335 research outputs found
Data Requirements for Oceanic Processes in the Open Ocean, Coastal Zone, and Cryosphere
The type of information system that is needed to meet the requirements of ocean, coastal, and polar region users was examined. The requisite qualities of the system are: (1) availability, (2) accessibility, (3) responsiveness, (4) utility, (5) continuity, and (6) NASA participation. The system would not displace existing capabilities, but would have to integrate and expand the capabilities of existing systems and resolve the deficiencies that currently exist in producer-to-user information delivery options
Ocean services user needs assessment. Volume 1: Survey results, conclusions and recommendations
An interpretation of environmental information needs of marine users, derived from a direct contact survey of eight important sectors of the marine user community is presented. Findings of the survey and results and recommendations are reported. The findings consist of specific and quantized measurement and derived product needs for each sector and comparisons of these needs with current and planned NOAA data and services. The following supportive and reference material are examined: direct contact interviews with industry members, analyses of current NOAA data gathering and derived product capabilities, evaluations of new and emerging domestic and foreign satellite data gathering capabilities, and a special commercial fishing survey conducted by the Jet Propulsion Laboratory (JPL)
Spin Density wave instability in a ferromagnet
Ferromagnetic (FM) and incommensurate spin-density wave (ISDW) states are an
unusual set of competing magnetic orders that are seldom observed in the same
material without application of a polarizing magnetic field. We report, for the
first time, the discovery of an ISDW state that is derived from a FM ground
state through a Fermi surface (FS) instability in FeGa. This was
achieved by combining neutron scattering experiments with first principles
simulations. Neutron diffraction demonstrates that FeGa is in an ISDW
state at intermediate temperatures and that there is a conspicuous re-emergence
of ferromagnetism above 360 K. First principles calculations show that the ISDW
ordering wavevector is in excellent agreement with a prominent nesting
condition in the spin-majority FS demonstrating the discovery of a novel
instability for FM metals; ISDW formation due to Fermi surface nesting in a
spin-polarized Fermi surface.Comment: 6 pages with 4 figures. Supplemental Materials Include
Design Concept for a Reusable/Propellantless MXER Tether Space Transportation System
The Momentum Exchange/Electrodynamic Reboost (MXER) tether facility is a transformational concept that significantly reduces the fuel requirements (and associated costs) in transferring payloads above low earth orbit (LEO). Facility reboost is accomplished without propellant by driving current against a voltage created by a conducting tether's interaction with the Earth's magnetic field (electrodynamic reboost). This system can be used for transferring a variety of payloads (scientific, cargo, and human space vehicles) to multiple destinations including geosynchronous transfer orbit, the Moon or Mars. MXER technology advancement requires development in two key areas: survivable, high tensile strength non-conducting tethers and reliable, lightweight payload catch/release mechanisms. Fundamental requirements associated with the MXER non-conducting strength tether and catch mechanism designs will be presented. Key requirements for the tether design include high specific-strength (tensile strength/material density), material survivability to the space environment (atomic oxygen and ultraviolet radiation), and structural survivability to micrometeoroid/orbital debris (MM/OD) impacts. The driving mechanism key,gequirements include low mass-to-capture-volume ratio, positional and velocity error tolerance, and operational reliability. Preliminary tether and catch mechanism design criteria are presented, which have been used as guidelines to "screen" and down-select initial concepts. Candidate tether materials and protective coatings are summarized along with their performance in simulated space environments (e.g., oxygen plasma, thermal cycling). A candidate catch mechanism design concept is presented along with examples of demonstration hardware
Dimensional crossover in the electrical and magnetic properties of the layered LaSb2 superconductor under pressure: The role of phase fluctuations
We present electrical transport, magnetization, and ac as well as dc magnetic susceptibility measurements of the highly anisotropic compound LaSb2. Our data display a very broad anisotropic transition upon cooling below 2.5 K into a clean superconducting state with a field-dependent magnetization that is consistent with type I behavior. We identify distinct features of two-dimensionality in both the transport and magnetic properties. Application of hydrostatic pressure induces a two- to three-dimensional crossover evidenced by a reduced anisotropy and transition width. The superconducting transition appears phase-fluctuation-limited at ambient pressure, with fluctuations observed for temperatures greater than eight times the superconducting critical temperature. © 2011 American Physical Society
Origin of the butterfly magnetoresistance in a Dirac nodal-line system
We report a study on the magnetotransport properties and on the Fermi
surfaces (FS) of the ZrSi(Se,Te) semimetals. Density Functional Theory (DFT)
calculations, in absence of spin orbit coupling (SOC), reveal that both the Se
and the Te compounds display Dirac nodal lines (DNL) close to the Fermi level
at symmorphic and non-symmorphic positions, respectively. We
find that the geometry of their FSs agrees well with DFT predictions. ZrSiSe
displays low residual resistivities, pronounced magnetoresistivity, high
carrier mobilities, and a butterfly-like angle-dependent magnetoresistivity
(AMR), although its DNL is not protected against gap opening. As in
CdAs, its transport lifetime is found to be 10 to 10 times
larger than its quantum one. ZrSiTe, which possesses a protected DNL, displays
conventional transport properties. Our evaluation indicates that both compounds
most likely are topologically trivial. Nearly angle-independent effective
masses with strong angle dependent quantum lifetimes lead to the butterfly AMR
in ZrSiSe
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