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Worst-case Scenario (worst-case + scenario)
Selected AbstractsPrediction of the maximum credible ground motion in Singapore due to a great Sumatran subduction earthquake: the worst-case scenarioEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 8 2002Kusnowidjaja Megawati Abstract Although Singapore is located in a low-seismicity region, huge but infrequent Sumatran subduction earthquakes might pose structural problems to medium- and high-rise buildings in the city. Based on a series of ground motion simulations of potential earthquakes that may affect Singapore, the 1833 Sumatran subduction earthquake (Mw=9.0) has been identified to be the worst-case scenario earthquake. Bedrock motions in Singapore due to the hypothesized earthquake are simulated using an extended reflectivity method, taking into account uncertainties in source rupture process. Random rupture models, considering the uncertainties in rupture directivity, slip distribution, presence of asperities, rupture velocity and dislocation rise time, are made based on a range of seismologically possible models. The simulated bedrock motions have a very long duration of about 250 s with a predominant period between 1.8 and 2.5 s, which coincides with the natural periods of medium- and high-rise buildings widely found in Singapore. The 90-percentile horizontal peak ground acceleration is estimated to be 33 gal and the 90-percentile horizontal spectral acceleration with 5% damping ratio is 100 gal within the predominant period range. The 90-percentile bedrock motion would generate base shear force higher than that required by the current design code, where seismic design has yet to be considered. This has not taken into account effects of local soil response that might further amplify the bedrock motion. Copyright © 2002 John Wiley & Sons, Ltd. [source] Comparative effects of pH and Vision® herbicide on two life stages of four anuran amphibian species,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2004Andrea N. Edginton Abstract Vision®, a glyphosate-based herbicide containing a 15% (weight:weight) polyethoxylated tallow amine surfactant blend, and the concurrent factor of pH were tested to determine their interactive effects on early life-stage anurans. Ninety-six-hour laboratory static renewal studies, using the embryonic and larval life stages (Gosner 25) of Rana clamitans, R. pipiens, Bufo americanus, and Xenopus laevis, were performed under a central composite rotatable design. Mortality and the prevalence of malformations were modeled using generalized linear models with a profile deviance approach for obtaining confidence intervals. There was a significant (p < 0.05) interaction of pH with Vision concentration in all eight models, such that the toxicity of Vision was amplified by elevated pH. The surfactant is the major toxic component of Vision and is hypothesized, in this study, to be the source of the pH interaction. Larvae of B. americanus and R. clamitans were 1.5 to 3.8 times more sensitive than their corresponding embryos, whereas X. laevis and R. pipiens larvae were 6.8 to 8.9 times more sensitive. At pH values above 7.5, the Vision concentrations expected to kill 50% of the test larvae in 96-h (96-h lethal concentration [LC50]) were predicted to be below the expected environmental concentration (EEC) as calculated by Canadian regulatory authorities. The EEC value represents a worst-case scenario for aerial Vision application and is calculated assuming an application of the maximum label rate (2.1 kg acid equivalents [a.e.]/ha) into a pond 15 cm in depth. The EEC of 1.4 mg a.e./L (4.5 mg/L Vision) was not exceeded by 96-h LC50 values for the embryo test. The larvae of the four species were comparable in sensitivity. Field studies should be completed using the more sensitive larval life stage to test for Vision toxicity at actual environmental concentrations. [source] Architecture design, performance analysis and VLSI implementation of a reconfigurable shared buffer for high-speed switch/router,INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2009Ling Wu Abstract Modern switches and routers require massive storage space to buffer packets. This becomes more significant as link speed increases and switch size grows. From the memory technology perspective, while DRAM is a good choice to meet capacity requirement, the access time causes problems for high-speed applications. On the other hand, though SRAM is faster, it is more costly and does not have high storage density. The SRAM/DRAM hybrid architecture provides a good solution to meet both capacity and speed requirements. From the switch design and network traffic perspective, to minimize packet loss, the buffering space allocated for each switch port is normally based on the worst-case scenario, which is usually huge. However, under normal traffic load conditions, the buffer utilization for such configuration is very low. Therefore, we propose a reconfigurable buffer-sharing scheme that can dynamically adjust the buffering space for each port according to the traffic patterns and buffer saturation status. The target is to achieve high performance and improve buffer utilization, while not posing much constraint on the buffer speed. In this paper, we study the performance of the proposed buffer-sharing scheme by both a numerical model and extensive simulations under uniform and non-uniform traffic conditions. We also present the architecture design and VLSI implementation of the proposed reconfigurable shared buffer using the 0.18 µm CMOS technology. Our results manifest that the proposed architecture can always achieve high performance and provide much flexibility for the high-speed packet switches to adapt to various traffic patterns. Furthermore, it can be easily integrated into the functionality of port controllers of modern switches and routers. Copyright © 2008 John Wiley & Sons, Ltd. [source] Risk of catastrophic terrorism: an extreme value approachJOURNAL OF APPLIED ECONOMETRICS, Issue 4 2009Hamid Mohtadi This paper models the stochastic behavior of large-scale terrorism using extreme value methods. We utilize a unique dataset composed of roughly 26,000 observations. These data provide a rich description of domestic and international terrorism between 1968 and 2006. Currently, a credible worst-case scenario would involve losses of about 5000 to 10,000 lives. Also, the return time for events of such magnitude is shortening every year. Today, the primary threat is from conventional weapons, rather than from chemical, biological and/or radionuclear weapons. However, pronounced tails in the distribution of these incidents suggest that this threat cannot be dismissed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Capacity of model biobeds to retain and degrade mecoprop and isoproturonPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 10 2003Vibeke V Henriksen Abstract Biobeds are used to increase the adsorption and degradation of pesticide spillage on sites used for mixing and loading and for cleaning of sprayers. The adsorption and the rate of degradation of 14C-labelled isoproturon and mecoprop (MCPP) at concentrations from 0.0005 to 25 000 mg kg,1 were determined in biobed soil. Further leaching of the two herbicides was determined in a model biobed with a surface area of 2 m2. The biobed material showed enhanced ability to adsorb the two herbicides. Kd was 5.2 litre kg,1 for isoproturon and 1.6 litre kg,1 for MCPP in biobed material, which is higher than in natural soil. In different experiments with natural soil, Kd ranges from 0.07 to 0.6 litre kg,1 for MCPP and from 1.5 to 4.6 litre kg,1 for isoproturon in soils with varying organic carbon content. Degradation of MCPP was rapid at concentrations from 0.0005 to 500 mg kg,1, delayed at 5000 mg kg,1, and very slow at 25 000 mg kg,1. For isoproturon, the relative degradation was most rapid at the lowest concentration and decreasing with increasing concentrations. After 120 days, between 55% and 8% 14C was evolved as 14CO2 at concentrations between 0.0005 and 25 000 mg kg,1. The rate of evolution of 14CO2 indicated that degradation rates at low concentrations were of first-order and at higher concentrations of zero-order. Leaching of MCPP and isoproturon was determined in a newly established model biobed during a 2-year period. About 13% of applied MCPP and 1.4% of applied isoproturon leached out during the winter following the first autumn application (worst-case scenario). Leaching was completely prevented when the biobed had a well-developed grass cover and was covered during the winter. Copyright © 2003 Society of Chemical Industry [source] Assessment of Emergency Physician Workforce Needs in the United States, 2005ACADEMIC EMERGENCY MEDICINE, Issue 12 2008Carlos A. Camargo Jr MD Abstract Objectives:, The objective was to estimate emergency physician (EP) workforce needs, taking into account the diversity of U.S. emergency departments (EDs) and various projections of EP supply and demand. Methods:, The 2005 National ED Inventory-USA (http://www.emnet-usa.org/) provided annual visit volumes for 4,828 U.S. EDs. The authors calculated annual supply based on existing emergency medicine (EM) board-certified EPs, adding newly board-certified EPs, and subtracting board-certified EPs who died or retired. Demand was estimated at each ED by dividing the number of visits by the average EP volume (based on 2.8 patients/hour, 40 hours/week, and 34% nonclinical time). The models assumed that at least 1 EP should be present 24/7 in each ED, which would require at least 5.35 full-time equivalents (FTEs) per ED. Based on annual EP attrition estimates, results for best-case, worst-case, and intermediate scenarios were calculated. Results:, In 2005, there were approximately 22,000 EM board-certified EPs, but 40,030 EPs would be needed to staff all 4,828 EDs (55% of demand met). A total of 2,492 (52%) EDs had a visit volume that required the minimum number (5.35) FTEs, of which 47% were rural. In the unrealistic (no attrition), best-case scenario, it would take until 2019 to staff all EDs with board-certified EPs. In the worst-case scenario (12% attrition), supply would never meet demand. Our intermediate scenario (2.5% attrition) suggested that board-certified EPs would satisfy workforce needs in 2038. Conclusions:, Supply of EM residency-trained, board-certified EPs is not likely to meet demand in the near future. Alternative EP staffing arrangements merit further consideration. [source] Sirolimus-eluting stents for the prevention of restenosis in a worst-case scenario of diffuse and recurrent in-stent restenosisCATHETERIZATION AND CARDIOVASCULAR INTERVENTIONS, Issue 3 2004Gerald S. Werner MD Abstract For recurrent in-stent restenosis (ISR), surgical revascularization or brachytherapy is still the principal therapeutic options. The present investigation explores the efficacy of a sirolimus-eluting stent to prevent restenosis in these lesions with a high risk of recurrence. In 22 consecutive patients with a recurrent and diffuse ISR, a sirolimus-eluting stent was implanted to cover the restenotic lesion. All patients were followed clinically for at least 1 year and underwent a repeat angiography after 7 months. A quantitative coronary angiographic analysis was done. The target vessel failure was 14% in the sirolimus-eluting stent group, with an angiographic late loss of only 0.39 ± 0.54. No subacute stent thrombosis was observed, and the 1-year event-free survival was 86%. The three cases with restenosis were all focal and could be successfully treated by additional drug-eluting stent implantation. This study showed the efficacy of a sirolimus-eluting stent for the prevention of restenosis in a worst-case scenario of recurrent and diffuse ISR. The observed restenosis rate is lower than that reported after brachytherapy and suggests that sirolimus-eluting stents are a promising treatment option for ISR. Catheter Cardiovasc Interv 2004;63:259,264. © 2004 Wiley-Liss, Inc. [source] Downy mildew (Plasmopara viticola) epidemics on grapevine under climate changeGLOBAL CHANGE BIOLOGY, Issue 7 2006SALINARI FRANCESCA Abstract As climate is a key agro-ecosystem driving force, climate change could have a severe impact on agriculture. Many assessments have been carried out to date on the possible effects of climate change (temperature, precipitation and carbon dioxide concentration changes) on plant physiology. At present however, likely effects on plant pathogens have not been investigated deeply. The aim of this work was to simulate future scenarios of downy mildew (Plasmopara viticola) epidemics on grape under climate change, by combining a disease model to output from two general circulation models (GCMs). Model runs corresponding to the SRES-A2 emissions scenario, characterized by high projections of both population and greenhouse gas emissions from present to 2100, were chosen in order to investigate impacts of worst-case scenarios, among those currently available from IPCC. Three future decades were simulated (2030, 2050, 2080), using as baseline historical series of meteorological data collected from 1955 to 2001 in Acqui Terme, an important grape-growing area in the north-west of Italy. Both GCMs predicted increase of temperature and decrease of precipitation in this region. The simulations obtained by combining the disease model to the two GCM outputs predicted an increase of the disease pressure in each decade: more severe epidemics were a direct consequence of more favourable temperature conditions during the months of May and June. These negative effects of increasing temperatures more than counterbalanced the effects of precipitation reductions, which alone would have diminished disease pressure. Results suggested that, as adaptation response to future climate change, more attention would have to be paid in the management of early downy mildew infections; two more fungicide sprays were necessary under the most negative climate scenario, compared with present management regimes. At the same time, increased knowledge on the effects of climate change on host,pathogen interactions will be necessary to improve current predictions. [source] The ,-reliable mean-excess regret model for stochastic facility location modelingNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 7 2006Gang Chen Abstract In this paper, we study a strategic facility location problem under uncertainty. The uncertainty associated with future events is modeled by defining alternative future scenarios with probabilities. We present a new model called the ,-reliable mean-excess model that minimizes the expected regret with respect to an endogenously selected subset of worst-case scenarios whose collective probability of occurrence is no more than 1 , ,. Our mean-excess risk measure is coherent and computationally efficient. Computational experiments also show that the ,-reliable mean-excess criterion matches the ,-reliable minimax criterion closely. © 2006 Wiley Periodicals, Inc. Naval Research Logistics 2006 [source] | ||||||||||||||||