A historical overview of nano-optics:From near-field optics to plasmonics

Nano-optics is an emergent research field in physics that appeared in the 1980s,which deals with light–matter optical interactions at the nanometer scale.In early studies of nano-optics,the main concern focus is to obtain higher optical resolution over the diffraction limit.The researches of near-field imaging and spectroscopy based on scanning near-field optical microscopy(SNOM)are developed.The exploration of improving SNOM probe for near-field detection leads to the emergence of surface plasmons.In the sense of resolution and wider application,there has been a significant transition from seeking higher resolution microscopy to plasmonic near-field modulations in the nano-optics community during the nano-optic development.Nowadays,studies of nano-optics prefer the investigation of plasmonics in different material systems.In this article,the history of the development of near-field optics is briefly reviewed.The difficulties of conventional SNOM to achieve higher resolution are discussed.As an alternative solution,surface plasmons have shown the advantages of higher resolution,wider application,and flexible nano-optical modulation for new devices.The typical studies in different periods are introduced and characteristics of nano-optics in each stage are analyzed.In this way,the evolution progress from near-field optics to plasmonics of nano-optics research is presented.The future development of nano-optics is discussed then.

Modeling Near-Field Impulsive Waves Generated by Deformable Landslide Using the HBP Model Based on the SPH Method

Landslide-generated impulsive waves(LGWs)in reservoir areas can seriously threaten waterway safety as well as hu-man life and properties around the two side slopes.The risk reduction and mitigation of such a hazard require the accurate prediction of near-field wave characteristics,such as wave amplitude and run-up.However,near-field LGW involves complicated fluid-solid interactions.Furthermore,the wave characteristics are closely related to various aspects,including the geometry and physical features of the slide,river,and body of water.However,the empirical or analytical methods used for rough estimation cannot derive accurate results,especially for deformable landslides,due to their significant geometry changes during the sliding process.In this study,the near-field waves generated by deformable landslides were simulated by smoothed particle hydrodynamics(SPH)based on multi-phase flow.The deformable landslides were generalized as a kind of viscous flow by adopting the Herschel-Bulkley-Papanastasiou(HBP)-based nonNewtonian rheology model.The HBP model is capable of producing deformable landslide dynamics even though the high-speed sliding process is involved.In this study,an idealized experiment case originating from Lituya LGW and a practical case of Gongjiafang LGW were reproduced for verification and demonstration.The simulation results of both cases show satisfactory consistency with the experiment/investigation data in terms of landslide movement and near-field impulsive wave characteristics,thus indicating the applicability and accuracy of the proposed method.Finally,the effects of the HBP model’s rheological parameters on the landslide dynamics and near-field wave characteristics are discussed,providing a parameter calibration method along with sug-gestions for further applications.

Influence of substrate effect on near-field radiative modulator based on biaxial hyperbolic materials

Relative rotation between the emitter and receiver could effectively modulate the near-field radiative heat transfer(NFRHT)in anisotropic media.Due to the strong in-plane anisotropy,natural hyperbolic materials can be used to construct near-field radiative modulators with excellent modulation effects.However,in practical applications,natural hyperbolic materials need to be deposited on the substrate,and the influence of substrate on modulation effect has not been studied yet.In this work,we investigate the influence of substrate effect on near-field radiative modulator based onα-MoO_(3).The results show that compared to the situation without a substrate,the presence of both lossless and lossy substrate will reduce the modulation contrast(MC)for different film thicknesses.When the real or imaginary component of the substrate permittivity increases,the mismatch of hyperbolic phonon polaritons(HPPs)weakens,resulting in a reduction in MC.By reducing the real and imaginary components of substrate permittivity,the MC can be significantly improved,reaching 4.64 forε_(s)=3 at t=10 nm.This work indicates that choosing a substrate with a smaller permittivity helps to achieve a better modulation effect,and provides guidance for the application of natural hyperbolic materials in the near-field radiative modulator.

Study on the influence of side-blown airflow velocities on plasma and combustion wave generated from fused silica induced by combined pulse laser

This study examines the impact of variations in side-blowing airflow velocity on plasma generation,combustion wave propagation mechanisms,and surface damage in fused silica induced by a combined millisecond-nanosecond pulsed laser.The airflow rate and pulse delay are the main experimental variables.The evolution of plasma motion was recorded using ultrafast time-resolved optical shadowing.The experimental results demonstrate that the expansion velocities of the plasma and combustion wave are influenced differently by the sideblowing airflow at different airflow rates(0.2 Ma,0.4 Ma,and 0.6 Ma).As the flow rate of the sideblow air stream increases,the initial expansion velocities of the plasma and combustion wave gradually decrease,and the side-blow air stream increasingly suppresses the plasma.It is important to note that the target vapor is always formed and ionized into plasma during the combined pulse laser action.Therefore,the side-blown airflow alone cannot completely clear the plasma.Depending on the delay conditions,the pressure of the side-blowing airflow,the influence of inverse Bremsstrahlung radiation absorption and target surface absorption mechanisms can lead to a phenomenon known as the double combustion waves when using a nanosecond pulse laser.Both simulation and experimental results are consistent,indicating the potential for further exploration of fused silica targets in the laser field.

The Influence of Airflow Transport Pathways on Precipitation during the Rainy Season in the Liupan Mountains of Northwest China

This study investigates the influence of airflow transport pathways on seasonal rainfall in the mountainous region of the Liupan Mountains(LM) during the rainy seasons from 2020 to 2022, utilizing observational data from seven ground gradient stations located on the eastern slopes, western slopes, and mountaintops combined with backward trajectory cluster analysis. The results indicate 1) that the LM's rainy season, characterized by overcast and rainy days, is mainly influenced by cold and moist airflows(CMAs) from the westerly direction and warm and moist airflows(WMAs) from a slightly southern direction. The precipitation amounts under four airflow transport paths are ranked from largest to smallest as follows: WMAs, CMAs, warm dry airflows(WDAs), and cold dry airflows(CDAs). 2) WMAs contribute significantly more to the intensity of regional precipitation than the other three types of airflows. During localized precipitation events,warm airflows have higher precipitation intensities at night than cold airflows, while the opposite is true during the afternoon. 3) During regional precipitation events, water vapor content is the primary influencing factor. Precipitation characteristics under humid airflows are mainly affected by high water vapor content, whereas during dry airflow precipitation, dynamic and thermodynamic factors have a more pronounced impact. 4) During localized precipitation events, the influence of dynamic and thermodynamic factors is more complex than during regional precipitation, with the precipitation characteristics of the four airflows closely related to their water vapor content, air temperature and humidity attributes, and orographic lifting. 5) Compared to regional precipitation, the influence of topography is more prominent in localized precipitation processes.

Near-field radiative heat transfer between nanoporous GaN films

Photon tunneling effects give rise to surface waves,amplifying radiative heat transfer in the near-field regime.Recent research has highlighted that the introduction of nanopores into materials creates additional pathways for heat transfer,leading to a substantial enhancement of near-field radiative heat transfer(NFRHT).Being a direct bandgap semiconductor,GaN has high thermal conductivity and stable resistance at high temperatures,and holds significant potential for applications in optoelectronic devices.Indeed,study of NFRHT between nanoporous GaN films is currently lacking,hence the physical mechanism for adding nanopores to GaN films remains to be discussed in the field of NFRHT.In this work,we delve into the NFRHT of GaN nanoporous films in terms of gap distance,GaN film thickness and the vacuum filling ratio.The results demonstrate a 27.2%increase in heat flux for a 10 nm gap when the nanoporous filling ratio is 0.5.Moreover,the spectral heat flux exhibits redshift with increase in the vacuum filling ratio.To be more precise,the peak of spectral heat flux moves fromω=1.31×10^(14)rad·s^(-1)toω=1.23×10^(14)rad·s^(-1)when the vacuum filling ratio changes from f=0.1 to f=0.5;this can be attributed to the excitation of surface phonon polaritons.The introduction of graphene into these configurations can highly enhance the NFRHT,and the spectral heat flux exhibits a blueshift with increase in the vacuum filling ratio,which can be explained by the excitation of surface plasmon polaritons.These findings offer theoretical insights that can guide the extensive utilization of porous structures in thermal control,management and thermal modulation.

Localization for mixed near-field and far-field sources under impulsive noise

In order to solve the problem that the performance of traditional localization methods for mixed near-field sources(NFSs)and far-field sources(FFSs)degrades under impulsive noise,a robust and novel localization method is proposed.After eliminating the impacts of impulsive noise by the weighted out-lier filter,the direction of arrivals(DOAs)of FFSs can be estimated by multiple signal classification(MUSIC)spectral peaks search.Based on the DOAs information of FFSs,the separation of mixed sources can be performed.Finally,the estimation of localizing parameters of NFSs can avoid two-dimension spectral peaks search by decomposing steering vectors.The Cramer-Rao bounds(CRB)for the unbiased estimations of DOA and range under impulsive noise have been drawn.Simulation experiments verify that the proposed method has advantages in probability of successful estimation(PSE)and root mean square error(RMSE)compared with existing localization methods.It can be concluded that the proposed method is effective and reliable in the environment with low generalized signal to noise ratio(GSNR),few snapshots,and strong impulse.

Near-Field Wireless Power Transfer, Sensing and Communication with Bessel Beams

The Bessel beam,characterized by its unique non-diffracting properties,holds promising applications.In this paper,we provide a detailed introduction and investigation into the theory and research of the Bessel beam,with a special focus on its generation and applications in the near-field region.We provide an introduction to the concepts,properties,and foundational theories of the Bessel beam.Additionally,the current study on generating Bessel beams and their applications is categorized and discussed,and potential research challenges are proposed in this paper.This review serves as a solid foundation for researchers to understand the concept of the Bessel beam and explore its potential applications.

Towards Near-Field Communications for 6G:Challenges and Opportunities

Extremely large-scale multiple-input multiple-output(XL-MIMO)and terahertz(THz)communications are pivotal candidate technologies for supporting the development of 6G mobile networks.However,these techniques invalidate the common assumptions of far-field plane waves and introduce many new properties.To accurately understand the performance of these new techniques,spherical wave modeling of near-field communications needs to be applied for future research.Hence,the investigation of near-field communication holds significant importance for the advancement of 6G,which brings many new and open research challenges in contrast to conventional far-field communication.In this paper,we first formulate a general model of the near-field channel and discuss the influence of spatial nonstationary properties on the near-field channel modeling.Subsequently,we discuss the challenges encountered in the near field in terms of beam training,localization,and transmission scheme design,respectively.Finally,we point out some promising research directions for near-field communications.

Near-Field Beam Training for Holographic MIMO Communications: Typical Methods, Challenges and Future Directions

Holographic multiple-input multiple-output(HMIMO)has become an emerging technology for achieving ultra-high frequency spectral efficiency and spatial resolution in future wireless systems.The increasing antenna aperture leads to a more significant characterization of the spherical wavefront in near-field communications in HMIMO scenarios.Beam training as a key technique for wireless communication is worth exploring in this near-field scenario.Compared with the widely researched far-field beam training,the increased dimensionality of the search space for near-field beam training poses a challenge to the complexity and accuracy of the proposed algorithm.In this paper,we introduce several typical near-field beam training methods:exhaustive beam training,hierarchical beam training,and multi-beam training that includes equal interval multi-beam training and hash multi-beam training.The performances of these methods are compared through simulation analysis,and their effectiveness is verified on the hardware testbed as well.Additionally,we provide application scenarios,research challenges,and potential future research directions for near-field beam training.

Modular Extremely Large-Scale Array Communication:Near-Field Modelling and Performance Analysis

This paper investigates the wireless communication with a novel architecture of antenna arrays,termed modular extremely large-scale array(XLarray),where array elements of an extremely large number/size are regularly mounted on a shared platform with both horizontally and vertically interlaced modules.Each module consists of a moderate/flexible number of array elements with the inter-element distance typically in the order of the signal wavelength,while different modules are separated by the relatively large inter-module distance for convenience of practical deployment.By accurately modelling the signal amplitudes and phases,as well as projected apertures across all modular elements,we analyse the near-field signal-to-noise ratio(SNR)performance for modular XL-array communications.Based on the non-uniform spherical wave(NUSW)modelling,the closed-form SNR expression is derived in terms of key system parameters,such as the overall modular array size,distances of adjacent modules along all dimensions,and the user's three-dimensional(3D)location.In addition,with the number of modules in different dimensions increasing infinitely,the asymptotic SNR scaling laws are revealed.Furthermore,we show that our proposed near-field modelling and performance analysis include the results for existing array architectures/modelling as special cases,e.g.,the collocated XL-array architecture,the uniform plane wave(UPW)based far-field modelling,and the modular extremely large-scale uniform linear array(XL-ULA)of onedimension.Extensive simulation results are presented to validate our findings.

Dynamic behavior of outburst two-phase flow in a coal mine T-shaped roadway:The formation of impact airflow and its disaster-causing effect

The study of the dynamic disaster mechanism of coal and gas outburst two-phase flow is crucial for improving disaster reduction and rescue ability of coal mine outburst accidents.An outburst test in a T-shaped roadway was conducted using a self-developed large-scale outburst dynamic disaster test system.We investigated the release characteristics of main energy sources in coal seam,and obtained the dynamic characteristics of outburst two-phase flow in a roadway.Additionally,we established a formation model for outburst impact flow and a model for its flow in a bifurcated structure.The results indicate that the outburst process exhibits pulse characteristics,and the rapid destruction process of coal seam and the blocking state of gas flow are the main causes of the pulse phenomenon.The outburst energy is released in stages,and the elastic potential energy is released in the vertical direction before the horizontal direction.In a straight roadway,the impact force oscillates along the roadway.With an increase in the solid–gas ratio,the two-phase flow impact force gradually increases,and the disaster range extends from the middle of the roadway to the coal seam.In the area near the coal seam,the disaster caused by the two-phase flow impact is characterized by intermittent recovery.In a bifurcated roadway,the effect of impact airflow on impact dynamic disaster is much higher than that of two-phase flow,and the impact force tends to weaken with increasing solid-gas ratio.The impact force is asymmetrically distributed;it is higher on the left of the bifurcated roadway.With an increase in the solid-gas ratio,the static pressure rapidly decreases,and the bifurcated structure accelerates the attenuation of static pressure.Moreover,secondary acceleration is observed when the shock wave moves along the T-shaped roadway,indicating that the bifurcated structure increases the shock wave velocity.

微米级类球形介孔材料用于乙烯聚合催化剂

采用2-(4-氯磺酰苯基)乙基三甲氧基硅烷对类球形介孔材料进行疏水处理,制备了疏水性类球形介孔材料,将其作为载体,通过气流式喷雾干燥技术制备了聚乙烯催化剂。对疏水处理前后的类球形介孔材料进行了XRD、N2吸附-脱附、TEM、SEM表征,考察了气流式喷雾干燥过程中载气流量和浆料浓度对聚乙烯催化剂的影响,并评价了催化剂的乙烯聚合性能。实验结果表明,类球形介孔材料在疏水处理后孔结构和微观结构稳定;最佳喷雾干燥条件为喷雾干燥器进、出风口温度分别为140,105℃,载气流量为30 L/s,浆料浓度为30%(w);在最佳喷雾干燥条件下制备的催化剂用于乙烯聚合时,催化活性为28000 g/g,远高于工业用TS-610硅胶制备的催化剂的活性(9000 g/g),反应得到的聚合物性能也优于TS-610硅胶制备的催化剂得到的聚乙烯粉料。

综掘面风流调控下的瓦斯与粉尘浓度双目标预测模型研究

针对综掘面瓦斯和粉尘浓度预测能力不足,导致瓦斯粉尘积聚难以提前解决,造成风筒出风口风流调控降尘排瓦效果不佳的问题,采用层次分析法确定了瓦斯和粉尘浓度分布的关键影响因素,建立了7-11-3结构的双目标预测神经网络模型,并进行出风口距端头5 m和10 m工况下的应用测试,结果表明:模型误差率最大9.85%,最小0.27%。瓦斯浓度最高降低了45%,粉尘浓度最高降低了40%,有效预防了瓦斯和粉尘浓度的积聚问题。

西安市一次雷暴过程的闪电活动特征

利用陕西省闪电定位数据、多普勒天气雷达资料及逐小时降水资料,分析2018年8月9日西安市一次雷暴过程中闪电与降水、雷达回波和气流切变的关系特征,并进行特征对比分析。结果表明:15:00左右初始闪电发生后,闪电频次逐渐增加,17:54达到最大峰值后,闪电频次逐渐减少。整个雷暴过程中,正地闪占比较高,为23.8%;闪电频次出现了2次明显峰值,最大闪电频次为124次/6min,出现时段为17:48-17:54。闪电主要集中在强降水发生区域和时段,且先有闪电活动后有降水发生,正地闪活动与降水有密切关系。60 dBZ以上反射率面积与闪电频次随时间变化趋势一致,65 dBZ强反射率的出现和消失伴随着闪电频次的增加和减少。闪电频次与50 dBZ和40 dBZ的反射率等值线变化有较好的对应关系。正、负地闪在不同反射率范围集中程度不同,正地闪主要活动在强回波区前部和后部,且主要发生在雷暴云发展成熟后,负地闪则集中在强回波区中部和后部。地闪发生区域与上升气流和风切变区域有密切关系,但并不完全发生在上升气流区,负地闪在上升气流和下沉气流区的占比,对对流系统发展阶段有一定指示作用。经过特征对比分析,3次雷暴过程中降水量与正地闪的相关性、闪电与雷达反射率的关系均与西安市雷暴过程有相似特征。

气流与激光联合作用铝合金板热响应研究

为了获得激光加工等应用中气流环境激光辐照材料的热响应特性和熔穿规律,采用面热源近似和不定常热传导分析方法构建了包括热传导、对流换热、熔化烧蚀等主要机制的物理模型,并通过实验校核后进行了气流环境激光辐照铝合金热学响应定量评估,获得气流环境不同激光功率密度下铝合金靶板温升和烧蚀熔穿规律。结果表明,相同靶参数下,熔穿时间随着激光功率密度增加而急剧减小,并且熔穿时间变化规律与热平衡积分方法气化烧蚀模型结果一致;不同条件下熔穿时间显示,在激光功率密度较小(500 W/cm^(2)附近)时,气流引起对流换热因素对激光烧蚀熔穿影响较大,而在激光功率密度较高(1500 W/cm^(2)以上)时,气流引起对流换热因素对激光烧蚀熔穿影响较小。建立的气流条件下激光辐照热响应模型与实际物理过程更接近,计算获得的熔穿规律为激光辐照模型合理简化提供了定量的参考依据。

湿热地区室内气流调控对人群健康的影响

气流调控在改善湿热地区夏季热环境质量方面发挥着关键作用。然而,多数研究主要关注气流对人体全身热舒适的积极作用,而忽略了气流作用于身体局部时对人体健康的潜在影响。本研究采用随机抽样方法,于2023年8—10月在广东省21个地级市开展了问卷调研,共收集1 349份有效问卷。统计分析结果显示:当气流温度过低或气流主要作用于人体额头、腹部、太阳穴等敏感部位时,最易引发头疼、流涕、面瘫等症状;在年龄与性别差异上,青年人群相较于其他年龄段人群更容易因气流影响而出现此类症状,女性相比男性更排斥被气流直吹身体。这些发现可为制定湿热地区不同人群的健康气流调控策略提供支撑,有利于提升城市居民的生活质量和健康水平。

煤气化渣气流分级提炭分质试验

煤气化渣提炭分质是实现其减量化、资源化、高值化利用的关键。基于此,提出研磨破碎-气流分级的干法提炭工艺,利用研磨使气化渣中炭灰结合物解离,再利用气流分级机内离心力和气体曳力作用,将解离所得的细颗粒进行高效分离。通过设计均匀试验并对各影响因素进行回归分析,获取优选试验条件并对该试验条件下的提炭效果进行验证。结果表明,气流分级提炭受多因素耦合作用影响,其中分级机频率和引风机频率是影响提炭效果的关键。均匀试验优选条件为分级机频率175 Hz、引风机频率5 Hz,喂料螺旋频率5 Hz,二次风口全开;该条件下所得富炭产品的收率为25.86%,烧失量49.76%,较原气化渣烧失量提高了26.91%,与试验预测值(49.64%)较一致,且试验效果明显优于未研磨破碎直接气流分级的气化渣。优选条件下气流分级得到的富炭产品的平均粒径(Dav)为5.95μm,满足橡胶补强填充料的粒度要求,其热值为16.73 MJ/kg,亦可作为细粉燃料等使用。同时,气流分级可实现较好的气化渣脱炭效果,所得脱炭渣烧失量低于10%,有利于其在建材等领域应用。研磨破碎-气流分级方法可实现气化渣的提炭分质,有利于其下游利用。

果蔬隧道式气流冲击干燥流场模拟及其设备结构优化

为解决隧道式气流冲击干燥设备中风速流场不均匀的问题,利用计算流体动力学对气流冲击干燥过程的流场进行模拟分析,提出2种改进方案,并且每种方案选择9组模型,通过对比分析每组模型的速度均匀性和流场分布情况,以速度不均匀性为指标,得到结构参数为高度H=630 mm、半径R=60 mm圆柱扰流装置,并在此基础上,进行气流分配口大小调整,将上层和下层气流分配口调整为25 mm,中层气流分配口调整为20 mm的模型为最优结构。最优结构气流分配口速度不均匀系数减小到20.4%,物料层截面速度不均匀系数减小到16.89%,极大地改善气流冲击干燥的均匀性。对改进的模型进行试验验证,模拟值与试验测量值的相对误差均在11%以内。研究为相关干燥设备的结构优化提供参考。

六盘山区地面碘化银发生器催化作业条件分析

利用数值模式模拟的1 km×1 km六盘山区2009年6月至2010年5月的垂直速度资料、宁夏173个加密自动气象站数据、云高观测资料等开展了六盘山区碘化银发生器催化作业条件研究。结果表明:有降水过程时,六盘山区2.0 km、2.5 km、3.0 km、3.5 km高度层均有明显上升气流;地面发生器释放的碘化银催化剂的有效扩散高度可达3000 m;降雪开始前6 h至降雪开始后12 h内,发生器作业点有明显上升气流,80%以上时间内上升气流速度分钟平均值大于0.3 m·s~(-1)。结合六盘山区云底、0℃层等特征层高度,综合分析得出了六盘山东西两侧及六盘山顶一年中不同时期开展碘化银发生器催化作业的适宜程度。