In river with non-regular cross sectional area or with turbulent flow, it is not possible to measure flow by usual methods. The tracing method is used in such circumstances.This method is applied in two ways: constant rate injection for small streams and slug injection for greater flows. These methods are based on tracer dilution in a stream. In this study a new equation is presented for discharge determination using constant rate injection in the laboratory and nonlinear regressions. Sodium chloride is used in this experiment as a tracer. This method is double-checked in the field.Experimental and field results confirm accuracy of the new equation.

This study explored the impact of solvent dielectric constant on the catalyst layer of proton exchange membrane fuel cell (PEMFC) cathodes during the oxygen reduction reaction. Electrochemical analyses were conducted at 25ºC in 2.0 M H2SO4 on electrodes that had been prepared with the same Nafion and Pt loadings, but different solvent dielectric constants for ink preparation of the catalyst layer. A Nafion loading of 0.5 mg cm-2 and Pt loading of 1 mg cm-2 were employed for all electrodes. The findings of the research revealed that the dielectric constant of the ink utilized for preparing the gas diffusion electrode reaction layer has an impact on the electrode's performance for the oxygen reduction reaction. This effect was evident in both the kinetics parameters linked to the oxygen reduction reaction and the physical characteristics of the electrode surface. In the preparation of the reaction layer, an optimal electrode performance result of 4.2 was achieved in relation to the dielectric constant.

In this study, the stability of trinitroglycerin (TNG) in polyethylene (PEG) 400 was investigated according to Arrhenius approach. The reaction rate constant (k) for the thermal disintegration of TNG in PEG 400 at various temperatures was counted based on the percents of remaining TNG at different intervals of time at a specific temperature. The results showed that “k” at 40, 50, 60, 70, 80 and 90 ºC were 6.5×10- 4, 3.57×1 0- 3, 4.7×1 0- 3, 3×1 0- 2, 6.2×10- 2 and 6.5×1 0- 2, respectively. By plotting “log k” against temperature (1/T), “k” was obtained at 5 and 20 oC which was 1.47×10- 5 and 7.94×10-5, respectively. The results showed the time required to attend 90, 80, 70, and 50 percent of the original TNG at 5 oC was 9.76, 20.7, 33, and 64.2 months, respectively. The results assist in the calculation of the expiration time of TNG/ PEG 400.

Magnetic resonance imaging (MRI) is a non-ionizing method for identification and evaluation of soft tissue lesions. Perfusion MRI evaluates soft tissues by measuring changes in magnetization of water molecules due to a contrast agent. To this end, concentration curves in the plasma and tissue are estimated by MRI and effective longitudinal relaxation time (T1eff) of the tissue was calculated. To interpret the results, the effects of water exchange on the effective longitudinal relaxation time should be studied. This work presents such a study in which the equations of two- and three-compartmental models of rat brain tissue are solved using Hion and Runge-Kutta numerical methods for different input functions and simulated by Monte Carlo method. Since the exchange of water and contrast agent among different tissue compartments is a diffusion phenomenon, Monte Carlo method is applicable. Results of the numerical methods were compared with those of Monte Carlo simulation. The results of the two methods were almost identical with a maximum relative difference of less than 1%. In this work, concentration of contrast agent in plasma is estimated from MRI of a rat brain tissue. This data is used in the Monte Carlo method to obtain T1eff and exchange rate constants. An advantage of our method is that T1eff is obtained from real data and not from the curve fitting method as commonly used. We derive concentration of contrast agent as a function of time in extravascular space for different constants (K). Then, the curves of simulated and real data were compared to obtain the exchange rate constant of each compartment. The results showed that K of an abnormal tissue was larger than that of the normal tissues. As such, this parameter may be used for diagnosis and treatment of the soft tissue diseases.

In this work, the reaction rate of molybdenite powder is calculated and the effects of temperature on the reaction rate and reaction time are investigated. The particle temperature is obtained by solving the heat transfer equation, including convection, conduction, and radiation terms. The particle diameter is assumed to be 100 μm and the porosity is 50%. The results show that the particle temperature reaches the fluidized bed temperature in 365 seconds and the reaction time is around 5000 seconds. According to the results, during the time interval between 500 seconds and 1800 seconds, the temperature of the particles is higher than 600 °C, which causes sintering in the molybdenum trioxide. The fluidized bed temperature must be decreased, and the gas velocity must be increased to prevent sintering. The results are in good agreement with the experimental data. This article is part of a study on the design and construction of a fluidized bed furnace. For the first time in the country, a pilot-scale fluidized bed roaster has been built based on these results.