5,805 research outputs found
Anti-depressants and Suicide
Does drug treatment for depression with selective serotonin reuptake inhibitors (SSRIs) increase or decrease the risk of completed suicide? The question is important in part because of recent government warnings that question the safety of SSRIs, one of the most widely prescribed medications in the world. While there are plausible clinical and behavioral arguments that SSRIs could have either positive or negative effects on suicide, randomized clinical trials have not been very informative because of small samples and other problems. In this paper we use data from 26 countries for up to 25 years to estimate the effect of SSRI sales on suicide mortality using just the variation in SSRI sales that can be explained by cross-country variation in the growth of drug sales more generally. We find that an increase in SSRI sales of 1 pill per capita (about a 12 percent increase over 2000 sales levels) is associated with a decline in suicide mortality of around 5 percent. These estimates imply a cost per statistical life far below most other government interventions to improve health outcomes.
BIRP: Software for interactive search and retrieval of image engineering data
Better Image Retrieval Programs (BIRP), a set of programs to interactively sort through and to display a database, such as engineering data for images acquired by spacecraft is described. An overview of the philosophy of BIRP design, the structure of BIRP data files, and examples that illustrate the capabilities of the software are provided
Synthesis of Colloidal Mn2+:ZnO Quantum Dots and High-TC Ferromagnetic Nanocrystalline Thin Films
We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots
and the preparation of room-temperature ferromagnetic nanocrystalline thin
films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation
reaction in DMSO under atmospheric conditions. Synthesis was monitored by
electronic absorption and electron paramagnetic resonance (EPR) spectroscopies.
Zn(OAc)2 was found to strongly inhibit oxidation of Mn2+ by O2, allowing the
synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from
the surfaces of as-prepared nanocrystals using dodecylamine to yield
high-quality internally doped Mn2+:ZnO colloids of nearly spherical shape and
uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and
Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic
susceptibilities, confirmed that the manganese is substitutionally incorporated
into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing
from bulk Mn2+:ZnO only in the magnitude of D-strain. Robust ferromagnetism was
observed in spin-coated thin films of the nanocrystals, with 300 K saturation
moments as large as 1.35 Bohr magneton/Mn2+ and TC > 350 K. A distinct
ferromagnetic resonance signal was observed in the EPR spectra of the
ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its
dependence on synthetic variables are discussed in the context of these and
previous theoretical and experimental results.Comment: To be published in the Journal of the American Chemical Society Web
on July 14, 2004 (http://dx.doi.org/10.1021/ja048427j
Cation composition effects on oxide conductivity in the Zr_2Y_2O_7-Y_3NbO_7 system
Realistic, first-principles-based interatomic potentials have been used in
molecular dynamics simulations to study the effect of cation composition on the
ionic conductivity in the Zr2Y2O7-Y3NbO7 system and to link the dynamical
properties to the degree of lattice disorder. Across the composition range,
this system retains a disordered fluorite crystal structure and the vacancy
concentration is constant. The observed trends of decreasing conductivity and
increasing disorder with increasing Nb5+ content were reproduced in simulations
with the cations randomly assigned to positions on the cation sublattice. The
trends were traced to the influences of the cation charges and relative sizes
and their effect on vacancy ordering by carrying out additional calculations in
which, for example, the charges of the cations were equalised. The simulations
did not, however, reproduce all the observed properties, particularly for
Y3NbO7. Its conductivity was significantly overestimated and prominent diffuse
scattering features observed in small area electron diffraction studies were
not always reproduced. Consideration of these deficiencies led to a preliminary
attempt to characterise the consequence of partially ordering the cations on
their lattice, which significantly affects the propensity for vacancy ordering.
The extent and consequences of cation ordering seem to be much less pronounced
on the Zr2Y2O7 side of the composition range.Comment: 22 pages, 8 figures, submitted to Journal of Physics: Condensed
Matte
Statistical analysis of galaxy surveys — II. The three-point galaxy correlation function measured from the 2dFGRS
We present new results for the three-point correlation function, ζ, measured as a function of scale, luminosity and colour from the final version of the 2dF Galaxy Redshift Survey (2dFGRS). The reduced three-point correlation function, Q3~ζ/ξ2, is estimated for different triangle shapes and sizes, employing a full covariance analysis. The form of Q3 is consistent with the expectations for the Λ cold dark matter model, confirming that the primary influence shaping the distribution of galaxies is gravitational instability acting on Gaussian primordial fluctuations. However, we find a clear offset in amplitude between Q3 for galaxies and the predictions for the dark matter. We are able to rule out the scenario in which galaxies are unbiased tracers of the mass at the 9σ level. On weakly non-linear scales, we can interpret our results in terms of galaxy bias parameters. We find a linear bias term that is consistent with unity, b1= 0.93+0.10-0.08 and a quadratic bias c2=b2/b1=-0.34+0.11-0.08. This is the first significant detection of a non-zero quadratic bias, indicating a small but important non-gravitational contribution to the three-point function. Our estimate of the linear bias from the three-point function is independent of the normalization of underlying density fluctuations, so we can combine this with the measurement of the power spectrum of 2dFGRS galaxies to constrain the amplitude of matter fluctuations. We find that the rms linear theory variance in spheres of radius 8 h−1 Mpc is σ8= 0.88+0.12-0.10, providing an independent confirmation of values derived from other techniques. On non-linear scales, where ξ > 1, we find that Q3 has a strong dependence on scale, colour and luminosit
Void Statistics in Large Galaxy Redshift Surveys: Does Halo Occupation of Field Galaxies Depend on Environment?
We use measurements of the projected galaxy correlation function w_p and
galaxy void statistics to test whether the galaxy content of halos of fixed
mass is systematically different in low density environments. We present new
measurements of the void probability function (VPF) and underdensity
probability function (UPF) from Data Release Four of the Sloan Digital Sky
Survey, as well as new measurements of the VPF from the full data release of
the Two-Degree Field Galaxy Redshift Survey. We compare these measurements to
predictions calculated from models of the Halo Occupation Distribution (HOD)
that are constrained to match both w_p and the space density of galaxies. The
standard implementation of the HOD assumes that galaxy occupation depends on
halo mass only, and is independent of local environment. For luminosity-defined
samples, we find that the standard HOD prediction is a good match to the
observations, and the data exclude models in which galaxy formation efficiency
is reduced in low-density environments. More remarkably, we find that the void
statistics of red and blue galaxies (at L ~ 0.4L_*) are perfectly predicted by
standard HOD models matched to the correlation function of these samples,
ruling out "assembly bias" models in which galaxy color is correlated with
large-scale environment at fixed halo mass. We conclude that the luminosity and
color of field galaxies are determined predominantly by the mass of the halo in
which they reside and have little direct dependence on the environment in which
the host halo formed. In broader terms, our results show that the sizes and
emptiness of voids found in the distribution of L > 0.2L_* galaxies are in
excellent agreement with the predictions of a standard cosmological model with
a simple connection between galaxies and dark matter halos. (abridged)Comment: 20 emulateapj pages, 9 figures. submitted to Ap
Experimental Tests of the Control System
Control Systems Laboratory changed its name to Coordinated Science LaboratoryDefense Department / DA-11-022-ORD-174, TB3-053
How covariant is the galaxy luminosity function?
We investigate the error properties of certain galaxy luminosity function
(GLF) estimators. Using a cluster expansion of the density field, we show how,
for both volume and flux limited samples, the GLF estimates are covariant. The
covariance matrix can be decomposed into three pieces: a diagonal term arising
from Poisson noise; a sample variance term arising from large-scale structure
in the survey volume; an occupancy covariance term arising due to galaxies of
different luminosities inhabiting the same cluster. To evaluate the theory one
needs: the mass function and bias of clusters, and the conditional luminosity
function (CLF). We use a semi-analytic model (SAM) galaxy catalogue from the
Millennium run N-body simulation and the CLF of Yang et al. (2003) to explore
these effects. The GLF estimates from the SAM and the CLF qualitatively
reproduce results from the 2dFGRS. We also measure the luminosity dependence of
clustering in the SAM and find reasonable agreement with 2dFGRS results for
bright galaxies. However, for fainter galaxies, L<L*, the SAM overpredicts the
relative bias by ~10-20%. We use the SAM data to estimate the errors in the GLF
estimates for a volume limited survey of volume V~0.13 [Gpc/h]^3. We find that
different luminosity bins are highly correlated: for L<L* the correlation
coefficient is r>0.5. Our theory is in good agreement with these measurements.
These strong correlations can be attributed to sample variance. For a
flux-limited survey of similar volume, the estimates are only slightly less
correlated. We explore the importance of these effects for GLF model parameter
estimation. We show that neglecting to take into account the bin-to-bin
covariances can lead to significant systematic errors in best-fit parameters.Comment: 19 pages, 12 figures. Accepted for publication in MNRAS. Refs
updated; Fig 6 added; Figs 7 and 10 improve
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