In this work we show that the Layzer theory for atomic calculations, not only provides a theoretical framework but also a powerful computational approach if correct rules for the calculation of the screening parameters are given. Using the virial as a model for potential energy and splitting of two-body operators as sum of onebody operators, a neat definition of screening is given, satisfying diverse physically indispensable properties. Many different experimental and theoretical results are reproduced with high accuracy, with no fitting procedure involving energy levels or numerical potentials. A C + + code and an executable file are available upon request.
The study of Infrared Light propagation in turbid media is of great interest because of its biomedical applications. This technique can provide information about both, lesions location and composition. The final goal is to find the distribution of inhomogeneities in tissues starting from a set of images obtained non - invasively. This is known as the inverse problem and it is extremely complex, since Light diffusion in tissues eliminates the spatial information. Even though it exist some proposals to solve the inverse problem, it is always necessary to compare results with known situations (direct problem). Additionally, apart from some special case, theoretical models have not been developed yet. This work presents a new approach of Monte Carlo calculations based in Graphics Processing Units (GPU), which are used in video games cards and which have been developed and optimized for parallel processing. Since in MC simulations each photon is independent of all others launched, they can be parallelized, and thus, using GPU’s can reduce calculation times in several orders of magnitude. In this way, it is possible to generate many simulations with different optical parameters in a reasonable time and to compare them to experiments. The set of parameters that best fit the experiments is thus the desired one. We present, as an example, the case of a plastic resin cylinder immersed in a turbid medium with optical properties similar to biological tissue.
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