52,436 research outputs found
Snakes and ladders: localized solutions of plane Couette flow
We demonstrate the existence of a large number of exact solutions of plane
Couette flow, which share the topology of known periodic solutions but are
localized in space. Solutions of different size are organized in a
snakes-and-ladders structure strikingly similar to that observed for simpler
pattern-forming PDE systems. These new solutions are a step towards extending
the dynamical systems view of transitional turbulence to spatially extended
flows.Comment: submitted to Physics Review Letter
Advanced dosimetry systems for the space transport and space station
Advanced dosimetry system concepts are described that will provide automated and instantaneous measurement of dose and particle spectra. Systems are proposed for measuring dose rate from cosmic radiation background to greater than 3600 rads/hr. Charged particle spectrometers, both internal and external to the spacecraft, are described for determining mixed field energy spectra and particle fluxes for both real time onboard and ground-based computer evaluation of the radiation hazard. Automated passive dosimetry systems consisting of thermoluminescent dosimeters and activation techniques are proposed for recording the dose levels for twelve or more crew members. This system will allow automatic onboard readout and data storage of the accumulated dose and can be transmitted to ground after readout or data records recovered with each crew rotation
Experimental active and passive dosimetry systems for the NASA Skylab program
Active and passive dosimetry instrumentation to measure absorbed dose, charged particle spectra, and linear energy transfer spectra inside the command module and orbital workshop on the Skylab program were developed and tested. The active dosimetry system consists of one integral unit employing both a tissue equivalent ionization chamber and silicon solid state detectors. The instrument measures dose rates from 0.2 millirad/hour to 25 rads/hour, linear energy transfer spectra from 2.8 to 42.4 Kev/micron, and the proton and alpha particle energy spectra from 0.5 to 75 Mev. The active dosimeter is equipped with a portable radiation sensor for use in astronaut on-body and spacecraft shielding surveys during passage of the Skylab through significant space radiations. Data are transmitted in real time or are recorded by onboard spacecraft tape recorder for rapid evaluation of the radiation levels. The passive dosimetry systems consist of twelve (12) hard-mounted assemblies, each containing a variety of passive radiation sensors which are recoverable at the end of the mission for analysis
Virtual chemical reactions for drug design
Two methods for the fast, fragment-based combinatorial molecule assembly were developed. The software COLIBREE® (Combinatorial Library Breeding) generates candidate structures from scratch, based on stochastic optimization [1]. Result structures of a COLIBREE design run are based on a fixed scaffold and variable linkers and side-chains. Linkers representing virtual chemical reactions and side-chain building blocks obtained from pseudo-retrosynthetic dissection of large compound databases are exchanged during optimization. The process of molecule design employs a discrete version of Particle Swarm Optimization (PSO) [2]. Assembled compounds are scored according to their similarity to known reference ligands. Distance to reference molecules is computed in the space of the topological pharmacophore descriptor CATS [3]. In a case study, the approach was applied to the de novo design of potential peroxisome proliferator-activated receptor (PPAR gamma) selective agonists. In a second approach, we developed the formal grammar Reaction-MQL [4] for the in silico representation and application of chemical reactions. Chemical transformation schemes are defined by functional groups participating in known organic reactions. The substructures are specified by the linear Molecular Query Language (MQL) [5]. The developed software package contains a parser for Reaction-MQL-expressions and enables users to design, test and virtually apply chemical reactions. The program has already been used to create combinatorial libraries for virtual screening studies. It was also applied in fragmentation studies with different sets of retrosynthetic reactions and various compound libraries
Noise Pollution? What\u27s the solution?: Understanding Traffic Noise Pollution in Gettysburg, Pennsylvania
Noise pollution can be damaging to a community by impacting its atmosphere as well as the health of its residents, local quality of life, and local economy. Our study sought to gain insight into the level of noise pollution in Gettysburg, both in-town and on the Gettysburg College campus, and how noise pollution may be affecting the local residents and students. We selected 9 sampling sites, 6 in-town and 3 on the college campus, and measured the noise pollution in dBA with portable sound meters three days a week and three times a day over a three week period. Our data showed no major trends in terms of time of day or day of the week, but there were clear differences in noise pollution levels between the different sites in that town sites were generally louder than on campus sites. Noise pollution in town was often louder than 70 dBA, the noise threshold that indicates possible hearing damage overtime set by the World Health Organization. Gettysburg has recently enacted a noise ordinance; our study suggests the Borough possibly could do more to mitigate traffic noise by repairing roads and manipulating road design
NLTE spectroscopic analysis of the He anomaly in subluminous B-type stars
Several B-type main-sequence stars show chemical peculiarities. A
particularly striking class are the He stars, which exhibit a remarkable
enrichment of He with respect to He. This isotopic anomaly has also
been found in blue horizontal branch (BHB) and subdwarf B (sdB) stars, which
are helium-core burning stars of the extreme horizontal branch. Using a hybrid
local/non-local thermodynamic equilibrium (LTE/NLTE) approach for B-type stars,
we analyzed high-quality spectra of two known He BHBs and nine known He
sdBs to determine their isotopic helium abundances and He/He abundance
ratios. We redetermined their atmospheric parameters and analyzed selected
neutral helium lines, including 4922 and 6678
, which are very sensitive to He/He. Most of the He
sdBs cluster in a narrow temperature strip between 26000 K and 30000 K and are
helium deficient in accordance with previous LTE analyses. BD+48 2721
is reclassified as a BHB star because of its low temperature
( 20700 K). Whereas He is almost absent
(He/He 0.25) in most of the known He stars, other sample stars
show abundance ratios up to He/He2.51. A search for He stars in
the ESO SPY survey led to the discovery of two new He sdB stars (HE
0929-0424 and HE 1047-0436). The observed helium line profiles of all BHBs and
of three sdBs are not matched by chemically homogeneous atmospheres, but hint
at vertical helium stratification. This phenomenon has been seen in other
peculiar B-type stars, but is found for the first time for sdBs. We estimate
helium to increase from the outer to the inner atmosphere by factors ranging
from 1.4 (SB 290) up to 8.0 (BD+48 2721).Comment: 19 pages, 79 figures submitted to Astronomy&Astrophysic
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