Mechanistic peculiarities of the N2O reduction by CH4 over Fe-silicalite

Transient isotopic studies in the temporal analysis of products (TAP) reactor evidenced the importance of the lifetime of oxygen species generated upon N₂O decomposition on extraframework iron sites of Fe-silicalite for methane oxidation at 723 K. Fe-silicalite effectively activates CH₄ when N₂O and CH₄ are pulsed together in the reactor. However, these oxygen species gradually become inactive for methane oxidation as the time delay between the N₂O and CH₄ pulses is increased from 0 to 2 s.     

Characterization of catalysts and membrane in DMFC lifetime testing

The lifetime and performance of a direct methanol fuel cell (DMFC) were investigated to understand the correlation between the structure of catalysts/membrane and cell performance versus time. The cell polarization and performance curves were obtained during the DMFC operation with the time. The catalysts and Nafion^® membrane of the membrane electrode assembly (MEA) from the lifetime test were comprehensively examined by XRD, HRTEM, FTIR and Raman spectroscopy techniques. The results revealed that there was significant performance degradation during the first 200 h operation; while the degradation was slowing down between 200 and 704 h operation. The degradation became worse after 1002 h operation. The increases of the catalyst particle size from both anode and cathode catalysts were observed after the DMFC lifetime test. The changes of microstructure, surface composition, the interfacial structure of the MEA, and the aging of Nafion^® under the DMFC lifetime tests were also observed.     

热障涂层失效机制和寿命预测研究概述

对热障涂层失效机制和寿命预测研究进行了概述,描述了导致热障涂层在服役过程中失效的几种主妻因素,并介绍了几种热障涂层寿命预测模型。     

A simple optode based method for imaging O2 distribution and dynamics in tap water biofilms

A ratiometric luminescence intensity imaging approach is presented, which enables spatial O₂ measurements in biofilm reactors with transparent planar O₂ optodes. Optodes consist of an O₂ sensitive luminescent dye immobilized in a 1-10 μm thick polymeric layer on a transparent carrier, e.g. a glass window. The method is based on sequential imaging of the O₂ dependent luminescence intensity, which are subsequently normalized with luminescent intensity images recorded under anoxic conditions. We present 2-dimensional O₂ distribution images at the base of a tap water biofilm measured with the new ratiometric method and compare the results with O₂ distribution images obtained in the same biofilm reactor with luminescence lifetime imaging. Using conventional digital cameras, such simple normalized luminescence intensity imaging can yield images of 2-dimensional O₂ distributions with a high signal-to-noise ratio and spatial resolution comparable or even surpassing those obtained with expensive and complex luminescence lifetime imaging systems. The method can be applied to biofilm growth incubators allowing intermittent experimental shifts to anoxic conditions or in systems, in which the O₂ concentration is depleted during incubation.     

Oxygen distribution on a multicrystalline silicon ingot grown from upgraded metallurgical silicon

Oxygen precipitation creates centers of recombination of carriers. Therefore, oxygen concentration and its chemical configuration must be controlled. In this study, the oxygen distribution on a multicrystalline silicon ingot produced by directional solidification of upgraded metallurgical silicon is investigated. The highest amount of oxygen was detected close to the bottom of the ingot. Most of the oxygen present was interstitial but there were approximately 5-10 ppma oxygen present as precipitates. FT-IR and TEM confirmed the presence of many oxygen precipitates, mainly segregated at grain boundaries and dislocations. Lifetime measurements by QSSPC were performed on as grown- and passivated wafers, and after P-gettering. A correlation between the lifetime values and the presence of oxygen precipitates has been found and it has been shown that the electrical properties could be improved if an appropriate annealing step would be applied. Oxygen content may dramatically reduce the solar cell performances and efficiencies (estimated reduction of 1-3% absolute values).     

The risk of power loss in crystalline silicon based photovoltaic modules due to micro-cracks

Micro-cracks in wafer based silicon solar cell modules are nowadays identified by a human observer with the electroluminescence (EL) method. However, the essential question of how the micro-cracks affect the PV module performance has yet to be answered. We experimentally analyze the direct impact of micro-cracks on the module power and the consequences after artificial aging. We show that the immediate effect of micro-cracks on the module power is small, whereas the presence of micro-cracks is potentially crucial for the performance of the module after artificial ageing. This confirms the necessity to develop the means of quantifying the risk of power loss in PV modules with cracked solar cells in their lifetime, in order to enable manufacturers to discard defective modules with high risk of failure while keeping modules with uncritical micro-cracks. As a first step towards risk estimation we develop an upper bound for the potential power loss of PV modules due to micro-cracks in the solar cells. This is done by simulating the impact of inactive solar cell fragments on the power of a common PV module type and PV array. We show that the largest inactive cell area of a double string protected by a bypass diode is most relevant for the power loss of the PV module. A solar cell with micro-cracks, which separate a part of less than 8% of the cell area, results in no power loss in a PV module or a PV module array for all practical cases. In between approximately 12 and 50% of inactive area of a single cell in the PV module the power loss increases nearly linearly from zero to the power of one double string.     

Oscillator strengths of allowed transitions for O III

The electric dipole oscillator strengths for lines in O III between some singlet and triplet levels have been calculated using the weakest bound electron potential model theory and the quantum defect orbital theory. In the calculations, both multiplet and fine-structure transitions are studied. The calculated oscillator strengths have been compared with available theoretical and experimental results. Good agreement with results in the literature has been obtained.     

Porous silicon and aluminum co-gettering experiment in p-type multicrystalline silicon substrate

The lifetimes of non-equilibrium minority carriers, which bound with the diffusion length, are considered as two important parameters of the low-quality multicrystalline silicon (mc-Si) substrate. Its value defines the quality of the initial substrate. It is also subjected to change as a result of many high-temperature operations during the device fabrication. Therefore, it is necessary to incorporate certain processing steps that either improve or preserve the electronic quality of the mc-Si substrate. In this study, a novel porous silicon and aluminum co-gettering experiment has been applied as a beneficial approach to improve the electronic quality of the low-resistivity mc-Si substrates. Porous silicon layers were prepared by anodization of the n⁺ silicon region by a simple electrochemical etching process using an aqueous HF-based electrolyte, which leads to the creation of porous silicon microcavities. Besides making porous silicon and aluminum co-gettered samples, both phosphorous and aluminum alloy-gettered samples and reference samples were made. The gettering-induced lifetime enhancement in the test samples was monitored by measuring the lifetime/diffusion length of the test samples using two independent methods such as photoconductivity decay (PCD) measurement and the photocurrent generation method (PCM), respectively. The result in both the measurements has shown a reasonably good agreement with each other. Therefore, it is inferred that the applied co-gettering experiment has a synergetic effect to improve the lifetime of the mc-Si substrate.     

I: Dispersibility of robust alumina particles in non-aqueous solution

This article presents the preparation of well dispersed alumina slurries containing relatively large alumina particles that can withstand accelerated weather conditions. Besides using conventional dispersants such as phosphate esters and menhaden fish oil, dispersants widely used in the surface coatings industries such as Disperbyk 110 and Triton X 100 have also been employed. However, sedimentation tests, sediment density, viscosity and gloss measurements indicate the failure of the anionic dispersants as well as menhaden fish oil to disperse the alumina particles in non-aqueous medium. Instead the binder polyvinyl butyral itself acts as the best dispersant. The well dispersed alumina slurry is stabilized in the presence of a commercially available rheology modifier, Bentone SD2 for a period of 144 h at 60 °C. The rheological behavior of the aged sample was studied under various conditions. Although a rise in viscosity of the suspension was observed when the slurry was exposed to accelerated weather conditions, a lower shear thinning index and higher gloss values indicate a better dispersion state with aging.     

Load balancing techniques for lifetime maximizing in wireless sensor networks

Energy consumption has been the focus of many studies on Wireless Sensor Networks (WSN). It is well recognized that energy is a strictly limited resource in WSNs. This limitation constrains the operation of the sensor nodes and somehow compromises the long term network performance as well as network activities. Indeed, the purpose of all application scenarios is to have sensor nodes deployed, unattended, for several months or years.This paper presents the lifetime maximization problem in “many-to-one” and “mostly-off” wireless sensor networks. In such network pattern, all sensor nodes generate and send packets to a single sink via multi-hop transmissions. We noticed, in our previous experimental studies, that since the entire sensor data has to be forwarded to a base station via multi-hop routing, the traffic pattern is highly non-uniform, putting a high burden on the sensor nodes close to the base station.In this paper, we propose some strategies that balance the energy consumption of these nodes and ensure maximum network lifetime by balancing the traffic load as equally as possible. First, we formalize the network lifetime maximization problem then we derive an optimal load balancing solution. Subsequently, we propose a heuristic to approximate the optimal solution and we compare both optimal and heuristic solutions with most common strategies such as shortest-path and equiproportional routing. We conclude that through the results of this work, combining load balancing with transmission power control outperforms the traditional routing schemes in terms of network lifetime maximization.