1,575 research outputs found
Molecular simulation of 2-dimensional microphase separation of single-component homopolymers grafted onto a planar substrate
The structural phase behavior of polymer brushes, single-component linear
homopolymers grafted onto a planar substrate, is studied using the molecular
Monte Carlo method in 3 dimensions. When simulation parameters of the system
are set in regions of macrophase separation of solution for the corresponding
non-grafted homopolymers, the grafted polymers also prefer segregation.
However, macrophase separation is disallowed due to the spatially-fixed
grafting points of the polymers. Such constraints on the grafting are similar
to connecting points between blocks of non-grafted diblock copolymers at the
microphase separation in the melt state. This results in "microphase
separation" of the homopolymer brush in the lateral direction of the substrate.
Here we extensively search the parameter space and reveal various lateral
domain patterns that are similar to those found in diblock copolymer melts at
microphase separation.Comment: 6 pages, 5 figures, accepted for publication in EP
Aerodynamic investigation of an air-cooled axial-flow turbine. Part 2: Rotor blade tip-clearance effects on overall turbine performance and internal gas flow conditions: Experimental results and prediction methods
Total turbine blade performance was investigated while changing the blade tip clearance in three ways. The internal flow at the moving blade outlet point was measured. Experimental results were compared with various theoretical methods. Increased blade clearance leads to decreased turbine efficiency
Molecular Dynamics Study of Orientational Cooperativity in Water
Recent experiments on liquid water show collective dipole orientation
fluctuations dramatically slower then expected (with relaxation time 50 ns)
[D. P. Shelton, Phys. Rev. B {\bf 72}, 020201(R) (2005)]. Molecular dynamics
simulations of SPC/E water show large vortex-like structure of dipole field at
ambient conditions surviving over 300 ps [J. Higo at al. PNAS, {\bf 98} 5961
(2001)]. Both results disagree with previous results on water dipoles in
similar conditions, for which autocorrelation times are a few ps. Motivated by
these recent results, we study the water dipole reorientation using molecular
dynamics simulations in bulk SPC/E water for temperatures ranging from ambient
300 K down to the deep supercooled region of the phase diagram at 210 K. First,
we calculate the dipole autocorrelation function and find that our simulations
are well-described by a stretched exponential decay, from which we calculate
the {\it orientational autocorrelation time} . Second, we define a
second characteristic time, namely the time required for the randomization of
molecular dipole orientation, the {\it self-dipole randomization time}
, which is an upper limit on ; we find that
. Third, to check if there are correlated domains
of dipoles in water which have large relaxation times compared to the
individual dipoles, we calculate the randomization time of the
site-dipole field, the net dipole moment formed by a set of molecules belonging
to a box of edge . We find that the {\it site-dipole randomization
time} for \AA, i.e.
it is shorter than the same quantity calculated for the self-dipole. Finally,
we find that the orientational correlation length is short even at low .Comment: 25 Pages, 10 figure
Surgery for thoracic myelopathy caused by ossification of the ligamentum flavum
ArticleSURGICAL NEUROLOGY. 69(2): 114-116 (2008)journal articl
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