Methods for estimating model parameters using likelihood techniques are examined and a model selection procedure is proposed for classifying the neighbourhood structure of the image. The techniques are investigated us...
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Methods for estimating model parameters using likelihood techniques are examined and a model selection procedure is proposed for classifying the neighbourhood structure of the image. The techniques are investigated using simulated data.
作者：
Woo, HCTaegu Univ
Sch Comp & Commun Engn Jinryang Kyungsan Kyungp 712714 South Korea
The performance of a stochastic gradient adaptive filter can be significantly improved by introducing a forgetting factor. The complexity of the original algorithm can also be reduced by using only the signs of error ...
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The performance of a stochastic gradient adaptive filter can be significantly improved by introducing a forgetting factor. The complexity of the original algorithm can also be reduced by using only the signs of error signals and input signals in the gradient adaptive step size computation.
An elastic matrix containing aligned, randomly positioned, penny-shaped cracks is considered. Admission that the cracks open under tension and close under compression introduces a nonlinearity in the form of an inequa...
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An elastic matrix containing aligned, randomly positioned, penny-shaped cracks is considered. Admission that the cracks open under tension and close under compression introduces a nonlinearity in the form of an inequality into the boundary conditions. The stress in the matrix is found in terms of the dynamic Green's function and a field of internal variables representing crack openness. The boundary conditions on the crack allow an exact variational principle to be written down. Proof is given that subsequent statistical averaging and search for a solution within a particular space of trial functions is equivalent to making a quasi-crystalline approximation on the original equation for the stress. The stress then depends on two-point statistics. A system of integro-differential inequalities on a set of averaged variables is written down. This system models the effective behaviour of the composite. The integral terms contain information about history of loading and effects of crack interaction. In the case of an isotropic matrix with mean wave parallel to the crack normal, the equations decouple and the frictional behaviour of the cracks is irrelevant. Simplifying approximations to the integral terms allow easy numerical solutions to initial-and boundary-value problems on the averaged variables when the statistics have a particular form. This work is intended as an extension to that of Smyshlyaev and Willis (1996) to include the effects of crack interaction through two-point statistics. (C) 1998 Elsevier Science Ltd. All rights reserved.
A theory is presented to predict the stress/strain relations and unload/reload hysteresis behavior during the evolution of multiple matrix cracking in unidirectional fiber reinforced ceramic matrix composites (CMCs). ...
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A theory is presented to predict the stress/strain relations and unload/reload hysteresis behavior during the evolution of multiple matrix cracking in unidirectional fiber reinforced ceramic matrix composites (CMCs). The theory is based on the similarity between multiple matrix cracking and fiber fragmentation in a single fiber composite, and determines the crack and strain evolution as a function of the statistical distribution of initial flaws in the material, the interfacial sliding resistance tau, and the thermal residual stresses in the composite. The model properly includes matrix fragments of all lengths, from lengths smaller than the current slip length delta(sigma) to larger than 2 delta(sigma), at applied stress sigma, and accounts for their respective and differing contributions to the overall strain and hysteresis behavior of the composite. The procedure by which experimental stress/strain and hysteresis data can be interpreted to derive values for the interfacial shear stress, thermal stresses, and intrinsic matrix flaw distribution is discussed. The actual physical crack spacing needs only to be determined at one load level, such as post-fracture, which greatly simplifies the data acquisition and analysis. Several detailed examples are presented, and the results compared with a widely-used approach in which the crack spacing is assumed constant and equal to the average spacing obtained directly from experiment. The discrepancy between the previous and present theories is manifest in an incorrect estimate for the interfacial sliding, but only by approximately 10%. The effect of changing temperature, and hence residual stresses, without changing either matrix flaws or interfacial sliding resistance, is studied. (C) 1997 Elsevier Science Ltd.
The mechanism of the statistical variation of the shearing behavior of soil specimens is investigated from the viewpoint of bifurcation, under the major assumption that these specimens undergo elastic bifurcation, and...
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The mechanism of the statistical variation of the shearing behavior of soil specimens is investigated from the viewpoint of bifurcation, under the major assumption that these specimens undergo elastic bifurcation, and that such variation is ascribed to the variation of initial imperfections among specimens. Through a synthesis and an extension of the pre-existing bifurcation theory, we advance a method to describe that variation. Two series of triaxial compression tests are conducted to construct a data bank of the shearing behavior of sand specimens. An imperfection sensitivity law is employed to describe the variation in their axial strain versus axial stress curves and volumetric strain versus axial stress curves, and hence to assess the validity of those assumptions to demonstrate the predominant role of elastic bifurcation in soil shearing behavior. The theory of the stochasticity of initial imperfections is employed to explain the probabilistic variation of the maximum strength. (C) 1997 Elsevier Science Ltd.
Exact equations are derived governing the evolution of fragments in a long fiber loaded according to the ''single Nament composite test.'' These equations are derived with no a priori assumptions regar...
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Exact equations are derived governing the evolution of fragments in a long fiber loaded according to the ''single Nament composite test.'' These equations are derived with no a priori assumptions regarding the distribution for fiber strength except that the distribution of fiber flaws along the length follows a compound Poisson process in terms of flaw strength. Furthermore, the interface model and the fiber stress profile in the exclusion zone around a fiber break can be arbitrary as long as the exclusion zone is well defined. Explicit and exact closed-form solutions of the governing equations are obtained under these general conditions including random initial breaks before load is applied, which have exponentially distributed spacings of a given normalized rate a along the fiber. We demonstrate this method by finding the exact closed-form solution for a bilinear stress interface model proposed earlier. Copyright (C) 1996 Elsevier Science Ltd.
A study has been made of the micro mechanical origins of the irrecoverable compression of aggregates which comprise brittle grains. The terms ''yielding'' and ''plastic hardening'' are ...
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A study has been made of the micro mechanical origins of the irrecoverable compression of aggregates which comprise brittle grains. The terms ''yielding'' and ''plastic hardening'' are used in the discipline of soil mechanics to describe the post-elastic behaviour of granular media. These ''plastic'' phenomena are here related to the successive splitting of grains. Grains are taken to split probabilistically, the likelihood increasing with applied (macroscopic) stress, but reducing with any increase in the co-ordination number and with any reduction in particle size. When the effect of the co-ordination number dominates, a simple numerical model confirms published findings that a fractal distribution of particle sizes evolves from the compression of an aggregate of uniform grains. Taking the production of new surface area from the particle size distributions produced by the numerical model, a work equation is used to deduce the plastic compression of voids, for one-dimensional compression of the aggregate. This too is shown to be in agreement with experimental data, and in particular confirms the linearity of plots of voids ratio versus the logarithm of stress. The gradient of these plots is for the first time related to fundamental material parameters. Copyright (C) 1996 Elsevier Science Ltd.
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