206 research outputs found
Evidence for Jet Collimation in SS 433 with the Chandra HETGS
High-resolution X-ray spectra of SS 433 obtained after a binary egress with
the Chandra High Energy Transmission Grating Spectrometer (HETGS) were studied.
Many Doppler-shifted X-ray emission lines from highly ionized elements were
detected. The initial temperature of the jets is estimated to be 20 keV. The
lines are found to generally be broader than the instrumented resolution. The
widths of the Fe XXV K-alpha and Si XIII K-alpha lines correspond to velocity
dispersions of 2100 (+600/-340) km/s and 840 (+180/-150) km/s respectively, in
terms of Gaussian sigma. Neither the measured line widths nor their dependence
on the atomic number can be explained by thermal broadening alone. Alternative
explanations of the observed line widths are discussed, including in particular
a progressive jet collimation along its axis.Comment: 20 pages, 8 figur
Magnetic properties of epitaxial FeO films with various crystal orientations and TMR effect in room temperature
FeO is a ferrimagnetic spinel ferrite that exhibits electric
conductivity at room temperature (RT). Although the material has been predicted
to be a half metal according to ab-initio calculations, magnetic tunnel
junctions (MTJs) with FeO electrodes have demonstrated a small tunnel
magnetoresistance effect. Not even the sign of the TMR ratio has been
experimentally established. Here, we report on the magnetic properties of
epitaxial FeO films with various crystal orientations. The films
exhibited apparent crystal orientation dependence on hysteresis curves. In
particular, FeO(110) films exhibited in-plane uniaxial magnetic
anisotropy. With respect to the squareness of hysteresis, FeO (111)
demonstrated the largest squareness. Furthermore, we fabricated MTJs with
FeO(110) electrodes, and obtained an TMR effect of -12\% at RT. The
negative TMR ratio corresponded to the negative spin polarization of
FeO predicted from band calculations
Suzaku and Optical Spectroscopic Observations of SS 433 in the 2006 April Multiwavelength Campaign
We report results of the 2006 April multi-wavelengths campaign of SS 433,
focusing on X-ray data observed with Suzaku at two orbital phases (in- and
out-of- eclipse) and simultaneous optical spectroscopic observations. By
analyzing the Fe25 K_alpha lines originating from the jets, we detect rapid
variability of the Doppler shifts, dz/dt ~ 0.019/0.33 day^-1, which is larger
than those expected from the precession and/or nodding motion. This phenomenon
probably corresponding to "jitter" motions observed for the first time in
X-rays, for which significant variability both in the jet angle and intrinsic
speed is required. From the time lag of optical Doppler curves from those of
X-rays, we estimate the distance of the optical jets from the base to be ~(3-4)
\times 10^14 cm. Based on the radiatively cooling jet model, we determine the
innermost temperature of the jets to be T_0 = 13 +/- 2 keV and 16 +/- 3 keV
(the average of the blue and red jets) for the out-of-eclipse and in-eclipse
phase, respectively, from the line intensity ratio of Fe25 K_alpha and Fe26
K_alpha. While the broad band continuum spectra over the 5--40 keV band in
eclipse is consistent with a multi-temperature bremsstrahlung emission expected
from the jets, and its reflection component from cold matter, the
out-of-eclipse spectrum is harder than the jet emission with the base
temperature determined above, implying the presence of an additional hard
component.Comment: 12 pages, 15 figures, accepted for publication in PAS
Tree hazards compounded by successive climate extremes after masting in a small endemic tree, Distylium lepidotum , on subtropical islands in Japan
連続して生じる異常気象は樹木の衰退を加速させる --地球温暖化の森林への影響を高精度に予測する道を開く成果--. 京都大学プレスリリース. 2021-09-28.Ongoing global warming increases the frequency and severity of tropical typhoons and prolonged drought, leading to forest degradation. Simultaneous and/or successive masting events and climatic extremes may thus occur frequently in the near future. If these climatic extremes occur immediately after mass seed reproduction, their effects on individual trees are expected to be very severe because mass reproduction decreases carbohydrate reserves. While the effects of either a single climate extreme or masting alone on tree resilience/growth have received past research attention, understanding the cumulative effects of such multiple events remains challenging and is crucial for predicting future forest changes. Here, we report tree hazards compound by two successive climate extremes, a tropical typhoon and prolonged drought, after mass reproduction in an endemic tree species (Distylium lepidotum Nakai) on oceanic islands. Across individual trees, the starch stored within the sapwood of branchlets significantly decreased with reproductive efforts (fruit mass/shoot mass ratio). Typhoon damage significantly decreased not only the total leaf area of apical shoots but also the maximum photosynthetic rates. During the 5-month period after the typhoon, the mortality of large branchlets (8–10-mm diameter) increased with decreasing stored starch when the typhoon hit. During the prolonged summer drought in the next year, the recovery of total leaf area, stored starch, and hydraulic conductivity was negatively correlated with the stored starch at the typhoon. These data indicate that the level of stored starch within branchlets is the driving factor determining tree regrowth or dieback, and the restoration of carbohydrates after mass reproduction is synergistically delayed by such climate extremes. Stored carbohydrates are the major cumulative factor affecting individual tree resilience, resulting in their historical effects. Because of highly variable carbohydrate levels among individual trees, the resultant impacts of such successive events on forest dieback will be fundamentally different among trees
Combined Spectral and Timing Analysis of the Black Hole Candidate MAXI J1659-152 Discovered by MAXI and Swift
We report on X-ray spectral and timing results of the new black hole
candidate (BHC) MAXI J1659-152 with the orbital period of 2.41 hours (shortest
among BHCs) in the 2010 outburst from 65 Rossi X-ray Timing Explorer (RXTE)
observations and 8 simultaneous Swift and RXTE observations. According to the
definitions of the spectral states in Remillard & McClintock (2006), most of
the observations have been classified into the intermediate state. All the
X-ray broadband spectra can be modeled by a multi-color disk plus a power-law
with an exponential cutoff or a multi-color disk plus a Comptonization
component. During the initial phase of the outburst, a high energy cutoff was
visible at 30-40 keV. The innermost radius of the disk gradually decreased by a
factor of more than 3 from the onset of the outburst and reached a constant
value of 35 d_10 cos i^-1/2 km, where d_10 is the distance in units of 10 kpc
and is the inclination. The type-C quasi-periodic oscillation (QPO)
frequency varied from 1.6 Hz to 7.3 Hz in association with a change of the
innermost radius, while the innermost radius remained constant during the
type-B QPO detections at 1.6-4.1 Hz. Hence, we suggest that the origin of the
type-B QPOs is different from that of type-C QPOs, the latter of which would
originate from the disk truncation radius. Assuming the constant innermost
radius in the latter phase of the outburst as the innermost stable circular
orbit, the black hole mass in MAXI J1659-152 is estimated to be 3.6-8.0 M_solar
for a distance of 5.3-8.6 kpc and an inclination angle of 60-75 degrees.Comment: 27 pages, 14 figures, accepted for publication in PAS
The Roles of Two IκB Kinase-related Kinases in Lipopolysaccharide and Double Stranded RNA Signaling and Viral Infection
Viral infection and stimulation with lipopolysaccharide (LPS) or double stranded RNA (dsRNA) induce phosphorylation of interferon (IFN) regulatory factor (IRF)-3 and its translocation to the nucleus, thereby leading to the IFN-β gene induction. Recently, two IκB kinase (IKK)–related kinases, inducible IκB kinase (IKK-i) and TANK-binding kinase 1 (TBK1), were suggested to act as IRF-3 kinases and be involved in IFN-β production in Toll-like receptor (TLR) signaling and viral infection. In this work, we investigated the physiological roles of these kinases by gene targeting. TBK1-deficient embryonic fibroblasts (EFs) showed dramatic decrease in induction of IFN-β and IFN-inducible genes in response to LPS or dsRNA as well as after viral infection. However, dsRNA-induced expression of these genes was residually detected in TBK1-deficient cells and intact in IKK-i–deficient cells, but completely abolished in IKK-i/TBK1 doubly deficient cells. IRF-3 activation, in response not only to dsRNA but also to viral infection, was impaired in TBK1-deficient cells. Together, these results demonstrate that TBK1 as well as, albeit to a lesser extent, IKK-i play a crucial role in the induction of IFN-β and IFN-inducible genes in both TLR-stimulated and virus-infected EFs
Toll-like receptor 9 mediates innate immune activation by the malaria pigment hemozoin
Malaria parasites within red blood cells digest host hemoglobin into a hydrophobic heme polymer, known as hemozoin (HZ), which is subsequently released into the blood stream and then captured by and concentrated in the reticulo-endothelial system. Accumulating evidence suggests that HZ is immunologically active, but the molecular mechanism(s) through which HZ modulates the innate immune system has not been elucidated. This work demonstrates that HZ purified from Plasmodium falciparum is a novel non-DNA ligand for Toll-like receptor (TLR)9. HZ activated innate immune responses in vivo and in vitro, resulting in the production of cytokines, chemokines, and up-regulation of costimulatory molecules. Such responses were severely impaired in TLR9−/− and myeloid differentiation factor 88 (MyD88)−/−, but not in TLR2, TLR4, TLR7, or Toll/interleukin 1 receptor domain–containing adaptor-inducing interferon β−/− mice. Synthetic HZ, which is free of the other contaminants, also activated innate immune responses in vivo in a TLR9-dependent manner. Chloroquine (CQ), an antimalarial drug, abrogated HZ-induced cytokine production. These data suggest that TLR9-mediated, MyD88-dependent, and CQ-sensitive innate immune activation by HZ may play an important role in malaria parasite–host interactions
Essential role of IPS-1 in innate immune responses against RNA viruses
IFN-β promoter stimulator (IPS)-1 was recently identified as an adapter for retinoic acid–inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (Mda5), which recognize distinct RNA viruses. Here we show the critical role of IPS-1 in antiviral responses in vivo. IPS-1–deficient mice showed severe defects in both RIG-I– and Mda5-mediated induction of type I interferon and inflammatory cytokines and were susceptible to RNA virus infection. RNA virus–induced interferon regulatory factor-3 and nuclear factor κB activation was also impaired in IPS-1–deficient cells. IPS-1, however, was not essential for the responses to either DNA virus or double-stranded B-DNA. Thus, IPS-1 is the sole adapter in both RIG-I and Mda5 signaling that mediates effective responses against a variety of RNA viruses
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