57 research outputs found
Hydrodynamics of driven granular gases
Hydrodynamic equations for granular gases driven by the Fokker-Planck
operator are derived. Transport coefficients appeared in Navier-Stokes order
change from the values of a free cooling state to those of a steady state.Comment: 5 pages, 3 figure
A numerical study of the Navier-Stokes transport coefficients for two-dimensional granular hydrodynamics
A numerical study that aims to analyze the thermal mechanisms of unsteady, supersonic granular flow by means of hydrodynamic simulations of the NavierâStokes granular equation is reported in this paper. For this purpose, a paradigmatic problem in granular dynamics such as the Faraday instability is selected. Two different approaches for the NavierâStokes transport coefficients for granular materials are considered, namely the traditional JenkinsâRichman theory for moderately dense quasi-elastic grains and the improved GarzĂłâDuftyâLutsko theory for arbitrary inelasticity, which we also present here. Both the solutions are compared with event-driven simulations of the same system under the same conditions, by analyzing the density, temperature and velocity field. Important differences are found between the two approaches, leading to interesting implications. In particular, the heat transfer mechanism coupled to the density gradient, which is a distinctive feature of inelastic granular gases, is responsible for a major discrepancy in the temperature field and hence in the diffusion mechanisms
Golexanolone improves fatigue, motor incoordination and gait and memory in rats with bile duct ligation
\ua9 2023 The Authors. Liver International published by John Wiley & Sons Ltd.Background and Aims: Many patients with the chronic cholestatic liver disease primary biliary cholangitis (PBC) show fatigue and cognitive impairment that reduces their quality of life. Likewise, rats with bile duct ligation (BDL) are a model of cholestatic liver disease. Current PBC treatments do not improve symptomatic alterations such as fatigue or cognitive impairment and new, more effective treatments are therefore required. Golexanolone reduces the potentiation of GABAA receptors activation by neurosteroids. Golexanolone reduces peripheral inflammation and neuroinflammation and improves cognitive and motor function in rats with chronic hyperammonemia. The aims of the present study were to assess if golexanolone treatment improves fatigue and cognitive and motor function in cholestatic BDL rats and if this is associated with improvement of peripheral inflammation, neuroinflammation, and GABAergic neurotransmission in the cerebellum. Methods: Rats were subjected to bile duct ligation. One week after surgery, oral golexanolone was administered daily to BDL and sham-operated controls. Fatigue was analysed in the treadmill, motor coordination in the motorater, locomotor gait in the Catwalk, and short-term memory in the Y-maze. We also analysed peripheral inflammation, neuroinflammation, and GABAergic neurotransmission markers by immunohistochemistry and Western blot. Results: BDL induces fatigue, impairs memory and motor coordination, and alters locomotor gait in cholestatic rats. Golexanolone improves these alterations, and this was associated with improvement of peripheral inflammation, neuroinflammation, and GABAergic neurotransmission in the cerebellum. Conclusion: Golexanolone may have beneficial effects to treat fatigue, and motor and cognitive impairment in patients with the chronic cholestatic liver disease PBC
Studies of Mass and Size Effects in Three-Dimensional Vibrofluidized Granular Mixtures
We examine the steady state properties of binary systems of driven inelastic
hard spheres. The spheres, which move under the influence of gravity, are
contained in a vertical cylinder with a vibrating base. We computed the
trajectories of the spheres using an event-driven molecular dynamics algorithm.
In the first part of the study, we chose simulation parameters that match those
of experiments performed by Wildman and Parker. Various properties computed
from the simulation including the density profile, granular temperature and
circulation pattern are in good qualitative agreement with the experiments. We
then studied the effect of varying the mass ratio and the size ratio
independently while holding the other parameters constant. The mass and size
ratio are shown to affect the distribution of the energy. The changes in the
energy distributions affect the packing fraction and temperature of each
component. The temperature of the heavier component has a non-linear dependence
on the mass of the lighter component, while the temperature of the lighter
component is approximately proportional to its mass. The temperature of both
components is inversely dependent on the size of the smaller component.Comment: 14 Pages, 12 Figures, RevTeX
A model for the atomic-scale structure of a dense, nonequilibrium fluid: the homogeneous cooling state of granular fluids
It is shown that the equilibrium Generalized Mean Spherical Model of fluid
structure may be extended to nonequilibrium states with equation of state
information used in equilibrium replaced by an exact condition on the two-body
distribution function. The model is applied to the homogeneous cooling state of
granular fluids and upon comparison to molecular dynamics simulations is found
to provide an accurate picture of the pair distribution function.Comment: 29 pages, 11 figures Revision corrects formatting of the figure
Self-diffusion in dense granular shear flows
Diffusivity is a key quantity in describing velocity fluctuations in granular
materials. These fluctuations are the basis of many thermodynamic and
hydrodynamic models which aim to provide a statistical description of granular
systems. We present experimental results on diffusivity in dense, granular
shear in a 2D Couette geometry. We find that self-diffusivities are
proportional to the local shear rate with diffusivities along the mean flow
approximately twice as large as those in the perpendicular direction. The
magnitude of the diffusivity is D \approx \dot\gamma a^2 where a is the
particle radius. However, the gradient in shear rate, coupling to the mean
flow, and drag at the moving boundary lead to particle displacements that can
appear sub- or super-diffusive. In particular, diffusion appears superdiffusive
along the mean flow direction due to Taylor dispersion effects and subdiffusive
along the perpendicular direction due to the gradient in shear rate. The
anisotropic force network leads to an additional anisotropy in the diffusivity
that is a property of dense systems with no obvious analog in rapid flows.
Specifically, the diffusivity is supressed along the direction of the strong
force network. A simple random walk simulation reproduces the key features of
the data, such as the apparent superdiffusive and subdiffusive behavior arising
from the mean flow, confirming the underlying diffusive motion. The additional
anisotropy is not observed in the simulation since the strong force network is
not included. Examples of correlated motion, such as transient vortices, and
Levy flights are also observed. Although correlated motion creates velocity
fields qualitatively different from Brownian motion and can introduce
non-diffusive effects, on average the system appears simply diffusive.Comment: 13 pages, 20 figures (accepted to Phys. Rev. E
Hydrodynamics and transport coefficients for Granular Gases
The hydrodynamics of granular gases of viscoelastic particles, whose
collision is described by an impact-velocity dependent coefficient of
restitution, is developed using a modified Chapman-Enskog approach. We derive
the hydrodynamic equations and the according transport coefficients with the
assumption that the shape of the velocity distribution function follows
adiabatically the decaying temperature. We show numerically that this
approximation is justified up to intermediate dissipation. The transport
coefficients and the coefficient of cooling are expressed in terms of the
elastic and dissipative parameters of the particle material and by the gas
parameters. The dependence of these coefficients on temperature differs
qualitatively from that obtained with the simplifying assumption of a constant
coefficient of restitution which was used in previous studies. The approach
formulated for gases of viscoelastic particles may be applied also for other
impact-velocity dependencies of the restitution coefficient.Comment: 16 pages, 4 figure
Validation of UVEDAI: An Index for Evaluating the Level of Inflammatory Activity in Uveitis
Introduction
Uveitis is the inflammation of the middle layer of the eye, the uvea, and is a major cause of blindness. None of the instruments used in clinical practice are, in themselves, sufficient to evaluate the course of uveitis. Therefore, it is necessary to develop instruments enabling standardized measurement of inflammatory activity. We developed a composite disease activity index for patients with uveitis known as UVEDAI, which considers the overall activity of the eye. The objective of this study was to validate the composite index of ocular inflammation, UVEDAI.
Methods
A multicenter cross-sectional study involving eight Spanish tertiary hospitals. Sixty-two patients agedââ„â18 years with acute uveitis were recruited. Participants gave informed consent before participating in the study. A full ophthalmological examination was performed by two ophthalmologists to determine inflammatory activity: one used the UVEDAI score and the other used clinical judgment. The ophthalmologists did not share their findings with each other to avoid introducing bias into the analysis. Construct validity was established by means of factor analysis. The criterion validity of the index was determined using an ordinal multivariate regression model, in which the dependent variable was the degree of uveal inflammation (mild, moderate, or high/severe). Cut-off points were determined for the UVEDAI and for the receiver operating characteristic (ROC) curves.
Results
Sixty-two patients were included. Total variance with the three components accounted for 80.32% of the construct validity. Each of the three components identified one type of eye involvement. The discriminatory capacity of UVEDAI was 0.867 (95% CI 0.778; 0.955 pâ<â0.001) for mild versus moderateâhigh and 0.946 (95% CI 0.879; 1.000 pâ<â0.001) for high versus mildâmoderate.
Conclusions
The variables included in UVEDAI enable ocular inflammatory activity to be described with a high degree of accuracy. The index may be used to evaluate and classify this activity with considerable discriminatory power.We would like to acknowledge the support of Abbvie: this study was conducted with an unrestricted grant from Abbvie. The Spanish Society of Rheumatology is the sponser and funder of this study and the journal's Rapid Service Fee, and has participated in the study design; in the analysis, and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication. The corresponding author had full access to all study data and had final responsibility for the decision to submit the manuscript for publication
Correlation of spin and velocity in the homogeneous cooling state of a granular gas of rough particles
Morphology and distribution of the external labial sensilla in Fulgoromorpha (Insecta: Hemiptera)
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