Sharif Digital Repository

In recent years, adjustable optical properties, simple and inexpensive synthesis, and excellent biocompatibility of carbon dots have attracted much attention. However, the widespread use of carbon dots in biomedical diagnostics, photoluminescence, and photocatalysis has been limited due to a lack of emission or excitation in the red or near-infrared region. Studies have shown that doping in carbon dots can affect the displacement and increase the light intensity. This study aims to use the engineering methods of optical properties of carbon points by doping heteroatoms and adjusting the surface state to synthesize biocompatible carbon dots with luminescence at long wavelengths with strong... 

In recent years, studies in luminescent carbon dots are overgrowing, the prominent features of carbon quantum dots include cheap and straightforward synthesis, excellent biocompatibility, and adjustable optical properties. However, the widespread use of carbon dots in biomedical diagnostics, photoluminescence, and photocatalysis has been limited due to a lack of emission and excitation in the red or near-infrared region.. However, the widespread use of carbon dots in biomedical diagnostics, photoluminescence, and photocatalysis has been limited due to a lack of emission and excitation in the red or near-infrared region. This research tried to produce carbon dots with redshift in emission... 

Novel zeolite-based micromotors consisted of silver-exchanged zeolite core and three different partial catalytic coatings (Mg/Au, Pt and Ag) were synthesized to eliminate the biological and chemical contamination from water in a fast and efficient way. These engines are benefited by the adsorption capacity and antibacterial activity of silver-zeolites in combination with the autonomous propulsion of catalytic micromotors. The remarkable bactericidal capacity of these particles relies on reactive silver ion released from zeolite and accordingly, increased chance of contact with bacteria during movement. These motors showed rapid killing of bacteria and effective elimination of the Pseudomonas... 

Iron oxide nanoparticles were synthesized using microemulsion technique as MRI contrast agents. Utilization of nanoparticles for biological applications and in this case as MRI contrast agents needs particles to be of small size and also narrow size distribution. For this aim, the effect of several parameters on size and size distribution has been studied. These parameters include water/surfactant ratio, precursor’s concentration and amount of polymer employed to improve nanoparticles colloidal stability. XRD, FE-SEM and TEM results reveal that the synthesized nanoparticles had small size (about 10 nm iron oxide core and 20 nm overall diameter) and possessed narrow size distribution (15-21... 

In this research, a facile, two-step synthesis was reported for 34-LCysteine- nanocomposites. The first step comprises the preparation of LCysteine functionalized magnetic nanoparticles (MNPs) core-shell structures via co-precipitation method. In the second step, graphene quantum dots (GQDs), which were synthesized by citric acid carbonization, added to the functionalized MNPs and finally refluxed at the appropriate time and temperature. LCysteine as a biocompatible, natural amino acid were used to link MNPs with GQDs. This nanocomposite was characterized by various techniques. XRD and FT-IR were used to investigate the formation of MNPs and LCysteine existence on the MNPs surface. XPS... 

Repair welding is one of the important maintenance processes that include build-up welding and surfacing.In this study, investigation of repair welding parameters has been conducted to achieve desired microstructure with the appropriate toughness and minimum residual stress.In this research, local post-weld heat treatment has been performed by Tungsten electrode arc on weld zone. Performing this process with optimum parameters leads to the best heat cycle with the tempered Martensite microstructure. Residual stress of the sample will be reduced. HAZ coarse grains will be refined to finer grains which result in to improved toughness and reduced hardness to the acceptable limit.
Results... 

A great deal of information are continuously generated by users in different contexts such as social networks and online service providers in terms of temporal marked events. These events indicate that what happened to who by when and where.Modeling such events and predicting future ones has interesting applications in different domains such as item recommendation in online service providers and trending topic prediction in online social networks. However, complex longitudinal dependencies among such events makes the prediction task challenging. Moreover, nonstationarity of generative model of events and large size of events, makes the modeling and learning the models challenging.In this... 

The emergence of applications such as spam detection and online advertising coupled with the dramatic growth of user-generated content has attracted more and more attention to stream classification. The data stream in such applications is large or even unbounded; moreover, the system is often required to respond in an online manner. Furthermore, one of the main challenges of stream classification is that often the process that generates the data is non-stationary. This phenomenon, known as concept drift, poses different challenges to the classification problem.Therefore, an adaptive approach is required that can manage concept drift in an online fashion. This thesis presents a probabilistic... 

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... 

During the most recent years, investigating novel nanomaterials based on porous strucures has become an interesting field of research. Among these kinds of materials, mesoporous silica has extensive applications in catalysis, absorbants and biomedical engineering. By combining specific surface characteristics of mesoporous silica with magnetic properties of iron oxide nanoparticles, new nanocomposites owing unique properties, can be obtained. In the present research, magnetic mesoporous nanocomposite has been synthesized. Iron oxide nanoparticles were produced through reduction of water solution containing Fe2+/Fe3+ ions, followed by hydrothermal treatment of precipitan. Then, iron oxide... 

In this study in-situ Al/Al3Ti was fabricated by mechanical alloying, hot extrusion and subsequent heat treatment. First, initial pure powders of Al and Ti were mechanically alloyed with 5 weight percentages of Ti for 40 hours. The as-hot extruded samples containing 5 wt% of initial Ti particles, were exposed to heating at 600 oC for various time intervals up to 10 hours. Microstructure analysis by OM and SEM proved that in-situ Al3Ti phase was formed as a layer around Ti particles by solid reactive diffusion between Al and Ti particles. After 10 hours of heating, all the Ti particles were consumed and transformed to Al3Ti. Mechanical properties of samples were investigated by Brinell... 

Age-related macular degeneration (AMD) is the most common cause of vision loss in those aged over 50. There are two main types of AMD, Wet and Dry form. Wet AMD is more severe though more treatable. There are three conventional treatments for AMD including laser therapy, surgery and intravitreal injection of anti-VEGF into the eye. Delivery of drugs to the posterior segment of the eye is still challenging and several implants and devices are currently under investigation for their ability to stimulate the retina, producing visual percepts. The application of intravitreal bevacizumab (Avastin) has expanded tremendously from the time of its introduction into ophthalmic care since 3 years ago.... 

A biocompatible ferrofluid have been prepared by co-precipitation of FeCl2.4H2O and FeCl3.6H2O under ultrasonic irradiation and with NaOH as alkaline agent. Also cystein was used as capping agent in the solution. Magnetic properties of the produced ferrofluid then determined by VSM test and magnetite nanoparticles were characterized by XRD and TEM techniques. Results indicate the presence of a biocompatible superparamagnetic ferrofluid including magnetite nanoparticles with particle size ranging under 15 nm. The effect of ultrasonic irradiation on presence of a sharp particle size distribution then denoted by comparing the condition with production without ultrasonic irradiation  

In this work, the effect of chemical composition on structural, mechanical, electrical and magnetic properties of nanocrystalline Finemet-type alloys with the composition of Fe73.5Si13.5B9Nb3Cu1 , Fe77Si11B9Nb2.4Cu0.6 and (〖Fe_0.5 Co_0.5)〗_77 Si_11 B_9 Nb_2.4 Cu_(0.6 )was investigated. The samples were prepared by vacuum arc melting of high purity constitution in order to obtain a nanocrystalline structure. The amorphous ribbons were then annealed under vacuum with the same conditions of temperatures and time to compare their properties. The structural and thermal properties of the samples were analyzed using various techniques such as X-ray Diffraction (XRD) and Differential Scanning... 

Al /Al3Ti in-situ composite have been fabricated by mechanical alloying and two-step hot pressing of powders containing Al and 20%wt Ti. Samples were characterized by using optical microscopy, density measurement, brinel hardness, XRD analysis. An increasing density was observed with increasing pressure until certain pressure and after that the density of composite decreased, which can be attributed to the increase in the level of porosity level and the amount of forming Al3Ti. The samples that hot pressed under cycle 5 and 6, showed the most volume fraction of in-situ phases on the matrix. The wear behavior of Al based composites reinforced with in situ Al3Ti particles has been investigated... 

Ferrofluids are special stable suspensions of magnetic nanoparticles dispersed in liquid phase. These materials have numerous biological applications such as drug delivery, magnetic hyperthermia and magnetic resonance imaging due to their special magnetic properties and fluidity. Particle size and magnetic properties of ferrofluids have an important role in these applications. In this work, magnetite-based ferrofluids have been synthesized via coprecipitation and hydrothermal methods. In the coprecipitation process, cysteine and dextran surfactants have been used as ferrofluid stabilizer and effect of synthesize temperature, time, pH and surfactant concentration have been investigated on... 

In the present research, a novel method for the fabrication of Al/Al3 Ti-Al2O3 composites and nanocomposites based on the thermal degradation of the refectory ceramic “Aluminium Titanate (AT)” or Al2TiO5 by powder metallurgy route. This research encompasses some precise subsequent steps. At first stage, nanostructured aluminium titanate nanofibers and particles were synthesized via a citrate sol gel process in which citric acid was used as a chelating agent. At second step, the possible chemical reactions between Al and aluminium titanate were taken into consideration both in powder form and in bulk form. Thermal analysis results indicated that it is feasible to decompose aluminium titanate... 

Recently, preparation of biofunctionalized nanoparticles with specific magnetic properties has received great attention for medical imaging. Targeting magnetic nanoparticles with high signal in magnetic resonance imaging (MRI) could be a powerful tissue imaging and cellular tracking agent. Main purpose of this research is the synthesis of Mn3O4@polymer composite nanoparticles as a positive MRI contrast agent. Nanoparticles were prepared by modified microwavepolyol and precipitation method with average particle size of 18 and 3nm.Respectivelythe effect of diffrent parameters such as time, surfactant and the presence of water in polyol method and the amount ofpolyethylene glycol as surfactant... 

In the present study, a simple synthesis route was used to obtain Titanium dioxide nanoparticles with aggregates different in size. The purpose was to study the effect of TiO2 nanoparticles size on photocatalytic activity and develop it to sonocatalytic properties. Surface modification with polymeric and/or anionic agents were carried out to stabilize titania nanoparticles in aqueous media with neutral pH, specifically in SBF. Sonocatalytic properties of modified and bare particles were compared to show if the particles may be used in future studies on sonodynamic therapy. Results showed that increment in size of the aggregates, similar to primary particles, lead to lower properties due to... 

Age-related macular degeneration (AMD) is the most common cause of vision loss in those aged over 50. There are two main types of AMD, Wet and Dry form. Wet AMD is more severe though more treatable. There are three conventional treatments for AMD including laser therapy, surgery and intravitreal injection of anti-VEGF into the eye. Delivery of drugs to the posterior segment of the eye is still challenging and several implants and devices are currently under investigation for their ability to stimulate the retina, producing visual percepts. The application of intravitreal bevacizumab (Avastin) has expanded tremendously from the time of its introduction into ophthalmic care since 3 years ago....