Generation of structured light beams with polarization variation along arbitrary spatial trajectories using tri-layer metasurfaces

Conventionally,the spatially structured light beams produced by metasurfaces primarily highlight the polarization modulation of the beams propagating along the optical axis or the beams'spatial transmission trajectory.In particular,along the optical axis,the polarization state is either constant or varies continuously in each output plane.Here,we develop innovative spatially structured light beams with continually changing polarization along any arbitrary spatial transmission trajectories.With tri-layer metallic metasurfaces,the geometric characteristics of each layer structure can be adjusted to modulate the phase and polarization state of the incident terahertz(THz)wave.The beam will converge to the predefined trajectory along several paths to generate a Bessel-like beam with longitudinal polarization changes.We demonstrate the versatility of the approach by designing two THz-band structured light beams with varying polarization states along the spatial helical transmission trajectory.Continuous linear polarization changes and linear polarization to right circular polarization(RCP)and back to linear polarization changes are realized respectively.The experimental results are basically consistent with the simulated results.Our proposal for arbitrary trajectory structured light beams with longitudinally varying polarization offers a practical method for continuously regulating the characteristics of spatial structured light beams with non-axial transmission.This technique has potential uses in optical encryption,particle manipulation,and biomedical imaging.

Occurrence and Control of Main Pest Groups in Allium tuberosum Fields in Shijiazhuang

[Objectives]This study was conducted to investigate the species and occurrence patterns of main pests in the Chinese chive(Allium tuberosum)fields in Shijiazhuang.[Methods]Our research group conducted a systematic investigation on the types and occurrence of major pests in Chinese chive fields in Shijiazhuang from April 2019 to November 2020 using the Malaise net method.[Results]The main pests harming Chinese chives in the region included Thrips tabaci,Bradysia odoriphaga,Luperomorpha suturalis,Acrolepla alliella,Liriomyza chinensis,and Neotoxoptera formosana.The pest populations in the region mainly experienced two peak periods,from mid June to mid July and from late August to late September.Meanwhile,corresponding green prevention and control measures were proposed based on the occurrence characteristics and biological characteristics of different pests in local chive fields.[Conclusions]Predicting the occurrence of pests in Chinese chive fields can provide basis for farmers to take timely prevention and control measures,reduce the damage of pests in the field to Chinese chives and realize high-quality production of Chinese chive.

Influence of equipment excitation on flexible carbody vibration of EMU

To study the vibration transmission character istics of a flexible carbody and its suspended equipment, a vertical mathematical model of highspeed electric multiple unit was established with equipment excitation considered. And the dynamic unbalance and impact turbulence excita tion from equipment were taken into account in a single stage and twostage vibration isolation system, respectively. Results show that the excitation transferred to carbody increases with suspension stiffness but decreases with the equipment mass increasing; the vibration transmission can be reduced by increasing the equipment mass or reduce the suspension stiffness. To avoid vibration resonance, the dynamic unbalance frequency of equipment should be out of the possible range of the carbody flexible modes, and a small stiffness should be applied to reduce the impact tur bulence. A small stiffness, however, would result in a large movement of the equipment which is limited by the static deflection requirement, while a great stiffness will transfer high frequency vibration. Therefore, a preferred stiffness should make the suspension frequency of equipment a bit greater than the first bending mode of carbody. Additionally, a 3D rigidflexible coupled dynamics model was built to verify the mathematical analysis, and they show good agreements. Results show that a twostage isolation could reduce the excitation transmission and make the vibration of carbody and equipment acceptable.

Polarization multiplexing for double images display

Metasurface provides subwavelength structures for manipulating wavefronts of light. The benefits of subwavelength components offer a continuous modulation of amplitude, phase, and polarization, thus eliminating the production of higher-order images and improving the utilization of light intensity. Despite the rapid progress in this field, multiparameter control of light using single layer metasurface is rarely reported. In fact, multiparameter control of light helps to improve information storage capacity and image fidelity. With simultaneous manipulation of polarization and amplitude at each pixel, it is possible to encode two separate images into one metasurface and reconstruct them under proper conditions. In a proof of concept experiment, we demonstrate an independent display of two binary images at the same position with polarization de-multiplexing from a single metasurface. This unique technology of encoding two images through amplitude and polarization manipulation provides a new opportunity for various applications in, such as encryption, information storage, polarization holograms, optical communications and fundamental physics.

野生型RET与RET/PTC融合基因检测对甲状腺乳头状癌中央区淋巴结清扫的指导意义

目的探讨野生型RET(WT-RET)与RET/甲状腺乳头状癌(PTC)融合基因检测对PTC中央区淋巴结清扫的指导意义。方法选取2020年10月至2022年10月行中央区淋巴结清扫的300例PTC患者,术后行野生型RET与RET/PTC融合基因检测,按照中央区淋巴结是否转移分为两组,转移组(155例)和无转移组(145例)。应用SPSS 25.0软件对数据进行统计学分析,通过多因素Logistic回归分析影响PTC患者中央区淋巴结转移的独立危险因素,并构建列线图预测模型。P<0.05为差异有统计学意义。结果两组患者的年龄、病灶直径、病灶数量、肿瘤分期、浸润被膜、野生型RET、RET/PTC融合基因、淋巴结肿大、病变腺叶差异性有统计学意义(P<0.05);多因素Logistic回归分析提示影响PTC患者中央区淋巴结转移的独立危险因素有年龄<45岁、病灶直径≥1.0 cm、多发病灶数、T_(3-4)期、有浸润被膜、野生型RET阳性、RET/PTC融合基因阳性、淋巴结肿大、病变腺叶单侧(P<0.05);列线图模型并验证,结果提示训练集和验证集的C-index分别为0.850、0.826,两集的曲线下面积分别为0.802、0.789,当阈值概率在0.01~0.91之间的决策曲线,净获益值比较高。结论野生型RET与RET/PTC融合基因是预测PTC患者发生中央区淋巴结转移的独立危险因素,能指导临床医生对这类患者谨慎选择中央区淋巴结清扫范围,基于临床特征及基因检测特征构建列线图风险预测模型,具有较高的预测性能,有助于指导临床决策。

Improved lateral-dynamics-intended railway vehicle model involving nonlinear wheel/rail interaction and car body flexibility

To study the vehicle hunting behavior and its coupling with car body vibrations,a simplified lateral-dynamics-intended railway vehicle model is developed.A two-truck vehicle is modeled as a 17 degrees-of-freedom rigid system,into which the car body flexural vibrations of torsion and bending modes are further integrated.The wheel/rail interaction employs a real-time calculation for the Hertzian normal contact,in which the nonlinear curvatures of wheel and rail profiles are presented as functions of wheelset lateral movement and/or yaw rotation.Then the tangential/creep forces are analytically expressed as the Hertzian contact patch geometry,and lead to a continuous and fast calculation compared to a look-up table interpolation.It is shown that the hunting frequencies of the vehicle model and a truck model differ significantly,which verifies the necessity of the whole vehicle model.In the case of low wheel/rail conicity,the hunting frequency increases linearly with vehicle speed,whereas it rises slowly at high speed for a large conicity.Comparison of hunting frequency and damping ratio between various conicities shows that first hunting(car body hunting)may occur when the vehicle is operated at a low speed in a small conicity case,while a second hunting(truck hunting)appears when the vehicle is operated at a high speed in a large conicity case.Stability analysis of linear and nonlinear vehicle models was carried out through coast down method and constant speed simulations.Results tell that the linear one overestimates the lateral vibrating.Whereas the structural vibrations of car body can be ignored in the stability analysis.Compared to existing simplified models for hunting stability study,the proposed simplified vehicle model released limitations in the nonlinear geometries of wheel/rail profiles,and it is suitable for a frequency-domain analysis by deriving the analytical expressions of the normal and tangential wheel/rail contact forces.