29,860 research outputs found
Coherent caloritronics in Josephson-based nanocircuits
We describe here the first experimental realization of a heat interferometer,
thermal counterpart of the well-known superconducting quantum interference
device (SQUID). These findings demonstrate, on the first place, the existence
of phase-dependent heat transport in Josephson-based superconducting circuits
and, on the second place, open the way to novel ways of mastering heat at the
nanoscale. Combining the use of external magnetic fields for phase biasing and
different Josephson junction architectures we show here that a number of heat
interference patterns can be obtained. The experimental realization of these
architectures, besides being relevant from a fundamental physics point of view,
might find important technological application as building blocks of
phase-coherent quantum thermal circuits. In particular, the performance of two
different heat rectifying devices is analyzed.Comment: 34 pages, 15 figures, review article for Ultra-low temperatures and
nanophysics ULTN2013. Microkelvin Proceeding
Luminosity segregation versus fractal scaling in the galaxy distribution
In this letter I present results from a correlation analysis of three galaxy
redshift catalogs: the SSRS2, the CfA2 and the PSCz. I will focus on the
observation that the amplitude of the two--point correlation function rises if
the depth of the sample is increased. There are two competing explanations for
this observation, one in terms of a fractal scaling, the other based on
luminosity segregation. I will show that there is strong evidence that the
observed growth is due to a luminosity dependent clustering of the galaxies.Comment: 7 pages, EPL in pres
Metastable states influence on the magnetic behavior of the triangular lattice: Application to the spin-chain compound Ca3Co2O6
It is known that the spin-chain compound Ca3Co2O6 exhibits very interesting
plateaus in the magnetization as a function of the magnetic field at low
temperatures. The origin of them is still controversial. In this paper we study
the thermal behavior of this compound with a single-flip Monte Carlo simulation
on a triangular lattice and demonstrate the decisive influence of metastable
states in the splitting of the ferrimagnetic 1/3 plateau below 10 K. We
consider the [Co2O6]n chains as giant magnetic moments described by large Ising
spins on planar clusters with open boundary conditions. With this simple
frozen-moment model we obtain stepped magnetization curves which agree quite
well with the experimental results for different sweeping rates. We describe
particularly the out-of-equilibrium states that split the low-temperature 1/3
plateau into three steps. They relax thermally to the 1/3 plateau, which has
long-range order at the equilibrium. Such states are further analyzed with
snapshots unveiling a domain-wall structure that is responsible for the
observed behavior of the 1/3 plateau. A comparison is also given of the exact
results in small triangular clusters with our Monte Carlo results, providing
further support for our thermal description of this compound.Comment: 8 pages, 11 figures, submitted to PR
Mass-radius relation for magnetized strange quark stars
We review the stability of magnetized strange quark matter (MSQM) within the
phenomenological MIT bag model, taking into account the variation of the
relevant input parameters, namely, the strange quark mass, baryon density,
magnetic field and bag parameter. A comparison with magnetized asymmetric quark
matter in -equilibrium as well as with strange quark matter (SQM) is
presented. We obtain that the energy per baryon for MSQM decreases as the
magnetic field increases, and its minimum value at vanishing pressure is lower
than the value found for SQM, which implies that MSQM is more stable than
non-magnetized SQM. The mass-radius relation for magnetized strange quark stars
is also obtained in this framework.Comment: 7 pages, 6 figures. To be published in the Proceedings of 4th
International Workshop on Relativistic Astrophysical and Astronomy IWARA0
A QCD sum rule calculation of the decay width
To understand the nature of the , recently observed in the mass
spectrum of the system by the D0 Collaboration, we have
investigated, in a previous work, a scalar tetraquark (diquak-antidiquark)
structure for it, within the two-point QCD sum rules method. The result found
for its mass agrees well with the experimental value. Encouraged by this
finding we now extend our calculations to obtain the decay width of
to using the three-point QCD sum rule. We obtain a value of
(20.4\pm8.7)\MeV, which, on comparing with the experimental value of
21.9\pm6.4 (\mbox{sta})^{+5.0}_{-2.5}(\mbox{syst}) \MeV/c^2, reinforces the
scalar four quark nature of .Comment: Minor modifications made. Some new discussions and references adde
Physical qubits from charged particles: IR divergences in quantum information
We consider soft photons effects (IR structure of QED) on the construction of
physical qubits. Soft-photons appear when we build charged qubits from the
asymptotic states of QED. This construction is necessary in order to include
the effect of soft photons on entanglement measures. The nonexistence of free
charged particles (due to the long range of QED interactions) lead us to
question the sense of the very concept of free charged qubit. In this letter,
using the "dressing" formalism, we build physical charged qubits from dressed
fields which have the correct asymptotic behavior, are gauge invariant, their
propagators have a particle pole structure and are free from infrared
divergences. Finally, we discuss the impact of the soft corrections on the
entanglement measures.Comment: 4 pages, 2 figures, RevTeX. Version 2: Some references update
Directed Random Markets: Connectivity determines Money
Boltzmann-Gibbs distribution arises as the statistical equilibrium
probability distribution of money among the agents of a closed economic system
where random and undirected exchanges are allowed. When considering a model
with uniform savings in the exchanges, the final distribution is close to the
gamma family. In this work, we implement these exchange rules on networks and
we find that these stationary probability distributions are robust and they are
not affected by the topology of the underlying network. We introduce a new
family of interactions: random but directed ones. In this case, it is found the
topology to be determinant and the mean money per economic agent is related to
the degree of the node representing the agent in the network. The relation
between the mean money per economic agent and its degree is shown to be linear.Comment: 14 pages, 6 figure
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