Sharif Digital Repository

The concept of a nonlinear transfer function of a fibre-optic communication link is reviewed. Also an approximation of the nonlinear transfer function is introduced, which allows to define an equivalent single-span model of a dispersion-managed multi-span system. In this paper we will show its limits of validity and try to extent these limits by enhancing the theoretical model. In this respect we will discuss the impact of dispersion precompensation and show the influence of residual dispersion per span, number of spans and local dispersion on transmission systems with on-off keying and differential phase-shift keying modulation formats. This approach allows fast assessment of the... 

Hydrogen technology through water electrolyzer systems has attracted a great attention to overcome the energy crisis. So, rationally designed non-noble metal based-electrocatalysts with high activity and durability can lead to high performance water electrolyzer systems and high purity hydrogen generation. Herein, a facile two-step method: hydrothermal and electrodeposition, respectively, are developed to decorate highly porous three-dimensional binder-free structure NiFeO/NiO nanosheets array on Ni foam (NiFeO/NiO/NF) with robust adhesion as a high-performance electrode for Hydrogen Evolution Reaction (HER). The electrodeposition process applied after the initial hydrothermal process... 

New techniques for Class-AB Operational Transconductance Amplifiers (OTAs) are presented. These new techniques are two topologies based on current boosting in class-AB stage which achieve considerable improvement of Slew Rate and Gain-Bandwidth while maintaining the same power consumption as the conventional design. Circuit level analysis and simulation results of proposed circuits in 0.18μm CMOS technology for gain, GBW, slew rate, and settling time are presented to prove the effectiveness of the proposed design method  

In this paper, first we shall define a list of technology transfer barriers in the biotechnology field through interviews and literature reviews. Next, we shall categorize them into four major categories of technology, and at last introduce all of the hypotheses on the existence of relationship between each part of technology and failure in the technology transfer process. Questionnaires consisting of two parts were created and handed out to all of the specialists and biotechnology idea-holders in the Iranian National Research center of Biotechnology, Lidco Co, Iran Pastor Institute, Biotechnology Department of University of Tehran, etc. Going on, we've evaluated the factors' validity... 

Most researches on the application of the adjoint method in turbine blade design are concentrated on the aerodynamic shape optimization without considering the heat transfer to/from the blade material. In this study, the adjoint method is extended to the conjugate heat transfer problems in which the viscous flow field is coupled to heat transfer in the solid region. Introducing a new adjoint variable in the solid domain, a heat adjoint equation is derived which is coupled with the energy adjoint equation in the fluid zone at the fluid/solid interface. The detailed mathematical description associated with the derivation of the heat adjoint equation with corresponding boundary conditions are... 

This article presents a novel identification approach which can deal with nonlinear and time-varying characteristics of complex dynamic systems, especially an aerial vehicle in the entire flight envelope. A set of local sub-models are first developed at different operating points of the system, and subsequently a self-organizing multi-model ensemble is introduced to aggregate the outputs of the local models as a single model. The number of employed local models in the proposed multi-model ensemble is optimized using a novel self-organizing approach. Also, wavelet neural networks, which combine both the universal approximation property of neural networks and the wavelet decomposition... 

L-tryptophan functionalized AgNPs were successfully fabricated using a one-pot synthesis method and assessed as a colorimetric probe for rapid and accurate determination of Mg2+ ions. The developed sensor showed a selective response towards Mg2+ with no interference from Ca2+ in the wide concentration range of 1–200 µM. The sensor's response was optimized in the pH range of 9–10, which can be attributed to the protonation of amine groups and their interaction with Mg2+ ions. The stability and selectivity of the sensor were examined in different salt (NaCl) and other metal ions, respectively. The L-tryptophan-AgNPs sensor detected Mg2+ with the limit of detection of 3 µM, which is way lower... 

In this paper, we propose what we believe is a novel sensitive micro-optoelectromechanical systems (MOEMS) accelerometer based on intensity modulation by using a one-dimensional photonic crystal. The optical sensing system of the proposed structure includes an air-dielectric multilayer photonic bandgap material, a laser diode (LD) light source, a typical photodiode (1550 nm) and a set of integrated optical waveguides. The proposed sensor provides several advantages, such as a relatively wide measurement range, good linearity in the whole measurement range, integration capability, negligible cross-axis sensitivity, high reliability, and low air-damping coefficient, which results in a wider... 

In the present work, the effect of brazing pa rameters on the properties of the brazed joint of pure titanium and 304 stainless steel (304SS) was investigated. Three different Ag-Cu filler metals were used, while the temperature and time of brazing were in the range of 800-950°C and 5-45 minutes, respectively. The microstructural observations show that, depending on the brazing conditions, different intermetallic phases such as CuTi2, CuTi, Cu3Ti4, and FeTi were formed at the phases interface. Based on the microstructural observations, a model was developed to characterize the formation of phases at the interfaces and brazed joint. The results show that, while some phases may form during the... 

Empirical drift capacity models for in-plane loaded unreinforced masonry (URM) walls are derived from results of quasi-static cyclic shear-compression tests. The experimentally determined drift capacities are, however, dependent on the applied demand, i.e., on the loading protocol that is used in the test. These loading protocols differ between test campaigns. The loading protocols applied in tests are also different from the displacement histories to which URM walls are subjected in real earthquakes. In the absence of experimental studies on the effect of loading histories on the wall response, this article presents numerical simulations of modern unreinforced clay block masonry walls that... 

Displacement-based assessment procedures require as input reliable estimates of the deformation capacity of all structural elements. For unreinforced masonry (URM) walls, current design codes specify the in-plane deformation capacity as empirical equations of interstory drift. National codes differ with regard to the parameters that are considered in these empirical drift capacity equations, but the inhomogeneity of datasets on URM wall tests renders it difficult to validate the hypotheses with the currently available experimental data. This paper contributes to the future development of such empirical relationships by investigating the sensitivity of the drift capacity to the shear span,... 

Current design codes provide empirical equations for the drift capacity of unreinforced masonry (URM) walls that are based on results of quasi-static cyclic shear-compression tests. Yet different experimental campaigns have used various approaches of imposing fixed-fixed boundary conditions at the wall top which may affect the test results. This article investigates, by means of numerical simulations, the influence of experimental setups on the force and drift capacities of in-plane loaded URM walls subjected to double-fixed conditions. It is shown that controlling the shear span or the top rotation while keeping the axial force constant leads to very similar results. Controlling the axial... 

Redistribution of alloying elements in the transient liquid phase (TLP) bonding zone of IN738LC/ BNi-3/IN738LC was studied to investigate microstructural evolution in this area. Wavelength dispersive spectrometry and electron probe microanalysis revealed that, during non-isothermal solidification in the TLP bonding zone, enrichment of residual liquid phase with the positive segregating elements caused formation of intermetallic in the bonding zone. Scanning electron microscopy observation Indicated that the redistribution of alloying elements, between TLP bonding zone and base alloy, resulted In formation of a γ′ boundary layer, containing high density of fine γ′, around the bonding zone.... 

Transient-liquid-phase (TLP) bonding of the IN-738LC base alloy with BNi-3 interlayer was investigated in this article. Effects of the TLP bonding thermal cycle on the base alloy were studied microstructurally and macrostructurally. Microscopic investigation revealed that the microstructural evolution in the TLP bonding area was affected substantially by the bonding temperature. Therefore, a critical bonding temperature (Tcr) was defined for TLP bonding of IN-738LC/ BNi-3/IN-738LC samples. Unlike bonding below Tcr, TLP bonding at temperatures higher than Tcr resulted in formation of individual γ-γ' colonies in the adjacent base alloy to TLP bonding zone and caused significant reduction in... 

In this paper, we present the design guidelines for a tunable optical isolator in an SOI-based ring resonator with two small time-modulated regions. By considering a physical model, the proper geometrical and modulation parameters are designed, based on a standard CMOS foundry process. The effect of the variation of the key parameters on the performance of the isolator is explained by two counter-acting mechanisms, namely the separation between the resonance frequencies of counter-rotating modes and energy transfer to the side harmonic. We show that there is a trade-off between these parameters to obtain maximum isolation. Consequently, by applying the quadrature phase difference one can... 

We propose an analytical circuit model for accurate analysis of one-dimensional periodic array of metallic strips. The proposed model is valid not only in subwavelength regime, but also for wavelengths shorter than the period of structure. The working frequency can reach the visible range and thus electromagnetic properties of periodic arrays of nano-slits can be analyzed by the proposed model. The proposed model remains valid for arbitrary incident angles even when nonspecular diffracted orders become propagating. Analytical expressions are derived explicitly in order to describe the parameters of the proposed circuit model. The circuit model is derived by assuming that only one guided mode... 

Nano sized ZnO on TiO 2 spherical core shells were prepared by using hydrothermal method. The particle size of initial TiO 2 was around 20 nm, and the specific surface area was 50 m2/gr. Different ratios of TiO 2 and ZnO applied to synthesize core shell particle. X-ray diffraction (XRD) used to phase characterization and crystalline size, scanning electron microscopy (SEM) to morphology and microstructure investigations. S. Brunauer, P. H. Emmett and E. Teller method (BET) to find specific surface area, Diffusive UV-visible-NIR spectrometry to bang gap calculations. The results indicate that powders with a shell of zinc oxide in specific range have the quantum size effect. Titanium oxide and... 

A circuit model has been proposed for two-dimensional metallic arrays of metallic square holes located on a homogeneous substrate. Although the proposed circuit model holds true, the surface admittance between the metallic hole array and the cover was erroneously calculated since the presence of the cross-polarization terms had been neglected. Furthermore, there have been mistakes in numerical simulation and in analytical calculations based on the presented formulas. The correct formulation is now given, and erroneous figures are replotted  

In this paper, combined effects of material degradation, p-delta, and foundation uplift are incorporated in a soil-structure-interaction (SSI) framework to assess seismic response of a single-degree-of-freedom system. The considered phenomenological systems represent a column with a lumped mass on top is placed on a rigid foundation. The foundation is mounted on Winkler springs and dashpots to take account of soil-foundation compliance and material/radiation damping. The springs are tensionless to guarantee that uplift is properly modelled. The model is verified for two specific limit cases with the code and literature to make sure that the model is capable of capturing SSI and foundation... 

This paper presents the results of a series of shake table tests carried out on a half-scale single-story unreinforced masonry building with asymmetric openings. First, the unretrofitted building is subjected to seven increasing steps of bidirectional seismic excitation. The damaged building is then rehabilitated using steel mesh and shotcrete layer with two walls retrofitted from the exterior face and the other two from the interior face. Afterward, the shake table test is again conducted on the retrofitted specimen in nine increasing excitation levels. Three cases of interior-to-interior, interior-to-exterior, and exterior-to-exterior shotcrete connections are considered at the...