Electron paramagnetic resonance measurements on the aquo complex of sperm whale skeletal myoglobin in solution at $T<\mathrm{}4\mathrm{}$ K show that, at phonon energies around 20 ${\mathrm{cm}}^{-1\mathrm{}}$, the density of vibrational states is that of a three-dimensional system.

Results of numerical simulations of the evolution of a network of interacting cosmic strings in an expanding universe are presented and compared with a simple model. The results lend weight to earlier speculations about the evolution of cosmic strings.

A problem of critical importance to space physics and astrophysics is the existence and properties of high—mach-number shocks. In this Letter we present the preliminary results of a simulation of a perpendicular shock with Alfvén Mach number 22. We show that for sufficiently small electron resistivity the dissipation for this shock is provided by a periodic, rather than time-stationary, reflection of ions. We discuss the problem of electron heating and the extension to higher Mach numbers.

We report a measurement of the ultrahigh-energy cosmic-ray spectrum using an atmospheric fluorescence technique for extensive-air-shower detection. The differential spectrum between 0.1 and 10 EeV (1 EeV = ${10}^{18}$ eV) is well fitted by a power law with slope 2.94±0.02. Above 10 EeV evidence is presented for the development of a spectral "bump" followed by a cutoff at 70 EeV.

It is shown that if the "standard quantum limit" is taken in a predictive sense, then a repeated measurement scheme involving contractive states, recently proposed by Yuen, does not break this limit.

Levinson's theorem relation phase shifts and bound states, developed for a short-range potential $V_{\mathrm{sh}}$, is extended to scattering by $V_{\mathrm{sh}}+V_{\mathrm{C}}$, where $V_{\mathrm{C}}$ is a repulsive Coulomb potential. The subtleties associated with $L=0\mathrm{}$, $E=0\mathrm{}$ bound states for $V_{\mathrm{sh}}$ alone are not present for $V_{\mathrm{sh}}+V_{\mathrm{C}}$. Information is also obtained on the relation between the nodal structure of the zero-incident-energy wave function and the number of bound states; some extensions to scattering by a compound target are possible.

The dynamics of an asymmetric double-well system coupled to a heat bath is studied at low temperatures where transitions between the wells involve quantum tunneling. The time evolution of the occupation probabilities of the wells is calculated by means of instanton techniques. For a wide range of parameters incoherent relaxation is found at a rate whose dependence both on temperature and bias is nonanalytic, in general.

We study quantum tunneling in a biased double-well potential in the presence of Ohmic dissipation with a friction coefficient $\alpha >1\mathrm{}$. The tunneling rate out of the metastable well is calculated in real time as a function of the temperature $T$ and bias energy $\epsilon$. The $T=0\mathrm{}$ result agrees with a droplet-model calculation in imaginary time. At low temperatures we find an enhancement to the $T=0\mathrm{}$ rate varying as ${\left(\frac{T}{\epsilon }\right)}^2$.

A study of intrinsic and noise-induced intermittency and low-frequency noise due to crises is reported for numerical simulations of the sinusoidally driven dampled pendulum and radiofrequency-driven Josephson junctions. The effects of fractal boundaries of the basins of attraction on the functional form, noise sensitivity, and noise scaling of low-frequency power spectra are considered.

Statistics of energy spectra are studied for quantum billiards, i.e., free motion of a particle in two dimensions surrounded by a hard wall. The transition from regular to irregular spectra observed in moments of nearest-neighbor spacing distributions for different shapes of the boundary is analyzed by a superposition of independent level sequences with Poisson and Wigner distributions. The rate of mixture of the two sequences is compared with the rate of phase volumes spanned by quasiperiodic and chaotic orbits of the corresponding classical motion.

A high-statistics measurement is presented of the cross section for the process $e^{+}{e}^{-}\to {\tau }^{+}{\tau }^{-}$ at $\sqrt{s}=29\mathrm{}$ GeV from the MAC detector at PEP. A fit to the angular distribution of our sample of 10 153 events with $\left|cos\theta \right|<\mathrm{}0.9\mathrm{}$ gives an asymmetry $A_{\tau \tau }=-0.055\mathrm{}\pm 0.012\pm 0.005$ from which we find the product of electron and tau axial-vector weak neutral couplings $g_A^e{g}_A^{\tau }=0.22\mathrm{}\pm 0.05$.

Precise results are reported for the $\tau$-lepton lifetime and several $\tau$ branching ratios obtained with the MAC detector operating at PEP at $\sqrt{s}=29\mathrm{}$ GeV. We find ${\tau }_{\tau }=(3.15\mathrm{}\pm 0.36\pm 0.4)\times {10}^{-13\mathrm{}}$ sec. Results for the topological branching ratios $B_1$, $B_3$, $B_5$ ($\tau$ decaying into 1, 3, 5 charged particles) are $B_3\equiv 1-B_1=0.133\mathrm{}\pm 0.003\pm 0.006$ and $B_5<0.0017\mathrm{}$ at the 95% confidence level. The fraction of all three-prong decays unaccompanied by ${\pi }^0\text{'}\mathrm{s}$ is found to be 0.61±0.03±0.05.

The value of $\frac{{\epsilon }^{\prime }}{\epsilon }$, a measure of the $\mathrm{CP}$-nonconserving direct transition from the $K_L^0$ state to the isospin-2 state of two pions, was determined to be 0.0017±0.0082, a result that excludes interesting models of $\mathrm{CP}$ nonconservation.

A measurement of the ratio of the $\mathrm{CP}$-nonconservation parameters, $\frac{{\epsilon }^{\prime }}{\epsilon }$, in the $K^0{\overline{K}}^0$ system was performed through a study of two-pion decays with and without a regenerator. To reduce systematic effects, $K_L$ and $K_S$ decays were recorded simultaneously with a double beam. Over 3100 $K_L\to 2{\pi }^0$ events were reconstructed leading to the result $\frac{{\epsilon }^{\prime }}{\epsilon }=-0.0046\mathrm{}\pm 0.0053\pm 0.0024$ (the first error is statistical, the second systematic). The measurement agrees with previous less precise determinations but, because of theoretical uncertainties, is not able to test decisively the Kobayashi-Maskawa mechanism.

The evolution of the quasicontinuum $\gamma$ decay in ${}_{}{}^{156}{}_{}{}^{}\mathrm{Er}$ is studied from $J\approx 24\hslash \mathrm{to} 48\hslash$ with a new particle-$\gamma$ coincidence technique. $\gamma$-ray-energy-dependent $\gamma$ multiplicities are used to identify spin-energy-correlated transitions characteristic of rotational motion for $J<~37\hslash$ and $J>~48\hslash$. No significant spin-energy-correlated transitions are observed in the intermediate spin range $37\hslash <~J<~42\hslash$ signaling the presence of single-particle behavior in this limited spin domain.

Differential cross sections for the reaction ${}_{}{}^2{}_{}{}^{}\mathrm{H}(\gamma , p)n$ were measured at five laboratory angles, from 32° to 130°, for photon energies 100, 140, 180, and 220 MeV. A quasimonochromatic photon beam was used and the photon spectrum was measured on line by a pair spectrometer. The absolute normalization uncertainty is within ±5%. Data agree within the total errors with the recent results of a tagged-photon experiment and of a measurement of the inverse process.

The transverse form factors are calculated for the reactions ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}(e, e){}_{}{}^{13}{}_{}{}^{}\mathrm{C}(\mathrm{g}.\mathrm{s}.\mathrm{})$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}(e, e^{\prime }){}_{}{}^{13}{}_{}{}^{}\mathrm{C}_{}^{*}{}_{}{}^{}$. It is found that the data for momentum transfers ≲2.2 ${\mathrm{fm}}^{-1\mathrm{}}$ can be explained purely in terms of configuration mixing within the $1p$ shell.

The presence and significance of three- and four-level correlation effects in nuclear spectra are demonstrated for the first time. New ways to study two-level properties are also presented. Agreement with random-matrix predictions is found.

From measurements of the total-absorption cross section for photon energies between 3 and 38 MeV we obtain values of the cross section for pair creation on the ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ nucleus. Theoretical values of the distorted-wave Born cross section for pair creation are available at 10 and 20 MeV. These, modified by radiative and screening corrections, are compared with ${\sigma }_{\kappa }$ obtained from the experiment. The agreement is within about 1% at 20 MeV. However, at 10 MeV the theoretical value is about 4% too small. The calculations likely can be improved by taking into account the finite size of the nucleus.

We report findings for high-multiplicity $0.9A$-GeV ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ on ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ events observed at the Bevalac streamer chamber. Observed azimuthal correlations cannot be explained by finite-multiplicity effects. Comparisons are made with Cugnon's cascade model, and with the explosion-evaporation simulation of Fai and Randrup. The widely used flow-angle methodology proves to be relatively insensitive to collective effects under the conditions of the present experiment.