Quantum Critical Point in the Spin Glass-Kondo Transition in Heavy Fermion Systems

The Kondo-Spin Glass competition is studied in a theoretical model of a Kondo lattice with an intra-site Kondo type exchange interaction treated within the mean field approximation, an inter-site quantum Ising exchange interaction with random couplings among localized spins and an additional transverse field in the x direction, which represents a simple quantum mechanism of spin flipping. We obtain two second order transition lines from the spin-glass state to the paramagnetic one and then to the Kondo state. For a reasonable set of the different parameters, the two second order transition lines do not intersect and end in two distinct QCP.Comment: 20 pages; 1 figure; to appear in Physical Review

Radiação solar no sub-bosque de sistema agrossilvipastoril com eucalipto em diferentes arranjos estruturais.

A radiação solar no sub-bosque de povoamentos de eucalipto torna-se decisiva para implantação de culturas intercalares e consórcio com pastagens em sistemas agrossilvipastoris. Objetivou-se determinar a incidência e distribuição da densidade de fluxo de fótons, radiação solar global e iluminância no sub-bosque de diferentes arranjos estruturais de sistema agrossilvipatoril com eucalipto. O experimento foi implantado em dezembro de 1999, em área de cerrado. Realizou-se o plantio de mudas clonais de um híbrido natural de Eucalyptus camaldulensis Dehnh com Eucalyptus urophylla S.T. Blake, em consórcio com arroz no primeiro ano, soja no segundo e pastagem de Brachiaria brizantha (Hochst. ex A. Rich.) Stapf cv. Marandu nos anos consecutivos. O delineamento utilizado foi blocos casualizados em esquema de parcelas subdivididas, com cinco repetições. Nas parcelas, estudou-se o efeito dos arranjos 3,33 x 2 m, 3,33 x 3 m, 5 x 2 m, 10 x 2 m, 10 x 3 m, 10 x 4 m, (3 x 4)+7 m, (3 x 3)+10 m, (3 x 4)+10 m e (3 x 3)+15 m. As subparcelas corresponderam às avaliações na linha e entrelinha de plantio, realizadas aos 27, 38 e 54 meses. A radiação solar no subbosque varia em função dos arranjos. Nos 3,33 x 2 m e 3,33 x 3 m, o fechamento do dossel promove sombreamento geral do sub-bosque aos dois anos. Nos arranjos mais amplos, a distribuição espacial da radiação solar e o sombreamento variam com a época do ano

Nanocompósitos de nanossílica obtida de equisetum arvense I. com poli(metacrilato de metila).

bitstream/CNPDIA-2009-09/11039/1/CT88_2007.pd

The TIGA technique for detecting gravitational waves with a spherical antenna

We report the results of a theoretical and experimental study of a spherical gravitational wave antenna. We show that it is possible to understand the data from a spherical antenna with 6 radial resonant transducers attached to the surface in the truncated icosahedral arrangement. We find that the errors associated with small deviations from the ideal case are small compared to other sources of error, such as a finite signal-to-noise ratio. An in situ measurement technique is developed along with a general algorithm that describes a procedure for determining the direction of an external force acting on the antenna, including the force from a gravitational wave, using a combination of the transducer responses. The practicality of these techniques was verified on a room-temperature prototype antenna.Comment: 15 pages, 14 figures, submitted to Physical Review

Generation of nonground-state Bose-Einstein condensates by modulating atomic interactions

A technique is proposed for creating nonground-state Bose-Einstein condensates in a trapping potential by means of the temporal modulation of atomic interactions. Applying a time-dependent spatially homogeneous magnetic field modifies the atomic scattering length. An alternating modulation of the scattering length excites the condensate, which, under special conditions, can be transferred to an excited nonlinear coherent mode. It is shown that there occurs a phase-transition-like behavior in the time-averaged population imbalance between the ground and excited states. The application of the suggested technique to realistic experimental conditions is analyzed and it is shown that the considered effect can be realized for experimentally available condensates.Comment: 6 pages, 2 figures, 1 tabl