541 research outputs found
Efficient electrocatalytic water oxidation at neutral and high pH by adventitious nickel at nanomolar concentrations
Electrolytic water oxidation using earth-abundant elements is a key challenge in the quest to develop cheap, large surface area arrays for solar-to-hydrogen conversion. There have been numerous studies in this area in recent years, but there remains an imperative to demonstrate that the current densities reported are indeed due to the species under consideration and not due to the presence of adventitious (yet possibly highly active) contaminants at low levels. Herein, we show that adventitious nickel at concentrations as low as 17 nM can act as a water oxidation catalyst in mildly basic aqueous solutions, achieving stable (tens of hours) current densities of 1 mA cm–2 at overpotentials as low as 540 mV at pH 9.2 and 400 mV at pH 13. This nickel was not added to the electrolysis baths deliberately, but it was found to be present in the electrolytes as an impurity by ICP-MS. The presence of nickel on anodes from extended-time bulk electrolysis experiments was confirmed by XPS. In showing that such low levels of nickel can perform water oxidation at overpotentials comparable to many recently reported water oxidation catalysts, this work serves to raise the burden of proof required of new materials in this field: contamination by adventitious metal ions at trace loadings must be excluded as a possible cause of any observed water oxidation activity
Explicit Integration of the Full Symmetric Toda Hierarchy and the Sorting Property
We give an explicit formula for the solution to the initial value problem of
the full symmetric Toda hierarchy. The formula is obtained by the
orthogonalization procedure of Szeg\"{o}, and is also interpreted as a
consequence of the QR factorization method of Symes \cite{symes}. The sorting
property of the dynamics is also proved for the case of a generic symmetric
matrix in the sense described in the text, and generalizations of tridiagonal
formulae are given for the case of matrices with nonzero diagonals.Comment: 13 pages, Latex
Ultra-high brilliance multi-MeV -ray beam from non-linear Thomson scattering
We report on the generation of a narrow divergence (
mrad), multi-MeV ( MeV) and ultra-high brilliance ( photons s mm mrad 0.1\% BW) -ray
beam from the scattering of an ultra-relativistic laser-wakefield accelerated
electron beam in the field of a relativistically intense laser (dimensionless
amplitude ). The spectrum of the generated -ray beam is
measured, with MeV resolution, seamlessly from 6 MeV to 18 MeV, giving clear
evidence of the onset of non-linear Thomson scattering. The photon source has
the highest brilliance in the multi-MeV regime ever reported in the literature
Bright X-ray radiation from plasma bubbles in an evolving laser wakefield accelerator
We show that the properties of the electron beam and bright x-rays produced
by a laser wakefield accelerator can be predicted if the distance over which
the laser self-focuses and compresses prior to self-injection is taken into
account. A model based on oscillations of the beam inside a plasma bubble shows
that performance is optimised when the plasma length is matched to the laser
depletion length. With a 200~TW laser pulse this results in an x-ray beam with
median photon energy of \unit[20]{keV}, photons above
\unit[1]{keV} per shot and a peak brightness of \unit[3 \times
10^{22}]{photons~s^{-1}mrad^{-2}mm^{-2} (0.1\% BW)^{-1}}.Comment: 5 pages, 4 figure
Darboux Coordinates and Liouville-Arnold Integration in Loop Algebras
Darboux coordinates are constructed on rational coadjoint orbits of the
positive frequency part \wt{\frak{g}}^+ of loop algebras. These are given by
the values of the spectral parameters at the divisors corresponding to
eigenvector line bundles over the associated spectral curves, defined within a
given matrix representation. A Liouville generating function is obtained in
completely separated form and shown, through the Liouville-Arnold integration
method, to lead to the Abel map linearization of all Hamiltonian flows induced
by the spectral invariants. Serre duality is used to define a natural
symplectic structure on the space of line bundles of suitable degree over a
permissible class of spectral curves, and this is shown to be equivalent to the
Kostant-Kirillov symplectic structure on rational coadjoint orbits. The general
construction is given for or , with
reductions to orbits of subalgebras determined as invariant fixed point sets
under involutive automorphisms. The case is shown to reproduce
the classical integration methods for finite dimensional systems defined on
quadrics, as well as the quasi-periodic solutions of the cubically nonlinear
Schr\"odinger equation. For , the method is applied to the
computation of quasi-periodic solutions of the two component coupled nonlinear
Schr\"odinger equation.Comment: 61 pg
Investigating the Effectiveness, Acceptability and Impact on Healthcare Usage of Providing a Cognitive-Behavioural Based Psychological Therapy Service for Patients with Primary Antibody Deficiency
PURPOSE: Patients with primary antibody deficiency report poorer quality of life and higher rates of anxiety and depression than the general population. Cognitive-behavioral therapy has been shown to be a valuable treatment for patients with other long-term physical health conditions, improving well-being and enabling them to manage their symptoms more effectively. The aim of this project was to establish the feasibility and effectiveness of providing cognitive-behavioral based therapy to patients with primary antibody deficiency. METHODS: Forty-four patients completed a course of psychological therapy. Participants completed a series of self-report measures examining psychological and physical health, and service usage, prior to starting treatment and following their final session. They also provided feedback on their experience of treatment. RESULTS: Patients showed improvements in anxiety, depression, insomnia and fatigue. There was a high level of acceptability of the service and the potential for long-term cost savings to the NHS. CONCLUSION: Psychological therapy based on the cognitive-behavioral model of treatment appears to be a valuable treatment for patients with primary antibody deficiency and comorbid mental health difficulties
Soft X-ray harmonic comb from relativistic electron spikes
We demonstrate a new high-order harmonic generation mechanism reaching the
`water window' spectral region in experiments with multi-terawatt femtosecond
lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving
uJ/sr pulses. Harmonics are collectively emitted by an oscillating electron
spike formed at the joint of the boundaries of a cavity and bow wave created by
a relativistically self-focusing laser in underdense plasma. The spike
sharpness and stability are explained by catastrophe theory. The mechanism is
corroborated by particle-in-cell simulations
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