Electronic excitations in solids studied using inelastic x-ray scattering

Inelastic x-ray scattering can be used to study the electronic structure of matter. The x rays scattered from the target both induce and carry information on the electronic excitations taking place in the system. These excitations are the manifestations of the electronic structure and the physics governing the many-body system. This work presents results of non-resonant inelastic x-ray scattering experiments on a range of materials including metallic, insulating and semiconducting compounds as well as an organic polymer. The experiments were carried out at the National Synchrotron Light Source, USA and at the European Synchrotron Radiation Facility, France. The momentum transfer dependence of the experimental valence- and core-electron excitation spectra is compared with the results of theoretical first principles computations that incorporate the electron-hole interaction. A recently developed method for analyzing the momentum transfer dependence of core-electron excitation spectra is studied in detail. This method is based on real space multiple scattering calculations and is used to extract the angular symmetry components of the local unoccupied density of final states.

Characterization of non-imaging semiconductor X-ray solar monitors

The first observations of solar X-rays date back to late 1940 s. In order to observe solar X-rays the instruments have to be lifted above the Earth s atmosphere, since all high energy radiation from the space is almost totally attenuated by it. This is a good thing for all living creatures, but bad for X-ray astronomers. Detectors observing X-ray emission from space must be placed on-board satellites, which makes this particular discipline of astronomy technologically and operationally demanding, as well as very expensive. In this thesis, I have focused on detectors dedicated to observing solar X-rays in the energy range 1-20 keV. The purpose of these detectors was to measure solar X-rays simultaneously with another X-ray spectrometer measuring fluorescence X-ray emission from the Moon surface. The X-ray fluorescence emission is induced by the primary solar X-rays. If the elemental abundances on the Moon were to be determined with fluorescence analysis methods, the shape and intensity of the simultaneous solar X-ray spectrum must be known. The aim of this thesis is to describe the characterization and operation of our X-ray instruments on-board two Moon missions, SMART-1 and Chandrayaan-1. Also the independent solar science performance of these two almost similar X-ray spectrometers is described. These detectors have the following two features in common. Firstly, the primary detection element is made of a single crystal silicon diode. Secondly, the field of view is circular and very large. The data obtained from these detectors are spectra with a 16 second time resolution. Before launching an instrument into space, its performance must be characterized by ground calibrations. The basic operation of these detectors and their ground calibrations are described in detail. Two C-flares are analyzed as examples for introducing the spectral fitting process. The first flare analysis shows the fit of a single spectrum of the C1-flare obtained during the peak phase. The other analysis example shows how to derive the time evolution of fluxes, emission measures (EM) and temperatures through the whole single C4 flare with the time resolution of 16 s. The preparatory data analysis procedures are also introduced in detail. These are required in spectral fittings of the data. A new solar monitor design equipped with a concentrator optics and a moderate size of field of view is also introduced.

Preliminary X-ray crystallographic analysis of 2-methylcitrate synthase from Salmonella typhimurium

Analysis of the genomic sequences of Escherichia coli and Salmonella typhimurium has revealed the presence of several homologues of the well studied citrate synthase (CS). One of these homologues has been shown to code for 2-methylcitrate synthase (2-MCS) activity. 2-MCS catalyzes one of the steps in the 2-methylcitric acid cycle found in these organisms for the degradation of propionate to pyruvate and succinate. In the present work, the gene coding for 2-MCS from S. typhimurium (StPrpC) was cloned in pRSET-C vector and overexpressed in E. coli. The protein was purified to homogeneity using Ni-NTA affinity chromatography. The purified protein was crystallized using the microbatch-under-oil method. The StPrpC crystals diffracted X-rays to 2.4 A resolution and belonged to the triclinic space group P1, with unit-cell parameters a = 92.068, b = 118.159, c = 120.659 A, alpha = 60.84, beta = 67.77, gamma = 81.92 degrees. Computation of rotation functions using the X-ray diffraction data shows that the protein is likely to be a decamer of identical subunits, unlike CSs, which are dimers or hexamers.

New computational approaches for inelastic x-ray scattering

Inelastic x-ray scattering spectroscopy is a versatile experimental technique for probing the electronic structure of materials. It provides a wealth of information on the sample's atomic-scale structure, but extracting this information from the experimental data can be challenging because there is no direct relation between the structure and the measured spectrum. Theoretical calculations can bridge this gap by explaining the structural origins of the spectral features. Reliable methods for modeling inelastic x-ray scattering require accurate electronic structure calculations. This work presents the development and implementation of new schemes for modeling the inelastic scattering of x-rays from non-periodic systems. The methods are based on density functional theory and are applicable for a wide variety of molecular materials. Applications are presented in this work for amorphous silicon monoxide and several gas phase systems. Valuable new information on their structure and properties could be extracted with the combination of experimental and computational methods.

The CaO-SrO-CuO-O-2 system: Phase equilibria and thermodynamic properties at 1123 K

Phase relationships in the CaO-SrO-CuO system in pure oxygen at 1.01 x 10(5) Pa pressure were determined by equilibrating different compositions at 1123 K for similar to 120 h and analyzing the phases present in the quenched samples using X-ray diffraction (XRD), optical and scanning electron microscopy, and energy dispersive analysis of X-rays (EDAX). Four solid solution series were observed in the system, The CawSr1-wO monoxide solid solution with rock-salt structure was found to exhibit an asymmetric miscibility gap, The mixing properties of the monoxide system were deduced using a subregular solution model, For the (CaxSr1-x)(2)CuO3 series, a complete solid solution range with orthorhombic space group Immm was obtained. Calcium substituted for strontium up to 68 at. % in SrCuO2+delta and 51.5 at. % in Sr14Cu24O41-delta. The tie lines between the solid solutions were determined accurately, The activity-composition relations in (CaxSr1-x)(2)CuO3, CaySr1-yCuO2+delta, and (Ca2Sr1-z)(14)Cu24O41-delta solid solutions were determined from experimental tie lines. Activities in the (CaxSr1-x)(2)CuO3 and CaySr1-yCuO2+delta series were close to the predictions of the Temkin model, The behavior of the (CazSr1-(z))(14)Cu24O41-delta solid solution was more complex, with the activity of SrCu(24/14)O-(41-delta/14) exhibiting both positive and negative deviations from ideality. Gibbs energy of formation of the CaCuO2+delta metastable phase at 1123 K was deduced from an analysis of the phase diagram.

Cloning, expression, purification and preliminary X-ray diffraction studies of a putative Mycobacterium smegmatis thiolase

Thiolases are important in fatty-acid degradation and biosynthetic pathways. Analysis of the genomic sequence of Mycobacterium smegmatis suggests the presence of several putative thiolase genes. One of these genes appears to code for an SCP-x protein. Human SCP-x consists of an N-terminal domain (referred to as SCP2 thiolase) and a C-terminal domain (referred as sterol carrier protein 2). Here, the cloning, expression, purification and crystallization of this putative SCP-x protein from M. smegmatis are reported. The crystals diffracted X-rays to 2.5 angstrom resolution and belonged to the triclinic space group P1. Calculation of rotation functions using X-ray diffraction data suggests that the protein is likely to possess a hexameric oligomerization with 32 symmetry which has not been observed in the other six known classes of this enzyme.

Preliminary X-ray crystallographic studies on acetate kinase (AckA) from Salmonella typhimurium in two crystal forms

Acetate kinase (AckA) catalyzes the reversible transfer of a phosphate group from acetyl phosphate to ADP, generating acetate and ATP, and plays a central role in carbon metabolism. In the present work, the gene corresponding to AckA from Salmonella typhimurium (StAckA) was cloned in the IPTG-inducible pRSET C vector, resulting in the attachment of a hexahistidine tag to the N-terminus of the expressed enzyme. The recombinant protein was overexpressed, purified and crystallized in two different crystal forms using the microbatch-under-oil method. Form I crystals diffracted to 2.70 angstrom resolution when examined using X-rays from a rotating-anode X-ray generator and belonged to the monoclinic space group C2, with unit-cell parameters a = 283.16, b = 62.17, c = 91.69 angstrom, beta = 93.57 degrees. Form II crystals, which diffracted to a higher resolution of 2.35 angstrom on the rotating-anode X-ray generator and to 1.90 angstrom on beamline BM14 of the ESRF, Grenoble, also belonged to space group C2 but with smaller unit-cell parameters (a = 151.01, b = 78.50, c = 97.48 angstrom, beta = 116.37 degrees). Calculation of Matthews coefficients for the two crystal forms suggested the presence of four and two protomers of StAckA in the asymmetric units of forms I and II, respectively. Initial phases for the form I diffraction data were obtained by molecular replacement using the coordinates of Thermotoga maritima AckA (TmAckA) as the search model. The form II structure was phased using a monomer of form I as the phasing model. Inspection of the initial electron-density maps suggests dramatic conformational differences between residues 230 and 300 of the two crystal forms and warrants further investigation.

Constraints on axino warm dark matter from X-ray observation at the Chandra telescope and SPI

A sufficiently long lived warm dark matter could be a source of X-rays observed by satellite based X-ray telescopes. We consider axinos and gravitinos with masses between 1 keV and 100 keV in supersymmetric models with sin all R-parity violation. We show that axino dark matter receives significant constraints from X-ray observations of Chandra and SPI, especially for the lower end of the allowed range of the axino decay constant f(a), while the gravitino dark matter remains unconstrained.

Compositional dependence properties change in S40Se60-x,Sb-x alloys

Bulk samples of S40Se60,Sb-x (with x=10, 20, 30 and 40 at. %) were prepared from high purity chemicals by melt quenching technique. The samples compositions were confirmed by using energy dispersive analysis of X-rays. X-ray diffraction studies revealed that all the samples have poly-crystalline phase. The variation in optical properties with compositional has been investigated by X-ray photoelectron spectroscopy and Raman spectroscopy. The optical band gap of the thin films is found to be decreased with composition. Increasing Sb content was found to affect the structural and optical properties of bulk samples. The intensity of core level spectra changes with the addition of Sb clearly interprets the optical properties change due to compositional variation. The Raman shift and new peak formation in these samples clearly show the structural modifications due to Sb addition.

Multiwavelength observations of the black hole candidate 1E 1740.7-2942

Observations of the Galactic center region black hole candidate 1E 1740.7-2942 have been carried out using the Caltech Gamma-Ray Imaging Payload (GRIP), the Röntgensatellit (ROSAT) and the Very Large Array (VLA). These multiwavelength observations have helped to establish the association between a bright emitter of hard X-rays and soft γ-rays, the compact core of a double radio jet source, and the X-ray source, 1E 1740.7-2942. They have also provided information on the X-ray and hard X-ray spectrum.

The Galactic center region was observed by GRIP during balloon flights from Alice Springs, NT, Australia on 1988 April 12 and 1989 April 3. These observations revealed that 1E 1740.7-2942 was the strongest source of hard X-rays within ~10° of the Galactic center. The source spectrum from each flight is well fit by a single power law in the energy range 35-200 keV. The best-fit photon indices and 100 keV normalizations are: γ = (2.05 ± 0.15) and K_(100) = (8.5 ± 0.5) x 10^(-5) cm^(-2) s^(-1) keV^(-1) and γ = (2.2 ± 0.3) and K_(100) = (7.0 ± 0.7) x 10^(-5) cm^(-2) s^(-1) keV^(-1) for the 1988 and 1989 observations respectively. No flux above 200 keV was detected during either observation. These values are consistent with a constant spectrum and indicate that 1E 1740.7-2942 was in its normal hard X-ray emission state. A search on one hour time scales showed no evidence for variability.

The ROSAT HRI observed 1E 1740.7-2942 during the period 1991 March 20-24. An improved source location has been derived from this observation. The best fit coordinates (J2000) are: Right Ascension = 17^h43^m54^s.9, Declination = -29°44'45".3, with a 90% confidence error circle of radius 8".5. The PSPC observation was split between periods from 1992 September 28- October 4 and 1993 March 23-28. A thermal bremsstrahlung model fit to the data yields a column density of N_H = 1.12^(+1.51)_(0.18) x cm^(-2) , consistent with earlier X- ray measurements.

We observed the region of the Einstein IPC error circle for 1E 1740.7-2942 with the VLA at 1.5 and 4.9 GHz on 1989 March 2. The 4.9 GHz observation revealed two sources. Source 'A', which is the core of a double aligned radio jet source (Mirabel et al. 1992), lies within our ROSAT error circle, further strengthening its identification with 1E 1740.7-2942.

Studying atomic-resolution by X-ray fluorescence holography

In this work, the results of numerical simulations of X-ray fluorescence holograms and the reconstructed atomic images for Fe single crystal are given. The influences of the recording angles ranges and the polarization effect on the reconstruction of the atomic images are discussed. The process for removing twin images by multiple energy fluorescence holography and expanding the energy range of the incident X-rays to improve the resolution of the reconstructed images is presented. (c) 2005 Elsevier B.V. All rights reserved.

Análise de tensões residuais pela técnica de difração de raios X em processos de soldagem MIG

Nesse trabalho foram realizados experimentos para determinar as tensões residuais introduzidas no Aço A36, que é uma liga de baixo carbono e que é muito utilizado em vários setores da produção industrial, quando esta é submetida à soldagem do tipo MIG (Metal Gas Inert). A escolha desse tipo de soldagem foi para manter constantes os parâmetros que pudessem influenciar nos resultados. Nessa análise foi verificada a distribuição das tensões residuais na zona termicamente afetada, a distribuição da tensão em relação a profundidade. Para isso usamos uma remoção eletrolítica e um corte transversal pelo processo de eletroerosão. Nesse trabalho foi usado o método do sen2, devido a sua facilidade para a análise dos dados do Programa PSD. O resultado das mediadas realizadas na região do cordão de solda, zona termicamente afetada (ZTA) e metal base próxima da ZTA, mostrou uma variação da distribuição da tensão em relação à profundidade do material e na distância do ponto de soldagem. No ponto de soldagem um aumento da tensão em relação à profundidade do material. Os fatores que influenciaram na introdução dessas tensões no processo de soldagem, foram causados pelo gradiente de temperatura, pelo resfriamento heterogêneo do material e também pelo resfriamento rápido da superfície

Aplicabilidade da Norma Regulamentadora 32: visão dos trabalhadores de enfermagem de um hospital público do RJ

Pesquisa de natureza descritiva e abordagem quantitativa de dados sobre a Aplicabilidade da Norma Regulamentadora-32 (NR 32) do Ministério do Trabalho e Emprego (MTE), visando mobilizar os trabalhadores de enfermagem para reduzir a exposição aos riscos inerentes do trabalho em estabelecimentos de saúde. Problema de pesquisa: Quais os fatores que interferem na implantação da Norma Regulamentadora-32 nas enfermarias de um Hospital Público Estadual do Rio de Janeiro, na visão dos trabalhadores de enfermagem? Teve como objetivo geral analisar os fatores que interferem na aplicabilidade da NR 32 pela enfermagem, em um hospital público do Rio de Janeiro. A população foi composta de 138 trabalhadores de enfermagem das enfermarias de clínica médica, cirúrgica e ortopédica. Utilizou-se para a coleta de dados um questionário estruturado com perguntas fechadas. Os dados foram coletados no período de 28 de janeiro a 14 de fevereiro de 2009, e analisados através do Programa Statical Package for the Social Sciences (SPSS) versão 13 for Windows e Microsoft Office Excel 2003. Os resultados apontaram que os trabalhadores de enfermagem desse hospital estão, em sua maioria, na faixa etária de 30-49 anos, com pelo menos 1 ano de atuação no mesmo setor e formaram-se há 15 anos ou mais, além disso, 68,1% são estatutários. Constatou-se que há recomendações da NR-32 e precauções-padrão não são seguidas pelos participantes da pesquisa. Os fatores que interferem no cumprimento da atual legislação vão desde o desconhecimento dos riscos ocupacionais e comportamento dos trabalhadores, até a falta de uma ação efetiva de Educação Continuada e da Comissão de Controle de Infecção Hospitalar (CCIH). Destacaram-se, entre outros, o uso de adornos (51,8%); calçado aberto (48,9%); alimentação no posto de trabalho (46,3%); uso da pia para outras finalidades (44,9%), reencape ou desconexão manual de agulhas (36,4%); sair do local de trabalho com uniforme ou Equipamento de Proteção Individual - EPI (21%); limite de recipiente de descarte de perfurocortantes não respeitado (11,8%), falta de uso de EPI quando auxilia no exame com Raios-X (32,6%) e na manipulação de quimioterápicos (7,8%). A instituição não fornece uniformes nem calçados. Outros fatores institucionais foram a falta de equipamentos, a falta de um política de prevenção e promoção da saúde, inexistência de serviço de saúde ocupacional e instalações físicas inadequadas. Tal descumprimento expõe, de forma excessiva, os trabalhadores de enfermagem aos mais variados fatores de riscos ocupacionais, podendo refletir na sua saúde e no processo de trabalho. Recomenda-se um trabalho efetivo e integrado dos Programas de Educação Continuada e CCIH para esclarecimento dos trabalhadores de enfermagem, e implantação do Serviço de Saúde do Trabalhador. Sugere-se aos gestores expandirem este estudo para os demais setores das unidades hospitalares e outras instituições públicas de saúde para o conhecimento da situação de trabalho, bem como a criação de espaços de discussão para a busca de soluções dos problemas com a participação dos trabalhadores.

Efeitos de raios-X de baixa energia em células mamárias

Doses de radiação de baixa energia podem induzir quebras de dupla fita no DNA assim como também produzir perfis alterados de expressão de genes relacionados a estas lesões. Os danos não reparados ou mal reparados levam a uma maior suscetibilidade à transformação oncogênica já que os efeitos biológicos mais importantes causados pela radiação ionizante são mutação e carcinogênese. As lesões no DNA provocadas pela radiação podem também ocasionar o surgimento micronúcleos e as células podem ser induzidas à apoptose. O objetivo deste trabalho é estudar in vitro a presença de micronúcleos e a apoptose ocasionados por Raios-X de baixa energia. Pretende-se analisar estes efeitos biológicos em relação à energia equivalente à utilizada em exames mamográficos usando duas linhagens estabelecias de células de mama: a MCF-7 (tumoral) e a HB-2 (não-tumoral). As células, em crescimento exponencial, foram irradiadas no equipamento de arranjo experimental de mamografia do LCR/UERJ. A dose de 5Gy na energia de 30 kV foi aplicada com taxa de 0,1 Gy/seg utilizando filtro de 0,03 mm de molibdênio. As irradiações foram realizadas duas vezes, após as irradiações, as células foram incubadas por 4, 24 ou 48 horas e posteriormente coradas com o corante Hoechst33258 para análise em microscopia de fluorescência. Para cada análise, 1000 células foram categorizadas pela morfologia do núcleo. Os resultados mostraram que a HB-2, utilizada neste estudo como célula mamária normal, apresentou maior sensibilidade aos efeitos da radiação, com 37 % das células em apoptose após 4 hs de incubação, enquanto a MCF-7 apresentou 6,5 %. Nas análises após 24 hs foi possível confirmar a radioresistência da MCF-7 tendo sido observadas 11% de células em apoptose no grupo irradiado. Houve um aumento crescente de micronúcleos radioinduzidos nas duas linhagens de acordo com os tempos de incubação. Na análise de 4 hs a HB-2 apresentou 3%, em 24 hs, 8,5% e 48 hs, 11,5 %. Diante destes resultados, foi possível concluir que a energia do feixe de raios-X utilizada na mamografia pode ser capaz de ocasionar aumento de ocorrência de apoptose e geração de micronúcleos nas duas linhagens estudadas

一个基于X射线摄像的智能图像诊断系统

针对用软件进行病态和可疑目标识别具有造价低、可维护性好等优点 ,提出了一种简单实用的图像子图像的提取、分割、去噪与增强的改进算法 ,设计和实现了一个实用的基于X射线摄影的智能图像处理系统。实验表明 ,该系统性能稳定 ,算法优越 ,可以大幅度提高图像质量 ,增强图像的视觉效果 ,提供更准确、分辨率更高、更满意的图像。在图像预处理等方面优于国内外同类系统。该系统的推广使用 ,将对无损检测产生深远的影响