3,019 research outputs found
Modeling scalar flux and the energy and dissipation equations
Closure models derived from the Two-Scale Direct-Interaction Approximation were compared with data from direct simulations of turbulence. Attention was restricted to anisotropic scalar diffusion models, models for the energy dissipation equation, and models for energy diffusion
Anomalous elastic softening of SmRu_{4}P_{12} under high pressure
The filled skutterudite compound SmRu_4P_{12} undergoes a complex evolution
from a paramagnetic metal (phase I) to a probable multipolar ordering insulator
(phase II) at T_{MI} = 16.5 K, then to a magnetically ordered phase (phase III)
at T_{N} = 14 K. Elastic properties under hydrostatic pressures were
investigated to study the nature of the ordering phases. We found that distinct
elastic softening above T_{MI} is induced by pressure, giving evidence of
quadrupole degeneracy of the ground state in the crystalline electric field. It
also suggests that quadrupole moment may be one of the order parameters below
T_{MI} under pressure. Strangely, the largest degree of softening is found in
the transverse elastic constant C_{T} at around 0.5-0.6 GPa, presumably having
relevancy to the competing and very different Gruneisen parameters \Omega of
T_{MI} and T_{N}. Interplay between the two phase transitions is also verified
by the rapid increase of T_{MI} under pressure with a considerably large \Omega
of 9. Our results can be understood on the basis of the proposed octupole
scenario for SmRu_4P_{12}.Comment: 7 pages, 7 figure
Commensurate-Incommensurate transition in the melting process of the orbital ordering in Pr0.5Ca0.5MnO3: neutron diffraction study
The melting process of the orbital order in
Pr0.5Ca0.5MnO3 single crystal has been studied in detail as a function of
temperature by neutron diffraction. It is demonstrated that a
commensurate-incommensurate (C-IC) transition of the orbital ordering takes
place in a bulk sample, being consistent with the electron diffraction studies.
The lattice structure and the transport properties go through drastic changes
in the IC orbital ordering phase below the charge/orbital ordering temperature
Tco/oo, indicating that the anomalies are intimately related to the partial
disordering of the orbital order, unlike the consensus that it is related to
the charge disordering process. For the same T range, partial disorder of the
orbital ordering turns on the ferromagnetic spin fluctuations which were
observed in a previous neutron scattering study.Comment: 5 pages, 2 figures, REVTeX, to be published in Phys. Rev.
Statistical model for intermittent plasma edge turbulence
The Probability Distribution Function of plasma density fluctuations at the
edge of fusion devices is known to be skewed and strongly non-Gaussian. The
causes of this peculiar behaviour are, up to now, largely unexplored. On the
other hand, understanding the origin and the properties of edge turbulence is a
key issue in magnetic fusion research. In this work we show that a stochastic
fragmentation model, already successfully applied to fluid turbulence, is able
to predict an asymmetric distribution that closely matches experimental data.
The asymmetry is found to be a direct consequence of intermittency. A
discussion of our results in terms of recently suggested BHP universal curve
[S.T. Bramwell, P.C.W. Holdsworth, J.-F. Pinton, Nature (London) 396, 552
(1998)], that should hold for strongly correlated and critical systems, is also
proposedComment: 13 pages. Physica Review E, accepte
Femtosecond relaxation kinetics of fluorescent and nonfluorescent states in blue- and red-phase polydiacetylenes
- …