5,289 research outputs found
Deciding logics of linear Kripke frames with scattered end pieces
We show that logics based on linear Kripke frames – with or without constant domains – that have a scattered end piece are not recursively enumerable.This is done by reduction to validity in all finite classical models
ICP polishing of silicon for high quality optical resonators on a chip
Miniature concave hollows, made by wet etching silicon through a circular
mask, can be used as mirror substrates for building optical micro-cavities on a
chip. In this paper we investigate how ICP polishing improves both shape and
roughness of the mirror substrates. We characterise the evolution of the
surfaces during the ICP polishing using white-light optical profilometry and
atomic force microscopy. A surface roughness of 1 nm is reached, which reduces
to 0.5 nm after coating with a high reflectivity dielectric. With such smooth
mirrors, the optical cavity finesse is now limited by the shape of the
underlying mirror
A Hard Medium Survey with ASCA. IV: the Radio-Loud Type 2 QSO AXJ0843+294 2
We discuss the X-ray, optical and radio properties of AX J0843+2942, a high
luminosity Type 2 AGN found in the ASCA Hard Serendipitous Survey. The X-ray
spectrum is best described by an absorbed power-law model with photon index of
Gamma = 1.72 (+0.3 -0.6) and intrinsic absorbing column density of NH = 1.44
(+0.33 -0.52) x 10E23 cm-2. The intrinsic luminosity in the 0.5-10 keV energy
band is ~ 3x10E45 erg s-1, well within the range of quasar luminosities. AX
J0843+2942, positionally coincident with the core of a triple and strong (S_1.4
GHz ~ 1 Jy; P_1.4 GHz ~ 9 x 10E33 erg s-1 Hz-1) radio source, is
spectroscopically identified with a Narrow Line object (intrinsic FWHM of all
the permitted emission lines <= 1200 km s-1) at z=0.398, having line features
and ratios typical of Seyfert-2 like objects. The high X-ray luminosity,
coupled with the high intrinsic absorption, the optical spectral properties and
the radio power, allow us to propose AX J0843+2942 as a Radio-Loud "Type 2
QSO". A discussion of the SED of this object is presented here together with a
comparison with the SED of Ultra Luminous Infrared Galaxies, other "Type 2 QSO"
candidates from the literature, and "normal" Radio-Quiet and Radio-Loud QSOs.Comment: 10 pages, 7 figures, Latex manuscript, Accepted for publication in
Ast ronomy and Astrophysic
Microfabricated high-finesse optical cavity with open access and small volume
We present a microfabricated optical cavity, which combines a very small mode volume with high finesse. In contrast to other micro-resonators, such as microspheres, the structure we have built gives atoms and molecules direct access to the high-intensity part of the field mode, enabling them to interact strongly with photons in the cavity for the purposes of detection and quantum-coherent manipulation. Light couples directly in and out of the resonator through an optical fiber, avoiding the need for sensitive coupling optics. This renders the cavity particularly attractive as a component of a lab-on-a-chip, and as a node in a quantum network
Methyl and T-Butyl Group Reorientation in Planar Aromatic Solids: Low-Frequency Nuclear Magnetic Resonance Relaxometry and X-Ray Diffraction
We have synthesized 3-t-butylchrysene and measured the Larmor frequency omega/2pi (= 8.50, 22.5, and 53.0 MHz) and temperature T (110-310 K) dependence of the proton spin-lattice relaxation rate R in the polycrystalline solid [low-frequency solid state nuclear magnetic resonance (NMR) relaxometry]. We have also determined the molecular and crystal structure in a single crystal of 3-t-butylchrysene using x-ray diffraction, which indicates the presence of a unique t-butyl group environment. The spin-1/2 protons relax as a result of the spin-spin dipolar interactions being modulated by the superimposed reorientation of the t-butyl groups and their constituent methyl groups. The reorientation is successfully modeled by the simplest motion; that of random hopping describable by Poisson statistics. The x-ray data indicate near mirror-plane symmetry that places one methyl group nearly in the aromatic plane and the other two almost equally above and below the plane. The NMR relaxometry data indicate that the nearly in-plane methyl group and the entire t-butyl group reorient with a barrier of 24.2 +/- 0.9 kJ mol(-1), and the two out-of-plane methyl groups reorient with a barrier of 14.2 +/- 0.6 kJ mol(-1). Following a brief review of methyl group rotation in simple ethyl-, and isopropyl-substituted one- and two-ring aromatic van der Waals molecular solids, the barriers for the out-of-plane methyl groups and the t-butyl group in 3-t-butylchrysene are compared with those barriers in three related molecular solids whose crystal structure is known: 4-methyl-2,6-di-t-butylphenol, 1,4-di-t-butylbenzene, and polymorph A of 2,6-di-t-butyl- naphthalene. A trend is observed in the reorientational barriers for the t-butyl and the out-of-plane methyl groups across this series of four compounds: as the t-butyl barriers decrease, the out-of-plane methyl barriers increase
A comprehensive analysis of the hard X-ray spectra of bright Seyfert galaxies
Hard X-ray spectra of 28 bright Seyfert galaxies observed with INTEGRAL were
analyzed together with the X-ray spectra from XMM-Newton, Suzaku and RXTE.
These broad-band data were fitted with a model assuming a thermal
Comptonization as a primary continuum component. We tested several model
options through a fitting of the Comptonized continuum accompanied by a complex
absorption and a Compton reflection. Both the large data set used and the model
space explored allowed us to accurately determine a mean temperature kTe of the
electron plasma, the Compton parameter y and the Compton reflection strength R
for the majority of objects in the sample. Our main finding is that a vast
majority of the sample (20 objects) is characterized by kTe < 100 keV, and only
for two objects we found kTe > 200 keV. The median kTe for entire sample is
48(-14,+57) keV. The distribution of the y parameter is bimodal, with a broad
component centered at ~0.8 and a narrow peak at ~1.1. A complex, dual absorber
model improved the fit for all data sets, compared to a simple absorption
model, reducing the fitted strength of Compton reflection by a factor of about
2. Modest reflection (median R ~0.32) together with a high ratio of Comptonized
to seed photon fluxes point towards a geometry with a compact hard X-ray
emitting region well separated from the accretion disc. Our results imply that
the template Seyferts spectra used in AGN population synthesis models should be
revised.Comment: 26 pages, 12 figures, accepted for publication in MNRA
In-flight calibration of the INTEGRAL/IBIS mask
Since the release of the INTEGRAL Offline Scientific Analysis (OSA) software
version 9.0, the ghost busters module has been introduced in the INTEGRAL/IBIS
imaging procedure, leading to an improvement of the sensitivity around bright
sources up to a factor of 7. This module excludes in the deconvolution process
the IBIS/ISGRI detector pixels corresponding to the projection of a bright
source through mask elements affected by some defects. These defects are most
likely associated with screws and glue fixing the IBIS mask to its support.
Following these major improvements introduced in OSA 9, a second order
correction is still required to further remove the residual noise, now at a
level of 0.2-1% of the brightest source in the field of view. In order to
improve our knowledge of the IBIS mask transparency, a calibration campaign has
been carried out during 2010-2012. We present here the analysis of these data,
together with archival observations of the Crab and Cyg X-1, that allowed us to
build a composite image of the mask defects and to investigate the origin of
the residual noise in the IBIS/ISGRI images. Thanks to this study, we were able
to point out a simple modification of the ISGRI analysis software that allows
to significantly improve the quality of the images in which bright sources are
detected at the edge of the field of view. Moreover, a refinement of the area
excluded by the ghost busters module is considered, and preliminary results
show improvements to be further tested. Finally, this study indicates further
directions to be investigated for improving the ISGRI sensitivity, such as
taking into account the thickness of the screws in the mask model or studying
the possible discrepancy between the modeled and actual mask element bridges.Comment: accepted for publication in the proceedings of "An INTEGRAL view of
the high-energy sky (the first 10 years)" 9th INTEGRAL Workshop, October
15-19, 2012, Paris, France, in Proceedings of Science (INTEGRAL 2012), Eds.
A. Goldwurm, F. Lebrun and C. Winkler,
(http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=176), id 154; 6 pages, 4
figures, see the PoS website for the full resolution versio
Sampling Distributions of Random Electromagnetic Fields in Mesoscopic or Dynamical Systems
We derive the sampling probability density function (pdf) of an ideal
localized random electromagnetic field, its amplitude and intensity in an
electromagnetic environment that is quasi-statically time-varying statistically
homogeneous or static statistically inhomogeneous. The results allow for the
estimation of field statistics and confidence intervals when a single spatial
or temporal stochastic process produces randomization of the field. Results for
both coherent and incoherent detection techniques are derived, for Cartesian,
planar and full-vectorial fields. We show that the functional form of the
sampling pdf depends on whether the random variable is dimensioned (e.g., the
sampled electric field proper) or is expressed in dimensionless standardized or
normalized form (e.g., the sampled electric field divided by its sampled
standard deviation). For dimensioned quantities, the electric field, its
amplitude and intensity exhibit different types of
Bessel sampling pdfs, which differ significantly from the asymptotic
Gauss normal and ensemble pdfs when is relatively
small. By contrast, for the corresponding standardized quantities, Student ,
Fisher-Snedecor and root- sampling pdfs are obtained that exhibit
heavier tails than comparable Bessel pdfs. Statistical uncertainties
obtained from classical small-sample theory for dimensionless quantities are
shown to be overestimated compared to dimensioned quantities. Differences in
the sampling pdfs arising from de-normalization versus de-standardization are
obtained.Comment: 12 pages, 15 figures, accepted for publication in Phys. Rev. E, minor
typos correcte
Influence of Habitat on Distribution and Abundance of the Eastern Woodrat in Kansas
Anthropogenic modification of native woodlands and grasslands in the Great Plains has altered the abundance and distribution of many species of mammals. To study habitat effects on the eastern woodrat (Neotoma floridana), we surveyed nests of the eastern woodrat in woodlands, grasslands, and croplands along 77 km of secondary roads in three counties in north-central Kansas. All nests were located in woodlands ( \u3c 2 %of habitat), although grasslands and croplands constituted 36% and 62% of habitat surveyed, respectively. In our survey, nests were associated positively with shelterbelts (3.6 nests per 100 m of road edge) but not with shrub patches (1.1 nests per 100 m of road edge) or riparian woodlands (0.3 nests per 100 m of road edge). Consequently, we specifically censused nests in an additional 12 riparian woodlands and 12 shelterbelts. Nests of eastern woodrats were less dense in riparian woodlands (9.4 nests/ha) than in shelterbelts (55.5 nests/ha). Density of woodrat nests decreased as width of a wooded area increased. Further, nests per 100 m of length of woodland did not increase as the width of woodland increased. These patterns suggest that woodland edge, not woodland interior, is the primary factor in abundance of eastern woodrats in this region. Although the eastern woodrat has previously been considered a woodland species, our results suggest that this assessment is incorrect. Our observations demonstrate that anthropogenic modification of the Great Plains, in the form of planted shelterbelts and expanded riparian woodland, likely has increased the distribution and abundance of eastern woodrats, compared to the mid-1800s
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