1,441 research outputs found
Dissipative particle dynamics study of solvent mediated transitions in pores decorated with tethered polymer brushes in the form of stripes
We study self-assembly of a binary mixture of components A and B confined in
a slit-like pore with the walls modified by the stripes of tethered brushes
made of beads of a sort A. The emphasis is on solvent mediated transitions
between morphologies when the composition of the mixture varies. For certain
limiting cases of the pore geometry we found that an effective reduction of the
dimensionality may lead to a quasi one- and two-dimensional demixing. The
change of the environment for the chains upon changing the composition of the
mixture from polymer melt to a good solvent conditions provides explanation for
the mechanism of development of several solvent mediated morphologies and, in
some cases, for switching between them. We found solvent mediated lamellar,
meander and in-lined cylinder phases. Quantitative analysis of morphology
structure is performed considering brush overlap integrals and gyration tensor
components.Comment: 14 pages, 12 figure
Isobaric-isothermal molecular dynamics computer simulations of the properties of water-1,2-dimethoxyethane model mixtures
Isothermal-isobaric molecular dynamics simulations have been performed to
examine a broad set of properties of the model water-1,2-dimethoxyethane (DME)
mixture as a function of composition. The SPC-E and TIP4P-Ew water models and
the modified TraPPE model for DME were applied. Our principal focus was to
explore the trends of behaviour of the structural properties in terms of the
radial distribution functions, coordination numbers and number of hydrogen
bonds between molecules of different species, and of conformations of DME
molecules. Thermodynamic properties, such as density, molar volume, enthalpy of
mixing and heat capacity at constant pressure have been examined. Finally, the
self-diffusion coefficients of species and the dielectric constant of the
system were calculated and analyzed.Comment: 14 pages, 9 figure
Did You Use This IUD? Legal Advice in Lawyer Advertising: Zauderer v. Office of Disciplinary Counsel
Employment in America's Charities: A Profile
This report presents the result of a study on employment in America's charities carried out by the Johns Hopkins Center for Civil Society Studies. This research covers the full non-profit workforce in health, education, civic, scientific and charitable organisations, including both paid and volunteer workers. Statistics as well as charts are also included
The dynamical equivalence of modified gravity revisited
We revisit the dynamical equivalence between different representations of
vacuum modified gravity models in view of Legendre transformations. The
equivalence is discussed for both bulk and boundary space, by including in our
analysis the relevant Gibbons-Hawking terms. In the f(R) case, the Legendre
transformed action coincides with the usual Einstein frame one. We then
re-express the R+f(G) action, where G is the Gauss-Bonnet term, as a second
order theory with a new set of field variables, four tensor fields and one
scalar and study its dynamics. For completeness, we also calculate the
conformal transformation of the full Jordan frame R+f(G) action. All the
appropriate Gibbons-Hawking terms are calculated explicitly.Comment: 17 pages; v3: Revised version. New comments added in Sections 3 & 5.
New results added in Section 6. Version to appear in Class. Quantum Gravit
The liquid-vapor interface of the restricted primitive model of ionic fluids from a density functional approach
We investigate the liquid-vapor interface of the restricted primitive model
for an ionic fluid using a density functional approach. The applied theory
includes the electrostatic contribution to the free energy functional arising
from the bulk energy equation of state and the mean spherical approximation for
a restricted primitive model, as well as the associative contribution, due to
the formation of pairs of ions. We compare the density profiles and the values
of the surface tension with previous theoretical approaches.Comment: 12 pages, 8 figure
Microscopic structure and thermodynamics of a core-softened model fluid from the second-order integral equations theory
We have studied the structure and thermodynamic properties of isotropic
three-dimensional core-softened fluid by using the second-order
Ornstein-Zernike integral equations completed by the hypernetted chain and
Percus-Yevick closures. The radial distribution functions are compared with
those from singlet integral equations and with computer simulation data. The
limits of the region of density anomaly resulting from different approximate
theories are established. The obtained results show that the second-order
hypernetted chain approximation can be used to describe both the structure and
the density anomaly of this model fluid. Moreover, we present the results of
calculations of the bridge functions.Comment: 12 pages, 6 figure
Evaporation and Step Edge Diffusion in MBE
Using kinetic Monte-Carlo simulations of a Solid-on-Solid model we
investigate the influence of step edge diffusion (SED) and evaporation on
Molecular Beam Epitaxy (MBE). Based on these investigations we propose two
strategies to optimize MBE-growth. The strategies are applicable in different
growth regimes: during layer-by-layer growth one can reduce the desorption rate
using a pulsed flux. In three-dimensional (3D) growth the SED can help to grow
large, smooth structures. For this purpose the flux has to be reduced with time
according to a power law.Comment: 5 pages, 2 figures, latex2e (packages: elsevier,psfig,latexsym
Effect of strontium and cooling rate upon eutectic temperatures of A319 aluminum alloy
DTA analysis was used to investigate the solidification reactions of alloy A319 with either 12 or 136 ppm of Sr added. Strontium does not affect primary solidification of (Al) dendrites but modifies the kinetics of the (Al)–Si eutectic. The effects of Sr level and of cooling rate on the characteristic temperatures for the (Al)–Si and other eutectic reactions are described
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