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See detailHydrogen fluoride total and partial column time series above the Jungfraujoch from long-term FTIR measurements: Impact of the line-shape model, characterization of the error budget and seasonal cycle, and comparison with satellite and model data
Duchatelet, Pierre ULg; Demoulin, Philippe ULg; Hase, Frank et al

in Journal of Geophysical Research. Atmospheres (2010), 115

Time series of hydrogen fluoride (HF) total columns have been derived from ground-based Fourier transform infrared (FTIR) solar spectra recorded between March 1984 and December 2009 at the International ... [more ▼]

Time series of hydrogen fluoride (HF) total columns have been derived from ground-based Fourier transform infrared (FTIR) solar spectra recorded between March 1984 and December 2009 at the International Scientific Station of the Jungfraujoch (Swiss Alps, 46.5°N, 8.0°E, 3580 m asl) with two high resolution spectrometers (one home-made and one Bruker 120-HR). Solar spectra have been inverted with the PROFFIT 9.5 algorithm, using the optimal estimation method. An inter-comparison of HF total columns retrieved with PROFFIT and SFIT-2 – the other reference algorithm in the FTIR community - is performed for the first time. The effect of a Galatry line shape model on HF retrieved total columns and vertical profiles, on the residuals of the fits and on the error budget is also quantified. Information content analysis indicates that, in addition to HF total vertical abundance, three independent stratospheric HF partial columns can be derived from our Bruker spectra. A complete error budget has been established and indicates that the main source of systematic error is linked to HF spectroscopy and that the random error affecting our HF total columns does not exceed 2.5%. Ground-based middle and upper stratospheric HF amounts have been compared to satellite data collected by the HALOE or ACE-FTS instruments. Comparisons of our FTIR HF total and partial columns with runs performed by two 3D numerical models (SLIMCAT and KASIMA) are also included. Finally, FTIR and model HF total and partial columns time series have been analyzed to derive the main characteristics of their seasonal cycles. [less ▲]

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See detailHydrogen in the atmosphere of the evolved WN3 Wolf-Rayet star WR 3: defying an evolutionary paradigm?
Marchenko, S. V.; Moffat, A. F. J.; Crowther, P. A. et al

in Monthly Notices of the Royal Astronomical Society (2004), 353(1), 153-161

WR 3 is the brightest very early-type WN star in the sky. Based on several years of time-resolved spectroscopy and precision photometry on various time-scales, we deduce that WR 3 is most likely a single ... [more ▼]

WR 3 is the brightest very early-type WN star in the sky. Based on several years of time-resolved spectroscopy and precision photometry on various time-scales, we deduce that WR 3 is most likely a single, weak-lined star of type WN3ha (contrary to its current catalogue-type of WN3 + O4), with H lines occurring both in emission and absorption in its wind. This conclusion is confirmed and strengthened via detailed modelling of the spectrum of WR 3. Given the similarity of WR 3 with numerous H-rich WNE stars in the Large Magellanic Cloud and especially the Small Magellanic Cloud, and its location towards the metal-deficient exterior of the Galaxy, we conclude that rotationally induced meridional circulation probably led to the apparently unusual formation of this hot Galactic WN star with enhanced hydrogen. Although we cannot completely rule out the possibility of a binary with a low orbital inclination and/or long period, we regard this latter possibility as highly unlikely. [less ▲]

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See detailHydrogen Loss from Mars: Seasonal and Sourced from Upper Atmospheric Water
Chaffin; Deighan; Stewart et al

Conference (2017, August 09)

Mars has lost a significant fraction of its initial water inventory to space over its history. This loss proceeds via a chemical chain initiated in the lower and middle atmosphere below 100 km altitude ... [more ▼]

Mars has lost a significant fraction of its initial water inventory to space over its history. This loss proceeds via a chemical chain initiated in the lower and middle atmosphere below 100 km altitude, which results in H escape to space in the collisionless corona above about 200 km altitude. Hydrogen loss from Mars is tracked via brigtness measurements of this corona in Lyman alpha light at 121.6 nm, which is scattered by neutral H orbiting and escaping the planet. Here we present observations of H escape variability made by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission's Imaging Ultraviolet Spectrograph (IUVS) that demonstrate the seasonal dependence of H escape, adding to evidence initially gathered by Mars Express and the Hubble Space Telescope. We show that for two Mars years the atmosphere has exhibited enhanced H escape in Southern Summer near perihelion. We also present the result of photochemical model calculations which demonstrate that this variation can be explained as a result of high concentrations of water vapor in the upper atmosphere, consistent with Mars Express solar occultation measurements and several general circulation models. Our results demonstrate that the large variations in H escape at high altitudes can be driven by lower atmospheric dynamics, suggesting that Mars hydrogen escape may depend on climate, in addition to the long-term evolution of Martian climate depending on atmospheric escape. [less ▲]

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See detailHydrogen Peroxide Hyperpolarizes Rat Ca1 Pyramidal Neurons by Inducing an Increase in Potassium Conductance
Seutin, Vincent ULg; Scuvée-Moreau, Jacqueline ULg; Massotte, Laurent ULg et al

in Brain Research (1995), 683(2), 275-8

It has been suggested that hydrogen peroxide is involved in cascades of pathological events affecting neural cells. The aim of this study was therefore to examine whether this molecule is able by itself ... [more ▼]

It has been suggested that hydrogen peroxide is involved in cascades of pathological events affecting neural cells. The aim of this study was therefore to examine whether this molecule is able by itself to modify membrane properties of pyramidal neurons in the CA1 region of the rat hippocampus. Intracellular recordings in the slice preparation showed that 3.3 mM hydrogen peroxide hyperpolarized all neurons tested (n = 41) by 11 +/- 3 mV. This effect persisted in the presence of tetrodotoxin. It developed slowly, was reversible and reproducible. In the presence of tetrodotoxin, the extrapolated reversal potential of this effect was -95 +/- 5 mV in 2.5 mM external potassium. This value was not significantly different from the one obtained with the GABAB agonist baclofen (10 microM) (-98 +/- 5 mV). It shifted when the concentration of external potassium was increased to 10.5 mM (from -96 +/- 5 to -62 +/- 4 mV), in close agreement with the Nernst equation potassium ions. The hyperpolarization was significantly reduced (by 65 +/- 22%) by the potassium channel blocker barium (100 microM). We suggest that hydrogen peroxide is able to induce an increase in potassium conductance in rat CA1 pyramidal neurons. The exact mechanism by which it produces this effect (direct action on channels or indirect effect) remains to be determined. [less ▲]

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See detailHydrogen peroxide increases transforming factor-β3 gene expression in human chondrocytes and reverses interleukin-1β inhibitory effect
Mathy-Hartert, Marianne ULg; Devel, P.; Hoormaert, S. et al

in Osteoporosis International (2002, November), 13(Suppl.3), 52

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See detailHydrogen peroxyde in breath condensate as marker of lower airway inflammation in an experimental model of feline asthma
Kirschvink, Nathalie; Malin, D.; Delvaux, Francois et al

Conference (2003)

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See detailHydrogen photo-evolution upon S deprivation stepwise: An illustration of microalgal photosynthetic and metabolic flexibility and a step stone for future biotechnological methods of renewable H2 production
Ghysels, Bart ULg; Franck, Fabrice ULg

in Photosynthesis Research (2010), 106

The metabolic flexibility of some photosynthetic microalgae enables them to survive periods of anaerobiosis in the light by developing a particular photofermentative metabolism. The latter entails ... [more ▼]

The metabolic flexibility of some photosynthetic microalgae enables them to survive periods of anaerobiosis in the light by developing a particular photofermentative metabolism. The latter entails compounds of the photosynthetic electron transfer chain and an oxygen-sensitive hydrogenase in order to reoxidise reducing equivalents and to generate ATP for maintaining basal metabolic function. This pathway results in the photo-evolution of hydrogen gas by the algae. A decade ago Melis and coworkers managed to reproduce such a condition in a laboratory context by depletion of sulfur in the algal culture media, making the photo-evolution by the algae sustainable for several days (Melis et al. 2000). This observation boosted research in algal H2 evolution. A feature, which due to its transient nature was long time considered as a curiosity of algal photosynthesis suddenly became a phenomenon with biotechnological potential. Although the Melis procedure has not been developed into a biotechnological process of renewable H2 generation so far, it has been a useful tool for studying microalgal metabolic and photosynthetic flexibility and a possible step stone for future H2 production procedures. Ten years later most of the critical steps and limitations of H2 production by this protocol have been studied from different angles particularly with the model organism C. reinhardtii, by introducing various changes in culture conditions and making use of mutants issued from different screens or by reverse genomic approaches. A synthesis of these observations with the most important conclusions driven from recent studies will be presented in this review. [less ▲]

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See detailHydrogen photoproduction by oxygenic photosynthetic microorganisms
Franck, Fabrice ULg; Ghysels, Bart ULg; Godaux, Damien ULg

in Darvishi, Farshad; Hiligsmann, Serge (Eds.) Microbial fuels: technologies and applications (in press)

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See detailHydrogen Storage and Carbon Dioxide Capture in an Iron-Based Sodalite-Type Metal-Organic Framework (Fe-BTT) Discovered via High-Throughput Methods
Sumida, Kenji; Horike, S; Kaye, S.S. et al

in Chemical Science (2010), 1

Using high-throughput instrumentation to screen conditions, the reaction between FeCl2 and H3BTT.2HCl(BTT3-=1,3,5-benzenetristetrazolate) in a mixture of DMF and DMSO was found to afford Fe3[(Fe4Cl)3(BTT ... [more ▼]

Using high-throughput instrumentation to screen conditions, the reaction between FeCl2 and H3BTT.2HCl(BTT3-=1,3,5-benzenetristetrazolate) in a mixture of DMF and DMSO was found to afford Fe3[(Fe4Cl)3(BTT)8]2.22DMF.32DMSO.11H2O. THis compound adopts a porous three-dimensional framework structure consisting of squre [Fe4CL]2+ units linked via triangulat BTT3- bridging ligands to give an anionic 3.8-net. Mossbauer spectroscopy carried out on a DMF-solvated version of the material indicated the framework to contain high-spin Fe2+ with a distribution of local environments and confirmed the presence of extra-framework iron cations. Upon soaking the compound in methanol and heating at 135 C for 24 h under dynamic vacuum, most of the solvent is removed to yield Fe3[(Fe4Cl)3(BTT)8(MeOH)4]2(Fe-BTT), a microporous solid with a BET surface area of 2010 m2g-1 and open Fe2+ coordination sites. Hydrogen adsorption data collected at 77 K show a steep rise in the isotherm, associated with an initial isosteric heat of adsorption of 11.9 kJ/mol, leading to a total storage capacity of 1.1 wt% and 8.4 g/L at 100 bar and 298 K. Powder neutron diffraction experiments performed at 4 K under various D2 loadings enabled identification of ten different adsorption sites. with the strongest binding site residing just 2.17(5) Å from the framework Fe2+ cation. Inelastic neutron scattering spectra are consistent with the strong rotational hindering of the H2 molecules at low loadings, and further reveal the catalytic conversion of ortho-H2 to para-H2 by the paramagnetic iron centers. The exposed Fe2+ cation sites within Fe-BTT also lead to the selective adsorption of CO2 over N2, with isotherms collected at 298 K indicating uptake ratios of 30.7 and 10.8 by weight at 0.1 and 1.0 bar, respectively. [less ▲]

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See detailHydrogen-bonded block copolymer complexes as possible precursors for thin films with hairy nanopores
Lefèvre, Nathalie ULg; Fustin, Charles-André; Gohy, Jean-François

Conference (2008)

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See detailHydrogen-Deficient Compact Pulsators: The GW Virginis Stars and the Variable DB White Dwarfs
Quirion, P*-O; Dupret, Marc-Antoine ULg; Fontaine, G. et al

in Hydrogen-Deficient Stars (2008, July 01)

We review briefly the basic properties of the GW Vir stars and of the V777 Her stars. We describe the classical kappa-mechanism operating in the GW Vir stars and the effects of the chemical composition ... [more ▼]

We review briefly the basic properties of the GW Vir stars and of the V777 Her stars. We describe the classical kappa-mechanism operating in the GW Vir stars and the effects of the chemical composition and of the interaction between diffusion and mass loss on the boundaries of the instability domain of these objects in the log g - T[SUB]eff[/SUB] diagram. Because of the presence of an extensive superficial convection zone in pulsating DB (V777 Her) white dwarfs, oscillation modes are not excited through a similar classical kappa-mechanism in those stars but, instead, involve pulsation-convection interactions. We describe the effects of a time-dependent convection (TDC) treatment on the driving mechanism of the V777 Her stars. We show how convection deeply affects the excitation of modes via the entropy transport mechanism or S-mechanism. Provisional blue and red edges are calculated for the V777 Her stars and are found at T[SUB]eff[/SUB] ~= 28,500 K and ~= 20,500 K, respectively, for a 0.6 M[SUB]o[/SUB] star under the assumption of ML2 convection. [less ▲]

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See detailHydrogen-Saturated Silicon Nanowires Heavily Doped with Interstitial and Substitutional Transition Metals
Durgun, E.; Bilc, Daniel ULg; Ciraci, S. et al

in Journal of Physical Chemistry C: Nanomaterials, Interfaces, and Hard Matter (2012), 116

We report a first-principles systematic study of atomic, electronic, and magnetic properties of hydrogen-saturated silicon nanowires (H-SiNW) that are heavily doped by transition metal (TM) atoms placed ... [more ▼]

We report a first-principles systematic study of atomic, electronic, and magnetic properties of hydrogen-saturated silicon nanowires (H-SiNW) that are heavily doped by transition metal (TM) atoms placed at various interstitial and substitutional sites. Our results obtained within the conventional GGA+U approach have been confirmed using a hybrid functional. To reveal the surface effects, we examined three different possible facets of HSiNW along the [001] direction with a diameter of ∼2 nm. The energetics of doping and resulting electronic and magnetic properties are examined for all alternative configurations. We found that except Ti, the resulting systems have a magnetic ground state with a varying magnetic moment. Whereas H-SiNWs are initially nonmagnetic semiconductor, they generally become ferromagnetic metal upon TM doping. They can even exhibit half-metallic behavior for specific cases. Our results suggest that H-SiNWs functionalized by TM impurities form a new type of dilute magnetic semiconductor potentially attractive for new electronic and spintronic devices on the nanoscale. [less ▲]

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See detailHydrogeochemical mechanisms driving the occurrence of elevated fluoride contents in crystalline aquifers in Benin, Western Africa
Tossou, Yao ULg; Orban, Philippe ULg; Gesels, Julie ULg et al

Conference (2016, July 24)

Elevated concentrations of fluoride in drinking water is the source of severe healthy problems such as dental or skeletal fluorosis. High concentrations of fluoride are often observed in fractured and ... [more ▼]

Elevated concentrations of fluoride in drinking water is the source of severe healthy problems such as dental or skeletal fluorosis. High concentrations of fluoride are often observed in fractured and altered crystalline aquifers around the world. However, the hydrogeochemical mechanisms leading to such elevated fluoride concentrations are usually not fully understood. In particular, it is important to make the link between these elevated concentrations and the geological context in order to make efficient recommendations on appropriate locations of further groundwater abstraction wells. This is the case in Benin, Western Africa, where groundwater from crystalline bed-rock aquifers is the main source for drinking-water supply. In this context, this research aims to identify the hydrogeochemical processes governing groundwater mineralization and the origin of the high fluoride concentrations. The investigations are based on groundwater samples collected in the central part of the country (Department of Collines), characterized by hard Precambrian aquifers. The hydrogeological system consists of a thin altered bedrock layer (shallow aquifer) and a deeper fractured crystalline bedrock (deep aquifer). The most significant groundwater quality problems in the area relate to the high fluoride (more than 7 mg / l) and nitrate (over 400 mg / l) concentrations in groundwater. The collected hydrogeochemical dataset was explored using geochemical approaches and multivariate statistics. The results reveal that the water mineralization derives from hydrolysis of silicate minerals, but it is also influenced by anthropogenic effects, particularly in the shallow reservoir. However, fluoride has a natural origin, essentially related to weathering of silicate minerals, mainly from biotite. Ion exchanges between groundwater and the rock matrix also contributes to increase fluoride concentrations in groundwater. Earlier saturation of water with calcite and the precipitation of this mineral due to bicarbonate excess reduce calcium activity are favorable of the release of fluoride by rocks. Further investigations are going on to make the link between crystalline rock types, associated primary minerals and fluoride concentrations in order to identify the geological contexts which are more prone to such problems. [less ▲]

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See detailHydrogeological assessment of diaphragm walls used to excavate deep shafts associated to tunnels construction
Pujades, Estanislao ULg; Jurado, Anna; Carrera, Jesus et al

Poster (2015, September 17)

Deep shafts are usually required during tunnels construction (for maintenance tasks when tunnel boring machines –TBM- are used) and/or the operation stage of tunnels (emergency exits). Generally, these ... [more ▼]

Deep shafts are usually required during tunnels construction (for maintenance tasks when tunnel boring machines –TBM- are used) and/or the operation stage of tunnels (emergency exits). Generally, these shafts are constructed below the water table and by the cut and cover method. Therefore, impervious diaphragm walls are desired for two main reasons: (1) to reduce risks (stability, inflows, flooding, etc.) and outside impacts (loose of groundwater resource, holes and sinkholes, etc.) during the excavation stage of a shaft and, (2) to avoid leaks and inflows of groundwater during the operation stage once the shaft is finished. Given that defects in diaphragm walls are frequent and can relatively easy be repaired before starting the excavation stage, a useful and new methodology to assess the state of enclosures before excavation is proposed. Its use would allow to reduce impacts on groundwater (construction and operation stages) and costs in case of defects as well as to increase the safety during the construction. The groundwater response regarding different scenarios of diaphragm walls is studied numerically in order to propose a successful procedure to evaluate underground enclosures imperviousness by internal pumping tests. The scenarios consist in circular and square enclosures where the diaphragm walls are assumed as homogeneous (with numerous defects) or heterogeneous (one discrete defect). The homogeneous cases are modeled by considering different effective hydraulic conductivities, while the size and position of the single defect is varied in the simulations of heterogeneous walls. An analysis of diagnostic plots and the comparison between the expected and measured groundwater evolutions inside the enclosure, is proposed to ascertain: (1) if the diaphragm walls can be considered as homogeneous or heterogeneous, (2) the effective hydraulic conductivity of the walls (if they are homogeneous) and, (3) the position of a defect (if they are heterogeneous). [less ▲]

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