A Simple Device for Lens-to-Sample Distance Adjustment in Laser-Induced Breakdown Spectroscopy (LIBS).

A simple device based on two commercial laser pointers is described to assist in the analysis of samples that present uneven surfaces and/or irregular shapes using laser-induced breakdown spectroscopy (LIBS). The device allows for easy positioning of the sample surface at a reproducible distance from the focusing lens that conveys the laser pulse to generate the micro-plasma in a LIBS system, with reproducibility better than ±0.2 mm. In this way, fluctuations in the fluence (J cm-2) are minimized and the LIBS analytical signals can be obtained with a better precision even when samples with irregular surfaces are probed.

Ring-oven based preconcentration technique for microanalysis: simultaneous determination of Na, Fe, and Cu in fuel ethanol by laser induced breakdown spectroscopy.

The ring-oven technique, originally applied for classical qualitative analysis in the years 1950s to 1970s, is revisited to be used in a simple though highly efficient and green procedure for analyte preconcentration prior to its determination by the microanalytical techniques presently available. The proposed preconcentration technique is based on the dropwise delivery of a small volume of sample to a filter paper substrate, assisted by a flow-injection-like system. The filter paper is maintained in a small circular heated oven (the ring oven). Drops of the sample solution diffuse by capillarity from the center to a circular area of the paper substrate. After the total sample volume has been delivered, a ring with a sharp (c.a. 350 µm) circular contour, of about 2.0 cm diameter, is formed on the paper to contain most of the analytes originally present in the sample volume. Preconcentration coefficients of the analyte can reach 250-fold (on a m/m basis) for a sample volume as small as 600 µL. The proposed system and procedure have been evaluated to concentrate Na, Fe, and Cu in fuel ethanol, followed by simultaneous direct determination of these species in the ring contour, employing the microanalytical technique of laser induced breakdown spectroscopy (LIBS). Detection limits of 0.7, 0.4, and 0.3 µg mL(-1) and mean recoveries of (109 ± 13)%, (92 ± 18)%, and (98 ± 12)%, for Na, Fe, and Cu, respectively, were obtained in fuel ethanol. It is possible to anticipate the application of the technique, coupled to modern microanalytical and multianalyte techniques, to several analytical problems requiring analyte preconcentration and/or sample stabilization.

Classification of Brazilian soils by using LIBS and variable selection in the wavelet domain.

This paper proposes a novel analytical methodology for soil classification based on the use of laser-induced breakdown spectroscopy (LIBS) and chemometric techniques. In the proposed methodology, linear discriminant analysis (LDA) is employed to build a classification model on the basis of a reduced subset of spectral variables. For the purpose of variable selection, three techniques are considered, namely the successive projection algorithm (SPA), the genetic algorithm (GA), and a stepwise formulation (SW). The use of a data compression procedure in the wavelet domain is also proposed to reduce the computational workload involved in the variable selection process. The methodology is validated in a case study involving the classification of 149 Brazilian soil samples into three different orders (Argissolo, Latossolo and Nitossolo). For means of comparison, soft independent modelling of class analogy (SIMCA) models are also employed. The best discrimination of soil types was attained by SPA-LDA, which achieved an average classification rate of 90% in the validation set and 72% in cross-validation. Moreover, the proposed wavelet compression procedure was found to be of value by providing a 100-fold reduction in computational workload without significantly compromising the classification accuracy of the resulting models.

Comparison of hard tissue density changes around implants assessed in digitized conventional radiographs and subtraction images.

OBJECTIVES: The aim of this in vivo study was to compare peri-implant bone density assessed by the mean gray value of the histogram in digitized conventional radiographs and two digital subtraction images (DSI) methods: linear and logarithmic. MATERIAL AND METHODS: Thirty-four patients were monitored by standardized periapical radiographs 1 week after surgery and 4 months later. The radiographs were digitized and manipulated by means of EMAGO software. Linear and logarithmic DSI were obtained, and a filter was added to the logarithmic image. Control and test regions were selected and the mean value of the gray level of the histogram of these selected areas was obtained. This process was carried out in the digitized conventional radiographs (DCR) and the two methods of DSI. After that, the images were divided into two groups, with and without bone loss, and statistical analysis was performed. RESULTS: The results indicate that differences between the jaws did not reach significance, in all the images and in the two groups with and without bone loss. Furthermore, there was no statistically significant difference between the radiographic density assessed in the DCR and the two methods of subtraction images. CONCLUSIONS: Monitoring of peri-implant bone density by the mean gray value of the histogram in a selected area can be assessed either by linear and logarithmic DSI or by DCR.

Os efeitos do turismo em Ilhabela na percepção da comunidade escolar / The effects of tourism in Ilhabela city in perception of the school community

Essa dissertação de mestrado tem como objetivo apreender a percepção dos alunos de uma escola pública de Ilhabela, no litoral paulista sobre ambiente, saúde e turismo. Para melhor discorrer sobre essa percepção foram levantadas informações sobre o processo de desenvolvimento do Litoral Norte do Estado de São Paulo, assim como as atuais políticas de gerenciamento costeiro que regulam esse litoral. Também foi elaborada uma descrição municipal e regional e elencados alguns efeitos do turismo sobre essa realidade. Essa situação, por sua vez, é cotejada com o perfil dos alunos e suas reflexões sobre o tema estudado. Como resultado dessa análise propõe-se um projeto de intervenção local junto à escola participante.(AU)

Os efeitos do turismo em Ilhabela na percepção da comunidade escolar / The effects of tourism in Ilhabela city in perception of the school community

Essa dissertação de mestrado tem como objetivo apreender a percepção dos alunos de uma escola pública de Ilhabela, no litoral paulista sobre ambiente, saúde e turismo. Para melhor discorrer sobre essa percepção foram levantadas informações sobre o processo de desenvolvimento do Litoral Norte do Estado de São Paulo, assim como as atuais políticas de gerenciamento costeiro que regulam esse litoral. Também foi elaborada uma descrição municipal e regional e elencados alguns efeitos do turismo sobre essa realidade. Essa situação, por sua vez, é cotejada com o perfil dos alunos e suas reflexões sobre o tema estudado. Como resultado dessa análise propõe-se um projeto de intervenção local junto à escola participante.