Monday, April 14, 2008

Earth Rise

This image is a still from a high-definition April 5, 2007 video of the Earth rising above the moon as seen by Japan's Kaguya lunar orbiter. The probe was about 236,121 miles (380,000 km) away from Earth at the time. Credit: JAXA/NHK.
High Resolution Video

John A. Wheeler Dies

John A. Wheeler, Physicist Who Coined the Term ‘Black Hole,’ Is Dead at 96 article in the New York Times.

Gecko Acrobatics

Active tails enhance arboreal acrobatics in geckos in PNAS.
Geckos are nature's elite climbers. Their remarkable climbing feats have been attributed to specialized feet with hairy toes that uncurl and peel in milliseconds. Here, we report that the secret to the gecko's arboreal acrobatics includes an active tail. We examine the tail's role during rapid climbing, aerial descent, and gliding. We show that a gecko's tail functions as an emergency fifth leg to prevent falling during rapid climbing. A response initiated by slipping causes the tail tip to push against the vertical surface, thereby preventing pitch-back of the head and upper body. When pitch-back cannot be prevented, geckos avoid falling by placing their tail in a posture similar to a bicycle's kickstand. Should a gecko fall with its back to the ground, a swing of its tail induces the most rapid, zero-angular momentum air-righting response yet measured. Once righted to a sprawled gliding posture, circular tail movements control yaw and pitch as the gecko descends. Our results suggest that large, active tails can function as effective control appendages. These results have provided biological inspiration for the design of an active tail on a climbing robot, and we anticipate their use in small, unmanned gliding vehicles and multisegment spacecraft.

Asian-American Birth Gender Bias

Son-biased sex ratios in the 2000 United States Census in PNAS.
We document male-biased sex ratios among U.S.-born children of Chinese, Korean, and Asian Indian parents in the 2000 U.S. Census. This male bias is particularly evident for third children: If there was no previous son, sons outnumbered daughters by 50%. By contrast, the sex ratios of eldest and younger children with an older brother were both within the range of the biologically normal, as were White offspring sex ratios (irrespective of the elder siblings' sex). We interpret the found deviation in favor of sons to be evidence of sex selection, most likely at the prenatal stage

Let's Not Have a Nuclear War, OK?

Total ozone deviations following 5-Tg soot injection in the upper troposphere.
Atmospheric consequences of nuclear exchange Nuclear winter has been hypothesized to dramatically alter the Earth's climate. Michael Mills et al. have studied ozone depletion as a result of regional nuclear war, developing a computational model that links climate to atmospheric chemistry, and conducting 10-year simulations. The fires that would result from a total exchange of 100 Hiroshima-equivalent nuclear devices (yield 15 kilotons) would generate 5 million tonnes of soot that firestorms and solar heating would loft into the stratosphere. At altitudes up to 60 km, the soot would absorb solar radiation and heat surrounding gases, thus increasing the rate constants for several reactions that break down ozone. The authors found that two chemical reactions in particular would dominate alterations in ozone after a nuclear war: (i) the Chapman cycle, in which an oxygen free radical and ozone combine to form two diatomic molecules; and (ii) a coupled pair of reactions catalyzed by NO and NO2 that similarly produces diatomic oxygen. In the year after a nuclear war, the Chapman cycle would account for the greatest ozone loss, but NOx catalysis would then become dominant and persist for several more years. Mills et al.'s model predicts that the net result in both hemispheres would be an ozone hole extending from 20° north or south latitude to the poles. — K.M.

Massive global ozone loss predicted following regional nuclear conflict in PNAS.
We use a chemistry-climate model and new estimates of smoke produced by fires in contemporary cities to calculate the impact on stratospheric ozone of a regional nuclear war between developing nuclear states involving 100 Hiroshima-size bombs exploded in cities in the northern subtropics. We find column ozone losses in excess of 20% globally, 25–45% at midlatitudes, and 50–70% at northern high latitudes persisting for 5 years, with substantial losses continuing for 5 additional years. Column ozone amounts remain near or <220 Dobson units at all latitudes even after three years, constituting an extratropical "ozone hole." The resulting increases in UV radiation could impact the biota significantly, including serious consequences for human health. The primary cause for the dramatic and persistent ozone depletion is heating of the stratosphere by smoke, which strongly absorbs solar radiation. The smoke-laden air rises to the upper stratosphere, where removal mechanisms are slow, so that much of the stratosphere is ultimately heated by the localized smoke injections. Higher stratospheric temperatures accelerate catalytic reaction cycles, particularly those of odd-nitrogen, which destroy ozone. In addition, the strong convection created by rising smoke plumes alters the stratospheric circulation, redistributing ozone and the sources of ozone-depleting gases, including N2O and chlorofluorocarbons. The ozone losses predicted here are significantly greater than previous "nuclear winter/UV spring" calculations, which did not adequately represent stratospheric plume rise. Our results point to previously unrecognized mechanisms for stratospheric ozone depletion.

Is the Solar System Stable?

On the Dynamical Stability of the Solar System
The experiments yielded one evolution in which Mercury falls onto the Sun at ~1.261Gyr from now, and another in which Mercury and Venus collide in ~862Myr. In the latter solution, as a result of Mercury's unstable behavior, Mars was ejected from the Solar System at ~822Myr. We have performed a number of numerical tests that confirm these results, and indicate that they are not numerical artifacts.

What is a Galaxy?

What is a galaxy? How Cold is Cold Dark Matter? Recent progress in Near Field Cosmology
These data show that there is a bimodal distribution in half-light radii, with stable star clusters always being smaller than 35pc, while stable galaxies are always larger than 120pc. We extend the previously known observational relationships and interpret them in terms of a more fundamental pair of intrinsic properties of dark matter itself: dark matter forms cored mass distributions, with a core scale length of greater than about 100pc, and always has a maximum central mass density with a narrow range.
Galaxies are embedded in dark matter halos with these properties; smaller systems containing dark matter are not observed


SS433 a strange object in our own Galaxy. Aligned Molecular Clouds towards SS433 and L=348.5 degrees; Possible Evidence for Galactic "Vapor Trail" Created by Relativistic Jet

High speed cameras

Nice "slow-motion" videos on the site Vision Research.