Sharif Digital Repository

In this paper, the synchronization of a pair of pacemaker cells as Sino-Atrial (SA) and Atrio-Ventricullar (AV) nodes have been studied and a new approach for synchronization, based on the concept of Phase Response Curve (PRC), has been proposed. The paper starts with presenting the necessary and sufficient conditions for synchronization in terms of the PRC parameters. Such conditions are time dependent and thus, the paper proceeds with deriving some sufficient conditions, which are not time dependent. The time-delay between the firing time of SA node and when it reaches the AV node is also considered. When the conditions for spontaneous synchronization are not valid, the synchronization is... 

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... 

In this paper, we investigate the influence of nonideal boundary conditions on the nonlinear vibration of damped Euler-Bernoulli beams subjected to harmonic loads. These nonidealities allow for small deflections and/or moments at the supports of the beam. Using the iteration perturbation method, analytical expressions for the case of simply supported beams with immovable end conditions are provided. The results reveal that the first order of approximation obtained by the proposed method is more accurate than the perturbation solutions. Moreover, compared with the previous studies, some interesting phenomenon is predicted. We have shown that in some special combinations of the nonidealities... 

Despite their simple structure and design, microcantilevers are receiving increased attention due to their unique sensing and actuation features in many MEMS and NEMS. Along this line, a non-linear distributed-parameters modeling of a microcantilever beam under the influence of a nanoparticle sample is studied in this paper. A long-range Van der Waals force model is utilized to describe the microcantilever-particle interaction along with an inextensibility condition for the microcantilever in order to derive the equations of motion in terms of only one generalized coordinate. Both of these considerations impose strong nonlinearities on the resultant integro-partial equations of motion. In... 

This paper deals with the in-plane dynamics of Horizontally Curved Beams (HCBs) supported by a visco-elastic foundation under the excitation induced by a moving mass. What has been included as worthy of detailed exposition is the inevitable contribution of the inertial actions of the mass object into the problem formulation. By taking into account the effect of Coriolis acceleration, centrifugal force and rotary inertia, the governing coupled non-linear differential equations of equilibrium for a simply supported HCB are derived. In the proposed solution, a new system of linear ordinary differential equations is distilled from the governing differential equations of motion, which can be... 

In this paper, an optical beam shaping system is theoretically and experimentally investigated. The optical system design software ZEMAX is used to simulate and analyze the reported beam shaping design. By using this software ray tracing diagrams are presented with the aim of studying the direct beam propagation, total reflection rays, and the lost rays. The prism duct output beam shape and radiance profiles in both position space and angle space are also studied. For experimental investigation, a two-stage beam shaping design including a fiber-bundle and a prism duct is used. A source light is used for the fiber-bundle illumination and the photograph image of the output beam is taken by a... 

Trolling mode atomic force microscopy (TR-AFM) has overcome many imaging problems in liquid environments by considerably reducing the liquid-resonator interaction forces. The finite element model of the TR-AFM resonator considering the effects of fluid and nanoneedle flexibility is presented in this research, for the first time. The model is verified by ABAQUS software. The effect of installation angle of the microbeam relative to the horizon and the effect of fluid on the system behavior are investigated. Using the finite element model, frequency response curve of the system is obtained and validated around the frequency of the operating mode by the available experimental results, in air... 

In this article, two optical-fibre probes used in displacement measurements are reported. In one arrangement, two optical fibres with protective buffer jackets are placed together, while in the second arrangement, the protective buffer jackets are removed and the two fibres are placed with the claddings in contact, with a concomitant smaller centrecentre distance. As the core and cladding diameters are the same in both probes, the effect of the centrecentre distance on double-fibre designs can be investigated. The reflected output powers are recorded for the probes as a function of the axial distance from a reflective surface. A theoretical model is also implemented, which considers the... 

Fiber core size determination from power transmission modulation for different fibers is reported.Three different fibers are tested and power variations of lateral displacement of the second fiber are obtained (lamp, red LED). From the averaged bandwidths of the response curves the core diameter of each fiber is determined. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1225-1229, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25967 Copyright  

Operation of two different optical fiber sensor designs for distance measurements with a good sensitivity, resolution, and wide dynamic range is reported. Design is based on the intensity modulation due to reflectance measurement from a target surface. Two reported designs are fabricated with a triple-fiber assembly, in which one uses a double-transmitter, while another one uses a double-receiver fiber design. Reflection signals from different targets are tested with these sensors and results for the mirror and A4 paper surfaces are described. The response curve for both experiments starts from a near zero level, shows a maximum at a certain distance and gradually drops to the background... 

The Endurance Time (ET) method is a dynamic analysis procedure in which structures are subjected to predesigned accelerograms that increase their intensity in time. The main advantage of the ET method over the standard time-history analysis, which uses ground motions as excitation, is its reduced computational effort. In this paper, the nonlinear rigid-perfectly plastic (RPP) spectra, instead of linear elastic spectra, are used to correlate the seismic hazard return period and the time in the ET analysis. Several elastic-perfectly plastic SDOF systems as well as two three-story steel frames-namely a moment-resisting frame and a frame equipped with friction dampers-are analyzed. The response...