3,871 research outputs found
Training Induced Positive Exchange Bias in NiFe/IrMn Bilayers
Positive exchange bias has been observed in the
NiFe/IrMn bilayer system via soft x-ray resonant
magnetic scattering. After field cooling of the system through the blocking
temperature of the antiferromagnet, an initial conventional negative exchange
bias is removed after training i. e. successive magnetization reversals,
resulting in a positive exchange bias for a temperature range down to 30 K
below the blocking temperature (450 K). This new manifestation of magnetic
training is discussed in terms of metastable magnetic disorder at the
magnetically frustrated interface during magnetization reversal.Comment: 4 pages, 3 figure
Cryogenic fluid management experiment
The cryogenic fluid management experiment (CFME), designed to characterize subcritical liquid hydrogen storage and expulsion in the low-q space environment, is discussed. The experiment utilizes a fine mesh screen fluid management device to accomplish gas-free liquid expulsion and a thermodynamic vent system to intercept heat leak and control tank pressure. The experiment design evolved from a single flight prototype to provision for a multimission (up to 7) capability. A detailed design of the CFME, a dynamic test article, and dedicated ground support equipment were generated. All materials and parts were identified, and components were selected and specifications prepared. Long lead titanium pressurant spheres and the flight tape recorder and ground reproduce unit were procured. Experiment integration with the shuttle orbiter, Spacelab, and KSC ground operations was coordinated with the appropriate NASA centers, and experiment interfaces were defined. Phase 1 ground and flight safety reviews were conducted. Costs were estimated for fabrication and assembly of the CFME, which will become the storage and supply tank for a cryogenic fluid management facility to investigate fluid management in space
Behavior of fluids in a weightless environment
Fluid behavior in a low-g environment is controlled primarily by surface tension forces. Certain fluid and system characteristics determine the magnitude of these forces for both a free liquid surface and liquid in contact with a solid. These characteristics, including surface tension, wettability or contact angle, system geometry, and the relationships governing their interaction, are discussed. Various aspects of fluid behavior in a low-g environment are then presented. This includes the formation of static interface shapes, oscillation and rotation of drops, coalescence, the formation of foams, tendency for cavitation, and diffusion in liquids which were observed during the Skylab fluid mechanics science demonstrations. Liquid reorientation and capillary pumping to establish equilibrium configurations for various system geometries, observed during various free-fall (drop-tower) low-g tests, are also presented. Several passive low-g fluid storage and transfer systems are discussed. These systems use surface tension forces to control the liquid/vapor interface and provide gas-free liquid transfer and liquid-free vapor venting
Candidate locations for SPS rectifying antennas
The feasibility of placing 120 Satellite Power System (SPS) rectifying antenna (rectenna) sites across the U.S. was studied. An initial attempt is made to put two land sites in each state using several land site selection criteria. When only 69 land sites are located, it is decided to put the remaining sites in the sea and sea site selection criteria are identified. An estimated projection of electrical demand distribution for the year 2000 is then used to determine the distribution of these sites along the Pacific, Atlantic, and Gulf Coasts. A methodology for distributing rectenna sites across the country and for fine-tuning exact locations is developed, and recommendations on rectenna design and operations are made
Dual Behavior of Antiferromagnetic Uncompensated Spins in NiFe/IrMn Exchange Biased Bilayers
We present a comprehensive study of the exchange bias effect in a model
system. Through numerical analysis of the exchange bias and coercive fields as
a function of the antiferromagnetic layer thickness we deduce the absolute
value of the averaged anisotropy constant of the antiferromagnet. We show that
the anisotropy of IrMn exhibits a finite size effect as a function of
thickness. The interfacial spin disorder involved in the data analysis is
further supported by the observation of the dual behavior of the interfacial
uncompensated spins. Utilizing soft x-ray resonant magnetic reflectometry we
have observed that the antiferromagnetic uncompensated spins are dominantly
frozen with nearly no rotating spins due to the chemical intermixing, which
correlates to the inferred mechanism for the exchange bias.Comment: 4 pages, 3 figure
decays to from new data on
Data on the reaction with ,
taken with unpolarized or polarized beams in combination with an unpolarized or
polarized proton-target, were analyzed within the Bonn-Gatchina (BnGa) partial
wave analysis. Differential cross sections, several spin density matrix
elements, the beam asymmetry , the normalized helicity difference ,
and the correlation between linear photon and longitudinal target
polarization were included in a large data base on pion and photo-induced
reactions. The data on photoproduction are used to determine twelve
branching ratios; most of these are determined for the first
time.Comment: 6 pages, 4 figures, 2 table
Rapid Response Plan for Management and Control of the Chinese Mitten Crab, Northeast United States and Atlantic Canada
The Rapid Response Plan for Management and Control of the Chinese Mitten Crab is intended to guide efforts to mitigate the further introduction and spread of the Chinese mitten crab in the northeastern United States and Canada. Due to the unique challenges of invasive species introductions to marine and coastal ecosystems, the mitten crab and other existing and potential marine invasive species are more difficult and often more costly to manage or control than freshwater aquatic or terrestrial invasive species. These challenges include ecosystem connectivity across vast geographic areas, ocean currents and tidal influence, and shipping- and ballast-related vectors for larvae. Warming ocean and coastal waters and species range expansions influenced by climate change will further compound these issues. Recent and historical efforts to control or eradicate invasive mitten crab populations in other countries and in other parts of the United States have not been effective. More than a century of efforts to control or eradicate other marine invasive species, such as the European green crab, has also proven unsuccessful. For these reasons, it is prudent to focus available funds and regional capacity for early detection and rapid response planning on prevention, as we must assume that eradication is not likely should Chinese mitten crabs enter Rhode Island, Massachusetts, New Hampshire, Maine or Maritime Canada. The Sea Grant Programs in Massachusetts, New Hampshire and Maine worked with local, state, regional and federal stakeholders to establish a foundation for prevention, early detection and rapid response efforts of the Chinese mitten crab
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