7,914 research outputs found
contraction for bounded (non-integrable) solutions of degenerate parabolic equations
We obtain new contraction results for bounded entropy solutions of
Cauchy problems for degenerate parabolic equations. The equations we consider
have possibly strongly degenerate local or non-local diffusion terms. As
opposed to previous results, our results apply without any integrability
assumption on the %(the positive part of the difference of) solutions. They
take the form of partial Duhamel formulas and can be seen as quantitative
extensions of finite speed of propagation local contraction results for
scalar conservation laws. A key ingredient in the proofs is a new and
non-trivial construction of a subsolution of a fully non-linear (dual)
equation. Consequences of our results are maximum and comparison principles,
new a priori estimates, and in the non-local case, new existence and uniqueness
results
Analysis and assessment of film materials and associated manufacturing processes for a solar sail
Candidate resin manufacturers and film producers were surveyed to determine the availability of key materials and to establish the capabilities of fabricators to prepare ultrathin films of these materials within the capacity/cost/time constraints of the Halley program. Infrared spectra of three candidate samples were obtained by pressing each sample against an internal reflection crystal with the polymer sandwiched between the crystal and the metal backing. The sample size was such that less than one-fourth of the surface of the crystal was covered with the sample. This resulted in weak spectra requiring a six-fold expansion. Internal reflection spectra of the three samples were obtained using both a KRS-5 and a Ge internal reflection crystal. Subtracted infrared spectra of the three samples are presented
Investigating CXOU J163802.6-471358: a new pulsar wind nebula in the Norma region?
We present the first analysis of the extended source CXOU J163802.6--471358,
which was discovered serendipitously during the {\em Chandra} X-ray survey of
the Norma region of the Galactic spiral arms. The X-ray source exhibits a
cometary appearance with a point source and an extended tail region. The
complete source spectrum is fitted well with an absorbed power law model and
jointly fitting the {\em Chandra} spectrum of the full source with one obtained
from an archived {\em XMM-Newton} observation results in best fit parameters
and
(90 confidence uncertainties). The unabsorbed
luminosity of the full source is then ergs
s with kpc, where a distance of 10 kpc is a lower bound
inferred from the large column density. The radio counterpart found for the
source using data from the Molonglo Galactic Plane Survey epoch-2 (MGPS-2)
shows an elongated tail offset from the X-ray emission. No infrared counterpart
was found. The results are consistent with the source being a previously
unknown pulsar driving a bow shock through the ambient medium
Continuous dependence estimates for nonlinear fractional convection-diffusion equations
We develop a general framework for finding error estimates for
convection-diffusion equations with nonlocal, nonlinear, and possibly
degenerate diffusion terms. The equations are nonlocal because they involve
fractional diffusion operators that are generators of pure jump Levy processes
(e.g. the fractional Laplacian). As an application, we derive continuous
dependence estimates on the nonlinearities and on the Levy measure of the
diffusion term. Estimates of the rates of convergence for general nonlinear
nonlocal vanishing viscosity approximations of scalar conservation laws then
follow as a corollary. Our results both cover, and extend to new equations, a
large part of the known error estimates in the literature.Comment: In this version we have corrected Example 3.4 explaining the link
with the results in [51,59
Strategies for aeroelastic parameter identification from bridge deck free vibration data
Author's manuscript version. The version of record is available from the publisher via: doi:10.1016/S0167-6105(01)00091-5. Copyright © 2001 Elsevier Science Ltd. All rights reserved.Several techniques for identification of aerodynamic derivatives (ADs) from free vibration test data are
compared using simulated data and test data obtained from wind tunnel tests. These identification methods
include system identification from one degree of freedom or two degree of freedom response to either
transient excitation or to turbulent buffeting. The experimental and analytical difficulties involved in each
method are highlighted and suggestions made for the best approach to determination of ADs in both model
and full-scale studies.
Time domain methods using step relaxation provided the best results as long as air-flow turbulence does not
cause severe signal to noise ratio problems with the free vibration decay. When, as in full-scale, the
turbulence is the primary forcing function, time domain and frequency domain methods can be used to
recover the full set of ADs concerning vertical and torsional respons
Copepod reaction to odor stimuli influenced by cestode infection
The cestode Schistocephalus solidus uses copepods as first and sticklebacks as second intermediate hosts. For transmission, an infected copepod has to be preyed upon by a stickleback. We used copepods of the species Macrocy albidus to test whether infected and uninfected copepods differ in their reaction to two kind of simultaneously presented odors: odors of sticklebacks and odors of sticklebacks and conspecificz. By giving this choice, we attempted to force the copepods to make a trade-off between the benefit of risk dilution and possible predator confusion and the costs of food competition and other disadvantages induced by conspecifics. Within 1-8 h after last feeding, uninfected copepods clearly preferred the odors of conspeciflcs under the chemically simulated threat of predation. This was in contrast to the infected copepods, who tended to avoid the odor of conspecifics. When the time between experiment and last feeding varied, infected copepods showed an increas preference for fish water only (or avoided conspecthcs) with increasing hunger level This suggests that S. solidus benefits from hunger-induced behavioral changes of its copepod host by influencing its microhabitat selection. The same effect could be found in both sexes; however, it was significantly more pronounced in male than in female copepods. We propose several hypotheses that could explain the difference between the sexes in their infection-dependent microhabitat selectio
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