HETEROGENEOUS POLYMERIZATION OF METHYL METHACRYLATE AT LOW TEMPERATURE IN DISPERSED SYSTEMS

ABSTRACT Title of thesis HETEROGENEOUS POLYMERIZATION OF METHYL METHACRYLATE AT LOW TEMPERATURE IN DISPERSED SYSTEMS Laleh Emdadi, Master of Science, 2011 Directed by: Professor, Dr. Kyu Yong Choi, Chemical and Biomolecular Engineering Department Dispersion polymerization is a unique method to prepare monodisperse polymer particles of 1-10 µm in a single step process. This process is usually carried out at high temperatures that are not cost effective and suitable for special applications such as encapsulation of bio materials. Production of uniform polymer particles at low temperatures via dispersion polymerization has not been studied widely yet. In this research, dispersion polymerization of methyl methacrylate (MMA) in a nonpolar solvent, n-hexane, using N,N-dimethylaniline (DMA) and lauroyl peroxide (LPO) as redox initiators at low temperature has been studied. The evolutions of monomer conversion, polymer molecular weight distribution (MWD), and particle morphology were determined. Under specific reaction conditions, monodisperse micron-sized polymer particles were produced. The same technique was applied in the confined reaction space of a monomer droplet. Using this new process, called micro dispersive suspension polymerization, polymer particles with different internal morphologies produced with various potential applications

Carbon Dots Dye-Sensitized Solar Cells Application

Carbon dots (CDs) are a series of non-dimensional carbon-based little particles, endowed with great photoluminescence, water- dissolved, good bio adaptability, and small toxicity. Carbon dots (CDs) are a unique class of fluorescent Nano materials, whose emissions can be tuned by manipulating the reaction conditions of their formation. Moreover, CDs act a significant duty in the transfer of electrons. On the one hand, the appropriate energy band value of CDs assists the charge segregation and transfer after the carbon point is excited. In addition, carbon dots depict explicit electrical conductivities analogous to graphene. An excellent utilization amount of fossil vigor has led to the crisis of energy as well as the surroundings. Thus, it is an immediate duty to research renewable scavenging energy to dissolve these issues. In this paper, I’ve strived to classify the application of carbon dots in dye-sensitized solar cells in recent years and explained the mechanisms of improving the performance of carbon dots. Among them, solar energy is reliable to be the most promising renewable energy resource due to its fascinating properties such as being inexhaustible and environmentally friendly. The growth of solar cells is already in the third stage, and investigation focuses contain dye-sensitized solar cells. Dye-sensitized solar cells make use of a similar sense, and light to electric power transformation efficiencies above 10% have been reached with DSCs

Some types of Solar Cells and their characters

A solar cell is a type of electronic device that directly converts solar energy from light into electricity. A current and a voltage are produced by the sun's light shining on the solar cell to produce electrical vigor. This process requires a material that, when exposed to light, elevates an electron's energy level in the first stage. Additionally, in the second stage, this stronger electron is transferred from the solar cell to an external circuit. As a result, the electron loses energy in the outside circuit before returning to the solar cell. The requirements for photovoltaic energy conversion can potentially be met by a variety of materials and techniques. Although not strictly speaking, nearly all photovoltaic energy conversion uses semiconductor materials in the form of a p-n link. Taking into account the increase in tolerable vigor. Solar energy is the best example to use to show this. We will examine the many types of solar cells and their characteristics in this essay

Influence of replacing fish meal with soybean meal on growth rate, feed conversion ratio and chemical composition of carcass, fillet and liver in juvenile stellate sturgeon (Acipenser stellatus)

This study was conducted to determine the effect of replacing fish meal with soybean meal on growth rate, feed conversion ratio and chemical composition of carcass, fillet and liver in juvenile stellate sturgeon (Acipenser stellatus). As in Treatments one (F), two (S1), three (S2), four (S3) and five (S4) 0, 10, 20, 30 and 40 percent of fish meal was replaced with soybean meal, respectively. Five isonitrogenous and isocaloric diets formulated containing 44 percent crude proteins and 4374 Kcal gross energy kg-1 diet. Individual body weights of fish were measured every three week. Fish were sampled randomly from each treatment for whole body, fillet and liver proximate analysis. Based on the results, weight gain (WG) and feed conversion ratio (FCR) had significant difference among the treatments (P0.05). Significant differences were found in fillet lipid content (P0.05). Liver proximate composition of fish did not significant difference (P>0.05)

Study of Droplet Impact on a Wall using a Sharp Interface Method and Different Contact Line Models

In this research, droplet impact on a surface is simulated by using a sharp method for interface modeling. The level-set method along with the ghost fluid method is used to model interface in a sharp fashion. Different contact line models are compared and evaluated at both low and high impact velocities. On a hydrophobic surface, dynamic models developed by Hoffman and Jiang represent a more accurate prediction of droplet behavior during the impact process than the static and molecular kinetic dynamic models, especially at rebounding stage. At lower impact velocities, the Hoffman’s model represents better predictions. However, at higher impact velocities, the Jiang’s model is somewhat more accurate. The molecular dynamic model is not appropriate for high impact velocities. On a hydrophilic surface, at low impact velocities, the Jiang’s model represents satisfactory results, whereas the static and the Hoffman’s models cannot produce accurate results, after initial stages of the impact process. At high impact velocities, the static model shows considerable deviation from the experimental results. The effect of the contact angle on the dynamic behavior of the droplet is investigated. At contact angles lower than 900, the droplet only spreads on the surface after impact. However, at contact angles higher than 900, the droplet starts to recoil after spreading. In this case, it is possible that droplet rebounds from surface after recoiling. Maximum spreading radius of the droplet decreases by an increase in contact angle. At higher contact angles, less time is needed for the droplet to rebound from surface

Wavelet based Adaptive RBF Method for Nearly Singular Poisson-Type Problems on Irregular Domains

We present a wavelet based adaptive scheme and investigate the efficiency of this scheme for solving nearly singular potential PDEs over irregularly shaped domains. For a problem defined over Ω ∈ ℜd, the boundary of an irregularly shaped domain, Γ, is defined as a boundary curve that is a product of a Heaviside function along the normal direction and a piecewise continuous tangential curve. The link between the original wavelet based adaptive method presented in Libre, Emdadi, Kansa, Shekarchi, and Rahimian (2008, 2009) or LEKSR method and the generalized one is given through the use of simple Heaviside masking procedure. In addition level dependent thresholding were introduced to improve the efficiency and convergence rate of the solution. We will show how the generalized wavelet based adaptive method can be applied for detecting nearly singularities in Poisson type PDEs over irregular domains. The numerical examples have illustrated that the proposed method is powerful to analyze the Poisson type PDEs with rapid changes in gradients and nearly singularities

Stable PDE Solution Methods for Large Multiquadric Shape Parameters

We present a new method based upon the paper of Volokh and Vilney (2000) that produces highly accurate and stable solutions to very ill-conditioned multiquadric (MQ) radial basis function (RBF) asymmetric collocation methods for partial differential equations (PDEs). We demonstrate that the modified Volokh-Vilney algorithm that we name the improved truncated singular value decomposition (IT-SVD) produces highly accurate and stable numerical solutions for large values of a constant MQ shape parameter, c, that exceeds the critical value of c based upon Gaussian elimination

Prevalence of vitamin d deficiency amongwomen of reproductive age: A multi centric study in tehran

Background and Objectives: The aim of this study was to determine the prevalence of vitaminDdeficiency among Iranianwomenof reproductive age. Methods: In this multicentric cross-sectional study, 300 women aged 15 - 45 years referring to Tehran branch of Islamic Azad university hospitals from 2013 to 2015 were recruited. The collected data included the demographic characteristics of the participants, including age, body mass index (BMI), parity, and serum level of vitamin D. Serum levels of 25-dihydroxy vitamin D were measured by radioimmunoassay. Vitamin D was defined as deficient < 20 nmol/L, mild 25 nmol/L, moderate 12.5 - 25 nmol/L and severe12.5 nmol/L. Statistical analysis was performed, using Excel software. Results: Amongthe300patients, 257 caseshadvitaminDdeficiency;amongwhom,122 caseshadsevere, 96hadmoderateand38hadmild deficiency. Conclusions: According to the results of this study, only 14.8 of the study population had normal serum vitamin D levels, indicating that the majority of Iranian women in the reproductive age have vitamin D deficiency. © 2016, Shiraz University of Medical Sciences

A Fast Adaptive Wavelet Scheme in RBF Collocation for Nearly Singular Potential PDEs

We present a wavelet based adaptive scheme and investigate the efficiency of this scheme for solving nearly singular potential PDEs. Multiresolution wavelet analysis (MRWA) provides a firm mathematical foundation by projecting the solution of PDE onto a nested sequence of approximation spaces. The wavelet coefficients then were used as an estimation of the sensible regions for node adaptation. The proposed adaptation scheme requires negligible calculation time due to the existence of the fast DiscreteWavelet Transform (DWT). Certain aspects of the proposed adaptive scheme are discussed through numerical examples. It has been shown that the proposed adaptive scheme can detect the singularities both in the domain and near the boundaries. Moreover, the proposed adaptive scheme can be utilized for capturing the regions with high gradient both in the solution and its spatial derivatives. Due to the simplicity of the proposed method, it can be efficiently applied to large scale nearly singular engineering problems