Mainly based on data for local susceptibilities and $3d$ spin rates of dilute Fe ions in many metals, we conclude that the existence and stability of Fe, Co, and Ni moments in Cu, Ag, Au, and certain transition-metal hosts are governed by impurity-$3d$ host-$d$ electron interactions. As the leading contribution to moment stability we propose ferromagnetic-$3d$ host-$d$ exchanges which in certain hosts successfully suppress spin fluctuations arising from antiferromagnetic $d-sp$ exchanges. All host-dependent trends of moment stability of Mn, Fe, Co, and Ni ions in metals are consistent with our proposal.

The nature of the metastable magnetic properties of a random Josephson-junction array in the presence of a constant transverse magnetic field is studied extensively by Monte Carlo simulations. The quenched magnetization and helicity modulus are calculated as a function of temperature, field, amounts of disorder, dimensionality, and time. The calculated quantities are found to be strongly thermal-history dependent, similar to the magnetic properties found in high-temperature oxide superconductors. We also suggest to test the results of this paper in artificially made arrays of random Josephson junctions.

We show that even in $d=\infty$ dimensions the Hubbard model, when scaled properly, describes nontrivial correlations among fermions. Diagrammatic treatments are found to be substantially simpler than in finite dimensions. The weak-coupling correlation energy is seen to be a good approximation for that in $d=3\mathrm{}$. Recent approximations based on slave-boson techniques are recovered by the exact evaluation of explicit variational wave functions in $d=\infty$.

We report mechanical measurements of the flux lattice in U${\mathrm{Pt}}_3$. In the superconducting state the flux lattice that is formed in the sample when a magnetic field is applied contributes a restoring force and a dissipation term to a high-$Q$ mechanical oscillator, when the oscillator and sample are tilted with respect to the static magnetic field. In addition to the characteristic response for a type-II superconductor that gives $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$, we observe an unexpected dissipation peak along two lines in the ($H, T$) plane within the superconducting state. The evidence suggests transitions between three different superconducting phases, and hence a complex phase diagram for U${\mathrm{Pt}}_3$ is proposed.

Measurements of the attenuation of longitudinal ultrasound in superconducting U${\mathrm{Pt}}_3$ show a peak, below $H_{c2\mathrm{}}$, which depends strongly on the orientation of the field relative to the $c$ axis. We propose an explanation of this peak in terms of a vortex phase transition in an unconventional superconducting state, which is consistent with recent neutron-scattering data.

uv-photoemission spectra ($h\nu =21.2\mathrm{}$ eV) of single-crystal specimens of the high-$T_c$ superconductor ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$Ca${\mathrm{Cu}}_2$${\mathrm{O}}_8$ have been measured with a resolution of 20 meV in the normal state at 105 K and in the superconducting state at 15 K. In a narrow energy range of 120 meV below the Fermi energy, the low-temperature spectra reveal unambiguously the low-lying quasiparticle excitations reflecting the superconducting state. A straightforward analysis of these spectra provides strong evidence for the existence of a superconducting gap with a reduced value $\frac{2\Delta }{k_B{T}_c}\simeq 8$.

We show that the presence of superconducting cosmic strings in the early Universe may have dramatic consequences for primordial nucleosynthesis. Due to the enormous currents that they potentially can carry, very large magnetic fields can be produced in the vicinity of such strings. As they then move through the primordial plasma, charged particles are deflected away by the magnetic pressure surrounding the strings. We show that the predicted primordial abundances can differ radically from standard big-bang predictions, and may even be consistent with an ${\Omega }_b=1\mathrm{}$ universe.

We study the overrelaxation algorithm developed by one of us (S.A.) for the SU(2) gauge theory in four dimensions. We find improvement in the decorrelation time for the plaquette by a factor of 2 to 3. However, our results suggest that the Monte Carlo application of overrelaxation behaves quite differently from the classical differential-equation analog. In particular, the optimum value of the overrelaxation parameter $\omega$ may depend on what order parameter one measures. In addition, there are order parameters that do not appear to improve by overrelaxation.

Using the data from Fermilab experiment 691, we have observed signals for the decays ${D_s}^{\pm }$ and $D^{\pm }\to {\pi }^{-}{\pi }^{+}{\pi }^{\pm }$ and have analyzed these modes for the fraction due to ${\rho }^0{\pi }^{\pm }$ and $f_0\mathrm{}\left(975\right)\mathrm{}{\pi }^{\pm }$. In addition, we have searched for the decays ${D_s}^{\pm }$ and $D^{\pm }\to {\pi }^{-}{\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{\pm }$. Values or upper limits are reported for the relative branching fractions for all of the above decays.

The mass splits in the fission decays of giant $E1\mathrm{}$, $\frac{E2\mathrm{}}{E0\mathrm{}}$, and $E3\mathrm{}$ multipole resonances have been studied in ${}_{}{}^{235,238}{}_{}{}^{}\mathrm{U}(e, e^{\prime }f)$ coincidence experiments. The fission width ratios $\frac{{\Gamma }_S}{{\Gamma }_A}$ have been determined as functions of excitation energy for separated multipoles. The isoscalar gaint $E2\mathrm{}$ resonances show a larger symmetric contribution than the $E1\mathrm{}$ and $E3\mathrm{}$ resonances.

A parameter-free method is proposed for the analysis of transfer reactions leading to an unbound three-body final state. The three-body dynamics are treated in the adiabatic approximation. The technique is applied successfully to new data for the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}({}_{}{}^3{}_{}{}^{}\mathrm{He}, pp){}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ reaction.

We show how, by resorting to a one-fermion realization of the Pauli operators, the Hamiltonian of the Jaynes-Cummings (JC) model can be identified as an element of the superalgebra u(1|1), which plays the role of a dynamical algebra. The extension of this notion to osp(2|2) allows adding both virtual and real two-photon processes to the JC Hamiltonian. The exact diagonalization problem is tackled here in the special case when the coupling constants of the fermionic terms of the "dressed" JC Hamiltonian are assumed to nilpotent Grassman-Banach numbers.

The electronic spectra of mass-specific dichloroanthracene · ${\mathrm{Kr}}_N$ clusters were interrogated by resonant two-photon two-color ionization. A novel effect of abrupt spectral line narrowing with increasing cluster size at $N=17\mathrm{}$ was observed, which signals the nonrigid-to-rigid, collective, three-dimensional, multistate isomerization in the heterocluster.

From an ${\mathrm{H}}_2$ photodissociation experiment the destruction of the $\mathrm{H}\mathrm{}\left(2S\right)\mathrm{}$ metastable fragments, colliding with an ${\mathrm{H}}_2$ molecule, is shown to proceed through two competitive processes: the $2S-2P$ mixing induced by the ${\mathrm{H}}_2$ quadrupole moment and a nonradiative process. This nonradiative process has a cross section of about 50 ${\mathrm{\AA }}^2$ for thermal velocities. Its identification as ${\mathrm{H}}_3^{+}$ production is discussed.

The feasibility of launching an acoustic directed energy pulse train was tested experimentally. Excellent agreement between theoretical and experimental results was obtained.

Experimental evidence of degenerate four-wave mixing in a plasma is presented for the first time. The thermal-force contribution to the signal reflectivity, as evidenced by its temporal shape and dependence on plasma density, pump and probe intensities, and polarizations, dominates that due to the ponderomotive force in the collisional plasma. The pump-pump grating, which is driven by a much stronger ponderomotive force, is found not to affect adversely the signal reflectivity.

We describe temporal and spectroscopic measurements of high-density plasmas produced by focusing intense, 160-fsec laser pulses on solids. Soft-x-ray emission with a duration of 2±2 psec is observed up to photon energies of a kilovolt. We observe reduced emission from long-lived spectral lines, indicating the presence of a short-lived, high-density plasma. Reflectivity measurements indicate that absorption of the laser pulse occurs at the surface of the solid before it expands.

An electrostatic method for controlling diverted particle fluxes in a stellarator has been demonstrated. Potentials applied to a defined set of divertor targets (shields) in contact with diverted flux bundles results in redistribution of plasma flow to any given divertor. Examination of the edge magnetic topology shows that E×B drifts just outside the last-closed magnetic surface account for the alteration of the diverted particle flows.

Using cluster and percolation concepts, we obtain a relation between relaxation times at critical points obtained from a new dynamical model introduced by Swendsen and Wang and those obtained from Glauber dynamics. This relation, which involves only static critical exponents, provides new insight into the physics underlying cluster acceleration methods such as the one introduced by Swendsen and Wang.

Recent experiments on spin waves in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$- ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixtures suggest that the interaction parameter $\lambda$, where $\lambda ={(1+F_0^a)}^{-1\mathrm{}}-{(1+\frac{F_1^a}{3})}^{-1\mathrm{}}$, vanishes for a value of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ concentration between 3% and 5%. At this concentration some new features in the dispersion and attenuation of the spin-wave modes will appear. Moreover, when $\lambda =0\mathrm{}$, the Leggett-Rice effect disappears. Measuring the dispersion of the spin-wave mode in this regime provides a unique experiment in which two Fermi-liquid parameters, $F_0^a$ and $F_1^a$, are obtained.