13,180 research outputs found
INCREASING CONCENTRATION IN THE U.S. HARD WHEAT MILLING INDUSTRY
This research shows that increased concentration in the U.S. wheat milling industry has not led to noncompetive pricing in upstream or downstream markets. Increased concentration has helped to reduce the marketing margin by $0.65 for every 100 pounds of flour produced. This is about 7% of the average marketing margin.Crop Production/Industries, Industrial Organization,
Are Business Cycles All Alike?
This paper examines two questions. The first is whether economic fluctuations-business cycles-are due to an accumulation of nall shocks or instead mostly to infrequent large shocks. The paper concludes that neither of these two extreme views accurately characterize fluctuations. The second question is whether fluctuations are due mostly to one source of shocks, for example monetary, or instead to many sources. The paper concludes that evidence strongly supports the hypothesis of many, about equally important, sources of shocks.To analyze the empirical evidence and to reach these conclusions, the paper uses two different statistical approaches. The first is estimation ofa structural model, using a set of just identifying restrictions. The secondis non-structural and may be described as a formalization of the Burns Mitchell techniques. Both approaches are somewhat novel and should be of independent interest.
"Barber pole turbulence" in large aspect ratio Taylor-Couette flow
Investigations of counter-rotating Taylor-Couette flow (TCF) in the narrow
gap limit are conducted in a very large aspect ratio apparatus. The phase
diagram is presented and compared to that obtained by Andereck et al. The
spiral turbulence regime is studied by varying both internal and external
Reynolds numbers. Spiral turbulence is shown to emerge from the fully turbulent
regime via a continuous transition appearing first as a modulated turbulent
state, which eventually relaxes locally to the laminar flow. The connection
with the intermittent regimes of the plane Couette flow (pCf) is discussed
Stride-to-stride variability while backward counting among healthy young adults
BACKGROUND: Little information exists about the involvement of attention in the control of gait rhythmicity. Variability of both stride time and stride length is closely related to the control of the rhythmic stepping mechanism. We sought 1) to determine whether backward counting while walking could provoke significant gait changes in mean values and coefficients of variation of stride velocity, stride time and stride length among healthy young adults; and 2) to establish whether change in stride-to-stride variability could be related to dual-task related stride velocity change, attention, or both. METHODS: Mean values and coefficients of variation of stride velocity, stride time and stride length were recorded using the Physilog(Ÿ)-system, at a self-selected walking speed in 49 healthy young adults (mean age 24.1 ± 2.8 years, women 49%) while walking alone and walking with simultaneous backward counting. Performance on backward counting was evaluated by recording the number of figures counted while sitting alone and while walking. RESULTS: Compared with walking alone, a significant dual-task-related decrease was found for the mean values of stride velocity (p < 0.001), along with a small but significant increase for the mean values and coefficients of variation of stride time (p < 0.001 and p = 0.015, respectively). Stride length parameters did not change significantly between both walking conditions. Dual-task-related increase of coefficient of variation of stride time was explained by changing stride velocity and variability between subjects but not by backward counting. The number of figures counted while walking decreased significantly compared to backward counting alone. Further, the dual-task related decrease of the number of enumerated figures was significantly higher than the dual-task related decrease of stride velocity (p = 0.013). CONCLUSION: The observed performance-changes in gait and backward counting while dual tasking confirm that certain aspects of walking are attention-demanding in young adults. In the tested group of 49 young volunteers, dual tasking caused a small decrease in stride velocity and a slight increase in the stride-to-stride variability of stride time, while stride velocity variability was not affected by the attention-demanding task. The increase in stride time variability was apparently the result of a change in gait speed, but not a result of dual tasking. This suggests that young adults require minimal attention for the control of the rhythmic stepping mechanism while walking
The Stackelberg equilibrium as a consistent conjectural equilibrium
We consider a static game with conjectural variations where some firms make conjectures while others do not. Two propositions are proved. We first show that there exists a continuum of conjectural variations such that the conjectural equilibrium locally coincides with the Stackelberg equilibrium (Proposition 1). Second, we define the conditions under which a conjectural equilibrium is a locally consistent equilibrium (i.e. such that conjectures are fulfilled). The concept of (local) consistency is restricted to firms making conjectures. Two conditions on consistency are featured: consistency within a cohort and consistency among cohorts. The Stackelberg equilibrium fulfills only the latter condition (Proposition 2). An example is provided.Consistent conjectural variations, reaction functions, Stackelberg competition
Nonlinear wavelength selection in surface faceting under electromigration
We report on the control of the faceting of crystal surfaces by means of
surface electromigration. When electromigration reinforces the faceting
instability, we find perpetual coarsening with a wavelength increasing as
. For strongly stabilizing electromigration, the surface is stable.
For weakly stabilizing electromigration, a cellular pattern is obtained, with a
nonlinearly selected wavelength. The selection mechanism is not caused by an
instability of steady-states, as suggested by previous works in the literature.
Instead, the dynamics is found to exhibit coarsening {\it before} reaching a
continuous family of stable non-equilibrium steady-states.Comment: 5 pages, 4 figures, submitte
Do followers really matter in Stackelberg competition?
In this note, we consider a generalized Tâstage Stackelberg oligopoly. We provide a proof and an interpretation that under the two necessary and sufficient conditions of linear aggregate demand and identical constant marginal costs, followers do not matter for leaders. Leaders act as rational myopic agents, voluntarily ignoring the number of followers and remaining stages, thereby behaving as Cournotian oligopolists. Strategies of incumbent firms are invariant to entry of new cohorts. Their profits can be studied by the way of two discount factors: the first impacting markup and the second impacting output supply. Some implications in terms of welfare and convergence toward competitive equilibrium are derived.Leaderâs markup discount factor, linear economy, followerâs output discount factor, myopic behavior
Critical bubbles and implications for critical black strings
We demonstrate the existence of gravitational critical phenomena in higher
dimensional electrovac bubble spacetimes. To this end, we study linear
fluctuations about families of static, homogeneous spherically symmetric bubble
spacetimes in Kaluza-Klein theories coupled to a Maxwell field. We prove that
these solutions are linearly unstable and posses a unique unstable mode with a
growth rate that is universal in the sense that it is independent of the family
considered. Furthermore, by a double analytical continuation this mode can be
seen to correspond to marginally stable stationary modes of perturbed black
strings whose periods are integer multiples of the Gregory-Laflamme critical
length. This allow us to rederive recent results about the behavior of the
critical mass for large dimensions and to generalize them to the charged black
string case.Comment: A reference to unpublished work for the case q=2, by J. Hovdebo adde
Freezing Out Early Dark Energy
A phenomenological model of dark energy that tracks the baryonic and cold
dark matter at early times but resembles a cosmological constant at late times
is explored. In the transition between these two regimes, the dark energy
density drops rapidly as if it were a relic species that freezes out, during
which time the equation of state peaks at +1. Such an adjustment in the dark
energy density, as it shifts from scaling to potential-domination, could be the
signature of a trigger mechanism that helps explain the late-time cosmic
acceleration. We show that the non-negligible dark energy density at early
times, and the subsequent peak in the equation of state at the transition,
leave an imprint on the cosmic microwave background anisotropy pattern and the
rate of growth of large scale structure. The model introduces two new
parameters, consisting of the present-day equation of state and the redshift of
the freeze-out transition. A Monte Carlo Markov Chain analysis of a
ten-dimensional parameter space is performed to compare the model with
pre-Planck cosmic microwave background, large scale structure and supernova
data and measurements of the Hubble constant. We find that the transition
described by this model could have taken place as late as a redshift z~400. We
explore the capability of future cosmic microwave background and weak lensing
experiments to put tighter constraints on this model. The viability of this
model may suggest new directions in dark-energy model building that address the
coincidence problem.Comment: 11 pages, 15 figure
Modeling pedestrian evacuation movement in a swaying ship
With the advance in living standard, cruise travel has been rapidly expanding
around the world in recent years. The transportation of passengers in water has
also made a rapid development. It is expected that ships will be more and more
widely used. Unfortunately, ship disasters occurred in these years caused
serious losses. It raised the concern on effectiveness of passenger evacuation
on ships. The present study thus focuses on pedestrian evacuation features on
ships. On ships, passenger movements are affected by the periodical water
motion and thus are quite different from the characteristic when walking on
static horizontal floor. Taking into consideration of this special feature, an
agent-based pedestrian model is formulized and the effect of ship swaying on
pedestrian evacuation efficiency is investigated. Results indicated that the
proposed model can be used to quantify the special evacuation process on ships.Comment: Traffic and Granular Flow'15, At Delft, the Netherland
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