1,620 research outputs found
The Evolution of Hetergeneous "Clumpy Jets": A Parameter Study
We investigate the role discrete clumps embedded in an astrophysical jet play
on the jet's morphology and line emission characteristics. By varying clumps'
size, density, position, and velocity, we cover a range of parameter space
motivated by observations of objects such as the Herbig Haro object HH~34. We
here extend the results presented in Yirak et al. 2009, including how analysis
of individual observations may lead to spurious sinusoidal variation whose
parameters vary widely over time, owing chiefly to interacts between clumps.
The goodness of the fits, while poor in all simulations, are best when
clump-clump collisions are minimal. Our results indicate that a large velocity
dispersion leads to a clump-clump collision-dominated flow which disrupts the
jet beam. Finally, we present synthetic emission images of H- and [SII]
and note an excess of [SII] emission along the jet length as compared to
observations. This suggests that observed beams undergo earlier processing, if
they are present at all.Comment: 18 pages, 7 figures. Submitted to the Astrophysical Journa
Differences in treatment for substance use disorders by insurance status: Self-help only versus outpatient medical treatment
Background: The role of insurance on substance use disorders (SUD) treatment utilization generally is poorly understood and still less is known on how insurance status relates to the use of evidence-based treatment (i.e., medicalization approach) compared to other treatments, like single self-help groups, where the research on effectiveness is less supportive. This study examines associations between health insurance and any SUD treatment utilization as well as use of single self- help versus medicalization approach.
Methods: A cross-sectional study design was used. Data were from the 2015-2017, public use National Surveys on Drug Use and Health (NSDUH). Adjusted logistic regressions were used to examine the associations controlling for socio-demographics, recent major depressive episode, and survey year. All analyses used survey weights to be representative of the US population and account for the NSDUH’s complex survey design.
Results: After adjustment for covariates, those with publicly insured remained more likely to use any SUD treatment in the past year (odd ratio [OR] 1.82; 95% CI: 1.36-2.43), compared to those without insurance. Further, compared with uninsured, those with public insurance reported lower odds of using only self-help treatment (OR 0.42; 95% CI: 0.23-0.74) versus medicalization approach utilization.
Conclusions: Publicly insured persons with SUD are more likely to use SUD treatment in the past year than the uninsured. Uninsured people with SUD are more likely to use single self-help as a substitute for medicalization approach.https://scholarscompass.vcu.edu/gradposters/1098/thumbnail.jp
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Using local ecological knowledge to assess the status of the Critically Endangered Chinese giant salamander Andrias davidianus in Guizhou Province, China
The Critically Endangered Chinese giant salamander Andrias davidianus, the world's largest amphibian, is severely threatened by unsustainable exploitation of wild individuals. However, field data with which to assess the salamander's status, population trends, or exploitation across its geographical range are limited, and recent field surveys using standard ecological field techniques have typically failed to detect wild individuals. We conducted community-based fieldwork in three national nature reserves (Fanjingshan, Leigongshan and Mayanghe) in Guizhou Province, China, to assess whether local ecological knowledge constitutes a useful tool for salamander conservation. We collected a sample of dated salamander sighting records and associated data from these reserves for comparative assessment of the relative status of salamander populations across the region. Although Fanjingshan and Leigongshan are still priority sites for salamander conservation, few recent sightings were recorded in either reserve, and respondents considered that salamanders had declined locally at both reserves. The species may already be functionally extinct at Mayanghe. Although respondent data on threats to salamanders in Guizhou are more difficult to interpret, overharvesting was the most commonly suggested explanation for salamander declines, and it is likely that the growing salamander farming industry is the primary driver of salamander extraction from Guizhou's reserves. Questionnaire-based surveys can collect novel quantitative data that provide unique insights into the local status of salamander populations, and we advocate wide-scale incorporation of this research approach into future salamander field programmes
Protostellar Outflow Evolution in Turbulent Environments
The link between turbulence in star formatting environments and protostellar
jets remains controversial. To explore issues of turbulence and fossil cavities
driven by young stellar outflows we present a series of numerical simulations
tracking the evolution of transient protostellar jets driven into a turbulent
medium. Our simulations show both the effect of turbulence on outflow
structures and, conversely, the effect of outflows on the ambient turbulence.
We demonstrate how turbulence will lead to strong modifications in jet
morphology. More importantly, we demonstrate that individual transient outflows
have the capacity to re-energize decaying turbulence. Our simulations support a
scenario in which the directed energy/momentum associated with cavities is
randomized as the cavities are disrupted by dynamical instabilities seeded by
the ambient turbulence. Consideration of the energy power spectra of the
simulations reveals that the disruption of the cavities powers an energy
cascade consistent with Burgers'-type turbulence and produces a driving
scale-length associated with the cavity propagation length. We conclude that
fossil cavities interacting either with a turbulent medium or with other
cavities have the capacity to sustain or create turbulent flows in star forming
environments. In the last section we contrast our work and its conclusions with
previous studies which claim that jets can not be the source of turbulence.Comment: 24 pages, submitted to the Astrophysical Journa
Determining Star Formation Thresholds from Observations
Most gas in giant molecular clouds is relatively low-density and forms star
inefficiently, converting only a small fraction of its mass to stars per
dynamical time. However, star formation models generally predict the existence
of a threshold density above which the process is efficient and most mass
collapses to stars on a dynamical timescale. A number of authors have proposed
observational techniques to search for a threshold density above which star
formation is efficient, but it is unclear which of these techniques, if any,
are reliable. In this paper we use detailed simulations of turbulent,
magnetised star-forming clouds, including stellar radiation and outflow
feedback, to investigate whether it is possible to recover star formation
thresholds using current observational techniques. Using mock observations of
the simulations at realistic resolutions, we show that plots of projected star
formation efficiency per free-fall time can detect the
presence of a threshold, but that the resolutions typical of current dust
emission or absorption surveys are insufficient to determine its value. In
contrast, proposed alternative diagnostics based on a change in the slope of
the gas surface density versus star formation rate surface density
(Kennicutt-Schmidt relation) or on the correlation between young stellar object
counts and gas mass as a function of density are ineffective at detecting
thresholds even when they are present. The signatures in these diagnostics
sometimes taken as indicative of a threshold in observations, which we
generally reproduce in our mock observations, do not prove to correspond to
real physical features in the 3D gas distribution.Comment: 10 pages, 7 figures, Accepted for publication in MNRA
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