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71.
72.
Russo I. Boccia L. Amendola G. Massa G.D. Hall P.S. 《Microwaves, Antennas & Propagation, IET》2009,3(5):877-881
A simple method for parametric analysis of grid amplifier performances is presented here. The proposed approach is based on the development of an equivalent transmission line model where each element of the grid is represented by an S-matrix derived from a full-wave simulation in an infinite array environment. The proposed technique makes it possible to investigate the dependency of grid amplifier performance on its major parameters taking into account the actual geometry of each part of the circuit while preserving the simulation efficiency. 相似文献
73.
This paper aims to clarify the difference between stores of energy in the form of non-rechargeable stores of energy such as fossil-fuels, and the storage of electricity by devices that are rechargeable. The existing scale of these two distinct types of storage is considered in the UK context, followed by a review of rechargeable technology options. The storage is found to be overwhelmingly contained within the fossil-fuel stores of conventional generators, but their scale is thought to be determined by the risks associated with long supply chains and price variability. The paper also aims to add to the debate regarding the need to have more flexible supply and demand available within the UK electrical network in order to balance the expected increase of wind derived generation. We conclude that the decarbonisation challenge facing the UK electricity sector should be seen not only as a supply and demand challenge but also as a storage challenge. 相似文献
74.
This paper studies the effects of the number and location of solid obstacles on the rate of propagation of turbulent premixed flames. A vented explosion chamber is constructed where controlled premixed flames are ignited from rest to propagate past grids or baffles plates as well as other solid obstacles strategically positioned in the chamber. Laser Induced Fluorescence (LIF) is used to image OH which is used as an indicator of the reaction zone while pressure transducers are used to obtain pressure-time traces. Single grids or baffle plates located at different distances from the ignition source are tested. Two as well as three baffle plates are also investigated in varying configurations. It is found that while the peak overpressure increases with increasing number of grids or baffle plates, a limit is reached where the pressure starts to decrease. The location of the obstacles is found to have a significant effect on the overpressure and the flame structure. Higher overpressures are obtained when the baffle plates and obstacles are stacked closer together hence not allowing turbulence to decay. LIF images for OH show that the reaction zones become more contorted with increasing number of baffle plates in the flame path. 相似文献
75.
76.
A. M. Barnett J. A. Rand R. B. Hall J. C. Bisaillon E. J. DelleDonne B. W. Feyock D. H. Ford A. E. Ingram M. G. Mauk J. P. Yaskoff P. E. Sims 《Solar Energy Materials & Solar Cells》2001,66(1-4)
Solar cells utilizing thin-film polycrystalline silicon can achieve photovoltaic power conversion efficiencies greater than 19%. These high efficiencies are a result of light trapping and back surface passivation. Optimum silicon thickness, for devices employing such technology, has been determined to be 20 μm (Blakers et al., Appl. Phys. Lett. 60 (1992) 2572) to 35 μm (Rand et al., Proceedings of the IEEE Photovoltaic Specialist Conference, Orlando, FL, May 1990, p. 263). Low cost is achieved by minimizing the required amount of silicon feedstock per watt of power output. The use of an electrically insulating supporting substrate allows for monolithic, series connected sub-modules. A solar cell with a 20 μm thick polycrystalline Si-layer on a ceramic substrate, utilizing both light trapping and back-surface passivation, was fabricated and characterized. A short-circuit current of 25.8 mA/cm2 was measured and verified by the National Renewable Energy Laboratory (NREL). 相似文献
77.
Allen Philip A.; Hall Rosali J.; Druley Jennifer A.; Smith Albert F.; Sanders Raymond E.; Murphy Martin D. 《Canadian Metallurgical Quarterly》2001,16(3):532
Several theories have suggested that age-related declines in cognitive processing are due to a pervasive unitary mechanism, such as a decline in processing speed. Structural equation model tests have shown some support for such common factor explanations. These results, however, may not be as conclusive as previously claimed. A further analysis of 4 cross-sectional data sets described in T. Salthouse, D. Hambrick, and K. McGuthry (1998) and T. Salthouse and S. Czaja (2000) found that although the best fitting model included a common factor in 3 of the data sets, additional direct age paths were significant, indicating the presence of specific age effects. For the remaining data set, a factor-specific model fit at least as well as the best fitting common factor model. Three simulated data sets with known structure were then tested with a sequence of structural equation models. Common factor models could not always be falsified-even when they were false. In contrast, factor-specific models were more easily falsified when the true model included a unitary common factor. These results suggest that it is premature to conclude that all age-related cognitive declines are due to a single mechanism. Common factor models may be particularly difficult to falsify with current analytic procedures. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
78.
非常高兴能为中国的读者出版我近期几篇论文的专集.当然,作为在英国和美国渡过了自己的职业生涯并从事专业工作的一名规划师,我在写作这些文章时会有一定的观点倾向. 相似文献
79.
80.
Sharon M Hall Gary L Humfleet Julie A Gorecki Ricardo F Mu?oz Victor I Reus Judith J Prochaska 《Nicotine & tobacco research》2008,10(3):463-470
Quitting smoking benefits older individuals, yet few recent studies have described older smokers. The goal of this paper was to test a series of hypotheses about differences between smokers aged 50 years or older (50+) and those younger than age 50 (<50) presenting to the same treatment facility during 2002-2004 for participation in two randomized clinical trials: one exclusively for smokers aged 50+, and a second open to smokers aged 18 or older. As predicted, smokers aged 50+ were more tobacco dependent, had better psychological functioning, and had poorer physical functioning than those aged <50. Contrary to predictions, we found no differences in motivation to quit cigarette smoking or in alcohol use. Women aged 50+ were less likely to report marijuana use than women aged <50, and less likely than men to receive a positive diagnosis for alcohol abuse. Despite higher scores on measures of tobacco dependence, older smokers were less likely to be diagnosed as tobacco dependent or as having tobacco withdrawal using DSM-IV criteria. Rates of DSM-IV alcohol abuse and dependence were high in both age groups but were higher for smokers aged <50. We found no striking differences between studies in reasons for exclusion, but in both the proportion of individuals excluded due to current antidepressant use was high. Implications for the assessment and treatment of older adults are discussed. 相似文献