92 research outputs found
The radiation properties of an accretion disk with a non-zero torque on its inner edge
The structure of the inner edge of the accretion disk around a black hole can
be altered, if the matter inside the marginally stable orbit is magnetically
connected to the disk. In this case, a non-zero torque is exerted on its inner
edge, and the accretion efficiency can be much higher than that in
the standard accretion disk model. We explore the radiation properties of an
accretion disk at its sonic point around a black hole with a time-steady torque
exerted on the inner edge of the disk. The local structure of the accretion
flow at the sonic point is investigated in the frame of general relativity. It
is found that the accretion flow will be optically thin at its sonic point for
most cases, if the additional accretion efficiency caused by
the torque is as high as 10 %. The results imply that the variable torque
may trigger transitions of the flow between different accretion types.Comment: 6 pages, to appear in PASJ, Vol. 55, No. 1 (February 25, 2003
Profiles of thermal line emission from advection dominated accretion flows
Recently, Narayan & Raymond (1999) proposed that the thermal emission lines
from the hot plasma in advection dominated accretion flows (ADAFs) are
potentially observable with the next generation of X-ray observatories, with
which the physical properties of some X-ray sources can be probed. In ADAFs,
the temperature of the ion is so high that the thermal broadening of the line
is important. We calculate the profiles of thermal line emission from ADAFs, in
which both the thermal and Doppler broadening have been considered. It is found
that the double-peaked profiles are present for high inclination angles between
the axis of disk and the line of sight. The double-peaked profiles are smeared
in low inclination cases, and completely disappear while the inclination angle
is less than , where the thermal and turbulent broadening dominated
on the line profiles. We also note that the thermal line profile is affected by
the location of the transition radius of ADAF. The self-similar
height-integrated disk structure and the emissivity with power-law dependence
of radius are adopted in our calculations. The results obtained in this work
can be used as a diagnosis on the future X-ray observations of the thermal
lines. Some important physical quantities of ADAFs could be inferred from
future thermal line observations.Comment: 7 page
Eco-physiological adaptation of dominant tree species at two contrasting karst habitats in southwestern China
The purpose of this study was to investigate the eco-physiological adaptation of indigenous woody species to their habitats in karst areas of southwestern China. Two contrasting forest habitats were studied: a degraded habitat in Daxiagu and a well-developed habitat in Tianlongshan, and the eco-physiological characteristics of the trees were measured for three growth seasons. Photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (Tr) of the tree species in Daxiagu were 2-3 times higher than those in Tianlongshan under ambient conditions. However, this habitat effect was not significant when measurements were taken under controlled conditions. Under controlled conditions, Pn, gs, and Tr of the deciduous species were markedly higher than those for the evergreen species. Habitat had no significant effect on water use efficiency (WUE) or photochemical characteristics of PSII. The stomatal sensitivity of woody species in the degraded habitat was much higher than that in the well-developed habitat. Similarly, the leaf total nitrogen (N) and phosphorus (P) contents expressed on the basis of either dry mass or leaf area were also much higher in Daxiagu than they were in Tianlongshan. The mass-based leaf total N content of deciduous species was much higher than that of evergreen species, while leaf area-based total N and P contents of evergreens were significantly higher than those of deciduous species. The photosynthetic nitrogen- and phosphorus-use efficiencies (PNUE and PPUE) of deciduous species were much higher than those of evergreens. Further, the PPUE of the woody species in Tianlongshan was much higher than that of the woody species in Daxiagu. The results from three growth seasons imply that the tree species were able to adapt well to their growth habitats. Furthermore, it seems that so-called âtemporary drought stressâ may not occur, or may not be severe for most woody plants in karst areas of southwestern China
Thermal expansion behavior of co-extruded wood-plastic composites with glass-fiber reinforced shells
Coextruded wood-plastic composites (WPCs) with glass-fiber (GF) filled shells were manufactured, and their thermal expansion behavior was studied. A three-dimensional finite element model (FEM) considering differential properties of both shell and core layers was developed to predict the linear coefficient of thermal expansion (LCTE) of the material. It was shown that the LCTE values varied with composite structure and composition (i.e., core-shell thicknesses and materials). The use of GF-filled shells helped lower overall composite LCTE values. The imbalance of shell and core LCTE, and their moduli led to complex stress fields within a given composite system. The FEM predicted a trend of LCTE change with varying composite structures, which was in good agreement with the experimental data. This study provides for the first time a finite element modeling technique to optimize raw material composition and composite structure for optimizing thermal expansion behavior of co-extruded WPCs
On the BL Lacertae objects/radio quasars and the FRI/II dichotomy
In the frame of unification schemes for radio-loud active galactic nuclei
(AGNs), FR I radio galaxies are believed to be BL Lacertae (BL Lac) objects
with the relativistic jet misaligned to our line of sight, and FR II radio
galaxies correspond to misaligned radio quasars. The Ledlow-Owen dividing line
for FR I/FR II dichotomy in the optical absolute magnitude of host galaxy-radio
luminosity (M_R-L_Rad) plane can be translated to the line in the black hole
mass-jet power (M_bh-Q_jet) plane by using two empirical relations: Q_jet-L_Rad
and M_bh}-M_R. We use a sample of radio quasars and BL Lac objects with
measured black hole masses to explore the relation of the jet power with black
hole mass, in which the jet power is estimated from the extended radio
emission. It is found that the BL Lac objects are clearly separated from radio
quasars by the Ledlow & Owen FR I/II dividing line in the M_bh-Q_jet plane.
This strongly supports the unification schemes for FR I/BL Lac object and FR
II/radio quasar. We find that the Eddington ratios L_bol/L_Edd of BL Lac
objects are systematically lower than those of radio quasars in the sample with
a rough division at L_bol/L_Edd 0.01, and the distribution of Eddington ratios
of BL Lac objects/quasars exhibits a bimodal nature, which imply that the
accretion mode of BL Lac objects may be different from that of radio quasars.Comment: 4 pages, 2 figures, accepted by ApJ
Physiological function of nerve injury-induced protein 1 and its role in relevant diseases
Nerve injury-induced protein 1 (NINJ1) is a cell-surface adhesion molecule containing an extracellular adhesion domain and two transmembrane domains. NINJ1 is named for its original discovery in damaged nerve endings. It is expressed in a variety of tissues and cells, with high expression in epithelial and myeloid cells. NINJ1 regulates nerve regeneration by promoting Schwann cell precursors and pluripotent pericytes to differentiate into Schwann cells. In diabetes-induced peripheral nerve and vascular damage, NINJ1 not only promotes nerve repair, but also regulates penile angiogenesis via angiopoietin 1 (ANG1)/tyrosine-protein kinase receptor tie-2 (TIE2) signaling pathway. NINJ1 also participates in the maturation of vitreous vascular network, which is associated with changes in the proportion of ANG1 and ANG2 in pericytes. NINJ1 mediates inflammatory cell migration across the endothelium through its extracellular adhesion domain, and thus aggravates central nervous system inflammation. However, NINJ1 cleaved by matrix metalloproteinase 9 (MMP9) can inhibit macrophage inflammatory activation, and its mimic peptide is expected to treat atherosclerosis. In addition to regulating the inflammatory phenotypes of myeloid cells, NINJ1 actively mediates plasma membrane rupture and regulates programmed cell death, which is involved in host defense against exogenous infection. Moreover, NINJ1 is up-regulated in a variety of tumor tissues, and regulates tumor suppressor P53 activity via the P53-NINJ1 loop, which mediates tumor growth and metastasis. The current review summarizes the physiological function of NINJ1 and its key regulatory roles in pathological processes, and discusses its potential value in immunomodulation and tissue regeneration, in order to provide new ideas for the prevention and treatment of injury, inflammation and tumor-related diseases
Unification of Radio Galaxies and Their Accretion/Jet Properties
We investigate the relation between black hole mass, M_bh, and jet power,
Q_jet, for a sample of BL Lacs and radio quasars. We find that BL Lacs are
separated from radio quasars by the FR I/II dividing line in M_bh-Q_jet plane,
which strongly supports the unification scheme of FR I/BL Lac and FR II/radio
quasar. The Eddington ratio distribution of BL Lacs and radio quasars exhibits
a bimodal nature with a rough division at L_bol/L_Edd~0.01, which imply that
they may have different accretion modes. We calculate the jet power extracted
from advection dominated accretion flow (ADAF), and find that it require
dimensionless angular momentum of black hole j~0.9-0.99 to reproduce the
dividing line between FR I/II or BL Lac/radio quasar if dimensionless accretion
rate mdot=0.01 is adopted, which is required by above bimodal distribution of
Eddington ratios. Our results suggest that black holes in radio galaxies are
rapidly spinning.Comment: To appear JAA in Jun
Associations between gut microbiota and sleep: a two-sample, bidirectional Mendelian randomization study
IntroductionPrevious research has reported that the gut microbiota performs an essential role in sleep through the microbiomeâgutâbrain axis. However, the causal association between gut microbiota and sleep remains undetermined.MethodsWe performed a two-sample, bidirectional Mendelian randomization (MR) analysis using genome-wide association study summary data of gut microbiota and self-reported sleep traits from the MiBioGen consortium and UK Biobank to investigate causal relationships between 119 bacterial genera and seven sleep-associated traits. We calculated effect estimates by using the inverse-variance weighted (as the main method), maximum likelihood, simple model, weighted model, weighted median, and MR-Egger methods, whereas heterogeneity and pleiotropy were detected and measured by the MR pleiotropy residual sum and outlier method, Cochranâs Q statistics, and MR-Egger regression.ResultsIn forward MR analysis, inverse-variance weighted estimates concluded that the genetic forecasts of relative abundance of 42 bacterial genera had causal effects on sleep-associated traits. In the reverse MR analysis, sleep-associated traits had a causal effect on 39 bacterial genera, 13 of which overlapped with the bacterial genera in the forward MR analysis.DiscussionIn conclusion, our research indicates that gut microbiota may be involved in the regulation of sleep, and conversely, changes in sleep-associated traits may also alter the abundance of gut microbiota. These findings suggest an underlying reciprocal causal association between gut microbiota and sleep
Growth of massive black holes at their late stage
We derive the black hole mass density as a function of redshift with the
bolometric luminosity function of AGN assuming that massive black holes grew
via accreting the circumnuclear gases, in which the derived black hole mass
density is required to match the measured local black hole mass density at z=0.
ADAFs are supposed to present in low luminosity AGNs/normal galaxies, which are
very hot and radiate mostly in the hard X-ray band. Most of the XRB is
contributed by bright AGNs, and a variety of AGN population synthesis models
were developed to model the observed XRB in the last two decades. Based on our
derived black hole mass density, we calculate the contribution to the XRB from
the ADAFs in faint AGNs/normal galaxies with a given Eddington ratio
distribution, which is mostly in hard X-ray energy band with an energy peak at
~200 keV. The growth of massive black holes during ADAF phase can therefore be
constrained with the observed XRB. Combining an AGN population synthesis model
with our results, we find that the fitting on the observed XRB, especially at
hard X-ray energy band with \ga 100 keV, is improved provided the contribution
of the ADAFs in low luminosity AGNs/normal galaxies is properly included. It is
found that less than ~15 per cent of local massive black hole mass density was
accreted during ADAF phases. We suggest that more accurate measurements of the
XRB in the energy band with \ga 100 keV in the future may help constrain the
growth of massive black holes at their late stage. We also calculate their
contribution to the extragalactic gamma-ray background, and find that less than
~1% of the observed EGRB is contributed by the ADAFs in these faint sources.Comment: 9 pages, 11 figures, accepted for publication in ApJ
Cosmological evolution of massive black holes: effects of Eddington ratio distribution and quasar lifetime
A power-law time-dependent lightcurve for active galactic nuclei (AGNs) is
expected by the self-regulated black hole growth scenario, in which the
feedback of AGNs expels gas and shut down accretion. This is also supported by
the observed power-law Eddington ratio distribution of AGNs. At high redshifts,
the AGN life timescale is comparable with (or even shorter than) the age of the
universe, which set a constraint on the minimal Eddington ratio for AGNs on the
assumption of a power-law AGN lightcurve. The black hole mass function (BHMF)
of AGN relics is calculated by integrating the continuity equation of massive
black hole number density on the assumption of the growth of massive black
holes being dominated by mass accretion with a power-law Eddington ratio
distribution for AGNs. The derived BHMF of AGN relics at z=0 can fit the
measured local mass function of the massive black holes in galaxies quite well,
provided the radiative efficiency ~0.1 and a suitable power-law index for the
Eddington ratio distribution are adopted. In our calculations of the black hole
evolution, the duty cycle of AGN should be less than unity, which requires the
quasar life timescale >0.5 giga-years.Comment: 7 pages, accepted by Ap
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