The unsteady pressure field and the aerodynamic performances of a Savonius rotor based on the discrete vortex method

The aim of this paper is to numerically explore the non-linear two-dimensional unsteady potential flow over a Savonius rotor and to develop a code for predicting its aerodynamics performances. In the model developed, the rotor is represented in a median plane by two semicircles, displaced along their common diameter. The two semicircles can be considered to produce lifting effects. As a result, they are modelled by a collection of discrete vortices on their contours. The flow field is then governed by the Laplace equation. The versatile Neumann boundary condition, applied over the contour of the semicircles and the Kutta Joukowsky condition applied at the four extremities of the semicircles have been used in the modelling. The torque distribution of the stationary rotor and the unsteady pressure field on the blades of the rotating rotor, predicted by the code developed, have been compared and validated by some experimental data.     

A prototype of a fuel cell PEM emulator based on a buck converter

After a brief introduction about fuel cell systems, and their modelling, this paper proposes a possible solution to emulate a proton exchange membrane fuel cell (PEM-FC) system by using a DC–DC buck converter. The fuel cell system, including all its auxiliaries and related control systems, is emulated by a buck converter realized experimentally and controlled in the DSPACE environment. The realization of the buck converter allows the behaviour of any fuel cells to be easily emulated since only the modification of the control law of the switch is necessary. The proposed emulator can be applied easily to other fuel cell systems if the polarization curve has the same current rate and maximum power. In this way it is possible to utilize the converter and perform the necessary tests to optimize a fuel cell system by avoiding the waste of hydrogen and the purchase of cells as well as any cell damage. With regard to current other types of emulators, the one presented here has the following characteristics: (1) all the auxiliaries of the system have been considered, each including its own control system, as in a real FCS, (2) the converter is a classical buck converter with a free-wheeling diode and is designed to have a high bandwidth and to be practically always in conduction mode (discontinuous mode appears only at very low currents) (3) the voltage control is made by a space-state controller, able to fix properly the closed loop poles of the system, thus guaranteeing the desired bandwidth of the control system and (4) it can be used in laboratory as a stand-alone low-cost system for design and experimental purposes.     

Method for reliable isolation of Lactobacillus sakei strains originating from Tunisian seafood and meat products

In Tunisia, several food products derived from meat or seafood are naturally processed, without any addition of bacterial starters. Such fermented, dried-cured, salted, or marinated products, as well as the raw meat or fish may thus provide a source to isolate the natural microflora colonizing such environments. We isolated lactic acid bacteria from a representative range of flesh-foods sold or manufactured in different parts of Tunisia, and selectively searched for Lactobacillus sakei, a lactic acid bacterium potentially useful as starter or protective culture. Eighty six (86) strains were isolated from various seafood (anchovy, sardine, sole, mullet, and octopus), or meat (pork, veal, beef, sheep, chicken, and turkey) products that were either fresh, or transformed by different traditional processes. Several methods were used in order to develop a rapid and reliable protocol for the direct identification of L. sakei. Amplified ribosomal DNA restriction analysis (ARDRA) classified the various isolates into 9 distinct groups. Search for the presence of the L. sakei specific katA gene indicated that all positive isolates were grouped in the same ARDRA group. Sequencing of 16S rDNA confirmed those isolates as L. sakei. Those 22 different L. sakei strains represent 25.6% of the total isolates, while other isolates found in the different ARDRA groups were tentatively ascribed to Lactobacillus plantarum, Lactococcus lactis/garviae, Enterococcus avium, Streptococcus parauberis, Hafnia alvei, Pediococcus pentosaceus, and Lactobacillus curvatus through 16S rDNA sequencing. A fast and reliable method to isolate and discriminate L. sakei from complex food environments is proposed.     

Polymerization compounding composites of nylon‐6,6/short glass fiber

Nylon‐6,6 was grafted onto the surface of short glass fibers through the sequential reaction of adipoyl chloride and hexamethylenediamine onto the fiber surface. Grafted and unsized short glass fibers (USGF) were used to prepare composites with nylon‐6,6 via melt blending. The glass fibers were found to act as nucleating agents for the nylon‐6,6 matrix. Grafted glass fiber composites have higher crystallization temperatures than USGF composites, indicating that grafted nylon‐6,6 molecules further increase crystallization rate of composites. Grafted glass fiber composites were also found to have higher tensile strength, tensile modulus, dynamic storage modulus, and melt viscosity than USGF composites. Property enhancement is attributed to improved wetting and interactions between the nylon‐6,6 matrix and the modified surface of glass fibers, which is supported by scanning electron microscopy (SEM) analysis. The glass transition (tan δ) temperatures extracted from dynamic mechanical analysis (DMA) are found to be unchanged for USGF, while in the case of grafted glass fiber, tan δ increases with increasing glass fiber contents. Moreover, the peak values (i.e., intensity) of tan δ are slightly lower for grafted glass fiber composites than for USGF composites, further indicating improved interactions between the grafted glass fibers and nylon‐6,6 matrix. The Halpin‐Tsai and modified Kelly‐Tyson models were used to predict the tensile modulus and tensile strength, respectively.     

Takagi–Sugeno fuzzy modeling for three-phase micro hydropower plant prototype

Micro hydropower plants (MHPP) are widely set up in off-grid sites to provide electrical power. The power quality in such site is a challenge and requires an accurate model for MHPP. The model has to be available for large operating points. Moreover, the model must take into consideration the non-linear character of the system. For these reasons, the present paper proposes a Takagi–Sugeno (T.S) fuzzy model approach for modeling the overall behavior of a three-phase MHPP prototype. This modeling is based on the identification of simple approximations by first and second order systems around several operating points of the system. These operating points depend on different water flows and electric load variations. The developed T.S fuzzy models were experimentally validated taking into consideration various working conditions. The results show that the approximation by the second order system has better accordance with the real system responses. Therefore, this approximation devotes more opportunities to synthesize suitable and robust controllers for MHPP compared to the first order one.     

Authenticated encryption on FPGAs from the static part to the reconfigurable part

Recently, techniques have been invented to combine encryption and authentication into a single algorithm which is called Authenticated Encryption (AE). Combining these two security services in hardware produces smaller area compared to two separate algorithms.     

Methane decomposition into COx-free hydrogen and carbon nanomaterials over ZrO2–M (M = MgO,Al2O3, SiO2, La2O3 or CeO2) binary oxides supported cobalt catalysts

Hydrogen production via methane decomposition has attracted great attention as a source of clean energy. In this work, the catalytic decomposition of undiluted methane into CO_x-free hydrogen and carbon nanomaterial over ZrO₂–M (M?=?MgO, Al₂O₃, SiO₂, La₂O₃ and CeO₂) binary oxides supported Co catalysts was studied. The fresh and spent catalysts were characterized by XRD, H₂-TPR, N₂ adsorption–desorption, TEM and Raman spectroscopy. The results revealed that the incorporation of secondary oxide to ZrO₂ support played a vital role in the activity and stability of cobalt metal. The activity results illustrated that Co/Zr–Mg exhibited better activity in terms of hydrogen yield compared with the other Zr–M supported catalysts. This is ascribed to the moderate cobalt oxide-support interaction and forming CoMgO_x species which enhance the Co₃O₄ dispersion and prevent its aggregation on the catalyst surface. On the other hand, the Co/Zr–Si catalyst showed the lowest activity due to the agglomeration of Co₃O₄ on the surface of the SiO₂ support. High-resolution TEM images illustrated that almost the deposited carbon on the surface of spent catalysts was in the form of multi-walled carbon nanotubes.     

Catalytic grafting: A new technique for polymer–fiber composites I. Polyethylene–asbestos composites

In this work we present a new technique to prepare polyolefin-fiber composites. This technique is based on chemical anchoring of a catalyst on reinforcing agents containing OH groups on their surface and then conducting an olefin polymerization on the supported catalyst. This technique offers the possibility to approach the challenging problems encountered in polymer composites, namely, the reinforcement-matrix adhesion, the dispersion, and the wetting of the reinforcement by the resin. As a first part of a systematic research, we report on the procedure of fixation of titanium tetrachloride on the surface of asbestos fibers and the Ziegler-Natta polymerization of ethylene on the surface-modified fibers. The procedure as well as the structure and properties of the composite were investigated by means of FTIR, atomic absorption, SEM, solvent extraction, and tensile testing. The experimental results show that the Ziegler-Natta catalyst can be efficiently anchored on the surface of the fibers to conduct successful polymerization and to “synthesize” a new class of polymer composites.