On the finite-size effects in two segregated Bose-Einstein condensates restricted by a hard wall

The finite-size effects in two segregated Bose-Einstein condensates (BECs) restricted by a hard wall is studied by means of the Gross-Pitaevskii equations in the double-parabola approximation (DPA). Starting from the consistency between the boundary conditions (BCs) imposed on condensates in confined geometry and in the full space, we find all possible BCs together with the corresponding condensate profiles and interface tensions. We discover two finite-size effects: a) The ground state derived from the Neumann BC is stable whereas the ground states derived from the Robin and Dirichlet BCs are unstable. b) Thereby, there equally manifest two possible wetting phase transitions originating from two unstable states. However, the one associated with the Robin BC is more favourable because it corresponds to a smaller interface tension.Comment: 14 pages, 7 figure

Phase Diagram of the Holstein-Hubbard Two-Leg Ladder

Using a functional renormalization group method, we obtain the phase diagram of the two-leg ladder system within the Holstein-Hubbard model, which includes both electron-electron and electron-phonon interactions. Our renormalization group technique allows us to analyze the problem for both weak and strong electron-phonon coupling. We show that, in contrast results from conventional weak coupling studies, electron-phonon interactions can dominate electron-electron interactions because of retardation effects.Comment: 4 page

Some estimates of Wang-Yau quasilocal energy

Given a spacelike 2-surface $\Sigma$ in a spacetime $N$ and a constant future timelike unit vector $T_0$ in $\R^{3,1}$, we derive upper and lower estimates of Wang-Yau quasilocal energy $E(\Sigma, X, T_0)$ for a given isometric embedding $X$ of $\Sigma$ into a flat 3-slice in $\R^{3,1}$. The quantity $E(\Sigma, X, T_0)$ itself depends on the choice of $X$, however the infimum of $E(\Sigma, X, T_0)$ over $T_0$ does not. In particular, when $\Sigma$ lies in a time symmetric 3-slice in $N$ and has nonnegative Brown-York quasilocal mass \mby(\Sigma), our estimates show that $\inf\limits_{T_0}E(\Sigma, X, T_0)$ equals \mby (\Sigma). We also study the spatial limit of $\inf\limits_{T_0}E(S_r,X_r,T_0)$, where $S_r$ is a large coordinate sphere in a fixed end of an asymptotically flat initial data set $(M, g, p)$ and $X_r$ is an isometric embeddings of $S_r$ into $\mathbb{R}^3 \subset \mathbb{R}^{3,1}$. We show that if $(M, g, p)$ has future timelike ADM energy-momentum, then $\lim\limits_{r\to\infty}\inf\limits_{T_0}E(S_r,X_r,T_0)$ equals the ADM mass of $(M, g, p)$.Comment: 17 page

The missing GeV {\gamma}-ray binary: Searching for HESS J0632+057 with Fermi-LAT

The very high energy (VHE; >100 GeV) source HESS J0632+057 has been recently confirmed as a \gamma-ray binary, a subclass of the high mass X-ray binary (HMXB) population, through the detection of an orbital period of 321 days. We performed a deep search for the emission of HESS J0632+057 in the GeV energy range using data from the Fermi Large Area Telescope (LAT). The analysis was challenging due to the source being located in close proximity to the bright \gamma-ray pulsar PSR J0633+0632 and lying in a crowded region of the Galactic plane where there is prominent diffuse emission. We formulated a Bayesian block algorithm adapted to work with weighted photon counts, in order to define the off-pulse phases of PSR J0633+0632. A detailed spectral-spatial model of a 5 deg circular region centred on the known location of HESS J0632+057 was generated to accurately model the LAT data. No significant emission from the location of HESS J0632+057 was detected in the 0.1-100 GeV energy range integrating over ~3.5 years of data; with a 95% flux upper limit of F_{0.1-100 GeV} < 3 x 10-8 ph cm-2 s-1. A search for emission over different phases of the orbit also yielded no significant detection. A search for source emission on shorter timescales (days--months) did not yield any significant detections. We also report the results of a search for radio pulsations using the 100-m Green Bank Telescope (GBT). No periodic signals or individual dispersed bursts of a likely astronomical origin were detected. We estimated the flux density limit of < 90/40 \mu Jy at 2/9 GHz. The LAT flux upper limits combined with the detection of HESS J0632+057 in the 136-400 TeV energy band by the MAGIC collaboration imply that the VHE spectrum must turn over at energies <136 GeV placing constraints on any theoretical models invoked to explain the \gamma-ray emission.Comment: 11 pages, 4 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS) Main Journa

The Fundamental Plane of Gamma-ray Globular Clusters

We have investigated the properties of a group of $\gamma$-ray emitting globular clusters (GCs) which have recently been uncovered in our Galaxy. By correlating the observed $\gamma$-ray luminosities $L_{\gamma}$ with various cluster properties, we probe the origin of the high energy photons from these GCs. We report $L_{\gamma}$ is positively correlated with the encounter rate $\Gamma_{c}$ and the metalicity $\left[{\rm Fe/H}\right]$ which place an intimate link between the gamma-ray emission and the millisecond pulsar population. We also find a tendency that $L_{\gamma}$ increase with the energy densities of the soft photon at the cluster location. Furthermore, the two-dimensional regression analysis suggests that $L_{\gamma}$, soft photon densities, and $\Gamma_{c}$/$\left[{\rm Fe/H}\right]$ possibly span fundamental planes which potentially provide better predictions for the $\gamma$-ray properties of GCs.Comment: 17 pages, 4 figures, 3 tables, published in Ap

Spin Waves in Detwinned BaFe2_2As2_2

Understanding magnetic interactions in the parent compounds of high-temperature superconductors forms the basis for determining their role for the mechanism of superconductivity. For parent compounds of iron pnictide superconductors such as $A$Fe$_2$As$_2$ ($A=$ Ba, Ca, Sr), although spin excitations have been mapped out throughout the entire Brillouin zone (BZ), measurements were carried out on twinned samples and did not allow for a conclusive determination of the spin dynamics. Here we use inelastic neutron scattering to completely map out spin excitations of $\sim$100\% detwinned BaFe$_2$As$_2$. By comparing observed spectra with theoretical calculations, we conclude that the spin excitations can be well described by an itinerant model with important contributions from electronic correlations.Comment: 6 pages, 4 figures, with supplemental materia

A Hubble Space Telescope Imaging Survey of Nearby Active Glactic Nuclei

We obtained 500-second F606W WFPC2 images of 256 of the nearest (z<0.035) Seyfert 1,Seyfert 2, and starburst galaxies. Less than 10% show tidal features or multiple nuclei. The incidence of inner starburst rings is about 10% in both classes of Sy galaxies. In contrast, galaxies with H II region emission line spectra appear substantially more irregular because of their much higher specific rates of star formation. An unresolved central continuum source in our HST images is a virtually perfect indicator of a Sy1 spectrum. 52% of these Sy1 point sources are saturated in our images; we use their wings to estimate their magnitudes. The converse is not however true, as over a third of Sy's with direct spectroscopic evidence for broad Balmer wings show no nuclear point source. Like the Sy2's, they have central surface brightnesses consistent with those expected for the bulges of normal galaxies. The frequency of bars in Sy1's and 2's and non-Sys are the same. The Sy2 galaxies are significantly more likely to show nuclear dust absorption, especially in lanes and patches which are irregular or reach close to the nucleus. The difference cannot be explained by different average redshifts or selection techniques. This is confirmed by our morphology classifications, which show that Sy1 nuclei reside in earlier type galaxies than Sy2 nuclei. This intrinsic difference in host galaxy properties may undermine the strong unification hypothesis for Sy galaxies that they appear different due to the orientation of their central engine. The excess galactic dust we see in Sy2's may cause substantial absorption which obscures their hypothesized broad emission-line regions and central nonstellar continua. This galactic dust could produce much of the absorption in Sy2 nuclei which had instead been attributed to a thick dusty accretion torus.Comment: The text of the paper is 23 pages (ms.tex), there are 8 tables, and 9 figures. Figures 1, 2, and 3 are the image gallery (45 pages) and are NOT included here. They can be ftp'ed from ftp.astro.ucla.edu. Log in as anonymous and give your e-mail address as the password. The images are in the /pub/submit/vg/AGNgallery . Figures 4-9 are in eps format and are included here and can be printed using the lpr command in unix system

Remote sensing and GIS-based analysis of cave development in the Suoimuoi Catchment (Son La - NW Vietnam)

Integration of remotely sensed imagery with ground surveys is a promising method in cave development studies. In this research a methodology was set up in which a variety of remote sensing and GIS techniques support cave analysis in the tropical karst area of the Suoimuoi catchment, NW Vietnam. In order to extract the maximum information from different remotely sensed data, the hue invariant IHS transformation was applied to integrate Landsat multispectral channels with the high resolution Landsat 7 ETM panchromatic channel. The resulting fused image was used, after enhancement, to visually and digitally extract lineaments. Aerial photos evaluated the extracted lineaments. Based on lineament density indices a fracture zone favorable for cave development is defined. The distance between caves and faults was investigated as well as the correspondence between the cave occurrence and the fracture zone