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991.
Dan Zhang Laixin Shi Ping Shen Qiaoli Lin Qichuan Jiang 《Applied Physics A: Materials Science & Processing》2010,98(3):601-607
The wetting behaviors of molten Mg drops on polycrystalline ZrO2 substrate surfaces were studied in a controlled Ar atmosphere at 948–1173 K using an improved sessile drop method. The ZrO2 substrate is virtually not wetted by molten Mg at temperatures below 1173 K. The wetting and evaporation stages according
to different variation behaviors of contact angle, contact diameter and drop height were identified. Six representative modes
were proposed to describe the evaporation-coupled wetting behaviors during different stages. The competitions between surface
oxidation, chemical reaction and drop evaporation were discussed to account for the mechanisms for various wetting behaviors
at different temperatures. The chemical reaction leads to the formation of more wettable MgO phase at the interface; however,
it yields only an inconspicuous improvement in the wetting due to enhanced Mg evaporation. 相似文献
992.
Dan Zhao 《Journal of luminescence》2010,130(3):424-428
This paper reports the growth and spectroscopic characterization of Er3+:Sr3Y(BO3)3 crystal. Er3+:Sr3Y(BO3)3 crystal with dimensions up to ∅20×35 mm3 has been grown by Czochralski method. The polarized spectroscopic properties of Er3+:Sr3Y(BO3)3 crystal were investigated. Based on the Judd-Ofelt theory, the effective intensity parameters Ωt were obtained: Ω2=1.71×10−20 cm2, Ω4=1.39×10−20 cm2, Ω6=0.74×10−20 cm2 for π-polarization, and Ω2=1.77×10−20 cm2, Ω4=1.44×10−20 cm2, Ω6=0.65×10−20 cm2 for σ-polarization. The emission cross-section σem was calculated to be 4.75×10−21 cm2 for π-polarization at 1536 nm and 6.30×10−21 cm2 for σ-polarization at 1537 nm. The investigated results showed that Er3+:Sr3Y(BO3)3 crystal may be regarded as a potential laser host material for 1.55 μm IR solid-state lasers. 相似文献
993.
We have studied systematically room-temperature photoluminescence (PL) properties of many nanostructured ZnO samples grown by chemical vapour deposition (CVD). Their PL spectra consist of two emissions peaked in the ultraviolet (UV) and green regions. The relative intensity of these emissions depends on the excitation energy density, size and morphology of ZnO nanostructures. Based on the excitation-density dependence of the integrated intensity ratio of UV-to-green emission, we could classify PL spectra of ZnO nanostructures into three groups characteristic of size and morphology. Our study also reveals that with increasing excitation density, the UV-peak position shifts slightly towards longer wavelengths while the green emission around 514-520 nm is almost unchanged. This green-luminescence emission is dominant when the nanostructure sizes range from 20 to 200 nm, which is related to a large surface-to-volume ratio. 相似文献
994.
We investigate the persistent holographic recording in triply doped LiNbO3:Mn:Ce:Fe crystals at different oxidation/reduction states. The experimental results show that there is an optimum oxidation/reduction state, which results in the best dynamic range M/#. Compared with doubly doped LiNbO3:Ce:Fe, we found that the nonvolatile diffraction efficiency and the best dynamic range M/# obtained in triply doped samples are larger than that obtained in doubly doped samples. The reason for the increase of the crystal about the nonvolatile diffraction efficiency and the dynamic range M/# was also explained. 相似文献
995.
Dan Yu 《Optics Communications》2010,283(21):4219-4223
Holographic storage stability is investigated experimentally in phenanthrenequinone (PQ) doped poly-(methyl methacrylate) (PMMA) photopolymer with high thickness and rigid polymer matrix. It is demonstrated that the stability consists of two continuous processes, dark enhancement and decay of holograms, which are corresponding to the diffusion of PQ and its photoproduct molecules, respectively. During dark enhancement the Bragg detuning of angle selectivity is observed. Therefore it is necessary to obtain steady holograms quality by adjusting the readout angle. After reaching steady state, the long-term stability of holograms is determined by the diffusion of photoproducts. Temperature is a most significant parameter for long-term stability, which can bring sufficient energy to increase the diffusion of photoproducts and reduce the stability. Finally low temperature and uniform exposure as alternative methods are proposed to optimize the storage stability after dark enhancement. Moreover the influence of humidity on the storage stability is neglectable. 相似文献
996.
Dan Bai 《Applied Surface Science》2010,256(8):2643-1994
Free-standing multiwall carbon nanotubes (MWNTs) films were coated, using chemical vapor deposition method, with a thin layer of nanostructural ZnO. The morphology and crystal structure of the as-grown products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman scattering analyses. Field emission (FE) results demonstrated that the needle-like and spherical ZnO-MWNTs composite structure films possessed good performance with a turn-on field of 1.3, 2.2 V μm−1 and a threshold field of 2.6, 4.5 V μm−1, respectively. The glucose-sensing characteristic has also been studied. The multi-layer electrode (PDDA/GOx/ZnO/MWNTs) exhibited significant electrocatalysis to the oxidation and reduction of H2O2 than the PDDA/GOx/MWNTs electrode, which provided wide potential applications in clinical, environmental, and food analysis. 相似文献
997.
Global analysis of an age-structured SEIR model with immigration of population and nonlinear incidence rate
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Epidemic models with infection age of infectious individuals have been extensively studied, however, most of the existing works ignore the combined effects of immigration and nonlinear incidence. In this paper, we incorporate both the effects of immigration and nonlinear incidence, based on which we formulate an SEIR epidemic model. We give a rigorous mathematical analysis on some necessary technical materials. Then, by constructing a Lyapunov functional, we show that the endemic equilibrium is globally asymptotically stable. Numerical simulations of an application are given to support our theoretical results. 相似文献
998.
本文选取白银、铝和铜三种供应链金融质物作为研究对象,在分析三种质物收益率统计特征的基础上,引入Copula模型刻画供应链金融业务中质物收益率的“尖峰厚尾”特征以及质物收益率之间的非线性相关结构;采用Monte Carlo模拟方法测度考虑到极端情况下的质物组合价格风险值CVaR;利用时间平方根法则测度长周期视角下质物组合的价格风险。将CVaR与VaR测度结果进行对比,比较分析短期价格风险与长期价格风险,将Copula模型与传统风险测度方法下计算出的风险值进行对比,以期选取最优测度供应链金融质物组合长期价格风险模型。研究结果表明:从单一质物价格波动特征来看,三种单一质物的收益率均存在非正态分布和“尖峰厚尾”特征,具有一般金融资产收益率分布的特点。从模型的有效性来看,第一,CVaR比VaR能够更好地、全面地测度供应链金融质物组合的价格风险;第二,基于Copula模型的风险测度结果比传统集成风险测度结果的准确性高;第三,平方欧式距离法结果表明在五种Copula模型中,t-Copula是最优刻画供应链金融质物组合收益率间的相依关系的模型。从长短期风险测度结果来看,随着风险期限的增加,质物组合的价格风险值随之增大,以往研究中用短期风险测度往往会低估商业银行所面临的价格风险,不利于商业银行资金信贷的优化配置。得到的结论对我国商业银行开展供应链金融业务防范价格风险提供了量化支持。 相似文献
999.
Uniqueness of meromorphic functions concerning sharing two small functions with their derivatives
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In this paper, we study the uniqueness of meromorphic functions that share two small functions with their derivatives. We prove the following result: Let $f$ be a nonconstant meromorphic function such that $\mathop {\overline{\lim}}\limits_{r\to\infty} \frac{\bar{N}(r,f)}{T(r,f)}<\frac{3}{128}$, and let $a$, $b$ be two distinct small functions of $f$ with $a\not\equiv\infty$ and $b\not\equiv\infty$. If $f$ and $f"$ share $a$ and $b$ IM, then $f\equiv f"$. 相似文献
1000.
Martin Andersson 《Journal of Chemometrics》2009,23(10):518-529
Nine PLS1 algorithms were evaluated, primarily in terms of their numerical stability, and secondarily their speed. There were six existing algorithms: (a) NIPALS by Wold; (b) the non‐orthogonalized scores algorithm by Martens; (c) Bidiag2 by Golub and Kahan; (d) SIMPLS by de Jong; (e) improved kernel PLS by Dayal; and (f) PLSF by Manne. Three new algorithms were created: (g) direct‐scores PLS1 based on a new recurrent formula for the calculation of basis vectors yielding scores directly from X and y; (h) Krylov PLS1 with its regression vector defined explicitly, using only the original X and y; (i) PLSPLS1 with its regression vector recursively defined from X and the regression vectors of its previous recursions. Data from IR and NIR spectrometers applied to food, agricultural, and pharmaceutical products were used to demonstrate the numerical stability. It was found that three methods (c, f, h) create regression vectors that do not well resemble the corresponding precise PLS1 regression vectors. Because of this, their loading and score vectors were also concluded to be deviating, and their models of X and the corresponding residuals could be shown to be numerically suboptimal in a least squares sense. Methods (a, b, e, g) were the most stable. Two of them (e, g) were not only numerically stable but also much faster than methods (a, b). The fast method (d) and the moderately fast method (i) showed a tendency to become unstable at high numbers of PLS factors. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献