On the mechanism of low-temperature water gas shift reaction on copper

Periodic, self-consistent density functional theory (DFT-GGA) calculations are used to investigate the water gas shift reaction (WGSR) mechanism on Cu(111). The thermochemistry and activation energy barriers for all the elementary steps of the commonly accepted redox mechanism, involving complete water activation to atomic oxygen, are presented. Through our calculations, we identify carboxyl, a new reactive intermediate, which plays a central role in WGSR on Cu(111). The thermochemistry and activation energy barriers of the elementary steps of a new reaction path, involving carboxyl, are studied. A detailed DFT-based microkinetic model of experimental reaction rates, accounting for both the previous and the new WGSR mechanism show that, under relevant experimental conditions, (1) the carboxyl-mediated route is the dominant path, and (2) the initial hydrogen abstraction from water is the rate-limiting step. Formate is a stable "spectator" species, formed predominantly through CO2 hydrogenation. In addition, the microkinetic model allows for predictions of (i) surface coverage of intermediates, (ii) WGSR apparent activation energy, and (iii) reaction orders with respect to CO, H2O, CO2, and H2.     

Synthesis,X-ray crystallographic studies,DFT calculations and nanostructural features of annulated imidazo[4,5-b]pyridine derivatives

Friedländer-type condensation of 5-amino-4-cyano-1-(phenyl/p-substitutedphenyl)imidazole with cycloalkanone was done by refluxing the mixture with a suspension of anhydrous aluminum chloride in dry 1,2-dichloroethane to produce 7-amino-3-aryl(5,6)cycloalkanoimidazolo[4,5-b]pyridine. Single X-ray crystallographic diffraction studies had shown that compounds had different types of heterodimeric, homodimeric π–π stacking, T-type stacking, and intermolecular hydrogen bonds which lead to nanostructure formation detected by scanning electron microscope. DFT calculation had also been performed to quantify heterodimeric π–π and T-stacking interactions.     

An IP transport and routing architecture for next-generationsatellite networks

Over the past several years, a number of new satellite systems have been proposed to provide high-speed Internet and multimedia services to businesses and home users. These proposals have been driven by the desire of network operators to reach end users that do not have cost effective access to other alternatives such as fiber, DSL, and cable, and by the availability of new spectrum (Ka-band) for use by new satellite services. The proposed systems generally employ multiple high-power spot beams, an onboard fast packet switch, and a demand-assigned multiple access scheme to provision IP-based services. In this article we concentrate on a geosynchronous satellite system where packet transport and switching within the satellite system are based on ATM. We describe an IP/ATM interworking and IP routing architecture that is driven by three main requirements: (1) the ability to support ATM SVCs between hundreds of thousands of satellite terminals by a single ATM switch located onboard; (2) a scalable IP routing architecture that does not result in large volumes of routing traffic to be transported over the satellite; and (3) the ability to segment the satellite terminals for routing and administrative control by ISPs and enterprise networks     

InGaAsPN-InP-based photodetectors for long wavelength(λ>1.65 μm) applications

We demonstrate InGaAsPN p-i-n photodetectors lattice-matched to InP substrates with cutoff wavelengths larger than 1.65 μm. The narrow bandgap InGaAsPN absorption layers were grown by gas source molecular beam epitaxy using an RF plasma nitrogen source. Optical absorption spectra reveal that InGaAsPN with 5% P and 2.8% N has a cutoff wavelength λ_CO=1.90 μm Background doping in the absorption layer for a detector with 1.5% N and 5% P is reduced from (1.5±0.5)×10¹⁷ cm^-3 for the as-grown device, to (5±0.5)×10¹⁶ cm^-3 for a thermally annealed device. The unintentional high background doping is due to N-H bond formation or local strain induced defects. Spectral response measurements indicate that λ_CO=1.85 μm is achieved for detectors annealed at 800°C with 2% N and 5% P in the InGaAsPN absorption layer, suggesting that annealed InGaAsPN alloys are promising for use in detectors with response in the near and mid-IR wavelength spectral range     

Generalizations of the Hermite–Biehler theorem: the complex case

The Hermite–Biehler theorem gives necessary and sufficient conditions for the Hurwitz stability of a polynomial in terms of certain interlacing conditions. In this paper, we extend our earlier generalization of the Hermite–Biehler theorem for real, not necessarily Hurwitz polynomials to the domain of polynomials with complex coefficients. This result, which is of interest in its own right, can also be used to analytically solve an important stabilization problem in control theory.     

Multi-channel curve crossing problems: analytically solvable model

We have proposed a general method for finding the exact analytical solution for the multi-channel curve crossing problem in the presence of delta function couplings. We have analysed the case where a potential energy curve couples to a continuum (in energy) of the potential energy curves.     

Wastewater treatment: a novel energy efficient hydrodynamic cavitational technique

A novel method of treating a dye solution has been studied by hydrodynamic cavitation using multiple hole orifice plates. The present work deals with the effect of geometry of the multiple hole orifice plates on the degradation of a cationic dye rhodamine B (rhB) solution. The efficiency of this technique has been compared with the cavitation generated by ultrasound and it has been found that there is substantial enhancement in the extent of degradation of this dye solution using hydrodynamic cavitation. Large-scale operation coupled with better energy efficiency makes this technique a viable alternative for conventional cavitational reactors.     

Numerical computations of internal flows for axisymmetric and two-dimensional nozzles

MacCormack's explicit time-marching scheme is used to solve the full Navier–Stokes unsteady, compressible equations for internal flows. The requirement of a very fine grid to capture shock as well as separated flows is circumvented by employing grid clustering. The numerical scheme is applied for axisymmetric as well as two-dimensional flows. Numerical predictions are compared with experimental data and the qualitative as well as the quantitative agreement is found to be quite satisfactory. © 1997 John Wiley & Sons, Ltd.     

Microwave-mediated synthesis of spinel CuAl2O4 nanocomposites for enhanced electrochemical and catalytic performance

Research on Chemical Intermediates - The present study explores synthesis of spinel copper aluminate nanocomposites (CuAl2O4 NCs) for electrochemical applications and solvent-free synthesis of...     

On the pivotal roles of non-covalent interactions in governing the conformational stability of halo-salicylic acids: an “atoms-in-molecules” perspective

Structural Chemistry - The present contribution elucidates the non-covalent interactions present within the molecular frameworks of a miscellany of mono and dihalo-salicylic acid derivatives from...