The scintillation and ionization yields in liquid argon by α particles and fission fragments have been measured as a function of the applied electric field (≤38 kV/cm). The quenching due to high excitation density does not depend on the field for ≳4 kV/cm for α particles. The scintillation due to α particles shows a maximum at about 1.5 kV/cm. This increase (2.5±0.7%) of the scintillation at low fields has not been observed heretofore and is ascribed to the presence of a quenching process at zero field.

Polarizing microscopy, optical activity, reflection, and transmission measurements are used to determine the phase diagram for the blue phases of chiral 4’’-(2-methylbutylphenyl)-4’ -(2-methylbutyl)-4-biphenylcarboxylate (CE2) mixed with nonchiral 4-n-pentylbenzenethio-4’-n-heptyloxybenzoate (7¯S5). These mixtures exhibit a chirality higher than previously investigated. The phase diagram shows two new features: (1) blue phase II becomes unstable at high concentrations of the chiral component, and (2) blue phase III possesses a wider temperature range than blue phase I for the most chiral mixtures.

A quasirandom object produced by a self-similar space-division model is examined. We find that abandoning small subspaces drastically changes the distribution function of single subspaces, but the power spectrum is only slightly changed. Examples of $k^{\mathrm{-}d}$ spectra are presented. These are made from photographs of several materials or phenomena, i.e., rocks, patterns in fluid motions, and pictures.

In radiationless transitions to atomic inner-shell hole states produced by threshold photoionization, the Auger electron energy is shifted up by post-collision interaction between the two continuum electrons. According to both semiclassical and quantum-mechanical models, this shift is expected to disappear if the photoelectron energy exceeds that of the Auger electron (the vanishing or ‘‘no-passing’’ effect). This effect, recently observed for a long-lived [4d] hole state of Xe, is now also demonstrated for the very fast Xe $L_2$-$L_3$$N_4$ (J=3) Coster-Kronig transition, excited with synchrotron radiation.

Spectra representing the relative cross sections for resonant absorption from the 3p subshell of laser-excited and ionized manganese have been obtained in the 47–52-eV range. The results show a marked change in the resonant structure and the appearance of new resonances which are attributed to 3p-4s transitions.

A first-order perturbation calculation is performed on a generalized nonlinear Schrödinger equation in order to investigate the degree of squeezing that can be obtained for a medium described by such a field theory. Expressions for the amount of squeezing in the normal and anomalous dispersion regimes are obtained. In particular, it is found that the amount of squeezing is greater in the anomalous dispersion region than in the normal dispersion region. By keeping fourth-order derivatives in the field, the squeezing when the pump is located at the zero-dispersion wavelength is also investigated.

We show experimental evidence of spontaneous oscillations in a single-transverse and single-longitudinal mode ${\mathrm{CO}}_2$ laser under conditions for which the plane-wave Maxwell-Bloch model predicts stable laser operation. These instabilities seem to result from transverse structure in the mode, as a model which accounts for the transverse profile of the field in the cavity predicts behavior in close agreement with our experimental results.

A quantum theory of nondegenerate multiwave mixing in a two-level atomic medium is formulated, with emphasis on traveling-wave interaction geometries. Two equivalent alternative methods are developed to treat, with some rigor, the spatial propagation of the interacting multimode traveling-wave field. The theory is applied to the case of a single beam propagating through the medium to obtain the spectrum of squeezing. The effects of spontaneous emission, propagation loss, atomic collisions, and pump-probe phase mismatch are comprehensively taken into account for the first time.

A possible class of traveling-wave solutions to the Maxwell-Bloch equations is presented and discussed. These are given by periodic solutions of the Lorenz equations; in particular, solutions for negative values of the parameter σ give stable traveling-wave solutions with phase velocity less than the speed of light.

We present complete results for the selected width of Saffman-Taylor fingers at large velocities with and without anisotropy in the surface tension. We solve a nonlinear eigenvalue problem to obtain the scaling laws and constants relating finger width, surface tension, and anisotropy. Excellent agreement with McLean’s numerical solution of the full isotropic problem is obtained. The effect of anisotropy is to allow all finger widths. We discuss the relevance of these results to recent experimental findings.

We present data for the onset of time dependence in convecting layers of a normal ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$He mixture with positive separation ratio ψ. The boundaries of the fluid were cylindrical; data were obtained for aspect ratios Γ of 6≲Γ≲13. Time dependence typically first occurs as finite-amplitude periodic oscillations with a vanishing frequency at the onset Rayleigh number $R_1$ of the instability. The amplitude at onset A and $R_1$ show regular variations with Γ which reflect variations in the number of convection rolls. From A(Γ) and $R_1$(Γ) we deduce the typical wave vectors α of the convection rolls at $R_1$; α decreases only slowly with ψ. Yet, theory and estimates of ψ indicate that α at the onset of convection should change by a factor of 3. We argue that the values of α at $R_1$ are different from those predicted to occur at the onset of convection.

We derive an eight-mode model with horizontal boundaries that are impermeable to the concentration current and free slip for the velocity. Its properties are elucidated and compared with theoretical results obtained for other boundaries. Impermeable boundaries cause an additional coupling between temperature and concentration gradients which significantly changes linear and nonlinear properties as compared to those of permeable boundaries.

The evolution of periodic patterns of parallel convective rolls in a fluid heated from below that grow inwards from a sidewall after applying a lateral heat pulse is determined from numerical solutions of the Oberbeck-Boussinesq equations. Propagation speed and intensity profile of the front between homogeneous conductive and periodic convective state and the wave number selected under the front are determined for several Rayleigh numbers.

An experimental study of the flow regimes observed when time-periodic convection is forced with an external frequency is reported and analyzed within the framework of amplitude equation formalism.

It is shown that the system of parametrically excited surface waves falls into the class of ‘‘critical flows’’ whose dynamics and transition to chaos can be understood from first-return maps derived in the vicinity of one saddle point in phase space. The onset of chaos is via ‘‘gluing bifurcations,’’ which are also common to Lorenz-like flows, but these are intermingled here with usual period-doubling bifurcations. Similar parametrically excited systems might show the full array of routes to chaos which appear in critical flows.

We present the first study of fractal growth in a solid-solid phase transition. A highly ramified, randomly branched crystalline phase was obtained by heating thin amorphous ${\mathrm{GeSe}}_2$ films. Our result for the fractal dimension of the above structure, D∼1.7, is in agreement with that of two-dimensional diffusion-limited aggregates. Possible mechanisms resulting in fractal growth are discussed.