Anomalous magnetic field dependence of the thermodynamic transition line in the isotropic superconductor (K,Ba)Bi03

Thermodynamic (specific heat, reversible magnetization, tunneling spectroscopy) and transport measurements have been performed on high quality (K,Ba)BiO$_3$ single crystals. The temperature dependence of the magnetic field $H_{Cp}$ corresponding to the onset of the specific heat anomaly presents a clear positive curvature. $H_{Cp}$ is significantly smaller than the field $H_\Delta$ for which the superconducting gap vanishes but is closely related to the irreversibility line deduced from transport data. Moreover, the temperature dependence of the reversible magnetization present a strong deviation from the Ginzburg--Landau theory emphasazing the peculiar nature of the superconducting transition in this material.Comment: 4 pages, 4 figures, 28 reference

A Bragg glass phase in the vortex lattice of a type II superconductor

Although crystals are usually quite stable, they are sensitive to a disordered environment: even an infinitesimal amount of impurities can lead to the destruction of the crystalline order. The resulting state of matter has been a longstanding puzzle. Until recently it was believed to be an amorphous state in which the crystal would break into crystallites. But a different theory predicts the existence of a novel phase of matter: the so-called Bragg glass, which is a glass and yet nearly as ordered as a perfect crystal. The lattice of vortices that can contain magnetic flux in type II superconductors provide a good system to investigate these ideas. Here we show that neutron diffraction data of the vortex lattice in type II superconductors provides unambiguous evidence for a weak, power-law decay of the crystalline order characteristic of a Bragg glass. The theory also predicts accurately the electrical transport properties of superconductors; it naturally explains the observed phase transition and the dramatic jumps in the critical current associated with the melting of the Bragg glass. Moreover the model explains experiments as diverse as X-ray scattering in disordered liquid crystals and conductivity of electronic crystals.Comment: 9 pages, 4 figure

Domain regime in two-dimensional disordered vortex matter

A detailed numerical study of the real space configuration of vortices in disordered superconductors using 2D London-Langevin model is presented. The magnetic field $B$ is varied between 0 and $B_{c2}$ for various pinning strengths $\Delta$. For weak pinning, an inhomogeneous disordered vortex matter is observed, in which the topologically ordered vortex lattice survives in large domains. The majority of the dislocations in this state are confined to the grain boundaries/domain walls. Such quasi-ordered configurations are observed in the intermediate fields, and we refer it as the domain regime (DR). The DR is distinct from the low-field and the high-fields amorphous regimes which are characterized by a homogeneous distribution of defects over the entire system. Analysis of the real space configuration suggests domain wall roughening as a possible mechanism for the crossover from the DR to the high-field amorphous regime. The DR also shows a sharp crossover to the high temperature vortex liquid phase. The domain size distribution and the roughness exponent of the lattice in the DR are also calculated. The results are compared with some of the recent Bitter decoration experiments.Comment: 9 pages, 9 figure

Expenditure Reform in Industrialised Countries: A Case Study Approach

This study examines reforms of public expenditure in industrialised countries over the past two decades. We distinguish ambitious and timid reformers and analyse in detail reform experiences in eight case studies of ambitious reform episodes. We find that ambitious reform countries reduce spending on transfers, subsidies and public consumption while largely sparing education spending. Such expenditure retrenchment is also typically part of a comprehensive reform package that includes improvements in fiscal institutions as well as structural and other macroeconomic reforms. The study finds that ambitious expenditure retrenchment and reform coincides with large improvements in fiscal and economic growth indicators

Roadless and Low-Traffic Areas as Conservation Targets in Europe

With increasing road encroachment, habitat fragmentation by transport infrastructures has been a serious threat for European biodiversity. Areas with no roads or little traffic (“roadless and low-traffic areas”) represent relatively undisturbed natural habitats and functioning ecosystems. They provide many benefits for biodiversity and human societies (e.g., landscape connectivity, barrier against pests and invasions, ecosystem services). Roadless and low-traffic areas, with a lower level of anthropogenic disturbances, are of special relevance in Europe because of their rarity and, in the context of climate change, because of their contribution to higher resilience and buffering capacity within landscape ecosystems. An analysis of European legal instruments illustrates that, although most laws aimed at protecting targets which are inherent to fragmentation, like connectivity, ecosystem processes or integrity, roadless areas are widely neglected as a legal target. A case study in Germany underlines this finding. Although the Natura 2000 network covers a significant proportion of the country (16%), Natura 2000 sites are highly fragmented and most low-traffic areas (75%) lie unprotected outside this network. This proportion is even higher for the old Federal States (western Germany), where only 20% of the low-traffic areas are protected. We propose that the few remaining roadless and low-traffic areas in Europe should be an important focus of conservation efforts; they should be urgently inventoried, included more explicitly in the law and accounted for in transport and urban planning. Considering them as complementary conservation targets would represent a concrete step towards the strengthening and adaptation of the Natura 2000 network to climate change