Sharif Digital Repository

In this paper concurrent design of Schottky diode based limiter and low noise amplifier (LNA), based on noise matching, is investigated to achieve minimum noise figure (NF) of the receiver chain. In design procedure of the LNA, the noise figure is minimum, gain at central frequency is 14.5 dB, and limiter structure tolerates up to 5 W continuous wave input power. In the proposed concurrent design, a pass-band filter is applied at the LNA output to attenuate undesired out-of-band signals. In the proposed design, the limiter-LNA is implemented with a 0.25 µm gate length AlGaAs/InGaAs pHEMT process. Measured noise figure of chain is 2.7 dB and average gain over 8.5–9.5 GHz frequency range and... 

In this paper concurrent design of Schottky diode based limiter and low noise amplifier (LNA), based on noise matching, is investigated to achieve minimum noise figure (NF) of the receiver chain. In design procedure of the LNA, the noise figure is minimum, gain at central frequency is 14.5 dB, and limiter structure tolerates up to 5 W continuous wave input power. In the proposed concurrent design, a pass-band filter is applied at the LNA output to attenuate undesired out-of-band signals. In the proposed design, the limiter-LNA is implemented with a 0.25 µm gate length AlGaAs/InGaAs pHEMT process. Measured noise figure of chain is 2.7 dB and average gain over 8.5–9.5 GHz frequency range and... 

Boiling of water/triethyleneglycol (TEG) binary solution has a wide-ranging application in the gas processing engineering. Design, operation and optimization of the involved boilers require accurate prediction of boiling heat transfer coefficient between surface and solution. In this investigation, nucleate pool boiling heat transfer coefficient has been experimentally measured on a horizontal rod heater in water/TEG binary solutions in a wide range of concentrations and heat fluxes under ambient condition. The present experimental data are correlated using major existing correlations. In addition a correlation is presented for prediction of pool boiling heat transfer for the system in which... 

The compounds α-lead oxide (α-PbO) and β-lead oxide (β-PbO) were purchased from Merck co. and used for thermal investigations in laboratory. The compound was heated in a thermogravimeter at different temperature, from 25 to 400 °C. The used gas atmosphere was O2. The received products were investigated by X-ray diffraction (XRD) technique. The received product Pb3O4 was confirmed by XRD. The textures of two different morphologies of α-PbO, β-PbO and the product Pb3O4 is investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. © 2018, Faculty of Metallurgy. All rights reserved  

Nucleate pool boiling heat transfer coefficient have been experimentally measured on a horizontal rod heater for various liquid binary mixtures. Measurements are based on more than three hundred data points on a wide range of concentrations and heat fluxes. In this investigation, it has been confirmed that the heat transfer coefficient in boiling solutions are regularly less than those in pure component liquids with same physical properties. Several reasons should be responsible for this phenomenon, but mainly it could be related to preferential evaporation of the more volatile component(s) during bubble formation. In this article, the performances of major existing correlations to the... 

A numerical study on mixing/segregation phenomena in a pressurized fluidized bed with large particles of Geldart D type of binary density but same diameter with high velocity gas was performed by the use of discrete particle simulation. Particle mixtures are composed of spherical particles with 2mm diameter and 1g/cm3 flotsam density and different jetsam densities of 1.25, 2 and 2.5g/cm3 with jetsam volume fraction of 0.5. The particles are initially packed approaching perfect mixing state in a rectangular bed and then fluidized by gas uniformly injected at the bottom of the bed. Effect of increase of pressure and density ratio was investigated and mixing/segregation behavior is discussed in... 

We obtain an exact analytical expression for magnetoresistance using noncommutative geometry and quantum groups. We then show there is a deep relationship between magnetoresistance and the quantum group suq(2), from which we understand the quantum interpretation of the quantum corrections to the conductivity  

We obtain an exact analytical expression for magnetoresistance using noncommutative geometry and quantum groups. Then we will show that there is a deep relationship between magnetoresistance and the quantum group su q(2), from which we understand the quantum interpretation of the quantum corrections to the conductivity. © 2003 Elsevier B.V. All rights reserved  

the development and enlargement of city structure has caused the environmental problems on watershed of Latian dam which is one of the drinking water resourses of Tehran. The enlargement of Lavasan town and existence of an army garrison that it's effluents of treatment plant discharge to this river necessitate a water quality surveillance in entrance area of the dam. The present research includes the survey of this river's self-purification in the mentioned-above area. Numerical analysis is used in different methods to explain self- purification. Frist, we have the numerical analysis and analytical methods for a known sample in order to determine the accuracy and deviation between two... 

An easy method for green and low-temperature (40 °C) reduction of graphene oxide (GO) by increasing the antioxidant activity of green tea polyphenols (GTPs) in the presence of iron was developed. The reduction level (obtained by X-ray photoelectron spectroscopy) and electrical conductivity (obtained by current-voltage measurement) of the GO sheets reduced by GTPs in the presence of iron were comparable to those of hydrazine-reduced GO and much better than those of the GO reduced by only GTPs (in the absence of iron) at reduction temperatures of 40-80 °C. Raman spectroscopy indicated that application of GTPs in the presence of iron, in contrast to hydrazine, resulted in better recovering of... 

In this study, a hybrid search algorithm combining genetic programming with orthogonal least squares (GP/OLS) is utilized to generate prediction models for compressive strength of high performance concrete (HPC) mixes. The GP/OLS models are developed based on a comprehensive database containing 1133 experimental test results obtained from previously published papers. A multiple least squares regression (LSR) analysis is performed to benchmark the GP/OLS models. A subsequent parametric study is carried out to verify the validity of the models. The results indicate that the proposed models are effectively capable of evaluating the compressive strength of HPC mixes. The derived formulas are... 

Static recrystallization and microstructural changes in austenitic stainless steel 304L were studied. The rolling experiments at 200 °C were carried out, and then, annealing treatment was made at temperatures ranging between 500 and 830 °C. A model was also developed to simulate the kinetics of non-isothermal recrystallization within the rolled steel. The distribution of plastic strains during rolling was predicted utilizing an elastic–plastic finite element formulation performed in ABAQUS/Explicit, while the predicted results were used to generate the as-rolled microstructure and to estimate the stored energy. Finally, microstructural–thermal model based on cellular automata was developed... 

In this work, non-isothermal annealing of cold-rolled 304L austenitic stainless steel was studied at temperatures ranging between 400 and 800 °C. In the first place, a dual-phase structure containing work-hardened austenite and strain-induced martensite was produced by means of multi-pass plate rolling, and then, the deformed steel was subjected to annealing heat treatments. To determine the distribution of stored strain energy in the rolling operations, an elastic–plastic finite-element modeling was conducted. Afterwards, an artificial neural network technique was coupled with the thermal-cellular automata model for prediction of martensite reversion, temperature history, and... 

1-Aminophosphonates are valuable compounds with wide range of applications in biological and industry. Various reaction conditions and catalysts have been reported for the synthesis of 1-aminophosphonates via three-component (dialkyl phosphite + aldehyde + amine) or two-component reaction (dialkyl phosphite + imine). Here a solvent-free synthesis of 1-aminophosphonates under very mild reaction conditions is reported. The three-component condensation reactions of dialkyl phosphite, carbonyl compound, and an amine gave 1- aminophosphonates in good to excellent yields under solvent- and catalyst-free conditions at ambient temperature. Hydrophosphorylation of imines in the presence of dialkyl... 

This article analyzes various roles of development practitioners (called outsiders) in five different cases of community-based development (CBD) in rural Iran. It provides a review of the literature on CBD and identifies three main types of roles fulfilled by outsiders to support indigenous development processes. These include preparing the ground, activating community-based organizations as participatory institutions, and taking on the role of brokers who bridge the gap between the local community and outside institutions—especially the state and market. From the analysis of empirical qualitative data collected during fieldwork in Iran, the article concludes that while the roles played by... 

Although there have been numerous studies of self-efficacy and collective efficacy in different contexts, little attention has been paid to proxy efficacy. In this article we propose that a person's self-efficacy may be related to proxy efficacy when achievement of personal goals is related to the performance of the proxy on the person's behalf. We argue this is important in team leadership. We further propose that the extent to which team members believe their leaders efficacious as their proxies may affect team processes and effectiveness. A team level construct, namely team proxy efficacy for the leader, referring to a shared proxy efficacy belief for the team leader, is also proposed.... 

Organizational change has become complex and challenging, and employee attitudes and beliefs toward change are even more important. This article proposes a theoretical framework on how authentic leadership may influence followers’ change-oriented attitudes, beliefs, and behaviors through follower psychological resources including hope, trust, optimism, self-efficacy, and resilience, which influence readiness for change and change implementation. We maintain that an authentic leader’s behavior can influence his or her followers’ change-oriented behaviors in participation in decision-making processes and change initiatives, organization citizenship behavior, organizational learning processes,... 

Few studies have been conducted about team members’ individual beliefs of their team’s collective efficacy (personal collective efficacy). We argue that this individual belief is a motivational factor for teamwork along with self-efficacy for teamwork. This study investigated relationships between personal collective efficacy, self-efficacy for teamwork, collective orientations and perceptions of self in relation to other team members. In addition, relationships between personal collective efficacy and team members’ perceptions of team activities namely evaluating and integrating were explored. Multilevel analysis was employed in order to account for team level variation when testing... 

Background. Although the relationship between collective efficacy and group performance has been frequently investigated, a few studies have investigated the development of collective efficacy. Aim. This paper proposes some determinants of collective efficacy in small university groups. Group level hypotheses and research questions relating collective efficacy to collective cognition activities, task interdependence, self-efficacy for group work, and collective orientation were posited. Sample. The sample comprised 145 university students in 40 work-groups. Method. A two-phase longitudinal design was employed in the context of university student groups. All groups were required to perform... 

The nanostructures under rotation have high promising future to be used in nanomachines, nano-motors and nano-turbines. They are also one of the topics of interests and it is new in designing of rotating nano-systems. In this paper, the scaledependent vibration analysis of a nanoplate with consideration of the axial force due to the rotation has been investigated. The governing equation and boundary conditions are derived using the Hamilton's principle based on nonlocal elasticity theory. The boundary conditions of the nanoplate are considered as free-free in y direction and two clamped-free (cantilever plate) and clamped-simply (propped cantilever) in x direction. The equations have been...