Numerical simulation on sand sedimentation and erosion characteristics around HDPE sheet sand barrier under different wind angles

For the safety of railroad operations,sand barriers are utilized to mitigate wind-sand disaster effects.These disasters,characterized by multi-directional wind patterns,result in diverse angles among the barriers.In this study,using numerical simulations,we examined the behavior of High Density Polyethylene(HDPE)sheet sand barriers under different wind angles,focusing on flow field distribution,windproof efficiency,and sedimentation erosion dynamics.This study discovered that at a steady wind speed,airflow velocity varies as the angle between the airflow and the HDPE barrier changes.Specifically,a 90°angle results in the widest low-speed airflow area on the barrier’s downwind side.If the airflow is not perpendicular to the barrier,it prompts a lateral airflow movement which decreases as the angle expands.The windproof efficiency correlates directly with this angle but inversely with the wind’s speed.Notably,with a wind angle of 90°,wind speed drops by 81%.The minimum wind speed is found at 5.1H(the sand barrier height)on the barrier’s downwind side.As the angle grows,the barrier’s windproof efficiency improves,extending its protective reach.Sedimentation is most prominent on the barrier’s downwind side,as the wind angle shifts from 30°to 90°,the sand sedimentation area on the barrier’s downwind side enlarges by 14.8H.As the angle grows,sedimentation intensifies,eventually overtakes the forward erosion and enlarges the sedimentation area.

Experimental Study on the Wavelengths of Two-Dimensional and Three-Dimensional Freak Waves

Freak waves are commonly characterized by strong-nonlinearity, and the wave steepness, which is calculated from the wavelength, is a measure of the degree of the wave nonlinearity. Moreover, the wavelength can describe the locally spatial characteristics of freak waves. Generally, the wavelengths of freak waves are estimated from the dispersion relations of Stokes waves. This paper concerns whether this approach enables a consistent estimate of the wavelength of freak waves. The two-(unidirectional, long-crested) and three-dimensional(multidirectional, shortcrested) freak waves are simulated experimentally through the dispersive and directional focusing of component waves, and the wavelengths obtained from the surface elevations measured by the wave gauge array are compared with the results from the linear, 3rd-order and 5th-order Stokes wave theories. The comparison results suggest that the 3rd-order theory estimates the wavelengths of freak waves with higher accuracy than the linear and 5th-order theories. Furthermore, the results allow insights into the dominant factors. It is particularly noteworthy that the accuracy is likely to depend on the wave period, and that the wavelengths of longer period freak waves are overestimated but the wavelengths are underestimated for shorter period ones. In order to decrease the deviation, a modified formulation is presented to predict the wavelengths of two-and three-dimensional freak waves more accurately than the 3rd-order dispersion relation, by regression analysis. The normalized differences between the predicted and experimental results are over 50% smaller for the modified model suggested in this study compared with the 3rd-order dispersion relation.

3D Echocardiogram Reconstruction Employing a Flip Directional Texture Pyramid

Three dimensional(3D)echocardiogram enables cardiologists to visua-lize suspicious cardiac structures in detail.In recent years,this three-dimensional echocardiogram carries important clinical value in virtual surgical simulation.However,this 3D echocardiogram involves a trade-off difficulty between accu-racy and efficient computation in clinical diagnosis.This paper presents a novel Flip Directional 3D Volume Reconstruction(FD-3DVR)method for the recon-struction of echocardiogram images.The proposed method consists of two main steps:multiplanar volumetric imaging and 3D volume reconstruction.In the crea-tion of multiplanar volumetric imaging,two-dimensional(2D)image pixels are mapped into voxels of the volumetric grid.As the obtained slices are discontin-uous,there are some missing voxels in the volume data.To restore the structural and textural information of 3D ultrasound volume,the proposed method creates a volume pyramid in parallel with theflip directional texture pyramid.Initially,the nearest neighbors of missing voxels in the multiplanar volumetric imaging are identified by 3D ANN(Approximate Nearest Neighbor)patch matching method.Furthermore,aflip directional texture pyramid is proposed and aggregated with distance in patch matching tofind out the most similar neighbors.In the recon-struction step,structural and textural information obtained from differentflip angle directions can reconstruct 3D volume well with the desired accuracy.Com-pared with existing 3D reconstruction methods,the proposed Flip Directional 3D Volume Reconstruction(FD-3DVR)method provides superior performance for the mean peak signal-to-noise ratio(40.538 for the proposed method I and 39.626 for the proposed method II).Experimental results performed on the cardi-ac datasets demonstrate the efficiency of the proposed method for the reconstruc-tion of echocardiogram images.

Alternating Direction Finite Volume Element Methods for Three-Dimensional Parabolic Equations

This paper presents alternating direction finite volume element methods for three-dimensional parabolic partial differential equations and gives four computational schemes, one is analogous to Douglas finite difference scheme with second-order splitting error, the other two schemes have third-order splitting error, and the last one is an extended LOD scheme. The L2 norm and H1 semi-norm error estimates are obtained for the first scheme and second one, respectively. Finally, two numerical examples are provided to illustrate the efficiency and accuracy of the methods.

Science Letters:Dynamic concision for three-dimensional reconstruction of human organ built with virtual reality modelling language (VRML)

This research studies the process of 3D reconstruction and dynamic concision based on 2D medical digital images using virtual reality modelling language (VRML) and JavaScript language, with a focus on how to realize the dynamic concision of 3D medical model with script node and sensor node in VRML. The 3D reconstruction and concision of body internal organs can be built with such high quality that they are better than those obtained from the traditional methods. With the function of dynamic concision, the VRML browser can offer better windows for man-computer interaction in real-time environment than ever before. 3D reconstruction and dynamic concision with VRML can be used to meet the requirement for the medical observation of 3D reconstruction and have a promising prospect in the fields of medical imaging.

Obstacle avoidance method of three-dimensional obstacle spherical cap

Focusing on obstacle avoidance in three-dimensional space for unmanned aerial vehicle(UAV), the direct obstacle avoidance method in dynamic space based on three-dimensional velocity obstacle spherical cap is proposed, which quantifies the influence of threatening obstacles through velocity obstacle spherical cap parameters. In addition, the obstacle avoidance schemes of any point on the critical curve during the multi-obstacles avoidance are given. Through prediction, the insertion point for the obstacle avoidance can be obtained and the flight path can be replanned. Taking the Pythagorean Hodograph(PH) curve trajectory re-planning as an example, the three-dimensional direct obstacle avoidance method in dynamic space is tested. Simulation results show that the proposed method can realize the online obstacle avoidance trajectory re-planning, which increases the flexibility of obstacle avoidance greatly.

Wide color gamut switchable autostereoscopic 3D display based on directional quantum-dot backlight

A switchable autostereoscopic 3-dimensional(3D) display device with wide color gamut is introduced in this paper. In conjunction with a novel directional quantum-dot(QD) backlight, the precise scanning control strategy, and the eye-tracking system, this spatial-sequential solution enables our autostereoscopic display to combine all the advantages of full resolution,wide color gamut, low crosstalk, and switchable 2D/3D. And also, we fabricated an autostereoscopic display prototype and demonstrated its performances effectively. The results indicate that our system can both break the limitation of viewing position and provide high-quality 3D images. We present two working modes in this system. In the spatial-sequential mode,the crosstalk is about 6%. In the time-multiplexed mode, the viewer should wear auxiliary and the crosstalk is about 1%,just next to that of a commercial 3D display(BENQ XL2707-B and View Sonic VX2268 WM). Additionally, our system is also completely compatible with active shutter glasses and its 3D resolution is same as its 2D resolution. Because of the excellent properties of the QD material, the color gamut can be widely extended to 77.98% according to the ITU-R recommendation BT.2020(Rec.2020).

Methods for Setting up a Three-Dimensional Industrial Surveying System of “Building Blocks Type”

This paper is to advance some relevant techniques to set up a three-dimensional industrial surveying system of “building blocks type”, making use of the electronic theodolite, standard ruler and portable computer.

OpenMP-Based PCG Solver for Three-Dimensional Heat Equation

As one of the most important mathematics-physics equations, heat equation has been widely used in engineering area and computing science research. Large-scale heat problems are difficult to solve due to computational intractability. The parallelization of heat equation is available to improve the simulation model efficiency. In order to solve the three-dimensional heat problems more rapidly, the OpenMP was adopted to parallelize the preconditioned conjugate gradient （PCG） algorithm in this paper. A numerical experiment on the three-dimensional heat equation model was carried out on a computer with four cores. Based on the test results, it is found that the execution time of the original serial PCG program is about 1.71 to 2.81 times of the parallel PCG program executed with different number of threads. The experiment results also demonstrate the available performance of the parallel PCG algorithm based on OpenMP in terms of solution quality and computational performance.

A novel method for geometric quality assurance of rock joint replicas in direct shear testing-Part 2:Validation and mechanical replicability

Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies.However,a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking.In this study,a novel method is presented for geometric quality assurance of replicas.The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results.In Part 1 of this study,two quality assurance parameters,smf and V_(Hp100),are derived and their usefulness for evaluation of geometric deviations,i.e.geometric reproducibility,is shown.In Part 2,the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior,which qualifies the parameters for usage in the quality assurance method.Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σ_(mf)<0.06 mm and
|V_(Hp100)|
<0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength.The wear in these replicas,which have similar morphology as the rock joint,is in the same areas as in the rock joint.The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties,possibly from differences in toughness.It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics,which makes them useful in parameter studies.

基于图分级的水下有向传感器网络栅栏覆盖策略

栅栏覆盖问题近年来已成为水下传感器网络研究的热点,但水下有向传感器网络的栅栏覆盖问题尚未得到足够的重视。随机部署前提下的水下静态有向传感器网络的栅栏覆盖难度较大,因此目前关于该问题的相关研究成果较少。为弥补这方面研究的不足,该文提出一种基于图分级的有向传感器网络首次栅栏覆盖策略。首先,该策略深入研究了多种位置关系下两个相邻节点之间满足强(弱)连接的条件;其次,利用位置关系条件构建分级图,从中选取合适节点进行栅栏的首次构建。仿真实验结果表明:采用该算法对静态有向传感器网络进行栅栏首次构建在确保较高成功率的前提下采用的节点数更少,保证了较高的网络检测概率和较长的网络寿命。

一种高效的持续有向栅栏覆盖算法

如何高效实现持续有向栅栏覆盖是无线充电传感器网络的研究热点,采用射频能量捕获技术可以解决栅栏中节点能量受限的问题。在已知网络区域中构建栅栏的节点分布和候选部署位置的情况下,研究射频能量源(Energy source,ES)的部署方案,从而满足所有节点的充电需求。首先,确定网络区域中的栅栏矩形;然后,提出一种基于有向发射的射频能量源最优部署算法(OdepD算法),根据候选位置与栅栏矩形的位置关系得到各个ES的射频能量发射方向和角度,根据有向能量发送模型和充电需求计算各个ES的发射功率;最后,以最小化网络充电总能耗为目标,通过离散粒子群优化充电部署位置,确定最终部署策略。仿真结果证明:OdepD算法可以明显降低网络充电总能耗,高效地实现持续栅栏覆盖。

新型双定子无刷双馈风力发电机直接功率控制

新型双定子无刷双馈发电机包括内外功率绕组和内外控制绕组,二者分别通过中间带隔磁环的背靠背笼障转子进行磁场耦合。针对该新型双定子无刷双馈风力发电机提出一种直接功率控制方法,内外功率绕组及内外控制绕组分别串联以保持各自同相绕组的电磁一致性,将功率绕组有功和无功功率滞环比较器输出值及控制绕组磁链扇区号综合,采用查找表得到控制绕组机侧变流器所需输出的电压空间矢量。通过定量对比研究12/8极50 kW样机控制系统阶跃信号作用下的特性仿真与实验结果,验证了所提双定子无刷双馈风力发电机直接功率控制在亚同步~超同步速度变化范围内变速恒频发电、最大功率跟踪、无功功率与单位功率因数控制等方面的正确性、可行性和有效性。

考虑输出约束及外部干扰的柔性航天器振动控制

针对具有输出约束及外部干扰的柔性航天器系统,提出一种直接关节力矩输入的振动控制方法。利用哈密顿原理,系统动力学特性由偏微分方程(PDE)和常微分方程(ODE)耦合组成的分布参数模型来描述。设计了非线性干扰观测器补偿外界干扰,并基于正切型障碍李雅普诺夫函数解决了航天器姿态角度误差和振动误差的多输出约束问题。利用扩展的拉塞尔不变集原理和半群理论证明了系统的渐近稳定性。不仅实现了姿态角的位置控制,还抑制了柔性航天器的弹性振动。通过对比仿真验证了所提方法的有效性。

负载单宁酸的双层壳聚糖屏障膜的制备及其生物相容性的研究

目的制备负载单宁酸的双层壳聚糖膜(CS@TA),测试其活性氧(ROS)清除能力、生物相容性及抗菌性能,研究其作为引导骨再生屏障膜的可行性。方法采用自蒸发技术先制备出致密的单层壳聚糖(CS)膜,随后采用蒸发干燥、取向冷冻和冷冻干燥技术在单层CS膜上制备出多孔的CS层,从而得到双层CS膜,利用扫描电镜观察其微观结构。将制备好的CS双层膜先接枝4-羧基苯硼酸形成中间体,按不同比例接枝单宁酸(TA),使用傅里叶红外光谱仪(FITR)分析TA与CS双层膜的相互作用。通过1,1-二苯基-2苦基肼(DPPH)测试ROS清除能力,选取负载TA后ROS清除效率在90%以上的双层膜进行后续体外细胞实验,利用CCK-8及活死细胞染色测试其生物相容性,利用扫描电镜观察MC3T3-E1细胞在双层膜多孔面上的黏附情况,通过菌落计数测试其对金黄色葡萄球菌(E.coli)和大肠埃希菌(S.aureus)的抗菌性能。结果CS@TA双层膜一面光滑致密,另一面粗糙疏松多孔,截面呈垂直薄膜方向的有序多孔结构,随着TA的加入,双层膜的ROS清除能力先迅速增加后缓慢稳定,CCK-8及活死细胞染色结果显示加入过多的TA会明显影响双层膜的生物相容性,细菌稀释涂板计数结果显示加入适量TA的双层膜与未负载TA的双层膜相比,对E.coli和S.aureus具有一定抗菌能力。结论负载适量TA的双层膜具有较强的ROS清除能力,良好的生物学性能,且对E.coli和S.aureus均具有一定的抗菌能力。

基于陈无择“运气十六方”探讨五运六气理论在皮肤病领域的辨治特色

运气学说肇基自《黄帝内经》,是用以寻求构建人类最佳生存空间的理论。皮肤疾患常迁延难愈、病程缠绵、瘥后易复,以运气理论诊疗皮肤疾患多有效验。通过论述运气建法与皮肤藩篱间之巨阳固护、节律运营的交互关系,提出先天五运六气禀赋影响皮肤疾患的易患性,后天五运六气流布影响肤疾患的易发性。又梳理前人既效之方,提出运气理论调摄皮肤疾患之时以运气十六方砌其藩篱、重视“欲解时”调其枢机、敷布“太阳”以固其腠理的观点,对于扩大皮肤疾患临床辨证思路有所裨益,为医家用运气学说指导皮肤病临床提供了范例。

Direct loading of atoms from a macroscopic quadrupole magnetic trap into a microchip trap

We demonstrate the direct loading of cold atoms into a microchip 2-mm Z-trap, where the evaporative cooling can be performed efficiently, from a macroscopic quadrupole magnetic trap with a high loading efficiency. The macroscopic quadrupole magnetic trap potential is designed to be moveable by controlling the currents of the two pairs of anti-Helrnholtz coils. The cold atoms are initially prepared in a standard six-beam magneto-optical trap and loaded into the macroscopic quadrupole magnetic trap, and then transported to the atom chip surface by moving the macroscopic trap potential. By means of a three-dimensional absorption imaging system, we are able to optimize the position alignment of the atom cloud in the macroscopic trap and the microchip Z-shaped wire. Consequently, with a proper magnetic transfer scheme, we load the cold atoms into the microchip Z-trap directly and efficiently. The loading efficiency is measured to be about 50%. This approach can be used to generate appropriate ultracold atoms sources, for example, for a magnetically guided atom interferometer based on atom chip.

Study of three-dimensional spatial diffuse discharge in contact electrode structure applied to air purification

In this work,based on the role of pre-ionization of the non-uniform electric field and its effect of reducing the collisional ionization coefficient,a diffuse dielectric barrier discharge plasma is formed in the open space outside the electrode structure at a lower voltage by constructing a three-dimensional non-uniform spatial electric field using a contact electrode structure.The air purification study is also carried out.Firstly,a contact electrode structure is constructed using a three-dimensional wire electrode.The distribution characteristics of the spatial electric field formed by this electrode structure are analyzed,and the effects of the non-uniform electric field and the different angles of the vertical wire on the generation of three-dimensional spatial diffuse discharge are investigated.Secondly,the copper foam contact electrode structure is constructed using copper foam material,and the effects of different mesh sizes on the electric field distribution are analyzed.The results show that as the mesh size of the copper foam becomes larger,a strong electric field region exists not only on the surface of the insulating layer,but also on the surface of the vertical wires inside the copper foam,i.e.,the strong electric field region shows a three-dimensional distribution.Besides,as the mesh size increases,the area of the vertical strong electric field also increases.However,the electric field strength on the surface of the insulating layer gradually decreases.Therefore,the appropriate mesh size can effectively increase the discharge area,which is conducive to improving the air purification efficiency.Finally,a highly permeable stacked electrode structure of multilayer wire-copper foam is designed.In combination with an ozone treatment catalyst,an air purification device is fabricated,and the air purification experiment is carried out.

Thermal Shock Property of Al/Ni-ZrO_2 Gradient Thennal Barrier Coatings

Al/Ni-ZrO2 gradient thennal barrier coatings are made on aluminum substrate using plasma spraying method and one direction thermal shock properties of the coatings are studied in this paper. The results show that pores in coatings link to form cracks vertical to coating surface. They go through the whole ZrO2 coating once vertical cracks form. When thermal shock cycles increase, horizontal cracks that result in coatings failure forms in the coatings and interface. And vertical cracks delay appearance of horizontal cracks and enhance thermal shock property of coatings. Failure mechanisms of coating thermal shock are discussed using experiments and finite element method.

投资壁垒对产业内投资的影响——基于美国国际直接投资数据的研究

以美国为研究对象,利用行业层面的面板数据,考察了美国及其主要经济伙伴投资壁垒强度对美国产业内投资的影响。研究发现:母国和东道国投资的综合投资壁垒强度对产业内投资有显著影响,综合投资壁垒强度越高,产业内投资水平越低;美国与主要经济伙伴的投资壁垒不对等程度对产业内投资也具有显著影响,对内对外壁垒差距越大,产业内投资水平越低;在壁垒不对等对产业内投资的影响机制中,美国经济发展水平发挥着正向调节效应;综合投资壁垒和壁垒不对等水平对产业内投资的影响程度因技术密集度的不同而不同。基于上述结论,对如何推动我国产业内投资发展,实现高质量“引进来”和高水平“走出去”提出了建议。