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81.
The thermal diffusivity and sound speed of binary refrigerant mixtures of R143a (1,1,1-trifluoroethane) and R125 (pentafluoroethane) have been determined for both the saturated liquid and vapor phase using dynamic light scattering (DLS). Measurements were performed for four quite different mixture compositions over a wide temperature range from 293 to 345 K approaching the vapor-liquid critical point. The results obtained corroborate the usefulness of a simple prediction method for the determination of different thermophysical properties of multicomponent mixtures in the two-phase region up to the critical point. Besides the information on the properties for the pure components, the successful application of the prediction method is also based on an exact knowledge of the critical temperature. The composition dependence of the critical temperature has been determined by observation of the vanishing meniscus between liquid and vapor phases. The mixture results are discussed in detail and compared with available literature data. 相似文献
82.
A. P. Fröba L. Penedo Pellegrino A. Leipertz 《International Journal of Thermophysics》2004,25(5):1323-1337
Light scattering by thermally excited capillary waves on liquid surfaces or interfaces can be used for the investigation of viscoelastic properties of fluids. In this work, the simultaneous determination of surface tension and liquid kinematic viscosity of n-pentane by surface light scattering (SLS) on a gas–liquid interface was carried out. The experiments are based on a heterodyne detection scheme and signal analysis by photon correlation spectroscopy (PCS). Measurements were performed under saturation conditions over a wide temperature range from about 233 to 363 K. For the whole temperature range the total uncertainty of the liquid kinematic viscosity and surface tension is estimated to be better than 1.0 and 1.2, respectively. The results obtained corroborate the reliability of the SLS technique for the determination of thermophysical properties. 相似文献
83.
Sébastien Hentz Laurent Daudeville Frédéric V. Donzé 《Canadian Metallurgical Quarterly》2004,130(6):709-719
The use of a three-dimensional discrete element method (DEM) is proposed to study concrete structures submitted to dynamic loading. The aim of this paper is to validate the model first in the quasistatic domain, and second in dynamic compression, at the sample scale. A particular growing technique is used to set a densely packed assembly of arbitrarily sized spherical particles interacting together, representing concrete. An important difference from classical DEMs where only contact interactions are considered, is the use of an interaction range. First, the correct identification of parameters of the DEM model to simulate elastic and nonlinear deformation including damage and rupture is made through quasistatic uniaxial compression and tension tests. The influence of the packing is shown. The model produces a quantitative match of strength and deformation characteristics of concrete in terms of Young’s modulus, Poisson’s coefficient, and compressive and tensile strengths. Then, its validity is extended through dynamic tests. The simulations exhibit complex macroscopic behaviors of concrete, such as strain softening, fractures that arise from extensive microcracking throughout the assembly, and strain rate dependency. 相似文献
84.
In sheep, recognition of the familiar lamb by the mother depends on the learning of its olfactory signature after parturition. The authors quantified Fos changes in order to identify brain regions activated during lamb odor memory formation. Brain activation was compared with those measured in anosmic ewes displaying maternal behavior but not individual lamb recognition. In intact ewes, parturition induced significant increase in Fos expression in olfactory cortical regions and in cortical amygdala, whereas in anosmic mothers, Fos expression was very low. In contrast, no difference was observed between intact and anosmic ewes in hypothalamic areas and medial amygdala, suggesting a differentiation between the neural network controlling maternal responsiveness and that involved in olfactory lamb memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
85.
86.
Wei Chen Jian Liu Flore Brue Frédéric Skoczylas C.A. Davy Xavier Bourbon Jean Talandier 《Cement and Concrete Research》2012,42(7):1001-1013
This experimental study aims at identifying the water retention properties of two industrial concretes to be used for long term underground nuclear waste storage structures. Together with water retention, gas transfer properties are identified at varying water saturation level, i.e. relative gas permeability is assessed directly as a function of water saturation level Sw. The influence of the initial de-sorption path and of the subsequent re-saturation are analysed both in terms of water retention and gas transfer properties. Also, the influence of concrete microstructure upon water retention and relative gas permeability is assessed, using porosity measurements, analysis of the BET theory from water retention properties, and MIP. Finally, a single relative gas permeability curve is proposed for each concrete, based on Van Genuchten–Mualem's statistical model, to be used for continuous modelling approaches of concrete structures, both during drying and imbibition. 相似文献
87.
Open-pit deposits are often characterised by a stack of layers of different geological nature. Some layers are worthless while the ore of the others is of a varying economic value depending on grade. To reach a layer, it is necessary to have first removed the upper layers above the extraction zone. This action results in uncovering the layer in this particular place and in facilitating access to the layers below. This extraction process involves a series of 2–7 basic operations; each one is performed by a machine, some of which are able to perform up to three different operations. Ensuring the consistency of mining extraction scheduling over a few months, in order to meet known or forecast demand, is a challenging task. A mining extraction model based on mathematical programming is proposed but it is hardly usable, due to its size. Therefore, a model based on a Discrete Event Simulation, is created to test how ore supplies are affected by the tactical and operational decisions relating to the choice of parcels to be processed and to the allocation of machines to the different basic operations. 相似文献
88.
Andrés Vignaga Frédéric Jouault María Cecilia Bastarrica Hugo Brunelière 《Software and Systems Modeling》2013,12(1):105-119
Model management is essential for coping with the complexity introduced by the increasing number and varied nature of artifacts involved in model-driven engineering-based projects. Global model management (GMM) addresses this issue by enabling the representation of artifacts, particularly transformation composition and execution, within a model called a megamodel. Type information about artifacts can be used for preventing type errors during execution. Built on our previous work, in this paper we present the core elements of a type system for GMM that improves its original typing approach and enables both typechecking and type inference on artifacts within a megamodel. This type system is able to deal with non-trivial situations such as the use of higher order transformations. We also present a prototypical implementation of such a type system. 相似文献
89.
Moisés Frías Holmer Savastano Ernesto Villar M. Isabel Sánchez de Rojas Sergio Santos 《Cement and Concrete Composites》2012,34(9):1019-1023
The worldwide production of bamboo generates large volumes of leaf wastes, which are deposited in landfills or burned in an uncontrolled manner, with negative effects in the environment. The ash obtained by calcining of the bamboo leaf waste, shows good qualities as supplementary cementing material for the production of blended cements.The current paper shows a detailed scientific study of a Brazilian bamboo leaf ash (BLA) calcined at 600 °C in small scale condition, by using different techniques (XRF, XRD, SEM/EDX, FT–IR, TG/DTG) and technical study in order to analyse the behaviour of this ash in blended cements elaborated with 10% and 20% by mass of BLA. The results stated that this ash shows a very high pozzolanic activity, with a reaction rate constant K of the order of 10?1/h and type I CSH gel was the main hydrated phase obtained from pozzolanic reaction. The BLA blended cements (10% and 20%) complied with the physical and mechanical requirements of the existing European standards. 相似文献
90.