Polymer Optical Fiber Photosensitivities and Highly Tunable Fiber Gratings

In this paper, recent progress in the investigation of photosensitivities of polymer optical fibers and the development of polymer optical fiber grating is reported. Photosensitivities in various polymer fibers, including doped and undoped, multimode and single-mode polymer fibers, have been experimentally characterized and evaluated for fiber grating application. In particular, the wavelength dependence of material absorption and photosensitivity has been found essential to the fabrication of polymer optical fiber grating. Based on the results of photosensitivity research, polymer optical fiber gratings have been successfully fabricated. More importantly, polymer optical fiber grating has been demonstrated highly tunable, with a tuning range more than 70 nm. The unique feature of high tunability in polymer optical fiber grating has great potential in various applications including optical fiber WDM systems and fiber sensor systems. Several important issues that remain to be investigated will also be discussed.     

原子相干性对 V型三能级原子自发辐射的影响

本文分别就两种模型,即三能级原子与单模场和双模场的V型相互作用,研究了原子相干性对原子自发辐射的影响.发现在单模情况,原子相干性导致原子自发辐射的消除;而在双模情况,两个跃迁通道的自发辐射是相互独立的,原子相干性不导致原子自发辐射的消除.     

A high-gain porous silicon metal–semiconductor–metal photodetector through rapid thermal oxidation and rapid thermal annealing

2 tungsten lamp at 1.83 mA excited by a 0.85-mW 675-nm laser diode. We also demonstrate that the dark current could be greatly reduced through rapid thermal oxidation and rapid thermal annealing. Received: 4 August 1997/Accepted: 28 May 1998     

Possible Critical Orientations of Interacting Composite Particles

We obtain possibly valuable information about the phase diagram linked to the critical orientations for composite matter subjected to interactions at high fermion as well as boson number density but low temperature, which is not easily accessible to experiments. Our results qualitatively resemble those proposed before by using other theories once we can calibrate our results by tuning the critical orientation and the rarefaction measure (relevant to the temperature).     

Parametric resonance of truncated conical shells rotating at periodically varying angular speed

Parametric resonance of a truncated conical shell rotating at periodically varying angular speed is studied in this paper. Based upon the Love?s thin shell theory and generalized differential quadrature (GDQ) method, the equations of motion of a rotating conical shell are derived. The time-dependent rotating speed is assumed to be a small and sinusoidal perturbation superimposed upon a constant speed. Considering the periodically rotating speed, the conical shell system is a parametric excited system of the Mathieu–Hill type. The improved Hill?s method is utilized for parametric instability analysis. Both the primary and combination instability regions for various natural modes and boundary conditions are obtained numerically. The effects of relative amplitude and constant part of periodically rotating speed and cone angle on the instability regions are discussed in detail. It is shown that for the natural mode with lower circumferential wavenumber, only the primary instability regions exist. With the increasing circumferential wavenumber, the instability widths are reduced significantly and the combination instability region might appear. The results for different boundary conditions are substantially similar. Increasing the constant rotating speed (or cone angle) all lead to the movements of instability regions and the appearance of combination instability region. The former will cause the instability width increasing, while the latter will reduce the instability width. The variation of length-to-radius ratio only causes the movements of instability regions.     

基于改进量子粒子群和主动PI模型的自适应无线传感器网络拥塞控制算法设计

针对无线传感器网络中路由节点需要转发大量数据导致网络拥塞,从而引起节点丢包率高和网络吞吐率过低的问题,提出了一种基于主动PI模型和改进量子粒子群优化算法的拥塞控制方法;首先定义了丢包率和队列长度计算方式;设计了改进的PI主动队列管理模型,然后,为了改进PI模型的控制效果,采用改进的量子粒子群算法对PI主动队列管理模型中的比例系数和积分系数kP和kI进行参数优化,从而得到能实现WSN自适应控制的主动PI控制模型;最后,对基于量子粒子群算法和PI主动队列模型的网络拥塞算法进行了描述和说明;仿真实验表明:文中提出的拥戴控制方法能有效实现WSN拥塞控制,是一种适用于WSN的有效拥塞控制方法,与其它方法相比,具有较短的平均队列长度和较大的网络吞吐率,具有很强的可行性。     

高光谱成像技术的柑橘植株叶片含氮量预测模型

氮素是果树生长发育的一种大量必需元素,及时准确地监控果树的氮营养状况,对果树的合理施肥、增产、优化果实品质以及减缓过量施氮引起的水资源污染具有重要意义。利用高光谱成像技术结合多变量统计学方法,建立了柑橘植株叶片的含氮量预测模型。研究步骤为：高光谱扫描、提取平均光谱曲线、预处理原始光谱数据、采用连续投影法提取特征波段和建立含氮量预测模型。从SG平滑、SNV、MSC、1-Der等11种预处理方法中筛选出的较优预处理方法是SG平滑、Detrending和SG平滑-Detrending。对应这三种最优预处理方法,先采用连续投影法挑选出各自的特征波长,然后将各特征波段下的光谱反射率作为偏最小二乘、多元线性回归和反向传播人工神经网络模型的输入,各自建立三个预测模型。从以上获得的9个预测模型中,得出两个最优模型SG平滑-Detrending-SPA-BPNN(R_p：0.851 3,RMSEP：0.188 1)和Detrending-SPA-BPNN(R_p：0.8609,RMSEP：0.159 5)。结果表明,利用高光谱数据测定柑橘叶片含氮量具有可行性。这为实时、准确地监控柑橘植株生长过程中叶片含氮量的变化以及合理科学的氮肥施加提供了一定的理论基础。     

Growth of strongly textured FeCO 3 thin films for application in research of nuclear quantum optics with ultrashort-pulsed laser deposition

Growth of strongly textured $\mathrm{FeCO}_{3}$ thin films on substrates was achieved with ultrashort-pulsed laser deposition using 810-nm, 46-fs ablation pulses. The crystallinity and composition were verified with X-ray diffraction and Raman spectroscopy. Using Mössbauer spectroscopy, it is shown that the deposited $\mathrm{FeCO}_{3}$ thin films possess the film quality required for application in research of nuclear quantum optics. It is found that a relatively low substrate temperature is crucial for growing a strongly textured film of $\mathrm{FeCO}_{3}$ while avoiding decomposition of $\mathrm{FeCO}_{3}$ into $\mathrm{Fe}_{2}\mathrm{O}_{3}$ and $\mathrm{CO}_{2}$ . This supports the importance of the use of ultrashort-pulsed laser deposition in providing adatoms with high mobility for attaining good crystallinity. The surface morphology was characterized by surface profilometry, scanning electron microscopy and atomic force microscopy. It is found to be significantly affected by changing the ablation laser parameters, including laser fluence, pulse duration, and on-target spot size. The results show that the peak deposition flux must be below approximately 0.03 nm/pulse in order to grow a flat film.     

ZnO three-dimensional hedgehog-like nanostructure: synthesis,growth mechanism and optical enhancement

The 3D hedgehog-like ZnO nanostructures were synthesized on Si substrate through chemical vapor deposition process. The morphology and structure of the products were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, as well as transmission electron microscopy. The ZnO 3D hedgehog-like architectures were found to consist of a central nucleus and multiple side-growing nanowires with diameter of 100–250 nm and length up to 10 µm. The growth mechanism of the hedgehog-like ZnO nanostructures was studied. It revealed a three-step process during the entire growth. Finally, room temperature photoluminescence spectra of ZnO 3D nanostructures showed that the center excitation would render much stronger PL emission intensity. Furthermore, simulation results indicated that the enhanced emission came from light-trapping-induced excitation light field enhancement.     

Irregular elliptical plasmonic rings for engineering near-field and phase

Metallic glasses find wide applications in nanotechnology and micro electro-mechanical systems because of their unique physical properties due to their amorphous structures. The material removal mechanism in nanometric cutting of Cu₅₀Zr₅₀, a typical metallic glass, is studied using molecular dynamics method. The chip formation, workpiece deformation and scratching forces under various scratching depths, scratching velocities and temperatures are investigated. The effect of void defect on the cutting behaviors of metallic glass is also explored. The results show that the material removal in nanometric cutting process is based on extrusion instead of shearing, achieving a good understanding of material removal at the nanoscale.