Universality class for bootstrap percolation with m=3m=3 on the cubic lattice

We study the $m=3$ bootstrap percolation model on a cubic lattice, using Monte Carlo simulation and finite-size scaling techniques. In bootstrap percolation, sites on a lattice are considered occupied (present) or vacant (absent) with probability $p$ or $1-p$, respectively. Occupied sites with less than $m$ occupied first-neighbours are then rendered unoccupied; this culling process is repeated until a stable configuration is reached. We evaluate the percolation critical probability, $p_c$, and both scaling powers, $y_p$ and $y_h$, and, contrarily to previous calculations, our results indicate that the model belongs to the same universality class as usual percolation (i.e., $m=0$). The critical spanning probability, $R(p_c)$, is also numerically studied, for systems with linear sizes ranging from L=32 up to L=480: the value we found, $R(p_c)=0.270 \pm 0.005$, is the same as for usual percolation with free boundary conditions.Comment: 11 pages; 4 figures; to appear in Int. J. Mod. Phys.

Tunnel and thermal c-axis transport in BSCCO in the normal and pseudogap state

We consider the problem of c-axis transport in double-layered cuprates, in particular with reference to Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ compounds. We exploit the effect of the two barriers on the thermal and tunnel transport. The resulting model is able to describe accurately the normal state c-axis resistivity in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$, from the underdoped side up to the strongly overdoped. We extend the model, without introducing additional parameters, in order to allow for the decrease of the barrier when an external voltage bias is applied. The extended model is found to describe properly the c-axis resistivity for small voltage bias above the pseudogap temperature $T^{*}$, the c-axis resistivity for large voltage bias even below $T_c$, and the differential $dI/dV$ curves taken in mesa structures.Comment: 12 pages, 6 figures. Submitted to Superconductor Science and Technolog

Improved magnetodielectric coefficient on polymer based composites through enhanced indirect magnetoelectric coupling

Particulate composites of ferrite and ferroelectric polymer phases with general formula [xCoFe2O4]/[(1-x) PVDF] were prepared for x = 0, 3, 11 and 20 wt.% by solution casting. The dielectric constant, dielectric loss and saturation magnetization of the polymer composite films increase with increasing CoFe2O4 (CFO) content, being 13, 0.13 and 13 emu.g-1 respectively, for x=20. The magnetodielectric (MD) coupling also depend on the CFO content, the change in the dielectric response (MDE(%)) being the highest for the x=20 sample (4.2%). On the other hand, the highest value of the MD coefficient (γ) is higher on the x=3 sample (0.015 emu-2g2). Those values are favourably compared with the ones found in the ceramic-based MD materials, being the highest reported for polymer composites. These facts, together with the flexibility and scalable production of the composites, leads to their large application potential in areas such as filters, magnetic field sensors and actuators, among others.The authors thank the Portuguese Fundação para a Ciência e Tecnologia (FCT) for financial support under projects PTDC/EEI-SII/5582/2014 and PTDC/CTM-ENE/5387/2014.P. M. and M. Silva acknowledges also support from FCT (SFRH/BPD/96227/2013 and SFRH/BD/70303/2010 grants respectively). Financial support from the Basque Government Industry Department under the ELKARTEK Program is also acknowledged. SLM thanks the Diputación Foral de Bizkaia for financial support under the Bizkaia Talent program; European Union’s Seventh Framework Programme; Marie Curie Actions – People; Grant agreement nº 267230

ARCHI: pipeline for light curve extraction of CHEOPS background star

High precision time series photometry from space is being used for a number of scientific cases. In this context, the recently launched CHEOPS (ESA) mission promises to bring 20 ppm precision over an exposure time of 6 hours, when targeting nearby bright stars, having in mind the detailed characterization of exoplanetary systems through transit measurements. However, the official CHEOPS (ESA) mission pipeline only provides photometry for the main target (the central star in the field). In order to explore the potential of CHEOPS photometry for all stars in the field, in this paper we present archi, an additional open-source pipeline module{\dag}to analyse the background stars present in the image. As archi uses the official Data Reduction Pipeline data as input, it is not meant to be used as independent tool to process raw CHEOPS data but, instead, to be used as an add-on to the official pipeline. We test archi using CHEOPS simulated images, and show that photometry of background stars in CHEOPS images is only slightly degraded (by a factor of 2 to 3) with respect to the main target. This opens a potential for the use of CHEOPS to produce photometric time series of several close-by targets at once, as well as to use different stars in the image to calibrate systematic errors. We also show one clear scientific application where the study of the companion light curve can be important for the understanding of the contamination on the main target.Comment: 14 pages, 13 figures, accepted for publication in MNRAS, all code available at https://github.com/Kamuish/arch

Índice de sustentabilidade do uso da água de cisternas no semi-árido brasileiro.

A disponibilidade hídrica no Semi-Árido brasileiro é baixa, embora, nos anos secos possam ocorrer, no mínimo, 300,Omm, que são suficientes para abastecer uma cisterna com capacidade de 16.000 litros e atender as necessidades básicas de uma família com cinco pessoas. Nesta região, a quantidade e a qualidade da água são indicadores que devem ser considerados na gestão sustentável da água, principalmente para consumo das famílias. Assim, este estudo avaliou os resultados obtidos pelo P1 MC/Ministério do Desenvolvimento Social - MDS, objetivando propor um índice de sustentabilidade do uso da água de cisterna. Foram utilizados procedimentos de análise fatorial em componentes principais e de agrupamento, integrando-se diferentes bases dados. A partir das variáveis analisadas foram definidos quatro indicadores de sustentabilidade da água das cisternas: a) uso da água de outras fontes; b) condições ecológicas dos domicílios; c) capacitação comunitária e d) qualidade da água. Os indicadores poderão auxiliar no monitoramento e gestão da água, no que concerne ao fornecimento da água necessária e sua qualidade, visando à melhoria da qualidade de vida dos usuários das cisternas. Os indicadores propostos poderão auxiliar na decisão dos gestores do P1 MC no sentido de revisar e reformular suas ações estratégias