179 research outputs found
Coorbital Satellites of Saturn: Congenital Formation
Saturn is the only known planet to have coorbital satellite systems. In the
present work we studied the process of mass accretion as a possible mechanism
for coorbital satellites formation. The system considered is composed of
Saturn, a proto-satellite and a cloud of planetesimals distributed in the
coorbital region around a triangular Lagrangian point. The adopted relative
mass for the proto-satellite was 10^-6 of Saturn's mass and for each
planetesimal of the cloud three cases of relative mass were considered, 10^-14,
10^-13 and 10^-12 masses of Saturn. In the simulations each cloud of
planetesimal was composed of 10^3, 5 x 10^3 or 10^4 planetesimals. The results
of the simulations show the formation of coorbital satellites with relative
masses of the same order of those found in the saturnian system (10^-13 -
10^-9). Most of them present horseshoe type orbits, but a significant part is
in tadpole orbit around L_4 or L_5. Therefore, the results indicate that this
is a plausible mechanism for the formation of coorbital satellites.Comment: 10 pages, 9 figures, 4 table
Terrestrial Planet Formation in a protoplanetary disk with a local mass depletion: A successful scenario for the formation of Mars
Models of terrestrial planet formation for our solar system have been
successful in producing planets with masses and orbits similar to those of
Venus and Earth. However, these models have generally failed to produce
Mars-sized objects around 1.5 AU. The body that is usually formed around Mars'
semimajor axis is, in general, much more massive than Mars. Only when Jupiter
and Saturn are assumed to have initially very eccentric orbits (e 0.1),
which seems fairly unlikely for the solar system, or alternately, if the
protoplanetary disk is truncated at 1.0 AU, simulations have been able to
produce Mars-like bodies in the correct location. In this paper, we examine an
alternative scenario for the formation of Mars in which a local depletion in
the density of the protosolar nebula results in a non-uniform formation of
planetary embryos and ultimately the formation of Mars-sized planets around 1.5
AU. We have carried out extensive numerical simulations of the formation of
terrestrial planets in such a disk for different scales of the local density
depletion, and for different orbital configurations of the giant planets. Our
simulations point to the possibility of the formation of Mars-sized bodies
around 1.5 AU, specifically when the scale of the disk local mass-depletion is
moderately high (50-75%) and Jupiter and Saturn are initially in their current
orbits. In these systems, Mars-analogs are formed from the protoplanetary
materials that originate in the regions of disk interior or exterior to the
local mass-depletion. Results also indicate that Earth-sized planets can form
around 1 AU with a substantial amount of water accreted via primitive
water-rich planetesimals and planetary embryos. We present the results of our
study and discuss their implications for the formation of terrestrial planets
in our solar system.Comment: Accepted for publication in The Astrophysical Journa
Terrestrial Planet Formation Constrained by Mars and the Structure of the Asteroid Belt
Reproducing the large Earth/Mars mass ratio requires a strong mass depletion
in solids within the protoplanetary disk between 1 and 3 AU. The Grand Tack
model invokes a specific migration history of the giant planets to remove most
of the mass initially beyond 1 AU and to dynamically excite the asteroid belt.
However, one could also invoke a steep density gradient created by inward drift
and pile-up of small particles induced by gas-drag, as has been proposed to
explain the formation of close-in super Earths. Here we show that the asteroid
belt's orbital excitation provides a crucial constraint against this scenario
for the Solar System. We performed a series of simulations of terrestrial
planet formation and asteroid belt evolution starting from disks of
planetesimals and planetary embryos with various radial density gradients and
including Jupiter and Saturn on nearly circular and coplanar orbits. Disks with
shallow density gradients reproduce the dynamical excitation of the asteroid
belt by gravitational self-stirring but form Mars analogs significantly more
massive than the real planet. In contrast, a disk with a surface density
gradient proportional to reproduces the Earth/Mars mass ratio but
leaves the asteroid belt in a dynamical state that is far colder than the real
belt. We conclude that no disk profile can simultaneously explain the structure
of the terrestrial planets and asteroid belt. The asteroid belt must have been
depleted and dynamically excited by a different mechanism such as, for
instance, in the Grand Tack scenario.Comment: Accepted for publication in MNRA
A Compound model for the origin of Earth's water
One of the most important subjects of debate in the formation of the solar
system is the origin of Earth's water. Comets have long been considered as the
most likely source of the delivery of water to Earth. However, elemental and
isotopic arguments suggest a very small contribution from these objects. Other
sources have also been proposed, among which, local adsorption of water vapor
onto dust grains in the primordial nebula and delivery through planetesimals
and planetary embryos have become more prominent. However, no sole source of
water provides a satisfactory explanation for Earth's water as a whole. In view
of that, using numerical simulations, we have developed a compound model
incorporating both the principal endogenous and exogenous theories, and
investigating their implications for terrestrial planet formation and
water-delivery. Comets are also considered in the final analysis, as it is
likely that at least some of Earth's water has cometary origin. We analyze our
results comparing two different water distribution models, and complement our
study using D/H ratio, finding possible relative contributions from each
source, focusing on planets formed in the habitable zone. We find that the
compound model play an important role by showing more advantage in the amount
and time of water-delivery in Earth-like planets.Comment: Accepted for publication in The Astrophysical Journa
Assessing the spin-orbit obliquity of low-mass planets in the breaking the chain formation model: A story of misalignment
The spin-orbit obliquity of a planetary system constraints its formation
history. A large obliquity may either indicate a primordial misalignment
between the star and its gaseous disk or reflect the effect of different
mechanisms tilting planetary systems after formation. Observations and
statistical analysis suggest that system of planets with sizes between 1 and 4
R have a wide range of obliquities (), and that
single- and multi-planet transiting have statistically indistinguishable
obliquity distributions. Here, we revisit the ``breaking the chains'' formation
model with focus in understanding the origin of spin-orbit obliquities. This
model suggests that super-Earths and mini-Neptunes migrate close to their host
stars via planet-disk gravitational interactions, forming chain of planets
locked in mean-motion resonances. After gas-disk dispersal, about 90-99\% of
these planetary systems experience dynamical instabilities, which spread the
systems out. Using synthetic transit observations, we show that if planets are
born in disks where the disk angular momentum is virtually aligned with the
star's rotation spin, their final obliquity distributions peak at about 5
degrees or less, and the obliquity distributions of single and multi-planet
transiting systems are statistically distinct. By treating the star-disk
alignment as a free-parameter, we show that the obliquity distributions of
single and multi-planet transiting systems only become statistically
indistinguishable if planets are assumed to form in primordially misaligned
natal disks with a ``tilt'' distribution peaking at 10-20 deg. We
discuss the origin of these misalignments in the context of star formation and
potential implications of this scenario for formation models.Comment: 11 pages, 9 figures, 2 tables. Accepted for publication in MNRA
Pyrolytic temperature evaluation of macauba biochar for uranium adsorption from aqueous solutions
Application of hyaluronic acid in non-surgical treatment of periodontitis
Poster apresentado no 2º Congresso Internacional do CiiEM: Translational Research and Innovation in Human in health Sciences. 11-13 Junho 2017, Campus Egas Moniz, Caparica, PortugalN/
Treatment of infra-bony periodontal defects using a collagen membrane and a bone substitute of equine origin : a pilot study
Abstract in proceedings of the Fourth International Congress of CiiEM: Health, Well-Being and Ageing in the 21st Century, held at Egas Moniz’ University Campus in Monte de Caparica, Almada, from 3–5 June 2019.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.info:eu-repo/semantics/publishedVersio
Tratamento da peri-implantite: conceitos atuais
Poster apresentado no XXIV Congresso da Ordem dos Médicos Dentistas. Lisboa, 12-14 Novembro de 2015Nos últimos anos a colocação de implantes tornou-se uma das técnicas mais preconizadas na reabilitação de desdentados totais ou parciais, sobretudo devido à elevada percentagem de sucesso que lhe está associada. Não obstante, existem algumas complicações, quer a curto, quer a longo prazo, que podem comprometer o êxito desta técnica. A peri-implantite é uma das complicações mais frequentes associadas aos implantes dentários. O objetivo desta revisão é apresentar o “estado da arte” no tratamento da peri-implantite.N/
Caracterização do uso de medicamentos pediátricos em crianças do ensino pré-primário e primário
Pais e/ou outros responsáveis recorrem habitualmente à utilização de medicação sem prescrição nas suas
crianças, o que pode ser considerado como um processo facilitador de intoxicações medicamentosas 1. No
entanto, a criança não é um adulto em tamanho pequeno. Nos primeiros anos de vida, o organismo possui
sistemas de reação e eliminação dos fármacos distintos do adulto, o que tem necessariamente implicações na
utilização dos medicamentos para garantir a segurança e a efetividade 2.
Objetivo: Identificar formas, motivos e fontes de influência na prática da automedicação na idade pediátrica pelos
pais/responsáveis e fatores associados; determinar a perceção do conhecimento dos encarregados relativamente
às prescrições médicas das suas crianças. Foi efetuado um estudo transversal, descritivo correlacional. Nele participaram 371 pais ou outros responsáveis, 81,9%
do sexo feminino e 18,1% do sexo do masculino, com idades abrangidas entre os 22 e os 58 anos, sendo a média de
idades de 37,84 anos.
A recolha de dados foi realizada, através de um questionário de autopreenchimento anónimo e voluntário, nos
estabelecimentos de ensino pré-escolar e do 1º ciclo do ensino básico da cidade de Bragança. Na análise estatística
aplicaram-se medidas de tendência central e de dispersão, e o teste do qui-quadrado considerando o nível de
significância de 5%.info:eu-repo/semantics/publishedVersio
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