9,309 research outputs found
Antenna Technology for QUASAT application
A hybrid growth version of the advanced Sunflower, or precision deployable, antenna was adopted as the configuration proposed for the QUASAT very long baseline interferometry mission. The antenna consists of rigid panels of graphite-epoxy facesheets covering aluminum honeycomb sandwich. The six main folding panels are hinged to a cantilevered support ring attached to the periphery of the center section. Six pairs of intermediate panels are located between these panels and are hinged to each other and to the main panels. The flight configuration, antenna weight, a mass properties, frequency, and contour tolerance are discussed. The advantages of the solid antenna surface cover an all-mesh contour are examined
Microscopic theory of solvent mediated long range forces: influence of wetting
We show that a general density functional approach for calculating the force
between two big particles immersed in a solvent of smaller ones can describe
systems that exhibit fluid-fluid phase separation: the theory captures effects
of strong adsorption (wetting) and of critical fluctuations in the solvent. We
illustrate the approach for the Gaussian core model, a simple model of a
polymer mixture in solution and find extremely attractive, long ranged solvent
mediated potentials between the big particles for state points lying close to
the binodal, on the side where the solvent is poor in the species which is
favoured by the big particles.Comment: 7 pages, 3 figures, submitted to Europhysics Letter
Improved analytic longitudinal response analysis for axisymmetric launch vehicles. Volume I - Linear analytic model
Improved analytic longitudinal response analysis for axisymmetric launch vehicles - linear mode
Sedimentation of a two-dimensional colloidal mixture exhibiting liquid-liquid and gas-liquid phase separation: a dynamical density functional theory study
We present dynamical density functional theory results for the time evolution
of the density distribution of a sedimenting model two-dimensional binary
mixture of colloids. The interplay between the bulk phase behaviour of the
mixture, its interfacial properties at the confining walls, and the
gravitational field gives rise to a rich variety of equilibrium and
non-equilibrium morphologies. In the fluid state, the system exhibits both
liquid-liquid and gas-liquid phase separation. As the system sediments, the
phase separation significantly affects the dynamics and we explore situations
where the final state is a coexistence of up to three different phases. Solving
the dynamical equations in two-dimensions, we find that in certain situations
the final density profiles of the two species have a symmetry that is different
from that of the external potentials, which is perhaps surprising, given the
statistical mechanics origin of the theory. The paper concludes with a
discussion on this
Dynamical density functional theory for the dewetting of evaporating thin films of nanoparticle suspensions exhibiting pattern formation
Recent experiments have shown that the striking structure formation in
dewetting films of evaporating colloidal nanoparticle suspensions occurs in an
ultrathin `postcursor' layer that is left behind by a mesoscopic dewetting
front. Various phase change and transport processes occur in the postcursor
layer, that may lead to nanoparticle deposits in the form of labyrinthine,
network or strongly branched `finger' structures. We develop a versatile
dynamical density functional theory to model this system which captures all
these structures and may be employed to investigate the influence of
evaporation/condensation, nanoparticle transport and solute transport in a
differentiated way. We highlight, in particular, the influence of the subtle
interplay of decomposition in the layer and contact line motion on the observed
particle-induced transverse instability of the dewetting front.Comment: 5 pages, 5 figure
Solvent mediated interactions between model colloids and interfaces: A microscopic approach
We determine the solvent mediated contribution to the effective potentials
for model colloidal or nano- particles dispersed in a binary solvent that
exhibits fluid-fluid phase separation. Using a simple density functional theory
we calculate the density profiles of both solvent species in the presence of
the `colloids', which are treated as external potentials, and determine the
solvent mediated (SM) potentials. Specifically, we calculate SM potentials
between (i) two colloids, (ii) a colloid and a planar fluid-fluid interface,
and (iii) a colloid and a planar wall with an adsorbed wetting film. We
consider three different types of colloidal particles: colloid A which prefers
the bulk solvent phase rich in species 2, colloid C which prefers the solvent
phase rich in species 1, and `neutral' colloid B which has no strong preference
for either phase, i.e. the free energies to insert the colloid into either of
the coexisting bulk phases are almost equal. When a colloid which has a
preference for one of the two solvent phases is inserted into the disfavored
phase at statepoints close to coexistence a thick adsorbed `wetting' film of
the preferred phase may form around the colloids. The presence of the adsorbed
film has a profound influence on the form of the SM potentials.Comment: 17 Pages, 13 Figures. Accepted for publication in Journal of Chemical
Physic
Modelling the evaporation of thin films of colloidal suspensions using Dynamical Density Functional Theory
Recent experiments have shown that various structures may be formed during
the evaporative dewetting of thin films of colloidal suspensions. Nano-particle
deposits of strongly branched `flower-like', labyrinthine and network
structures are observed. They are caused by the different transport processes
and the rich phase behaviour of the system. We develop a model for the system,
based on a dynamical density functional theory, which reproduces these
structures. The model is employed to determine the influences of the solvent
evaporation and of the diffusion of the colloidal particles and of the liquid
over the surface. Finally, we investigate the conditions needed for
`liquid-particle' phase separation to occur and discuss its effect on the
self-organised nano-structures
A model colloidal fluid with competing interactions: bulk and interfacial properties
Using a simple mean-field density functional theory theory (DFT), we
investigate the structure and phase behaviour of a model colloidal fluid
composed of particles interacting via a pair potential which has a hard core of
diameter , is attractive Yukawa at intermediate separations and
repulsive Yukawa at large separations. We analyse the form of the asymptotic
decay of the bulk fluid correlation functions, comparing results from our DFT
with those from the self consistent Ornstein-Zernike approximation (SCOZA). In
both theories we find rich crossover behaviour, whereby the ultimate decay of
correlation functions changes from monotonic to long-wavelength damped
oscillatory decay on crossing certain lines in the phase diagram, or sometimes
from oscillatory to oscillatory with a longer wavelength. For some choices of
potential parameters we find, within the DFT, a -line at which the
fluid becomes unstable with respect to periodic density fluctuations. SCOZA
fails to yield solutions for state points near such a -line. The
propensity to clustering of particles, which is reflected by the presence of a
long wavelength , slowly decaying oscillatory pair correlation
function, and a structure factor that exhibits a very sharp maximum at small
but non zero wavenumbers, is enhanced in states near the -line. We
present density profiles for the planar liquid-gas interface and for fluids
adsorbed at a planar hard wall. The presence of a nearby -transition
gives rise to pronounced long-wavelength oscillations in the one-body densities
at both types of interface.Comment: 14 pages, 11 figure
Structure-activity relationships in nitrosamine carcinogenesis.
Statistically significant correlations have been demonstrated between carcinogenic activity, toxicity and number of carbons per molecule for an extensive set of nitrosamines. Such correlations, involving only bulk molecular properties indicate that the chemical nature of the alkyl substituents need not be the sole determinants of carcinogenic activity. These structure-activity relationships can be used to estimate carcinogenic activity with some degree of confidence
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