We report here the observation of non-ohmic behavior in the dominant oscillatory component (the cigar component) of ρ('H) in ultrapure magnesium when the magnetic field, 'H, is parallel to [0001] and the current density, 'J, lies in the basal plane. In order to study this new phenomenon systematically, we had to overcome two experimental problems. The first was the design of an experimental probe which could reproducibly control, at low temperatures, the contact resistance at one of the points where current is injected into the sample without disturbing the sample's orientation with respect to 'H. Special micromanipulators, controlled by helium gas pressure, were designed into the probe for this purpose. The second problem was the construction of a detector which had the sensitivity to measure small signals from the magnesium samples in an effort to investigate the low current regime where the oscillations appear to satisfy Ohm's Law. A superconducting chopper amplifier was built which had the sensitivity to measure 10⁻¹¹ volt signals. We present evidence which directly relates this non-ohmic behavior to the long-range influence of a relatively large contact resistance at a point where current is injected into the sample. Data are presented which indicate that when this non-ohmic behavior is present, the corresponding oscillation amplitudes are proportional to the contact resistance. Measurements are also presented which show that the effects of this local current injection are so nonlocal that they extend over distances which are comparable to the dimensions of the sample.

In most South African schools Grade 12 Physical Sciences learners are generally not performing well. As Examiners’ Reports reveal, they are particularly weak on the topic of electrical circuits. Because of this, the Examiners recommended that conventional practical activities and revision should be implemented to improve learners’ performance whilst they are in Grade 11. These factors contributed to the rationale of this study in using the ‘straw electricity’ analogy in conjunction with a conventional practical activity to mediate learners’ sense making of Ohm’s law. The study falls within the interpretive paradigm, whose focus is on the understanding of human world-views. Within the interpretive paradigm a qualitative case study approach was employed. It is a case study because it aimed to investigate a group of learners in a given context. This qualitative case study used purposive sampling to select participants. Various data gathering techniques were employed, namely, documents, observations and stimulated recall interviews. The gathered data was analysed so as to determine the indicators of how learners made sense of Ohm’s law. The findings of this study are that learners were able to construct new knowledge within a social context where the ‘straw electricity’ analogy, using easily accessible resources, was incorporated in tandem with a conventional practical classroom task. Moreover, the ‘straw electricity’ analogy enabled a better understanding of science concepts as it tested and supported different learning skills.

Reverse engineering, defined as extracting information about a product from the product itself, is a common industry practice for gaining insight into innovative products. Both the original designer and those reverse engineering the original design can benefit from estimating the time and barrier to reverse engineer a product. This thesis presents a set of metrics and parameters that can be used to calculate the barrier to reverse engineer any product as well as the time required to do so. To the original designer, these numerical representations of the barrier and time can be used to strategically identify and improve product characteristics so as to increase the difficulty and time to reverse engineer them. One method for increasing the time and barrier to reverse engineer a product – presented in this thesis – is to treat material microstructures (crystallographic grain size, orientation, and distribution) as continuous design variables that can be manipulated to identify unusual material properties and to design devices with unexpected mechanical performance. A practical approach, carefully tied to proven manufacturing strategies, is used to tailor material microstructures by strategically orienting and laminating thin anisotropic metallic sheets. This approach, coupled with numerical optimization, manipulates material microstructures to obtain desired material properties at designer-specified locations (heterogeneously) or across the entire part (homogeneously). As the metrics and parameters characterizing the reverse engineering time and barrier are also quantitative in nature, they can also be used in conjunction with numerical optimization techniques, thereby enabling products to be developed with a maximum reverse engineering barrier and time – at a minimum development cost. On the other hand, these quantitative measures enable competitors who reverse engineer original designs to focus their efforts on products that will result in the greatest return on investment. While many products were analyzed in an empirical study demonstrating that the characterization of the time to reverse engineer a product has an average error of 12.2%, we present the results of three different products. Two additional examples are also presented showing how microstructure manipulation leads to product hardware with unexpected mechanical performance effectively increasing reverse engineering time and barrier.

Submitted by Larissa Vitoria Cardoso Cusielo (larissavitoria@id.uff.br) on 2017-09-06T18:50:23Z No. of bitstreams: 3 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) DISSERTACAO FABIANO.pdf: 2044410 bytes, checksum: 2ec958dba6d2bb7bbf465dd3233e2530 (MD5) produto MNPEF - Fabiano - professor.pdf: 861178 bytes, checksum: 0436e722a0896e5ddf5c279878e9e201 (MD5) / Approved for entry into archive by Biblioteca do Aterrado BAVR (bavr@ndc.uff.br) on 2017-09-27T21:20:56Z (GMT) No. of bitstreams: 3 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) DISSERTACAO FABIANO.pdf: 2044410 bytes, checksum: 2ec958dba6d2bb7bbf465dd3233e2530 (MD5) produto MNPEF - Fabiano - professor.pdf: 861178 bytes, checksum: 0436e722a0896e5ddf5c279878e9e201 (MD5) / Made available in DSpace on 2017-09-27T21:20:56Z (GMT). No. of bitstreams: 3 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) DISSERTACAO FABIANO.pdf: 2044410 bytes, checksum: 2ec958dba6d2bb7bbf465dd3233e2530 (MD5) produto MNPEF - Fabiano - professor.pdf: 861178 bytes, checksum: 0436e722a0896e5ddf5c279878e9e201 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Universidade Federal Fluminense. Instituto de Ciências Exatas. Programa de Pós-Graduação em Ensino de Física. Volta Redonda, RJ. / Com o objetivo de criar um ambiente que propicie uma discussão filosófica incipiente dos conceitos físicos que são apresentados aos aprendizes da Educação Básica, abordaremos algumas correntes filosóficas que estão presentes nesses conceitos de uma forma geral, e em particular, no desenvolvimento das Leis de Ohm da eletricidade. Nosso trabalho baseia-se em uma discussão sobre a construção e o constante refinamento, ao longo dos anos, de duas formas de fazer ciência, isto é, a vertente do Empirismo, que tem como representante inicial, o Filósofo grego Aristóteles e em oposição ideológica aos ensinamentos do também Filósofo grego Platão que defendia o Racionalismo. Pretendemos, portanto, estabelecer um diálogo diante dessas duas formas de interpretar a natureza e reforçar para os alunos que, ao longo do tempo, esse diálogo entre diversas interpretações científicas não cessa, e o que existe é um contínuo refinamento das propostas de se explicar o mundo ao longo da História da humanidade. Destacaremos a proposta de Immanuel Kant que apresenta para o mundo uma visão singular de como fazer ciência, e sugere através de suas obras, entre outras coisas, a fusão entre o Racionalismo continental (René Descartes) e o Empirismo Britânico (Francis Bacon). Na sequência, pretendemos construir um entendimento mais amplo sobre a obra do Físico Alemão George Simon Ohm, que se notabilizou através das leis que recebem seu nome e são de grande importância dentro do ensino de física. / In order to create an environment that fosters an incipient philosophical discussion of the physical concepts that are presented to learners of Basic Education will discuss some philosophical currents that are present these concepts in general, and particularly in the development of Ohm's electricity Laws . Our work is based on a discussion of the construction and the constant refinement over the years, of two ways of doing science, that is, the side of empiricism, whose initial representative, the Greek philosopher Aristotle and ideological opposition the teachings of the Greek philosopher Plato also argued that Rationalism. We intend, therefore, to establish a dialogue on these two ways of interpreting the nature and reinforce for students who, over time, this dialogue between different scientific interpretations does not cease, and that there is a continuous refinement of proposals to explain world throughout human history. We highlight the proposal of Immanuel Kant presenting to the world a unique view of how to do science, and suggests through his works, among other things, the merger between Continental Rationalism (René Descartes) and the British Empiricism (Francis Bacon). Further, we plan to build a broader understanding of the work of the German physicist Georg Ohm, who distinguished himself through laws that are named and are of great importance in the physics teaching.

Orientador: Prof. Dr. Francisco Eugenio Mendonça da Silveira / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2014. / Neste trabalho, discutimos o efeito de uma relaxação finita para a corrente sobre a instabilidade axialmente simetrica de uma coluna de plasma com perfil parabólico na aproximacão não indutiva. A forma funcional da densidade de momento angular específico é dada por L = ar2+br..1=2, onde a e b s~ao constantes. Isto signica que L possui um valor mnimo para uma dada coordenada radial r, limitada pelas paredes do vaso que contem o uido. Como consequ^encia, o sistema pode se tornar instavel se a frequ^encia epicclica k = [2 (2 + r 0)]1=2 for um numero imaginario, onde denota a velocidade angular do uido e a linha, uma derivada total em relac~ao a r. Uma analise de instabilidade linear e desenvolvida para os limites de grande e pequena resistividade do uido. Os resultados apresentados aqui podem contribuir para tornar a noc~ao da aproximac~ao n~ao indutiva em um conceito mais preciso. Finalmente, apresentamos uma proposta de continuidade natural deste trabalho. / In this work, we discuss the efect of a fnite relaxation for the current on the axisymmetric instability of a plasma column with parabolic profile in the inductionless approximation. The functional form of the specic angular momentum density is given by L = ar2 + br..1=2, where a and b are constants. As a consequence, the system may become unstable if the epicyclic frequency k = [2 (2 + r 0)]1=2 is an imaginary number, where denotes the angular velocity of the uid and the prime, a total derivative with respect to r. A linear stability analysis is developed for the limits of large and of small resistivity of the uid. The results presented here may contribute to turn the notion of the inductionless approximation into a more precise concept. Finally, we present a proposal of natural continuity of this work.

Orientador: Prof. Dr Eugenio Mendonça da Silveira / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2014. / Neste trabalho, discutimos o efeito combinado de uma relaxção infinita para a corrente e da formação de uma camada de corrente-vórtice sobre a instabilidade magneto-rotacional em um uido condutor. Mostramos que a amplificação relativa da viscosidade magnética, desde a estabilidade marginal até a instabilidade determinada pela taxa de crescimento máxima da perturbação, é de aproximadamente 924% quando efeitos resistivos são dominantes e que ela é de aproximadamente 220% no limite ideal. Isto significa que o efeito combinado é muito mais efciente para amplicar viscosidade magnética que a simples in uência devida à tensãoo magnética usual. Os resultados apresentados aqui podem contribuir para a compreensão dos vários processos que desempenham um papel significativo no mecanismo da viscosidade anômala observada em discos de acreção keplerianos. Argumentamos que o novo efeito deve ser relevante em discos de acreação delgados. Finalmente, apresentamos uma proposta de continuidade natural deste trabalho.

Orientador: Prof. Dr Eugenio Mendonça da Silveira / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2014. / Neste trabalho, discutimos o efeito combinado de uma relaxção infinita para a corrente e da formação de uma camada de corrente-vórtice sobre a instabilidade magneto-rotacional em um uido condutor. Mostramos que a amplificação relativa da viscosidade magnética, desde a estabilidade marginal até a instabilidade determinada pela taxa de crescimento máxima da perturbação, é de aproximadamente 924% quando efeitos resistivos são dominantes e que ela é de aproximadamente 220% no limite ideal. Isto significa que o efeito combinado é muito mais efciente para amplicar viscosidade magnética que a simples in uência devida à tensãoo magnética usual. Os resultados apresentados aqui podem contribuir para a compreensão dos vários processos que desempenham um papel significativo no mecanismo da viscosidade anômala observada em discos de acreção keplerianos. Argumentamos que o novo efeito deve ser relevante em discos de acreação delgados. Finalmente, apresentamos uma proposta de continuidade natural deste trabalho.