Sharif Digital Repository

Development of a model for optimal power generation from the thermal oxidation of a low concentration coal bed mine has been considered as the main objective of this investigation. The model has been applied to identify the optimal thermodynamic characteristics of the power generation system through using a mixture with 1.6% methane concentration in a recuperative lean-burn gas turbine and coupling a gas engine to the system for more power generation from the remaining coal bed methane. The implementation of the model based on the real site condition would lead to the generation of 6.97 MW electricity in Tabas coal mine of Iran. © 2016 Taylor & Francis  

In this paper, a novel method of retrofit design in total site cogeneration systems based on constructal theory is presented. In this regard, the total site cogeneration system is decomposed into three constructs: turbines, turbine arrays, and steam generators. The objective function to be minimised is the total annual cost of existing total site. Using constructal theory simplifies the optimisation procedure of total site in addition to reaching better conceptual design especially in more sophisticated systems. A case study from literatures has been taken up to examine the applicability of the algorithm and excellent agreement has been observed. Copyright  

In this research, the influence of anionic surfactant sodium dodecyl sulfate (SDS), pH, substrate finishing, and annealing temperature on the surface morphology and hardness of the electroless nickel phosphorus (ENi-P) coatings were studied. Taguchi's experimental design method was used. Parameters selected in three levels and L9 from orthogonal robust array design were employed. Surface roughnesses of the deposits were measured using a stylus instrument. Scanning electron microscope and x-ray diffraction analysis were implemented to study surface morphologies and phase composition, respectively. Microhardness of the ENi-P deposits was measured using a microhardness tester at three trials... 

In an electronic warfare environment, an electronic support system receives signals emitted by different radars. One of the key tasks in an electronic support system is detection of Pulse Repetition Interval Modulation for these signals. In this paper we present a new robust and yet simple method for detection of complex PRI Modulation. Simulation results show that the proposed method is more robust against noise (spurious and missing pulses) and unwanted jitter than previous methods  

Phase noise is one of the most important specifications of microwave oscillators. External factors such as mechanical vibrations increase the phase noise of the oscillator. A novel technique is introduced to reduce vibration-induced phase noise using inter-injection locking of two coupled oscillators. Two similar oscillators with equal free running frequencies are chosen and are subjected to sinusoidal vibration. The mechanical configuration is such that vibration sensitivity vector increases the frequency of one oscillator and decreases the other one's frequency of oscillation. Coupling these two oscillators using inter-injection locking, the common after-lock frequencies of both... 

In this paper, a novel travelling-wave printed Frequency Scanning Antenna (FSA), which can be used for imaging purposes, is proposed. All sample designs scan the space symmetrically about the broadside direction. For different scanning ranges, two low profile antennas are designed on a 6.6 mils thick Rogers 4350 board substrate layer. Impedance bandwidth of the first one covers 6.5GHz, from 29.5GHz to 36GHz, and this antenna scans 56° in angular space. The second antenna has 5.6GHz bandwidth from 30.6GHz to 36.2GHz, and scans 98° in angular space by means of switching the input port. The average gain and the Side-lobe level (SLL) of the first and the second antennas are 11.46dBi, 12.8dB, and... 

This paper describes the design procedure and measurement results of a single-layer low-cost, and wideband frequency scanning antenna, which exhibits a nearly symmetrical beam-steering around broadside direction. The measured antenna bandwidth ranges from 27.5 to 40 GHz, which covers most of the Ka-band. In addition, the antenna main beam scans from − 52° to + 42° as the frequency sweeps from 27.5 to 36.5 GHz, showing 94° beam-steering range. At the center frequency of 32 GHz, the beam points to the broadside direction. The measured radiation patterns verify that the beam-pointing error is less than 2° over the scanning range. Furthermore, the measured gain for a 10-cell structure with 6-cm... 

Purpose: The purpose of this study is to use correlation analysis to understand how knowledge structure, task structure and collaboration affect collective knowledge (CK) by the mediating mechanism of communication. Design/methodology/approach: Drawing on an existing gap in the literature related to CK, a research model with five hypotheses is proposed. The hypotheses were analyzed based on data collected from 114 work-team practitioners using structural equation modeling. Findings: The results indicate that communication, knowledge structure, task structure and collaboration significantly contribute to CK and that communication partially mediates the impact of these constructs on CK.... 

An analysis of resonant modes in ladder networks is performed using difference equations. Linear and loop configurations are studied and analytical relations are derived for the mode distributions and resonant frequencies of these networks, having arbitrary elements. Furthermore, it is shown that a) Modes with an exponential distribution along network nodes may exist in some cases and b) The mode distributions in loop networks are independent of network elements. Finally, a simple criterion is obtained for a loop structure to control the spacing between resonant frequencies. © Sharif University of Technology, April 2008  

In the present work, a non-linear distributed circuit model for superconducting rectangular-spiral resonators is proposed. This is based on an accurate non-linear circuit model for superconducting parallel coupled lines, which is simultaneously considered both quadratic and modulus non-linear dependencies. The non-linearity in superconducting devices depends on the current distribution, which is mainly determined by the geometrical structure of the device. The current distribution in the superconducting spiral resonators can be computed by a numerical approach based on three-dimensional finite element method. This computed current distribution is used to produce a non-linear circuit model... 

Quarter-wavelength superconducting spiral resonators have been used to realize a coplanar waveguide bandpass filter and bandstop filter around the center frequency of 6 GHz. These compact coplanar waveguide filters have been made from 300-nm-thick NbTiN thin film on a 525-μm-thick silicon substrate. The bandpass filter is a six-pole Chebyshev filter with two zero transmissions due to nonadjacent coupling in its structure. Accurately microfabricated air-bridges have been used to suppress the undesired slot-line mode in this filter. The bandstop filter is a very simple two-pole structure that used wire bonding to suppress the slot-line mode. Measurements have been done at a temperature of 4.2... 

Design of an Ultra-Wideband 3-dB quadrature (90°) Hybrid using ADS and HFSS softwares plus Measurement report are presented. Simultaneous Use of these two softwares lead to fast and accurate design procedure. The coupler is realized in broadside stripline and with the connection of coupled regions in tandem structure. The measured data agrees well with the expected values from simulations, and shows a good ultra wide bandwidth response over the frequency range of 1-10 GHz. Measurements showed an amplitude unbalance of ±1.5 dB, a phase unbalance of 90°±7° , and an isolation and a return loss characteristics of more than 14 dB over the frequency of 1 to 10 GHz  

In the present work, a non-linear distributed circuit model for superconducting rectangular-spiral resonators is proposed. This is based on an accurate non-linear circuit model for superconducting parallel coupled lines, which is simultaneously considered both quadratic and modulus non-linear dependencies. The non-linearity in superconducting devices depends on the current distribution, which is mainly determined by the geometrical structure of the device. The current distribution in the superconducting spiral resonators can be computed by a numerical approach based on three-dimensional finite element method. This computed current distribution is used to produce a non-linear circuit model... 

Purpose: The purpose of this research is to propose a framework for developing business intelligence systems (BIS). Design/methodology/approach: Following a qualitative research method, a comprehensive framework at organizational and individual level, as well as team level, was developed. Findings: The findings revealed that team-level influential factors play a more significant role in BIS development success. The results also indicate that BIS development relies on suppliers, customers and their relationships, whereas the supplier side has a more significant impact on determining successful development. Drawing on these findings, embedded knowledge, knowledge management process capability... 

The solvent-based process appears to be an increasingly feasible technology for the extraction of heavy oil reserves. However, there is a lack of fundamental understanding of how fracture geometrical characteristics control the oil recovery efficiency in this type of enhanced oil recovery (EOR) technique. In this work, a series of experiments were performed whereby the pure and mixed hydrocarbon solvents (HCS) displaced heavy oil in fractured five-spot glass micro-models. Successive images of the solvent injection process were recorded. The oil recovery factor, as a function of injected pore volume of solvents, was measured using image analysis of the provided pictures. It has been observed... 

Properly terminating a transmission line, in order to transfer the maximum available power to the load, is an important issue. The problem, fully analyzed in linear lines, is still considered as a persisting problem in the area of nonlinear transmission lines (NLTLs). In this paper, an accurate analysis is presented which gives a closed-form formula for the matching efficiency of the NLTLs. Using this analysis, optimal resistive terminating load for the NLTLs was extracted. These results will considerably ease the design of all kinds of the NLTL-based systems, such as high-frequency oscillators and ultrashort pulse generators. This consistent analysis also gives the reflection coefficient... 

Micromodel is small-scale artificial model of porous medium which is known as a novel approach for simulating flow and transport in porous media. For better understanding the effect of fracture geometrical properties on oil recovery efficiency, a series of first contact miscible solvent injection process were conducted on horizontal glass micromodels at several fixed flow rate conditions. The micromodels were initially saturated with the heavy crude oil. The produced oil as a function of injected volume of solvents was measured using image analysis of the provided pictures. The concentration calibration curves of solvents in heavy crude oil were used for evaluating the solvents... 

After receiving emitted signals from various radars by electronic support measures (ESM) system, several processes are applied to signals such as: deinterleaving, recognition of pulse repetition interval (PRI) modulation, PRI estimation and etc. Indeed, recognition of PRI modulation is an essential task of ESM system. In this paper a novel and robust method for recognition of complicated PRI Modulations is presented. This method uses specifications such as distribution related to members of sequences obtained from first and second order derivation of TOAs around a constant value and continuity of these sequences to recognize the PRI modulation. Some numerical simulations are performed to...