Elastic twisting metamaterial for perfect longitudinal-torsional wave mode conversion

In this work,we design a twisting metamaterial for longitudinal-torsional(L-T)mode conversion in pipes through exploring the theory of perfect transmodal FabryPerot interference(TFPI).Assuming that the axial and radial motions in pipes can be decoupled,we find that the metamaterial can be designed in a rectangular coordinate system,which is much more convenient than that in a cylindrical system.Numerical calculation with detailed microstructures shows that an efficient L-T mode conversion can be obtained in pipes with different radii.In addition,we fabricate mode-converting microstructures on an aluminum pipe and conduct ultrasonic experiments,and the results are in good agreement with the numerical calculations.We expect that the proposed LT mode-converting metamaterial and its design methodology can be applied in various ultrasonic devices.

Mode Conversion and Diffraction of Guided Optical Waves from Magnetostatic Waves under Inclined Bias Magnetic Field

The noncollinear interaction of guided optical waves with magnetostatic waves under inclined bias magnetic field is theoretically studied in detail. Similar approach can also be applied to the collinear interaction. Calculation results indicate that the diffraction efficiency (DE) in magnitude is equal to the mode-conversion efficiency (MCE) under vertical bias magnetic field, but they differ greatly under inclined bias magnetic field. By comparison to the case of vertical magnetization, the DE or the MCE can be greatly increased under inclined magnetic field. The characteristic of the DE curves obtained is basically in agreement with the experimental result.

Realizing mode conversion and optical diode effect by coupling photonic crystal waveguides with cavity

We propose a novel two-dimensional photonic crystal structure consisting of two line defect waveguides and a cavity to realize mode conversion based on the coupling effect. The W1/cavity/W2 structure breaks the spatial symmetry and successfully converts the even（odd） mode to the odd（even） mode in the W2 waveguide during the forward（backward）transmission. When considering the incidence of only the even mode, the optical diode effect emerges and achieves approximate 35 d B unidirectionality at the resonant frequency. Moreover, owing to the narrow bandpass feature and the flexibility of the tuning cavity, utilization of the proposed structure as a wavelength filter is demonstrated in a device with a Y-branch splitter. Here, we provide a heuristic design for a mode converter, optical diode, and wavelength filter derived from the coupling effect between a cavity and adjacent waveguides, and expect that the proposed structure can be applied as a building block in future all-optical integrated circuits.

Numerical Research of Mode Conversion in an Inhomogeneous Plasma

The linear mode conversion of electromagnetic waves in the hot, unmagnetized inhomogeneous plasma is studied numerically for different density profiles, and the dependence of the absorption coefficient on the incident angles and the wave frequencies are obtained for different electrons＇ temperature. The results show that the shapes of the density profiles and the electron＇s temperature create a certain effect on the coefficients of absorption, which reaches its peak value （about 50%） for appropriate parameters. Effective absorption occurs in a limited range of parameter q.

Influence of mode conversions in the skull on transcranial focused ultrasound and temperature fields utilizing the wave field separation method： A numerical study

Transcranial focused ultrasound is a booming noninvasive therapy for brain stimuli. The Kelvin–Voigt equations are employed to calculate the sound field created by focusing a 256-element planar phased array through a monkey skull with the time-reversal method. Mode conversions between compressional and shear waves exist in the skull. Therefore, the wave field separation method is introduced to calculate the contributions of the two waves to the acoustic intensity and the heat source, respectively. The Pennes equation is used to depict the temperature field induced by ultrasound. Five computational models with the same incident angle of 0？and different distances from the focus for the skull and three computational models at different incident angles and the same distance from the focus for the skull are studied. Numerical results indicate that for all computational models, the acoustic intensity at the focus with mode conversions is 12.05%less than that without mode conversions on average. For the temperature rise, this percentage is 12.02%. Besides, an underestimation of both the acoustic intensity and the temperature rise in the skull tends to occur if mode conversions are ignored. However, if the incident angle exceeds 30？, the rules of the over-and under-estimation may be reversed. Moreover,shear waves contribute 20.54% of the acoustic intensity and 20.74% of the temperature rise in the skull on average for all computational models. The percentage of the temperature rise in the skull from shear waves declines with the increase of the duration of the ultrasound.

Adaptive Fuzzy Sliding Mode Controller for Grid Interface Ocean Wave Energy Conversion

This paper presents a closed-loop vector control structure based on adaptive Fuzzy Logic Sliding Mode Controller (FL-SMC) for a grid-connected Wave Energy Conversion System (WECS) driven Self-Excited Induction Generator (SEIG). The aim of the developed control method is to automatically tune and optimize the scaling factors and the membership functions of the Fuzzy Logic Controllers (FLC) using Multi-Objective Genetic Algorithms (MOGA) and Multi-Objective Particle Swarm Optimization (MOPSO). Two Pulse Width Modulated voltage source PWM converters with a carrier-based Sinusoidal PWM modulation for both Generator- and Grid-side converters have been connected back to back between the generator terminals and utility grid via common DC link. The indirect vector control scheme is implemented to maintain balance between generated power and power supplied to the grid and maintain the terminal voltage of the generator and the DC bus voltage constant for variable rotor speed and load. Simulation study has been carried out using the MATLAB/Simulink environment to verify the robustness of the power electronics converters and the effectiveness of proposed control method under steady state and transient conditions and also machine parameters mismatches. The proposed control scheme has improved the voltage regulation and the transient performance of the wave energy scheme over a wide range of operating conditions.

Scheme for implementing frequency up-conversion between two collective atomic modes

This paper presents a scheme for realizing the frequency up-conversion between two collective atomic modes. In the scheme two atomic samples are coupled to a cavity mode. Under the large detuning condition, the two collective atomic modes are coupled via the virtual excitation of the cavity mode and the effective Hamiltonian corresponds to the frequency up-conversion. In the scheme the cavity mode is only virtually excited and thus the process is insensitive to cavity decay.

HG-LG Mode Conversion with Stressed 3-Mode Fibers under Polarization

We have coupled an upright HG mode into a fiber-optic waveguide and used the application of stress to generate a Laguerre-Gaussian laser mode. We have generalized previous results by McGloin et al. by using a polarized input beam, a true 3-mode fiber and by applying the stress on a stripped piece of the optical waveguide. These generalizations are necessary in order to perform quantum information experiments and obtain reliable information on the stress imposed on the optical fiber.

LP modes exchange based on multiplane light conversion

Data exchange between different mode channels is essential in the optical communication network with mode-division multiplexing(MDM).However,there are challenges in realizing mode exchange with low insert loss,low mode crosstalk,and high integration.Here,we designed and fabricated a mode exchange device based on multiplane light conversion(MPLC),which supports the transmission of LP01,LP11a,LP11b,and LP21 modes in the C-band and L-band.The simulated exchanged mode purities are greater than 85%.The phase masks were fabricated on a silicon substrate to facilitate the integration with optical systems,with an insert loss of less than 2.2 dB and mode crosstalk below-21 dB due primarily to machining inaccuracies and alignment errors.We carried out an optical communication experiment with 10 Gbit/s OOK and QPSK data transmission at the wavelength of 1550 nm and obtained excellent performance with the device.It paves the way for flexible data exchange as a building block in MDM optical communication networks.

A Novel Hybrid MPPT for Wind Energy Conversion Systems Operating under Low Variations in Wind Speed

This manuscript presents a new approach MPPT (Maximum Power Point Tracking) for improving and optimizing the performance of a Wind Energy Conversion System (WECS) operating for small variations in wind speed by combining sliding mode control and fuzzy logic control. The proposed method consists of optimizing the sliding mode controller by the fuzzy controller. The main purpose of the Sliding Mode control-Fuzzy Logic controller (SM-FL) is to ensure the robustness (by eliminating certain disadvantages of the sliding mode control such as the phenomenon of chattering) and the stability of the control system in the case of small variations in conditions atmospheric (here variation of the wind). Our system consists of a wind turbine, a Permanent Magnet Synchronous Generator (PMSG) and a DC-DC boost converter connected to a continuous load. The performances of the method suggested are compared with those of fuzzy logic and fuzzy-Proportional Integral (FL-PI) in term speed of convergence, of tracking time and tracking efficiency. The results of numerical simulation of our system confirmed the best performance of this method.

Modes to Open a Conversation

All of us make conversations with others in a certain social context every day, though the mode to start them is various from different persons, occasions and circumstances. This paper is an attempt to analyze the variety of modes to open a conversation in different situations from the viewpoint of discourse analysis.

Experimental Investigation of Multi-Mode Vortex-Induced Vibration of Flexible Risers with Different Mass Ratios

Experiments were conducted on risers with different mass ratios to study the effect of mode conversion and spanwise correlation. The slenderness ratio of the riser model was set as 169, and the Reynolds numbers are 1600-14400. The dynamic responses of riser models versus reduced velocity were analyzed, and the spanwise displacement, frequency,and trajectory of the mode conversion from the lower to the higher mode were explored. The results revealed that the riser model with a higher mass ratio excites a higher number of modes. The conversion region of multi-mode competition exists and narrows with the increasing mass ratio. Mode conversion is continuous and manifests as the transmission of peaks and troughs in mode shape: the peaks and troughs of mode shape move up in the mode stable development region and move down in the mode conversion region. The single-mode dominating vibration exhibits a standing wave feature, and the traveling wave feature is significant in the mode conversion region. Furthermore, the frequency jump is always transmitted from the trough to the peak of the mode shape, and finally, all the axial positions vibrate at the same frequency. The trajectory in the mode conversion region deviates from the 8-shape and recovers the standard8-shape at the middle and late stages of the mode stable development region.

经济政策不确定性、投资者情绪与银行系统性风险传染

面对经济政策不确定性和投资者情绪,银行业需承担应对经济衰退、化解银行风险和实现经济高质量稳定增长的责任。本文利用MVMQ-CAViaR模型测度了2008—2021年所有上市银行的系统性风险,构建面板门限回归模型和面板平滑转换模型,研究在投资者情绪转换作用下经济政策不确定性影响银行系统性风险多重传染的边际效应结构变化。研究表明:投资者情绪具有显著的区制转换效应,使经济不确定性影响银行系统性风险多重传染的净边际效应,以指数转换模式发生结构变化。据此提出正确处理经济政策不确定性与银行系统性风险的关系,投资者要保持理性情绪以及监管部门要加强监管的建议。

高重现毛细管电泳的研究进展

毛细管电泳(CE)因具有微量、快速、高效、分离模式丰富等特点得以快速发展并逐渐走向成熟,但在其推广应用过程中一直伴随着出峰稳定性或重现性不佳的问题。CE长期采用信号强度对迁移时间作图的测量模式,但迁移时间并非自变量,受诸多直接和间接因素的影响,故很难测得稳定或精密的电泳谱图。为解决此类问题,国内外很早就开展了不同层次的研究,出现了至少三类解决策略:一是设法控制和稳定电泳特别是影响电渗的条件,以提高出峰的重复性;二是设法调整电泳峰参数,主要是利用内标来校正出峰位置,以提高出峰的重现性,如作时间比例谱、校正时间谱、有效淌度谱、校正淌度谱等;三是寻找建立高重现CE(HRCE)实时测量的新理论、新原理、新方法,从根本上彻底解决问题,如本团队提出的加权淌度谱、迁移电量谱、电密度谱、偏摩尔电密度谱及其比例谱等,这些新式CE方法在适当范围内可以抵抗CE条件或参数的波动,给出高重现的电泳谱图。本综述旨在总结构建HRCE的理论表述和研究进展,阐明影响CE重现性的一些关键因素,核心是电泳峰的表述方式。综述简要归纳分析了CE发展以来文献中对电泳峰表述方式的研究,但不直接涉及和讨论通过仪器改进、实用方法相关的参数的优化、改善等提升CE重复性或重现性的研究及其进展。

《敦煌乐谱》乐曲调式释疑

自林谦三率先对《敦煌乐谱》进行研究以来,有一个问题始终困扰着研究者们,正如林氏所言:“又据唐代中期的通说,《伊州》应该是商调,而在这乐谱里反倒不能理解为商调。”作者长期以来一直对乐谱第二、三组乐曲进行技术性的“宫”与“商”调式转换,后来又对唐的“侧商调”进行了研究。作者认为,如果按第二、三组乐曲实际解译的宫调式理解,从乐调理论上来加以论证,或许更符合当时的实际。说明唐代极有可能于某一个时期,在乐调(调性、调式)概念上有将“侧商调式”作为“黄钟宫调式”的代称或另称现象,这些都是从日本留存的唐代乐曲解译中得到的启发。

住院医师规范化培训手术操作指导教学的模式转换与分层递进方法探讨

提高手术操作能力是当前住院医师规范化培训进入质量内涵建设阶段的重要内容之一。指导医师手术教学能力是提升培训质量的重要保障措施。“扶放有度”是手术操作指导教学的理论基础,按住院医师能力可以采用示教模式、带教模式、协助模式和督导模式四种模式。可以采用一种模式为主体,多种模式联合应用,在手术的不同阶段灵活选择、随时切换。四种模式是分层递进的具体表现,符合学习一般规律,也是缩短学习曲线的有效方法。

模式转换型超声扭转焊接振子的研究

基于超声振动的模式转换理论,结合有限元方法设计了谐振频率为20 kHz的超声扭转焊接振子。该振子主要由夹心式压电换能器与模式转换变幅杆组成,模式转换变幅杆的互推杆和传振杆通过螺栓连接。为减少振子的漏波,设计了一种特殊结构的减振型法兰,并保证模式转换变幅杆输出端产生扭转振动。利用有限元分析软件进行模态分析和谐响应分析,仿真出振子的扭转频率为19.877 kHz,得到振子的频率响应曲线,通过模式转换变幅杆处完成振动模式的转换。最后,通过阻抗分析仪测得研制的振子谐振频率为19.69 kHz,与理论值和仿真值相差较小。激光测振仪测量振子互推杆端面处的纵向振幅为10.2μm,与仿真值接近,验证了设计方法的可行性,可为设计其他超声扭转焊接振子提供参考。

三模式掘进机选型及模式转换技术研究——以广州市地铁7号线为例

为解决复杂多变地层条件下单一模式或双模式掘进机适应性不足的问题,依托广州地铁7号线萝岗站—水西站区间三模式掘进机施工案例,开展三模式掘进机选型及模式转换技术研究。该区间包含软土、富水砂层、硬岩等复杂多变的地质,通过对区间地质特征、掘进风险、模式适应性等方面的综合分析,结合三模式掘进机工程应用效果的反馈和进一步探究,确定三模式掘进机选型及模式转换方案。结果表明:1)长距离、高强度硬岩地层适合采用敞开式硬岩模式,沉降要求高的富水砂层适合采用泥水平衡模式,带孤石的软土地层适合采用土压平衡模式;2)集3种模式于一体的三模式掘进机能有效解决地铁盾构区间穿越多种复杂地层(软土地层、沉降控制要求高的地层以及硬岩地层)时的盾构选型和地层适应性问题,实现掘进机多模式一体、一键切换、一机多用;3)掘进模式转换流程、工艺的工程应用,形成了掘进模式快速、安全转换技术;4)硬岩掘进的双排渣方案能有效解决一般硬岩条件下的高效排渣(硬岩掘进螺旋输送机出渣模式)和硬岩富水条件下的防喷涌(硬岩掘进泥水出渣模式)问题。

基于滑模自抗扰的储能变流器控制策略

为了提高储能变流器(PCS)的动态性能,设计基于降阶级联扩张状态观测器(ESO)和互补滑模控制(CSMC)的改进自抗扰控制(ADRC)策略,将改进ADRC策略应用于PCS的双向DC/AC变流器电压外环.改进ESO为降阶级联ESO以提高状态变量和系统总扰动的估计速度,增加扰动估计能力;更改PD控制为CSMC以设计状态误差反馈律,提升PCS的系统鲁棒性;设计改进指数趋近律以抑制抖振现象.为了证明改进ADRC策略相较于PI控制和传统ADRC的优越性,建立仿真模型并搭建相关实验平台.仿真与实验结果表明,改进ADRC策略减小了PCS暂态时直流母线电压波动,提高了PCS交流侧功率响应速度,改善了交流侧的输出电能质量.

级联声光器件与回音壁模式微腔实现非对称传输

本文提出利用级联声光效应器和耦合回音壁模式微球腔的方案来实现非对称传输效果,并进行理论和实验验证.实验中利用加热拉锥的方式制备了两段式光纤,可同时实现声光效应的激发和回音壁模式的耦合.利用光纤中声光效应将纤芯基模中的矢量模式转换到包层高阶模式,由于基模中不同矢量模式转换包层模式的矢量模式也不同,从而产生类似双折射效果,使输出的包层模式产生偏振变化.而后通过耦合回音壁模式微腔将包层模式转换回纤芯基模.由于回音壁模式的偏振选择效果,使得相反方向入射光能量具有不同的透射特性,其传输隔离度可达17 d B.此外,对两个方向传输的透射率随偏振角度变化进行测试,测得声光效应带来的偏振变化约为80°.本文的非对称传输方案继承了声光器件响应迅速、调谐性良好的优势,同时具有全光纤结构和无工作阈值的特点,在光开关、光隔离器等场景具有重要的应用潜力.