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Optimal Selection (optimal + selection)
Selected AbstractsRetrospective selection bias (or the benefit of hindsight)GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2001Francesco Mulargia SUMMARY The complexity of geophysical systems makes modelling them a formidable task, and in many cases research studies are still in the phenomenological stage. In earthquake physics, long timescales and the lack of any natural laboratory restrict research to retrospective analysis of data. Such ,fishing expedition' approaches lead to optimal selection of data, albeit not always consciously. This introduces significant biases, which are capable of falsely representing simple statistical fluctuations as significant anomalies requiring fundamental explanations. This paper identifies three different strategies for discriminating real issues from artefacts generated retrospectively. The first attempts to identify ab initio each optimal choice and account for it. Unfortunately, a satisfactory solution can only be achieved in particular cases. The second strategy acknowledges this difficulty as well as the unavoidable existence of bias, and classifies all ,anomalous' observations as artefacts unless their retrospective probability of occurrence is exceedingly low (for instance, beyond six standard deviations). However, such a strategy is also likely to reject some scientifically important anomalies. The third strategy relies on two separate steps with learning and validation performed on effectively independent sets of data. This approach appears to be preferable in the case of small samples, such as are frequently encountered in geophysics, but the requirement for forward validation implies long waiting times before credible conclusions can be reached. A practical application to pattern recognition, which is the prototype of retrospective ,fishing expeditions', is presented, illustrating that valid conclusions are hard to find. [source] Analytical approach to the optimal adaptation rate of reconfigurable radio networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 7 2008R. Fraile Abstract Flexible radio resource management schemes are nowadays used within a wide range of systems. However, the optimal selection for their adaptation rate is still an open research issue. This paper presents an analytical approach to such problem, which consists in a combined analysis of the dynamics of the session-arrival process and the estimation of the mean traffic load from network measurements. From this study, it is concluded that both aspects pose an upper limit on the optimal system adaptation rate, being the most restrictive the one depending on the mean traffic load estimation. A specific procedure for deriving such limit on adaptation rate is provided. It is shown that the derived value directly depends on the mean service duration. The application of the whole analysis is illustrated with an example based on a set of measurements from a live network. Copyright © 2008 John Wiley & Sons, Ltd. [source] Scheduling multistage batch plants with sequence-dependent changeoversAICHE JOURNAL, Issue 8 2009Pedro M. Castro Abstract This article deals with the optimal short-term scheduling of multistage batch plants with parallel units and sequence-dependent changeovers, together with the optimal selection of the number and size of batches to be produced. A new resource-task network-based, multiple time-grid continuous-time formulation is proposed that explicitly considers a virtual, shared, intermediate storage unit per stage to keep track of material transfer between processing units belonging to consecutive stages of production. Adequate material transfer is implicitly ensured through mass balances and timing constraints relating the times of event points of dissimilar grids. The new formulation is compared with a conceptually different approach from another research group. The results for several example problems show that the new formulation is tighter, typically requiring fewer event points to find the global optimal solution, and is significantly more efficient computationally. The results also show that for single batch problems other approaches are preferable. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] SCREENING FOR CARDIOVASCULAR DISEASE IN PATIENTS WITH ADVANCED CHRONIC KIDNEY DISEASEJOURNAL OF RENAL CARE, Issue 2010Rajan Sharma BSc SUMMARY Cardiovascular disease remains the major cause of mortality and morbidity in patients with advanced chronic kidney disease (CKD) and after renal transplantation. The mechanisms for cardiotoxicity are multiple. Identifying high-risk patients remains a challenge. Given, the poor long-term outcome of dialysis patients who do not receive renal transplantation and the lower supply of donor kidneys relative to demand, optimal selection of renal transplantation candidates is crucial. This requires a clear understanding of the validity of cardiac tests in this patient group. This paper explores the strengths and weaknesses of currently available diagnostic tools in patients with advanced CKD. Echocardiography is very useful for the detection of cardiomyopathy and prognosis. Stress echocardiography, myocardial perfusion imaging and coronary angiography are the best tools for the assessment of coronary artery disease. All predict outcome. No single gold standard investigation exists. At present, there is not an optimal technique for predicting sudden cardiac death in this patient group. Ultimately, the choice of cardiac test will always be determined by patient preference, local expertise and availability. [source] Determinants of the optimal first-line therapy for follicular lymphoma: A decision analysis,AMERICAN JOURNAL OF HEMATOLOGY, Issue 4 2010Rebecca L. Olin Combination immunochemotherapy is the most common approach for initial therapy of patients with advanced-stage follicular lymphoma, but no consensus exists as to the optimal selection or sequence of available regimens. We undertook this decision analysis to systematically evaluate the parameters affecting the choice of early therapy in patients with this disease. We designed a Markov model incorporating the three most commonly utilized regimens (RCVP, RCHOP, and RFlu) in combinations of first- and second-line therapies, with the endpoint of number of quality-adjusted life years (QALYs) until disease progression. Data sources included Phase II and Phase III trials and literature estimates of long-term toxicities and health state utilities. Meta-analytic methods were used to derive the values and ranges of regimen-related parameters. Based on our model, the strategy associated with the greatest number of expected quality-adjusted life years was treatment with RCHOP in first-line therapy followed by treatment with RFlu in second-line therapy (9.00 QALYs). Strategies containing RCVP either in first- or second-line therapy resulted in the lowest number of QALYs (range 6.24,7.71). Sensitivity analysis used to determine the relative contribution of each model parameter identified PFS after first-line therapy and not short-term QOL as the most important factor in prolonging overall quality-adjusted life years. Our results suggest that regimens associated with a longer PFS provide a greater number of total QALYs, despite their short-term toxicities. For patients without contraindications to any of these regimens, use of a more active regimen may maximize overall quality of life. Am. J. Hematol. 2010. © 2010 Wiley-Liss, Inc. [source] Methodology for the optimal component selection of electronic devices under reliability and cost constraintsQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 8 2007E. P. Zafiropoulos Abstract The objective of this paper is to present an efficient computational methodology for the reliability optimization of electronic devices under cost constraints. The system modeling for calculating the reliability indices of the electronic devices is based on Bayesian networks using the fault tree approach, in order to overcome the limitations of the series,parallel topology of the reliability block diagrams. Furthermore, the Bayesian network modeling for the reliability analysis provides greater flexibility for representing multiple failure modes and dependent failure events, and simplifies fault diagnosis and reliability allocation. The optimal selection of components is obtained using the simulated annealing algorithm, which has proved to be highly efficient in complex optimization problems where gradient-based methods can not be applied. The reliability modeling and optimization methodology was implemented into a computer program in Matlab using a Bayesian network toolbox. The methodology was applied for the optimal selection of components for an electrical switch of power installations under reliability and cost constraints. The full enumeration of the solution space was calculated in order to demonstrate the efficiency of the proposed optimization algorithm. The results obtained are excellent since a near optimum solution was found in a small fraction of the time needed for the complete enumeration (3%). All the optimum solutions found during consecutive runs of the optimization algorithm lay in the top 0.3% of the solutions that satisfy the reliability and cost constraints. Copyright © 2007 John Wiley & Sons, Ltd. [source] Liquid chromatography/triple quadrupole tandem mass spectrometry with multiple reaction monitoring for optimal selection of transitions to evaluate nutraceuticals from olive-tree materialsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2008Rafael Japón Luján Optimal transitions have been selected for the identification and quantitation of the most interesting hydrophilic biophenols in extracts from olive-tree materials, which are of interest because of their nutraceutical properties. The tested materials were extra virgin olive oil, waste from oil production (known as alperujo), and olive-tree materials such as leaves, small branches and fruit stones. The identification and determination steps of the target biophenols are based on liquid chromatography/tandem mass spectrometry (LC/MS/MS) with a triple quadrupole (QQQ) mass detector. The interface between the chromatograph and the QQQ was an electrospray ionization source operated in the negative ion mode. Highly selective identification of the biophenols was confirmed by multiple reaction monitoring (MRM) using the most representative transitions from the precursor ion to the different product ions. Quantitative MS/MS analysis was carried out by optimization and selection of the most sensitive transition for each analyte, which resulted in estimated detection limits of 5.10 to 11.65,ng/mL for the extracts. The biophenols were extracted from the tested samples by different methods: liquid-liquid extraction for virgin olive oil, microwave-assisted leaching for olive leaves, branches and stones, and pressurized liquid leaching for alperujo. This study provides valuable information about the most suitable source for the isolation of each nutraceutical biophenol and enables us to obtain a complete profile of them in Olea Europaea. Copyright © 2008 John Wiley & Sons, Ltd. [source] Identification of cascaded systems with linear and quantized observations,ASIAN JOURNAL OF CONTROL, Issue 1 2010Le Yi Wang Abstract This paper studies identification of systems that can be decomposed into cascaded subsystems. The benefits of using additional sensors for identifying subsystems are investigated in terms of identification accuracy and time complexity. Identification algorithms, input design, and time complexity are first developed for subsystems, under various sensor types and locations. Overall reduction in estimation errors and time complexity is then analyzed to understand optimal selection of sensor locations and impact of sensor types on identification accuracy and time complexity. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] N-linked glycosylation is an important parameter for optimal selection of cell lines producing biopharmaceutical human IgGBIOTECHNOLOGY PROGRESS, Issue 1 2009Patrick H. C. van Berkel Abstract We studied the variations in N-linked glycosylation of human IgG molecules derived from 105 different stable cell lines each expressing one of the six different antibodies. Antibody expression was based on glutamine synthetase selection technology in suspension growing CHO-K1SV cells. The glycans detected on the Fc fragment were mainly of the core-fucosylated complex type containing zero or one galactose and little to no sialic acid. The glycosylation was highly consistent for the same cell line when grown multiple times, indicating the robustness of the production and glycan analysis procedure. However, a twofold to threefold difference was observed in the level of galactosylation and/or non-core-fucosylation between the 105 different cell lines, suggesting clone-to-clone variation. These differences may change the Fc-mediated effector functions by such antibodies. Large variation was also observed in the oligomannose-5 glycan content, which, when present, may lead to undesired rapid clearance of the antibody in vivo. Statistically significant differences were noticed between the various glycan parameters for the six different antibodies, indicating that the variable domains and/or light chain isotype influence Fc glycosylation. The glycosylation altered when batch production in shaker was changed to fed-batch production in bioreactor, but was consistent again when the process was scaled from 400 to 5,000 L. Taken together, the observed clone-to-clone glycosylation variation but batch-to-batch consistency provides a rationale for selection of optimal production cell lines for large-scale manufacturing of biopharmaceutical human IgG. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Optimal Synthesis of Protein Purification ProcessesBIOTECHNOLOGY PROGRESS, Issue 4 2001Elsa Vásquez-Alvarez There has been an increasing interest in the development of systematic methods for the synthesis of purification steps for biotechnological products, which are often the most difficult and costly stages in a biochemical process. Chromatographic processes are extensively used in the purification of multicomponent biotechnological systems. One of the main challenges in the synthesis of purification processes is the appropriate selection and sequencing of chromatographic steps that are capable of producing the desired product at an acceptable cost and quality. This paper describes mathematical models and solution strategies based on mixed integer linear programming (MILP) for the synthesis of multistep purification processes. First, an optimization model is proposed that uses physicochemical data on a protein mixture, which contains the desired product, to select a sequence of operations with the minimum number of steps from a set of candidate chromatographic techniques that must achieve a specified purity level. Since several sequences that have the minimum number of steps may satisfy the purity level, it is possible to obtain the one that maximizes final purity. Then, a second model that may use the total number of steps obtained in the first model generates a solution with the maximum purity of the product. Whenever the sequence does not affect the final purity or more generally does not impact the objective function, alternative models that are of smaller size are developed for the optimal selection of steps. The models are tested in several examples, containing up to 13 contaminants and a set of 22 candidate high-resolution steps, generating sequences of six operations, and are compared to the current synthesis approaches. [source] | ||||||||||||||||