Y. Ueda

The University of Tokyo, 白山, Tōkyō, Japan

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Publications (653)1398.77 Total impact

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    ABSTRACT: An enigmatic group of objects, unabsorbed Seyfert 2s may have intrinsically weak broad line regions, obscuration in the line of sight to the BLR but not to the X-ray corona, or so much obscuration that the X-ray continuum is completely suppressed and the observed spectrum is actually scattered into the line of sight from nearby material. NGC 3660 has been shown to have weak broad optical/near-infrared lines, no obscuration in the soft X-ray band, and no indication of “changing look” behavior. The only previous hard X-ray detection of this source by Beppo-SAX seemed to indicate that the source might harbor a heavily obscured nucleus. However, our analysis of a long-look Suzaku observation of this source shows that this is not the case, and that this source has a typical power-law X-ray continuum with normal reflection and no obscuration. We conclude that NGC 3660 is confirmed to have no unidentified obscuration and that the anomolously high Beppo-SAX measurement must be due to source confusion or similar, being inconsistent with our Suzaku measurements as well as non-detections from Swift-Burst Alert Telescope (BAT) and Rossi X-ray Timing Explorer (RXTE).
    No preview · Article · Jan 2016 · Publications- Astronomical Society of Japan
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    ABSTRACT: Heavily obscured accretion is believed to represent an important stage in the growth of supermassive black holes and to play an important role in shaping the observed spectrum of the cosmic X-ray background. Hard X-ray (E > 10 keV) selected samples are less affected by absorption than samples selected at lower energies, and are therefore one of the best ways to detect and identify Compton-thick (CT, ) active galactic nuclei (AGNs). In this letter we present the first results of the largest broadband (0.3-150 keV) X-ray spectral study of hard X-ray selected AGNs to date, focusing on the properties of heavily obscured sources. Our sample includes the 834 AGNs (728 non-blazar, average redshift z ≃ 0.055) reported in the 70-month catalog of the all-sky hard X-ray Swift/Burst Alert Monitor survey. We find 55 CT AGNs, which represent of our non-blazar sample. Of these, 26 are reported as candidate CT AGNs for the first time. We correct for selection bias and derive the intrinsic column density distribution of AGNs in the local universe in two different luminosity ranges. We find a significant decrease in the fraction of obscured Compton-thin AGNs for increasing luminosity, from 46 ± 3% (for = 40-43.7) to 39 ± 3% (for = 43.7-46). A similar trend is also found for CT AGNs. The intrinsic fraction of CT AGNs with = 24-25 normalized to unity in the = 20-25 range is 27 ± 4%, and is consistent with the observed value obtained for AGNs located within 20 Mpc. © 2015. The American Astronomical Society. All rights reserved..
    No preview · Article · Dec 2015
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    ABSTRACT: We study the correlation between the [O III]$\lambda 5007$ and X-ray luminosities of local Active Galactic Nuclei (AGNs), using a complete, hard X-ray ($>10$ keV) selected sample in the Swift/BAT 9-month catalog. From our optical spectroscopic observations at the South African Astronomical Observatory and the literature, a catalog of [O III]$\lambda 5007$ line flux for all 103 AGNs at Galactic latitudes of $|b|>15^\circ$ is complied. Significant correlations with intrinsic X-ray luminosity ($L_{\rm X}$) are found both for observed ($L_{\rm [O~III]}$) and extinction-corrected ($L_{\rm [O~III]}^{\rm cor}$) luminosities, separately for X-ray unabsorbed and absorbed AGNs. We obtain the regression form of $L_{\rm [O~III]}$ $\propto L_{\rm 2-10\; keV}^{1.18\pm0.07}$ and $L_{\rm [O~III]}^{\rm cor}$ $\propto L_{\rm 2-10\; keV}^{1.16\pm0.09}$ from the whole sample. The absorbed AGNs with low ($<$0.5\%) scattering fractions in soft X-rays show on average smaller $L_{\rm [O~III]}/L_{\rm X}$ and $L_{\rm [O~III]}^{\rm cor}/L_{\rm X}$ ratios than the other absorbed AGNs, while those in edge-on host galaxies do not. These results suggest that a significant fraction of this population are buried in tori with small opening angles. By using these $L_{\rm [O~III]}$ vs. $L_{\rm X}$ correlations, the X-ray luminosity function of local AGNs (including Compton thick AGNs) in a standard population synthesis model gives much better agreement with the [O III]$\lambda 5007$ luminosity function derived from the Sloan Digital Sky Survey than previously reported. This confirms that hard X-ray observations are a very powerful tool to find AGNs with high completeness.
    Preview · Article · Oct 2015 · The Astrophysical Journal
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    ABSTRACT: We present X-ray observations of the active galactic nucleus (AGN) in NGC 4785. The source is a local Seyfert 2 which has not been studied so far in much detail. It was recently detected with high significance in the 15–60 keV band in the 66-month Swift/BAT (Burst Array Telescope) all sky survey, but there have been no prior pointed X-ray observations of this object. With Suzaku, we clearly detect the source below 10 keV, and find it to have a flat continuum and prominent neutral iron fluorescence line with equivalent width ≳1 keV. Fitting the broad-band spectra with physical reflection models shows the source to be a Compton-thick AGN with NH of at least 2 × 1024 cm−2 and absorption-corrected 2–10 keV X-ray power L2−10 ∼ few times 1042 erg s−1. Realistic uncertainties on L2−10 computed from the joint confidence interval on the intrinsic power-law continuum photon index and normalization are at least a factor of 10. The local bona fide Compton-thick AGN population is highly heterogeneous in terms of WISE mid-infrared source colours, and the nucleus of NGC 4785 appears especially sub-dominant in the mid-infrared when comparing to other Compton-thick AGN. Such sources would not be easily found using mid-infrared selection alone. The extent of host galaxy extinction to the nucleus is not clear, though NGC 4785 shows a complex core with a double bar and inner disc, adding to the list of known Compton-thick AGN in barred host galaxies.
    No preview · Article · Apr 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We construct the rest-frame 2--10 keV intrinsic X-ray luminosity function of Active Galactic Nuclei (AGNs) from a combination of X-ray surveys from the all-sky Swift BAT survey to the Chandra Deep Field-South. We use ~3200 AGNs in our analysis, which covers six orders of magnitude in flux. The inclusion of the XMM and Chandra COSMOS data has allowed us to investigate the detailed behavior of the XLF and evolution. In deriving our XLF, we take into account realistic AGN spectrum templates, absorption corrections, and probability density distributions in photometric redshift. We present an analytical expression for the overall behavior of the XLF in terms of the luminosity-dependent density evolution, smoothed two power-law expressions in 11 redshift shells, three-segment power-law expression of the number density evolution in four luminosity classes, and binned XLF. We observe a sudden flattening of the low luminosity end slope of the XLF slope at z>~0.6. Detailed structures of the AGN downsizing have been also revealed, where the number density curves have two clear breaks at all luminosity classes above log LX>43. The two break structure is suggestive of two-phase AGN evolution, consisting of major merger triggering and secular processes.
    Full-text · Article · Feb 2015 · The Astrophysical Journal
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    ABSTRACT: We report a photoemission study at room temperature on BaFe2X3 (X = S and Se) and CsFe2Se3 in which two-leg ladders are formed by the Fe sites. The Fe 2p core-level peaks of BaFe2X3 are broad and exhibit two components, indicating that itinerant and localized Fe 3d sites coexist similar to KxFe2-ySe2. The Fe 2p core-level peak of CsFe2Se3 is rather sharp and is accompanied by a charge-transfer satellite. The insulating ground state of CsFe2Se3 can be viewed as a Fe2+ Mott insulator in spite of the formal valence of +2.5. The itinerant versus localized behaviors can be associated with the stability of chalcogen p holes in the two-leg ladder structure.
    Full-text · Article · Jan 2015 · Physical Review B
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    ABSTRACT: In this white paper we describe the prospects for ASTRO-H for the study of outflows from active galactic nuclei. The most important breakthroughs in this field are expected to arise from the high spectral resolution and sensitivity in the Fe-K band, combined with broad-band sensitivity over the full X-ray band and spectral capabilities also at lower energies. The sensitivity in the Fe-K region allows to extend the absorption measure distribution of the outflow out to the highest ionisation states accessible, where observations with current X-ray missions indicate that most of the outflowing gas is to be found. Due to the high-resolution and sensitivity it will also be able to give the definitive proof for the existence of ultra-fast outflows, and if so, characterise their physical properties in great detail. These ultra-fast outflows carry very large amounts of energy and momentum, and are of fundamental importance for feedback studies. We show how the ASTRO-H observations in general can help to constrain numerical models for outflows. The link to reflection and emission processes is also discussed, as well as the possible relation between outflows and relativistic emission lines. Finally, we discuss the prospects for other related categories of objects like BAL quasars, partially covered sources and Compton thick outflows.
    Full-text · Article · Dec 2014
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    ABSTRACT: X-ray observations provide a powerful tool to probe the central engines of active galactic nuclei (AGN). A hard X-ray continuum is produced from deep within the accretion flow onto the supermassive black hole, and all optically thick structures in the AGN (the dusty torus of AGN unification schemes, broad emission line clouds, and the black hole accretion disk) "light up" in response to irradiation by this continuum. This White Paper describes the prospects for probing AGN physics using observations of these X-ray reflection signatures. High-resolution SXS spectroscopy of the resulting fluorescent iron line in type-2 AGN will give us an unprecedented view of the obscuring torus, allowing us to assess its dynamics (through line broadening) and geometry (through the line profile as well as observations of the "Compton shoulder"). The broad-band view obtained by combining all of the ASTRO-H instruments will fully characterize the shape of the underlying continuum (which may be heavily absorbed) and reflection/scattering, providing crucial constraints on models for the Cosmic X-ray Background with a subsequent impact on understanding of supermassive black hole evolution. ASTRO-H will also permit the relativistically broadened reflection spectrum from the inner accretion disk to be robustly studied, even in complex systems with, for example, warm absorption and composite soft excesses. Finally, the HXI will allow the detection and study of reverberation delays between the continuum and the Compton reflection hump from the inner disk.
    Full-text · Article · Dec 2014
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    ABSTRACT: Thanks to extensive observations with X-ray missions and facilities working in other wavelengths, as well as rapidly--advancing numerical simulations of accretion flows, our knowledge of astrophysical black holes has been remarkably enriched. Rapid progress has opened new areas of enquiry, including measurements of black hole spin, the properties and driving mechanisms of jets and disk winds, the impact of feedback into local environments, the origin of periodic and aperiodic X-ray variations, and the nature of super-Eddington accretion flows, among others. The goal of this White Paper is to illustrate how ASTRO-H can make dramatic progress in the study of astrophysical black holes, particularly the study of black hole X-ray binaries.
    Full-text · Article · Dec 2014
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    ABSTRACT: The magnetism of magnetoelectric $S=\frac{3}{2}$ pyroxenes ${\mathrm{LiCrSi}}_{2}{\mathrm{O}}_{6}$ and ${\mathrm{LiCrGe}}_{2}{\mathrm{O}}_{6}$ is studied by density functional theory calculations, quantum Monte Carlo (QMC) simulations, neutron diffraction, as well as low- and high-field magnetization measurements. In contrast with earlier papers, we find that the two compounds feature remarkably different, albeit nonfrustrated magnetic models. In ${\mathrm{LiCrSi}}_{2}{\mathrm{O}}_{6}$, two relevant exchange integrals, ${J}_{1}$ $$\simeq${}9$ K along the structural chains and ${J}_{\text{ic1}}$ $$\simeq${}2$ K between the chains, form a two-dimensional anisotropic honeycomb lattice. In contrast, the spin model of ${\mathrm{LiCrGe}}_{2}{\mathrm{O}}_{6}$ is constituted of three different exchange couplings. Surprisingly, the leading exchange ${J}_{\text{ic1}}$ $$\simeq${}2.3$ K operates between the chains, while ${J}_{1}$ $$\simeq${}1.2$ K is about two times smaller. The additional interlayer coupling ${J}_{\text{ic2}}$ $$\simeq${}$ ${J}_{1}$ renders this model three dimensional. QMC simulations reveal excellent agreement between our magnetic models and the available experimental data. Underlying mechanisms of the exchange couplings, magnetostructural correlations, as well as implications for other pyroxene systems are discussed.
    Full-text · Article · Dec 2014 · Physical Review B
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    ABSTRACT: A large fraction of the AGN output power is emitted in the X-rays, in a region very close to the supermassive black hole (SMBH). The most distinctive feature of the X-ray spectra of AGN is the iron Kα line, often observed as the superposition of a broad and a narrow component. While the broad component is found in only ~ 35–45% of bright nearby AGN, the narrow component has been found to be ubiquitous. The narrow Fe Kα line is thought to be produced in the circumnuclear material, likely in the molecular torus. Given its origin, this feature is possibly the most important tracer of neutral matter surrounding the SMBH. One of the most interesting characteristics of the narrow Fe Kα line is the decrease of its equivalent width with the continuum luminosity, the so-called X-ray Baldwin effect (Iwasawa & Taniguchi 1993). This trend has been found by many studies of large samples of type-I AGN, and very recently also in type-II AGN (Ricci et al. 2013c, submitted to ApJ). The slope of the X-ray Baldwin effect in type-II AGN is the same of their unobscured counterparts, which implies that the mechanism at work is the same. Several hypothesis have been put forward in the last decade to explain the X-ray Baldwin effect: i) a luminosity-dependent variation in the ionisation state of the iron-emitting material (Nandra et al. 1997); ii) the decrease of the number of continuum photons in the iron line region with the Eddington ratio, as an effect of the well known correlation between the photon index and the Eddington ratio (Ricci et al. 2013b, submitted to MNRAS); iii) the decrease of the covering factor of the torus with the luminosity (e.g., Page et al. 2004, Ricci et al. 2013a A&A 553, 29) as expected by luminosity-dependent unification models (e.g., Ueda et al. 2003). In my talk I will review the main characteristics of the narrow Fe K? line, and present the results of our recent works aimed at explaining the X-ray Baldwin effect using iron-line emitting physical torus models (Ricci et al. 2013a, b), and at understanding the origin of the Fe K? line (Ricci et al. 2013c). I will focus in particular on the importance of the Fe Kα line as a probe of the evolution of the physical characteristics of the molecular torus with the luminosity.
    No preview · Article · Oct 2014 · Proceedings of the International Astronomical Union
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    ABSTRACT: We explore the relationships between the 3.3 μm polycyclic aromatic hydrocarbon (PAH) feature and active galactic nucleus (AGN) properties of a sample of 54 hard X-ray selected bright AGNs, including both Seyfert 1 and Seyfert 2 type objects, using the InfraRed Camera (IRC) on board the infrared astronomical satellite AKARI. The sample is selected from the 9-month Swift/BAT survey in the 14-195 keV band and all of them have measured X-ray spectra at E ≲ 10 keV. These X-ray spectra provide measurements of the neutral hydrogen column density (N H) towards the AGNs. We use the 3.3 μm PAH luminosity (L 3.3μm) as a proxy for star formation activity and hard X-ray luminosity (L 14-195keV) as an indicator of the AGN activity. We searched for possible difference of star-formation activity between type 1 (un-absorbed) and type 2 (absorbed) AGNs. Our regression analysis of log L 14-195keV versus log L 3.3μm shows a positive correlation and the slope seems steeper for type 1/unobscured AGNs than that of type 2/obscured AGNs. The same trend has been found for the log (L 14-195keV/M BH) versus log (L 3.3μm/MBH) correlation. Our analysis show that the circum-nuclear star-formation is more enhanced in type 2/absorbed AGNs than type 1/un-absorbed AGNs for low X-ray luminosity/low Eddington ratio AGNs.
    No preview · Article · Oct 2014 · Proceedings of the International Astronomical Union
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    ABSTRACT: We present data products from the 300 ks Chandra survey in the AKARI North Ecliptic Pole Deep Field. This field has a unique set of nine-band infrared photometry covering 2–24 μm from the AKARI Infrared Camera, including mid-infrared (MIR) bands not covered by Spitzer. The survey is one of the deepest ever achieved at ∼15 μm, and is by far the widest among those with similar depths in the MIR. This makes this field unique for the MIR-selection of AGN at z ∼ 1. We design a source detection procedure, which performs joint maximum likelihood PSF (point spread function) fits on all of our 15 mosaicked Chandra pointings covering an area of 0.34 deg2. The procedure has been highly optimized and tested by simulations. We provide a point source catalogue with photometry and Bayesian-based 90 per cent confidence upper limits in the 0.5–7, 0.5–2, 2–7, 2–4, and 4–7 keV bands. The catalogue contains 457 X-ray sources and the spurious fraction is estimated to be ∼1.7 per cent. Sensitivity and 90 per cent confidence upper flux limits maps in all bands are provided as well. We search for optical–MIR counterparts in the central 0.25 deg2, where deep Subaru Suprime-Cam multiband images exist. Among the 377 X-ray sources detected there, ∼80 per cent have optical counterparts and ∼60 per cent also have AKARI MIR counterparts. We cross-match our X-ray sources with MIR-selected AGN from Hanami et al. Around 30 per cent of all AGN that have MIR SEDs purely explainable by AGN activity are strong Compton-thick AGN candidates.
    Preview · Article · Sep 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We present X-ray observations of the active galactic nucleus (AGN) in NGC 4785. The source is a local Seyfert 2 which has not been studied so far in much detail. It was recently detected with high significance in the 15-60 keV band in the 66 month Swift/BAT all sky survey, but there have been no prior pointed X-ray observations of this object. With Suzaku, we clearly detect the source below 10 keV, and find it to have a flat continuum and prominent neutral iron fluorescence line with equivalent width >~1 keV. Fitting the broadband spectra with physical reflection models shows the source to be a bona fide Compton thick AGN with Nh of at least 2x10^{24} cm^{-2} and absorption-corrected 2-10 keV X-ray power L(2-10) ~ few times 10^{42} erg s^{-1}. Realistic uncertainties on L(2-10) computed from the joint confidence interval on the intrinsic power law continuum photon index and normalization are at least a factor of 10. The local bona fide Compton thick AGN population is highly heterogeneous in terms of WISE mid-infrared source colours, and the nucleus of NGC 4785 appears especially sub-dominant in the mid-infrared when comparing to other Compton thick AGN. Such sources would not be easily found using mid-infrared selection alone. The extent of host galaxy extinction to the nucleus is not clear, though NGC 4785 shows a complex core with a double bar and inner disk, adding to the list of known Compton thick AGN in barred host galaxies.
    Full-text · Article · Aug 2014
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    ABSTRACT: Recent X-ray observations show absorbing winds with velocities up to mildly relativistic values of the order of ∼0.1c in a limited sample of six broad-line radio galaxies. They are observed as blueshifted Fe xxv–xxvi K-shell absorption lines, similarly to the ultrafast outflows (UFOs) reported in Seyferts and quasars. In this work we extend the search for such Fe K absorption lines to a larger sample of 26 radio-loud active galactic nuclei (AGN) observed with XMM–Newton and Suzaku. The sample is drawn from the Swift Burst Alert Telescope 58-month catalogue and blazars are excluded. X-ray bright Fanaroff–Riley Class II radio galaxies constitute the majority of the sources. Combining the results of this analysis with those in the literature we find that UFOs are detected in >27 per cent of the sources. However, correcting for the number of spectra with insufficient signal-to-noise ratio, we can estimate that the incidence of UFOs is this sample of radio-loud AGN is likely in the range f ≃ (50 ± 20) per cent. A photoionization modelling of the absorption lines with xstar allows us to estimate the distribution of their main parameters. The observed outflow velocities are broadly distributed between vout ≲ 1000 km s−1 and vout ≃ 0.4c, with mean and median values of vout ≃ 0.133c and vout ≃ 0.117c, respectively. The material is highly ionized, with an average ionization parameter of logξ ≃ 4.5 erg s−1 cm, and the column densities are larger than NH > 1022 cm−2. Overall, these characteristics are consistent with the presence of complex accretion disc winds in a significant fraction of radio-loud AGN and demonstrate that the presence of relativistic jets does not preclude the existence of winds, in accordance with several theoretical models.
    Preview · Article · Jun 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We report on the results from Suzaku observations of the Galactic black hole X-ray binary H1743–322 in the low/hard state during its outburst in 2012 October. We appropriately take into account the effects of dust scattering to accurately analyze the X-ray spectra. The time-averaged spectra in the 1-200 keV band are dominated by a hard power-law component of a photon index of 1.6 with a high-energy cutoff at 60 keV, which is well described with the Comptonization of the disk emission by the hot corona. We estimate the inner disk radius from the multi-color disk component, and find that it is 1.3-2.3 times larger than the radius in the high/soft state. This suggests that the standard disk was not extended to the innermost stable circular orbit. A reflection component from the disk is detected with R = Ω/2π 0.6 (Ω is the solid angle). We also successfully estimate the stable disk component independent of the time-averaged spectral modeling by analyzing short-term spectral variability on a ~1 s timescale. A weak low-frequency quasi-periodic oscillation at 0.1-0.2 Hz is detected, whose frequency is found to correlate with the X-ray luminosity and photon index. This result may be explained by the evolution of the disk truncation radius.
    No preview · Article · Jun 2014 · The Astrophysical Journal
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    ABSTRACT: Introduction and Aims: Patients with chronic kidney disaeses (CKD) suffer from accelered vascular calcification (VC) and vitamin K defficiency. The vitamin K-dependent matrix Gla protein (MGP) is one of the most powerful inhibitors of VC. This prospective randomized intervention study assessed the impact of vitamin K2 supplementation on levels of the inactive form of MGP desphospho-uncarboxylated MGP (dp-ucMGP) in non-dialyzed 3 -5 stages CKD patients. Methods: Common carotid intima media thickness (CCA-IMT), coronary artery calcification score (CACS), serum mineral parameters, matrix Gla protein (MGP), desphospho-uncarboxylated MGP (dp-ucMGP), osteocalcin (OC) were measured at baseline and after 270±12 days of supplementation of 90 μg of vitamin K2 (menaquinone-7, MK-7) with 10 μg cholecalciferol (K+D group) or 10 μg vitamin D (group D) in 42 non-dialyzed CKD patients. Results: During the treatment period no significant changes of eGFR in both groups were observed. The significantly lower increase of CCA-IMT during the intervention period was noticed in group K+D: from 0.95±0.2 mm at the beginning to 1.01±0.3 mm, p=0.003 at the end, and in D group: from 1.02±0.2 mm to 1.16±0.3 mm, p=0.003. The change of CACS was numerically less in vitamin K+D treated patients than in D group (ΔCACS: 63.1±108.5 A.u. vs 74.4±127.1, p=0.7; 16% and 15.8%, p=0.91, respectively). After nine months of MK-7 supplementation a significant decrease of dp-ucMGP was found 1077.1±507.7 pmol/L vs 961.5±506.7, p=0.02. This effect was not observed in D group: 793.9±400.3 pmol/L vs 820.7±565.2, p=0.7 respectively. The serum level of dp-ucMGP positively correlated with serum creatinine r=0.4, p=0,02, negatively with eGFR r=-0,5, p=0.003 at the beginning and r=0.4, p=0.03; r=-0.6, p=0.0001, respectively at the end of the study in both group. The positive correlation of dp-ucMGP and PTH level was noticed in all examined patients at the beginning and at the end of the study: r=0.4, p=0.04; r=0.4, p=0.01 respectively. Similar correlations were noticed between dp-ucMGP and OC: r=0.47, p=0.005; r=0.5; p=0.004 respectively. Any correlation between dp-ucMGP and estimated vascular changes was not find. Conclusions: The main determinant of dp-ucMGP level is the kidney function. Circulating level of dp-ucMGP may be a marker of vascular vitamin K status in CKD patients. The mechanisms by which vitamin K2 may exert the protective effect on progression of vessels damage are still uncertain, but may be connected with the impact of MK-7 on calcification’s regulators, including the impact on the MGP carboxylation process.
    Full-text · Article · May 2014 · Nephrology Dialysis Transplantation
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    ABSTRACT: The magnetism of magnetoelectric $S$ = 3/2 pyroxenes LiCrSi$_2$O$_6$ and LiCrGe$_2$O$_6$ is studied by density functional theory (DFT) calculations, quantum Monte Carlo (QMC) simulations, neutron diffraction, as well as low-field and high-field magnetization measurements. In contrast with earlier reports, we find that the two compounds feature remarkably different, albeit non-frustrated magnetic models. In LiCrSi$_2$O$_6$, two relevant exchange integrals, $J_1 \simeq$ 9 K along the structural chains and $J_{\text{ic1}}$ $\simeq$ 2 K between the chains, form a 2D anisotropic honeycomb lattice. In contrast, the spin model of LiCrGe$_2$O$_6$ is constituted of three different exchange couplings. Surprisingly, the leading exchange $J_{\text{ic1}}$ $\simeq$ 2.3 K operates between the chains, while $J_1$ $\simeq$ 1.2 K is about two times smaller. The additional interlayer coupling $J_{\text{ic2}}$ $\simeq$ $J_1$ renders this model 3D. QMC simulations reveal excellent agreement between our magnetic models and the available experimental data. Underlying mechanisms of the exchange couplings, magnetostructural correlations, as well as implications for other pyroxene systems are discussed.
    Full-text · Article · Feb 2014
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    ABSTRACT: X-ray surveys have revealed a new class of active galactic nuclei (AGN) with a very low observed fraction of scattered soft X-rays, f_scat < 0.5%. Based on X-ray modeling these "X-ray new-type", or low observed X-ray scattering (hereafter:"low-scattering") sources have been interpreted as deeply-buried AGN with a high covering factor of gas. In this paper we address the questions whether the host galaxies of low-scattering AGN may contribute to the observed X-ray properties, and whether we can find any direct evidence for high covering factors from the infrared (IR) emission. We find that X-ray low-scattering AGN are preferentially hosted by highly-inclined galaxies or merger systems as compared to other Seyfert galaxies, increasing the likelihood that the line-of-sight toward the AGN intersects with high columns of host-galactic gas and dust. Moreover, while a detailed analysis of the IR emission of low-scattering AGN ESO 103-G35 remains inconclusive, we do not find any indication of systematically higher dust covering factors in a sample of low-scattering AGN based on their IR emission. For ESO 103-G35, we constrained the temperature, mass and location of the IR emitting dust which is consistent with expectations for the dusty torus. However, a deep silicate absorption feature probably from much cooler dust suggests an additional screen absorber on larger scales within the host galaxy. Taking these findings together, we propose that the low f_scat observed in low-scattering AGN is not necessarily the result of circumnuclear dust but could originate from interference of host-galactic gas with a column density of the order of 10^22 cm^-2 with the line-of-sight. We discuss implications of this hypothesis for X-ray models, high-ionization emission lines, and observed star-formation activity in these objects.
    Full-text · Article · Nov 2013 · Monthly Notices of the Royal Astronomical Society
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    C. Ricci · S. Paltani · Y. Ueda · H. Awaki
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    ABSTRACT: The X-ray Baldwin effect is the inverse correlation between the equivalent width (EW) of the narrow component of the iron Kα line and the X-ray luminosity of active galactic nuclei (AGN). A similar trend has also been observed between Fe Kα EW and the Eddington ratio (λEdd). Using Chandra/High Energy Grating results of Shu et al. and bolometric corrections we study the relation between EW and λEdd, and find that log EW = ( − 0.13 ± 0.03)log λEdd + 1.47. We explore the role of the known positive correlation between the photon index of the primary X-ray continuum Γ and λEdd on the X-ray Baldwin effect. We simulate the iron Kα line emitted by populations of unabsorbed AGN considering three different geometries of the reflecting material: toroidal, spherical–toroidal and slab. We find that the Γ–λEdd correlation cannot account for the whole X-ray Baldwin effect, unless a strong dependence of Γ on λEdd, such as the one recently found by Risaliti et al. and Jin et al., is assumed. No clear correlation is found between EW and Γ. We conclude that a good understanding of the slope of the Γ–λEdd relation is critical to assess whether the trend plays a leading or rather a marginal role in the X-ray Baldwin effect.
    Full-text · Article · Nov 2013 · Monthly Notices of the Royal Astronomical Society

Publication Stats

8k Citations
1,398.77 Total Impact Points

Institutions

  • 1991-2015
    • The University of Tokyo
      • • Institute for Solid State Physics
      • • Laboratory for Materials Design and Characterization
      • • Department of Physics
      白山, Tōkyō, Japan
    • Himeji Institute of Technology
      Himezi, Hyōgo, Japan
  • 1976-2015
    • Kyoto University
      • • Department of Astronomy
      • • Department of Physics II
      • • Division of Chemistry
      Kioto, Kyoto, Japan
  • 2013
    • University of Maryland, College Park
      • Department of Astronomy
      Maryland, United States
  • 1997-2012
    • Kure National College of Technology
      Kure, Hiroshima, Japan
  • 2010
    • Nihon University
      • Department of Physics
      Edo, Tōkyō, Japan
  • 2009
    • Japan Science and Technology Agency (JST)
      Edo, Tokyo, Japan
  • 2007
    • Japan Aerospace Exploration Agency
      • Institute of Space and Astronautical Science (ISAS)
      Chōfu, Tokyo, Japan
  • 1996-2007
    • Hiroshima University
      • • Graduate School of Science
      • • Physical Chemistry Laboratory
      Hirosima, Hiroshima, Japan
  • 2005
    • Okayama University
      • Department of Physics
      Okayama, Okayama, Japan
  • 2002
    • Moscow State Forest University
      Mytishi, Moskovskaya, Russia
    • Institute of Physics Belgrade
      Beograd, Central Serbia, Serbia
    • Kochi University
      • Faculty of Science
      Kôti, Kochi, Japan
  • 2001
    • Tokyo Institute of Technology
      • Department of Physics
      Edo, Tōkyō, Japan
    • Iowa State University
      Ames, Iowa, United States
  • 2000
    • Simon Fraser University
      • Department of Physics
      Burnaby, British Columbia, Canada
    • Lomonosov Moscow State University
      • Low Temperature Physics Department
      Moskva, Moscow, Russia
    • High Energy Accelerator Research Organization
      Tsukuba, Ibaraki, Japan
    • NASA
      Washington, West Virginia, United States
  • 1999
    • Leibniz-Institut für Analytische Wissenschaften
      Dortmund, North Rhine-Westphalia, Germany
  • 1998-1999
    • Tokyo Metropolitan University
      • Department of Physics
      Edo, Tokyo, Japan
    • RIKEN
      Вако, Saitama, Japan
    • University of California, Berkeley
      Berkeley, California, United States
    • Hiroshima International University
      Hirosima, Hiroshima, Japan
  • 1990-1996
    • Tokuyama College of Technology
      Kakuyama, Yamaguchi, Japan
  • 1995
    • Hiroshima Institute of Technology
      Hirosima, Hiroshima, Japan
  • 1994
    • Kyushu Institute of Technology
      • Faculty of Computer Science & Systems Engineering
      Kitakyūshū, Fukuoka, Japan