Zur Bestimmung des Volumens des Fundamentalbereichs der unimodularen Gruppe

Ohne Zusammenfassung     

Ten-fold spin-orbital degeneracy in the true d-electron Hubbard model of the Mott metal-insulator transition

The ten-fold spin-orbital degeneracy of true d-electrons is included in the non-spin-orbitally degenerate Hubbard model treatment theory of the Mott metal-insulator transition of Rice and Brinkman, and Gutzwiller. The Rice-Brinkman and Kohn phase diagrams of the Mott metal-insulator transition are shown to shift due to spin-orbital degeneracy of true d-electrons so as to increase the available phase space in the temperature-“interaction” Mott phase diagram for the formation of the antiferromagnetic insulator, superlattice metal or superlattice insulator states in these phase diagrams.     

Strings with dimension-dependent intercept

By changing the boundary conditions of the relativistics string in extra dimensions, the intercept α(0) is lowered to $\text{1 ?}\text{1}\text{16}\text{(26 ?D}{}_0\text{)}$ in the modified orbital model, where D₀ is the dimensionality of the Poincaré-invariant subspace of space-time. In the modified model of the spinning string, the boson intercept becomes $\text{1}\text{2}\text{?}\text{1}\text{8}\text{(10 ? D}{}_{\mathrm{o}}\text{)}$, while the fermion intercept stays at zero. The projective invariance of the ground state is broken, giving the “photon” mass by a Higgs-like mechanism. Unfortunately, the strings have a negative “G parity”, so the usual, unshifted strings appear as intermediate states in the scattering amplitudes. Also, some of the amplitudes are not dual.     

A biophysical model of an inner hair cell

Whole-cell patch-clamp recordings on isolated inner hair cells (IHCs) of guinea pig cochleae have revealed the presence of voltage-gated potassium channels. A biophysical model of an IHC is presented that indicates activation of slow voltage-gated potassium channels may lead to receptor potentials whose dc component decreases during the stimulus, and membrane potential hyperpolarizes when the stimulus is turned off. Both the decreasing dc and the hyperpolarization are, respectively, consistent with rapid adaptation and suppression of spontaneous rate in the auditory nerve. Receptor potentials recorded in vivo do not show these features, and when a nonspecific leak is included in the model to simulate microelectrode impalement, the model's receptor potentials become similar to those in vivo. The nonspecific leak creates an electrical shunt that masks slow channel activity and allows the cell to depolarize. Both the decreasing dc and the hyperpolarization are sensitive to the resting potential. Because the reported resting potentials in vivo and in vitro differ greatly, the model is used to investigate homeostatic mechanisms responsible for the resting potential. It is found that the voltage-gated potassium channels have the greatest influence on the resting potential, but that the standing transducer current may be sufficient to eliminate the decreasing dc and after-stimulus hyperpolarization.     

Linewidth and tuning characteristics of terahertz quantum cascade lasers

We have measured the spectral linewidths of three continuous-wave quantum cascade lasers operating at terahertz frequencies by heterodyning the free-running quantum cascade laser with two far-infrared gas lasers. Beat notes are detected with a GaAs diode mixer and a microwave spectrum analyzer, permitting very precise frequency measurements and giving instantaneous linewidths of less than -30 kHz. Characteristics are also reported for frequency tuning as the injection current is varied.