40 research outputs found
Explosive Nucleosynthesis in GRB Jets Accompanied by Hypernovae
Two-dimensional hydrodynamic simulations are performed to investigate
explosive nucleosynthesis in a collapsar using the model of MacFadyen and
Woosley (1999). It is shown that 56Ni is not produced in the jet of the
collapsar sufficiently to explain the observed amount of a hypernova when the
duration of the explosion is \sim 10 sec, which is considered to be the typical
timescale of explosion in the collapsar model. Even though a considerable
amount of 56Ni is synthesized if all explosion energy is deposited initially,
the opening angles of the jets become too wide to realize highly relativistic
outflows and gamma-ray bursts in such a case. From these results, it is
concluded that the origin of 56Ni in hypernovae associated with GRBs is not the
explosive nucleosynthesis in the jet. We consider that the idea that the origin
is the explosive nucleosynthesis in the accretion disk is more promising. We
also show that the explosion becomes bi-polar naturally due to the effect of
the deformed progenitor. This fact suggests that the 56Ni synthesized in the
accretion disk and conveyed as outflows are blown along to the rotation axis,
which will explain the line features of SN 1998bw and double peaked line
features of SN 2003jd. Some fraction of the gamma-ray lines from 56Ni decays in
the jet will appear without losing their energies because the jet becomes
optically thin before a considerable amount of 56Ni decays as long as the jet
is a relativistic flow. We show that abundance of nuclei whose mass number \sim
40 in the ejecta depends sensitively on the energy deposition rate. So it may
be determined by observations of chemical composition in metal poor stars which
model is the proper one as a model of a gamma-ray burst accompanied by a
hypernova.Comment: 29 pages with 16 figures. ApJ, accepte
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Successful Interdisciplinary Collaborations: The Contributions of Shared Socio-Emotional-Cognitive Platforms to Interdisciplinary Synthesis
Available theories concerning interdisciplinary collaborations tend to focus on either the cognitive or the social dimension of such interchange. We propose the theoretical construct of "shared socio-emotional-cognitive (SSEC) platforms" to capture what defines successful interdisciplinarity. The paper elaborates on this theoretical concept, which is informed by an extensive empirical study of nine research networks supported by three institutions: the Canadian Institute for Advanced Research, the MacArthur Foundation, and the Santa Fe Institute. We also analyze the conditions that enable or impede individuals to conduct interdisciplinary research together successfully, focusing on intellectual, interactional and institutional conditions. We first review relevant literature on interdisciplinary collaborations, and then advance a definition of SSEC platforms, describing three key dimensions and the theoretical assumptions on which they stand. These dimensions are: the cognitive-intellectual (most exclusively concerned with substance); the emotional (concerned with reactions to individuals and ideas); and the socio-interactional (concerned primarily with interaction, meaning-making, and group styles). These dimensions are also described as conditions enabling successful interdisciplinarity. They operate together with institutional conditions for success, which concern the rules, practices and expectations of funding organizations and the academic fields. After showing that these dimensions and conditions are present in the nine groups studied, but in varying proportions, we conclude by comparing our construct with the notion of "trading zones" (Galison 1997) to specify our constructsâ usefulness and contribution to the field.African and African American StudiesSociolog