Densification rate and phase structure changes during sintering of zinc titanate ceramics

Densification rate and phase structure changes during sintering of nanosized ZnTiO₃ were studied. Sintering was performed in a dilatometer in two regimes: the first to 900 °C (heating rates 5, 10 and 15 °C/min) and the second to 1200 °C (heating rates 3, 5 and 10 °C/min). XRD analysis of samples sintered at both temperatures combined with Rietveld structure refinement enabled determination of all phases present and their structure parameters. Samples sintered to 900 °C contained ZnTiO₃ and Zn₂TiO₄ with traces of r-TiO₂ (rutile) and Zn₂Ti₃O₈, while samples sintered to1200 °C contained only r-TiO₂ and Zn₂TiO₄. A master sintering curve was defined for sintering to 900 °C enabling determination of the sintering process activation energy as 313 kJ/mol.     

Robust Coupled-Quantum-Well Structure for Use in Electrorefraction Modulators

In this letter, an InGaAs/InAlAs coupled-quantum-well structure that is very robust to layer thickness and the compositional variations is reported. The robustness occurs because the structure's electrorefraction (ER) is based on the anticrossing of the two lowest energy light-hole wave functions. The structure is, thus, more appropriate for use in transverse magnetic modulators rather than in transverse electric modulators. The robustness of the structure is shown to be superior to that of a similar structure that has its ER effect based on the anticrossing of the two lowest energy electron wave functions     

Rheological properties of partially hydrolyzed ethylene–vinyl acetate copolymers

Studies have been made of steady-shear and dynamic viscosities for melts of two ethylene–vinyl acetate copolymers and their partially hydrolyzed derivatives using a Weissenberg rheogoniometer over the temperature range of 123–150°C with some tests at 160°C. The flow activation energy of all samples studied was essentially independent of shear stress. The introduction of hydroxyl groups in controlled concentrations, however, produced a complicated flow behavior. At low concentrations, there is a marked increase in Newtonian viscosity, flow activation energy, and shear dependence of viscosity. In contrast to previous reports, a further increase in all three functions was not observed with increasing vinyl alcohol concentration. Dynamic viscosities, in contrast, show monotonic increases with increasing hydroxyl group content, as do activation energies derived from the temperature dependence of the dynamic viscosity. These data may result from an increased chain cohesion due to hydrogen bonding of hydroxyl groups.     

A rheological study of long branching in polyethylene by blending

Steady shear viscosities, dynamic viscosities and moduli, and the corresponding activation energies for flow were examined for a branched polyethylene, a linear polyethylene, and three of their blends at 150° and 190°C. The polyethylenes were chosen to have closely matched molecular weights and distributions. An R-17 Weissenberg rheogoniometer and an Instron capillary rheometer were used. At lower stress, the branched polymer had a higher viscosity than the linear one, possibly because of the contribution of long branches to entanglements. At high stress, this contribution is reduced and the inherently smaller coil dimensions likely become responsible for the lower viscosity of the branched polymer. The activation energy for the branched polymer is high and decreases with stress, in contrast to the low and almost-constant value for the linear polymer. The effects here of pressure on compression are considered. The entanglements of long branches may also decrease with increasing temperature. With decreasing stress, the activation energy for branched polymer tends to become constant, corresponding to an absence of pressure effects and an equilibrium entanglement of long branches for a given temperature range. The linear relationship between activation energy and blend composition problably means that any compressional effects, like free volume, are additive and that long-branch entanglements rearrange with added linear molecules. The linearity may be the result, in part, of a broad distribution for the lengths of long branches.     

The effect of the photopolymerization method on the quality of composite resin samples

Although heart transplantation is by now considered an established procedure in patients with terminal heart failure, there has been a stagnation or even a decline in the number of transplantations performed due to the decreased willingness of the public to provide organs. As a consequence of this development patients have to wait for a donor organ for a much larger time. The aim of this study was to examine patients especially during this very stressful period. From July 1995 to February 1997, 62 patients who had been continuously added to the waiting list were examined regarding their quality of life and emotional state. Completely assessed were 53 patients (participation rate: 85%). As compared to a healthy control group, patients with terminal heart failure on the waiting list reported their quality of life in the physical as well as the psychological area as significantly lower (p < 0.001). The areas of depression (p < 0.001) and anxiety (p < 0.001) also showed a significant difference. There was an obvious correlation (p < 0.01) between the key symptom of terminal heart failure-- dyspnoea--and the measured level of depression. This served to support the notion that there is a connection between the psychological and the somatic state in these severely ill patients. These results point to the necessity of supportive psychotherapeutic treatment during this very stressful time.     

Design parameters of Ti:LiNbO3 waveguides for optimumacoustooptic interaction efficiency

A computer model of optical and surface acoustic wave modes in titanium indiffused Y-cut LiNbO₃ guiding structures is used to produce several graphs for the design of guided-wave acoustooptic devices with optimum interaction characteristics. The design concentrates on waveguide fabrication parameters in order to achieve the optimum acoustic frequency and the acoustooptic interaction bandwidth. The optimum acoustic frequency for a given value of Ti film thickness and diffusion depth is defined as the frequency causing the maximum value of the overlap integral     

Sintering of mechanically activated Zno-TiO2 powders

Zinc oxide and titanium dioxide powders mixed in an equimolar ratio are mechanically activated in a planetary ball mill and sintered under nonisothermal and isothermal conditions. Nonisothermal sintering is studied using dilatometry and SEM. The activation energy of sintering is determined using the method based on different heating rates and Dorn’s method as well. The phase composition of the isothermally sintered samples is determined using x-ray powder diffraction. Published in Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 55–62, 2008.     

Reactionary processes during mechanical treatment of mixtures of ZnO and MnO<Subscript>2</Subscript>. I. Formation of defects and solid solution

Kinetics of defects formation, reaction process and formation of solid solution in powder mixtures of ZnO and MnO₂ induced by prolonged mechanical treatment (MT) have been investigated (X-ray, FTIR, EPR). At MT in zones of deformation-destruction the different defects (\( {\text{V}}_{{\text{Zn}}}^ - :{\text{Zn}}_{\text{i}}^{\text{0}} \) (I), \( {\text{V}}_{{\text{Zn}}}^ - \) (II), and \( {\text{(V}}_{{\text{Zn}}}^ - {\text{)}}_{\text{2}}^ - \) (III) centers at all) are forming. The defects have various physical and chemical properties, and have different activation energies of annealing, E_act The part of these defects is responsible for the processes of hydration and carbonation of samples. In turn, the formation of defects is accompanied by development of various mechanothermical processes, which increase temperature of the sample, T _MT, with the increasing of duration of MT, t _MT. The increasing of t _MT activates the reactionary processes: promotes a consecutive annealing the «low-temperature» defects having small values of E_act (I, II and III) and also leads to formation of Mn²⁺-doped Zn(OH)₂. With the further increase of t _MT, the process of MT is accompanied by an increasing of temperature of samples up to equilibrium, T _eq and accumulation of “high-temperature” defects in the sample. As a result, in the sample the conditions for intensification of volumetric diffusion processes and formation of Mn²⁺-doped ZnO were created.     

System for enhancing supply chain agility through exception handling

With the emergence of a new business era characterized by continuous and unpredictable changes and tough global competition, an agile supply chain has been recognized as a competitive strategy for companies to survive and prosper. Co-OPERATE, an on-going IST project, is aimed at developing concepts and tools for coordination of production planning and control activities in the complex and distributed supply network, and is targeted in the automotive supply and the semiconductor industries. Since the work reported here is based on the project, a framework for manufacturing coordination in the distributed supply network is proposed for the project. As an important part of the project, exception handling is further described. First, through boundary investigation, the scope of this business solution is clarified. Second, a methodology is developed to help understand the mechanism behind the exception handling process. Third, guiding design principles are described to direct the detailed business process design. Finally, rush-order handling is chosen as part of the concept prototype for implementation and evaluation. Extensive feedback from industrial business partners has been collected and taken into account for further implementation.