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111.
Yuxiang Qin Ming Hu Haiyan Li Zhisheng Zhang Qiang Zou 《Applied Surface Science》2007,253(8):4021-4024
A new preparation process for carbon nanotubes (CNTs) cold cathode was studied through the replacement of traditional organic or inorganic binder with Ag nano-particles. This method has the advantages of low preparation temperature and fine electrical contact between CNTs paste and substrate. A mixture paste of CNTs, Ag nano-particles and other organic solvents was spreaded on Si substrate. By melting and connecting of Ag nano-particles after sintered 30 min at 250 °C, a flat CNTs films with good field emission properties was obtained. The measurements reveal that the turn on electric field and the threshold electric field of as-prepared CNTs cathode are 2.1 and 3.9 V/μm respectively and the field emission current density is up to 41 mA/cm2 at an applied electric field of 4.7 V/μm. 相似文献
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任一几何平均收缩比率小于1(简称g-收缩映射)的由完备的非空度量空间M到M的复合序列映射,复合周期映射有在M中的唯一的不动点,文中给出定理应用于一组非线性微分方程以及扁壳轴对称弯曲的耦合的积分方程的解的存在和唯一性证明的应用例子。 相似文献
114.
采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法, 计算了In2O3电子结构和光学线性响应函数, 系统研究了In2O3电子结构与光学性质的内在关系. 利用计算的能带结构和态密度分析了带间跃迁占主导地位的In2O3材料的能量损失函数、介电函数、反射图谱, 根据电荷密度差分图分析了In2O3材料的化学和电学特性. 研究结果表明In2O3光学透过率在可见光范围内高达85%, 可作为优异的透明导电薄膜材料. 同时, 计算结果为我们制备基于In2O3透明导电材料的设计与大规模应用提供了理论依据, 也为监测和控制这一类透明导电材料的生长过程提供了可能性. 相似文献
115.
金融衍生产品的力学方法分析(Ⅰ)——期指价格基本方程 总被引:5,自引:2,他引:3
类似连续介质力学方法,将期指价格变化看成是连续、有规律可寻的。根据期指特点,建立期指价格变化的基本方程。这是一个微分方程,其解显示时间与价格呈对数圆形关系。若将时间理解为相应价格的概率,则这一关系与基于统计理论分析的、著名的诺贝尔经济学奖(1997)获得者的期权定价Black-Scholes公式中主要假设-基础资产(在此为期指)价格呈对数正态分布-完全一致。表明了依据完全不同的两种分析方法,也会得到相同的结果。只是Black-Scholes是用假设给出,而作者则从微分方程的解推出。 相似文献
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采用二步成胶工艺制备ZnO-SnO2透明导电薄膜,应用X射线衍射、原子力显微镜、紫外-可见分光光度计、薄膜分析仪及四探针仪等对薄膜的结构、表面微观形貌、透过率和导电性能进行表征.结果表明,锌锡摩尔比为9/12,退火温度为500 ℃时,薄膜的透过率达90%,电阻率为3.15×10-3 Ω·cm.与其它工艺相比,二步成胶工艺所制备出的ZnO-SnO2透明导电薄膜性能优异. 相似文献
119.
Zhao Z Xu B Zhou XF Wang LM Wen B He J Liu Z Wang HT Tian Y 《Physical review letters》2011,107(21):215502
A novel carbon allotrope of C-centered orthorhombic C(8) (Cco-C(8)) is predicted by using a recently developed particle-swarm optimization method on structural search. Cco-C(8) adopts a sp(3) three-dimensional bonding network that can be viewed as interconnected (2,2) carbon nanotubes through 4- and 6-member rings and is energetically more favorable than earlier proposed carbon polymorphs (e.g., M carbon, bct-C(4), W carbon, and chiral C(6)) over a wide range of pressures studied (0-100 GPa). The simulated x-ray diffraction pattern, density, and bulk modulus of Cco-C(8) are in good accordance with the experimental data on structurally undetermined superhard carbon recovered from cold compression of carbon nanotube bundles. The simulated hardness of Cco-C(8) can reach a remarkably high value of 95.1 GPa, such that it is capable of cracking diamond. 相似文献
120.
In fully three-dimensional (3D) positron emission tomography (PET) imaging, the scatter fraction (SF) is about 40%-60%, which may degrade the imaging quality severely. Scatter correction is important for high quality image reconstruction. Model-based scatter correction has been proved to be accurate and available in clinical PET. However, it does not correct the scatter from out of the field of view (OFOV) and multiple scatters. In this study, we demonstrate the radial and axial distribution of scatters from OFOV when the source is located in different radial positions. In order to apply the above conclusions to different PET systems, we characterize the scatters from OFOV as a function of the ratio of the scanner diameter to the length of the axial field of view (AFOV) by modeling several typical whole-body and micro PET systems. The proportions of true events (S0-0), single scatter of one photon (S1-0) , single scatter of both photons (S1-1) , double scatter of one photon (S2-0) and multiple scatter (Sm) are also calculated and compared. Here the 3D-PET Monte Carlo simulations are performed with the Geant4 Application for Tomography Emission (GATE). In summary, the scatters from OFOV tend to be recorded on the lines of response (LOR) far away from the source. They have a much more serious impact on whole-body PET than micro PET depending on the ratio of scanner diameter to the length of AFOV. In whole-body PET, twice scatters including single scatter of both photons (S1-1) and double scatter of one photon (S2-0) add up to about 12% so that twice scatter correction must be taken into account to acquire a high quality reconstruction image. 相似文献