27,225 research outputs found
Different steady states for spin currents in noncollinear multilayers
We find there are at least two different steady states for transport across
noncollinear magnetic multilayers. In the conventional one there is a
discontinuity in the spin current across the interfaces which has been
identified as the source of current induced magnetic reversal; in the one
advocated herein the spin torque arises from the spin accumulation transverse
to the magnetization of a magnetic layer. These two states have quite different
attributes which should be discerned by current experiments.Comment: 8 pages, no figure. Accepted for publication in Journal of Physics:
Condensed Matte
The steady state in noncollinear magnetic multilayers
There are at least two different putative steady state solutions for current
across noncollinear magnetic multilayers; one has a discontinuity in the spin
current at the interface the other is continuous. We compare the resistance of
the two and find the solution with the continuous spin currents is lower. By
using the entropic principle we can state that this solution is a better
estimate of the resistance for a noncollinear magneticComment: 14 pages, 4 figures,Submitted to Physical Review
All-electrical control of single ion spins in a semiconductor
We propose a method for all-electrical initialization, control and readout of
the spin of single ions substituted into a semiconductor. Mn ions in GaAs form
a natural example. In the ion's ground state the Mn core spin magnetic moment
locks antiparallel to the spin and orbital magnetic moment of a bound valence
hole from the GaAs host. Direct electrical manipulation of the ion spin is
possible because electric fields manipulate the orbital wave function of the
hole, and through the spin-orbit coupling the spin is reoriented as well.
Coupling two or more ion spins can be achieved using electrical gates to
control the size of the valence hole wave function near the semiconductor
surface. This proposal for coherent manipulation of individual ionic spins and
controlled coupling of ionic spins via electrical gates alone may find
applications in extremely high density information storage and in scalable
coherent or quantum information processing.Comment: 5 pages, 3 figure
Oceanic CO2 increase in Baffin Bay
Measurements of the total inorganic carbon in the water of Baffin Bay are interpreted to reflect increases in atmospheric carbon dioxide due to fossil fuel combustion. The increases are indicated by differences at various depths in the alkalinity and total inorganic carbon values after correction for calcium carbonate dissolution and decay of organic matter. These differences are comparable to the changes reported for GEOSECS Atlantic and Pacific Stations
Capillarity Theory for the Fly-Casting Mechanism
Biomolecular folding and function are often coupled. During molecular
recognition events, one of the binding partners may transiently or partially
unfold, allowing more rapid access to a binding site. We describe a simple
model for this flycasting mechanism based on the capillarity approximation and
polymer chain statistics. The model shows that flycasting is most effective
when the protein unfolding barrier is small and the part of the chain which
extends towards the target is relatively rigid. These features are often seen
in known examples of flycasting in protein-DNA binding. Simulations of
protein-DNA binding based on well-funneled native-topology models with
electrostatic forces confirm the trends of the analytical theory
PowerAqua: fishing the semantic web
The Semantic Web (SW) offers an opportunity to develop novel, sophisticated forms of question answering (QA). Specifically, the availability of distributed semantic markup on a large scale opens the way to QA systems which can make use of such semantic information to provide precise, formally derived answers to questions. At the same time the distributed, heterogeneous, large-scale nature of the semantic information introduces significant challenges. In this paper we describe the design of a QA system, PowerAqua, designed to exploit semantic markup on the web to provide answers to questions posed in natural language. PowerAqua does not assume that the user has any prior information about the semantic resources. The system takes as input a natural language query, translates it into a set of logical queries, which are then answered by consulting and aggregating information derived from multiple heterogeneous semantic sources
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