The diploma thesis deals with a temperature field in a solid fuel during the combustion process. At the beginning of this thesis, research of available literature was conducted to obtain information about the composition of wood, properties affecting the combustion process, and the basics of heat transfer. Afterward, the temperature profiles of the samples were recorded during the measurement in the observation furnace. The temperature profiles of samples of six different sizes which were made of spruce and beech wood were subsequently evaluated and compared. Based on experimentally obtained data, a mathematical model was created in the OpenModellica software. Finally, the results of the mathematical model were compared with experimentally obtained data and appropriate conclusions were deduced.

Les renforts à base de fibres de lin sont aujourd’hui une alternative capable de concurrencer les fibres synthétiques conventionnelles puisqu’ils sont écologiques, économiques et présentent des propriétés mécaniques intéressantes. Cependant, leur inconvénient majeur est leur absorption d’eau potentiellement importante qui affecte leurs propriétés mécaniques. Ce projet de recherche propose d’étudier le comportement hygroscopique et le couplage hygro-mécanique dans les composites lin / époxy. Cette étude repose sur une approche expérimentale multi-échelle et une modélisation du comportement visco-élasto-plastique avec prise en compte du couplage hygro-mécanique des composites renforcés par des fibres de lin. Les cinétiques de diffusion dans l’époxy et dans le composite ont été modélisées par une loi de type Langmuir et Fick respectivement. Les coefficients d’hygro-expansion des composites et des fils élémentaires qui constituent le renfort tissu ont été déterminés expérimentalement. Une étude de l’influence du conditionnement jusqu’à saturation à différentes humidités relatives sur le comportement mécanique dans les trois directions du stratifié a également été menée. Cette étude a montré l’existence d’une teneur en eau optimale pour laquelle les propriétés mécaniques sont optimales. L’émergence d’un comportement à deux régions linéaires a été mise en évidence et attribuée à la présence d’hétérogénéités locales au sein du renfort tissu. Des essais de fluage / recouvrance et de relaxation / effacement ont permis de mettre en place un modèle visco-élasto-plastique avec prise en compte du couplage hygro-mécanique. Ce modèle offre de bonnes capacités de prédiction et permettra de prévoir le comportement des structures composites renforcés par des fibres de lin en atmosphère humide. / Flax fibre reinforcements are nowadays an alternative able to compete with conventional synthetic fibres since they are ecological, economic and have interesting mechanical properties. However, their major drawback is their potentially significant water absorption which affects their mechanical properties. This research project proposes to study the hygroscopic behaviour and hygro-mechanical coupling in flax / epoxy composites. This study is based on a multi-scale experimental approach. A modelling of visco-elasto-plastic behaviour taking into account the hygro-mechanical coupling within flax /epoxy composites is established. The diffusion kinetics in composites were modelled by a Fick law. However, the diffusion kinetics in epoxy were modelled by a Langmuir law. The hygro-expansion coefficients of the composites and the elementary yarns that constitute the fabric reinforcement were determined experimentally. A study of the influence of conditioning until saturation at different relative humidities on the mechanical behaviour in the three main directions of the laminates was conducted. This study showed the existence of an optimal water content for which the mechanical properties are maximum. The emergence of a two-linear-region behaviour was pointed out and attributed to the presence of local heterogeneities within the fabric reinforcement. Creep / recovery and stress relaxation tests were exploited in order to develop a visco-elastoplastic model with consideration of the hygro-mechanical coupling. This model offers good predictive capabilities and could be used to predict the behaviour of flax fibres reinforced composite structures in humid atmospheres.

Purpose – The unexpected yet drastic influence of the COVID-19 pandemic resulted in a rapid transition of education to be conducted in digital environments. Replacing face-to-face classrooms with synchronous online learning requires a number of appropriate adjustments which were heavily restricted by the urgency of this global change taking place. With theobserved issues of student participation and involvement in online learning, the purpose ofthis research was to investigate the potential that digital collaborative tools have and if theycan improve the quality of online group discussions among students aged 12 to 16 years old. Method – This study employs a quantitative data collection approach and makes use of the Community of Inquiry framework. A close-ended questionnaire based on the Community of Inquiry survey tool was used to collect students’ impressions and attitudes after they hadparticipated in the experimental study. The experiment consisted of control and experimental groups that partook in online group discussions as part of a regularly scheduled lesson. Findings – Digital collaborative tools were found to change the way in which students experience online group discussions. The attained rates of the Community of Inquiry were overall higher among students in the experimental group. Our findings tested to be statistically significant together with the effect size falling between medium to large extent. This further supports the notion that digital collaborative tools bring in a positive difference into online group discussions and have a potential to increase the quality of online learning when implemented carefully and thoughtfully. Implications – This study emphasizes the importance of developing a clear strategy of how to implement suitable digital collaborative tools into online learning in the most optimal manner that would increase the quality of online learning. This paper can be considered as a startingpoint for future research that could construct further knowledge within the field and extend our findings by investigating other aspects that have an influence on and can have beneficial effects for younger students in online education.

Background: Psilocybin is today the most studied psychedelic substance in neuroscience for its psychotomimetic and therapeutic effects. One of the institutions in the Czech Republic that studies this substance is the National Institute of Mental Health, where a clinical evaluation of its effects and safety is underway. The action and safety of this substance is examined here in terms of acute intoxication, but also in terms of long-term effects. Aim: To determine how volunteers perceive the experience with psilocybin administered in a controlled experimental study environment and whether they have experienced any afterglow effects after the cessation of acute intoxication for 28 days after administration, as well as how these effects occur and how long they persist. Methods: Data was obtained using semi-structured interviews. The research group consists of 20 interviews with 10 healthy volunteers of the clinical study at NUDZ. Interviews were conducted on day 28 after administration of an active dose of psilocybin or placebo. A qualitative thematic analysis of these interviews was performed in order to identify topics within the framework set by the research questions. Results: The results showed that for the respondents, the experience with the active dose of psilocybin was significant in terms of...

In the last few years educational computer games have gained attention as a tool for facilitating learning in different sectors of society including but not limited to military, health, and education. However, advances in computer game technology continue to outpace research on its effectiveness. Few empirical studies have investigated the effects of educational games in the context of formal K-12 settings. The purpose of this study was to examine the effects of a series of mathematics computer games on mathematics achievement and motivation of high school students. In addition, the role of prior mathematics knowledge, computer skill, and English language skill of the participants on their mathematics achievement and motivation when they played the games were investigated. A total of 193 students and 10 teachers from an urban high school in the southeast of the United States of the America participated in this study. The teachers were randomly assigned to treatment and control groups. Students' mathematics achievement was measured using school district benchmark exams and a game performance test generated by the developers of the mathematics games. A mathematics motivation questionnaire based on Keller's (1987a) ARCS model of motivational design measured students' mathematics motivation. Multivariate Analysis of Co-Variance (MANCOVA) was conducted to analyze the data. In addition, interviews were conducted to cross validate the results of the quantitative data. The MANCOVA results indicated significant improvement of the mathematics achievement of the experimental versus control group. No significant improvement was found in the motivation of the experimental versus control group. However, a significant improvement was found on the motivation scores of the students who played the games in their school lab and classrooms compared to the ones who played the games only in the school labs. In addition, the findings indicated that prior mathematics knowledge, computer skill and English language skill did not play significant roles in achievement and motivation of the experimental group. Teachers' interviews revealed that these individual differences had indeed played significant roles in game-playing at the beginning of using the games, but the impacts gradually diminished as the students gained the required game-playing skills. The overall results indicated that the mathematics games used in this study were effective teaching and learning tools to improve the mathematics skills of the students. Using the games in mathematics education was suggested by the teachers as an appropriate alternative way of teaching, as one of the teachers stated: "This is definitely the way that we have to go to teach mathematics in the future." Mathematics games should be integrated with classroom activities if teachers want to increase mathematics class motivation. Teachers' helps and supports are vital in using the games effectively in a population with different prior mathematics knowledge, computer skills, and English language skills.

No / We have probed the coupling between flow and concentration fluctuations in polymer blends using small-angle neutron scattering. We utilized a recirculating cell with a slot die, enabling us to measure the behavior at the entrance, within and at the exit of a contraction-expansion flow. While, as expected, anisotropy was observed in all nonquiescent experiments, the correlation lengths associated with the concentration fluctuations are found to be "stretched" more in the direction perpendicular to the flow at all positions along the centerline of the flow, except at the slot die exit. To gain insight into the observations, we present calculations of the scattering based on a multiscale approach, which bridges the gap between macroscopic Newtonian fluid dynamics and the convection of nanoscale concentration fluctuations. However, we find that this model contains insufficient physics to correctly describe our observations. Consequently, we argue that the deformation of the correlation length is primarily due to the coupling between weakly non-Newtonian stresses and thermodynamics

No / Auditory signals have been shown to exert a marked influence on visual perception in a wide range of tasks. However, the mechanisms of these interactions are, at present, poorly understood. Here we present a series of experiments where a temporal cue within the auditory domain can significantly affect the localisation of a moving visual target. To investigate the mechanism of this interaction, we first modulated the spatial positional uncertainty of the visual target by varying its size. When visual positional uncertainty was low (small target size), auditory signals had little or no influence on perceived visual location. However, with increasing visual uncertainty (larger target sizes), auditory signals exerted a significantly greater influence on perceived visual location. We then altered the temporal profile of the auditory signal by modulating the spread of its Gaussian temporal envelope. Introducing this temporal uncertainty to the auditory signal greatly reduced its effect on visual localisation judgements. These findings support the view that the relative uncertainty in individual sensory domains governs the perceptual outcome of multisensory integration.

In this investigation, a single phase fluid is used to study the coupling between natural convection heat transfer within an enclosure and forced convection through computer covering case to cool the electronic chip. Two working fluids are used (water and air) within a rectangular enclosure and the air flow through the computer case is created by an exhaust fan installed at the back of the computer case. The optimum enclosure size configuration that keeps a maximum temperature of the heat source at a safe temperature level (85℃) is determined. The cooling system is tested for varying values of applied power in the range of 15−40𝑊. The study is based on both numerical models and experimental observations. The numerical work was developed using the commercial software (ANSYS-Icepak) to simulate the flow and temperature fields for the desktop computer and the cooling system. The numerical simulation has the same physical geometry as those used in the experimental investigations. The experimental work was aimed to gather the details for temperature field and use them in the validation of the numerical prediction. The results showed that, the cavity size variations influence both the heat transfer process and the maximum temperature. Furthermore, the experimental results ii compared favourably with those obtained numerically, where the maximum deviation in terms of the maximum system temperature, is within 3.5%. Moreover, it is seen that using water as the working fluid within the enclosure is capable of keeping the maximum temperature under 77℃ for a heat source of 40𝑊, which is below the recommended electronic chips temperature of not exceeding 85℃. As a result, the noise and vibration level is reduced. In addition, the proposed cooling system saved about 65% of the CPU fan power.

No description available.

[pt] Esta dissertação tem como objetivo avaliar o comportamento estrutural de um sistema misto pré-fabricado através de um estudo teórico-experimental. O modelo estrutural é composto por dois perfis I laminados que são ligados através de conectores localizados na alma do perfil I e preenchidos por concreto armado. Foi realizado um estudo teórico baseado na análise linear elástica e formulações não lineares através do Método dos Elementos Finitos (MEF) com o uso do software ABAQUS avaliando o comportamento estrutural submetido à flexão no eixo não-múltiplo. Foi analisado o comportamento carga x deslocamento, bem como a carga última do sistema. Foi desenvolvido um programa experimental no Laboratório de Estruturas e Materiais da PUC-Rio, para avaliar o comportamento estrutural do sistema proposto, quando submetido à flexão, a fim de validar os resultados obtidos na análise numérica. Os resultados experimentais foram comparados com os resultados obtidos computacionalmente e os teóricos calculados com base na norma ABNT NBR 8800:2008. Por fim, foram avaliadas as condições econômicas para implementação do sistema e analisada a eficiência estrutural visando um método construtivo industrializado. / [en] This study aims to evaluate the structural behavior of a pre-fabricated composite system by developing a theoretical and experimental study. The structural model consists of a rolled double I section connected by its webs and filled with reinforced concrete. A theoretical study, based on linear and nonlinear static analysis considering the Finite Element Method (FEM), was done using ABAQUS software. Based on this study, an experimental programme was developed at the Structure and Materials Laboratory of PUC-Rio, to evaluate the structural behavior of the proposed system submitted to a bending test, in order to validate the numerical results obtained in the numerical analysis. The experimental results were compared to the numerical results and the design recommendations of the Brazilian standards ABNT NBR 8800:2008. Finally, the economic conditions for the implementation of the system and its structural efficiency were evaluated, aiming to industrialization of construction.