4,163 research outputs found
Formation of shear bands in drying colloidal dispersions
In directionally dried colloidal dispersions regular bands can appear behind the drying front, inclined at ±45° to the drying line. Although these features have been noted to share visual similarities with shear bands in metal, no physical mechanism for their formation has ever been suggested, until very recently. Here, through microscopy of silica and polystyrene dispersions, dried in Hele-Shaw cells, we demonstrate that the bands are indeed associated with local shear strains. We further show how the bands form, that they scale with the thickness of the drying layer, and that they are eliminated by the addition of salt to the drying dispersions. Finally, we reveal the origins of these bands in the compressive forces associated with drying
Associations of sitting accumulation patterns with cardio-metabolic risk biomarkers in Australian adults
Backgroun
Jump-like unravelings for non-Markovian open quantum systems
Non-Markovian evolution of an open quantum system can be `unraveled' into
pure state trajectories generated by a non-Markovian stochastic (diffusive)
Schr\"odinger equation, as introduced by Di\'osi, Gisin, and Strunz. Recently
we have shown that such equations can be derived using the modal (hidden
variable) interpretation of quantum mechanics. In this paper we generalize this
theory to treat jump-like unravelings. To illustrate the jump-like behavior we
consider a simple system: A classically driven (at Rabi frequency )
two-level atom coupled linearly to a three mode optical bath, with a central
frequency equal to the frequency of the atom, , and the two side
bands have frequencies . In the large limit we
observed that the jump-like behavior is similar to that observed in this system
with a Markovian (broad band) bath. This is expected as in the Markovian limit
the fluorescence spectrum for a strongly driven two level atom takes the form
of a Mollow triplet. However the length of time for which the Markovian-like
behaviour persists depends upon {\em which} jump-like unraveling is used.Comment: 11 pages, 5 figure
Critical dimensions of the diffusion equation
We study the evolution of a random initial field under pure diffusion in
various space dimensions. From numerical calculations we find that the
persistence properties of the system show sharp transitions at critical
dimensions d1 ~ 26 and d2 ~ 46. We also give refined measurements of the
persistence exponents for low dimensions.Comment: 4 pages, 5 figure
Energy Barriers for Flux Lines in 3 Dimensions
I determine the scaling behavior of the free energy barriers encountered by a
flux line in moving through a three-dimensional random potential. A combination
of numerical simulations and analytic arguments suggest that these barriers
scale with the length of the line in the same way as the fluctuation in the
free energy.Comment: 12 pages Latex, 4 postscript figures tarred, compressed, uuencoded
using `uufiles', coming with a separate fil
Hydrodynamic simulations of the KT Eridani nova super-remnant
A nova super-remnant (NSR) is an immense structure associated with a nova
that forms when frequent and recurrent nova eruptions sweep up surrounding
interstellar material (ISM) into a high density and distant shell. The
prototypical NSR, measuring over 100 pc across, was discovered in 2014 around
the annually erupting nova M31N 2008-12a. Hydrodynamical simulations
demonstrated that the creation of a dynamic NSR by repeated eruptions
transporting large quantities of ISM is not only feasible but that these
structures should exist around all novae, whether the white dwarf (WD) is
increasing or decreasing in mass. But it is only the recurrent nova (RNe) with
the highest WD masses and accretion rates that should host observable NSRs. KT
Eridani is, potentially, the eleventh RNe recorded in the Galaxy and is also
surrounded by a recently unveiled H{\alpha} shell tens of parsecs across,
consistent with a NSR. Through modelling the nova ejecta from KT Eri, we
demonstrate that such an observable NSR could form in approximately 50,000
years, which fits with the proper motion history of the nova. We compute the
expected H{\alpha} emission from the KT Eri NSR and predict that the structure
might be accessible to wide-field X-ray facilities.Comment: 9 pages, 7 figures; Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Anomalous Roughness in Dimer-Type Surface Growth
We point out how geometric features affect the scaling properties of
non-equilibrium dynamic processes, by a model for surface growth where
particles can deposit and evaporate only in dimer form, but dissociate on the
surface. Pinning valleys (hill tops) develop spontaneously and the surface
facets for all growth (evaporation) biases. More intriguingly, the scaling
properties of the rough one dimensional equilibrium surface are anomalous. Its
width, , diverges with system size , as
instead of the conventional universal value . This originates
from a topological non-local evenness constraint on the surface configurations.Comment: Published version in PR
Hierarchical model for the scale-dependent velocity of seismic waves
Elastic waves of short wavelength propagating through the upper layer of the
Earth appear to move faster at large separations of source and receiver than at
short separations. This scale dependent velocity is a manifestation of Fermat's
principle of least time in a medium with random velocity fluctuations. Existing
perturbation theories predict a linear increase of the velocity shift with
increasing separation, and cannot describe the saturation of the velocity shift
at large separations that is seen in computer simulations. Here we show that
this long-standing problem in seismology can be solved using a model developed
originally in the context of polymer physics. We find that the saturation
velocity scales with the four-third power of the root-mean-square amplitude of
the velocity fluctuations, in good agreement with the computer simulations.Comment: 7 pages including 3 figure
Wild hummingbirds can use the geometry of a flower array
This research was supported in part by ASAB to SDH, and a Natural Sciences and Engineering Research Council of Canada Discovery Grant to TAH.Animals use cues from their environment to orient in space and to navigate their surroundings. Geometry is a cue whose informational content may originate from the metric properties of a given environment, and its use has been demonstrated in the laboratory in nearly every species of animal tested. However, it is not clear whether geometric information, used by animals typically tested in small, rectangular boxes, is directly relevant to animals in their natural environment. Here we present the first data that confirm the use of geometric cues by a free-living animal in the wild. We trained rufous hummingbirds to visit a rectangular array of four artificial flowers, one of which was rewarded. In some trials a conspicuous landmark cued the reward. Following array translocation and rotation, we presented hummingbirds with three tests. When trained and tested with the landmark, or when trained and tested without it, hummingbirds failed to show geometric learning. However, when trained with a landmark but tested without it, hummingbirds produced the classic geometric response, showing that they had learned the geometric relationships (distance and direction) of several non-reward visual elements of the environment. While it remains that the use of geometry to relocate a reward may be an experimental artefact, it is one cue that is not confined to the laboratory.PostprintPeer reviewe
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