Synthesis and Microstructural Characterization of Substoichiometric Ti2Al(CxNy) Solid Solutions and Related Ti2AlCx and Ti2AlN End‐Members

Ti, TiC, Al and AlN powders were mixed to synthesize Ti₂Al(C_xN_y) (x + y < 1) solid solutions, Ti₂AlC_x (x < 1) and Ti₂AlN‐related end‐members by hot isostatic pressing at 1400°C/80 MPa for 4 h. For the pure carbides, it is demonstrated that single‐phased samples can only be obtained when about 15% of substoichiometry on the carbon site is applied. Such a result likely implies that Ti₂AlC_x can only exist in a narrow range of carbon composition. Ti₂AlN nitride can be synthesized with y = 1. Assuming that vacancy content varies linearly from 0 to 0.15 going from Ti₂AlN to Ti₂AlC_0.85 in the solid solutions, element concentrations have been calculated to synthesize different solid solutions. Thus, it is demonstrated that single‐phased and fully dense Ti₂Al(C_0.23N_0.71), Ti₂Al(C_0.45N_0.45), and Ti₂Al(C_0.66N_0.22) carbonitrides can be synthesized.     

Analysis of the Shrinkage Effect on Mass Transfer During Convective Drying of Sawdust/Sludge Mixtures

Convective drying of wastewater sludges and sawdust/sludge mixtures was studied. The first part of this work was an experimental study performed in a cross-flow convective dryer using 500 g of wet material extruded through a disk with circular dies of 12 mm. The results showed that the sawdust addition has a positive impact on the drying process from a mass ratio of 2/8, on a dry basis, with observed drying rates higher than the original sludge. The second part of this work consisted of developing a drying model in order to identify the internal diffusion coefficient and convective mass transfer coefficient from the experimental data. A comparison was made between fitted drying curves, well represented by the Newton's model, and the analytical solutions of the diffusion equation applied to a finite cylinder. Variations of dimensional characteristics, such as the volume and exchange surface of the sample bed, were obtained by X-ray tomography. This technique allowed us to confirm that shrinkage, which is an important phenomenon occurring during sludge and sawdust/sludge mixture drying, must be taken into account. The results showed that both the internal diffusion coefficient and convective mass transfer coefficient were affected by mixing and sawdust addition. The internal diffusion coefficient changed from 7.77 × 10^?9 m²/s for the original sludge to 7.01 × 10^?9 m²/s for the mixed sludge and then increased to 8.35 × 10^?9 m²/s for the mixture of a mass ratio of 4/6. The convective mass transfer coefficient changed from 9.70 × 10^?8 m/s for the original sludge to 8.67 × 10^?8 m/s for the mixed sludge and then increased to 12.09 × 10^?8 m/s for the mixture of a mass ratio of 4/6. These results confirmed that sawdust addition was beneficial to the sludge drying process as the mass transfer efficiency between the air and material increased. Reinforcing the texture of sludge by adding sawdust can increase the drying rate and decrease the drying time, and then the heat energy supply will be reduced significantly. The study also showed that neglecting shrinkage phenomenon resulted in an overestimation for the internal diffusion coefficient for the convective drying of sludges and sawdust/sludge mixtures.     

An axiomatic characterization of the ranking based on the h-index and some other bibliometric rankings of authors

In the last few years, many new bibliometric rankings or indices have been proposed for comparing the output of scientific researchers. We propose a formal framework in which rankings can be axiomatically characterized. We then present a characterization of some popular rankings. We argue that such analyses can help the user of a ranking to choose one that is adequate in the context where she/he is working.     

Image segmentation by a contrario simulation

Segmenting an image into homogeneous regions generally involves a decision criterion to establish whether two adjacent regions are similar. Decisions should be adaptive to get robust and accurate segmentation algorithms, avoid hazardous a priori and have a clear interpretation. We propose a decision process based on a contrario reasoning: two regions are meaningfully different if the probability of observing such a difference in pure noise is very low. Since the existing analytical methods are intractable in our case, we extend them to allow a mixed use of analytical computations and Monte-Carlo simulations. The resulting decision criterion is tested experimentally through a simple merging algorithm, which can be used as a post-filtering and validation step for existing segmentation methods.     

Effect of initial powder type on the hydrogen storage properties of high-pressure torsion consolidated Mg

While severe plastic deformation (SPD) on bulk samples has been widely applied for modifying the H-sorption properties, there has been little attention towards the use of SPD on powder materials. In this context, the aim of the present work was to compare the H-storage properties of high-pressure torsion (HPT) consolidated products obtained from two distinct Mg powder precursors: atomized micro-sized and condensed ultrafine powder particles. The results showed that the nature of the initial powder precursor had a pronounced effect on the H-sorption behavior. The HPT product obtained from the condensed ultrafine powder showed faster absorption kinetics than the consolidated product obtained from the atomized powder. However, the HPT product obtained from atomized powder could absorb more hydrogen and showed faster desorption kinetics corresponding to a lower activation energy. These results are discussed by taking into account the effectiveness of the HPT process to refine the grain sizes and differences in the dispersion of fine MgO oxide particles.     

Experimental and Molecular Dynamics Simulations of Tribochemical Reactions with ZDDP: Zinc Phosphate–Iron Oxide Reaction

Zinc phosphate glass is considered to be the main constituent of tribofilms generated under boundary lubrication with zinc dialkyldithiophosphate (ZDDP), a well-known antiwear additive. The reaction occurring during friction between zinc phosphate glasses and steel native iron oxide layer is investigated by both an experimental approach and by Molecular Dynamics simulations (MD). The importance of this “tribochemical” reaction in the general ZDDP antiwear process is discussed.     

光学仿真分析在光电传感器开发过程中的应用

1 引言 光电传感器是指利用光电效应作为传感原理的传感器件,它主要由光源、光学通路、光电探测器等部分.光源发出的光照射到待检测的目标物体上,被目标物体调制后被光电探测器所接收.     

A simple analytical model to study and control azimuthal instabilities in annular combustion chambers

This study describes a simple analytical method to compute the azimuthal modes appearing in annular combustion chambers and help analyzing experimental, acoustic and large eddy simulation (LES) data obtained in these combustion chambers. It is based on a one-dimensional zero Mach number formulation where N burners are connected to a single annular chamber. A manipulation of the corresponding acoustic equations in this configuration leads to a simple dispersion relation which can be solved by hand when the interaction indices of the flame transfer function are small and numerically when they are not. This simple tool is applied to multiple cases: (1) a single burner connected to an annular chamber (N = 1), (2) two burners connected to the chamber (N = 2), and (3) four burners (N = 4). In this case, the tool also allows to study passive control methods where two different types of burners are mixed to control the azimuthal mode. Finally, a complete helicopter chamber (N = 15) is studied. For all cases, the analytical results are compared to the predictions of a full three-dimensional Helmholtz solver and a very good agreement is found. These results show that building very simple analytical tools to study azimuthal modes in annular chambers is an interesting path to control them.     

Zinc Dialkyl Phosphate (<Emphasis Type="Bold">ZP</Emphasis>) as an Anti-Wear Additive: Comparison with <Emphasis Type="Bold">ZDDP</Emphasis>

In this study, we are interested in the anti-wear properties of zinc dialkyl phosphate additive (ZP) in comparison with ‘classical’ zinc dialkyldithiophosphate (ZDDP). Friction tests were performed on a reciprocating tribometer using both ball-on-flat and cylinder-on-flat configurations under a Hertzian contact pressure of 0.9 GPa. Experiments were carried out as a function of temperature (25 and 100 °C), sliding speed (25, 50 and 100 mm/s) and additives concentrations. Ball wear scar diameters as well as friction coefficient were measured. In order to better understand the anti-wear mechanisms of these additives, friction tests were followed by surface analyses such as AES (Auger Electron Spectroscopy) and XPS (X-Ray Photoelectron Spectroscopy). Transmission Electron Microscopy (TEM) observations of the ZDDP and ZP tribofilms were also carried out to visualise the generated layers. The anti-wear capability of ZP molecule is discussed.     

On‐line acoustic attenuation spectroscopy of emulsions stabilized by vinyl alcohol–vinyl acetate copolymers: a model system for the suspension polymerization of vinyl chloride

BACKGROUND: Poly[(vinyl alcohol)‐co‐(vinyl acetate)] (PVA) copolymers obtained by partial hydrolysis of poly(vinyl acetate) are currently used as industrial stabilizers in the suspension polymerization of vinyl chloride monomer (VCM). Their molecular characteristics, mainly the average degree of hydrolysis (DH ) and average degree of polymerization (DPw ), have a major influence on the monomer droplet size and the properties of the final poly(vinyl chloride) resin. RESULTS: The average droplet size and size distribution of chlorobutane/water emulsions, as a model system for VCM/water emulsions, were studied using acoustic attenuation spectroscopy on‐line with an agitated laboratory reactor. The emulsions were stabilized by PVA with DH values between 73 and 88 mol% and DPw values between 450 and 2500. The effects of agitation speed, stirring time and concentration of the PVA copolymers were investigated. An attempt was made to correlate the interfacial tension and the droplet size. CONCLUSION: On‐line acoustic spectroscopy appears to be a suitable technique for the real‐time control of the droplet size of monomer suspensions. The advantages and limitations of the technique are outlined. The validity and the application limits of the commonly cited correlation between the droplet size and the Weber number are established for polymeric surfactant‐stabilized emulsions. Copyright © 2009 Society of Chemical Industry