The ordering in the Cu-O basal plane of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathrm{z}}$ is investigated as a function of oxygen content and temperature. A phase diagram is calculated by application of the cluster variation method to an asymmetric two-dimensional Ising model. The interaction parameters selected guarantee the stability of the experimentally observed double-cell structure around z=6.5. The transition temperatures at various oxygen partial pressures are in good agreement with experiment. The pair probabilities along the Cu-O chains show a plateau with varying oxygen concentration, not unlike the dependence of ${\mathrm{T}}_{\mathrm{c}}$ on oxygen content.

We report the positron-annihilation lifetime and Doppler-broadening energy spectra in ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_4$ superconductors for 10<T<297 K. A strong temperature dependence in positron lifetime and momentum distribution parameters is observed for positron-electron annihilation data while the sample is in the superconducting state, but not while it is in the normal state. We show experimental evidence that the superconducting mechanisms in ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_4$ and ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ are similar and suggest that this is a consequence of a common physics involving the delicate balance between localized and itinerant-electron behavior.

Positive-muon spin-rotation and -relaxation measurements of the oxygen-deficient perovskite ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathrm{x}}$ have revealed local antiferromagnetic order for 6.0≲x≲6.4 with a Néel temperature $T_{\mathrm{N}}$ that decreases rapidly with increasing oxygen content x. For slowly annealed samples with 6.35≲x≲6.5 the superconducting transition temperature $T_c$ increases smoothly with x from 25 K at x=6.348 to 60 K at x=6.507. Two such samples with x=6.348 and x=6.400 appear to ‘‘switch’’ from superconductivity to antiferromagnetic order at lower temperatures.

We report systematic calculations based on the full-potential linearized augmented-plane-wave method for the whole transition-metal series (V,Cr,Mn,Fe,Co,Ni) as overlayers on the Pd(001) surface. An energy analysis shows that Fe, Co, and Ni overlayers favor the ferromagnetic p(1×1) configuration, but V, Cr, and Mn, the antiferromagnetic c(2×2) superstructure. We conjecture that this result is a general trend which should also be found on the (001) surfaces of Pt and the noble metals.

The one-dimensional, discrete Schrödinger equation is studied when the potential is allowed to take on two values, $V_A$ and $V_B$, which are arranged according to a generalized Fibonacci sequence. The problem is reduced to a dynamical map for the traces of the transfer matrices which are given recursively by $M_{l+1\mathrm{}}$=$M_{l\mathrm{-}1}$$M_l^n$, where n is a positive integer. A related class of sequences whose transfer matrices obey the recursion formula $M_{l+1\mathrm{}}$=$M_{l\mathrm{-}1}^n$$M_l$ is also investigated.

We have been able to observe the enhanced Raman scattering from copper phthalocyanine molecules deposited on layers of gas-evaporated GaP small particles. It is found that the enhancement factor increases as the average particle size increases; a maximum enhancement factor obtained in the size range between 400 and 1100 Å is as high as 700. We show by calculating the efficiency of electric field enhancement at the surface of a GaP sphere that the electromagnetic mechanism of enhancement can operate even for a nonmetallic particle, in which surface plasmon modes are not excited.

Recently, a macroscopic theory of N-channel disordered condeuctors showed that the statistical distribution of the transfer matrix for a system of length L evolves with L according to a diffusion equation in N dimensions. It is proved here that the recently observed universal conductance fluctuations in normal metals at very low temperatures are a rigorous consequence of that diffusion equation, in the regime in which L≫ (mean free path) and N≫1. The value found for the fluctuation coincides with the one obtained from elaborate microscopic calculations.

The magnetic scattering rate of Kondo alloys with a finite concentration of magnetic impurities is measured by means of weak localization. The three investigated systems—Fe in Mg and Co on the surface of Mg and Cu—show magnetic interactions at liquid-helium temperatures. At much lower temperatures the magnetic scattering rate decreases drastically with a ${\mathrm{T}}^{1/2}$ temperature dependence in the experimental range. This suggests a cooperative effect between the differnt impurities which appears to suppress the magnetic moments, although the condition for a Landau Fermi liquid is not fulfilled.

We study ultrasmall Josephson junctions using the coherent picture to describe the pair dynamics and the semiclassical approach for the quasiparticles. We find that the dynamics depends crucially on the ratio of the superconducting gap energy Δ(T) to the charging energy ${\mathrm{e}}^2$/2C. The pair ‘‘Bloch oscillations’’ can be practically observed when 2Δ(T)>${\mathrm{e}}^2$/2C; for 2Δ(T)<${\mathrm{e}}^2$/2C the ${\mathrm{I}}_{\mathrm{dc}/\mathrm{e}}$ oscillations due to quasiparticle tunneling can be observed. We discuss under what conditions the I-V characteristic will be S-shaped, exhibiting both oscillations at different values of the current.

We study the significance of a pronounced Cantori structure in classical phase space for the level statistics of the associated quantum system. As an example we choose the anisotropic Kepler problem. For high excitations, we find that the level statistics tend to the predictions of random matrix theory, but the convergence is rather slow.

An adaptation of lattice-gas cellular automata to the simulation of solid-fluid suspensions is described. The method incorporates both dissipative hydrodynamic forces and thermal fluctuations. At low solid densities, theoretical results for the drag force on a single disk and the viscosity of a suspension of disks are reproduced. The zero–shear-rate viscosity has been obtained over a range of packing fractions and results indicate that simulations of three-dimensional suspensions are feasible.

An increase in fractal dimension is shown to occur in filtered chaotic signals. The dependence of the Lyapunov dimension on the filter parameters is used to predict the behavior of the information dimension which is directly evaluated for two experimental systems: the NMR laser and Rayleigh-Bénard convection. Good quantitative agreement with the theoretical predictions is found. The understanding of the role of filtering not only clarifies aspects relevant in the calculation of fractal dimensions, but also yields an indirect but precise way of evaluating Lyapunov exponents.

A scalar model of two-dimensional Navier-Stokes turbulence first proposed by Gledzer is shown to realize the power law E(k)∼$k^{\mathrm{-}3}$ in its chaotic state, which is found to obey the same scaling law as that of the enstrophy-cascade theory. All the Lyapunov exponents are calculated for several values of viscosity, and they are found to have a scaling property in the interior of attractor. The calculated distribution function of the Lyapunov exponents appears to have a singularity at null Lyapunov exponent.

A method is proposed to analyze the Bose-Einstein effect in lepton-hadron and $e^{+}$-$e^{\mathrm{-}}$ collisions in such a way as to measure longitudinal source extensions. A model is used which predicts measurable longitudinal source extensions as a function of excitation energy and meson-pair energy.

The azimuthal dependence of the flow of hadronic energy about the momentum-transfer direction in charged-current deep-inelastic neutrino-nucleon scattering is used to study gluon emission and the transverse momentum 〈$k_T$〉 of partons confined inside the nucleon. A 7-standard-deviation azimuthal asymmetry is observed indicating an average 〈$k_T$〉=0.303±0.041 GeV/c.

We have measured the neutron lifetime using a superconducting electron spectrometer and a pulsed beam of cold neutrons. Spatially defined neutron bunches are completely contained within the spectrometer’s active volume while the β decay rate is measured. The flux is determined from the radioactivity of nearly totally absorbing thick samples of cobalt and gold exposed to the neutron beam. We obtain ${\tau }_n$=876±21 sec.

Experiments to determine the characteristics of electromagnetic dissociation (ED) has been extended to high projectile charge and ultrarelativistic energies using ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ projectiles on ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ targets. The gross features are reproduced in a Weizsäcker-Williams calculation but significant systematic deviations appear. The results are used as a guide in extending the calculations to the regime of energies and projectiles expected for planned heavy-ion colliders where Ed effects should comprise a major fraction of the total cross section.

A two-dimensional generalization of the one-dimensional kicked-rotor model is introduced. As in one dimension, this model can be mapped on a two-dimensional Anderson model for localization. It is found that all the states are localized in momentum space and that the localization length grows exponentially with the mean free path, as expected from the scaling theory for localization. This suggests that the correspondence between the quantum dynamics of chaotic systems and Anderson localization that was found in one dimension holds in two dimensions as well.

This paper presents a new method for the solution of diffusion-reaction problems in one dimension. The method is used to derive some new exact results for the polymerization (cl-cl aggregation) and annihilation processes on openR and openZ. Through well-known dualities, these results have implications for the T=0 limit of the kinetic Ising model and for two interacting particle processes, the invasion and voter models. Prospectively, the method may be useful in providing one-dimensional verification for speculations in the theory of diffusion reaction.

A heuristic argument predicting the existence and critical temperature of a phase transition in the Coulomb gas in any dimensionality D>1 is advanced. Numerical simulations are reported, corroborating these predictions in two and three dimensions. They lead to an interpretation of the Kosterlitz-Thouless transition, different from the standard one, of dipole dissociation. In three dimensions, the transition is interpreted as the first-order liquid-gas one, across which the density is discontinuous.