Monday, October 05, 2009

The Deep Ocean was Oxygenated Late

Anoxygenic photosynthesis modulated Proterozoic oxygen and sustained Earth's middle age in PNAS.
Molecular oxygen (O2) began to accumulate in the atmosphere and surface ocean ca. 2,400 million years ago (Ma), but the persistent oxygenation of water masses throughout the oceans developed much later, perhaps beginning as recently as 580–550 Ma. For much of the intervening interval, moderately oxic surface waters lay above an oxygen minimum zone (OMZ) that tended toward euxinia (anoxic and sulfidic).

Economic Downturns are Good for Your Health?

Life and death during the Great Depression in PNAS.
Recent events highlight the importance of examining the impact of economic downturns on population health. The Great Depression of the 1930s was the most important economic downturn in the U.S. in the twentieth century. We used historical life expectancy and mortality data to examine associations of economic growth with population health for the period 1920–1940. We conducted descriptive analyses of trends and examined associations between annual changes in health indicators and annual changes in economic activity using correlations and regression models. Population health did not decline and indeed generally improved during the 4 years of the Great Depression, 1930–1933, with mortality decreasing for almost all ages, and life expectancy increasing by several years in males, females, whites, and nonwhites. For most age groups, mortality tended to peak during years of strong economic expansion (such as 1923, 1926, 1929, and 1936–1937). In contrast, the recessions of 1921, 1930–1933, and 1938 coincided with declines in mortality and gains in life expectancy. The only exception was suicide mortality which increased during the Great Depression, but accounted for less than 2% of deaths. Correlation and regression analyses confirmed a significant negative effect of economic expansions on health gains. The evolution of population health during the years 1920–1940 confirms the counterintuitive hypothesis that, as in other historical periods and market economies, population health tends to evolve better during recessions than in expansions.

Cosmic Rays - mysteries of the sources

IceCube: The Rationale for Kilometer-Scale Neutrino Detectors
At a time when IceCube is nearing completion, we revisit the rationale for constructing kilometer-scale neutrino detectors. We focus on the prospect that such observatories reveal the still-enigmatic sources of cosmic rays. While only a "smoking gun" is missing for the case that the Galactic component of the cosmic-ray spectrum originates in supernova remnants, the origin of the extragalactic component remains a mystery. We speculate on neutrino emission from gamma-ray bursts and active galaxies.

Supernova Cosmology

Foundations of Supernova Cosmology
This is a brief sketch of the use of supernovae to measure cosmological parameters. It traces the early work, the events surrounding the discovery and verification of cosmic acceleration using SN Ia, and the efforts today to make sound inferences about the nature of dark energy. The prospects for minimizing systematics by using near-infrared observations in the supernova restframe are emphasized. This could be an important point in the design of a JDEM that employs supernovae to measure the history of cosmic expansion.

Tycho's Nova

The Periodic Table and Group Theory

From the Mendeleev periodic table to particle physics and back to the periodic table
We briefly describe in this paper the passage from Mendeleev's chemistry (1869) to atomic physics (in the 1900's), nuclear physics (in the 1932's) and particle physics (from 1953 to 2006). We show how the consideration of symmetries, largely used in physics since the end of the 1920's, gave rise to a new format of the periodic table in the 1970's. More specifically, this paper is concerned with the application of the group SO(4,2)xSU(2) to the periodic table of chemical elements. It is shown how the Madelung rule of the atomic shell model can be used for setting up a periodic table that can be further rationalized via the group SO(4,2)xSU(2) and some of its subgroups. Qualitative results are obtained from this nonstandard table.