518 research outputs found
Onset of Patterns in an Ocillated Granular Layer: Continuum and Molecular Dynamics Simulations
We study the onset of patterns in vertically oscillated layers of
frictionless dissipative particles. Using both numerical solutions of continuum
equations to Navier-Stokes order and molecular dynamics (MD) simulations, we
find that standing waves form stripe patterns above a critical acceleration of
the cell. Changing the frequency of oscillation of the cell changes the
wavelength of the resulting pattern; MD and continuum simulations both yield
wavelengths in accord with previous experimental results. The value of the
critical acceleration for ordered standing waves is approximately 10% higher in
molecular dynamics simulations than in the continuum simulations, and the
amplitude of the waves differs significantly between the models. The delay in
the onset of order in molecular dynamics simulations and the amplitude of noise
below this onset are consistent with the presence of fluctuations which are
absent in the continuum theory. The strength of the noise obtained by fit to
Swift-Hohenberg theory is orders of magnitude larger than the thermal noise in
fluid convection experiments, and is comparable to the noise found in
experiments with oscillated granular layers and in recent fluid experiments on
fluids near the critical point. Good agreement is found between the mean field
value of onset from the Swift-Hohenberg fit and the onset in continuum
simulations. Patterns are compared in cells oscillated at two different
frequencies in MD; the layer with larger wavelength patterns has less noise
than the layer with smaller wavelength patterns.Comment: Published in Physical Review
Continuum simulations of shocks and patterns in vertically oscillated granular layers
We study interactions between shocks and standing-wave patterns in vertically
oscillated layers of granular media using three-dimensional, time-dependent
numerical solutions of continuum equations to Navier-Stokes order. We simulate
a layer of grains atop a plate that oscillates sinusoidally in the direction of
gravity. Standing waves form stripe patterns when the accelerational amplitude
of the plate's oscillation exceeds a critical value. Shocks also form with each
collision between the layer and the plate; we show that pressure gradients
formed by these shocks cause the flow to reverse direction within the layer.
This reversal leads to an oscillatory state of the pattern that is subharmonic
with respect to the plate's oscillation. Finally, we study the relationship
between shocks and patterns in layers oscillated at various frequencies and
show that the pattern wavelength increases monotonically as the shock strength
increases.Comment: 12 pages, 9 figure
Walmart Impact on the Finance and Insurance Industry
Purpose
This paper investigates the effect of Walmart presence on professional service firms within the finance and insurance sector. This paper also discusses the finance and insurance industry’s place within the Walmart ripple effect—changed retail sector leads to changed professional support services resulting in altered levels of social capital within the community.
Design/Methodology
The study uses county-level data from the state of Nebraska to examine the relationship between cumulative Walmart exposure and the number of firms, number of employees, and payroll levels within the finance and insurance (F&I) sector. These same variables are also investigated within two specific F&I industries—insurance and banking.
Findings
The study documents a negative association between cumulative Walmart presence and the number of employees in the finance and insurance industry and a positive relationship between Walmart exposure and F&I payroll levels. The insurance industry results are consistent with the F&I sector result relating to payroll, but show a significant positive relationship between cumulative Walmart exposure and number of insurance agencies. Empirical results from the commercial banking industry are consistent with both the F&I sector and insurance industries with a positive relationship between Walmart presence over time and payroll levels.
Originality/value
This study contributes to the Walmart effect literature by considering the impact of Walmart presence beyond the retail sector. The paper investigates the effect of Walmart on the finance and insurance profession, a sector that 1) competes directly with Walmart Supercenters for money services, 2) provides support services for retail businesses impacted by Walmart services, and 3) potentially suffers from centralized benefits provided to employees by Walmart headquarters rather than local insurers. The paper concludes that the mixed impact on professional firms results in social capital that could be both strengthened and challenged by Walmart presence
Resonance tongues and patterns in periodically forced reaction-diffusion systems
Various resonant and near-resonant patterns form in a light-sensitive
Belousov-Zhabotinsky (BZ) reaction in response to a spatially-homogeneous
time-periodic perturbation with light. The regions (tongues) in the forcing
frequency and forcing amplitude parameter plane where resonant patterns form
are identified through analysis of the temporal response of the patterns.
Resonant and near-resonant responses are distinguished. The unforced BZ
reaction shows both spatially-uniform oscillations and rotating spiral waves,
while the forced system shows patterns such as standing-wave labyrinths and
rotating spiral waves. The patterns depend on the amplitude and frequency of
the perturbation, and also on whether the system responds to the forcing near
the uniform oscillation frequency or the spiral wave frequency. Numerical
simulations of a forced FitzHugh-Nagumo reaction-diffusion model show both
resonant and near-resonant patterns similar to the BZ chemical system
Symmetries and novel universal properties of turbulent hydrodynamics in a symmetric binary fluid mixture
We elucidate the universal properties of the nonequilibrium steady states
(NESS) in a driven symmetric binary fluid mixture, an example of active
advection, in its miscible phase. We use the symmetries of the equations of
motion to establish the appropriate form of the structure functions which
characterise the statistical properties of the NESS of a driven symmetric
binary fluid mixture. We elucidate the universal properties described by the
scaling exponents and the amplitude ratios. Our results suggest that these
exponents and amplitude ratios vary continuously with the degree of
crosscorrelations between the velocity and the gradient of the concentration
fields. Furthermore, we demonstrate, in agreement with Celani et al, Phys. Rev.
Lett., 89, 234502 (2002, that the conventional structure functions as used in
passive scalar turbulence studies exhibit only simple scaling in the problem of
symmetric binary fluid mixture even in the weak concentration limit. We also
discuss possible experimental verifications of our results.Comment: To appear in JSTAT (letters) (2005
Synchronisation in Coupled Sine Circle Maps
We study the spatially synchronized and temporally periodic solutions of a
1-d lattice of coupled sine circle maps. We carry out an analytic stability
analysis of this spatially synchronized and temporally periodic case and obtain
the stability matrix in a neat block diagonal form. We find spatially
synchronized behaviour over a substantial range of parameter space. We have
also extended the analysis to higher spatial periods with similar results.
Numerical simulations for various temporal periods of the synchronized
solution, reveal that the entire structure of the Arnold tongues and the
devil's staircase seen in the case of the single circle map can also be
observed for the synchronized coupled sine circle map lattice. Our formalism
should be useful in the study of spatially periodic behaviour in other coupled
map lattices.Comment: uuencoded, 1 rextex file 14 pages, 3 postscript figure
Some , And Possibly All, Scalar Inferences Are Not Delayed: Evidence For Immediate Pragmatic Enrichment
Scalar inferences are commonly generated when a speaker uses a weaker expression rather than a stronger alternative, e.g., John ate some of the apples implies that he did not eat them all. This article describes a visual-world study investigating how and when perceivers compute these inferences. Participants followed spoken instructions containing the scalar quantifier some directing them to interact with one of several referential targets (e.g., Click on the girl who has some of the balloons). Participants fixated on the target compatible with the implicated meaning of some and avoided a competitor compatible with the literal meaning prior to a disambiguating noun. Further, convergence on the target was as fast for some as for the non-scalar quantifiers none and all. These findings indicate that the scalar inference is computed immediately and is not delayed relative to the literal interpretation of some. It is argued that previous demonstrations that scalar inferences increase processing time are not necessarily due to delays in generating the inference itself, but rather arise because integrating the interpretation of the inference with relevant information in the context may require additional time. With sufficient contextual support, processing delays disappear
Breathing Spots in a Reaction-Diffusion System
A quasi-2-dimensional stationary spot in a disk-shaped chemical reactor is
observed to bifurcate to an oscillating spot when a control parameter is
increased beyond a critical value. Further increase of the control parameter
leads to the collapse and disappearance of the spot. Analysis of a bistable
activator-inhibitor model indicates that the observed behavior is a consequence
of interaction of the front with the boundary near a parity breaking front
bifurcation.Comment: 4 pages RevTeX, see also http://chaos.ph.utexas.edu/ and
http://t7.lanl.gov/People/Aric
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