Sharif Digital Repository

A decade after discovery of graphene, the unique properties and characteristics of two-dimensional materials, particularly an emerging family of carbides and nitrides (MXenes), have attracted the attention of researchers. MXenes are two-dimensional structures of two or more layers of transition metals, with interstitial carbon and/or nitrogen atoms, with exceptional properties such as high specific surface area, excellent elastic modulus, metallic conductivity, and various termination groups. These properties can be altered by various factors, including chemical composition and synthesis processes, and any changes in these factors significantly affect the properties of MXene sheets. In this... 

The amount of fresh water suitable for various uses is decreasing day by day. This may be due to evaporation or contamination of water or such. Heavy metal cations, dyes, oils and solvents are the most important substances that contaminate water. There are various ways to remove these contaminants, one of which is the absorption of these substances by suitable absorbents. Carbon compounds have attracted much attention among all the absorbents used so far. The aim of this study is to produce carbon aerogels from an economic and modify its structure and properties by adding graphene nanosheets. In this study, Novalak-graphene oxide (GO) gel was fabricated using solvent-saturated vapor... 

Type IV high pressure vessels are composite vessels with a polymeric liner, which are the best choice for storing hydrogen in hydrogen vehicles. The defect of these vessels is the penetration of light hydrogen molecules in the polymeric liner and the composite part. When depressurization the vessel, these molecules cannot release from the polymeric liner and the composite part according to the emptying rate of the vessel. Thus, concentration of the hydrogen molecules in the polymeric liner becomes more than inside the vessel which leads to a pressure difference between the two sides of the polymeric liner that causes the liner collapse. In this research, the partial differential equation for... 

Biodegradable implants are new generation of implants that require no secondary surgery for their removal. Mg exhibits a great potential to be used as the biodegradable implant. However, mechanical properties and biocorrosion behavior of Mg are not suitable for being used as biodegradable implants. In this study, effects of Sr additions, heat treatments (T4 and T6), and multi-directional forging on the microstructural evolution, mechanical properties and biocorrosion behavior of Mg-4Zn-xSr alloys, and also the effect of hydrothermal coating on the biocorrosion behavior of Mg-4Zn-0.3Sr alloy were investigated. Potentiodynamic polarization and hydrogen evolution methods were used to... 

In Mg–Si alloys, both primary and eutectic Mg2Si particles normally appear with sharp edges, which can lead to weak mechanical properties as the result of stress concentration at the sharp corners of these brittle particles. On the other hand, the morphology, size and distribution of Mg2Si particles affect corrosion behavior of Mg–Si alloys. Thus, it would be of great importance to modify the morphology of these particles. In this study, microstructure modification mechanisms after 0.5 wt% Y addition and heat treatment (HT) at 420 ◦C for 24 h are comprehensively studied in hypo-eutectic Mg–1Si and hyper-eutectic Mg–2Si alloys. Microstructural observations were performed using optical and... 

The use of polymers is increasing day by day due to low density, reasonable price and ability to produce different products. On the other hand, the accumulation of polymer wastes in nature is one of the environmental concerns in today's world, which is mainly due to the widespread use of polymers in the packaging industry and disposable applications. In order to solve this problem, recycling is recommended as the most appropriate and economical solution. Because in addition to consuming polymer waste, it also saves energy and reduces carbon footprint.Polyethylene terephthalate (PET) is one of the polymeric materials which; It has a special place in the packaging industry and is widely used... 

Crack propagation problem is one of the most important problems that are being investigated for a long time. Plenty of various approaches have been utilized to simulate the crack propagation phenomenon. Continuum based methods like Finite element (FE), Extended Finite element (XFEM), have been successfully applied, and the obtained results are valid in macro scale. However, the stress filed near crack tip in FEM modeling of crack, is not exquisite enough due to inability of continuum based approaches in revealing atomistic aspects of the material.
In order to gather efficiency of the continuum based domain and the accuracy of the atomistic based domain, Multiscale methods are employed.... 

It is generally believed that the only utility of tests as a critical instrument is to be at the service of educational institutions. To broadly consider their different usefulness, tests can serve other purposes like focusing on the ethical and moral issues. As it is called Critical Language Testing, tests are not reliable instruments and they have the capacity of being used not only in educational, but also in political contexts. This philosophy has not been brought into perspective, and, as a result, the literature deserves more comprehensive attention. This study, guided by the principles of Grounded Theory and Qualitative research design, pursued three purposes: To investigate the... 

Biodegradable Mg-Ag alloys are promising implants for bone tissue regeneration due to their unique ability to reduce inflammation and infection after implantation with the presence of silver. However, their biological performance, including biodegradability, needs further improvement. In this regard, the effects of adding yttrium element, solution heat treatment and coating on the microstructure, biodegradability behavior, mechanical properties and biological characteristics of a cast Mg-2Ag alloy were studied. Addition of 1 wt% of yttrium caused grain refinement in the microstructure and solid solution heat treatment led to a significant decrease in the volume fraction of secondary phases.... 

Ultralight aircraft (VLA category) are usually piloted by novice pilots under Visual Flight Rules (VFR). In this work, we demonstrate how newly developed techniques in robotics could be used to enhance flight safety in this category of aircraft, especially during landing around sunset. In this research we have investigated the ability of Simultaneous Localization And Mapping (SLAM) algorithms in low level flight just before touch-down. Different case-studies show that SLAM algorithm is efficient in detecting the runway threshold. Comparing five different methods of parameterizations for landmarks detection including: (1) Plucker, (2) Anchored Plucker, (3) Homogeneous, (4) Anchored... 

Magnesium and its alloys have gained a lot of interest recently in the field of biodegradable implants, particularly in the field of orthopedics, mainly due to their excellent compatibility, low density and similarity of their mechanical properties with the human bone. However, the main weakness of magnesium for such applications is that it corrodes faster than the time required for complete healing of the tissue. Different properties of Mg can be improved by making composites. In this research, 1% and 2% of MgO microparticles were added to the Mg-1Zn-0.2Ag alloy. These composites were made by the stir casting technique, and after that, the samples' microstructure, mechanical... 

Polylactic acid (PLA) is considered as a great option to be employed as 3D porous scaffold in tissue engineering applications owing to its excellent biocompatibility and processability. However, relatively weak mechanical properties, low degradation rate and inappropriate biodegradability limit its extensive usage. In order to overcome the mentioned challenges, micrometric magnesium (Mg) particles were incorporated into the PLA matrix by the fused deposition modeling (FDM) technique. The effects of various Mg contents (i.e., 2, 4, 6, 8 and 10 wt%) on the mechanical, thermal, structural, wettability, rheological, biodegradability characteristics and cellular behavior of the 3D porous PLA-Mg... 

Three-dimensional biological scaffolds, as an emerging strategy in bone tissue engineering, enable the treatment of bone injuries without the need for grafting and implantation. The selection of suitable materials and fabrication methods for producing bone scaffolds is one of the key challenges in bone tissue engineering. This research focuses on the production of poly-lactic acid-bioactive glass S58 composite scaffolds using 3D printing. A solvent-based method was employed to produce poly-lactic acid composites containing bioactive glass particles (0.5, 1, and 1.5 weight percent). The composites were printed after the extrusion process and filament production for evaluating microstructural,... 

In this study, the effects of calcium addition and T4 heat treatment at 450°C for 36 hours on the microstructure, mechanical properties, and corrosion resistance of the Mg-2.5Y alloy were comprehensively investigated. The studied alloys included the base Mg-2.5Y alloy and the Mg-2.5Y-0.2Ca alloy, which were prepared through casting. Microstructural analysis using optical microscopy, scanning electron microscopy, and X-ray diffraction revealed that the addition of 0.2 wt% calcium significantly reduced the grain size from 732±34 µm in the base alloy to 475±12 µm. After heat treatment, the dissolution of dendritic branches and secondary phases (Mg24Y5 and Mg2Ca) resulted in finer, more equiaxed... 

Single nucleotide polymorphs, There are changes caused by a mutation in a nucleotide in the Dena sequence. Mononucleotide polymorphisms are the most common type of genetic variation. Some of these changes have little or no effect on cells, while others cause significant changes in the expression of cell genes that can lead to disease or resistance to certain diseases. Because of the importance of these changes and their effect on cell function, the relationships between these changes are also important. Over the past decade, thousands of single disease-related mononucleotide polymorphisms have been identified in genome-related studies. Studies in this field have shown that the expression of... 

In the past few years, many research works on the controllable integration of metal nanoparticles and metal-organic frameworks were done, since the obtained composite material shows a synergism effect in catalysis and photocatalysis, drug delivery applications, gas, and energy storage, as well as sensing. For the first time, in this study, we employed template-assisted growth to synthesize Au-HKUST-1 Nanocomposite. XRD analysis entirely confirms that employing this strategy in synthesizing Au-HKUST-1 was wholly successful, and the plasmonic properties of this nanostructure were studied via UV-visible spectroscopy. In the course of synthesis, gold nanoparticles with 70nm diameter were... 

Nowadays, video streaming over peer-to-peer networks has become an interesting field to deliver video in large scale networks. As multi-channel live video streaming networks increase,distributing video with high quality among channels faces many challenges. The most significant challenges cause from frequent channel churns, unbalanced channel resources, network heterogeneity and diversity of users’ bandwidths. They include: nodes’ unstability, low users participations, large startup and playback delays, low video quality received by users and lack of resources in unpopular channels.In order to solve the above problems, we have proposed several solutions such as: 1- using distribution groups... 

The fast growth of social networks and their wide range of applications have made the anal-ysis of them an interesting field of research. The growth of concern in modeling large social networksand investigation of their structural features leads studies towards community detec-tion in such networks. In recent years, a great amount of effort has been done for introducing community detection algorithms, many of which are based on optimization of a global cri-terion which needs network’s topology. However, because of big size of most of the social networks , accessing their global information tends to be impossible. Hence, local commu-nity detection algorithms have been introduced. In this... 

Semi-supervised Learning (SSL) is an extremely useful approach in many applications where unlabeled data can be easily obtained. Graph based methods are among the most studied branches in SSL. Since neighborhood graph is a key component in these methods, we focus on methods of graph construction in this project. Graph construction methods based on Euclidean distance have the common problem of creating shortcut edges. Shortcut edges refer to the edges which connect two nearby points that are far apart on the manifold. Specifically, we show both in theory and practice that using geodesic distance for selecting and weighting edges results in more appropriate neighborhood graphs. We propose an... 

At first the killing vector fields will be investigated. Conditions are introduced for the hypersurface of a Riemannian manifold with a killing vector field to be equipped with the same killing vector field. Then 2-killing vector field is studied and its relation with killing vector fields and monotone vector fields is presented. After that conformal vector fields are discussed and conditions are introduced in order that the Riemannian manifold equipped with a conformal vector field, isisometric to n-dimensional sphere with constant curvature. Finally we will present the conditions which conformal vector field is a 2-killing vector field. Then we will present the results in which the...