996 research outputs found
A Longitudinal Study of Use of Health Care Services Among Older Women
Article discussing a longitudinal study of the use of health care services among older women
Density, Velocity, and Magnetic Field Structure in Turbulent Molecular Cloud Models
We use 3D numerical MHD simulations to follow the evolution of cold,
turbulent, gaseous systems with parameters representing GMC conditions. We
study three cloud simulations with varying mean magnetic fields, but identical
initial velocity fields. We show that turbulent energy is reduced by a factor
two after 0.4-0.8 flow crossing times (2-4 Myr), and that the magnetically
supercritical cloud models collapse after ~6 Myr, while the subcritical cloud
does not collapse. We compare density, velocity, and magnetic field structure
in three sets of snapshots with matched Mach numbers. The volume and column
densities are both log-normally distributed, with mean volume density a factor
3-6 times the unperturbed value, but mean column density only a factor 1.1-1.4
times the unperturbed value. We use a binning algorithm to investigate the
dependence of kinetic quantities on spatial scale for regions of column density
contrast (ROCs). The average velocity dispersion for the ROCs is only weakly
correlated with scale, similar to the mean size-linewidth relation for clumps
within GMCs. ROCs are often superpositions of spatially unconnected regions
that cannot easily be separated using velocity information; the same difficulty
may affect observed GMC clumps. We analyze magnetic field structure, and show
that in the high density regime, total magnetic field strengths increase with
density with logarithmic slope 1/3 -2/3. Mean line-of-sight magnetic field
strengths vary widely across a projected cloud, and do not correlate with
column density. We compute simulated interstellar polarization maps at varying
orientations, and determine that the Chandrasekhar-Fermi formula multiplied by
a factor ~0.5 yields a good estimate of the plane-of sky magnetic field
strength provided the dispersion in polarization angles is < 25 degrees.Comment: 56 pages, 25 figures; Ap.J., accepte
Multiphase Gas and the Fractal Nature of Radiative Turbulent Mixing Layers
A common situation in galactic and intergalactic gas involves cold dense gas
in motion relative to hot diffuse gas. Kelvin-Helmholtz instability creates a
turbulent mixing layer and populates the intermediate-temperature phase, which
often cools rapidly. The energy lost to cooling is balanced by the advection of
hot high enthalpy gas into the mixing layer, resulting in growth and
acceleration of the cold phase. This process may play a major role in
determining the interstellar medium and circumgalactic medium phase structure,
and accelerating cold gas in galactic winds and cosmic filaments. Cooling in
these mixing layers occurs in a thin corrugated sheet, which we argue has an
area with fractal dimension and a thickness that adjusts to match the
hot phase mixing time to the cooling time. These cooling sheet properties form
the basis of a new model for how the cooling rate and hot gas inflow velocity
depend on the size , cooling time , relative velocity , and density contrast of the system.
Entrainment is expected to be enhanced in environments with short , large , and large . Using
a large suite of three dimensional hydrodynamic simulations, we demonstrate
that this fractal cooling layer model accurately captures the energetics and
evolution of turbulent interfaces and can therefore be used as a foundation for
understanding multiphase mixing with strong radiative cooling.Comment: 11 pages, 5 figures, submitted to ApJL. Movies can be found here
https://dfielding14.github.io/movies
MetaBlast! Virtual Cell: A Pedagogical Convergence between Game Design and Science Education
MetaBlast! Virtual Cell (from now on referred to as VC) is a game design solution to a specific scientific and educational problem; expressly, how to make advanced, university level plant biology instruction on molecular and anatomical levels an exciting, efficient learning experience. The advanced technologies of 3D modeling and animation, computer programming and game design are united and tempered with strong, scientific guidance for accuracy and art direction for a powerful visual and audio simulation. The additional strength of intense gaming as a powerful tool aiding memory, logic and problem solving has recently become well recognized. Virtual Cell will provide a unique gaming experience, while transparently teaching scientifically accurate facts and concepts about, in this case, a soybean plant’s inner workings and dependant mechanisms on multiple scales and levels of complexity. Virtual Cell (from now on referred to as VC) in the future may prove to be a reference for other scientific/education endeavors as scientists battle for a more prominent mind share among average citizens. This paper will discuss the difficulties of developing VC, its structure, intended game and educational goals along with additional benefits to both the sciences and gaming industry
Spectral Properties of Compressible Magnetohydrodynamic Turbulence from Numerical Simulations
We analyze the spectral properties of driven, supersonic compressible
magnetohydrodynamic (MHD) turbulence obtained via high-resolution numerical
experiments, for application to understanding the dynamics of giant molecular
clouds. Via angle-averaged power spectra, we characterize the transfer of
energy from the intermediate, driving scales down to smaller dissipative
scales, and also present evidence for inverse cascades that achieve
modal-equipartition levels on larger spatial scales. Investigating compressive
versus shear modes separately, we evaluate their relative total power, and find
that as the magnetic field strength decreases, (1) the shear fraction of the
total kinetic power decreases, and (2) slopes of power-law fits over the
inertial range steepen. To relate to previous work on incompressible MHD
turbulence, we present qualitative and quantitative measures of the
scale-dependent spectral anisotropy arising from the shear-Alfv\'{e}n cascade,
and show how these vary with changing mean magnetic field strength. Finally, we
propose a method for using anisotropy in velocity centroid maps as a diagnostic
of the mean magnetic field strength in observed cloud cores.Comment: 22 pages, 11 figures; Ap.J., accepte
Delivering a “Dose of Hope”: A Faith-Based Program to Increase Older African Americans’ Participation in Clinical Trials
Background: Underrepresentation of older-age racial and ethnic minorities in clinical research is a significant barrier to health in the United States, as it impedes medical research advancement of effective preventive and therapeutic strategies. Objective: The objective of the study was to develop and test the feasibility of a community-developed faith-based intervention and evaluate its potential to increase the number of older African Americans in clinical research. Methods: Using a cluster-randomized design, we worked with six matched churches to enroll at least 210 persons. We provided those in the intervention group churches with three educational sessions on the role of clinical trials in addressing health disparity topics, and those in the comparison group completed surveys at the same timepoints. All persons enrolled in the study received ongoing information via newsletters and direct outreach on an array of clinical studies seeking participants. We evaluated the short-, mid-, and longer-term effects of the interventional program on clinical trial-related outcomes (ie, screening and enrollment)
Communitas and the commons: The open access movement and the dynamics of restructuration in scholarly publishing
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