Multilayers of ultrathin superconducting a-${\mathrm{Mo}}_{79}$${\mathrm{Ge}}_{21}$ and normal Ge-rich a-${\mathrm{Mo}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Ge}}_{\mathrm{x}}$ were prepared to study the effects of disorder on superconductivity in reduced dimensions. The superconducting transition temperatures of the multilayers as a function of composition and thickness of the normal metal show a systematic enhancement over the single film ${\mathrm{T}}_{\mathrm{c}}$. This effect can be attributed to a crossover from 2D single-film behavior to 3D bulk behavior as electron diffusion between individual superconducting layers increases. The nature of this crossover sheds light on the microscopic mechanisms reducing ${\mathrm{T}}_{\mathrm{c}}$.

We use neutron diffraction to show that superconductivity affects the magnetic order in ${\mathrm{UPt}}_3$. The different superconducting states identified in previous bulk measurements can be associated with different behaviors of the magnetic order parameter. The data suggest that the coupling between multicomponent superconducting and magnetic order parameters leads to the variety of superconducting phases of ${\mathrm{UPt}}_3$.

In a spin-1/2 Heisenberg model with short-range antiferromagnetic order, a hole making a closed loop on one sublattice is subject to a slowly varying spin-quantization axis and picks up a phase equal to half the solid angle subtended by the spin orientation around the loop. The phase can be represented by an Aharonov-Bohm flux resulting in a U(1) gauge theory. For a finite hole density this model leads to superconductivity even in the presence of Coulomb repulsion. The gauge field also enhances low-energy particle-hole excitations, leading to a $T^{4/3}$ law for the normal-state resitivity.

A theory of spiral waves is presented that includes nonlocal effects due to wave-front interactions. Evolution equations for the spiral wave front are derived from the basic reaction-diffusion system, using a singular perturbation method. It is shown that nonlocal effects play a crucial role in stabilizing the dynamics of spiral waves and may substantially affect their spatiotemporal behavior. In particular, conditions are found under which spiral cores expand in time. An expression for the normal velocity is derived and compared with previous results.

We consider the problem of multiplication in a diffusive random medium. For time-independent one-dimensional white-noise multiplication ‘‘potential’’ we find asymptotic growth ∼exp(${\mathrm{t}}^3$), while for a ‘‘potential’’ with finite-range correlation we find asymptotic growh ∼exp(${\mathrm{t}}^2$).

We study the phenomena of self-organized criticality originally proposed by Bak, Tang, and Wiesenfeld. A continuous-energy model is introduced. Using numerical simulations, we find that energy is homogeneously and isotropically distributed in space, and that it is concentrated around discrete values. We propose a scaling theory to estimate the various exponents. The activation cluster size distribution is found to be D(s)∼1/$s^{\tau }$, τ=2-2/d; and the dispersion relation t∼$r^z$, z=(d+2)/3.

We find a representation for the finite Fourier series of a vector whereby any constant constraint on its magnitude is completely solved and automatically satisfied. The representation is a product of rotations, one set for each harmonic, such that the independent degrees of freedom are identified as rotational angles and an infinite series is replaced by an infinite product. This can be applied to the study of relativistic strings, and other applications and generalizations are anticipated.

It is argued that the superstring tension is not renormalized in perturbation theory for vacua which preserve N=1 spacetime supersymmetry. Some implications of this result for macroscopic superstrings are discussed, as well as some analogies between macroscopic superstrings and solitons in supersymmetric theories.

By using the well-known expression for the vacuum polarization as the low-energy effective Lagrangian, photon pairing and condensation are discussed. Above a certain critical coupling, pairing instability occurs and magnetic-type condensation is realized with 〈:$F_{\mu \nu }^2$:〉>0. A possible confining property of the condensed vacuum is suggested by the use of the dual potential.

We study CP violation in a chiral color model with exotic fermions transforming as singlets of the weak-isospin group SU(2${)}_{\mathrm{L}}$. The Higgs sector consists of a nonet of chiral color and the usual doublet of SU(2${)}_{\mathrm{L}}$×U(1${)}_{\mathrm{Y}}$. In the limit in which the mixings between the third generation with the first two generations are small, CP-violating interactions are dominated by the exchange of neutral Higgs bosons. The CP-violating parameters ε and ε’/ε for the kaon system are easily accommodated. The neutron electric dipole moment is generated at the one-loop level and is ∼${10}^{\mathrm{-}25}$–${10}^{\mathrm{-}26}$e cm.

We have measured the polarizations and the differential cross sections of the produced Λ’s at backward angles (70°<${\theta }_{\mathrm{lab}<145\mathrm{}\mathrm{°}}$) using a large-aperture spectrometer. The angular range is kinematically not accessible in interactions of the incident pions with free nucleons. The calculated polarizations in terms of superposition of an elementary process incorporating Fermi motion of nucleons in the nucleus are opposite in sign to the observed ones, while a quark-parton model of Λ production with a Thomas precession effect reproduces both the polarizations and the cross sections well.

The dependence of multifragment-emission processes upon linear momentum transfer to the target residue is determined for ${}_{}{}^{36}{}_{}{}^{}\mathrm{induced}$ reactions on ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ at E/A=35 MeV. Significantly more intermediate-mass fragments are emitted in central collisions. Multiplicity distributions for intermediate-mass fragments emitted behind the grazing angle resemble Poisson distributions and are consistent with a stochastic production process. Exit channels with up to five intermediate-mass fragments and two fission fragments were observed.

Differential and absolute cross sections for the coherent reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(γ,${\pi }^0$${)}^{40}$Ca g.s., as well as for the incoherent reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(γ,${\mathrm{\pi }}^0$${)}^{40}$Ca(g.s.), have been measured with monochromatic photons in the threshold region ($E_{\gamma }$=157–169 MeV). The differential cross section for the coherent process exhibits a diffraction minimum due to the nuclear mass form factor while the incoherent cross section is rather structureless. The cross sections are in good agreement with recent distorted-wave impulse-approximation calculations.

A new method is described which is capable of determining ‖Δ${\mathrm{E}}_{0\mathrm{-}1}$‖, the absolute value of the fine-structure splitting of the interval $2^3$${\mathrm{P}}_0$-$2^3$${\mathrm{P}}_1$ from the hyperfine quenched lifetime of the $2^3$${\mathrm{P}}_0$ state of heliumlike ions with nuclear spin. Based on this method a measurement is reported of ‖Δ${\mathrm{E}}_{0\mathrm{-}1}$‖ in the heliumlike ion ${}_{}{}^{107}{}_{}{}^{}$${\mathrm{Ag}}^{45+}$ with the result ‖Δ${\mathit{E}}_{0\mathrm{-}1}$‖=0.${74}_{\mathrm{-}0.19}^{+0.16\mathrm{}}$ eV. The error in the measurement is substantially smaller than the natural linewidth of 1.1 eV.

Two pulse photon echoes were observed in organic dye molecules in solution using 6-fs optical pulses. The results show an initial rapid dephasing of the echo due to level multiplicity followed by quantum beaks. The temporal decay of the quantum beats is characterized by a ${\mathrm{T}}_2$ of about 60 fs.

We discuss the possibility of the coexistence of two states with different wavelengths in the framework of phase dynamics. We investigate in detail this phenomenon which is intrinsically nonlinear and we give a Lyapunov functional for the case of a phase associated with a stationary pattern. The relationship of the confined states discussed here with recent experimental observations of localized states posessing a wavelength different from that in the bulk of the container for the case of slot convection and for the Taylor instability between co-rotating cylinders is critically examined.

Theoretical analysis of vorticity disturbances in axisymmetric elongational flow of dilute polymer solutions shows that polymers decrease the vorticity near the symmetry axis and increase it away from this axis, at distances larger than the square root of the ratio betwen the kinematic viscosity and the strain rate of the fluid. Enhancement of large-scale vorticity is a consequence of elastic energy storage by macromolecules that inhibits the energy cascade towards the dissipative scales. A similar mechanism may be expected to play an important role in turbulence modification by polymers.

Stability of a klystron-type free-electron laser as a new microwave source in the two-beam concept is analyzed by means of a macroparticle approach. A universal gain equation for initially bunched beams is derived and proved to have a limit cycle. Motion of the macroparticle which represents the bunch center is straightforwardly reconstructed from the solution for the gain equation and the stability analysis shows that the macroparticle’s motion is very stable over many periods.

Central ion temperatures up to 30 keV and rotation speeds up to 8×${10}^5$ m/sec have been confirmed with new diagnostic measurements in the TFTR hot-ion enhanced-confinement regime, and the ion thermal diffusivity is found to be non-neoclassical and comparable to the anomalous electron thermal diffusivity. The dominant effect of strong rotation is the down-shifting of the neutral beam energies in the plasma frame, which results in reduced ion and electron heating on axis, and the presence of off-axis ion heating from viscous damping of the plasma rotation.

Spectra of 90° scattered light from underdense plasmas evidence a line close to the second harmonic of laser frequency, whose red shift is consistent with frequency sum between incident laser light and Brillouin backscattered light. Time-resolved spectra give information on the dynamics of the process.