Search results for "Temporal"
showing 10 items of 1095 documents
Synchronized rotation in swarms of magnetotactic bacteria.
2017
Self-organizing behavior has been widely reported in both natural and artificial systems, typically distinguishing between temporal organization (synchronization) and spatial organization (swarming). Swarming has been experimentally observed in systems of magnetotactic bacteria under the action of external magnetic fields. Here we present a model of ensembles of magnetotactic bacteria in which hydrodynamic interactions lead to temporal synchronization in addition to the swarming. After a period of stabilization during which the bacteria form a quasiregular hexagonal lattice structure, the entire swarm begins to rotate in a direction opposite to the direction of the rotation of the magnetic …
Software Timing Calibration of the ARGO-YBJ Detector
2009
The ARGO-YBJ experiment is mainly devoted to search for astronomical gamma sources. The arrival direction of air showers is reconstructed thanks to the times measured by the pixels of the detector. Therefore, the timing calibration of the detector pixels is crucial in order to get the best angular resolution and pointing accuracy. Because of the large number of pixels a hardware timing calibration is practically impossible. Therefore an off-line software calibration has been adopted. Here, the details of the procedure and the results are presented. (C) 2008 Elsevier B.V. All rights reserved.
Detailed diagnostics of an X-ray flare in the single giant HR 9024
2007
We analyze a 96 ks Chandra/HETGS observation of the single G-type giant HR 9024. The high flux allows us to examine spectral line and continuum diagnostics at high temporal resolution, to derive plasma parameters. A time-dependent 1D hydrodynamic model of a loop with half-length $L = 5 \times 10^{11}$ cm ($\sim R_{\star}/2$), cross-section radius $r = 4.3 \times 10^{10}$ cm, with a heat pulse of 15 ks and $2 \times 10^{11}$~erg cm$^{-2}$ s$^{-1}$ deposited at the loop footpoints, satisfactorily reproduces the observed evolution of temperature and emission measure, derived from the analysis of the strong continuum emission. For the first time we can compare predictions from the hydrodynamic …
Giant collective incoherent shock waves in strongly nonlinear turbulent flows
2016
Contrary to conventional coherent shocks, we show theoretically and experimentally that nonlocal turbulent flows lead to the emergence of large-scale incoherent shock waves, which constitute a collective phenomenon of the incoherent field as a whole.
Wavelength-multiplexed computational temporal ghost imaging
2017
Ghost imaging is a novel imaging technique based on correlation measurements between a structured illumination pattern (the reference) and the total intensity transmitted or reflected by an object [1]. The reference illumination patterns may be either randomly generated by a spatially incoherent light source, or pre-programmed e.g. with a spatial light modulator. Light transmitted (or reflected) by the object is measured by a single-pixel “bucket” detector with null spatial resolution. A unique feature associated with ghost imaging is that (i) neither the bucket detector nor the reference measurement caries enough information to retrieve the object shape and (ii) it is insensitive to distor…
Temporal ghost imaging with photon pairs
2017
International audience; We present an experiment of temporal ghost imaging based on the spatial properties of twin photons. The retrieval of a binary time signal of 8 bits is performed with an error rate of 0.70%.
Source linewidth effects in temporal imaging of Gaussian Schell-model pulses
2006
A transform-limited Gaussian pulse generated from an externally modulated stationary source is launched within a temporal imaging system composed of a second-order dispersion followed by a time lens and a subsequent quadratic dispersion. We consider the effect of the statistical properties of the emitted light for temporal imaging. In particular, it is shown that the design parameters that ensure a received signal with the minimum root-mean-square (rms) width achievable, which is called the temporal image of the incident pulse, are strongly dependent on the coherence properties of the input waveform. Finally, limitations on the temporal resolution of the setup are highlighted and a realisti…
Impact of slow gain dynamics on soliton molecules in mode-locked fiber lasers
2012
International audience; We theoretically demonstrate and experimentally confirm the major influence of gain dynamics on soliton molecules that self-assemble in mode-locked lasers. Both slow gain recovery and depletion play a pivotal role in the formation of chirped soliton molecules characterized by an increasing separation from leading to trailing pulses. These chirped molecules actually consist of many pulses and may be termed macromolecules. They are experimentally observed in a fiber laser and numerically modeled by an approach that properly includes the slow gain dynamics. Furthermore, it is shown that these processes stabilize soliton trains in fiber lasers by inhibiting internal osci…
Red-green vs. blue-yellow spatio-temporal contrast sensitivity across the visual field
2011
We measured contrast sensitivity (CS) to sinusoidal spatio-temporal patterns isolating the red-green and blue-yellow mechanisms, at 21 locations in the visual field (including the fovea). These measurements complete the available data for the red-green mechanism at fovea and for both mechanisms outside fovea with non-stationary patterns. Chromatic detection surfaces are low-pass at fovea and CS decreases with eccentricity at a rate that depends on the spatial and temporal frequencies. Our results confirm that, in general, sensitivities decrease with eccentricity at different rates for stationary red-green and blue-yellow patterns at each point of the spatio-temporal domain and that the chro…
Condensation and thermalization of classsical optical waves in a waveguide
2011
http://pra.aps.org/; International audience; We consider the long-term evolution of a random nonlinear wave that propagates in a multimode optical waveguide. The optical wave exhibits a thermalization process characterized by an irreversible evolution toward an equilibrium state. The tails of the equilibrium distribution satisfy the property of energy equipartition among the modes of the waveguide. As a consequence of this thermalization, the optical field undergoes a process of classical wave condensation, which is characterized by a macroscopic occupation of the fundamental mode of the waveguide. Considering the nonlinear Schrödinger equation with a confining potential, we formulate a wav…