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

Collapse of the Mott gap and emergence of a nodal liquid in lightly doped Sr2_2IrO4_4

Superconductivity in underdoped cuprates emerges from an unusual electronic state characterised by nodal quasiparticles and an antinodal pseudogap. The relation between this state and superconductivity is intensely studied but remains controversial. The discrimination between competing theoretical models is hindered by a lack of electronic structure data from related doped Mott insulators. Here we report the doping evolution of the Heisenberg antiferromagnet Sr$_2$IrO$_4$, a close analogue to underdoped cuprates. We demonstrate that metallicity emerges from a rapid collapse of the Mott gap with doping, resulting in lens-like Fermi contours rather than disconnected Fermi arcs as observed in cuprates. Intriguingly though, the emerging electron liquid shows nodal quasiparticles with an antinodal pseudogap and thus bares strong similarities with underdoped cuprates. We conclude that anisotropic pseudogaps are a generic property of two-dimensional doped Mott insulators rather than a unique hallmark of cuprate high-temperature superconductivity

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

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

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

Produtividade de genótipos de girassol em diferentes épocas de semeadura no oeste da Bahia.

bitstream/item/31477/1/comunicado-208.pd

Ring closing reaction in diarylethene captured by femtosecond electron crystallography

The photoinduced ring-closing reaction in diarylethene, which serves as a model system for understanding reactive crossings through conical intersections, was directly observed with atomic resolution using femtosecond electron diffraction. Complementary ab initio calculations were also performed. Immediately following photoexcitation, subpicosecond structural changes associated with the formation of an open-ring excited-state intermediate were resolved. The key motion is the rotation of the thiophene rings, which significantly decreases the distance between the reactive carbon atoms prior to ring closing. Subsequently, on the few picosecond time scale, localized torsional motions of the carbon atoms lead to the formation of the closed-ring photoproduct. These direct observations of the molecular motions driving an organic chemical reaction were only made possible through the development of an ultrabright electron source to capture the atomic motions within the limited number of sampling frames and the low data acquisition rate dictated by the intrinsically poor thermal conductivity and limited photoreversibility of organic materials

Search for the Lepton-Flavor-Violating Decay τ−→μ−η\tau^- \to \mu^- \eta at Belle

We have searched for the Lepton Flavor Violating decay $\tau^- \to \mu^- \eta$ using a data sample of 84.3 fb$^{-1}$ accumulated with the Belle detector at KEK. The $\eta$-meson was detected through the decay modes: $\eta \to \gamma\gamma$ and $\pi^+\pi^-\pi^0$. No signal candidates are found, and we obtain an upper limit for the branching fraction ${\cal B}(\tau^- \to \mu^- \eta)<3.4\times 10^{-7}$ at the 90% confidence level.Comment: Submitted to Phys.Rev.Let

Search for B+ -> J/psi eta' K+ and B0 -> J/psi eta' Ks0 Decays

We report the results of searches for B+ -> J/psi eta' K+ and B0 -> J/psi eta' Ks0 decays, using a sample of 388 x 10^6 BBbar pairs collected with the Belle detector at the Upsilon(4S) resonance. No statistically significant signal is found for either of the two decay modes and upper limits for the branching fractions are determined to be B(B+ -> J/psi eta' K+) < 8.8 x 10^-5 and B(B0 -> J/psi eta' Ks0) < 2.5 x 10^-5 at 90% confidence level.Comment: 5 pages, 6 figures, submitted to PRD Brief Repor

Observation of Radiative Decay D0→ϕγD^0 \to \phi \gamma

We report the observation of the decay $D^{0} \to \phi \gamma$ with a statistical significance of $5.4\sigma$ in 78.1 \ifb of data collected by the Belle experiment at the KEKB $e^+ e^-$ collider. This is the first observation of a flavor-changing radiative decay of a charmed meson. The Cabibbo- and color-suppressed decays $D^0 \to \phi \pi^0$, $\phi \eta$ are also observed for the first time. We measure branching fractions \br(D^{0} \to \phi \gamma) = [ 2.60^{+0.70}_{-0.61} \stat {}^{+0.15}_{-0.17} \syst ] \times 10^{-5}, \br(D^{0} \to \phi \pi^{0}) = [ 8.01 \pm 0.26 \stat \pm 0.47 \syst ] \times 10^{-4}, and \br(D^{0} \to \phi \eta) = [ 1.48 \pm 0.47 \stat \pm 0.09 \syst ] \times 10^{-4}.Comment: 9 pages, 4 figures, Belle Preprint 2003-24, KEK Preprint 2003-75, updated version of BELLE-CONF-0346 (contributed paper to the XXI International Symposium on Lepton and Photon Interactions at High Energies,Fermilab Aug 11-16,2003). to appear in Phys. Rev. Let