Sharif Digital Repository

Due to recent advancements and wide usage of location detection devices, huge amount of data are collected by GPS and cellular technologies which exhibits moving objects trajectories. Using this information, it is possible to track a set of objects over a long period of time, as happens for instance in studying animal migration. Always, in these situations it is undesirable or even impossible (due to process and storage limits) to store the complete stream of positioning data. Then, simplifying a trajectory as a data reduction technique is the option for resolving such problems. Moreover, there is an increasing interest in queries capturing ”aggregate” behavior of trajectories as groups like... 

According to the growth in the world population and the decrease in fossil fuels resources and also according to the pollution caused by these unrenewable resources, using hydrogen as an alternative energy resource seems to be unavoidable. In the past decades, semi-conductor metal oxides were being used widely in the energy domain of study, due to their appropriate band gap in the ultra-violet and visible spectra. Among these metal oxides, ZnO has been under special attention because of its electron mobility and its reasonable production cost and also its friendliness to environment. But the high band gap of ZnO (3.2 eV) has impeded its use in visible light spectrum. In this project,... 

The sustainable development in societies and the global energy challenge requires usage of clean energy systems that have attracted the attention of many researchers in recent decades. One of the major challenges in generating renewable resources is the problem of energy storage and imbalance between supply and demand cycles. Hydrogen as one of the clean energy carriers and due to having the highest energy density in terms of weight, is one of the important research topics. From this point of view, the preparation of electrocatalysts for hydrogen production, based on available materials, via simple and environmentally friendly production methods, was considered in this research.... 

Recently, Supercapacitors, as one of the most important energy storage devices, have attracted attensions by the scientists. Supercapcitor devices with appoporate design can store energy by two different mechanisms: i) physical (like conventional capacitors, i.e. by using polarization of the electrolyte, and ii) formation of electric double layer) and chemical mechanisms (like batteries, with reversible faradic reactions). These energy storage mechanisms allow these devices not only store high energy density but also they can provide high power density. In this project, two Co3O4/Co(OH)2 and Co3O4@Sponge-like rGO electrodes are made with chemical and electrochemical methods. To characterize... 

Due to the increasing demand for clean energy, layered double hydroxides (LDHs) have gained attention as electrocatalytic materials for water splitting into hydrogen and oxygen. Nickel-cobalt-based LDHs are favored for their ease of production and environmental compatibility, but they face challenges such as a lack of active sites and structural instability. The use of a core-shell structure can enhance the specific surface area and electroactive sites while preventing structural degradation. Furthermore, this structure can improve electrochemical performance and facilitate the oxygen evolution reaction (OER). In this research, a core-shell structure based on nickel-cobalt was developed,... 

Hexavalent chromium ion (Cr+6) is a very toxic type of heavy metal in industrial effluents which is not biodegradable and accumulates in the human body that can cause genetic mutations and cancer. The aim of this project is to investigate the effect of wavelength and intensity of appropriate light on the reaction rate of photocatalytic reduction of Cr+6 ion to less toxic materials. In this project, we first designed and constructed a photocatalytic reactor to investigate the effect of wavelength and intensity of incident light on the reaction rate. The home-made photocatalytic reactor consisted of 120 LEDs in 12 different wavelengths, which has ability to control the intensity and... 

Due to imminent shortage of fossil fuels, environmental issues that occur from their intensive use, population growth and industrialization of societies moving towards renewable energy sources is inevitable. Sun is the most clean and abundant source of energy but it is needed to be accompanied with an energy storage system as it is intermittent and cannot supply our required energies on demand. Water splitting electrochemical cells are promising solutions to cope with this problem by producing hydrogen as a clean fuel. The overpotential imposed by anode is the bottleneck of the water splitting reaction. The anodes with sufficient efficiency that are used today are made from precious and... 

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... 

Fighting contagious microbial diseases is considered a serious health issue, which has attracted much attention in worldwide. Thus, development of new materials based on nanostructures as a new generation of antibiotics to address this challenge has been of interest to researchers in recent years. Nanostructures based on metallic oxide semiconductors such as oxides with light absorption, production of electron-hole pairs in needle like structures cause tearing bacterial membrane and eventually destroy the bacterium. To this end, we designed experiments to study mechanism and physics governing the process of bacterial degradation to determine the best conditions for inhibiting bacteria... 

The optimized geometry and structure of iron oxide(Fe2O3) nanorod arrays as the photoanodes of photoelectrochemical cells have been calculated. Using finite element method, different structures have been studied in order to maximize the photocurrent density generated by the photoanodes. Two main characteristics of nanorod arrays namely the aspect ratio of nanorod and the density of nanorods in array have been selected as the variables. The absorbance of the photoanode has been calculated using Electromagnetic Waves Physics in COMSOL Multiphysics software. In this study, nanorods with aspect ratio of 3.6 to 40 have been varied and compared. The results reveal that the current density has a... 

Solar cells can be a solution to the challenges of energy and the environment. Perovskite solar cells are currently very popular, with an efficiency of around 25%. Silver nanowires are being considered as the next generation of flexible transparent electrodes in solar cells. Their stability is the most important challenge. Perovskite cells were fabricated in the laboratory, and the best efficiency of 14.3% was achieved with a gold electrode. Silver nanowires were synthesized using the polyol method with an average diameter of approximately 65 nanometers and an average length of about 13 micrometers. The spray method was used to deposit nanowires at temperatures between 100 and 200°C. When... 

The aim of conducting this research is to study, fabrication and photocatalytic application of electrospun ZnO-based composite nanofibers. One of the most important challenges is to apply photocatalyst under solar irradiation and improve its activity for pollutant degradation. ZnO is a wide band gap semiconductor, hence, it is not active under the visible light. In Iran, we have at least 300 sunny days in a year. Therefore, fabrication and application of photocatalytic material with activity under the sunlight which contains 47% of visible light is so vital in our country. Since CuO is a visible light active photocatalyst and its interface with ZnO forms a type I heterojunction, this... 

A Balanced Scorecard (BSC) model is proposed to evaluate performance of Health, Safety and Environment (HSE) management systems. This model includes key performance indicators at three integrated levels. It has been tested and verified in a project-based organization in Iran, active in the area of power and energy. Results show that the company has done well in implementing HSE management processes, but no so well in growth and learning. This model may be used as a basis for comparing different companies and various proposed programs in the field of HSE management systems. The model includes indicators and sub-indicators in each category particularly related to stakeholders, processes, and... 

Fischer-Tropsch process (FT ) is one of the most important processes gas-to-liquid (GTL) conversion. This process converts synthesis gas into hydrocarbons. Depending on the catalyst and operating conditions of the process, heavy paraffins (Wax) are the most important products in this process. These products can be used to heavy paraffin catalyst hydrocracking in a process for the production of diesel fuel and gasoline to lighter products are suitable to be converted. The aim of this project is to develop a suitable kinetic model to describe the process of producing heavy paraffin hydrocracking process Fisher - Tropsch to be lighter products. In this regard, each 5 continuous mass model... 

Articular cartilage Function is vital to joint tasks and its motion. The main biomechanical tasks of articular cartilage are a) the distribution of loads occurred in joints; b) providing joints with frictionless surface. The particular mechanical properties of articular cartilage make it possible for the Cartilage tissue to do its duty successfully. The biological factor that causes articular cartilage to damage is still unknown. It is believed that mechanical factors are the main reason for the cartilage destruction in osteoarthritis. Factors like age, heavy exercises and impact can begin tissue destructions and result in change in mechanical properties. To study the process of the... 

Ease of solar hydrogen production using water splitting and its environmental benefits, distinct hydrogen from other energy carriers. Hydrogen is the most abundant material in the world that make up more than 90% of the world compounds. So applying this material as a clean fuel is the best way to prevent environmental problems caused by fossil fuels. For efficient hydrogen production from water, a suitable electrocatalyst with low overpotential, high mechanical strength and reasonable catalytic activity must be utilized. In this research, cobalt based electrocatalyst was used considering that electrodepositon conditions play an important role in its final efficiency. On the other hand,... 

Regarding increasing world population, air pollution and depletion of fossil fuels supplies, hydrogen production via photoelectrochemical water splitting is a promising approach for providing a clean and renewable source of energy. Hematite (α-Fe2O3), the most common natural form of iron oxide, with a suitable band gap, high stability, earth-abundant nature and low cost has been widely acknowledged as a photoanode. However, intrinsic drawbacks of hematite like low electrical conductivity, short hole diffusion length and high recombination rate of electron-hole pairs hinder its photoelectrochemical performance with high efficiency. In this research, hematite nanostructures were synthesized...