17,026 research outputs found
FIR Filter Implementation by Efficient Sharing of Horizontal and Vertical Common Sub-expressions
No abstract availabl
Piezoelectric and optical setup to measure an electrical field: Application to the longitudinal near-field generated by a tapered coax
We propose a new setup to measure an electrical field in one direction. This
setup is made of a piezoelectric sintered lead zinconate titanate film and an
optical interferometric probe. We used this setup to investigate how the shape
of the extremity of a coaxial cable influences the longitudinal electrical
near-field generated by it. For this application, we designed our setup to have
a spatial resolution of 100 um in the direction of the electrical field.
Simulations and experiments are presented
Transmission of hand, foot and mouth disease and its potential driving factors in Hong Kong
published_or_final_versio
Differential Forms and Wave Equations for General Relativity
Recently, Choquet-Bruhat and York and Abrahams, Anderson, Choquet-Bruhat, and
York (AACY) have cast the 3+1 evolution equations of general relativity in
gauge-covariant and causal ``first-order symmetric hyperbolic form,'' thereby
cleanly separating physical from gauge degrees of freedom in the Cauchy problem
for general relativity. A key ingredient in their construction is a certain
wave equation which governs the light-speed propagation of the extrinsic
curvature tensor. Along a similar line, we construct a related wave equation
which, as the key equation in a system, describes vacuum general relativity.
Whereas the approach of AACY is based on tensor-index methods, the present
formulation is written solely in the language of differential forms. Our
approach starts with Sparling's tetrad-dependent differential forms, and our
wave equation governs the propagation of Sparling's 2-form, which in the
``time-gauge'' is built linearly from the ``extrinsic curvature 1-form.'' The
tensor-index version of our wave equation describes the propagation of (what is
essentially) the Arnowitt-Deser-Misner gravitational momentum.Comment: REVTeX, 26 pages, no figures, 1 macr
Slow spin relaxation in a highly polarized cooperative paramagnet
We report measurements of the ac susceptibility of the cooperative paramagnet
Tb2Ti2O7 in a strong magnetic field. Our data show the expected saturation
maximum in chi(T) and also an unexpected low frequency dependence (< 1 Hz) of
this peak, suggesting very slow spin relaxations are occurring. Measurements on
samples diluted with nonmagnetic Y3+ or Lu3+ and complementary measurements on
pure and diluted Dy2Ti2O7 strongly suggest that the relaxation is associated
with dipolar spin correlations, representing unusual cooperative behavior in a
paramagnetic system.Comment: Accepted for publication in Physical Review Letter
Helical Tubes in Crowded Environments
When placed in a crowded environment, a semi-flexible tube is forced to fold
so as to make a more compact shape. One compact shape that often arises in
nature is the tight helix, especially when the tube thickness is of comparable
size to the tube length. In this paper we use an excluded volume effect to
model the effects of crowding. This gives us a measure of compactness for
configurations of the tube, which we use to look at structures of the
semi-flexible tube that minimize the excluded volume. We focus most of our
attention on the helix and which helical geometries are most compact. We found
that helices of specific pitch to radius ratio 2.512 to be optimally compact.
This is the same geometry that minimizes the global curvature of the curve
defining the tube. We further investigate the effects of adding a bending
energy or multiple tubes to begin to explore the more complete space of
possible geometries a tube could form.Comment: 10 page
Brown-York Energy and Radial Geodesics
We compare the Brown-York (BY) and the standard Misner-Sharp (MS) quasilocal
energies for round spheres in spherically symmetric space-times from the point
of view of radial geodesics. In particular, we show that the relation between
the BY and MS energies is precisely analogous to that between the
(relativistic) energy E of a geodesic and the effective (Newtonian) energy
E_{eff} appearing in the geodesic equation, thus shedding some light on the
relation between the two. Moreover, for Schwarzschild-like metrics we establish
a general relationship between the BY energy and the geodesic effective
potential which explains and generalises the recently observed connection
between negative BY energy and the repulsive behaviour of geodesics in the
Reissner-Nordstrom metric. We also comment on the extension of this connection
between geodesics and the quasilocal BY energy to regions inside a horizon.Comment: v3: 7 pages, shortened and revised version to appear in CQ
A randomised controlled study on the rehabilitation of rheumatoid arthrits patients with the use of psychological and occupational therapy
published_or_final_versio
Contextual CMA-ES
Many stochastic search algorithms are designed to optimize a fixed objective function to learn a task, i.e., if the objective function changes slightly, for example, due to a change in the situation or context of the task, relearning is required to adapt to the new context. For instance, if we want to learn a kicking movement for a soccer robot, we have to relearn the movement for different ball locations. Such relearning is undesired as it is highly inefficient and many applications require a fast adaptation to a new context/situation. Therefore, we investigate contextual stochastic search algorithms
that can learn multiple, similar tasks simultaneously. Current contextual stochastic search methods are based on policy search algorithms and suffer from premature convergence and the need for parameter tuning. In this paper, we extend the well known CMA-ES algorithm to the contextual setting and illustrate its performance on several contextual
tasks. Our new algorithm, called contextual CMAES, leverages from contextual learning while it preserves all the features of standard CMA-ES such as stability, avoidance of premature convergence, step size control and a minimal amount of parameter tuning
- …