Resumo Um problema importante no estudo de materiais magnéticos é saber como esses sistemas se comportam na presença de um campo magnético externo. A resposta para esse problema está na susceptibilidade magnética. Neste trabalho realizamos uma abordagem estatística das propriedades magnéticas dos materiais levando em consideração suas interações microscópicas. Nosso intuito é apresentar de maneira didática e acessível para um estudante de graduação as origens do fenômeno magnético e suas fases termodinâmicas, paramagnética, ferromagnética e antiferromagnética, calculando suas susceptibilidades e analisando seu comportamento em função da temperatura.

Abstract An important problem in studying magnetic materials is to know how these systems behave in the presence of an external magnetic field. The answer to that problem is in the magnetic susceptibility. In this work, we performed a statistical approach of the magnetic properties of materials that take into account their microscopic interactions. Our intent is to present in a didactic and accessible way to an undergraduate student the origins of the magnetic phenomenon and its thermodynamic, paramagnetic, ferromagnetic and antiferromagnetic phases, calculating its susceptibilities and analyzing its behavior as a function of temperature.

Neste trabalho abordaremos dois problemas teóricos, não muito discutidos na maioria das universidades brasileiras, envolvendo a Teoria da Relatividade Especial (TRE) e a Teoria do Eletromagnetismo (TEM). Tais exemplos são de fundamental importância para uma completa compreensão da natureza dos campos elétrico e magnético induzidos, bem como para o desenvolvimento dos conceitos da TRE. Eles podem ser discutidos em sala de aula juntamente com uma contextualização histórica acerca da evolução dos conceitos de eletricidade e magnetismo que culminaram na elaboração da Teoria do Eletromagnetismo.

In this paper we discuss two theoretical problems, not much discussed in most Brazilian universities, involving the Theory of Special Relativity (TSR) and the Electromagnetic Theory (EMT). Such examples are of fundamental importance to a complete understanding of the nature of the induced electric and magnetic fields, as well as for the development of concepts of TSR. These can be discussed in the classroom along with a historical contextualization on the evolution of electricity and magnetism concepts which culminated in the elaboration of Electromagnetic Theory.

O presente trabalho discute o modelo do átomo de Sommerfeld não relativístico no contexto da mecânica quântica antiga. No intuito de deixar o trabalho completo são também discutidas as energias da partícula na caixa, rotor rígido e oscilador harmônico. Uma introdução histórica da mecânica quântica antiga e uma discussão qualitativa do correspondente modelo relativístico são também elaborados. O texto apresentado pode ser acompanhado por estudantes de graduação.

The present work discuss the Sommerfeld atom in the non-relativistic domain, using the old quantum mechanics formulation. The particle in a box, rigid rotor and harmonic oscillator energies are considered, to make the text complete. An historical introduction and a qualitative presentation of the relativistic formulation are also discussed. The text was prepared in a way to make it acessible to an undergraduated student.

The main objective of the present study was to upgrade a clinical gamma camera to obtain high resolution tomographic images of small animal organs. The system is based on a clinical gamma camera to which we have adapted a special-purpose pinhole collimator and a device for positioning and rotating the target based on a computer-controlled step motor. We developed a software tool to reconstruct the target’s three-dimensional distribution of emission from a set of planar projections, based on the maximum likelihood algorithm. We present details on the hardware and software implementation. We imaged phantoms and heart and kidneys of rats. When using pinhole collimators, the spatial resolution and sensitivity of the imaging system depend on parameters such as the detector-to-collimator and detector-to-target distances and pinhole diameter. In this study, we reached an object voxel size of 0.6 mm and spatial resolution better than 2.4 and 1.7 mm full width at half maximum when 1.5- and 1.0-mm diameter pinholes were used, respectively. Appropriate sensitivity to study the target of interest was attained in both cases. Additionally, we show that as few as 12 projections are sufficient to attain good quality reconstructions, a result that implies a significant reduction of acquisition time and opens the possibility for radiotracer dynamic studies. In conclusion, a high resolution single photon emission computed tomography (SPECT) system was developed using a commercial clinical gamma camera, allowing the acquisition of detailed volumetric images of small animal organs. This type of system has important implications for research areas such as Cardiology, Neurology or Oncology.

Single-photon emission computed tomography (SPECT) is a non-invasive imaging technique, which provides information reporting the functional states of tissues. SPECT imaging has been used as a diagnostic tool in several human disorders and can be used in animal models of diseases for physiopathological, genomic and drug discovery studies. However, most of the experimental models used in research involve rodents, which are at least one order of magnitude smaller in linear dimensions than man. Consequently, images of targets obtained with conventional gamma-cameras and collimators have poor spatial resolution and statistical quality. We review the methodological approaches developed in recent years in order to obtain images of small targets with good spatial resolution and sensitivity. Multipinhole, coded mask- and slit-based collimators are presented as alternative approaches to improve image quality. In combination with appropriate decoding algorithms, these collimators permit a significant reduction of the time needed to register the projections used to make 3-D representations of the volumetric distribution of target’s radiotracers. Simultaneously, they can be used to minimize artifacts and blurring arising when single pinhole collimators are used. Representation images are presented, which illustrate the use of these collimators. We also comment on the use of coded masks to attain tomographic resolution with a single projection, as discussed by some investigators since their introduction to obtain near-field images. We conclude this review by showing that the use of appropriate hardware and software tools adapted to conventional gamma-cameras can be of great help in obtaining relevant functional information in experiments using small animals.

Um algoritmo geral para resolver problemas inversos lineares e não lineares, baseado em redes neurais recursivas, é discutido neste trabalho. O procedimento será aplicado a problemas físico-químicos modelados por equações integrais, diferenciais e de autovalor. As aplicações são discutidas em espectroscopia de aniquilação de pósitrons, cinética química e espectroscopia vibracional. O método é robusto com relação a erros nas condições iniciais ou em dados experimentais. A presente abordagem é simples, numericamente estável e tem uma grande aplicabilidade.

A general algorithm to solve linear and nonlinear inverse problems, based on recursive neural networks, is discussed in this work. The procedure will be applied to physical chemical problems modeled by integral, differential and eigenvalue equations. Representative applications discussed are in positron lifetime spectroscopy, chemical kinetics and vibrational spectroscopy. The method is robust with respect to errors in the initial condition or in the experimental data. The present approach is simple, numerically stable and has a broad range of applicability.

A simple analysis of glory and rainbow effects, together with the description of their trajectories is given by the geometric model. The energy dependence of glory and rainbow impact parameters and the energy dependence of the rainbow angle are determined analytically within the model. An universal function for glory and rainbow trajectories can be easily determined.

This paper deals with Carathédory's formulation of the second law of thermodynamics. The material is presented in a didatical way, which allows a second year undergraduate student to follow the formalism. An application is made to an ideal gas with two independent variables. A criticism to Carnot formulation of the second law and an investigation of the historical origins of the Carathéodory formalism are also presented.