38,433 research outputs found
Carbonate Formation in Non-Aqueous Environments by Solid-Gas Carbonation of Silicates
We have produced synthetic analogues of cosmic silicates using the Sol Gel
method, producing amorphous silicates of composition Mg(x)Ca(1-x)SiO3. Using
synchrotron X-ray powder diffraction on Beamline I11 at the Diamond Light
Source, together with a newly-commissioned gas cell, real-time powder
diffraction scans have been taken of a range of silicates exposed to CO2 under
non-ambient conditions. The SXPD is complemented by other techniques including
Raman and Infrared Spectroscopy and SEM imaging.Comment: 5 pages, 3 figures. Contribution to the Proceedings of the First
European Conference on Laboratory Astrophysics (ECLA
Transparent polymeric laminates
Laminate prepared from epoxy-boroxine and phenolphthalein polycarbonate has high mechanical strength at elevated temperature and is resistant to impact, fire, and high-energy thermal radiation. Polycarbonate is prepared by reaction of phenolphthalein with phosgene in presence of amine catalyst and immiscible organic solvent phase
The Generation of Magnetic Fields Through Driven Turbulence
We have tested the ability of driven turbulence to generate magnetic field
structure from a weak uniform field using three dimensional numerical
simulations of incompressible turbulence. We used a pseudo-spectral code with a
numerical resolution of up to collocation points. We find that the
magnetic fields are amplified through field line stretching at a rate
proportional to the difference between the velocity and the magnetic field
strength times a constant. Equipartition between the kinetic and magnetic
energy densities occurs at a scale somewhat smaller than the kinetic energy
peak. Above the equipartition scale the velocity structure is, as expected,
nearly isotropic. The magnetic field structure at these scales is uncertain,
but the field correlation function is very weak. At the equipartition scale the
magnetic fields show only a moderate degree of anisotropy, so that the typical
radius of curvature of field lines is comparable to the typical perpendicular
scale for field reversal. In other words, there are few field reversals within
eddies at the equipartition scale, and no fine-grained series of reversals at
smaller scales. At scales below the equipartition scale, both velocity and
magnetic structures are anisotropic; the eddies are stretched along the local
magnetic field lines, and the magnetic energy dominates the kinetic energy on
the same scale by a factor which increases at higher wavenumbers. We do not
show a scale-free inertial range, but the power spectra are a function of
resolution and/or the imposed viscosity and resistivity. Our results are
consistent with the emergence of a scale-free inertial range at higher Reynolds
numbers.Comment: 14 pages (8 NEW figures), ApJ, in press (July 20, 2000?
Series-hybrid bearing - An approach to extending bearing fatigue life at high speeds
Fluid film bearing of hybrid device consists of orifice compensated annular thrust bearing and self-acting journal bearing. In series hybrid bearing, both ball bearing and annular thrust bearing carry full system thrust load, but two bearings share speed. Operation of system is stable and automatically fail-safe
Hawking radiation by Kerr black holes and conformal symmetry
The exponential blueshift associated with the event horizon of a black hole
makes conformal symmetry play a fundamental role in accounting for its thermal
properties. Using a derivation based on two-point functions, we show that the
spectrum of thermal radiation of scalar particles by Kerr (and Schwarzschild)
black holes can be explicitly derived on the basis of a -dimensional
conformal symmetry arising in the wave equation near the horizon. This result
reinforces the recently conjectured relation between Kerr geometry and a
-dimensional conformal field theory.Comment: Version published in Phys. Rev. Let
In situ apparatus for the study of clathrate hydrates relevant to solar system bodies using synchrotron X-ray diffraction and Raman spectroscopy
Clathrate hydrates are believed to play a significant role in various solar
system environments, e.g. comets, and the surfaces and interiors of icy
satellites, however the structural factors governing their formation and
dissociation are poorly understood. We demonstrate the use of a high pressure
gas cell, combined with variable temperature cooling and time-resolved data
collection, to the in situ study of clathrate hydrates under conditions
relevant to solar system environments. Clathrates formed and processed within
the cell are monitored in situ using synchrotron X-ray powder diffraction and
Raman spectroscopy. X-ray diffraction allows the formation of clathrate
hydrates to be observed as CO2 gas is applied to ice formed within the cell.
Complete conversion is obtained by annealing at temperatures just below the ice
melting point. A subsequent rise in the quantity of clathrate is observed as
the cell is thermally cycled. Four regions between 100-5000cm-1 are present in
the Raman spectra that carry features characteristic of both ice and clathrate
formation. This novel experimental arrangement is well suited to studying
clathrate hydrates over a range of temperature (80-500K) and pressure
(1-100bar) conditions and can be used with a variety of different gases and
starting aqueous compositions. We propose the increase in clathrate formation
observed during thermal cycling may be due to the formation of a quasi
liquid-like phase that forms at temperatures below the ice melting point, but
which allows easier formation of new clathrate cages, or the retention and
delocalisation of previously formed clathrate structures, possibly as amorphous
clathrate. The structural similarities between hexagonal ice, the quasi
liquid-like phase, and crystalline CO2 hydrate mean that differences in the
Raman spectrum are subtle; however, all features out to 5000cm-1 are diagnostic
of clathrate structure.Comment: Astronomy & Astrophysics, in press. 6 page
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