Sharif Digital Repository

Nanodiamond (ND)/polylactic acid (PLA) nanocomposites have the potential for biomedical applications and bone tissue engineering. In this research, nanodiamond/poly lactic acid nanocomposites were prepared by mechanical mixing solution method and applying ultrasonication. Also, PLA-based nanofiber scaffold reinforced by nanodiamond were prepared by electrospinning methods. To find the optimum value of parameters to prepare this nanocomposite sample, the effect of nanofiller concentration, mixing rate and duration, the role of solute and ultrasonication, and solvent evaporation conditions were investigated and then it compared to the neat polylactic acid sample. By means of Fourier transform... 

Polymeric membranes based on polyaniline and PVDF were prepared by using cast-solvent film method. The effects of various parameters including polyaniline synthesis temparature, thickness of the PANI/PVDF films and feed pressure were investigated. The results obtained from exprimental data showed increasing permeability with reducing the thickness of the film and increasing feed pressure. Increasing polyaniline synthesis temprature increased the permeability of PANI/PVDF films. Reducing the films thikcness and increasing the feed pressure decreased the selectivity of films for the , and . The results showed increasing selectivity for PANI/PVDF films by using PANI produced at 10°C.... 

Semi-crystalline polylactic acid (PLA) and amorphous polymethyl methacrylate can form a soluble and miscible alloy in which the crystalline regions in the polylactic acid act as the fixed and immutable region and amorphous regions of the two polymers act as the changeable region. The two polymers can form a lattice structure with physical connections having shape-memory. So that the deformed polymer returns to its original shape above a certain temperature. These materials are used in sensors, smart materials, and medicine. On the other hand, Polyethylene glycol (PEG) is compatible with polylactic acid (PLA) and it seems that adding it will increase the ductility of polylactic acid (PLA). In... 

PVDF (polyvinylidene fluoride) magnetic nanocomposite films were prepared by solution casting using two types of nanomagnetic particles: (i) magnetic nanoparticles synthesized by using an alkaline solution of mixed ferrous/ferric salts along with oleic acid as a coating agent at 70˚C; (ii) Fe3O4 nanoparticles prepared by hydrolysis of aqueous solution of ferrous/ferric salts with potassium hydroxide at room temprature. Scanning electron microscopy (SEM) showed that the PVDF magnetic nanocomposite had a porous structure with Fe3O4 nanoparticles dispersed inside the porous polymer matrix. The presence of crystalline magnetite within the polymer matrix was confirmed by X-Ray diffraction method... 

Polylactic acid (PLA) nanocomposite films reinforced with surface-modified carbon nanotube (CNT) particles were prepared by solution-phase methods. In order to enhance the flexibility of the film, and to improve nanoparticle dispersion throughout the final material, polyvinyl acetate (PVA) was also added to the polymeric backbone during the nanocomposite preparation process. Characteristics of the former nanocomposite films were investigated by Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR) Spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), mechanical testing, and electrical resistance measurement. In this study, our results showed that increasing... 

Nanocomposites of PLA/Ag, PLA/PEG/Ag and PLA/PEG/Oleic acid were synthesized via chemical reduction of AgNO3.The formation of nano-silver particles (Ag-NPs) started in the aqueous phase (using NaBH4 as a reducing agent) followed by transfer of the silver nanoparticles into the organic phase (PLA solution in chloroform) due to the presence of van der waals interactions between the hydroxyl groups of the PLA and the particles charges surrounded in the surface of the Ag-NPs. The nanocomposites films were prepared by the solution casting method. The XRD patterns and UV-Vis spectra of the nanocomposites demonstrated face–centered cubic (fcc) silver crystals and spherical nanoparticles... 

Oxygen barrier properties of poly (lactic acid) (PLA) films were improved by blending it with hydrolyzed poly (vinyl acetate). Poly (vinyl acetate-co-vinyl alcohol) with vinyl alcohol contents of 0, 5, 10 and 15% was prepared using acid-catalyzed hydrolysis of poly (vinyl acetate). The Blend films of PLA/poly (VAc-co-VA) containing 0, 5, 10 and 15% of the copolymer with various degree of hydrolysis was prepared by solution-casting method. Effect of gamma irradiation on the films was examined by exposing them to radiation doses of 0, 20, 35 and 50 kGy. The films remained colorless and transparent after irradiation. Morphology of the samples characterized by optical microscopy displayed not... 

Poly (vinylidene Fluoride) (PVDF)/organoclay nanocomposite films were prepared via melt mixing, solution casting and Co-precipitation techniques. The effects of different kinds of nanoclay, sample preparation techniques and electron beam irradiation on PVDF/Nanoclay nanocomposite are reported in this research project. Differential scanning calorimetry was used to study thermal properties and crystallinity of the PVDF and its nanocomposites. The chemical and crystalline structure of the samples was analysed by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) and the mechanical properties of the PVDF nanocomposite were characterized by stress strain test. The degree of... 

Biocompatible porous polymeric scaffolds provide a suitable 3-D environment for proliferation of stem cells in human body. For instance, growth and proliferation concurrent with differentiation of stem cells in such scaffolds can regenerate the tissues or organs. In this attitude we fabricated a porous Gelatin-based scaffold using both of freeze-drying and freeze-extraction methods.Also, effect fo gamma irradiation on microstructure of scaffolds was investigated. In addition, poly(ethylene glycol) was employed to make the scaffold softer. Moreover, effects of various parameters including freezing temperature, cross-linking agent concentration, gelatin and PEG concentrations and their... 

The present work investigates a novel approach for improving the oxygen-barrier property of PLA-based film using vinyl acetate-vinyl alcohol copolymer [Poly(VAc-co-VA)] and the nanoclay Nanolin DK4. The permeability, thermal and mechanical properties are studied. To synthesize poly(VAc-co-VA), the hydrolysis of PVAc was done. The nanocomposite blend of PLA/Poly(VAc-co-VA)/Nanolin DK4 was prepared by the solution casting method. The prepared nanocomposite films were optically transparent regardless of poly(Vac-co-VA) and Nanolin DK4 concentrations. The gamma irradiated Poly(VAc-co-VA) was incorporated in the PLA films to probe the effect of cross-linked copolymer on the permeability of the... 

Multiwall carbon nanotubes (MWCNTs) and carbon black (CB) reinforced polypropylene/polyamide6 (75/25) nanocomposites were prepared by melt compounding approach. Polypropylene grafted with maleic anhydride (PP-g-MA) was used as compatibilizer. Different amount of fillers were introduced into the polymer blends. The morphology, mechanical, rheological properties and crystallization behavior of the composites were investigated. Scanning electron microscopy was employed to study the microstructure. Differential scanning calorimetry (DSC) results showed that the addition of MWNT or CB to PP/PA6 blend resultes increase in crystallinity degree of PA6. The fillers were found to be located... 

Gas hydrates are ice-like clathrate compounds. Methane and carbon dioxide can form gas hydrate and plug pipelines, in order to preventing of gas hydrate formation, inhibitors like salts and alcohols are added to the natural gas pipelines. In this work a molecular thermodynamic model based on statistical mechanics, is employed to predict the hydrate formation conditions for carbon dioxide and methane in the presence of aqueous ionic liquid solutions. The statistical model of Van der Waals and Platteeuw mixed with Holder model is employed for hydrate phase. An equation of state applicable to the systems containing electrolyte developed by coupling the statistical associating fluid theory... 

The notable share of housing sector in GDP (approximately five percent) shows this sector’s relation with macroeconomic activities. On the other hand, House as an asset leads housing sector to be affected by monetary and fiscal variables. A dynamic panel data was used in this study to evaluate the relations between housing sector and some macroeconomic variables in metropolises of Iran. As results show, in long term growth of liquidity, GDP per capita and sharp ratio have positive effects, and land per capita has negative effect on housing price in metropolises of Iran. Price increases have not been equal in different cities. Inequality of land price between metropolises and between... 

In this research, an Index of Iran informal economy in response to the government interventions in credit, labor and product markets is stimated by EMIMIC model. To do this, first these interventions are measured using principal components analysis. In the model, the variables GDP and employment are used as indicators and taxation rates, government distortions in credit, labor and product markets, government expenditure, per capita income, unemployment and inflation as causes of the informal economy. We conclude these government interventions have affected Iran informal economy and their influence is more than indirect interventions influence such as taxation. The estimated index of Iran... 

With altering natural state and increasing impervious surfaces, traditional urbanization leads to deteriorating the environment and water catchments. During the years most efforts in order to control the urban runoff outflow, have been focused on quantity; and awareness about improving water quality has been raised just in the last few years and, which emphasizes on pollution source control. Standard water quality sampling methods are time consuming, expensive and because of sampling in broad geographic areas, difficult; however modeling is a more efficient way in assessing water quality and as worries about non-point source pollution grows, different kinds of models have been used to... 

The role of government in economy has been a controversial subject in economics. Lately, there has been some fundamental change in evaluating this subject. One could mention two of these as 1) realizing the importance of micro-founded macro model for evaluating policy, and 2) taking into consideration the rent-seeking behavior of politicians. In this research, a general equilibrium in a micro-founded macro model will be discussed and then in political economics framework, the effect of government on this equilibrium will be investigated. Only the redistribution role of government has been considered. First, the model in which a benevolent government is seeking optimal policy is Discussed.... 

Gini coefficient is the most prevalent index for the measurement of inequality and is usually extracted by means of nominal variables based on income or expenditures of households. In this study we have extracted more accurate Gini coefficients. By using the raw data of Households Budget Survey (HBS) and STATA software, a special CPI for each household of the sample is extracted. Subsequently nominal expenditures are deflated by these special CPIs, and at last, Gini coefficients are extracted from real expenditures. Our findings indicate that in recent years, extracted Gini coefficients are remarkably higher than prevailing ones.
 

This paper investigates the behavior of the Y-shaped bracing system. Because of the special type of eccentricity in this system, the behavior of the frame is strongly dependent on the geometrical changes of the braces. So that even in the elastic region, it shows the geometrically nonlinear behavior. The amount of eccentricity is very effective on the nonlinear behavior of the frame. Also the ratio of cross sections of the bracing members has a very important impact on the expected performance of the frame. The results show that this system tolerates large displacements, and can act like a base isolation system. Firstly, using a two-dimensional accurate modeling related to the geometrical... 

The Overstrength, Ductility and the Response Modification Factor (R) for 70 steel X-braced , Inverted-V-Braced and Offcenter Bracing System frames were evaluated by performing pushover analysis of model structure with various stories (3,6,9,12&15 story) and span length (4,6&8 meter). Some result were compared with those from nonlinear dynamic analysis. According to the analysis result the R factors obtained from nonlinear dynamic analysis are 15% more than obtained from pushover analysis and R factors computed from pushover analysis were generally smaller than the values given in the design codes. R factors in Irregular structure in height are about 90% of R values in regular structure in... 

Maghemite (γ-Fe2O3) nanoparticles were produced after high temperature oxidation of gelatin-Fe3O4 nanocomposite, obtained from a common coprecipitation process of Fe2+ and Fe3+ ions in an alkaline medium in the presence of a gelatin protein as an effective mediator. Size, shape, surface morphology and magnetic properties of the prepared γ-Fe2O3 nanoparticles were characterized using XRD, FTIR, TEM, SEM and VSM data. The results revealed that primary, gelatin-Fe3O4 nanocomposite had been formed and next, the gelatin decomposition in furnace produced a spinel structure of γ-Fe2O3. The effects of furnace temperature and time of heating together with the amount of gelatin on the produced...