Conception in silico d'une nouvelle phase de carbure de bore

The goal of this work is to reinforce the boron carbide B 4 C in its use for shielding.This thesis has been devoted to the theoretical study of new boron carbides using abinitio methods based on the density functional theory (DFT) using the local densityapproximation (LDA) and generalized gradient approximation (GGA). These have firstbeen validated by comparing the calculated results with the experimental data on theboron carbide B 4 C. They were then used to design new materials.The idea was to reinforce C-B-C chains with respect to vacancies formation. In thenew material, (B 11 C p )C-C, chains are C-C. With the help of Wade’s ionic model, I havealso found that increasing the carbon concentration in the icosaedra, (B 10 C 2 )C-C, formsanother metastable phase. The concentration in the latter phase, 28.6% carbon concentra-tion, is however outside the domain of concentration were icosahedral phases are knownto exist.Once the structures were designed, the second step was to chek their (meta)stability.This required the calculation of their formation energies, their elastic constants and ofphonons dispersion curves. The third step was to check mechanical strengthening. To thisend, I have shown that these materials are less subject to vacancy formation, and thatvacancies can withstand a huge hydostatic pressure without a discontinuous change ofvolume, at variance with vacancies in B 4 C. The calculated elastic properties showed alarge increase in the bulk modulus, Young modulus and shear modulus.I have shown that different methods can be used to distinguish materials with C-Cchains, especially (B 11 C p )C-C, from B 4 C. These methods are the X-ray diffraction, Ramanand infrared vibrational spectroscopy. In particular, I have identified all of the modes of(B 11 C p )C-C by projecting their eigenvectors onto those of B 4 C and I have calculatedtheir Raman scattering spectrum in a polycrystalline average. I have also studied theRaman spectrum of B 4 C under pressure, and the results are in excellent agreement withexperiment. This enables me to confirm the mode identifications made at ambiant pressureand to understand the difference between calcultions in a monoclinic symmetry and theexperimental data which exhibit a rhombohedral average.In order to provide a method of synthesis, I then studied the phase transition that canoccur under pressure between the material (B 11 C p )CC ( represents a vacancy) andthe material (B 11 C p )C-C. A synthesis method has been elaborated in order to synthesizethis last material. This method is magnesiothermic reaction under high pressure.Le but de ce travail est de renforcer le carbure de bore à 20% d’atomes de carbone B 4 Cpour son utilisation pour le blindage. Cette thèse a été consacrée à l’étude théorique d’unenouvelle phase de carbure de bore à l’aide des méthodes ab initio basées sur la théoriede la fonctionnelle de la densité (DFT), en utilisant l’approximation de la densité locale(LDA) et du gradient généralisé (GGA). Les méthodes employées ont tout d’abord étévalidées en comparant les résultats calculés aux résultats expérimentaux sur le carbure debore B 4 C. Elles ont ensuite été utilisées pour concevoir de nouveaux matériaux.L’idée a été de renforcer les chaînes C-B-C par rapport à la formation de lacunes. Dansle nouveau matériau, (B 11 C p )C-C, les chaînes sont C-C. En me basant sur le modèle io-nique de Wade, j’ai aussi trouvé qu’augmenter la concentration en carbone sur l’icosaèdre,(B 10 C 2 )C-C, forme une deuxième phase métastable. La concentration obtenue (28% enatomes de carbone) sort toutefois du domaine connu d’existence des phases icosaédriques.Une fois les structures conçues, la deuxième étape a été de vérifier leur (méta)stabilité.Cela a nécessité le calcul de leurs énergies de formation, de leurs constantes élastiques etdes courbes de dispersion des phonons. La troisième étape a été de vérifier le renforcementmécanique. Pour cela, j’ai démontré que ces matériaux sont moins sujets à la formationde lacunes, et que les lacunes qui peuvent se former ne subissent pas de réduction dis-continue de volume sous pression hydrostatique contrairement à ce qu’il se passe pourB 4 C. De plus, les propriétés élastiques calculées ont montré une augmentation du moduled’incompressibilité, du module de Young et du module de cisaillement.J’ai montré que différentes méthodes peuvent permettre de différencier les matériaux àchaînes C-C, et plus particulièrement (B 11 C p )C-C, de B 4 C. Ces méthodes sont la diffrac-tion des rayons X et la spectroscopie vibrationnelle Raman et infrarouge. En particulier,j’ai identifié tous les modes propres de (B 11 C p )C-C en projetant leurs vecteurs propressur ceux de B 4 C et j’ai calculé leur spectre de diffusion Raman en moyenne polycris-talline. J’ai aussi étudié le spectre Raman de B 4 C sous pression et les résultats sont enexcellent accord avec l’expérience. Cela m’a permis de valider les identifications des modesréalisées à pression ambiante et de comprendre la différence entre le calcul en symétriemonoclinique et l’expérience en moyenne rhomboédrique.Dans le but de proposer une méthode de synthèse, j’ai ensuite étudié la transition dephase pouvant se produire sous pression entre le matériau (B 11 C p )CC ( représente unelacune) et le matériau (B 11 C p )C-C. Une méthode de synthèse a été élaborée dans le butde réaliser ce matériau. Cette méthode est une magnésiothermie sous haute pression

Overcoming the challenges of cancer drug resistance through bacterial-mediated therapy.

Despite tremendous efforts to fight cancer, it remains a major public health problem and a leading cause of death worldwide. With increased knowledge of cancer pathways and improved technological platforms, precision therapeutics that specifically target aberrant cancer pathways have improved patient outcomes. Nevertheless, a primary cause of unsuccessful cancer therapy remains cancer drug resistance. In this review, we summarize the broad classes of resistance to cancer therapy, particularly pharmacokinetics, the tumor microenvironment, and drug resistance mechanisms. Furthermore, we describe how bacterial-mediated cancer therapy, a bygone mode of treatment, has been revitalized by synthetic biology and is uniquely suited to address the primary resistance mechanisms that confound traditional therapies. Through genetic engineering, we discuss how bacteria can be potent anticancer agents given their tumor targeting potential, anti-tumor activity, safety, and coordinated delivery of anti-cancer drugs

Simulation of Single Particle Displacement Damage in Silicon – Part I: Global Approach and Primary Interaction Simulation

A comprehensive approach is developed for the simulation of Single Particle Displacement Damage in silicon, from the incident particle interaction in silicon, to the resulting electrical effect observed experimentally. The different steps of the global approach are described. The paper then focuses on the first step corresponding to Monte Carlo simulation of the primary interaction. The characteristics of the Primary Knock-On Atom (PKA) generated by neutron- or proton-silicon interactions for different energies are explored, analyzing in particular the PKA range in energies and species. This leads to the selection of 1 and 10 keV silicon atoms as good candidates to best represent the displacement cascades generated by all PKA. These PKA characteristics will be used as input in the following Molecular Dynamics simulation step, developed in a separate paper to simulate the displacement cascade generation and evolution. Monte Carlo simulations are also performed in a geometry representative of an image sensor, analyzing the distribution of non-ionizing deposited energy. The obtained distributions appear very similar for incident neutrons from 3 to 18 MeV and incident protons of 200 MeV, in agreement with similarities observed in experimentally measured dark current distributions in image sensors. The effect of geometric parameters on these distributions is finally explored

Integrated weed management systems with herbicide-tolerant crops in the European Union: lessons learnt from home and abroad

Conventionally bred (CHT) and genetically modified herbicide-tolerant (GMHT) crops have changed weed management practices and made an important contribution to the global production of some commodity crops. However, a concern is that farm management practices associated with the cultivation of herbicide-tolerant (HT) crops further deplete farmland biodiversity and accelerate the evolution of herbicide-resistant (HR) weeds. Diversification in crop systems and weed management practices can enhance farmland biodiversity, and reduce the risk of weeds evolving herbicide resistance. Therefore, HT crops are most effective and sustainable as a component of an integrated weed management (IWM) system. IWM advocates the use of multiple effective strategies or tactics to manage weed populations in a manner that is economically and environmentally sound. In practice, however, the potential benefits of IWM with HT crops are seldom realized because a wide range of technical and socio-economic factors hamper the transition to IWM. Here, we discuss the major factors that limit the integration of HT crops and their associated farm management practices in IWM systems. Based on the experience gained in countries where CHT or GMHT crops are widely grown and the increased familiarity with their management, we propose five actions to facilitate the integration of HT crops in IWM systems within the European Union

Radiation Induced Variable Retention Time in Dynamic Random Access Memories

The effect of gamma-ray and neutron radiations on the Variable Retention Time (VRT) phenomenon occurring in Dynamic Random Access Memory (DRAM) is studied. It is shown that both ionizing radiation and non-ionizing radiation induce VRT behaviors in DRAM cells. It demonstrates that both Si/SiO2 interface states and silicon bulk defects can be a source of VRT. It is also highlighted that radiation induced VRT in DRAMs is very similar to radiation induced Dark Current Random Telegraph Signal (DC-RTS) in image sensors. Both phenomena probably share the same origin but high magnitude electric fields seem to play an important role in VRT only. Defect structural fluctuations (without change of charge state) seem to be the root cause of the observed VRT whereas processes involving trapping and emission of charge carriers are unlikely to be a source of VRT. VRT also appears to be the most probable cause of intermittent stuck bits in irradiated DRAMs

Human Immunodeficiency Virus and Malaria in a Representative Sample of Childbearing Women in Kigali, Rwanda

In 1986-1987 a consecutive sample of 3702 women presenting to prenatal and pediatric clinics at the only hospital in Kigali, Rwanda, was screened for human immunodeficiency virus (HIV) and malaria infection. The prevalence of HIV antibodies was 29%, and that of malaria parasites was 9%. HIV antibodies were more prevalent in women from the urban center than in those from the outskirts (31% vs. 20%, P < .001), and malaria parasites showed the opposite prevalence pattern (8% vs. 15%, P < .001); after stratifying by location, there was no association between HIV and the presence or degree of malaria parasitemia. HIV prevalence was 45% in women who had received a blood transfusion between 1980-1985 (before screening of donated blood began), and 28% among the great majority (94%) who had never been transfused. HIV prevalence was 44% in single mothers, 34% in women in common law unions, and 20% in those in legal marriages. These high rates of infection in the general population of Kigali highlight the need to develop effective programs for preventing further spread of sexually transmitted HI

Surprisingly Strong K-band Emission Found in Low Luminosity Active Galactic Nuclei

We examine the near-infrared (NIR) emission from low-luminosity AGNs (LLAGNs). Our galaxy sample includes 15 objects with detected 2-10 keV X-ray emission, dynamical black hole mass estimates from the literature, and available Gemini/NIFS integral field spectroscopy (IFU) data. We find evidence for red continuum components at the center of most galaxies, consistent with the hot dust emission seen in higher luminosity AGN. We decompose the spectral data cubes into a stellar and continuum component, assuming the continuum component comes from thermal emission from hot dust. We detect nuclear thermal emission in 14 out of 15 objects. This emission causes weaker CO absorption lines and redder continuum ($2.05-2.28\:\mu$m) in our $K$-band data, as expected from hot dust around an AGN. The NIR emission is clearly correlated with the 2-10 keV X-ray flux, with a Spearman coefficient of $r_{spearman}=0.69$ suggesting a $>99\%$ significance of correlation, providing further evidence of an AGN origin. Our sample has typical X-ray and NIR fluxes $3-4$ orders of magnitude less luminous than previous work studying the NIR emission from AGN. We find that the ratio of NIR to X-ray emission increases towards lower Eddington ratios. The NIR emission in our sample is often brighter than the X-ray emission, with our $K$-band AGN luminosities comparable to or greater than the 2-10 keV X-ray luminosities in all objects with Eddington ratios below $0.01\%$. The nature of this LLAGN NIR emission remains unclear, with one possibility being an increased contribution from jet emission at these low luminosities. These observations suggest JWST will be a useful tool for detecting the lowest luminosity AGN.Comment: Submitted to ApJ, manuscript after resubmissio

Short-term risk of anaemia following initiation of combination antiretroviral treatment in HIV-infected patients in countries in sub-Saharan Africa, Asia-Pacific, and central and South America

BACKGROUND:The objective was to examine the short-term risk and predictors of anaemia following initiation of combination antiretroviral therapy (cART) in HIV-infected patients from the Western Africa, Eastern Africa, Southern Africa, Central Africa, Asian-Pacific, and Caribbean and Central and South America regions of the International Epidemiologic Databases to Evaluate AIDS (IeDEA) collaboration. METHODS: Anaemia was defined as haemoglobin of = 10 g/dL, and had one or more follow-up haemoglobin tests. Factors associated with anaemia up to 12 months were examined using Cox proportional hazards models and stratified by IeDEA region. RESULTS: Between 1998 and 2008, 19,947 patients initiated cART with baseline and follow-up haemoglobin tests (7358, 7289, 2853, 471, 1550 and 426 in the Western Africa, Eastern Africa, Southern Africa, Central Africa, Asian-Pacific, and Caribbean and Central and South America regions, respectively). At initiation, anaemia was found in 45% of Western Africa patients, 29% of Eastern Africa patients, 21% of Southern Africa patients, 36% of Central Africa patients, 15% of patients in Asian-Pacific and 14% of patients in Caribbean and Central and South America. Among patients with haemoglobin of > = 10 g/dL at baseline (13,445), the risks of anaemia were 18.2, 6.6, 9.7, 22.9, 11.8 and 19.5 per 100 person-years in the Western Africa, Eastern Africa, Southern Africa, Central Africa, Asian, and Caribbean and Central and South America regions, respectively. Factors associated with anaemia were female sex, low baseline haemoglobin level, low baseline CD4 count, more advanced disease stage, and initial cART containing zidovudine. CONCLUSIONS: In data from 34 cohorts of HIV-infected patients from sub-Saharan Africa, Central and South America, and Asia, the risk of anaemia within 12 months of initiating cART was moderate. Routine haemoglobin monitoring was recommended in patients at risk of developing anaemia following cART initiation

A Security Model and Fully Verified Implementation for the IETF QUIC Record Layer

We investigate the security of the QUIC record layer, as standardized by the IETF in draft version 30. This version features major differences compared to Google\u27s original protocol and prior IETF drafts. We model packet and header encryption, which uses a custom construction for privacy. To capture its goals, we propose a security definition for authenticated encryption with semi-implicit nonces. We show that QUIC uses an instance of a generic construction parameterized by a standard AEAD-secure scheme and a PRF-secure cipher. We formalize and verify the security of this construction in F*. The proof uncovers interesting limitations of nonce confidentiality, due to the malleability of short headers and the ability to choose the number of least significant bits included in the packet counter. We propose improvements that simplify the proof and increase robustness against strong attacker models. In addition to the verified security model, we also give concrete functional specification for the record layer, and prove that it satisfies important functionality properties (such as successful decryption of encrypted packets) after fixing more errors in the draft. We then provide a high-performance implementation of the record layer that we prove to be memory safe, correct with respect to our concrete specification (inheriting its functional correctness properties), and secure with respect to our verified model. To evaluate this component, we develop a provably-safe implementation of the rest of the QUIC protocol. Our record layer achieves nearly 2 GB/s throughput, and our QUIC implementation\u27s performance is within 21% of an unverified baseline

Guidance on Noncorticosteroid Systemic Immunomodulatory Therapy in Noninfectious Uveitis : Fundamentals Of Care for UveitiS (FOCUS) Initiative

Supplemental material available at www.aaojournal.org. Supported by AbbVie, Inc., and the Fundamentals of Care for Uveitis Initiative National Faculty. This manuscript was developed subsequent to an AbbVie-sponsored literature review of noninfectious, nonanterior uveitis. The meeting was conducted to understand the available literature regarding the management of patients with noninfectious, nonanterior uveitis. The program involved a total of 139 experts from 28 countries, who were selected for participation by AbbVie. However, AbbVie was not involved in the development of the manuscript. The authors maintained complete control over the content and this manuscript reflects the opinions of the authors. AbbVie selected the discussion participants and reviewed the final manuscript draft for scientific accuracy, but the authors determined the final content. All authors made substantial contributions to the article or critically revised it for important intellectual content and approved the final manuscript. AbbVie provided funding to invited participants, including honoraria for their attendance at the meetings. Travel to and from the meetings was reimbursed. No payments were made to the authors for the development of this manuscript. Dhinakaran Sambandan, PhD, and Shula Sarner, PhD, of Lucid Partners, Burleighfield House, Buckinghamshire, United Kingdom, provided medical writing and editorial support to the authors in the development of this manuscript; financial support for these services was provided by AbbVie. AbbVie reviewed the manuscript, but was not involved in the methodology, data collection and analysis, or completion of this manuscript.Peer reviewedPublisher PD