An Anisotropic Model of Damage and Unilateral Effect for Brittle Materials

This work deals with the initial applications and formulation of an aniscitropic plastic-damage constitutive model proposed for non-linear analysis of reinforced concrete structures submitted to a loading with change of the sign. The original constitutive model is based on the fundamental hypothesis of energy equivalence between real and continuous medium following the concepts of the Continuum Damage Mechanics. The concrete is assumed as an initial elastic isotropic medium presenting anisotropy, permanent strains and bimodularity (distinct elastic responses whether traction or compression stress states prevail) induced by damage evolution. In order to take into account the bimodularity, two damage tensors governing the rigidity in tension or compression regimes are introduced. Then, some conditions are introduced in the original version of the model in order to simulate the damage unilateral effect. The three-dimensional version of the proposed model is analyzed in order to validate its formulation when compared to micromechanical theory. The one-dimensional version of the model is applied in the analyses of a reinforced concrete beam submitted to a loading with change of the sign. Despite the parametric identification problems, the initial applications show the good performance of the model.

Open photoacoustic cell for thermal diffusivity measurements of a fast hardening cement used in dental restoring

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effects of fetuin on zona pellucida hardening, fertilization and embryo development in cattle

Mammalian oocytes can undergo spontaneous meiotic maturation when they are liberated from their follicles and cultured in vitro; however, the zona pellucida (ZP) becomes resistant to chymotrypsin digestion, or hardens, when spontaneous maturation occurs in serum-free medium. Schroeder et al. [Biol. Reprod. 43 (1990) 891] described that fetuin, a component of fetal calf serum (FCS), inhibits ZP hardening during oocyte maturation. The aim of this experiment was to study the effect of the presence of cumulus cells and addition of hormones to maturation media on bovine zona hardening and embryo development in medium with and without fetuin. In Experiment 1, different concentrations of fetuin were added to the maturation medium. The time necessary for digestion of 50% of the ZP (d50) was not different when oocytes were matured in presence of 10% FCS, 1 mg/ml polyvinyl alcohol (PVA), or 4, 1 and 0.25 mg/ml of fetuin; cleavage rates were also similar. However, significantly more blastocysts (P < 0.05) were formed when FCS was used compared to PVA and 0.25 mg/ml of fetuin. In Experiment 11, we examined the influence of the presence of cumulus cells and hormones during the maturation of oocytes in media with PVA, BSA, FCS and fetuin. The d50 was significantly higher (P < 0.05) when oocytes were matured in presence of cumulus cells. The cleavage rate of cumulus-intact oocytes was similar for all groups. However, when oocytes were partially stripped before maturation, the cleavage rate was significantly higher (P < 0.05) when FCS or fetuin was used. In both stripped and non-stripped groups, significantly more blastocysts (P < 0.05) were formed when oocytes were matured with FCS compared to BSA and PVA. These results indicate that zona hardening, as described for mouse and human oocytes, does not have a large effect on bovine cumulus-intact oocytes. Apparently fetuin can be used as a substitute for FCS during bovine oocyte maturation, since it leads to similar developmental rates as FCS in intact and partially stripped oocytes. (C) 2002 Published by Elsevier B.V. B.V.

Modal analysis of anisotropic diffused-channel waveguide by a scalar finite element method

A procedure to model optical diffused-channel waveguides is presented in this work. The dielectric waveguides present anisotropic refractive indexes which are calculated from the proton concentration. The proton concentration inside the channel is calculated by the anisotropic 2D-linear diffusion equation and converted to the refractive indexes using mathematical relations obtained from experimental data, the arbitrary refractive index profile is modeled by a. nodal expansion in the base functions. The TE and TM-like propagation properties (effective index) and the electromagnetic fields for well-annealed proton-exchanged (APE) LiNbO3 waveguides are computed by the finite element method.

Hardening of a dual-cure resin cement using QTH and LED curing units

Objective: This study evaluated the surface hardness of a resin cement (RelyX ARC) photoactivated through indirect composite resin (Cristobal) disks of different thicknesses using either a light- emitting diode (LED) or quartz tungsten halogen (QTH) light source. Material and Methods: Eighteen resin cement specimens were prepared and divided into 6 groups according to the type of curing unit and the thickness of resin disks interposed between the cement surface and light source. Three indentations (50 g for 15 s) were performed on the top and bottom surface of each specimen and a mean Vickers hardness number (VHN) was calculated for each specimen. The data were analyzed using two-way ANOVA and Tukey-Kramer test was used for post-hoc pairwise comparisons. Results: Increased indirect resin disk thickness resulted in decreased mean VHN values. Mean VHN values for the top surfaces of the resin cement specimens ranged from 23.2 to 46.1 (QTH) and 32.3 to 41.7 (LED). The LED curing light source produced higher hardness values compared to the QTH light source for 2- and 3-mm-thick indirect resin disks. The differences were clinically, but not statistically significant. Increased indirect resin disk thickness also resulted in decreased mean VHN values for the bottom surfaces of the resin cement: 5.8 to 19.1 (QTH) and 7.5 to 32.0 (LED). For the bottom surfaces, a statistically significant interaction was also found between the type of curing light source and the indirect resin disk thickness. Conclusions: Mean surface hardness values of resin cement specimens decreased with the increase of indirect resin disk thickness. The LED curing light source generally produced higher surface hardness values.

Anisotropic sound and shock waves in dipolar Bose-Einstein condensate

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Fortran programs for the time-dependent Gross-Pitaevskii equation in a fully anisotropic trap

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

C programs for solving the time-dependent Gross-Pitaevskii equation in a fully anisotropic trap

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Triangular-lattice anisotropic dimerized Heisenberg antiferromagnet: Stability and excitations of the quantum paramagnetic phase

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Surface equilibrium angle for anisotropic grain growth in SnO2 systems

Usually, the kinetic models used in the study of sintered ceramic are performed by means of indirect physical tests, such as, results obtained from data of linear shrinkage and mass loss. This fact is justified by the difficulty in the determinations of intrinsic parameters of ceramic materials along every sintering process. In this way, the technique of atomic force microscopy (AFM) was used in order to determine the importance and the evolution of the dihedral angle in the sintering of 0.5 mol% MnO2-doped tin dioxide obtained by the polymeric precursor method.

Coexistence of different types of vortex lines in anisotropic superconductors

We considered a system of two vortex lines running in different directions with their average vortex direction making an arbitrary angle theta with respect to the crystal c axis. The free energy of this system is calculated as a function of the relative angle 2 alpha between the two inclined vortex lines with respect to each other. For sufficiently high anisotropy, it is shown that, as the induction is tilted away from the crystal c axis (theta not equal 0), the inclined vortex lines (alpha not equal 0) suddenly becomes more stable than that with parallel vortex lines (alpha = 0). While theta is increased, the system continuously changes towards the parallel configuration before the angle theta approaches 90 degrees.

Anisotropic growth of oxide nanocrystals: Insights into the rutile TiO2 phase

In this work, we report the synthesis of titanium oxide nanocrystals, especially the rutile TiO2 phase with nanorod morphology, by a method based on peroxotitanium complex decomposition. The results indicate that the anisotropic morphology reported for rutile TiO2 nanocrystals is related to the oriented attachment process. Despite the predominance of rutile nanocrystals at longer treatment times, the nanocrystals were obtained also in the anatase type, according to the degradation time adopted. XANES results evidenced the absence of structural correlation between the peroxytitanium complex and phase evolution, and the coexistence of the two phases strongly suggests a correlation of the oriented attachment mechanism and the rutile phase stabilization.

Magnetic susceptibility of an exactly solvable anisotropic spin ladder system

We investigate the thermodynamics of an integrable spin ladder model which possesses a free parameter besides rung and leg couplings. The model is exactly solvable by means of the Bethe ansatz and exhibits a phase transition between a gapped and a gapless spin excitation spectrum. The magnetic susceptibility is obtained numerically and its dependence on the anisotropy parameter is determined. The spin gap obtained from the susceptibility curve and the one obtained from the Bethe ansatz equations are in very good agreement. Our results for the magnetic susceptibility fit well the experimental data for the organometallic compounds (5IAP)(2)CuBr4 . 2H(2)O (Landee C. P. et al., Phys. Rev. B, 63 (2001) 100402(R)) Cu-2(C5H12N2)(2)Cl-4 (Hayward C. A., Poilblanc D. and Levy L. P., Phys. Rev. B, 54 (1996) R12649, Chaboussant G. et al., Phys. Rev. Lett., 19 ( 1997) 925; Phys. Rev. B, 55 ( 1997) 3046.) and (C5H12N)(2)CuBr4 (Watson B. C. et al., Phys. Rev. Lett., 86 ( 2001) 5168) in the strong-coupling regime.

Integrable anisotropic spin-ladder model

We present an integrable spin-ladder model, which possesses a free parameter besides the rung coupling J. Wang's system based on the SU(4) symmetry can be obtained as a special case. The model is exactly solvable by means of the Bethe ansatz method. We determine the dependence on the anisotropy parameter of the phase transition between gapped and gapless spin excitations and present the phase diagram. Finally, we show that the model is a special case of a more general Hamiltonian with three free parameters.

Anisotropic Lifshitz point at O(epsilon(2)(L))

We present the critical exponents nu (L2), eta (L2) and gamma (L) for an m-axial Lifshitz point at second order in an epsilon (L) expansion. We introduce a constraint involving the loop momenta along the m-dimensional subspace in order to perform two- and three-loop integrals. The results are valid in the range 0 less than or equal to m less than or equal to d. The case m = 0 corresponds to the usual Ising-like critical behaviour.