An improved second moment method for solution of pure advection problems

The second moment numerical method (SMM) of Egan and Mahoney [Numerical modeling of advection and diffusion of urban area source pollutant. Journal of Applied Meteorology 1972; 11 : 312–322] is adapted to solve for the pure advection transport equation in a variety of flow fields. SMM eliminates numerical diffusion by employing a procedure that takes into account the first and second moments of mass distribution in each grid element. For pure translational flow fields, the method is conservative, positive definite and shape‐preserving. In rotational and/or shear flows, the accuracy of SMM is significantly reduced. Two improvements are presented to make the SMM applicable to a wider range of flow problems. It is shown that the improved SMM (ISMM) is less diffusive and more shape‐preserving than the SMM in rotational and/or deformational flows. The ISMM can also be used to solve for a color function in compressible flow fields. The computational efficiency of this method is compared with that of other methods and, for a given accuracy, it is shown that ISMM is a cost‐effective, non‐diffusive and shape‐preserving method. Copyright © 2000 John Wiley & Sons, Ltd.     

Changing emission of divalent samarium doped into barium octoborate as a function of firing time

Barium octoborate has been synthesized by air firing of co-precipitated borates with additional boric acid. During the firing process, samarium ions doped into the matrix are reduced to the divalent state. Two different divalent samarium emission spectra have been observed from the material as a function of the firing history, even though the structure, as identified by powder X-ray diffraction remained consistent. A minor barium pentaborate impurity, in conjunction with significant thermal variability in the strength of the divalent samarium emission generated by the different sites in the two borate materials, appears to give rise to this phenomenon.     

Novel optical polarizer design based on metasurface nano aperture for biological sensing in mid-infrared regime

Since Metasurfaces are playing important roles in optical devices such as optical polarizers and detectors, in this article, we have proposed a novel shape of nano aperture antenna for mid-infrared applications such as bio-sensing and other potential optical applications based on plasmonic characteristic of the gold layer over the SiN substrate. The transmittance tensor is obtained for vertical and horizontal linear polarization and base on boundary condition of the metasurface, the circular polarizations are extracted which are confirmed by the electric field distributions. We have shown by the parametric studies that the phase difference is altered by the gap and slot width and so with the dimension modification, we are able to achieve circular polarizer in the optical range. The biological materials with a thickness of 80 nm have then been placed over the metasurface layer and the figures of merits have been obtained. We have revealed that when the circular polarization is osculated to the metasurface at a special frequency the linear polarization is obtained in the other side of the metasurface. The nano aperture has been modeled and the finite difference time domain calculations are performed in CST Microwave Studio as a commercial full wave simulation software.     

Evaluation of spectral dispersion of optical constants of a-Se films from their normal-incidence transmittance spectra using Swanepoel algebraic envelope approach

Spectral dispersions of index of refraction \({n(\lambda )}\) and extinction coefficient \({\kappa (\lambda )}\) of undoped amorphous selenium (a-Se) films of three thicknesses (d?≈?0.5, 0.75, and 1.0 µm) were evaluated by analyzing experimental room-temperature normal-incidence transmittance-wavelength (\({{T_{{\text{exp}}}}(\lambda )} - \lambda\)) data (λ =?400–1100 µm) of their air-supported {a-Se film/thick glass slide}-stacks using Swanepoel’s transmission envelope theory of uniform films. Above a wavelength \({{\lambda _c}\,\, \approx \,\,640\;{\text{nm}}}\), as-measured \({{T_{{\text{exp}}}}(\lambda )}\,\, - \,\lambda\) spectra display well-resolved maxima and minima, with minor shrinkage in transparent and weak absorption regions (750–1100 nm). Below \({\lambda _{\text{c}}}\), a smeared sharp decline of \({{T_{{\text{exp}}}}(\lambda )}\) with decreasing λ, signifying strong absorption in a-Se films and existence of band-tail localized states. For λ > λ _c, the \({n\,(\lambda )}\, - \,\lambda\) data retrieved from algebraic envelope procedures followed a Sellmeier-like dispersion relation, with the best-fit values of high-frequency dielectric constant \({{\varepsilon _\infty }\, \approx \,\,{\text{4.9}}}\), static index of refraction \({{n_{\text{0}}} = n\left( {E\, \to \,{\text{0}}} \right)\,\, \approx \,\,{\text{2.43}}}\), and resonance wavelength \({{\lambda _0}\, \approx \,490\,\,{\text{nm}}}\), which may be assigned to onset of photogeneration in a-Se. Urbach-like dependency of absorption coefficient \({\alpha (h{{\nu }})}\) of a-Se films on photon energy \({h{{\nu }}}\) was realized with an Urbach-tail breadth of 85 meV. All achieved optical parameters were found to be slightly dependent on film thickness. Findings of present algebraic analysis are consistent with reported literature results obtained on the basis of other optical analytical approaches.     

MHD stagnation point flow towards a stretching sheet

The steady two-dimensional MHD stagnation point flow towards a stretching sheet with variable surface temperature is investigated. The governing system of partial differential equations are transformed into ordinary differential equations, which are then solved numerically using a finite-difference scheme known as the Keller-box method. The effects of the governing parameters on the flow field and heat transfer characteristics are obtained and discussed. It is found that the heat transfer rate at the surface increases with the magnetic parameter when the free stream velocity exceeds the stretching velocity, i.e. ε>1, and the opposite is observed when ε<1.     

A sulfonic acid functionalized ionic liquid as a homogeneous and recyclable catalyst for the one-pot synthesis of α-aminophosphonates

A sulfonic acid functionalized ionic liquid is used as a Brønsted acid catalyst for the one-pot, three-component synthesis of α-aminophosphonates from aldehydes and ketones at room temperature in water. This homogeneous catalytic procedure is simple and efficient and the catalyst can be reused at least six times without any noticeable decrease in catalytic activity.     

Roots of C*-algebra elements under numerical range condition

Let be a C*-algebra with unit 1. For each a ∈ , the C*-algebra numerical range is defined by V(a) = {φ(a): φ ∈ , φ ≥ 0,φ(1) = 1}. In a 2003 paper Li, Rodman and Spitkovsky have found the ω-th roots of elements in C*-algebra under a numerical range condition, when ω ∈ [1,∞). In this paper, we will give a short proof of the above result in the case of ω is a positive integer number. We also give a simple proof for ω-th root of an element a ∈ , when ω ∈ [1,∞) and V(a)∩ {z ∈ ℂ: z ≤ 0} = . The first author was supported by the Shiraz university Research Council Grant No. 86-GRSC-32.     

Two-Dimensional Legendre Wavelets for Solving Time-Fractional Telegraph Equation

In this paper, we develop an accurate and efficient Legendre wavelets method for numerical solution of the well known time-fractional telegraph equation. In the proposed method we have employed both of the operational matrices of fractional integration and differentiation to get numerical solution of the time-telegraph equation. The power of this manageable method is confirmed. Moreover, the use of Legendre wavelet is found to be accurate, simple and fast.     

Spherical Kadomtsev-Petviashvili Solitons in a Suprathermal Complex Plasma

The nonlinear aspects of nonplanar dust acoustic (DA) solitary waves are investigated in an unmagnetized complex plasma comprising of cold dust grains, kappa-distributed ions as well as electrons. The nonplanar DA solitons are studied based on the reductive perturbation technique. It is shown that the evolution of DA solitons is governed by a spherical Kadomtsev-Petviashvili (sKP) equation and then the impact of suprathermality on the spatial structure as well as the nature of DA soliton is studied. It seems that the properties of DA solitons in nonplanar geometry are quite different from that of the planar solitons.     

Composition and in vitro antibacterial activity of essential oils from four Satureja species growing in Iran

The composition and in?vitro antibacterial activity of essential oils from four Satureja species (S. bachtiarica, S. khuzistanica, S. mutica and S. rechingeri) growing in Iran were determined. According to the results of GC-FID and GC-MS analysis, all oil samples were principally composed of phenolic constituents (carvacrol and/or thymol) with the percentages ranging from 41.2% (S. bachtiarica) to 77.7% (S. rechingeri). Determining antibacterial activities by the disc diffusion method against two Gram-positive and two Gram-negative bacteria revealed the maximum activity against Bacillus cereus with a range of minimum inhibitory concentration values from 0.25 to 1?mg?mL(-1) and minimum bactericidal concentration values from 0.5 to 1?mg?mL(-1). The oils of S. khuzistanica and S. rechingeri appeared to be more active in general than those of other species. In conclusion, the essential oils of studied Satureja species have the potential to be considered as alternatives for synthetic food preservatives.