29,863 research outputs found
An Efficient Block Circulant Preconditioner For Simulating Fracture Using Large Fuse Networks
{\it Critical slowing down} associated with the iterative solvers close to
the critical point often hinders large-scale numerical simulation of fracture
using discrete lattice networks. This paper presents a block circlant
preconditioner for iterative solvers for the simulation of progressive fracture
in disordered, quasi-brittle materials using large discrete lattice networks.
The average computational cost of the present alorithm per iteration is , where the stiffness matrix is partioned into
-by- blocks such that each block is an -by- matrix, and
represents the operational count associated with solving a block-diagonal
matrix with -by- dense matrix blocks. This algorithm using the block
circulant preconditioner is faster than the Fourier accelerated preconditioned
conjugate gradient (PCG) algorithm, and alleviates the {\it critical slowing
down} that is especially severe close to the critical point. Numerical results
using random resistor networks substantiate the efficiency of the present
algorithm.Comment: 16 pages including 2 figure
Excitation of surface plasmon-polaritons in metal films with double periodic modulation: anomalous optical effects
We perform a thorough theoretical analysis of resonance effects when an
arbitrarily polarized plane monochromatic wave is incident onto a double
periodically modulated metal film sandwiched by two different transparent
media. The proposed theory offers a generalization of the theory that had been
build in our recent papers for the simplest case of one-dimensional structures
to two-dimensional ones. A special emphasis is placed on the films with the
modulation caused by cylindrical inclusions, hence, the results obtained are
applicable to the films used in the experiments. We discuss a spectral
composition of modulated films and highlight the principal role of
``resonance'' and ``coupling'' modulation harmonics. All the originating
multiple resonances are examined in detail. The transformation coefficients
corresponding to different diffraction orders are investigated in the vicinity
of each resonance. We make a comparison between our theory and recent
experiments concerning enhanced light transmittance and show the ways of
increasing the efficiency of these phenomena. In the appendix we demonstrate a
close analogy between ELT effect and peculiarities of a forced motion of two
coupled classical oscillators.Comment: 24 pages, 17 figure
Phase transition in the Higgs model of scalar dyons
In the present paper we investigate the phase transition
"Coulomb--confinement" in the Higgs model of abelian scalar dyons -- particles
having both, electric and magnetic , charges. It is shown that by dual
symmetry this theory is equivalent to scalar fields with the effective squared
electric charge e^{*2}=e^2+g^2. But the Dirac relation distinguishes the
electric and magnetic charges of dyons. The following phase transition
couplings are obtained in the one--loop approximation:
\alpha_{crit}=e^2_{crit}/4\pi\approx 0.19,
\tilde\alpha_{crit}=g^2_{crit}/4\pi\approx 1.29 and \alpha^*_{crit}\approx
1.48.Comment: 16 pages, 2 figure
Unique gap structure and symmetry of the charge density wave in single-layer VSe
Single layers of transition metal dichalcogenides (TMDCs) are excellent
candidates for electronic applications beyond the graphene platform; many of
them exhibit novel properties including charge density waves (CDWs) and
magnetic ordering. CDWs in these single layers are generally a planar
projection of the corresponding bulk CDWs because of the quasi-two-dimensional
nature of TMDCs; a different CDW symmetry is unexpected. We report herein the
successful creation of pristine single-layer VSe, which shows a () CDW in contrast to the (4 4) CDW for the layers in
bulk VSe. Angle-resolved photoemission spectroscopy (ARPES) from the single
layer shows a sizable () CDW gap of 100 meV at the
zone boundary, a 220 K CDW transition temperature twice the bulk value, and no
ferromagnetic exchange splitting as predicted by theory. This robust CDW with
an exotic broken symmetry as the ground state is explained via a
first-principles analysis. The results illustrate a unique CDW phenomenon in
the two-dimensional limit
Charge sensing in carbon nanotube quantum dots on microsecond timescales
We report fast, simultaneous charge sensing and transport measurements of
gate-defined carbon nanotube quantum dots. Aluminum radio frequency single
electron transistors (rf-SETs) capacitively coupled to the nanotube dot provide
single-electron charge sensing on microsecond timescales. Simultaneously, rf
reflectometry allows fast measurement of transport through the nanotube dot.
Charge stability diagrams for the nanotube dot in the Coulomb blockade regime
show extended Coulomb diamonds into the high-bias regime, as well as even-odd
filling effects, revealed in charge sensing data.Comment: 4 pages, 4 figure
Thermodynamics of the superfluid dilute Bose gas with disorder
We generalize the Beliaev-Popov diagrammatic technique for the problem of
interacting dilute Bose gas with weak disorder. Averaging over disorder is
implemented by the replica method. Low energy asymptotic form of the Green
function confirms that the low energy excitations of the superfluid dirty Boson
system are sound waves with velocity renormalized by the disorder and
additional dissipation due to the impurity scattering. We find the
thermodynamic potential and the superfluid density at any temperature below the
superfluid transition temperature and derive the phase diagram in temperature
vs. disorder plane.Comment: 4 page
A Solvable Model of Two-Dimensional Dilaton-Gravity Coupled to a Massless Scalar Field
We present a solvable model of two-dimensional dilaton-gravity coupled to a
massless scalar field. We locally integrate the field equations and briefly
discuss the properties of the solutions. For a particular choice of the
coupling between the dilaton and the scalar field the model can be interpreted
as the two-dimensional effective theory of 2+1 cylindrical gravity minimally
coupled to a massless scalar field.Comment: 6 pages, RevTeX, to be published in Phys. Rev.
Doping-Dependent Raman Resonance in the Model High-Temperature Superconductor HgBa2CuO4+d
We study the model high-temperature superconductor HgBa2CuO4+d with
electronic Raman scattering and optical ellipsometry over a wide doping range.
The resonant Raman condition which enhances the scattering cross section of
"two-magnon" excitations is found to change strongly with doping, and it
corresponds to a rearrangement of inter-band optical transitions in the 1-3 eV
range seen by ellipsometry. This unexpected change of the resonance condition
allows us to reconcile the apparent discrepancy between Raman and x-ray
detection of magnetic fluctuations in superconducting cuprates. Intriguingly,
the strongest variation occurs across the doping level where the antinodal
superconducting gap reaches its maximum.Comment: 4 pages, 4 figures, contact authors for Supplemental Materia
Observing sub-microsecond telegraph noise with the radio frequency single electron transistor
Telegraph noise, which originates from the switching of charge between
meta-stable trapping sites, becomes increasingly important as device sizes
approach the nano-scale. For charge-based quantum computing, this noise may
lead to decoherence and loss of read out fidelity. Here we use a radio
frequency single electron transistor (rf-SET) to probe the telegraph noise
present in a typical semiconductor-based quantum computer architecture. We
frequently observe micro-second telegraph noise, which is a strong function of
the local electrostatic potential defined by surface gate biases. We present a
method for studying telegraph noise using the rf-SET and show results for a
charge trap in which the capture and emission of a single electron is
controlled by the bias applied to a surface gate.Comment: Accepted for publication in Journal of Applied Physics. Comments
always welcome, email [email protected], [email protected]
Quantum fluctuations of Cosmological Perturbations in Generalized Gravity
Recently, we presented a unified way of analysing classical cosmological
perturbation in generalized gravity theories. In this paper, we derive the
perturbation spectrums generated from quantum fluctuations again in unified
forms. We consider a situation where an accelerated expansion phase of the
early universe is realized in a particular generic phase of the generalized
gravity. We take the perturbative semiclassical approximation which treats the
perturbed parts of the metric and matter fields as quantum mechanical
operators. Our generic results include the conventional power-law and
exponential inflations in Einstein's gravity as special cases.Comment: 5 pages, revtex, no figure
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