Nonlinear viscoelastic modeling of soft polymers

A one‐dimensional phenomenological constitutive model, representing the nonlinear viscoelastic behavior of polymers is developed in this study. The proposed model is based on a modification of the well‐known three element standard solid model. The linear dashpot is replaced by an Eyring type one, while the nonlinearity is enhanced by a nonlinear, strain dependent spring constant. The new constitutive model was proved to be capable of capturing the main aspects of nonlinear viscoelastic response, namely, monotonic and cyclic loading, creep and stress relaxation, with the same parameter values. Model validation was tested on the experimental results at various modes of deformation for two elastomeric type materials, performed elsewhere. A very good agreement between model simulations and experimental data was obtained in all cases. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42141.     

Mint and pomegranate extracts/oils as antibacterial agents against Escherichia coli O157:H7 and Listeria monocytogenes on shredded carrots

Among minimally processed vegetables, shredded carrots are particularly popular. The aim of this study was to evaluate the antimicrobial activity of different washing treatments with aqueous solutions of mint essential oil (EO) (1:1000), mint hydrosol (1:10), and pomegranate juice (1:10) against two major foodborne pathogens on shredded carrots as well as their effect on carrot's quality. The results of this study indicate that the tested washing treatments resulted in a small but significant decrease of the microbial load of Escherichia coli and Listeria monocytogenes on the sixth day of storage. Pomegranate juice and mint hydrosol were more effective against L.   monocytogenes, whereas mint EO was more effective against E.   coli. Furthermore, an increase in carrot's total phenolics and antioxidants was observed with the application of mint hydrosol and pomegranate juice, whereas mint EO resulted in a decrease on the sixth day of storage. Additionally, a decreased chroma of the shredded carrots were observed during the application of mint hydrosol on the sixth day. Total carotenoids, ascorbic acid, total soluble solids, and tritratable acidity were not differing after six days of storage of shredded carrots. These washing products can be used for the partial disinfection of shredded carrots.

Practical applications

Pomegranate and mint natural products solution can be used for the partial disinfection of minimally processed fresh produce as an alternative to chlorine, and these products can be a part of the sanitation process.     

Revisiting the cutting of the firing squad synchronization

Various synchronization algorithms have been introduced in literature during the last decades to deal with the firing squad synchronization problem on cellular automata (CA). Among others defective CA algorithms, where the CA cell is able to transmit information without previous processing, have been also presented. In our case, originating from the classical Mazoyer’s paper, where a minimum-time solution is presented with 6 states, a one-dimensional CA where one cell may permanently fail is presented. In the proposed algorithm, the defective cell can neither process nor transmit information any longer, while it is considered that such dynamic defects may become apparent in any time step of computation. A thorough analysis of the synchronization, in terms of location and time at which cell fails, for the cells found in both sides of defective cell is delivered to decipher the corresponding maximal possible number of synchronized cells in each part of the cut, due to defect, CA array. The proposed algorithm is properly extended to consider more than one defective cells that may occur in the under study one-dimensional CA. Based on the aforementioned analysis, we provide the generalization of synchronization with multiple totally defective cells, while application examples of the generalized CA algorithm in case of two defective cells are also presented. Finally, another intriguing aspect refers to handling of states that could be tentatively characterized as unknown, in a confrontation similar to the previous defective state but also different, since now this(these) cell(s) are not stated as faulty but unknown. As a result, a new one-dimensional CA with less states, compared to the previous CA defective algorithms, able to synchronize the maximal possible number of cells in each part occurs.     

Characterization of a water-dispersible metal protective coating with Fourier transform infrared spectroscopy, modulated differential scanning calorimetry, and ellipsometry

An ethylene-methacrylic acid copolymer, formulated by BASF as a waterborne suspension of its alkylammonium salt and used, among other applications, in art conservation as a temporary protective coating was characterized using Fourier transform infrared (FT-IR) spectroscopy aided by modulated differential scanning calorimetry (MDSC) and ellipsometry. The thermal conversion of thin copolymer films from the freshly applied state, where carboxylic acid and carboxylate ion functional groups co-exist, to a purely acidic working state was spectroscopically followed. Transmission mid-infrared data of the working state showed a 1 : 12 ratio of methacrylic acid towards ethylene units. The glass transition temperature (T(g)) in the same state was found at 45 °C. Copolymer films spin-coated on mechanically polished bronze and iron coupons were characterized with transflection infrared spectroscopy and compared to corresponding transmission mid-infrared spectra of copolymer films spin-coated on silicon wafers. In the case of bronze coupons, evidence for interaction of the carboxylate ion with the copper substrate was obtained. The chemical structure and the thermal behavior of the coating, as well as some implications on its protective capability towards iron and copper alloys, is discussed as this material has received considerable attention in the field of metal conservation and coatings.     

Mathematical investigation of interfacial property in fiber reinforced model composites

In the current paper, we have investigated the dependence of the effective elastic properties of a composite material on the fiber/matrix interface elastic property. The model composite consists of a single cylindrical fiber embedded in a concentric cylindrical matrix material. A three dimensional mathematical method has been developed connecting the interface properties with the effective axial Young’s modulus of the composite structure. Special effort has been devoted to decode information about the quality of the interface by exploiting the information provided by the elastic effective parameters. In particular, the effective modulus vs. stiffness coefficient curves have been generated for Ti/SiC composites. The aforementioned curves reveal the characteristics of the transition from the regime of perfect interface to the realm of complete debonding.     

On the gradient elastic wave propagation in cylindrical waveguides with microstructure

The present work describes the development of a complete theoretical framework of wave propagation in cylindrical waveguides possessing microstructure. In parallel, a thorough investigation of the full 3-D model of wave propagation in cylinders is presented. The first step is the spectral decomposition of the boundary value problem emerging via wave propagation analysis. The spectral representation of the specific gradient elasticity problem reflects the ability to construct all the possible propagating modes in cylindrical geometry. Several byproducts arise along the present work, which constitute generalizations of well known important features of classical elasticity and are indispensable for modeling the gradient elasticity problem. We note the construction of the set of dyadic Navier eigenfunctions which constitute the generalization of the Navier eigenvectors. The restriction of the Navier eigendyadics on cylindrical surfaces gives birth to the dyadic cylindrical harmonics, which constitute the generalization of the well known vector harmonics. This set is also a basis in the sense that the trace of every dyadic field on a cylindrical surface can be represented as a countable superposition of dyadic cylindrical harmonics. The method aims at providing the necessary theoretical establishment for the determination of the dispersion curves emerging in cortical bones.