Sharif Digital Repository

Fourier-based modal methods are among the most effective numerical tools for the accurate analysis of crossed gratings. However, leading to computationally expensive eigenvalue equations significantly restricts their applicability, particularly when large truncation orders are required. The resultant eigenvalues are the longitudinal propagation constants of the grating and play a key role in applying the boundary conditions, as well as in the convergence and stability analyses. This paper aims to propose simple techniques for the fast estimation of propagation constants in crossed gratings, predominantly with no need to solve an eigenvalue equation. In particular, we show that for regular... 

The application of regularized jump points has been proposed [Khavasi and Mehrany in Opt Commun 284(13):3211–3215, 6] as an adaptive spatial resolution (ASR) technique to improve the convergence of the Fourier modal method (FMM) in the analysis of one-dimensional periodic structures. We extend this approach to obtain the optical response of metal–dielectric crossed gratings, two-dimensional periodic structures with a high-contrast permittivity distribution. A metallic grid and a slab of split-ring resonators are analyzed using the proposed ASR technique, and the results compared with those obtained using the conventional ASR technique and FMM. The results show that, by adequately choosing... 

Recently, an approximate boundary condition [Opt. Lett. 38, 3009 (2013)] was proposed for fast analysis of onedimensional periodic arrays of graphene ribbons by using the Fourier modal method (FMM). Correct factorization rules are applicable to this approximate boundary condition where graphene is modeled as surface conductivity. We extend this approach to obtain the optical properties of two-dimensional periodic arrays of graphene. In this work, optical absorption of graphene squares in a checkerboard pattern and graphene nanodisks in a hexagonal lattice are calculated by the proposed formalism. The achieved results are compared with the conventional FMM, in which graphene is modeled as a... 

Recently, an approximate formalism [Opt. Express 23, 2764, (2015)] called diffractive interface theory has been reported for the fast analysis of the optical response of metasurfaces, subwavelength two-dimensional periodic arrays. In this method, the electromagnetic boundary conditions are derived using the susceptibility distribution of the metasurface, such that the analysis of metasurface is possible without solving any eigenvalue equation inside the grating layer. In this paper, we modify the boundary conditions to achieve more accurate results. In addition, in this paper, correct Fourier factorization rules are also applied leading to faster convergence rate. The obtained results are... 

An accurate and fast method for guided modes extraction in monolayer colloidal crystals and their inverse replicas is presented. These three-dimensional structures are composed of a monolayer of spherical particles that can easily and simply be prepared by self-assembly method in close packed hexagonal lattices. In this work, we describe how the guided modes, even or odd modes and light cone boundary can be easily determined using phase variations of reflection and transmission coefficients. These coefficients are quickly calculated by Fourier modal method. The band structures are obtained for a monolayer of polystyrene particles and two-dimensional TiO2 inverse opal by this proposed method  

We propose a new method to extract the modes of photonic crystal slabs and, thus, obtain their band structures. These slabs, which are 2-D periodic structures with finite thickness, can completely confine light and have the important advantage of simple construction for applications in integrated optic devices. In this paper, reflection pole method (RPM) is utilized to analyze photonic crystal slabs. Modes are poles of reflection and transmission coefficients of multilayered structures. According to this principle, modes can be detected by only pursuing phase variations of transmission coefficients that are equal to π rad. Therefore, extraction of modes becomes fast and simple through... 

Fourier-based modal methods are among the most significant tools for accurate numerical analysis of grating structures. However, they mostly lead to time consuming and memory hungry eigenvalue problems, particularly when large dielectric constants or high contrasts are involved. We have found an asymptotic semi-empirical relationship for the propagation constants of a lamellar grating, obtained from Fourier-based modal methods. Hence, given any truncation order, it is possible to estimate propagation constants without having to solve the eigenvalue equation. We observed propagation constants only depend on permittivities, filling factors, and the unit cell size, while the dependence on the... 

Simultaneous reductions in inventory of raw materials, work-in-process, and finished items have recently become a major focus in supply chain management. Vendor-managed inventory is a well-known practice in supply chain collaborations, in which manufacturer manages inventory at the retailer and decides about the time and replenishment. In this paper, an integrated vendor-managed inventory model is presented for a two-level supply chain structured as a single capacitated manufacturer at the first level and multiple retailers at the second level. Manufacturer produces different products where demands are assumed decreasing functions of retail prices. In this chain, both the manufacturer and... 

High molecular mass of naphthalene make it non-biodegradable and the biological methods for treated the pollutant are much time consuming. In this paper, two methods of ozonation and aeration are used to remove naphthalene. Because of the industrial wastewater has a great range of pH, in this study different concentrations of soluble naphthalene are placed in variable pH conditions, different contact times and changes in amount of aeration and ozonation. ANOVA results indicated a significant difference between two methods. The average removal of naphthalene by use of ozonation is 55 % and 37 % for aeration. As results, the best conditions that naphthalene are removed is in acidic environment... 

In this study, a series of highly swelling hydrogels based on sodium alginate (NaAlg) and polymethacrylamide (PMAM) was prepared through free radical polymerization. The graft copolymerization reaction was performed in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator andN,N′-methylenebisacrylamide (MBA) as a crosslinker. The crosslinked graft copolymer, alginate-graft-polymethacrylamide (Alg-g-PMAM), was then partially hydrolyzed by NaOH solution to yield a hydrogel, hydrolyzed alginate-graft-polymethacrylamide (H-Alg-g-PMAM). During alkaline hydrolysis, the carboxamide groups of Alg-g-PMAM were converted into hydrophilic carboxylate anions. Either the... 

Malaysian secondary schools are facing a shortage of male teachers. Almost 70% of the teaching profession is dominated by female teachers. There is an obvious gap in the reason why teaching is not preferred by the male gender. This study intends to find the determinants of career success among male teachers with the hope of revealing the career success factors that are associated with male teachers. A survey was done among 140 male teachers in secondary schools in the state of Malacca, Malaysia. Results showed that 4out of 5 of the determinants factors are significantly explaining career success among the teachers (Emotional Intelligence, Person-Job-Fit, Career Adaptability & Work-Life... 

We studied the flow stress and microstructural changes of nanostructured Al-6063 alloy produced by mechanical alloying at various temperatures and strain rates. The analysis of flow curves was performed by a constitutive equation, and the stress exponent and activation energy were determined as functions of strain. The deformation mechanisms were elaborated through microstructural observations by electron backscattering diffraction and transmission electron microscopy. Coarsening of the subgrains and grain growth upon deformation was monitored and related to the Zener–Hollomon parameter  

An ultrafine-grained Al6063/Al2O3 (0.8 vol.%, 25 nm) nanocomposite was prepared via powder metallurgy route through reactive mechanical alloying and hot powder extrusion. Scanning electron microcopy, transmission electron microscopy, and back scattered electron diffraction analysis showed that the grain structure of the nanocomposite is trimodal and composed of nano-size grains (< 0.1 μm), ultrafine grains (0.1–1 μm), and micron-size grains (> 1 μm) with random orientations. Evaluation of the mechanical properties of the nanocomposite based on the strengthening-mechanism models revealed that the yield strength of the ultrafine-grained nanocomposite is mainly controlled by the high-angle... 

Ultrafine-grained (UFG) Al6063/Al2O3 (0.8 vol%, 25 nm) nanocomposite was prepared via powdr metallurgy route. The grain structure of the nanocomposite composed of nano-size grains (< 0.1 μm), ultrafine grains (0.1-1 μm) and micron-size grains (>1 μm) with random orientations. It was found that the yield strength of the UFG nanocomposite is mainly controlled by the Orowan mechanism rather than the grain boundaries. The deformation activation energy at temperature ranges of T <300 ˚C and 300 ˚C ≤T < 450 ˚C was determined to be 74 and 264 kJ mol-1, respectively. At the higher temperatures, significant deformation softening was observed due to dynamic recrystallization of non-equilibrium grain... 

Ultrafine-grained (UFG) Al6063 alloy reinforced with 0.8 vol% nanometric alumina particles (25 nm) was prepared by reactive mechanical alloying and direct powder extrusion. Transmission electron microscopy and electron backscatter diffraction analysis showed that the grain structure of the nanocomposite composed of nanosize grains (<0.1 μm), ultrafine grains (0.1–1 μm) and micronsize grains (>1 μm) with random orientations. Mechanical properties of the material were examined at room and high temperatures by compression test. It was found that the yield strength of the UFG composite material is mainly controlled by the Orowan mechanism rather than the grain boundaries. The deformation... 

Nanostructured AA6063 (NS-Al) powder with an average grain size of ∼100 nm was synthesized by high-energy attrition milling of gas-atomized AA6063 powder followed by hot extrusion. The microstructural features of the consolidated specimen were studied by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques and compared with those of coarse-grained AA6063 (CG-Al) produced by hot powder extrusion of gas-atomized powder (without using mechanical milling). The consolidated NS-Al alloy consisted of elongated ultrafine grains (aspect ratio of ∼2.9) and equiaxed nanostructured grains. A high fraction (∼78%) of high-angle grain boundaries with average... 

The preparation of microcapsules containing perphenazine by solvent evaporation using ethyl cellulose is described. The microparticles are formed after solvent evaporation and polymer precipitation. The drug was dissolved in a polymer solution and emulsified into an aqueous phase to form microcapsules. To study the effects on particle size, encapsulation efficiency and morphology, three different molecular weights of ethyl cellulose (Mw=47000, 71000 and 99000) were used. Covalent bonding of drugs to polymers via hydrolytically or enzymatically cleavable covalent bond was achieved for sustained drug delivery. The release rate of perphenazine from these systems was investigated  

Models capable of accurate simulation of microcantilever dynamics coupled with complex tip–sample interactions are essential for interpretation and prediction of the imaging results in amplitude modulation or tapping-mode atomic-force microscopy (AM-AFM or TM-AFM). In this paper, four approaches based on combinations of lumped and finite element methods for modelling of cantilever dynamics, and van der Waals and molecular dynamics for modelling of tip–sample interactions, are used to simulate the precise imaging by AM-AFM. Based on the simulated imaging and force determination, the efficiency of different modelling schemes is evaluated. This comparison is performed considering their...