960 research outputs found
Room temperature ferromagnetic behavior in the hollandite-type titanium oxide
A hollandite-type K(x)Ti(8)O(16) polycrystalline sample has been prepared and studied by magnetization, resistivity and x-ray photoelectron spectroscopy (XPS). Room temperature ferromagnetic behavior is observed in the magnetic hysteresis measurement. The sample shows a semiconductive temperature dependence in the resistivity measurement. Analysis of the Ti 2p(3/2) core-level XPS spectrum indicates that the titanium ions have a mixed valence of Ti(4+) and Ti(3+). In addition, the valence band spectrum reveals that the 3d electrons tend to localize on Ti(3+) ions in the hollandite-type TiO(2) lattice. Also, analysis of the valence band spectrum shows that the prepared sample is a wide-gap oxide with a band gap of 3.6 eV. These results indicate that the present hollandite-type K(x)Ti(8)O(16) sample can be classified as a TiO(2)-based wide-gap semiconductor with Curie temperature above room temperature. Room temperature ferromagnetism (RTFM) decreases in the sample prepared under a strong reducing gas atmosphere, accompanied with the decrease in the resistivity. The results imply that the localized 3d electrons are responsible for the RTFM of the K(x)Ti(8)O(16) sample
A General Optimization Technique for High Quality Community Detection in Complex Networks
Recent years have witnessed the development of a large body of algorithms for
community detection in complex networks. Most of them are based upon the
optimization of objective functions, among which modularity is the most common,
though a number of alternatives have been suggested in the scientific
literature. We present here an effective general search strategy for the
optimization of various objective functions for community detection purposes.
When applied to modularity, on both real-world and synthetic networks, our
search strategy substantially outperforms the best existing algorithms in terms
of final scores of the objective function; for description length, its
performance is on par with the original Infomap algorithm. The execution time
of our algorithm is on par with non-greedy alternatives present in literature,
and networks of up to 10,000 nodes can be analyzed in time spans ranging from
minutes to a few hours on average workstations, making our approach readily
applicable to tasks which require the quality of partitioning to be as high as
possible, and are not limited by strict time constraints. Finally, based on the
most effective of the available optimization techniques, we compare the
performance of modularity and code length as objective functions, in terms of
the quality of the partitions one can achieve by optimizing them. To this end,
we evaluated the ability of each objective function to reconstruct the
underlying structure of a large set of synthetic and real-world networks.Comment: MAIN text: 14 pages, 4 figures, 1 table Supplementary information: 19
pages, 8 figures, 5 table
Determination of the local structure of SrMIrO (M = K, La) as a function of doping and temperature
The local structure of correlated spin-orbit insulator SrMIrO
(M = K, La) has been investigated by Ir L-edge extended x-ray absorption
fine structure measurements. The measurements were performed as a function of
temperature for different dopings induced by substitution of Sr with La or K.
It is found that Ir-O bonds have strong covalency and they hardly show any
change across the N\'eel temperature. In the studied doping range, neither Ir-O
bonds nor their dynamics, measured by their mean square relative displacements,
show any appreciable change upon carrier doping, indicating possibility of a
nanoscale phase separation in the doped system. On the other hand, there is a
large increase of the static disorder in Ir-Sr correlation, larger for K doping
than La doping. Similarities and differences with respect to the local lattice
displacements in cuprates are briefly discussed.Comment: Main text: 6 pages, 4 figures, Supplemental information: 2 pages, 2
figure
Proximity to Fermi-surface topological change in superconducting LaO0.54F0.46BiS2
The electronic structure of nearly optimally-doped novel superconductor
LaOFBiS ( = 0.46) was investigated using
angle-resolved photoemission spectroscopy (ARPES). We clearly observed band
dispersions from 2 to 6 eV binding energy and near the Fermi level (), which are well reproduced by first principles calculations when
the spin-orbit coupling is taken into account. The ARPES intensity map near
shows a square-like distribution around the (Z) point
in addition to electronlike Fermi surface (FS) sheets around the X(R) point,
indicating that FS of LaOFBiS is in close proximity to
the theoretically-predicted topological change.Comment: 6 pages, 3 figures, + supplemental materia
Metallic phase in stoichiometric CeOBiS 2 revealed by space-resolved ARPES
Recently CeOBiS2 system without any fluorine doping is found to show superconductivity posing question on its origin. Using space resolved ARPES we have found a metallic phase embedded in the morphological defects and at the sample edges of stoichiometric CeOBiS2. While bulk of the sample is semiconducting, the embedded metallic phase is characterized by the usual electron pocket at X point, similar to the Fermi surface of doped BiS2-based superconductors. Typical size of the observed metallic domain is larger than the superconducting correlation length of the system suggesting that the observed superconductivity in undoped CeOBiS2 might be due to this embedded metallic phase at the defects. The results also suggest a possible way to develop new systems by manipulation of the defects in these chalcogenides with structural instability
Remote detection of fumarolic gas chemistry at Vulcano, Italy, using an FT-IR spectral radiometer
An infrared absorption spectroscopy remote sensing technique was used to determine the S02/HCl ratio in fumarolic
plumes at Vulcano, Italy. The measurements were made from the southern crater rim of Fossa Grande Crater, about 400 m
from the fumarolic area in the crater. Infrared absorption spectra of HCl and SO, were observed for four fumaroles a few
tens of metres apart using the hot fumarolic surface as an infrared light source. The measured S02/HCl ratios in the FA,
F47, FW and lower parti of the F21 fumaroles were 4.5-5.4, 3.5, 9.5-11.2 and 5.8 respectively. The S02/HCl ratio of the
FA fumarole was higher than that of the gas collected directly in the fumarolic vent (S02/HCl ratio = 2.9), and was closer
to the S~,,,,,,/HCl ratio (= 4.6) of the collected gas. Our results show that the SO,/HCl ratios of two fumaroles only a few
tens of metres apart exhibits differences of about twofold. This suggests that this remote monitoring technique is capable of
detecting spatial distribution in the S02/HCl ratios of volcanic plumes. Because temporal variations in S/Cl ratios can
provide precursory signals for volcanic eruptions [l-31, this remote sensing technique can used efficiently for evaluation of
volcanic activity
Asymptotics of a discrete-time particle system near a reflecting boundary
We examine a discrete-time Markovian particle system on the quarter-plane
introduced by M. Defosseux. The vertical boundary acts as a reflecting wall.
The particle system lies in the Anisotropic Kardar-Parisi-Zhang with a wall
universality class. After projecting to a single horizontal level, we take the
longtime asymptotics and obtain the discrete Jacobi and symmetric Pearcey
kernels. This is achieved by showing that the particle system is identical to a
Markov chain arising from representations of the infinite-dimensional
orthogonal group. The fixed-time marginals of this Markov chain are known to be
determinantal point processes, allowing us to take the limit of the correlation
kernel.
We also give a simple example which shows that in the multi-level case, the
particle system and the Markov chain evolve differently.Comment: 16 pages, Version 2 improves the expositio
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