395 research outputs found
Charge and Spin Density Waves observed through their spatial fluctuations by coherent and simultaneous X-ray diffraction
Spatial uctuations of spin density wave (SDW) and charge density wave (CDW)
in chromium have been compared by combining coherent and simultaneous X-ray
diffraction experiments. Despite their close relationship, spatial fluctuations
of the spin and of the charge density waves display a very different behavior:
the satellite reflection associated to the charge density displays speckles
while the spin one displays an impressive long-range order. This observation is
hardly compatible with the commonly accepted magneto-elastic origin of CDW in
chromium and is more consistent with a purely electronic scenario where CDW is
the second harmonic of SDW. A BCS model taking into account a second order
nesting predicts correctly the existence of a CDW and explains why the CDW is
more sensitive to punctual defects.Comment: 4 pages, 4 figures; Accepted in Phys. Rev.
Gravitational waves from binary systems in circular orbits: Convergence of a dressed multipole truncation
The gravitational radiation originating from a compact binary system in
circular orbit is usually expressed as an infinite sum over radiative multipole
moments. In a slow-motion approximation, each multipole moment is then
expressed as a post-Newtonian expansion in powers of v/c, the ratio of the
orbital velocity to the speed of light. The bare multipole truncation of the
radiation consists in keeping only the leading-order term in the post-Newtonian
expansion of each moment, but summing over all the multipole moments. In the
case of binary systems with small mass ratios, the bare multipole series was
shown in a previous paper to converge for all values v/c < 2/e, where e is the
base of natural logarithms. In this paper, we extend the analysis to a dressed
multipole truncation of the radiation, in which the leading-order moments are
corrected with terms of relative order (v/c)^2 and (v/c)^3. We find that the
dressed multipole series converges also for all values v/c < 2/e, and that it
coincides (within 1%) with the numerically ``exact'' results for v/c < 0.2.Comment: 9 pages, ReVTeX, 1 postscript figur
Alignment procedure for the VIRGO Interferometer: experimental results from the Frascati prototype
A small fixed-mirror Michelson interferometer has been built in Frascati to
experimentally study the alignment method that has been suggested for VIRGO.
The experimental results fully confirm the adequacy of the method. The minimum
angular misalignment that can be detected in the present set-up is 10
nrad/sqrt{Hz}Comment: 10 pages, LaTex2e, 4 figures, 5 tables. Submitted to Phys. Lett.
Data analysis strategies for the detection of gravitational waves in non-Gaussian noise
In order to analyze data produced by the kilometer-scale gravitational wave
detectors that will begin operation early next century, one needs to develop
robust statistical tools capable of extracting weak signals from the detector
noise. This noise will likely have non-stationary and non-Gaussian components.
To facilitate the construction of robust detection techniques, I present a
simple two-component noise model that consists of a background of Gaussian
noise as well as stochastic noise bursts. The optimal detection statistic
obtained for such a noise model incorporates a natural veto which suppresses
spurious events that would be caused by the noise bursts. When two detectors
are present, I show that the optimal statistic for the non-Gaussian noise model
can be approximated by a simple coincidence detection strategy. For simulated
detector noise containing noise bursts, I compare the operating characteristics
of (i) a locally optimal detection statistic (which has nearly-optimal behavior
for small signal amplitudes) for the non-Gaussian noise model, (ii) a standard
coincidence-style detection strategy, and (iii) the optimal statistic for
Gaussian noise.Comment: 5 pages RevTeX, 4 figure
The Kepler equation for inspiralling compact binaries
Compact binaries consisting of neutron stars / black holes on eccentric orbit
undergo a perturbed Keplerian motion. The perturbations are either of
relativistic origin or are related to the spin, mass quadrupole and magnetic
dipole moments of the binary components. The post-Newtonian motion of such
systems decouples into radial and angular parts. We present here for the first
time the radial motion of such a binary encoded in a generalized Kepler
equation, with the inclusion of all above-mentioned contributions, up to linear
order in the perturbations. Together with suitably introduced parametrizations,
the radial motion is solved completely
Scattering of Woods-Saxon Potential in Schrodinger Equation
The scattering solutions of the one-dimensional Schrodinger equation for the
Woods-Saxon potential are obtained within the position-dependent mass
formalism. The wave functions, transmission and reflection coefficients are
calculated in terms of Heun's function. These results are also studied for the
constant mass case in detail.Comment: 14 page
To the practical design of the optical lever intracavity topology of gravitational-wave detectors
The QND intracavity topologies of gravitational-wave detectors proposed
several years ago allow, in principle, to obtain sensitivity significantly
better than the Standard Quantum Limit using relatively small anount of optical
pumping power. In this article we consider an improved more ``practical''
version of the optical lever intracavity scheme. It differs from the original
version by the symmetry which allows to suppress influence of the input light
amplitude fluctuation. In addition, it provides the means to inject optical
pumping inside the scheme without increase of optical losses.
We consider also sensitivity limitations imposed by the local meter which is
the key element of the intracavity topologies. Two variants of the local meter
are analyzed, which are based on the spectral variation measurement and on the
Discrete Sampling Variation Measurement, correspondingly. The former one, while
can not be considered as a candidate for a practical implementation, allows, in
principle, to obtain the best sensitivity and thus can be considered as an
ideal ``asymptotic case'' for all other schemes. The DSVM-based local meter can
be considered as a realistic scheme but its sensitivity, unfortunately, is by
far not so good just due to a couple of peculiar numeric factors specific for
this scheme.
From our point of view search of new methods of mechanical QND measurements
probably based on improved DSVM scheme or which combine the local meter with
the pondermotive squeezing technique, is necessary.Comment: 27 pages, 6 figure
Estimation of parameters of gravitational waves from coalescing binaries
In this paper we deal with the measurement of the parameters of the
gravitational wave signal emitted by a coalescing binary signal.
We present the results of Monte Carlo simulations carried out for the case of
the initial LIGO, incorporating the first post-Newtonian corrections into the
waveform. Using the parameters so determined, we estimate the direction to the
source. We stress the use of the time-of-coalescence rather than the
time-of-arrival of the signal to determine the direction of the source. We show
that this can considerably reduce the errors in the determination of the
direction of the source.Comment: 5 pages, REVTEX, 2 figures (bundled via uufiles command along with
this paper) submitted to Praman
Parametric instabilities and their control in advanced interferometer GW detectors
A detailed simulation of Advanced LIGO test mass optical cavities shows that
parametric instabilities will excite acoustic modes in the test masses in the
frequency range 28-35 kHz and 64-72 kHz. Using nominal Advanced LIGO optical
cavity parameters with fused silica test masses, parametric instability excites
7 acoustic modes in each test mass, with parametric gain R up to 7. For the
alternative sapphire test masses only 1 acoustic mode is excited in each test
mass with R ~ 2. Fine tuning of the test mass radii of curvature cause the
instabilities to sweep through various modes with R as high as ~2000. Sapphire
test mass cavities can be tuned to completely eliminate instabilities using
thermal g-factor tuning with negligible degradation of the noise performance.
In the case of fused silica test mass, instabilities can be minimized but not
eliminated.Comment: 5 pages, 4 figure
Gravitational waves from inspiraling compact binaries: Second post-Newtonian waveforms as search templates II
We present further evidence that the second post-Newtonian (pN) approximation
to the gravitational waves emitted by inspiraling compact binaries is
sufficient for the detection of these systems. This is established by comparing
the 2-pN wave forms to signals calculated from black hole perturbation theory.
Results are presented for different detector noise curves. We also discuss the
validity of this type of analysis.Comment: 5 pages, 3 Figures, RevTe
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