Melting temperature of screened Wigner crystal on helium films by molecular dynamics

Using molecular dynamics (MD) simulation, we have calculated the melting temperature of two-dimensional electron systems on $240$\AA-$500$\AA helium films supported by substrates of dielectric constants $\epsilon_{s}=2.2-11.9$ at areal densities $n$ varying from $3\times 10^{9}$ cm$^{-2}$ to $1.3\times 10^{10}$ cm$^{-2}$. Our results are in good agreement with the available theoretical and experimental results.Comment: 4 pages and 4 figure

A thorough analysis of the short- and mid-term activity-related variations in the solar acoustic frequencies

The frequencies of the solar acoustic oscillations vary over the activity cycle. The variations in other activity proxies are found to be well correlated with the variations in the acoustic frequencies. However, each proxy has a slightly different time behaviour. Our goal is to characterize the differences between the time behaviour of the frequency shifts and of two other activity proxies, namely, the area covered by sunspots and the 10.7cm flux. We define a new observable that is particularly sensitive to the short-term frequency variations. We then compare the observable when computed from model frequency shifts and from observed frequency shifts obtained with the Global Oscillation Network Group (GONG) for cycle 23. Our analysis shows that on the shortest time-scales the variations in the frequency shifts seen in the GONG observations are strongly correlated with the variations in the area covered by sunspots. However, a significant loss of correlation is still found. We verify that the times when the frequency shifts and the sunspot area do not vary in a similar way tend to coincide with the times of the maxima of the quasi-biennial variations seen in the solar seismic data. A similar analysis of the relation between the 10.7cm flux and the frequency shifts reveals that the short-time variations in the frequency shifts follow even more closely those of the 10.7cm flux than those of the sunspot area. However, a loss of correlation between frequency shifts and 10.7cm flux variations is still found around the same times.Comment: 7 pages, 6 figures, accepted for publication in MNRA

On the relation between activity-related frequency shifts and the sunspot distribution over the solar cycle 23

The activity-related variations in the solar acoustic frequencies have been known for 30 years. However, the importance of the different contributions is still not well established. With this in mind, we developed an empirical model to estimate the spot-induced frequency shifts, which takes into account the sunspot properties, such as area and latitude. The comparison between the model frequency shifts obtained from the daily sunspot records and those observed suggests that the contribution from a stochastic component to the total frequency shifts is about 30%. The remaining 70% is related to a global, long-term variation. We also propose a new observable to investigate the short- and mid-term variations of the frequency shifts, which is insensitive to the long-term variations contained in the data. On the shortest time scales the variations in the frequency shifts are strongly correlated with the variations in the total area covered by sunspots. However, a significant loss of correlation is still found, which cannot be fully explained by ignoring the invisible side of the Sun when accounting for the total sunspot area. We also verify that the times when the frequency shifts and the sunspot areas do not vary in a similar way tend to coincide with the times of the maximum amplitude of the quasi-biennial variations found in the seismic data.Comment: 4 pages, 2 figures, proceedings of the Joint TASC2 - KASC9 Workshop - SPACEINN - HELAS8 Conference "Seismology of the Sun and the Distant Stars 2016: Using Today's Successes to Prepare the Future". To be published by the EPJ Web of Conference

New Constraints on the Variable Equation of State Parameter from X-Ray Gas Mass Fractions and SNe Ia

Recent measurements are suggesting that we live in a flat Universe and that its present accelerating stage is driven by a dark energy component whose equation of state may evolve in time. Assuming two different parameterizations for the function $\omega(z)$, we constrain their free parameters from a joint analysis involving measurements from X-Ray luminosity of galaxy clusters and SNe type Ia data.Comment: paper, 6 pages, 1 figure Accepted by Int. Journal of Modern Physics D (IJPMD

Intraventricular Thrombi with Systemic Embolization: Two Clinical Cases

A formação de trombos intraventriculares é um complicação frequente nos doentes com miocardiopatia dilatada e enfarte agudo do miocárdio, sendo o risco de embolização sistémica muito variável em função da patologia subjacente e características subjacentes dos trombos. Os autores descrevem dois casos clínicos relativos a dois doentes internados no mesmo dia com trombos intraventriculares, volumosos, protuberantes e muito móveis, no contexto de miocardiopatia dilatada e enfarte agudo do miocárdio, que embolizaram para os membros inferiores. Salientam a importância da ecocardiografia no diagnóstico, caracterização morfológica inicial e controlo evolutivo dos trombos intraventriculares, aspectos fundamentais na avaliação do risco embólico. Na ausência de recomendações específicas quanto às opções terapêuticas – anticoagulação, trombólise ou remoção cirúrgica, os autores sublinham a necessidade de avaliação individualizada, «caso a caso», tendo em conta o risco embólico, hemorrágico, e cirúrgico

Pristine CNO abundances from Magellanic Cloud B stars II. Fast rotators in the LMC cluster NGC 2004

We present spectroscopic abundance analyses of three main-sequence B stars in the young Large Magellanic Cloud cluster NGC 2004. All three targets have projected rotational velocities around 130 km/s. Techniques are presented that allow the derivation of stellar parameters and chemical abundances in spite of these high v sin i values. Together with previous analyses of stars in this cluster, we find no evidence among the main-sequence stars for effects due to rotational mixing up to v sin i around 130 km/s. Unless the equatorial rotational velocities are significantly larger than the v sin i values, this finding is probably in line with theoretical expectations. NGC 2004/B30, a star of uncertain evolutionary status located in the Blue Hertzsprung Gap, clearly shows signs of mixing in its atmosphere. To verify the effects due to rotational mixing will therefore require homogeneous analysis of statistically significant samples of low-metallicity main-sequence B stars over a wide range of rotational velocities.Comment: 12 pages, 5 figures, 2 tables; accepted for publication in ApJ (vol. 633, p. 899

Spin-polarized transport in ferromagnetic multilayered semiconductor nanostructures

The occurrence of inhomogeneous spin-density distribution in multilayered ferromagnetic diluted magnetic semiconductor nanostructures leads to strong dependence of the spin-polarized transport properties on these systems. The spin-dependent mobility, conductivity and resistivity in (Ga,Mn)As/GaAs,(Ga,Mn)N/GaN, and (Si,Mn)/Si multilayers are calculated as a function of temperature, scaled by the average magnetization of the diluted magnetic semiconductor layers. An increase of the resistivity near the transition temperature is obtained. We observed that the spin-polarized transport properties changes strongly among the three materials.Comment: 3 pages, 4 figure

Phase selective growth of Cu12Sb4S13 and Cu3SbS4 thin films by chalcogenization of simultaneous sputtered metal precursors

In this work, it is presented a procedure to grow single phase Cu12Sb4S13 and Cu3SbS4 thin films consisting on the annealing of simultaneously sputtered metal precursors fllowed by a annealing treatment in a sulphur atmosphere. The selection of the ternary phase which is intended to grow is performed by adjusting the sulfur evaporation temperature in chalcogenization process. It is shown that for a sulphur evaporation temperature of 140 ◦C the predominant phase is Cu12Sb4S13 and for 180 ◦C the predominant phase is Cu3SbS4. In order to ensure precursor composition homogeneity, the Cu-Sb metallic precursors are deposited simultaneously by rf magnetron sputtering using adjustable segmented targets. The morphological characterization of the films was made by scanning electron microscopy and the composition was analysed by energy dispersive spectroscopy. The structural analysis and phase identification were performed by X-ray diffraction and Raman scattering. The optical properties were studied through spectrophotometry on films deposited directly on bare glass.publishe

Características físico-químicas de raízes de mandioca mansa (Manihot esculenta Crantz).

A mandioca apresenta uma grande diversidade genética e a caracterização físico-química é uma importante ferramenta de avaliação para poder selecionar genótipos promissores para fins de melhoramento genético. Por isso, objetivou-se caracterizar diferentes genótipos de mandioca mansa pertencentes ao banco ativo de germoplasma (BAG) da Embrapa Amazônia Oriental, no qual, foram coletados 12 genótipos de raízes de mandioca mansa em triplicata, pertencentes ao BAG-Embrapa, Belém, Pará, Brasil. Após a colheita das raízes, estas passaram por lavagem, descasque e armazenamento até o momento de utilização nas analises físico-químicas. O teor de proteínas variou entre 0,4-1,3%; lipídios 0,3-1,9%; umidade 55,3-64,4%; cinzas 0,4-0,6%; fibras 0,4-1,2%;carboidratos 32,4-42,7%; pH 6,6-7,0 e sólidos solúveis totais entre 1,0-1,4 ºBrix. Com exceção de cinzas, fibras e pH, os demais parâmetros apresentaram diferenças significativas. Tais características podem variar devido às propriedades intrínsecas das raízes de mandioca, em relação aos seus diferentes genótipos

Generic point-free lenses

Lenses are one the most popular approaches to define bidirectional transformations between data models. A bidirectional transformation with view-update, denoted a lens, encompasses the definition of a forward transformation projecting concrete models into abstract views, together with a backward transformation instructing how to translate an abstract view to an update over concrete models. In this paper we show that most of the standard point-free combinators can be lifted to lenses with suitable backward semantics, allowing us to use the point-free style to define powerful bidirectional transformations by composition. We also demonstrate how to define generic lenses over arbitrary inductive data types by lifting standard recursion patterns, like folds or unfolds. To exemplify the power of this approach, we “lensify” some standard functions over naturals and lists, which are tricky to define directly “by-hand” using explicit recursion