Observations of the dynamics of a single-mode, traveling-wave laser under bad-cavity conditions are reported. The sequence of instabilities occurring on resonator tuning corresponds in detail to the transition to chaos of the logistic equation. Period-doubling cascade, reverse ("noisy") cascade, and the regular period-3 and -5 windows in the chaotic range are observed. At presumably homogeneous broadening conditions the transition from cw to chaotic emission is abrupt on pump variation. All of the observed features including instability pump thresholds and characteristics of the chaotic laser pulses agree with predictions of the Lorenz equations.

MHD surface waves of $m=-1\mathrm{}$ (poloidal mode number of left-hand rotation) compressional Alfvén waves in cylindrical finite-$\beta$ plasma have been observed for the first time to propagate together with shear Alfvén waves. These modes also show a distinctive feature of the dispersion merging with that of shear Alfvén waves at the center of a plasma column when a limiting frequency below the ion cyclotron frequency is reached. The experimental results confirm a recent prediction concerning surface-wave properties of the first radial eigenmode of a nonaxisymmetric compressional wave in a plasma surrounded by an insulating boundary.

A medium driven sufficiently far off equilibrium so that it is wave turbulent can support a propagating energy mode with similarities to second sound. Conditions for the transition from parabolic to hyperbolic energy transport as well as consequences for plasma confinement are discussed.

The decay time of stored energy was measured when additional heating power decreased abruptly. The energy decay time is almost constant at 15 ms, irrespective of the gross energy confinement time ${\tau }_E^G$, which is changed by ion-cyclotron range of frequency heating up to 1.5 MW. The decay time coincides with a confinement time of the additionally heated power defined by ${\tau }_{\mathrm{ad}}=\frac{\Delta W_T}{\Delta P_{\mathrm{tot}}}$, which indicates that the incremental energy from the additional heating behaves independently of the gross plasma energy. It is also shown that ${\tau }_{\mathrm{ad}}$ is almost independent of density and plasma current as well as heating power.

The cause for anomalous electron-energy confinement in tokamaks in an active area of research. In this Letter we present a model for the anomalous electron-energy transport and compare it with experimental results.

The potential for H isotopes in $\alpha$-phase (hexagonal) ${\mathrm{YH}\left(\mathrm{D}\right)\mathrm{}}_{0.18}$ has been probed by neutron spectroscopy. The results reveal a highly unusual potential, which is considerably softer and anharmonic along the $c$ axis than in the basal plane, even though the near-neighbor arrangement of metal atoms is only slightly distorted from regular tetrahedral symmetry. Low-temperature results show a splitting of the $c$-axis vibrational modes, consistent with the pairing of hydrogen on either side of yttrium atoms.

NMR data show that the deuteron "pseudo spin-glass" transition in ${\mathrm{Rb}}_{1-x}{\left(\mathrm{N}{\mathrm{D}}_4\right)}_x{\mathrm{D}}_2\mathrm{P}{\mathrm{O}}_4$ is not just a simple kinetic slowing down process but is characterized by a gradual condensation of randomly polarized clusters as expected if we deal with a percolation transition in eigenstate space. The results provide novel information on the temperature dependence and distribution of local random fields and their dynamics. The spin-lattice and motional-narrowing data further suggest that the "pseudospin" O—D--O deuteron intrabond motion determines the freezing dynamics.

We report light-scattering measurements under pressures up to 1000 bars of nematic short-range order in the isotropic phase of the lyotropic liquid-crystal system cesium perfluoro-octanoate and water. The nematic-to-isotropic transition temperature is a nonlinear function of pressure which changes strongly with concentration and $\frac{d{T}_{\mathrm{NI}}}{\mathrm{dp}}$ is from 10 to 100 times smaller than in typical thermotropic nematics. We also find the bare correlation length in the isotropic phase to be 12.5 ± 2 Å.

We observe via freeze-fracture transmission electron microscopy the transition from the disklike micellar nematic phase to the lamellar smectic phase of decylammonium chloride-ammonium chloridewater as a function of temperature. We show direct visual evidence of the size and shape of the aggregates in the nematic phase, the mechanism of the nematic-smectic transition, and the origin of the residual in-plane order in the smectic phase. These observations are consistent with previous scattering, conductivity, and NMR measurements on this system.

The elastic properties of cadmium arachidate films, 11 to 401 monolayers thick, prepared on molybdenum and glass substrates by the Langmuir-Blodgett dipping technique, have been investigated by Brillouin scattering. Measurements of the dispersion of the guided acoustic waves with film thickness indicate an anomalously small ratio of the shear to the compressional elastic constants. Evidence for molecular reorientational fluctuations in the depolarized spectrum was also observed.

Convergent beam diffraction patterns from a bcc blue-phase (I) monocrystal in an electric field applied in the [110] direction show this twofold axis transforming through an orthorhombic distortion to become, at a critical field, the fourfold axis of a tetragonal crystal. The implication on structures of blue phase I is important. Although the transition is weakly first order because the two order parameters describing it are coupled, the diffraction pattern changes continuously through the transition.

Employing a long-range potential model we investigate nucleation of crystalline droplets near the limit of stability of the metastable liquid. The nucleation process is found to differ considerably from what is predicted in standard models. In contrast to the classical nucleation mechanism this process provides a qualitative explanation of the results of molecular-dynamics simulations of systems undergoing deep quenches.

Mössbauer emission spectra of LiNb${\mathrm{O}}_3$:${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ single crystals in magnetic fields up to 5 T at 4.2 K show initial populations of the ${}_{}{}^6{}_{}{}^{}A_{1\mathrm{g}}^{}{}_{}{}^{}$ Zeeman substates of ${\mathrm{Fe}}^{3+}$ which depend strongly on the angle between the crystallographic $c$ axis and the magnetic field. This is interpreted in terms of a crystal-field effect on excited states which influences the initial populations of the Zeeman sublevels of the ${}_{}{}^6{}_{}{}^{}A_{1\mathrm{g}}^{}{}_{}{}^{}$ ground term after the electron-capture decay of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$. An intersystem crossing process due to orbit-lattice interaction can fairly well explain the angular dependence.

A model of an open quantum system is presented in which irreversibility is introduced via boundary conditions on the Wigner function. The model is applied to the quantum-well resonant-tunneling diode. The calculations reproduce the negative-resistance characteristic of the device, and indicate that the tunneling current approaches steady state within a few hundred femtoseconds of a sudden change in applied voltage.

We report the evolution from resonant Raman scattering (RS) due to longitudinal-optical and acoustic phonons to excitonic-polariton luminescence in ZnTe at low temperature by picosecond time-resolved spectroscopy. The resonant RS lines deform with decay time of 300 ps into the ordinary polariton luminescence. The finite decay time of the RS lines shows evidence of a real transition on the polariton branch in the resonant RS process.

A neural network model which is capable of recalling time sequences and cycles of patterns is introduced. In this model, some of the synaptic connections, $J_{\mathrm{ij}}$, between pairs of neurons are asymmetric ($J_{\mathrm{ij}}\ne J_{\mathrm{ji}}$) and have slow dynamic response. The effects of thermal noise on the generated sequences are discussed. Simulation results demonstrating the performance of the network are presented. The model may be also useful in understanding the generation of rhythmic patterns in biological motor systems.

This Letter discusses the recent measurement of the number of galaxies versus red shift and flux for cosmological models with a nonzero cosmological constant $\Lambda$ and pressureless matter. The main conclusions are these: (1) If space is flat as the inflationary model predicts, then the density parameter $\Omega ={0.9}_{-0.2\mathrm{}}^{+0.4\mathrm{}}$ and $\frac{\Lambda }{\left(3\mathrm{}{H}_0^2\right)}={0.1}_{-0.4\mathrm{}}^{+0.2\mathrm{}}$. (95%-confidence intervals are used throughout.) (2) For both inflationary and $\Lambda =0\mathrm{}$ models, the present result and primordial nucleosynthesis are consistent only if a large density of nonbaryonic matter exists. (3) Without any assumptions about $\Lambda$, the age of the Universe $t$ and Hubble's constant $H_0$ are constrained by $0.60<t{H}_0<0.88\mathrm{}$.

The semiclassical approximation serves as an ideal basis for Monte Carlo evaluation of Euclidean path integrals. When the semiclassical approximation is good, the averaging converges rapidly. Comparison with conventional techniques shows a great advantage in computational efficiency. A simple one-dimensional example is presented, along with a discussion of how the technique is extended to several degrees of freedom.

A new Monte Carlo method is presented for simulations of systems with quenched random interactions. The approach greatly reduces the long correlation times characteristic of standard methods, allowing the investigation of lower temperatures with less computer time than previously necessary.

We present a variant of the Stueckelberg formalism for Yang-Mills theory where the Stueckelberg scalar field is eliminated in favor of the gauge potential. Normally this leads to nonpolynomial interactions. However, we point out that it is possible to pick a gauge where the nonpolynomiality disappears and the resulting theory is power-counting renormalizable and unitary. This procedure allows one to construct an electroweak model without the Higgs boson.