375 research outputs found
Weakly coupled, antiparallel, totally asymmetric simple exclusion processes
We study a system composed of two parallel totally asymmetric simple
exclusion processes with open boundaries, where the particles move in the two
lanes in opposite directions and are allowed to jump to the other lane with
rates inversely proportional to the length of the system. Stationary density
profiles are determined and the phase diagram of the model is constructed in
the hydrodynamic limit, by solving the differential equations describing the
steady state of the system, analytically for vanishing total current and
numerically for nonzero total current. The system possesses phases with a
localized shock in the density profile in one of the lanes, similarly to
exclusion processes endowed with nonconserving kinetics in the bulk. Besides,
the system undergoes a discontinuous phase transition, where coherently moving
delocalized shocks emerge in both lanes and the fluctuation of the global
density is described by an unbiased random walk. This phenomenon is analogous
to the phase coexistence observed at the coexistence line of the totally
asymmetric simple exclusion process, however, as a consequence of the
interaction between lanes, the density profiles are deformed and in the case of
asymmetric lane change, the motion of the shocks is confined to a limited
domain.Comment: 14 pages, 15 figures, to appear in Phys. Rev.
Direct observation of the tube model in F-actin solutions
Mutual uncrossability of polymers generates topological constraints on their
conformations and dynamics, which are generally described using the tube model.
We imaged confinement tubes for individual polymers within a F-actin solution
by sampling over many successive micrographs of fluorescently labeled probe
filaments. The resulting average tube width shows the predicted scaling
behavior. Unexpectedly, we found an exponential distribution of tube curvatures
which is attributed to transient entropic trapping in network void spaces.Comment: 6 pages, 4 figure
A diffusive system driven by a battery or by a smoothly varying field
We consider the steady state of a one dimensional diffusive system, such as
the symmetric simple exclusion process (SSEP) on a ring, driven by a battery at
the origin or by a smoothly varying field along the ring. The battery appears
as the limiting case of a smoothly varying field, when the field becomes a
delta function at the origin. We find that in the scaling limit, the long range
pair correlation functions of the system driven by a battery turn out to be
very different from the ones known in the steady state of the SSEP maintained
out of equilibrium by contact with two reservoirs, even when the steady state
density profiles are identical in both models
Archeologische evaluatie en waardering van een site uit de bandkeramiek (Riemst, provincie Limburg)
Archeologisch onderzoek op de paddock aan de Toekomststraat in Riemst toonde in 2009 aan dat op een vlakker deel van de uitloper van dit leemplateau resten van een vroege bandkeramische nederzetting bewaard bleven in de vorm van aardewerk, lithische artefacten en verbrand bot. Bovendien werd toen het grondplan van een bandkeramische boerderij opgetekend en voor een deel ook een tweede boerderij. Op basis van deze waarnemingen ging het om één van de eerste en weinige getuigen van de vroegste kolonisatie van onze gewesten in het vroegneolithicum. In de loop van 2011 voerde het onderzoeks- en adviesbureau Triharch een bijkomende studie uit in functie van een eventuele bescherming van deze site. Dit rapport presenteert de resultaten hiervan. Uitgebreid magnetometer-onderzoek gaf duidelijke aanwijzingen over de aanwezigheid van verschillende plattegronden van LBK-boerderijen binnen de site. De archeologische boringen, gericht op de geofysische anomalieën lieten toe de minimale omvang van de site te bepalen (minstens 1,7 ha), maar vermoedelijk strekt ze zich nog uit in verschillende richtingen. De bewaringstoestand werd vooral bepaald door de historische erosie in kaart te brengen. Hieruit bleek ze goed tot vrij goed bewaard binnen haar minimale afbakening en hoogstwaarschijnlijk ook nauwelijks gecontamineerd door recentere archeologische sporen. Daarvan werden er alleszins nauwelijks gevonden. De grootste recente verstoorder was vermoedelijk de ruilverkaveling uit 1956. Er volgen enkele aanbevelingen voor toekomstig beheer. Op basis van het waarderingsonderzoek besluit het rapport dat de site zeker binnen haar minimale omvang beschermenswaardig is
Limited Lifespan of Fragile Regions in Mammalian Evolution
An important question in genome evolution is whether there exist fragile
regions (rearrangement hotspots) where chromosomal rearrangements are happening
over and over again. Although nearly all recent studies supported the existence
of fragile regions in mammalian genomes, the most comprehensive phylogenomic
study of mammals (Ma et al. (2006) Genome Research 16, 1557-1565) raised some
doubts about their existence. We demonstrate that fragile regions are subject
to a "birth and death" process, implying that fragility has limited
evolutionary lifespan. This finding implies that fragile regions migrate to
different locations in different mammals, explaining why there exist only a few
chromosomal breakpoints shared between different lineages. The birth and death
of fragile regions phenomenon reinforces the hypothesis that rearrangements are
promoted by matching segmental duplications and suggests putative locations of
the currently active fragile regions in the human genome
Effect of molecular and electronic structure on the light harvesting properties of dye sensitizers
The systematic trends in structural and electronic properties of perylene
diimide (PDI) derived dye molecules have been investigated by DFT calculations
based on projector augmented wave (PAW) method including gradient corrected
exchange-correlation effects. TDDFT calculations have been performed to study
the visible absorbance activity of these complexes. The effect of different
ligands and halogen atoms attached to PDI were studied to characterize the
light harvesting properties. The atomic size and electronegativity of the
halogen were observed to alter the relaxed molecular geometries which in turn
influenced the electronic behavior of the dye molecules. Ground state molecular
structure of isolated dye molecules studied in this work depends on both the
halogen atom and the carboxylic acid groups. DFT calculations revealed that the
carboxylic acid ligands did not play an important role in changing the
HOMO-LUMO gap of the sensitizer. However, they serve as anchor between the PDI
and substrate titania surface of the solar cell or photocatalyst. A
commercially available dye-sensitizer, ruthenium bipyridine (RuBpy), was also
studied for electronic and structural properties in order to make a comparison
with PDI derivatives for light harvesting properties. Results of this work
suggest that fluorinated, chlorinated, brominated, and iyodinated PDI compounds
can be useful as sensitizers in solar cells and in artificial photosynthesis.Comment: Single pdf file, 14 pages with 7 figures and 4 table
Greedy Solution of Ill-Posed Problems: Error Bounds and Exact Inversion
The orthogonal matching pursuit (OMP) is an algorithm to solve sparse
approximation problems. Sufficient conditions for exact recovery are known with
and without noise. In this paper we investigate the applicability of the OMP
for the solution of ill-posed inverse problems in general and in particular for
two deconvolution examples from mass spectrometry and digital holography
respectively.
In sparse approximation problems one often has to deal with the problem of
redundancy of a dictionary, i.e. the atoms are not linearly independent.
However, one expects them to be approximatively orthogonal and this is
quantified by the so-called incoherence. This idea cannot be transfered to
ill-posed inverse problems since here the atoms are typically far from
orthogonal: The ill-posedness of the operator causes that the correlation of
two distinct atoms probably gets huge, i.e. that two atoms can look much alike.
Therefore one needs conditions which take the structure of the problem into
account and work without the concept of coherence. In this paper we develop
results for exact recovery of the support of noisy signals. In the two examples
in mass spectrometry and digital holography we show that our results lead to
practically relevant estimates such that one may check a priori if the
experimental setup guarantees exact deconvolution with OMP. Especially in the
example from digital holography our analysis may be regarded as a first step to
calculate the resolution power of droplet holography
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Complexity within an oil palm monoculture: The effects of habitat variability and rainfall on adult dragonfly (Odonata) communities
Recent expansion of oil palm agriculture has resulted in loss of forest habitat and forest-dependent species. However, large numbers of species – particularly insects – can persist within plantations. This study focuses on Odonata (dragonflies and damselflies): a charismatic indicator taxon, and a potentially valuable pest control agent. We surveyed adult Odonata populations biannually over three years within an industrial oil palm plantation in Sumatra, Indonesia. We assessed the effects of rainfall (including an El Niño Southern Oscillation-associated drought), the role of roadside ditches, and the importance of understory vegetation on Odonata populations. To assess the impacts of vegetation we took advantage of a long-term vegetation management experiment that is part of the Biodiversity and Ecosystem Function in Tropical Agriculture (BEFTA) Programme. We found 41 Odonata species, and communities varied between plantation core and roadside edge microhabitats, and between seasons. Abundance was significantly related to rainfall levels four months before surveys, probably indicating the importance of high water levels in roadside ditches for successful larval development. We found no significant effect of the BEFTA understory vegetation treatments on Odonata abundance, and only limited effects on community composition, suggesting that local understory vegetation structure plays a relatively unimportant role in determining communities. Our findings highlight that there are large numbers of Odonata species present within oil palm plantations, and suggest that their abundance could potentially be increased by maintaining or establishing waterbodies. As Odonata are predators, this could bring pest control benefits, in addition to enhancing biodiversity within intensive agricultural landscapes.This work was funded by The Isaac Newton Trust Cambridge, Golden Agri Resources, and the Natural Environment Research Council [grant number NE/P00458X/1]
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