<p>The development of fuel efficient internal combustion engines (ICE)have resulted in a variety of different solutions. One of those are the variable valve timing and an implemenation of such is the Continuous Variable Cam Phasing (CVCP). This thesis have used a simulation package, psPack, for the simulation of the gas exchange process for an ICE with CVCP. The purpose of the simulations was to investigate what kind of design parameters, e.g. the length of an intake pipe or the duration of combustion, that were significant for the gas exchange process with the alternation of intake pressure, engine speed and valve setting. The parameters that showed a vast impact were those who affected the amount of residual gas and the temperature of the air charge. Furthermore a validation was made between simulation data acquired from psPack and measured data provided in Heywood (1988). The validation showed that for the general behaviour the simulation results from psPack corresponded well to the measured data.</p>

We experimentally demonstrate an eight-state continuous-variable quantum key distribution (CV-QKD) over atmospheric turbulence channels. The high secret key rate (SKR) is enabled by 4-D multiplexing of 96 channels, i.e., six-channel wavelength-division multiplexing, four-channel orbital angular momentum multiplexing, two-channel polarization multiplexing, and two-channel spatial-position multiplexing. The atmospheric turbulence channel is emulated by a spatial light modulator on which a series of azimuthal phase patterns yielding Andrews' spectrum are recorded. A commercial coherent receiver is implemented at Bob's side, followed by a phase noise cancellation stage, where channel transmittance can be monitored accurately and phase noise can be effectively eliminated. Compared to four-state CV-QKD, eight-state CV-QKD protocol potentially provides a better performance by offering higher SKR, better excess noise tolerance, and longer secure transmission distance. In our proposed CV-QKD system, the minimum transmittances of 0.24 and 0.26 are required for OAM states of 2 (or -2) and 6 (or -6), respectively, to guarantee the secure transmission. A maximum SKR of 3.744 Gb/s is experimentally achievable, while a total SKR of 960 Mb/s can be obtained in case of mean channel transmittances.

The development of fuel efficient internal combustion engines (ICE)have resulted in a variety of different solutions. One of those are the variable valve timing and an implemenation of such is the Continuous Variable Cam Phasing (CVCP). This thesis have used a simulation package, psPack, for the simulation of the gas exchange process for an ICE with CVCP. The purpose of the simulations was to investigate what kind of design parameters, e.g. the length of an intake pipe or the duration of combustion, that were significant for the gas exchange process with the alternation of intake pressure, engine speed and valve setting. The parameters that showed a vast impact were those who affected the amount of residual gas and the temperature of the air charge. Furthermore a validation was made between simulation data acquired from psPack and measured data provided in Heywood (1988). The validation showed that for the general behaviour the simulation results from psPack corresponded well to the measured data.

Ce manuscrit porte sur l’étude théorique de techniques expérimentales récemment développées pour réaliser des protocoles d’information quantique en variables continues. Les états Gaussiens multi-modes produits par conversion paramétrique de peignes de fréquences optiques jouent un rôle centrale dans ce travail. Ce phénomène permet de générer de façon déterministe un grand nombre d’états Gaussiens de la lumière. L’état de sortie peut ensuite être de-Gaussifié par soustraction ou addition d’un photon dans une superposition cohérente de modes du champ, puis mesuré par détection homodyne. La thèse est organisée en trois projets principaux. Le premier concerne l’optimisation du spectre du laser de pompe pour manipuler l’état de sortie de la conversion paramétrique. Nous avons développé les outils mathématiques pour traiter des profils spectraux avec amplitude et phase spectrales arbitraires. On a ensuite utilisé un algorithme d’optimisation pour trouver les spectres maximisant des différentes propriétés de l’état de sortie. Une importance particulière est donnée à la production d’"états cluster" en variables continues. Les optimisations ont été développées pour prendre en compte les limitations expérimentales pour assurer la faisabilité des forme spectrales dans les expériences. Dans le deuxième projet nous avons étudié comment les états non-Gaussiens obtenus par soustraction d’un photon d’un état comprimé peuvent être utilisés pour le calcul quantique. Nous proposons un protocole inspiré par le paradigme de "calcul quantique basé sur la mesure" qui combine l’état de-Gaussifié et la mesure homodyne pour approximer des opérateurs unitaires non-Gaussiens. On montre que les mêmes résultats peuvent être obtenus avec des mesure projectives sur des états de photon unique. Finalement, le troisième projet porte sur le partage de secret quantique ("quantum secret sharing"). Dans les protocoles de partage de secret quantique un donneur veut distribuer de l’information codée dans un système quantique à plusieurs joueurs d’une façon qui oblige des sous-ensembles de joueurs à collaborer s’ils veulent retrouver l’information originale. Nous avons développé un protocole qui peut être transféré aux expériences de notre groupe et nous avons participé à la formulation d’une preuve de concept expérimentale. À partir de cela, nous avons dérivé des résultats généraux sur le partage et la reconstruction d’états arbitraires de la lumière en utilisant des ressources Gaussiennes. / The present manuscript reports theoretical investigations about the use of recently developed experimental techniques in the realization of quantum information protocols with continuous variables. The focus of the work is on the multi-mode Gaussian states produced by spontaneous parametric down-conversion of optical frequency combs. Such setup allows to deterministicallyengineer many different Gaussian states of light. The output state can be de-Gaussified subtracting or adding a photon coherently on a superposition of modes and finally measured with pulse-shaped and wavelength-multiplexed homodyne detection. The thesis encompasses three projects. The first concerns the optimization of the spectrum of the pump laser field to engineer the Gaussian output state. We developed mathematical techniques to treat spectral profiles with arbitrary amplitude and spectral phase. We thenran an optimization algorithm to find the spectra maximizing several interesting properties of the state of the down-converted field. A particular emphasis was put on the production of continuous-variable cluster states. The optimizations were developed in such a way as to ensure the experimental feasibility of the optimized pump spectra. In the second project we studied how the non-Gaussian states produced subtracting a photon from a squeezed state can be used for quantum computation. We propose a protocol inspired by the measurement-based paradigm for quantum computation combining the photon subtracted states and homodyne detectionto approximate unitary non-Gaussian operations. We show that the same results can be obtained with projective measurements onsingle-photon states. Finally, the third project deals with quantum secret sharing. In quantum secret sharing schemes a dealer wants to share information encoded in some quantum system with a group of players in such a way that subsets of players need to collaborate if they want to retrieve the information. We devised a secret sharing protocol that could be mapped to the experimental setups developed in our group and participated in the formulation of an experimental proof of principle of such protocol. Starting from this we derived general results for sharing and reconstructing arbitrary quantum states using Gaussian resources.

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In clinical research, it is sometimes desirable to dichotomize a continuous variable so that the information expressed using a dichotomous variable is more straightforward for clinicians to interpret and communicate. The distribution of a continuous variable can differ between two populations defined by the case status. Under such a scenario, the dichotomization process can be based on distributions of the continuous variable in two distinct populations. The resulting dichotomous variable can be used as an endpoint in future studies. Even though dichotomization has not been extensively studied, dichotomization has been commonly carried out in clinical trials. We developed a methodology on dichotomization based on maximizing the correlation between the two populations and the dichotomous variable. We have investigated several commonly assumed distributions (e.g., normal, log-normal and gamma distribution) of the continuous variable for the two populations and developed a numerical algorithm for the proposed method to determine the optimal cutoff point. The two populations can differ in form and/or parameters. The proposed method of finding the optimal cutoff was also extended to adjust for covariates. In real world scenarios where the two samples from the two populations are not completely identified, we recommended using the EM method to first estimate the parameters associated with the two populations before applying the proposed method to find the optimal cutoff point. The performance of the proposed method with the numerical algorithm and the EM method has been studied for several theoretical distributions and using simulated data. These methods were also applied to a varicella vaccine example. / Statistics

Orientador: Júlio Carlos Teixeira / Dissertação (mestrado) - Universidade Federal do ABC. Programa de Pós-Graduação em Energia

We experimentally demonstrate a RF-assisted four-state continuous-variable quantum key distribution (CV-QKD) system in the presence of turbulence. The atmospheric turbulence channel is emulated by two spatial light modulators (SLMs) on which two randomly generated azimuthal phase patterns are recorded yielding Andrews' azimuthal phase spectrum. Frequency and phase locking are not required in our system thanks to the proposed digital phase noise cancellation (PNC) stage. Besides, the transmittance fluctuation can be monitored accurately by the DC level in this PNC stage, which is free of post-processing noise. The mean excess noise is measured to be 0.014, and the maximum secret key rate of >20Mbit/s can be obtained with the transmittance of 0.85, while employing the commercial PIN photodetectors.

The compromise between ride comfort and handling for a passive suspension system is a well-known and often researched problem. Semi-active suspension systems offer significant improvements to this compromise. One example of a semi-active system, that can change both spring and damper characteristics between two discrete values is the 4-state semi-active hydro-pneumatic suspension system. This system can switch between a ”ride comfort mode” (soft spring and low damping) and a ”handling mode” (stiff spring and high damping) within 100ms, improving both ride comfort and handling. The discrete 4S4 could be improved upon further by adding continuous variable damping. Work on this topic showed great promise but also posed its challenges in achieving this in a safe and controllable manner. In order to make continuous variable damping a reality a new configuration for the 4S4 is proposed. This new configuration incorporates a blow-off damper in parallel with a proportional flow control valve. The system ensures that, in the highly non-linear closing region of the proportional flow control valve, adequate damping for handling is maintained and uncontrollable peak pressure differences are avoided. Experimental work conducted showed that the system was capable of achieving the required spring and variable damping characteristics in a safe and controllable manner. The experimental data was used for parametrizing and validating a physics based mathematical model of the suspension system. The mathematical model incorporates the: pressure drop vs: flow characteristics for both the blow-off and proportional valves, response time for the on-off valves as well as the gas pressure vs: flow characteristic incorporating the compressibility of the oil and thermal properties of the gas. This model can be used to make informed decisions on further prototype development or in full vehicle simulations. The system makes continuous variable damping possible ranging from the optimal damping characteristic for handling to the low damping characteristic required for ride comfort. The system also shows a significant reduction in friction. / Dissertation (MEng)--University of Pretoria, 2020. / VDG / University of Pretoria / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Les évolutions récentes de la cryptographie quantique ont permis de proposer sur le marché des appareils de distribution quantique de clé secrète (QKD). Ceci est obtenu en utilisant soit des variables discrètes et des compteurs de photons (DV), soit des variables continues et des systèmes de détection cohérente (CV). Les avancées technologiques s'orientent maintenant vers la réalisation de dispositifs plus petits, moins chers, et plus commodes à utiliser.L'objectif de cette thèse est de mettre en oeuvre un protocole CV-QKD sur un circuit optique intégré en silicium, en utilisant une modulation Gaussienne d'états cohérents. Deux approches sont utilisées: dans la première l'émetteur Alice et le récepteur Bob sont sur le même circuit photonique (chip) pour une validation de principe, et dans la deuxième ils sont séparés.Les valeurs mesurées des paramètres de la communication permettent d'échanger une clé secrète. / During recent years there have been significant developments in quantum cryptography, bringing quantum key distribution (QKD) devices on the market. This can be done by using either discrete variables (DV) and photon counting, or continuous variables (CV) and coherent detection. Current technological evolutions are now aiming at developing smaller, cheaper and more user-friendly devices.This work focuses on the implementation of CV-QKD using silicon photonics techniques, which provide a high degree of integration. This is exploited to build an on-chip realization of a cryptographic protocol, using Gaussian modulation of coherent states. Two different approaches have been used, first by physically implementing the sender (Alice) and the receiver (Bob) on the same chip for validation purposes, and then by having them onto two separate chips. The measured communication parameters give the possibility to extract a secret key