14,374 research outputs found
Introduction to the computational structural mechanics testbed
The Computational Structural Mechanics (CSM) testbed software system based on the SPAR finite element code and the NICE system is described. This software is denoted NICE/SPAR. NICE was developed at Lockheed Palo Alto Research Laboratory and contains data management utilities, a command language interpreter, and a command language definition for integrating engineering computational modules. SPAR is a system of programs used for finite element structural analysis developed for NASA by Lockheed and Engineering Information Systems, Inc. It includes many complementary structural analysis, thermal analysis, utility functions which communicate through a common database. The work on NICE/SPAR was motivated by requirements for a highly modular and flexible structural analysis system to use as a tool in carrying out research in computational methods and exploring computer hardware. Analysis examples are presented which demonstrate the benefits gained from a combination of the NICE command language with a SPAR computational modules
High Temperature Ferromagnetism with Giant Magnetic Moment in Transparent Co-doped SnO2-d
Occurrence of room temperature ferromagnetism is demonstrated in pulsed laser
deposited thin films of Sn1-xCoxO2-d (x<0.3). Interestingly, films of
Sn0.95Co0.05O2-d grown on R-plane sapphire not only exhibit ferromagnetism with
a Curie temperature close to 650 K, but also a giant magnetic moment of about 7
Bohr-Magneton/Co, not yet reported in any diluted magnetic semiconductor
system. The films are semiconducting and optically highly transparent.Comment: 12 pages, 4 figure
Extended Standard Map with Spatio-Temporal Asymmetry
We analyze the transport properties of a set of symmetry-breaking extensions
%, both spatial and temporal, of the Chirikov--Taylor Map. The spatial and
temporal asymmetries result in the loss of periodicity in momentum direction in
the phase space dynamics, enabling the asymmetric diffusion which is the origin
of the unidirectional motion. The simplicity of the model makes the calculation
of the global dynamical properties of the system feasible both in phase space
and in controlling-parameter space. We present the results of numerical
experiments which show the intricate dependence of the asymmetric diffusion to
the controlling parameters.Comment: 6 pages latex 2e with 12 epsf fig
Risk factors for wound infection in surgery for spinal metastasis
Wound infection rates are generally higher in patients undergoing surgery for spinal metastasis. Risk factors of wound infection in these patients are poorly understood.
Purpose
To identify demographic and clinical variables that may be associated with patients experiencing a higher wound infection rate.
Study design
Retrospective study with prospectively collected data of spinal metastasis patients operated consecutively at a University Teaching Hospital, adult spine division which is a tertiary referral centre for complex spinal surgery.
Patient sample
Ninety-eight patients were all surgically treated, consecutively from January 2009 to September 2011. Three patients had to be excluded due to inadequate data.
Outcome measures
Physiological measures, with presence or absence of microbiologically proven infection.
Methods
Various demographic and clinical data were recorded, including age, serum albumin level, blood total lymphocyte count, corticosteroid intake, Malnutrition Universal Screening Tool (MUST) score, neurological disability, skin closure material used, levels of surgery and administration of peri-operative corticosteroids. No funding was received from any sources for this study and as far as we are aware, there are no potential conflict of interest-associated biases in this study.
Results
Higher probabilities of infection were associated with low albumin level, seven or more levels of surgery, use of delayed/non-absorbable skin closure material and presence of neurological disability. Of these factors, levels of surgery were found to be statistically significant at the 5 % significance level.
Conclusion
Risk of infection is high (17.9 %) in patients undergoing surgery for spinal metastasis. Seven or more vertebral levels of surgery increase the risk of infection significantly (p < 0.05). Low albumin level and presence of neurological disability appear to show a trend towards increased risk of infection. Use of absorbable skin closure material, age, low lymphocyte count, peri-operative administration of corticosteroids and MUST score do not appear to influence the risk of infection
Superstrings and Topological Strings at Large N
We embed the large N Chern-Simons/topological string duality in ordinary
superstrings. This corresponds to a large duality between generalized gauge
systems with N=1 supersymmetry in 4 dimensions and superstrings propagating on
non-compact Calabi-Yau manifolds with certain fluxes turned on. We also show
that in a particular limit of the N=1 gauge theory system, certain
superpotential terms in the N=1 system (including deformations if spacetime is
non-commutative) are captured to all orders in 1/N by the amplitudes of
non-critical bosonic strings propagating on a circle with self-dual radius. We
also consider D-brane/anti-D-brane system wrapped over vanishing cycles of
compact Calabi-Yau manifolds and argue that at large they induce a shift in
the background to a topologically distinct Calabi-Yau, which we identify as the
ground state system of the Brane/anti-Brane system.Comment: 30 pages, some minor clarifications adde
Parametric Resonance in an Expanding Universe
Parametric resonance has been discussed as a mechanism for copious particle
production following inflation. Here we present a simple and intuitive
calculational method for estimating the efficiency of parametric amplification
as a function of parameters. This is important for determining whether resonant
amplification plays an important role in the reheating process. We find that
significant amplification occurs only for a limited range of couplings and
interactions.Comment: 18 pages, Latex, 4 figure
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Group A Streptococcal S Protein Utilizes Red Blood Cells as Immune Camouflage and Is a Critical Determinant for Immune Evasion.
Group A Streptococcus (GAS) is a human-specific pathogen that evades the host immune response through the elaboration of multiple virulence factors. Although many of these factors have been studied, numerous proteins encoded by the GAS genome are of unknown function. Herein, we characterize a biomimetic red blood cell (RBC)-captured protein of unknown function-annotated subsequently as S protein-in GAS pathophysiology. S protein maintains the hydrophobic properties of GAS, and its absence reduces survival in human blood. S protein facilitates GAS coating with lysed RBCs to promote molecular mimicry, which increases virulence in vitro and in vivo. Proteomic profiling reveals that the removal of S protein from GAS alters cellular and extracellular protein landscapes and is accompanied by a decrease in the abundance of several key GAS virulence determinants. In vivo, the absence of S protein results in a striking attenuation of virulence and promotes a robust immune response and immunological memory
The CWKB Method of Particle Production in Periodic Potential
In this work we study the particle production in time dependent periodic
potential using the method of complex time WKB (CWKB) approximation. In the
inflationary cosmology at the end of inflationary stage, the potential becomes
time dependent as well as periodic. Reheating occurs due to particle production
by the oscillating inflaton field. Using CWKB we obtain almost identical
results on catastrophic particle production as obtained by others.Comment: 17 pages, latex, 2 figure
Tracing the Arguello Submarine Canyon System from Shelf Origins to an Abyssal Sink
The Arguello submarine canyon/channel system extends over 300 km from the continental shelf off Point Arguello and Point Conception in southern California westward onto the oceanic crust of the Pacific plate. In the northernmost reaches where the canyon system originates, all stages in the evolution of seafloor morphologic fluid flow features—from pockmarks to gullies to converging rills—are observed, similar to what has been described for the Ascension slope, north of Monterey Bay. These features appear to be active today and are linked to fluid leakage from the underlying hydrocarbon basin. The channel dissects a continental slope that exhibits features consistent with large-scale mass wasting. Upslope scarps may be the source of the morphological feature at the base of the slope previously referred to as the "Arguello submarine fan," with topographic expressions (e.g., large channel meanders, ridges) that are more consistent with mass transport deposits than with deep-sea fan depositional lobes. The modern canyon crosscuts these deposits and parallels an older, meandering channel/canyon to the west. Modern seismicity along the shelf and slope may have, and potentially still can, trigger landslides on the slope. Seismicity associated with seamount volcanism, past subduction, and Borderland transrotational and extensional processes most likely played a role in stimulating mass wasting. The presence of abundant nearby petroleum suggests that gas venting and hydrate dissociation cannot be ruled out as a triggering mechanism for the slope destabilization occurring today. The canyon/channel continues due south on a path possibly determined by the structural grain of north–south-aligned abyssal hills underlying oceanic basement. At latitude 33deg 18min N, the channel makes a 90deg turn (bend) to the west at the E–W-striking Arguello transform fault wall and develops into a meandering channel system that crosses over abyssal hill crustal fabric. The system ultimately straightens as it continues west before veering north, curving around a thickened crustal bulge at a corner offset in the Arguello fracture zone in complex basement structure, and then finally empties into an 800-m-deep basin depocenter
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