627 research outputs found
Electromagnetic emissions from near-horizon region of an extreme Kerr-Taub-Nut black hole
We have studied electromagnetic line emissions from near-horizon region in
the extremal Kerr-Taub-NUT black hole spacetime and then probe the effects of
NUT charge on the electromagnetic line emissions. Due to the presence of the
NUT charge, the equatorial plane is no more a symmetry plane of the KTN
spacetime, which leads to that the dependence of electromagnetic line emission
on the NUT charge for the observer in the Southern Hemisphere differs from that
in the Northern one. Our result indicate that the electromagnetic line emission
in the Kerr-Taub-NUT black hole case is brighter than that in the case of Kerr
black hole for the observer in the equatorial plane or in the Southern
Hemisphere, but it becomes more faint as the observer's position deviates far
from the equatorial plane in the Northern one. Moreover, we also probe effects
of redshift factor on electromagnetic emission from near-horizon region in the
extremal Kerr-Taub-NUT black hole spacetime.Comment: 18 pages, 7 figure
A compilation of known QSOs for the Gaia mission
Quasars are essential for astrometric in the sense that they are spatial
stationary because of their large distance from the Sun. The European Space
Agency (ESA) space astrometric satellite Gaia is scanning the whole sky with
unprecedented accuracy up to a few muas level. However, Gaia's two fields of
view observations strategy may introduce a parallax bias in the Gaia catalog.
Since it presents no significant parallax, quasar is perfect nature object to
detect such bias. More importantly, quasars can be used to construct a
Celestial Reference Frame in the optical wavelengths in Gaia mission. In this
paper, we compile the most reliable quasars existing in literatures. The final
compilation (designated as Known Quasars Catalog for Gaia mission, KQCG)
contains 1843850 objects, among of them, 797632 objects are found in Gaia DR1
after cross-identifications. This catalog will be very useful in Gaia mission
Exploring Foreign Language Anxiety in the Chinese EFL Classroom: A Case Study
This study aimed to examine the factors affecting foreign language anxiety (FLA) in Chinese tertiary EFL classrooms. This study adopted a descriptive case study design involving 490 EFL students from one public university in China. Data were collected via a self-reported questionnaire and semi-structured interviews. The findings reported a moderate level of FLA among the students. Internal and external factors affected the studentβs FLA, including performance anxiety, perceived lack of proficiency, low motivation, relationship challenges, and learning environment-related challenges. These findings implied universities should enhance the physical and pedagogical learning environment to sustain quality EFL teaching and learning
Telomere Recombination Accelerates Cellular Aging in Saccharomyces cerevisiae
Telomeres are nucleoprotein structures located at the linear ends of eukaryotic chromosomes. Telomere integrity is required for cell proliferation and survival. Although the vast majority of eukaryotic species use telomerase as a primary means for telomere maintenance, a few species can use recombination or retrotransposon-mediated maintenance pathways. Since Saccharomyces cerevisiae can use both telomerase and recombination to replicate telomeres, budding yeast provides a useful system with which to examine the evolutionary advantages of telomerase and recombination in preserving an organism or cell under natural selection. In this study, we examined the life span in telomerase-null, post-senescent type II survivors that have employed homologous recombination to replicate their telomeres. Type II recombination survivors stably maintained chromosomal integrity but exhibited a significantly reduced replicative life span. Normal patterns of cell morphology at the end of a replicative life span and aging-dependent sterility were observed in telomerase-null type II survivors, suggesting the type II survivors aged prematurely in a manner that is phenotypically consistent with that of wild-type senescent cells. The shortened life span of type II survivors was extended by calorie restriction or TOR1 deletion, but not by Fob1p inactivation or Sir2p over-expression. Intriguingly, rDNA recombination was decreased in type II survivors, indicating that the premature aging of type II survivors was not caused by an increase in extra-chromosomal rDNA circle accumulation. Reintroduction of telomerase activity immediately restored the replicative life span of type II survivors despite their heterogeneous telomeres. These results suggest that telomere recombination accelerates cellular aging in telomerase-null type II survivors and that telomerase is likely a superior telomere maintenance pathway in sustaining yeast replicative life span
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