196,439 research outputs found
Sound insulation measurements on noise barriers across their entire extension: a preliminary study
No full textEN 1793-6 allows measuring the in-situ sound insulation of installed noise barriers at selected
positions, but it would be desirable to check the quality of the installation or the decrease in
performance over time over the whole length of a noise barrier. For this purpose it is necessary
to carry out measurements along the entire extension of the noise barrier and not just at few
positions taken as representative. This work presents a preliminary study of a quick method
for evaluating airborne sound insulation along the entire length of a noise barrier and finding weak points, like assembly errors. Preliminary measurements were made by moving in the horizontal direction a linear antenna of microphones, kept vertical, along the entire width of the barrier in 0.25 m steps. On the opposite side of the barrier (noise source side) a loudspeaker was held in axis with the microphones, at fixed height, for each step. The entire surface of a 9 m wide, 4 m high sample barrier was analysed. Processing the measured impulse responses
between the loudspeaker and the microphones, global images of the local airborne sound insulation can be obtained in each frequency band
The slope of the gamma-ray burst variability/peak luminosity correlation
No full textFirst using a sample of 32 gamma-ray bursts (GRBs) with known redshift and then a sample of 551 BATSE GRBs with derived pseudo-redshift, the time variability/peak luminosity correlation (V versus L), originally found by Reichart et al. using a sample of 18 GRBs, was tested. For both samples the correlation is still found is but less relevant because of a much higher spread of the data. Assuming a straight line in the logL-logV plane (logL = m logV + b), both Guidorzi et al. and Guidorzi found that the line slope for both samples is much lower than that derived by Reichart et al.: m = 1.3+0.8-0.4 and 0.85 +/- 0.02, to be compared with m = 3.3+1.1-0.9 by Reichart et al. Reichart & Nysewander discuss our results and attribute the different slope to the fact that we do not take into account the variance of the sample in the fit (also called the slop), and demonstrate that, using the method presented by Reichart, the expanded data set in the logL-logV plane is still well described by a line with slope m = 3.4+0.9-0.6. Here we compare the results of two methods accounting for the slope of the sample: the method implemented by Reichart and that by D'Agostini. We demonstrate that the first method provides an inconsistent estimate of the parameter when the sample variance is comparable to the interval of values covered by the GRB variability. We also demonstrate that, using the second method, the slope of the logL-logV correlation is still consistent with that derived by us earlier and inconsistent with that derived by Reichart & Nysewander. Finally we discuss the implications on the interpretations proposed for the V-L correlation and show that our results are in agreement with the peak energy/variability correlation found by Lloyd-Ronning & Ramirez-Ruiz and the peak energy/peak luminosity correlation found by Yonetoku et al. and Ghirlanda et al
Confronto tra misure di isolamento acustico secondo la normativa ISO-140 e tramite misure impulsive
No full textIn questo lavoro si analizzano alcune misure di isolamento acustico, svolte in camera semi-riverberante. Le misure sono state effettuate simultaneamente mediante due sistemi di misura: un analizzatore Larson Davis modello 2900 e un sistema di acquisizione basato su PC, scheda audio e software di misura e analisi.
Con il presente lavoro si è trovata verifica sperimentale che, in condizioni normali (ambienti semi-riverberanti) si ha una sostanziale equivalenza tra le misure di fonoisolamento effettuate con un fonometro e con un sistema basato su personal computer e scheda audio. Il vantaggio nell'utilizzo di un sistema software risiede soprattutto nel costo, sensibilmente inferiore rispetto al fonometro. Il metodo di misura della risposta impulsiva con segnale MLS inoltre presenta alcuni vantaggi, il più evidente dei quali risiede nell'elevata immunità dal rumore di fondo. Per misure in laboratorio, in ambiente controllato, questa peculiarità del metodo MLS non è essenziale, ma nel caso di misure in opera o in cantiere, in presenza di forti sorgenti disturbanti, l'impiego di questo metodo
presenta indubbi vantaggi
A Low-Cost System for Quick Measurements on Noise Barriers in Situ
No full textThis paper describes the development of a low-cost device for measuring the acoustic intrinsic characteristics of noise barriers. The system is based on the Teensy 4.1 microcontroller combined with a few other components. The measurements are carried out using a vertical linear microphone antenna housing 6 microphones and a lightweight loudspeaker, wireless connected to the main unit. Both the main system unit and the amplified loudspeaker are powered from normal 5 V USB battery packs, which are easily rechargeable and interchangeable. The system measures 6 impulse responses using an MLS signal and performs a series of calculations and frequency analyses to characterize the device under test, following a simplified version of the European standards EN 1793-5 and EN 1793-6 (commonly referred to as the ’Adrienne method’). One measurement takes few minutes, obtaining results comparable to those obtained with the Adrienne method, which requires a more complicated and heavy measuring equipment and is much more expensive and time consuming
Thermal field measurements of heat sinks through a novel three-dimensional method based on acoustic waves
No full textNatural convection heat sinks are still important in many industrial applications thanks to their simple design, effectiveness and noise-free operation. In this paper we present some case studies of experimental determination of the thermal characteristics of such devices, carried out using an innovative three-dimensional method of position detection for the temperature transducer (thermocouple). The three-dimensional position detection system uses acoustic waves emitted by a small grid of four loudspeakers, which simultaneously emit pseudo-random noise sequences orthogonal to one another. A small microphone samples the sounds coming from the four loudspeakers and its position in the three-dimensional space is obtained through trilateration calculations and signal analysis. Microphone and thermocouple are mounted on the same movable support, so that by measuring the position of the microphone, the position of the thermocouple is also detected. In this way it is possible to measure the temperature in a cloud of points of known position in space and obtain the three-dimensional thermal field around the heat sink. From these measurements it is possible to evaluate the thermal field around the heat sink and to easily compare different construction geometries. The position detection system has good precision and is inexpensive, allowing this type of measurement to be carried out even in low-budget situations. It also differs from thermal imaging systems such as IR cameras, in that it allows measurement of the temperature in the fluid surrounding the heat sink and not on its surface only
Measurement of sound reflection and sound insulation of installed noise barriers using the SOPRANOISE quick method
No full textThis paper presents the preliminary results of a study on the new possibilities emerging from the analysis of measurements on installed noise barriers following the quick method designed in the frame of the SOPRANOISE project. Measurements of sound reflection and sound insulation were done in laboratory on a full-scale acoustic barrier and on an acoustic barrier installed along the Brennero motorway in northern Italy. The measurements were carried out using the SOPRANOISE quick system device, designed and engineered to provide a fast and lightweight version of the Adrienne method (i.e., EN 1793-5 and EN 1793-6), and then checked by applying the standardized Adrienne method, using instrumentation and procedures validated during the round-robin test performed in the frame of the QUIESST project. The preliminary results of the measurements are presented
Existence and regularity of minimizers of nonconvex integrals with growth
No full textWe show that local minimizers of integral functionals featuring p-q growth at infinity and satisfying appropriate convexity properties are locally Lipschitz continuous. As a consequence of this, we obtain an existence result for a related nonconvex minimum problem
Necessary conditions and non-existence results for autonomous nonconvex variational problems
No full textAbstractClassical one-dimensional, autonomous Lagrange problems are considered. In absence of any smoothness, convexity or coercivity condition on the energy density, we prove a DuBois-Reymond type necessary condition, expressed as a differential inclusion involving the subdifferential of convex analysis. As a consequence, a non-existence result is obtained
: Experimental verification and comparison with laboratory data
No full textIn the frame of the 1994-1997 Standard, Measurement and Testing program, the European Commission funded a research project, named Adrienne, to define new test methods for measuring the intrinsic characteristics of road traffic noise reducing devices in situ. The research team produced innovative methods for testing the sound reflection/absorption and the airborne sound insulation characteristics of noise barriers. These methods are now under consideration at CEN (European Committee for Standardization), to become European standards. The present work reports a detailed verification of the test method for airborne sound insulation over a selection of 17 noise barriers, representative of the Italian and European production. The samples were tested both outdoors, using the new Adrienne method, and in laboratory, following the European standard EN 1793-2. In both cases the single number rating for airborne sound insulation recommended by the European standard was calculated. The new method proved to be easy to use and reliable for all kinds of barriers. It has been found sensitive to quality of mounting, presence of seals, and other details typical of outdoor installations. The comparison between field and laboratory results shows a good correlation, while existing differences can be explained with the different sound fields and mounting conditions between the outdoor and laboratory tests. It is concluded that the Adrienne method is adequate for its intended use. (C) 2000 Acoustical Society of America
Existence of Minimizers of Free Autonomous Variational Problems Via Solvability of Constrained Ones
No full textWe consider the following autonomous variational problem:
minimize {\int_a^b f(v(x), v′(x))dx: v ∈ W^{1,1}(a, b), v(a) = α, v(b) = β} where the Lagrangian f is assumed to be continuous, but not necessarily coercive, nor convex. We show that the existence of the minimum is linked to the solvability of certain constrained variational problems. This allows us to derive existence theorems covering a wide class of nonconvex noncoercive problems
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