Optimisation of sintering processes for porcelain using in-situ measuring methods

By monitoring the thermal conductivity of ceramic materials during sintering, direct insight into the microstructural evolution can be gained. Using an in-situ thermooptical measuring system for measurement of thermal conductivities and densification rates and a high-temperature X-ray diffractometer, sintering mechanisms of porcelain have been examined. For the investigation of fast biscuit and glost firing cycles of whiteware, a firing process of a continuosly gas fired kiln with a firing atmosphere containing water vapourwas simulated in a resistance heated laboratory fumace. The sintering properties deviate significantly from results obtained in dry air. From densification data, a „kinetic field" for the glost firing of whiteware has been setup to calculate optimal fast firing cydes and to determine the activation energy for the densification. The activation energy increases in the intermediate sintering stage

Hydrogels and Their Role in Biosensing Applications

Hydrogels play an important role in the field of biomedical research and diagnostic medicine. They are emerging as a powerful tool in the context of bioanalytical assays and biosensing. In this context, this review gives an overview of different hydrogels and the role they adopt in a range of applications. Not only are hydrogels beneficial for the immobilization and embedding of biomolecules, but they are also used as responsive material, as wearable devices, or as functional material. In particular, the scientific and technical progress during the last decade is discussed. The newest hydrogel types, their synthesis, and many applications are presented. Advantages and performance improvements are described, along with their limitations

Clarifications to the limitations of the s-α equilibrium model for gyrokinetic computations of turbulence

In the context of gyrokinetic flux-tube simulations of microturbulence in magnetized toroidal plasmas, different treatments of the magnetic equilibrium are examined. Considering the Cyclone DIII-D base case parameter set [Dimits et al., Phys. Plasmas 7, 969 (2000)], significant differences in the linear growth rates, the linear and nonlinear critical temperature gradients, and the nonlinear ion heat diffusivities are observed between results obtained using either an $s-\alpha$ or an MHD equilibrium. Similar disagreements have been reported previously [Redd et al., Phys. Plasmas 6, 1162 (1999)]. In this paper it is shown that these differences result primarily from the approximation made in the standard implementation of the $s-\alpha$ model, in which the straight field line angle is identified to the poloidal angle, leading to inconsistencies of order $\varepsilon$ ($\varepsilon=a/R$ is the inverse aspect ratio, $a$ the minor radius and $R$ the major radius). An equilibrium model with concentric, circular flux surfaces and a correct treatment of the straight field line angle gives results very close to those using a finite $\varepsilon$, low $\beta$ MHD equilibrium. Such detailed investigation of the equilibrium implementation is of particular interest when comparing flux tube and global codes. It is indeed shown here that previously reported agreements between local and global simulations in fact result from the order $\varepsilon$ inconsistencies in the $s-\alpha$ model, coincidentally compensating finite $\rho^*$ effects in the global calculations, where $\rho^*=\rho _s / a$ with $\rho_s$ the ion sound Larmor radius. True convergence between local and global simulations is finally obtained by correct treatment of the geometry in both cases, and considering the appropriate $\rho^* \rightarrow 0$ limit in the latter case

Flux- and gradient-driven global gyrokinetic simulation of tokamak turbulence

The Eulerian gyrokinetic turbulence code GENE has recently been extended to a full torus code. Moreover, it now provides Krook-type sources for gradient-driven simulations where the profiles are maintained on average as well as localized heat sources for a flux-driven type of operation. Careful verification studies and benchmarks are performed successfully. This setup is applied to address three related transport issues concerning nonlocal effects. First, it is confirmed that in gradient-driven simulations, the local limit can be reproduced-provided that finite aspect ratio effects in the geometry are treated carefully. In this context, it also becomes clear that the profile widths (not the device width) may constitute a more appropriate measure for finite-size effects. Second, the nature and role of heat flux avalanches are discussed in the framework of both local and global, flux-and gradient-driven simulations. Third, simulations dedicated to discharges with electron internal barriers are addressed. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3567484

Particle transport in density gradient driven TE mode turbulence

The turbulent transport of main ion and trace impurities in a tokamak device in the presence of steep electron density gradients has been studied. The parameters are chosen for trapped electron (TE) mode turbulence, driven primarily by steep electron density gradients relevant to H-mode physics, but with a transition to temperature gradient driven turbulence as the density gradient flattens. Results obtained through non-linear (NL) and quasilinear (QL) gyrokinetic simulations using the GENE code are compared with results obtained from a fluid model. Main ion and impurity transport is studied by examining the balance of convective and diffusive transport, as quantified by the density gradient corresponding to zero particle flux (peaking factor). Scalings are obtained for the impurity peaking with the background electron density gradient and the impurity charge number. It is shown that the impurity peaking factor is weakly dependent on impurity charge and significantly smaller than the driving electron density gradient.Comment: 11 pages, 6 figures. Submitted to Nuclear Fusion SP