A. L. Ribeiro Filho

The Cangemi–Jackiw Manifold in High Dimensions and Symplectic Structure

Abstract The notion of Poincare gauge manifold ( G ), proposed in the context of an (1+1) gravitational theory by D. Cangemi and R. Jackiw (1993, Ann. Phys. (N.Y.)225, 229), is explored from a geometrical point of view. First G is defined for arbitrary dimensions and in the sequence a symplectic structure is attached to T* G . Treating then the case of five dimensions, a (4, 1) de-Sitter space, applications are presented studing representations of the Poincare group in association with kinetic theory and the Weyl operators in phase space. The central extension in the Aghassi–Roman–Santilli group (J. J. Aghassi, P. Roman, and R. M. Santilli, 1970, Phys. Rev. D1, 2753) is derived as a subgroup of linear transformations in G with six dimensions.

Relação entre comprimento craniocaudal e diâmetro da vesícula embrionária/fetal com idade de gestação por meio de avaliação ultra-sonográfica em ovino da raça Bergamácia

This study aimed to relate embryonic/fetal vesicle diameter (EVD) and crown-rump length (CRL) to gestational age in ewes from the 15th to the 45th day of pregnancy. Nineteen adult Bergamacia ewes with synchronized estrus were mated by the same male. Ultrasonographic evaluations were performed every 24 hours from the 15th to the 30th day after mating and every five days from the 30th to the 45th day using 5.0 and 7.5MHZ linear transducers. Average daily growth of EVD and CRL were 1.40mm and 1.33mm, respectively. The inverse calibration obtained for EVD was: Days = -11 + 50(0.1 + 0.04log EVD)1/2 with R2 = 0.85, and for CRL was: Days = 13.63 + 12.5(- 0.71 + 0.16CRL)1/2 with R2 = 0.93. Both EVD and CRL obtained by ultrasonography are useful measurements that allow the prediction of gestational age in Bergamacia ewes.

Hamiltonian dynamics of the Landau-Ginzburg model for the phase transition in (NH4)2BeF4

We present a Hamiltonian treatment of the Landau-Ginzburg theory of phase transitions in the case of incommensurate ferroelectric systems like (NH4)2BeF4. This formulation has the advantage of treating the system as an example of a nonlinear dynamical system.

New Calculations of ICDW Eigenmode Frequencies of 2H-TaSe2

Using an extended expression for the Landau-Lifshitz free-energy density we have computed order-parameter fluctuation eigenmodes for the triple hexagonal incommensurate charge-density-wave (ICDW) phase in 2H-TaSe 2 . Phasons and amplitudons have been obtained for two particular directions and we have performed some numerical calculations.

Phase Transitions in Two‐Dimensional Incommensurate Systems

Analytical and numerical calculations are performed in order to get free energies and critical temperature expressions for dichalcogenide transition metals which are incommensurate systems and present charge density waves (CDW). General results are obtained and compared with those of other authors.

Eigenmode frequencies calculations in the charge-density-wave states of 2H-TaSe2

We have performed some calculations involving two eigenmode frequencies of 2H - TaSe2. We have obtained a good comparison with some well established Raman scattering data for the commensurate and incommensurate charge-density-wave phases in this compound. We outline an approximated method to compute the determinantal equation.