The interaction of three-level atoms with a two-mode classical electromagnetic field is considered in the case when transitions between all levels are allowed. It is found that for exact resonance with field frequencies the dynamics is chaotic in the rotating-wave approximation, i.e., for an arbitrarily small atomic density. The possibility of experimental observation of this phenomenon for Rydberg atoms is discussed.

The free massless field in 2 + 1 dimensions is written as an "integral" over free massless fields in 1 + 1 dimensions. With the operators with fractional dimension in the Gaussian model as a spring-board, operators with fractional statistics in the former theory are constructed.

Recently, Fischbach et al. suggested that the accelerations of various materials to the Earth may be different depending on their compositions, on the basis of their reanalysis of the results of the experiment of Eötvös, Pekár, and Fekete. We find that systematic effects due to thermal gradients can account for the experimental data.

A procedure is developed for transcription of any measure for the integration over metric fields in the continuum to the Regge-calculus lattice.

An investigation of pure U(1) gauge theory is made based on block-spin transformations for configurations of lattice size ${16}^4$ down to size $8^4$ and $4^4$. Even operators (five types in the first three representations) and ten renormalized couplings are determined on these smaller lattices. This allows the mapping of the renormalization flow. An interesting fixed-point structure and results on the leading critical exponent are found.

We present a simple set of rules for constructing ultraviolet-finite closed-fermionic-string models. In particular, the method easily gives four-dimensional models which possess $N=1\mathrm{}$ super-symmetry, chiral fermions, and phenomenologically interesting gauge groups.

We measure an inclusive branching fraction of (13.9 ± ${2.0}_{-2.2\mathrm{}}^{+1.9\mathrm{}}$)% for the decay ${\tau }^{-}\to {\nu }_{\tau }{\pi }^{-}{\pi }^0+n{h}^0(n>~1)$, where $h^0$ is a ${\pi }^0$ or an $\eta$. The data sample, obtained with the time-projection-chamber detector facility at the SLAC $e^{+}{e}^{-}$ storage ring PEP, corresponds to an integrated luminosity of 72 ${\mathrm{pb}}^{-1\mathrm{}}$ at 29 GeV center-of-mass energy. The measured branching fraction is somewhat greater than the theoretical prediction and, with errors taken into account, could resolve the present difference between the inclusive and the sum of the exclusive ${\tau }^{\pm }$ branching fractions into one charged prong.

The analog of the 4.7-MeV state of the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ nucleus has been observed in its mirror ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ by the reaction ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}({}_{}{}^3{}_{}{}^{}\mathrm{He},\alpha ){}_{}{}^9{}_{}{}^{}\mathrm{B}\left(\alpha \right){}_{}{}^3{}_{}{}^{}\mathrm{Li}_{(\mathrm{g}.\mathrm{s}.\mathrm{})}^{}{}_{}{}^{}$ at $E\left({}_{}{}^3{}_{}{}^{}\mathrm{He}\right)=2.3\mathrm{} \mathrm{and} 5.0$ MeV. The excitation energy and width of the state have been deduced. The value of 1.5 ± 0.3 MeV found for the width is in line with the value deduced by the reaction ${}_{}{}^7{}_{}{}^{}\mathrm{Li}({}_{}{}^3{}_{}{}^{}\mathrm{He},n){}_{}{}^9{}_{}{}^{}\mathrm{B}$, but it is larger by a factor of about 4 than the one measured by the proton following the ${\beta }^{+}$ decay of the ${}_{}{}^9{}_{}{}^{}\mathrm{C}$ nucleus.

The spectral function for the knockout of $1f$ protons from ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ leading to the ${\left(1\mathrm{}{f}_{\frac{7}{2}}\right)}^2$ quadruplet in ${}_{}{}^{50}{}_{}{}^{}\mathrm{Ti}$ has been measured in a high-resolution ($e,e^{\prime }p$) experiment. In the distorted-wave impulse approximation the $1f$ spectroscopic strength observed in the $0^{+}$, $2^{+}$, $4^{+}$, $6^{+}$ quadruplet of ${}_{}{}^{50}{}_{}{}^{}\mathrm{Ti}$ is 1.11(14). This is considerably lower than predicted by shell-model calculations. In addition the rms radius of the $1f_{\frac{7}{2}}$ orbit, 4.20(14) fm, is deduced. With this rms radius, recent ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}\left(d{}_{}{}^3{}_{}{}^{}\mathrm{He}\right){}_{}{}^{50}{}_{}{}^{}\mathrm{Ti}$ data yield a similar low value of the $1f$ strength.

A large ${\mu }^{-}$ polarization was achieved in muonic Bi atoms with the help of the strong hyperfine field in a polarized nuclear target. Using ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ nuclei polarized to (59 ± 9)% in ferromagnetic BiMn, we observed a $\mu -e$ decay asymmetry of (13.1 ± 3.9)%, which gives ${\mu }^{-}$ polarization per nuclear polarization equal to -1.07 ± 0.35. This value is almost consistent with -0.792 calculated for nuclei with spin $I=\frac{9}{2}$ and a positive magnetic moment under the assumption that the hyperfine interaction becomes effective in the lowest muonic states.

The ${\mathrm{Na}}_3$ photodissociation spectrum is studied by depletion spectroscopy. For the first time a predissociated state is observed in ${\mathrm{Na}}_3$ and detected both by depletion and by recording of the related photofragments. The method is promising for photodissociation studies in clusters.

The energy dependence of the spin asymmetry in elastic scattering of polarized electrons from Li atoms has been studied for scattering angles of 65°, 90°, and 107.5° and collision energies from 1 to 30 eV. The measured asymmetry shows variations between its extreme values of + 1 and - ⅓, and its behavior can best be described by close-coupling calculations.

Dielectronic recombination is shown to be a dominant process for determining the charge state of fast heavy ions passing through plasma. Calculated dielectronic rates are compared with rates of competing processes, including effects of high plasma density. Equilibrium charge states are determined for a typical ion-target system.

Microwave resonance transitions between the $\mathrm{}(0,1)10G_5$ and $\mathrm{}(0,1)10H_6$ states of ${\mathrm{H}}_2$ have been observed with a fast-beam technique and have been used to determine an energy difference of 10 031.24(10) MHz between these two Rydberg states. The observations show partial resolution of the magnetic fine and hyperfine structure which appears to conform to a simple model. It should prove possible to deduce new precise information about the ${\mathrm{H}}_2^{+}$ ion from measurements of this type.

A space- and time-resolved coherent anti-Stokes Raman spectroscopy technique gives direct access to the propagation and loss of coherence of picosecond phonon-polariton pulses of widely varying wave vector and frequency in noncentrosymmetric crystals.

The growth and saturation of spontaneous emission and coherent radiation in a long undulator are studied by use of the 3D Maxwell-Klimontovich equation. Electron correlation, transverse radiation profiles, spectral features, transverse coherence, and intensity characteristics are discussed. The results, which agree with recent microwave experiments, are applied to proposed schemes for generation of short-wavelength coherent radiation.

Viscous fingers (VF) and diffusion-limited aggregates (DLA) are shown to exhibit different features when they grow on dilute percolating networks. On the infinite incipient cluster at the site-percolation threshold $p_c$ on the square lattice, both fractal dimensionalities are $D_{\mathrm{VF}}\simeq D_{\mathrm{DLA}}\simeq 1.3$, but the mass amplitudes obey $\frac{A_{\mathrm{VF}}}{A_{\mathrm{DLA}}}\simeq 1.3$. The effective $D_{\mathrm{VF}}^{\mathrm{eff}}$ seems to increase for wider pores, while $D_{\mathrm{DLA}}^{\mathrm{eff}}$ remains 1.3. For $p>\mathrm{}{p}_c$, the crossover to homogeneous behavior is very slow, and $1.3<\mathrm{}{D}_{\mathrm{DLA}}^{\mathrm{eff}}<D_{\mathrm{VF}}^{\mathrm{eff}}<1.7\mathrm{}$.

Scalar-wave localization characteristics in a two-component composite are calculated as a function of frequency, relative volume fraction, and impedance contrast between the components. It is found that the occurrence of localization requires a minimum impedance contrast whose value is defined by a critical point on the localization phase diagram. Furthermore, localization is shown to be closely tied to resonant scattering, and there is a multitude of mobility edges and localization regions associated with resonance harmonics.

2D Navier-Stokes solutions are generated for a periodic shear layer with a fundamental ($m=0\mathrm{}$) and a single subharmonic ($m>\mathrm{}0\mathrm{}$) disturbance. For $m=2, 3, \mathrm{and} 4$ we find clusters with $m+1\mathrm{}$ vortices without the formation of vortex pairs. This implies enhanced spreading in a spatially growing mixing layer. However, when $m=5\mathrm{}$ we find a different dynamical clustering due to nondirect energy transfer from the fundamental to the subharmonic. Additionally, if we force the layer with a wavelength smaller than the fundamental we find a new mechanism called "collective interaction."

We have made numerical calculations with a new nonlocal fluid treatment of Coulomb collisional electron transport which self-consistently accounts for the nonthermal high-energy electrons arising from the spatial transport of thermal electrons whose range is not short compared with the temperature scale length. Heat fluxes associated with steep gradients are reduced from classical, while ahead of a temperature front there is preheating which exceeds classical.