1,722,057 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
CONSIDERAZIONI SUI METODI PER IL CALCOLO DELL'ISOLAMENTO ACUSTICO AL CALPESTIO
No full textLa norma UNI EN 12354-2, per il calcolo dell'isolamento acustico al calpestio di un massetto galleggiante, prevede di utilizzare i valori di ΔL o ΔLw calcolati partendo dalla frequenza di risonanza del sistema massa molla o dai valori misurati sul solaio di riferimento UNI EN ISO 10140. Nel presente lavoro, partendo dell'esperienza fatta finora dal Laboratorio di Acustica Edilizia dell'Università di Bologna, si metteranno a confronto i valori dell'attenuazione del livello di calpestio calcolati, utilizzando i valori della rigidità dinamica determinati in accordo con la UNI EN 29052-1 e quelli misurati sperimentalmente in camera acustica. Scopo degli autori è quello di valutare l'equivalenza dei due metodi
Dall’incertezza di misura al confronto con valori limite
Full text linkIn acustica applicata si pone spesso il problema di provare la conformità o la non conformità di un valore misurato a valori limite di specifica, che possono essere indicati da leggi, regolamenti, norma tecniche o documenti di tipo contrattuale. Considerando che il valore misurato è sempre affetto da incertezza, la soluzione di questo problema è tutt’altro che ovvia, ed implica la scelta di regole decisionali che dipendono dall’obiettivo del confronto. Si propone qui una metodologia opportuna, declinando le principali regole decisionali nello specifico settore dell’acustica applicata e fornendo inoltre le regole da adottare nei casi in cui non può essere presa una decisione certa
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
Pass-by characterization of noise emitted by different categories of seagoing ships in ports
Full text linkIn the light of sustainability, satisfactory living conditions is an important factor for people's positive feedback in their own living environment. Acoustic comfort and noise exposure should then be carefully monitored in all human settlements. Furthermore, it is already well-known that high or prolonged noise levels may lead to unwanted health effects. Unfortunately, while in the last decades scientists and public authorities have investigated the noise produced by roads, trains, and airports, not enough efforts have been spent in studying what happens around the coastal and port areas. Following the attention brought to the subject by recent European projects on noise in port areas, the present paper characterizes the sound power level and 1/3 octave band sound power spectrum of seagoing ships while moving at low speeds. Five different categories have been distinguished: Roll-on/roll-off (RORO), container ship, oil tanker, chemical tanker, and ferry. The analysis is based on a continuous noise measurement lasting more than three months, performed in the industrial canal of the port of Livorno (Italy). The resulting noise emissions are new and useful data that could be inserted in acoustic propagation models to properly assess the noise in the areas affected by port activities. Thus, the present work can act as a supporting tool in planning ship traffic in ports towards better sustainability
Port noise and complaints in the North Tyrrhenian sea and framework for remediation
Full text linkCompared to the other relevant noise sources such as railways, roads, and airplanes, the regulation regarding port noise is lagging behind. The absence of specific laws is likely one of the main causes of the increasingly high number of complaints reported by the citizens living nearby the ports. At the same time, scientific literature concerning the impact of port noise and its mitigation is not so widespread and only a few studies are available at the moment. However, the volume of maritime traffic has increased in the last years and consequently, Port Authorities are required to assess the impact of port operations on the city soundscape without using specific directives or guidelines. In this context, the INTERREG Maritime programme projects RUMBLE, MON ACUMEN, and REPORT aim to fill this gap, by investigating the state-of-the-art of port noise in the north Tyrrhenian sea and developing helpful instruments. Data were collected via a survey sent to the Port Authorities, local environmental protection agencies and universities involved in the projects. The survey was focused on monitoring systems, previous measurement campaigns, noise maps, and citizens’ complaints already taken. The results confirmed both a lack of awareness among residents and authorities and the absence of actions aimed at reducing port noise. In this framework, the difficulties encountered by the Port Authorities in managing the ports sustainably are highlighted. An underestimation of citizens’ exposure to noise in port areas could be expected
Port noise impact and citizens' complaints evaluation in rumble and mon acumen interreg projects
No full textAfter the publications of the European Environmental Noise Directive in 2002, many noise maps and action plans, as well as a consistent number of scientific papers, emerged for roads, railways, airports and industrial noise. Unfortunately, noise produced by ports in their surrounding areas seems to be forgotten at present, even though there could be many areas affected by it. Relevant attention from authorities and scientific community seems to be devoted to noise produced underwater for its interference with wildlife, rather than noise produced in the urban portion, that is causing disturbance and consequent complaints by some citizens. The INTERREG Maritime projects MON ACUMEN and RUMBLE aim to study noise originating from port activity in order to assess the currently unexplored situation and then identify solutions for a long-term environmental sustainability. More specifically, RUMBLE aims to effectively and efficiently implement small mitigation interventions, while MON ACUMEN will gather the preliminary knowledge on the issue of noise generated by ports. In this context, questionnaires submitted to north Tyrrhenian port authorities concerning the description of the port area, the present monitoring systems, the measurement campaigns and acoustics maps performed are discussed. Furthermore, by analyzing the citizen's complaints where present, the critical aspects of the analyzed ports will be studied © Proceedings of the 26th International Congress on Sound and Vibration, ICSV 2019. All rights reserved
Evaluation of Acoustic Comfort and Sound Energy Transmission in a Yacht
Full text linkAfter 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
Full text linkThe 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
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