Probing ferroelectricity in highly conducting materials through their elastic response: persistence of ferroelectricity in metallic BaTiO3-d

The question whether ferroelectricity (FE) may coexist with a metallic or highly conducting state, or rather it must be suppressed by the screening from the free charges, is the focus of a rapidly increasing number of theoretical studies and is finally receiving positive experimental responses. The issue is closely related to the thermoelectric and multiferroic (also magnetic) applications of FE materials, where the electrical conductivity is required or spurious. In these circumstances, the traditional methods for probing ferroelectricity are hampered or made totally ineffective by the free charges, which screen the polar response to an external electric field. This fact may explain why more than 40 years passed between the first proposals of FE metals and the present experimental and theoretical activity. The measurement of the elastic moduli, Young's modulus in the present case, versus temperature is an effective method for studying the influence of doping on a FE transition because the elastic properties are unaffected by electrical conductivity. In this manner, it is shown that the FE transitions of BaTiO3-d are not suppressed by electron doping through O vacancies; only the onset temperatures are depressed, but the magnitudes of the softenings, and hence of the piezoelectric activity, are initially even increased

Quantum Electrodynamics vacuum polarization solver

The self-consistent modeling of vacuum polarization due to virtual electron-positron fluctuations is of relevance for many near term experiments associated with high intensity radiation sources and represents a milestone in describing scenarios of extreme energy density. We present a generalized finite-difference time-domain solver that can incorporate the modifications to Maxwell's equations due to vacuum polarization. Our multidimensional solver reproduced in one dimensional configurations the results for which an analytic treatment is possible, yielding vacuum harmonic generation and birefringence. The solver has also been tested for two-dimensional scenarios where finite laser beam spot sizes must be taken into account. We employ this solver to explore different types of counter-propagating configurations that can be relevant for future planned experiments aiming to detect quantum vacuum dynamics at ultra-high electromagnetic field intensities

Avaliação da qualidade do efluente gerado pelas ETE do Estado de Pernambuco em relação aos contaminantes emergentes.

Existem alguns compostos orgânicos presentes na água que ainda não são investigados pelas legislações ambientais brasileiras, mas que estão presentes mesmo em baixas concentrações (?g.L-1 ou ng.L-1) e causam efeitos adversos à saúde humana e dos animais, denominados contaminantes emergentes. Estes compostos são introduzidos no meio ambiente através de esgoto doméstico e efluentes de ETE. As classes de substâncias que são consideradas persistentes são: fármacos, produtos de cuidado pessoal e limpeza, interferentes endócrinos e subprodutos da desinfecção de água potável. O derramamento de esgoto sem tratamento é um grave problema ambiental, pois ocasiona poluição em rios, águas represadas, abastecimento de cidades e irrigação de plantações, e mesmo que as ETE disponham de diversas formas de tratamento, estas são insuficientes para garantir a ausência de poluição. Neste trabalho foi realizado um monitoramento em quatro estações de tratamento de esgoto (ETE) da Região Metropolitana do Recife, a saber: Caçote, Mangueira, Jardim Paulista e Cabanga. Foram quantificados cinco contaminantes classificados como interferentes endócrinos, foram selecionados para quantificação: progesterona e 17?-etinilestradiol (hormônios), dibutilftalato e dietilfitalato (plastificantes) e nonilfenol (surfactantes). Para a identificação e quantificação foi empregado LC/MS-MS de alta resolução e os dados tratados por análise por componentes principais e constatado a ineficiência da remoção dos micropoluentes do tratamento empregado pelas estações de tratamento de esgoto estudadas

Some new class of Chaplygin Wormholes

Some new class of Chaplygin wormholes are investigated in the framework of a Chaplygin gas with equation of state $p = - \frac{A}{\rho}$, $A>0$. Since empty spacetime ($p = \rho = 0$) does not follow Chaplygin gas, so the interior Chaplygin wormhole solutions will never asymptotically flat. For this reason, we have to match our interior wormhole solution with an exterior vacuum solution i.e. Schwarzschild solution at some junction interface, say $r = a$. We also discuss the total amount of matter characterized by Chaplygin gas that supplies fuel to construct a wormhole.Comment: 14 pages, 12 figures, Accepted for publication in Mod.Phys.Lett.

A nonextensive insight to the stellar initial mass function

the present paper, we propose that the stellar initial mass distributions as known as IMF are best fitted by $q$-Weibulls that emerge within nonextensive statistical mechanics. As a result, we show that the Salpeter's slope of $\sim$2.35 is replaced when a $q$-Weibull distribution is used. Our results point out that the nonextensive entropic index $q$ represents a new approach for understanding the process of the star-forming and evolution of massive stars.Comment: 5 pages, 2 figures, Accepted to EP