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Notes: When the charge overlap between interacting molecules or ions A and B is weak or negligible, the first-order interaction energy depends only upon the molecular positions, orientations, and the unperturbed charge distributions of the molecules. In contrast, the first-order force on a nucleus in molecule A as computed from the Hellmann–Feynman theorem depends not only on the unperturbed charge distribution of molecule B, but also on the electronic polarization induced in A by the field from B. At second order, the interaction energy depends on the first-order, linear response of each molecule to its neighbor, while the Hellmann–Feynman force on a nucleus in A depends on second-order and nonlinear responses to B. One purpose of this work is to unify the physical interpretations of interaction energies and Hellmann–Feynman forces at each order, using nonlocal polarizability densities and connections that we have recently established among permanent moments, linear response, and nonlinear response tensors. Our theory also yields new information on the origin of terms in the long-range forces on molecules, through second order in the interaction.One set of terms in the force on molecule A is produced by the field due to the unperturbed charge distribution of B and by the static reaction field from B, acting on the nuclear moments of A. This set originates in the direct interactions between the nuclei in A and the charge distribution of B. A second set of terms results from the permanent field and the reaction field of B acting on the permanent electronic moments of A. This set results from the attraction of nuclei in A to the electronic charge in A itself, polarized by linear response to B. Finally, there are terms in the force on A due to the perturbation of B by the static reaction field from A; these terms stem from the attraction of nuclei in A to the electronic charge in A, hyperpolarized by the field from B. For neutral, dipolar molecules A and B at long range, the forces on individual nuclei vary as R−3 in the intermolecular separation R; but when the forces are summed over all of the nuclei, the vector sum varies as R−4. This result, an analogous conversion at second order (from R−6 forces on individual nuclei to an R−7 force when summed over the nuclei), and the long-range limiting forces on ions are all derived from new sum rules obtained in this work.

Notes: From extensive simulation of simple local fluid models of long wavelength drift wave turbulence in tokamaks, it is found that conventional notions concerning directions of cascades, locality and isotropy of spectral transfer, frequencies of fluctuations, and stationarity of saturation do not hold for moderate to long wavelengths (kρs≤1). In particular, at long wavelengths, where spectral transfer of energy is dominated by the E×B nonlinearity, energy is carried to short scale (even in two dimensions) in a manner that is anisotropic and highly nonlocal (energy is efficiently passed between modes separated by the entire spectrum range in a correlation time). At short wavelengths, transfer is dominated by the polarization drift nonlinearity. While the standard dual cascade applies in this subrange, it is found that finite spectrum size can produce cascades that are reverse directed (i.e., energy to high k) and are nonconservative in enstrophy and energy similarity ranges (but conservative overall). In regions where both nonlinearities are important, cross-coupling between the nonlinearities gives rise to large nonlinear frequency shifts which profoundly affect the dynamics of saturation by modifying the growth rate and nonlinear transfer rates. These modifications produce a nonstationary saturated state with large amplitude, long period relaxation oscillations in the energy, spectrum shape, and transport rates. Methods of observing these effects are presented.

Notes: A self-consistent model of the low to high ("L'' to "H'') transition is derived from coupled nonlinear envelope equations for the fluctuation level and radial electric field shear, Er', as determined by ion pressure gradient, ∇Pi, and poloidal flow. These equations extend the phase transition model of the L to H bifurcation by including ∇Pi effects. In this model, the transition occurs when the turbulence drive is large enough to overcome the damping of the total E×B flow. Near the critical power for transition, poloidal flow shear dominates Er', but at high power, ∇Pi gives the main contribution. The inclusion of ∇Pi also introduces a quenched fluctuation state that is accessible at high power and may be the experimentally observed H-mode state for P(very-much-greater-than)Pcrit. In this state, the radial electric field is determined only by ∇Pi because no fluctuation energy is available to produce a turbulent Reynolds stress. © 1994 American Institute of Physics.

Notes: Insulating diamond films were imaged by scanning tunneling microscopy (STM) utilizing photoinduced bulk carrier transport to establish tunneling currents. General comparisons of topographic STM images and atomic force microscopy images acquired on the same sample demonstrate that submicrometer structures obtained in the images can be correlated. This observation establishes that the topography of an insulating surface such as diamond can be imaged under illumination by STM. The results suggest that local electronic structure of illuminated insulating surfaces can be probed using scanning tunneling spectroscopy.

Notes: We report the electronic properties, stability, and microstructure of a-Si:H films grown at high substrate temperature (320–440 °C) by dc reactive magnetron sputtering. The initial defect state density, determined by the constant photocurrent method, varies from 2–5×1015 cm−3 with H content changing from 15–10 at. % as Ts increases from 320–375 °C. For 100 h of white light exposure at 1 W/cm2, the midgap state density reached an apparent saturation at 2–3×1016 cm−3 over this temperature range. By contrast, films grown at 230–300 °C saturate at 9×1016 cm−3.

Notes: The two-nonlinearity model of dissipative trapped-electron drift wave turbulence [Y.-M. Liang et al., Phys. Fluids B 5, 1128 (1993)] is generalized to include the effects of a sheared magnetic field. Because of the coupling of drift waves with the damped ion-acoustic modes, the eigenmode k has a radial structure centered on its rational surface characterized by a mode width Δk. In this work, both the linear properties of the model, and the multiple-helicity nonlinear dynamics, including the interactions of the two nonlinearities, i.e., the E×B drift and the polarization drift nonlinearities, are analyzed in detail. In particular, a one-point renormalization is performed to investigate the nonlinear eigenmode properties and the saturation of the system in the multiple-helicity limit. It is shown that, for the ultrastrong magnetic shear limit where Δk≤2ρs, the polarization drift nonlinearity is the dominant nonlinear transfer mechanism. However, for the moderate-to-weak magnetic shear limit where Δk(very-much-greater-than)2ρs, both nonlinearities and cross-coupling effects will affect the nonlinear transfer processes. An analytic explanation of previous computational observation of the suppression of magnetic shear damping by turbulence [D. Biskamp and M. Walter, Phys. Lett. A 109, 34 (1985)] is also given.