23,170 research outputs found
Lightning mapping system
A Lightning Detection and Ranging (LDAR) System is being implemented at KSC in Florida. The first operational use is expected in the late summer of 1991. The system is designed to map the location of in-cloud and cloud-to-ground lightning based on the time of arrival (TOA) of electromagnetic radiation. The system detects very high frequency (VHF) radiation and designed to map the volumetric extent of lightning. The system implements two independent antenna arrays to provide a fast data quality check, as necessary for a real-time warning system. The system performance goals and a comparison with a similar system implemented in the mid-1970's is made
The Effects of Weak Spatiotemporal Noise on a Bistable One-Dimensional System
We treat analytically a model that captures several features of the
phenomenon of spatially inhomogeneous reversal of an order parameter. The model
is a classical Ginzburg-Landau field theory restricted to a bounded
one-dimensional spatial domain, perturbed by weak spatiotemporal noise having a
flat power spectrum in time and space. Our analysis extends the Kramers theory
of noise-induced transitions to the case when the system acted on by the noise
has nonzero spatial extent, and the noise itself is spatially dependent. By
extending the Langer-Coleman theory of the noise-induced decay of a metastable
state, we determine the dependence of the activation barrier and the Kramers
reversal rate prefactor on the size of the spatial domain. As this is increased
from zero and passes through a certain critical value, a transition between
activation regimes occurs, at which the rate prefactor diverges. Beyond the
transition, reversal preferentially takes place in a spatially inhomogeneous
rather than in a homogeneous way. Transitions of this sort were not discovered
by Langer or Coleman, since they treated only the infinite-volume limit. Our
analysis uses higher transcendental functions to handle the case of finite
volume. Similar transitions between activation regimes should occur in other
models of metastable systems with nonzero spatial extent, perturbed by weak
noise, as the size of the spatial domain is varied.Comment: 16 page
Charge transfer statistics of a molecular quantum dot with strong electron-phonon interaction
We analyze the nonequilibrium transport properties of a quantum dot with a
harmonic degree of freedom (Holstein phonon) coupled to metallic leads, and
derive its full counting statistics (FCS). Using the Lang-Firsov (polaron)
transformation, we construct a diagrammatic scheme to calculate the cumulant
generating function. The electron-phonon interaction is taken into account
exactly, and the employed approximation represents a summation of a diagram
subset with respect to the tunneling amplitude. By comparison to Monte Carlo
data the formalism is shown to capture the basic properties of the strong
coupling regime
Daily activities and survival at older ages
This study tested the hypothesis that time spent on regenerative (e.g., resting), productive (e.g., housework), and consumptive activities (e.g., meeting friends) is associated with survival in persons aged 70 and older. An observational study with semi-annual mortality follow-ups was carried out in the former West Berlin, Germany. The sample was stratified by age and sex and consisted of 473 persons aged 70 to 103 years. Study participants lived in the community as well as in institutions. Activity measures were assessed in 1990-1993 by structured interviews in the participants´ homes. Cox regression was used to model survival from time of interview. The main outcome measure was survival on 3 February 2000. Consumptive activities were related to survival (relative risk = 0.76, 95% confidence interval 0.58 to 1.00) after several confounding factors were controlled for. There were indications that the greatest survival benefit is achieved with a medium amount of time devoted to consumptive activities. Our results support the idea that daily activities are linked to survival via a psychosocial pathway, which might involve perceived quality of life. Consumptive activities (e.g., meeting friends, reading a novel) may contribute considerably to maintaining health and achieving longevity, because they are performed on a daily basis and their effects may accumulate over the life course.
Cluster induced quenching of galaxies in the massive cluster XMMXCSJ2215.9-1738 at z~1.5 traced by enhanced metallicities inside half R200
(Abridged) We explore the massive cluster XMMXCSJ2215.9-1738 at z~1.5 with
KMOS spectroscopy of Halpha and [NII] covering a region that corresponds to
about one virial radius. Using published spectroscopic redshifts of 108
galaxies in and around the cluster we computed the location of galaxies in the
projected velocity vs. position phase-space to separate our cluster sample into
a virialized region of objects accreted longer ago (roughly inside half R200)
and a region of infalling galaxies. We measured oxygen abundances for ten
cluster galaxies with detected [NII] lines in the individual galaxy spectra and
compared the MZR of the galaxies inside half R200 with the infalling galaxies
and a field sample at similar redshifts. We find that the oxygen abundances of
individual z~1.5 star-forming cluster galaxies inside half R200 are comparable,
at the respective stellar mass, to the higher local SDSS metallicity values. We
find that the [NII]/Halpha line ratios inside half R200 are higher by 0.2 dex
and that the resultant metallicities of the galaxies in the inner part of the
cluster are higher by about 0.1 dex, at a given mass, than the metallicities of
infalling galaxies and of field galaxies at z~1.5. The enhanced metallicities
of cluster galaxies at z~1.5 inside half R200 indicate that the density of the
ICM in this massive cluster becomes high enough toward the cluster center such
that the ram pressure exceeds the restoring pressure of the hot gas reservoir
of cluster galaxies. This can remove the gas reservoir initiating quenching;
although the galaxies continue to form stars, albeit at slightly lower rates,
using the available cold gas in the disk which is not stripped.Comment: Accepted for publication in A&
Electromagnetic energy transport along arrays of closely spaced metal rods as an analogue to plasmonic devices
The transport of electromagnetic energy along structures consisting of arrays of closely spaced metal rods (spacing = 0.2 cm) was investigated in the microwave regime at 8.0 GHz (lambda= 3.7 cm). The dispersion relation shows that information transport occurs at a group velocity of 0.6c. The electromagnetic energy is highly confined to the arrays (90% within a distance of 0.05lambda from the array). The propagation loss in a straight array is 3 dB/8 cm. Routing of energy around 90° corners is possible with a power loss of 3–4 dB. Analogies to plasmon wires consisting of arrays of nm-size metal clusters are discussed
Noise-Activated Escape from a Sloshing Potential Well
We treat the noise-activated escape from a one-dimensional potential well of
an overdamped particle, to which a periodic force of fixed frequency is
applied. We determine the boundary layer behavior, and the physically relevant
length scales, near the oscillating well top. We show how stochastic behavior
near the well top generalizes the behavior first determined by Kramers, in the
case without forcing. Both the case when the forcing dies away in the weak
noise limit, and the case when it does not, are examined. We also discuss the
relevance of various scaling regimes to recent optical trap experiments.Comment: 9 pages, no figures, REVTeX, expanded versio
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