89 research outputs found
Origin of G Magnetic Fields in the Central Engine of Gamma Ray Bursts
Various authors have suggested that the gamma-ray burst (GRB) central engine
is a rapidly rotating, strongly magnetized, G) compact
object. The strong magnetic field can accelerate and collimate the relativistic
flow and the rotation of the compact object can be the energy source of the
GRB. The major problem in this scenario is the difficulty of finding an
astrophysical mechanism for obtaining such intense fields. Whereas, in
principle, a neutron star could maintain such strong fields, it is difficult to
justify a scenario for their creation. If the compact object is a black hole,
the problem is more difficult since, according to general relativity it has "no
hair" (i.e., no magnetic field). Schuster, Blackett, Pauli, and others have
suggested that a rotating neutral body can create a magnetic field by
non-minimal gravitational-electromagnetic coupling (NMGEC). The
Schuster-Blackett form of NMGEC was obtained from the Mikhail and Wanas's
tetrad theory of gravitation (MW). We call the general theory NMGEC-MW.
We investigate here the possible origin of the intense magnetic fields G in GRBs by NMGEC-MW. Whereas these fields are difficult to
explain astrophysically, we find that they are easily explained by NMGEC-MW. It
not only explains the origin of the G fields when the
compact object is a neutron star, but also when it is a black hole.Comment: 9 pages, accepted for publication in JCA
LEAP2 changes with body mass and food intake in humans and mice
Acyl-ghrelin administration increases food intake, body weight, and blood glucose. In contrast, mice lacking ghrelin or ghrelin receptors (GHSRs) exhibit life-threatening
hypoglycemia during starvation-like conditions but do not consistently exhibit overt metabolic phenotypes when given ad libitum food access. These results, and findings of
ghrelin resistance in obese states, imply nutritional state-dependence of ghrelin’s metabolic actions. Here, we hypothesized that LEAP2 (liver enriched antimicrobial
peptide-2), a recently-characterized endogenous GHSR antagonist, blunts ghrelin action during obese states and post-prandially. To test this hypothesis, we determined
changes in plasma LEAP2 and acyl-ghrelin due to fasting, eating, obesity, Roux-en-Y gastric bypass (RYGB), vertical sleeve gastrectomy (VSG), oral glucose administration,
and type 1 diabetes mellitus (T1DM) using humans and/or mice. Our results suggest that plasma LEAP2 is regulated by metabolic status: its levels increase with body mass
and blood glucose, and decrease with fasting, RYGB, and in post-prandial states following VSG. These changes were mostly opposite to those of acyl-ghrelin. Furthermore, using electrophysiology, we showed that LEAP2 both hyperpolarizes and prevents acyl-ghrelin from activating arcuate NPY neurons. We predict that the plasma LEAP2:acyl-ghrelin molar ratio may be a key determinant modulating acyl-ghrelin
activity in response to body mass, feeding status, and blood glucose
Late-time evolution and modeling of the off-axis gamma-ray burst candidate FIRST J141918.9+394036
High Energy Astrophysic
Guided self-assembly of lateral InAs/GaAs quantum-dot molecules for single molecule spectroscopy
We report on the growth and characterization of lateral InAs/GaAs (001) quantum-dot molecules (QDMs) suitable for single QDM optical spectroscopy. The QDMs, forming by depositing InAs on GaAs surfaces with self-assembled nanoholes, are aligned along the [] direction. The relative number of isolated single quantum dots (QDs) is substantially reduced by performing the growth on GaAs surfaces containing stepped mounds. Surface morphology and X-ray measurements suggest that the strain produced by InGaAs-filled nanoholes superimposed to the strain relaxation at the step edges are responsible for the improved QDM properties. QDMs are Ga-richer compared to single QDs, consistent with strain- enhanced intermixing. The high optical quality of single QDMs is probed by micro-photoluminescence spectroscopy in samples with QDM densities lower than 108 cm−2
The emergence of a new source of X-rays from the binary neutron star merger GW170817
The binary neutron-star (BNS) merger GW170817 is the first celestial object
from which both gravitational waves (GWs) and light have been detected enabling
critical insight on the pre-merger (GWs) and post-merger (light) physical
properties of these phenomena. For the first years after the merger
the detected radio and X-ray radiation has been dominated by emission from a
structured relativistic jet initially pointing degrees away from
our line of sight and propagating into a low-density medium. Here we report on
observational evidence for the emergence of a new X-ray emission component at
days after the merger. The new component has luminosity at 1234 days, and represents a - excess compared to the expectations from the off-axis
jet model that best fits the multi-wavelength afterglow of GW170817 at earlier
times. A lack of detectable radio emission at 3 GHz around the same time
suggests a harder broadband spectrum than the jet afterglow. These properties
are consistent with synchrotron emission from a mildly relativistic shock
generated by the expanding merger ejecta, i.e. a kilonova afterglow. In this
context our simulations show that the X-ray excess supports the presence of a
high-velocity tail in the merger ejecta, and argues against the prompt collapse
of the merger remnant into a black hole. However, radiation from accretion
processes on the compact-object remnant represents a viable alternative to the
kilonova afterglow. Neither a kilonova afterglow nor accretion-powered emission
have been observed before.Comment: 66 pages, 12 figures, Submitte
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