Stress/strain development around a spherical inclusion in a polymeric matrix: The effects of particle and matrix mechanical characteristics and thermal expansivity difference

For a spherical inclusion embedded in an infinite polymeric matrix, the Goodier Model, combined with thermal stress contribution, is applied to establish the stress/strain fields around a spherical particle in different particle/matrix combinations, including TiO₂, alumina, silica, steel, polystyrene, and polyvinyl butyral particles embedded in a range of polymeric matrices. This approach provides the basis for examining the effects of different parameters such as Young's modulus and Poisson's ratio of the particle and matrix, and the thermal history of samples on the failure‐initiation criteria. An explanation is provided for divergent results obtained for very soft and elastic particles. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Free vibration analysis of functionally graded plates with multiple circular and non-circular cutouts

Cutouts are inevitable in structures due to practical consideration.In order to investigate the free vibration of functionally graded plates with multiple circular and non-circular cutouts,finite eleme...     

Assessment of mean and fluctuating velocity and temperature of CuO/water nanofluid in a horizontal channel: Large eddy simulation

Abstract

A comprehensive investigation applying the large eddy simulation approach to turbulent forced convection of CuO/water nanofluid flowing through a horizontal channel is carried out. Dealing with the sub-grid scale stress tensor and heat flux vector, the wall-adopting local eddy-viscosity model is employed. The periodic boundary condition is imposed to the streamwise and spanwise directions, while the no-slip and constant heat flux are applied to the walls. The results indicate that adding nanoparticles into the base fluid increases the dimensionless mean velocity and fluctuations of velocity and temperature. This increment is more evident for turbulent Reynolds stress and turbulent heat flux in the streamwise direction than the other directions. Therefore, higher energy is transferred between nanofluid layers which results in a higher amount of heat transfer than the pure water. It is also observed that the nanoparticles enhance the turbulence energy at all frequencies, and the decay in the fluctuations occurs at the higher wavenumbers.     

Endosomal Escape of Polymer‐Coated Silica Nanoparticles in Endothelial Cells

Current investigations into hazardous nanoparticles (i.e., nanotoxicology) aim to understand the working mechanisms that drive toxicity. This understanding has been used to predict the biological impact of the nanocarriers as a function of their synthesis, material composition, and physicochemical characteristics. It is particularly critical to characterize the events that immediately follow cell stress resulting from nanoparticle internalization. While reactive oxygen species and activation of autophagy are universally recognized as mechanisms of nanotoxicity, the progression of these phenomena during cell recovery has yet to be comprehensively evaluated. Herein, primary human endothelial cells are exposed to controlled concentrations of polymer‐functionalized silica nanoparticles to induce lysosomal damage and achieve cytosolic delivery. In this model, the recovery of cell functions lost following endosomal escape is primarily represented by changes in cell distribution and the subsequent partitioning of particles into dividing cells. Furthermore, multilamellar bodies are found to accumulate around the particles, demonstrating progressive endosomal escape. This work provides a set of biological parameters that can be used to assess cell stress related to nanoparticle exposure and the subsequent recovery of cell processes as a function of endosomal escape.     

Applying simulated annealing for designing cellular manufacturing systems using MDmTSP

The design of cellular manufacturing systems involves many structural and operational issues. One of the important design steps is the formation of part families and machine cells (cell formation). Despite a large number of papers on cell formation published worldwide, only a handful incorporates operation sequence in layout design (intra-cell move calculations). We propose a solution to solve the part-family and machine-cell formation problem considering the within-cell layout problem, simultaneously. In this paper, the cellular manufacturing system is formulated as a multiple departures single destination multiple travelling salesman problem (MDmTSP) and a solution methodology based on simulated annealing is proposed to solve the formulated model. Numerical examples show that the proposed method is efficient and effective in finding optimal solutions. The results also indicate that the proposed approach performs well compared to some well-known cell formation methods.     

Microstructured silicon membrane with soft suspension beams for a high performance MEMS microspeaker

This study presents a novel approach to MEMS microspeakers design aiming to tackle two main drawbacks of conventional microspeakers: their poor sound quality and their weak efficiency. For this purpose, an acoustic emissive surface based on a very light but very stiff structured silicon membrane was designed and microfabricated. This architecture, for which the membrane undesirable vibration modes were reduced to only three within the microspeaker bandwidth, is promising to let the microspeaker produce high sound quality from 300?Hz to 20?kHz. This silicon membrane is suspended by a whole set of silicon springs designed to enable out-of-plane displacements as large as 300?μm. Different geometries of springs were considered and the material maximum stress was analyzed in each case by finite element modeling. The proposed structure promises an efficiency of 10^?4, that is to say ten times higher than that of conventional microspeakers.     

Effect of partial replacement of chitosan with halloysite nanotubes on the properties of polylactic acid hybrid biocomposites

In this study, hybrid chitosan/halloysite nanotubes (Cs/HNTs) reinforced polylactic acid (PLA) were prepared via melt compounding and compression molding techniques. In the fabrication of PLA/Cs/HNTs hybrid biocomposites, the partial replacement of Cs with HNTs was performed at filler loading of 2.5 parts per hundred parts of polymer (php), proceeding from the highest tensile strength of PLA/Cs obtained in our previous study. Cs was partially replaced with different HNTs loadings (0.5, 1, 1.5, 2, and 2.5) php and its effects on the functional group, thermal, tensile, morphological, and water absorption properties were investigated systematically. The results revealed that the combined loading of 1 php Cs and 1.5 php HNTs hybrid fillers into PLA showed the best performance in all properties. Fourier transform infrared spectroscopy (FTIR) analysis indicated that the siloxane (Si O) group of HNTs had chemically interacted with the amine group of Cs. The thermal analysis demonstrated that partial replacement of Cs with 1.5 php HNTs improved the thermal stability of PLA/2.5Cs/0HNTs biocomposite by ~12%. Yet, the percentage of crystallinity (χ_c) reduced with HNTs addition due to the phase adhesion improvement. Moreover, PLA/1Cs/1.5HNTs hybrid biocomposites showed the highest tensile strength and elongation at break of 59 MPa and 2.72%, respectively. This correlated with the uniform dispersion and better interfacial adhesion between Cs/HNTs fillers in the PLA matrix, as confirmed by the field emission scanning electron microscopy (FESEM). In addition, partial replacement of Cs with HNTs exhibited a lower water absorption percentage, which suggested the advantage of hybrid fillers to reduce water uptake, and is beneficial in a wide range of applications.     

Characteristics of the pH-influenced adaptation of methanogenic sludge to ammonium toxicity

Increasing ammonium-nitrogen concentrations caused failure of methanogenesis at 1900-2000 mg dm^?3. After an adaptation period characterised by an almost nil methane production, methanogenesis appeared to be possible at even higher concentrations. A kinetic analysis of methane production during the adaptation process indicated that the adaptation was the result of a metabolic change in the methanogenic bacteria already present, rather than of growth of new bacteria. A high pH value causing toxic concentrations of un-ionised ammonia during the adaptation period appeared to result in a decreased maximum specific methanogenic activity of the adapted sludge. A low pH value during the adaptation period resulted in a retarded degradation of propionic acid, probably due to inhibition of the hydrogen consuming methanogenic bacteria by undissociated volatile fatty acids, but this did not result in a decreased maximum specific methanogenic activity in the adapted sludge. The maximum specific methanogenic activity at an ammonium-nitrogen concentration of 2315 mg dm^?3 after adaptation as a percentage of that at 1000 mg dm^?3 before adaptation was 31, 65 and 61% for a pH during the adaptation period of 7.6, 7.25 and 7.0 respectively. Except for the sludge which was maintained at pH 7.6 during the adaptation period, after adaptation the maximum specific methanogenic activity at an ammonium-nitrogen concentration of 2315 mg dm^?3 was higher than the maximum specific methanogenic activity at an ammonium nitrogen concentration of 1900 mg dm^?3 before adaptation.