Using a multiparameter multicoincidence spectrometer, we have measured the coplanar (e,3e) angular distributions following the double ionization of helium at an incident energy of Ϸ5.6 keV and under a small projectile's scattering angle of 0.45°. The two ejected electrons have been detected with equal energies E b ϭE c ϭ10 eV. The absolute value of the cross section is determined with an accuracy of 25%. The origin of dips and peaks in the spectra is exposed by analyzing the corresponding theoretical calculations. These calculations have been done using a four-body final-state wave function for the three electrons moving in the field of He 2ϩ. The dipolar limit is investigated and the manifestation of the deviation from this limit are pointed out. General features and possible trends for other targets are proposed. ͓S1050-2947͑99͒02805-X͔

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We calculate the ground and excited electron and hole levels in spherical Si quantum dots inside SiO 2 in a multiband effective mass approximation. The Luttinger Hamiltonian is used for holes, and the strong anisotropy of the conduction electron effective mass in Si is taken into account. As the boundary conditions for the electron and hole wave functions, we use the continuity of the wave functions and the flux at the boundaries of the quantum dots.

The temporal and spatial controllability of charge distribution in submicron structures opens new avenues for potential applications and for the understanding of nonequilibrium processes. Here we suggest a novel way to trigger and control within picoseconds charge currents and magnetic moments in nanoscopic and mesoscopic ring structures by applying two shaped, time-delayed light pulses. Our quantum dynamic calculations show that the magnitude and direction of the induced currents are tunable by varying the time delay and strengths of the pulses. Furthermore, in an array of rings desirable magnetic orders are generated depending on the ring sizes and particle number.