We present analytic properties of the power spectrum for a class of chaotic dynamical systems (Axiom-A systems). The power spectrum is meromorphic in a strip; the position of the poles (resonances) depends on the system considered, but only their residues depend on the observable monitored. In relation with these results we also discuss the exponential or nonexponential decay of correlation functions at infinity. In conclusion, it appears desirable to analyze the decay of correlation functions and the possible analyticity of power spectra for physical time evolutions, and for computer generated simple dynamical systems (non-Axiom-A in general).

We argue that the mass gap in the O(3) σ model is produced by condensation of vortices of topological charge (1/2) (merons). This mechanism is not effective at topological angle theta=π, supporting arguments that this model is massless. These two models are the large-spin limit of integer (half-integer) quantum spin chains.

We present a new approach for calculations of the electronic structure of atoms and molecules. The main features are (1) a functional-integral formulation on a lattice in space and imaginary time, (2) renormalization-group transformations which increase lattice spacings to reduce the number of degrees of freedom, (3) perturbation-theory treatments of core electrons, and (4) a Monte Carlo technique using the Langevin equation for nonpertubative calculations of valence-electron properties at low temperatures.

A simple scaling description of the ordering transition in random-field Ising systems is developed and supported by renormalization-group arguments in terms of a zero-temperature critical fixed point. The main prediction is that the characteristic relaxation time τ will diverge extremely rapidly as the critical point is approached: τ∼exp(${\xi }^{\mathrm{theta}}$) with ξ the correlation length and theta the ‘‘violation of hyperscaling’’ exponent (d-theta)ν=2-α. Recent experiments which exhibit onset of hysteresis in a very narrow temperature range are discussed.

A theory of quantum tunneling with dissipation is constructed. The frequency-dependent transmission coefficient is calculated at zero and finite temperatures. A fluctuation-dissipation theorem for tunneling particles is derived.

We argue that the massive modes of the superstring can play an important role in the last stages of black-hole evaporation. If the Bekenstein-Hawking entropy is the true statistical entropy of an evaporating black hole, it becomes probable for a black hole to disappear by making a transition to an excited string state. This excited string state can then decay to massless radiation, avoiding the naked singularity of the semiclassical picture. We also construct the energy-volume phase diagram separating the three phases: pure radiation, black hole and radiation, and massive string modes and radiation.

We present the three-flavor formalism for scattering of pseudoscalar mesons from baryons in the class of models in which the baryon is viewed as a ‘‘hedgehog’’ soliton in the meson field. To test this formalism, we apply it to πN scattering in the Skyrme model. The result, as compared with the two-flavor Skyrme model, is an overall improvement in agreement with experiment.

We discuss how realistic low-energy physics can arise from the ${\mathrm{E}}_8$×${\mathrm{E}}_8$ superstring. A key role is played by the discrete symmetries which typically arise after compactification. Cosmological problems are avoided because the discrete symmetry we employ is shown to be effectively embedded in a Peccei-Quinn symmetry. The models we present seem to satisfy the known phenomenological and cosmological constraints. In particular they possess a harmless axion. The existence of topologically stable superconducting vortices (strings), surviving until today, is also predicted.

The nucleon mass is computed in the skyrmion model. Starting with a parameter-free nonlinear chiral Lagrangean containing the effects of heavy mesons ( ρ,σ,ω), we find that the computed mass is a factor of 2 too large compared with the measured value.

Becchi-Rouet-Stora invariance is used to second quantize the free superstring covariantly in the Neveu-Schwarz-Ramond formalism. The massless sector is shown to be the gauge-fixed supersymmetric Yang-Mills theory. A method to find a gauge-covariant local formulation is also discussed.

We have observed that the positrons associated with a narrow peak in the positron spectrum from U+Th collisions are correlated with the simultaneous emission of electrons whose energy spectrum also contains a narrow peak. The mean energies and widths of the two peaks are equal within measurement errors. Neither the coincidence peak intensity nor the energy distributions of the positrons and electrons can be accounted for by known nuclear internal conversion processes. Similar observations have also been made in the Th+Th and Th+Cm collision systems.

Muonic x-ray spectra from aqueous solutions of alkali halides have been measured and compared with spectra from the respective solid salts. In the solutions the higher members of the Lyman series are enhanced. From this and from p+${\mathrm{\pi }}^{\mathrm{-}}$→n+${\mathrm{\pi }}^0$ data on hydrogen-containing compounds it is concluded that transfer involving pμ or pπ atoms, respectively, is responsible for the hydrogen effects while mechanisms involving mesomolecular orbitals are ruled out.

The experimental observation of the behavior of acoustically rotated free drops in the microgravity environment of low earth orbit has yielded the first data which meet the restrictions of existing theoretical treatments. Rotating drops displayed both ‘‘axisymmetric’’ and ‘‘two-lobed’’ shapes in the presence and absence of applied torques. Their dimensions and general development confirm the existence of the distinct shape families and the bifurcation point between them. The data also indicate that the secular instability in the axisymmetric family occurs at a lower rotation velocity than predicted.

Because of relativistic nonlinear effects large amplitude cyclotron motion of a free electron can be excited by two laser beams with frequencies much higher than the cyclotron frequency Ω. The laser frequencies can differ either by Ω (three-photon resonance) or 2Ω (four-photon resonance). The excited cyclotron motion displays a hysteretic resonance based solely on the relativistic mass effect. To observe three-photon hysteretic excitation, a He-Ne laser with a few microwatts of power is sufficient.

X-ray diffraction measurements were performed at atmospheric pressure on a high-density form of amorphous ice obtained by pressurizing crystalline ice Ih at 77 K, up to 2 GPa. The low–momentum-transfer region of the determined structure factor is quite different from that corresponding to the low-density form of amorphous ice. However, the nearest-neighbor distance and coordination number are almost unchanged. The high density of this form of amorphous ice is explained by the strong distortion of the 0-0-0 angles from the ideal tetrahedral value.

For a given temperature below the smectic-A (SmA)–chiral–smectic-C (${\mathrm{SmC}}^{\mathrm{*}}$) transition of DOBAMBC, polarization (P) and tilt-angle (theta) have been measured almost simultaneously with high resolution. The ratio P/theta stays fairly constant for ${\mathrm{T}}_{\mathrm{c}}$-T>2 K and shows a precipitous drop near the transition temperature (${\mathrm{T}}_{\mathrm{c}}$). A calculation based on a generalized mean-field model, similar to the one proposed by Zeks, is in good agreement with our result. This generalized mean-field model also gives the prominent feature of the helical pitch anomaly just below the SmA-${\mathrm{SmC}}^{\mathrm{*}}$ transition.

It is shown that the icosahedral quasicrystal and the recently observed T phase are closely related to each other. The latter is a periodic stacking of two-dimensional quasilattices with mirror symmetry. Their diffraction patterns, though appearing very different, can be indexed by a set of primary vectors that are only small deformations of each other. However, because of the mirror symmetry, their quasilattices are not related by small deformations. A calculation based on the model free energy of Kalugin et al. shows that this periodic quasicrystal is very competitive with (and in fact energetically more favorable than) the icosahedral quasicrystal.

Complete wetting and critical wetting transitions are studied in d-dimensional systems with quenched random impurities and general interactions. New but more universal singular behavior is predicted: e.g., under random fields the wetting-layer thickness at complete wetting should diverge as ${\mathrm{h}}^{\mathrm{-}1/2}$ for d=3, where h measures the deviation from the bulk-phase boundary. Wetting exponents are expressed in terms of a single spatial anisotropy or roughness exponent, ζ, defined via ${\xi }_{\mathrm{\perp }}$∼${\xi }_{\mathrm{?}}^{\mathrm{\zeta }}$ where ${\xi }_{\mathrm{\perp }}$ and ${\xi }_{\mathrm{?}}$ are the wetting correlation lengths.

It is shown that an external electric field can appreciably affect local-defect reactions in semiconductors. A phenomenological model in terms of elementary reaction dipolar moments is presented and the importance of defect orientation and electronic structure is stressed. Experimental evidence of this field effect was clearly obtained for several deep-center reactions in electron-irradiated InP. In particular it is shown that the behavior of the main defect annealing event is well understood by a field-induced orientation of a dynamic Jahn-Teller system.

Rayleigh linewidth data gathered at small scattering angles on critical-mixture films of thickness 2L are found to collapse about a single universal curve, ${\mathrm{\Gamma }}^{\mathrm{*}}$(K${\xi }^{\mathrm{eff}}$), where ${\mathrm{\Gamma }}^{\mathrm{*}}$(x) is the 3D reduced Rayleigh linewidth function, and ${\xi }^{\mathrm{eff}}$ is an effective correlation length obeying a general finite-size scaling relation, ${\xi }^{\mathrm{eff}/\mathrm{L}=\mathrm{F}(\xi /\mathrm{L})}$. The latter reveals that ${\xi }^{\mathrm{eff}}$ grows with ξ until ξ≊L, when its growth terminates, implying the existence of surface layers of thickness ξ formed by preferential wall-fluid interactions.