Insights on finite size effects in Ab-initio study of CO adsorption and dissociation on Fe 110 surface

Adsorption and dissociation of hydrocarbons on metallic surfaces represent crucial steps to carburization of metal. Here, we use density functional theory total energy calculations with the climbing-image nudged elastic band method to estimate the adsorption energies and dissociation barriers for different CO coverages with surface supercells of different sizes. For the absorption of CO, the contribution from van der Waals interaction in the computation of adsorption parameters is found important in small systems with high CO-coverages. The dissociation process involves carbon insertion into the Fe surface causing a lattice deformation that requires a larger surface system for unrestricted relaxation. We show that, in larger surface systems associated with dilute CO-coverages, the dissociation barrier is significantly decreased. The elastic deformation of the surface is generic and can potentially applicable for all similar metal-hydrocarbon reactions and therefore a dilute coverage is necessary for the simulation of these reactions as isolated processes.Comment: 12 pages, 6 figures. Submitted to Journal of Applied Physic

Dislocation interaction with C in alpha-Fe: a comparison between atomic simulations and elasticity theory

The interaction of C atoms with a screw and an edge dislocation is modelled at an atomic scale using an empirical Fe-C interatomic potential based on the Embedded Atom Method (EAM) and molecular statics simulations. Results of atomic simulations are compared with predictions of elasticity theory. It is shown that a quantitative agreement can be obtained between both modelling techniques as long as anisotropic elastic calculations are performed and both the dilatation and the tetragonal distortion induced by the C interstitial are considered. Using isotropic elasticity allows to predict the main trends of the interaction and considering only the interstitial dilatation will lead to a wrong interaction

Threshold concentration for H blistering in defect free W

Lattice distortion induced by high concentration of H is believed to be precursor of H blistering in single crystalline W (SCW) during H isotope irradiation. However, the critical H concentration needed to trigger bond-breaking of metal atoms presents a challenge to measure. Using density functional theory, we have calculated the formation energy of a vacancy and a self-interstitial atom (SIA) in supersaturated defect-free SCW with various H concentrations. When the ratio of H:W exceeds 1:2, the formation of both vacancies and self-interstitials becomes exothermic, meaning that spontaneous formation of micro-voids which can accommodate molecular H2 will occur. Molecular H2 is not allowed to form, and it is not needed either at the very initial stage of H blistering in SCW. With supersaturated H, the free volume at the vacancy or SIA is greatly smeared out with severe lattice distortion and more H can be trapped than in the dilute H case.Comment: 13 pages, 4 figure

Study of hydrogen isotopes behavior in tungsten by a multi trapping macroscopic rate equation model

International audienceDensity functional theory (DFT) studies show that in tungsten a mono vacancy can contain up to six hydrogen isotopes (HIs) at 300 K with detrapping energies varying with the number of HIs inthe vacancy. Using these predictions, a multi trapping rate equation model has been built and used to model thermal desorption spectrometry (TDS) experiments performed on single crystaltungsten after deuterium ions implantation. Detrapping energies obtained from the model to adjust temperature of TDS spectrum observed experimentally are in good agreement with DFTvalues within a deviation below 10%. The desorption spectrum as well as the diffusion of deuterium in the bulk are rationalized in light of the model results

Quantitative NanoSIMS provides subcellular concentration and distribution of oligonucleotide therapeutics

Antisense oligonucleotides (ASOs) represent a powerful therapeutic modality that can selectively modulate gene expression. However, ASOs face two major hurdles that restrict their use in the clinic. The first issue is delivery of the ASO to a tissue of therapeutic interest while reducing exposure to unrelated tissues. Additionally, inefficient escape of ASOs from endolysosomal compartments affects their activity since ASOs are unable to reach their intracellular RNA target in the nucleus and/or cytosol. Despites the variety of chemical modifications developed to tackle these delivery issues, it remains challenging to reach particular tissues and/or cell types outside of the liver, and there are still no non-toxic solutions to the endosomal escape problem. To fully realize the therapeutic potential of this class of molecules, it is crucial to understand the mechanisms underlying how ASOs enter cells and exit the endosomal space. Therefore, this thesis focuses on the use of nanoscale secondary ion mass spectrometry (NanoSIMS), in combination with electron microscopy, to investigate the subcellular distribution and accumulation of ASOs. It was necessary to develop a NanoSIMS method capable of absolute quantification of the intracellular exposure of ASO. Thus, external standards were developed to quantify several halogenated compounds (iodine, bromine, and fluorine) as well as a sulfur isotope (34S). Results showed that the uptake of different ASOs was saturable, but conjugation to a N-acetylgalactosamine targeting domain enhanced cellular uptake and improved target knockdown. NanoSIMS data also showed that upon colchicine treatment, the uptake and localization of ASOs were affected. It was also possible to quantifying both the targeting domain and ASO components of an engineered glucagon-like peptide 1 ASO conjugate. That highlighted that fine tuning of ASO chemistry can be used to affect the productive uptake of ASOs. Overall, these findings contribute to a better understanding of the cellular delivery, uptake and trafficking mechanisms of ASOs, which is valuable for the future development of more effective oligonucleotide-based therapeutics

Disorder-Driven Pretransitional Tweed in Martensitic Transformations

Defying the conventional wisdom regarding first--order transitions, {\it solid--solid displacive transformations} are often accompanied by pronounced pretransitional phenomena. Generally, these phenomena are indicative of some mesoscopic lattice deformation that ``anticipates'' the upcoming phase transition. Among these precursive effects is the observation of the so-called ``tweed'' pattern in transmission electron microscopy in a wide variety of materials. We have investigated the tweed deformation in a two dimensional model system, and found that it arises because the compositional disorder intrinsic to any alloy conspires with the natural geometric constraints of the lattice to produce a frustrated, glassy phase. The predicted phase diagram and glassy behavior have been verified by numerical simulations, and diffraction patterns of simulated systems are found to compare well with experimental data. Analytically comparing to alternative models of strain-disorder coupling, we show that the present model best accounts for experimental observations.Comment: 43 pages in TeX, plus figures. Most figures supplied separately in uuencoded format. Three other figures available via anonymous ftp

Cell-free (RNA) and cell-associated (DNA) HIV-1 and postnatal transmission through breastfeeding

<p>Introduction - Transmission through breastfeeding remains important for mother-to-child transmission (MTCT) in resource-limited settings. We quantify the relationship between cell-free (RNA) and cell-associated (DNA) shedding of HIV-1 virus in breastmilk and the risk of postnatal HIV-1 transmission in the first 6 months postpartum.</p> <p>Materials and Methods - Thirty-six HIV-positive mothers who transmitted HIV-1 by breastfeeding were matched to 36 non-transmitting HIV-1 infected mothers in a case-control study nested in a cohort of HIV-infected women. RNA and DNA were quantified in the same breastmilk sample taken at 6 weeks and 6 months. Cox regression analysis assessed the association between cell-free and cell-associated virus levels and risk of postnatal HIV-1 transmission.</p> <p>Results - There were higher median levels of cell-free than cell-associated HIV-1 virus (per ml) in breastmilk at 6 weeks and 6 months. Multivariably, adjusting for antenatal CD4 count and maternal plasma viral load, at 6 weeks, each 10-fold increase in cell-free or cell-associated levels (per ml) was significantly associated with HIV-1 transmission but stronger for cell-associated than cell-free levels [2.47 (95% CI 1.33–4.59) vs. aHR 1.52 (95% CI, 1.17–1.96), respectively]. At 6 months, cell-free and cell-associated levels (per ml) in breastmilk remained significantly associated with HIV-1 transmission but was stronger for cell-free than cell-associated levels [aHR 2.53 (95% CI 1.64–3.92) vs. 1.73 (95% CI 0.94–3.19), respectively].</p> <p>Conclusions - The findings suggest that cell-associated virus level (per ml) is more important for early postpartum HIV-1 transmission (at 6 weeks) than cell-free virus. As cell-associated virus levels have been consistently detected in breastmilk despite antiretroviral therapy, this highlights a potential challenge for resource-limited settings to achieve the UNAIDS goal for 2015 of eliminating vertical transmission. More studies would further knowledge on mechanisms of HIV-1 transmission and help develop more effective drugs during lactation.</p&gt

Ab initio study of the modification of elastic properties of alpha-iron by hydrostatic strain and by hydrogen interstitials

The effect of hydrostatic strain and of interstitial hydrogen on the elastic properties of $\alpha$-iron is investigated using \textit{ab initio} density-functional theory calculations. We find that the cubic elastic constants and the polycrystalline elastic moduli to a good approximation decrease linearly with increasing hydrogen concentration. This net strength reduction can be partitioned into a strengthening electronic effect which is overcome by a softening volumetric effect. The calculated hydrogen-dependent elastic constants are used to determine the polycrystalline elastic moduli and anisotropic elastic shear moduli. For the key slip planes in $\alpha$-iron, $[1\bar{1}0]$ and $[11\bar{2}]$, we find a shear modulus reduction of approximately 1.6% per at.% H.Comment: Updated first part of 1009.378

Interdisciplinarity and infectious diseases : an Ebola case study

International audienceHigh-profile epidemics such as Ebola, avian influenza, and severe acute respiratory syndrome (SARS) repeatedly thrust infectious diseases into the limelight. Because the emergence of dis-eases involves so many factors, the need for interdisciplinary approaches to studying emerging infections, particularly those originating from animals (i.e., zoonoses), is frequently discussed. However, effective integration across disciplines is challenging in practice. Ecological ideas, for example, are rarely considered in biomedical research, while insights from biomedicine are often neglected in ecological studies of infectious diseases. One practical reason for this is that researchers in these fields focus on vastly different scales of biological organization, which are difficult to bridge both intellectually and methodologically. Nevertheless, integration across biological scales is increasingly needed for solving the complex problems zoonotic diseases pose to human and animal well-being. Motivated by current events, we use Ebola virusas a case study to highlight fundamental questions about zoonoses that can be addressed by integrating insights and approaches across scales

La sinodalidad, un camino de conversión comunitaria

Synodality is a path of discernment in common, listening to the Spirit. It is a call to personal, communitarian and ecclesial conversion. It is also a path of spiritual and pastoral conversion. Therefore, synodality supposes and demands spiritual attitudes for its implementation, which could be summarized in a spirituality of the “ecclesial we” that has as its objective the construction of a people, a fraternal and missionary ecclesial community at the service of the common good of society. In this article we would like to offer some reflections to help us understand synodality as a process of conversion that invites us to learn the art of discernment in order to walk together in the Church.La sinodalidad es un camino de discernimiento en común, a la escucha del Espíritu. Es una llamada a la conversión personal, comunitaria y eclesial. También es un camino de conversión espiritual y pastoral. Por ello, la sinodalidad supone y exige actitudes espirituales para su puesta en práctica, que podría resumirse en una espiritualidad del «nosotros eclesial» que tiene como objetivo la construcción de un pueblo, una comunidad eclesial fraterna y misionera al servicio del bien común de la sociedad. En este artículo queremos ofrecer algunas reflexiones que nos ayuden a comprender la sinodalidad como un proceso de conversión que nos invita a aprender el arte del discernimiento con el fin de caminar juntos en la Iglesia