Sharif Digital Repository

Mutually coupled oscillator arrays may be used for power combining at the millimeter-wave region. In addition, these arrays have the capability of beam steering without the use of any phase shifter. Using the strong coupling method is inevitable to obtain synchronization between all elements in the large arrays. One of the challenges in strongly coupled oscillators is the multi-moding problem or oscillation at undesired frequencies. In this thesis, we obtain mode distributions in a one-dimensional and a two-dimensional array with rectangular boundary, using a method based on circuit equations in the frequency domain. Then, we compared the results with the previous works and also verified... 

Crumb rubber, produced from shredding of scrap or refused tires, is one of the most commonly used modifiers of asphalt. Asphalt rubber, in addition to mitigating some of the environmental problems of disposing scrap tire, improves the flexural strength of pavement, extends the life of pavement and reduces the maintenance costs. The properties of asphalt rubber are highly dependent on the type and composition of base asphalt, type and amount of crumb rubber, and the production method.The goal of this research is to investigate the performance properties of asphalt rubbers produced from Iranian asphalt and crumb rubber, using an industrially feasible method. The Superpave testing procedure was... 

Pulsating heat pipes have been more studied in recent two decades as effective tools in dissipating waste heat from electronic components. Due to oscillating fluid flow model, these tubes have the potential of converting waste energy to power. This research presents a system that makes this potential to act. In this system, the oscillating slug-plug fluid flow pattern in an open-looped pulsating heat pipe makes a permanent magnet which is levitated in Ferrofluid to vibrate in an electromagnetic vibration-based generator in order to induce electro motive force. The fluid flow regime in pulsating heat pipe has been simulated numerically with finite element scheme. The model results for fluid... 

Aquatic canopy zones play an important role in maintenance of ecosystems. These areas are ubiquitous near rivers, lakes, lagoons, estuaries and shore lines. Governing dynamical systems through these areas have direct influence on, how nutrients and other vital materials for living things disperse. Also, they can control the amount of dissolved oxygen within the body of water in these regions. Nowadays, investigating the effects of vegetation grabbed the attention of many scientists and is a very important burgeoning field. In this study, the effects of surface cooling which resulting from mild wind blow have been investigated. In fact, two type of different currents form when wind blows... 

Sensibility of parameters that influence the Interaction between crossing tunnel at different level such as Soil charactristic, Construction procedure,Method of excavation,Rigidity of lining,Distance between tunnels and angle of intersection is studied. For comparison above parameters the surface settlement and bending moment during the excavation is measured .In order to simulate the Interaction between Crossing tunnels, use 3D finite element model with Abaqus program. The soil govern elasto-plastic mohr-coloumb constitutive equation.Parametric Analysis shows the great and different influence of each parameter that we can able to minimize this interaction with correct choose of this... 

Increasing demand in power systems necessitates the Generation Expansion Planning (GEP) which is to determine the type, size, and location of new generating units in a planning horizon. The final solution of GEP is based on the minimum cost and/or optimum reliability taking into account various constraints such as capacity of units and lines, operating constraints, and budget restrictions. This paper presents a model based on scenarios for generation expansion planning and units retirement decision. The proposed model could be used by vertically integrated utilities as well as the ISOs in electricity markets to obtain generation expansion schemes. In this approach, uncertainty of units are... 

Modern communication and space systems such as satellite communication devices, radars, SAR and radio astronomy interferometers are realized with large antenna arrays since this kind of radiating systems are able to generate radiation patterns with high directivity and resolution. In such a framework, conventional arrays with uniform inter-element spacing could be not satisfactory in terms of costs and dimensions. An interesting alternative is to reduce the array elements obtaining the so called ‘ thinned arrays’. Large thinned arrays have been exploited because of their advantages in terms of weight,consumption, hardware complexity, and cost over the... 

As time has passed, the cost of maintaining expert human resources has been increasing worldwide; as a result, factories and stakeholder has sought ways to exploit the expertise of their human resources as much as possible so they can reduce their costs and, of course, raise their profits. To achieve this, managers decided to assign their human resources to tasks that demands their expertise and knowledge and therefore provides added value for their companies; nevertheless, this decision needs proper alternatives to do routine and predetermined jobs as substitutions for expert human resources.As the technology and the science has been growing day by day, the use of robots has been extremely... 

The growing number of disasters in recent years has become a significant threat to hospital buildings' resilience and preparedness. Besides, the stochastic nature of these disasters and the complexity of the hospital building systems exacerbate the difficulty of making appropriate decisions during and after disasters. To address the issue, this research proposes a novel model that utilizes the capabilities of Bayesian Networks (BNs) and Building Information Modeling (BIM). This model helps decision-makers in hospitals and medical centers measure various effects of disasters on utility systems and analyze the consequences of their decisions. The capabilities of the proposed model are tested... 

Willingness to communicate (WTC) has recently received great attention in the area of second language learning. Thus, the concept of willingness to communicate and what would influence the students' willingness to communicate gain importance. The current study employed a hybrid design to probe Iranian students' willingness to communicate. First, self-report questionnaires were administered to 431 language learners to collect quantitative data. Then, interviews were conducted with 41 randomly selected learners who had already completed the questionnaires. Pearson correlation coefficient, one-way ANOVA, independent t-test through SPSS .16 and the Structural Equation Model (SEM) analyses... 

Since speaking seems to be the foremost skill in language learning, the evaluation of speaking ability has become increasingly important in recent years. Moreover, research on rater effect in speaking performance assessment has provided evidence for a considerable degree of variability among raters. This study investigated the use of holistic vs. nalytic rating scales in rating Iranian EFL learners‟ speaking performance. Moreover, the current study explored the effects of gender and experience on raters‟ rating in rating Iranian EFL learners‟ speaking performance applying holistic vs. analytic rating scales. The effects of ater variables (gender and experience) on weighing components of... 

The gaps in the existing studies on L2 listening comprehension have been highlighted in the literature of second language learning. Accordingly, the necessity of the qualitative investigations in this field has been frequently addressed by the scholars (e.g., Vandergrift, 2007). The primary purpose of this study was to investigate the use of dynamic assessment (DA) in L2 listening comprehension within a group of six advanced EFL learners to extract the patterns of teacher mediation and learner reciprocity moves through a dyadic examination of their interactions. The examination of listening self-regulation was another incentive behind this study. This research also investigated learners’... 

Critical thinking has been the center of attention in education and academia over the last several decades. It can be fostered at different rates and extents in different academic disciplines given the diverse cognitive processes that students need to go through. Hence, an understanding over the extent to which a specific field of study in higher education aids the development of critical thinking might help educators and educational system to see what should be revised, substituted, and/or added in a curriculum. Accordingly, the major thrust of the current study was to compare the critical thinking ability of 296 humanities and engineering undergraduate students at four Iranian...