19,025 research outputs found
Irreversibility and the arrow of time in a quenched quantum system
Irreversibility is one of the most intriguing concepts in physics. While
microscopic physical laws are perfectly reversible, macroscopic average
behavior has a preferred direction of time. According to the second law of
thermodynamics, this arrow of time is associated with a positive mean entropy
production. Using a nuclear magnetic resonance setup, we measure the
nonequilibrium entropy produced in an isolated spin-1/2 system following fast
quenches of an external magnetic field and experimentally demonstrate that it
is equal to the entropic distance, expressed by the Kullback-Leibler
divergence, between a microscopic process and its time-reverse. Our result
addresses the concept of irreversibility from a microscopic quantum standpoint.Comment: 8 pages, 7 figures, RevTeX4-1; Accepted for publication Phys. Rev.
Let
Experimental Determination of Thermal Entanglement in Spin Clusters using Magnetic Susceptibility Measurements
The present work reports an experimental observation of thermal entanglement
in a clusterized spin chain formed in the compound NaCuSiO.
The presence of entanglement was investigated through two measured quantities,
an Entanglement Witness and the Entanglement of Formation, both derived from
the magnetic susceptibility. It was found that pairwise entanglement exists
below K. Tripartite entanglement was also observed below K. A theoretical study of entanglement evolution as a function of applied
field and temperature is also presented.Comment: Submited to Phys. Rev.
Preparo de amostras padrão para controle de qualidade laboratorial.
Diante da necessidade do controle de qualidade para os ensaios de fertilidade do solo (K, Ca, Mg, Mn, Fe, Al, Zn, P, Cu, matéria orgânica, H+Al, pH) realizados pelo Laboratório de Análise Agroambiental produziu-se 3 amostras padrão em diferentes níveis de fertilidade. Selecionou-se estas amostras em diferentes pontos da Fazenda Capivara e Fazenda Palmital, coletou-se cerca de 5 kg e em seguida, as amostras foram secas, moídas e peneiradas.Pôster - graduação
Polarization and Strong Infra-Red Activity in Compressed Solid Hydrogen
Under a pressure of ~150 GPa solid molecular hydrogen undergoes a phase
transition accompanied by a dramatic rise in infra-red absorption in the vibron
frequency range. We use the Berry's phase approach to calculate the electric
polarization in several candidate structures finding large, anisotropic dynamic
charges and strongly IR-active vibron modes. The polarization is shown to be
greatly affected by the overlap between the molecules in the crystal, so that
the commonly used Clausius-Mossotti description in terms of polarizable,
non-overlapping molecular charge densities is inadequate already at low
pressures and even more so for the compressed solid.Comment: To appear in Phys. Rev. Let
Bacterial selection for biological control of plantdisease: criterion determination and validation.
This study aimed to evaluate the biocontrol potential of bacteria isolated from different plant species and soils. The production of compounds related to phytopathogen biocontrol and/or promotion of plant growth in bacterial isolates was evaluated by measuring the production of antimicrobial compounds (ammonia and antibiosis) and hydrolytic enzymes (amylases, lipases, proteases, and chitinases) and phosphate solubilization. Of the 1219 bacterial isolates, 92% produced one or more of the eight compounds evaluated, but only 1% of the isolates produced all the compounds. Proteolytic activity was most frequently observed among the bacterial isolates. Among the compounds which often determine the success of biocontrol, 43% produced compounds which inhibit mycelial growth of Monilinia fructicola, but only 11% hydrolyzed chitin. Bacteria from different plant species (rhizosphere or phylloplane) exhibited differences in the ability to produce the compounds evaluated. Most bacterial isolates with biocontrol potential were isolated from rhizospheric soil. The most ef?cient bacteria (producing at least ?ve compounds related to phytopathogen biocontrol and/or plant growth), 86 in total, were evaluated for their biocontrol potential by observing their ability to kill juvenile Mesocriconema xenoplax. Thus, we clearly observed that bacteria that produced more compounds related to phytopathogen biocontrol and/or plant growth had a higher ef?cacy for nematode biocontrol, which validated the selection strategy used
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