Magnetically-induced electric polarization in an organo-metallic magnet

The coupling between magnetic order and ferroelectricity has been under intense investigation in a wide range of transition-metal oxides. The strongest coupling is obtained in so-called magnetically-induced multiferroics where ferroelectricity arises directly from magnetic order that breaks inversion symmetry. However, it has been difficult to find non-oxide based materials in which these effects occur. Here we present a study of copper dimethyl sulfoxide dichloride (CDC), an organo-metallic quantum magnet containing $S = 1/2$ Cu spins, in which electric polarization arises from non-collinear magnetic order. We show that the electric polarization can be switched in a stunning hysteretic fashion. Because the magnetic order in CDC is mediated by large organic molecules, our study shows that magnetoelectric interactions can exist in this important class of materials, opening the road to designing magnetoelectrics and multiferroics using large molecules as building blocks. Further, we demonstrate that CDC undergoes a magnetoelectric quantum phase transition where both ferroelectric and magnetic order emerge simultaneously as a function of magnetic field at very low temperatures

Viscous dark fluid Universe: a unified model of the dark sector?

The Universe is modeled as consisting of pressureless baryonic matter and a bulk viscous fluid which is supposed to represent a unified description of the dark sector. In the homogeneous and isotropic background the \textit{total} energy density of this mixture behaves as a generalized Chaplygin gas. The perturbations of this energy density are intrinsically nonadiabatic and source relative entropy perturbations. The resulting baryonic matter power spectrum is shown to be compatible with the 2dFGRS and SDSS (DR7) data. A joint statistical analysis, using also Hubble-function and supernovae Ia data, shows that, different from other studies, there exists a maximum in the probability distribution for a negative present value of the deceleration parameter. Moreover, the unified model presented here favors a matter content that is of the order of the baryonic matter abundance suggested by big-bang nucleosynthesis. A problem of simple bulk viscous models, however, is the behavior of the gravitational potential and the reproduction of the CMB power spectrum.Comment: 12 pages, 3 figures, contributed paper to 8th Friedmann Seminar, 30 May to 3 June 2011, Rio de Janeiro, Brazi

On general features of warm dark matter with reduced relativistic gas

Reduced Relativistic Gas (RRG) is a useful approach to describe the warm dark matter (WDM) or the warmness of baryonic matter in the approximation when the interaction between the particles is irrelevant. The use of Maxwell distribution leads to the complicated equation of state of the J\"{u}ttner model of relativistic ideal gas. The RRG enables one to reproduce the same physical situation but in a much simpler form. For this reason RRG can be a useful tool for the theories with some sort of a "new Physics". On the other hand, even without the qualitatively new physical implementations, the RRG can be useful to describe the general features of WDM in a model-independent way. In this sense one can see, in particular, to which extent the cosmological manifestations of WDM may be dependent on its Particle Physics background. In the present work RRG is used as a complementary approach to derive the main observational exponents for the WDM in a model-independent way. The only assumption concerns a non-negligible velocity $v$ for dark matter particles which is parameterized by the warmness parameter $b$. The relatively high values of $b$ ( $b^2\gtrsim 10^{-6}$) erase the radiation (photons and neutrinos) dominated epoch and cause an early warm matter domination after inflation. Furthermore, RRG approach enables one to quantify the lack of power in linear matter spectrum at small scales and in particular, reproduces the relative transfer function commonly used in context of WDM with accuracy of $\lesssim 1\%$. A warmness with $b^2\lesssim 10^{-6}$ (equivalent to $v\lesssim 300 km/s$) does not alter significantly the CMB power spectrum and is in agreement with the background observational tests.Comment: 15 pages, 8 figures. Essential improvements in style and presentatio

Viscous Cosmology

We discuss the possibility to implement a viscous cosmological model, attributing to the dark matter component a behaviour described by bulk viscosity. Since bulk viscosity implies negative pressure, this rises the possibility to unify the dark sector. At the same time, the presence of dissipative effects may alleviate the so called small scale problems in the $\Lambda$CDM model. While the unified viscous description for the dark sector does not lead to consistent results, the non-linear behaviour indeed improves the situation with respect to the standard cosmological model.Comment: Latex file, 7 pages, 6 figures. To appear in the proceedings of the XIIth International Conference on Gravitation, Astrophysics and Cosmology, June 28-July 5, 2015, PFUR, Moscow, Russi

VERNACULAR ARCHITECTURE AS A FORM OF RESILIENCE IN CHINESE COUNTRYSIDE TRANSITION. EVIDENCE FROM A RURAL SETTLEMENT IN THE FUJIAN PROVINCE

Abstract. Chinese rural settlements face different critical challenges in the current framework of rapid transformation. Tangible and intangible elements related to the traditional spatial organisation of siting and living are threatened by a socio-economic transition which appears to be indifferent to local specificities. Such aspects express and shape the rural built fabric, which shows no resistance to the pressures of both planned and spontaneous development. The few exceptions are mainly represented by the survived vernacular architectures, whose function goes beyond practical uses, such as the ancestral halls. Their spatial principles persisted in the malleable rural patterns, making such buildings the physical carrier of local traditions. This paper takes a rural village in the Fujian Province, China, as a paradigmatic case study to explore the settlement pattern's degree of resilience. The data collected in two years of fieldworks allows authors to assert the prominent role played by the fifteen ancestral halls of the village. After introducing the current patterns of change, with a focus on the phenomenon of rural hollowing, the paper emphasises both the spatial rules and the contextual relationships of vernacular buildings. In the conclusions, we remark their importance against the backdrop of current land use development, suggesting to reconsider the vernacular buildings as an alternative approach for more conscious and sustainable development

Observational constraints on Rastall's cosmology

Rastall's theory is a modification of General Relativity, based on the non-conservation of the stress-energy tensor. The latter is encoded in a parameter $\gamma$ such that $\gamma = 1$ restores the usual $\nabla_\nu T^{\mu\nu} = 0$ law. We test Rastall's theory in cosmology, on a flat Robertson-Walker metric, investigating a two-fluid model and using the type Ia supernovae Constitution dataset. One of the fluids is pressureless and obeys the usual conservation law, whereas the other is described by an equation of state $p_x = w_x\rho_x$, with $w_x$ constant. The Bayesian analysis of the Constitution set does not strictly constrain the parameter $\gamma$ and prefers values of $w_x$ close to -1. We then address the evolution of small perturbations and show that they are dramatically unstable if $w_x \neq -1$ and $\gamma \neq 1$, i.e. General Relativity is the favored configuration. The only alternative is $w_x = -1$, for which the dynamics becomes independent from $\gamma$.Comment: Latex file, 14 pages, 6 figures in eps format. Substantial modifications performed, main conclusions change

The chiral Anomalous Hall effect in re-entrant AuFe alloys

The Hall effect has been studied in a series of AuFe samples in the re-entrant concentration range, as well as in part of the spin glass range. An anomalous Hall contribution linked to the tilting of the local spins can be identified, confirming theoretical predictions of a novel topological Hall term induced when chirality is present. This effect can be understood in terms of Aharonov-Bohm-like intrinsic current loops arising from successive scatterings by canted local spins. The experimental measurements indicate that the chiral signal persists, meaning scattering within the nanoscopic loops remains coherent, up to temperatures of the order of 150 K.Comment: 7 pages, 11 eps figures Published version. Minor change

Magnetic Breakdown in the electron-doped cuprate superconductor Nd2−x_{2-x}Cex_xCuO4_4: the reconstructed Fermi surface survives in the strongly overdoped regime

We report on semiclassical angle-dependent magnetoresistance oscillations (AMRO) and the Shubnikov-de Haas effect in the electron-overdoped cuprate superconductor Nd$_{2-x}$Ce$_x$CuO$_4$. Our data provide convincing evidence for magnetic breakdown in the system. This shows that a reconstructed multiply-connected Fermi surface persists, at least at strong magnetic fields, up to the highest doping level of the superconducting regime. Our results suggest an intimate relation between translational symmetry breaking and the superconducting pairing in the electron-doped cuprate superconductors.Comment: 5 pages, 4 figures, submitted to PR

Predição de estruturas e modelagem molecular de BIP (Binding Protein da soja (Glycine max L. (Merrill) usando biologia computacional.

xSuplemento. Edição dos resumos do 43º Congresso Nacional de Genética

Compositional and structural variabilities of MG-rich iron oxide spinels from tuffite.

A maghemita (yFe2O3) de tufito e, excepcionalmente, rica em magnesio, se comparada as comumente encontradas em outros litossistemas maficos. Na tentativa de investigar em detalhes a variabilidade composicional e estrutural desses oxidos naturais de ferro, alguns conjuntos de cristais foram separados de amostras coletadas a diferentes posicoes de um manto de intemperismo de tufito. Esses conjuntos de cristais foram, individualmente, estudados por difracao de raios-X, espectroscopia Mossbauer, medidas de magnetizacao e analise quimica. Da difratometria de raios-X, observou-se que o parametro da celula cubica (ao) varia de 0,834(1) a 0,8412(1) nm. Os valores mais baixos de ao sao caracteristicos de maghemita; os mais altos sao atribuidos a magnetita, mineral magnetico precursor. Os teores de Fe0 alcancam 17 mass % e os valaores de magnetizacao espontanea variam de 8 a 32 J T1 kg1. Os espectros Mossbauer, obtidos com a amostra mantida a temperatura do ambiente, na ausencia de campo magnetico aplicado, sao bastante complexos, om indicacoes de ocorrencia de superposicao de distribuicoes de campo hiperfino, devidas ao Fe3+ e ao ion de valencia mista Fe3+12+. A variabilidade estrutural dos oxidos de ferro, isoestruturais ao espinelio e ricos em Mg e Ti, e, essencialmente, relacionada com os graus variaveis de oxidacao do mineral precursor, a magnetita rica em Mg e Ti