2,063,069 research outputs found
Characteristic temperatures of exchange biased systems
Characteristic temperatures in ferromagnetic - antiferromagnetic exchange
biased systems are analyzed. In addition to usual blocking temperature of
exchange bias , and the N\'{e}el temperature of an antiferromagnet
, the inducing temperature , i.e., the temperature, at which
the direction of exchange anisotropy is established, has been recently
proposed. We demonstrate that this temperature is in general case different
from and . Physics and experimental approaches to measure the
inducing temperature are discussed. Measurements of , in addition to
, and , provide important information about exchange interactions
in ferromagnetic - antiferromagnetic heterostructures
Phase separation in double exchange systems
Ferromagnetic systems described by the double exchange model are
investigated. At temperatures close to the Curie temperature, and for a wide
range of doping levels, the system is unstable toward phase separation. The
chemical potential decreases upon increasing doping, due to the significant
dependence of the bandwidth on the number of carriers. The reduction of the
electronic bandwidth by spin disorder leads to an enormously enhanced
thermopower which peaks near T_c, with a sign opposite that predicted by a
rigid band model.Comment: 4 pages, 2 encapsulated PostScript figure
A Functional Architecture Approach to Neural Systems
The technology for the design of systems to perform extremely complex combinations of real-time functionality has developed over a long period. This technology is based on the use of a hardware architecture with a physical separation into memory and processing, and a software architecture which divides functionality into a disciplined hierarchy of software components which exchange unambiguous information. This technology experiences difficulty in design of systems to perform parallel processing, and extreme difficulty in design of systems which can heuristically change their own functionality. These limitations derive from the approach to information exchange between functional components. A design approach in which functional components can exchange ambiguous information leads to systems with the recommendation architecture which are less subject to these limitations. Biological brains have been constrained by natural pressures to adopt functional architectures with this different information exchange approach. Neural networks have not made a complete shift to use of ambiguous information, and do not address adequate management of context for ambiguous information exchange between modules. As a result such networks cannot be scaled to complex functionality. Simulations of systems with the recommendation architecture demonstrate the capability to heuristically organize to perform complex functionality
Resolution exchange simulation
We extend replica exchange simulation in two ways, and apply our approaches
to biomolecules. The first generalization permits exchange simulation between
models of differing resolution -- i.e., between detailed and coarse-grained
models. Such ``resolution exchange'' can be applied to molecular systems or
spin systems. The second extension is to ``pseudo-exchange'' simulations, which
require little CPU usage for most levels of the exchange ladder and also
substantially reduces the need for overlap between levels. Pseudo exchanges can
be used in either replica or resolution exchange simulations. We perform
efficient, converged simulations of a 50-atom peptide to illustrate the new
approaches.Comment: revised manuscript: 4.2 pages, 3 figure
The NASA-IGES geometry data exchange standard
Described here are the data exchange efforts and plans supported by the NASA Steering Committee for Surface Modeling and Grid Generation. Current methods for geometry data exchange between computer aided design (CAD) systems and NASA computational fluid dynamics (CFD) analysis systems are tedious and induce errors. A Geometry Data Exchange Standard is proposed, utilizing a subset of an existing national standard titled Initial Graphic Exchange Standard (IGES). Future plans for data exchange standardization include all aspects of CFD data. Software systems to utilize this NASA-IGES Geometry Data Exchange Specification are under development
First-principles calculation of the intersublattice exchange interactions and Curie temperatures of full Heusler alloys Ni2MnX (X=Ga, In, Sn, Sb)
The interatomic exchange interactions and Curie temperatures in Ni-based full
Heusler alloys Ni2MnX with X=Ga, In, Sn and Sb are studied within the framework
of the density-functional theory. The calculation of the exchange parameters is
based on the frozen-magnon approach. Despite closeness of the experimental
Curie temperatures for all four systems their magnetism appeared to differ
strongly. This difference involves both the Mn-Mn and Mn-Ni exchange
interactions. The Curie temperatures, Tc, are calculated within the mean-field
approximation by solving a matrix equation for a multi-sublattice system. Good
agreement with experiment for all four systems is obtained. The role of
different exchange interactions in the formation of Tc of the systems is
discussed.Comment: 6 pages, 4 figure
- …