Strong electron correlations in the normal state of FeSe0.42Te0.58

We investigate the normal state of the '11' iron-based superconductor FeSe0.42Te0.58 by angle resolved photoemission. Our data reveal a highly renormalized quasiparticle dispersion characteristic of a strongly correlated metal. We find sheet dependent effective carrier masses between ~ 3 - 16 m_e corresponding to a mass enhancement over band structure values of m*/m_band ~ 6 - 20. This is nearly an order of magnitude higher than the renormalization reported previously for iron-arsenide superconductors of the '1111' and '122' families but fully consistent with the bulk specific heat.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let

Controlling crystal cleavage in Focused Ion Beam shaped specimens for surface spectroscopy

Our understanding of quantum materials is commonly based on precise determinations of their electronic spectrum by spectroscopic means, most notably angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). Both require atomically clean and flat crystal surfaces which traditionally are prepared by in-situ mechanical cleaving in ultrahigh vacuum chambers. We present a new approach that addresses three main issues of the current state-of-the-art methods: 1) Cleaving is a highly stochastic and thus inefficient process; 2) Fracture processes are governed by the bonds in a bulk crystal, and many materials and surfaces simply do not cleave; 3) The location of the cleave is random, preventing data collection at specified regions of interest. Our new workflow is based on Focused Ion Beam (FIB) machining of micro-stress lenses in which shape (rather than crystalline) anisotropy dictates the plane of cleavage, which can be placed at a specific target layer. As proof-of-principle we show ARPES results from micro-cleaves of Sr$_2$RuO$_4$ along the ac plane and from two surface orientations of SrTiO$_3$, a notoriously difficult to cleave cubic perovskite

Model for the hydration of non-polar compounds and polymers

We introduce an exactly solvable statistical-mechanical model of the hydration of non-polar compounds, based on grouping water molecules in clusters where hydrogen bonds and isotropic interactions occur; interactions between clusters are neglected. Analytical results show that an effective strengthening of hydrogen bonds in the presence of the solute, together with a geometric reorganization of water molecules, are enough to yield hydrophobic behavior. We extend our model to describe a non-polar homopolymer in aqueous solution, obtaining a clear evidence of both ``cold'' and ``warm'' swelling transitions. This suggests that our model could be relevant to describe some features of protein folding.Comment: REVTeX, 6 pages, 3 figure

Optical switching of radical pair conformation enhances magnetic sensitivity

The yield of chemical reactions involving intermediate radical pairs is influenced by magnetic fields well beyond the levels expected from energy considerations. This dependence can be traced back to the microscopic dynamics of electron spins and constitutes the basis of the chemical compass. Here we propose a new experimental approach based on molecular photoswitches to achieve additional control on the chemical reaction and to allow short-time resolution of the spin dynamics. Our proposal enables experiments to test some of the standard assumptions of the radical pair model and improves the sensitivity of chemical magnetometers by two orders of magnitude

Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides

The iron pnictide and chalcogenide compounds are a subject of intensive investigations due to their high temperature superconductivity.\cite{a-LaFeAsO} They all share the same structure, but there is significant variation in their physical properties, such as magnetic ordered moments, effective masses, superconducting gaps and T$_c$. Many theoretical techniques have been applied to individual compounds but no consistent description of the trends is available \cite{np-review}. We carry out a comparative theoretical study of a large number of iron-based compounds in both their magnetic and paramagnetic states. We show that the nature of both states is well described by our method and the trends in all the calculated physical properties such as the ordered moments, effective masses and Fermi surfaces are in good agreement with experiments across the compounds. The variation of these properties can be traced to variations in the key structural parameters, rather than changes in the screening of the Coulomb interactions. Our results provide a natural explanation of the strongly Fermi surface dependent superconducting gaps observed in experiments\cite{Ding}. We propose a specific optimization of the crystal structure to look for higher T$_c$ superconductors.Comment: 5 pages, 3 figures with a 5-page supplementary materia

ELF3 is an antagonist of oncogenic-signalling-induced expression of EMT-TF ZEB1

Background: Epithelial-to-mesenchymal transition (EMT) is a key step in the transformation of epithelial cells into migratory and invasive tumour cells. Intricate positive and negative regulatory processes regulate EMT. Many oncogenic signalling pathways can induce EMT, but the specific mechanisms of how this occurs, and how this process is controlled are not fully understood. Methods: RNA-Seq analysis, computational analysis of protein networks and large-scale cancer genomics datasets were used to identify ELF3 as a negative regulator of the expression of EMT markers. Western blotting coupled to siRNA as well as analysis of tumour/normal colorectal cancer panels was used to investigate the expression and function of ELF3. Results: RNA-Seq analysis of colorectal cancer cells expressing mutant and wild-type β-catenin and analysis of colorectal cancer cells expressing inducible mutant RAS showed that ELF3 expression is reduced in response to oncogenic signalling and antagonizes Wnt and RAS oncogenic signalling pathways. Analysis of gene-expression patterns across The Cancer Genome Atlas (TCGA) and protein localization in colorectal cancer tumour panels showed that ELF3 expression is anti-correlated with β-catenin and markers of EMT and correlates with better clinical prognosis. Conclusions: ELF3 is a negative regulator of the EMT transcription factor (EMT-TF) ZEB1 through its function as an antagonist of oncogenic signalling

Estudos de diferentes espaçamentos na cultura do girassol.

Com o objetivo de avaliar o comportamento do girassol em diferentes espaçamentos em condição de sequeiro na região Oeste da Bahia, foi instalado um ensaio no município de São Desidério-BA. O delineamento estatístico foi o de blocos ao acaso, em esquema fatorial 2 x 4 (dois espaçamentos e quatro genótipos). Os espaçamentos avaliados foram 0,50 m e 0,76 m e os genótipos utilizados foram: Agrobel 972, M 734, Hélio 250 (híbridos) e Embrapa 122 (variedade). A semeadura foi realizada manualmente no dia 16/12/2008. Os parâmetros avaliados foram: produtividade de grãos, massa de 1000 sementes, tamanho do capítulo, altura de planta, estande final e ciclo de maturação. Nos espaçamentos avaliados as maiores produtividade foram alcançadas no de 0,76 m para todos os genótipos, obtendo-se média de 2.149 kg.ha-1 enquanto que, no espaçamento de 0,50 m foram obtidas produtividades de 1.460 kg.ha-1. O M 734 e o Hélio 250 foram os genótipos mais produtivos no espaçamento de 0,50 m. Independente do espaçamento o genótipo M 734 esteve sempre entre os mais produtivos. Na massa de 1000 sementes não foram detectadas diferenças entre os espaçamentos. O Hélio 250 e o Embrapa 122 produziram maiores capítulos no espaçamento de 0,76 m. Não houve diferenças na altura de plantas e no estande final dentro e entre espaçamentos. Os genótipos completaram sua maturação por volta de 89 dias

Uniaxial Tensile Stress-Strain Relationships of RC Elements Strengthened with FRP Sheets

The shear behavior of fiber-reinforced-polymer–strengthened reinforced concrete (FRP-strengthened RC) members is not fully developed and accurately predicted because of the lack of accurate constitutive laws for the components of the composite members. This paper presents experimental and analytical investigations of tensile stress-strain relationships of concrete and steel in FRP-strengthened RC members. These stress-strain relationships are required in formulations of softened truss models to predict the shear behavior of the FRP-strengthened RC element. Thirteen full-scale FRP-strengthened RC prismatic specimens with different FRP reinforcement ratios, steel reinforcement ratios, and FRP wrapping schemes were tested under uniaxial tension loading. The results show that the tensile behavior of the concrete and steel is altered because of the externally bonded FRP sheets. Modified constitutive laws are proposed and incorporated in the softened membrane model (SMM) to demonstrate through two tests the behavior of FRP-strengthened RC element subjected to pure shear. Moreover, crack spacing and crack width were studied and compared with existing code provisions

Competição de híbridos e variedades de girassol comerciais em safrinha no oeste da Bahia.

Foi instalado um experimento no município de São Desidério-BA com objetivo de avaliar o comportamento de híbridos e variedades de girassol comerciais em safrinha no Oeste da Bahia. A semeadura foi realizada em 09/03/2009 utilizando 18 genótipos: NTO3.0, NTO2.0, M 734, Hélio 250, Agrobel 962, Hélio 358, Agrobel 960, Hélio 253, Hélio 251, DAS 735, Paraíso 20, Agrobel 972, Paraíso 33, Paraíso 22, Agrobel 967, Paraíso 102CL (híbridos), Embrapa 122 e IAC Iarama (variedades). O delineamento experimental foi o de blocos ao acaso com cinco repetições. Os parâmetros avaliados foram: produtividade de grãos, estande final de plantas, massa de 1000 sementes, altura de planta, tamanho do capítulo, duração do ciclo de maturação. O ensaio teve média de produtividade de 2.344,6 kg/ha, onde estas variaram de 1.543,1 kg/ha (IAC Iarama) a 3.367,8 kg/ha (NTO3.0), estando acima da média da produtividade nacional de 1.400 kg/ha. Nos parâmetros avaliados houve variações entre os diversos genótipos para estande final de plantas (22.631,6 a 33.157,9 plantas/ha), massa de mil sementes (60 a 96 g), altura de planta (133 a 182 cm), tamanho do capítulo (42 a 58 cm) e ciclo (90 a 106 dias), sendo observadas diferenças estatísticas significativas para todas as características avaliadas