Supramolecular Magnetic Brushes: The Impact of Dipolar Interactions on the Equilibrium Structure

The equilibrium structure of supramolecular magnetic filament brushes is analyzed at two different scales. First, we study the density and height distributions for brushes with various grafting densities and chain lengths. We use Langevin dynamics simulations with a bead-spring model that takes into account the cross-links between the surface of the ferromagnetic particles, whose magnetization is characterized by a point dipole. Magnetic filament brushes are shown to be more compact near the substrate than nonmagnetic ones, with a bimodal height distribution for large grafting densities. This latter feature makes them also different from brushes with electric dipoles. Next, in order to explain the observed behavior at the filament scale, we introduce a graph theory analysis to elucidate for the first time the structure of the brush at the scale of individual beads. It turns out that, in contrast to nonmagnetic brushes, in which the internal structure is determined by random density fluctuations, magnetic forces introduce a certain order in the system. Because of their highly directional nature, magnetic dipolar interactions prevent some of the random connections to be formed. On the other hand, they favor a higher connectivity of the chains' free and grafted ends. We show that this complex dipolar brush microstructure has a strong impact on the magnetic response of the brush, as any weak applied field has to compete with the dipole-dipole interactions within the crowded environment.This research has been partially supported by the Austrian Research Fund (FWF): START-Projekt Y 627-N27. The authors are grateful to the Ural Federal University stimulating programme. S.S.K, E.S.P., and E.V.N. are supported by RFBR mol-a-ved 15-32-20549. The work of E.V.N. was partially supported by the President of RF, Grant NO MK-5216.2015.2. S.S.K. is supported by the Ministry of Education and Science of the Russian Federation (Contract 02.A03.21.000, Project 3.12.2014/K) and EU-Project 642774 ETN-Colldense. P.A.S. acknowledges financial support from the Universitat de les Illes Balears within its Programa de foment de la recerca. T.S. and J.J.C. were supported by the project FIS2012-30634 (funded by the Spanish Mineco). J.J.C. and T.S. also acknowledge funding from a grant awarded by the Conselleria d’Educació, Cultura i Universitats del Govern de les Illes Balears and the European Social Fund (ESF).Peer Reviewe

Implications of Extreme Life Span in Clonal Organisms: Millenary Clones in Meadows of the Threatened Seagrass Posidonia oceanica

The maximum size and age that clonal organisms can reach remains poorly known, although we do know that the largest natural clones can extend over hundreds or thousands of metres and potentially live for centuries. We made a review of findings to date, which reveal that the maximum clone age and size estimates reported in the literature are typically limited by the scale of sampling, and may grossly underestimate the maximum age and size of clonal organisms. A case study presented here shows the occurrence of clones of slow-growing marine angiosperm Posidonia oceanica at spatial scales ranging from metres to hundreds of kilometres, using microsatellites on 1544 sampling units from a total of 40 locations across the Mediterranean Sea. This analysis revealed the presence, with a prevalence of 3.5 to 8.9%, of very large clones spreading over one to several (up to 15) kilometres at the different locations. Using estimates from field studies and models of the clonal growth of P. oceanica, we estimated these large clones to be hundreds to thousands of years old, suggesting the evolution of general purpose genotypes with large phenotypic plasticity in this species. These results, obtained combining genetics, demography and model-based calculations, question present knowledge and understanding of the spreading capacity and life span of plant clones. These findings call for further research on these life history traits associated with clonality, considering their possible ecological and evolutionary implications

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1.

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field

Black holes, gravitational waves and fundamental physics: a roadmap

The grand challenges of contemporary fundamental physics—dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem—all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics'

Pair Interaction between End-Grafted Polymers onto Spherical Surfaces: A Monte Carlo Study

We present the results of extensive three-dimensional off-lattice Monte Carlo simulations of two interacting spherical brushes. We have measured the interacting force in systems where curvature effects are important. Our results support a description of the force profile divided into two regimes. At short separating distances between the brushes the force is well described by the theory of Witten and Pincus, whereas at larger distances the interaction is reproduced by extending the theory of Flory for dilute polymer solutions. The overall behavior is also compared with the predictions of the phenomenological theory of Doroszkowski and Lambourne. The characteristic radial size of an unperturbed brush follows the same scaling relationship found in the star polymer systems approximation

Ranked proportions of the genets (X) belonging to an MLG present in the meadows.

<p>from X = 1, the original genet, to X = 2…n representing the genets derived from somatic mutations, ranked by abundance of ramets. The results are derived from somatic mutations in meadows growing over 400 to 500 years with an overall probability (across nine loci) pM = 10-6. The original ramet, X = 1, is the most abundant one, P(X = 1) = 0.99978, whereas the abundance of mutants, P(X>1), follow a power-law decay that strongly depends on the somatic mutation probability.</p

Relationship between maximum clonal size detected and distance sampled in studies reporting very large clones.

<p>The solid line shows the fitted regression line of clonal size (S, m) over distance (D, m): log10 S = −0.14 (±0.10)+1.15 (±0.26) log10 D (R2 = 0.91, N = 8, p<0.001). The regression intercept and slope do not differ significantly from 0 and 1, respectively (t-test, p>0.05), thus not rejecting the hypothesis that there is a general tendency for the maximum clonal size detected to be limited by the maximum distance sampled.</p