10,766 research outputs found
Scattering of second sound waves by quantum vorticity
A new method of detection and measurement of quantum vorticity by scattering
second sound off quantized vortices in superfluid Helium is suggested.
Theoretical calculations of the relative amplitude of the scattered second
sound waves from a single quantum vortex, a vortex ring, and bulk vorticity are
presented. The relevant estimates show that an experimental verification of the
method is feasible. Moreover, it can even be used for the detection of a single
quantum vortex.Comment: Latex file, 9 page
GRANAT/WATCH catalogue of cosmic gamma-ray bursts: December 1989 to September 1994
We present the catalogue of gamma-ray bursts observed with the WATCH all-sky
monitor on board the GRANAT satellite during the period December 1989 to
September 1994. The cosmic origin of 95 bursts comprising the catalogue is
confirmed either by their localization with WATCH or by their detection with
other GRB experiments. For each burst its time history and information on its
intensity in the two energy ranges 8-20 keV and 20-60 keV are presented. Most
events show hardening of the energy spectrum near the burst peak. In part of
the bursts an X-ray precursor or a tail is seen at 8-20 keV. We have determined
the celestial positions of the sources of 47 bursts. Their localization regions
(at 3-sigma confidence level) are equivalent in area to circles with radii
ranging from 0.2 to 1.6 deg. The burst sources appear isotropically distributed
on the sky on large angular scales.Comment: 18 pages (including 3 tables and 7 figures), LaTeX, l-aa style.
Accepted by Astronomy and Astrophysics Suppl. Serie
Scattering of dislocated wavefronts by vertical vorticity and the Aharonov-Bohm effect II: Dispersive waves
Previous results on the scattering of surface waves by vertical vorticity on
shallow water are generalized to the case of dispersive water waves. Dispersion
effects are treated perturbatively around the shallow water limit, to first
order in the ratio of depth to wavelength. The dislocation of the incident
wavefront, analogous to the Aharonov-Bohm effect, is still observed. At short
wavelengths the scattering is qualitatively similar to the nondispersive case.
At moderate wavelengths, however, there are two markedly different scattering
regimes according to wether the capillary length is smaller or larger than
times depth. The dislocation is characterized by a parameter that
depends both on phase and group velocity. The validity range of the calculation
is the same as in the shallow water case: wavelengths small compared to vortex
radius, and low Mach number. The implications of these limitations are
carefully considered.Comment: 30 pages, 11 figure
Financial conservatism, firm value and international business risk: Evidence from emerging economies around the global financial crisis
The increase in debt-free or under-levered firms (financial conservatism) is one of the most recent stylized puzzles that cannot be explained within the context of extant capital structure theories. In this paper, we exploit the 2008â09 contractions in credit supply in a quasi-natural experiment to examine whether financial conservatism affects firm value. Using a large sample of firms from seven African countries over the period 2003â2012, we find strong evidence that financial conservatism mitigates the adverse effect of contractions in credit supply on firm value for both local and international firms. Our results suggest that financial conservatism is an effective strategy for managing risks arising from contractions in credit supply and international business exposure. These findings provide novel empirical evidence on the value relevance of financial conservatism which shields firms from the adverse and far-reaching effects of contractions in credit supply
Elevated cerebral spinal fluid biomarkers in children with mucopolysaccharidosis I-H.
Mucopolysaccharidosis (MPS) type-IH is a lysosomal storage disease that results from mutations in the IDUA gene causing the accumulation of glycosaminoglycans (GAGs). Historically, children with the severe phenotype, MPS-IH (Hurler syndrome) develop progressive neurodegeneration with death in the first decade due to cardio-pulmonary complications. New data suggest that inflammation may play a role in MPS pathophysiology. To date there is almost no information on the pathophysiologic changes within the cerebral spinal fluid (CSF) of these patients. We evaluated the CSF of 25 consecutive patients with MPS-IH. While CSF glucose and total protein were within the normal range, we found a significantly mean elevated CSF opening pressure at 24âcm H2O (range 14-37âcm H2O). We observed a 3-fold elevation in CSF heparan sulfate and a 3-8 fold increase in MPS-IH specific non-reducing ends, I0S0 and I0S6. Cytokine analyses in CSF of children with MPS-IH showed significantly elevated inflammatory markers including: MCP-1 SDF-1a, IL-Ra, MIP-1b, IL-8, and VEGF in comparison to unaffected children. This is the largest report of CSF characteristics in children with MPS-IH. Identification of key biomarkers may provide further insight into the inflammatory-mediated mechanisms related to MPS diseases and perhaps lead to improved targeted therapies
Systematic trends in beta-delayed particle emitting nuclei: The case of beta-p-alpha emission from 21Mg
We have observed beta+-delayed alpha and p-alpha emission from the
proton-rich nucleus 21Mg produced at the ISOLDE facility at CERN. The
assignments were cross-checked with a time distribution analysis. This is the
third identified case of beta-p-alpha emission. We discuss the systematic of
beta-delayed particle emission decays, show that our observed decays fit
naturally into the existing pattern, and argue that the patterns are to a large
extent caused by odd-even effects.Comment: 6 pages, 5 figure
Elastic forces that do no work and the dynamics of fast cracks
Elastic singularities such as crack tips, when in motion through a medium
that is itself vibrating, are subject to forces orthogonal to the direction of
motion and thus impossible to determine by energy considerations alone. This
fact is used to propose a universal scenario, in which three dimensionality is
essential, for the dynamic instability of fast cracks in thin brittle
materials.Comment: 8 pages Latex, 1 Postscript figur
Evidence for 1122 Hz X-Ray Burst Oscillations from the Neutron-Star X-Ray Transient XTE J1739-285
We report on millisecond variability from the X-ray transient XTE J1739-285.
We detected six X-ray type I bursts and found evidence for oscillations at 1122
+/- 0.3 Hz in the brightest X-ray burst. Taking into consideration the power in
the oscillations and the number of trials in the search, the detection is
significant at the 99.96% confidence level. If the oscillations are confirmed,
the oscillation frequency would suggest that XTE J1739-285 contains the fastest
rotating neutron star yet found. We also found millisecond quasiperiodic
oscillations in the persistent emission with frequencies ranging from 757 Hz to
862 Hz. Using the brightest burst, we derive an upper limit on the source
distance of about 10.6 kpc.Comment: To appear in ApJL, 4 page
The complex Sine-Gordon equation as a symmetry flow of the AKNS Hierarchy
It is shown how the complex sine-Gordon equation arises as a symmetry flow of
the AKNS hierarchy. The AKNS hierarchy is extended by the ``negative'' symmetry
flows forming the Borel loop algebra. The complex sine-Gordon and the vector
Nonlinear Schrodinger equations appear as lowest negative and second positive
flows within the extended hierarchy. This is fully analogous to the well-known
connection between the sine-Gordon and mKdV equations within the extended mKdV
hierarchy.
A general formalism for a Toda-like symmetry occupying the ``negative''
sector of sl(N) constrained KP hierarchy and giving rise to the negative Borel
sl(N) loop algebra is indicated.Comment: 8 pages, LaTeX, typos corrected, references update
MOBSTER â III. HDâ62658: a magnetic Bp star in an eclipsing binary with a non-magnetic âidentical twinâ
HDâ62658 (B9pâV) is a little-studied chemically peculiar star. Light curves obtained by the Kilodegree Extremely Little Telescope (KELT) and Transiting Exoplanet Survey Satellite (TESS) show clear eclipses with a period of about 4.75 d, as well as out-of-eclipse brightness modulation with the same 4.75 d period, consistent with synchronized rotational modulation of surface chemical spots. High-resolution ESPaDOnS circular spectropolarimetry shows a clear Zeeman signature in the line profile of the primary; there is no indication of a magnetic field in the secondary. PHOEBE modelling of the light curve and radial velocities indicates that the two components have almost identical masses of about 3 M_â. The primaryâs longitudinal magnetic fieldâ©B_zâȘ varies between about +100 and â250 G, suggesting a surface magnetic dipole strength B_d = 850 G. Bayesian analysis of the Stokes V profiles indicates B_d = 650 G for the primary and B_d < 110 G for the secondary. The primaryâs line profiles are highly variable, consistent with the hypothesis that the out-of-eclipse brightness modulation is a consequence of rotational modulation of that starâs chemical spots. We also detect a residual signal in the light curve after removal of the orbital and rotational modulations, which might be pulsational in origin; this could be consistent with the weak line profile variability of the secondary. This system represents an excellent opportunity to examine the consequences of magnetic fields for stellar structure via comparison of two stars that are essentially identical with the exception that one is magnetic. The existence of such a system furthermore suggests that purely environmental explanations for the origin of fossil magnetic fields are incomplete
- âŠ