Quantum Effects in the Spacetime of a Magnetic Flux Cosmic String

In this work we compute the vacuum expectation values of the energy-momentum tensor and the average value of a massive, charged scalar field in the presence of a magnetic flux cosmic string for both zero- and finite-temperature cases.Comment: To appear in the Int. Journal of Modern Phys. A (special issue). Proceedings of the Second International Londrina Winter School on Mathematical Methods in Physics, Londrina, Brazil, August 200

Cosmic String in Scalar-Tensor Gravity

The gravitational properties of a local cosmic string in the framework of scalar-tensor gravity are examined. We find the metric in the weak-field approximation and we show that, contrary to the General Relativity case, the cosmic string in scalar-tensor gravitation exerces a force on non-relativistic, neutral test particle. This force is proportional to the derivative of the conformal factor $A^{2}(\phi)$ and it is always attractive. Moreover, this force could have played an important role at the Early Universe, although nowadays it can be neglegible. It is also shown that the angular separation $\delta\varphi$ remains unaltered for scalar-tensor cosmic strings.Comment: 15 pages, LATEX, no figure

Carbon nanotube: a low-loss spin-current waveguide

We demonstrate with a quantum-mechanical approach that carbon nanotubes are excellent spin-current waveguides and are able to carry information stored in a precessing magnetic moment for long distances with very little dispersion and with tunable degrees of attenuation. Pulsed magnetic excitations are predicted to travel with the nanotube Fermi velocity and are able to induce similar excitations in remote locations. Such an efficient way of transporting magnetic information suggests that nanotubes are promising candidates for memory devices with fast magnetization switchings

Experimental observation of quantum entanglement in low dimensional spin systems

We report macroscopic magnetic measurements carried out in order to detect and characterize field-induced quantum entanglement in low dimensional spin systems. We analyze the pyroborate MgMnB_2O_5 and the and the warwickite MgTiOBO_3, systems with spin 5/2 and 1/2 respectively. By using the magnetic susceptibility as an entanglement witness we are able to quantify entanglement as a function of temperature and magnetic field. In addition, we experimentally distinguish for the first time a random singlet phase from a Griffiths phase. This analysis opens the possibility of a more detailed characterization of low dimensional materials

Relativistic Approach to Superfluidity in Nuclear Matter

Pairing correlations in symmetric nuclear matter are studied within a relativistic mean-field approximation based on a field theory of nucleons coupled to neutral ($\sigma$ and $\omega$) and to charged ($\varrho$) mesons. The Hartree-Fock and the pairing fields are calculated in a self-consistent way. The energy gap is the result of a strong cancellation between the scalar and vector components of the pairing field. We find that the pair amplitude vanishes beyond a certain value of momentum of the paired nucleons. This fact determines an effective cutoff in the gap equation. The value of this cutoff gives an energy gap in agreement with the estimates of non relativistic calculations.Comment: 21 pages, REVTEX, 8 ps-figures, to appear in Phys.Rev.C. e-mail: [email protected]

Massive scalar field near a cosmic string

The $\zeta$ function of a massive scalar field near a cosmic string is computed and then employed to find the vacuum fluctuation of the field. The vacuum expectation value of the energy-momentum tensor is also computed using a point-splitting approach. The obtained results could be useful also for the case of self-interacting scalar fields and for the finite-temperature Rindler space theory.Comment: 15 pages, standard LaTeX, no figures. Reference [14] correcte

Desenvolvimento de dietas para a criação massal de moscas-das-frutas do gênero Anastrepha (Diptera: Tephritidae).

bitstream/CNPAT-2010/11572/1/Bd-33.pd

Interceptação da radiação solar por genótipos de feijão sob deficiência hídrica.

O objetivo deste trabalho foi o de avaliar a interceptação da radiação solar pelas linhagens elite de feijoeiro do programa de melhoramento dessa cultura na Embrapa, sob deficiência hídrica, na Estação Experimental da Emater, em Porangatu, GO.CONAFE

Estudo genético quantitativo de características relacionadas à velocidade de crescimento de bovinos Nelore Mocho.

Pesquisas efetivas que avaliam a eficiência produtiva de bovino da raça Nelore, variedade mocho, são incipientes. Por isto, este estudo foi realizado com o objetivo de estimar (co)variâncias e parâmetros genéticos para as características de dias para se ganhar 160 kg (D160) na fase pré-desmama, e dias para se ganhar 240 kg (D240) na fase pós-desmama, em bovinos da raça Nelore, variedade mocho, criados na região de Mato Grosso. Os componentes de (co)variância e parâmetros genéticos foram estimados por meio do software MTDFREML. As estimativas de herdabilidade para D160, devido ao efeito genético aditivo e maternal foram 0,15±0,027 e 0,08±0,031 respectivamente. Para D240, a estimativa de herdabilidade para efeito genético aditivo foi 0,16±0,26. As estimativas de herdabilidade evidenciaram a existência de variabilidade suficiente para promover melhoria do rebanho em estudo, Embora estas características não sejam adotadas como critérios de seleção, sua utilização proporcionaria melhoria do rebanho, por meio da seleção de animais mais precoces e com maior velocidade de crescimento