130,680 research outputs found
Time-consistent policy and politics: does voting matter when individuals are identical?
No full textWe consider the implications of a lack of policy commitment when policies are chosen through a political process and individuals are ex-ante identical. We show that politics, by allowing ex-post distributional tensions to shape policy, can make it possible to sustain non-trivial equilibria in which the commitment problem is alleviated or fully eliminated. How effective politics can be at countering collective commitment problems in homogeneous groups depends on the nature of the political process and on the extent to which private choices are public information
Interplay between singlet and triplet pairings in multiband two-dimensional oxide superconductors
No full textWe theoretically study the superconducting properties of multiband two-dimensional transition metal oxide superconductors by analyzing not only the role played by conventional singlet pairings, but also by the triplet order parameters, favored by the spin-orbit couplings present in these materials. In particular, we focus on the two-dimensional electron gas at the (001) interface between and band insulators where the low electron densities and the sizable spin-orbit couplings affect the superconducting features. Our theoretical study is based on an extended superconducting mean-field analysis of the typical multiband tight-binding Hamiltonian, as well as on a parallel analysis of the effective electronic bands in the low-momentum limit, including static on-site and intersite intraband attractive potentials under applied magnetic fields. The presence of triplet pairings is able to strongly reduce the singlet order parameters which, as a result, are no longer a monotonic function of the charge density. The interplay between the singlet and the triplet pairings affects the dispersion of quasiparticle excitations in the Brillouin zone and also induces anisotropy in the superconducting behavior under the action of an in-plane and of an out-of-plane magnetic fields. Finally, nontrivial topological superconducting states become stable as a function of the charge density, as well as of the magnitude and of the orientation of the magnetic field. In addition to the chiral, time-reversal breaking, topological superconducting phase, favored by the linear Rashba couplings and by the on-site attractive potentials in the presence of an out-of-plane magnetic field, we find that a time-reversal invariant topological helical superconducting phase is promoted by nonlinear spin-orbit couplings and by the intersite attractive interactions in the absence of magnetic field
Interplay between singlet and triplet pairings in multiband two-dimensional oxide superconductors
No full textWe theoretically study the superconducting properties of multiband two-dimensional transition metal oxide superconductors by analyzing not only the role played by conventional singlet pairings, but also by the triplet order parameters, favored by the spin-orbit couplings present in these materials. In particular, we focus on the two-dimensional electron gas at the (001) interface between LaAlO3 and SrTiO3 band insulators where the low electron densities and the sizable spin-orbit couplings affect the superconducting features. Our theoretical study is based on an extended superconducting mean-field analysis of the typical multiband tight-binding Hamiltonian, as well as on a parallel analysis of the effective electronic bands in the low-momentum limit, including static on-site and intersite intraband attractive potentials under applied magnetic fields. The presence of triplet pairings is able to strongly reduce the singlet order parameters which, as a result, are no longer a monotonic function of the charge density. The interplay between the singlet and the triplet pairings affects the dispersion of quasiparticle excitations in the Brillouin zone and also induces anisotropy in the superconducting behavior under the action of an in-plane and of an out-of-plane magnetic fields. Finally, nontrivial topological superconducting states become stable as a function of the charge density, as well as of the magnitude and of the orientation of the magnetic field. In addition to the chiral, time-reversal breaking, topological superconducting phase, favored by the linear Rashba couplings and by the on-site attractive potentials in the presence of an out-of-plane magnetic field, we find that a time-reversal invariant topological helical superconducting phase is promoted by nonlinear spin-orbit couplings and by the intersite attractive interactions in the absence of magnetic field
Pseudo-automorphisms of positive entropy on the blowups of products of projective spaces
No full text10.1007/s00208-013-0992-4Mathematische Annalen3591-2189-20
Rashba quantum wire: exact solution and ballistic transport
No full textThe effect of Rashba spin-orbit interaction in quantum wires with hard-wall boundaries is discussed. The exact wavefunction and eigenvalue equation are worked out, pointing out the mixing between the spin and spatial parts. The spectral properties are also studied within perturbation theory with respect to the strength of the spin-orbit interaction and diagonalization procedure. A comparison is made with the results of a simple model, the two-band model, that takes account only of the first two sub-bands of the wire. Finally, the transport properties within the ballistic regime are analytically calculated for the two-band model and through a tight-binding Green function for the entire system. Single and double interfaces separating regions with different strengths of spin-orbit interaction are analysed by injecting carriers into the first and the second sub-band. It is shown that in the case of a single interface the spin polarization in the Rashba region is different from zero, and in the case of two interfaces the spin polarization shows oscillations due to spin-selective bound states
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ground state features of the Fröhlich model
No full textFollowing the ideas behind the Feynman approach, a variational wave function is proposed for the Fröhlich model. It is shown that it provides, for any value of the electron-phonon coupling constant, an estimate of the polaron ground state energy better than the Feynman method based on path integrals. The mean number of phonons, the average electronic kinetic and interaction energies, the ground state spectral weight and the electron-lattice correlation function are calculated and successfully compared with the best available results. Copyright Springer-Verlag Berlin/Heidelberg 2003
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