Sharif Digital Repository

Considering high potential of solar energy and exhaustibility of fossil fuels in Iran, using solar energy seems to be inevitable. But one of the main problems in the application of these systems is high investment and maintenance costs. So, in this thesis, suitable solution is presented for decreasing cost and optimizing of a solar absorption refrigerator based on developed energy model. This system consists of two CPC solar collectors and a thermal energy storage system using phase change materials that provides input energy to the generator of absorption refrigerator. The exergy efficiency of system components is calculated by relations of energy model and exergy analysis. Then... 

The applications of science and technology of materials grows rapidly nowadays One of the major aspect of this science discuss about the growth of thin films via deposition of molecules and atoms. By this way we can diagnose physical and chemical properties of thin films whose applications in electronics, computer, microelectronic industry, material engineering telecommunications and so advances every day. In this way we smell out the process of the growth of diamond like carbon (DLC) thin films whose importance is extended nowadays. By acknowledgement of variables that influence the dynamics of film formation we make a big jump in attaining the optical, physical and electrical properties of... 

Optimized structure of the chlorophyll a and b molecules was obtained for LDA and GGA approximation by SIESTA package. Calculation illustrate that tails are curved in the optimized structure for both chlorophyll a and chlorophyll b molecules; in addition, Antennas, which are attached to the head of molecules, are located in optimized-spatial state. This optimized structure of chlorophyll a is similar to the calculated structure in ref [42]. Electrical dipole are calculated from ground state electron density of chlorophylls. Total electrical dipole of chlorophyll a for GGA and LDA approximation are 4.662 and 4.813 Debay, and these value for chlorophyll b are 1.435 and 1.302 Debay,... 

The Fuel cell is an energy converter which converts the chemical energy of a chemical reaction to electricity and heat directly and without any pollution. One of the most important types of fuel cells is the proton exchange membrane (PEM) fuel cell. The importance of PEM fuel cells is a result of their high energy density, quick start up ability, lower operating temperature, high efficiency and low or zero emissions. Catalysts play an important role in both costs and durability of PEM fuel cells. Alloying the Pt with other metals can increase the activity of the catalysts of the fuel cells and also reduces the amount of costly Pt. In this study, the nanoparticles of Ni were added to the... 

The  aim  of  this  work  is  to  investigate  some  theoretical  models  developed  in  recent years for describing electronic correlation and apply them to some special problems  and  metallicity  and  insulating  behavior  of  one  type  of  paramagnetic  systems. One  of  the  vast‐applied  and  effective  routines  for  investigating  the  strongly  correlated electron systems is Dynamical Mean Field Theory (DMFT). In the first part,  the  equations  of  DMFT  are  solved  on  nearly  real  frequency  axis  with  a  effective and more reliable solver a little parameter γ above the real axis. This approach  appears  fine  structures  that  can’t  be  captured  with  the ... 

The silicon vacancy in silicon carbide is a strong emergent candidate for applications in quantum information processing. 4H, 6H and 3C polytypes of SiC all host coherent and optically addressable defect spin states. Electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) investigations suggest that silicon vacancy point defects in SiC possess properties similar to those of the NV center in diamond. We provide a new theoretical frame to explain a wider range of experimental results. Employing a proposed generalized Hubbard model, with the help of electronic structure programs, DFT, second quantization, and various computational approaches, we obtain new... 

The Pulse Laser Deposition (PLD), Sputtering, Evaporation and Metal-Organic Chemical Vapor Deposition are the common methods for thin film fabrication. The mentioned methods are very costly for commercials application. Due to the importance of cost in large thin film fabrication, scientist tried to find a low-cost method. The low-cost non-hazardious Metal Organic Deposition (MOD), method which is based on chemical manufacturing method was developed. The type of the solvent and removal the destructive residual materials are the main challenge in this method. In this project, by utilizing acetyl acetone method, high quality MOD YBCO superconducting thin film has been fabricated and will be... 

Photostrictive type of opto-thermo-electro-mechanical materials, called PbLaZrTi (PLZT), are a recently emerged family of smart materials, that are able to generate strains under illumination of near violet light and attract much attention in a variety of wireless and remote control applicati-ons, including the areas of material science and engineering, micro-electro-mechanical system (MEMS) and Optical MEMS, and smart structures. This research presents an analytical and finite element investigation into ultraviolet photo-induced multi-physics responses of 0-3 polarized PLZT photocantilever and a comparison of the measured bending displacement. The finite element formulation of the... 

A Flying Electric Generator (FEG) can be a wind turbine which operates at high altitudes, where there is a continuous fast flow of air and converts wind energy to electrical power.The related field is an interdisciplinary area and is mostly related to the Aerospace Engineering and Energy Conversion. We focused on Iran, as one of the few lands in the northern hemisphere that has a high overall amount of high altitude wind energy for at least half of the year over it, according to the information of atlas of airborne wind energy in this work.So to install the FEGs in Iran, we had to find, places with a safe aerial space overhead which grant us reliable spots over country. These places found by... 

Nitrogen-Vacancy (NV) consists of a substitutional nitrogen located at a lattice site adjacent to a carbon vacancy. It has attracted much attention due to its application in solid state quantum information processing. Its long coherence time and ability to be used in ambient temperature made it a major candidate for quantum bit (Qbit). Due to its importance, a lot of theoretical studies for the NV’s properties based on the DFT and other single particle approaches have been done, while many-body approaches are not expanded so. For the first time, a generalized Hubbard Hamiltonian was used as a many-body approach to study NV defects. The obtained wavefunctions and states result to good... 

Purpose of ongoing thesis is providing a tool for suitable modeling, increase efficiency and decrease construction cost of solar absorption heat pump. At first, the solar absorption heat pump is modeled by the thermodynamic laws. Then, this model is converted to the new standard mathematical programming model using exergy and thermodynamic Analysis with considering all technical and economic constrains. This mathematical model is optimized by Genetic algorithm (GA). Because of the nonlinear objective function and the constraint, GA is used as optimization algorithm. After applying GA, optimized parameters of cycle heat exchanger designing and its electricity consumption are calculated.... 

In this thesis, we are focusing on the heat transport mechanism in one of the most applicable kinds of superconducting detectors called, YBa2Cu3O7-x (YBCO) transition-edge bolometer. The Time Domain Thermoreflectance (TDTR) method is described as a tool for investigating the thermal boundary conductance and thermal conductivity of the materials, and the measured thermal conductivity of our YBCO films is reported here. Although some recent papers have shown a dependence of the thermal conductivity of the YBCO films to their thickness, our results on many samples with different substrates didn’t show the reported thickness dependency and we have obtained the thermal conductivity of the YBCO... 

Motion of magnetic flux, as a result of exerting electrical current, causes dissipation and voltage difference in the type II superconducting slab. So fixing these vortices by pinning centers will increase the critical current . Enhancing the critical current by different kinds of pinning centers is interesting for a lot of theoretical and experimental research groups. At first in this project dynamics of vortices in a triangular lattice is investigated by changing the pinning force. For the case of fp=2f0 we have seen two phase transition in velocity-force plot. And also a practical pinning array of parallel lines is presented. The effect of pinning force, pinning potential width and the... 

One of the methods for the stability of the projectile is its rotation. The rotational velocity of the body surface induces velocity to the adjacent flow, thus changing the shape of the boundary layer, and due to the change in the thickness distribution of the boundary layer, the effective aerodynamic shape of the body also changes, which causes a force perpendicular to the angle of attack.This effect is called the Magnus effect. Since the force created by the rotation is an undamped force, the possibility of dynamic instability is very likely. There is no comprehensive analytical method that can accurately calculate its value for a wide range of projectiles.Due to the effect of Magnus...