3,672 research outputs found
Use of microwave satellite data to study variations in rainfall over the Indian Ocean
The University of Wisconsin Space Science and Engineering Center mapped rainfall over the Indian Ocean using a newly developed Scanning Multichannel Microwave Radiometer (SMMR) rain-retrieval algorithm. The short-range objective was to characterize the distribution and variability of Indian Ocean rainfall on seasonal and annual scales. In the long-range, the objective is to clarify differences between land and marine regimes of monsoon rain. Researchers developed a semi-empirical algorithm for retrieving Indian Ocean rainfall. Tools for this development have come from radiative transfer and cloud liquid water models. Where possible, ground truth information from available radars was used in development and testing. SMMR rainfalls were also compared with Indian Ocean gauge rainfalls. Final Indian Ocean maps were produced for months, seasons, and years and interpreted in terms of historical analysis over the sub-continent
The Differential Impact of a Basic Public Speaking Course on Perceived Communication Competencies in Class, Work, and Social Contexts
Communication departments generally choose between a public speaking and a hybrid course of their basic course. Previous research has shown that students\u27 perceptions of their communication competencies increase after completing a hybrid course (Ford & Wolvin, 1992, 1993). After noting similarities between public speaking and hybrid courses, this study examines students\u27 perceptions of their competencies after completing a public a speaking course.
Results indicated that students\u27 perceptions of their competencies changed significantly in class, work, and social contacts in such areas as public speaking, interpersonal and group communication, interviewing, listening, and self-confidence. The largest gains were in perceptions of their classroom competencies
Interpolating between the Bose-Einstein and the Fermi-Dirac distributions in odd dimensions
We consider the response of a uniformly accelerated monopole detector that is
coupled to a superposition of an odd and an even power of a quantized, massless
scalar field in flat spacetime in arbitrary dimensions. We show that, when the
field is assumed to be in the Minkowski vacuum, the response of the detector is
characterized by a Bose-Einstein factor in even spacetime dimensions, whereas a
Bose-Einstein as well as a Fermi-Dirac factor appear in the detector response
when the dimension of spacetime is odd. Moreover, we find that, it is possible
to interpolate between the Bose-Einstein and the Fermi-Dirac distributions in
odd spacetime dimensions by suitably adjusting the relative strengths of the
detector's coupling to the odd and the even powers of the scalar field. We
point out that the response of the detector is always thermal and we, finally,
close by stressing the apparent nature of the appearance of the Fermi-Dirac
factor in the detector response.Comment: RevTeX, 7 page
Response of finite-time particle detectors in non-inertial frames and curved spacetime
The response of the Unruh-DeWitt type monopole detectors which were coupled
to the quantum field only for a finite proper time interval is studied for
inertial and accelerated trajectories, in the Minkowski vacuum in (3+1)
dimensions. Such a detector will respond even while on an inertial trajctory
due to the transient effects. Further the response will also depend on the
manner in which the detector is switched on and off. We consider the response
in the case of smooth as well as abrupt switching of the detector. The former
case is achieved with the aid of smooth window functions whose width, ,
determines the effective time scale for which the detector is coupled to the
field. We obtain a general formula for the response of the detector when a
window function is specified, and work out the response in detail for the case
of gaussian and exponential window functions. A detailed discussion of both and limits are given and several
subtlities in the limiting procedure are clarified. The analysis is extended
for detector responses in Schwarzschild and de-Sitter spacetimes in (1+1)
dimensions.Comment: 29 pages, normal TeX, figures appended as postscript file, IUCAA
Preprint # 23/9
Massive Dirac particles on the background of charged de-Sitter black hole manifolds
We consider the behavior of massive Dirac fields on the background of a
charged de-Sitter black hole. All black hole geometries are taken into account,
including the Reissner-Nordstr\"{o}m-de-Sitter one, the Nariai case and the
ultracold case. Our focus is at first on the existence of bound quantum
mechanical states for the Dirac Hamiltonian on the given backgrounds. In this
respect, we show that in all cases no bound state is allowed, which amounts
also to the non-existence of normalizable time-periodic solutions of the Dirac
equation. This quantum result is in contrast to classical physics, and it is
shown to hold true even for extremal cases. Furthermore, we shift our attention
on the very interesting problem of the quantum discharge of the black holes.
Following Damour-Deruelle-Ruffini approach, we show that the existence of
level-crossing between positive and negative continuous energy states is a
signal of the quantum instability leading to the discharge of the black hole,
and in the cases of the Nariai geometry and of the ultracold geometries we also
calculate in WKB approximation the transmission coefficient related to the
discharge process.Comment: 19 pages, 11 figures. Macro package: Revtex4. Changes concern mainly
the introduction and the final discussion in section VI; moreover, Appendix D
on the evaluation of the Nariai transmission integral has been added.
References adde
Cavity method for quantum spin glasses on the Bethe lattice
We propose a generalization of the cavity method to quantum spin glasses on
fixed connectivity lattices. Our work is motivated by the recent refinements of
the classical technique and its potential application to quantum computational
problems. We numerically solve for the phase structure of a connectivity
transverse field Ising model on a Bethe lattice with couplings, and
investigate the distribution of various classical and quantum observables.Comment: 27 pages, 9 figure
Exploring the nature of the unidentified VHE gamma-ray source HESS J1507-622
The nature of the first unidentified VHE gamma-ray source with significant
angular offset from the Galactic plane of 3.5 degrees, HESS J1507-622, is
explored. Fermi-LAT data in the high-energy (HE, 100 MeV < E < 100 GeV)
gamma-ray range collected over 34 month are used to describe the spectral
energy distribution (SED) of the source. HESS J1507-622 is detected in the
Fermi energy range and its spectrum is best described by a power law in energy
with Gamma=1.7 +/- 0.1 stat +/- 0.2_sys and integral flux between (0.3-300) GeV
of F = (2.0 +/-0.5_stat +/- 1.0_sys) x 10^-9 cm^-2 s^-1. With the available
data it is not possible to discriminate between a hadronic and a leptonic
scenario for HESS J1507-622. The location and compactness of the source
indicate a considerable physical offset from the Galactic plane for this
object. In case of a multiple-kpc distance, this challenges a pulsar wind
nebula (PWN) origin for HESS J1507-622 since the time of travel for a pulsar
born in the Galactic disk to reach such a location would exceed the inverse
Compton (IC) cooling time of electrons that are energetic enough to produce VHE
gamma-rays. However, an origin of this gamma-ray source connected to a pulsar
that was born off the Galactic plane in the explosion of a hypervelocity star
cannot be excluded. The nature of HESS J1507-622 is still unknown to date, and
a PWN scenario cannot be ruled out in general. On the contrary HESS J1507-622
could be the first discovered representative of a population of spatially
extended VHE gamma-ray emitters with HE gamma-ray counterpart that are located
at considerable offsets from the Galactic plane. Future surveys in the VHE
gamma-ray range are necessary to probe the presence or absence of such a source
population.(abridged)Comment: accepted for publication in A&A, 7 pages, 3 figure
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