2,693 research outputs found
A Secular Relativistic Model For Solar System's Numerical Simulations
Using Gauss' averaged equations, we compute the secular relativistic effects
generated by the Sun on the argument of the perihelion and the mean anomaly of
an orbit. Then we test different alternative simpler models that have been
proposed to reproduce the secular relativistic effects in the orbital elements.
Generally, models introduce artificial perturbations that are
velocity-independent but that depend on the heliocentric distance. If these
perturbations are set as an impulse in a constant timestep integrator, when the
particle approaches perihelion the generated impulse could be very strong and
badly sampled, originating a spurious orbital evolution. In order to overcome
this setback, we propose two new models based on a constant,
distance-independent, perturbation. With these models we obtain the correct
secular drift in the argument of perihelion and the expected secular orbital
evolution is reproduced. We also discuss with some detail the secular effect
generated on the mean anomaly by different models.Comment: This work is an expanded version of Venturini and Gallardo (2010
Bayesian analysis of interiors of HD 219134b, Kepler-10b, Kepler-93b, CoRoT-7b, 55 Cnc e, and HD 97658b using stellar abundance proxies
Using a generalized Bayesian inference method, we aim to explore the possible
interior structures of six selected exoplanets for which planetary mass and
radius measurements are available in addition to stellar host abundances:
HD~219134b, Kepler-10b, Kepler-93b, CoRoT-7b, 55~Cnc~e, and HD~97658b. We aim
to investigate the importance of stellar abundance proxies for the planetary
bulk composition (namely Fe/Si and Mg/Si) on prediction of planetary interiors.
We performed a full probabilistic Bayesian inference analysis to formally
account for observational and model uncertainties while obtaining confidence
regions of structural and compositional parameters of core, mantle, ice layer,
ocean, and atmosphere. We determined how sensitive our parameter predictions
depend on (1) different estimates of bulk abundance constraints and (2)
different correlations of bulk abundances between planet and host star. [...]
Although the possible ranges of interior structures are large, structural
parameters and their correlations are constrained by the sparse data. The
probability for the tested exoplanets to be Earth-like is generally very low.
Furthermore, we conclude that different estimates of planet bulk abundance
constraints mainly affect mantle composition and core size.Comment: Astronomy & Astrophysics, 597, A38 (15 pages, 9 figures
Beam Induced Electron Cloud Resonances in Dipole Magnetic Fields
The buildup of low energy electrons in an accelerator, known as electron
cloud, can be severely detrimental to machine performance. Under certain beam
conditions, the beam can become resonant with the cloud dynamics, accelerating
the buildup of electrons. This paper will examine two such effects:
multipacting resonances, in which the cloud development time is resonant with
the bunch spacing, and cyclotron resonances, in which the cyclotron period of
electrons in a magnetic field is a multiple of bunch spacing. Both resonances
have been studied directly in dipole fields using retarding field analyzers
installed in the Cornell Electron Storage Ring (CESR). These measurements are
supported by both analytical models and computer simulations
Critical core mass for enriched envelopes: the role of H2O condensation
Context. Within the core accretion scenario of planetary formation, most
simulations performed so far always assume the accreting envelope to have a
solar composition. From the study of meteorite showers on Earth and numerical
simulations, we know that planetesimals must undergo thermal ablation and
disruption when crossing a protoplanetary envelope. Once the protoplanet has
acquired an atmosphere, the primordial envelope gets enriched in volatiles and
silicates from the planetesimals. This change of envelope composition during
the formation can have a significant effect in the final atmospheric
composition and on the formation timescale of giant planets.
Aims. To investigate the physical implications of considering the envelope
enrichment of protoplanets due to the disruption of icy planetesimals during
their way to the core. Particular focus is placed on the effect on the critical
core mass for envelopes where condensation of water can occur.
Methods. Internal structure models are numerically solved with the
implementation of updated opacities for all ranges of metallicities and the
software CEA to compute the equation of state. CEA computes the chemical
equilibrium for an arbitrary mixture of gases and allows the condensation of
some species, including water. This means that the latent heat of phase
transitions is consistently incorporated in the total energy budget.
Results. The critical core mass is found to decrease significantly when an
enriched envelope composition is considered in the internal structure
equations. A particular strong reduction of the critical core mass is obtained
for planets whose envelope metallicity is larger than Z=0.45 when the outer
boundary conditions are suitable for condensation of water to occur in the top
layers of the atmosphere. We show that this effect is qualitatively preserved
when the atmosphere is out of chemical equilibrium.Comment: Accepted for publication in A&
Borderline leprosy: in situ and cytokine profile in supernatant of mononuclear of cell culture
In order to contribute to a better understanding of cytokine participation in borderline leprosy, in the present study we determined - by in vitro and in situ examinations - the production of these cytokine mediation in non-treated borderline tuberculoid (BT) patients and borderline lepromatous (BL) patients. Seven non-treated BT patients, 12 non-treated BL patients, besides 19 healthy individuals (control group), were evaluated. Peripheral blood mononuclear cells (PBMC) were stimulated or not with specific-M. leprae stimulus (whole and sonicated M. leprae antigens) and a non-specific stimulus. After 48 hours, supernatant was collected for TNF-alpha, IFN-gamma, IL-10 and TGF-beta1 cytokine determination by ELISA. Biopsies from cutaneous lesions were submitted to histological analysis and hematoxylin-eosin and Fite-Faraco stainings; the sections then underwent iNOS, IL-10 and TGF-beta1 in situ detection by immunohistochemistry. Cytokine quantification in PBMC supernatants from patients showed that BT patients produced higher levels of IFN-gamma. Compared to healthy individuals, both borderline patient groups produced lower levels of TGF-beta1 while BL patients generated lower IL-10 levels. The in situ iNOS expression was higher in BT patients compared to BL individuals. on the order hand, TGF-beta1 cytokine revealed a higher proportion of immunostained cells in BL patients. There was no significant difference in IL-10 level between BT and BL patients. Regarding cutaneous lesions, in BL patients there was a negative correlation between TGF-beta1 tissue expression and IL-10. Independently of the clinical form, we observed a positive correlation between TGF-beta1 and bacterial index as well as a negative correlation between the TGF-beta1 tissue expression and iNOS. The results even showed a positive correlation between iNOS tissue expression and production of IFN-gamma by PBMC stimulated with M. leprae antigens. Taken together, the histopathological and immunological observations reinforce the notion of immunological instability in borderline leprosy patients and indicating the participation of mixed cytokines profiles in these individuals, specifically a Th1 profile in BT patients and Th2 profile in BL patients, with a possible participation of T-regulatory lymphocytes
A generalized bayesian inference method for constraining the interiors of super Earths and sub-Neptunes
We aim to present a generalized Bayesian inference method for constraining
interiors of super Earths and sub-Neptunes. Our methodology succeeds in
quantifying the degeneracy and correlation of structural parameters for high
dimensional parameter spaces. Specifically, we identify what constraints can be
placed on composition and thickness of core, mantle, ice, ocean, and
atmospheric layers given observations of mass, radius, and bulk refractory
abundance constraints (Fe, Mg, Si) from observations of the host star's
photospheric composition. We employed a full probabilistic Bayesian inference
analysis that formally accounts for observational and model uncertainties.
Using a Markov chain Monte Carlo technique, we computed joint and marginal
posterior probability distributions for all structural parameters of interest.
We included state-of-the-art structural models based on self-consistent
thermodynamics of core, mantle, high-pressure ice, and liquid water.
Furthermore, we tested and compared two different atmospheric models that are
tailored for modeling thick and thin atmospheres, respectively. First, we
validate our method against Neptune. Second, we apply it to synthetic
exoplanets of fixed mass and determine the effect on interior structure and
composition when (1) radius, (2) atmospheric model, (3) data uncertainties, (4)
semi-major axes, (5) atmospheric composition (i.e., a priori assumption of
enriched envelopes versus pure H/He envelopes), and (6) prior distributions are
varied. Our main conclusions are: [...]Comment: Astronomy & Astrophysics, 597, A37, 17 pages, 11 figure
Distribution-aware compressed full-text indexes
In this paper we address the problem of building a compressed self-index that, given a distribution for the pattern queries and a bound on the space occupancy, minimizes the expected query time within that index space bound. We solve this problem by exploiting a reduction to the problem of finding a minimum weight K-link path in a properly designed Directed Acyclic Graph. Interestingly enough, our solution can be used with any compressed index based on the Burrows-Wheeler transform. Our experiments compare this optimal strategy with several other known approaches, showing its effectiveness in practice
Characterization of Brazilian table wines from american varieties
The Brazilian wine industry has a remarkable characteristic that distinguishes from other
markets. While the foreign market only accepts products originating from European cultivars
(cv) (Vitis vinifera), in Brazil, products originating from American cv (Vitis labrusca and Vitis
bourquina) and hybrids are also accepted. Dry and sweet varietal wines from red grapes cv
Bordô, Isabel and Máximo and white grapes cv Niágara and Lorena were analyzed, by the
following chemical standard analyses: total, volatile and fixed acidity; ethanol content;
density; pH; dry and reduced dry extract; ratio ethanol/reduced dry extract; reducing sugars;
total and free sulfur dioxide. Additionally, major volatile compounds were analyzed by gas
chromatography, directly, without any previous treatment, after the addition of the internal
standard (4-nonanol).A indústria de vinho brasileira tem uma caracterÃstica notável que a distingui dos outros
mercados. Enquanto o mercado estrangeiro só aceita produtos originários das cultivares (cv)
européias (V. vinifera), no Brasil, produtos originários das cv americanas (V. labrusca e V.
bourquina) e hÃbridos também são aceitos. Vinhos varietais secos e suaves das uvas tintas
das cv Bordô, Isabel e Máximo, e das uvas brancas das cv Niágara e Lorena foram
avaliados pelas seguintes análises quÃmicas: acidez total, volátil e fixa; teor alcoólico, massa
volúmica, pH, extrato seco total e reduzido; relação álcool em peso/extrato seco reduzido,
açúcares redutores; dióxido de enxofre total e livre. Adicionalmente, os compostos voláteis
maioritários foram avaliados por cromatografia gasosa, diretamente, sem qualquer
tratamento prévio, após a adição do padrão interno (4-nonanol)
Vinhos de mesa varietais de uvas americanas: análises quÃmicas e energética
A indústria brasileira de vinhos tem uma caracterÃstica notável que a distingui dos outros mercados. Enquanto o mercado estrangeiro só aceita produtos originários das variedades europeias (V. vinifera), no Brasil, produtos originários das variedades americanas (V. labrusca e V. bourquina) e hÃbridos também são aceitos. Vinhos varietais secos e suaves das variedades Bordô (seco e suave), Isabel (suave) e Máximo (seco), foram avaliados pelas seguintes determinações quÃmicas: teor alcoólico; densidade; extrato seco total e reduzido; relação álcool em massa/extrato seco reduzido, açúcares redutores; acidez total, volátil e fixa; pH; dióxido de enxofre total e livre; e valor energético. Todos os vinhos analisados apresentaram resultados dentro dos parâmetros estipulados pela legislação brasileira, fato positivo, uma vez que são comercializados. O vinho varietal Máximo apresentou um teor baixo de dióxido de enxofre livre e total, podendo acarretar problemas futuros com sua sanidade.The Brazilian wine industry has a remarkable characteristic that distinguishes from other markets, while the foreign market only accepts products originating from European varieties (Vitis vinifera), in Brazil, products originating from American varieties (Vitis labrusca and Vitis bourquina) and hybrids are also accepted. Dry and sweet varietal wines from varieties Bordô (dry and sweet), Isabel (sweet) e Máximo (dry) were analyzed, by the following chemical standard analyses: alcohol content; density; total and reduced dry matter; alcohol/reduced dry extract ratio; reducing sugars; total, volatile and fixed acidity; pH; total and free sulfur dioxide; and energy value. All analyzed wines presented results within the parameters set forth by Brazilian law, a positive fact, once they are commercialized. The varietal wine Máximo presented a low content of total and free sulfur dioxide, which may cause future problems with its sanity.info:eu-repo/semantics/publishedVersio
Origin of ferroelectricity in the multiferroic barium fluorides BaMF4
We present a first principles study of the series of multiferroic barium
fluorides with the composition BaMF4, where M is Mn, Fe, Co, or Ni. We discuss
trends in the structural, electronic, and magnetic properties, and we show that
the ferroelectricity in these systems results from the "freezing in" of a
single unstable polar phonon mode. In contrast to the case of the standard
perovskite ferroelectrics, this structural distortion is not accompanied by
charge transfer between cations and anions. Thus, the ferroelectric instability
in the multiferroic barium fluorides arises solely due to size effects and the
special geometrical constraints of the underlying crystal structure.Comment: 8 pages, 6 figures, 3 table
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