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991.
以随机分析的知识和最优控制理论为基础,讨论了一类带停时的奇异型随机控制的折扣费用模型,在原模型的状态过程的基础上添加了漂移因子和扩散因子,并在λ<δα的情况下讨论了该问题相应的变分方程的解,给出了此随机控制问题的最优策略,即最优控制和最优停时,并且证明了变分方程的解即为最优费用函数. 相似文献
992.
993.
超细氧化硅纳米线阵列的制备和发光特性 总被引:2,自引:0,他引:2
以液态金属Ca作为催化剂合成了大量的非晶SiO2纳米线阵列。这些纳米线具有高度取向性,直径分布均匀,平均约8nm,长度大于300μm。研究发现,载气的湿度对非晶SiO2纳米线阵列的生长有重大影响,提出了一种可能的生长模型,以解释这一与传统的VLS机制不同的生长过程。对样品的光致荧光(PL)谱的测量表明,非晶SiO2纳米线阵列在蓝光波段附近存在两个很强且稳定的发射峰,它们直接与样品中的缺陷和空位有关。首次发现了一个稳定的PL峰,存在于红外波段,作为光源,非晶SiO2纳米线阵列可能会在纳米光电子器件中得到应用。由于SiO2是传统的光纤材料,单根SiO2纳米线也有希望应用于近场光学扫描显微镜(SNOM)之中。 相似文献
994.
995.
ZnO薄膜的分子束外延生长及性能 总被引:2,自引:0,他引:2
利用分子束外延(MBE)和氧等离子体源辅助MBE方法分别在Si(100)、GaAs(100)和蓝宝石Al2O3(0001)衬底上用Zn、ZnS或以一定Zn-O化学计量比作缓冲层,改变衬底生长温度和氧压,并在氧气氛下,进行原位退火处理,得到ZnO薄膜。依据X射线衍射(XRD)图,表明样品的结晶性能尚好,且呈c轴择优取向;实验结果表明在不同衬底上生长的ZnO薄膜,由于晶格失配度不同,其衍射峰也有区别。用原子力显微镜(AFM)观测薄膜的表面形貌,为晶粒尺寸约几十纳米的ZnO纳米晶,且ZnO晶粒呈六边形柱状垂直于衬底的表面。采用掠入射X射线反射率法测膜厚。在360nm激发下,样品的发光光谱是峰值为410,510nm的双峰谱,是与样品表面氧缺陷有关的深能级发光。 相似文献
996.
V. I. BOROVKOV V. A. BAGRYANSKY I. V. YELETSKIKH YU. N. MOLIN 《Molecular physics》2013,111(9):1379-1384
The time-resolved magnetic field effect in the recombination fluorescence of spin-correlated radical ion pairs has been measured to study n-alkane radical cations in irradiated solutions at room temperature. The magnetic field effect was recorded as a ratio of fluorescence decay curves in the 0.1 T and zero magnetic fields for solutions of C8, C9, C10, C12, and C16 n-alkanes in n-hexane with addition of 3 × 10?5 M p-terphenyl-d 14. A distinct maximum at 10–30 ns followed by a slowly decaying plateau was observed for all the solutions. Simulation shows that the maximum corresponds to an unresolved ESR spectrum with the peak-to-peak line-width ranging from about 1.6mT to 0.5mT for C8 to C16 radical cations. The unresolved structure is believed to result from the hyperfine couplings with many protons of the radical cation, the increase in the number of interacting protons compared with low temperature matrices being caused by the methyl group rotation and conformational motion of the carbon chain. With increase in concentration of dissolved n-alkane, the maximum in the curves first moves to longer times and finally disappears; this was attributed to the narrowing of ESR spectrum contour due to degenerate electron exchange. 相似文献
997.
998.
H. Y. PAN D. P. YU G. J. LIAN G. C. XIONG X. P. ZHANG X. C. SUN 《Molecular physics》2013,111(19):3049-3054
A study is reported on the growth mechanism of YBa2Cu3O7 with different growth speeds by high resolution transmission microscopy (HRTEM) and analysis of the interface and thin film microstructure. Two thin films were synthesized by pulse laser deposition on [100], miscut 5°, SrTiO3 substrate at 820 °C, one with a pulse laser frequency of 1 Hz and one with 6 Hz. Cross-sections were studied by an H-9000 NAR HRTEM along the [010] direction. The growth process of the sample made at 1 Hz was as follows. First, distorted step flow growth occurred on a step-mediated substrate surface of 3–4 cells thickness. Second, about a 15 nm thickness of island shape growth becomes superimposed on the area of the step flow layer. Finally, thin film growth occurred but with growth fluctuation. The sample made at 6 Hz showed the characteristics of island growth; the growth area of island or ball shape was of small size and dense distribution, and seemed to be a confused mosaic stack. The influence of growth speed on YBCO epitaxial film microstructure was studied explicitly by HRTEM. 相似文献
999.
Mixed second refractivity virial coefficients B ab R (ω) are determined in the infrared spectral range from the analysis of the buffer gas-induced intensity redistribution in the ν3 absorption band at ω ? 930 cm?1 of 34SF6 perturbed by the rare gases Ar, Kr, and Xe at relative densities up to 140 Amagat. The values of the refractivity virial coefficients are found to be several orders of magnitude greater than those observed in the spectral regions far removed from single-photon resonances. The undamped dynamic dipole—induced-dipole (DID) model is shown to qualitatively correctly reproduce the observed unusual dispersion of the B ab R (ω) functions. A new estimate of the integrated band intensity S(ν3) of SF6 is also obtained. 相似文献
1000.
The multilayer Laue lens (MLL) is a novel diffraction optics which can realize nanometer focusing of hard X-rays with high efficiency. In this paper, a 7.9 μm-thick MLL with the outmost layer thickness of 15 nm is designed based on dynamical diffraction theory. The MLL is fabricated by first depositing the depth-graded multilayer using direct current (DC) magnetron sputtering technology. Then, the multilayer sample is sliced, and both cross-sections are thinned and polished to a depth of 35-41 μm. The focusing property of the MLL is measured at the Shanghai Synchrotron Facility (SSRF). One-dimensional (1D) focusing resolutions of 205 nm and 221 nm are obtained at E=14 keV and 18 keV, respectively. It demonstrates that the fabricated MLL can focus hard X-rays into nanometer scale. 相似文献