5,334 research outputs found
Electrochemically Modulated Permeability of Poly(aniline) and Composite Poly(aniline)−Poly(styrenesulfonate) Membranes
The influence of oxidation state on the permeability of several probe molecules through conducting polymer membranes comprising composites of poly(aniline) and poly(styrenesulfonate) was examined in aqueous solution. Pure poly(aniline) membranes displayed a characteristic increase in permeability between reduced and half-oxidized states for neutrally charged phenol and negatively charged 4-hydroxybenzenesulfonate. In contrast, positively charged pyridine experienced decreased permeability through the membrane when poly(aniline) was switched from the reduced to the half-oxidized state. This behavior can be explained by a combination of oxidation-induced film swelling and the anion-exchange character of the positively charged membrane. The membrane composition was modified to include a fixed negative charge by the addition of poly(styrenesulfonate) during synthesis. The incorporation of this negatively charged component introduced cation-exchange character to the film and substantially reduced membrane permeability to 4-hydroxybenzenesulfonate in both oxidation states. In addition, increasing the fraction of poly(styrenesulfonate) in the membrane served to decrease film permeability for all species because of a densification of the membrane. This work demonstrates how both film composition and oxidation state can be used to tune the permeability of conducting polymer membranes
Ion-neutral decoupling in the nonlinear Kelvin–Helmholtz instability: Case of field-aligned flow
This is the author accepted manuscript. The final version is available from AIP Publishing via the DOI in this recordThe nonlinear magnetic Kelvin-Helmholtz instability (KHi), and the turbulence it creates, appears in many astrophysical
systems. This includes those systems where the local plasma conditions are such that the plasma is not fully ionised,
for example in the lower solar atmosphere and molecular clouds. In a partially ionised system, the fluids couple
via collisions which occur at characteristic frequencies, therefore neutral and plasma species become decoupled for
sufficiently high-frequency dynamics. Here we present high-resolution 2D two-fluid simulations of the nonlinear KHi
for a system that traverses the dynamic scales between decoupled fluids and coupled dynamics. We discover some
interesting phenomena, including the presence of a density coupling that is independent of the velocity coupling. Using
these simulations we analyse the heating rate, and two regimes appear. The first is a regime where the neutral flow
is decoupled from the magnetic field that is characterised with a constant heating rate, then at larger scales the strong
coupling approximation holds and the heating rate. At large scales with the KHi layer width to the 2 power. There is
an energy cascade in the simulation, but the nature of the frictional heating means the heating rate is determined by the
largest scale of the turbulent motions, a fact that has consequences for understanding turbulent dissipation in multi-fluid
systems.Science and Technology Facilities Council (STFC
Random Walks Along the Streets and Canals in Compact Cities: Spectral analysis, Dynamical Modularity, Information, and Statistical Mechanics
Different models of random walks on the dual graphs of compact urban
structures are considered. Analysis of access times between streets helps to
detect the city modularity. The statistical mechanics approach to the ensembles
of lazy random walkers is developed. The complexity of city modularity can be
measured by an information-like parameter which plays the role of an individual
fingerprint of {\it Genius loci}.
Global structural properties of a city can be characterized by the
thermodynamical parameters calculated in the random walks problem.Comment: 44 pages, 22 figures, 2 table
Measurement of the production branching ratios following nuclear muon capture for palladium isotopes using the in-beam activation method
Background: The energy distribution of excited states populated by the
nuclear muon capture reaction can facilitate an understanding of the reaction
mechanism; however, experimental data are fairly sparse. Purpose: We developed
a new methodology, called the in-beam activation method, to measure the
production probability of residual nuclei by muon capture. For the first
application of the new method, we have measured muon-induced activation of five
isotopically-enriched palladium targets. Methods: The experiment was conducted
at the RIKEN-RAL muon facility of the Rutherford Appleton Facility in the UK.
The pulsed muon beam impinged on the palladium targets and gamma rays from the
beta and isomeric decays from the reaction residues were measured using
high-purity germanium detectors in both the in-beam and offline setups.
Results: The production branching ratios of the residual nuclei of muon capture
for five palladium isotopes with mass numbers A = 104, 105, 106, 108, and 110
were obtained. The results were compared with a model calculation using the
particle and heavy ion transport system (PHITS) code. The model calculation
well reproduces the experimental data. Conclusion: For the first time, this
study provides experimental data on the distribution of production branching
ratios without any theoretical estimation or assumptions in the interpretation
of the data analysisComment: 20 pages, 11 figure
Global modelling of X-ray spectra produced in O-type star winds
High-resolution X-ray spectra of O-type stars revealed less wind absorption
than expected from smooth winds with conventional mass-loss rates. Various
solutions have been proposed, including porous winds, optically thick clumps or
an overall reduction of the mass-loss rates. The latter has a strong impact on
the evolution of the star. Our final goal is to analyse high resolution X-ray
spectra of O-type stars with a multi temperature plasma model in order to
determine crucial wind parameters such as the mass loss rate, the CNO
abundances and the X-ray temperature plasma distribution in the wind. In this
context we are developing a modelling tool to calculate synthetic X-ray
spectra. We present, here, the main ingredients and physics necessary for a
such work. Our code uses the AtomDB emissivities to compute the intrinsic
emissivity of the hot plasma as well as the CMFGEN model atmosphere code to
evaluate the opacity of the cool wind. Following the comparison between two
formalisms of stellar wind fragmentation, we introduce, for the first time in
X-rays, the effects of a tenuous inter-clump medium. We then explore the
quantitative impact of different model parameters on the X-ray spectra such as
the position in the wind of the X-ray emitting plasma. For the first time, we
show that the two formalisms of stellar wind fragmentation yield different
results, although the differences for individual lines are small and can
probably not be tested with the current generation of X-ray telescopes. As an
illustration of our method, we compare various synthetic line profiles to the
observed O VIII {\lambda} 18.97{\AA} line in the spectrum of {\zeta} Puppis. We
illustrate how different combinations of parameters can actually lead to the
same morphology of a single line, underlining the need to analyse the whole
spectrum in a consistent way when attempting to constrain the parameters of the
wind.Comment: accepted for publication in Ap
X-ray Line Emission from the Hot Stellar Wind of theta 1 Ori C
We present a first emission line analysis of a high resolution X-ray spectrum
of the stellar wind of theta 1 Ori C obtained with the High Energy Transmission
grating Spectrometer onboard the Chandra X-ray Observatory. The spectra are
resolved into a large number of emission lines from H- and He-like O, Ne, Mg,
Si, S, Ar and Fe ions. The He-like Fe XXV and Li-like Fe XXIV appear quite
strong indicating very hot emitting regions. From H/He flux ratios, as well as
from Fe He/Li emission measure ratios we deduce temperatures ranging from 0.5
to 6.1 x 10^7 K. The He-triplets are very sensitive to density as well. At
these temperatures the relative strengths of the intercombination and forbidden
lines indicate electron densities well above 10^12 cm^-3. The lines appear
significantly broadened from which we deduce a mean velocity of 770 km/s with a
spread between 400 and 2000 km/s. Along with results of the deduced emission
measure we conclude that the X-ray emission could originate in dense and hot
regions with a characteristic size of less then 4 x 10^10 cm.Comment: 4 pages, 3 figure
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