314 research outputs found
Magnetic screening in proximity effect Josephson-junction arrays
The modulation with magnetic field of the sheet inductance measured on
proximity effect Josephson-junction arrays (JJAs) is progressively vanishing on
lowering the temperature, leading to a low temperature field-independent
response. This behaviour is consistent with the decrease of the two-dimensional
penetration length below the lattice parameter. Low temperature data are
quantitatively compared with theoretical predictions based on the XY model in
absence of thermal fluctuations. The results show that the description of a JJA
within the XY model is incomplete and the system is put well beyond the weak
screening limit which is usually assumed in order to invoke the well known
frustrated XY model describing classical Josephson-junction arrays.Comment: 6 pages, 5 figure
Bone Remodelling in BioShape
AbstractMany biological phenomena are inherently multiscale, i.e. they are characterised by interactions involving different scales at the same time. This is the case of bone remodelling, where macroscopic behaviour (at organ and tissue scale) and microstructure (at cell scale) strongly influence each other. Consequently, several approaches have been defined to model such a process at different spatial and temporal levels and, in particular, in terms of continuum properties, abstracting in this way from a realistic – and more complex – cellular scenario. While a large amount of information is available to validate such models separately, more work is needed to integrate all levels fully in a faithful multiscale model.In this scenario, we propose the use of BioShape, a 3D particle-based, scale-independent, geometry and space oriented simulator. It is used to define and integrate a cell and tissue scale model for bone remodelling in terms of shapes equipped with perception, interaction and movement capabilities. Their in-silico simulation allows for tuning continuum-based tissutal and cellular models, as well as for better understanding – both in qualitative and in quantitative terms – the blurry synergy between mechanical and metabolic factors triggering bone remodelling
Resource Windfalls, Political Regimes, and Political Stability
We study theoretically and empirically whether natural resource windfalls affect political regimes. We show that windfalls have no effect on democracies, while they have heterogeneous political consequences in autocracies. In deeply entrenched autocracies, the effect of windfalls is virtually nil, while in moderately entrenched autocracies, windfalls significantly exacerbate the autocratic nature of the political system. To frame the empirical work, we present a simple model in which political incumbents choose the degree of political contestability and potential challengers decide whether to try to unseat the incumbents. The model uncovers a mechanism for the asymmetric impact of resource windfalls on democracies and autocracies, as well as the the differential impact within autocracies
Mapping the dynamic interactions between vortex species in highly anisotropic superconductors
Here we use highly sensitive magnetisation measurements performed using a
Hall probe sensor on single crystals of highly anisotropic high temperature
superconductors to study the dynamic interactions
between the two species of vortices that exist in such superconductors. We
observe a remarkable and clearly delineated high temperature regime that
mirrors the underlying vortex phase diagram. Our results map out the parameter
space over which these dynamic interaction processes can be used to create
vortex ratchets, pumps and other fluxonic devices.Comment: 7 pages, 3 figures, to be published in Supercond. Sci. Techno
Deformation processes, textural evolution and weakening in retrograde serpentinites
Serpentinites play a key role in controlling fault rheology in a wide range of geodynamic settings, from oceanic and continental rift zones to subduction zones. In this paper, we provide a summary of the most common deformation mechanisms and frictional strengths of serpentine minerals and serpentinites. We focus on deformation mechanisms in retrograde serpentinites, which show a progressive evolution from undeformed mesh and bastite pseudomorphic textures to foliated, ribbon-like textures formed by lizardite with strong crystallographic and shape preferred orientations. We also discuss the possible mechanical significance of anastomosing slickenfibre veins containing ultraweak fibrous serpentines or relatively strong splintery antigorite. Our review and new observations indicate that pressure solution and frictional sliding are the most important deformation mechanisms in retrograde serpentinite, and that they are frictionally weak (ÎĽ~0.3). The mineralogical and microstructural evolution of retrograde serpentinites during shearing suggests that a further reduction of the friction coefficient to ÎĽ of 0.15 or less may occur during deformation, resulting in a sort of continuous feedback weakening mechanism
Guar gum/borax hydrogel: Rheological, low field NMR and release characterizations
Guar gum (GG) and Guar gum/borax (GGb) hydrogels are studied by means of rheology, Low Field Nuclear Magnetic Resonance (LF NMR) and model drug release tests. These three approaches are used to estimate the mesh size (ζ) of the polymeric network. A comparison with similar Scleroglucan systems is carried out. In the case of GGb, the rheological and Low Field NMR estimations of ζ lead to comparable results, while the drug release approach seems to underestimate ζ. Such discrepancy is attributed to the viscous effect of some polymeric chains that, although bound to the network to one end, can freely fluctuate among meshes. The viscous drag exerted by these chains slows down drug diffusion through the polymeric network. A proof for this hypothesis is given by the case of Scleroglucan gel, where the viscous contribution is not so significant and a good agreement between the rheological and release test approaches was found
Fault structure and slip localization in carbonate-bearing normal faults: An example from the Northern Apennines of Italy
Carbonate-bearing normal faults are important structures for controlling fluid flow and seismogenesis
within the brittle upper crust. Numerous studies have tried to characterize fault zone structure and
earthquake slip processes along carbonate-bearing faults. However, due to the different scales of
investigation, these studies are not often integrated to provide a comprehensive fault image. Here we
present a multi-scale investigation of a normal fault exhumed from seismogenic depths. The fault extends
for a length of 10 km with a maximum width of about 1.5 km and consists of 5 sub-parallel and
interacting segments. The maximum displacement (370e650 m) of each fault segment is partitioned
along sub-parallel slipping zones extending for a total width of about 50 m. Each slipping zone is
characterized by slipping surfaces exhibiting different slip plane phenomena. Fault rock development is
controlled by the protolith lithology. In massive limestone, moving away from the slip surface, we
observe a thin layer (<2 cm) of ultracataclasite, cataclasite (2e10 cm) and fault breccia. In marly limestone,
the fault rock consists of a cataclasite with hydrofractures and smectite-rich pressure solution
seams. At the micro-nanoscale, the slip surface consists of a continuous and thin (<300 mm) layer
composed of coarse calcite grains (~5e20 mm in size) associated with sub-micrometer grains showing
fading grain boundaries, voids and/or vesicles, and suggesting thermal decomposition processes.
Micrometer-sized calcite crystals show nanoscale polysynthetic twinning affected by the occurrence of
subgrain boundaries and polygonalized nanostructures. Investigations at the kilometres-tens of meter
scale provide fault images that can be directly compared with high-resolution seismological data and
when combined can be used to develop a comprehensive characterization of seismically active fault
structures in carbonate lithologies. Micro and nanoscale investigations along the principal slipping zone
suggest that different deformation processes, including plastic deformation and thermal decomposition,
were active during seismic slip
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