Oscillatory magnetoresistance as a function of the Fe layer thickness has been found in Fe/Cr(100) multilayers deposited on MgO(100). It is mainly attributed to an oscillatory interlayer exchange coupling between adjacent Fe layers as a function of the Fe layer thickness. Further, oscillatory variation of the saturation resistivity with Fe layer thickness was also observed. Both the oscillation periods are approximately 8 Å. These two oscillations can be understood in terms of the partial confinement of the perpendicular motion to the layer plane of Fe majority spin electrons.

Absolute magnetic moments of Cr are determined from in situ magnetometer measurements during growth of ultrathin Cr films on Fe(100). Cr moments in the first atomic layer are aligned antiparallel to the Fe moments and amount to ≥4${\mathrm{\mu }}_{\mathit{B}}$ for submonolayer coverage and 3${\mathrm{\mu }}_{\mathit{B}}$ for the first complete monolayer. This is the first experimental evidence of the huge moment enhancement predicted for Cr interfaces by band theory. Monte Carlo simulations indicate a drastic deviation from layer-antiferromagnetic order within the first 2–3 Cr atomic layers.

Ag(111) and Ag(110) surfaces exposed to oxygen at elevated temperatures (∼800 K) exhibit strongly enhanced Raman bands at 803 and 627 ${\mathrm{cm}}^{\mathrm{-}1}$ which are attributed to O atoms strongly chemisorbed on the surface (${\mathrm{O}}_{\gamma }$) or held in subsurface sites (${\mathrm{O}}_{\mathrm{\beta }}$), respectively. In contrast to usual experience, surface-enhanced Raman scattering is occurring here under well-defined conditions up to temperatures of 900 K which is attributed to the joint operation of delocalized electromagnetic enhancement (caused by surface roughness provided by oxygen-induced faceting) and local resonance due to the particular electronic properties of the surface sites.

We present Raman spectra of a series of isotopic ${}_{}{}^{70}{}_{}{}^{}$(Ge${)}_{\mathit{n}}^{74}$(Ge${)}_{\mathit{n}}$ superlattices with 2≤n≤32. In these novel structures only the phonons are subject to a periodic isotopic mass modulation, whereas the electrons retain their bulklike character. This differs substantially from conventional superlattices where both electronic and vibronic properties are affected by the reduction in dimensionality. Our results show clear evidence for optic phonon confinement in each of the two superlattice constituents. Observed frequencies, relative intensities, and mode mixing compare favorably with calculations based on a planar bond-charge model and the bond polarizability approach.

A formalism is developed for studying genetic algorithms by considering the evolution of the distribution of fitness in the population. The effects of selection on the population are problem independent. The formalism predicts the optimal amount of selection. Crossover is solved for a model problem-finding low energy states of the one dimensional Ising spin glass. The theory is found to be in good agreement with simulations.

Time-independent wave-packet forms of the Schrödinger equation (TIWSE) and Lippmann-Schwinger equation (TIWLSB) have been derived by a partial time-to-energy Fourier transform of ${\mathit{L}}^2$ wave-packet solutions to the time-dependent Schrödinger equation. The new equations retain the initial wave packet χ(${\mathit{t}}_0$) as a ‘‘universal source’’ of scattered waves, which applies for all collision energies E contained in the initial wave packet. The relationship between the solution ${\mathrm{\Psi }}_{\mathit{t}0}$(E) of the TIWSE or TIWLSE and the scattering solution ${\mathrm{\Psi }}^{\mathrm{}(+)\mathrm{}}$(E) of the standard time-independent Lippmann-Schwinger or Schrödinger equation is given and the method illustrated by a computational application.

We present the first calculations of the gravitational radiation produced by nonaxisymmetric dynamical instability in rapidly rotating compact star. The star deforms into a bar shape, shedding ∼4% of its mass and ∼17% of its angular momentum. The gravitational radiation is calculated in the quadrupole approximation. For a mass M∼1.4${\mathit{M}}_{\mathrm{\odot }}$ and radius R∼10 km, the gravitational waves have frequency ∼4 kHz and amplitude h∼2×${10}^{\mathrm{-}22}$ at the distance of the Virgo Cluster. They carry off energy ΔE/M∼0.1% and radiate angular momentum ΔJ/J∼0.7%.

The differential cross sections dσ/${\mathit{dx}}_{\mathit{F}}$ for J/ψ produced inclusively in 800 GeV/c p-Cu and p-Be collisions have been measured in the kinematic range 0.30≤${\mathit{x}}_{\mathit{F}}$≤0.95 through the decay mode J/ψ→${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{\mathrm{-}}$. They are compared with the predictions of the semilocal duality model for several sets of parton density functions. No evidence for a suggested intrinsic charm contribution to the cross section is observed. The ratio of the differential cross sections for Cu and Be targets confirms the suppression of J/ψ production in heavy nuclei at large ${\mathit{x}}_{\mathit{F}}$.

A precision measurement of the masses of the ${\mathrm{\Lambda }}^0$ and Λ${\mathrm{¯}}^0$ hyperons is obtained from Gaussian fits to the invariant mass distributions for 20 138 ${\mathrm{\Lambda }}^0$’s and 18 309 Λ${\mathrm{¯}}^0$’s. The Gaussians have standard deviations of 0.49 and 0.51 MeV/${\mathit{c}}^2$ for the ${\mathrm{\Lambda }}^0$ and Λ${\mathrm{¯}}^0$, respectively. Systematic errors were reduced by calibrating the spectrometer with 60 000 exclusive events containing a ${\mathit{K}}_{\mathit{S}}^0$. We find ${\mathit{M}}_{\mathrm{\Lambda }}$=1115.678±0.006±0.006 MeV/${\mathit{c}}^2$ and ${\mathit{M}}_{\mathrm{\Lambda }\mathrm{¯}}$=1115.690±0.008±0.006 MeV/${\mathit{c}}^2$. The ${\mathrm{\Lambda }}^{0\mathrm{-}}$Λ${\mathrm{¯}}^0$ mass difference testing CPT invariance is -0.012±0.010 MeV/${\mathit{c}}^2$.

We investigate the α- and γ-decay properties of states belonging to the ground state ‘‘band’’ of ${}_{}{}^{212}{}_{}{}^{}\mathrm{Po}$, using an α-cluster model with parameter values taken from an earlier study of α decay of heavy nuclei. The known lifetimes of these states, which vary from 5.5×${10}^{\mathrm{-}10}$ s to 45 s, are reproduced to within a factor of ∼2. The (approximately) known α branching ratios, which vary from 3.3×${10}^{\mathrm{-}4}$ to 0.71, are reproduced to within a factor ∼5. These results strongly suggest a large amount of α clustering in this heavy nucleus.

Fine structure has been observed in the α decay of ${}_{}{}^{202}{}_{}{}^{}\mathrm{Rn}$, ${}_{}{}^{194,196,198}{}_{}{}^{}\mathrm{Po}$, ${}_{}{}^{186,188}{}_{}{}^{}\mathrm{Pb}$, and ${}_{}{}^{180,182,184}{}_{}{}^{}\mathrm{Hg}$ and has led to the identification of low-lying $0^{+}$ states in ${}_{}{}^{198}{}_{}{}^{}\mathrm{Po}$, ${}_{}{}^{190,192,194}{}_{}{}^{}\mathrm{Pb}$, ${}_{}{}^{182,184}{}_{}{}^{}\mathrm{Hg}$, and ${}_{}{}^{176,178,180}{}_{}{}^{}\mathrm{Pt}$. The large variation in the hindrance factors of the α decay to the exicted $0^{+}$ state is a proof for the persistence of the Z=82 shell closure at the neutron-deficient side. Comparing the reduced widths of the α decays to the ground and excited states offers a unique way to probe the proton particle-hole character of the $0^{+}$ states in this region.

We present the first experimental evidence that near-resonant perturbations produce a destabilizing shift of a subcritical bifurcation. This is in direct contrast to supercritical bifurcations, where near-resonant perturbations always suppress the instability. Using a normal form analysis we derive a generic scaling law relating the magnitude of the destabilizing shift μ to the perturbation amplitude ɛ and detuning frequency δ. The predictions are in excellent agreement with our experiments. In the limit of very small δ the shift obeys a pure scaling law, μ∝(ɛ${)}^{2/3}$.

We consider a system in which a classical oscillator is interacting with a purely quantum mechanical oscillator, described by the Lagrangian L=1/2x${\mathrm{̇}}^2$+1/2A${\mathrm{̇}}^2$-1/2(${\mathit{m}}^2$+${\mathit{e}}^2$${\mathit{A}}^2$)${\mathit{x}}^2$, where A is a classical variable and x is a quantum operator. With 〈x(t)〉=0, the relevant variable for the quantum oscillator is 〈x(t)x(t)〉=G(t). The classical Hamiltonian dynamics governing the variables A(t),${\mathrm{\Pi }}_{\mathit{A}}$(t),G(t), and ${\mathrm{\Pi }}_{\mathit{G}}$(t) is chaotic so that the results of making measurements on the quantum system at later times are sensitive to initial conditions. This system arises as the zero momentum part of the problem of pair production of charged scalar particles by a strong external electric field.

We describe the application of path integrals to the problem of light propagation in turbid media. The photon propagation process is separated into an absorption dependent part and a part that depends only on scattering. We determine the nonabsorption photon path and nonabsorption probability distribution function, from which other measurable optical parameters can be obtained. As an example, we calculate the diffuse reflectance for a semi-infinite medium and obtain a new result which reduces to a previously derived expression in the approximate limiting case.

The Kadomtsev-Petviashvili equation with positive dispersion has well known flat as well as two dimensional soliton solutions. The two dimensional solitons, however, involve regions of depressed as well as of excess density. It might therefore seem to be an open question if flat solitons, known to be unstable, would decompose into these rather strange structures. The present paper definitely answers this question in the affirmative by describing a numerical simulation.

We report the first measurements of single-pass propagation of intense (>1-GW, 20-ns) microwaves through a high-density [${\mathit{n}}_{\mathit{e}}$=(0.5–2.4)×${10}^{20}$${\mathrm{m}}^{\mathrm{-}3}$] tokamak plasma at 140 GHz, the fundamental electron cyclotron resonance frequency. Compared with low-power pulses, these free-electron-laser generated intense pulses were not as strongly absorbed by the plasma, in agreement with predictions of nonlinear theory. Enhanced absorption of intense pulses was achieved by increasing the gradient in the parallel index of refraction (${\mathit{N}}_{\mathrm{\parallel }}$) of the microwave beam.

Quantitative measurements of oxygen octahedra local rotation angles are reported for the antiferrodistortive type perovskites, ${\mathrm{Na}}_{0.82}$${\mathrm{K}}_{0.18}$${\mathrm{TaO}}_3$ and ${\mathrm{NaTaO}}_3$. The results were obtained using a detailed analysis of x-ray absorption fine structure spectra. These results show that the oxygen octahedra rotation angle at the peak of the rotation angle distribution function of an antiferrodistortive crystal is nonzero and large, hundreds of degrees above the transition temperature.

The translational energy of ${\mathrm{D}}_2$ desorbed from Si(100) and Si(111) surfaces was measured and found roughly equal to the thermal expectation at the surface temperature ${\mathit{T}}_{\mathit{s}}$. Combining these results with previously measured internal state distributions, the total energy of the desorbed molecules is approximately equal to the equilibrium expectation at ${\mathit{T}}_{\mathit{s}}$. Thus adsorption experiments, which suggest a large energetic barrier, are at variance with desorption experiments, which exhibit a trivial adsorption barrier, and the applicability of detailed balance for this system needs to be reexamined.

Optical observations, Raman scattering, and single-crystal synchrotron x-ray measurements demonstrate the stability of a new stoichiometric compound, Ar(${\mathrm{H}}_2$${)}_2$. This is a Laves phase with a hexagonal structure isomorphous to ${\mathrm{MgZn}}_2$. A first order phase transition, wihch is associated with the sudden disappearance of the vibron and a visual increase absorbance of the sample, was observed around 175 GPa in three different experiments, two on Ar(${\mathrm{H}}_2$${)}_2$ and one on Ar(${\mathrm{D}}_2$${)}_2$. Optical absorption measurements up to 200 GPa in Ar(${\mathrm{D}}_2$${)}_2$ have revealed the onset of a possible Drude type metallic behavior above the transition.

Time-resolved photoelectron spectroscopy is used to directly observe the energy relaxation of optically excited electrons in silicon with 150 fsec resolution. We observe an electron-electron thermalization time of <120 fsec, an extremely fast initial electron cooling rate, followed by an electron-phonon thermalization time of ∼1 psec, and overall a strong energy dependence to the electron scattering rate. Here, we also report a new effect in two-photon photoemission unique to ultrashort laser pulses, resulting in a sensitive new monitor of electron dynamics.