27,702 research outputs found
Long-range behavior of the optical potential for the elastic scattering of charged composite particles
The asymptotic behavior of the optical potential, describing elastic
scattering of a charged particle off a bound state of two charged, or
one charged and one neutral, particles at small momentum transfer
or equivalently at large intercluster distance
, is investigated within the framework of the exact three-body
theory. For the three-charged-particle Green function that occurs in the exact
expression for the optical potential, a recently derived expression, which is
appropriate for the asymptotic region under consideration, is used. We find
that for arbitrary values of the energy parameter the non-static part of the
optical potential behaves for as
. From this we derive for the
Fourier transform of its on-shell restriction for the behavior , i.e.,
dipole or quadrupole terms do not occur in the coordinate-space asymptotics.
This result corroborates the standard one, which is obtained by perturbative
methods. The general, energy-dependent expression for the dynamic
polarisability is derived; on the energy shell it reduces to the
conventional polarisability which is independent of the energy. We
emphasize that the present derivation is {\em non-perturbative}, i.e., it does
not make use of adiabatic or similar approximations, and is valid for energies
{\em below as well as above the three-body dissociation threshold}.Comment: 35 pages, no figures, revte
Changes in heart rate variability and QT variability during the first trimester of pregnancy
The risk of new-onset arrhythmia during pregnancy is high, presumably relating to changes in both haemodynamic and cardiac autonomic function. The ability to non-invasively assess an individual's risk of developing arrhythmia during pregnancy would therefore be clinically significant. We aimed to quantify electrocardiographic temporal characteristics during the first trimester of pregnancy and to compare these with non-pregnant controls.Ninety-nine pregnant women and sixty-three non-pregnant women underwent non-invasive cardiovascular and haemodynamic assessment during a protocol consisting of various physiological states (postural manoeurvres, light exercise and metronomic breathing). Variables measured included stroke volume, cardiac output, heart rate, heart rate variability, QT and QT variability and QTVI (a measure of the variability of QT relative to that of RR).Heart rate (p < 0.0005, p < 0.0005, p < 0.0005) and cardiac output (p = 0.043, p < 0.0005, p < 0.0005) were greater in pregnant women in all physiological states (respectively for the supine position, light exercise and metronomic breathing state), whilst stroke volume was lower in pregnancy only during the supine position (p < 0.0005). QTe (Q wave onset to T wave end) and QTa (T wave apex) were significantly shortened (p < 0.05) and QTeVI and QTaVI were increased in pregnancy in all physiological states (p < 0.0005). QT variability (p < 0.002) was greater in pregnant women during the supine position, whilst heart rate variability was reduced in pregnancy in all states (p < 0.0005).Early pregnancy is associated with substantial changes in heart rate variability, reflecting a reduction in parasympathetic tone and an increase in sympathetic activity. QTVI shifted to a less favourable value, reflecting a greater than normal amount of QT variability. QTVI appears to be a useful method for quantifying changes in QT variability relative to RR (or heart rate) variability, being sensitive not only to physiological state but also to gestational age. We support the use of non-invasive markers of cardiac electrical variability to evaluate the risk of arrhythmic events in pregnancy, and we recommend the use of multiple physiological states during the assessment protocol
On a stationary spinning string spacetime
The properties of a stationary massless string endowed with intrinsic spin
are discussed. The spacetime is Minkowskian geometrically but the topology is
nontrivial due to the horizon located on the surface , similar with
Rindler's case. For less than the Planck length , has the
same sign as and closed timelike curves are possible.
We assume an elementary particles' spin originates in the frame dragging
effect produced by the rotation of the source. The Sagnac time delay is
calculated and proves to be constant.Comment: revised version of hep-th/0602014 v1, 7 pages, title changed, sec.5
removed, talk given at "Recent Developments in Gravity" (NEB XII), Nafplio,
Greece, 29 June 200
SN1993J VLBI (I): The Center of the Explosion and a Limit on Anisotropic Expansion
Phase-referenced VLBI observations of supernova 1993J at 24 epochs, from 50
days after shock breakout to the present, allowed us to determine the
coordinates of the explosion center relative to the quasi-stationary core of
the host galaxy M81 with an accuracy of 45 micro-arcsec, and to determine the
nominal proper motion of the geometric center of the radio shell with an
accuracy of 9micro-arcsec/yr. The uncertainties correspond to 160 AU for the
position and 160 km/s for the proper motion at the distance of the source of
3.63 Mpc. After correcting for the expected galactic proper motion of the
supernova around the core of M81 using HI rotation curves, we obtain a peculiar
proper motion of the radio shell center of only 320 +/- 160 km/s to the south,
which limits any possible one-sided expansion of the shell. We also find that
the shell is highly circular, the outer contours in fact being circular to
within 3%. Combining our proper motion values with the degree of circular
symmetry, we find that the expansion of the shockfront from the explosion
center is isotropic to within 5.5% in the plane of the sky. This is a more
fundamental result on isotropic expansion than can be derived from the
circularity of the images alone. The brightness of the radio shell, however,
varies along the ridge and systematically changes with time. The degree of
isotropy in the expansion of the shockfront contrasts with the asymmetries and
polarization found in optical spectral lines. Asymmetric density distributions
in the ejecta or more likely in the circumstellar medium, are favored to
reconcile the radio and optical results. We see no sign of any disk-like
density distribution of the circumstellar material, with the average axis ratio
of the radio shell of SN1993J being less than 1.04.Comment: 21 pages, LaTex + 5 Figures (encapulsated PostScript), Accepted for
Publication in the Astrophysical Journa
Movement and Aggregation of Eastern Hudson Bay Beluga Whales (Delphinapterus leucas): A Comparison of Patterns Found through Satellite Telemetry and Nunavik Traditional Ecological Knowledge
Traditional Ecological Knowledge (TEK) consists of the collective knowledge, experience, and values of subsistence communities, while Western science relies on hypothesis testing to obtain information on natural processes. Both approaches provide important ecological information, but few studies have directly compared the two. We compared information on movements and aggregation of beluga whales obtained from TEK interview records (n = 3253) and satellite telemetry records of 30 whales tagged in eastern Hudson Bay, Canada, using geographic information system (GIS) approaches that allowed common formatting of the data sets. Estuarine centres of aggregation in the summer were evident in both data sets. The intensive use of offshore areas seen in the telemetry data, where 76% of the locations were more than 15 km from mainland Quebec, was not evident in the TEK data, where only 17% of the records indicated offshore locations. Morisitaâs index of similarity indicated that TEK and telemetry data distributions varied with season, with the highest similarity in winter (0.74). Location and movement data from the telemetry study were limited by small sample size and short tag deployment times, while TEK data were biased by spatial coverage and coastal travel habits. Although the two data sets can provide complementary information, both suffer from weaknesses that need to be acknowledged when these data are adapted for use in resource management.Les connaissances Ă©cologiques traditionnelles (CĂT) consistent en lâensemble des connaissances, de lâexpĂ©rience et des valeurs des communautĂ©s de subsistance, tandis que la science occidentale sâappuie sur la mise Ă lâĂ©preuve dâhypothĂšses dans le but dâobtenir de lâinformation sur les processus naturels. Bien que ces deux dĂ©marches permettent dâobtenir dâimportants renseignements sur lâĂ©cologie, peu dâĂ©tudes ont Ă©tabli une comparaison directe entre ces deux dĂ©marches. Nous avons comparĂ© des donnĂ©es sur les mouvements et le rassemblement des bĂ©lugas, donnĂ©es obtenues Ă partir de CĂT prĂ©levĂ©es au moyen dâentrevues (n = 3253) ainsi quâĂ partir de rĂ©sultats de tĂ©lĂ©mĂ©trie par satellite sur 30 baleines marquĂ©es dans lâest de la baie dâHudson, au Canada, Ă lâaide de systĂšmes dâinformation gĂ©ographique (SIG) qui ont permis le formatage commun des ensembles de donnĂ©es. Pendant lâĂ©tĂ©, les centres de rassemblement en estuaire Ă©taient Ă©vidents dans les deux ensembles de donnĂ©es. Lâutilisation intensive des zones au large en ce qui a trait aux donnĂ©es de tĂ©lĂ©mĂ©trie, oĂč 76 % des localisations se situaient Ă plus de 15 km du continent quĂ©bĂ©cois, nâĂ©tait pas Ă©vidente dans le cas des donnĂ©es des CĂT, oĂč seulement 17 % des rĂ©sultats indiquaient des localisations au large. Lâindice de similaritĂ© de Morisita indiquait que la rĂ©partition des donnĂ©es obtenues par CĂT et par tĂ©lĂ©mĂ©trie variait dâune saison Ă lâautre, la similaritĂ© la plus grande ayant Ă©tĂ© atteinte lâhiver (0,74). Les donnĂ©es de localisation et de mouvement dĂ©coulant de lâĂ©tude de tĂ©lĂ©mĂ©trie Ă©taient limitĂ©es par la petite taille de lâĂ©chantillon et les courtes durĂ©es de dĂ©ploiement des Ă©tiquettes, tandis que les donnĂ©es provenant des CĂT Ă©taient biaisĂ©es par lâespace Ă couvrir et les habitudes de dĂ©placement sur la cĂŽte. Bien que les deux ensembles de donnĂ©es puissent fournir de lâinformation complĂ©mentaire, tous deux possĂšdent des faiblesses quâil y a lieu de reconnaĂźtre lorsque ces donnĂ©es sont adaptĂ©es Ă des fins de gestion des ressources
Atom chip for BEC interferometry
We have fabricated and tested an atom chip that operates as a matter wave interferometer. In this communication we describe the fabrication of the chip by ion-beam milling of gold evaporated onto a silicon substrate. We present data on the quality of the wires, on the current density that can be reached in the wires and on the smoothness of the magnetic traps that are formed. We demonstrate the operation of the interferometer, showing that we can coherently split and recombine a BoseâEinstein condensate with good phase stability
Microlensing of Relativistic Knots in the Quasar HE1104-1805
We present 3 years of photometry of the ``Double Hamburger'' lensed quasar,
HE1104-1805, obtained on 102 separate nights using the OGLE 1.3-m telescope.
Both the A and B images show variations, but with substantial differences in
the lighcurves at all time delays. At the 310 day delay reported by Wisotzki
and collaborators the difference lightcurve has an rms amplitude of 0.060 mag.
The structure functions for the A and B images are quite different, with image
A more than twice as variable as image B (a factor of 4 in structure function)
on timescales of less than a month. Adopting microlensing as a working
hypothesis for the uncorrelated variability, the short timescale argues for the
relativistic motion of one or more components of the source. We argue that the
small amplitude of the fluctuations is due to the finite size of the source
with respect to the microlenses.Comment: As accepted for publication in ApJ. 22 pages. The discussion of
microlensing at high optical depth has been shortened and a few minor points
have been clarifie
Free Boundary Poisson Bracket Algebra in Ashtekar's Formalism
We consider the algebra of spatial diffeomorphisms and gauge transformations
in the canonical formalism of General Relativity in the Ashtekar and ADM
variables. Modifying the Poisson bracket by including surface terms in
accordance with our previous proposal allows us to consider all local
functionals as differentiable. We show that closure of the algebra under
consideration can be achieved by choosing surface terms in the expressions for
the generators prior to imposing any boundary conditions. An essential point is
that the Poisson structure in the Ashtekar formalism differs from the canonical
one by boundary terms.Comment: 19 pages, Latex, amsfonts.sty, amssymb.st
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