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Model Design (model + design)
Selected AbstractsA covariance-adaptive approach for regularized inversion in linear modelsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2007Christopher Kotsakis SUMMARY The optimal inversion of a linear model under the presence of additive random noise in the input data is a typical problem in many geodetic and geophysical applications. Various methods have been developed and applied for the solution of this problem, ranging from the classic principle of least-squares (LS) estimation to other more complex inversion techniques such as the Tikhonov,Philips regularization, truncated singular value decomposition, generalized ridge regression, numerical iterative methods (Landweber, conjugate gradient) and others. In this paper, a new type of optimal parameter estimator for the inversion of a linear model is presented. The proposed methodology is based on a linear transformation of the classic LS estimator and it satisfies two basic criteria. First, it provides a solution for the model parameters that is optimally fitted (in an average quadratic sense) to the classic LS parameter solution. Second, it complies with an external user-dependent constraint that specifies a priori the error covariance (CV) matrix of the estimated model parameters. The formulation of this constrained estimator offers a unified framework for the description of many regularization techniques that are systematically used in geodetic inverse problems, particularly for those methods that correspond to an eigenvalue filtering of the ill-conditioned normal matrix in the underlying linear model. Our study lies on the fact that it adds an alternative perspective on the statistical properties and the regularization mechanism of many inversion techniques commonly used in geodesy and geophysics, by interpreting them as a family of ,CV-adaptive' parameter estimators that obey a common optimal criterion and differ only on the pre-selected form of their error CV matrix under a fixed model design. [source] A modular approach to addressing model design, scale, and parameter estimation issues in distributed hydrological modellingHYDROLOGICAL PROCESSES, Issue 2 2002G. H. Leavesley Abstract A modular approach to model design and construction provides a flexible framework in which to focus the multidisciplinary research and operational efforts needed to facilitate the development, selection, and application of the most robust distributed modelling methods. A variety of modular approaches have been developed, but with little consideration for compatibility among systems and concepts. Several systems are proprietary, limiting any user interaction. The US Geological Survey modular modelling system (MMS) is a modular modelling framework that uses an open source software approach to enable all members of the scientific community to address collaboratively the many complex issues associated with the design, development, and application of distributed hydrological and environmental models. Implementation of a common modular concept is not a trivial task. However, it brings the resources of a larger community to bear on the problems of distributed modelling, provides a framework in which to compare alternative modelling approaches objectively, and provides a means of sharing the latest modelling advances. The concepts and components of the MMS are described and an example application of the MMS, in a decision-support system context, is presented to demonstrate current system capabilities. Copyright © 2002 John Wiley & Sons, Ltd. [source] Analysis of low content drug tablets by transmission near infrared spectroscopy: Selection of calibration ranges according to multivariate detection and quantitation limits of PLS modelsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2008Manel Alcalą Abstract The content uniformity of low dose products is a major concern in the development of pharmaceutical formulations. Near infrared spectroscopy may be used to support the design and optimization of potent drug manufacturing processes through the analysis of blends and tablets in a relatively short time. A strategy for the selection of concentration ranges in the development of multivariate calibration is presented, evaluating the detection and quantitation limits of the obtained multivariate models. The strategy has been applied to the determination of an active principle in pharmaceutical tablets of low concentration (0,5%, w/w), using Fourier Transform Near Infrared (FT-NIR) transmission spectroscopy. The quantitation and detection limits decreased as the upper concentration level of the calibration models was reduced. The results obtained show that the selection of concentration ranges is a critical aspect during model design. The selection of wide concentration ranges with high levels is not recommended for the determination of analytes at minor levels (<1%, w/w), even when the concentration of interest is within the range of the model. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:5318,5327, 2008 [source] Region, Local Context, and Voting at the 1997 General Election in EnglandAMERICAN JOURNAL OF POLITICAL SCIENCE, Issue 3 2007Ron Johnston There has been considerable debate in recent work on voting patterns in Great Britain regarding the importance of regional effects: are these "real" or are they simply statistical artifacts of decision-making processes at smaller spatial scales which are aggregated up to the regional scale if not incorporated directly into any modeling? Using a multilevel model design, this article reports on analyses of survey data for the 1997 general election in England which allows tests of whether regional variations are no more than aggregation effects. Individual voters are nested within households, neighborhoods, constituencies, and regions and when all of the smaller-scale spatial levels are included in the model, the observed regional effects are statistically insignificant. At the 1997 general election, at least, regional variations within England in support for the three main parties,basically, a north-south divide,are aggregation effects. [source] On a robust synchronization problem via internal model approach,ASIAN JOURNAL OF CONTROL, Issue 1 2010Weijie Sun Abstract This paper formulates the synchronization of the Duffing system and the Van der Pol oscillator as a robust output regulation problem and presents the solution to this problem based on the internal model design. The controller thus obtained is able to achieve the synchronization of the outputs of these two systems in the presence of the parameter uncertainty of the Duffing system. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Trust management in wireless sensor networksEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 4 2010Theodore Zahariadis The range of applications of wireless sensor networks is so wide that it tends to invade our every day life. In the future, a sensor network will survey our health, our home, the roads we follow, the office or the industry we work in or even the aircrafts we use, in an attempt to enhance our safety. However, the wireless sensor networks themselves are prone to security attacks. The list of security attacks, although already very long, continues to augment impeding the expansion of these networks. The trust management schemes consist of a powerful tool for the detection of unexpected node behaviours (either faulty or malicious). Once misbehaving nodes are detected, their neighbours can use this information to avoid cooperating with them, either for data forwarding, data aggregation or any other cooperative function. A variety of trust models which follow different directions regarding the distribution of measurement functionality, the monitored behaviours and the way measurements are used to calculate/define the node's trustworthiness has been presented in the literature. In this paper, we survey trust models in an attempt to explore the interplay among the implementation requirements, the resource consumption and the achieved security. Our goal is to draw guidelines for the design of deployable trust model designs with respect to the available node and network capabilities and application peculiarities. Copyright © 2010 John Wiley & Sons, Ltd. [source] Population pharmacokinetic modelling of carbamazepine in epileptic elderly patients: implications for dosageJOURNAL OF CLINICAL PHARMACY & THERAPEUTICS, Issue 3 2006I. B. Bondareva PhD Summary Background:, Proper use of antiepileptic drugs in the elderly involves knowledge of their pharmacokinetics to ensure a patient-specific balance between efficacy and toxicity. However, populations of epileptic patients on chronic carbamazepine (CBZ) therapy which have been studied have included data of relatively few elderly patients. Aims:, The aim of the present study was to evaluate the population pharmacokinetics of CBZ in elderly patients on chronic monotherapy. Methods:, We have used the non-parametric expectation maximization (NPEM) program in the USC*PACK collection of PC programs to estimate individual and population post-induction pharmacokinetics of CBZ in epileptic elderly patients who received chronic CBZ monotherapy. Age-related changes of CBZ population pharmacokinetics were evaluated from routine therapeutic drug monitoring (TDM) data of 37 elderly and 35 younger patients with epilepsy. As a ,historical control' we used previously published population modelling results from 99 young epileptic patients on chronic CBZ monotherapy. In that control group, TDM was performed in the same pharmacokinetic (PK) laboratory, using the same sampling strategy as in the present study, and the same PK population modelling software was used for data analysis. Results and conclusions:, A poor correlation was found between daily CBZ dose and serum concentrations in the elderly patients (r = 0·2, P = 0·25). Probably statistically significant difference in the median values of the CBZ metabolic rate constant (P < 0·001) between elderly and relatively young epileptic patients was found. Our results showed that age-related influences in CBZ pharmacokinetics in elderly patients should be considered in the optimal planning of CBZ dosage regimens. Most elderly patients with epilepsy will usually need CBZ dosages lower than those based on the median population PK parameter values obtained from younger patients. The present population model is also uniquely well suited for the new ,multiple model' design of dosage regimens to hit target therapeutic goals with maximum precision. [source] | ||||||||||