Warped band and anisotropy of the hot-hole drift velocity in Si between 300 and 430 K

Experimental evidence of the anisotropy in the hot-hole drift velocity v_d of Si between 300 and 430°K has been theoretically proved to be strongly correlated to the warped shape of the heavy valence band. The comparison between theory and experiments permits a valuable check on the competitive role played by the strong nonparabolicity of the Si valence band and the lattice scattering mechanisms.     

Working without accumulation membrane in flow field-flow fractionation. Effect of sample loading on retention

Membraneless hyperlayer flow field-flow fractionation (Hyp FIFFF) has shown improved performance with respect to Hyp FIFFF with membrane. The conditions for high recovery and recovery independent of sample loading in membraneless Hyp FIFFF have been previously determined. The effect of sample loading should be also investigated in order to optimize the form of the peaks for real samples. The effect of sample loading on peak retention parameters is of prime importance in applications such as the conversion of peaks into particle size distributions. In this paper, a systematic experimental work is performed in order to study the effect of sample loading on retention parameters. A procedure to regenerate the frit operating as accumulation wall is described. High reproducibility is obtained with low system conditioning time.     

The index of symmetry of compact naturally reductive spaces

We introduce a geometric invariant that we call the index of symmetry, which measures how far is a Riemannian manifold from being a symmetric space. We compute, in a geometric way, the index of symmetry of compact naturally reductive spaces. In this case, the so-called leaf of symmetry turns out to be of the group type. We also study several examples where the leaf of symmetry is not of the group type. Interesting examples arise from the unit tangent bundle of the sphere of curvature 2, and two metrics in an Aloff-Wallach 7-manifold and the Wallach 24-manifold.     

Electron energy relaxation time in Si and Ge

The electron energy relaxation time τ_? has been analytically evaluated as a function of lattice temperature taking into account the electron-lattice scattering mechanisms for Si and Ge. Calculations have been carried on in the deformation potential approach including nonparabolicity and overlap corrections with a Maxwell-Boltzmann distribution function, and have been limited to the warm electron range. Since theoretical results agree only qualitatively, even accounting for different approaches, with available data, τ_? has been related to β a physical quantity given by a wealth of experimental data. Theoretical results agree satisfactorily with β and seem to indicate that the present theory is essentially sound. A comparative study of lattice scattering for Si and Ge evidences the different effects of the various electron-phonon scattering mechanisms upon τ_?.     

MHD fluctuations and low energy solar neutrinos

We analyze here how future solar neutrino experiments could detect neutrino flux fluctuations due to magnetohydrodynamics (MHD) perturbations on the solar plasma. We state that if such time fluctuations are detected, this would provide a unique signature of the resonant spin-flavor precession (RSFP) mechanism as a solution to the solar neutrino problem. Received: 2 July 2001 / Revised version: 4 April 2002 / Published online: 20 August 2002