The contribution to electron-impact ionization cross sections from excitations to high-nl shells and a consequent autoionization is investigated. We perform relativistic subconfiguration-average and detailed level-to-level calculations for this process. Ionization cross sections for the W27+ ion are presented to illustrate the large influence of the high shells (n ^ 9) and orbitals (/ > 4) in the excitation-autoionization process. The obtained results show that the excitations to the high shells (n ^ 9) increase cross sections of the indirect ionization process by a factor of 2 compared to the excitations to the lower shells (n < 8). The excitations to the shells with orbital quantum number l = 4 give the largest contribution compared with the other orbital quantum numbers /. Radiative damping reduces the cross sections of the indirect process approximately twofold in the case of the level-to-level calculations. Determined data show that the excitation-autoionization process contributes approximately 40 % to the total ionization cross sections.

The energy spectra and the electric dipole transitions in the boron isoelectronic sequence (Z = 8 -26) between the levels of the ls22s22p, ls22s2p2 and ls22p3 configurations were considered. The stationary second-order many-body perturbation theory (MBPT) was used to account for the electron correlations. The relativistic corrections were included in the Breit-Pauli approximation. Method Term El E2 E3 Term El E2 E3 (O+ 1) -1.6888 -0.42 -1.9534 -0.73 (O+ 1 + 2) -1.8347 -0.20 -2.1831 -0.35 MCHF ls22s22p 2P -1.7113 ls22s2p2 2P -2.0006 HF 2.33445 -1.7073 -0.40 -2.0006 -0.70 HPT 2.32753 -1.8349 2.47744 -2.1821 (O+ 1) -1.8878 -0.53 -2.1790 -0.78 (O+ 1 +2) -1.9926 -0.35 -2.3073 -0.56 MCHF ls22s2p2 4P -1.9005 is22p3 4 s o -2.194 1 HF -1.9005 -0.46 -2.1941 -0.68 HPT 2.38954 -1.9926 2.52277 -2.3071 -1.9614 -0.61 -2.2558 -0.82 (O+ 1 +2) -2.1363 -0.36 -2.4476 -0.56 MCHF ls22s2p2 2D -1.9835 1s22p3 200 -2.2765 HF -1.9835 ~~ ~ ~

The electric quadrupole (E2) and magnetic dipole (M1) transitions in the nitrogen isoelectronic sequence (Z \ 10È30) between the levels of the 1s22s22p3, 1s22s2p4 and 1s22p5 conÐgurations are investigated. The results include wavelengths and radiative E2 and M1 transition probabilities. The stationary second-order many-body perturbation theory (MBPT) was used to account for the electron correlations. A non-local potential was used to calculate the radial part of the e †ective Hamiltonian. Relativistic corrections were included in the BreitÈPauli approximation. The lowest-order correlation corrections to the one-body part of the spinÈorbit interaction operator were also included.

A correlation velocity log (CVL) is an acoustic navigation aid that estimates the velocity of a maritime vehicle using a transmitter and a receiving array. The CVL discussed here operates by calculating the correlation coefficient between the echoes from a pair of consecutive acoustic pulses transmitted towards the seafloor, across all combinations of receiver pairings in the array. A correlation surface is constructed by plotting the correlation coefficients versus the spatial separation vector of all the receiver pairings. The coordinates of the peak of this surface provide an estimate of the velocity vector of the vessel. However, the correlation coefficient surface exhibits high variance within a modest distance from the peak position, and individual datasets tend to be asymmetric about the peak position. Since each dataset consists of a sparsely sampled set of discrete measurements, the variance makes the task of peak estimation very challenging. This paper outlines the operating principles of CVLs and describes peak-finding techniques that are used to improve the accuracy and precision of the instrument. Three peak estimation techniques are considered, namely the highest point, and fitting of an axisymmetric quadratic model using either least squares or a nonlinear implementation of maximum likelihood estimation. It is shown that the maximum likelihood approach offers some advantages when the peak is controlled to lie near the centre of the receiver array, but the advantages are small compared to the additional computational load required.

The electric dipole (E1) transitions between the levels of the 1s22s22p4, 1s22s2p5 and 1s22p6 Configurations have been considered in the oxygen isoelectronic sequence. The second-order stationary perturbation theory of the effective Hamiltonian has been adopted. Relativistic corrections were included in the Breit-Pauli approximation. E1 transition energies, line strengths, oscillator strengths, probabilities and lifetimes obtained in various approximations are compared with experimental values and with results of other theoretical calculations for Z = 10 – 26.