54,695 research outputs found
Force and cavitation characteristics of the NACA 4412 hydrofoil
This report covers Water Tunnel measurements of the infinite aspect ratio characteristics and cavitation characteristics of a hydrofoil section. The profile tested is identical to the 4412 airfoil section of the National Advisory Committee for Aeronautics and is called the NACA 4412 hydrofoil in this report. Measurements and observations include lift, drag, and pitching moment and the inception and development of cavitation as functions of the angle of attack, velocity, and pressure of the flow. The purpose of this report is to present these measurements of the characteristics of this section in water, to compare the results with other available information on this shape, and to evaluate the Water Tunnel method for obtaining the complte hydrodynamic characteristics of hydrofoils
New Minimal Distortion Shift Gauge
Based on the recent understanding of the role of the densitized lapse
function in Einstein's equations and of the proper way to pose the thin
sandwich problem, a slight readjustment of the minimal distortion shift gauge
in the 3+1 approach to the dynamics of general relativity allows this shift
vector to serve as the vector potential for the longitudinal part of the
extrinsic curvature tensor in the new approach to the initial value problem,
thus extending the initial value decomposition of gravitational variables to
play a role in the evolution as well. The new shift vector globally minimizes
the changes in the conformal 3-metric with respect to the spacetime measure
rather than the spatial measure on the time coordinate hypersurfaces, as the
old shift vector did.Comment: 5 page ReVTeX4 twocolumn latex file, no figures; slight revision:
last sentence of section 2 deleted and replaced, citations reordered,
additonal paragraph added to introduction with short explanation of the
initial value problem and its thin sandwich variation, Yvonne Choquet-Bruhat
reference added and acknowledgment expanded to include he
Structural performance of two aerobrake hexagonal heat shield panel concepts
Structural sizing and performance are presented for two structural concepts for an aerobrake hexagonal heat shield panel. One concept features a sandwich construction with an aluminum honeycomb core and thin quasi-isotropic graphite-epoxy face sheets. The other concept features a skin-rib isogrid construction with thin quasi-isotropic graphite-epoxy skins and graphite-epoxy ribs oriented at 0, +60, and -60 degs along the panel. Linear static, linear bifurcation buckling, and nonlinear static analyses were performed to compare the structural performance of the two panel concepts and assess their feasibility for a lunar transfer vehicle aerobrake application
Mass in anti-de Sitter spaces
The boundary stress tensor approach has proven extremely useful in defining
mass and angular momentum in asymptotically anti-de Sitter spaces with CFT
duals. An integral part of this method is the use of boundary counterterms to
regulate the gravitational action and stress tensor. In addition to the
standard gravitational counterterms, in the presence of matter we advocate the
use of a finite counterterm proportional to phi^2 (in five dimensions). We
demonstrate that this finite shift is necessary to properly reproduce the
expected mass/charge relation for R-charged black holes in AdS_5.Comment: 15 pages, late
Are Risk Regulators Rational' Evidence from Hazardous Waste Cleanup Decisions
Using original data on the cleanup of 130 hazardous waste sites, W. Kip Viscusi of Harvard Law School and James T. Hamilton of Duke University's Sanford Institute of Public Policy examine the extent that political decisions and quantitative risk assessments influence cleanup and remediation decisions. They conclude that target risk levels chosen by regulators are largely a function of political variables and risk-perception biases. Communities with higher voter turnouts are more likely at times to have lower risks remaining after final site cleanup and to have more spent to avert expected cases of cancer. They find these political influences are most significant for the least cost-effective site cleanups and the lowest site risks. By basing its policies on an individual risk approach that does not reflect the size of the exposed population or whether the population exists at the site, the Environmental Protection Agency often fails to recognize important aspects of the overall beneficial consequences of its efforts. The mean cost per case of cancer averted at the sample of 130 EPA sites is 418 million. These estimates use EPA conservative risk assumptions and assume no latency period. With such adjustments, the median cost rises to above $1 billion per cancer case. The most effective 5 percent of all cleanup expenditures eliminate over 99 percent of the cancer risk. Put somewhat differently, 95% of the costs are spent to address less than 1 percent of the risks.
Neuronal Control of Swimming Behavior: Comparison of Vertebrate and Invertebrate Model Systems
Swimming movements in the leech and lamprey are highly analogous, and lack homology. Thus, similarities in mechanisms must arise from convergent evolution rather than from common ancestry. Despite over 40 years of parallel investigations into this annelid and primitive vertebrate, a close comparison of the approaches and results of this research is lacking. The present review evaluates the neural mechanisms underlying swimming in these two animals and describes the many similarities that provide intriguing examples of convergent evolution. Specifically, we discuss swim initiation, maintenance and termination, isolated nervous system preparations, neural-circuitry, central oscillators, intersegmental coupling, phase lags, cycle periods and sensory feedback. Comparative studies between species highlight mechanisms that optimize behavior and allow us a broader understanding of nervous system function
Prediction of LDEF ionizing radiation environment
The Long Duration Exposure Facility (LDEF) spacecraft flew in a 28.5 deg inclination circular orbit with an altitude in the range from 172 to 258.5 nautical miles. For this orbital altitude and inclination two components contribute most of the penetrating charge particle radiation encountered - the galactic cosmic rays and the geomagnetically trapped Van Allen protons. Where shielding is less than 1.0 g/sq cm geomagnetically trapped electrons make a significant contribution. The 'Vette' models together with the associated magnetic filed models were used to obtain the trapped electron and proton fluences. The mission proton doses were obtained from the fluence using the Burrell proton dose program. For the electron and bremsstrahlung dose we used the Marshall Space Flight Center (MSFC) electron dose program. The predicted doses were in general agreement with those measured with on-board thermoluminescent detector (TLD) dosimeters. The NRL package of programs, Cosmic Ray Effects on MicroElectronics (CREME), was used to calculate the linear energy transfer (LET) spectrum due to galactic cosmic rays (GCR) and trapped protons for comparison with LDEF measurements
A large scale prediction of bacteriocin gene blocks suggests a wide functional spectrum for bacteriocins
Bacteriocins are peptide-derived molecules produced by bacteria, whose
recently-discovered functions include virulence factors and signalling
molecules as well as their better known roles as antibiotics. To date, close to
five hundred bacteriocins have been identified and classified. Recent
discoveries have shown that bacteriocins are highly diverse and widely
distributed among bacterial species. Given the heterogeneity of bacteriocin
compounds, many tools struggle with identifying novel bacteriocins due to their
vast sequence and structural diversity. Many bacteriocins undergo
post-translational processing or modifications necessary for the biosynthesis
of the final mature form. Enzymatic modification of bacteriocins as well as
their export is achieved by proteins whose genes are often located in a
discrete gene cluster proximal to the bacteriocin precursor gene, referred to
as \textit{context genes} in this study. Although bacteriocins themselves are
structurally diverse, context genes have been shown to be largely conserved
across unrelated species. Using this knowledge, we set out to identify new
candidates for context genes which may clarify how bacteriocins are
synthesized, and identify new candidates for bacteriocins that bear no sequence
similarity to known toxins. To achieve these goals, we have developed a
software tool, Bacteriocin Operon and gene block Associator (BOA) that can
identify homologous bacteriocin associated gene clusters and predict novel
ones. We discover that several phyla have a strong preference for bactericon
genes, suggesting distinct functions for this group of molecules. Availability:
https://github.com/idoerg/BOAComment: Accepted for publication in BMC Bioinformatic
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