2,252 research outputs found
Mean and mean square measurements of nonstationary random processes
Mean and mean square measurements of nonstationary random processes - orthogonal function analysis and computer simulatio
Surface coupling effects on the capacitance of thin insulating films
A general form for the surface roughness effects on the capacitance of a
capacitor is proposed. We state that a capacitor with two uncoupled rough
surfaces could be treated as two capacitors in series which have been divided
from the mother capacitor by a slit. This is in contrast to the case where the
two rough surfaces are coupled. When the rough surfaces are coupled, the type
of coupling decides the modification of the capacitance in comparison to the
uncoupled case. It is shown that if the coupling between the two surfaces of
the capacitor is positive (negative), the capacitance is less (higher) than the
case of two uncoupled rough plates. Also, we state that when the correlation
length and the roughness exponent are small, the coupling effect is not
negligible
A summary of methods for analyzing nonstation- ary data
Estimation of nonstationary mean values, spectral density, and correlation functions - summary of methods for analyzing nonstationary dat
A method for vibration-based structural interrogation and health monitoring based on signal cross-correlation
Vibration-based structural interrogation and health monitoring is a field which is concerned with the estimation of the current state of a structure or a component from its vibration response with regards to its ability to perform its intended function appropriately. One way to approach this problem is through damage features extracted from the measured structural vibration response. This paper suggests to use a new concept for the purposes of vibration-based health monitoring. The correlation between two signals, an input and an output, measured on the structure is used to develop a damage indicator. The paper investigates the applicability of the signal cross-correlation and a nonlinear alternative, the average mutual information between the two signals, for the purposes of structural health monitoring and damage assessment. The suggested methodology is applied and demonstrated for delamination detection in a composite beam
A method for vibration-based structural interrogation and health monitoring based on signal cross-correlation
Vibration-based structural interrogation and health monitoring is a field which is concerned with the estimation of the current state of a structure or a component from its vibration response with regards to its ability to perform its intended function appropriately. One way to approach this problem is through damage features extracted from the measured structural vibration response. This paper suggests to use a new concept for the purposes of vibration-based health monitoring. The correlation between two signals, an input and an output, measured on the structure is used to develop a damage indicator. The paper investigates the applicability of the signal cross-correlation and a nonlinear alternative, the average mutual information between the two signals, for the purposes of structural health monitoring and damage assessment. The suggested methodology is applied and demonstrated for delamination detection in a composite beam
Probability Functions for Random Responses: Prediction of Peaks, Fatigue Damage, and Catastrophic Failures
This report reviews a number of theoretical matters in random process theory which can be applied to physical problems such as predicting peaks, structural fatigue damage, and catastrophic structural failures. The presentation emphasizes the basic assumptions which are involved, and discusses how to properly interpret the theoretical results. Various engineering examples are given as illustrations
Extensions of Lieb's concavity theorem
The operator function (A,B)\to\tr f(A,B)(K^*)K, defined on pairs of bounded
self-adjoint operators in the domain of a function f of two real variables, is
convex for every Hilbert Schmidt operator K, if and only if f is operator
convex. As a special case we obtain a new proof of Lieb's concavity theorem for
the function (A,B)\to\tr A^pK^*B^{q}K, where p and q are non-negative numbers
with sum p+q\le 1. In addition, we prove concavity of the operator function
(A,B)\to \tr(A(A+\mu_1)^{-1}K^* B(B+\mu_2)^{-1}K) on its natural domain
D_2(\mu_1,\mu_2), cf. Definition 4.1Comment: The format of one reference is changed such that CiteBase can
identify i
Some issues when using Fourier analysis for the extraction of modal parameters
It is sometimes necessary to determine the manner in which structures deteriorate with respect to time; for instance when quantifying a material's ability to withstand sustained dynamic loads. In such cases, it is well established that loss of structural integrity is reflected by variations in modal characteristics such as stiffness. This paper addresses some practical limitations of Fourier analysis with respect to temporal resolution and the uncertainties associated with extracting variations in modal parameters. The statistical analysis of numerous numerical experiments shows how techniques, such as data overlapping and zero-padding, can be used to improve the sensitivity of modal parameter extraction
The principle of a virtual multi-channel lock-in amplifier and its application to magnetoelectric measurement system
This letter presents principles and applications of a virtual multi-channel
lock-in amplifier that is a simple but effective method to recover small ac
signal from noise with high presison. The fundamentals of this method are based
on calculation of cross-correlation function. Via this method, we successfully
built up a magnetoelectric measurement system which can perform precise and
versatile measurements without any analog lock-in amplifier. Using the virtual
multi-channel lock-in amplifier, the output of the magnetoelectric measurement
system is extensively rich in magnetoelectric coupling behaviors, including
coupling strength and phase lag, under various dc bias magnetic field and ac
magnetic field.Comment: 11 pages, 6 figures. To be submitted to Rev. Sci. Instr
Concavity of Eigenvalue Sums and the Spectral Shift Function
It is well known that the sum of negative (positive) eigenvalues of some
finite Hermitian matrix is concave (convex) with respect to . Using the
theory of the spectral shift function we generalize this property to
self-adjoint operators on a separable Hilbert space with an arbitrary spectrum.
More precisely, we prove that the spectral shift function integrated with
respect to the spectral parameter from to (from
to ) is concave (convex) with respect to trace class perturbations.
The case of relative trace class perturbations is also considered
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