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The spread of a source host is the number of distinct destinations that it has sent packets to during a measurement period. A spread estimator is a software/hardware module on a router that inspects the arrival packets and estimates the spread of each source. It has important applications in detecting port scans and DDoS attacks, measuring the infection rate of a worm, assisting resource allocation in a server farm, determining popular web contents for caching, to name a few. The main technical challenge is to fit a spread estimator in a fast but small memory (such as SRAM) in order to operate it at the line speed in a high-speed network. In this paper, we design a new spread estimator that delivers good performance in tight memory space where all existing estimators no longer work. The new estimator not only achieves space compactness but operates more efficiently than the existing ones. Its accuracy and efficiency come from a new method for data storage, called virtual vectors, which allow us to measure and remove the errors in spread estimation. We perform experiments on real Internet traces to verify the effectiveness of the new estimator.

An ionic-polymer–metal composite (IPMC) consists of an ionic polymer membrane and metallic electrodes plated on both surfaces. When it bends, a voltage is generated between the two electrodes across the membrane. Since it works not only in aqueous solution similar to in vivo but also in air, it can be used for embedded biomedical as well as surface-mounted sensors. The present study investigates the effect of solvent evaporation and mechanisms of electrode degradation of an IPMC when it is operated as a sensor. The output voltages and electrode resistances were measured with several cyclic bending motions applied on the sensor in both aqueous solution and air. There was a good correlation between the sensor voltage and the bending angle when the sensor was tested in aqueous solution. The sensor worked for a long time without attenuation in the output voltage in an aqueous solution. The output voltage, however, decreased rapidly when the sensor was operated in air. The results of resistance measurement showed that the electrode on the compressive side deformed more and generated more cracks than on the tensile side. Optical microscopic images taken on the electrode surfaces validated the results. The results provided very useful information needed to understand electrode degradation and solvent evaporation and to improve the performance of IPMC sensors.

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Many air, less-than-truck load and intermodal transportation and telecommunication networks incorporate hubs in an effort to reduce total cost. These hubs function as make bulk/break bulk or consolidation/deconsolidation centres. In this paper, a new hub location and network design formulation is presented that considers the fixed costs of establishing the hubs and the arcs in the network, and the variable costs associated with the demands on the arcs. The problem is formulated as a mixed integer programming problem embedding a multicommodity flow model. The formulation can be transformed into some previously modelled hub network design problems. We develop a dual-based heuristic that exploits the multi-commodity flow problem structure embedded in the formulation. The test results indicate that the heuristic is an effective way to solve this computationally complex problem.