792 research outputs found
Mg II Absorption Systems in SDSS QSO Spectra
We present the results of a MgII absorption-line survey using QSO spectra
from the SDSS EDR. Over 1,300 doublets with rest equivalent widths greater than
0.3\AA and redshifts were identified and measured. We
find that the rest equivalent width ()
distribution is described very well by an exponential function , with
and \AA. Previously reported power law
fits drastically over-predict the number of strong lines. Extrapolating our
exponential fit under-predicts the number of \AA systems,
indicating a transition in near \AA. A combination of
two exponentials reproduces the observed distribution well, suggesting that
MgII absorbers are the superposition of at least two physically distinct
populations of absorbing clouds. We also derive a new redshift parameterization
for the number density of \AA lines:
and \AA. We find that the distribution steepens with decreasing redshift,
with decreasing from \AA at to \AA at
. The incidence of moderately strong MgII lines does not
show evidence for evolution with redshift. However, lines stronger than
\AA show a decrease relative to the no-evolution prediction with
decreasing redshift for . The evolution is stronger for
increasingly stronger lines. Since in saturated absorption lines is an
indicator of the velocity spread of the absorbing clouds, we interpret this as
an evolution in the kinematic properties of galaxies from moderate to low z.Comment: 50 pages, 26 figures, accepted for publication in Ap
Implementation of an Online Feedback-Path-Modelling Active Noise Control System
Active Noise Control (ANC) systems have proved to be a very efficient way to reduce low-frequency acoustic noise. On this domain, passive techniques like enclosures, barriers and silencers tend to be relatively large, costly and ineffective. Although many studies and articles have been published in order to improve performance and stability, the implementation of a real-time, stable and robust system still faces several theoretical and practical challenges
Hierarchical Model for the Evolution of Cloud Complexes
The structure of cloud complexes appears to be well described by a "tree
structure" representation when the image is partitioned into "clouds". In this
representation, the parent-child relationships are assigned according to
containment. Based on this picture, a hierarchical model for the evolution of
Cloud Complexes, including star formation, is constructed, that follows the
mass evolution of each sub-structure by computing its mass exchange
(evaporation or condensation) with its parent and children, which depends on
the radiation density at the interphase. For the set of parameters used as a
reference model, the system produces IMFs with a maximum at too high mass (~2
M_sun) and the characteristic times for evolution seem too long. We show that
these properties can be improved by adjusting model parameters. However, the
emphasis here is to illustrate some general properties of this nonlinear model
for the star formation process. Notwithstanding the simplifications involved,
the model reveals an essential feature that will likely remain if additional
physical processes are included. That is: the detailed behavior of the system
is very sensitive to variations on the initial and external conditions,
suggesting that a "universal" IMF is very unlikely. When an ensemble of IMFs
corresponding to a variety of initial or external conditions is examined, the
slope of the IMF at high masses shows variations comparable to the range
derived from observational data. (Abridged)Comment: Latex, 29 pages, 13 figures, accepted for publication in Ap
Damped Lyman Alpha Systems at z<1.65: The Expanded SDSS HST Sample
We present results of our HST Cycle 11 Survey for low-redshift (z<1.65) DLAs
in the UV spectra of quasars selected from the SDSS Early Data Release. These
quasars have strong intervening MgII-FeII systems which are known signatures of
high column density neutral gas. In total, UV observations of Ly-alpha
absorption in 197 MgII systems with z<1.65 and rest equivalent width (REW)
W2796 \ge 0.3A have now been obtained. The main results are: (1) 36(+/- 6)% of
systems with W2796 \ge 0.5 A and FeII W2600 \ge 0.5 A are DLAs. This increases
to 42(+/- 7)% for systems with W2796/W2600 0.1 A. (2) The
mean N(HI) of MgII systems with 0.3 A \le W2796 < 0.6 A is a factor of ~36
lower than that of systems with W2796 \ge 0.6 A. (3) The DLA incidence per unit
redshift is consistent with no evolution for z <~ 2 (Omega_L=0.7, Omega_M =
0.3), but exhibits significant evolution for z >~ 2. (4) Omega_{DLA} is
constant for 0.5<z<5.0 to within the uncertainties. This is larger than
Omega_{gas}(z=0) by a factor of ~2. (5) The slope of the N(HI) distribution
does not change significantly with redshift. However, the low redshift
distribution is marginally flatter due to the higher fraction of high N(HI)
systems in our sample. (6) Finally, using the precision of MgII survey
statistics, we find that there may be evidence of a decreasing Omega_{DLA} from
z=0.5 to z=0. We reiterate the conclusion of Hopkins, Rao, & Turnshek that very
high columns of neutral gas might be missed by DLA surveys because of their
very small cross sections, and therefore, that Omega_{DLA} might not include
the bulk of the neutral gas mass in the Universe. (Abridged)Comment: Accepted for publication in ApJ. 22 pages, 22 figure
Optical properties and spatial distribution of MgII absorbers from SDSS image stacking
We present a statistical analysis of the photometric properties and spatial
distribution of more than 2,800 MgII absorbers with 0.37<z<1 and rest
equivalent width W_0(\lambda2796)>0.8\AA detected in SDSS quasar spectra. Using
an improved image stacking technique, we measure the cross-correlation between
MgII gas and light (in the g, r, i and z-bands) from 10 to 200 kpc and infer
the light-weighted impact parameter distribution of MgII absorbers. Such a
quantity is well described by a power-law with an index that strongly depends
on W_0, ranging from ~-1 for W_0~ 1.5\AA. At redshift
0.37<z<0.55, we find the average luminosity enclosed within 100 kpc around MgII
absorbers to be M_g=-20.65+-0.11 mag, which is ~0.5 L_g*. The global
luminosity-weighted colors are typical of present-day intermediate type
galaxies. However, while the light of weaker absorbers originates mostly from
red passive galaxies, stronger systems display the colors of blue star-forming
galaxies. Based on these observations, we argue that the origin of strong MgII
absorber systems might be better explained by models of metal-enriched gas
outflows from star-forming/bursting galaxies. Our analysis does not show any
redshift dependence for both impact parameter and rest-frame colors up to z=1.
However, we do observe a brightening of the absorbers related light at high
redshift (~50% from z~0.4 to 1). We argue that MgII absorbers are a phenomenon
typical of a given evolutionary phase that more massive galaxies experience
earlier than less massive ones, in a downsizing fashion. (abridged)Comment: ApJ in press, 28 pages, 16 figures, using emulateapj. Only typo
corrections wrt the original submission (v1
Lupus autoantibodies act as positive allosteric modulators at GluN2A-containing NMDA receptors and impair spatial memory
Systematic analysis of different experimental approaches to measure electronic stopping of very slow hydrogen ions
The electronic stopping cross section (SCS) of Ni for slow H+, H2 +, D+ and D2 + ions has been investigated for different types of targets in two complementary experimental geometries, i.e., in transmission and backscattering. To warrant sample purity, both a high purity nickel sheet and nanometer Ni layers were prepared in-situ under ultra-high-vacuum conditions. In an alternative approach, ultra-thin samples were prepared ex-situ as self-supporting foils and as nanometer films on a polished substrate (silicon). Identical SCS results are obtained in backscattering using the in-situ prepared film and the high purity sheet. The ex-situ prepared targets contained considerable concentrations of impurities of low atomic numbers, whose contribution to the SCS can be rectified by applying Bragg's rule using TRIM stopping for the impurities. In this way for the ex-situ targets the accuracy of the resulting SCS data is improved considerably. Concordant stopping cross section data are obtained in both geometries. The achieved accuracy does, however, not permit to spot a possible influence of different impact parameter regimes explored in transmission and in backscattering geometries.Fil: Roth, D.. Johannes Kepler Universitat Linz; AustriaFil: Celedon, C. E.. Universidad Técnica Federico Santa María; Chile. Johannes Kepler Universitat Linz; Austria. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; ArgentinaFil: Goebl, D.. Johannes Kepler Universitat Linz; AustriaFil: Sánchez, Esteban Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; ArgentinaFil: Bruckner, B.. Johannes Kepler Universitat Linz; AustriaFil: Steinberger, R.. Johannes Kepler Universitat Linz; AustriaFil: Guimpel, Julio Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; ArgentinaFil: Arista, Nestor Ricardo. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; ArgentinaFil: Bauer, P.. Johannes Kepler Universitat Linz; Austri
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