A spectroelectrochemical study of conducting pyrrole-N-methylpyrrole copolymers in nonaqueous solution

Conducting poly(pyrrole-N-methylpyrrole) (P(Py-NMPy)) was electrochemically synthesized on a gold electrode in a lithium perchlorate-containing acetonitrile electrolyte solution and compared with polypyrrole (PPy) and poly(N-methylpyrrole) (PNMPy) prepared under the same conditions. The obtained polymers were characterized with cyclic voltammetry, in situ resistance measurements, in situ UV–vis spectroscopy, FTIR spectroscopy, and scanning electron microscopy. The onset potentials for pyrrole and N-methylpyrrole monomer oxidation differ by about 0.1 V. Nucleation processes initiated by the radical cations are followed by growth of nuclei into continuous films. The oxidation and reduction peaks for the P(Py-NMPy) copolymer synthesized at 1:1 M concentration ratio of the comonomers are between those of PPy and PNMPy. A decreased [Py]/[NMPy] comonomer concentration ratio yields in the copolymers shifts of peak potentials to more positive values. The in situ resistance of copolymers measured from ?0.20 to 0.90 V vs. Ag/AgCl decreased with increasing [Py]/[NMPy] concentration ratio. In situ UV–vis and ex situ FTIR spectra of copolymers show spectroscopic behavior intermediate between those of the homopolymers. Scanning electron microscopy micrographs of the samples show fundamental differences between the morphology of the homo- and copolymers.     

Selective Sensing Characteristics of Ca Doped BeO Nano-sized Tube toward H20 and NH3

By means of density functional calculations, the structural and electronic properties of chemical modification of pristine and Ca-doped BeO nanotubes were investigated with NH3 and H20 molecules. It was found that the NH3 and H20 molecules can be adsorbed on the Be atom of the tube sidewall with the adsorption energies of about 36.1 and 39.0 kcal/mol, respectively. Density of states analysis shows that the electronic properties of the BeONT are slightly changed after the adsorption processes. Substitution of a Be atom in the tube surface with a Ca atom increases the adsorption energies by about 7.4 and 14.7 kcal/mol for NH3 and H20, respectively. Unlike the pristine tube, the electronic properties of Ca-doped BeONT are sensitive to NH3 and H20 molecules. Also, the Ca-doped tube is much more sensitive to H20 molecule than NH3 one.     

Understanding of the flow behaviour on a Helmholtz resonator excited by grazing flow

In this study, a large eddy simulation of the three-dimensional shear flow over a flow-excited Helmholtz resonator has been implemented. The simulations have been performed over a wide range of flow speeds to analyse the effect of the inlet flow properties on the excitation condition. For validation proposes, the results obtained from the numerical simulations have been compared with published experimental data and show that numerical modelling provides an accurate representation of the pressure fluctuations inside the cavity. The main objective of this paper is to gain an understanding of the flow features over a flow-excited Helmholtz resonator. To this end, using the numerical model, the interaction of a turbulent boundary layer with a Helmholtz resonator has been considered, and the characteristics of the flow inside the resonator and over the orifice for various flow conditions are also analysed.     

Investigation of flow and heat transfer of nanofluid in microchannel with variable property approach

Laminar flow and heat transfer of water-Al₂O₃ nanofluid under constant heat flux have been investigated numerically. Single-phase with temperature dependant effective properties has been assumed for fluid. Enhancement in heat transfer and increase in friction factor have been obtained by the use of nanofluid. Heat transfer enhancement is more obvious by the use of variable properties. Also, effects of temperature variation on nanofluid heat transfer are greater than the pure water.     

Working Mechanism of a BC3 Nanotube Carbon Monoxide Gas Sensor

Carbon and BN nanotubes have previously demonstrated extreme sensitivity to several molecules, but they cannot be used to detect highly toxic molecules of CO. In this work, we examine the possibility of a BC₃ nanotube (BC₃NT) as a potential gas sensor for CO detection by using density functional theory calculations. It is found that CO molecule can be absorbed on B and C atoms of BC₃NT wall with adsorption energies in the range of -1.0 to -25.9 kcal/mol and it can donate finite charge to the tube. By comparing the HOMO/LUMO energy gaps of the bare and CO adsorbed nanotubes, we deduce that molecular CO can induce significant change in the electrical conductivity of the tube. The conductivity change can generate an electrical signal, which might be useful for CO detection.     

Aluminum nitride nanotubes

An AlN nanotube (AlNNT) was theoretically predicted in 2003. In comparison with the carbon nanotubes, the AlNNTs are wide-band-gap nanostructures with high reactivity, high thermal stability and sharp electronic sensitivity toward some chemicals. The B3LYP predicts an HOMO–LUMO gap of 3.74–4.27 eV for zigzag AlNNTs, while the experimental bad gap of bulk AlN is about 6.28 eV. The lowest strain energy of AlNNTs relative to its AlN nanosheet compared to the nanosheets of carbon and BN nanotubes with an equivalent diameter suggests the feasibility of AlNNT synthesis from its nanosheet. Theoretical methods predict a Young’s Modulus of about 453 GPa for AlNNTs that is smaller than that of carbon (1 TPa), BN (870 GPa) and GaN (796 GPa) nanotubes. In 2003, the faceted single-crystalline hexagonal AlNNTs were synthesized and extensively explored by means of density functional theory calculations. Several works have suggested different potential applications for AlNNTs including chemical sensors, hydrogen storage, gas adsorbent, and electron field emitter. This review is a comprehensive study on the latest achievements in the structural analyses, synthesis, and property evaluations based on the computational methods on the AlNNTs in the light of the development of nanotubes.     

Local nonglobal minima for solving large-scale extended trust-region subproblems

We study large-scale extended trust-region subproblems (eTRS) i.e., the minimization of a general quadratic function subject to a norm constraint, known as the trust-region subproblem (TRS) but with an additional linear inequality constraint. It is well known that strong duality holds for the TRS  and that there are efficient algorithms for solving large-scale TRS  problems. It is also known that there can exist at most one local non-global minimizer (LNGM) for TRS. We combine this with known characterizations for strong duality for eTRS  and, in particular, connect this with the so-called hard case for TRS. We begin with a recent characterization of the minimum for the TRS  via a generalized eigenvalue problem and extend this result to the LNGM. We then use this to derive an efficient algorithm that finds the global minimum for eTRS  by solving at most three generalized eigenvalue problems.     

Two-phase Flow Dynamics at the Interface Between GDL and Gas Distributor Channel Using a Pore-Network Model

Transport in Porous Media - For improved operating conditions of a polymer electrolyte membrane (PEM) fuel cell, a sophisticated water management is crucial. Therefore, it is necessary to...