36,478 research outputs found
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
Multi-feed cone Cassegrain antenna Patent
Design and operation of multi-feed cone Cassegrain antenn
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 Fractal Dimension of SAT Formulas
Modern SAT solvers have experienced a remarkable progress on solving
industrial instances. Most of the techniques have been developed after an
intensive experimental testing process. Recently, there have been some attempts
to analyze the structure of these formulas in terms of complex networks, with
the long-term aim of explaining the success of these SAT solving techniques,
and possibly improving them.
We study the fractal dimension of SAT formulas, and show that most industrial
families of formulas are self-similar, with a small fractal dimension. We also
show that this dimension is not affected by the addition of learnt clauses. We
explore how the dimension of a formula, together with other graph properties
can be used to characterize SAT instances. Finally, we give empirical evidence
that these graph properties can be used in state-of-the-art portfolios.Comment: 20 pages, 11 Postscript figure
Focusing of Intense Subpicosecond Laser Pulses in Wedge Targets
Two dimensional particle-in-cell simulations characterizing the interaction
of ultraintense short pulse lasers in the range 10^{18} \leq I \leq 10^{20}
W/cm^{2} with converging target geometries are presented. Seeking to examine
intensity amplification in high-power laser systems, where focal spots are
typically non-diffraction limited, we describe key dynamical features as the
injected laser intensity and convergence angle of the target are systematically
varied. We find that laser pulses are focused down to a wavelength with the
peak intensity amplified by an order of magnitude beyond its vacuum value, and
develop a simple model for how the peak location moves back towards the
injection plane over time. This performance is sustained over hundreds of
femtoseconds and scales to laser intensities beyond 10^{20} W/cm^{2} at 1 \mu m
wavelength.Comment: 5 pages, 6 figures, accepted for publication in Physics of Plasma
Electrical manipulation of an electronic two-state system in Ge/Si quantum dots
We calculate that the electron states of strained self-assembled Ge/Si
quantum dots provide a convenient two-state system for electrical control. An
electronic state localized at the apex of the quantum dot is nearly degenerate
with a state localized at the base of the quantum dot. Small electric fields
shift the electronic ground state from apex-localized to base-localized, which
permits sensitive tuning of the electronic, optical and magnetic properties of
the dot. As one example, we describe how spin-spin coupling between two Ge/Si
dots can be controlled very sensitively by shifting the individual dot's
electronic ground state between apex and base
Mechanism for bipolar resistive switching in transition metal oxides
We introduce a model that accounts for the bipolar resistive switching
phenomenom observed in transition metal oxides. It qualitatively describes the
electric field-enhanced migration of oxygen vacancies at the nano-scale. The
numerical study of the model predicts that strong electric fields develop in
the highly resistive dielectric-electrode interfaces, leading to a spatially
inhomogeneous oxygen vacancies distribution and a concomitant resistive
switching effect. The theoretical results qualitatively reproduce non-trivial
resistance hysteresis experiments that we also report, providing key validation
to our model.Comment: Accepted for publication in Physical Review B, 6 twocolumn pages, 5
figure
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