370 research outputs found
Hubble-COS Observations of Galactic High-Velocity Clouds: Four AGN Sight Lines through Complex C
We report ultraviolet spectra of Galactic high-velocity clouds (HVCs) in
Complex C, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space
Telescope (HST), together with new 21-cm spectra from the Green Bank Telescope.
The wide spectral coverage and higher S/N, compared to previous HST spectra,
provide better velocity definition of the HVC absorption, additional ionization
species, and improved abundances in this halo gas. Complex C has a metallicity
of 0.1-0.3 solar and a wide range of ions, suggesting dynamical and thermal
interactions with hot gas in the Galactic halo. Spectra in the COS
medium-resolution G130M (1133-1468 A) and G160M (1383-1796 A) gratings detect
ultraviolet absorption lines from 8 elements in low ionization stages (O I, N
I, C II, S II, Si II, Al II, Fe II, P II) and 3 elements in intermediate and
high-ionization states (Si III, Si IV, C IV, N V). Our four AGN sight lines
toward Mrk 817, Mrk 290, Mrk 876, and PG1259+593 have high-velocity H I and O
VI column densities, log N_HI = 19.39-20.05 and log N_OVI = 13.58-14.10, with
substantial amounts of kinematically associated photoionized gas. The high-ion
abundance ratios are consistent with cooling interfaces between photoionized
gas and collisionally ionized gas: N(C IV)/N(O VI) = 0.3-0.5, N(Si IV)/N(O VI)
= 0.05-0.11, N(N V)/N(O VI) = 0.07-0.13, and N(Si IV)/N(Si III) = 0.2.Comment: 43 pages, 11 figures (appearing in ApJ, Sept 1, 2011
Does training with amplitude modulated tones affect tone-vocoded speech perception?
Temporal-envelope cues are essential for successful speech perception. We asked here whether training on stimuli containing temporal-envelope cues without speech content can improve the perception of spectrally-degraded (vocoded) speech in which the temporal-envelope (but not the temporal fine structure) is mainly preserved. Two groups of listeners were trained on different amplitude-modulation (AM) based tasks, either AM detection or AM-rate discrimination (21 blocks of 60 trials during two days, 1260 trials; frequency range: 4Hz, 8Hz, and 16Hz), while an additional control group did not undertake any training. Consonant identification in vocoded vowel-consonant-vowel stimuli was tested before and after training on the AM tasks (or at an equivalent time interval for the control group). Following training, only the trained groups showed a significant improvement in the perception of vocoded speech, but the improvement did not significantly differ from that observed for controls. Thus, we do not find convincing evidence that this amount of training with temporal-envelope cues without speech content provide significant benefit for vocoded speech intelligibility. Alternative training regimens using vocoded speech along the linguistic hierarchy should be explored
Numerical studies of the phase diagram of layered type II superconductors in a magnetic field
We report on simulations of layered superconductors using the
Lawrence-Doniach model in the framework of the lowest Landau level
approximation. We find a first order phase transition with a dependence
which agrees very well with the experimental ``melting'' line in YBaCuO. The
transition is not associated with vortex lattice melting, but separates two
vortex liquid states characterised by different degrees of short-range
crystalline order and different length scales of correlations between vortices
in different layers. The transition line ends at a critical end-point at low
fields. We find the magnetization discontinuity and the location of the lower
critical magnetic field to be in good agreement with experiments in YBaCuO.
Length scales of order parameter correlations parallel and perpendicular to the
magnetic field increase exponentially as 1/T at low temperatures. The dominant
relaxation time scales grow roughly exponentially with these correlation
lengths. We find that the first order phase transition persists in the presence
of weak random point disorder but can be suppressed entirely by strong
disorder. No vortex glass or Bragg glass state is found in the presence of
disorder. The consistency of our numerical results with various experimental
features in YBaCuO, including the dependence on anisotropy, and the temperature
dependence of the structure factor at the Bragg peaks in neutron scattering
experiments is demonstrated.Comment: 25 pages (revtex), 19 figures included, submitted to PR
On the galaxy stellar mass function, the mass-metallicity relation, and the implied baryonic mass function
A comparison between published field galaxy stellar mass functions (GSMFs)
shows that the cosmic stellar mass density is in the range 4--8 per cent of the
baryon density (assuming Omega_b = 0.045). There remain significant sources of
uncertainty for the dust correction and underlying stellar mass-to-light ratio
even assuming a reasonable universal stellar initial mass function. We
determine the z < 0.05 GSMF using the New York University - Value-Added Galaxy
Catalog sample of 49968 galaxies derived from the Sloan Digital Sky Survey and
various estimates of stellar mass. The GSMF shows clear evidence for a low-mass
upturn and is fitted with a double Schechter function that has alpha_2 =~ -1.6.
At masses below ~ 10^8.5 Msun, the GSMF may be significantly incomplete because
of missing low surface-brightness galaxies. One interpretation of the stellar
mass-metallicity relation is that it is primarily caused by a lower fraction of
available baryons converted to stars in low-mass galaxies. Using this
principal, we determine a simple relationship between baryonic mass and stellar
mass and present an `implied baryonic mass function'. This function has a
faint-end slope, alpha_2 =~ -1.9. Thus, we find evidence that the slope of the
low-mass end of the galaxy mass function could plausibly be as steep as the
halo mass function. We illustrate the relationship between halo baryonic mass
function --> galaxy baryonic mass function --> GSMF. This demonstrates the
requirement for peak galaxy formation efficiency at baryonic masses ~ 10^11
Msun corresponding to a minimum in feedback effects. The baryonic-infall
efficiency may have levelled off at lower masses.Comment: Changes to section 4.3 and figs 12, 13; 15 pages (10 pages excluding
Appendix and refs), accepted by MNRAS; binned GSMF data file is available at
http://www.astro.ljmu.ac.uk/~ikb/research/gsmf-paper.htm
The Role of Environment in the Mass-Metallicity Relation
Using a sample of 57,377 star-forming galaxies drawn from the Sloan Digital
Sky Survey, we study the relationship between gas-phase oxygen abundance and
environment in the local Universe. We find that there is a strong relationship
between metallicity and environment such that more metal-rich galaxies favor
regions of higher overdensity. Furthermore, this metallicity-density relation
is comparable in strength to the color-density relation along the blue cloud.
After removing the mean dependence of environment on color and luminosity, we
find a significant residual trend between metallicity and environment that is
largely driven by galaxies in high-density regions, such as groups and
clusters. We discuss the potential source of this relationship between
metallicity and local galaxy density in the context of feedback models, with
special attention paid to quantifying the impact of environment on the scatter
in the mass-metallicity relation. We find that environment is a non-negligible
source of scatter in this fundamental relation, with > 15% of the measured
scatter correlated with environment.Comment: Submitted to MNRA
The Impact of Feedback on Disk Galaxy Scaling Relations
We use a disk galaxy evolution model to investigate the impact of mass
outflows (a.k.a. feedback) on disk galaxy scaling relations. Our model follows
the accretion, cooling, star formation and ejection of baryonic mass inside
growing dark matter haloes, with cosmologically motivated specific angular
momentum distributions. Models without feedback produce disks that are too
small and rotate too fast. Feedback reduces the baryonic masses of galaxies,
resulting in larger disks with lower rotation velocities. Models with feedback
can reproduce the zero points of the scaling relations between rotation
velocity, stellar mass and disk size, but only in the absence of adiabatic
contraction. Our feedback mechanism is maximally efficient in expelling mass,
but our successful models require 25% of the SN energy, or 100% of the SN
momentum, to drive the outflows. It remains to be seen whether such high
efficiencies are realistic or not. Our energy and momentum driven wind models
result in different slopes of various scaling relations, such as size - stellar
mass, stellar mass - halo mass, and metallicity - stellar mass. Observations
favor the energy driven wind at stellar masses below Mstar = 10^{10.5} Msun,
but the momentum driven wind model at high masses. The ratio between the
specific angular momentum of the baryons to that of the halo, (j_gal/m_gal), is
not unity in our models. Yet this is the standard assumption in models of disk
galaxy formation. Feedback preferentially ejects low angular momentum material
because star formation is more efficient at smaller galactic radii. This
results in (j_gal/m_gal) increasing with decreasing halo mass. This effect
helps to resolve the discrepancy between the high spin parameters observed for
dwarf galaxies with the low spin parameters predicted from LCDM. [Abridged]Comment: 27 pages, 16 figures, accepted to MNRAS, two new figure
Satellite content and quenching of star formation in galaxy groups at z ~ 1.8
We study the properties of satellites in the environment of massive star-forming galaxies at z ~ 1.8 in the COSMOS field, using a sample of 215 galaxies on the main sequence of star formation with an average mass of ~1011Mâ. At z> 1.5, these galaxies typically trace halos of mass âł1013Mâ. We use optical-near-infrared photometry to estimate stellar masses and star formation rates (SFR) of centrals and satellites down to ~ 6 Ă 109Mâ. We stack data around 215 central galaxies to statistically detect their satellite halos, finding an average of ~3 galaxies in excess of the background density. We fit the radial profiles of satellites with simple ÎČ-models, and compare their integrated properties to model predictions. We find that the total stellar mass of satellites amounts to ~68% of the central galaxy, while spectral energy distribution modeling and far-infrared photometry consistently show their total SFR to be 25-35% of the central's rate. We also see significant variation in the specific SFR of satellites within the halo with, in particular, a sharp decrease at <100 kpc. After considering different potential explanations, we conclude that this is likely an environmental signature of the hot inner halo. This effect can be explained in the first order by a simple free-fall scenario, suggesting that these low-mass environments can shut down star formation in satellites on relatively short timescales of ~0.3 Gyr
Stress-Induced Reinstatement of Drug Seeking: 20 Years of Progress
In human addicts, drug relapse and craving are often provoked by stress. Since 1995, this clinical scenario has been studied using a rat model of stress-induced reinstatement of drug seeking. Here, we first discuss the generality of stress-induced reinstatement to different drugs of abuse, different stressors, and different behavioral procedures. We also discuss neuropharmacological mechanisms, and brain areas and circuits controlling stress-induced reinstatement of drug seeking. We conclude by discussing results from translational human laboratory studies and clinical trials that were inspired by results from rat studies on stress-induced reinstatement. Our main conclusions are (1) The phenomenon of stress-induced reinstatement, first shown with an intermittent footshock stressor in rats trained to self-administer heroin, generalizes to other abused drugs, including cocaine, methamphetamine, nicotine, and alcohol, and is also observed in the conditioned place preference model in rats and mice. This phenomenon, however, is stressor specific and not all stressors induce reinstatement of drug seeking. (2) Neuropharmacological studies indicate the involvement of corticotropin-releasing factor (CRF), noradrenaline, dopamine, glutamate, kappa/dynorphin, and several other peptide and neurotransmitter systems in stress-induced reinstatement. Neuropharmacology and circuitry studies indicate the involvement of CRF and noradrenaline transmission in bed nucleus of stria terminalis and central amygdala, and dopamine, CRF, kappa/dynorphin, and glutamate transmission in other components of the mesocorticolimbic dopamine system (ventral tegmental area, medial prefrontal cortex, orbitofrontal cortex, and nucleus accumbens). (3) Translational human laboratory studies and a recent clinical trial study show the efficacy of alpha-2 adrenoceptor agonists in decreasing stress-induced drug craving and stress-induced initial heroin lapse
Oynophagia in patients after dental extraction: surface electromyography study
OBJECTIVES: Surface electromyographic (sEMG) studies were performed on 40 adult patients following extraction of lower third and second molars to research the approach and limitations of sEMG evaluation of their odynophagia complaints. METHODS: Parameters evaluated during swallowing and drinking include the timing, number of swallows per 100 cc of water, and range (amplitude) of EMG activity of m. masseter, infrahyoid and submental-submandibular group. The above mentioned variables (mean + standard deviation) were measured for the group of dental patients (n = 40) and control group of healthy adults (n = 40). RESULTS: The duration of swallows and drinking in all tests showed increase in dental patients' group, in which this tendency is statistically significant. There was no statistically significant difference between male and female adults' duration and amplitude of muscle activity during continuous drinking in both groups (p = 0.05). The mean of electric activity (in ÎŒV) of m. masseter was significantly lower in the dental patients' group in comparison with control group. The electric activity of submental-submandimular and infrahyoid muscle groups was the same in both groups. CONCLUSION: Surface EMG of swallowing is a simple and reliable noninvasive method for evaluation of odynophagia/dysphagia complaints following dental extraction with low level of discomfort of the examination. The surface EMG studies prove that dysphagia following dental extraction and molar surgery has oral origin, does not affect pharingeal segment and submental-submandibular muscle group. This type of dysphagia has clear EMG signs: increased duration of single swallow, longer drinking time, low range of electric activity of m. masseter, normal range of activity of submental-submandibular muscle group, and the "dry swalow" aftereffect. The data can be used for evaluation of complaints and symptoms, as well as for comparison purposes in pre- and postoperative stages and in EMG monitoring during treatment of post-surgical oral cavity discomfort and dysphagia
Structure of visible and dark matter components in spiral galaxies at redshifts z = 0.5-0.9
We have constructed self-consistent light and mass distribution models for
four disk galaxies at redshifts z = 0.48, 0.58, 0.81 and 0.88, using the HST
archive WFPC2 observations and rotation curves measured by Vogt et al. (1996)
and Rigopoulou et al. (2002). The models consist of three components: a bulge,
a disk and a dark matter halo. Similarly to the sample studied in Paper I (Tamm
& Tenjes, 2003), light distribution of the galaxies in the outer parts is
clearly steeper than a simple exponential disk. After applying k-corrections,
calculated mass-to-light ratios for galactic disks within the maximum disk
assumption are M/L_B = 0.9, 7.4, 4.3 and 1.4, respectively. Together with the
galaxies from Paper I, the mean = 2.5 at ~0.9, indicating no
significant evolution of M/L_B with redshift. Central densities of dark matter
halos for an isothermal model are 0.008, 0.035, 0.013, and 0.022 in units
M_sun/pc^3, respectively. Together with the galaxies from Paper I, the DM
central density of the four galaxies at mean readshift ~0.9 is rho(0) =
(0.012-0.028) M_sun/pc^3, also showing no significant evolution with redshift.Comment: 11 pages, 10 figures, Astron. Astrophys. accepte
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