204 research outputs found
Longitudinal Structure Functions in Decaying and Forced Turbulence
In order to reliably compute the longitudinal structure functions in decaying
and forced turbulence, local isotropy is examined with the aid of the isotropic
expression of the incompressible conditions for the second and third order
structure functions. Furthermore, the Karman-Howarth-Kolmogorov relation is
investigated to examine the effects of external forcing and temporally
decreasing of the second order structure function. On the basis of these
investigations, the scaling range and exponents of the longitudinal
structure functions are determined for decaying and forced turbulence with the
aid of the extended-self-similarity (ESS) method. We find that 's are
smaller, for , in decaying turbulence than in forced turbulence. The
reasons for this discrepancy are discussed. Analysis of the local slopes of the
structure functions is used to justify the ESS method.Comment: 15 pages, 16 figure
Statistics of Dissipation and Enstrophy Induced by a Set of Burgers Vortices
Dissipation and enstropy statistics are calculated for an ensemble of
modified Burgers vortices in equilibrium under uniform straining. Different
best-fit, finite-range scaling exponents are found for locally-averaged
dissipation and enstrophy, in agreement with existing numerical simulations and
experiments. However, the ratios of dissipation and enstropy moments supported
by axisymmetric vortices of any profile are finite. Therefore the asymptotic
scaling exponents for dissipation and enstrophy induced by such vortices are
equal in the limit of infinite Reynolds number.Comment: Revtex (4 pages) with 4 postscript figures included via psfi
Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory
Data from the Pierre Auger Observatory are analyzed to search for
anisotropies near the direction of the Galactic Centre at EeV energies. The
exposure of the surface array in this part of the sky is already significantly
larger than that of the fore-runner experiments. Our results do not support
previous findings of localized excesses in the AGASA and SUGAR data. We set an
upper bound on a point-like flux of cosmic rays arriving from the Galactic
Centre which excludes several scenarios predicting sources of EeV neutrons from
Sagittarius . Also the events detected simultaneously by the surface and
fluorescence detectors (the `hybrid' data set), which have better pointing
accuracy but are less numerous than those of the surface array alone, do not
show any significant localized excess from this direction.Comment: Matches published versio
Quantum Turbulence
The present article reviews the recent developments in the physics of quantum
turbulence. Quantum turbulence (QT) was discovered in superfluid He in the
1950s, and the research has tended toward a new direction since the mid 90s.
The similarities and differences between quantum and classical turbulence have
become an important area of research. QT is comprised of quantized vortices
that are definite topological defects, being expected to yield a model of
turbulence that is much simpler than the classical model. The general
introduction of the issue and a brief review on classical turbulence are
followed by a description of the dynamics of quantized vortices. Then, we
discuss the energy spectrum of QT at very low temperatures. At low wavenumbers,
the energy is transferred through the Richardson cascade of quantized vortices,
and the spectrum obeys the Kolmogorov law, which is the most important
statistical law in turbulence; this classical region shows the similarity to
conventional turbulence. At higher wavenumbers, the energy is transferred by
the Kelvin-wave cascade on each vortex. This quantum regime depends strongly on
the nature of each quantized vortex. The possible dissipation mechanism is
discussed. Finally, important new experimental studies, which include
investigations into temperature-dependent transition to QT, dissipation at very
low temperatures, QT created by vibrating structures, and visualization of QT,
are reviewed. The present article concludes with a brief look at QT in atomic
Bose-Einstein condensates.Comment: 13 pages, 5 figures, Review article to appear in J. Phys. Soc. Jp
An upper limit to the photon fraction in cosmic rays above 10^19 eV from the Pierre Auger Observatory
An upper limit of 16% (at 95% c.l.) is derived for the photon fraction in cosmic rays with energies above 10^19 eV, based on observations of the depth of shower maximum performed with the hybrid detector of the Pierre Auger Observatory. This is the first such limit on photons obtained by observing the fluorescence light profile of air showers. This upper limit confirms and improves on previous results from the Haverah Park and AGASA surface arrays. Additional data recorded with the Auger surface detectors for a subset of the event sample, support the conclusion that a photon origin of the observed events is not favoured
On the Alignment of Strain, Vorticity and Scalar Gradient in Turbulent, Buoyant, Nonpremixed Flames
The alignment of vorticity and scalar gradient with the eigendirections of the rate of strain tensor is investigated in turbulent buoyant nonpremixed horizontal and vertical flames. The uniqueness of a buoyant nonpremixed flame is that it contains regions with distinct alignment characteristics. The strain-enstrophy angle Psi is used to identify these regions. Examination of the vorticity field and the vorticity production in these different regions indicates that Psi and consequently the alignment properties near the flame surface identified by the mixture fraction band F approximately equals F(sub st) differ from those in the fuel region, F > F(sub st) and the oxidizer region, F F(sub st) (and F < F(sub st) for the vertical flame) band(s) show(s) vorticity/beta alignment. The implication of this result is that the scalar dissipation, epsilon(sub F), attains its maximum value always near F approximately equals F(sub st). These results are also discussed within the framework of recent dynamical results [Galanti et al., Nonlinearity 10, 1675 (1997)] suggesting that the Navier-Stokes equations evolved towards an attracting solution. It is shown that the properties of such an attracting solution are also consistent with our results of buoyant turbulent nonpremixed flames
Patterns of Productivity Growth and the Wage Cycle in Turkish Manufacturing
In this paper we investigate the distributional consequences of the post-1980 accumulation patterns and technological change in the Turkish manufacturing industries. We utilise two quantitative techniques. First, we make use of the Hodrick-Prescott filter to disintegrate the cyclical variations in productivity growth and wage rates from their respective historical trends, and study the evolution of the wage cycle against the long term productivity patterns in the sector. Next, we decompose the fundamental characteristics of the contributions of productivity growth of the manufacturing sub-sectors to the overall total. Our results suggest very little structural change in the sectoral composition and nature of productivity advances under the post-1980 structural adjustment reforms and outward-orientation, and underscore that the gains in productivity in this period did not materialise as gains in remunerations of wage labour. Contrary to the prognostications of the orthodox theory, the post-1980 export orientation of Turkish manufacturing was not found to lend itself to productivity contributions, and could not be sustained as a viable strategy of 'export-led industrialisation'.
- …