6,313 research outputs found
Prioritized Sweeping Neural DynaQ with Multiple Predecessors, and Hippocampal Replays
During sleep and awake rest, the hippocampus replays sequences of place cells
that have been activated during prior experiences. These have been interpreted
as a memory consolidation process, but recent results suggest a possible
interpretation in terms of reinforcement learning. The Dyna reinforcement
learning algorithms use off-line replays to improve learning. Under limited
replay budget, a prioritized sweeping approach, which requires a model of the
transitions to the predecessors, can be used to improve performance. We
investigate whether such algorithms can explain the experimentally observed
replays. We propose a neural network version of prioritized sweeping
Q-learning, for which we developed a growing multiple expert algorithm, able to
cope with multiple predecessors. The resulting architecture is able to improve
the learning of simulated agents confronted to a navigation task. We predict
that, in animals, learning the world model should occur during rest periods,
and that the corresponding replays should be shuffled.Comment: Living Machines 2018 (Paris, France
Anatomical features, fiber morphological, physical and mechanical properties of three years old new hybrid Paulownia: green Paulownia
Objective: Green Paulownia (hybridization of Paulownia elongata × Paulownia fotunei and tropical Paulownia spp.) is new hybrid claimed as one of the fast-growing woody plants with the high potential as a fiber material or lignocellulosic material. The material for this study originates from the area of Nanning in China.
Methodology: Cell morphology and anatomical appearances were observed and evaluated under the image analysis system (Leica DMLS). Physical and mechanical properties were evaluated based on the American Society for Testing and Materials (ASTM) standards.
Results: From the results, average value of the mean fiber length was 0.905 mm, mean fiber length 34.59 μm, lumen thickness 26.80 μm and cell wall thickness 3.89 μm. Fiber dimensions of green Paulownia are in the normal range for hardwoods. The physical and mechanical properties of 3 years old green Paulownia have similar properties than those 7-11 years old Paulownia published in China.
Conclusion: The 3 years old green Paulownia timbers can be used as materials for furniture
Design of an electrochemical micromachining machine
Electrochemical micromachining (μECM) is a non-conventional machining process based on the phenomenon of electrolysis. μECM became an attractive area of research due to the fact that this process does not create any defective layer after machining and that there is a growing demand for better surface integrity on different micro applications including microfluidics systems, stress-free drilled holes in automotive and aerospace manufacturing with complex shapes, etc. This work presents the design of a next generation μECM machine for the automotive, aerospace, medical and metrology sectors. It has three axes of motion (X, Y, Z) and a spindle allowing the tool-electrode to rotate during machining. The linear slides for each axis use air bearings with linear DC brushless motors and 2-nm resolution encoders for ultra precise motion. The control system is based on the Power PMAC motion controller from Delta Tau. The electrolyte tank is located at the rear of the machine and allows the electrolyte to be changed quickly. This machine features two process control algorithms: fuzzy logic control and adaptive feed rate. A self-developed pulse generator has been mounted and interfaced with the machine and a wire ECM grinding device has been added. The pulse generator has the possibility to reverse the pulse polarity for on-line tool fabrication.The research reported in this paper is supported by the European Commission within the project “Minimizing Defects in Micro-Manufacturing Applications (MIDEMMA)” (FP7-2011-NMPICT- FoF-285614)
Decaying Dark Matter in Supersymmetric Model and Cosmic-Ray Observations
We study cosmic-rays in decaying dark matter scenario, assuming that the dark
matter is the lightest superparticle and it decays through a R-parity violating
operator. We calculate the fluxes of cosmic-rays from the decay of the dark
matter and those from the standard astrophysical phenomena in the same
propagation model using the GALPROP package. We reevaluate the preferred
parameters characterizing standard astrophysical cosmic-ray sources with taking
account of the effects of dark matter decay. We show that, if energetic leptons
are produced by the decay of the dark matter, the fluxes of cosmic-ray positron
and electron can be in good agreements with both PAMELA and Fermi-LAT data in
wide parameter region. It is also discussed that, in the case where sizable
number of hadrons are also produced by the decay of the dark matter, the mass
of the dark matter is constrained to be less than 200-300 GeV in order to avoid
the overproduction of anti-proton. We also show that the cosmic gamma-ray flux
can be consistent with the results of Fermi-LAT observation if the mass of the
dark matter is smaller than nearly 4 TeV.Comment: 24 pages, 5 figure
Enhancement of the Nernst effect by stripe order in a high-Tc superconductor
The Nernst effect in metals is highly sensitive to two kinds of phase
transition: superconductivity and density-wave order. The large positive Nernst
signal observed in hole-doped high-Tc superconductors above their transition
temperature Tc has so far been attributed to fluctuating superconductivity.
Here we show that in some of these materials the large Nernst signal is in fact
caused by stripe order, a form of spin / charge modulation which causes a
reconstruction of the Fermi surface. In LSCO doped with Nd or Eu, the onset of
stripe order causes the Nernst signal to go from small and negative to large
and positive, as revealed either by lowering the hole concentration across the
quantum critical point in Nd-LSCO, or lowering the temperature across the
ordering temperature in Eu-LSCO. In the latter case, two separate peaks are
resolved, respectively associated with the onset of stripe order at high
temperature and superconductivity near Tc. This sensitivity to Fermi-surface
reconstruction makes the Nernst effect a promising probe of broken symmetry in
high-Tc superconductors
On the Beaming of Gluonic Fields at Strong Coupling
We examine the conditions for beaming of the gluonic field sourced by a heavy
quark in strongly-coupled conformal field theories, using the AdS/CFT
correspondence. Previous works have found that, contrary to naive expectations,
it is possible to set up collimated beams of gluonic radiation despite the
strong coupling. We show that, on the gravity side of the correspondence, this
follows directly (for arbitrary quark motion, and independently of any
approximations) from the fact that the string dual to the quark remains
unexpectedly close to the AdS boundary whenever the quark moves
ultra-relativistically. We also work out the validity conditions for a related
approximation scheme that proposed to explain the beaming effect though the
formation of shock waves in the bulk fields emitted by the string. We find that
these conditions are fulfilled in the case of ultra-relativistic uniform
circular motion that motivated the proposal, but unfortunately do not hold for
much more general quark trajectories.Comment: 1+33 pages, 2 figure
Planet Populations as a Function of Stellar Properties
Exoplanets around different types of stars provide a window into the diverse
environments in which planets form. This chapter describes the observed
relations between exoplanet populations and stellar properties and how they
connect to planet formation in protoplanetary disks. Giant planets occur more
frequently around more metal-rich and more massive stars. These findings
support the core accretion theory of planet formation, in which the cores of
giant planets form more rapidly in more metal-rich and more massive
protoplanetary disks. Smaller planets, those with sizes roughly between Earth
and Neptune, exhibit different scaling relations with stellar properties. These
planets are found around stars with a wide range of metallicities and occur
more frequently around lower mass stars. This indicates that planet formation
takes place in a wide range of environments, yet it is not clear why planets
form more efficiently around low mass stars. Going forward, exoplanet surveys
targeting M dwarfs will characterize the exoplanet population around the lowest
mass stars. In combination with ongoing stellar characterization, this will
help us understand the formation of planets in a large range of environments.Comment: Accepted for Publication in the Handbook of Exoplanet
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