22,854 research outputs found
Bifurcation-based parameter tuning in a model of the GnRH pulse and surge generator
We investigate a model of the GnRH pulse and surge generator, with the
definite aim of constraining the model GnRH output with respect to a
physiologically relevant list of specifications. The alternating pulse and
surge pattern of secretion results from the interaction between a GnRH
secreting system and a regulating system exhibiting fast-slow dynamics. The
mechanisms underlying the behavior of the model are reminded from the study of
the Boundary-Layer System according to the "dissection method" principle. Using
singular perturbation theory, we describe the sequence of bifurcations
undergone by the regulating (FitzHugh-Nagumo) system, encompassing the rarely
investigated case of homoclinic connexion. Basing on pure dynamical
considerations, we restrict the space of parameter search for the regulating
system and describe a foliation of this restricted space, whose leaves define
constant duration ratios between the surge and the pulsatility phase in the
whole system. We propose an algorithm to fix the parameter values to also meet
the other prescribed ratios dealing with amplitude and frequency features of
the secretion signal. We finally apply these results to illustrate the dynamics
of GnRH secretion in the ovine species and the rhesus monkey
Edge and waveguide THz surface plasmon modes in graphene micro-ribbons
Surface plasmon modes supported by graphene ribbon waveguides are studied and
classified. The properties of both modes with the field concentration within
the ribbon area (waveguiding modes) and on the edges (edge modes) are
discussed. The waveguide and edge modes are shown to be separated from each
other by a gap in wavenumbers. The even-parity hybridized edge mode results to
be the fundamental electromagnetic mode of the ribbon, possessing also the
lowest losses. All the plasmonic modes in the ribbons have an optimum
frequency, at which the absorption losses are minimum, due to competition
between the plasmon confinement and the frequency dependence of absorption in
graphene.Comment: 4 pages, 4 figure
Asymptotic entanglement capacity of the Ising and anisotropic Heisenberg interactions
We compute the asymptotic entanglement capacity of the Ising interaction ZZ,
the anisotropic Heisenberg interaction XX + YY, and more generally, any
two-qubit Hamiltonian with canonical form K = a XX + b YY. We also describe an
entanglement assisted classical communication protocol using the Hamiltonian K
with rate equal to the asymptotic entanglement capacity.Comment: 5 pages, 1 figure; minor corrections, conjecture adde
Numerical study of the hard-core Bose-Hubbard Model on an Infinite Square Lattice
We present a study of the hard-core Bose-Hubbard model at zero temperature on
an infinite square lattice using the infinite Projected Entangled Pair State
algorithm [Jordan et al., Phys. Rev. Lett. 101, 250602 (2008)]. Throughout the
whole phase diagram our values for the ground state energy, particle density
and condensate fraction accurately reproduce those previously obtained by other
methods. We also explore ground state entanglement, compute two-point
correlators and conduct a fidelity-based analysis of the phase diagram.
Furthermore, for illustrative purposes we simulate the response of the system
when a perturbation is suddenly added to the Hamiltonian.Comment: 8 pages, 6 figure
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