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Rainbow trapping based on long-range plasmonic Bragg gratings at telecom frequencies

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Chinese Physics B 2013年第7期22卷 440-443页

作者：陈林张天 li xun Wuhan National Laboratory for Optoelectronics School of Optoelectronic Science and EngineeringHuazhong University of Science and Technology Department of Electrical and Computer Engineering McMaster University

The group velocity of long-range surface plasmon polaritons （LRSPPs） in a wide frequency bandwidth at infrared frequencies is significantly reduced by dielectric gratings of graded thickness on both sides of a thin metal film. This structure can reduce the propagation loss of slow surface plasmons in ＂rainbow trapping＂ systems based on plasmonic Bragg gratings. Compared with dielectric gratings of graded thickness on a single side of a metal film, the proposed structure is able to guide slow light with a much longer propagation distance for the same group index factor. Finite- difference time-domain simulation results show that slow LRSPPs with the group velocity of c/14.5 and the propagation distance of 10.4 μm are achieved in dielectric gratings of uniform thickness on both sides of a thin metal film at 1.62 μm.

关键词： surface plasmon polaritons slow light photonic integrated circuits

Estimation of the J-resistance curve for Cr2Ni2MoV steel using the modified load separation parameter S_(pb) method

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2010年第10期11卷 782-788页

作者： Chen BAO li-xun CAI School of Mechanics and Engineering Southwest Jiaotong University Chengdu 610031 China

Based on load separation theory, the load separation parameter Spb method is an effective approach for estimating the J-resistance curve from records of load versus displacement directly, using one sharp cracked specimen and an additional reference blunt cracked specimen. However, the effect of the reference blunt cracked specimen on J-resistance determination was not explicitly considered in past work. In this paper, a modified load separation parameter Spb method was developed to eliminate this effect, and then a unique estimation of instantaneous crack length for one sharp cracked specimen could be obtained. Furthermore, a forced blunting calibration method was also adopted to determine the instantaneous crack length in the load inseparable region, referring to a normalization method. Experiments on steam turbine rotator steel Cr2Ni2MoV were carried out to estimate J-resistance curves using an unloading compliance method. By removing unload and reload data from load-displacement records, the J-resistance curve for the same sharp cracked specimen was estimated using the modified separation parameter Spb method. The results indicate that the modified Spb method completely eliminates the effect of the reference blunt cracked specimen on the instantaneous crack length determination of the sharp cracked specimen. However, different J-resistance curves in a small range of crack extension are present when different blunting coefficients are used in the blunting line equation. The J-resistance curve obtained from the modified Spb method agrees well with that obtained from the compliance method.

关键词： Load separation J-resistance curve Separation parameter Spb Blunt cracked specimen Forced blunting calibration

A novel evasion guidance for hypersonic morphing vehicle via intelligent maneuver strategy

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Chinese Journal of Aeronautics 2024年第5期37卷 441-461页

作者： xun li Xiaogang WANG Hongyu ZHOU Yu li Department of Aerodynamics Harbin Institute of TechnologyHarbin 150001China Beijing Aerospace Technology Institute Beijing 100074China

This paper presents a novel evasion guidance law for hypersonic morphing vehicles,focusing on determining the optimized wing's unfolded angle to promote maneuverability based on an intelligent ***,the pursuit-evasion problem is modeled as a Markov decision *** the agent's action consists of maneuver overload and the unfolded angle of wings,which is different from the conventional evasion guidance designed for fixed-shape *** reward function is formulated to ensure that the miss distances satisfy the prescribed bounds while minimizing energy ***,to maximize the expected cumulative reward,a residual learning method is proposed based on proximal policy optimization,which integrates the optimal evasion for linear cases as the baseline and trains to optimize the performance for nonlinear engagement with multiple ***,offline training guarantees improvement of the constructed evasion guidance law over conventional ***,the guidance law for online implementation includes only analytical *** maps from the confrontation state to the expected angle of attack and the unfolded angle while retaining high computational *** show that the proposed evasion guidance law can utilize the change of unfolded angle to extend the maximum overload *** it surpasses conventional maneuver strategies by ensuring better evasion efficacy and higher energy efficiency.

关键词： Hypersonic vehicles Variable-sweep wings Evasion guidance Reinforcement learning Pursuit-evasion problem

Surface integrity of GH4169 affected by cantilever finish grinding and the application in aero-engine blades

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Chinese Journal of Aeronautics 2015年第5期28卷 1539-1545页

作者： li xun Ma Shuang Meng Fanjun School of Mechanical Engineering and Automation Beihang University

GH4169 is the main material for aero-cngine blades and integrated blisks. Because GH4169 has a poor milling performance, the profile precision and surtace integrity of blades and integrated blisks are difficult to be met by utilizing the conventional milling process, which directly influence the global performance and reliability of aero-engines. Through grinding experiments on parameters and surface integrity optimization, the helical cantilever grinding process utilizing a 300# CBN RB wheel is presented and applied in finish machining of GH4169 blades. The profile errors of the blade surface are within ±0.01 mm, the roughness is less than 0.4μm, the residual compressive stresses and the hardening rate are appropriate, there are no phenomena of burr and smearing with the grinding chips, and the leading/trailing edge can be smoothly connected with the suction/pressure surface. All the experimental results indicate that this grinding process is greatly suitable for the profile finish machining of GH4169 blades.

关键词： Blade:Cantilever:GH4169:Grinding:Surface integrity

Influences of milling and grinding on machined surface roughness and fatigue behavior of GH4169 superalloy workpieces

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Chinese Journal of Aeronautics 2018年第6期31卷 1399-1405页

作者： xun li Chunming GUAN Peng ZHAO School of Mechanical Engineering and Automation Beihang University

Surface topography of superalloy GH4169 workpieces machined by milling and grinding is different significantly. Meanwhile, surface roughness, as one of the main indicators of machined surface integrity, has a great influence on the fatigue behavior of workpieces. Based on analyzing the formation mechanism and characteristics of surface roughness utilizing different machining processes and parameters, the machined surface roughness curve can be decoupled into two parts utilizing frequency spectrum analysis, which are kinematic surface roughness curve and stochastic surface roughness curve. The kinematic surface roughness curve is influenced by machining process,parameters, geometry of the cutting tool or wheel, the maximum height of which is expressed as Rz＇.By subtracting the kinematic part from the measurement curve, the stochastic surface roughness curve and its maximum height Rz＂ can be obtained, which is influenced by the defects of cutting tool edge or abrasive grains, built-up edges（BUE）, cracks, high frequency vibration and so on. On the other hand, the results of decoupling analysis of surface roughness curves indicate that Raand Rz values of milling GH4169 are 2–5 times and 1–3 times as high as those of grinding, while Rz＂ value of milling is 13.85%–37.7% as high as that of grinding. According to the results of fatigue life tests of specimens machined by milling and grinding, it can be concluded that fatigue behavior of GH4169 decreases with the increase of Rz＂monotonically, even utilizing different machining processes.

关键词： Fatigue life GH4169 Grinding Milling Surface integrity

Suppression of Surface Burn in Grinding of Titanium Alloy TC4 Using a Self-inhaling Internal Cooling Wheel

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Chinese Journal of Aeronautics 2011年第1期24卷 96-101页

作者： li xun CHEN Zhitong CHEN Wuyi School of Mechanical Engineering and Automation Beijing University of Aeronautics and Astronautics Beijing 100191 China

Based on analysis of surface average temperature and burn degree, this article obtains the threshold temperature of surface burn in grinding titanium alloy with cup wheels. Meanwhile, the impact of the burn degree on the metallographic structure of workpiece surface and metallurgical phase transformations is investigated. In order to reduce the grinding temperature and improve the grinding efficiency, a self-inhaling structure cup segmented wheel is developed to generate internal cooling effect. The internal cooling technology is compared with traditional cooling conditions in the grinding experiments on TC4 （Ti-6Al-4V）. The results indicate that the self-inhaling internal cooling wheel can reduce the grinding surface temperature by 30% or more, and the grinding efficiency doubles. Utilizing water-based semi-synthetic coolant, the segmented wheel with the self-inhaling structure can further reduce the grinding temperature by about 50%.

关键词： grinding temperature measurement surface burn internal cooling self-inhaling

Design and experimental study of a micro-groove grinding wheel with spray cooling effect

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Chinese Journal of Aeronautics 2014年第2期27卷 407-412页

作者： Shi Chaofeng li xun Chen Zhitong School of Mechanical Engineering and Automation Beihang University China Precision Engineering Institute for Aircraft Industry

The effectiveness of grinding fluid supply has a crucial impact on grinding quality and efficiency in high speed grinding. In order to improve the cooling and lubrication, through in-depth research of self-inhaling internal cooling method and intermittent grinding mechanism, a new spray cooling method used in high speed grinding is proposed. By referring to the structure of bowl- shaped dispersion disk, the grinding wheel matrix with atomization ability is designed; through studying heat transfer of droplet collision and the influence of micro-groove on the boiling heat transfer, grinding segment with micro-groove is designed to enhance the heat flux of coolant and achieve maximum heat transfer between droplets and grinding contact zone. High-speed grinding experiments on GH4169 with the developed grinding wheel are carried out. The results show that with the micro-groove grinding wheel just 5.4% of pump outlet flow rate and 0.5% of spindle energy is needed to reduce the grinding temperature to 200℃, which means the developed grinding wheel makes cooling high efficient and low energy consuming.

关键词： Cooling Droplet Grinding Micro grooveSpray cooling

Boundedness and liveness enforcement for labeled Petri nets using transition priority

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Journal of Electronic Science and Technology 2023年第4期21卷 75-90页

作者： Ye-Jia liu xun-Bo li School of Mechanical and Electrical Engineering University of Electronic Science and Technology of ChinaChengdu611731China

This paper deals with the supervisory control problem of discrete event systems modeled by labeled Petri nets. The system is originally unbounded. First, the solvability of the problem is confirmed. A necessary condition is given and proven for the existence of a feasible priority-based controller based on the notions of liveness and transition invariants. Next, a cyclic behavior graph is constructed, which shows the reachable markings that guarantee the maximum liveness of the system within a given bound vector. Finally, an on-line control strategy is proposed to enforce boundedness and liveness to the given system by appending priority relations to transitions. The dynamic priority relation changes flexibly according to the current state of the system and enforces the system evolving in a bounded and live manner. In addition, numerical examples are studied to verify the validity of the proposed approach that remains the structure of the plant net and is efficient for on-line control.

关键词： Boundedness Control strategy liveness Petri nets Priority Transition invariant

Primitive to conventional geometry projection for efficient phonon transport calculations

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npj Computational Materials 2023年第1期9卷 365-371页

作者： xun li Simon Thébaud Lucas lindsay Materials Science and Technology Division Oak Ridge National LaboratoryOak RidgeTNUSA Univ Rennes INSA RennesCNRSInstitut FOTON-UMR 6082RennesFrance

The primitive Wigner-Seitz cell and corresponding first Brillouin zone(FBZ)are typically used in calculations of lattice vibrational and transport properties as they contain the smallest number of degrees of freedom and thus have the cheapest computational ***,in complex materials,the FBZ can take on irregular shapes where lattice symmetries are not ***,conventional cells(with more atoms and regular shapes)are often used to describe materials,though dynamical and transport calculations are more *** we discuss an efficient anharmonic lattice dynamic method that maps conventional cell dynamics to primitive cell dynamics based on translational *** symmetries have not been utilized in typical lattice dynamical *** leads to phase interference conditions that act like conserved quantum numbers and a conservation rule for phonon scattering that is hidden in conventional dynamics which significantly reduces the computational *** demonstrate this method for phonon transport in a variety of materials with inputs from first-principles calculations and attribute its efficiency to reduced scattering phase space and fewer summations in scattering matrix element calculations.

关键词： phonon conventional primitive