Fatigue crack analysis in a bolster of a metro train

A Metro train is one of the heavily designed structures and is capable of having long life span of 20–30 years. The occurrence of fatigue crack in the bolster of a metro train is very unusual. In this paper, a series of fatigue damage assessments on a bolster was performed to understand the possibility of fatigue crack initiation under normal operating conditions. Additionally, fatigue crack growth analysis was performed to check for the possibility of unstable crack growth during normal service operation. In the fatigue damage assessment, minimum safety margin of 2.71 was calculated until the end of design life span of 30 years. In the crack growth analysis, operable years of 6.9 was calculated even a 30 mm-sized-initial-crack grows to unstable crack growth. From these two results, we can conclude that the cracks found at the bolster thought to initiate due to accidental over loadings during service, and even though the 30 mm-sized-initial-crack can be detected before it brings unstable crack growth considering maintenance period of normally every 3 years.     

地铁车辆段上盖物业车致振动分析

为研究地铁列车进出车辆段对上盖物业振动的影响,先结合两个实际工程,对武汉某车辆段和宁波某车辆段内运用库列车振动荷载进行现场实测,并对两车辆段内运用库列车振动荷载进行对比分析,探讨车辆段内运用库列车振动荷载特性。然后改善了基于弱振情况下结构精细化有限元模型构建方法和荷载输入方法,并基于实测数据验证了其合理性。最后建立了武汉某车辆段上盖物业精细化有限元模型,计算分析上盖物业的振动响应。计算结果表明：地铁列车进出车辆段引起上盖建筑物的振动高频成分较丰富,其主频率在40Hz附近,列车振动荷载特性决定了建筑物内振动的频域分布;建筑内楼板跨中各方向振级沿高度方向的变化是不同的,铅垂向Z振级沿楼层的上升呈现先减小后增大的特点,而在水平方向振级总体上呈现随楼层增大而增大的特点。本文的研究成果可为精确预测、分析和评价地铁车辆段上盖物业振动舒适度提供基础。     

Silo quake response spectrum of iron ore train load out bin

Silo quaking is a very complex industrial phenomenon and is often occurred in silo structures during discharge. There are three variants of the silo quaking phenomenon such as silo honking, silo shock and silo pulsation. Accelerometers are often used in practice to measure the responses of the structure. The accelerations generated by the silo structure during discharge are of non-linear and non-stationary nature. Therefore traditional algorithm, such as Fast Fourier Transform, which was designed to analyse linear and stationary signals and often used to analyse the collected acceleration data, is not suitable for signals generated by the silo structure during discharge. In the present research, Hilbert-Huang Transform and Hilbert Marginal Spectrum created by Norden Huang, a mathematician at NASA to analyse non-linear and non-stationary signals, were used to analyse the accelerograms collected from the experimental silo. The results revealed the existence of a silo quake spectrum which lays a solid foundation for further research into the silo quaking phenomenon and especially structural design methods to mitigate the effects of silo quaking on the silo structure.     

谱线比值法测量接收信号的频率

在声信号处理系统中，需要实时地测量接收信号的频率。文章利用谱线比值法测量接收信号的频率。该方法具有实时性好、结构简单、准确率高等优点。作者根据论文提出的方法进行了计算机的仿真研究，研究结果验证了这种方法的可行性。     

广州地铁二号线列车空调系统分析

通过介绍二号线列车空调系统的新设计理念、新型控制技术和各种新型元件特性，对比分析广州地铁一、二号线列车空调系统。     

Talbot effect of a grating with different kinds of flaws

The Talbot effect of a grating with different kinds of flaws is analyzed with the finite-difference time-domain (FDTD) method. The FDTD method can show the exact near-field distribution of different flaws in a high-density grating, which is impossible to obtain with the conventional Fourier transform method. The numerical results indicate that if a grating is perfect, its Talbot imaging should also be perfect; if the grating is distorted, its Talbot imaging will also be distorted. Furthermore, we evaluate high-density gratings by detecting the near-field distribution with the scanning near-field optical microscopy technique. Experimental results are also given.     

Fano-like line shape of spontaneous emission spectrum in a weakly driven two-level atom

It has been shown that the Fano-like profile of spontaneous emission spectrum can be obtained in a weakly driven two-level atom under certain conditions. Coherent control of the spectral ‘hole’ or dark line generated in the asymmetric line shape can also be achieved by varying those conditions.     

Talbot effect of selective reflection from a homogeneous atomic vapour

In the present work, the Talbot effect of selective reflection (SR) modified by the coupling fields is examined. It is shown that SR Talbot (SRT) patterns can be dramatically modified by the detuning, the strength and the incident angles of the coupling fields. SRT patterns at the integer and the half integer planes are similar to conventional Talbot images. However, the manifest change in fractional SRT patterns can be observed at several planes, e.g. at the quarter and the three quarters planes, the spatial frequency of those patterns is doubled comparing to that of the original output plane, and the carpets become blurring with an increasing asymmetry as the coupling fields are detuned away from the resonant transition of atoms, or as its strength increases. These peculiar Talbot patterns are mainly from a combined contribution of real and imaginary parts of source SR field modified by the coupling light. The SRT images may have potential applications in the detection of atom–surface interactionsand the processing of optical information.     

metaXCMS: second-order analysis of untargeted metabolomics data

Mass spectrometry-based untargeted metabolomics often results in the observation of hundreds to thousands of features that are differentially regulated between sample classes. A major challenge in interpreting the data is distinguishing metabolites that are causally associated with the phenotype of interest from those that are unrelated but altered in downstream pathways as an effect. To facilitate this distinction, here we describe new software called metaXCMS for performing second-order ("meta") analysis of untargeted metabolomics data from multiple sample groups representing different models of the same phenotype. While the original version of XCMS was designed for the direct comparison of two sample groups, metaXCMS enables meta-analysis of an unlimited number of sample classes to facilitate prioritization of the data and increase the probability of identifying metabolites causally related to the phenotype of interest. metaXCMS is used to import XCMS results that are subsequently filtered, realigned, and ultimately compared to identify shared metabolites that are up- or down-regulated across all sample groups. We demonstrate the software's utility by identifying histamine as a metabolite that is commonly altered in three different models of pain. metaXCMS is freely available at http://metlin.scripps.edu/metaxcms/.     

高速列车“通过噪声”的测试分析

为了评估高速列车运行时对轨道周围环境的噪声污染程度,对高速列车以不同速度工况通过时的车外辐射噪声(称为"通过噪声")进行了测试,得到了以最大A声级和1/3倍频程A声级标志的列车通过噪声的测量数据。分析了通过噪声的频谱特性、及其与列车速度的关系。测试数据表明高速列车通过噪声是宽频噪声,最大A声级在标准规定测试点上的值达到约90 dB,对铁路附近的噪声污染比较大;通过噪声随着列车速度增大而增大,在时速370 km以上增幅变大。     

公路与轨道交通载荷作用下隧道动力响应分析

为研究公路和轨道交通荷载共同作用下隧道的动态响应,本文引入微观交通流模型中的元胞自动机模型来模拟公路车流荷载,利用多体动力学模型来模拟轨道车辆荷载,以上海某公铁两用隧道为例建立隧道-土体系统的三维动力有限元模型,对公路和轨道交通载荷单独作用及共同作用时的隧道动力响应进行分析,获得了公铁两用隧道的动力响应规律,为其设计提供参考。     

Efficiency of capturing a phase image using cone-beam x-ray Talbot interferometry

We assesses the efficiency of x-ray Talbot interferometry (XTI), a technique based on the Talbot effect for measuring a wavefront gradient, in terms of how quickly it can capture a high-quality phase image with a large signal-to-noise ratio for a given incident photon number. Photon statistics cause errors in the phase of the moiré fringes and impose a detection limit on the wavefront gradient. The relation between the incident photon number and the detection limit is determined, and a figure of merit of XTI for a monochromatic cone beam is then defined. The dependence of the figure of merit on optical system parameters, such as grating pitch and position, is then discussed. The effects of varying the pattern height and linewidth of the second grating are shown for rectangular and trapezoidal teeth. Finally, we show how to design a practical cone-beam Talbot interferometer for certain boundary conditions.     

White-light-modified Talbot array illuminator with a variable density of light spots

A flexible array illuminator, comprising only two conventional optical elements, with a variable density of bright white-light spots is presented. The key to our method is to obtain with a single diffractive lens an achromatic version of different fractional Talbot images, produced by free-space propagation, of the amplitude distribution at the back focal plane of a periodic refractive microlens array under a broadband point-source illumination. Some experimental results of our optical procedure are also shown.     

Number of phase levels in a two-dimensional separable Talbot array illuminator

The number of phase levels in a Talbot array illuminator (TAIL) is an important factor for estimation of practical fabrication complexity and cost. We show that the number of phase levels in a two-dimensional TAIL (2D-TAIL) has a simple relation to the prime number. When the output array is alternatively pi phase modulated, there are similar simple relations. These simple relations should be highly interesting for practical use. An experiment with the 2D-TAIL based on the joint-Talbot effect is given as well.     

一种估计船舶线谱的联合分析法

线谱是船舶辐射噪声中重要的特征信息，线谱提取是水中目标识别的关键技术。文章简述了船舶辐射噪声的物理成因和频谱特征，利用经典谱估计法与现代谱估计法在短时序列谱估计中的特点，结合Matlab仿真试验的结果，提出了一种对船舶辐射噪声0．100Hz低频段线谱估计的联合分析法。并用该方法对两艘实船噪声进行了谱分析，提取了A型船在中速航行时5．25Hz的特征线谱，B型船存在65．5Hz和69．2Hz两条特征线谱。实验结果表明该方法对低频段的线谱特征提取有明显的实用效果。     

风屏障对高架桥上列车气动特性影响机理分析

基于同步测压技术,以京沪高速铁路典型高架桥和CRH2列车为背景,研究风屏障对典型车桥组合状态下列车的风压分布和各面气动力分布特征的影响,以分析风屏障的气动影响机理,并从流体力学角度进行解释。研究结果表明:风屏障对上游列车气动特性影响较大,下游列车由于处于尾流中,受之影响较小;设置风屏障后,上游列车由于迎风面风压由正变负,使得该面的侧力与背风面相反,故使总体侧力减小,车顶平均风压显著减小,使得车顶升力约增大50%,背风面和车底风压变化较小;风屏障透风率及高度取值需根据具体环境进行优化,并需注意防风效果并不与减小平均风速等同。     

Red-excitation dispersive Raman spectroscopy is a suitable technique for solid-state analysis of respirable pharmaceutical powders

Dispersive Raman spectroscopy with excitation by a red diode laser is suitable for quantitative crystallinity measurements in powders for pulmonary drug delivery. In spray-dried mixtures of salmon calcitonin and mannitol, all three crystalline polymorphs of mannitol and amorphous mannitol were unambiguously identified and their mass fractions were measured with a limit of quantification of about 5%. The instrument design offered high sensitivity and adequate background suppression, resulting in a low limit of detection in the range of 0.01% to 1%. This spectroscopy method has significant advantages over established techniques regarding specificity, sensitivity, and sample requirements.