Ring opening polymerization of oxetane by the use of a montmorillonite clay as catalyst

Maghnite-H⁺ was found to be an effective solid catalyst for the ring opening polymerization of oxetane. Maghnite-H⁺ is a proton exchanged montmorillonite clay. Effect of weight ratio of initiator/monomer and reaction time on the conversion of monomer and the molecular weight is investigated. Increasing maghnite-H⁺ proportion produced an increase in oxetane conversion and a decrease in Mn. A cationic mechanism for the reaction was proposed.     

Improvement of the heat transfer quality by air cooling of three-heated obstacles in a horizontal channel using the lattice Boltzmann method

This study focuses on the cooling of three heated obstacles with different heights mounted on the bottom of the channel wall using different aspects that influence the enhancement of the heat exchange, as is known in the concept of cooling electronic devices. The lattice Boltzmann method associated with multiple relaxation times (LBM-MRT) was adopted to simulate the physical configurations of the studied system. In this context, the D2Q9 and D2Q5 models are applied to describe the fluid flow behavior and conjugate heat transfer, respectively. The evaluation of heat exchange between the cold fluid and three-heated obstacles has been accurately analyzed under the effect of several parameters such as Reynolds number, obstacle spacing, and thermal conductivity ratio. In addition, the setting of two and three fluids flow inlets were also studied. The results are presented in terms of streamlines, isotherms, and local Nusselt curves. The heat transfer increases with increasing solid-fluid thermal conductivity. It is also more pronounced for large Reynolds numbers. Moreover, the heat transfer significantly enhances for the second and third obstacles when obstacle spacing increases. The improvement of the heat transfer is performed by the implementation of several jet flows in the studied system.     

On the producibility of composite position tolerance specifications for patterns of holes

A composite position tolerance verification algorithm is embedded in a simulation program to explore the producibility of three composite position tolerance variants for patterns of holes. The influence of some selective design and manufacturing variables on producibility is simulated and evaluated. It is shown that design variables such as specification variant, material condition modifier and number of holes in the pattern have a significant influence on producibility. The influence of manufacturing variables such as orientation error and numerical control path programming in the presence of axis reversal error are also simulated and discussed. Detailed graphs of these effects are presented and discussed.     

Fluorescence quenching of fluoranthene by maleic anhydride in solution and during nonreactive and reactive twin‐screw extrusion

Fluorescence quenching of fluoranthene by maleic anhydride (MAH) in polypropylene (PP) during twin‐screw extrusion (TSE) was investigated using an online fluorescence measurement system. The fluorescence quenching effect was clearly seen from the decrease of the peak intensity and integrated area of the residence time distribution (RTD) curves when MAH was introduced into PP. Fluorescence quenching effect in TSE was compared with that in chloroform solution and in both cases, it followed the linear Stern‐Volmer equation although it showed lower quenching effect in TSE than in solution. Using this quenching phenomenon, it was possible to measure online the grafting degree of PP with MAH in the TSE. The obtained results showed that MAH grafting degree and total conversion measured by both fluorescence technique and by Fourier transform infrared spectroscopy were in good agreement for MAH weight concentrations up to 0.8 wt%. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Structural and elastic properties of TiN and AlN compounds: first-principles study

First-principles calculations of the lattice constants, bulk modulus, pressure derivatives of the bulk modulus and elastic constants of AlN and TiN compounds in rock-salt (B1) and wurtzite (B4) structures are presented. We have used the fullpotential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT) in the generalized gradient approximation (GGA) for the exchange-correlation functional. Moreover, the elastic properties of cubic TiN and hexagonal AlN, including elastic constants, bulk and shear moduli are determined and compared with previous experimental and theoretical data. Our results show that the structural transition at 0 K from wurtzite to rock-salt phase occurs at 10 GPa and ?26 GPa for AlN and TiN, respectively. These results are consistent with those of other studies found in the literature.     

Simulating microstructure evolution during passive mixing

The prediction of microstructure evolution during passive mixing is of major interest in order to qualify and quantify mixing devices as well as to predict the final morphology of the resulting blend. Direct numerical simulation fails because of the different characteristic lengths of the microstructure and the process itself. Micro-macro approaches could be a valuable alternative but the computational cost remains tremendous. For this reason many authors proposed the introduction of some microstructural variables able to qualify and quantify the mixing process at a mesoscale level. Some proposals considered only the effects induced by the flow kinematics, other introduced also the effects of shape relaxation due to the surface tension and coalescence. The most advanced integrate also the break-up process. However, the derivation of the evolution equations governing the evolution of such microstructural variables needs the introduction of some closure relations whose impact on the computed solution should be evaluated before applying it for simulating complex mixing flows. In this work we consider the Lee and Park??s model that considers the flow kinematics, the surface tension, the coalescence and the break-up mechanisms in the evolution of the area tensor. The accuracy of both a quadratic closure and an orthotropic relations will be analyzed in the first part of this work, and then the resulting closed model by using a quadratic closure will be used for simulating complex mixing flows.     

Proper generalized decomposition of time-multiscale models

Models encountered in computational mechanics could involve many time scales. When these time scales cannot be separated, one must solve the evolution model in the entire time interval by using the finest time step that the model implies. In some cases, the solution procedure becomes cumbersome because of the extremely large number of time steps needed for integrating the evolution model in the whole time interval. In this paper, we considered an alternative approach that lies in separating the time axis (one-dimensional in nature) in a multidimensional time space. Then, for circumventing the resulting curse of dimensionality, the proper generalized decomposition was applied allowing a fast solution with significant computing time savings with respect to a standard incremental integration. Copyright © 2011 John Wiley & Sons, Ltd.     

Revealing the Atomic Origin of Heterogeneous Li‐Ion Diffusion by Probing Na

Tracing the dynamic process of Li‐ion transport at the atomic scale has long been attempted in solid state ionics and is essential for battery material engineering. Approaches via phase change, strain, and valence states of redox species have been developed to circumvent the technical challenge of direct imaging Li; however, all are limited by poor spatial resolution and weak correlation with state‐of‐charge (SOC). An ion‐exchange approach is adopted by sodiating the delithiated cathode and probing Na distribution to trace the Li deintercalation, which enables the visualization of heterogeneous Li‐ion diffusion down to the atomic level. In a model LiNi_1/3Mn_1/3Co_1/3O₂ cathode, dislocation‐mediated ion diffusion is kinetically favorable at low SOC and planar diffusion along (003) layers dominates at high SOC. These processes work synergistically to determine the overall ion‐diffusion dynamics. The heterogeneous nature of ion diffusion in battery materials is unveiled and the role of defect engineering in tailoring ion‐transport kinetics is stressed.     

Application-specific multiprocessor Systems-on-Chip

It often happens that designers have to integrate different instruction-set processors on a single chip. Typical applications are wireless, image processing, xDSL, network and game processors. This paper deals with the three main problems that make the design of application-specific heterogeneous multiprocessor Systems-on-Chip very hard and expensive:

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higher level specification;

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software support packages design;

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on-chip HW/SW communication design.