31,197 research outputs found
Linking numbers of measured foliations
We generalise the average asymptotic linking number of a pair of
divergence-free vector fields on homology three-spheres by considering the
linking of a divergence-free vector field on a manifold of arbitrary dimension
with a codimension two foliation endowed with an invariant transverse measure.
We prove that the average asymptotic linking number is given by an integral of
Hopf type. Considering appropriate vector fields and measured foliations, we
obtain an ergodic interpretation of the Godbillon-Vey invariant of a family of
codimension one foliations discussed in math.GT/0111137.Comment: minor corrections, to appear in Ergodic Theory and Dynamical System
Multi-mode density matrices of light via amplitude and phase control
A new method is described for determining the quantum state of correlated
multimode radiation by interfering the modes and measuring the statistics of
the superimposed fields in four-port balanced homodyne detection. The full
information on the -mode quantum state is obtained by controlling both the
relative amplitudes and the phases of the modes, which simplifies the
reconstruction of density matrices to only Fourier transforms. In
particular, this method yields time-correlated multimode density matrices of
optical pulses by superimposing the signal by a sequence of short
local-oscillator pulses.Comment: 6 pages, late
Why the meson might be a difficult messenger for the restoration of chiral symmetry
We perform a theoretical analysis of the resonance mass spectrum in
ultra-relativistic heavy ion collisions within a hadron/string transport
approach. Predictions for the yield and its mass distribution are given
for the GSI-FAIR and the critRHIC energy regime. The potential of the
meson as a signal for chiral symmetry restoration is explored. In view of the
latest discussion, we investigate the decay channel in
detail and find a strong bias towards low masses. This apparent mass
shift of the if observed in the channel might render a
possible mass shift due to chiral symmetry restoration very difficult to
disentangle from the decay kinematics.Comment: 4 pages, 5 figure
Numerical solution of flowfields behind rectangular wings
The numerical solution of flow fields behind rectangular wings is described. Subjects discussed are: (1) evaluation of various differencing methods applied to the hyperbolic partial differential equations encountered in gas dynamics, (2) application of the numerical differencing techniques to the wedge flow, two dimensional shock reflection for the three dimensional finite thickness wing at zero degrees angle of attack, and (3) calculation of preliminary results for wedge flows using optimum differencing methods
XMM-Newton observations of EF Eridani: the textbook example of low-accretion rate polars
Archival X-ray observations of EF Eridani obtained in a low state revealed
distinct X-ray detections at a luminosity L_X ~ 2 10^{29} erg/s, three orders
of magnitude below its high state value. The plasma temperature was found to be
as low as kT \loa 2 keV, a factor 10 below the high state. The X-ray/UV/IR
spectral energy distribution suggests faint residual accretion rather than
coronal emission as being responsible for the low-state X-ray emission. EF Eri
thus showed a clear transition from being shock-dominated in the high state to
be cyclotron-dominated in the low state. From the optical/UV spectral energy
distribution we re-determine the photospheric temperature of the white dwarf to
\~10000K. Contrary to earlier claims, WD model atmospheres produce sufficient
UV flux to reproduce the published GALEX flux and orbital modulation.Comment: A&A, in pres
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