High-resolution spectra of Fe xxv have been observed from Princeton Large Torus tokamak discharges and are used for a detailed comparison with theoretical predictions of Bely-Dubau, Gabriel, and Volonté for the ($1s^{2}nl-1s2pnl$, $n>~3$) dielectronic satellites at 1.85 Å. The theory predicts a significant apparent broadening of the resonance lines of high-$Z$ heliumlike ions in high-temperature plasmas due to the dielectronic capture of electrons into outer atomic shells. The experimental results and theoretical predictions are in good general agreement.

We have observed photoinduced reactions between pairs of zinc and oxygen impurities in gallium phosphide. From photoluminescence studies we find that the nearest-neighbor (Zn, O) pairs are dissociating, after which they re-form as further separated pairs. The activation energy for the dissociation is found to be 0.60±0.07 eV for the photoinduced reaction, and 2.6±0.6 eV for the purely thermal reaction. We tentatively identify the photoinduced reaction as being due to excitation of local phonon modes by nonradiative electron-hole recombination.

Traces of preadsorbed oxygen on a metal surface will induce a high degree of azimuthal order in adsorbed molecules which are disordered azimuthally on the clean surface. This azimuthal-ordering effect has been studied for both N${\mathrm{H}}_3$ and ${\mathrm{H}}_2$O on Ni(111).

The azimuthal variations in the photoemission cross section for the $1e$ molecular orbital of N${\mathrm{H}}_3$ adsorbed on Ni(111) are used to identify the angular orientation of the adsorbed molecules. From comparison of experiment and theory, it is possible to determine the NH-bond directions relative to the substrate. In addition, it is found that the observed strong azimuthal anisotropy comes mainly from direct interference of emissions from the $1e$ molecular orbital rather than from backscattering off the substrate.

It is proposed that the spin-glass phase is described by two order parameters $q\left(x\right)={\left[〈S_i\mathrm{}\right(0\left)\mathrm{}{S}_i\right(t_x\left)〉\right]}_{\mathrm{a}\mathrm{v}}$ and $\chi \mathrm{}\left(x\right)=\int 0^{t_x}\chi \mathrm{}\left(t\right)\mathrm{}\mathrm{dt}$, that measure the relaxations of the average autocorrelation and susceptibility along macroscopic time scales, $t_x$, which are parametrized in a decreasing order by $x\in \mathrm{}[0,1]\mathrm{}$. The function $q$ decays from a finite value at $t_1$ to zero at $t_0$, while $\chi$ increases from $\chi \mathrm{}\left(1\right)\mathrm{}$ to a value $\chi \mathrm{}\left(0\right)\mathrm{}$ which is independent of temperature in the mean-field limit. The equilibrium results agree with Parisi's replica solution.

The spin polarization $P$ of electrons at Cr and Ni surfaces is measured with electron-capture spectroscopy. With use of one-electron capture at magnetized Cr(100)-$c(2\mathrm{}\times 2)$ surfaces at 293 K ($T_N=310\mathrm{}$ K), $P$ values up to -18% are found revealing ferromagnetic order at this surface. Utilizing two-electron capture at demagnetized Ni surfaces we find at 293 K ($T_C=631\mathrm{}$ K) $\mathrm{}\left|P\right|=94\%$ for Ni(110), $\mathrm{}\left|P\right|=72\%$ for Ni(100), $\mathrm{}\left|P\right|=47\%$ for Ni(111), and $\mathrm{}\left|P\right|=14\%$ for Ni(120). There is evidence that "local" ferromagnetic order at Ni surfaces exists even at $2T_C$.

An unusual linear dependence of the nuclear-spin relaxation rate upon the magnetic field is observed in the incommensurate linear-chain mercury compound ${\mathrm{Hg}}_{3-\delta }\mathrm{As}{\mathrm{F}}_6$. It is shown that in two-dimensional metals the planar cyclotron motion of the conduction electrons in a strong magnetic field gives rise to a divergence of the spin-spin correlation function. This new effect, combined with the small orbits resulting from the incommensurate structure, can explain the observed nuclear-spin relaxation behavior in the pseudo two-dimensional metal ${\mathrm{Hg}}_{3-\delta }\mathrm{As}{\mathrm{F}}_6$.

At low pressure and at a commensurability of 3 (at ∼19 kbar) the low-temperature thermopower of TTF-TCNQ is large, negative, and varying $\sim \frac{1}{T}$. At 17 kbar it is smaller, positive, and independent of temperature. At 22 kbar it is similar to that at 17 kbar but of opposite sign. For $P\lesssim 19$ kbar pulling of the distortion wave vector from $2k_{\mathrm{F}}$ to a commensurate value ($\frac{b^{*}}{3}$) leaves the TCNQ valence band underfilled and TTF valence band overfilled. For $P\gtrsim 19$ kbar the reverse holds. We suggest that the excess carriers are charged solitons or polarons.

We introduce a procedure which considerably simplifies the calculation of clusters like those commonly appearing in real-space renormalization-group treatments of bond-percolation and pure and random Ising and Potts problems. The method is illustrated through two applications for the $q$-state Potts ferromagnet.

The rate of anneal of stress-induced ordering of isolated substitutional nitrogen impurities in diamond, measured in the temperature range $78 \mathrm{K}<T<\mathrm{}200\mathrm{} \mathrm{K}$, shows large deviations from Arrhenius-type behavior. It is concluded that in the temperature range considered, reorientation of the centers occurs by tunneling between thermally populated excited vibrational states. Two parameters serve to describe reorientations by thermal activation, by tunneling, and by the combined process.

It is shown that a metal-insulator transition takes place in a Peierls system with half-filled bands at a critical concentration, $c_{\mathrm{cr}}$, of excess electrons. At $c<\mathrm{}{c}_{\mathrm{cr}}$ the electrons form pinned (chaotic) soliton states; at $c>\mathrm{}{c}_{\mathrm{cr}}$ the solitons form an unpinned conducting lattice. We find $c_{\mathrm{cr}}=\frac{a^2}{{\pi }^2{l_0}^2}$, where $l_0$ is the width of the solitons. The theory may explain the metal-insulator transition observed in doped polyacetylene at $c_{\mathrm{cr}}\sim 1$%.

This paper reports measurements of electrical impedance versus frequency on photoelectrochemical solar cells and metal-insulator-semiconductor junctions using polycrystalline, electrodeposited $n$-CdSe electrodes. A simple power law in frequency for the photoelectrochemical cell impedance is interpreted in terms of a percolation conduction at the semiconductor-electrolyte interface with use of arguments supported by measurements on this and related systems.

The excitation spectrum of an antiferromagnetic chain exhibiting the effects of both dimerization and frustration is studied. The method used is based on an exact solution for the doubly degenerate ground state, and views the excitations as propagating defect boundaries between the two exact ground states. These excitations are analogous to "solitons," and can bind into a second type of excitation, analogous to "breathers."

The quantum analog of Kramers's classical theory of the rate of activated events is presented. By means of a path-integral approach, the correlation function expression for the rate of barrier crossing by a quantum mechanical particle coupled to a heat bath is evaluated for finite temperatures. Tunneling effects are dramatically diminished by the frictional influence of the heat bath.

The quantum limitations on measurements of the relative positions of the two mirrors in a Michelson gravity-wave detector are derived. The effects of intensity fluctuations in the two light beams and radiation pressure on the mirrors are modeled in a unified calculation. The radiation-pressure uncertainty in mirror position differs in general from earlier work, but gives agreement for coherent input light.

The amplitude for the ($p$,${\pi }^{+}$) reaction is calculated in a relativistic one-nucleon model with use of a distorted-wave Born-approximation approach. The nucleon continuum and bound-state wave functions are solutions of Dirac equations with appropriate vector and scalar nuclear potentials. Calculations with the pseudovector $\pi \mathrm{NN}$ coupling, which satisfies the constraints of partial conservation of axial-vector current, are in much better agreement with the data than calculations with the simple pseudoscalar coupling.

Measurements of $4d$, $5p$, and $5s$ subshell cross sections have been performed on polycrystalline Ba. These results essentially confirm many-body atomic calculations including the resonant enhancement of photoemission from the outer shells at the $4d$ threshold. Evidence is also presented for a two-electron discrete excited state about 20 eV above the $4d$ threshold.

Subnatural linewidth in the optical transitions of Na $D_2$ lines was directly observed with use of phase switching of the optical field and gating of the photon counter. A linewidth as narrow as 4.5 MHz compared with the natural width of 10 MHz was obtained.

Electron capture accompanied by simultaneous $K$-shell excitation has been observed for 70-MeV ${\mathrm{S}}^{13+}$ + Ar collisions. This process is analogous to dielectronic recombination for the case of free electrons incident on highly charged ions. In addition, radiation following capture into high-$n$ states without accompanying excitation is measured for charge states $q=14+ \mathrm{to} 16+$. The results are used to determine the fraction of capture events which result in $K$-shell radiation, and the fraction of $K$ x rays resulting from capture events.

The universal velocity profile for wall-bounded turbulent flows is verified by numerical integration of the incompressible Navier-Stokes euqations. Mean velocity profiles, Reynolds stresses, and turbulent intensities are in good agreement with experiment. Von Kármán's constant is calculated to be $\kappa =0.46\mathrm{}\pm 0.05$.