35 research outputs found
Local Void vs Dark Energy: Confrontation with WMAP and Type Ia Supernovae
It is now a known fact that if we happen to be living in the middle of a
large underdense region, then we will observe an "apparent acceleration", even
when any form of dark energy is absent. In this paper, we present a "Minimal
Void" scenario, i.e. a "void" with minimal underdensity contrast (of about
-0.4) and radius (~ 200-250 Mpc/h) that can, not only explain the supernovae
data, but also be consistent with the 3-yr WMAP data. We also discuss
consistency of our model with various other measurements such as Big Bang
Nucleosynthesis, Baryon Acoustic Oscillations and local measurements of the
Hubble parameter, and also point out possible observable signatures.Comment: Minor numerical errors and typos corrected, references adde
Apoptosis Regulates ipRGC Spacing Necessary for Rods and Cones to Drive Circadian Photoentrainment
SummaryThe retina consists of ordered arrays of individual types of neurons for processing vision. Here, we show that such order is necessary for intrinsically photosensitive retinal ganglion cells (ipRGCs) to function as irradiance detectors. We found that during development, ipRGCs undergo proximity-dependent Bax-mediated apoptosis. Bax mutant mice exhibit disrupted ipRGC spacing and dendritic stratification with an increase in abnormally localized synapses. ipRGCs are the sole conduit for light input to circadian photoentrainment, and either their melanopsin-based photosensitivity or ability to relay rod/cone input is sufficient for circadian photoentrainment. Remarkably, the disrupted ipRGC spacing does not affect melanopsin-based circadian photoentrainment but severely impairs rod/cone-driven photoentrainment. We demonstrate reduced rod/cone-driven cFos activation and electrophysiological responses in ipRGCs, suggesting that impaired synaptic input to ipRGCs underlies the photoentrainment deficits. Thus, for irradiance detection, developmental apoptosis is necessary for the spacing and connectivity of ipRGCs that underlie their functioning within a neural network
Toward an internally consistent astronomical distance scale
Accurate astronomical distance determination is crucial for all fields in
astrophysics, from Galactic to cosmological scales. Despite, or perhaps because
of, significant efforts to determine accurate distances, using a wide range of
methods, tracers, and techniques, an internally consistent astronomical
distance framework has not yet been established. We review current efforts to
homogenize the Local Group's distance framework, with particular emphasis on
the potential of RR Lyrae stars as distance indicators, and attempt to extend
this in an internally consistent manner to cosmological distances. Calibration
based on Type Ia supernovae and distance determinations based on gravitational
lensing represent particularly promising approaches. We provide a positive
outlook to improvements to the status quo expected from future surveys,
missions, and facilities. Astronomical distance determination has clearly
reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press
(chapter 8 of a special collection resulting from the May 2016 ISSI-BJ
workshop on Astronomical Distance Determination in the Space Age