27,796 research outputs found

### Broad-line and Multi-wave Band Emission from Blazars

We study the correlations of the flux of the broad-line emission ($F_{BLR}$)
with the X-ray emission flux, optical emission flux at 5500 \AA and radio
emission flux at 5 GHz, respectively, for a large sample of 50 Blazars (39
flat-spectrum radio quasars (FSRQs) and 11 BL Lac objects). Our main results
are as follows. There are very strong correlations between $F_{BLR}$ and
$F_{X}$ and between $L_{BLR}$ and $L_{X}$ in both states for 39 FSRQs and the
slopes of the linear regression equations are almost equal to 1. There are weak
correlations between $F_{BLR}$ and $F_{X}$ and between $L_{BLR}$ and $L_{X}$
for 11 BL Lac objects in both states, and the slopes of the linear regression
equations are close to 1. There are significant correlations between $F_{BLR}$
and $F_{X}$ and between $L_{BLR}$ and $L_{X}$ for 50 blazars in both states,
the slopes of both the linear regression equations are also close to 1. These
results support a close link between relativistic jets and accretion on to the
central Kerr black hole. On the other hand, we find that BL Lac objects have
low accretion efficiency $\eta$, whereas FSRQs have high accretion efficiency
$\eta$. The unified model of FSRQs and BL Lac objects is also discussed.Comment: 15 pages, 8 figure

### Dynamical properties of dipolar Fermi gases

We investigate dynamical properties of a one-component Fermi gas with
dipole-dipole interaction between particles. Using a variational function based
on the Thomas-Fermi density distribution in phase space representation, the
total energy is described by a function of deformation parameters in both real
and momentum space. Various thermodynamic quantities of a uniform dipolar Fermi
gas are derived, and then instability of this system is discussed. For a
trapped dipolar Fermi gas, the collective oscillation frequencies are derived
with the energy-weighted sum rule method. The frequencies for the monopole and
quadrupole modes are calculated, and softening against collapse is shown as the
dipolar strength approaches the critical value. Finally, we investigate the
effects of the dipolar interaction on the expansion dynamics of the Fermi gas
and show how the dipolar effects manifest in an expanded cloud.Comment: 14 pages, 8 figures, submitted to New J. Phy

### Spectral Transition and Torque Reversal in X-ray Pulsar 4U 1626-67

The accretion-powered, X-ray pulsar 4U 1626-67 has recently shown an abrupt
torque reversal accompanied by a dramatic spectral transition and a relatively
small luminosity change. The time-averaged X-ray spectrum during spin-down is
considerably harder than during spin-up. The observed torque reversal can be
explained by an accretion flow transition triggered by a gradual change in the
mass accretion rate. The sudden transition to spin-down is caused by a change
in the accretion flow rotation from Keplerian to sub-Keplerian. 4U 1626-67 is
estimated to be near spin equilibrium with a mass accretion rate Mdot~2x10**16
g/s, Mdot decreasing at a rate ~6x10**14 g/s/yr, and a polar surface magnetic
field of ~2b_p**{-1/2} 10^**12G where b_p is the magnetic pitch. During
spin-up, the Keplerian flow remains geometrically thin and cool. During
spin-down, the sub-Keplerian flow becomes geometrically thick and hot. Soft
photons from near the stellar surface are Compton up-scattered by the hot
accretion flow during spin-down while during spin-up such scattering is
unlikely due to the small scale-height and low temperature of the flow. This
mechanism accounts for the observed spectral hardening and small luminosity
change. The scattering occurs in a hot radially falling column of material with
a scattering depth ~0.3 and a temperature ~10^9K. The X-ray luminosity at
energies >5keV could be a poor indicator of the mass accretion rate. We briefly
discuss the possible application of this mechanism to GX 1+4, although there
are indications that this system is significantly different from other
torque-reversal systems.Comment: 10 pages, 1 figure, ApJ

### The momentum distribution of J/psi in B decays

The discrepancy between theory and data in the momentum distribution of slow
J/psi in B decays has been several times addressed as a puzzle. Using the most
recent results on exclusive B decays into J/psi and heavy kaons or exotic
mesons and reconsidering the non-relativistic-QCD calculation of the color
octet fragmentation component, we show that an improvement in the comparison
between data and theory can be obtained. There is still room for a better fit
to data and this may imply that new exotic mesons of the XYZ kind have yet to
be discovered.Comment: 4 pages, 2 figures, 2 tables. To appear in Physical Review

### A note on entropic force and brane cosmology

Recently Verlinde proposed that gravity is an entropic force caused by
information changes when a material body moves away from the holographic
screen. In this note we apply this argument to brane cosmology, and show that
the cosmological equation can be derived from this holographic scenario.Comment: 5 pages, no figures;references adde

### Spin freezing and dynamics in Ca_{3}Co_{2-x}Mn_{x}O_{6} (x ~ 0.95) investigated with implanted muons: disorder in the anisotropic next-nearest neighbor Ising model

We present a muon-spin relaxation investigation of the Ising chain magnet
Ca_{3}Co_{2-x}Mn_{x}O_{6} (x~0.95). We find dynamic spin fluctuations
persisting down to the lowest measured temperature of 1.6 K. The previously
observed transition at around T ~18 K is interpreted as a subtle change in
dynamics for a minority of the spins coupling to the muon that we interpret as
spins locking into clusters. The dynamics of this fraction of spins freeze
below a temperature T_{SF}~8 K, while a majority of spins continue to
fluctuate. An explanation of the low temperature behavior is suggested in terms
of the predictions of the anisotropic next-nearest-neighbor Ising model.Comment: 4 pages, 2 figure

### Scanning Tunneling Spectroscopy and Vortex Imaging in the Iron-Pnictide Superconductor BaFe$_{1.8}$Co$_{0.2}$As$_2$

We present an atomic resolution scanning tunneling spectroscopy study of
superconducting BaFe$_{1.8}$Co$_{0.2}$As$_2$ single crystals in magnetic fields
up to $9 \text{Tesla}$. At zero field, a single gap with coherence peaks at
$\overline{\Delta}=6.25 \text{meV}$ is observed in the density of states. At $9
\text{T}$ and $6 \text{T}$, we image a disordered vortex lattice, consistent
with isotropic, single flux quantum vortices. Vortex locations are uncorrelated
with strong scattering surface impurities, demonstrating bulk pinning. The
vortex-induced sub-gap density of states fits an exponential decay from the
vortex center, from which we extract a coherence length $\xi=27.6\pm 2.9
\text{\AA}$, corresponding to an upper critical field $H_{c2}=43 \text{T}$.Comment: 4 pages, 4 figure

### Integral Human Pose Regression

State-of-the-art human pose estimation methods are based on heat map
representation. In spite of the good performance, the representation has a few
issues in nature, such as not differentiable and quantization error. This work
shows that a simple integral operation relates and unifies the heat map
representation and joint regression, thus avoiding the above issues. It is
differentiable, efficient, and compatible with any heat map based methods. Its
effectiveness is convincingly validated via comprehensive ablation experiments
under various settings, specifically on 3D pose estimation, for the first time

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