RESUMEN
The solar photon sail (SPS) allows space missions without propellant that would otherwise not be feasible. Thrust models frequently used in the literature for the calculation of trajectories often underestimate the effect that the surface roughness has on SPS dynamics. A small variation of the thrust vector can induce a large modification of sail flight. In this work, the variation of the photon momentum vector (PMV) is computed as resulting from the incident Sun radiation, taking into account the absorbed and reflected photons. The momentum resulting from diffuse light has been modeled by using vectorial scattering theories in the limit of a quasi-smooth sail where the first-order of Rayleigh-Rice can be applied. In particular, the momentum change resulting from diffuse radiation causes a PMV reduction as well as a deviation of its direction from what is foreseen in the case of an ideally smooth sail.
RESUMEN
The investigations employed in the diagnosis of oesophageal achalasia have been assessed critically. Although electromanometry contributes most to diagnosis and pinpoints with absolute precision the physiopathological elements that characterise the disease, radioisotopic study of oesophageal transit is an important diagnostic aid. More readily than any other, this technique permits morphofunctional evaluation in selected patients; it also represents the most physiological investigation and the best tolerated and, second only to manometry, the most reliable. Oesophagography with baritate meal and oesophagoscopy also play a diagnostic role in oesophageal achalasia. The former makes it possible to document the cardial stop and the presence or otherwise of mega-oesophagus, the second excludes the presence of organic dysphagias and also has a therapeutic use because cycles of dilatation of the oesophago-cardial junction can be carried out.