RESUMO
We report on the optical characterization of three-dimensional opal-like photonic crystals made by self-organized nanospheres of poly[styrene-(co-2-hydroxyethyl methacrylate)] having a face centred cubic (fcc) structure oriented along the [111] direction. A detailed optical characterization of the samples is presented using angle resolved reflection spectroscopy in specular geometry. The investigated energies are between a/lambda=0.5 and a/lambda=1.5 (where a is the lattice parameter and lambda is the light wavelength), a region in which both first and second-order Bragg diffraction are expected. Some interesting features as branching of the Bragg peak dispersion and high energy reflection peaks are revealed. We compare the experimental data with theoretical calculations using both Bragg diffraction and band structure approach. A comparison with recent results reported in the literature is also presented.
Assuntos
Tecnologia de Fibra Óptica/instrumentação , Modelos Químicos , Nanosferas/química , Polímeros/química , Refratometria/métodos , Análise Espectral/métodos , Simulação por Computador , Teste de Materiais , Conformação Molecular , Nanosferas/ultraestrutura , Tamanho da PartículaRESUMO
Gastric volvulus is an infrequent event and few clinical cases are an important experience. Diagnosis, both clinical and radiological, is not difficult if you think of gastric volvulus; abdomen X-ray is often sufficient to clear up diagnostic doubts. First diagnosis can be quickly confirmed by X-ray examination of digestive organs that provides us with further information: contemporaneous ulcerative of neoplastic lesions, characteristics of bowels whirling round. Endoscopic and manometric evaluation must be performed only in recurrent or chronic cases, when there's no symptom of clinical urgency. Authors describe their experience of three cases observed in the last ten years and underline the importance of deciding and performing the surgical treatment quickly to avoid serious complications, in all doubtful cases. It is important to carry out an operation compared to the pathogenesis of volvulus: generally gastropexy is sufficient while radical operations are executed only in cae of gastric necrosis or in the presence of gastric neoplasms or ulcerative lesions.