13,337 research outputs found
Nonequilibrium Thermodynamics of Porous Electrodes
We reformulate and extend porous electrode theory for non-ideal active
materials, including those capable of phase transformations. Using principles
of non-equilibrium thermodynamics, we relate the cell voltage, ionic fluxes,
and Faradaic charge-transfer kinetics to the variational electrochemical
potentials of ions and electrons. The Butler-Volmer exchange current is
consistently expressed in terms of the activities of the reduced, oxidized and
transition states, and the activation overpotential is defined relative to the
local Nernst potential. We also apply mathematical bounds on effective
diffusivity to estimate porosity and tortuosity corrections. The theory is
illustrated for a Li-ion battery with active solid particles described by a
Cahn-Hilliard phase-field model. Depending on the applied current and porous
electrode properties, the dynamics can be limited by electrolyte transport,
solid diffusion and phase separation, or intercalation kinetics. In
phase-separating porous electrodes, the model predicts narrow reaction fronts,
mosaic instabilities and voltage fluctuations at low current, consistent with
recent experiments, which could not be described by existing porous electrode
models
Phase Transformation Dynamics in Porous Battery Electrodes
Porous electrodes composed of multiphase active materials are widely used in
Li-ion batteries, but their dynamics are poorly understood. Two-phase models
are largely empirical, and no models exist for three or more phases. Using a
modified porous electrode theory based on non-equilibrium thermodynamics, we
show that experimental phase behavior can be accurately predicted from free
energy models, without artificially placing phase boundaries or fitting the
open circuit voltage. First, we simulate lithium intercalation in porous iron
phosphate, a popular two-phase cathode, and show that the zero-current voltage
gap, sloping voltage plateau and under-estimated exchange currents all result
from size-dependent nucleation and mosaic instability. Next, we simulate porous
graphite, the standard anode with three stable phases, and reproduce
experimentally observed fronts of color-changing phase transformations. These
results provide a framework for physics-based design and control for
electrochemical systems with complex thermodynamics
A discussion of the scaling effect in numerical simulation of the extrusion process
The main objective of the work of this paper is to study the possibility of using a small scale geometrical model in the numerical simulation of aluminium extrusion. The advantages and shortcomings of the application of the
geometrically similar model in FEM simulation are discussed. Thermal – mechanical and metallurgical combined
simulations are performed within two tests using geometrically similar models and assessment is made in terms of mechanical and material properties. It was found that small scale simulation could not reproduce most of the
important forming parameters of the original process, although it could help to bring about significant savings in
computation time
Particle-Level Modeling of the Charge-Discharge Behavior of Nanoparticulate Phase-Separating Li-Ion Battery Electrodes
In nanoparticulate phase-separating electrodes, phase separation inside the
particles can be hindered during their charge/discharge cycles even when a
thermodynamic driving force for phase separation exists. In such cases,
particles may (de)lithiate discretely in a process referred to as mosaic
instability. This instability could be the key to elucidating the complex
charge/discharge dynamics in nanoparticulate phase-separating electrodes. In
this paper, the dynamics of the mosaic instability is studied using Smoothed
Boundary Method simulations at the particle level, where the concentration and
electrostatic potential fields are spatially resolved around individual
particles. Two sets of configurations consisting of spherical particles with an
identical radius are employed to study the instability in detail. The effect of
an activity-dependent exchange current density on the mosaic instability, which
leads to asymmetric charge/discharge, is also studied. While we show that our
model reproduces the results of a porous-electrode model for the simple setup
studied here, it is a powerful framework with the capability to predict the
detailed dynamics in three-dimensional complex electrodes and provides further
insights into the complex dynamics that result from the coupling of
electrochemistry, thermodynamics, and transport kinetics
A lower bound in Nehari's theorem on the polydisc
By theorems of Ferguson and Lacey (d=2) and Lacey and Terwilleger (d>2),
Nehari's theorem is known to hold on the polydisc D^d for d>1, i.e., if H_\psi
is a bounded Hankel form on H^2(D^d) with analytic symbol \psi, then there is a
function \phi in L^\infty(\T^d) such that \psi is the Riesz projection of \phi.
A method proposed in Helson's last paper is used to show that the constant C_d
in the estimate \|\phi\|_\infty\le C_d \|H_\psi\| grows at least exponentially
with d; it follows that there is no analogue of Nehari's theorem on the
infinite-dimensional polydisc
Lexical Derivation of the PINT Taxonomy of Goals: Prominence, Inclusiveness, Negativity Prevention, and Tradition
What do people want? Few questions are more fundamental to psychological science than this. Yet, existing taxonomies disagree on both the number and content of goals. We thus adopted a lexical approach and investigated the structure of goal-relevant words from the natural English lexicon. Through an intensive rating process, 1,060 goal-relevant English words were first located. In Studies 1-2, two relatively large and diverse samples (total n = 1,026) rated their commitment to approaching or avoiding these goals. Principal component analyses yielded 4 replicable components: Prominence, Inclusiveness, Negativity prevention, and Tradition (the PINT Taxonomy). Study 3-7 (total n = 1,396) supported the 4-factor structure of an abbreviated scale and found systematic differences in their relationships with past goal-content measures, the Big 5 traits, affect, and need satisfaction. This investigation thus provides a data-driven taxonomy of higher-order goal-content and opens up a wide variety of fascinating lines for future research
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Political Ideology and Public Views of the Energy Transition in Australia and the UK
We explore the relationship between political ideology and public attitudes towards a range of energy technologies (namely: biomass, coal, shale (or coal seam) gas, natural gas, carbon capture and storage, hydroelectricity, nuclear, solar thermal and photovoltaic, wave and wind energy). Our empirical analysis draws on the results of two similar nationally representative public surveys that were conducted in Australia and the UK in 2017. Our findings suggest that political ideology is significantly associated with public attitudes towards energy technologies. Specifically, supporters of left-leaning political parties tend to be more supportive of renewables and opposed to biomass, shale (coal seam) gas, nuclear and fossil fuel energies compared to right-leaning individuals. We also create an alternative ideological proxy to capture the relative emphasis that parties place on the environment and economy and find that supporters of environmentally focused parties generally express similar energy preferences to left-leaning individuals and economy-focused respondents align with right-leaning attitudes. Our findings are robust to different choices of proxy
Morphology and biomechanics of the nests of the Common Blackbird Turdus merula
Capsule Common blackbirds select different materials, with varying biomechanical properties, to construct different parts of their nest.
Aims This study tested the hypothesis that outer components of a nest have a more structural role and so are stronger than materials used to line the cup.
Methods Blackbird nests were measured prior to being dismantled to isolate structural components which were tested for mechanical strength and rigidity.
Results Outer nest wall materials were significantly thicker, stronger and more rigid than materials in the inner structural wall or the cup lining. In the vertical plane materials used in the structural wall did not differ. By contrast, lining materials from the bottom of the nest cup were significantly thicker, stronger and more rigid than materials from the top of the cup.
Conclusion Blackbirds use different materials in nest construction roles suited to their properties and so may be able to recognise the structural properties of these materials. Materials on the outside of the nest may have a key structural role during construction
Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators
We investigate magnetization dynamics in a spin-Hall oscillator using a direct current measurement as well as conventional microwave spectrum analysis. When the current applies an anti-damping spin-transfer torque, we observe a change in resistance which we ascribe mainly to the excitation of incoherent exchange magnons. A simple model is developed based on the reduction of the effective saturation magnetization, quantitatively explaining the data. The observed phenomena highlight the importance of exchange magnons on the operation of spin-Hall oscillators
Sunspot observations from the SOUP instrument on Spacelab 2
A series of white light images obtained by the SOUP instrument on Spacelab 2 of active region 4682 on August 5, 1985 were analyzed in the area containing sunspots. Although the umbra of the spot is underexposed, the film is well exposed in the penumbral regions. These data were digitally processed to remove noise and to separate p-mode oscillations from low velocity material motions. The results of this preliminary investigation include: (1) proper motion measurements of a radial outflow in the photospheric granulation pattern just outside the penumbra; (2) discovery of occasional bright structures (streakers) that appear to be ejected outward from the penumbra; (3) broad dark clouds moving outward in the penumbra in addition to the well known bright penumbral grains moving inward; (4) apparent extensions and contractions of penumbral filaments over the photosphere; and (5) observation of a faint bubble or loop-like structure which seems to expand from two bright penumbral filaments into the photosphere
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