Superfluid 4He: brief notes on collective energy excitations and specific heat.

These brief notes about some amazing properties of the helium superfluid have been written to graduate and postgraduate students of physics. We have estimated some collective energy excitations (linear vortices, energy spectrum of the quasiparticles and solitons) and calculated the specific heat of the superfluid helium assuming that the transition superfluid liquid → liquid is an order-disorder transition

Optical activity of a dilute dielectric medium: Pasteur and the molecular symmetries

Em 1848 Pasteur conjeturou que a rotação do plano de polarização da luz em um meio diluído é gerada pelas propriedades de simetria das moléculas do meio no qual a luz se propaga. O objetivo do nosso artigo é de mostrar que Pasteur estava correto usando conhecimentos de eletromagnetismo e mecânica quântica de um curso de graduação em física. Faremos um breve retrospecto das ideias básicas da teoria eletromagnética necessárias para o estudo da atividade óptica. A seguir, usando a teoria de perturbações em mecânica quântica e levando em conta as simetrias das moléculas calcularemos a atividade óptica do meio. Mostraremos que as previsões teóricas, que estão plenamente de acordo com os resultados experimentais, comprovam a hipótese de Pasteur.Pasteur proposed in 1848 that the rotation of the polarization plane of the light in a dilute medium is generated by the symmetry properties of the molecules of the medium where the light propagates. Our objective is to show that Pasteur hypothesis was correct using the basic knowledge of electromagnetism and quantum mechanics of the undergraduate physics course. We present a brief review of the fundamental concepts of the electromagnetic theory necessary to understand the optical activity. Next, using the quantum mechanical perturbation theory and taking into account the molecular symmetries we calculate the optical activity of the medium. It will be shown that the theoretical predictions, which are in good agreement with the experimental results, give support to the Pasteur conjecture

História da propagação das citações originais do artigo do Journal of Quantitative Spectroscopy & Radiative Transfer 102/441/2006.

Neste artigo procuraremos descrever a história cronológica das citações originais (aquelas que os nomes dos autores aparecem apenas uma vez, portanto, excluídas as autocitações) da publicação do artigo: M. Cattani and J. M. F. Bassalo, Racemization, Chiral Stability and Weak Interactions, Journal of Quantitative Spectroscopy & Radiative Transfer 102, pp. 441-449, 2006 (CB: JQS&RT 102/441/2006). Para realizar essa história, usamos a WEB OF SCIENCE (acessado: 08/02/2013) disponibilizado pela CAPES/UFPA

Solitrons Hidrodinâmicos de Korteweg-de Vries.

Esse artigo foi escrito para alunos de graduação e pós- graduação em Física e para alunos de Engenharia. Primeiramente mostramos como construir a equação diferencial não-linear de Korteweg e de Vries a partir das equações básicas da hidrodinâmica. Em seguida mostramos como resolvê-la obtendo as ondas denominadas de solitons

Crônica dos Potenciais Vetor e Quântico.

Neste artigo, vamos apresentar o desenvolvimento histórico dos\ud conceitos dos potenciais vetor e quântico formulados, respectivamente, por\ud Maxwell e Bohm. Em suas concepções iniciais, eles foram considerados\ud apenas como um artifício matemático. Contudo, enquanto o potencial vetor já\ud apresenta uma grande evidência experimental (efeito Aharonov-Bohm) sobre\ud a sua interpretação física, o potencial quântico ainda aguarda a sua, muito\ud embora esse efeito e alguns resultados teóricos sinalizem a sua existência\ud física. Este artigo já foi publicado na revista MensAgitat vol.1(2),pp.93-\ud 108(2006) da Academia Roraimense e Paraense de Ciências. Está sendo\ud publicado novamente como e-print no IFUSP para que ele tenha uma\ud divulgação mais ampla e mais ágil pela internet

Surface modification by metal ion implantation forming metallic nanoparticles in insulating matrix.

There is special interest in the incorporation of metallic nanoparticles in a surrounding dielectric matrix for obtaining composites with desirable characteristics such as for surface plasmon resonance, which can be used in photonics and sensing, and controlled surface electrical conductivity. We investigated nanocomposites produced through metallic ion implantation in insulating substrate, where the implanted metal self-assembles into nanoparticles. During the implantation, the excess of metal atom concentration above the solubility limit leads to nucleation and growth of metal nanoparticles, driven by the temperature and temperature gradients within the implanted sample including the beam-induced thermal characteristics. The nanoparticles nucleate near the maximum of the implantation depth profile (projected range), that can be estimated by computer simulation using the TRIDYN. This is a Monte Carlo simulation program based on the TRIM (Transport and Range of Ions in Matter) code that takes into account compositional changes in the substrate due to two factors: previously implanted dopant atoms, and sputtering of the substrate surface. Our study suggests that the nanoparticles form a bidimentional array buried few nanometers below the substrate surface. More specifically we have studied Au/PMMA (polymethylmethacrylate), Pt/PMMA, Ti/alumina and Au/alumina systems. Transmission electron microscopy of the implanted samples showed the metallic nanoparticles formed in the insulating matrix. The nanocomposites were characterized by measuring the resistivity of the composite layer as function of the dose implanted. These experimental results were compared with a model based on percolation theory, in which electron transport through the composite is explained by conduction through a random resistor network formed by the metallic nanoparticles. Excellent agreement was found between the experimental results and the predictions of the theory. It was possible to conclude, in all cases, that the conductivity process is due only to percolation (when the conducting elements are in geometric contact) and that the contribution from tunneling conduction is negligible

Gold ion implantation into alumina using an “inverted ion source” configuration.

We describe an approach to ion implantation in which the plasma and its electronics are held at\ud ground potential and the ion beam is injected into a space held at high negative potential, allowing\ud considerable savings both economically and technologically. We used an “inverted ion implanter”\ud of this kind to carry out implantation of gold into alumina, with Au ion energy 40 keV and dose\ud (3–9) × 1016 cm−2. Resistivity was measured in situ as a function of dose and compared with predictions\ud of a model based on percolation theory, in which electron transport in the composite is\ud explained by conduction through a random resistor network formed by Au nanoparticles. Excellent\ud agreement is found between the experimental results and the theory.FAPESPCNP