A multi‐access method for BPL based on orthogonal pulse division multiplexing,barker‐code‐based spectrum spreading and orthogonal frequency division multiplexing

A highly efficient multi‐access scheme of broadband power line (BPL) communication, named as OFDM‐BPS‐OPDMA, is proposed based on the Orthogonal Pulse Division Multiplexing Access (OPDMA), Barker‐code‐based Spectrum Spreading (BSS) and Orthogonal Frequency Division Multiplexing (OFDM) method. The orthogonal pulses are generated by using the eigenvectors of Hermitian matrix. At the same time, a specific pulse will be allocated to every user of the communication system. The transmitting data are first modulated by OFDM. Then, it is processed with OPDMA and BSS. Finally, the data is sent to the power line channel. On the receiving side, the data is processed with BSS demodulation, OPDMA demodulation and OFDM demodulation, and the receiving data for each user is acquired. Because of the orthogonality between these pulses, the multi‐user interference could be eliminated; when BSS is used, the waveform restoration is enhanced. Meanwhile, with the help of OFDM, the multi‐path interference is mitigated. Particularly, all users can share the resources of time and spectrum without interfering with others, and get excellent reliability in the concerned scheme. When OFDM is used, the sub‐carriers may be allocated dynamically, and the legal radio frequency band could be shunned by sharing the common bandwidth with other communication systems. Copyright © 2009 John Wiley & Sons, Ltd.     

缺陷光子晶格局限光现象的研究

利用成像法在自散焦LiNbO3:Fe晶体中诱导出了线形缺陷结构的(2+1)维光折变光子晶格,并发现该缺陷晶格对光波具有一定的局域作用。又对三角与四方点阵缺陷晶格的局域光能力作了对比,结果显示三角点阵缺陷晶格的局域光能力要更好一些。最后,根据光子带隙理论对晶格局限光的现象进行了初步的解释。这对光子晶体的进一步研究与应用有一定的意义。     

Synthesis and characterization of imine‐coupled polyphenols containing carbazole units

Imine coupled phenolic monomers containing carbazole unit were synthesized in four steps. The monomers were polymerized via oxidative polycondensation by air as oxidant in an aqueous alkaline medium at 50°C. The structures of compounds were confirmed by ultraviolet–visible (UV–vis), Fourier transform infrared, and ¹H‐ and ¹³C‐NMR techniques. The conductivity measurements of these polymers were made by the four‐point probe technique and iodine was used as doping agent. The highest occupied molecular orbital, the lowest unoccupied molecular orbital, and electrochemical and optical band gap values were calculated by the results of the UV–vis and the cyclic voltammetry measurement, respectively. The number‐average molecular weight, weight‐average molecular weight, and polydispersity index values were determined by the size exclusion chromatography technique. Also, thermal behavior of these polymers was determined by thermogravimetric/differential thermal analysis measurements in a N₂ atmosphere between 20 and 1000°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

杭兰公路某滑坡稳定性综合分析

以某公路滑坡为研究对象,在对其影响因素进行分析的基础上,研究其形成机制。建立滑坡地质模型并确定相应的计算方案。经分析,用极限平衡法和强度折减法确定的滑动面位置基本一致;天然状态和饱水状态下的稳定性计算结果也基本一致,天然状态下滑坡稳定,饱水状态下会失稳。采取锚杆支护措施后饱水状态下该滑坡也满足工程设防等级要求。     

Influence of interstitial fluid viscosity on transport phenomenon in sheared granular materials

We report experimental measurements of transport properties on sheared granular materials with different interstitial fluids to study the granular flow behaviors. Four kinds of interstitial fluids are used in the experiments. The ensemble velocities, fluctuation velocities, granular temperature and self-diffusion coefficients are successfully measured by PTV method. The results indicate that the interstitial fluid plays an important role in determining the transport properties of the granular flow. The particles motions are more random and interactive collisions are more serious in a dry system (interstitial fluid of air). The values of fluctuations and granular temperatures are smaller as the interstitial fluid is more viscous resulting in the larger viscous force. The thickness of shear band is about three to eight particle diameters and increases with the decreasing interstitial fluid viscosity. The self-diffusion coefficient of granular materials is also discussed in this study. Both the self-diffusion coefficients and the granular temperature increase with the increasing shear rate. The average streamwise self-diffusion coefficient and granular temperature increase with the increase in Stokes number and Bagnold number.     

Thermophoresis of axisymmetric aerosol particles along their axes of revolution

The axisymmetric thermophoretic motion of an aerosol particle of revolution in a uniformly prescribed temperature gradient is studied theoretically. The Knudsen number is assumed to be small so that the fluid flow is described by a continuum model. A method of distribution of a set of spherical singularities along the axis of revolution within a prolate particle or on the fundamental plane within an oblate particle is used to find the general solutions for the temperature distribution and fluid velocity field. The jump/slip conditions on the particle surface are satisfied by applying a boundary‐collocation technique to these general solutions. Numerical results for the thermophoretic velocity of the particle are obtained with good convergence behavior for various cases. For the axisymmetric thermophoresis of an aerosol spheroid with no temperature jump and frictional slip at its surface, the agreement between our results and the available analytical solutions is very good. The thermophoretic velocity of a spheroid along its axis of revolution in general increases with an increase in its axial‐to‐radial aspect ratio, but there are exceptions. For most practical cases of a spheroid with a specified aspect ratio, its thermophoretic mobility is not a monotonic function of its relative jump/slip coefficients and thermal conductivity. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

间歇式膨胀加强带在某超长混凝土工程中的应用

通过对采用间歇式膨胀加强带的工程进行理论分析及现场监测试验,给出了间歇式膨胀加强带的应力计算和应变监测结果,以对结构安全性进行评价.并进一步阐述了施工过程中质量控制措施.技术经济分析表明,该工程采用间歇式膨胀加强带施工方便,可节约投资并缩短工期.     

微穿孔板吸声结构的研究进展

在介绍马大猷开创的微穿孔板吸声结构基础理论的前提下,综述了微穿孔板吸声结构的理论发展、吸声系数实验测量方法以及微穿孔板吸声结构在实际工程领域的一些应用。最后提出微穿孔板研究发展的方向。     

新型U型外包钢-混凝土组合梁薄弱截面分析

新型U型钢-混凝土组合粱强度高、延性好且便于施工、应用前景广阔。针对这种新型U型钢-混凝土组合梁的两个受力薄弱截面,并根据试验,分析其具体位置和形成原因,对薄弱截面采取抗剪、抗滑移措施,效果良好。     

超长大板结构的无缝施工

阐述了超长大板结构无缝施工的经验和理论,并结合工程实例说明超长大板结构无缝施工过程的质量控制点,提出了混凝土温差控制的措施,介绍了大底板地下室的抗浮设计,以积累超长大板结构施工经验。