微振法在斜拉桥拉索索力测试中的应用

斜拉桥索力测定的准确与否直接关系到斜拉桥施工控制的顺利实施和桥梁在运行期间的安全监测,所以索力正确且精确的测定也越来越被引起重视。重庆万安大桥采用微振法对拉索索力进行了测试,并对主桥索力的分布及受力变化进行了分析,为桥梁结构健康提供了可靠的依据。

关于斜拉桥索力测定的分析

在全面详细总结了当今几种斜拉桥斜拉索索力的检测方法和其优缺点后,重点讨论了当今应用最为广泛的索力检测法—微振法的原理、应用及所存在的诸多理论问题.最后提出了解决这些问题的主要方法.

Asymmetrical Fabry-Perot cavity slot micro-ring resonator and its sensing characteristics

To achieve high quality factor and high-sensitivity refractive index sensor,a slot micro-ring resonator(MRR)based on asymmetric Fabry-Perot(FP)cavity was proposed.The structure consisted of a pair of elliptical holes to form an FP cavity and a microring resonator.The two different optical modes generated by the micro-ring resonator were destructively interfered to form a Fano line shape,which improved the system sensitivity while obtaining a higher quality factor and extinction ratio.The transmission principle of the structure was analyzed by the transfer matrix method.The transmission spectrum and mode field distribution of the proposed structure were simulated by the finite difference time domain(FDTD)method,and the key structural parameters affecting the Fano line shape in the device were optimized.The simulation results show that the quality factor of the device reached 22037.1,and the extinction ratio was 23.9 dB.By analyzing the refractive index sensing characteristics,the sensitivity of the structure was 354 nm·RIU−1,and the detection limit of the sensitivity was 2×10−4 RIU.Thus,the proposed compact asymmetric FP cavity slot micro-ring resonator has obvious advantages in sensing applications owing to its excellent performance.

小间距下穿高铁隧道控制爆破技术

因2015年雨季兰渝高铁龙凤隧道内地下水涌出,致其停运,故在线下增建泄水洞,要求必须在2016年雨季前贯通。该泄水洞距上方运营高铁仅5 m,为保证高铁的运营安全,对爆破振速控制要求极为严格。介绍了此工程中所采用的爆破方法、爆破参数和起爆方式,并最终引入了电子雷管错相减振技术以及相应的起爆时差。由于施工区域地质复杂,围岩等级较高,岩石硬度大。通过试爆段的多次爆破监测数据显示,爆破振速以及主频都远远大于一般类似工程。传统非电毫秒延时方式已彻底无法满足工程要求,普通电子雷管逐孔起爆方法亦无法使得振速得到有效控制,所以最终采取了数码电子雷管错相减振技术。施工过程表明,电子雷管错相减振方式的工程爆破效果良好,减振效果明显,保证了泄水洞如期贯通,避免了高铁再次因雨停运。可为类似的工程作为参考。

A novel method for measuring the moisture content of coal powder by microwave resonator

A novel technique for the quick measurement moisture content of coal powder by microwave was studied. The effects of the various moisture contents on the measurement results were also discussed. The experimental results show that the standard deviation is less than 0.36% when the moisture content of coal powder is 0.74%-16.90% and the standard deviation is less than 0.16% when the moisture content is 0.31%-1.49%. The experimental results indicate that a process of quick measurement moisture content of coal powder by microwave is practical.

Advantages and Drawbacks of Quantum Mechanical Static and Dynamic Approaches to Modelling Infrared Spectra

We present quantum mechanical vibrational computations beyond the harmonic approximation from effective second order perturbative and variation perturbation treatments defined as static approaches, as well as vibrational analysis from density functional theory molecular dynamics trajectories at 300 and 600 K. The four schemes are compared in terms of prediction of fundamental transitions, and simulation of the corresponding medium infrared spectrum at the same level of theory using the B3LYP/6-31＋G（d,p） description of the electronic structure. We summarize conclusions about advantages and drawbacks of these two approaches and report the main results obtained for semi-rigid and flexible molecules.

Studies of Structure, Microstructure and Magnetic Properties of Fe70Si20Cr10 Nanocrystalline Alloy

Nanostructured Fe70Si20Cr10 alloy was produced by high energy planetary ball milling, starting from elemental powders. The structural, microstructural and magnetic properties of the milled powders were characterized by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer and 57Fe M6ssbauer. After 5 h of milling, it is observed the formation of a bcc solid solutions ~t-Fe （Si, Cr）. Its grain size decreases with increasing milling time attaining 20 nm after 15 h of milling time. Analysis of M6ssbauer spectra shows an increasing broad magnetic component when the milling time increases. Its mean hyperfme field is about 25.5 T at 15 h of milling. M-H hysteresis loop curves reveal a room temperature ferromagnetic behaviour with a saturation magnetisation reaching 143 emu/g after 15 hours of milling, which is 20% lower than that of bulk iron; i.e., 1800 emu/g, due to effect of alloying elements after the formation of ct-Fe （Si, Cr） solid solution.

Nonlinear vibration of edged cracked FGM beams using differential quadrature method

This paper investigated the nonlinear vibration of functionally graded beams containing an open edge crack based on Timoshenko beam theory.The cracked section is modeled by a massless elastic rotational spring.It is assumed that material properties follow exponential distributions through the beam thickness.The differential quadrature(DQ) method is employed to discretize the nonlinear governing equations which are then solved by a direct iterative method to obtain the nonlinear vibration frequencies of beams with different boundary conditions.The effects of the material gradient,crack depth and boundary conditions on nonlinear free vibration characteristics of the cracked FGM beams are studied in detail.

Controlled fabrication and microwave absorbing mechanism of hollow Fe3O4@C microspheres

Uniform core-shell SiO2@Fe_3O_4@C microspheres were prepared by a one-step hydrothermal method with SiO_2 microspheres as the template, and the hollow Fe_3O_4@C(HFC) microspheres were achieved via etching SiO_2 template. By changing the sizes of SiO_2 microspheres, a series of HFC microspheres with variable cavity sizes were obtained to study the relationship between cavity size and microwave absorbing(MA) performance for the first time. The morphology and structure of samples were characterized in detail. The results showed that the MA performance of HFC sample depended on its cavity size. In particular, the hollow structure was good for improving MA performance and could make MA move to the high-frequency region. More importantly, as the cavity size increases, the resonance frequency of HFC-i(i=1,2, 3, 4) samples moved to a low frequency, and the optimal matching thickness of HFC-i samples was increasing. Among all HFC-i samples, HFC-3 showed the most excellent MA performance,which could be mainly explained by the quarter-wavelength matching model, intrinsical magnetic and dielectric loss. Furthermore,the MA performance of HFC mixture blended by the equal mass fraction of HFC-2, HFC-3 and HFC-4 was the comprehensive results of three HFC-i samples. All the above suggested that the cavity size in HFC sample had a great influence on the MA performance.

Fluorescence enhancement of Tb^(3+) complexes by adding silica-coated silver nanoparticles

Six kinds of terbium ternary complexes with halo-benzoic acids were synthesized. Their compositions were determined by C, H elemental analyzer and EDTA titration. The infrared spectra, ultraviolet absorption spectra, and fluorescence spectra were also measured to identify the complexes. Elemental analysis showed that the compositions of these complexes were Tb（p-BrBA）3- H20, Tb（p-CIBA）3- 2H20, Tb（p-FBA）3- H20, Tb（o-FBA）3·2H20, Tb（o-CIBA）3· H20, and Tb（o-BrBA）3. H20, respectively. The monodispersed Ag@SiO2 core-shell nanoparticles with silica thicknesses of 10, 15, and 25 nm were success- fully prepared and characterized by transmission-electron microscopy. Fluorescence intensities of the complexes were detected before and after Ag@SiO2core-shell nanoparticles were added; the enhancement times were related to the silica-shell thick- ness. The fluorescence enhancement times were largest when the thickness of the silica shell was 25 nm. The mechanism may be attributed to the localized surface-plasmon resonance. Furthermore, the enhancement effect of terbium fluoro-benzoate complexes was the strongest in these complexes. This result may be attributed to the hydrogen bond between the hydroxyl on the surface of the silica shell and the fluorine atom.