Identifying interlinkages between urbanization and Sustainable Development Goals

Urbanization and Sustainable Development Goals(SDGs)are important global issues in the current“Anthropocene”.Climate change and the COVID-19 pandemic have exacerbated global urban problems and hindered the ability to meet SDGs on time,while the broad interlinkages between urbanization and the SDGs remain poorly understood.This study shows that among the interlinkages of urbanization with 17 SDGs,synergies are observed with 151 targets(89%),among which 67(40%)have stronger synergies,and trade-offs are observed with 66 targets(39%),among which 31(18%)have stronger trade-offs.Furthermore,the synergies and trade-offs between urbanization and the achievement of SDGs are specifically analyzed based on four fundamental interaction fields:(a)public health and social welfare equality;(b)energy consumption and economic growth;(c)natural resource use and ecological/environmental impacts;and(d)international cooperation for development.Finally,based on these analyses,we propose four recommendations for sustainable urbanization,including(a)shared well-being and spatial justice for urban and rural residents;(b)guiding green and low-carbon urban development;(c)building resilient cities;and(d)promoting multilateral cooperation in cities,which can contribute to the achievement of SDGs by 2030.

Liquid Crystal Based Label-Free Optical Sensors forBiochemical Application

Biochemical sensors have important applications in biology,chemistry,and medicine.Nevertheless,many biochemical sensors are hampered by intricate techniques,cumbersome procedures,and the need for labeling.In the past two decades,it has been discovered that liquid crystals can be used to achieve the optical amplification of biological interactions.By modifying recognition molecules,a variety of label-free biochemical sensors can be created.Consequently,biochemical sensors based on the amplification of liquid crystals have become one of the most promising sensors.This paper describes in detail the optical sensing principle of liquid crystals,sensing devices,and optical detection technologies.Meanwhile,the latest research findings are elucidated.Finally,the challenges and future research directions are discussed.

Side Polished Fiber:A Versatile Platform for Compact Fiber Devices and Sensors

Side polished fiber(SPF)has a controllable average roughness and length of the side-polishing region,which becomes a versatile platform for integrating multiple materials to interact with the evanescent field to fabricate all-fiber devices and sensors.It has been widely used in couplers,filters,polarizers,optical attenuators,photodetectors,modulators,and sensors for temperature,humidity,strain,biological molecules,chemical gas,and vector magnetic monitoring.In this article,an overview of the development history,fabrication techniques,fiber types,transmission characteristics,and varied recent applications of SPFs are reviewed.Firstly,the fabrication techniques of SPFs are reviewed,including the V-groove assisted polishing technique and wheel polishing technique.Then,the different types of SPFs and their characteristics are discussed.Finally,various applications of SPFs are discussed and concluded theoretically and experimentally,including their principles and structures.When designing the device,the residual thickness and polishing lengths of the SPF need to be appropriately selected in order to obtain the best performance.Developing all-fiber devices and sensors is aimed at practical usability under harsh environments and allows to avoid the high coupling loss between optical fibers and on-chip integrated devices.

High-sensitivity and fast-response fiber optic temperature sensor using an anti-resonant reflecting optical waveguide mechanism

Temperature sensing is essential for human health monitoring.High-sensitivity(>1 nm∕℃)fiber sensors always require long interference paths and temperature-sensitive materials,leading to a long sensor and thus slow response(6–14 s).To date,it is still challenging for a fiber optic temperature sensor to have an ultrafast(~ms)response simultaneously with high sensitivity.Here,a side-polished single-mode/hollow/single-mode fiber(SPSHSF)structure is proposed to meet the challenge by using the length-independent sensitivity of an anti-resonant reflecting optical waveguide mechanism.With a polydimethylsiloxane filled sub-nanoliter volume cavity in the SP-SHSF,the SP-SHSF exhibits a high temperature sensitivity of 4.223 nm/℃ with a compact length of 1.6 mm,allowing an ultrafast response(16 ms)and fast recovery time(176 ms).The figure of merit(FOM),defined as the absolute ratio of sensitivity to response time,is proposed to assess the comprehensive performance of the sensor.The FOM of the proposed sensor reaches up to 263.94(nm/℃)∕s,which is more than two to three orders of magnitude higher than those of other temperature fiber optic sensors reported previously.Additionally,a threemonth cycle test shows that the sensor is highly robust,with excellent reversibility and accuracy,allowing it to be incorporated with a wearable face mask for detecting temperature changes during human breathing.The high FOM and high stability of the proposed sensing fiber structure provide an excellent opportunity to develop both ultrafast and highly sensitive fiber optic sensors for wearable respiratory monitoring and contactless in vitro detection.

Effect of SiO_(2) nano film deposited on copper and aluminium electrodes on the power frequency breakdown voltage of SF_(6) gas

In order to reveal the effect of insulating nano film on the insulation strength of SF_(6) gas gap,SiO_(2) nano film was deposited on the electrode surface by the plasma-enhanced chemical vapour deposition technique.The power frequency breakdown characteristics of SF_(6) gas under Cu and Al electrodes were obtained before and after coating.The results showed that when the Cu electrode was coated,the breakdown voltage was up to at most 11.5% higher than that of an uncoated Cu electrode in the pressure range of 0.2-0.5 MPa.When the Al electrode was coated,the breakdown voltage of SF_(6) gas was lower than that of an uncoated one in the pressure range of 0.2-0.5 MPa.The breakdown voltage of SF_(6) gas under the Cu electrode was slightly lower than that under the Al electrode,but the breakdown voltages under the coated Cu electrode were significantly higher than that under the coated Al electrode.Through SEM tests,it was found that the surface roughness of the electrode decreases after coating,but particles were formed on the surface of the Al electrode.The content of metal fluoride formed on the coated Al electrode under multiple breakdowns was significantly higher than that on the coated Cu electrode.The research results could provide references for improving insulation performance of GIS equipment.

浙江美丽乡村空间格局及可持续发展模式研究

浙江美丽乡村建设系全国稳步推进乡村振兴战略的地方经典模式。基于浙江2016年以来3个批次美丽乡村“示范村”数据,运用洛伦兹曲线、平均最近邻指数、核密度分析和地理探测器等方法定量识别美丽乡村空间特征及影响因素,并构建乡村振兴可持续发展模式,揭示具有强烈资源禀赋约束的各类乡村如何在政策与资本双重驱动下从示范走向全域。结果表明:(1)美丽乡村示范村空间上整体呈凝聚型分布,已形成“杭嘉湖”和“金衢”两大集聚区,且其时空演化特征稳中有变,后两批较第一批分布范围更广;(2)美丽乡村具有农业服务型、工业发展型、休闲旅游型、文化传承型和综合治理型等五大类型,不同类型的空间分布特征差异显著,且与已有要素禀赋和产业基础关联密切;(3)区位条件、文化旅游资源、经济发展水平和地形是影响示范村区位的重要因素;(4)美丽乡村建设从局部到全域推进过程遵循优先发展资源禀赋示范村、辐射引领周边村落的路径,并倡导政府引导、资本驱动、“农户+公司”和村民创业并存的多元主体发展模式。

面向学习云空间的认知投入量化研究

在全面推进"网络学习空间人人通"的建设背景下,学习云空间的应用不断深入。但正如其他在线学习平台一样,学习云空间也存在辍学率高、学习投入不足等问题。本文聚焦学习云空间中学习主体认知投入相关数据的获取,提出了基于机器学习的认知投入量化方法。首先,分析了认知投入的构成要素,并基于班杜拉的社会认知理论,建立了面向学习云空间的认知投入模型。然后构建了围绕"数据采集-数据处理-量化实现-量化应用"的认知投入量化框架,并设计了一个基于支持向量机的认知投入量化算法。最后以世界大学城系统平台数据为支撑,通过与其他机器学习算法的对比得到研究结果,基于SVM算法具有较高的量化精确率,本研究希望能为教育领域深层认知投入量化提供一种可行的参考方案。

Photonic cavity enhanced high-performance surface plasmon resonance biosensor

Herein we propose a novel strategy to enhance surface plasmon resonance(SPR)by introducing a photonic cavity into a total-internal-reflection architecture.The photonic cavity,which is comprised of a highly reflective photonic crystal(PC),defect layers,and a gold(Au)film,enables Fabry–Perot(FP)resonances in the defect layers and therefore narrows the SPR resonance width in the metallic surface as well as increases the electric field intensity and penetration depth in the evanescent region.The fabricated sensor exhibits a 5.7-fold increase in the figure of merit and a higher linear coefficient as compared with the conventional Au-SPR sensor.The demonstrated PC/FP cavity/metal structure presents a new design philosophy for SPR performance enhancement.

Sensitivity-enhanced surface plasmon resonance sensor utilizing a tungsten disulfide (WS_2) nanosheets overlayer

Tungsten disulfide （WS2）, as a representative layered transition metal dichalcogenide （TMDC） material, possesses important potential for applications in highly sensitive sensors. Here, a sensitivity-enhanced surface plasmon resonance （SPR） sensor with a metal film modified by an overlayer of WS2 nanosheets is proposed and demo onstrated. The SPR sensitivity is related to the thickness of the WS2 overlayer, which can be tailored by coating a WS2 ethanol suspension with different concentrations or by the number of times of repeated post-coating. Benefitting from its large surface area, high refractive index, and unique optoelectronic properties, the WS2 nanosheet overlayer coated on the gold film significantly improves the sensing sensitivity. The highest sensitivity （up to 2459.3 nm/RIU） in the experiment is achieved by coating the WS2 suspension once. Compared to the case without a WS2 overlayer, this result shows a sensitivity enhancement of 26.6%. The influence of the WS2 nano- sheet overlayer on the sensing performance improvement is analyzed and discussed. Moreover, the proposed WS2 SPR sensor has a linear correlation coefficient of 99.76% in refractive index range of 1.333 to 1.360. Besides sensitivity enhancement, the WS2 nanosheet overlayer is able to show additional advantages, such as protection of metal film from oxidation, tunability of the resonance wavelength region, biocompatibility, capability of vapor, and gas sensing.

Tunable spin splitting of Laguerre–Gaussian beams in graphene metamaterials

Optical spin splitting has attracted significant attention owing to its potential applications in quantum information and precision metrology. However, it is typically small and cannot be controlled efficiently. Here, we enhance the spin splitting by transmitting higher-order Laguerre–Gaussian(LG) beams through graphene metamaterial slabs. The interaction between LG beams and metamaterial results in an orbital-angularmomentum-(OAM) dependent spin splitting. The upper bound of the OAM-dependent spin splitting is found,which varies with the incident OAM and beam waist. Moreover, the spin splitting can be flexibly tuned by modulating the Fermi energy of the graphene sheets. This tunable spin splitting has potential applications in the development of spin-based applications and the manipulation of mid-infrared waves.

High-performance fiber-integrated multifunctional graphene-optoelectronic device with photoelectric detection and optic-phase modulation

In graphene-based optoelectronic devices,the ultraweak interaction between a light and monolayer graphene leads to low optical absorption and low responsivity for the photodetectors and relative high half-wave voltage for the phase modulator.Here,an integration of the monolayer graphene onto the side-polished optical fiber is demonstrated,which is capable of providing a cost-effective strategy to enhance the light–graphene interaction,allowing us to obtain a highly efficient optical absorption in graphene and achieve multifunctions:photodetection and optical phase modulation.As a photodetector,the device has ultrahigh responsivity(1.5×10^(7) A/W)and high external quantum efficiency(>1.2×10^(9)%).Additionally,the polybutadiene/polymethyl methacrylate(PMMA)film on the graphene can render the device an optical phase modulator through the large thermo-optic effect of the PMMA.As a phase modulator,the device has a relatively low half-wave voltage of 3 V with a 16 dB extinction ratio in Mach–Zehnder interferometer configuration.

Optimized weak measurement of orbital angular momentum-induced beam shifts in optical reflection

Tiny but universal beam shifts occur when a polarized light beam is reflected upon a planar interface.Although the beam shifts of Gaussian beams have been measured by the weak measurement technique, the weak measurement for orbital angular momentum(OAM)-induced spatial shifts of vortex beams is still missing.Here, by elaborately choosing the preselection and postselection states, the tiny OAM-induced Goos–H?nchen and Imbert–Fedorov shifts are amplified at an air–prism interface. The maximum shifts along directions both parallel and perpendicular to the incident plane are theoretically predicted and experimentally verified with optimal preselection and postselection states. These maximum shifts can be used to determine the OAM of vortex beams.

Distance-controllable and direction-steerable opto-conveyor for targeting delivery

Opto-conveyors have attracted widespread interest in various fields because of their non-invasive and non-contact delivery of micro/nanoparticles.However,the flexible control of the delivery distance and the dynamic steering of the delivery direction,although very desirable in all-optical manipulation,have not yet been achieved by optoconveyors.Here,using a simple and cost-effective scheme of an elliptically focused laser beam obliquely irradiated on a substrate,a direction-steerable and distance-controllable opto-conveyor for the targeting delivery of microparticles is implemented.Theoretically,in the proposed scheme of the opto-conveyor,the transverse and longitudinal resultant forces of the optical gradient force and the optical scattering force result in the transverse confinement and the longitudinal transportation of microparticles,respectively.In this study,it is experimentally shown that the proposed opto-conveyor is capable of realizing the targeting delivery for microparticles.Additionally,the delivery distance of microparticles can be flexibly and precisely controlled by simply adjusting the irradiation time.By simply rotating the cylindrical lens,the proposed opto-conveyor is capable of steering the delivery direction flexibly within a large range of azimuthal angles,from-75°to 75°.This study also successfully demonstrated the real-time dynamic steering of the delivery direction from-45°to 45°with the dynamical rotation of the cylindrical lens.Owing to its simplicity,flexibility,and controllability,the proposed method is capable of creating new opportunities in bioassays as well as in drug delivery.

Resonance-assisted light–control–light characteristics of SnS_2 on a microfiber knot resonator with fast response

An all-optical light–control–light functionality with the structure of a microfiber knot resonator (MKR) coated with tin disulfide (SnS_2) nanosheets is experimentally demonstrated. The evanescent light in the MKR [with a resonance Q of ～59,000 and an extinction ratio (ER) of ～26 dB] is exploited to enhance light–matter interaction by coating a two-dimensional material SnS_2 nanosheet onto it. Thanks to the enhanced light–matter interaction and the strong absorption property of SnS_2, the transmitted optical power can be tuned quasi-linearly with an external violet pump light power, where a transmitted optical power variation rate ΔT with respect to the violet light power of ～0.22 dB∕mW is obtained. In addition, the MKR structure possessing multiple resonances enables a direct experimental demonstration of the relationship between resonance properties (such as Q and ER), and the obtained ΔT variation rate with respect to the violet light power. It verifies experimentally that a higher resonance Q and a larger ER can lead to a higher ΔT variation rate. In terms of the operating speed, this device runs as fast as ～3.2 ms. This kind of all-optical light–control–light functional structure may find applications in future all-optical circuitry, handheld fiber sensors, etc.

Methods for alleviation of impacts of axial diffusion on decomposition products monitoring in gas‐insulated transmission lines

Considering the long length of gas‐insulated transmission lines(GILs),novel methods are required to alleviate the impacts of axial diffusion on decomposition products'moni-toring.The diffusion process of two typical decomposition products,SO2 and SO2F2,was studied.During the diffusion experiments,SO2 and SO2F2 were generated by partial discharges.Based on Fick’s law,an axial diffusion model of SO2 and SO2F2 was proposed.By combining the experiment and simulation results,it was found that the diffusion coefficient of SO2 was greater than that of SO2F2.In addition,the concentration variation at different positions would experience some delay and decay in axial direction.The delay and decay were inversely related to the diffusion coefficient and increased with prolongation of the distance.Based on the diffusion characteristics determined,methods for optimising the monitoring positions,correcting concentration,and using the concentration ratio and generation rate were proposed to alleviate the impacts of diffusion.The methods could allow the decomposition products to be monitored in 1 month and reduce the monitoring error to 10%or less.The diffusion model and the methods could be useful for monitoring decomposition products in GILs.