We describe a semi-analytical method to calculate the total radiance received form a black body, between two frequencies. As has been done before, the method takes advantage of the fact that the solution simplifies with the use of polylogarithm functions. We then use it to study the amount of radiation from the sun received by bodies at Earths surface.

Complete optoelectronic devices present major difficulties to be built by aqueous chemical deposition. In this work, a ITO/CdS/PbSe heterostructure was developed, depositing CdS over an ITO-coated substrate via a chemical bath deposition (CBD) technique. The next step involved the growth of a plumbonacrite film over CdS via CBD, where the film acted as a precursor film to be converted to PbSe via ion exchange. The characterization of each material involved in the heterostructure were as follows: the CdS thin films presented a hexagonal crystalline structure and bandgap of 2.42 eV; PbSe had a cubic structure and a bandgap of 0.34 eV. I vs. V measurements allowed the observation of the electrical behavior, which showed a change from an ohmic to diode response by applying a thermal annealing at 150 °C for 5 min. The forward bias of the diode response was in the order of 0.8 V, and the current-voltage characteristics were analyzed by using the modified Shockley model, obtaining an ideality factor of 2.47, being similar to a Schottky diode. Therefore, the reported process to synthesize an ITO/CdS/PbSe heterostructure by aqueous chemical methods was successful and could be used to develop optoelectronic devices.

We present a simulation of the orbits of Galactic Centre stars, also known as ‘S-stars’, with the purpose of describing the motion of those bodies for which complete orbits are known with greater accuracy. The aim is to have a better understanding of the inner parts of the Galactic potential. The simulation assumes that the spacetime around the central black hole of the Galaxy may be modelled by the Schwarzschild metric, while stellar interactions are approximated classically. We model the central object as a black hole with mass 4.31 × 106 M⊙, fix the Galactic Centre distance at R = 8.33 kpc and include 37 orbiting stars, all of which have masses of 10 M⊙, except for S2, which has a mass of 20 M⊙. Our method allows us to predict the semimajor axis, a; eccentricity, ϵ; and period, T for these stars and predict their periastron shift, δΘ. In particular for S2, the most scrutinized star, we find δΘ = 11.9342 arcmin, in strong agreement with the observed value.