2,016 research outputs found
Multiple-access phased array antenna simulator for a digital beam forming system investigation
Future versions of data relay satellite systems are currently being planned by NASA. Being given consideration for implementation are on-board digital beamforming techniques which will allow multiple users to simultaneously access a single S-band phased array antenna system. To investigate the potential performance of such a system, a laboratory simulator has been developed at NASA's Lewis Research Center. This paper describes the system simulator, and in particular, the requirements, design, and performance of a key subsystem, the phased array antenna simulator, which provides realistic inputs to the digital processor including multiple signals, noise, and nonlinearities
Increasing Availability of Benzodiazepines Among People Who Inject Drugs in a Canadian Setting
Background: Benzodiazepine misuse is associated with mortality and is common among people who inject drugs (PWID). This study aimed to examine the temporal trends in the availability of benzodiazepines among PWID in a Canadian setting, and to identify factors associated with more immediate access to benzodiazepines.
Methods: Data were derived from three prospective cohorts of PWID in Vancouver, Canada, between June 2012 and May 2015. The primary outcome was the perceived availability of benzodiazepines, measured in three levels: not available, delayed availability (available in ≥10 min), and immediate availability (available in <10 min). We used multivariable generalized estimating equations to identify factors associated with availability of benzodiazepines.
Results: In total, 1641 individuals were included in these analyses. In multivariable analyses, factors associated with immediate benzodiazepine availability included incarceration (adjusted odds ratio (AOR): 1.42, 95% CI1.06, 1.89) and participation in methadone maintenance therapy (MMT) (AOR: 1.35, 95% CI 1.14, 1.60). Factors associated with delayed benzodiazepine availability included incarceration (AOR: 1.45, 95% CI 1.02, 2.07) and MMT (AOR: 1.77, 95% CI 1.48, 2.12). Benzodiazepine availability increased throughout the study period for both immediate (AOR: 1.14, 95% CI 1.10, 1.18 per 6-month follow-up period) and delayed availability (AOR: 1.17, 95% CI 1.12, 1.22 per 6-month follow-up period).
Conclusions: Among our sample of PWID, benzodiazepine availability is increasing and was associated with health and criminal justice system characteristics. Our findings indicate a need to examine prescribing practices and educate both PWID and healthcare providers about the risks associated with benzodiazepine use
On the Nature of the X-ray Emission from the Ultraluminous X-ray Source, M33 X-8: New Constraints from NuSTAR and XMM-Newton
We present nearly simultaneous NuSTAR and XMM-Newton observations of the
nearby (832 kpc) ultraluminous X-ray source (ULX) M33 X-8. M33 X-8 has a 0.3-10
keV luminosity of LX ~ 1.4 x 10^39 erg/s, near the boundary of the
"ultraluminous" classification, making it an important source for understanding
the link between typical Galactic X-ray binaries and ULXs. Past studies have
shown that the 0.3-10 keV spectrum of X-8 can be characterized using an
advection-dominated accretion disk model. We find that when fitting to our
NuSTAR and XMM-Newton observations, an additional high-energy (>10 keV)
Comptonization component is required, which allows us to rule out single
advection-dominated disk and classical sub-Eddington models. With our new
constraints, we analyze XMM-Newton data taken over the last 17 years to show
that small (~30%) variations in the 0.3-10 keV flux of M33 X-8 result in
spectral changes similar to those observed for other ULXs. The two most likely
phenomenological scenarios suggested by the data are degenerate in terms of
constraining the nature of the accreting compact object (i.e., black hole
versus neutron star). We further present a search for pulsations using our
suite of data; however, no clear pulsations are detected. Future observations
designed to observe M33 X-8 at different flux levels across the full 0.3-30 keV
range would significantly improve our constraints on the nature of this
important source.Comment: Accepted for publication in ApJ (15 pages, 4 tables, 6 figures
Climate Projections Very Likely Underestimate Future Volcanic Forcing and Its Climatic Effects
Standard climate projections represent future volcanic eruptions by a constant forcing inferred from 1850 to 2014 volcanic forcing. Using the latest ice-core and satellite records to design stochastic eruption scenarios, we show that there is a 95% probability that explosive eruptions could emit more sulfur dioxide (SO2) into the stratosphere over 2015–2100 than current standard climate projections (i.e., ScenarioMIP). Our simulations using the UK Earth System Model with interactive stratospheric aerosols show that for a median future eruption scenario, the 2015–2100 average global-mean stratospheric aerosol optical depth (SAOD) is double that used in ScenarioMIP, with small-magnitude eruptions (<3 Tg of SO2) contributing 50% to SAOD perturbations. We show that volcanic effects on large-scale climate indicators, including global surface temperature, sea level and sea ice extent, are underestimated in ScenarioMIP because current climate projections do not fully account for the recurrent frequency of volcanic eruptions of different magnitudes
Glutamatergic dysfunction leads to a hyper-dopaminergic phenotype through deficits in short-term habituation: a mechanism for aberrant salience
Psychosis in disorders like schizophrenia is commonly associated with aberrant salience and elevated striatal dopamine. However, the underlying cause(s) of this hyper-dopaminergic state remain elusive. Various lines of evidence point to glutamatergic dysfunction and impairments in synaptic plasticity in the etiology of schizophrenia, including deficits associated with the GluA1 AMPAR subunit. GluA1 knockout (Gria1−/−) mice provide a model of impaired synaptic plasticity in schizophrenia and exhibit a selective deficit in a form of short-term memory which underlies short-term habituation. As such, these mice are unable to reduce attention to recently presented stimuli. In this study we used fast-scan cyclic voltammetry to measure phasic dopamine responses in the nucleus accumbens of Gria1−/− mice to determine whether this behavioral phenotype might be a key driver of a hyper-dopaminergic state. There was no effect of GluA1 deletion on electrically-evoked dopamine responses in anaesthetized mice, demonstrating normal endogenous release properties of dopamine neurons in Gria1−/− mice. Furthermore, dopamine signals were initially similar in Gria1−/− mice compared to controls in response to both sucrose rewards and neutral light stimuli. They were also equally sensitive to changes in the magnitude of delivered rewards. In contrast, however, these stimulus-evoked dopamine signals failed to habituate with repeated presentations in Gria1−/− mice, resulting in a task-relevant, hyper-dopaminergic phenotype. Thus, here we show that GluA1 dysfunction, resulting in impaired short-term habituation, is a key driver of enhanced striatal dopamine responses, which may be an important contributor to aberrant salience and psychosis in psychiatric disorders like schizophrenia
Geometry of Frictionless and Frictional Sphere Packings
We study static packings of frictionless and frictional spheres in three
dimensions, obtained via molecular dynamics simulations, in which we vary
particle hardness, friction coefficient, and coefficient of restitution.
Although frictionless packings of hard-spheres are always isostatic (with six
contacts) regardless of construction history and restitution coefficient,
frictional packings achieve a multitude of hyperstatic packings that depend on
system parameters and construction history. Instead of immediately dropping to
four, the coordination number reduces smoothly from as the friction
coefficient between two particles is increased.Comment: 6 pages, 9 figures, submitted to Phys. Rev.
Applying Recent Argumentation Methods to Some Ancient Examples of Plausible Reasoning
Plausible (eikotic) reasoning known from ancient Greek (late Academic) skeptical philosophy is shown to be a clear notion that can be analyzed by argu- mentation methods, and that is important for argumentation studies. It is shown how there is a continuous thread running from the Sophists to the skeptical philosopher Carneades, through remarks of Locke and Bentham on the subject, to recent research in artificial intelligence. Eleven characteristics of plausible reasoning are specified by analyzing key examples of it recognized as important in ancient Greek skeptical philosophy using an artificial intelligence model called the Carneades Argumentation System (CAS). By applying CAS to ancient examples it is shown how plausible reasoning is especially useful for gaining a better understanding of evidential reasoning in law, and argued that it can also be applied to everyday argumentation. Our analysis of the snake and rope example of Carneades is also used to point out some ways CAS needs to be extended if it is to more fully model the views of this ancient philosopher on argumentation
VIS: the visible imager for Euclid
Euclid-VIS is a large format visible imager for the ESA Euclid space mission
in their Cosmic Vision program, scheduled for launch in 2019. Together with the
near infrared imaging within the NISP instrument it forms the basis of the weak
lensing measurements of Euclid. VIS will image in a single r+i+z band from
550-900 nm over a field of view of ~0.5 deg2. By combining 4 exposures with a
total of 2240 sec, VIS will reach to V=24.5 (10{\sigma}) for sources with
extent ~0.3 arcsec. The image sampling is 0.1 arcsec. VIS will provide deep
imaging with a tightly controlled and stable point spread function (PSF) over a
wide survey area of 15000 deg2 to measure the cosmic shear from nearly 1.5
billion galaxies to high levels of accuracy, from which the cosmological
parameters will be measured. In addition, VIS will also provide a legacy
imaging dataset with an unprecedented combination of spatial resolution, depth
and area covering most of the extra-Galactic sky. Here we will present the
results of the study carried out by the Euclid Consortium during the Euclid
Definition phase.Comment: 10 pages, 6 figure
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