辊速差对连铸连轧7075铝板显微组织、织构及力学性能的影响

研究辊速差对连铸连轧7075铝板显微组织、织构及力学性能的影响。采用3种不同上辊/下辊转速比(ω/ω0,ω为上辊转速,ω0为下辊转速)1:1、1:1.2及1:1.4进行多次试验。结果显示,在最大辊速差条件下(ω/ω0=1:1.4),7075铝板在轧制方向的屈服强度和极限抗拉强度分别提高41.5%和21.9%。此外,当辊速比ω/ω0为1:1.4时,成品轧制板的平均晶粒尺寸减小36%,横剖面平均硬度增加约9.2%。织构研究结果显示,辊速差越大,成品各向同性及硬度越大。然而,采用不同辊速度的连铸连轧会导致变形板伸长率降低约6%。     

YOLSO: You Only Look Small Object

Small object detection is challenging and far from satisfactory. Most general object detectors suffer from two critical issues with small objects: (1) Feature extractor based on classification network cannot express the characteristics of small objects reasonably due to insufficient appearance information of targets and a large amount of background interference around them. (2) The detector requires a much higher location accuracy for small objects than for general objects. This paper proposes an effective and efficient small object detector YOLSO to address the above problems. For feature representation, we analyze the drawbacks in previous backbones and present a Half-Space Shortcut(HSSC) module to build a background-aware backbone. Furthermore, a coarse-to-fine Feature Pyramid Enhancement(FPE) module is introduced for layer-wise aggregation at a granular level to enhance the semantic discriminability. For loss function, we propose an exponential L1 loss to promote the convergence of regression, and a focal IOU loss to focus on prime samples with high classification confidence and high IOU. Both of them significantly improves the location accuracy of small objects. The proposed YOLSO sets state-of-the-art results on two typical small object datasets, MOCOD and VeDAI, at a speed of over 200 FPS. In the meantime, it also outperforms the baseline YOLOv3 by a wide margin on the common COCO dataset.     

腔磁力系统中的诱导透明和快慢光传播

为了在腔磁力系统中实现可控的磁子诱导透明、磁力诱导透明以及快慢光传播,建立了一个混合腔磁力系统.该系统由一个含有YIG球的微波腔和在z方向对球施加一个均匀的偏置磁场组成,并用强泵浦场驱动磁子和弱探测场驱动微波腔.研究表明,通过调节腔与磁子之间的相互作用强度和微波腔与磁子的耗散比,可以增加磁子诱导透明(MIT)、磁力诱导透明(MMIT)的效果和提高快慢光传播的速度.该研究结果可为磁力诱导放大、量子光学操纵和量子信息存储以及灵敏光开关的研究提供参考.     

Strong tribocatalysis of strontium titanate nanofibers through harvesting friction energy for dye decomposition

Friction is a common clean energy and can be harvested and converted into electricity energy via triboelectricity, which can electrochemically drive dye decomposition in theory. In this work, the tribocatalytic Rhodamine B dye decomposition has been experimentally realized in strontium titanate (SrTiO₃) nanofibers, which are synthesized via a hydrothermal method. In the tribocatalytic dye decomposition process, the friction is exerted in the interface between catalyst surface and a polytetrafluoroethylene (PTFE) Teflon rod setup with the different stirring speed. The RhB dye decomposition ratios of SrTiO₃ nanofibers at these stirring speeds of 200 rpm, 400 rpm, 600 rpm, and 800 rpm are respectively 24.2%, 51.8%, 73.9% and 88.6%, yielding to these reaction rate constants of ～0.0112 h^?1, ～0.0260 h^?1, ～0.0562 h^?1 and ～0.0877 h^?1. The main active species, which play an important role in tribocatalytic process, are the superoxide radicals and holes on basis of the active species quenching experiment results. The excellent tribocatalysis activity makes SrTiO₃ nanofibers potential for application in dye wastewater treatment through utilizing the environmental friction energy.     

An Improved Torque Sensorless Speed Control Method for Electric Assisted Bicycle With Consideration of Coordinate Conversion

In this paper, we propose an improved torque sensorless speed control method for electric assisted bicycle, this method considers the coordinate conversion. A low-pass filter is designed in disturbance observer to estimate and compensate the variable disturbance during cycling. A DC motor provides assisted power driving, the assistance method is based on the real-time wheel angular velocity and coordinate system transformation. The effect of observer is proved, and the proposed method guarantees stability under disturbances. It is also compared to the existing methods and their performances are illustrated through simulations. The proposed method improves the performance both in rapidity and stability.      

定子分段式永磁直线同步电机速度波动抑制方法研究

为了解决定子分段式永磁直线同步电机(PMLSM)存在的因磁阻效应、负载阻力、摩擦力、参数摄动以及动子进出定子时耦合面积变化所造成的控制性能下降的难题,根据动子和定子的耦合状态,提出一种在完全耦合阶段和动子退出定子阶段的分段式控制方法。首先,在动子与定子完全耦合阶段采用改进滑模控制器减小推力波动导致的速度波动,再通过加入扰动观测器降低滑模切换项所带来的抖振现象;在动子退出定子阶段,建立相关电磁参数与动子位置的函数关系,实时补偿由耦合面积变化引起的动子失速,使动子速度在退出时接近给定值。仿真及实验结果表明动定子完全耦合过程中的速度稳态误差为0.005 m/s,收敛时间为0.3 s,动子退出定子阶段的速度波动不超过0.04 m/s,满足定子分段式PMLSM用于长行程自动运输系统对平稳性及快速性的需求。     

Design of energy‐efficient train speed profiles considering fixed‐block signaling system

In dense traffic railway networks, trains may often slow down or stop between stations owing to previous train delays. If preceding train trajectory can be predicted, energy‐efficient driving can be achieved by suppressing unnecessary speed changes. In this paper, we propose an algorithm to find energy‐efficient driving considering fixed‐block signaling (FBS) system by using dynamic programming (DP). DP is suitable for use because it can optimize the control inputs with discrete and state constraints. In this paper, we discuss energy‐efficient driving by considering a FBS system using some case studies of simulation. In the simulation, we examine a technique to drive an express train in an energy‐efficient way when the preceding local train is running toward the station with passing loops. The results show that the proposed method can derive complex speed profiles for energy‐efficient driving and the train can be operated with a maximum reduced energy consumption of 8.3%.     

风速时间序列混沌判定方法比较研究

混沌识别是对非线性时间序列进行混沌预测的前提。针对时间序列风速确定性与随机性相结合的复杂非线性特征,研究了不同的混沌识别方法,并对风速时间序列进行混沌特征识别。应用随机噪声、周期运动及经典混沌系统的时间序列对所选方法进行可靠性验证。对美国国家风能研究中心M2测风塔实测时间序列风速数据进行非线性混沌特征识别。结果表明:风速时间序列具有明显的混沌特征;各风速时间序列表现出不同程度的混沌特征;各混沌识别方法对风速时间序列混沌特征的表达形式不同,互为补充,相互验证。     

An up to date review of continuously variable speed wind turbines with mechatronic variable transmissions

As a promising and potential alternative to conventional fixed or variable speed wind turbines, continuously variable speed wind turbines (CVSWTs) with variable transmissions offer improved power efficiency and enhanced power control capabilities. The CVSWTs can be generally achieved by adapting mechatronic variable transmissions in the turbine drive train for continuously variable speed operations for wind turbines. Therefore, this paper serves to provide an up to date and exhaustive review of the CVSWTs with mechatronic variable transmissions such as mechanical variable transmission, electrical variable transmission, and power splitting transmission. In this paper, the analysis of CVSWTs with different mechatronic transmission topologies is performed regarding basic configurations, dynamic characteristics, control principles, and experimental or simulation results. Review results indicate the feasibility of applying CVSWTs with such mechatronic transmissions and highlight superiorities of the CVSWTs with power splitting transmission. The CVSWT with power splitting transmission will be particularly suitable for megawatt‐scale turbine systems and will hence increase the economic competitiveness of these turbines due to its large power capacity and high reliability. The directions or challenges for future investigations of CVSWTs with such mechatronic transmissions are also presented to foster in‐depth understanding of such CVSWTs and their control strategies.