253 research outputs found
The imprint of the interaction between dark sectors in large scale cosmic microwave background anisotropies
Dark energy interacting with dark matter is a promising model to solve the
cosmic coincidence problem. We study the signature of such interaction on large
scale cosmic microwave background (CMB) temperature anisotropies. Based on the
detail analysis in perturbation equations of dark energy and dark matter when
they are in interaction, we find that the large scale CMB, especially the late
Integrated Sachs Wolfe effect, is a useful tool to measure the coupling between
dark sectors. We also discuss the possibility to detect the coupling by
cross-correlating CMB maps with tracers of the large scale structure. We
finally perform the global fitting to constrain the coupling by using the CMB
power spectrum data together with other observational data. We find that in the
range, the constrained coupling between dark sectors can solve the
coincidence problem.Comment: 17 pages, 9 figures, revised version, more discussions added,
accepted for publication in PR
The ergodicity bias in the observed galaxy distribution
The spatial distribution of galaxies we observed is subject to the given
condition that we, human beings are sitting right in a galaxy -- the Milky Way.
Thus the ergodicity assumption is questionable in interpretation of the
observed galaxy distribution. The resultant difference between observed
statistics (volume average) and the true cosmic value (ensemble average) is
termed as the ergodicity bias. We perform explicit numerical investigation of
the effect for a set of galaxy survey depths and near-end distance cuts. It is
found that the ergodicity bias in observed two- and three-point correlation
functions in most cases is insignificant for modern analysis of samples from
galaxy surveys and thus close a loophole in precision cosmology. However, it
may become non-negligible in certain circumstances, such as those applications
involving three-point correlation function at large scales of local galaxy
samples. Thus one is reminded to take extra care in galaxy sample construction
and interpretation of the statistics of the sample, especially when the
characteristic redshift is low.Comment: Revised version published as JCAP08(2010)01
The Mechanism of Secretion and Metabolism of Gut-Derived 5-Hydroxytryptamine
Serotonin, also known as 5-hydroxytryptamine (5-HT), is a metabolite of tryptophan and is reported to modulate the development and neurogenesis of the enteric nervous system, gut motility, secretion, inflammation, sensation, and epithelial development. Approximately 95% of 5-HT in the body is synthesized and secreted by enterochromaffin (EC) cells, the most common type of neuroendocrine cells in the gastrointestinal (GI) tract, through sensing signals from the intestinal lumen and the circulatory system. Gut microbiota, nutrients, and hormones are the main factors that play a vital role in regulating 5-HT secretion by EC cells. Apart from being an important neurotransmitter and a paracrine signaling molecule in the gut, gut-derived 5-HT was also shown to exert other biological functions (in autism and depression) far beyond the gut. Moreover, studies conducted on the regulation of 5-HT in the immune system demonstrated that 5-HT exerts anti-inflammatory and proinflammatory effects on the gut by binding to different receptors under intestinal inflammatory conditions. Understanding the regulatory mechanisms through which 5-HT participates in cell metabolism and physiology can provide potential therapeutic strategies for treating intestinal diseases. Herein, we review recent evidence to recapitulate the mechanisms of synthesis, secretion, regulation, and biofunction of 5-HT to improve the nutrition and health of humans
Nonlinear Transport of Graphene in the Quantum Hall Regime
We have studied the breakdown of the integer quantum Hall (QH) effect with
fully broken symmetry, in an ultra-high mobility graphene device sandwiched
between two single crystal hexagonal boron nitride substrates. The evolution
and stabilities of the QH states are studied quantitatively through the
nonlinear transport with dc Hall voltage bias. The mechanism of the QH
breakdown in graphene and the movement of the Fermi energy with the electrical
Hall field are discussed. This is the first study in which the stabilities of
fully symmetry broken QH states are probed all together. Our results raise the
possibility that the v=6 states might be a better target for the quantum
resistance standard.Comment: 15 pages,6 figure
The Sunyaev Zel'dovich effect: simulation and observation
The Sunyaev Zel'dovich effect (SZ effect) is a complete probe of ionized
baryons, the majority of which are likely hiding in the intergalactic medium.
We ran a CDM simulation using a moving mesh hydro code to
compute the statistics of the thermal and kinetic SZ effect such as the power
spectra and measures of non-Gaussianity. The thermal SZ power spectrum has a
very broad peak at multipole with temperature fluctuations
K. The power spectrum is consistent with available
observations and suggests a high and a possible role of
non-gravitational heating. The non-Gaussianity is significant and increases the
cosmic variance of the power spectrum by a factor of for .
We explore optimal driftscan survey strategies for the AMIBA CMB
interferometer and their dependence on cosmology. For SZ power spectrum
estimation, we find that the optimal sky coverage for a 1000 hours of
integration time is several hundred square degrees. One achieves an accuracy
better than 40% in the SZ measurement of power spectrum and an accuracy better
than 20% in the cross correlation with Sloan galaxies for . For
cluster searches, the optimal scan rate is around 280 hours per square degree
with a cluster detection rate 1 every 7 hours, allowing for a false positive
rate of 20% and better than 30% accuracy in the cluster SZ distribution
function measurement.Comment: 34 pages, 20 figures. Submitted to ApJ. Simulation maps have been
replaced by high resolution images. For higher resolution color images,
please download from http://www.cita.utoronto.ca/~zhangpj/research/SZ/ We
corrected a bug in our analysis. the SZ power spectrum decreases 50% and y
parameter decrease 25
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