Search

Pulmonary surfactant phospholipids play an important role in the surface tension activity of the lung. Incorporation of [32P]orthophosphate into rat-lung pulmonary-surfactant phospholipids was studied in vitro and in vivo after separation on silicic-acid-column chromatography and by one and two-dimensional thin-layer chromatography. While they represent a small part of the phospholipids of the whole lung, pulmonary-surfactant phospholipids show a rapid turnover, particularly in vitro. After in vitro incubation, phosphatidylcholine and lysophosphatidylcholine show very important specific activities; by contrast, phosphatidylethanolamine and sphingomyelin have a very low turnover. Thus phosphatidyldimethylmethanolamine-methylation pathway, demonstrated in the lung, is not very important. Phosphatidylglycerol is labeled more markedly in vivo than in vitro indicating, for this lipid, a possible transfer from lung tissue to pulmonary-surfactant cells. In diphosphatidylglyceroI specific activities are always very low. The incorporation of radioactive phosphate into phosphatidylinositol, more important in vitro than in vivo, is probably related to the phagocytosis activity of these cells. Our work demonstrates the existence of a phospholipid biosynthesis into pulmonary surfactant but cannot explain the metabolic relations between lung tissue and macrophagic alveolar cells investigated as a possibility in our results. [ABSTRACT FROM AUTHOR]

The scattering of electromagnetic waves and plasma waves by a space vehicle, excited by a ground source, in an isotropic warm plasma is studied. By considering the propagation constant for the induced current and charge on the vehicle due to ground excitation to be general, expressions for scattered power and radar cross section of the vehicle are obtained and the effect of generation of electroacoustic waves by the vehicle on the scattered power and radar cross section is discussed. By giving three different values to the general propagation constant, different theoretical curves for the radar cross section are obtained and compared with the available experimental graphs, and the possibility of neglecting the presence of current having propagation constant equal to is explored. The power re-radiated by the space vehicle is also computed and it is shown that the behavior of power re-radiated by a cylindrical space vehicle is similar to the power radiated by a thin cylindrical antenna in plasma.
7. Discussions and concluding remarks
A similar problem has been considered by Seshadri (1964), but his expressions for the scattered power are in the form of infinite series. Using a propagation constant equal to that of the EM wave in plasma, Chen (1965) has determined induced current and charge on the surface of a space vehicle and their effect on the radar cross sections of the vehicle. It is pointed out here that the expressions for scattered power W and W given in (35) and (38) do not involve any approximation in the evaluation of integrals. The phase propagation constant is general and can be put equal to , , or any other value determined experimentally. The corresponding values for W and W can then be found out. Equations (41) and (42), in which the functions of Si, Ci and Cin are approximated for very large values of c/v=10, are for the case when... [ABSTRACT FROM AUTHOR]