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Structure and Roles of the Various Layers in the Shells of Conch Conus litteratus

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Journal of Bionic Engineering 2016年第1期13卷 124-131页

作者： Xiaojuan Hong xiaoxiang wang College of Materials Science and Engineering Zhejiang University Hangzhou 310027 China

Mollusc shells are renowned for their mechanical strength and toughness. To better understand the mineralization process of the shell, structure of the body whorl and base of Conus litteratus （Conus shell） were in detail investigated by using scanning electron microscopy. Three-point bending tests were taken to demonstrate that each layer of crossed-lamellar structures is indispensable to enhance the whole strength of the shells. The results show that the conch shell is composed of hierarchical structure from nano scale to macro scale, and the basic constituent is long rod-shaped aragonite. Different positions of the shell have varied structures, and the base is more complicated than the body whorl. The mechanical properties of Conus are highly anisotropic and the arrangement of middle layer has a great influence on the bending strength. The outer and inner layers are very thin but play a protective role for the middle layer.

关键词： crossed-lamellar mechanical properties aragonite mollusc shell

Mobility-Aware Caching Strategy in an SDN-Based Cooperative Caching Network

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China Communications 2023年第9期20卷 196-214页

作者： Qi Li xiaoxiang wang Dongyu wang Information and Communication Engineering Beijing University of TechnologyBeijing 100124China Beijing University of Posts and Telecommunications Beijing 100876China

The upsurge of mobile multimedia traf-fic puts a heavy burden on the cellular network,and wireless caching has emerged as a powerful tech-nique to overcome the backhaul bottleneck and al-leviate the network ***,most previ-ous works ignored user mobility,thus not reaping the caching gain from user mobility and having lim-ited practical *** this paper,a mobility-aware caching strategy for the software-defined net-work(SDN)-based network is ***,since typical mobile user(MU)has multiple opportunities to connect with the nearby MUs and Small-base stations(SBSs),the contact times between MUs as well as be-tween MU and SBSs are derived as the Poisson distri-bution and Gamma ***,we propose a two-tier cooperative caching strategy,where SBSs cache the rateless Fountain code encoded video blocks probabilistically and nonrepeatedly while MUs just store the whole encoded video received last *** corresponding four-stage transmission process is ana-lyzed,where the key intermediate step is the deriva-tion of the service and the failing probabilities of each transmission ***,we derive the success-ful offloading rate and average data offloading ra-tio(ADOR)as performance metrics.A system op-timization problem based on ADOR is formulated,and two solutions are proposed,namely,derivativebased solution(DB-Solution)and long-tail distribution approximation(LTD-Approximation).Simulation results demonstrate that the effectiveness of LTDApproximation is similar to the DB-Solution,and the proposed caching strategy can achieve quasi-optimal performance compared with other contrast schemes.

关键词： wireless caching mobility SDN

Conformal minimal two-spheres in Q_n

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Science China Mathematics 2011年第4期54卷 817-830页

作者： JIAO xiaoxiang wang Jun School of Mathematics Graduate UniversityChinese Academy of SciencesBeijing 100049China

In this paper we study,using moving frames,conformal minimal two-spheres S2 immersed into a complex hyperquadric Qn equipped with the induced Fubini-Study metric from a complex projective n+1-space CPn+*** associated functions τX and τY are introduced to classify the problem into several *** is proved that τX or τY must be identically zero if f:S2 → Qn is a conformal minimal *** the Gaussian curvature K and the Khler angle θ are constant if the conformal immersion is totally *** is also shown that the conformal minimal immersion is totally geodesic holomorphic or antiholomorphic if K = *** the case K = 4,conformal minimal immersion f:S2 → Q2 with Gaussian curvature K2 must be totally geodesic with(K,θ) ∈ {(2,0),(2,π/2),(2,π)}.

关键词： complex hyperquadric Gaussian curvature Khler angle minimal immersion totally geodesic

Joint subcarrier and power allocation with threshold in cooperative multiuser networks

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High Technology Letters 2011年第4期17卷 360-365页

作者： Tang Mingwei wang xiaoxiang Key Laboratory of Universal Wireless Communications Ministry of Education Beijing University of Posts and Telecommunications Beijing 100876 P.R.China

In this paper, we investigate a resource allocation issue in OFDMA-based decode-and-forward cooperative multiuser networks and propose joint subcarrier and power allocation schemes. The optimal solution of this combinable allocation shows high computational complexity, so we allocate subcarriers and power separately. At firstly, we distribute subcarriers to relays and users under the assumption of equal power distribution. Here, we propose an equal capacity increment （ECI） allocation strategy to achieve tradeoff between total throughput and fairness. To further improve the system performance, we introduce threshold into ECI strategy, named ECI strategy with threshold （ECI-T）, where subcarriers with bad performance are prevented from transmitting. Subsequently, a water-filling method is adopted to distribute the power to cooperative links in order to fully utilize the limited power. Simulation results show that system performance of the proposed schemes is significantly enhanced compared with an existing resource allocation scheme. Besides, the resource allocation schemes with the water- filling method notably outperform schemes with equal power allocation.

关键词： cooperative communication orthogonal ~equency division multiplexing access (OFDMA) resource allocation threshold

Performance analysis of opportunistic amplify-and-forward two-way relaying in two-wave with diffuse power fading channels

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The Journal of China Universities of Posts and Telecommunications 2015年第2期22卷 7-14页

作者： Zhou Jia wang xiaoxiang Qi Yanyan Key Laboratory of Universal Wireless Communications Beijing University of Posts and Telecommunications

This paper considers cooperative amplify-and-forwards （AF） two-way relay networks （TWRNs） with opportunistic relay selection （ORS） in two-wave with diffuse power （TWDP） fading channels. To investigate the system performance, we first derive an easy-to-computer approximated expression for the exact outage probability to reduce computational cost. Furthermore, we presented compact expressions for the asymptotic outage probability and asymptotic symbol error rate, which characterizes two factors goveming the network performance at high signal-to-noise ratio （SNR） in terms of diversity order and coding gain. Additionally, based on the asymptotic outage probability, we determine the optimal power allocation solution between the relay and the sources to minimize the overall outage probability under the assumption that both the sources have identical transmit power. The correctness of the analysis is validated through Monte Carlo simulations. Our derived results can be applied to general operating scenarios with distinct TWDP fading parameters which encompass Rayleigh and Rician fading as special cases and arbitrary number of relays.

关键词： two-way relay opportunistic relay TWDP TWDP AF

Online Learning-Based Offloading Decision and Resource Allocation in Mobile Edge Computing-Enabled Satellite-Terrestrial Networks

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China Communications 2024年第3期21卷 230-246页

作者： Tong Minglei Li Song Han Wanjiang wang xiaoxiang School of Information and Communication Engineering Beijing University of Posts and TelecommunicationsBeijing 100876China Key Laboratory of Universal Wireless Communications Ministry of EducationBeijing University of Posts and TelecommunicationsBeijing 100876China School of Information and Control Engineering China University of Mining and TechnologyXuzhou 221116China School of Computer Science(National Pilot Software Engineering School) Beijing University of Posts and TelecommunicationsBeijing 100876China

Mobile edge computing(MEC)-enabled satellite-terrestrial networks(STNs)can provide Internet of Things(IoT)devices with global computing ***,the network state information is uncertain or *** deal with this situation,we investigate online learning-based offloading decision and resource allocation in MEC-enabled STNs in this *** problem of minimizing the average sum task completion delay of all IoT devices over all time periods is *** decompose this optimization problem into a task offloading decision problem and a computing resource allocation problem.A joint optimization scheme of offloading decision and resource allocation is then proposed,which consists of a task offloading decision algorithm based on the devices cooperation aided upper confidence bound(UCB)algorithm and a computing resource allocation algorithm based on the Lagrange multiplier *** results validate that the proposed scheme performs better than other baseline schemes.

关键词： computing resource allocation mobile edge computing satellite-terrestrial networks task offloading decision

New insights into the relationships between performance and physicochemical properties of FeO_(x)-NbO_(x)mixed oxide catalysts for the NH_(3)-SCR reactions

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Waste Disposal and Sustainable Energy 2021年第2期3卷 97-106页

作者： Dong Ye xiaoxiang wang Hui Liu Haining wang College of Quality and Safety Engineering China Jiliang UniversityHangzhou 310018China Key Laboratory of Biomass Chemical Engineering of Ministry of Education Institute of Industrial Ecology and EnvironmentCollege of Chemical and Biological EngineeringZhejiang UniversityHangzhou 310027China

In this study,we prepared Fe_(2)O_(3)-Nb_(2)O_(5)binary mixed oxide catalysts using co-precipitation(CP),sol-gel(SG),and solid process(SR)methods and tested their *** the catalysts exhibited over 75%NO_(x)removal efficiency between 250℃and 400℃.Compared with the samples prepared by the SR method,catalyst synthesized using CP and SG methods possessed a larger specific surface area,which could compensate for the lower surface area-normalized reaction rate originat-ing from the insufficient reactive surface oxygen species,hence exhibiting a relatively high low-temperature apparent deNO_(x)***,at a high-temperature region,limited amount of reactive surface oxygen species,together with abundant strong acid sites,facilitated the proceeding of NH_(3)reduction of NO_(x),which well explained the higher apparent activity of the catalyst prepared by SG method than the other two *** seemed that specific surface area had an important role to play in the low-temperature apparent performance of the catalysts,while chemical properties mainly decided the activity at an elevated temperature.

关键词： Selective Catalytic Reduction Fe_(2)O_(3)-Nb_(2)O_(5) Surface area Preparation methods Chemical properties

Excellent thermal shock resistance of NiCrAlY coatings on copper substrate via laser cladding

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Journal of Materials Science & Technology 2022年第35期130卷 93-102页

作者： Mingyu Gao Shunchao Li Weimian Guan Hongbin Xie xiaoxiang wang Jiabin Liu Hongtao wang State Key Laboratory of Silicon Materials School of Materials Science and EngineeringZhejiang UniversityHangzhou 310027China Center for X-mechanics School of Aeronautics and AstronauticsZhejiang UniversityHangzhou 310027China

Coatings are widely used to protect substrates in extreme thermal environments(e.g., arc heaters), and thermal shock resistance is a crucial parameter for the coatings, which requires tight interlayer bonding between coatings and substrates. In this work, Ni Cr Al Y coatings were highly required for the pure copper substrate to restrict the electric arc in arc heaters. To overcome the bonding difculty of coating on the copper surface, the Ni Cr Al Y coatings were prepared by two laser cladding methods: conventional laser cladding(CLC) and high-speed laser cladding(HSLC). The microstructure, composition, and thermal shock resistance of Ni Cr Al Y cladding layers prepared by both methods were investigated. Benefitting from the high cooling rate and high energy density, the HSLC-layer has better composition uniformity and tighter interlayer bonding than the CLC-layer, achieving a 30%–45% improvement in thermal cycling lifetime. Besides, the Ni Cr Al Y layers prepared on copper substrate by both laser cladding methods exhibit3–10 times better thermal shock resistance than those Ni Cr Al Y layers prepared by conventional spraying methods. It further confirms the great effects of metallurgical bonding and composition uniformity on the thermal shock resistance of coatings. The Ni Cr Al Y layers fail in the form of internal cracking and interface peeling, and the corresponding failure mechanism is discussed.

关键词： Laser cladding NiCrAlY Thermal shock resistance Microstructure

Mechanistic investigation on the Hg^(0)elimination ability of MnO_(x)-CeO_(x)nanorod adsorbents:effects of Mn/Ce molar ratio

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Waste Disposal and Sustainable Energy 2024年第2期6卷 185-196页

作者： Shujie Gao xiaoxiang wang Yaolin wang Kai Zhu Changxing Hu Dong Ye College of Quality and Safety Engineering China Jiliang UniversityHangzhou 310018China Key Laboratory of Biomass Chemical Engineering of Ministry of Education Institute of Industrial Ecology and EnvironmentCollege of Chemical and Biological EngineeringZhejiang UniversityHangzhou 310027China Department of Electrical Engineering and Electronics University of LiverpoolLiverpool L693GJUK Ningbo Tech University No.1 Qianhu South RoadNingbo 315100China

Mercury pollution is created by coal combustion processes in multi-component *** injection was identified as a potential strategy for capturing Hg^(0)from waste gases,with adsorbents serving as the primary *** hydro-thermal approach was used to synthesize a series of MnO_(x)-CeO_(x)nanorod adsorbents with varying Mn/Ce molar ratios to maximize the Hg^(0)capture *** CeO,had weak Hg elimination activity;<8%Hg^(0)removal efficiency was obtained from 150℃to 250℃.With the addition of MnOr,the amount of surface acid sites and the relative concentration of Mn4+*** ensured the sufficient adsorption and oxidation of Hg while overcoming the limitations of restricted adsorbate-adsorbent interactions caused by the lower surface area,endowing MnO_(x)-CeO_(x)with increased Hg^(0)removal *** the molar ratio of Mn/Ce reached 6/4,the adsorbent's Hg^(0)removal efficiency remained over 92%at 150℃and 200℃.As the molar ratio of Mn/Ce grew,the adsorbent's Hg^(0)elimination capacity declined due to decreased surface area,weakened acidity,and decreased activity of Mn^(4+);<75%Hg^(0)removal efficiency was reached between 150℃and 250℃for virgin *** the overall Hg'elimination reactions,Mn4+and *** in charge of oxidizing Hg^(0)to Hg^(0),with Ce^(4+)acting as a promoter to aid in the regeneration of Mn^(4+),Because of its limited adaptability to flue gas components,further optimization of the MnO_(x)-CeO_(x)nanorod adsorbent is required.

关键词： Hg^(0)capture MnO_(x)-CeO_(x)nanorods Mn/Ce molar ratio Acid properties Redox behaviors