Summary: Syndiotactic polystyrene (sPS)/organophilic clay nanocomposites were obtained by in situ coordination‐insertion polymerization of styrene. Two cationic surfactants (alkylammonium and alkylphosphonium) were used for the intercalation of montmorillonite (MMT). For each organically modified clay, three protocols were performed using an MAO‐activated hemi‐metallocene catalyst, in order to compare the influence of experimental conditions on the composite microstructure and on its thermal stability. The microstructures of nanocomposites were investigated by wide angle X‐ray scattering and DSC. Partially exfoliated or intercalated materials were obtained in all cases and a decrease of crystallinity is observed. Thermal properties were also studied by DSC and thermogravimetric analysis. The presence of clay does not have a strong influence on the sPS thermal transitions but the thermal decomposition process of the material was slowed down in the presence of few organoclay percents, particularly in the degradation beginning. The influence of these two organically modified clays on the thermal stability of the material is discussed.
Gel and suspension formed from the combination of cloisite with toluene (left) and styrene (right), respectively. 相似文献
The NLP community has shown a renewed interest in deeper semantic analyses, among them automatic recognition of semantic relations
in text. We present the development and evaluation of a semantic analysis task: automatic recognition of relations between
pairs of nominals in a sentence. The task was part of SemEval-2007, the fourth edition of the semantic evaluation event previously
known as SensEval. Apart from the observations we have made, the long-lasting effect of this task may be a framework for comparing
approaches to the task. We introduce the problem of recognizing relations between nominals, and in particular the process
of drafting and refining the definitions of the semantic relations. We show how we created the training and test data, list
and briefly describe the 15 participating systems, discuss the results, and conclude with the lessons learned in the course
of this exercise. 相似文献
Wind energy systems have been considered for Canada's remote communities in order to reduce their costs and dependence on diesel fuel to generate electricity. Given the high capital costs, low-penetration wind–diesel systems have been typically found not to be economic. High-penetration wind–diesel systems have the benefit of increased economies of scale, and displacing significant amounts of diesel fuel, but have the disadvantage of not being able to capture all of the electricity that is generated when the wind turbines operate at rated capacity.Two representative models of typical remote Canadian communities were created using HOMER, an NREL micro-power simulator to model how a generic energy storage system could help improve the economics of a high-penetration wind–diesel system. Key variables that affect the optimum system are average annual wind speed, cost of diesel fuel, installed cost of storage and a storage systems overall efficiency. At an avoided cost of diesel fuel of 0.30 $Cdn/kWh and current installed costs, wind generators are suitable in remote Canadian communities only when an average annual wind speed of at least 6.0 m/s is present. Wind energy storage systems become viable to consider when average annual wind speeds approach 7.0 m/s, if the installed cost of the storage system is less than 1000 $Cdn/kW and it is capable of achieving at least a 75% overall energy conversion efficiency. In such cases, energy storage system can enable an additional 50% of electricity from wind turbines to be delivered. 相似文献
This paper presents an innovative concept for optimized air diffusion in buildings. The method uses passive control of air jet through lobed diffusers. An analysis is done experimentally at different scales for a lobed shaped geometry. A cross-shaped jet is characterized first through an isolated orifice and then at the scale of one perforated panel. An intermediary analysis of two coalescent and a row of cross-shaped jets is also proposed. All the results lead to the same conclusion. The lobed diffuser favors the self-induction compared to a reference conventional circular perforated diffuser. The air flow induced in the case of the lobed perforated panel is in average twice as the one of the circular perforated panel. Despite the consequent gain in air induction for the lobed perforated panel flow, the streamwise maximum velocities display comparable values in the far field which signifies comparable throws for the two flows. Consequently, the presented lobed perforated panel concept can be generalized to different type of diffusers to improve mixing ventilation in buildings. 相似文献
This paper presents an overview of the results obtained at the Industrial Materials Institute (IMI) on the numerical simulation of the gas‐assisted injection molding and co‐injection molding. For this work, the IMI's three‐dimensional (3D) finite element flow analysis code was used. Non‐Newtonian, non‐isothermal flow solutions are obtained by solving the momentum, mass and energy equations. Two additional transport equations are solved to track polymer/air and skin/core materials interfaces. Solutions are shown for different thin parts and then for thick three‐dimensional geometries. Different operating conditions are considered and the influence of various processing parameters is analyzed. 相似文献
This paper deals with the methods of three-dimensional fixed-point wind speed real-time simulation modelled in large band, in order to use them in test rigs for experimental investigation of the wind energy conversion systems. The medium- and long-term components of the non-stationary wind speed are considered as known, being issued from measured data or by adopting a generic model. The spectral characteristics of three-dimensional turbulence are described either by the Kaimal or the von Karman models. The turbulence intensity and the length scale that take part in these models are calculated by the site parameters, using current standards. The basic idea of the methods for large-band three-dimensional wind simulation is to use rational shaping filters that approximate non-integer orders shaping filters issued from the Kaimal and the von Karman models. All the synthesized rational shaping filters use one time constant, automatically adapted to the medium- and long-term components that pilot the other time constants of the shaping filters by a set of parameters practically constant. Some numerical results concerning time series that simulate the non-stationary wind speed with three-dimensional turbulence components based on Kaimal and von Karman models are presented. 相似文献
The general context of the present study is the design of high induction HVAC air diffusers by means of passive jet control. When the diffuser is a perforated panel with lobed orifices (Meslem et al. 2010), the optimization of jet induction consists in improving the orifice’s geometry, the spacing between orifices and their arrangement on the panel. In this study, the flow field of a turbulent twin cross-shaped jet is investigated numerically using the standard k-ε model, the Shear Stress Transport (SST) k-ω model and the Reynolds Stress Model (RSM). The results are compared with PIV measurements. The objective is to assess their capability and limitations to predict the significant features of twin jet flow when the flow is numerically resolved through a lobed diffuser. It is shown that the k-ε and RSM models are more appropriate for predicting potential jet core length, the change in jet centreline streamwise velocity, and flow expansion in the symmetry plane of the twin jet flow. However, these models overestimate the overall flow expansion and the jet volumetric flow rate. The SST k-ω model seems more appropriate for the prediction of such dynamic integral quantities. A high level of turbulent kinetic energy predicted by the k-ε and RSM models in the near field of jets is probably the reason for this overestimation of jet induction. The SST k-ω model would appear to be the most appropriate tool for optimizing orifice design, orifice to orifice spacing and relative orifice orientation on a perforated panel diffuser. 相似文献
This paper presents a finite element model for the three-dimensional simulation of industrial mold filling and solidification problems. The finite element solutions of mold filling problems involve highly convective fluid flow coupled with free surface, heat transfer, nonconstant material properties, and complex three-dimensional geometries. They present unusual challenges for both the finite element modeling and numerical solution algorithms. In this work a segregated algorithm is proposed to solve Navier-Stokes, energy, and front tracking equations. The streamline upwind Petrov-Galerkin formulation is used to obtain stable solutions. The position of the free surface is modeled using a level-set approach. The whole procedure is shown to present the accuracy, robustness, and cost-effectiveness needed for complex three-dimensional industrial applications. 相似文献