3,027 research outputs found
Visual Spike-based Convolution Processing with a Cellular Automata Architecture
this paper presents a first approach for
implementations which fuse the Address-Event-Representation
(AER) processing with the Cellular Automata using FPGA and
AER-tools. This new strategy applies spike-based convolution
filters inspired by Cellular Automata for AER vision
processing. Spike-based systems are neuro-inspired circuits
implementations traditionally used for sensory systems or
sensor signal processing. AER is a neuromorphic
communication protocol for transferring asynchronous events
between VLSI spike-based chips. These neuro-inspired
implementations allow developing complex, multilayer,
multichip neuromorphic systems and have been used to design
sensor chips, such as retinas and cochlea, processing chips, e.g.
filters, and learning chips. Furthermore, Cellular Automata is a
bio-inspired processing model for problem solving. This
approach divides the processing synchronous cells which
change their states at the same time in order to get the solution.Ministerio de Educación y Ciencia TEC2006-11730-C03-02Ministerio de Ciencia e Innovación TEC2009-10639-C04-02Junta de Andalucía P06-TIC-0141
Constraining the properties of neutron star crusts with the transient low-mass X-ray binary Aql X-1
Aql X-1 is a prolific transient neutron star low-mass X-ray binary that
exhibits an accretion outburst approximately once every year. Whether the
thermal X-rays detected in intervening quiescent episodes are the result of
cooling of the neutron star or due to continued low-level accretion remains
unclear. In this work we use Swift data obtained after the long and bright 2011
and 2013 outbursts, as well as the short and faint 2015 outburst, to
investigate the hypothesis that cooling of the accretion-heated neutron star
crust dominates the quiescent thermal emission in Aql X-1. We demonstrate that
the X-ray light curves and measured neutron star surface temperatures are
consistent with the expectations of the crust cooling paradigm. By using a
thermal evolution code, we find that ~1.2-3.2 MeV/nucleon of shallow heat
release describes the observational data well, depending on the assumed
mass-accretion rate and temperature of the stellar core. We find no evidence
for varying strengths of this shallow heating after different outbursts, but
this could be due to limitations of the data. We argue that monitoring Aql X-1
for up to ~1 year after future outbursts can be a powerful tool to break model
degeneracies and solve open questions about the magnitude, depth and origin of
shallow heating in neutron star crusts.Comment: 14 pages, 5 figures, 3 tables, accepted to MNRA
Experimental violation of a spin-1 Bell inequality using maximally-entangled four-photon states
We demonstrate the first experimental violation of a spin-1 Bell inequality.
The spin-1 inequality is a calculation based on the Clauser, Horne, Shimony and
Holt formalism. For entangled spin-1 particles the maximum quantum mechanical
prediction is 2.552 as opposed to a maximum of 2, predicted using local hidden
variables. We obtained an experimental value of 2.27 using the
four-photon state generated by pulsed, type-II, stimulated parametric
down-conversion. This is a violation of the spin-1 Bell inequality by more than
13 standard deviations.Comment: 5 pages, 3 figures, Revtex4. Problem with figures resolve
Experimental noise-resistant Bell-inequality violations for polarization-entangled photons
We experimentally demonstrate that violations of Bell's inequalities for
two-photon polarization-entangled states with colored noise are extremely
robust, whereas this is not the case for states with white noise. Controlling
the amount of noise by using the timing compensation scheme introduced by Kim
et al. [Phys. Rev. A 67, 010301(R) (2003)], we have observed violations even
for states with very high noise, in excellent agrement with the predictions of
Cabello et al. [Phys. Rev. A 72, 052112 (2005)].Comment: REVTeX4, 5 pages, 4 figure
Type I X-ray bursts, burst oscillations and kHz quasi-periodic oscillations in the neutron star system IGR J17191-2821
We present a detailed study of the X-ray energy and power spectral properties
of the neutron star transient IGR J17191-2821. We discovered four instances of
pairs of simultaneous kilohertz quasi-periodic oscillations (kHz QPOs). The
frequency difference between these kHz QPOs is between 315 Hz and 362 Hz. We
also report on the detection of five thermonuclear type-I X-ray bursts and the
discovery of burst oscillations at ~294 Hz during three of them. Finally, we
report on a faint and short outburst precursor, which occurred about two months
before the main outburst. Our results on the broadband spectral and variability
properties allow us to firmly establish the atoll source nature of IGR
J17191-2821.Comment: 9 pages, 7 figures - accepted for publication in MNRA
Description of Be, Li and Be nuclei within the Gamow Shell Model
In this work we study spectra of Be, Li, Be and elastic
scattering cross sections He(He, He)He, He(H,
H)He within the Gamow shell model (GSM) in the coupled-channel
formulation (GSM-CC). The evolution of channel amplitudes and the alignment of
the many-body state with the decay channel in the vicinity of the channel
threshold is studied for selected states. The GSM-CC in multi-mass partition
formulation applied to a translationally invariant Hamiltonian with an
effective finite-range two-body interaction reproduce well the spectra of
Be, Li, Be and elastic scattering reactions: He(He,
He)He, He(H, H)He. Detailed analysis of the dependence
of reaction channel amplitudes on the distance from the particle decay
threshold allowed to demonstrate the alignment of the wave function in the
vicinity of the decay threshold. This analysis also demonstrates the appearance
of clustering in the GSM-CC wave function in the vicinity of the cluster decay
threshold. We demonstrated that GSM formulated in the basis of reaction
channels including both cluster and proton/neutron channels allows to describe
both the spectra of nuclei with low-energy cluster thresholds and the
low-energy elastic scattering reactions with proton, H, and He
projectiles. Studying dependence of the reaction channel amplitude in a
many-body state on distance from the threshold, we showed an evolution of the
He, He clustering with increasing separation energy from the cluster
decay threshold and demonstrated a mechanism of the alignment of many-body wave
function with the decay threshold, i.e. the microscopic reorganization of the
wave function in the vicinity of the cluster decay threshold which leads to the
appearance of clustering in this state.Comment: 20 pages, 12 figure
Study of the one-dimensional off-lattice hot-monomer reaction model
Hot monomers are particles having a transient mobility (a ballistic flight)
prior to being definitely absorbed on a surface. After arriving at a surface,
the excess energy coming from the kinetic energy in the gas phase is dissipated
through degrees of freedom parallel to the surface plane. In this paper we
study the hot monomer-monomer adsorption-reaction process on a continuum
(off-lattice) one-dimensional space by means of Monte Carlo simulations. The
system exhibits second-order irreversible phase transition between a reactive
and saturated (absorbing) phases which belong to the directed percolation (DP)
universality class. This result is interpreted by means of a coarse-grained
Langevin description which allows as to extend the DP conjecture to transitions
occurring in continuous media.Comment: 13 pages, 5 figures, final version to appear in J. Phys.
- …