3,554 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
Low-level accretion in neutron-star X-ray binaries
We search the literature for reports on the spectral properties of
neutron-star low-mass X-ray binaries when they have accretion luminosities
between 1E34 and 1E36 ergs/s. We found that in this luminosity range the photon
index (obtained from fitting a simple absorbed power-law in the 0.5-10 keV
range) increases with decreasing 0.5-10 keV X-ray luminosity (i.e., the
spectrum softens). Such behaviour has been reported before for individual
sources, but here we demonstrate that very likely most (if not all)
neutron-star systems behave in a similar manner and possibly even follow a
universal relation. When comparing the neutron-star systems with black-hole
systems, it is clear that most black-hole binaries have significantly harder
spectra at luminosities of 1E34 - 1E35 erg/s. Despite a limited number of data
points, there are indications that these spectral differences also extend to
the 1E35 - 1E36 erg/s range. This observed difference between the neutron-star
binaries and black-hole ones suggests that the spectral properties (between
0.5-10 keV) at 1E34 - 1E35 erg/s can be used to tentatively determine the
nature of the accretor in unclassified X-ray binaries. We discuss our results
in the context of properties of the accretion flow at low luminosities and we
suggest that the observed spectral differences likely arise from the
neutron-star surface becoming dominantly visible in the X-ray spectra. We also
suggest that both the thermal component and the non-thermal component might be
caused by low-level accretion onto the neutron-star surface for luminosities
below a few times 1E34 erg/s.Comment: Accepted for publication in MNRA
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
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