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991.
The dynamical properties of a noise-driven tumor cell growth system are investigated when there exist two different kinds
of time delays, in the deterministic and fluctuating forces, respectively. Using the approximation probability density approach,
the delayed Fokker-Planck equation is obtained. The effects of two different time delays on the stationary probability distribution
(SPD), the mean value and the mean passage time (MFPT) are discussed. It is found that the time delay τ1 in the deterministic force can enhance tumor cell number, while the time delay τ2 in the fluctuating force can induce a decrease in tumor cell numbers. On the other hand, while τ1 can hold back the extinction of tumor cells, τ2 can speed up their extinction. 相似文献
992.
The magnetoresistivity and critical current density of well characterized Si-nanoparticle doped and undoped Cu-sheathed MgB2 tapes have been measured at temperatures T≥28 K in magnetic fields B≤0.9 T. The irreversibility line Birr(T) for doped tape shows a stepwise variation with a kink around 0.3 T. Such Birr(T) variation is typical for high-temperature superconductors with columnar defects (a kink occurs near the matching field B?) and is very different from a smooth Birr(T) variation in undoped MgB2 samples. The microstructure studies of nanoparticle doped MgB2 samples show uniformly dispersed nanoprecipitates, which probably act as a correlated disorder. The observed difference between the field variations of the critical current density and pinning force density of the doped and undoped tape supports the above findings. 相似文献
993.
Dou Tao Feng Fangxia Xiao Yongzhuang Cao Jinghui 《Reaction Kinetics and Catalysis Letters》1997,61(1):97-101
Silicalite-1 has first been synthesized from a dry powder system with an adsorbedstate template, and is presented as a convincing
example for direct solid-solid transformation process. 相似文献
994.
995.
空间目标的可见光散射与红外辐射 总被引:22,自引:6,他引:16
利用Lowtran7大气传输模型计算了0.4~0.8μm可见光波段的太阳辐射、大气自身的热辐射以及天地背景辐射。利用粗糙面光散射理论与双向反射分布函数计算了空中目标表面对太阳辐射、云层对阳光反射的散射。并利用传热学和背景辐射理论,根据能量守恒定律建立了空间目标表面温度的热平衡方程。以气球为例,计算了不同表面涂层材料的气球在不同地理位置、不同高度、不同时间、温度及辐射功率的变化。分析了空间目标红外辐射特性的一般规律和特征。 相似文献
996.
报导了ZnSCu水溶液和ZnSCu/PVA复合膜的制备过程,分析了分散剂所起的作用.研究了室温下复合膜的激发光谱和发射光谱,以及室温和液氮温度下的分时光谱.初步探讨了ZnSCu纳米超微粒的发光过程. 相似文献
997.
In this paper simple closed form expressions of surface wave fields for microstrip dipoles on grounded substrates are presented.
The surface power, radiated power and radiation efficiency are calculated. It is shown that the radiation efficiency decreases
with the increase of substrate electrical thickness. Hence new type antennas are needed to radiate millimeter wave because
of the effect of the surface waves in substrate. 相似文献
998.
Qizheng Dou Xiaomin Zhu Karin Peter Dan E. Demco Martin Möller Claudiu Melian 《Journal of Sol-Gel Science and Technology》2008,48(1-2):51-60
Based on a volatile-free silica liquid precursor polymer—hyperbranched polyethoxysiloxane (PEOS), an industrial compatible in situ sol–gel process for the preparation of polymer/silica nanocomposites has been developed. It has been shown that in the presence of a catalyst water vapor induced a fast conversion of liquid PEOS to solid silica in polypropylene (PP) melt in a twin-screw microcompounder. Solid state NMR showed that the in situ conversion of PEOS proceeded to a large extent. With small amounts of PEOS this procedure yielded PP/silica composites with particle size less than 100 nm. The particle size increased with the PEOS amount blended with PP. Nevertheless, the particles were observed to be homogeneously dispersed within the polymer matrix. PP/silica composites prepared by in situ sol–gel technology showed improved thermal properties, but almost not affected mechanical properties in comparison with pure PP. 相似文献
999.
In this communication a note on the coupling efficiency between an antenna and a Gaussian beam is presented. The calculations of the coupling efficiency from both methods, a nomorlized inner product between the antenna radiation pattern and the Gaussian-beam pattern or alternatively, between the electric field at the antenna aperture and a two-dimensional field representation of a Gaussian beam, are compared for different aperture size in wavelength. How a correct solution can be gotten is stated. 相似文献
1000.
Several kinds of waveguide components such as curved waveguide bends, arbitrary angle waveguide bends and T-junctions have been analyzed with boundary element method in this paper. A new discretization method for the boundary element method to solve the waveguide discontinuities has been given. The numerical results obtained agree well with the experimental results and numerical results in other literature. Especially, the scattering characteristics of Forded E-, H-plane T-junctions in 3mm band have been analyzed using boundary element method and the calculation results are presented. 相似文献