Sharif Digital Repository

In this thesis, we investigate some transport and many body properties of the 2DEG at the interface of LaAlO3=SrTiO3. First, following Boltzmann approach,we calculate conductivity and mobility of the system. We find that the mobility varies inversely with the cubic power of the carrier density ( / n3 2D) in good agreement with the experimental results. Taking in to account the variations of the dielectric constant of SrTiO3 with carrier density together with the variable impurity density are remarkably important in order to explain the abrupt decrease of the mobility with increasing the density in this system. We find that although the multiband nature of the system and interband... 

In today’s world the growth in population make food production and also the packaging industry increase. Finding new ways to enhance the efficiency of packaging is become so important beyond researchers. As the randomized co-polypropylene is the most suitable materials for this industry many attempts have been made to control its melting behavior with the aim of expanding their application in the packaging industry. The study in this field indicate the dependence of the melting behavior on the structural characteristics of the material such as molecular mass, chain structure, type of crystalline structure, and the amount of dispersion of the crystals thickness. Due to the lack of proper... 

Molybdenum disulfide (MoS2) nanoflakes, a two-dimensional crystal with tunable bandgap depends on number of layers, is a promising candidate for future nanoelectronic devices. In the present research, flower shaped MoS2 nanoflakes have been synthesized via hydrothermal method. As part of the research, the growth of triangular MoS2 monolayer up to 10 micrometers has optimized by carring out several chemical vapor deposition experiments with varying deposition parameters. The prepared samples were characterized using optical, scanning electron, and atomic force microscopes, x-ray diffraction analysis, and Raman spectroscopy. Based on the experimental results, the growth mechanism has been... 

All supersonic intakes with external compression, having a good level of performance at all the critical poin t. Exhibit a marked instability of flow in subcritical operation below some value of the flow ratio, in the form of an oscillation of the shock system, colloquially known as “buzz", which can lead to thrust loss, engine surge or even structural damages. Therefore the effort to understand the nature and cause of this phenomenon is important in order that the starting of buzz can be predicted and more effectively avoided without losing performance. This phenomenon has been the subject of many studies, mainly experimental. In this research, we design and build an axisymmetric supersonic... 

A global concern has arisen owing to rapid industrial development and population growth, resulting in energy scarcity and earth pollution. In this regard, developing green and sustainable methods for producing clean energy and solving environmental pollution problems have absorbed enormous attention. Among various auspicious strategies, semiconductor photocatalysis has been widely studied in recent years owing to its capabilities to obtain hydrogen as an energy carrier, to remove organic pollutants, and to reduce CO2 emission by converting solar energy into chemical energy. Recently, a metal-free semiconductor photocatalyst based on graphitic carbon nitride, g-C3N4, has received much... 

Many efforts have been put into increasing the efficiency of dye-sensitized solar cells that part of it has been devoted to structure and chemical composition of photoanode electrode. In this thesis, the effect of changes in the composition and its influence on light scattering ability in photoanode of dye sensitized solar cells was studied.First, the nanoparticles of titanium dioxide powder through solvothermal method as well as spherical particle and barium titanate powder by sol-gel method were synthesized. XRD and FE-SEM analyses indicated that synthesized powders are in good size and morphology regarding the intended chemical composition. Optical properties of TiO2 particles were... 

In this study, mechanical properties of neat isotactic polypropylene (iPP) were evaluated on local and global scales. Depth-sensing indentation with nanoscale resolution (nanoindentation) and traditional macromechanical tests were incorporated for this purpose at different temperatures and strain rates. Various morphologies and crystalline structures of iPP was obtained via changing processing conditions in melt state. A certain relation was found between the local and global mechanical properties, i. e. yield stress, modulus of elasticity and hardness. Moreover, developed yield models were evaluated on the local scale. The results showed that while crystal plasticity theory is not valid for... 

In this project, the ionization and dissociation of methane molecule by intense femto-second lasers has been studied. Dissociation probability is calculated for interacting CH4 molecule under Ti: Sapphire laser pulse with pulse durations of 10- 40fs in intensities at the range of 1014-1016 Wcm-2. Calculations are carried out with time-dependent density functional theory using Gaussian03 and Octopus packages as powerful computational chemical physics programs. Due to importance of the dependence of interaction dynamics to laser parameters, the effect of these parameters including different intensities, polarization, various pulse durations and pulse envelopes are investigated. The optimal... 

Fine-tuning language models has become a prevalent approach to tackling various natural language processing tasks. However, fine-tuning a model sequentially on a series of tasks leads to catastrophic forgetting: as the model learns a new task, it tends to forget the previously learned tasks. This research aims to address this issue by proposing a soft prompt tuning approach, a parameter-efficient fine-tuning method introduced in recent years. We introduce an improved version called SuperPositon Prompts, which is evaluated on the T5 model using tasks from the GLUE and SuperGLUE benchmarks. The results demonstrate the superior performance of the proposed method compared to previous approaches....