Effects of manganese oxide addition and reductive atmosphere annealing on the phase stability and microstructure of yttria stabilized zirconia

The effects of Mn₃O₄ addition and reductive atmosphere (N₂:H₂ = 97:3) annealing on the microstructure and phase stability of yttria stabilized zirconia (YSZ) ceramics during sintering at 1500 °C for 3 h in air and subsequent annealing in a reductive atmosphere were investigated. Mn₃O₄ added 6 mol% YSZ (6YSZ) and 10 mol% YSZ (10YSZ) ceramics were prepared via the conventional solid-state reaction processes. The X-ray diffraction results showed that a single cubic phase of ZrO₂ was obtained in 1 mol% Mn₃O₄ added 6YSZ ceramic at a sintering temperature of 1500 °C for 3 h. A trace amount of monoclinic ZrO₂ phases were observed for 1 mol% Mn₃O₄ added 6YSZ ceramics after annealing at 1300 °C for 60 cycles in a reductive atmosphere by transmission electron microscopy. Furthermore, a single cubic ZrO₂ phase existed stably as Mn₃O₄ added 10YSZ ceramics was annealed at 1300 °C for 60 cycles in reductive atmosphere.     

Assessment of redox behavior of nickel ferrite as oxygen carriers for chemical looping process

This study investigated the suitability of using nickel ferrite (NiFe₂O₄) oxygen carriers for a chemical looping process. NiFe₂O₄ powder was prepared by ball milling equimolar NiO and Fe₂O₃ in a high temperature solid-state reaction. Material characteristics of NiFe₂O₄ samples were investigated by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area measurements, and scanning electron microscopy (SEM). Redox cycling of NiFe₂O₄ oxygen carriers was performed by thermogravimetric (TGA) measurement under pure CH₄ gas and O₂/Air atmospheres, respectively. After five successive cycles, NiFe₂O₄ powder with a single phase of spinel structure demonstrated higher redox cycling behavior and better stability than standard NiO and Fe₂O₃. We also addressed the mechanism underlying the redox cycling by NiFe₂O₄ spinel powder. Our results demonstrate the feasibility of using the proposed preparation of NiFe₂O₄ as an oxygen carrier in a reversible chemical looping process (CLP).     

A Review of Pinealectomy-Induced Melatonin-Deficient Animal Models for the Study of Etiopathogenesis of Adolescent Idiopathic Scoliosis

Adolescent idiopathic scoliosis (AIS) is a common orthopedic disorder of unknown etiology and pathogenesis. Melatonin and melatonin pathway dysfunction has been widely suspected to play an important role in the pathogenesis. Many different types of animal models have been developed to induce experimental scoliosis mimicking the pathoanatomical features of idiopathic scoliosis in human. The scoliosis deformity was believed to be induced by pinealectomy and mediated through the resulting melatonin-deficiency. However, the lack of upright mechanical spinal loading and inherent rotational instability of the curvature render the similarity of these models to the human counterparts questionable. Different concerns have been raised challenging the scientific validity and limitations of each model. The objectives of this review follow the logical need to re-examine and compare the relevance and appropriateness of each of the animal models that have been used for studying the etiopathogenesis of adolescent idiopathic scoliosis in human in the past 15 to 20 years.     

Morphological studies of randomized dispersion magnetite nanoclusters coated with silica

In this study, we report a simple way to produce randomized dispersion magnetite nanoclusters coated with silica (RDMNS) via Stöber process with minor modifications. The morphology of silica coated magnetite nanoclusters was emphasized by studying various reaction parameters including alcohols with different polarities as co-solvents, concentration of alcohol-water, concentration of alkaline catalyst (ammonia), and concentration of TEOS monomer. The results of transmission electron microscope (TEM) showed that the sizes and morphological behaviour of the magnetite nanoclusters vary accordingly with the different reaction parameters investigated. The results showed that ethanol would be the best candidate as co-solvent in the preparation of randomized dispersion magnetite nanoclusters. Besides, the optimum alcohol-water ratio has been determined to be 70-30% v/v as this concentration range could render desired shape of randomized dispersion magnetite nanoclusters. The volume of ammonia (NH₃) catalyst in the reaction media also strongly governs the formation of silica coated magnetite nanoclusters in a desired shape. Apart from that, the addition of TEOS monomer into the reaction media has to be well-controlled as the excess amount of monomer added might affect the thickness of the silica layer that is coated on the magnetite nanoparticles. Prior to silica coating, the bare magnetite nanoparticles were first treated with trisodium citrate (0.5 M) to enhance the particles’ dispersibility. Improvement in the size distribution and dispersibility of the magnetite nanoparticles after the citrate treatment has been examined using TEM. The XRD results show that the magnetite samples retained good crystallinity although they have been surface-modified with citrate group and silica. The Fourier transform infrared (FT-IR) and thermogravimetric analysis (TGA) prove that the magnetite nanoparticles have been successfully coated with citrate and silica. The superparamagnetic behaviour of the magnetite samples was confirmed by VSM. The produced silica coated magnetite nanoclusters possess great potential to be applied in bio-medical research and clinical diagnosis application.     

Differences in curing behavior of cocured and IPN materials

This study addressed the blending and cocuring of resole and epoxy, using NaOH and 4,4′‐diaminodiphenylmethane as curing agents. IR band shifts regarding the molecular interactions were investigated with FTIR. Exothermic peak shifts during cocuring reactions were studied with dynamic DSC. Viscosity increases were measured with a Brookfield LVT viscometer at 100°C. The dynamic mechanical properties of the cocured samples were investigated using rheometric dynamic spectroscopy (RDS). Experimental results revealed that the molecular interactions between resole and epoxy resulted in good compatibility as shown by the single damping peak in the RDS curve and the single glass transition for each cocured sample. Also apparent were accelerated curing rates, leading to shifts of the exothermic peaks to lower temperature and faster viscosity increases. Nevertheless, enhanced gel fractions and increased glass‐transition temperatures (T_g) of the samples were generally observed for this cocured system. The average molecular weight between crosslinked points calculated for the cocured materials also showed much less than the two components. These curing behaviors were quite different from those of the Interpenetrating Polymer Network (IPN) materials, which usually indicated lowered gel fractions, decreased T_g, and higher average molecular weight between crosslinkings than for components. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 963–969, 2001     

Triple-shape memory properties of thermoplastic polyurethane/olefin block copolymer/polycaprolactone blends

Thermoplastic polyurethane (TPU)/olefin block copolymer (OBC)/polycaprolactone (PCL) blends (70/20/10 and 50/30/20) were melt-blended to form the first environmental OBC-based triple-shape memory polymer blends. In this work, PCL with low crystalline temperature (switching phase), OBC with medium crystalline temperature (switching phase), and TPU with high crystalline temperature (fixed phase) could form an alternative triple-shape memory polymer (TSMP). Two compatibilizers, OBC-g-glycidyl methacrylate (OBC-g-GMA) and dicumyl peroxide, were confirmed to show a synergistic effect in enhancing the compatibility further through the morphological observation. Crystallinity of both OBC and PCL in the blends with or without modification decreased in comparison with that of pure resin. For dual-shape behaviors, the shape fixing ratio (R_f) and shape recovery ratio (R_r) were up to 96.3% and 91.2% for the GMA and peroxide-modified blends (50/30/20). The higher amount of TPU didn’t give higher recovery ratio, but instead slightly lower R_r due to the morphology difference. For triple-shape behaviors, both TPU/OBC/PCL blend compositions with or without GMA or peroxide modifications gave high R_f(C→B) values in the first fixing stage, but slightly lower values R_f(B→A) in the second fixing stage, especially for (70/20/10) case. On the other hand, a reverse trend was observed for two recovery stages. To enhance the R_f(B→A) in the second fixing stage, higher deformation temperatures were considered, and a measurable increment on R_f(B→A) was attained. Through this subtle adjustment on the temperature difference between high and low deformation temperatures, the theoretical multi-shape memory shape could be readily tailored to meet different applications.     

Comparative study of different numerical models of packed bed thermal energy storage systems

This paper presents, compares and validates two different mathematical models of packed bed storage with PCM, more specifically the heat transfer during charge of the PCM. The first numerical model is a continuous model based on the Brinkman equation and the second numerical model treats the PCM capsules as individual particles (energy equation model). Using the Brinkman model the flow field inside the porous media and the heat transfer mechanisms present in the packed bed systems can be described. On the other hand, using the energy equation model the temperature gradient inside the PCM capsules can be analysed. Both models are validated with experimental data generated by the authors. The experimental set up consists mainly of a cylindrical storage tank with a capacity of 3.73 L full of spherically encapsulated PCM. The PCM used has a storage capacity of 175 kJ/kg between ?2–13 °C. The results from the energy equation model show a basic understanding of cold charging. Moreover, three different Nu correlations found in the literature were analysed and compared. All of them showed the same temperature profile of the PCM capsules; hence any of them could be used in future models. The comparison between both mathematical models indicated that free convection is not as important as forced convection in the studied case.     

Maximum bandwidth routing and maximum flow routing in wireless mesh networks

The emergence of nomadic multimedia applications, such as multimedia conferencing, distance learning, video phones, video/movie-on-demand, and education-on-demand, has recently generated much interest in multi-hop wireless mesh networks (WMNs) to support diverse Quality-of-Service (QoS). In the existing WMN QoS routing protocols, the methods of bandwidth calculation and allocation were proposed to determine routes with bandwidth guaranteed for QoS applications. This paper studies two NP-hard problems, the maximum bandwidth routing problem (abbreviated to MBRP) and the maximum flow routing problem (abbreviated to MFRP). Given a source node s and a destination node d in a multi-hop wireless mesh network, the MBRP is to determine an s-to-d path that can carry a maximum amount of traffic from s to d and the MFRP is to determine the maximum flow from s to d, both retaining the network bandwidth-satisfied. In this paper, heuristic algorithms for the two problems are proposed. Upper bounds on their optimal values are derived, and a lower bound is derived on the feasible value obtained for the MBRP. With the upper bound and the lower bound, an approximation ratio for the heuristic algorithm of the MBRP is obtained. The effectiveness of the heuristic algorithms is further verified by experiments. A generalized interference model is also discussed.