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

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

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

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

Spectroscopic evidence of the formation of (V,Ti)O₂ solid solution in VO₂ thinner films grown on TiO₂(001) substrates

We have prepared VO2 thin films epitaxially grown on TiO2(001) substrates with thickness systematically varied from 2.5 to 13 nm using a pulsed laser deposition method, and studied the transport property and electronic states of the films by means of resistivity and in situ synchrotron photoemission spectroscopy (SRPES). In resistivity measurements, the 13-nm-thick film exhibits a metal-insulator transition at around 290 K on cooling with change of three orders of magnitudes in resistivity. As the film thickness decreases, the metal-insulator transition broadens and the transition temperature increases. Below 4 nm, the films do not show the transition and become insulators. In situ SRPES measurements of near the Fermi level valence band find that the electronic state of the 2.5-nm-thick film is different than that of the temperature-induced insulator phase of VO2 itself although these two states are insulating. Ti 2p core-level photoemission measurements reveal that Ti ions exist near the interface between the films and TiO2 substrates, with a chemical state similar to that in (V,Ti)O-2 solid solution. These results indicate that insulating (V,Ti)O-2 solid solution is formed in the thinner films. We propose a simple growth model of a VO2 thin film on a TiO2(001) substrate. Near the interface, insulating (V,Ti) O-2 solid solution is formed due to the diffusion of Ti ions from the TiO2 substrate into the VO2 film. The concentration of Ti in (V,Ti) O-2 is relatively high near the interface and decreases toward the surface of the film. Beyond a certain film thickness (about 7 nm in the case of the present 13-nm-thick film), the VO2 thin film without any Ti ions starts to grow. Our work suggests that developing a technique for preparing the sharp interface between the VO2 thin films and TiO2 substrates is a key issue to study the physical property of an ultrathin film of "pure" VO2, especially to examine the presence of the novel electronic state called a semi-Dirac point phase predicted by calculations