Variation of magnetic properties in sedimentary rocks hosting the Foum Zguid dyke (southern Morocco): Combined effects of re-crystallization and Fe-metasomatism

The effects of dyke intrusion on the magnetic properties of host sedimentary rocks are still poorly understood. Therefore, we have evaluated bulk magnetic parameters of standard palaeomagnetic samples collected along several sections across the sediments hosting the Foum Zguid dyke in southern Morocco. The study has been completed with the evaluation of the magnetic fabric after laboratory application of sequential heating experiments. The present study shows that: (1) close to Fourn Zguid dykes, the variations of the bulk magnetic parameters and of the magnetic fabric is strongly related with re-crystallization and Fe-metasomatism intensity. (2) The thermal experiments on AMS of samples collected farther from the dyke and, thus, less affected by heating during dyke emplacement, indicate that 300-400 degrees C is the minimum experimental temperature necessary to trigger appreciable transformations of the pre-existing magnetic fabrics. For temperatures higher than ca. 580 degrees C, the magnetic fabric transformations are fully realized, with complete transposition of the initial fabric to a fabric similar to that of samples collected close to the dyke. Therefore, measured variations of the magnetic fabric can be used to evaluate re-crystallization temperatures experienced by the host sedimentary rock during dyke emplacement. The distinct magnetic behaviour observed along the cross-sections strongly suggests that samples collected farther from the dyke margins did not experience thermal episodes with temperatures higher than 300 degrees C after dyke emplacement. (3) AMS data shows a gradual variation of the magnetic fabric with distance from the dyke margin, from sub-horizontal K-3 away from the dyke to vertical K3 close to the dyke. Experimental heating shows that heat alone can be responsible for this strong variation. Therefore, such orientation changes should not be unequivocally interpreted as the result of a stress field (resulting from the emplacement of the dyke, for instance). (4) Magnetic studies prove to be a very sensitive tool to assess rock magnetic transformations, thermally and chemically induced by dyke intrusion in hosting sediments.

Novel structure for large area image sensing

This work presents preliminary results in the study of a novel structure for a laser scanned photodiode (LSP) type of image sensor. In order to increase the signal output, a stacked p-i-n-p-i-n structure with an intermediate light-blocking layer is used. The image and the scanning beam are incident through opposite sides of the sensor and their absorption is kept in separate junctions by an intermediate light-blocking layer. As in the usual LSP structure the scanning beam-induced photocurrent is dependent on the local illumination conditions of the image. The main difference between the two structures arises from the fact that in this new structure the image and the scanner have different optical paths leading to an increase in the photocurrent when the scanning beam is incident on a region illuminated on the image side of the sensor, while a decreasing in the photocurrent was observed in the single junction LSP. The results show that the structure can be successfully used as an image sensor even though some optimization is needed to enhance the performance of the device.

Optical confinement and colour separation in a double colour laser scanned photodiode (D/CLSP)

Large area n-i-p-n-i-p a-SiC:H heterostructures are used as sensing element in a double colour laser scanned photodiode image sensor (D/CLSP). This work aims to clarify possible improvements, physical limits and performance of CLSP image sensor when used as non-pixel image reader. Here, the image capture device and the scanning reader are optimized and the effects of the sensor structure on the output characteristics discussed. The role of the design of the sensing element, the doped layer composition and thickness, the read-out parameters (applied voltage and scanner frequency) on the image acquisition and the colour detection process are analysed. A physical model is presented and supported by a numerical simulation of the output characteristics of the sensor.

Optical confinement and colour separation in a double colour laser scanned photodiode (D/CLSP)

Large area n-i-p-n-i-p a-SiC:H heterostructures are used as sensing element in a Double Color Laser Scanned Photodiode image sensor (D/CLSP). This work aims to clarify possible improvements, physical limits and performance of CLSP image sensor when used as non-pixel image reader. Here, the image capture device and the scanning reader are optimized and the effects of the sensor structure on the output characteristics discussed. The role of the design of the sensing element, the doped layer composition and thickness, the read-out parameters (applied voltage and scanner frequency) on the image acquisition and the color detection process are analyzed. A physical model is presented and supported by a numerical simulation of the output characteristics of the sensor.

Sensor element for a metal-insulator-semiconductor camera system (MISCam)

We discuss the operation of a new type of optical sensor (MISCam) based on a metal-insulator-semiconductor (MIS) structure. The operation principle relies on light-induced changes of the band bending and barrier height at the interface between semiconductor and insulator. An image is obtained from the quenching of the ac signal in analogy to the principle of the laser-scanned photodiode (LSP). Lateral resolution depends on the semiconductor material chosen. We have characterised the MIS structures by C-V, I-V, and spectral response measurements testing different types of insulators like a-Si3N4, SiO2, and AlN. The presence of slow interface charges allows for image memory. Colour sensors can be realised by controlling sign and magnitude of the electric fields in the base and the interface region.

Percepção de exposição a cargas de trabalho e riscos de acidentes em Pelotas, RS (Brasil)

OBJETIVO: Investigar a associação entre a percepção de exposição às cargas de trabalho e o risco de acidentes. MÉTODOS: O delineamento do estudo foi o tipo de casos e controles. Os casos (n=264) incluíram os acidentes de trabalho típicos notificados no Instituto Nacional de Seguridade Social, de Pelotas, RS (Brasil), de janeiro a julho de 1996. Foram excluídos os óbitos (dois), os acidentes ocorridos na zona rural, e os que afastaram o trabalhador de suas atividades por menos de sete dias. Para cada caso foram selecionados três tipos de controles: um trabalhador da mesma empresa, um vizinho e um controle populacional. Os controles foram emparelhados com os casos por idade e sexo e precisavam ter vínculo empregatício formal e não ter sofrido acidente no último mês. Os dados foram analisados usando regressão logística condicional. RESULTADOS E CONCLUSÕES: Os trabalhadores que relatavam enfrentar situações de emergência, o trabalho em altura, perigo constante, ou ambientes ruidosos tinham cerca de duas vezes mais risco de acidentar-se. O trabalho em posições incômodas ou com esforço físico intenso aumentaram em 50% o risco de acidentes. As demais cargas de trabalho estudadas não se constituíram como fatores de risco para os acidentes. Os resultados foram ajustados para fatores de confusão.

Nutrição materna e duração da amamentação em uma coorte de nascimento de Pelotas, RS

OBJETIVO: Os efeitos da situação nutricional materna sobre a duração da amamentação são inconsistentes na literatura. O estudo realizado objetivou investigar esses efeitos em uma coorte de nascimentos hospitalares. MÉTODOS: Foram estudadas 977 mulheres que tiveram filhos no ano de 1993, em Pelotas (representando 20% dos nascimentos ocorridos nesse ano). Os efeitos da situação nutricional materna e de variáveis socioeconômicas e demográficas sobre a prevalência de amamentação aos seis meses de idade e sobre a duração da amamentação foram analisados pela regressão logística e de Cox, respectivamente. RESULTADOS: A análise multivariada mostrou que a prevalência de amamentação foi mais alta entre mulheres que iniciaram a gestação com 49 kg ou mais (RO = 1,31; IC95% 1,04 - 1,64), e a associação com altura materna foi no limiar da significância (p=0,06). A regressão de Cox mostrou um efeito protetor, no limiar da significância, do maior peso pré-gestacional sobre o desmame (RR = 0,91; IC95% 0,82 -- 1,01). Não houve diferença na duração da amamentação quanto à altura materna. O ganho de peso gestacional não mostrou associação com prevalência ou duração da amamentação. Idade materna, paridade, hábito de tabagismo e idade gestacional estiveram associadas significativamente com a amamentação em ambas as análises. Renda familiar mostrou associação com a prevalência de amamentação aos seis meses e o peso ao nascer com a duração da amamentação. CONCLUSÕES: Peso pré-gestacional foi um melhor preditor para duração da amamentação do que o ganho de peso gestacional.

Critérios de escolha de postos de saúde para acompanhamento pré-natal em Pelotas, RS

OBJETIVO: Caracterizar o cuidado pré-natal em uma amostra representativa de mães, identificando o serviço de saúde onde estas realizaram o acompanhamento da gestação e os motivos que as levaram a escolher este local. MÉTODOS: Estudo transversal, realizado nos meses de março e abril de 1997, nas quatro principais maternidades de Pelotas, RS, através de entrevista a 401 mães no pós-parto imediato. RESULTADOS: Fizeram acompanhamento pré-natal, em um posto de saúde 51% das mães, sendo a proximidade geográfica o critério mais freqüentemente referido para tal escolha (46,8%). Para 85% das mães, o serviço de saúde mais próximo de casa era um posto de saúde. No entanto, 52,2% dessas não utilizaram esse local para as consultas pré-natais alegando a má qualidade do atendimento (37,4%). Conforme referido pelas mães, entre os procedimentos de rotina do pré-natal recomendados pelo programa de saúde da rede pública, incluindo a promoção do aleitamento materno, apenas a imunização anti-tetânica foi realizada mais freqüentemente nos postos do que nos demais locais. CONCLUSÕES: Tendo em vista a expressiva utilização da rede pública para o acompanhamento pré-natal, necessitam ser implementados investimentos em educação continuada dos profissionais, com ênfase no cumprimento de normas técnicas pré-estabelecidas.

Validação de equações de predição da taxa metabólica basal em mulheres residentes em Porto Alegre, RS, Brasil

OBJETIVO: Medir a taxa metabólica basal em mulheres de 20 a 40 anos, não-gestantes ou lactantes, e comparar o valor medido com os valores de taxa metabólica basal estimados por equações de predição. MÉTODOS: A taxa metabólica basal foi medida por calorimetria indireta, pela manhã, durante a fase folicular do ciclo menstrual, em 60 voluntárias residentes no município de Porto Alegre, RS, sob condições padronizadas de jejum, repouso e ambiente. RESULTADOS: A média (± desvio-padrão) da taxa metabólica basal medida foi 1.185,3±148,6 kcal em 24 horas. A taxa metabólica basal, estimada por equações, foi significativamente maior (7% a 17%) do que a taxa metabólica basal medida. CONCLUSÕES: Os dados evidenciaram que as equações de predição não são adequadas para estimar a taxa metabólica basal nas mulheres avaliadas. O emprego dessas equações podem superestimar os requerimentos energéticos para mulheres com características semelhantes.

Prevalência e determinantes de anemia em crianças de Porto Alegre, RS, Brasil

OBJETIVO: O estudo foi realizado com o objetivo de verificar a prevalência de anemia e seus possíveis determinantes em crianças de 0 a 36 meses de idade que freqüentam escolas municipais infantis. MÉTODOS: Realizou-se um estudo transversal pelo qual foram estudadas 557 crianças de 0 a 36 meses de idade de todas as escolas municipais infantis de Porto Alegre, RS. Foi feita antropometria e dosagem de hemoglobina pelo fotômetro portátil HemoCue, considerando-se anemia níveis inferiores a 11 g/dl. As informações sobre as crianças foram obtidas por questionário aplicado às mães. A associação das variáveis estudadas com a anemia foi analisada pela técnica de regressão log-binomial aplicada ao modelo hierárquico. RESULTADOS: Encontrou-se uma prevalência de anemia de 47,8% entre toda a população estudada, cujos determinantes foram: famílias com renda per capita igual ou inferior a um salário-mínimo (razão de prevalência [RP] = 1,6), faixa etária de 12 a 23 meses (RP=1,4) e presença de dois ou mais irmãos com menos de cinco anos (RP=1,4). CONCLUSÕES: A prevalência de anemia na população estudada é bastante elevada, especialmente nas crianças de nível socioeconômico mais baixo, na faixa etária de 12 a 23 meses, e nas crianças com dois ou mais irmãos com menos de cinco anos, indicando a necessidade urgente de medidas efetivas visando o seu combate e a sua prevenção.

Cr2O3 thin films grown at room temperature by low pressure laser chemical vapour deposition

Chromia (Cr2O3) has been extensively explored for the purpose of developing widespread industrial applications, owing to the convergence of a variety of mechanical, physical and chemical properties in one single oxide material. Various methods have been used for large area synthesis of Cr2O3 films. However, for selective area growth and growth on thermally sensitive materials, laser-assisted chemical vapour deposition (LCVD) can be applied advantageously. Here we report on the growth of single layers of pure Cr2O3 onto sapphire substrates at room temperature by low pressure photolytic LCVD, using UV laser radiation and Cr(CO)(6) as chromium precursor. The feasibility of the LCVD technique to access selective area deposition of chromia thin films is demonstrated. Best results were obtained for a laser fluence of 120 mJ cm(-2) and a partial pressure ratio of O-2 to Cr(CO)(6) of 1.0. Samples grown with these experimental parameters are polycrystalline and their microstructure is characterised by a high density of particles whose size follows a lognormal distribution. Deposition rates of 0.1 nm s(-1) and mean particle sizes of 1.85 mu m were measured for these films. (C) 2011 Elsevier B.V. All rights reserved.

A new chemical route to synthesise TM-doped (TM = Co, Fe) TiO2 nanoparticles

Since the discovery of ferromagnetism well above room temperature in the Co-doped TiO2 system, diluted magnetic semiconductors based on TiO2 doped with transition metals have generated great interest because of their potential use in the development of spintronic devices. The purpose of this paper is to report on a new and swift chemical route to synthesise highly stable anatase single-phase Co- and Fe-doped TiO2 nanoparticles, with dopant concentrations of up to 10 at.-% and grain sizes that range between 20 and 30 nm. Complementary structural, microstructural and chemical analyses of the different nanopowders synthesised strongly support the hypothesis that a homogeneous distribution of the dopant element in the substitutional sites of the anatase structure has been achieved. Moreover, UV/Vis diffuse reflectance spectra of powder samples show redshifts to lower energies and decreasing bandgap energies with increasing Co or Fe concentration, which is consistent with n-type doping of the TiO2 anatase matrix. Films of Co-doped TiO2 were successfully deposited onto Si (100) substrates by the dip-coating method, with suspensions of Ti1-xCOxO2 nanoparticles in ethylene glycol. ((C)Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

KrF pulsed laser deposition of chromium oxide thin films from Cr8O21 targets

Chromium oxides, CrxOy, are of great interest due to the wide variety of their technological applications. Among them, CrO2 has been extensively investigated in recent years because it is an attractive compound for use in spintronic heterostructures. However, its synthesis at low temperatures has been a difficult task due to the metastable nature of this oxide. This is indeed essential to ensure interface quality and the ability to coat thermal-sensitive materials such as those envisaged in spintronic devices. Pulsed Laser Deposition (PLD) is a technique that has the potential to meet the requirements stated above. In this work, we describe our efforts to grow chromium oxide thin films by PLD from Cr8O21 targets, using a KrF excimer laser. The as-deposited films were investigated by X-ray diffraction and Rutherford backscattering spectrometry. Structural and chemical composition studies showed that the films consist of a mixture of amorphous chromium oxides exhibiting different stoichiometries depending on the processing parameters, where nanocrystals of mainly Cr2O3 are dispersed. The analyses do not exclude the possibility of co-deposition of Cr2O3 and a low fraction of CrO2.

Laser-assisted deposition of thin films from photoexcited vapour phases

Laser-assisted chemical vapour deposition (LCVD) has been extensively studied in the last two decades. A vast range of applications encompass various areas such as microelectronics, micromechanics, microelectromechanics and integrated optics, and a variety of metals, semiconductors and insulators have been grown by LCVD. In this article, we review briefly the LCVD process and present two case studies of thin film deposition related to laser thermal excitation (e.g., boron carbide) and non-thermal excitation (e.g., CrO(2)) of the gas phase.

Femtosecond laser ablation of dentin

The surface morphology, structure and composition of human dentin treated with a femtosecond infrared laser (pulse duration 500 fs, wavelength 1030 nm, fluences ranging from 1 to 3 J cm(-2)) was studied by scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The average dentin ablation threshold under these conditions was 0.6 +/- 0.2 J cm(-2) and the ablation rate achieved in the range 1 to 2 mu m/pulse for an average fluence of 3 J cm(-2). The ablation surfaces present an irregular and rugged appearance, with no significant traces of melting, deformation, cracking or carbonization. The smear layer was entirely removed by the laser treatment. For fluences only slightly higher than the ablation threshold the morphology of the laser-treated surfaces was very similar to the dentin fracture surfaces and the dentinal tubules remained open. For higher fluences, the surface was more porous and the dentin structure was partially concealed by ablation debris and a few resolidified droplets. Independently on the laser processing parameters and laser processing method used no sub-superficial cracking was observed. The dentin constitution and chemical composition was not significantly modified by the laser treatment in the processing parameter range used. In particular, the organic matter is not preferentially removed from the surface and no traces of high temperature phosphates, such as the beta-tricalcium phosphate, were observed. The achieved results are compatible with an electrostatic ablation mechanism. In conclusion, the high beam quality and short pulse duration of the ultrafast laser used should allow the accurate preparation of cavities, with negligible damage of the underlying material.