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51.
The efficacy of photodynamic therapy is dependent upon the optical dose rate or upon the fractionation schedule on the light. These effects are thought to be limited by the time required for oxygen diffusion from the capillaries, since this therapy can consume oxygen faster than it can be supplied to tissues distant from the blood vessels. Oxygen diffusion and consumption by metabolic and photochemical mechanisms have been modeled here to compare theoretical predictions with experimental results of varying light fractionations and delivered dose rates. The mathematics of the problem have been described in the literature, and the present study extends these calculations to allow a more direct and quantitative comparison with fractionation experiments, using both analytical and numerical arguments. The optimum fraction time was found to depend only on the intercapillary spacing and not on the intensity of irradiation or the concentration of photosensitizer. The calculations indicate that experimentally observed optimum fractionation times of 30 and 60 s correspond to a distance from capillary to cell of approximately 1 mm. These results suggest that the fractionated light irradiation experiments need careful interpretation, and some possible reasons for longer optimum fractionation times are discussed.  相似文献   
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There are now more than 1,000 constructed wetland systems (CWs) in the UK. The first UK CW database was constructed by Water Research Centre (WRc) and Severn Trent Water Ltd to accompany a book on the design and performance of these systems. In that database, constructed by Gareth Job et al., only 154 beds were listed, most of which were tertiary sewage treatment sites in Severn Trent Water. The Constructed Wetland Association (CWA) was formed in 2000 as a UK water industry body in response to problems caused by unscrupulous constructors. A group of experienced, reputable designers and constructors formed the CWA to bring together best UK practice in order to counteract this problem. The group contains major water companies, designers, constructors, academics, plant growers and operators. They decided that one of the best ways of countering the problem was to assemble a database of design and performance from well-designed systems. After negotiation the CWA group took over responsibility for the database from WRc. The CWA has produced eight updates of the database which now contains information from more than 900 beds. It contains examples of the different variants of CWs in use in the UK. Most of these sites treat sewage/domestic wastewater but the database also includes examples of systems for the treatment of minewater, sludge, landfill leachate, industrial effluents, surface runoff and road runoff. Particular treatment applications are illustrated by case studies which are summary articles describing design, construction and performance.  相似文献   
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The storage times of FET-accessed GaAs dynamic RAM cells are limited to less than 1 min at room temperature by gate leakage in the access transistor. These transistor leakage mechanisms have been eliminated by designing a vertically integrated DRAM cell in which an n-p-n bipolar access transistor is merged with a p-n-p storage capacitor. Storage times of 4.5 h are obtained at room temperature, a 1000-fold increase over the best FET-accessed cells  相似文献   
55.
Back pain is an important public health problem but there is a paucity of knowledge about risk factors and causal mechanisms. Previous studies have shown that tall men are more at risk of back pain, although observations in women have been less consistent. This paper presents findings from a national longitudinal study of 3262 men and women aged 43 yr. Standing height and sitting height were related to 18-month reported prevalence of 'sciatica, lumbago or severe backache' in both men and women. The paper investigates explanations for these findings using previously collected data on childhood growth and detailed lifetime occupational histories. Neither greater susceptibility of tall men to heavy lifting, nor the timing of growth, were able to account for these relationships. To assess further the association between height and back pain, information is needed on the relationship between stature and characteristics of spinal structure.  相似文献   
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In order to select the optimal device for a particular application, designers must carefully analyze the tradeoffs between competing devices. Recent progress in SiC power rectifiers has resulted in the demonstration of high-voltage PiN and Schottky barrier diodes (SBDs). With both technologies maturing, power electronics engineers will soon face the task of selecting between these two devices. Until recently, the choice was simple, since silicon SBDs are only available for relatively low voltage applications. The choice is not as clear when considering SiC diodes, and guidelines for determining the proper application of each are needed. The purpose of this paper is to provide such guidelines, based on an analysis of the most significant tradeoffs involved.  相似文献   
59.
A study was undertaken to examine the sensitivity of a wastewater population of coliphage, total coliforms and total flora present in raw sewage and secondary effluent after irradiating with similar doses delivered by a high-energy electron beam and y -radiation. The electron beam study was conducted on a large scale at the Virginia Key Wastewater Treatment Plant, Miami, Fla. The facility is equipped with a 1.5 MeV, 50 mA electron accelerator, with a wastewater flow rate of 8 ls−1. Concurrent y-radiation studies were conducted at laboratory scale using a 5000 Ci, 60Co y -source. Three logs reduction of all three test organisms were observed at an electron beam dose of 500 krads, while at least four logs reduction were observed at the same dose utilizing the y-source.  相似文献   
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