1,044 research outputs found
Hydrous Manganese Oxide Doped Gel Probe Sampler for Measuring In Situ Reductive Dissolution Rates. 2. Field Deployment
In situ rates of reductive dissolution in submerged shoreline sediments at Lake Tegel (Berlin, Germany) were measured with a novel hydrous manganese (Mn) oxide-doped gel probe sampler in concert with equilibrium gel probe and sequential extraction measurements. Rates were low in the top 8 cm, then showed a peak from 8 to 14 cm, with a maximum at 12 cm depth. This rate corresponded with a peak in dissolved porewater iron (Fe) at 11 cm depth. Below 14 cm, the reductive dissolution rate reached an intermediate steady value. Lower rates at depth corresponded with increases in operationally defined fractions of carbonate-bound and organic- and sulfide-bound Mn and Fe as detected by sequential extraction. Observed rates of reductive dissolution, which reflect a capacity for Mn reduction rather than actual rates under ambient conditions, appear to correlate with porewater chemistry and sequential extraction fractions as expected in early sediment diagenesis, and are consistent with previous measurements of in situ reductive dissolution rates. Significant downward advection in this bank filtration setting depletes the Mn and Fe oxides in the sediments and enhances the transport of dissolved Fe and Mn into the infiltrating water
On the role of the Knudsen layer in rapid granular flows
A combination of molecular-dynamics simulations, theoretical predictions, and
previous experiments are used in a two-part study to determine the role of the
Knudsen layer in rapid granular flows. First, a robust criterion for the
identification of the thickness of the Knudsen layer is established: a rapid
deterioration in Navier-Stokes-order prediction of the heat flux is found to
occur in the Knudsen layer. For (experimental) systems in which heat flux
measurements are not easily obtained, a rule-of-thumb for estimating the
Knudsen layer thickness follows, namely that such effects are evident within
2.5 (local) mean free paths of a given boundary. Second, comparisons of
simulation and experimental data with Navier-Stokes order theory are used to
provide a measure as to when Knudsen layer effects become non-negligible.
Specifically, predictions that do not account for the presence of a Knudsen
layer appear reliable for Knudsen layers collectively composing up to 20% of
the domain, whereas deterioration of such predictions becomes apparent when the
domain is fully comprised of the Knudsen layer.Comment: 9 figures, accepted to Journal of Fluid Mechanic
Studies of Mass and Size Effects in Three-Dimensional Vibrofluidized Granular Mixtures
We examine the steady state properties of binary systems of driven inelastic
hard spheres. The spheres, which move under the influence of gravity, are
contained in a vertical cylinder with a vibrating base. We computed the
trajectories of the spheres using an event-driven molecular dynamics algorithm.
In the first part of the study, we chose simulation parameters that match those
of experiments performed by Wildman and Parker. Various properties computed
from the simulation including the density profile, granular temperature and
circulation pattern are in good qualitative agreement with the experiments. We
then studied the effect of varying the mass ratio and the size ratio
independently while holding the other parameters constant. The mass and size
ratio are shown to affect the distribution of the energy. The changes in the
energy distributions affect the packing fraction and temperature of each
component. The temperature of the heavier component has a non-linear dependence
on the mass of the lighter component, while the temperature of the lighter
component is approximately proportional to its mass. The temperature of both
components is inversely dependent on the size of the smaller component.Comment: 14 Pages, 12 Figures, RevTeX
Status and specifications of a Project X front-end accelerator test facility at Fermilab
This paper describes the construction and operational status of an
accelerator test facility for Project X. The purpose of this facility is for
Project X component development activities that benefit from beam tests and any
development activities that require 325 MHz or 650 MHz RF power. It presently
includes an H- beam line, a 325 MHz superconducting cavity test facility, a 325
MHz (pulsed) RF power source, and a 650 MHz (CW) RF power source. The paper
also discusses some specific Project X components that will be tested in the
facility.Comment: 3 pp. Particle Accelerator, 24th Conference (PAC'11) 2011. 28 Mar - 1
Apr 2011. New York, US
An integrated study of earth resources in the State of California based on ERTS-1 and supporting aircraft data
There are no author-identified significant results in this report
Close-packed floating clusters: granular hydrodynamics beyond the freezing point?
Monodisperse granular flows often develop regions with hexagonal close
packing of particles. We investigate this effect in a system of inelastic hard
spheres driven from below by a "thermal" plate. Molecular dynamics simulations
show, in a wide range of parameters, a close-packed cluster supported by a
low-density region. Surprisingly, the steady-state density profile, including
the close-packed cluster part, is well described by a variant of Navier-Stokes
granular hydrodynamics (NSGH). We suggest a simple explanation for the success
of NSGH beyond the freezing point.Comment: 4 pages, 5 figures. To appear in Phys. Rev. Let
Population Distributions of Thymic Function in Adults: Variation by Sociodemographic Characteristics and Health Status
The thymus is critical for mounting an effective immune response and maintaining health. However, epidemiologic studies characterizing thymic function in the population setting are lacking. Using data from 263 adults in the Detroit Neighborhood Health Study, we examined thymic function as measured by the number of signal joint T-cell receptor excision circles (sjTREC) and assessed associations with established indicators of physiological health. Overall, increasing age and male gender were significantly associated with reduced thymic function. Adjusting for covariates, individuals with elevated levels of the pro-inflammatory biomarkers C-reactive protein (β: −0.50 [95% CI: −0.82, −0.18] for moderate elevation; β: −0.29 [95% CI: −0.59, 0.00] for high elevation) and interleukin-6 (β: −0.60 [95% CI: −0.92, −0.28] for moderate elevation; β: −0.43 [95% CI: −0.77, −0.08] for severe elevation) also had lower thymic function. Compared to individuals with a BMI <25, individuals who were overweight (β: 0.36 [95% CI: 0.07, 0.64]) or obese (β: 0.27 [95% CI: −0.03, 0.56]) had higher thymic function. Differences by self-rated health were not statistically significant. Our findings underscore demographic- and health-related gradients in thymic function among adult residents of Detroit, suggesting thymic function may be an important biomarker of health status in adults at the population level
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