25,236 research outputs found
Improved superlensing in two-dimensional photonic crystals with a basis
We study propagation of light in square and hexagonal two-dimensional
photonic crystals. We show, that slabs of these crystals focus light with
subwavelength resolution. We propose a systematic way to increase this
resolution, at an essentially fixed frequency, by employing a hierarchy of
crystals of the same structure, and the same lattice constant, but with an
increasingly complex basis.Comment: 16 Pages, 5 Figure
The branch processes of vortex filaments and Hopf Invariant Constraint on Scroll Wave
In this paper, by making use of Duan's topological current theory, the
evolution of the vortex filaments in excitable media is discussed in detail.
The vortex filaments are found generating or annihilating at the limit points
and encountering, splitting, or merging at the bifurcation points of a complex
function . It is also shown that the Hopf invariant of knotted
scroll wave filaments is preserved in the branch processes (splitting, merging,
or encountering) during the evolution of these knotted scroll wave filaments.
Furthermore, it also revealed that the "exclusion principle" in some chemical
media is just the special case of the Hopf invariant constraint, and during the
branch processes the "exclusion principle" is also protected by topology.Comment: 9 pages, 5 figure
Recurrence interval analysis of high-frequency financial returns and its application to risk estimation
We investigate the probability distributions of the recurrence intervals
between consecutive 1-min returns above a positive threshold or
below a negative threshold of two indices and 20 individual stocks in
China's stock market. The distributions of recurrence intervals for positive
and negative thresholds are symmetric, and display power-law tails tested by
three goodness-of-fit measures including the Kolmogorov-Smirnov (KS) statistic,
the weighted KS statistic and the Cram\'er-von Mises criterion. Both long-term
and shot-term memory effects are observed in the recurrence intervals for
positive and negative thresholds . We further apply the recurrence interval
analysis to the risk estimation for the Chinese stock markets based on the
probability , Value-at-Risk (VaR) analysis and VaR analysis
conditioned on preceding recurrence intervals.Comment: 17 pages, 10 figures, 1 tabl
Plasmon assisted transmission of high dimensional orbital angular momentum entangled state
We present an experimental evidence that high dimensional orbital angular
momentum entanglement of a pair of photons can be survived after a
photon-plasmon-photon conversion. The information of spatial modes can be
coherently transmitted by surface plasmons. This experiment primarily studies
the high dimensional entangled systems based on surface plasmon with
subwavelength structures. It maybe useful in the investigation of spatial mode
properties of surface plasmon assisted transmission through subwavelength hole
arrays.Comment: 7 pages,6 figure
Oxidation Behavior of a Pd_(43)Cu_(27)Ni_(10)P_(20) Bulk Metallic Glass and Foam in Dry Air
The oxidation behavior of both Pd_(43)Cu_(27)Ni_(10)P_(20) bulk metallic glass (Pd4-BMG) and its amorphous foam containing 45 pct porosity (Pd4-AF) was investigated over the temperature range of 343 K (70 °C) to 623 K (350 °C) in dry air. The results showed that virtually no oxidation occurred in the Pd4-BMG at T < 523 K (250 °C), revealing the alloy’s favorable oxidation resistance in this temperature range. In addition, the oxidation kinetics at T ≥ 523 K (250 °C) followed a parabolic-rate law, and the parabolic-rate constants (k_p values) generally increased with temperature. It was found that the oxidation k_p values of the Pd4-AF are slightly lower than those of the Pd4-BMG, indicating that the porous structure contributes to improving the overall oxidation resistance. The scale formed on the alloys was composed exclusively of CuO at T ≥ 548 K (275 °C), whose thickness gradually increased with increasing temperature. In addition, the amorphous structure remained unchanged at T ≤ 548 K (275 °C), while a triplex-phase structure developed after the oxidation at higher temperatures, consisting of Pd_2Ni_2P, Cu_3P, and Pd_3P
Strongly-coupled quantum critical point in an all-in-all-out antiferromagnet
Dimensionality and symmetry play deterministic roles in the laws of Nature.
They are important tools to characterize and understand quantum phase
transitions, especially in the limit of strong correlations between spin,
orbit, charge, and structural degrees of freedom. Using newly-developed,
high-pressure resonant x-ray magnetic and charge diffraction techniques, we
have discovered a quantum critical point in Cd2Os2O7 as the all-in-all-out
(AIAO) antiferromagnetic order is continuously suppressed to zero temperature
and, concomitantly, the cubic lattice structure continuously changes from space
group Fd-3m to F-43m. Surrounded by three phases of different time reversal and
spatial inversion symmetries, the quantum critical region anchors two phase
lines of opposite curvature, with striking departures from a mean-field form at
high pressure. As spin fluctuations, lattice breathing modes, and quasiparticle
excitations interact in the quantum critical region, we argue that they present
the necessary components for strongly-coupled quantum criticality in this
three-dimensional compound
Possibility of Unconventional Pairing Due to Coulomb Interaction in Fe-Based Pnictide Superconductors: Perturbative Analysis of Multi-Band Hubbard Models
Possibility of unconventional pairing due to Coulomb interaction in
iron-pnictide superconductors is studied by applying a perturbative approach to
realistic 2- and 5-band Hubbard models. The linearized Eliashberg equation is
solved by expanding the effective pairing interaction perturbatively up to
third order in the on-site Coulomb integrals. The numerical results for the
5-band model suggest that the eigenvalues of the Eliashberg equation are
sufficiently large to explain the actual high Tc for realistic values of
Coulomb interaction and the most probable pairing state is spin-singlet s-wave
without any nodes just on the Fermi surfaces, although the superconducting
order parameter changes its sign between the small Fermi pockets. On the other
hand the 2-band model is quite insufficient to explain the actual high Tc.Comment: 2 pages, 3 figures. Proceedings of the Intl. Symposium on
Fe-Oxypnictide Superconductors (Tokyo, 28-29th June 2008
Neutron scattering study of magnetic phase separation in nanocrystalline LaCaMnO
We demonstrate that magnetic phase separation and competing spin order in the
colossal magnetoresistive (CMR) manganites can be directly explored via tuning
strain in bulk samples of nanocrystalline LaCaMnO. Our results
show that strain can be reversibly frozen into the lattice in order to
stabilize coexisting antiferromagnetic domains within the nominally
ferromagnetic metallic state of LaCaMnO. The measurement of
tunable phase separation via magnetic neutron powder diffraction presents a
direct route of exploring the correlated spin properties of phase separated
charge/magnetic order in highly strained CMR materials and opens a potential
avenue for realizing intergrain spin tunnel junction networks with enhanced CMR
behavior in a chemically homogeneous material.Comment: 6 pages, 4 figures. New figure and text added to manuscrip
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