ABSTRACT
Monte Carlo simulations and integral equation techniques allow for the flexible and efficient computation of drag and diffusion coefficients for virus mimetic particles. We highlight a Monte Carlo method that is useful for computing the drag on biomimetic particles in the free-molecular regime and a numerical technique to solve a boundary integral equation (related to the Stokes equation) in the hydrodynamic limit. The free-molecular and the continuum results allow the construction of an approximation for the drag applicable over the full range of Knudsen numbers. Finally, we outline how this work will be useful in modeling viral transport in air and fluids and in viral morphology measurements and in viral separations via electrospray-differential mobility analyzers (ES-DMA).
ABSTRACT
AIM: The objective of this research was to estimate the dose distribution delivered by radioactive gold nanoparticles (198AuNPs or 199AuNPs) to the tumor inside the human prostate as well as to normal tissues surrounding the tumor using the Monte-Carlo N-Particle code (MCNP-6.1.1 code). BACKGROUND: Radioactive gold nanoparticles are emerging as promising agents for cancer therapy and are being investigated to treat prostate cancer in animals. In order to use them as a new therapeutic modality to treat human prostate cancer, accurate radiation dosimetry simulations are required to estimate the energy deposition in the tumor and surrounding tissue and to establish the course of therapy for the patient. MATERIALS AND METHODS: A simple geometrical model of a human prostate was used, and the dose deposited by 198AuNPs or 199AuNPs to the tumor within the prostate as well as to the healthy tissue surrounding the prostate was calculated using the MCNP code. Water and A-150 TEP phantoms were used to simulate the soft and tumor tissues. RESULTS: The results showed that the dose due to 198AuNPs or 199AuNPs, which are distributed homogenously in the tumor, had a maximal value in the tumor region and then rapidly decreased toward the prostate-tumor interface and surrounding organs. However, the dose deposited by 198Au is significantly higher than the dose deposited by 199Au in the tumor region as well as normal tissues. CONCLUSIONS: According to the MCNP results, 198AuNPs are a promising modality to treat prostate cancer and other cancers and 199AuNPs could be used for imaging purposes.
ABSTRACT
Here we examine Langmuir's conjecture (1918) regarding hindered diffusion in the context of the computation of a diffusion coefficient for iodine in air from experimental results. Using an expression that he derived for diffusion from a small sphere in an infinite nonabsorbing medium, Langmuir calculated a diffusion coefficient based on the measured (Morse, 1910) rate of mass loss from a small sphere of iodine sitting on the flat pan of a microbalance. He obtained a diffusion coefficient of 0.053 cm(2)/s under the experimental conditions but noted that due to the pan of the microbalance, diffusion in all directions was hindered, and that the actual diffusion coefficient was more likely closer to 0.07 cm(2)/s. To examine how the pan of the microbalance might have hindered the evaporation, we have considered a two-sphere model in which one sphere is evaporating. The other sphere is purely absorbing and comparatively large compared to the evaporating sphere so a flat surface can be approximated. For generality in future applications with arbitrary geometries, we solve the diffusion equation in the volume surrounding the spheres using Green's function to obtain the normalized evaporation rate of the sphere and compare it to that of an evaporating sphere surrounded by a large volume of air. In doing so, we have reinterpreted the experimental data, accounting for the hindered diffusion, obtaining a diffusion coefficient of 0.072 cm(2)/s, which supports Langmuir's conjecture.
