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We present in this work a heuristic expression for the density of prime numbers. Our expression leads to results which possesses approximately the same precision of the Riemann's function in the domain that goes from 2 to 1010 at least. Instead of using a constant as was done by Legendre and others in the formula of Gauss, we try to adjust the data through a function. This function has the remarkable property: its points of discontinuity are the prime numbers.

The effect of thermal fluctuations in the resonance fluorescence of a three-level system is studied. The damped three-level system is driven by two strong incident classical fields near resonances frequencies. The simulation of a thermal bath is obtained with a large system of harmonic oscillators that represent the normal modes of the thermal radiation field. The time evolution of the fluorescent light intensities are obtained solving by a iterative method the Heisenberg equations of motion in the integral form. The results show that the time development of the intensity of the fluorescence light is strongly affected by the interaction of the system with the thermal bath., Comment: 25 pages, 7 figures

In this work we present a "vision" model for blind people, preferentially for those ones of birth origin. The model should be implemented using the available computational resources at the moment. The model uses a simulation of an optical image by an appropriate sonorous "image" according to certain rules.