A mathematical analysis of the evolution of perturbations in a modified Chaplygin gas model

One approach in modern cosmology consists in supposing that dark matter and dark energy are different manifestations of a single `quartessential' fluid. Following such idea, this work presents a study of the evolution of perturbations of density in a flat cosmological model with a modified Chaplygin gas acting as a single component. Our goal is to obtain properties of the model which can be used to distinguish it from another cosmological models which have the same solutions for the general evolution of the scale factor of the universe, without the construction of the power spectrum. Our analytical results, which alone can be used to uniquely characterize the specific model studied in our work, show that the evolution of the density contrast can be seen, at least in one particular case, as composed by a spheroidal wave function. We also present a numerical analysis which clearly indicates as one interesting feature of the model the appearence of peaks in the evolution of the density constrast.Comment: 21 pages, accepted for publication in General Relativity and Gravitatio

Newly-discovered interactions between bacteriophages and the process of calcium carbonate precipitation

Although it has been suggested that viruses may induce precipitation of carbonate, the exact mechanisms involved and the roles they might play in the nucleation of carbonates are still unknown. Experimental evidence is reported here demonstrating that bacteriophages are an important factor in calcium carbonate formation. Short-term experiments were designed to induce viral-mediated mineral precipitation at different fluid compositions. The precipitates obtained, analysed with fluorescence and electron microscopes and X-Ray diffraction, and evaluated by statistics, clearly show that bacteriophages strongly affect the process of carbonate precipitation. We demonstrate that as a result of the coalescence of the phages, the carbonate precipitates form large aggregates consisting of spheroids. The spheroids are constructed of angular nanoparticles resembling viral-like particles. In control experiments spheroids were also observed; however, they consist of irregular nanoparticles and additionally they do not form large aggregates. We also demonstrate that bacteriophages strongly influence the mineral composition of the precipitates, with vaterite being the dominant form, and they likely control vaterite stability

Perfil epidemiológico de pacientes com degeneração macular relacionada à idade na cidade de Niterói, Brasil: considerações sobre o atendimento no Hospital Universitário Antonio Pedro da Universidade Federal Fluminense

Objetivo: Demonstrar o perfil epidemiológico e fatores de riscos de pacientes com degeneração macular relacionada à idade (DMRI) na cidade de Niterói, estado do Rio de Janeiro, sudeste do Brasil. Métodos: Estudo observacional e seccional. Incluído um olho de cada paciente com maior comprometimento visual por DMRI atendido no Hospital Universitário Antônio Pedro. A variável principal a ser comparada foi a presença de DMRI dividida em estágios inexpressivo, inicial, intermediário e avançado, segundo classificação do estudo AREDS. As variáveis secundárias foram os dados demográficos (sexo, idade, raça, faixa etária), índice de massa corporal, cor da íris, história familiar de DMRI, status do cristalino, longo tempo exposição à luz ultravioleta e tabagismo. Foram realizados testes estatísticos com análises de Kruskal-Wallis e Qui-quadrado e teste t de Student. O nível de significância foi definido em 5%. Resultados: Após os critérios de inclusão e exclusão, 126 pacientes foram incluídos neste estudo, sendo 20 pacientes com DMRI inexpressiva, 30 pacientes com DMRI inicial, 30 pacientes com DMRI intermediária e 46 pacientes com DMRI avançada. Dentre todos os fatores de risco pesquisados, apenas o tabagismo se mostrou estatisticamente significativo (p = 0,03).SimPurpose: To demonstrate the epidemiological profile and risk factors of patients with age-related macular degeneration (ARMD) in the city of Niterói, state of Rio de Janeiro, southeastern Brazil. Methods: Observational and sectional study. One eye of each patient with greater visual impairment due to AMD treated at the University Hospital Antônio Pedro was included. The main variable to be compared was the presence of AMD divided into inexpressive, initial, intermediate, and advanced stages, according to the classification of the AREDS study. Secondary variables were demographics (gender, age, race, age group), body mass index, iris color, family history of ARMD, lens status, long-term exposure to ultraviolet light and smoking. Statistical tests were performed with Kruskal-Wallis and Chi-square analyzes and Student's t test. The significance level was set at 5%. Results: After the inclusion and exclusion criteria, 126 patients were included in this study, 20 patients with non-expressive AMD, 30 patients with early AMD, 30 patients with intermediate AMD and 46 patients with advanced AMD. Among all risk factors surveyed, only smoking was statistically significant (p = 0.03). Conclusion: smoking as a risk factor for AMD had significant importance prevalent in this research and even as a preventive factor for this ocular morbidit