In an optical fiber, nonlinear optical interactions couple the sideband modes of two strong pump waves at different frequencies just as required for a quantum nondemolition measurement. Experimental measurements demonstrate that 37% of the rms phase fluctuations of one wave are caused by the quantum amplitude fluctuations of the other.

For a simple Lorentz gas, viz., a random walk on a square lattice with randomly excluded sites, we present an exact calculation of the diffusion coefficient, the static conductivity, and the long-time tail of the velocity autocorrelation function $\phi \mathrm{}\left(t\right)\mathrm{}\simeq -\frac{\beta \mathrm{}\left(c\right)\mathrm{}}{t^2}$, exact to $O\left(c^2\right)$ terms included, by making a systematic expansion in the density of impurities $c$ (fraction of excluded sites). To $O\left(c\right)\mathrm{}$ the velocity auto-correlation function is calculated exactly for all times, and shows negative correlations (cage effect).

We prove that the motion of a tagged particle in a one-dimensional fluid of hard point particles in an external potential $U$ may be asymptotically described by a diffusion process. The process is spatially homogeneous or inhomogeneous according to whether $U$ varies on a microscopic or macroscopic scale. The latter process can still be described by a simple Langevin equation, provided that one interprets it in the sense of Stratonovich.

Spherically symmetric gravitational equilibria of self-interacting scalar fields $\phi$ with interaction potential $V\left(\phi \right)=\frac{1}{4}\lambda {\left|\phi \right|}^4$ are determined. Surprisingly, the resulting configuration may differ markedly from the noninteracting case even when $\lambda \ll 1$. Contrary to generally accepted astrophysical folklore, it is found that the maximum masses of such boson stars may be comparable to the Chandrasekhar mass for fermions of mass $m_{\mathrm{fermion}}\sim {\lambda }^{-\frac{1}{4}}{m}_{\mathrm{boson}}$.

Compactification of ten-dimensional $E_8\otimes E_8^{\prime }$ heterotic string theory on coset manifolds is discussed. It is pointed out that $N=1\mathrm{}$ supersymmetry can be preserved on $\frac{G_2}{\mathrm{SU}\mathrm{}\left(3\right)\mathrm{}}$, SO(5)/SU(2)⊗U(1), and SU(3)/U(1)⊗U(1) if gauge-fermion condensation occurs and the third-rank antisymmetric field strength is nonzero. In particular, three generations of chiral fermions can be obtained.

The action for a string moving on a group manifold is related to the form of the Wess-Zumino action as studied by Witten. It is shown that the proper setting for a nonanomalous formulation of the model is a Kac-Moody group.

It is proposed that a dynamical mass for a fourth family of quarks is responsible for breaking of the weak interactions, and for breaking of the extended technicolor interactions which provide mass to the third family. This greatly simplifies the extended technicolor sector and avoids fermions with exotic quantum numbers. A technicolor sector is still required but it is lighter than usual. The most attractive-channel hypothesis for symmetry breakdown is relied on.

Two-photon production of $K_S^0{K}^{\pm }{\pi }^{\mp }$ states has been studied by the TPC/Two-Gamma experiment at the SLAC storage ring PEP. A resonance of mass 1.42 GeV was seen when one of the photons was quite virtual but not when both photons were nearly real. Production of a spin-1 meson, which cannot be made by two real photons, would fit these observations. The $Q^2$ dependence of the data in the resonance region agrees with this spin assignment and is incompatible with a spin-0 hypothesis. The mass and width of the resonance are similar to those of the $E$ meson, which has been assigned $J^P=0^{-}$ and $J^P=1^{+}$ by different experiments.

Antiprotons from the Low Energy Antiproton Ring of CERN are slowed from 21 MeV to below 3 keV by being passed through 3 mm of material, mostly Be. While still in flight, the kiloelectronvolt antiprotons are captured in a Penning trap created by the sudden application of a 3-kV potential. Antiprotons are held for 100 s and more. Prospects are now excellent for much longer trapping times under better vacuum conditions. This demonstrates the feasibility of a greatly improved measurement of the inertial mass of the antiproton and opens the way to other intriguing experiments.

Apparent anomalously short mean free paths observed in relativistic heavy-ion collisions are given a plausible explanation by a parameter-free theory in which input parameters are experimentally measurable physical quantities. A new theoretical analysis is carried out for a specific case of the anomalous behavior of $Z=2\mathrm{}$ secondary nuclei recently observed in a hydrogen bubble chamber in order to demonstrate the validity of the new theory. Implications of the new theory for other cases are also discussed.

We report the observation of sequences of from 1- to as many as 28-photon transitions between potassium $\mathrm{}(n+2\mathrm{})s$ states and the lowest-energy Stark states of the $n$ manifolds for $n=15\mathrm{}-18$. The sequences are observed by the scanning of a static electric field from the field at which these pairs of levels nearly cross, to zero field where they are well separated. The maximum number of photons absorbed is observed to be proportional to the microwave field.

The second-harmonic spectrum of the output of an optical parametric emitter at degeneracy exhibits a narrow peak, much sharper than the spectrum of the parametric light. This peak is a manifestation of the second-order correlations in parametric light. Alternatively, it can be considered as resulting from the recombination of simultaneously generated (twin) wave packets. The twin-wave-packet correlation time is shown to be limited by the first-order coherence time of parametric light.

Squeezed states of the electromagnetic field are generated by degenerate parametric down conversion in an optical cavity. Noise reductions greater than 50% relative to the vacuum noise level are observed in a balanced homodyne detector. A quantitative comparison with theory suggests that the observed squeezing results from a field that in the absence of linear attenuation would be squeezed by greater then tenfold.

A transition from heat transfer by conduction directly to turbulent convective flow is observed in a rotating cryogenic Bénard cell. Near the critical Rayleigh number the power spectra are characterized by broad features, falling off as approximately $f^{-4\mathrm{}}$ at high frequencies. The turbulent flow at onset is predicted as a result of the Küppers-Lortz instability. We report new heat-transfer measurements of this instability, complementing previous visualization experiments, and also report preliminary effects of applying white-noise modulation.

The explosive phase of mode growth observed in multihelicity tearing-mode simulations of tokamak plasmas can be accounted for by a nonphysical feedback mechanism. It is shown that spatially discretized magnetohydrodynamic (MHD) equations admit both attracting finite-time singularities and exponential, but bounded, deviations from solutions of differential MHD. Finally, means of avoiding the nonphysical behavior, which is characterized by poor energy conservation, are given.

In activated chemisorption occurring both by direct impact from the gas and by conversion from a precursor on the surface, the measured activation energy can provide information about the mechanism of activation. If translational motion is dominant in promoting passage over the adsorption barrier, a single activation energy describes the reaction whether gas and surface are isothermal or hot gas strikes a cold surface. When internal degrees of freedom must be excited for chemisorption to occur, different activation energies characterize these two regimes of measurement.

We investigated impurity- (water-) controlled dendritic solidification of dimethyl sulfoxide in narrow gaps. The dendritic structures are stable only for gap widths $d_0>d_{0,c}$, where the remaining liquid phase wets the glass walls completely. A surface-pressure-induced transition from complete to partial wetting occurs at constant temperature at a critical gap width $d_{0,c}\simeq 2$ μm which is related to the interfacial energies and the van der Waals energy of the wetting film. The films were made visible by evanescent-wave-induced fluorescence of added dye molecules which are enriched in the liquid phase.

Cadmium-vacancy complexes are formed in Al single crystals after implantation of Cd ions at 293 K. Postirradiation of these implants with ${\mathrm{H}}^{+}$ and ${\mathrm{Kr}}^{+}$ ions even at 5 K leads to an increase of the substitutional component ($f_s$) of Cd in Al. The increase of $f_s$ is attributed to disassociation of neighboring Cd-vacancy pairs and serves as a quantitative measure for unstable pair recombination in the relaxation phase of the collision cascade. Our data support the results of molecular-dynamics calculations.

The elastic shear constant and the internal friction of three mixed crystals ${\left(\mathrm{KBr}\right)}_{1-x}{\left(\mathrm{KCN}\right)}_x$ have been determined from the resonance of a torsion pendulum in the ${10}^2$-Hz range. Two glass-forming samples ($x=0.20,0.50\mathrm{}$) and one sample ($x=0.75\mathrm{}$) which orders ferroelastically have been investigated. Two regimes of loss have been observed; the primary one is related to domain-wall motion, the secondary one to dipolar reorientations.

Room-temperature adsorption of atomic hydrogen on Cu(110) initially yields a (1×2)* phase visible with low-energy electron diffraction but not with atom diffraction; this surprising observation suggests that H moves below the surface and induces a reconstruction in deeper layers. Upon further H uptake the (1×2) periodicity extends to the surface and also becomes visible with atom diffraction. Low-temperature phases, in which H adsorbs above the surface, transform at ∼240 K into the (1×2) reconstructed phases, proving that H subsurface movement requires thermal activation.