Transport measurements show that the critical current in the c direction, ${\mathit{J}}_{\mathit{c}}^{\mathit{c}}$ of ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ single crystals increases with temperature for low temperature zero field cooled (ZFC) measurements. As a consequence, the c direction electrical resistance of the ZFC critical state, at a given dc current, is finite, goes to zero with increasing temperature, and becomes finite again at higher temperatures. The results are consistent with a loss of the c axis long range correlation induced by the critical current flowing in the ab planes, ${\mathit{J}}_{\mathit{c}}^{\mathit{a}\mathit{b}}$, and an increase of that correlation with temperature, as a consequence of the corresponding decrease of ${\mathit{J}}_{\mathit{c}}^{\mathit{a}\mathit{b}}$.

We report the observation of the excitonic recombination of degenerate quasi-two-dimensional electrons with localized photoexcited holes. Low-temperature photoluminescence and magnetophotoluminescence spectra exhibit a well resolved Mahan exciton resonance which is sensitive to electron density ${\mathit{n}}_{\mathit{s}}$. We observe a sharp decrease in the exciton oscillator strength and linewidth with the concomitant formation of biexcitons and a large discontinuity in the exciton ground-state energy at ${\mathit{n}}_{\mathit{s}}$≊1.9×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$. An abrupt transition from excitonic to free-electron–localized-hole recombination occurs at ${\mathit{n}}_{\mathit{s}}$≊2.2×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$.

Impact of ${\mathrm{C}}_{60}^{+}$ ions onto an epitaxially grown crystalline fullerite target is studied at a primary kinetic energy of 275 eV as a function of the angle of incidence. Scattered ions are investigated by velocity selective time-of-flight mass spectrometry at a fixed scattering angle of 140°. In addition to scattering of intact ${\mathrm{C}}_{60}^{+}$ ions we also see desorbed ${\mathrm{C}}_{70}^{+}$ as well as larger ions ${\mathrm{C}}_{100}^{+}$ to ${\mathrm{C}}_{130}^{+}$ arising from reactive processes (fusion, coalescence). The velocity distribution of the receding ${\mathrm{C}}_{60}^{+}$ ions reveals a range of processes from nearly elastic to fully inelastic. The angular dependence exhibits rich structure. This may be attributed to rainbow scattering, as confirmed by a simple classical trajectory calculation.

We establish chemical-shift low-energy photoelectron diffraction as a novel and powerful method for the determination of clean surface structures. Combined with a new theoretical approach based on full multiple scattering theory with complex potential, the method is applied to the case of the InP(110) clean surface relaxation. The extreme sensitivity of this technique to structural parameters allows us to measure with good accuracy both the first layer and the second layer relaxation angle (respectively 23° and -5°).

We give a wide class of Lie-Poisson systems for which explicit, Lie-Poisson integrators, preserving all Casimirs, can be constructed. The integrators are extremely simple and have widespread applicability. Examples are the free rigid body, a moment truncation, and a new, fast algorithm for the sine-bracket truncation of the 2D Euler equations.

The number of levels with energy less than E of an integrable quantum system with two degrees of freedom is equal to λE+${\mathit{sE}}^{1/4}$, where λ is a constant and s a fluctuating quantity with a non-Gaussian distribution. The probability distribution of s decreases roughly like exp(-${\mathit{s}}^4$) when s is large. The number of levels between E and E+z √E is equal to λz √E +${\mathit{rE}}^{1/4}$ where r is another fluctuating quantity. The distribution of r tends to a Gaussian distribution as z→0 and oscillates around some limiting non-Gaussian distribution as z→∞.

Evolution of inhomogeneities in the axion field around the QCD epoch is studied numerically, including for the first time important nonlinear effects. It is found that perturbations on scales corresponding to causally disconnected regions at T∼1 GeV can lead to very dense axion clumps, with present density ${\mathrm{\rho }}_{\mathit{a}}$≳${10}^{\mathrm{-}8}$ g ${\mathrm{cm}}^{\mathrm{-}3}$. This is high enough for the collisional 2a→2a process to lead to Bose-Einstein relaxation in the gravitationally bound clumps of axions, forming Bose stars.

Thermal amplitudes exhibit mass singularities when particle(s) with vanishing mass is (are) involved. We show that such singularities do not appear in the perturbation expansions of the thermal reaction rates, provided the theory in consideration does not bring about such mass singularities in zero-temperature reaction rates. The latter is supposed to be the case for physically sensible quantities in a wide class of theories, including QED and QCD (Kinoshita-Lee-Nauenberg theorem).

We present results of a detailed investigation of the temperature dependence of the spatial string tension in SU(2) gauge theory. We show, for the first time, that the spatial string tension is scaling on the lattice and thus is nonvanishing in the continuum limit. It is temperature independent below ${\mathit{T}}_{\mathit{c}}$ and rises rapidly above. For temperatures larger than 2${\mathit{T}}_{\mathit{c}}$ we find a scaling behavior consistent with ${\mathrm{\sigma }}_{\mathit{s}}$(T)=(0.136±0.011)${\mathit{g}}^4$(T)${\mathit{T}}^2$, where g(T) is the two-loop running coupling constant with a scale parameter determined as ${\mathrm{\Lambda }}_{\mathit{T}}$=(0.076±0.013)${\mathit{T}}_{\mathit{c}}$.

The scaling behavior of pure gauge SU(3) in the region β=5.85-7.60 is examined by a Monte Carlo renormalization group analysis. The coupling shifts induced by factor 2 blocking are measured on both ${32}^4$ and ${16}^4$ lattices with high statistics. A systematic deviation from naive 2-loop scaling is clearly seen. The mean field and effective coupling constant schemes explain part, but not all, of the deviation. It can be accounted for by a suitable change of coupling constant, including a correction term O(${\mathit{g}}^7$) in the 2-loop lattice β function. Based on this improvement, √σ /${\mathrm{\Lambda }}_{\mathrm{MS}\mathrm{¯}\mathit{f}}^{\mathit{n}}$=0 is estimated to be 2.2±0.1 from the analysis of the string tension σ.

We observe that quantities like (${\mathit{f}}_{\mathit{B}\mathit{s}}$/${\mathit{f}}_{\mathit{B}}$)/(${\mathit{f}}_{\mathit{D}\mathit{s}}$/${\mathit{f}}_{\mathit{D}}$) are predicted to be unity both by heavy quark and by light quark flavor symmetries. Hence, the deviation from the symmetry prediction must be simultaneously small in both symmetry breaking parameters, i.e., order of the ratio of light to heavy quark masses. We estimate the size of the correction. We observe that the ratio of (ΔM/Γ) for ${\mathit{B}}_{\mathit{s}\mathrm{-}}$B${\mathrm{¯}}_{\mathit{s}}$ to B-B¯ mixing can be expressed in terms of the measurable ratio ${\mathit{f}}_{\mathit{D}\mathit{s}}$/${\mathit{f}}_{\mathit{D}}$ with good precision. We comment on applications of these ideas to other processes.

Using 1.79 ${\mathrm{fb}}^{\mathrm{-}1}$ of data recorded by the CLEO II detector we have measured the absolute branching fraction for ${\mathit{D}}^0$→${\mathit{K}}^{\mathrm{-}}$${\mathrm{\pi }}^{+}$. The angular correlation between the ${\mathrm{\pi }}^{+}$ emitted in the decay ${\mathit{D}}^{\mathrm{*}+}$→${\mathit{D}}^0$${\mathrm{\pi }}^{+}$, and the jet direction in ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$→cc¯ events, is used to determine the total number of inclusive ${\mathit{D}}^0$ mesons produced from this source. The subsequent reconstruction of the decay chain ${\mathit{D}}^{\mathrm{*}+}$→${\mathit{D}}^0$${\mathrm{\pi }}^{+}$,${\mathit{D}}^0$→${\mathit{K}}^{\mathrm{-}}$${\mathrm{\pi }}^{+}$ allows a measurement of the absolute ${\mathit{D}}^0$→${\mathit{K}}^{\mathrm{-}}$${\mathrm{\pi }}^{+}$ branching fraction. Correcting for decay radiation in the final state, we find scrB(${\mathit{D}}^0$→${\mathit{K}}^{\mathrm{-}}$${\mathrm{\pi }}^{+}$)=[3.95±0.08(stat)±0.17(syst)]%.

The dependence on invariant mass M and transverse momentum ${\mathit{q}}_{\mathrm{\perp }}$ of lepton pairs emitted by quarks during the early stage of central collisions between gold nuclei at √s =200A GeV is investigated within the parton cascade model. For fixed transverse mass ${\mathit{M}}_{\mathrm{\perp }}$ between 2 and 3 GeV, the spectrum is thermal shaped at low ${\mathit{q}}_{\mathrm{\perp }}$ and exhibits a power law behavior at larger ${\mathit{q}}_{\mathrm{\perp }}$. A suspected ${\mathit{M}}_{\mathrm{\perp }}$ scaling is not observed in the calculated distribution, but the significant shape of the spectrum and the large yield from preequilibrium emission may nevertheless serve as a characteristic signal for a parton plasma formation.

Relativistic mean field theory in the rotating frame is used to describe superdeformed nuclei. Nuclear currents and the resulting spatial components of the vector meson fields are fully taken into account. Identical bands in neighboring rare earth nuclei are investigated and excellent agreement with recent experimental data is observed.

A curved mirror for atoms was made from an evanescent wave, formed by internal reflection of a quasiresonant laser beam at a curved glass surface. A cold cloud of cesium atoms was dropped onto the mirror and observed to rebound more than 8 times. The mirror size and reflectivity were studied, and reasonable agreement with a simple theory obtained. With 800 mW of laser power and a mirror of 1 mm diameter, we observed up to 73% of the atoms returning after each bounce, the losses being mostly during the free flight between bounces.

We report a 1D study of optical forces on atoms in a two-frequency laser field. The light couples two ground state hyperfine structure levels to a common excited state of ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$, thus forming a Λ system. We observe a new type of sub-Doppler coupling with blue-tuned light that uses neither polarization gradients nor magnetic fields, efficient heating with red tuning, and the spatial phase dependence of these. We observed deflection from a rectified dipole force and determined its velocity dependence and capture range. We report velocity selective resonances associated with Raman transitions. A simplified semiclassical calculation agrees qualitatively with our measurements.

We have determined the exchange splitting of the 1${\mathrm{\sigma }}_{\mathit{g}}^{\mathrm{-}1}$3${\mathrm{\sigma }}_{\mathit{u}}$ shape resonance excitation of gas phase ${\mathrm{O}}_2$, which cannot unambiguously be identified using conventional absorption spectroscopy. By identifying the electronic decay spectrum of the shape resonance excitation we could separately monitor the decay of the ${\mathrm{\sigma }}^{\mathrm{*}}$ shape resonance and the Rydberg states. Using this fingerprint method we measured the pure core to 3${\mathrm{\sigma }}_{\mathit{u}}$ bound state absorption spectrum in partial secondary electron yield spectroscopy.

A scheme for the preparation of general coherent superpositions of photon-number states is proposed. By strongly coupling an atom to a cavity field, atomic ground-state Zeeman coherence can be transferred by (coherent) adiabatic passage to the cavity mode and a general field state can be generated without atomic projection noise.

Nonlinear optical generation using electromagnetically induced transparency is demonstrated with atomic hydrogen as a test medium. With the application of a strong-coupling laser field to the 3p-2s transition, the resonant Lyman-β (3p-1s) transition becomes transparent. The generated-sum-frequency Lyman-β radiation at 103 nm can continue to grow without suffering resonant absorption and phase mismatching.

A new route is described for eliminating chaos in nonlinear oscillators by changing only the shape of a weak nonlinear periodic perturbation and illustrated with the example of the Duffing-Holmes oscillator forced with the Jacobian elliptic function sn. Two techniques are used in the illustration: applying the Melnikov-Holmes analysis, and studying the behavior of the Lyapunov exponent from a simple recursion relation which models an unstable limit cycle. The connection with related previously described routes is also discussed in a general setting.