Sharif Digital Repository

In this paper, we report on a periodic metallo-dielectric structure that supports geometry-induced surface plasmons in the sub-terahertz regime. The proposed structure is made up of a dielectric-coated metallic grating sandwiched by parallel metal plates. Based on the modal analysis of 2D and 3D structures, the impact of a metal cladding and a customized dielectric coating on the dispersion relation and field distribution of the guided surface wave is investigated. It is found that modal field confinement is improved in the presence of a metal cladding without narrowing the operational bandwidth of the waveguide. Moreover, a customized subwavelength-sized dielectric coating based on... 

In this paper, we present a Gaussian to tophat beam shaper (GTBS) based on an all-dielectric metasurface lens for sub terahertz (sub-THz) applications. In order to calculate the required phase profile of the GTBS, we use an analytical procedure based on the geometrical transformation technique. The calculated phase profile is then realized by a silicon (Si) metasurface lens consisting of rectangular-shaped pillars of subwavelength dimensions. Because of large solution domain relative to the operation wavelength, we combined the beam envelope and the finite element methods to simulate the structure with a high precision. By designing an anti-reflection metasurface made up of periodically... 

In this paper, we report on the design, simulation and measurement of a flat-top beam shaper (FBS) lens for a millimeter-wave (mm-wave) antenna coupled source. The beam shaper is designed to transform the pseudo-Gaussian beam of the mm-wave source into a flat-top beam of sharp roll-off at a specific distance in the Fresnel region. Firstly, relying on the geometrical optics principles, we propose an analytical formulation for the design of lens profiles. Next, a simple optimization method based on the full-wave simulation of the lens and the mm-wave antenna is suggested to tune the analytically extracted lens profile. The optimized lens profile is then studied to assess its performance... 

In this paper, we report on a periodic metallo-dielectric structure that supports geometry-induced surface plasmons in the sub-terahertz regime. The proposed structure is made up of a dielectric-coated metallic grating sandwiched by parallel metal plates. Based on the modal analysis of 2D and 3D structures, the impact of a metal cladding and a customized dielectric coating on the dispersion relation and field distribution of the guided surface wave is investigated. It is found that modal field confinement is improved in the presence of a metal cladding without narrowing the operational bandwidth of the waveguide. Moreover, a customized subwavelength-sized dielectric coating based on... 

In this paper, we report on the design, simulation and measurement of a flat-top beam shaper (FBS) lens for a millimeter-wave (mm-wave) antenna coupled source. The beam shaper is designed to transform the pseudo-Gaussian beam of the mm-wave source into a flat-top beam of sharp roll-off at a specific distance in the Fresnel region. Firstly, relying on the geometrical optics principles, we propose an analytical formulation for the design of lens profiles. Next, a simple optimization method based on the full-wave simulation of the lens and the mm-wave antenna is suggested to tune the analytically extracted lens profile. The optimized lens profile is then studied to assess its performance... 

Dielectric gratings (DGs) have recently been introduced as a new platform for guiding dielectric-based geometrically-induced surface plasmons (SPs) called spoof SPs (SSPs). In this paper, we report on the modal analysis of a metal-clad DG waveguide and compare its performance with other counterparts including the dielectric image guide (IG) and the metal grating (MG) waveguide. The proposed DG waveguide is made up of a periodic array of high-resistivity silicon (HR-Si) pillars on a metal plate with a metal cladding at a proper distance above the structure. By modal analysis of 2D and 3D structures, we show that the presence of the metal cladding enhances the modal field confinement without... 

Dielectric grating-based spoof surface plasmonic (SSP) structures are among the recent low-loss and subwavelength field-concentrating solutions for realizing high-density terahertz (THz) and sub-THz integrated circuits. In this paper, we report on a novel waveguide structure capable of supporting highly confined SSP mode while exhibiting much lower propagation loss compared to other similar SSP structures. The proposed structure is composed of two perfectly aligned identical silica ridges placed on the inner faces of the metallic plates of a parallel plate waveguide with a proper plate distancing in order to leave an empty gap region between the ridges. Each of the ridges embodies a periodic... 

In this paper, we discuss some recent results on graphs attached to rings. In particular, we deal with comaximal graphs, unit graphs, and total graphs. We then define the notion of cototal graph and, using this graph, we characterize the rings which are additively generated by their zero divisors. Finally, we glance at graphs attached to other algebraic structures  

The energy of a graph G, denoted by E(G), is defined as the sum of absolute values of all eigenvalues of G. In (MATCH Commun. Math. Comput. Chem. 83 (2020) 631{633) it was conjectured that for every graph G with maximum degree Δ(G) and minimum degree Δ (G) whose adjacency matrix is non-singular, E(G) +δ (G) + Δ (G) and the equality holds if and only if G is a complete graph. Here, we prove the validity of this conjecture for planar graphs, triangle-free graphs and quadrangle-free graphs. © 2021 University of Kragujevac, Faculty of Science. All rights reserved  

The energy of a graph G, denoted by E(G), is defined as the sum of absolute values of all eigenvalues of G. In (MATCH Commun. Math. Comput. Chem. 83 (2020) 631{633) it was conjectured that for every graph G with maximum degree Δ(G) and minimum degree Δ (G) whose adjacency matrix is non-singular, E(G) +δ (G) + Δ (G) and the equality holds if and only if G is a complete graph. Here, we prove the validity of this conjecture for planar graphs, triangle-free graphs and quadrangle-free graphs. © 2021 University of Kragujevac, Faculty of Science. All rights reserved  

Background: Warts are the most common clinical manifestation of the human papilloma-virus infection in the skin and mucous membranes. In spite of the various therapeutic modalities for nongenital skin warts, there is still no single method to be used as an approved treatment. In this study, we compared the efficacy of immunotherapy and cryotherapy on wart lesions. Methods: Sixty patients with verruca vulgaris and plantar warts were randomly divided into two groups. One group received intralesional injection of candida antigen repeated every 3 weeks until complete improvement of all warts or for a maximum of three sessions. The second group was treated by cryotherapy with liquid nitrogen for... 

A novel intelligent semi-active control system for an eleven degrees of freedom passenger car's suspension system using magnetorheological (MR) damper with neuro-fuzzy (NF) control strategy to enhance desired suspension performance is proposed. In comparison with earlier studies, an improvement in problem modeling is made. The proposed method consists of two parts: a fuzzy control strategy to establish an efficient controller to improve ride comfort and road handling (RCH) and an inverse mapping model to estimate the force needed for a semi-active damper. The fuzzy logic rules are extracted based on Sugeno inference engine. The inverse mapping model is based on an artificial neural network... 

Using CNG as an additive for gasoline is a proper choice due to higher octane number of CNG enriched gasoline with respect to that of gasoline. As a result, it is possible to use gasoline with lower octane number in the engine. This would also mean the increase of compression ratio in SI engines resulting in higher performance and lower gasoline consumption. Over the years, the use of simulation codes to model the thermodynamic cycle of an internal combustion engine have developed tools for more efficient engine designs and fuel combustion. In this study, a thermodynamic cycle simulation of a conventional four-stroke spark-ignition engine has been developed. The model is used to study the... 

With the declining energy resources and increase of pollutant emissions, a great deal of efforts has been focused on the development of alternatives for fossil fuels. One of the promising alternative fuels to gasoline in the internal combustion engine is natural gas [1-5]. The application of natural gas in current internal combustion engines is realistic due to its many benefits. The higher thermal efficiency due to the higher octane value and lower exhaust emissions including CO2 as a result of the lower carbon to hydrogen ratio of the fuel are the two important feature of using CNG as an alternative fuel. It is well known that computer simulation codes are valuable economically as a cost... 

Gaining insight into possible vibratory responses of dynamical systems around their stable equilibria is an essential step, which must be taken before their design and application. The results of such a study can significantly help prevent instability in closed-loop stabilized systems by avoiding the excitation of the system in the neighborhood of its resonance. This paper investigates nonlinear oscillations of a rotary inverted pendulum (RIP) with a full-state feedback controller. Lagrange’s equations are employed to derive an accurate 2-DoF mathematical model, whose parameter values are extracted by both the measurement and 3D modeling of the real system components. Although the governing... 

A suction-controlled ring device has been developed to continuously measure the coefficient of lateral soil pressure in deformable unsaturated soil samples from the at-rest to the active condition under application of increasing vertical pressure and controlled matric suction. The device incorporates a thin aluminum specimen ring equipped with horizontal strain gages for recording the lateral soil strains. In addition, a sensor recording water volume changes is utilized to continuously monitor the degree of saturation of the soil sample during tests. The matric suction within the soil texture is controlled using the axis translation technique. In order to verify the performance of the ring... 

We introduce a new smooth, non-toxic, biocompatible method for cross-linking of gum tragacanth (GT), a polysaccharide of natural origin, in order to serve as a new supporting matrix for immobilization systems. The modified gum is used as a matrix for the catalysis of the conversion of benzyl penicillin to 6-aminopenicillanic acid (6-APA) by means of Escherichia coli ATCC11105 with penicillin G acylase (PGA) activity. The results show that GT beads can not only serve as a proper matrix for immobilization, but show enhanced hydrolysis rate and stability compared to other immobilization systems used for this reaction. This signifies the potential of GT as a biocompatible matrix for... 

The Class-E power amplifier has been widely studied and formulated in the literature. Although the majority of reported inductive coupling wireless power transfer (WPT) systems use a class-E power amplifier for driving the primary coil, still there is a lack of a comprehensive study on class-E circuit dedicated to WPT, providing a set of closed form design equations for proper class-E operation. This paper presents the required design equations needed to design a 'true' class-E circuit for WPT applications. Equations for the series-tuned secondary coil WPT system are presented, as well as two different design procedures for the parallel-tuned secondary coil. The derived equations have been... 

Pole Side Impact Tes is one out of three crash tests described by Euro NCAP standard for star rating of a vehicle and is required for assessing the Adult Occupant Protection. In this paper the goal is to determine the crashworthiness of side doors and B pillar in a Pole Side Impact Test based on Euro New Car Assessment Program (Euro-NCAP) using computer and simulation method. In this matter, a vehicle model has been prepared and meshed using Hypermesh and CATIA. The velocity of 29 km/h has been assigned to the vehicle which was on top of a cart while the pole has been assigned as a rigid static object based on Euro NCAP requirements specifically. Results show that different amounts of energy...