1,090 research outputs found
Anodized aluminium pressure sensitive paint: effect of paint application technique
The porous surface of the Anodized Aluminium Pressure Sensitive Paint (AA-PSP) is what differentiates it from conventional sol–gel based PSPs, leading to a faster response time of the paint. The objective of the current study is to examine the effect of the paint application technique, i.e., whether the AA substrate is dipped or sprayed, on the pressure and temperature sensitivity. A more practical procedure for preparing the AA samples is also presented. Scanning Electron Microscope (SEM) images are acquired together with the calibration of the AA-PSP at various temperatures and pressures to determine the effectiveness of each application technique. The results revealed that the AA sample which was dipped in the PSP solution shows a higher pressure sensitivity than the sprayed one. The SEMs show that spraying leads to the covering up of the micropores created on the surface and undermining the benefit of anodization
Unwrapping of DNA-protein complexes under external stretching
A DNA-protein complex modelled by a semiflexible chain and an attractive
spherical core is studied in the situation when an external stretching force is
acting on one end monomer of the chain while the other end monomer is kept
fixed in space. Without stretching force, the chain is wrapped around the core.
By applying an external stretching force, unwrapping of the complex is induced.
We study the statics and the dynamics of the unwrapping process by computer
simulation and simple phenomenological theory. We find two different scenarios
depending on the chain stiffness: For a flexible chain, the extension of the
complex scales linearly with the external force applied. The sphere-chain
complex is disordered, i.e. there is no clear winding of the chain around the
sphere. For a stiff chain, on the other hand, the complex structure is ordered,
which is reminiscent to nucleosome. There is a clear winding number and the
unwrapping process under external stretching is discontinuous with jumps of the
distance-force curve. This is associated to discrete unwinding processes of the
complex. Our predictions are of relevance for experiments, which measure
force-extension curves of DNA-protein complexes, such as nucleosome, using
optical tweezers.Comment: 8 pages, 7 figure
Ring polymers in melts and solutions: scaling and crossover
We propose a simple mean-field theory for the structure of ring polymer
melts. By combining the notion of topological volume fraction and a classical
van der Waals theory of fluids, we take into account many body effects of
topological origin in dense systems. We predict that although the compact
statistics with the Flory exponent is realized for very long chains,
most practical cases fall into the crossover regime with the apparent exponent
during which the system evolves toward a topological dense-packed
limit.Comment: 4 pages, 3 figure
How does torsional rigidity affect the wrapping transition of a semiflexible chain around a spherical core?
We investigated the effect of torsional rigidity of a semiflexible chain on
the wrapping transition around a spherical core, as a model of nucleosome, the
fundamental unit of chromatin. Through molecular dynamics simulation, we show
that the torsional effect has a crucial effect on the chain wrapping around the
core under the topological constraints. In particular, the torsional stress (i)
induces the wrapping/unwrapping transition, and (ii) leads to a unique complex
structure with an antagonistic wrapping direction which never appears without
the topological constraints. We further examine the effect of the stretching
stress for the nucleosome model, in relation to the unique characteristic
effect of the torsional stress on the manner of wrapping
Unifying model of driven polymer translocation
We present a Brownian dynamics model of driven polymer translocation, in
which non-equilibrium memory effects arising from tension propagation (TP)
along the cis side subchain are incorporated as a time-dependent friction. To
solve the effective friction, we develop a finite chain length TP formalism,
expanding on the work of Sakaue [Sakaue, PRE 76, 021803 (2007)]. The model,
solved numerically, yields results in excellent agreement with molecular
dynamics simulations in a wide range of parameters. Our results show that
non-equilibrium TP along the cis side subchain dominates the dynamics of driven
translocation. In addition, the model explains the different scaling of
translocation time w.r.t chain length observed both in experiments and
simulations as a combined effect of finite chain length and pore-polymer
interactions.Comment: 7 pages, 3 figure
Maxwell stress in fluid mixtures
We examine the structure of Maxwell stress in binary fluid mixtures under an
external electric field and discuss its consequence. In particular, we show
that, in immiscible blends, it is intimately related to the statistics of
domain structure. This leads to a compact formula, which may be useful in the
investigation of electro-rheological effects in such systems. The stress tensor
calculated in a phase separated fluid under a steady electric field is in a
good agreement with recent experiments.Comment: 5 page
Correlation, Breit and Quantum Electrodynamics effects on energy level and transition properties of W ion
The electron correlation effects and Breit interaction as well as Quantum
Electro-Dynamics (QED) effects were expected to have important contribution to
the energy level and transition properties of heavy highly charged ions. The
ground states [Ne] and first excited states
[Ne]3s of W ion have been studied by using
Multi-Configuration Dirac-Fock method with the implementation of Grasp2K
package. A restricted active space was employed to investigate the correlation
contribution from different models. The Breit interaction and QED effects were
taken into account in the relativistic configuration interaction calculation
with the converged wavefunction. It is found that the correlation contribution
from 3s and 3p orbital have important contribution to the energy level,
transition wavelength and probability of the ground and the first excited state
of W ion
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