Numerical modeling of solid-liquid phase change in a closed 2D cavity with density change, elastic wall and natural convection

In this paper, the solidification of water near its density extremum is simulated while taking into account the expansion of the phase change material resulting from the different density of the solid and liquid phases. A thermo-mechanical coupling is achieved through one of the boundaries of the cavity behaving as an elastic wall. A methodology is introduced in which the problem is adapted in order to be solved with commercial CFD software (ANSYS Fluent 17.0). It is shown that when both the density variations and interaction of the phase change material with its boundaries are taken into account, significant differences may be observed in the flow pattern and the thermal behavior of the system, as opposed to an approach where a free ceiling or a constant density would be used. The pressure buildup inside the cavity resulting from the expansion of the phase change material as it pushes against the elastic wall causes the melting temperature to drop, which hinders solidification. It is shown that this effect becomes more pronounced as the spring constant of the elastic wall increases. It is also demonstrated that, with the assumptions made in the present model, the pressure rise may significantly influence the buoyancy forces within the cavity and change the relative size of the two counter rotating convective cells in the liquid phase. In some cases, when the pressure rises very quickly, the density extremum in the cavity disappears which strongly changes the flow pattern, i.e., only a single counter-clockwise convective cell is present in the cavity. This, in turn, changes the shape and position of the solidification front considerably

Various ways to take into account density change in solid-liquid phase change models : formulation and consequences

In this paper, a classification of different methods for accommodating volume variations during solid–liquid phase change is presented. The impact of each method is analyzed with the help of a scale analysis. Neglecting fluid velocity at the interface or allowing fluid to enter/exit the domain may result in either local (at the solid–liquid interface) or global (within the system) mass imbalance. This can lead to significant differences in the transient phase change process itself (e.g., 19% more time and 9% more energy to completely solidify a given mass of water with models for which the total mass of the system is conserved). This paper aims at addressing this issue by deriving two new models of thermo-mechanical coupling between the PCM and its container. The first model is that of a PCM bounded by an elastic wall, whereas the second model assumes that a compressible air gap is adjacent to the PCM, which allows the PCM to expand more easily. Analytical expressions are developed for both models and can be used to predict important quantities at equilibrium, such as the position of the solid–liquid interface and the pressure rise within the system. Finally, the two thermo-mechanical coupling models are implemented numerically with a finite volume moving mesh method. Numerical simulations are performed to show the limits of the two models. It is observed that volume variations during phase change can have significant impacts on the evolution of the process

Le trouble d'anxiété généralisée modèles conceptuels et applications cliniques

Si le trouble d'anxiété généralisée (TAG) représente une problématique fréquemment rencontrée par les cliniciens dans le réseau de la santé, il demeure pourtant un trouble anxieux pour lequel l'efficacité du traitement reste mitigée. Aussi, certains chercheurs proposent des modèles conceptuels du TAG ou font des ajouts aux traitements cognitivo-comportementaux traditionnels afin de les adapter à cette problématique, à la lumière des connaissances acquises au fil des ans. Le premier article, Modèles conceptuels du trouble d'anxiété généralisée : caractéristiques et applications cliniques, présente les quatre principaux modèles conceptuels du TAG en précisant leurs caractéristiques, le déroulement du traitement et offre une réflexion sur les apports et les faiblesses apparentes pour chacun d'eux. Une adaptation d'un traitement cognitivocomportemental au TAG est également décrite. Tout au long de l'article, un cas typique offre des exemples concrets de l'application clinique des principaux concepts mis de l'avant par les modèles présentés. Ce premier article se termine en identifiant des aspects convergents des divers modèles, dont l'exposition à la source d'anxiété. Le second article, Identification of Recurrent Themes in Imaginal Exposure Scenarios During the Cognitive-Behavioral Treatment of Generalized Anxiety Disorder, rapporte les résultats d'une étude sur les thèmes qui ressortent des scénarios catastrophiques utilisés lors de séance d'exposition dans le traitement d'individus souffrant de TAG. Des cliniciens (N = 28) évaluent le niveau de présence de 26 thèmes dans 29 scénarios d'exposition utilisés auprès d'individus souffrant du TAG, identifient les 3 thèmes les plus représentatifs dans chaque scénario et, à la fin, choisissent les 5 thèmes les plus représentatifs des scénarios qu'ils ont lus. Un thème émerge de façon significative à travers ces 3 niveaux d'analyse : le sentiment d'impuissance face aux événements. D'autres thèmes émergent, à l'un ou l'autre des niveaux d'analyse : la présence de sensations physiques, le sentiment d'être coincé, le sentiment d'incompétence, ainsi que le sentiment d'être incapable de faire face émotivement à un événement. Ces thèmes peuvent orienter les cliniciens dans la création de scénarios d'exposition du TAG. La conclusion présente la convergence possible des différents modèles et de l'utilisation de l'exposition dans le traitement du TAG. Si les visées de l'exposition sont différentes selon les modèles et les traitements adaptés, le cadre d'intervention demeure semblable

Correlations between dynamic thermal properties, energy consumption, and comfort in wood, concrete, and lightweight buildings

An office building located in Québec City (QC, Canada) with different envelope assemblies has been simulated to determine the energy consumption and thermal comfort that they provide. The resistance, thermal mass, and materials (concrete, cross-laminated timbers (CLT), and light-frame) were varied in a series of 164 different scenarios, and the energy intensities for heating and cooling were determined in each case, along with the discomfort index. Results show that the materiel used to provide thermal mass has a larger impact on comfort and energy consumption than the value of the thermal mass thickness itself. It was also attempted to correlate the performance of the envelope assessed through energy simulations with four dynamic thermal properties (i.e., dynamic transmittance, areal heat capacity, decrement factor, and time lag). The internal areal heat capacity appeared to be the most important variable to explain variations of performance of the envelope.Un immeuble de bureaux situé à Québec (QC, Canada) avec différents assemblages d’enveloppes a été simulé afin de déterminer la consommation d’énergie et le confort thermique qu’ils procurent. La résistance, la masse thermique et les matériaux (béton, bois lamellés-croisés (CLT) et charpente légère) varient selon une série de 164 scénarios différents et les intensités énergétiques pour le chauffage et le refroidissement sont déterminées dans chaque cas, ainsi que l’indice d’inconfort. Les résultats montrent que le matériau utilisé pour fournir la masse thermique a un impact plus important sur le confort et la consommation d’énergie que la valeur de l’épaisseur de la masse thermique elle-même. On a également tenté de corréler la performance de l’enveloppe évaluée par des simulations énergétiques avec quatre propriétés thermiques dynamiques (c’est-à-dire la transmission dynamique, la capacité thermique surfacique, le facteur de décrémentation et le décalage dans le temps). La capacité thermique aréolaire interne est apparue comme la variable la plus importante pour expliquer les variations de performance de l’envelopp

Interdisciplinary teaching in family medicine teaching units: the residents’ points of view

Background:  Interdisciplinary teaching (IDT) is the norm in Canadian family medicine residency programs. Literature on IDT reports many academic, collaborative and organizational benefits, but little is known about family medicine residents’ own perspectives of IDT. The purpose of this study was to explore family medicine residents’ points of view on IDT in family medicine teaching units (FMTU).       Methods: A mixed methods design combined interviews and self-completed online questionnaires to explore participants’ perceptions of IDT during residency. Content analysis was conducted on the qualitative data and univariate analysis statistical tests on means and proportions were conducted on the quantitative survey questions.Results: A total of 125 family medicine residents from 12 FMTU affiliated with Université Laval (Quebec City) participated in the study (11 interviews and 114 online questionnaires). Participants perceived significant benefits of IDT, including clinical knowledge, complementary perspectives and interprofessional collaboration skills. However, they believe that IDT works best when the educators adapt their teaching to the specific needs of residents in family medicine.Conclusion: These findings support those of previous IDT research and highlight the positive impacts of interdisciplinary education in family medicine residency, especially on interprofessional collaboration. IDT should remain an essential component of the family medicine curricula._____ Contexte: L’enseignement interdisciplinaire (EID) constitue une norme dans les programmes canadiens de résidence en médecine familiale. La littérature disponible sur l’EID fait état de plusieurs bénéfices académiques, collaboratifs et organisationnels, mais elle rend peu compte des points de vue des résidents sur ce type d’enseignement. Cette étude a pour objectif d’explorer les points de vue des résidents en médecine familiale quant à l’EID offert dans les unités de médecine familiale (UMF).Méthodes: Un devis mixte a été utilisé, s’appuyant sur des entrevues semi-dirigées et des questionnaires auto-administrés en ligne. Une analyse de contenu a été effectuée pour le volet qualitatif, et des analyses univariées et bi-variées ont été réalisées pour les données obtenues dans les questionnaires auto-administrés.Résultats: Un total de 125 résidents en médecine familiale, rattachés aux 12 UMF relevant de l’Université Laval (Québec), a participé à l’étude (11 entrevues et 114 questionnaires en ligne). Les participants reconnaissent des bénéfices significatifs à l’EID, tels l’acquisition et l’approfondissement de connaissances cliniques essentielles, l’intégration de perspectives complémentaires sur les problèmes de santé, et le développement d’habiletés à la collaboration interprofessionnelle. Ils estiment toutefois que l’EID peut s’optimiser en s’adaptant davantage aux besoins spécifiques des résidents en médecine familiale.Conclusions: À l’instar des études antérieures, les résultats de cette recherche mettent en relief les impacts positifs de l’EID pendant la résidence en médecine familiale, particulièrement ceux qui sont liés à l’apprentissage de la collaboration interprofessionnelle. L’EID devrait par conséquent demeurer une caractéristique essentielle des programmes de résidence en médecine familiale

Optimization of geothermal power plant design for evolving operating conditions

The main goal of this work is to determine optimal geothermal power plant designs by taking into account the transient evolution of the plant/reservoir system. To do so, a geothermal reservoir model is developed, where the permeability of the ground is represented by a series of parallel pipes inside which the underground water can flow. The reservoir model is coupled to an evolving Organic Ranking Cycle (ORC), where the pressure at the condenser adapts to the conditions in the geothermal reservoir (temperature of the brine and mass flow rate) based on the Stodola equation. The system is then optimized in order to maximize the total energy output of the power plant over its lifetime. A series of parametric analyses was performed for relevant design parameters (e.g., overall conductance of the heat exchanger at the evaporator, turbine sizes, number of years of operation, etc.), while other parameters were optimized, namely the working fluid to geofluid mass flow rate ratio, the pressure at the evaporator, and the geofluid mass flow rate. The optimal values that were found were values that yielded viable cycles over the entire exploitation period of the plant and that did not deplete the thermal reservoir prior to the end of the plant lifetime. ORC cycles that were optimized by considering the time evolution of the system were then compared against cycles optimized under the assumption of constant geothermal reservoir properties. It was also demonstrated that by allowing key design parameters to change over the course of the exploitation of the plant, it was possible to further increase the plant performance

Braak neurofibrillary tangle staging prediction from in vivo MRI metrics

INTRODUCTION: Alzheimer’s disease (AD) diagnosis requires postmortem visualization of amyloid and tau deposits. As brain atrophy can provide assessment of consequent neurodegeneration, our objective was to predict postmortem neurofibrillary tangles (NFT) from in vivo MRI measurements. METHODS: All participants with neuroimaging and neuropathological data from the Alzheimer’s Disease Neuroimaging Initiative, the National Alzheimer’s Coordinating Center and the Rush Memory and Aging Project were selected (n=186). 232 variables were extracted from last MRI before death using FreeSurfer. Nonparametric correlation analysis and multivariable support vector machine classification were performed to provide a predictive model of Braak NFT staging. RESULTS: We demonstrated that 59 of our MRI variables, mostly temporal lobe structures, were significantly associated with Braak NFT stages (p<.005). We obtained a 62.4% correct classification rate for discrimination between transentorhinal, limbic and isocortical groups. DISCUSSION: Structural neuroimaging may therefore be considered as a potential biomarker for early detection of AD-associated neurofibrillary degeneration

An open vibration platform to evaluate postural control using a simple reinforcement learning agent

In this paper, our research team proposes an inexpensive open vibration platform built from easily available electronic components to be used as a tool by physiotherapists in order to help them in their evaluation of the postural control of individuals at risk of postural imbalance which could lead to falls. The platform has been thought to be easily reproducible and all the code necessary to make it work is made available on the researchers’ websites. In addition, a simple reinforcement learning agent has been developed and tested to automatically calibrate the vibration motors for optimal stimulation. Finally, we present in this paper pilot experiments done on 7 healthy participants (40.8 years old) to validate the proper functioning of the platform

Re-evaluation of blood mercury, lead and cadmium concentrations in the Inuit population of Nunavik (Québec): a cross-sectional study

<p>Abstract</p> <p>Background</p> <p>Arctic populations are exposed to mercury, lead and cadmium through their traditional diet. Studies have however shown that cadmium exposure is most often attributable to tobacco smoking. The aim of this study is to examine the trends in mercury, lead and cadmium exposure between 1992 and 2004 in the Inuit population of Nunavik (Northern Québec, Canada) using the data obtained from two broad scale health surveys, and to identify sources of exposure in 2004.</p> <p>Methods</p> <p>In 2004, 917 adults aged between 18 and 74 were recruited in the 14 communities of Nunavik to participate to a broad scale health survey. Blood samples were collected and analysed for metals by inductively coupled plasma mass spectrometry, and dietary and life-style characteristics were documented by questionnaires. Results were compared with data obtained in 1992, where 492 people were recruited for a similar survey in the same population.</p> <p>Results</p> <p>Mean blood concentration of mercury was 51.2 nmol/L, which represent a 32% decrease (p < 0.001) between 1992 and 2004. Mercury blood concentrations were mainly explained by age (partial r²= 0.20; p < 0.0001), and the most important source of exposure to mercury was marine mammal meat consumption (partial r²= 0.04; p < 0.0001). In 2004, mean blood concentration of lead was 0.19 μmol/L and showed a 55% decrease since 1992. No strong associations were observed with any dietary source, and lead concentrations were mainly explained by age (partial r²= 0.20.; p < 0.001). Blood cadmium concentrations showed a 22% decrease (p < 0.001) between 1992 and 2004. Once stratified according to tobacco use, means varied between 5.3 nmol/L in never-smokers and 40.4 nmol/L in smokers. Blood cadmium concentrations were mainly associated with tobacco smoking (partial r²= 0.56; p < 0.0001), while consumption of caribou liver and kidney remain a minor source of cadmium exposure among never-smokers.</p> <p>Conclusion</p> <p>Important decreases in mercury, lead and cadmium exposure were observed. Mercury decrease could be explained by dietary changes and the ban of lead cartridges use likely contributed to the decrease in lead exposure. Blood cadmium concentrations remain high and, underscoring the need for intensive tobacco smoking prevention campaigns in the Nunavik population.</p