Suppression of matching field effects by splay and pinning energy dispersion in YBa_2Cu_3O_7 with columnar defects

We report measurements of the irreversible magnetization M_i of a large number of YBa_2Cu_3O_7 single crystals with columnar defects (CD). Some of them exhibit a maximum in M_i when the density of vortices equals the density of tracks, at temperatures above 40K. We show that the observation of these matching field effects is constrained to those crystals where the orientational and pinning energy dispersion of the CD system lies below a certain threshold. The amount of such dispersion is determined by the mass and energy of the irradiation ions, and by the crystal thickness. Time relaxation measurements show that the matching effects are associated with a reduction of the creep rate, and occur deep into the collective pinning regime.Comment: 7 pages, 5 figures, submitted to Phys. Rev.

Properties of the Bose glass phase in irradiated superconductors near the matching field

Structural and transport properties of interacting localized flux lines in the Bose glass phase of irradiated superconductors are studied by means of Monte Carlo simulations near the matching field B_Phi, where the densities of vortices and columnar defects are equal. For a completely random columnar pin distribution in the xy-plane transverse to the magnetic field, our results show that the repulsive vortex interactions destroy the Mott insulator phase which was predicted to occur at B = B_Phi. On the other hand, for ratios of the penetration depth to average defect distance lambda/d <= 1, characteristic remnants of the Mott insulator singularities remain visible in experimentally accessible quantities as the magnetization, the bulk modulus, and the magnetization relaxation, when B is varied near B_Phi. For spatially more regular disorder, e.g., a nearly triangular defect distribution, we find that the Mott insulator phase can survive up to considerably large interaction range \lambda/d, and may thus be observable in experiments.Comment: RevTex, 17 pages, eps files for 12 figures include

Environment and Rural Affairs Monitoring & Modelling Programme ERAMMP - Report-32: National Forest in Wales - Evidence Review

This review was commissioned by Welsh Government (WG) from the Environment and Rural Affairs Monitoring and Modelling Programme (ERAMMP) to provide key evidence of potential benefits and disbenefits of woodland creation, woodland expansion and managing undermanaged woodland, to provide an evidence base to inform the development of a National Forest for Wales. During the commissioning process, WG emphasised that the evidence provided must reflect the collective views of the community by reviewing the literature in an objective way highlighting where evidence is contradictory or weak. Within the time available, evidence of causality of impacts, the likely timescales and magnitude of these impacts should be also be presented, for both positive and negative impacts of woodland expansion and management of undermanaged woodlands. This Evidence Pack should also build on the evidence put forward in the ERAMMP Sustainable Farm Scheme (SFS) (https://erammp.wales/en/resources) which included a range of assessments of the value of intervention measures which promoted trees within a landscape setting for a range of environmental, economic and social outcomes. The required rapid production of the review in four months meant an expert approach of key evidence was expected rather than a systematic review. Key topics to cover were selected, in partnership with WG, focussing on issues that could fundamentally change decision-making going forward. The final agreed list was arranged under a series of high-level subject headings, and the individual reviews published as ERAMMP Reports 33 to 38 and include; Biodiversity; Managing Undermanaged Woodland; Future-proofing our Woodland; Climate Change Mitigation; Ecosystem Services, and Economics and Natural Capital Accounting. An Integrated Assessment was also commissioned to provide a synthesis of cross-cutting themes and dependencies between topics. These ERAMMP reports are all provided as Annexes to this report

Not all activated satellite cell progeny commit to differentiation

Satellite cells provide skeletal muscle with a remarkable capacity for repeated repair and regeneration. Quiescent satellite cells are MyoD-ve, with MyoD being induced in >98% of satellite cells within 24hrs of activation (Zammit, Exp. Cell Res. 281, 39, 2002). Here, we explore the subsequent fate of these satellite cells, as they proliferate and begin to differentiate. Satellite cells associated with myofibres, cultured without exposure to serum/CEE, still activated MyoD but the majority failed to divide, demonstrating an uncoupling of the two events. In contrast, myofibres cultured with serum/CEE had clones of satellite cells. MyoD-ve cells were detected in these clones, in which the rest of the cells were MyoD+ve, implying they had arisen after division but were not adopting the same fate. Three possible explanations for MyoD-ve cells were explored: phosphorylated histone markers and BrdU labelling showed that the lack of MyoD was not cell cycle dependent; myogenin immunostaining demonstrated that satellite cells committing to differentiation initially contained MyoD; Pax7 expression was generally down-regulated in the majority of satellite cells by 72hrs, but some remained strongly Pax7+ve. Together, these data suggest that MyoD-ve cells are returning to a quiescent state

Maintaining the regenerative compartment of adult skeletal muscle

Skeletal muscle is predominantly composed of highly specialised contractile myofibres, each maintained by hundreds of postmitotic myonuclei. Throughout adult life, new myonuclei are required to meet the persistent demands of myofibre turnover, growth and repair. These are provided by the differentiation of myoblasts, generated from the satellite cells that reside between the plasmalemma and surrounding basal lamina of mature myofibres. Although the progression from satellite cell to myonucleus is well established, the mechanisms by which an effective regenerative compartment is maintained remain controversial. Indeed, it has been suggested that satellite cells are “arrested” myogenic precursors that are replenished from other stem cells located within the muscle interstitium and/or from outside the tissue. Using an isolated myofibre culture system to investigate early events of satellite cell activation, proliferation and differentiation, we have shown that in the context of the sublaminal niche, satellite cell progeny can adopt divergent fates. In this model system, quiescent Pax7+ve/MyoD-ve satellite cells are synchronously activated to produce a homogenous Pax7+ve/MyoD+ve population. These cells proliferate and generate clusters of myoblasts, most of which become Pax7-ve/myogenin+ve and are fated to undergo terminal differentiation. Significantly, some cells within the clusters maintain expression of Pax7 and down regulate MyoD, apparently returning to a state of quiescence comparable to that of the initial Pax7+ve/MyoD-ve population. Our observations demonstrate that satellite cells have the potential to generate both myonuclei and new satellite cells and suggest that the alternate fate decisions may be extrinsically imposed on a homogeneous population. Most importantly, these findings suggest that the satellite cell pool may be maintained by self-renewal and does not necessarily require a contribution from elsewhere