967 resultados para Laser-induced breakdown spectroscopy
Resumo:
Two different theories of migraine aura exist: In the vascular theory of Wolff, intracerebral vasoconstriction causes migraine aura via energy deficiency, whereas in the neuronal theory of Leão and Morison, spreading depression (SD) initiates the aura. Recently, it has been shown that the cerebrovascular constrictor endothelin-1 (ET-1) elicits SD when applied to the cortical surface, a finding that could provide a bridge between the vascular and the neuronal theories of migraine aura. Several arguments support the notion that ET-1-induced SD results from local vasoconstriction, but definite proof is missing. If ET-1 induces SD via vasoconstriction/ischemia, then neuronal damage is likely to occur, contrasting with the fact that SD in the otherwise normal cortex is not associated with any lesion. To test this hypothesis, we have performed a comprehensive histologic study of the effects of ET-1 when applied topically to the cerebral cortex of halothane-anesthetized rats. Our assessment included histologic stainings and immunohistochemistry for glial fibrillary acidic protein, heat shock protein 70, and transferase dUTP nick-end labeling assay. During ET-1 application, we recorded (i) subarachnoid direct current (DC) electroencephalogram, (ii) local cerebral blood flow by laser-Doppler flowmetry, and (iii) changes of oxyhemoglobin and deoxyhemoglobin by spectroscopy. At an ET-1 concentration of 1 muM, at which only 6 of 12 animals generated SD, a microarea with selective neuronal death was found only in those animals demonstrating SD. In another five selected animals, which had not shown SD in response to ET-1, SD was triggered at a second cranial window by KCl and propagated from there to the window exposed to ET-1. This treatment also resulted in a microarea of neuronal damage. In contrast, SD invading from outside did not induce neuronal damage in the absence of ET-1 (n = 4) or in the presence of ET-1 if ET-1 was coapplied with BQ-123, an ET(A) receptor antagonist (n = 4). In conclusion, SD in presence of ET-1 induced a microarea of selective neuronal necrosis no matter where the SD originated. This effect of ET-1 appears to be mediated by the ET(A) receptor.
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In this study, we present a detailed structural characterization by means of transmission electron microscopy and Raman spectroscopy of polymorphous silicon (pm-Si:H) thin films deposited using radio-frequency dust-forming plasmas of SiH4 diluted in Ar. Square-wave modulation of the plasma and gas temperature was varied to obtain films with different nanostructures. Transmission electron microscopy and electron diffraction have shown the presence of Si crystallites of around 2 nm in the pm-Si:H films, which are related to the nanoparticles formed in the plasma gas phase coming from their different growth stages, named particle nucleation and coagulation. Raman scattering has proved the role of the film nanostructure in the crystallization process induced ¿in situ¿ by laser heating.
Resumo:
In this work we report the observation of the blue visible fluorescence at 420 nm in rubidium vapour as a result of two-photon absorption excited by femtosecond laser pulses 790 nm. After experimental investigation of the spa-tial and spectral characteristics of the obtained emission we can claim that mechanism of this coherent fluorescence at 420 nm was not caused by ampli-fied spontaneous emission, but represents the nondegenerate four-wave mixing. As a probable outcome of this investigation an opportunity of creation an ultrafast all-optical switcher might appear.
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The time-course changes of the responsiveness of glycogen breakdown to a- and ß-adrenergic agonists during insulin-induced hypoglycemia (IIH) were investigated. Blood glucose levels were decreased prior to the alteration in the hepatic responsiveness to adrenergic agonists. The activation of hepatic glucose production and glycogenolysis by phenylephrine (2 µM) and isoproterenol (20 µM) was decreased in IIH. The changes in the responsiveness of glycogen catabolism were first observed for isoproterenol and later for phenylephrine. Hepatic ß-adrenergic receptors showed a higher degree of adrenergic desensitization than did a-receptors. Liver glycogen synthase activity, glycogen content and the catabolic effect of dibutyryl cyclic AMP (the ß-receptor second messenger) were not affected by IIH.
Resumo:
The responsiveness of glycogen breakdown to cAMP was investigated in isolated perfused liver from male Wistar fed rats (200-220 g) with insulin-induced hypoglycemia. The activation of glycogenolysis by 3 µM cAMP was decreased (P<0.05) in livers from rats with hypoglycemia induced by the administration of insulin or during the direct infusion of insulin into the isolated liver. The direct effect of insulin on glycogen catabolism promoted by 3 µM cAMP occurred as early as 3 min after starting insulin infusion. In contrast, the cAMP agonists resistant to phosphodiesterases, 8Br-cAMP and 6MB-cAMP, used at the same concentration as cAMP, i.e., 3 µM, did not modify the effect of insulin. The data suggest that the decreased hepatic responsiveness of glycogen breakdown during insulin-induced hypoglycemia is a direct effect of insulin decreasing the intracellular levels of cAMP.
Investigation of femtosecond laser technology for the fabrication of drug nanocrystals in suspension
Resumo:
La technique du laser femtoseconde (fs) a été précédemment utilisée pour la production de nanoparticules d'or dans un environnement aqueux biologiquement compatible. Au cours de ce travail de maîtrise, cette méthode a été investiguée en vue d'une application pour la fabrication de nanocristaux de médicament en utilisant le paclitaxel comme modèle. Deux procédés distincts de cette technologie à savoir l'ablation et la fragmentation ont été étudiés. L'influence de la puissance du laser, de point de focalisation, et de la durée du traitement sur la distribution de taille des particules obtenues ainsi que leur intégrité chimique a été évaluée. Les paramètres ont ainsi été optimisés pour la fabrication des nanoparticules. L’évaluation morphologique et chimique a été réalisée par microscopie électronique et spectroscopie infrarouge respectivement. L'état cristallin des nanoparticules de paclitaxel a été caractérisé par calorimétrie differentielle et diffraction des rayons X. L'optimisation du procédé de production de nanoparticules par laser fs a permis d'obtenir des nanocristaux de taille moyenne (400 nm, polydispersité ≤ 0,3). Cependant une dégradation non négligeable a été observée. La cristallinité du médicament a été maintenue durant la procédure de réduction de taille, mais le paclitaxel anhydre a été transformé en une forme hydratée. Les résultats de cette étude suggèrent que le laser fs peut générer des nanocristaux de principe actif. Cependant cette technique peut se révéler problématique pour des médicaments sensibles à la dégradation. Grâce à sa facilité d'utilisation et la possibilité de travailler avec des quantités restreintes de produit, le laser fs pourrait représenter une alternative valable pour la production de nanoparticules de médicaments peu solubles lors des phases initiales de développement préclinique. Mots-clés: paclitaxel, nanocristaux, laser femtoseconde, ablation, fragmentation
Resumo:
Near-infrared spectroscopy can be a workhorse technique for materials analysis in industries such as agriculture, pharmaceuticals, chemicals and polymers. A near-infrared spectrum represents combination bands and overtone bands that are harmonics of absorption frequencies in the mid-infrared. Near-infrared absorption includes a combination-band region immediately adjacent to the mid-infrared and three overtone regions. All four near-infrared regions contain "echoes" of the fundamental mid-infrared absorptions. For example, vibrations in the mid-infrared due to the C-H stretches will produce four distinct bands in each of the overtone and combination regions. As the bands become more removed from the fundamental frequencies they become more widely separated from their neighbors, more broadened and are dramatically reduced in intensity. Because near-infrared bands are much less intense, more of the sample can be used to produce a spectra and with near-infrared, sample preparation activities are greatly reduced or eliminated so more of the sample can be utilized. In addition, long path lengths and the ability to sample through glass in the near-infrared allows samples to be measured in common media such as culture tubes, cuvettes and reaction bottles. This is unlike mid-infrared where very small amounts of a sample produce a strong spectrum; thus sample preparation techniques must be employed to limit the amount of the sample that interacts with the beam. In the present work we describe the successful the fabrication and calibration of a linear high resolution linear spectrometer using tunable diode laser and a 36 m path length cell and meuurement of a highly resolved structure of OH group in methanol in the transition region A v =3. We then analyse the NIR spectrum of certain aromatic molecules and study the substituent effects using local mode theory
Resumo:
Femtosecond laser pulses are applied to the study of the dynamics and the pathways of multiphoton-induced ionization, autoionization, and fragmentation of Na_2 in molecular-beam experiments. In particular, we report on first results obtained studying electronic autoionization (leading to Na_2{^+} + {e ^-}) and autoionization-induced fragmentation (leading to Na{^+} + Na + {e ^-}) of a bound doubly excited molecular state. The final continuum states are analyzed by photoelectron spectroscopy and by measuring the mass and the released kinetic energy of the corresponding ionic fragments with a time-of-flight arrangement.
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Femtosecond laser pulses generated from an amplified coiliding pulse modelocked ring dye laser have been employed in molecular beam experiments to study the dynamics and the pathways of multiphoton induced ionization, autoionization and fragmentation of Na2 . Energy distributions of photoelectrons arising from these processes and the mass and released kinetic energy of the corresponding fragment ions are measured by time-of-flight spectroscopy.
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The real-time dynamics of multiphoton ionization and fragmentation of molecules Na_2 and Na_3 has been studied in molecular beam experiments employing ion and electron spectroscopy together with femtosecond pump-probe techniques. Experiments with Na_2 and Na_3 reveal unexpected features of the dynamics of the absorption of several photons as seen in the one- and three-dimensional vibrational wave packet motion in different potential surfaces and in high laser fields: In Na_2 a second major resonance-enhanced multiphoton ionization (REMPI) process is observed, involving the excitation of two electrons and subsequent electronic autoionization. The possibility of controlling a reaction by controlling the duration of propagation of a wave packet on an electronically-excited surface is demonstrated. In high laser fields, the contributions from direct photoionization and from the second REMPI process to the total ion yield change, due to different populations in the electronic states participating in the multiphoton ionization (MPI) processes. In addition, a vibrational wave packet motion in the electronic ground state is induced through stimulated emission pumping by the pump laser. The 4^1 \summe^+_g shelf state of Na_2 is given as an example for performing frequency spectroscopy of highlying electronic states in the time domain. Pure wave packet effects, such as the spreading and the revival of a vibrational wave packet, are investigated. The three-dimensional wave packet motion in the Na_3 reflects the normal modes in the X and B states, and shows in addition the pseudorotational motion in the B state in real time.
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This thesis concerns with the main aspects of medical trace molecules detection by means of intracavity laser absorption spectroscopy (ICLAS), namely with the equirements for highly sensitive, highly selective, low price, and compact size sensor. A novel two modes semiconductor laser sensor is demonstrated. Its operation principle is based on the competition between these two modes. The sensor sensitivity is improved when the sample is placed inside the two modes laser cavity, and the competition between the two modes exists. The effects of the mode competition in ICLAS are discussed theoretically and experimentally. The sensor selectivity is enhanced using external cavity diode laser (ECDL) configuration, where the tuning range only depends on the external cavity configuration. In order to considerably reduce the sensor cost, relative intensity noise (RIN) is chosen for monitoring the intensity ratio of the two modes. RIN is found to be an excellent indicator for the two modes intensity ratio variations which strongly supports the sensor methodology. On the other hand, it has been found that, wavelength tuning has no effect on the RIN spectrum which is very beneficial for the proposed detection principle. In order to use the sensor for medical applications, the absorption line of an anesthetic sample, propofol, is measured. Propofol has been dissolved in various solvents. RIN has been chosen to monitor the sensor response. From the measured spectra, the sensor sensitivity enhancement factor is found to be of the order of 10^(3) times of the conventional laser spectroscopy.
Resumo:
In this thesis, a dual mode tunable gas sensor based on intracavity laser absorption spectroscopy (ICLAS) principle is investigated, both, numerically and experimentally. In order to minimize the cost and size of the gas sensor, relative intensity noise (RIN) is implemented as a detection parameter. Investigation is performed to determine the effect of injection current, operating temperature, mode spacing, and cavity length on RIN. It has been found that it is best to operate the gas sensor at smaller mode spacing and near the threshold current or at larger mode spacing and far above the threshold current for the use of RIN as the readout parameter.
Resumo:
IntraCavity Laser Absorption Spectroscopy (ICLAS) is a high-resolution, high sensitivity spectroscopic method capable of measuring line positions, linewidths, lineshapes, and absolute line intensities with a sensitivity that far exceeds that of a traditional multiple pass absorption cell or Fourier Transform spectrometer. From the fundamental knowledge obtained through these measurements, information about the underlying spectroscopy, dynamics, and kinetics of the species interrogated can be derived. The construction of an ICLA Spectrometer will be detailed, and the measurements utilizing ICLAS will be discussed, as well as the theory of operation and modifications of the experimental apparatus. Results include: i) Line intensities and collision-broadening coefficients of the A band of oxygen and previously unobserved, high J, rotational transitions of the A band, hot-band transitions, and transitions of isotopically substituted species. ii) High-resolution (0.013 cm-1) spectra of the second overtone of the OH stretch of trans-nitrous acid recorded between 10,230 and 10,350 cm-1. The spectra were analyzed to yield a complete set of rotational parameters and an absolute band intensity, and two groups of anharmonic perturbations were observed and analyzed. These findings are discussed in the context of the contribution of overtone-mediated processes to OH radical production in the lower atmosphere.
Resumo:
Intracavity photoacoustic overtone spectrum of monofluoroacetylene, HCCF, has been recorded in the wave number region 10 750–14 500 cm−1 with a titanium:sapphire ring laser. The spectrum contains many dense vibration–rotation band systems which can be resolved with Doppler limited resolution. Altogether 58 individual overtone bands have been analyzed rotationally. Many of the observed bands show perturbations of which some have been attributed to anharmonic resonance interactions. A Fermi resonance model based on conventional rectilinear normal coordinate theory has been used to assign vibrationally bands from this work and from earlier studies. Many of the observed vibrational term values and rotational constants can be reproduced well with this model. The results show the importance of the Fermi resonance interactions at the high overtone excitations.