Safety and reliability are one of the key objectives for future Generation IV nuclear energy systems. The neutron flux monitoring system forms an integral part of the safety design of a nuclear reactor and must be able to detect any irregularities during all states of reactor operation. The work in this thesis mainly concerns the detection of in-core perturbations arising from unwanted movements of control rods with in-vessel neutron detectors in a sodium-cooled fast reactor. Feasibility study of self-powered neutron detectors (SPNDs) with platinum emitters as in-core power profile monitors for SFRs at full power is performed. The study shows that an SPND with a platinum emitter generates a prompt current signal induced by neutrons and gammas of the order of 600 nA/m, which is large enough to be measurable. Therefore, it is possible for the SPND to follow local power fluctuations at full power operation. Ex-core and in-core detector locations are investigated with two types of detectors, fission chambers and self-powered neutron detectors (SPNDs) respectively, to study the possibility of detection of the spatial changes in the power profile during two different transient conditions, i.e. inadvertent withdrawal of control rods (IRW) and one stuck rod during reactor shutdown (OSR). It is shown that it is possible to detect the two simulated transients with this set of ex-core and in-core detectors before any melting of the fuel takes place. The detector signal can tolerate a noise level up to 5% during an IRW and up to 1% during an OSR.

Message Authentication Codes (MACs) are valuable tools for ensuring the integrity of messages. MACs may be built around a keyed hash function. Our main motivation was to prove that universal hash functions can be employed as underlying primitives of MACs in order to provide provable security in ultra-low-power applications such as the next generation self-powered sensor networks. The idea of using a universal hash function (NH) was explored in the construction of UMAC. This work presents three variations on NH, namely PH, PR and WH. The first hash function we propose, PH, produces a hash of length 2w and is shown to be 2^(-w)-almost universal. The other two hash functions, i.e. PR and WH, reach optimality and are proven to be universal hash functions with half the hash length of w. In addition, these schemes are simple enough to allow for efficient constructions. To the best of our knowledge the proposed hash functions are the first ones specifically designed for low-power hardware implementations. We achieve drastic power savings of up to 59% and speedup of up to 7.4 times over NH. Note that the speed improvement and the power reduction are accomplished simultaneously. Moreover, we show how the technique of multi- hashing and the Toeplitz approach can be combined to reduce the power and energy consumption even further while maintaining the same security level with a very slight increase in the amount of key material. At low frequencies the power and energy reductions are achieved simultaneously while keeping the hashing time constant. We develope formulae for estimation of leakage and dynamic power consumptions as well as energy consumption based on the frequency and the Toeplitz parameter t. We introduce a powerful method for scaling WH according to specific energy and power consumption requirements. This enables us to optimize the hash function implementation for use in ultra-low-power applications such as "Smart Dust" motes, RFIDs, and Piconet nodes. Our simulation results indicate that the implementation of WH-16 consumes only 2.95 ìW 500 kHz. It can therefore be integrated into a self- powered device. By virtue of their security and implementation features mentioned above, we believe that the proposed universal hash functions fill an important gap in cryptographic hardware applications.

Climate change is a significant issue in today's society as countries work towards decarbonising the economic sectors that contribute to significant greenhouse gas emissions. The electric vehicle (EV) is proposed as a solution to reduce the level of emissions in the transport sector. However, if an EV is powered by an electrical fossil fuelled source, their penetration into the UK market will have minimal mitigating effects, as emissions will simply shift from the transport sector to the energy production sector. Limited research has evaluated the loss of propulsion energy as a result of operating on-board climate control systems, and has focused more on traction energy. Unlike conventional fossil fuelled vehicles, EVs do not produce waste heat to warm the interior space of the vehicle. The present research found that up to 30% of a vehicle's total energy consumed per trip is allocated to heating requirements, thus the present research developed a temperature predicting numerical algorithm to compute indoor cabin temperatures. The vehicle was exposed to ambient climate conditions with an auxiliary heating or cooling system to evaluate this thermal model. The numerical algorithm could predict the temperature of a cabin space under solar space heating conditions with 62% more accuracy than previously developed models when comparing the Root Mean Square Error performance indicator. The presently developed temperature prediction algorithm may be applied to a route planning application, thus indicating the electrical energy required by the vehicle's battery for users to increase or decrease the desired temperature level. Additionally, this study investigated the ability of a renewable energy resource to decarbonise the vehicle's built-in climate control system. Integrating solar panels on the roof and bonnet of an EV to power an auxiliary climate control system reduced the electrical loading required to reach the occupant's thermal comfort. By installing an auxiliary heating system to increase cabin temperature by 2 or 5°C, the present research found that energy consumption of the built-in climate control system was reduced by 22% or 57%, respectively. This illuminates the potential an auxiliary climate control system has in improving the thermal performance of EVs.

With the rapid progress of nanotechnologies, there are two developing trends for the next generation of sensors: miniaturization and multi-functionality. Device miniaturization requires less power consumption, or even self-powered system. Multi-functional devices are usually based on multi-property coupling effects. Piezoelectric semiconductors have been considered to be potential candidates for self-powered/multi-functional devices due to their piezotronic coupling effect. In this dissertation, ZnO and CdSe nanowire arrays have been synthesized as the piezoelectric semiconductor materials to develop the following self-powered/multi-functional sensors: (1) self-powered gas sensors of ZnO/SnO2, ZnO/In2O3, ZnO/WO3 and CdSe nanowire arrays have been assembled. All these gas sensors are capable of detecting oxidizing gas and reducing gas without any external power supply owing to piezotronic effect which can convert mechanical energies to electrical energy to power the sensors; (2) a self-powered ZnO/ZnSe core/shell nanowire array photodetector has been fabricated. This photodetector is able to detect the entire range of the visible spectrum as well as UV light because of its type II heterostructure. The absolute sensitivity and the percentage change in responsivity of the photodetector were significantly enhanced resulting from the piezo-phototronic effect. The photodetector also exhibited self-powered photodetection behavior; (3) three dimensional nanowire arrays, such as ZnO and ZnO/Co3O4, have been synthesized to investigate piezo-magnetotronic and piezo-photo-magnetotronic effects. Under magnetic field, the magnetic-induced current of ZnO nanowire array decreased as magnetic field increased, and the current difference was magnified by one order of magnitude caused by piezo-magnetotronic effect through applying a stress. In contrast, under UV light illumination, the current response increased with an increment of magnetic field. The current difference was enhanced by at least two orders of magnitude attributed to piezo-photo-magnetotronic effect. Furthermore, ZnO/Co3O4 core/shell structure was employed to further improve the magnetic-induced current difference. This phenomenon projects a potential for multi-functional piezo-magnetotronic and piezo-photo-magnetotronic device development.

A linear covariance analysis is conducted to assess closed-loop guidance, navigation, and control system (GN&C) performance of the Altair vehicle during lunar powered descent. Guidance algorithms designed for lunar landing are presented and incorporated into the closed-loop covariance equations. Navigation-based event triggering is also included in the covariance formulation to trigger maneuvers and control dispersions. Several navigation and guidance trade studies are presented demonstrating the influence of triggering and guidance and study parameters on the vehicle GN&C performance.

In this thesis, X-ray and optical observations of accretion powered pulsars are presented. By using archival RXTE observations we work on the X-ray spectral and pulse timing analysis of 4U 1538-52, 4U 1907+09, SMC X-1 to have more detailed information about their orbital and spin parameters. For 4U 1538-52 and SMC X-1, we determined new orbital epochs. By using long term pulse history of 4U 1907+09, we were able to work spin-down trend of the system and also calculate the change in the spin-down rate. Using Fermi/GBM observations we can monitor bright accreting pulsar systems. We are producing long term histories of pulse frequency and flux of 20 continuosly monitoring systems. Adding Swift/BAT observations to GBM observations, for 4U 1626-67, we did reveal the characteristics belong to spin-down trend before and spin-up behaviour after torque reversal seen in 2008 February. Two newly discovered IGRJ06074+2205 and IGRJ01583+6713 sources are identified as X-ray binary systems and we found parameters of them like distance, magnitudes, by using both optical photometric and spectroscopic observations.

Energy harvesting and energy storage are two most important technologies in today's green and renewable energy science. As for energy harvesting, the fundamental science and practically applicable technologies are not only essential in realizing the self-powered electronic devices and systems, but also tremendously helpful in meeting the rapid-growing world-wide energy consumptions. Mechanical energy is one of the most universally-existing, diversely-presenting, but usually-wasted energies in the natural environment. Owing to the limitations of the traditional technologies for mechanical energy harvesting, it is highly desirable to develop new technology that can efficiently convert different types of mechanical energy into electricity. On the other hand, the electricity generated from environmental energy often needs to be stored before used to drive electronic devices. For the energy storage units such as Li-ion batteries as the power sources, the limited lifetime is the prominent problem. Hybridizing energy harvesting devices with energy storage units could not only provide new solution for this, but also lead to the realization of sustainable power sources. In this dissertation, the research efforts have led to several critical advances in a new technology for mechanical energy harvesting—triboelectric nanogenerators (TENGs). Previous to the research of this dissertation, the TENG only has one basic mode—the contact mode. Through rational structural design, we largely improved the output performance of the contact-mode TENG and systematically studied their characteristics as a power source. Beyond this, we have also established the second basic mode for TENG—the lateral sliding mode, and demonstrated sliding-based disk TENGs for harvesting rotational energy and wind-cup-based TENGs for harvesting wind energy. In order to expand the application and versatility of TENG by avoid the connection of the electrode on the moving part, we further developed another basic mode—freestanding-layer mode, which is capable of working with supreme stability in non-contact mode and harvesting energy from any free-moving object. Both the grating structured and disk-structured TENGs based on this mode also display much improved long-term stability and very high energy conversion efficiency. For the further improvement of the TENG’s output performance from the material aspect, we introduced the ion-injection method to study the maximum surface charge density of the TENG, and for the first time unraveled its dependence on the structural parameter—the thickness of the dielectric film. The above researches have largely propelled the development of TENGs for mechanical energy harvesting and brought a big potential of impacting people’s everyday life. Targeted at developing sustainable and independent power sources for electronic devices, efforts have been made in this dissertation to develop new fundamental science and new devices that hybridize the nanogenerator-based mechanical energy harvesting and the Li-ion-battery-based energy storage process into a single-step process or in a single device. Through hybridizing a piezoelectric nanogenerator with a Li-ion battery, a self-charging power cell has been demonstrated based on a fundamentally-new mechanical-to-electrochemcial process. The triboelectric nanogenerator as a powerful technology for mechanical energy harvesting has also been hybridized with a Li-ion battery into a self-charging power unit. This new concept of device can sustainably provide a constant voltage for the non-stop operation of electronic devices.

Submitted by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2018-09-17T17:22:44Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_impressao.pdf: 2956113 bytes, checksum: e6a4b36626de2a1892da7e9ffd7ac14a (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2018-09-17T17:22:55Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_impressao.pdf: 2956113 bytes, checksum: e6a4b36626de2a1892da7e9ffd7ac14a (MD5) / Made available in DSpace on 2018-09-17T17:22:55Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_impressao.pdf: 2956113 bytes, checksum: e6a4b36626de2a1892da7e9ffd7ac14a (MD5) Previous issue date: 2018-08-10 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Currently, diverse existing training environments help new users of electric powered wheelchairs (EPW) learn how to drive, acquaint and improve their abilities with these assistive devices. Several authors are developing such environments, and most of them use virtually simulated wheelchairs. Despite the similarities between virtual and real wheelchairs, it is easier to drive the real device because representation of the wheelchair physical behavior is still a problem for virtual simulated environments. Concerning the driving methods, most of them are based on a joystick, which does not give the opportunity for users to test, practice and acquaint themselves with new technologies, such as driving through eye movements. This work implements and tests a more realistic approach for a training environment dedicated to new users of EPW. The proposed system is based on a real EPW controlled by teleoperation, and it is flexible enough to attend to multiple driving methods. An architecture that allows a user to send command messages to control a real EPW through the Internet was implemented to validate the system. The implemented driving methods were conventional joystick, eye-tracker and a generic human-machine interface. For the system’s evaluation, scenarios were created considering the implemented driving methods, and also scenarios considering a long distance teleoperation. The experimental results suggest that new users can practice safely using a real EPW through the Internet, even in a situation with a communication delay of 130.2 ms (average). Furthermore, the proposed system showed potential for attending new EPW users with different types of disabilities and to be a low-cost approach that could be applied in developing countries. / Atualmente, diversos ambientes de treinamento existentes ajudam novos usuários de cadeira de rodas motorizada (CRM) a aprender a comandar, se familiarizar e aprimorar suas habilidades. Vários autores estão desenvolvendo esses ambientes, e a maioria deles está usando CRM virtualmente simulada. Apesar das semelhanças entre a CRM virtual e a real, observouse que é mais fácil comandar o dispositivo real. Isso ocorre porque nesses ambientes virtuais, a representação do comportamento físico da CRM ainda é um problema. Outro aspecto observado, foi a respeito dos métodos de condução, onde a maioria dos trabalhos utiliza apenas o joystick. Porém, esse método não oferece a oportunidade a usuários com deficiência severa de aprender a comandar a partir de novas tecnologias, como por exemplo, o rastreamento ocular. Para superar essas dificuldades, este trabalho propõe, implementa e valida uma abordagem mais realista, a qual é baseada em treinamento por teleoperação e por múltiplos métodos de condução. Foi implementada uma arquitetura que permite ao usuário enviar comandos remotamente para comandar uma CRM real a longas distâncias. Os métodos de condução implementados foram por joystick, eye-tracker e por meio de uma interface humanomáquina genérica. Para a avaliação do sistema, foram criados cenários considerando diferentes configurações. Os resultados experimentais sugerem que novos usuários podem praticar com segurança utilizando uma CRM real através da Internet, mesmo em uma situação com delay de 130,2 ms (média). O sistema proposto mostrou potencial em atender novos usuários de CRM com diferentes tipos de deficiência, bem como de ser uma abordagem de baixo custo com possibilidade de ser aplicada em países em desenvolvimento.

Cette dissertation modélise et analyse les flux de trafic hétérogènes, avec une attention particulière portée à la circulation de voitures et de deux-roues. L'augmentation du nombre de congestions de trafic a forcé les personnes désirant se déplacer à se diriger vers les le deux-roues (appelé ici PTWs = powered two wheelers), comme les motos, les mopeds et les scooters, du fait de leur facilité de manoeuvre et leur efficacité dans l'espace. L'augmentation du nombre de PTWs combinée au caractère unique de certaines de leurs fonctionnalités a résulté en un trafic complexe, donc les particularités sont difficiles à recréer avec les approches de modélisation existantes. Nous développerons ici un modele analytique permettant de reproduire de manière pertinente les particularités d'un flux de véhicules mêlant à la fois les voitures et les deux-roues. Le trafic se décompose en deux classes de véhicules : les PTWs et les voitures. Les propriétés fondamentales sont déduites en employant une approche "porous flow". On suppose que la vitesse d'un véhicule d’une certaine classe est dictée par les propriétés physiques et motrices du véhicule, ainsi que la distribution d'espace vide sur la route. Nous proposons une méthode d'approximation pour dériver la distribution d'espace vide. Dans le but d'explorer plus largement les caractéristiques du flux de trafic notamment requis par les applications de système de transport intelligent (ITS), nous formulons le modèle dans les cadres lagrangien et eulérien. Puis, nous feront appel à une méthode numérique pour la discrétisation du modèle mathématique. Se basant sur le modèle développé nous analyserons les caractéristiques du flux de trafic pour en identifier les propriétés les plus importantes qui nous permettrons de prédire de futures ITS applications et d'organisations du trafic. La possibilité d'appliquer le modèle pour les différentes ITS applications est illustrée par des exemples. Finalement, le modèle développé est validé à l'aide de l'outil de microsimulation. / This dissertation models and analyzes heterogeneous traffic flow, with a particular focus on mixed traffic flow consisting of cars and two-wheelers. The increase in traffic congestion induces commuters to switch to powered two wheelers (PTWs), i.e. motorcycle, mopeds and scooters, because of their high maneuverability and space efficiency. The growth in number of PTWs, combined with their unique mobility features, results in complex traffic characteristics which are difficult to recreate with the existing modeling approaches. We develop an analytical model that can accurately reproduce the traffic features in a mixed flow of cars and PTWs. The traffic stream is decomposed into two vehicle classes, PTWs and cars. The fundamental properties are derived by employing a porous flow approach. It is assumed that the speed of a vehicle class is dictated by the physical and motion properties of the vehicle class, and the distribution of free spaces on the road. We propose an approximation method to derive the free-space distribution. In order to explore broader aspects of the traffic flow characteristics, notably required by intelligent transport system (ITS) applications, we formulate the model in the Lagrangian and the Eulerian frameworks. Further, we provide a numerical method for the discretization of the mathematical model. We analyze the flow characteristics of mixed PTWs and cars traffic and identify important properties, which give insights for future ITS solutions and traffic policy makers. The applicability of the model for different ITS applications is illustrated. Finally, the developed model is validated using a microsimulation tool.

The aim of this diploma thesis is the design of the differential of a road vehicle driven by a human force, intended for daily driving in the city with a focus on older users. The vehicle for which the differential is designed is strictly a pedal tricycle. The introduction of this thesis briefly outlines the history of pedal tricycles. The second chapter explains some technical terms relating to tricycles and bicycles in general. Further chapters of the research part describe the current structures of tricycles, the principle of a differential function in motor vehicles and design possibilities of the differential for pedal tricycles. The practical part of my work includes the design of a differential for pedal tricycle, the strength analysis of selected parts of the differential, drawings of the differential assembly, production drawings of selected parts and proposal of the torque transfer from pedals to the differential.