7,719 research outputs found
Autoresonant control of the magnetization switching in single-domain nanoparticles
The ability to control the magnetization switching in nanoscale devices is a
crucial step for the development of fast and reliable techniques to store and
process information. Here we show that the switching dynamics can be controlled
efficiently using a microwave field with slowly varying frequency
(autoresonance). This technique allowed us to reduce the applied field by more
than compared to competing approaches, with no need to fine-tune the
field parameters. For a linear chain of nanoparticles the effect is even more
dramatic, as the dipolar interactions tend to cancel out the effect of the
temperature. Simultaneous switching of all the magnetic moments can thus be
efficiently triggered on a nanosecond timescale
Regional assessment of groundwater recharge in the lower Mekong Basin
Groundwater recharge remains almost totally unknown across the Mekong River Basin, hindering the evaluation of groundwater potential for irrigation. A regional regression model was developed to map groundwater recharge across the Lower Mekong Basin where agricultural water demand is increasing, especially during the dry season. The model was calibrated with baseflow computed with the local-minimum flow separation method applied to streamflow recorded in 65 unregulated sub-catchments since 1951. Our results, in agreement with previous local studies, indicate that spatial variations in groundwater recharge are predominantly controlled by the climate (rainfall and evapotranspiration) while aquifer characteristics seem to play a secondary role at this regional scale. While this analysis suggests large scope for expanding agricultural groundwater use, the map derived from this study provides a simple way to assess the limits of groundwater-fed irrigation development. Further data measurements to capture local variations in hydrogeology will be required to refine the evaluation of recharge rates to support practical implementations
A few simple steps to improve the description of group results in neuroscience
No abstract available
Spin-torque switching and control using chirped oscillating currents
We propose to use oscillating spin currents with slowly varying frequency
(chirp) to manipulate and control the magnetization dynamics in a nanomagnet.
By recasting the Landau-Lifshitz-Slonczewski equation in a quantum-like
two-level formalism, we show that a chirped spin current polarized in the
direction normal to the anisotropy axis can induce a stable precession of the
magnetic moment at any angle (up to ) with respect to the anisotropy
axis. The drive current can be modest ( or lower) provided
the chirp rate is sufficiently slow. The induced precession is stable against
thermal noise, even for small nano-objects at room temperature. Complete
reversal of the magnetization can be achieved by adding a small external
magnetic field antiparallel to the easy axis. Alternatively, a combination of
chirped ac and dc currents with different polarization directions can also be
used to trigger the reversal
Geometric Exponents of Dilute Logarithmic Minimal Models
The fractal dimensions of the hull, the external perimeter and of the red
bonds are measured through Monte Carlo simulations for dilute minimal models,
and compared with predictions from conformal field theory and SLE methods. The
dilute models used are those first introduced by Nienhuis. Their loop fugacity
is beta = -2cos(pi/barkappa}) where the parameter barkappa is linked to their
description through conformal loop ensembles. It is also linked to conformal
field theories through their central charges c = 13 - 6(barkappa +
barkappa^{-1}) and, for the minimal models of interest here, barkappa = p/p'
where p and p' are two coprime integers. The geometric exponents of the hull
and external perimeter are studied for the pairs (p,p') = (1,1), (2,3), (3,4),
(4,5), (5,6), (5,7), and that of the red bonds for (p,p') = (3,4). Monte Carlo
upgrades are proposed for these models as well as several techniques to improve
their speeds. The measured fractal dimensions are obtained by extrapolation on
the lattice size H,V -> infinity. The extrapolating curves have large slopes;
despite these, the measured dimensions coincide with theoretical predictions up
to three or four digits. In some cases, the theoretical values lie slightly
outside the confidence intervals; explanations of these small discrepancies are
proposed.Comment: 41 pages, 32 figures, added reference
Time- and Space-Efficient Evaluation of Some Hypergeometric Constants
The currently best known algorithms for the numerical evaluation of
hypergeometric constants such as to decimal digits have time
complexity and space complexity of or .
Following work from Cheng, Gergel, Kim and Zima, we present a new algorithm
with the same asymptotic complexity, but more efficient in practice. Our
implementation of this algorithm improves slightly over existing programs for
the computation of , and we announce a new record of 2 billion digits for
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