Parametric phase transition in one dimension

We calculate analytically the phase boundary for a nonequilibrium phase transition in a one-dimensional array of coupled, overdamped parametric harmonic oscillators in the limit of strong and weak spatial coupling. Our results show that the transition is reentrant with respect to the spatial coupling in agreement with the prediction of the mean field theory.Comment: to appear in Europhysics letter

Domain wall propagation and nucleation in a metastable two-level system

We present a dynamical description and analysis of non-equilibrium transitions in the noisy one-dimensional Ginzburg-Landau equation for an extensive system based on a weak noise canonical phase space formulation of the Freidlin-Wentzel or Martin-Siggia-Rose methods. We derive propagating nonlinear domain wall or soliton solutions of the resulting canonical field equations with superimposed diffusive modes. The transition pathways are characterized by the nucleations and subsequent propagation of domain walls. We discuss the general switching scenario in terms of a dilute gas of propagating domain walls and evaluate the Arrhenius factor in terms of the associated action. We find excellent agreement with recent numerical optimization studies.Comment: 28 pages, 16 figures, revtex styl

Spatial Pattern Formation in External Noise: Theory and Simulation

Spatial pattern formation in excitable fluctuating media was researched analytically from the point of view of the order parameters concept. The reaction-diffusion system in external noise is considered as a model of such medium. Stochastic equations for the unstable mode amplitudes (order parameters), dispersion equations for the unstable mode averaged amplitudes, and the Fokker-Planck equation for the order parameters have been obtained. The developed theory makes it possible to analyze different noise-induced effects, including the variation of boundaries of ordering and disordering phase transitions depending on the parameters of external noiseComment: 22 pages, 10 figure

Dynamics of modal power distribution in a multimode semiconductor laser with optical feedback

The dynamics of power distribution between longitudinal modes of a multimode semiconductor laser subjected to external optical feedback is experimentally analyzed in the low-frequency fluctuation regime. Power dropouts in the total light intensity are invariably accompanied by sudden activations of several longitudinal modes. These activations are seen not to be simultaneous to the dropouts, but to occur after them. The phenomenon is statistically analysed in a systematic way, and the corresponding delay is estimated.Comment: 3 pages, 4 figures, revte

Generalized Casimir forces in non-equilibrium systems

In the present work we propose a method to determine fluctuation induced forces in non equilibrium systems. These forces are the analogue of the well known Casimir forces, which were originally introduced in Quantum Field theory and later extended to the area of Critical Phenomena. The procedure starts from the observation that many non equilibrium systems exhibit long-range correlations and the associated structure factors diverge in the long wavelength limit. The introduction of external bodies into such systems in general modifies the spectrum of these fluctuations and leads to the appearance of a net force between these bodies. The mechanism is illustrated by means of a simple example: a reaction diffusion equation with random noises.Comment: Submitted to Europhysics Letters. 7 pages, 2 figure

The wideband backend at the MDSCC in Robledo. A new facility for radio astronomy at Q- and K- bands

The antennas of NASA's Madrid Deep Space Communications Complex (MDSCC) in Robledo de Chavela are available as single-dish radio astronomical facilities during a significant percentage of their operational time. Current instrumentation includes two antennas of 70 and 34 m in diameter, equipped with dual-polarization receivers in K (18 - 26 GHz) and Q (38 - 50 GHz) bands, respectively. We have developed and built a new wideband backend for the Robledo antennas, with the objectives (1) to optimize the available time and enhance the efficiency of radio astronomy in MDSCC; and (2) to tackle new scientific cases impossible to that were investigated with the old, narrow-band autocorrelator. The backend consists of an IF processor, a FFT spectrometer (FFTS), and the software that interfaces and manages the events among the observing program, antenna control, the IF processor, the FFTS operation, and data recording. The whole system was end-to-end assembled in August 2011, at the start of commissioning activities, and the results are reported in this paper. Frequency tunings and line intensities are stable over hours, even when using different synthesizers and IF channels; no aliasing effects have been measured, and the rejection of the image sideband was characterized. The first setup provides 1.5 GHz of instantaneous bandwidth in a single polarization, using 8192 channels and a frequency resolution of 212 kHz; upgrades under way include a second FFTS card, and two high-resolution cores providing 100 MHz and 500 MHz of bandwidth, and 16384 channels. These upgrades will permit simultaneous observations of the two polarizations with instantaneous bandwidths from 100 MHz to 3 GHz, and spectral resolutions from 7 to 212 kHz.Comment: 9 pages, 8 figures. Accepted to Astronomy and Astrophysic

Effect of External Noise Correlation in Optical Coherence Resonance

Coherence resonance occurring in semiconductor lasers with optical feedback is studied via the Lang-Kobayashi model with external non-white noise in the pumping current. The temporal correlation and the amplitude of the noise have a highly relevant influence in the system, leading to an optimal coherent response for suitable values of both the noise amplitude and correlation time. This phenomenon is quantitatively characterized by means of several statistical measures.Comment: RevTeX, 4 pages, 7 figure

Resonance and frequency-locking phenomena in spatially extended phytoplankton-zooplankton system with additive noise and periodic forces

In this paper, we present a spatial version of phytoplankton-zooplankton model that includes some important factors such as external periodic forces, noise, and diffusion processes. The spatially extended phytoplankton-zooplankton system is from the original study by Scheffer [M Scheffer, Fish and nutrients interplay determines algal biomass: a minimal model, Oikos \textbf{62} (1991) 271-282]. Our results show that the spatially extended system exhibit a resonant patterns and frequency-locking phenomena. The system also shows that the noise and the external periodic forces play a constructive role in the Scheffer's model: first, the noise can enhance the oscillation of phytoplankton species' density and format a large clusters in the space when the noise intensity is within certain interval. Second, the external periodic forces can induce 4:1 and 1:1 frequency-locking and spatially homogeneous oscillation phenomena to appear. Finally, the resonant patterns are observed in the system when the spatial noises and external periodic forces are both turned on. Moreover, we found that the 4:1 frequency-locking transform into 1:1 frequency-locking when the noise intensity increased. In addition to elucidating our results outside the domain of Turing instability, we provide further analysis of Turing linear stability with the help of the numerical calculation by using the Maple software. Significantly, oscillations are enhanced in the system when the noise term presents. These results indicate that the oceanic plankton bloom may partly due to interplay between the stochastic factors and external forces instead of deterministic factors. These results also may help us to understand the effects arising from undeniable subject to random fluctuations in oceanic plankton bloom.Comment: Some typos errors are proof, and some strong relate references are adde

Critical Behaviour of Non-Equilibrium Phase Transitions to Magnetically Ordered States

We describe non-equilibrium phase transitions in arrays of dynamical systems with cubic nonlinearity driven by multiplicative Gaussian white noise. Depending on the sign of the spatial coupling we observe transitions to ferromagnetic or antiferromagnetic ordered states. We discuss the phase diagram, the order of the transitions, and the critical behaviour. For global coupling we show analytically that the critical exponent of the magnetization exhibits a transition from the value 1/2 to a non-universal behaviour depending on the ratio of noise strength to the magnitude of the spatial coupling.Comment: 4 pages, 5 figure

Spatiotemporal communication with synchronized optical chaos

We propose a model system that allows communication of spatiotemporal information using an optical chaotic carrier waveform. The system is based on broad-area nonlinear optical ring cavities, which exhibit spatiotemporal chaos in a wide parameter range. Message recovery is possible through chaotic synchronization between transmitter and receiver. Numerical simulations demonstrate the feasibility of the proposed scheme, and the benefit of the parallelism of information transfer with optical wavefronts.Comment: 4 pages, 5 figure