This Week in Science

Science  13 Aug 2004:
Vol. 305, Issue 5686, pp. 913
  1. Forecasting the Heat


    Heat waves are one of the most dramatic expressions of warm weather. Meehl and Tebaldi (p. 994) use a global climate model to show that heat waves in the 21st century should be more intense, more frequent, and last longer than they do now. Moreover, future heat waves will instead exhibit a distinct geographical pattern directly related to the average climate change associated with an increase in greenhouse gases. Certain areas of Europe and North America will be affected particularly strongly.

  2. Black Hole Jets

    Candidate black holes can be identified and characterized by the relativistic jets of plasma that form from material pulled in from the surrounding accretion disk that then accelerates out from the poles. Unfortunately, theorists and modelers have had difficulty generating jets from spinning black holes. Semenov et al. (p. 978; see the news story by Irion) present a model in which a nonlinear string (flux tube of plasma) gets wound around a Kerr black hole. Because of differential rotation of the plasma caused by frame dragging (Lens-Thirring effect), the plasma coils into a relativistic jet released at the poles of the black hole. This model would conclude that the source of the energy for the jets is the black hole rather than the accretion disk.

  3. Faster Through the DNA Hairpins

    Membranes have been fabricated that facilitate the transport of particular DNA sequences. Kohli et al. (p. 984) electroplated polycarbonate membranes with gold to create arrays of nanotubes with inside diameters of 12 nanometers. These nanotubes were then functionalized with 30-nucleotide DNA strands that were thiol-derivatized at one end that contained 18-base DNA hairpins. The presence of the internal hairpin increased the DNA flux relative to an open tube by about a factor of 5, but only slightly increased the flux of strands with a single sequence mismatch.

  4. Imaging Fractional Charge


    The localization of charge plays a major role in describing the behavior of two-dimensional electron gases subjected to a magnetic field. In the fractional quantum Hall effect, the Hall resistance exhibits a series of plateaus in the current that arise through the formation of quasiparticles that have only a fraction of electron charge e. Fractionally charged particles have been verified in transport measurements, but the quasiparticles that localize have been more elusive. Using a scanning single-electron transistor, Martin et al. (p. 980) directly image the quasiparticles with charge e/3 and find that they localize to submicrometer areas.

  5. Small Is Relative

    At what point is a particle small enough that its surfaces influence the mechanical properties of the bulk atoms? It might be reasonable to expect no changes until samples approached the nanoscale, but Uchic et al. (p. 986) show that for the deformation of nickel and some of its alloys, sample size and shape alters the strength and plasticity for samples at the tens-of-micrometers scale. In general terms, it may be important to specify all sample dimensions when discussing the measurement of a metals strength and plasticity.

  6. Ganymede Mass Anomalies

    Radio Doppler data collected by the Galileo spacecraft during fly-bys of the Jovian satellite Ganymede show two mass anomalies. Anderson et al. (p. 989) located the anomalies at a depth of about 800 kilometers with associated isostatic compensation at the surface. They infer that the anomalies are near the rock-ice interface but within the rock. Thus, the density and hence composition of the rock is different in these regions. The depth of the anomalies is consistent with an estimated thickness of the ice of about 800 kilometers.

  7. Magmatic Memories

    The volcanic eruption of Toba, Sumatra, was likely Earth's largest in the past 2 million years. In all, 2800 cubic kilometers of magma were erupted 74,000 years ago. A record of how such a large body of magma formed, accumulated, and then erupted is partly contained in minerals that grew from the erupted magma prior to the eruption. Vazquez and Reid (p. 991) used ion probe methods to date the sequence of chemical changes preserved in individual allanite crystals from the Toba eruption. These minerals show complex zoning, and together with the dates, imply that a primary magma formed about 150,000 years before the eruption. At about 35,000 years before the eruption, other magmas were generated and merged to form a huge magma body.

  8. Live and in Full Color

    Imaging of internal structures in intact biological specimens such as developing embryos still presents a technical challenge. Huisken et al. (p. 1007) describe a microscopic set-up, selective plane illumination microscopy (SPIM), that allows high-resolution multi-dimensional imaging of intact living specimens. Using SPIM, they observed the developmental changes within embryos of Drosophila melanogaster, and could monitor the internal workings of a beating heart in intact Medaka fish embryos.

  9. Enhancing Stem Cell Homing

    The efficiency with which hematopoietic stem cells (HSC) home to the bone marrow is a critical factor determining clinical outcome in transplantation. Christopherson II et al. (p. 1000) show that efficiency of stem cell homing can be significantly enhanced by interrupting the activity of a peptidase, CD26, on the donor cell surface. Under normal circumstances, CD26 appears to negatively regulate HSC homing by cleavage of the chemokine CXCL12, thereby preventing binding to its receptor on the surface of HSC. The potential ability to increase the efficiency of HSC homing rather than having to isolate greater numbers of the stem cells may help bone marrow transplantation.

  10. Stomaching Helicobacter pylori Infection

    Helicobacter pylori infects about one in every two individuals and can cause gastric malignancy and stomach ulcers. However, given the large population that is infected, the small fraction who exhibit significant pathology suggests that mucosal defense in the stomach normally contains the pathogenic activity of H. pylori.Kawakubo et al. (p. 1003) found a component of the gastric mucins, the mucin-type O-glycan, that occurs within deeper regions of the gastric mucosa and that can inhibit growth and motility of H. pylori in culture by interfering with cell-wall biosynthesis. Thus, cells of the gastric mucosa appear to protect themselves from H. pylori infection by secreting O-glycans that possess strong antibiotic activity.

  11. Protecting Damaged Axons


    Degeneration of axons that have been severed from their neuronal cell bodies can follow a specific course of progressive fragmentation called Wallerian degeneration. Various neurodegenerative diseases are also characterized by axonal degeneration. Araki et al. (p. 1010; see the Perspective by Bedalov and Simon) provide new insight into what directs the course of organized axonal degeneration. Analysis of a fusion protein resulting from a mutation that slows axon degeneration implicates the nicotinamide adenine dinucleotide biosynthetic pathway in this type of axonal degeneration.

  12. From Use to Abuse

    Only a minority of the people who use potentially addictive drugs become addicts. A better understanding of the biological basis of addiction has been hampered by a dearth of robust animal models of addiction, as opposed to self-administration (see the Perspective by Robinson). Deroche-Gamonet et al. (p. 1014) developed a behavioral model to examine addictive behavior in rats. The authors find that both the amount of exposure to drugs and also the degree of vulnerability in the exposed individual are key to developing addiction. Vanderschuren and Everitt (p. 1017) show that cocaine-seeking in rats can be suppressed by presentation of an aversive stimulus, but after extended exposure to self-administered cocaine, drug-seeking became resistant to adversity. This effect did not occur after prolonged exposure to sucrose. Thus, prolonged cocaine self-administration contributes an inflexible compulsive dimension to drug-seeking.

  13. The Fly, the Eye, and the Complex Pattern

    Are visual processing mechanisms in the small nervous system of the fruit fly Drosophila melanogaster analogous to higher level perceptual mechanisms like the ones found in primates? Tang et al. (p. 1020) measured fly behavior in a purpose-built flight simulator. Just like more complex animals, Drosophila associated invariably positioned visual cues that were specifically selected to test various aspects of pattern discrimination with punishment. The flies could generalize this concept for future encounters of similar stimuli across the visual fields. This ability requires selective attention and inter-ocular memory transfer.

  14. Coral's Daytime Glow

    The hard Caribbean coral Montastraea cavernosa not only possesses symbiotic zooxanthella (dinoflagellates), but also harbors endocellular symbiotic cyanobacteria. Lesser et al. (p. 997) confirm this finding in their investigation of the characteristic orange daytime fluorescence of this coral. The pigment involved is the cyanobacterial protein, phycoerythrin, rather than one of the photoprotective coral pigments. Further analysis revealed that the cyanobacterial symbionts express components of the nitrogenase enzyme complex and have the potential to fix nitrogen, presumably to the benefit of their coral hosts.