Search results for "ACOUSTIC"
showing 10 items of 1590 documents
On the convergent parts of high order spectral moments of stationary structural responses
1986
The paper deals with the evaluation of the convergent parts of the high spectral moments of linear systems subjected to stationary random input. An adequate physical meaning of these quantities in both the time and frequency domains is presented. Recurrence formulas to obtain the high convergent cross spectral moments of any order are given in the case of white noise input.
Analytic evaluation of spectral moments
1988
In this paper an analytic procedure that drastically reduces the computational effort in evaluating the spectral moments of the response of multi-degree-of-freedom systems is presented. It is shown that the cross-spectral moments of any order of two oscillators subjected to a filtered stochastic process can be obtained in a recursive manner as a linear combination of the spectral moment of each oscillator up to the third order separately taken. A numerical procedure is also presented in order to evaluate such first few spectral moments.
Non-stationary pre-envelope covariances of non-classically damped systems
1991
Abstract A new formulation is given to evaluate the stationary and non-stationary response of linear non-classically damped systems subjected to multi-correlated non-separable Gaussian input processes. This formulation is based on a new and more suitable definition of the impulse response function matrix for such systems. It is shown that, when using this definition, the stochastic response of non-classically damped systems involves the evaluation of quantities similar to those of classically damped ones. Furthermore, considerations about non-stationary cross-covariances, spectral moments and pre-envelope cross-covariances are presented for a monocorrelated input process.
Risuonatore Acustico Biomorfo Triplanare
2019
Triplanar Biomorph Acoustic Resonator
A noise analyzer for monitoring static electrification current
2005
Abstract This paper presents a static electrification current signal analyzer used for measuring and processing of the variable component of the changes in electrostatic charge that occur on a solid-body/liquid boundary interface. Due to high sensitivity and low uncertainty, the analyzer allows a precise evaluation of the phenomenon generated. The device operates in a spinning-disk system. The tests carried out indicate that it is possible to measure random components which depend, to a large extent, on hydrodynamic conditions and on the properties of the liquid phase. The device can be applied to the testing of transformer oils. It can be also used for measurements of other liquids having …
Detection of lung cancer bio-markers in human breath using a micro-fabricated air analyzer
2015
International audience; The analysis of volatile organic compounds (VOCs) that are linked to lung cancer is a very promising way in medical diagnostics because it is non-invasive and potentially inexpensive. In that sense, a silicon micro-analytical platform consisting of a three-dimensional micro-preconcentrator coupled to a silicon spiral gas chromatographic micro-column was built. A metal oxide-based gas sensor acted as a miniaturized gas detector. This system allowed selective detection of VOCs at the sub-ppm level. The present study is focused first on the chromatographic air analyzer fabrication and second on the selection of an appropriate adsorbent. Various adsorbents such as activa…
Element-specific ferromagnetic resonance in epitaxial Heusler spin valve systems
2011
Time-resolved x-ray magnetic circular dichroism was used to investigate epitaxial MgO(100)/Co2Cr0.6Fe0.4Al and MgO(100)/Co2Cr0.6Fe0.4Al/Cr/CoFe films. The precessional motion of the individual sublattice magnetization, excited by continuous microwave excitation in the range 2–10 GHz, was detected by tuning the x-ray photon energy to the L 3 absorption edges of Cr, Fe and Co. The relative phase angle of the sublattice magnetization's response is smaller than the detection limit of 2°. A weakly antiferromagnetically coupled CoFe layer causes an increase in the ferromagnetic resonance linewidth consisting of a constant offset and a component linearly increasing with frequency that we partly at…
Uncertainty in 2-point correlation function estimators and baryon acoustic oscillation detection in galaxy surveys
2012
Abstract We study the uncertainty in different two-point correlation function (2PCF) estimators in currently available galaxy surveys. This is motivated by the active subject of using the baryon acoustic oscillations (BAOs) feature in the correlation function as a tool to constrain cosmological parameters, which requires a fine analysis of the statistical significance. We discuss how estimators are affected by both the uncertainty in the mean density n and the integral constraint 1 V 2 ∫ V 2 ξ ˆ ( r ) d 3 r = 0 which necessarily causes a bias. We quantify both effects for currently available galaxy samples using simulated mock catalogues of the Sloan Digital Sky Survey (SDSS) following a lo…
Steady-state dynamic response of various hysteretic systems endowed with fractional derivative elements
2019
In this paper, the steady-state dynamic response of hysteretic oscillators comprising fractional derivative elements and subjected to harmonic excitation is examined. Notably, this problem may arise in several circumstances, as for instance, when structures which inherently exhibit hysteretic behavior are supplemented with dampers or isolators often modeled by employing fractional terms. The amplitude of the steady-state response is determined analytically by using an equivalent linearization approach. The procedure yields an equivalent linear system with stiffness and damping coefficients which are related to the amplitude of the response, but also, to the order of the fractional derivativ…
Cosmic microwave background constraints on secret interactions among sterile neutrinos
2017
Secret contact interactions among eV sterile neutrinos, mediated by a massive gauge boson $X$ (with $M_X \ll M_W$), and characterized by a gauge coupling $g_X$, have been proposed as a mean to reconcile cosmological observations and short-baseline laboratory anomalies. We constrain this scenario using the latest Planck data on Cosmic Microwave Background anisotropies, and measurements of baryon acoustic oscillations (BAO). We consistently include the effect of secret interactions on cosmological perturbations, namely the increased density and pressure fluctuations in the neutrino fluid, and still find a severe tension between the secret interaction framework and cosmology. In fact, taking i…