Contribution of the Patagonia Icefields of South America to sea level rise

Digital elevation models of the Northern and Southern Patagonia Icefields of South America generated from the 2000 Shuttle Radar Topography Mission were compared with earlier cartography to estimate the volume change of the largest 63 glaciers. During the period 1968/1975-2000, these glaciers lost ice at a rate equivalent to a sea level rise of 0.042 +/- 0.002 millimeters per year. In the more recent years 1995-2000, average ice thinning rates have more than doubled to an equivalent sea level rise of 0.105 +/- 0.011 millimeters per year. The glaciers are thinning more quickly than can be explained by warmer air temperatures and decreased precipitation, and their contribution to sea level per unit area is larger than that of Alaska glaciers.     

Preserved feedforward but impaired top-down processes in the vegetative state

Frontoparietal cortex is involved in the explicit processing (awareness) of stimuli. Frontoparietal activation has also been found in studies of subliminal stimulus processing. We hypothesized that an impairment of top-down processes, involved in recurrent neuronal message-passing and the generation of long-latency electrophysiological responses, might provide a more reliable correlate of consciousness in severely brain-damaged patients, than frontoparietal responses. We measured effective connectivity during a mismatch negativity paradigm and found that the only significant difference between patients in a vegetative state and controls was an impairment of backward connectivity from frontal to temporal cortices. This result emphasizes the importance of top-down projections in recurrent processing that involve high-order associative cortices for conscious perception.     

Spontaneous cortical activity reveals hallmarks of an optimal internal model of the environment

The brain maintains internal models of its environment to interpret sensory inputs and to prepare actions. Although behavioral studies have demonstrated that these internal models are optimally adapted to the statistics of the environment, the neural underpinning of this adaptation is unknown. Using a Bayesian model of sensory cortical processing, we related stimulus-evoked and spontaneous neural activities to inferences and prior expectations in an internal model and predicted that they should match if the model is statistically optimal. To test this prediction, we analyzed visual cortical activity of awake ferrets during development. Similarity between spontaneous and evoked activities increased with age and was specific to responses evoked by natural scenes. This demonstrates the progressive adaptation of internal models to the statistics of natural stimuli at the neural level.     

Piecing together the biggest puzzle of all

In this month's essay, the last in the Pathways of Discovery series, Martin J. Rees celebrates the way astronomers and cosmologists have systematically uncovered the biography of the universe. Rife with neutron stars, black holes, and multiple universes that emerge from quantum fluctuation, it's a story as grand as it is strange.     

Airborne lead and carbon monoxide at 45th Street, New York City

Daily business-day traffic determines the diurnal lead concentration as well as diurnal carbon monoxide concentration. Daily averages of 7.5 micrograms per cubic meter for lead and 13 parts per million of carbon monoxide were found for the 10-week period of the study. Correlations were demonstrated for lead and traffic and lead and carbon monoxide.     

A chromium terephthalate-based solid with unusually large pore volumes and surface area

We combined targeted chemistry and computational design to create a crystal structure for porous chromium terephthalate, MIL-101, with very large pore sizes and surface area. Its zeotype cubic structure has a giant cell volume (approximately 702,000 cubic angstroms), a hierarchy of extra-large pore sizes (approximately 30 to 34 angstroms), and a Langmuir surface area for N2 of approximately 5900 +/- 300 square meters per gram. Beside the usual properties of porous compounds, this solid has potential as a nanomold for monodisperse nanomaterials, as illustrated here by the incorporation of Keggin polyanions within the cages.     

Plant circadian clocks increase photosynthesis, growth, survival, and competitive advantage

Circadian clocks are believed to confer an advantage to plants, but the nature of that advantage has been unknown. We show that a substantial photosynthetic advantage is conferred by correct matching of the circadian clock period with that of the external light-dark cycle. In wild type and in long- and short-circadian period mutants of Arabidopsis thaliana, plants with a clock period matched to the environment contain more chlorophyll, fix more carbon, grow faster, and survive better than plants with circadian periods differing from their environment. This explains why plants gain advantage from circadian control.