Antenna pattern of DUAL detectors of gravitational waves and its exploitation in a network of advanced interferometers

We investigate the directional sensitivity to plane gravitational waves (GWs) of DUAL detectors of cylindrical shape. Calculations make use of the finite element method to simulate the responses to the GW Riemann tensor of a single-mass DUAL (SMD) and of a tapered cylinder (TC) in their wide sensitivity bandwidth. We show that one SMD or a pair of TCs is able to cover both GW polarization amplitudes from almost all incoming directions. We discuss the achievable enhancement in tackling the inverse problem for high frequency [~(2–5) kHz] GWs by adding a TC detector to the future advanced LIGO–VIRGO network

False discovery rate: setting the probability of false claim of detection

When testing multiple hypothesis in a survey --e.g. many different source locations, template waveforms, and so on-- the final result consists in a set of confidence intervals, each one at a desired confidence level. But the probability that at least one of these intervals does not cover the true value increases with the number of trials. With a sufficiently large array of confidence intervals, one can be sure that at least one is missing the true value. In particular, the probability of false claim of detection becomes not negligible. In order to compensate for this, one should increase the confidence level, at the price of a reduced detection power. False discovery rate control is a relatively new statistical procedure that bounds the number of mistakes made when performing multiple hypothesis tests. We shall review this method, discussing exercise applications to the field of gravitational wave surveys.Comment: 7 pages, 3 table, 3 figures. Prepared for the Proceedings of GWDAW 9 (http://lappc-in39.in2p3.fr/GWDAW9) A new section was added with a numerical example, along with two tables and a figure related to the new section. Many smaller revisions to improve readibilit

Inhomogeneous mechanical losses in micro-oscillators with high reflectivity coating

We characterize the mechanical quality factor of micro-oscillators covered by a highly reflective coating. We test an approach to the reduction of mechanical losses, that consists in limiting the size of the coated area to reduce the strain and the consequent energy loss in this highly dissipative component. Moreover, a mechanical isolation stage is incorporated in the device. The results are discussed on the basis of an analysis of homogeneous and non-homogeneous losses in the device and validated by a set of Finite-Element models. The contributions of thermoelastic dissipation and coating losses are separated and the measured quality factors are found in agreement with the calculated values, while the absence of unmodeled losses confirms that the isolation element integrated in the device efficiently uncouples the dynamics of the mirror from the support system. Also the resonant frequencies evaluated by Finite-Element models are in good agreement with the experimental data, and allow the estimation of the Young modulus of the coating. The models that we have developed and validated are important for the design of oscillating micro-mirrors with high quality factor and, consequently, low thermal noise. Such devices are useful in general for high sensitivity sensors, and in particular for experiments of quantum opto-mechanics

Detection of weak stochastic force in a parametrically stabilized micro opto-mechanical system

Measuring a weak force is an important task for micro-mechanical systems, both when using devices as sensitive detectors and, particularly, in experiments of quantum mechanics. The optimal strategy for resolving a weak stochastic signal force on a huge background (typically given by thermal noise) is a crucial and debated topic, and the stability of the mechanical resonance is a further, related critical issue. We introduce and analyze the parametric control of the optical spring, that allows to stabilize the resonance and provides a phase reference for the oscillator motion, yet conserving a free evolution in one quadrature of the phase space. We also study quantitatively the characteristics of our micro opto-mechanical system as detector of stochastic force for short measurement times (for quick, high resolution monitoring) as well as for the longer term observations that optimize the sensitivity. We compare a simple, naive strategy based on the evaluation of the variance of the displacement (that is a widely used technique) with an optimal Wiener-Kolmogorov data analysis. We show that, thanks to the parametric stabilization of the effective susceptibility, we can more efficiently implement Wiener filtering, and we investigate how this strategy improves the performance of our system. We finally demonstrate the possibility to resolve stochastic force variations well below 1% of the thermal noise

An ultra-low dissipation micro-oscillator for quantum opto-mechanics

Generating non-classical states of light by opto-mechanical coupling depends critically on the mechanical and optical properties of micro-oscillators and on the minimization of thermal noise. We present an oscillating micro-mirror with a mechanical quality factor Q = 2.6x10^6 at cryogenic temperature and a Finesse of 65000, obtained thanks to an innovative approach to the design and the control of mechanical dissipation. Already at 4 K with an input laser power of 2 mW, the radiation-pressure quantum fluctuations become the main noise source, overcoming thermal noise. This feature makes our devices particularly suitable for the production of pondero-motive squeezing.Comment: 21 pages including Supplementary Informatio

A longitudinal study of neck and upper limb musculoskeletal disorders and alternative measures of vibration exposure

Objective \u2013 To investigate the exposure-response relationships between alternative frequency weightings of hand-transmitted vibration (HTV) and neck and upper limb musculoskeletal disorders (MSDs) in a cohort of HTV workers. Methods \u2013 In a 3-year longitudinal study, the occurrence of neck and upper limb MSDs were investigated in 249 HTV workers and 138 control men. In the HTV workers, MSDs were related to measures of daily vibration exposure expressed in terms of 8-hour energy-equivalent frequency-weighted acceleration magnitude [A(8)]. To calculate A(8), the acceleration magnitudes of vibration were weighted by means of four alternative frequency weightings of HTV. The associations between MSDs, individual characteristics, physical work load other than vibration and psychological strain were also investigated. Results \u2013 The occurrence of upper limb MSDs was greater in the HTV workers than in the controls. After adjustment for potential confounders, the occurrence of elbow/forearm and wrist/hand MSDs increased with the increase of vibration exposure. A measure of model selection did not reveal any substantial difference in the performance of the alternative frequency weightings of HTV for the prediction of neck and upper limb MSDs. In the study population, age, hard physical work load and poor psychological well-being were associated with both neck and upper limb MSDs. Conclusions \u2013 In this study there was evidence for significant exposure-response relationships between HTV exposure and MSDs in the distal sites of the upper limbs. There were no differences in the prediction of neck and upper limb MSDs between measures of daily vibration exposure calculated with alternative frequency weightings of acceleration magnitude

Pressure-induced Spin-Peierls to Incommensurate Charge-Density-Wave Transition in the Ground State of TiOCl

The ground state of the spin-Peierls system TiOCl was probed using synchrotron x-ray diffraction on a single-crystal sample at T = 6 K. We tracked the evolution of the structural superlattice peaks associated with the dimerized ground state as a function of pressure. The dimerization along the b axis is rapidly suppressed in the vicinity of a first-order structural phase transition at Pc = 13.1(1) GPa. The high-pressure phase is characterized by an incommensurate charge density wave perpendicular to the original spin chain direction. These results show that the electronic ground state undergoes a fundamental change in symmetry, indicating a significant change in the principal interactions.Comment: 5 pages, 4 figure

Selective readout and back-action reduction for wideband acoustic gravitational wave detectors

We present the concept of selective readout for broadband resonant mass gravitational wave detectors. This detection scheme is capable of specifically selecting the signal from the contributions of the vibrational modes sensitive to the gravitational waves, and efficiently rejecting the contribution from non gravitationally sensitive modes. Moreover this readout, applied to a dual detector, is capable to give an effective reduction of the back-action noise within the frequency band of interest. The overall effect is a significant enhancement in the predicted sensitivity, evaluated at the standard quantum limit for a dual torus detector. A molybdenum detector, 1 m in diameter and equipped with a wide area selective readout, would reach spectral strain sensitivities 2x10^{-23}/sqrt{Hz} between 2-6 kHz.Comment: 9 pages, 4 figure

Dynamical two-mode squeezing of thermal fluctuations in a cavity opto-mechanical system

We report the experimental observation of two-mode squeezing in the oscillation quadratures of a thermal micro-oscillator. This effect is obtained by parametric modulation of the optical spring in a cavity opto-mechanical system. In addition to stationary variance measurements, we describe the dynamic behavior in the regime of pulsed parametric excitation, showing enhanced squeezing effect surpassing the stationary 3dB limit. While the present experiment is in the classical regime, our technique can be exploited to produce entangled, macroscopic quantum opto-mechanical modes