The effect of a CNT interface on the thermal resistance of contacting surfaces

Experimental and theoretical analyses were used to study the effect of thermal contact resistance in two materials, aluminum and graphite. Experimental investigation included the use of a modern laser flash device to measure the effective thermal conductivity of each material for three different cases: in direct contact, with a graphite coating and with a thin sheet of carbon nanotube (CNT) thermal interface material (TIM). For both materials total thermal resistance values were determined corresponding to different cases for same contact pressure. Results showed that the CNT TIM produced the minimum thermal contact resistance. A theoretical study was carried out to compare the experimental results with thermal resistance models from the literature. Based on the surface roughness of the materials tested, two models were used. Both models showed reasonable agreement with the experimental results with an error of less than 6.5%. The results demonstrate the effectiveness of CNT materials in improving the thermal conductance of contacting surfaces.     

Use of exfoliated graphite filler to enhance polymer physical properties

Three sets of exfoliated graphite filled polymers, having three different particle sizes, were prepared with load levels from 0.1-20% by weight. After sieving, the particles were reduced to nanometer size through exfoliation, shear mixing, and ultrasonication, which further breaks and delaminates them. The electrical, thermal and mechanical properties of the nanoparticle filled polymers were measured. In addition, light, scanning electron, and atomic force microscope characterization were performed. The exfoliated graphite filled polymer material could be tailored to be high modulus and vary from insulating to highly conducting. Compared with the pure polymer, the polymers filled with 20% wt. exfoliated graphite has seen an significant reduction in electrical resistivity from 1.5⁸ to 0.5 Ω cm. The thermal conductivity for the polymers containing 20% wt exfoliated graphite has also been drastically improved, increasing from 0.2 to 5 W/m K. The flexural modulus achieved a maximum increase of 3.8 GPa which is a 60% above the value for the pure polymer (2.4 GPa).     

Fischer–Tropsch Synthesis: Oxidation of a Fraction of Cobalt Crystallites in Research Catalysts at the Onset of FT at Partial Pressures Mimicking 50 % CO Conversion

Freshly H₂-reduced catalyst samples and FTS catalyst samples (i.e., freshly reduced and immediately exposed to the onset of FTS conditions corresponding to 50 % CO conversion) were prepared. Each sample was coated in situ using molten polywax and solidified so that an air-protected sample was obtained, which was stored in inert gas. XAS was utilized to investigate the oxidation state of cobalt. A fraction of cobalt crystallites in the freshly reduced research catalysts having lower-than-commercial loading and smaller crystallites undergoes a degree of oxidation to CoO at the onset of FTS conditions simulating 50 % CO conversion (i.e., the H₂O partial pressure is high enough to induce some oxidation). Therefore, by decreasing Co content with the aim of improving the dispersion of cobalt and Co efficiency, very small Co crystallites are obtained. Their reoxidation at the onset of FTS is an unintended consequence. Thus, catalysts should be designed to have an optimum narrow cluster size range—small enough to increase Co surface site densities, but large enough to avoid reoxidation, and the stability problems that arise from having unreduced Co in the working catalyst (e.g., a complex coalescence and reduction mechanism).     

Experimental analysis of applicability of a picosecond laser for micro-polishing of micromilled Inconel 718 superalloy

An increasing number of recent technological advancement is linked to the widespread adoptions of ultra-short picosecond (ps) pulsed laser in various applications of material processing. The superior capability of this laser is associated with the precise control of laser–material interaction as an outcome of extremely short interaction times resulting in almost-negligible heat affected zones. In this context, the present study explores the applicability of a picosecond laser in laser micro-polishing (LμP) of Ni-based superalloy Inconel 718 (IN718). The specific research goals of the present study constitute determination of melting regime—a mandatory phase for LμP, establishing the concept of polishability of the spatial contents of the initial surface topography and experimental demonstration of the process capability of a ps laser for potential micro-polishing applications. The initial surface topography was prepared by micromilling operation with a step-over of 50 μm and scallop height of 2 μm. The LμP experiments were performed at five different levels of fluence associated with the melting regime by changing the focal offset, a parameter denoting the working distance between workpiece surface and focusing lens focal plane. The LμP performance was evaluated based on the line profiling average surface roughness (R _a) spectrum distributed at different spatial wavelength intervals along the laser path trajectory. Furthermore, additional statistical metrics such as material ratio and power spectral density functions were analyzed in order to establish the process parameters associated with best achievable surface finish. The applicability of ps LμP was demonstrated in two regimes—1D (line) and 2D (area) polishing. During 1D LμP, significant (～52 %) improvement of the surface quality was achieved by reducing an R _a value from 0.50 μm before polishing to an R _a value of 0.24 μm across the laser path trajectory on initially ground surface. In addition, an initially micromilled area of 4.5?×?4.5 mm was LμPed resulting in the reduction of an areal topography surface roughness (S _a) value from 0.435 to 0.127 μm (70.8 % surface quality improvement).     

Synthesis and characterization of polyurethane/bentonite nanoclay based nanocomposites using toluene diisocyanate

Polyurethanes (PUs) prepolymers blended with bentonite nanoclay and without bentonite nanoclay were prepared by the reaction of toluene-2,4-diisocyanate (TDI) and hydroxyl terminated polybutadiene (HTPB), and the chain was further extended with 1,4-butane diol (1,4-BDO) to get final polyurethane nanocomposites (PUNC). A mixture of polymer and bentonite clay enriched in montmorillonite (MMT) was formed in solution polymerization, in which MMT dispersed depending on interaction of MMT with polymer chains. The molecular structure of the monomers and the prepared PU nanocomposites was confirmed by FTIR. A series of PUNCs were prepared by varying the percent compositions of bentonite nanoclay into the PU matrix. The existence of the clay in to the PU was confirmed by scanning electron microscope (SEM). SEM images verified the good dispersion of the bentonite nanoclay in PU matrix.     

Improvement of blown film extrusion of poly(Lactic Acid): Structure–Processing–Properties relationships

The blown extrusion of poly(lactic acid) (PLA) presents several challenges mainly due to the poor shear and elongation properties of this biopolymer. This article highlights some promising routes to enhance the processability of PLA for blown extrusion. To achieve this objective, various formulations of PLA with multifunctionalized epoxy, nucleating agents, and plasticizer were elaborated and studied on the basis of their linear viscoelasticity and elongational properties. We further characterized both the structure and thermomechanical properties of blown films produced with these PLA formulations. Stability charts for the film blowing of neat and modified PLA were thus established at different processing conditions. On the basis of these results, we managed to achieve a large enhancement of the blown processing windows of PLA with high blow‐up ratio (BUR) and take‐up ratio attained. We were able to demonstrate that a higher kinetic of crystallization can also be reached for chain‐extended and branched PLA formulated with adequate amounts of nucleating agents and plasticizers. Induced crystallization during process was also demonstrated. Through this work, blown films with interesting thermomechanical and mechanical properties have been elaborated using an optimal formulation for PLA. POLYM. ENG. SCI., 54:840–857, 2014. © 2013 Society of Plastics Engineers     

Study of ac impedance spectroscopy of Al doped MnFe2−2xAl2xO4

We have reported electrical properties of Al doped MnFe₂O₄ ferrite using ac impedance spectroscopy as a function of frequency (42 Hz to 5 MHz) at different temperatures (300–473 K). XRD analysis shows that all the compositions are single phase cubic spinel in structure. The complex impedance analysis has been used to separate the grain and grain boundary resistance of MnFe_2−2xAl_2xO₄. From the analysis of impedance spectra it is found that the real (Z′), and imaginary (Z″) part of the impedance decrease with increasing frequency and both are found to decrease with Al doping up to 20%, and thereafter, these increase with further increasing the Al concentration. Experimental results have been fitted with two parallel RC equivalent circuits in series.     

3D experimental quantification of fabric and fabric evolution of sheared granular materials using synchrotron micro-computed tomography

Many experimental studies have demonstrated that mechanical response of granular materials is highly influenced by micro-structural fabric and its evolution. In the current literature, quantification of fabric and its evolution has been developed based on micro-structural observations using Discrete Element Method or 2D experiments with simple particle shapes. The emergence of X-ray computed tomography technique has made quantification of such experimental micro-structural properties possible using 3D high-resolution images. In this paper, synchrotron micro-computed tomography was used to acquire 3D images during in-situ conventional triaxial compression experiments on granular materials with different morphologies. 3D images were processed to quantify fabric and its evolution based on experimental measurements of contact normal vectors between particles. Overall, the directional distribution of contact normals exhibited the highest degree of isotropy at initial state (i.e., zero global axial strain). As compression progressed, contact normals evolved in the direction of loading until reaching a constant fabric when experiments approached the critical state condition. Further assessment of the influence of confining pressure, initial density state, and particle-level morphology on fabric and its evolution was formed. Results show that initial density state and applied confining pressure significantly influence the fabric-induced internal anisotropy of tested specimens at initial states. Relatively, a higher applied confining pressure and a looser initial density state resulted in a higher degree of fabric-induced internal anisotropy. Influence of particle-level morphology was also found to be significant particularly on fabric evolution.     

Robust Parameter Design of an EDM Process

The paper details a robust parameter design of an electrical discharge machining process. The influence of capacitance, pulse off‐time, pulse on‐time and pulse current on both the average and variability of surface roughness and material removal rate of a titanium alloy was investigated. The analysis revealed that to attain robustness against the impact of noise parameters, no capacitance should be applied. Furthermore, increasing pulse on‐time and its current increased the average of both the surface roughness and material removal rate. Two approaches were suggested to deal with the trade‐off between minimizing the former and maximizing the latter. The study confirmed empirically the inferiority of Taguchi's S/N ratios to a robust design method involving the use of log(s) together with a simple graphical tool for determining the appropriate data transformation called lambda plot. In fact, it was revealed that the employed S/N ratios were driven mainly by the average and involved unaided, unexplained and unjustified transformations. The log(s), on the other hand, provided an independent means of quantifying the variability and, when integrated with lambda plot, rendered not only a simplified analysis but also a better process understanding. The study is the first to report the use of this powerful approach in the context of electrical discharge machining parameter design. Copyright © 2012 John Wiley & Sons, Ltd.     

MicroRNAs and their target mRNAs as potential biomarkers among smokers and non‐smokers with lung adenocarcinoma

Lung adenocarcinoma is one of the major causes of mortality. Current methods of diagnosis can be improved through identification of disease specific biomarkers. MicroRNAs are small non‐coding regulators of gene expression, which can be potential biomarkers in various diseases. Thus, the main objective of this study was to gain mechanistic insights into genetic abnormalities occurring in lung adenocarcinoma by implementing an integrative analysis of miRNAs and mRNAs expression profiles in the case of both smokers and non‐smokers. Differential expression was analysed by comparing publicly available lung adenocarcinoma samples with controls. Furthermore, weighted gene co‐expression network analysis is performed which revealed mRNAs and miRNAs significantly correlated with lung adenocarcinoma. Moreover, an integrative analysis resulted in identification of several miRNA–mRNA pairs which were significantly dysregulated in non‐smokers with lung adenocarcinoma. Also two pairs (miR‐133b/Protein Kinase C Zeta (PRKCZ) and miR‐557/STEAP3) were found specifically dysregulated in smokers. Pathway analysis further revealed their role in important signalling pathways including cell cycle. This analysis has not only increased the authors’ understanding about lung adenocarcinoma but also proposed potential biomarkers. However, further wet laboratory studies are required for the validation of these potential biomarkers which can be used to diagnose lung adenocarcinoma.Inspec keywords: cancer, molecular biophysics, patient diagnosis, tumours, RNA, proteins, lung, genetics, medical diagnostic computing, molecular configurationsOther keywords: miRNAs expression profiles, mRNAs expression profiles, smokers, nonsmokers, integrative analysis, lung adenocarcinoma, microRNAs, disease specific biomarkers, noncoding regulators, genetic abnormalities, weighted gene coexpression network analysis