7,618 research outputs found
Long-term health effects after DES exposure in utero
No full textLeeuwen, F.E. [Promotor]van Helmerhorst, Th.J.M. [Promotor]Rookus, M.A. [Copromotor
Cancer risks and hormonal modifiers of risks in BRCA1 and BRCA2 mutation carriers: Knowing the genes, what are the risks?
No full textLeeuwen, F.E. [Promotor]van Veer, L.J. van 't [Promotor]Rookus, M.A. [Copromotor
Modifiers of breast cancer risk in BRCA1/2 mutation carriers: diagnostic radiation, physical activity, and body weight
No full textLeeuwen, F.E. van [Promotor]Rookus, M.A. [Copromotor
Deep anisotropic dry etching of silicon microstructures by high-density plasmas
No full textThis thesis deals with the dry etching of deep anisotropic microstructures in monocrystalline silicon by high-density plasmas. High aspect ratio trenches are necessary in the fabrication of sensitive inertial devices such as accellerometers and gyroscopes. The etching of silicon in fluorine-based plasmas is isotropic. To obtain anisotropy the addition of sidewall passivation is necessary. This is achieved with both oxygen passivation at low temperatures and fluorocarbon passivation at room temperature. A quantitative approach was pursued to explain the etching mechanism. The etch results were analysed using the measured plasma species fluxes and the surface composition. Moreover, the transport of the plasma species in narrow anisotropic structures is a fundamental factor determining the etch rate and the profile evolution. The experimental methods such as the etching equipment, plasma diagnostics, surface analysis and sample preparation are described in chapter 2. Three etching processes were investigated: the cryogenic etching process with oxygen passivation at low temperatures, the Bosch process with fluorocarbon passivation at room temperature and the novel triple pulse process that was developed in our laboratory. The polymer deposition mechanism and the characteristic role of the ions are also explained. The cryogenic etching process is discussed in chapter 3. Fluorine radicals, oxygen radicals and ion bombardment are responsible for the three main sub-processes, that is, etching, sidewall passivation and depassivation of the trench bottom, respectively. Etching experiments with an extremely low ion-to-radical flux ratio were used to reveal the etching mechanism. Crystal orientation dependent etching leading to Si(111) crystal facets is observed in a surface kinetics controlled regime. By varying the plasma conditions it is possible to adjust the etching mechanism from fluorine-limited to ion-limited. Controlled etching is obtained because the etching is tuned from aspect ratio dependent in the fluorine-limited domain to aspect ratio independent in the ion-limited domain. The transport of radicals in high aspect ratio trenches is an important limiting factor and was investigated with special structures. The etch results are described by an analytic model that is based on the surface site balance of fluorine and oxygen radicals. The results are further explained with a Monte Carlo simulation model. The Bosch process is clarified in chapter 4. The anisotropy of the etched structures is controlled by balancing the etching and passivation pulse. However, the maximal obtainable aspect ratio is limited by convergence of the trench sidewalls due to excessive passivation. The maximal obtainable aspect ratio increases if the ion-to-radical flux ratio increases. The transport of ions is an important limiting factor in the depassivation of the bottom of the trench. Divergence of the ion beam leads to a reduction of the ion flux, so that the fluorocarbon passivation is insufficiently removed near the base of the sidewalls. The average ion angle was measured and correlated to the maximal obtainable aspect ratio. The Bosch process was improved at the depassivation side with the triple pulse process and at the passivation side with preferential sidewall deposition. The triple pulse process that is described in chapter 5 has the aim to improve the depassivation in deep trenches. The three main sub-processes are decoupled using a separate depassivation pulse directly after the etching and passivation pulses. The fluorocarbon passivation is efficiently removed with low-pressure, high-density, oxygen-based plasmas. The investigated plasma chemistries include O2, CO2 and SO2. The triple pulse process leads to better profile control with a straight trench bottom. However, the maximal obtainable aspect ratio is comparable to the Bosch process because a larger etch depth and a small lateral etch cancel out. The polymer deposition mechanism is treated in chapter 6 with the aim to understand the fluorocarbon passivation in deep trenches. The deposition on plane surfaces and on special structures was investigated to distinguish between the radical-induced and ion-enhanced components. A simple analytical model, which explains the main deposition characteristics, was developed. Preferential sidewall deposition is obtained for higher ion fluxes and higher bias voltages where sputtering plays an important role. In this case no fluorocarbon passivation has to be removed from the bottom of the trench. The trench profile was optimised in the Bosch process by tuning the bias voltage during etching and passivation independently. It resulted in perfectly anisotropic trenches but the maximal obtainable aspect ratio was still limited by a small lateral etch. The characteristic role of the ions in the etching mechanism is explained in chapter 7. Ion-induced etching of both SiC in a SF6-O2 plasma and Si in a Cl2 plasma were investigated. The impact of the ions on the profile evolution can be examined more explicitly because spontaneous chemical reactions are absent for these plasma-material systems. The etching mechanism varies from fluorine-limited to ion-limited depending on the radical-to-ion flux ratio. Microtrenches are observed for an ion-limited etching mechanism. Fluorine-limited SiC etching is aspect ratio dependent in contrast to ion-limited SiC etching, which is aspect ratio independent. The etching of high aspect ratio SiC structures is limited by the positive sidewall taper. This is presumably caused by insufficient removal of the thin fluorocarbon layer on the surface. Si etching in a Cl2 plasma is always aspect ratio independent in contrast to SiC etching because of the low reaction probability. The conclusions and recommendations of this thesis are given in chapter 8.Applied Science
Body mass index in young Dutch adults : its development and the etiology of its development
No full textFollow-up studies of long duration have shown a U-shaped relationship between mortality/morbidity and the body mass index (BMI, weight/height 2). The risk to health posed by obesity appears to be larger in younger subjects than in older subjects. Though this might suggest that a moderate weight gain after the termination of growth may not increase the risk to health, this contention is not supported by other observations (Chapter 1). These are: (1) the range of relative weight associated with minim= mortality does not seem to shift to higher values with increasing age, at least not in men. (2) Diseases associated with overweight at younger ages need not be the same as those associated with overweight at older ages. (3) Cohort effects may bias the age trend in the risk associated with overweight. (4) Longitudinal studies on adults show that changes in body weight are associated with changes in risk factors of diseases. (5) Anthropometric studies show that even at the same weight, the fat mass increases with increasing age. In addition, several studies suggest that weight gained during adulthood mainly accumulates in the abdomen, which means a shift to a fat distribution more strongly associated with risk to health. The risk to health therefore does not seem to remain constant if body weight increases during adulthood.As part of an extensive mixed-longitudinal study (Chapter 2), this thesis deals with the development of the BMI and the etiology of this development in young adults. In addition, one methodological study is described. These studies build m cross-sectional observations that were made in the first examination of the study.In spring 1980, all residents of Dutch nationality in the county of Ede, born in 1948-1950, 1953-1955, 1958-1960 were invited by mail to participate in the study. Participants in spring 1980 (N=3936) were followed for four years (1980-1984) in two groups, the follow-up group (N=1670) and the control group (N=2266). From spring 1981 onward the follow-up group was approached twice a year in seven consecutive examinations. The control group was re-measured in spring 1984 only. At each examination a questionnaire was completed and body weight in light indoor clothing and without shoes was measured to the nearest 0.5 kg. Body height was measured to the nearest 0.1 cm in spring 1980. Subgroups of the follow-up and control groups were additionally examined for the studies described in Chapter 7 and 8.The development of the BMI is dealt with in Chapter 3, in which the mixed-longitudinal design of the study was utilized, and Chapter 4, in which the data were analyzed longitudinally. Over the four years, the change in BMI of the follow-up group was the same as that of the control group. Prom 19 to 35 years of age the median BMI increased from 22.1 kg/m 2to 24.4 kg/m 2in men and from 21.1 kg/m 2to 23.0 kg/m 2in women (Chapter 3). This increment in BMI gave rise to an incidence of moderate overweight (BMI>25 kg/m 2) which increased from 4.8% per 4 years to 15.5% per 4 years in men, and was more stable (5.3-5.7% per 4 years) in women (Chapter 4). Thus, especially in men, young adulthood appears to be a critical period for the development of overweight.The age-reference curves (Chapter 3) suggested that the variation of the BMI over subjects was independent of age. In accordance, the longitudinal analyses showed that the initial BMI and the rate of gain in BMI were unrelated in men and only slightly negatively related in women. Thus, overweight subjects did not appear to gain more or less body mass than non-overweight subjects.The within-subjects standard deviation of the yearly measured BMI was 0.69 kg/m 2in men and 0.74 kg/m 2in women (Chaper 4). This fluctuation was larger in overweight subjects than in normal-weight subjects and was larger in subjects with a larger long-term change (gain or loss) in BMI than in subjects who had a more stable BMI. The considerable fluctuation in BMI may mask the gradual long-term increment in BMI and may thus hinder young adults from being aware that they are becoming overweight.The effect of dieting is dealt with in Chapter 5. After two years of follow-up, the average decrease in body mass as a result of dieting was -0.5 kg/m 2(95% confidence interval (CI):-1.0,+0.0) in men and -0.4 kg/m 2(95%CI:-0.8,+0.0) in women. This approximately amounts to an average weight reduction of 1.5 kg in men and 1.0 kg in women. The effect of dieting was most pronounced in men whose initial BMI was high, who dieted during the summer, or who dieted more frequently, and in women who were older than 30 or who dieted on medical advice. Though subjects who have already developed severe overweight may achieve a larger reduction in the risk to health by losing the same amount of body mass as subjects who are only moderately overweight, it is unlikely that the benefit is large unless they persist. However, the effect of dieting may be enough to prevent the age-related gain in body mass and thus dieting may especially play a part in the prevention of overweight.Chapter 6 deals with the changes in BMI in relation to number of life events experienced. During the first year of follow-up several subgroups of men and women who experienced many life events and several subgroups of men who experienced few life events showed a gain in body mass. After another year of follow-up this gain in body mass had disappeared in almost all subgroups; compared with dieting ran with an intermediate number of life events, dieting men with few life events gained +1.3 kg/m 2(95%CI:+0.0,+2.6) more body mass, whereas dieting men with many life events gained +1.8 kg/m 2(95%CI: +0.5,+3.0) more body mass. Thus, life events seem to have an impact on the etiology of overweight in men.One life event in women is considered more specifically (Chapter 7); i.e. pregnancy. Women who breastfed their child for more than two months gained more body mass than was expected from aging. Nine months postpartum they were +0.6 kg/m 2(90%CI: +0.1,+1.0) heavier than expected. This difference was slightly smaller (not significantly) in women who breastfed their child for 0-2 months. Women who used bromocriptine to stop lactation lost body mass unexpectedly.In a methodological study (Chapter 8) the impact of adjustment of the BMI for body diameters (i.e. knee, wrist, elbow, shoulder, pelvis and hip) on the prediction of body fatness was examined. In addition to what was explained by the BMI, 6% of the variation in body fatness was explained by the shoulder diameter in men, and also 6% by the knee diameter in women. This improvement in estimating body fatness by the diameters, used as continuous variables, was considered too small to justify frame categories being included in weight-height tables. Instead of frame size, fat distribution might be a more useful attribute in these tables.In the last chapter (Chapter 9) several aspects relating to the validity of the mixed-longitudinal study are discussed. The main conclusions of this thesis are:- Young adulthood seems to be a critical period in the development of moderate overweight, expecially in men.- The age-related gain in BMI of overweight young adults and of young adults of normal weight is similar.- Overweight subjects are unlikely to decrease their risk to health markedly by dieting as generally practiced, unless they persist. Dieting may be more effective in preventing overweight.- The experience of many life events may play a part in the etiology of overweight in men, as does the experience of few life events.- Women who breastfeed their child for more than two months may gain more body mass than expected from aging. - In weight-height tables the fat distribution might be a more useful attribute than frame size categories.</TT
Assessment of Models for Near Wall Behavior and Swirling Flows in Nuclear Reactor Sub-system Simulations
No full textAccurate simulation of turbulence remains one of the most challenging problems in nuclear reactor analysis and design. Due to limitations in computing resources, Reynolds averaged Navier Stokes models (RANS) continue to play an important role in reactor simulations. The Consortium for advanced simulations of light water reactors (CASL) is a Department of Energy technology hub that is investing in research and developmentof a state-of-the-art computational fluid dynamics capabilityto meet the challenges of turbulent simulation of nuclear reactors. In this presentation, we assess several RANS eddy viscosity models appropriate for single-phase incompressible turbulent flows. Specifically, we compare the single equation Splalart-Allmaras to several variations of the model. The assessment takes into consideration elements of full system reactor cores such as complex geometries, heterogeneous meshes, swirling flow, near wall flow behavior, heat transfer and robustness issues. The goal of this strategically oriented assessment is to provide an accurate and robust turbulent simulation capability for the CASL community. Metrics of performance will be constructed by comparing different models on a strategically chosen set of problems that represent reactor core sub-systems
O zarubežnoj dejatel'nosti professora M.A. Kumaxova
No full textOn professor M.A. Kumakhov's work and research abroad (in Russian)
Professor Mukhadin A. Kumakhov and the author collaborated in the area of Northwest Caucasian languages under a period from 1991 to 2008. The fruitful collaboration at Lund and Malmö universities resulted in three joint monographs and a number of articles, which is outlined in the article. Mukhadin A. Kumakhov became Honorary Doctor of the Philosophical Faculty of Lund University in 1998
Bringing clouds into our lab!: The influence of turbulence on early stage rain droplets
No full textWe are investigating a droplet-laden flow in an air-filled turbulence chamber, forced by speaker-driven air jets. The speakers are running in a random manner; yet they allow us to control and define the statistics of the turbulence. We study the motion of droplets with tunable size in a turbulent flow, mimicking the early stages of raindrop formation. 3D Particle Tracking Velocimetry (PTV) is chosen as the experimental method to track the droplets and collect data for statistical analysis. Thereby it is possible to study the spatial distribution of the droplets in turbulence using the so-called Radial Distribution Function (RDF), a statistical measure to quantify the clustering of particles. Additionally, this technique allows us to measure velocity statistics of the droplets and the influence of the turbulence on droplet trajectories, both individually and collectively. In this contribution, we will present velocity statistics of the droplets and quantify their clustering using the RDF for different turbulence conditions
The Story about the constructed SARS COV-2 Virus - A Review of three Research Groups
No full textAbstract
A literature research on synthetic recombinant SARS Coronavirus was made to answer two questions. Is the SARS CoV-2 virus designed in a laboratory? And why has the SARS CoV-2 such a high mutation rate? A total of 12 research articles, 2 reviews and 10 experimental studies were attributed to three Research Groups, the Wadsworth Center New York, the Vanderbilt Medical Center, and the Chapel Hill North Carolina. The research papers were published between 1991 and 2014. All 12 research papers reported the successful construction of recombinant SARS Coronaviruses based on RNA reverse genetic and molecular techniques. The Research group from the Medical Center at Vanderbilt University proved how an engineered SARS Coronavirus with an impaired Exonuclease resulted in a progeny virus with high mutation rate. Furthermore, the review showed that a zoonotic-human transmission was just possible with specific genetic manipulations at the SARS CoV virus genome through selection of virus species for recombination, and targeted manipulation at non-structural virus domains. But importantly, the studies showed that a SARS Coronavirus cross-species infection such as between zoonotic and humans or between different animal species without the exchange of the virus spike protein domain with the host-specific receptor-binding domain (RBD) and additional point mutations was not possible. Therefore, the SARS CoV-2 was deliberately constructed to overcome the receptor limiting factor for animal-human infection. Interestingly, the review revealed that the study purpose of constructed recombinant SARS CoV changed from the scientific research point of view to vaccine production and development. Competing interests for all reviewed studies by grants from private investors such as the Gates Foundation and vaccine production companies were part of the discussion. Keywords: SARS CoV-2, Covid19, Spike protein, gene sequencing, Vanderbilt University, University North Carolina, Wadsworth Research Center, New York Health Department, Coronavirus, Bill & Melinda Gates Foundation, WHO, Pfizer, Merck, Novartis, AlphaVaxThe author declares no competing interests.
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