As the demand for green energy and fuel cells grows, more attention is drawn towards Solid Oxide Fuel Cells (SOFCs). Random and complex structure of composite electrodes and underlying electrochemical process has not been completely unveiled yet and further study is required to acquire more understanding. Modeling in this regard plays an important role as it pinpoints key parameters in optimum design of the cell without resorting to costly and uncertain experiments which might even lead to misinterpretations due to random nature of experimental data. The aim of this work is to develop a new rigorous model to study the structure performance relationship of (SOFC) composite electrodes. The work has been conducted in two phases, a two-dimensional continuous approach and three-dimensional discrete model. A new two-dimensional, geometrical model which captures the inhomogeneous nature of the location of electrochemical reactions based on random packing of electronic and ionic conducting particles has been developed. The results show that the concentration of oxygen inside the cathode in the two-dimensional model is not only a function of the electrode depth but also changes along the width of the electrode. Furthermore the effect of composition of the electrode on the length of three phase boundary (TPB) and total polarization resistance has been demonstrated. A parametric study of the effect of the conductivity of ionic conductor and diffusion coefficient on the performance of the electrode has been given. To make a more realistic analysis, a three-dimensional reconstruction of (SOFC) composite electrodes was developed to evaluate the performance and further investigate the effect of microstructure on the performance of electrodes. To enhance connectivity between particles and increase the length of TPB, sintering process is mimicked by enlarging particles to certain degree. Geometrical characteristics such as length of TBP and active contact area as well as porosity can easily be calculated using the current model. Electrochemical process is simulated using resistor-network model and complete Butler-Volmer equation is used to deal with charge-transfer process on TBP. The model shows that TPBs are not uniformly distributed across the electrode and location of TPBs as well as amount of electrochemical reaction is not homogeneous. Effects of particle size, electrode thickness, particle size ratio, electron and ion conductor conductivities and rate of electrochemical reaction on overall electrochemical performance of electrode are investigated. / Chemical Engineering

Bandgap reference circuits are used in a host of analog, digital, and mixed-signal systems to establish an accurate voltage reference for the entire IC. The most used CMOS implementation for voltage references is the bandgap circuit due to its high predictability, and low dependence of the supply voltage and temperature of operation. This work studies a CMOS implementation of a resistor-less bandgap reference, which consumes low power. The most relevant and traditional approaches usually employed to implement bandgap voltage references are investigated. The impact of process, power-supply, load and temperature variations has been analyzed and simulated. The functionality of critical components of the circuit has been verified through chip implementation. / text

No description available.

Submitted by Marco Antônio de Ramos Chagas (mchagas@ufv.br) on 2017-02-07T09:44:57Z No. of bitstreams: 1 texto completo.pdf: 699097 bytes, checksum: 8f579eaacf25441c936f22bf65466f29 (MD5) / Made available in DSpace on 2017-02-07T09:44:57Z (GMT). No. of bitstreams: 1 texto completo.pdf: 699097 bytes, checksum: 8f579eaacf25441c936f22bf65466f29 (MD5) Previous issue date: 2002-03-23 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Os objetivos deste trabalho foram: coletar dados referentes à radiação global refletida para dois diferentes tipos de superfícies, isto é com vegetação (plantas daninhas dicotiledôneas e monocotiledôneas) e sem vegetação (palhada de trigo e solo), utilizando dois tipos de filtro (verde e transparente), desenvolver um programa computacional em linguagem assembly para o sistema eletrônico de baixo custo, que detecta a presença de plantas daninhas e controle da vazão do herbicida, bem como determinar o tempo de resposta do sistema, a resolução da área de visão do sensor e testá-lo em condições ambientais simuladas (temperatura, umidade relativa e poeira) e em campo. Na medida da resistência elétrica na coleta de dados estáticos a radiação global incidente (X) tem correlação com a radiação global refletida (Y), para as superfícies recobertas com plantas daninhas dicotiledôneas, em que Y = 63,72X - 8.711,83 (r 2 = 0,97) para o filtro verde e Y = 25,10X - 3.056,55 (r 2 = 0,97) para o filtro transparente e, para a grama - seda, Y = 71,00X - 9.636,74 (r 2 = 0,98) para o filtro verde e Y = 25,84X - 2.852,53 (r 2 = 0,99) para o filtro transparente, enquanto para a palhada de trigo Y = 45,64X - 5.985,84 (r 2 = 0,98) para o filtro verde e Y = 12,58X - 1.243,26 (r 2 = 0,99) para o filtro transparente e, para o solo, Y = 37,77X - 5.259,39 (r 2 = 0,97) para o filtro verde e Y = 9,87X - 1.002,79 (r 2 = 0,98) para o filtro transparente. Foram desenvolvidos dois programas computacionais, sendo um para o filtro verde e o outro para o transparente, utilizando-se, como referência, a equação da palhada pelo fato de refletir mais luz que as folhas e menos que o solo. A resolução da área de visão do sensor foi 23% para o filtro transparente e 73% para o filtro verde, devido à não otimização das equações para este filtro. O tempo de resposta foi determinado, somente, para o filtro transparente sendo de 0,08 segundos porque este filtro apresentou menor área de sensibilidade. Os testes feitos em condições simuladas não apresentaram nenhuma anomalia quanto ao funcionamento do protótipo, enquanto os testes de campo mostraram uma eficácia de 100% no controle das plantas daninhas. / The objectives of this work were: to collect referring data to the global radiation contemplated for two different types of surfaces, that is with vegetation (plants harmful dicotyledon and monocotyledon) and without vegetation (wheat strow and soil), using two filter types (green and transparent), to develop a program computation in language assembly for the electronic system of low cost, that detects the presence of harmful plants and control of the flow of the herbicides, as well as to determine the time of answer of the system, the resolution of the area of vision of the sensor and to test it in simulate environmental conditions (temperature, relative humidity and dust) and in field. In the measure of the electric resistance in the collection of static data the incident global radiation (X) he/she has correlation with the reflected global radiation (Y), for the surfaces covered with plants harmful dicotyledon, in that Y = 63,72X - 8.711,83 (r 2 = 0,97) for the green filter and Y = 25,10X - 3.056,55 (r 2 = 0,97) for the transparent filter and, for the gram - silk, Y = 71,00X - 9.636,74 (r 2 = 0,98) for the green filter and Y = 25,84X - 2.852,53 (r 2 = 0,99) for the transparent filter, while for the wheat strow Y = 45,64X - 5.985,84 (r 2 = 0,98) for the green filter and Y = 12,58X - 1.243,26 (r 2 = 0,99) for the transparent filter and, for the soil, Y = 37,77X - 5.259,39 (r 2 = 0,97) for the green filter and Y = 9,87X - 1.002,79 (r 2 = 0,98) for the transparent filter. Two programs computation was developed, being one for the green filter and the another for the transparent, being used, as reference, the equation of the strow for the fact of reflecting more light than the leaves and less than the soil. The resolution of the area of vision of the sensor was 23% for the transparent filter and 73% for the green filter, due to the non optimization of the equations for this filter. The time of answer was determined, only, for the transparent filter being of 0,08 seconds because this filter presented smaller sensibility area. The tests done in simulate conditions didn't present any anomaly with relationship to the operation of the prototype, while the field tests showed an effectiveness of 100% in the control of the harmful plants. / Tese importada do Alexandria

Building Information Modeling, abbreviated BIM, is a process of information sharing which enhances communication and which helps in visualizing complex problems in the building industry. BIM has not been used in a larger extent in the production phase of civil works. The purpose of the study is therefore to investigate driving forces behind the use of BIM and the resistors against it and to investigate in what ways BIM could be used in the production phase. The theoretical framework is based on one licentiate thesis, two degree projects, three research papers and three books. A qualitative method with semi-structured interviews was used. The interviews were made with a calculator, a supervisor and a CAD planner from Skanska, a constructor and project manager from ELU, a Project Information Officer from Tyréns and a VDC coordinator and VDC business developer from Veidekke who all have been working with BIM. This was to get a good representation from different actors and people with different professional roles. The study shows that the driving forces behind a use of BIM are that it enhances collaboration and communication between the actors, it makes it easier to visualize the project and the scope, and it provides a higher degree of accuracy of coordination’s. BIM also makes the work more effective and results in fewer errors. Above all, BIM give a possibility for a shorter production phase, shorter total project duration and a lower total cost. The study also shows that the resistors against the use of BIM are employee’s negative attitude against administrative work, that it is hard to measure profitability of using BIM, the uncertainty of who has the legal ownership of the data, and who has the responsibility of the accuracy of it. 3 That the implementation cost and the design phase are more expensive is also a resistor against a use of BIM. BIM could be used in visualization with 3D models in collision controls and co-reviews in meetings, work preparations and at site. A workplace outline could also be printed from the 3D model to be placed on the site for visualization. 4D scheduling and 4D animations could be used for visualization in meetings, work preparations and at site. The study showed that quantity takeoff and cost estimation with 5D is only reconciled in the meetings in the production phase and that the programs for it are not needed in this phase. RFID tags could be used at site for logistics and tracking materials, and field verifications could be used to verify that a work task is executed according to exact coordination’s in the 3D model. Furthermore tablet computers could be used for bringing the technique of BIM to the site which enables a better understanding of complex work tasks for the workers. A BIM coordinator who understands the process of working with BIM and who could work as a bridge between the users and the technical development team is important in a successful implementation. The study also shows that the focus of BIM should lie on how to make use of the technique. The examples of how BIM could be used in the production phase of civil works have to be useful and meet the needs and demands of the users. The processes of using 3D models, 4D scheduling, 4D animations, RFID tags, field verifications and tablet computers should therefore be studied thoroughly to find how the technique could be applicable at site, in meetings and work preparations and how it could enhance the daily activities and work tasks. If the demands are met it will be accepted by both the user and the organization. Further research should therefore lie on how 3D models, 4D scheduling, 4D animations, RFID tags, field verifications and tablet computers could be useful in the production phase. These BIM techniques should then be tested on a real project to investigate how the processes could be useful at site, in meetings and in work preparations. Further research should also be made on how countries like Norway, Finland and USA have made use of BIM in the production of civil works.

A human body can carry out many physiological complex processes which can be mechanical, electrical or bio-chemical. Each mechanical activity generates a signal that describes the characteristics of the particular action in the form of pressure or temperature. Any irregularity in the process changes the usual functioning thus affecting the performance of the system. Several techniques were introduced to evaluate these muscular signals in order to get a deeper understanding of the medical abnormalities. Displacement sensors, laser optics, electrodes, accelerometers and microphones are some of the widely used devices in measuring the electrical and mechanical activities produced in the muscles. The aim of this thesis project was to find and implement a simple non-contact optical method to measure and monitor the displacements caused on the surface of the skin due to muscular movements. In this study, a device was developed using photo electric sensors that can record surface changes caused on the skin due to the movements forearm muscles.

A current meter has been designed, intended for surveillance of low-power battery driven devices with a large dynamic range in their current consumption. Among such devices may, for example, be nodes in a wireless sensor network (WSN). The large dynamic range originates in the nodes’ states from an active mode for data collection and communication to a sleep mode for preserving very limited energy and prolonging the lifetime of the device. The active mode draws current up to hundreds of milliamperes whilst the sleep mode’s current may be as low as 22 nA. This makes the dynamic range larger than 6 orders of magnitude. To perform measurements that prevail over noise sources and resolution of involved components, an increase in the SNR must be made. If the current is measured with a shunt resistor, this may be done by varying its resistance as required. The resistance should be as high as possible to maximize the SNR, but low enough such that the burden voltage of the current meter is kept within tolerances of the device. A literature study was done, and with the gained knowledge a circuit was designed and simulated in LTSpice. Then a printed circuit board (PCB) of the circuit was designed and implemented using Altium Designer (an ECAD program), manufactured and hand-soldered. The final PCB was tested but shown to have some design flaws that deteriorated the performance, for example too frequent switching of the current range.

This project entails the design and development of a digitally controlled, modular electronic load. The proposed load is unique from existing designs because it has the added ability to increase its maximum current level by adding identical modules in parallel. Each module is designed to sink a maximum of 5A at 60V but more modules allow for more current. The cost and simplicity of the design are considered such that it can be reproduced in-house to replace, whenever possible, the resistor box for load testing of any analog circuits but more specifically power electronic circuits. The design process as well as the hardware development is explained in detail in this report. Results from hardware testing are also provided.

No description available.

No description available.