3,277 research outputs found
Collapse dynamics of copolymers in a poor solvent: Influence of hydrodynamic interactions and chain sequence
We investigate the dynamics of the collapse of a single copolymer chain, when
the solvent quality is suddenly quenched from good to poor. We employ Brownian
dynamics simulations of a bead-spring chain model and incorporate fluctuating
hydrodynamic interactions via the Rotne-Prager-Yamakawa tensor. Various
copolymer architectures are studied within the framework of a two-letter HP
model, where monomers of type H (hydrophobic) attract each other, while all
interactions involving P (polar or hydrophilic) monomers are purely repulsive.
The hydrodynamic interactions are found to assist the collapse. Furthermore,
the chain sequence has a strong influence on the kinetics and on the
compactness and energy of the final state. The dynamics is typically
characterised by initial rapid cluster formation, followed by coalescence and
final rearrangement to form the compact globule. The coalescence stage takes
most of the collapse time, and its duration is particularly sensitive to the
details of the architecture. Long blocks of type P are identified as the main
bottlenecks to find the globular state rapidly.Comment: 25 pages, 13 figures, Submitted to Macromolecule
Energy-stable linear schemes for polymer-solvent phase field models
We present new linear energy-stable numerical schemes for numerical
simulation of complex polymer-solvent mixtures. The mathematical model proposed
by Zhou, Zhang and E (Physical Review E 73, 2006) consists of the Cahn-Hilliard
equation which describes dynamics of the interface that separates polymer and
solvent and the Oldroyd-B equations for the hydrodynamics of polymeric
mixtures. The model is thermodynamically consistent and dissipates free energy.
Our main goal in this paper is to derive numerical schemes for the
polymer-solvent mixture model that are energy dissipative and efficient in
time. To this end we will propose several problem-suited time discretizations
yielding linear schemes and discuss their properties
Particle rearrangements during transitions between local minima of the potential energy landscape of a supercooled Lennard-Jones liquid
The potential energy landscape (PEL) of supercooled binary Lennard-Jones
(BLJ) mixtures exhibits local minima, or inherent structures (IS), which are
organized into meta-basins (MB). We study the particle rearrangements related
to transitions between both successive IS and successive MB for a small 80:20
BLJ system near the mode-coupling temperature T_MCT. The analysis includes the
displacements of individual particles, the localization of the rearrangements
and the relevance of string-like motion. We find that the particle
rearrangements during IS and MB transitions do not change significantly at
T_MCT. Further, it is demonstrated that IS and MB dynamics are spatially
heterogeneous and facilitated by string-like motion. To investigate the
mechanism of string-like motion, we follow the particle rearrangements during
suitable sequences of IS transitions. We find that most strings observed after
a series of transitions do not move coherently during a single transition, but
subunits of different sizes are active at different times. Several findings
suggest that the occurrence of a successful string enables the system to exit a
MB. Moreover, we show that the particle rearrangements during two consecutive
MB transitions are basically uncorrelated. Specifically, different groups of
particles are highly mobile during subsequent MB transitions. Finally, the
relation between the features of the PEL and the relaxation processes in
supercooled liquids is discussed.Comment: 13 pages, 10 figure
D-region blunt probe data analysis using hybrid computer techniques
The feasibility of performing data reduction techniques with a hybrid computer was studied. The data was obtained from the flight of a parachute born probe through the D-region of the ionosphere. A presentation of the theory of blunt probe operation is included with emphasis on the equations necessary to perform the analysis. This is followed by a discussion of computer program development. Included in this discussion is a comparison of computer and hand reduction results for the blunt probe launched on 31 January 1972. The comparison showed that it was both feasible and desirable to use the computer for data reduction. The results of computer data reduction performed on flight data acquired from five blunt probes are also presented
Solubility of water in molten alkali chlorides
The solubility of water in molten mixtures of lithium chloride and potassium chloride containing 50.0, 53.0, 60.0, and 68.6 mole per cent lithium chloride was determined at 480 and 390oC in the pressure range zero to 26 mm. Melts were dried by alternate hydrogen chloride flushing and evacuation, and the solubility was determined by measuring the quantity of water vapor absorbed by the melt
Intestinal current measurements to diagnose cystic fibrosis
AbstractElectrophysiological techniques are essential for the diagnosis of cystic fibrosis. In the past ten years intestinal current measurements has emerged as valuable tool for this purpose. This overview highlights the objectives, methodology and current protocols to diagnose cystic fibrosis by intestinal current measurement on rectal biopsies
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