ABSTRACT
In this study, Monte Carlo simulations were created to investigate the distribution of Raman signals in tissue phantoms and to validate the arctk code that was used. The aim was to show our code is capable of replicating experimental results in order to use it to advise similar future studies and to predict the outcomes. The experiment performed to benchmark our code used large volume liquid tissue phantoms to simulate the scattering properties of human tissue. The scattering agent used was Intralipid (IL), of various concentrations, filling a small quartz tank. A thin sample of PTFE was made to act as a distinct layer in the tank; this was our Raman signal source. We studied experimentally, and then reproduced via simulations, the variation in Raman signal strength in a transmission geometry as a function of the optical properties of the scattering agent and the location of the Raman material in the volume. We have also found that a direct linear extrapolation of scattering coefficients between concentrations of Intralipid is an incorrect assumption at lower concentrations when determining the optical properties. By combining experimental and simulation results, we have calculated different estimates of these scattering coefficients. The results of this study give insight into light propagation and Raman transport in scattering media and show how the location of maximum Raman signal varies as the optical properties change. The success of arctk in reproducing observed experimental signal behaviour will allow us in future to inform the development of noninvasive cancer screening applications (such as breast and prostate cancers) in vivo.
Subject(s)
Soybean Oil , Spectrum Analysis, Raman , Emulsions , Humans , Male , Monte Carlo Method , Phantoms, Imaging , Phospholipids , Scattering, RadiationABSTRACT
Young stars are surrounded by a circumstellar disk of gas and dust, within which planet formation can occur. Gravitational forces in multiple star systems can disrupt the disk. Theoretical models predict that if the disk is misaligned with the orbital plane of the stars, the disk should warp and break into precessing rings, a phenomenon known as disk tearing. We present observations of the triple-star system GW Orionis, finding evidence for disk tearing. Our images show an eccentric ring that is misaligned with the orbital planes and the outer disk. The ring casts shadows on a strongly warped intermediate region of the disk. If planets can form within the warped disk, disk tearing could provide a mechanism for forming wide-separation planets on oblique orbits.
ABSTRACT
Photothermal therapy using nanoparticles is a promising new approach for the treatment of cancer. The principle is to utilise plasmonic nanoparticle light interaction for efficient heat conversion. However, there are many hurdles to overcome before it can be accepted in clinical practice. One issue is a current poor characterization of the thermal dose that is distributed over the tumour region and the surrounding normal tissue. Here, we use Monte Carlo simulations of photon radiative transfer through tissue and subsequent heat diffusion calculations, to model the spatial thermal dose in a skin cancer model. We validate our heat rise simulations against experimental data from the literature and estimate the concentration of nanorods in the tumor that are associated with the heat rise. We use the cumulative equivalent minutes at 43 °C (CEM43) metric to analyse the percentage cell kill across the tumour and the surrounding normal tissue. Overall, we show that computer simulations of photothermal therapy are an invaluable tool to fully characterize thermal dose within tumour and normal tissue.
Subject(s)
Hot Temperature , Molecular Dynamics Simulation , Monte Carlo Method , Nanoparticles/chemistry , Phototherapy , Skin Neoplasms/therapy , HumansABSTRACT
Deuterium-to-hydrogen (D/H) enrichments in molecular species provide clues about their original formation environment. The organic materials in primitive solar system bodies generally have higher D/H ratios and show greater D/H variation when compared to D/H in solar system water. We propose this difference arises at least in part due to (1) the availability of additional chemical fractionation pathways for organics beyond that for water, and (2) the higher volatility of key carbon reservoirs compared to oxygen. We test this hypothesis using detailed disk models, including a sophisticated, new disk ionization treatment with a low cosmic-ray ionization rate, and find that disk chemistry leads to higher deuterium enrichment in organics compared to water, helped especially by fractionation via the precursors CH 2 D + / CH 3 + . We also find that the D/H ratio in individual species varies significantly depending on their particular formation pathways. For example, from ~20-40 au, CH4 can reach D/H ~ 2 × 10-3, while D/H in CH3OH remains locally unaltered. Finally, while the global organic D/H in our models can reproduce intermediately elevated D/H in the bulk hydrocarbon reservoir, our models are unable to reproduce the most deuterium-enriched organic materials in the solar system, and thus our model requires some inheritance from the cold interstellar medium from which the Sun formed.
ABSTRACT
Identifying the source of Earth's water is central to understanding the origins of life-fostering environments and to assessing the prevalence of such environments in space. Water throughout the solar system exhibits deuterium-to-hydrogen enrichments, a fossil relic of low-temperature, ion-derived chemistry within either (i) the parent molecular cloud or (ii) the solar nebula protoplanetary disk. Using a comprehensive treatment of disk ionization, we find that ion-driven deuterium pathways are inefficient, which curtails the disk's deuterated water formation and its viability as the sole source for the solar system's water. This finding implies that, if the solar system's formation was typical, abundant interstellar ices are available to all nascent planetary systems.
