Orbits and masses in the young triple system TWA 5

We aim to improve the orbital elements and determine the individual masses of the components in the triple system TWA 5. Five new relative astrometric positions in the H band were recorded with the adaptive optics system at the Very Large Telescope (VLT). We combine them with data from the literature and a measurement in the Ks band. We derive an improved fit for the orbit of TWA 5Aa-b around each other. Furthermore, we use the third component, TWA 5B, as an astrometric reference to determine the motion of Aa and Ab around their center of mass and compute their mass ratio. We find an orbital period of 6.03+/-0.01 years and a semi-major axis of 63.7+/-0.2 mas (3.2+/-0.1 AU). With the trigonometric distance of 50.1+/-1.8 pc, this yields a system mass of 0.9+/-0.1 Msun, where the error is dominated by the error of the distance. The dynamical mass agrees with the system mass predicted by a number of theoretical models if we assume that TWA5 is at the young end of the age range of the TW Hydrae association. We find a mass ratio of M_Ab / M_Aa = 1.3 +0.6/-0.4, where the less luminous component Ab is more massive. This result is likely to be a consequence of the large uncertainties due to the limited orbital coverage of the observations.Comment: 9 pages, 8 figures, accepted by Astronomy and Astrophysic

Corrections to the Boltzmann mean free path in disordered systems with finite size scatterers

The mean free path is an essential characteristic length in disordered systems. In microscopic calculations, it is usually approximated by the classical value of the elastic mean free path. It corresponds to the Boltzmann mean free path when only isotropic scattering is considered, but it is different for anisotropic scattering. In this paper, we work out the corrections to the so called Boltzmann mean free path due to multiple scattering effects on finite size scatterers, in the s-wave approximation, ie. when the elastic mean free path is equivalent to the Boltzmann mean free path. The main result is the expression for the mean free path expanded in powers of the perturbative parameter given by the scatterer density.Comment: 12 page

Ab-initio study of the relation between electric polarization and electric field gradients in ferroelectrics

The hyperfine interaction between the quadrupole moment of atomic nuclei and the electric field gradient (EFG) provides information on the electronic charge distribution close to a given atomic site. In ferroelectric materials, the loss of inversion symmetry of the electronic charge distribution is necessary for the appearance of the electric polarization. We present first-principles density functional theory calculations of ferroelectrics such as BaTiO3, KNbO3, PbTiO3 and other oxides with perovskite structures, by focusing on both EFG tensors and polarization. We analyze the EFG tensor properties such as orientation and correlation between components and their link with electric polarization. This work supports previous studies of ferroelectric materials where a relation between EFG tensors and polarization was observed, which may be exploited to study ferroelectric order when standard techniques to measure polarization are not easily applied.Comment: 9 pages, 6 figures, 5 tables, corrected typos, as published in Phys. Rev.

Fertility Care Provided by a Public Health Hospital to Viral-Infected Couples: A Case-Control Study

Objective: To evaluate the results of ART (clinical pregnancies and baby home rates) in couples infected with HBV, HCV, HIV or mixed in a Referral center. Patients: The study is a retrospective case-control study comprising 1587 cycles/1064 couples in the control group and 237 cycles/164 couples in the infected group, submitted to in vitro fertilization, intracytoplasmic sperm injection and embryo transfer. Two branches from the infected group were created: the HIV subgroup, comprising couples with one or both partners infected with HIV-1 (84 cycles/67 couples), and the HCV subgroup, including at least one partner infected with HCV (45 cycles/29 couples). Results: The infected group presented higher infertility duration (P < 0.001) and so did the HCV subgroup (P < 0.001). Tubal infertility was increased in the infected group (P < 0.001), and in the HIV (P < 0.001) and HCV (P = 0.01) subgroups. Oocytes and oocytes in metaphase II numbers were lower in the infected group, but not in the HIV and HCV subgroups. Clinical pregnancy rate was lower in the infected group (25.74%) when compared to the control (34.66%), probably due to the contribution of HCV individuals (17.78%), but not of HIV (28.57%). Baby home rate was lower in the infected group (21.52%) relative to the control group (28.42%), but no differences were found in the HIV (27.38%) and HCV (15.56%) subgroups. Conclusions: Despite the low clinical pregnancy rate in the HCV subgroup, baby home rates did not change from control. These data seem promising for couples with viral infections who wish to conceive.info:eu-repo/semantics/publishedVersio

Stellar and circumstellar properties of visual binaries in the Orion Nebula Cluster

Our general understanding of multiple star and planet formation is primarily based on observations of young multiple systems in low density regions like Tau-Aur and Oph. Since many, if not most, of the stars are born in clusters, observational constraints from young binaries in those environments are fundamental for understanding both the formation of multiple systems and planets in multiple systems throughout the Galaxy. We build upon the largest survey for young binaries in the Orion Nebula Cluster (ONC) which is based on Hubble Space Telescope observations to derive both stellar and circumstellar properties of newborn binary systems in this cluster environment. We present Adaptive Optics spatially-resolved JHKL'-band photometry and K-band R$\sim$\,5000 spectra for a sample of 8 ONC binary systems from this database. We characterize the stellar properties of binary components and obtain a census of protoplanetary disks through K-L' color excess. For a combined sample of ONC binaries including 7 additional systems with NIR spectroscopy from the literature, we derive mass ratio and relative age distributions. We compare the stellar and circumstellar properties of binaries in ONC with those in Tau-Aur and Oph from samples of binaries with stellar properties derived for each component from spectra and/or visual photometry and with a disk census obtained through K-L color excess. The mass ratio distribution of ONC binaries is found to be indistinguishable from that of Tau-Aur and, to some extent, to that of Oph in the separation range 85-560\,AU and for primary mass in the range 0.15 to 0.8\,M_{\sun}.A trend toward a lower mass ratio with larger separation is suggested in ONC binaries which is not seen in Tau-Aur binaries.The components of ONC binaries are found to be significantly more coeval than the overall ONC population and as coeval as components of binaries in Tau-Aur and Oph[...]Comment: Accepted for publication in Astronomy & Astrophysic

Chitosan membranes exhibiting shape memory capability by the action of controlled hydration

Chitosan membranes can undergo a glass transition at room temperaturetriggered by hydration. The mechanical properties of the membranes were followed by atension test and dynamic mechanical analysis (DMA), with the sample in wet conditionsafter being immersed in varying compositions of water/ethanol mixtures. Results show thatwith the increasing of water content, the Young’s and storage modulus decreasesystematically. For water contents of ca. 35 vol%, chitosan (CHT) exhibits a glasstransition, showing an elastomeric plateau in the elastic modulus above this hydration leveland the occurrence of a peak in the loss factor. Due to the semi-crystalline nature of CHT,membranes of this biomaterial present a shape memory capability induced by water uptake.By fixation of the permanent shape by further covalent cross-linking, the membranes canhave different permanent shapes appropriate for different applications, including in thebiomedical area.This work was supported by the Portuguese Foundation for Science and Technology Foundation (FCT) through project PTDC/FIS/115048/2009

Modeling of the performance of scintillator based x-ray detectors

Over the last years several prototypes of detectors for digital radiography have been developed. One of the several approaches is based on scintillating crystals. Generally, these prototypes have been developed in a purely experimental basis, with a lack of mathematical and physical support. In the present work we have performed a systematic study of the various interactions and processes essential to the construction of x-ray sensors based in scintillator crystals. These results are an important help in the simulation of the performance of the whole sensor before its construction, which allows a better selection of the materials, the dimensions, shape and fabrication process