无线网络中的扩频传输和微蜂房结构技术

计算机无线局域网是计算机网络技术与现代通讯技术相结合的产物，如同移动电话一样，它可使计算机与网络的通信变得非常灵活和方便。支持无线局域网的关键技术是扩频传输技术和微蜂房技术。     

Ground-penetrating radar as a tool to detect rock heterogeneities (channels, cemented layers and fractures) in the Luxembourg Sandstone Formation (Grand-Duchy of Luxembourg)

A combined study of radar profiles and thin section analysis supported by modelling of synthetic radar traces reveals that ground-penetrating radar (GPR) reflections generated in diagenetically altered sandstones cannot always be interpreted unequivocally. This is illustrated in the Luxembourg Sandstone Formation, which has been altered diagenetically by selective carbonate cementation and fracturing. Cemented lenses and concretions developed along the bedding planes, especially at places with high primary carbonate content. Cementation resulted in the alternation of cemented carbonate-rich sandy layers (thickness 30–50 cm and variable length) and uncemented carbonate-poor sandstone layers. The ability of GPR to detect the geometry of these lenses and vertical fractures with centimetre apertures has been tested at several antenna frequencies (100, 200, 250 and 500 MHz). Relative dielectric permittivity calculations were carried out to assess variations of this electric property within the cemented and uncemented layers as a function of porosity, calcite and water content in the pores. Two-dimensional full waveform modelling was also carried out to study the effect of conductivity in the sandstones and the effect of interlayer clay seams. At the penetration depth of the radar (7 m with 250 MHz), cemented lenses and concretions could only be detected with GPR when the porosity contrast was sufficiently high, which is not always the case. This conclusion is supported by the modelling. The data also proved the ability of radar to detect large open vertical fractures along which sandstones are weathered. The study has implications for investigations which will use GPR to detect three-dimensional distribution of diagenetic pore filling precipitates as well as secondary porosity development along fractures.     

Complexity in a cellular model of river avulsion

We propose a new model of river avulsion that emphasizes simplicity, self-organization, and unprogrammed behavior rather than detailed simulation. The model runs on a fixed cellular grid and tracks two elevations in each cell, a high elevation representing the channel (levee) top and a low one representing the channel bottom. The channel aggrades in place until a superelevation threshold for avulsion is met. After an avulsion is triggered a new flow path is selected by steepest descent based on the low values of elevation. Flow path depends sensitively on floodplain topography, particularly the presence of former abandoned channels. Several behavioral characteristics emerge consistently from this simple model: (1) a tendency of the active flow to switch among a small number of channel paths, which we term the active channel set, over extended periods, leading to clustering and formation of multistory sand bodies in the resulting deposits; (2) a tendency for avulsed channels to return to their previous paths, so that new channel length tends to be generated in relatively short segments; and (3) avulsion-related sediment storage and release, leading to pulsed sediment output even for constant input. Each of these behaviors is consistent with observations from depositional river systems. A single-valued threshold produces a wide variety of avulsion sizes and styles. Larger “nodal” avulsions are rarer because pre-existing floodplain topography acts to steer flow back to the active channel. Channel stacking pattern is very sensitive to floodplain deposition. This work highlights the need to develop models of floodplain evolution at large time and space scales to complement the improving models of river channel evolution.     

The politics of design: architecture, tall buildings and the skyline of central London

After 2000 a handful of very tall buildings were approved in central London, a circumstance that challenged well-established planning practices in that part of the city. Their promotion by Ken Livingstone, the mayor, but opposition to them by conservation groups, seemed to signal a fierce campaign ahead; in fact, it was all over in an instant. This article examines how this debate was framed to dismiss the arguments and concerns of those who oppose tall buildings. To make tall buildings acceptable, London's mayor drew on the merits associated with iconic architecture and high-profile architects. Under Livingstone's incumbency tall buildings were affirmed by the expertise and clout of global architects who provided legitimacy for mayoral ambitions to reach for the sky. Stressing the significance of high-quality design and iconic architecture helped to wear down deep-rooted antagonism and to channel the debate to improving the aesthetic qualities of London, a goal that enjoys wide consensus.     

Stratigraphic Dip Analysis – A Novel Application for Detailed Geological Modeling of Point Bars,and Predicting Bitumen Grade,McMurray Formation,Muskeg River Mine,Northeast Alberta

At the Muskeg River Mine, bitumen is hosted in the clastic sediments of the lower Cretaceous McMurray Formation. Within the mine area, the McMurray Formation is divided informally into mappable units representing fluvial, continental floodplain, open estuarine, estuarine channel complex (ECC), and marine environments. Fluvial, open estuarine, and ECC deposits host more than 90% of the mineable bitumen reserves. Bitumen grade is more consistent within the fluvial and open estuarine units (12–15 mass%), whereas ECC sediments are characterized by significant lateral and vertical grade variability (0–15 mass%). In the ECC deposits, bitumen grade is controlled by significant reservoir heterogeneity. Facies assemblages including point-bar deposits (PB), abandoned channel-fills (AC), and tidal flat deposits (TF), create complex internal geometries, architectures and associated reservoir properties. Traditional facies mapping and correlation has proven to be difficult even in closely spaced wells for the ECC deposits of the McMurray Formation; thus, an alternative technique using concepts of Stratigraphic Dip Analysis (SDA) was developed to assess bitumen grade for the deposits at the Muskeg River Mine. This approach involves three main steps: (l) juxtaposing azimuth maps (rose diagrams) over horizon slice facies maps for selected stratigraphic intervals to identify major channel trends (paleo-current directions); (2) comparison of dips, with corresponding sedimentary structures allows for a better prediction and geometries of point bars and abandoned channel-fills; and (3) comparison of dip trends with dominant lithology of facies assemblages and available bitumen grades provides a base for accurate delineation of architectural elements. A detailed case study is presented and shows that this approach provides a base for accurate delineation of architectural elements and confirms that bitumen grade decreases laterally with inferred maturity of point bar successions.     

构造断阶对沉积的控制:来自地震、测井和露头的实例

构造断阶是裂谷盆地(特别是裂谷盆地发育早期)或断陷盆地边缘发育的一种构造样式,反映盆地边缘因断块差异沉降所形成的沉积斜坡地形的阶梯变化。在地震剖面可以解释出许多不同类型的断阶带,并在此框架下根据地震反射结构解释地震相和沉积相。构造断阶带的不同类型控制了不同的沉积样式。构造断阶的识别约束了地震解释的多解性。测井资料的运用可以证实断阶带的沉积控制作用,约束地震解释,也可以进行沉积微相及空间分布的精细研究.地震、测井的实例分别来自松辽盆地徐家围子断陷和渤海湾盆地沾化凹陷。来自胶莱盆地野外露头的实例从另一方面证实了这种控制作用。与钻井或测井资料相比,露头资料具有连续性。露头的详细分析可得到构造断阶对沉积和地层结构控制的细节。构造断阶(带)与沉积作用关系的模式可以提供油气勘探的地质模型。     

Thirteen plus one: a comparison of global climate policy architectures

We critically review the Kyoto Protocol and thirteen alternative policy architectures for addressing the threat of global climate change. We employ six criteria to evaluate the policy proposals: environmental outcome, dynamic efficiency, cost-effectiveness, equity, flexibility in the presence of new information, and incentives for participation and compliance. The Kyoto Protocol does not fare well on a number of criteria, but none of the alternative proposals fare well along all six dimensions. We identify several major themes among the alternative proposals: Kyoto is “too little, too fast”; developing countries (DCs) should play a more substantial role and receive incentives to participate; implementation should focus on market-based approaches, especially those with price mechanisms; and participation and compliance incentives are inadequately addressed by most proposals. Our investigation reveals tensions among several of the evaluative criteria, such as between environmental outcome and efficiency, and between cost-effectiveness and incentives for participation and compliance.     

Polyvocalism and the public: 'doing' a critical historical geography of architecture

Loretta Lees' recent call for a 'critical geography of architecture' argued that a more nuanced and truly interpretative methodology for analysing the relationship between space, place and architecture would involve active engagement with such architectural spaces. This paper argues that, in the same way, by broadening our approach to historical architectural geographies more meaningful interpretations will result. Utilizing a 'polyvocal' methodological approach, by which not only architects and planners but also residents of these spaces are considered as important actors, will facilitate this 'critical' engagement with architectural spaces. Further, by taking this polyvocal approach, interesting conclusions can be reached about the production, consumption and re-production of space, both in the past and also in the present.     

空间物流信息系统体系结构研究

信息技术尤其是以 GIS、GPS等为代表的空间信息技术的发展 ,对物流管理产生了重大的影响 ,空间物流信息系统已经成为一个新的研究热点。本文着重介绍了空间信息系统的体系结构 ,在此基础上 ,对空间物流信息系统的总体框架、集成平台设计等进行了研究和探讨 ,最后提出了基于 CORBA的空间物流信息系统的平台结构设计框架