Sharif Digital Repository

In this paper, methods for reduction of coupling between receiving and transmitting antenna arrays are proposed and tested. Coupling between RX and TX causes saturation and a higher noise level in IF. So, coupling reduction improves image quality of system. Antenna element of arrays are printed antipodal Yagi-Uda antenna with greater than 8 dBi gain and higher than 4 GHz bandwidth. Frequency bandwidth of this imaging system is 27 to 30.5 GHz. Half power beamwidth of this antenna element is larger than 90 dB. Front to back ratio of this antenna is improved in this paper to 30 dB at 29 GHz. © 2019 IEEE  

In this paper, the coupling coefficient of two waveguides with conducting interfaces is calculated analytically. It is shown that the control of interface charge densities via a transverse voltage leads to the control of the coupling. To derive the coupling coefficient, the basic Coupled Mode Theory (CMT) with paraxial approximation is improved to include the effect of conducting interfaces. The analysis is performed independently for TE and TM polarizations. Several direct applications of this effect including a multiplexer, a coupler and a modulator/switch and programmable grating are introduced. © Sharif University of Technology, October 2003  

An improved coupled wave approach is presented for the analysis of diffraction behavior of a two-dimensional spatially periodic or almost periodic dielectric layer illuminated by TE polarized plane waves. This method applies to any simultaneous composition of arbitrarily modulated planar transmission gratings with any permittivity in neighboring regions. Two major improvements have been made. In the first part, the eigenvalues and eigenvectors of coupled wave system of equations are first-order corrected to reduce the inherent errors generated by neglecting second-order derivatives. In the second part, a scattering matrix method is used to model the effect of boundaries. Using this method,... 

The present paper deals with the design and optimization of a heat driven thermoacoustic refrigerator. A simplified model is developed which enables to pinpoint and examine the most important physical characteristics of a compact traveling wave thermoacoustic refrigerator driven by a traveling wave thermoacoustic engine. The model can explain the so-called traveling standing wave effect in thermoacoustics very well. The position, length and hydraulic radius of the refrigerator are optimized for the maximum total COP. The prime mover efficiency, refrigerator COP and dimensionless dissipation and their impacts on total COP are investigated and discussed. The results indicate that a COP of... 

Owing to the inherent incompatibility with water, cyanation of aryl halides may be the most challenging category of palladium-catalyzed coupling reactions. The major challenges are attributed to the catalyst deactivation by the soluble cyanide (CN−) ions and desirable conversions only could be obtained by employing toxic organic solvents. The current minireview highlights mechanistic insights and breakthrough achievements for this reaction in the aqueous media  

The system, Pd(OAc)2/imidazolium salts (L2), was found as an efficient catalyst in the Heck coupling reaction of olefins with aryl halides and Suzuki reactions of various aryl halides with aryl boronic acids under aerobic condition. This catalytic system demonstrates great tolerance to a wide range of groups on all substrates of aryl halides, alkenes and aryl boronic acids  

One of the main applications of citation is to find articles that are relevant to a particular article. However, not all citations are equally relevant to the target article. This paper presents an approach to identify the most relevant citation(s). To this end, the Normalized Similarity Index (NSI) is proposed to quantify the similarity between the source and target of a citation base on the co-citations and references shared by them. To validate the method, NSI was calculated for five citation networks and was compared with the peer review grades for the relevancy between the source and the target articles. The results showed a significant correlation between the NSI ranks and those of... 

The idea of pure coupled mode approach is extended to the analysis of volume grating structures. In this approach, diffraction orders inside the grating are expanded over TE and TM components and unperturbed wavevectors are used instead of Floquet wavevectors of conventional coupled wave approach. Coupling between these orders are considered to model the diffraction. Three-dimensional grating structures are analyzed, and comparisons with rigorous coupled wave analysis are made to verify the accuracy and determine the range of applicability of the proposed method. © 2004 IEEE  

Identification of chatter free cutting conditions, the chatter stability lobes, requires a measurement of the frequency response function (FRF) of each tool mounted on the spindle. This paper presents a method of assembling known dynamics of the spindle-tool holder with an analytically modeled end mill using the receptance coupling technique. The classical receptance technique is enhanced by proposing a method of identifying the end mill-spindle/tool holder joint dynamics, which include both translational and rotational degrees of freedom. The method requires measurement of FRFs with impact tests applied on the spindle-tool holder assembly and blank calibration cylinders attached to the... 

An improved coupled mode approach is presented for the analysis of plane-wave interaction with a spatially periodic permittivity dielectric layer. The method consists of two parts, in the first part the eigenvalues and eigenvectors of coupled mode system of equations are corrected to reduce the inherent errors, which arise by neglecting second-order derivatives. In the second part, a scattering matrix representation of cascaded systems is used to model the effect of boundaries. The problem under consideration is a 2-D planar grating structure illuminated by a TE polarized incident wave, but the method can be applied to other grating structures such as couplers, or any other structure for... 

Optomechanical and electromechanical cavities have been widely used in quantum memories and quantum transducers. We theoretically investigate the robustness of optomechanical and electromechanical quantum memories against the noise of the control laser. By solving the Langevin equations and using the covariance matrix formalism in the presence of laser noise, the storing fidelity of Gaussian states is obtained. It is shown that the destructive effect of phase noise is more significant in higher values of coupling laser amplitude and optomechanical coupling strength G. However, by further increasing the coupling coefficient, the interaction time between photons and phonons decreases below the... 

In this paper, we investigate cooling of a levitated nanosphere in a system of coupled cavities in the resolved sideband regime. Thanks to the presence of an extra resonance in the coupled cavity cooling system, the coupling strength can be maximized at the optimum detuning. In this fashion, the intracavity photon number is increased, and thereby the cooling rate is enhanced and the strong coupling regime is achieved without resorting to increased driving laser power. The underlying physics of the increased cooling efficiency in the system of coupled cavities in the resolved sideband regime proposed here and that of the already reported system of coupled cavities in the unresolved sideband... 

Recently, a group of novel devices based on conducting interfaces is proposed. These conducting interfaces can be implemented by using the inversion layer of MOS structures, trapped charges or depletion layer charges. It has been shown that these structures can support surface electromagnetic waves. In this paper, the coupling of surface electromagnetic waves supported by conducting interfaces is analyzed and an analytical formula is driven by using the coupled mode theory. It is shown that one can program the coupling length of this structure by applying a transverse voltage and obtain a new type of optical modulator. The results obtained by coupled mode theory are verified by solving... 

The glucose-based ligand, N-salicylidene-d-glucosamine (Sal-d-glsmN), was readily obtained by reaction of salicylaldehyde (Hsal) with the d-glucosamine hydrochloride. Ligand Sal-d-glsmN was found to be an efficient ligand in the palladium-catalyzed Suzuki and Heck C-C coupling reactions in aqueous medium under aerobic condition. It was found that the use of Sal-d-glsmN/Pd(OAc) 2 system as a catalyst, aryl halides undergo Suzuki and Heck cross-couplings, respectively, with arylboronic acids and olefins to give the desired products in moderate to excellent yields  

In this paper a time-domain response and Nyquist stability criterion to acquire dependence of degree of crosstalk relative stability based on transmission lines modeling (TLM) is investigated for coupled multilayer graphene nanoribbon (MLGNR) interconnects. This is the first instance that such an analysis has been presented for coupled MLGNR consisting of both capacitive and mutual-inductive couplings. The near-end and far-end outputs of coupled MLGNR individually are compared in two cases, with considering both couplings and without them (single MLGNR). It is observed that the near-end output of the system together with both couplings is more stable and at its far-end output, an induced... 

An easy-to-design single-stub nano-coupler is proposed to increase the direct coupling efficiency between metal-insulator-metal (MIM) plasmonic and high-index dielectric waveguides. The modal reflection and transmission from the junction are exploited to provide a circuit description for the structure. The return loss of direct coupling is then minimized by loading the MIM waveguide with a single stub. Numerical examples are given, and the accuracy of the model is examined via finite-difference time-domain method  

Effect of openings' dimensions on the relative flexural behavior of adjacent piers (independent or conjugate) in perforated shear walls is addressed. 384 designed models were made and exposed to lateral loads. For middle openings, in addition to the alpha parameter in the literature, the relative flexural behavior of piers in medium-rise buildings can be predicted as function of thickness-to-length ratio of the coupling beam and the ratio of the coupling beam length to the pier length; but in high-rise buildings, it is always conjugate. For corner openings, the alpha parameter must be modified with respect to the number of stories  

Although many complex real-world networks are weighted, unweighted networks are used in many applications such as sensor networks. In this Letter it is shown using properly weighted networks the performance can be greatly enhanced by reducing the time necessary for the average consensus. Random geographical models are adapted as network models and a method based on mutually coupled phase oscillators is used for providing average consensus over the network. The consensus time is calculated by numerically solving the network's differential equations and monitoring the average error. The simulation results on some sample networks show that the consensus time is dramatically reduced when the... 

New binuclear palladium (II) complex featuring ONO pincer type hydrazone ligand was synthesized and characterized by spectroscopic and single-crystal XRD analysis. This complex showed excellent catalytic activity towards the copper-free Sonogashira cross coupling reaction. The main advantages over previous methodologies include low catalyst loading, less problematic reaction media (H2O–DMSO) and reusability in homogenous systems for optimal performance