38 research outputs found
Adapter les ANB en se basant sur les processus cognitifs conformes au SB5 pour les enfants avec (DAM)
No full textCette recherche s'inscrit dans le cadre des recherches bibliographiques exploratoires. Elle est basée sur des études empiriques menées dans les domaines de la psychologie cognitive et de la neuropsychologie, qui ont pour objet l'intervention auprès des enfants en difficulté d'apprentissage en mathématiques (DAM). Son objectif est d'identifier des modèles d'enseignement efficace, statistiquement significatifs, ainsi que des lignes directrices méthodologiques, permettant de proposer des étapes possibles à suivre pour diagnostiquer les DAM liées aux compétences numériques de base (CNB) et aux processus cognitifs généraux (PCG), et adapter les activités numériques de base (ANB). La plupart des études rapportées dans cette recherche ont montré l'importance de l’instruction directe, des stratégies explicites et de l'utilisation d’heuristiques, en plus des stratégies métacognitives et des stratégies de compensation spécifiques aux déficiences au niveau des PCG. Il est également crucial que l'enseignant « orthopédagogue » soit bien informé tant sur la cognition numérique que sur les dysfonctionnements sous-jacents des (DAM). Tout cela a permis de formuler un scénario, comprenant des étapes d'adaptation des ANB, en réponse à la question problématique sur la possibilité d'une adaptation fondée sur les PCG et les CNB, au profit des enfants avec DAM, et ensuite, fournir des modèles d’activités numériques pour remédier à une des difficultés diagnostiquées dans le cas de « Banafsaj », qui est la difficulté "de correspondance terme à terme"
Conceptual Design of a Flameless Combustor for Aircraft Engines
No full textThe thesis presents a feasibility study of a proposed combustion methodology by means of two-dimensional Computational Fluid Dynamics on the application of Flameless Combustion to an aircraft engine with the objective to achieve ultra-low pollutant emissions. The geometrical design started from scratch while taking the philosophy of the proposed methodology into account. The combustor’s entry conditions and global size were estimated based on a conventional turbofan engine and corrected at atmospheric pressure. The most important parameter to achieve flameless combustion was considered to be the recirculation ratio in order for it to be sustained. Therefore a cold flow simulation was carried out first with the objective to fulfil this requirement by using RANS-based turbulence models. The models were first validated by attempting to reproduce the measured flow velocities of three wind tunnel cases with similar geometry. All models under predicted maximum recirculation. The k-? Realizable model was closest to determine maximum recirculation and its axial position. This model also showed a similar linear trend in maximum recirculation ratio with respect to different channel-to-inlet area ratios, and also the reattachment point was well predicted, which aided in the prediction of the flow paths. Attempts were also made to reproduce the measured velocity profiles with the Large Eddy Simulation derived models. The Embedded Large Eddy Simulation model did not give better results, probably due to the mesh resolution still being too coarse and the Detached Eddy Simulation model even performed worse which made it not suitable for such flow cases. Within the engine’s size limits the annular type combustor could achieve a maximum recirculation ratio up to a value of 1.3 in the cold flow while a can type combustor could achieve a value of 3.2. In the literature a value of at least 3 was required. The simulations of the reacting flow were first applied to the can combustor and were carried out with the Eddy Dissipation Concept model, using a detailed reaction mechanism. Combustion reduced the cold flow’s recirculation ratio by a factor 2. By studying the results and understanding the reacting flow, the combustion could be controlled with qualitative refinement of the combustors geometry and repositioning of the inlets of the fuel and secondary air. With the help of using vitiated air as oxidant, these rough alterations led to CO emissions to reduce to less than 50 ppm and NOX to less than 2 ppm, both for cruise and take-off conditions. The more realistic annular combustor did not perform as good when using the final geometry of the can combustor, which led to an increase of CO emissions by an order of magnitude. Due to the area ratio of the annular combustor being roughly six times smaller than that of the can combustor, the velocity of the recirculated flow increased from 24 m/s to nearly 140 m/s, which led to high heat dissipation and a residence time five times as short. Further geometry improvement was more difficult making the emissions harder to control. However CO emissions were eventually reduced to below 200 ppm and NOX below 65 ppm. The annular combustor was also tested to simulate actual flight conditions by also pressurising the inlet air. This led to an improved reaction rate and the CO emissions were further reduced to below 100 ppm. The NOX emissions reduced to below 20 ppm and the pressure loss was less than 3% which was below the imposed requirement of an aero engine combustor.Flight Performance and PropulsionPropulsion and PowerAerospace Engineerin
Quantitative analysis of myofiber type composition in human and mouse skeletal muscles
No full textSkeletal muscles are composed of different myofiber types characterized by the expression of myosin heavy chain isoforms, which can be affected by physical activity, aging, and pathological conditions. Here, we present a step-by-step high-throughput semi-automated approach for performing myofiber type quantification of entire human or mouse muscle tissue sections, including immunofluorescence staining, image acquisition, processing, and quantification. For complete details on the use and execution of this protocol, please refer to Abbassi-Daloii et al. (2022).(1
Modelling Turbulent Combustion Coupled with Conjugate Heat Transfer in OpenFOAM
No full textThis paper verifies a mathematical model that is developed for the open source CFD-toolbox OpenFOAM, which couples turbulent combustion with conjugate heat transfer. This feature already exists in well-known commercial codes. It permits the prediction of the flame’s characteristics, its emissions, and the consequent heat transfer between fluids and solids via radiation, convection, and conduction. The verification is based on a simplified 2D axisymmetric cylindrical reactor. In the first step, the combustion part of the solver is compared against experimental data for an open turbulent flame. This shows good agreement when using the full GRI 3.0 reaction mechanism. Afterwards, the flame is confined by a cylindrical wall and simultaneously conjugate heat transfer is activated and analysed. It is shown that the combustion and conjugate heat transfer are successfully coupled.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Numerical AnalysisMathematical Physic
The Effect of Variable Air–Fuel Ratio on Thermal NOx Emissions and Numerical Flow Stability in Rotary Kilns Using Non-Premixed Combustion
No full textOne of the quickest ways to influence both the wall temperature and thermal NOx emissions in rotary kilns is to change the air–fuel ratio (AFR). The normalized counterpart of the AFR, the equivalence ratio, is usually associated with premixed flames and studies of its influence on diffusion flames are inconsistent, depending on the application. In this paper, the influence of the AFR is investigated numerically for rotary kilns by conducting steady-state simulations. We first conduct three-dimensional simulations where we encounter statistically unstable flow at high inflow conditions, which may be caused by vortex stretching. As vortex stretching vanishes in two-dimensional flow, the 2D simulations no longer encounter convergence problems. The impact of this simplification is shown to be acceptable for the thermal behaviour. It is shown that both the wall temperature and thermal NOx emissions peak at the fuel-rich and fuel-lean side of the stoichiometric AFR, respectively. If the AFR continues to increase, the wall temperature decreases significantly and thermal NOx emissions drop dramatically. The NOx validation, however, shows different results and indicates that the simulation model is simplified too much, as the measured NOx formation peaks at significantly fuel-lean conditions.Numerical AnalysisMathematical Physic
Non-premixed combustion in rotary kilns using OpenFOAM: the effect of conjugate heat transfer and external radiative heat loss on the reacting flow and the wall
No full textThe wish to reduce the environmental footprint and to enhance economic gains of rotary kilns pushes the numerical simulation of combustion to include conjugate heat transfer. In this paper we study the influence of the refractory wall and radiative heat loss to the ambient, on the combustion process of a reference kiln model. Numerical results show that the inclusion of the refractory lining and the external radiative heat loss allows the inner wall temperature distribution to vary, with 60 % difference between its minimum and maximum. This is in sharp contrast with models that assume a fixed temperature at the wall. Consequently the maximum inner wall temperature increases by more than 200 %, the maximum flame temperature by nearly 13 % and maximum freeboard gas temperature by up to 90 %. It is thus important to account for these effects when modeling rotary kilns.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Numerical AnalysisMathematical Physic
Mitigating Thermal NOx by Changing the Secondary Air Injection Channel: A Case Study in the Cement Industry
No full textThis work studies how non-premixed turbulent combustion in a rotary kiln depends on thegeometry of the secondary air inlet channel. We target a kiln in which temperatures can reach values above 1800 degrees Kelvin. Monitoring and possible mitigation of the thermal nitric-oxide (NOx) formation is of utmost importance. The performed reactive flow simulations result in detailed maps of the spatial distribution of the flow, thermodynamics and chemical conditions of the kiln. These maps provide valuable information to the operator of the kiln. The simulations show the difference between the existing and the newly proposed geometry of the secondary air inlet. In the existing configuration, the secondary air inlet is rectangular and located above the base of the burner pipe. The secondary air flows into the furnace from the top of the flame. The heat release by combustion is unevenly distributed throughout the flame. In the new geometry, the secondary air inlet is an annular ring placed around the burner pipe. The secondary air flows circumferentially around the burner pipe. The new secondary air inlet geometry is shown to result in a more homogeneous spatial distribution of the heat release throughout the flame. The peak temperatures of the flame and the production of thermal NOx are significantly reduced. Further research is required to resolve limitations of various choices in our modeling approach.Mathematical PhysicsNumerical Analysi
Platinum contacts for 9-atom-wide armchair graphene nanoribbons
No full textCreating a good contact between electrodes and graphene nanoribbons (GNRs)
has been a longstanding challenge in searching for the next GNR-based
nanoelectronics. This quest requires the controlled fabrication of sub-20 nm
metallic gaps, a clean GNR transfer minimizing damage and organic contamination
during the device fabrication, as well as work function matching to minimize
the contact resistance. Here, we transfer 9-atom-wide armchair-edged GNRs
(9-AGNRs) grown on Au(111)/mica substrates to pre-patterned platinum
electrodes, yielding polymer-free 9-AGNR field-effect transistor devices. Our
devices have a resistance in the range of to in the
low-bias regime, which is 2 to 4 orders of magnitude lower than previous
reports. Density functional theory (DFT) calculations combined with the
non-equilibrium Green's function method (NEGF) explain the observed p-type
electrical characteristics and further demonstrate that platinum gives strong
coupling and higher transmission in comparison to other materials such as
graphene.Comment: 6 pages, 5 figure
Sleep Disorders and Sleep Quality in Moroccan Adult Patients with Cancer during Treatment
No full textA generalized neural network approach for separation of molecular breaking traces
No full textBreak-junction experiments are used to statistically study the electronic properties of individual molecules. The measurements consist of repeatedly breaking and merging a gold wire while measuring the conductance as a function of displacement. When a molecule is captured, a plateau is observed in the conductance traces otherwise exponentially decaying tunnel traces are measured. Clustering methods are widely used to separate these traces and identify potential sub-populations in the data corresponding to different molecular junction configurations. As these configurations are typically a priori unknown, unsupervised methods are most suitable for the classification. However, most of the unsupervised methods used for the classification perform poorly in the identification of these small sub-populations of molecular traces. Robust removal of tunnelling-only traces before clustering is thus of great interest. Neural networks have been proven to be powerful in the classification of data samples with predictable behaviour, but often show large sensitivity to the underlying training data. In this study we report on a neural network method for the separation of tunnelling-only traces in conductance vs. displacement measurements that achieves excellent classification performance for complete and unseen data sets. This method is particularly useful for data sets in which the yield of molecular traces is low or which comprise of a significant number of traces displaying a jump from tunneling features to a molecular plateau.QN/van der Zant La
