Modified 802.11-Based Opportunistic Spectrum Access in Cognitive Radio Networks

Linbo Zhai,Xiaomin Zhang 한국전자통신연구원 2012 ETRI Journal Vol.34 No.2

In this letter, a modified 802.11-based opportunistic spectrum access is proposed for single-channel cognitive radio networks where primary users operate on a slot-by-slot basis. In our opportunistic spectrum access, control frames are used to reduce the slot-boundary impact and achieve channel reservation to improve throughput of secondary users. An absorbing Markov chain model is used to analyze the throughput of secondary users. Simulation results show that the analysis accurately predicts the saturation throughput.

A Fiber Spool’s Vibration Sensitivity Optimization Based on Orthogonal Experimental Design

Jing Gao,Linbo Zhang,Dongdong Jiao,Guanjun Xu,Xue Deng,Qi Zang,Honglei Yang,Ruifang Dong,Tao Liu,Shougang Zhang 한국광학회 2024 Current Optics and Photonics Vol.8 No.1

A fiber spool with ultra-low vibration sensitivity has been demonstrated for the ultra-narrowlinewidth fiber-stabilized laser by the multi-object orthogonal experimental design method, which can achieve the optimization object and analysis of influence levels without extensive computation. According to a test of 4 levels and 4 factors, an L 16 (4 4 ) orthogonal table is established to design orthogonal experiments. The vibration sensitivities along the axial and radial directions and the normalized sums of the vibration sensitivities are determined as single objects and comprehensive objects, respectively. We adopt the range analysis of object values to obtain the influence levels of the four design parameters on the single objects and the comprehensive object. The optimal parameter combinations are determined by both methods of comprehensive balance and evaluation. Based on the corresponding fractional frequency stability of ultra-narrow-linewidth fiber-stabilized lasers, we obtain the final optimal parameter combination A3B1C2D1, which can achieve the fiber spool with vibration sensitivities of 10 −12 /g magnitude. This work is the first time to use an orthogonal experimental design method to optimize the vibration sensitivities of fiber spools, providing an approach to design the fiber spool with ultra-low vibration sensitivity.

Loading-unloading model of contact between elastic-plastic ellipsoid and rigid plane

Jian Chen,Wangyang Zhang,Di Liu,Chenglong Wang,Linbo Zhu 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.8

The mechanical behaviour of the ellipsoidal asperity and rigid planes during loading and unloading are fundamental problems in contact mechanics. This study investigates the contact between elastic-perfectly plastic ellipsoidal asperity for different ellipticities and rigid planes under normal conditions during the loading and unloading process using the finite element method. The results show that the changing trend of the contact load, residual displacement, contact area, and plastic work with displacement under different ellipticities is similar, but the magnitude is different. The contact area during unloading is not always smaller than that during loading with the same displacement. Moreover, the initial unloading stage contact area is larger than that of the loading stage. Based on the numerical model calculation results, analytical dimensionless expressions are proposed for the residual displacement, plastic work, contact area, and contact load after fully unloading the ellipsoids with different ellipticities for a wide range of displacements. The prediction results from previous models are used to verify the effectiveness and correctness of the proposed equations. These empirical relations can be combined with statistical or fractal methods to study the contact behaviour of macroscopic rough surfaces.

A Numerical Investigation on Restrained High Strength Q460 Steel Beams Including Creep Eff ect

Wei-Yong Wang,Linbo Zhang,Pingzhao He 한국강구조학회 2018 International Journal of Steel Structures Vol.18 No.5

Most of previous studies on fi re resistance of restrained steel beams neglected creep eff ect due to lack of suitable creep model. This paper presents a fi nite element model (FEM) for accessing the fi re resistance of restrained high strength Q460 steel beams by taking high temperature Norton creep model of steel into consideration. The validation of the established model is verifi ed by comparing the axial force and defl ection of restrained beams obtained by fi nite element analysis with test results. In order to explore the creep eff ect on fi re response of restrained Q460 steel beams, the thermal axial force and defl ection of the beams are also analyzed excluding creep eff ect. Results from comparison infer that creep plays a crucial role in fi re response of restrained steel beam and neglecting the eff ect of creep may lead to unsafe design. A set of parametric studies are accomplished by using the calibrated FEM to evaluate the governed factors infl uencing fi re response of restrained Q460 steel beams. The parametric studies indicate that load level, rotational restraint stiff ness, span–depth ratio, heating rate and temperature distribution pattern are key factors in determining fi re resistance of restrained Q460 steel beam. A simplifi ed design approach to determine the moment capacity of restrained Q460 steel beams is proposed based on the parametric studies by considering creep eff ect.

An accurate solution of a hemisphere contact against a rigid flat under varying elastic moduli and yield strengths and comparison with previous model

Jian Chen,Wangyang Zhang,Chenglong Wang,Di Liu,Linbo Zhu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.9

The contact behavior of hemisphere pressed by a rigid flat is analyzed based on the finite element method under the condition of independent varying elastic moduli (E) and yield strengths (Y). The contact behavior is related to the ratio of E/Y. The mean contact pressure (p*) first increases and then decreases with the increasing interference, and this trend is more obvious for the contact of materials with the comparatively small ratio of E/Y. The end of the elastoplastic range or the inception of the fully plastic range is determined according to the interference corresponding to the peak value of the p*. The contact load and area in elastoplastic and fully plastic ranges are determined by the interference and the ratio of E/Y. Then, a new contact model to accurately predict the contact load and area for a wide range of E and Y is proposed, and compared with the previous models. The correctness of the current model is verified by the experimental measurement results recorded in previous literature.

Letters to the Editor : Evaluation of the Potential Association between NOS Gene Polymorphisms (iNOS G-954C and eNOS G894T) and Psoriasis

( Xi Duan ),( Yan Cheng ),( Linbo Gao ),( Lijuan Li ),( Tao Wang ),( Min Zhang ) 대한피부과학회 2016 Annals of Dermatology Vol.28 No.1

Adaptive Virtual Impedance of Grid-Tied Inverters to Enhance the Stability in a Weak Grid

Yan Du,Qingqing Sun,Xiangzhen Yang,Linbo Cui,Jian Zhang,Fei Wang 대한전기학회 2019 Journal of Electrical Engineering & Technology Vol.14 No.3

In a weak grid, especially with a grid-voltage proportional feedforward controller, the grid-tied inverter tends to interact with the grid impedance and thus suff ers from poor power quality and even instability. In order to improve the stability, serial-parallel virtual impedance based on the derivative controllers of grid current and voltage is proposed in this paper. With the aim of optimizing the performance of the inverter for a variety of grid impedance, these derivative coeffi cients are adaptively tuned by the constraint of a minimum leading phase which is determined by the phase margin and the current tracking response. With this proposed adaptive virtual impedance, the grid-tied inverter can operate stably under a wide variety of grid impedance and voltage harmonic rejection performance is also improved. Simulation and experimental results validate the eff ectiveness of the proposed method and design methodology.

Comparison of Acyrthosiphon pisum probing behaviors on different alfalfa cultivars

Yu Liangbin,Cui Jin,Wang Danyang,Zhang Quanyi,Xu Linbo 한국응용곤충학회 2023 Journal of Asia-Pacific Entomology Vol.26 No.1

Acyrthosiphon pisum (Harris) is a major pest of alfalfa worldwide. Here, we evaluated the resistance of eight alfalfa cultivars to A. pisum to identify resistant cultivars. The Giga-8 DC-EPG technique was used to record differences in electrical waveform patterns of probing behavior to identify cultivars with higher resistance. The frequency and average duration of EPG waveforms significantly differed among the cultivars, with eight docu mented waveforms (np, C, pd, E1, E2, sE2, F, and G). The longer duration of np, C, F and E1 waveforms reflected stronger resistance, whereas longer sE2 waveforms reflected weaker resistance. The resistance-related wave forms, np and C, occurred most frequently with Sardi 7, the time of the first E waveforms were the latest, duration of G waveforms and F waveforms were the longest, the feeding waveforms E2 and sE2 were the shortest, the time of reaching phloem for feeding was the latest, with notable resistance in leaf epidermis, mesophyll and phloem. The number of C waveforms occurring with Gibraltar were the least, duration of np waveforms was short, feeding waveforms were long, time to reach the phloem for feeding was early, and the resistance was not pronounced in various tissues. After comprehensive evaluation, the resistance levels of 8 alfalfa cultivars were as follows: High resistance, Sardi 7; Resistance, Zhongcao No. 3, Derby, WL319HQ; Low resistance, Golden Empress, Algonquin, Zhaodong; Susceptible, Gibraltar. In conclusion, evaluation of cultivar resistance to aphids can provide baseline data for selecting and planting cultivars with high local resistance

A Novel Self-Healing Polyurethane with High Transparency and Strength: Effects of Multiple Supermolecular Forces

Yuan Liu,Yanmei Liao,Yintao Long,Yuxiang Qian,Shengqiang Nie,Yi Wang,Jia Zeng,Chunmei Zhang,Linbo Tian,Jun Luo 한국고분자학회 2022 폴리머 Vol.46 No.3

It is a considerable challenge for expanding the applications of self-healing polyurethane because of the dilemma in balancing its mechanical and self-healing properties. Herein, a series of self-healing polyurethane systems (PUT-x) with short-range ordered rigid aromatic structures were synthesized by simply adjusting two kinds of diisocyanates, and by ingenious addition of aromatic chain extender. We hope to regulate the π-π interactions and further to manipulate the properties of obtained polyurethanes via adjusting the amount of the benzene rings in the molecular chains of the PUT-x systems. The PUT-5 with decent self-healing ability, optimal mechanical properties, acceptable thermal stability and favorable transparency was selected to incorporate liquid metal and fluorescent powder to fabricate conductive wire and anti-counterfeiting film. Significantly, the liquid metal could be recycled from the conductive wire conveniently without using strong acids or strong bases. Moreover, PUT-5 exemplarily withstood long-term soaking in normal saline, and no deformation could be identified.