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At least 1,387 records · Page 77Linked to original sources
PubMed2005

Postcollision interaction in noble gas clusters: observation of differences in surface and bulk line shapes.

The surface and bulk components of the x-ray photoelectron spectra of free noble gas clusters are shown to display differences in the influence of postcollision interaction between the photoelectron and the Auger electron on the spectral line shape; the bulk component is observed to be less affected than the surface and atomic parts of the spectra. A model for postcollision interaction in nonmetallic solids and clusters is also provided which takes the polarization screening into account. Core-level photoelectron spectra of Ar, Kr, and Xe have been recorded to verify the dependence of the postcollision interaction effect on the polarizability of the sample.

Argon↗
PubMed2006

Simulation of vibrational dephasing of I(2) in solid Kr using the semiclassical Liouville method.

In this paper, we present simulations of the decay of quantum coherence between vibrational states of I(2) in its ground (X) electronic state embedded in a cryogenic Kr matrix. We employ a numerical method based on the semiclassical limit of the quantum Liouville equation, which allows the simulation of the evolution and decay of quantum vibrational coherence using classical trajectories and ensemble averaging. The vibrational level-dependent interaction of the I(2)(X) oscillator with the rare-gas environment is modeled using a recently developed method for constructing state-dependent many-body potentials for quantum vibrations in a many-body classical environment [J. M. Riga, E. Fredj, and C. C. Martens, J. Chem. Phys. 122, 174107 (2005)]. The vibrational dephasing rates gamma(0n) for coherences prepared between the ground vibrational state mid R:0 and excited vibrational state mid R:n are calculated as a function of n and lattice temperature T. Excellent agreement with recent experiments performed by Karavitis et al. [Phys. Chem. Chem. Phys. 7, 791 (2005)] is obtained.

Algorithms↗
PubMed2006

Cross sections for electron trapping by DNA and its component subunits I: Condensed tetrahydrofuran deposited on Kr.

We report cross sections for electron capture processes occurring in condensed tetrahydrofuran (THF) for incident electron energies in the range of 0-9 eV. The charge trapping cross section for 6-9 eV electrons is very small, and an upper limit of 4 x 10(-19) cm2 is estimated from our results. This latter is thus also an upper bound for the cross section for dissociative electron attachment process that is known to occur at these energies for condensed THF. At energies close to zero eV electron trapping proceeds via intermolecular stabilization. The cross section for this process is strongly dependent on the quantity of deposited THF. Since THF may model the furyl ring found in deoxyribose, these measurements indicate that this ring likely plays little role in either initiating or enhancing strand break damage via the attachment of the low energy secondary electrons produced when DNA is exposed to ionizing radiation.

Chemical Phenomena↗
PubMed1983

Effects of a transfusion with a blood substitute (Fluosol-DA, 20%). Part II: Human cerebral blood flow.

In 24 patients suffering from cerebrovascular diseases, alteration of the cerebral blood flow was investigated by means of the 133Xe clearance technique before and after the intravenous infusion of perfluorochemical suspension (Fluosol-DA, 20%, 10 ml/kg). Since perfluorochemicals exhibit high solubilities for not only oxygen but other kinds of gases, the partition coefficient of Xe (lambda tb) is considered to change depending on the amount of perfluorochemicals contained in the blood (Fct). The solubilities of Xe in the perfluorochemicals contained in the solution were then measured by gas chromatography to obtain an equation for lambda tb: lambda tb = 1.50/(Hct/100 + 12.48Fct/100 + 0.95). The cerebral blood flow was found to increase significantly by 10.1% in the lesional hemisphere and by 10.8% in the healthy one. The cortical small artery with a diameter between 0.1 and 0.2 mm appeared to dilate by 13% after its administration. From these results, the decrease of blood viscosity and some vasodilating effect of the solution might be responsible for the increase of the cerebral blood flow.

Blood Substitutes↗
PubMed1980

Lung ventilation model for radioactive tracer itdal breathing.

A mathematical lung ventilation model for radioactive tracer tidal breathing is developed on the basis of the previously established simple mathematical lung model for quantitative regional ventilation measurements. In the present model, the periodicity of breathing is completely taken into account. A precise definition of the effective specific ventilation is given. This was found to be related to the ratio of tidal volume (TV) and functional residual capacity (FRC). The determination of the regional effective specific ventilation is reduced to a simple fitting to a straight line. A description is given of the method of measurement (in the framework of radioisotope dynamic studies) that makes it possible to use the mathematical model for the actual determination of lung ventilation and volume parameters. The model is experimentally verified on healthy subjects, and the value of the effective specific ventilation obtained is in agreement with comparable parameters in the literature. Furthermore, the value for TV/FRC is comparable with that determined by classical spirometrical methods.

Humans↗
PubMed1986

Dual isotope (81Krm and 99Tcm) SPECT in lung function diagnosis.

A method is presented for deriving regional values for lung volume, ventilation, perfusion and dV/dQ ratios suitably plotted for clinical interpretation. Necessary data are obtained from a 12 min dual-head, dual isotope (81Krm and 99Tcm) SPECT acquisition and subsequent graphics and image processing. Computed histograms make possible a detailed quantitative impression of lung function.

Capillaries↗
PubMed1982

Quantitative comparison of 99Tcm-aerosol and 81Krm ventilation images.

Quantitative indices are described for assessing the distribution of ventilation imaging agents (radioaerosols, in particular) within the lung. They have been applied to images obtained with 99Tcm aerosol particles (0.5-2.0 micrometer diameter) and with 81Krm gas in 12 patients with a wide range of lung function. In patients with normal lung function aerosol distribution was similar to that of 81Krm. In patients with airways obstruction, the aerosol tended to penetrate less well than 81Krm to the lung periphery and to show a less homogeneous distribution there. Quantitative analysis confirms that the aerosol technique is an effective substitute for 81Krm in patients with normal lung function. When lung function is impaired aerosol images may still be valuable particularly in confirming a diagnosis of pulmonary embolism though they must be interpreted with caution in attempting to exclude that diagnosis. We conclude that small particle radioactive aerosols provide a readily available ventilation technique for clinical ventilation-perfusion imaging.

Adult↗
PubMed1986

Distributions of an ultra-fine 99Tcm aerosol and 81Krm gas in human lungs compared using a gamma camera.

A 99Tcm aerosol of particle size 0.12 micron and the gas 81Krm were administered to four normal subjects and to eleven patients with airway disease. Posterior-anterior gamma camera images of erect lungs were compared qualitatively and quantitatively, and 99Tcm clearance rates were measured. Qualitatively the two images were similar in normal subjects but differed in most patients owing to small regions of high count density in the 99Tcm images. In a few patients, regional variations in ventilation were defined more finely by the aerosol. In both groups a significant vertical gradient in 99Tcm count density relative to 81Krm count density was found. Penetration of 99Tcm to the lung periphery relative to the hilar region was similar to that of 81Krm in the normal subjects and less than that of 81Krm in the patients. Possible causes of the differing distributions are discussed. The images obtained with the aerosol in the two groups studied were similar to those reported for larger particle aerosols.

Adult↗
PubMed1988

Lung volume calculations from 81Krm SPECT for the quantification of regional ventilation.

Lung volumes, calculated from 81Krm single-photon emission computed tomography (SPECT) of the lungs, were compared with functional residual capacity (FRC), measured with the helium dilution technique in controls and in patients with various pulmonary diseases. SPECT volume was greater than FRC, which was attributed to non-gas-containing structures in the lung such as the alveolar walls, the interstitium, the blood vessels and the blood, included in the SPECT volume. A good correlation (r = 0.91) was found between the two volumes and there was no difference in this relationship between patients and controls. It was concluded that the relative volume distribution, calculated from SPECT, can be used for the quantification of ventilation from 81Krm SPECT steady-state count distributions.

Adult↗
PubMed2004

Principles of lasers and biophotonic effects.

In this review, we discuss how, due to a variety of different interactions between laser radiation and biological tissue, the laser has become an established instrument in most medical fields. Depending on the interaction time and the effective power density, three types of laser tissue interaction can be distinguished: photochemical effects, photothermal effects, and photomechanical and photoionizing effects. After a description of the physical mechanisms, the typical parameters, and the medical applications of these effects, a review of the laser types used in medicine is given. For percutaneous laser disc decompression (PLDD), lasers in the near-infrared region (Nd:YAG, Ho:YAG, and diode lasers) and with visible green radiation (frequency doubled Nd:YAG, called "KTP laser") were reported to be effective.

Argon↗