44,473 research outputs found
Experimental demonstration of coupled optical springs
Optical rigidity will play an important role in improving the sensitivity of future generations of gravitational wave (GW) interferometers, which employ high laser power in order to reach and exceed the standard quantum limit. Several experiments have demonstrated the combined effect of two optical springs on a single system for very low-weight mirror masses or membranes. In this paper we investigate the complex interactions between multiple optical springs and the surrounding apparatus in a system of comparable dynamics to a large-scale GW detector. Using three 100 g mirrors to form a coupled cavity system capable of sustaining two or more optical springs, we demonstrate a number of different regimes of opto-mechanical rigidity and measurement techniques. Our measurements reveal couplings between each optical spring and the control loops that can affect both the achievable increase in sensitivity and the stability of the system. Hence this work establishes a better understanding of the realisation of these techniques and paves the way to their application in future GW observatories, such as upgrades to Advanced LIGO
Adaptive interpolation of discrete-time signals that can be modeled as autoregressive processes
This paper presents an adaptive algorithm for the restoration of lost sample values in discrete-time signals that can locally be described by means of autoregressive processes. The only restrictions are that the positions of the unknown samples should be known and that they should be embedded in a sufficiently large neighborhood of known samples. The estimates of the unknown samples are obtained by minimizing the sum of squares of the residual errors that involve estimates of the autoregressive parameters. A statistical analysis shows that, for a burst of lost samples, the expected quadratic interpolation error per sample converges to the signal variance when the burst length tends to infinity. The method is in fact the first step of an iterative algorithm, in which in each iteration step the current estimates of the missing samples are used to compute the new estimates. Furthermore, the feasibility of implementation in hardware for real-time use is established. The method has been tested on artificially generated auto-regressive processes as well as on digitized music and speech signals
Energy Harvesting From Bistable Systems Under Random Excitation
The transformation of otherwise unused vibrational energy into electric energy through the use of piezoelectric energy harvesting devices has been the subject of numerous investigations. The mechanical part of such a device is often constructed as a cantilever beam with applied piezo patches. If the harvester is designed as a linear resonator the power output relies strongly on the matching of the natural frequency of the beam and the frequency of the harvested vibration which restricts the applicability since most vibrations which are found in built environments are broad-banded or stochastic in nature. A possible approach to overcome this restriction is the use of permanent magnets to impose a nonlinear restoring force on the beam that leads to a broader operating range due to large amplitude motions over a large range of excitation frequencies.
In this paper such a system is considered introducing a refined modeling with a modal expansion that incorporates two modal functions and a refined modeling of the magnet beam interaction. The corresponding probability density function in case of random excitation is calculated by the solution of the corresponding Fokker-Planck equation and compared with results from Monte Carlo simulations. Finally some measurements of ambient excitations are discussed.DFG, 253161314, Untersuchung des nichtlinearen dynamischen Verhaltens von stochastisch erregten Energy Harvesting Systemen mittels Lösung der Fokker-Planck-Gleichun
Imaging the Radio Photospheres of Mira Variables
We have used the VLA at 43 GHz to image the radio continuum emission from o
Ceti, R Leo, and W Hya and to precisely locate their SiO maser emission with
respect to the star. The radio continuum emission region for all three stars
has a diameter close to 5.6 AU. These diameters are similar to those measured
at infrared wavelengths in bands containing strong molecular opacity and about
twice those measured in line-free regions of the infrared spectrum. Thus, the
radio photosphere and the infrared molecular layer appear to be coextensive.
The 43 GHz continuum emission is consistent with temperatures near 1600 K and
opacity from H-minus free-free interactions. While the continuum image of o
Ceti appears nearly circular, both R Leo and W Hya display significant
elongations. The SiO masers for all three stars show partial rings with
diameters close to 8 AU.Comment: 14 pages; 3 figure
A 6D interferometric inertial isolation system
We present a novel inertial-isolation scheme based on six degree-of-freedom
(6D) interferometric sensing of a single reference mass. It is capable of
reducing inertial motion by more than two orders of magnitude at 100\,mHz
compared with what is achievable with state-of-the-art seismometers. This will
enable substantial improvements in the low-frequency sensitivity of
gravitational-wave detectors. The scheme is inherently two-stage, the reference
mass is softly suspended within the platform to be isolated, which is itself
suspended from the ground. The platform is held constant relative to the
reference mass and this closed-loop control effectively transfers the low
acceleration-noise of the reference mass to the platform. A high loop gain also
reduces non-linear couplings and dynamic range requirements in the
soft-suspension mechanics and the interferometric sensing
Investigation of the thermal stability of Mg/Co periodic multilayers for EUV applications
We present the results of the characterization of Mg/Co periodic multilayers
and their thermal stability for the EUV range. The annealing study is performed
up to a temperature of 400\degree C. Images obtained by scanning transmission
electron microscopy and electron energy loss spectroscopy clearly show the good
quality of the multilayer structure. The measurements of the EUV reflectivity
around 25 nm (~49 eV) indicate that the reflectivity decreases when the
annealing temperature increases above 300\degreeC. X-ray emission spectroscopy
is performed to determine the chemical state of the Mg atoms within the Mg/Co
multilayer. Nuclear magnetic resonance used to determine the chemical state of
the Co atoms and scanning electron microscopy images of cross sections of the
Mg/Co multilayers reveal changes in the morphology of the stack from an
annealing temperature of 305\degreee;C. This explains the observed reflectivity
loss.Comment: Published in Applied Physics A: Materials Science \& Processing
Published at
http://www.springerlink.com.chimie.gate.inist.fr/content/6v396j6m56771r61/ 21
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A CONSTRAINED MATCHING PURSUIT APPROACH TO AUDIO DECLIPPING
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