5,650 research outputs found
COMPARISON ANALYSIS OF CORRELATIONS FOR INTERFACIAL FRICTION FACTOR APPLIED IN GAS-LIQUID ANNULAR FLOW IN VERTICAL PIPES
Gas-liquid flows in pipes can occur in the form of an annular pattern in which the liquid flows as a thin film at pipe wall and the gas flows as a core in pipe center. This flow pattern is often encountered at boiling and condensation processes, for example, in industries of steam generation, cooling or petroleum. In annular flow, the interfacial friction factor is one of the important closing parameters for the definition of the interfacial shear stress and consequently the pressure gradient. In the literature, several correlations are found to estimate the interfacial friction factor. The main objective of this work is to carry out a comparative analysis of some these correlations against experimental data also obtained from the literature. The features and limitations of each correlation were observed, as well as the accuracy of each in relation to experimental data. The results obtained demonstrate that correlations analyzed, present relatively satisfactory results, despite the different characteristics of the correlations, however, it is necessary to carry out more extensive analyses involving others correlations and sets of experimental data
Numerical Simulation of Magnetic Interactions in Polycrystalline YFeO3
The magnetic behavior of polycrystalline yttrium orthoferrite was studied
from the experimental and theoretical points of view. Magnetization
measurements up to 170 kOe were carried out on a single-phase YFeO3 sample
synthesized from heterobimetallic alkoxides. The complex interplay between
weak-ferromagnetic and antiferromagnetic interactions, observed in the
experimental M(H) curves, was successfully simulated by locally minimizing the
magnetic energy of two interacting Fe sublattices. The resulting values of
exchange field (H_E = 5590 kOe), anisotropy field (H_A = 0.5 kOe) and
Dzyaloshinsky-Moriya antisymmetric field (H_D = 149 kOe) are in good agreement
with previous reports on this system.Comment: 26 pages, 9 figure
COMPARISON ANALYSIS OF CORRELATIONS FOR INTERFACIAL FRICTION FACTOR APPLIED IN GAS-LIQUID ANNULAR FLOW IN VERTICAL PIPES
Gas-liquid flows in pipes can occur in the form of an annular pattern in which the liquid flows as a thin film at pipe wall and the gas flows as a core in pipe center. This flow pattern is often encountered at boiling and condensation processes, for example, in industries of steam generation, cooling or petroleum. In annular flow, the interfacial friction factor is one of the important closing parameters for the definition of the interfacial shear stress and consequently the pressure gradient. In the literature, several correlations are found to estimate the interfacial friction factor. The main objective of this work is to carry out a comparative analysis of some these correlations against experimental data also obtained from the literature. The features and limitations of each correlation were observed, as well as the accuracy of each in relation to experimental data. The results obtained demonstrate that correlations analyzed, present relatively satisfactory results, despite the different characteristics of the correlations, however, it is necessary to carry out more extensive analyses involving others correlations and sets of experimental data
Gemini and Chandra observations of Abell 586, a relaxed strong-lensing cluster
We analyze the mass content of the massive strong-lensing cluster Abell 586
(). We use optical data (imaging and spectroscopy) obtained with the
Gemini Multi-Object Spectrograph (GMOS) mounted on the 8-m Gemini-North
telescope, together with publicly available X-ray data taken with the
\textit{Chandra} space telescope. Employing different techniques -- velocity
distribution of galaxies, weak gravitational lensing, and X-ray spatially
resolved spectroscopy -- we derive mass and velocity dispersion estimates from
each of them. All estimates agree well with each other, within a 68% confidence
level, indicating a velocity dispersion of 1000 -- 1250 \kms. The projected
mass distributions obtained through weak-lensing and X-ray emission are
strikingly similar, having nearly circular geometry. We suggest that Abell 586
is probably a truly relaxed cluster, whose last major merger occurred more than
Gyr agoComment: ApJ accepted, 20 pages, 11 figures; Figure 1 fixe
Nonextensive Thermostatistics and the H-Theorem
The kinetic foundations of Tsallis' nonextensive thermostatistics are
investigated through Boltzmann's transport equation approach. Our analysis
follows from a nonextensive generalization of the ``molecular chaos
hypothesis". For , the -transport equation satisfies an -theorem
based on Tsallis entropy. It is also proved that the collisional equilibrium is
given by Tsallis' -nonextensive velocity distribution.Comment: 4 pages, no figures, corrected some typo
Accelerating Cold Dark Matter Cosmology ()
A new kind of accelerating flat model with no dark energy that is fully
dominated by cold dark matter (CDM) is investigated. The number of CDM
particles is not conserved and the present accelerating stage is a consequence
of the negative pressure describing the irreversible process of gravitational
particle creation. A related work involving accelerating CDM cosmology has been
discussed before the SNe observations [Lima, Abramo & Germano, Phys. Rev. D53,
4287 (1996)]. However, in order to have a transition from a decelerating to an
accelerating regime at low redshifts, the matter creation rate proposed here
includes a constant term of the order of the Hubble parameter. In this case,
does not need to be small in order to solve the age problem and the
transition happens even if the matter creation is negligible during the
radiation and part of the matter dominated phase. Therefore, instead of the
vacuum dominance at redshifts of the order of a few, the present accelerating
stage in this sort of Einstein-de Sitter CDM cosmology is a consequence of the
gravitational particle creation process. As an extra bonus, in the present
scenario does not exist the coincidence problem that plagues models with
dominance of dark energy. The model is able to harmonize a CDM picture with the
present age of the universe, the latest measurements of the Hubble parameter
and the Supernovae observations.Comment: 9 pages, 6 figures, typos corrected, references added, discussion in
Appendix B extende
Extended DFT+U+V method with on-site and inter-site electronic interactions
In this article we introduce a generalization of the popular DFT+U method
based on the extended Hubbard model that includes on-site and inter-site
electronic interactions. The novel corrective Hamiltonian is designed to study
systems for which electrons are not completely localized on atomic states
(according to the general scheme of Mott localization) and hybridization
between orbitals from different sites plays an important role. The application
of the extended functional to archetypal Mott - charge-transfer (NiO) and
covalently bonded insulators (Si and GaAs) demonstrates its accuracy and
versatility and the possibility to obtain a unifying and equally accurate
description for a broad range of very diverse systems
Two spectroscopically confirmed galaxy structures at z=0.61 and 0.74 in the CFHTLS Deep~3 field
Adami et al. (2010) have detected several cluster candidates at z>0.5 as part
of a systematic search for clusters in the Canada France Hawaii Telescope
Legacy Survey, based on photometric redshifts. We focus here on two of them,
located in the D3 field: D3-6 and D3-43. We have obtained spectroscopy with
Gemini/GMOS and measured redshifts for 23 and 14 galaxies in the two
structures. These redshifts were combined with those available in the
literature. A dynamical and a weak lensing analysis were also performed,
together with the study of X-ray Chandra archive data. Cluster D3-6 is found to
be a single structure of 8 spectroscopically confirmed members at an average
redshift z=0.607, with a velocity dispersion of 423 km/s. It appears to be a
relatively low mass cluster. D3-43-S3 has 46 spectroscopically confirmed
members at an average redshift z=0.739. It can be decomposed into two main
substructures, having a velocity dispersion of about 600 and 350 km/s. An
explanation to the fact that D3-43-S3 is detected through weak lensing (only
marginally, at the ~3sigma level) but not in X-rays could be that the two
substructures are just beginning to merge more or less along the line of sight.
We also show that D3-6 and D3-43-S3 have similar global galaxy luminosity
functions, stellar mass functions, and star formation rate (SFR) distributions.
The only differences are that D3-6 exhibits a lack of faint early type
galaxies, a deficit of extremely high stellar mass galaxies compared to
D3-43-S3, and an excess of very high SFR galaxies. This study shows the power
of techniques based on photometric redshifts to detect low to moderately
massive structures, even at z~0.75.Comment: Accepted in A&A, final version, shortened abstrac
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