Neutron Charge Radius: Relativistic Effects and the Foldy Term

The neutron charge radius is studied within a light-front model with different spin coupling schemes and wave functions. The cancellation of the contributions from the Foldy term and Dirac form factor to the neutron charge form factor is verified for large nucleon sizes and it is independent of the detailed form of quark spin coupling and wave function. For the physical nucleon our results for the contribution of the Dirac form factor to the neutron radius are insensitive to the form of the wave function while they strongly depend on the quark spin coupling scheme.Comment: 12 pages, 5 figures, Latex, Int. J. Mod. Phys.

Two Kerr black holes with axisymmetric spins: An improved Newtonian model for the head-on collision and gravitational radiation

We present a semi-analytical approach to the interaction of two (originally) Kerr black holes through a head-on collision process. An expression for the rate of emission of gravitational radiation is derived from an exact solution to the Einstein's field equations. The total amount of gravitational radiation emitted in the process is calculated and compared to current numerical investigations. We find that the spin-spin interaction increases the emission of gravitational wave energy up to 0.2% of the total rest mass. We discuss also the possibility of spin-exchange between the holes.Comment: 8 pages, RevTeX, 2 figures, psbox macro include

Ensacamento de frutos de abiu visando à proteção contra o ataque da mosca-das-frutas.

O abiu (Pouteria caimito) é fruto bastante conhecido nos trópicos e consumido in natura. Dentre os principais problemas que afetam a qualidade dos frutos, estão os danos causados por ataque da larva de mosca-das-frutas. O objetivo do trabalho foi determinar o diâmetro do fruto de abiu para efetivar a prática do ensacamento, visando à proteção contra o ataque da mosca. Para isto, foram estabelecidas seis classes de diâmetros: a) frutos com diâmetro menor que 1 cm; b) frutos com diâmetro de 1 a 2 cm; c) frutos com diâmetro de 2 a 3 cm; d) frutos com diâmetro de 3 a 4 cm; e) frutos com diâmetro de 4 a 5 cm; f) frutos com diâmetro maior que 5 cm, e o tratamento-testemunha, que constou de frutos sem proteção. Os sacos para a cobertura dos frutos foram confeccionados em TNT, na cor branca. Após a colheita, os frutos foram medidos e pesados, e depois partidos nos sentidos longitudinal e transversal e avaliados por meio da observação visual, quanto à presença ou ausência de larva da mosca-das-frutas. A eficiência dos tratamentos foi avaliada pela porcentagem de frutos caídos ao chão, e de frutos colhidos com ausência e presença da larva. Foram observados 96,7; 88,3 e 40,0% de queda nos frutos ensacados com diâmetro menor que 1 cm; 1-2 cm, e 2-3 cm, respectivamente. O ensacamento de frutos de abiu com diâmetro entre 1 e 2 cm não é viável devido à alta porcentagem de frutos caídos (96,7%). A maior porcentagem de frutos colhidos sem larva da mosca-dasfrutas (83,3%) é verificada quando os frutos foram ensacados com diâmetro entre três e cinco centímetros

Quantum dot to disordered wire crossover: A complete solution in all length scales for systems with unitary symmetry

We present an exact solution of a supersymmetric nonlinear sigma model describing the crossover between a quantum dot and a disordered quantum wire with unitary symmetry. The system is coupled ideally to two electron reservoirs via perfectly conducting leads sustaining an arbitrary number of propagating channels. We obtain closed expressions for the first three moments of the conductance, the average shot-noise power and the average density of transmission eigenvalues. The results are complete in the sense that they are nonperturbative and are valid in all regimes and length scales. We recover several known results of the recent literature by taking particular limits.Comment: 4 page

Nonequilibrium Zaklan model on Apollonian Networks

The Zaklan model had been proposed and studied recently using the equilibrium Ising model on Square Lattices (SL) by Zaklan et al (2008), near the critica temperature of the Ising model presenting a well-defined phase transition; but on normal and modified Apollonian networks (ANs), Andrade et al. (2005, 2009) studied the equilibrium Ising model. They showed the equilibrium Ising model not to present on ANs a phase transition of the type for the 2D Ising model. Here, using agent-based Monte-Carlo simulations, we study the Zaklan model with the well-known majority-vote model (MVM) with noise and apply it to tax evasion on ANs, to show that differently from the Ising model the MVM on ANs presents a well defined phase transition. To control the tax evasion in the economics model proposed by Zaklan et al, MVM is applied in the neighborhood of the critical noise $q_{c}$ to the Zaklan model. Here we show that the Zaklan model is robust because this can be studied besides using equilibrium dynamics of Ising model also through the nonequilibrium MVM and on various topologies giving the same behavior regardless of dynamic or topology used here.Comment: 11 pages, 6 figures. arXiv admin note: substantial text overlap with arXiv:1204.0386 and arXiv:0910.196