Sharif Digital Repository

In this paper, the influence of the van der Waals force on two main parameters describing an instability point of cantilever type nanomechanical switches, which are the pull-in voltage and deflection are investigated by using a distributed parameter model. The fringing field effect is also taken into account. The nonlinear differential equation of the model is transformed into the integral form by using the Green's function of the cantilever beam. The integral equation is solved analytically by assuming an appropriate shape function for the beam deflection. The detachment length and the minimum initial gap of the cantilever type switches are given, which are the basic design parameters for... 

In this paper, the influence of the Casimir force on two main parameters describing an instability point of cantilever type nanomechanical switches, which are the pull-in voltage and deflection are investigated by using a distributed parameter beam model. The nonlinear differential equation of the model is transformed into the integral form by using the Green's function of the cantilever beam. The integral equation is solved analytically by assuming an appropriate shape function for the beam deflection. The detachment length and the minimum initial gap of the cantilever type switches are given, which are the basic design parameters for NEMS switches. The pull-in parameters of micromechanical... 

An efficient hybrid method is presented for the analysis of the interference phenomenon in high frequency communication circuits. The method is based on the transmission line matrix (TLM) method, augmented with a time domain integral formulation using the free space Green's function to account for the radiation of equivalent sources on boundary surfaces. The method is highly effective in reducing the dispersion effects in the TLM method and drastically reduces its computational intensity. © 2003 IEEE  

An efficient hybrid method for the analysis of the interference phenomenon in high frequency communication circuits is presented. This method is based on the Transmission Line Matrix (TLM) method augmented with a time-domain integral equation formulation to account for the radiation of equivalent sources on boundary surfaces. As such, wide band effects are easily and accurately modeled since its formulation is in the time domain  

Let G be a graph and I be an interval. In this paper, we present bounds for the number mGI of Laplacian eigenvalues in I in terms of structural parameters of G. In particular, we show that mG(n−α(G),n]≤n−α(G) and mG(n−d(G)+3,n]≤n−d(G)−1, where α(G) and d(G) denote the independence number and the diameter of G, respectively. Also, we characterize bipartite graphs that satisfy mG[0,1)=α(G). Further, in the case of triangle-free or quadrangle-free, we prove that mG(n−1,n]≤1. © 2021 Elsevier Inc  

Drill strings are subjected to complex coupled dynamics. Therefore, accurate dynamic modeling, which can represent the physical behavior of real drill strings, is of great importance for system analysis and control. The most widely used dynamic models for such systems are the lumped element models, which neglect the system distributed feature. In this paper, a dynamic model called neutral-type time delay model is modified to investigate the coupled axial–torsional vibrations in drill strings. This model is derived directly from the distributed parameter model by employing the d’Alembert method. Coupling of axial and torsional vibration modes occurs in the bit–rock interface. For the first... 

In this paper, a Kalman filter technique which is operated in time is introduced for noise reduction on CT set of projections to reconstruct medical images. The experiments were done on medical image of kidneys and the simulated projections are captured by CT scanner. Evaluation results indicated that as the number of projections increase in the collected ray sums corrupted by noise the quality of reconstructed image becomes better in terms of contrast and transparency. However, for the comparison issue, the same conditions are applied for reconstruction of medical image in frequency domain using filter back projection technique. It observes that filter back projection technique does not... 

This paper proposes a control strategy for the autonomous (islanded) operation of a four-wire, electronically-coupled distributed generation (DG) unit which can feed a highly unbalanced load, e.g., due to the presence of single-phase loads. In the grid-connected mode, the power-electronic interface of the DG unit enables the exchange of real and reactive power with the distribution network, based on the conventional dq-frame current control strategy. The current control scheme is disabled subsequent to the detection of an islanding event, and the proposed controller is activated. The proposed control strategy utilizes: i) an internal oscillator to maintain the island frequency and ii) a... 

Here, a case study of natural gas network is conducted. We design an optimal distribution network of natural gas. Our proposed network is composed of stations reducing gas pressure to desirable pressure using consumer's viewpoint. By using minimum spanning tree (MST) technique, an optimal distribution network among stations and consumers is constructed. Our aim is to determine both locations and types of stations minimizing location-allocation costs in the network. A case study in Mazandaran Gas Company in Iran is made to assess the validity and effectiveness of the proposed model  

E-learning environments are being used more efficiently by the rapid growth in internet and multimedia technologies. Adaptive learning is a kind of learning environment which provides individual learning. It can customize the learning style according to the individual's personality and characteristics. Although there are a lot of e-learning systems having adaptive learning feature, they do not satisfy all adaptive learning aspects. This paper proposes a new method which tries to help learners find educational contents adapted to their personalities in an efficient manner. Our proposed method has four essential parts: 1) It finds out learner's features by Bayesian networks. 2) Then It tries... 

A continuous-discrete Distributed and Decentralized Switching Kalman Filter (DDSKF) is designed for estimation of spatial profiles in Pressure Swing Adsorption (PSA) processes. The introduced observer is an integral part of the control strategy of hybrid systems in general and PSA systems in particular. A reduced order model is developed based on the mechanistic model of the process. The sensors are optimally located and observability of the process is studied. The proposed observer is used to estimate the spatial profiles of various states of a two-bed, six-step PSA system used for production of pure H2 from a H2–CH4 gas mixture. The spatial profiles of the system have been estimated using... 

We introduce a universal and systematic way of defining a generalized B-spline based on a linear shift-invariant (LSI) operator L (a.k.a. Fourier multiplier). The generic form of the B-spline is . βL=LdL-1δ where . L-1δ is the Green's function of L and where . Ld is the discretized version of the operator that has the smallest-possible null space. The cornerstone of our approach is a main construction of . Ld in the form of an infinite product that is motivated by Weierstrass' factorization of entire functions. We show that the resulting Fourier-domain expression is compatible with the construction of all known B-splines. In the special case where L is the derivative operator (linked with... 

This work presents a new necessary and sufficient condition for robust stability and robust performance of positive linear time invariant (LTI) systems with structured uncertainties. It is known that robustness analysis of LTI systems with structured uncertainties requires evaluation of structured singular value (SSV), which is known to be NP-hard. This paper shows that for positive systems, the structured singular value can be estimated efficiently using linear programming. Thus, the robustness analysis of positive systems is simplified to easily verifiable conditions that scale linearly with the dimensions of the system. This property finds great utility in analysis and synthesis of large... 

Demand response is envisioned as a key solution to increase network efficiency as well as to alleviate challenges such as growing demand. In this paper, domestic electric water heater (EWH) and heating, ventilation, and air-conditioning (HVAC) are considered for potential demand response applications. An interaction between the system operator and consumers is considered to facilitate managing cyclic operation of consumers' heating loads. A centralized control model is first developed and formulated to achieve potential benefits of demand response of EWH and HVAC loads. Then, a distributed control algorithm is designed for practical implementation. In the proposed algorithm, house-wide... 

We introduce a universal and systematic way of defining a generalized B-spline based on a linear shift-invariant (LSI) operator L (a.k.a. Fourier multiplier). The generic form of the B-spline is βL=LdL−1δ where L−1δ is the Green's function of L and where Ld is the discretized version of the operator that has the smallest-possible null space. The cornerstone of our approach is a main construction of Ld in the form of an infinite product that is motivated by Weierstrass’ factorization of entire functions. We show that the resulting Fourier-domain expression is compatible with the construction of all known B-splines. In the special case where L is the derivative operator (linked with... 

Trolling mode atomic force microscopy (TR-AFM) has resolved many imaging problems by a considerable reduction of the liquid-resonator interaction forces in liquid environments. The present study develops a nonlinear model of the meniscus force exerted to the nanoneedle of TR-AFM and presents an analytical solution to the distributed-parameter model of TR-AFM resonator utilizing multiple time scales (MTS) method. Based on the developed analytical solution, the frequency-response curves of the resonator operation in air and liquid (for different penetration length of the nanoneedle) are obtained. The closed-form analytical solution and the frequency-response curves are validated by the... 

Synthesis of the optimum conventional (with non-sharp separations) distillation column sequence (DCS) is a challenging problem, in the field of chemical process design and optimization, due to its huge search space and combinatorial nature. In this paper, a novel procedure for the synthesis of optimum Conventional Distillation Column Sequence is proposed. The proposed method is based on evolutionary algorithms. The main criterion used to screen alternative DCS's is the Total Annual Cost (TAC). In order to estimate the TAC of each DCS alternative all columns that exist in the DCS are designed using short-cut methods. The performance of the proposed method and other alternatives are compared... 

With the introduction of restructuring concepts to traditional power systems, a great deal of attention is given to utilization of distributed generation. Integration of DG units has been known as an alternative for distribution network reinforcement and purchasing energy from transmission network. Considering these facts, in the planning procedure of DG, determination of optimal sizing and sitting is a very important issue. This work presents a comprehensive framework for integration of distributed generations into a distribution network, regarding various technical and economical issues such as reduction of active power losses, environmental pollutions, investment and running costs while...