113 research outputs found
Permeability of a bubble assembly: From the very dry to the wet limit
We measure the permeability of a fluidized bed of monodispersed bubbles with
soap solution characteristic of mobile and non-mobile interfaces. These
experimental data extend the permeability curves previously published for foam
in the dry limit. In the wet limit, these data join the permeability curves of
a hard sphere suspension at porosity equal to 0.4 and 0.6 in the cases of
mobile and non-mobile interfaces respectively. We show that the model of
permeability proposed by Kozeny and Carman and originally validated for packed
beds of spheres (with porosity around 0.4) can be successfully applied with no
adjustable parameters to liquid fractions from 0.001 up to 0.85 for systems
made of monodisperse and deformable entities with non-mobile interfaces
Navier-Stokes transport coefficients of -dimensional granular binary mixtures at low density
The Navier-Stokes transport coefficients for binary mixtures of smooth
inelastic hard disks or spheres under gravity are determined from the Boltzmann
kinetic theory by application of the Chapman-Enskog method for states near the
local homogeneous cooling state. It is shown that the Navier-Stokes transport
coefficients are not affected by the presence of gravity. As in the elastic
case, the transport coefficients of the mixture verify a set of coupled linear
integral equations that are approximately solved by using the leading terms in
a Sonine polynomial expansion. The results reported here extend previous
calculations [V. Garz\'o and J. W. Dufty, Phys. Fluids {\bf 14}, 1476 (2002)]
to an arbitrary number of dimensions. To check the accuracy of the
Chapman-Enskog results, the inelastic Boltzmann equation is also numerically
solved by means of the direct simulation Monte Carlo method to evaluate the
diffusion and shear viscosity coefficients for hard disks. The comparison shows
a good agreement over a wide range of values of the coefficients of restitution
and the parameters of the mixture (masses and sizes).Comment: 6 figures, to be published in J. Stat. Phy
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
Molecular dynamics simulations of vibrated granular gases
We present molecular dynamics simulations of mono- or bidisperse inelastic
granular gases driven by vibrating walls, in two dimensions (without gravity).
Because of the energy injection at the boundaries, a situation often met
experimentally, density and temperature fields display heterogeneous profiles
in the direction perpendicular to the walls. A general equation of state for an
arbitrary mixture of fluidized inelastic hard spheres is derived and
successfully tested against numerical data. Single-particle velocity
distribution functions with non-Gaussian features are also obtained, and the
influence of various parameters (inelasticity coefficients, density...)
analyzed. The validity of a recently proposed Random Restitution Coefficient
model is assessed through the study of projected collisions onto the direction
perpendicular to that of energy injection. For the binary mixture, the
non-equipartition of translational kinetic energy is studied and compared both
to experimental data and to the case of homogeneous energy injection
(``stochastic thermostat''). The rescaled velocity distribution functions are
found to be very similar for both species
Scaling, Multiscaling, and Nontrivial Exponents in Inelastic Collision Processes
We investigate velocity statistics of homogeneous inelastic gases using the
Boltzmann equation. Employing an approximate uniform collision rate, we obtain
analytic results valid in arbitrary dimension. In the freely evolving case, the
velocity distribution is characterized by an algebraic large velocity tail,
P(v,t) ~ v^{-sigma}. The exponent sigma(d,epsilon), a nontrivial root of an
integral equation, varies continuously with the spatial dimension, d, and the
dissipation coefficient, epsilon. Although the velocity distribution follows a
scaling form, its moments exhibit multiscaling asymptotic behavior.
Furthermore, the velocity autocorrelation function decays algebraically with
time, A(t)= ~ t^{-alpha}, with a non-universal dissipation-dependent
exponent alpha=1/epsilon. In the forced case, the steady state Fourier
transform is obtained via a cumulant expansion. Even in this case, velocity
correlations develop and the velocity distribution is non-Maxwellian.Comment: 10 pages, 3 figure
Report of the 12th Liaison Meeting
The 12th Liaison meeting was held in Brussels on 8th and 9th October 2015 to address the following Terms
of Reference:
TOR 1. Discussion on possible follow-‐‑up to the main outputs/recommendations of:
• The 2015 RCMs -‐‑ specific recommendations addressed to the Liaison Meeting
• PGECON, PGDATA, PGMed – outcomes and recommendations from their 2015 meeting
• STECF EWG and STECF Plenary -‐‑ outcomes and recommendations from their 2015 meetings
• Data end users (ICES, STECF, RFMOs – GFCM, IATTC, ICCAT, IOTC, WCPFC, NAFO,
SPRFMO, CECAF, WECAFC)
TOR2. End user feedback on data transmission and related issues
• Discuss feedback received from data end-‐‑users on data transmission: main issues and possible
harmonization of end user feedback to the Commission
• JRC data transmission IT platform: experience gained and future steps
• Discuss best practices on automatization of data upload by MS: data validation tools used by
end users
• Discussion on new set-‐‑up for STECF evaluation of AR2014 & data transmission 2014 used in
2015 – continue like this next year?
• Harmonisation and dissemination of DCF metadata: codelists, metiers, nomenclatures, best
practices, standards
• RCM data calls – overview of how MS responded
TOR 3. Regional cooperation
• Call for proposals MARE/2014/19 'ʹStrengthening Regional Cooperation in the area of fisheries
data collection– state of play'ʹ. Presentation by a representative of the two RCG grants and
discussions by LM thereafter. What should be the way forward?
• Regional databases
• Overview of use of the Regional Databases for RCMs in 2015 and problems identified
• Other developments (RDB trainings in 2015, RDB Med&BS development)
• Changes for the future – any recommendations from the LM?
• Future role of RCMs and DCF-‐‑related meetings: best practices, coordination, cohesion and
common structure in line with emerging needs of DCF
TOR 4. EU MAP
• Discuss recommendations/ output of RCMs: List of proposed stocks, landing obligation, metiers
• Discuss design-‐‑based sampling in relation to DCF: does it fulfil DCF requirements?
TOR 5. Availability of data
• Overview of latest developments (DCF Database Feasibility Study and plans for a follow-‐‑up
study to this)
TOR 6. AOB
• Agree on a list of recommendations relating to DCF (that MS will need to report on in their
AR2015) – COM will provide a compilation of proposed recommendations from LM & STECF
Plenaries in 2014 as input
• Prepare a list of recommended meetings for 2016 as guidance for MS
• Review and prioritize DCF-‐‑related study proposals from RCMs, PGECON, EGs etc
• ICES update on workshop on concurrent sampling and plans to re-‐‑evaluate survey
NMR Experiments on a Three-Dimensional Vibrofluidized Granular Medium
A three-dimensional granular system fluidized by vertical container
vibrations was studied using pulsed field gradient (PFG) NMR coupled with
one-dimensional magnetic resonance imaging (MRI). The system consisted of
mustard seeds vibrated vertically at 50 Hz, and the number of layers N_ell <= 4
was sufficiently low to achieve a nearly time-independent granular fluid. Using
NMR, the vertical profiles of density and granular temperature were directly
measured, along with the distributions of vertical and horizontal grain
velocities. The velocity distributions showed modest deviations from
Maxwell-Boltzmann statistics, except for the vertical velocity distribution
near the sample bottom which was highly skewed and non-Gaussian. Data taken for
three values of N_ell and two dimensionless accelerations Gamma=15,18 were fit
to a hydrodynamic theory, which successfully models the density and temperature
profiles including a temperature inversion near the free upper surface.Comment: 14 pages, 15 figure
Granular fluid thermostatted by a bath of elastic hard spheres
The homogeneous steady state of a fluid of inelastic hard spheres immersed in
a bath of elastic hard spheres kept at equilibrium is analyzed by means of the
first Sonine approximation to the (spatially homogeneous) Enskog--Boltzmann
equation. The temperature of the granular fluid relative to the bath
temperature and the kurtosis of the granular distribution function are obtained
as functions of the coefficient of restitution, the mass ratio, and a
dimensionless parameter measuring the cooling rate relative to the
friction constant. Comparison with recent results obtained from an iterative
numerical solution of the Enskog--Boltzmann equation [Biben et al., Physica A
310, 308 (202)] shows an excellent agreement. Several limiting cases are also
considered. In particular, when the granular particles are much heavier than
the bath particles (but have a comparable size and number density), it is shown
that the bath acts as a white noise external driving. In the general case, the
Sonine approximation predicts the lack of a steady state if the control
parameter is larger than a certain critical value that
depends on the coefficient of restitution and the mass ratio. However, this
phenomenon appears outside the expected domain of applicability of the
approximation.Comment: 16 pages, 7 figures; minor changes; to be published in Phys. Rev.
Report of the 12th Liaison Meeting
The 12th Liaison meeting was held in Brussels on 8th and 9th October 2015 to address the following Terms
of Reference:
TOR 1. Discussion on possible follow-‐‑up to the main outputs/recommendations of:
• The 2015 RCMs -‐‑ specific recommendations addressed to the Liaison Meeting
• PGECON, PGDATA, PGMed – outcomes and recommendations from their 2015 meeting
• STECF EWG and STECF Plenary -‐‑ outcomes and recommendations from their 2015 meetings
• Data end users (ICES, STECF, RFMOs – GFCM, IATTC, ICCAT, IOTC, WCPFC, NAFO,
SPRFMO, CECAF, WECAFC)
TOR2. End user feedback on data transmission and related issues
• Discuss feedback received from data end-‐‑users on data transmission: main issues and possible
harmonization of end user feedback to the Commission
• JRC data transmission IT platform: experience gained and future steps
• Discuss best practices on automatization of data upload by MS: data validation tools used by
end users
• Discussion on new set-‐‑up for STECF evaluation of AR2014 & data transmission 2014 used in
2015 – continue like this next year?
• Harmonisation and dissemination of DCF metadata: codelists, metiers, nomenclatures, best
practices, standards
• RCM data calls – overview of how MS responded
TOR 3. Regional cooperation
• Call for proposals MARE/2014/19 'ʹStrengthening Regional Cooperation in the area of fisheries
data collection– state of play'ʹ. Presentation by a representative of the two RCG grants and
discussions by LM thereafter. What should be the way forward?
• Regional databases
• Overview of use of the Regional Databases for RCMs in 2015 and problems identified
• Other developments (RDB trainings in 2015, RDB Med&BS development)
• Changes for the future – any recommendations from the LM?
• Future role of RCMs and DCF-‐‑related meetings: best practices, coordination, cohesion and
common structure in line with emerging needs of DCF
TOR 4. EU MAP
• Discuss recommendations/ output of RCMs: List of proposed stocks, landing obligation, metiers
• Discuss design-‐‑based sampling in relation to DCF: does it fulfil DCF requirements?
TOR 5. Availability of data
• Overview of latest developments (DCF Database Feasibility Study and plans for a follow-‐‑up
study to this)
TOR 6. AOB
• Agree on a list of recommendations relating to DCF (that MS will need to report on in their
AR2015) – COM will provide a compilation of proposed recommendations from LM & STECF
Plenaries in 2014 as input
• Prepare a list of recommended meetings for 2016 as guidance for MS
• Review and prioritize DCF-‐‑related study proposals from RCMs, PGECON, EGs etc
• ICES update on workshop on concurrent sampling and plans to re-‐‑evaluate survey
Human Cryptochrome-1 Confers Light Independent Biological Activity in Transgenic Drosophila Correlated with Flavin Radical Stability
Cryptochromes are conserved flavoprotein receptors found throughout the biological kingdom with diversified roles in plant development and entrainment of the circadian clock in animals. Light perception is proposed to occur through flavin radical formation that correlates with biological activity in vivo in both plants and Drosophila. By contrast, mammalian (Type II) cryptochromes regulate the circadian clock independently of light, raising the fundamental question of whether mammalian cryptochromes have evolved entirely distinct signaling mechanisms. Here we show by developmental and transcriptome analysis that Homo sapiens cryptochrome - 1 (HsCRY1) confers biological activity in transgenic expressing Drosophila in darkness, that can in some cases be further stimulated by light. In contrast to all other cryptochromes, purified recombinant HsCRY1 protein was stably isolated in the anionic radical flavin state, containing only a small proportion of oxidized flavin which could be reduced by illumination. We conclude that animal Type I and Type II cryptochromes may both have signaling mechanisms involving formation of a flavin radical signaling state, and that light independent activity of Type II cryptochromes is a consequence of dark accumulation of this redox form in vivo rather than of a fundamental difference in signaling mechanism
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