Experimental investigation of the flow-induced motion of a square-section cylinder

The flow-induced motion(FIM)of an elastically mounted square-section cylinder is experimentally investigated over a wide range of Reynolds numbers(1.5×104＜Re＜7....     

Synthesis and thermal stability of (Co,Ni)O solid solutions

(Co,Ni)O solid solutions are considered as promising protective materials of O₂-evolving anodes for Al production. In this context, two solid-state synthesis methods, namely high-energy ball milling (HEBM) and calcination, have been evaluated for the synthesis of (Co,Ni₎O solid solutions. In all cases, Co_xNi_1−xO solid solutions can be formed over the whole composition range. However, undesired WC contaminant is observed using the HEBM method due to the erosion of the milling tools. Their thermal stability in air has been analyzed by thermogravimetric analyzes (TGA) complemented by X-ray diffraction (XRD) analyses. It is shown that Co_xNi_1−xO solid solutions are stable at 1000°C over the whole composition range whereas they are only stable for x ≤ 46 and x ≤ 22 at 800°C and 700°C, respectively. For higher Co contents, the formation of Co₃O₄ is observed. This is a relevant information for their future use for Al production, which can be done at different temperatures (~700-1000°C) depending of the electrolyte composition.     

Robust non-aggressive three-axis attitude control of spacecraft: dynamic sliding mode approach

Conventional sliding mode control (SMC) has been extensively applied in controlling spacecrafts because of its appealing characteristics such as robustness and a simple design procedure. Several methods such as second-order sliding modes and discontinuous controllers are applied for the SMC implementation. However, the main problems of these methods are convergence and error tracking in a finite amount of time. This paper combines an improved dynamic sliding mode controller and model predictive controller for spacecrafts to solve the chattering phenomenon in traditional sliding mode control. To this aim, this paper develops dynamic sliding mode control for spacecraft’s applications to omit the chattering issue. The proposed approach shows robust attitude tracking by a set of reaction wheels and stabilizes the spacecraft subject to disturbances and uncertainties. The proposed method improves the performance of the SMC for spacecraft by avoiding chattering. A set of simulation results are provided that show the advantages and improvements of this approach (in some sense) compared to SMC approaches.     

Design of explicit model predictive control for constrained linear systems with disturbances

On-line model predictive control approaches require the online solution of an optimization problem. In contrast, the explicit model predictive control moves major part of computation offline. Therefore, eMPC enables one to implement a MPC in real time for wide range of fast systems. The eMPC approach requires the exact system model and results a piecewise affine control law defined on a polyhedral partition in the state space. As an important limitation, disturbances may reduce performance of the explicit model predictive control. This paper presents efficient approach for handling the problem of using eMPC for constrained systems with disturbances. It proposes an approach to improve performance of the closed loop system by designing a suitable state and disturbance estimator. Conditions for observability of the disturbances are considered and it is depicted that applying the disturbance’s estimation leads to rejection of the response error. It is also shown that the proposed approach prevents the reduction of feasible space. Simulation results illustrate the advantages of this approach.     

Microwave absorption characterization and wettability of magnetic nano iron oxide/recycled PET nanofibers web

This paper describes the microwave characterization and wettability of a uniform and light magnetic nanofibers web. Iron oxide nanoparticles/recycled poly (ethylene terephthalate) nanofibers web (Fe₃O₄ NPs/RPET NFs web) were fabricated from bath-sonication solution via electrospinning method. For environmental conservation and economic reasons, RPET instead of virgin material was used. After synthesizing magnetic Fe₃O₄ NPs with an average diameter of 35?nm by precipitation method using iron sulfate and sodium hydroxide, Fe₃O₄ NPs/RPET NFs web was made. The main objective of this work is to show how Fe₃O₄ NPs are able to significantly modify electromagnetic properties at X-band frequencies. Microwave characterization is based on the microwave scattering parameters measured in the X-band (8–12?GHz). Various characterization methods, including field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM), have been used to study morphologies, crystalline structure, magnetic, and wettability properties of NFs web. The saturation magnetization of the Fe₃O₄ NPs/RPET NFs web at a concentration of 5% was 2.79?emu/g. The mathematical model was estimated for magnetization, diameter and concentration by MathWorks Model Predictive Control Toolbax Software. The wettability, reflection coefficient, absorption coefficient, and EMI shielding of Fe₃O₄ NPs/RPET NFs web have been improved compared to RPET NFs web.     

Microwave absorption and photocatalytic properties of magnetic nickel nanoparticles/recycled PET nanofibers web

Abstract

The use of nanoparticles in electrospun web has always been of great interest for a wider and easier application especially for microwave absorption and photocatalytic activity. In this work, nickel nanoparticles/recycled poly (ethylene terephthalate) nanofibers web (Ni NPs/RPET NFs web) were electrospun from a homogeneous sonicated RPET solution containing Ni NPs with an average diameter of 32.5?nm synthesizedthrough the chemical reduction method. To study morphologies, crystalline structure, magnetic, wettability, microwave absorption and photocatalytic activities of the web, field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and electromagnetic properties were used. The saturation magnetization of the Ni NPs/RPET NFs web at a nickel concentration of 3% was 0.5?emu/g. In addition, the wettability, the reflection coefficient, the absorption coefficient, the EMI shielding and the photocatalytic activities of the Ni NPs/RPET NFs web were improved compared to the RPET NFs web.     

Enhancement of Chilling Stress Tolerance of Tomato Fruit by Postharvest Brassinolide Treatment

Tomatoes, originally a tropical fruit, cannot easily be stored at low temperatures, due to the risk of chilling injury (CI). To develop an effective technique to reduce CI, the effects of treatment with 0, 3, and 6 μM brassinolide (BR) on chilling injury, electrolyte leakage (EL), contents of malondialdehyde (MDA) and proline, and activities of phospholipase D (PLD) and lipoxygenase (LOX) were investigated in tomato fruit stored at 1 °C for 21 days. Treatment with BR, especially at 6 μM, significantly alleviated chilling injury, reduced EL and MDA content, and increased proline content. Also, fruit treated with BR exhibited significantly lower PLD and LOX activities as compared with the control fruit. These results suggest that PLD and LOX are associated with the induction of CI in tomato fruit. BR might reduce CI by inhibiting PLD and LOX activities and by enhancing membrane integrity.     

Turbo Interference Mitigation in Layered Space-Time MIMO DS-CDMA Uplink with TTCM(Turbo Trellis Coded Modulation)

In this paper we propose the use of a turbo receiver for the uplink of a MIMO CDMA system employing layered space-time transmission. The proposed receiver consists of a low complexity layered space-time multi-user detector using minimum mean squared error (MMSE) filtering with a-priori information and a bank of MAP SISO decoders. Using the soft estimates from a bank of MAP decoders we obtain soft values of the interfering symbols. The SISO multiuser detector subtracts the vector of the interfering symbols from the incoming signal. The resulting vector is then filtered by an adaptive MMSE filter to reduce the residual MAI. This process iterates by exchanging extrinsic informations between the bank of MAP decoders and the SISO multiuser detector. Turbo Trellis Coded Modulation (TTCM) is used as Forward Error Correcting (FEC) code due to its high bandwidth efficiency. Our computer simulations show that the proposed structure outperforms a classical iterative receiver based on parallel interference cancellation (PIC) as well as a non-iterative MMSE receiver. Furthermore, in a multiuser context, the proposed receiver offers an error performance similar to that of single-user case at high SNR. Jean-Pierre Cances graduated in electrical engineering from ENST Bretagne in 1990. He received his Ph.D degree from Télécom Paris in satellite communication engineering in 1993. He is now an assistant Professor at the Ecole Nationale Supérieure d'Ingénieurs de Limoges (ENSIL). His current research interests include satellite communication systems, multicarrier detection and synchronization algorithms, MIMO communication systems. Gholam Reza Mohammad-khani received his BSc. and MSc. degrees in communication engineering from Sharif University of Technology, Tehran, Iran, respectively in 1992 and 1994. He worked as a lecturer in Mashhad University in 1997. His current research interests include satellite communication systems, multiuser detection and synchronization algorithms. Vahid Meghdadi received his BSc. and MSc. degrees in communication engineering from Sharif University of Technology, Tehran, Iran, respectively in 1989 and 1992. He worked as a lecturer in Mashhad University in 1993. Since 1994, he has been a Ph.D. student inEcole nationale Supérieure d'Ingenieurs de Limoges (ENSIL) where he is now an assistant professor. His current research interests include satellite communication systems, multiuserdetection and synchronization algorithms, MIMO communication systems.     

High-Stability Platinum Nano-Electrocatalyst Synthesized by Cyclic Voltammetry for Oxygen Reduction Reaction

Cyclic voltammetry as a simple electrochemical deposition method was developed in order to prepare a platinum nano-electrocatalyst for oxygen reduction reaction (ORR) in low-temperature fuel cell systems. The morphology of the prepared platinum was evaluated by scanning electron microscopy and energy dispersive x-ray analysis. The effects of platinum concentration in electrodeposition solution and scan numbers of cyclic voltammetry (scan rate: 50 m V s^?1, between 1.489 and ??0.311 versus reversible hydrogen electrode) on the performance of prepared electrocatalysts for ORR were studied. The fabricated electrodes were evaluated by cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The results revealed that the optimum conditions for the preparation of electrocatalysts were 2E?3 M H₂PtCl₆ and 30 scan numbers. The optimized electrode showed high stability after 1200 cycles.     

Nano-magnetic-iron Oxides@choline Acetate as a Heterogeneous Catalyst for the Synthesis of 1,2,3-Triazoles

In this research, four cholines supported on core–shell iron oxides, Fe₂O₃@MgO@Ch.OAc (choline acetate), Fe₂O₃@MgO@Ch.OH (choline hydroxide), Fe₃O₄@Ch.OAc, Fe₃O₄@Ch.OH, were synthesized. The synthesized catalysts were tested in 1,2,3-triazoles synthesis by the reaction of nitromethane, aldehyde, and benzyl azide in EtOH as a green solvent. Among four synthesized heterogeneous catalysts, the Fe₂O₃@MgO@ch.OAc showed superior catalytic activity for the reaction and afforded the desired triazoles in good isolated yields under mild reaction conditions.

Graphic Abstract