Mechanical properties and porosity of dental glass-ceramics hot-pressed at different temperatures

The objective of this work was to evaluate biaxial-flexural-strength (σf), Vickers hardness (HV), fracture toughness (K Ic), Young's modulus (E), Poisson's ratio (ν) and porosity (P) of two commercial glass-ceramics, Empress (E1) and Empress 2 (E2), as a function of the hot-pressing temperature. Ten disks were hot-pressed at 1065, 1070, 1075 and 1080 °C for E1; and at 910, 915, 920 and 925 °C for E2. The porosity was measured by an image analyzer software and s f was determined using the piston-on-three-balls method. K Ic and HV were determined by an indentation method. Elastic constants were determined by the pulse-echo method. For E1 samples treated at different temperatures, there were no statistical differences among the values of all evaluated properties. For E2 samples treated at different temperatures, there were no statistical differences among the values of σf, E, and ν, however HV and K Ic were significantly higher for 910 and 915 °C, respectively. Regarding P, the mean value obtained for E2 for 925 °C was significantly higher compared to other temperatures.

Effect of insertion method on knoop hardness of high viscous glass ionomer cements

The aim of this study was to assess the Knoop hardness of three high viscous glass ionomer cements: G1 - Ketac Molar; G2 - Ketac Molar Easymix (3M ESPE) and G3 - Magic Glass ART (Vigodent). As a parallel goal, three different methods for insertion of Ketac Molar Easymix were tested: G4 - conventional spatula; G5 - commercial syringe (Centrix) and G6 - low-cost syringe. Ten specimens of each group were prepared and the Knoop hardness was determined 5 times on each specimen with a HM-124 hardness machine (25 g/30 s dwell time) after 24 h, 1 and 2 weeks. During the entire test period, the specimens were stored in liquid paraffin at 37ºC. Significant differences were found between G3 and G1/G2 (two-way ANOVA and Tukey's post hoc test; p<0.01). There was no significant difference in the results among the multiple ways of insertion. The glass ionomer cement Magic Glass ART showed the lowest hardness, while the insertion technique had no significant influence on hardness.

Resíduos de sisal como reforço em compósitos de polipropileno virgem e reciclado

Foram estudadas as propriedades térmicas e mecânicas de compósitos de polipropileno, virgem e reciclado, reforçados com 30% em massa de fibras residuais de sisal, assim como o perfil de processamento e a morfologia da matriz polimérica. Para tanto, foram determinadas a resistência à tração, o módulo de Young, alongamento na ruptura, e energia de impacto. As amostras também foram caracterizadas por MEV, DMTA e TG. Para ambos os compósitos de polipropileno, virgem e reciclado, com a adição das fibras, o alongamento na ruptura mostrou uma queda significativa, enquanto que a resistência à tração não sofreu grandes variações. Houve um aumento significativo nos valores de tração na ruptura e de energia de impacto com a adição das fibras de sisal na matriz de polipropileno. As análises térmicas mostraram ligações secundárias, como as ligações polares, entre as fibras e a matriz, concordando com o comportamento mecânico dos compósitos. Constatou-se que a temperatura de transição vítrea não variou após a adição da fibra.

Minas-type fresh cheese developed from buffalo milk with addition of L. acidophilus

Effective incorporation of a probiotic into foods requires the culture to remain viable all along processing and storage, without adverse alterations to sensory characteristics. The objective of this work was developing Minas-type fresh cheese with probiotic properties from buffalo milk. Four batches of Minas-type fresh cheese were prepared using buffalo milk: batch T1 in which neither culture nor lactic acid added; batch T3 in which only lactic acid added; batches T2 and T4 , both added of Lactobacillus acidophilus LAC 4, but T4 was also acidified. Resulting cheeses were evaluated for probiotic culture stability, texture profile, sensory acceptance, and changes in pH. The T4 probiotic cheese presented hardness, gumminess, and chewiness significantly lower than the other treatments. However, values for springiness and cohesiveness did not differ between all cheeses, and no sensory differences (p > 0.05) were found between treatments for texture, taste, and overall acceptance. The addition of probiotic to the acidified cheese (T4) yielded best aroma. The populations of L. acidophilus were greater than 10(6) CFU g-1 after 28 days of storage all products. Minas-type fresh cheese from buffalo milk is a suitable food for the delivery of L. acidophilus, since the culture remained viable during the shelf life of the products and did not negative affect analysed parameters.

Evaluation of elephant grass silage with the addition of cassava scrapings

The objective of this experiment was to evaluate the effects of adding cassava scrapings on gas and effluent losses, dry matter recovery, pH, contents of N-NH3, organic acids and volatile fatty acids and the bromatological composition of elephant grass silages. It was used a randomized complete design, with four levels of cassava scrapings (0, 7, 15 or 30% natural matter) each one with four replications per level. The grass was cut at 50 days of regrowth and ensiled in 15-L silos, equipped with a Bunsen valve to allow gas outflow. The gas losses decreased quadratically with the addition of cassava scrapings, whereas effluent losses decreased linearly. Dry matter recovery increased quadratically with the addition of cassava scrapings. Dry matter (DM) concentration increased but crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF) and hemicellulose (HEM) decreased linearly with the addition of cassava scrapings. The pH value and lactic acid concentration increased quadratically with the addition of cassava scrapings. Contents of N-NH3 and butyric acid decreased quadratically with the addition of cassava scrapings, whereas acetic acid content decreased linearly. Addition of cassava scrapings reduced gas and effluent losses and improved the fermentation profile of elephant grass silages and the level of 7% already ensures this improvement.

Prediction of good glass formers in the Al-Ni-La and Al-Ni-Gd systems using topological instability and electronegativity

A new criterion has been recently proposed combining the topological instability (lambda criterion) and the average electronegativity difference (Delta e) among the elements of an alloy to predict and select new glass-forming compositions. In the present work, this criterion (lambda.Delta e) is applied to the Al-Ni-La and Al-Ni-Gd ternary systems and its predictability is validated using literature data for both systems and additionally, using own experimental data for the Al-La-Ni system. The compositions with a high lambda.Delta e value found in each ternary system exhibit a very good correlation with the glass-forming ability of different alloys as indicated by their supercooled liquid regions (Delta T(x)) and their critical casting thicknesses. In the case of the Al-La-Ni system, the alloy with the largest lambda.Delta e value, La(56)Al(26.5)Ni(17.5), exhibits the highest glass-forming ability verified for this system. Therefore, the combined lambda.Delta e criterion is a simple and efficient tool to select new glass-forming compositions in Al-Ni-RE systems. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3563099]

Enhanced luminescence of Tb(3+)/Eu(3+) doped tellurium oxide glass containing silver nanostructures

We report on energy transfer studies in terbium (Tb(3+))-europium (Eu(3+)) doped TeO(2)-ZnO-Na(2)O-PbO glass containing silver nanostructures. The samples excitation was made using ultraviolet radiation at 355 nm. Luminescence spectra were recorded from approximate to 480 to approximate to 700 nm. Enhanced Eu(3+) luminescence at approximate to 590 nm (transition (5)D(0)-(7)F(1)) and approximate to 614 nm (transition (5)D(0)-(7)F(2)) are observed. The large luminescence enhancement was obtained due to the simultaneous contribution of the Tb(3+)-Eu(3+) energy transfer and the contribution of the intensified local field on the Eu(3+) ions located near silver nanostructures.

Melting and freezing of spherical bismuth nanoparticles confined in a homogeneous sodium borate glass

The melting temperature and the crystallization temperature of Bi nanoclusters confined in a sodium borate glass were experimentally determined as functions of the cluster radius. The results indicate that, on cooling, liquid Bi nanodroplets exhibit a strong undercooling effect for a wide range of radii. The difference between the melting temperature and the freezing temperature decreases for decreasing radius and vanishes for Bi nanoparticles with a critical radius R = 1.9 nm. The magnitude of the variation in density across the melting and freezing transitions for Bi nanoparticles with R = 2 nm is 40% smaller than for bulk Bi. These experimental results support a basic core-shell model for the structure of Bi nanocrystals consisting of a central crystalline volume surrounded by a structurally disordered shell. The volume fraction of the crystalline core decreases for decreasing nanoparticle radius and vanishes for R = 1.9 nm. Thus, on cooling, the liquid nanodroplets with R < 1.9 nm preserve, across the liquid-to-solid transformation, their homogeneous and disordered structure without crystalline core.

Femtosecond third-harmonic generation in a glass ceramic containing sodium niobate nanocrystals

The third-harmonic optical susceptibility, chi((3))(3 omega; omega, omega, omega) of a silicate glass ceramic containing sodium niobate nanocrystals was measured for incident broadband light with central frequency omega corresponding to 1900nm. Absolute values of |chi((3))| and the dispersion of the refractive index from 600 to 1900nm were measured using the spectrally resolved femtosecond Maker fringes technique. The experiments show that |chi((3))| is 1 order of magnitude larger than silica, and it grows by similar to 50% when the volume fraction occupied by the nanocrystals increases up to 40%. (C) 2011 Optical Society of America

Evolutionary dynamics on rugged fitness landscapes: Exact dynamics and information theoretical aspects

The parallel mutation-selection evolutionary dynamics, in which mutation and replication are independent events, is solved exactly in the case that the Malthusian fitnesses associated to the genomes are described by the random energy model (REM) and by a ferromagnetic version of the REM. The solution method uses the mapping of the evolutionary dynamics into a quantum Ising chain in a transverse field and the Suzuki-Trotter formalism to calculate the transition probabilities between configurations at different times. We find that in the case of the REM landscape the dynamics can exhibit three distinct regimes: pure diffusion or stasis for short times, depending on the fitness of the initial configuration, and a spin-glass regime for large times. The dynamic transition between these dynamical regimes is marked by discontinuities in the mean-fitness as well as in the overlap with the initial reference sequence. The relaxation to equilibrium is described by an inverse time decay. In the ferromagnetic REM, we find in addition to these three regimes, a ferromagnetic regime where the overlap and the mean-fitness are frozen. In this case, the system relaxes to equilibrium in a finite time. The relevance of our results to information processing aspects of evolution is discussed.

Influence of temperature and excitation procedure on the athermal behavior of Nd(3+)-doped phosphate glass: Thermal lens, interferometric, and calorimetric measurements

In this work, thermal and optical properties of the commercial Q-98 neodymium-doped phosphate glass have been measured at low temperature, from 50 to 300 K. The time-resolved thermal lens spectrometry together with the optical interferometry and the thermal relaxation calorimetry methods were used to investigate the glass athermal characteristics described by the temperature coefficient of the optical path length change, ds/dT. The thermal diffusivity was also determined, and the temperature coefficients of electronic polarizability, linear thermal expansion, and refractive index were calculated and used to explain ds/dT behavior. ds/dT measured via thermal lens method was found to be zero at 225 K. The results provided a complete characterization of the thermo-optical properties of the Q-98 glass, which may be useful for those using this material for diode-pumped solid-state lasers. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3234396]

Thermal lens and interferometric method for glass transition and thermo physical properties measurements in Nd(2)O(3) doped sodium zincborate glass

In this work the time resolved thermal lens method is combined with interferometric technique, the thermal relaxation calorimetry, photoluminescence and lifetime measurements to determine the thermo physical properties of Nd(2)O(3) doped sodium zincborate glass as a function of temperature up to the glass transition region. Thermal diffusivity, thermal conductivity, fluorescence quantum efficiency, linear thermal expansion coefficient and thermal coefficient of electronic polarizability were determined. In conclusion, the results showed the ability of thermal lens and interferometric methods to perform measurements very close to the phase transition region. These techniques provide absolute values for the measured physical quantities and are advantageous when low scan rates are required. (c) 2008 Optical Society of America

Polarization effects in molecular dynamics simulations of glass-formers Ca(NO(3))(2)center dot nH(2)O, n=4, 6, and 8

Thermodynamics, equilibrium structure, and dynamics of glass-forming liquids Ca(NO(3))(2)center dot nH(2)O, n=4, 6, and 8, have been investigated by molecular dynamics (MD) simulations. A polarizable model was considered for H(2)O and NO(3)- on the basis of previous fluctuating charge models for pure water and the molten salt 2Ca(NO(3))(2)center dot 3KNO(3). Similar thermodynamic properties have been obtained with nonpolarizable and polarizable models. The glass transition temperature, T(g), estimated from MD simulations was dependent on polarization, in particular the dependence of T(g) with electrolyte concentration. Significant polarization effects on equilibrium structure were observed in cation-cation, cation-anion, and water-water structures. Polarization increases the diffusion coefficient of H(2)O, but does not change significantly the diffusion coefficients of ions. Viscosity decreases upon inclusion of polarization, but the conductivity calculated with the polarizable model is smaller than the nonpolarizable model because polarization enhances anion-cation interactions.

Dual contactless conductivity and amperometric detection on hybrid PDMS/glass electrophoresis microchips

A new approach for the integration of dual contactless conductivity and amperometric detection with an electrophoresis microchip system is presented. The PDMS layer with the embedded channels was reversibly sealed to a thin glass substrate (400 mu m), on top of which a palladium electrode had been previously fabricated enabling end-channel amperometric detection. The thin glass substrate served also as a physical wall between the separation channel and the sensing copper electrodes for contactless conductivity detection. The latter were not integrated in the microfluidic device, but fabricated on an independent plastic substrate allowing a simpler and more cost-effective fabrication of the chip. PDMS/glass chips with merely contactless conductivity detection were first characterized in terms of sensitivity, efficiency and reproducibility. The separation efficiency of this system was found to be similar or slightly superior to other systems reported in the literature. The simultaneous determination of ionic and electroactive species was illustrated by the separation of peroxynitrite degradation products, i.e. NO(3)(-) (non-electroactive) and NO(2)(-) (electroactive), using hybrid PDMS/glass chips with dual contactless conductivity and amperometric detection. While both ions were detected by contactless conductivity detection with good efficiency, NO(2)(-) was also simultaneously detected amperometrically with a significant enhancement in sensitivity compared to contactless conductivity detection.

Role of Glycerol Addition on Xylose-to-Xylitol Bioconversion by Candida guilliermondii

The effect of glycerol on xylose-to-xylitol bioconversion by Candida guilliermondii was evaluated by its addition (0.7 and 6.5 g/l) to semidefined media (xylose as a substrate). The glycerol concentrations were chosen based on the amounts produced during previous studies on xylitol production by C. guilliermondii. Medium without glycerol addition (control) and medium containing glycerol (53 g/l) in substitution to xylose were also evaluated. According to the results, the addition of 0.7 g/l glycerol to the fermentation medium favored not only the yield (Y (P/S) = 0.78 g/g) but also the xylitol productivity (Q (P) = 1.13 g/l/h). During the xylose-to-xylitol bioconversion, the formation of byproducts (glycerol and ethanol) was observed for all conditions employed. In relation to the cellular growth, glycerol as the only carbon source for C. guilliermondii was better than xylose or xylose and glycerol mixtures, resulting in a maximum cellular concentration (5.34 g/l).