فهرست مطالب abolfazl khodadadi

In this study, the thermoelectric properties of (6, 0) two sided-closed single-walled boron nitride nanotube ((6, 0) TSC-SWBNNT) in the state without impurity and a single carbon atom impurity instead of boron and nitrogen atoms in the center, left and right The nanotube was investigated in the energy range of -5.5 to 5.5 eV and temperatures of 200, 300, 500, 700, 900, 1100 and 1300 K. The results show that, with the increase in temperature and the creation of impurity, the band gap is affected and becomes noticeably smaller. The highest decrease in band gap is at 1300 K. With increasing temperature, the number of peaks has decreased, which shows that the mobility of electrons and holes has increased and their localization has decreased. As the temperature increases, the height of the thermal conduction peaks increases. But in general, the thermal conduction values are in the range of 9-10 nanoscale. Merit coefficient (ZT) values have increased with the increase in temperature, and the highest values are related to the temperature of 1300 K. The high values of 1 for ZT especially at high temperatures indicates that (6, 0) TSC-SWBNNT are suitable for choosing as thermoelectric material.

In this research, MNPs were fabricated and coated by the co-precipitation method. The study of this process was performed in a two-level factorial design framework. The effect of a polymeric agent, the strength of the alkaline solution, and the temperature on the magnetic properties MNPs were studied in this design. the structure, morphology, size, appearance, and magnetic behavior of modified MNPs were investigated using XRD, FT-IR, TEM, and VSM. The results obtained from the spectra show the modified MNPs have superparamagnetic behavior with high saturation magnetization (𝑀𝑠) and small coercivity (𝐻𝑐). The mean size of coated MNPs was determined 10 nm, saturation magnetization 60.98 emu/g, and magnetic coercivity 8.26 G.

We have calculated the branching ratio of the non-resonant B→D^- π^+ π^+ π^- four body decay using a simple model based on the framework of the naïve factorization approach where one can ommit the nonfactorization effects. In naive factorization approach, according to the Feynman diagram, there are only two tree diagrams for this decay mode. In the first diagram, the matrix element of decay mode is factorized into a B→D form factor multiplied by a 3π decay constant and in the second diagram, the matrix element is factorized into a B→Dπ form factor multiplied by a 2π decay constant, According to the rest mass of the particles, we assume that in the rest frame of B meson, the D meson remains stationary, so we obtain the value (3.47±0.14)×10^(-3) for the branching ratio of the B→D^- π^+ π^+ π^- decay mode in naive factorization approach, while the experimental results is (3.9±1.9)×10^(-3).

Magnetic nanoparticles were synthesized and coated by the situ-coprecipitation method with FeCl3.6H2O and FeCl2.4H2O precursors in the presence of NH4OH (or NaOH) reduction and PEG coated agent. Preparation of modified magnetic nanoparticles were performed at two different temperatures under the influence of different alkaline media. The effect of strength of alkaline media and reaction temperature of the magnetic properties (Magnetic saturation, Magnetic remanent, coercive force (of modified MNPs were investigated. To study structure, morphology, optic and magnetic properties MNPs were characterized by XRD, FTIR, TEM and VSM analyzes.The results showed that modified magnetic nanoparticles have superparamagnetic properties and have high magnetic saturation and small coercive force, so the magnetic properties of the modified MNPs are depended to the strength of the alkaline remanent directly. The saturation magnetization of the synthesized sample in NH4OH and NaOH at 80° C was determined as 60.94 and 49.39 emu/g, respectively. Also increasing temperature, improves magnetic properties coated MNPs) at temperatures below the blocking temperature. (The results of the XRD analysis showed that the structure of the modified magnetic nanoparticles is inverted spinel and the size of the nanoparticles synthesized in the ammonia media is smaller than the other media. The results of FTIR optical analysis revealed that the peaks at ~570 and ~440 cm^(-1) indicates the bond Fe-O. TEM analysis indicated that the shape of the MNPs is pseudo-spherical. VSM analysis indicated that the magnetic nanoparticles synthesized in stronger alkaline media (ammonia) and high temperature showed better magnetic behavior by higher magnetic properties.

Iron oxide (Fe3O4) nanoparticles (NPs) are the most important group of magnetic nanoparticles. This study modifies iron oxide (Fe3O4) magnetic nanoparticles (MNPs) by polyethylene glycol (PEG) and polyvinyl alcohol (PVA) coating co-precipitation method. MNPs were characterized by XRD, FTIR, TEM, DLS, and VSM analyses to study their structure, morphology, and magnetic properties. The results showed the superior properties of PEG and PVA-coated Fe3O4 compared to the pristine sample. It is illustrated that modified Fe3O4 MNPs improved magnetic saturation. The particle size of PEG-coated Fe3O4 nanoparticles was estimated at 11 nm with magnetic saturation of 60.98 emu/g and coercivity of 8.26G.

This study doped alumina with iron impurities by co-precipitation and sol-gel methods compared with pure alumina. Precursors of aluminum and iron metal salts employ the surfactant and new stabilizers used for synthesizing samples. Several analysewere performed on different properties of the synthesized samples and the effect of iron impurities on them. The presence of different phases was confirmed in the XRD spectrum of nanoparticles made by co-precipitate method. As the percentage of impurities increases, the unstable and intermediate phases decrease and eventually tend to the stable phase of α-alumina, the resulting hexagonal structure is obtained. The FESEM spectra of samples synthesized by both methods showed that a decrease in particle size occurs with an increase in the percentage of impurities. TEM analysis of nanoparticles with 5% impurity shows the shape of the particles as quasi-spherical, about agglomerate. It is the reason for removing the stabilizing agent in the high-temperature heating process. Also, increasing the intermolecular gravitation force, the particles stick together in a lump. UV-DSR analysis showed that with increasing impurity percentage, the energy band gap decreases and the absorption wavelength  increases. In samples fabricated in both methods, the value of  obtained is close to each other. The VSM spectrum showed that ferromagnetic properties occur when iron enters alumina sites.

In this study, iron-doped alumina (Fe-Al2O3) nanoparticles (NPs) containing 2 mol%, 4 mol%, and 6 mol% iron impurities were fabricated by the co-precipitation method in the presence of Al2(SO4)3.9H2O and Fe2(SO4)3.9H2O precursors. The prepared nanoparticles were heated at 1000 oC to study their physicochemical properties. The XRD results pointed out the multiphase for the samples. The morphological results revealed that the uniformity increased by increasing iron atoms rate. TEM analysis revealed that the particle with a size of 40 nm was obtained for 4% of the sample. The results of FT-IR analysis indicated that when the 2% impurity increases the AlO4 tetrahedra and AlO6 octahedral vibrational bond grow.

As more people live in cities and urban areas, evaluation of urban environmental quality is nowadays an unavoidable necessity. Urbanization gives off heavy metals into urban soils and threatens the human health. In this study, urban soil samples were acquired from different locations (Public parks, streets, and squares) from Borujerd, Iran. The levels of Cd and Pb in the soils, along with soil pH, electrical conductivity (EC), and particle size distribution (texture), were analyzed. Kriging method by Surfer software was employed to create the spatial distribution maps of Cd, Pb, and geoaccumulation index (Igeo). The average Cd and Pb concentrations in the surface soil samples were 2.50±1.14, and 50.37±34.77 mg/kg dry weight, respectively. The highest mean concentration of Cd was found in street soils and as for Pb in square soils. The interpolation maps illustrated the same behavior for Cd and Pb with elevated concentrations located in the southeast. The mean values of geoaccumulation index (Igeo) showed that soils are moderately/strongly contaminated with Cd and moderately contaminated with Pb. In this study, traffic emission, textile industries and probably released untreated municipal wastewater into the soil are anthropogenic sources of Pb and Cd.