337 research outputs found
Velocity distribution of fluidized granular gases in presence of gravity
The velocity distribution of a fluidized dilute granular gas in the direction
perpendicular to the gravitational field is investigated by means of Molecular
Dynamics simulations. The results indicate that the velocity distribution can
be exactly described neither by a Gaussian nor by a stretched exponential law.
Moreover, it does not exhibit any kind of scaling. In fact, the actual shape of
the distribution depends on the number of monolayers at rest, on the
restitution coefficient and on the height at what it is measured. The role
played by the number of particle-particle collisions as compared with the
number of particle-wall collisions is discussed
Energy fluctuations in vibrated and driven granular gases
We investigate the behavior of energy fluctuations in several models of
granular gases maintained in a non-equilibrium steady state. In the case of a
gas heated from a boundary, the inhomogeneities of the system play a
predominant role. Interpreting the total kinetic energy as a sum of independent
but not identically distributed random variables, it is possible to compute the
probability density function (pdf) of the total energy. Neglecting correlations
and using the analytical expression for the inhomogeneous temperature profile
obtained from the granular hydrodynamic equations, we recover results which
have been previously observed numerically and which had been attributed to the
presence of correlations. In order to separate the effects of spatial
inhomogeneities from those ascribable to velocity correlations, we have also
considered two models of homogeneously thermostated gases: in this framework it
is possible to reveal the presence of non-trivial effects due to velocity
correlations between particles. Such correlations stem from the inelasticity of
collisions. Moreover, the observation that the pdf of the total energy tends to
a Gaussian in the large system limit, suggests that they are also due to the
finite size of the system.Comment: 13 pages, 10 figure
Decorated vertices with 3-edged cells in 2D foams: exact solutions and properties
The energy, area and excess energy of a decorated vertex in a 2D foam are
calculated. The general shape of the vertex and its decoration are described
analytically by a reference pattern mapped by a parametric Moebius
transformation. A single parameter of control allows to describe, in a common
framework, different types of decorations, by liquid triangles or 3-sided
bubbles, and other non-conventional cells. A solution is proposed to explain
the stability threshold in the flower problem.Comment: 13 pages, 17 figure
Self-Similarity in Random Collision Processes
Kinetics of collision processes with linear mixing rules are investigated
analytically. The velocity distribution becomes self-similar in the long time
limit and the similarity functions have algebraic or stretched exponential
tails. The characteristic exponents are roots of transcendental equations and
vary continuously with the mixing parameters. In the presence of conservation
laws, the velocity distributions become universal.Comment: 4 pages, 4 figure
Review of the catch and catch-at-age estimation for the E-BFT catch inflated estimates 1998-2007
During the 2022 Eastern Atlantic and Mediterranean Bluefin Tuna Data Preparatory Meeting, the Bluefin Species Group (BFTSG) agreed to revise the assumptions and update the catch-atsize/catch-at-age (CAS/CAA) intersessionally by replacing the "NEI (inflated)" partial catches component (1998-2007) with a new set of combined Mediterranean size samples. An ad-hoc small group was formed to carry out this task and proposed an alternative CAS/CAA for the 2022 E-BFT stock assessment, this document summarizes these analyses. This document provides the revised CAS (version 2b), and two CAA based on the von Bertalanffy and the Richards growth
curves. The small group agreed that this revised CAS is a better estimate of the size distribution for the NEI-inflated catch and proposed to be adopted by the BFTSG, and aso recommended that this revision would be applied only to VPA (Virtual Population Analysis) and possibly ASAP (Age Structured Assessment Program)
Velocity correlations in dense granular gases
We report the statistical properties of spherical steel particles rolling on
an inclined surface being driven by an oscillating wall. Strong dissipation
occurs due to collisions between the particles and rolling and can be tuned by
changing the number density. The velocities of the particles are observed to be
correlated over large distances comparable to the system size. The distribution
of velocities deviates strongly from a Gaussian. The degree of the deviation,
as measured by the kurtosis of the distribution, is observed to be as much as
four times the value corresponding to a Gaussian, signaling a significant
breakdown of the assumption of negligible velocity correlations in a granular
system.Comment: 4 pages, 4 Figure
Final data, explorations, model set-up and diagnostics for the 2022 VPA stock assessment of the eastern and Mediterranean Atlantic bluefin tuna stock
This document presents the modeling work done for the 2022 stock assessment for the Eastern and Mediterranean Bluefin tuna stock, during informal modeling subgroup meetings in June 2022. This document presents various runs built upon the base case for the 2017 stock assessment. These runs aim at addressing issues identified in the 2020 update assessment and aspects discussed during the
informal meetings held in june 2022, regarding the inclusion of updated catch at age data, improvement of model stability in relation to Fratio estimates, the selection of the age for the plus group, inclusion of the WMED_GBYP_AER index. Following several explorations, the present work contains two runs that displayed improved diagnostics compared to previous runs. These models have improved retrospective patterns and no problematic issue was found through jittering the random number generator, jittering the starting values for the terminal F estimate, bootstrapping
or through jackknife analysis
Entropic Tightening of Vibrated Chains
We investigate experimentally the distribution of configurations of a ring
with an elementary topological constraint, a ``figure-8'' twist. Using vibrated
granular chains, which permit controlled preparation and direct observation of
such a constraint, we show that configurations where one of the loops is tight
and the second is large are strongly preferred. This agrees with recent
predictions for equilibrium properties of topologically-constrained polymers.
However, the dynamics of the tightening process weakly violate detailed
balance, a signature of the nonequilibrium nature of this system.Comment: 4 pages, 4 figure
Data and initial model set-up for the 2022 VPA stock assessment of the eastern Atlantic and Mediterranean bluefin tuna
This document presents the data and initial model set-up for the 2022 Stock Assessment for the
Eastern Atlantic and Mediterranean bluefin tuna stock. During the 2017 Data Preparatory
meetings, several changes in the data used for previous assessments have been presented, among
which the revision of the Task 1 and Task 2 statistics and the selection of the indices of abundance.
This led to completely revisiting the catch at age matrix and the model specifications for the 2017
assessment. For the present document, the data over the historical period (1968-2015) were
nearly identical, whereas the data for the years 2016-2020 and abundance indices were updated.
As agreed in previous meetings, the initial model specifications were kept identical to the 2017
assessment as no change has been agreed on since then
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