The angular distribution of electrons ejected from He with about the projectile velocity in coincidence with the capture of the other electron by the projectile in 1-MeV proton-He collisions has been measured. The signature of the proton-electron-electron scattering leading to transfer ionization has been observed for the first time as a peak at about 90° in the angular distribution of the ejected electrons. The effect is in qualitative agreement with theoretical predictions.

This paper addresses the development of a new high-voltage-gradient linear accelerator. This accelerator was energized by a modulated intense relativistic electron beam with power in the multigigawatt range. A 0.2-cm-diam electron beam emerged from the accelerator with a peak current of ∼200 A and peak kinetic energy ≥60 MeV. The length of the accelerating structure was 1 m. Simple scaling laws suggest that similar accelerators with much higher average electric fields can be built.

We have used relativistic klystron technology to extract 290 MW of peak power at 11.4 GHz from an induction linac beam, and to power a short 11.4-GHz high-gradient accelerator. We have measured rf phase stability, field emission, and the momentum spectrum of an accelerated electron beam. An average accelerating gradient of 84 MV/m has been achieved with 80 MW of relativistic klystron power.

Excitation of Alfvén waves in the TCA tokamak using an external antenna structure produces a radially inward propagating and strongly damped wave which is observable through its associated density oscillations. It is found to have the properties of the kinetic Alfvén wave predicted to be created by resonant mode conversion at shear Alfvén wave resonance layers. Our experimental results are compared with the original theory of Hasegawa and Chen and with numerical calculations in cylindrical geometry.

An analytic many-body potential is derived for the bond order of s-valent systems which allows the influence of the local atomic environment on the bond strength to be determined directly. The importance of the three-membered- and four-membered-ring terms on the topology of four-atom clusters is demonstrated. The simplicity of the potential’s analytic form will allow the much used embedded atom potentials to be extended to include explicit three-body and four-body terms.

A two-dimensional quasiperiodic structure, based on tiles of three different shapes, has been generated using a modified strip-projection method. This structure belongs to the 4mm point symmetry group and can be viewed as an ordered derivative of fcc. The constituent tiles have been identified to be unimolecular subunit cells of three well known ordered structures of the fcc 1(1/20 family. The concept of a ‘‘rational modification of a truly quasiperiodic structure’’ is introduced.

Self-consistent calculations show that S and Al adatoms form directional bonds to Al(001) in four-fold hollows. If substrate nearest-neighbor nuclei are allowed to move, each adatom approaches the surface, as its square of neighbors expands and moves slightly into the metal. These relaxations approximately preserve adatom-Al bond lengths. They open Al-adatom-Al bond angles slightly, and shorten the bonds between first- and second-neighbor atoms in the outer Al layer, as expected for a surface under tensile stress.

A theoretical groundwork has been laid for modeling dopant diffusion and distribution in semiconductor heterostructures. The driving force for the diffusion of a dopant is no longer simply given by its concentration gradient as in homogeneous semiconductors, but by the gradient of its chemical potential that derives from several contributions to the free energy of the solid solution, including two sources of strain energy and the variation of band gap with the composition of the heterostructure. Expressions for dopant flux and segregation are given.

We show that the energy of adsorbate resonant states observed in a number of electron spectroscopies is profoundly affected by the multiple scattering of the incident and/or emitted electrons participating in the resonance. High-resolution electron-energy loss spectroscopy is used to investigate the X ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{\mathrm{-}}{}_{}{}^{}$->a ${}_{}{}^1{}_{}{}^{}\mathrm{\Delta }_{\mathrm{g}}^{}{}_{}{}^{}$ electronic excitation of ${\mathrm{O}}_2$ physisorbed in two different monolayer phases on graphite. The observed 2-eV shift in the resonance energy between the ζ 2 and δ phases is shown to be produced by elastic multiple scattering within the molecular overlayers. This phenomenon, in other electron spectroscopies, will lead to disagreement in the location of resonance energies as determined by different experimental techniques.

A molecular-orbital method is used to analyze the early stages of the K-GaAs(110) interface formation. From our analysis we conclude that the first K atoms deposited on the semiconductor are bonded to Ga, while for a full monolayer coverage a disordered metal geometry may appear. Our results also show a slight evolution in the Fermi level; that for a small K coverage is around 0.9 eV, while that for a monolayer is 0.65 eV. We find that in all the cases the Fermi level is pinned by the adatom-induced density of states in the semiconductor energy gap: The Fermi-level shift as a function of the metal coverage is explained as due to the modification of the semiconductor charge-neutrality level.

A new method of analytic continuation from a Matsubara single-particle Green’s function to a spectral function is presented. We recast this problem onto a new one where we dynamically minimize a suitably defined potential. Our method allows the imposition of physical constraints such as smoothness and adherence to the sum rule. The method is applied to the symmetric Anderson impurity model. We show how the spectral function changes with the Kondo temperature $T_K$, the hybridization witdth Δ, and the Coulomb potential U.

We report, for the first time, measurements of a current-to-current coupling between 2D and 3D electron-gas (EG) layers in the AlGaAs/GaAs system, utilizing an ${\mathrm{n}}^{+}$ GaAs gate as the 3DEG layer. Current driven through either of the layers, which are only 30 nm apart, induces current flow in the other layer. Current-to-current transfer ratios of the order of 3×${10}^{\mathrm{-}5}$ have been observed, and there is a sign reversal of the interaction at temperatures below 40 K. This and other effects can be explained by invoking Coulomb mutual scattering to couple energy and momentum between the two layers.

The effect of magnetoelastic dissipation upon the tunneling and coherence of the total magnetization in small (∼100 Å) single-domain ferromagnetic particles is investigated. Such tunneling would be an example of a macroscopic quantum phenomenon. It is shown that the dissipation has a super-Ohmic spectral density, J(ω)∼${\omega }^3$, and that the dissipation is weak for reasonable material parameters. Corrections to the rates, and the damping rate for coherent oscillations are obtained. A key feature is the inclusion of the elastic waves in the medium surrounding the particle.

Measurements of the superconducting critical temperature ${\mathrm{T}}_{\mathrm{c}}$ are reported for the (${\mathrm{Y}}_{1\mathrm{-}\mathit{x}\mathrm{-}\mathit{y}}$${\mathrm{Ca}}_{\mathit{y}}$)${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ system as a function of x and y. The ${\mathit{T}}_{\mathit{c}}$ vs c curves at fixed values of x can be resolved into two contributions: (1) the counteracting effects of generation and filling of holes in the ${\mathrm{CuO}}_2$ sheets by ${\mathrm{Ca}}^{2+}$ and ${\mathrm{Pr}}^{4+}$ ions, respectively, and (2) the depairing of superconducting electrons via exchange scattering of the mobile holes in the ${\mathrm{CuO}}_2$ sheets by the Pr magnetic moments.

We have performed a detailed anisotropy study of the superconducting properties of untwinned single crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ for δ≊0.1 and δ≊0.4 in magnetic fields up to 22 T using a rf method giving critical fields ${\mathrm{H}}^{\mathrm{*}}$ which are determined by the onset of flux-line motion. For δ≊0.1 we find the highest ${\mathrm{H}}^{\mathrm{*}}$ along the b axis; the a-b anisotropy amounts to 20% at 85 K. The 60-K superconductivity for δ≊0.4 is characterized by the largest ${\mathrm{H}}^{\mathrm{*}}$ along the a axis and pronounced 2D behavior as manifested by a cusp in the angular dependence of ${\mathrm{H}}^{\mathrm{*}}$ and by the extremely steep slope of ${\mathrm{H}}^{\mathrm{*}}$(T) perpendicular to c. We discuss our experimental results with respect to the significance of the Cu-O chains for the high-${\mathrm{T}}_{\mathrm{c}}$ superconductivity of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$.

Using a non-mean-field approach the triangular lattice S=(1/2 Heisenberg antiferromagnet with nearest- and next-nearest-neighbor coupling is shown to undergo an Ising-type phase transition into a chiral symmetry broken phase (Kalmeyer-Laughlin–like state) at small T. Removal of next-nearest-neighbor coupling introduces a local $Z_2$ symmetry, thereby suppressing any finite-T chiral order.

We present observations of time-dependent electrophoretic mobility as large DNA molecules are being deformed in agarose gels under an applied electric field by means of movement of fluorescence pattern after photobleaching (MOFPAP). The short-time (∼min) averaged mobility initially increased with increasing electric-field-on time, and finally reached a steady state. We observed a transition behavior in electrophoretic mobility as the ratio of the gel pore size and the DNA size became smaller. Furthermore, an unusual fluctuating fine structure was observed to superimpose on the oscillating pattern of MOFPAP during the initial period when the electric field was turned on.

We show that the Aharonov-Bohm effect requires that the vector potential couple minimally to matter, not that it be a gauge field: The effect is present in massive (finite-range) electrodynamics, reducing smoothly to the original result in the limit of infinite range. Indeed, it may be used to provide an experimental bound on the range which is much larger than the ‘‘table-top’’ apparatus, namely a lower limit of order ${10}^2$ km.

We consider in this note the time dependence of a system for which two levels (which are not in general decoupled) accidentally cross (or almost cross) for some value of the parameters of the Hamiltonian. We show that for a well-defined class of crossings or narrowly avoided crossings, in which the Hamiltonian changes slowly on its own scale, the system will behave oppositely to the usual adiabatic rule.

A new class of generally covariant gauge theories is introduced. The only field in addition to the gauge connection is a scalar-density Lagrange multiplier. For the group SO(3,C) [SO(3,R)] in four dimensions and particular coupling constants, the theory is equivalent to complex [Euclidean] general relativity, modulo an important degeneracy. The spacetime metric is constructed from the curvature in a solution. A canonical analysis leads directly to Ashtekar’s Hamiltonian formalism. The general solution to the four diffeomorphism constraints in the nondegenerate case is given.