25 research outputs found
A study of the effect of water management and electrode flooding on the dimensional change of polymer electrolyte fuel cells
AbstractWater management and flooding play an important role in the performance and durability of polymer electrolyte fuel cells (PEFCs). In this study, a dynamic electro-mechanical analysis is performed to examine the performance of a working PEFC during hydration transients and flooding events. Cell resistance is measured using electrochemical impedance spectroscopy (EIS), and the stress/strain characteristics – cell compression and membrane electrode assembly (MEA) dimensional change – are studied using a controlled compression unit (CCU).Ex-situ measurements of membrane thickness as a function of hydration level provide a direct correlation between ionic conductivity and thickness. During initial hydration of Nafion membranes there is a direct relationship between membrane conductivity and dimensional change (swelling) of MEAs. Electrode flooding is found to result in membrane hydration and an increase in stress or strain, depending on the compression mode of the fuel cell. Results suggest that hydration cycles and flooding events can lead to cell degradation due to the stresses imposed
Vacancies, disorder-induced smearing of the electronic structure, and its implications for the superconductivity of anti-perovskite MgCNi
The anti-perovskite superconductor MgCNi was studied using
high-resolution x-ray Compton scattering combined with electronic structure
calculations. Compton scattering measurements were used to determine
experimentally a Fermi surface that showed good agreement with that of our
supercell calculations, establishing the presence of the predicted hole and
electron Fermi surface sheets. Our calculations indicate that the Fermi surface
is smeared by the disorder due to the presence of vacancies on the C and Ni
sites, but does not drastically change shape. The 20\% reduction in the Fermi
level density-of-states would lead to a significant () suppression
of the superconducting for pair-forming electron-phonon coupling.
However, we ascribe the observed much smaller reduction at our
composition (compared to the stoichiometric compound) to the suppression of
pair-breaking spin fluctuations.Comment: 11 pages, 3 figure
Magnetic frustration, short-range correlations and the role of the paramagnetic Fermi surface of PdCrO<sub>2</sub>
Frustrated interactions exist throughout nature, with examples ranging from protein folding through to frustrated magnetic interactions. Whilst magnetic frustration is observed in numerous electrically insulating systems, in metals it is a rare phenomenon. The interplay of itinerant conduction electrons mediating interactions between localised magnetic moments with strong spin-orbit coupling is likely fundamental to these systems. Therefore, knowledge of the precise shape and topology of the Fermi surface is important in any explanation of the magnetic behaviour. PdCrO2, a frustrated metallic magnet, offers the opportunity to examine the relationship between magnetic frustration, short-range magnetic order and Fermi surface topology. By mapping the short-range order in reciprocal space and experimentally determining the electronic structure, we have identified the dual role played by the Cr electrons in which the itinerant ones on the nested paramagnetic Fermi surface mediate the frustrated magnetic interactions between local moments
Extreme Fermi surface smearing in a maximally disordered concentrated solid solution
We show that the Fermi surface can survive the presence of extreme compositional disorder in the equiatomic alloy Ni0.25Fe0.25Co0.25Cr0.25. Our high-resolution Compton scattering experiments reveal a Fermi surface which is smeared across a significant fraction of the Brillouin zone (up to 40% of 2Ï€/a). The extent of this smearing and its variation on and between different sheets of the Fermi surface have been determined, and estimates of the electron mean free path and residual resistivity have been made by connecting this smearing with the coherence length of the quasiparticle states
Electron-phonon coupling and superconducting critical temperature of the YIr<sub>2</sub>Si<sub>2</sub> and LaIr<sub>2</sub>Si<sub>2</sub> high-temperature polymorphs from first-principles
Increasing frailty is associated with higher prevalence and reduced recognition of delirium in older hospitalised inpatients: results of a multi-centre study
Purpose:
Delirium is a neuropsychiatric disorder delineated by an acute change in cognition, attention, and consciousness. It is common, particularly in older adults, but poorly recognised. Frailty is the accumulation of deficits conferring an increased risk of adverse outcomes. We set out to determine how severity of frailty, as measured using the CFS, affected delirium rates, and recognition in hospitalised older people in the United Kingdom.
Methods:
Adults over 65 years were included in an observational multi-centre audit across UK hospitals, two prospective rounds, and one retrospective note review. Clinical Frailty Scale (CFS), delirium status, and 30-day outcomes were recorded.
Results:
The overall prevalence of delirium was 16.3% (483). Patients with delirium were more frail than patients without delirium (median CFS 6 vs 4). The risk of delirium was greater with increasing frailty [OR 2.9 (1.8–4.6) in CFS 4 vs 1–3; OR 12.4 (6.2–24.5) in CFS 8 vs 1–3]. Higher CFS was associated with reduced recognition of delirium (OR of 0.7 (0.3–1.9) in CFS 4 compared to 0.2 (0.1–0.7) in CFS 8). These risks were both independent of age and dementia.
Conclusion:
We have demonstrated an incremental increase in risk of delirium with increasing frailty. This has important clinical implications, suggesting that frailty may provide a more nuanced measure of vulnerability to delirium and poor outcomes. However, the most frail patients are least likely to have their delirium diagnosed and there is a significant lack of research into the underlying pathophysiology of both of these common geriatric syndromes
Increasing frailty is associated with higher prevalence and reduced recognition of delirium in older hospitalised inpatients: results of a multi-centre study
Purpose Delirium is a neuropsychiatric disorder delineated by an acute change in cognition, attention, and consciousness. It is common, particularly in older adults, but poorly recognised. Frailty is the accumulation of deficits conferring an increased risk of adverse outcomes. We set out to determine how severity of frailty, as measured using the CFS, affected delirium rates, and recognition in hospitalised older people in the United Kingdom. Methods Adults over 65 years were included in an observational multi-centre audit across UK hospitals, two prospective rounds, and one retrospective note review. Clinical Frailty Scale (CFS), delirium status, and 30-day outcomes were recorded. Results The overall prevalence of delirium was 16.3% (483). Patients with delirium were more frail than patients without delirium (median CFS 6 vs 4). The risk of delirium was greater with increasing frailty [OR 2.9 (1.8–4.6) in CFS 4 vs 1–3; OR 12.4 (6.2–24.5) in CFS 8 vs 1–3]. Higher CFS was associated with reduced recognition of delirium (OR of 0.7 (0.3–1.9) in CFS 4 compared to 0.2 (0.1–0.7) in CFS 8). These risks were both independent of age and dementia. Conclusion We have demonstrated an incremental increase in risk of delirium with increasing frailty. This has important clinical implications, suggesting that frailty may provide a more nuanced measure of vulnerability to delirium and poor outcomes. However, the most frail patients are least likely to have their delirium diagnosed and there is a significant lack of research into the underlying pathophysiology of both of these common geriatric syndromes
UCoGe
Determination of spin and orbital magnetisation in the ferromagnetic superconductor UCoG
BaSn5
Calculations of the electronic band structure, Fermi surface, and electron-phonon coupling in BaSn
PdCrO2
Support data for Compton scattering, neutron and first principles calculations on PdCrO