Simulation of Heme using DFT+U: a step toward accurate spin-state energetics

We investigate the DFT+U approach as a viable solution to describe the low-lying states of ligated and unligated iron heme complexes. Besides their central role in organometallic chemistry, these compounds represent a paradigmatic case where LDA, GGA, and common hybrid functionals fail to reproduce the experimental magnetic splittings. In particular, the imidazole pentacoordinated heme is incorrectly described as a triplet by all usual DFT flavors. In this study we show that a U parameter close to 4 eV leads to spin transitions and molecular geometries in quantitative agreement with experiments, and that DFT+U represents an appealing tool in the description of iron porphyrin complexes, at a much reduced cost compared to correlated quantum-chemistry methods. The possibility of obtaining the U parameter from first-principles is explored through a self-consistent linear-response formulation. We find that this approach, which proved to be successful in other iron systems, produces in this case some overestimation with respect to the optimal values of U.Comment: To be published in The Journal of Physical Chemistry B 30 pages, 15 figure

Aqueous systems from first-principles : structure, dynamics and electron-transfer reactions

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (p. 127-141).In this thesis, we show for the first time how it is possible to calculated fully from first-principles the diabatic free-energy surfaces of electron-transfer reactions. The excitation energy corresponding to the transfer of an electron at any given ionic configuration (the Marcus energy gap) is accurately assessed within ground-state density-functional theory via a novel penalty functional for oxidation-reduction reactions that appropriately acts on the electronic degrees of freedom alone. The self-interaction error intrinsic to common exchange-correlation functionals is also corrected by the same penalty functional. The diabatic free-energy surfaces are then constructed from umbrella sampling on large ensembles of configurations. As a paradigmatic case study, the self-exchange reaction between ferrous and ferric ions in water is studied in detail. Since the solvent plays an central role in mediating the process, studying electron-transfer reactions requires us to first understand the structure and dynamics of the solvent molecules (water molecules in our case). Therefore, we have also studied the static and dynamical properties of (heavy) water at ambient conditions with extensive first-principles molecular-dynamics simulations in the canonical ensemble, with temperatures ranging between 325 K and 400 K.(cont.) Density-functional theory, paired with a modern exchange-correlation functional (PBE), provides an excellent agreement for the structural properties and binding energy of the water monomer and dimer. On the other hand, contrary to a long-standing belief, the structural and dynamical properties of the bulk liquid show a clear enhancement of the local structure compared to experimental results; a distinctive transition to liquid-like diffusion occurs in the simulations only at the elevated temperature of 400 K. The local coordination and structure of water is still a very debated matter and in collaboration with experimentalists at the European Synchrotron Radiation Facility in Grenoble, we have characterized the structure and the local environment in water with a combination of inelastic X-ray scattering and first-principles calculations, under conditions ranging from the normal state to the supercritical regime. The same temperature dependence of the Compton profile is observed in experiment and simulation. A well-defined linear correlation is identified between Compton profile differences and changes in the number of hydrogen bonds per molecule, that is consistent with well-established structural models, and that confirms the prevailing picture of hydrogen bonding under normal conditions.(cont.) While close to the critical point we observe a clear signature of density fluctuations, supercritical water is characterized by a sharp increase in under-coordinated clusters, with a significant number of dimers and trimers. Last, we implemented a Hubbard U correction in our first-principles molecular dynamics to improve the hybridization between a transition metal ion and its surroundings. The implementation has been tested for ferrous and ferric ions solvation in water. The effects of the Hubbard U correction on the electron-transfer reaction is also studied.by Patrick Hoi Land Sit.Ph.D

Hydrogen bonding and coordination in normal and supercritical water from X-ray inelastic scattering

A direct measure of hydrogen bonding in water under conditions ranging from the normal state to the supercritical regime is derived from the Compton scattering of inelastically-scattered X-rays. First, we show that a measure of the number of electrons $n_e$ involved in hydrogen bonding at varying thermodynamic conditions can be directly obtained from Compton profile differences. Then, we use first-principles simulations to provide a connection between $n_e$ and the number of hydrogen bonds $n_{HB}$. Our study shows that over the broad range studied the relationship between $n_e$ and $n_{HB}$ is linear, allowing for a direct experimental measure of bonding and coordination in water. In particular, the transition to supercritical state is characterized by a sharp increase in the number of water monomers, but also displays a significant number of residual dimers and trimers.Comment: 14 pages, 5 figures, 1 tabl

Chlamydia trachomatis prevalence in undocumented migrants undergoing voluntary termination of pregnancy: a prospective cohort study

BACKGROUND: Chlamydia trachomatis infection (CTI) is the most frequent sexual transmitted disease (STI) in Switzerland but its prevalence in undocumented migrants is unknown. We aimed to compare CTI prevalence among undocumented migrants undergoing termination of pregnancy (ToP) to the prevalence among women with residency permit. METHODS: This prospective cohort study included all pregnant, undocumented women presenting from March 2005 to October 2006 to the University hospital for ToP. The control group consisted of a systematic sample of pregnant women with legal residency permit coming to the same hospital during the same time period for ToP. RESULTS: One hundred seventy five undocumented women and 208 women with residency permit (controls) were included in the study. Mean ages were 28.0 y (SD 5.5) and 28.2 y (SD 7.5), respectively (p = 0.77). Undocumented women came primarily from Latin-America (78%). Frequently, they lacked contraception (23%, controls 15%, OR 1.8, 95% CI 1.04;2.9). Thirteen percent of undocumented migrants were found to have CTI (compared to 4.4% of controls; OR 3.2, 95% CI 1.4;7.3). CONCLUSION: This population of undocumented, pregnant migrants consisted primarily of young, Latino-American women. Compared to control women, undocumented migrants showed higher prevalence rates of genital CTI, which indicates that health professionals should consider systematic screening for STI in this population. There is a need to design programs providing better access to treatment and education and to increase migrants' awareness of the importance of contraception and transmission of STI

BeaverCube: Coastal Imaging with VIS/LWIR CubeSats

BeaverCube is a student-built 3U CubeSat that has two main objectives: one science objective and one technology objective. The science goal of BeaverCube is to demonstrate that it is possible to develop and apply platforms that can leverage statistical relationships between temperature and co-varying bio-optical properties, such as light absorption by colored dissolved organic matter. The technology goal of BeaverCube is to demonstrate electrospray propulsion for CubeSats, enabling more coordinated and targeted science missions among multiple spacecraft. The science objective for BeaverCube involves measuring temperature and color, which are key oceanographic properties, through a low-cost platform. Temperature and salinity are used to determine the density of watermasses. This is then used to physically classify them. Thermohaline circulation is a part of large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. Thermohaline circulation plays an important role in supplying heat to the polar regions; it influences the rate of sea ice formation near the poles, which in turn affects other aspects of the climate system, such as the albedo, and thus solar heating, at high latitudes. Small- and meso-scale ocean features such as fronts and eddies canal so be identified and tracked solely using sea surface temperature properties. BeaverCube will track warm core rings on the Northeastern section of the US coast, one of the regions in the world that is heating the fastest due to climate change. Wide geospatial coverage with near-simultaneous measurements of thermal and bio-optical ocean properties by a CubeSat has the potential to address many important oceanographic questions for both basic science and Naval applications. The majority of space-borne optical oceanographic parameters observed from CubeSats rely on atmospheric corrections to provide useful data. BeaverCube will both obtain data and help determine to what extent supplemental data will still be required for atmospheric corrections. BeaverCube will make sea surface and cloud top temperature measurements using three cameras: one visible and two FLIR Boson LWIR cameras. In-situ measurements will be coordinated with an array of ocean buoys to support calibration and validation. The student team successfully tested the LWIR camera on a high-altitude balloon launch in November 2019 to an altitude of 110,000 feet, demonstrating the imaging functionality in a near-space environment. The technology goal for BeaverCube is to demonstrate the operation of the Tiled Ionic Liquid Electrospray (TILE2) propulsion technology from Accion Systems, Inc. for orbital maneuvering. BeaverCube will be deployed in Low Earth Orbit from the International Space Station. The plan is to change the altitude of BeaverCube by 480 meters using 50 micro-Newtons of thrust, detected by an onboard GPS receiver. With a goal of launching in late 2020 or early 2021, BeaverCube passed Critical Design Review in Spring 2020, with subsystems designed and procured, including components from AAC Clyde Space (power), ISIS (ADCS), Near Space Launch (BlackBox with GlobalStar simplex radio and NovAtel GPS), and others (OpenLST radio and Raspberry Pi based C&DH board). Assembly and integration prior to environmental testing are planned for late summer 2020

Cross-ancestry genome-wide association analysis of corneal thickness strengthens link between complex and Mendelian eye diseases

Central corneal thickness (CCT) is a highly heritable trait associated with complex eye diseases such as keratoconus and glaucoma. We perform a genome-wide association meta-analysis of CCT and identify 19 novel regions. In addition to adding support for known connective tissue-related pathways, pathway analyses uncover previously unreported gene sets. Remarkably, >20% of the CCT-loci are near or within Mendelian disorder genes. These included FBN1, ADAMTS2 and TGFB2 which associate with connective tissue disorders (Marfan, Ehlers-Danlos and Loeys-Dietz syndromes), and the LUM-DCN-KERA gene complex involved in myopia, corneal dystrophies and cornea plana. Using index CCT-increasing variants, we find a significant inverse correlation in effect sizes between CCT and keratoconus (r =-0.62, P = 5.30 × 10-5) but not between CCT and primary open-angle glaucoma (r =-0.17, P = 0.2). Our findings provide evidence for shared genetic influences between CCT and keratoconus, and implicate candidate genes acting in collagen and extracellular matrix regulation

2017 HRS/EHRA/ECAS/APHRS/SOLAECE expert consensus statement on catheter and surgical ablation of atrial fibrillation: executive summary.

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2017 HRS/EHRA/ECAS/APHRS/SOLAECE expert consensus statement on catheter and surgical ablation of atrial fibrillation: executive summary.

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withdrawn 2017 hrs ehra ecas aphrs solaece expert consensus statement on catheter and surgical ablation of atrial fibrillation

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