2,750 research outputs found
Discovery of a Quasar with Double-Peaked Broad Balmer Emission Lines
Most massive galaxies contain a supermassive black hole (SMBH) at their
center. When galaxies merge, their SMBHs sink to the center of the new galaxy
where they are thought to eventually merge. During this process an SMBH binary
is formed. The presence of two sets of broad emission lines in the optical
spectrum of an active galactic nucleus (AGN) has been interpreted as evidence
for two broad line regions (BLR), one surrounding each SMBH in a binary. We
modeled the broad Balmer emission lines in SDSS spectra of 373 extreme
variability AGNs using one broad and several narrow Gaussian components. We
report on the discovery of SDSS J021647.53011341.5 (hereafter J0216) as a
double-peaked broad emission line source. Among the 373 AGNs there were five
sources that are known double-peaked emission line sources. Three of these have
been reported as candidate SMBH binaries in previous studies. We present all
six objects and their double-peaked broad Balmer emission lines, and discuss
the implications for a tidal disruption event (TDE) interpretation of the
extreme variability assuming the double-peaked sources are SMBH binaries.Comment: 6 pages, 1 figure, 1 table. Accepted for publication in MNRA
Origin of the large thermoelectric power in oxygen-variable RBaCo_{2}O_{5+x} (R=Gd, Nd)
Thermoelectric properties of GdBaCo_{2}O_{5+x} and NdBaCo_{2}O_{5+x} single
crystals have been studied upon continuous doping of CoO_2 planes with either
electrons or holes. The thermoelectric response and the resistivity behavior
reveal a hopping character of the transport in both compounds, providing the
basis for understanding the recently found remarkable divergence of the Seebeck
coefficient at x=0.5. The doping dependence of the thermoelectric power evinces
that the configurational entropy of charge carriers, enhanced by their spin and
orbital degeneracy, plays a key role in the origin of the large thermoelectric
response in these correlated oxides.Comment: 5 pages, 4 figures, accepted for publication in PR
Low Temperature Magnetic Properties of the Double Exchange Model
We study the {\it ferromagnetic} (FM) Kondo lattice model in the strong
coupling limit (double exchange (DE) model). The DE mechanism proposed by Zener
to explain ferromagnetism has unexpected properties when there is more than one
itinerant electron. We find that, in general, the many-body ground state of the
DE model is {\it not} globally FM ordered (except for special filled-shell
cases). Also, the low energy excitations of this model are distinct from spin
wave excitations in usual Heisenberg ferromagnets, which will result in unusual
dynamic magnetic properties.Comment: 5 pages, RevTeX, 5 Postscript figures include
The hard quiescent spectrum of the neutron-star X-ray transient EXO 1745-248 in the globular cluster Terzan 5
We present a Chandra observation of the globular cluster Terzan 5 during
times when the neutron-star X-ray transient EXO 1745-248 located in this
cluster was in its quiescent state. We detected the quiescent system with a
(0.5-10 keV) luminosity of ~2 x 10^{33} ergs/s. This is similar to several
other neutron-star transients observed in their quiescent states. However, the
quiescent X-ray spectrum of EXO 1745--48 was dominated by a hard power-law
component instead of the soft component that usually dominates the quiescent
emission of other neutron-star X-ray transients. This soft component could not
conclusively be detected in EXO 1745-248 and we conclude that it contributed at
most 10% of the quiescent flux in the energy range 0.5-10 keV. EXO 1745-248 is
only the second neutron-star transient whose quiescent spectrum is dominated by
the hard component (SAX J1808.4-3658 is the other one). We discuss possible
explanations for this unusual behavior of EXO 1745-248, its relationship to
other quiescent neutron-star systems, and the impact of our results on
understanding quiescent X-ray binaries. We also discuss the implications of our
results on the way the low-luminosity X-ray sources in globular clusters are
classified.Comment: Accepted by ApJ Main Journal, September 22, 2004. Figure 2 is a color
figur
Spin Excitation Spectrum of LaMnO
As an effective model to describe perovskite-type manganates (La,)MnO,
the double-exchange model on a cubic lattice is investigated. Spin excitation
spectrum of the model in the ground state is studied using the spin wave
approximation. Spin wave dispersion relation observed in the inelastic neutron
scattering experiment of LaPbMnO is reproduced. Effective
values for the electron bandwidth as well as Hund's coupling is estimated from
the data.Comment: 10 pages LaTeX including 4 PS figure
A robust subspace based approach to feedforward control of broadband disturbances on a six-degrees-of-freedom vibration isolation set-up
The contribution of this paper is twofold. First, the paper introduces a novel hybrid vibration isolation approach which uses a combination of passive and active vibration control techniques to provide additional design freedom. The approach can be used to meet higher design requirements with respect to vibration isolation. To illustrate the feasibility of the approach, a stiff hybrid sixdegrees-of-freedom vibration isolation set-up will be presented. The objective of the set-up is to investigate if the receiver structure can be isolated from the source structure by six hybrid vibration isolation mounts, such that disturbances induced by the source structure are isolated from the receiver structure. Vibration isolation is established by minimizing signals from six acceleration sensor outputs and by steering six piezo-electric actuator inputs. Our second contribution is that a state space based fixed gain H2 controller is designed, implemented and validated. Real-time broadband feedforward control results are presented (between 0 - 1 kHz) which show that an average reduction of 8.0 dB is achieved in the error sensor outputs in real-time
Electronic and magnetic states in doped LaCoO_3
The electronic and magnetic states in doped perovskite cobaltites, (La,
Sr)CoO_3, are studied in the numerically exact diagonalization method on
Co_2O_{11} clusters. For realistic parameter values, it is shown that a high
spin state and an intermediate spin state coexist in one-hole doped clusters
due to strong p-d mixing. The magnetic states in the doped cobaltites obtained
in the calculation explain various experimental results.Comment: 4 pages, 2 figures, epsfj.st
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