25,488 research outputs found
Band structure and atomic sum rules for x-ray dichroism
Corrections to the atomic orbital sum rule for circular magnetic x-ray
dichroism in solids are derived using orthonormal LMTOs as a single-particle
basis for electron band states.Comment: 7 pages, no figure
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Changing the way we learn: towards agile learning and co-operation
This paper addresses the need for learning and competence development in industrial organizations. The people that enter professional organizations today are part of a gamer generation that have some or much experience with on-line games. Therefore they are more open to e-learning and in general more open to access anything on-line. At the same time industrial organizations experience a pressure on their ability to train employees faster due to the increase in complexity. We argue that games are not yet mature enough to support this training challenge as stand alone efforts. But games can support the training and competence development in a synchronized setup with other means
Simple stochastic models showing strong anomalous diffusion
We show that {\it strong} anomalous diffusion, i.e. \mean{|x(t)|^q} \sim
t^{q \nu(q)} where is a nonlinear function of , is a generic
phenomenon within a class of generalized continuous-time random walks. For such
class of systems it is possible to compute analytically nu(2n) where n is an
integer number. The presence of strong anomalous diffusion implies that the
data collapse of the probability density function P(x,t)=t^{-nu}F(x/t^nu)
cannot hold, a part (sometimes) in the limit of very small x/t^\nu, now
nu=lim_{q to 0} nu(q). Moreover the comparison with previous numerical results
shows that the shape of F(x/t^nu) is not universal, i.e., one can have systems
with the same nu but different F.Comment: Final versio
Evolution of magnetic fields and energetics of flares in active region 8210
To better understand eruptive events in the solar corona, we combine sequences of multi-wavelength observations and modelling of the coronal magnetic field of NOAA AR 8210, a highly flare-productive active region. From the photosphere to the corona, the observations give us information about the motion of magnetic elements (photospheric magnetograms), the location of flares (e.g., H, EUV or soft X-ray brightenings), and the type of events (H blueshift events). Assuming that the evolution of the coronal magnetic field above an active region can be described by successive equilibria, we follow in time the magnetic changes of the 3D nonlinear force-free (nlff) fields reconstructed from a time series of photospheric vector magnetograms. We apply this method to AR 8210 observed on May 1, 1998 between 17:00 UT and 21:40 UT. We identify two types of horizontal photospheric motions that can drive an eruption: a clockwise rotation of the sunspot, and a fast motion of an emerging polarity. The reconstructed nlff coronal fields give us a scenario of the confined flares observed in AR 8210: the slow sunspot rotation enables the occurence of flare by a reconnection process close to a separatrix surface whereas the fast motion is associated with small-scale reconnections but no detectable flaring activity. We also study the injection rates of magnetic energy, Poynting flux and relative magnetic helicity through the photosphere and into the corona. The injection of magnetic energy by transverse photospheric motions is found to be correlated with the storage of energy in the corona and then the release by flaring activity. The magnetic helicity derived from the magnetic field and the vector potential of the nlff configuration is computed in the coronal volume. The magnetic helicity evolution shows that AR 8210 is dominated by the mutual helicity between the closed and potential fields and not by the self helicity of the closed field which characterizes the twist of confined flux bundles. We conclude that for AR 8210 the complex topology is a more important factor than the twist in the eruption process
Bursts and Shocks in a Continuum Shell Model
We study a "burst" event, i. e. the evolution of an initial condition having
support only in a finite interval of k-space, in the continuum shell model due
to Parisi. We show that the continuum equation without forcing or dissipation
can be explicitly written in characteristic form and that the right and left
moving parts can be solved exactly. When this is supplemented by the
appropriate shock condition it is possible to find the asymptotic form of the
burst.Comment: 15 pages, 2 eps figures included, Latex 2e. Contribution to the
proceedings of the conference: Disorder and Chaos, in honour of Giovanni
Paladin, September 22-24, 1997, in Rom
The Dreaming Variational Autoencoder for Reinforcement Learning Environments
Reinforcement learning has shown great potential in generalizing over raw
sensory data using only a single neural network for value optimization. There
are several challenges in the current state-of-the-art reinforcement learning
algorithms that prevent them from converging towards the global optima. It is
likely that the solution to these problems lies in short- and long-term
planning, exploration and memory management for reinforcement learning
algorithms. Games are often used to benchmark reinforcement learning algorithms
as they provide a flexible, reproducible, and easy to control environment.
Regardless, few games feature a state-space where results in exploration,
memory, and planning are easily perceived. This paper presents The Dreaming
Variational Autoencoder (DVAE), a neural network based generative modeling
architecture for exploration in environments with sparse feedback. We further
present Deep Maze, a novel and flexible maze engine that challenges DVAE in
partial and fully-observable state-spaces, long-horizon tasks, and
deterministic and stochastic problems. We show initial findings and encourage
further work in reinforcement learning driven by generative exploration.Comment: Best Student Paper Award, Proceedings of the 38th SGAI International
Conference on Artificial Intelligence, Cambridge, UK, 2018, Artificial
Intelligence XXXV, 201
Three-dimensional MgB-type superconductivity in hole-doped diamond
We substantiate by calculations that the recently discovered
superconductivity below 4 K in 3% boron-doped diamond is caused by
electron-phonon coupling of the same type as in MgB, albeit in 3
dimensions. Holes at the top of the zone-centered, degenerate -bonding
valence band couple strongly to the optical bond-stretching modes. The increase
from 2 to 3 dimensions reduces the mode-softening crucial for reaching
40 K in MgB Even if diamond had the same \emph{bare} coupling constant
as MgB which could be achieved with 10% doping, would only be 25
K. Superconductivity above 1 K in Si (Ge) requires hole-doping beyond 5% (10%).Comment: revised version, accepted by PR
The Stability Balloon for Two-dimensional Vortex Ripple Patterns
Patterns of vortex ripples form when a sand bed is subjected to an
oscillatory fluid flow. Here we describe experiments on the response of regular
vortex ripple patterns to sudden changes of the driving amplitude a or
frequency f. A sufficient decrease of f leads to a "freezing" of the pattern,
while a sufficient increase of f leads to a supercritical secondary "pearling"
instability. Sufficient changes in the amplitude a lead to subcritical
secondary "doubling" and "bulging" instabilities. Our findings are summarized
in a "stability balloon" for vortex ripple pattern formation.Comment: 4 pages, 5 figure
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