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71.
It has been shown that information collected from and about links between web pages and web sites can reflect real world phenomena
and relationships between the organizations they represent. Yet, government linking has not been extensively studied from
a webometric point of view. The aim of this study was to increase the knowledge of governmental interlinking and to shed some
light on the possible real world phenomena it may indicate. We show that interlinking between local government bodies in Finland
follows a strong geographic, or rather a geopolitical pattern and that governmental interlinking is mostly motivated by official
cooperation that geographic adjacency has made possible. 相似文献
72.
Estimations of the effectiveness of remedial treatments in road safety analysis are frequently bedevilled by the problem of regression to the mean (RTM). The number of accidents x observed at a site in the “before” period is a “noisy” quantity: x is Poisson distributed about an (unknown) true mean m for that site, so that x = m + e. Sites selected for treatment tend to have a positive random error component e, which will on average be zero in the “after” period, even if no treatment is applied.Methods for estimating RTM usually require some assumption about the underlying (prior) between-site distribution of the true means f0(m): for example, in the empirical Bayes method, a gamma distribution is assumed. The paper considers the impact of different assumptions for this distribution and, indeed, whether any distributional form needs to be assumed. Using Markov Chain Monte Carlo methods, a variety of distributional forms are assumed for f0(m) and applied to each of a number of real data sets, including that from a major study on the effectiveness of speed cameras. It is shown that, in some cases, the size of the estimated RTM effect can be quite sensitive to the choice of distribution. 相似文献
73.
Sarah J. Wakes Tanja Maegli Katharine J. Dickinson Mike J. Hilton 《Environmental Modelling & Software》2010,25(2):237-247
Numerical modelling of wind flow over complex dune topography is an ambitious prospect. There is an increasing need to understand wind flow over complex topography for land planning purposes to enable prediction of sediment transport at a particular site. New surveying techniques permit the rapid development of digital terrain models, however a stumbling block is the ability of Computational Fluid Dynamics (CFD) to emulate the wind flow over such a landscape. To overcome these difficulties, it is important to establish the parameters within which such simulations can operate. This paper details an initial two-dimensional numerical model developed in order to test various modelling assumptions against experimental field wind data. Mason Bay, Stewart Island, New Zealand was chosen as an undisturbed but accessible experimental site with a prevalent on-shore wind perpendicular to a simple foredune and a complex down-wind parabolic dune system. A complex topographical two-dimensional model with vegetation represented as a roughness was compared against field data along a transect dissecting a dune system.This paper establishes that:
- * Replicating the roughness patterns at the surface is important
- * The inlet profile should be duplicated with care
- * Modelling only a portion of the domain can have an effect on the flow patterns due to outflow effects
- * There is a modelling decision to be made between the complexity of the topography and the sophistication of the turbulence model and degree to which vegetation and sand transportation are modelled.
74.
75.
Mike Santarni 《电子设计技术》2009,16(9):82-82,83
并非只有宇宙才诞生于大爆炸。目前硅谷最火的汽车电子新创企业PLX Devices也诞生于创始人的引擎爆炸。PLX最新的产品是一款能够监测汽油使用状况,鼓励节油驾驶的插入式器件。它源自公司28岁的首席执行官Paul Lowchareonkul在驾车与奔驰赛车跑坏了引擎后发明的一个空气燃油比测量仪。这两款器件均采用了赛灵思FPGA平台。 相似文献
76.
欧洲化学品管理局(ECHA)现已将重铬酸盐列入了高关注物质(SVHC)的名单.用含有重铬酸钾和重铬酸钠等的媒介染料染制羊毛的工厂正面临着越来越大的压力.这意味着采用这种技术的染厂未来可能要得到特别授权才能使用这种化学品. 相似文献
77.
Osborn TJ Hulme M 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2002,360(1796):1313-1325
Daily precipitation in the UK has changed over the period 1961-2000, becoming on average more intense in winter and less intense in summer. Recent increases in total winter precipitation are shown to be mainly due to an increase in the amount of precipitation on wet days, with a smaller contribution in the western UK from a trend towards more wet days. If the wet-day amounts are modelled using a gamma distribution, then positive trends in its scale parameter are found across almost all of the UK, consistent with an increased frequency of heavy winter precipitation. Non-parametric analyses confirm an increase in the contribution of heavy events to winter precipitation totals. Analysis of multi-day sequences of heavy rainfall indicate a corresponding increase in their frequency. Results for summer show almost opposite trends: decreased precipitation totals (driven more equally by fewer wet days and reduced wet-day amounts), decreases in gamma scale parameter (although accompanied by a trend towards a less positively skewed distribution) and decreases in the occurrence of heavy precipitation (whether defined parametrically or non-parametrically). A more sparse network of weather stations with data back to 1901 suggests that the recent winter changes are unusual, while the recent summer changes are not, though the poorer coverage reduces the confidence in these longer-period results. 相似文献
78.
The essential fatty acid arachidonate is oxidized by cytochrome P-450 epoxygenases to four epoxyeicosatrienoic acids (EETs): 14,15-, 11,12-, 8,9-, and 5,6-EETs. Each of the four EET regioisomers and their hydrolysis products (DHETs) has multiple paracrine and autocrine functions and may also potently dilate blood vessels and activate potassium channels. The present work describes a method to resolve EETs and DHETs by capillary electrophoresis (CE) using trimethyl-beta-cyclodextrin and CH3CN as buffer additives. While stored at 25 degrees C, most of the EET and DHET regioisomers remained intact when suspended in alkaline vehicle. However, under these same conditions, 5,6-EET rapidly broke down to a lactone and was slowly converted to 5,6-DHET. When subjected to CE, the EET and DHET regioisomers were baseline resolved (R > or = 1.3); 10 pg of an EET or a DHET regioisomer was readily detectable at 194 nm. In addition, the UV spectra were regiospecific and identical to those obtained during HPLC except that an additional, weak absorption occurred at 235 nm. Together, the high-sensitivity, high-resolution, and differential UV spectra permitted the identification and quantification of EETs in phospholipids isolated from murine liver. Thus, CE was successfully used for the trace analysis of eicosanoids. 相似文献
79.
We examine the light-activation properties of micrometer-sized gear structures fabricated with polysilicon surface micromachining techniques. The gears are held in place on a substrate through a capped anchor post and are free to rotate about the post. The light-activation technique is modeled on photon radiation pressure, and the equation of motion of the gear is solved for this activation technique. Experimental measurements of torque and damping are found to be consistent with expected results for micrometer-scale devices. Design optimization for optically actuated microstructures is discussed. 相似文献
80.
Miniature cylindrical ion trap mass spectrometer 总被引:4,自引:0,他引:4
Patterson GE Guymon AJ Riter LS Everly M Griep-Raming J Laughlin BC Ouyang Z Cooks RG 《Analytical chemistry》2002,74(24):6145-6153
A miniature cylindrical ion trap mass spectrometer is described, and preliminary data are presented. Functionality and performance of laboratory-scale instruments have been maintained to the extent possible in this battery-operated mass spectrometer. Capabilities include tandem mass spectrometry experiments. Custom-designed electronic components include the RF scanning and amplification system, data acquisition components, and lens power supplies, as well as a custom-software application. Direct leak and membrane introduction inlet systems are used for sample introduction. A mass/charge range of approximately 250 Th with unit mass resolution has been demonstrated. 相似文献