The effects of aging of scientists on their publication and citation patterns

The average age at which U.S. researchers get their first grant from NIH has increased from 34.3 in 1970, to 41.7 in 2004. These data raise the crucial question of the effects of aging on the scientific creativity and productivity of researchers. Those who worry about the aging of scientists usually believe that the younger they are the more creative and productive they will be. Using a large population of 13,680 university professors in Quebec, we show that, while scientific productivity rises sharply between 28 and 40, it increases at a slower pace between 41 and 50 and stabilizes afterward until retirement for the most active researchers. The average scientific impact per paper decreases linearly until 50-55 years old, but the average number of papers in highly cited journals and among highly cited papers rises continuously until retirement. Our results clearly show for the first time the natural history of the scientific productivity of scientists over their entire career and bring to light the fact that researchers over 55 still contribute significantly to the scientific community by producing high impact papers.Comment: 12 pages, 4 figure

Re–Os and U–Pb geochronology of the Shazigou Mo polymetallic ore field, Inner Mongolia: Implications for Permian–Triassic mineralization at the northern margin of the North China Craton

The recently discovered polymetallic Shazigou Mo–W–Pb–Zn ore field is located at the northern margin of the North China Craton. This integrated metallogenic system is comprised of quartz vein mineralization in three deposits: Shazigou Mo–W, Jindouzishan Pb–Zn and Mantougou Pb–Zn. The total reserves are estimated to be 50 kt Mo, 626 t WO3, 244 kt Pb and 150 kt Zn. Molybdenite Re–Os dating of five quartz vein-type ores yielded a mean model age of 243.8 ± 1.6 Ma (MSWD = 0.81) and hydrothermal zircons yielded a concordant U–Pb age of 245 ± 2.6 Ma (MSWD = 0.65). These results suggest that the mineralization was formed in the early Triassic and could be related to Paleo-Asian Ocean subduction. Microthermometry and quartz fluid inclusion compositions indicate that fluids related to the Mo–W mineralization were mainly derived from magmatic sources and precipitated under relatively high temperature (280–340 °C) and salinity conditions (6–9 wt% NaCl equiv.), whereas subsequent Pb–Zn mineralization-related fluids may have been modified by metamorphic and meteoric waters. The discovery of the Shazigou ore field suggests conditions may be favourable for more extensive mineralization in the western Xilamulun Mo metallogenic belt at the northern margin of the North China Craton

Development of a Low-Aspect Ratio Fin for Flight Research Experiments

A second-generation flight test fixture, developed at NASA Dryden Flight Research Center, offers a generic testbed for aerodynamic and fluid mechanics research. The new fixture, a low-aspect ratio vertical fin shape mounted on the centerline of an F-15B aircraft lower fuselage, is designed for flight research at Mach numbers up to 2.0. The new fixture is a composite structure with a modular configuration and removable components for functional flexibility. This report describes the multidisciplinary design and analysis approach used to develop the fixture. The approach integrates conservative assumptions with simple analysis techniques to minimize the time and cost associated with its development. Presented are the principal disciplines required for this effort, which include aerodynamics, structures, stability, and operational considerations. In addition, preliminary results from the first phase of flight testing are presented. Acceptable directional stability and flow quality are doc..

Evolution of arc‐continent collision in the southeastern margin of the South China Sea: insight From the Isugod Basin in Central‐Southern Palawan

The evolution of arc‐continent collision between the Palawan microcontinental block and the Cagayan Ridge in the southeastern margin of the South China Sea (SCS) is vital to understand how this collision correlated with seafloor spreading of the SCS. To address the evolution of arc‐continent collision, we studied the biostratigraphy and provenance of syn‐collisional sediments in the Isugod Basin in central‐southern Palawan. Microfossil analysis indicates a Late Miocene age (11.5–5.6 Ma) for the Isugod and Alfonso XIII Formations and rapid subsidence during initiation of the basin which may have been triggered by local extensional collapse of the wedge in response to forearc uplift. Multidisciplinary provenance analysis reveals that the Isugod and Alfonso XIII Formations were derived from the Middle Eocene–lower Oligocene Panas‐Pandian Formation on the Palawan wedge and the Late Eocene Central Palawan Ophiolite. These results suggest the emergence of both the orogenic wedge and obducted forearc ophiolite at ∼11.5 Ma, implying collision onset before ∼11.5 Ma. The collision initiation in Palawan could be better constrained to ∼18 Ma, based on the drowning of the Nido carbonate platform in the foreland. Therefore, the gravitational collapse of the Palawan wedge and the subsidence/formation of the Isugod Basin might reflect a significant uplift pulse in the hinterland of the wedge beginning within 13.4–11.5 Ma in the late stage of collision. It indicates that although compression originated from spreading of the SCS had ceased at 16–15 Ma, arc‐continent collision in Palawan did not stop and was sustained by compression from the upper plate afterward