This Week in Science

Science  27 Aug 2004:
Vol. 305, Issue 5688, pp. 1210
  1. Deep Seismic Swarm

    CREDIT: SMITH ET AL.

    The Lake Tahoe Basin in eastern California and western Nevada formed as a down-dropped block of crust between the uplifted Sierra Nevada mountains to the west and the Carson Range to the east. Volcanism related to the tectonics and subsequent glaciations have left one of the deepest lakes in North America surrounded by high mountain peaks. Smith et al. (p. 1277, published online 5 August 2004) measured an extremely deep (25 to 35 kilometers) earthquake swarm beneath Lake Tahoe that was coincident with geodetic displacement measured at one station near the swarm. They infer that the two observations are related to an extremely deep magmatic intrusion, which provides information about the state of volcanic activity and the state of stress beneath the lake.

  2. Testing a Gravity Lens

    The numerous lines of sight that traverse dense stellar fields can provide opportunities for observing a foreground star aligning with a background star. Gravitational microlensing can magnify and bend the light from the background star into an annular ring image. Abe et al. (p. 1264) used the microlensing event, MOA 2003-BLG-32/OGLE 2003-BLG-219, to search for asperities in the ring image that might be created by an extrasolar planet orbiting the background star. They found no extrasolar planets, but they showed that the technique is precise and useful for planet searches.

  3. Riding the Light Waves

    Existing measurement techniques for characterizing light fields and pulses generally provide cycle-averaged properties, such as the frequency, wavelength, or envelope amplitude. Determining the oscillatory nature of the electric field under the carrier envelope pre- sents a significant problem, however, not least because the electric field oscillates at around 1015 cycles per second for visible light. Extending the classical route of determining electric field by looking at the force on a test charge, Goulielmakis et al. (p. 1267) use a bunch of electrons created by a 250-attosecond extreme ultraviolet pulse as a probe to determine and characterize the dynamical evolution of the electric field of a several-optical-cycle femtosecond laser pulse. Having the strength and temporal variation of the electric field available should prove a useful spectroscopic tool to probe ultrafast electron dynamics within solids.

  4. Caught on Large Films

    CREDIT: WU ET AL.

    High specific surface area, high intrinsic conductivity, and high aspect ratio are some of the outstanding characteristics of single-walled carbon nanotubes (SWNTs). These properties also enable the fabrication of highly conductive and highly transparent freestanding SWNT films. The major challenge now is making large-area films. Wu et al. (p. 1273) show they can make highly conductive, optically transparent films on the order of 80 square centimeters through a method that should be scaleable to much larger sizes. The films are prepared by vacuum filtration of a dilute SWNT solution onto a membrane. In regions where the films initially thicken, the filtration rate decreases, so there is a natural tendency to form films that are uniformly thick. The authors use the films to construct an electric field-activated optical modular, which is the optical analog of a field-effect transistor.

  5. Nanoribbon Optical Waveguides

    The decrease in size of optical components as well as efforts aimed at integrating them into optical chips and networks will require efficient methods for getting the light from one component to another. Law et al. (p. 1269) show that nanoribbon oxide structures, which have rectangular cross sections typically on the scale of several hundred nanometers and are millimeters in length, can be used as optical waveguides and coupled to nanoscale optical components. The strength and flexibility of the nanoribbons also allow them to be physically manipulated for the creation of complex optical networks.

  6. Fuel Cells That Like CO

    The production of hydrogen from hydrocarbons for fuel cell applications also creates CO and CO2. The CO is especially a problem because it poisons the fuel cell catalysts. It can be removed via the water-gas shift reaction, which creates CO2 and additional hydrogen, but the reaction is slow. Kim et al. (p. 1280; see the news story by Service) now show that polyoxometalate (POM) compounds such as H3PMo12O40 react in aqueous solution with CO in the presence of gold nanotubes. The reduced POM compounds can then be reoxidized at the fuel cell anode to generate electricity.

  7. A Return on Investment

    Humans often engage in cooperative activities, not only with family members and friends, but even with strangers. They do so in the expectation that generous behavior will be reciprocated, resulting in mutual gains, and that those who take but do not give will be sanctioned. How such behavior arose evolutionarily has been debated because the individual who metes out punishment usually incurs a cost without receiving a direct benefit. De Quervain et al. (p. 1254; see the cover and the Perspective by Gutscher) use brain imaging to show that in a game situation, the punisher does in fact enjoy the satisfaction of correcting violators of cultural norms. An individual who experienced a greater sense of satisfaction was willing to spend more money in order to punish the offender.

  8. The Wheres and Hows of Memory

    The hippocampus plays a fundamental role in encoding, consolidating, and retrieving episodic and semantic memory (see the Perspective by Bilkey). Fyhn et al. (p. 1258) show that precise spatial information exists and arises in neural activity upstream of the hippocampus in a hitherto unexplored dorsocaudal area in the medial entorhinal cortex, and that this information is being computed within this area. The entorhinal cortex may thus have the processing power to compute and represent position. To understand the functional differentiation underlying structural differences in the patterns of neuronal connectivity within the hippocampus, Leutgeb et al. (p. 1295, published online 22 July 2004) performed ensemble recordings in hippocampal areas CA1 and CA3 when rats were placed in varying enclosures in different recording rooms. The ensemble codes in CA3 were independently organized, whereas codes in CA1 overlapped one another, especially when the animals were placed in familiar-looking surroundings. The CA1 appears to register more general features, whereas CA3 appears to store overlapping but different memories with minimal interference.

  9. Controlling GAS

    The “flesh eating bacteria” group A streptococci (GAS, S. pyogenes) are responsible for sore throats, for complications of rheumatic fever and glomerulonephritis, and for necrotizing fasciitis. Like most microbial pathogens, the range of host species that can be infected by a particular GAS is highly restricted. Sun et al. (p. 1283) now find that this host target restriction relies on the highly specific interaction between bacterial streptokinase and host plasminogen. Mice expressing a human plasminogen transgene showed increased sensitivity and mortality to human GAS pathogens. In these mice, streptokinase activation of human-derived plasminogen facilitated blood clot dissolution and enhanced bacterial spread.

  10. Gene Silencing in Leukemia?

    CREDIT: ZHANG ET AL.

    About 15% of acute myeloid leukemia display a chromosomal translocation with high- level expression of leukemogenic AML1-ETO fusion proteins. AML1-ETO contains a conserved TAF4-homology domain (TAFH) for which in vivo function is unknown, but which might be expected to complex with other transcription factors. Zhang et al. (p. 1286) now show that the TAFH domain AML1-ETO, and nonleukemic factor ETO, associates with HEB protein, a transcription factor of the E protein family. The domain by which ETO interacts with E protein coincides with the site targeted by p300/CBP histone acetyltransferase. The association of HEB and ETO may sterically block p300/CBP recruitment in vivo and allow recruitment of negative co-factors such as HDACs for gene silencing of HEB-responsive promoters in leukemic cells.

  11. Autophagy and Parkinson's Disease

    The cause of Parkinson's disease, the second most common neurodegenerative disorder, remains unknown. It is widely suspected that Lewy bodies, the intraneuronal signature of the disease, and perhaps neuronal death, result from aberrant degradation of synuclein, a protein that is known to play a role in the pathogenesis of Parkinson's disease. Cuervo et al. (p. 1292) now show that wild-type synuclein is degraded in lysosomes by chaperone-mediated autophagy. In contrast, the pathogenic synuclein mutants are not degraded, and actually block chaperone-mediated autophagy. This finding may explain the basis by which mutant synucleins cause familial Parkinson's disease.

  12. Protecting the Genome?

    In plants, the yeast Schizosaccharomyces pombe, and Drosophila, small interfering (si)RNAs that are generated as part of the RNA interference process can silence gene expression either posttranscriptionally, by the cleavage of homologous target RNAs, or transcriptionally, by inducing the formation of heterochromatin and/or the methylation of homologous DNA sequences. Morris et al. (p. 1289), published online 5 August 2004) now show that siRNAs can mediate transcriptional gene silencing in human cells when the siRNAs are delivered to the nucleus. siRNAs directed against gene promoter sequences result in methylation of the DNA. Transcriptional gene silencing probably plays a role in defending the genome from transposons and repeated sequences.