Theory of bound polarons in oxide compounds

We present a multilateral theoretical study of bound polarons in oxide compounds MgO and \alpha-Al_2O_3 (corundum). A continuum theory at arbitrary electron-phonon coupling is used for calculation of the energies of thermal dissociation, photoionization (optically induced release of an electron (hole) from the ground self-consistent state), as well as optical absorption to the non-relaxed excited states. Unlike the case of free strong-coupling polarons, where the ratio \kappa of the photoionization energy to the thermal dissociation energy was shown to be always equal to 3, here this ratio depends on the Froehlich coupling constant \alpha and the screened Coulomb interaction strength \beta. Reasonable variation of these two parameters has demonstrated that the magnitude of \kappa remains usually in the narrow interval from 1 to 2.5. This is in agreement with atomistic calculations and experimental data for hole O^- polarons bound to the cation vacancy in MgO. The thermal dissociation energy for the ground self-consistent state and the energy of the optically induced charge transfer process (hops of a hole between O^{2-} ions) have been calculated using the quantum-chemical method INDO. Results obtained within the two approaches for hole O$^-$ polarons bound by the cation vacancies (V^-) in MgO and by the Mg^{2+} impurity (V_{Mg}) in corundum are compared to experimental data and to each other. We discuss a surprising closeness of the results obtained on the basis of independent models and their agreement with experiment.Comment: 13 pages, 2 figures, 2 tables, E-mail addresses: [email protected], [email protected]

A key to fuzzy-logic inference

AbstractClassically, whether to effect inference, one uses a small set of axioms and modus ponens, or a set of rules of inference including modus ponens, one is going beyond what can be derived with the explicit operations of logic alone. Carrying this concept over to fuzzy logic we construct a fuzzy modus ponens and other rules of inference that include modus tollens and reductio ad absurdum. These in turn are based on (and greatly facilitated by) a choice for the operation of implication that preserves the (logic) symmetry implicit in its definition. Extensions including conditional quantification, cut rules (single, multiple, and implicitory), and fuzzy mathematical induction are sketched. As an example, a fuzzy-logic treatment of the Yale shooting problem is discussed. The results suggest that the implicit processes of inference, as distinct from the explicit processes of decision (control) theory and systems theory, can be effected in fuzzy logic if, as in classical logic, one ventures outside the scope of (fuzzy) logic operations

DIRECT MEASUREMENT OF VELOCITY OVERSHOOT BY HOT-ELECTRON, SUBMILLIMETER WAVE CONDUCTIVITY IN Si INVERSION LAYERS

Nous décrivons des mesures à large bande en ondes sousmillimétriques (5-30 cm-1) de la conductivité d'électron chaud dans un transistor à effet de champ métal-oxyde-semiconducteur (MOSFET) Si aux températures basses (~ 1.5 K). Le dépassement de vitesse est observé directement dans le domaine des fréquences. Par transformée de Fourier, la dynamique électronique est montrée sur une échelle de temps de .5 à 3.5 psec et ici le dépassement de vitesse est signalé aussi.We describe broadband (5-30 cm-1) submillimeter wave measurements of the hot electron conductivity in a Si metal-oxide-semiconductor-field-effect-transistor (MOSFET), at low temperatures (~ 1.5 K ) Velocity overshoot is directly observed in the frequency domain. By Fourier transform the electron dynamics are displayed on a time scale from .5 to 3.5 psecs and velocity overshoot revealed here as well