Similarity-type decay-mode solutions of the two-dimensional Korteweg-de Vries equation, ${(u_t+6u{u}_x+u_{\mathrm{xxx}})}_x+3\mathrm{}{\alpha }^2{u}_{\mathrm{yy}}=0\mathrm{}$, with $\alpha$ being constant, have been obtained explicitly in the simple analytic functions. Solutions of this decay mode have nonlinear superposition property similar to soliton solutions. Generalization of the customary Bäcklund transform enables one to produce multiple-soliton, multiple-decay-mode solutions.

It is shown that the acceleration of the sine-Gordon solitons by a constant torque increases as $t^2$ for small times $t$. For larger times, the velocity behaves like tanh $t^3$. Thus the soliton dynamical behavior is not Newtonian. Analytical arguments are given based on the linear perturbation theory which generalize this conclusion to any weak external perturbation of sine-Gordon solitons.

For the two-dimensional Ising model at arbitrary temperature, a system of quadratic difference equations is presented, involving the correlations of $n$ order variables and that of $n-2\mathrm{}$ order and two disorder variables. With suitable boundary conditions these equations specify the correlations.

Results are reported of an experiment to measure the cross section for production of the $D^{{*}^{+}}$ ($D^{{*}^{-}}$) in 200-GeV/c ${\pi }^{-}N$ interactions. We observe 78 ± 26 events corresponding to a $D^{*}$-production cross section $\frac{d\sigma }{\mathrm{dy}}=1.6\mathrm{}\pm 0.5$ μb at $y=0\mathrm{}$.

It is pointed out that the recently discovered dip in elastic $p\overline{p}$ cross section is related to the dips at lower $\mathrm{}\left|t\right|\mathrm{}$ and lower energies, consistent with the geometrical picture of high-energy scattering. At 30 GeV/c incoming energy, the dip is predicted by interpolation to occur at $-t=1.1\mathrm{}$ (GeV/${\mathit{c})}^2$. The curve for dip position versus ${\sigma }_T$ is discussed.

Experimental results on the change of electron spin polarization due to elastic scattering are reported. Measurements with a mercury target have been made at electron energies between 30 and 350 eV at a scattering angle of 90°. In conjunction with results for the differential cross section and the Sherman function, such measurements yield the maximum possible information on the scattering process.

It is shown that quasilinear diffusion in velocity space can fully account for the formation of a high-energy ion tail in current-driven ion-acoustic instability. The mechanism is effective for a relatively small turbulence level, $\frac{W}{n{T}_e}\simeq {10}^{-3\mathrm{}}$.

The vibrational excitations, both in the Si-bulk band mode region and above it at the impurity centers in the various configurations for the $a$-Si: F and $a$-Si: (F,H) alloys, have been obtained by using a cluster Bethe-lattice method. The predicted frequencies are in excellent agreement with the available experimental data.

In molecular-dynamics simulations of Be${\mathrm{F}}_2$ glass, it is observed that a few percent of the ions are capable of displacements of the order of 1 Å in 10 ps at temperatures lower than 300 K. It is shown that these ions are located at well-defined defect sites in the glass. The activation energy for such motion is between 0.03 and 0.2 eV. Ions making large displacements often return to their starting points after a few picoseconds (periodic motion). It is suggested that such mobile ions are responsible for the low-temperature anomalous properties of glass.

Extra Si density of states has been observed within about 3-4 Å of the ${\mathrm{Pd}}_2$Si-Si(111) interface. Spectral analysis indicated that most of these states exist near the Si band-gap region and originate from an atomic environment more Si rich than ${\mathrm{Pd}}_2$Si. Transmission-electron-microscopy lattice images showed a structurally sharp ${\mathrm{Pd}}_2$Si-Si interface with misfit dislocations and atomic-step imperfections. It is suggested that the interfacial bonding in such a structure can account for the observed interface states.

Is is found that nonlinear effects give rise to anomalies in the spectrum of the antiferromagnetic Heisenberg chain in an external field, even at low temperatures. Divergences in the two-magnon density of states are responsible for additional resonances, besides the usual spin-wave peak, in the dynamic structure factor.

A physically interesting nonlinear singular integro-differential equation which is an intermediary between the Korteweg-de Vries and Benjamin-Ono equations is considered via the inverse-scattering transform. Novel aspects of the theory and limits to the Benjamin-Ono equation are discussed.

Horizontal flavor chirality and a minimal Higgs system are combined for uniquely establishing a "canonical" fermion mass matrix, reflecting pure nearest-neighbor Yukawa interactions, for any arbitrary number of generations. The quark-mass matrices then become tightly correlated by the anomaly-free equations, admitting neither strong nor weak $\mathrm{CP}$ nonconservation. The resulting horizontal $\mathrm{CP}$ nonconservation is then truly superweak, signifying the existence of an energy oasis around a few hundred teraelectronvolts.

The ${\beta }^{+}$ branch of ${}_{}{}^{18}{}_{}{}^{}\mathrm{Ne}$ to the 1081-keV $J^{\pi }=0^{-}$, $I=0\mathrm{}$ level of ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$ is observed to have an intensity of (1.71 ± 0.41)×${10}^{-4\mathrm{}}$ times that of the superallowed Fermi transition to the 1042-keV $J^{\pi }=0^{+}$, $I=1\mathrm{}$ level. This result plus the previously measured upper limit on parity mixing in the $0^{+}$, $0^{-}$ doublet of ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$ yields an upper limit of ± (0.5 ± 1.3) × ${10}^{-6\mathrm{}}$ for $F_{\pi }$. This limit is largely independent of details of nuclear structure.

A simple relationship between the one-body and exchange-current contributions to the axial charge operator may allow a separation of these amplitudes in the $\beta$-decay transition ${}_{}{}^{18}{}_{}{}^{}\mathrm{Ne}(J^{\pi }I=0^{+}1)\to {}_{}{}^{18}{}_{}{}^{}\mathrm{F}(J^{\pi }I=0^{-}0)$. Since the exchange-current operator is related by isospin rotation to the pion-exchange component of the parity-nonconserving nucleon-nucleon potential, this suggests that the parity-nonconserving pion coupling can be extracted, with minimal dependence on nuclear models, from circular-polarization measurements for the analog $\gamma$ decay in ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$.

This Letter suggests that $\overline{p}$-nucleus scattering might display resonant phenomena at certain energies, arising from the orbiting of the $\overline{p}$ in a pocket of nuclear attraction extending beyond the region of strong absorption. This results in resonances of typical widths 15-150 MeV in the 180° excitation function and large polarizations for large-angle elastic scattering.

Inelastic electron scattering is used to identify $M8\mathrm{}$ transitions and assign $J^{\pi }=8^{-}$ to states at $E_x=8.314, 8.949, 9.974, 10.677, \mathrm{and} 13.263$ MeV excitations. Shell-model calculations within the model space ${[g_{\frac{9}{2}}\otimes ({f_{\frac{7}{2}}}^{-3\mathrm{}}\left)\right]}_{8^{-}}$ suggest that the four lowest states are $T=1\mathrm{}$ and the strongest excitation, to the state at 13.263 MeV, is $T=2\mathrm{}$.

The microscopic basis of the proton-neutron interacting-boson model is studied by comparison with exact shell-model calculations. These calculations show that the $0^{+}$ and $2^{+}$ collective nucleon pairs, which correspond, respectively, to $s$ and $d$ bosons, play dominant roles in quadrupole collective states. The boson Hamiltonian is constructed microscopically from these pairs, while effects of other pairs are also included by renormalization of the Hamiltonian. Resultant boson spectra agree well with the exact ones.

A first-order correction is presented to a previously derived zeroth-order approximate eikonal exchange amplitude for electron-hydrogen scattering and both the modulus and the phase are compared with those of the exact eikonal exchange amplitude for elastic scattering. The correction term dramatically improves the approximation, even at energies as low as 50 eV.

A beam of 400-eV positrons is partially transmitted through a 40-Å C film in vacuum. Measuring the $\gamma$-ray energy spectrum with a downstream Ge(Li) detector, a new $\gamma$-ray peak is observed, the energy of which can be changed by applying a voltage to a grid behind the film. Attributing the new peak to a Doppler-shifted annihilation $\gamma$ implies a mass-to-charge ratio $3.011\left(14\right)\mathrm{}\frac{m}{e}$, thus signaling the presence of the $e^{-}{e}^{+}{e}^{-}$ positronium negative ion, ${\mathrm{Ps}}^{-}$. The ${\mathrm{Ps}}^{-}$ conversion efficiency of the C film is (2.8±0.3)×${10}^{-4\mathrm{}}$.