3,936 research outputs found
Doping dependence of the vortex-core energy in ultra-thin films of cuprates
No full textDoping dependence of the vortex-core energy in bilayer films of cuprates BENFATTO, L., CASTELLANI, C., GIAMARCHI, Thierry The energy needed to create a vortex core is the basic ingredient to address the physics of thermal vortex fluctuations in underdoped cuprates. Here, we theoretically investigate its role in the occurrence of the Beresinskii-Kosterlitz-Thouless transition in a bilayer film with inhomogeneity. From the comparison with recent measurements of the penetration depth in two-unit-cell thin films, we can extract the value of the vortex-core energy μ and show that μ scales linearly with Tc at low doping. BENFATTO, L., CASTELLANI, C., GIAMARCHI, Thierry. Doping dependence of the vortex-core energy in bilayer films of cuprates. Physical Review. B, Condensed Matter, 2008, vol. 77, no. 1
RECENT DEVELOPMENTS IN LAND TENURE LAW IN ERITREA, HORN OF AFRICA
No full textAfter a historical sketch of the evolution of land tenure systems in the Eritrean highlands, this paper describes the main features of the new Eritrean land law and its operative assumption that the legislation is meant to extend state control over land. The legal devices employed by the law are widely used in sub-Saharan Africa (and were largely inspired by colonial policies). The State of Eritrea frequently asserts that its recent independence gives it the opportunity to learn from other developing countries' mistakes and to avoid them. The basic patterns of the new land law, however, are common to the rest of Africa, notwithstanding the evident poor results. The central government wants its control to be widespread and pervasive. The fight against traditional social groups controlling land, at least in the highlands, is severe. Apart from a formal repeal of customary law, the state's acquisition of the power to modify village boundaries according to a scheme already completed at higher administrative levels and to introduce equal rights on land for women entails a disruption of the villages' social identity. Mandatory state control over landed property in Eritrea is, as usual, motivated by the necessity to address higher social needs. The ultimate intent, of course, is that the evolution from communal property to state property will eventually result in the widespread introduction of individual property once a sufficient level of economic development is achieved. This unfavorable attitude toward communal property is not supported by the evidence, which shows that, in fact, efficient land management can be obtained through renovation of traditional institutions.Land tenure -- Eritrea, Land tenure -- Government policy -- Eritrea, Land tenure -- Law and legislation -- Eritrea, Customary law -- Eritrea, Tenure types, Traditional -- Eritrea, Land reform -- Eritrea, Land Economics/Use,
Degree Variance And Emotional Strategies Catalyze Cooperation In Dynamic Signed Networks
No full textWe study the problem of the emergence of cooperation in dynamic signed networks where agent strategies coevolve with relational signs and network topology. Running simulations based on an agent-based model, we compare results obtained in a regular lattice initialization with those obtained on a comparable random network initialization. We show that the increased degree heterogeneity at the outset enlarges the parametric conditions in which cooperation survives in the long run. Furthermore, we show how the presence of sign-dependent emotional strategies catalyze the evolution of cooperation with both network topology initializations. Proceedings 28th European Conference on Modelling and Simulation © ECMS Flaminio Squazzoni, Fabio Baronio, Claudia Archetti, Marco Castellani (Editors)
Energetic balance of the superconducting transition across the BCS-Bose Einstein crossover in the attractive Hubbard model
No full textWe investigate by means of Dynamical mean-field theory the crossover from BCS superconductivity to Bose-Einstein (BE) condensation of preformed pairs which occurs in the attractive Hubbard model by increasing the attraction strength. Fixing the density to a generic value n=0.75, we follow the evolution of the two energy scales underlying the superconducting phenomenon, the gap Delta(0), and the superfluid stiffness D-S, which controls the phase coherence. The BCS-BE crossover is clearly mirrored in a change in the hierarchy of these two scales, the smallest of the two controlling the critical temperature. In the whole intermediate-to-strong-coupling region T-c scales with D-S, while T-C is proportional to Delta(0) only in the BCS regime. This evolution as a function of the interaction qualitatively resembles what happens in the cuprates when the doping is decreased towards the Mott insulator. This continuous change reflects also in the energetic balance at the superconducting transition. While, as it is well known, superconductivity is stabilized by a potential energy gain in the BCS regime, the strong-coupling superconductivity is made stable by a reduction of kinetic energy. Interestingly the intermediate-coupling region, where the maximum T-c is achieved, behaves similarly to the strong-coupling regime, and its gain in kinetic energy is the largest as a function of the coupling. Since the integral of the optical conductivity is proportional to the kinetic energy, the above finding implies that the attractive Hubbard model can account qualitatively for the anomalous behavior of optical spectra around T-c, where an increase of spectral weight is observed in under and optimally doped cuprates, while the overdoped samples have a more standard behavior. This qualitative agreement is lost in the normal phase, specifically at strong coupling, calling for the inclusion of strong correlation effects in the theoretical description. RI Capone, Massimo/A-7762-200
The BKT Universality Class in the Presence of Correlated Disorder
No full textThe correct detection of the Berezinskii-Kosterlitz-Thouless (BKT) transition in quasi-two-dimensional superconductors still remains a controversial issue. Its main signatures, indeed, are often at odds with the theoretical expectations. In a recent work (Maccari, I.; Benfatto, L.; Castellani, C. Phys. Rev. B 2017, 96, 060508), we have shown that the presence of spatially correlated disorder plays a key role in this sense because it is the reason underlying the experimentally-observed smearing of the universal superfluid-density jump. In the present paper we closely investigate the effects of correlated disorder on the BKT transition, specifically addressing the issue of whether or not it changes the BKT universality class
Anderson localization in bipartite lattices
No full textWe study the localization properties of a disordered tight-binding Hamiltonian on a generic bipartite lattice close to the band center. By means of a fermionic replica trick method, we derive the effective non-linear sigma-model describing the diffusive modes, which we analyse by using the Wilson-Polyakov renormalization group. In addition to the standard parameters which define the non-linear sigma-model, namely, the conductance and the external frequency, a new parameter enters, which may be related to the fluctuations of the staggered density of states. We find that, when both the regular hopping and the disorder only couple one sublattice to the other, the quantum corrections to the Kubo conductivity vanish at the band center, thus implying the existence of delocalized states. In two dimensions, the RG equations predict that the conductance flows to a finite value, while both the density of states and the staggered density of states fluctuations diverge. In three dimensions, we find that, sufficiently close to the band center, all states are extended, independently of the disorder strength. We also discuss the role of various symmetry breaking terms, as a regular hopping between same sublattices, or an on-site disorder. (C) 2000 Elsevier Science B.V. All rights reserved
Paring and Superconductivity from weak to strong coupling in the Attractive Hubbard model
No full textThe finite-temperature phase diagram of the attractive Hubbard model is studied by means of the dynamical mean-field theory. We first consider the normal phase of the model by explicitly frustrating the superconducting ordering. In this case, we obtain a first-order pairing transition between a metallic phase and a paired phase formed by strongly coupled incoherent pairs. The transition line ends in a finite temperature critical point, but a crossover between two qualitatively different solutions still occurs at higher temperature. Comparing the superconducting- and the normal-phase solutions, we find that the superconducting instability always occurs before the pairing transition in the normal phase, i.e. T-c > T-pairing. Nevertheless, the high-temperature phase diagram at T > T-c is still characterized by a crossover from a metallic phase to a preformed pair phase. We characterize this crossover by computing different observables that can be used to identify the pseudogap region, like the spin susceptibility, the specific heat and the single-particle spectral function. RI Capone, Massimo/A-7762-2008; Barone, Paolo/C-8918-201
Eurados-ideas guidelines (version 2) for the estimation of committed doses from incorporation monitoring data
No full textDose assessment after intakes of radionuclides requires application of biokinetic and dosimetric models and assumptions about factors influencing the final result. In 2006, a document giving guidance for such assessment was published, commonly referred to as the IDEAS Guidelines. Following its publication, a working group within the European networks CONRAD and EURADOS was established to improve and update the IDEAS Guidelines. This work resulted in Version 2 of the IDEAS Guidelines, which was published in 2013 in the form of a EURADOS report. The general structure of the original document was maintained; however, new procedures were included, e.g. the direct dose assessment method for 3H or special procedure for wound cases applying the NCRP wound model. In addition, information was updated and expanded, e.g. data on dietary excretion of U, Th, Ra and Po for urine and faeces or typical and achievable values for detection limits for different bioassay measurement techniques. © The Author 2015. Published by Oxford University Press. All rights reserved
Francesco Clemente: Fiori d’Inverno a New York, catalogo della mostra a cura di M. Seidel con C. Castellani, Complesso museale Santa Maria della Scala (29 giugno-2 ottobre 2016), Sillabe, Livorno 2016.
No full textCatalogo della mostra Francesco Clemente: Fiori d’Inverno a New York, Complesso museale Santa Maria della Scala (29 giugno-2 ottobre 2016)
- …
