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Figure 5 presents the cross-receptance of the wire for both sub-critical (α = 0.6) and overcritical velocities (α = 1.2). The angular frequency of the moving harmonic load corresponds to Ω = 0.8. At sub-critical velocity, the elastic waves of the wire are propagating waves, meanwhile at the overcritical velocity, the wire experiences standing waves behind moving load. CONCLUSIONS In this paper the dynamic behaviour of an infinite wire on visco-elastic support due to a moving harmonic load is studied. To this end, the Green’s functions method has been applied. There are two cases, the sub-critical one, when the force velocity is lower than the critical velocity (the elastic wave velocity) and the over-critical one, when the velocity of the force is higher than the critical velocity. The wire response under a stationary harmonic load is similar to the one of the system with a single degree of freedom, excepting the phase resonance. When the harmonic load moves at sub-critical velocities, the resonance frequency decreases and the wire response becomes higher. Also, the propagating waves travel at both ends of the wire. At the overcritical velocities, the wire has only standing waves behind moving harmonic load. Further research will extend the application of this method (Green’s functions method) to the case of the pantograph-catenary interaction. REFERENCES [1.] G. Poetsch et al. 1997, Pantograph – catenary dynamics and control, Vehicle System Dynamics 28 159-195. [2.] G. Bucca, A. Collina, 2009, A procedure for the wear prediction of collector strip and contact wire in pantograph–catenary system, Wear 266, 46–59. ACTA TECHNICA CORVINIENSIS – Bulletin of Engineering [3.] T. X. Wu, M. J. Brennan 1998, Basic Analytical Study of Pantograph-catenary System Dynamics, Vehicle System Dynamics, 30 443- 456. [4.] J.-W. Kim et al. 2007, State sensitivity analysis of the pantograph system for a high-speed rail vehicle considering span length and static uplift force, Journal of Sound and Vibration 303, 405-427. [5.] O. Lopez-Garcia, A. Carnicero, J.L. Marono, 2007. Influence of stiffness and contact modelling on catenary–pantograph system dynamics, Journal of Sound and Vibration 303, 405-427. [6.] L. Fryba, 1972, Vibration of Solids and Structures under Moving Loads, Noordhoff International, Groningen. [7.] A. V. Metrikine, 2004, Steady state response of an infinite string on a non-linear visco-elastic foundation to moving point loads, Journal of Sound and Vibration 272, 1033-1046. [8.] A.V. Metrikine, A. L. Bosch, 2006, Dynamic response of a two-level catenary to a moving load, Journal of Sound and Vibration 292, 676- 693. [9.] T. Mazilu, 2010, Application of Green’s functions in analysis of the response of an infinite homogenous structure to moving load, U.P.B. Scientific Bulletin, Series A, 72, 139- 152. [10.] T. Mazilu, 2010, New method for calculating response of a periodic structure due to moving loads, Proceedings of the Romanian Academy, Series A 11, 340-346. [11.] T. Mazilu, 2008, Wheel – Rail Vibrations (in Romanian), Matrixrom, Bucharest. ACTA TECHNICA CORVINIENSIS – BULLETIN of ENGINEERING ISSN: 2067-3809 [CD-Rom, online] copyright © UNIVERSITY POLITEHNICA TIMISOARA, FACULTY OF ENGINEERING HUNEDOARA, 5, REVOLUTIEI, 331128, HUNEDOARA, ROMANIA http://acta.fih.upt.ro 38 2013. Fascicule 2 [April–June]
1. Abdelmajid Sadiki LAMARI, 2. Anass El FATTOUH, 3. Salah Eddine El QOUATLI, 4 Rachida NAJIH, 5. Abdelilah CHTAINI ELECTROCHEMICAL DETECTION OF ASCORBIC ACID USING A POLYMER MODIFIED CARBON PASTE ELECTRODE 1-5. EQUIPE D’ELECTROCHIMIE MOLECULAIRE ET MATERIAUX INORGANIQUES, FACULTE DES SCIENCES ET TECHNIQUES DE BENI MELLAL, UNIVERSITE SULTAN MOLUAY SLIMANE, BP : 523, BENI MELLAL, MAROCCO ABSTRACT: Ascorbic acid (Vitamin C) is a water soluble organic compound that participates in many biological processes. This paper reports the synthesis of polymer modified carbon paste electrode and its application for the electrochemical detection of ascorbic acid (AA). The cyclic voltammetry results obtained corrobate with square wave voltammetry. The influence of variables such the concentration of ascorbic acid adsorbed onto polymer, and the pH of solution were tested. The capacity of prepared electrode (P-CPE) for selective detection of AA was confirmed in a sufficient amount of ascorbic acid. The observed linear range for the determination of AA concentration was from 0.2 mM to 9 mM. The detection limit was estimated to be 5. 48 mM. KEYWORDS: Ascorbic acid; Carbon paste electrode; Cyclic voltammetry; Electrochemical detection INTRODUCTION Ascorbic acid AA (vitamin C) is a water soluble organic compound involved in many biological processes. AA is used in large scale as an antioxidant in food, animal feed, beverages, pharmaceutical formulations and cosmetic applications. It is also important in helping to produce collagen, a protein needed in the development and maintenance of bones, cartilage, joint limings, skin, teeth, gums and blood vessels [1 – 3]. Due to the above importance of AA, its determination in their solution is more important. Many analytical techniques including sensors and biosensors [4 – 6] have been suggested for a detection of ascorbic acid in very varied types of samples. Other methods, based on the most commontly employed physico-chemical methods for identification of AA such high performance liquid chromatography [7-9] or capillary electrophoresis [10-13]. Investigations aimed at the development of modern analytical techniques for AA determination are directed towards increasing their sensitivity, specificity, simplicity and rapidity [14-15]. Electrochemical detection is an attractive alternative method for detection of electroactive species, because of its inherent advantages of simplicity, ease of miniaturization, high sensitivity and relatively low cost. In this paper, we describe the electrochemical analysis of ascorbic acid on a polymer modified carbon paste electrode. The electrochemical characterization of adsorbed electroactive AA was evaluated using cyclic voltammetric and square wave voltammetric (SWV) analysis. EXPERIMENTAL. Reagents and instrumentation All chemicals were of analytical grade and used without further purification. Na 2 SO 4 , KOH, eugenol and ascorbic acid were purcharged form Fluka. Carbon powder (Carbone, Lorraine, ref. 9900, French) was used for the preparation of electrode. All solutions were prepared with doubly distilled water. Preparation of CPE Substrates of commercial stainless steel metal 1 x 1 x 0.1 cm 3 in size were grinded, and cleaned in pure acetone and distilled water. An anodic oxidation system was composed of anode and cathode plates of steel, electrolyte of carbon solution contained in glass chamber and an extended range direct current (DC) power supply system. Substrates of stainless steel metal were fixed on the anode using steel wire and immersed in H 2 SO 4 solution for 5 min to dissolve the air-formed oxide film on the surface. Then, they were immersed in electrolyte of carbon gel contained glass chamber, and subjected to anodic oxidation by applying DC for 72h at room temperature. The anodic oxidation was processed at 25 V. Apparatus Voltammetric experiments were investigated with a potentiostat (model PGSTAT 100,Eco Chemie B.V., The Netherlands), equipped with a three electrode system mounted on cell. Working electrode was polymer modified carbon paste electrode, the counter electrode was a platinum plate and SCE served as reference. The pH-meter (Radiometer Copenhagen, PHM210, Tacussel, French) was used for adjusting pH values. © copyright FACULTY of ENGINEERING ‐ HUNEDOARA, ROMANIA 39
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