Photoinduced magnetic bound state in itinerant correlated electron system with spin-state degree of freedom

Photo-excited state in correlated electron system with spin-state degree of freedom is studied. We start from the two-orbital extended Hubbard model where energy difference between the two orbitals is introduced. Photo-excited metastable state is examined based on the effective model Hamiltonian derived by the two-orbital Hubbard model. Spin-state change is induced by photo-irradiation in the low-spin band insulator near the phase boundary. High-spin state is stabilized by creating a ferromagnetic bound state with photo-doped hole carriers. An optical absorption occurs between the bonding and antibonding orbitals inside of the bound state. Time-evolution for photo-excited states is simulated in the time-dependent mean-field scheme. Pair-annihilations of the photo-doped electron and hole generate the high-spin state in a low-spin band insulator. We propose that this process is directly observed by the time-resolved photoemission experiments.Comment: 15 pages, 16 figure

Competing Ground States of a Peierls-Hubbard Nanotube

Motivated by iodo platinum complexes assembled within a quadratic-prism lattice, [Pt(C$_2$H$_8$N$_2$)(C$_{10}$H$_8$N$_2$)I]$_4$(NO$_3$)$_8$, we investigate the ground-state properties of a Peierls-Hubbard four-legged tube. Making a group-theoretical analysis, we systematically reveal a variety of valence arrangements, including half-metallic charge-density-wave states. Quantum and thermal phase competition is numerically demonstrated with particular emphasis on doping-induced successive insulator-to-metal transitions with conductivity increasing stepwise.Comment: 6 pages, 4 figures. to be published in Europhys. Lett. 87 (2009) 1700

Dominant aerosol processes during high-pollution episodes over Greater Tokyo

This paper studies two high-pollution episodes over Greater Tokyo: 9 and 10 December 1999, and 31 July and 1 August 2001. Results obtained with the chemistry-transport model (CTM) Polair3D are compared to measurements of inorganic PM2.5. To understand to which extent the aerosol processes modeled in Polair3D impact simulated inorganic PM2.5, Polair3D is run with different options in the aerosol module, e.g. with/without heterogeneous reactions. To quantify the impact of processes outside the aerosol module, simulations are also done with another CTM (CMAQ). In the winter episode, sulfate is mostly impacted by condensation, coagulation, long-range transport, and deposition to a lesser extent. In the summer episode, the effect of long-range transport largely dominates. The impact of condensation/evaporation is dominant for ammonium, nitrate and chloride in both episodes. However, the impact of the thermodynamic equilibrium assumption is limited. The impact of heterogeneous reactions is large for nitrate and ammonium, and taking heterogeneous reactions into account appears to be crucial in predicting the peaks of nitrate and ammonium. The impact of deposition is the same for all inorganic PM2.5. It is small compared to the impact of other processes although it is not negligible. The impact of nucleation is negligible in the summer episode, and small in the winter episode. The impact of coagulation is larger in the winter episode than in the summer episode, because the number of small particles is higher in the winter episode as a consequence of nucleation.Comment: Journal of Geophysical Research D: Atmospheres (15/05/2007) in pres

A hybrid Si@FeSiy/SiOx anode structure for high performance lithium-ion batteries via ammonia-assisted one-pot synthesis

Synthesised via planetary ball-milling of Si and Fe powders in an ammonia (NH3) environment, a hybrid Si@FeSiy/SiOx structure shows exceptional electrochemical properties for lithium-ion battery anodes, exhibiting a high initial capacity of 1150 mA h g−1 and a retention capacity of 880 mA h g−1 after 150 cycles at 100 mA g−1; and a capacity of 560 mA h g−1 at 4000 mA g−1. These are considerably high for carbon-free micro-/submicro-Si-based anodes. NH3 gradually turns into N2 and H2 during the synthesis, which facilitates the formation of highly conductive FeSiy (y = 1, 2) phases, whereas such phases were not formed in an Ar atmosphere. Milling for 20–40 h leads to partial decomposition of NH3 in the atmosphere, and a hybrid structure of a Si core of mixed nanocrystalline and amorphous Si domains, shelled by a relatively thick SiOx layer with embedded FeSi nanocrystallites. Milling for 60–100 h results in full decomposition of NH3 and a hybrid structure of a much-refined Si-rich core surrounded by a mantle of a relatively low level of SiOx and a higher level of FeSi2. The formation mechanisms of the SiOx and FeSiy phases are explored. The latter structure offers an optimum combination of the high capacity of a nanostructural Si core, relatively high electric conductivity of the FeSiy phase and high structural stability of a SiOx shell accommodating the volume change for high performance electrodes. The synthesis method is new and indispensable for the large-scale production of high-performance Si-based anode materials

Liquid-like thermal conduction in a crystalline solid

A solid conducts heat through both transverse and longitudinal acoustic phonons, but a liquid employs only longitudinal vibrations. Here, we report that the crystalline solid AgCrSe2 has liquid-like thermal conduction. In this compound, Ag atoms exhibit a dynamic duality that they are exclusively involved in intense low-lying transverse acoustic phonons while they also undergo local fluctuations inherent in an order-to-disorder transition occurring at 450 K. As a consequence of this extreme disorder-phonon coupling, transverse acoustic phonons become damped as approaching the transition temperature, above which they are not defined anymore because their lifetime is shorter than the relaxation time of local fluctuations. Nevertheless, the damped longitudinal acoustic phonon survives for thermal transport. This microscopic insight might reshape the fundamental idea on thermal transport properties of matter and facilitates the optimization of thermoelectrics.Comment: four figures, supplemental informatio

Preferential dipeptide incorporation of Porphyromonas gingivalis mediated by proton-dependent oligopeptide transporter (Pot)

Multiple dipeptidyl-peptidases (DPPs) are present in the periplasmic space of Porphyromonas gingivalis, an asaccharolytic periodontopathic bacterium. Dipeptides produced by DPPs are presumed to be transported into the bacterial cells and metabolized to generate energy and cellular components. The present study aimed to identify a transporter responsible for dipeptide uptake in the bacterium. A real-time metabolic analysis demonstrated that P. gingivalis preferentially incorporated Gly-Xaa dipeptides, and then,single amino acids, tripeptides, and longer oligopeptides to lesser extents. Heterologous expression of the P. gingivalis serine/threonine transporter (SstT) (PGN_1460), oligopeptide transporter (Opt) (PGN_1518), and proton-dependent oligopeptide transporter (Pot) (PGN_0135) genes demonstrated that Escherichia coli expressing Pot exclusively incorporated Gly-Gly, while SstT managed Ser uptake and Opt was responsible for Gly-Gly-Gly uptake. Dipeptide uptake was significantly decreased in a P. gingivalis Δpot strain and further suppressed in a Δpot-Δopt double-deficient strain. In addition, the growth of the Δpot strain was markedly attenuated and the Δpot-Δopt strain scarcely grew, whereas the ΔsstT strain grew well almost like wild type. Consequently, these results demonstrate that predominant uptake of dipeptide in P. gingivalis is mostly managed by POT. We thus propose that Pot is a potential therapeutic target of periodontal disease and P. gingivalis related systemic diseases

Expanded substrate specificity supported by P1′ and P2′ residues enables bacterial dipeptidyl-peptidase 7 to degrade bioactive peptides

Dipeptide production from extracellular proteins is crucial for Porphyromonas gingivalis, a pathogen related to chronic periodontitis, because its energy production is entirely dependent on the metabolism of amino acids predominantly incorporated as dipeptides. These dipeptides are produced by periplasmic dipeptidyl-peptidase (DPP)4, DPP5, DPP7, and DPP11. Although the substrate specificities of these four DPPs cover most amino acids at the penultimate position from the N terminus (P1), no DPP is known to cleave penultimate Gly, Ser, Thr, or His. Here, we report an expanded substrate preference of bacterial DPP7 that covers those residues. MALDI-TOF mass spectrometry analysis demonstrated that DPP7 efficiently degraded incretins and other gastrointestinal peptides, which were successively cleaved at every second residue, including Ala, Gly, Ser, and Gln, as well as authentic hydrophobic residues. Intravenous injection of DPP7 into mice orally administered glucose caused declines in plasma glucagon-like peptide-1 and insulin, accompanied by increased blood glucose levels. A newly developed coupled enzyme reaction system that uses synthetic fluorogenic peptides revealed that the P1′ and P2′ residues of substrates significantly elevated kcat values, providing an expanded substrate preference. This activity enhancement was most effective toward the substrates with nonfavorable but nonrepulsive P1 residues in DPP7. Enhancement of kcat by prime-side residues was also observed in DPP11 but not DPP4 and DPP5. Based on this expanded substrate specificity, we demonstrate that a combination of DPPs enables proteolytic liberation of all types of N-terminal dipeptides and ensures P. gingivalis growth and pathogenicity