2,847 research outputs found
Turbulence without pressure in d dimensions
The randomly driven Navier-Stokes equation without pressure in d-dimensional
space is considered as a model of strong turbulence in a compressible fluid. We
derive a closed equation for the velocity-gradient probability density
function. We find the asymptotics of this function for the case of the gradient
velocity field (Burgers turbulence), and provide a numerical solution for the
two-dimensional case. Application of these results to the velocity-difference
probability density function is discussed.Comment: latex, 5 pages, revised and enlarge
Dynamical Anomalies and Intermittency in Burgers Turbulence
We analyze the field theory of fully developed Burgers turbulence. Its key
elements are shock fields, which characterize the singularity statistics of the
velocity field. The shock fields enter an operator product expansion describing
intermittency. The latter is found to be constrained by dynamical anomalies
expressing finite dissipation in the inviscid limit. The link between dynamical
anomalies and intermittency is argued to be important in a wider context of
turbulence.Comment: revised version, 4 pp., 1 fig., to appear in PR
Thermal Process Integration in the AVDU A12/2 Crude Distillation Unit during Winter Operation
A pinch analysis of the AVDU A12/2 crude distillation unit processing 2 million tons of crude oil per year is made. A pinch retrofit of the recuperative heat-exchange system of the unit is performed. It is shown that the implementation of the proposed project will reduce the arbitrary energy consumption by 60 %, which corresponds to a reduction in specific fuel consumption from 36 to 13 kg per ton of refined oil
Extreme Plasma Astrophysics
This is a science white paper submitted to the Astro-2020 and Plasma-2020
Decadal Surveys. The paper describes the present status and emerging
opportunities in Extreme Plasma Astrophysics -- a study of
astrophysically-relevant plasma processes taking place under extreme conditions
that necessitate taking into account relativistic, radiation, and QED effects.Comment: A science white paper submitted to the Astro-2020 and Plasma-2020
Decadal Surveys. 7 pages including cover page and references. Paper updated
in late March 2019 to include a several additional co-authors and references,
and a few small change
A Turbulent Origin for Flocculent Spiral Structure in Galaxies
The flocculent structure of star formation in 7 galaxies has a Fourier
transform power spectrum for azimuthal intensity scans with a power law slope
that increases systematically from -1 at large scales to -1.7 at small scales.
This is the same pattern as in the power spectra for azimuthal scans of HI
emission in the Large Magellanic Clouds and for flocculent dust clouds in
galactic nuclei. The steep part also corresponds to the slope of -3 for
two-dimensional power spectra that have been observed in atomic and molecular
gas surveys of the Milky Way and the Large and Small Magellanic Clouds. The
same power law structure for star formation arises in both flocculent and grand
design galaxies, which implies that the star formation process is the same in
each. Fractal Brownian motion models that include discrete stars and an
underlying continuum of starlight match the observations if all of the emission
is organized into a global fractal pattern with an intrinsic 1D power spectrum
having a slope between 1.3 and 1.8. We suggest that the power spectrum of
optical light in galaxies is the result of turbulence, and that large-scale
turbulent motions are generated by sheared gravitational instabilities which
make flocculent spiral arms first and then cascade to form clouds and clusters
on smaller scales.Comment: accepted for ApJ, 31 pg, 9 figure
Radio-Frequency Measurements of Coherent Transition and Cherenkov Radiation: Implications for High-Energy Neutrino Detection
We report on measurements of 11-18 cm wavelength radio emission from
interactions of 15.2 MeV pulsed electron bunches at the Argonne Wakefield
Accelerator. The electrons were observed both in a configuration where they
produced primarily transition radiation from an aluminum foil, and in a
configuration designed for the electrons to produce Cherenkov radiation in a
silica sand target. Our aim was to emulate the large electron excess expected
to develop during an electromagnetic cascade initiated by an ultra high-energy
particle. Such charge asymmetries are predicted to produce strong coherent
radio pulses, which are the basis for several experiments to detect high-energy
neutrinos from the showers they induce in Antarctic ice and in the lunar
regolith. We detected coherent emission which we attribute both to transition
and possibly Cherenkov radiation at different levels depending on the
experimental conditions. We discuss implications for experiments relying on
radio emission for detection of electromagnetic cascades produced by ultra
high-energy neutrinos.Comment: updated figure 10; fixed typo in equation 2.2; accepted by PR
Yield, plasticity, stability and homeostasis of spring barley cultivars in the Non-Black Earth Region
Background. The expansion of agrometeorological factors negatively affecting the productivity of spring barley has oriented plant breeders towards developing adaptable forms capable of realizing their genetic potential for higher yield under unfavorable conditions. Applying several methods of statistical data analysis helps to perform a more accurate assessment of the material differentiated according to its adaptability indicators. The objective of this study was to assess the adaptability of spring barley cultivars on the basis of their yield, plasticity, stability and homeostasis.Materials and methods. The resulting data were obtained for ten spring barley cultivars developed at Nemchinovka FRC.Results. High yield potential of more than 8.5 t/ha was disclosed in barley cultivars ‘Yaromir’, ‘Nur’, ‘Nadezhny’, ‘Sudar’, ‘Zlatoyar’ and ‘Znatny’. Cvs. ‘Luboyar’, ‘Nadezhny’ and ‘Rafael’ showed the highest adaptability to the worst growing conditions (4.65–5.04 t/ha) as well as high adaptive and compensatory ability. Cvs. ‘Sudar’, ‘Nur’ and ‘Zlatoyar’ were identified for high environmental plasticity (Cvi = 24.1–25.9%; bi = 1.02–1.16; σ = 1.52–1.59), while ‘Lyuboyar’, ‘Znatny’ and ‘Vladimir’ for their stability parameters (S2di = 0.05–0.19; σ2CACi = 1.60–1.78; σ2(G×E)gi = 0.05–0.15). The highest values of homeostasis (BVGi = 3.45– 3.53; CSLi = 138.7–139.4; Homi = 9.02–9.85) were registered for cvs. ‘Rafael’ and ‘Lyuboyar’. The calculated rating of the tested cultivars identified ‘Nadezhny’ as the best in productivity, while ‘Zlatoyar’ was the best in environmental plasticity. The highest levels of stability and homeostasis were recorded for cvs. ‘Rafael’ and ‘Lyuboyar’.Conclusion. Comprehensive assessment of productivity and adaptability indicators in the tested spring barley cultivars showed that ‘Lyuboyar’, ‘Nadezhny’, ‘Zlatoyar’ and ‘Rafael’ were the best under the conditions of the Non-Black Earth Region
Simulating Supersonic Turbulence in Magnetized Molecular Clouds
We present results of large-scale three-dimensional simulations of weakly
magnetized supersonic turbulence at grid resolutions up to 1024^3 cells. Our
numerical experiments are carried out with the Piecewise Parabolic Method on a
Local Stencil and assume an isothermal equation of state. The turbulence is
driven by a large-scale isotropic solenoidal force in a periodic computational
domain and fully develops in a few flow crossing times. We then evolve the flow
for a number of flow crossing times and analyze various statistical properties
of the saturated turbulent state. We show that the energy transfer rate in the
inertial range of scales is surprisingly close to a constant, indicating that
Kolmogorov's phenomenology for incompressible turbulence can be extended to
magnetized supersonic flows. We also discuss numerical dissipation effects and
convergence of different turbulence diagnostics as grid resolution refines from
256^3 to 1024^3 cells.Comment: 10 pages, 3 figures, to appear in the proceedings of the DOE/SciDAC
2009 conferenc
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