Sharif Digital Repository

A novel and general formulation for wave propagation in time-varying media is presented. Unlike previousreports, our formalism is able to solve propagation in media with arbitrary time variations of permittivity orpermeability, for both transient and steady-state periodic variations. The formulation is approximate yet strikingly accurate in most practical cases. The provided closed-form expressions show that the normalized averagepower after the transition of the permittivity does not depend on the details of the transition, while the energydensity does. Some important discussions are made about time-periodic media, and it is shown that there is anaccumulation of energy when the temporal... 

Feed-forward is one of the main methods for linearising microwave power amplifiers. The level of inter-modulation rejection (IMR) values can be predicted by appropriate modelling of the feed-forward microwave amplifier. Here, we have presented closed form expressions, which can be used for predicting the IMR for the first and second adjacent channels. Fifth- and third-order nonlinear models have been used for the main and error amplifiers, respectively. The predicted values have been verified using ADS simulator and a MATLAB program. © The Institution of Engineering and Technology 2007  

In this paper, we investigate the diversity-multiplexing tradeoff (DMT) for multi-relay channels in finite-SNR regime. In our analysis, we consider the decode and forward (DF) relaying strategy and a line of sight path from source to destination. First, we determine the outage probability in a multi-relay scenario and obtain its exact analytical expressions. Then, the outage probability of a multi-relay channel with relay selection is calculated and provided as a closed-form expression. Based on these results, we determine the DMT in finite-SNR regime. Finally, using simulation results, we show that our analysis has accurate results which coincides with that of obtained from Monte-Carlo... 

In this paper, two circuit models are proposed for analytical investigation of extraordinary transmission through periodic array of subwavelength stepped slits in a thick metallic plate. A cascade model is first developed and then a stub model is suggested for cases that the cascade model is not accurate. The parameters of the proposed circuits are given by closed-form expressions. Both symmetric and asymmetric stepped slits are considered  

A circuit model is proposed for periodic 1-D array of metallic strips in the sub-wavelength regime. The parameters of the proposed circuit and their dependence on frequency are all explicitly given by closed form expressions. The necessity of using numerical simulation to extract model parameters is thus sidestepped. It is demonstrated that the proposed model is valid at different incident angles and for arbitrary surrounding mediums given that there is only one propagating diffracted order outside the grating and only one guided mode supported by the slits. Both major polarizations are studied in this paper  

Infinite series solutions are obtained for electrical potential, electroosmotic velocity, ionic conductance, and surface physicochemical properties of long pH-regulated rectangular nanochannels of low surface potential utilizing the double finite Fourier transform method. Closed form expressions are also obtained for channels of large height to width ratio for which the depthwise variations vanish. Neglecting the Stern layer impact, the effects of EDL (Electric Double Layer) overlap, multiple ionic species, and association/dissociation reactions on the surface are all taken into account. Moreover, finite-element-based numerical simulations are conducted to account for the end effects as well... 

This work is about the total variation (TV) minimization which is used for recovering gradient-sparse signals from compressed measurements. Recent studies indicate that TV minimization exhibits a phase transition behavior from failure to success as the number of measurements increases. In fact, in large dimensions, TV minimization succeeds in recovering the gradient-sparse signal with high probability when the number of measurements exceeds a certain threshold; otherwise, it fails almost certainly. Obtaining a closed-form expression that approximates this threshold is a major challenge in this field and has not been appropriately addressed yet. In this work, we derive a tight lower-bound on... 

In this article, we propose a lightweight security scheme for ensuring both information confidentiality and transmission resiliency in the Internet-of-Things (IoT) communication. A single-Antenna transmitter communicates with a half-duplex single-Antenna receiver in the presence of a sophisticated multiple-Antenna-Aided passive eavesdropper and a multiple-Antenna-Assisted hostile jammer (HJ). A low-complexity artificial noise (AN) injection scheme is proposed for drowning out the eavesdropper. Furthermore, for enhancing the resilience against HJ attacks, the legitimate nodes exploit their own local observations of the wireless channel as the source of randomness to agree on shared secret... 

Oscillatory condition in LTI dynamic systems is generally expressed as possessing purely imaginary solutions by their characteristic equations. Dealing with the class of fractional order systems, such a condition is equivalently restated as owing complex roots with specific arguments by a polynomial defined based on the system characteristic equation. The degree of this polynomial can be unboundedly high. Consequently, such statement for the oscillatory condition in fractional order systems, which is based on arguments of the roots of a polynomial with an unbounded degree, cannot be viewed as a closed-form expression. To tackle this challenge, this brief introduces an approach to obtain a... 

In this paper, an extended dynamic model of peripheral milling process including process damping, structural and cutting force nonlinearities is presented. Cutting forces are described through a third-order polynomial function of chip thickness while a cubic nonlinear function is considered for the structural stiffness. Under stable and regenerative chatter conditions and using Fourier series components, closed form expressions for the nonlinear cutting forces are derived. Parameters of the proposed model are identified through a set of experiments. For this purpose, modal experiments and measurement of cutting forces (at various feed rates) are performed to determine the modal parameters... 

In this study, the authors propose a novel power allocation scheme in time division multiple access (TDMA)-based distributed multiple-input multiple-output (MIMO) channels. By modelling the problem with a TDMA MIMO interference channel, the authors have derived closed-form expressions for power and time slot assigned to each MIMO transmission. Although our scheme is sub-optimal, with the aid of Jensen's inequality, it is shown to be superior to solutions based on channel inversion. In addition, the proposed scheme is compared with the optimal solution, and also with the scheme proposed by Dohler. By applying our proposed power allocation to the hierarchical cooperation strategy, the authors... 

There are unusual nonlinear behaviors in superconducting materials, especially at low temperatures. This paper describes the procedure to reliably predict this nonlinearity in superconducting microstrip transmission lines (SMTLs). An accurate nonlinear distributed circuit model, based on simultaneously considering of both quadratic and modulus nonlinearity dependences, is proposed. All parameters of the equivalent circuit can be calculated analytically using proposed closed-form expressions. A numerical method based on Harmonic Balance approach is used to predict nonlinear phenomena like intermodulation distortions and third harmonic generations. Nonlinear analyses of the SMTLs at the... 

A rigorous approach is proposed to improve the resolution of integral imaging (InI) by finding the appropriate form of irregularity in the arrangement of the InI lenslets. The improvement of the resolution is achieved through redistribution of the sampling points in a uniform manner. The optimization process for finding the optimum pattern of the lens-array irregularity is carried out by minimizing a cost function, whose mathematical closed-form expression is provided. The minimization of the proposed cost function ensures the uniform distribution of sampling points and thus improves the resolution within the desired depth of field (DOF) and field of view (FOV). A set of standard resolution... 

In this study, the authors optimise the outage probability of amplify and forward incremental relaying (IR) scheme using two different power allocation methods in the presence of channel estimation errors. The authors find the outage probability of IR scheme and minimise it subject to traditional power (TP) constraint in which the sum of nodes' powers is fixed and outage-dependent power (ODP) constraint which is compatible with the physical concept of IR and takes into account the quality of the direct path in the optimisation problem. The authors provide closed-form expressions to allocate power to pilot and data symbols of both the source and the relay. Although, their analysis uses high... 

The present investigation considers the fully developed electro-osmotic flow of power-law fluids in a planar microchannel subject to constant wall heat fluxes. Using an approximate velocity distribution, closed form expressions are obtained for the transverse distribution of temperature and Nusselt number. The approximate solution is found to be quite accurate, especially for the values of higher than ten for the dimensionless Debye-Huckel parameter where the exact values of Nusselt number are predicted. The results demonstrate that a higher value of the dimensionless Debye-Huckel parameter is accompanied by a higher Nusselt number for wall cooling, whereas the opposite is true for wall... 

In this study, the authors propose a novel Filon-type integration method that uses error-controllable and frequency-independent closed-form expression to evaluate highly oscillatory physical optics (PO) surface integrals on smooth conducting surfaces. In this method, the phase and amplitude functions of PO integrals for a general parametric surface and incident wave are approximated by second order polynomials, first. Although there are some complicated closed-form expressions for these integrals in the literature, the authors present simple and computationally efficient closed-form expressions for them. For this end, the parametric domain of each resulted integral is meshed by triangular... 

In this study, the authors present an analytical approach to find the axisymmetric buckling load of two joined isotropic conical shells under axial compression. The problem of two joined conical shells may be considered as the generalized form of joined cylindrical and conical shells with constant or stepped thicknesses. Thickness of each cone is constant; however it may be different from the thickness of the other cone. The boundary conditions are assumed to be simply supported with rigid rings. The governing equations for the conical shells are obtained and solved with an analytical approach. A simple closed-form expression is obtained for the buckling load of two joined truncated conical... 

This study presents an efficient fractional frequency reuse scheme for macrocell network which uses six directional antennas to cover the outer region and analyses the performance. Cross-tier interference between macrocell and femtocell networks leading to throughput and outage probability degradation is a major issue in two-tier networks when femtocells are deployed in co-channel with macrocells. In this study, the received interference from the macrocell network to femtocell network is analysed. Then, based on the degree of received interference, an algorithm for orthogonal resource allocation to femtocells with low cross-tier interference is presented. According to the introduced scheme,... 

It is has been long known that the curved space in the presence of gravitation can be described as a non-homogeneous anisotropic medium in flat geometry with different constitutive equations. In this article, we show that the eigenpolarizations of such medium can be exactly solved, leading to a pseudo-isotropic description of curved vacuum with two refractive index eigenvalues having opposite signs, which correspond to forward and backward travel in time. We conclude that for a rotating universe, time-reversal symmetry is broken. We also demonstrate the applicability of this method to Schwarzschild metric and derive exact forms of refractive index. We derive the subtle optical anisotropy of... 

This paper investigates the outage probability and the throughput of relay networks with joint information and energy transfer where the relay harvests energy from transmitted radio-frequency (RF) signal of the source. Considering different power consumption models, we derive the outage probability of the systems for both adaptive and non-adaptive power allocations at the relay. With a total energy consumption constraint at the source, we provide closed-form expressions for the optimal time sharing and power allocation between the source energy and information transfer signals. The analytical and simulation results demonstrate the efficiency of joint energy and information transfer systems...