Doping induced inhomogeneity in high-Tc superconductors

Doping and disorder are inseparable in the superconducting cuprates. Assuming the simplest possible disordered doping, we construct a semiphenomenological model and analyze its experimental consequences. Among the affected experimental quantities are the ARPES spectra and thermodynamic properties. From our model we make a prediction for the width of the local superconducting gap distribution with the only experimentally unknown parameter being the superconducting correlation length. Thus, our model provides a direct way of determining the superconducting correlation length from a known experimental gap distribution.Comment: 5 pages, 3 eps figures. Expanded version of talk presented by AVB at the ISS 2000, Oct 14-16, Tokyo, Japa

First videos of endemic Zanzibar servaline genet Genetta servalina archeri, African palm civet Nandinia binotata (Mammalia: Carnivora: Viverridae) and other small carnivores on Unguja Island, Tanzania

The faunal diversity of the densely populated island of Unguja, Zanzibar archipelago, Tanzania, includes several endemic mammals. Camera-trapping in Jozani-Chwaka Bay National Park and Kiwengwa–Pongwe Forest Reserve in September 2017 captured the first video footage of the Zanzibar Servaline Genet Genetta servalina archeri, an endemic subspecies first formally described in 1998. Other native small carnivores were also recorded on video for the first time during this survey, including the African Palm Civet Nandinia binotata, which was first documented in print as present in Unguja in 2004. Also camera-trapped in 2017 were the Zanzibar Slender Mongoose Herpestes sanguineus rufescens and the Zanzibar Bushy-tailed Mongoose Bdeogale crassicauda tenuis. Follow-up cameratrapping in Jozani-Chwaka Bay National Park in August 2018 captured additional video of the Zanzibar Servaline Genet and the African Palm Civet. No images were obtained of the African Civet Civettictis civetta, or of the two introduced species—the Banded Mongoose Mungos mungo and the Small Indian Civet Viverricula indica—in either year. As the remaining natural habitat in Zanzibar shrinks in size and becomes fragmented, it is increasingly urgent to document the archipelago’s carnivores and other fauna, so that sound conservation measures can be implemented

Decentralized Language Learning Through Acting

This paper presents an algorithm for learning the meaning of messages communicated between agents that interact while acting optimally towards a cooperative goal. Our reinforcement-learning method is based on Bayesian filtering and has been adapted for a decentralized control process. Empirical results shed light on the complexity of the learning problem, and on factors affecting the speed of convergence. Designing intelligent agents able to adapt their mutual interpretation of messages exchanged, in order to improve overall task-oriented performance, introduces an essential cognitive capability that can upgrade the current state of the art in multi-agent and human-machine systems to the next level. Learning to communicate while acting will add to the robustness and flexibility of these systems and hence to a more efficient and productive performance

Collisionless magnetic reconnection in a plasmoid chain

The kinetic features of plasmoid chain formation and evolution are investigated by two dimensional Particle-in-Cell simulations. Magnetic reconnection is initiated in multiple X points by the tearing instability. Plasmoids form and grow in size by continuously coalescing. Each chain plasmoid exhibits a strong out-of plane core magnetic field and an out-of-plane electron current that drives the coalescing process. The disappearance of the X points in the coalescence process are due to anti-reconnection, a magnetic reconnection where the plasma inflow and outflow are reversed with respect to the original reconnection flow pattern. Anti-reconnection is characterized by the Hall magnetic field quadrupole signature. Two new kinetic features, not reported by previous studies of plasmoid chain evolution, are here revealed. First, intense electric fields develop in-plane normally to the separatrices and drive the ion dynamics in the plasmoids. Second, several bipolar electric field structures are localized in proximity of the plasmoid chain. The analysis of the electron distribution function and phase space reveals the presence of counter-streaming electron beams, unstable to the two stream instability, and phase space electron holes along the reconnection separatrices.Comment: accepted for publication in special issue "Magnetic reconnection and turbulence in space, laboratory and astrophysical systems" of Nonlinear Processes in Geophysic

Testing the Unitarity of the CKM Matrix with a Space-Based Neutron Decay Experiment

If the Standard Model is correct, and fundamental fermions exist only in the three generations, then the CKM matrix should be unitary. However, there remains a question over a deviation from unitarity from the value of the neutron lifetime. We discuss a simple space-based experiment that, at an orbit height of 500 km above Earth, would measure the kinetic-energy, solid-angle, flux spectrum of gravitationally bound neutrons (kinetic energy K<0.606 eV at this altitude). The difference between the energy spectrum of neutrons that come up from the Earth's atmosphere and that of the undecayed neutrons that return back down to the Earth would yield a measurement of the neutron lifetime. This measurement would be free of the systematics of laboratory experiments. A package of mass $<25$ kg could provide a 10^{-3} precision in two years.Comment: 10 pages, 4 figures. Revised and updated for publicatio

Kondo effect in a double quantum-dot molecule under the effect of an electric and magnetic field

Electron tunneling through a double quantum dot molecule, in the Kondo regime, under the effect of a magnetic field and an applied voltage, is studied. This system possesses a complex response to the applied fields characterized by a tristable solution for the conductance. The different nature of the solutions are studied in and out thermodynamical equilibrium. It is shown that the interdot coupling and the fields can be used to control the region of multistability. The mean-field slave-boson formalism is used to obtain the solution of the problem.Comment: 5 pages, 4 figures. To appear in Sol. State Com