Leech neurons are attached to metal-free field-effect transistors in electrolyte. The voltage in a neuron is controlled through a pipette fused to its membrane. Gaussian transients and ac voltages are applied. The response of the source-drain current is measured. Two types of neuron-transistor couplings are observed. (A) Efficient coupling above 100 Hz with a phase shift of 90°. (B) Efficient coupling from 0.1–1000 Hz without a phase shift. The responses are described by a circuit made of capacitance and resistance of the membrane, by the gate capacitance and by the resistance of the junction.

A simple and robust model of biological evolution of an ecology of interacting species is introduced. The model self-organizes into a critical steady state with intermittent coevolutionary avalanches of all sizes; i.e., it exhibits ‘‘punctuated equilibrium’’ behavior. This collaborative evolution is much faster than non-cooperative scenarios since no large and coordinated, and hence prohibitively unlikely, mutations are involved.

A simple dynamical model for Darwinian evolution on its slowest time scale is analyzed. Its mean field theory is formulated and solved. A random neighbor version of the model is simulated, as is a one-dimensional version. In one dimension, the dynamics can be described in terms of a ‘‘repetitious random walker’’ and anomalous diffusion with exponent 0.4. In all cases the model self-organizes to a robust critical attractor.

We present a continuum theory for the self-assembly of cylindrical tubules from chiral lipid bilayers in any tilted fluid phase. This theory shows that tubule formation is driven by an intrinsic bending force due to molecular chirality, and gives the radius in terms of the continuum parameters. The radius diverges as an untilted phase is approached. The theory also predicts that the tilt direction is modulated in a helical striped pattern on the tubule. This striped pattern is consistent with helical patterns observed in electron micrographs of lipid tubules.

We present the analytic solution of the self-organized critical (SOC) forest-fire model in one dimension proving SOC in systems without conservation laws by analytic means. Under the condition that the system is in the steady state and very close to the critical point, we calculate the probability that a string of n neighboring sites is occupied by a given configuration of trees. The critical exponent describing the size distribution of forest clusters is exactly τ=2 and does not change under certain changes of the model rules. Computer simulations confirm the analytic results.

If black hole formation evaporation can be described by an S matrix, information would be expected to come out in black hole radiation. An estimate shows that it may come out initially so slowly, or else be so spread out, that it would never show up in an analysis perturbative in ${\mathit{M}}_{\mathrm{Planck}}$/M, or in 1/N for two-dimensional dilatonic black holes with a large number N of minimally coupled scalar fields.

We analyze the Gamma Ursae Minoris (GUM) and Mu Pegasii scans of the millimeter-wave anisotropy experiment in the context of cold dark matter (CDM) models of structure formation, paying particular attention to the two-dimensional nature of the GUM scan. If all of the structure in the (foreground subtracted) data is attributed to cosmic microwave background anisotropy, then there is a detection in each scan. For a standard CDM model, the amplitudes of the signals are individually compatable with the Cosmic Background Explorer measurement, but marginally inconsistent with each other.

We present a conformal field theory which describes a homogeneous four dimensional Lorentz-signature space-time. The model is an ungauged Wess-Zumino-Witten model based on a central extension of the Poincaré algebra. The central charge of this theory is exactly four, just like four dimensional Minkowski space. The model can be interpreted as a four dimensional monochromatic plane wave. As there are three commuting isometries, other interesting geometries are expected to emerge via O(3,3) duality.

We show that many of the recently proposed supersymmetric p-brane solutions of d=10 and d=11 supergravity have the property that they interpolate between Minkowski spacetime and a compactified spacetime, both being supersymmetric supergravity vacua. Our results imply that the effective world-volume action for small fluctuations of the super p-brane is a supersingleton field theory for (p+2)-dimensional anti–de Sitter spacetime, as has been often conjectured in the past.

We demonstrate that QED exhibits a previously unobserved noncovariant, nonlocal symmetry. Some consequences are discussed.

Phase shift parameters for p-d elastic scattering are extracted from new measurements of spin observables at ${\mathit{E}}_{\mathit{p}}$=3 MeV. The experimental phase shifts are compared with predictions obtained from Faddeev calculations. The agreement between theory and experiment is generally good. However, we find that there are significant discrepancies for the ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2}$ phase shift and for the S-D mixing parameters.

Inelastic scattering of 50 MeV/nucleon ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ on ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ was measured in coincidence with protons in order to investigate the excitation and decay of highly excited states in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. The proton decay pattern corresponding to an excitation region around 34 MeV shows the characteristic behavior expected of the direct decay of a two-phonon state. Thus, by using this novel method, the presence of a double-phonon state built with isoscalar giant resonances in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ is demonstrated.

Angular distributions of high energy photoelectrons from Xe and Kr, excited by a 50 ps, 1.05 μm laser, are presented. In Xe, strong, narrow rings ∼45 ° off the polarization axis appear in a limited energy range centered around 9${\mathit{U}}_{\mathit{p}}$, where ${\mathit{U}}_{\mathit{p}}$ is the ponderomotive energy. This effect is much weaker in Kr. Single active electron calculations agree well with these observations. We conclude that the rings result from single-electron ionization dynamics, most likely involving rescattering from the ion core of the tunneling component of the continuum wave function.

We report the first observation of amplification of spontaneous emission on the Lyman-α transition of hydrogenlike lithium ions by optical-field-induced ionization. Using a subpicosecond KrF laser (0.5 ps, 50 mJ) focused at ${10}^{17}$ W/${\mathrm{cm}}^2$, singly ionized lithium ions have been further ionized to fully stripped states, resulting in the population inversion with respect to the ground state of the hydrogenic ions. A small signal gain coefficient of 20 ${\mathrm{cm}}^{\mathrm{-}1}$ was obtained.

Resonancelike intensity variations of the impact radiation were observed at electric-field anticrossings of 1snl ${}_{}{}^1{}_{}{}^{}$L and ${}_{}{}^3{}_{}{}^{}$L Stark sublevels (n=5, 6, 7; l≥2), when investigating excitation of helilium atoms by 12.5 keV proton impact. The measured signal amplitudes provide strong evidence that the collision process excites the electron selectively to the (${\mathit{n}}_1$ , ${\mathit{n}}_2$, m) hydrogenic Stark states (0, n-1, 0) and (0, n-2, ±1), indicating that the electron is promoted along in-saddle sequences of ${\mathrm{H}}_2^{+}$-like molecular orbitals during the final phase of the collision.

A new search for a permanent electric dipole moment of ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ has yielded the null result d${(}^{199}$Hg)=-(2.7±5.8)×${10}^{\mathrm{-}28}$e cm where the statistical and systematic uncertainty have been combined. This gives an upper limit of d${(}^{199}$Hg)<1.3×${10}^{\mathrm{-}27}$e cm (95% confidence). The measurement sets the most stringent limits to date on several possible sources of time-reversal symmetry violation. We look for a relative shift in Larmor-precession frequency between two optically pumped ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ atomic oscillators in the presence of applied electric fields. We have attained a statistical uncertainty on the relative shift in frequency between the oscillators of 2×${10}^{\mathrm{-}9}$ Hz.

The Maass operator for automorphic forms is interpreted as the Hamiltonian of a charged particle moving in a constant magnetic field on a Riemann surface of constant negative curvature. A careful analysis of the classical trajectories in the presence of the magnetic field shows that the action on a periodic orbit is related to the action on a free periodic geodesic. This identification provides a semiclassical interpretation of the Selberg-Maass trace formula for automorphic forms.

The exponential decay of correlations in chaotic systems is often modulated and shows up as broad peaks in the power spectrum. For a particle sliding freely on a compact surface of constant negative curvature, we show that these classical resonances are directly related to the quantal eigenenergies of the system. We use this as the basis for proposing a quantization scheme which requires the knowledge of a single arbitrary ergodic classical trajectory. Our results are substantiated numerically.

A model one-dimensional drift-wave equation driven by a sinusoidal wave is used to study controlling chaos in partial differential equations. By injecting negative feedback through a monochromatic wave or pinning at a certain x-space point we can successfully stabilize unstable steady states and control chaos. In the case of bistability, an unstable steady state in the middle branch can be also stabilized by these controlling approaches. The methods used in this Letter can be applied to general continuous spatiotemporal systems.

Coherent enhancement of the spontaneous undulator radiation by several orders of magnitude has been observed in a free-electron laser at wavelengths from 40 to 100 μm. The coherent emission can be explained by details of the electron-beam micropulse structure. Furthermore, it has been found that the phase of the optical micropulses is fixed by the electron pulse structure and that the coherence extends over successive optical micropulses, which gives rise to interference effects as a function of the optical cavity length in a laser oscillator.