Large deflection of viscoelastic beams using fractional derivative model

This paper deals with large deflection of viscoelastic beams using a fractional derivative model. For this purpose, a nonlinear finite element formulation of viscoelastic beams in conjunction with the fractional derivative constitutive equations has been developed. The four-parameter fractional derivative model has been used to describe the constitutive equations. The deflected configuration for a uniform beam with different boundary conditions and loads is presented. The effect of the order of fractional derivative on the large deflection of the cantilever viscoelastic beam, is investigated after 10, 100, and 1000 hours. The main contribution of this paper is finite element implementation for nonlinear analysis of viscoelastic fractional model using the storage of both strain and stress histories. The validity of the present analysis is confirmed by comparing the results with those found in the literature.     

Novel synthesis of Zn2GeO4/graphene nanocomposite for enhanced electrochemical hydrogen storage performance

For the first time, a novel technique of preparing Zn₂GeO₄ nanostructures has been developed by using chemical precipitation method of GeCl₄ as a Ge precursor and acacen as a capping agent. Uniform and fine Zn₂GeO₄ nanoparticle was synthesized. The optimized Zn₂GeO₄ nanostructures anchored onto graphene sheets and Zn₂GeO₄/graphene nanocomposite synthesized through pre-graphenization, successfully. Hydrogen storage capacities of Zn₂GeO₄ nanoparticle and Zn₂GeO₄/graphene nanocomposite were compared, for the first time. Obtained results represent that Zn₂GeO₄/graphene nanocomposites have higher electrochemical hydrogen storage capacity than Zn₂GeO₄ nanoparticles. It was found that the synergistic effect between Zn₂GeO₄ nanoparticles and graphene sheets can improve the electrochemical performance of this hybrid composite electrode. After 29 cycles, the discharging capacities of the electrode reached to 2695 mAh/g. These results indicate that the Zn₂GeO₄/graphene nanocomposite can be potentially applied for electrochemical hydrogen storage.     

Temporal development of melt-pool morphology and clad geometry in laser powder deposition

A transient finite element approach is developed to simulate the temporal evolution of the melt-pool morphology and dimensions during laser powder deposition. The in-process addition of material is numerically carried out in a coupled manner through activation of a new set of elements within each solution time step. The geometry of the deposited material is finely predicted without assuming any of the geometrical characteristics, such as height, width, and/or the general shape, as a priori. Experimental verification of the model for deposition of AISI 304L reveals a good agreement between the predicted and measured temperature and geometry of the deposited material. The model presents a high accuracy in simulation of 3D melt-pool morphology and geometry in deposition of Ti45Nb on Ti–6Al–4V. It is shown, using the developed model, that local solidification conditions, i.e., the temperature gradient and interface velocity, can be accurately evaluated along the predicted solid/liquid interface. Moreover, the presented model is able to show the effect of the laser scan velocity on the amount of dilution from the substrate.     

A novel lutetium(III) PVC membrane sensor based on a new symmetric S–N Schiff's base for Lu(III) analysis in real sample

A novel Lu(III) PVC membrane sensor has been constructed based on a new synthesized symmetric S–N Schiff's base, namely N-[(Z)-1-(2-thienyl)methylidene]-N-[4-(4-{[(Z)-1-(2-thienyl) methylidene]amino}benzyl)phenyl] amine (TBPA). The electrode showed a Nernstian slope of 19.8 ± 0.5 mV per decade across a wide concentration range of 1.0 × 10^? 6 to 1.0 × 10^? 2 mol L^? 1 with a detection limit of 7.2 × 10^? 7 mol L^? 1. The proposed sensor showed high selectivity toward Lu(III) ion in comparison with common alkaline, alkaline earth, transition, and heavy metals specially lanthanide ions, and could be used over a pH range of 2.7–10.6. It can be used for at least 2 months without any considerable divergency in potentials and it has a relatively fast response time of < 10 s. The sensor was effectively used as an indicator electrode in the potentiometric titration of Lu(III) ions with EDTA. The constructed sensor accuracy was investigated by the monitoring of Lu(III) ion in mixtures of two and three different ions.     

Iodide selective membrane electrodes based on a Molybdenum–Salen as a neutral carrier

A new polymeric membrane electrode (PME) and a coated platinum disk electrode (CPtE) based on Schiff base complex of Mo(VI) as a suitable carrier for I^? ion were described. The influence of membrane composition, pH and possible interfering anions were investigated on the response properties of the electrodes. The electrodes exhibited a Nernstian slope of 63.0 ± 0.5 (CPtE) and 60.3 ± 0.4 (PME) mV decade^? 1 in I^? ion over a wide concentration range from 7.9 × 10^? 7 to 1.0 × 10^? 1 M for CPtE and 9.1 × 10^? 6 to 1.0 × 10^? 1 M I^? for PME. The potentiometric response of the electrodes was independent of the pH of the test solution in the pH range 2.0–8.5 with a fast response time (< 10 s). The process of transfer of iodide across the membrane interface was investigated by use of the AC impedance technique. The proposed sensors were successfully applied to direct determination of iodide in samples containing interfering anions, waste water and as indicator electrodes in precipitation titrations.     

Synthesis and characterization of nanocrystalline merwinite (Ca3Mg(SiO4)2) via sol-gel method

In this research, the synthesis of nanocrystalline merwinite (2SiO₂-3CaO-MgO) bioactive ceramic was carried out by the sol-gel method. After crushing, obtained sol-gel derived bioceramic powder pressed uniaxially to produce cylindrical-like pellets, followed by sintering at 1300 °C. Via immersion in simulated body fluid (SBF) for various time intervals, the formation of apatite was characterized. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Fourier transform infrared spectroscopy (FT-IR) studies were conducted both before and after immersion in SBF. The crystallization temperature of the merwinite was determined by thermal analysis. Attained results confirmed formation of apatite layer within the first day of soaking. Accordingly it can be concluded that merwinite is bioactive and might be used for preparation of implantable biomaterials.     

Novel nanofiber-based triple-layer proton exchange membranes for fuel cell applications

New types of triple-layer membranes were fabricated using multi-step impregnation of Nafion in electrospun webs based on bead-free nanofibers of sulfonated poly(ether sulfone) (SPES). The results showed that the fabricated nanofiber-filled membrane owing to its reduced methanol permeability as well as sufficient proton conductivity and membrane selectivity can be used as a promising proton exchange membrane for direct methanol fuel cell (DMFC) applications. The single cell DMFC performance results revealed that the SPES nanofiber-based triple-layer membranes have higher electrochemical performance than commercial Nafion membranes.     

The effects of yeasts involved in the fermentation of Coffea arabica in East Africa on growth and ochratoxin A (OTA) production by Aspergillus ochraceus

The effects of Pichia anomala, Pichia kluyveri and Hanseniaspora uvarum predominant during coffee processing on growth of Aspergillus ochraceus and production of ochratoxin A (OTA) on malt extract agar (MEA) and on coffee agar (CA) were studied. The three yeasts were able to inhibit growth of A. ochraceus when co-cultured in MEA and CA. Growth inhibition was significantly higher on MEA than on CA. Furthermore, P. anomala and P. kluyveri were found to have a stronger effect on growth of A. ochraceus than H. uvarum. The three yeasts were able to prevent spore germination of A. ochraceus in yeast glucose peptone (MYGP) broth. In yeast-free supernatant of MYGP broth after an incubation period of 72 h, spores of A. ochraceus were able to germinate with very short germ tubes, but further development of the germ tubes was inhibited. The three yeasts decreased the pH of MYGP broth from 5.6 to a range of 4.4-4.7, which was found to have no effect on spore germination of A. ochraceus. P. anomala, P. kluyveri and H. uvarum were able to prevent production of OTA by A. ochraceus when co-cultured on MEA. On CA medium, P. anomala and P. kluyveri prevented A. ochraceus from producing OTA. H. uvarum did not affect production of OTA by A. ochraceus on CA medium.     

Use of hyperspectral imaging for evaluation of the shelf-life of fresh white button mushrooms (Agaricus bisporus) stored in different packaging films

The shelf life of mushrooms packaged using different polymer top-films (PVC, PET with different levels of perforations) was investigated using hyperspectral imaging (HSI). Packaged mushrooms were stored at 4 ± 0.2 °C for 14 days and weight loss, Hunter L, a, b values, maturity index and in-pack gas composition (% CO₂ and O₂) were also measured. The results obtained showed that the PET film perforated with small holes (1 mm in diameter) was generally superior in terms of maintaining overall mushroom quality. Regression models were built to correlate HSI data with measured quality parameters. Prediction maps were generated from hyperspectral data to show the model performance at pixel level. Results presented in this work show hyperspectral imaging can be used to evaluate the effect of different packaging systems on mushroom quality and that perforated PET packaging film is a viable alternative to the conventional PVC packaging, facilitating an increase in shelf life from 10 to 14 days.Industrial relevanceThe present study demonstrates HSI can be used for rapid evaluation of mushroom quality facilitating non-destructive evaluation of the effect of packaging systems on mushroom shelf-life. In addition, this work suggests an effective packaging solution to extend shelf life of mushrooms during storage. The proposed solution potentially improves the packaging recyclability as the same polymer material (PET) is used for the tray and top film, compared to conventional mushroom packaging where PVC is used for the top film and polypropylene (PP) for the tray.     

A qualitative X-ray analysis of white and grey mineral trioxide aggregate using compositional imaging

Mineral trioxide aggregate (MTA) is used in endodontics as a filling and sealant material. An earlier commercial formulation Grey MTA (GMTA) was liable to became progressively discoloured, and a whiter version (WMTA) has been introduced for cosmetic reasons. This study compares the composition and particle size distribution of the two formulations using energy dispersive X-ray analysis in a scanning electron microscope. Particle size is smaller in WMTA. X-ray analysis reveals similar major peaks (calcium, silicon and bismuth) but those of the minor elements aluminium, magnesium and particularly iron are considerably less in WMTA, which may account for the colour difference. Neither contains phosphorus, a major constituent of the original formulation. Author to whom all correspondence should be addressed