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61.
In this note, we investigate different concepts of nonlinear identifiability in the generic sense. We work in the linear algebraic framework. Necessary and sufficient conditions are found for geometrical identifiability, algebraic identifiability and identifiability with known initial conditions. Relationships between different concepts are characterized. Constructive procedures are worked out for both generic geometrical and algebraic identifiability of nonlinear systems. As an application of the theory developed, we study the identifiability properties of a four dimensional model of HIV/AIDS. The questions answered in this study include the minimal number of measurement of the variables for a complete determination of all parameters and the best period of time to make such measurements. This information will be useful in formulating guidelines for clinical practice. 相似文献
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The main difficulty with EM algorithm for mixture model concerns the number of components, say g. This is the question of model selection, and the EM algorithm itself could not estimate g. On the contrary, the algorithm requires g to be specified before the remaining parameters can be estimated. To solve this problem, a new algorithm, which is called stepwise split-and-merge EM (SSMEM) algorithm, is proposed. The SSMEM algorithm alternately splits and merges components, estimating g and other parameters of components simultaneously. Also, two novel criteria are introduced to efficiently select the components for split or merge. Experimental results on simulated and real data demonstrate the effectivity of the proposed algorithm. 相似文献
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Chouping Luo Marek Klisinski 《International journal for numerical methods in engineering》2004,61(2):159-188
The present study is a continuation of our previous work with the aim to reduce problems caused by standard higher order elements in contact problems. The difficulties can be attributed to the inherent property of the Galerkin method which gives uneven distributions of nodal forces resulting in oscillating contact pressures. The proposed remedy is use of piece‐wise linear weight functions. The methods to establish stiffness and/or mass matrix for 8‐node quadrilateral element in 2D are presented, i.e. the condensing and direct procedures. The energy and nodal displacement error norms are also checked to establish the convergence ratio. Interpretation of calculated contact pressures is discussed. Two new 2D 8‐node quadrilateral elements, QUAD8C and QUAD8D, are derived and tested in many examples, which show their good performance in contact problems. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
66.
Grain refinement of Al-7Si alloys and the efficiency assessment by recognition of cooling curves 总被引:5,自引:0,他引:5
Under sand cup solidification condition, the influence of Ti, B concentration, and holding time on the grain size of a high-purity
Al-7Si alloy has been systematically studied. It is found that the grain size decreases rapidly at lower Ti or B additions,
and is almost constant at the higher concentrations. For Al-3B refined Al-7Si alloys, the grain size increases at the initial
period of holding time, and then rapidly becomes independent of holding time; while for Al-7Si alloys refined with Al-5Ti-1B,
the grain size increases with holding time throughout. To evaluate the refinement efficiency, a new method named “intelligent
evaluating of melt quality by pattern recognition of thermal analysis cooling curves” has also been introduced in this article.
The results show that comparing the cooling curve of the evaluated melt with those in a database to find the most similar
one to it can precisely assess the grain refinement efficiency of the measured Al-7Si alloy. In addition, the influence of
Ti, B addition levels, and pouring temperatures on some characteristic parameters of cooling curve has also been discussed. 相似文献
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