53,401 research outputs found
Theoretical and Experimental Adsorption Studies of Polyelectrolytes on an Oppositely Charged Surface
Using self-assembly techniques, x-ray reflectivity measurements, and computer
simulations, we study the effective interaction between charged polymer rods
and surfaces. Long-time Brownian dynamics simulations are used to measure the
effective adhesion force acting on the rods in a model consisting of a planar
array of uniformly positively charged, stiff rods and a negatively charged
planar substrate in the presence of explicit monovalent counterions and added
monovalent salt ions in a continuous, isotropic dielectric medium. This
electrostatic model predicts an attractive polymer-surface adhesion force that
is weakly dependent on the bulk salt concentration and that shows fair
agreement with a Debye-Huckel approximation for the macroion interaction at
salt concentrations near 0.1 M. Complementary x-ray reflectivity experiments on
poly(diallyldimethyl ammonium) chloride (PDDA) monolayer films on the native
oxide of silicon show that monolayer structure, electron density, and surface
roughness are likewise independent of the bulk ionic strength of the solution.Comment: Revtex, prb format; uses amssym
Combinatorial classification of quantum lens spaces
We answer the question of how large the dimension of a quantum lens space
must be, compared to the primary parameter , for the isomorphism class to
depend on the secondary parameters. Since classification results in C*-algebra
theory reduces this question to one concerning a certain kind of
-equivalence of integer matrices of a special form, our approach is
entirely combinatorial and based on the counting of certain paths in the graphs
shown by Hong and Szyma\'nski to describe the quantum lens spaces.Comment: 27 pages, 2 figure
1/z-renormalization of the mean-field behavior of the dipole-coupled singlet-singlet system HoF_3
The two main characteristics of the holmium ions in HoF_3 are that their
local electronic properties are dominated by two singlet states lying well
below the remaining 4f-levels, and that the classical dipole-coupling is an
order of magnitude larger than any other two-ion interactions between the
Ho-moments. This combination makes the system particularly suitable for testing
refinements of the mean-field theory. There are four Ho-ions per unit cell and
the hyperfine coupled electronic and nuclear moments on the Ho-ions order in a
ferrimagnetic structure at T_C=0.53 K. The corrections to the mean-field
behavior of holmium triflouride, both in the paramagnetic and ferrimagnetic
phase, have been calculated to first order in the high-density 1/z-expansion.
The effective medium theory, which includes the effects of the single-site
fluctuations, leads to a substantially improved description of the magnetic
properties of HoF_3, in comparison with that based on the mean-field
approximation.Comment: 26pp, plain-TeX, JJ
Dimensional reduction in a model with infinitely many absorbing states
Using Monte Carlo method we study a two-dimensional model with infinitely
many absorbing states. Our estimation of the critical exponent beta=0.273(5)
suggests that the model belongs to the (1+1) rather than (2+1)
directed-percolation universality class. We also show that for a large class of
absorbing states the dynamic Monte Carlo method leads to spurious dynamical
transitions.Comment: 6 pages, 4 figures, Phys.Rev. E, Dec. 199
Synthesis of imide/arylene ether copolymers for adhesives and composite matrices
A series of imide/arylene ether copolymers were prepared from the reaction of an amorphous arylene ether oligomer and a semi-crystalline imide oligomer. These copolymers were thermally characterized and mechanical properties were measured. One block copolymer was endcapped and the molecular weight was controlled to provide a material that displayed good compression moldability and attractive adhesion and composite properties
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