4,278 research outputs found
The 1984 NASA/ASEE summer faculty fellowship program
An overview is given of the program management and activities. Participants and research advisors are listed. Abstracts give describe and present results of research assignments performed by 31 fellows either at the Johnson Space Center, at the White Sands test Facility, or at the California Space Institute in La Jolla. Disciplines studied include engineering; biology/life sciences; Earth sciences; chemistry; mathematics/statistics/computer sciences; and physics/astronomy
Summer Workshop on Near-Earth Resources
The possible large scale use of extraterrestrial resources was addressed, either to construct structures in space or to return to Earth as supplements for terrestrial resources. To that end, various specific recommendations were made by the participants in the summer study on near-Earth resources, held at La Jolla, California, 6 to 13 August, 1977. The Moon and Earth-approaching asteroids were considered. Summaries are included of what is known about their compositions and what needs to be learned, along with recommendations for missions designed to provide the needed data. Tentative schedules for these projects are also offered
Responses of Hyalella azteca and Ceridaphnia dubia to reservoir sediments following Chelated Copper Herbicide Applications
In response to nuisance growths of algae and vascular
plants, such as dioecious hydrilla (
Hydrilla verticillata
L.f.
Royle), copper formulations have been applied in lakes and
reservoirs for a number of years. Concerns have arisen regarding
the long-term consequences of copper applications
and those concerns have appropriately focused on sediment
residues. In this study, we evaluated the toxicity of sediments
from treated (for a decade) and untreated areas in Lake
Murray, South Carolina and estimated the capacity of those
sediments to bind additional copper. Two sentinel aquatic invertebrates,
Hyalella azteca
Saussure and
Ceriodaphnia dubia
Richard, were used to measure residual toxicity of treated
and untreated sediments from the field and after laboratory
amendments. (PDF has 5 pages.
Workshop on Science and the Human Exploration of Mars
The exploration of Mars will be a multi-decadal activity. Currently, a scientific program is underway, sponsored by NASA's Office of Space Science in the United States, in collaboration with international partners France, Italy, and the European Space Agency. Plans exist for the continuation of this robotic program through the first automated return of Martian samples in 2014. Mars is also a prime long-term objective for human exploration, and within NASA, efforts are being made to provide the best integration of the robotic program and future human exploration missions. From the perspective of human exploration missions, it is important to understand the scientific objectives of human missions, in order to design the appropriate systems, tools, and operational capabilities to maximize science on those missions. In addition, data from the robotic missions can provide critical environmental data - surface morphology, materials composition, evaluations of potential toxicity of surface materials, radiation, electrical and other physical properties of the Martian environment, and assessments of the probability that humans would encounter Martian life forms. Understanding of the data needs can lead to the definition of experiments that can be done in the near-term that will make the design of human missions more effective. This workshop was convened to begin a dialog between the scientific community that is central to the robotic exploration mission program and a set of experts in systems and technologies that are critical to human exploration missions. The charge to the workshop was to develop an understanding of the types of scientific exploration that would be best suited to the human exploration missions and the capabilities and limitations of human explorers in undertaking science on those missions
Systematic Variation in Willingness to Pay for Agricultural Land Preservation and Implications for Benefit Transfer: A Meta-Analysis
Despite prior studies examining willingness to pay for farmland preservation there has been no quantitative, systematic analysis of findings across the literature. This paper presents the first statistical meta-analysis of farmland preservation values. Results confirm systematic variations in willingness to pay, with value surfaces corresponding to theoretical expectations. Findings also provide significant insight into the potential for valid meta-analytic, function based benefit transfer. Results suggest, for example, that transfer validity is critically dependent on jurisdictional scale. Transfer errors are modest for community scale farmland preservation, but large for state scale preservation policies in which per acre welfare estimates are small.Land Economics/Use,
Mars Surface Mission Workshop
A workshop was held at the Lunar and Planetary Institute on September 4-5, 1997, to address the surface elements of the Mars Reference Mission now being reviewed by NASA. The workshop considered the current reference mission and addressed the types of activities that would be expected for science and resource exploration and facilities operations. A set of activities was defined that can be used to construct "vignettes" of the surface mission. These vignettes can form the basis for describing the importance of the surface mission, for illustrating aspects of the surface mission, and for allowing others to extend and revise these initial ideas. The topic is rich with opportunities for additional conceptualization. It is recommended that NASA consider supporting university design teams to conduct further analysis of the possibilities
Spin-polarized tunneling through randomly transparent magnetic junctions: Reentrant magnetoresistance approaching the Julliere limit
Electron conductance in planar magnetic tunnel junctions with long-range
barrier disorder is studied within Glauber-eikonal approximation enabling exact
disorder ensemble averaging by means of the Holtsmark-Markov method. This
allows us to address a hitherto unexplored regime of the tunneling
magnetoresistance effect characterized by the crossover from
momentum-conserving to random tunneling as a function of the defect
concentration. We demonstrate that such a crossover results in a reentrant
magnetoresistance: It goes through a pronounced minimum before reaching
disorder- and geometry-independent Julliere's value at high defect
concentrations.Comment: 7 pages, 5 figures, derivation of Eq. (39) added, errors in Ref. 7
correcte
Impurity-induced tuning of quantum well states in spin-dependent resonant tunneling
We report exact model calculations of the spin-dependent tunneling in double
magnetic tunnel junctions in the presence of impurities in the well. We show
that the impurity can tune selectively the spin channels giving rise to a wide
variety of interesting and novel transport phenomena. The tunneling
magnetoresistance, the spin polarization and the local current can be
dramatically enhanced or suppressed by impurities. The underlying mechanism is
the impurity-induced shift of the quantum well states (QWS) which depends on
the impurity potential, impurity position and the symmetry of the QWS.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Report of the Terrestrial Bodies Science Working Group. Volume 4: The moon
A rationale for furture exploration of the moon is given. Topics discussed include the objectives of the lunar polar orbiter mission, the mission profile, and general characteristics of the spacraft to be used
High-frequency spin valve effect in ferromagnet-semiconductor-ferromagnet structure based on precession of injected spins
New mechanism of magnetoresistance, based on tunneling-emission of spin
polarized electrons from ferromagnets (FM) into semiconductors (S) and
precession of electron spin in the semiconductor layer under external magnetic
field, is described. The FM-S-FM structure is considered, which includes very
thin heavily doped (delta-doped) layers at FM-S interfaces. At certain
parameters the structure is highly sensitive at room-temperature to variations
of the field with frequencies up to 100 GHz. The current oscillates with the
field, and its relative amplitude is determined only by the spin polarizations
of FM-S junctions at relatively large bias voltage.Comment: 5 pages, 2 figures, (v2) new plot with a dependence of current J on
magnetic field H added in Fig.2 (top panel), minor amendments in the text;
(v3) minor typos corrected. To appear in Phys. Rev. Letter
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