The ${\mathit{B}}^0$ B¯ ${}_{}{}^0{}_{}{}^{}$ average mixing parameter χ has been extracted from eμ and ee events produced in pp¯ collisions at √s =1.8 TeV. In a sample of 900 eμ events, the like-sign to opposite-sign charge ratio R is measured to be 0.556±0.048(stat${)}_{\mathrm{-}0.042}^{+0.035\mathrm{}}$(syst). In the absence of mixing, the expected value of R would be 0.23±0.06. The corresponding number for 212 ee events is 0.573±0.116(stat)±0.047(syst) with an expected nonmixing value of 0.24±0.07. The observed excess in R leads to a combined determination of χ=0.176±0.031(stat+syst) ±0.032 (model), where the last uncertainty is due to Monte Carlo modeling.

We report the observation of a large asymmetry in the elastic scattering of 100 MeV ${\mathrm{\pi }}^{+}$ from a polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ target. Measurements have been made at laboratory angles of 60°, 80°, and 100°, with the largest value ${\mathit{A}}_{\mathit{y}}$=0.89±0.12 occurring at 80°, near a cross-section minimum. This asymmetry is the largest observed to date in pion scattering from a spin-1/2 nucleus. The ${\mathit{A}}_{\mathit{y}}$ data are qualitatively reproduced by a schematic model; however, agreement with the data is significantly improved when realistic three-body Faddeev wave functions and a full nonlocal distorted-wave impulse approximation reaction model are used.

Experimental evidence testifying to the existence of a limiting temperature for the observation of gamma decay from the giant dipole resonance in hot nuclei is interpreted as indicating a remarkable constancy with temperature of the width with which the giant resonance couples to the compound nucleus.

Exclusive measurements of two- and three-body events were performed for the system ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$${+}^{100}$Mo at 19.1 MeV/nucleon. Most ternary events are consistent with sequential processes in which one of the two deep-inelastic fragments fissions. For such events large differences are found between the fission probabilities of projectilelike and targetlike fragments of a given mass, this probability being larger for the nucleus which gained nucleons. This behavior demonstrates that there is a lack of equilibrium at the end of the deep-inelastic collision.

The commonly held view that fusion excitation functions are featureless and do not provide a good test of models is challenged by high-precision measurements for the reaction ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$${+}^{16}$O. The data yield a well-defined distribution of barrier heights using a recently proposed, novel analysis technique. The measured distribution is that expected from the quadrupole deformation of ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$ and models using significantly different distributions cannot reproduce the measured excitation functions.

Is it possible to number squeeze an already sub-Poissonian electromagnetic field? This work presents a system able to squeeze the sub-Poissonian photon statistics of a beam from the down-conversion luminescence produced in a nonlinear crystal by laser pumping. Parameters are shown to stress the experimental difficulties inherent to the process. Even if this sub-Poissonian proposition for the down-converted light-state turns out to be unrealistic, the proposed system is, in principle, a singular tool in noise reduction processes.

Self-consistent Xα multiple-scattering calculations for ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ reveal a close connection between the prominent multiple-scattering ${\mathrm{\sigma }}^{\mathrm{*}}$ shape resonances found near threshold and the weak single-scattering extended x-ray-absorption fine-structure (EXAFS) oscillations at higher energy. The ${\mathrm{\sigma }}^{\mathrm{*}}$ shape resonance may be interpreted as the first, enhanced, EXAFS wiggle while the valence electron potential is found to significantly influence the EXAFS, signifying a breakdown of the conventional picture.

Three-dimensionally periodic dielectric structures, photonic crystals, possessing a forbidden gap for electromagnetic wave propagation, a photonic band gap, are now known. If the perfect 3D periodicity is broken by a local defect, local electromagnetic modes can occur within the forbidden band gap. Addition of extra dielectric material locally, inside the photonic crystal, produces ‘‘donor’’ modes. Conversely, local removal of dielectric material from the crystal produces ‘‘acceptor’’ modes. It is now possible to make high-Q electromagnetic cavities of ∼1 cubic wavelength, for short wavelengths at which metallic cavities are useless. These new dielectric cavities can cover the range from mm waves to UV wavelengths.

We show that the photoacoustic pressure in one, two, and three dimensions can be found as mappings of the optical deposition of heat in space for short optical radiation pulses. In addition, we find the photoacoustic pressure to be proportional to the zeroth derivative in one dimension, the one-half derivative in two dimensions, and the first derivative in three dimensions of the optical radiation intensity for long pulses. Experiments with fluid layers, cylinders, and droplets give ultrasonic wave forms that are in general agreement with the theorems.

We report experimental and theoretical results for the absolute and convective instability boundaries in Taylor-Couette flow with imposed axial flow as a function of the axial Reynolds number. Experiment and theory agree quantitatively. In the downstream region of a large-aspect-ratio system, noise-sustained structures of traveling vortices exist in much of the convectively unstable regime. These structures have a nearly time-independent amplitude, but a noisy phase. The phase noise ceases abruptly upon crossing the absolute instability boundary.

A noise-sustained and noise-modulated structure of propagating Taylor vortices (PTV) in a convectively unstable regime of Couette-Taylor flow with a superimposed axial flow was observed and studied. The structure differs drastically from PTV in an absolutely unstable regime in its noisy power spectrum and in the noisy temporal dynamics of the front. Interaction of perturbations with the interface causes an amplitude modulation near the front and a noisy phase further to the outlet. The dependence of the front location on the control parameter indicates that perturbations from the inlet are responsible for the PTV existence.

Simulation results of toroidal ${\mathrm{\eta }}_{\mathit{i}}$-mode turbulence are analyzed using mathematical tools of nonlinear dynamics. Low-dimensional chaotic attractors are found in the strongly nonlinear regime while in the weakly interacting regime the dynamics is high dimensional. In both regimes, the solutions are found to display sensitive dependence on initial conditions, characterized by a positive largest Liapunov exponent.

A novel linear electro-optic effect is observed in a surface-stabilized chiral nematic cell above the Fréedericksz transition threshold field. The slow dynamic response indicates that this effect arises from the interfacial region which elastically couples to the bulk, rather than directly from the bulk. Moreover, evidence suggests that the primary effect is a spontaneous electric polarization very near the interface. Other possible contributions to this effect are discussed.

We investigate the effect of a finite heat current Q on the superfluid transition of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. We perform a renormalization-group (RG) calculation of the temperature profile and of the critical thermal conductivity ${\lambda }_{\mathit{T}}$(Q) in the nonlinear-response regime. In the experimentally accessible region close to ${\mathit{T}}_{\lambda }$ we predict the divergence ${\lambda }_{\mathit{T}}$(Q)∼${\mathit{Q}}_{\lambda }^{\mathrm{-}\mathit{y}}$ with the effective exponent ${\mathit{y}}_{\lambda }$≊0.31. An experiment is proposed to detect this nonlinear effect. We also present the exact RG result x=(2ν${)}^{\mathrm{-}1}$ for the depression of the transition temperature ${\mathit{T}}_{\lambda }$-${\mathit{T}}_{\lambda }$(Q)∼${\mathit{Q}}^{\mathit{x}}$.

We have carried out x-ray reflectivity and adsorption measurements on thermally evaporated silver and gold films deposited onto substrates held at 80, 300, and 500 K to investigate whether the surfaces of such films are fractal in nature. Both techniques indicate self-affine fractal scaling for Ag films deposited at near-normal incidence onto substrates held at 80 K.

Dynamical growth aspects of symmetry-breaking, first-order phase transitions for which the primary order parameter is a second-rank tensor, e.g., strain describing diffusionless structural phase transitions, are considered. It is found that a single domain does not always grow inside the parent phase matrix, but instead a perpetually twinning interface propagates through the system, a result of the system attempting to minimize its kinetic energy.

Scanning tunneling microscopy and low-energy electron diffraction of clean Ir(110) reveal a surprising novel route for the (110) surface of a fcc metal to stabilize its surface configuration: The Ir(110) surface is characterized by mesoscopic grooves of several 100 nm length along the direction of the close-packed rows and depths between 0.5 and 1.5 nm. Extended (331) facets on the walls and local unreconstructed (110) structures on the ridges are observed. Ir(110) obviously strongly differs from Au(110) and Pt(110), which exhibit (1×2) missing-row-type reconstructions with (111) microfacets.

A new phase-modulation technique for nonlinear laser spectroscopy is applied with a relative resolving power in the sub-Hz range to measure fundamental relaxation processes of the N-V center in diamond. Complementary EPR experiments versus temperature establish the spin character of the ground state in the absence of optical illumination and show that spin-lattice decay occurs via two-phonon processes involving the dominant vibrational mode. The combined results permit deduction of reliable fine-structure assignments for three states of the center and accurate values for zero-field intersystem crossing and spin-lattice relaxation rates from linewidths of individual resonances in the four-wave-mixing spectrum.

It is well known that Frenkel excitons are not true bosons or fermions. I show that the fundamental electronic excitations in a linear (noncyclic) one-dimensional molecular aggregate consisting of N coupled two-level absorbers with site disorder are in fact fermions, allowing one to calculate IallR of the $2^{\mathit{N}}$ excited-state eigenfunctions and eigenenergies with a single N×N matrix diagonalization. As an application, the third-order nonlinear absorption coefficient for a molecular aggregate with site disorder is calculated.

The dispersion relation for magnetoplasmons propagating perpendicular to the magnetic field is investigated for a quasi-three-dimensional electron system. The magnetic field is in the plane of a ≃100-nm-wide electron slab which is confined by a wide ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As parabolic quantum well. A minimum is found in the magnetoplasma dispersion relation indicating the existence of a magnetoroton excitation for wave vector q about twice the inverse magnetic length. Calculations of the dispersion relation within the single-mode approximation are in good qualitative agreement with the measurements.