A main challenge in the field of special effects is to create special effects in real time in a way that the user can preview the effect before taking the actual picture or movie sequence. There are many techniques currently used to create computer-simulated special effects, however current techniques in computer graphics do not provide the option for the creation of real-time texture synthesis. Thus, while computer graphics is a powerful tool in the field of special effects, it is neither portable nor does it provide work in real-time capabilities. Real-time special effects may, however, be created optically. Such approach will provide not only real-time image processing at the speed of light but also a preview option allowing the user or the artist to preview the effect on various parts of the object in order to optimize the outcome. The work presented in this dissertation was inspired by the idea of optically created special effects, such as painterly effects, encoded in images captured by photographic or motion picture cameras. As part of the presented work, compact relay optics was assessed, developed, and a working prototype was built. It was concluded that even though compact relay optics can be achieved, further push for compactness and cost-effectiveness was impossible in the paradigm of bulk macro-optics systems. Thus, a paradigm for imaging with multi-aperture micro-optics was proposed and demonstrated for the first time, which constitutes one of the key contributions of this work. This new paradigm was further extended to the most general case of magnifying multi-aperture micro-optical systems. Such paradigm allows an extreme reduction in size of the imaging optics by a factor of about 10 and a reduction in weight by a factor of about 500. Furthermore, an experimental quantification of the feasibility of optically created special effects was completed, and consequently raytracing software was developed, which was later commercialized by SmARTLens(TM). While the art forms created via raytracing were powerful, they did not predict all effects acquired experimentally. Thus, finally, as key contribution of this work, the principles of scalar diffraction theory were applied to optical imaging of extended objects under quasi-monochromatic incoherent illumination in order to provide a path to more accurately model the proposed optical imaging process for special effects obtained in the hardware. The existing theoretical framework was generalized to non-paraxial in- and out-of-focus imaging and results were obtained to verify the generalized framework. In the generalized non-paraxial framework, even the most complex linear systems, without any assumptions for shift invariance, can be modeled and analyzed.

No description available.

In the context of an aviation industry whose top priority is to face the sustainability challenge, the growing civil UAV branch is not an exception. Hydrogen-powered UAVs equipped with PEM (Polymer Electrolyte Membrane) fuel cells are more and more frequently identified as the most convincing and promising technology, particularly for long-endurance mission requirements. However, the onboard carriage of a hydrogen fuel cell leads to unexplored internal flow characteristics, including the introduction of water vapour. The purpose of this master thesis is to develop a valid CFD model and methodology for the internal flow simulation of hydrogen-powered UAVs. Given the strict environmental operational requirements of PEM fuel cells, the intended application of the model is to effectively assess the evolution of the internal bay flow temperature and humidity fields. An explicit-time fourth-order Runge-Kutta projection method is tested successfully on a sample 2D case setup. The case geometry and flow conditions are inspired by the Green Raven UAV project conceived by the Department of Aeronautical and Vehicle Engineering at KTH. / I samband med en flygindustri vars högsta prioritet är att bemöta hållbarhetsutma- ningen är den växande civila UAV-sektorn inget undantag. Vätgasdrivna UAV:er utrustade med PEM (Polymer Electrolyte Membrane) bränsleceller betecknas allt oftare som den mest övertygande och lovande teknologin, särskilt för att de ska kunna utföra långvariga uppdrag. Den ombordgående transporten av en vätebränslecell leder emellertid till outforskade inre flödesfenomen, inklusive alstrad vattenånga. Syftet med detta examensarbete är att utveckla en lämplig CFD-modell och metodik för intern flödesimulering av vätgasdrivna UAV. Med tanke på de strikta miljökraven för PEM-bränsleceller är modellens avsedda tillämpning att eektivt utvärdera utvecklingen av de inre flödestemperaturerna och luftfuktighetsfälten. En tidsexplicit Runge-Kutta-projektionsmetod av fjärde ordningen testas framgångsrikt på ett 2D-exempel. Fallets geometri och flödesförhållanden är inspirerade av Green Raven UAV-projektet som utförts på Farkost och Flyg avdelningen på KTH.

<p dir="ltr">This thesis presents advances in numerical methods for partial differential equations (PDEs) and optimization problems, with a focus on improving efficiency, stability, and accuracy across various applications. We begin by addressing 3D Poisson-type equations, developing a GPU-accelerated spectral-element method that utilizes the tensor product structure to achieve extremely fast performance. This approach enables solving problems with over one billion degrees of freedom in less than one second on modern GPUs, with applications to Schrödinger and Cahn<i>–</i>Hilliard equations demonstrated. Next, we focus on parabolic PDEs, specifically the Cahn<i>–</i>Hilliard equation with dynamical boundary conditions. We propose an efficient energy-stable numerical scheme using a unified framework to handle both Allen<i>–</i>Cahn and Cahn<i>–</i>Hilliard type boundary conditions. The scheme employs a scalar auxiliary variable (SAV) approach to achieve linear, second-order, and unconditionally energy stable properties. Shifting to a machine learning perspective for PDEs, we introduce an unsupervised learning-based numerical method for solving elliptic PDEs. This approach uses deep neural networks to approximate PDE solutions and employs least-squares functionals as loss functions, with a focus on first-order system least-squares formulations. In the realm of optimization, we present an efficient and robust SAV based algorithm for discrete gradient systems. This method modifies the standard SAV approach and incorporates relaxation and adaptive strategies to achieve fast convergence for minimization problems while maintaining unconditional energy stability. Finally, we address optimization in the context of machine learning by developing a structure-guided Gauss<i>–</i>Newton method for shallow ReLU neural network optimization. This approach exploits both the least-squares and neural network structures to create an efficient iterative solver, demonstrating superior performance on challenging function approximation problems. Throughout the thesis, we provide theoretical analysis, efficient numerical implementations, and extensive computational experiments to validate the proposed methods. </p>

In order to find quantum corrections to the de Sitter entropy, a new approach to higher loop Feynman integral computations on the sphere is presented. Arbitrary scalar Feynman integrals on a spherical background are brought into the generalized Euler integral (A-hypergeometric series/GKZ systems) form by expressing the massive scalar propagator as a bivariate radial Mellin transform of the massless scalar propagator in one higher dimensional Euclidean flat space. This formulation is expanded to include massive and massless vector fields by construction of similar embedding space propagators. Vector Feynman integrals are shown to be sums over generalized Euler integral formed of underlying scalar Feynman integrals. Granting existence of general spin embedding space propagators, general spin Feynman integrals are shown, by the construction of a "master" integral, to also be sums over generalized Euler integral representations of scalar Feynman integrals. Finding exact embedding space propagator expressions for fields of integer spin ≥ 2 and half integer spin is left to future work.

Cette thèse de doctorat composée de trois chapitres contribue au développement de tests statistiques et à analyser la transmission financière dans un cadre multivarié hétéroscédastique. Le premier chapitre propose deux tests du multiplicateur de Lagrange de constance des corrélations conditionnelles dans les modèles GARCH multivariés. Si l'hypothèse nulle repose sur des corrélations conditionnelles constantes, l'hypothèse alternative propose une première spécification basée sur des réseaux de neurones artificiels et une seconde représentée par une forme fonctionnelle inconnue qui est linéarisée à l'aide d'un développement de Taylor.Dans le deuxième chapitre, un nouveau modèle est introduit dans le but de tester la non-linéarité des (co)variances conditionnelles. Si l'hypothèse nulle repose sur une fonction linéaire des innovations retardées au carré et des (co)variances conditionnelles, l'hypothèse alternative se caractérise quant à elle par une fonction de transition non-linéaire : exponentielle ou logistique ; une configuration avec effets de levier est également proposée. Dans les deux premiers chapitres, les expériences de simulations et les illustrations empiriques montrent les bonnes performances de nos tests de mauvaise spécification.Le dernier chapitre étudie la transmission d'information en séance et hors séance de cotation en termes de rendements et de volatilités entre la Chine, l'Amérique et l'Europe. Le problème d'asynchronicité est considéré avec soin dans la modélisation bivariée avec la Chine comme référence. / This Ph.D. thesis composed by three chapters contributes to the development of test statistics and to analyse financial transmission in a multivariate heteroskedastic framework.The first chapter proposes two Lagrange multiplier tests of constancy of conditional correlations in multivariate GARCH models. Whether the null hypothesis is based on constant conditional correlations, the alternative hypothesis proposes a first specification based on artificial neural networks, and a second specification based on an unknown functional form linearised by a Taylor expansion.In the second chapter, a new model is introduced in order to test for nonlinearity in conditional (co)variances. Whether the null hypothesis is based on a linear function of the lagged squared innovations and the conditional (co)variances, the alternative hypothesis is characterised by a nonlinear exponential or logistic transition function; a configuration with leverage effects is also proposed.In the two first chapters, simulation experiments and empirical illustrations show the good performances of our misspecification tests.The last chapter studies daytime and overnight information transmission in terms of returns and volatilities between China, America and Europe. The asynchronicity issue is carefully considered in the bivariate modelling with China as benchmark.

Wards occupy significant proportions of hospital floor areas and due to their constant use, represent a worthwhile focus of study. Single-bed wards are specifically of interest owing to the isolation aspect they bring to infection control, including airborne pathogens, but threats posed by airborne pandemics and family-involvement in hospital care means cross-infection is still a potential problem. In its natural mode, ventilation driven by combined wind and buoyancy forces can lead to energy savings and achieve thermal comfort and high air change rates through secure openings. These are advantageous for controlling indoor airborne pathogens and external air and noise pollution. However, there is lack of detailed evidence and guidance is needed to gain optimum performance from available natural ventilation systems. This research is a proof of concept investigation into the feasibility and impact of natural ventilation systems targeting airflow rates, thermal comfort, heating energy and control of pathogenic bio-aerosols in hospital wards. In particular, it provides insights into the optimal areas of vent openings which could satisfy the complex three-pronged criteria of contaminant dilution, low heating energy and acceptable thermal comfort for occupants in a naturally ventilated single bed ward. The main aim of this thesis is the structured study of four systems categorised into three groups: Simple Natural Ventilation (SNV) in which single and dual-openings are used on the same external wall; Advanced Natural Ventilation (ANV) which is an emerging concept; and finally Natural Personalised Ventilation (NPV) which is an entirely new concept borne out of the limitations of previous systems and gaps in literature. The focus of this research is in the exploratory study of the weaknesses and potentials of the four systems, based on multi-criteria performances metrics within three architecturally distinct single-bed ward designs. In contributing to the body of existing knowledge, this thesis provides a better understanding of the performances of three existing systems while presenting the new NPV system. The analysis is based on dynamic thermal modelling and computational fluid dynamics and in the case of the NPV system, salt-bath experiments for validation and visualisation of transient flows. In all cases, wards were assumed to be free of mechanical ventilation systems that might influence the natural flow of air. The thesis meets three major objectives which have resulted in the following contributions to current knowledge: An understanding of the limitations and potentials of same-side openings, especially why and how dual-openings can be useful when retrofitted into existing wards. Detailed analysis of bulk airflow, thermal comfort, heating energy and room air distribution achievable from existing SNV and ANV systems, including insights to acceptable trickle ventilation rates, which will be particular useful in meeting minimum dilution and energy requirements in winter. This also includes qualitative predictions of the airflow pattern and direction obtainable from both systems. The innovation and study of a new natural ventilation system called Natural Personalised Ventilation (NPV) which provides fresh air directly over a patient s bed, creating a mixing regime in the space and evaluation of its comfort and energy performances. A low-energy solution for airborne infection control in clinical spaces is demonstrated by achieving buoyancy-driven mixing ventilation via the NPV system, and a derivative called ceiling-based natural ventilation (CBNV) is shown. A comparative analysis of four unique natural ventilation strategies including their performance rankings for airflow rates, thermal comfort, energy consumption and contaminant dilution or removal using an existing single-bed ward design as case study. Development of design and operational recommendations for future guidelines on utilising natural ventilation in single-bed wards either for refurbishment or for proposed designs. These contributions can be extended to other clinical and non-clinical spaces which are suitable to be naturally ventilated including treatment rooms, office spaces and waiting areas. The findings signify that natural ventilation is not only feasible for ward spaces but that there is opportunity for innovation in its application through further research. Future work could focus on related aspects like: impacts of fan-assisted ventilation for a hybrid flow regime; pre-heating of supply air; integration with passive heat recovery systems as well the use of full-scale experiments to fine-tune and validate findings.

We discuss a full-waveform based material profile reconstruction in two-dimensional heterogeneous semi-infinite domains. In particular, we try to image the spatial variation of shear moduli/wave velocities, directly in the time-domain, from scant surficial measurements of the domain's response to prescribed dynamic excitation. In addition, in one-dimensional media, we try to image the spatial variability of elastic and attenuation properties simultaneously. To deal with the semi-infinite extent of the physical domains, we introduce truncation boundaries, and adopt perfectly-matched-layers (PMLs) as the boundary wave absorbers. Within this framework we develop a new mixed displacement-stress (or stress memory) finite element formulation based on unsplit-field PMLs for transient scalar wave simulations in heterogeneous semi-infinite domains. We use, as is typically done, complex-coordinate stretching transformations in the frequency-domain, and recover the governing PDEs in the time-domain through the inverse Fourier transform. Upon spatial discretization, the resulting equations lead to a mixed semi-discrete form, where both displacements and stresses (or stress histories/memories) are treated as independent unknowns. We propose approximant pairs, which numerically, are shown to be stable. The resulting mixed finite element scheme is relatively simple and straightforward to implement, when compared against split-field PML techniques. It also bypasses the need for complicated time integration schemes that arise when recent displacement-based formulations are used. We report numerical results for 1D and 2D scalar wave propagation in semi-infinite domains truncated by PMLs. We also conduct parametric studies and report on the effect the various PML parameter choices have on the simulation error. To tackle the inversion, we adopt a PDE-constrained optimization approach, that formally leads to a classic KKT (Karush-Kuhn-Tucker) system comprising an initial-value state, a final-value adjoint, and a time-invariant control problem. We iteratively update the velocity profile by solving the KKT system via a reduced space approach. To narrow the feasibility space and alleviate the inherent solution multiplicity of the inverse problem, Tikhonov and Total Variation (TV) regularization schemes are used, endowed with a regularization factor continuation algorithm. We use a source frequency continuation scheme to make successive iterates remain within the basin of attraction of the global minimum. We also limit the total observation time to optimally account for the domain's heterogeneity during inversion iterations. We report on both one- and two-dimensional examples, including the Marmousi benchmark problem, that lead efficiently to the reconstruction of heterogeneous profiles involving both horizontal and inclined layers, as well as of inclusions within layered systems. / text

為了探討注意力與年齡因素對計時行為的影響，本實驗選用事前知道計時派典（prospective paradigm）與不涉及人為時間單位之知識的計時複製方式。針對注意力的因素，本研究採用雙重作業以操弄注意力資源集中或分散，檢測其對計時作業的影響。另針對年齡的因素，本研究比較低年級小學生、高年級小學生、及大學生成人三種不同年齡組的受試。 本研究利用四種計時作業，針對三個不同年齡層的受試進行對兩種不等的時距計時資料收集。計時作業及年齡因子的實驗設計採受試者間設計，而時距因子則採受試者內設計。研究結果發現（1）低年級組的計時準確性較高年級組或成人組差；（2）受試在雙重作業的計時表現的確較單一作業差，這個計時受干擾的結果，在複雜的雙重作業又較在簡單雙重作業明顯，且年紀愈小的受試所受干擾影響愈大；（3）三年齡層受試在雙重作業中皆有低估目標時距的現象，其中以低年級在複雜雙重作業中的低估程度最明顯；（4）低年級組的計時能力之穩定性較高年級或成人組低；（5）在無需對不斷出現之無意義刺激作偵測反應時，三年齡受試的計時準確性未受影響。 這些結果顯示計時的誤差的確隨著注意力需分派於非時間作業的增加，受試所複製的時距也隨之縮短。這項由於注意力分散所致的計時誤差在國小低年級組最明顯，但隨著年齡的成長及腦發展愈臻成熟，這項影響效果愈趨式微，致使計時的表現愈正確。 關鍵詞：時間複製、年齡與發展、雙重作業、注意力、小學生、純量計時 / The purpose of this study was to investigate the effects of the attention and age on time estimation based on the prospective timing paradigm. Four timing tasks, with different degrees of attentional requirement, were utilized to test timing of reproducing the target intervals in three groups of different ages including the lower-grade (M= 7.5 years), higher-grade (M= 11.2 years) elementary school students and adult (M= 20.1 years). The subjects in this work were asked to estimate a stimulus duration lasting for 7 or 14 s, during which they are required to either do or do not perform a concurrent non-temporal task. Thus, the experimental design for the present study was mixed with between-subject factors (age and task) and a within-subject factor (target interval). The results showed (1) the lower-grade children performed less accurate than the higher-grade children; (2) all subjects had worse timing performance in the dual-task condition than the single-task or control condition, which effect was most evident in the lower-grade children; (3) all subjects reproduced shorter interval as compared to the target interval, which effect was most apparently observed from the dual-task for the lower-grade children; (4) the lower-grade children had less reliability in timing; and (5) the effect of age on the single-task and control condition is not significant. Together, these data indicate that concurrent non-temporal task cause temporal reproduction shorter, especially under high attention demand in lower-grade children. In addition to the influence by the task complexity, the accuracy of timing estimation depends on the age. Keywords: time reproduction、age and development、dual task、attention、elementary school student、Scalar expectancy theory(SET)

Cette étude s'intéresse aux risques associés à la formation d'une ATmosphère EXplosive (ATEX) née d'une fuite d'hydrogène et de sa dispersion dans l'air ambiant. La fuite a été modélisée par un jet turbulent à densité variable libre, impactant sur une sphère de diamètre 20mm ou sur une plaque plane. Dans un premier temps, les champs de vitesses et de concentration ont été obtenus expérimentalement en proche sortie grâce à des mesures de Vélocimétrie par Images de Particules (PIV) et de Fluorescence Induite par Plan Laser sur l'acétone (PLIF). La turbulence et le mélange ont été caractérisés pour le cas d'un jet libre ou en présence d'un obstacle. A partir de ces mesures, la structure générale de l'écoulement a été étudiée à partir des champs moyens et fluctuants par comparaison avec les données de la bibliographie. Puis, les données issues des fluctuations ont été analysées statistiquement par l'étude des fonctions de densité de probabilité du scalaire. Ces travaux se sont poursuivis avec la mise en relation des résultats expérimentaux avec ceux obtenues par des simulations numériques DNS (Direct Numerical Simulation) utilisant la méthode Boltzmann sur Réseau (LBM) d'un scalaire passif dans un jet d'air. Cette étude a permis de recueillir et d'analyser des données supplémentaires sur le mélange d'un jet à masse volumique variable libre ou impactant. Ces données sont directement applicables à la maitrise des risques liés aux fuites d'hydrogène. / This study examines the risks associated with the formation of an explosive atmosphere from a hydrogen leak and its dispersion into the air. We considered the leak as a turbulent jet with density variable, free and impinging a $20,mm$ diameter sphere or a flat plate. Firstly, velocity and scalar fields have been measured experimentally in the near field through Particle Image Velocimetry (PIV) and acetone Planar Laser Induced Fluorescence (LIF). Turbulence and mixing have been defined in the case of free jet and impinging jet. From this measurements, the flow structure has been presented from the mean and fluctuating flow measurements by comparison with literature data. Next, the fluctuation scalar fields are studied with the probability density function method. Finally, a comparison has been conducted between the experiments and direct numerical simulation (DNS) of turbulence based on the lattice Boltzmann method (LBM) for passive scalar in air jet. This study is gathering and analyzing data on the mixing of jet with density variable, free and impinging jet. Such data is directly useful to identify and control risks incurred due to hydrogen leak.