Physical Review Letters

Sommerer, John C; Ditto, William L; Grebogi, Celso L; Ott, Edward L; Spano, Mark L

doi: 10.1103/PhysRevLett.66.1947pmid: 10043351

We investigate experimentally the scaling of the average time τ between intermittent, noise-induced bursts for a chaotic mechanical system near a crisis. The system studied is a periodically driven (frequency f ) magnetoelastic ribbon. Theory predicts that for deterministic crises where τ scales as τ∼‖ f - f c ‖ - γ ( f < f c , f = f c at crisis), the characteristic time between noise-induced bursts ( f ≥ f c ) should scale as τ∼ σ - γ g (‖ f - f c ‖/σ), where σ is the noise strength and γ is the same in both cases. We determine γ for the low-noise (‘‘deterministic’’) system, then add noise and observe that the scaling for τ is as predicted.

Orito, S; Ichinose, H; Nakamura, S; Kuwahara, K; Doke, T; Ogura, K; Tawara, H; Imori, M; Yamamoto, K; Yamakawa, H; Suzuki, T; Anraku, K; Nozaki, M; Sasaki, M; Yoshida, T

Distler, Jacques

doi: 10.1103/PhysRevLett.66.1955pmid: 10043353

We formulate two-dimensional topological gravity starting from local N =2 superconformal geometry. The theory is free from the very beginning. The usual ‘‘twisting’’ of the N =2 algebra emerges from symmetry breaking when we expand about a nonzero value for one of the ghost fields. The mysterious linear term in the supercurrent emerges automatically, as does a full superfield formalism for the whole system including ghosts. We analyze the moduli space of the ‘‘semirigid’’ super Riemann surfaces associated with this theory, including their allowed degenerations.

Yen, Yi-Fen ; Brinkmöller, B; Dehnhard, D; Sterbenz, S. M; Yu, Yi-Ju M

doi: 10.1103/PhysRevLett.66.1959pmid: 10043354

Analyzing powers A y were measured for π + and π - elastic scattering from polarized C 13 at energies near the P 33 resonance. At T π =132 MeV the values of A y are significantly different from zero for π - . For π + at 132 MeV and for both π - and π + at all other energies, the A y are mostly consistent with zero. These data differ from the predictions of present pion-nucleus reaction theories, especially at large momentum transfers.

Richardson, W. H; Yamamoto, Y. H

doi: 10.1103/PhysRevLett.66.1963pmid: 10043355

The photon-number fluctuation of the external field from a semiconductor laser—which was reduced to below the standard quantum limit—is shown to be correlated with the measured junction-voltage noise. The spectral density of the sum of the photon-number fluctuation and junction-voltage fluctuation falls below the squeezed photon-number fluctuation. This confirms the theoretical predictions that this correlation, which originates in the dipole interaction between the internal field and electron-hole pairs, extends into the quantum regime.

Ohkuma, Juzo ; Okuda, Shuichi ; Tsumori, Kunihiko

doi: 10.1103/PhysRevLett.66.1967pmid: 10043356

High-intensity Cherenkov radiation (CR), emitted in air from a high-current 30-MeV electron bunch (2× 10 11 electrons/bunch) of the linear accelerator at the Institute of Scientific and Industrial Research was observed at wavelengths from 0.4 to 3 mm. The radiation was emitted at an angle of 38 mrad, with some spread, from the beam axis. The radiation measured was about 10 11 times as intense as that calculated for ordinary CR. Such enhancement is attributed to the coherence which appears in CR emitted from electron bunches of relatively short length.

DuBois, D. F; Rose, Harvey A; Russell, David A

doi: 10.1103/PhysRevLett.66.1970pmid: 10043357

We report results of two-dimensional numerical solutions of Zakharov’s model for strong Langmuir turbulence excited by powerful electromagnetic pump waves at subcritical densities, as in hf modification of the ionisphere and laser-plasma interactions. The results show that truncated parametric decay cascades can coexist with caviton collapse for moderate pump power. A high level of ion density fluctuations, driven primarly by caviton collapse, produces energy and power spectra which are not consistent with conventional weak turbulence theory.

Hanada, K; Tanaka, H; Iida, M; Ide, S; Minami, T; Nakamura, M; Maekawa, T; Terumichi, Y; Tanaka, S

doi: 10.1103/PhysRevLett.66.1974pmid: 10043358

Sawtooth oscillations (STO) in the Ohmically heated WT-3 tokamak are strongly modified or suppressed by localized-electron cyclotron resonance heating (ECH) near the q =1 surface, where q refers to the safety factor. The efect of ECH is much stronger when it is applied on the high-field side as compared to the low-field side. Complete suppression of the STO is achieved for the duration of the ECH, in most cases, when it is applied on the high-field side of a low-density plasma, provided the ECH power exceeds a threshold value. The STO stabilization is attributed to a modification of the current-density profile by hot electrons generated by ECH, which reduces the shear in the q =1 region.

Brener, Efim ; Levine, Herbert ; Tu, Yuhai

doi: 10.1103/PhysRevLett.66.1978pmid: 10043359

We present a new mean-field theory of diffusion-limited aggregation (DLA). We apply our approach to calculate the ensemble-averaged structure seen in recent experiments in a two-dimensional channel geometry. Our method explains the similarity between the average DLA occupancy and the Saffman-Taylor finger pattern.

Hentschel, H. G; Family, Fereydoon G

doi: 10.1103/PhysRevLett.66.1982pmid: 10043360

The scaling behavior of open dissipative systems including the Kim-Kosterlitz exponents for interfacial growth, and the current fluctuations in a flowing sandpile are derived using a generalization of the arguments applied by Kolmogorov to the inertial range of turbulence. The approach may be considered a nonequilibrium equivalent to Flory theory.