7,143 research outputs found
Phase and Charge reentrant phase transitions in two capacitively coupled Josephson arrays with ultra-small junction
We have studied the phase diagram of two capacitively coupled Josephson
junction arrays with charging energy, , and Josephson coupling energy,
. Our results are obtained using a path integral Quantum Monte Carlo
algorithm. The parameter that quantifies the quantum fluctuations in the i-th
array is defined by . Depending on
the value of , each independent array may be in the semiclassical or
in the quantum regime: We find that thermal fluctuations are important when
and the quantum fluctuations dominate when . We have extensively studied the interplay between vortex and charge
dominated individual array phases. The two arrays are coupled via the
capacitance at each site of the lattices. We find a {\it
reentrant transition} in , at low temperatures, when one of
the arrays is in the semiclassical limit (i.e. ) and the
quantum array has , for the values considered for
the interlayer capacitance. In addition, when , and
for all the inter-layer couplings considered above, a {\it novel} reentrant
phase transition occurs in the charge degrees of freedom, i.e. there is a
reentrant insulating-conducting transition at low temperatures. We obtain the
corresponding phase diagrams and found some features that resemble those seen
in experiments with 2D JJA.Comment: 25 Latex pages including 8 encapsulated poscript figures. Accepted
for publication in Phys. Rev B (Nov. 2004 Issue
Structural Changes in Data Communication in Wireless Sensor Networks
Wireless sensor networks are an important technology for making distributed
autonomous measures in hostile or inaccessible environments. Among the
challenges they pose, the way data travel among them is a relevant issue since
their structure is quite dynamic. The operational topology of such devices can
often be described by complex networks. In this work, we assess the variation
of measures commonly employed in the complex networks literature applied to
wireless sensor networks. Four data communication strategies were considered:
geometric, random, small-world, and scale-free models, along with the shortest
path length measure. The sensitivity of this measure was analyzed with respect
to the following perturbations: insertion and removal of nodes in the geometric
strategy; and insertion, removal and rewiring of links in the other models. The
assessment was performed using the normalized Kullback-Leibler divergence and
Hellinger distance quantifiers, both deriving from the Information Theory
framework. The results reveal that the shortest path length is sensitive to
perturbations.Comment: 12 pages, 4 figures, Central European Journal of Physic
Variaciones sedimentarias durante el Eoceno medio en la sierra de AndÃa (Navarra)
In this paper, tkie stratigraphical and lithological character- istics of the Middle Eocene are established, in the Sierra de Andia (Navarra, Spain). Examples of the cross-stratification are described and the directional data analyzed. A study of the basin evolution is elaborated. It is pro- posed a correlation with the youngest sediments of the Sierra de Urbasa, situated more to the West
Pulmonary thromboembolism and alveolar hemorrhage as initial manifestations of systemic lupus erythematosus
Systemic lupus erythematosus (SLE) is an autoimmune disease that affects multiple organs. SLE can affect the lung, the pulmonary vasculature, and the pleura. A 38-year-old female with limb pain and ecchymosis who later developed pulmonary thromboembolism and alveolar hemorrhage is presented here. Clinical, imaging, laboratory, and histopathological evidence is presented. The patient met the European League Against Rheumatism (EULAR) and the American College of Rheumatology (ACR) criteria for SLE. Furthermore, the patient had a Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) score of 35; thus, indicating severe disease. This case is an example of concomitant venous and arterial lung complications in an SLE patient
Rare-gas solids under pressure: A path-integral Monte Carlo simulation
Rare-gas solids (Ne, Ar, Kr, and Xe) under hydrostatic pressure up to 30 kbar
have been studied by path-integral Monte Carlo simulations in the
isothermal-isobaric ensemble. Results of these simulations have been compared
with available experimental data and with those obtained from a quasiharmonic
approximation (QHA). This comparison allows us to quantify the overall
anharmonicity of the lattice vibrations and its influence on several structural
and thermodynamic properties of rare-gas solids. The vibrational energy
increases with pressure, but this increase is slower than that of the elastic
energy, which dominates at high pressures. In the PIMC simulations, the
vibrational kinetic energy is found to be larger than the corresponding
potential energy, and the relative difference between both energies decreases
as the applied pressure is raised. The accuracy of the QHA increases for rising
pressure.Comment: 9 pages, 6 figure
Unexpected impact of D waves in low-energy neutral pion photoproduction from the proton and the extraction of multipoles
Contributions of waves to physical observables for neutral pion
photoproduction from the proton in the near-threshold region are studied and
means to isolate them are proposed. Various approaches to describe the
multipoles are employed
--a phenomenological one, a unitary one, and heavy baryon chiral perturbation
theory. The results of these approaches are compared and found to yield
essentially the same answers. waves are seen to enter together with
waves in a way that any means which attempt to obtain the multipole
accurately must rely on knowledge of waves and that consequently the latter
cannot be dismissed in analyses of low-energy pion photoproduction. It is shown
that waves have a significant impact on double-polarization observables
that can be measured. This importance of waves is due to the soft nature of
the wave and is a direct consequence of chiral symmetry and the
Nambu--Goldstone nature of the pion. -wave contributions are shown to be
negligible in the near-threshold region.Comment: 38 pages, 13 figures, 19 tables. Version to be published in Physical
Review
Solid helium at high pressure: A path-integral Monte Carlo simulation
Solid helium (3He and 4He) in the hcp and fcc phases has been studied by
path-integral Monte Carlo. Simulations were carried out in the
isothermal-isobaric (NPT) ensemble at pressures up to 52 GPa. This allows one
to study the temperature and pressure dependences of isotopic effects on the
crystal volume and vibrational energy in a wide parameter range. The obtained
equation of state at room temperature agrees with available experimental data.
The kinetic energy, E_k, of solid helium is found to be larger than the
vibrational potential energy, E_p. The ratio E_k/E_p amounts to about 1.4 at
low pressures, and decreases as the applied pressure is raised, converging to
1, as in a harmonic solid. Results of these simulations have been compared with
those yielded by previous path integral simulations in the NVT ensemble. The
validity range of earlier approximations is discussed.Comment: 7 pages, 5 figure
Bilepton effects on the WWV^* vertex in the 331 model with right-handed neutrinos via a SU_L(2)XU_Y(1) covariant quantization scheme
In a recent paper, we investigated the effects of the massive charged gauge
bosons (bileptons) predicted by the minimal 331 model on the off-shell vertex
WWV^* (V=gamma, Z) using a SU_L(2) X U_Y(1) covariant gauge-fixing term for the
bileptons. We proceed along the same lines and calculate the effects of the
gauge bosons predicted by the 331 model with right-handed neutrinos. It is
found that the bilepton effects on the WWV^* vertex are of the same order of
magnitude than those arising from the SM and several of its extensions,
provided that the bilepton mass is of the order of a few hundred of GeVs. For
heavier bileptons, their effects on the WWV^* vertex are negligible. The
behavior of the form factors at high energies is also discussed as it is a
reflect of the gauge invariance and gauge independence of the WWV^* Green
function obtained via our quantization method.Comment: Replaced to match published versio
Granulation in K-type Dwarf Stars. II. Hydrodynamic simulations and 3D spectrum synthesis
We construct a 3D radiative-hydrodynamic model atmosphere of parameters Teff
= 4820 K, log g = 4.5, and solar chemical composition. The theoretical line
profiles computed with this model are asymmetric, with their bisectors having a
characteristic C-shape and their core wavelengths shifted with respect to their
laboratory values. The line bisectors span from about 10 to 250 m/s, depending
on line strength, with the stronger features showing larger span. The
corresponding core wavelength shifts range from about -200 m/s for the weak Fe
I lines to almost +100 m/s in the strong Fe I features. Based on observational
results for the Sun, we argue that there should be no core wavelength shift for
Fe I lines of EW > 100 mA. The cores of the strongest lines show contributions
from the uncertain top layers of the model, where non-LTE effects and the
presence of the chromosphere, which are important in real stars, are not
accounted for. The comparison of model predictions to observed Fe I line
bisectors and core wavelength shifts for a reference star, HIP86400, shows
excellent agreement, with the exception of the core wavelength shifts of the
strongest features, for which we suspect inaccurate theoretical values. Since
this limitation does not affect the predicted line equivalent widths
significantly, we consider our 3D model validated for photospheric abundance
work.Comment: A&A, in pres
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