2,266 research outputs found
State-Dependent Computation Using Coupled Recurrent Networks
Although conditional branching between possible behavioral states is a hallmark of intelligent behavior, very little is known about the neuronal mechanisms that support this processing. In a step toward solving this problem, we demonstrate by theoretical analysis and simulation how
networks of richly interconnected neurons, such as those observed in the superficial layers of the neocortex, can embed reliable, robust finite state machines. We show how a multistable neuronal network containing a number of states can be created very simply by coupling two recurrent
networks whose synaptic weights have been configured for soft winner-take-all (sWTA) performance. These two sWTAs have simple, homogeneous, locally recurrent connectivity except for a small fraction of recurrent cross-connections between them, which are used to embed the required states. This coupling between the maps allows the network to continue to express the current state even after the input that elicited that state iswithdrawn. In addition, a small number of transition neurons implement the necessary input-driven transitions between the embedded states. We provide simple rules to systematically design and construct neuronal state machines of this kind. The significance of our finding is that it offers a method whereby the cortex could construct networks supporting a broad range of sophisticated processing by applying only small specializations to the same generic neuronal circuit
Generating derivative structures: Algorithm and applications
We present an algorithm for generating all derivative superstructures--for
arbitrary parent structures and for any number of atom types. This algorithm
enumerates superlattices and atomic configurations in a geometry-independent
way. The key concept is to use the quotient group associated with each
superlattice to determine all unique atomic configurations. The run time of the
algorithm scales linearly with the number of unique structures found. We show
several applications demonstrating how the algorithm can be used in materials
design problems. We predict an altogether new crystal structure in Cd-Pt and
Pd-Pt, and several new ground states in Pd-rich and Pt-rich binary systems
The story of supernova 'Refsdal' told by MUSE
We present MUSE observations in the core of the HFF galaxy cluster MACS
J1149.5+2223, where the first magnified and spatially-resolved multiple images
of SN 'Refsdal' at redshift 1.489 were detected. Thanks to a DDT program with
the VLT and the extraordinary efficiency of MUSE, we measure 117 secure
redshifts with just 4.8 hours of total integration time on a single target
pointing. We spectroscopically confirm 68 galaxy cluster members, with redshift
values ranging from 0.5272 to 0.5660, and 18 multiple images belonging to 7
background, lensed sources distributed in redshifts between 1.240 and 3.703.
Starting from the combination of our catalog with those obtained from extensive
spectroscopic and photometric campaigns using the HST, we select a sample of
300 (164 spectroscopic and 136 photometric) cluster members, within
approximately 500 kpc from the BCG, and a set of 88 reliable multiple images
associated to 10 different background source galaxies and 18 distinct knots in
the spiral galaxy hosting SN 'Refsdal'. We exploit this valuable information to
build 6 detailed strong lensing models, the best of which reproduces the
observed positions of the multiple images with a rms offset of only 0.26". We
use these models to quantify the statistical and systematic errors on the
predicted values of magnification and time delay of the next emerging image of
SN 'Refsdal'. We find that its peak luminosity should should occur between
March and June 2016, and should be approximately 20% fainter than the dimmest
(S4) of the previously detected images but above the detection limit of the
planned HST/WFC3 follow-up. We present our two-dimensional reconstruction of
the cluster mass density distribution and of the SN 'Refsdal' host galaxy
surface brightness distribution. We outline the roadmap towards even better
strong lensing models with a synergetic MUSE and HST effort.Comment: 21 pages, 9 figures, 6 tables; accepted for publication in the
Astrophysical Journal - extra information on data analysis added, all model
predictions and results unchange
A highly-ionized region surrounding SN Refsdal revealed by MUSE
Supernova (SN) Refsdal is the first multiply-imaged, highly-magnified, and
spatially-resolved SN ever observed. The SN exploded in a highly-magnified
spiral galaxy at z=1.49 behind the Frontier Fields Cluster MACS1149, and
provides a unique opportunity to study the environment of SNe at high z. We
exploit the time delay between multiple images to determine the properties of
the SN and its environment, before, during, and after the SN exploded. We use
the integral-field spectrograph MUSE on the VLT to simultaneously target all
observed and model-predicted positions of SN Refsdal. We find MgII emission at
all positions of SN Refsdal, accompanied by weak FeII* emission at two
positions. The measured ratios of [OII] to MgII emission of 10-20 indicate a
high degree of ionization with low metallicity. Because the same high degree of
ionization is found in all images, and our spatial resolution is too coarse to
resolve the region of influence of SN Refsdal, we conclude that this high
degree of ionization has been produced by previous SNe or a young and hot
stellar population. We find no variability of the [OII] line over a period of
57 days. This suggests that there is no variation in the [OII] luminosity of
the SN over this period, or that the SN has a small contribution to the
integrated [OII] emission over the scale resolved by our observations.Comment: 5 pages, 4 figures, accepted for publication in A&
Laughlin liquid - Wigner solid transition at high density in wide quantum wells
Assuming that the phase transition between the Wigner solid and the Laughlin
liquid is first-order, we compare ground-state energies to find features of the
phase diagram at fixed . Rather than use the Coulomb interaction, we
calculate the effective interaction in a square quantum well, and fit the
results to a model interaction with length parameter roughly
proportional to the width of the well. We find a transition to the Wigner solid
phase at high density in very wide wells, driven by the softening of the
interaction at short distances, as well as the more well-known transition to
the Wigner solid at low density, driven by Landau-level mixing.Comment: RevTeX 3.0, 3 Postscript figures appended in uuencoded forma
Freezing of the quantum Hall liquid at 1/7 and 1/9
We compare the free energy computed from the ground state energy and
low-lying excitations of the 2-D Wigner solid and the fractional quantum Hall
liquid, at magnetic filling factors and 1/9. We find that the
Wigner solid melts into the fractional quantum Hall liquid at roughly the same
temperature as that of some recent luminescence experiments, while it remains a
solid at the lower temperatures characteristic of the transport experiments. We
propose this melting as a consistent interpretation of both sets of
experiments.Comment: uses RevTeX 2.0 or 3.
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