Lattice stability and formation energies of intrinsic defects in Mg2Si and Mg2Ge via first principles simulations

We report an ab initio study of the semiconducting Mg2X (with X = Si, Ge) compounds and in particular we analyze the formation energy of the different point defects with the aim to understand the intrinsic doping mechanisms. We find that the formation energy of Mg2Ge is 50 % larger than the one of Mg2Si, in agreement with the experimental tendency. From the study of the stability and the electronic properties of the most stable defects taking into account the growth conditions, we show that the main reason for the n-doping in these materials comes from interstitial magnesium defects. Conversely, since other defects acting like acceptors such as Mg vacancies or multivacancies are more stable in Mg2Ge than in Mg2Si, this explains why Mg2Ge can be of n or p type, contrary to Mg2Si. The finding that the most stable defects are different in Mg2Si and Mg2Ge and depend on the growth conditions is important and must be taken into account in the search of the optimal doping to improve the thermoelectric properties of these materials.Comment: 25 pages, 6 Table

Suivi de la cinétique associée à la phase gamma' dans le superalliage N18 en utilisant des mesures de résisitivité électrique in situ

International audienceIn nickel-based superalloys, temperatures related to the formation or the dissolution of the different types of γ' precipitates are important parameters for optimizing the mechanical properties of components but also for developing models which can reproduce the kinetics of their phase transformation. We showed that the electrical resistivity variations during heat treatment of the N18 superalloy was sufficient to monitor the kinetics related to secondary and tertiary γ' precipitates. In particular, the effects of the heating rate and the initial microstructure on the dissolution kinetics of the γ' phase were investigated. Experimental results were also compared to outputs of a precipitation model developed for the N18 alloy showing that in situ electrical resistivity measurements can be used for calibration and validation purposes

Van der Waals epitaxy of two-dimensional single-layer h-BN on graphite by molecular beam epitaxy: electronic properties and band structure

We report on the controlled growth of h-BN/graphite by means of molecular beam epitaxy. X-Ray photoelectron spectroscopy suggests the presence of an interface without any reaction or intermixing, while the angle resolved photoemission spectroscopy (ARPES) measurements show that the h-BN layers are epitaxially aligned with graphite. A well-defined band structure is revealed by ARPES measurements, reflecting the high quality of the h-BN films. The measured valence band maximum located at 2.8 eV below the Fermi level reveals the presence of undoped h-BN films (band gap 6 eV). These results demonstrate that, although only weak van der Waals interactionsare present between h-BN and graphite, a long range ordering of h-BN can be obtained even on polycrystalline graphite via van der Waals epitaxy, offering the prospect of large area, single layer h-BN

Population genetics of trypanosoma brucei rhodesiense: clonality and diversity within and between foci

African trypanosomes are unusual among pathogenic protozoa in that they can undergo their complete morphological life cycle in the tsetse fly vector with mating as a non-obligatory part of this development. Trypanosoma brucei rhodesiense, which infects humans and livestock in East and Southern Africa, has classically been described as a host-range variant of the non-human infective Trypanosoma brucei that occurs as stable clonal lineages. We have examined T. b. rhodesiense populations from East (Uganda) and Southern (Malawi) Africa using a panel of microsatellite markers, incorporating both spatial and temporal analyses. Our data demonstrate that Ugandan T. b. rhodesiense existed as clonal populations, with a small number of highly related genotypes and substantial linkage disequilibrium between pairs of loci. However, these populations were not stable as the dominant genotypes changed and the genetic diversity also reduced over time. Thus these populations do not conform to one of the criteria for strict clonality, namely stability of predominant genotypes over time, and our results show that, in a period in the mid 1990s, the previously predominant genotypes were not detected but were replaced by a novel clonal population with limited genetic relationship to the original population present between 1970 and 1990. In contrast, the Malawi T. b. rhodesiense population demonstrated significantly greater diversity and evidence for frequent genetic exchange. Therefore, the population genetics of T. b. rhodesiense is more complex than previously described. This has important implications for the spread of the single copy T. b. rhodesiense gene that allows human infectivity, and therefore the epidemiology of the human disease, as well as suggesting that these parasites represent an important organism to study the influence of optional recombination upon population genetic dynamics

Neglected Tropical Diseases in Sub-Saharan Africa: Review of Their Prevalence, Distribution, and Disease Burden

The neglected tropical diseases (NTDs) are the most common conditions affecting the poorest 500 million people living in sub-Saharan Africa (SSA), and together produce a burden of disease that may be equivalent to up to one-half of SSA's malaria disease burden and more than double that caused by tuberculosis. Approximately 85% of the NTD disease burden results from helminth infections. Hookworm infection occurs in almost half of SSA's poorest people, including 40–50 million school-aged children and 7 million pregnant women in whom it is a leading cause of anemia. Schistosomiasis is the second most prevalent NTD after hookworm (192 million cases), accounting for 93% of the world's number of cases and possibly associated with increased horizontal transmission of HIV/AIDS. Lymphatic filariasis (46–51 million cases) and onchocerciasis (37 million cases) are also widespread in SSA, each disease representing a significant cause of disability and reduction in the region's agricultural productivity. There is a dearth of information on Africa's non-helminth NTDs. The protozoan infections, human African trypanosomiasis and visceral leishmaniasis, affect almost 100,000 people, primarily in areas of conflict in SSA where they cause high mortality, and where trachoma is the most prevalent bacterial NTD (30 million cases). However, there are little or no data on some very important protozoan infections, e.g., amebiasis and toxoplasmosis; bacterial infections, e.g., typhoid fever and non-typhoidal salmonellosis, the tick-borne bacterial zoonoses, and non-tuberculosis mycobaterial infections; and arboviral infections. Thus, the overall burden of Africa's NTDs may be severely underestimated. A full assessment is an important step for disease control priorities, particularly in Nigeria and the Democratic Republic of Congo, where the greatest number of NTDs may occur

Etudes microstructurales d'oxydes désordonnés et modélisation de leurs propriétés thermiques

Cette thèse concerne la modélisation d'oxydes fortement désordonnés à l'aide de simulations numériques de type Monte Carlo et Dynamique Moléculaire, en relation avec des mesures d'ordre à courte distance par diffusion diffuse de rayons X et de neutrons. Les oxydes à base de zircone sont caractérisés par une cinétique de diffusion très lente pour les cations et rapide pour les anions. Comme ce sont des matériaux ioniques, les interactions dominantes sont des interactions électrostatiques à longue portée. Des mesures d'ordre local ont montré que les atomes ne sont pas disposés au hasard dans le système: il existe donc de fortes corrélations chimiques en plus des distorsions de réseau introduites par la présence de lacunes structurelles. La technique de Dynamique Moléculaire hors d'équilibre (NEMD) a été utilisée pour calculer la conductivité thermique à partir des configurations atomiques. Cependant, elle ne peut suivre les mouvements des atomes que durant quelques nanosecondes. C'est pourquoi, afin d'améliorer la description des propriétés microstructurales et d'analyser l'effet de l'ordre local sur la conductivité thermique, nous avons développé un code de calcul de type Monte Carlo traitant aussi bien des effets élastiques que des effets chimiques et adapté à des solides ioniques. La confrontation de l'ordre à courte distance reproduit dans les simulations numériques avec celui mesuré par diffusion diffuse a montré un très bon accord simulations-expériences ainsi que la nécessité d'utiliser des simulations Monte Carlo afin rendre compte de la mise en ordre locale des défauts notamment à forte concentration en dopant. D'autre part, les résultats des calculs de conductivité thermique se sont révélés en excellent accord avec les mesures, puisque que la différence entre valeurs calculées et valeurs mesurées est inférieure à 20%. Enfin, l'influence de l'ordre local sur le comportement de la conductivité a été analysée numériquement et expérimentalement.This thesis is devoted to the modelling of disordered oxides by Monte Carlo and Molecular Dynamics simulations, in relation with short-range order investigations by neutrons and X-rays diffuse scattering measurements. In zirconia based oxides the kinetics of cations is very slow, whereas it is very fast for anions. These materials are ionic systems. Thus, the largest contribution to the energy of the system is given by long-range electrostatic interactions (1/r). Local order measurements have shown that chemical species are not randomly placed in the crystal structure. Due to the presence of structural vacancies, created by a charge compensation mechanism, lattice distortions are also important. Thus, the chemical ordering is strongly correlated to the atomic displacements. The Non Equilibrium Molecular Dynamics technique has been used to compute the thermal conductivity from atomic configurations. However, this method can only reproduce the movement of particles during several nanoseconds. Therefore, in order to ameliorate the description of micro structural properties and to analyze the influence on the conductivity of the local order, we developed a code based on a Monte Carlo approach, which is adapted to ionic systems and which can describe the strong elastic effects as well as the chemical effects. The short-range order reproduced in the Monte Carlo simulations is very closed to the one measured. We also show that Molecular Dynamics simulations cannot reproduce the correct local order between defects, observed at high doping concentrations. Moreover, the thermal conductivity computations have shown a good agreement with the experimental data. Indeed, the error between simulations and measurements are below 20%. Finally, this study also discusses the influence of the short-range order on the conductivity behaviour using numerical results, diffuse scattering investigations and thermal conductivity measurements.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Evaluation of the Activity of a Combination of Three Bacteriophages Alone or in Association with Antibiotics on Staphylococcus aureus Embedded in Biofilm or Internalized in Osteoblasts

Staphylococcus aureus is responsible for difficult-to-treat bone and joint infections (BJIs). This is related to its ability to form biofilm and to be internalized and persist inside osteoblasts. Recently, bacteriophage therapy has emerged as a promising option to improve treatment of such infections, but data on its activity against the specific bacterial lifestyles presented above remain scarce. We evaluated the activity of a combination of three bacteriophages, recently used for compassionate treatment in France, against S. aureus HG001 in a model of staphylococcal biofilm and a model of osteoblasts infection, alone or in association with vancomycin or rifampin. The activity of bacteriophages against biofilm-embedded S. aureus was dose dependent. In addition, synergistic effects were observed when bacteriophages were combined with antibiotics used at the lowest concentrations. Phage penetration into osteoblasts was observed only when the cells were infected, suggesting a S. aureus-dependent Trojan horse mechanism for internalization. The intracellular bacterial count of bacteria in infected osteoblasts treated with bacteriophages as well as with vancomycin was significantly higher than in cells treated with lysostaphin, used as a control condition, owing to the absence of intracellular activity and the rapid killing of bacteria released after the death of infected cells. These results suggest that bacteriophages are both inactive in the intracellular compartment after being internalized in infected osteoblasts and present a delayed killing effect on bacteria released after cell lysis into the extracellular compartment, which avoids preventing them from infecting other osteoblasts. The combination of bacteriophages tested was highly active against S. aureus embedded in biofilm but showed no activity against intracellular bacteria in the cell model used

Implémentation de filtres à résonateurs coaxiaux en bande Ka et X dans un substrat multicouche

International audienceL'intérêt de la miniaturisation des systèmes de télécommunications est indéniable. Dans cette communication, deux filtres à résonateurs coaxiaux d'ordre 3 et de bande passante de 70 % sont présentés : le premier en bande Ka et le second en bande X. Ils sont intégrés dans un substrat multicouche de type Megtron6. Les trous métallisés réalisés avec des microvias laser permettent d'implémenter les résonateurs coaxiaux dans l'épaisseur du substrat. Les mesures des filtres en bande Ka et en bande X montrent un bon accord avec la simulation

Compact X -Band Filter Based on Substrate Integrated Coaxial Line Stubs Using Advanced Multilayer PCB Technology

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Salvage Debridement, Antibiotics and Implant Retention ("DAIR") With Local Injection of a Selected Cocktail of Bacteriophages: Is It an Option for an Elderly Patient With Relapsing Staphylococcus aureus Prosthetic-Joint Infection?

[PubMed Central:\hrefhttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC6240628PMC6240628] [DOI:\hrefhttps://dx.doi.org/10.1093/ofid/ofy26910.1093/ofid/ofy269] [PubMed:\hrefhttps://www.ncbi.nlm.nih.gov/pubmed/3029248130292481]International audienceLocal injection of a bacteriophages mix during debridement, antibiotics and implant retention ("DAIR") was performed to treat a relapsing Staphylococcus aureus chronic prosthetic joint infection (PJI). This salvage treatment was safe and associated with a clinical success. Scientific evaluation of the potential clinical benefit of bacteriophages as antibiofilm treatment in PJI is now feasible and required