89 research outputs found
Reduced model for droplet dynamics in shear flows at finite capillary numbers
No full textWe propose an extension of the Maffettone-Minale (MM) model to predict droplet dynamics in shear flow. The parameters of the MM model are traditionally retrieved in the framework of the perturbation theory for small deformations, i.e., small capillary numbers (Ca << 1) applied to Stokes equations. In this work, we take a novel route, in that we determine the model parameters at finite capillary numbers (Ca - O(1)) without relying on perturbation theory results, while retaining a realistic representation in loading time and steady deformation attained by the droplet for different realizations of the viscosity ratio lambda between the inner and the outer fluids. This extended MM (EMM) model hinges on an independent characterization of the process of droplet deformation via fully three-dimensional numerical simulations of Stokes equations employing the immersed boundary-lattice Boltzmann numerical techniques. Issues on droplet breakup are also addressed and discussed within the EMM model
Droplet dynamics in homogeneous isotropic turbulence with the immersed boundary–lattice Boltzmann method
No full textWe develop a numerical method for simulating the dynamics of a droplet immersed in a generic time-dependent velocity gradient field. This approach is grounded on the hybrid coupling between the lattice Boltzmann (LB) method, employed for the flow simulation, and the immersed boundary (IB) method, utilized to couple the droplet with the surrounding fluid. We show how to enrich the numerical scheme with a mesh regularization technique, allowing droplets to sustain large deformations. The resulting methodology is adapted to simulate the dynamics of droplets in homogeneous and isotropic turbulence, with the characteristic size of the droplet being smaller than the characteristic Kolmogorov scale of the outer turbulent flow. We report statistical results for droplet deformation and orientation collected from an ensemble of turbulent trajectories, as well as comparisons with theoretical models in the limit of small deformation
Projective Invariance of Dual-Resonance Models from Spin Analyticity and Lorentz Invariance
No full textOn the Transformation Functions from the jm-Basis to the z-Basis for the Unitary Representations of SL_2C
No full textDeformation of ellipsoidal droplets in homogeneous and isotropic turbulence
No full textWe study the statistics of deformation of neutrally buoyant droplets in homogeneous isotropic turbulence (HIT), wherein the characteristic droplet size R is smaller than the characteristic Kolmogorov scale eta of the turbulent flow. We systematically focus on the characterization of droplet deformation statistics obtained with various phenomenological (reduced-order) ellipsoidal models (EMs)-assuming that the droplet preserves the ellipsoidal shape at all times-with the droplet moving as a passive tracer in the turbulent flow. The predictions of the EMs are compared with ground-truth data obtained with three-dimensional fully resolved simulations without any ad hoc assumption on the droplet shape. Our work helps in elucidating the applicability of the EMs in describing droplet deformation in HIT at changing the capillary number Ca = tau sigma/tau eta, weighting the relative importance of the droplet characteristic time tau sigma with respect to the turbulent flow characteristic time tau eta
METHYLPREDNISOLONE ESTER OF HYALURONAN AS A DELIVERY SYSTEM: PROTEIN RESISTANCE, CELL ADHESION AND DRUG RELEASE
No full textShort-range structure of solid and liquid AgBr determined by multiple-edge X-ray Absorption Spectroscopy
No full textX-ray absorption measurements of solid and liquid AgBr in the T = 30-927 K range of temperature have been performed using synchrotron radiation. Accurate short-range structural parameters are determined using simultaneous Ag and Br K-edge EXAFS refinement in the framework of the GNXAS method for data analysis. Results are discussed in light of the peculiar structural and ionic conduction properties of AgBr and taking into account previous x-ray, neutron diffraction (ND), molecular-dynamics (MD), and EXAFS results. Detailed information about the asymmetry of the first-neighbor g(r) distribution is given, showing that anharmonic effects are important even at moderate temperatures. The foot and the most probable value of the first neighbor g(r) are found to shift up to about 0.25 Å toward shorter distances from 30 K to 670 K, while the long-range part of the distribution broadens at high temperatures. The average bondlength is found to be in agreement with known thermal expansion diffraction data correcting previous EXAFS results. Accurate EXAFS measurements of liquid AgBr as a function of temperature are presented and compared with existing ND and MD structural models. The reconstructed EXAFS signals related to previous structural models are shown to differ considerably with present experimental data, due to the extreme EXAFS sensitivity to short-range correlations. The first-neighbor peak of the Ag-Br partial distribution function is accurately determined in this work. The short-distance side of the distribution, probing the repulsive part of the interaction, shows a steeper onset located at about 2.4 Å, clearly shifted toward shorter distances with respect to previous broader MD simulations. The reconstructed g(r) broadens gradually at higher temperatures (up to 927 K). Existence of short-range Ag-Ag correlations resulting in a well-defined Ag-Ag short-distance peak in solid and liquid AgBr as suggested by recent ND reverse Monte Carlo data analysis is not confirmed
LATTICE GAUGE FIXING FOR PARAMETER DEPENDENT COVARIANT GAUGES.
No full textWe propose a nonperturbative procedure to fix generic covariant gauges on the lattice. Varying the gauge parameter, this gauge fixing provides a concrete method to check numerically the gauge dependence of correlators measured on the lattice. The new algorithm turns out to converge with a good efficiency. As a preliminary physical result, we find a sensitive dependence of the gluon propagator on the gauge parameter. ©2000 The American Physical Society
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