24,653 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
ALMA Observations of a Candidate Molecular Outflow in an Obscured Quasar
We present Atacama Large Millimeter/Submillimeter Array (ALMA) CO (1-0) and
CO (3-2) observations of SDSS J135646.10+102609.0, an obscured quasar and
ultra-luminous infrared galaxy (ULIRG) with two merging nuclei and a known
20-kpc-scale ionized outflow. The total molecular gas mass is M_{mol} ~
9^{+19}_{-6} x 10^8 Msun, mostly distributed in a compact rotating disk at the
primary nucleus (M_{mol} ~ 3 x 10^8 Msun) and an extended tidal arm (M_{mol} ~
5 x 10^8 Msun). The tidal arm is one of the most massive molecular tidal
features known; we suggest that it is due to the lower chance of shock
dissociation in this elliptical/disk galaxy merger. In the spatially resolved
CO (3-2) data, we find a compact (r ~ 0.3 kpc) high velocity (v ~ 500 km/s)
red-shifted feature in addition to the rotation at the N nucleus. We propose a
molecular outflow as the most likely explanation for the high velocity gas. The
outflowing mass of M_{mol} ~ 7 x 10^7 Msun and the short dynamical time of
t_{dyn} ~ 0.6 Myr yield a very high outflow rate of \dot{M}_{mol} ~ 350 Msun/yr
and can deplete the gas in a million years. We find a low star formation rate
(< 16 Msun/yr from the molecular content and < 21 Msun/yr from the far-infrared
spectral energy distribution decomposition) that is inadequate to supply the
kinetic luminosity of the outflow (\dot{E} ~ 3 x 10^43 erg/s). Therefore, the
active galactic nucleus, with a bolometric luminosity of 10^46 erg/s, likely
powers the outflow. The momentum boost rate of the outflow (\dot{p}/(Lbol/c) ~
3) is lower than typical molecular outflows associated with AGN, which may be
related to its compactness. The molecular and ionized outflows are likely two
distinct bursts induced by episodic AGN activity that varies on a time scale of
10^7 yr.Comment: 16 pages, 7 figures, ApJ accepte
Quantum anti-Zeno effect without rotating wave approximation
In this paper, we systematically study the spontaneous decay phenomenon of a
two-level system under the influences of both its environment and continuous
measurements. In order to clarify some well-established conclusions about the
quantum Zeno effect (QZE) and the quantum anti-Zeno effect (QAZE), we do not
use the rotating wave approximation (RWA) in obtaining an effective
Hamiltonian. We examine various spectral distributions by making use of our
present approach in comparison with other approaches. It is found that with
respect to a bare excited state even without the RWA, the QAZE can still happen
for some cases, e.g., the interacting spectra of hydrogen. But for a physical
excited state, which is a renormalized dressed state of the atomic state, the
QAZE disappears and only the QZE remains. These discoveries inevitably show a
transition from the QZE to the QAZE as the measurement interval changes.Comment: 14 pages, 8 figure
The influential factor studies on the cooling rate of roller quenching for ultra-heavy plate
In this paper, the gradient temperature rolling (GTR) method is used to establish the 12-pass rolling model by Deform- 3D finite element (FE) software. The variation of temperature field and strain field of ultra-heavy plate slab under different conditions is systematically studied. The result shows that the more the number of water cooling between the passes during the rolling process, the greater the deformation of the core of slab, and the one of plate rolling with large temperature difference does not appear on near surface but gradually moves to the central part of the plate as cooling times increase
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
Efficiency optimization in a correlation ratchet with asymmetric unbiased fluctuations
The efficiency of a Brownian particle moving in periodic potential in the
presence of asymmetric unbiased fluctuations is investigated. We found that
there is a regime where the efficiency can be a peaked function of temperature,
which proves that thermal fluctuations facilitate the efficiency of energy
transformation, contradicting the earlier findings (H. kamegawa et al. Phys.
Rev. Lett. 80 (1998) 5251). It is also found that the mutual interplay between
asymmetry of fluctuation and asymmetry of the potential may induce optimized
efficiency at finite temperature. The ratchet is not most efficiency when it
gives maximum current.Comment: 10 pages, 7 figure
Clinicopathological features of extranodal lymphomas: Kuwait experience
A total of 935 patients with extranodal non-Hodgkin lymphoma (NHL) diagnosed in the period between January 1985 and December 2000 in Kuwait Cancer Center, serving the whole population of Kuwait, were used to describe the clinicopathological and epidemiological features of extranodal lymphomas in Kuwait. Extranodal lymphomas accounted for 45% of all NHL observed during this time. All NHL cases from Kuwait Cancer registry were analyzed and pathologically reclassified using the latest WHO ( 2000) classification. The most common lymphoma observed was diffuse large B-cell lymphoma (58.60%) followed by Burkitt's lymphoma (BL) (3.80%). In the pediatric group, BL comprises more than two thirds of all patients (77.20%). The most common extranodal sites were stomach (19.70%) and skin (17.80%) in the adult group, large intestine (29.80%) and small intestine (19.30%) in the pediatric age group. The majority (73.40%) of adult extranodal lymphomas was in stage IE - IIE and had a very good prognosis. On the contrary, the majority of pediatric extranodal lymphomas were found to be in stage III and IV. Variations in treatment policies ( single agent or combined chemotherapy, radiotherapy, combined modality treatment) adopted and changed during the time period of 16 years of this retrospective study were documented. Copyright (C) 2004 S. Karger AG, Basel
- …