2,009 research outputs found
Boundary regularity for the Poisson equation in reifenberg-flat domains
This paper is devoted to the investigation of the boundary regularity for the
Poisson equation {{cc} -\Delta u = f & \text{in} \Omega u= 0 & \text{on}
\partial \Omega where belongs to some and is a
Reifenberg-flat domain of More precisely, we prove that given an
exponent , there exists an such that the
solution to the previous system is locally H\"older continuous provided
that is -Reifenberg-flat. The proof is based on
Alt-Caffarelli-Friedman's monotonicity formula and Morrey-Campanato theorem
Modeling, system identification, and control of ASTREX
The modeling, system identification and controller design aspects of the ASTREX precision space structure are presented in this work. Modeling of ASTREX is performed using NASTRAN, TREETOPS and I-DEAS. The models generated range from simple linear time-invariant models to nonlinear models used for large angle simulations. Identification in both the time and frequency domains are presented. The experimental set up and the results from the identification experiments are included. Finally, controller design for ASTREX is presented. Simulation results using this optimal controller demonstrate the controller performance. Finally the future directions and plans for the facility are addressed
Nitrogen dioxide radical generated by the myeloperoxidase-hydrogen peroxide-nitrite system promotes lipid peroxidation of low density lipoprotein
AbstractMyeloperoxidase, a heme protein secreted by activated phagocytes, is present and enzymatically active in human atherosclerotic lesions. In the current studies, we explored the possibility that reactive nitrogen species generated by myeloperoxidase promote lipid peroxidation of low density lipoprotein (LDL) – a modification that may render the lipoprotein atherogenic. We found that myeloperoxidase, an H2O2-generating system and nitrite (NO2−) peroxidized LDL lipids. The process required NO2− and each component of the enzymatic system; it was inhibited by catalase, cyanide and ascorbate, a potent scavenger of aqueous phase radicals. LDL peroxidation did not require chloride ion, and it was little affected by the hypochlorous acid scavenger taurine. Collectively, these results suggest that lipid peroxidation is promoted by a nitrogen dioxide radical-like species. These observations indicate that myeloperoxidase, by virtue of its ability to form reactive nitrogen intermediates, may promote lipid peroxidation and atherogenesis
Modeling nitrous acid and its impact on ozone and hydroxyl radical during the Texas Air Quality Study 2006
Nitrous acid (HONO) mixing ratios for the Houston metropolitan area were simulated with the Community Multiscale Air Quality (CMAQ) Model for an episode during the Texas Air Quality Study (TexAQS) II in August/September 2006 and compared to in-situ MC/IC (mist-chamber/ion chromatograph) and long path DOAS (Differential Optical Absorption Spectroscopy) measurements at three different altitude ranges. Several HONO sources were accounted for in simulations, such as gas phase formation, direct emissions, nitrogen dioxide (NO<sub>2</sub>) hydrolysis, photo-induced formation from excited NO<sub>2</sub> and photo-induced conversion of NO<sub>2</sub> into HONO on surfaces covered with organic materials. Compared to the gas-phase HONO formation there was about a tenfold increase in HONO mixing ratios when additional HONO sources were taken into account, which improved the correlation between modeled and measured values. Concentrations of HONO simulated with only gas phase chemistry did not change with altitude, while measured HONO concentrations decrease with height. A trend of decreasing HONO concentration with altitude was well captured with CMAQ predicted concentrations when heterogeneous chemistry and photolytic sources of HONO were taken into account. Heterogeneous HONO production mainly accelerated morning ozone formation, albeit slightly. Also HONO formation from excited NO<sub>2</sub> only slightly affected HONO and ozone (O<sub>3</sub>) concentrations. Photo-induced conversion of NO<sub>2</sub> into HONO on surfaces covered with organic materials turned out to be a strong source of daytime HONO. Since HONO immediately photo-dissociates during daytime its ambient mixing ratios were only marginally altered (up to 0.5 ppbv), but significant increase in the hydroxyl radical (OH) and ozone concentration was obtained. In contrast to heterogeneous HONO formation that mainly accelerated morning ozone formation, inclusion of photo-induced surface chemistry influenced ozone throughout the day
The TAOS Project: Statistical Analysis of Multi-Telescope Time Series Data
The Taiwanese-American Occultation Survey (TAOS) monitors fields of up to
~1000 stars at 5 Hz simultaneously with four small telescopes to detect
occultation events from small (~1 km) Kuiper Belt Objects (KBOs). The survey
presents a number of challenges, in particular the fact that the occultation
events we are searching for are extremely rare and are typically manifested as
slight flux drops for only one or two consecutive time series measurements. We
have developed a statistical analysis technique to search the multi-telescope
data set for simultaneous flux drops which provides a robust false positive
rejection and calculation of event significance. In this paper, we describe in
detail this statistical technique and its application to the TAOS data set.Comment: 15 pages, 14 figures. Submitted to PAS
The Taiwanese-American Occultation Survey Project Stellar Variability. II. Detection of 15 Variable Stars
The Taiwanese-American Occultation Survey (TAOS) project has collected more than a billion photometric measurements since 2005 January. These sky survey data—covering timescales from a fraction of a second to a few hundred days—are a useful source to study stellar variability. A total of 167 star fields, mostly along the ecliptic plane, have been selected for photometric monitoring with the TAOS telescopes. This paper presents our initial analysis of a search for periodic variable stars from the time-series TAOS data on one particular TAOS field, No. 151 (R.A. = 17^(h)30^(m)6^(s).7, decl. = 27°17'30", J2000), which had been observed over 47 epochs in 2005. A total of 81 candidate variables are identified in the 3 deg^2 field, with magnitudes in the range 8 < R < 16. On the basis of the periodicity and shape of the light curves, 29 variables, 15 of which were previously unknown, are classified as RR Lyrae, Cepheid, δ Scuti, SX Phonencis, semi-regular, and eclipsing binaries
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