Carbon nanotube-DNA nanoarchitectures and electronic functionality

Biological molecules such as deoxyribonucleic acid (DNA) possess inherent recognition and self-assembly capabilities, and are attractive templates for constructing functional hierarchical material structures as building blocks for nanoelectronics. Here we report the assembly and electronic functionality of nanoarchitectures based on conjugates of single-walled carbon nanotubes (SWNTs) functionalized with carboxylic groups and single-stranded DNA (ssDNA) sequences possessing terminal amino groups on both ends, hybridized together through amide linkages by adopting a straightforward synthetic route. Morphological and chemical-functional characterization of the nanoarchitectures are investigated using scanning electron microscopy, transmission electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy. Electrical measurements (I-V characterization) of the nanoarchitectures demonstrate negative differential resistance in the presence of SWNT/ssDNA interfaces, which indicates a biomimetic route to fabricating resonant tunneling diodes. I-V characterization on platinum-metallized SWNT-ssDNA nanoarchitectures via salt reduction indicates modulation of their electrical properties, with effects ranging from those of a resonant tunneling diode to a resistor, depending on the amount of metallization. Electron transport through the nanoarchitectures has been analyzed by density functional theory calculations. Our studies illustrate the great promise of biomimetic assembly of functional nanosystems based on biotemplated materials and present new avenues toward exciting future opportunities in nanoelectronics and nanobiotechnology.     

Computational Analysis of Reacting Flows in Afterburner

Abstract

Gas turbine afterburner is used during take-off, combat, maneuvers, and emergencies when the aircraft engine needs more thrust than normal. A 60° sector full-scaled afterburner, with extended domain of three times the nozzle diameter in the axial direction and two times the nozzle diameter in the radial direction, is modeled. The numerical calculations are performed using SIMPLE algorithm and k–ε model has been used for turbulence. Kerosene (C₁₂H₂₃) is taken as fuel and virtual injectors are specified for fuel injection. Energy equation and species transport with the Discrete Phase model is selected for computations. Maximum density of 1.25?kg/m³ is observed and the density of the fluid reduced to 0.2?kg/m³ at the exit of nozzle after combustion. The desired Mach number of 1.1 could be observed at the exit of the nozzle. The CO₂ mass fraction increased from 0 to 0.075 whereas the O₂ mass fraction decreased from 0.23 to 0.145 from the inlet to the exit of afterburner. The maximum temperature of 2500?K is observed radially at 0.2?m, from the center of the afterburner and axially at a distance of 0.9?m of afterburner. The obtained results are validated with published experimental and computational fluid dynamics results.     

Preparation of CdS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> films by brush plating technique and their characteristics

CdS _x Se_1−x films were deposited for the first time by the brush plating technique from aqueous precursors. X-ray diffraction patterns of the films indicated polycrystalline structure with peaks corresponding to the hexagonal phase. Optical absorption measurements indicated the band gap to shift from 1.68 to 2.39 eV as the value of x is increased. XPS spectra indicated the peaks corresponding to Cd (3d_5/2 and 3d_3/2), Se (3d_5/2 and 3d_3/2) and S (3d_5/2 and 3d_3/2) levels. Surface morphology studies indicated the grain size to increase with increase of selenium concentration. The resistivity of the films changed from 20 ohm cm to 250 ohm cm as the sulphur content increased.     

Effect of surface radiation on conjugate natural convection in a horizontal annulus driven by inner heat generating solid cylinder

This paper reports a numerical study of the laminar conjugate natural convection heat transfer with and without the interaction of the surface radiation in a horizontal cylindrical annulus formed between an inner heat generating solid circular cylinder and an outer isothermal circular boundary. Numerical solutions are obtained by solving the governing equations with a pressure correction method on a collocated (non-staggered) mesh. Steady-state results are presented for the flow and temperature distributions and Nusselt numbers for the heat generation based Grashof number ranging from , solid-to-fluid thermal conductivity ratios of 1, 5, 10, 50 and 100, radius ratios of 0.226 and 0.452 and surface emissivities of 0–0.8 with air as the working medium. It is observed that surface radiation reduces the convective heat transfer in the annulus compared to the pure natural convection case and enhances the overall Nusselt number.