Atomistic deconstruction of current flow in graphene based hetero-junctions

We describe the numerical modeling of current flow in graphene heterojunctions, within the Keldysh Landauer Non-equilibrium Green’s function (NEGF) formalism. By implementing a k-space approach along the transverse modes, coupled with partial matrix inversion using the Recursive Green’s function Algorithm (RGFA), we can simulate on an atomistic scale current flow across devices approaching experimental dimensions. We use the numerical platform to deconstruct current flow in graphene, compare with experimental results on conductance, conductivity and quantum Hall, and deconstruct the physics of electron ‘optics’ and pseudospintronics in graphene pn junctions. We also demonstrate how to impose exact open boundary conditions along the edges to minimize spurious edge reflections.     

Experimental study on permanent deformation characteristics of coarse-grained soil under repeated dynamic loading

Practical assessment of subgrade settlement induced by train operation requires developing suitable models capable of describing permanent deformation characteristics of subgrade filling under repeated dynamic loading. In this paper, repeated load triaxial tests were performed on coarse-grained soil (CGS), and the axial permanent strain of CGS under different confining pressures and dynamic stress amplitudes was analysed. Permanent deformation behaviors of CGS were categorized based on the variation trend of permanent strain rate with accumulated permanent strain and the shakedown theory. A prediction model of permanent deformation considering stress state and number of load cycles was established, and the ranges of parameters for different types of dynamic behaviors were also divided. The results indicated that the variational trend of permanent strain rate with accumulated permanent strain can be used as a basis for classifying dynamic behaviors of CGS. The stress state (confining pressure and dynamic stress amplitude) has significant effects on the permanent strain rate. The accumulative characteristics of permanent deformation of CGS with the number of load cycles can be described by a power function, and the model parameters can reflect the influence of confining pressure and dynamic stress amplitude. The study’s results could help deepen understanding of the permanent deformation characteristics of CGS.

     

Polyoxometalates in the Design of Effective and Tunable Water Oxidation Catalysts

Water oxidation catalysts (WOCs) are of core importance in several green energy production technologies, including water splitting and water reduction of CO₂ driven by electrochemical potential and/or photons (radiant energy). General challenges in solar fuel generating structures, WOC design concepts, and some success-limiting considerations in WOC development are described. The first class of WOCs are presented that combine the stability benefits of heterogeneous WOCs with the reactivity and other benefits of homogeneous WOCs.     

Ionic interdiffusion as interaction mechanism between Al and Si3N4

Al-Si₃N₄ couples were heat-treated at 850-1150°C for 250 hours. The thickness of the interacted area was measured by scanning electron microscopy (SEM) and scanning/transmission electron microscopy (TEM/STEM). The interaction rate increases exponentially with inverse temperature, with an activation energy of 194.23 kJ/mol and diffusion pre-coefficient of 5 × 10⁻⁹ m²/s, indicating that the interaction is diffusion-dependent. As the results showed, the interfacial area is comprised of Al alloy channels, Si precipitates, and AlN grains. Al-Si transfer through the solid solution (Si_3-xAl_xN_4-y) at the interface of Al alloy and β-Si₃N₄ grains controls the kinetic of the interaction. When concentration of Al in solid solution exceeds a certain amount, it undergoes a topotactic phase transformation to form Al_1-xSi_xN_1+y (viz., AlN). Next, the Al_1-xSi_xN_1+y grains detach from the β-Si₃N₄ grains and subsequently new Al-Si₃N₄ interfaces are established. These interfaces repeat the interaction process, continuing until all the reactant is depleted. Thus, the interaction kinetics consist of a sequence of associated parabolic stages, precluding the observation of parabolic kinetics.     

Pervaporation of toluene and iso‐octane through poly(vinyl alcohol)/graphene oxide nanoplate mixed matrix membranes: Comparison of crosslinked and noncrosslinked membranes

Removal of aromatic compounds from fuel is an essential requirement in new environmental policies. In the present study, poly(vinyl alcohol)/graphene oxide (GO) mixed matrix membranes were prepared and applied to the separation of toluene from iso‐octane by pervaporation, considering the similarity and interaction between graphene and aromatics. The effects of crosslinking and GO content on separation efficiency have been investigated in detail. Owing to the high affinity of GO with toluene through s and π bonds, the selectivity of the membranes was increased by incorporating a low amount of GO. The results also indicated that noncrosslinked membranes have higher selectivity and permeation flux due to higher crystallinity and also have lower mechanical properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45853.     

Variants in the PPARGC1A Gene may Influence the Effect of Fat Intake on Resting Metabolic Rate in Obese Women

Recent studies have shown that dietary intake and genetic variants play a decisive role in the risk of obesity. Therefore, this study was designed to examine the interaction between dietary fat and PPARGC1A polymorphisms on the level of resting metabolic rate (RMR). We enrolled 288 Iranian overweight and obese women in this cross‐sectional study. We sequenced the 648 b.p. DNA in Exon 8 of PPARGC1A gene. We analyzed the two single‐nucleotide polymorphisms, namely rs11290186 and rs2970847, in this region. All participants were assessed for RMR, dietary intake, and body composition. This study demonstrated that total cholesterol and insulin levels were positively associated with T allele carriers of rs2970847. Moreover, the A‐deletion allele carrier of the rs11290186 genotype had higher triacylglycerol and insulin concentrations. The current study revealed that, after adjustment for energy intake, the AA genotype of PPARGC1A (rs11290186) had a direct association with polyunsaturated fatty acids and linoleic acid intakes. Another important finding in our study was that there was an interaction seen between fat and saturated fatty acids intake with the PPARGC1A genotypes. Women with fat intakes of more than 30% of calorie intake per day and the A‐deletion genotype had a lower RMR and RMR/fat free mass (FFM). It seems that the PPARGC1A polymorphisms lead to the downregulation of insulin signaling and subsequently insulin resistance. In addition, the interactions between the PPARGC1A polymorphisms (rs11290186) and the level of dietary fat intake probably can have an effect on RMR and RMR/FFM in obese women.     

Digital printing of acrylic fabric with cationic dyes using conventional inkjet printer

A special printing ink formulation based on cationic dyes is developed for digital printing of acrylic fabrics using a conventional inkjet printer. In order to investigate the contribution of color gamut boundary of printer colorants to printing efficiency, customized color targets containing 3164 color patches in 25 different hues were generated. The printed color patches were then fixed through steaming for 30 minutes followed by washing with hot soap and water and finally drying. To show the influence of dye fixation on colorimetric changes as well as color gamut boundary of samples, the L*a*b* values of color patches before and after fixation process were compared. Results demonstrate that color saturation of samples is enhanced dramatically after the dye fixation process. In fact, 3D color gamut of color patches has been drastically expanded as a direct consequence of adsorption to absorption transition. Additionally, dye fixation changes the structure of printed image from halftone superimposed dots to contone superimposed dyes. Strictly speaking, during fixation process, colors inside the halftone dots diffuse through the interfacial area to make the individual printed dots integrated. This is in analogy to the chromogenic photography films and dye‐sublimation thermal transfer processes by which contone images are produced. Moreover, dye fixation improves the washing fastness of digitally printed acrylic fabrics to the level comparable with the traditional screen printing method. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 244–249, 2017