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排序方式: 共有479条查询结果,搜索用时 31 毫秒
81.
Guang Lin RANG Zhi Yuan HUANG 《数学学报(英文版)》2007,23(5):895-904
In this paper a complete proof for the existence of generalized operators satisfying abstract 02 dynamical equations of quantum motions δ^2/δt^2Ф(t, x) + ( △- m^2)Ф(t, x) = -λ :Ф^3(t, x), subject to a suitable initial condition, is given under the framework of white noise analysis. Also some important commutation relations related to Ф44 quantum fields are discussed and proved in detail. 相似文献
82.
A method for the determination of colorimetric uncertainties has been developed in order to meet the requirements for accreditation by the UK accreditation service (UKAS), which include a statement of uncertainty for all certified quantities. The values of the principal sources of spectrophotometric uncertainty are first determined and are used to calculate corresponding components of colorimetric uncertainty using a simple model. The components of uncertainty analysed are 100% level (diffuse reflectance), photometric non-linearity, dark level and wavelength error. Bandwidth error is not significant for NPL surface colour standards because a small bandwidth is always used.
The gloss trap error and specular beam error are determined and corrected so that only the uncertainties after correction need be considered. These can be treated as components of dark level uncertainty. The uncertainties are determined for the following colour data: x, y, Y, u′, v′, L*, a* and b* for the CIE 10° Standard Observer and the CIE Standard Illuminant D65 for three geometries: specular included, specular excluded and 0°/45°. These are now quoted routinely on NPL certificates for ceramic colour standards, white and black ceramic tile standards and Russian opal standards. 相似文献
83.
多基色混合白光LED显色性优化研究 总被引:1,自引:0,他引:1
为优化多基色混合白光LED的显色性,得到色彩生动的白光LED照明效果,以评价饱和红色的特殊显色指数R9为研究对象,通过多基色光源混合白光LED的光谱功率分布的高斯数学模型,选取峰值波长λm、半波宽Δλ和幅值A为基色光源光谱功率分布的主要参量,并以“蓝光芯片+YAG黄色荧光粉”和“红、绿和蓝基色LED”为分析模型分别进行二基色和三基色混合白光LED显色性研究,讨论两种基色混合情况下三个参量对混色白光LED的显色性R9贡献。结果表明:为使多基色混合白光LED的显色性更好,首先确定光源S1的峰值波长λm1、半波宽Δλ1及幅值A1;然后设定其他基色光源幅值Ai以求此条件下峰值波长λmi和半波长Δλi取值范围;最后在求得的峰值波长λmi和半波长Δλi取值范围,反求基色光源的最佳幅值Aiopt,从而使多基色混合白光LED的显色性达到最佳效果。该方法对分析基色混合白光LED的显色性具有理论参考价值。 相似文献
84.
Sandra M. Meyers Cornelia Laule Irene M. Vavasour Shannon H. Kolind Burkhard Mädler Roger Tam Anthony L. Traboulsee Jimmy Lee David K.B. Li Alex L. MacKay 《Magnetic resonance imaging》2009
This study compared region of interest (ROI) and voxel-based analysis (VBA) methods to determine the optimal method of myelin water fraction (MWF) analysis. Twenty healthy controls were scanned twice using a multi-echo T2 relaxation sequence and ROIs were drawn in white and grey matter. MWF was defined as the fractional signal from 15 to 40 ms in the T2 distribution. For ROI analysis, the mean intensity of voxels within an ROI was fit using non-negative least squares. For VBA, MWF was obtained for each voxel and the mean and median values within an ROI were calculated. There was a slightly higher correlation between Scan 1 and 2 for the VBA method (R2=0.98) relative to the ROI method (R2=0.95), and the VBA mean square difference between scans was 300% lower, indicating VBA was the most consistent between scans. For the VBA method, mean MWF was found to be more reproducible than median MWF. As the VBA method is more reproducible and gives more options for visualization and analysis of MWF, it is recommended over the ROI method of MWF analysis. 相似文献
85.
Vera Novak Mareile Haertle Peng Zhao Kun Hu Medha Munshi Peter Novak Amir Abduljalil David Alsop 《Magnetic resonance imaging》2009
Background
White matter hyperintensities (WMHs) on MRI have been associated with age, cardiovascular risk factors and falls in the elderly. This study evaluated the relationship between WMHs and dynamics of postural control in older adults without history of falls.Methods
We studied 76 community-living subjects without history of falls (age 64.5±7.3 years). Brain and WMH volume calculations and clinical rating were done on fluid-attenuation inversion recovery (FLAIR) and MP-RAGE MR images on 3 T. Balance was assessed from the center of pressure displacement using the force platform during 3 min of quiet standing using traditional and dynamic measures (using stabilogram-diffusion analysis). Gait speed was measured from 12-min walk.Results
Age-adjusted periventricular and focal WMHs were associated with changes in certain dynamic balance measures, including reduced range of postural sway in anteroposterior direction (fronto-temporal WMHs, P=.045; parieto-occipital WMHs, P=.009) and more irregular long-term mediolateral fluctuations (P=.046). Normal walking speed was not affected by WMHs.Conclusions
Periventricular and focal WMHs affect long-term dynamics of postural control, which requires engagement of feedback mechanisms, and may contribute to mobility decline in the elderly. 相似文献86.
3种菊花茶中6种微量元素的初级形态及溶出特性研究 总被引:4,自引:1,他引:3
按照传统的花茶饮用方法对杭白菊茶、野菊花茶、贡菊茶3种菊花茶中钙、镁、铁、锰、铜、锌6种元素进行浸取;用0.45μm微孔滤膜分离浸取液中的可溶态和悬浮态;采用电感耦合等离子体原子发射光谱法对此3种菊花茶中微量元素的初级形态进行了测定。结果显示:菊花茶中6种元素的提取率在12.4%—80.4%之间,可溶态在水浸液中的比率在74.3%—96.5%之间。 相似文献
87.
A series of Dy3+-doped calcium magnesium silicate phosphors: CaMgSi2O6:Dy3+, Ca2MgSi2O7:Dy3+, and Ca3MgSi2O8:Dy3+ with white long-lasting afterglow were prepared and investigated. The characteristic intra-configurational 4f emissions of Dy3+ were observed in the emission spectra as well as the afterglow spectra under ultraviolet excitation. The combination of the 480 nm blue emission corresponding to the 4F9/2→6H15/2 transition and the 575 nm yellow emission corresponding to the 4F9/2→6H13/2 transition yielded white-light emission. The white-coloured afterglow emission can last more than 1 h for most of the samples under study. The concentration dependence of the ratio of the yellow emission intensity with blue emission intensity was also examined and found to be varied for the different hosts. The thermoluminescence spectra above room temperature are employed for the discussion of the origin of the traps and the mechanism of the persistent luminescence. 相似文献
88.
Interlayer-free phosphorescent white organic light-emitting diodes (PHWOLEDs) with a mixed-host emitting structure in red emitting layer were developed and device performances were investigated according to the host composition in the red emitting layer. Device performances could be effectively managed by a simple change of host materials in the red emitting layer. A high quantum efficiency was obtained in PHWOLEDs with electron transport-type host in the red emitting layer and red emission was strong in PHWOLEDs with mixed-host in the red emitting layer. In addition, stable color performances were obtained in electron transport-type host rich devices. 相似文献
89.
高质量CdTe量子点的水相快速合成 总被引:3,自引:0,他引:3
系统考察了水相合成CdTe量子点的主要影响因素, 通过改变无水乙醇-水体系的体积, 提高NaHTe的合成质量, 并调整反应温度, 改变反应的初始pH值, 在水相中快速合成了量子产率高、粒径分布范围窄的CdTe量子点, 实现了对量子点发光性质的调控, 在最佳条件(无水乙醇3 mL, 水1 mL, 反应初始pH 8.0, 反应温度40 ℃)下, 最高量子产率达68%. 量子点胶体溶液在回流过程中有时产生白色沉淀, 放置7 d后, 未过滤白色沉淀的量子点比过滤后的量子点荧光强度提高15%, 白色沉淀还有减小粒径分布的作用. 相似文献
90.
Baoling Wang Liuzheng Sun Haidong Ju Shilong Zhao Degang Deng Huanping Wang Shiqing Xu 《Journal of Sol-Gel Science and Technology》2009,50(3):368-371
CaAl2Si2O8: Eu2+, Mn2+ phosphors have been prepared by a sol–gel method. X-ray diffractometer, spectrofluorometer and UV–Vis spectrometer were used
to characterize structural and optical properties of the samples. The results indicate that anorthite (CaAl2Si2O8) directly crystallizes at 1000 °C in the sol–gel process. CaAl2Si2O8: Eu2+, Mn2+ phosphors show two emission bands excited by ultraviolet light. Blue (around 415 nm) and yellow (around 575 nm) emissions
originate from Eu2+ and Mn2+, respectively. With appropriate tuning of Mn2+ content, CaAl2Si2O8: Eu2+, Mn2+ phosphors exhibit different hues and relative color temperatures. 相似文献