A multimaterial Eulerian approach for fluid-solid interaction

This thesis is devoted to understanding and modeling multimaterial interactions, and to develop accordingly a robust scheme taking into account the largest variety of those, with a particular interest in resolving solid/fluid configurations. This very general frame of studies can be tackled with numerous different approaches as several issues arise and need to be addressed before attempting any modelisation of these problems. A first questioning should be the frame of reference to be used for the materials considered. Eulerian shock-capturing schemes have advantages for modeling problems involving complex non-linear wave structures and large deformations. If originally reserved mostly to fluids components, recent work has focused on extending Eulerian schemes to other media such as solid dynamics, as long as the set of equations employed is written under a hyperbolic system of conservation laws. Another matter of interest when dealing with multiple immiscible materials it the necessity to include some means of tracking material boundaries within a numerical scheme. Interface tracking methods based on the use of level set functions are an attractive alternative for problems with sliding interfaces since it allows discontinuous velocity profiles at the material boundaries whilst employing fixed grids. However, its intrinsic lack of variables conservation needs to be circumvented by applying an appropriate fix near the interface, where cells might comprise multiple components. Another requirement is the ability to correctly predict the physical interaction at the interface between the materials. For that purpose, the Riemann problem corresponding to the interfacial conditions needs to be formulated and solved. This implies in turn the need of appropriate Riemann solvers; if they are largely available when the materials are identical (i.e. governed by the same set of equations), a specific Riemann solver will be developed to account for fluid/solid interaction. Eventually, these newly developed methods will be tested on a wide range of different multimaterial problems, involving several materials undergoing large deformations. The materials used, whether modelling fluid/fluid or solid/fluid interactions, will be tested using various initial conditions from both sides of the interface, to demonstrate the robustness of the solver and its flexibility. These testcases will be carried out in 1D, 2D and 3D frames, and compared to exact solutions or other numerical experiments conducted in previous studies.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Antibiotic use in urological surgeries: a six years review at Muhimbili National Hospital, Dar es salaam-Tanzania

Introduction: Antimicrobial prophylaxis for urologic procedures is a major issue, as potential   advantages of antibiotic administration should be carefully weighed against potential side effects,   microbial resistance, and health care costs. This study aimed to review a six years trend of antibiotic  use  in urological surgeries at Muhimbili National Hospital (MNH) being an experience in a typical third  world environment.Methods: This was a six years hospital based descriptive, retrospective study conducted of which all case notes of urological patients operated on in between January 2007 to December, 2012 were reviewed by using a structured data collecting tool. The data were analyzed using SPSS software.Results: Male patients were the majority at 62% (450). The age range was 0 - 90 years, with a mean of 30 ± 22.09. Among the urological surgeries done at MNH 86.5% (628) received prophylactic antibiotics  regardless of the type surgery done. Majority 63.7% (463) received antibiotics during induction.  Ceftriaxone was the commonly given antibiotic regardless of the type of urological surgery done. Most of patients (86.4%) were given antibiotics for five days regardless whether it was for prophylactic or  treatment intention.Conclusion: Antibiotic use is still a challenge at our hospital with over use of prophylactic antibiotics  without obvious indications. Prolonged use of prophylactic antibiotics beyond five days was the main finding. Ceftriaxone was the most given antibiotic regardless of the urological surgery done and its level of contamination. Antibiotic stewardship needs to be addressed urgently to avoid serious drug resistances leaving alone the cost implication.Key words: Antibiotics, urological surgeries, Tanzania

Antibiotic use in urological surgeries: a six years review at Muhimbili National Hospital, Dar es salaam-Tanzania

Introduction: Antimicrobial prophylaxis for urologic procedures is a major issue, as potential   advantages of antibiotic administration should be carefully weighed against potential side effects,   microbial resistance, and health care costs. This study aimed to review a six years trend of antibiotic  use  in urological surgeries at Muhimbili National Hospital (MNH) being an experience in a typical third  world environment.Methods: This was a six years hospital based descriptive, retrospective study conducted of which all case notes of urological patients operated on in between January 2007 to December, 2012 were reviewed by using a structured data collecting tool. The data were analyzed using SPSS software.Results: Male patients were the majority at 62% (450). The age range was 0 - 90 years, with a mean of 30 ± 22.09. Among the urological surgeries done at MNH 86.5% (628) received prophylactic antibiotics  regardless of the type surgery done. Majority 63.7% (463) received antibiotics during induction.  Ceftriaxone was the commonly given antibiotic regardless of the type of urological surgery done. Most of patients (86.4%) were given antibiotics for five days regardless whether it was for prophylactic or  treatment intention.Conclusion: Antibiotic use is still a challenge at our hospital with over use of prophylactic antibiotics  without obvious indications. Prolonged use of prophylactic antibiotics beyond five days was the main finding. Ceftriaxone was the most given antibiotic regardless of the urological surgery done and its level of contamination. Antibiotic stewardship needs to be addressed urgently to avoid serious drug resistances leaving alone the cost implication.Key words: Antibiotics, urological surgeries, Tanzania

Novel Drosophila Viruses Encode Host-Specific Suppressors of RNAi

Contains fulltext : 136405.pdf (publisher's version ) (Open Access)The ongoing conflict between viruses and their hosts can drive the co-evolution between host immune genes and viral suppressors of immunity. It has been suggested that an evolutionary 'arms race' may occur between rapidly evolving components of the antiviral RNAi pathway of Drosophila and viral genes that antagonize it. We have recently shown that viral protein 1 (VP1) of Drosophila melanogaster Nora virus (DmelNV) suppresses Argonaute-2 (AGO2)-mediated target RNA cleavage (slicer activity) to antagonize antiviral RNAi. Here we show that viral AGO2 antagonists of divergent Nora-like viruses can have host specific activities. We have identified novel Nora-like viruses in wild-caught populations of D. immigrans (DimmNV) and D. subobscura (DsubNV) that are 36% and 26% divergent from DmelNV at the amino acid level. We show that DimmNV and DsubNV VP1 are unable to suppress RNAi in D. melanogaster S2 cells, whereas DmelNV VP1 potently suppresses RNAi in this host species. Moreover, we show that the RNAi suppressor activity of DimmNV VP1 is restricted to its natural host species, D. immigrans. Specifically, we find that DimmNV VP1 interacts with D. immigrans AGO2, but not with D. melanogaster AGO2, and that it suppresses slicer activity in embryo lysates from D. immigrans, but not in lysates from D. melanogaster. This species-specific interaction is reflected in the ability of DimmNV VP1 to enhance RNA production by a recombinant Sindbis virus in a host-specific manner. Our results emphasize the importance of analyzing viral RNAi suppressor activity in the relevant host species. We suggest that rapid co-evolution between RNA viruses and their hosts may result in host species-specific activities of RNAi suppressor proteins, and therefore that viral RNAi suppressors could be host-specificity factors

A multimaterial Eulerian approach for fluid-solid interaction

This thesis is devoted to understanding and modeling multimaterial interactions, and to develop accordingly a robust scheme taking into account the largest variety of those, with a particular interest in resolving solid/fluid configurations. This very general frame of studies can be tackled with numerous different approaches as several issues arise and need to be addressed before attempting any modelisation of these problems. A first questioning should be the frame of reference to be used for the materials considered. Eulerian shock-capturing schemes have advantages for modeling problems involving complex non-linear wave structures and large deformations. If originally reserved mostly to fluids components, recent work has focused on extending Eulerian schemes to other media such as solid dynamics, as long as the set of equations employed is written under a hyperbolic system of conservation laws. Another matter of interest when dealing with multiple immiscible materials it the necessity to include some means of tracking material boundaries within a numerical scheme. Interface tracking methods based on the use of level set functions are an attractive alternative for problems with sliding interfaces since it allows discontinuous velocity profiles at the material boundaries whilst employing fixed grids. However, its intrinsic lack of variables conservation needs to be circumvented by applying an appropriate fix near the interface, where cells might comprise multiple components. Another requirement is the ability to correctly predict the physical interaction at the interface between the materials. For that purpose, the Riemann problem corresponding to the interfacial conditions needs to be formulated and solved. This implies in turn the need of appropriate Riemann solvers; if they are largely available when the materials are identical (i.e. governed by the same set of equations), a specific Riemann solver will be developed to account for fluid/solid interaction. Eventually, these newly developed methods will be tested on a wide range of different multimaterial problems, involving several materials undergoing large deformations. The materials used, whether modelling fluid/fluid or solid/fluid interactions, will be tested using various initial conditions from both sides of the interface, to demonstrate the robustness of the solver and its flexibility. These testcases will be carried out in 1D, 2D and 3D frames, and compared to exact solutions or other numerical experiments conducted in previous studies

dsRNA uptake in adult Drosophila

International audienceRNA interference (RNAi) is a conserved sequence-specific gene silencing mechanism that is induced by double-stranded RNA (dsRNA). The development of methods that allow internalization of dsRNA and concomitant silencing of the desired gene has not stopped since the first demonstration of RNAi in Caenorhabditis elegans. In this chapter, we describe how to introduce exogenous dsRNA into adult Drosophila in order to interfere with endogenous or viral gene expression

Microbial Quantity Impacts Drosophila Nutrition, Development, and Lifespan

Summary: In Drosophila, microbial association can promote development or extend life. We tested the impact of microbial association during malnutrition and show that microbial quantity is a predictor of fly longevity. Although all tested microbes, when abundantly provided, can rescue lifespan on low-protein diet, the effect of a single inoculation seems linked to the ability of that microbial strain to thrive under experimental conditions. Microbes, dead or alive, phenocopy dietary protein, and the calculated dependence on microbial protein content is similar to the protein requirements determined from fly feeding studies, suggesting that microbes enhance host protein nutrition by serving as protein-rich food. Microbes that enhance larval growth are also associated with the ability to better thrive on fly culture medium. Our results suggest an unanticipated range of microbial species that promote fly development and longevity and highlight microbial quantity as an important determinant of effects on physiology and lifespan during undernutrition. : Nutrition in Life Cycle; Microbiology; Microbiome Subject Areas: Nutrition in Life Cycle, Microbiology, Microbiom

Probabilistic Invasion Underlies Natural Gut Microbiome Stability.

Species compositions of gut microbiomes impact host health [1-3], but the processes determining these compositions are largely unknown. An unexplained observation is that gut species composition varies widely between individuals but is largely stable over time within individuals [4, 5]. Stochastic factors during establishment may drive these alternative stable states (colonized versus non-colonized) [6, 7], which can influence susceptibility to pathogens, such as Clostridium difficile. Here we sought to quantify and model the dose response, dynamics, and stability of bacterial colonization in the fruit fly (Drosophila melanogaster) gut. Our precise, high-throughput technique revealed stable between-host variation in colonization when individual germ-free flies were fed their own natural commensals (including the probiotic Lactobacillus plantarum). Some flies were colonized while others remained germ-free even at extremely high bacterial doses. Thus, alternative stable states of colonization exist even in this low-complexity model of host-microbe interactions. These alternative states are driven by a fundamental asymmetry between the inoculum population and the stably colonized population that is mediated by spatial localization and a population bottleneck, which makes stochastic effects important by lowering the effective population size. Prior colonization with other bacteria reduced the chances of subsequent colonization, thus increasing the stability of higher-diversity guts. Therefore, stable gut diversity may be driven by inherently stochastic processes, which has important implications for combatting infectious diseases and for stably establishing probiotics in the gut