6,352 research outputs found
The Early Evolution of Primordial Pair-Instability Supernovae
The observational signatures of the first cosmic explosions and their
chemical imprint on second-generation stars both crucially depend on how heavy
elements mix within the star at the earliest stages of the blast. We present
numerical simulations of the early evolution of Population III pair-instability
supernovae with the new adaptive mesh refinement code CASTRO. In stark contrast
to 15 - 40 Msun core-collapse primordial supernovae, we find no mixing in most
150 - 250 Msun pair-instability supernovae out to times well after breakout
from the surface of the star. This may be the key to determining the mass of
the progenitor of a primeval supernova, because vigorous mixing will cause
emission lines from heavy metals such as Fe and Ni to appear much sooner in the
light curves of core-collapse supernovae than in those of pair-instability
explosions. Our results also imply that unlike low-mass Pop III supernovae,
whose collective metal yields can be directly compared to the chemical
abundances of extremely metal-poor stars, further detailed numerical
simulations will be required to determine the nucleosynthetic imprint of very
massive Pop III stars on their direct descendants.Comment: submitted to ApJ, comments welcom
Generalised Umbral Moonshine
Umbral moonshine describes an unexpected relation between 23 finite groups
arising from lattice symmetries and special mock modular forms. It includes the
Mathieu moonshine as a special case and can itself be viewed as an example of
the more general moonshine phenomenon which connects finite groups and
distinguished modular objects. In this paper we introduce the notion of
generalised umbral moonshine, which includes the generalised Mathieu moonshine
[Gaberdiel M.R., Persson D., Ronellenfitsch H., Volpato R., Commun. Number
Theory Phys. 7 (2013), 145-223] as a special case, and provide supporting data
for it. A central role is played by the deformed Drinfel'd (or quantum) double
of each umbral finite group , specified by a cohomology class in
. We conjecture that in each of the 23 cases there exists a rule
to assign an infinite-dimensional module for the deformed Drinfel'd double of
the umbral finite group underlying the mock modular forms of umbral moonshine
and generalised umbral moonshine. We also discuss the possible origin of the
generalised umbral moonshine
Addressing a global epidemic: Opportunities for adult education to assist suicide loss survivors
Globally 800,000 people die by suicide every year. The worldwide prevalence of suicide has led to an increase in suicide prevention educational programming, but suicide bereavement education is rarely addressed. The upward trend of suicide rates has direct implications at the personal, community, societal, and global levels. The purpose of this literature review is to bring together empirical studies of those bereaved by suicide from various fields, so that researchers in adult education have a direction for this much-needed area of exploration. Three themes emerged during this research: (a) unique bereavement challenges, (b) barriers to obtaining support, and (c) sources of effective support. The studies were conducted in the fields of death and dying, mental health, public health, nursing, and suicidology with only one study conducted in the field of adult education. The results of this literature review can serve as a starting point for synergistic endeavors between adult education researchers and scholars in these fields to create programing that will serve the needs of suicide loss survivors. Such endeavors will bridge the gap between adult education theories and praxis
Hexabromocyclododecane decreases tumor-cell-binding capacity and cell-surface protein expression of human natural killer cells
Hexabromocyclododecane (HBCD) is a flame retardant that decreases the lytic function of human natural killer (NK) cells. NK cells defend against tumor cells and virally infected cells. Thus, HBCD has the potential to increase cancer incidence and viral infections. NK cells must bind to their targets for lysis to occur. Thus, concentrations of HBCD that decrease lytic function were examined for their ability to alter NK binding to tumor targets. Levels of HBCD that caused a loss of binding function were examined for effects on expression of cell surface proteins needed for binding. NK cells exposed to HBCD for 24 h, 48 h or 6 days or to HBCD for 1 h followed by 24 h, 48 h or 6 days in HBCD-free media were examined for binding function and cell surface protein expression. The results indicated that exposure of NK cells to 10 μM HBCD for 24 h (which caused a greater than 90% loss of lytic function) caused a very significant decrease in NK cell binding function (70.9%), and in CD16 and CD56 cell-surface protein expression (57.8 and 24.6% respectively). NK cells exposed to 10 μM HBCD for 1 h followed by 24 h in HBCD-free media (which caused a 89.3% loss of lytic function) showed decreased binding function (79.2%), and CD 16 expression (48.1%). Results indicate that HBCD exposures decreased binding function as well as cell-surface marker expression in NK cells and that these changes may explain the losses of lytic function induced by certain HBCD exposures
Hexabromocyclododecane decreases the lytic function and ATP levels of human natural killer cells
This study investigates the effect of hexabromocyclododecane (HBCD) on the lytic function of human natural killer (NK) cells and on ATP levels in NK cells. NK cells are capable of lysing tumor cells, virally infected cells, and antibody-coated cells. HBCD is a brominated cyclic alkane used primarily as an additive flame retardant. If HBCD interferes with NK cell function, this could increase risk of tumor development and/or viral infection. NK cells were exposed to various concentrations of HBCD for 24 and 48 h and 6 days before determining lytic function and ATP levels. ATP levels and lytic function were also determined in NK cells that were exposed to HBCD for 1 h followed by 24 and 48 h, and 6 days in HBCD-free media. The results indicated that exposure of NK cells to 10 µm HBCD for 24 h causes a very significant decrease in both NK cell lytic function and ATP levels (93.5 and 90.5%, respectively). Exposure of NK cells to 10 µm HBCD for 1 h followed by 24 h in HBCD-free media showed a progressive and persistent loss of lytic function (89.3%) as well as a decrease in ATP levels (46.1%). The results indicate that HBCD exposures decreased lytic function as well as ATP levels. However, a decrease in lytic function was not necessarily accompanied by a similar decrease in ATP. Importantly, these results also indicate that a brief (1 h) exposure to HBCD causes a progressive loss of lytic function over a 6 day period
How the First Stars Regulated Star Formation. II. Enrichment by Nearby Supernovae
Metals from Population III (Pop III) supernovae led to the formation of less
massive Pop II stars in the early universe, altering the course of evolution of
primeval galaxies and cosmological reionization. There are a variety of
scenarios in which heavy elements from the first supernovae were taken up into
second-generation stars, but cosmological simulations only model them on the
largest scales. We present small-scale, high-resolution simulations of the
chemical enrichment of a primordial halo by a nearby supernova after partial
evaporation by the progenitor star. We find that ejecta from the explosion
crash into and mix violently with ablative flows driven off the halo by the
star, creating dense, enriched clumps capable of collapsing into Pop II stars.
Metals may mix less efficiently with the partially exposed core of the halo, so
it might form either Pop III or Pop II stars. Both Pop II and III stars may
thus form after the collision if the ejecta do not strip all the gas from the
halo. The partial evaporation of the halo prior to the explosion is crucial to
its later enrichment by the supernova.Comment: Accepted to Ap
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