Combination of a standard viscoelastic model and fractional derivate calculus to the characterization of polymers

Polymeric materials are known to be more or less dispersive and absorptive. In the field of mechanical vibrations, dispersion has for consequence that the dynamic modulus is frequency dependent, and absorption is exhibited by the fact that these materials have the ability to absorb energy under vibratory motion. The phenomenon of dispersion in conjunction with the notion of complex Modulus of Elasticity, permits to establish the relation between the real and the imaginary components of the Modulus of Elasticity, i.e. respectively the dynamic and loss moduli. The loss factor is simply determined through taking the quote of these two components of the Modulus of Elasticity. The theoretical background for the interrelations between the dynamic modulus and the loss modulus is found in the Kramers–Kronig relations. However, and due to the mathematical difficulties encountered in using the exact expressions of these relations, approximations are necessary for applications in practical situations. On the other hand, several simple models have been proposed to explain the viscoelastic behaviour of materials, but all fail in giving a full account of the phenomenon. Among these models, the standard viscoelastic model, or more known as the Zener model, is perhaps the most attractive one. To improve the performance of this model, the concept of fractional derivates has been incorporated into it, and which results in a four-parameter model. Applications have also shown the superiority of this model when theoretical predictions are compared to experimental data of different polymeric materials. The aim of this paper is to present the results of applying this model to rubber, both natural and filled, and to some other selected more general polymer. Electronic Publication     

Extension of the shelf life of beef steaks packaged in a modified atmosphere by treatment with rosemary and displayed under UV-free lighting

Fresh beef steaks, either sprayed on the surface with a solution of rosemary and vitamin C or not sprayed, were packaged in 70%O₂₊20%CO₂₊10%N₂ and displayed at 1±1 °C without illumination or illuminated by a standard fluorescent lamp, a low-UV, colour-balanced lamp (Promolux®), or the fluorescent lamp with a UV filter. Metmyoglobin formation, lipid oxidation (2-thiobarbituric acid reactive substances), instrumental colour (CIE L*, a*, b*), psychrotrophic bacterial counts (PCA) and sensory discolouration and off-odour were determined. Results showed that the use of the antioxidant mixture of rosemary and vitamin C together with the absence of UV radiation significantly reduced the rates of metmyoglobin formation and lipid oxidation, as well as microbial growth, and extended the display life from about 10 to about 20 days.     

Display life of beef packaged with an antioxidant active film as a function of the concentration of oregano extract

Fresh beef steaks were packaged with a new antioxidant active system containing increasing concentrations (0.5, 1, 2 and 4%) of an oregano extract. Control samples were packaged without the active film. Additional samples were sprayed with the extract and packaged as the control samples. Packages were filled with a 80%O(2)/20%CO(2) atmosphere and displayed under illumination (14 h) at 1 ± 1 °C for 28 days. Metmyoglobin formation, lipid oxidation (TBARS), instrumental colour (CIE a*) and sensory colour, discoloration, off-odour and oregano smell were determined. Active packaging significantly (P < 0.05) enhanced oxidative stability of beef steaks, depending on the oregano concentration of the active film. The display life of beef samples demonstrated that at least 1% oregano was needed for obtaining a significant increase of display life from 14 to 23 days. A concentration of 4% gave rise to unacceptable oregano smell. As a consequence, most suitable oregano extract concentrations for optimum active packaging in this system should be within the range 1-2%.     

2D‐DOA estimation performance using split vertical linear and circular arrays

This paper presents a new approach to reduce the computational complexity in two‐dimensional (2D) matrix pencil (MP) method for direction of arrival (DOA) estimation of plane wave signals using a combination of vertical uniform linear array (VULA) and uniform circular array (UCA). By applying phase mode excitation based beamforming to the UCA, we can apply the matrix pencil (MP) method to the beamspace data using only a single snapshot. The technique is based on the split array, which is composed of two perpendicular arrays. The vertical uniform linear array used to determine the elevation DOA components is located perpendicularly at the center of the uniform circular array in the horizontal plane used to calculate the azimuth angles. Unlike common planar and circular arrays, this antenna array with its particular geometry requires no pair‐matching between the azimuth and the elevation angle estimation and can also remove the drawbacks of estimation failure problems. Using this particular geometry for the 2D MP method leads to an efficient computational methodology for real‐time implementation on a digital signal processor. The obtained simulation results of the MP method applied to both uncorrelated and correlated narrow‐band sources in the presence of white noise show good performance estimation. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Numerical study of mixed convection in a ventilated square enclosure with the lattice Boltzmann method

In this article, numerical study of heat transfer by convection in a square cavity was investigated. The vertical walls of the cavity are differentially heated and the horizontal walls are considered adiabatic. A ventilation jet is created by a fan placed in the cavity. A lattice Boltzmann model for incompressible flow equation is used to simulate the problem. A parametric study was performed presenting the influence of Reynolds number (20 ≤ Re?≤?500), Rayleigh number (10≤Ra?≤?10⁺⁶), and fan position (0.2?≤?L_F≤0.8). It has been observed that heat transfer rate increases with the Reynolds number increasing and it is maximal for the L_F=0.2.     

Study of the miscibility of poly(ethyl methacrylate-co-4-vinylpyridine)/poly(styrene-co-cinnamic acid) blends

Summary The miscibility of a series of poly(ethyl methacrylate-co-4-vinylpyridine) with poly(styrene-co-cinnamic acid), is investigated by differential scanning calorimetry. The results show that each blend is miscible as ascertained by a single composition dependent glass transition temperature. The Tg's of the blends exhibit positive deviations from the weight average Tg's of the blend components. The thermograms data exploited according to the Kwei and Schneider approaches suggest the occurrence of strong specific intermolecular attractive interactions within the binary systems. The strength of these interactions, as estimated from the Kwei q-values, increases with the proton donor and proton acceptor contents in the copolymers. Received: 23 January 1999/Revised version: 29 April 1999/Accepted: 1 June 1999     

Computing Shear Flow and Sludge Blanket in Secondary Clarifiers

Recent developments in computing turbulent and buoyant flow in sedimentation tanks are introduced. The test case is a circular, center-feed secondary clarifier with inclined bottom and central sludge withdrawal. Axisymmetry is assumed, and the flow and settling processes are modeled in a radial section by using the k-ε turbulence model on a two-dimensional, nonorthogonal grid. The computation domain includes the sludge blanket where the viscosity is affected by the rheological behavior of the sludge. The aim of the present study is to evaluate the sensitivity of the flow and concentration fields to parameters that characterize (1) the rheological properties of highly concentrated regions; (2) the settling of sludge; and (3) the effect of stratification on the turbulent diffusion. The overall appearance of the fields proves to be similar, whereas the regions of high velocities and high gradients are strongly affected by using different parameters or approaches on rheology, settling, and diffusive transport, resulting in different sludge blanket heights.     

Numerical analysis of earth air heat exchangers at operating conditions in arid climates

This paper presents the modeling and simulation of an earth air heat exchanger (EAHE), employed as an air-conditioning device for buildings in the climate conditions of the south of Algeria. The earth tubes buried in the ground can offer considerable advantages in terms of energy savings. The appropriate depth of the buried tubes was calculated taking into account the physical properties of the soil in the region under study and using a specific program developed by the authors. A parametric analysis was carried out taking into account the length and the radius of the pipe and the velocity of the air in the pipe. The results of performance and overall energy savings are presented. The maximum daily cooling capacity of the EAHE studied was 1.755 kWh. Results showed that a simple EAHE system can provide 246.815 kWh in a period of one year.     

Miniaturized six-ring elliptical monopole-based MIMO antenna for ultrawideband applications

This paper proposes a miniature two-element Multiple Input Multiple Output (MIMO) antenna dedicated to UWB applications. The proposed MIMO design has a very low profile of 30 × 20 × 1.6 mm³. The proposed antenna is carefully designed and optimized using HFSS simulation software. As a proof of concept, the proposed design is realized and experimentally tested for MIMO applications. The proposed structure, printed on an FR4 substrate, comprises two symmetrical elliptical conductive patches on the upper side and a modified ground plane on the lower one. Each radiating element includes six elliptical rings. The modified ground plane consists of a T-shaped strip and two semielliptical slots etched opposite the feed line. All the parameters of the design are carefully optimized to achieve an ultrawide bandwidth antenna spanning from (136.08%) 3.1 to 16.3 GHz. The results are discussed and analyzed in terms of bandwidth, gain, efficiency, radiation pattern, diversity gain, envelope correlation coefficient (ECC), total active reflection coefficient (TARC), and mean effective gain (MEG). All simulated results are found to be in good accordance with experiments. The design reveals attractive features for UWB applications. A good isolation (17 dB) between the two radiators is achieved despite the close proximity using the suggested ground plane geometry.     

Chitosan nanoparticles with controlled size and zeta potential

Optimization of chitosan nanoparticles (ChNs) production process employing a 2^(5–2) fractional factorial design was performed to analyze the influence of viscosity average molecular weight (40–120 kDa), the initial concentration of chitosan (2–5 g/L), the initial tripolyphosphate (TPP) concentration (0.8–1.2 g/L), the ratio chitosan/TPP (4/1–10/1) (V/V), and the stirring speed (300–700 rpm), on final nanoparticles size and zeta potential. The measured responses of average particle size and surface charge were determined on Zetasizer Nano ZS. ChNs were prepared using ionotropic cross-linking of chitosan and TPP and were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and differential scanning calorimetry (DSC). The experiments showed that the size of synthesized nanoparticles depended on initial concentration and molecular weight of chitosan, TPP concentration and stirring speed within the chosen levels. However, the zeta potential was significantly influenced by chitosan molecular weight, chitosan concentration and stirring speed. The FTIR analysis confirmed the interaction between negative charge of TPP with positive charge of chitosan through the appearance of new peaks at 1222 and 895 cm⁻¹ in produced ChNs. XRD and DSC analysis were used to evaluate the effect of crosslinking of chitosan on crystal structure of ChNs.