605,231 research outputs found
A Microscopic Model of Gemini Surfactants: Self-assemblies in Water and at Air-Water Interface
We report the results of large scale Monte Carlo (MC) simulations of novel
microscopic models of gemini surfactants to elucidate (i) their spontaneous
aggregation in bulk water and (ii) their spatial organization in a system where
water is separated from the air above it by a sharp well defined interface. We
study the variation of the critical micellar concentration (CMC) with the
variation of the (a) length of the spacer, (b) length of the hydrophobic tail
and (c) the bending rigidity of the hydrocarbon chains forming the spacer and
the tail; some of the trends of variation are counter-intuitive but are in
excellent agreement with the available experimental results. Our simulations
elucidate the effects of the geometrical shape, size and density of the
surfactant molecules, the ionic nature of the heads and
hydrophobicity/hydrophilicity of the spacer not only on the shapes of the
micellar aggregates and the magnitude of the CMC, but also on their
conformations close to the air-water interface.Comment: 19 pages in REVTEX, 25 Postscript Figures (now included
Invariants of Welded Virtual Knots Via Crossed Module Invariants of Knotted Surfaces
We define an invariant of welded virtual knots from each finite crossed
module by considering crossed module invariants of ribbon knotted surfaces
which are naturally associated with them. We elucidate that the invariants
obtained are non trivial by calculating explicit examples. We define welded
virtual graphs and consider invariants of them defined in a similar way.Comment: New results. A perfected version will appear in Compositio
Mathematic
On Exchangeability in Network Models
We derive representation theorems for exchangeable distributions on finite
and infinite graphs using elementary arguments based on geometric and
graph-theoretic concepts. Our results elucidate some of the key differences,
and their implications, between statistical network models that are finitely
exchangeable and models that define a consistent sequence of probability
distributions on graphs of increasing size.Comment: Dedicated to the memory of Steve Fienber
Recommended from our members
Midwinter suppression of baroclinic storm activity on Mars: observations and models
We present results from assimilated analyses of observations from the Mars Global Surveyor Thermal Emission Spectrometer showing evidence for a regular suppression of baroclinic circumpolar storm activity in both hemispheres of Mars around winter solstice. General circulation model simulations are then used to elucidate the structure and possible causes of this suppression, for which the local ‘Eady growth rate’ appears to be a good predictor
Symmetries and novel universal properties of turbulent hydrodynamics in a symmetric binary fluid mixture
We elucidate the universal properties of the nonequilibrium steady states
(NESS) in a driven symmetric binary fluid mixture, an example of active
advection, in its miscible phase. We use the symmetries of the equations of
motion to establish the appropriate form of the structure functions which
characterise the statistical properties of the NESS of a driven symmetric
binary fluid mixture. We elucidate the universal properties described by the
scaling exponents and the amplitude ratios. Our results suggest that these
exponents and amplitude ratios vary continuously with the degree of
crosscorrelations between the velocity and the gradient of the concentration
fields. Furthermore, we demonstrate, in agreement with Celani et al, Phys. Rev.
Lett., 89, 234502 (2002, that the conventional structure functions as used in
passive scalar turbulence studies exhibit only simple scaling in the problem of
symmetric binary fluid mixture even in the weak concentration limit. We also
discuss possible experimental verifications of our results.Comment: To appear in JSTAT (letters) (2005
Antinucleus Production at RHIC
Light antinuclei may be formed in relativistic heavy ion collisions via final
state coalescence of antinucleons. The yields of antinuclei are sensitive to
primordial antinucleon production, the volume of the system at kinetic
freeze-out, and space-momentum correlations among antinucleons at freeze-out.
We report here preliminary STAR results on antideuteron and antihelion
production in 130A GeV Au+Au collisions. These results are examined in a
coalescence framework to elucidate the space-time structure of the antinucleon
source.Comment: 4 pages, 3 figures, talk given at Quark Matter 200
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