5,204 research outputs found
Thermodynamics, Structure, and Dynamics of Water Confined between Hydrophobic Plates
We perform molecular dynamics simulations of 512 water-like molecules that
interact via the TIP5P potential and are confined between two smooth
hydrophobic plates that are separated by 1.10 nm. We find that the anomalous
thermodynamic properties of water are shifted to lower temperatures relative to
the bulk by K. The dynamics and structure of the confined water
resemble bulk water at higher temperatures, consistent with the shift of
thermodynamic anomalies to lower temperature. Due to this shift, our
confined water simulations (down to K) do not reach sufficiently low
temperature to observe a liquid-liquid phase transition found for bulk water at
K using the TIP5P potential. We find that the different
crystalline structures that can form for two different separations of the
plates, 0.7 nm and 1.10 nm, have no counterparts in the bulk system, and
discuss the relevance to experiments on confined water.Comment: 31 pages, 14 figure
Interplay Between Time-Temperature-Transformation and the Liquid-Liquid Phase Transition in Water
We study the TIP5P water model proposed by Mahoney and Jorgensen, which is
closer to real water than previously-proposed classical pairwise additive
potentials. We simulate the model in a wide range of deeply supercooled states
and find (i) the existence of a non-monotonic ``nose-shaped'' temperature of
maximum density line and a non-reentrant spinodal, (ii) the presence of a low
temperature phase transition, (iii) the free evolution of bulk water to ice,
and (iv) the time-temperature-transformation curves at different densities.Comment: RevTeX4, 4 pages, 4 eps figure
Effect of water-wall interaction potential on the properties of nanoconfined water
Much of the understanding of bulk liquids has progressed through study of the
limiting case in which molecules interact via purely repulsive forces, such as
a hard-core potential. In the same spirit, we report progress on the
understanding of confined water by examining the behavior of water-like
molecules interacting with planar walls via purely repulsive forces and compare
our results with those obtained for Lennard-Jones (LJ) interactions between the
molecules and the walls. Specifically, we perform molecular dynamics
simulations of 512 water-like molecules which are confined between two smooth
planar walls that are separated by 1.1 nm. At this separation, there are either
two or three molecular layers of water, depending on density. We study two
different forms of repulsive confinements, when the interaction potential
between water-wall is (i) and (ii) WCA-like repulsive potential. We
find that the thermodynamic, dynamic and structural properties of the liquid in
purely repulsive confinements qualitatively match those for a system with a
pure LJ attraction to the wall. In previous studies that include attractions,
freezing into monolayer or trilayer ice was seen for this wall separation.
Using the same separation as these previous studies, we find that the crystal
state is not stable with repulsive walls but is stable with WCA-like
repulsive confinement. However, by carefully adjusting the separation of the
plates with repulsive interactions so that the effective space
available to the molecules is the same as that for LJ confinement, we find that
the same crystal phases are stable. This result emphasizes the importance of
comparing systems only using the same effective confinement, which may differ
from the geometric separation of the confining surfaces.Comment: 20 pages, 10 figure
The COMPTEL instrumental line background
The instrumental line background of the Compton telescope COMPTEL onboard the
Compton Gamma-Ray Observatory is due to the activation and/or decay of many
isotopes. The major components of this background can be attributed to eight
individual isotopes, namely 2D, 22Na, 24Na, 28Al, 40K, 52Mn, 57Ni, and 208Tl.
The identification of instrumental lines with specific isotopes is based on the
line energies as well as on the variation of the event rate with time,
cosmic-ray intensity, and deposited radiation dose during passages through the
South-Atlantic Anomaly. The characteristic variation of the event rate due to a
specific isotope depends on its life-time, orbital parameters such as the
altitude of the satellite above Earth, and the solar cycle. A detailed
understanding of the background contributions from instrumental lines is
crucial at MeV energies for measuring the cosmic diffuse gamma-ray background
and for observing gamma-ray line emission in the interstellar medium or from
supernovae and their remnants. Procedures to determine the event rate from each
background isotope are described, and their average activity in spacecraft
materials over the first seven years of the mission is estimated.Comment: accepted for publication in A&A, 22 pages, 21 figure
A comparative framework: how broadly applicable is a 'rigorous' critical junctures framework?
The paper tests Hogan and Doyle's (2007, 2008) framework for examining critical junctures. This framework sought to incorporate the concept of ideational change in understanding critical junctures. Until its development, frameworks utilized in identifying critical junctures were subjective, seeking only to identify crisis, and subsequent policy changes, arguing that one invariably led to the other, as both occurred around the same time. Hogan and Doyle (2007, 2008) hypothesized ideational change as an intermediating variable in their framework, determining if, and when, a crisis leads to radical policy change. Here we test this framework on cases similar to, but different from, those employed in developing the exemplar. This will enable us determine whether the framework's relegation of ideational change to a condition of crisis holds, or, if ideational change has more importance than is ascribed to it by this framework. This will also enable us determined if the framework itself is robust, and fit for the purposes it was designed to perform â identifying the nature of policy change
The Image of Taiwan as a Travel Destination: Perspectives from Mainland China
This study presents the perceived and projected image of Taiwan as a travel destination from perspectives from Mainland China. The perceived image of Taiwan was examined by interviewing 28 Mainland Chinese; the projected image of Taiwan was investigated by analyzing articles in China's most popular travel magazines. The different types of images of Taiwan among visitors, nonvisitors, and travel magazines were compared. The projected image changed notably after the opening of Taiwan's tourism to travelers from Mainland China. The results of this study could help destination marketing organizations to assess their marketing strategies for the Mainland Chinese travel market
Many Roads to Synchrony: Natural Time Scales and Their Algorithms
We consider two important time scales---the Markov and cryptic orders---that
monitor how an observer synchronizes to a finitary stochastic process. We show
how to compute these orders exactly and that they are most efficiently
calculated from the epsilon-machine, a process's minimal unifilar model.
Surprisingly, though the Markov order is a basic concept from stochastic
process theory, it is not a probabilistic property of a process. Rather, it is
a topological property and, moreover, it is not computable from any
finite-state model other than the epsilon-machine. Via an exhaustive survey, we
close by demonstrating that infinite Markov and infinite cryptic orders are a
dominant feature in the space of finite-memory processes. We draw out the roles
played in statistical mechanical spin systems by these two complementary length
scales.Comment: 17 pages, 16 figures:
http://cse.ucdavis.edu/~cmg/compmech/pubs/kro.htm. Santa Fe Institute Working
Paper 10-11-02
QCSE and carrier blocking in P-modulation doped InAs/InGaAs quantum dots
The quantum confined Stark effect in InAs/InGaAs QDs using an undoped and p-modulation doped active region was investigated. Doping potentially offers more than a 3x increase in figure of merit modulator performance up to 100°C
A possible mechanism for cold denaturation of proteins at high pressure
We study cold denaturation of proteins at high pressures. Using
multicanonical Monte Carlo simulations of a model protein in a water bath, we
investigate the effect of water density fluctuations on protein stability. We
find that above the pressure where water freezes to the dense ice phase
( kbar), the mechanism for cold denaturation with decreasing
temperature is the loss of local low-density water structure. We find our
results in agreement with data of bovine pancreatic ribonuclease A.Comment: 4 pages for double column and single space. 3 figures Added
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