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991.
Shawn E. Gano John E. Renaud Jay D. Martin Timothy W. Simpson 《Structural and Multidisciplinary Optimization》2006,32(4):287-298
Many optimization methods for simulation-based design rely on the sequential use of metamodels to reduce the associated computational burden. In particular, kriging models are frequently used in variable fidelity optimization. Nevertheless, such methods may become computationally inefficient when solving problems with large numbers of design variables and/or sampled data points due to the expensive process of optimizing the kriging model parameters in each iteration. One solution to this problem would be to replace the kriging models with traditional Taylor series response surface models. Kriging models, however, were shown to provide good approximations of computer simulations that incorporate larger amounts of data, resulting in better global accuracy. In this paper, a metamodel update management scheme (MUMS) is proposed to reduce the cost of using kriging models sequentially by updating the kriging model parameters only when they produce a poor approximation. The scheme uses the trust region ratio (TR-MUMS), which is a ratio that compares the approximation to the true model. Two demonstration problems are used to evaluate the proposed method: an internal combustion engine sizing problem and a control-augmented structural design problem. The results indicate that the TR-MUMS approach is very effective; on the demonstration problems, it reduced the number of likelihood evaluations by three orders of magnitude compared to using a global optimizer to find the kriging parameters in every iteration. It was also found that in trust region-based method, the kriging model parameters need not be updated using a global optimizer—local methods perform just as well in terms of providing a good approximation without affecting the overall convergence rate, which, in turn, results in a faster execution time. 相似文献
992.
993.
Managing database server performance to meet QoS requirements in electronic commerce systems 总被引:1,自引:0,他引:1
Patrick Martin Wendy Powley Hoi-Ying Li Keri Romanufa 《International Journal on Digital Libraries》2002,3(4):316-324
The performance of electronic commerce systems has a major impact on their acceptability to users. Different users also demand
different levels of performance from the system, that is, they will have different Quality of Service (QoS) requirements. Electronic commerce systems are the integration of several different types of servers and each server must
contribute to meeting the QoS demands of the users. In this paper we focus on the role, and the performance, of a database server within an electronic commerce system.
We examine the characteristics of the workload placed on a database server by an electronic commerce system and suggest a
range of QoS requirements for the database server based on this analysis of the workload. We argue that a database server
must be able to dynamically reallocate its resources in order to meet the QoS requirements of different transactions as the
workload changes. We describe Quartermaster, which is a system to support dynamic goal-oriented resource management in database
management systems, and discuss how it can be used to help meet the QoS requirements of the electronic commerce database server.
We provide an example of the use of Quartermaster that illustrates how the dynamic reallocation of memory resources can be
used to meet the QoS requirements of a set of transactions similar to transactions found in an electronic commerce workload.
We briefly describe the memory reallocation algorithms used by Quartermaster and present experiments to show the impact of
the reallocations on the performance of the transactions.
Published online: 22 August 2001 相似文献
994.
Injuries trends of passenger car drivers in head-on collisions are identified based on crash data extracted from the National Automotive Sampling System. Annual injury incidence levels are estimated for years 1990-2007. Over that period, the number of crashes is predicted to rise by 71%. However, the number of serious injuries to drivers is expected to rise by only 41% and driver fatalities are anticipated to decrease by 9%. Meantime, the types of injuries suffered by drivers are changing. Year-to-year shifts in injury patterns result from changes in vehicle size classes within the US vehicle fleet population and increases in seat belt use and air bag availability. The effectiveness of air bags in saving lives is estimated to be 30%, and with more air bag-equipped cars on the road, the probability of sustaining a life-threatening head or a torso injury is reduced. Air bags, however, are not as effective in preventing upper and lower extremity injuries, and thus arm and leg injuries will become more prevalent in years to come. 相似文献
995.
John Sheffield Thomas M. Antonsen Jr. Lee A. Berry Michael R. Brown Jill P. Dahlburg Ronald C. Davidson Martin Greenwald Chris C. Hegna William McCurdy David E. Newman Claudio Pellegrini Cynthia K. Phillips Douglass E. Post Marshall N. Rosenbluth Thomas C. Simonen James Van Dam 《Journal of Fusion Energy》2000,19(3-4):229-244
This Panel was set up by the Fusion Energy Sciences Advisory Committee (FESAC) at its November 2000 meeting for the purpose of addressing questions from the Department of Energy concerning the theory and computing/simulation program of the Office of Fusion Energy Sciences. Although the Panel primarily addressed programmatic questions, it acknowledges that the theory and computing in fusion energy sciences has a stellar record of research successes. (A recent FESAC report entitled Opportunities in the Fusion Energy Sciences Program listed a number of theory and computing research highlights.) Last year the National Research Council performed an assessment of the quality of the fusion energy sciences program—including theory and computing—and concluded that the quality of its research is on a par with that of other leading areas of contemporary physical science. 相似文献
996.
Tkalcic S Brown CA Harmon BG Jain AV Mueller EP Parks A Jacobsen KL Martin SA Zhao T Doyle MP 《Journal of food protection》2000,63(12):1630-1636
Calves inoculated with Escherichia coli O157:H7 and fed either a high-roughage or high-concentrate diet were evaluated for rumen proliferation and fecal shedding of E. coli O157:H7. Calves fed the high-roughage diet had lower mean rumen volatile fatty acid concentrations and higher rumen pH values than did calves fed the high-concentrate diet. Despite these differences in rumen conditions, the calves fed the high-roughage diet did not have greater rumen populations of E. coli O157: H7 and did not exhibit increased or longer fecal shedding compared with the calves fed the high-concentrate diet. Two calves shedding the highest mean concentrations of E. coli O157:H7 were both fed the high-concentrate diet. There was a significant (P < 0.05) positive correlation between fecal shedding and rumen volatile fatty acid concentration in calves fed a high-concentrate diet. The effects of diet on E. coli O157:H7 proliferation and acid resistance were investigated using an in vitro rumen fermentation system. Rumen fluid collected from steers fed a high-roughage diet, but not from steers fed a high-concentrate diet, supported the proliferation of E. coli O157:H7. Rumen fluid from steers fed a high-concentrate diet rapidly induced acid resistance in E. coli O157:H7. The impact of diet on fecal shedding of E. coli O157:H7 is still unclear and may depend on dietary effects on fermentation in the colon and on diet-induced changes in the resident microflora. However, rapid development of acid tolerance by E. coli O157:H7 in the rumens of calves fed high-concentrate diets, allowing larger populations to survive passage through the acidic abomasum to proliferate in the colon, may be one factor that influences fecal shedding in cattle on feed. 相似文献
997.
Increased prevalence of Alzheimer's disease-like beta-amyloid deposits in the neuropil and within neurons occurs in the brains of non-demented individuals with heart disease. Heart disease is a prevalent finding in Alzheimer's disease, and may be a forerunner to the dementing disorder. In the cholesterol-fed rabbit model of human coronary heart disease there is production and accumulation of beta-amyloid in the brain. This accumulation of beta-amyloid can be reversed by removing cholesterol from the rabbits' diet. In culture cells, a cholesterol challenge has been shown to increase production of beta-amyloid, and dramatic reductions of cholesterol produced by HMG Co-A reductase inhibitors decrease production of beta-amyloid. Increased beta-amyloid production is also produced by dietary cholesterol in a number of transgenic mouse models of Alzheimer's disease. Administration of HMG Co-A reductase inhibitors may block beta-amyloid production caused by dietary cholesterol in rabbits. Clinical trials testing the benefit of HMG Co-A reductase inhibitors in the treatment of Alzheimer's disease are underway. 相似文献
998.
Acoustic plate modes (APM) on various quartz substrates have been investigated in order to determine their usefulness for liquid-sensing applications. The modes have been characterized in terms of their mass sensitivity, mode separation, temperature sensitivity, and reproducibility of the experimental results. Promising characteristics are found for rotated Y-cuts of quartz with the direction of acoustic mode propagation being perpendicular to the X-axis of the quartz crystal. Experiments on the detection of immunochemical reactions are performed using different quartz APM sensors, and the results are compared to similar experiments utilizing APM devices on ZX-LiNbO3. 相似文献
999.
Carbon-carbon composites were coated with Calcium Magnesium Zirconium Phosphate (CMZP) and Mg-doped Al2TiO5 sol-gels in order to form an oxygen barrier at temperatures above 650°C. The coatings were applied using a dipping technique and controlled drying procedures. It was determined that 10 coats of CMZP sol-gel fired every other coat created crack free coatings and oxidation protection. Mg-doped AlTi2O5 coatings produced were unsuccessful as oxidation barriers. 相似文献
1000.
In the current era of critical-organ shortage, one of the most controversial questions facing transplantation teams is whether hepatic retransplantation, which has historically been associated with increased resource utilization and diminished survival, should be offered to a patient whose first allograft is failing. Retransplantation effectively denies access to orthotopic liver transplantation (OLT) to another candidate and further depletes an already-limited organ supply. The study group was comprised of 1,356 adults undergoing hepatic retransplantation in the United States between 1990 and 1996 as reported to the United Network for Organ Sharing (UNOS). We analyzed numerous donor and recipient variables and created Cox proportional-hazards models on 900 randomly chosen patients, validating the results on the remaining cohort. Five variables consistently provided significant predictive power and made up the final model: age, bilirubin, creatinine, UNOS status, and cause of graft failure. Although both hepatitis C seropositivity and donor age were significant by univariate and multivariate analyses, neither contributed independently to the estimation of prognosis when added to the final model. The final model was highly predictive of survival (whole model chi2 = 139.63). The risk scores for individual patients were calculated, and patients were assigned into low-, medium-, and high-risk groups (P <.00001). The low degree of uncertainty in the probability estimates as reflected by confidence intervals, even in our high-risk patients, underscores the applicability of our model as an adjunct to clinical judgment. We have developed and validated a model that uses five readily accessible "bedside" variables to accurately predict survival in patients undergoing liver retransplantation. 相似文献