13,718 research outputs found
Evaluation of a Gas Chromatograph-Differential Mobility Spectrometer for Potential Water Monitoring on the International Space Station
Environmental monitoring for manned spaceflight has long depended on archival sampling, which was sufficient for short missions. However, the longer mission durations aboard the International Space Station (ISS) have shown that enhanced, real-time monitoring capabilities are necessary in order to protect both the crewmembers and the spacecraft systems. Over the past several years, a number of real-time environmental monitors have been deployed on the ISS. Currently, volatile organic compounds (VOCs) in the station air are monitored by the Air Quality Monitor (AQM), a small, lightweight gas chromatograph-differential mobility spectrometer. For water monitoring, real-time monitors are used for total organic carbon (TOC) and biocide analysis. No information on the actual makeup of the TOC is provided presently, however. An improvement to the current state of environmental monitoring could be realized by modifying a single instrument to analyze both air and water. As the AQM currently provides quantitative, compound-specific information for VOCs in air samples, this instrument provides a logical starting point to evaluate the feasibility of this approach. The major hurdle for this effort lies in the liberation of the target analytes from the water matrix. In this presentation, we will discuss our recent studies, in which an electro-thermal vaporization unit has been interfaced with the AQM to analyze target VOCs at the concentrations at which they are routinely detected in archival water samples from the ISS. We will compare the results of these studies with those obtained from the instrumentation routinely used to analyze archival water samples
Investigation of gene–environment interactions in relation to tic severit
Tourette syndrome (TS) is a neuropsychiatric disorder with involvement of genetic and environmental factors. We investi gated genetic loci previously implicated in Tourette syndrome and associated disorders in interaction with pre- and perinatal
adversity in relation to tic severity using a case-only (N=518) design. We assessed 98 single-nucleotide polymorphisms
(SNPs) selected from (I) top SNPs from genome-wide association studies (GWASs) of TS; (II) top SNPs from GWASs
of obsessive–compulsive disorder (OCD), attention-defcit/hyperactivity disorder (ADHD), and autism spectrum disorder
(ASD); (III) SNPs previously implicated in candidate-gene studies of TS; (IV) SNPs previously implicated in OCD or ASD;
and (V) tagging SNPs in neurotransmitter-related candidate genes. Linear regression models were used to examine the main
efects of the SNPs on tic severity, and the interaction efect of these SNPs with a cumulative pre- and perinatal adversity
score. Replication was sought for SNPs that met the threshold of signifcance (after correcting for multiple testing) in a rep lication sample (N=678). One SNP (rs7123010), previously implicated in a TS meta-analysis, was signifcantly related to
higher tic severity. We found a gene–environment interaction for rs6539267, another top TS GWAS SNP. These fndings were
not independently replicated. Our study highlights the future potential of TS GWAS top hits in gene–environment studies
Communication: Studies of the Lennard-Jones fluid in 2, 3, and 4 dimensions highlight the need for a liquid-state 1/d expansion
The recent theoretical prediction by Maimbourg and Kurchan [arXiv:1603.05023]
that for regular pair-potential systems the virial potential-energy correlation
coefficient increases towards unity as the dimension goes to infinity is
investigated for the standard 12-6 Lennard-Jones fluid. This is done by
computer simulations for going from the critical point along the
critical isotherm/isochore to higher density/temperature. In all cases the
virial potential-energy correlation coefficient increases significantly. For a
given density and temperature relative to the critical point, with increasing
number of dimension the Lennard-Jones system conforms better to the
hidden-scale-invariance property characterized by high virial potential-energy
correlations (a property that leads to the existence of isomorphs in the
thermodynamic phase diagram, implying that it becomes effectively
one-dimensional in regard to structure and dynamics). The present paper also
gives the first numerical demonstration of isomorph invariance of structure and
dynamics in four dimensions. Our findings emphasize the need for a universally
applicable expansion in liquid-state theory; we conjecture that the
systems known to obey hidden scale invariance in three dimensions are those for
which the yet-to-be-developed expansion converges rapidly
Soft spin waves in the low temperature thermodynamics of Pr_{0.7}Ca_{0.3}MnO_{3}
We present a detailed magnetothermal study of Pr(0.7)Ca(0.3)MnO(3), a
perovskite manganite in which an insulator-metal transition can be driven by
magnetic field, but also by pressure, visible light, x-rays, or high currents.
We find that the field-induced transition is associated with an enormous
release of energy which accounts for its strong irreversibility. In the
ferromagnetic metallic state, specific heat and magnetization measurements
indicate a much smaller spin wave stiffness than that seen in any other
manganite, which we attribute to spin waves among the ferromagnetically ordered
Pr moments. The coupling between the Pr and Mn spins may also provide a basis
for understanding the low temperature phase diagram of this most unusual
manganite.Comment: 10 pages, LATEX, 5 PDF figures, corrected typo
Constraining the epoch of reionization with the variance statistic: simulations of the LOFAR case
Several experiments are underway to detect the cosmic redshifted 21-cm signal
from neutral hydrogen from the Epoch of Reionization (EoR). Due to their very
low signal-to-noise ratio, these observations aim for a statistical detection
of the signal by measuring its power spectrum. We investigate the extraction of
the variance of the signal as a first step towards detecting and constraining
the global history of the EoR. Signal variance is the integral of the signal's
power spectrum, and it is expected to be measured with a high significance. We
demonstrate this through results from a simulation and parameter estimation
pipeline developed for the Low Frequency Array (LOFAR)-EoR experiment. We show
that LOFAR should be able to detect the EoR in 600 hours of integration using
the variance statistic. Additionally, the redshift () and duration
() of reionization can be constrained assuming a parametrization. We
use an EoR simulation of and to test the
pipeline. We are able to detect the simulated signal with a significance of 4
standard deviations and extract the EoR parameters as and in 600 hours,
assuming that systematic errors can be adequately controlled. We further show
that the significance of detection and constraints on EoR parameters can be
improved by measuring the cross-variance of the signal by cross-correlating
consecutive redshift bins.Comment: 13 pages, 14 figures, Accepted for publication in MNRA
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