78 research outputs found
A Parameter Study of the Dust and Gas Temperature in a Field of Young Stars
We model the thermal effect of young stars on their surrounding environment
in order to understand clustered star formation. We take radiative heating of
dust, dust-gas collisional heating, cosmic-ray heating, and molecular cooling
into account. Using Dusty, a spherical continuum radiative transfer code, we
model the dust temperature distribution around young stellar objects with
various luminosities and surrounding gas and dust density distributions. We
have created a grid of dust temperature models, based on our modeling with
Dusty, which we can use to calculate the dust temperature in a field of stars
with various parameters. We then determine the gas temperature assuming energy
balance. Our models can be used to make large-scale simulations of clustered
star formation more realistic.Comment: 29 pages, 19 figures. Submitted to Ap
A Parameter Study Of The Dust And Gas Temperature In A Field Of Young Stars
We model the thermal effect of young stars on their surrounding environment in order to understand clustered star formation. We take radiative heating of dust, dust-gas collisional heating, cosmic-ray heating, and molecular cooling into account. Using DUSTY, a spherical continuum radiative transfer code, we model the dust temperature distribution around young stellar objects with various luminosities and surrounding gas and dust density distributions. We have created a grid of dust temperature models, based on our modeling with DUSTY, which we can use to calculate the dust temperature in a field of stars with various parameters. We then determine the gas temperature assuming energy balance. Our models can be used to make large-scale simulations of clustered star formation more realistic.NSF AST-0307250, AST-0607793Research Corporation (SDD)Astronom
Constraining the structure of the non-spherical preprotostellar core L1544
A series of self-consistent, three-dimensional continuum radiative transfer
models are constructed of the pre-protostellar core L1544, with the results
compared with existing SCUBA and ISO data. The source is well-fit by a prolate
spheroid, having an ellipsoidal power-law density distribution of index m ~ 2
(1.75 < m < 2.25) in to at least r ~ 1600AU. For r<1600 AU, the data are
consistent with either an extension of the power law to smaller radii, or a
flattened (Bonner-Ebert like) density distribtion. We can further constrain the
optical depth along the short axis at 1300um to be ~ 5e-3, the central
luminosity to be L < 1e-3 solar luminosities, the long axis diameter D ~ 0.1
pc, the axis ratio to be q ~ 2, and the external ISRF to be similar to that
defined by Mathis, Mezger, & Panagia (1983) to within 50 per cent. The outer
diameter and axis ratio may each be somewhat larger due to potential on-source
chopping in the observations, and the projection of the long axis onto the
plane of the sky. While these results are similar to those inferred directly
from observations or spherical modeling due to the source transparency at
submillimeter wavelengths, we infer a smaller size, lower mass, and higher
optical depth / column density, exposed to a stronger external radiation field
than previously assumed. Finally, we find that both the spectral energy
distribution (SED) and surface brightness distribution are necessary to
constrain the source properties in this way.Comment: 9 pages; 8 figures; accepted for publication in MNRA
Chemical history of molecules in circumstellar disks
The chemical composition of a protoplanetary disk is determined not only by
in situ chemical processes during the disk phase, but also by the history of
the gas and dust before it accreted from the natal envelope. In order to
understand the disk's chemical composition at the time of planet formation,
especially in the midplane, one has to go back in time and retrace the
chemistry to the molecular cloud that collapsed to form the disk and the
central star. Here we present a new astrochemical model that aims to do just
that. The model follows the core collapse and disk formation in two dimensions,
which turns out to be a critical upgrade over older collapse models. We predict
chemical stratification in the disk due to different physical conditions
encountered along different streamlines. We argue that the disk-envelope
accretion shock does not play a significant role for the material in the disk
at the end of the collapse phase. Finally, our model suggests that complex
organic species are formed on the grain surfaces at temperatures of 20 to 40 K,
rather than in the gas phase in the T>100 K hot corino.Comment: 10 pages, 5 figures, to appear in the proceedings of IAU Symposium
280: "The Molecular Universe
Structural Correlates of Taste and Smell Loss in Encephalitis Disseminata
BACKGROUND: Olfactory dysfunction in MS patients is reported in the literature. MRI of the olfactory bulb (OB) is discussed as a promising new testing method for measuring olfactory function (OF). Aim of this study was to explore reasons for and optimize the detection of olfactory dysfunction in MS patients with MRI. MATERIALS AND METHODS: OB and olfactory brain volume was assessed within 34 MS patients by manual segmentation. Olfactory function was tested using the Threshold-Discrimination-Identification-Test (TDI), gustatory function was tested using Taste Strips (TST). RESULTS: 41% of the MS patients displayed olfactory dysfunction (8% of the control group), 16% displayed gustatory dysfunction (5% of the control group). There was a correlation between the OB volume and the number and volume of MS lesions in the olfactory brain. Olfactory brain volume correlated with the volume of lesions in the olfactory brain and the EDSS score. The TST score correlated with the number and volume of lesions in the olfactory brain. CONCLUSION: The correlation between a higher number and volume of MS lesions with a decreased OB and olfactory brain volume could help to explain olfactory dysfunction
The Effect of Medicare Eligibility on Spousal Insurance Coverage
A majority of married couples in the United States take advantage of the fact that employers often provide health insurance coverage to spouses. When the older spouses become eligible for Medicare, however, many of them can no longer provide their younger spouses with coverage. In this paper, we study how spousal eligibility for Medicare affects the health insurance and health care access of the younger spouse. We find spousal eligibility for Medicare results in the younger spouse having worse insurance coverage and reduced access to health care services
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Identifying Treatments for Taste and Smell Disorders: Gaps and Opportunities.
The chemical senses of taste and smell play a vital role in conveying information about ourselves and our environment. Tastes and smells can warn against danger and also contribute to the daily enjoyment of food, friends and family, and our surroundings. Over 12% of the US population is estimated to experience taste and smell (chemosensory) dysfunction. Yet, despite this high prevalence, long-term, effective treatments for these disorders have been largely elusive. Clinical successes in other sensory systems, including hearing and vision, have led to new hope for developments in the treatment of chemosensory disorders. To accelerate cures, we convened the Identifying Treatments for Taste and Smell Disorders conference, bringing together basic and translational sensory scientists, health care professionals, and patients to identify gaps in our current understanding of chemosensory dysfunction and next steps in a broad-based research strategy. Their suggestions for high-yield next steps were focused in 3 areas: increasing awareness and research capacity (e.g., patient advocacy), developing and enhancing clinical measures of taste and smell, and supporting new avenues of research into cellular and therapeutic approaches (e.g., developing human chemosensory cell lines, stem cells, and gene therapy approaches). These long-term strategies led to specific suggestions for immediate research priorities that focus on expanding our understanding of specific responses of chemosensory cells and developing valuable assays to identify and document cell development, regeneration, and function. Addressing these high-priority areas should accelerate the development of novel and effective treatments for taste and smell disorders
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