One-photo excitation pathway in 2D in-plane heterostructures for effective visible-light-driven photocatalytic degradation

Broad-spectrum absorption and highly effective charge-carrier separation are two essential requirements to improve the photocatalytic performance of semiconductor-based photocatalysts.In this work,a fascinating one-photon system is reported by rationally fabricating 2D in-plane Bi_(2)O_(3)/BiOCl(i-Cl)heterostructures for efficient photocatalytic degradation of RhB and TC.Systematic investigations revealed that the matched band structure generated an internal electric field and a chemical bond connection between the Bi_(2)O_(3)and BiOCl in the Bi_(2)O_(3)/BiOCl composite that could effectively improve the utilization ratio of visible light and the separation effectivity of photo-generated carriers in space.The formed interactions at the 2D in-plane heterojunction interface induced the one-photon excitation pathway which has been confirmed by the experiment and DFT calculations.As a result,the i-Cl samples showed significantly enhanced photocatalytic efficiency towards the degradation of RhB and TC(RhB:0.106 min^(-1);TC:0.048 min^(-1))under visible light.The degradation activities of RhB and TC for i-Cl were 265.08 and 4.08times that of pure BiOCl,as well as 9.27 and 2.14 times that of mechanistically mixed Bi_(2)O_(3)/BiOCl samples,respectively.This work provides a logical strategy to construct other 2D in-plane heterojunctions with a one-photon excitation pathway with enhanced performance.

Strength failure of spatial reticulated structures under multi-support excitation

Under strong earthquakes, long-span spatial latticed structures may collapse due to dynamic instability or strength failure. The elasto-plastic dynamic behaviors of three spatial latticed structures, including two double-layer cylindrical shells and one spherical shell constructed for the 2008 Olympic Games in Beijing, were quantitatively examined under multi-support excitation （MSE） and uniform support excitation （USE）. In the numerical analyses, several important parameters were investigated such as the peak acceleration and displacement responses at key joints, the number and distribution of plastic members, and the deformation of the shell at the moment of collapse. Analysis results reveal the features and the failure mechanism of the spatial latticed structures under MSE and USE. In both scenarios, the double-layer reticulated shell collapses in the ＂overflow＂ mode, and the collapse is governed by the number of invalid plastic members rather than the total number of plastic members, beginning with damage to some of the local regions near the supports. By comparing the numbers and distributions of the plastic members under MSE to those under USE, it was observed that the plastic members spread more sufficiently and the internal forces are more uniform under MSE, especially in cases of lower apparent velocities in soils. Due to the effects of pseudo-static displacement, the stresses in the members near the supports under MSE are higher than those under USE.

Condition assessment of structures under unknown support excitation

A new method is proposed to assess the condition of structures under unknown support excitation by simultaneously detecting local damage and identifying the support excitation from several structural dynamic responses. The support excitation acting on a structure is modeled by orthogonal polynomial approximations, and the sensitivities of structural dynamic response with respect to its physical parameters and orthogonal coefficients are derived. The identification equation is based on Taylor＇s first order approximation, and is solved with the damped least-squares method in an iterative procedure. A fifteen-story shear building model and a five-story three-dimensional steel frame structure are studied to validate the proposed method. Numerical simulations with noisy measured accelerations show that the proposed method can accurately detect local damage and identify unknown support excitation from only several responses of the structure. This method provides a new approach for detecting structural damage and updating models with unknown input and incomplete measured output information.

Seismic Response Analysis of Long-Span Suspen-Dome under Multi-Support Excitations

A practical suspen-dome project, Changzhou Gym roof, is adopted as an example and its transient analysis based on the multi-support excitations of the earthquake wave is carried out. Compared with the single support excitation, the position and value of the maximum stress under multi-support excitations both change and the amount of elements with obvious changes is large and more than 70% of the total. Moreover, when other terms are not changed, this influence will decrease as the span decreases, but increa...

Semi-active control of a cable-stayed bridge under multiple-support excitations

This paper presents a semi-active strategy for seismic protection of a benchmark cable-stayed bridge with consideration of multiple-support excitations. In this control strategy, Magnetorheological (MR) dampers are proposed as control devices, a LQG-clipped-optimal control algorithm is employed. An active control strategy, shown in previous researches to perform well at controlling the benchmark bridge when uniform earthquake motion was assumed, is also used in this study to control this benchmark bridge with consideration of multiple-support excitations. The performance of active control system is compared to that of the presented semi-active control strategy. Because the MR fluid damper is a con-trollable energy- dissipation device that cannot add mechanical energy to the structural system, the proposed control strategy is fail-safe in that bounded-input, bounded-output stability of the controlled structure is guaranteed. The numerical results demonstrated that the performance of the presented control design is nearly the same as that of the active control system; and that the MR dampers can effectively be used to control seismically excited cable-stayed bridges with multiple-support excitations.

Research on the random seismic response analysis for multi- and large-span structures to multi-support excitations

The pseudo excitation method(PEM) has been improved into a more practical form,on which the analytic formulae of seismic response power spectral density(PSD) of simplified large-span structural models have been derived.The analytic formulae and numerical computing results of seismic response PSD have been derived to study the mechanism of multi-support excitation effects,such as the wave-passage effect and incoherence effect,for the seismic response of multiand large-span structures.By using a multi-span truss as an example,the influence of multi-support excitation effects on the seismic response of such structures is studied.

Shaking table test and numerical simulation of an isolated cylindrical latticed shell under multiple-support excitations

In order to study the infl uence of the ground motion spatial eff ect on the seismic response of large span spatial structures with isolation bearings, a single-layer cylindrical latticed shell scale model with a similarity ratio of 1/10 was constructed. An earthquake simulation shaking table test on the response under multiple-support excitations was performed with the high-position seismic isolation method using high damping rubber (HDR) bearings. Small-amplitude sinusoidal waves and seismic wave records with various spectral characteristics were applied to the model. The dynamic characteristics of the model and the seismic isolation eff ect on it were analyzed at varying apparent wave velocities, namely infi nitely great, 1000 m/s, 500 m/s and 250 m/s. Besides, numerical simulations were carried out by Matlab software. According to the comparison results, the numerical results agreed well with the experimental data. Moreover, the results showed that the latticed shell roof exhibited a translational motion as a rigid body after the installation of the HDR bearings with a much lower natural frequency, higher damping ratio and only 1/2~1/8 of the acceleration response peak values. Meanwhile, the structural responses and the bearing deformations at the output end of the seismic waves were greatly increased under multiple-support excitations.

基于测量阻抗动态轨迹的大型调相机失磁保护

大型调相机失磁故障严重影响设备本体安全以及电网稳定,现有基于静态阈值的低电压与无功反向判据可靠性与选择性不足。文中提出一种可反映调相机运行状态的机端测量阻抗全局动态轨迹智能识别的失磁保护原理,从运动学角度建立能够准确反映失磁与其他工况下测量阻抗轨迹的特征量时间序列,基于统计学提取解释性强的特征量。利用自适应权重的全局与局部核函数组合训练多核支持向量机(multiple kernel learning support vector machine,MKL-SVM),在保证模型学习能力的同时增强其泛化能力;提出基于分类核空间距离的两阶段识别策略,可在保证可靠性的前提下提高保护速动性。基于PSCAD仿真平台搭建调相机接入电网模型进行验证,结果表明所提失磁保护方案无须采集转子侧电气量,识别准确,面对新能源接入和未知扰动时仍具有优良的适用性。

基于小波包能量曲率的环境激励下简支梁损伤识别方法

为了识别环境激励下简支梁的损伤时刻及损伤位置,提出一种基于小波包能量的简支梁损伤识别方法.首先采用小波包技术处理环境激励下健康状态和未知状态的简支梁位移响应时程数据,获得其小波包能量;然后根据各子频带的能量占比筛选出最优频带,并进行归一化处理得到能量曲率;最后以健康状态下的小波包能量曲率计算的损伤识别指标作为参考,对比未知状态下简支梁的损伤识别指标,获得结构中的单点或多点损伤状况,包括损伤时刻、损伤位置和相对损伤程度.简支梁数值模拟结果表明,该方法在信噪比≥40 dB条件下可以准确识别结构的损伤状况.

基于混合采样和SE_ResNet_SVM的不平衡多分类研究

针对结构化多分类算法中不平衡数据集类别分布不均导致分类难度增加的问题,本文提出了一种基于混合采样、压缩与激励(squeeze and excitation, SE)模块、改进深度残差网络和支持向量机(support vector machines, SVM)的网络模型SNSMRS (SMOTEENNmixed residual networks-SVM network)。首先,通过合成少数过采样和编辑最近邻技术来改善数据分布;然后,构建融合SE模块与通过融合批次归一化和群组归一化的深度残差网络来提取特征;最后,通过SVM进行输出网络模型。其中,SE模块增强了模型对特征的区分能力,提升了模型的鲁棒性;基于融合归一化的残差网络受批次大小的影响较小,并且避免了传统神经网络梯度消失和精度退化等问题,增强了网络的稳定性与准确度;SVM可以根据特征向量在空间上的分布进行全部特征的分割,特征利用率高,提高了模型的分类精度。在7个不同规模和领域的非平衡公开数据集上进行了对比和消融实验,结果表明,本文所提的网络模型SNSMRS不仅优于其他深度学习模型,而且相对于未改良的ResNet,Macro-F1和G-mean值分别提升了约3%和4%,同时在4个数据集上的Macro-F1和G-mean值均超过了95%。

航空液压管路系统振动疲劳寿命评估的响应谱方法

目的实现航空液压管路系统在一致/多点激励作用下,高周疲劳寿命的准确高效获取。方法考虑管内流体Coriolis力和夹具的附加阻尼效应,建立一致/多点激励作用下,航空液压管路系统振动疲劳寿命评估的响应谱方法。首先,采用复模态叠加法,在状态空间对其控制方程进行降阶,推导出一致/多点激励作用下航空液压管路随机应力响应的显式表达。然后,基于现有的疲劳响应谱方法,依次引入与模态速度与基础激励相关的广义相关系数,并计入非比例阻尼以及多点激励效应,建立一致/多点激励作用下航空液压管路系统疲劳响应谱方法组合格式。结果采用雨流计数法验证了本文方法的计算精度,并讨论了分析效率。同时,探究了管内流体流速与激励的部分相干性对于管路系统疲劳寿命的影响。结论本文方法计算效率极高,且计算精度稳定,并考虑了管内流体负载与多点激励效应对疲劳寿命影响,能够满足工程中复杂管路系统振动疲劳的分析需求。

基于WOA-VMD-MSE-SVM的海水泵激励源识别方法

针对海水泵的复杂多激励源难以准确识别问题,提出一种基于变分模态分解(VMD)、鲸鱼优化算法(WOA)、多尺度熵(MSE)和支持向量机(SVM)相结合的海水泵激励源识别方法。基于海水泵振动信号,首先采用VMD和WOA算法获取分解层数K与惩罚系数α两个重要参数,并对信号进行分解重组;然后提取重组信号的多尺度熵,作为WOA-SVM模型的输入特征向量,并对SVM的惩罚因子c和核系数g两个重要参数进行寻优,最后将得到的参数代入SVM模型进行训练与激励源识别。通过实船海水泵激励源识别及对比分析,验证识别方法的有效性。研究结果表明提出的WOA-VMD-MSE-SVM算法满足海水泵激励源识别准确要求。

基础激励下的弹性支承-转子系统振动行为的试验研究

转子系统在实际运行过程中由于复杂的工作环境会随机承受来自基础的外部激励,一定概率下这将导致转子系统振动异常,严重时甚至还会影响到转子系统的正常运转。本文以弹支转子系统为研究对象,设计搭建带有鼠笼弹支的转子试验平台,采用激振器加载模拟不同模式的基础激励,实验研究了不同基础激励对弹支转子系统的振动行为的影响规律。研究结果表明,基础激励具有传递性,能够通过基础传递到支承和转子;弹支-转子系统的振动特性在基础激励方向上变化明显,其频谱中存在激励频率及其倍频成分,且振动幅值随激振频率增加(40~80Hz)呈增大趋势;瞬态激励下随激振频率增大(0Hz,1Hz和2Hz),转轴和转盘的工频振动幅值、鼠笼的工频应变幅值均增大,转轴和转盘的2倍工频振动幅值、鼠笼的2倍工频应变幅值呈降低趋势。

基于三维荧光光谱耦合平行因子法的菊花特征组分快速无损鉴别

为提高菊花特征组分的检测效率,提出一种基于三维荧光光谱(three-dimensional excitation emission matrix spectroscopy,3DEEM)耦合平行因子分析(parallel factor analysis,PARAFAC)的快速鉴别方法。以4种菊花为研究对象,在分别获取样品3DEEM矩阵(EEMs)后,首先通过数据预处理去除如拉曼散射和瑞利散射等干扰数据,并剔除异常值,分析光谱特征。然后,采用PARAFAC进行特征提取,通过方差解释率和残差分析法,确定菊花两种特征荧光组分为氨基酸和黄酮类化合物。最后利用支持向量机(support vector machines,SVM)和BP神经网络(back propagation neural network,BPNN)对特征变量进行分析,建立菊花快速无损鉴别模型。SVM和BPNN训练集结果分别为100%、95.93%,测试集结果分别为94.50%、89.61%。结果表明,3DEEM-PARAFAC结合SVM可以实现对菊花特征组分的定性定量分析,能够对菊花进行快速鉴别。

基于拉梅模谐振器的无线式石英测温系统设计

本文提出一种采用单端支撑型拉梅(Lamé)模石英热敏谐振器的无线式石英测温系统的设计。它包括一体式热敏-载波双模谐振组件、同步激励式双模相干振荡组件、调频与整形滤波组件、无线发射、接收与鉴频组件、STM32F407型单片机软硬件信号处理单元等。详述了频率为1.8 MHz的Lamé模石英热敏谐振器、频率为98 MHz泛音厚度切变模的超小型载波石英谐振器的设计与创新点。实验结果表明:典型样品Lamé模热敏谐振器的Q值可达6.5×10^(4),测温系统分辨率为0.01℃,精度为0.2℃,达到设计要求。

汽车传动轴万向节摩擦引起的自激振动与稳定性分析

针对某四驱车急加速工况传动轴撞击中间支撑限位问题,建立考虑万向节内部摩擦的传动轴系统横向运动方程,识别原因为万向节内部摩擦引起的传动轴自激振动。建立包含万向节摆动Dahl摩擦的传动系ADAMS模型,利用仿真失稳转速评价主要参数变化对系统稳定性的影响,并进行实车验证,结果表明:减小万向节摩擦、增加中间支撑刚度、优化传动轴夹角可提升系统稳定性。采用将万向节更改为DO节、优化中间支撑刚度的组合方案,消除了传动轴自激振动现象,验证了方法的有效性。

Parametrically excited oscillation of stay cable and its control in cable-stayed bridges＂

This paper presents a nonlinear dynamic model for simulation and analysis of a kind of parametrically excited vibration of stay cable caused by support motion in cable-stayed bridges. The sag, inclination angle of the stay cable are considered in the model, based on which, the oscillation mechanism and dynamic response characteristics of this kind of vibration are analyzed through numerical calculation. It is noted that parametrically excited oscillation of a stay cable with certain sag, inclination angle and initial static tension force may occur in cable-stayed bridges due to deck vibration under the condition that the natural frequency of a cable approaches to about half of the first model frequency of the bridge deck system. A new vibration control system installed on the cable anchorage is proposed as a possible damping system to suppress the cable parametric oscillation. The numerical calculation results showed that with the use of this damping system, the cable oscillation due to the vibration of the deck and/or towers will be considerably reduced.

A new spatial coherence model and analytical coeffi cients for multi-support response spectrum combination

In this paper, a new spatial coherence model of seismic ground motions is proposed by a fitting procedure. The analytical expressions of modal combination （correlation） coefficients of structural response are developed for multi-support seismic excitations. The coefficients from both the numerical integration and analytical solutions are compared to verify the accuracy of the solutions. It is shown that the analytical expressions of numerical modal combination coefficients are of high accuracy. The results of random responses of an example bridge show that the analytical modal combination coefficients developed in this paper are accurate enough to meet the requirements needed in practice. In addition, the computational efficiency of the analytical solutions of the modal combination coefficients is demonstrated by the response computation of the example bridge. It is found that the time required for the structural response analysis by using the analytical modal combination coefficients is less than 1/20 of that using numerical integral methods.

Synchrophasing Vibration Control of Machines Supported by Discrete Isolators

This paper describes an analytical investigation into synchrophasing,a vibration control strategy on a machinery installation in which two rotational machines are attached to a beam-like raft by discrete resilient isolators.Forces and moments introduced by sources are considered,which effectively represent a practical engineering system.Adjusting the relative phase angle between the machines has been theoretically demonstrated to greatly reduce the cost function,which is defined as the sum of velocity squares of attaching points on the raft at each frequency of interest.The effect of the position of the machine is also investigated.Results show that altering the position of the secondary source may cause a slight change to the mode shape of the composite system and therefore change the optimum phase between the two machines.Although the analysis is based on a one-dimensional Euler– Bernoulli beam and each machine is considered as a rigid-body,a key principle can be derived from the results.However,the factors that can influence the synchrophasing control performance would become coupled and highly complicated.This condition has to be considered in practice.

Phase diagram and collective modes in Rashba spin–orbit coupled BEC: Effect of in-plane magnetic field

We studied the system of pure Rashba spin–orbit coupled Bose gas with an in-plane magnetic field. Based on the mean field theory, we obtained the zero temperature phase diagram of the system which exhibits three phases, plane wave（PW） phase, striped wave（SW） phase, and zero momentum（ZM） phase. It was shown that with a growing in-plane field,both SW and ZM phases will eventually turn into the PW phase. Furthermore, we adopted the Bogoliubov theory to study the excitation spectrum as well as the sound speed.