258,874 research outputs found
Gibbsian Hypothesis in Turbulence
We show that Kolmogorov multipliers in turbulence cannot be statistically
independent of others at adjacent scales (or even a finite range apart) by
numerical simulation of a shell model and by theory. As the simplest
generalization of independent distributions, we suppose that the steady-state
statistics of multipliers in the shell model are given by a
translation-invariant Gibbs measure with a short-range potential, when
expressed in terms of suitable ``spin'' variables: real-valued spins that are
logarithms of multipliers and XY-spins defined by local dynamical phases.
Numerical evidence is presented in favor of the hypothesis for the shell model,
in particular novel scaling laws and derivative relations predicted by the
existence of a thermodynamic limit. The Gibbs measure appears to be in a
high-temperature, unique-phase regime with ``paramagnetic'' spin order.Comment: 19 pages, 9 figures, greatly expanded content, accepted to appear in
J. Stat. Phy
Comparison of the Geometrical Characters Inside Quark- and Gluon-jet Produced by Different Flavor Quarks
The characters of the angular distributions of quark jets and gluon jets with
different flavors are carefully studied after introducing the cone angle of
jets. The quark jets and gluon jets are identified from the 3-jet events which
are produced by Monte Carlo simulation Jetset7.4 in e+e- collisions at =91.2GeV. It turns out that the ranges of angular distributions of gluon jets
are obviously wider than that of quark jets at the same energies. The average
cone angles of gluon jets are much larger than that of quark jets. As the
multiplicity or the transverse momentum increases, the cone-angle distribution
without momentum weight of both the quark jet and gluon jet all increases, i.e
the positive linear correlation are present, but the cone-angle distribution
with momentum weight decreases at first, then increases when n > 4 or p_t > 2
GeV. The characters of cone angular distributions of gluon jets produced by
quarks with different flavors are the same, while there are obvious differences
for that of the quark jets with different flavors.Comment: 13 pages, 6 figures, to be published on the International Journal of
Modern Physics
Equation-free dynamic renormalization in a glassy compaction model
Combining dynamic renormalization with equation-free computational tools, we
study the apparently self-similar evolution of void distribution dynamics in
the diffusion-deposition problem proposed by Stinchcombe and Depken [Phys. Rev.
Lett. 88, 125701 (2002)]. We illustrate fixed point and dynamic approaches,
forward as well as backward in time.Comment: 4 pages, 4 figures (Minor Modifications; Submitted Version
Resonant Interactions in Rotating Homogeneous Three-dimensional Turbulence
Direct numerical simulations of three-dimensional (3D) homogeneous turbulence
under rapid rigid rotation are conducted to examine the predictions of resonant
wave theory for both small Rossby number and large Reynolds number. The
simulation results reveal that there is a clear inverse energy cascade to the
large scales, as predicted by 2D Navier-Stokes equations for resonant
interactions of slow modes. As the rotation rate increases, the
vertically-averaged horizontal velocity field from 3D Navier-Stokes converges
to the velocity field from 2D Navier-Stokes, as measured by the energy in their
difference field. Likewise, the vertically-averaged vertical velocity from 3D
Navier-Stokes converges to a solution of the 2D passive scalar equation. The
energy flux directly into small wave numbers in the plane from
non-resonant interactions decreases, while fast-mode energy concentrates closer
to that plane. The simulations are consistent with an increasingly dominant
role of resonant triads for more rapid rotation
Measurement of surface potential decay of corona-charged polymer films using the pulsed electroacoustic method
In this paper, the pulsed electroacoustic (PEA) technique that allows the determination of space charge in a dielectric material has been used to monitor the electrical potential decay of corona-charged polyethylene films of different thicknesses. To prevent possible disturbance on the surface charge during the PEA measurements, two thin polyethylene films were placed on both sides of the corona-charged sample. Charge profiles measured at different times were used to calculate the potential across the sample. The obtained potential decay was compared with the potential measured using the conventional method. A good agreement has been obtained. More importantly, the charge profile obtained using the PEA technique indicates that bipolar charge injection has taken place
Calibration of the Pulsed Electroacoustic Technique in the Presence of Trapped Charge
The influence of pulse voltage on the accuracy of charge density distribution in the pulsed electroacoustic technique (PEA) is discussed. It is shown that significant error can be introduced if a low dc voltage and high pulse voltage are used to calibrate charge density. However, our main focus in the present paper is to deal with one of the practical situations where space charge exists in the material prior to any measurements. The conventional calibration method can no longer be used to calibrate charge density due to the interference by the charge on the electrode induced by space charge. A method has been proposed which is based on two measurements. Firstly, the sample containing charge is measured without any applied voltage. The second measurement is carried out with a small external applied voltage. The applied voltage should be small enough so there is no disturbance of the existing charge in the sample. The difference of the two measurements can be used for calibration. An additional advantage of the proposed method avoids the influence of the pulse voltage on calibration and therefore gives a more accurate representation of space charge. The proposed method has been validated
The GTC exoplanet transit spectroscopy survey X. Stellar spots versus Rayleigh scattering: the case of HAT-P-11b
Rayleigh scattering in a hydrogen-dominated exoplanet atmosphere can be
detected from ground or space based telescopes, however, stellar activity in
the form of spots can mimic Rayleigh scattering in the observed transmission
spectrum. Quantifying this phenomena is key to our correct interpretation of
exoplanet atmospheric properties. We obtained long-slit optical spectroscopy of
two transits of HAT-P-11b with the Optical System for Imaging and
low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at Gran Telescopio
Canarias (GTC) on August 30 2016 and September 25 2017. We integrated the
spectrum of HAT-P-11 and one reference star in several spectroscopic channels
across the 400-785 nm region, creating numerous light curves of
the transits. We fit analytic transit curves to the data taking into account
the systematic effects and red noise present in the time series in an effort to
measure the change of the planet-to-star radius ratio
() across wavelength. By fitting both transits
together, we find a slope in the transmission spectrum showing an increase of
the planetary radius towards blue wavelengths. A closer inspection to the
transmission spectrum of the individual data sets reveals that the first
transit presents this slope while the transmission spectrum of the second data
set is flat. Additionally we detect hints of Na absorption in the first night,
but not in the second. We conclude that the transmission spectrum slope and Na
absorption excess found in the first transit observation are caused by
unocculted stellar spots. Modeling the contribution of unocculted spots to
reproduce the results of the first night we find a spot filling factor of
and a spot-to-photosphere temperature difference
of K.Comment: Accepted for publication in Astronomy & Astrophysics, 13 page
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