11,729 research outputs found
Turbulent-like fluctuations in quasistatic flow of granular media
We analyze particle velocity fluctuations in a simulated granular system
subjected to homogeneous quasistatic shearing. We show that these fluctuations
share the following scaling characteristics of fluid turbulence in spite of
their different physical origins: 1) Scale-dependent probability distribution
with non-Guassian broadening at small time scales; 2) Power-law spectrum,
reflecting long-range correlations and the self-affine nature of the
fluctuations; 3) Superdiffusion with respect to the mean background flow
Strain versus stress in a model granular material: a Devil's staircase
The series of equilibrium states reached by disordered packings of rigid,
frictionless discs in two dimensions, under gradually varying stress, are
studied by numerical simulations. Statistical properties of trajectories in
configuration space are found to be independent of specific assumptions ruling
granular dynamics, and determined by geometry only. A monotonic increase in
some macroscopic loading parameter causes a discrete sequence of
rearrangements. For a biaxial compression, we show that, due to the statistical
importance of such events of large magnitudes, the dependence of the resulting
strain on stress direction is a Levy flight in the thermodynamic limit.Comment: REVTeX, 4 pages, 5 included PostScript figures. New version altered
throughout text, very close to published pape
Mobile particles in an immobile environment: Molecular Dynamics simulation of a binary Yukawa mixture
Molecular dynamics computer simulations are used to investigate thedynamics
of a binary mixture of charged (Yukawa) particles with a size-ratio of 1:5. We
find that the system undergoes a phase transition where the large particles
crystallize while the small particles remain in a fluid-like (delocalized)
phase. Upon decreasing temperature below the transition, the small particles
become increasingly localized on intermediate time scales. This is reflected in
the incoherent intermediate scattering functions by the appearance of a plateau
with a growing height. At long times, the small particles show a diffusive
hopping motion. We find that these transport properties are related to
structural correlations and the single-particle potential energy distribution
of the small particles.Comment: 7 pages, 5 figure
Emergence of Quintet Superfluidity in the Chain of Partially Polarized Spin-3/2 Ultracold Atom
The system of ultracold atoms with hyperfine spin might be unstable
against the formation of quintet pairs if the interaction is attractive in the
quintet channel. We have investigated the behavior of correlation functions in
a model including only s-wave interactions at quarter filling by large-scale
density-matrix renormalization-group simulations. We show that the correlations
of quintet pairs become quasi-long-ranged, when the system is partially
polarized, leading to the emergence of various mixed superfluid phases in which
BCS-like pairs carrying different magnetic moment coexist.Comment: 4 pages, 4 figures; significantly rewritten compared to the first
versio
Production and reproduction norms of fine woolled Merino sheep on natural pastures in the Karoo
The objective of this study was to establish a fine woolled Merino flock at the Grootfontein Agricultural Development Institute in order to evaluate the production and reproduction performance of fine woolled animals against a control line on natural pastures in the Karoo. Data collected from 1989 to 1999 were used to evaluate the production and reproduction performance of these two lines. It is evident from the results of this study that the control lambs had a slightly better growth rate than the fine woolled lambs. However, body weight and reproduction of the adult ewes did not differ. The fine woolled animals produced significantly less wool compared to the control line. It can therefore be concluded that it would be possible to produce finer wool effectively under natural pastures in the Karoo. Keywords: Fibre diameter, body weight, fleece weight South African Journal of Animal Science Vol. 37 (1) 2007: pp. 31-3
Multimer formation in 1D two-component gases and trimer phase in the asymmetric attractive Hubbard model
We consider two-component one-dimensional quantum gases at special imbalanced
commensurabilities which lead to the formation of multimer (multi-particle
bound-states) as the dominant order parameter. Luttinger liquid theory supports
a mode-locking mechanism in which mass (or velocity) asymmetry is identified as
the key ingredient to stabilize such states. While the scenario is valid both
in the continuum and on a lattice, the effects of umklapp terms relevant for
densities commensurate with the lattice spacing are also mentioned. These ideas
are illustrated and confronted with the physics of the asymmetric
(mass-imbalanced) fermionic Hubbard model with attractive interactions and
densities such that a trimer phase can be stabilized. Phase diagrams are
computed using density-matrix renormalization group techniques, showing the
important role of the total density in achieving the novel phase. The effective
physics of the trimer gas is as well studied. Lastly, the effect of a parabolic
confinement and the emergence of a crystal phase of trimers are briefly
addressed. This model has connections with the physics of imbalanced
two-component fermionic gases and Bose-Fermi mixtures as the latter gives a
good phenomenological description of the numerics in the strong-coupling
regime.Comment: 17 pages, 15 figure
Scaling Laws of Stress and Strain in Brittle Fracture
A numerical realization of an elastic beam lattice is used to obtain scaling
exponents relevant to the extent of damage within the controlled, catastrophic
and total regimes of mode-I brittle fracture. The relative fraction of damage
at the onset of catastrophic rupture approaches a fixed value in the continuum
limit. This enables disorder in a real material to be quantified through its
relationship with random samples generated on the computer.Comment: 4 pages and 6 figure
Parameterized Littlewood-Paley operators with variable kernels on Hardy spaces and weak Hardy spaces
In this paper, by using the atomic decomposition theory of Hardy space and
weak Hardy space, we discuss the boundedness of parameterized Littlewood-Paley
operator with variable kernel on these spaces.Comment: 15 pages. arXiv admin note: text overlap with arXiv:1711.0961
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