Dissipative Quantum Ising model in a cold atomic spin-boson mixture

Using cold bosonic atoms with two (hyperfine) ground states, we introduce a spin-boson mixture which allows to implement the quantum Ising model in a tunable dissipative environment. The first specie lies in a deep optical lattice with tightly confining wells and forms a spin array; spin-up/down corresponds to occupation by one/no atom at each site. The second specie forms a superfluid reservoir. Different species are coupled coherently via laser transitions and collisions. Whereas the laser coupling mimics a transverse field for the spins, the coupling to the reservoir sound modes induces a ferromagnetic (Ising) coupling as well as dissipation. This gives rise to an order-disorder quantum phase transition where the effect of dissipation can be studied in a controllable manner.Comment: 4 pages, 2 figures, 1 table; Title modified and cosmetic change

Tendency of spherically imploding plasma liners formed by merging plasma jets to evolve toward spherical symmetry

Three dimensional hydrodynamic simulations have been performed using smoothed particle hydrodynamics (SPH) in order to study the effects of discrete jets on the processes of plasma liner formation, implosion on vacuum, and expansion. The pressure history of the inner portion of the liner was qualitatively and quantitatively similar from peak compression through the complete stagnation of the liner among simulation results from two one dimensional radiationhydrodynamic codes, 3D SPH with a uniform liner, and 3D SPH with 30 discrete plasma jets. Two dimensional slices of the pressure show that the discrete jet SPH case evolves towards a profile that is almost indistinguishable from the SPH case with a uniform liner, showing that non-uniformities due to discrete jets are smeared out by late stages of the implosion. Liner formation and implosion on vacuum was also shown to be robust to Rayleigh-Taylor instability growth. Interparticle mixing for a liner imploding on vacuum was investigated. The mixing rate was very small until after peak compression for the 30 jet simulation.Comment: 28 pages, 16 figures, submitted to Physics of Plasmas (2012

The Line Emission Region in III Zw 2: Kinematics and Variability

We have studied the Ly-al, Hbeta, Halpha and Mg II2798 line profiles of the Seyfert 1 galaxy III Zw 2. The shapes of these broad emission lines show evidence of a multicomponent origin and also features which may be identified as the peaks due to a rotating disk. We have proposed a two-component Broad Line Region (BLR) model consisting of an inner Keplerian relativistic disk and an outer structure surrounding the disk. The results of the fitting of the four Broad Emission Lines (BELs) here considered, are highly consistent in both the inner and outer component parameters. Adopting a mass of approx. 2 E8 sollar masses for the central object we found that the outer radius of the disk is approximately equal for the four considered lines (approx 0.01 pc). However, the inner radius of the disk is not the same: 0.0018 pc for Ly-alpha, 0.0027 pc for Mg II, and 0.0038 pc for the Balmer lines. This as well as the relatively broad component present in the blue wings of the narrow [OIII] lines indicate stratification in the emission-line region. Using long-term Hbeta observations (1972-1990, 1998) we found a flux variation of the BEL with respect to the [OIII] lines.Comment: ApJ, accepted, 22 pages, 10 figure

On acoustic scattering by a shell-covered seafloor

Author Posting. © Acoustical Society of America, 2000. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 108 (2000): 551-555, doi:10.1121/1.429585.Acoustic scattering by the seafloor is sometimes influenced, if not dominated, by the presence of discrete volumetric objects such as shells. A series of measurements of target strength of a type of benthic shelled animal and associated scattering modeling have recently been completed (Stanton et al., "Acoustic scattering by benthic and planktonic shelled animals," J. Acoust. Soc. Am., this issue). The results of that study are used herein to estimate the scattering by the seafloor with a covering of shells at high acoustic frequencies. A simple formulation is derived that expresses the area scattering strength of the seafloor in terms of the average reduced target strength or material properties of the discrete scatterers and their packing factor (where the reduced target strength is the target strength normalized by the geometric cross section of the scatterers and the averaging is done over orientation and/or a narrow range of size or frequency). The formula shows that, to first order, the backscattering at high acoustic frequencies by a layer of shells (or other discrete bodies such as rocks) depends principally upon material properties of the objects and packing factor and is independent of size and acoustic frequency. Estimates of area scattering strength using this formula and measured values of the target strength of shelled bodies from Stanton et al. (this issue) are close to or consistent with observed area scattering strengths due to shell-covered seafloors published in other papers.This research was supported by the U.S. Office of Naval Research Grant No. N00014-95-1-0287

Genotoxic potential of Cotinus coggygria Scop. (Anacardiaceae) stem extract in vivo

The intention was to evaluate the possible in vivo genotoxic potential in different cell-types, of a methanol extract obtained from the plant stem of Cotinus coggygria Scop., using the sex-linked recessive lethal (or SLRL) test and alkaline comet assay. The SLRL test, revealed the genotoxic effect of this extract in postmeiotic and premeiotic germ-cell lines. The comet assay was carried out on rat liver and bone marrow at 24 and 72 h after intraperitoneal administration. For genotoxic evaluation, three concentrations of the extract were tested, viz., 500, 1000 and 2000 mg/kg body weight (bw), based on the solubility limit of the extract in saline. Comet tail moment and total scores in the group treated with 500 mg/kg bw, 24 and 72 h after treatment, were not significantly different from the control group, whereas in the groups of animals, under the same conditions, but with 1000 and 2000 mg/kg bw of the extract, scores were statistically so. A slight decrease in the comet score and tail moment observed in all the doses in the 72 h treatment, gave to understand that DNA damage induced by Cotinus coggygria extract decreased with time. The results of both tests revealed the genotoxic effect of Cotinus coggygria under our experimental conditions

Optically Selected BL Lacertae Candidates from the Sloan Digital Sky Survey Data Release Seven

We present a sample of 723 optically selected BL Lac candidates from the SDSS DR7 spectroscopic database encompassing 8250 deg^2 of sky; our sample constitutes one of the largest uniform BL Lac samples yet derived. Each BL Lac candidate has a high-quality SDSS spectrum from which we determine spectroscopic redshifts for ~60% of the objects. Redshift lower limits are estimated for the remaining objects utilizing the lack of host galaxy flux contamination in their optical spectra; we find that objects lacking spectroscopic redshifts are likely at systematically higher redshifts. Approximately 80% of our BL Lac candidates match to a radio source in FIRST/NVSS, and ~40% match to a ROSAT X-ray source. The homogeneous multiwavelength coverage allows subdivision of the sample into 637 radio-loud BL Lac candidates and 86 weak-featured radio-quiet objects. The radio-loud objects broadly support the standard paradigm unifying BL Lac objects with beamed radio galaxies. We propose that the majority of the radio-quiet objects may be lower-redshift (z<2.2) analogs to high-redshift weak line quasars (i.e., AGN with unusually anemic broad emission line regions). These would constitute the largest sample of such objects, being of similar size and complementary in redshift to the samples of high-redshift weak line quasars previously discovered by the SDSS. However, some fraction of the weak-featured radio-quiet objects may instead populate a rare and extreme radio-weak tail of the much larger radio-loud BL Lac population. Serendipitous discoveries of unusual white dwarfs, high-redshift weak line quasars, and broad absorption line quasars with extreme continuum dropoffs blueward of rest-frame 2800 Angstroms are also briefly described.Comment: 24 pages, 14 figures, 8 tables. Accepted for publication in A

Molecular Gas in Infrared Ultraluminous QSO Hosts

We report CO detections in 17 out of 19 infrared ultraluminous QSO (IR QSO) hosts observed with the IRAM 30m telescope. The cold molecular gas reservoir in these objects is in a range of 0.2--2.1$\times 10^{10}M_\odot$ (adopting a CO-to-${\rm H_2}$ conversion factor $\alpha_{\rm CO}=0.8 M_\odot {\rm (K km s^{-1} pc^2)^{-1}}$). We find that the molecular gas properties of IR QSOs, such as the molecular gas mass, star formation efficiency ($L_{\rm FIR}/L^\prime_{\rm CO}$) and the CO (1-0) line widths, are indistinguishable from those of local ultraluminous infrared galaxies (ULIRGs). A comparison of low- and high-redshift CO detected QSOs reveals a tight correlation between L$_{\rm FIR}$ and $L^\prime_{\rm CO(1-0)}$ for all QSOs. This suggests that, similar to ULIRGs, the far-infrared emissions of all QSOs are mainly from dust heated by star formation rather than by active galactic nuclei (AGNs), confirming similar findings from mid-infrared spectroscopic observations by {\it Spitzer}. A correlation between the AGN-associated bolometric luminosities and the CO line luminosities suggests that star formation and AGNs draw from the same reservoir of gas and there is a link between star formation on $\sim$ kpc scale and the central black hole accretion process on much smaller scales.Comment: 30 pages, 9 figures, accepted for publication in The Astrophysical Journa

Violent quenching : Molecular Gas Blown to 1000 km s -1 during a Major Merger

Accepted for publication in ApJ LettersWe present Atacama Large Millimeter/submillimeter Array observations of a massive () compact ( pc) merger remnant at z = 0.66 that is driving a 1000 km s -1 outflow of cool gas, with no observational trace of an active galactic nucleus (AGN). We resolve molecular gas on scales of approximately 1-2 kpc, and our main finding is the discovery of a wing of blueshifted CO J(2 → 1) emission out to-1000 km s -1 relative to the stars. We argue that this is the molecular component of a multiphase outflow, expelled from the central starburst within the past 5 Myr through stellar feedback, although we cannot rule out previous AGN activity as a launching mechanism. If the latter is true, then this is an example of a relic multiphase AGN outflow. We estimate a molecular mass outflow rate of approximately 300 M o yr -1, or about one third of the 10 Myr-Averaged star formation rate. This system epitomizes the multiphase "blowout" episode following a dissipational major merger-a process that has violently quenched central star formation and supermassive black hole growth.Peer reviewedFinal Accepted Versio