基于继电特性函数的互联电力系统混沌控制

电力系统中的混沌振荡对整个互联电网具有极大危害.本文利用Lyapunov指数、分岔图、相平面图和功率谱等分析一个简单互联电力系统的动力学行为,研究电力系统对电磁功率扰动幅值的敏感性.同时,提出一种基于继电特性函数的准滑动模态控制方法,对系统进行混沌振荡抑制,使系统快速平滑地到达控制目标.实验表明,该方法不仅能够缩短控制时间,减少因参数过大带来的系统冲击,而且对高频抖动也有很好的抑制作用,具有较强的鲁棒性.     

Laser-induced damage of the optical films prepared by electron beam evaporation and ion beam sputtering in vacuum

The laser-induced damage characteristics and adsorption effects of organic contamination molecules of two high reflectors (HR) prepared by electron beam evaporation (EB) and ion beam sputtering (IBS) method at 1064 nm is investigated in vacuum. It is found that EB films show the performance degradation of laser induced damages in vacuum while for IBS film, seems to have no this effect, in comparison with air environment. In addition, EB coatings also have the strong affinity with organic contamination molecules, in contrast of IBS films. The results reveal that ion beam sputtering (IBS) method seem to be one of the favorite film deposition techniques of the optical films used in vacuum and space environments.     

Linear and nonlinear optical properties of carbon nanotube-coated single-mode optical fiber gratings

Single-wall carbon nanotube deposition on the cladding of optical fibers has been carried out to fabricate an all-fiber nonlinear device. Two different nanotube deposition techniques were studied. The first consisted of repeatedly immersing the optical fiber into a nanotube supension, increasing the thickness of the coating in each step. The second deposition involved wrapping a thin film of nanotubes around the optical fiber. For both cases, interaction of transmitted light through the fiber core with the external coating was assisted by the cladding mode resonances of a tilted fiber Bragg grating. Ultrafast nonlinear effects of the nanotube-coated fiber were measured by means of a pump-probe pulses experiment.     

Surface modification and characterization of magnesium hydroxide sulfate hydrate nanowhiskers

In order to enhance the compatibility with plastic polymers, magnesium hydroxide sulfate hydrate (MHSH) nanowhiskers were modified through grafting methyl methacrylate (MMA) on the surface of the nanowhiskers by emulsion polymerization. The influences of the reaction time, MMA monomer content, adding speed of monomer and the reaction temperature on the grafting ratio were investigated. Thermogravimetry (TG), Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray (EDX) spectroscopy and surface contact angle measurement were used to characterize the effect of surface modification. The results showed that the MHSH nanowhiskers were uniformly coated by polymethyl methacrylate (PMMA), and a well-defined core-shell hybrid structure of MHSH/PMMA was obtained. The surface contact angle of the hybrid whiskers increased to 87.32° from 12.71° and the whiskers surface was changed from hydrophilic to lipophilic.     

The significant digit law in statistical physics

The occurrence of the nonzero leftmost digit, i.e., 1,2,…,9, of numbers from many real world sources is not uniformly distributed as one might naively expect, but instead, the nature favors smaller ones according to a logarithmic distribution, named Benford’s law. We investigate three kinds of widely used physical statistics, i.e., the Boltzmann-Gibbs (BG) distribution, the Fermi-Dirac (FD) distribution, and the Bose-Einstein (BE) distribution, and find that the BG and FD distributions both fluctuate slightly in a periodic manner around Benford’s distribution with respect to the temperature of the system, while the BE distribution conforms to it exactly whatever the temperature is. Thus Benford’s law seems to present a general pattern for physical statistics and might be even more fundamental and profound in nature. Furthermore, various elegant properties of Benford’s law, especially the mantissa distribution of data sets, are discussed.     

Cytotoxic effects and in vitro reversal of multidrug resistance by therapeutic ultrasound in human hepatocarcinoma cell line (HepG2)

Multidrug resistance (MDR) is one of the major obstacles to successful chemotherapy of human malignancies. Although many strategies have been explored to overcome MDR, none of them have been proven to be clinically useful until now. The aim of this study was to investigate whether a novel therapeutic ultrasound (US) approach would have useful effects on the reversal of MDR in cancer cells. Wild-type and MDR phenotype (HepG2/ADM) cells of the human hepatocarcinoma cell line HepG2 were exposed to 0.8 MHz US at an intensity of 0.43 W/cm² for a 9 s exposure (total energy density: 3.87 J/cm²). After US exposure, cell number and viability were counted immediately, and flow cytometry was performed to measure retention of rhodamine 123 and adriamycin in HepG2 and HepG2/MDR cells. Both cell lines were then incubated in suspension with adriamycin, vincristine, etoposide, cisplatin and 5-fluorouracil, respectively, and the MTT assay was used to determine cytotoxicity. The results showed that US exposure could significantly increase the uptake of Rh123 and ADM by HepG2/ADM tumor cells. The resistant index for the chemotherapeutic drugs was significantly lower in the US-exposed HepG2/ADM cells than in those not exposed to US. It was therefore concluded that US exposure could enhance the sensitivity of HepG2/ADM tumor cells to these chemotherapeutic agents, and the functional and structural changes induced by previous US exposure in MDR tumor cells may be responsible for it. However, further study is needed to investigate the mechanism behind US-mediated reversal of MDR.     

Novel optical orthogonally modulation scheme for superimposing DPSK signals on dark RZ signals

A configuration of transmitter for superimposing DPSK signals on dark RZ signals was proposed. The transmitter comprises two optical phase modulators and a delayed line Mach-Zehnder interferometer. A new orthogonally modulation format with tunable duty cycle and extinction ratio in the optical domain was generated and discussed. The results show that the proposed modulation format offers significant advantages in offering high spectral efficiency values, high extinction ratio, and requiring electronics with reduced bandwidth.     

Solution-combusting preparation of mono-dispersed Mn3O4 nanoparticles for electrochemical applications

Manganese oxide (Mn₃O₄) nanoparticles with average diameter of 15 nm were prepared using alcohol solution of manganese chloride as starting material via a facile solution-combusting method. The flame core zone was chosen to prepare mono-dispersed and high crystalline products, which were employed to modify glassy carbon electrode and detect dopamine via cyclic voltammetry. The results exhibited excellent electrochemical sensitivity. A linear relationship between the concentration of dopamine and its oxidation peak current was obtained by differential pulse voltammetry, which will find wide application in the biological detection.     

电子束放射照相的特性与参数优化

短脉冲强激光产生的电子束具有源尺寸小、脉宽窄、准单能谱等特点, 在放射照相诊断中具有独特作用. 本文通过分析电子在材料中散射并采用蒙特卡罗方法数值模拟, 研究了100 keV到几百MeV能量电子束对有厚度起伏或存在界面的靶的透视, 并与质子、X射线束透视结果比较, 给出了电子束放射照相的特性与参数优化: 基于电子在材料中非弹性散射或能量损失, 选用能量使其射程与靶厚度接近的电子束来诊断靶厚度不均匀性; 基于电子在材料中的弹性散射, 选用射程超过靶厚度的电子束来诊断靶界面.     

质子交换光波导生长动力学研究

分析了质子交换光波导的生长动力学并给出了波导层厚度与生长时间的计算公式。