Regression estimators in simulation

sampling;simulation;queuing systems;operations research

Importance sampling in systems simulation: A practical failure?

sampling;queuing theory;operations research

Effect of blue and red radiation on cycling stomata of bean.

Differences in the effect of blue and red radiation of low radiant flux density on sustained stomatal cycling were studied in Phaseolus vulgaris cv. Vroege Wagenaar. Stomatal behaviour in a constant environment was observed indirectly by recording the differences between leaf and air temperature. In radiation with equal radiant flux densities of 1.75 W/m2 and with equal estimated absorbed quantum flux densities of 0.73 nE/cm2 s of both colours, cycling was more rapid and peak-to-trough differences were smaller in red than in blue radiation. Blue radiation from below caused more rapid cycling with larger peak-to-trough differences than radiation from above. In red radiation the direction of radiation had a much smaller influence on period and peak-to-trough difference. To explain these qualitatively different effects of both colours on cycling stomata, the hypothesis is proposed that blue light increases the osmotic pressure in the guard cells more effectively than red light. In blue light the permeability for water transport of the guard cell membranes is lower than in red light. (Abstract retrieved from CAB Abstracts by CABI’s permission

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

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