Discretizing the deformation parameter in the su(q)(2) quantum algebra

Inspired in recent works of Biedenham [1, 2] on the realization of the q-algebra su(q)(2), We show in this note that the condition [2j + 1](q) = N-q(j) = integer, implies the discretization of the deformation parameter alpha, where q = e(alpha). This discretization replaces the continuum associated to ct by an infinite sequence alpha(1), alpha(2), alpha(3),..., obtained for the values of j, which label the irreps of su(q)(2). The algebraic properties of N-q(j) are discussed in some detail, including its role as a trace, which conducts to the Clebsch-Gordan series for the direct product of irreps. The consequences of this process of discretization are discussed and its possible applications are pointed out. Although not a necessary one, the present prescription is valuable due to its algebraic simplicity especially in the regime of appreciable values of alpha.

Rapidly varying boundaries in equations with nonlinear boundary conditions. The case of a Lipschitz deformation

We analyze the behavior of solutions of nonlinear elliptic equations with nonlinear boundary conditions of type partial derivative u/partial derivative n + g( x, u) = 0 when the boundary of the domain varies very rapidly. We show that the limit boundary condition is given by partial derivative u/partial derivative n+gamma(x) g(x, u) = 0, where gamma(x) is a factor related to the oscillations of the boundary at point x. For the case where we have a Lipschitz deformation of the boundary,. is a bounded function and we show the convergence of the solutions in H-1 and C-alpha norms and the convergence of the eigenvalues and eigenfunctions of the linearization around the solutions. If, moreover, a solution of the limit problem is hyperbolic, then we show that the perturbed equation has one and only one solution nearby.

VERY RAPIDLY VARYING BOUNDARIES IN EQUATIONS WITH NONLINEAR BOUNDARY CONDITIONS. THE CASE of A NON UNIFORMLY LIPSCHITZ DEFORMATION

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

Theoretical analysis of the structural deformation in Mn-doped BaTiO3

An alternative theoretical method to simulate the structural deformation induced by Mn-doping in BaTiO3 is proposed. The periodic quantum-mechanical method is based on density functional theory at B3LYP level. The structural models were obtained from Rietveld refinement of the undoped and Mn doped BaTiO3 X-ray diffraction data. This modelization gives access to the dopant General effect on the electronic structure. In fact, the influence of the doing element itself on the electronic configuration is barely local: therefore, it is not included in the simulation. The simplicity of the model makes it available for working within a wide range of materials.(C) 2004 Published bv Elsevier B.V.

BARRIER VOLTAGE DEFORMATION OF ZNO VARISTORS BY CURRENT PULSE

The phenomenon of electrical degradation in ZnO varistors was studied by application of high-intensity current pulses. A wave shape of 8 X 20-mu-s and rectangular waves of 1 and 2 ms were used. The degradation was estimated by reference electric-field variation and by Schottky voltage barrier deformation. The results showed that current pulses reduce both the height and the width of the barrier voltage. It was also observed that the donor density N(d) did not change but the surface states density N(s) decreased with degradation.

Short-range order kinetics in alpha-AgZn for various states of post-deformation defect annealing after cold-rolling

Kinetics of short-range ordering (SRO) in Ag with 21, 23 and 28 at% Zn is investigated by residual resistometry during isochronal and isothermal heat treatment for different states of post-deformation defect annealing after cold-rolling to about 30 and 60% thickness reduction. Resistivity changes due to pure ordering can be separated from the as-measured total resistivity change which includes defect annealing. Although the initial state of SRO of the as-rolled material can be estimated to be comparably low, for as-rolled and partially annealed states by appropriate thermal treatment evolution of SRO is achieved which corresponds quite well to that of recrystallized samples. It is observed, however, that quenched-in surplus vacancies contribute considerably to the ordering process for the recrystallized state and that this contribution is still increased by the grain growth during the final stage of annealing. It therefore turns out that SRO-kinetics under equilibrium vacancy conditions can be better observed in a state of post-deformation annealing, for which deformation induced point defects are annealed-out, but a relatively high dislocation density is still present to act as a vacancy sink. Copyright (C) 1996 Acta Metallurgica Inc.

Effect of thermocycling on bond strength and elasticity of 4 long-term soft denture liners

Statement of problem. Two problems found in prostheses with soft liners are bond failure to the acrylic resin base and loss of elasticity due to material aging.Purpose. This in vitro study evaluated the effect of thermocycling on the bond strength and elasticity of 4 long-term soft denture liners to acrylic resin bases.Material and methods. Four soft lining materials (Molloplast-B, Flexor, Permasoft, and Pro Tech) and 2 acrylic resins (Classico, and Lucitone 199) were processed for testing according to manufacturers' instructions. Twenty rectangular specimens (10 X 10-mm(2) cross-sectional area) and twenty cylinder specimens (12.7-mm diameter X 19.0-mm height) for each liner/resin combination were used for the tensile and deformation tests, respectively. Specimen shape and liner thickness were standardized. Samples were divided into a test group that was thermocycled 3000 times and a control group that was stored for 24 hours in water at 37degreesC. Mean bond strength, expressed in megapascals (Wa), was determined in the tensile test with the use of a universal testing machine at a crosshead speed of 5 mm/min. Elasticity, expressed as percent of permanent deformation, was calculated with an instrument for measuring permanent deformation described in ADA/ANSI specification 18. Data from both tests were examined with 1-way analysis of variance and a Tukey test, with calculation of a Scheffe interval at a 95% confidence level.Results. In the tensile test under control conditions, Molloplast-B (1.51 +/- 0.28 MPa [mean SD]) and Pro Tech (1.44 +/- 0.27 MPa) liners had higher bond strength values than the others (P < .05). With regard to the permanent deformation test, the lowest values were observed for Molloplast-B (0.48% +/- 0.19%) and Flexor (0.44% +/- 0.14%) (P < .05). Under thermocycling conditions, the highest bond strength occurred with Molloplast-B (1.37 +/- 0.24 MPa) (P < .05) With regard to the deformation test, Flexor (0.46% +/- 0.13%) and Molloplast-B (0.44% +/- 0.17%) liners had lower deformation values than the others (P < .05).Conclusion. The results of this in vitro study indicated that bond strength and permanent deformity values of the 4 soft denture liners tested varied according to their chemical composition. These tests are not completely valid for application to dental restorations because the forces they encounter are more closely related to shear and tear. However, the above protocol serves as a good method of investigation to evaluate differences between thermocycled and control groups.

Comparison of the tensile bond strengths of cast metal crowns luted with resin cements

The limitation of photoactivation of dual-polymerized resin cements along the margins of metal restorations may adversely affect the mechanical properties of these cements, thus impairing the retention of restorations. The aim of this study was to assess the bond strength of cast metal crowns cemented with three dual-polymerized resin cements, using a chemically-activated resin cement and zinc phosphate as controls. Fifty nickel-chromium alloy crowns were cast and randomly assigned to five groups of equal size. Castings were cemented on their corresponding metal dies with one of the tested luting agents: Scotchbond Resin Cement, Enforce and Panavia F (dual-polymerized resin cements), Cement-It (chemically-activated resin cement) and Zinc Phosphate Cement (zinc phosphate cement). Specimens were stored in distilled water at 37 degreesC for 24 h and then loaded in tension until failure. Panavia F and Zinc Phosphate Cement provided the highest and lowest bond strength means, respectively. Scotchbond Resin Cement, Enforce and Cement-It cements exhibited similar intermediate values, but with statistically significant difference compared to the other materials (P < 0.05). Even with the restriction or absence of light activation, all tested dual-polymerized resin cements produced significantly higher bond strength than did the zinc phosphate cement and yielded similar or better results than the chemically activated cement. It should be pointed out that the findings of this study relate to a test scenario which does not mimic clinical circumstances and that further work is required to identify the clinical significance of the reported tensile bond strength differences between the different luting materials.

The influence of internal surface treatments on tensile bond strength for two ceramic systems

Statement of the Problem: the ceramic composition and surface microstructure of all-ceramic restorations are important components of an effective bonding substrate. Hydrofluoric acid and sandblasting are well-known procedures for surface treatment; however, surface treatment for high alumina-containing and lithium disilicate ceramics have not been fully investigated.Purpose: This in vitro study evaluated the tensile bond strength of resin cement to two types of ceramic systems with different surface treatments.Methods and Materials: Thirty specimens of each ceramic system were made according to the manufacturer's instructions and embedded in polyester resin. Specimens of In-Ceram Alumina [1] and IPS Empress 2 [E] were distributed to three groups with differing surface treatments (n=10): sandblasting with 50 jam aluminum oxide (APA); sandblasting with 110 pm aluminum oxide modified with silica particles (ROCATEC System-RS); a combination of sandblasting with APA and 10% hydrofluoric acid etching (HA) for two minutes on In-Ceram and for 20 seconds for IPS Empress 2. After the respective surface treatments, all the specimens were silanated, and Rely-X resin cement was injected onto the ceramic surface and light polymerized. The specimens were stored in distilled water at 37 degrees C for 24 hours and thermally cycled 1,100 times (5 degrees C/55 degrees C). The tensile bond strength test was performed in a universal testing machine at a 0.5 mm/minute crosshead speed.Results: the mean bond strength values (AWa) for IPS Empress 2 were 12.01 +/- 5.93 (EAPA), 10.34 +/- 1.77 (ERS) and 14.49 +/- 3.04 (EHA). The mean bond strength values for In-Ceram Alumina were 9.87 +/- 2.40 JAPA) and 20.40 +/- 6.27 (IRS). All In-Ceram specimens treated with 10% hydrofluoric acid failed during thermal cycling.Conclusion: the Rocatec system was the most effective surface treatment for In-Ceram Alumina ceramics; whereas, the combination of aluminum oxide sandblasting and hydrofluoric acid etching for 20 seconds worked more effectively for Empress 2 ceramics.

Different responses in bulk density and saturated hydraulic conductivity to soil deformation by logging machinery on a Ferralsol under native forest

Ferralsols have high structural stability, although structural degradation has been observed to result from forest to tillage or pasture conversion. An experimental series of forest skidder passes in an east Amazonian natural forest was performed for testing the effects of mechanical stress during selective logging operations on a clay-rich Ferralsol under both dry and wet soil conditions. Distinct ruts formed up to 25 cm depth only under wet conditions. After nine passes the initially very low surface bulk density of between 0.69 and 0.80 g cm(-3) increased to 1.05 g cm(-3) in the wet soil and 0.92 g cm(-3) in the dry soil. Saturated hydraulic conductivities, initially > 250 mm h(-1), declined to a minimum of around 10 mm h(-1) in the wet soil after the first pass, and in the dry soil more gradually after nine passes. The contrasting response of bulk density and saturated hydraulic conductivity is explained by exposure of subsoil material at the base of the ruts where macrostructure rapidly deteriorated under wet conditions. We attribute the resultant moderately high hydraulic conductivities to the formation of stable microaggregates with fine sand to coarse silt textures. We conclude that the topsoil macrostructure of Ferralsols is subject to similar deterioration to that of Luvisols in temperate zones. The stable microstructure prevents marked compaction and decrease in hydraulic conductivity under wetter and more plastic soil conditions. However, typical tropical storms may regularly exceed the infiltration capacity of the deformed soils. In the deeper ruts water may concentrate and cause surface run-off, even in gently sloping areas. To avoid soil erosion, logging operations in sloping areas should therefore be restricted to dry soil conditions when rut formation is minimal.