19,616 research outputs found
Global pointwise decay estimates for defocusing radial nonlinear wave equations
We prove global pointwise decay estimates for a class of defocusing
semilinear wave equations in dimensions restricted to spherical symmetry.
The technique is based on a conformal transformation and a suitable choice of
the mapping adjusted to the nonlinearity. As a result we obtain a pointwise
bound on the solutions for arbitrarily large Cauchy data, provided the
solutions exist globally. The decay rates are identical with those for small
data and hence seem to be optimal. A generalization beyond the spherical
symmetry is suggested.Comment: 9 pages, 1 figur
Anomalously small wave tails in higher dimensions
We consider the late-time tails of spherical waves propagating on
even-dimensional Minkowski spacetime under the influence of a long range radial
potential. We show that in six and higher even dimensions there exist
exceptional potentials for which the tail has an anomalously small amplitude
and fast decay. Along the way we clarify and amend some confounding arguments
and statements in the literature of the subject.Comment: 13 page
The Geoff Egan Memorial Lecture 2011. Artefacts, art and artifice: reconsidering iconographic sources for archaeological objects in early modern Europe
A first systematic analysis of historic domestic material culture depicted in contemporaneous Western painting and prints, c.1400-1800. Drawing on an extensive data set, the paper proposes to methodologies and hermeneutics for historical analysis and archaeological correspondence
Internal mode mechanism for collective energy transport in extended systems
We study directed energy transport in homogeneous nonlinear extended systems
in the presence of homogeneous ac forces and dissipation. We show that the
mechanism responsible for unidirectional motion of topological excitations is
the coupling of their internal and translation degrees of freedom. Our results
lead to a selection rule for the existence of such motion based on resonances
that explains earlier symmetry analysis of this phenomenon. The direction of
motion is found to depend both on the initial and the relative phases of the
two harmonic drivings, even in the presence of noise.Comment: Final version, to appear in Physical Review Letter
EVA Glove Research Team
The goal of the basic research portion of the extravehicular activity (EVA) glove research program is to gain a greater understanding of the kinematics of the hand, the characteristics of the pressurized EVA glove, and the interaction of the two. Examination of the literature showed that there existed no acceptable, non-invasive method of obtaining accurate biomechanical data on the hand. For this reason a project was initiated to develop magnetic resonance imaging as a tool for biomechanical data acquisition and visualization. Literature reviews also revealed a lack of practical modeling methods for fabric structures, so a basic science research program was also initiated in this area
Searching For Integrated Sachs-Wolfe Effect Beyond Temperature Anisotropies: CMB E-mode Polarization-Galaxy Cross Correlation
The cross-correlation between cosmic microwave background (CMB) temperature
anisotropies and the large scale structure (LSS) traced by the galaxy
distribution, or sources at different wavelengths, is now well known. This
correlation results from the integrated Sachs-Wolfe (ISW) effect in CMB
anisotropies generated at late times due to the dark energy component of the
Universe. In a reionized universe, the ISW quadrupole rescatters and
contributes to the large-scale polarization signal. Thus, in principle, the
large-scale polarization bump in the E-mode should also be correlated with the
galaxy distribution. Unlike CMB temperature-LSS correlation that peaks for
tracers at low redshifts this correlation peaks mostly at redshifts between 1
and 3. Under certain conditions, mostly involving a low optical depth to
reionization, if the Universe reionized at a redshift around 6, the cross
polarization-source signal is marginally detectable, though challenging as it
requires all-sky maps of the large scale structure at redshifts between 1 and
3. If the Universe reionized at a redshift higher than 10, it is unlikely that
this correlation will be detectable even with no instrumental noise all-sky
maps. While our estimates do not guarantee a detection unknown physics related
to the dark energy as well as still uncertain issues related to the large
angular scale CMB and polarization anisotropies may motivate attempts to
measure this correlation using upcoming CMB polarization E-mode maps.Comment: 13 pages; 3 figure panels, JCAP submitte
The -cleus experiment: A gram-scale fiducial-volume cryogenic detector for the first detection of coherent neutrino-nucleus scattering
We discuss a small-scale experiment, called -cleus, for the first
detection of coherent neutrino-nucleus scattering by probing nuclear-recoil
energies down to the 10 eV-regime. The detector consists of low-threshold
CaWO and AlO calorimeter arrays with a total mass of about 10 g and
several cryogenic veto detectors operated at millikelvin temperatures.
Realizing a fiducial volume and a multi-element target, the detector enables
active discrimination of , neutron and surface backgrounds. A first
prototype AlO device, operated above ground in a setup without
shielding, has achieved an energy threshold of eV and further
improvements are in reach. A sensitivity study for the detection of coherent
neutrino scattering at nuclear power plants shows a unique discovery potential
(5) within a measuring time of weeks. Furthermore, a site
at a thermal research reactor and the use of a radioactive neutrino source are
investigated. With this technology, real-time monitoring of nuclear power
plants is feasible.Comment: 14 pages, 19 figure
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