Improving the Physicochemical Properties of Fe–25Cr Ferritic Steel for SOFC Interconnects via Y-Implantation and Y2O3-Deposition

The present study investigated the role of the reactive-element effect (REE) in improving the corrosion resistance, chromium vaporization rate, and electrical conductivity of the Fe–25Cr ferritic steel modified either by means of yttrium implantation or chemical deposition of yttrium oxide from metaloorganic compound vapors. The corrosion kinetics of the Fe–25Cr steel, both pure and modified, were determined under isothermal conditions in air and an Ar–H₂–H₂O gas mixture at 1,073 K. A significant improvement in corrosion resistance was observed after surface modification. XRD and SEM–EDS investigations showed that the protective Cr₂O₃ layer formed the main part of the scale. Measurements of Cr vaporization rate in the air–H₂O gas mixture revealed that both surface modifications of the steel significantly suppressed the formation of volatile chromium compounds to a large degree. The yttrium-implanted steels oxidized both in air and the Ar–H₂–H₂O mixture were characterized by the lowest area specific resistance and thereby did not exceed the acceptable ASR level (0.1 Ω cm²) for interconnect materials in the temperature range of 973–1,073 K, unlike pure steel and the steel coated with Y₂O₃.     

A new formula for determining a minimum recommended value of inlet air velocity from UFAD system to prevent occupants from draught risk

During the winter period the natural convection flow along a cold window surface can be the cause of thermal discomfort. Warm air blown into the room near the window prevents occupants from draught risk. The paper presents a new formula for determining a minimum recommended value of inlet air velocity. A balance of a momentum flux of flow of the down draught currents and the warm air jet inflow from the UFAD (under floor air distribution) system was a base for the analytical solution. In order to estimate air movement in a typical room, numerical simulations are executed. A computational model of the room with the UFAD system is constructed within the CFD environment developed by Fluent Inc. Ten cases with varying inlet air parameters and a window U$U$-value are considered. The analytical estimation of minimum inlet air velocity is confirmed by simulation results of temperature and velocity distributions.     

The accuracy of a solid packing fraction model in recognizing zones of different dendritic structures

A front tracking method on a fixed control-volume grid, based on assumed dendrite tip kinetics, is applied to discuss the accuracy of a numerical model where the coherency solid fraction is used in the identification of diverse dendritic regions developing within a mushy zone during binary alloy solidification driven by diffusion and thermo-solutal buoyancy forces. It is shown that this critical value of a solid volume fraction is not constant but changes with time and along the border separating the regions.     

Determination of thoron equilibrium factor from simultaneous long-term thoron and its progeny measurements

With 3-month simultaneous measurements of thoron and its progeny concentrations in the lowest floors of 109 homes, the geometric mean (GM) of thoron equilibrium factor was determined to be 0.019 with a geometric standard deviation (GSD) of 3.63. Combined with the analysis from results obtained from a previous study in 138 homes, the GM of thoron equilibrium factor was determined to be 0.022 with a GSD of 3.02. The results indicate that the F value of 0.02 for thoron recommended by UNSCEAR is a reasonable value for those Canadian homes tested.     

On Nonparametric Identification of Wiener Systems

In this paper, a new method for the identification of the Wiener nonlinear system is proposed. The system, being a cascade connection of a linear dynamic subsystem and a nonlinear memoryless element, is identified by a two-step semiparametric approach. The impulse response function of the linear part is identified via the nonlinear least-squares approach with the system nonlinearity estimated by a pilot nonparametric kernel regression estimate. The obtained estimate of the linear part is then used to form a nonparametric kernel estimate of the nonlinear element of the Wiener system. The proposed method permits recovery of a wide class of nonlinearities which need not be invertible. As a result, the proposed algorithm is computationally very efficient since it does not require a numerical procedure to calculate the inverse of the estimate. Furthermore, our approach allows non-Gaussian input signals and the presence of additive measurement noise. However, only linear systems with a finite memory are admissible. The conditions for the convergence of the proposed estimates are given. Computer simulations are included to verify the basic theory     

Minimizing the Distortion of Steel Profiles by Controlled Cooling

A complex thermomechanical model is introduced for the simulation of the transient fields of temperature and stresses during the quenching of steel products. The material behaviour is an extension of the classical J₂‐plasticity theory with the extension of temperature and phase fraction dependent yield criteria. The coupling effects, i.e., dissipation of mechanical energy, transformation induced plasticity (TRIP), and phase transformation enthalpy, are considered. The model is used for the determination of the optimal cooling or quenching for reducing the distortion in the long steel profiles. The simulation results are presented in order to investigate the effects of material properties, boundary conditions, profile size and geometry. In the simulations, L‐, T‐ and U‐profiles made of steel C45 and steel C80 are considered. It is demonstrated that with a higher cooling rate in the mass lumped regions of the profiles, the distortion can be reduced.     

Spatially resolved luminescence properties of ZnO tetrapods

ZnO tetrapods were prepared by Zn-vapour deposition at 740 °C in Argon and subsequent oxidation in air for 1–30 min. The photoluminescence (PL) and cathodoluminescence (CL) spectra were measured from ZnO particles collected at various distances from the Zn source representing decreasing dimensions. The ZnO tetrapods showed a green emission centred at 516 nm (2.40 eV) band and the exciton emission at 387 nm (3.20 eV). The measured data suggested that the green emission is strongly increased for particle sizes below 500 nm, whereas the exciton emission is dominant for particle size larger than 500 nm. Spatially resolved CL-measurement on individual tetrapod legs showed, that the green emission increases with decreasing ZnO leg diameter. To our knowledge, the local CL spectroscopic measurements were correlated with the dimensions of the individual ZnO tetrapods for the first time.     

Tagung „Frontiers of E-Voting“, 29. Juli bis 3. August auf Schloss Dagstuhl

Ohne Zusammenfassung     

Purification and characterization of aPenicillium sp. lipase which discriminates against diglycerides

A lipase was isolated fromPenicillium sp. strain UZLM-4 and characterized. This lipase has a molecular weight of 27,344 (determined by mass spectrometry) and hydrolyzes triglycerides in preference to mono- and diglyceride substrates. Among various triglyceride substrates, tributyrin is hydrolyzed about four times faster than any other tested. The lipase has a preference for hydrolysis at the 1,3 positions of the lipids and shows a weak stereoselectivity for the S enantiomer. Unlike most other lipases, this lipase is stable and has a high activity at low surface pressures (5–10 mN/m).     

负气门叠开方式下天然气的均质压燃(HCCI)

天然气的自燃温度较高,要达到其自燃必须采用高压缩比和进气加热,另外一种方法是利用负气门叠开在缸内驻留废气,以减少所需要的进气加热量。本文采用特殊阀的策略,通过与汽油进行对比,发现在相同的发动机负荷下,天然气HCCI需要使用较迟后的气门定时,这导致缸内将截获较少量的废气,因而减小了稀释的效果,使得NOx的排放增加。