Surface analysis and adsorption behavior of caffeine as an environmentally friendly corrosion inhibitor at the copper/aqueous chloride solution interface

Abstract

Corrosion inhibitors based on environmentally friendly and harmless products are currently being studied and developed. The corrosion inhibition properties of caffeine (1,3,7-trimethylxanthine) on copper corrosion in aqueous chloride solution (3.5?wt.% NaCl) are analysed here using stationary and transient electrochemical methods, and a theoretical study based on density functional theory is carried out. Caffeine is a very competitive compared to the chemical inhibitors that are often used for copper protection. Electrochemical and impedance experiments reveal that the protective efficiency of caffeine reaches a value of 96% at a concentration of 10^?2?mol L^?1. Based on these results, the Langmuir model appears to be the best representation of the adsorption of caffeine onto the copper surface. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction (XRD) were used to determine the surface morphology and the chemical composition of the copper surface in chloride media, in the absence and presence of caffeine. The results show the development of a mechanism of corrosion inhibition. In order to confirm the correlation between the inhibitory effect and the molecular structure of caffeine, quantum chemical parameters are used to calculate its electronic properties.     

Academic effectiveness of podcasting: A comparative study of integrated versus supplemental use of podcasting in second language classes

With podcasting gaining more mainstream adoption in higher education, it’s critical to examine its effectiveness in improving the student learning experience. To this end, this paper examines the effectiveness of podcasts integrated into the curriculum (PIC) versus podcasts as supplemental material (PSM). Considering recent empirical work on the effectiveness of podcasting, this study collected data from students enrolled in lower level and upper level language courses. Results revealed an inconclusive relationship among PIC students’ learning outcomes (as measured by their final grades). In contrast, however, our findings indicate a strong relationship between the use of PSM and students’ final grades, particularly in upper level courses.     

Discontinuous Galerkin error estimation for hyperbolic problems on unstructured triangular meshes

We extend the error analysis of Adjerid and Baccouch [1], [2] for the discontinuous Galerkin discretization error to variable-coefficient linear hyperbolic problems as well as nonlinear hyperbolic problems on unstructured meshes. We further extend this analysis to transient hyperbolic problems and prove that the local superconvergence results presented in [1] still hold for both steady and transient variable-coefficient linear and nonlinear problems. This local error analysis allows us to construct asymptotically correct a posteriori error estimates by solving local hyperbolic problems with no boundary conditions on each element of general unstructured meshes. We illustrate the superconvergence and the efficiency of our a posteriori error estimates by showing computational results for several linear and nonlinear numerical examples.     

Nonlinear multi-scale decomposition by EMD for Co-Channel speaker identification

Multimedia Tools and Applications - A multi-scale analysis method, called Empirical Mode Decomposition (EMD), has been proposed for analysis of nonlinear and non stationary data. The empirical mode...     

Learner outcomes and satisfaction: A comparison of live video-streamed instruction,satellite broadcast instruction,and face-to-face instruction

This study examined the final grade and satisfaction level differences among students taking specific courses using three different methods: face-to-face in class, via satellite broadcasting at remote sites, and via live video-streaming at home or at work. In each case, the same course was taught by the same instructor in all three delivery methods, and an attempt was made to survey students taking the course via the three different delivery methods. MANOVA results indicated no grade or satisfaction level differences among the three populations. Self-reported computer literacy skills revealed a slight fit between the chosen delivery mode and the reported computer literacy skills. These results provide additional evidence to support both the “no significant difference” phenomenon and the use of distance education as a viable, convenient and flexible alternative delivery mode capable of extending learning opportunities to non-traditional students.     

The Discontinuous Galerkin Method for Two-Dimensional Hyperbolic Problems. Part I: Superconvergence Error Analysis

In this paper we investigate the superconvergence properties of the discontinuous Galerkin method applied to scalar first-order hyperbolic partial differential equations on triangular meshes. We show that the discontinuous finite element solution is O(h ^p+2) superconvergent at the Legendre points on the outflow edge for triangles having one outflow edge. For triangles having two outflow edges the finite element error is O(h ^p+2) superconvergent at the end points of the inflow edge. Several numerical simulations are performed to validate the theory. In Part II of this work we explicitly write down a basis for the leading term of the error and construct asymptotically correct a posteriori error estimates by solving local hyperbolic problems with no boundary conditions on more general meshes.     

Robustness study of emerged communities from exchanges in peer-to-peer networks

The study of emerged community structure is an important challenge in networks analysis. In fact, several methods have been proposed in the literature to statistically determine the significance of discovered structures. Nevertheless, most of existing analysis models consider only the structural aspect of emerged communities. We are interested in studying the robustness of emerged communities in peer-to-peer (P2P) networks. More precisely, we consider the emerged communities in the induced graph by all the exchanges in these networks. Hence, rather than examining the robustness only on the structural properties of the graph, we will focus on the parameters that allow the emergence of community structures. In fact, perturbing these parameters might destroy most of the obtained properties at the emerged level. To the best of our knowledge, robustness of networks has never been considered from this angle before. In this paper, we study the impact of perturbing the content and the profile of nodes on the emerged communities in P2P networks. We show how these alterations affect both structure and information supported by the emerged structures.     

Cancellation technique to reduce intercarrier interference in OFDM

Orthogonal frequency division multiplexing (OFDM) systems are sensitive to frequency errors, which cause intercarrier interference among subcarriers. A new cancellation method to reduce the effects of frequency offset errors is presented. The main feature is to map each data symbol a_k which is to be transmitted onto a pair of non-adjacent subcarriers, with weightings +1 and -1, rather than to a single subcarrier. The carrier-to-interference ratio gain of the proposed method over normal OFDM varies between 10 to 30 dB. This method also offers a frequency diversity effect in a multipath fading channel     

Bandwidth efficiency of MC-CDMA signals

The bandwidth efficiency of MC-CDMA signals is evaluated and compared to that of DS-CDMA signals. For the same available bandwidth, the achievable processing gain of the two systems with and without filtering is evaluated and then compared     

Physical and chemical characterization of adsorbed protein onto gold electrode functionalized with Tunisian coral and nacre

Bone substitutes are more and more used in bone surgery because of their biologic safety, clinic efficiency and facility to synthesize. Bone substitutes with active osteogenic properties, associating biomaterials with organic macromolecule components of the extracellular matrix (protein, GAG) are recommended. Nevertheless, we should have a simple technique to control interactions between proteins and the material. Natural coral and nacre have been found to be impressive bone graft substitutes. In this work, we characterize nacre and coral powder using energy dispersive X-ray analysis (EDX). We used electrochemical impedance spectroscopy (EIS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to evaluate bovine serum albumin (BSA) as model protein, adsorbed to these biomaterial surfaces. In order to understand the nacre/coral-protein interfacial compatibility, it is necessary to investigate the wettability.