We report 230Th-238U disequilibrium data on mid-ocean ridge basalts recovered 5 to 40 kilometers off the ridge axis near 9 degrees 30'N of the East Pacific Rise. These data indicate near-symmetrical eruptions of normal mid-ocean ridge basalts (NMORBs) and incompatible element-enriched mid-ocean ridge basalts (EMORBs) as far as 20 kilometers off axis. Our results suggest large-scale subsurface l...

How much dissolved oxygen was present in the mid-Proterozoic oceans between 1.8 and 1.0 billion years ago is debated vigorously. One model argues for oxygenation of the oceans soon after the initial rise of atmospheric oxygen approximately 2.3 billion years ago. Recent evidence for H(2)S in some mid-Proterozoic marine basins suggests, however, that the deep ocean remained anoxic until much late...

Cross-spectral techniques are used to analyze the relationship between gravity and bathymetry at the Mid-Atlantic Ridge and the East Pacific Rise crests. The resulting transfer functions were used to study the nature of the isostatic mechanism operative at these ridge crests. The most satisfactory results were obtained for models in which the oceanic lithosphere is treated as a thin elastic pla...

In Chile, office buildings are typically reinforced concrete (RC) structures whose lateral load-resisting system comprises core structural walls and perimeter moment frames (i.e., dual wall-frame system). the last 20 years, nearly 800 new have been built in country roughly 70% of them less than ten stories. Although seismic performance these was deemed satisfactory previous earthquakes, their a...

Professional liability insurance crises in medicine have been intermittent, reaching magnitudes sucient to generate widespread concern only in the mid-1970s, the mid-1980s, and 2002-2003. It is easy for health policymakers and the public to view each crisis as an upswing of the same pendulum. Malpractice premiums rise, doctors accuse lawyers, lawyers point back at doctors, and legislatures deb...

The mathematical study of genealogies has yielded important insights in population biology, such as the ability to estimate the time to the most recent common ancestor (MRCA) of a sample of genetic sequences or of a group of individuals. Here we introduce a model of cultural genealogies that is a step toward answering similar questions for cultural traits. In our model individuals can inherit f...