Sharif Digital Repository

Fundamental constraints imposing power-frequency trade-offs in conventional electronics have stimulated research on alternative technologies for millimeter-wave and sub-millimeter-wave applications. In this work, we use the picosecond threshold firing of nanoplasma switches to demonstrate on-chip millimeter-wave modulators that rely only on a single metal layer. We show amplitude shift keying (ASK) modulation with self-synthesized carrier frequencies up to 66 GHz (limited by the bandwidth of our experimental setup), with output powers up to 30 dBm. These all-metal nanoplasma modulators are low cost, and generally compatible with different platforms, from CMOS and III-V compounds to flexible... 

The transformerless single-phase semi-quasi-Z-source inverter (SqZSI) has a nonlinear gain curve and requires nonlinear sinusoidal pulse width modulation (NLSPWM) to achieve sinusoidal voltage at the output AC terminal. Although the SqZSI provides some advantages, for example, leakage current elimination, doubly grounded, low volume, and low cost, it needs nonlinear modulation control. The NLSPWM is relatively complex among single-phase modulation methods and it is considered a disadvantage for this topology, so this paper presents a model-driven processor programming method that facilitates the implementation of NLSPWM. The developed programming method utilizes a Blockset environment in... 

Due to size minimization and increment in the frequency of electronic devices, efficient and reliable methods for thermal management are required to reduce operating temperature, enhance stability, increase lifetime and user comfort. To prevent the damages of leakage and corrosion which occur in conventional heat sinks, proposing innovative thermal management methods has always been welcomed. Regarding these issues and based on the energy storage unit concept, in this study, a passive heat sink (HS) is fabricated and characterized for electronic chipset cooling with heat fluxes of 2000 to 4000 W/m2 utilizing phase change material (PCM) and nano-additive PCM (NPCM). The presented cooling... 

Photothermally heated and mesh-gridded membrane distillation (PHMD) system is proposed for desalination of high saline aqueous solutions. A triple-layered membrane, composed of a photothermal top nanofibrous layer containing polyacrylonitrile and dispersed carbon black nanoparticles and a polyvinylidene fluoride porous membrane supported on a nonwoven polyester, was prepared. A polypropylene mesh was used to hold the membrane. A 3D numerical simulation of the PHMD system was carried out by COMSOL and the appropriate length of the membrane module was determined. The effects of various operating parameters including solar radiation intensity on the permeate flux and thermal efficiency were... 

This article is concerned with remote monitoring and control of the 2-degrees of freedom (DoF) robotic manipulators, which have nonlinear dynamics over the packet erasure channel, which is an abstract model for communication over the Internet, WiFi, or Zigbee modules. This type of communication is subject to imperfections, such as random packet dropout and rate distortion. These imperfections cause a significant challenge for monitoring and control of robotic manipulators in the industrial environments because sensitive data, such as sensor data and control commands may not ever reach to their destination resulting in significant performance degradation. Therefore, the effects of these... 

The lipid membranes of living cells form an integral part of biological systems, and the mechanical properties of these membranes play an important role in biophysical investigations. One interesting problem to be evaluated is the effect of protein insertion in one leaflet of a bilayer on the physical properties of lipid membrane. In the present study, an all atom (fine-grained) molecular dynamics simulation is used to investigate the binding of cytotoxin A3 (CTX A3), a cytotoxin from snake venom, to a phosphatidylcholine lipid bilayer. Then, a 5 ms coarse-grained molecular dynamics simulation is carried out to compute the pressure tensor, lateral pressure, surface tension, and first moment... 

Miscellaneous sorts of renewable energies, despite of their positive impacts on the power system operation cost and environmental concerns, could jeopardize the system reliability due to introducing significant degrees of intermittency and uncertainty. This challenge could be overcome by composing various sources of renewable energies with complimentary natures. This paper devises an explicit mathematical framework to compromise the contribution of wind and solar energies. The optimization problem is to maximize the system reliability subject to a fixed monetary investment associated with both wind and solar. The problem formulation is based on mixed-integer programming (MIP) format in which... 

We present the results of a bolometric transition-edge sensor made of a high-Tc superconductor YBCO thin film prepared by fluorine-free metal-organic deposition. The structure of the films was characterized by X-ray diffraction and scanning electron microscopy, and the superconducting properties were determined by R-T measurements. The applicability of the resulting film as an infrared sensor is reported here. The optical response in the range of near infrared and the noise characteristics of the patterned bolometer are measured and analyzed. The dependence of device sensitivity on the bias current and modulation frequency is also investigated. As it is presented in this paper, the results... 

This paper describes a novel Direct Torque Control (DTC) method for adjustable speed Doubly-Fed Induction Machine (DFIM) drives which is supplied by a two-level Space Vector Modulation (SVM) voltage source inverter (DTC-SVM) in the rotor circuit. The inverter reference voltage vector is obtained by using input-output feedback linearization control and a DFIM model in the stator a-b axes reference frame with stator currents and rotor fluxes as state variables. Moreover, to make this nonlinear controller stable and robust to most varying electrical parameter uncertainties, a two layer recurrent Artificial Neural Network (ANN) is used to estimate a certain function which shows the machine... 

The finite element method and molecular dynamics simulations are used for modeling the AFM microcantilever dynamics and the tip-sample interaction forces, respectively. Molecular dynamics simulations are conducted to calculate the tip-sample force data as a function of tip height at different lateral positions of the tip with respect to the sample. The results demonstrate that in the presence of nonlinear interaction forces, higher eigenmodes of the microcantilever are excited and play a significant role in the tip and sample elastic deformations. Using comparisons between the results of FEM and lumped models, how some aspects of the system behavior can be hidden when the point-mass model is... 

This paper presents an investigation of the dynamics of two coupled non-identical FitzHugh-Nagumo neurons with delayed synaptic connection. We consider coupling strength and time delay as bifurcation parameters, and try to classify all possible dynamics which is fairly rich. The neural system exhibits a unique rest point or three ones for the different values of coupling strength by employing the pitchfork bifurcation of non-trivial rest point. The asymptotic stability and possible Hopf bifurcations of the trivial rest point are studied by analyzing the corresponding characteristic equation. Homoclinic, fold, and pitchfork bifurcations of limit cycles are found. The delay-dependent stability... 

In this study, the authors evaluate the performance of asynchronous optical multi-carrier code division multiple access (MC-CDMA) for intensity modulated/direct detection systems to be used in next-generation optical access networks. The proposed system employs Gold sequence in frequency-domain to provide asynchronous resource sharing. In long-reach passive optical networks, fibre impairments degradation to the performance of ordinary optical CDMA can be avoided by frequency-domain digital compensation methods in the proposed MC-CDMA. In comparison with orthogonal frequency division multiple access, peak-to-average power ratio in the proposed MC-CDMA is reduced and asynchronous resource... 

A matrix converter is a voltage/current source AC/AC frequency converter. In grid-connected operation of a variable-speed permanent magnet synchronous wind power generator, the matrix converter is normally controlled as a voltage source converter. In this control method, the generator-side voltage is synthesized from the grid-side voltage source. However, in the stand-alone mode of operation, the grid-side stiff voltage source is not available, and the input filter of the matrix converter is unstable. In this article, a new control method is presented that controls a permanent magnet synchronous wind generator in a stand-alone mode with a matrix converter as a current source converter. The... 

Differential pulse polarography (DPP) was applied for the determination of the herbicide Tribenuron-methyl (TBM). This is a first study for various parameters affecting the reduction peak current were simultaneously optimized using experimental design and these results are different from other reports. The effect of factors such as voltage step, voltage step time, pulse amplitude, pulse time, sample pH, concentration of the supporting electrolyte and the mercury drop size were assessed by means of a (27-2) fractional factorial design. It was found that the effects and interactions of four out of seven factors were significant. Consequently, a central composite design (CCD) with four factors,... 

Challenging problems in the design and analysis of photovoltaic (PV) systems stem from the nonlinear current–voltage (I–V) characteristics of solar cells. This paper presents an analytical analysis based on a describing function method to investigate the transient and steady-state characteristics of a three-phase single-stage grid-connected PV system. In this study, the nonlinear I–V characteristic of the PV array is linearized around the operating point. The nonlinear dynamic of the maximum power point tracking controller is divided into two parts of continuous and discrete. For the continuous part, the common small-signal linearization is applied, while for the discontinuous part, a... 

Background: Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation tool suited to alter cortical excitability and activity via the application of weak direct electrical currents. An increasing number of studies in the addiction literature suggests that tDCS modulates subjective self-reported craving through stimulation of dorsolateral prefrontal cortex (DLPFC). The major goal of this study was to explore effects of bilateral DLPFC stimulation on resting state networks (RSNs) in association with drug craving modulation. We targeted three large-scale RSNs; the default mode network (DMN), the executive control network (ECN), and the salience network (SN). Methods:... 

We investigate the problem of energy-efficient resource allocation constrained to quality of service and physical requirements in orthogonal frequency division multiplexing (OFDM)-based elastic optical networks and propose a fast two-stage algorithm to solve it. The first stage of the proposed algorithm deals with routing, traffic grooming, and traffic ordering and mainly aims at minimization of the number of deployed optical amplifiers and transponders. We provide an integer linear program for routing and traffic grooming and propose a heuristic procedure, which yields its near-optimum solution in a shorter runtime. In the second stage, we optimize transponder parameters to minimize total... 

A binary differential impulse radio-ultra wide band (IR-UWB) communication scheme over a single-mode optical fibre is examined. For a receiver structure, the conventional electrical receiver as well as an optical receiver structure, which is similar to the optical receiver used for digital, optically phase-modulated differential phase shift keying, are considered. The optical receiver can alleviate the IR-UWB receiver implementation challenges and it is studied for the first time in the context of IR-UWB. Considering various important noises, for example, phase noise, laser intensity noise, thermal noise and shot noise, analytical expressions for the error probability of the aforementioned... 

We present a new approach for analytical modeling and calculating the response of high-Tc superconductive transition edge sensors in a wide range of modulation frequencies for different configurations of the film patterns. The method used here is based on solving the heat transfer differential equation for two different time varying heat sources, which are related to the absorbed radiated power. The used method employs two-dimensional boundary conditions for describing meander-line patterned devices. The results from the applied method are in better agreement with those obtained from the frequency response measurements of the characterized samples, than the previously developed models. In...