Real-time payments for mobile IP

The mobile IP protocol has evolved from providing mobility support for portable computers to support for wireless handheld devices with high mobility patterns. A new category of micromobility protocols has been proposed to deal with the increased signaling loads that will be generated with large populations of such devices on a network. We argue that the authentication schemes presently employed in these networks do not scale well for large numbers of nodes, and that the lack of accounting procedures prevents the mass deployment of these networks. We envisage that future access networks will be operated by independent service providers, who will charge users for access to services in the fixed network but may not have long-term contractual relationships with them. These access networks may also employ a variety of micromobility protocols for fast handover support. We present a scheme based on hash chains, which allows for fast authentication of datagrams for secure updating of router entries within the access network, and real-time accounting of network usage by mobile nodes. Such a system will alleviate problems of fraud in mobile networks and eliminate the need for interoperator billing agreements.     

Active surveillance of health and safety in microbiology laboratories

In microbiology laboratories highly infectious material is handled alongside complex and potentially dangerous equipment, and staff are therefore at risk of infections and accidents. Acts of parliament and regulations exist to protect staff in the workplace, including those exposed to biological agents. The current monitoring of health and safety in laboratories seeks to ensure that employers and employees comply with existing regulations, but this form of passive surveillance is of limited value because it does not highlight shortcomings in techniques, equipment, premises, or personnel. We propose a scheme for the surveillance of health and safety in microbiology laboratories that will actively seek information about laboratory incidents and practices, in order to enable appropriate preventive measures to be instituted.     

Utility of ischemic scores in the differential diagnosis of Alzheimer's disease and ischemic vascular dementia

Despite new developments in the concept of vascular dementia, the Hachinski Ischemic Score (HIS) and its modified versions continue to be widely used in the clinical differentiation of Alzheimer's disease (AD) and ischemic vascular dementia (IVD). The sensitivity of the HIS and two modified versions in the diagnosis of AD, IVD, and single infarcts in a large, geriatric population with mild cognitive impairment (N = 100) was evaluated. Sensitivity for identification of AD was greater than 90% but was less than 70% for IVD. Over one third of patients with one or more infarcts on computed tomographic brain scans and 63% of mixed cases were classified as having probable AD. It is concluded that ischemic scores may be useful at predicting prevalence rates if individual case accuracy is ignored. Despite being sensitive to identifying AD, ischemic scores are insensitive to both cerebral infarction and IVD and cannot reliably exclude IVD. Finally, patients with mixed dementia should not be expected to have intermediate scores.     

Assessment of oxygen levels in convenience‐style muscle‐based sous vide products through optical means and impact on shelf‐life stability

An optical oxygen analyser was used in two small‐scale industrial trials to non‐destructively assess the quality of packaged convenience foods and packaging process. Beef lasagne packed under 70% vacuum and cooked under standard sous vide conditions was monitored for residual oxygen, using disposable sensors incorporated in each pack and a benchtop optical oxygen analyser. High levels of residual oxygen close to ambient were determined in the majority of packs after packaging, as opposed to anticipated levels of 4–5%. Residual oxygen was monitored over product shelf‐life (4 weeks at +4–10°C) along with measurement of microbial growth and lipid oxidation in food by conventional destructive methods. Oxygen levels in packs went down to almost zero between weeks 2 and 3 indicating deterioration of packaged product. Correlation between oxygen profiles and the rate of microbial growth and lipid oxidation was established. The optical oxygen sensor system was shown to provide valuable information about performance of the packaging process, product storage conditions and food quality in a convenient and cost‐efficient fashion and non‐destructively. Copyright © 2004 John Wiley & Sons, Ltd.     

Feedback min–max model predictive control using robust one-step sets

A solution to the infinite-horizon min–max model predictive control (MPC) problem of constrained polytopic systems has recently been defined in terms of a sequence of free control moves over a fixed horizon and a state feedback law in the terminal region using a time-varying terminal cost. The advantage of this formulation is the enlargement of the admissible set of initial states without sacrificing local optimality, but this comes at the expense of higher computational complexity. This article, by means of a counterexample, shows that the robust feasibility and stability properties of such algorithms are not, in general, guaranteed when more than one control move is adopted. For this reason, this work presents a novel formulation of min–max MPC based on the concept of within-horizon feedback and robust contractive set theory that ensures robust stability for any choice of the control horizon. A parameter-dependent feedback extension is also proposed and analysed. The effectiveness of the algorithms is demonstrated with two numerical examples.     

Bitumens modified with recycled polymers

Increasing traffic loading and volumes on roads has led to the use of polymer modified binders to improve the performance of bitumen in terms of additional strength, durability and increased resistance to rutting and fatigue cracking. Generally those modifiers currently in use are virgin polymers but the research investigates the possibility of using waste polymers instead. The aim was to find a recycled polymer modified binder that would be similar to a proven modified binder (Polyflex 75) or would augment the properties of 100 penetration grade bitumen. A wide range of recycled polymers was tested including polyethylenes, polypropylenes, polyetherpolyurethane, ground rubber and truck tyre rubber. Although there were some problems with stability in the bitumen some were found to be successful. The blend with 3% by mass of low density polyethlyene substituted for 1% by mass of sytrene butadiene styrene had similar properties to that of Polyflex 75 although it had a lower stiffness. A combination of ethylene vinyl acetate with low density polyethylene showed similar viscosity to that of a 100 penetration bitumen while having an increased softening point. The blends showing promise need to be subjected to further investigation, in particular to evaluate how these blends perform in optimised bituminous mixes.

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Résumé La charge et le volume croissants de la circulation routière ont conduit à l'emploi de liants modifiés aux polymères pour améliorer les propriétés performantielles du bitume, à savoir le renforcement de la solidité, la durabilité et l'accroissement de la résistance à l'orniérage et aux criques de fatigue. En général les agents modifiants actuellement utilisés sont des polymères vierges, toutefois notre recherche était axée sur la possibilité d'utiliser des déchets plastiques émulsifiés. Le but était de trouver un liant modifié au polymère recyclé similaire à un liant modifié ayant fait ses preuves (Polyflex 75) ou pouvant améliorer les propriétés du bitume de pénétration qualité 100. Une gamme variée de polymères recyclés a été mise à l'essai, comprenant des polyéthylènes, des polypropylènes des polyuréthanes de polyéther, du caoutchouc pilé et du caoutchouc de pneus poids lourds. Bien que certains problèmes de stabilité bitumineuse se soient manifestés, certaines expériences se sont avérées fructueuses. Le mélange à 3% par masse de polyéthylène basse densité substitué à un mélange à 1% par masse de styrène-butadiène-styrène s'est avéré avoir des propriétés similaires à celles du Polyflex 75, en dépit d'une rigidité inférieure. On a obtenu une viscosité similaire à celle d'un bitume de pénétration qualité 100 en mélangeant un acétate de vinyle à l'éthylène avec un polyéthylène à basse densité, tout en maintenant un point de ramollissement supérieur. Les mélanges prometteurs doivent être soumis à de nouvelles analyses, dans le but spécifique d'évaluer la performance de tels mélanges dans des matériaux optimisés au liant hydrocarboné.

     

Picosecond pulse response of a travelling-wave semiconductor laser amplifier

The dynamic pulse response of a travelling-wave semiconductor laser amplifier has been investigated. Peak output powers greater than 100 mW, with a fibre-to-fibre gain of 10 dB, have been observed for narrow pulses (<50ps FWHM) at low repetition rates. The dynamic bandwidth of the amplifier has been shown to be at least 50 GHz.     

Modeling of surface acoustic wave strain sensors using coupling-of-modes analysis

SAW devices may be configured as strain sensors, providing passive, wireless strain measurement in demanding conditions. A key consideration is the modeling of the sensors, enabling different device designs to be considered. This paper presents a simulation scheme using coupling-of-modes (COM) analysis which allows both the frequency response of a SAW strain sensor and its bias sensitivity to be evaluated. Example applications are presented to demonstrate the use of the model.