Climate crystal ball?
Recent research has indicated that ocean temperatures and other properties of the North Atlantic region vary on a decadal scale. These results suggest that long-term climate in this region may be predictable if the origins of the patterns can be understood. Griffies and Bryan (p. 181) used a global climate model to examine the long-term response of the ocean to short-term fluctuations in atmospheric forcing. The results suggest that predictability of the Atlantic climate depends in part on variations in high-latitude ocean temperatures.
Massive astrophysical objects can bend light, a phenomenon known as gravitational lensing. Einstein published a short communication on this phenomenon in Science in 1936, but earlier derivations by others are also known. Now, Renn et al. (p. 184) have unearthed Einstein's research notes on gravitational lensing that date back to 1912, 3 years before he put the finishing touches on his theory of general relativity. Einstein finally published the work 24 years later at the urging of an amateur scientist.
Nanotubes and quantum effects
Electronic effects that arise from the confinement of electrons along a quantum wire have been observed from single wall carbon nanotubes (SWNTs). Rao et al. (p. 187) obtained Raman spectra from highly pure SWNTs and assigned peaks for different diameter tubes through model calculations. Changes in peak intensity at different excitation frequencies indicate that a resonant Raman scattering process occurs. As the electronic densities of states change with diameter, different sizes of SWNTs couple to the laser field, which enhances their spectral intensity.
Rift in action
A mid-ocean rift system is exposed in Iceland and thus can be easily observed with geodetic instruments. Vadon and Sigmundsson (p. 193) used satellite radar interferometry to observe the deformation associated with rifting and volcanism from 1992 to 1995 where the ridge comes onshore in southwest Iceland. The results show that the plate boundary subsided during this period when spreading was not fully compensated by inflow of new magma.
More from Mariner
Mariner 10, the only satellite to visit Mercury, mapped about one-half of the surface. Robinson and Lucey (p. 197) recalibrated the Mariner 10 images to produce images that include more of the ultraviolet to visible color spectral data. They interpret the variations in the colors using correlations derived from more detailed maps of the moon. They infer that the plains deposits on Mercury are derived from volcanism and suggest that the smallest terrestrial planet in our solar system may have undergone differentiation.
Keeps on ticking
In higher organisms, circadian rhythms are controlled by clock proteins, which use a feedback loop to keep time—the protein is transported back to the nucleus, where it can disrupt its own expression. Prokaryotes can divide much faster than the circadian cycle time and lack a nuclear membrane, but Kondo et al. (p. 224) found evidence for circadian rhythms in wild-type and period-mutant reporter strains of the cyanobacterium Synechococcus. Even though these cells could have doubling times as short as 5 or 6 hours, their bioluminescence exhibited circadian oscillations.
A few grapes a day...
An important goal of cancer research is to identify chemopreventive agents, chemicals that reduce the risk of carcinogenesis and that can be safely ingested. Jang et al. (p. 218) have isolated and characterized a candidate chemopreventive agent from grapes. This agent, called resveratrol, was shown to inhibit a variety of biochemical and cellular events associated with carcinogenesis in experimental models. These results raise the possibility that resveratrol, a naturally occurring dietary component, may have chemopreventive activity in humans.
The decapentaplegic (DPP) protein of Drosophila is related to transforming growth factor-β (TGF-β) and functions during development to regulate differentiation. Penton et al. (p. 203) report that in the developing Drosophila eye, DPP has a different role. Rather than controlling cell fate, DPP promotes synchronization of the cell division cycle. Although in other instances TGF-β family members cause arrest of the cell cycle in the G1 phase, DPP appears to act in the developing eye to promote progression through the G2 and M phases of the cell cycle.
Neuronal give and take
Single neurons are complex computational devices. In two reports in this issue (Magee and Johnston, p. 209, and Markram et al., p. 213), also discussed in a Perspective by Sejnowski on p. 178, neurons of the hippocampus and cortex are shown to send, along with an action potential to the next downstream neuron, a feedback signal from the cell body to the dendrites that alters the efficacy of the dendritic input synapses. Other work, in part presented by Abbott et al. on p. 221 and discussed in a Perspective by Thomson on p. 179, examines the summed effect of many such plastic synapses on cortical neurons both experimentally and by constructing models. The results suggest that under certain circumstances these neurons act as coincidence detectors, but at other times they can respond to changes in the frequency of their input.