Importance sampling in systems simulation: A practical failure?

sampling;queuing theory;operations research

Regression estimators in simulation

sampling;simulation;queuing systems;operations research

Aquifer Vulnerability Modeling in New Jersey Through the Use of Modified DRASTIC Methodology

Due to the global average increase in temperature over the last 50 years, sea levels have been rising and making coastal aquifers more susceptible to saltwater intrusion. The average rate of sea level rise has increased from 2 mm/year to 3.5 mm/year during the twentieth century. The state of New Jersey is not only densely populated but the development along coastlines makes inundation a potential serious threat. New Jersey is diverse in aquifer types, in addition to the types of water bodies surrounding New Jersey, and makes for an interesting case study for groundwater vulnerability. The EPA has a universal model used to identify potentially contaminated aquifers, the DRASTIC model. This model, however, does not include saltwater intrusion as a potential contaminant and we therefore propose to modify the DRASTIC model in order to address saltwater intrusion as a potential aquifer contaminant, making coastal aquifers more vulnerable to contamination. This study will investigate and compare the aquifer vulnerability mapping ability of the DRASTIC method and a modified DRASTIC method for the state of New Jersey

Exploring the Changing Landscape of Surgical Residency Training

Within the past decade, the structure and format of surgical residency training has changed radically by the introduction of competency-based training programs, the progressive fragmentation of general surgery into subspecialties, and the implementation of stringent work hour restrictions. The aim of this thesis was to explore how these developments have transformed the landscape of surgical residency training within the past years. The research described in this thesis has been conducted in a surgical training region located in the Southwest of the Netherlands, consisting of 1 university hospital and 6 affiliated district hospitals. Conclusions resulting from this research may be helpful for stakeholders responsible for the organization of training in general surgery in the Netherlands and could be used for continuous improvement of the surgical residency training program and to guide future directions in surgical training, hence ensuring high-quality training and well-balanced education for the next generation of surgeons

Impact of Climate Change on Irrigation Water Availability, Crop Water Requirements and Soil Salinity in the SJV, CA

We examine potential regional-scale impacts of global climate change on sustainability of irrigated agriculture, focusing on the western San Joaquin Valley in California. We consider potential changes in irrigation water demand and supply, and quantify impacts on cropping patterns, groundwater pumping, groundwater levels, soil salinity, and crop yields. Our analysis is based on archived output from General Circulation Model (GCM) climate projections through 2100, which are downscaled here to the scale of the study area (~30 km across). We account for uncertainty in GCM climate projections by considering output from two different GCM\u27s, each using three greenhouse gas emission scenarios. Significant uncertainty in projected precipitation translates into uncertainty of future water supply, ranging from an increase of 10% to a decrease of 30% in 2100. On the other hand, temperature projections are much less variable, resulting in consistent projections of crop water demand for all climate change scenarios. Crop water demand is expected to change very little, due to compensating effects of rising temperature on evaporative demand and crop growth rate. Reductions in surface water supply are projected to be offset by groundwater pumping and land fallowing. Simulations of subsurface flow and salt transport with a regional-scale hydro-salinity model suggest a small expansion in salt-affected area, compared to current conditions. However, in all scenarios salinity is expected to increase in downslope areas, thereby limiting crop production. This is especially significant given an anticipated demand-driven switch to high-value, salt-sensitive crops. Results show that technological adaptation, such as improvements in irrigation efficiency, may partly mitigate these effects

Sustainable Habitat Restoration: Fish, Farms, and Ecosystem Services

Biomass burning impacts biogeochemical cycling, vegetation dynamics and climate. However, interactions between fire, climate and vegetation are not well understood and therefore studies have attempted to reconstruct fire and vegetation history under different climatic conditions using sedimentary archives. Here we focus on levoglucosan, a thermal by-product of cellulose generated during biomass burning, and, therefore, a potential fire biomarker in the marine sedimentary archive. However, before levoglucosan can be applied as a biomass burning proxy in marine sediments, there is a need for studies on how levoglucosan is transported to the marine environment, how it is reflecting biomass burning on continents, as well as the fate of levoglucosan in the marine water column and during deposition in marine sediments. Here we present analyses of levoglucosan, using an improved Ultra High Pressure Liquid Chromatography-Electro Spray Ionization/High Resolution Mass Spectrometry (UHPLC-ESI/HRMS) method, in atmospheric particles, in particulate matter settling through the water column and in marine surface sediments on a longitudinal transect crossing the tropical North Atlantic Ocean at 12°N. Levoglucosan was detected in the atmosphere, although in low concentration, possibly due to the sampled particle size, the source area of the aerosols, or the short time interval of sampling by which large burning events may have been missed. In sinking particles in the tropical North Atlantic Ocean we find that levoglucosan deposition is influenced by a mineral ballast effect associated with marine biogenic particles, and that levoglucosan is not transported in association with mineral dust particles. Highest levoglucosan concentrations and seasonal differences in sinking particles were found close to continents and low concentrations and seasonal differences were found in the open ocean. Close to Africa, levoglucosan concentration is higher during winter, reflecting seasonal burning in northwestern Africa. However, close to South America levoglucosan concentrations appear to be affected by riverine transport from the Amazon River. In surface sediments close to South America, levoglucosan concentration is higher than in the middle of the Atlantic Ocean, implying that here the influence from the South American continent is important and perennial. Our study provides evidence that degradation of levoglucosan during settling in the marine water column is not substantial, but is substantial at the sediment–water interface. Nevertheless, levoglucosan was detected in all surface sediments throughout the tropical North Atlantic, indicating its presence in the marine sedimentary record, which reveals the potential for levoglucosan as a biomass burning proxy in marine sediments

Penetrômetro Combinado com Sensor de Umidade por TDR para Estudo da Compactação dos Solos.

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