25,901 research outputs found
Suppression of magnetism in Ba5AlIr2O11: interplay of Hund's coupling, molecular orbitals and spin-orbit interaction
The electronic and magnetic properties of BaAlIrO containing
Ir-Ir dimers are investigated using the GGA and GGA+SOC calculations. We found
that strong suppression of the magnetic moment in this compound recently found
in [J. Terzic {\it et al.}, Phys. Rev. B {\bf 91}, 235147 (2015)] is not due to
charge-ordering, but is related to the joint effect of the spin-orbit
interaction and strong covalency, resulting in the formation of metal-metal
bonds. They conspire and act against the intra-atomic Hund's rule exchange
interaction to reduce total magnetic moment of the dimer. We argue that the
same mechanism could be relevant for other and dimerized transition
metal compounds
Long-Range Plasmon Assisted Energy Transfer Between Fluorescent Emitters
We demonstrate plasmon assisted energy transfer between fluorophores located
at distances up to m on the top of a thin silver film. Thanks to the
strong confinement and large propagation length of surface plasmon polaritons,
the range of the energy transfer is almost two orders of magnitude larger than
the values reported in the literature so far. The parameters driving the energy
transfer range are thoroughly characterized and are in very good agreement with
theoretically expected values.Comment: 5 pages, 4 figures, accepted for publication in Physical Review
Letter
Effective macroscopic dynamics of stochastic partial differential equations in perforated domains
An effective macroscopic model for a stochastic microscopic system is
derived. The original microscopic system is modeled by a stochastic partial
differential equation defined on a domain perforated with small holes or
heterogeneities. The homogenized effective model is still a stochastic partial
differential equation but defined on a unified domain without holes. The
solutions of the microscopic model is shown to converge to those of the
effective macroscopic model in probability distribution, as the size of holes
diminishes to zero. Moreover, the long time effectivity of the macroscopic
system in the sense of \emph{convergence in probability distribution}, and the
effectivity of the macroscopic system in the sense of \emph{convergence in
energy} are also proved
Resonances in 1D disordered systems: localization of energy and resonant transmission
Localized states in one-dimensional open disordered systems and their
connection to the internal structure of random samples have been studied. It is
shown that the localization of energy and anomalously high transmission
associated with these states are due to the existence inside the sample of a
transparent (for a given resonant frequency) segment with the minimal size of
order of the localization length. A mapping of the stochastic scattering
problem in hand onto a deterministic quantum problem is developed. It is shown
that there is no one-to-one correspondence between the localization and high
transparency: only small part of localized modes provides the transmission
coefficient close to one. The maximal transmission is provided by the modes
that are localized in the center, while the highest energy concentration takes
place in cavities shifted towards the input. An algorithm is proposed to
estimate the position of an effective resonant cavity and its pumping rate by
measuring the resonant transmission coefficient. The validity of the analytical
results have been checked by extensive numerical simulations and wavelet
analysis
Random Resonators and Prelocalized Modes in Disordered Dielectric Films
Areal density of disorder-induced resonators with a high quality factor,
, in a film with fluctuating refraction index is calculated
theoretically. We demonstrate that for a given , where is the light
wave vector, and is the transport mean free path, when {\em on average} the
light propagation is diffusive, the likelihood for finding a random resonator
increases dramatically with increasing the correlation radius of the disorder.
Parameters of {\em most probable} resonators as functions of and are
found.Comment: 6 pages including 2 figure
Friedmann Equations from Entropic Force
In this note by use of the holographic principle together with the
equipartition law of energy and the Unruh temperature, we derive the Friedmann
equations of a Friedmann-Robertson-Walker universe.Comment: latex, 8 pages, v2: minor modifications and to appear in PRD (Rapid
Communication
Magnetic anomalies in single crystalline ErPd2Si2
Considering certain interesting features in the previously reported 166Er
Moessbauer effect and neutron diffraction data on the polycrystalline form of
ErPd2Si2 crystallizing in ThCr2Si2-type tetragonal structure, we have carried
out magnetic measurements (1.8 to 300 K) on the single crystalline form of this
compound. We observe significant anisotropy in the absolute values of
magnetization (indicating that the easy axis is c-axis) as well as in the
features due to magnetic ordering in the plot of magnetic susceptibility (chi)
versus temperature (T) at low temperatures. The chi(T) data reveal that there
is a pseudo-low dimensional magnetic order setting in at 4.8 K, with a
three-dimensional antiferromagnetic ordering setting in at a lower temperature
(3.8 K). A new finding in the chi(T) data is that, for H//, but not for
H//, there is a broad shoulder in the range 8-20 K, indicative of the
existence of magnetic correlations above 5 K as well, which could be related to
the previously reported slow-relaxation-dominated Moessbauer spectra.
Interestingly, the temperature coefficient of electrical resistivity is found
to be isotropic; no feature due to magnetic ordering could be detected in the
electrical resistivity data at low temperatures, which is attributed to
magnetic Brillioun-zone boundary gap effects. The results reveal complex nature
of the magnetism of this compound
Hierarchical growing neural gas
“The original publication is available at www.springerlink.com”. Copyright Springer.This paper describes TreeGNG, a top-down unsupervised learning method that produces hierarchical classification schemes. TreeGNG is an extension to the Growing Neural Gas algorithm that maintains a time history of the learned topological mapping. TreeGNG is able to correct poor decisions made during the early phases of the construction of the tree, and provides the novel ability to influence the general shape and form of the learned hierarchy
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