Effects of vertical central stabilizers on nonlinear wind-induced stabilization of a closed-box girder suspension bridge with various aspect ratios

The aerodynamic shape of a closed-box girder plays an important role in the wind-induced stabilization of long-span suspension bridges. The purpose of this study is to investigate the effects of the combination of five aspect ratios and a downward vertical central stabilizer (DVCS) on nonlinear flutter and aerostatic behaviors of a super long-span suspension bridge with closed-box girders. Through conducting a series of wind-tunnel tests and nonlinear finite element analysis, the results show that the nonlinear self-excited forces and the critical wind speed (U_cr) gradually increase as the increase of the aspect ratio (i.e. the width to depth ratios). Furthermore, the application of 20% deck depth DVCS could significantly increase the nonlinear self-excited forces and U_cr for small aspect ratios of 7.9 and 7.1. Particularly, the installation of the DVCS could change the flutter divergence patterns of the bridge from soft flutter to hard flutter, especially for a relatively small aspect ratio. In addition, the aerostatic force coefficients and torsional divergence critical wind speeds of the larger aspect ratio with DVCS are significantly larger than that without DVCS. A relatively small aspect ratio of the bridge has better aerostatic performance than that with a larger aspect ratio.

     

现代桥梁抗风理论及其应用

介绍了在国家自然科学基金``九五'重大项目(59895410)研究中探索的桥梁抗风理论以及近10 年来在完成中国大跨度桥梁抗风研究项目中所积累的实践经验,主要包括桥梁风环境及其模拟、 桥梁抗风研究方法、风振机理及控制方法、大跨度桥梁抗风设计与评价等,反映了 中国现代桥梁抗风理论与实践的最新研究进展.     

γ-Mo2N催化剂上H2及NO吸附性质的TPD-MS研究

采用TPD-MS方法研究了H2及NO在γ-Mo2N上的吸附状况．单独的H2-TPD结果表明,当H2在673K吸附时,在443K、573K及723K得到了三个H2脱附峰,表明γ-Mo2N上有三种不同能量的H2吸附位．NO－TPD结果表明,NO吸附后亦有三个脱附峰（383K、493K、543K）,对应着γ-Mo2N上三种不同能量的NO吸附位：低、中、高能吸附位．NO既可以以解离状态,又可以以一种NO三聚态（dimerordinitrosyl）的形式吸附在γ－Mo2N上,这些吸附物种在脱附过程中产生大量的N2及少量的N2O.对比NO吸附在不同处理条件的γ-Mo2N上的TPD结果可知,NO是吸附在γ-Mo2N上的MO的配位不饱和中心上,这些吸附中心既可通过还原催化剂,又可通过在773K抽空钝化态的γ－Mo2N而产生,H2和NO共吸附的结果表明,预吸附H2再吸附NO后,H2和NO的脱附量均大大减少,且只有两个脱附峰出现.NO只在363K及493K出现两个脱附峰,表明预吸附氢占据了NO的强吸附位,且NO很难取代它,从而使NO只能吸附在能量较低的吸附位上;而H2只在523K及723K出现两个脱附峰,且伴随着H2的脱出有N2和H2O的产生,表明在γ－Mo2N上NO可能与预吸附氢形成了一种复合相MoHx（NO）y,它在脱附时分解为H2、N2及H2O.     

Application of a Direct Stiffness Method to Wave Propagation in Multiphase Poroelastic Media

In this paper, it is demonstrated how a direct stiffness method for wavepropagation in multilayered saturated poroelastic media, based on integraltransform techniques, can be modified to account for a small amount of gasin the pores. Unsaturated media with small gas fractions can be treatedusing Smeulders extension of Biots poroelastic theory. The effect of thepresence of gas bubbles on the fluid bulk modulus and the dispersioncharacteristics of a water-saturated sand of Mol is demonstrated. Thedirect stiffness method is illustrated with a numerical example wheretransient wave propagation in a dry, saturated and unsaturated halfspaceis considered.     

Experimental implementation of an all-optical OFDM system based on time lenses

<正>Experimental implementations of continuous optical time domain Fourier transformation based on time lenses and optical orthogonal frequency-division multiplexing(OFDM) system are carried out.Such a system is verified through 100-km transmission of 10-Gb/s non-return-to-zero(NRZ) intensity-modulated direct-detection(IM-DD) without any dispersion compensation.The system's bit error rate(BER) and power penalty are 10~(-12) and 4 dBm,respectively.     

一类非线性Schrodinger方程的整体解和自相似解

对于α的某一取值范围,应用广义Strichartz不等式和压缩映射原理研究了初值在弱Lp空间中足够小的条件下,非线性Schr(o)dinger方程Cauchy问题整体解和自相似解的存在性.     

Amine‐Catalyzed [3+2] Huisgen Cycloaddition Strategy for the Efficient Assembly of Highly Substituted 1,2,3‐Triazoles

An enamine‐catalyzed strategy has been utilized to fully promote the Huisgen [3+2] cycloaddition with a broad spectrum of carbonyl compounds and azides, thereby permitting the efficient assembly of a vast pool of highly substituted 1,2,3‐triazoles. In particular, the employment of commonly used and commercially available carbonyl compounds has resulted in the introduction of a diverse set of functional groups, such as alkyl, aryl, nitrile, ester, and ketone groups, at the 1‐, 4‐, or 5‐positions of the 1,2,3‐triazole scaffold. This approach might be manipulated to access more useful and sophisticated heterocyclic compounds. Most significantly, the reaction process exhibits complete regioselectivity, with the formation of only one regioisomer.     

Expeditious diastereoselective construction of a thiochroman skeleton via a cinchona alkaloid-derived catalyst

An example of diastereoselective and enantioselective synthesis of thiochroman derivatives through a sulfa-Michael-Michael cascade sequence is disclosed. This is a significant complement of the quinine-thiourea catalyzed sulfa-Michael-Michael cascade reaction. The densely functionalized target thiochromans were obtained in high diastereoselectivities, and with high to excellent enantioselectivities.     

Blind frequency offset estimation based on cyclic prefix and virtual subcarriers in CO-OFDM system

A new blind frequency offset estimation method based on cyclic prefix and virtual subcarriers in coherent optical orthogonal frequency division multiplexing （CO-OFDM） system is presented. It is able to estimate the fractional part and integral part of frequency offset at the same time. Its estimation range is about [-3.5 GHz, 3.5 GHz]. The influence of the integral frequency offset is comprehensively analyzed in COOFDM system. Its performances in the additive white Gaussian noise （AWGN） channel and the dispersive channel are investigated, respectively. Simulation results indicate that even in the dispersive channel, when the optical signal-to-noise ratio （OSNR） is low, it can still work very well.