In the parametric regression model, the covariate missing problem under missing at random is considered. It is often desirable to use flexible parametric or semiparametric models for the covariate distribution, which ...
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In the parametric regression model, the covariate missing problem under missing at random is considered. It is often desirable to use flexible parametric or semiparametric models for the covariate distribution, which can reduce a potential misspecification problem. Recently, a completely nonparametric approach was developed by [H.Y. Chen, Nonparametric and semiparametric models for missing covariates in parameter regression, J. Amer. Statist. Assoc. 99 (2004), pp. 1176-1189;Z. Zhang and H.E. Rockette, On maximum likelihood estimation in parametric regression with missing covariates, J. Statist. Plann. Inference 47 (2005), pp. 206-223]. Although it does not require a model for the covariate distribution or the missing data mechanism, the proposed method assumes that the covariate distribution is supported only by observed values. Consequently, their estimator is a restricted maximum likelihood estimator (MLE) rather than the global MLE. In this article, we show the restricted semiparametric MLE could be very misleading in some cases. We discuss why this problem occurs and suggest an algorithm to obtain the global MLE. Then, we assess the performance of the proposed method via some simulation experiments.
In this paper, we introduce a retrial queueing problem for wireless cellular networks applying the Fractional Guard Channel (FGC) admission control policy and propose a new algorithm to solve the retrial queue problem...
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In this paper, we introduce a retrial queueing problem for wireless cellular networks applying the Fractional Guard Channel (FGC) admission control policy and propose a new algorithm to solve the retrial queue problem involving the FGC policy. A comparison between analytical and simulation results shows that our algorithm is accurate and fast to evaluate the performance of the system. (C) 2010 Elsevier Ltd. All rights reserved.
We introduce a new solution technique for closed product-form queueing networks that generalizes the Method of Moments (MoM), a recently proposed exact algorithm that is several orders of magnitude faster and memory e...
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We introduce a new solution technique for closed product-form queueing networks that generalizes the Method of Moments (MoM), a recently proposed exact algorithm that is several orders of magnitude faster and memory efficient than the established Mean Value Analysis (MVA) algorithm. Compared to MVA, moM recursively computes higher-order moments of queue lengths instead of mean values, an approach that remarkably reduces the computational costs of exact solutions, especially on models with large numbers of jobs. In this paper, we show that the MoM recursion can be generalized to include multiple recursive branches that evaluate models with different numbers of queues, a solution approach inspired by the Convolution algorithm. Combining the approaches of MoM and Convolution simplifies the evaluation of normalizing constants and leads to large computational savings with respect to the recursive structure originally proposed for MOM. (C) 2010 Elsevier B.V. All rights reserved.
In the present paper an algorithmic implementation of a generalized plasticity model is presented with reference to a material behaviour at finite strains. A return mapping algorithm is implemented for an elastoplasti...
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ISBN:
(纸本)9788489925731
In the present paper an algorithmic implementation of a generalized plasticity model is presented with reference to a material behaviour at finite strains. A return mapping algorithm is implemented for an elastoplastic material behaviour in large deformations. A computationally efficient algorithmic scheme is described and the performance of a generalized plasticity model at finite deformations is illustrated. Numerical results and examples are finally reported.
The problem of switching stabilizability of linear uncertain switched systems with unstable modes has recently attracted increased interest. For a given collection of unstable linear uncertain subsystems, the problem ...
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The problem of switching stabilizability of linear uncertain switched systems with unstable modes has recently attracted increased interest. For a given collection of unstable linear uncertain subsystems, the problem is to determine asymptotically stabilizing switching signals or to ascertain the absence of such laws. In this paper, we deal with the switching stabilizability problem for a class of autonomous continuous-time switched linear systems with time-varying parametric uncertainties in the presence of additional state constraints. With a special emphasis on two-dimensional systems we extend previous relevant results in the literature, and we propose a computational technique that generates piecewise linear Lyapunov functions of a convex or non-convex nature. The algorithm is graph-based and consists of determining controlled invariant polytopes induced by systematic conic decompositions of the state-space and corresponding state-dependent switching control actions. Further extension of this computational tool to higher dimensional systems is also discussed.
In this technical note, we show how to use the analysis of the controllability Lie algebra of a quantum mechanical system to study its dynamics and facilitate the design of controls. We give algorithms to decompose th...
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In this technical note, we show how to use the analysis of the controllability Lie algebra of a quantum mechanical system to study its dynamics and facilitate the design of controls. We give algorithms to decompose the dynamics and describe an example of application to two coupled spin 1/2's.
Physiological cross-sectional area (PCSA) is used to compare force-producing capabilities of muscles. A limitation of PCSA is that it cannot be measured directly from a specimen, as there is usually no area within the...
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Physiological cross-sectional area (PCSA) is used to compare force-producing capabilities of muscles. A limitation of PCSA is that it cannot be measured directly from a specimen, as there is usually no area within the muscle traversed by all fibres. Traditionally, a formula requiring averaged architectural parameters has been used. The purpose of this paper is to describe the development of a fibre bundle element (FBE) method to calculate PCSA from digitised fibre bundle data of five architecturally distinct muscles and compare the FBE and PCSA formula. An FBE method was developed that used a serially arranged set of cylinders as the volumetric representation of each fibre bundle, and PCSA was computed as the summation of the cross-sectional area of each FBE. Four of five muscles had significantly different PCSA between FBE and formula methods. The FBE method provides an approach that considers architectural variances while minimising the need for averaged architectural parameters.
Efficient data visualization techniques are critical for many scientific applications. Centroidal Voronoi tessellation(CVT) based algorithms offer a convenient vehicle for performing image analysis,segmentation and co...
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Efficient data visualization techniques are critical for many scientific applications. Centroidal Voronoi tessellation(CVT) based algorithms offer a convenient vehicle for performing image analysis,segmentation and compression while allowing to optimize retained image quality with respect to a given *** experimental science with data counts following Poisson distributions,several CVT-based data tessellation algorithms have been recently *** they surpass their predecessors in robustness and quality of reconstructed data,time consumption remains to be an issue due to heavy utilization of the slowly converging Lloyd *** paper discusses one possible approach to accelerating data visualization *** relies on a multidimensional generalization of the optimization based multilevel algorithm for the numerical computation of the CVTs introduced in[1],where a rigorous proof of its uniform convergence has been presented in 1-dimensional *** multidimensional implementation employs barycentric coordinate based interpolation and maximal independent set coarsening *** is shown that when coupled with bin accretion algorithm accounting for the discrete nature of the data,the algorithm outperforms Lloyd-based schemes and preserves uniform convergence with respect to the problem *** numerical demonstrations provided are limited to spectroscopy data analysis,the method has a context-independent setup and can potentially deliver significant speedup to other scientific and engineering applications.
We present analytical algorithms for computing the ultimate bending strength of superhard composite materials based on WC-Co hardmetals. The study is performed for fine-grained materials (where mean particle size of t...
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We present analytical algorithms for computing the ultimate bending strength of superhard composite materials based on WC-Co hardmetals. The study is performed for fine-grained materials (where mean particle size of the dispersed superhard phase d (C) and that of carbide grains d (WC) are of the same order of magnitude) and coarse-grained materials (with d (C) a parts per thousand << d (WC) ). The strength of the composite is assumed to be governed by the strength of its hardmetal matrix. The stressed state of the matrix is assessed through volume-average microstresses for fine-grained materials and interface-average stresses for coarse-grained composites. The calculated results presented in the form of tables and graphs have been analyzed. The strength has been found to decrease drastically with increasing particle size of the superhard phase and its concentration in the composite.
Architectural parameters and physiological cross-sectional area (PCSA) are important determinants of muscle function. Extensor carpi radialis longus (ECRL) and brevis (ECRB) are used in muscle transfers;however, their...
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Architectural parameters and physiological cross-sectional area (PCSA) are important determinants of muscle function. Extensor carpi radialis longus (ECRL) and brevis (ECRB) are used in muscle transfers;however, their regional architectural differences have not been investigated. The aim of this study is to develop computational algorithms to quantify and compare architectural parameters (fiber bundle length, permation angle, and volume) and PCSA of ECRL and ECRB. Fiber bundles distributed throughout the volume of ECRL (75 +/- 20) and ECRB (110 +/- 30) were digitized in eight formalin embalmed cadaveric specimens. The digitized data was reconstructed in Autodesk (R) May (R) with computational algorithms implemented in Python. The mean PCSA and fiber bundle length were significantly different between ECRL and ECRB (p <= 0.05). Superficial ECRL had significantly longer fiber bundle length than the deep region, whereas the PCSA of superficial ECRB was significantly larger than the deep region. The regional quantification of architectural parameters and PCSA provides a framework for the exploration of partial tendon transfers of ECRL and ECRB. (C) 2009 Elsevier Ireland Ltd. All rights reserved.
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