4,518 research outputs found
Proposal to the Council of the British Psychological Society for the formation of a new Section of the Society on ‘Qualitative Methods in Psychology’
[FIRST PARAGRAPH] In this proposal we argue that qualitative psychology is growing in popularity and that there is a need to support this development within the framework of the British Psychological Society as qualitative psychologists have a set of unique, identifiable, and specific needs. We envisage this support in the form of a Section on Qualitative Methods in Psychology that will provide a focus for researchers interested in qualitative approaches
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
Induced-charge Electrokinetic Phenomena: Theory and Microfluidic Applications
We give a general, physical description of ``induced-charge electro-osmosis''
(ICEO), the nonlinear electrokinetic slip at a polarizable surface, in the
context of some new techniques for microfluidic pumping and mixing. ICEO
generalizes ``AC electro-osmosis'' at micro-electrode arrays to various
dielectric and conducting structures in weak DC or AC electric fields. The
basic effect produces micro-vortices to enhance mixing in microfluidic devices,
while various broken symmetries -- controlled potential, irregular shape,
non-uniform surface properties, and field gradients -- can be exploited to
produce streaming flows. Although we emphasize the qualitative picture of ICEO,
we also briefly describe the mathematical theory (for thin double layers and
weak fields) and apply it to a metal cylinder with a dielectric coating in a
suddenly applied DC field.Comment: 4 pages, 4 figs; revsion with more refs, one new fig, and more
emphasis on microfluidic
Induced-Charge Electro-Osmosis
We describe the general phenomenon of `induced-charge electro-osmosis' (ICEO)
-- the nonlinear electro-osmotic slip that occurs when an applied field acts on
the ionic charge it {\sl induces} around a polarizable surface. Motivated by a
simple physical picture, we calculate ICEO flows around conducting cylinders in
steady (DC), oscillatory (AC), and suddenly-applied electric fields. This
picture, and these systems, represent perhaps the clearest example of nonlinear
electrokinetic phenomena. We complement and verify this physically-motivated
approach using a matched asymptotic expansion to the electrokinetic equations
in the thin double-layer and low potential limits. ICEO slip velocities vary
like , where is the field strength and is a
geometric length scale, and are set up on a time scale , where is the screening length and is the ionic diffusion
constant. We propose and analyze ICEO microfluidic pumps and mixers that
operate without moving parts under low applied potentials. Similar flows around
metallic colloids with fixed total charge have been described in the Russian
literature (largely unnoticed in the West). ICEO flows around conductors with
fixed potential, on the other hand, have no colloidal analog and offer further
possibilities for microfluidic applications.Comment: 36 pages, 8 figures, to appear in J. Fluid Mec
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
Effects of Growth Temperatures on the Fatty Acid Composition of Isolated Chloroplasts From Two Species Differing in Heat Sensitivity
Lipid analyses of chloroplasts isolated from wheat (Triticum aestivum L. cv. Arthur) and milo (Sorghum bicolor cv. Funk\u27s hybrid 522) suggest no major heat effect on lipid class distribution. Assuming milo is more heat tolerant than wheat and that increased saturated/unsaturated fatty acid values increase thermal stability, changes in sulfoquinovosyldiglyceride (SL) appear to be more important than phosphatidylglycerol (PG) in conferring thermal stability to isolated chloroplasts
Ultrafast High-pressure AC Electro-osmotic Pumps for Portable Biomedical Microfluidics
This paper details the development of an integrated AC electro-osmotic (ACEO)
microfluidic pump for dilute electrolytes consisting of a long serpentine
microchannel lined with three dimensional (3D) stepped electrode arrays. Using
low AC voltage (1 Volt rms, 1 kHz), power (5 mW) and current (3.5 mA) in water,
the pump is capable of generating a 1.4 kPa head pressure, a 100-fold increase
over prior ACEO pumps, and a 1.37 mm/sec effective slip velocity over the
electrodes without flow reversal. The integrated ACEO pump can utilize low
ionic strength solutions such as distilled water as the working solution to
pump physiological strength (100 mM) biological solutions in separate
microfluidic devices, with potential applications in portable or implantable
biomedical microfluidic devices. As a proof-of-concept experiment, the use of
the ACEO pumps for DNA hybridization in a microfluidic microarray is
demonstrated
Climate change and Australia’s comparative advantage in broadacre agriculture
Australia has long been a major exporter of the products of broadacre agriculture, a production system well suited to the economic and climatic conditions of the country. According to the conventional wisdom, Australia holds a comparative advantage in these products, among which wheat and livestock products predominate. However, the future validity of this proposition is sensitive to the projected impacts of climate change. This paper develops a framework with which to quantify the future patterns of comparative advantage in broadacre agriculture given the projections of several global climate models. We find empirical support for the conventional wisdom, and note substantial resilience in Australia’s comparative advantage to adverse yield change.Comparative advantage, climate change, broadacre agriculture, Agricultural and Food Policy, Environmental Economics and Policy, Land Economics/Use, Livestock Production/Industries,
Climate change and Australia’s comparative advantage in wheat
Australia has long been a major exporter of wheat, a commodity well suited to the economic and climatic conditions of Australia. According to the conventional wisdom, Australia holds a comparative advantage in wheat. However, the future validity of this proposition is sensitive to the proposed impacts of climate change. This paper develops a framework with which to examine the future patterns of comparative advantage in wheat given the projections of several global climate models. We find support for the conventional wisdom, and identify the presence of substantial resilience in Australia’s comparative advantage to adverse yield change.International Relations/Trade,
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