In the current research, thermal CONDUCTIVITY of magnetite (Fe3O4) has been calculated using molecular dynamic simulation. The rNEMD Molecular Dynamics Method provided in the LMMPS package is used for the simulation of the thermal CONDUCTIVITY. The effects of magnetite layer size and temperature on the thermal CONDUCTIVITY have been investigated. The numerical results have been validated by experimental data. Results show that the thermal CONDUCTIVITY of magnetite can be predicted appropriately using Buckingham potential function. Moreover, Thermal CONDUCTIVITY of magnetite is shown to be a decreasing function of temperature. The obtained results provide a benchmark for magnetite ferrofluid heat transfer simulations, which has been extensively increased in recent years.

The present research work was aimed at developing conductive polymer-based composites in order to have a higher CONDUCTIVITY than the standard level of the Energy Institute of America. In this case, the composites can be applied to make electrodes. For this purpose, carbon clack particles, carbon nanotube and expanded graphite with different weight percentages (5%, 10%, 15%, 25%, and 35%) were added to the epoxy resin and the electrical CONDUCTIVITY of the samples was measured according to the four-point standard method. The average electrical CONDUCTIVITY threshold for carbon clack particles, carbon nanotube and expanded graphite was determined at 25, 10, and 15, respectively. Furthermore, the effect of different construction parameters such as the use of vacuum pumps and heating on the electrical CONDUCTIVITY of the composite samples was also investigated. The experiments revealed that the use of the vacuum pump increased the electrical CONDUCTIVITY by 10. 8%, 11. 4% and 9. 6% in carbon black, carbon nanotube, and expanded graphite samples, respectively. In order to increase the mechanical strength of the conductive polymer samples, ten layers of unidirectional carbon fabric were used. The results obtained showed that the use of carbon fibers enhanced the electrical CONDUCTIVITY by 23. 2%, 27. 3%, and 24. 7% for carbon black, expanded graphite, and carbon nanotube samples, respectively. Ultimately, using the scanned electron microscopy images, the quality of the nanoparticle distribution in the samples was investigated.

Hydraulic CONDUCTIVITY is one of the soil"s dynamic properties, which plays a major role in water flow and salts transport within the soil. A saturated hydraulic CONDUCTIVITY value is needed for drainage projects design, which is almost constant. Different methods can be used in determining insitu hydraulic CONDUCTIVITY and they can be divided into two groups, e.g. above and below water table methods. Preliminary investigations showed that there was a significant difference between the results of these methods. The objectives of this study were 1) to investigate and compare the hydraulic CONDUCTIVITY values obtained using the above-mentioned methods in Iran and other countries; 2) to find the reasons of differences between the results of these two methods; and 3) to present practical solutions to minimize these differences. Generally, the results obtained by the above water table method were lower than those of under water table one. Based on the results of this research, values of under water table method were 0.5 to 32 times bigger than those of the above water table method. The reason for such a difference can be explained by various factors, e.g. water quality, the collapse of well walls, trapped air bubbles within soil pore, and the difference in flow patterns. Lower values obtained by the above water table method compare with under water table one may indicate that the saturated hydraulic CONDUCTIVITY cannot be accurately determined using the above water table method. Therefore, the results of this kind of method need to be closer to those of under water table one. In this regard, the suitable methods can be ranked as following: Natural model method, field model method, geostatitical method, Macnill method and correlation between texture and structure method.

Direct measurement of soil unsaturated hydraulic CONDUCTIVITY (K (h) or K (q)) is difficult and time-consuming, and often in many applied models, predicting hydraulic CONDUCTIVITY is carried out according to measurements of soil retention curve and saturated hydraulic CONDUCTIVITY (Ks). However, using KS as a matching point in many procedures may result in over-estimation of unsaturated hydraulic CONDUCTIVITY in dry regions. Therefore, the unsaturated hydraulic CONDUCTIVITY at inflection point of retention curve (Ki) and Ks was used as a matching point to predict K (h). For measurement of K (h), 30 soil samples were collected based on variety of soil texture (8 texture classes from sandy to clay) and other chemical and physical properties. In addition to Ks, K (q) values of undisturbed samples were measured using multi-step outflow method at matric suctions of 0.1, 0.2, 0.3, 0.5 0.7, 1 bar and inflection point of retention curve by using hanging water column and pressure plate. Then, the measured K (h), and water diffusivity (D (q)) values were compared to the predicted values of van Genuchten and Brooks and Corey models (with Mualem and Burdine constraint). The results showed that for 80% of the samples, the van Genuchten-Mualem model with Ki was the best model for predicting K (h) (i.e. using Ki as a matching point in the van Genuchten-Mualem model resulted in best fitting to measured data). Also, in 6.7% of samples (two sandy clay samples), Brooks and Corey-Mualem model with Ki and in 13.3% soil samples (2 silty clay and 2 silty clay loam samples), van Genouchten-Mualem model had a best fitting to K (h) measured data. Furthermore, in 20% samples (4 clay loam, and 2 silt loam textures), the accuracy and efficiency of van Genuchten-Mualem with Ki and van Genuchten-Mualem models in predicting K (h) were almost similar. According to t-Student test, the mean of RMSE and GSDER of van Genuchten-Mualem model with Ki was significantly less than van Genuchten-Mualem model at P<0.01. In 90 percent of samples, van Genuchten-Mualem and Brooks and Corey-Burdine theory had the best fitting to the measured data of water diffusivity, but in some cases van Genuchten-Burdine model with Ki was the best model for predicting D(q).

In this research, Graphene was synthesized by chemical vapor deposition (CVD) method in atmosphere pressure (14.7 psi). Different functionalization method was used for oxidizing of graphene such as acid and alkaline treatments. The Functionalized graphene (FG) was characterized by FTIR and Raman spectroscopy. Nanofluid with water and different concentration (0.05, 0.15 and 0.25 wt %) of FG were prepared. Thermal CONDUCTIVITY of nanofluids was measured by transient hot wire method. The acid functionalization introduces significant defects in graphene structure, degrading its unique properties such as superior carrier mobility, mechanical strength and chemical stability. In alkali functionalization method, the graphene is not effectively defected. Therefore, the transport properties of graphene maintained and this method showed enhancement in thermal CONDUCTIVITY more than acid fictionalization in same conditions. In optimum condition (0.25 wt % graphene of alkaline method in water), thermal CONDUCTIVITY ratio were increased (24.4% at 20oC and 33.9% at 60oC).

The growth processes of Tetragonal single crystals of solid solution (Cd0. 6Zn0. 32Mn0. 08)3As2, space group P42/nmc, has been synthesized by Bridgman method. CONDUCTIVITY and magnetoresistance of (Cd0. 6Zn0. 32Mn0. 08)3As2 were measured in the range 1. 6K to 300K and in magnetic field up to 25 T. Crossover from Mott variable-range-hopping CONDUCTIVITY mechanism close to helium temperatures. In this work, we found the width of the coulomb D = 0. 21 meV and a rigid gap δ = 0. 026 meV in the density of localized states, concentration and localization radius of charge carriers.

We report details of calculation of the lattice thermal CONDUCTIVITY in wurtzite GaN in the wide temperature range of 5-300 K. Our analysis shows that on the basis of the Debye specific heat model, this material has a characteristic temperature of 616 K. This quantity affects the probability of phonon-phonon umklapp (u) scattering process at temperatures above 150 K. At lower temperatures, dislocations and ionised impurities becoming the dominant mechanisms for phonons scattering, respectively. Although the peak CONDUCTIVITY (kmax) in a sample reported by Jezowski et al [9] has the highest reported value (17 W.cm-1K-1), it is expected that by reduction both in the density of dislocations and ionised impurities by an amount of one order of magnitude this peak value will be increased by a factor of 10.

A simple equivalent circuit to explain the electrical response of an ionic conductor is a parallel circuit consisting of an electrical resistance and a capacitor. Impedance semicircle of such a circuit is exactly a semicircle, but the impedance semicircle of experimental data is a depressed one. To explain this deformed shape of semicircle, usually CPE (constant phase element) is used in equivalent circuit instead of the capacitor. There are just a few theoretical researches about this element, which explain the deformed shape by fractals based on the surface roughness. The present work investigated the surface roughness and rejected its influence on the shape of impedance semicircle by using experimental data. An equivalent circuit is offered for ionic conductors based on the CMR “Concept of Mismatch and Relaxation” model.