Unmanned Aerial Vehicles (UAVs) are getting closer to becoming ubiquitous in everyday life. Among them, Micro Aerial Vehicles (MAVs) have seen an outburst of attention recently, specifically in the area with a demand for autonomy. A key challenge standing in the way of making MAVs autonomous is that researchers lack the comprehensive understanding of how performance, power, and computational bottlenecks affect MAV applications. MAVs must operate under a stringent power budget, which severely limits their flight endurance time. As such, there is a need for new tools, benchmarks, and methodologies to foster the systematic development of autonomous MAVs. In this paper, we introduce the "MAVBench" framework which consists of a closed-loop simulator and an end-to-end application benchmark suite. A closed-loop simulation platform is needed to probe and understand the intra-system (application data flow) and inter-system (system and environment) interactions in MAV applications to pinpoint bottlenecks and identify opportunities for hardware and software co-design and optimization. In addition to the simulator, MAVBench provides a benchmark suite, the first of its kind, consisting of a variety of MAV applications designed to enable computer architects to perform characterization and develop future aerial computing systems. Using our open source, end-to-end experimental platform, we uncover a hidden, and thus far unexpected compute to total system energy relationship in MAVs. Furthermore, we explore the role of compute by presenting three case studies targeting performance, energy and reliability. These studies confirm that an efficient system design can improve MAV's battery consumption by up to 1.8X.

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A new 2D numerical model of a single U-tube ground heat exchanger is proposed and a four-thermal-resistance model is adopted to evaluate the effective pipe-to-borehole, pipe-to-pipe, and borehole-to-borehole thermal resistances. The influence of temperature distributions on both borehole surface and outer diameter of two pipes to these thermal resistances has been thoroughly studied. The best-fit correlations of effective pipe-to-borehole, pipe-to-pipe, and borehole-to-borehole thermal resistances are proposed and compared with the available equations in the literature. It is found that the present correlations of thermal resistances for ground heat exchanger are more accurate than those of available formulas. Furthermore, based on these obtained thermal resistance correlations, an analytical model is proposed to evaluate the heat transfer performance of the ground heat changer.

The underground temperature distribution and variation are important for the development and utilization of shallow geothermal energy and underground space. In this paper, a remote ground temperature monitoring system was established in Chongqing, located in southwest China and the ground temperature distribution and its variation with seasons of the 100m underground depth was measured from June 2010 to June 2011. The results show that, in the typical geo-structure of Chongqing, the variational ground temperature zone is from 0m to 10m, where the ground temperature is strongly affected by the change of ambient temperature. Below 11m depth, the ground temperature does not change with seasons, i.e., it is the constant ground temperature zone. In the constant temperature zone below 40 meter depth, the geothermal gradient is about 0.02°C/m. Baggs’s empirical formula was applied to predict the ground temperature distribution history at different ground depths. The results show a good agreement with the measured data.

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