91,616 research outputs found
Recommended from our members
Product line design
We characterize the product line choice and pricing of a monopolist from the upper envelope of net marginal revenue curves to the individual product demand functions. The equilibrium product line constitutes those varieties yielding the highest upper envelope. In a generalized vertical differentiation framework, the equilibrium line is exactly the same as the first-best socially optimal line. These upper envelope and first-best optimal line findings extend to symmetric Cournot oligopoly
Fermiology of Cuprates from First Principles: From Small Pockets to the Luttinger Fermi surface
Fermiology, the shape and size of the Fermi surface, underpins the
low-temperature physical properties of a metal. Recent investigations of the
Fermi surface of high-Tc superconductors, however, show a most unusual
behavior: upon addition of carriers, ``Fermi'' pockets appear around nodal
(hole doping) and antinodal (electron doping) regions of the Brillouin zone in
the ``pseudogap'' state. With progressive doping, p, these evolve into
well-defined Fermi surfaces around optimal doping (p_opt), with no pseudogap.
Correspondingly, various physical responses, including d-wave
superconductivity, evolve from highly anomalous, up to p_opt, to more
conventional beyond. Describing this evolution holds the key to understanding
high-temperature superconductivity. Here, we present ab initio quantum chemical
results for cuprates, providing a quantitative description of the evolution of
the Fermi surface with doping. Our results constitute an ab initio
justification for several, hitherto proposed semiphenomenological theories,
offering an unified basis for understanding of various, unusual physical
responses of doped cuprates
Effects of antiferromagnetic planes on the superconducting properties of multilayered high-Tc cuprates
We propose a mechanism for high critical temperature (T_c) in the coexistent
phase of superconducting- (SC) and antiferromagnetic (AF) CuO_2 planes in
multilayered cuprates. The Josephson coupling between the SC planes separated
by an AF insulator (Mott insulator) is calculated perturbatively up to the
fourth order in terms of the hopping integral between adjacent CuO_2 planes. It
is shown that the AF exchange splitting in the AF plane suppresses the
so-called pi-Josephson coupling, and the long-ranged 0-Josephson coupling leads
to coexistence with a rather high value of T_c.Comment: 4 pages including 4 figure
Use of ERTS data for a multidisciplinary analysis of Michigan resources
There are no author-identified significant results in this report
Instabilities in asymmetric nuclear matter
The existence of phase transitions from liquid to gas phases in asymmetric
nuclear matter (ANM) is related with the instability regions which are limited
by the spinodals. In this work we investigate the instabilities in ANM
described within relativistic mean field hadron models, both with constant and
density dependent couplings at zero and finite temperatures. In calculating the
proton and neutron chemical potentials we have used an expansion in terms of
Bessel functions that is convenient at low densities. The role of the isovector
scalar -meson is also investigated in the framework of relativistic
mean field models and density dependent hadronic models. It is shown that the
main differences occur at finite temperature and large isospin asymmetry close
to the boundary of the instability regions.Comment: 13 pages, 5 figures; to appear in Phys. Rev.
Modular Equations and Distortion Functions
Modular equations occur in number theory, but it is less known that such
equations also occur in the study of deformation properties of quasiconformal
mappings. The authors study two important plane quasiconformal distortion
functions, obtaining monotonicity and convexity properties, and finding sharp
bounds for them. Applications are provided that relate to the quasiconformal
Schwarz Lemma and to Schottky's Theorem. These results also yield new bounds
for singular values of complete elliptic integrals.Comment: 23 page
Competition between Antiferromagnetism and Superconductivity in High Cuprates
Using variational cluster perturbation theory we study the competition
between d-wave superconductivity (dSC) and antiferromagnetism (AF) in the the
t-t'-t''-U Hubbard model. Large scale computer calculations reproduce the
overall ground state phase diagram of the high-temperature superconductors as
well as the one-particle excitation spectra for both hole- and electron-doping.
We identify clear signatures of the Mott gap as well as of AF and of dSC that
should be observable in photoemission experiments.Comment: 4 pages, 4 figure
Persistent current formation in a high-temperature Bose-Einstein condensate: an experimental test for c-field theory
Experimental stirring of a toroidally trapped Bose-Einstein condensate at
high temperature generates a disordered array of quantum vortices that decays
via thermal dissipation to form a macroscopic persistent current [T. W. Neely
em et al. arXiv:1204.1102 (2012)]. We perform 3D numerical simulations of the
experimental sequence within the Stochastic Projected Gross-Pitaevskii equation
using ab initio determined reservoir parameters. We find that both damping and
noise are essential for describing the dynamics of the high-temperature Bose
field. The theory gives a quantitative account of the formation of a persistent
current, with no fitted parameters.Comment: v2: 7 pages, 3 figures, new experimental data and numerical
simulation
Effect of nuclear quadrupole interactions on the dynamics of two-level systems in glasses
The standard tunneling model describes quite satisfactorily the thermal
properties of amorphous solids at temperatures in terms of an ensemble
of two-level systems possessing logarithmically uniform distribution over their
tunneling amplitudes and uniform distribution over their asymmetry energies. In
particular, this distribution explains the observable logarithmic temperature
dependence of the dielectric constant. Yet, experiments have shown that at
ultralow temperatures such a temperature behavior breaks down and the
dielectric constant becomes temperature independent (plateau effect). In this
letter we suggest an explanation of this behavior exploiting the effect of the
nuclear quadrupole interaction on tunneling. We show that below a temperature
corresponding to the characteristic energy of the nuclear quadrupole
interaction the effective tunneling amplitude is reduced by a small overlap
factor of the nuclear quadrupole ground states in the left and right potential
wells of the tunneling system. It is just this reduction that explains the
plateau effect . We predict that the application of a sufficiently large
magnetic field should restore the logarithmic dependence because of the
suppression of the nuclear quadrupole interaction.Comment: To appear in the Physical Review Letter
Superconductivity in the repulsive Hubbard model: an asymptotically exact weak-coupling solution
We study the phase diagram of the Hubbard model in the limit where U, the
onsite repulsive interaction, is much smaller than the bandwidth. We present an
asymptotically exact expression for T, the superconducting transition
temperature, in terms of the correlation functions of the non-interacting
system which is valid for arbitrary densities so long as the interactions are
sufficiently small. Our strategy for computing T involves first integrating
out all degrees of freedom having energy higher than an unphysical initial
cutoff . Then, the renormalization group (RG) flows of the resulting
effective action are computed and T is obtained by determining the scale
below which the RG flows in the Cooper channel diverge. We prove that T is
independent of . Using this method, we find a variety of
unconventional superconducting ground states in two and three dimensional
lattice systems and present explicit results for T and pairing symmetries
as a function of the electron concentration.Comment: 18 pages, 17 figure
- …