3,695 research outputs found
Bayesian estimation for selective trace gas detection
We present a Bayesian estimation analysis for a particular trace gas
detection technique with species separation provided by differential diffusion.
The proposed method collects a sample containing multiple gas species into a
common volume, and then allows it to diffuse across a linear array of optical
absorption detectors, using, for example, high-finesse Fabry-Perot cavities.
The estimation procedure assumes that all gas parameters (e.g. diffusion
constants, optical cross sections) are known except for the number population
of each species, which are determined from the time-of-flight absorption
profiles in each detector
Oxygen Gas Abundances at 0.4<z<1.5: Implications for the Chemical Evolution History of Galaxies
We report VLT-ISAAC and Keck-NIRSPEC near-infrared spectroscopy for a sample
of 30 0.47<z<0.92 CFRS galaxies and five [OII]-selected, M_B,AB<-21.5, z~1.4
galaxies. We have measured Halpha and [NII] line fluxes for the CFRS galaxies
which have [OII], Hbeta and [OIII] line fluxes available from optical
spectroscopy. For the z~1.4 objects we measured Hbeta and [OIII] emission line
fluxes from J-band spectra, and Halpha line fluxes plus upper limits for [NII]
fluxes from H-band spectra. We derive the extinction and oxygen abundances for
the sample using a method based on a set of ionisation parameter and oxygen
abundance diagnostics, simultaneously fitting the [OII], Hbeta, [OIII], Halpha
and [NII] line fluxes. Our most salient conclusions are: a) the source of gas
ionisation in the 30 CFRS and in all z~1.4 galaxies is not due to AGN activity;
b) about one third of the 0.47<z<0.92 CFRS galaxies in our sample have
substantially lower metallicities than local galaxies with similar luminosities
and star formation rates; c) comparison with a chemical evolution model
indicates that these low metallicity galaxies are unlikely to be the
progenitors of metal-poor dwarf galaxies at z~0, but more likely the
progenitors of massive spirals; d) the z~1.4 galaxies are characterized by the
high [OIII]/[OII] line ratios, low extinction and low metallicity that are
typical of lower luminosity CADIS galaxies at 0.4<z<0.7, and of more luminous
Lyman Break Galaxies at z~3.1, but not seen in CFRS galaxies at 0.4<z<1.0; e)
the properties of the z~1.4 galaxies suggest that the period of rapid chemical
evolution takes place progressively in lower mass systems as the universe ages,
and thus provides further support for a downsizing picture of galaxy formation,
at least from z~1.4 to today.Comment: Proceedings contribution for "The Fabulous Destiny of Galaxies;
Bridging Past and Present", Marseille, 200
Lithium in the prevention of suicide in mood disorders: updated systematic review and meta-analysis
Objective To assess whether lithium has a specific preventive effect for suicide and self harm in people with unipolar and bipolar mood disorders. Design Systematic review and meta-analysis. Data sources Medline, Embase, CINAHL, PsycINFO, CENTRAL, web based clinical trial registries, major textbooks, authors of important papers and other experts in the discipline, and websites of pharmaceutical companies that manufacture lithium or the comparator drugs (up to January 2013). Inclusion criteria Randomised controlled trials comparing lithium with placebo or active drugs in long term treatment for mood disorders. Review methods Two reviewers assessed studies for inclusion and risk of bias and extracted data. The main outcomes were the number of people who completed suicide, engaged in deliberate self harm, and died from any cause. Results 48 randomised controlled trials (6674 participants, 15 comparisons) were included. Lithium was more effective than placebo in reducing the number of suicides (odds ratio 0.13, 95% confidence interval 0.03 to 0.66) and deaths from any cause (0.38, 0.15 to 0.95). No clear benefits were observed for lithium compared with placebo in preventing deliberate self harm (0.60, 0.27 to 1.32). In unipolar depression, lithium was associated with a reduced risk of suicide (0.36, 0.13 to 0.98) and also the number of total deaths (0.13, 0.02 to 0.76) compared with placebo. When lithium was compared with each active individual treatment a statistically significant difference was found only with carbamazepine for deliberate self harm. Lithium tended to be generally better than the other active comparators, with small statistical variation between the results. Conclusions Lithium is an effective treatment for reducing the risk of suicide in people with mood disorders. Lithium may exert its antisuicidal effects by reducing relapse of mood disorder, but additional mechanisms should also be considered because there is some evidence that lithium decreases aggression and possibly impulsivity, which might be another mechanism mediating the antisuicidal effect
Stellar Populations of Luminous Evolved Galaxies at z~1.5
Observational evidence has been mounting over the past decade that at least
some luminous (~2 L*) galaxies have formed nearly all of their stars within a
short period of time only 1-2x10^9 years after the Big Bang. These are examples
of the first major episodes of star formation in the Universe and provide
insights into the formation of the earliest massive galaxies. We have examined
in detail the stellar populations of six z~1.5 galaxies that appear to be
passively evolving, using both ground and space-based photometry covering
rest-frame UV to visible wavelengths. In addition, we have obtained
medium-resolution spectroscopy for five of the six galaxies, covering the
rest-frame UV portion of the spectrum. Spectral synthesis modeling for four of
these galaxies favors a single burst of star formation more than 1 Gyr before
the observed epoch. The other two exhibit slightly younger ages with a higher
dust content and evidence for a small contribution from either recent star
formation or active nuclei. The implied formation redshifts for the oldest of
these sources are consistent with previous studies of passive galaxies at high
redshift, and improved stellar modeling has shown these results to be quite
robust. It now seems clear that any valid galaxy formation scenario must be
able to account for these massive (2x10^11 M_sun) galaxies at very early times
in the Universe.Comment: 10 pages, 3 figures (2 in color), accepted for publication in Ap
Tensor polarizability and dispersive quantum measurement of multilevel atoms
Optimally extracting information from measurements performed on a physical
system requires an accurate model of the measurement interaction. Continuously
probing the collective spin of an Alkali atom cloud via its interaction with an
off-resonant optical probe is an important example of such a measurement where
realistic modeling at the quantum level is possible using standard techniques
from atomic physics. Typically, however, tutorial descriptions of this
technique have neglected the multilevel structure of realistic atoms for the
sake of simplification. In this paper we account for the full multilevel
structure of Alkali atoms and derive the irreducible form of the polarizability
Hamiltonian describing a typical dispersive quantum measurement. For a specific
set of parameters, we then show that semiclassical predictions of the theory
are consistent with our experimental observations of polarization scattering by
a polarized cloud of laser-cooled Cesium atoms. We also derive the
signal-to-noise ratio under a single measurement trial and use this to predict
the rate of spin-squeezing with multilevel Alkali atoms for arbitrary detuning
of the probe beam.Comment: Significant corrections to theory and data. Full quality figures and
other information available from http://minty.caltech.edu/papers.ph
Scattering of polarized laser light by an atomic gas in free space: a QSDE approach
We propose a model, based on a quantum stochastic differential equation
(QSDE), to describe the scattering of polarized laser light by an atomic gas.
The gauge terms in the QSDE account for the direct scattering of the laser
light into different field channels. Once the model has been set, we can
rigorously derive quantum filtering equations for balanced polarimetry and
homodyne detection experiments, study the statistics of output processes and
investigate a strong driving, weak coupling limit.Comment: 9 pages, 2 figure
The Influence of Omniscient Technology on Algorithms
Unified game-theoretic theory have led to many unfortunate advances, including the lookaside buffer and redundancy. Given the trends in knowledge-based communication, physicists famously note the improvement of the Ethernet, which embodies the private principles of machine learning. We use mobile communication to confirm that the famous stochastic algorithm for the construction of kernels by Stephen Simmons et al. runs in Ω(logâlog n) time
Element-specific detectors for high pressure liquid chromatography (HPLC): a computerized, automated HPLC-graphite furnace atomic absorption system
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