1,714 research outputs found
On the scaling of temperature fluctuations induced by frictional heating
The temperature fluctuations generated by viscous dissipation in an isotropic
turbulent flow are studied using direct numerical simulation. It is shown that
their scaling with Reynolds number is at odds with predictions from recent
investigations. The origin of the discrepancy is traced back to the anomalous
scaling of the dissipation rate fluctuations. Phenomenological arguments are
presented which explain the observed results. The study shows that previously
proposed models underpredict the variance of frictional temperature
fluctuations by a factor proportional to the square of the Taylor-scale
Reynolds number
Multifrequency Method for Mapping Active Galactic Nuclei with Allowance for the Frequency-Dependent Image Shift
We consider the problem of multifrequency VLBA image synthesis and
spectral-index mapping for active galactic nuclei related to the necessity of
taking into account the frequency-dependent image shift. We describe our
generalized multifrequency synthesis algorithm with a spectral correction based
on the maximum entropy method. The results of our processing of multifrequency
VLBI data for the radio sources J2202+4216, J0336+3218, and J1419+5423 are
presented.Comment: 12 pages, 2 tables, 6 figure
Numerical Verification of the Weak Turbulent Model for Swell Evolution
The purpose of this article is numerical verification of the theory of weak
turbulence. We performed numerical simulation of an ensemble of nonlinearly
interacting free gravity waves (swell) by two different methods: solution of
primordial dynamical equations describing potential flow of the ideal fluid
with a free surface and, solution of the kinetic Hasselmann equation,
describing the wave ensemble in the framework of the theory of weak turbulence.
In both cases we observed effects predicted by this theory: frequency
downshift, angular spreading and formation of Zakharov-Filonenko spectrum
. To achieve quantitative coincidence of the
results obtained by different methods, one has to supply the Hasselmann kinetic
equation by an empirical dissipation term modeling the coherent
effects of white-capping. Using of the standard dissipation terms from
operational wave predicting model ({\it WAM}) leads to significant improvement
on short times, but not resolve the discrepancy completely, leaving the
question about optimal choice of open. In a long run {\it WAM}
dissipative terms overestimate dissipation essentially.Comment: 41 pages, 37 figures, 1 table. Submitted in European Journal of
Mechanics B/Fluid
A lower bound for Garsia's entropy for certain Bernoulli convolutions
Let be a Pisot number and let denote Garsia's
entropy for the Bernoulli convolution associated with . Garsia, in 1963
showed that for any Pisot . For the Pisot numbers which
satisfy (with ) Garsia's entropy has been
evaluated with high precision by Alexander and Zagier and later improved by
Grabner, Kirschenhofer and Tichy, and it proves to be close to 1. No other
numerical values for are known.
In the present paper we show that for all Pisot , and
improve this lower bound for certain ranges of . Our method is
computational in nature.Comment: 16 pages, 4 figure
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