Sharif Digital Repository

A periodic arrangement of 1-D slits carved in a perfect electric conductor is investigated, and an equivalent model which features sinusoidal surface conductivity on its upper and lower interfaces is derived. Therefore, and in sheer contrast to all the previous attempts that were successful in mimicking only the zeroth-order diffracted waves, it is capable of emulating both specular and nonspecular diffraction orders. The accuracy of the model is verified by the full-wave simulations. The proposed model is used to study the sharp Fano-type extraordinary transmission resonances arising in the structure. The transmission spectrum near these resonances is derived in terms of Fano resonance... 

In the present study, the shock-disturbances interaction in hypersonic inviscid flows with real gas effects is studied by applying a high-order accurate numerical method with the shock capturing technique. To consider real gas effects, the equilibrium air model is utilized here. The strong conservative form of the unsteady compressible Euler equations in the 2D generalized curvilinear coordinates is formulated and the resulting system of equations for the equilibrium air model is discretized by using the fifth-order finite-difference WENO scheme in space and the explicit third-order TVD Runge–Kutta scheme in time to provide a highly accurate and robust equilibrium airflow solver. The... 

Today, due to rapid development of construction of hydraulic structures like dams, the constituent material used in concrete and its durability in these kinds of structures has gained dominant interests and importance. One of the important factors of concrete durability in these structures is its resistance against abrasion due to crash of particles carried out as hydrated crystalline particulate matter. To enhance the abrasion resistance of concrete, different methods have been offered and investigated by many research3ers/ The aim of present article is to investigate the important parameter i.e. water-cement ratio on abrasive strength, porosity and the coefficient of hydraulic conductivity... 

One of the major shortcomings of conventional and rather high-rise structures is increasing lateral displacements arising from lateral forces which finally make the entire project un-economical. In this research, effort has been made to investigate the effect of shear walls arrangements on the lateral displacement of the structure. Two types of structures including 16 and 32-storeys frameswith different arrangements of shear panels were examined. The findings indicate that compared to other frames, the performance of frame no. 1 in both types of structures was poor in controlling the overall displacement of structure. Furthermore, more number of shear panels are not necessarily effective in... 

Submarine pipelines as the principal structural components are prone to fail by circumferential buckling under the effect of hydrostatic external pressure. Basically, the buckling capacity of a thin-walled pipe is dependent on "radius to thickness" ratio. At least two modes of local and overall buckling are possible in any pipeline system, which could be developed in pipe wall. A method of strengthening of pipes is developed in this paper to stop the failure. A total of 21 stiffened models are generated and analyzed using the well-known finite element program ABAQUS. In this study, the buckling and post-buckling behaviour of stiffened pipes are investigated by carrying out linear and... 

We propose an effective medium theory for a one-dimensional periodic array of rectangular grooves covered by a graphene sheet. Parameters of the effective medium model are given by explicit analytical expressions for both major polarizations TM and TE, and for all incident angles. In extraction of this model, we assumed single mode approximation inside the grooves. The effect of non-specular diffraction orders outside the grating, as well as the plasmonic response of the graphene sheet in the far-infrared spectrum, is addressed by introducing an effective surface conductivity at the interface of the metallic grating and the ambient environment. It is shown that surface plasmons in graphene... 

A simple approach to acquire wide-band/angle blazing operation in one-dimensional metallic gratings is investigated by means of mode-matching and equivalent circuit analysis. The gratings are single-groove perfectly conducting gratings that support two propagating guided modes (opposed to typical single mode cases). It is shown under what conditions, one can achieve blazing over a wide range of frequencies and angles. Most importantly, it is identified what governs blazing, in particular the true matching condition that needs to be satisfied, and how the structures’ multiple resonances play role in achieving such matching and tailoring the bandwidth. Parameters of the proposed equivalent... 

A simple approach to acquire wide-band/angle blazing operation in 1-D metallic gratings is investigated by means of mode-matching and equivalent circuit analysis. The gratings are single-groove perfectly conducting gratings that support two propagating guided modes (opposed to typical single-mode cases). It is shown under what conditions one can achieve blazing over a wide range of frequencies and angles. Most importantly, it is identified what governs blazing, in particular the true matching condition that needs to be satisfied, and how the structures' multiple resonances play role in achieving such matching and tailoring the bandwidth. Parameters of the proposed equivalent circuit model... 

In the present study, the potential of doxorubicin hydrochloride (DOX)-loaded electrospun chitosan/cobalt ferrite/titanium oxide nanofibers was studied to investigate the simultaneous effect of hyperthermia and chemotherapy against melanoma cancer B16F10 cell lines. The cobalt ferrite nanoparticles were synthesized via microwave heating method. The titanium oxide nanoparticles were mixed with cobalt ferrite to control the temperature rise. The synthesized nanoparticles and nanofibers were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and vibrating sample magnetometer (VSM) analysis. The DOX loading efficiency and in vitro drug release of... 

One of challenging problems in the domain of web services is the web service composition (i.e the task of composing web services to create new services, capable of fulfilling a need that no single service can satisfy). In real application, there will be a lot of relevant web services for a simple goal, so the search space for such a problem is huge. In this research statement, we show how by extracting some prior knowledge and using simple heuristics, search space and search time can be reduced significantly  

Optimal control of large-scale uncertain dynamic systems with time delays in states is considered in this paper. For this purpose, a two-level strategy is proposed to decompose the large-scale system into several interconnected subsystems at the first level. Then optimal control inputs are obtained by minimization of convex performance indices in presence of uncertainties, in the form of states and interactions feedback. The solution is achieved by bounded data uncertainty problems, where the uncertainties are only needed to be bounded and it is not required to satisfy the so-called 'matching conditions'. At the second level, a simple substitution-type interaction prediction method is used... 

In this paper, a fully coupled three-dimensional dynamic analysis is carried out to investigate the dynamic behavior of pile foundations in liquefied ground. A critical state bounding surface plasticity model is used to model soil skeleton, while a fully coupled (u- P) formulation is employed to analyze soil displacements and pore water pressures. Furthermore, in this study, variation of permeability coefficient during liquefaction is taken into account; the permeability coefficient is related to excess pore water pressure ratio. Results of a centrifuge test on pile foundations are used to demonstrate the capability of the model for reliable analysis of piles under dynamic loading. Then, the... 

In large-scale power systems, classical centralized control approaches may fail due to geographically distribution of information and decentralized controllers result in sub-optimal solution for load-frequency control (LFC) problems. In this paper, a two-level structure is presented to obtain optimal solution for LFC problems and also reduce the computational complexity of centralized controllers. In this approach, an interconnected multi-area power system is decomposed into several sub-systems (areas) at the first-level. Then an optimization problem in each area is solved separately, with respect to its local information and interaction signals coming from other areas. At the second-level,... 

In this study, a hierarchical optimal robust controller is presented for the power system load-frequency control problem. In this approach, the multi-area power system is first decomposed into several sub-systems (areas). Then by using a two-level control strategy, the overall optimal solution is obtained. At the first level, the optimal control of each area is obtained with respect to local information and also considering interactions coming from other areas. At the second level, by using a coordination strategy, the local controllers will converge to global solution and optimal robust controller is achieved. This approach is applicable to both single-area and multi-area interconnected... 

Nickel-base superalloys such as René 80 are widely used in manufacturing aircraft turbine blades. They are usually coated in order to increase their wear, oxidation, erosion, and hot corrosion properties against environmental degradation. In this article, the mechanical behavior (tensile and low-cycle fatigue (LCF)) of uncoated and aluminide-coated (CODEP-B) René 80 has been studied at 871 °C and 982 °C. Experimental results show that the tensile properties of coated specimens are relatively lower than those of uncoated ones in the same conditions, but application of coating increases the LCF life of René 80 at T = 871 °C, 982 °C, R = (εmin/εmax) = 0, strain rate of 2 × 10-3 s-1, and Δεt =... 

In a deregulated environment of power distribution industry, a comprehensive economic evaluation for the implementation of distribution automation (DA) systems is inevitable. Using the presented methodology in this paper and system dynamics approach, it is efficiently possible to deal with variation of the economic parameters such as the interest rate, inflation rate, energy supply cost, load growth, etc. In this paper, economic short-run and long-run impacts of DA systems are evaluated from utility point of view. Also economic benefits from customers' point of view are analyzed. A practical pricing strategy for maximizing the utility profit is suggested depending on the underlying market... 

Ni-base superalloys such as René 80 are widely used for aircraft turbine blades manufacture, due to possesses suitable mechanical, oxidation and hot corrosion properties. It is usually coated in order to increase its wear, oxidation, erosion and hot corrosion properties against environmental degradation. One the most important properties of coatings is its DBTT. In this paper the behavior of uncoated and coated (CODEP-B) René 80 has been studied near the DBTT (871 °C), R = (εmin/εmax) = 0 and strain rate of about 2 × 10-3 s-1. Experimental results show that in coated specimens while the total cyclic strain is lower than 1%, coating leaves longer fatigue life, at this condition the nucleation... 

Mach’s principle asserts that the inertial mass of a body is related to the distribution of other distant bodies. This means that in the absence of other bodies, a single body has no mass. In this case, talking about motion is not possible, because the detection of motion is possible only relative to other bodies. But in physics we are faced with situations that are not fully Machian. As in the case of general theory of relativity where geodesics exist in the absence of any matter, the motion has meaning. Another example which is the main topic of our discussion, refers to Bohmian quantum mechanics, where the inertial mass of a single particle does not vanish, but is modified. We can call... 

One of the important and famous topics in general theory of relativity and gravitation is the problem of geodesic deviation and its related singularity theorems. An interesting subject is the investigation of these concepts when quantum effects are considered. Since the definition of trajectory is not possible in the framework of standard quantum mechanics (SQM), we investigate the problem of geodesic equation and its related topics in the framework of Bohmian quantum mechanics in which the definition of trajectory is possible. We do this in a fixed background and we do not consider the backreaction effects of matter on the space-time metric. © 2018 World Scientific Publishing Company  

Ni-base superalloy René 80 is widely used in manufacturing aircraft turbine blades. The service temperature of this alloy is in the range of 760-982 °C. Although this alloy possesses suitable mechanical, oxidation and hot corrosion properties, it is coated in order to increase its wear, oxidation, erosion and hot corrosion properties against harmful environmental service conditions. In this paper the influence of applying diffusion coating (CODEP-B) on the tensile properties of René 80 has been studied in the temperature range of 22-982 °C. Experimental results show that the tensile properties of the coated specimens are relatively lower than that of uncoated ones in the same conditions. But...