1,089 research outputs found
Observation of resonant interactions among surface gravity waves
We experimentally study resonant interactions of oblique surface gravity
waves in a large basin. Our results strongly extend previous experimental
results performed mainly for perpendicular or collinear wave trains. We
generate two oblique waves crossing at an acute angle, while we control their
frequency ratio, steepnesses and directions. These mother waves mutually
interact and give birth to a resonant wave whose properties (growth rate,
resonant response curve and phase locking) are fully characterized. All our
experimental results are found in good quantitative agreement with four-wave
interaction theory with no fitting parameter. Off-resonance experiments are
also reported and the relevant theoretical analysis is conducted and validated.Comment: 11 pages, 7 figure
Observation of intermittency in wave turbulence
We report the observation of intermittency in gravity-capillary wave
turbulence on the surface of mercury. We measure the temporal fluctuations of
surface wave amplitude at a given location. We show that the shape of the
probability density function of the local slope increments of the surface waves
strongly changes across the time scales. The related structure functions and
the flatness are found to be power laws of the time scale on more than one
decade. The exponents of these power laws increase nonlinearly with the order
of the structure function. All these observations show the intermittent nature
of the increments of the local slope in wave turbulence. We discuss the
possible origin of this intermittency.Comment: new version to Phys. Rev. Let
On the origin of intermittency in wave turbulence
Using standard signal processing tools, we experimentally report that
intermittency of wave turbulence on the surface of a fluid occurs even when two
typical large-scale coherent structures (gravity wave breakings and bursts of
capillary waves on steep gravity waves) are not taken into account. We also
show that intermittency depends on the power injected into the waves. The
dependence of the power-law exponent of the gravity-wave spectrum on the
forcing amplitude cannot be also ascribed to these coherent structures.
Statistics of these both events are studied.Comment: To be published in EP
Experimental study of the inverse cascade in gravity wave turbulence
We perform experiments to study the inverse cascade regime of gravity wave
turbulence on the surface of a fluid. Surface waves are forced at an
intermediate scale corresponding to the gravity-capillary wavelength. In
response to this forcing, waves at larger scales are observed. The spectrum of
their amplitudes exhibits a frequency-power law at high enough forcing. Both
observations are ascribed to the upscale wave action transfers of gravity wave
turbulence. The spectrum exponent is close to the value predicted by the weak
turbulence theory. The spectrum amplitude is found to scale linearly with the
mean injected power. We measure also the distributions of the injected power
fluctuations in the presence of upscale (inverse) transfers or in the presence
of a downscale (direct) cascade in gravity wave turbulence.Comment: in press in EPL (2011
Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-Type Galaxies from the SMAKCED Project. I. Kinematically Decoupled Cores and Implications for Infallen Groups in Clusters
We present evidence for kinematically decoupled cores (KDCs) in two dwarf
early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied
as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey.
These KDCs have radii of 1.8'' (0.14 kpc) and 4.2'' (0.33 kpc), respectively.
Each of these KDCs is distinct from the main body of its host galaxy in two
ways: (1) inverted sense of rotation; and (2) younger (and possibly more
metal-rich) stellar population. The observed stellar population differences are
probably associated with the KDC, although we cannot rule out the possibility
of intrinsic radial gradients in the host galaxy. We describe a statistical
analysis method to detect, quantify the significance of, and characterize KDCs
in long-slit rotation curve data. We apply this method to the two dE galaxies
presented in this paper and to five other dEs for which KDCs have been reported
in the literature. Among these seven dEs, there are four significant KDC
detections, two marginal KDC detections, and one dE with an unusual central
kinematic anomaly that may be an asymmetric KDC.The frequency of occurence of
KDCs and their properties provide important constraints on the formation
history of their host galaxies. We discuss different formation scenarios for
these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas
accretion can explain the properties of these KDCs. Both of these mechanisms
require that the progenitor had a close companion with a low relative velocity.
This suggests that KDCs were formed in galaxy pairs residing in a poor group
environment or in isolation whose subsequent infall into the cluster quenched
star formation.Comment: 14 pages, accepted for publication in Ap
Wave turbulence on the surface of a fluid in a high-gravity environment
International audienceWe report on the observation of gravity-capillary wave turbulence on the surface of a fluid in a high-gravity environment. By using a large-diameter centrifuge, the effective gravity acceleration is tuned up to 20 times the Earth gravity. The transition frequency between the gravity and capillary regimes is thus increased up to one decade as predicted theoretically. A frequency power-law wave spectrum is observed in each regime and is found to be independent of the gravity level and of the wave steepness. While the timescale separation required by weak turbulence is well verified experimentally regardless of the gravity level, the nonlinear and dissipation timescales are found to be independent of the scale, as a result of the finite size effects of the system (large-scale container modes) that are not taken currently into account theoretically
Axisymmetric solitary waves on the surface of a ferrofluid
We report the first observation of axisymmetric solitary waves on the surface
of a cylindrical magnetic fluid layer surrounding a current-carrying metallic
tube. According to the ratio between the magnetic and capillary forces, both
elevation and depression solitary waves are observed with profiles in good
agreement with theoretical predictions based on the magnetic analogue of the
Korteweg-deVries equation. We also report the first measurements of the
velocity and the dispersion relation of axisymmetric linear waves propagating
on the cylindrical ferrofluid layer that are found in good agreement with
theoretical predictions.Comment: to be published in Phys. Rev. Let
Observational constraints to boxy/peanut bulge formation time
Boxy/peanut bulges are considered to be part of the same stellar structure as
bars and both could be linked through the buckling instability. The Milky Way
is our closest example. The goal of this letter is determining if the mass
assembly of the different components leaves an imprint in their stellar
populations allowing to estimate the time of bar formation and its evolution.
To this aim we use integral field spectroscopy to derive the stellar age
distributions, SADs, along the bar and disc of NGC 6032. The analysis shows
clearly different SADs for the different bar areas. There is an underlying old
(>=12 Gyr) stellar population for the whole galaxy. The bulge shows star
formation happening at all times. The inner bar structure shows stars of ages
older than 6 Gyrs with a deficit of younger populations. The outer bar region
presents a SAD similar to that of the disc. To interpret our results, we use a
generic numerical simulation of a barred galaxy. Thus, we constrain, for the
first time, the epoch of bar formation, the buckling instability period and the
posterior growth from disc material. We establish that the bar of NGC 6032 is
old, formed around 10 Gyr ago while the buckling phase possibly happened around
8 Gyr ago. All these results point towards bars being long-lasting even in the
presence of gas.Comment: Accepted for publication in MNRAS Letter
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