302 research outputs found
Effects of an embedding bulk fluid on phase separation dynamics in a thin liquid film
Using dissipative particle dynamics simulations, we study the effects of an
embedding bulk fluid on the phase separation dynamics in a thin planar liquid
film. The domain growth exponent is altered from 2D to 3D behavior upon the
addition of a bulk fluid, even though the phase separation occurs in 2D
geometry. Correlated diffusion measurements in the film show that the presence
of bulk fluid changes the nature of the longitudinal coupling diffusion
coefficient from logarithmic to algebraic dependence of 1/s, where s is the
distance between the two particles. This result, along with the scaling
exponents, suggests that the phase separation takes place through the Brownian
coagulation process.Comment: 6 pages, 5 figures. Accepted for publication in Europhys. Let
Maturation of biomimetic hydroxyapatite in physiological fluids: a physicochemical and proteomic study
Biomimetic calcium-deficient hydroxyapatite (CDHA) as a bioactive material exhibits exceptional intrinsic osteoinductive and osteogenic properties because of its nanostructure and composition, which promote a favorable microenvironment. Its high reactivity has been hypothesized to play a relevant role in the in vivo performance, mediated by the interaction with the biological fluids, which is amplified by its high specific surface area. Paradoxically, this high reactivity is also behind the in vitro cytotoxicity of this material, especially pro-nounced in static conditions. The present work explores the structural and physicochemical changes that CDHA undergoes in contact with physiological fluids and to investigate its interaction with proteins. Calcium-deficient hydroxyapatite discs with different micro/nanostructures, coarse (C) and fine (F), were exposed to cell-free complete culture medium over extended periods of time: 1, 7, 14, 21, 28, and 50 days. Precipitate formation was not observed in any of the materials in contact with the physiological fluid, which would indicate that the ionic exchanges were linked to incorporation into the crystal structure of CDHA or in the hydrated layer. In fact, CDHA experienced a maturation process, with a progressive increase in crystallinity and the Ca/P ratio, accompanied by an uptake of Mg and a B-type carbonation process, with a gradual propagation into the core of the samples. However, the reactivity of biomimetic hydroxyapatite was highly dependent on the specific surface area and was amplified in nanosized needle-like crystal structures (F), whereas in coarse specimens the ionic exchanges were restricted to the surface, with low penetration in the material bulk. In addition to showing a higher protein adsorption on F substrates, the proteomics study revealed the existence of protein selectivity to-ward F or C microstructures, as well as the capability of CDHA, and more remarkably of F-CDHA, to concentrate specific proteins from the culture medium. Finally, a substantial improvement in the material's ability to support cell proliferation was observed after the CDHA maturation process
Velocity autocorrelation function of a Brownian particle
In this article, we present molecular dynamics study of the velocity
autocorrelation function (VACF) of a Brownian particle. We compare the results
of the simulation with the exact analytic predictions for a compressible fluid
from [6] and an approximate result combining the predictions from hydrodynamics
at short and long times. The physical quantities which determine the decay were
determined from separate bulk simulations of the Lennard-Jones fluid at the
same thermodynamic state point.We observe that the long-time regime of the VACF
compares well the predictions from the macroscopic hydrodynamics, but the
intermediate decay is sensitive to the viscoelastic nature of the solvent.Comment: 7 pages, 6 figure
Coupled coarse graining and Markov Chain Monte Carlo for lattice systems
We propose an efficient Markov Chain Monte Carlo method for sampling
equilibrium distributions for stochastic lattice models, capable of handling
correctly long and short-range particle interactions. The proposed method is a
Metropolis-type algorithm with the proposal probability transition matrix based
on the coarse-grained approximating measures introduced in a series of works of
M. Katsoulakis, A. Majda, D. Vlachos and P. Plechac, L. Rey-Bellet and
D.Tsagkarogiannis,. We prove that the proposed algorithm reduces the
computational cost due to energy differences and has comparable mixing
properties with the classical microscopic Metropolis algorithm, controlled by
the level of coarsening and reconstruction procedure. The properties and
effectiveness of the algorithm are demonstrated with an exactly solvable
example of a one dimensional Ising-type model, comparing efficiency of the
single spin-flip Metropolis dynamics and the proposed coupled Metropolis
algorithm.Comment: 20 pages, 4 figure
On the variational limits of lattice energies on prestrained elastic bodies
We study the asymptotic behaviour of the discrete elastic energies in
presence of the prestrain metric , assigned on the continuum reference
configuration . When the mesh size of the discrete lattice in
goes to zero, we obtain the variational bounds on the limiting (in the sense of
-limit) energy. In case of the nearest-neighbour and
next-to-nearest-neibghour interactions, we derive a precise asymptotic formula,
and compare it with the non-Euclidean model energy relative to
Primary cilia elongation in response to interleukin-1 mediates the inflammatory response
Primary cilia are singular, cytoskeletal organelles present in the majority of mammalian cell types where they function as coordinating centres for mechanotransduction, Wnt and hedgehog signalling. The length of the primary cilium is proposed to modulate cilia function, governed in part by the activity of intraflagellar transport (IFT). In articular cartilage, primary cilia length is increased and hedgehog signaling activated in osteoarthritis (OA). Here, we examine primary cilia length with exposure to the quintessential inflammatory cytokine interleukin-1 (IL-1), which is up-regulated in OA. We then test the hypothesis that the cilium is involved in mediating the downstream inflammatory response. Primary chondrocytes treated with IL-1 exhibited a 50 % increase in cilia length after 3 h exposure. IL-1-induced cilia elongation was also observed in human fibroblasts. In chondrocytes, this elongation occurred via a protein kinase A (PKA)-dependent mechanism. G-protein coupled adenylate cyclase also regulated the length of chondrocyte primary cilia but not downstream of IL-1. Chondrocytes treated with IL-1 exhibit a characteristic increase in the release of the inflammatory chemokines, nitric oxide and prostaglandin E2. However, in cells with a mutation in IFT88 whereby the cilia structure is lost, this response to IL-1 was significantly attenuated and, in the case of nitric oxide, completely abolished. Inhibition of IL-1-induced cilia elongation by PKA inhibition also attenuated the chemokine response. These results suggest that cilia assembly regulates the response to inflammatory cytokines. Therefore, the cilia proteome may provide a novel therapeutic target for the treatment of inflammatory pathologies, including OA
Multi-Particle Collision Dynamics -- a Particle-Based Mesoscale Simulation Approach to the Hydrodynamics of Complex Fluids
In this review, we describe and analyze a mesoscale simulation method for
fluid flow, which was introduced by Malevanets and Kapral in 1999, and is now
called multi-particle collision dynamics (MPC) or stochastic rotation dynamics
(SRD). The method consists of alternating streaming and collision steps in an
ensemble of point particles. The multi-particle collisions are performed by
grouping particles in collision cells, and mass, momentum, and energy are
locally conserved. This simulation technique captures both full hydrodynamic
interactions and thermal fluctuations. The first part of the review begins with
a description of several widely used MPC algorithms and then discusses
important features of the original SRD algorithm and frequently used
variations. Two complementary approaches for deriving the hydrodynamic
equations and evaluating the transport coefficients are reviewed. It is then
shown how MPC algorithms can be generalized to model non-ideal fluids, and
binary mixtures with a consolute point. The importance of angular-momentum
conservation for systems like phase-separated liquids with different
viscosities is discussed. The second part of the review describes a number of
recent applications of MPC algorithms to study colloid and polymer dynamics,
the behavior of vesicles and cells in hydrodynamic flows, and the dynamics of
viscoelastic fluids
Littoral cell angioma of the spleen in a patient with previous pulmonary sarcoidosis: a TNF-α related pathogenesis?
<p>Abstract</p> <p>Background</p> <p>Littoral cell angioma (LCA) is a rare vascular tumor of the spleen. Generally thought to be benign, additional cases of LCA with malignant features have been described. Thus, its malignant potential seems to vary and must be considered uncertain. The etiology remains unclear, but an immune dysregulation for the apparent association with malignancies of visceral organs or immune-mediated diseases has been proposed.</p> <p>Case Presentation</p> <p>We report a case of LCA in a 43-year old male patient who presented with a loss of appetite and intermittent upper abdominal pain. Computed tomography showed multiple hypoattenuating splenic lesions which were hyperechogenic on abdominal ultrasound. Lymphoma was presumed and splenectomy was performed. Pathological evaluation revealed LCA.</p> <p>Conclusions</p> <p>LCA is a rare, primary vascular neoplasm of the spleen that might etiologically be associated with immune dysregulation. In addition, it shows a striking association with synchronous or prior malignancies. With about one-third of the reported cases to date being co-existent with malignancies of visceral organs or immune-mediated diseases, this advocates for close follow-ups in all patients diagnosed with LCA. To our knowledge, this report is the first one of LCA associated with previous pulmonary sarcoidosis and hypothesizes a TNF-α related pathogenesis of this splenic tumor.</p
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