1,732 research outputs found
Laser-induced thermal acoustics (LITA) signals from finite beams
Laser-induced thermal acoustics (LITA) is a four-wave mixing technique that may be employed to measure sound speeds, transport properties, velocities, and susceptibilities of fluids. It is particularly effective in high-pressure gases (>1 bar). An analytical expression for LITA signals is derived by the use of linearized equations of hydrodynamics and light scattering. This analysis, which includes full finite-beam-size effects and the optoacoustic effects of thermalization and electrostriction, predicts the amplitude and the time history of narrow-band time-resolved LITA and broadband spectrally resolved (multiplex) LITA signals. The time behavior of the detected LITA signal depends significantly on the detection solid angle, with implications for the measurement of diffusivities by the use of LITA and the proper physical picture of LITA scattering. This and other elements of the physics of LITA that emerge from the analysis are discussed. Theoretical signals are compared with experimental LITA data
Explosive synchronization in weighted complex networks
The emergence of dynamical abrupt transitions in the macroscopic state of a
system is currently a subject of the utmost interest. Given a set of phase
oscillators networking with a generic wiring of connections and displaying a
generic frequency distribution, we show how combining dynamical local
information on frequency mismatches and global information on the graph
topology suggests a judicious and yet practical weighting procedure which is
able to induce and enhance explosive, irreversible, transitions to
synchronization. We report extensive numerical and analytical evidence of the
validity and scalability of such a procedure for different initial frequency
distributions, for both homogeneous and heterogeneous networks, as well as for
both linear and non linear weighting functions. We furthermore report on the
possibility of parametrically controlling the width and extent of the
hysteretic region of coexistence of the unsynchronized and synchronized states
Relay synchronization in multiplex networks
Relay (or remote) synchronization between two not directly connected
oscillators in a network is an important feature allowing distant coordination.
In this work, we report a systematic study of this phenomenon in multiplex
networks, where inter-layer synchronization occurs between distant layers
mediated by a relay layer that acts as a transmitter. We show that this
transmission can be extended to higher order relay configurations, provided
symmetry conditions are preserved. By first order perturbative analysis, we
identify the dynamical and topological dependencies of relay synchronization in
a multiplex. We find that the relay synchronization threshold is considerably
reduced in a multiplex configuration, and that such synchronous state is mostly
supported by the lower degree nodes of the outer layers, while hubs can be
de-multiplexed without affecting overall coherence. Finally, we experimentally
validated the analytical and numerical findings by means of a multiplex of
three layers of electronic circuits.the analytical and numerical findings by
means of a multiplex of three layers of electronic circuits
Synchronization centrality and explosive synchronization in complex networks
Synchronization of networked oscillators is known to depend fundamentally on
the interplay between the dynamics of the graph's units and the microscopic
arrangement of the network's structure. For non identical elements, the lack of
quantitative tools has hampered so far a systematic study of the mechanisms
behind such a collective behavior. We here propose an effective network whose
topological properties reflect the interplay between the topology and dynamics
of the original network. On that basis, we are able to introduce the
"synchronization centrality", a measure which quantifies the role and
importance of each network's node in the synchronization process. In
particular, we use such a measure to assess the propensity of a graph to
synchronize explosively, thus indicating a unified framework for most of the
different models proposed so far for such an irreversible transition. Taking
advantage of the predicting power of this measure, we furthermore discuss a
strategy to induce the explosive behavior in a generic network, by acting only
upon a small fraction of its nodes
Transient polarization dynamics in a CO laser
We study experimentally and theoretically the polarization alternation during
the switch-on transient of a quasi-isotropic CO laser emitting on the
fundamental mode. The observed transient dynamics is well reproduced by means
of a model which provides a quantitative discrimination between the intrinsic
asymmetry due to the kinetic coupling of molecules with different angular
momenta, and the extrinsic anisotropies, due to a tilted intracavity window.
Furthermore, the experiment provides a numerical assignment for the decay rate
of the coherence term for a CO laser.Comment: 14 pages, 6 figures, submitted to Opt. Com
- …