The electrodynamical response of the spin-density-wave state is examined in (TMTSF${)}_2$${\mathrm{PF}}_6$ by conducting experiments in the microwave and millimeter-wave spectral range. We present the first complete optical spectrum of the ground state, and show that both the collective-mode response and single-particle excitations contribute to the frequency-dependent conductivity. The analysis of the ac response leads to a significant spin-density-wave mass enhancement.

The electronic structure of a vortex line in a type-II superconductor is calculated in the low-magnetic-field limit in the framework of the Bogoliubov–de Gennes theory. It is found that breaking the rotational invariance of a vortex line by means of either an anisotropic crystal potential or by the presence of neighboring vortices induces an angular band structure in the low-energy part of the quasiparticle spectrum. The associated quasiparticle amplitudes become distorted and exhibit a characteristic ‘‘star’’ shape whose orientation is energy dependent. This explains recent scanning-tunneling-microscopy experiments by Hess, Robinson, and Waszczak [Phys. Rev. Lett. 64, 2711 (1990)] on ${\mathrm{NbSe}}_2$.

Using perturbed γγ angular correlations of ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ in the La site, we report a structurally disordered phase in oxygen stoichiometric ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4+\mathrm{\delta }}$. So far this phase has been defined for 0≤x≤0.07, involves a reversible order-disorder transition at ${\mathit{T}}_{\mathit{d}}$=150(20) K, and is observed by changes in the electric-field gradient (EFG). These changes involve a continuous broadening of the EFG distribution and decrease of the average EFG asymmetry parameter as T→0. The new disordered phase is associated with a loss of three dimensional magnetic order in the range 0.015<x<0.018, and may be due to short-range disorder in the tilting of the ${\mathrm{CuO}}_6$ octahedra as proposed by Egami et al.

We examine the question of accurately determining Lyapunov exponents for a time series. We find that it is advantageous to use local mappings with higher-order Taylor series, rather than linear maps as done earlier. We demonstrate this procedure for the Ikeda map and the Lorenz system. We present methods for identifying spurious exponents by analyzing data-set singularities and by determining the Lyapunov direction vectors. The behavior of spurious exponents in the presence of noise is also investigated, and found to be different from that of the true exponents.

For a chaotic system, a noisy trajectory diverges rapidly from the true trajectory with the same initial condition. To understand in what sense the noisy trajectory reflects the true dynamics of the actual system, we developed a rigorous procedure to show that some true trajectories remain close to the noisy one for long times. The procedure involves a combination of containment, which establishes the existence of an uncountable number of true trajectories close to the noisy one, and refinement, which produces a less noisy trajectory. Our procedure is applied to noisy chaotic trajectories of the standard map and the driven pendulum.

Using the CLEO detector at the Cornell Electron Storage Ring (CESR), we have determined the ratio Γ(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathit{l}}^{+}$ν)/Γ(${\mathit{D}}_{\mathit{s}}^{+}$ →φ${\mathrm{\pi }}^{+}$)=0.49±0.${10}_{\mathrm{-}0.14}^{+0.10\mathrm{}}$. We use this measurement to derive B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$).

The analytic next-to-leading-order correction [O(${\mathrm{\alpha }}_{\mathit{s}}^2$)] to the longitudinal structure function in QCD is presented in the form of kernels that give ${\mathit{F}}_{\mathit{L}}$ after convolution with the partonic densities. This final complete result, which corrects previous partial calculations, can be easily used for phenomenological applications, which are briefly discussed.

The method of scaled factorial moments is used to study fluctuations of the fragment-size distribution in the percolation model and in nuclear multifragmentation following the breakup of high-energy nuclei in nuclear emulsion. The percolation model accounts well for the fluctuations in the nuclear fragmentation process. An intermittent pattern of fluctuations is found in the data, suggesting a self-similarity in the fragment-size distribution and a random character for the scaling law. However, no evidence of the critical behavior in nuclear multifragmentation is found.

Motivated by a recent measurement of β-delayed fission in the ${}_{}{}^{180}{}_{}{}^{}\to _{}^{180}{}_{}{}^{}$Hg chain, we have calculated the β strength distribution ${\mathit{S}}_{\mathrm{\beta }}$ of the neutron-deficient nuclide ${}_{}{}^{180}{}_{}{}^{}\mathrm{Tl}$ within the framework of the proton-neutron quasiparticle random phase approximation (pn-QRPA). The fission barrier height is then deduced from the measured β-delayed fission probability ${\mathit{P}}_{\mathrm{\beta }\mathrm{DF}}$. In addition, as a test for the reliability of the theoretical strength distributions, ${\mathrm{\beta }}^{+}$/EC half-lives of some isotopic chains are calculated using the pn-QRPA including both particle-hole and particle-particle Gamow-Teller residual interactions.

Four, possibly five, superdeformed bands have been observed in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Hg}$. Two of these bands have strikingly different dynamical moments of inertia from all previously observed superdeformed bands in this region. This behavior can be understood in terms of a level or band crossing. Evidence for transitions between two superdeformed bands is observed for the first time. This, together with the reduced alignments observed and the strong interaction between the crossing bands, is the first experimental evidence supporting the prediction for strong octupole correlations in superdeformed nuclei.

Pulsed twin beams of light have been generated using an optical-parametric amplifier that is pumped by the second harmonic of a mode-locked and Q-switched neodymium:yttrium aluminum garnet laser. The intensity noise levels on the direct-detected signal and idler beams are found to be correlated by more than 15 dB, and the subtracted noise falls below the quantum limit by more than 6 dB (75%). To our knowledge, this is the first observation of pulsed twin beams of light, and yields the highest quantum-noise reduction observed in any experiment to date. Our measurements are in excellent agreement with the quantum theory of a nondegenerate optical-parametric amplifier.

We have studied the statistics of the absorption of photons by atoms by measuring the momentum distribution of an atomic beam that is deflected by a laser beam. We observe the transition from a Poissonian to a sub-Poissonian distribution, as we vary the detuning of the laser. The largest observed fractional deviation of the variance from Poissonian statistics is Q=-0.51±0.05, in agreement with theoretical predictions for our experimental conditions.

Photon-number statistics in resonance fluorescence is studied through the deflection of a beam of neon atoms in the metastable ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_2$ state by radiation pressure. An analysis of the deflection profile leads to experimental values for the Mandel Q parameter as a function of laser intensity and detuning for different laser polarizations. The results confirm the predicted predominantly sub-Poissonian statistics. Good agreement is demonstrated with the results of a Monte Carlo calculation based on a pure-state analysis of resonance fluorescence.

If velocity-selective optical excitation in a gas is followed by rapid collisional deexcitation, the result may be called velocity-selective heating. Through the temperature dependence of the transport coefficients, this process gives rise to a new type of kinetic effect. This is experimentally demonstrated using hot-band rovibrational excitation of ${\mathrm{CO}}_2$ gas by a ${\mathrm{CO}}_2$ laser tuned in the Doppler wing. Upon R- or P-branch excitation, rotational- to kinetic-energy conversion yields velocity-selective heating or cooling. This results in a light-induced flow for nonuniform illumination.

A direct connection between the solid-liquid transition in atomic clusters and the macroscopic phase transition is established through analysis of the size scaling of the latent heat and transition rounding. The transition occurs without phase separation, leading to remarkable consequences in caloric experiments. These features are all quantified through the characteristic shape of the classical state density, computed by a new Monte Carlo method.

We have produced a very cold sample of spin-polarized trapped atoms. The technique used dramatically simplifies the production of laser-cooled atoms. In this experiment, 1.8×${10}^7$ neutral cesium atoms were optically captured directly from a low-pressure vapor in a small glass cell. We then cooled the <1-${\mathrm{mm}}^3$ cloud of trapped atoms and loaded it into a low-field magnetic trap in the same cell. The magnetically trapped atoms had an effective temperature as low as 1.1±0.2 μK, which is the lowest kinetic temperature ever observed and far colder than any previous sample of trapped atoms.

A subset of lasers in an array of coupled lasers can produce identical, synchronized, chaotic signals. Beyond a critical coupling strength, synchronization fails, and spatiotemporal chaos results. The transition to spatiotemporal chaos is signaled by spatial symmetry breaking. Quantitative measures of the transition from synchronized chaos are provided by Lyapunov exponents, sub-Lyapunov exponents, and the mutual information content.

We report experiments on weakly nonlinear traveling-wave convection in an annular cell. The evolution of small-amplitude waves consists of the repetitive formation and sudden collapse of spatially localized pulses. This leads to continuously erratic dynamics with no stable saturated state, even near onset, and even when convection begins with a unidirectional, nearly spatially uniform state. Such behavior is reminiscent of simulations of the complex Ginzburg-Landau equation in the limit of strong nonlinear dispersion.

Analytical solutions are derived for the quasisteady shape and speed of a single wormhole resulting from the coupled processes of Darcian fluid motion and chemical dissolution in a soluble permeable material. For an initially unsaturated medium, two-dimensional solutions are obtained by addressing an inverted free-boundary problem in which the spatial coordinates are treated as dependent variables on the plane of a complex potential. For initially saturated materials, solutions are obtained by analogy to Ivantsov’s problem of dendrite growth.

The baroeffect is analyzed including a third nondiffusing component (gas 3). Gas 3 reduces the pressure drop in all cases, whether it raises or lowers the mean density. Four distinct regimes are identified for diffusive slip: positive slip directed from heavy to light gas; negative slip directed from light to heavy gas; a no-slip regime; and a fourth regime characterized by a maximum in diffusive slip and (contrary to the other regimes) an increase in positive slip upon addition of low-molecular-weight gas 3. Unlike binary gases alone, gas 3 leads to nonzero diffusive slip even in the limit of very disparate masses for the diffusing gases. Implications for controlling concentration creep in crystal growth are discussed.