Measurements are reported of the sublimation rate of cobalt in the vicinity of its Curie temperature ($T_{\mathrm{C}}=1400\mathrm{}$ K) which show a relatively large change (∼0.8 eV/atom) in the apparent activation energy for sublimation near $T_{\mathrm{C}}$. The results can be accounted for in terms of a simple model that incorporates into the sublimation process the temperature dependence of the magnetic contribution to the binding energy of a cobalt surface atom.

This paper reports investigation of the photoinduced mechanical response of a mono-layer consisting of the copolymer poly(methyl methacrylate)-spiropyran (molecular weight 215 000, 5.1 mole% spiropyran) at an air-water interface. Irradiation with uv-light pulses isomerizes the spiropyran chromophore and leads to a relative surface-pressure increase up to 10% at saturation. The photoexcited state has a typical decay time constant of 20 min. Irradiation with visible light returns the chromophore to the initial state making the mechanical process fully reversible.

Experimental evidence is presented in support of a recent suggestion by Baraff, Kane, and Schlüter that the isolated lattice vacancy in silicon is an Anderson negative-$U$ system. The second donor level (+/++) (of charge state + if defect level is occupied by an electron; ++, if unoccupied) is located at $E_v+0.13\mathrm{}$ eV, above a first donor level (0/+) at $E_v+0.05\mathrm{}$ eV. Evidence is presented that interstitial boron has negative-$U$ properties with a single donor level (0/+) at $E_c-0.13\mathrm{}$ eV, above a single acceptor level (-/0) at $E_c-0.45\mathrm{}$ eV.

The ac susceptibility of a sequence of amorphous Fe-Mn alloys shows lines of both spin-glass and ferromagnetic transitions. A detailed scaling-law analysis, treating the common point on the two magnetic phase boundaries as a multicritical point, verifies the scaling hypothesis and yields multicritical, spin-glass, and crossover exponents. The observed behavior compares quite will with position-space renormalization results.

Exciton dynamics in Tb${\mathrm{}\left(\mathrm{OH}\right)\mathrm{}}_3$ is shown to depend upon the excitation location within the $k\simeq 0$ inhomoheneously broadened absorption profile. The dynamics is observed by monitoring the populations of the different $k$ states from time-resolved band-to-band luminescence. The results indicate the presence of experimentally separable microscopic regions within which delocalized exciton states occur with well-defined $k$ values.

A polarized- neutron study of the compound U${\mathrm{Ge}}_3$ has revealed that the susceptibility at the Ge atom is paramagnetic and highly aspherical. A fit to experiment has been obtained with a single $4d_{z^2}$ orbital at the Ge site. Such an effect probably arises from charge transfer from U to Ge and strong hybridization with the unoccupied Ge $4d$ states.

Emission rates and hole-capture cross sections for the Au donor center in silicon are reported and from entropy considerations this center is shown to be similar in behavior to the Pt donor center. In contrast, the gold and platinum acceptor states display significantly different entropy changes on electron emission. A similar chemical structure for both these defects is proposed which is then used to interpret differences in electron emission behavior from the acceptor forms of the two defects.

The contribution of phason and amplitudon excitations to the spin-lattice relaxation rate in structurally incommensurable ($I$) systems as well as the NMR line shapes in these systems have been evaluated and compared with the ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ NMR data for ${\mathrm{Rb}}_2$Zn${\mathrm{Cl}}_4$. The presence of a strong, temperature-independent relaxation mechanism, which disappears below the "lockin" transition, demonstrates that in the $I$ phase of ${\mathrm{Rb}}_2$Zn${\mathrm{Cl}}_4$ the spin-lattice relaxation rate is dominated by phasons.

Photoemission indicates that the formation of the surface states (surface resonances) on the (111) face of ultrathin Pd overlayers on a recrystallized Nb foil commences with the deposition of the third atomic layer and is completely established at the full fourth layer. It also shows the formation of two resonant $d$ states at submonolayer coverages, corresponding to the interaction of Pd $d$ levels with the Nb bulk bands and to the Pd bulk $d$-band resonance, respectively.

New analytic results are presented for the low-$T$ thermodynamics of the Ising-Heisenberg linear ferromagnetic in a magnetic field $H_0$. For small $H_0$ the thermodynamic functions show unexpected and interesting structure as a function of $H_0$ and the anisotropy $\Delta$. The thermal and magnetic energy gaps have singularities, not necessarily at the same $\Delta -H_0$ location, as changes occur in the type of excitation dominating the low-$T$ behavior. The results may relate to quantum solitons in the linear ferromagnet.

The relevance of finite-temperature gauge-theory effects on computations of the cosmological baryon-to-entropy ratio is discussed.

It is shown that the requirements of spontaneous $\mathrm{CP}$ breaking and natural flavor conservation lead to a class of theories where $\mathrm{CP}$ nonconservation is due solely to Higgs exchange, for an arbitrary number of fermion generations.

Evidence of bottom-quark-state production has been searched for in $p$-Fe interactions at 400 GeV/c by looking for multimuon final states. Muons in such final states could come from $B\to \psi \to 2\mu$ decay accompanied by a muonic decay of $\overline{B}$ (or $\overline{B}\to \overline{D}\to \mu$ chain) or from a combination of $B$ and $D$ muonic decays. With the assumption of a 10% branching ratio for $B\to \mu X$, a search for several specific decay modes yields an upper limit for the $B$ production cross section of ≲ 50 nb/nucleon.

This Letter reports measurements of the ratios of $\pi$, $K$, and $p$ production at large values of transverse momentum in ${\pi }^{-}-p$ collisions. The charge ratios, such as $\frac{{\pi }^{-}}{{\pi }^{+}}$, $\frac{K^{-}}{K^{+}}$, and $\frac{\overline{p}}{p}$ are seen to be quite different from those measured in $p-p$ collisions. These ratios are sensitive tests of hard-scattering models, and are compared with the-oretical predictions. The particle ratios have also been studied as a function of center-of-mass angle (${\theta }^{*}$) at ${\theta }^{*}=90\mathrm{}°, 77°, \mathrm{and} 60°$.

New results for parton transverse momentum obtained from two-jet high-$p_T$ hadron events are presented. These results, and results for quark structure functions in the pion, are compared with results from dimuon production experiments. The results for the two types of experiments are very similar. This indicates that jet pairs give direct information on parton-parton scattering.

A simple space-time description of high-energy hadron-nucleus collisions is presented. The model is based on the two-sheet description of soft multiparticle production in hadron-hadron collisions, and can be formulated in a parton framework. This zero-parameter model agrees well with the general features of hadron-nucleus data.

This paper reports on a search for ${\overline{\nu }}_e$ from ${\mu }^{+}\to e^{+}{\overline{\nu }}_e{\nu }_{\mu }$, allowed by multiplicative but not additive muon conservation, and for ${\nu }_e$ from ${\mu }^{+}\to e^{+}{\nu }_e{\overline{\nu }}_{\mu }$, allowed by both. Neutrinos from the Clinton P. Anderson Meson Physics Facility have been used, together with a six-ton Cherenkov counter filled with ${\mathrm{H}}_2$O (${\mathrm{D}}_2$O) to look for ${\nu }_{e}p\to n{e}^{+}({\nu }_{e}d\to \mathrm{pp}{e}^{-})$. The branching ratio $\frac{({\mu }^{+}\to e^{+}{\nu }_e{\nu }_{\mu })}{({\mu }^{+}\to \mathrm{all})}=-0.001\mathrm{}\pm 0.040$ is in excellent agreement with the additive law. The cross section $〈\sigma ({\nu }_{e}d\to \mathrm{pp}{e}^{-})〉=(0.52\mathrm{}\pm 0.18)\times {10}^{-40\mathrm{}}$ ${\mathrm{cm}}^2$ agrees with theory.

Using a proportional-chamber spectrometer and an array of lead-glass photon detectors, we have observed four examples of the decay ${K_L}^0\to e^{+}{e}^{-}\gamma$, and one candidate for ${K_L}^0\to {\mu }^{+}{\mu }^{-}\gamma$. The corresponding branching ratios are (17.4±8.7)×${10}^{-6\mathrm{}}$ and (2.8±2.8)×${10}^{-7\mathrm{}}$, respectively. In addition we have established 90%-confidence-level upper limits of $b({K_L}^0\to e^{+}{e}^{-}{\pi }^0)<\mathrm{}2.3\mathrm{}\times {10}^{-6\mathrm{}}$ and $b({K_L}^0\to {\mu }^{+}{\mu }^{-}{\pi }^0)<\mathrm{}1.2\mathrm{}\times {10}^{-6\mathrm{}}$.

Using a proportional-chamber spectrometer and an array of lead-glass photon detectors, we have observed 1070 ${K_L}^0\to {\pi }^{+}{\pi }^{-}\gamma$ events. We have extracted the branching ratios of the inner-bremsstrahlung component $b{({K_L}^0\to {\pi }^{+}{\pi }^{-}\gamma , k>\mathrm{}20\mathrm{} \mathrm{MeV})}_{\mathrm{IB}}=(1.52\mathrm{}\pm 0.16)\times {10}^{-5\mathrm{}}$, which agrees within errors with the theoretical prediction, and of the directemission component, $b{({K_L}^0\to {\pi }^{+}{\pi }^{-}\gamma )}_{\mathrm{DE}}=(2.89\mathrm{}\pm 0.28)\times {10}^{-5\mathrm{}}$. The $\gamma$-energy spectrum for direct emission shows possible evidence for a deviation from the pure $M1\mathrm{}$ shape.

It is shown that the boson expansion theory can describe very well various features of nuclei in the Os-Pt region. In particular it fits the sign and magnitude of the static quadrupole moment of the $2_1^{+}$ state, where the O(6) theory encounters difficulties.