8,314 research outputs found
A Model for Force Fluctuations in Bead Packs
We study theoretically the complex network of forces that is responsible for
the static structure and properties of granular materials. We present detailed
calculations for a model in which the fluctuations in the force distribution
arise because of variations in the contact angles and the constraints imposed
by the force balance on each bead of the pile. We compare our results for force
distribution function for this model, including exact results for certain
contact angle probability distributions, with numerical simulations of force
distributions in random sphere packings. This model reproduces many aspects of
the force distribution observed both in experiment and in numerical simulations
of sphere packings
Predicting Variation in Endowment Effect Magnitudes
Hundreds of studies demonstrate human cognitive biases that are both inconsistent with “rational” decisionmaking and puzzlingly patterned. One such bias, the “endowment effect” (also known as “reluctance to trade”), occurs when people instantly value an item they have just acquired at a much higher price than the maximum they would have paid to acquire it. This bias impedes a vast range of real-world transactions, making it important to understand. Prior studies have documented items that do or do not generate endowment effects, and have noted that the effects vary in magnitude. But none has predicted any of the substantial between-item variation in those magnitudes across a large and novel set of items. Working from evolutionary theory, we derived six factors that predicted 52% of the between- item variation in magnitudes for a novel set of 24 items. These results deepen understanding of both the causes of and patterns in endowment effects. More broadly, they suggest that many other cognitive biases may be similarly approached, and potentially linked by a common theoretical framework
Creep motion in a granular pile exhibiting steady surface flow
We investigate experimentally granular piles exhibiting steady surface flow.
Below the surface flow, it has been believed exisitence of a `frozen' bulk
region, but our results show absence of such a frozen bulk. We report here that
even the particles in deep layers in the bulk exhibit very slow flow and that
such motion can be detected at an arbitrary depth. The mean velocity of the
creep motion decays exponentially with depth, and the characteristic decay
length is approximately equal to the particle-size and independent of the flow
rate. It is expected that the creep motion we have seeen is observable in all
sheared granular systems.Comment: 3 pages, 4 figure
Rapid analysis of Förster resonance energy transfer by two-color global fluorescence correlation spectroscopy: Trypsin proteinase reaction
AbstractIn this study we introduce the combination of two-color global fluorescence correlation spectroscopy (2CG-FCS) and Förster resonance energy transfer (FRET) as a very powerful combination for monitoring biochemical reactions on the basis of single molecule events. 2CG-FCS, which is a new variation emerging from the family of fluorescence correlation spectroscopy, globally analyzes the simultaneously recorded auto- and cross-correlation data from two photon detectors monitoring the fluorescence emission of different colors. Overcoming the limitations inherent in mere auto- and cross-correlation analysis, 2CG-FCS is sensitive in resolving and quantifying fluorescent species that differ in their diffusion characteristics and/or their molecular brightness either in one or both detection channels. It is able to account for effects that have often been considered as sources of severe artifacts in two-color and FRET measurements, the most prominent artifacts comprising photobleaching, cross talk, or concentration variations in sample preparation. Because of its very high statistical accuracy, the combination of FRET and 2CG-FCS is suited for high-throughput applications such as drug screening. Employing beam scanning during data acquisition even further enhances this capability and allows measurement times of <2s. The improved performance in monitoring a FRET sample was verified by following the protease cleavage reaction of a FRET-active peptide. The FRET-inactive subpopulation of uncleaved substrate could be correctly assigned, revealing a substantial portion of inactive or missing acceptor label. The results were compared to those obtained by two-dimensional fluorescence intensity distribution analysis
Subdiffusion and cage effect in a sheared granular material
We investigate experimentally the diffusion properties of a bidimensional
bidisperse dry granular material under quasistatic cyclic shear.The comparison
of these properties with results obtained both in computer simulations of hard
spheres systems and Lenard-Jones liquids and experiments on colloidal systems
near the glass transition demonstrates a strong analogy between the behaviour
of granular matter and these systems. More specifically, we study in detail the
cage dynamics responsible for the subdiffusion in the slow relaxation regime,
and obtain the values of relevant time and length scales.Comment: 4 pages, 6 figures, submitted to PR
Stratified horizontal flow in vertically vibrated granular layers
A layer of granular material on a vertically vibrating sawtooth-shaped base
exhibits horizontal flow whose speed and direction depend on the parameters
specifying the system in a complex manner. Discrete-particle simulations reveal
that the induced flow rate varies with height within the granular layer and
oppositely directed flows can occur at different levels. The behavior of the
overall flow is readily understood once this novel feature is taken into
account.Comment: 4 pages, 6 figures, submitte
Acute Onset of Intermittent Claudication Caused by Complete Occlusion of a Persistent Sciatic Artery
Power-Laws in Nonlinear Granular Chain under Gravity
The signal generated by a weak impulse propagates in an oscillatory way and
dispersively in a gravitationally compacted granular chain. For the power-law
type contact force, we show analytically that the type of dispersion follows
power-laws in depth. The power-law for grain displacement signal is given by
where and denote depth and the exponent of contact
force, and the power-law for the grain velocity is . Other
depth-dependent power-laws for oscillation frequency, wavelength, and period
are given by combining above two and the phase velocity power-law
. We verify above power-laws by comparing with the data
obtained by numerical simulations.Comment: 12 pages, 3 figures; Changed conten
Clustering and Non-Gaussian Behavior in Granular Matter
We investigate the properties of a model of granular matter consisting of
Brownian particles on a line subject to inelastic mutual collisions. This model
displays a genuine thermodynamic limit for the mean values of the energy and
the energy dissipation. When the typical relaxation time associated with
the Brownian process is small compared with the mean collision time
the spatial density is nearly homogeneous and the velocity probability
distribution is gaussian. In the opposite limit one has
strong spatial clustering, with a fractal distribution of particles, and the
velocity probability distribution strongly deviates from the gaussian one.Comment: 4 pages including 3 eps figures, LaTex, added references, corrected
typos, minimally changed contents and abstract, to published in
Phys.Rev.Lett. (tentatively on 28th of October, 1998
Aging and multiscaling in out of equilibrium dynamical processes in granular media
In the framework of recently introduced frustrated lattice gas models, we
study the out of equilibrium dynamical processes during the compaction process
in granular media. We find irreversible-reversible cycles in agreement with
recent experimental observations. Moreover in analogy with the phenomenology of
the glass transition we find aging effects during the compaction process In
particular we find that the two time density correlation function
asymptotically scales as a function of the single variable .
This result is interpreted in terms of multiscaling properties of the system.Comment: 4 page
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