Wireless LANs: From WarChalking to Open Access Networks

This work discusses the evolution of W-LANs from their current status of wireless termination of LAN services to a possible global infrastructure where the access networks become open to multiple operators and a vehicle of a win-win scenario, where both users and operators benefit from the new network architecture. The idea of Open Access Networks (OANs) can go beyond wireless HotSpots and be generalized to a generic shared access infrastructure that fosters service operators competition and drastically reduces the cost of last mile coverage.The general concept of Open Access Networks is detailed, highlighting its difference with the more traditional model of vertical integration of the access network into the global service. About the OANs development, it is shown how to support the quick and smooth evolution of the infrastructure toward a widespread and reliable communication support.Business models are discussed by mentioning the different actors, the market organization and the different organization forms.The final part of the paper is devoted to technical challenges such as access control, security, privacy, roaming, resource exploitation and service differentiation. As an example of how to tackle these problems, we discuss a pricing technique devoted to resource management and billing support.In addition we present a simulation on how the OAN concept can speed-up the deployment of broadband access in a real case.A preliminary version of this paper with the title “Global Growth of Open Access Networks: from WarChalking and Connection Sharing to Sustainable Business” was presented at WMASH 2003. Roberto Battiti received the Laurea degree from the University of Trento, Italy, in 1985 and the Ph.D. degree from the California Institute of Technology (Caltech), USA, in 1990. He has been a consultant in the area of parallel computing and pattern recognition and since 1991 he has been a faculty member at the University of Trento, where he is now full professor of Computer Networks. His main research interests are heuristic algorithms for optimization problems, in particular reactive search algorithms for maximum clique, maximum satisfiability, graph coloring, networks and massively parallel architectures, code assignment in wireless and cellular networks, protocols for pricing and Quality of Service in wireless networks.Prof. R. Battiti is currently Dean of the international Graduate School in Information and Communication Technologies at Trento, Deputy Dean at the Faculty of Science, member of the advisory committee for the future Telecommunications Plan of the Autonomous Province of Trento. Prof. R. Battiti is associate editor of various scientific journals. He is the author of more than fifty scientific publications, including special issues dedicated to experimental algorithmics and wireless on-demand networks.R. Battiti is a member of IEEE Computer Society and ACM Sigmobile. Renato Lo Cigno is Associate Professor at the Department of Computer Science and Telecommunications (DIT) of the University of Trento, Italy. He received a Dr. Ing. degree in Electronic Engineering from Politecnico di Torino in 1988. From 1989 to 2002 has been with the Telecommunication Research Group of the Electronics Department of Politecnico di Torino.From June 1998 to February 1999, he was at the CS Department at UCLA as Visiting Scholar under grant CNR 203.15.8. He is coauthor of more than 90 journal and conference papers in the area of communication networks and systems. His curent research interests are in performance evaluation of wired and wireless networks, modeling and simulation techniques, flow and congestion control, as well as network management and architecture. Renato Lo Cigno is member of the IEEE Communication Society and ACM Sigcomm. Mikalai Sabel received his master degree in radio physics from Belorussian State University in 2002. He is now pursuing his Ph.D. at the international Graduate School of Information and Communication Technologies at University of Trento, Italy. His research interest include wireless LANs, pricing and incentive engineering, IEEE802.11 MAC protocol. His current research is focused on optimization algorithms that can provide stability and maximum global welfare in a non-cooperative environment where singles tries to maximize their own benefit function. Experimentation of such schemes to pricing techniques and micro-payments in TLC networks provides the application environment of the fundamental research. Fredrik Orava is associate professor at KTH, Stockholm, Sweden. He conducts research into scalable (in terms of cost, capacity, number of users and devices etc.) communication system architectures and technologies. He has a MSc in engineering physics from Uppsala University and a PhD in computer systems also from Uppsala University. He previously held positions as researcher at the Swedish Institute for Computer Science (SICS); senior lecturer and manager of the telecommunications systems laboratory at the department for teleinformatics, KTH; acting professor in telecomunication systems at KTH; director for the Swedish Centre for Internet Technologies; and vice president of Dynarc AB with world wide responsibility for product management. Dynarc AB develops, manufactures and sells IP routers for optical IP networks. Bjorn Pehrson is a professor of telecommunication systems at KTH, the Royal Institute of Technology in Stockholm, since 1992, where he has also served as a department chairman and vice dean. He had his PhD from Uppsala University 1975 where he also served as senior lecturer and established a research group in computer and communication technology. During the period 1985-1992 he participated in the establishment of the Swedish Institute of Computer Science. Björn Pehrson research interests are currently focussed on open network topologies allowing different actors forming new value chains to build networks together based on different, sometimes very local business models. The results are applied in testbeds, especially in rural areas and in developing countries.This revised version was published online in August 2005 with a corrected cover date.     

NONLINEAR DIFFRACTION FORCES ON LARGE MULTICYLINDRICAL OFFSHORE STRUCTURES

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Coherent structures near the boundary between excitable and oscillatory media

We investigate reaction–diffusion systems near parameter values that mark the transition from an excitable to an oscillatory medium. We analyse the existence and stability of travelling waves near a steep pulse that arises as the limit of excitation pulses when parameters cross into the oscillatory regime. Travelling waves near this limiting profile are obtained by analysing a codimension-two homoclinic saddle-node/orbit-flip bifurcation. The main result shows that there are precisely two generic scenarios for such a transition, distinguished by the sign of an interaction coefficient between pulses. In both scenarios, we find stable fast fronts, unstable slow fronts, stable excitation pulses, and trigger and phase waves. Both trigger and phase waves are stable for repulsive interaction and both are unstable for attractive interaction.     

Dynamic impedance of pile and caisson foundations

Abstract

The dynamic impedance of a pile or caisson foundation embedded in a homogeneous visco elastic half‐space was evaluated using the hybrid method. The soil‐foundation system is partitioned into a near‐field and a far‐field by choosing a cylindrical interface passing through the soil region very close to the foundation. The near‐field is modeled by the finite element method while the far‐field is characterized by a frequency‐dependent impedance matrix through the continuum approach. From the results presented, it is shown that the proposed method is very effective and can be widely used for parameter studies in engineering applications.     

基于增秩Kalman滤波的移动车辆荷载在线识别

提出了一种基于增秩Kalman滤波(augmented Kalman filter,AKF)的移动车辆荷载在线识别方法.将车辆荷载向量与桥梁结构状态向量联立构成增秩状态向量,基于AKF算法,利用桥梁状态空间方程和少量振动响应获得增秩状态向量的无偏最小方差估计,进而实时识别车辆荷载.以简支梁-弹簧质量车桥耦合系统为数值分...     

试论北方游牧民族饮食文化的交流

一个民族或群体由于各自有较稳定的生存地域和生计方式，因而具有相对独立的饮食文化，这是其饮食文化的主要特征。事实上。每个民族或群体的饮食生活是动态的，反映在文化上是相互交流的。在不同民族、地域、国家之间的文化传播、渗透、吸收、整合、流变中，饮食文化不断发展变化，这在北方游牧民族的饮食文化中显得非常突出。主要表现在与中原地区、周边民族和西方国家的饮食文化交流状况。形成你中有我、我中有你的文化现象。     

Are disulphide bonds formed during acid gelation of preheated milk?

The role of thiol/disulphide exchanges during acid gelation of preheated milk was studied with milk samples with or without N‐ethylmaleimide (NEM), a thiol‐blocking agent, and acidified to pH 4 by the addition of glucono‐delta‐lactone at 20 °C. Active or total thiol groups, particle size with light scattering measurements in a dissociating solvent or by SDS‐agarose electrophoresis were determined on acidified milk samples. Diffusing wave spectroscopy and rheology in low strain were applied during acidification of sample, while rheology in large strain was applied on final acid gels. The only effect of the presence of NEM was a reduced firmness of acid gels as measured at large strain and a reduced tendency to form large aggregates at pH<5.5. In conclusions, thiol/disulphide exchanges during acidification of milk played only a minor role in the building of acid gel networks from heated milk.     

英语自主学习教学与实践论析

自主学习倡导以学生发展为本、培养学生自主获取知识和创新探究思维能力。目前为止,学界对自主学习理论尚存在多种阐释和理解,自主学习理论有待进一步得到实践的检验。基于计算机网络多媒体交互式新型大学英语教学模式为学生自主学习和英语语言教学双向互动提供了可行性。本文对自主学习理论进行了梳理,以大学英语教学资源和教学主体为研究对象,对高校大学英语开展自主学习可行性进行分析研究,提出大学英语开展自主学习的新思考。     

反胶束萃取大豆蛋白前萃过程的动力学研究

系统研究了影响总传质系数的各个主要因素(缓冲溶液pH、反胶束含水量W0、表面活性剂浓度、KCl浓度、振荡速度操作温度),探讨了以丁二酸二异辛酯磺酸钠(AOT)/异辛烷反胶束体系萃取大豆蛋白前萃过程的动力学。结果表明,大豆蛋白前萃过程中总传质系数随缓冲溶液pH和KCl浓度的升高先增大后减小,分别在pH7.0和KCl浓度0.1mol/L附近出现最大值;随W0和AOT浓度的增加而增大,当W0大于12时,总传质系数基本不变;随温度的变化总传质系数变化不大。由此可以推断出蛋白质的加溶过程,不仅与蛋白质分子和表面活性剂之间的静电相互作用力和疏水力有关,而且与界面阻力有关。