We report the fabrication of microporous thin film membranes with two-dimensionally arranged submicron pores whose size can be varied by changing pH of aqueous medium. A solution containing poly(2-vinylpyridine) partially quaternized with 1,4-diiodobutane (qP2VP) and unreacted 1,4-diodobutane (DIB) was used for the formation and deposition of the membranes on solid substrates. The membranes were spin-coated onto solid substrates in a controlled humid environment. The presence of water vapor in air was found to be a necessary condition for the pore formation. We studied the influence of relative humidity on the membrane morphology and proposed a mechanism of pore formation. Cross-linking the qP2VP membranes with DIB made them insoluble (stable) in organic solvents and acidic water. The cross-linked membranes demonstrated pHdependent swelling, which had a strong influence on the pore size. IntroductionMicroporous polymer membranes (pore size 0.01-20 µm) are widely used in industry, medicine, pharmacology, and research for separation and concentration of particles, colloids, proteins, enzymes, and cells. Phase inversion and track etching are well-established, commercially implemented techniques for the fabrication of such membranes. In the phase inversion technique, a solvent for a polymer turns into a nonsolvent causing the polymer precipitation; the nonsolvent serves as a porogen that evaporates after the membrane formation. Phase inversion is usually achieved by immersion of a solution film into a coagulation bath with a nonsolvent (immersion precipitation), by exposure to nonsolvent vapor, or by temperature change (temperature-induced phase separation). Membranes prepared by this technique exhibit a highly porous inner structure represented by a continuous network of interconnected tortuous pores. Furthermore, the structure is usually asymmetric with a thin dense surface layer and a thick spongelike basic layer. The surface layer determines the separation properties and the overall flow resistance of the membrane, while the basic layer acts as a mechanical support. 1 The track etch (TE) membranes are prepared using a two-step fabrication procedure. 2 First, a polymer film (polycarbonate or polyester) is exposed to a collimated beam of heavy ions that produce parallel tracks across the film. The tracks are then chemically etched, forming cylindrical pores. Unlike the phase inversion membranes, the track etch membranes are characterized by uniform pore size and relatively low pore density, resulting in the high flow resistance.In addition to the above-mentioned techniques, various template-assisted methods for the fabrication of microporous polymer membranes have been reported in the literature. Colloidal crystals 3-8 and emulsion droplets 9 have been successfully implemented as templates for the fabrication of selfstanding membranes. Microcontact molding 10 and casting of polymer layers on solid substrates with 2D pillar arrays 11 were found to be feasible for the fabrication of thin film membranes.
Falls are currently a leading cause of death from injury in the elderly. The usage of the conventional assistive cane devices is critical in reducing the risk of falls and is relied upon by over 4 million patients in the U.S.. While canes provide physical support as well as supplementary sensing feedback to patients, at the same time, these conventional aids also exhibit serious adverse effects that contribute to falls. The falls due to the improper usage of the canes are particularly acute in the elderly and disabled where reduced cognitive capacity accompanied by the burden of managing cane motion leads to increased risk. This paper describes the development of the SmartCane assistive system that encompasses broad engineering challenges that will impact general development of individualized, robust assistive and prosthetic devices. The SmartCane system combines advances in signal processing, embedded computing, and wireless networking technology to provide capabilities for remote monitoring, local signal processing, and real-time feedback on the cane usage. This system aims to reduce risks of injuries and falls by enabling training and guidance of patients in proper usage of assistive devices.
Abstract-Dual-radio, dual-processor nodes are an emerging class of Wireless Sensor Network devices that provide both lowenergy operation as well as substantially increased computational performance and communication bandwidth for applications. In such systems, the secondary radio and processor operates with sufficiently low power that it may remain always vigilant, while the the main processor and primary, high-bandwidth radio remain off until triggered by the application. By exploiting the high energy efficiency of the main processor and primary radio along with proper usage, net operating energy benefits are enabled for applications. The secondary radio provides a constantly available multi-hop network, while paths in the primary network exist only when required. This paper describes a topology control mechanism for establishing an end-to-end path in a network of dual-radio nodes using the secondary radios as a control channel to selectively wake up nodes along the required end-to-end path. Using numerical models as well as testbed experimentation, we show that our proposed mechanism provides significant energy savings of more than 60% compared to alternative approaches, and that it incurs only moderately greater application latency.
A driving scenario for sensor networks is environmental monitoring: nodes gather data and send it back to a sink (i.e., a basestation with an internet connection or persistent storage) via a multi-hop tree topology. In order to form the data-gathering tree, and in order to configure the sensor nodes, the sink periodically disseminates messages into the network. For scaling, robustness, and load-balancing reasons, it is desirable to introduce multiple sinks and have nodes send data to their closest sink (under a metric, such as hop-count or energy cost) rather than all nodes sending to a unique sink. With multiple sinks, it becomes important to constrain dissemination of queries so that each sink does not flood the whole network. In this work we propose Voronoi scoping, a distributed algorithm to constrain the dissemination of messages from different sinks. It has the property that a query originated by a given sink will be forwarded only to the nodes for which that sink is the closest sink (under the chosen metric). Thus each query is forwarded to the smallest possible number of nodes, and per-node dissemination overhead does not grow with network size or with number of sinks. The algorithm has a simple distributed implementation and requires only a few bytes of state at each node. Experiments over a network of 55 motes confirm the algorithm's effectiveness.
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