We study the dynamics of Staffman-Taylor fingering in terms of topological defects of the flow field. The defects are created and/or annihilated at the interface. The route towards the single-finger steady state is characterized by a detailed mechanism for defect annihilation. For small viscosity contrast this mechanism is impeded, and creation of new defects leads the system away from a single-finger solution. Strong evidence for a drastic reduction of the basin of attraction of the Saffman-Taylor finger is presented.

A complete theory of wave-particle interactions is presented whereby both circulating and trapped energetic ions can destabilize kinetic ballooning modes in tokamaks. For qualitatively different types of resonances, involving wave-precessional drift, wave-transit, wave-bounce, and precessional drift-bounce interactions, are identified, and the destabilization potential of each is assessed. For a characteristic slowing-down distribution function, the dominant interaction is that which taps those resonant ions with the highest energy. Implications of the theory for present and future-generation fusion experiments are discussed.

We demonstrate experimentally the effects of plasma rotation and particle thermal velocities on cyclotron resonance in a long cylindrical pure electron plasma column of low density (${\mathrm{\omega }}_{\mathit{p}}^2$≪${\mathrm{\omega }}_{\mathit{c}}^2$). A single m=1 mode (${\mathit{e}}^{\mathit{i}\mathit{m}\mathrm{\theta }\mathrm{-}\mathit{i}\mathrm{\omega }\mathit{t}}$) is found whose frequency ω is down-shifted from ${\mathrm{\omega }}_{\mathit{c}}$=eB/${\mathit{m}}_{\mathit{e}}$ by an amount equal to the low-frequency diocotron mode frequency (〈${\mathrm{\omega }}_{\mathit{p}}^2$〉/2${\mathrm{\omega }}_{\mathit{c}}$). For m=2,3,4,. . . sets of modes are found which are Doppler shifted upward from ${\mathrm{\omega }}_{\mathit{c}}$. We explain these as radially trapped and azimuthally propagating Bernstein modes.

A slowly decaying fluorescence [lifetime ≃13.3(5) μs] induced by implanted positive muons has been observed in KBr by using the time-resolved direct-photon-counting method with a total yield of one photon per four incident muons below 30 K. The temperature dependence of the fluorescence yield shows a remarkable coincidence with that of the amplitude of the anomalous muonium center in KBr observed by the muon-spin-rotation method, strongly suggesting a coupled state between muonium centers and radiation-induced relaxed excited states as a model for the anomalous muonium centers.

Theoretical interatomic potentials for KCl and NaCl are tested at energies 5–350 eV against experimental data from intrinsic collision cascades. The collisional scattering of Cl with Cl, K, and Na atoms was observed from Doppler-shifted γ rays depopulating an excited state in recoiling ${}_{}{}^{36}{}_{}{}^{}\mathrm{Cl}$ produced through the thermal neutron capture ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$(n,γ${)}^{36}$Cl. The collisional scattering was simulated with molecular dynamics. Interatomic potentials from the present Iab initioP atomic cluster calculations are proposed for the Cl-Cl, Cl-K, and Cl-Na interactions in KCl and NaCl.

We perform the first analysis of the morphological instability of a growing epitaxially strained dislocation-free olid film. We derive an evolution equation for the film surface based on surface diffusion driven by a stress-dependent chemical potential. From the time-dependent linear stability problem we determine the conditions for which a growing film is unstable. Our results reveal that the critical film thickness for instability depends on the growth rate of the film itself, and that the instability we describe exhibits many of the observed features of the onset of the ‘‘island instability.’’

Raman echoes are observed for the first time in the liquid phase. The symmetric methyl stretch of acetonitrile is shown to be homogeneously broadened, in disagreement with time-resolved coherent Raman scattering experiments and recent theory, but in agreement with line-shape studies and computer simulations. The vibration interacts primarily with rapid, collisional solvent motions, not with long-lived structural features.

We observed tunneling in a system of interacting electrons confined to a two-dimensional layer. The effects of correlations on the tunneling were studied by varying the electron density from the single-particle limit to the highly correlated Wigner-crystal regime. For low densities the tunneling is well described by a model in which the interactions are represented by an effective potential.

We have observed for the first time a drastic enhancement of the normally forbidden second-harmonic generation signal when twice the incident-photon energy is resonant with the excitation energy of a 2P exciton in thin ZnSe crystals. Measurements were performed, using a titanium sapphire laser, at 4.2 K in such a geometrical configuration, x(zz, x or y) or x(yy, x or y)z, that transitions are forbidden by the usual selection rules. The results are shown to be well accounted for in the framework of a time-dependent perturbation formalism.

Clear fine-structure oscillations in magnetoresistance and torque magnetization are observed at low temperatures in the anisotropic organic superconductor (TMTSF${)}_2$${\mathrm{ClO}}_4$ as a function of sample orientation in a fixed magnetic field. At 0.1 K, these fine structures appear as resistance minima and torque maxima at specific orientations of the field in the ${\mathit{b}}^{\mathrm{*}}$-${\mathit{c}}^{\mathrm{*}}$ sample plane, with one-to-one correspondence. The angular positions of the feature are independent of magnetic field, temperature, and cooling rate (disorder), while their magnitudes depend strongly on all three. We compare these observations with a recent prediction by Lebed’ and Bak of resistance, but not magnetization, anomalies expected to arise at special ‘‘magic’’ orientations in field.

We report the first direct and comprehensive determination of the energy levels involved in the Haldane gap occurrence: the singlet ground state and the first triplet excited state. Precise values of the parameters are obtained from the analysis of the magneto-optical resonance transitions observed in the far infrared for frequencies ranging from 70 to 1000 GHz and magnetic fields up to 18 T.

We compute the current as a function of voltage for resonant tunneling through an Anderson impurity in the low-temperature, Kondo, regime. The differential conductance curve has the same structure as the zero-bias spectral function, but is sharper because a finite voltage tends to destroy the Kondo resonance. This destruction of the Kondo resonance cannot be mapped onto an increase in the effective temperature at the impurity site. The calculation is performed in the symmetric Anderson model using perturbation theory in the Hubbard U repulsion.

The characteristic temperature dependence of the electronic transport properties of heavy-fermion systems can be reproduced within the self-consistent second-order U-perturbation treatment of the periodic Anderson model. This approach, within which explicit calculations are possible in the limit of a large spatial dimension d for correlated lattice electrons, properly fulfills the Luttinger sum rules. Here we present the first explicit calculations of transport quantities and show that an excellent reproduction of the typical experimental results is possible by simply using the d=∞ result for d=3.

Raman spectra of untwinned ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ with ${\mathit{T}}_{\mathit{c}}$=91 K indicate a 2.2-eV resonance for incident light polarized in the CuO chain direction. The resonance is characterized by the appearance of nominally forbidden phonon modes at 232 and 597 ${\mathrm{cm}}^{\mathrm{-}1}$. Below 100 K the forbidden modes can be optically bleached if the photon energy exceeds 2.2 eV. The resulting optically induced low-temperature state is metastable; upon warming the crystal to T>200 K the forbidden modes reappear as before.

We obtain an improved cosmological mass bound of the axino (fermionic partner of the axion), and observe that the axion energy crisis problem is modified for ${\mathit{F}}_{\mathit{a}}$≥${10}^{12}$ GeV, from the consideration of the photon reheating due to decay of the saxino (scalar partner of the axion) in supergravity models.

A gauge theory of the Virasoro group is constructed as a theory of ‘‘internal’’ strings, and a spontaneous symmetry-breaking mechanism of the Virasoro group down to its Cartan subgroup is discussed. It is shown that the mass spectrum of the gauge bosons after the symmetry breaking becomes that of a harmonic oscillator. After a supersymmetric generalization, the theory could serve as a simple model for the hadrons.

An estimate is made of the corrections of order 1/${\mathit{N}}_{\mathit{c}}$ (where ${\mathit{N}}_{\mathit{c}}$ is the number of colors in quantum chromodynamics) to the axial vector coupling of the quark.

An investigation of the space-time extension of particle sources in the current-ensemble formalism shows that under quite general assumptions exist a quantum statistical (${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^{\mathrm{-}}$) correlation and a difference between (${\mathrm{\pi }}^0$${\mathrm{\pi }}^0$) and (${\mathrm{\pi }}^{\mathrm{-}}$${\mathrm{\pi }}^{\mathrm{-}}$) Bose-Einstein correlations. These effects are found to be enhanced for small momenta and radii.

It is shown that the recently reported strong enhancement of the axial-charge matrix element in first-forbidden β decay in heavy nuclei (A=205–212) can be simply explained in terms of an effective Lagrangian that incorporates approximate chiral and scale invariances of QCD. We suggest this as an evidence for the scaling property of hadrons in dense medium as predicted by effective chiral Lagrangians that are consistent with the symmetries of QCD.

We have modeled and experimentally investigated the ‘‘Zeeman tuned slowing’’ of rubidium using ${\mathrm{\sigma }}^{\mathrm{-}}$ polarized laser light. Previous studies have all used ${\mathrm{\sigma }}^{+}$ light. We find that important details of the slowing process enable this new method to produce significantly slower and more intense atomic beams than for the ${\mathrm{\sigma }}^{+}$ case. An additional advantage: ${\mathrm{\sigma }}^{\mathrm{-}}$ slowing exhibits much weaker dependence on laser wavelength and intensity.