Transient Binding and Dissipation in Cross-Linked Actin Networks

In contrast with entangled actin solutions, transiently cross-linked actin networks can provide highly elastic properties while still allowing for local rearrangements in the microstructure-on biological relevant time scales. Here, we show that thermal unbinding of transient cross-links entails local stress relaxation and energy dissipation in an intermediate elasticity dominated frequency regime. We quantify the viscoelastic response of an isotropically cross-linked actin network by experimentally tuning the off rate of the transiently cross-linking molecules, their density, and the solvent viscosity. We reproduce the measured frequency response by a semiphenomenological model that is predicated on microscopic unbinding events

Mechanics of bundled semiflexible polymer networks

While actin bundles are used by living cells for structural fortification, the microscopic origin of the elasticity of bundled networks is not understood. Here, we show that above a critical concentration of the actin binding protein fascin, a solution of actin filaments organizes into a pure network of bundles. While the elasticity of weakly crosslinked networks is dominated by the affine deformation of tubes, the network of bundles can be fully understood in terms of non-affine bending undulations.Comment: 5 pages, 3 figures, final version as publishe

Cytoskeletal Polymer Networks: Viscoelastic Properties are Determined by the Microscopic Interaction Potential of Cross-links

AbstractAlthough the structure of cross-linking molecules mainly determines the structural organization of actin filaments and with that the static elastic properties of the cytoskeleton, it is largely unknown how the biochemical characteristics of transiently cross-linking proteins (actin-binding proteins (ABPs)) affect the viscoelasticity of actin networks. In this study, we show that the macroscopic network response of reconstituted actin networks can be traced back to the microscopic interaction potential of an individual actin/ABP bond. The viscoelastic response of cross-linked actin networks is set by the cross-linker off-rate, the binding energy, and the characteristic bond length of individual actin/ABP interactions

PERC rule to exclude the diagnosis of pulmonary embolism in emergency low-risk patients: study protocol for the PROPER randomized controlled study.

BACKGROUND: The diagnosis of Pulmonary Embolism (PE) in the emergency department (ED) is crucial. As emergency physicians fear missing this potential life-threatening condition, PE tends to be over-investigated, exposing patients to unnecessary risks and uncertain benefit in terms of outcome. The Pulmonary Embolism Rule-out Criteria (PERC) is an eight-item block of clinical criteria that can identify patients who can safely be discharged from the ED without further investigation for PE. The endorsement of this rule could markedly reduce the number of irradiative imaging studies, ED length of stay, and rate of adverse events resulting from both diagnostic and therapeutic interventions. Several retrospective and prospective studies have shown the safety and benefits of the PERC rule for PE diagnosis in low-risk patients, but the validity of this rule is still controversial. We hypothesize that in European patients with a low gestalt clinical probability and who are PERC-negative, PE can be safely ruled out and the patient discharged without further testing. METHODS/DESIGN: This is a controlled, cluster randomized trial, in 15 centers in France. Each center will be randomized for the sequence of intervention periods: a 6-month intervention period (PERC-based strategy) followed by a 6-month control period (usual care), or in reverse order, with 2 months of "wash-out" between the 2 periods. Adult patients presenting to the ED with a suspicion of PE and a low pre test probability estimated by clinical gestalt will be eligible. The primary outcome is the percentage of failure resulting from the diagnostic strategy, defined as diagnosed venous thromboembolic events at 3-month follow-up, among patients for whom PE has been initially ruled out. DISCUSSION: The PERC rule has the potential to decrease the number of irradiative imaging studies in the ED, and is reported to be safe. However, no randomized study has ever validated the safety of PERC. Furthermore, some studies have challenged the safety of a PERC-based strategy to rule-out PE, especially in Europe where the prevalence of PE diagnosed in the ED is high. The PROPER study should provide high-quality evidence to settle this issue. If it confirms the safety of the PERC rule, physicians will be able to reduce the number of investigations, associated subsequent adverse events, costs, and ED length of stay for patients with a low clinical probability of PE. TRIAL REGISTRATION: NCT02375919

Nonaffine rubber elasticity for stiff polymer networks

We present a theory for the elasticity of cross-linked stiff polymer networks. Stiff polymers, unlike their flexible counterparts, are highly anisotropic elastic objects. Similar to mechanical beams stiff polymers easily deform in bending, while they are much stiffer with respect to tensile forces (``stretching''). Unlike in previous approaches, where network elasticity is derived from the stretching mode, our theory properly accounts for the soft bending response. A self-consistent effective medium approach is used to calculate the macroscopic elastic moduli starting from a microscopic characterization of the deformation field in terms of ``floppy modes'' -- low-energy bending excitations that retain a high degree of non-affinity. The length-scale characterizing the emergent non-affinity is given by the ``fiber length'' $l_f$, defined as the scale over which the polymers remain straight. The calculated scaling properties for the shear modulus are in excellent agreement with the results of recent simulations obtained in two-dimensional model networks. Furthermore, our theory can be applied to rationalize bulk rheological data in reconstituted actin networks.Comment: 12 pages, 10 figures, revised Section II

Coevolution of religious and political authority in Austronesian societies

Authority, an institutionalized form of social power, is one of the defining features of the large-scale societies that evolved during the Holocene. Religious and political authority have deep histories in human societies and are clearly interdependent, but the nature of their relationship and its evolution over time is contested. We purpose-built an ethnographic dataset of 97 Austronesian societies and used phylogenetic methods to address two long-standing questions about the evolution of religious and political authority: first, how these two institutions have coevolved, and second, whether religious and political authority have tended to become more or less differentiated. We found evidence for mutual interdependence between religious and political authority but no evidence for or against a long-term pattern of differentiation or unification in systems of religious and political authority. Our results provide insight into how political and religious authority have worked synergistically over millennia during the evolution of large-scale societies

Simulations of the High-Energy Beam-Transport (HEBT) section at FRANZ

The neutron source FRANZ (Frankfurter Neutronenquelle am Stern-Gerlach-Zentrum), which is currently under construction, will be the neutron source with the highest intensity in the nuclear-astrophysically relevant energy region. The TraceWin code was used to design the High-Energy Beam-Transport section with regard to the experimental requirements at different target positions

Adapting Nyando smallholder farming systems to climate change and variability through modeling

This study was done in Nyando, Kenya to model maize production under different climate scenarios and project the yields up to 2030 and 2050 using Decision Support System for Agrotechnology Transfer (DSSAT) under rain fed conditions. Three maize varieties were used; Katumani Comp B as early maturing variety, Hybrid 511 as a medium maturing variety and Hybrid 614 as a late maturing variety. Global coupled model Hadley Centre Global Environment Model version 2 (HadGEM2-ES) under representative concentration pathways (RCP) 4.5 and 8.5 was used to downscale Nyando’s climate data for the years 2030 and 2050. Past climate data for 53 years and current data was obtained from Kisumu Meteorological station while crop growth and farm management data was obtained from 70 farmers in Nyando. Results showed a decrease in yields across the years from 2015, 2030 and 2050 under both RCP 4.5 and 8.5. Average simulated yields for 2015 were 2519 kg ha-1 while projected yields under RCP 4.5 were 2212 and 2081 kg ha-1 in 2030 and 2050 respectively. Average yield projections under RCP 8.5 were 2184 and 1806 kg ha-1 for the years 2030 and 2050 consecutively. The study found out that temperatures will increase and rainfall duration will reduce. In addition, Katumani Comp B maize variety was not very much affected by these changes in temperatures and rainfall compared to H511 and H614

Projet Nassonia : mise en place d'un inventaire forestier des arbres d'intérêt

Au sein du massif forestier de Saint-Hubert, 1 650 hectares de forêt domaniale sont cogérés, depuis plus de 2 ans, dans un schéma inédit de partenariat public-privé, par le DNF (SPW ARNE) et la Fondation Pairi Daiza. Ce projet Nassonia, d’une durée de 20 ans trois fois renouvelable, s’inscrit dans le temps long de la forêt. Il a pour objectif principal de placer la biodiversité et la naturalité au centre des enjeux de gestion au sein de ce territoire. Le présent article explique les résultats et la méthode d’un inventaire mis en place par l’équipe en charge du projet dans le but de fournir des données importantes pour la rédaction du nouveau plan d’aménagement forestier. Un des enjeux majeurs est effectivement de disposer, dans toute une série de domaines, d’un état des lieux initial, un t0

Pollination strategy of Gennaria diphylla (Orchidaceae) on the Canary Islands and on Madeira

Gennaria diphylla (Link) Parl. is a terrestrial, inconspicuous green orchid. Its distribution includes the central and western Mediterranean region as well as the Canary Islands and Madeira. Investigations on its pollination biology are scarce. In literature, there are mentions of autogamy and of allogamy. Pollination and pollen import and export were studied on Tenerife and Madeira. The investigations showed autogamy plays a less important role than thought, although a caging experiment showed that the species is well capable of self-pollination. The orchid is pollinated by a variety of small moths, especially of the families Geometridae, Pyralidae and Crambidae. It is flowering in a period when few other plants flower, so there is little competition for pollinators. Complemented by autogamy this seems to be a successful strategy, as the species shows a relatively high average fruit set of 73 %.Naturali