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Specific Assumptions (specific + assumption)
Selected AbstractsA Kharitonov-like theorem for robust stability independent of delay of interval quasipolynomialsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 6 2010Onur Toker Abstract In this paper, a Kharitonov-like theorem is proved for testing robust stability independent of delay of interval quasipolynomials, p(s)+,eqk(s), where p and qk's are interval polynomials with uncertain coefficients. It is shown that the robust stability test of the quasipolynomial basically reduces to the stability test of a set of Kharitonov-like vertex quasipolynomials, where stability is interpreted as stability independent of delay. As discovered in (IEEE Trans. Autom. Control 2008; 53:1219,1234), the well-known vertex-type robust stability result reported in (IMA J. Math. Contr. Info. 1988; 5:117,123) (See also (IEEE Trans. Circ. Syst. 1990; 37(7):969,972; Proc. 34th IEEE Conf. Decision Contr., New Orleans, LA, December 1995; 392,394) does contain a flaw. An alternative approach is proposed in (IEEE Trans. Autom. Control 2008; 53:1219,1234), and both frequency sweeping and vertex type robust stability tests are developed for quasipolynomials with polytopic coefficient uncertainties. Under a specific assumption, it is shown in (IEEE Trans. Autom. Control 2008; 53:1219,1234) that robust stability independent of delay of an interval quasipolynomial can be reduced to stability independent of delay of a set of Kharitonov-like vertex quasipolynomials. In this paper, we show that the assumption made in (IEEE Trans. Autom. Control 2008; 53:1219,1234) is redundant, and the Kharitonov-like result reported in (IEEE Trans. Autom. Control 2008; 53:1219,1234) is true without any additional assumption, and can be applied to all quasipolynomials. The key idea used in (IEEE Trans. Autom. Control 2008; 53:1219,1234) was the equivalence of Hurwitz stability and , -o -stability for interval polynomials with constant term never equal to zero. This simple observation implies that the well-known Kharitonov theorem for Hurwitz stability can be applied for , -o -stability, provided that the constant term of the interval polynomial never vanishes. However, this line of approach is based on a specific assumption, which we call the CNF-assumption. In this paper, we follow a different approach: First, robust , -o -stability problem is studied in a more general framework, including the cases where degree drop is allowed, and the constant term as well as other higher-orders terms can vanish. Then, generalized Kharitonov-like theorems are proved for , -o -stability, and inspired by the techniques used in (IEEE Trans. Autom. Control 2008; 53:1219,1234), it is shown that robust stability independent of delay of an interval quasipolynomial can be reduced to stability independent of delay of a set of Kharitonov-like vertex quasipolynomials, even if the assumption adopted in (IEEE Trans. Autom. Control 2008; 53:1219,1234) is not satisfied. Copyright © 2009 John Wiley & Sons, Ltd. [source] Association tests using kernel-based measures of multi-locus genotype similarity between individualsGENETIC EPIDEMIOLOGY, Issue 3 2010Indranil Mukhopadhyay Abstract In a genetic association study, it is often desirable to perform an overall test of whether any or all single-nucleotide polymorphisms (SNPs) in a gene are associated with a phenotype. Several such tests exist, but most of them are powerful only under very specific assumptions about the genetic effects of the individual SNPs. In addition, some of the existing tests assume that the direction of the effect of each SNP is known, which is a highly unlikely scenario. Here, we propose a new kernel-based association test of joint association of several SNPs. Our test is non-parametric and robust, and does not make any assumption about the directions of individual SNP effects. It can be used to test multiple correlated SNPs within a gene and can also be used to test independent SNPs or genes in a biological pathway. Our test uses an analysis of variance paradigm to compare variation between cases and controls to the variation within the groups. The variation is measured using kernel functions for each marker, and then a composite statistic is constructed to combine the markers into a single test. We present simulation results comparing our statistic to the U -statistic-based method by Schaid et al. ([2005] Am. J. Hum. Genet. 76:780,793) and another statistic by Wessel and Schork ([2006] Am. J. Hum. Genet. 79:792,806). We consider a variety of different disease models and assumptions about how many SNPs within the gene are actually associated with disease. Our results indicate that our statistic has higher power than other statistics under most realistic conditions. Genet. Epidemiol. 34: 213,221, 2010. © 2009 Wiley-Liss, Inc. [source] Determining controller benefits via probabilistic optimizationINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 7-9 2003Y. Zhou Abstract For the most part, process control research has focussed on the synthesis and tuning of controllers, which has provided a plethora of techniques that can address virtually any application. With each new control technique, a steady stream of ,successful' application results are generated and reported. Recently, a considerable number of control researchers have turned their attention to assessing the performance of installed control systems and to the diagnosis of controller performance problems. Despite successes in the areas of controller synthesis, tuning and performance analysis, almost no research has addressed the fundamental issue of determining whether the economic performance gains that are expected accrue from a proposed process control project are sufficient to justify its execution. The work presented here proposes an optimization-based technique for calculating the expected economic performance of a given control system; a method, which is analogous to analysis of variance, for determining the expected economic benefit that will arise from a particular controller improvement effort; and a sensitivity analysis approach for determining the effect of specific assumptions on control system improvement decisions. Copyright © 2003 John Wiley & Sons, Ltd. [source] Racing to Theory or Retheorizing Race?JOURNAL OF SOCIAL ISSUES, Issue 1 2009Understanding the Struggle to Build a Multiracial Identity Theory Empirical research on the growing multiracial population in the United States has focused largely on the documentation of racial identification, analysis of psychological adjustment, and understanding the broader political consequences of mixed-race identification. Efforts toward theory construction on multiracial identity development, however, have been largely disconnected from empirical data, mired in disciplinary debates, and bound by historically specific assumptions about race and racial group membership. This study provides a critical overview of multiracial identity development theories, examines the links between theory and research, explores the challenges to multiracial identity theory construction, and proposes considerations for future directions in theorizing racial identity development among the mixed-race population. [source] DEMAND POLICIES FOR LONG-RUN GROWTH: BEING KEYNESIAN BOTH IN THE SHORT AND IN THE LONG RUN?METROECONOMICA, Issue 1 2007Article first published online: 8 FEB 200, Marco Missaglia ABSTRACT The idea of demand-led growth is defended by neo-Kaleckians and neo-Keynesians using very specific assumptions. In their models the paradox of costs is always valid in the long run. The central message of this paper is that these specific and strong assumptions are not needed to defend the Kaleckian perspective of a demand-driven long-run growth. What is needed is simply a less demanding theory of flexible mark-ups in an open economy. The formal model developed in this paper shows that long-run growth may be demand driven even when the paradox of costs does not hold in the long run. [source] A predator's perspective of nest predation: predation by red squirrels is learned, not incidentalOIKOS, Issue 5 2010Shawna A. Pelech Nest predation has been used to explain aspects of avian ecology ranging from nest site selection to population declines. Many arguments rely on specific assumptions regarding how predators find nests, yet these predatory mechanisms remain largely untested. Here we combine artificial nest experiments with behavioural observations of individual red squirrels Tamiasciurus hudsonicus to differentiate between two common hypotheses: predation is incidental versus learned. Specifically, we tested: 1) whether nest survival could be explained solely by a squirrel's activity patterns or habitat use, as predicted if predation was incidental; or 2) if predation increased as a squirrel gained experience preying on a nest, as predicted if predation was learned. We also monitored squirrel activity after predation to test for evidence of two search mechanisms: area-restricted searching and use of microhabitat search images. Contrary to incidental predation and in support of learning, squirrels did not find nests faster in areas with high use (e.g. forest edges). Instead, survival of artificial nests was strongly related to a squirrel's prior experience preying on artificial nests. Experience reduced nest survival times by over half and increased predation rates by 150,200%. Squirrels returned to and doubled their activity at the site of a previously preyed on nest. However, neither area-restricted searching nor microhabitat search images can explain how squirrels located artificial nests more readily with experience. Instead, squirrels likely used cues associated with the nests or eggs themselves. Learning implies that squirrels could be increasingly effective predators as the density or profitability of nests increases. Our results add support to the view that nest predation is complex and broadly influenced (e.g. by predator experience, motivation), and is unlikely to be predicted consistently by simple relationships with predator activity, abundance or habitat. [source] A basic study design for expedited safety signal evaluation based on electronic healthcare data,PHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 8 2010Sebastian Schneeweiss MD Abstract Active drug safety monitoring based on longitudinal electronic healthcare databases (a Sentinel System), as outlined in recent FDA-commissioned reports, consists of several interlocked processes, including signal generation, signal strengthening, and signal evaluation. Once a signal of a potential drug safety issue is generated, signal strengthening and signal evaluation have to follow in short sequence in order to quickly provide as much information about the triggering drug-event association as possible. This paper proposes a basic study design based on the incident user cohort design for expedited signal evaluation in longitudinal healthcare databases. It will not resolve all methodological issues nor will it fit all study questions arising within the framework of a Sentinel System. It should rather be seen as a guidance that will fit the majority of situations and serve as a starting point for adaptations to specific studies. Such an approach will expedite and structure the process of study development and highlight specific assumptions, which is particularly valuable in a Sentinel System where signals are by definition preliminary and evaluation of signals is time critical. Copyright © 2010 John Wiley & Sons, Ltd. [source] The promise of geometric morphometricsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue S35 2002Joan T. Richtsmeier Abstract Nontraditional or geometric morphometric methods have found wide application in the biological sciences, especially in anthropology, a field with a strong history of measurement of biological form. Controversy has arisen over which method is the "best" for quantifying the morphological difference between forms and for making proper statistical statements about the detected differences. This paper explains that many of these arguments are superfluous to the real issues that need to be understood by those wishing to apply morphometric methods to biological data. Validity, the ability of a method to find the correct answer, is rarely discussed and often ignored. We explain why demonstration of validity is a necessary step in the evaluation of methods used in morphometrics. Focusing specifically on landmark data, we discuss the concepts of size and shape, and reiterate that since no unique definition of size exists, shape can only be recognized with reference to a chosen surrogate for size. We explain why only a limited class of information related to the morphology of an object can be known when landmark data are used. This observation has genuine consequences, as certain morphometric methods are based on models that require specific assumptions, some of which exceed what can be known from landmark data. We show that orientation of an object with reference to other objects in a sample can never be known, because this information is not included in landmark data. Consequently, a descriptor of form difference that contains information on orientation is flawed because that information does not arise from evidence within the data, but instead is a product of a chosen orientation scheme. To illustrate these points, we apply superimposition, deformation, and linear distance-based morphometric methods to the analysis of a simulated data set for which the true differences are known. This analysis demonstrates the relative efficacy of various methods to reveal the true difference between forms. Our discussion is intended to be fair, but it will be obvious to the reader that we favor a particular approach. Our bias comes from the realization that morphometric methods should operate with a definition of form and form difference consistent with the limited class of information that can be known from landmark data. Answers based on information that can be known from the data are of more use to biological inquiry than those based on unjustifiable assumptions. Yrbk Phys Anthropol 45:63,91, 2002. © 2002 Wiley-Liss, Inc. [source] Body and Soul: Oskar Kokoschka's The Warrior, truth, and the interchangeability of the physical and psychological in fin-de-siècle ViennaART HISTORY, Issue 1 2000Claude Cernuschi This essay examines the interpretive issues raised by Oskar Kokoschka's sculpted bust The Warrior, in light of Kokoschka's rejection of Gustav Klimt's decorative use of ornament in favour of an Expressionist visual language of formal distortion and physiognomic exaggeration. Among the most salient properties introduced by Kokoschka's mode of Expressionist portraiture is the depiction of human flesh as if it were transparent, with veins, arteries and nerve endings left visible on the surface of the skin. The essay also focuses on how Kokoschka's experiments were patronized by the architect Adolf Loos, and how Loos and Kokoschka could have construed this new idiom as an evocation of psychological ,truth', an evocation consistent with the architect's own obsession with truth to materials in architectural structures. The essay further argues that the association of Kokoschka's suggestion of physical decay with psychological truth was essentially rhetorical; that this association could only have been made against time-bound and culturally specific assumptions about the interchangeability of the physical and psychological; and that this association was culled from a broad panoply of ideas prominent in nineteenth-century philosophy, medicine and psychiatry. [source] Particle Sizes from Sectional DataBIOMETRICS, Issue 1 2009k Pawlas Summary We propose a new statistical method for obtaining information about particle size distributions from sectional data without specific assumptions about particle shape. The method utilizes recent advances in local stereology. We show how to estimate separately from sectional data the variance due to the local stereological estimation procedure and the variance due to the variability of particle sizes in the population. Methods for judging the difference between the distribution of estimated particle sizes and the distribution of true particle sizes are also provided. [source] Parameter Estimation in a Gompertzian Stochastic Model for Tumor GrowthBIOMETRICS, Issue 4 2000L. Ferrante Summary. The problem of estimating parameters in the drift coefficient when a diffusion process is observed continuously requires some specific assumptions. In this paper, we consider a stochastic version of the Gompertzian model that describes in vivo tumor growth and its sensitivity to treatment with antiangiogenic drugs. An explicit likelihood function is obtained, and we discuss some properties of the maximum likelihood estimator for the intrinsic growth rate of the stochastic Gompertzian model. Furthermore, we show some simulation results on the behavior of the corresponding discrete estimator. Finally, an application is given to illustrate the estimate of the model parameters using real data. [source] | |||||||||||||