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排序方式: 共有350条查询结果,搜索用时 15 毫秒
211.
Bebbington Mark Zitikis Ričardas 《Methodology and Computing in Applied Probability》2004,6(4):441-462
While there are a number of methods for estimating the intensity of a cyclic point process, these assume prior estimation of the period itself. The standard method for the latter is the periodogram, or spectral analysis, approach. This is a parametric method which is sensitive to the form, in particular the number of peaks per cycle, of the intensity. We construct a family of nonparametric estimators for the period of a cyclic Poisson process, with the object of robustness against the form of the intensity. These are tested, along with the standard periodogram estimate and an earlier nonparametric estimator, on simulated data from a range of intensity functions. While the nonparametric estimators presently lack the well-developed asymptotic and statistical properties of the periodogram, the best of them is almost as accurate as the periodogram for the unimodal intensity cycles on which the latter is based. Whereas the periodogram cannot handle multimodal cycles at all, the better nonparametric estimators are reasonably accurate, and sometimes err by estimating multiples of the period rather than divisors, errors that are arguably less damaging. We conclude with some remarks concerning the derivation of asymptotic properties for our nonparametric estimator. 相似文献
212.
J. Rička 《Experiments in fluids》1987,5(6):381-384
A streaming fluid containing a bleachable fluorescent tracer is illuminated by an intense laser beam having a steep intensity profile and a wavelength suitable to induce either the fluorescence or the bleaching reaction. Providing the beam intensity is sufficiently high to bleach all the dye molecules crossing the beam, the fluorescence intensity is proportional to the rate of transport of the dye into the illuminated region. This phenomenon makes it possible to measure out two-dimensional cross-sections of complex velocity fields with microscopic spatial resolution and within fractions of a second. The measurable velocity range is limited only by the diffusion of the dye on its lower end and by the bleaching sensitivity and the available laser power on the upper end. The applicability of this principle is illustrated in the example of Bénard-Marangoni flow. 相似文献
213.
Ashish A. Rokade Jong Hwa Kim Se Ri Lim Seong Il Yoo Young Eup Jin Seong Soo Park 《Journal of Cluster Science》2017,28(4):2017-2026
We report a facile, cost effective, and environmentally friendly green chemistry method for preparing silver nanoparticles (AgNPs) using Rubus crataegifolius bge (RCB) fruit extract. The amount of the fruit extract used was found to be important parameters in the growth of AgNPs. In this study, the effect of RCB fruit extract on the synthesis of AgNPs was studied using UV–Vis spectroscopy, transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction (XRD), and dynamic light scattering analyses were performed to characterize the RCB fruit extract-stabilized AgNPs. The formation of the AgNPs was confirmed by the color change of the reaction medium and the absorbance peak observed at 420 nm. The XRD analysis confirmed the face centered cubic structure of the AgNPs. The catalytic property of the as-synthesized AgNPs was analyzed for the reduction of 4-nitrophenol to 4-aminophenol. 相似文献
214.
Lee KS Kim SR Park HS Park SJ Min KH Lee KY Choe YH Hong SH Han HJ Lee YR Kim JS Atlas D Lee YC 《Experimental & molecular medicine》2007,39(6):756-768
Reactive oxygen species (ROS) play an important role in the pathogenesis of airway inflammation and hyperresponsiveness. Recent studies have demonstrated that antioxidants are able to reduce airway inflammation and hyperreactivity in animal models of allergic airway disease. A newly developed antioxidant, small molecular weight thiol compound, N-acetylcysteine amide (AD4) has been shown to increase cellular levels of glutathione and to attenuate oxidative stress related disorders such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. However, the effects of AD4 on allergic airway disease such as asthma are unknown. We used ovalbumin (OVA)-inhaled mice to evaluate the role of AD4 in allergic airway disease. In this study with OVA-inhaled mice, the increased ROS generation, the increased levels of Th2 cytokines and VEGF, the increased vascular permeability, the increased mucus production, and the increased airway resistance in the lungs were significantly reduced by the administration of AD4. We also found that the administration of AD4 decreased the increases of the NF-kappaB and hypoxia-inducible factor-1alpha (HIF-1alpha) levels in nuclear protein extracts of lung tissues after OVA inhalation. These results suggest that AD4 attenuates airway inflammation and hyperresponsiveness by regulating activation of NF-kappaB and HIF-1alpha as well as reducing ROS generation in allergic airway disease. 相似文献
215.
216.
Recently,severalkindsoftotalsyntheticmethodsfornaturallyoccurringfuranoidfattyacids(F-acids)whichhavemanybiologicalactivities1havebeendeveloped2.Inthepresentpapertheauthorswishtoreportanewsimplerouteofsynthesizing9-(5-pentyl-carbomethoxyheptyl)triphenylphosphoniumbromideinthepresenceofpotassiumcarbonateandl,2-butyleneoxideinanunexpectedlylowyield(34%),mainlyduetotheextremelyunstablecharacterof2inbasicconditions,especiallyforstrongbaselikesodiummethoxidewhichgaverisetoconsiderableresinification… 相似文献
217.
218.
稀土/高分子复合材料的研究进展 总被引:31,自引:4,他引:31
详述了稀土/高分子复合材料的特异性能。着重说明了该复合材料的射线屏蔽性能和磁性能。指出稀土/高分子复合材料在X射线屏蔽应用中可有效弥补铅的弱吸收区;具有高稀土含量的复合高分子屏蔽材料具有强的热中子吸收能力;含稀土的共聚物具有强顺磁性,提出了制备磁性和磁智能稀土/高分子复合材料的可行性。此外,概述了稀土/高分子复合材料的3种主要制备方法:聚合法,简单掺混法和反应加工法。分析了稀土/高分子配位前体结构和配位数目对光性能的影响;指出了稀土/高分子复合材料可能具有的离聚物结构及其特征;提出原位生成稀土/高分子纳米复合结构的可行性,还对稀土/高分子复合材料的结构与性能的关系进行了详细的探讨,并对制备稀土/高分子复合材料所存在的问题进行了一定的说明。 相似文献
219.
本文在40℃下制得了5-氯水杨醛,使其与硫脲缩合合成了一种含N、O、S的新型Schiff碱配体,该配体与铜(Ⅱ),锌(Ⅱ)能形成稳定的配合物,其组成,结构已由元素分析和红外光谱所表征。 相似文献
220.
DMD (Digital Micro-mirror Device) is a new device, which has hundreds of thousands of micro-mirrors in one chip. We developed
a DMD reflection-type CCD camera that we call ‘DMD camera’ previously. In this optical system of the DMD camera, each mirror
of the DMD is corresponded to each pixel of the CCD. As a result, each DMD mirror works as a high-speed controllable shutter
of the corresponding CCD pixel. However, corresponding each mirror of the DMD to each pixel of the CCD cannot readily be done
since the pixel sizes of DMD and CCD are very small. In this paper, a pixel-to-pixel correspondence adjustment method, which
can perform accurate adjustment of the DMD camera optical system by moiré methodology is proposed. The proposed method is
easy and visual by observing the moiré pattern. This method enables DMD camera to adjust pixel-to-pixel correspondence less
than one pixel accuracy of the CCD. An experiment of phase analysis to demonstrate the improvement of the resolution and accuracy
was performed. 相似文献