Broadband high-efficiency dielectric metalenses based on quasi-continuous nanostrips

Benefiting from the abrupt phase changes within subwavelength thicknesses,metasurfaces have been widely applied for lightweight and compact optical systems.Simultaneous broadband and high-efficiency characteristics are highly attractive for the practical implementation of metasurfaces.However,current metasurface devices mostly adopt discrete micro/nano structures,which rarely realize both merits simultaneously.In this paper,dielectric metasurfaces composed of quasi-continuous nanostrips are proposed to overcome this limitation.Via quasi-continuous nanostrips metasurface,a normal focusing metalens and a superoscillatory lens overcoming the diffraction limit are designed and experimentally demonstrated.The quasi-continuous metadevices can operate in a broadband wavelength ranging from 450 nm to 1000nm and keep a high power efficiency.The average efficiency of the fabricated metalens reaches 54.24%,showing a significant improvement compared to the previously reported metalenses with the same thickness.The proposed methodology can be easily extended to design other metadevices with the advantages of broadband and high-efficiency in practical optical systems.

基于Quasi-continuous高阶滑模理论的高超声速飞行器控制

针对高度非线性、强耦合、参数不确定性的高超声速飞行器数学模型,首先应用精确线性化将其非线性的数学模型转化成符合控制设计要求的等效线性模型,然后引入了Quasi-continuous高阶滑模控制理论,同时采用鲁棒精确微分器来克服测量的困难。模拟结果表明所设计的控制器对参数不确定性具有很好的鲁棒性,而且达到了期望的性能指标。

Control method based on DRFNN sliding mode for multifunctional flexible multistate switch

To address the low accuracy and stability when applying classical control theory in distribution networks with distributed generation,a control method involving flexible multistate switches(FMSs)is proposed in this study.This approach is based on an improved double-loop recursive fuzzy neural network(DRFNN)sliding mode,which is intended to stably achieve multiterminal power interaction and adaptive arc suppression for single-phase ground faults.First,an improved DRFNN sliding mode control(SMC)method is proposed to overcome the chattering and transient overshoot inherent in the classical SMC and reduce the reliance on a precise mathematical model of the control system.To improve the robustness of the system,an adaptive parameter-adjustment strategy for the DRFNN is designed,where its dynamic mapping capabilities are leveraged to improve the transient compensation control.Additionally,a quasi-continuous second-order sliding mode controller with a calculus-driven sliding mode surface is developed to improve the current monitoring accuracy and enhance the system stability.The stability of the proposed method and the convergence of the network parameters are verified using the Lyapunov theorem.A simulation model of the three-port FMS with its control system is constructed in MATLAB/Simulink.The simulation result confirms the feasibility and effectiveness of the proposed control strategy based on a comparative analysis.

Quasi-continuous synthesis of cobalt single atom catalysts for transfer hydrogenation of quinoline

Improving the transfer hydrogenation of N-heteroarenes is of key importance for various industrial pro-cesses and remains a challenge so far.We reported here a microcapsule-pyrolysis strategy to quasi-continuous synthesis S,N co-doped carbon supported Co single atom catalysts(Co/SNC),which was used for transfer hydrogenation of quinoline with formic acid as the hydrogen donor.Given the unique ge-ometric and electronic properties of the Co single atoms,the excellent catalytic activity,selectivity and stability were observed.Benefiting from the quasi-continuous synthesis method,the as-obtained cata-lysts provide a reference for the large-scale preparation of single atom catalysts without amplification ef-fect.Highly catalytic performances and quasi-continuous preparation process,demonstrating a new and promising approach to rational design of atomically dispersed catalysts with maximum atomic efficiency in industrial.

Characterization and formation mechanisms of fractures and their significance to hydrocarbon accumulation: A case study of Lower Ordovician mid-assemblage Formations in central Ordos Basin, China

The lower Ordovician mid-assemblage Formations in the central Ordos Basin of China host prolific gas resources,and most hydrocarbon reserves are stored in naturally-fractured reservoirs.Thus,fracture pathway systems may have a significant impact on reservoir performance.This article focuses on the core-and laboratory-based characterization of fractures.Through the developmental degrees,extended scale,output state and filling characteristics of various types of fractures,the results show that there are three distinct fracture types:1)nearly vertical fractures,2)oblique fractures,and 3)horizontal fractures.Based on a systematic study of the characterization of reservoir space,the main geologic setting of natural gas accumulation and the regional tectonic background,type 1 is mainly driven by the tectonic formation mechanism,and type 3 and parts of low-angle fractures in type 2 are induced by the diagenetic formation mechanism.While recovered paleopressure for methane-rich aqueous inclusions trapped in fracture-filling cement indicates that the fracture opening and growth are consistent with gas maturation and charge and such high-angle fractures in type 2 are caused by the compound formation mechanism.The fractures to hydrocarbon accumulation may play a more significant role in improving the quality of reservoir porosity.Furthermore,connected fractures,dissolved pores and cavities together constitute the three-dimensional pore-cave-fracture network pathway systems,with faults serving as the dominant charge pathways of highly pressurized gas in the study area.Our results demonstrate that protracted growth of a pervasive fracture system is not only the consequence of various formation mechanisms but also intrinsic to quasi-continuous accumulation reservoirs.

Strong Law of Large Numbers under an Upper Probability

Strong law of large numbers is a fundamental theory in probability and statistics. When the measure tool is nonadditive, this law is very different from additive case. In 2010 Chen investigated the strong law of large numbers under upper probabilityVby assumingVis continuous. This assumption is very strong. Upper probabilities may not be continuous. In this paper we prove the strong law of large numbers for an upper probability without the continuity assumption whereby random variables are quasi-continuous and the upper probability is generated by a weakly compact family of probabilities on a complete and separable metric sample space.

基于高阶滑模的舰载机着舰动力补偿系统仿真

将舰载机模型视为多输入多输出系统,基于Quasi-Continuous高阶滑模同时设计姿态稳定系统和迎角恒定的动力补偿系统。为避免传统微分环节对输入噪声的放大作用,采用鲁棒精确微分器对滑模面的高阶导数进行计算;为使系统有较快的响应速度,基于ITAE准则,对Quasi-Continuous高阶滑模控制器中参数的选取进行优化。仿真结果表明,在舰尾流存在的情况下,所设计的动力补偿系统能使航迹角准确快速地响应姿态角指令。

高超声速飞行器高阶滑模控制器设计

针对高度非线性、强耦合、参数不确定性的高超声速飞行器纵向运动数学模型,设计了一种基于Quasi-continuous高阶滑模理论的控制器,并与传统滑模控制器进行了分析和比较。仿真结果表明,Quasi-continu-ous高阶滑模控制在高度阶跃响应时间上比传统滑模控制减少了30%,速度阶跃响应时间比传统滑模控制减少了约56%。说明所设计的控制器能较好地满足在极端环境中飞行的高超声速飞行器对控制指令响应时间的要求。因此,该项研究对高超声速飞行器控制系统的设计有十分重要的参考价值。

Petroleum accumulation:from the continuous to discontinuous

Based on the extensive studies of conventional and unconventional hydrocarbon accumulations,the concept,classification and formation as well as distribution of petroleum reservoirs are discussed.The revised concept defined the petroleum reservoir as a continuous hydrocarbon accumulation in a single or a set of reservoirs with an independent or uniform pressure system.In terms of the pattern of hydrocarbon accumulation and distribution,the hydrocarbon accumulations are classified into three basic types,i.e.,the continuous accumulation,the quasi-continuous accumulation and the discontinuous accumulation.The hydrocarbon accumulation was demonstrated as a process from continuous accumulation to discontinuous accumulation,and therefore these three basic types of hydrocarbon accumulations were identified.The continuous hydrocarbon accumulation is principally formed in source rocks,and typical examples are shale hydrocarbon reservoirs and coal-bed methane reservoirs;it is mainly characterized by tight-ultra tight reservoirs with permeability of nanodarcy to millidarcy;the hydrocarbons occurred in free,adsorbed or dissolved state;a continuous accumulation comprises actually only a single reservoir,and hydrocarbons are extensively and continuously distributed within the scope of effective source rocks;the accumulation has neither defined boundaries nor bottom or edge water;oil and gas mainly accumulate in situ or near the generation of hydrocarbons with no prominent migration;this hydrocarbon accumulation process is basically not controlled by traps.The quasicontinuous hydrocarbon accumulation mostly occurs in the tight reservoirs adjacent to source rocks,and typical examples are most of tight hydrocarbon reservoirs;the hydrocarbons are distributed quasicontinuously in large areas,and each quasi-continuous hydrocarbon accumulation includes numerous adjacent small-to medium-size reservoirs;reservoirs of this kind of hydrocarbon accumulation have no defined boundaries,no or only local edge and bottom water distribution,and no regional oil-gas-water inversion;hydrocarbons are pervasively charged in large areas,and oil and gas accumulation is caused by primary migration and short-distance secondary migration;the hydrocarbon migration and accumulation is principally driven by non-buoyant forces in non-Darcy flow;and the hydrocarbon accumulation is basically not controlled by anticline traps,but largely by non-anticline traps,especially lithological traps.The discontinuous hydrocarbon accumulation is also named as the hydrocarbon accumulation of the conventional-trap type,and typically occurs in conventional reservoirs,but some tight hydrocarbon reservoirs,coalbed methane reservoirs and even possible shale hydrocarbon reservoirs also belong to this kind of hydrocarbon accumulation;the hydrocarbon reservoirs are distributed discontinuously,and have clear boundaries and complete edge water or bottom water;the hydrocarbon migration and accumulation is mainly driven by buoyancy and secondary migration is usually indispensable;the hydrocarbon accumulation is strictly controlled by various traps,especially structural traps.In a petroliferous basin,above three types of hydrocarbon accumulation may coexist,andhydrocarbons are often derived from a common source kitchen(s).Therefore,these three types of hydrocarbon accumulation should be considered and studied as a whole to maximize hydrocarbon exploration efficiencvy.