10,879 research outputs found
A differential memristive synapse circuit for on-line learning in neuromorphic computing systems
Spike-based learning with memristive devices in neuromorphic computing
architectures typically uses learning circuits that require overlapping pulses
from pre- and post-synaptic nodes. This imposes severe constraints on the
length of the pulses transmitted in the network, and on the network's
throughput. Furthermore, most of these circuits do not decouple the currents
flowing through memristive devices from the one stimulating the target neuron.
This can be a problem when using devices with high conductance values, because
of the resulting large currents. In this paper we propose a novel circuit that
decouples the current produced by the memristive device from the one used to
stimulate the post-synaptic neuron, by using a novel differential scheme based
on the Gilbert normalizer circuit. We show how this circuit is useful for
reducing the effect of variability in the memristive devices, and how it is
ideally suited for spike-based learning mechanisms that do not require
overlapping pre- and post-synaptic pulses. We demonstrate the features of the
proposed synapse circuit with SPICE simulations, and validate its learning
properties with high-level behavioral network simulations which use a
stochastic gradient descent learning rule in two classification tasks.Comment: 18 Pages main text, 9 pages of supplementary text, 19 figures.
Patente
Plasmon interactions in the quark-gluon plasma
Yang-Mills theory at finite temperature is rewritten as a theory of plasmons
which provides a Hamiltonian framework for perturbation theory with resummation
of hard thermal loops.Comment: 12 pages, LaTeX, minor typos corrected, discussion adde
Large Magnetoresistance and Jahn Teller effect in SrFeCoO
Neutron diffraction measurement on the spin glass double perovskite
SrFeCoO reveals site disorder as well as Co intermediate spin
state. In addition, multiple valence states of Fe and Co are confirmed through
M\"{o}ssbauer and X-ray photoelectron spectroscopy. The structural disorder and
multiple valence lead to competing ferromagnetic and antiferromagnetic
interactions and subsequently to a spin glass state, which is reflected in the
form of an additional -linear contribution at low temperatures in specific
heat. A clear evidence of Jahn-Teller distortion at the Co-O complex
is observed and incorporating the physics of Jahn-Teller effect, the presence
of localized magnetic moment is shown. A large, negative and anomalous
magnetoresistance of 63% at 14K in 12T applied field is observed for
SrFeCoO. The observed magnetoresistance could be explained by applying
a semi-empirical fit consisting of a negative and a positive contribution and
show that the negative magnetoresistance is due to spin scattering of carriers
by localized magnetic moments in the spin glass phase
Massive Spin-2 fields of Geometric Origin in Curved Spacetimes
We study the consistency of a model which includes torsion as well as the
metric as dynamical fields and has massive spin-2 particle in its spectrum. The
massive spin-2 mode resides in the torsion, rather than in the metric. It is
known that this model is tachyon- and ghost-free in Minkowski background. We
show that this property remains valid and no other pathologies emerge in de
Sitter and anti-de Sitter backgrounds, with some of our results extending to
arbirary Einstein space backgrounds. This suggests that the model is
consistent, at least at the classical level, unlike, e.g., the Fierz--Pauli
theory.Comment: 17 pages, Clarifying remarks added in section 5, minor changes,
version to be published in the Phys. Rev.
A neuromorphic systems approach to in-memory computing with non-ideal memristive devices: From mitigation to exploitation
Memristive devices represent a promising technology for building neuromorphic
electronic systems. In addition to their compactness and non-volatility
features, they are characterized by computationally relevant physical
properties, such as state-dependence, non-linear conductance changes, and
intrinsic variability in both their switching threshold and conductance values,
that make them ideal devices for emulating the bio-physics of real synapses. In
this paper we present a spiking neural network architecture that supports the
use of memristive devices as synaptic elements, and propose mixed-signal
analog-digital interfacing circuits which mitigate the effect of variability in
their conductance values and exploit their variability in the switching
threshold, for implementing stochastic learning. The effect of device
variability is mitigated by using pairs of memristive devices configured in a
complementary push-pull mechanism and interfaced to a current-mode normalizer
circuit. The stochastic learning mechanism is obtained by mapping the desired
change in synaptic weight into a corresponding switching probability that is
derived from the intrinsic stochastic behavior of memristive devices. We
demonstrate the features of the CMOS circuits and apply the architecture
proposed to a standard neural network hand-written digit classification
benchmark based on the MNIST data-set. We evaluate the performance of the
approach proposed on this benchmark using behavioral-level spiking neural
network simulation, showing both the effect of the reduction in conductance
variability produced by the current-mode normalizer circuit, and the increase
in performance as a function of the number of memristive devices used in each
synapse.Comment: 13 pages, 12 figures, accepted for Faraday Discussion
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Ion beam induced enhanced diffusion from gold thin films in silicon
Enhanced diffusion of gold atoms into silicon substrate has been studied in
Au thin films of various thicknesses (2.0, 5.3, 10.9 and 27.5 nm) deposited on
Si(111) and followed by irradiation with 1.5 MeV Au2+ at a flux of 6.3x10^12
ions cm-2 s-1 and fluence up to 1x10^15 ions cm-2. The high resolution
transmission electron microscopy measurements showed the presence of gold
silicide formation for the above-mentioned systems at fluence greater than
equal to 1x1014 ions cm-2. The maximum depth to which the gold atoms have been
diffused at a fluence of 1x10^14 ions cm-2 for the cases of 2.0, 5.3, 10.9 and
27.5 nm thick films has been found to be 60, 95, 160 and 13 nm respectively.
Interestingly, at higher fluence of 1x1015 ions cm-2 in case of 27.5 nm thick
film, gold atoms from the film transported to a maximum depth of 265 nm in the
substrate. The substrate silicon is found to be amorphous at the above fluence
values where unusually large mass transport occurred. Enhanced diffusion has
been explained on the basis of ion beam induced, flux dependent amorphous
nature of the substrate, and transient beam induced temperature effects. This
work confirms the absence of confinement effects that arise from spatially
confined structures and existence of thermal and chemical reactions during ion
irradiation.Comment: 15 pages, 3 figure
Observations on the developmental stages of the smooth dogfish, Eridacnis radcliffei Smith from Gulf of Mannar.
The structure of mature reproductive organs of fifteien adult females of
Eridacn'.s radcliffei. ranging in total length from 150 to 218 mm collected from
the trawl catches off Mandapam in Gulf of Mannar during February, 1972 at a
depth ranging frori 100 to 150 fathoms were studied and the various stages of
intra-uterine embryos are described and discussed. A close examination of different
stages of embryos revealed that this species exhibits ovoviviparous type of
development. The intra-uterine egg is enclosed in a thin shell membrane which
disappears when the embryo develops inside the uterus. The embryos are seen
free inside the uterus and no placental connection has been observed in any
stage of development
The Bramble shark Echinorhinus brucus (Bonnaterre) landed at Cochin
Two female sharks having the diagnostic characters of Echinorhinus brucus (Bonnaterre) were caught by hooks and line fishermen southwest of Cochin about 60 km from the shore from depths of 120-160 metres. The bramble shark Echinorhinus brucus (Bonnaterre) usually occurs in the upper conitnental slope and the deeper neritic waters of the Atlantic, Mediterranean and Indo-Pacific. These deep water sharks were caught when the artisanal fishermen from Colachel were fishing with hooks and line in the hitherto under exploited fishing grounds in deeper waters
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