Sharif Digital Repository

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... 

During the past 20 years, there has been an ever¬increasing interest in searching for anomalies or features beyond the standard scale¬invariant Gaussian spectrum of the CMB in the hope of finding signals of new physics. In this study, a new type of anomaly on the cosmic microwave background called the Inflationary Cherenkov effect is studied. By first simulating the expected effects and using machine learning methods such as convolutional neural networks, we obtain methods to detect this effect. Afterward, with the help of the detector, we study real data, namely temperature anisotropies of the CMB. Finally, we infer the speed of propagation of scalar field perturbations whose energy runs... 

Internet of things (IOT) interconnects a system of low power embedded devices that each of them has a unique identifier, without human intervention. The number of devices of IOT increases every day, therefor routing in the network of IOT is an important challenge. So, Internet Engineering Task Force (IETF) propose a protocol for routing low power and lossy networks in 2012, which is named RPL. Considering the power supply limitation of devices in the network, utilizing energy-aware policies within the RPL is so important. Meanwhile, objective functions have a vital role in the consuming energy. Also, energy consumption determines the lifetime of nodes. Since many of devices are placed in... 

The formation of gas hydrates in oil and gas industries has been the subject of long-standing problems. For example, the hydrate formation may occur and block gas pipelines which can lead to safety hazards. All of these will result in catastrophic economic losses and ecological risks. Therefore, various methods were developed to mitigate the formation of gas hydrate. In many cases, the hydrate inhibition by adding kinetic and thermodynamic inhibitors to the system is the only viable option. But recently using ionic liquids as novel hydrate inhibitors and the discovery of dual function thermo-kinetic inhibitors have been studied. In this project the performance of six imidazolium-based ionic... 

Uptake characteristics of alginate microcapsules containing D2EHPA/TOPO for adsorption of uranium from industrial effluent were examined using batch, stirred and column method .stable alginate microcapsules in dried form was developed by immobilizing of D2EHPA/TOPO in porous matrix of calcium alginate. Characteristics of microcapsules were carrying out by destructive chemical analysis, BET, SEM and TG .the synthesized microcapsules showed a good column properties and high selectivity and reusability. In addition, isotherm adsorption of calcium alginate and microcapsules were fitted with frendlich's equation .the microcapsules also demonstrated that, the uptake percentage was constantly high... 

Plant layout and siting are the earliest steps in any process design that may have significant effects on the further required level of safety and costs. Extensive carried out studies have been published in literatures in which, the safety factor has been taken into account in the form of prediction the severity of likely accidents. Majority of these studies are based on the accident consequence and other important parameters such as the accident frequency and the density of vulnerable items have been ignored. This recent negligence may lead to over conservative designs. To eliminate this recent deficiency, quantitative risk assessment (QRA) is the best procedure than can be suggested.... 

This thesis is divided into three parts: In part I, structure and electronic properties of ionic liquids based on N7, N9-dimethylguaninium cation and α-amino acid (Gly, His, Phe, Try, and Tyr) anions and also ionic liquids based on 1-ethyl-3-methylimidazolium [emim]+ cation and alkyl-trifluoroborate ([RBF3]-, R=n-CmH2m+1 (m=1-5)) anions were discussed at the DFT(B3LYP)/6-311++G(d,p) level of theory. Then, the effect of chain length in anion on the nature and strength of interaction between cation and anion was investigated. Our results indicated that interaction energy values decrease with the increase in side chain size in anion. NBO and QTAIM results indicated that the interaction in these... 

During the over balanced drilling operation in high permeability or fractured formations, drilling fluid loss and in more severe occasions fluid lost occurs which causes many problems and dangers and delayed the drilling operation until it was repaired. On the one hand, because of the high value of this material, and on the other hand, due to the increase in rig/day costs resulting from lost circulation control, leads to a significant increase in drilling costs. In this research, polymer-fiber composites have been designed and manufactured using extrusion method and have been investigated as fluid lost control agent in the laboratory scale for the first time in Iran. The effective parameters... 

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... 

Bone is one of the most vital parts of the body for almost any functional movement. Due to its many involved diseases, traumas and injuries, bone maintenance and regeneration are of high importance. Engineering and design of complex tissues, with impeccable mimicry of the native ones, are always accounted as the solution to dysfunction of body organs due to aging, various diseases, etc. However, the inability to complete mimicry of the native tissue architecture and cell microenvironment are the main barriers to functional tissue regeneration. In this project, in order to design a suitable scaffold for bone regeneration, hydrogel nanocomposites with polysaccharide basis were developed by... 

With the increasing development of Internet of Things (IoT) devices, issues such as establishing effective communication, optimizing energy consumption, ensuring reliability and improving the quality of services provided by these devices become more and more complex and critical challenges. With the introduction of fog computing model by Cisco in 2012, some of these challenges were successfully managed. Fog computing is a distributed computing paradigm that acts as a middle layer between cloud data centers and IoT-based devices/sensors. By distributing computing resources closer to edge devices, fog computing enables real-time data processing and analysis. However, one of the key aspects in... 

Memristor is a modern circuit element that demonstrates resistance memory function and can have important applications in emerging memories and artificial synapses. Binary oxides and perovskite oxides are two major classes of materials that are promising for memory resistances. Among the binary oxides, TiO2, and among the perovskite oxides, SrTiO3 (STO), are particularly promising in research on electrical resistance switching. In this thesis, by using two deposition techniques of sputtering and pulsed laser deposition (PLD), we have constructed single-layer and multi-layer memristor devices based on these two materials. Two general mechanisms control the behavior of memristors: bulk-control... 

The process of aging is accompanied by problems that can affect the daily activities of an elderly. Recent studies have shown that the use of virtual reality technology provides a variety of diagnostic methods and clinical systems to prevent and delay cognitive aging to ensure the normal life of the elderly. In this project, efforts have been made to design some virtual reality-based games focusing on memory and recall in the form of three scenarios of finding address, finding car, and virtual-reality based maze game for the elderly to prevent cognitive decline and developing the dementia so that the difficulty of the game level ahead of each elderly can be adjusted according to his or her... 

In this study, biosorption of selenium by Pseudomonas putida bacteria was investigated in both single and binary uptake systems. Bacteria cells were immobilized in the chitosan beads, to study impact of microorganism entrapment on the sorption capacity of the fabricated adsorbent. Uptake capacity increased by the entrapped bacterial weight percent up to 20 wt. %; but thereafter, sorption capacity gradually leveled off with an increase in the loading percentage of the bacterial cells.The effects of the three process variables including pH (2-6), biomass dosage (0.5-2.5 g/L) and initial concentration of selenium (50-250 mg/L) on the uptake performance of adsorbent were investigated, and... 

In this thesis, we study the observability and stability problems of networked control systems (the control systems which communicate through communication channels) to answer two important questions about different system models. The first is that what is the constraints implied by the stability or observability of systems? (necessary condition on the observability and stability). The second is that under which constraints can we present a design for system to guarantee the observability or stability of systems? (sufficient condition on the observability and stability). Clearly, an efficient design is the one that presents a tight sufficient condition.One of system models addressed in this... 

Emotions are one of the most important issues which affects daily life and activities. On the other hand, robots play an increasing role in human life and play a fundamental role in meeting our needs. One of these basic roles is empathy and verbal interaction between the robot and human. In this research, participant's emotions were stimulated in two ways: by using OASIS and GAPED image data sets and by instructing the participants to remind about their good or bad memories. During emotional stimulation, EEG signals have been recorded for the training and testing process. The preprocessing of training data includes filtering, removing bad parts of data, removing bad channels and... 

This thesis is divided into three parts: In part I, interactions of neutral and anionic forms of histidine with coinage metal nano clusters M3 (M = Au, Ag and Cu) are investigated. Results demonstrate that nonconventional M…H-O hydrogen bonds and M-X bonds (X = N, O) play stabilization roles in interactions of histidine and metal nano clusters. Presence of negative charge in ligand leads to increase of binding energy of complexes. In the next step, the effects of coinage metal nano clusters on the gas-phase acidity of weak organic acid (histidine) have been explored. The acidity of isolated histidine is compared with the acidity of its Au3–, Ag3– and Cu3–complexed species. Moreover, pKa... 

The purpose of this thesis is to find upper bounds for the eigenvalues of natural operators acting on functions on a compact Riemannian man-ifold (M, g) such as the Laplace–Beltrami operator and Laplace-type operators. In the case of the Laplace–Beltrami operator, two aspects are investigated:
The first aspect is to study relationships between the intrinsic geometry and eigenvalues of the Laplace–Beltrami operator. In this regard, we obtain upper bounds depending only on the dimension and a conformal invariant called min-conformal volume. Asymptotically, these bounds are consistent with the Weyl law. They improve previous results by Korevaar and Yang and Yau. The proof relies on the...