Distributed Sparse Signal Recovery For Sensor Networks

We propose a distributed algorithm for sparse signal recovery in sensor networks based on Iterative Hard Thresholding (IHT). Every agent has a set of measurements of a signal x, and the objective is for the agents to recover x from their collective measurements at a minimal communication cost and with low computational complexity. A naive distributed implementation of IHT would require global communication of every agent's full state in each iteration. We find that we can dramatically reduce this communication cost by leveraging solutions to the distributed top-K problem in the database literature. Evaluations show that our algorithm requires up to three orders of magnitude less total bandwidth than the best-known distributed basis pursuit method

A Guide to ITS Operations: Useful Spells and Incantations

It is said that it is not wise to dabble in the Arts without care and caution, for the spell is at once subtle and dangerous: Look herein! For if you read carefully and closely, you can incant a Word of Magic, and the system might be revived. This working paper describes crash recovery procedures for a DEC KA-10 computer running ITS, the Incompatible Timesharing System. It is intended for people not intimately familiar with the system internals who need to handle emergency operation program when a system maintaner is not available.MIT Artificial Intelligence Laborator

A state of change : an historical archaeology of Doukhobor identity at Kirilovka village site (FcNs-1)

A migration of over seven thousand Russian immigrants belonging to the Christian sect known as the Doukhobors arrived in western Canada beginning in early 1899. Three colonies of at least 61 villages in total were established in the Districts of Saskatchewan and Assiniboia in the Northwest Territories. Due to internal tensions in the sect and conflicts with the Department of the Interior, most of these villages were abandoned by 1920. Although the Doukhobors in Saskatchewan are an integral part of the province's agricultural and settlement history, no substantial archaeological investigation of village sites took place until the site of Kirilovka (FcNs-I) was excavated in August and September of 1996. Kirilovka village was located along the North Saskatchewan River, west of the community of Langham, and was occupied by 30-35 families at the peak of its population. An archaeological sample representing the locations of four households is investigated in this thesis. Historical characterizations of the Doukhobors in Saskatchewan tend to be uncertain as to whether the Doukhobors were an ethnic group and/or religious sect, and to the degree of internal cohesion and homogeneity at the community level. Combined archaeological and historical investigations here suggest that the Doukhobor identity in Saskatchewan cannot be defined simply in terms of Russian ethnicity, but involves a combination of philosophical, ethnic, economic, and geographical factors. Further, the Doukhobor identity is characterized by the constant change brought about through repeated mass migrations spanning two centuries. One of the material implication of this identity was a tendency to readily adopt certain new technologies and styles into Doukhobor activities. This thesis examines the possible social implication of such material acquisitions. Only further archaeological investigation of Saskatchewan Doukhobor village sites may contribute to or contradict the findings of this research. It is hoped, however, that this thesis provides a necessary contribution to the growing field of Settlement Period Archaeology in western Canada

Microwave scattering and emission properties of large impact craters on the surface of Venus

Many of the impact craters on Venus imaged by the Magellan synthetic aperture radar (SAR) have interior floors with oblique incidence angle backscatter cross sections 2 to 16 times (3 dB to 12 dB) greater than the average scattering properties of the planet's surface. Such high backscatter cross sections are indicative of a high degree of wavelength-scale surface roughness and/or a high intrinsic reflectivity of the material forming the crater floors. Fifty-three of these (radar) bright floored craters are associated with 93 percent of the parabolic-shaped radar-dark features found in the Magellan SAR and emissivity data, features that are thought to be among the youngest on the surface of Venus. It was suggested by Campbell et al. that either the bright floors of the parabolic feature parent craters are indicative of a young impact and the floor properties are modified with time to a lower backscatter cross section or that they result from some property of the surface or subsurface material at the point of impact or from the properties of the impacting object. As a continuation of earlier work we have examined all craters with diameters greater than 30 km (except 6 that were outside the available data) so both the backscatter cross section and emissivity of the crater floors could be estimated from the Magellan data

Storage requirement definition study

A dish Stirling solar receiver (DSSR) and a heat pipe solar receiver with TES (HPSR) for a 25 kWe dish Stirling solar power system are described. The thermal performance and cost effectiveness of each are analyzed minute by minute over the equivalent of one year of solar insolation. Existing designs of these two systems were used as a basis for the study; TES concepts for the DSSR and alternative TES concepts for the HPSR are presented. Parametric performance and cost studies were performed to determine the operating and cost characteristics of these systems. Data are reported for systems (1) without TES and with varying amounts of TES, (2) with and without a fossil fuel combustor, (3) with varying solar to fossil power input, and (4) with different system control assumptions. The principal effects of TES duration, collector area, engine efficiency, and fuel cost sensitivity are indicated. Development needs for each of the systems are discussed and the need and nature of possible future TES solar modular experiments are presented and discussed