12,713 research outputs found
Recurrent backpropagation and the dynamical approach to adaptive neural computation
Error backpropagation in feedforward neural network models is a popular learning algorithm that has its roots in nonlinear estimation and optimization. It is being used routinely to calculate error gradients in nonlinear systems with hundreds of thousands of parameters. However, the classical architecture for backpropagation has severe restrictions. The extension of backpropagation to networks with recurrent connections will be reviewed. It is now possible to efficiently compute the error gradients for networks that have temporal dynamics, which opens applications to a host of problems in systems identification and control
The static potential: lattice versus perturbation theory in a renormalon-based approach
We compare, for the static potential and at short distances, perturbation
theory with the results of lattice simulations. We show that a
renormalon-dominance picture explains why in the literature sometimes
agreement, and another disagreement, is found between lattice simulations and
perturbation theory depending on the different implementations of the latter.
We also show that, within a renormalon-based scheme, perturbation theory agrees
with lattice simulations.Comment: 18 pages, 11 figures, lattice data of Necco and Sommer introduced,
references added, some lengthier explanations given, physical results
unchange
The static potential in {\cal N}=4 supersymmetric Yang-Mills at weak coupling
We compute the static potential associated to the locally 1/2 BPS Wilson loop
in =4 supersymmetric Yang-Mills theory with
accuracy. We also resum the leading logarithms, of , and show the structure of the renormalization
group equation at next-to-leading order in the multipole expansion. In order to
obtain these results it is crucial the use of an effective theory for the
ultrasoft degrees of freedom. We develop this theory up to next-to-leading
order in the multipole expansion. Using the same formalism we also compute the
leading logarithms, of , of the static
potential associated to an ordinary Wilson loop in the same theory.Comment: 6 pages, 1 figure. Two references added, misprints corrected.
Computation of the static potential associated to the ordinary static Wilson
loop incorporate
A Panchromatic View of Brown Dwarf Aurorae
Stellar coronal activity has been shown to persist into the low-mass star
regime, down to late M-dwarf spectral types. However, there is now an
accumulation of evidence suggesting that at the end of the main sequence there
is a transition in the nature of the magnetic activity from chromospheric and
coronal to planet-like and auroral, from local impulsive heating via flares and
MHD wave dissipation to energy dissipation from strong large-scale
magnetospheric current systems. We examine this transition and the prevalence
of auroral activity in brown dwarfs through a compilation of multi-wavelength
surveys of magnetic activity, including radio, X-ray, and optical. We compile
the results of those surveys and place their conclusions in the context of
auroral emission as the consequence of large-scale magnetospheric current
systems that accelerate energetic electron beams and drive the particles to
impact the cool atmospheric gas. We explore the different manifestation of
auroral phenomena in brown dwarf atmospheres, like H, and define their
distinguishing characteristics. We conclude that large amplitude photometric
variability in the near infrared is most likely a consequence of clouds in
brown dwarf atmospheres, but that auroral activity may be responsible for
long-lived stable surface features. We report a connection between auroral
H emission and quiescent radio emission in ECMI pulsing brown dwarfs,
suggesting a potential underlying physical connection between the quiescent and
auroral emissions. We also discuss the electrodynamic engines powering brown
dwarf aurorae and the possible role of satellites around these systems to both
power the aurorae and seed the magnetosphere with plasma.Comment: 26 pages, 17 figures, and 2 tables; accepted to Ap
Preparing the bound instance of quantum entanglement
Among the possibly most intriguing aspects of quantum entanglement is that it
comes in "free" and "bound" instances. Bound entangled states require entangled
states in preparation but, once realized, no free entanglement and therefore no
pure maximally entangled pairs can be regained. Their existence hence certifies
an intrinsic irreversibility of entanglement in nature and suggests a
connection with thermodynamics. In this work, we present a first experimental
unconditional preparation and detection of a bound entangled state of light. We
consider continuous-variable entanglement, use convex optimization to identify
regimes rendering its bound character well certifiable, and realize an
experiment that continuously produced a distributed bound entangled state with
an extraordinary and unprecedented significance of more than ten standard
deviations away from both separability and distillability. Our results show
that the approach chosen allows for the efficient and precise preparation of
multimode entangled states of light with various applications in quantum
information, quantum state engineering and high precision metrology.Comment: The final version accounts for a recent comment in Nature Physics
[24] clarifying that a previous claim of having generated bound entanglement
[23] was not supported by the authors' data. We also extended our
introduction and discussion and also added reference
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