2,048 research outputs found
Elastic response of filamentous networks with compliant crosslinks
Experiments have shown that elasticity of disordered filamentous networks
with compliant crosslinks is very different from networks with rigid
crosslinks. Here, we model and analyze filamentous networks as a collection of
randomly oriented rigid filaments connected to each other by flexible
crosslinks that are modeled as worm-like chains. For relatively large
extensions we allow for enthalpic stretching of crosslinks' backbones. We show
that for sufficiently high crosslink density, the network linear elastic
response is affine on the scale of the filaments' length. The nonlinear regime
can become highly nonaffine and is characterized by a divergence of the elastic
modulus at finite strain. In contrast to the prior predictions, we do not find
an asymptotic regime in which the differential elastic modulus scales linearly
with the stress, although an approximate linear dependence can be seen in a
transition from entropic to enthalpic regimes. We discuss our results in light
of the recent experiments.Comment: 10 pages, 11 figure
Electronic structure and magnetism in the frustrated antiferromagnet LiCrO2
LiCrO2 is a 2D triangular antiferromagnet, isostructural with the common
battery material LiCoO2 and a well-known Jahn-Teller antiferromagnet NaNiO2. As
opposed to the latter, LiCrO2 exibits antiferromagnetic exchange in Cr planes,
which has been ascribed to direct Cr-Cr d-d overlap. Using LDA and LDA+U first
principles calculations I confirm this conjecture and show that (a) direct d-d
overlap is indeed enhanced compared to isostructural Ni and Cr compounds, (b)
p-d charge transfer gap is also enhanced, thus suppressing the ferromagnetic
superexchange, (c) the calculated magnetic Hamiltonian maps well onto the
nearest neighbors Heisenberg exchange model and (d) interplanar inteaction is
antiferromagnetic.Comment: 5 pages, 4 figure
Multi-scale strain-stiffening of semiflexible bundle networks
Bundles of polymer filaments are responsible for the rich and unique
mechanical behaviors of many biomaterials, including cells and extracellular
matrices. In fibrin biopolymers, whose nonlinear elastic properties are crucial
for normal blood clotting, protofibrils self-assemble and bundle to form
networks of semiflexible fibers. Here we show that the extraordinary
strain-stiffening response of fibrin networks is a direct reflection of the
hierarchical architecture of the fibrin fibers. We measure the rheology of
networks of unbundled protofibrils and find excellent agreement with an affine
model of extensible wormlike polymers. By direct comparison with these data, we
show that physiological fibrin networks composed of thick fibers can be modeled
as networks of tight protofibril bundles. We demonstrate that the tightness of
coupling between protofibrils in the fibers can be tuned by the degree of
enzymatic intermolecular crosslinking by the coagulation Factor XIII.
Furthermore, at high stress, the protofibrils contribute independently to the
network elasticity, which may reflect a decoupling of the tight bundle
structure. The hierarchical architecture of fibrin fibers can thus account for
the nonlinearity and enormous elastic resilience characteristic of blood clots.Comment: 27 pages including 8 figures and Supplementary Dat
Influence of single-neutron stripping on near-barrier <sup>6</sup>He+<sup>208</sup>Pb and <sup>8</sup>He+<sup>208</sup>Pb elastic scattering
The influence of single-neutron stripping on the near-barrier elastic scattering angular distributions for the 6,8He+208Pb systems is investigated through coupled reaction channels (CRC) calculations fitting recently published data to explore the differences in the absorptive potential found in the scattering of these two neutron-rich nuclei. The inclusion of the coupling reduces the elastic cross section in the Coulomb-nuclear interference region for 8He scattering, whereas for 6He its major impact is on the large-angle elastic scattering. The real and imaginary dynamic polarization potentials are obtained by inverting the CRC elastic scattering S-matrix elements. These show that the main absorptive features occur between 11 and 12 fm for both projectiles, while the attractive features are separated by about 1 fm, with their main structures occurring at 10.5 fm for 6He and 11.5 fm for 8He
Magnetic and electric properties of double-perovskites and estimation of their Curie temperatures by ab initio calculations
First principles electronic structure calculations have been carried out on
ordered double perovskites Sr_2B'B"O_6 (for B' = Cr or Fe and B" 4d and 5d
transition metal elements) with increasing number of valence electrons at the
B-sites, and on Ba_2MnReO_6 as well as Ba_2FeMoO_6. The Curie temperatures are
estimated ab initio from the electronic structures obtained with the local
spin-density functional approximation, full-potential generalized gradient
approximation and/or the LDA+U method (U - Hubbard parameter). Frozen
spin-spirals are used to model the excited states needed to evaluate the
spherical approximation for the Curie temperatures. In cases, where the induced
moments on the oxygen was found to be large, the determination of the Curie
temperature is improved by additional exchange functions between the oxygen
atoms and between oxygen and B' and B" atoms.
A pronounced systematics can be found among the experimental and/or
calculated Curie temperatures and the total valence electrons of the transition
metal elements.Comment: 8 pages, 11 figures. Submitted to the Physical Review
Network Structures and Dynamics Of Early Dementia Events Recorded in Primary Care Electronic Health Records
Background: Identifying early signs of heterogeneous conditions like dementia is challenging. We used electronic health records (EHR) and data-driven methods in order to represent prodromal dementia as a dynamic temporal network of healthcare events and move beyond reductionist representations of complex syndromes. / Methods: We used UK primary care EHR data from Clinical Practice Research Datalink (CPRD) through the CALIBER resource and identified patients with a dementia diagnosis. We constructed a weighted, undirected network. We calculated centrality measures of the network and compared three community detection algorithms, Louvain, InfoMAP and Walktrap. Distinctive temporal communities of events in two year windows were derived, and we explored community membership, interactions and dynamics using evaluation measures including Jaccard distance, modularity, Rand Index and Normalised Mutual Information. / Results: We analysed data from 89,102 patients, where nodes (n=816) were connected to edges (n=392,345) based on the frequency with which two features were recorded in the same time window. Across the whole prodrome, repeated cardiovascular medications accounted for 22% of the network edges, followed by repeated central nervous system medications, accounting for 5% of edges. Cardiovascular conditions had the highest eigen centrality (influence on the entire network structure) and QRISK2 and malignant neoplasms had the greatest betweenness centrality (bridge between events). Louvin had the highest modularity and clustered the temporal network into six communities: The largest community was enriched for respiratory diseases (late-prodrome) and circulatory conditions (mid). Community 2 was enriched for musculoskeletal conditions (late), and Community 3 for administrative events (early) and nervous system conditions (late). In the early prodrome, there were more transitions between communities, however from 10 years to diagnosis, most events occurred within communities. / Conclusion: By understanding the interdependencies of conditions and associated medications across a disease network, we can deepen our understanding of prodromal dementia and create an accurate phenotype of the earliest stages of cognitive decline
Actively Contracting Bundles of Polar Filaments
We introduce a phenomenological model to study the properties of bundles of
polar filaments which interact via active elements. The stability of the
homogeneous state, the attractors of the dynamics in the unstable regime and
the tensile stress generated in the bundle are discussed. We find that the
interaction of parallel filaments can induce unstable behavior and is
responsible for active contraction and tension in the bundle. Interaction
between antiparallel filaments leads to filament sorting. Our model could apply
to simple contractile structures in cells such as stress fibers.Comment: 4 pages, 4 figures, RevTex, to appear in Phys. Rev. Let
Barrier and internal wave contributions to the quantum probability density and flux in light heavy-ion elastic scattering
We investigate the properties of the optical model wave function for light
heavy-ion systems where absorption is incomplete, such as Ca
and O around 30 MeV incident energy. Strong focusing effects
are predicted to occur well inside the nucleus, where the probability density
can reach values much higher than that of the incident wave. This focusing is
shown to be correlated with the presence at back angles of a strong enhancement
in the elastic cross section, the so-called ALAS (anomalous large angle
scattering) phenomenon; this is substantiated by calculations of the quantum
probability flux and of classical trajectories. To clarify this mechanism, we
decompose the scattering wave function and the associated probability flux into
their barrier and internal wave contributions within a fully quantal
calculation. Finally, a calculation of the divergence of the quantum flux shows
that when absorption is incomplete, the focal region gives a sizeable
contribution to nonelastic processes.Comment: 16 pages, 15 figures. RevTeX file. To appear in Phys. Rev. C. The
figures are only available via anonynous FTP on
ftp://umhsp02.umh.ac.be/pub/ftp_pnt/figscat
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