Fundamental study of crystallization,orientation, and electrical conductivity of electrospun PET/carbon nanotube nanofibers

The morphology, structure, and properties of polyethylene terephthalate (PET)/Carbon Nanotubes (CNT) conductive nanoweb were studied in this article. Nanocomposite nanofibers were obtained through electrospinning of PET solutions in trifluoroacetic acid (TFA)/dichloromethane (DCM) containing different concentrations and types of CNTs. Electrical conductivity measurements on nanofiber mats showed an electrical percolation threshold around 2 wt % multi‐wall carbon nanotubes (MWCNT). The morphological analysis results showed smoother nanofibers with less bead structures development when using a rotating drum collector especially at high concentrations of CNTs. From crystallographic measurements, a higher degree of crystallinity was observed with increasing CNT concentrations above electrical percolation. Spectroscopy results showed that both PET and CNT orientation increased with the level of alignment of the nanofibers when the nanotube concentration was below the electrical percolation threshold; while the orientation factor was reduced for aligned nanofibers with higher content in CNT. Considerable enhancement in mechanical properties, especially tensile modulus, was found in aligned nanofibers; at least six times higher than the modulus of random nanofibers at concentrations below percolation. The effect of alignment on the mechanical properties was less important at higher concentrations of CNTs, above the percolation threshold. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2052–2064, 2010     

Electron transfer in quantum-dot-sensitized ZnO nanowires: ultrafast time-resolved absorption and terahertz study

Photoinduced electron injection dynamics from CdSe quantum dots to ZnO nanowires is studied by transient absorption and time-resolved terahertz spectroscopy measurements. Ultrafast electron transfer from the CdSe quantum dots to ZnO is proven to be efficient already on a picoseconds time scale (τ = 3-12 ps). The measured kinetics was found to have a two-component character, whose origin is discussed in detail. The obtained results suggest that electrons are injected into ZnO via an intermediate charge transfer state.     

Projection iterative method for solving general variational inequalities

In this paper, we suggest and analyze a new projection iterative method for solving general variational inequalities by using a new step size. We also prove the global convergence of the proposed method under some suitable conditions. Some preliminary numerical experiments are included to illustrate the advantage and efficiency of the proposed method.     

Palladium(0)-catalyzed amination of allylic natural terpenic functionalized olefins

The palladium(0) catalyzed amination of allylic acetates and carbonates derivatives from terpenic olefins was carried out under mild conditions. The reaction offers a very good method for the preparation of allylic amines and thus to provide a useful entry to new functionalized terpenic olefin products. The mechanism involving a formation of p-allyl-palladium intermediate complex is in good agreement with the results obtained with the optically active substrates, as well as via an analysis of the observed regio-and stereoselectivity.      

Surface analysis for catalyst layer (PT/PTFE/C) and diffusion layer (PTFE/C) for proton exchange membrane fuel cells systems (PEMFCs)

X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) studies have been used to analyze the surface of diffusion layer (PTFE/C) and catalyst layer (Pt/C/PTFE) of electrode. Detail analysis of carbon C_1s peak showed that the carbon was of the form of C, C-O, CO, CF, CF₂ and CF₃ with CF₂ is more dominated on the surface compared to CF and CF₃. The oxygen O_1s photoelectron peak showed that the oxygen was of the form of CO and C-O. The platinum was of the form of Pt⁰ with some Pt oxidized to PtO. The scanning electron microscopy was used to observe the dispersion of Teflon in the diffusion layer, the distribution of platinum in the catalyst layer loaded with 0.38 mg Pt/cm² and also the cross section of the membrane electrode assembly. The prepared electrode delivers a superior performance compared with the commercial electrode (E-TEK). The difference in performance between the two electrodes is due to the good localization of the platinum particles.     

Constrained stabilization: an enlargement technique of positively invariant sets

This paper presents a new technique of enlargement of positivelyinvariant sets for linear systems with input saturation. Thistechnique is based on the use of the convex hull of the unionof N preconstructed positively invariant sets. It is shown thatthe obtained region is a stability region where the controlis always admissible.     

Equivariant functions and integrals of elliptic functions

In this paper, we introduce the theory of equivariant functions by studying their analytic, geometric and algebraic properties. We also determine the necessary and sufficient conditions under which an equivariant form arises from modular forms. This study was motivated by observing examples of functions for which the Schwarzian derivative is a modular form on a discrete group. We also investigate the Fourier expansions of normalized equivariant functions, and a strong emphasis is made on the connections to elliptic functions and their integrals.     

A new analytical formula to compute the step length of Padé approximants in the ANM: Application to buckling structures

In this paper, we propose a new analytical formula to define the next branch in the Asymptotic Numerical Method (ANM) using the Padé approximants. The proposed formula is based on the computation of the relative error of two consecutive Padé approximants. This formula is obtained by developing the relative error with respect to the path parameter. An appropriate matrix formulation is adopted for the computation of this relative error. A comparison between the analytical formula proposed in this paper and the classical continuation Padé approximants using the step length computed numerically using dichotomy method is presented for examples of buckling structures.     

Study of corrosion-erosion behaviour of stainless alloys in industrial phosphoric acid medium

The corrosion and corrosion-abrasion resistance of some stainless steels in industrial phosphoric acid 30% P₂O₅ has been studied using electrochemical techniques. The corrosion rate of materials increases with the increase of temperature. Alloys which contain chromium, molybdenum and nitrogen in sufficient quantities present the best behaviour.In the abrasion-corrosion conditions, the experimental device set up allowed to follow continually samples electrochemical behaviour. Under dynamic conditions and without solid particles, the increase of acid projection speed has no effect on the alloys corrosion behaviour. The adding of abrasive leads to a general increase of corrosion rate and to a decrease of material resistance. Under these conditions, materials attack is controlled by synergistic effect between the abrasion and the impurities. The cast 30% Cr shows good resistance according to his high chromium content.