33 research outputs found
Orbital Perturbations of the Galilean Satellites During Planetary Encounters
The Nice model of the dynamical instability and migration of the giant
planets can explain many properties of the present Solar System, and can be
used to constrain its early architecture. In the jumping-Jupiter version of the
Nice model, required from the terrestrial planet constraint and dynamical
structure of the asteroid belt, Jupiter has encounters with an ice giant. Here
we study the survival of the Galilean satellites in the jumping-Jupiter model.
This is an important concern because the ice-giant encounters, if deep enough,
could dynamically perturb the orbits of the Galilean satellites, and lead to
implausible results. We performed numerical integrations where we tracked the
effect of planetary encounters on the Galilean moons. We considered three
instability cases from Nesvorny & Morbidelli (2012) that differed in the number
and distribution of encounters. We found that in one case, where the number of
close encounters was relatively small, the Galilean satellite orbits were not
significantly affected. In the other two, the orbital eccentricities of all
moons were excited by encounters, Callisto's semimajor axis changed, and, in a
large fraction of trials, the Laplace resonance of the inner three moons was
disrupted. The subsequent evolution by tides damps eccentricities and can
recapture the moons in the Laplace resonance. A more important constraint is
represented by the orbital inclinations of the moons, which can be excited
during the encounters and not appreciably damped by tides. We find that one
instability case taken from Nesvorny & Morbidelli (2012) clearly fails this
constraint. This shows how the regular satellites of Jupiter can be used to set
limits on the properties of encounters in the jumping-Jupiter model, and help
us to better understand how the early Solar System evolved.Comment: The Astronomical Journal, in pres
Dynamical Evolution of Planetary Systems
Planetary systems can evolve dynamically even after the full growth of the
planets themselves. There is actually circumstantial evidence that most
planetary systems become unstable after the disappearance of gas from the
protoplanetary disk. These instabilities can be due to the original system
being too crowded and too closely packed or to external perturbations such as
tides, planetesimal scattering, or torques from distant stellar companions. The
Solar System was not exceptional in this sense. In its inner part, a crowded
system of planetary embryos became unstable, leading to a series of mutual
impacts that built the terrestrial planets on a timescale of ~100 My. In its
outer part, the giant planets became temporarily unstable and their orbital
configuration expanded under the effect of mutual encounters. A planet might
have been ejected in this phase. Thus, the orbital distributions of planetary
systems that we observe today, both solar and extrasolar ones, can be different
from the those emerging from the formation process and it is important to
consider possible long-term evolutionary effects to connect the two.Comment: Review to appear as a chapter in the "Handbook of Exoplanets", ed. H.
Deeg & J.A. Belmont
Elevated Risk for HIV-1 Infection in Adolescents and Young Adults in São Paulo, Brazil
Background. Recent studies have sought to describe HIV infection and transmission characteristics around the world. Identification of early HIV-1 infection is essential to proper surveillance and description of regional transmission trends. In this study we compare people recently infected (RI) with HIV-1, as defined by Serologic Testing Algorithm for Recent HIV Seroconversion (STARHS), to those with chronic infection. Methodology/Principal Findings Subjects were identified from 2002-2004 at four testing sites in São Paulo. Of 485 HIV-1-positive subjects, 57 (12%) were defined as RI. Of the participants, 165 (34.0%) were aware of their serostatus at the time of HIV-1 testing. This proportion was statistically larger (p<0.001) among the individuals without recent infection (n = 158, 95.8%) compared to 7 individuals (4.2%) with recently acquired HIV-1 infection. In the univariate analysis, RI was more frequent in <25 and >59 years-old age strata (p<0.001). The majority of study participants were male (78.4%), 25 to 45 years-old (65.8%), white (63.2%), single (61.7%), with family income of four or more times the minimum wage (41.0%), but with an equally distributed educational level. Of those individuals infected with HIV-1, the predominant route of infection was sexual contact (89.4%), with both hetero (47.5%) and homosexual (34.5%) exposure. Regarding sexual activity in these individuals, 43.9% reported possible HIV-1 exposure through a seropositive partner, and 49.4% reported multiple partners, with 47% having 2 to 10 partners and 37.4% 11 or more; 53.4% of infected individuals reported condom use sometimes; 34.2% reported non-injecting, recreational drug use and 23.6% were reactive for syphilis by VDRL. Subjects younger than 25 years of age were most vulnerable according to the multivariate analysis. ) Conclusions/Significance In this study, we evaluated RI individuals and discovered that HIV-1 has been spreading among younger individuals in São Paulo and preventive approaches should, therefore, target this age stratu
Cladistical analysis of the Jovian and Saturnian satellite systems
Jupiter and Saturn each have complex systems of satellites and rings. These satellites can be classified into dynamical groups, implying similar formation scenarios. Recently, a larger number of additional irregular satellites have been discovered around both gas giants that have yet to be classified. The aim of this paper is to examine the relationships between the satellites and rings of the gas giants, using an analytical technique called cladistics. Cladistics is traditionally used to examine relationships between living organisms, the 'tree of life.' In this work, we perform the first cladistical study of objects in a planetary science context. Our method uses the orbital, physical, and compositional characteristics of satellites to classify the objects in the Jovian and Saturnian systems. We find that the major relationships between the satellites in the two systems, such as families, as presented in previous studies, are broadly preserved. In addition, based on our analysis of the Jovian system, we identify a new retrograde irregular family, the Iocaste family, and suggest that the Phoebe family of the Saturnian system can be further divided into two subfamilies. We also propose that the Saturnian irregular families be renamed, to be consistent with the convention used in Jovian families. Using cladistics, we are also able to assign the new unclassified irregular satellites into families. Taken together, the results of this study demonstrate the potential use of the cladistical technique in the investigation of relationships between orbital bodies
Effects of the planetary migration on some primordial satellites of the outer planets
Context. During the first hundred million years after the formation of our solar system, the four giant planets are believed to have migrated significantly (by up ≈ 20 AU). The current scenario and dynamics of the satellites of these planets must be the result of both the initial conditions of their formation and this early extensive migrational episode.
Aims. We examine the effects of the migration on the primordial satellites of Uranus.
Methods. We use the Nice model to generate templates for the evolution of the four giant planets and record the time history of these planets and important close encounters. The satellites are then added to Uranus and these objects are integrated according to the dynamics stored in the templates.
Results. We show that Oberon is the outermost regular satellite of Uranus that is able to resist the close encounters during the extensive migrational episode. Some theories predict that Uranus’ satellites can form out to a 57 RU distance from the planet, but we show that even those at ≈ 27 RU from the planet cannot support the instabilities that appeared during migration. Close objects, such as the current regular satellites of Uranus, can survive quite stably and we are able to place some constraints on the masses of the planetesimals that have close encounters. For instance, if an object with mass ≥ 10-9 M⊙ approaches at distances ≲ 23 RU from Uranus, the regular satellites can be destabilized or their eccentricities or inclinations excited to some non-compatibles values. We also find that planet-planetesimal close encounters can generate capture. In this way, we present a promising means of explaining the origin of the irregular satellites of Uranus. The importance of the oblateness of the planet, and the Sun for just-captured planetesimals is also shown
Proposta de aplicação do método de solução de problemas na assistência de enfermagem em Centro de Terapia Intensiva
Consiste numa proposta de adaptação do modelo de Método de Solução de Problemas, proposto por Bailey & Claus, na sistematização da assistência de enfermagem em Centro de Terapia Intensiva. Utilizou-se a metodologia de estudo de caso, com a aplicação do modelo em um paciente de terapia intensiva. Para isso, elaboramos um instrumento que possibilitasse a aplicação do modelo na prática assistencial do enfermeiro de C.T.I., e discutimos os passos propostos por este modelo. Concluímos que sua aplicação é viável, desde que sejam efetuadas adaptações nos passos propostos, e se desenvolva numa estrutura com enfermeiros qualificados, recursos técnicos e materiais adequados
Proposta de aplicação do método de solução de problemas na assistência de enfermagem em Centro de Terapia Intensiva
Consiste numa proposta de adaptação do modelo de Método de Solução de Problemas, proposto por Bailey & Claus, na sistematização da assistência de enfermagem em Centro de Terapia Intensiva. Utilizou-se a metodologia de estudo de caso, com a aplicação do modelo em um paciente de terapia intensiva. Para isso, elaboramos um instrumento que possibilitasse a aplicação do modelo na prática assistencial do enfermeiro de C.T.I., e discutimos os passos propostos por este modelo. Concluímos que sua aplicação é viável, desde que sejam efetuadas adaptações nos passos propostos, e se desenvolva numa estrutura com enfermeiros qualificados, recursos técnicos e materiais adequados
Proposta de aplicação do método de solução de problemas na assistência de enfermagem em Centro de Terapia Intensiva
Consiste numa proposta de adaptação do modelo de Método de Solução de Problemas, proposto por Bailey & Claus, na sistematização da assistência de enfermagem em Centro de Terapia Intensiva. Utilizou-se a metodologia de estudo de caso, com a aplicação do modelo em um paciente de terapia intensiva. Para isso, elaboramos um instrumento que possibilitasse a aplicação do modelo na prática assistencial do enfermeiro de C.T.I., e discutimos os passos propostos por este modelo. Concluímos que sua aplicação é viável, desde que sejam efetuadas adaptações nos passos propostos, e se desenvolva numa estrutura com enfermeiros qualificados, recursos técnicos e materiais adequados
Corneal collagen cross-linking for progressive keratoconus in patients aged 9 to 14
RESUMO Objetivo: Determinar a segurança e eficácia do cross-linking corneano (CXL) em pacientes de 9 a 14 anos de idade com ceratocone progressivo. Métodos: Dezesseis olhos de onze pacientes (8 homens e 3 mulheres) com ceratocone progressivo foram submetidos ao CXL, de acordo com o protocolo padrão de Dresden. A média do tempo de seguimento foi de 26 meses (variando de 12 a 60 meses). Os exames pré e pós-operatórios incluíram: acuidade visual sem correção (AVSC), melhor acuidade visual com correção (AVCC), topografia corneana, tonometria, refração, paquimetria corneana, e contagem de células endoteliais. Resultados: Na última visita de acompanhamento ambulatorial, a AVCC melhorou pelo menos uma linha na tabela de Snellen em 6 olhos (37,5%) e permaneceu estável em 9 olhos (56,25%). Dois olhos (12,5%) de pacientes que coçam os olhos com frequência, exigiram retratamento devido à progressão do ceratocone, 15 e 28 meses após o primeiro CXL. A refração e contagem de células endoteliais mantiveram-se estáveis. Os resultados topográficos mostraram melhora estatisticamente significativa nos valores do K máximo até dois anos após o CXL. No entanto, houve perda de significância ao longo do tempo. Nenhuma complicação peroperatória foi observada. Dois olhos (12,5%) apresentaram haze grau I, que regrediu após um mês de terapia com esteróide tópico. Conclusão: Neste estudo com pacientes selecionados, de 9 a 14 anos de idade, o CXL mostrou ser uma opção segura e eficaz para o tratamento do ceratocone progressivo. No entanto, o efeito pode não ser duradouro, podendo ser necessário um novo tratamento. Maior amostragem e maior seguimento são necessários para verificar esta tendência