Correlated enhancement of Hc2 and Jc in carbon nanotube-doped MgB2

The use of MgB2 in superconducting applications still awaits for the development of a MgB2-based material where both current-carrying performance and critical magnetic field are optimized simultaneously. We achieved this by doping MgB2 with double-wall carbon nanotubes (DWCNT) as a source of carbon in polycrystalline samples. The optimum nominal DWCNT content for increasing the critical current density, Jc is in the range 2.5-10%at depending on field and temperature. Record values of the upper critical field, Hc2(4K) = 41.9 T (with extrapolated Hc2(0) ~ 44.4 T) are reached in a bulk sample with 10%at DWCNT content. The measured Hc2 vs T in all samples are successfully described using a theoretical model for a two-gap superconductor in the dirty limit first proposed by Gurevich et al.Comment: 12 pages, 3 figure

Distinguishing the albedo of exoplanets from stellar activity

Light curves show the flux variation from the target star and its orbiting planets as a function of time. In addition to the transit features created by the planets, the flux also includes the reflected light component of each planet, which depends on the planetary albedo. This signal is typically referred to as phase curve and could be easily identified if there were no additional noise. As well as instrumental noise, stellar activity, such as spots, can create a modulation in the data, which may be very difficult to distinguish from the planetary signal. We analyze the limitations imposed by the stellar activity on the detection of the planetary albedo, considering the limitations imposed by the predicted level of instrumental noise and the short duration of the observations planned in the context of the CHEOPS mission. As initial condition, we have assumed that each star is characterized by just one orbiting planet. We built mock light curves that included a realistic stellar activity pattern, the reflected light component of the planet and an instrumental noise level, which we have chosen to be at the same level as predicted for CHEOPS. We then fit these light curves to try to recover the reflected light component, assuming the activity patterns can be modeled with a Gaussian process.We estimate that at least one full stellar rotation is necessary to obtain a reliable detection of the planetary albedo. This result is independent of the level of noise, but it depends on the limitation of the Gaussian process to describe the stellar activity when the light curve time-span is shorter than the stellar rotation. Finally, in presence of typical CHEOPS gaps in the simulations, we confirm that it is still possible to obtain a reliable albedo.Comment: Accepted for publication in A&A, 14 pages, 12 figure

Lattice Properties of PbX (X = S, Se, Te): Experimental Studies and ab initio Calculations Including Spin-Orbit Effects

During the past five years the low temperature heat capacity of simple semiconductors and insulators has received renewed attention. Of particular interest has been its dependence on isotopic masses and the effect of spin- orbit coupling in ab initio calculations. Here we concentrate on the lead chalcogenides PbS, PbSe and PbTe. These materials, with rock salt structure, have different natural isotopes for both cations and anions, a fact that allows a systematic experimental and theoretical study of isotopic effects e.g. on the specific heat. Also, the large spin-orbit splitting of the 6p electrons of Pb and the 5p of Te allows, using a computer code which includes spin-orbit interaction, an investigation of the effect of this interaction on the phonon dispersion relations and the temperature dependence of the specific heat and on the lattice parameter. It is shown that agreement between measurements and calculations significantly improves when spin-orbit interaction is included.Comment: 25 pages, 12 Figures, 1 table, submitted to PR

A entrega de um filho em adoção e as vicissitudes de ser mãe

This study aimed to investigate the feelings and experiences of motherhood of a woman who delivered two daughters for adoption. Furthermore, investigate their experiences in relation to her other children not delivered and with the condition of being a mother in this context. Using a semi-structured interview, we conducted a single case study, qualitative, through clinical report. The main results indicated the social and emotional vulnerability of the participant as an important influence on the delivery and a differentiation between children who remained in their care and daughters delivered for adoption. It was also noted the maternal role strongly related to maternal care and the different emotional reactions to experiences of delivery. We conclude the relevance of providing space for these mothers elaborate their stories, beyond the need for public policies that give legal and emotional support to mothers/families who wish to make delivery of children

The deep-pocket effect of internal capital markets

We provide evidence that incumbent and entrant firms' access to business group deep pockets affects entry patterns in product markets. Relying on a unique French data set on business groups, our paper shows that entry in manufacturing industries is negatively related to the cash hoarded by incumbent-affiliated groups, and positively related to entrant groups' cash. In line with theoretical predictions, we find that the impact on entry of group cash holdings is more important in environments where financial constraints are pronounced and in more financially dependent sectors. The cash holdings of incumbent and entrant groups also affect the survival rate of entrants in the 3 to 5 year post-entry window. Overall, our findings suggest that internal capital markets operate within corporate groups and affect the product market behavior of affiliated firms by mitigating financial constraints