Motion of a rod-like particle between parallel walls with application to suspension rheology

We study the dynamics of elongated axisymmetric particles undergoing shear flow between two parallel planar walls, under creeping-flow conditions. Particles are modeled as linear chains of touching spheres and it is assumed that walls are separated by a distance comparable to particle length. The hydrodynamic interactions of the chains with the walls are evaluated using our Cartesian-representation algorithm Bhattacharya et al., Physica A 356, 294–340 2005b . We find that when particles are far from both walls in a weakly confined system, their trajectories are qualitatively similar to Jeffery orbits in unbounded space. In particular, the periods of the orbits and the evolution of the azimuthal angle in the flow-gradient plane are nearly independent of the initial orientation of the particle. For stronger confinements, however, i.e., when the particle is close to one or both walls a significant dependence of the angular evolution on the initial particle configuration is observed. The phases of particle trajectories in a confined dilute suspension subject to a sudden onset of shear flow are thus slowly randomized due to unequal trajectory periods, even in the absence of interparticle hydrodynamic interactions. Therefore, stress oscillations associated with initially coherent particle motions decay with time. The effect of near contact particle-wall interactions on the suspension behavior is also discussed

Study of the enzymatic activity inhibition on the saccharification of acid pretreated corn stover

The inhibition of the enzymatic saccharification of acid pretreated corn stover (PCS) biomass due to several compounds either present in PCS or produced during saccharification has been studied. The prospective inhibitors tested were glucose ( 110 g L1 ), celobiose ( 24 g L1 ), xylose ( 50 g L1 ), arabinose ( 1.5 g L1 ), furfural ( 2gL1 ), hydroxymethylfurfural ( 1gL1 ), acetic acid ( 4gL1 ), and lignin ( 50 g L1 ). Each of these compounds was added at three different concentrations, being the concentration intervals different according to standard maximum concentrations of such compounds in the reaction medium, previously measured and described in literature. In addition, these experiments were employed to evaluate the standard error present during the evaluation of the results obtained in the inhibition reactions. Those results show that significant inhibition was only detected for lignin (more than 25 g L1 ) and it was also appreciable for glucose at high concentrations (above 75 g L1 ), although it was not remarkable at medium concentrations (40 g L1 ). On the other hand, neither of the remaining compounds tested presented any significant inhibitory effect at the usual process concentration range

Numerical Analysis of Degradation and Capacity Loss in Graphite Active Particles of Li-Ion Battery Anodes

It is well known that the performance and durability of lithium-ion batteries (LIBs) can be severely impaired by fracture events that originate in stresses due to Li ion diffusion in fast charge–discharge cycles. Existing models of battery damage overlook either the role of particle shape in stress concentration, the effect of material disorder and preexisting defects in crack initiation and propagation, or both. In this work we present a novel, three-dimensional, and coupled diffusive-mechanical numerical model that simultaneously accounts for all these phenomena by means of (i) a random particle generator and (ii) a stochastic description of material properties implemented within the lattice method framework. Our model displays the same complex fracture patterns that are found experimentally, including crack nucleation, growth, and branching. Interestingly, we show that irregularly shaped active particles can suffer mechanical damage up to 60% higher than that of otherwise equivalent spherical particles, while material defects can lead to damage increments of up to 110%. An evaluation of fracture effects in local Li-ion diffusivity shows that effective diffusion can be reduced up to 25% at the particle core due to lithiation, while it remains at ca. 5% below the undamaged value at the particle surface during delithiation. Using a simple estimate of capacity loss, we also show that the C-rate has a nonlinear effect on battery degradation, and the estimated capacity loss can surpass 10% at a 2C charging rate

A Numerical Study of Mechanical Degradation of Carbon-Coated Graphite Active Particles in Li-ion Battery Anodes

Current trends in portable electronic devices,1,2 electric vehicles,3–5 or renewable energy systems6–8 demand the development of lithium-ion batteries (LIBs) with improved capacity and performance.9–12 One critical component in LIBs is the negative electrode (i.e., anode),13 whose behavior has an important impact on the cell’s performance since it hosts the active materials in which Li intercalation and deintercalation occurs. During operation, both chemical and mechanical degradation occurs inside LIBs, resulting in a decreased battery performance and shortened battery life.14 The former is caused by the side reactions within the LIB that consume the number of lithium ions available for successive battery cycles and, therefore, cause battery capacity loss. The latter is due to the mechanical stresses originated within the electrode materials that may lead to fracture.15–17 Cracks in the active material that composes the electrode can isolate parts where intercalation will not occur

Stratified rod network model of electrical conductance in ultrathin polymer-carbon nanotube multilayers

The electronic conductance of polymer–carbon nanotube multilayered composite films assembled by the spin-spray layer-by-layer method is investigated. Our measurements show that the film conductance per bilayer σ1 vanishes for film thickness below a critical value, and above this threshold it grows logarithmically with the number of polyelectrolyte bilayers kl. The results of our experiments are interpreted using a stratified quasi-two-dimensional conducting-network model, in which the junction resistance between nanotubes deposited in different bilayers is a function of the interlayer distance. Using scaling arguments and numerical simulations, we show that the linear dependence of the junction resistance on the layer separation leads to the logarithmic behavior σ1 ∼ log kl for large kl, as observed in our experiments. Properties of our stratified-network model are investigated, and we show that with proper rescaling, different sets of experimental measurements can be collapsed onto a master curve. The overall shape of the master curve is determined by a single dimensionless parameter characterizing the slope of the junction-resistance function

Creación de recursos prácticos y digitales de meteorología y clima a través de Metolab

Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasFALSEsubmitte