5,755 research outputs found
The H Beta Index as an Age Indicator of Old Stellar Systems: The Effects of Horizontal-Branch Stars
The strength of the H index has been computed for the integrated
spectra of model globular clusters from the evolutionary population synthesis.
These models take into account, for the first time, the detailed systematic
variation of horizontal-branch (HB) morphology with age and metallicity. Our
models show that the H index is significantly affected by the presence
of blue HB stars. Because of the contribution from blue HB stars, the H
does not monotonically decrease as metallicity increases at a given age.
Instead, it reaches a maximum strength when the distribution of HB stars is
centered around 9500 K, the temperature where the H index becomes
strongest. Our models indicate that the strength of the H index
increases as much as 0.75 {\AA} due to the presence of blue HB stars.
The comparison of the recent Keck observations of the globular cluster system
in the Milky Way Galaxy with those in giant elliptical galaxies, NGC 1399 and
M87, shows a systematic shift in the H against metallicity plane. Our
models suggest that this systematic difference is understood if the globular
cluster systems in giant elliptical galaxies are several billion years older,
in the mean, than the Galactic counterpart. Further observations of globular
cluster systems in the external galaxies from the large ground-based telescopes
and space UV facilities will enable to clarify whether this difference is
indeed due to the age difference or other explanations are also possible.Comment: 21 pages, 8 figures, Accepted for publication in the Astronomical
Journal, August 2000 issue, Postscript files are available at
http://csaweb.yonsei.ac.kr/~hclee/Hbet
Men and talk about legal abortion in South Africa: equality, support and rights discourses undermining reproductive âchoiceâ
Discursive constructions of abortion are embedded in the social and gendered power relations of a particular socio-historical space. As part of research on public discourses concerning abortion in South Africa where there has been a radical liberalisation of abortion legislation, we collected data from male group discussions about a vignette concerning abortion, and newspaper articles written by men about abortion. Our analysis revealed how discourses of equality, support and rights may be used by men to subtly undermine womenâs reproductive right to âchooseâ an abortion. Within an Equal Partnership discourse, abortion, paired with the assumption of foetal personhood, was equated with violating an equal heterosexual partnership and a manâs patriarchal duty to protect a child. A New Man discourse, which positions men as supportive of women, was paired with the assumption of men as rational and women as irrational in decision-making, to allow for the possibility of men dissuading women from terminating a pregnancy. A Rights discourse was invoked to suggest that abortion violates menâs paternal rights
Electron kinetic effects on raman backscatter in plasmas
We augment the usual three-wave cold-fluid equations governing Raman backscatter (RBS) with a new kinetic thermal correction, proportional to an average of particle kinetic energy weighted by the ponderomotive phase. From closed-form analysis within a homogeneous kinetic three-wave model and ponderomotively averaged kinetic simulations in a more realistic pulsed case, the magnitude of these new contributions is shown to be a measure of the dynamical detuning between the pump laser, seed laser, and Langmuir wave. Saturation of RBS is analyzed, and the role of trapped particles illuminated. Simple estimates show that a small fraction of trapped particles (similar to 6%) can significantly suppress backscatter. We discuss the best operating regime of the Raman plasma amplifier to reduce these deleterious kinetic effects.open282
Does Sensationalism Affect Executive Compensation? Evidence from Pay Ratio Disclosure Reform
Beginning in 2018, publicly-traded U.S. firms were required to report the ratio of the chief executive officerâs (CEO) compensation to that of the median employeeâs compensation in the annual proxy statement. Our study examines the effect of the mandated pay ratio disclosure on executive compensation. We find that pay ratio disclosure leads to declines in both total compensation and pay-for-performance sensitivity for CEOs relative to chief financial officers (CFOs). Our effects are strongest for firms that are more sensitive to political pressure. Taken together, our paper provides the first evidence that pay ratio disclosure achieves regulatorsâ goal of curtailing CEO compensation but also leads to an unintended decline in pay-for-performance sensitivity
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