10 research outputs found
Short-term Effects of Gamma Ray Bursts on Earth
The aim of the present work is to study the potential short-term atmospheric
and biospheric influence of Gamma Ray Bursts on the Earth. We focus in the
ultraviolet flash at the planet's surface, which occurs as a result of the
retransmission of the radiation through the atmosphere. This would be
the only important short-term effect on life. We mostly consider Archean and
Proterozoic eons, and for completeness we also comment on the Phanerozoic.
Therefore, in our study we consider atmospheres with oxygen levels ranging from
to 1% of the present atmospheric level, representing different
moments in the oxygen rise history. Ecological consequences and some strategies
to estimate their importance are outlined.Comment: 13 pp., to appear in Astrophysics and Space Scienc
Inhomogeneous models of interacting dark matter and dark energy
We derive and analyze a class of spherically symmetric cosmological models
whose source is an interactive mixture of inhomogeneous cold dark matter (DM)
and a generic homogeneous dark energy (DE) fluid. If the DE fluid corresponds
to a quintessense scalar field, the interaction term can be associated with a
well motivated non--minimal coupling to the DM component. By constructing a
suitable volume average of the DM component we obtain a Friedman evolution
equation relating this average density with an average Hubble scalar, with the
DE component playing the role of a repulsive and time-dependent term.
Once we select an ``equation of state'' linking the energy density () and
pressure () of the DE fluid, as well as a free function governing the radial
dependence, the models become fully determinate and can be applied to known
specific DE sources, such as quintessense scalar fields or tachyonic fluids.
Considering the simple equation of state with , we show that the free parameters and boundary conditions can be selected
for an adequate description of a local DM overdensity evolving in a suitable
cosmic background that accurately fits current observational data. While a DE
dominated scenario emerges in the asymptotic future, with total and
tending respectively to 1 and -1/2 for all cosmic observers, the effects of
inhomogeneity and anisotropy yield different local behavior and evolution rates
for these parameters in the local overdense region. We suggest that the models
presented can be directly applied to explore the effects of various DE
formalisms on local DM cosmological inhomogeneities.Comment: 15 pages, revtex4, 10 eps figure
Follow-Up Study Confirms the Presence of Gastric Cancer DNA Methylation Hallmarks in High-Risk Precursor Lesions
Intestinal metaplasia confers an increased risk of progression to gastric cancer. However, some intestinal metaplasia patients do not develop cancer. The development of robust molecular biomarkers to stratify patients with advanced gastric precursor lesions at risk of cancer progression will contribute to guiding programs for prevention. Starting from a genome-wide methylation study, we have simplified the detection method regarding candidate-methylation tests to improve their applicability in the clinical environment. We identified CpG methylation at the ZNF793 and RPRM promoters as a common event in intestinal metaplasia and intestinal forms of gastric cancer. Furthermore, we also showed that Helicobacter pylori infection influences DNA methylation in early precursor lesions but not in intestinal metaplasia, suggesting that therapeutic strategies to prevent epigenome reprogramming toward a cancer signature need to be adopted early in the precursor cascade. To adopt prevention strategies in gastric cancer, it is imperative to develop robust biomarkers with acceptable costs and feasibility in clinical practice to stratified populations according to risk scores. With this aim, we applied an unbiased genome-wide CpG methylation approach to a discovery cohort composed of gastric cancer (n = 24), and non-malignant precursor lesions (n = 64). Then, candidate-methylation approaches were performed in a validation cohort of precursor lesions obtained from an observational longitudinal study (n = 264), with a 12-year follow-up to identify repression or progression cases. H. pylori stratification and histology were considered to determine their influence on the methylation dynamics. As a result, we ascertained that intestinal metaplasia partially recapitulates patterns of aberrant methylation of intestinal type of gastric cancer, independently of the H. pylori status. Two epigenetically regulated genes in cancer, RPRM and ZNF793, consistently showed increased methylation in intestinal metaplasia with respect to earlier precursor lesions. In summary, our result supports the need to investigate the practical utilities of the quantification of DNA methylation in candidate genes as a marker for disease progression. In addition, the H. pylori-dependent methylation in intestinal metaplasia suggests that pharmacological treatments aimed at H. pylori eradication in the late stages of precursor lesions do not prevent epigenome reprogramming toward a cancer signature
Short-term effects of gamma ray bursts on oceanic photosynthesis
We continue our previous work on the potential
short-term influence of a gamma ray bursts on Earthâs
biosphere, focusing on the only important short-term effect
on life: the ultraviolet flash which occurs as a result of the
retransmission of the Îł radiation through the atmosphere.
Thus, in this work we calculate the ultraviolet irradiances
penetrating the first hundred meters of the water column, for
Jerlovâs ocean water types I, II and III. Then we estimate the
UV flash potential for photosynthesis inhibition in the whole
photic zone, showing that it can be important in the first tens
of meters of the water column.Peer reviewe
On the Habitability of Aquaplanets
An Aquatic Habitability Index is proposed, based on Quantitative Habitability Theory, and considering a very general model for life. It is a primary habitability index, measuring habitability for phytoplankton in the first place. The index is applied to some case studies, such as the habitability changes in Earth due to environmental perturbations caused by asteroid impacts.We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).Peer reviewe