2,068 research outputs found
From low-rank approximation to an efficient rational Krylov subspace method for the Lyapunov equation
We propose a new method for the approximate solution of the Lyapunov equation
with rank- right-hand side, which is based on extended rational Krylov
subspace approximation with adaptively computed shifts. The shift selection is
obtained from the connection between the Lyapunov equation, solution of systems
of linear ODEs and alternating least squares method for low-rank approximation.
The numerical experiments confirm the effectiveness of our approach.Comment: 17 pages, 1 figure
The continuum gauge field-theory model for low-energy electronic states of icosahedral fullerenes
The low-energy electronic structure of icosahedral fullerenes is studied
within the field-theory model. In the field model, the pentagonal rings in the
fullerene are simulated by two kinds of gauge fields. The first one,
non-abelian field, follows from so-called K spin rotation invariance for the
spinor field while the second one describes the elastic flow due to pentagonal
apical disclinations. For fullerene molecule, these fluxes are taken into
account by introducing an effective field due to magnetic monopole placed at
the center of a sphere. Additionally, the spherical geometry of the fullerene
is incorporated via the spin connection term. The exact analytical solution of
the problem (both for the eigenfunctions and the energy spectrum) is found.Comment: 9 pages, 2 figures, submitted to European Physical Journal
Nanomechanical displacement detection using coherent transport in ordered and disordered graphene nanoribbon resonators
Graphene nanoribbons provide an opportunity to integrate phase-coherent
transport phenomena with nanoelectromechanical systems (NEMS). Due to the
strain induced by a deflection in a graphene nanoribbon resonator, coherent
electron transport and mechanical deformations couple. As the electrons in
graphene have a Fermi wavelength \lambda ~ a_0 = 1.4 {\AA}, this coupling can
be used for sensitive displacement detection in both armchair and zigzag
graphene nanoribbon NEMS. Here it is shown that for ordered as well as
disordered ribbon systems of length L, a strain \epsilon ~ (w/L)^2 due to a
deflection w leads to a relative change in conductance \delta G/G ~ (w^2/a_0L).Comment: 4 Pages, 4 figure
Rapidly rotating neutron star progenitors
Rotating proto-neutron stars can be important sources of gravitational waves
to be searched for by present-day and future interferometric detectors. It was
demonstrated by Imshennik that in extreme cases the rapid rotation of a
collapsing stellar core may lead to fission and formation of a binary
proto-neutron star which subsequently merges due to gravitational wave
emission. In the present paper, we show that such dynamically unstable
collapsing stellar cores may be the product of a former merger process of two
stellar cores in a common envelope. We applied population synthesis
calculations to assess the expected fraction of such rapidly rotating stellar
cores which may lead to fission and formation of a pair of proto-neutron stars.
We have used the BSE population synthesis code supplemented with a new
treatment of stellar core rotation during the evolution via effective
core-envelope coupling, characterized by the coupling time, . The
validity of this approach is checked by direct MESA calculations of the
evolution of a rotating 15 star. From comparison of the calculated
spin distribution of young neutron stars with the observed one, reported by
Popov and Turolla, we infer the value years. We
show that merging of stellar cores in common envelopes can lead to collapses
with dynamically unstable proto-neutron stars, with their formation rate being
of the total core collapses, depending on the common envelope
efficiency.Comment: 10 pages, 4 figures, accepted for publication in MNRA
Conductance through the disclination dipole defect in metallic carbon nanotubes
The electronic transport properties of a metallic carbon nanotube with the
five-seven disclination pair characterized by a lattice distortion vector are
investigated. The influence of the disclination dipole includes induced
curvature and mixing of two sublattices. Both these factors are taken into
account via a self-consistent perturbation approach. The conductance and the
Fano factor are calculated within the transfer-matrix technique. PACS:
73.63.Fg, 72.80.Rj, 72.10.F
Stability and hyperfine structure of the four- and five-body muon-atomic clusters and
Based on the results of accurate variational calculations we demonstrate
stability of the five-body negatively charged ions . Each of these five-body ions contains two electrons , one
negatively charged muon and two nuclei of the hydrogen isotopes . The bound state properties of these five-body ions, including
their hyperfine structure, are briefly discussed. We also investigate the
hyperfine structure of the ground states of the four-body muonic quasi-atoms
. In particular, we determine the hyperfine
structure splittings for the ground state of the four-body muonic quasi-atoms:
and
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