Radial distribution function of Lennard-Jones fluids in shear flows from intermediate asymptotics

Determining the microstructure of colloidal suspensions under shear flows has been a challenge for theoreticaland computational methods due to the singularly perturbed boundary-layer nature of the problem. Previousapproaches have been limited to the case of hard-sphere systems and suffer from various limitations in theirapplicability. We present an alternative analytic scheme based on intermediate asymptotics which solves theSmoluchowski diffusion-convection equation including both intermolecular and hydrodynamic interactions. Themethod is able to recover previous results for the hard-sphere fluid and to predict the radial distribution function(rdf) of attractive fluids such as the Lennard-Jones (LJ) fluid. In particular, a new depletion effect is predictedin the rdf of the LJ fluid under shear. This method can be used for the theoretical modeling and understandingof real fluids subjected to flow, with applications ranging from chemical systems to colloids, rheology, plasmas,and atmospherical science

IMPACT OF TURBULENCE MODELING ON FLUID/SOLID HEAT TRANSFER INSIDE INDUSTRIAL AUTOCLAVES

This work is centred on the analysis of the impact of different turbulence modeling approaches on the fluid/solid heat exchange inside a commercial size autoclave. This project proposes itself to be a first step towards the optimization of the turbulent flow inside this kind of machinery to improve the curing treatment of Carbon-Fiber Reinforced Plastics (CFRP). The setup of the CFD simulations includes the presence of a metallic sample object inside the autoclave, where air will be recirculated with velocity, pressure and temperature typically adopted for this type of treatments. The analysis takes advantage of parallel CFD simulations, conducted by using the open-source software openFOAM v2106. Two turbulence models have been adopted: one is the well-known Reynolds-Average Navier-Stokes approach (RANS), which is currently used to model the turbulence inside this type of machinery. The second one is the Delayed Detached Eddy Simulations (DDES), which allows the full resolution of the majority of turbulent scales around the sample object. First, we propose the difference between the local heat flux distribution at the air/solid interface computed by using RANS and DDES, next we analyse the overall heat flux entering the sample object: the resolution of the turbulent scales does not influence the local heat flux only, but also the overall heat flux entering the object; an average increase of 35% is reported when the velocity fluctuations are neglected. Future steps of the research foresee the analysis of the heat flux and temperature distributions on the surface of realistic shapes and common-use CFRP. Afterwards, the autoclave design will be optimized by adding multiple inlets and aerodynamic devices to guarantee a more homogeneous heat flux distribution on the surface of realistic shapes of actual CFRP

Live-cell super-resolution microscopy reveals a primary role for diffusion in polyglutamine-driven aggresome assembly

The mechanisms leading to self-assembly of misfolded proteins into amyloid aggregates have been studied extensively in the test tube under well-controlled conditions. However, to what extent these processes are representative of those in the cellular environment remains unclear. Using super-resolution imaging of live cells, we show here that an amyloidogenic polyglutamine-containing protein first forms small, amorphous aggregate clusters in the cytosol, chiefly by diffusion. Dynamic interactions among these clusters limited their elongation and led to structures with a branched morphology, differing from the predominantly linear fibrils observed in vitro. Some of these clusters then assembled via active transport at the microtubule-organizing center and thereby initiated the formation of perinuclear aggresomes. Although it is widely believed that aggresome formation is entirely governed by active transport along microtubules, here we demonstrate, using a combined approach of advanced imaging and mathematical modeling, that diffusion is the principal mechanism driving aggresome expansion. We found that the increasing surface area of the expanding aggresome increases the rate of accretion caused by diffusion of cytosolic aggregates and that this pathway soon dominates aggresome assembly. Our findings lead to a different view of aggresome formation than that proposed previously. We also show that aggresomes mature over time, becoming more compacted as the structure grows. The presence of large perinuclear aggregates profoundly affects the behavior and health of the cell, and our super-resolution imaging results indicate that aggresome formation and development are governed by highly dynamic processes that could be important for the design of potential therapeutic strategies

Two Years of Arc-Tunnel Experience at Centrospazio", 3 rd European Symposium on Aerothermodynamics for Space Vehicles

Centrospazio has recently developed a small archeated wind tunnel (High Enthalpy Arc-heated Tunnel, HEAT) whose flexible configuration is particularly suited for cost-effective experimentation and research on a wide variety of aerothermodynamic phenomena occurring in high speed flows. The design and operation of the HEAT has involved a number of critical aspects, ranging from the feasibility and realisation of the proposed concept, to the effectiveness and performance of pulsed arc tunnels for hypersonic aerothermodynamic testing and the applicability of the necessary instrumentation in the hostile environment of the tunnel test section. The present article reviews some of the experience and results recently got a

Predictive model of polymer reaction kinetics and coagulation behavior in seeded emulsion co- and ter-polymerizations

A mathematical model to describe the emulsion polymerization kinetics of co- and ter-polymerizations is developed. The model uses the well-known pseudo-homopolymerization approach together with recently developed models for radical entry and desorption in order to monitor crucial kinetic variables such as conversion and latex composition. The model includes a series of unknown parameters related to monomer-specific gel-effect coefficients, that are needed to compute the bimolecular termination reaction rates. The unknown parameters are determined through extensive calibration of the model on literature data for homo- and co-polymerizations of n-butyl acrylate (n-BA) and methyl methacrylate (MMA). The so-obtained predictive model is then applied to the modelling of the ter-polymerization of n-BA and MMA with 2-hydroxyethyl methacrylate (2-HEMA) with sodium persulphate (SPR) as initiator: predictions for the time-evolution of particle size and conversion are in excellent agreement with experimental measurements using Dynamic Light Scattering (DLS) and Gas Chromatography (GC), upon tuning the gel-effect coefficient related to 2-HEMA. The developed model is used to quantify the surfactant surface coverage of the particles as well as the total concentration of counterions in the system throughout the entire polymerization process. This key information provides a way to rationalize and control the coagulation behavior during the whole polymerization process

Homogenization of turbulent flows inside industrial environments: an application to the curing of Carbon Fiber Reinforced Polymers

This work proposes a study of turbulence homogenization inside large industrial environments, with a first application to the curing treatment of Carbon-Fiber-Reinforced Polymers, which are composite materials widely spread in the aerospace industry. The state-of-the-art design of these machineries causes a highly anisotropic turbulent flow, that leads to an heterogeneous heat exchange between the air and the mold containing the material to be treated, which causes the curing procedure to be inhomogeneous. Aim of this work is to propose innovative methods to homogenize the turbulence inside a 16 m3 autoclave and analyse their impact on the air/mold heat exchange under different operating conditions. The first designs include the addition of random (both in location and number) velocity perturbations generated at the walls of the chamber. The impact of these sources has been examined by conducting hybrid DNS-LES simulations in an empty chamber where the circulating flow has a Reynolds number Re = O(106); the computational analysis has been carried out by using the open-source software PLUTO 4.4.2. Aim of this analysis is the mapping of the kinetic energy and enstrhophy inside the system,together with the distribution of a tracer within the chamber. Afterwards, the impact of the velocity perturbations is analysed by simulating different stages of a realistic curing scenario, where a rectangular mold made of steel is located inside the chamber. It will be showed that a more homogeneous turbulence leads to an improvement of the heat flux distribution uniformity on the surface of the solid sample

Extended Charge-On-Particle Optimized Potentials for Liquid Simulation Acetone Model: The Case of Acetone–Water Mixtures

It is well-known that classical molecular dynamics simulations of acetone–water mixtures lead to a strong phase separation when using most of the standard all-atom force fields, despite the well-known experimental fact that acetone is miscible with water in any proportion at room temperature. We describe here the use of a charge-on-particle model for accounting for the induced polarization effect in acetone–water mixtures which can solve the demixing problem at all acetone molar fractions. The polarizability effect is introduced by means of a virtual site (VS) on the carbonyl group of the acetone molecule, which increases its dipole moment and leads to a better affinity with water molecules. The VS parameter is set by fitting the density of the mixture at different acetone molar fractions. The main novelty of the VS approach lies on the transferability and universality of the model because the polarizability can be controlled without modifying the force field adopted, like previous efforts did. The results are satisfactory also in terms of the transport properties, that is, diffusivity and viscosity coefficients of the mixture

Live-cell super-resolution microscopy reveals a primary role for diffusion in polyglutamine-driven aggresome assembly

The mechanisms leading to self-assembly of misfolded proteins into amyloid aggregates have been studied extensively in the test tube under well-controlled conditions. However, to what extent these processes are representative of those in the cellular environment remains unclear. Using super-resolution imaging of live cells, we show here that an amyloidogenic polyglutamine-containing protein first forms small, amorphous aggregate clusters in the cytosol, chiefly by diffusion. Dynamic interactions among these clusters limited their elongation and led to structures with a branched morphology, differing from the predominantly linear fibrils observed in vitro Some of these clusters then assembled via active transport at the microtubule-organizing center and thereby initiated the formation of perinuclear aggresomes. Although it is widely believed that aggresome formation is entirely governed by active transport along microtubules, here we demonstrate, using a combined approach of advanced imaging and mathematical modeling, that diffusion is the principal mechanism driving aggresome expansion. We found that the increasing surface area of the expanding aggresome increases the rate of accretion caused by diffusion of cytosolic aggregates and that this pathway soon dominates aggresome assembly. Our findings lead to a different view of aggresome formation than that proposed previously. We also show that aggresomes mature over time, becoming more compacted as the structure grows. The presence of large perinuclear aggregates profoundly affects the behavior and health of the cell, and our super-resolution imaging results indicate that aggresome formation and development are governed by highly dynamic processes that could be important for the design of potential therapeutic strategies