Surface characterization of zirconium titanate (ZrTiO4) powder by measurements of electrical photoconductance and photoassisted oxygen isotope exchange

The photosensitivity of a ZrTiO₄ sample (33 m²/g) prepared by a sol-gel method has been assessed in the presence of O₂ by both photoconductance and oxygen isotope exchange (OIE) measurements at room temperature at wavelengths > 290 nm. For oxygen pressures < ca. 13.3 Pa, the steady-state photoconductance of ZrTiO₄ was unaffected by , which indicated that the direct recombination of the photoproduced charges played the dominant role. At higher pressures, varied as the reciprocal of , which was consistent with the fact that the electronic equilibrium was then governed by O₂ + e^– O ₂ ^– . OIE over ZrTiO₄ occurred predominantly via the overall mechanism which involves the exchange of two surface oxygen atoms for each exchange act. It was very slow as compared with OIE over photocatalytically active anatase samples which, in addition, occurs via another mechanism. These results allow one to predict that this ZrTiO₄ sample is a poorly active photocatalyst for oxidations involving gaseous oxygen, and further illustrate the interest of and OIE measurements to evaluate the photosensitivity of semiconductor oxide samples.     

Reinforcement of poly(dimethylsiloxane) networks by montmorillonite platelets

A PDMS network, synthesized from a vinyl‐terminated precursor, was reinforced by plate‐like montmorillonite (volclay) particles with different surface cations. The optimal ratio of crosslinker‐to‐PDMS precursor was ascertained from the mechanical properties of networks prepared with different crosslinker concentrations. The elastic modulus of the polymer was enhanced by the montmorillonite particles. The increase in modulus was higher in the Li– than in the Na–volclay composites. The ultimate strength of the composites was also strongly enhanced by the small platelets, especially in presence of surface Li⁺. The stronger influence of Li–volclay on the mechanical properties of the composites can be attributed to the partial formation of an intercalated structure, which leads to thinner particles with a high aspect ratio. Both composite strength and modulus were proportional to the filler‐volume‐fraction, but the increase in strength was limited by rising particle agglomeration at high loading. In contrast to organic‐modified montmorillonite, the inorganic surface of volclay catalyzed the thermal degradation of PDMS. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2175–2183, 2002     

Wood-Derived Porous SiC Ceramics by Sol Infiltration and Carbothermal Reduction

A new method for transforming wood structures into ceramic by carbothermal reduction of silica and carbonized wood has been developed. Application of this technique allows the preservation of wood microstructures in the ceramic state and the conversion of wood components without constraints in component size. The chosen infiltration technique of silica sol incorporation into carbonized wood structures is examined in terms of sol and wood type, carbonization conditions of the wood, and thickness of the infiltrated carbon body. Ceramization conditions were optimized, and the reaction mechanism is discussed.     

Einfluß der Diffusion auf die Selektivität der Schleppmittel-Destillation

Influence of diffusion on the selectivity of entrainer distillation . The selectivity of azeotropic distillation generally depends not only on the relative volatility but also upon the rate of diffusion of the participating components in the liquid and the gaseous phase. If the less volatile material diffuses faster in the gas phase than the more volatile material, then the former can also accumulate in the gas phase. In such a case the azeotropic points do not necessarily represent separation limits. This effect might also be utilized in the separation of azeotropic mixtures in specific cases. On the other hand, a large diffusion resistance in the liquid phase can override any selectivity. An estimate shows that selective drying of porous materials containing binary solvent mixtures is therefore practically impossible. Azeotropic distillation is also suitable for investigating column plates and packings with the aim of isolating the hydraulic and kinetic reasons for the imperfect equilibration always observed. These questions, overcoming azeotropic points, non-selective drying, and the reasons for imperfect equilibration in separation columns, are discussed in the light of theoretical results and experimental data obtained for practical azeotropic distillations.     

Simulating electron energy loss spectroscopy with the MNPBEM toolbox

Within the MNPBEM toolbox, we show how to simulate electron energy loss spectroscopy (EELS) of plasmonic nanoparticles using a boundary element method approach. The methodology underlying our approach closely follows the concepts developed by García de Abajo and coworkers (Garcia de Abajo, 2010). We introduce two classes eelsret and eelsstat that allow in combination with our recently developed MNPBEM toolbox for a simple, robust, and efficient computation of EEL spectra and maps. The classes are accompanied by a number of demo programs for EELS simulation of metallic nanospheres, nanodisks, and nanotriangles, and for electron trajectories passing by or penetrating through the metallic nanoparticles. We also discuss how to compute electric fields induced by the electron beam and cathodoluminescence.     

Performance of CPU/GPU compiler directives on ISO/TTI kernels

GPUs are slowly becoming ubiquitous devices in High Performance Computing, as their capabilities to enhance the performance per watt of compute intensive algorithms as compared to multicore CPUs have been identified. The primary shortcoming of a GPU is usability, since vendor specific APIs are quite different from existing programming languages, and it requires a substantial knowledge of the device and programming interface to optimize applications. Hence, lately a growing number of higher level programming models are targeting GPUs to alleviate this problem. The ultimate goal for a high-level model is to expose an easy-to-use interface for the user to offload compute intensive portions of code (kernels) to the GPU, and tune the code according to the target accelerator to maximize overall performance with a reduced development effort. In this paper, we share our experiences of three of the notable high-level directive based GPU programming models—PGI, CAPS and OpenACC (from CAPS and PGI) on an Nvidia M2090 GPU. We analyze their performance and programmability against Isotropic (ISO)/Tilted Transversely Isotropic (TTI) finite difference kernels, which are primary components in the Reverse Time Migration (RTM) application used by oil and gas exploration for seismic imaging of the sub-surface. When ported to a single GPU using the mentioned directives, we observe an average 1.5–1.8x improvement in performance for both ISO and TTI kernels, when compared with optimized multi-threaded CPU implementations using OpenMP.     

The asymptotic stability of stable and time-autonomous discrete multidimensional behaviors

We generalize the important paper of Napp et al. (Automatica 47, 2373–2382, 2011), to discrete time-autonomous (ta) (=time-relevant), but not necessarily square-autonomous behaviors in arbitrary dimensions. This paper and therefore also the present one were essentially influenced by the papers of Wood et al. (SIAM J Control Optim 43, 1493–1520 2005), and Willems (Proceedings of the International Conference on Multidimensional (nD) Systems, Aveiro, 2007). In the present paper the discrete domain of the independent variables is the lattice of vectors of integers of arbitrary (but fixed) length whose first component is a natural number and interpreted as a discrete time instant. The stability of an autonomous behavior is defined by a spectral condition on its characteristic variety. The behavior is time autonomous if each trajectory is determined by a fixed number of its initial values. Under a weak additional condition, a discrete stable and time-autonomous behavior is asymptotically stable in the sense that under suitable initial conditions its trajectories converge to zero when the time tends to infinity. We derive algorithms for the constructive verification of the assumptions of most of our results and in particular establish a constructive normal form of ta behaviors in arbitrary dimensions. The Fourier transform on finitely generated free abelian groups plays an important part in the derivations as it already did in the quoted papers. Stability and stabilization of multidimensional discrete behaviors were previously discussed by various colleagues, for instance by Bisiacco, Bose, Fornasini, Lin, Marchesini, Pillai, Quadrat, Rogers, Shankar, Sule, Valcher, Wood, but only partly from the analytic point of view.     

Temperature dependant dielectric breakdown of sputter-deposited AlN thin films using a time-zero approach

In MEMS (micro electromechanical system) devices, piezoelectric aluminum nitride (AlN) thin films are commonly used as functional material for sensing and actuating purposes. Additionally, AlN features excellent dielectric properties as well as a high chemical and thermal stability, making it also a good choice for passivation purposes for microelectronic devices. With those aspects and current trends towards minimization in mind, the dielectric reliability of thin AlN films is of utmost importance for the realization of advanced device concepts. In this study, we present results on the transversal dielectric strength of 100 nm AlN thin films deposited by dc magnetron sputtering. The dielectric strength is measured using a time-zero approach, using a fast voltage ramp to stress the film up to the point of breakdown. The measurements are performed at different device temperatures. In order to achieve statistical significance, at least 12 measurements are performed for each environment parameter set and the results are analyzed using the Weibull approach. Basically, lower breakdown fields are observed with increasing temperatures up to 300 °C with a characteristic breakdown field strength E ₀ following the relationship $\sqrt {E_{0} } \propto T$ as reported in literature for similar measurements performed at silicon nitride thin films. From the intersection of this linear behavior, the Poole–Frenkel (PF) barrier height ? _B is determined to 0.54 eV, which is reasonable for AlN thin films. The slope of this relation is similar to values reported for silicon nitride thin films. This allows an estimation of the breakdown field at higher temperatures by extrapolation. Leakage current measurements show a dominant PF type conduction mechanism, verifying the applicability of $\sqrt {E_{0} } \propto T$ . No breakdown occurs in negative field direction, which is attributed to the metal–insulator–semiconductor configuration of the sample and hence, the presence of a depletion layer forming in the n-doped silicon and dominating the leakage current behavior.     

CLASSIFICATION OF REACTIVE DISTILLATION PROCESSES BY DIMENSIONLESS NUMBERS

In the present paper a comparative consideration is given for the physico-chemical phenomena involved in homogeneously and heterogeneously catalyzed reactive distillation processes (RDP). The processes are classified qualitatively by dimensionless parameter groups derived from the balances for vapor, liquid and solid phases according to the principles of irreversible thermodynamics. The groups are applied to analyze industrial processes and experimental data for esterification, etherification and alkylation regarding different catalysts, operating conditions and configurations of plants. The mathematical models published until today and the experimental results are contrasted taking the parameter groups as a basis. This gives a discrimination of the models and some recommendations for their applicability.     

Cytotoxic effects of ether lipids and derivatives in human nonneoplastic bone marrow cells and leukemic cells in vitro

The effects of 2-lysophosphatidylcholine (2-LPC), the alkyl lysophospholipid derivatives (ALP) 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH₃) and 1-O-hexadecyl-sn-glycero-3-phospho-trimethyl-ammonio-hexanol, the 2-acetamide analog of platelet-activating factor (PAF) 1-O-octadecyl-2-acetamide-sn-glycero-3-phosphocholine, the thioether lysophospholipid derivative (TLP) BM 41.440 and the ether-linked lipoidal amine CP-46,665 on tritiated thymidine uptake and trypan blue dye exclusion were tested in vitro in various freshly explanted cell samples from human nonneoplastic bone marrow and human leukemias. In both assay systems, a dose range of 1–20 μg/ml of the compounds was tested after 24, 48 and 72 hr of coincubation with the cells. The trypan blue dye exclusion revealed statistically significant preferential cytotoxicity in leukemic cells for three compounds with the order of quantitative selectiveness: ET-18-OCH₃>BM41.440>2-acetamide analog of PAF. CP-46,665 was the most toxic compound, but did not reveal significant differences between nonneoplastic bone marrow and leukemic cells when added in concentrations greater than 1 μg/ml. The trimethyl-ammoniohexanol compound showed only minor activity in the majority of tests, when added at concentrations <20 μg/ml. 2-LPC was rather ineffective. The tritiated thymidine uptake showed only preferential antiproliferative effects towards leukemic cells of ET-18-OCH₃ and, sometimes, within the dose time frame tested of BM 41.440. All compounds tested except 2-LPC and the trimethyl-ammonio-hexanol compound were active also in this assay (inhibition of uptake>50% of the controls). Based on these results, ET-18-OCH₃ and BM 41.440 are recommended for experimental bone marrow purging.