1,111 research outputs found
What is the Astrophysical Meaning of the Intermediate Subgroup of GRBs?
Published articles concerning the intermediate (third) subgroup of GRBs are
surveyed. From a statistical perspective this subgroup may exist, however its
significance depends on which data set is used. Its astrophysical meaning is
unclear because the occurrence of this subgroup can also be an artificial
selection effect. Hence, GRBs from this subgroup need not be given by a
physically different phenomenon. The aim of this contribution is to search for
the answer to the question in the title.Comment: journal: Proceedings of Science, Swift: 10 Years of Discovery;
conference date: 2-5 December 2014; location: La Sapienza University, Rome,
Italy; 6 pages, 4 figures, 1 table; accepted for publication in July 9 201
A curious relation between the flat cosmological model and the elliptic integral of the first kind
The dependence of the luminosity distance on the redshift has a key
importance in the cosmology. This dependence can well be given by standard
functions for the zero cosmological constant. The purpose of this article is to
present such a relation also for the non-zero cosmological constant, if the
universe is spatially flat. A definite integral is used. The integration ends
in the elliptic integral of the first kind. The result shows that no numerical
integration is needed for the non-zero cosmological constant, if the universe
is spatially flat.Comment: Accepted for publication in Astronomy & Astrophysics. 2 page
On the properties of the RHESSI intermediate-duration gamma-ray bursts
The intermediate-duration gamma-ray bursts (GRBs) identified in the data of
the RHESSI satellite are investigated with respect to their spectral lags, peak
count rates, redshifts, supernova observations, and star formation rates of
their host galaxies. Standard statistical tests like Kolmogorov-Smirnov and
Student t-test are used. It is discussed whether these bursts belong to the
group of so-called short or long GRBs, or if they significantly differ from
both groups.Comment: 4 pages, 4 figures, 2 table
On the relation between the non-flat cosmological models and the elliptic integral of first kind
Recently we have found an analytic integration formula that describes the
dependence of the luminosity distance on the redshift for the flat cosmological
model with a non-zero cosmological constant. The purpose of this article is to
search for a similar relation for the non-flat models. A Taylor series was
used. The elliptic integral of the first kind can indeed be applied. The result
shows that a combination of the numerical integration with the previous
analytic formula can also be useful for the nearly flat cosmological models.Comment: two pages, published in Astronomy & Astrophysics, Volume 573, A5
Cell cycle dynamics during diapause entry and exit in an annual killifish revealed by FUCCI technology
Background: Annual killifishes are adapted to surviving and reproducing over alternating dry and wet seasons. During the dry season, all adults die and desiccation-resistant embryos remain encased in dry mud for months or years in a state of diapause where their development is halted in anticipation of the months that have to elapse before their habitats are flooded again. Embryonic development of annual killifishes deviates from canonical teleost development. Epiblast cells disperse during epiboly, and a "dispersed phase" precedes gastrulation. In addition, annual fish have the ability to enter diapause and block embryonic development at the dispersed phase (diapause I), mid-somitogenesis (diapause II) and the final phase of development (diapause III). Developmental transitions associated with diapause entry and exit can be linked with cell cycle events. Here we set to image this transition in living embryos. Results: To visibly explore cell cycle dynamics during killifish development in depth, we created a stable transgenic line in Nothobranchius furzeri that expresses two fluorescent reporters, one for the G1 phase and one for the S/G2 phases of the cell cycle, respectively (Fluorescent Ubiquitination-based Cell Cycle Indicator, FUCCI). Using this tool, we observed that, during epiboly, epiblast cells progressively become quiescent and exit the cell cycle. All embryos transit through a phase where dispersed cells migrate, without showing any mitotic activity, possibly blocked in the G1 phase (diapause I). Thereafter, exit from diapause I is synchronous and cells enter directly into the S phase without transiting through G1. The developmental trajectories of embryos entering diapause and of those that continue to develop are different. In particular, embryos entering diapause have reduced growth along the medio-lateral axis. Finally, exit from diapause II is synchronous for all cells and is characterized by a burst of mitotic activity and growth along the medio-lateral axis such that, by the end of this phase, the morphology of the embryos is identical to that of direct-developing embryos. Conclusions: Our study reveals surprising levels of coordination of cellular dynamics during diapause and provides a reference framework for further developmental analyses of this remarkable developmental quiescent state
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