Image-Aided Analysis of Ballast Particle Movement Along a High-Speed Railway

As a core infrastructure of high-speed railways,ballast layers constituted by graded crushed stones feature noteworthy particle movement compared with normal railways,which may cause excessive settlement and have detrimental effects on train operation.However,the movement behavior remains ambiguous due to a lack of effective measurement approaches and analytical methods.In this study,an image-aided technique was developed in a full-scale model test using digital cameras and a colorbased identification approach.A total of 1274 surface ballast particles were manually dyed by discernible colors to serve as tracers in the test.The movements of the surface ballast particles were tracked using the varied pixels displaying tracers in the photos that were intermittently taken during the test in the perpendicular direction.The movement behavior of ballast particles under different combinations of train speeds and axle loads was quantitatively evaluated.The obtained results indicated that the surface ballast particle movements were slight,mainly concentrated near sleepers under low-speed train loads and greatly amplified and extended to the whole surface when the train speed reached 360 km.h-1.Additionally,the development of ballast particle displacement statistically resembled its rotation.Track vibration contributed to the movements of ballast particles,which specifically were driven by vertical acceleration near the track center and horizontal acceleration at the track edge.Furthermore,the development trends of ballast particle movements and track settlement under long-term train loading were similar,and both stabilized at nearly the same time.The track performance,including the vibration characteristics,accumulated settlement,and sleeper support stiffness,was determined to be closely related to the direction and distribution of ballast particle flow,which partly deteriorated under high-speed train loads.

PIV analysis and high-speed photographic observation of cavitating flow field behind circular multi-orifice plates

Based on a self-developed hydrodynamic cavitation device with different geometric parameters for circular multi-orifice plates,turbulence characteristics of cavitating flow behind multi-orifice plates,including the effects of orifice number and orifice layout on longitudinal velocity,turbulence intensity,and Reynolds stress,were measured with the particle image velocimetry(PIV)technique.Flow regimes of the cavitating flow were also observed with high-speed photography.The experimental results showed the following:(1)high-velocity multiple cavitating jets occurred behind the multi-orifice plates,and the cavitating flow fields were characterized by topological structures;(2)the longitudinal velocity at each cross-section exhibited a sawtooth-like distribution close to the multi-orifice plate,and each sawtooth indicated one jet issuing from one orifice;(3)there were similar magnitudes and forms for the longitudinal and vertical turbulence intensities at the same cross-section;(4)the variation in amplitude of Reynolds stress increased with an increase in orifice number;and(5)the cavitation clouds in the flow fields became denser with the increase in orifice number,and the clouds generated by the staggered layout of orifices were greater in number than those generated by the checkerboard-type one for the same orifice number.The experimental results can be used to analyze the mechanism of killing pathogenic microorganisms through hydrodynamic cavitation.

PLIF技术测量浓度场及其二维数字校正

推导了ＰＬＩＦ技术测量浓度场时液地内荧光强度的分布，提出了ＰＬＩＦ技术的二维数字校正方程和校正方法来消除激光片光的高斯分布和沿光程衰减的影响．在此基础上，对圆形紊动射流的浓度场进行了测量和校正．此外，还将测量结果与前人的半经验理论进行了分析和比较。

Preliminary study of the electrospray DPE peculiarities from the liquid surface in the presence of the CSWs

The Ultrasonic Electric Propulsion(UEP)system is a cutting-edge propulsion technology that is mostly used on platforms for small satellites(less than 10 kg).The characteristics of droplet partial emissions(DPEs)in the UEP system are investigated using a high-speed imaging technique(an ultra-high speed camera(NAC HX-6)and a long-distance microscope)in this work.The experiments demonstrate that there are a few partial emission modes,including left-side emission,double-side emission,and right-side emission,that are present in the droplet emission process of the UEP system.These modes are primarily caused by the partial formation of capillary standing waves(CSWs)on the emission surface of the ultrasonic nozzle.The emission rate for single-and double-sided emissions varies at different times,indicating that there are different CSWs engaged in droplet emission due to variations in the liquid film thickness and charge state of the liquid cones.Additionally,as the droplets emit continuously,a raised area on the emission surface appears,with several droplets emitting there as a result of charge accumulation.Additionally,photos of the CSWs with emitting droplets are obtained,which highlights the CSWs'distinctive wave morphology.

超燃冲压发动机点火过程10kHz PLIF测量技术

应用自主研制的10kHz OH-PLIF(Planar laser-induced fluorescence)系统实现超燃冲压发动机点火过程的可视化。在直连式脉冲燃烧风洞上开展了超燃冲压发动机自点火、电火花和激光诱导等离子体三种点火方式的火焰结构演变过程OH-PLIF测试,采集了时间间隔为100μs的高分辨率火焰图像,进一步计算得到火焰OH基荧光强度和火焰面积的时间演化特性及火焰质心发展轨迹。研究发现:三种点火方式的初始火核发展时间均小于1ms;点火过程中,火焰均先沿凹腔壁面向下游传播,在斜坡附近转向上游传播,火焰质心运动速度为100~450m/s;相对其它两种点火过程,自点火存在强烈振荡现象。研究表明,高频PLIF技术是发动机点火过程可视化最有潜力的手段之一,是发动机燃烧机理和设计方法研究的重要支撑。

搅拌釜内液-液混合溶析沉淀法制备纳米姜黄素颗粒

研究了在搅拌釜内利用溶析沉淀法制备姜黄素纳米颗粒的过程,分别探讨了搅拌釜尺寸、搅拌形式、初始浓度以及搅拌转速对制备结果的影响。通过平面激光诱导荧光技术定量测量釜内液液混合行为,揭示了流体混合环境的控制是决定溶析沉淀产品过程的关键因素。实验表明,搅拌速度过低无法保证流体混合效率,将导致颗粒黏结;搅拌速度过高带来颗粒与流场的强剪切作用,引起颗粒破碎;局部过饱和度过大,引起颗粒的生长和聚团。搅拌釜内纳米颗粒制备需提供适度强化的流体混合环境。

Design of a 20-Gsps 12-bit time-interleaved analog-to-digital conversion system

The time-interleaved analog-to-digital conversion(TIADC)technique is an effective method for increasing the sampling rate in a waveform digitization system.In this study,a 20-Gsps TIADC system was designed.A wide-bandwidth performance was achieved by optimizing the analog circuits,and a sufficient effective number of bits(ENOB)performance guaranteed using the perfect reconstruction algorithm for mismatch error correction.The proposed system was verified by tests,and the results indicated that a-3 dB bandwidth of 6 GHz and the ENOB performance of 8.7 bits at 1 GHz and 7.6 bits at6 GHz were successfully achieved.

Meta-Analysis of Clinical Outcomes of Lumbar Fusion Surgical Interventions for Degenerative Spondylolisthesis

Introduction: Surgical interventions for degenerative spondylolisthesis are varied with comparable claims of success. Fusion based technique is one of the most commonly used surgical interventions in treating this condition. The aim of this meta-analysis is to compare the effectiveness of the Lumbar Interbody Fusion techniques (specifically Posterolateral Interbody approach—PLIF) versus Posterolateral Instrumented Fusion (PLF). The clinical outcomes investigated were: back pain, leg pain, function, Oswestery Disability Index (ODI), Disability Rating Index (DRI), fusion and revision rates if reported. Methods: Combinations of keywords and MeSH terms, where appropriate, were used to search for studies in Medline via Ovid, Embase, Cochrane Library, and Google scholar. The initial search was conducted on 10 August 2016 and updated on 13 June 2017. Eligibility criteria for the studies to be selected for this meta-analysis were: Randomised Controlled Trials (RCTs), cohort and consecutive cases studies that compared at PLIF versus PLF surgical interventions at the lumbar region. Heterogeneity indicators and Forest plot were computed using RevMan 5. Results: Out of the initial hits of 3021, 5 articles were selected as relevant and assessed for risk of bias and then data was extracted and tabulated. These 5 studies reported data from (900 patients’ records, follow up ranges from 6 months to 5 years) undergone one of 2 interventions (PLIF or PLF). The overall effect for ODI and leg pain showed no advantage of any intervention over the other while there was a greater odd ratio of fusion if the operation applied PLIF techniques (Overall Z = 2.86, p = 0.004). Conclusions: There is a need for more high quality clinical trials to compare these two interventions. However, available data indicate that there are comparable results in the main clinical outcomes between PLIF and PLF. PLIF has superior fusion rate which does not seem to affect post-operative pain ratings.

Boundary Induced Inductive Delay in Transmission of Electromagnetic Signals

When an electromagnetic signal transmits through a coaxial cable, it propagates at speed determined by the dielectrics of insulator between the cooper core wire and the metallic shield. However, we demonstrate here that, once the shielding layer of the coaxial cable is cut into two parts leaving a small gap, while the copper core wire is still perfectly connected, a remarkable transmission delay immediately appears in the system. We have revealed by both computational simulation and experiments that, when the gap spacing between two parts of the shielding layer is small, this delay is mostly determined by the overall geometrical parameters of the conductive boundary which connects two parts of the cut shielding layer. A reduced analytic formula for the transmission delay related with geometrical parameters, which is based on an inductive model of the transmission system, matches well with the fitted formula of the simulated delay. This above structure is analog to the situation that an interconnect is between two inter-modules in a circuit. The results suggest that for high speed circuits and systems, parasitic inductance should be taken into full consideration, and compact conductive packaging is favorable for reducing transmission delay of inter-modules, therefore enhancing the performance of the system.

Diffusion Process of High Concentration Spikes in a Quasi-Homogeneous Turbulent Flow

When a mass spreads in a turbulent flow, areas with obviously high concentration of the mass compared with surrounding areas are formed by organized structures of turbulence. In this study, we extract the high concentration areas and investigate their diffusion process. For this purpose, a combination of Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) techniques was employed to obtain simultaneously the two fields of the concentration of injected dye and of the velocity in a water turbulent channel flow. With focusing on a quasi-homogeneous turbulence in the channel central region, a series of PLIF and PIV images were acquired at several different downstream positions. We applied a conditional sampling technique to the PLIF images to extract the high concentration areas, or spikes, and calculated the conditional-averaged statistics of the extracted areas such as length scale, mean concentration, and turbulent diffusion coefficient. We found that the averaged length scale was constant with downstream distance from the diffusion source and was smaller than integral scale of the turbulent eddies. The spanwise distribution of the mean concentration was basically Gaussian, and the spanwise width of the spikes increased linearly with downstream distance from the diffusion source. Moreover, the turbulent diffusion coefficient was found to increase in proportion to the spanwise distance from the source. These results reveal aspects different from those of regular mass diffusion and let us conclude that the diffusion process of the spikes differs from that of regular mass diffusion.

改良Jaslow技术与PLIF治疗峡部裂型腰椎滑脱症比较

[目的]比较改良Jaslow技术与PLIF治疗峡部裂型腰椎滑脱症的效果。[方法]回顾性分析2014年12月~2017年3月手术治疗的L5 S1单节段中、重度峡部裂型腰椎滑脱症患者87例。其中49例采用改良Jaslow技术;38例采用PLIF。比较两组临床与影像资料。[结果]两组患者均顺利手术,Jaslow组的手术时间、术中出血量、术后引流量均显著低于PLIF组(P<0.05)。随访(18.31±2.25)个月,术后两术式组JOA、VAS、ODI评分均显著改善(P<0.05)。影像方面,采用K-Means聚类分析,依据PT、SS相对比值分为平衡型和失平衡型。平衡型两术式△SP、△SA、△LL、△PT、CS之间差异无统计学意义(P>0.05);而失平衡组中,Jaslow组的△SP、△SA、△LL、△PT均显著大于PLIF组(P<0.05);Jaslow组中CS和SR显著低于PLIF组(P<0.05)。[结论]对于峡部裂型腰椎滑脱症,改良Jaslow技术和PLIF同样可获得满意的临床疗效,改良Jaslow技术能更有效地恢复腰椎前凸角及矢状位平衡。

Experimental study of hypervapotron under conditions of high heat flux

In the light of the needs to develop high-performance heat transfer component for nation-level large-scale scientific projects of China,a hypervapotron experimental platform with supply of heat flux 1 10 MW m-2 was established.With this platform,the multiphase flow and heat transfer phenomena on the surface of triangular fin when the subcooled water flowed through were observed and measured with the planar laser induced fluorescence(PLIF) and high-speed photography techniques.The temperature contour on the slice plane of fin symmetry was measured and the heat flux contour was processed based on gradient computation.It is confirmed that:1) PLIF with high-speed photography is very powerful technique to investigate the multiphase flow of hypervapotron quantitatively;2) evaporation is the primary way in heat transfer mechanism of hypervapotron flow under the condition of high heat flux.The techniques and results obtained will provide useful reference in the R&D of hypervapotron technology in China.

波形板壁面液膜的神经网络及混沌特性分析

波形板干燥器是船用核动力系统中重要的汽水分离设备,其壁面上自由下降液膜的流动特性对干燥器的汽水分离效率及船用核动力装置的安全性指标有着较大的影响。基于平面激光诱导荧光技术(PLIF)对不同雷诺数下的壁面薄层液膜厚度进行测量。通过小数据量法计算不同工况下的液膜厚度时间序列的最大Lyapunov指数,分析壁面液膜的混沌特性并进行相空间重构。利用反向传播(BP)神经网络解决非线性问题的优势对液膜厚度进行预测,完成了单隐层BP神经网络预测模型的建立并实现了自由液膜厚度的非线性特征分析。结果显示:最大Lyapunov指数与液膜雷诺数呈正相关关系;在大雷诺数区生成的孤立峰同重力及液膜间的叠加作用相互耦合,使液膜混沌特性变得更加明显。