Sharif Digital Repository

The present study deals with the analysis of Atomic Microscope with crack by making use of Strain Gradient Elasticity theory. Empirical observations represent that in micro dimensions, materials show behaviors, which the classic continuum mechanics theories are not able to explain. Thus, taking advantage of non-classic theories, which are capable of explaining such phenomena or behaviors in analyzing materials in micro dimensions seems necessary and of much significance. In this direction, by applying an Euler-Bernoulli beam assumption and neglecting the shear effects, governing equations and boundary conditions of the problem were obtained via taking advantage of variations in Hamilton... 

Antioxidants are compounds with anti-cancer, anti-bacterial, anti-viral, anti-aging and anti-allergic properties. In the present study, a quantum mechanical approach has been used to shed light on the presence effect of glycoside group on the antioxidant ability of chrysin as one of the most important consumable flavonoids and two glycoside derivatives, chrysin-6-C-fucopyranoside and chrysin-3-malonyl-6-C-fucopyranoside which has electron-withdrawing group (EWG) in its C3 of glycoside group. Density functional theory (DFT) using B3LYP and UB3LYP functional and split-valance 6-311++G ** basis set were used to optimize chrysin, its different derivatives, and their radicals. Analysis of... 

Endothelium is the interior layer of an artery made up of tremendous number of endothelial cells which are located side by side. Finding the effective parameters that cause the cells to obtain mechanical strength in different morphologies is a major effort in cell engineering studies. In this work a numerical model for endothelial cells is developed. This model has included cell's plasma membrane (the outer membrane of the cell), nucleus and cytoskeleton main components including intermediate and actin filaments as well as microtubules. The model has been validated by simulating the adhesion of the cells to a flat substrate and also atomic force microscopy (AFM) experiments. The two most... 

Atomic force microscope (AFM) has a significant capability of imaging surface topography on an atomic scale. It is also widely used for Nanolithography in MEMS/NEMS (micro/nanoelectromechanical systems). Conventional AFMs consist of a cantilever with a sharp conical or pyramidal tip located at the free end of the cantilever that plays an important role in AFM measurements. Scanning across a surface, AFM interacts with the sample surface through its tip. Although the dynamic behavior of the AFM cantilever is complicated, the researchers have been interested in studying AFM dynamic behavior because it has a great influence on the surface imaging process. The imaging rate and contrast of... 

Liquid atomization have broad range of usage in different industries. Colliding two jets is one method for atomization of different kind of fluids especially high viscose and viscoelastic fluids. Here, we experimentally investigated the effect of skewness and velocity differential of two Newtonian viscose colliding jets on formation of a special oscillating liquid sheet pattern with periodic fragmentation called “fishbone”. For this work, four liquid sheet regimes; triple chain, double chain, close rim, and open rim which fishbone pattern could be observed were produced and Skewness and jets velocity differential were applied to them. A synced CCD camera and stroboscope illumination source... 

In this thesis ،molecular dynamics simulation of structural and mechanical properties of pure aluminium and copper crystals as well as of the alloyed crystals including 10%,30%,50%,70% and 90% aluminium alloyed have been investigated using two various all-atom and coarse-grained models. Molecular dynamics simulations calculate the realistic behavior of the system and then use them in order to calculate the time average properties of the system. Embedded atom method (eam) and the numerical iterative Boltzmann Inversion method are employed to describe the interaction between atoms. The results are then compared with coarse-grained model. The demonstrated peaks in the radial distribution... 

Nano/Micro-structure of rapidly solidified (products of Atomizing and Melt Spinning processes) Al-20Si-(5Fe) alloys has been investigated at the present work. Moreover, the effect of cooling rate on microstructure and growth morphology of these alloys has been studied. Microstructure of the products was examined by using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction.At the present work some models have been proposed for driving a relationship between microstructure and rapid solidification parameters during Atomizing and Melt Spinning processes. These models are based on macroscopic heat transfer during the processes. Model for... 

In this project, the aim is finding the corrosion behavior and biocompatibility of metallic biomaterials in simulated body fluids.by this study we can have a wide knowledge about the behavior and use of metallic biomaterials.in this project we use three base metals. Ti (grade 5 and grade 2), stainless steel (316L and 316) and Mg alloy(AZ91 and AZ31). the media was six physiological environment( Cigada solution, Hank solution, SBF solution, Fusayama solution, Ringer solution and Tyrod’s solution). all of these environments are related to the body fluids except Fusayama solution that is an artificial saliva and is a mouth fluid. we used polarization tests to determine the corrosion behavior... 

In this work a theoretical overview of Parity-Time symmetry and its application in multilevel atomic systems are presented. Because of equivalence between the Schrodinger equation and the paraxial propagation equation, complex index of refraction plays the role of complex potential. On the other side, the possibility to manipulate loss, gain and the index of refraction simultaneously, Optics is a fertile ground to investigate Parity-Time symmetry and one of this symmetry’s applications is reduction of loss in optical systems. Furthermore, In order to realize Parity time symmetry a four level atomic system under electromagnetically induced transparency condition is proposed. Optical gain... 

Hydrogen bonding is an important weak interaction encountered in gas, liquid, as well as solid phases. The hydrogen bond plays a very vital role in many life processes and is one of the most frequently used terms in chemistry and biology.
Polyols or polyhydric alcohols are, strictly speaking, simply organic chemicals containing more than two hydroxyl groups. Each hydroxyl is attached to separate carbon atoms of an aliphatic skeleton.They may also contain ester, ether, amide, acrylic, metal, metalloid and other functionalities; along with hydroxyl groups. Polyols are obtained from many plant and animal sources and are synthesized by a variety of methods. Among important properties of... 

We carry out computer simulations in the hope of understanding the properties of assemblies of molecules in terms of their structure and the microscopic interactions between them. This serves as a complement to conventional experiments, enabling us to learn something new, something that cannot be found out in other ways. One of the main families of simulation technique are molecular dynamics (MD). Over the last decade , nanoscience and nanotechnology have emerged as two of the pillars of the research that will lead us to the next industrial revolution. The fundamental entities of interest to nanoscience and nanotechnology are the isolated individual nanostructures and their assemblies. Nano... 

This thesis deals with the theoretical and experimental investigation of quantum interference and coherence, and electromagnetic induced transparency (EIT) in multi-level atomic systems such as hot and cold Rb atoms, semiconductor quantum dots and wells. Optical properties of atomic media in presence of coherent laser fields and incoherent fields are studied.
Theoretical studies verify the crucial role of atomic coherence due to quantum interference in modifying optical properties of atomic media. Suitable and efficient models based on multi-level atomic systems to investigate the optical properties and, optical bistability and multistability are proposed. The most advantages of these... 

To account for certain essential features of material such as micro-structure effects and dispersive behaviour and optical branches in dispersion curves, a fundamental departure from classical elasticity to generalized continuum theories is required. Among the generalized continuum mechanics, micromorphic elasticity is capable of capturing these physical phenomena completely. In the mathematical framework of micromorphic elasticity, in addition to the traditional elastic moduli tensors, some additional tensors are introduced in the pertinent governing equations of motion. A precise evaluation of the numerical values of the aforementioned elastic moduli tensors in the realm of the... 

In present research forming process of nanopowders, which is a part of powder metallurgy was investigated by molecular dynamics method. Powder metallurgy is a relatively new method for production of industrial parts by pouring powder into die and compaction to desired density. One can reach parts with higher quality and strength by decreasing size of powder’s particles and entering the nano scale. Particle with smaller size have higher specific surface and due more intensity to react. Classic methods for investigation of this process don’t cover the atomic scale effects, so using newer procedures such as molecular dynamics is highly recommended. In present research, at first compaction of... 

In the contemporary pursuit of sustainable energy solutions to address the escalating demand for electrical power, a crucial focus lies on the exploration of renewable energies and the harnessing of wasted energy in industrial processes. This research contributes to this imperative by investigating active cooling methods, specifically employing jet impingement and spray techniques, for the cooling of thermoelectric generators and the recovery of wasted heat. The study empirically assesses three distinct cooling approaches, encompassing a heat pipe relying on free convective heat transfer with air, a heat pipe cooled by water jet impingement, and a heat pipe incorporating spray application.... 

City of Karaj with 2 million population used to enjoy very clean and accommodating air and environment . This congenial condition was due to agricultural and gardening activities of the local population . This way of life has undergone a profound change due to a change in the economic activities of the local population from farming and agriculture to industrial activities . And this has brought particulate matter wich has been exacerbated in the recent years . With the additional onslaught of the dust storms coming from the neighboring countries due to drying up of rivers and lagoons .The main object of this work was to obtain the spectrum of the PM and the additional component of PM that... 

In order to obtain more insight into the enzymatic oxygen-atom-transfer (OAT) process and elucidate the relation between the structure and function of the synthetic model complexes, new molybdenum and tungsten complexes containing different chelating ligands were systematically prepared and investigated. Herein, the cis-dioxo-molybdenum(VI) complexes with new aromatic dithiolene ligands, formulated as [MoO2(2,3ppdt)2]NR4 and [MoO2(3,4ppdt)2]NR4, (2,3ppdt= pyrido-2,3-pyrazine-2,3-dithiolato, 3,4ppdt= pyrido-3,4-pyrazine-2,3-dithiol and R= Et or Bu) were prepared and investigated by elemental analysis, IR, 1H NMR and UV-Vis spectroscopic methods. An OAT reaction of [MoO2(2,3ppdt)2]2– with PPh3... 

Hypereutectic A390 alloy has some exclusive specification among aluminum alloys because of its' excellent properties such as high wear resistance and low thermal expansion. In this research powder-thixoforming method, a compilation of powder and thixoforming methods is used for production of parts. In this method gas atomized powder of pre-fabricated alloy was consolidated by hot pressing under argon atmosphere and converted to an acceptable feedstock for thixoforming stage. The feedstock is reheated to semi solid region and rapidly transferred to a injection sleeve with central runner. The semi-solid feedstock is injected in a step die by a hydraulic press of 1 m/s ram speed. According to... 

In this thesis, a coarse-grained multi-scale method for 2D crystallyn solids based-on finite element consepts has presented. In this method, both scales are atomic scale and similar to what we see in non-local QC method, the entire atomic structure will be intact. Accordingly, calculations of potential functions and forces in the domain will have the atomic accuracy. In the presented method to reduce the domain’s degrees of freedom, the classical finite-element meshing concept to mesh the elastic linear areas in the domain is used and the MD calculations will done on the mesh nodes. Therefore, degrees of freedom in the system will reduce and consequently, the computational cost will reduce.... 

In this dissertation, Hydrogen storage in the solids based was investigated. The carbon-based structure used is the graphene that decorated with metal atoms to increase intermolecular interactions and increase the adsorption weight capacity. The structure of graphene has been considered due to its properties such as low density, high heat transfer coefficient and high specific surface area. Initially, the structure of pure graphene was investigated using the molecular dynamics method for hydrogen storage and it was shown that the interaction between hydrogen molecules and pure graphene is very weak and it can’t be a good option for use in cars. Then, the structures of graphene reinforced...