An investigation of a polymetamorphic terrain using ⁴⁰Ar-³⁹Ar geochronology

This research is an exploration both of the Precambrian metamorphic geology of south-western Montana and the Wlaser ablation microprobe 40At-39At geochronological technique. Using the high spatial resolution of the UV laser microprobe it has been possible to produce systematic 40At-39Ar ages within individual mica grains. Further, the UV laser has been used to drill into biotite inclusions within garnet to look at the shielding effect of the garnet lattice, and to drill depth profiles into garnet to measure helium diffusion in laboratory experiments. The south-western Montana region of the Precambrian Wyoming Province was believed to have undergone at least three separate periods of metamorphism: M1- granulite facies in the Archaean, M2 - amphibolite facies in the Early Proterozoic, and M3 - greenschist to epidote-amphibolite facies in the Mid-Proterozoic. Because of the relatively low blocking temperature of the 40Ar- 39Ar geochronological system in mica (c.300-350 °C), it is readily reset by regional metamorphic events and previous K-Ar and 4OAr_38 Atgeochronology had found that the Early Proterozoic event dominated the ages obtained. UV laser 4OAt-39At dating of the matrix mica constrained the timing of cooling from the Early Proterozoic metamorphic event to between 1780 to 1740 Ma with a cooling rate between 1 and 8 °C/m.y. 40Ar-39Ar analyses of individual biotite inclusions in garnet also produced similar ages. However, Pb-Pb step leach dating of a small subset of garnet yielded ages between 1808 and 1765 Ma, demonstrating that the garnet did not grow during an Archaean event but, rather, during the Early Proterozoic metamorphic event. Thus, the shielding properties of garnet on biotite inclusions could not be easily assessed in these samples. However, where matrix biotite had been partially reset by the Cretaceous plutons, there was some evidence to suggest that a minority of the biotite inclusions in the same sample had been shielded from resetting. The influence of fractures, defects and other fast diffusion paths is believed to have prevented most of the inclusions from being shielded. No evidence was found to show that the rocks in south-western Montana were metamorphosed during the Archaean and it seems likely that the M1 and M2 events were not greatly separated in time and were both Early ProterozoiC in age. The high spatial resolution of the UV laser microprobe was used in order to date highly altered biotite within rocks that had undergone later (M3) greenschist metamorphism. Biotite was interlayered with chlorite, clinozoisite and prehnite but using the UV laser it was possible to separately analyse areas of unaltered biotite and areas of alteration within a single mineral and produce ages from both. It was thus possible to measure two ages from one sample: an unaltered age consistent with the timing of the Early Proterozoic metamorphism, and a younger age that could be linked to the c.1500-1360 Ma timing of Belt basin formation to the north and west of the region. This technique therefore was able to overcome the difficulties associated with producing meaningful ages from altered samples whilst constraining the timing of the M3 metamorphic event

Not just a number: examining coverage and content of antenatal care in low-income and middle-income countries.

Introduction: Antenatal care (ANC) provides a critical opportunity for women and babies to benefit from good-quality maternal care. Using 10 countries as an illustrative analysis, we described ANC coverage (number of visits and timing of first visit) and operationalised indicators for content of care as available in population surveys, and examined how these two approaches are related. Methods: We used the most recent Demographic and Health Survey to analyse ANC related to women's most recent live birth up to 3 years preceding the survey. Content of care was assessed using six components routinely measured across all countries, and a further one to eight additional country-specific components. We estimated the percentage of women in need of ANC, and using ANC, who received each component, the six routine components and all components. Results: In all 10 countries, the majority of women in need of ANC reported 1+ ANC visits and over two-fifths reported 4+ visits. Receipt of the six routine components varied widely; blood pressure measurement was the most commonly reported component, and urine test and information on complications the least. Among the subset of women starting ANC in the first trimester and receiving 4+ visits, the percentage receiving all six routinely measured ANC components was low, ranging from 10% (Jordan) to around 50% in Nigeria, Nepal, Colombia and Haiti. Conclusion: Our findings suggest that even among women with patterns of care that complied with global recommendations, the content of care was poor. Efficient and effective action to improve care quality relies on development of suitable content of care indicators

Iterative stochastic subspace self-consistent field method

We propose a new self-consistent field (SCF) algorithm based on an iterative, partially stochastic “Divide & Conquer”-type approach. This new SCF algorithm is a simple variant of the usual SCF procedure and can be easily implemented in parallel. A detailed description of the algorithm is reported. We illustrate this new method on one-dimensional hydrogen chains and three-dimensional hydrogen clusters.PFL thanks the NCI National Facility for a generous grant of supercomputer time, and the Australian Research Council for funding (Grant DP140104071) and a Discovery Early Career Researcher Award (Grant DE130101441). XA would like to thank the Research School of Chemistry of the Australian National University for a visiting fellowship during the construction of this manuscript

Interaction of Iron II Complexes with B-DNA. Insights from Molecular Modeling, Spectroscopy, and Cellular Biology

We report the characterization of the interaction between B-DNA and three terpyridin iron II complexes. Relatively long time-scale molecular dynamics is used in order to characterize the stable interaction modes. By means of molecular modeling and UV-vis spectroscopy, we prove that they may lead to stable interactions with the DNA duplex. Furthermore, the presence of larger π-conjugated moieties also leads to the appearance of intercalation binding mode. Non-covalent stabilizing interactions between the iron complexes and the DNA are also characterized and evidenced by the analysis of the gradient of the electronic density. Finally, the structural deformations induced on the DNA in the different binding modes are also evidenced. The synthesis and chemical characterization of the three complexes is reported, as well as their absorption spectra in presence of DNA duplexes to prove the interaction with DNA. Finally, their effects on human cell cultures have also been evidenced to further enlighten their biological effects

Calculation of Wave-functions with Frozen Orbitals in Mixed Quantum Mechanics/Molecular Mechanics methods. I. Application of the Huzinaga Equation.

Mixed quantum mechanics/quantum mechanics (QM/QM) and quantum mechan- ics/molecular mechanics (QM/MM) methods make computations feasible for extended chemical systems by separating them into subsystems that are treated at different level of sophistication. In many applications the subsystems are covalently bound and the use of frozen localized orbitals at the boundary is a possible way to separate the sub- systems and to ensure a sensible description of the electronic structure near to the boundary. A complication in these methods is that orthogonality between optimized and frozen orbitals has to be warranted and this is usually achieved by an explicit or- thogonalization of the basis set to the frozen orbitals. An alternative to this approach is proposed by calculating the wave-function from the Huzinaga-equation that guaranties orthogonality to the frozen orbitals without basis set orthogonalization. The theoreti- cal background and the practical aspects of the application of the Huzinaga equation in mixed methods is discussed. Forces have been derived to perform geometry opti- mization with wave-functions from the Huzinaga-equation. Various properties have been calculated applying the Huzinaga-equation for the central QM subsystem, repre- senting the environment by point charges and using frozen strictly localized orbitals to connect the subsystems. It is shown that a 2-3 bond separation of the chemical or physical event from the frozen bonds allows a very good reproduction (typically around 1 kcal/mol) of standard Hartree-Fock-Roothaan results. The proposed scheme provides an appropriate framework for mixed QM/QM and QM/MM methods

NHC-Based Iron Sensitizers for DSSCs

Nanostructured dye-sensitized solar cells (DSSCs) are promising photovoltaic devices because of their low cost and transparency. Ruthenium polypyridine complexes have long been considered as lead sensitizers for DSSCs, allowing them to reach up to 11% conversion efficiency. However, ruthenium suffers from serious drawbacks potentially limiting its widespread applicability, mainly related to its potential toxicity and scarcity. This has motivated continuous research efforts to develop valuable alternatives from cheap earth-abundant metals, and among them, iron is particularly attractive. Making iron complexes applicable in DSSCs is highly challenging due to an ultrafast deactivation of the metal-ligand charge-transfer (MLCT) states into metal-centered (MC) states, leading to inefficient injection into TiO2. In this review, we present our latest developments in the field using Fe(II)-based photosensitizers bearing N-heterocyclic carbene (NHC) ligands, and their use in DSSCs. Special attention is paid to synthesis, photophysical, electrochemical, and computational characterization

Etude théorique de réactions chimiques en phase liquide à l'aide du modèle du champ de réaction auto-cohérent

Non disponible / Not availableL'objectif principal de ce travail était la mise au point d'une méthode permettant l'étude théorique de la réactivité chimique en phase liquide à l'aide du modèle du champ de réaction auto-cohérent. Pour cela, nous avons été amenés à développer un algorithme de calcul des dérivées secondes de l'énergie de solvatation par rapport aux coordonnées nucléaires qui permet la localisation des structures de transition en solution. Nous avons appliqué cette méthodologie à l'étude de quelques réactions chimiques que l'on peut classer en trois catégories suivant l'intensité des effets du solvant mis en jeu: 1) réactions faisant intervenir des états de transition peu polaires et, par conséquent, ne devant pas subir de fortes modifications sous l'effet du solvant; 2) réactions à intermédiaires zwitterioniques, fortement favorisées dans les milieux polaires (réaction de Staudinger); 3) réactions avec formation d'ions, donc à forte séparation de charges, possibles uniquement dans un milieu polaire et dans lesquelles le solvant participe activement à la coordonnée de réaction (bromation de l'éthylène). La conclusion principale de ce travail est que le modèle à cavité constitue une approche theorique extrêmement utile pour l'étude des réactions chimiques en solution. Sa rapidité d'exécution et sa précision (en ce qui concerne les effets électrostatiques du solvant) en font une méthode aisée à mettre en oeuvre