Reactivity between liquid Si or Si alloys and graphite

The fundamental issues of the reaction at liquid Si/graphite interfaces between Si melting point (1412 °C) and 1600 °C are studied on the basis of results obtained with polycrystalline graphite concerning the growth kinetics of the interfacial reaction layer and the microstructure and morphology of this layer. Experiments were also performed using vitreous carbon substrates. Results are also reported for Si–Al alloys at 1000 °C. The elementary process controlling the growth kinetics is determined and a model is proposed to describe the different stages of the interfacial reaction.     

Identification of equivalent topography in an open channel flow using Lagrangian data assimilation

We present a Lagrangian data assimilation experiment in an open channel flow above a broad-crested weir. The observations consist of trajectories of particles transported by the flow and extracted from a video film, in addition to classical water level measurements. However, the presence of vertical recirculations on both sides of the weir actually conducts to the identification of an equivalent topography corresponding to the lower limit of a surface jet. In addition, results on the identification of the Manning coefficient may allow to detect the presence of bottom recirculations.     

Relationships between processing conditions and mechanical properties of PA12 tubes. The EWF approach

In polyamide 12 (PA12) tube extrusion, calibration is the key step of the process that affects the subsequent mechanical properties. In previous work it has been shown that according to the calibration conditions, a very oriented skin layer may be created, which has been correlated to an important decrease of elongation at break. In this paper, we present new results showing a good correlation between molecular orientation and fracture toughness, as evaluated by the EWF (Essential Work of Fracture) approach. They concern notched specimens and confirm the results obtained in classical tensile testing. The specific essential work of fracture is very sensitive to the orientation generated in the skin region by appropriate processing conditions: it decreases from the external to the inner regions of the tube, and increases with skin orientation.     

Dynamic modelling for thermal micro-actuators using thermal networks

Thermal actuators are extensively used in microelectromechanical systems (MEMS). Heat transfer through and around these microstructures are very complex. Knowing and controlling them in order to improve the performance of the micro-actuator, is currently a great challenge. This paper deals with this topic and proposes a dynamic thermal modelling of thermal micro-actuators. Thermal problems may be modelled using electrical analogy. However, current equivalent electrical models (thermal networks) are generally obtained considering only heat transfers through the thickness of structures having considerable height and length in relation to width (walls). These models cannot be directly applied to micro-actuators. In fact, micro-actuator configurations are based on 3D beam structures, and heat transfers occur through and around length. New dynamic and static thermal networks are then proposed in this paper. The validities of both types of thermal networks have been studied. They are successfully validated by comparison with finite elements simulation and analytical calculations.     

Reaction kinetics of the combined pyrolysis and steam-gasification of carbonaceous waste materials

Synthesis gas production by steam-gasification of carbonaceous waste materials with high volatile contents (e.g., sewage and industrial sludge, fluff, and scrap tire powder) is kinetically examined. A multiple pseudo-component first-order reaction model is formulated to describe the rates of the combined pyrolysis and gasification processes. Arrhenius-type kinetic parameters are determined by dynamic thermogravimetric experimental runs conducted in the temperature range 473-1476 K.     

Method for Accurate Surface Temperature Measurements During Fast Induction Heating

A robust method is proposed for the measurement of surface temperature fields during induction heating. It is based on the original coupling of temperature-indicating lacquers and a high-speed camera system. Image analysis tools have been implemented to automatically extract the temporal evolution of isotherms. This method was applied to the fast induction treatment of a 4340 steel spur gear, allowing the full history of surface isotherms to be accurately documented for a sequential heating, i.e., a medium frequency preheating followed by a high frequency final heating. Three isotherms, i.e., 704, 816, and 927°C, were acquired every 0.3 ms with a spatial resolution of 0.04 mm per pixel. The information provided by the method is described and discussed. Finally, the transformation temperature Ac1 is linked to the temperature on specific locations of the gear tooth.     

Restricted dissolution and derivatization capacities of cellulose fibres under uniaxial elongational stress

Cellulose is a future major source of materials and biofuel but its extraction and its chemical or enzymatic treatments are difficult, polluting and inefficient tasks. The accessibility of the reagents to cellulose chains is indeed limited. Classical evocated reasons for this lack of accessibility are pore structure, tight hydrogen bond arrays, crystallinity and presence of resistant materials like lignin. Studying dissolution of cotton hairs and regenerated cellulose fibres in various solvents under uniaxial tension, we found that tension is preventing these fibres to dissolve in chemicals that would dissolve the same cellulose fibres tension-free. We show that what is controlling dissolution is not the degree of swelling since, at the same degree of swelling, fibres under tension do not dissolve while fibres without tension do. An important result is that when a fibre under tension (thus swollen but not dissolved) is breaking, it is immediately dissolving. Under tension, when the solvent is present around cellulose chains, it is activated to solvate the chains only when tension stress is released. A chemical reaction like acetylation of cellulose fibre under tension also gives an interesting result. The degree of substitution remains very low while the same experiment performed without tension leads to higher degree of substitution followed by the dissolution of the fibre (even increasing further the DS due to homogeneous reaction). We postulate that the lack of dissolution capacity or reacting activity under tension can be due to the hampering of local conformational movements, cellulose chains being not able to perform axial movements. The availability of performing local conformational movements could be a main component of cellulose activation.     

Incumbency Bonus in Election News Coverage Explained: The Logics of Political Power and the Media Market

This article investigates the determinants of the incumbency bonuses in news coverage. Two main factors are identified: the distribution of political power and changes in the media market. To test these assumptions, a content analysis of the news coverage of 5 national election campaigns in Denmark was conducted (4,592 news stories). First, the more unevenly political power is distributed, the more visible the government is. Second, results suggest a trade‐off between the incumbency bonus and the coverage of nonsubstantive issues. Third, changes in news coverage seem to be more driven by changes in the political system than by changes in the media market. Finally, it is discussed how future research can further our understanding of political imbalances in news coverage.     

盘式制动器尖叫声单模态和多模态不稳定性非线性稳态动力学的研究(二)

本文重点说明和讨论制动系统承受摩擦诱导的振动,由于多不稳定模式可能发生的非线性动力学特性。采用具有摩擦副的有限元模型分析制动系统的稳定性和预测尖叫声稳态非线性波动。尖叫声不稳定机理看成是一模式偶合现象,它通常看成为一种组合。