Sharif Digital Repository

The Cu2ZnSnS4 (CZTS) quaternary compound, with suitable optical and electrical properties, is one of the most interesting materials for absorber layer of thin film solar cell. Since all constituents of CZTS, are abundant in earth’s crust and non-toxic, it is a proper replacement for the materials like CdTe and CuInSe2. The CZTS pellet was synthesized by the solid-state reaction and deposited on soda lime glass substrates by pulsed laser deposition (PLD) method. PLD technique has the advantages of offering stoichiometric preservation during the materials transformation from target to substrate and good crystallinity due to the highly energetic species. CZTS has was deposited in order to... 

In this study, the effect of temperature on the microstructure and electrochemical properties of the NMC batteries has been studied. An extensive set of accelerated aging tests has been carried out employing a Li-ion high energy 18650 system (2.2 Ah, negative electrode: carbon, positive electrode: Li(Ni0.5Mn0.3Co0.2) O2. Different influence factors on cycle aging, such as temperature and discharge rate have been investigated. The aged 18650 cells have been inspected via scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), impedance spectroscopy, and X-ray diffraction (XRD) after disassembly to find more information about the chemical reasons of the degradation and... 

Geothermal piles are being used to serve dual purposes: transfer the structural load to the ground and act as heat exchanger elements to harvest and reject heat from and to the ground. Thermal loading can change the mechanical performance and bearing capacity of the geothermal piles during heating and cooling cycles. Therefore the thermo-mechanical responses of the geothermal piles should be comprehensively studied. In this paper the thermo-mechanical performance of a geothermal pile was analyzed using a 3D finite difference model in FLAC. The energy pile tests performed at Lambeth College, London were simulated using the developed numerical model. Comparison of both thermal strain and... 

Reducing the size of transistors has dramatically increased the impacts of NBTI, HCI, and EM phenomena in comparison with decade ago. These phenomena are able to have influence on properties of different parts of a chip to make it changed gradually; including threshold voltage of a transistor and electrical conductivity of interconnections. These changes are known as the aging of a transistors that diminish the performance and reliability of a chip. A common reason that plays a significant role in all these phenomena is temperature. The temperature becomes more important when the power density increases per unit area due to decreased size of transistors, which is a trend in multi-core... 

In this study, four parameters were investigated including temperature, inlet flow rate, gas composition (oxygen) and particle size on the roasting of Bama company zinc sulfide concentrate in Fluidized bed reactor. Initially, primary sample was heated in electric furnace at 125℃ for 24 hours until the moisture content dried. Then roasting operation was done at 700 and 900℃. The operation was carried out on three range of particle size including 300-500, 500-700 and 700-1000 microns and flow rate was greater than the minimum flow rate of Fluencing. To investigate the effect of flow rate and gas composition input, 500-700 micron particle size range was selected. The effect of 155, 172 and 188... 

One of the main problems associated with the oil production is asphaltene precipitate in the reservoirs. In order to plan for the EOR methods, production scenario, and selection of completion technology, it is necessary to study the initiation of asphaltene precipitation called onset. Since the experimental methods is not only is so expensive and time consuming, the required materials are not available. Consequently, modeling approaches as new methods are proper substitutes for laboratory procedure. These methods need less costs and time and higher accuracy compared to the experimental investigations which are the advantages of these methods. Computational operations for onset determination... 

Hyperscale cloud data center (HCDC) (a.k.a., hyperscale data center) is the backbone of a wide variety of Internet services such as web-hosting, ecommerce, social networking, software as a service (SaaS), platform as a service (PaaS), application as a service (AaaS), and cloud computing.HCDC platforms consist of massive parallel processing, high utilization rate, and high volume storage that cost hundreds of million dollars.The increased demand for various Internet services and the subsequent dramatic growth in HCDC platforms, have caused an exponential increase in utilization of energy. With energy costs on the rise and global attention focused on carbon footprints, organizations are... 

Nowadays, due to gearbox drawbacks, the direct-drive wind turbines have received much more attention. Permanent magnet synchronous machines are commonly used for this purpose. The flux reversal machine with a magnetic gearbox and high power density could be an appropriate alternative. Due to placement of permanent magnets on the stator, the machine has a simple and robust structure and provides more reliability. There is limited study on optimization of the flux reversal machine and the existing papers are not complete and many parameters like PM dimension, working temperature, and winding reactance are not considered in the optimization process.Considering the flux reversal machine... 

Nowadays the performance of multi-core systems is increasing; however, the limited off-chip bandwidth of DRAMs is the biggest limiting factor for keeping up this trend. 3D stacked memories are good alternatives for current memories as they utilize high-bandwidth low-power through silicon via (TSV) connections. The main problem of these structures is significant rise of temperature as heat cannot be dissipated easily from the middle layers. As a result, utilizing thermal and power-aware management techniques is one of the most critical design goals of these systems. DRAM manufacturers consider timing parameters of memory controller conservatively high to guarantee the true functionality of... 

Improving the discharge process of phase-change materials (PCMs) is of great importance. In this study, the process of acetone drop impact on molten paraffin, as a direct-contact solidification method, is experimentally investigated. Four Weber numbers (corresponding to heights of 10, 20, 30, and 40 cm) for the acetone drop and six surface temperatures (66, 68, 70, 75, 80, and 90 °C) for the molten paraffin are considered. As the acetone drop impacts the molten paraffin, the drop absorbs heat from the melting paraffin and boils, solidifying a portion of the molten paraffin. Two important parameters that govern the acetone drop dynamics and the solidification of the molten paraffin are the... 

Double cantilever beam (DCB) specimens were prepared according to standard surface mount technology (SMT). The samples were stored inside an environmental chamber at two different relative humidity values (i.e. 40 or 100%) for either 2 or 4 hours. Then they were aged at 25ºC, 75ºC or 125℃ for the same time. Finally, after being cooled to room temperature, fracture tests were performed under mode-I loading conditions at a strain rate of 0.03 s-1 at room temperature. Storage time did not have a significant effect on the fracture behavior. The fracture load and energy of the solder joints decreased significantly when the temperature was increased from 25 to 75℃. By further increase in the... 

Preserving and promoting the health of citizens in a society is one of the most important problems addressed in any country. The power sector discharges a huge volume of carbon dioxide which intensifies the climate change and consequent human health problems.The goal of this study is to evaluate the ultimate effect of climate change caused by power plant emissions on the human health using life cycle analysis approach for different provinces in Iran. An integrated model has been developed to evaluate the impact of climate change due to power plant emissions on the human health. This model includes the equations regarding the variations in carbon dioxide concentration in the atmosphere,... 

Cyber-Physical Systems, including embedded systems, have become essential components of various applications in modern life. Due to this fact, cyber-physical and embedded systems must be reliable, safe, and meet timing constraints. Task replication is an effective approach to improve reliability and safety, but it may violate the real-time constraints of the executing tasks and aggravate the aging effects of the system due to elevating the on-chip temperature. Moreover, since embedded systems have time, reliability, power, and thermal constraints, the appropriate number of replicas should be determined to handle the extra overheads. Existing works determine the number of replicas at design... 

The use of renewable energy sources has received much attention due to the increasing need for energy, limited energy resources and the pollution of fossil fuels. Among all types of solar energy conversion technology, photovoltaics has the highest technical potential and Iran’s geographical location is very suitable for benefiting from this energy. So, in this thesis, the fabrication and characterization of nanostructured solar cells based on organic-inorganic perovskites have been investigated. Many research goups have tried to increase the efficiency of perovskite solar cells. The efficiency of this kind of solar cells depends mainly on the light-absorbing layer (perovskite) and its... 

Precipitation in the water year 1396-1397 is the lowest in the past decade. The present study is conducted during this water year and focuses on the effects of climate variables such as temperature and precipitation on child labor supply between Tir 1397 and Farvardin 1398. Children and household characteristics are also taken into account when evaluating child labor supply using OLS and Logit methods. Estimation results indicate that both child work hours and participation in the job market decline with an increase in precipitation. Furthermore, how much time children spend working or studying is heavily influenced by parents' income. The temperature variable does not have a significant...