We report a synchrotron magnetic x-ray scattering study of the temperature evolution of the magnetic long range order (LRO) of ${\mathrm{Mn}}_{0.75}$${\mathrm{Zn}}_{0.25}$${\mathrm{F}}_2$ in a magnetic field with emphasis on the behavior after zero field cooling (ZFC). We show that with increasing temperature the metastable ZFC LRO vanishes continuously at a temperature well above the equilibrium ${\mathit{T}}_{\mathit{N}}$; the LRO follows a rounded power law with exponent ${\mathrm{\beta }}_{\mathrm{ZFC}}$=0.20±0.02 and a transition width which scales as ∼${\mathit{H}}^2$ but with no divergent critical fluctuations. We argue that this behavior is generic to the random field Ising model.

Steplike phonon structures are observed in the luminescence spectrum of porous Si under excitation within the luminescence band at liquid He temperature. The shape of the phonon structures are successfully interpreted in terms of a model based on phonon assisted indirect transitions. From the spacing of the structures, it is concluded that the luminescence occurs in an entity which has a phonon spectrum very similar to crystalline Si. The broad spectrum of luminescence is attributed to an inhomogeneous distribution of the indirect band gap energy of Si particles.

It is found that a change of the photoionization matrix element with the binding energy in the valence band can cause a substantial discrepancy between the density of states and the photoemission spectrum for d-band metals and alloys even in the x-ray photoemission spectroscopy regime. This is the main cause of the controversial discrepancy between photoemission spectra and theoretical density of states predicted in the Korringa-Kohn-Rostoker coherent-potential approximation for Cu-Pd alloys, rather than the local lattice relaxation around Pd atomic sites.

Optimal strategies for predicting correctly the output of a few new random inputs, when various feedforward networks are trained by noise-free random training examples, are examined analytically and numerically. The existence of a universal strategy for various generalization tasks is discussed, and indicates that the Bayes algorithm is not always the optimal strategy.

We use nonlinear methods to predict changes in cardiac rhythms over periods of up to several hours. The patterns of measured premature heart beats which correspond to return cycles of a 1D map are found to be organized into a devil’s staircase when plotted against heart rate. Throughout the data collections, changes in patterns with heart rate agree with the computed dynamics. This result, typical of the majority of patients examined, demonstrates that (1) simple recursions can model complex biological rhythms and (2) mode locking can play a dominant role in the patterning of arrhythmias.

A nonperturbative method for solving differential equations and for finding limit cycles is proposed and is illustrated on the anharmonic oscillator and on the Van der Pol equation. It is shown to give the amplitude, period, and equation of the limit cycle with a better accuracy than any perturbative results so far obtained.

Lower and upper bounds are derived for the decay and transitions of quantum states, evolving under a time-dependent Hamiltonian, in terms of the energy uncertainty of the initial and final state. The bounds are simultaneously a rigorous version of Fermi’s golden rule and of the time-energy uncertainty relation. They are sharp, refer to short times, and are compared with recent long-time results for time-independent Hamiltonians. Illustrations for tunneling systems, laser-driven processes, and neutron interferometry in time-dependent magnetic fields are given.

It is shown that joint measurements of certain commuting operators, performed on pre- and postselected quantum systems, invariably disturb each other. This result is applied to recent assertions that quantum theory has no realistic Lorentz-invariant interpretation (even without requiring locality).

We show that the strong ${\mathit{Q}}^2$ dependence of the Gerasimov-Drell-Hearn sum rule is naturally described by using the Schwinger sum rules and the contribution of the ${\mathit{g}}_2$ structure function. The deep inelastic proton longitudinal asymmetry is expected to change sign around ${\mathit{Q}}^2$=0.2 ${\mathrm{GeV}}^2$; this important result should be checked experimentally.

We show that long-wavelength excitations of the quark-gluon plasma are described by simple kinetic equations which represent the exact equations of motion at leading order in g. Properties of the so-called ‘‘hard thermal loops,’’ i.e., the dominant contributions to amplitudes with soft external lines, find a natural explanation in this approach. In particular, their generating functional appear here as the effective action describing long-wavelength excitations of the plasma.

We have derived explicit expressions in the one-dimensional Ising model for multiplicity distributions ${\mathit{P}}_{\mathrm{\delta }\xi }$(n) and factorial moments ${\mathit{F}}_{\mathit{q}}$(δξ). We identify the salient features of ${\mathit{P}}_{\mathrm{\delta }\xi }$(n) that lead to scaling, ${\mathit{F}}_{\mathit{q}}$(δξ)=F${\mathrm{̃}}_{\mathit{q}}$[${\mathit{F}}_2$], and universality. These results compare well with the presently available high-energy data. We point out the important features that should be studied in future higher-energy experiments of multiparticle productions in pp, p¯p, ep, ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$, and NN. We also make comments on comparisons with Koba-Nielsen-Olesen and negative-binomial distributions.

It is argued that color transparency in quasielastic scattering of electrons and hadrons on nuclei is possible only due to Fermi motion. We found a strong dependence of nuclear transparency on Bjorken x in (e,e’p); it is close to the Glauber model expectations at x>1, but increases and even exceeds one at x<1. It is argued that color transparency is accompanied by large longitudinal momentum transfer to nuclear matter during the passage of the small size wave packet.

The dynamics of a wave packet in the nuclear degree of freedom of a sodium dimer have been studied via the time- and frequency-resolved spectrum of spontaneous emission. This technique allows one to track the nuclear wave packet dynamics in a single excited electronic state over a substantial fraction of its periodic trajectory. The quantum beats in the spectrum may be partially interpreted in terms of the classical-like evolution of an initially random distribution of internuclear separations. We observe the expansion and contraction of the wave packet that is characteristic of a quadrature squeezed state.

We have measured the state-to-state differential scattering cross section (DCS) for a rotationally inelastic process using an entirely spectroscopic method. The system studied was ${\mathrm{Li}}_2$(${\mathit{A}}^1$${\mathrm{\Sigma }}_{\mathit{u}}^{+}$)-Xe and the method utilizes two color sub-Doppler double resonance. Analysis of the shape of the double resonance line yields the final distribution of relative velocity vectors. This represents the first measurement of a state-to-state DCS using thermal cell spectroscopy. In addition we have determined, also for the first time, the dependence of the state-to-state DCS on initial relative velocity. Results are presented for the Δj=6 rotationally inelastic process.

Unpolarized particles with spin may spontaneously polarize during their flight through a resonant cavity, due to their interaction with the cavity’s quantized radiation field. This effect, of purely electromagnetic origin, could, if not recognized as such, be mistaken for a parity violating weak interaction effect. For a better understanding of this effect we have simulated it, as well as the related quantum field effects of collapse, revival, and hidden coherence, with a beam of polarized neutrons and a set of classical magnetic fields.

A number-phase interaction is suggested that is analogous to the usual quadrature squeezing Hamiltonian for a mode of the electromagnetic field. Applied to an initial coherent state, it produces number-phase squeezed states. For moderate squeezing in either direction the result is close to a minimum uncertainty state. Two different ${\mathrm{\chi }}^{\mathrm{}\left(3\right)\mathrm{}}$ approximations to the ideal interaction are found, appropriate for the different directions of squeezing. Even with the approximate interaction, the fluctuations in photon number can be reduced to less than half a photon for an arbitrarily intense field.

We demonstrate all-optical techniques for position measurement and localization of moving atoms with suboptical wavelength precision. Spatial resolution of 200 nanometers, with linearity over a few microns, is obtained by the methods which ultimately will scale to yield nanometer resolution limited by the uncertainty principle.

We report an interesting phenomenon of wavelength doubling bifurcations in the model of coupled (logistic) map lattices. The temporal and spatial periods of the observed patterns undergo successive period doubling bifurcations with decreasing coupling strength. The universality constants α and δ appear to be the same as in the case of period doubling route to chaos in the uncoupled logistic map. The analysis of the stability matrix shows that period doubling bifurcation occurs when an eigenvalue whose eigenvector has a structure with doubled spatial period exceeds unity.

The first experimental observation of limit-cycle power oscillations in a short-pulse free-electron laser is presented. These are due to a nonlinear modulation of the optical micropulse shape and phase by the electrons, which leads to the formation of a train of subpulses. Experimentally, the oscillations have been found to depend on the slippage distance and on the desynchronism between optical pulses and electron bunches, comparing well with theoretical predictions.

Scaling behavior in turbulence is studied on the basis of its relation to the wrinkling, or fractalization, of the graph of the velocity field in 3+3 dimensions. We propose a novel mechanism for deviations from the Kolmogorov exponents, which is realized if the fine structure of turbulence tends locally towards two dimensionality. It is argued that some of the popular fractal and multifractal models of intermittency in turbulence are not consistent with fluid mechanics, and miss some essential physics.