30,587 research outputs found
Delay-dependent robust stability of stochastic delay systems with Markovian switching
In recent years, stability of hybrid stochastic delay systems, one of the important issues in the study of stochastic systems, has received considerable attention. However, the existing results do not deal with the structure of the diffusion but estimate its upper bound, which induces conservatism. This paper studies delay-dependent robust stability of hybrid stochastic delay systems. A delay-dependent criterion for robust exponential stability of hybrid stochastic delay systems is presented in terms of linear matrix inequalities (LMIs), which exploits the structure of the diffusion. Numerical examples are given to verify the effectiveness and less conservativeness of the proposed method
The monodromy groups of Dolgachev's CY moduli spaces are Zariski dense
Let be the coarse moduli space of CY manifolds arising
from a crepant resolution of double covers of branched along
hyperplanes in general position. We show that the monodromy group of a
good family for is Zariski dense in the corresponding
symplectic or orthogonal group if . In particular, the period map does
not give a uniformization of any partial compactification of the coarse moduli
space as a Shimura variety whenever . This disproves a conjecture of
Dolgachev. As a consequence, the fundamental group of the coarse moduli space
of ordered points in is shown to be large once it is not a
point. Similar Zariski-density result is obtained for moduli spaces of CY
manifolds arising from cyclic covers of branched along
hyperplanes in general position. A classification towards the geometric
realization problem of B. Gross for type bounded symmetric domains is
given.Comment: 48 page
Internal Variations in Empirical Oxygen Abundances for Giant HII Regions in the Galaxy NGC 2403
This paper presents a spectroscopic investigation of 11 HII regions in the
nearby galaxy NGC 2403. The HII regions are observed with a long-slit
spectrograph mounted on the 2.16 m telescope at XingLong station of National
Astronomical Observatories of China. For each of the HII regions, spectra are
extracted at different nebular radii along the slit-coverage. Oxygen abundances
are empirically estimated from the strong-line indices R23, N2O2, O3N2, and N2
for each spectrophotometric unit, with both observation- and model-based
calibrations adopted into the derivation. Radial profiles of these diversely
estimated abundances are drawn for each nebula. In the results, the oxygen
abundances separately estimated with the prescriptions on the basis of
observations and models, albeit from the same spectral index, systematically
deviate from each other; at the same time, the spectral indices R23 and N2O2
are distributed with flat profiles, whereas N2 and O3N2 exhibit apparent
gradients with the nebular radius. Because our study naturally samples various
ionization levels which inherently decline at larger radii within individual
HII regions, the radial distributions indicate not only the robustness of R23
and N2O2 against ionization variations but also the sensitivity of N2 and O3N2
to the ionization parameter. The results in this paper provide observational
corroboration of the theoretical prediction about the deviation in the
empirical abundance diagnostics. Our future work is planned to investigate
metal-poor HII regions with measurable T_e, in an attempt to recalibrate the
strong-line indices and consequently disclose the cause of the discrepancies
between the empirical oxygen abundances.Comment: 16 pages, 10 figures, 5 tables; accepted for publication in The
Astrophysical Journal; with a minor correction in the tex
Characterizing Ultraviolet and Infrared Observational Properties for Galaxies. II. Features of Attenuation Law
Variations in the attenuation law have a significant impact on observed
spectral energy distributions for galaxies. As one important observational
property for galaxies at ultraviolet and infrared wavelength bands, the
correlation between infrared-to-ultraviolet luminosity ratio and ultraviolet
color index (or ultraviolet spectral slope), i.e., the IRX-UV relation (or
IRX-beta relation), offered a widely used recipe for correcting dust
attenuation in galaxies, but the usability appears to be in doubt now because
of considerable dispersion in this relation found by many studies. In this
paper, on the basis of spectral synthesis modeling and spatially resolved
measurements of four nearby spiral galaxies, we provide an interpretation of
the deviation in the IRX-UV relation with variations in the attenuation law.
From both theoretical and observational viewpoints, two components in the
attenuation curve, the linear background and the 2175 Angstrom bump, are
suggested to be the parameters in addition to the stellar population age
(addressed in the first paper of this series) in the IRX-UV function; different
features in the attenuation curve are diagnosed for the galaxies in our sample.
Nevertheless, it is often difficult to ascertain the attenuation law for
galaxies in actual observations. Possible reasons for preventing the successful
detection of the parameters in the attenuation curve are also discussed in this
paper, including the degeneracy of the linear background and the 2175 Angstrom
bump in observational channels, the requirement for young and dust-rich systems
to study, and the difficulty in accurate estimates of dust attenuations at
different wavelength bands.Comment: 25 pages, 23 figures, 5 tables; accepted for publication in The
Astrophysical Journa
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