104,553 research outputs found
On the role of chemical synapses in coupled neurons with noise
We examine the behavior in the presence of noise of an array of Morris-Lecar
neurons coupled via chemical synapses. Special attention is devoted to
comparing this behavior with the better known case of electrical coupling
arising via gap junctions. In particular, our numerical simulations show that
chemical synapses are more efficient than gap junctions in enhancing coherence
at an optimal noise (what is known as array-enhanced coherence resonance): in
the case of (nonlinear) chemical coupling, we observe a substantial increase in
the stochastic coherence of the system, in comparison with (linear) electrical
coupling. We interpret this qualitative difference between both types of
coupling as arising from the fact that chemical synapses only act while the
presynaptic neuron is spiking, whereas gap junctions connect the voltage of the
two neurons at all times. This leads in the electrical coupling case to larger
correlations during interspike time intervals which are detrimental to the
array-enhanced coherence effect. Finally, we report on the existence of a
system-size coherence resonance in this locally coupled system, exhibited by
the average membrane potential of the array.Comment: 7 pages, 7 figure
Correlated hopping of bosonic atoms induced by optical lattices
In this work we analyze a particular setup with ultracold atoms trapped in
state-dependent lattices. We show that any asymmetry in the contact interaction
translates into one of two classes of correlated hopping. After deriving the
effective lattice Hamiltonian for the atoms, we obtain analytically and
numerically the different phases and quantum phase transitions. We find for
weak correlated hopping both Mott insulators and charge density waves, while
for stronger correlated hopping the system transitions into a pair superfluid.
We demonstrate that this phase exists for a wide range of interaction
asymmetries and has interesting correlation properties that differentiate it
from an ordinary atomic Bose-Einstein condensate.Comment: 24 pages with 9 figures, to appear in New Journal of Physic
Detecting ground state qubit self-excitations in circuit QED: slow quantum anti-Zeno effect
In this work we study an ultrastrong coupled qubit-cavity system subjected to
slow repeated measurements. We demonstrate that even under a few imperfect
measurements it is possible to detect transitions of the qubit from its free
ground state to the excited state. The excitation probability grows
exponentially fast in analogy with the quantum anti-Zeno effect. The dynamics
and physics described in this paper is accessible to current superconducting
circuit technology.Comment: 6 pages, 6 figures. v2: extended published versio
Computability of the causal boundary by using isocausality
Recently, a new viewpoint on the classical c-boundary in Mathematical
Relativity has been developed, the relations of this boundary with the
conformal one and other classical boundaries have been analyzed, and its
computation in some classes of spacetimes, as the standard stationary ones, has
been carried out.
In the present paper, we consider the notion of isocausality given by
Garc\'ia-Parrado and Senovilla, and introduce a framework to carry out
isocausal comparisons with standard stationary spacetimes. As a consequence,
the qualitative behavior of the c-boundary (at the three levels: point set,
chronology and topology) of a wide class of spacetimes, is obtained.Comment: 44 pages, 5 Figures, latex. Version with minor changes and the
inclusion of Figure
Heat fluxes between the Guadalquivir river and the Gulf of Cádiz Continental Shelf
An 18-year time series of daily sea surface temperature of Gulf of Cadiz and an 18-month time series of temperature collected in the vicinity of the Guadalquivir estuary mouth have been analyzed to investigate the heat exchange between the estuary and the adjacent continental shelf. The first time identifies a continental shelf area where seasonal thermal oscillation signal (amplitudes and phase) changes abruptly.
In order to explain this anomaly, the second data set allows a description of thermal fluctuations in a wide range of frequencies and an estimation of the upstream heat budget of the Guadalquivir estuary. Results show that high frequency thermal signal, diurnal and semidiurnal, and water flux signal through Guadalquivir mouth, mainly semidiurnal, apparently interact randomly to give a small exchange of thermal energy at high frequency. There is no trace, at the estuary's mouth, of daily heat exchanges with intertidal mudflats probably because it tends to cancel on daily time scales. Results also show that fluctuations of estimated air-sea fluxes force fluctuations of temperature in a quite homogeneous estuarine, with a delay of 20 days. The along-channel thermal energy gradient reaches magnitudes of 300-400 J m-4 near the mouth during the summer and winter and drives the estuary-shelf exchange of thermal energy at seasonal scale. Particularly, the thermal heat imported by the estuary from the shelf area during late fall-winter-early spring of 2008/2009 is balanced by the thermal heat that the estuary exports to the shelf area during late spring-summer of 2008. In summary, Guadalquivir river removes/imports excess of thermal energy towards/from the continental shelf seasonally, as a mechanism to accommodate excess of heat from one side respect to the other side.Universidad de Málaga. Campus de Excelencia Internacional AndalucĂa Tech. Autoridad Portuaria de Sevilla (APS
Quantum computation with unknown parameters
We show how it is possible to realize quantum computations on a system in
which most of the parameters are practically unknown. We illustrate our results
with a novel implementation of a quantum computer by means of bosonic atoms in
an optical lattice. In particular we show how a universal set of gates can be
carried out even if the number of atoms per site is uncertain.Comment: 3 figure
Isocausal spacetimes may have different causal boundaries
We construct an example which shows that two isocausal spacetimes, in the
sense introduced by Garc\'ia-Parrado and Senovilla, may have c-boundaries which
are not equal (more precisely, not equivalent, as no bijection between the
completions can preserve all the binary relations induced by causality). This
example also suggests that isocausality can be useful for the understanding and
computation of the c-boundary.Comment: Minor modifications, including the title, which matches now with the
published version. 12 pages, 3 figure
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