50,663 research outputs found
Dissecting the quasar main sequence: insight from host galaxy properties
The diverse properties of broad-line quasars appear to follow a well-defined
main sequence along which the optical FeII strength increases. It has been
suggested that this sequence is mainly driven by the Eddington ratio (L/L_Edd)
of the black hole (BH) accretion. Shen & Ho demonstrated with quasar clustering
analysis that the average BH mass decreases with increasing FeII strength when
quasar luminosity is fixed, consistent with this suggestion. Here we perform an
independent test by measuring the stellar velocity dispersion sigma* (hence the
BH mass via the M-sigma* relation) from decomposed host spectra in low-redshift
Sloan Digital Sky Survey quasars. We found that at fixed quasar luminosity,
sigma* systematically decreases with increasing FeII strength, confirming that
Eddington ratio increases with FeII strength. We also found that at fixed
luminosity and FeII strength, there is little dependence of sigma* on the broad
Hbeta FWHM. These new results reinforce the framework put forward by Shen & Ho
that Eddington ratio and orientation govern most of the diversity seen in
broad-line quasar properties.Comment: ApJL in press; 5 pages and 4 figure
The Impact of Road Configuration on V2V-based Cooperative Localization
Cooperative localization with map matching has been shown to reduce Global
Navigation Satellite System (GNSS) localization error from several meters to
sub-meter level by fusing the GNSS measurements of four vehicles in our
previous work. While further error reduction is expected to be achievable by
increasing the number of vehicles, the quantitative relationship between the
estimation error and the number of connected vehicles has neither been
systematically investigated nor analytically proved. In this work, a
theoretical study is presented that analytically proves the correlation between
the localization error and the number of connected vehicles in two cases of
practical interest. More specifically, it is shown that, under the assumption
of small non-common error, the expected square error of the GNSS common error
correction is inversely proportional to the number of vehicles, if the road
directions obey a uniform distribution, or inversely proportional to logarithm
of the number of vehicles, if the road directions obey a Bernoulli
distribution. Numerical simulations are conducted to justify these analytic
results. Moreover, the simulation results show that the aforementioned error
decrement rates hold even when the assumption of small non-common error is
violated
Optimal control of nonlinear partially-unknown systems with unsymmetrical input constraints and its applications to the optimal UAV circumnavigation problem
Aimed at solving the optimal control problem for nonlinear systems with
unsymmetrical input constraints, we present an online adaptive approach for
partially unknown control systems/dynamics. The designed algorithm converges
online to the optimal control solution without the knowledge of the internal
system dynamics. The optimality of the obtained control policy and the
stability for the closed-loop dynamic optimality are proved theoretically. The
proposed method greatly relaxes the assumption on the form of the internal
dynamics and input constraints in previous works. Besides, the control design
framework proposed in this paper offers a new approach to solve the optimal
circumnavigation problem involving a moving target for a fixed-wing unmanned
aerial vehicle (UAV). The control performance of our method is compared with
that of the existing circumnavigation control law in a numerical simulation and
the simulation results validate the effectiveness of our algorithm
Segregation by Race in Public Schools Retrospect and Prospect
Solar energy conversion has been intensively studied in past decades and has been shown to be greatly effective for solving the serious environmental pollution and energy shortage problems. Photoelectrocatalysis and photovoltaics have been considered as the two main approaches for solar energy conversion and utilization, which are generally involved with nanostructured materials and/or catalytic processes, greatly affecting the efficiencies for solar energy conversion. Then, it is necessary to understand the relationship between the physical and chemical properties of nanomaterials and their performances for solar energy conversion. It is also important to explore the fundamentals in catalytic processes for solar energy conversion and make breakthrough in design and synthesis of nanomaterials or nanostructures, characterization of material properties, and performance of novel devices and systems. The aim of this special issue is to present some recent progress in the field of advanced catalysis and nanostructure design for solar energy conversion. A brief summary of all accepted papers is provided below
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