137 research outputs found
A ferroelectric memristor
Memristors are continuously tunable resistors that emulate synapses.
Conceptualized in the 1970s, they traditionally operate by voltage-induced
displacements of matter, but the mechanism remains controversial. Purely
electronic memristors have recently emerged based on well-established physical
phenomena with albeit modest resistance changes. Here we demonstrate that
voltage-controlled domain configurations in ferroelectric tunnel barriers yield
memristive behaviour with resistance variations exceeding two orders of
magnitude and a 10 ns operation speed. Using models of ferroelectric-domain
nucleation and growth we explain the quasi-continuous resistance variations and
derive a simple analytical expression for the memristive effect. Our results
suggest new opportunities for ferroelectrics as the hardware basis of future
neuromorphic computational architectures
Evolving unipolar memristor spiking neural networks
© 2015 Taylor & Francis. Neuromorphic computing â brain-like computing in hardware â typically requires myriad complimentary metal oxide semiconductor spiking neurons interconnected by a dense mesh of nanoscale plastic synapses. Memristors are frequently cited as strong synapse candidates due to their statefulness and potential for low-power implementations. To date, plentiful research has focused on the bipolar memristor synapse, which is capable of incremental weight alterations and can provide adaptive self-organisation under a Hebbian learning scheme. In this paper, we consider the unipolar memristor synapse â a device capable of non-Hebbian switching between only two states (conductive and resistive) through application of a suitable input voltage â and discuss its suitability for neuromorphic systems. A self-adaptive evolutionary process is used to autonomously find highly fit network configurations. Experimentation on two robotics tasks shows that unipolar memristor networks evolve task-solving controllers faster than both bipolar memristor networks and networks containing constant non-plastic connections whilst performing at least comparably
Evidence of Activity-Specific, Radial Organization of Mitotic Chromosomes in Drosophila
A fluorescently labeled protein specifically binding to genes was reproducibly found at the periphery of condensed mitotic fruit fly chromosomes, illustrating preservation of a radial structure between consecutive divisions
SPOrt: an Experiment Aimed at Measuring the Large Scale Cosmic Microwave Background Polarization
SPOrt (Sky Polarization Observatory) is a space experiment to be flown on the
International Space Station during Early Utilization Phase aimed at measuring
the microwave polarized emission with FWHM = 7deg, in the frequency range 22-90
GHz. The Galactic polarized emission can be observed at the lower frequencies
and the polarization of Cosmic Microwave Background (CMB) at 90 GHz, where
contaminants are expected to be less important. The extremely low level of the
CMB Polarization signal (< 1 uK) calls for intrinsically stable radiometers.
The SPOrt instrument is expressly devoted to CMB polarization measurements and
the whole design has been optimized for minimizing instrumental polarization
effects. In this contribution we present the receiver architecture based on
correlation techniques, the analysis showing its intrinsic stability and the
custom hardware development carried out to detect such a low signal.Comment: 9 pages, 5 figures, conference proceeding, to appear in "Polarimetry
in Astronomy", SPIE Symposium on 'Astronomical Telescopes and
Instrumentation', Waikoloa, August 22-28 200
First Detection of Polarization of the Submillimetre Diffuse Galactic Dust Emission by Archeops
We present the first determination of the Galactic polarized emission at 353
GHz by Archeops. The data were taken during the Arctic night of February 7,
2002 after the balloon--borne instrument was launched by CNES from the Swedish
Esrange base near Kiruna. In addition to the 143 GHz and 217 GHz frequency
bands dedicated to CMB studies, Archeops had one 545 GHz and six 353 GHz
bolometers mounted in three polarization sensitive pairs that were used for
Galactic foreground studies. We present maps of the I, Q, U Stokes parameters
over 17% of the sky and with a 13 arcmin resolution at 353 GHz (850 microns).
They show a significant Galactic large scale polarized emission coherent on the
longitude ranges [100, 120] and [180, 200] deg. with a degree of polarization
at the level of 4-5%, in agreement with expectations from starlight
polarization measurements. Some regions in the Galactic plane (Gem OB1,
Cassiopeia) show an even stronger degree of polarization in the range 10-20%.
Those findings provide strong evidence for a powerful grain alignment mechanism
throughout the interstellar medium and a coherent magnetic field coplanar to
the Galactic plane. This magnetic field pervades even some dense clouds.
Extrapolated to high Galactic latitude, these results indicate that
interstellar dust polarized emission is the major foreground for PLANCK-HFI CMB
polarization measurement.Comment: Submitted to Astron. & Astrophys., 14 pages, 12 Fig., 2 Table
Specific heat and heat conductivity of the BaTiO3 polycrystalline films with the thickness in the range 20 - 1100 nm
Thermal properties - specific heat and heat conductivity coefficient - of
polycrystalline BaTiO3 films on massive substrates were studied as a function
of the temperature and the film thickness by ac-hot probe method. The anomalies
of specific heat with decreasing of the film thickness from 1100 to 20 nm
revealed the reducing of critical temperature (Tc) and excess entropy of the
ferroelectric phase transition, which becomes diffused. The critical thickness
of the film at which Tc = 0 estimated as 2.5 nm.Comment: 12 pages, 7 figures, 2 tables, 450kb; submitted to J.Phys.:Cond.Mat
The Cosmic Microwave Background Anisotropy Power Spectrum measured by Archeops
We present a determination by the Archeops experiment of the angular power
spectrum of the cosmic microwave background anisotropy in 16 bins over the
multipole range l=15-350. Archeops was conceived as a precursor of the Planck
HFI instrument by using the same optical design and the same technology for the
detectors and their cooling. Archeops is a balloon-borne instrument consisting
of a 1.5 m aperture diameter telescope and an array of 21 photometers
maintained at ~100 mK that are operating in 4 frequency bands centered at 143,
217, 353 and 545 GHz. The data were taken during the Arctic night of February
7, 2002 after the instrument was launched by CNES from Esrange base (Sweden).
The entire data cover ~ 30% of the sky.This first analysis was obtained with a
small subset of the dataset using the most sensitive photometer in each CMB
band (143 and 217 GHz) and 12.6% of the sky at galactic latitudes above 30
degrees where the foreground contamination is measured to be negligible. The
large sky coverage and medium resolution (better than 15 arcminutes) provide
for the first time a high signal-to-noise ratio determination of the power
spectrum over angular scales that include both the first acoustic peak and
scales probed by COBE/DMR. With a binning of Delta(l)=7 to 25 the error bars
are dominated by sample variance for l below 200. A companion paper details the
cosmological implications.Comment: A&A Letter, in press, 6 pages, 4 figures, see also
http://www.archeops.or
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