793 research outputs found
Optimum number of oocytes for a successful first IVF treatment cycle
No full textOvarian stimulation in IVF allows selection of embryos for transfer, but may have detrimental effects on oocyte and embryo quality and endometrial receptivity. This study investigated the optimal response to ovarian stimulation in terms of number of oocytes for achieving pregnancy in a first IVF cycle. Data from 7422 women who underwent their first IVF cycle for standard indications were analysed. All had been treated with exogenous gonadotrophins and gonadotrophin releasing hormone (GnRH) agonist co-treatment in a long down-regulation protocol between 1990 and 1995. Pregnancy rates in relation to the number of obtained oocytes were adjusted for age, fecundity, subfertility cause, gonadotrophin dosage, type of luteal support, and number of transferred embryos by multivariate analysis. Of the 7422 women who underwent oocyte retrieval, overall 85% had an embryo transfer and 24% conceived. The highest pregnancy rates per embryo transfer and per started cycle were observed when 13 oocytes were obtained (31 and 28%, respectively). This study supports the concept of an optimal range of oocytes obtained in response to ovarian stimulation for IVF, below and above which outcomes are compromised
The Impact of Petri Nets on System-of-Systems Engineering
No full textThe successful engineering of a large-scale system-of-systems project towards deterministic behaviour depends on integrating autonomous components using international communications standards in accordance with dynamic requirements. To-date, their engineering has been unsuccessful: no combination of top-down and bottom-up engineering perspectives is adopted, and information exchange protocol and interfaces between components are not being precisely specified. Various approaches such as modelling, and architecture frameworks make positive contributions to system-of-systems specification but their successful implementation is still a problem.
One of the most popular modelling notations available for specifying systems, UML, is intuitive and graphical but also ambiguous and imprecise. Supplying a range of diagrams to represent a system under development, UML lacks simulation and exhaustive verification capability. This shortfall in UML has received little attention in the context of system-of-systems and there are two major research issues:
1. Where the dynamic, behavioural diagrams of UML can and cannot be used to model and analyse system-of-systems
2. Determining how Petri nets can be used to improve the specification and analysis of the dynamic model of a system-of-systems specified using UML
This thesis presents the strengths and weaknesses of Petri nets in relation to the specification of system-of-systems and shows how Petri net models can be used instead of conventional UML Activity Diagrams. The model of the system-of-systems can then be analysed and verified using Petri net theory. The Petri net formalism of behaviour is demonstrated using two case studies from the military domain. The first case study uses Petri nets to specify and analyse a close air support mission. This case study concludes by indicating the strengths, weaknesses, and shortfalls of the proposed formalism in system-of-systems specification. The second case study considers specification of a military exchange network parameters problem and the results are compared with the strengths and weaknesses identified in the first case study.
Finally, the results of the research are formulated in the form of a Petri net enhancement to UML (mapping existing activity diagram elements to Petri net elements) to meet the needs of system-of-systems specification, verification and validation
Towards Genetic Prediction of Coronary Heart Disease in Familial Hypercholesterolemia
No full textFamilial hypercholesterolemia (FH) is an autosomal dominant disorder of lipid metabolism caused by mutations in the gene coding for the low-density lipoprotein (LDL) receptor. The LDL receptor is a transmembrane protein that regulates plasma cholesterol levels by uptake of LDL particles from the blood circulation (Figure). Mutations in the LDL receptor gene cause insufficient uptake of circulating LDL particles, which raises the endogenous cholesterol production by the hepatocytes, resulting in twofold increased plasma concentrations of LDL cholesterol in patients with the heterozygous form of FH. The rare (1/million) homozygous FH patients have severely reduced or completely absent residual function of the LDL receptor causing extremely raised plasma LDL cholesterol concentrations. These patients develop tendon
xanthomas in childhood and massive atherosclerosis occurs frequently at a very young age. This thesis, however, focuses on patients with heterozygous FH, which is more common with a prevalence of 1/500 in Western societies. The typical heterozygous FH patients develop
tendon xanthomas and have accelerated atherosclerosis and coronary heart disease (CHD) at a young age. Nevertheless, substantial variation is seen in the age of onset of CHD among patients with heterozygous FH
Influence of sand characteristics on the piping process
No full textOne of the failure mechanisms of a dike is piping. A water level difference between the two sides of a dike causes a groundwater flow in the sand layer under the (clay)dike. This flow can transport sand from under the dike to the exit point of the groundwater flow. The formula of Sellmeijer is derived mathematically from the equation of continuity, Poiseuille flow in the slit and equilibrium of grains on the bed of the channel, modeled with the equation of White. The influence of D70 on the critical gradient is linear in the Sellmeijer formula. However, coarse-grained sands are generally more permeable than fine-grained sands, which generally results in a net influence of the grain size on the critical gradient to be less than linear, but still positive. De Wit did experimental research and found that coarse grained sands have a higher critical gradient than fine grained sands. In the framework of Strength and Solicitation Flood Defences (SBW), experiments with piping were performed. It was found the influence of D70 on the critical gradient is less than is predicted with the Sellmeijer model. 1. Problem definition and objective of the research The objective of this thesis is to research the influence of the grain size and other sand characteristics on the critical head of piping, and to find an explanation for the difference found between SBW results and the Sellmeijer formula. Besides the mean objective of this thesis, a theoretical research to the velocity in the channel according to the current Sellmeijer model has been done. 2. Approach and results of the study of variables A study is performed to variables which are considered to have influence on the critical gradient. A multi variate analysis (MVA) has been performed successfully on SBW. The influence of the D70 is less than is predicted with the Sellmeijer formula. For fine sands, the Sellmeijer formula agreed quite well with the experiments, for coarse sands, it gives an unsafe prediction. Based on the MVA on SBW, an adapted Sellmeijer formula was formulated by Sellmeijer (Sellmeijer 2010a). The MVA was also tried on the dataset of de Wit, but was not successful. The data of de Wit was inserted in the adapted Sellmeijer formula. The outcome did not agree, this may be because the data of de Wit was possibly not corrected for the filter resistance, or because the range of variables in the de Wit dataset is different than the range of variables in the dataset of SBW. 3. Approach and results of research to the erosion mechanism In the Sellmeijer model, the equilibrium of grains is according to the model of White, which assumes individual grain erosion. It is researched if this is correct. A test facility was built to research the erosion process experimentally. It was found the grains are dislodged from the granular matrix as mass erosion, with a layer thickness of roughly 7 grains. The transport of sand in the test facility occurs in the pipe in mass transport, in waves, called slurry flow. It is not sure that the observed erosion of the grains from the sand matrix is normative for determining the critical gradient, as the observed erosion may be the erosion type that is present when the critical gradient has already been exceeded. This is still under discussion. The implication of the found dislodging mechanism is that the Sellmeijer formula may possibly describe the dislodging of grains and the piping process in an improper way, however more research is needed to validate if the observed erosion process is normative for determining the critical gradient.Hydraulic Engineering + GeotechnologyCivil Engineering and Geoscience
Modelling epidemiological and economic consequences of bovine respiratory disease in dairy heifers
No full textBovine respiratory disease (BRD) is an important health problem in dairy heifers. BRD causes considerable losses, particularly on farms that experience high levels of the disease. However, an exact quantification of the economic losses due to BRD was not available yet. Despite this lack of economic insight, dairy farmers have to make decisions with regard to prevention of the disease. To make these decisions as economically sound as possible, more accurate insight is necessary into the economic consequences of BRD on the individual dairy farm.The main objective of the research project described in this thesis was to obtain insight into the on-farm economic consequences of BRD in dairy heifers by means of a PC-based simulation model. The second objective was to collect information on the epidemiological consequences of the disease indispensable for model input.The research started with a literature review aimed at obtaining the necessary qualitative and quantitative information on both the effects of BRD on the productivity of dairy heifers and risk factors of the disease. Because relevant literature turned out to be scarce, a formal expert judgement study was held to obtain additional data on the(se) variables of interest.As a next step, a simulation model was developed that calculates the economic losses due to BRD in dairy heifers for individual dairy farm conditions in the Netherlands. Following the results of the expert judgement study, the model distinguishes between two BRD types, being calf pneumonia and a seasonal BRD outbreak.Model calculations showed that for most dairy farms in the Netherlands the economic losses due to BRD will be relatively small: around 1 % of the farm's net return to labour and management for average situations, increasing up to 3-4 % at worst. For individual farms that experience high levels of BRD, the associated losses can be as high as 10-15 % of the farm's net return to labour and management, up to 25 % for large farms. Besides for calculation of the economic losses due to BRD, the model showed also to be useful for evaluation of the on-farm cost-effectiveness of prevention of the disease. Moreover, the model is flexible and user-friendly, hence, can be used as a tool to support decision-making in dairy practice.</p
Natural Resources: Curse or Blessing?
No full textAre natural resources a “curse” or a “blessing”? The empirical evidence suggests either outcome is possible. The paper surveys a variety of hypotheses and supporting evidence for why some countries benefit and others lose from the presence of natural resources. These include that a resource bonanza induces appreciation of the real exchange rate, deindustrialization and bad growth prospects, and that these adverse effects are more severe in volatile countries with bad institutions and lack of rule of law, corruption, presidential democracies, and underdeveloped financial systems. Another hypothesis is that a resource boom reinforces rent grabbing and civil conflict especially if institutions are bad, induces corruption especially in non-democratic countries, and keeps in place bad policies. Finally, resource rich developing economies seem unable to successfully convert their depleting exhaustible resources into other productive assets. The survey also offers some welfare-based fiscal rules for harnessing resource windfalls in developed and developing economies.resource curse, cross-country, panel and quasi-experimental evidence, Dutch disease, institutions, corruption, financial development, volatility, Hotelling rule, genuine saving, Hartwick rule, natural resource wealth management, sustainable development
Capital accumulation, inflation and long-run conflict in international objectives
No full textMacroeconomic Models;Economic Policy
Capacitated single stage production planning with storage constraints and sequence-dependent setup times
No full textAspects of protein metabolism in children in acute and chronic illness
No full textIn critically ill children, a negative protein balance is associated with an increased incidence of infections, fewer ventilator-free days, and increased length of stay in the pediatric intensive care unit. Additionally, a malnourished state due to chronic illness increases the risk of respiratory infections, length of hospitalization, and is associated with an increase in economic burden. The principal aim of this thesis was to investigate the effect of high (5 g/kg/d) versus age-related, normal protein intake on whole-body protein synthesis (WBPS), -breakdown (WBPB), and net balance in children with acute or chronic disease. In this thesis, we demonstrated that in young children following cardiac surgery, early enteral nutrition with normal protein (NP) intake of 2 g/kg/d, but not high carbohydrate intake-induced hyperinsulinemia, can reverse negative net whole-body protein balance in the immediate postoperative phase. High protein (HP) intake of 5 g/kg/d does not serve to improve WBPS or net protein balance, and therefore cannot be recommended over standard protein intake. In contrast, in school-age children with chronic illness (CF with stunted growth), WBPS and net protein balance can be improved by provision of a higher (5 g/kg/d) than currently recommended intake of protein. Further studies are necessary to demonstrate a possible effect on increased LBM and improved linear growth and body composition. Finally, the implementation of a nurse-driven feeding algorithm, together with the institution of an NST, increases early prescription and consecutive delivery of calories and macronutrients to patients in the first days following admission to a PICU
Studying biosphere-atmosphere exchange of CO2 through Carbon-13 stable isotopes
No full textSummary Thesis ‘Studying biosphere-atmosphere exchange of CO2 through carbon-13 stable isotopes’ Ivar van der Velde Making predictions of future climate is difficult, mainly due to large uncertainties in the carbon cycle. The rate at which carbon is stored in the oceans and terrestrial biosphere is not keeping pace with the rapid increase in fossil fuel combustion and deforestation, resulting in an increase of atmospheric carbon dioxide (CO2). To gain a better understanding of the global carbon cycle we need to combine multiple sources of data into one consistent analysis, such as, forest and agricultural statistics, satellite data, atmospheric and ecological observations, and mechanistic models. This thesis describes fundamental research on some of the key components of the terrestrial carbon cycle, i.e., gross primary production (GPP) and terrestrial ecosystem respiration (TER) of CO2, which forms the key to improved prediction of net exchange. Droughts have been shown to strongly influence this exchange, and to interpret these responses adequately we have turned to a large collection of new atmospheric observations of CO2, and its 13C isotope (13CO2), to constrain key model components. In Chapter 2 we studied the global budget of atmospheric CO2 and the ratio of 13CO2/12CO2 (δ13C) and investigated the main terrestrial drivers of interannual variability (IAV) responsible for the observed atmospheric δ13C variations. In this chapter we introduced the SiBCASA biogeochemical model that we provided with a detailed isotopic discrimination scheme (to calculate the natural preference of 12CO2 over 13CO2 in uptake processes), separate 12C and 13C biogeochemical pools, and satellite-observed fire disturbances. This model was able to calculate uptake of 13CO2 and 12CO2 and produced return fluxes from its differently aged carbon pools, contributing to the so-called disequilibrium flux. Our simulated terrestrial isotope processes, plant discrimination and disequilibrium, closely resembled previously published values and similarly suggested that discrimination variations in C3 type plants and year-to-year variations in C3 and C4 productivity are the main drivers of IAV. The year-to-year variability in the terrestrial disequilibrium flux was much lower than required to match variations in atmospheric observations, under the common assumption of low variability in net ocean CO2 exchange, constant discrimination, and a closed CO2 budget. It was unclear how to increase IAV in the terrestrial biosphere, which suggested that SiBCASA missed adequate drought responses resulting in a latent isotope discrimination and variability in C3/C4 plant productivity. Implementation of carbon isotope cycling, biomass burning, and SiBCASA’s drought response were closely studied in Chapter 3. Our biomass burning emissions were similar as in CASA-GFED; both in magnitude and spatial patterns, and the implementation of isotope exchange gave a global mean discrimination value of approximately 15 ‰, and varied spatially depending on the photosynthetic pathway in the plant. These values compared well (annually and seasonally) with other published results. Similarly, the size of the terrestrial isotopic disequilibrium was close to that of other studies. As plants experience drought stress, they respond by closing their stomata to prevent the loss of water. This process also inhibits the uptake of CO2 and reduces the isotope discrimination against 13CO2 molecules. We found that the amplitude of drought response in SiBCASA was smaller than suggested by the measured isotope signatures. We also found that a slight increase in stomatal closure for large vapor pressure deficits amplified the variations in the respired isotope signature. Finally, we saw the need for modified starch/sugar storage pools to improve the propagation of isotopic discrimination anomalies to respiration on short-term time scales. In Chapter 4 we developed a multi-tracer inversion system to interpret signals in atmospheric CO2 and δ13C observations simultaneously. We wanted to know whether drought stress in plants can induce changes in atmospheric δ13C and whether they are interpretable. Using inverse modeling we were able to refine the discrimination parameter for plants as it reflected detectable variations in atmospheric δ13C. The results showed that the isotope discrimination values were consistently smaller during large severe droughts in the Northern Hemisphere, exceeding the estimates from SiBCASA (i.e., a larger reduction). Decreased discrimination suggested an increase in the regional intrinsic water use efficiency, which was also recorded at a large number of measurement sites. The IAV in net ecosystem exchange was relatively insensitive as we allowed the variability of the discrimination parameter to increase more than 8-fold, but it also allowed significant correlation between annual net exchange and discrimination. This study suggested a larger effect of droughts on discrimination than previously thought and that the treatment of drought response in biosphere models needs to be improved. Carbon cycle research is far from complete as many components are still largely uncertain, which prevents us from making better predictions of future climate. This thesis, however, highlights the importance of isotope observations to assess and improve biogeochemical models, especially with regard to the allocation and turnover of carbon, and responses to droughts.</p
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