An improved algorithm based on equivalent sound velocity profile method at large incident angle

With the development of ultra-wide coverage technology,multibeam echo-sounder(MBES)system has put forward higher requirements for localization accuracy and computational efficiency of ray tracing method.The classical equivalent sound speed profile(ESSP)method replaces the measured sound velocity profile(SVP)with a simple constant gradient SVP,reducing the computational workload of beam positioning.However,in deep-sea environment,the depth measurement error of this method rapidly increases from the central beam to the edge beam.By analyzing the positioning error of the ESSP method at edge beam,it is discovered that the positioning error increases monotonically with the incident angle,and the relationship between them could be expressed by polynomial function.Therefore,an error correction algorithm based on polynomial fitting is obtained.The simulation experiment conducted on an inclined seafloor shows that the proposed algorithm exhibits comparable efficiency to the original ESSP method,while significantly improving bathymetry accuracy by nearly eight times in the edge beam.

Novel Method for Spatial Angle Measurement Based on Rotating Planar Laser Beams

Spatial angle measurement, especially the measurement of horizontal and vertical angle, is a basic method used for industrial large-scale coordinate measurement. As main equipments in use, both theodolites and laser trackers can provide very high accuracy for spatial angle measurement. However, their industrial applications are limited by low level of automation and poor parallelism. For the purpose of improving measurement efficiency, a lot of studies have been conducted and several alternative methods have been proposed. Unfortunately, all these means are either low precision or too expensive. In this paper, a novel method of spatial angle measurement based on two rotating planar laser beams is proposed and demonstrated. Photoelectric receivers placed on measured points are used to receive the rotating planner laser signals transmitted by laser transmitters. The scanning time intervals of laser planes were measured, and then measured point＇s horizontal/vertical angles can be calculated. Laser plane＇s angle parameters are utilized to establish the abstract geometric model of transmitter. Calculating formulas of receiver＇s horizontal/vertical angles have been derived. Measurement equations＇ solvability conditions and judgment method of imaginary solutions are also presented after analyzing. Proposed method for spatial angle measurement is experimentally verified through a platform consisting of one laser transmitter and one optical receiver. The transmitters used in new method are only responsible for providing rotating light plane signals carrying angle information. Receivers automatically measure scanning time of laser planes and upload data to the workstation to calculate horizontal angle and vertical angle. Simultaneous measurement of multiple receivers can be realized since there is no human intervention in measurement process .Spatial angle measurement result indicates that the repeatable accuracy of new method is better than 10＂. Proposed method can improve measurement＇s automation degree and speed while ensuring measurement accuracy.

Simulation on Heating and Current Drive Using Neutral Beam Injection with Variable Injection Angle on EAST

The heating and current drive using NBI （neutral beam injection） with a variable injection angle （the angle between the axis of the NBI system with the center axis of the injection window） on EAST is simulated by using NBEAMS code. The influence of the injection angle on the neutral beam current drive, heating efficiency and beam shinethrough power is discussed to explore the optimum injection angle for the EAST NBI system. According to the simulation, an injection angle of 19.5° is the optimum for EAST with its typical experimental parameters. With this injection angle, the increase in both the beam energy and power can improve the current drive and heating efficiency. The problem that the beam shinethrough power increases with the higher injection energy and power could be controlled through an increase of the plasma density.

Effects of laser beam divergence angle on airborne LIDAR positioning errors

The influence of laser beam divergence angle on the positioning accuracy of scanning airborne light detection and ranging （LIDAR） is analyzed and simulated. Based on the data process and positioning principle of airborne LIDAR, the errors from pulse broadening induced by laser beam di vergence angle are modeled and qualitatively analyzed for different terrain surfaces. Simulated results of positioning errors and suggestions to reduce them are given for the flat surface, the downhill of slope surface, and the uphill surface.

Investigation on the effect of beam divergence angle upon output waveform based on stimulated Brillouin scattering optical limiting

This paper investigates the effect of beam divergence angle on output waveform based on stimulated Brillouin scattering optical limiting.Output waveforms in the case of different pump divergence angles are numerically simulated,and validated in a Nd：YAG seed-injected laser system.The results indicate that a small pump divergence angle can lead to good interaction between pump and Stokes,and a platform can be easily realized in the transmitted waveform.In contrast,a peak followed by the platform appears when the divergence angle becomes large.

Local dynamical characteristics of Bessel beams upon reflection near the Brewster angle

We analytically and numerically study the local dynamical characteristics of the Bessel beams reflected from an airglass interface near the Brewster angle.A Taylor series expansion based on the angular spectrum component is applied to correct the reflection coefficients near the Brewster angle.Using a hybrid angular spectrum representation and vector potential method,the explicit expressions for the electric and magnetic field components of the reflected Bessel beams are derived analytically under paraxial approximation.The local energy,momentum,spin,and orbital angular momentum of the Bessel beams upon reflection near the Brewster angle are examined numerically by utilizing a canonical approach.Numerical simulation results show that the properties of these dynamical quantities for the Bessel beams near Brewster angle incidence change abruptly,and are significantly affected by their topological charge,half-cone angle,and polarization state.The present study has its importance in understanding the dynamical aspects of optical beams with vortex structure and diffraction-free nature during the reflection process.

Bragg-Angle Diffraction in Slant Gratings Fabricated by Single-Beam Interference Lithography

A single-beam interference-lithography scheme is demonstrated for the fabrication of large-area slant gratings, which requires exposure of the photoresist thin film spin-coated on a glass plate with polished side-walls to a single laser beam in the ultraviolet and requires small coherence length of the laser. No additional beam splitting scheme and no adjustments for laser-beam overlapping and for optical path-length balancing are needed. Bragg-angle diffractions are observed as strong optical extinction that is tunable with changing the angle of incidence. This device is important for the design of efficient filters, beam splitters, and photonic devices.

成人Angle Ⅱ~2错畸形患者髁突位置及颞下颌关节形态的CBCT观察研究

目的:利用锥形束CT(CBCT)评估成人Angle Ⅰ与Angle Ⅱ2错畸形患者颞下颌关节的形态特征及与颞下颌关节窝的关系。方法:通过对30例Angle Ⅰ与30例Angle Ⅱ2类错畸形成人患者行TMJ的CBCT扫描,在GALILEOS工作站分析测量颞下颌关节窝间隙、髁突相关指标,进行统计学分析,比较Angle Ⅰ与Angle Ⅱ2TMJ形态学之间的差异。结果:①Angle Ⅰ、An-gle Ⅱ2类左右两侧髁突在各自颞下颌关节窝内的位置均无明显差异(P>0.05)。②Angle Ⅱ2组颞下颌关节窝深度、前间隙、上间隙均大于Angle Ⅰ组,后间隙小于Angle Ⅰ组(P<0.05)。结论:Angle Ⅰ与Angle Ⅱ2患者两侧髁突在颞下颌关节窝内位置对称,Angle Ⅱ2颞下颌关节窝深度,上间隙及前间隙比Angle Ⅰ大,后间隙比Angle Ⅰ小。

Optimizing depth of field in 3D light-field display by analyzing and controlling light-beam divergence angle

A concept of divergence angle of light beams(DALB)is proposed to analyze the depth of field(DOF)of a 3D light-field display system.The mathematical model between DOF and DALB is established,and the conclusion that DOF and DALB are inversely proportional is drawn.To reduce DALB and generate clear depth perception,a triple composite aspheric lens structure with a viewing angle of 100°is designed and experimentally demonstrated.The DALB-constrained 3D light-field display system significantly improves the clarity of 3D images and also performs well in imaging at a 3D scene with a DOF over 30 cm.

Investigation of fast pitch angle scattering of runaway electrons in the EAST tokamak

This paper reports that an experimental investigation of fast pitch angle scattering （FPAS） of runaway electrons in the EAST tokamak has been performed. From the newly developed infrared detector （HgCdTe） diagnostic system, the infrared synchrotron radiation emitted by relativistic electrons can be obtained as a function of time. The FPAS is analysed by means of the infrared detector diagnostic system and the other correlative diagnostic systems （including electron-cyclotron emission, hard x-ray, neutrons）. It is found that the intensity of infrared synchrotron radiation and the electron-cyclotron emission signal increase rapidly at the time of FPAS because of the fast increase of pitch angle and the perpendicular velocity of the energetic runaway electrons. The Parail and Pogutse instability is a possible mechanism for the FPAS.

全景片与锥形束CT对诊断AngleⅡ~2错牙合畸形颞下颌关节改变的研究

目的比较全景片和锥形束CT（CBCT）对AngleⅡ~2错牙合畸形患者的髁突骨质改变检测的准确性,为临床合理运用X线片进行诊断提供依据。方法 60例AngleⅡ~2错牙合畸形患者根据临床检查分为有症状组（A组）和无症状组（B组）,分别对双侧颞下颌关节进行全景片和CBCT检查,对髁突骨质改变进行检测,并对二者差异进行统计学分析。结果 CBCT对髁突骨质改变的诊断一致性较高,全景片一致性诊断存在一定差异;以CBCT对髁突骨质改变的检测结果为金标准,该两组与CBCT检测结果比较,A组全景片正确诊断率为66.7%,B组全景片正确诊断率为85.7%。结论全景片在筛选AngleⅡ~2错牙合畸形患者TMD的临床诊断中具有一定的应用价值,但其灵敏度低于CBCT。

新型外包波纹钢-混凝土组合梁抗火性能研究

文中利用ABAQUS建立了组合梁热-力耦合模型,通过分析组合梁跨中挠度、耐火极限随温度变化曲线研究了荷载比、波纹钢腹板厚度、下翼缘钢板厚度和预应力筋保护层厚度对其抗火性能的影响.结果表明:高温作用下,新型组合梁的钢腹板未发生鼓曲、角钢连接件起到较好的抗滑移,耐火性能显著增强.荷载比越大,临界温度越低,当荷载比取0.3~0.5时,新型组合梁具备较好的变形性能,临界状态为形成塑性铰的强度破坏.随波纹钢腹板厚度增加,新型组合梁的耐火极限提升,且提升幅度随荷载比的增大而减小;随下翼缘钢板厚度增加,新型组合梁的耐火极限提升,且提升幅度随荷载比的增大而增大;预应力筋保护层厚度小于40 mm时,组合梁的耐火极限随厚度的减小而降低,大于40 mm时,影响较小.

杭州电竞中心结构设计重难点概述

杭州电竞中心内圈主体结构采用钢框架-支撑结构,外圈采用“大倾角梭形斜柱+多段钢折梁框架”,是集承重与抗侧力于一体的结构体系,屋盖采用车辐式索承网格自平衡结构形式。详细介绍了地下结构、中央场馆结构的设计要点,门厅处利用建筑造型空间设计为多段钢折梁与跨层桁架相结合的结构形式;室内二层至三层楼面设计一浮空弧形人行桥,截面形式为薄壁钢箱梁,桥宽2.2m,跨度57m,采用“上挂下支”的稳定结构形式。对整体结构进行了静力弹性、动力弹塑性、振动台试验、典型节点有限元、整体稳定以及局部稳定等系列分析与试验。结果表明:结构在静力荷载和地震作用下强度和刚度均满足规范要求;典型节点极限承载力为荷载设计值的4.17倍;结构整体稳定性安全系数为3.79;斜柱局部稳定安全系数为2.52。合理的设计保证了结构的安全、经济和实用性。

光学相控阵性能参数仿真分析与实验研究

详细介绍了一维光学相控阵的扫描特性,仿真分析了各参数之间的理论关系。通过各参数与波长之间的关系研究,可知波长调制实现纵向角度控制不会明显改变光学相控阵参数变化,论证在波导上刻蚀光栅,利用光栅的衍射特性可实现二维光学相控阵光束扫描。通过实验,实现了一种256通道光栅二维光学相控阵系统,验证了探测距离大于50 m,测距精度优于5 cm,光束发散角小于0.25°,在1515~1595 nm波长范围内,可实现41.2°×11.9°的二维扫描范围。这些理论分析和实验研究为该领域的科研工作者提供理论指导和技术支持,具有重要的应用价值。

基于PSO−ELM的综采工作面液压支架姿态监测方法

针对基于惯性测量单元的液压支架姿态解算方法会产生累计误差、校正结果不准确的问题,提出一种基于粒子群优化(PSO)−极限学习机(ELM)的综采工作面液压支架姿态监测方法。以液压支架顶梁俯仰角为监测对象,采用倾角传感器和陀螺仪采集液压支架顶梁支护姿态实时信息,对采集到的数据进行预处理,将处理后的数据输入PSO−ELM误差补偿模型中,得到解算误差预测值;同时通过卡尔曼滤波融合进行液压支架姿态解算,得到解算值;再用误差预测值对解算值进行误差补偿,从而求得更加准确的顶梁支护姿态数据。该方法只考虑加速度和角速度数据与解算误差的关系,不依赖具体的物理模型,可有效降低姿态解算累计误差。实验结果表明:液压支架顶梁俯仰角平均绝对误差由补偿前的1.4208°减少到0.0580°,且误差曲线具有良好的收敛性,验证了所提方法可持续稳定地监测液压支架的支护姿态。

基于改进可微分域转换的双域锥束计算机断层扫描重建网络用于锥角伪影校正

目的 提出一种基于改进可微分域转换的双域锥束计算机断层扫描(CBCT)重建框架DualCBR-Net用于锥角伪影校正。方法 所提出的双域CBCT重建框架DualCBR-Net包含3个模块:投影域预处理、可微分域转换和图像后处理。投影域预处理模块首先对投影数据进行排方向扩充,使被扫描物体能够被X射线完全覆盖。可微分域转换模块引入重建和前投影算子去完成双域网络的前向和梯度回传过程,其中几何参数对应扩大的数据维度,扩大几何在网络前向过程中提供了重要先验信息,在反向过程中保证了回传梯度的精度,使得锥角区域的数据学习更为精准。图像域后处理模块对域转换后的图像进一步微调以去除残留伪影和噪声。结果 在Mayo公开的胸部数据集上进行的验证实验结果显示,本研究提出的DualCBR-Net在伪影去除和结构细节保持方面均优于其他竞争方法;定量上,这种DualCBR-Net方法在PSNR和SSIM上相对于最新方法分别提高了0.6479和0.0074。结论 本研究提出的基于改进可微分域转换的双域CBCT重建框架DualCBR-Net用于锥角伪影校正方法使有效联合训练CBCT双域网络成为可能,尤其是对于大锥角区域。

温湿变参数旋转复合材料薄壁梁扭转振动特性

复合材料梁具有强度高、质量轻、耐腐蚀、耐高温以及抗疲劳等诸多优良性能,在工程中有广泛的应用,如风力机叶片、直升机螺旋桨等.基于湿热环境下旋转复合材料薄壁梁振动方程,研究了梁的扭转运动.采用Rayleigh-Ritz法求解振动特性,分析了温度、湿度、转速、安装角、铺层角等因素对固有频率和模态振型的影响.采用有限元方法验证了计算结果的精确性.研究表明:前2阶频率随着温度和湿度的升高而降低;与湿度相比,温度对频率的影响更为显著;T=325~425 K且铺层角为15°~30°时,温度对频率的影响略小;铺层角在0°或90°附近时,湿度对频率的影响不大;频率随转速增大而增大,随安装角增大而降低;铺层角对频率有较大影响;温度、湿度、转速、铺层角和安装角对前2阶模态振型影响很小.

错[牙合]畸形患者髁突位置及正畸治疗前后髁突位置变化的CBCT评估

口颌系统的功能健康、稳定是口腔正畸治疗的基本目标之一。健康人群的下颌处于牙尖交错位(in-tercuspal position,ICP)时髁突位置基本位于关节窝的中央,颞下颌关节功能稳定。错[牙合]畸形患者由于正畸牙齿移动及咬合改变,可能发生颞下颌关节的相关改建,特别是髁突位置的改变。传统的髁突位置的评估方法是通过架来转移下颌位置,然后在髁突位置测量仪上进行测量,但此方法得到的髁突位置变化缺乏一致性。近年来,锥形束CT(cone beam computed tomography,CBCT)成为正畸治疗检查的首选,CBCT可精准地测量关节间隙,确定髁突位置的改变。本文对髁突位置的CBCT评估及正畸治疗前后的错[牙合]畸形髁突位置变化的研究进行综述。文献复习结果表明,不同错[牙合]畸形患者的髁突位置存在差异,正畸治疗前后髁突位置也可能发生变化,使用CBCT可以较低的辐射剂量和更高的精确度评价错[牙合]畸形的髁突位置,有助于进一步研究错畸[牙合]形患者髁突位置变化的机制,并为患者治疗提供更准确、个性化的指导。

碳类粒子对固体推进剂束流发散角度影响的实验研究

以石墨烯和碳粉两种碳类粒子作为掺杂剂定向改性固体推进剂,借助高速摄影技术和自搭建的束流发散角度测量系统,对比并分析不同掺杂比例和工作条件对改性推进剂束流发散角度的影响,确定了掺杂粒子的最优掺杂比例和工作条件。结果表明,石墨烯和碳粉的最优掺杂比例均为7%,且石墨烯的束流发散角度更小,生成稳定等离子体流的响应时间更短。同时,石墨烯更适配于小激光能量供给下的工作条件,而碳粉更适配于大激光能量供给下的工作条件。

离子束抛光对单晶硅表面质量影响的分子动力学模拟研究

离子束抛光作为一种超精密加工技术,被应用于材料表面抛光的精抛阶段,而其原子量级的去除效果使得它的加工过程与加工效果难以直接观察,因此为了能够从微观尺度研究离子束抛光的加工效果以及加工参数对材料表面粗糙度与表面损伤的影响,提出使用分子动力学模拟的方法研究离子束抛光过程,通过对氩离子轰击单晶硅的仿真模拟,分析加工参数对单晶硅表面粗糙度与晶格损伤的影响规律,指导实际的加工工艺设计.研究发现,在不同加工角度下,离子剂量对于表面粗糙度的影响规律不同,低角度(0°~40°)低剂量以及高角度(>50°)高剂量的加工有助于达到较低的表面粗糙度;随着加工角度的增加,离子束对晶体表面造成的损伤逐渐减少,当加工角度大于40°时能够大幅度减少晶格损伤.模拟结果显示在实际的离子束抛光过程中,为了得到高质量的表面,应该采取高角度高剂量的加工方式以达到既降低材料表面粗糙度又减小对材料表面晶格产生损伤的目的.