6,944 research outputs found
Dynamics of Enceladus and Dione inside the 2:1 Mean-Motion Resonance under Tidal Dissipation
In a previous work (Callegari and Yokoyama 2007, Celest. Mech. Dyn. Astr.
vol. 98), the main features of the motion of the pair Enceladus-Dione were
analyzed in the frozen regime, i.e., without considering the tidal evolution.
Here, the results of a great deal of numerical simulations of a pair of
satellites similar to Enceladus and Dione crossing the 2:1 mean-motion
resonance are shown. The resonance crossing is modeled with a linear tidal
theory, considering a two-degrees-of-freedom model written in the framework of
the general three-body planar problem. The main regimes of motion of the system
during the passage through resonance are studied in detail. We discuss our
results comparing them with classical scenarios of tidal evolution of the
system. We show new scenarios of evolution of the Enceladus-Dione system
through resonance not shown in previous approaches of the problem.Comment: 36 pages, 12 figures. Accepted in Celestial Mechanics and Dynamical
Astronom
Larval condition and growth of Sardinella brasiliensis (Steindachner, 1879): preliminary results from laboratory studies
Brazilian sardine, the most important resource along the southeastern Brazilian coast, presented great variations and declines in its stocks. The main factors contributing to this are: oceanographic structure changes; recruitment failures; excessive catches of juveniles and increase in fishery effort. In spite of this, no alterations in the density-dependent parameters were detected. Consequently, methods analysing the condition of the larvae coupled with methods determining growth using sagittae otolith increment width were applied to evaluate growth under experimental conditions. The results of the readings on the sagittae were compared with the age of the laboratory-reared sardine larvae and confirmed that increments are formed on a daily basis. Under poor feeding conditions, sardine larvae showed a low growth expressed by dry weight, RNA/DNA ratio and tryptic enzyme activity and by the narrow and low contrast increments in the otoliths. The results of the biochemical indices showed an unexpected decline in the feeding group coupled with a decrease in width of increment numbers 8 and 10. Other factors than food availability were affecting the condition of the larvae and might be indicative of physiological processes and ontogenetic changes occurring in sardine larvae
Initial pseudo-steady state & asymptotic KPZ universality in semiconductor on polymer deposition
The Kardar-Parisi-Zhang (KPZ) class is a paradigmatic example of universality
in nonequilibrium phenomena, but clear experimental evidences of asymptotic
2D-KPZ statistics are still very rare, and far less understanding stems from
its short-time behavior. We tackle such issues by analyzing surface
fluctuations of CdTe films deposited on polymeric substrates, based on a huge
spatio-temporal surface sampling acquired through atomic force microscopy. A
\textit{pseudo}-steady state (where average surface roughness and spatial
correlations stay constant in time) is observed at initial times, persisting up
to deposition of monolayers. This state results from a fine
balance between roughening and smoothening, as supported by a phenomenological
growth model. KPZ statistics arises at long times, thoroughly verified by
universal exponents, spatial covariance and several distributions. Recent
theoretical generalizations of the Family-Vicsek scaling and the emergence of
log-normal distributions during interface growth are experimentally confirmed.
These results confirm that high vacuum vapor deposition of CdTe constitutes a
genuine 2D-KPZ system, and expand our knowledge about possible
substrate-induced short-time behaviors.Comment: 13 pages, 8 figures, 2 table
Certificação IEA.
Dada a dimensão territorial ocupada pelo cultivo da cana, pelos impactos ambientais e sociais gerados pelo setor sucroalcooleiro, pela existência de iniciativas de certificação e devido ao fato da não adoção até o momento de certificação socioambiental por nenhum grupo empresarial do setor, é clara a necessidade de se discutir este tema assim como deixar clara a necessidade de gerar subsídios para a implementação de políticas públicas nesta direção. O intuito deste trabalho é justamente o de apresentar informações para colocar em discussão como políticas de pesquisa e tecnológicas podem levar a modos de produção mais desejáveis e auxiliar na definição de políticas públicas que auxiliem na elaboração de certificação socioambiental para o setor sucroalcooleiro. No decorrer do texto são relatados dados da situação atual do setor, bem como cenários futuros, inclusive de opções tecnológicas, como argumento para justificar as propostas de políticas e agendas de pesquisas futuras, que são apresentadas no final
Dissipation in planar resonant planetary systems
Close-in planetary systems detected by the Kepler mission present an excess
of periods ratio that are just slightly larger than some low order resonant
values. This feature occurs naturally when resonant couples undergo dissipation
that damps the eccentricities. However, the resonant angles appear to librate
at the end of the migration process, which is often believed to be an evidence
that the systems remain in resonance.
Here we provide an analytical model for the dissipation in resonant planetary
systems valid for low eccentricities. We confirm that dissipation accounts for
an excess of pairs that lie just aside from the nominal periods ratios, as
observed by the Kepler mission. In addition, by a global analysis of the phase
space of the problem, we demonstrate that these final pairs are non-resonant.
Indeed, the separatrices that exist in the resonant systems disappear with the
dissipation, and remains only a circulation of the orbits around a single
elliptical fixed point. Furthermore, the apparent libration of the resonant
angles can be explained using the classical secular averaging method. We show
that this artifact is only due to the severe damping of the amplitudes of the
eigenmodes in the secular motion.Comment: 18 pages, 20 figures, accepted to A&
Age-related increase of kynurenic acid in human cerebrospinal fluid-IgG and beta(2)-microglobulin changes
Kynurenic acid (KYNA) is an endogenous metabolite in the kynurenine pathway of tryptophan degradation and is an antagonist at the glycine site of the N-methyl-D-aspartate as well as at the alpha 7 nicotinic cholinergic receptors. In the brain tissue KYNA is synthesised from L-kynurenine by kynurenine aminotransferases (KAT) I and II. A host of immune mediators influence tryptophan degradation. In the present study, the levels of KYNA in cerebrospinal fluid (CSF) and serum in a group of human subjects aged between 25 and 74 years were determined by using a high performance liquid chromatography method. In CSF and serum KAT I and II activities were investigated by radioenzymatic assay, and the levels of β2-microglobulin, a marker for cellular immune activation, were determined by ELISA. The correlations between neurochemical and biological parameters were evaluated. Two subject groups with significantly different ages, i.e. 50 years, p < 0.001, showed statistically significantly different CSF KYNA levels, i.e. 2.84 ± 0.16 fmol/μl vs. 4.09 ± 0.14 fmol/μl, p < 0.001, respectively; but this difference was not seen in serum samples. Interestingly, KYNA is synthesised in CSF principally by KAT I and not KAT II, however no relationship was found between enzyme activity and ageing. A positive relationship between CSF KYNA levels and age of subjects indicates a 95% probability of elevated CSF KYNA with ageing (R = 0.6639, p = 0.0001). KYNA levels significantly correlated with IgG and β2-microglobulin levels (R = 0.5244, p = 0.0049; R = 0.4253, p = 0.043, respectively). No correlation was found between other biological parameters in CSF or serum. In summary, a positive relationship between the CSF KYNA level and ageing was found, and the data would suggest age-dependent increase of kynurenine metabolism in the CNS. An enhancement of CSF IgG and β2-microglobulin levels would suggest an activation of the immune system during ageing. Increased KYNA metabolism may be involved in the hypofunction of the glutamatergic and/or nicotinic cholinergic neurotransmission in the ageing CNS
Ward identities for the Anderson impurity model: derivation via functional methods and the exact renormalization group
Using functional methods and the exact renormalization group we derive Ward
identities for the Anderson impurity model. In particular, we present a
non-perturbative proof of the Yamada-Yosida identities relating certain
coefficients in the low-energy expansion of the self-energy to thermodynamic
particle number and spin susceptibilities of the impurity. Our proof underlines
the relation of the Yamada-Yosida identities to the U(1) x U(1) symmetry
associated with particle number and spin conservation in a magnetic field.Comment: 8 pages, corrected statements about infintite flatband limi
The Strange Man in Random Networks of Automata
We have performed computer simulations of Kauffman's automata on several
graphs such as the regular square lattice and invasion percolation clusters in
order to investigate phase transitions, radial distributions of the mean total
damage (dynamical exponent ) and propagation speeds of the damage when one
adds a damaging agent, nicknamed "strange man". Despite the increase in the
damaging efficiency, we have not observed any appreciable change at the
transition threshold to chaos neither for the short-range nor for the
small-world case on the square lattices when the strange man is added in
comparison to when small initial damages are inserted in the system. The
propagation speed of the damage cloud until touching the border of the system
in both cases obeys a power law with a critical exponent that strongly
depends on the lattice. Particularly, we have ckecked the damage spreading when
some connections are removed on the square lattice and when one considers
special invasion percolation clusters (high boundary-saturation clusters). It
is seen that the propagation speed in these systems is quite sensible to the
degree of dilution.Comment: AMS-LaTeX v1.2, 7 pages with 14 figures Encapsulated Postscript, to
be publishe
Renormalization of the BCS-BEC crossover by order parameter fluctuations
We use the functional renormalization group approach with partial
bosonization in the particle-particle channel to study the effect of order
parameter fluctuations on the BCS-BEC crossover of superfluid fermions in three
dimensions. Our approach is based on a new truncation of the vertex expansion
where the renormalization group flow of bosonic two-point functions is closed
by means of Dyson-Schwinger equations and the superfluid order parameter is
related to the single particle gap via a Ward identity. We explicitly calculate
the chemical potential, the single-particle gap, and the superfluid order
parameter at the unitary point and compare our results with experiments and
previous calculations.Comment: 5 pages, 3 figure
Field-theoretical renormalization group for a flat two-dimensional Fermi surface
We implement an explicit two-loop calculation of the coupling functions and
the self-energy of interacting fermions with a two-dimensional flat Fermi
surface in the framework of the field theoretical renormalization group (RG)
approach. Throughout the calculation both the Fermi surface and the Fermi
velocity are assumed to be fixed and unaffected by interactions. We show that
in two dimensions, in a weak coupling regime, there is no significant change in
the RG flow compared to the well-known one-loop results available in the
literature. However, if we extrapolate the flow to a moderate coupling regime
there are interesting new features associated with an anisotropic suppression
of the quasiparticle weight Z along the Fermi surface, and the vanishing of the
renormalized coupling functions for several choices of the external momenta.Comment: 16 pages and 22 figure
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