Sharif Digital Repository

In this paper a directive mesh network operating in the 60 GHz unlicensed band is considered for backhaul support for a small cell mobile network in an urban environment and interference between network links is analyzed. It is observed that while non-line-of-sight stations are adequately isolated by antenna directivity, interference can affect link performance in links that fall in line with each other, namely, line-of-sight links. Seeing as back-to-back links may occur in the proposed network between stations situated within long straight streets, the resulting interference can cause a decrease in network capacity by preventing simultaneous transmission on links. Here, the use of... 

Because of their exclusive features, millimeter wave directive mesh networks can be considered for small cell backhaul support in urban environments. For this purpose, a network of closely spaced stations has been considered with very directive line-of-sight links operating in the 60-GHz band. An attempt is made to evaluate channel response and interference behavior in such a network, taking into account the effect of building blockage. A simple grid of building blocks is considered as the propagation environment, and wave propagation is simulated using 2.5-dimensional (2.5D) ray tracing (2D with ground effect) to calculate the received signal at different nodes in the network. The results... 

The nature of alumazine⋯M (M = Li+, Na+, K+, Be2+, Mg2+, AND Ca2+) interactions was studied by ab initio calculations. The interaction energies were calculated at MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p) level. The calculations suggest that the size and charge of cation are two important factors that affect the interaction energy, charge transfer values and the variation in aromaticity of alumazine ring upon complexation. The theory of atoms in molecules (AIM) and natural bond orbital (NBO) analyses of complexes indicate that the variation of densities and the extent of charge shifts upon complexation correlate well with the obtained interaction energies. Finally, nucleus independent chemical... 

It is shown that negative capacitance (NC) circuits can be systematically used to improve the gain-bandwidth product of the operational amplifiers (opamps). The NC circuit moves the nondominant pole of the opamp to higher frequency by decreasing the parasitic capacitance of the critical node. The impedance at the input of the NC circuits is neither purely capacitive nor negative at all frequencies. A design guide is presented by deriving the circuit model for a conventional NC circuit and investigating the extent of the improvement that can be achieved in a circuit by the use of the NC circuit. The model is then used to present the design guide for widebanding the multistage opamps with... 

The required linearity of wideband receivers for applications, such as software-defined radio in the absence of input surface-acoustic wave (SAW) filters, is studied. It is shown that the required linearity of wideband SAW-less receivers is surprisingly higher than what has been commonly assumed. For these receivers, although the out-of-band blockers can reduce the compression point of the receiver, they can also potentially generate interferers that appear in the desired frequency band, resulting in higher noise floor and signal corruption. The required out-of-band IIP2 and IIP3 of low-noise amplifier (LNA) and mixer for single and concurrent applications are analytically derived. The... 

Elimination of the surface acoustic wave (SAW) filter from the input of a receiver can render it extremely vulnerable to various blockers and interferers. The presence of large out-of-band (OOB) blockers will result in the required linearity of the SAW-less receiver to be considerably higher than that of the conventional receivers with the input SAW filter. The ever-present undesirable signals that arise in the absence of the input SAW filter can be divided into two classes of far and near OOB blockers and interferers. Removal of these harmful signals requires two distinct approaches according to their nature. Two different methods for blocker and interferer rejection are introduced in this... 

In this paper, an effort has been made to model the 60 GHz wireless channel using a precise yet fast and simple method for short outdoor links that are a possible area for the use of 60 GHz wireless connectivity for high data rate services with dense frequency reuse. Considering the certain properties of this frequency band, it is possible to obtain a simple channel model to replace time consuming ray tracing methods with simpler models by disregarding low power multipath components. The street canyon model has been considered here as a replacement for ray tracing in an urban environment with below rooftop antennas to predict received power along streets and the results have been compared to... 

Channel characterization is an important step in the design of wireless communication systems. While channel sounding procedures are a useful method in determining channel behavior, they also require expensive and time consuming procedures and equipment. Ray tracing has been an important substitute for measurement in deterministic channel modeling and characterization of the wireless channel. Much has been done to improve the precision and efficiency of this method for lower frequency bands (generally below 5 GHz) over the years. Recently, with the worldwide announcement of a broad unlicensed band in the millimeter wave spectrum around 60 GHz, a great amount of attention has been paid to... 

In this article, a particular off-center bracing system is introduced. In this system, the tensile diagonal strut is not straight. When the load is applied, the original geometry changes and thus causes the system to harden. Based on this behavior, a step-by-step analytical method is developed. Using this method, a Geometrically Nonlinear Analysis Program (GNAP) is designed to analyze the elastic force-displacement relation. Extension of this program to dynamic analysis led to a Dynamic Nonlinear Analysis Program (DNAP). The object of this article is to show that such bracing systems will lead to less seismic force on such structures compared to classic concentric bracing systems. On the... 

It is widely accepted that the presence of a lossy network, such as a SAW filter or balun, at the input of LNA increases NF of the overall circuit by an amount equal to the insertion loss of the lossy network. In this work it is shown that this idea is not exactly true and it considerably underestimates the overall NF. To verify this claim, Z-model of the lossy network is added before the LNA and the overall noise figure is recalculated for some commonly used LNA topologies. It is shown that in common gate LNA and common source LNA with resistive feedback the accepted equation underestimates the overall NF by 1.3 dB for an insertion loss of 2 dB. In common source with resistive matching and... 

In this paper, the nonlinear cylindrical bending of a functionally graded plate is studied. The material properties of the plate are assumed to be graded continuously in the direction of thickness. The variation of the material properties follows a simple power-law distribution in terms of the volume fractions of constituents. The von Karman strains are used to construct the nonlinear equilibrium equations of the plates subjected to in-plane and transverse loadings. The governing equations are reduced to linear differential equation with nonlinear boundary conditions yielding a simple solution procedure. The results show that the functionally graded plates exhibit different behavior from... 

In this paper, based on Kirchhoff plate theory (CLPT), vibration analysis of an arbitrary nonlinear variable thickness annular isotropic plate which is covered with piezoelectric layers on the top and bottom surfaces in a short circuit state is performed using a semi-analytic method, named modified wave method (MWM). The plate is partitioned into several continuous segments with constant thicknesses, for which there exists exact analytical solutions. Considering wave method, the solution of each segment is assumed to be the combination of waves moving forward and backward, and at each step, waves in positive and negative directions are obtained in terms of waves at the inner edge of the... 

An energy based formulation of piezocomposites and a general 3-dimensional Ritz method for the analysis of piezocomposite solids of arbitrary shape and arbitrary width to thickness ratio are developed. The displacement fields and the electric potential function are approximated using special base functions, which satisfy boundary conditions through pb-3 method. Furthermore, an innovative remedy will be given to treat the problem of the discontinuities in strain fields and in electric displacement across the interfaces. An important feature of the present method is that, it can be used to analyze arbitrary shaped piezoelectric plates with high accuracy without the need of mesh generations and... 

The geometries of the complexes of Be 2+, Mg 2+, and Ca 2+ metal cations with borazine ring were studied. The complexes were optimized at the B3LYP level and the 6-311++G(d,p) basis set. Then, the interaction energies corrected by basis set super position error were calculated in the same level. The results show that interaction energy is strongly dependent on the charge-to-size ratio of the cation. Therefore, Be 2+ cation has the most interaction energy value with respect to Mg 2+ and Ca 2+ metal cations. Natural bond orbital analysis was performed to calculate the charge transfer and natural population analysis of the complexes. Quantum theory of atoms in molecules was also applied to... 

Pushover analysis is a simplified nonlinear analysis technique that can be used to estimate the dynamic demands imposed on a structure under earthquake excitations. One of the first steps taken in this approximate solution is to assess the maximum roof displacement, known as target displacement, using the base shear versus roof displacement diagram. That could be done by the socalled dynamic pushover analysis, i.e. a dynamic time history analysis of an equivalent single degree of freedom model of the original system, as well as other available approximate static methods. In this paper, a number of load patterns, including a new approach, are considered to construct the related pushover... 

Corrosion of steel rebars in concrete can reduce the durability of concrete structures in coastal environments. The corrosion rate of these concrete structures can be reduced by using suitable concrete additives and coating on rebars. This paper investigates the corrosion resistance of steel rebars by the addition of pozzolanic materials including fly ash, silica fume, polypropylene fibers, and industrial 2-dimethylaminoethanol (FerroGard 901) inhibitors to the concrete mixture. Three different types of rebars including mild steel rebar st37, and two stainless steel reinforcements, AISI 304 and AISI 316, were used. Various types of primer and coating including alkyd based primer, hot-dip...