8,898 research outputs found
Astrometry of mutual approximations between natural satellites. Application to the Galilean moons
Typically we can deliver astrometric positions of natural satellites with
errors in the 50-150 mas range. Apparent distances from mutual phenomena, have
much smaller errors, less than 10 mas. However, this method can only be applied
during the equinox of the planets. We developed a method that can provide
accurate astrometric data for natural satellites -- the mutual approximations.
The method can be applied when any two satellites pass close by each other in
the apparent sky plane. The fundamental parameter is the central instant
of the passage when the distances reach a minimum.
We applied the method for the Galilean moons. All observations were made with
a 0.6 m telescope with a narrow-band filter centred at 889 nm with width of 15
nm which attenuated Jupiter's scattered light. We obtained central instants for
14 mutual approximations observed in 2014-2015. We determined with an
average precision of 3.42 mas (10.43 km). For comparison, we also applied the
method for 5 occultations in the 2009 mutual phenomena campaign and for 22
occultations in the 2014-2015 campaign. The comparisons of determined by
our method with the results from mutual phenomena show an agreement by less
than 1-sigma error in , typically less than 10 mas. This new method is
particularly suitable for observations by small telescopes.Comment: 13 pages, 11 figures and 8 tables. Based on observations made at the
Laborat\'orio Nacional de Astrof\'isica (LNA), Itajub\'a-MG, Brazi
The Cosmological Evolution of Domain Wall Networks
We have studied the cosmological evolution of domain wall networks in two,
three and four spatial dimensions using high-resolution field theory
simulations. The dynamical range and number of our simulations is larger than
in previous works, but does not allow us to exclude previous hints of
deviations to the naively expected scale-invariant evolution. These results
therefore suggest that the approach of domain wall networks to linear scaling
is a much slower process than that of cosmic strings, which has been previously
characterized in detail.Comment: 7 pages, submitted to Phys Rev
Complex networks generated by the Penna bit-string model: emergence of small-world and assortative mixing
The Penna bit-string model successfully encompasses many phenomena of population evolution, including inheritance, mutation, evolution, and aging. If we consider social interactions among individuals in the Penna model, the population will form a complex network. In this paper, we first modify the Verhulst factor to control only the birth rate, and introduce activity-based preferential reproduction of offspring in the Penna model. The social interactions among individuals are generated by both inheritance and activity-based preferential increase. Then we study the properties of the complex network generated by the modified Penna model. We find that the resulting complex network has a small-world effect and the assortative mixing property
First Trimester Prediction of Pre-Eclampsia in Low Risk Pregnancies: Determining the Cut-Off in a Portuguese Group
Objective:We aimed to identify the cut-off for risk of pre-eclampsia (PE) in Portuguese population by applying the first trimester prediction model from Fetal Medicine Foundation (FMF) in a prospective enrolled cohort of low risk pregnant women.
Population and methods: A prospective cohort of low risk singleton pregnancies underwent routine first-trimester scree -
ning from 2011 through 2013. Maternal characteristics, blood pressure, uterine artery Doppler, levels of pregnancy-associated plasma protein-A (PAPP-A) and free b-human chorionic gonadotropin were evaluated. The prediction of PE in first trimester was calculated through software Astraia, the outcome obtained from medical records and the cutoff value was subse quently calculated.
Results:Of the 273 enrolled patients, 7 (2.6%) developed PE. In first trimester women who developed PE presented higher uterine arteries resistance, represented by higher values of lowest and mean uterine pulsatility index, p <0.005. There was no statistical significance among the remaining maternal characteristics, body mass index, blood pressure and PAPP-A. Using the FMF first trimester PE algorithm, an ideal cut-off of 0.045 (1/22) would correctly detect 71% women who developed PE for a 12% false positive rate and a likelihood ratio of 12.98 (area under the curve: 0.69; confidence interval 95%: 0.39-0.99). By applying the reported cutoff to our cohort, we would obtain 71.4% true positives, 88.3% true negatives, 11.4% false positives and 28.6% false negatives.
Conclusion: By applying a first trimester PE prediction model to low risk pregnancies derived from a Portuguese population, a significant proportion of patients would have been predicted as high risk. New larger studies are required to confirm the present findings
The reinfection threshold regulates pathogen diversity: the case of influenza
The awareness that pathogens can adapt and evolve over relatively short time-scales is changing our view of infectious disease epidemiology and control. Research on the transmission dynamics of antigenically diverse pathogens is progressing and there is increasing recognition for the need of new concepts and theories. Mathematical models have been developed considering the modelling unit in two extreme scales: either diversity is not explicitly represented or diversity is represented at the finest scale of single variants. Here, we use an intermediate approach and construct a model at the scale of clusters of variants. The model captures essential properties of more detailed systems and is much more amenable to mathematical treatment. Specificities of pathogen clusters and the overall potential for transmission determine the reinfection rates. These are, in turn, important regulators of cluster dynamics. Ultimately, we detect a reinfection threshold (RT) that separates different behaviours along the transmissibility axis: below RT, levels of infection are low and cluster substitutions are probable; while above RT, levels of infection are high and multiple cluster coexistence is the most probable outcom
Catastrophic senescence and semelparity in the Penna aging model
The catastrophic senescence of the Pacific salmon is among the initial tests
used to validate the Penna aging model. Based on the mutation accumulation
theory, the sudden decrease in fitness following reproduction may be solely
attributed to the semelparity of the species. In this work, we report other
consequences of mutation accumulation. Contrary to earlier findings, such
dramatic manifestation of aging depends not only on the choice of breeding
strategy but also on the value of the reproduction age, R, and the mutation
threshold, T. Senescence is catastrophic when . As the organism's
tolerance for harmful genetic mutations increases, the aging process becomes
more gradual. We observe senescence that is threshold dependent whenever T>R.
That is, the sudden drop in survival rate occurs at age equal to the mutation
threshold value
Whole-rock geochemistry of the Vila Pouca de Aguiar granitic porphyries (northern Portugal), integrated with petrographic and SEM-EDS analysis
Optical and structural properties of GaAs/GaInP quantum wells grown by Chemical Beam Epitaxy
In this work we investigated the optical and structural properties of GaAs/GaInP quantum wells (QW) grown by Chemical Beam Epitaxy (CBE). The samples were characterized by photoluminescence (PL), photoluminescence excitation (PLE) and transmission electron microscopy (TEM). Simulations of the quantum well potential profiles, using the Van De Walle-Martin model, supplemented by our experimental results, allowed us to associate the interface properties with the growth procedures. We concluded that a thin GaP layer grown at the interface improves its quality and also that the observed broad emission band in the PL spectrum is related to quaternary Ga1-xIn xAs1-yPy.620622Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento CientÃfico e Tecnológico (CNPq)Fundação para o Desenvolvimento da UNESP (FUNDUNESP
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