A study of an animal model of Attention-Deficit/ Hyperactivity Disorder using in vivo chronoamperometry and behavioural responses to methylphenidate and guanfacine

Includes abstract.~Includes bibliographical references (leaves 119-147).Attention-Deficit/Hyperactivity Disorder (ADHD) is a childhood disorder that is behaviorally characterized by developmentally inappropriate levels of inattention, impulsivity and hyperactivity. Among several hypotheses of ADHD etiology the prevailing hypothesis implicates a hypodopaminergic system due largely to the successes of the use of psychostimulants such as methylphenidate, that increase extracellular levels of dopamine (DA) and/or norepinephrine (NE) for the treatment of symptoms. In this study, the spontaneously hypertensive rat (SHR), the most widely accepted model for ADHD, is compared with the Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rat strains as control

The Effect of Ethnic Identity and Bilingual Confidence on Chinese Youth’s Self-Esteem

This study examines the interrelated issues of private and public domains of self-esteem, ethnic identity formation, and bilingual confidence among youth of a minority group in a city in western Canada. One hundred, ten Chinese students aged 11-18 from a Chinese-language school were randomly surveyed. Most items of the instrument are derived from the Rosenberg Self-Esteem Scale, the Cultural-Free Self-Esteem Inventories, and the Multigroup Ethnic Identity Measure. Participants’ self-confidence with the English and Chinese languages is also investigated. Zero-order correlate analysis and a two-way MACOVA controlling for GPA are used to examine potential factors that influence Chinese youth’s global, academic, and social self-esteem. The results confirm the importance of ethnic identity on minority youth’s global self-esteem. Moreover, self-confidence with bilingual proficiency has a great effect on Chinese youth’s global, academic, and social self-esteem.Cette étude porte sur plusieurs questions tant privées que publiques et reliées entre elles : l’estime de soi, la formation de l’identité ethnique et la confiance par rapport à ses compétences bilingues, chez un groupe de jeunes minoritaires dans une ville de l’Ouest canadien. L’enquête a porté sur 110 élèves chinois âgés de 11 à 18 ans, choisis au hasard, qui fréquentent une école de langue chinoise. La majorité des questions proviennent des questionnaires suivants qui évaluent l’estime de soi: Échelle de mesure de l’estime de soi de Rosenberg, CulturalFree SelfEsteem Inventories et Multigroup Ethnic Identity Measure. Nous avons également évalué la confiance en soi que ressentent les participants par rapport aux langues anglaise et chinoise. Une analyse corrélée d’ordre 0 et une MACOVA bidirectionnelle contrôlant la MPC ont servi dans l’étude des facteurs pouvant influencer l’estime de soi académique, sociale et générale des jeunes Chinois. Les résultats confirment l’importance de l’identité ethnique sur l’estime de soi globale des jeunes minoritaires. De plus, la confiance en ses capacités bilingues influence beaucoup l’estime de soi générale, académique et sociale des jeunes Chinois

Numerical simulation of flame acceleration and deflagration-to-detonation transition in hydrogen-air mixtures with concentration gradients

The present study aims to test the capability of our newly developed density-based solver, ExplosionFoam, for flame acceleration (FA) and deflagration-to-detonation transition (DDT) in mixtures with concentration gradients which is of important safety concern. The solver is based on the open source computational fluid dynamics (CFD) platform OpenFOAM® and uses the hydrogen-air single-step chemistry and the corresponding transport coefficients developed by the authors. Numerical simulations have been conducted for the experimental set up of Ettner et al. [7], which involves flame acceleration and DDT in both homogeneous hydrogen-air mixture as well as an inhomogeneous mixture with concentration gradients in an obstucted channel. The predictions demonstrate good quantitative agreement with the experimental measurements in flame tip position, speed and pressure profiles. Qualitatively, the numerical simulations have reproduced well the flame acceleration and DDT phenomena observed in the experiment. The results have revealed that in the computed cases, DDT is induced by the interaction of the precursor inert shock wave with the wall close to high hydrogen concentration rather than with the obstacle. Some vortex pairs appear ahead of the flame due to the interaction between the obstacles and the gas flow caused by combustion-induced expansion, but they soon disappear after the flame passes through them. Hydrogen cannot be completely consumed especially in the fuel rich region. This is of additional safety concern as the unburned hydrogen can be potentially re-ignited once more fresh air is available in an accidental scenario, resulting in subsequent explosions

Numerical characterization of under-expanded cryogenic hydrogen gas jets

High-resolution direct numerical simulations are conducted for under-expanded cryogenic hydrogen gas jets to characterize the nearfield flow physics. The basic flow features and jet dynamics are analyzed in detail, revealing the existence of four stages during early jet development, namely, (a) initial penetration, (b) establishment of near-nozzle expansion, (c) formation of downstream compression, and (d) wave propagation. Complex acoustic waves are formed around the under-expanded jets. The jet expansion can also lead to conditions for local liquefaction from the pressurized cryogenic hydrogen gas release. A series of simulations are conducted with systematically varied nozzle pressure ratios and systematically changed exit diameters. The acoustic waves around the jets are found to waken with the decrease in the nozzle pressure ratio. The increase in the nozzle pressure ratio is found to accelerate hydrogen dispersion and widen the regions with hydrogen liquefaction potential. The increase in the nozzle exit diameter also widens the region with hydrogen liquefaction potential but slows down the evolution of the flow structures

Modeling thermal response of polymer composite hydrogen cylinders subjected to external fires

With the anticipated introduction of hydrogen fuel cell vehicles to the market, there is an increasing need to address the fire resistance of hydrogen cylinders for onboard storage. Sufficient fire resistance is essential to ensure safe evacuation in the event of car fire accidents. The authors have developed a Finite Element (FE) model for predicting the thermal response of composite hydrogen cylinders within the frame of the open source FE code Elmer. The model accounts for the decomposition of the polymer matrix and effects of volatile gas transport in the composite. Model comparison with experimental data has been conducted using a classical one-dimensional test case of polymer composite subjected to fire. The validated model was then used to analyze a type-4 hydrogen cylinder subjected to an engulfing external propane fire, mimicking a published cylinder fire experiment. The external flame is modelled and simulated using the open source code FireFOAM. A simplified failure criteria based on internal pressure increase is subsequently used to determine the cylinder fire resistance

Non-grey radiative heat transfer modelling in LES-CFD simulated methanol pool fires

Non-grey radiation modelling of gas-phase combustion products is performed during runtime of large eddy simulations (LES) of 30cm, 20kW methanol pool fires, based on the experiments of Klassen and Gore (1992) and Weckman and Strong (1996). FireFOAM, the turbulent flame solver part of open source CFD platform OpenFOAM®, was modified to include a new array of gas radiation models. Two grey and three non-grey implementations of the weighted-sum-of-grey-gases (WSGG) are compared in terms of both accuracy and CPU efficiency, along with a 'box' model based on the exponential wide band model (EWB) but specially optimised for fire scenarios. Turbulence-radiation interactions (TRI) are taken into account for the self-correlation of temperature in the emission term of the radiative transfer equation (RTE). Non-grey WSGG models consistently performed better than their grey counterparts, but the two newer WSGG correlations based on up-to-date spectral databases did not perform noticeably better or worse than the older WSGG model, which is a departure from other studies in oxy-fuel conditions. The work also showed that TRI is very important for the accurate prediction of the pool surface radiant feedback and the total radiant output. Some recommendations are made for the fire and radiation community

Characterization of behaviour and hazards of fire and deflagration for high-energy Li-ion cells by over-heating

Fire and deflagration are extreme manifestation of thermal runaway (TR) of Li-ion cells, and they are characterized for fully charged LiNiCoAlO2 (LNCA) 18650 cells in this investigation. The cells are over-heated using a cone calorimeter under different incident heat fluxes. When the cells are exposed to the incident heat flux larger than 35 kW m−2, both fire and deflagration present. The pressure valve opens when the temperature of the cell is higher than 132 °C. The fire occurs with the valve opening when the concentration of the venting vapour in the air is higher than the lower flammability limit. The deflagration happens after the cell temperature arrives about 200 °C, and is mainly arising from the cathode decomposition, the combustion of solvents and the anode relevant thermal reactions. The extreme temperatures of the cell and the flame during deflagration are over than 820 and 1035 °C, respectively. The production of COx, mass loss, heat release rate (HRR) are quantitative identified, and are found increase as the increasing incident heat flux. Based on revised oxygen consumption method, the HRR and liberated heat during the fire and deflagration for the cells are up to 11.8 ± 0.05 kW and 163.1 ± 1.5 kJ, respectively

Numerical modelling of vented lean hydrogen deflagations in an ISO container

Hydrogen process equipment are often housed in 20-foot or 40-foot container either be at refueling stations or at the portable standalone power generation units. Shipping Container provide an easy to install, cost effective, all weather protective containment. Hydrogen has unique physical properties, it can quickly form an ignitable cloud for any accidental release or leakages in air, due to its wide flammability limits. Identifying the hazards associated with these kind of container applications are very crucial for design and safe operation of the container hydrogen installations. Recently both numerical studies and experiment have been performed to ascertain the level of hazards and its possible mitigation methods for hydrogen applications. This paper presents the numerical modelling and the simulations performed using the HyFOAM CFD solver for vented deflagrations processes. HyFOAM solver is developed in-house using the opensource CFD toolkit OpenFOAM libraries. The turbulent flame deflagrations are modelled using the flame wrinkling combustion model. This combustion model is further improved to account for flame instabilities dominant role in vented lean hydrogen-air mixtures deflagrations. The 20-foot ISO containers of dimensions 20′ × 8′ × 8′.6″ filled with homogeneous mixture of hydrogen-air at different concentration, with and without model obstacles are considered for numerical simulations. The numerical predictions are first validated against the recent experiments carried out by Gexcon as part of the HySEA project supported by the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH 2 JU) under the Horizon 2020 Framework Programme for Research and Innovation. The effects of congestion within the containers on the generated overpressures are investigated. The preliminary CFD predictions indicated that the container walls deflections are having considerable effect on the trends of generated overpressures, especially the peak negative pressure generated within the container is overestimated. Hence to account for the container wall deflections, the fluid structure interactions (FSI) are also included in the numerical modelling. The final numerical predictions are presented with and without the FSI. The FSI modelling considerably improved the numerical prediction and resulted in better match of overpressure trends with the experimental results

Large eddy simulation of upward flame spread on PMMA walls with a fully coupled fluid–solid approach

A fully coupled fluid–solid approach has been developed within FireFOAM 2.2.x, a large eddy simulation (LES) based fire simulation solver within the OpenFOAM® toolbox. Due consideration has been given to couple the radiative heat transfer and soot treatment with pyrolysis calculations. Combustion is modeled using the newly extended eddy dissipation concept (EDC) for the LES published by the authors’ group. Soot formation and oxidation are handled by the published extension of the laminar smoke point concept to turbulent fires using the partially stirred reactor (PaSR) concept also from the authors’ group. The gases radiation properties are evaluated using the established weighted sum of grey gas model while soot absorption coefficient is calculated using a single Planck-mean absorption coefficient. The effect of in-depth radiation is treated with the relatively simple Beer's law and the solid surface regression length is calculated from the local pyrolysis rate. Systematic validation studies have been conducted with several published experiments including simple pyrolysis test without the gaseous region, small scale wall fires and large scale flame spread. The predictions are in very good agreement with the relevant experimental data, demonstrating that the present modeling approach can be used to predict upward flame spread over PMMA with reasonable accuracy. Further parametric studies have also been conducted to demonstrate the effectiveness of the present modifications to capture the underlying physics. The detailed field predictions for vortex structures and flame volume including laminar–turbulent transition have also been analysed to uncover further insight of the unsteady flame spread phenomena. Potentially, the model can be used to aid further fundamental studies of the flame spread phenomena such as investigating the effects of width, inclination angles and side walls on flame spread as well as the predictions of flame spread in practical applications

Numerical modelling of vented lean hydrogen–air deflagrations using HyFOAM

Hydrogen is being considered as a sustainable future energy carrier with least environmental impact in terms of combustion by-products. It has unique physical properties of very wide flammability range, between 4% to 75% by volume and high flame speeds, which are challenging factors in designing safe hydrogen installations. An accidental release in enclosures can easily result in the formation of flammable mixtures, which may upon ignition lead to fast turbulent deflagrations or even transition to detonation. Explosion venting is frequently used to mitigate explosions in industry, but it is not straightforward to design vent systems that will reduce the explosion pressure sufficiently to prevent collapse of structures and formation of projectiles. Validated predictive techniques will be of assistance to quantified analysis of possible accidental scenarios and designing effective mitigation measures such as vents. While explosion venting has been previous studied experimentally and numerically, relatively little information has been gathered about the configurations used in hydrogen energy applications and in the presence of obstacles; a viable predictive technique for such scenario is still lacking. The use of standard 20 feet ISO shipping containers for self-contained portable hydrogen fuel cell power units is being widely considered. Fresh experiments for this configuration have been carried out by GexCon AS as part of the HySEA project supported by the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH 2 JU) under the Horizon 2020 Framework Program for Research and Innovation. In the present study, numerical modelling and simulations have been conducted to aid our understanding of the vented gas explosion in these self-contained portable power units using HyFOAM, an in-house modified version of the open source Computational Fluid Dynamics (CFD) code OpenFOAM for vented hydrogen explosions. The convective and diffusive terms are discretised using Gaussian-Gamma bounded and Gaussian linear corrected numerical schemes with in OpenFOAM. The temporal terms are discretised using Euler implicit scheme making the solver second order accurate both in spatial and time coordinates