8,142 research outputs found
Polyimide from bis(n-isoprenyl)s of aryl diamides
A process and polyimide product formed by the reaction of a bismaleimide with a bis(amidediene) is disclosed wherein the bis(amidediene) is formed by reacting an excess of an acid chloride with 1,4-N,N'-diisoprenyl 2,3,5,6-tetramethy1 benzene
Predictions from Star Formation in the Multiverse
We compute trivariate probability distributions in the landscape, scanning
simultaneously over the cosmological constant, the primordial density contrast,
and spatial curvature. We consider two different measures for regulating the
divergences of eternal inflation, and three different models for observers. In
one model, observers are assumed to arise in proportion to the entropy produced
by stars; in the others, they arise at a fixed time (5 or 10 billion years)
after star formation. The star formation rate, which underlies all our observer
models, depends sensitively on the three scanning parameters. We employ a
recently developed model of star formation in the multiverse, a considerable
refinement over previous treatments of the astrophysical and cosmological
properties of different pocket universes. For each combination of observer
model and measure, we display all single and bivariate probability
distributions, both with the remaining parameter(s) held fixed, and
marginalized. Our results depend only weakly on the observer model but more
strongly on the measure. Using the causal diamond measure, the observed
parameter values (or bounds) lie within the central of nearly all
probability distributions we compute, and always within . This success
is encouraging and rather nontrivial, considering the large size and dimension
of the parameter space. The causal patch measure gives similar results as long
as curvature is negligible. If curvature dominates, the causal patch leads to a
novel runaway: it prefers a negative value of the cosmological constant, with
the smallest magnitude available in the landscape.Comment: 68 pages, 19 figure
Dewetting of thin-film polymers
In this paper we present a theoretical model for the dewetting of ultra-thin
polymer films. Assumming that the shear-thinning properties of these films can
be described by a Cross-type constitutive equation, we analyze the front
morphology of the dewetting film, and characterize the time evolution of the
dry region radius, and of the rim height. Different regimes of growth are
expected, depending on the initial film thickness, and on the power-law index
involved in the constitutive equation. In the thin-films regime, the dry radius
and the rim height obey power-law time dependences. We then compare our
predictions with the experimental results obtained by Debr\'egeas {\it et al.}
[Phys. Rev. Lett. {\bf 75}, 3886 (1995)] and by Reiter [Phys. Rev. Lett. {\bf
87}, 186101 (2001)].Comment: 12 pages, 14 figure
Dewetting on porous media with aspiration
We consider a porous solid covered with a water film (or with a drop) in
situations where the liquid is pumped in, either spontaneously (if the porous
medium is hydrophilic) or mechanically (by an external pump). The dynamics of
dewetting is then strongly modified. We analyse a few major examples: a)
horizontal films, which break at a certain critical thickness, b) the "modified
Landau-Levich problem" where a porous plate moves up from a bath and carries a
film: aspiration towards the plate limits the height H reached by the film, c)
certain situation where the hysteresis of contact angles is important.Comment: Revised version: The analysis of the 'modified Landau-Levich problem'
(section 3) has been significantly revised. It is now treated as a singular
perturbation problem (using boundary-layer techniques), leading to a more
accurate physical pictur
Hydrodynamics of Binary Fluid Mixtures - An Augmented Multiparticle Collison Dynamics Approach
The Multiparticle Collision Dynamics technique (MPC) for hydrodynamics
simulations is generalized to binary fluid mixtures and multiphase flows, by
coupling the particle-based fluid dynamics to a Ginzburg-Landau free-energy
functional for phase-separating binary fluids. To describe fluids with a
non-ideal equation of state, an additional density-dependent term is
introduced. The new approach is verified by applying it to thermodynamics near
the critical demixing point, and interface fluctuations of droplets. The
interfacial tension obtained from the analysis of the capillary wave spectrum
agrees well with the results based on the Laplace-Young equation.
Phase-separation dynamics follows the Lifshitz-Slyozov law
Preparation of bis(4-(3,4 dimethylene pyrrolidyl) phenyl) methane as a high temperature reactive oligomer
A major goal in the field of high temperature polymers was to prepare aromatic polyimides that can be easily fabricated with the required thermal and physical properties for aerospace applications. Recent research was directed to achieve polyimides that are: soluable in a common organic solvent; melt-processable; and thermally curable without the evolution of volatile by-products. A monomer, N-phenyl 3,4-dimethylene pyrrolidine, that can be modified to form a bis (exocyclodiene) I for the preparation of polyimides by the Diels-Alder process was developed. Preparation of high temperature polymeric materials by Diels-Alder polymerization that will maintain their integrity and toughness during long exposure time at elevated temperature is sought
Dynamics of a driven probe molecule in a liquid monolayer
We study dynamics of a probe molecule, driven by an external constant force
in a liquid monolayer on top of solid surface. In terms of a microscopic,
mean-field-type approach, we calculate the terminal velocity of the probe
molecule. This allows us to establish the analog of the Stokes formula, in
which the friction coefficient is interpreted in terms of the microscopic
parameters characterizing the system. We also determine the distribution of the
monolayer particles as seen from the stationary moving probe molecule and
estimate the self-diffusion coefficient for diffusion in a liquid monolayer.Comment: Latex, 7 pages, 1 figur
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