The effect of sintering time on the densification and mechanical properties of a mechanically alloyed Cr–Mn–N stainless steel

Sintering is an essential stage in powder metallurgy, which affects the final microstructure and performance of the part. This study is concerned with the sintering and mechanical behaviors of Fe–18Cr–8Mn–0.9N stainless steel prepared from mechanically alloyed amorphous/nanocrystalline powders. The contribution of sintering time to the densification at 1100 °C is considered and a sluggish densification is found for the alloy. Furthermore, the correlation between the microstructure and mechanical properties of the fabricated porous parts is studied. It is found that the yield stress is affected by both porosity and the material’s intrinsic yield strength. Nonetheless, the effect of porosity on the overall hardness typically prevails over the effect of matrix hardness. Interestingly, even after sintering at 1100 °C for up to 20 h, the nanometric structure of the material is retained.     

Effects of dielectric substrate thickness on plasma immersion ion implantation

A one-dimensional plasma fluid model is developed for investigating the effects of dielectric substrate thickness on plasma immersion ion implantation. By considering the effects of secondary electron emission from the dielectric substrate and using finite difference schemes, evolution of plasma sheath, ion fluence and dielectric surface potential versus time and substrate thickness are evaluated. It was demonstrated that with the increasing dielectric thickness, sheath width and ion fluence over the dielectric surface decrease and surface potential reduces. These effects can be attributed to the accumulation of positive ions and ejection of secondary electrons from the dielectric surface and thereby lessening the strength of the electric field over the dielectric substrate. It is also shown that the secondary electrons have a profound effect on implantation results and must be considered in plasma immersion ion implantation of dielectric materials.     

Effects of strong magnetic field on plasma immersion ion implantation of dielectric substrates

In this paper the effects of a strong magnetic field on plasma immersion ion implantation (PHI) of dielectric substrates were investigated. A plasma fluid model and finite difference schemes were used to simulate a one-dimensional system of plasma immersion ion implantation. The effect of secondary electron emission from the electrode on PHI was also taken into consideration. It was found that the magnitude and direction of the magnetic field have slight effects on sheath thickness but have considerable effects on current densities in the y and z directions which are perpendicular to the direction of the electric field (the x direction). The simulations showed that the current densities in the y and z directions increased significantly with increasing magnitude of the magnetic field at a given fixed angle, the reason being attributed to the rotational force exerted on the ions by the magnetic field. With a fixed magnetic field, increasing the angle of the magnetic field, θ, with respect to the electric field produced a continuous increase in current density in the y direction from zero to its maximum at θ = 90° but the current density in the z direction could be described as saddle-shaped being zero at both ends.     

CFD study of non-premixed swirling burners: Effect of turbulence models

This research investigates a numerical simulation of swirling turbulent non-premixed combustion. The effects on the combustion characteristics are examined with three turbulence models: namely as the Reynolds stress model, spectral turbulence analysis and Re-Normalization Group. In addition, the P-1 and discrete ordinate (DO) models are used to simulate the radiative heat transfer in this model. The governing equations associated with the required boundary conditions are solved using the numerical model. The accuracy of this model is validated with the published experimental data and the comparison elucidates that there is a reasonable agreement between the obtained values from this model and the corresponding experimental quantities. Among different models proposed in this research, the Reynolds stress model with the Probability Density Function (PDF) approach is more accurate (nearly up to 50%) than other turbulent models for a swirling flow field. Regarding the effect of radiative heat transfer model, it is observed that the discrete ordinate model is more precise than the P-1 model in anticipating the experimental behavior. This model is able to simulate the subcritical nature of the isothermal flow as well as the size and shape of the internal recirculation induced by the swirl due to combustion.     

Controlled release from polyurethane films: Drug release mechanisms

In this study, polyurethane-films loaded with diclofenac were used to analyze the drug release kinetics and mechanisms. For this purpose, the experimental procedures were developed under static and dynamic conditions with different initial drug loads of 10, 20, and 30%. In the dynamic condition, to better simulate the biological flow, drug release measurements were investigated at flow rates of 7.5 and 23.5 ml/s. These values indicate the flow rate of the internal carotid artery (ICA) for a normal state of a body and for a person during the exercise, respectively. The experimental data were analyzed and adjusted by Higuchi, Korsmeyer–Peppas, First-order, zero-order, and Peppas–Sahlin models in order to understand the mechanisms contributed. Finally, drug release mechanisms were specified by investigating the model correlation coefficients. Experimental results showed that increasing the flow rate and initial drug loads enhance drug liberation. In addition, the rate of release is more influenced by the drug dosage in the static state. The analysis revealed that diffusion, burst, and osmotic pressure are the principal mechanisms contributed. Moreover, Fickian type was the dominant mechanism at all duration of release. However, it was discovered using Peppas–Sahlin model that the contribution of the diffusion mechanism decreases with increasing flow rate and initial dosage. Furthermore, the tests at different drug dosages showed that the number of stages in medication release profile is independent of the flow rate and the medicine percentage. One can conclude that the drug release kinetic in static state is more influenced by drug dosage compared with dynamic state.     

Antimicrobial Ionic Liquid-Based Materials for Biomedical Applications

Excessive and unwarranted administration of antibiotics has invigorated the evolution of multidrug-resistant microbes. There is, therefore, an urgent need for advanced active compounds. Ionic liquids with short-lived ion-pair structures are highly tunable and have diverse applications. Apart from their unique physicochemical features, the newly discovered biological activities of ionic liquids have fascinated biochemists, microbiologists, and medical scientists. In particular, their antimicrobial properties have opened new vistas in overcoming the current challenges associated with combating antibiotic-resistant pathogens. Discussions regarding ionic liquid derivatives in monomeric and polymeric forms with antimicrobial activities are presented here. The antimicrobial mechanism of ionic liquids and parameters that affect their antimicrobial activities, such as chain length, cation/anion type, cation density, and polymerization, are considered. The potential applications of ionic liquids in the biomedical arena, including regenerative medicine, biosensing, and drug/biomolecule delivery, are presented to stimulate the scientific community to further improve the antimicrobial efficacy of ionic liquids.     

Instability analysis of bi-axial micro-scanner under electromagnetic actuation including small scale and damping effects

Microsystem Technologies - The objective of this work is to create an analytical framework to study the problem of instability and squeezed film damping in bi-axial micro-scanners under...     

Elbs反应合成的多核芳香族化合物先驱体的碳化研究

研究了芘与甲基苯甲酰氯或２，５－二甲基对苯二甲酰氯通过Ｅｌｂｓ反应合成的先驱体的碳化．与其它方法相比，用此种新方法可得高质、高产的碳。     

Reliability analysis of a flexible machining cell

Introduction of flexible machining systems incorporating robotic manipulators for high speed transfer of tools and workpieces entails high capital investment. This is an important constraint which limits the scope for experimentation and emphasises the importance of reliability as a deciding factor in the use of such systems. This paper describes a typical flexible machining cell configuration. Operational details relating to its elements and their components are included. A large amount of data concerning the failure characteristics of various subsystem elements are gathered and processed. Using a representative sample, qualitative and quantitative analyses of the system reliability are carried out using various reliability evaluation techniques. These include block diagram analysis (BDA), fault tree analysis (FTA) and a discrete Markov model. In particular attention is paid to the availability of the robot-assisted tool delivery system, including sensing, measuring and signal conditioning devices.     

Measurement of dominant eigenvalues in cracked body problems

A refined optimal method consisting of the tandem application of frozen stress photoelasticity and high density moire interferometry for studying three dimensional effects in cracked bodies is briefly reviewed. It is then employed to measure the dominant eigenvalue at the right angle intersection of a straight front crack with a free surface under mode I loading. The variation of the eigenvalue through a transition zone near the free surface is also determined. The free surface result is found to be in agreement with analytical results.

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Résumé On expose brièvement une méthode optique consistant à appliquer en parallèle la photo-élasticité sous contraintes figées et l'interférométrie sur bandes de Moiré à hautes densités, pour l'étude des effets tridimensionnels dans les solides fissurés. On utilise ensuite cette méthode à la mesure de l'eigenvalue dominante à l'intersection suivant un angle droit d'un front de fissure droit avec une surface libre, sous une sollicitation de Mode I. On détermine également la variation de l'eigenvalue dans une zone de transition au voisinage de la surface libre. Le résultat relatif à cette dernière est en bonne concordance avec les résultats analytiques.