This Week in Science

Science  14 Jun 2002:
Vol. 296, Issue 5575, pp. 1925
  1. In Brevia

    High-surface-energy, mesoporous oxide templates have been used by Steinhart et al. (p. 1997) to synthesize nanotubes from many polymeric materials with uniform size and length distributions.

  2. The Timing Is Crucial

    Plastic modification of synaptic connections that depends on the precise timing of pre-and postsynaptic action potentials has been described in several in vitro preparations. However, it is unclear if the same phenomenon can also be observed in vivo. Fu et al. (p. 1999) describe timing-dependent plasticity of synaptic connectivity as well as of receptive field topography in the adult cat visual cortex. They also provide psychophysical evidence that comparable effects occur in the human visual system.

  3. Elements of Magnetic Logic

    A magnetic-based switching architecture has been proposed to operate at much lower power consumption than conventional electronics-based circuitry. However, viable demonstrations of dynamical logical elements that can couple to similar magnetic elements have so far been lacking. Combining the motion of a magnetic domain wall in a rotating magnetic field and micropatterned magnetic wires, Allwood et al. (p. 2003; see the news story by Cho) demonstrate a logical NOT-gate, or inverter, by patterning thin layers of ferromagnetic permalloy. As the domain wall moved through the junction, the magnetization in the wires on either side of the junction was reversed. Scalability was also demonstrated by coupling several of these inverter junctions together to form a shift register.

  4. Excited But Orderly

    Many physical and biological systems contain an excitable medium that can support wave propagation, and several approaches have been used to control their direction. Sakurai et al. (p. 2009; see the cover) now demonstrate a very high level of wave front control in the chemical waves that form in the Belousov-Zhabotinsky reaction. By using feedback methods, they can use light to create gradients in the concentration of photosensitive catalysts in a thin-film gel realization of this reaction. The wave fronts can then be steered to form complex patterns.

  5. Getting Oriented

    Layered ferroelectric thin films have potential applications as dynamic random access memory (DRAM). One material that has been studied for this purpose is a La-substituted Bi4Ti3O12, known as BLT. Although BLT will readily grow onto substrates, it does so with an orientation that causes the remnant polarizability to lie in the plane of the substrate. However, for DRAM applications, the remnant polarizability needs to be perpendicular to the substrate. Lee et al. (p. 2006; see the Perspective by Ramesh and Schlom) demonstrate the growth of BLT crystals with the preferred (100) orientation, almost to the exclusion of all other orientations.

  6. Large Slip in the Tibetan Plateau

    The collision of India into Eurasia created several parallel east-to-west trending strike-slip faults on the Tibetan plateau that accommodate some of the head-on, continent-to-continent collisions. Although there have been many large-magnitude earthquakes on these faults, geographic isolation has limited both seismic monitoring and field studies. Lin et al. (p. 2015) measured a 400-kilometer-long rupture zone that had as much as 16 meters of left-lateral strike-slip motion caused by the November 2001 Central Kunlun earthquake, which had a surface wave magnitude of 8.1. This study documents the importance of these strike-slip faults for accommodating some of the collision by eastward extrusion of tectonic blocks and provides vital ground truth to supplement remote geophysical modeling.

  7. Coral Fates Corralled

    The determination of species boundaries has been a continuous source of controversy in coral systematics. Using molecular techniques, Vollmer and Palumbi (p. 2023; see the news story by Pennisi) show that some Caribbean coral species generate morphologically distinct first-generation sterile hybrids that have little evolutionary potential but can asexually propagate effectively immortal clones. Many of these clones are sufficiently distinct to have been given their own species names, despite being evolutionary dead-ends. These results not only pave the way for more rational systematics of corals, but also have implications for evolutionary theory in general.

  8. More Rapid Retreat

    Continental ice sheets that extend into the sea, like those in Antarctica, begin to float at a location called the grounding line. Rignot and Jacobs (p. 2020) surveyed 22 glaciers that flow off the Antarctic Ice Sheet and examine their interactions with the ocean. Their satellite interferometry observations show that grounding lines often lie tens of kilometers landward of their previously estimated locations. Rapid basal melting occurs near the grounding lines of these ice shelves, and floating glacier tongues make the ice sheets vulnerable to ongoing ocean warming. The 0.2°C increase in ocean temperature that has been measured near the edges of Antarctic ice sheets during recent decades is sufficient to have increased rates of basal melting by 2 meters per year and may explain the rapid thinning observed for ice shelves in some parts of Antarctica.

    CREDIT: RIGNOT AND JACOBS
  9. Microbial Forensics

    In the wake of the recent bioterrorism incidents involving the contamination of the mail with Bacillus anthracis, there has been renewed interest in establishing relationships among isolates of organisms with highly conserved genomes. Read et al. (p. 2028; see the Perspective by Cummings and Relman and the 10 May news story by Enserink) have used comparative whole-genome sequencing and polymorphism analysis to classify nine closely related isolates of B. anthracis that were not distinguishable with existing genotype data.

  10. AIDing and Abetting Mutation

    The proposed RNA editing enzyme, activation-induced cytidine deaminase (AID), plays a critical role in increasing antigen affinity both by switching gene segments that encode different classes of antibody and in the somatic hypermutation (SHM) of variable coding segments of the same genes. Is AID activity sufficient for generating SHM? Yoshikawa et al. (p. 2033) show that AID can induce mutation in an artificial reporter gene cotransfected in a non-B cell line. That AID can act autonomously of B cell-specific factors suggests further clues about its mode of function in regulating antibody mutation in B cells.

  11. One Tyrosine Short

    LAT is an intracellular adaptor protein that becomes phosphorylated on multiple tyrosine residues after T cell receptor activation. Aguado et al. (p. 2036) and Sommers et al. (p. 2040) report that a single tyrosine residue in LAT, which couples to the downstream signaling molecule phospholipase C-γ1, plays a crucial role in maintaining T cell homeostasis, regulating both early and late T cell development and differentiation. Replacement of endogenous LAT in mice with a form in which Tyr136 was mutated to Phe caused a partial block in early T cell development. However, over time, the mice developed a fatal lymphoproliferative disorder featuring an overabundance of a particular TH2-type cell. One consequence of this paradoxical phenotype was an autoimmune response. The analyses suggest that while a single LAT residue may have a positive function during early T cell development, it may negatively regulate signaling pathways later on during T cell selection and differentiation of TH2 effector cells.

  12. Human Motor Skills and the Cerebellum

    The role of the cerebellum in motor learning and performance is still controversial. Seidler et al. (p. 2043; see the Perspective by Hazeltine and Ivry) used functional magnetic resonance imaging and a sophisticated set of behavioral tasks and manipulations to investigate the involvement of the cerebellum in motor learning. They found that the cerebellum does not play a role in motor sequence learning. It is, however, heavily involved in the expression of information about motor sequences and thus in the modification of performance.

  13. Plants Coping with Stress

    Plants use hydrogen peroxide (H2O2) as a second messenger in their responses to hormones, pathogen infection, and abiotic stresses. Baxter-Burrell et al. (p. 2026) have elucidated a Rop guanosine triphosphatase rheostat, RopGAP4, that fine-tunes the output of H2O2 in Arabidopsis in response to oxygen deprivation, which happens to plants when their roots are transiently flooded. The H2O2 signal in this case induces expression of alcohol dehydrogenase, which enables tolerance to the stressor, and RopGAP4, which represses further H2O2 production. As transient flooding, as well as other abiotic stressors, diminishes yield in many crops, manipulation of this Rop rheostat may be useful in developing crops better able to withstand these stressors.

    CREDIT: BAXTER-BURRELL ET AL.
  14. Detecting a Balmy Day

    Researchers have identified the receptor that senses cold temperatures (also triggered by menthol, accounting for menthol's cooling sensation) and hot temperatures (also activated by capsaicin, the “heat” in chili peppers). Both are members of a family of ion channels called transient receptor potential (TRP) channels. Peier et al. (p. 2046) now identify another family member, TRPV3, as a “warm” receptor. This cation-selective, outwardly rectifying channel is activated by temperatures between 33° and 42°C and is expressed in the keratinocytes and hair follicles of skin but not in neurons. Although it is not yet known how warm skin cells convey their response to temperature to the nervous system, the identification of this receptor accounts for our ability to discern pleasantly warm temperatures.

  15. Lithium Intercalation at Low Potentials

    The reversible electrochemical intercalation of lithium occurs readily for a number of materials that act as positive electrodes, but the main choice for negative electrodes that act through intercalation has been graphite. Souza et al. (p. 2012) now report the low-potential, reversible intercalation of lithium into MnP4 at room temperature. Unlike other materials, the redox reaction occurs at the anionic site through the breaking and reforming of a P-P bond.

  16. A Prevailing Wind

    The orientation and sedimentary structure of sand dunes depend on the strength and direction of the prevailing winds, so ancient dunes should contain important clues to paleoatmospheric circulation patterns—if their ages can actually be determined. Preusser et al. (p. 2018) used difficult luminescence techniques to construct a 160,000-year record of dune formation in Oman. Their results indicate that models of past atmospheric circulation over southern Arabia during times of high-latitude glaciation, which assume that the intensity of the prevailing westerly winds strengthens during these periods, need to be revised. The dominant wind direction was from South to North, and general atmospheric circulation was not very different from present conditions.

  17. Neuronal Activity in the Newborn

    The activity and spiking patterns of neurons in the developing brain is very different from that of the adult central nervous system. Leinekugel et al. (p. 2049) made neuronal recordings from both awake and behaving, as well as anesthetized, neonatal rats. They observed spontaneously occurring periodic bursts of synchronized activity in the hippocampus. This activity was mediated by glutamatergic and by GABAergic inputs that are excitatory at this developmental stage. Similar discharge patterns, called giant depolarizing potentials, have been observed previously in in vitro preparations. These endogenous synchronous activities may play an important role in the maturation and maintenance of cortical circuits in the newborn.

  18. Global Allocation Rules for Patterns of Biomass Partitioning

    Enquist and Niklas (Reports, 22 February 2002, p. 1517) quantified the allocation of plant biomass among stems, leaves, and roots for a broad range of seed plants inhabiting diverse ecosystems, and they proposed a general allometric model that predicts how these plant organs should scale in relation to one another and “helps identify the biophysical constraints acting on allocation tradeoffs in plant biology.” Sack et al. comment that the model “falls short in a number of important respects” when applied to plants during early ontogeny, “a crucial period for plant establishment,” during which biomass allocation and scaling follow rules different from those for mature plants. In response, Enquist and Niklas acknowledge that “allometric relationships for early ontogeny may be very different,” but maintain that their model is robust and accurately predicts scaling relationships among leaf, stem, and root biomass for multiple plant species across several orders of magnitude.

    The full text of these comments can be seen at www.sciencemag.org/cgi/content/full/296/5575/1923a

Log in to view full text

Via your Institution

Log in through your institution

Log in through your institution