37,591 research outputs found
Three-dimensional fluid motion in Faraday waves: creation of vorticity and generation of two-dimensional turbulence
We study the generation of 2D turbulence in Faraday waves by investigating
the creation of spatially periodic vortices in this system. Measurements which
couple a diffusing light imaging technique and particle tracking algorithms
allow the simultaneous observation of the three-dimensional fluid motion and of
the temporal changes in the wave field topography. Quasi-standing waves are
found to coexist with a spatially extended fluid transport. More specifically,
the destruction of regular patterns of oscillons coincides with the emergence
of a complex fluid motion whose statistics are similar to that of
two-dimensional turbulence. We reveal that a lattice of oscillons generates
vorticity at the oscillon scale in the horizontal flow. The interaction of
these vortices explain how 2D turbulence is fueled by almost standing waves.
Remarkably, the curvature of Lagrangian trajectories reveals a "footprint" of
the forcing scale vortices in fully developed turbulence. 2D Navier-Stokes
turbulence should be considered a source of disorder in Faraday waves. These
findings also provide a new paradigm for vorticity creation in 2D flows
Searches for Gauge-Mediated SUSY Breaking Topologies with the L3 Detector at LEP
Searches for topologies predicted by gauge-mediated SUSY breaking models were
performed using data collected with the L3 detector at LEP. All possible
lifetimes of the next-to-lightest SUSY particle (NLSP), neutralino or scalar
tau, were considered. No evidence for these new phenomena was found and limits
on the production cross sections and sparticle masses were derived. A scan over
the parameters of the minimal GMSB model was performed, leading to lower limits
of 62.2 GeV, 11 TeV, and 0.07 eV on the NLSP mass, the mass scale parameter
Lambda, and the gravitino mass, respectively. The status of the LEP combined
searches is also discussed.Comment: 4 pages, 2 figures, 1 table; to appear in Proceedings of SUSY06, the
14th International Conference on Supersymmetry and the Unification of
Fundamental Interactions, UC Irvine, California, 12-17 June 200
Strong ExB shear flows in the pedestal region in H-mode plasma
We report the first experimental observation of stationary zonal flows in the
pedestal region of the H-mode plasma in the H-1 toroidal heliac. Strong peaks
in E_r shear mark the top and foot of the density pedestal. Strong m=n=0
low-frequency (f < 0.6 kHz) zonal flows are observed in regions of increased
E_r, suggesting substantial contribution of zonal flows to the spatial
modulation of E_r radial profiles. Radial localization of zonal flows is
correlated with a region of zero magnetic shear and low-order (7/5) rational
surfaces.Comment: 4 pages, 5 figure
Radiance and Doppler shift distributions across the network of the quiet Sun
The radiance and Doppler-shift distributions across the solar network provide
observational constraints of two-dimensional modeling of transition-region
emission and flows in coronal funnels. Two different methods, dispersion plots
and average-profile studies, were applied to investigate these distributions.
In the dispersion plots, we divided the entire scanned region into a bright and
a dark part according to an image of Fe xii; we plotted intensities and Doppler
shifts in each bin as determined according to a filtered intensity of Si ii. We
also studied the difference in height variations of the magnetic field as
extrapolated from the MDI magnetogram, in and outside network. For the
average-profile study, we selected 74 individual cases and derived the average
profiles of intensities and Doppler shifts across the network. The dispersion
plots reveal that the intensities of Si ii and C iv increase from network
boundary to network center in both parts. However, the intensity of Ne viii
shows different trends, namely increasing in the bright part and decreasing in
the dark part. In both parts, the Doppler shift of C iv increases steadily from
internetwork to network center. The average-profile study reveals that the
intensities of the three lines all decline from the network center to
internetwork region. The binned intensities of Si ii and Ne viii have a good
correlation. We also find that the large blue shift of Ne viii does not
coincide with large red shift of C iv. Our results suggest that the network
structure is still prominent at the layer where Ne viii is formed in the quiet
Sun, and that the magnetic structures expand more strongly in the dark part
than in the bright part of this quiet Sun region.Comment: 10 pages,9 figure
Parametric survey of longitudinal prominence oscillation simulations
It is found that both microflare-sized impulsive heating at one leg of the
loop and a suddenly imposed velocity perturbation can propel the prominence to
oscillate along the magnetic dip. An extensive parameter survey results in a
scaling law, showing that the period of the oscillation, which weakly depends
on the length and height of the prominence, and the amplitude of the
perturbations, scales with , where represents the
curvature radius of the dip, and is the gravitational acceleration of
the Sun. This is consistent with the linear theory of a pendulum, which implies
that the field-aligned component of gravity is the main restoring force for the
prominence longitudinal oscillations, as confirmed by the force analysis.
However, the gas pressure gradient becomes non-negligible for short
prominences. The oscillation damps with time in the presence of non-adiabatic
processes. Compared to heat conduction, the radiative cooling is the dominant
factor leading to the damping. A scaling law for the damping timescale is
derived, i.e., , showing
strong dependence on the prominence length , the geometry of the magnetic
dip (characterized by the depth and the width ), and the velocity
perturbation amplitude . The larger the amplitude, the faster the
oscillation damps. It is also found that mass drainage significantly reduces
the damping timescale when the perturbation is too strong.Comment: 17 PAGES, 8FIGURE
Spectroscopy of reflection-asymmetric nuclei with relativistic energy density functionals
Quadrupole and octupole deformation energy surfaces, low-energy excitation
spectra and transition rates in fourteen isotopic chains: Xe, Ba, Ce, Nd, Sm,
Gd, Rn, Ra, Th, U, Pu, Cm, Cf, and Fm, are systematically analyzed using a
theoretical framework based on a quadrupole-octupole collective Hamiltonian
(QOCH), with parameters determined by constrained reflection-asymmetric and
axially-symmetric relativistic mean-field calculations. The microscopic QOCH
model based on the PC-PK1 energy density functional and -interaction
pairing is shown to accurately describe the empirical trend of low-energy
quadrupole and octupole collective states, and predicted spectroscopic
properties are consistent with recent microscopic calculations based on both
relativistic and non-relativistic energy density functionals. Low-energy
negative-parity bands, average octupole deformations, and transition rates show
evidence for octupole collectivity in both mass regions, for which a
microscopic mechanism is discussed in terms of evolution of single-nucleon
orbitals with deformation.Comment: 36 pages, 21 figures, Accepted for Publication in Physical Review
Multivariate adaptive regression splines for estimating riverine constituent concentrations
Regression-based methods are commonly used for riverine constituent concentration/flux estimation, which is essential for guiding water quality protection practices and environmental decision making. This paper developed a multivariate adaptive regression splines model for estimating riverine constituent concentrations (MARS-EC). The process, interpretability and flexibility of the MARS-EC modelling approach, was demonstrated for total nitrogen in the Patuxent River, a major river input to Chesapeake Bay. Model accuracy and uncertainty of the MARS-EC approach was further analysed using nitrate plus nitrite datasets from eight tributary rivers to Chesapeake Bay. Results showed that the MARS-EC approach integrated the advantages of both parametric and nonparametric regression methods, and model accuracy was demonstrated to be superior to the traditionally used ESTIMATOR model. MARS-EC is flexible and allows consideration of auxiliary variables; the variables and interactions can be selected automatically. MARS-EC does not constrain concentration-predictor curves to be constant but rather is able to identify shifts in these curves from mathematical expressions and visual graphics. The MARS-EC approach provides an effective and complementary tool along with existing approaches for estimating riverine constituent concentrations
The effect of 3He impurities on the nonclassical response to oscillation of solid 4He
We have investigated the influence of impurities on the possible supersolid
transition by systematically enriching isotopically-pure 4He (< 1 ppb of 3He)
with 3He. The onset of nonclassical rotational inertia is broadened and shifts
monotonically to higher temperature with increasing 3He concentration,
suggesting that the phenomenon is correlated to the condensation of 3He atoms
onto the dislocation network in solid 4He.Comment: 4 page
- …