82,121 research outputs found
Commuting charges and symmetric spaces
Every classical sigma-model with target space a compact symmetric space
(with classical) is shown to possess infinitely many local, commuting,
conserved charges which can be written in closed form. The spins of these
charges run over a characteristic set of values, playing the role of exponents
of , and repeating modulo an integer which plays the role of a Coxeter
number.Comment: LaTeX, 16 pages; v2: footnote adde
Magentically actuated compressor
A vibration free fluid compressor particularly adapted for Stirling cycle cryogenic refrigeration apparatus comprises a pair of identical opposing ferromagnetic pistons located in a housing and between a gas spring including a sealed volume of a working fluid such as gas under pressure. The gas compresses and expands in accordance with movement of the pistons to generate a compression wave which can be vented to other apparatus, for example, a displacer unit in a Stirling cycle engine. The pistons are urged outwardly due to the pressure of the gas; however, a fixed electromagnetic coil assembly located in the housing adjacent the pistons, is periodically energized to produce a magnetic field which interlinks the pistons in such a fashion that the pistons are mutually attracted to one another. The mass of the pistons, in conjunction with the compressed gas between them, form a naturally resonant system which, when the pistons are electromagnetically energized, produces an oscillating compression wave in the entrapped fluid medium
Dynamical density functional theory and its application to spinodal decomposition
We present an alternative derivation of the dynamical density functional
theory for the one body density profile of a classical fluid developed by
Marconi and Tarazona [J. Chem. Phys., 110, 8032 (1999)]. Our derivation
elucidates further some of the physical assumptions inherent in the theory and
shows that it is not restricted to fluids composed of particles interacting
solely via pair potentials; rather it applies to general, multi-body
interactions. The starting point for our derivation is the Smoluchowski
equation and the theory is therefore one for Brownian particles and as such is
applicable to colloidal fluids. In the second part of this paper we use the
dynamical density functional theory to derive a theory for spinodal
decomposition that is applicable at both early and intermediate times. For
early stages of spinodal decomposition our non-linear theory is equivalent to
the (generalised) linear Cahn-Hilliard theory, but for later times it
incorporates coupling between different Fourier components of the density
fluctuations (modes) and therefore goes beyond Cahn-Hilliard theory. We
describe the results of calculations for a model (Yukawa) fluid which show that
the coupling leads to the growth of a second maximum in the density
fluctuations, at a wavenumber larger than that of the main peak.Comment: 23 pages, 3 figure
Templated mineralization by charge-modified cowpea mosaic virus
Templated mineralization of virus particles provides routes to narrowly dispersed nanoparticles that are not readily prepared by other means. The templated mineralization of metal or metal oxide on the external surface of wild-type cowpea mosaic virus (CPMV), a plant virus, is facilitated by increasing the external surface negative charge. This is achieved by the chemical modification of surface lysine groups by succinic anhydride. Hence, for example, treatment of charge-modified CPMV succinamate with a 1:2 mixture of iron(II) and iron(III) salts, followed by raising the pH to 10.2, led to the formation of narrowly dispersed, CPMV-templated, magnetite (Fe3O4) nanoparticles
Soft core fluid in a quenched matrix of soft core particles: A mobile mixture in a model gel
We present a density-functional study of a binary phase-separating mixture of
soft core particles immersed in a random matrix of quenched soft core particles
of larger size. This is a model for a binary polymer mixture immersed in a
crosslinked rigid polymer network. Using the replica `trick' for
quenched-annealed mixtures we derive an explicit density functional theory that
treats the quenched species on the level of its one-body density distribution.
The relation to a set of effective external potentials acting on the annealed
components is discussed. We relate matrix-induced condensation in bulk to the
behaviour of the mixture around a single large particle. The interfacial
properties of the binary mixture at a surface of the quenched matrix display a
rich interplay between capillary condensation inside the bulk matrix and
wetting phenomena at the matrix surface.Comment: 20 pages, 5 figures. Accepted for Phys. Rev.
Swift J004427.3-734801- a probable Be/white dwarf system in the Small Magellanic Cloud
Swift J004427.3-734801 is an X-ray source in the Small Magellanic Cloud (SMC)
that was first discovered as part of the Swift S-CUBED programme in January
2020. It was not detected in any of the previous 3 years worth of observations.
The accurate positional determination from the X-ray data have permitted an
optical counterpart to be identified which has the characteristics of an
O9V-B2III star. Evidence for the presence of an IR excess and significant
I-band variability strongly suggest that this is an OBe type star. Over 17
years worth of optical monitoring by the OGLE project reveal periods of time in
which quasi-periodic optical flares occur at intervals of ~21.5d. The X-ray
data obtained from the S-CUBED project reveal a very soft spectrum, too soft to
be that from accretion on to a neutron star or black hole. It is suggested here
that this a rarely identified Be star-white dwarf binary in the SMC.Comment: 6 Pages, 8 Figures. Accepted by MNRAS 2020 June 8. Received 2020 June
5; in original form 2020 April 2
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