GeV Gamma-Ray Attenuation and the High-Redshift UV Background

We present new calculations of the evolving UV background out to the epoch of cosmological reionization and make predictions for the amount of GeV gamma-ray attenuation by electron-positron pair production. Our results are based on recent semi-analytic models of galaxy formation, which provide predictions of the dust-extinguished UV radiation field due to starlight, and empirical estimates of the contribution due to quasars. We account for the reprocessing of ionizing photons by the intergalactic medium. We test whether our models can reproduce estimates of the ionizing background at high redshift from flux decrement analysis and proximity effect measurements from quasar spectra, and identify a range of models that can satisfy these constraints. Pair-production against soft diffuse photons leads to a spectral cutoff feature for gamma rays observed between 10 and 100 GeV. This cutoff varies with redshift and the assumed star formation and quasar evolution models. We find only negligible amounts of absorption for gamma rays observed below 10 GeV for any emission redshift. With observations of high-redshift sources in sufficient numbers by the Fermi Gamma-ray Space Telescope and new ground-based instruments it should be possible to constrain the extragalactic background light in the UV and optical portion of the spectrum.Comment: 19 pages, 12 figures, Accepted for publication in MNRAS, this version includes minor correction

Mixing of Active and Sterile Neutrinos

We investigate mixing of neutrinos in the $\nu$MSM (neutrino Minimal Standard Model), which is the MSM extended by three right-handed neutrinos. Especially, we study elements of the mixing matrix $\Theta_{\alpha I}$ between three left-handed neutrinos $\nu_\alpha$ ($\alpha = e,\mu,\tau$) and two sterile neutrinos $N_I$ ($I=2,3$) which are responsible to the seesaw mechanism generating the suppressed masses of active neutrinos as well as the generation of the baryon asymmetry of the universe (BAU). It is shown that $\Theta_{eI}$ can be suppressed by many orders of magnitude compared with $\Theta_{\mu I}$ and $\Theta_{\tau I}$, when the Chooz angle $\theta_{13}$ is large in the normal hierarchy of active neutrino masses. We then discuss the neutrinoless double beta decay in this framework by taking into account the contributions not only from active neutrinos but also from all the three sterile neutrinos. It is shown that $N_2$ and $N_3$ give substantial, destructive contributions when their masses are smaller than a few 100 MeV, and as a results $\Theta_{e I}$ receive no stringent constraint from the current bounds on such decay. Finally, we discuss the impacts of the obtained results on the direct searches of $N_{2,3}$ in meson decays for the case when $N_{2,3}$ are lighter than pion mass. We show that there exists the allowed region for $N_{2,3}$ with such small masses in the normal hierarchy case even if the current bound on the lifetimes of $N_{2,3}$ from the big bang nucleosynthesis is imposed. It is also pointed out that the direct search by using $\pi^+ \to e^+ + N_{2,3}$ and $K^+ \to e^+ + N_{2,3}$ might miss such $N_{2,3}$ since the branching ratios can be extremely small due to the cancellation in $\Theta_{eI}$, but the search by $K^+ \to \mu^+ + N_{2,3}$ can cover the whole allowed region by improving the measurement of the branching ratio by a factor of 5.Comment: 30 pages, 32 figure

Regulation of the High Affinity IgE Receptor (FcεRI) in Human Neutrophils: Role of Seasonal Allergen Exposure and Th-2 Cytokines

The high affinity IgE receptor, FcεRI, plays a key role in the immunological pathways involved in allergic asthma. Previously we have demonstrated that human neutrophils isolated from allergic asthmatics express a functional FcεRI, and therefore it was of importance to examine the factors regulating its expression. In this study, we found that neutrophils from allergic asthmatics showed increased expression of FcεRI-α chain surface protein, total protein and mRNA compared with those from allergic non asthmatics and healthy donors (p<0.001). Interestingly, in neutrophils isolated from allergic asthmatics, FcεRI-α chain surface protein and mRNA expression were significantly greater during the pollen season than outside the pollen season (n = 9, P = 0.001), an effect which was not observed either in the allergic non asthmatic group or the healthy donors (p>0.05). Allergen exposure did not affect other surface markers of neutrophils such as CD16/FcγRIII or IL-17R. In contrast to stimulation with IgE, neutrophils incubated with TH2 cytokines IL-9, GM-CSF, and IL-4, showed enhanced FcεRI-α chain surface expression. In conclusion, these results suggest that enhanced FcεRI expression in human neutrophils from allergic asthmatics during the pollen season can make them more susceptible to the biological effects of IgE, providing a possible new mechanism by which neutrophils contribute to allergic asthma

Detection of intergalactic red-giant-branch stars in the Virgo cluster

It has been suspected for nearly 50 years that clusters of galaxies contain a population of intergalactic stars, ripped from galaxies during cluster formation or when the galaxies' orbits take them through the cluster center. Support for the existence of such a population of free-floating stars comes from measurements of the diffuse light in clusters, and from recent detections of planetary nebulae with positions and/or velocities far removed from any observed cluster galaxy. But estimates for the mass of the diffuse population and its distribution relative to the galaxies are still highly uncertain. Here we report the direct detection of intergalactic stars in deep images of a blank field in the Virgo Cluster. The data suggest that approximately 10% of the stellar mass of the cluster is in intergalactic stars. We observe a relatively homogeneous distribution of stars, with evidence of a slight gradient toward M87.Comment: Accepted for publication in Nature. 10 pages, 2 postscript figures included. Uses nature.sty and astrobib.sty. (Astrobib is available from http://www.stsci.edu/software/TeX.html.

Bayesian analysis of cosmic structures

We revise the Bayesian inference steps required to analyse the cosmological large-scale structure. Here we make special emphasis in the complications which arise due to the non-Gaussian character of the galaxy and matter distribution. In particular we investigate the advantages and limitations of the Poisson-lognormal model and discuss how to extend this work. With the lognormal prior using the Hamiltonian sampling technique and on scales of about 4 h^{-1} Mpc we find that the over-dense regions are excellent reconstructed, however, under-dense regions (void statistics) are quantitatively poorly recovered. Contrary to the maximum a posteriori (MAP) solution which was shown to over-estimate the density in the under-dense regions we obtain lower densities than in N-body simulations. This is due to the fact that the MAP solution is conservative whereas the full posterior yields samples which are consistent with the prior statistics. The lognormal prior is not able to capture the full non-linear regime at scales below ~ 10 h^{-1} Mpc for which higher order correlations would be required to describe the matter statistics. However, we confirm as it was recently shown in the context of Ly-alpha forest tomography that the Poisson-lognormal model provides the correct two-point statistics (or power-spectrum).Comment: 11 pages, 1 figure, report for the Astrostatistics and Data Mining workshop, La Palma, Spain, 30 May - 3 June 2011, to appear in Springer Series on Astrostatistic

f(R) theories

Over the past decade, f(R) theories have been extensively studied as one of the simplest modifications to General Relativity. In this article we review various applications of f(R) theories to cosmology and gravity - such as inflation, dark energy, local gravity constraints, cosmological perturbations, and spherically symmetric solutions in weak and strong gravitational backgrounds. We present a number of ways to distinguish those theories from General Relativity observationally and experimentally. We also discuss the extension to other modified gravity theories such as Brans-Dicke theory and Gauss-Bonnet gravity, and address models that can satisfy both cosmological and local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in Relativity, Published version, Comments are welcom

Cognitive and psychological science insights to improve climate change data visualization

Visualization of climate data plays an integral role in the communication of climate change findings to both expert and non-expert audiences. The cognitive and psychological sciences can provide valuable insights into how to improve visualization of climate data based on knowledge of how the human brain processes visual and linguistic information. We review four key research areas to demonstrate their potential to make data more accessible to diverse audiences: directing visual attention, visual complexity, making inferences from visuals, and the mapping between visuals and language. We present evidence-informed guidelines to help climate scientists increase the accessibility of graphics to non-experts, and illustrate how the guidelines can work in practice in the context of Intergovernmental Panel on Climate Change graphics

Skeletal carbonate mineralogy of Scottish bryozoans

This paper describes the skeletal carbonate mineralogy of 156 bryozoan species collected from Scotland (sourced both from museum collections and from waters around Scotland) and collated from literature. This collection represents 79% of the species which inhabit Scottish waters and is a greater number and proportion of extant species than any previous regional study. The study is also of significance globally where the data augment the growing database of mineralogical analyses and offers first analyses for 26 genera and four families. Specimens were collated through a combination of field sampling and existing collections and were analysed by X-ray diffraction (XRD) and micro-XRD to determine wt% MgCO3 in calcite and wt% aragonite. Species distribution data and phylogenetic organisation were applied to understand distributional, taxonomic and phylo-mineralogical patterns. Analysis of the skeletal composition of Scottish bryozoans shows that the group is statistically different from neighbouring Arctic fauna but features a range of mineralogy comparable to other temperate regions. As has been previously reported, cyclostomes feature low Mg in calcite and very little aragonite, whereas cheilostomes show much more variability, including bimineralic species. Scotland is a highly variable region, open to biological and environmental influx from all directions, and bryozoans exhibit this in the wide range of within-species mineralogical variability they present. This plasticity in skeletal composition may be driven by a combination of environmentally-induced phenotypic variation, or physiological factors. A flexible response to environment, as manifested in a wide range of skeletal mineralogy within a species, may be one characteristic of successful invasive bryozoans

Novel insights into the aetiology and pathophysiology of increased airway inflammation during COPD exacerbations

Airway inflammation increases during acute exacerbations of COPD. Extrinsic factors, such as airway infections, increased air pollution, and intrinsic factors, such as increased oxidative stress and altered immunity may contribute to this increase. The evidence for this and the potential mechanisms by which various aetiological agents increase inflammation during COPD exacerbations is reviewed. The pathophysiologic consequences of increased airway inflammation during COPD exacerbations are also discussed. This review aims to establish a cause and effect relationship between etiological factors of increased airway inflammation and COPD exacerbations based on recently published data. Although it can be speculated that reducing inflammation may prevent and/or treat COPD exacerbations, the existing anti-inflammatory treatments are modestly effective