Current Issue : July - September Volume : 2015 Issue Number : 3 Articles : 4 Articles
Sub-Saharan Africa contains the highest number of people affected by droughts.\nAlthough this can easily be mitigated through the provision of timely, reliable and relevant\nweather forecasts, the sparse network of weather stations in most of these countries makes this\ndifficult. Rapid development in wireless sensor networks has resulted in weatherboards capable\nof capturing weather parameters at the micro-level. Although these weatherboards offer a\nviable solution to Africa�s drought, the acceptability of such data by meteorologists is only\npossible if these sensors are calibrated and their field readiness scientifically evaluated. This\nis the contribution of this paper; we present results of a calibration exercise that was carried\nout to: (1) measure and correct lag, random and systematic errors; (2) determine if Perspex\nwas an ideal material for building sensor boards� enclosures; and (3) identify sensor boards�\nbattery charging and depletion rates. The result is a calibration report detailing actual error\nand uncertainty values for atmospheric pressure, humidity and temperature sensors, as well\nas the recharge and discharge curves of the batteries. The results further ruled out the use of\nPerspex for enclosing the sensor boards. These experiments pave the way for the design and\nimplementation of a sensor-based weather monitoring system (SenseWeather) that was piloted\nin two regions in Kenya....
In this paper, a dual band planar inverted F antenna (PIFA) has been investigated\nfor cooperative on- and off-body communications. Free space and on-body performance\nparameters like return loss, bandwidth, radiation pattern and efficiency of this antenna are\nshown and investigated. The on- and off-body radio propagation channel performance at\n2.45 GHz and 1.9 GHz have been investigated, respectively. Experimental investigations are\nperformed both in the anechoic chamber and in an indoor environment. The path loss exponent\nhas been extracted for both on- and off-body radio propagation scenarios. For on-body\npropagation, the path loss exponent is 2.48 and 2.22 in the anechoic chamber and indoor\nenvironment, respectively. The path loss exponent is 1.27 for off-body radio propagation\nsituation. For on-body case, the path loss has been characterized for ten different locations\non the body at 2.45 GHz, whereas for off-body case radio channel studies are performed for\nfive different locations at 1.9 GHz. The proposed antenna shows a good on- and off-body\nradio channel performance....
The mechanical model of the shape memory alloy (SMA) composite film with silicon (Si) substrate was established by the method\nof mechanics of composite materials. The coupled action between the SMA film and Si substrate under thermal loads was analyzed\nby combining static equilibrium equations, geometric equations, and physical equations. The material nonlinearity of SMA and\nthe geometric nonlinearity of bending deformation were both considered. By simulating and analyzing the actuation performance\nof the SMA composite film during one cooling-heating thermal cycle, it is found that the final cooling temperature, boundary\ncondition, and the thickness of SMA film have significant effects on the actuation performance of the SMA composite film. Besides,\nthe maximum deflection of the SMA composite film is affected obviously by the geometric nonlinearity of bending deformation\nwhen the thickness of SMA film is very large....
Network coding techniques are usually applied upon network-layer protocols\nto improve throughput in wireless networks. In scenarios with multiple unicast sessions,\nfairness is also an important factor. Therefore, a network coding-aware packet-scheduling\nalgorithm is required. A packet-scheduling algorithm determines which packet to send\nnext from a nodeââ?¬â?¢s packet backlog. Existing protocols mostly employ a basic round-robin\nscheduling algorithm to give ââ?¬Å?equalââ?¬Â opportunities to different packet flows. In fact, this\nââ?¬Å?equalââ?¬Â-opportunity scheduling is neither fair, nor efficient. This paper intends to accentuate\nthe importance of a coding-aware scheduling scheme. With a good scheduling scheme,\nwe can gain more control over the per-flow throughput and fairness. Specifically, we\nfirst formulate a static scheduling problem and propose an algorithm to find the optimal\nscheduling scheme. We then extend the technique to a dynamic setting and, later, to practical\nrouting protocols. Results show that the algorithm is comparatively scalable, and it can\nimprove the throughput gain when the network is not severely saturated. The fairness among\nflows is drastically improved as a result of this scheduling scheme....
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