Treatment of body forces in boundary element design sensitivity analysis

The inclusion of body forces has received a good deal of attention in boundary element research. The consideration of such forces is essential in the desgin of high performance components such as fan and turbine disks in a gas turbine engine. Due to their critical performance requirements, optimal shapes are often desired for these components. The boundary element method (BEM) offers the possibility of being an efficient method for such iterative analysis as shape optimization. The implicit-differentiation of the boundary integral equations is performed to obtain the sensitivity equations. The body forces are accounted for by either the particular integrals for uniform body forces or by a surface integration for non-uniform body forces. The corresponding sensitivity equations for both these cases are presented. The validity of present formulations is established through a close agreement with exact analytical results

Detection and predictive modeling of chaos in finite hydrological time series

International audienceThe ability to detect the chaotic signal from a finite time series observation of hydrologic systems is addressed in this paper. The presence of random and seasonal components in hydrological time series, like rainfall or runoff, makes the detection process challenging. Tests with simulated data demonstrate the presence of thresholds, in terms of noise to chaotic-signal and seasonality to chaotic-signal ratios, beyond which the set of currently available tools is not able to detect the chaotic component. The investigations also indicate that the decomposition of a simulated time series into the corresponding random, seasonal and chaotic components is possible from finite data. Real streamflow data from the Arkansas and Colorado rivers are used to validate these results. Neither of the raw time series exhibits chaos. While a chaotic component can be extracted from the Arkansas data, such a component is either not present or can not be extracted from the Colorado data. This indicates that real hydrologic data may or may not have a detectable chaotic component. The strengths and limitations of the existing set of tools for the detection and modeling of chaos are also studied

Direct and indirect costs of nephrolithiasis in an employed population: Opportunity for disease management?

Direct and indirect costs of nephrolithiasis in an employed population: Opportunity for disease management?BackgroundMore than 5% of the United States population has been diagnosed with nephrolithiasis and about one half of (first-time) stone formers will have a recurrence within 5 years. The prevalence of nephrolithiasis is concentrated among working age adults, yet little prior work has examined the economic burden of the disease on employers and their employees. We sought to estimate the direct and indirect costs of nephrolithiasis for working age adults (18-64) with employer-provided insurance.MethodsThis was an observational study using retrospective claims data. Detailed medical and pharmacy claims from 25 large employers and absentee data from a subset of firms were used to estimate the direct and indirect costs associated with nephrolithiasis in a privately insured, nonelderly population. Multivariate regression models were used to predict health care expenditures for persons with and without the condition, controlling for differences in patient (health status) and plan characteristics.ResultsMore than 1% of working-age adults were treated for nephrolithiasis in 2000. Prevalence was considerably higher among men and employees age 55 to 64. About one third of employees treated for nephrolithiasis in 2000 missed work due to the condition, with an average work loss for the entire treated population of 19 hours per person. Conditional on receiving treatment, the incremental costs of nephrolithiasis were $3,494 per person in 2000.ConclusionThe direct and indirect costs of nephrolithiaisis are substantial among working-age adults. Interventions that prevent recurrence among known stone formers may be a cost-effective component of disease management programs

The symmetric N-matrix completion problem

An $n\times n$ matrix is called an $N$-matrix if all its principal minors are negative. In this paper, we are interested in the symmetric $N$-matrix completion problem, that is, when a partial symmetric $N$-matrix has a symmetric $N$-matrix completion. Here, we prove that a partial symmetric $N$-matrix has a symmetric $N$-matrix completion if the graph of its specified entries is chordal. Furthermore, if this graph is not chordal, then examples exist without symmetric $N$-matrix completions. Necessary and sufficient conditions for the existence of a symmetric $N$-matrix completion of a partial symmetric $N$-matrix whose associated graph is a cycle are given.Fundação para a Ciência e a Tecnologia (FCT) - Programa Operacional "Ciência, Tecnologia, Inovação" (POCTI). Spanish DGI - grant number BFM2001-0081-C03-02. Generalitat Valenciana - GRUPOS03/062

Numerical Construction of LISS Lyapunov Functions under a Small Gain Condition

In the stability analysis of large-scale interconnected systems it is frequently desirable to be able to determine a decay point of the gain operator, i.e., a point whose image under the monotone operator is strictly smaller than the point itself. The set of such decay points plays a crucial role in checking, in a semi-global fashion, the local input-to-state stability of an interconnected system and in the numerical construction of a LISS Lyapunov function. We provide a homotopy algorithm that computes a decay point of a monotone op- erator. For this purpose we use a fixed point algorithm and provide a function whose fixed points correspond to decay points of the monotone operator. The advantage to an earlier algorithm is demonstrated. Furthermore an example is given which shows how to analyze a given perturbed interconnected system.Comment: 30 pages, 7 figures, 4 table