The Hybrid Finite Element Mixing Cell Method: A New Flexible Method for Modelling Mine Ground Water Problems

Dewatering operations often stop at mine closure. The ground water rebound can have undesirable consequences, which numerical models can help one understand and manage. However, classical modelling techniques are relatively unsuitable to these contexts. While spatially distributed and physically based models suffer difficulties due to the lack of data and the complexity of geological and hydrogeological conditions, black-box models are too simple to deal with the problems effectively. A new modelling method is proposed to simulate ground water environments in which water flows through mined (exploited) and unmined (unexploited) areas. Exploited zones are simulated using a group of mixing cells possibly interconnected by pipes. Unexploited zones are simultaneously simulated using classical finite elements. This combined approach allows explicit calculation of ground water flows around the mine and mean water levels in the exploited zones. Water exchanges between exploited zones and unexploited zones are simulated in the model using specifically defined internal boundary conditions. The method is tested on synthetic cases of increasing complexity, and first results from a real case study are presented.     

Excess enthalpy data for the ternary system methane—ethylene—carbon dioxide by flow calorimetry

Excess enthalpy data for the ternary system methane – ethylene – carbon dioxide was obtained utilizing an isothermal flow calorimeter. The measurements were made at three temperatures: 293.15, 305.15 and 313.15 K and pressures of 1.114, 1.520 and 3.445 MPa (11, 15 and 34 atm). The determination of excess enthalpies for the binary systems methane—ethylene, ethylene—carbon dioxide and methane—carbon dioxide has been reported in three preceeding articles, respectively: Gagné et al., 1985; Ba et al., 1979 and Barry et al., 1982a. The binary interaction coefficients k_ij obtained for these systems have been utilized as initial values for the optimization procedure leading to the k_ij for the ternary system. For the case of the ternary system studied in this investigation, two types of binary interaction coefficients k_ij have been determined from experimental data: k_ij independent of temperature and pressure and k_ij adjusted as function of temperature and pressure. Experimental data were compared with the predictions from Benedict—Webb—Rubin and Redlich—Kwong equations of state. In both cases, the coefficients k_ij dependent on temperature and pressure led to better prediction of excess enthalpies.     

Development of a questionnaire to assay recalled liking for salt,sweet and fat

Liking for a sweet, salty or fatty diet may induce overconsumption of simple carbohydrates, sodium or lipids. Measuring overall liking of the corresponding sensory sensations contributes to understanding the determinants of dietary behaviours. However, no standardized validated questionnaire assaying these sensations is currently available. In the present study, we developed a web-based questionnaire, “PrefQuest”, which measures recalled liking for the following four sensations: salt, fat and salt, sweet, fat and sweet. PrefQuest included four types of items: (1) liking for sweet, fatty-sweet and fatty-salty foods, (2) preferences in the level of seasoning by adding salt, sweeteners, or fat, (3) preferences for types of dishes in a restaurant menu and (4) overall questions about sweet-, salt- and fat-related behaviours. A development study (n = 198) demonstrated that PrefQuest was feasible, well-perceived, only lasted about 20 min and that items were repeatable (overall mean intra-class correlation coefficient: 0.77, SD 0.08). Construct validity was then evaluated on a larger population sample (n = 47 803). The underlying structure within each of the four sensations was determined by exploratory factor analysis and then internally validated by confirmatory factor analysis. After a selection of the most relevant items, the salt, fat-and-salt, sweet, and fat-and-sweet scales exhibited a theoretically meaningful factor structure, unidimensional for the salt scale and with interrelated sub-dimensions for the sweet, fat-and-salt, and fat-and-sweet scales. Based on the fat-and-sweet and fat-and-salt scales, a fat model was also unveiled. For each factor, internal consistency as well as convergent and divergent validities were demonstrated. Overall, PrefQuest is an internally valid and original tool that can be used to assay recalled liking for sweet, salt, and fat considered altogether or separately as fat and salt or fat and sweet, and can be applied to large population surveys.     

Electron Model of Solid Oxygen-Ionic Electrolytes Used in Gas Sensors

Yttria-stabilized zirconia (YSZ)-based ceramic gas sensors operating at high temperatures have been well established in many applications over the last 30 years. This article aims to provide an electron model of the solid electrolytes with oxygen-ionic conductivity used in gas sensors to simulate contact phenomena on the boundary of a YSZ/metal electrode interface within the solid-state zone theory. The primary focus of this article is modelling and assessment of the ability of a YSZ-based electrolyte to control oxygen potentials at low temperatures in different environments. The proposed model allows the necessary information with regard to the electrolyte/metal electrode interface and about the character of the electronic conductivity to be obtained. The model also describes that the character of the electronic conductivity in solid electrolytes usually depends on two mechanisms of charge transfer: electrons transfer in the conductivity zone, separated from the valent zone in the solid electrolyte by the wide enough forbidden zone, and the spasmodic transitions of electrons from one local level to another within the forbidden zone.     

Addition of trace metals increases denitrification rate in closed marine systems

We investigated the effect of trace metals (Fe, Mn, Cu, Zn and Mo) on the denitrification unit at the Montreal Biodome. Two dosages of the five trace metals were tested on a denitrifying bacterial population which was extracted from the denitrification unit and cultured in 250 mL chemostats with artificial seawater. The low dosage showed a 20% increase in the denitrification rate whereas the high dosage had a more pronounced effect with a 250% increase. No increase in bacterial growth was observed, suggesting that the trace metals had an effect on the denitrification activity. When the trace metals were tested separately, only iron had a significant effect similar to the increase in the denitrification rate observed when the five trace metals were added. The combination of Fe and Mn caused a small but significant increase compared to the five trace metals. We then tested the effect of adding Fe, Mn and Cu to the denitrification unit at the Montreal Biodome. A high dosage of these trace metals showed a 250% increase in the denitrification rate, which went from 200 to 700 g NO(x)-N/d. Our results showed that the addition of trace metals is crucial for denitrification activities.     

Cross-Linking Organic and Polyoxometalate Chemistries

This paper is a choral personal account on a longstanding and fruitful collaboration of organic and inorganic chemists to develop new hybrid polyoxometallic systems. .We explain our motivation and the context of our work that led to polyoxometalates with highly functional and reactive organic groups. Our approach yielded catalytically, biologically, and photochemically active systems.     

The Role of Pericytes in Neurovascular Unit Remodeling in Brain Disorders

Neurons are extremely vulnerable cells that tightly rely on the brain’s highly dynamic and complex vascular network that assures an accurate and adequate distribution of nutrients and oxygen. The neurovascular unit (NVU) couples neuronal activity to vascular function, controls brain homeostasis, and maintains an optimal brain microenvironment adequate for neuronal survival by adjusting blood-brain barrier (BBB) parameters based on brain needs. The NVU is a heterogeneous structure constituted by different cell types that includes pericytes. Pericytes are localized at the abluminal side of brain microvessels and contribute to NVU function. Pericytes play essential roles in the development and maturation of the neurovascular system during embryogenesis and stability during adulthood. Initially, pericytes were described as contractile cells involved in controlling neurovascular tone. However, recent reports have shown that pericytes dynamically respond to stress induced by injury upon brain diseases, by chemically and physically communicating with neighboring cells, by their immune properties and by their potential pluripotent nature within the neurovascular niche. As such, in this paper, we would like to review the role of pericytes in NVU remodeling, and their potential as targets for NVU repair strategies and consequently neuroprotection in two pathophysiologically distinct brain disorders: ischemic stroke and Alzheimer’s disease (AD).