An Expanded Multi-scale Monte Carlo Simulation Method for Personalized Radiobiological Effect Estimation in Radiotherapy: a feasibility study

A novel and versatile “bottom-up� approach is developed to estimate the radiobiological effect of clinic radiotherapy. The model consists of multi-scale Monte Carlo simulations from organ to cell levels. At cellular level, accumulated damages are computed using a spectrum-based accumulation algorithm and predefined cellular damage database. The damage repair mechanism is modeled by an expanded reaction-rate two-lesion kinetic model, which were calibrated through replicating a radiobiological experiment. Multi-scale modeling is then performed on a lung cancer patient under conventional fractionated irradiation. The cell killing effects of two representative voxels (isocenter and peripheral voxel of the tumor) are computed and compared. At microscopic level, the nucleus dose and damage yields vary among all nucleuses within the voxels. Slightly larger percentage of cDSB yield is observed for the peripheral voxel (55.0%) compared to the isocenter one (52.5%). For isocenter voxel, survival fraction increase monotonically at reduced oxygen environment. Under an extreme anoxic condition (0.001%), survival fraction is calculated to be 80% and the hypoxia reduction factor reaches a maximum value of 2.24. In conclusion, with biological-related variations, the proposed multi-scale approach is more versatile than the existing approaches for evaluating personalized radiobiological effects in radiotherapy

Modeling and analysis of current harmonic distortion from grid connected PV inverters under different operating conditions

Due to the fast growth of photovoltaic (PV) installations, concerns are rising about the harmonic distortion generated from PV inverters. High current total harmonic distortion (THD) occurs when PV inverters operate under light load conditions due to low solar insolation. A general model modified from the conventional control structure diagram is introduced to analyze the harmonic formation process. Causes of the current harmonics are summarized and its relationship with output power levels is analyzed. The field measurement for current harmonics is carried out at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) microgrid to validate the analysis results. In particular for two-stage inverter, unlike previous papers that assume the DC-link voltage is constant, the DC-link voltage ripple is identified as the source of a series of odd harmonics. A mew periodic time-varying model is proposed by including the DC-link voltage ripple into the conventional current control loop model. This model is able to simulate the characteristics of the harmonic components and show their dependence on the DC-link voltage ripple. © 2013 Elsevier Ltd

Making pathogens sociable: the emergence of high relatedness through limited host invasibility

Cooperation depends upon high relatedness, the high genetic similarity of interacting partners relative to the wider population. For pathogenic bacteria, which show diverse cooperative traits, the population processes that determine relatedness are poorly understood. Here, we explore whether within-host dynamics can produce high relatedness in the insect pathogen Bacillus thuringiensis. We study the effects of host/pathogen interactions on relatedness via a model of host invasion and fit parameters to competition experiments with marked strains. We show that invasibility is a key parameter for determining relatedness and experimentally demonstrate the emergence of high relatedness from well-mixed inocula. We find that a single infection cycle results in a bottleneck with a similar level of relatedness to those previously reported in the field. The bottlenecks that are a product of widespread barriers to infection can therefore produce the population structure required for the evolution of cooperative virulence