Intelligent Handoff for Mobile Wireless Internet

This paper presents an intelligent mobility management scheme for Mobile Wireless InterNet – MWIN. MWIN is a wireless service networks wherein its core network consisting of Internet routers and its access network can be built from any Internet-capable radio network. Two major standards are currently available for MWIN, i.e., the mobile IP and wireless LAN. Mobile IP solves address mobility problem with the Internet protocol while wireless LAN provides a wireless Internet access in the local area. However, both schemes solve problems independently at different layers, thereby some additional problems occur, e.g., delayed handoff, packet loss, and inefficient routing. This paper identifies these new problems and performs analyses and some real measurements on the handoff within MWIN. Then, a new handoff architecture that extends the features of both mobile IP and wireless LAN handoff mechanism was proposed. This new architecture consists of mobile IP extensions and a modified wireless LAN handoff algorithm. The effect of this enhancement provides a linkage between different layers for preventing packet loss and reducing handoff latency. Finally, some optimization issues regarding network planning and routing are addressed.     

Habitat fragmentation has interactive effects on the population genetic diversity and individual behaviour of a freshwater salmonid fish

Sufficient genetic diversity can aid populations to persist in dynamic and fragmented environments. Understanding which mechanisms regulate genetic diversity of riverine fish can therefore advance current conservation strategies. The aim of this study was to investigate how habitat fragmentation interacted with population genetic diversity and individual behaviour of freshwater fish in large river systems. We studied a population of the long‐distance migratory, iteroparous freshwater salmonid European grayling (Thymallus thymallus) in south‐eastern Norway. Genotyping (n = 527) and radio‐tracking (n = 54) of adult fish throughout a 169‐km river section revealed three major migration barriers limiting gene flow and depleting genetic diversity upstream. Individuals from upstream areas that had dispersed downstream of barriers showed different movement behaviour than local genotypes. No natal philopatry was found in a large unfragmented river section, in contrast to strong fidelity to spawning tributaries known for individuals overwintering in lakes. We conclude that (a) upstream sub‐populations in fragmented rivers show less genetic variation, making it less likely for them to adapt to environmental changes; (b) fish with distinct genotypes in the same habitat can differ in their behaviour; (c) spawning site selection (natal philopatry) can differ between fish of the same species living in different habitats. Together this implies that habitat loss and fragmentation may differently affect individual fish of the same species if they live in different types or sections of habitat. Studying behaviour and genetic diversity of fish can unravel their complex ecology and help minimize human impact.     

Phage‐mediated transfer of virulence genes

Bacteriophages as accessory genetic elements play a crucial role in the dissemination of genes and the promotion of genetic diversity within bacterial populations. Such horizontal transfer of DNA is critical in the emergence of new pathogenic organisms, through the dissemination of genes encoding virulence factors such as toxins, adhesins and agressins. Phages can transfer genes that are not necessary for bacteriophage persistence and are generally recognised by their ability to convert their host bacteria to new phenotypes. This phenomenon is known as phage conversion. If such converting genes encode for virulence factors, the consequences of phage infection may include increased virulence of the host bacteria, and the conversion of a non‐pathogenic strain to a potentially dangerous pathogen. A number of virulence factors in bacteria causing diseases in plants, animals and humans are encoded by converting phages, the vast majority of which are temperate as opposed to lytic in nature. © 2001 Society of Chemical Industry     

Modeling shallow marine carbonate depositional systems

Geological Process Models (GPMs) have been used in the past to simulate the distinctive stratigraphies formed in carbonate sediments, and to explore the interaction of controls that produce heterogeneity. Previous GPMs have only indirectly included the supersaturation of calcium carbonate in seawater, a key physicochemical control on carbonate production in reef and lagoon environments, by modifying production rates based on the distance from open marine sources. We here use the residence time of water in the lagoon and reef areas as a proxy for the supersaturation state of carbonate in a new process model, Carbonate GPM. Residence times in the model are calculated using a particle-tracking algorithm. Carbonate production is also controlled by water depth and wave power dissipation. Once deposited, sediment can be eroded, transported and re-deposited via both advective and diffusive processes. We show that using residence time as a control on production might explain the formation of non-ordered, three-dimensional carbonate stratigraphies by lateral shifts in the locus of carbonate deposition on timescales comparable to so-called 5th-order sea-level oscillations. We also show that representing supersaturation as a function of distance from open marine sources, as in previous models, cannot correctly predict the supersaturation distribution over a lagoon due to the intricacies of the flow regime.     

Quantification of margins and uncertainties: Example analyses from reactor safety and radioactive waste disposal involving the separation of aleatory and epistemic uncertainty

In 2001, the National Nuclear Security Administration (NNSA) of the U.S. Department of Energy (DOE) in conjunction with the national security laboratories (i.e., Los Alamos National Laboratory, Lawrence Livermore National Laboratory, and Sandia National Laboratories) initiated development of a process designated quantification of margins and uncertainties (QMU) for the use of risk assessment methodologies in the certification of the reliability and safety of the nation's nuclear weapons stockpile. A previous presentation, “Quantification of Margins and Uncertainties: Conceptual and Computational Basis,” describes the basic ideas that underlie QMU and illustrates these ideas with two notional examples. The basic ideas and challenges that underlie NNSA's mandate for QMU are present, and have been successfully addressed, in a number of past analyses for complex systems. To provide perspective on the implementation of a requirement for QMU in the analysis of a complex system, three past analyses are presented as examples: (i) the probabilistic risk assessment carried out for the Surry Nuclear Power Station as part of the U.S. Nuclear Regulatory Commission's (NRC's) reassessment of the risk from commercial nuclear power in the United States (i.e., the NUREG-1150 study), (ii) the performance assessment for the Waste Isolation Pilot Plant carried out by the DOE in support of a successful compliance certification application to the U.S. Environmental Agency, and (iii) the performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada, carried out by the DOE in support of a license application to the NRC. Each of the preceding analyses involved a detailed treatment of uncertainty and produced results used to establish compliance with specific numerical requirements on the performance of the system under study. As a result, these studies illustrate the determination of both margins and the uncertainty in margins in real analyses.     

Computer Systems Based on Silicon Photonic Interconnects

We present a computing microsystem that uniquely leverages the bandwidth, density, and latency advantages of silicon photonic interconnect to enable highly compact supercomputer-scale systems. We describe and justify single-node and multinode systems interconnected with wavelength-routed optical links, quantify their benefits vis-a-vis electrically connected systems, analyze the constituent optical component and system requirements, and provide an overview of the critical technologies needed to fulfill this system vision. This vision calls for more than a hundredfold reduction in energy to communicate an optical bit of information. We explore the power dissipation of a photonic link, suggest a roadmap to lower the energy-per-bit of silicon photonic interconnects, and identify the challenges that will be faced by device and circuit designers towards this goal.