3,514 research outputs found
The Post-Merger Magnetized Evolution of White Dwarf Binaries: The Double-Degenerate Channel of Sub-Chandrasekhar Type Ia Supernovae and the Formation of Magnetized White Dwarfs
Type Ia supernovae (SNe Ia) play a crucial role as standardizable
cosmological candles, though the nature of their progenitors is a subject of
active investigation. Recent observational and theoretical work has pointed to
merging white dwarf binaries, referred to as the double-degenerate channel, as
the possible progenitor systems for some SNe Ia. Additionally, recent
theoretical work suggests that mergers which fail to detonate may produce
magnetized, rapidly-rotating white dwarfs. In this paper, we present the first
multidimensional simulations of the post-merger evolution of white dwarf
binaries to include the effect of the magnetic field. In these systems, the two
white dwarfs complete a final merger on a dynamical timescale, and are tidally
disrupted, producing a rapidly-rotating white dwarf merger surrounded by a hot
corona and a thick, differentially-rotating disk. The disk is strongly
susceptible to the magnetorotational instability (MRI), and we demonstrate that
this leads to the rapid growth of an initially dynamically weak magnetic field
in the disk, the spin-down of the white dwarf merger, and to the subsequent
central ignition of the white dwarf merger. Additionally, these magnetized
models exhibit new features not present in prior hydrodynamic studies of white
dwarf mergers, including the development of MRI turbulence in the hot disk,
magnetized outflows carrying a significant fraction of the disk mass, and the
magnetization of the white dwarf merger to field strengths
G. We discuss the impact of our findings on the origins, circumstellar media,
and observed properties of SNe Ia and magnetized white dwarfs.Comment: Accepted ApJ version published on 8/20/13, with significant
additional text added discussing the nature of the magnetized outflows, and
possible CSM observational features relevant to NaID detection
The Importance of Community in a Fully Online Program: Establishing Equity, Inclusion, and Access with Nontraditional Students in an Early Childhood Licensure Program
This mixed method study examined nontraditional preservice teachers’ perception of community in an online bachelors’ program. Previous research supports the idea that nontraditional students face a variety of barriers in higher education including but not limited to feelings of comfortability and financial concerns. This study utilized the Community of Practice theory to best understand participants’ experiences. The findings suggest that most of the participants in this online program felt they received support when transitioning into the program in addition to feeling connected to others while in the program. Finally, it is important that preservice teacher programs make meaningful efforts to create a sense of community and culture within the program, disseminate information that provides support to students transitioning, and continually establish opportunities for professional development for faculty
Arousal from death feigning by vibrational stimuli: comparison of Tribolium species
Death feigning (or tonic immobility) is an effective antipredator strategy. However, prolonged immobility on the ground increases the risk of being parasitized or eaten by predators, and thus, insects must rouse themselves when appropriate stimulation is provided. Very few studies on the effect of stimulus intensity on arousal from death feigning have been conducted. A previous study using Tribolium castaneum showed an existing threshold for the intensity of the stimulus that causes arousal from death feigning. Whether there are differences between species in the threshold for arousal is an interesting question. In the present study, we, therefore, compared the effect of stimulus strength on arousal from death feigning in two closely related species, namely, T. confusum and T. freemani, which are established strains that have been artificially selected for longer duration of death feigning. Also, part of the study was to determine whether there was a positive association between intensity of stimulus needed to rouse and the duration of death feigning. We discuss why there is a difference in the strength of the stimulus needed for arousal from death feigning among Tribolium species, for which we included the data for T. castaneum from a previous study
Inhomogeneous Galactic Chemical Evolution: Modelling Ultra-Faint Dwarf Galaxies of the Large Magellanic Cloud
Ultra-faint dwarf galaxies are among the oldest and most metal-poor galaxies
in the cosmos, observed to contain no gas and a high dark matter mass fraction.
Understanding the chemical abundance dispersion in such extreme environments
could shed light on the very first generations of stars. We present a novel
inhomogeneous chemical evolution model, {\tt i-GEtool}, that we apply to two
ultra-faint dwarf galaxies, Carina II and Reticulum II, both satellites of the
Large Magellanic Cloud. Our model is based on the Monte Carlo sampling of the
initial mass function as star formation proceeds in different gas cells of the
galaxy volume. We account for the chemical enrichment of Supernova bubbles as
they spread in the interstellar medium, causing dispersion in the elemental
abundances. We recreate the abundance patterns of - and
odd- elements, predicting two sequences in [C/Fe] and [N/Fe] at all
metallicities. Our models underestimate [C/Fe] and [Ti/Fe] because of the large
uncertainty in the adopted stellar nucleosynthesis yields. We discuss that the
observed C and N abundances had likely been affected by internal mixing
processes, which changed the initial surface abundances in the red giants. Our
Supernova feedback scheme is responsible for driving galactic outflows, which
quench the star formation activity at early times. We predict an average
outflow mass-loading factor , which extrapolates towards very
low galaxy stellar masses the trend observed at high masses. Finally, by
combining our model with the MIST isochrone database, we compare our synthetic
colour-magnitude diagrams to observations.Comment: 19 Pages, 12 Figures, 1 Table, Accepted to MNRA
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Amphiregulin-EGFR Signaling Mediates the Migration of Bone Marrow Mesenchymal Progenitors toward PTH-Stimulated Osteoblasts and Osteocytes
Intermittent administration of parathyroid hormone (PTH) dramatically increases bone mass and currently is one of the most effective treatments for osteoporosis. However, the detailed mechanisms are still largely unknown. Here we demonstrate that conditioned media from PTH-treated osteoblastic and osteocytic cells contain soluble chemotactic factors for bone marrow mesenchymal progenitors, which express a low amount of PTH receptor (PTH1R) and do not respond to PTH stimulation by increasing cAMP production or migrating toward PTH alone. Conditioned media from PTH-treated osteoblasts elevated phosphorylated Akt and p38MAPK amounts in mesenchymal progenitors and inhibition of these pathways blocked the migration of these progenitors toward conditioned media. Our previous and current studies revealed that PTH stimulates the expression of amphiregulin, an epidermal growth factor (EGF)-like ligand that signals through the EGF receptor (EGFR), in both osteoblasts and osteocytes. Interestingly, conditioned media from PTH-treated osteoblasts increased EGFR phosphorylation in mesenchymal progenitors. Using several different approaches, including inhibitor, neutralizing antibody, and siRNA, we demonstrate that PTH increases the release of amphiregulin from osteoblastic cells, which acts on the EGFRs expressed on mesenchymal progenitors to stimulate the Akt and p38MAPK pathways and subsequently promote their migration in vitro. Furthermore, inactivation of EGFR signaling specifically in osteoprogenitors/osteoblasts attenuated the anabolic actions of PTH on bone formation. Taken together, these results suggest a novel mechanism for the therapeutic effect of PTH on osteoporosis and an important role of EGFR signaling in mediating PTH's anabolic actions on bone
One-step immortalization of primary human airway epithelial cells capable of oncogenic transformation
BACKGROUND: The ability to transform normal human cells into cancer cells with the introduction of defined genetic alterations is a valuable method for understanding the mechanisms of oncogenesis. Easy establishment of immortalized but non-transformed human cells from various tissues would facilitate these genetic analyses.
RESULTS: We report here a simple, one-step immortalization method that involves retroviral vector mediated co-expression of the human telomerase protein and a shRNA targeting the CDKN2A gene locus. We demonstrate that this method could successfully immortalize human small airway epithelial cells while maintaining their chromosomal stability. We further showed that these cells retain p53 activity and can be transformed by the KRAS oncogene.
CONCLUSIONS: Our method simplifies the immortalization process and is broadly applicable for establishing immortalized epithelial cell lines from primary human tissues for cancer research
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