Reynolds number effects on the Reynolds-stress budgets in turbulent channels

Budgets for the nonzero components of the Reynolds-stress tensor are presented for numerical channels with Reynolds numbers in the range Reτ ≤180–2000. The scaling of the different terms is discussed, both above and within the buffer and viscous layers. Above (x_2^+)≈150, most budget components scale reasonably well with u_t^3/h, but the scaling with (u_t^4)/v is generally poor below that level. That is especially true for the dissipations and for the pressure-related terms. The former is traced to the effect of the wall-parallel large-scale motions, and the latter to the scaling of the pressure itself. It is also found that the pressure terms scale better near the wall when they are not separated into their diffusion and deviatoric components, but mostly only because the two terms tend to cancel each other in the viscous sublayer. The budgets, together with their statistical uncertainties, are available electronically from http://torroja.dmt.upm.es/channels

The relationship between microsomal enzyme induction and liver tumour formation : a study on the effects of xenobiotic and naturally occurring microsomal enzyme inducers on livers of male CF-1 mice

The effects of naturally occurring microsomal enzyme inducers on important hepatocellular pathways for the metabolism of foreign compounds (xenobiotics) and also upon the incidence of liver tumours in CF-1 mice treated or not with 10 mg dieldrin.kg -1diet were investigated using animals maintained on semi-synthetic diet and filter paper bedding as controls. The results of the study indicate that dieldrin administration to mice results in a generalized liver enlargement predominantly due to hyperplasia. Liver enlargement in dieldrin-treated mice was followed by the appearance of nodular liver tumours, first observed at the age of 43 weeks. Conventional rodent diet and sawdust bedding were shown to contain agents that induce the microsomal mono-oxygenase system of mouse liver. However, the extent of mono-oxygenase induction by these factors was less pronounced than that caused by dieldrin. In contrast to the effects of dieldrin, conventional diet and sawdust bedding did not cause any significant induction of secondary drug-metabolizing enzyme systems, e.g. epoxide hydratase, glutathione S-epoxide transferase and UDP-glucuronyl transferase. Histopathological examination of livers demonstrated a low incidence of tumours in the livers of mice not treated with dieldrin. These tumours were generally benign in character although a few showed morphological characteristics associated with malignant liver cell tumours. The overall incidence of liver tumours was significantly increased in dieldrin-treated animals. Both benign and malignant liver tumours were found in dieldrin-treated mice; the latter type of lesion showing evidence of lung metastasis. Conventional diet and sawdust bedding did not exert any obvious influence on the development of 'spontaneous' tumours in the livers of male CF-1 mice.It is concluded that microsomal enzyme inducers such as dieldrin act by facilitating the expression of a pre-existing oncogenic factor, probably by inducing hyperplasia

tmap: Thematic Maps in R

Thematic maps show spatial distributions. The theme refers to the phenomena that is shown, which is often demographical, social, cultural, or economic. The best known thematic map type is the choropleth, in which regions are colored according to the distribution of a data variable. The R package tmap offers a coherent plotting system for thematic maps that is based on the layered grammar of graphics. Thematic maps are created by stacking layers, where per layer, data can be mapped to one or more aesthetics. It is also possible to generate small multiples. Thematic maps can be further embellished by configuring the map layout and by adding map attributes, such as a scale bar and a compass. Besides plotting thematic maps on the graphics device, they can also be made interactive as an HTML widget. In addition, the R package tmaptools contains several convenient functions for reading and processing spatial data

Wat donoren zien in good governance : discoursanalyse van het ontwikkelingsbeleid van Nederland en Duitsland

First, this study is about the policy process and policy discourse of two donors: the Netherlands and Germany. By comparing two policy processes, I hope to better understand which practices are really important. Germany forms a good contrast with the Netherlands, because of its clear-cut distinctions in the policy process, for example, in\ud terms of the actors involved. Second, this study is about the process of, and discourses on, bilateral aid policy. I am interested in the process within donor countries. An analysis of the policy process on multilateral level like the World Bank or the EU would be outside that\ud focus. Third, I analyze the bilateral policy on good governance with respect to a particular region in the World, namely Sub-Saharan Africa. Two development cooperation relationships, with Kenya and Uganda, I have analyzed in greater detail

Extreme Lagrangian acceleration in confined turbulent flow

A Lagrangian study of two-dimensional turbulence for two different geometries, a periodic and a confined circular geometry, is presented to investigate the influence of solid boundaries on the Lagrangian dynamics. It is found that the Lagrangian acceleration is even more intermittent in the confined domain than in the periodic domain. The flatness of the Lagrangian acceleration as a function of the radius shows that the influence of the wall on the Lagrangian dynamics becomes negligible in the center of the domain and it also reveals that the wall is responsible for the increased intermittency. The transition in the Lagrangian statistics between this region, not directly influenced by the walls, and a critical radius which defines a Lagrangian boundary layer, is shown to be very sharp with a sudden increase of the acceleration flatness from about 5 to about 20

Immunomodulation by diet : individual differences in sensitivity in layer hens

Enhancing relevant immunity of production animals to achieve more robust animals is receiving more and more attention. Several epidemics have hit production animals recently and with devastating consequences, but enhancing diseases resistance increasingly provides new opportunities. Furthermore, welfare and health of production animals is becoming a more and more consumer driven topic. Several routes are being used to approach the possibility of enhancing immunity such as selective breeding, enriched and altered housing conditions, vaccination programs, diet supplementation with immune stimulating components, and other management procedures. Disease susceptibility has been shown to be related to stress reactivity, which in turn is related to differences in HPA axis reactivity. Interestingly, independent of selection criteria used, the extremes of various selection procedures result in a recurrent dichotomy in HPA axis reactivity, either being hyperresponsive or hyporesponsive to stress. Animals with a hyperresponsive HPA axis show greater environmental sensitivity, while the hyporeactive animals are more intrinsically regulated. Often, research on immunomodulation is performed with compromised animals and/or exaggerated supplementation of dietary components in one generation of animals, but epigenetics by definition seems to be the mechanism for mothers to prepare their offspring for the environment they will be born into. Enhancing immunity through normal diet in uncompromised animals is rarely investigated, let alone over generations. In this thesis the aim was to induce immunomodulation through diet in selection lines of chicken that have previously been selected on their antibody response to sheep red blood cells over two generations of chicken. First, potential HPA axis differences were examined in these selection lines to establish their environmental sensitivity, whereafter immunomodulation through normal diet was investigated in humoral and cellular parameters of immunity. As humoral immunocompentence was not easily modulated, an immune trigger was used to detect potential differences in humoral reactivity. The selection lines showed differential sensitivity to immunomodulation by diet in both generations, suggesting that adaptation to environmental factors may be a line-specific (genetically based) process, with differential neuroendocrine regulation. Most interestingly, the second generation showed effects of the diets in all the selection lines, albeit in different manners. It is concluded that normal diet can cause immunomodulation, mainly in animals with hyper HPA axis reactivity, and that introducing such practices may be more beneficial when mothers are treated, as all offspring showed immunomodulation, irrespective of selection line. While genetic background and/or epigenetic processes on neuroendocrine and immune regulation of the individual form the framework wherein individual immunomodulation by diet can take place, environmental conditions determine if the modulation is beneficial or not. <br/

Assessing dot-map aggregations

Compositional geospatial data can be visualized as dot maps, where the color of each dot represents its class. For interactive dots maps, where it is possible to zoom out in order to see the global picture, it is often needed to aggregate the dots. Hence, we face the following aggregation problem: let M be an input matrix where each cell is assigned a class; find an aggregated matrix A in which each cell aligns with k by k cells of M such that A is a good summary of M.We distinguish three dimensions of “good summary”: class  balance, representation and presence. The first is holistic, whereas the othertwo capture spatial aspects. We propose a simple heuristic algorith

Flow organization in non-Oberbeck-Boussinesq Rayleigh-Benard convection in water

Non-Oberbeck-Boussinesq (NOB) effects on the flow organization in two-dimensional Rayleigh-Benard turbulence are numerically analyzed. The working fluid is water. We focus on the temperature profiles, the center temperature, the Nusselt number, and on the analysis of the velocity field. Several velocity amplitudes (or Reynolds numbers) and several kinetic profiles are introduced and studied; these together describe the various features of the rather complex flow organization. The results are presented both as functions of the Rayleigh number Ra (with Ra up to 10^8) for fixed temperature difference (Delta) between top and bottom plates and as functions of Delta ("non-Oberbeck-Boussinesqness") for fixed Ra with Delta up to 60 K. All results are consistent with the available experimental NOB data for the center temperature Tc and the Nusselt number ratio Nu_{NOB}/Nu_{OB} (the label OB meaning that the Oberbeck-Boussinesq conditions are valid). Beyond Ra ~ 10^6 the flow consists of a large diagonal center convection roll and two smaller rolls in the upper and lower corners. In the NOB case the center convection roll is still characterized by only one velocity scale.Comment: 31 pages, 22 figure

Changes in turbulent dissipation in a channel flow with oscillating walls

Harmonic oscillations of the walls of a turbulent plane channel flow are studied by direct numerical simulations to improve our understanding of the physical mechanism for skin-friction drag reduction. The simulations are carried out at constant pressure gradient in order to define an unambiguous inner scaling: in this case, drag reduction manifests itself as an increase of mass flow rate. Energy and enstrophy balances, carried out to emphasize the role of the oscillating spanwise shear layer, show that the viscous dissipations of the mean flow and of the turbulent fluctuations increase with the mass flow rate, and the relative importance of the latter decreases. We then focus on the turbulent enstrophy: through an analysis of the temporal evolution from the beginning of the wall motion, the dominant, oscillation-related term in the turbulent enstrophy is shown to cause the turbulent dissipation to be enhanced in absolute terms, before the slow drift towards the new quasi-equilibrium condition. This mechanism is found to be responsible for the increase in mass flow rate. We finally show that the time-average volume integral of the dominant term relates linearly to the drag reduction