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181.
火焰原子吸收光谱法对同一人体黑、白头发中微量元素Cu、Zn、Fe、Mn进行了测定,试验准确度高,相对标准偏差RSD不超过5.04%,回收率在96%~103%之间,结果显示,Cu、Mn缺乏可能是产生白发的重要原因。 相似文献
182.
Considering the stochastic exchange rate, a four-factor futures model with the underling asset, convenience yield, instantaneous
risk free interest rate and exchange rate, is established. These processes follow jump-diffusion processes (Weiner process
and Poisson process). The corresponding partial differential equation (PDE) of the futures price is derived. The general solution
of the PDE with parameters is drawn. The weight least squares approach is applied to obtain the parameters of above PDE. Variance
is substituted by semi-variance in Markowitzs portfolio selection model. Therefore, a class of multi-period semi-variance
model is formulated originally. Then, a continuous-time mean-variance portfolio model is also considered. The corresponding
stochastic Hamilton-Jacobi-Bellman (HJB) equation of the problem with nonlinear constraints is derived. A numerical algorithm
is proposed for finding the optimal solution in this paper. Finally, in order to demonstrate the effectiveness of the theoretical
models and numerical methods, the fuel futures in Shanghai exchange market and the Brent crude oil futures in London exchange
market are selected to be examples. 相似文献
183.
高精度检测球面面形的方法研究 总被引:7,自引:3,他引:4
短波光学的迅猛发展和高精密光学仪器的需求日益增多,对高精度表面的加工与检测也随之重要起来。而在一般的干涉检测中,球面镜检测精度主要依赖参考镜的精度。利用Jensen提出的干涉仪绝对校准理论可以去除参考镜的误差和干涉仪的附加波像差,从而提高被测件测量精度。在研究Jensen绝对校准理论的基础上,提出一种利用泽尼克(Zernike)多项式进行波面相位转换的方法进行波面处理,并提出具体实施方案。对面形精度优于A/37小凸球面进行测量得出了较好的结果,打破了标准镜头最优A/20的局限,使这一理论简单易行地赋予应用。从而实现了高精度检测球面面形。 相似文献
184.
描述了散斑干涉高温物体应变测试实验装置工作原理及其实验结果,对钨和石墨的测量表明,该装置可实现高温状态下材料应变测试,测试精度达1μm,选择波长632.8nm,半宽2.4nm的窄带滤光片,配之预处理电路,对632.8nm辐射散射能力较强的材料(诸如钨带等)可实现2300℃高温非接触应变测量,对632.8nm辐射散射能力较好的材料(诸如石墨等)可实现1500℃高温接触应变测量。 相似文献
185.
本文提出一个解线性规划问题的新算法.其最优解是通过求一个相容方程组的非负解而得到.这算法的计算量在最坏情况下是O(mnτ),其中τ是相应方程的m×n矩阵非零元素的个数. 相似文献
186.
A Ni/TiO2(TBT) catalyst was prepared through in situ precipitation, using tetrabutyl titanate(TBT) as the TiO2 precursor, and was studied in CO methanation. A Ni catalyst supported on commercial TiO2 was also prepared through post precipitation and studied to compare the influence of Ni precipitation conditions on the catalyst's performance. To gain insight on their structure and physicochemical properties, the catalysts were characterized with N2-adsorption, X-ray diffraction, transimission electron microscopy, H2 temperature programmed reduction and temperature programmed desorption. The results showed that the in situ precipitation method was beneficial to the dispersion of Ni and the formation of more active sites on the Ni/TiO2 catalyst. In addition, the density of the metal-support boundary and its interaction with the active component were also increased. These characteristics of Ni/TiO2(TBT) led to a lower light-off temperature and a suppression of Ni sintering during CO methanation. As a consequence, the Ni/TiO2(TBT) exhibited better catalytic behavior, with a CO conversion of 99.4% and CH4 selecti-vity of 90.4% under the following conditions:p=1 MPa, t=320℃, n(H2)/n(CO)=3, gas hour space velocity (GHSV)=2×104 mL·g-1·h-1. The life test results of the two catalysts showed that Ni/TiO2(TBT) was more stable and the catalytic activity remained at its initial level after being used for 30 h. 相似文献
187.
In this paper, we investigate the solvability of infinite-point boundary value problems for a class of higher-order factional differential equations on the half-line involving Riemann–Liouville derivatives. Under a new compactness criterion, some new results are obtained by means of the properties of the Green’s function and some appropriate fixed point theorems on cone. 相似文献
188.
189.
Tongxing Li Zhenlai Han Chenghui Zhang Shurong Sun 《Journal of Applied Mathematics and Computing》2011,37(1-2):601-610
In this paper, we study the following second-order Emden-Fowler neutral delay differential equation $$(r(t)z'(t) )'+q(t)|x(\sigma(t))|^{\gamma-1}x(\sigma(t))=0,$$ where $z(t)=x(t)+p(t)x(t-\tau),\ \int_{t_{0}}^{\infty}\frac{1}{r(t)}\mathrm{d}t<\infty$ . We establish some new oscillation results which handle some cases not covered by known criteria. 相似文献
190.
食品和环境中兽药残留问题时有发生,对人类健康构成很大的潜在威胁。随着人们对美好生活和同一健康的向往和不断追求,对微量甚至痕量兽药残留的分析检测已显得日益迫切和重要。因此,构建对兽药残留进行灵敏、准确、稳定、简便、快速检测的方法已成为一个热点研究领域。稀土掺杂上转换纳米材料(REEs-UCNPs)作为一种新兴的纳米荧光材料,具有独特的反斯托克斯发光性质,由于其具有荧光寿命长、光散射小、激发光生物组织穿透深度大且对组织损伤小等显著优点,在分析检测领域逐步凸显出巨大优势。本文重点介绍了基于REEs-UCNPs构建荧光共振能量转移核酸适配体传感器、磁性纳米颗粒结合核酸装配体传感器、荧光免疫探针以及现场快速检测等在兽药残留检测方面的研究进展,并对其应用前景进行了探讨和展望。 相似文献