14,682 research outputs found
Residual based adaptivity and PWDG methods for the Helmholtz equation
We present a study of two residual a posteriori error indicators for the
Plane Wave Discontinuous Galerkin (PWDG) method for the Helmholtz equation. In
particular we study the h-version of PWDG in which the number of plane wave
directions per element is kept fixed. First we use a slight modification of the
appropriate a priori analysis to determine a residual indicator. Numerical
tests show that this is reliable but pessimistic in that the ratio between the
true error and the indicator increases as the mesh is refined. We therefore
introduce a new analysis based on the observation that sufficiently many plane
waves can approximate piecewise linear functions as the mesh is refined.
Numerical results demonstrate an improvement in the efficiency of the
indicators
Feasibility of the optical fiber clock
We explore the feasibility of a compact high-precision Hg atomic clock based
on a hollow core optical fiber. We evaluate the sensitivity of the
- clock transition in Hg and other divalent atoms to the fiber
inner core surface at non-zero temperatures. The Casimir-Polder interaction
induced - transition frequency shift is calculated for the atom
inside the hollow capillary as a function of atomic position, capillary
material, and geometric parameters. For atoms on the axis
of a silica capillary with inner radius and
optimally chosen thickness , the atom-surface
interaction induced - clock transition frequency shift can be
kept on the level . We also estimate
the atom loss and heating due to the collisions with the buffer gas, lattice
intensity noise induced heating, spontaneous photon scattering, and residual
birefringence induced frequency shifts.Comment: 8 pages, 5 figures, submitte
One Hour of Chemical Demonstrations
This article describes a diverse set of chemistry demonstrations especially selected to encourage student interaction and to be easily transported. The demonstrations may be presented at a level that can be tailored to any audience– from very young children to high school students planning careers in science. An ideal environment is a small classroom with 20-30 students where everyone can take part in the discussion. Once the chemicals are prepared, the collection of demonstrations takes about ten minutes to set-up, and one hour (or less) to perform. Very little is needed at the visiting site, no more than a table and a pitcher of water. A single electrical outlet is useful, but not essential. In Table 2 th
Storage Ring Probes of Dark Matter and Dark Energy
We show that proton storage ring experiments designed to search for proton
electric dipole moments can also be used to look for the nearly dc spin
precession induced by dark energy and ultra-light dark matter. These
experiments are sensitive to both axion-like and vector fields. Current
technology permits probes of these phenomena up to three orders of magnitude
beyond astrophysical limits. The relativistic boost of the protons in these
rings allows this scheme to have sensitivities comparable to atomic
co-magnetometer experiments that can also probe similar phenomena. These
complementary approaches can be used to extract the micro-physics of a signal,
allowing us to distinguish between pseudo-scalar, magnetic and electric dipole
moment interactions.Comment: 19 pages, 7 figure
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