oncogenic when aberrantly expressed in immature T cells, functions as a bifunctional transcriptional regulator, being capable of activation or repression depending on cell type and/or promoter context. However, the detailed mechanisms by which it regulates the transcription of target genes such as ALDH1A1 remains to be elucidated. We therefore functionally assessed the ability of TLX1 to regulate ALDH1A1 expression in two hematopoietic cell lines, PER-117 T-leukemic cells and human erythroleukemic (HEL) cells, by use of luciferase reporter and mobility shift assays. We showed that TLX1 physically interacts with the general transcription factor TFIIB via its homeodomain, and identified two activities in respect to TLX1-mediated regulation of the CCAAT box-containing ALDH1A1 promoter. The first involved CCAAT-dependent transcriptional repression via perturbation of GATA factor-containing protein complexes assembled at a non-canonical TATA (GATA) box. A structurally intact homeodomain was essential for repression by TLX1 although direct DNA binding was not required. The second activity, which involved CCAAT-independent transcriptional activation did not require an intact homeodomain, indicating that the activation and repression functions of TLX1 are distinct. These findings confirm ALDH1A1 gene regulation by TLX1 and support an indirect model for TLX1 function, in which protein-protein interactions, rather than DNA binding at specific sites, are crucial for its transcriptional activity

Truncation of a 2-dimensional Fermi surface due to quasiparticle gap formation at the saddle points

We study a two-dimensional Fermi liquid with a Fermi surface containing the saddle points $(\pi,0)$ and $(0,\pi)$. Including Cooper and Peierls channel contributions leads to a one-loop renormalization group flow to strong coupling for short range repulsive interactions. In a certain parameter range the characteristics of the fixed point, opening of a spin and charge gap and dominant pairing correlations are similar to those of a 2-leg ladder at half-filling. An increase of the electron density we argue leads to a truncation of the Fermi surface with only 4 disconnected arcs remaining.Comment: Reference added. RevTeX 4 pages incl. 4 ps file

Radial Velocity Variability of Field Brown Dwarfs

We present paper six of the NIRSPEC Brown Dwarf Spectroscopic Survey, an analysis of multi-epoch, high-resolution (R ~ 20,000) spectra of 25 field dwarf systems (3 late-type M dwarfs, 16 L dwarfs, and 6 T dwarfs) taken with the NIRSPEC infrared spectrograph at the W. M. Keck Observatory. With a radial velocity (RV) precision of ~2 km s^−1, we are sensitive to brown dwarf companions in orbits with periods of a few years or less given a mass ratio of 0.5 or greater. We do not detect any spectroscopic binary brown dwarfs in the sample. Given our target properties, and the frequency and cadence of observations, we use a Monte Carlo simulation to determine the detection probability of our sample. Even with a null detection result, our 1σ upper limit for very low mass binary frequency is 18%. Our targets included seven known, wide brown dwarf binary systems. No significant RV variability was measured in our multi-epoch observations of these systems, even for those pairs for which our data spanned a significant fraction of the orbital period. Specialized techniques are required to reach the high precisions sensitive to motion in orbits of very low-mass systems. For eight objects, including six T dwarfs, we present the first published high-resolution spectra, many with high signal to noise, that will provide valuable comparison data for models of brown dwarf atmospheres

Client Satisfaction Survey for HIV/AIDS Dental Care Services: An Example from Rural Texas

The challenges to examining client satisfaction are demonstrated through an evaluation of dental services provided by a regional service provider to people living with HIV/AIDS. The process of developing and administering a measure of client satisfaction is discussed. Forty-one of 350 (11.7%) dental clients chose to participate. Quantitative and qualitative data suggests that overall participants are satisfied with services. Identified concerns included a lack of specialized dental, medical, mental health, and case management services. Implications of the study for service delivery, future evaluations, and rural social work practice are addressed

Collective modes and sound propagation in a p-wave superconductor: Sr2_2RuO4_4

There are five distinct collective modes in the recently discovered p-wave superconductor Sr$_2$RuO$_4$; phase and amplitude modes of the order parameter, clapping mode (real and imaginary), and spin wave. The first two modes also exist in the ordinary s-wave superconductors, while the clapping mode with the energy $\sqrt{2} \Delta(T)$ is unique to Sr$_2$RuO$_4$ and couples to the sound wave. Here we report a theoretical study of the sound propagation in a two dimensional p-wave superconductor. We identified the clapping mode and study its effects on the longitudinal and transverse sound velocities in the superconducting state. In contrast to the case of $^3$He, there is no resonance absorption associated with the collective mode, since in metals $\omega/(v_F |{\bf q}|) \ll 1$, where $v_F$ is the Fermi velocity, {\bf q} is the wave vector, and $\omega$ is the frequency of the sound wave. However, the velocity change in the collisionless limit gets modified by the contribution from the coupling to the clapping mode. We compute this contribution and comment on the visibility of the effect. In the diffusive limit, the contribution from the collective mode turns out to be negligible. The behaviors of the sound velocity change and the attenuation coefficient near $T_c$ in the diffusive limit are calculated and compared with the existing experimental data wherever it is possible. We also present the results for the attenuation coefficients in both of the collisionless and diffusive limits at finite temperatures.Comment: RevTex, 12 pages, 2 figures, Replaced by the published versio

Fermi surface renormalization in Hubbard ladders

We derive the one-loop renormalization equations for the shift in the Fermi-wavevectors for one-dimensional interacting models with four Fermi-points (two left and two right movers) and two Fermi velocities v_1 and v_2. We find the shift to be proportional to (v_1-v_2)U^2, where U is the Hubbard-U. Our results apply to the Hubbard ladder and to the t_1-t_2 Hubbard model. The Fermi-sea with fewer particles tends to empty. The stability of a saddle point due to shifts of the Fermi-energy and the shift of the Fermi-wavevector at the Mott-Hubbard transition are discussed.Comment: 5 pages, 4 Postscript figure

Imaging and optical properties of single core-shell GaAs-AlGaAs nanowires

We study the optical properties of a single core-shell GaAs-AlGaAs nanowire (grown by VLS method) using the technique of micro-photoluminescence and spatially-resolved photoluminescence imaging. We observe large linear polarization anisotropy in emission and excitation of nanowires.Comment: IEEE Nano 2006 Proceeding

Temperature dependence of photoluminescence from single core-shell GaAs–AlGaAs nanowires

Temperature-dependent polarized microphotoluminescencemeasurements of single GaAs∕AlGaAs core-shell nanowires are used to probe their electronic states. The low-temperature emission from these wires is strongly enhanced compared with that observed in bare GaAsnanowires and is strongly polarized, reflecting the dielectric mismatch between the nanowire and the surrounding air. The temperature-dependentband gap of the nanowires is seen to be somewhat different from that observed in bulk GaAs, and the PL rapidly quenches above 120K, with an activation energy of 17meV reflecting the presence of nonradiative defects.This work was supported by the University of Cincinnati. Australian authors gratefully acknowledge the financial support from the Australian Research Council

Half-quantum vortex and d-soliton in Sr2_2RuO4_4

Assuming that the superconductivity in Sr$_2$RuO$_4$ is described by a planar p-wave order parameter, we consider possible topological defects in Sr$_2$RuO$_4$. In particular, it is shown that both of the ${\hat d}$-soliton and half-quantum vortex can be created in the presence of the magnetic field parallel to the $a$-$b$ plane. We discuss how one can detect the ${\hat d}$-soliton and half-quantum vortex experimentally.Comment: 8 pages, 3 figure