A fractal-looking basin boundary for forced periodic motions of a particle in a two-well potential is observed in numerical simulation. The fractal structure seems to be correlated with the appearance of homoclinic orbits in the Poincaré map as calculated by Holmes using the method of Melnikov. Below this critical forcing amplitude the basin boundary appears to be smooth and nonfractal. This example raises questions about predictability in nonchaotic dynamics of nonlinear systems.

This Letter presents a model for tunneling-induced disorder in solids which encompasses both hindered rotors (such as ${\mathrm{H}}_2$ and C${\mathrm{H}}_4$) and hydrogen-bonded ferroelectrics (such as K${\mathrm{H}}_2$P${\mathrm{O}}_4$). The model indicates that while the interaction between tunneling systems decreases tunneling, coupling to phonons actually increases tunneling.

The use of generalized twisted Eguchi-Kawai models is proposed to determine the $\beta$ function of large-$N$ lattice gauge theory.

We use the SU(3) ⊗ SU(2) ⊗ U(1) renormalization-group equations to place upper limits on the scale where new physics beyond the standard model must emerge. Our bounds rely solely on the structure of the renormalization-group equations and on the magnitudes of heavy-quark masses. For example, if $\Sigma m_q^2>~{\left(450\mathrm{} \mathrm{GeV}\right)}^2$, new physics must be found below ${10}^5$ GeV.

Inclusive neutron spectra at 0° were measured from both 390- and 790-MeV/u Ne ions on targets of Pb and NaF. A striking peak at a neutron energy slightly below the beam energy per nucleon has a width (in the projectile rest frame) of ∼58 MeV/c, which is essentially the same for these two energies and these two targets. We suggest that this narrow peak is projectile evaporation and that it is superimposed on the broader fragmentation process predicted by statistical models. The high-momentum region of the cross section may reflect collective behavior.

Supersymmetry has been proposed as a mechanism for the simultaneous description of nuclear systems differing by one or two nucleons. Likewise, $F$-spin multiplets relate properties of neigh-boring even-even nuclei. We present possible evidence that both are manifestitations of a single, higher-lying group structure.

Studies of phase formation in rapidly solidified Al-Mn alloys (composition range 18-22 at.% Mn) show that an icosahedral phase is replaced by another noncrystallographic phase, a decagonal phase. The decagonal phase is another example of quasicrystal: It has a noncrystallographic point group ($\frac{10}{m}$ or $\frac{10}{\mathrm{mmm}}$) together with long-range orientational order and one-dimensional translational symmetry. The decagonal phase is an intermediate phase between an icosahedral phase and a crystal both from the symmetry and from the solidification condition points of view.

Nitrogen is observed to remain a molecular solid up to 130 GPa, contrary to recent theoretical predictions of metallization below 100 GPa. Raman scattering reveals three new phases at 20, 66, and 100 GPa, which are distinguished by branching of existing vibronic modes. One mode increases in frequency to a broad maximum at 66 GPa and then decreases, similar to the case of ${\mathrm{H}}_2$. In ${\mathrm{H}}_2$, such behavior was attributed to a weakening of the H-H bond. In ${\mathrm{N}}_2$, three other vibronic frequencies continue to increase, showing the situation to be more complicated than just a weakening of the N-N bond.

Comparison of x-ray-fluorescence-yield and electron-yield surface extended x-ray-absorption fine-structure spectra above the S $K$ edge for $c(2\mathrm{}\times 2)\mathrm{S}$ on Ni(100) reveals an order-of-magnitude higher sensitivity for the former technique. Thiophene (${\mathrm{C}}_4$${\mathrm{H}}_4$S) chemisorption on Ni(100) is studied with S coverages down to 0.08 monolayer. The molecule dissociates at temperatures as low as 100 K by interaction with fourfold hollow Ni sites. Blocking of these sites by oxygen leaves the molecule intact.

The decay rate $\Gamma$ for a micellar solution pentaethylene glycol mono $n$-dodecyl ether + water has been examined near the critical mixing point by light scattering. We find that the dynamic scaling behavior of ${\Gamma }^{*}\left[\frac{6\pi \eta \mathrm{}\left(T\right)\mathrm{}}{k_{\mathrm{B}}T}\right]\left(\frac{\Gamma }{k^3}\right)$ as a function of $k\xi$ over the range of $0.14\lesssim k\xi \lesssim 6.2$ has an obvious kinship with that for a fluid mixture near the critical mixing point, where $\eta \mathrm{}\left(T\right)\mathrm{}$ is the shear viscosity and $\xi$ the correlation length. It is also found that the shear viscosity exhibits a critical-like power-law singularity and depends explicitly on shear gradients.

The first observation of a smectic-$A$ phase with two collinear incommensurate density modulations is reported. X-ray diffraction studies of this incommensurate phase reveal reflections corresponding to both partially bilayer ($A_d$) and bilayer ($A_2$) periodicities, the relative intensities of the two reflections being strongly temperature dependent.

Using the new concept of survival probability we generalize the Flory approach to compute the second independent exponent in polymer statistics with excluded volume. We obtain $\gamma =3-d\nu$; and for the $\theta$ point, ${\gamma }^{\theta }=2(2-{\nu }^{\theta }d)$. These results bring to completion the mean-field theory for the exponents of polymer statistics.

Bombardment with 0.6-3-MeV ${\mathrm{Ne}}^{+}$ ions has been employed to stimulate solid-phase epitaxial growth of amorphous silicon at temperatures 200-500°C. Two distinctly different regrowth regimes have been identified. In the temperature range 200-400°C the activation energy for beaminduced regrowth is 0.24 eV, whereas, in the temperature range above 400°C, it is higher (>0.5 eV), but less well defined because of competing thermal effects. Results indicate that ion irradiation generates (athermally) nucleation sites for crystal growth, a process which has a high (∼ 2.4 eV) activation energy in the absence of ion-beam excitation.

The Si(111)-$\sqrt{3}\times \sqrt{3}R30°$-Au structure has been analyzed by low-energy alkali-ion-scattering spectroscopy. It has been derived that (1) Au triplet clusters form the $\sqrt{3}\times \sqrt{3}R30°$ lattice and (2) the Si first layer of honeycomb structure lies slightly below the Au layer.

The nuclear magnetization of hcp solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ has been measured for molar volumes ranging from 18.1 to 19.4 ${\mathrm{cm}}^3$/mol and at temperatures down to 43 μK. The magnetization follows the Curie-Weiss law with a positive Weiss temperature, indicating that the dominant spin interactions are ferromagnetic.

Although our understanding of superfluid turbulence has increased dramatically, the nature of the continuous transition at the second critical heat current remains a mystery. We report the first measurements of fluctuations in the dissipation near this transition. The fluctuations appear as broad-band noise without sharp spectral features. A most striking aspect of the data is the structure present in the noise-power amplitude. The results suggest that superfluid turbulence may be a unique system in which to study dynamical transitions.

Ground-state total energies and spins have been calculated for all interstitial and substitutional $3d$ ions in crystalline Si by use of spin-unrestricted density-functional theory plus the linear muffintin-orbital Green's-function method. The calculated deep donor and acceptor levels reproduce for the first time all experimentally observed transitions. The early $3d$ interstitial ions and the late $3d$ substitutional ions are calculated to have low spin. This is in conflict with the generally accepted model due to Ludwig and Woodbury.

The first ab initio theory of structure-independent interatomic potentials in $d$-electron transition metals has been developed from a multi-ion expansion of the total energy within the density-functional formalism. Explicit results for the volume term and two-ion and three-ion potentials entering this expansion have been obtained and successfully tested for $3d$-series metals.

With use of a first-principles unrestricted Hartree-Fock cluster procedure, it is demonstrated that a (${\mu }^{+}{e}^{-}$) center trapped near a vacancy has all the features of the hyperfine tensors for anomalous muonium in diamond and silicon obtained from muon-spin-rotation measurements.

This paper reports the observation of light-induced magnetization in ${\mathrm{Hg}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ by a novel technique combining optical pumping and superconducting quantum interference detection. We show that the magnetization is due to orientation of Mn ions caused by spin transfer from polarized electrons and holes to Mn centers in the process of spin-flip exchange scattering. This interpretation goes beyond a mean-field approach. The effect furnishes direct information on the spin-lattice relaxation in dilute magnetic semiconductors.