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Non-saturated throughput analysis of IEEE 802.11-based cognitive radio networks

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The Journal of China universities of Posts and Telecommunications 2012年第6期19卷 6-13页

作者： ZHAO Yuan JIN Shun-fu TIAN Nai-shuo College of Information Science and Engineering Yanshan University College of Science Yanshan University

Technology of cognitive radio networks has emerged as an effective method to enhance the utilization of the radio spectrum where the primary users have priority to use the spectrum, and the secondary users try to exploit the spectrum unoccupied by the primary users. In this paper, considering the non-saturated condition, the performance analysis for the IEEE 802.11-based cognitive radio networks is presented with single-channel and multi-channel, respectively. For the single-channel case, an absorbing Markov chain model describing the system transitions is constructed, and one-step transition probability matrix of the Markov chain is given. By using the method of probability generating function, the non-saturated throughput of the secondary users is obtained. For the multi-channel case, taking into account the negotiation-based sensing policy, the mean number of unused channels perceived by the second users is given, and then the non-saturated aggregate throughput of the secondary users is derived. Finally, numerical examples are provided to show the influences of the non-saturated degree, the number of the secondary users and the channel utilization of the primary users on the performance measures for the non-saturated throughput with single-channel and the non-saturated aggregate throughput with multi-channel.

关键词： cognitive radio networks IEEE 802.11 non-saturated throughput absorbing Markov chain probability generating function

Effects of mischmetal addition on phase transformation and as-cast microstructure characteristics of M2 high-speed steel

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Journal of Rare Earths 2013年第6期31卷 628-633页

作者：曲明贵王振华李慧吕知清孙淑华傅万堂 State Key Laboratory of Metastable Materials Science and Technology College of Materials Science and EngineeringYanshan University College of Mechanical Engineering Yanshan University College of Sciences Yanshan University

The influence of mischmetal （Ce-La） addition on phase transformation and as-cast microstructure characteristics of M2 high-speed steel （HSS） was investigated using Thermo-Calc software, differential scanning calorimetry, X-ray diffractometry and scanning electron microscopy with energy dispersive spectrometry. The results showed that the measured phase transition points of M2 HSS were broadly consistent with the theoretical results. After mischmetal addition, the liquidus peak temperature, the peak temperature of the eutectic precipitation of M6C and MC were all increased, especially for the M6C which was affected significantly and increased about 31 °C. The contents of Mo and V in the eutectic carbide decreased and that of Fe increased, while in the matrix, the Mo, V and Cr contents all increased slightly. Furthermore, the microstructure of as-cast dendrite and ledeburite were refined, the total eutectic carbide content decreased and distributed into a discontinuous network, the lamellar spacing of M2C was reduced and the lamellae became thinner.

关键词： M2 high-speed steel mischmetal phase transformation as-cast microstructure carbide rare earths

Performance Analyses of Production Inventory Systems Considering Service Time and Product Returns of Online Shopping

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Journal of Systems Science & Complexity 2019年第3期32卷 888-906页

作者： QIN Yaling YUE Dequan School of Economics and Management Yanshan University Qinhuangdao 066004 China LiRen College Yanshan University Qinhuangdao 066004 China College of Science Yanshan University Qinhuangdao 066004 China

This paper considers a production inventory system with service time and product returns, dependent on the characteristics of online shopping beliaviors. The customers arrive according to a Poisson process, in which the arriving customer requires an item in the inventory, as well as a server service that the service time is exponentially distributed. Moreover, there is one production facility to produce items according to (s, S) policy, and the production time also follows an exponential (listribution. In the beginning, the stationary joint distribution is obtained in the product form for the queue length and the on-hand inventory level. Additionally, the resulting distribution is applied to derive some performance measures, which can be adopted to numerically calculate the optimal (s, S) policy. Finally, numerical analyses are processed to investigate the effects of some system parameters on the performance measures. The numerical results clearly indicate that the product return rate has a significantly monotonic effect on the optimal policy and optimal cost.

关键词： Online shopping production inventory return service time (s, S) policy

Shape Discrimination Analysis of Rolled Strip Based on Strip Element Method

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Journal of Iron and Steel Research International 2004年第1期11卷 29-32页

作者： PENG Yan CHU Yu-peng LIU Hong-min yanshan university

Based on load-oriented manufacturing control theory, different combining modes and slab storage calculation method for continuous casting and hot rolling were discussed. The buffer capacity index of continuous casting-rolling was introduced, and the reasonable slab storage under different combining modes was calculated with buffer capacity index of 120.00 h for CCR, 79.20 h for HCR, 19.68 h for DHCR and 3.84 h for DR. Thin slab is 1.20 h, and the strip is zero. Theory gist was provided for steel enterprise to decrease storage.

关键词： continuous casting hot rolling production control slab storage

THE M/M/1 QUEUE WITH WORKING VACATIONS AND VACATION INTERRUPTIONS

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Journal of Systems Science and Systems Engineering 2007年第1期16卷 121-127页

作者： Jihong LI Naishuo TIAN College of Economics and Management Yanshan University College of Sciences Yanshan University Qinhuangdao Hebei 066004 China

In this paper, we study the M/M/1 queue with working vacations and vacation interruptions. The working vacation is introduced recently, during which the server can still provide service on the original ongoing work at a lower rate. Meanwhile, we introduce a new policy：, the server can come back from the vacation to the normal working level once some indices of the system, such as the number of customers, achieve a certain value in the vacation period. The server may come back from the vacation without completing the vacation. Such policy is called vacation interruption. We connect the above mentioned two policies and assume that if there are customers in the system after a service completion during the vacation period, the server will come back to the normal working level. In terms of the quasi birth and death process and matrix-geometric solution method, we obtain the distributions and the stochastic decomposition structures for the number of customers and the waiting time and provide some indices of systems.

关键词： Working vacation vacation interruption matrix-geometric solution stochastic decomposition

Effect of disorders on topological phases in one-dimensional optical superlattices

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Chinese Physics B 2016年第7期25卷 382-386页

作者：王志宙吴一东杜会静井西利 School of Science Yanshan University

In a recent paper, Lang et al. proposed that edge states and topological phases can be observed in one-dimensional optical superlattices. They showed that the topological phases can be revealed by observing the density profile of a trapped fermion system, which displays plateaus with their positions. However, disorders are not considered in their model. To study the effect of disorders on the topological phases, we introduce random potentials to the model for optical *** calculations show that edge states are robust against the disorders. We find the edge states are very sensitive to the number of the sites in the optical superlattice and we propose a simple rule to describe the relationship between the edge states and the number of sites. The density plateaus are also robust against weak disorders provided that the average density is calculated over a long interval. The widths of the plateaus are proportional to the widths of the bulk energy gaps when there are disorders. The disorders can diminish the bulk energy gaps. So the widths of the plateaus decrease with the increase of disorders and the density plateaus disappear when disorders are too strong. The results in our paper can be used to guide the experimental detection of topological phases in one-dimensional systems.

关键词： edge state topological phase optical superlattices

Fast Smallest Lowest Common Ancestor Computation Based on Stable Match

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Journal of Computer Science & Technology 2013年第2期28卷 366-381页

作者：周军锋蓝国翔陈子阳汤显 School of Information Science and Engineering Yanshan University Key Laboratory for Computer Virtual Technology and System Integration of Hebei Province Yanshan University School of Economics and Management Yanshan University

In this paper, we focus on efficient processing of XML keyword queries based on smallest lowest common ancestor （SLCA） semantics. For a given query Q with m keywords, we propose to use stable matches as the basis for SLCA computation, where each stable match M consists of m nodes that belong to the m distinct keyword inverted lists of Q. M satisfies that no other lowest common ancestor （LCA） node of Q can be found to be located after the first node of M and be a descendant of the LCA of M, based on which the operation of locating a stable match can skip more useless nodes. We propose two stable match based algorithms for SLCA computation, i.e., BSLCA and HSLCA. BSLCA processes two keyword inverted lists each time from the shortest to the longest, while HSLCA processes all keyword inverted lists in a holistic way to avoid the problem of redundant computation invoked by BSLCA. Our extensive experimental results verify the performance advantages of our methods according to various evaluation metrics.

关键词： XML keyword search smallest lowest common ancestor

Nonlinear Dynamics of Torsional Vibration for Rolling Mill′s Main Drive System Under Parametric Excitation

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Journal of Iron and Steel Research International 2013年第1期20卷 7-12页

作者： SHI Pei-ming LI Ji-zhao JIANG Jin-shui LIU Bin HAN Dong-ying College of Electrical Engineering Yanshan University College of Vehicles and Energy Yanshan University

The jointed shaft in the drivelines of the rolling mill, with its angle continuously varying in the production, has obvious impact on the stability of the main drive system. Considering the effect caused by the joint angle and friction force of roller gap, the nonlinear vibration model of the main drive system which contains parametric excitation stiffness and nonlinear friction damping was established. The amplitude-frequency characteristic equation and bifurcation response equation were obtained by using the method of multiple scales. Depending on the bifurcation response equation, the transition set and the topology structure of bifurcation curve of the system were obtained by using the singularity theory. The transition set can separate the system into seven areas, which has different bifurcation forms respectively. By taking the 1 780 rolling mill of Chengde Steel Co for example, the simulation and analysis were performed. The amplitude-frequency curves under different joint angles, damping coefficients, and nonlinear stiffness were given. The variations of these parameters have strong influences on the stability of electromechanical resonances and the characteristic of the response curves. The best angle of the jointed shaft is 4.761 3° in this rolling mill.

关键词： rolling mill main drive system torsional vibration parametric excitation joint angle singularity

A DISCRETE-TIME Geo/G/1 RETRIAL QUEUE WITH J-VACATION POLICY AND GENERAL RETRIAL TIMES

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Journal of Systems Science & Complexity 2013年第4期26卷 556-571页

作者： YUE Dequan ZHANG Feng College of Science Yanshan University College of Economics and Management Yanshan University College of Science North University of China

The authors discuss a discrete-time Geo/G/1 retrial queue with J-vacation policy and general retrial *** soon as the orbit is empty,the server takes a ***,the server is allowed to take a maximum number J of vacations,if the system remains empty after the end of a *** there is at least one customer in the orbit at the end of a vacation,the server begins to serve the new arrivals or the arriving customers from the *** this model,the authors focus on the steady-state analysis for the considered queueing ***,the authors obtain the generating functions of the number of customers in the orbit and in the ***,the authors obtain the closed-form expressions of some performance measures of the system and also give a stochastic decomposition result for the system ***,the relationship between this discrete-time model and the corresponding continuous-time model is also ***,some numerical results are provided.

关键词： Discrete-time generating function J-vacation policy Markov chain retrial queue.