The temperature variation of the relaxation rate ${\mathrm{\Gamma }}_{\mathit{w}}$ of the domain walls about their transition at T=${\mathit{T}}^{\mathrm{*}}$ from the Bloch to the linear Bulaevskii-Ginzburg structure has been investigated in the uniaxial ferrimagnet ${\mathrm{SrFe}}_{12}$${\mathrm{O}}_{19}$. The significant suppression of ${\mathit{T}}^{\mathrm{*}}$ below the mean-field approximation (MFA) value along with the speeding up of ${\mathrm{\Gamma }}_{\mathit{w}}$(T≤${\mathit{T}}^{\mathrm{*}}$), which is much stronger than that predicted by the MFA, reveals the first evidence for critical fluctuations in a domain wall. The speeding up can be almost quantitatively explained by taking two dimensional fluctuations of the transverse magnetization in the wall into account.

Experimentally, the magnetic coupling strength in Co/TM and Fe/TM multilayer systems, for which TM is a nonmagnetic transition metal, increases dramatically as a function of the electron per atom ratio, e/a, in the TM spacer layers. On the basis of simple model calculations we argue that this effect is a finite resonant increase of the coupling due to the variation of the band offset between the TM spacer and the magnetic host. We find that the specific form of the correlation is strongly influenced by the resonant coincidence of the TM bands with either the spin up or the spin down bands of the host, for particular values of e/a. We suggest new experiments to test the model.

We report photoinduced antiferromagnetic (AF) interlayer coupling in sputtered Fe/(Fe-Si) superlattices. The superlattices are intrinsically AF coupled at room temperature and become increasingly ferromagnetically coupled when cooled below 100 K, but the AF coupling is restored at low temperature by exposure to visible light of sufficient intensity (>10 mW/${\mathrm{mm}}^2$). These effects are due to charge carriers in the Fe-Si spacer layer which, when thermally or optically generated, are capable of communicating spin information between the Fe layers.

Elastic moduli of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ diamond, deduced from the Brillouin shifts experienced by inelastically scattered monochromatic radiation, are ∼0.5% higher than the corresponding values for natural diamond. This suggests ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ diamond is harder than natural diamond. A simple model incorporating the zero-point motion and the anharmonicity of the interatomic forces is proposed; it explains quantitatively the increase in the elastic moduli, the decrease in the lattice parameter, and a correction to the Raman frequency beyond its ${\mathit{M}}^{\mathrm{-}1/2}$ dependence (where M is the average atomic mass) observed for ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ diamond with respect to their values for natural diamond.

Inelastic neutron scattering and molecular dynamics simulations provide evidence for the existence of low-frequency floppy modes in the high-temperature phase of cristobalite, which are analogous to those found in network glasses. The behavior is similar to that observed in computer simulations of orientationally disordered crystals.

Simple models for the formation dynamics of two scales of sand features are proposed. In the simulation of the small scale model, a ripple pattern is spontaneously formed by the saltation of sand grains when the wind force exceeds a critical value. With the large scale model, the dynamics of sand dunes is discussed.

Large-scale cosmic microwave background temperature fluctuations are calculated for a universe with the topology of a 3-torus. In such a universe only perturbations which are harmonics of the fundamental mode are permitted. By comparison with data from the Cosmic Background Explorer satellite, we find that the minimum (comoving) scale of a cubic toroidal universe is 2400${\mathit{h}}^{\mathrm{-}1}$ Mpc for an n=1 inflationary model. This is approximately an order of magnitude greater than previous limits and 80% of the horizon scale, implying that a topologically ‘‘small’’ universe is no longer an interesting cosmological model.

Validity of perturbative estimation of renormalization factors in weak matrix element calculations in lattice QCD is examined for the ${\mathit{K}}^{0\mathrm{-}}$K${\mathrm{¯}}^0$ mixing matrix by comparing results for gauge invariant and noninvariant operators. A large disagreement found for uncorrected results for the two cases is shown to be removed by the one-loop renormalization factor. This indicates that the large scaling violation in the mixing matrix previously reported is not due to an artifact of prescription of lattice calculations. Our estimate of B${\mathrm{^}}_{\mathit{K}}$ for the continuum in quenched QCD is 0.61(13)–0.83(7).

Employing the decay chain ${\mathit{K}}^{+}$→${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^0$, ${\mathrm{\pi }}^0$→${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ we have observed the decay ${\mathrm{\pi }}^0$→${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$. With a signal sample of ≊21 events we measure the branching ratio for ${\mathrm{\pi }}^0$→${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ to be (6.9±2.3±0.6)×${10}^{\mathrm{-}8}$, normalized to the decay ${\mathit{K}}^{+}$→${\mathrm{\pi }}^{+}$${\mathrm{\pi }}^0$, ${\mathrm{\pi }}^0$→${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$γ. This result is consistent with the unitarity lower bound and the published 90% confidence level upper limit of 13×${10}^{\mathrm{-}8}$.

The Fermilab E799 Collaboration has carried out a search for the rare decay ${\mathrm{\pi }}^0$→${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ using ${\mathrm{\pi }}^0$’s produced from ${\mathit{K}}_{\mathit{L}}$→${\mathrm{\pi }}^0$${\mathrm{\pi }}^0$${\mathrm{\pi }}^0$ decays in flight. We observe a signal of nine events with an ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ mass close to the ${\mathrm{\pi }}^0$ mass where only one event is predicted from other known processes. From this, we measure B(${\mathrm{\pi }}^0$→${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$,(${\mathit{m}}_{\mathit{e}\mathit{e}}$/${\mathit{m}}_{\mathrm{\pi }}^0$${)}^2$≳0.95) =[7.$6_{\mathrm{-}2.8}^{+3.9\mathrm{}}$(stat)±0.5(syst)]×${10}^{\mathrm{-}8}$, over and above the contribution from ${\mathrm{\pi }}^0$ Dalitz decays. Correcting for radiative effects, we find this result consistent with theoretical expectations from standard-model processes.

We report on a measurement of the branching ratio for the ${\mathit{K}}_{\mathit{L}}$ double Dalitz decay ${\mathit{K}}_{\mathit{L}}$→${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$. The result, based on the observation of six events, is B(${\mathit{K}}_{\mathit{L}}$→${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$) =(3.07±1.25±0.26)×${10}^{\mathrm{-}8}$.

Inclusive momentum spectra of charged particles in three-fold symmetric three-jet (qqg) and two-jet +γ(qqγ) events taken from ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ annihilation at center-of-mass energy of 58 GeV were compared. The spectrum of gluon jets was found to be significantly softer than that of quark jets with the same energy and topology.

All currently available data on the pionic double charge exchange reaction (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{\mathrm{-}}$) on nuclei exhibit a very peculiar energy dependence near ${\mathit{T}}_{\mathrm{\pi }}$=50 MeV, while the angular distributions behave quite regularly. We demonstrate that these features find their natural explanation by a narrow resonance in the πNN subsystem with ${\mathit{J}}^{\mathit{P}}$=$0^{\mathrm{-}}$ and a mass of 2.065 GeV.

We discuss two different approximation schemes for the self-consistent solution of the relativistic Brueckner-Hartree-Fock equation for finite nuclei. The results obtained by the two methods are very similar. Employing a realistic one-boson-exhange potential (Bonn A), the predictions for energies and radii of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ come out in substantially better agreement with experiment as compared to nonrelativistic approaches. As a by-product of our study, it turns out that the Fock exchange terms, ignored in a previous investigation, are not negligible.

In this paper, we investigate a family of one-dimensional multicomponent quantum many-body systems. The interaction is an exchange interaction based on the familiar family of integrable systems which includes the inverse square potential. We show these systems to be integrable, and exploit this integrability to completely determine the spectrum including degeneracy, and thus the thermodynamics. The perioidic inverse square case is worked out explicitly. Next, we show that in the limit of strong interaction of the ‘‘spin’’ degrees of freedom decouple. Taking this limit for our example, we obtain a complete solution to a lattice system introduced recently by Shastry and by Haldane; our solution reproduces the numerical results. Finally, we emphasize the simple explanation for the high multiplicities found in this model.

The ratio of double to single ionization by photoabsorption is calculated for photon impact energies in the range 2–18 keV. Employing the acceleration form of the dipole operator and representing the electron-electron correlation in the final state by a Coulomb distortion factor, R=${\mathrm{\sigma }}^{++}$/${\mathrm{\sigma }}^{+}$ approaches an asymptotic value of 1.66% and reaches a value of about 2.5% at 2 keV photon energy. Comparison with experimental data shows good agreement when contributions due to Compton scattering are taken into account.

Reported here is a newly developed cw-infrared pump-probe method for studying the vibrational predissociation of weakly bound complexes at the state-to-state level. This method is suitable for studying the wide range of dynamical processes possible in these systems. We discuss preliminary results for two systems, ${\mathrm{N}}_2$-HF and ${\mathrm{CO}}_2$-HF, which illustrate the versatility of the method and the richness of the accessible dynamics.

Two rational numbers are associated to each periodic orbit of Smale’s horseshoe, and practical algorithms are given for their calculation. Using these quantities, it is possible to decide in many cases whether or not a given orbit must always be created after some other given orbit in any two-dimensional transition to chaos. A statement of ‘‘weak universality’’ for the bifurcation sequence as a whole is formulated.

We introduce a novel technique to find the asymptotic time behavior of deterministic systems exhibiting anomalous diffusion. The procedure is tested for various classes of simple but physically relevant 1D maps and the possible relevance of our findings for more complicated problems is briefly discussed.

An analog circuit implementation of the chaotic Lorenz system is described and used to demonstrate two possible approaches to private communications based on synchronized chaotic systems.