Phonon-modulated magnetic interactions and spin Tomonaga-Luttinger liquid in the p-orbital antiferromagnet CsO2

The magnetic response of antiferromagnetic CsO2, coming from the p-orbital S=1/2 spins of anionic O2- molecules, is followed by 133Cs nuclear magnetic resonance across the structural phase transition occuring at Ts1=61 K on cooling. Above Ts1, where spins form a square magnetic lattice, we observe a huge, nonmonotonic temperature dependence of the exchange coupling originating from thermal librations of O2- molecules. Below Ts1, where antiferromagnetic spin chains are formed as a result of p-orbital ordering, we observe a spin Tomonaga-Luttinger-liquid behavior of spin dynamics. These two interesting phenomena, which provide rare simple manifestations of the coupling between spin, lattice and orbital degrees of freedom, establish CsO2 as a model system for molecular solids.Comment: 9 pages, 5 figures (with Supplemental Material), to appear in Physical Review Letter

Coeficientes culturais de consórcio milho-feijão e milho-braquiária.

Para estabelecer os riscos climáticos para consórcios milho-feijão e milho-pastagens, é necessário que se conheça os seus respectivos coeficientes culturais. Objetivando determinar esses coeficientes, foram instalados, em três épocas, ensaios de campo onde determinou-se, o consumo de água pelas cultura no consórcio por meio do balanço hídrico do solo e a demanda potencial de água por meio da metodologia proposta por Penman-Monteith. Os resultados mostraram que os coeficiente culturais dos consórcios foram muito maiores que das culturas isoladamente, o que permite concluir que o consórcio demanda maior disponibilidade de água no solo. Portanto, a implantação do consorcio dependente grandemente da distribuição das chuvas na região e da a capacidade de retenção de umidade do solo. Assim sendo haverá restrição da época e da área a ser plantada por esse sistema produtivo comparado com a cultura isolada

One-dimensional quantum antiferromagnetism in the p−p-orbital CsO2_2 compound revealed by electron paramagnetic resonance

Recently it was proposed that the orbital ordering of $\pi_{x,y}^*$ molecular orbitals in the superoxide CsO$_2$ compound leads to the formation of spin-1/2 chains below the structural phase transition occuring at $T_{\rm{s1}}=61$~K on cooling. Here we report a detailed X-band electron paramagnetic resonance (EPR) study of this phase in CsO$_2$ powder. The EPR signal appears as a broad line below $T_{\rm{s1}}$, which is replaced by the antiferromagnetic resonance below the N\'{e}el temperature $T_{\rm N}=8.3$~K. The temperature dependence of the EPR linewidth between $T_{\rm{s1}}$ and $T_{\rm{N}}$ agrees with the predictions for the one-dimensional Heisenberg antiferromagnetic chain of $S=1/2$ spins in the presence of symmetric anisotropic exchange interaction. Complementary analysis of the EPR lineshape, linewidth and the signal intensity within the Tomonaga-Luttinger liquid (TLL) framework allows for a determination of the TLL exponent $K=0.48$. Present EPR data thus fully comply with the quantum antiferromagnetic state of spin-1/2 chains in the orbitally ordered phase of CsO$_2$, which is, therefore, a unique $p-$orbital system where such a state could be studied.Comment: 6 pages, 3 figure

Attitudes de consommateurs de viande bovine vis-à-vis du bien-être animal : une comparaison régionale dans la zone pyrénéenne

Attitudes towards animal welfare (AW) are investigated in two Spanish and two French regions located on both sides of the Pyrenees (n=1213). Two scores are used: one measuring the importance of 11 good practices for AW and one capturing the consumers´ trust regarding stakeholder behaviour. Items linked with animal life conditions get the highest scores of importance. Trust scores are of a lower magnitude and statistically significant differences are found across regions. Finally, socio-demographic characteristics and meat purchase and consumption habits explain part of the observed attitudinal differences found among respondent

Spin-Exchange Interaction in ZnO-based Quantum Wells

Wurtzitic ZnO/(Zn,Mg)O quantum wells grown along the (0001) direction permit unprecedented tunability of the short-range spin exchange interaction. In the context of large exciton binding energies and electron-hole exchange interaction in ZnO, this tunability results from the competition between quantum confinement and giant quantum confined Stark effect. By using time-resolved photoluminescence we identify, for well widths under 3 nm, the redistribution of oscillator strengths between the A and B excitonic transitions, due to the enhancement of the exchange interaction. Conversely, for wider wells, the redistribution is cancelled by the dominant effect of internal electric fields, which dramatically reduce the exchange energy.Comment: 14 pages, 3 figure

Cultivo do milho: clima e solo.

bitstream/CNPMS/15594/1/Com_38.pd

A1-512 Efecto del laboreo mínimo sobre el rendimiento, la abundancia de la flora arvense y el balance energético y económico en una rotación de espelta, garbanzos y trigo en la Región Mediterránea

El laboreo mínimo en sistemas herbáceos extensivos ecológicos en Europa, se ha llevado a cabo sobre todo en climas templados. El equipo de investigación Ecología de los Sistemas Agrícolas de la Universidad de Barcelona estableció un experimento a largo plazo en 2011 que tiene el objetivo de evaluar la viabilidad del laboreo mínimo en cultivos herbáceos extensivos ecológicos en clima mediterráneo. Este trabajo analiza el efecto del tipo de laboreo y la fertilización con estiércol compostado sobre el rendimiento de los cultivos de cereales y leguminosas, la abundancia de la flora arvense y el balance económico y energético. El laboreo mínimo no afectó los rendimientos de los cultivos y la fertilización favoreció a los cultivos de cereales. Los balances económico y energético no mostraron diferencias significativas con el tipo de laboreo ni con la fertilización, con la excepción de una mayor cantidad de salida de energía en las parcelas fertilizadas en el cultivo de trigo

The distribution and nature of soils with low phosphorus in the Brazilian savannas.

Editado por Robert E. Schaffert