Studying effects of gold nanoparticle on dose enhancement in megavoltage radiation

Background: Gold nanoparticles are emerging as promising agents for cancer therapy and are being investigated as drug carriers, photothermal agents, contrast agents and radiosensitisers. Objective: The aim of this study is to understand characteristics of secondary electrons generated from interaction of gold nanoparticles GNPs with x-rays as a function of nanoparticle size and beam energy and thereby further understanding of GNPenhanced radiotherapy. Methods: Effective range, defection angle, dose deposition, energy, and interaction processes of electrons produced from the interaction of x-rays with a GNP were calculated by Monte Carlo simulations. The MCNPX code was used to simulate and track electrons generated from 30 and 50 nm diameter GNP when it is irradiated with a cobalt-60 and 6MV photon and electron beam in water. Results: When a GNP was present, depending on beam types used, secondary electron production increased by 10- to 2000-fold compared to absence of a GNP. Conclusion: GNPs with larger diameters also contributed to more doses. © 2015, Shiraz University of Medical Sciences. All rights reserved

Effects of Gas Cross-over through the Membrane on Water Management in the Cathode and Anode Sides of PEM Fuel Cell

Water management in a proton exchange membrane fuel cell (PEMFC) is numerically modeled by considering the 2D, non-isothermal steady flow assumptions. Governing equations are solved in all cell layers including cathode and anode electrodes by finite volume method using a single-region approach. The effect of gas cross-over through the membrane is studied on cell performance. This consideration, not only improves the general accuracy of modeling but also makes it possible to model energy losses due to direct reaction of reactant gases. The effect of some key variables such as liquid water diffusivity, current density, membrane thickness, etc. on PEMFC conditions such as the amount of saturated liquid water, power density, cell temperature, cross-over efficiency and so on are examined. It was observed that the amount of saturated liquid water on the anode side is considerably important. This observation addresses needs for further investigation of liquid water behavior in the anode electrode. The amount of liquid water saturation in both the cathode and anode electrodes is increased with increasing the current density. The results showed that at the current density of 0.2 A/cm2, cross-over effect causes about 10% reduction in cell efficiency and by decreasing the current density this effect is enhanced