1,016 research outputs found
Determining Returns to Storage: USDA Data versus Micro Level Data
USDA data are commonly used to determine producers' returns to storage. Aggregating data may result in a loss of information, leading to underestimated returns. This study compares USDA and elevator data from Oklahoma to determine how much USDA data underestimates returns. Results indicate USDA data only slightly underestimate returns to storage.Research Methods/ Statistical Methods,
The Preference for Round Number Prices
This study determines if a preference for round prices exists in the wheat market and how wheat sales react to price movements around whole dollar amounts. The results show round prices are slightly more prevalent than non-round prices and that transactions increase when price moves above a whole dollar amount.Demand and Price Analysis,
Stochastic simulations of cargo transport by processive molecular motors
We use stochastic computer simulations to study the transport of a spherical
cargo particle along a microtubule-like track on a planar substrate by several
kinesin-like processive motors. Our newly developed adhesive motor dynamics
algorithm combines the numerical integration of a Langevin equation for the
motion of a sphere with kinetic rules for the molecular motors. The Langevin
part includes diffusive motion, the action of the pulling motors, and
hydrodynamic interactions between sphere and wall. The kinetic rules for the
motors include binding to and unbinding from the filament as well as active
motor steps. We find that the simulated mean transport length increases
exponentially with the number of bound motors, in good agreement with earlier
results. The number of motors in binding range to the motor track fluctuates in
time with a Poissonian distribution, both for springs and cables being used as
models for the linker mechanics. Cooperativity in the sense of equal load
sharing only occurs for high values for viscosity and attachment time.Comment: 40 pages, Revtex with 13 figures, to appear in Journal of Chemical
Physic
Transport by molecular motors in the presence of static defects
The transport by molecular motors along cytoskeletal filaments is studied
theoretically in the presence of static defects. The movements of single motors
are described as biased random walks along the filament as well as binding to
and unbinding from the filament. Three basic types of defects are
distinguished, which differ from normal filament sites only in one of the
motors' transition probabilities. Both stepping defects with a reduced
probability for forward steps and unbinding defects with an increased
probability for motor unbinding strongly reduce the velocities and the run
lengths of the motors with increasing defect density. For transport by single
motors, binding defects with a reduced probability for motor binding have a
relatively small effect on the transport properties. For cargo transport by
motors teams, binding defects also change the effective unbinding rate of the
cargo particles and are expected to have a stronger effect.Comment: 20 pages, latex, 7 figures, 1 tabl
Dynamic Boundaries in Asymmetric Exclusion Processes
We investigate the dynamics of a one-dimensional asymmetric exclusion process
with Langmuir kinetics and a fluctuating wall. At the left boundary, particles
are injected onto the lattice; from there, the particles hop to the right.
Along the lattice, particles can adsorb or desorb, and the right boundary is
defined by a wall particle. The confining wall particle has intrinsic forward
and backward hopping, a net leftward drift, and cannot desorb. Performing Monte
Carlo simulations and using a moving-frame finite segment approach coupled to
mean field theory, we find the parameter regimes in which the wall acquires a
steady state position. In other regimes, the wall will either drift to the left
and fall off the lattice at the injection site, or drift indefinitely to the
right. Our results are discussed in the context of non-equilibrium phases of
the system, fluctuating boundary layers, and particle densities in the lab
frame versus the frame of the fluctuating wall.Comment: 13 page
Traffic of Molecular Motors
Molecular motors perform active movements along cytoskeletal filaments and
drive the traffic of organelles and other cargo particles in cells. In contrast
to the macroscopic traffic of cars, however, the traffic of molecular motors is
characterized by a finite walking distance (or run length) after which a motor
unbinds from the filament along which it moves. Unbound motors perform Brownian
motion in the surrounding aqueous solution until they rebind to a filament. We
use variants of driven lattice gas models to describe the interplay of their
active movements, the unbound diffusion, and the binding/unbinding dynamics. If
the motor concentration is large, motor-motor interactions become important and
lead to a variety of cooperative traffic phenomena such as traffic jams on the
filaments, boundary-induced phase transitions, and spontaneous symmetry
breaking in systems with two species of motors. If the filament is surrounded
by a large reservoir of motors, the jam length, i.e., the extension of the
traffic jams is of the order of the walking distance. Much longer jams can be
found in confined geometries such as tube-like compartments.Comment: 10 pages, latex, uses Springer styles (included), to appear in the
Proceedings of "Traffic and Granular Flow 2005
Asymmetric Coupling in Two-Channel Simple Exclusion Processes
Simple exclusion processes for particles moving along two parallel lattices
and jumping between them are theoretically investigated for asymmetric rates of
transition between the channels. An approximate theoretical approach, that
describes the particle dynamics exactly in any vertical cluster of two parallel
sites and neglects the correlations between the different vertical clusters, is
applied to calculate stationary-state density profiles, currents and phase
diagrams. Surprisingly, it is found that asymmetry in the coupling between the
channels leads to a very complex phase behavior that is very different from
two-channel simple exclusion processes with symmetric coupling. There are seven
stationary-state phases in the simple exclusion processes with asymmetric
transition rates between the channels, in contrast to three phases found for
the systems with symmetric coupling. In addition, a new maximal-current phase
with a domain wall in the middle of the lattices, that has no analogs in other
exclusion processes, is observed. Although the explicit calculations are
presented only for the case of full asymmetry, when the particles can only jump
between the channels in one direction, the properties of two-channel simple
exclusion systems with general asymmetry are also discussed. Theoretical
predictions are in excellent agreement with extensive computer Monte Carlo
simulations.Comment: 12 pages, 6 figure
Cooperative Cargo Transport by Several Molecular Motors
The transport of cargo particles which are pulled by several molecular motors
in a cooperative manner is studied theoretically. The transport properties
depend primarily on the maximal number, , of motor molecules that may pull
simultaneously on the cargo particle. Since each motor must unbind from the
filament after a finite number of steps but can also rebind to it again, the
actual number of pulling motors is not constant but varies with time between
zero and . An increase in the maximal number leads to a strong increase
of the average walking distance (or run length) of the cargo particle. If the
cargo is pulled by up to kinesin motors, e.g., the walking distance is
estimated to be micrometers which implies that seven or eight
kinesin molecules are sufficient to attain an average walking distance in the
centimeter range. If the cargo particle is pulled against an external load
force, this force is shared between the motors which provides a nontrivial
motor-motor coupling and a generic mechanism for nonlinear force-velocity
relationships. With increasing load force, the probability distribution of the
instantenous velocity is shifted towards smaller values, becomes broader, and
develops several peaks. Our theory is consistent with available experimental
data and makes quantitative predictions that are accessible to systematic in
vitro experiments.Comment: 24 pages, latex, 6 figures, includes Supporting Tex
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