4,899 research outputs found
Characterization of rutile passivation layers formed on Magnéli-phase titanium oxide inert anodes
An ex situ characterization study has been performed on rutile passivation layers on inert anodes used for molten salt electrochemical studies. Rutile layer thicknesses were estimated using a number of ex situ methods, including laboratory and synchrotron X-ray diffraction and optical microscopy. The only phases in the anode detected by diffraction were the Magnéli phases (TinO2n-1, n = 5-6) of the unreacted anode and rutile (TiO2), which forms on electrolysis. These measurements validate a previously developed in situ energy-dispersive X-ray diffraction analysis technique [Scarlett, Madsen, Evans, Coelho, McGregor, Rowles, Lanyon & Urban (2009). J. Appl. Cryst. 42, 502-512]
Sample-displacement correction for whole-pattern profile fitting of powder diffraction data collected in capillary geometry
Abstract: Recent in situ experimentation at the Australian Synchrotron resulted in the nucleation and crystallization of material on the walls of the capillary reaction vessels. This lining of the capillary walls, without filling the bulk of the capillary volume, produced an artefact in the diffraction data due to sample displacement across the capillary. In effect, the experiment was examining simultaneously two samples displaced by equal and opposite amounts from the diffractometer centre. This was exaggerated by the fact that large-diameter (1 mm) capillaries had been used in order to increase the total sample volume and hence maximize the amount of material formed and examined. The effect of this displacement was to shift the diffraction peaks simultaneously to both lower and higher angles than their `ideal' positions, causing peak splitting in many instances. A model has been developed which considers the sample as being effectively two flat plate samples, thus allowing for correction through the use of sample displacement. An additional problem resulted from the oriented growth of the material on the capillary walls, producing preferred orientation in the observed data. The correction model can also be extended to model such anisotropic peak splitting caused by this preferential orientation of the crystallites on the capillary wall
Semiclassical two-step model for strong-field ionization
We present a semiclassical two-step model for strong-field ionization that
accounts for path interferences of tunnel-ionized electrons in the ionic
potential beyond perturbation theory. Within the framework of a classical
trajectory Monte-Carlo representation of the phase-space dynamics, the model
employs the semiclassical approximation to the phase of the full quantum
propagator in the exit channel. By comparison with the exact numerical solution
of the time-dependent Schr\"odinger equation for strong-field ionization of
hydrogen, we show that for suitable choices of the momentum distribution after
the first tunneling step, the model yields good quantitative agreement with the
full quantum simulation. The two-dimensional photoelectron momentum
distributions, the energy spectra, and the angular distributions are found to
be in good agreement with the corresponding quantum results. Specifically, the
model quantitatively reproduces the fan-like interference patterns in the
low-energy part of the two-dimensional momentum distributions as well as the
modulations in the photoelectron angular distributions.Comment: 31 pages, 7 figure
Nucleation of quark matter bubbles in neutron stars
The thermal nucleation of quark matter bubbles inside neutron stars is
examined for various temperatures which the star may realistically encounter
during its lifetime. It is found that for a bag constant less than a critical
value, a very large part of the star will be converted into the quark phase
within a fraction of a second. Depending on the equation of state for neutron
star matter and strange quark matter, all or some of the outer parts of the
star may subsequently be converted by a slower burning or a detonation.Comment: 13 pages, REVTeX, Phys.Rev.D (in press), IFA 93-32. 5 figures (not
included) available upon request from [email protected]
Lattice QCD Constraints on Hybrid and Quark Stars
A QCD-motivated dynamical-quasiparticle model with parameters adjusted to
reproduce the lattice-QCD equation of state is extrapolated from region of high
temperatures and moderate baryonic densities to the domain of high baryonic
densities and zero temperature. The resulting equation of state matched with
realistic hadronic equations of state predicts a phase transition into the
quark phase at higher densities than those reachable in neutron star interiors.
This excludes the possibility of the existence of hybrid (hadron-quark) stars.
Pure quark stars are possible and have low masses, small radii and very high
central densities. Similar results are obtained for a simple bag model with
massive quarks, fitted to reproduce the same lattice results. Self-bound quark
matter is also excluded within these models. Uncertainties in the present
extrapolation re discussed. Comparison with standard bag models is made.Comment: 13 p., 8 figs., 7 tables, Version accepted by Phys. Rev.
Synthesis of Two Tetrasaccharide Pentenyl Glycosides Related to the Pectic Rhamnogalacturonan I Polysaccharide
The synthesis of two protected tetrasaccharide pentenyl glycosides with diarabinan and digalactan branching related to the pectic polysaccharide rhamnogalacturonan I is reported. The strategy relies on the coupling of N-phenyl trifluoroacetimidate disaccharide donors to a common rhamnosyl acceptor. The resulting trisaccharide thioglycosides were finally coupled to an n-pentenyl galactoside acceptor to access the two protected branched tetrasaccharides
Masses of Multiquark Droplets
The mass formulae for finite lumps of strange quark matter with , and
quarks, and non-strange quark matter consisting of and quarks are
derived in a non-relativistic potential model. The finite-size effects
comprising the surface, curvature and even, the Gauss curvature were
consistently obtained, which shows a converging trend. It is found that there
is a possibility for the formation of metastable strangelets of large mass. The
model predicts low charge to mass ratio as the characteristic signature of
strange matter in agreement with the relativistic studies. This study also
yields an independent estimate for the bag energy density , which is in
agreement with the M.I.T bag model value.Comment: 24pages + 5 figures available upon request,Latex,IP/BBSR/93-3
A furnace and environmental cell for the in situ investigation of molten salt electrolysis using high-energy X-ray diffraction
This paper describes the design, construction and implementation of a relatively large controlled-atmosphere cell and furnace arrangement. The purpose of this equipment is to facilitate the in situ characterization of materials used in molten salt electrowinning cells, using high-energy X-ray scattering techniques such as synchrotron-based energy-dispersive X-ray diffraction. The applicability of this equipment is demonstrated by quantitative measurements of the phase composition of a model inert anode material, which were taken during an in situ study of an operational Fray-Farthing-Chen Cambridge electrowinning cell, featuring molten CaCl(2) as the electrolyte. The feasibility of adapting the cell design to investigate materials in other high-temperature environments is also discussed
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