A theoretical study of the modal dispersion characteristics of an annular circular waveguide with helical winding as the outer cladding

In this present communication, we introduce a new type of annular optical waveguide whose outer cladding is made of sheath helix. The sheath helix is made up of the dielectric material of lower refractive index than the core materials. Using vector approach, the general characteristic equation for the proposed waveguide has been derived. The modal dispersion characteristics for the lowest-order modes for different pitch angles are determined and analyzed. We observe that there is no effect of pitch angles on dispersion curve nearly up to 89° but drastic change is observed at 90° and above pitch angle. On comparison of helically inner cladded annular circular waveguide, we have found that there is not the existence of the negative dispersion curve and photonic band gap in the helically outer cladded annular circular waveguide. It means only the inner cladding is responsible for the negative dispersion as well as photonic band gap. There is no effect of the outer cladding.     

Imaging characteristics of a birefringent lens under broadband illumination

This paper reports the imaging characteristics of an optical system consisting of a lens made of a uniaxial birefringent crystal sandwiched between two linear polarizers under polychromatic input illumination. The optic axis of the birefringent crystal is perpendicular to the lens axis and for an initial investigation, the spectral profile of the input beam is considered to be uniform for all wavelengths. The study reveals that if the variation of the birefringence parameters of the device with the wavelength is less, a larger bandwidth may be used without considerably deviating from the imaging characteristics under strictly monochromatic illumination. The nonlinear variation of birefringence with wavelength results in an asymmetric axial irradiance distribution. This obviates an optimal operating wavelength as well as a proper choice of the lens material. It is found that no appreciable change in image quality under diffraction-limited condition results for an input beam having 632 nm operating wavelength and 60 nm bandwidth. Therefore, it may be feasible to use this system with a white light source in conjunction with a wavelength-selective filter.     

Ultrahigh Electron Emissive Carbon Nanotubes with Nano-sized RuO2 Particles Deposition

Multi-wall carbon nanotubes (MWNTs) have a great commercial potential as electron field emitters, but suffer from fundamental problems such as stability and brightness. By depositing the MWNTs with nano-sized ruthenium dioxide (RuO₂) particles, a new high performance emitter has been developed. When compared to MWNTs, the MWNTs impregnated with 1–2 nm sized RuO₂ have superior and more efficient electrical characteristics. MWNTs supported by a silicon substrate showed a reduction in the onset voltage from 5.4 to 4 V/μm after RuO₂ impregnation. The long-term stability of the impregnated MWNTs is also demonstrated with only a 20% increase in applied voltage required after 700 h operation at 40 mA/cm².     

Perturbation Analysis of Dielectric Grating Antenna with LHM Substrate

A dielectric grating leaky wave antenna with a substrate consisted of left handed material (LHM) is presented in this paper, the case where the n = −1 space harmonic of TM mode radiating into the space is carefully investigated through the improved perturbation analysis, which tremendously simplifies the analysis procedure with good calculation accuracy and brings considerable physical insight into the overall behavior of the dielectric grating antenna. It has been found that the new leaky wave antenna is of larger leakage constant than that of the traditional antenna with substrate of the right handed material (RHM). As a result the dimension of the antenna could be largely reduced, which is of practical significance for some applications. Extensive numerical results of the radiation characteristics are given to establish useful guidelines for the design of the new grating antenna.     

微通道内给定壁面热流的气体换热研究

本文利用实施给定热流边界条件的DSMC方法,对短通道内给定壁面热流边界条件下的气体换热情况进行了模拟.结果表明,壁面热流密度增大导致通道内压力分布非线性程度增加.随着热流密度的增大,截面速度分布趋于平缓,滑移速度增大.给定热流密度的通道壁面温度与气流截面平均温度的差值沿程增大,温度梯度沿程下降,气体稀薄性增大时,通道换热减弱.     

Research on Propagation Characteristics of Millimeter Wave in Tunnels

This paper analyzes the propagation characteristics of the millimeter wave in various circular section tunnels. The received power, path loss and delay spread are discussed in detail using the verified software of Wireless InSite. The investigated tunnel models with circular section include the long straight tunnel, the tunnel with train inside and the curved tunnels with different curvature. The simulated results are verified by the experimental value in the actual tunnel. Several valuable conclusions are obtained, which would offer theoretical and practical references for the millimeter wave communication in limited spaces.     

外界辐射对浸没在多孔介质中的液体燃料燃烧特性的影响

本文研究了不同辐射通量下浸没在沙床中的液体燃料的燃烧特性.探讨了辐射通量对液体燃料浸没在多孔沙床中的燃烧特性的影响,获得了不同辐射通量下的火焰特性、床层温度分布、离表面最近测点处蒸气区的下边界到达时间、燃烧持续时间及燃料消耗规律.实验结果揭示了浸没在多孔床中的液体燃料在不同辐射通量下燃烧时的特殊规律.     

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介绍了自行研制的直流非转移弧等离子体炬的结构和工作原理。运用相似理论,研究了该等离子体炬的电热特性与运行参数,比如气体流量、弧功率的关系,并将计算值与实验结果进行了比较。结果表明,计算值与实验结果吻合较好,可以利用获得的公式来对炬进行结构改进和参数优化。     

Ce:KNSBN晶体光扇效应的入射光强度阈值特性研究

采用非同时读出条件下的两波耦合实验装置,以单束光入射Ce:KNSBN光折变晶体,系统研究了Ce:KNSBN晶体中光扇效应随入射光偏振态、入射光强度、光入射角的变化情况.结果表明异常偏振光入射晶体时光扇效应明显,且存在明显的入射光强度阈值特性,入射光强度阈值为38.2 mW/cm2;相同光入射角下,稳态光扇强度随入射光强度的增强而明显变大;对应相同的入射光强度,稳态光扇强度随光入射角θ的增大而增大,当θ为15°时到达峰值,而后随θ的增大而逐渐减小.同时对光扇效应的入射光强度阈值特性以及稳态光扇强度随入射光偏振态、入射光强度、光入射角的变化作出了相应的物理解释.     

Laser synthesis of thin layers of In4Se3, In4Te3 and modification of their structure and characteristics

Trends of structural modifications and phase composition occurring in In₄Se₃ thin films and In₄Se₃-In₄Te₃ epitaxial heterojunctions under laser irradiations have been investigated. Dynamics of the layer structure modification, depending on laser modes, i.e. pulse duration τ = 2-4 ms, irradiation intensity I₀ = 10-50 kW/cm², number of pulses N = 5-50, was studied by electron microscopy. An increase in laser influence promotes enlargement of the layer grains and transformation of their polycrystalline structure towards higher degree of stoichiometry. As a result of laser solid restructuring heterojunctions of In₄Se₃-In₄Te₃, being photosensitive within 1.0-2.0 μm and showing fast time of response, have been obtained. Laser modification of structure enables one to optimize electrical and optical properties of functional elements on the base of thin films and layers of In₄Se₃, In₄Te₃, widely used as infrared detectors and filters.