1,708 research outputs found
Principles of gravitational wave detection
No full textThe principles of gravitational wave detection are presented. The measurement of the propagating minute deformation of space-Time remains an extraordinary experimental challenge. After a brief introduction to signals and noise, fundamental disturbances in the measurement are discussed, outlining how these have been sufficiently reduced to achieve detection
In silico broadband mechanical spectroscopy of amorphous tantala
No full textAdopting an agnostic approach, the quality factor Q of tantala glass is drawn via in silico mechanical spectroscopy in wide ranges of temperature (10–300 K) and frequency (500 MHz f 1 THz). At the highest frequencies, Q ∝ f −3, consistent with Rayleigh sound scattering. For frequencies lower than terahertz, losses exhibit a weak power-law frequency dependence Q ∝ f −α with α ∼ 0.1 to 0.2, depending on glass preparation and temperature. Arguing the validity of the power law down to 1 kHz, we show striking agreement with the losses measured in annealed amorphous films in the whole temperature range, revealing similitude between disordered structures created by different routes (quench cooling and deposition). Our results do not support the scenario of the mechanical loss due to activated relaxation of independent two-level system
Giuseppe and Maria Fidecaro inside the spark chamber apparatus in the South Hall of PS to search for the decay
No full textThe lens, the so-called front view (see album https://cds.cern.ch/record/1974123), was used in the S30 experiment to converge onto a camera parallel light rays from the front of a large spark chamber. A second identical lens, the so-called top view, and a large mirror were used to take pictures at 90 degrees in such a way to determine the x,y coordinates in the horizontal plane of each spark. Details of the optics are reported in the note: A -ray detector for the study of the electromagnetic decay of resonances, INFN/AE - 67/7, 20 Jun 1967, by F. Bradamante, G. Fidecaro, M. Fidecaro, M. Giorgi, F. Sauli, P. Schiavon
Evidence of negative thermal expansion in supercooled tantala
No full textA density anomaly, i.e. a temperature region with negative thermal expansion (NTE) bounded by a density maximum and a density minimum at lower temperatures, is revealed and characterised in tantala for the first time by Molecular Dynamics simulations. The NTE region is evidenced in the metastable supercooled liquid and rather close to the glass transition. Since NTE is suppressed by poor structural equilibration, highlighting these phenomena is highly challenging due to the need for fulfilling competing constraints of slow cooling and avoidance of the crystallization. We find that the density anomaly is signalled by a decrease of the partial coordination numbers nTa,Ta and nO,O when lowering the temperature. The NTE magnitude is comparable to the ones of both stable water and solid-state materials with giant NTE
Evaluation of Acoustic Comfort and Sound Energy Transmission in a Yacht
No full textAfter being neglected for a long time, in the last years, ships have been recognized and studied as sound emitters. The sound energy they generate impacts the outside, but it can also affect the indoor quality of life if the environments are not properly designed. In fact, acoustic comfort plays a pivotal role, particularly in recreational crafts. In the present work, room acoustics and acoustic camera measurements were performed, inside a 50 m length overall yacht, chosen as a case study in order to evaluate the acoustic comfort. The Italian classification procedure UNI 11367:2010 for buildings was applied, and results have been compared to other international comfort classes. However, all of these are based on prescription for standard buildings, and the present work highlights that they do not account for the effective ship’s acoustic issues: sound energy transfer from impacts over ceilings and sound energy leakage. While attention of shipbuilders in acoustic comfort is shown in the measured good reverberation times, the acoustic camera revealed sound energy leakages corresponding to hidden escape ways that have been poorly insulated. This compromises the standardized sound difference between contiguous compartments and also the thermal insulation, as leakage involves air passages. The present work attempts to evolve the classification procedure by also including, for the first time, the reverberation time, but future studies focused on finding correct standardized impact level noise for ship cases are needed. In fact, their values were very high and not comparable with those measured in actual buildings and for which reference values have been designed
Non-local cooperative atomic motions that govern dissipation in amorphous tantala unveiled by dynamical mechanical spectroscopy
No full textThe mechanisms governing mechanical dissipation in amorphous tantala are studied at microscopic scale via Molecular Dynamics simulations, namely by mechanical spectroscopy in a wide range of temperature and frequency. We find that dissipation is associated with irreversible atomic rearrangements with a sharp cooperative character, involving tens to hundreds of atoms arranged in spatially extended clusters of polyhedra. Remarkably, at low temperature we observe an excess of plastically rearranging oxygen atoms which correlates with the experimental peak in the macroscopic mechanical losses. A detailed structural analysis reveals preferential connections of the irreversibly rearranging polyhedra, corresponding to edge and face sharing. These results might lead to microscopically informed design rules for reducing mechanical losses in relevant materials for structural, optical, and sensing applications
ACOUSTIC COMFORT IN YACHTS: MEASUREMENTS WITH ACOUSTIC CAMERA
No full textShipowners have become more sensitive to noise issues, leading to consider acoustic comfort as an important parameter in the design of private boats. In the last years, manufacturers have been requested more attention to the living environments of leisure ships. Especially for luxury vessels, it has been seen that only the respect of the acoustic limits for the health safety of the crew, does not imply a good quality of life on board. Some naval country agencies have developed criteria based on the acoustic indexes used for the buildings, having in mind the different scopes of the various environments. Unfortunately, a common international line has still not been defined. The present work reports the analysis of data acquired with an acoustic camera in the process of the acoustic comfort evaluation of a 50 m long yacht. Due to the cabins' dimensions, the measurements were performed with an antenna of 0.28 m radius. This allowed the localization of noise with a Beamforming technique in the frequency range higher than 1 kHz. Its main use has been to localize different “sound leakage” routes that could compromise noise insulation mitigation
Efficient GW Chirp Estimation via Wigner-Ville Representation and Generalized Hough Transform
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