We report the first observation of magnetic resonance of oriented rare-earth nuclei in a rare-earth host. Radioactive ${}_{}{}^{160}{}_{}{}^{}\mathrm{Tb}$ implanted in a single crystal of ferromagnetic terbium was subjected to magnetic resonance detected by perturbation of the gamma-ray anisotropy. The open Tb $4f$ shell gives rise to a strong electric quadrupole interaction in addition to the magnetic interaction; the resulting resonance signal has six components, of which the first was detected at 480.0(4) MHz. The derived quadrupole interaction frequency is 167.7(2.6) MHz, giving $Q=3.56\mathrm{}\left(10\right)\mathrm{} \mathrm{b}$.

The occurrence of magnetic order in the heavy-fermion system Ce${\mathrm{Pb}}_3$ has been demonstrated by means of neutron scattering. The magnetic structure is antiferromagnetic with a moment modulation in the cubic (001) plane. The magnetic moments are aligned along the [001] axis, parallel to the antiferromagnetism direction. The local character of $4f$ electrons is evidenced by the observation of crystal-field transitions. The characteristics of Ce${\mathrm{Pb}}_3$ are discussed in terms of competition between usual $4f$ properties and Kondo-type couplings.

The vibrational and thermal-desorption spectra of the terminal and $\pi$-bonded adsorption states of ${\mathrm{N}}_2$ on clean and potassium-promoted Fe(111) at 74 K are reported. Submonolayer precoverages of potassium dramatically enhance the sticking coefficient of ${\alpha }_1-{\mathrm{N}}_2$, the $\pi$-bonded precursor to dissociation. As potassium promotion of surface reactions has been previously attributed to bond weakening in the dissociation precursor, an increase of the precursor population, with no evident bond weakening, is an important new result.

Kinetic simulations of the interaction between two collisionless shocks are presented. During the collision of two perpendicular shocks, the shock electromagnetic field structures pass through each other, while the previously shocked ions are kept separate by the electric fields arising in the collision. When two supercritical shocks collide, a fraction of ions are accelerated up to an order of magnitude in energy by first being reflected at one shock, then interacting with the electric fields of the other shock.

It is proposed that the superstring and its spectrum may not be fundamental but may themselves correspond to an approximate solution to a self-consistent dynamical theory built from the basic principles of $S$-matrix unitarity, analyticity, and crossing. In particular, it is shown that a simple approximate dual unitary scheme based on these principles does generate linear Regge trajectories and selects closed (rather than open) strings.

Axion photoproduction, particularly laser and wiggler induced, is suggested as a systematic technique for probing the couplings of new elementary pseudoscalar (or scalar) particles in the megaelectronvolt mass range to leptons, photons, and hadronic matter.

We report final results for the $D^{\pm }$, $F^{\pm }$, and $\Lambda _c^{}{}_{}{}^{+}$ lifetimes measured with a hybrid emulsion spectrometer in the wide-band neutrino beam at Fermilab. In total, 3886 neutrino and antineutrino interactions were located in the fiducial volume of the emulsion. From these interactions we have unambiguously identified $6 F^{\pm }$ and $13 \Lambda _c^{}{}_{}{}^{+}$ decays, for which the fitted lifetimes are $\tau \left(F^{\pm }\right)=\left({2.6}_{-0.9\mathrm{}}^{+1.6\mathrm{}}\right)\times {10}^{-13\mathrm{}}$ s and $\tau \left(\Lambda _c^{}{}_{}{}^{+}\right)=\left({2.0}_{-0.5\mathrm{}}^{+0.7\mathrm{}}\right)\times {10}^{-13\mathrm{}}$ s. 28 other decays are consistent with a $D^{+}$ or $D^{-}$ hypothesis. From these events, we obtain a $D^{\pm }$ lifetime of (${11.1}_{-2.9\mathrm{}}^{+4.4\mathrm{}}$) × ${10}^{-13\mathrm{}}$s.

We report final results for the $D^0$ lifetime measured with a hybrid emulsion spectrometer in the wide-band neutrino beam at Fermilab. In a total of 3886 neutrino and antineutrino interactions located in the emulsion fiducial volume, we have found 58 $D^0$ decays, from which we determine the lifetime to be (${4.3}_{-0.5-0.2\mathrm{}}^{+0.7+0.1\mathrm{}}$) × ${10}^{-13\mathrm{}}$ s.

The lifetime of the $F^{\pm }$ meson has been measured to be (${3.5}_{-1.8\mathrm{}}^{+2.4\mathrm{}}$±0.9) × ${10}^{-13\mathrm{}}$ s by means of the $F^{\pm }\to {\phi \pi }^{\pm }$ decay mode. The measurement was made with the High Resolution Spectrometer at the SLAC $e^{+}{e}^{-}$ storage ring PEP at a center-of-mass energy of 29 GeV.

Accurate measurements of the left-right asymmetry in ${\pi }^{-}p\to \gamma n$ at $p_{\pi }=427-625\mathrm{}$ MeV/c with a transversely polarized target are reported. Results are compared with the predictions from the Arai and Fujii single-pion photoproduction partial-wave analysis and with data on the inverse process measured with a deuterium target. The agreement is poor, casting doubt on the correctness of the value for the radiative-decay amplitude of the neutral Roper resonance now in use.

Gamma-ray transition-energy spectra up to $E_{\gamma }\simeq 33$ MeV have been measured for the decay of the compound nucleus ${}_{}{}^{111}{}_{}{}^{}\mathrm{S}\mathrm{n}*$ populated at excitation energies up to $E^{*}\simeq 100$ MeV. Above $E_{\gamma }\simeq 20$ MeV an excess of gamma rays over the contribution from the isovector giant dipole resonance is observed in the energy range where the isovectors giant quadrupole resonance built on excited states is expected. The width of the giant dipole resonance in ${}_{}{}^{108,111}{}_{}{}^{}\mathrm{S}\mathrm{n}*$ shows a large increase with increasing nuclear temperature and angular momentum.

An efficient method to build periodic orbits of the time-dependent Hartree-Fock equations is presented. A numerical application to monopole vibrations in the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ nucleus is discussed.

Differences between the rates of ${}_{}{}^{241}{}_{}{}^{}\mathrm{Pu}$ decay in the free ions ${\mathrm{Pu}}^{1+}$${-\mathrm{P}\mathrm{u}}^{5+}$ are predicted. Two mechanisms modifying these differences when the ions are present in an ionic solid are elucidated. ${}_{}{}^{241}{}_{}{}^{}\mathrm{Pu}$ is predicted to decay 0.3% faster in solid PuO than in solid Pu${\mathrm{O}}_2$. Chemical variations of this magnitude may be a contributing factor to the observed discrepancies between different experimental determinations of the half-life of ${}_{}{}^{241}{}_{}{}^{}\mathrm{Pu}$ but are unlikely on their own to account completely for the anomaly.

We report measurements of the axial variation of the wave number $q$ of Taylor-vortex flow in a system with aspect ratio $17\lesssim L\lesssim 25$ containing ten vortex pairs between rigid nonrotating ends. Near the critical Reynolds number $R_c$, $q$ is very nonuniform when its average value $\overline{q}$ differs significantly from its critical value $q_c$. For sufficiently small $|\overline{q}-q_c|$, the finite geometry eliminates the Eckhaus instability. Our results agree quantitatively with solutions of the Ginzburg-Landau equation.

We investigate laser cooling of phonons in a low-density crystal of ions. If the linewidth of the optical transition covers the range of phonon frequencies, the rate of decrease of mechanical energy per one ion in the crystal is found to be essentially the same as in an ideal gas of two-level systems, but the cooling is concentrated on a subset of the phonon modes. A broad phonon spectrum tends to counteract the cooling.

Two new results are presented on the development of convective flow in a finite Hele-Shaw cell. First, it is shown that within a certain range of Rayleigh numbers there exist three regions in the fluid layer: the center region having a steady flow and the two end regions exhibiting time-dependent flow. Second, in the two end regions each flow oscillation is always found to be monoperiodic and the two are not correlated. Transition to a more complicated oscillation is not observed, and the flow never becomes chaotic. The time-dependent flow regime is bounded at low and high Rayleigh number by transitions to steady-state flow.

We report the first operation of a high-gain, long-pulse (> 1 μsec), free-electron-laser oscillator. The growth rate is measured by variation of the interaction length of the electron beam within the oscillator cavity. The observed power gain per pass of up to ${10}^4$ and the buildup of cavity power to multimegawatt levels are in agreement with high-gain oscillator theory. Growth rates have also been measured as a function of wiggler field strength.

A radiative-transfer equation describing the propagation of light in a disordered medium is presented. The equation includes the effects of weak localization and polarization of the light. The polarization of the light in coherent backscattering from a disordered medium is discussed. It is found that for circularly or elliptically polarized light the interference in the backward direction is partially destructive. For linearly polarized light the depolarized scattered component does not contain coherent backscattering, in qualitative accord with observations.

We show that the atomic dispersion and therefore the efficiency of the nonlinear generation at a given frequency can be controlled by the addition of an extra resonant laser field. Using this change in dispersion, we explain some of the recent observations on the vacuum ultraviolet generation in Xe and Hg.

A radial profile of plasma potential is successfully controlled by the use of circular concentric segmented electrodes at both ends in a simple axisymmetric electron cyclotron resonance mirror plasma. An enhancement of radial nonambipolar ion transport is clearly observed under a condition where the ion Larmor motion is strongly modified by a radial electric field directed outward.