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Evaluation of Femtosecond Laser-Induced Breakdown Spectroscopy for Analysis of Animal Tissues

SANTOS JR., Dario; SAMAD, Ricardo Elgul; TREVIZAN, Lilian Cristina; FREITAS, Anderson Zanardi de; VIEIRA JR., Nilson Dias; KRUG, Francisco Jost
Fonte: SOC APPLIED SPECTROSCOPY Publicador: SOC APPLIED SPECTROSCOPY
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.2734%
The aim of this work was to evaluate the performance of femtosecond laser-induced breakdown spectroscopy (fs-LIBS) for the determination of elements in animal tissues. Sample pellets were prepared from certified reference materials, such as liver, kidney, muscle, hepatopancreas, and oyster, after cryogenic grinding assisted homogenization. Individual samples were placed in a two-axis computer-controlled translation stage that moved in the plane orthogonal to a beam originating from a Ti:Sapphire chirped-pulse amplification (CPA) laser system operating at 800 mu and producing a train of 840 mu J and 40 fs pulses at 90 Hz. The plasma emission was coupled into the optical fiber of a high-resolution intensified charge-coupled device (ICCD)-echelle spectrometer. Time-resolved characteristics of the laser-produced plasmas showed that the best results were obtained with delay times between 80 and 120 ns. Data obtained indicate both that it is a matrix-independent sampling process and that fs-LIBS can be used for the determination of Ca, Cu, Fe, K, Mg, Na, and P, but efforts must be made to obtain more appropriate detection limits for Al, Sr, and Zn.; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[98/14270-8]; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[00/15135-9]; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[04/15965-2]; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[05/50773-0]; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[06/06466-8]; Conselho Nacional de Desenvolvinnento Cientifico e Tecnologico (CNPq)[477385/2006-0]; Conselho Nacional de Desenvolvinnento Cientifico e Tecnologico (CNPq)[301285/2006-3]

Simultaneous optimization by neuro-genetic approach for analysis of plant materials by laser induced breakdown spectroscopy

NUNES, Lidiane Cristina; SILVA, Gilmare Antonia da; TREVIZAN, Lilian Cristina; SANTOS JUNIOR, Dario; POPPI, Ronei Jesus; KRUG, Francisco Jose
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.304456%
A simultaneous optimization strategy based on a neuro-genetic approach is proposed for selection of laser induced breakdown spectroscopy operational conditions for the simultaneous determination of macronutrients (Ca, Mg and P), micro-nutrients (B, Cu, Fe, Mn and Zn), Al and Si in plant samples. A laser induced breakdown spectroscopy system equipped with a 10 Hz Q-switched Nd:YAG laser (12 ns, 532 nm, 140 mJ) and an Echelle spectrometer with intensified coupled-charge device was used. Integration time gate, delay time, amplification gain and number of pulses were optimized. Pellets of spinach leaves (NIST 1570a) were employed as laboratory samples. In order to find a model that could correlate laser induced breakdown spectroscopy operational conditions with compromised high peak areas of all elements simultaneously, a Bayesian Regularized Artificial Neural Network approach was employed. Subsequently, a genetic algorithm was applied to find optimal conditions for the neural network model, in an approach called neuro-genetic, A single laser induced breakdown spectroscopy working condition that maximizes peak areas of all elements simultaneously, was obtained with the following optimized parameters: 9.0 mu s integration time gate, 1.1 mu s delay time...

Correlação entre a espectroscopia de fluorescência induzida pelo laser e as alterações histológicas na isquemia e reperfusão renal em ratos; Correlations between the laser-induced fluorescence spectroscopy and histological changes in kidney ischemia and reperfusion in rats.

Cassini, Marcelo Ferreira
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 21/09/2012 PT
Relevância na Pesquisa
36.328762%
Introdução: O transplante renal é amplamente reconhecido como a melhor forma de tratamento para os pacientes que necessitam de terapia de substituição renal. Frequentemente a equipe transplantadora se depara com a difícil questão de determinar se órgãos, provenientes de doadores falecidos e limítrofes ou em parada cardíaca, estão aptos para serem transplantados. É difícil quantificar a intensidade do dano provocado pela isquemia no enxerto a ser utilizado, especialmente se o doador apresentou quadro de instabilidade hemodinâmica com queda significativa da perfusão tecidual e aumento do risco de diminuir a função do enxerto e afetar adversamente sua sobrevida. Desta forma torna-se justificável a utilização da técnica de espectroscopia de fluorescência induzida pelo laser, na tentativa de se avaliar a correlação entre os seus achados e o grau de lesão histológica renal experimental, uma vez que se trata de um método objetivo, não invasivo, rápido e em tempo real que, futuramente, pode ser aplicada nos transplantes renais em humanos. Objetivos: Avaliar a correlação entre os dados da espectroscopia de fluorescência induzida pelo laser e alterações histológicas na isquemia e reperfusão renal em ratos...

Avaliação das lesões císticas da neurocisticercose na difusão e espectroscopia de prótons pela ressonância magnética; Evaluation of the cystic lesions of the neurocysticercosis on diffusion and magnetic resonance proton spectroscopy

Raffin, Luciana Sanchez
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 27/10/2004 PT
Relevância na Pesquisa
36.328762%
OBJETIVO: O objetivo deste estudo é descrever as características do sinal nas lesões císticas da neurocisticercose nas imagens ponderadas em difusão e os metabólitos encontrados na espectroscopia de prótons. MATERIAL E MÉTODOS: Estudaram-se 38 pacientes (39 lesões) com neurocisticercose, usando-se difusão e espectroscopia de prótons. Os exames foram realizados em um magneto de 1,5 T (Signa Horizon LX: GE Medical Systems). A difusão foi realizada no plano axial, com múltiplos cortes com seqüência eco planar. A espectroscopia de prótons utilizou a seqüência PRESS (point-resolved spectroscopy) com TR of 1500 ms e TE de 30/135 ms. RESULTADOS: Os cistos apresentaram intensidade de sinal similar a do líquido cefalorraqueano (LCR) na difusão e valores de CDA sobreponíveis, variando de 1,36 a 3,18 x 10-3 mm2/s. Os picos detectáveis na espectroscopia foram lactato (96,3%), succinato (48%), alanina (40%), lipídeos (15%), aminoácidos citosólicos (7,5%) e acetato (3,7%). CONCLUSÃO: As lesões císticas da neurocisticercose apresentaram hipossinal na difusão e os picos encontrados na espectroscopia de prótons, em ordem decrescente de freqüência, foram lactato, succinato, alanina, lipídeos, aminoácidos citosólicos e acetato; PURPOSE: The objective of this study is to describe the signal behavior of cystic neurocysticercotic lesions on diffusion-weighted imaging (DWI) and single voxel proton spectroscopy findings. MATERIALS AND METHODS: We studied 38 patients (39 lesions) with neurocysticercosis...

Phase transition in poly(vinylidene fluoride) investigated with micro-Raman spectroscopy

Constantino, CJL; Job, A. E.; Simoes, R. D.; Giacometti, J. A.; Zucolotto, V; Oliveira, O. N.; Gozzi, G.; Chinaglia, D. L.
Fonte: Soc Applied Spectroscopy Publicador: Soc Applied Spectroscopy
Tipo: Artigo de Revista Científica Formato: 275-279
ENG
Relevância na Pesquisa
46.23232%
The phase transition from the non-polar a-phase to the polar beta-phase of poly(vinylidene fluoride) (PVDF) has been investigated using micro-Raman spectroscopy, which is advantageous because it is a nondestructive technique. Films of alpha-PVDF were subjected to stretching under controlled rates at 80 degrees C, while the transition to P-PVDF was monitored by the decrease in the Raman band at 794 cm(-1) characteristic of the a-phase, along with the concomitant increase in the 839 cm-1 band characteristic of the P-phase. The alpha ->beta transition in our PVDF samples could be achieved even for the sample stretched to twice (2 X -stretched) the initial length and it did not depend on the stretching rate in the range between 2.0 and 7.0 mm/min. These conclusions were corroborated by differential scanning calorimetry (DSC) and X-ray diffraction experiments for PVDF samples processed under the same conditions as in the Raman scattering measurements. Poling with negative corona discharge was found to affect the a-PVDF morphology, improving the Raman bands related to this crystalline phase. This effect is minimized for films stretched to higher ratios. Significantly, corona-induced effects could not be observed with the other experimental techniques...

Raman Spectroscopy and Scanning Electron Microscopy Characterizations of Fission Track Method Datable Zircon Grains

Resende, Rosana Silveira; Tello Saenz, Carlos Alberto; Campos Curvo, Eduardo Augusto; Leopoldo Constantino, Carlos Jose; Aroca, Ricardo F.; Nakasuga, Wagner Massayuki
Fonte: Soc Applied Spectroscopy Publicador: Soc Applied Spectroscopy
Tipo: Artigo de Revista Científica Formato: 549-556
ENG
Relevância na Pesquisa
46.175444%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Spectroscopic and morphological studies, designed to improve our understanding of the physicochemical phenomena that occur during zircon crystallization, are presented. The zircon fission track method (ZFTM) is used routinely in various laboratories around the world; however, there are some methodological difficulties needing attention. Depending on the surface fission track density observed under an optical microscope, the zircon grain surfaces are classified as homogeneous, heterogeneous, hybrid, or anomalous. In this study, zircon grain surfaces are characterized using complementary techniques such as optical microscopy (OM), micro-Raman spectroscopy, and scanning electron microscopy (SEM), both before and after chemical etching. Our results suggest that anomalous grains have subfamilies and that etching anisotropy related to heterogeneous grains is due to different crystallographic faces within the same polished surface that cannot be observed under an optical microscope. The improved methodology was used to determine the zircon fission track ages of samples collected from the Bauru Group located in the north of Parana Basin...

Characterization of wine fermentations using fiber optic-mediated UV-VIS-SWNIR spectroscopy

Silva, J. S.; Castro, C. C.; Mendes, Inês; Duarte, Ricardo Franco; Vicente, A. A.; Schuller, Dorit; Martins, Rui C.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2011 ENG
Relevância na Pesquisa
36.364355%
Spectroscopy is widely used in biological sciences, being applied to liquids, pastes, powders, films, fibers, gases and surfaces. It makes possible to characterize proteins, peptides, lipids, membranes and carbohydrates in pharmaceuticals, foods, plants or animal tissues. It can also provide detailed information about the structure and mechanism of action of molecules. UV-VIS-SWNIR spectroscopy has not been used for fermentations characterization. This is possibly attributed to the fact that UV-VIS spectroscopy records transmissions between electron energy levels from molecular orbitals, which do not have a direct relationship with the presence/concentration of compounds, instead of vibrational or structural oscillation of molecular groups as in the infrared region, where such relationship is more straightforward. UV-VIS-SWNIR spectroscopy registers many features such as fluorescence and vibrational resonances due to energy decay of exited electrons, which may provide highly accurate fingerprinting of metabolites and metabolic state of the fermentation, provided that an adequate data treatment and interpretation system is available. In this work we explore the use of fiber optics UV-VIS-SWNIR spectroscopy to characterize wine fermentations of a Saccharomyces cerevisiae collection. This collection comprises 114 strains (among which almost 40 are sequenced strains)...

Observation Volumes and γ-Factors in Two-Photon Fluorescence Fluctuation Spectroscopy

Nagy, Attila; Wu, Jianrong; Berland, Keith M.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.328762%
Fluorescence fluctuation spectroscopy has become an important measurement tool for investigating molecular dynamics, molecular interactions, and chemical kinetics in biological systems. Although the basic theory of fluctuation spectroscopy is well established, it is not widely recognized that saturation of the fluorescence excitation can dramatically alter the size and profile of the fluorescence observation volume from which fluorescence fluctuations are measured, even at relatively modest excitation levels. A precise model for these changes is needed for accurate analysis and interpretation of fluctuation spectroscopy data. We here introduce a combined analytical and computational approach to characterize the observation volume under saturating conditions and demonstrate how the variation in the volume is important in two-photon fluorescence correlation spectroscopy. We introduce a simple approach for analysis of fluorescence correlation spectroscopy data that can fully account for the effects of saturation, and demonstrate its success for characterizing the observed changes in both the amplitude and relaxation timescale of measured correlation curves. We also discuss how a quantitative model for the observed phenomena may be of broader importance in fluorescence fluctuation spectroscopy.

SEIRA Spectroscopy on a Membrane Receptor Monolayer Using Lipoprotein Particles as Carriers

Zaitseva, Ekaterina; Saavedra, Marcia; Banerjee, Sourabh; Sakmar, Thomas P.; Vogel, Reiner
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 06/10/2010 EN
Relevância na Pesquisa
36.328762%
Surface-enhanced infrared absorption (SEIRA) difference spectroscopy can probe reactions in a protein monolayer tethered to a nanostructured gold surface. SEIRA studies of membrane proteins, however, remain challenging due to sample stability, effects of the metal surface on function, and the need for a membrane-mimicking environment. Here we demonstrate and characterize a model system for membrane receptor investigations using SEIRA spectroscopy. The system employs nanoscale apolipoprotein bound bilayer (NABB) particles, similar to discoidal high-density lipoprotein particles, as soluble carriers for the G-protein-coupled receptor rhodopsin. The His-tag of the engineered apolipoprotein allows for selective binding of the NABBs to a Ni-NTA modified surface, while the lipid environment of the particle ensures stability and protection of the embedded receptor. Using SEIRA spectroscopy, we followed specific binding of rhodopsin-loaded NABB particles to the surface and formation of a membrane protein monolayer. Functionality of the photoreceptor in the immobilized NABBs was probed by SEIRA difference spectroscopy confirming protein conformational changes associated with photoactivation. Orientation of the immobilized NABB particles was assessed by comparing SEIRA data with polarized attenuated total reflection-Fourier-transform infrared spectroscopy. Thus...

Scalable NMR Spectroscopy with Semiconductor Chips

Ha, Dongwan
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
EN_US
Relevância na Pesquisa
36.421467%
Conventional nuclear magnetic resonance (NMR) spectrometers—the electronic brain that orchestrates and monitors nuclear spin motions—are bulky, expensive, thus, not scalable. In this thesis, we report on scalable 4-mm2 silicon spectrometer chips that perform a broad range of two-dimensional NMR spectroscopy—e.g., correlation spectroscopy, J-resolved spectroscopy, and heteronuclear quantum coherence spectroscopy—as well as one-dimensional spectroscopy and relaxometry. In this way, they examine a wealth of nuclear spin behaviors and interactions in biological, organic, and pharmaceutical compound molecules, elucidating their structures and dynamics. This semiconductor-based NMR spectroscopy opens up new exciting vistas with two prime advantages. First, with size/cost economy and scalability, the spectrometer chips can be parallelized sharing the same bore of a magnet—whether a large superconducting or small permanent magnet—to greatly simplify multi-channel spectroscopy and vastly increase the spectroscopy throughput, overcoming the intrinsic slowness of NMR spectroscopy; such parallelism may enable the much-desired high-throughput NMR paradigm for drug discovery, metabolomics/metabonomics, and structural biology. We demonstrate the concept of this parallelism by 2-channel heteronuclear quantum coherence NMR experiments...

In-situ monitoring of the structure of a goethite-based catalyst during methane oxidation by X-ray absorption near-edge structure (XANES) spectroscopy assisted by chemometric methods

Fonte: Society for Applied Spectroscopy Publicador: Society for Applied Spectroscopy
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.23232%
A goethite-based catalyst was evaluated using in-situ X-ray absorption near-edge structure (XANES) spectroscopy during methane oxidation under increasing reaction temperature. Determination of rank by median absolute deviation (DRMAD), evolving factor analysis (EFA), and multivariate curve resolution (MCR) were used to detect the species present in the catalyst during the reaction and determine their concentration profiles and their pure spectra. The reactants and reaction products were monitored on-line by mass spectrometer. The goethite-based catalyst was active for methane oxidation, with CO(2) and H(2)O as the main products. DRMAD and EFA were useful to determine the number of chemical species present in the catalyst structure during reactions. The catalyst presented phase transition during the reaction from goethite to maghemite according to XANES spectra determined by MCR. On the other hand, it was verified that the catalyst presented phase transition from goethite to wüstite in the process in the absence of the oxidant (O(2)).

Cerebral oxygenation monitoring by near-infrared spectroscopy is not clinically useful in patients with severe closed-head injury: a comparison with jugular venous bulb oximetry

Lewis, S.; Myburgh, J.; Thornton, E.; Reilly, P.
Fonte: Williams & Wilkins Publicador: Williams & Wilkins
Tipo: Artigo de Revista Científica
Publicado em //1996 EN
Relevância na Pesquisa
36.348303%
OBJECTIVE: To compare continuous jugular venous bulb oximetry and cerebral near-infrared spectroscopy in patients with severe closed head injury. DESIGN: A prospective observational study. SETTING: Intensive care unit of a major teaching hospital. PATIENTS: Adults (n = 10) with severe closed-head injury (Glasgow Coma Scale score of < or = 8). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Jugular venous bulb oximetry, cerebral near-infrared spectroscopy, and cerebral perfusion pressure were measured continuously. A total of 3,691 paired measurements of near-infrared spectroscopy and jugular venous bulb oximetry were analyzed. Poor correlation (r2 = .04) between paired measurements and wide limits of agreement (-13% to +21%) were demonstrated. The mean difference between measurements was +/- 4% and the standard deviation of the mean difference was +/- 8.69%. The data were subsequently grouped according to three clinically significant subgroups of jugular venous bulb oxygen saturation reflecting low ( < 55%), normal (55% to 75%) and high ( > 75%) saturation values. Poor correlation and wide limits of agreement between the two methods of measurement were observed in all groups. Values recorded by near-infrared spectroscopy did not significantly change between the groups...

Infrared spectroscopy and advanced spectral data analyses to better describe sorption of pesticides in soils.

Forouzangohar, Mohsen
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2009
Relevância na Pesquisa
36.414888%
The fate and behaviour of hydrophobic organic compounds (e.g. pesticides) in soils are largely controlled by sorption processes. Recent findings suggest that the chemical properties of soil organic carbon (OC) significantly control the extent of sorption of such compounds in soil systems. However, currently there is no practical tool to integrate the effects of OC chemistry into sorption predictions. Therefore, the K [subscript]oc model, which relies on the soil OC content (foc), is used for predicting soil sorption coefficients (K[subscript]d) of pesticides. The K[subscript]oc model can be expressed as K[subscript]d = K[subscript]oc × foc, where K[subscript]oc is the OC-normalized sorption coefficient for the compound. Hence, there is a need for a prediction tool that can effectively capture the role of both the chemical structural variation of OC as well as foc in the prediction approach. Infrared (IR) spectroscopy offers a potential alternative to the K[subscript]oc approach because IR spectra contain information on the amount and nature of both organic and mineral soil components. The potential of mid-infrared (MIR) spectroscopy for predicting K[subscript]d values of a moderately hydrophobic pesticide, diuron, was investigated. A calibration set of 101 surface soils from South Australia was characterized for reference sorption data (K[subscript]d and K[subscript]oc) and foc as well as IR spectra. Partial least squares (PLS) regression was employed to harness the apparent complexity of IR spectra by reducing the dimensionality of the data. The MIR-PLS model was developed and validated by dividing the initial data set into corresponding calibration and validation sets. The developed model showed promising performance in predicting K[subscript]d values for diuron and proved to be a more efficacious than the K[subscript]oc model. The significant statistical superiority of the MIR-PLS model over the K[subscript]oc model was caused by some calcareous soils which were outliers for the K[subscript]oc model. Apart from these samples...

Low-frequency spectroscopic analysis of monomeric and fibrillar lysozyme

Zakaria, H.; Fischer, B.; Bradley, A.; Jones, I.; Abbott, D.; Middelberg, A.; Falconer, R.
Fonte: Soc Applied Spectroscopy Publicador: Soc Applied Spectroscopy
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
36.328762%
Terahertz time-domain spectroscopy (THz-TDS) and Fourier transform infrared (FT-IR) spectroscopy were used to generate far-infrared and low-frequency spectral measurements of monomeric lysozyme and lysozyme fibrils. The formation of lysozyme fibrils was verified by the Thioflavin T assay and transmission electron microscopy (TEM). It was evident in the FT-IR spectra that between 150 and 350 cm−1 the two spectra diverge, with the lysozyme fibrils showing higher absorbance intensity than the monomeric form. The broad absorption phenomenon is likely due to light scattered from the fibrillar architecture of lysozyme fibrils as supported by simulation of Rayleigh light scattering. The lack of discrete phonon-like peaks suggest that far-infrared spectroscopy cannot detect vibrational modes between the highly ordered hydrogen-bonded beta-pleated sheets of the lysozyme subunit.; Hidayatul A. Zakaria, Bernd M. Fischer, Andrew P. Bradley, Inke Jones, Derek Abbott, Anton P.J. Middelberg, Robert J. Falconer

Sodium and potassium released from burning particles of brown coal and pine wood in a laminar premixed methane flame using quantitative laser-induced breakdown spectroscopy

Hsu, L.J.; Alwahabi, Z.; Nathan, G.; Li, Y.; Li, Z.; Alden, M.
Fonte: Soc Applied Spectroscopy Publicador: Soc Applied Spectroscopy
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
46.175444%
A quantitative point measurement of total sodium ([Na]total) and potassium ([K]total) in the plume of a burning particle of Australian Loy Yang brown coal (23 ± 3 mg) and of pine wood pellets (63 ± 3 mg) was performed using laser-induced breakdown spectroscopy (LIBS) in a laminar premixed methane flame at equivalence ratios ( U ) of 1.149 and 1.336. Calibration was performed using atomic sodium or potassium generated by evaporation of droplets of sodium sulfite (Na2SO3) or potassium sulfate (K2SO4) solutions seeded into the flame. The calibration compensated for the absorption by atomic alkalis in the seeded flame, which is significant at high concentrations of solution. This allowed quantitative measurements of sodium (Na) and potassium (K) released into the flame during the three phases of combustion, namely devolatilization, char, and ash cooking. The [Na]total in the plume released from the combustion of pine wood pellets during the devolatilization was found to reach up to 13 ppm. The maximum concentration of total sodium ([Na]maxMtotal) and potassium ([K]maxtotal) released during the char phase of burning coal particles for φ = 1.149 was found to be 9.27 and 5.90 ppm, respectively. The [Na]maxtotal and [K]maxtotal released during the char phase of burning wood particles for φ = 1.149 was found to be 15.1 and 45.3 ppm...

In vivo 1H NMR spectroscopy of the rat brain at 16.4 T; In vivo 1H NMR Spektroskopie im Rattenhirn bei 16.4 T

Hong, Sung-Tak
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
36.328762%
Since the discovery of nuclear magnetic resonance (NMR) in the middle of the 1940s, this phenomenon has become a crucial tool for investigating chemical compounds and protein structures. The introduction of imaging gradients for phase- and frequency-encoding made it possible to acquire spatial information giving rise to magnetic resonance imaging (MRI), which has been utilized widely in clinical and preclinical applications. Complementary to MRI, the development of sequences that use gradients to select a specific volume-of-interest (VOI) established magnetic resonance spectroscopy (MRS) for detecting the biochemical information in a specific location or a selected tissue type within a living subject. In contrast to MRI, which is based on the abundant signal from water, 1H MRS detects signals from protons attached to biologically more interesting molecules, suppressing the water signal, which leads to long measurement times due to the inherently low concentrations (millimolar) of the metabolites of interest. One of the fundamental approaches to solve this problem is to increase the static field strength. The goal of this thesis was to develop and optimize a localization sequence for in vivo 1H NMR spectroscopy at 16.4 T, aiming for accurate quantification of metabolites. To increase the localization performance...

Spektroskopie an Silberelektroden auf yttriumstabilisiertem Zirkondioxid; Spectroscopy on Silver Electrodes on Yttria Stabilized Zirconia

Rösch, Martin
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
36.328762%
Ein neuer Messaufbau für in situ Spektroskopie an Elektroden auf Oxidionenleitern wurde entwickelt, der ein Referenzsystem aus porösen Platinelektroden und gasförmigem Sauerstoff besitzt und elektrochemisch gut definierte Messbedingungen ermöglicht. Die Austrittsarbeit von Silberelektroden auf yttriumstabilisiertem Zirkondioxid wurde mit Ultraviolett-Photoelektronenspektroskopie bestimmt, die chemische Natur der Oberflächenspezies mit Röntgen-Photoelektronenspektroskopie. Die Austrittsarbeit einer dichten Silberelektrode lässt sich durch elektrochemische Bildung von Oberflächendipolschichten aus Sauerstoffspezies beeinflussen. Die Eigenschaften der beobachteten Sauerstoffspezies decken sich mit den in der Literatur beschriebenen Eigenschaften von Sauerstoffspezies auf Silber, die durch Adsorption bei hohen Temperaturen erzeugt wurden. Bei Messungen an porösen Elektroden auf Ionenleitern muss der Einfluss des Elektrolyten berücksichtigt werden. Man findet eine Überlagerung der Eigenschaften der Silberelektrode und der des YSZ. Bei der Bestimmung der Austrittsarbeit poröser Elektroden mit UPS wird eine effektive Austrittsarbeit bestimmt. Die Ergebnisse der elektrochemischen Charakterisierung zeigen keine signifikanten Unterschiede im Elektrodenmechanismus zwischen dichter und poröser Elektrode. Die Erfassung des frequenzabhängigen Verhaltens von Druckschwankungen in der Analysenkammer des UHV-Systems liefert zur elektrochemischen Impedanzspektroskopie komplementäre Informationen zum Elektrodenmechanismus. Diese neue Methode wird als Oberflächenimpedanzspektroskopie bezeichnet. Die Messergebnisse zeigen...

Application of Micro-Raman Spectroscopy to the Study of Yttria-Stabilized Tetragonal Zirconia Polycrystal (Y-TZP) Phase Transformation

Ramos, Carla MüeIler; Tabata, Américo Sheitiro; Cesar, Paulo Francisco; Rubo, José Henrique; Fracisconi, Paulo Afonso Silveira; Borges, Ana Flávia Sanches
Fonte: Soc Applied Spectroscopy Publicador: Soc Applied Spectroscopy
Tipo: Artigo de Revista Científica Formato: 810-814
ENG
Relevância na Pesquisa
46.2734%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 2011/18061-0; The aim of this study was to perform micro-Raman spectroscopy as an alternative and nondestructive method to identify the phase transformation of zirconia after mechanical stress. The groups evaluated were experimental zirconia, zirconcad, IPS e.max ZirCad, and In Ceram YZ. Ten specimens were constructed for each group (n = 30) and subjected to a three-point bending test with a crosshead speed of 0.5 mm/min. The fractured surfaces were analyzed by micro-Raman spectroscopy. The laser power was kept at 10 mW, and scanning was performed in three regions of the fractured surface: (i) near the source of the failure (region of tensile stress), (ii) central to the fractured surface, and (iii) far from the source of failure. All materials showed the characteristic bands of tetragonal and monoclinic phases of zirconia. All zirconia studied showed a monoclinic phase in the tensile stress region. Micro-Raman spectroscopy was effective in detecting the presence of crystalline phases in polycrystals ceramics.

Terahertz spectroscopy and modelling of biotissue.

Png, Gretel Markris Wei Na
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2010
Relevância na Pesquisa
36.328762%
Pulsed terahertz (THz, or T-ray) research has burgeoned since its inception in the mid 1980s when the first pulses of THz radiation were emitted via electro-optic sampling. At the time, this discovery was a milestone for time domain spectroscopy because existing microwave and Fourier Transform Infrared (FTIR) spectrometers were not sensitive in the 0.1–10 THz frequency range. However, it would take several years before THz generation would become practical for spectroscopic use. In recent years, THz research has progressed to such a great extent that THz generation and detection techniques are now reliable and relatively low-cost, therefore THz has the potential to be used in a vast array of real-world applications ranging from security reinforcement (detection of weapons and explosives) to medical diagnosis (identifying melanomas). Indeed many bodies of research work have successfully demonstrated the efficacy of THz, although many challenges still exist before THz matures beyond the realm of research into everyday life. This Thesis focuses on the area of THz spectroscopy and modelling of biotissue, with the aim of broadening the application of THz in medicine, particularly in the early diagnosis of Alzheimer’s disease (AD). Since the nature of biotissue is complex...

Rotational spectroscopy of DO2 by FIR LMR and millimeter-wave absorption

Sears, Trevor; Takacs, Gerald; Howard, Carleton; Crownover, Richard; Helminger, Paul; De Lucia, Frank
Fonte: Elsevier: Journal of Molecular Spectroscopy Publicador: Elsevier: Journal of Molecular Spectroscopy
Tipo: Abstract Formato: 37365 bytes; application/pdf
EN_US
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We report the measurement of approximately 50 rotational transitions in the DO2 radical between 230 and 2530 GHz by high-resolution millimeter-wave and far-infrared laser magnetic resonance spectroscopy. The radical was generated in the gas phase by the reaction of chlorine atoms and oxygen or discharged oxygen with deuterated methanol. The data were analyzed in conjunction with previously published high-resolution spectra of the molecule in the ground vibronic state in order to extract the best set of parameters in the effective Hamiltonian describing the model. The fine structure (spin-rotation) parameters derived in the present work were used together with those for HO2 [A. Charo and F.C. De Lucia, J. Mol. Spectrosc. 94, 426-436 (1982)] in order to determine all of the symmetry-allowed spin-rotation tensor components for the hydroperoxyl radical. The results cannot be interpreted in terms of contamination of the ground state wavefunction by the lowest lying A~2A' state alone and information from quantum chemical calculations of spin-orbit matrix elements between the ground and higher excited states or additional experimental data involving high excited electronic states are necessary before a complete rationalization of the results is possible.