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Recent advances in miniaturization and low-cost, low-power design have led to active research in large-scale networks of small, wireless, low-power sensors and actuators. Time synchronization is critical in sensor networks for diverse purposes including sensor data fusion, coordinated actuation, and power-efficient duty cycling. Though the clock accuracy(More)
We present Asirra (Figure 1), a CAPTCHA that asks users to identify cats out of a set of 12 photographs of both cats and dogs. Asirra is easy for users; user studies indicate it can be solved by humans 99.6% of the time in under 30 seconds. Barring a major advance in machine vision, we expect computers will have no better than a 1/54,000 chance of solving(More)
Wireless sensor networks (WSNs) consist of large populations of wirelessly connected nodes, capable of computation, communication, and sensing. Sensor nodes cooperate in order to merge individual sensor readings into a high-level sensing result, such as integrating a time series of position measurements into a velocity estimate. The physical time of sensor(More)
As new fabrication and integration technologies reduce the cost and size of micro-sensors and wireless interfaces, it becomes feasible to deploy densely distributed wireless networks of sensors and actuators. These systems promise to revolutionize biological, earth, and environmental monitoring applications, providing data at granularities unrealizable by(More)
Many Wireless Sensor Network (WSN) applications are composed of a mixture of deployed devices with varying capabilities, from extremely constrained 8-bit “Motes” to less resource-constrained 32-bit “Microservers”. EmStar is a software environment for developing and deploying complex WSN applications on networks of 32-bit embedded Microserver platforms, and(More)
As the cost of embedded sensors and actuators drops, new applications will arise that exploit high density networks of small devices capable of a variety of sensing tasks. Although individual devices may have limited functionality, the true value of the system comes from the emergent behavior that arises when data from many places in the system is combined.(More)
Mugshot is a system that captures every event in an executing JavaScript program, allowing developers to deterministically replay past executions of web applications. Replay is useful for a variety of reasons: failure analysis using debugging tools, performance evaluation, and even usability analysis of a GUI. Because Mugshot can replay every execution step(More)
Recently deployed Wireless Sensor Network systems (WSNs) are increasingly following <i>heterogeneous</i> designs, incorporating a mixture of elements with widely varying capabilities. The development and deployment of WSNs rides heavily on the availability of simulation, emulation, visualization and analysis support. In this work, we develop tools(More)
Flat Datacenter Storage (FDS) is a high-performance, fault-tolerant, large-scale, locality-oblivious blob store. Using a novel combination of full bisection bandwidth networks, data and metadata striping, and flow control, FDS multiplexes an application’s large-scale I/O across the available throughput and latency budget of every disk in a cluster. FDS(More)