Sharif Digital Repository

polyamides have found great attractions in wide variety of applications due to their desirable mechanical and tribological properties and appropriate processability. Pure polymers are not suitable for this kind of application due to their low mechanical strength. High strength materials are needed for abrasive applications. Polytetrafluoroethylene (PTFE) is one of the most popular materials for abrasive applications. In this study the effect of PTFE and surface modification on PA/PTFE composite properties is investigated. duo to modification of PTFE powder, PTFE is exposed to sodium naphtalenide (Na/naphtha) etchant so as to deflurinate the surface for obtaining carbonyl, carboxyl and... 

Polyamides have found great attraction in the wide variety of application due to their desireable and tribological properties and appropriate processability. Due to their low mechanical strength reinforcing of these types of polymers has always been one of the important academic and industrial issues. In order to improve mechanical properties of such polymers, different kinds of reinforcement particles such as titaniom diaoxide, Nano clay, glass fibers (Short or long glass fiber), etc were used. Carbon nano tubes have high thermal and electrical conduction and mechanical properties; they are widely used as a reinforcement particle for polymer matrix. In this study, carbon nano tube and... 

In recent years the rapid rise of polymer consumption especially in the form of packaging materials became a real menace for the environment. Polyolefin are some of the most dominant packaging materials and responsible by part of the problems in the disposal of one-trip packaging. One of the possible ways of solving this problem is the introduction of additives increasing their susceptibility to environmental degradation into non-biodegradable polymers. One such additive is starch- the natural, cheap, and easily biodegradable polymer. Starch was already used as a filler or as a blend with polyolefin. Addition of dry starch granules to polyolefin follows the general trend of filler effects on... 

Plasma electrolytic oxidation (PEO) is currently recognized as an effective coating method on active metals such as magnesium. In this method, through occurrence of strong electric discharges on the surface of the anode accompanied by electrochemical and thermo-chemical reactions at plasma environment, a relatively thick ceramic coating with complex compounds grows on the metal surface which significantly improves its properties. Regarding the influence of PEO electrical parameters on the morphology and other properties of the coating, the objective of the present study is to prepare a quality ceramic coating on AZ31 magnesium alloy substrate via setting the process parameters, such as... 

Different types of morphologies and phase structures of crystalline TiO2 were synthesized by hydrothermal methods. For the first time, dandelion-like rutile TiO2 powder composed of numerous single crystalline nanorods was synthesized using TiCl4 as the main precursor. TiO2 Nanoparticles were produced using TTIP and 2-propanol, as precursor and solvent, respectively. Field emission scanning electron microscopy analyses revealed that the synthesized TiO2 nanoparticles had average crystallite size in the range 21–70 nm, whereas dandelion-like TiO2 showed diameter in the range 2-10 µm. According to the significant refractive index of TiO2, in particular rutile phase, it can be used in the... 

Considering the tremendous development in imaging systems’ industry, today we can afford to have imaging equipment, capable of taking multispectral images in very high resolution. One of the remarkable benefits of this technology is in the realm of arts and particularly in museums. Taking advantage of the potentials of multispectral, highquality imaging, curators will be able to probe their priceless works of art ( e.g. paintings ) without putting them in danger through invasive research. Besides, one can investigate and control the transformation of these works through time by using this new imaging method. Recently, Multispectral Imaging of paintings, in different frequency bands from... 

Improvement of semiconductors photocatalytic activity by different means has always been one of the challenges for researchers. Semiconductors doping for band-gap engineering and changing morphology to increase specific surface area and photocatalytic reaction sites are amongst these efforts. In this research simultaneous effect of these two parameters for three morphologies containing nanoparticle, nanowire and micro dandelion, simultaneously doped with carbon and nitrogen has been investigated. Final purpose of this thesis is to decrease the band-gap energy close to soft UV photon energies to make surface photodynamic therapy possible. Nanoparticle morphology with size distribution between... 

The increasing role of nanotechnology in our every-day-life, has aroused global concern regarding their hazardous potential, resulting in a demand for parallel risk assessment. Quatitative structure-activity relationships enable researches to use unique properties of nanoparticles as predictors for their toxicity or any other biological response. Extracting rational correlations between physicochemical properties of nanoparticles and their biological response, not only reveals the way that nanoparticles behave upon entering into biological media, but also leads to the design of safer and efficient nanoparticles for various applications of interest. This PhD dissertation presents QSAR tools... 

Enhancement of photocatalytic characteristics of semiconductors have been always a challenge for the researchers. Doping semiconductors for adjusting their energy gap and changing their morphology in order to increase their effective surface area and reaction sites are examples of their endeavor to overcome the challenge. In this research, nanostructured Aluminum Titanate powder was synthesized with Sol-Gel process and by altering synthesis parameters, the best synthesis condition to get the best possible band gap was discovered. Moreover, we examined the photocatalytic properties of the recently developed material “tialite”, which were not studied before and also evaluated the effect... 

Human brain is one the most efficient biological neural network that is capable of performing most complicated tasks in very short time. Visual system as a part of the brain can process the visual records from the environment and perform very useful processes on them. The information provided from visual system processes play important roles in human intelligence. In this thesis we introduce and investigate one of the well-known theories about visual system called gestalt theories. These theories tried to define how a biological neural network can perform such results. Gestalt theorists developed rules of perception to explain their ideas including Law of Pragnanz, Similarity, Closure,... 

In this thesis, the theoretical foundation, the way of implementation and the uses of Pars Morph, a Persian morphological analyzer is introduced. Pars Morph is a rule-based Persian morphological analysis system, which analyzes the internal structure of word in Persian and determines the grammatical category and function of the word parts. Pars Morph being in link with a lexicon covering about 45000 lexemes and based on morphological rules in Persian can analyze the structure of complex lexemes and their possible inflected forms and even out-of-lexicon words.
Accuracy rate of the first version of Pars Morph is about 95% which could be enhanced to 100% by applying the regulations on... 

Vibration is one of the most important factors in design, operation and lifetime of drill strings. There for, investigation of vibrations in drill string, like every other rotary machine, is very important. The main goal of this research is developing a nonlinear model for a drill string system dynamics in an inclined well. Effects of drilling mud flow rate, weight on bit, angular velocity along with viscous damping, on the stability and vibration of a drill string are studied. Dynamic equation of the model is developed considering axial displacement and lateral bending geometric nonlinear coupling. The effect of drilling mud flow is modeled using Paidoussis formulations. Equation of motion... 

In this work two shapes of silver nanostructures including silver nanowires and silver nanocubeswere synthesized by polyol method. Silver nanostructures were characterized by SEM, XRD and UV-Vis spectroscopy. Afterwards the morphology-dependent electrocatalyticperformance of these nanocrystals on the differential pulse behavior of naltrexone (NAL) was investigated. To this aim the differential pulse voltammetric behavior of NAL on a glassy carbon electrode modified with electrochemical deposited gold nanoparticles conjugated with different shapes of silver nanostructures and nafion was investigated. It was proved that silver nanowires show more effective electrocatalytic activity toward... 

The fascinating size-dependent properties of noble metal nanop articles have created a great promise for their use in a different applications specially chemical sensing. Gold nanorods (GNRs), specifically, have received a great deal of attention due to their unusual optical properties. The nanoscale confinement of electrons on the surface of gold nanorods grants them aspect ratio-dependent properties not seen in larger particles. Due to the intriguing properties of GNRs, significant work has gone into the application of nanorods for sensing and detection of various an alytes in biological and other systems. The major modalities which have been developed for... 

Syntheses of coats including nickel nano-particles by electrodeposition have been
investigated for over 10 years. A method of testing according to surface reply was chosen
to reveal the effect of each pulse parameters (including duty cycle, frequency, average
current density, off time (toff) and on time (ton)) and the effect of saccharin concentration
on electroplating cathode efficiency, nanostructure. Pulse electroplating test of nickel was
composed by 30 tests. Pulse electroplating with relatively high peak current density was
employed and saccharine was added to increase deposition and rate of nickel nucleation on
surface. According to the results of cathode... 

Drop deformation and breakup are of great importance in a wide variety of applications, from fuel combustion to agriculture, pharmaceutical processes, and coating. In this experimental study, droplet secondary bag breakup has been investigated. By conducting experiments on different fluids with a wide range of properties and in different conditions, the effects of different parameters on secondary bag breakup have been addressed. For this purpose, the breakup of these fluids, water, ethanol, glycerin, and SDS solution were scrutinized and by comparing their trajectory and morphological parameters, results are driven. Experimental conditions were such that the Weber number are from 11 to 17... 

Machine translation has been an important subject in the field of natural language processing (NLP). In recent years, because of providing essential linguistic data resources, statistical approached have been deployed in machine translation. Although there have been several attempt to create English to Persian automatic translator, there has not been sufficient effort in the reverse direction. In this project, we reviewed previous works in machine translator for Persian and implemented a statistical machine translator from Persian to English. We needed a bilingual corpus for building the translator. For this purpose, we used a corpus of Phd and MSc abstracts in Persian and their translation... 

Bulk metallic glasses (BMGs), in contrast to conventional crystalline materials, are defined as metals with an amorphous and disordered atomic-scale structure. Due to the absence of dislocations and grain boundaries, BMGs have considerably unique mechanical properties such as high strength and elastic strain, high wear resistance and desirable corrosion resistance. However, they generally suffer from poor plasticity caused by an inhomogeneous deformation which leads to catastrophic failure by localization of strain into narrow regions, known as shear bands. This factor has extremely restricted their application as advanced structural materials. Furthermore, the recently discovered phenomenon... 

Silver nanopowder is of great importance for various medical and industrial applications. Due to the significance of the solubility of silver nanoparticles in these applications as well as the high impact of the nanophysical morphology of the powder on their solubility, we prepared nanoparticles with plate morphology by the chemical reduction of silver nitrate in a soluble phase. Then we measure its solubility in a phosphate buffer salt, which greatly resembles the human blood chemically. The size and shape of the resulting nanosilver powder and also the use of non-toxic materials in their synthesis are important factors in the production of nanosilver powder.We confirmed the successful... 

One of the most important factors affecting the performance of the vehicle's brake disc is its stiffening coefficient. To improve this feature, many researches have been carried out by leading automotive companies, whose scientific aspects have not yet been widely disseminated. Brake discs are often made of cast iron and are more likely to produce gray iron with type A graphite. However, according to available resources, factors such as graphite morphology, their length-to-thickness ratios, cast iron and heat treatment on the piece affect this important feature. One of the most important factors that make changes in the above mentioned cases is the chemical composition and freezing rate. In...