73,897 research outputs found
Detecting relic gravitational waves in the CMB: A statistical bias
Analyzing the imprint of relic gravitational waves (RGWs) on the cosmic
microwave background (CMB) power spectra provides a way to determine the signal
of RGWs. In this Letter, we discuss a statistical bias, which could exist in
the data analysis and has the tendency to overlook the RGWs. We also explain
why this bias exists, and how to avoid it.Comment: 4 pages, 1 figur
A New Kind of Uniformly Accelerated Reference Frames
A new kind of uniformly accelerated reference frames with a line-element
different from the M{\o}ller and Rindler ones is presented, in which every
observer at consts. has the same constant acceleration. The laws of
mechanics are checked in the new kind of frames. Its thermal property is
studied. The comparison with the M{\o}ller and Rindler uniform accelerated
reference frames is also made.Comment: 10 pages, 2 figures. to appear in Int. J. Mod. Phys.
CARS spectroscopy of the () band in
Molecular hydrogen is a benchmark system for bound state quantum calculation
and tests of quantum electrodynamical effects. While spectroscopic measurements
on the stable species have progressively improved over the years, high
resolution studies on the radioactive isotopologues , and
have been limited. Here we present an accurate determination of
transition energies in the fundamental vibrational
band of the ground electronic state, by means of high resolution Coherent
Anti-Stokes Raman Spectroscopy. With the present experimental uncertainty of
, which is a fivefold improvement over previous
measurements, agreement with the latest theoretical calculations is
demonstrated.Comment: 9 pages, 3 figure
Spectral properties, generation order parameters and luminosities for spin-powered X-ray pulsars
We show the spectral properties of 15 spin-powered X-ray pulsars, and the
correlation between the average power-law photon index and spin-down rate.
Generation order parameters (GOPs) based on polar-cap models are introduced to
characterize the X-ray pulsars. We calculate three definitions of generation
order parameters due to the different effects of magnetic and electric fields
on photon absorption during cascade processes, and study the relations between
the GOPs and spectral properties of X-ray pulsars. There exists a possible
correlation between the photon index and GOP in our pulsar sample. Furthermore,
we present a method due to the concept of GOPs to estimate the non-thermal
X-ray luminosity for spin-powered pulsars. Then X-ray luminosity is calculated
in the context of our polar-cap accelerator model which is well consistent with
the most observed X-ray pulsar data. The ratio between X-ray luminosity
estimated by our method and the pulsar's spin-down power is well consistent
with the feature.Comment: 20 pages, 8 figures, 1 table, revised version for the publication in
Ap
Effects of Neighboring Nectar-Producing Plants on Populations of Pest Lepidoptera and Their Parasitoids in Broccoli Plantings
Eggs and larvae of the imported cabbageworm, Pieris rapae, were much more abundant in broccoli interplanted with nectar-producing plants than in broccoli monoculture. More diamondback moth larvae, Plutella xylostella, occurred in broccoli interplanted with or adjacent to nectar-producing plants than in broccoli monoculture. Density of cabbage looper larvae, Trichoplusia ni, was similar among the three types of broccoli plantings. For Cotesia rubecula, established in Michigan after introduction from Yugoslavia, pupae were more numerous in broccoli interplanted with nectar-producing plants than in other plots. High parasitism rates of diamondback moth, mainly by Diadegma insulare, were observed in every plot, but there were no differences in parasitism of diamondback moth between the treatments. Results indicate that the interactions between pests, parasitoids and nectar-producing plants are complex and may be different for each species
Tidal Destruction of The First Dark Microhalos
We point out that the usual self-similarity in cold dark matter models is
broken by encounters with individual normal galactic stars on sub-pc scale.
Tidal heating and stripping must have redefined the density and velocity
structures of the population of the Earth-mass dark matter halos, which are
likely to have been the first bound structures to form in the Universe. The
disruption rate depends strongly on {\it galaxy types} and the orbital
distribution of the microhalos; in the Milky Way, stochastic radial orbits are
destroyed first by stars in the triaxial bulge, microhalos on non-planar
retrograde orbits with large pericenters and/or apocenters survive the longest.
The final microhalo distribution in the {\it solar neighborhood} is better
described as a superposition of filamentry microstreams rather than as a set of
discrete spherical clumps in an otherwise homogeneous medium. We discuss its
important consequences to our detections of microhalos by direct recoil signal
and indirect annihilation signal.Comment: 13 pages, 3 figures, Astrophysical Journal, accepte
Chemical composition of 90 F and G disk dwarfs
High resolution, high S/N spectra have been obtained for a sample of 90 F and
G main-sequence disk stars covering the metallicity range -1.0 < [Fe/H] < +0.1,
and have been analysed in a parallel way to the work of Edvardsson et al.
(1993). Effective temperatures are based on the Alonso et al. (1996)
calibration of color indices and surface gravities are calculated from
Hipparcos parallaxes, which also allow more accurate ages to be calculated. In
addition, more reliable kinematical parameters are derived from Hipparcos
distances and proper motions. Finally, a larger spectral coverage, 5600 - 8800
A, makes it possible to improve the abundance accuracy by studying more lines
and to discuss several elements not included in the work of Edvardsson et al.
The present paper provides the data and discusses some general results of the
abundance survey. A group of stars in the metallicity range of -1.0 < [Fe/H] <
-0.6 having a small mean Galactocentric distance in the stellar orbits, Rm < 7
kpc, are shown to be older than the other disk stars and probably belong to the
thick disk. Excluding these stars, a slight decreasing trend of [Fe/H] with
increasing Rm and age is found, but a large scatter in [Fe/H] (up to 0.5 dex)
is present at a given age and Rm. The derived trends of O, Mg, Si, Ca, Ti, Ni
and Ba as a function of [Fe/H] agree rather well with those of Edvardsson et
al., but the overabundance of Na and Al for metal-poor stars found in their
work is not confirmed. Furthermore, the Galactic evolution of elements not
included in Edvardsson et al., K, V and Cr, is studied.Comment: 16 pages with 10 figures. Accepted for publication in A&A
Spatial oscillations in the spontaneous emission rate of an atom inside a metallic wedge
A method of images is applied to study the spontaneous emission of an atom
inside a metallic wedge with an opening angle of , where N is an
arbitrary positive integer. We show the method of images gives a rate formula
consistent with that from Quantum Electrodynamics. Using the method of images,
we show the correspondence between the oscillations in the spontaneous emission
rate and the closed-orbits of emitted photon going away and returning to the
atom inside the wedge. The closed-orbits can be readily constructed using the
method of images and they are also extracted from the spontaneous emission
rate.Comment: 8 figure
Isospin breaking in scalar and pseudoscalar channels of radiative -decays
In the framework of simple assumption on factorizing a mixing of vector state
with isoscalar components in effective amplitudes of isospin breaking caused by
the electromagnetic quark current, a branching fraction of radiative transition is evaluated at the level of .Comment: 3 pages, revtex4 class, 2 eps-figures; reference, comment and
acknowledgement adde
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