15,878 research outputs found
A Note on the Slim Accretion Disk Model
We show that when the gravitational force is correctly calculated in dealing
with the vertical hydrostatic equilibrium of black hole accretion disks, the
relationship that is valid for geometrically thin disks, i.e., constant, where is the sound speed, is the Keplerian
angular velocity, and is the half-thickness of the disk, does not hold for
slim disks. More importantly, by adopting the correct vertical gravitational
force in studies of thermal equilibrium solutions, we find that there exists a
maximally possible accretion rate for each radius in the outer region of
optically thick accretion flows, so that only the inner region of these flows
can possibly take the form of slim disks, and strong outflows from the outer
region are required to reduce the accretion rate in order for slim disks to be
realized.Comment: 14 pages, 5 figures, accepted by Ap
Tyrosine dephosphorylation of H2AX modulates apoptosis and survival decisions.
Life and death fate decisions allow cells to avoid massive apoptotic death in response to genotoxic stress. Although the regulatory mechanisms and signalling pathways controlling DNA repair and apoptosis are well characterized, the precise molecular strategies that determine the ultimate choice of DNA repair and survival or apoptotic cell death remain incompletely understood. Here we report that a protein tyrosine phosphatase, EYA, is involved in promoting efficient DNA repair rather than apoptosis in response to genotoxic stress in mammalian embryonic kidney cells by executing a damage-signal-dependent dephosphorylation of an H2AX carboxy-terminal tyrosine phosphate (Y142). This post-translational modification determines the relative recruitment of either DNA repair or pro-apoptotic factors to the tail of serine phosphorylated histone H2AX (gamma-H2AX) and allows it to function as an active determinant of repair/survival versus apoptotic responses to DNA damage, revealing an additional phosphorylation-dependent mechanism that modulates survival/apoptotic decisions during mammalian organogenesis
Global Dynamics of Advection-Dominated Accretion Revisited
We numerically solve the set of dynamical equations describing
advection-dominated accretion flows (ADAF) around black holes, using a method
similar to that of Chakrabarti (1996a). We choose the sonic radius of the flow
and the integration constant in angular momentum equation as free
parameters, and integrate the equations from the sonic point inwards to see if
the solution can extend supersonically to the black hole horizon, and outwards
to see if and where an acceptable outer boundary of the flow can be found. We
recover the ADAF-thin disk solution constructed in Narayan, Kato, & Honma
(1997, NKH97), an representative paper of the previous works on global ADAF
solutions, although in that paper an apparently very different procedure was
adopted. We obtain a complete picture in the form of parameter space
which sums up the situation of ADAF solution at a glance. For comparison we
also present the distribution of global solutions for inviscid flows in the
space, which supports the view that there should be some similarities
between the dynamical behavior of ADAF and that of adiabatic flows, and that
there should be a continuous change from the properties of viscous flows to
those of inviscid ones.Comment: 24 pages with 15 figures, to appear in ApJ Vol. 52
Calorimetric Evidence for Nodes in the Overdoped Ba(FeCo)As
We present low-temperature specific heat of the electron-doped
Ba(FeCo)As, which does not show any indication of
an upturn down to 400 mK, the lowest measuring temperature. The lack of a
Schottky-like feature at low temperatures or in magnetic fields up to 9 Tesla
enables us to identify enhanced low-temperature quasiparticle excitations and
to study anisotropy in the linear term of the specific heat. Our results can
not be explained by a single or multiple isotropic superconducting gap, but are
consistent with multi-gap superconductivity with nodes on at least one Fermi
surface sheet.Comment: 5 pages 4 figure
EM Decay of X(3872) as the charmonium
The recently BaBar results raise the possibility that X(3872) has negative
parity. This makes people reconsider assigning X(3872) to the state. In this paper we give a general form of the wave function of
mesons. By solving the instantaneous Bethe-Salpeter equation, we get
the mass spectrum and corresponding wave functions. We calculate
electromagnetic decay widths of the first state which we assume to be
the X(3872) particle. The results are keV, eV and keV. The ratio of branch fractions
of the second and first channel is about 0.002, which is inconsistent with the
experimental value . So X(3872) is unlikely to be a
charmonium state. In addition, we obtain a relatively large decay width for
channel which is keV.Comment: Revised versio
The role of in and reactions
The near threshold meson production in proton-proton and
collisions is studied with the assumption that the production mechanism is due
to the sub--threshold resonance. The , and
-meson exchanges for proton-proton collisions are considered. It is
shown that the contribution to the reaction from the t-channel
meson exchange is dominant. With a significant
coupling ( = 0.13), both and
data are very well reproduced. The significant coupling of
the resonance to is compatible with previous indications
of a large component in the quark wave function of the
resonance and may be the real origin of the significant enhancement of the
production over the naive OZI-rule predictions.Comment: 15 pages, 6 figure
Structural insights into the role of the Smoothened cysteine-rich domain in Hedgehog signalling.
Smoothened (Smo) is a member of the Frizzled (FzD) class of G-protein-coupled receptors (GPCRs), and functions as the key transducer in the Hedgehog (Hh) signalling pathway. Smo has an extracellular cysteine-rich domain (CRD), indispensable for its function and downstream Hh signalling. Despite its essential role, the functional contribution of the CRD to Smo signalling has not been clearly elucidated. However, given that the FzD CRD binds to the endogenous Wnt ligand, it has been proposed that the Smo CRD may bind its own endogenous ligand. Here we present the NMR solution structure of the Drosophila Smo CRD, and describe interactions between the glucocorticoid budesonide (Bud) and the Smo CRDs from both Drosophila and human. Our results highlight a function of the Smo CRD, demonstrating its role in binding to small-molecule modulators
Boundary K-matrices and the Lax pair for 1D open XYZ spin-chain
We analysis the symmetries of the reflection equation for open model
and find their solutions case by case. In the general open boundary
conditions, the Lax pair for open one-dimensional spin-chain is given.Comment: LaTeX, 17 pages, errors in references correcte
Production and optical properties of liquid scintillator for the JSNS experiment
The JSNS (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron
Source) experiment will search for neutrino oscillations over a 24 m short
baseline at J-PARC. The JSNS inner detector will be filled with 17 tons
of gadolinium-loaded liquid scintillator (LS) with an additional 31 tons of
unloaded LS in the intermediate -catcher and outer veto volumes.
JSNS has chosen Linear Alkyl Benzene (LAB) as an organic solvent because
of its chemical properties. The unloaded LS was produced at a refurbished
facility, originally used for scintillator production by the RENO experiment.
JSNS plans to use ISO tanks for the storage and transportation of the LS.
In this paper, we describe the LS production, and present measurements of its
optical properties and long term stability. Our measurements show that storing
the LS in ISO tanks does not result in degradation of its optical properties.Comment: 7 pages, 4 figures
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