3,349 research outputs found
Graphoidal Tree d - Cover
Acharya and Sampathkumar defined a graphoidal cover as a partition of edges into internally disjoint (not necessarily open) paths. If we consider only open paths in
the above definition then we call it as a graphoidal path cover
Spatial control of irreversible protein aggregation
Liquid cellular compartments spatially segregate from the cytoplasm and can
regulate aberrant protein aggregation, a process linked to several medical
conditions, including Alzheimer's and Parkinson's diseases. Yet the mechanisms
by which these droplet-like compartments affect protein aggregation remain
unknown. Here, we combine kinetic theory of protein aggregation and
liquid-liquid phase separation to study the spatial control of irreversible
protein aggregation in the presence of liquid compartments. We find that, even
for weak interactions between the compartment constituents and the aggregating
monomers, aggregates are strongly enriched inside the liquid compartment
relative to the surrounding cytoplasm. We show that this enrichment is caused
by a positive feedback mechanism of aggregate nucleation and growth which is
mediated by a flux maintaining the phase equilibrium between the compartment
and the cytoplasm. Our model predicts that the compartment volume that
maximizes aggregate enrichment in the compartment is determined by the reaction
orders of aggregate nucleation. The underlying mechanism of aggregate
enrichment could be used to confine cytotoxic protein aggregates inside
droplet-like compartments suggesting potential new avenues against aberrant
protein aggregation. Our findings could also represent a common mechanism for
the spatial control of irreversible chemical reactions in general
Transitions to Nematic states in homogeneous suspensions of high aspect ratio magnetic rods
Isotropic-Nematic and Nematic-Nematic transitions from a homogeneous base
state of a suspension of high aspect ratio, rod-like magnetic particles are
studied for both Maier-Saupe and the Onsager excluded volume potentials. A
combination of classical linear stability and asymptotic analyses provides
insight into possible nematic states emanating from both the isotropic and
nematic non-polarized equilibrium states. Local analytical results close to
critical points in conjunction with global numerical results (Bhandar, 2002)
yields a unified picture of the bifurcation diagram and provides a convenient
base state to study effects of external orienting fields.Comment: 3 Figure
Electronic Structure of Sr_2FeMoO_6
We have analysed the unusual electronic structure of Sr_2FeMoO_6 combining
ab-initio and model Hamiltonian approaches. Our results indicate that there are
strong enhancements of the intraatomic exchange strength at the Mo site as well
as the antiferromagnetic coupling strength between Fe and Mo sites. We discuss
the possibility of a negative effective Coulomb correlation strength (U_{eff})
at the Mo site due to these renormalised interaction strengths.Comment: To appear in Phys. Rev. Let
The predictability of large-scale wind-driven flows
International audienceThe singular values associated with optimally growing perturbations to stationary and time-dependent solutions for the general circulation in an ocean basin provide a measure of the rate at which solutions with nearby initial conditions begin to diverge, and hence, a measure of the predictability of the flow. In this paper, the singular vectors and singular values of stationary and evolving examples of wind-driven, double-gyre circulations in different flow regimes are explored. By changing the Reynolds number in simple quasi-geostrophic models of the wind-driven circulation, steady, weakly aperiodic and chaotic states may be examined. The singular vectors of the steady state reveal some of the physical mechanisms responsible for optimally growing perturbations. In time-dependent cases, the dominant singular values show significant variability in time, indicating strong variations in the predictability of the flow. When the underlying flow is weakly aperiodic, the dominant singular values co-vary with integral measures of the large-scale flow, such as the basin-integrated upper ocean kinetic energy and the transport in the western boundary current extension. Furthermore, in a reduced gravity quasi-geostrophic model of a weakly aperiodic, double-gyre flow, the behaviour of the dominant singular values may be used to predict a change in the large-scale flow, a feature not shared by an analogous two-layer model. When the circulation is in a strongly aperiodic state, the dominant singular values no longer vary coherently with integral measures of the flow. Instead, they fluctuate in a very aperiodic fashion on mesoscale time scales. The dominant singular vectors then depend strongly on the arrangement of mesoscale features in the flow and the evolved forms of the associated singular vectors have relatively short spatial scales. These results have several implications. In weakly aperiodic, periodic, and stationary regimes, the mesoscale energy content is usually relatively low and the predictability of the wind-driven circulation is determined by the large-scale structure of the flow. In the more realistic, strongly chaotic regime, in which energetic mesoscale eddies are produced by the meandering of the separated western boundary current extension, the predictability of the flow locally tends to be a stronger function of the local mesoscale eddy structure than of the larger scale structure of the circulation. This has a broader implication for the effectiveness of different approaches to forecasting the ocean with models which sequentially assimilate new observations
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