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41.
42.
Grosnick D Wright SC Bolton RD Cooper MD Frank JS Hallin AL Heusi PA Hoffman CM Hogan GE Mariam FG Matis HS Mischke RE Piilonen LE Sandberg VD Sanders GH Sennhauser U Werbeck R Williams RA Wilson SL Hofstadter R Hughes EB Ritter MW Highland VL McDonough J 《Physical review letters》1986,57(26):3241-3244
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The upper limit of momentum transfer by a proton to K-shell electrons is calculated in a restricted three-body classical model. The model shows that the infinite upper limit used in practice, is generally good except for low energy protons passing through an extremely rarefied gas. 相似文献
45.
M S Patterson S J Madsen B C Wilson 《Journal of photochemistry and photobiology. B, Biology》1990,5(1):69-84
Singlet oxygen (1O2) is thought to be the cytotoxic agent in photodynamic therapy (PDT) with current photosensitizers. Direct monitoring of 1O2 concentration in vivo would be a valuable tool in studying biological response. Attempts were made to measure 1O2 IR luminescence during PDT of cell suspensions and two murine tumour models using the photosensitizers Photofrin II and aluminium chlorosulphonated phthalocyanine. Instrumentation was virtually identical to that devised by Parker in the one positive report of in vivo luminescence detection in the literature. Despite the fact that our treatments caused cell killing and tissue necrosis, we were unable to observe 1O2 emission under any conditions. We attribute this negative result to a reduction in 1O2 lifetime in the cellular environment. Quantitative calibration of our system allowed us to estimate that the singlet oxygen lifetime in tissue is less than 0.5 microsecond. Some technical improvements are suggested which would improve detector performance and perhaps make such measurements feasible. 相似文献
46.
A Study of the Uptake of Toluidine Blue O by Porphyromonas gingivalis and the Mechanism of Lethal Photosensitization 总被引:2,自引:1,他引:2
Manpreet Bhatti Alexander MacRobert Sajeda Meghji Brian Henderson Michael Wilson 《Photochemistry and photobiology》1998,68(3):370-376
The purpose of the study was to determine the distribution of the photosensitizer toluidine blue O (TBO) within Porphyromonas gingivalis and the possible mechanism(s) involved in the lethal photosensitization of this organism. The distribution of TBO was determined by incubating P. gingivalis with tritiated TBO (3H-TBO) and fractionating the cells into outer membrane (OM), plasma membrane (PM), cytoplasmic proteins, other cytoplasmic constituents and DNA. The percentage of TBO in each of the fractions was found to be, 86.7, 5.4, 1.9, 5.7 and 0.3%, respectively. The involvement of cytotoxic species in the lethal photosensitization induced by light from a helium-neon (HeNe) laser and TBO was investigated by using deuterium oxide (D2O), which prolongs the lifetime of singlet oxygen, and the free radical and singlet oxygen scavenger L-tryptophan. There were 9.0 log10 and 2 log10 reductions in the presence of D2O and H2O (saline solutions), respectively, at a light dose of 0.44 J (energy density = 0.22 J/cm2), suggesting the involvement of singlet oxygen. Decreased kills were attained in the presence of increasing concentrations of L-tryptophan. The effect of lethal photosensitization on whole cell proteins was determined by measuring tryptophan fluorescence, which decreased by 30% using 4.3 J (energy density = 4.3 J/ cm2) of light. Effects on the OM and PM proteins were determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. There was evidence of change in the molecular masses of several PM proteins and OM proteins compared to controls. There was evidence of damage to the DNA obtained from irradiated cells. Scanning electron microscopic studies showed that there was coaggre-gation of P. gingivalis cells when sensitized and then exposed to laser light. These results suggest that lethal photosensitization of P. gingivalis may involve changes in OM and/or PM proteins and DNA damage mediated by singlet oxygen. 相似文献
47.
I. Alex Vitkin Joshua Woolsey Brian C. Wilson R. Rox Anderson 《Photochemistry and photobiology》1994,59(4):455-462
Abstract The optical properties and the thermal diffusivity of natural cuttlefish ( Sepia officinalis ) melanin have been measured. The optical absorption and scattering properties of melanin particles were determined at 580 nm and 633 nm, using photometric and photothermal techniques. For the photometric studies, the absorption and the transport scattering coefficients were determined from the measurements of diffuse reflectance and transmittance. The scattering anisotropy was obtained from an additional measurement of the total attenuation coefficient and independently obtained by goniometry. For photothermal studies, pulsed photothermal radiometry was used to deduce the absorption and transport scattering coefficients via a model based on optical diffusion theory. Pulsed photothermal radiometry was also used to provide the thermal diffusivity of solid melanin pressed pellets. 相似文献
48.
A. E. S. Green G. B. Findley Jr. K. F. Klenk W. M. Wilson T. Mo 《Photochemistry and photobiology》1976,24(4):353-362
Abstract— We correlate annual ultraviolet dose estimates with age specific and age adjusted incidence data for non-melanoma skin cancer in the United States, United Kingdom, Canada and Australia. We first examine (1) a reciprocity or photographic model in which incidence rates (R) are related to exposure (E) which is the product of age (T) and annual dose (D). We also test several models which violate reciprocity including models identified by the labels: (2) Dose potency; (3) Double cause; (4) Age-exposure and (5) separable. Our analyses together with the recent National Cancer Institute study favors the age-exposure model and/or the double cause models. All models lead to biological amplification factors (defined as the ratio of the percent increase in skin cancer incidence due to a 1% increase in dose) greater than unity. For the U.S. we find the biological amplification to be approximately 1.8 for the population center but greater in regions of higher UV annual dose, and less in regions of lower annual UV dose. 相似文献
49.
Six proficiency tests have now been completed in an ongoing program of the UK Food Analysis Performance Assessment Scheme (FAPAS) for the analysis of acrylamide in a range of food matrixes. Homogeneous test material samples were requested by laboratories throughout the world, with 29 to 45 submitting results for each test. Results were analyzed by appropriate statistical procedures, and z-scores were awarded for reported values. In the absence of both legislation and collaborative trial data, the target standard deviation was derived from the Horwitz equation, although it is acknowledged that there is a need to establish a "fit for purpose" target standard deviation specifically for acrylamide analysis. Participants were encouraged to use the analytical method routinely used in their own laboratory and to provide details of their procedure. Close examination of the data submitted indicates that performance is generally acceptable in terms of accuracy. There is no significant difference between results submitted by gas chromatography and liquid chromatography (GC and LC) methods, and no method dependency on the use of internal standards or sample size. However, choice of extraction solvent may be important, with indications that plain water is an acceptable extraction method. There is evidence from the most recent test that direct (underivatized) GC methodology may present problems, but more data are required and this aspect will be monitored in the continuing proficiency testing program. 相似文献
50.
In vivo near-infrared Raman spectroscopy: demonstration of feasibility during clinical gastrointestinal endoscopy 总被引:7,自引:0,他引:7
Raman spectroscopy (RS) has potential for disease classification within the gastrointestinal tract (GI). A near-infrared (NIR) fiber-optic RS system has been developed previously. This study reports the first in vivo Raman spectra of human gastrointestinal tissues measured during routine clinical endoscopy. This was achieved by using this system with a fiber-optic probe that was passed through the endoscope instrument channel and placed in contact with the tissue surface. Spectra could be obtained with good signal-to-noise ratio in 5 s. The effects on the spectra of varying the pressure of the probe tip on the tissue and of the probe-tissue angle were determined and shown to be insignificant. The limited set of spectra from normal and diseased tissues revealed only subtle differences. Therefore, powerful spectral-sorting algorithms, successfully implemented in prior ex vivo studies, are required to realize the full diagnostic potential of RS for tissue classification in the GI. 相似文献