http://dspace.mit.edu:80 The DSpace@MIT digital repository system captures, stores, indexes, preserves, and distributes digital research material. 2013-05-23T23:39:03Z http://hdl.handle.net/1721.1/78935 Thermogravimetry-Mass Spectrometry for Carbon Nanotube Detection in Complex Mixtures Plata, Desiree Louise; Reddy, Christopher M.; Gschwend, Philip M. In spite of the growth of the carbon nanotube (CNT) industry, there are no established analytical methods with which to detect or quantify CNTs in environmental matrices. Given that CNTs have relatively high thermal stabilities, we investigated the use of thermal techniques to isolate and quantify single wall carbon nanotubes (SWCNTs). Test materials included ten types of commercial SWCNTs, representative biological macromolecules (bovine serum albumin and methylcellulose), soot, natural coastal sediments, and SWCNT-amended sediments. Different SWCNTs exhibited widely diverse degradation temperatures, and thermal analytical methods may require SWCNT-type specific parameters. To improve quantification capabilities, evolved gases were monitored by mass spectrometry. SWCNTs produced diagnostic ion ratios reflective of their high carbon and low hydrogen and oxygen contents. Current detection limits are roughly 4 μgSWCNT per sample (e.g., 100 μgSWCNT g–1sediment and 40 mg sample), controlled by interfering ions associated with the instrument’s non-airtight design. Although future modifications could improve this limitation, the current method is sufficient for quantifying SWCNTs in laboratories and industrial sites where SWCNTs are handled. Furthermore, the method shows promise to distinguish between incidental (e.g., soot) and engineered (e.g., SWCNTs) nanoparticles, which is not possible with current state-of-the-art techniques. 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78934 Ocean Renewable Energy Storage (ORES) System: Analysis of an Undersea Energy Storage Concept Slocum, Alexander H.; Fennell, Gregory E.; Dundar, Gokhan; Hodder, Brian; Meredith, James D. C.; Sager, Monique A. Due to its higher capacity factor and proximity to densely populated areas, offshore wind power with integrated energy storage could satisfy > 20% of U.S. electricity demand. Similar results could also be obtained in many parts of the world. The offshore environment can be used for unobtrusive, safe, and economical utility-scale energy storage by taking advantage of the hydrostatic pressure at ocean depths to store energy by pumping water out of concrete spheres and later allowing it to flow back in through a turbine to generate electricity. The storage spheres are an ideal complement to energy harvesting machines, such as floating wind turbines (FWTs). The system could provide near-base-load-quality utility-scale renewable energy and do double duty as the anchoring point for the generation platforms. Analysis indicates that storage can be economically feasible at depths as shallow as 200 m, with cost per megawatt hour of storage dropping until 1500 m before beginning to trend upward. The sweet spot occurs when the concrete wall thickness to withstand the hydrostatic pressure provides enough ballast mass, and this will depend on the strength of used concrete and reinforcement. In addition, the required concrete would use significant amounts of fly ash from coal-fired power plants, and the spheres can serve as artificial reefs. 2013-03-01T00:00:00Z http://hdl.handle.net/1721.1/78933 Mapping Complex Marine Environments with Autonomous Surface Craft Leedekerken, Jacques C.; Fallon, Maurice Francis; Leonard, John Joseph This paper presents a novel marine mapping system using an Autonomous Surface Craft (ASC). The platform includes an extensive sensor suite for mapping environments both above and below the water surface. A relatively small hull size and shallow draft permits operation in cluttered and shallow environments. We address the Simultaneous Mapping and Localization (SLAM) problem for concurrent mapping above and below the water in large scale marine environments. Our key algorithmic contributions include: (1) methods to account for degradation of GPS in close proximity to bridges or foliage canopies and (2) scalable systems for management of large volumes of sensor data to allow for consistent online mapping under limited physical memory. Experimental results are presented to demonstrate the approach for mapping selected structures along the Charles River in Boston. 2010-12-01T00:00:00Z http://hdl.handle.net/1721.1/78932 Lamb’s problem at its simplest Kausel, Eduardo A. This article revisits the classical problem of horizontal and vertical point loads suddenly applied onto the surface of a homogeneous, elastic half-space, and provides a complete set of exact, explicit formulae which are cast in the most compact format and with the simplest possible structure. The formulae given are valid for the full range of Poisson's ratios from 0 to 0.5, and they treat real and complex poles alike, as a result of which a single set of formulae suffices and also exact formulae for dipoles can be given. 2012-10-01T00:00:00Z