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81.
82.
In this article, a brief introduction to the development of tunable filters was given. A classical design technique based on a combline filter approach was shown, where minimum degradation in passband performance could be obtained across a broad-tuning range. The fundamental disadvantages associated with the conventional resonator tuning approaches were also discussed, recognizing the importance of developing new techniques for realizing tunable microwave filters. It was shown that there is a possibility in realizing an electronically reconfigurable microwave filter based on parallel- coupled switched-delay lines, which possesses the important property of maintaining constant absolute bandwidth over almost an octave of tuning bandwidth. Furthermore, the filter has the ability to incorporate active switching elements in the filter circuit, without sacrificing its loss and linearity performance. With the exceptional linearity performance and power handling capability, the filter is readily adapted to poor environments. Although the use of p-i-n diodes as switching elements would result in large dc consumption, the approach could also be readily adapted for use with any switches, such as pHEMT or RF MEMS switches, to achieve extremely low power consumption. The integration of switchable couplings to enable both bandwidth and center frequency to be reconfigurable would be an enhancement. 相似文献
83.
Andrew D. Gronewold Anne H. Clites Timothy S. Hunter Craig A. Stow 《Journal of Great Lakes research》2011,37(3):577-583
Great Lakes water level forecasts are used to inform decisions ranging from personal choices of recreational activities to corporate evaluations of alternative cargo transport options. For effective decision-making it is important that these model-based forecasts include an accurate expression of the forecast uncertainty, as well as information regarding the model forecasting skill. We provide an assessment of water level forecasts from 1997 through 2009 that were made using the National Oceanic and Atmospheric Administration (NOAA) Great Lakes Environmental Research Laboratory (GLERL) Advanced Hydrologic Prediction System (AHPS). A visual comparison between observed and forecast water levels suggests that AHPS generally captures seasonal and inter-annual patterns. A more quantitative assessment based on the percentage of observations within 90% prediction intervals, however, indicates that AHPS generally underestimates the observed variability of Great Lakes water levels. This assessment provides a benchmark for forecast performance against which alternative model structures (including future evolutions of AHPS) can be tested, and a basis to identify and prioritize the implementation of those alternatives. Including a calibrated model error term into the AHPS framework, to accommodate the underestimated variability, is a priority for short-term development and research, and represents one step toward more accurately quantifying forecast uncertainty. Our results also underscore the importance of storing historical forecasts and the data from which they were derived to serve as a basis for assessing model performance and prioritizing future model improvements. 相似文献
84.
Bielak Allison A. M.; Hultsch David F.; Strauss Esther; MacDonald Stuart W. S.; Hunter Michael A. 《Canadian Metallurgical Quarterly》2010,25(3):575
In this study, the authors addressed the longitudinal nature of intraindividual variability over 3 years. A sample of 304 community-dwelling older adults, initially between the ages of 64 and 92 years, completed 4 waves of annual testing on a battery of accuracy- and latency-based tests covering a wide range of cognitive complexity. Increases in response-time inconsistency on moderately and highly complex tasks were associated with increasing age, but there were significant individual differences in change across the entire sample. The time-varying covariation between cognition and inconsistency was significant across the 1-year intervals and remained stable across both time and age. On occasions when intraindividual variability was high, participants' cognitive performance was correspondingly low. The strength of the coupling relationship was greater for more fluid cognitive domains such as memory, reasoning, and processing speed than for more crystallized domains such as verbal ability. Variability based on moderately and highly complex tasks provided the strongest prediction. These results suggest that intraindividual variability is highly sensitive to even subtle changes in cognitive ability. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
85.
K Hunter 《Canadian Metallurgical Quarterly》1997,13(4):327-335
This work is devoted to the comprehension of the sorption mechanism of uranyl ions on chitosan particle dispersions. The uranyl concentration measurements were obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) and we considered the role of various physicochemical parameters (pH; nature and concentration of added salts; degree of acetylation, DA). The use of appropriate calculation software allowed us to determine the chemical nature of uranyl species in solution in relation to these different parameters. The optimal pH of fixation has been found to be within 6.5-7.5 and can be related to the necessity of having both deprotonated amino groups and no carbonate ions, which are a strong complexant of uranyl ions, thus inhibiting their interaction with chitosan. The decrease of metal uptake with an increase of DA and the lack of influence of ionic strength, confirm the results obtained with pH and allowed us to suppose the formation of a complex with chitosan amino groups rather than interactions of an electrostatic nature. 相似文献
86.
87.
This article asks why the analogy between humans and computers was understood by cognitive psychologists to mean that "minds exist and that it is our job as psychologists to study them." Earlier psychologists, such as Clark Hull, used analogies between humans and complex machines such as telephone switchboards to defend a rigorous behaviorism. How, then, did the computer metaphor of mind come to be seen as the root concept underlying a paradigm shift from behaviorism to cognitivism? To answer this question, this article examines the life and work of George A. Miller, one of the most prominent of a generation of psychologists who began their careers as "good behaviorists" but later came to embrace cognitivism. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
88.
A statnet Tutorial 总被引:1,自引:0,他引:1
Goodreau SM Handcock MS Hunter DR Butts CT Morris M 《Journal of statistical software》2008,24(9):1-27
The statnet suite of R packages contains a wide range of functionality for the statistical analysis of social networks, including the implementation of exponential-family random graph (ERG) models. In this paper we illustrate some of the functionality of statnet through a tutorial analysis of a friendship network of 1,461 adolescents. 相似文献
89.
An improved closed-form approximation to the inverse black body radiation problem at microwave frequencies 总被引:1,自引:0,他引:1
A function is derived which approximates Planck's black body radiation law more closely at microwave frequencies than either the Rayleigh-Jeans or the recent Hamid-Ragheb approximations. The function leads to an improved closed-form approximation to the inverse black body radiation problem in the microwave region. 相似文献
90.
Christopher J. Howard Brett A. Hunter Dae-Joon Kim 《Journal of the American Ceramic Society》1998,81(1):241-243
A survey of the available data on the oxygen positions in various tetragonal zirconias reveals a simple, approximate relationship between the departure of the oxygen from the position it would have in the ideal fluorite structure, and the tetragonality ( c/a ) of the material. This relationship can be understood on the basis that the two oxygen—oxygen contact distances are very nearly equal. The relationship may be used to estimate the oxygen position from the lattice parameters, and from that all the bond lengths in the structure. 相似文献