RESUMO
Silicon dominates the electronics industry, but its poor optical properties mean that III-V compound semiconductors are preferred for photonics applications. Photoluminescence at visible wavelengths was observed from porous Si at room temperature in 1990, but the origin of these photons (do they arise from highly localized defect states or quantum confinement effects?) has been the subject of intense debate ever since. Attention has subsequently shifted from porous Si to Si nanocrystals, but the same fundamental question about the origin of the photoluminescence has remained. Here we show, based on measurements in high magnetic fields, that defects are the dominant source of light from Si nanocrystals. Moreover, we show that it is possible to control the origin of the photoluminescence in a single sample: passivation with hydrogen removes the defects, resulting in photoluminescence from quantum-confined states, but subsequent ultraviolet illumination reintroduces the defects, making them the origin of the light again.
Assuntos
Cristalização/métodos , Hidrogênio/química , Medições Luminescentes/métodos , Magnetismo , Nanoestruturas/química , Nanotecnologia/métodos , Silício/química , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Nanoestruturas/efeitos da radiação , Tamanho da Partícula , Espalhamento de Radiação , Propriedades de SuperfícieRESUMO
The aim of the present study was to determine by standard cultivation procedures the detection frequencies of Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum, Actinobacillus actinomycetemcomitans, Bacteroides forsythus, and Capnocytophaga species as well as various enteric rods in subgingival plaque samples form Romanian adult periodontitis patients. DNA probe analysis (Affirm DP Microbial Identification Test) was also used, parallel to cultivation, to identify P. gingivalis, A. actinomycetemcomitans, and B. forsythus, in deep (> or = 6 mm) and intermediate (4-5 mm) pockets in some of the subjects investigated. Paper points were used to sample 86 deep pockets in 36 patients and 27 intermediate pockets in 9 of the 36 patients. The chi 2 test was used to test for significance of differences between results obtained by cultivation and DNA analysis in both intermediate and deep pockets. P. gingivalis was recovered in a high percentage of the patients (75.8%) and sites (63.6%) examined, followed by P. intermedia, F. nucleatum, and A. actinomycetemcomitans, respectively. Capnocytophaga species were present in almost all subjects. Enteric rods were recovered in 61.1% of the patients and 55.8% of the sites. Except for this high prevalence of enteric rods, the present group of patients had the periodontal species monitored in %s similar to those commonly perceived in the West. The Affirm DP Test and cultivation showed poor correlation in detecting P. gingivalis, A. actinomycetemcomitans, and B. forsythus. The cultivation prevalence of P. gingivalis and P. intermedia in deep pockets was similar to their prevalence in intermediate ones. Overall, the prevalence of the periodontal pathogens investigated in the present Romanian periodontitis patients is similar to what has been revealed in matching Norwegian and other Western periodontitis patient populations. The high prevalence of enteric rods in the Romanian patients may have been an artifact resulting from prolonged transport of the samples in VMGA III.
Assuntos
Bactérias/isolamento & purificação , Placa Dentária/microbiologia , Periodontite/microbiologia , Adulto , Idoso , Aggregatibacter actinomycetemcomitans/genética , Aggregatibacter actinomycetemcomitans/isolamento & purificação , Artefatos , Bactérias/classificação , Técnicas Bacteriológicas , Bacteroides/genética , Bacteroides/isolamento & purificação , Capnocytophaga/genética , Capnocytophaga/isolamento & purificação , Contagem de Colônia Microbiana , Meios de Cultura , Sondas de DNA , DNA Bacteriano/análise , Enterobacteriaceae/genética , Enterobacteriaceae/isolamento & purificação , Feminino , Fusobacterium nucleatum/genética , Fusobacterium nucleatum/isolamento & purificação , Gengiva/microbiologia , Humanos , Masculino , Pessoa de Meia-Idade , Bolsa Periodontal/microbiologia , Porphyromonas gingivalis/genética , Porphyromonas gingivalis/isolamento & purificação , Prevalência , Prevotella intermedia/genética , Prevotella intermedia/isolamento & purificação , Romênia , Manejo de EspécimesRESUMO
With a view to extend the range of biologically active preparations for the direct and the indirect capping of the dental pulp the authors have used a paste made from an alcoholic solution of propolis and zincoxyde. The study was carried on in 150 teeth with indirect capping of deep cavities, and 50 teeth with direct capping. The evolution of the cappings was followed clinically, radiologically and morphologically. The results obtained showed that the paste with propolis exerts effects similar to those of zinc eugenate. The morphologic study of the indirect capping showed that secondary dentin developed shortly after the application of the paste, and that it was followed by the development of pulpolites and the sclerous transformation of the pulp. In teeth with direct capping a protective film developed at the opening of the dental chamber. With time the pulpal wound undergoes cicatrization by a process of fibrosis and there is a trend to remineralization. No areas of pulpal degenerescence were found the rest of the pulpal tissue, and this suggests that the paste is more histophilic than the pastes based on calcium hydroxide, with which an area of necrosis occurred at the opening of the chamber, and calcium and fibrous degenerescence occurred in the coronal pulp.
