565 research outputs found
An Experimental Study of Micron-scale Droplet Aerosols Produced via Ultrasonic Atomization
In the last 10 years, laser-driven fusion experiments performed on atomic clusters of deuterium have shown a surprisingly high neutron yield per joule of input laser energy. Results indicate that the optimal cluster size for maximizing fusion events should be in the 0.01–μm diameter range, but an appropriate source of droplets of this size does not exist. In an attempt to meet this need, we use ultrasonic atomization to generate micron-scale droplet aerosols of high average density, and we have developed and refined a reliable droplet sizing technique based on Mie scattering. Harmonic excitation of the fluid in the MHz range yields an aerosol of droplets with diameters of a few microns. The droplet diameter distribution is well-peaked and the relationship between average droplet size and forcing frequency follows an inviscid scaling law, predictable by dimensional analysis and consistent with the linear theory for Faraday excitation of an infinitely deep fluid
Using Ultrasonic Atomization to Produce an Aerosol of Micron-scale Particles
A device that uses ultrasonic atomization of a liquid to produce an aerosol of micron-scale droplets is described. This device represents a new approach to producing targets relevant to laser-driven fusion studies, and to rare studies of nonlinear optics in which wavelength-scale targets are irradiated. The device has also made possible tests of fluid dynamics models in a novel phase space. The distribution of droplet sizes produced by the device and the threshold power required for droplet production are shown to follow scaling laws predicted by fluid dynamics
The African Women's Protocol: Bringing Attention to Reproductive Rights and the MDGs
Andrew Gibbs and colleagues discuss the African Women's Protocol, a framework for ensuring reproductive rights are supported throughout the continent and for supporting interventions to improve women's reproductive health, including the MDGs
A Strategy for Finding Near Earth Objects with the SDSS Telescope
We present a detailed observational strategy for finding Near Earth Objects
(NEOs) with the Sloan Digital Sky Survey (SDSS) telescope. We investigate
strategies in normal, unbinned mode as well as binning the CCDs 2x2 or 3x3,
which affects the sky coverage rate and the limiting apparent magnitude. We
present results from 1 month, 3 year and 10 year simulations of such surveys.
For each cadence and binning mode, we evaluate the possibility of achieving the
Spaceguard goal of detecting 90% of 1 km NEOs (absolute magnitude H <= 18 for
an albedo of 0.1). We find that an unbinned survey is most effective at
detecting H <= 20 NEOs in our sample. However, a 3x3 binned survey reaches the
Spaceguard Goal after only seven years of operation. As the proposed large
survey telescopes (PanStarss; LSST) are at least 5-10 years from operation, an
SDSS NEO survey could make a significant contribution to the detection and
photometric characterization of the NEO population.Comment: Accepted by AJ -- 12 pages, 11 figure
Blood Supply to the Human Spinal Cord. II. Imaging and Pathology
The blood supply of the spinal cord is a complex system based on multilevel sources and anastomoses. Diseases often affect this vascular supply and imaging has been developed that better investigates these structures. The authors review the literature regarding pathology and imaging modalities for the blood supply of the spinal cord. Knowledge of the disease processes and imaging modalities used to investigate these arterial lesions of the spinal cord will assist the clinician when treating patients with spinal cord lesions
Particle Stirring in Turbulent Gas Disks: Including Orbital Oscillations
We describe the diffusion and random velocities of solid particles due to
stochastic forcing by turbulent gas. We include the orbital dynamics of
Keplerian disks, both in-plane epicycles and vertical oscillations. We obtain a
new result for the diffusion of solids. The Schmidt number (ratio of gas to
particle diffusivity) is Sc = 1 + (Omega t_stop)^2, in terms of the particle
stopping time, t_stop, and the orbital frequency, Omega. The standard result,
Sc = 1 + t_stop/t_eddy, in terms of the eddy turnover time, t_eddy, is shown to
be incorrect. The main difference is that Sc rises quadratically, not linearly,
with stopping time. Consequently, particles larger than ~ 10 cm in
protoplanetary disks will suffer less radial diffusion and will settle closer
to the midplane. Such a layer of boulders would be more prone to gravitational
collapse. Our predictions of RMS speeds, vertical scale height and diffusion
coefficients will help interpret numerical simulations. We confirm previous
results for the vertical stirring of particles (scale heights and random
velocities), and add a correction for arbitrary ratios of eddy to orbital
times. The particle layer becomes thinner for t_eddy > 1/Omega, with the
strength of turbulent diffusion held fixed. We use two analytic techniques --
the Hinze-Tchen formalism and the Fokker-Planck equation with velocity
diffusion -- with identical results when the regimes of validity overlap. We
include simple physical arguments for the scaling of our results.Comment: 17 pages, 7 figures, 2 tables, accepted to Icaru
Far Ultraviolet Morphology of Star Forming Filaments in Cool Core Brightest Cluster Galaxies
We present a multiwavelength morphological analysis of star forming clouds and filaments in the central (<50 kpc) regions of 16 low redshift ( \Msol) stars reveals filamentary and clumpy morphologies, which we quantify by means of structural indices. The FUV data are compared with X-ray, Ly, narrowband H, broadband optical/IR, and radio maps, providing a high spatial resolution atlas of star formation locales relative to the ambient hot ( K) and warm ionised ( K) gas phases, as well as the old stellar population and radio-bright AGN outflows. Nearly half of the sample possesses kpc-scale filaments that, in projection, extend toward and around radio lobes and/or X-ray cavities. These filaments may have been uplifted by the propagating jet or buoyant X-ray bubble, or may have formed {\it in situ} by cloud collapse at the interface of a radio lobe or rapid cooling in a cavity's compressed shell. The morphological diversity of nearly the entire FUV sample is reproduced by recent hydrodynamical simulations in which the AGN powers a self-regulating rain of thermally unstable star forming clouds that precipitate from the hot atmosphere. In this model, precipitation triggers where the cooling-to- freefall time ratio is . This condition is roughly met at the maxmial projected FUV radius for more than half of our sample, and clustering about this ratio is stronger for sources with higher star formation rates
Gravitational Radiation From Cosmological Turbulence
An injection of energy into the early Universe on a given characteristic
length scale will result in turbulent motions of the primordial plasma. We
calculate the stochastic background of gravitational radiation arising from a
period of cosmological turbulence, using a simple model of isotropic
Kolmogoroff turbulence produced in a cosmological phase transition. We also
derive the gravitational radiation generated by magnetic fields arising from a
dynamo operating during the period of turbulence. The resulting gravitational
radiation background has a maximum amplitude comparable to the radiation
background from the collision of bubbles in a first-order phase transition, but
at a lower frequency, while the radiation from the induced magnetic fields is
always subdominant to that from the turbulence itself. We briefly discuss the
detectability of such a signal.Comment: 20 pages. Corrections for an errant factor of 2 in all the gravity
wave characteristic amplitudes. Accepted for publication in Phys. Rev.
- …