4,332 research outputs found
Interfaces between highly incompatible polymers of different stiffness: Monte Carlo simulations and self-consistent field calculations
We investigate interfacial properties between two highly incompatible
polymers of different stiffness. The extensive Monte Carlo simulations of the
binary polymer melt yield detailed interfacial profiles and the interfacial
tension via an analysis of capillary fluctuations. We extract an effective
Flory-Huggins parameter from the simulations, which is used in self-consistent
field calculations. These take due account of the chain architecture via a
partial enumeration of the single chain partition function, using chain
conformations obtained by Monte Carlo simulations of the pure phases. The
agreement between the simulations and self-consistent field calculations is
almost quantitative, however we find deviations from the predictions of the
Gaussian chain model for high incompatibilities or large stiffness. The
interfacial width at very high incompatibilities is smaller than the prediction
of the Gaussian chain model, and decreases upon increasing the statistical
segment length of the semi-flexible component.Comment: to appear in J.Chem.Phy
Monte Carlo simulations of copolymers at homopolymer interfaces: Interfacial structure as a function of the copolymer density
By means of extensive Monte Carlo simulations of the bond fluctuation model,
we study the effect of adding AB diblock copolymers on the properties of an
interface between demixed homopolymer phases. The parameters are chosen such
that the homopolymers are strongly segregated, and the whole range of copolymer
concentrations in the two phase coexistence region is scanned. We compare the
``mushroom'' regime, in which copolymers are diluted and do not interact with
each other, with the ``wet brush'' regime, where copolymers overlap and
stretch, but are still swollen by the homopolymers. A ``dry brush'' regime is
never entered for our choice of chain lengths. ``Intrinsic'' profiles are
calculated using a block analysis method introduced by us in earlier work. We
discuss density profiles, orientational profiles and contact number profiles.
In general, the features of the profiles are similar at all copolymer
concentrations, however, the profiles in the concentrated regime are much
broader than in the dilute regime. The results compare well with
self-consistent field calculations.Comment: to appear in J. Chem. Phy
The Christmas Island Seamount Province, Indian Ocean: Origin of Intraplate Volcanism by Shallow Recycling of Continental Lithosphere?
The east-west-trending Christmas Island Seamount
Province (CHRISP, 1800x600 km) in the northeastern Indian
Ocean is elongated orthogonal to present-day plate motion,
posing the question if a mantle plume formed this volcanic
belt. Here we report the first age (Ar/Ar) and geochemical (Sr-
Nd-Hf-Pb DS isotopic data) from the CHRISP seamount
chain. A crude E-W age decrease from the Argo Basin (136
Ma), to the Eastern Wharton Basin (115-94 Ma) to the
Vening-Meinesz seamounts (96-64 Ma) to the Cocos-Keeling
seamounts (56-47 Ma) suggests spatial migration of melting.
Christmas Island, however, yields much younger ages (44-4
Ma), inconsistent with an age progression. The isotopic
compositions (e.g. 206Pb/204Pb = 17.3-19.3; 207Pb/204Pb = 15.49-
15.67; 143Nd/144Nd = 0.51220-0.51295; 176Hf/177Hf = 0.28246-
0.28319) range from enriched MORB (or “C”) to very
enriched mantle (EM1) type compositions more typical of
continental than oceanic volcanism. Lamproitic and
kimberlitic rocks from western Australia, India and other
continental areas, derived from metasomatized subcontinental
lithospheric mantle, could serve as the EM1 type endmembers.
The morphology, ages and chemical composition of the
CHRISP, combined with plate tectonic reconstructions, cannot
be easily explained within the framework of the mantle plume
hypotheses. We therefore propose that the seamounts are
derived through the recycling of continental lithosphere
(mantle ± lower crust) delaminated during the breakup of
Gondwana and brought to the surface at the former spreading
centers separating Argoland (western Burma), Greater India
and Australia
Effect of long range forces on the interfacial profiles in thin binary polymer films
We study the effect of surface fields on the interfacial properties of a
binary polymer melt confined between two parallel walls. Each wall attracts a
different component of the blend by a non-retarded van der Waals potential. An
interface which runs parallel to the surfaces is stabilized in the center of
the film. Using extensive Monte Carlo simulations we study the interfacial
properties as a function of the film thickness, the strength of the surface
forces and the lateral size over which the profiles across the film are
averaged. We find evidence for capillary wave broadening of the apparent
interfacial profiles. However, the apparent interfacial width cannot be
described quantitatively by a simple logarithmic dependence on the film
thickness. The Monte Carlo simulations reveal that the surface fields give rise
to an additional reduction of the intrinsic interfacial width and an increase
of the effective interfacial tension upon decreasing the film thickness. These
modifications of the intrinsic interfacial properties are confirmed by
self-consistent field calculations. Taking account of the thickness dependence
of the intrinsic interfacial properties and the capillary wave broadening, we
can describe our simulation results quantitatively.Comment: to appear in J.Chem.Phy
Theory of nuclear excitation by electron capture for heavy ions
We investigate the resonant process of nuclear excitation by electron
capture, in which a continuum electron is captured into a bound state of an ion
with the simultaneous excitation of the nucleus. In order to derive the cross
section a Feshbach projection operator formalism is introduced. Nuclear states
and transitions are described by a nuclear collective model and making use of
experimental data. Transition rates and total cross sections for NEEC followed
by the radiative decay of the excited nucleus are calculated for various heavy
ion collision systems
First Experiences with Black Fungus Gnats (Sciaridae) to Biological Control of Broad-Leaved Dock (Rumex obtusifolius L.)
In sieben von acht überprüften Beständen des Stumpfblättrigen Ampfers (Rumex obtusifolius L.) waren in den Pfahlwurzeln Larven von Trauermücken (Sciaridae) vorhanden. Vereinzelt traten in und an den Pfahlwurzeln Larven von Rüsselkäfern und Schmetterlingsraupen auf. Durch das fortlaufende Fressen der Trauermückenlarven in den Pfahlwurzeln nimmt in den nachfolgenden Aufwüchsen und Jahren die Höhe der Ampferpflanzen ab, es werden keine Blütentriebe mehr gebildet und die Anzahl und Größe der Blätter verringert sich bis die völlig zerstörte Pfahlwurzel nicht mehr austreibt. In dem Ampferbestand mit dem Erstfund von Trauermücken hat sich die ampferfreie Fläche in dreieinhalb Jahren von 110 m² auf 499 m² erhöht. Der kleine Ampferbestand in Bermbach ist nach zwei Jahren, die Ampferbestände am Henneberger Haus bei Schmalkalden und in Themar sind nach fünf Jahren erloschen.Eine erfolgreiche biologische Bekämpfung des Stumpfblättrigen Ampfers ist möglich, wenn Larven von Trauermücken in den Pfahlwurzeln vorhanden sind und durch die Bewirtschaftungsmaßnahmen das Reifen der Ampfersamen unterbunden wird. DOI: 10.5073/JfK.2015.04.04, https://doi.org/10.5073/JfK.2015.04.04In seven out of eight examined stocks of broad-leaved dock larvae of black fungus gnats existed in the tap roots. Rarely, larvae of weevils and caterpillars occurred in and around the tap roots. The continuous eating of the larvae of black fungus gnats in the tap roots has the following effects in subsequent regrowths and years: the height of dock plants decreases, no more flowering shoots are formed, and the number and size of leaves reduces until the completely destroyed tap roots do no longer sprout. In the stock of dock where black fungus gnats have been detected first, the area clear of dock increased from 110 m² to 499 m² within three and a half years. The small stock of dock in Bermbach extinguished after two years, the stocks at Henneberger Haus near Schmalkalden and at Themar disappeared after five years.Successful biological control of broad-leaved dock is possible when larvae of black fungus gnats are present in the tap roots and farming prevents the dock seeds from ripening. DOI: 10.5073/JfK.2015.04.04, https://doi.org/10.5073/JfK.2015.04.0
The impact of main belt asteroids on infrared--submillimetre photometry and source counts
> Among the components of the infrared and submillimetre sky background,
the closest layer is the thermal emission of dust particles and minor bodies in
the Solar System. This contribution is especially important for current and
future infrared and submillimetre space instruments --like those of Spitzer,
Akari and Herschel -- and must be characterised by a reliable statistical
model. > We describe the impact of the thermal emission of main belt
asteroids on the 5...1000um photometry and source counts, for the current and
future spaceborne and ground-based instruments, in general, as well as for
specific dates and sky positions. > We used the statistical asteroid model
(SAM) to calculate the positions of main belt asteroids down to a size of 1km,
and calculated their infrared and submillimetre brightness using the standard
thermal model. Fluctuation powers, confusion noise values and number counts
were derived from the fluxes of individual asteroids. > We have constructed
a large database of infrared and submillimetre fluxes for SAM asteroids with a
temporal resolution of 5 days, covering the time span January 1, 2000 --
December 31, 2012. Asteroid fluctuation powers and number counts derived from
this database can be obtained for a specific observation setup via our public
web-interface. > Current space instruments working in the mid-infrared
regime (Akari and Spitzer Space Telescopes) are affected by asteroid confusion
noise in some specific areas of the sky, while the photometry of space infrared
and submillimetre instruments in the near future (e.g. Herschel and Planck
Space Observatories) will not be affected by asteroids. Faint main belt
asteroids might also be responsible for most of the zodiacal emission
fluctuations near the ecliptic.Comment: accepted for publication in Astronomy & Astrophysics; Additional
material (appendices) and the related web-interface can be found at:
"http://kisag.konkoly.hu/solarsystem/irsam.html
Reactions at polymer interfaces: A Monte Carlo Simulation
Reactions at a strongly segregated interface of a symmetric binary polymer
blend are investigated via Monte Carlo simulations. End functionalized
homopolymers of different species interact at the interface instantaneously and
irreversibly to form diblock copolymers. The simulations, in the framework of
the bond fluctuation model, determine the time dependence of the copolymer
production in the initial and intermediate time regime for small reactant
concentration . The results are compared to
recent theories and simulation data of a simple reaction diffusion model. For
the reactant concentration accessible in the simulation, no linear growth of
the copolymer density is found in the initial regime, and a -law is
observed in the intermediate stage.Comment: to appear in Macromolecule
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