7,965 research outputs found
The relationship between noise and annoyance around Orly
The extent to which annoyance estimated by an isopsophic index is a good forecaster for annoyance perceived near airport approaches was investigated. An index of sensed annoyance is constructed, and the relationship between the annoyance index and the isopsophic index is studied
The Be/X-ray Transient V0332+53: Evidence for a tilt between the orbit and the equatorial plane?
We present optical and infrared observations of BQ Cam, the optical
counterpart to the Be/X-ray transient system V0332+53. BQ Cam is shown to be an
O8-9Ve star, which places V0332+53 at a distance of ~7 kpc. H-alpha
spectroscopy and infrared photometry are used to discuss the evolution of the
circumstellar envelope. Due to the low inclination of the system, parameters
are strongly constrained. We find strong evidence for a tilt of the orbital
plane with respect to the circumstellar disc (pressumably on the equatorial
plane). Even though the periastron distance is only ~ 10 R_*, during the
present quiescent state the circumstellar disc does not extend to the distance
of periastron passage. Under these conditions, X-ray emission is effectively
prevented by centrifugal inhibition of accretion. The circumstellar disc is
shown to be optically dense at optical and infrared wavelengths, which together
with its small size, is taken as an indication of tidal truncation.Comment: 9 pages, 3 figures, uses mn.sty and epsfig Accepted for publication
in MNRA
Vortex spectrum in superfluid turbulence: interpretation of a recent experiment
We discuss a recent experiment in which the spectrum of the vortex line
density fluctuations has been measured in superfluid turbulence. The observed
frequency dependence of the spectrum, , disagrees with classical
vorticity spectra if, following the literature, the vortex line density is
interpreted as a measure of the vorticity or enstrophy. We argue that the
disagrement is solved if the vortex line density field is decomposed into a
polarised field (which carries most of the energy) and an isotropic field
(which is responsible for the spectrum).Comment: Submitted for publication
http://crtbt.grenoble.cnrs.fr/helio/GROUP/infa.html
http://www.mas.ncl.ac.uk/~ncfb
Quantum turbulence at finite temperature: the two-fluids cascade
To model isotropic homogeneous quantum turbulence in superfluid helium, we
have performed Direct Numerical Simulations (DNS) of two fluids (the normal
fluid and the superfluid) coupled by mutual friction. We have found evidence of
strong locking of superfluid and normal fluid along the turbulent cascade, from
the large scale structures where only one fluid is forced down to the vorticity
structures at small scales. We have determined the residual slip velocity
between the two fluids, and, for each fluid, the relative balance of inertial,
viscous and friction forces along the scales. Our calculations show that the
classical relation between energy injection and dissipation scale is not valid
in quantum turbulence, but we have been able to derive a temperature--dependent
superfluid analogous relation. Finally, we discuss our DNS results in terms of
the current understanding of quantum turbulence, including the value of the
effective kinematic viscosity
The X-ray Transient XTE J2012+381
We present optical and infrared observations of the soft X-ray transient
(SXT) XTE J2012+381 and identify the optical counterpart with a faint red star
heavily blended with a brighter foreground star. The fainter star is coincident
with the radio counterpart and appears to show weak H alpha emission and to
have faded between observations. The RXTE/ASM lightcurve of XTE J2012+381 is
unusual for an SXT in that after an extended linear decay, it settled into a
plateau state for about 40 days before undergoing a weak mini-outburst. We
discuss the nature of the object and suggest similarities to long orbital
period SXTs.Comment: 5 pages, 7 postscript figures included, uses mn.sty. Accepted for
publication in MNRA
Vortex density spectrum of quantum turbulence
The fluctuations of the vortex density in a turbulent quantum fluid are
deduced from local second-sound attenuation measurements. These measurements
are performed with a micromachined open-cavity resonator inserted across a flow
of turbulent He-II near 1.6 K. The power spectrum of the measured vortex line
density is compatible with a (-5/3) power law. The physical interpretation,
still open, is discussed.Comment: Submitted to Europhys. Let
Induced fission of 240Pu
We study the fission dynamics of 240Pu within an implementation of the
Density Functional Theory (DFT) extended to superfluid systems and real-time
dynamics. We demonstrate the critical role played by the pairing correlations.
The evolution is found to be much slower than previously expected in this fully
non-adiabatic treatment of nuclear dynamics, where there are no symmetry
restrictions and all collective degrees of freedom (CDOF) are allowed to
participate in the dynamics.Comment: 8 pages, 4 figures, talk given at The 6th International Conference on
Fission and Properties of Neutron-Rich Nuclei, Sanibel Island, Florida,
November 6-2 (2016
High mass X-ray binaries in the NIRorbital solutions of two highly obscured systems
The maximum mass of a neutron star (NS) is poorly defined. Theoretical
attempts to define this mass have thus far been unsuccessful. Observational
results currently provide the only means of narrowing this mass range down.
Eclipsing X-ray binary (XRB) pulsar systems are the only interacting binaries
in which the mass of the NS may be measured directly. Only 10 such systems are
known to exist, 6 of which have yielded NS masses in the range 1.06 - 1.86
M.We present the first orbital solutions of two further eclipsing
systems, OAO 1657-415 and EXO 1722-363, whose donor stars have only recently
been identified. Using observations obtained using the VLT/ISAAC NIR
spectrograph, our initial work was concerned with providing an accurate
spectral classification of the two counterpart stars, leading to a consistent
explanation of the mechanism for spin period evolution of OAO 1657-415.
Calculating radial velocities allowed orbital solutions for both systems to be
computed. These are the first accurate determinations of the NS and counterpart
masses in XRB pulsar systems to be made employing NIR spectroscopy.Comment: 5 pages, 3 figures, contribution to the proceedings of "The
multi-wavelength view of hot, massive stars", 39th Li`ege Int. Astroph.
Coll., 12-16 July 201
Mesoscale Equipartition of kinetic energy in Quantum Turbulence
The turbulence of superfluid helium is investigated numerically at finite
temperature. Direct numerical simulations are performed with a "truncated HVBK"
model, which combines the continuous description of the
Hall-Vinen-Bekeravich-Khalatnikov equations with the additional constraint that
this continuous description cannot extend beyond a quantum length scale
associated with the mean spacing between individual superfluid vortices. A good
agreement is found with experimental measurements of the vortex density.
Besides, by varying the turbulence intensity only, it is observed that the
inter-vortex spacing varies with the Reynolds number as , like the
viscous length scale in classical turbulence. In the high temperature limit,
Kolmogorov's inertial cascade is recovered, as expected from previous numerical
and experimental studies. As the temperature decreases, the inertial cascade
remains present at large scales while, at small scales, the system evolves
towards a statistical equipartition of kinetic energy among spectral modes,
with a characteristic velocity spectrum. The accumulation of superfluid
excitations on a range of mesoscales enables the superfluid to keep dissipating
kinetic energy through mutual friction with the residual normal fluid, although
the later becomes rare at low temperature. It is found that most of the
superfluid vorticity can concentrate on these mesoscales at low temperature,
while it is concentrated in the inertial range at higher temperature. This
observation should have consequences on the interpretation of decaying
turbulence experiments, which are often based on vortex line density
measurements.Comment: 6 pages, 5 figure
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