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The negative ion of cerium is investigated experimentally with tunable infrared laser photodetachment spectroscopy and theoretically with relativistic configuration interaction in the continuum formalism. The relative cross section for neutral atom production is measured with a crossed ionbeam-laser-beam apparatus over the photon energy range 0.54 -0.75 eV. A rich resonance spectrum is revealed near threshold, with at least twelve peaks observed due to transitions from bound states of Ce − to either bound or quasi-bound excited states of the negative ion. Theoretical calculations of the photodetachment cross sections enable identification of the transitions responsible for the measured peaks. Two of the peaks are due to electric-dipole-allowed bound-bound transitions in Ce − , making cerium only the second atomic negative ion that has been demonstrated to support multiple bound states of opposite parity. In addition, combining the experimental data with the theoretical analysis determines the electron affinity of cerium to be 0.628(10) eV and the fine structure splitting of the ground state of Ce − ( 4 H 7/2 -4 H 9/2 ) to be 0.09775(4) eV.

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Higher-order correlations and spectra may be used for detection, time delay estimation, classification, and discrimination of signals. For these applications, a detailed knowledge of their attributes can be highly useful. In this paper, the properties of the bicorrelation and tricorrelation of bandlimited deterministic transients, i.e., energy signals, and their spectra, the bispectrum and trispectrum are studied. Bandlimited transients that contain frequencies down to and including zero and those that have a nonzero lower cutoff frequency are both considered. Using symmetries inherent in the bispectrum of a signal, the entire bispectrum can be mapped from bispectral elements defined in two polygons, one for the unaliased and one for the aliased domain, each of which is one-twelfth the area of its total domain. The nonredundant unaliased region of the trispectrum is contained in two principal unaliased polyhedra, each replicated 48 times to reproduce the full trispectrum. If there is aliasing in the trispectrum, then the total aliased domain can similarly be mapped from two principal aliased polyhedra. It is shown that the critical sampling interval for the bicorrelation, i.e., the sampling interval sufficient to avoid aliasing, is 2/3 the critical sampling interval for the ordinary correlation, and the critical sampling interval for the tricorrelation is 1/2 the critical sampling interval for the ordinary correlation. If the lowest frequency of the bandlimited transient fb is greater than half the highest frequency ft, then there is no unaliased bispectrum. The unaliased trispectrum is made up of two different replicated domains, one of which disappears for 3fb>ft.

Higher order statistical blind deconvolution methods are implemented for use in removing multipath distortion from passively received underwater acoustic transient signals. Using single channel data and simulations, it is demonstrated that a fourth order method based on cumulant maximization can work well if the associated multipath Green's function is sufficiently "sparse." The iterative method is parameterized by filter length, and while there is a range of values at which the best solutions are obtained with conventional convergence criteria, useful solutions exist across a much broader range of filter lengths if the iterations are not always allowed to proceed to convergence. The fourth order objective functional is generalized to arbitrary order, and the method is shown to also produce good results for the third order objective functional.