22,423 research outputs found
A comparative study of optical/ultraviolet variability of narrow-line Seyfert 1 and broad-line Seyfert 1 active galactic nuclei
The ensemble optical/ultraviolet variability of narrow-line Seyfert 1 (NLS1)
type active galactic nuclei (AGNs) is investigated, based on a sample selected
from the Sloan Digital Sky Survey (SDSS) Stripe-82 region with multi-epoch
photometric scanning data. As a comparison a control sample of broad-line
Seyfert 1 (BLS1) type AGNs is also incorporated. To quantify properly the
intrinsic variation amplitudes and their uncertainties, a novel method of
parametric maximum-likelihood is introduced, that has, as we argued, certain
virtues over previously used methods. The majority of NLS1-type AGNs exhibit
significant variability on timescales from about ten days to a few years with,
however, on average smaller amplitudes compared to BLS1-type AGNs. About 20
NLS1- type AGNs showing relatively large variations are presented, that may
deserve future monitoring observations, for instance, reverberation mapping.
The averaged structure functions of variability, constructed using the same
maximumlikelihood method, show remarkable similarity in shape for the two types
of AGNs on timescales longer than about 10 days, which can be approximated by a
power-law or an exponential function. This, along with other similar
properties, such as the wavelength-dependent variability, are indicative of a
common dominant mechanism responsible for the long-term optical/UV variability
of both NLS1- and BLS1-type AGNs. Towards the short timescales, however, there
is tentative evidence that the structure function of NLS1-type AGNs continues
declining, whereas that of BLS1-type AGNs flattens with some residual
variability on timescales of days. If this can be confirmed, it may suggest
that an alternative mechanism, such as X-ray reprocessing, starts to become
dominating in BLS1-type AGNs, but not in NLS1-, on such timescales.Comment: 53 pages, 13 figures, 3 tables, accepted for pulication in A
A Microscopic Mechanism for Muscle's Motion
The SIRM (Stochastic Inclined Rods Model) proposed by H. Matsuura and M.
Nakano can explain the muscle's motion perfectly, but the intermolecular
potential between myosin head and G-actin is too simple and only repulsive
potential is considered. In this paper we study the SIRM with different complex
potential and discuss the effect of the spring on the system. The calculation
results show that the spring, the effective radius of the G-actin and the
intermolecular potential play key roles in the motion. The sliding speed is
about calculated from the model which well agrees with
the experimental data.Comment: 9 pages, 6 figure
On the Stability and Structural Dynamics of Metal Nanowires
This article presents a brief review of the nanoscale free-electron model,
which provides a continuum description of metal nanostructures. It is argued
that surface and quantum-size effects are the two dominant factors in the
energetics of metal nanowires, and that much of the phenomenology of nanowire
stability and structural dynamics can be understood based on the interplay of
these two competing factors. A linear stability analysis reveals that metal
nanocylinders with certain magic conductance values G=1, 3, 6, 12, 17, 23, 34,
42, 51, 67, 78, 96, ... times the conductance quantum are exceptionally stable.
A nonlinear dynamical simulation of nanowire structural evolution reveals a
universal equilibrium shape consisting of a magic cylinder suspended between
unduloidal contacts. The lifetimes of these metastable structures are also
computed.Comment: 8 pages, 6 figure
Optimization of six strand tundish based on inclusions motion
Inclusion transport and the influence of structural parameters of baffle holes on inclusion removal rate are discussed. The physical modeling experiments give two optimal integrated tundish structural parameters of baffle holes. From the further study of Inclusion trajectories, the tundish should be optimized in the structural parameters of baffle holes in the condition of height 300 mm, angle 30° and diameter 20 mm
Sensitive Chemical Compass Assisted by Quantum Criticality
The radical-pair-based chemical reaction could be used by birds for the
navigation via the geomagnetic direction. An inherent physical mechanism is
that the quantum coherent transition from a singlet state to triplet states of
the radical pair could response to the weak magnetic field and be sensitive to
the direction of such a field and then results in different photopigments in
the avian eyes to be sensed. Here, we propose a quantum bionic setup for the
ultra-sensitive probe of a weak magnetic field based on the quantum phase
transition of the environments of the two electrons in the radical pair. We
prove that the yield of the chemical products via the recombination from the
singlet state is determined by the Loschmidt echo of the environments with
interacting nuclear spins. Thus quantum criticality of environments could
enhance the sensitivity of the detection of the weak magnetic field.Comment: 4 pages, 3 figure
On the classification of Kahler-Ricci solitons on Gorenstein del Pezzo surfaces
We give a classification of all pairs (X,v) of Gorenstein del Pezzo surfaces
X and vector fields v which are K-stable in the sense of Berman-Nystrom and
therefore are expected to admit a Kahler-Ricci solition. Moreover, we provide
some new examples of Fano threefolds admitting a Kahler-Ricci soliton.Comment: 21 pages, ancillary files containing calculations in SageMath; minor
correction
A Statistical Study on Force-Freeness of Solar Magnetic Fields in the Photosphere
It is an indisputable fact that solar magnetic fields are force-free in the
corona, where force free fields means that current and magnetic fields are
parallel and there is no Lorentz force in the fields. While the force-free
extent of photospheric magnetic fields remains open. In this paper, the
statistical results about it is given. The vector magnetograms (namely,
, and in heliocentric coordinates) are employed, which
are deduced and calibrated from Stokes spectra, observed by Solar Magnetic
Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS) are used. We
study and calibrated 925 magnetograms calibrated by two sets of calibration
coefficients, that indicate the relations between magnetic fields and the
strength of Stokes spectrum and can be calculated either theoretically or
empirically. The statistical results show that the majority of active region
magnetic fields are not consistent with the force-free model.Comment: 10 pages, 5 figures, has been accepted by PAS
Risk Identification And Analysis Of Precast Concrete Structure Based On Work Breakdown Structure-Risk Breakdown Structure
Because the prefabricated building started late in China, and subject to management and technical restrictions, the safety problems during the construction of the prefabricated building have not been solved effectively. In view of the problems of complex environments in precast concrete structure and many influencing factors which makes the construction risks are difficult to identify. The work breakdown structure (WBS) - risk breakdown structure (RBS) method is introduced to solve the problem. By means of analyzing the investigation data of the prefabricated building accidents, its risks during construction are identified and coupled. Then the judgment matrix is obtained and the corresponding risk factors can be established. In the meanwhile, the fault tree analysis method has been being used to analyze the sensitivity of three kinds of accidents, such as falling, striking by object and electrocution. The sensitive coefficients of risk factors are calculated and sorted. The result shows that the main risk factors of falling accident are verticality deviation of component installation, deviation of component position and unsecured mechanics. The main risk factors of striking by object/equipment are insufficient strength of components supporting, overturning components and unreasonable of suspension point. The main risk factors of electrocution are improper welding operation and short circuit. Finally, corresponding control measures are put forward according to the risk accidents. The research results provided a good theoretical basis for the risk identification of prefabricated building construction
An Unobscured type II quasar candidate: SDSS J012032.19-005501.9
We report the finding of an unobscured type II Active Galactic Nuclei (AGN)
candidate, SDSS J012032.19-005501.9 at a relatively high redshift of
0.601,which shows a number of unusual properties. It varies significantly on
timescales of years as typical type I AGNs and marginally on timescales of
weeks. The color-magnitude relation and the structure function are also
consistent with that of type I AGNs, which imply that its variability likely
originates from the black hole accretion system .However, no broad emission
line is detected in the SDSS spectrum, and the upper limit of the equivalent
width of the H broad emission line is much less than that of type I
AGNs. These properties suggest that SDSS J012032.19-005501.9 may be an
unobscured quasar without broad emission lines intrinsically, namely an
unobscured type II AGN or "true" type II AGN. Furthermore, its continuum
luminosity is at least one order of magnitude fainter than the average value of
thepast century expected from the [OIII] emission line. It indicates that SDSS
J012032.19-005501.9 may be switching off. Additional possible scenarios to
explain this intriguing source are also discussed. Future deep observations at
multi-wavelengths are needed to reveal the nature of this peculiar and
intriguing AGN.Comment: 8 pages, 7 figures, 1 table, accepted for publication in The
Astronomical Journa
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