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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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See detailHydrogeological assessment of non-linear underground enclosures
Pujades, Estanislao ULg; Jurado Elices, Anna ULg; Carrera, Jesus et al

in Engineering Geology (2016), 207

Excavations below the water table are usually undertaken by combining the protection of retaining walls with dewatering by pumping wells. Severe difficulties may arise if the retaining walls have defects ... [more ▼]

Excavations below the water table are usually undertaken by combining the protection of retaining walls with dewatering by pumping wells. Severe difficulties may arise if the retaining walls have defects. Therefore, their state must be determined and, if needed, the defects repaired or the dewatering system redesigned. The state of underground retaining walls can be evaluated using hydrogeological methods, but these methods are well-established only for linear excavations. The objective of this work is to propose a procedure to evaluate the state of non-linear underground enclosures by analyzing the groundwater response to pumping inside the enclosure. The proposed method, which is based on diagnostic plots (derivative of drawdown with respect to the logarithm of time), allows (1) determining if an underground non-linear enclosure has isolated openings or numerous defects and (2) computing its effective conductance or effective hydraulic conductivity. The methodology is tested with data collected during the excavation of a shaft required for the construction of the high speed train (HST) tunnel in Barcelona, Spain. The procedure can be applied using the wells drilled for dewatering. Although a test before the excavation is recommended to evaluate the underground retaining walls (Watertightness Assessment Test), the method can be applied using data collected at the beginning of the dewatering stage. [less ▲]

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See detailHydrogeological conditions required for Underground Pumping Storage Hydroelectricity (UPSH) in old mines
Bodeux, Sarah ULg; Pujades, Estanislao ULg; Orban, Philippe ULg et al

in Abstract book (2016, January 26)

Renewable energy sources, because of their intermittence, could not afford a stable production and an adequate variability according to the energy demand. Underground Pumped Storage Hydroelectricity (UPSH ... [more ▼]

Renewable energy sources, because of their intermittence, could not afford a stable production and an adequate variability according to the energy demand. Underground Pumped Storage Hydroelectricity (UPSH) using abandoned mine works is an interesting alternative, in flat regions, to store energy during low demand periods by pumping water from an underground mine to an upper reservoir. From the hydrogeological point of view, two considerations can arise for studying the feasibility before constructing an UPSH plant: 1) the alteration of the natural conditions of surrounding aquifers, and (2) the efficiency of the plant depending on possible leakage in the cavities from the hydrogeological environment. A potential old slate mine was selected through a multi-criterion method and its geometrical and hydrogeological characteristics are used to build a simple but typical model. With the help of the HFEMC approach implemented in the code SUFT3D (HEG-ULg), the groundwater flows are modelled for a representative cavity. Simulations of groundwater flow induced by a UPSH system are performed and the main variables are identified. Piezometric heads around the reservoir oscillate, the magnitude of the oscillations and the time to achieve a pseudo-steady state (magnitude and head reached during oscillations not varying anymore with time) depend on the boundaries, the parameters of the aquifer and the characteristics of the underground reservoir. The required hydrogeological conditions are deduced and a screening methodology can be proposed to assess the main impacts caused in aquifers by UPSH plants. Their efficiency regarding the water level evolution inside the reservoir is also considered accommodating the cyclic pumped storage schemes. [less ▲]

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See detailHydrogeological data requirements for assessment of natural attenuation
Haerens, Bruno; Dassargues, Alain ULg

in Proceedings of the National Colloquium CBGI-BCGI ‘Réhabilitation des zones polluées, inventaire, gestion et assainissement / Herinrichting van verontreinigdde zones, inventaris, beheer en sanering (2002)

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See detailHydrogeological investigations at the Membach station, Belgium, and application to correct long periodic gravity variations
Van Camp, Michel; Vanclooster, Marnik; Crommen, O. et al

in Journal of Geophysical Research (2006), 111(B10),

A comprehensive hydrogeological investigation regarding the influence of variations in local and regional water mass on superconducting gravity measurements is presented for observations taken near the ... [more ▼]

A comprehensive hydrogeological investigation regarding the influence of variations in local and regional water mass on superconducting gravity measurements is presented for observations taken near the geodynamic station of Membach, Belgium. Applying a regional water storage model, the gravity contribution due to the elastic deformation of the Earth was derived. In addition, the Newtonian gravity effect induced by the local water mass variations was calculated, using soil moisture observations taken at the ground surface (about 48 m above the gravimeters). The computation of the gravimetric effect is based on a digital elevation model with spatially discretized rectangular prisms. The obtained results are compared with the observations of a superconducting gravimeter (SG). We find that the seasonal variations can be reasonably well predicted with the regional water storage model and the local Newtonian effects. Shorter-period effects depend on the local changes in hydrology. This result shows the sensitivity of SG observations to very local water storage changes. [less ▲]

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See detailHydrogeological mapping of the Walloon Region (Belgium) – Now on the Web !!
Ruthy, Ingrid ULg; Bouezmarni, Mohamed ULg; Dossin, Frédéric et al

in 5th European Congress on Regional Geoscientific Cartography and Information Systems. Earht and Water (2006, June)

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See detailHydrogeological mapping of the Walloon region (Belgium).
Bouezmarni, Mohamed ULg

in Proceedings of the 5th european congress on regional geoscientific cartography and information systems. (2006)

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See detailHydrogeological modeling of radionuclide transport in heterogeneous low-permeability media: a comparison between Boom Clay and Ieper Clay
Huysmans, Marijke; Dassargues, Alain ULg

in Soares, A.; Pereira, M. J.; Dimitrakopoulos, R. (Eds.) GeoENV VI: Geostatistics for Environmental Applications (2006)

Deep low-permeability clay layers are considered as possible suitable environments for disposal of high-level radioactive waste. In Belgium, the Boom Clay is the reference host formation and the Ieper ... [more ▼]

Deep low-permeability clay layers are considered as possible suitable environments for disposal of high-level radioactive waste. In Belgium, the Boom Clay is the reference host formation and the Ieper Clay an alternative host formation for research and safety and feasibility assessment of deep disposal of nuclear waste. In this study, two hydrogeological models are built to calculate the radionuclide fluxes that would migrate from a potential repository through these two clay formations. Transport parameters heterogeneity is incorporated in the models using stochastic sequential simulation of hydraulic conductivity, diffusion coefficient and diffusion accessible porosity, using primary information and several types of secondary information, i.e. resistivity, gamma ray and grain size. The calculated radionuclide fluxes in the two clay formations are compared. Results show that in the Ieper Clay larger differences between the fluxes through the lower and the upper clay boundary occur, larger total output radionuclide amounts are calculated, and a larger effect of parameter heterogeneity on the calculated fluxes is observed, compared to the Boom Clay. [less ▲]

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See detailHydrogeological modeling of radionuclide transport in low permeability media: a comparison between Boom Clay and Ypresian Clay
Huysmans, Marijke; Dassargues, Alain ULg

in Environmental Geology (2006), 50(1), 122-131

Deep low-permeability clay layers are considered as suitable environments for disposal of high-level radioactive waste. In Belgium, the Boom Clay is the reference host formation and the Ypresian Clay an ... [more ▼]

Deep low-permeability clay layers are considered as suitable environments for disposal of high-level radioactive waste. In Belgium, the Boom Clay is the reference host formation and the Ypresian Clay an alternative host formation for research and safety and feasibility assessment of deep disposal of nuclear waste. In this study, two hydrogeological models are built to calculate the radionuclide fluxes that would migrate from a potential repository through these two clay formations. Transport parameter heterogeneity is incorporated in the models using geostatistical co-simulations of hydraulic conductivity, diffusion coefficient and diffusion accessible porosity. The calculated radionuclide fluxes in the two clay formations are compared. The results show that in the Ypresian Clay larger differences between the fluxes through the lower and the upper clay boundary occur, larger total output radionuclide amounts are calculated and a larger effect of parameter heterogeneity on the calculated fluxes is observed, compared to the Boom Clay. [less ▲]

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See detailHydrogeological processes in fractured and porous media: insights from geophysical case studies
Robert, Tanguy ULg; Hermans, Thomas ULg; Nguyen, Frédéric ULg

Conference (2013, January 18)

This presentation focuses on geophysical case studies with the aim to highlight the possibilities to study and monitor hydrogeological processes in the subsurface, including transport processes in ... [more ▼]

This presentation focuses on geophysical case studies with the aim to highlight the possibilities to study and monitor hydrogeological processes in the subsurface, including transport processes in fractured or in porous media. The presentation emphasizes two geoelectrical methods, namely electrical resistivity tomography (ERT) which images the electrical resistivity distribution of the subsurface and self-potential (SP) whose measured signal is directly sensitive to groundwater fluxes. The first case study concerns the geophysical identification and characterization of large hydraulically-active fractured areas in calcareous synclines and in particular the assessment of the joint use of ERT and SP to set up new piezometers in fractured limestone. This assessment shows that piezometers drilled inside less resistive areas and/or in negative SP anomalies presented high hydraulic capacities. Inversely, piezometers drilled inside more resistive zones and/or outside an SP anomaly presented low hydraulic capacities. The SP anomaly related to preferential flow in fractures was thus demonstrated for the first time. All these fractures information, obtained with geophysics, improved the conceptualization and calibration of the groundwater flow model of the calcareous valley. A seasonal monitoring of SP signals proved to be a successful methodology to better understand the hydrodynamics of calcareous aquifers and in particular to follow the seasonal drawdown of the water table in the calcareous valley. Different methodologies to delineate the main groundwater flow direction were also tested. The latter can be achieved for example by drawing an SP map showing the main hydraulic gradients or by monitoring a salt tracer test with ERT to highlight preferential flow in fractures. The second case study concerns the ERT monitoring of a shallow geothermal test conducted in a porous medium (sand). The main objective of this study was to derive temperature from a series of electrical resistivity images since the electrical resistivity is directly sensitive to temperature changes. This field work demonstrates that surface electric resistivity tomography can monitor heat injection and storage experiments in shallow aquifers providing a number of practical applications, such as the monitoring or the design of shallow geothermal systems or the use of heated water to replace salt water in tracer tests. Through these two different case studies, this presentation also emphasizes in a practical way on the importance of data inversion and image appraisal since these issues are crucial to quantitatively study hydrogeological processes. [less ▲]

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See detailHydrogeological study and modelling to implement a groundwater restoration plan near leaking soda industry landfills
Brouyère, Serge ULg; Dassargues, Alain ULg; Michiels, Thierry

in 2nd Int. Symp. on Environmental Contamination, Budapest (1994)

Detailed reference viewed: 28 (12 ULg)