The resistances of $K$Rb alloys have been measured by new high-precision techniques (1 part in ${10}^7$) from 180 mK to 4 K. Below 1.3 K a term proportional to the residual resistivity and to $T^2$ is positively identified. It is believed that this is the long sought for contribution to the resistivity from inelastic impurity scattering of electrons.

Measurements are reported of resonant nonradiative energy transfer in the $R_1$ line of ruby at 5 K using a fast Stark shifting technique. The transfer rate for 0.8% ruby is found to be slow, ∼ 1 ${\mathrm{msec}}^{-1\mathrm{}}$, contrary to the much more rapid rates proposed earlier by several workers but in fair agreement with the results of Heber. Implications of the results for the occurrence of an Anderson transition in ruby are discussed.

Nonradiative resonant energy transfer has been directly observed in ruby. However, the transfer rate is much slower than previously thought. For example, at 0.25% Cr concentration, an excitation will transfer roughly once in the radiative lifetime. We conclude ruby is unsuitable for observing an Anderson transition.

Far-infrared magneto-absorption experiments performed in semimetallic InAs-GaSb superlattices are presented. The results are interpreted in terms of cyclotron resonance and interband transitions from the valence subbands to the conduction subbands. The resulting energy gaps of the superlattices are found to be negative, demonstrating directly their semimetallic nature. The observed electron mass is enhanced as a result of the conduction-band nonparabolicity.

Zero-temperature metallic conductivities have been measured above and below Mott's minimum value ${\sigma }_{min}$ in bulk crystals of P-doped Si. Conductivities below ${\sigma }_{min}$ increase by over ${10}^3$ as the density is raised by less than 1%, and do not rule out a discontinuous transition. However, over a wider density range the data can be fitted with a scaling form with a characteristic length that tends to diverge with the same exponent in the metal and insulator.

In this paper the observation of sharp and very weak emission lines in phosphorousdoped silicon near twice the band-gap energy is reported. The line with the highest energy can be attributed to the total radiative annihilation of a free biexciton. The other three lines originate from the decay of two electron-hole pairs in a multiple bound exciton complex of two, three, and four excitons.

The temperature ($T$), frequency ($f$), and electric field ($E$) dependent conductivity ($\sigma$) of iodine-doped polyacetylene is reported for the concentration regime which encompasses the metal-insulator transition. No $f$ dependence was observed for $f<\mathrm{}500\mathrm{}$ MHz. The resistance varied logarithmically with $E$, while $\sigma \sim \ln T$ and $\sigma \sim \exp [-{\left(\frac{T_A}{T}\right)}^{0.25}]$ were observed. This $\sigma \mathrm{}(T,E,f)\mathrm{}$ is inconsistent with simple models of metallic regions separated by large barriers and suggests that the known strong disorder plays a dominant role.

The concentration of free charge carriers $p$ as a function of the doping level $C$ [$p\left(C\right)\mathrm{}$ characteristic] is calculated for a semiconductor containing defects with negative correlation energy $U$ of bound charge carrier pairs. It is shown that in a certain interval $p\sim C^{\frac{1}{2}}$ in contrast to the behavior of defects with positive correlation energy $U$ and of singly charged defects. Therefore, one has a simple criterion to prove experimentally whether a given kind of defect level has the negative-$U$ property or not.

Recent baryon magnetic moment measurements are used to isolate individual quark magnetic moment contributions, including nonstatic effects. The pattern of symmetry breaking observed is that quarks in spin-triplet states preserve SU(3), while quarks in spin-singlet states break SU(3). Relativistic effects are suggested as the dominant symmetry breaking mechanism. The present ${\Sigma }^{-}$ moment determination is incompatible with this analysis.

This Letter carries out a sensitive (∼5 events/nb) search for narrow $\overline{p}p$ states at the Brookhaven National Laboratory multiparticle spectrometer. No evidence is found for such states in the mass range 1900-2400 ${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{c}}^2$ in the reaction ${\pi }^{-}p\to p{\pi }^{-}\overline{p}p$ at 16 GeV/c. In particular, the $\overline{p}p$ states at 2020 and 2200 ${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{c}}^2$ previously reported in a CERN $\Omega$-spectrometer experiment are not observed.

Coincidence measurements of electrodisintegration products have been used to simultaneously study the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^8{}_{}{}^{}\mathrm{Be}$, and ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$+$\alpha$ decay channels of ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$. Asymmetric fission into ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^8{}_{}{}^{}\mathrm{Be}$, is concentrated between 18 and 28 MeV in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ and exhibits resonances with cross sections ten times those of symmetric fission. There is little correlation among resonances in the three decay channels. The fission yields are not consistent with statistical decays from giant resonances, and suggest highly clustered states in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$.

The transition charge density for the octupole vibration of ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ has been determined with an unprecedented accuracy for an inelastic transition. A comparison with some of the best theoretical calculations shows a persistent discrepancy in the interior of the nucleus which offers a measure of the limitations of the various theoretical approaches considered.

Theoretical estimates of total cross sections for the coherent production of isobars in a relativistic heavy-ion projectile with concomitant excitation of the target to a giant resonance at two appreciably different energies/nucleon are presented and comparisons are made to estimated experimental total cross sections for pion production.

The nonlinear evolution of oblique collisions is investigated experimentally on plane ion-acoustic solitons in two-dimensional space. Many of the observed characteristics of inelastic collisions of solitons are found to be similar to those of resonance interactions described by nonlinear ion-acoustic waves.

The form of the stress tensor and of the ponderomotive force in a dispersive medium in which there is a fast-varying electromagnetic field present is discussed. By carefully taking into account the symmetry of the stress tensor, an extra contribution to the ponderomotive force, not found so far by other authors, has been found, which can lead to the self-generation of magnetic fields in a turbulent plasma.

The erosion of water ice films by fast H and He ions has been found to depend on the electronic energy loss of the ion. At low temperatures the erosion yield is temperature independent and varies quadratically with the electronic stopping power, consistent with a Coulomb repulsion model of ejection. At temperatures above ∼100 °K the erosion is found to be temperature dependent and linear with the electronic stopping power. The erosion in this regime can be associated with defect formation and migration in the ice.

The polymer network of a gel, under certain conditions, undergoes a discrete transition in equilibrium volume with changes in solvent composition or temperature. This Letter demonstrates that ionization of the gel network plays an essential role in the phase transition. The volume collapse is also observed when the $p\mathrm{H}$ within the gel is varied.

Mössbauer cross section isotherms of Sn${\left(\mathrm{C}{\mathrm{H}}_3\right)}_4$ adsorbed on graphite show a two-step melting process which suggest the formation of two-dimensional moving islands in the intermediate phase. Above 0.65 of a monolayer and $T\lesssim 85$ K, the cross section increases sharply which we tentatively interpret as a coalescence of the islands into a large, still "continent." At ≃ 100 K, the islands melt into an isotropic fluid.

It is shown that the coordinates $\Delta N$ and $\overline{N}$, where $N$ is the periodic-table group number, effect a much better crystal-structure separation than do the coordinates of Zunger for 91 transition-metal-transition-metal compounds. It is concluded that there is no evidence from structure maps to support the assumption that $s-p$ electrons control the crystal structure dependent part of the energy of this class of compounds nor is there evidence to deny that $d$ electrons effectuate this control.

The temperature dependence of the orientational parameter was measured by ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ NMR techniques on solutions of polystyrene dissolved in nematic liquid crystals. This temperature dependence is different from that one of pure nematogens or of solutions of small molecules in nematic phases. These results are consistent with the concept of a pseudo clearing temperature introduced theoretically by Brochard. These are general results for solutes in nematic solvents, including those previously obtained on dissolved small molecules.