17,913 research outputs found
Biochemistry and Waste Treatment
Paper by E. D. Schroeder, a graduate student in Environmental Science and Engineering at Rice Universit
Molecular Model of the Contractile Ring
We present a model for the actin contractile ring of adherent animal cells.
The model suggests that the actin concentration within the ring and
consequently the power that the ring exerts both increase during contraction.
We demonstrate the crucial role of actin polymerization and depolymerization
throughout cytokinesis, and the dominance of viscous dissipation in the
dynamics. The physical origin of two phases in cytokinesis dynamics ("biphasic
cytokinesis") follows from a limitation on the actin density. The model is
consistent with a wide range of measurements of the midzone of dividing animal
cells.Comment: PACS numbers: 87.16.Ka, 87.16.Ac
http://www.ncbi.nlm.nih.gov/pubmed/16197254
http://www.weizmann.ac.il/complex/tlusty/papers/PhysRevLett2005.pd
Optical links in the angle-data assembly of the 70-meter antennas
In the precision-pointing mode the 70 meter antennas utilize an optical link provided by an autocollimator. In an effort to improve reliability and performance, commercial instruments were evaluated as replacement candidates, and upgraded versions of the existing instruments were designed and tested. The latter were selected for the Neptune encounter, but commercial instruments with digital output show promise of significant performance improvement for the post-encounter period
Small Displacement, Long Life On-Orbit Compressor Design and Fabrication
The focus is the generation of technology and fabrication of prototype hardware applicable to seven Space Station compressor system applications. The compressors are of the single acting reciprocating piston type and, in general, may be termed miniature in size compared with normal commercially available equipment. The initial technology development is focused on improved valve designs, and the control of pulsations and heating effects in order to increase compressor efficiency and reduce cycle temperatures, thus permitting significantly increased stage pressure ratios. The initial test compressor was successfully operated at pressure ratios of up to 50:1, and this significant extension of allowable pressure ratio will result in a reduction of the number of required stages and, hence, total hardware thereby reducing system weight and volume. These experiments have also identified the need to employ low shaft speeds, on the order of 250 to 500 rpm, to enhance heat transfer and increase life. The prototype compressor currently being designed, is to be driven by a low-speed brushless dc motor sealed in a case common to the compressor drive mechanism case. The compressor and motor case will communicate with stage suction pressure so that any minor gas leakage past the piston rings will be returned to the suction. Emphasis in this prototype design is being placed on simplicity, durability, commonality of components, and high efficiency
Photoelasticity of sodium silicate glass from first principles
Based on density-functional perturbation theory we have computed the
photoelastic tensor of a model of sodium silicate glass of composition
(NaO)(SiO) (NS3). The model (containig 84 atoms) is
obtained by quenching from the melt in combined classical and Car-Parrinello
molecular dynamics simulations. The calculated photoelastic coefficients are in
good agreement with experimental data. In particular, the calculation
reproduces quantitatively the decrease of the photoelastic response induced by
the insertion of Na, as measured experimentally.
The extension to NS3 of a phenomenological model developed in a previous work
for pure a-SiO indicates that the modulation upon strain of other
structural parameters besides the SiOSi angles must be invoked to explain the
change in the photoelstic response induced by Na
Neurogenic Fever after Acute Traumatic Spinal Cord Injury: A Qualitative Systematic Review.
STUDY DESIGN: Systematic review.
OBJECTIVE: To determine the incidence, pathogenesis, and clinical outcomes related to neurogenic fevers following traumatic spinal cord injury (SCI).
METHODS: A systematic review of the literature was performed on thermodysregulation secondary to acute traumatic SCI in adult patients. A literature search was performed using PubMed (MEDLINE), Cochrane Central Register of Controlled Trials, and Scopus. Using strict inclusion and exclusion criteria, seven relevant articles were obtained.
RESULTS: The incidence of fever of all origins (both known and unknown) after SCI ranged from 22.5 to 71.7% with a mean incidence of 50.6% and a median incidence of 50.0%. The incidence of fever of unknown origin (neurogenic fever) ranged from 2.6 to 27.8% with a mean incidence of 8.0% and a median incidence of 4.7%. Cervical and thoracic spinal injuries were more commonly associated with fever than lumbar injuries. In addition, complete injuries had a higher incidence of fever than incomplete injuries. The pathogenesis of neurogenic fever after acute SCI is not thoroughly understood.
CONCLUSION: Neurogenic fevers are relatively common following an acute SCI; however, there is little in the scientific literature to help physicians prevent or treat this condition. The paucity of research underscored by this review demonstrates the need for further studies with larger sample sizes, focusing on incidence rate, clinical outcomes, and pathogenesis of neurogenic fever following acute traumatic SCI
Counter Rotating Open Rotor Animation using Particle Image Velocimetry
This article describes the two accompanying fluid dynamics videos for the
"Counter rotating open rotor flow field investigation using stereoscopic
Particle Image Velocimetry" presented at the 64th Annual Meeting of the APS
Division of Fluid Dynamics in Baltimore, Maryland, November 20-22, 2011.Comment: Videos are include
Screened thermonuclear reactions and predictive stellar evolution of detached double-lined eclipsing binaries
The low energy fusion cross sections of charged-particle nuclear reactions
(and the respective reaction rates) in stellar plasmas are enhanced due to
plasma screening effects. We study the impact of those effects on predictive
stellar evolution simulations for detached double-lined eclipsing binaries. We
follow the evolution of binary systems (pre-main sequence or main sequence
stars) with precisely determined radii and masses from 1.1Mo to 23Mo (from
their birth until their present state). The results indicate that all the
discrepancies between the screened and unscreened models (in terms of
luminosity, stellar radius, and effective temperature) are within the
observational uncertainties. Moreover, no nucleosynthetic or compositional
variation was found due to screening corrections. Therefore all thermonuclear
screening effects on the charged-particle nuclear reactions that occur in the
binary stars considered in this work (from their birth until their present
state) can be totally disregarded. In other words, all relevant
charged-particle nuclear reactions can be safely assumed to take place in a
vacuum, thus simplifying and accelerating the simulation processes.Comment: 5 RevTex pages,no figures. Accepted for publication in Phys.Rev.
Kinetic Roughening in Growth Models with Diffusion in Higher Dimensions
We present results of numerical simulations of kinetic roughening for a
growth model with surface diffusion (the Wolf-Villain model) in 3+1 and
4+1~dimensions using lattices of a linear size up to in 3+1~D and
in 4+1~D. The effective exponents calculated both from the surface width and
from the height--height correlation function are much larger than those
expected based on results in lower dimensions, due to a growth instability
which leads to the evolution of large mounded structures on the surface. An
increase of the range for incorporation of a freshly deposited particle leads
to a decrease of the roughness but does not suppress the instability.Comment: 8 pages, LaTeX 2.09, IC-DDV-93-00
Scaling of Local Slopes, Conservation Laws and Anomalous Roughening in Surface Growth
We argue that symmetries and conservation laws greatly restrict the form of
the terms entering the long wavelength description of growth models exhibiting
anomalous roughening. This is exploited to show by dynamic renormalization
group arguments that intrinsic anomalous roughening cannot occur in local
growth models. However some conserved dynamics may display super-roughening if
a given type of terms are present.Comment: To appear in Phys. Rev. Lett., 4 pages in RevTeX style, no fig
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