Enhancement of distillate selectivity in Fischer-Tropsch synthesis by using iron and cobalt catalysts in a novel dual-bed reactor ?

Summary An integrated process for producing liquid fuels from synthesis gas via a two-stage Fischer-Tropsch (FT) reaction is disclosed. An iron catalyst was used in the first bed of a fixed-bed reactor followed by a ruthenium promoted cobalt catalyst in the second bed. The activity and selectivity of the dual-bed system were assessed and compared with those using catalysts in a single bed system, separately. The methane selectivity in the dual-bed reactor was about 11% less compared to that of the single-bed system. The C₅⁺ selectivity for the dual-bed reactor was 19.7% higher than that of the single-bed system.     

Dynamic Response of a Grid-Stiffened Composite Cylindrical Shell Reinforced with Carbon Nanotubes to a Radial Impulse Load

Mechanics of Composite Materials - Equilibrium equations of a rib grid-stiffened composite cylindrical shell reinforced with carbon nanotubes (CNTs) are derived based on the first-order shear...     

Characterization of high purity GaAs far-infrared photoconductors

In this paper we report the results of an extensive study on the far-infrared photoconductivity of high purityn-type GaAs. The crystal, which was grown at Max-Plank-Institute for Solid State Physics using liquid-phase epitaxy, exhibited the fine structures of the excited state transitions of the residual shallow level impurities. The major peak in the spectral response belongs to the 1s-2p transition, with its responsivity about thirty five times higher than the continuum. At 3.4K detector temperature, 625 mV bias, and 100 Hz chopping frequency the detector responsivity at 35.4 cm^–1 (279 µm) was measured to be 0.017 A/W. Under these same conditions, the NEP was 5.9×10^–14 W/Hz. The (DC) dark current at 25 mV bias was 5.6×10^–14 A.     

Flow field of a third-grade non-Newtonian fluid in the annulus of rotating concentric cylinders in the presence of magnetic field

In this paper, the flow field of a third-grade non-Newtonian fluid in the annulus of rotating concentric cylinders has been investigated in the presence of magnetic field. For this purpose, the constitutive equation of such a fluid flow was simplified, and the existence of the solution to the governing equation was established using Schauder's fixed point theorem. Using the finite difference method, the numerical solution of the non-dimensionalized form of the established governing equation was obtained. The effect of sundry parameters such as the rotating speed of the cylinders, the physical properties of fluid, and magnetic field intensity on the fluid velocity field was studied as well.     

Broadband dielectric relaxation study of 6CB and 6CB-aerosil dispersions in the nematic and isotropic phases

Experimental studies of dielectric relaxation in the nematic and isotropic phases of 6CB (4-hexyl-4′-cyanobiphenyl) and two mixtures of 6CB perturbed by 160 Å hydrophobic silica aerosil are presented. The measurements have been made from 1 MHz to 1 GHz in the temperature range from 19 to 40°C. For bulk 6CB, the dynamic aspect in the isotropic phase as well as the principal dielectric permittivities ε ∥ * (ω) and ε ┴ * (ω) in the nematic phase have been fully explored. For the mixtures, measurements on the isotropic phase and also on homeotropically aligned samples in the nematic phase have been made, and these results are systematically compared with those for the bulk. The possible molecular reorientational movements corresponding to the different absorption domains in the dielectric spectrum are discussed and compared with the previously proposed interpretations.     

Optimization based design of a wideband near zero refractive index metasurface for gain improvement of planar antennas in the terahertz band

Optical and Quantum Electronics - A high-sensitive refractive index (RI) measuring method is proposed through the combined use of elliptical core photonic crystal fiber (PCF) and Sagnac...     

Nonlinear free dynamic response of laminated compressible cylindrical shell panels

The governing equations for a free dynamic response of a symmetrically laminated composite shell are used to analyze a nonlinear differential panel. The FEM and the Lindstedt–Poincare perturbation technique are invoked to construct a uniform asymptotic expansion of the solution to a nonlinear differential equation ofmotion. A comparison between numerical and finite-element methods for analyzing a symmetrically laminated graphite/epoxy shell panel is performed to show that the nonlinearities are of hardening type and are more repeated for smaller opening angles. It is also shown that large-amplitude motions are dominated by lower modes.