6,267 research outputs found
Cluster synchronization in an ensemble of neurons interacting through chemical synapses
In networks of periodically firing spiking neurons that are interconnected
with chemical synapses, we analyze cluster state, where an ensemble of neurons
are subdivided into a few clusters, in each of which neurons exhibit perfect
synchronization. To clarify stability of cluster state, we decompose linear
stability of the solution into two types of stabilities: stability of mean
state and stabilities of clusters. Computing Floquet matrices for these
stabilities, we clarify the total stability of cluster state for any types of
neurons and any strength of interactions even if the size of networks is
infinitely large. First, we apply this stability analysis to investigating
synchronization in the large ensemble of integrate-and-fire (IF) neurons. In
one-cluster state we find the change of stability of a cluster, which
elucidates that in-phase synchronization of IF neurons occurs with only
inhibitory synapses. Then, we investigate entrainment of two clusters of IF
neurons with different excitability. IF neurons with fast decaying synapses
show the low entrainment capability, which is explained by a pitchfork
bifurcation appearing in two-cluster state with change of synapse decay time
constant. Second, we analyze one-cluster state of Hodgkin-Huxley (HH) neurons
and discuss the difference in synchronization properties between IF neurons and
HH neurons.Comment: Notation for Jacobi matrix is changed. Accepted for publication in
Phys. Rev.
Comment on ``Effective Mass and g-Factor of Four Flux Quanta Composite Fermions"
In a recent Letter, Yeh et al.[Phys. Rev. Lett. 82, 592 (1999)] have shown
beautiful experimental results which indicate that the composite fermions with
four flux quanta (CF) behave as fermions with mass and spin just like those
with two flux quanta. They observed the collapse of the fractional quantum Hall
gaps when the following condition is satisfied with some integer ,
, where and
are the g-factor and the cyclotron frequency of the CF,
respectively. However, in their picture the gap at the Fermi energy remains
always finite even if the above condition is satisfied, thus the reason of the
collapse was left as a mystery. In this comment it is shown that part of the
mystery is resolved by considering the electron-hole symmetry properly.Comment: 2 pages, RevTeX. Minor chang
Systematic Analysis of Frustration Effects in Anisotropic Checkerboard Lattice Hubbard Model
We study the ground state properties of the geometrically frustrated Hubbard
model on the anisotropic checkerboard lattice with nearest-neighbor hopping
and next nearest-neighbor hopping . By using the path-integral
renormalization group method, we study the phase diagram in the parameter space
of the Hubbard interaction and the frustration-control parameter .
Close examinations of the effective hopping, the double occupancy, the momentum
distribution and the spin/charge correlation functions allow us to determine
the phase diagram at zero temperature, where the plaquette-singlet insulator
emerges besides the antiferromagnetic insulator and the paramagnetic metal.
Spin-liquid insulating states without any kind of symmetry breaking cannot be
found in our frustrated model.Comment: 7pages, 5figure
Monolithic superconducting emitter of tunable circularly polarized terahertz radiation
We propose an approach to control the polarization of terahertz (THz)
radiation from intrinsic Josephson-junction stacks in single crystalline
high-temperature superconductor . By monolithically
controlling the surface current distributions in the truncated square mesa
structure, we can modulate the polarization of the emitted THz wave as a result
of two orthogonal fundamental modes excited inside the mesa. Highly polarized
circular terahertz waves with a degree of circular polarization of more than
99% can be generated using an electrically controlled method. The emitted
radiation has a high intensity and a low axial ratio (AR<1 dB). The intuitive
results obtained from the numerical simulation based on the conventional
antenna theory are consistent with the observed emission characteristics.Comment: Submitted to PRApplie
Polarization Enhancement of terahertz radiation generated by intrinsic Josephson junctions in a truncated edge square Bi_{2}Sr_{2}CaCu_{2}O_{8+{\delta}} mesa
In this study, we investigated the terahertz radiation from a truncated edge
square mesa structure made from a superconducting
Bi_{2}Sr_{2}CaCu_{2}O_{8+{\delta}} . Using a commercial software, the
polarization characteristics were determined, and introduced, while accounting
for the skin effect. The axial ratio was enhanced in the simulation by
performing a parametric study on the design.Comment: Proceedings of the 28th International Symposium on Superconductivity,
ISS 2015, November 16-18, 2015, Tokyo, Japa
Hall Crystal States at and Moderate Landau Level Mixing
The quantum Hall state at low Zeeman coupling is well-known to be a
translationally invariant singlet if Landau level mixing is small. At zero
Zeeman interaction, as Landau level mixing increases, the translationally
invariant state becomes unstable to aninhomogeneous state. This is the first
realistic example of a full Hall crystal, which shows the coexistence of
quantum Hall order and density wave order. The full Hall crystal differs from
the more familiar Wigner crystal by a topological property, which results in it
having only linearly dispersing collective modes at small , and no
magnetophonon. I present calculations of the topological number and the
collective modes.Comment: Final version to appear in PRL. Two references added, minor changes
to figures and tex
Anisotropic two-dimensional Heisenberg model by Schwinger-boson Gutzwiller projected method
Two-dimensional Heisenberg model with anisotropic couplings in the and
directions () is considered. The model is first solved in the
Schwinger-boson mean-field approximation. Then the solution is Gutzwiller
projected to satisfy the local constraint that there is only one boson at each
site. The energy and spin-spin correlation of the obtained wavefunction are
calculated for systems with up to sites by means of the
variational Monte Carlo simulation. It is shown that the antiferromagnetic
long-range order remains down to the one-dimensional limit.Comment: 15 pages RevTex3.0, 4 figures, available upon request, GWRVB8-9
- …