A Numerical Analysis on Nanofluid Mixed Convection in Triangular Cross-Sectioned Ducts Heated by a Uniform Heat Flux:

In this paper, results obtained by the numerical investigation on laminar mixed convection in triangular ducts, filled with nanofluids, are presented in order to evaluate the fluid dynamic and thermal features of the considered geometry by considering Al 2 O 3 /water based nanofluids. The system is heated by a constant and uniform heat flux also along the perimeter of the triangular duct section in H2 mode as thermal boundary condition and the single-phase model has been assigned for a Reynolds number value equal to 100. Results are given for different nanoparticle volume concentrations and Richardson number values ranging from 0% to 5% and from 0 to 5, respectively. Results, presented for the fully developed regime flow, show the enhancement of average convective heat transfer coefficients values for increasing values of Richardson number and particle fractions. However, wall shear stress and required pumping power profiles increase as expected. The PEC analysis showed that the use of nanofluids in mixed convection seems slightly convenient. It should be underlined that, at the moment, experimental data are not available to compare the numerical proposed model for mixed convection in horizontal triangular ducts with nanofluids

Quantification of optical pulsed-plane-wave-shaping by chiral sculptured thin films

The durations and average speeds of ultrashort optical pulses transmitted through chiral sculptured thin films (STFs) were calculated using a finite-difference time-domain algorithm. Chiral STFs are a class of nanoengineered materials whose microstructure comprises parallel helicoidal nanowires grown normal to a substrate. The nanowires are $\sim$10-300 nm in diameter and $\sim1-10 \mu$m in length. Durations of transmitted pulses tend to increase with decreasing (free-space) wavelength of the carrier plane wave, while average speeds tend to increase with increasing wavelength. An increase in nonlinearity, as manifested by an intensity-dependent refractive index in the frequency domain, tends to increase durations of transmitted pulses and decrease average speeds. The circular Bragg phenomenon exhibited by a chiral STFs manifests itself in the frequency domain as high reflectivity for normally incident carrier plane waves whose circular polarization state is matched to the structural handedness of the film and whose wavelength falls in a range known as the Bragg regime; films of the opposite structural handedness reflect such plane waves little. This effect tends to distort the shapes of transmitted pulses with respect to the incident pulses, and such shaping can cause sharp changes in some measures of average speed with respect to carrier wavelength. A local maximum in the variation of one measure of the pulse duration with respect to wavelength is noted and attributed to the circular Bragg phenomenon. Several of these effects are explained via frequency-domain arguments. The presented results serve as a foundation for future theoretical and experimental studies of optical pulse propagation through causal, nonlinear, nonhomogeneous, and anisotropic materials.Comment: To appear in Journal of Modern Optic

Surface-plasmon-polariton wave propagation guided by a metal slab in a sculptured nematic thin film

Surface-plasmon-polariton~(SPP) wave propagation guided by a metal slab in a periodically nonhomogeneous sculptured nematic thin film~(SNTF) was studied theoretically. The morphologically significant planes of the SNTF on both sides of the metal slab could either be aligned or twisted with respect to each other. The canonical boundary-value problem was formulated, solved for SPP-wave propagation, and examined to determine the effect of slab thickness on the multiplicity and the spatial profiles of SPP waves. Decrease in slab thickness was found to result in more intense coupling of two metal/SNTF interfaces. But when the metal slab becomes thicker, the coupling between the two interfaces reduces and SPP waves localize to one of the two interfaces. The greater the coupling between the two metal/SNTF interfaces, the smaller is the phase speed.Comment: 17 page

Surface-plasmon-polariton wave propagation supported by anisotropic materials: multiple modes and mixed exponential and linear localization characteristics

The canonical boundary-value problem for surface-plasmon-polariton (SPP) waves guided by the planar interface of a dielectric material and a plasmonic material was solved for cases wherein either partnering material could be a uniaxial material with optic axis lying in the interface plane.Numerical studies revealed that two different SPP waves, with different phase speeds, propagation lengths, and penetration depths, can propagate in a given direction in the interface plane; in contrast, the planar interface of isotropic partnering materials supports only one SPP wave for each propagation direction. Also, for a unique propagation direction in each quadrant of the interface plane, it was demonstrated that a new type of SPP wave--called a surface-plasmon-polariton-Voigt (SPP-V) wave--can exist. The fields of these SPP-V waves decay as the product of a linear and an exponential function of the distance from the interface in the anisotropic partnering material; in contrast, the fields of conventional SPP waves decay only exponentially with distance from the interface. Explicit analytic solutions of the dispersion relation for SPP-V waves exist and help establish constraints on the constitutive-parameter regimes for the partnering materials that support SPP-V-wave propagation

Theory of Dyakonov-Tamm waves at the planar interface of a sculptured nematic thin film and an isotropic dielectric material

In order to ascertain conditions for surface-wave propagation guided by the planar interface of an isotropic dielectric material and a sculptured nematic thin film (SNTF) with periodic nonhomogeneity, we formulated a boundary-value problem, obtained a dispersion equation therefrom, and numerically solved it. The surface waves obtained are Dyakonov-Tamm waves. The angular domain formed by the directions of propagation of the Dyakonov--Tamm waves can be very wide (even as wide as to allow propagation in every direction in the interface plane), because of the periodic nonhomogeneity of the SNTF. A search for Dyakonov-Tamm waves is, at the present time, the most promising route to take for experimental verification of surface-wave propagation guided by the interface of two dielectric materials, at least one of which is anisotropic. That would also assist in realizing the potential of such surface waves for optical sensing of various types of analytes infiltrating one or both of the two dielectric materials.Comment: accepted for publication in J. Opt.

Down-Regulation of the Canonical Wnt β-Catenin Pathway in the Airway Epithelium of Healthy Smokers and Smokers with COPD

Background: The Wnt pathway mediates differentiation of epithelial tissues; depending on the tissue types, Wnt can either drive or inhibit the differentiation process. We hypothesized that key genes in the Wnt pathway are suppressed in the human airway epithelium under the stress of cigarette smoking, a stress associated with dysregulation of the epithelial differentiated state. Methodology/Principal Findings: Microarrays were used to assess the expression of Wnt-related genes in the small airway epithelium (SAE) obtained via bronchoscopy and brushing of healthy nonsmokers, healthy smokers, and smokers with COPD. Thirty-three of 56 known Wnt-related genes were expressed in the SAE. Wnt pathway downstream mediators b-catenin and the transcription factor 7-like 1 were down-regulated in healthy smokers and smokers with COPD, as were many Wnt target genes. Among the extracellular regulators that suppress the Wnt pathway, secreted frizzled-related protein 2 (SFRP2), was up-regulated 4.3-fold in healthy smokers and 4.9-fold in COPD smokers, an observation confirmed by TaqMan Real-time PCR, Western analysis and immunohistochemistry. Finally, cigarette smoke extract mediated up-regulation of SFRP2 and down-regulation of Wnt target genes in airway epithelial cells in vitro. Conclusions/Significance: Smoking down-regulates the Wnt pathway in the human airway epithelium. In the context that Wnt pathway plays an important role in differentiation of epithelial tissues, the down-regulation of Wnt pathway ma

Mixed convection boundary layer flow over a moving vertical flat plate in an external fluid flow with viscous dissipation effect

The steady boundary layer flow of a viscous and incompressible fluid over a moving vertical flat plate in an external moving fluid with viscous dissipation is theoretically investigated. Using appropriate similarity variables, the governing system of partial differential equations is transformed into a system of ordinary (similarity) differential equations, which is then solved numerically using a Maple software. Results for the skin friction or shear stress coefficient, local Nusselt number, velocity and temperature profiles are presented for different values of the governing parameters. It is found that the set of the similarity equations has unique solutions, dual solutions or no solutions, depending on the values of the mixed convection parameter, the velocity ratio parameter and the Eckert number. The Eckert number significantly affects the surface shear stress as well as the heat transfer rate at the surface