The validity of form-factor, modified-form-factor and anomalous-scattering-factor approximations in predictions of elastic photon-atom scattering is assessed with the aid of the state-of-the-art numerical calculation of Rayleigh scattering obtained using the second-order Smatrix theory, in the photon energy range from 100 eV to 1 MeV. A comparison is made with predictions from Smatrix theory in the same atomic model for representative low-Z (carbon, Z = 6) and high-Z (lead, Z = 82) elements to get a general idea of the validity of these simpler more approximate methods. The importance of bound-bound contributions and the angle dependence of the anomalous scattering factors is discussed. A prescription is suggested, with the assumption of angle independence, that uses simpler approaches to obtain the elastic scattering cross sections in the soft-X-ray regime at the level of accuracy of the S-matrix calculation, failing at large momentum transfers for high-Z elements. Predictions from this prescription are compared with experiment. With starting point the many-body elastic scattering amplitude, a detailed discussion is presented of the partition of the elastic scattering amplitude into Rayleigh and Delbrtick scattering components. This partition of the optical theorem reveals contributions from bound-bound atomic transitions, bound pair annihilation and bound pair production that are not usually associated with elastic scattering. In the parti-* Present address: 395 Henry Street, Apartment IN, Brooklyn, New York 11201, USA. tioned optical theorem for Rayleigh scattering, as in the many-body optical theorem for scattering from excited states, subtracted cross sections naturally appear. These terms are needed, in addition to the familiar terms for photoionization, to relate the real and imaginary parts of the scattering amplitude.

The major advantage of inhaled milrinone is its pulmonary selectivity, thereby avoiding systemic side effects and ventilation-perfusion mismatch. Inhaled milrinone is an effective pulmonary vasodilator and appears to be an alternative promising approach in addressing the problem of right-ventricular decompensation following cardiopulmonary bypass.

The state-resolved differential cross sections for both the 1s 2 1 S 0 → 1s2s 1 S 0 monopolar transition and the 1s 2 1 S 0 → 1s2p 1 P 1 dipolar transition of atomic helium had been measured over a large momentum transfer region by high-resolution inelastic x-ray scattering (IXS). The almost-perfect match of the present measurement with the theoretical calculations gives a stringent test of the theoretical method and the calculated wave functions. Our results demonstrate that high-resolution IXS is a powerful tool for studying the excitations in atoms and molecules.

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