3,209 research outputs found
Time of primordial Be-7 conversion into Li-7, energy release and doublet of narrow cosmological neutrino lines
One of the important light elements created during the big bang
nucleosynthesis is Be-7 which then decays to Li-7 by electron capture when
recombination becomes effective but well before the Saha equilibrium
recombination is reached. This means that Be-7 should wait until its
recombination epoch even though the half-life of the hydrogenic beryllium atom
is only 106.4 days. We calculate when the conversion from primordial Be-7 to
Li-7 occurs taking into account the population of the hyperfine structure
sublevels and solving the kinetic equations for recombination, photoionization
and conversion rate. We also calculate the energies and the spectrum of narrow
neutrino doublet lines resulting from Be-7 decay.Comment: Minor typos correcte
Phonon sidebands of color centers in hexagonal boron nitride
Low temperature photoluminescence spectra of a color center in hexagonal
boron nitride are analyzed. The acoustic phonon sideband can be described by a
deformation coupling proportional to strain to a phonon bath that is
effectively two dimensional. The optical phonon band is described by Frohlich
coupling to the LO-branches, and a deformation coupling proportional to lattice
displacement for the TO-branch. The resonances expressed in the optical band
vary from defect to defect, in some emitters, coupling to out-of-plane
polarized phonons is reported.Comment: 7 pages, 4 fig
Preventing stroke at door step– need for a paradigm shift in delivery of preventive healthcare
Although stroke is a preventable disease, it is increasing globally. Only few risk factors are responsible for much of the leading noncommunicable diseases, yet those remain poorly controlled, despite being the most affordable way of promoting health and preventing disease [1]. Lifestyle modification including cessation of smoking, making aerobic physical activity a routine, certain changes in diet, and aggressive management of risk factors are all part of stroke prevention strategies [2]
Pulsing corals: A story of scale and mixing
Effective methods of fluid transport vary across scale. A commonly used
dimensionless number for quantifying the effective scale of fluid transport is
the Reynolds number, Re, which gives the ratio of inertial to viscous forces.
What may work well for one Re regime may not produce significant flows for
another. These differences in scale have implications for many organisms,
ranging from the mechanics of how organisms move through their fluid
environment to how hearts pump at various stages in development. Some
organisms, such as soft pulsing corals, actively contract their tentacles to
generate mixing currents that enhance photosynthesis. Their unique morphology
and intermediate scale where both viscous and inertial forces are significant
make them a unique model organism for understanding fluid mixing. In this
paper, 3D fluid-structure interaction simulations of a pulsing soft coral are
used to quantify fluid transport and fluid mixing across a wide range of Re.
The results show that net transport is negligible for , and continuous
upward flow is produced for .Comment: 8 pages, 8 figure
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