14,526 research outputs found
A tool for cutting ultra thin slits in metals
Tool produces slits of 0.0305 mm widths in materials up to RC 50 hardness, minimizes material waste and improves precision. Device may be used for general metal cutting and for producing simulated cracks in metal samples used in fatigue tests
Universal basic education : an overall strategy of investment priorities for economic growth
Includes bibliographical references (p. 27-28)
Apollo experience report: Guidance and control systems: CSM service propulsion system gimbal actuators
The service propulsion system gimbal actuators of the Apollo command and service module were developed, modified, and qualified between February 1962 and April 1968. The development of these actuators is described as the result of extensive testing, retesting, and modification of the initial design. Successful completion of each mission without anomalies attributable to the actuators indicated that the particular configuration (modification) in use was adequate for the flight profile imposed
Scale factor gage for fiber optics inspection device
Flexible wire device, fastened along outside of fiber bundle from viewing portion to tip, positions calibrated adjustable gage in field of view. Scale factor is determined from known magnification characteristics of fiber optics system or from graduations on gage tip
Quick release acoustic sensor holding fixture
Quick-release spring holder secures acoustic sensor to test material surface eliminating adhesive bonding to test material and achieving acoustic emission evaluation from tensile tests. Reusability of sensors reduces test cost
Measured electron contribution to Shuttle plasma environment: Abbreviated update
The differential energy spectra of electrons between 1 and 100 eV were measured by an electron spectrometer flown on an early shuttle. This energy range was scanned in 64 incremental steps with a resolution of 7%. The most striking feature that was observed throughout these spectra was a relatively flat distribution of the higher energy electrons out to 100 eV. This is in contrast to normal ambient spectra which consistently show a rapid decline in quantitative flux beyond 50 to 55 eV. The lower energy (1 to 2 eV) end of these spectra showed steep thermal trails comparable to normal ambient spectral structure. In general, daytime fluxes were significantly higher than those obtained during nighttime measurements. Quantitative flux excursions which may possibly be associated with thruster firing were frequently observed. Spectral structure suggestive of the N2 vibrational excitation energy loss mechanism was also seen in the data from some measurement periods. Examples of these spectra are shown and possible correlations are discussed
Functional connectivity of coral reef fishes in a tropical seascape assessed by compound-specific stable isotope analyses
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2011The ecological integrity of tropical habitats, including mangroves, seagrass beds and
coral reefs, is coming under increasing pressure from human activities. Many coral reef
fish species are thought to use mangroves and seagrass beds as juvenile nurseries before
migrating to coral reefs as adults. Identifying essential habitats and preserving functional
linkages among these habitats is likely necessary to promote ecosystem health and
sustainable fisheries on coral reefs. This necessitates quantitative assessment of
functional connectivity among essential habitats at the seascape level. This thesis presents
the development and first application of a method for tracking fish migration using amino
acid (AA) δ13C analysis in otoliths. In a controlled feeding experiment with fish reared on
isotopically distinct diets, we showed that essential AAs exhibited minimal trophic
fractionation between consumer and diet, providing a δ13C record of the baseline
isoscape. We explored the potential for geochemical signatures in otoliths of snapper to
act as natural tags of residency in seagrass beds, mangroves and coral reefs in the Red
Sea, Caribbean Sea and Eastern Pacific Ocean. The δ13C values of otolith essential AAs
varied as a function of habitat type and provided a better tracer of residence in juvenile
nursery habitats than conventional bulk stable isotope analyses (SIA). Using our otolith
AA SIA approach, we quantified the relative contribution of coastal wetlands and reef
habitats to Lutjanus ehrenbergii populations on coastal, shelf and oceanic coral reefs in
the Red Sea. L. ehrenbergii made significant ontogenetic migrations, traveling more than
30 km from juvenile nurseries to coral reefs and across deep open water. Coastal
wetlands were important nurseries for L. ehrenbergii; however, there was significant
plasticity in L. ehrenbergii juvenile habitat requirements. Seascape configuration played
an important role in determining the functional connectivity of L. ehrenbergii populations
in the Red Sea. The compound-specific SIA approach presented in this thesis will be
particularly valuable for tracking the movement of species and life-stages not amenable
to conventional tagging techniques. This thesis provides quantitative scientific support
for establishing realistic population connectivity models that can be used to design
effective marine reserve networks.I have been supported by an
Ocean Life Institute Fellowship, a National Science Foundation Graduate Research
Fellowship, and the WHOI Academic Programs Office. The research presented in this
thesis was supported by an Ocean Life Institute student research grant to K. McMahon,
an International Society for Reef Studies-Ocean Conservancy Coral Reef Research
Fellowship to K. McMahon, and King Abdullah University of Science and Technology
(KAUST) Award Nos. USA 00002 and KSA 00011 to S. Thorrold. Additional support
came from the Woods Hole Oceanographic Institution, the Large Pelagics Research
Center at the University of New Hampshire, the Carnegie Institution of Washington and
the W.M. Keck Foundation
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