This Week in Science

Science  06 Jun 2008:
Vol. 320, Issue 5881, pp. 1257
  1. Collisions for a Longer Lifetime


    Cold atoms confined to low dimensions can give rise to surprising effects such as bosons behaving as fermions and repelling each other. Elastic collisions were thought to be a necessary condition for such an effect, and much effort has been directed towards achieving elastic-collision regimes. In contrast, inelastic collisions have tended to be avoided. However, Syassen et al. (p. 1329; see the Perspective by Porto) now show that inelastic collisions between particles can also give rise to correlation effects. Starting with a condensate of molecules confined to a one-dimensional tube, they add a weak periodic potential along the axis and show that the lifetime of the molecules in the tube is extended by over an order of magnitude. The results should prove useful for exploring more of the parameter space in which inelastic collisions dominate that were once regimes to be avoided.

  2. Mountain High

    The Andes represent one of the longest, highest mountain ranges on Earth. Their topography affects the climate of much of South America, and their uplift history thus impacts the ecological development of the continent.

    Garzione et al. (p. 1304) review recent evidence for their history of uplift. Before about 10 million years ago, the Andes were of moderate elevation. Between 10 and 6 million years ago, the elevation of the Andes increased abruptly, perhaps because dense material at the base of the crust detached and subsided into the mantle.

  3. Earthquake Running at the Speed of Sound

    Some particularly destructive earthquakes, which produce sound waves, seem to rupture at faster than the local speed of sound through the crust. Bouchon and Karabulut (p. 1323) now show that the aftershocks of these tremors are also different. Instead of clustering on the fault plane, as is common, they cluster on secondary structures. The lack of aftershocks on the fault plane shows that friction along the fault plane itself is relatively uniform.

  4. Foresight Among E. coli

    Many natural signals progress in a readily predictable sequence. For instance, after being eaten, a bacterium will perceive a sudden temperature rise followed by a drop in oxygen levels. Tagkopoulos et al. (p. 1313, published online 8 May; see the Perspective by Baliga) investigated E. coli's predictive powers in a combination of in silico and chemostat experiments. On exposure to a large temperature change, E. coli can shift from aerobiosis to anaerobiosis even in the presence of 18% oxygen. This might seem maladaptive, but it means that the organism will have a competitive edge as soon as it encounters the zoo of microorganisms in the oxygen-starved lower gut. Furthermore, the authors were able to “train” the organisms to adapt metabolically to “unnatural” sequences of events, e.g., elevated temperature followed by high oxygen.

  5. Exploring Alternatives in Catalysis

    Many industrial catalytic systems are based on precious metals, and the search is on for substitute catalysts based on less expensive and more abundant metals and alloys. Studt et al. (p. 1320) have examined one reaction, the selective hydrogenation of acetylene, and show how insights from density functional theory (DFT) could be used to identify a candidate alloy. Acetylene, a trace contaminant of the commodity chemical ethylene, is hydrogenated to ethylene by palladium catalysts that do not convert the ethylene to ethane. By examining trends in the heats of adsorption of hydrocarbons on metals and alloys, the authors identified zinc-nickel alloys as possible alternatives and demonstrate their selective hydrogenation activity in experimental studies of these alloys dispersed on oxide supports.

  6. Eccentric Pulsar Performance


    Binary pulsars are rapidly spinning neutron stars that emit a beam of radio waves that co-rotate with a companion star. Two main types have been seen, one spinning more slowly with an eccentric orbit around the companion star, the other spinning rapidly with a circular orbit. Champion et al. (p. 1309, published online 15 May; see the Perspective by van den Heuvel) have now discovered a rapidly spinning pulsar with a highly eccentric orbit that does not fit into these classes and thus challenges models for formation of pulsars. Possible alternative models for the formation of this pulsar include a triple stellar system.

  7. Observing Cataclysmic Variables

    A variety of astrophysical objects such as binary stars involve one star accreting matter from another. In many cases, the collected matter heats up and is ejected in the form of a powerful jet. But some accreting objects, in particular so-called cataclysmic variables, seem to show no jet activity. Körding et al. (p. 1318) have gathered radio observations on the prototypical dwarf nova, SS Cyg, that show all the earmarks of an astrophysical jet. The American Association of Variable Star Observers sent out an alert that triggered data collection from the Very Large Array radio telescope. The results suggest that jet activity and the underlying mechanisms are similar in all accreting objects.

  8. Entangling Diamond

    Entanglement is a key ingredient in quantum information processing and quantum computation. While entanglement has been demonstrated for photons, cold atoms systems, and quantum dots at cryogenic temperatures, there are efforts to look to other systems that can extend entanglement to room temperature in solid state systems. By demonstrating the ability to generate and detect 2-qubit and 3-qubit entangled states with the optically active nitrogen vacancies in diamond, Neumann et al. (p. 1326) show that diamond can meet these requirements.

  9. Poring over the Nuclear Pore

    Light microscopy is a powerful tool in cell biology, and the view is improving with “super-resolution” techniques that have broken the 200- to 300-nm resolution barrier. Now Schermelleh et al. (p. 1332) describe the application of three-dimensional structured illumination microscopy (3D-SIM), an imaging technique that can produce multicolor images of whole cells with enhanced resolution in both the lateral and axial directions. They used the technique to simultaneously map nuclear pores, nuclear lamins, and chromatin at a resolution of about 100 nm and observed several features not detected by conventional microscopy.

  10. Flexible Organ Building Blocks

    Building an animal with distinct organs requires the coordination of cell identity and cell behavior during embryogenesis. Christiaen et al. (p. 1349) have tracked expression of genes controlling migration of the heart precursor cells in the sea squirt, Ciona intestinalis. In order to move forward, migrating cells must be polarized, extend protrusions, adhere to the substrate, and then detach. Heart regulatory factors control these events by regulating only subsets of genes to specify the combination of cellular activities required for migration. These properties of the regulation and behavior interface may account for the morphogenetic diversity observed in development and evolution.

  11. Dissecting X Inactivation

    The silencing of one of the two X chromosomes in mammalian females is regulated by the noncoding RNAs Xist and Tsix. These RNAs overlap for at least part of their length, leading to the speculation that RNA interference (RNAi), a pervasive gene silencing mechanism that targets double-stranded RNA, might be involved in X inactivation. Ogawa et al. (p. 1336) show in mouse cells that Xist and Tsix do indeed form an RNA duplex that can be targeted by Dicer, the RNA endonuclease at the heart of the RNA interference machinery, and give rise to small RNA species. Knocking down Dicer prevents Xist from coating the inactive X chromosome, which would generate heterochromatic marks. Thus X inactivation and RNA interference are mechanistically linked.

  12. From Impulsive to Compulsive

    Individual differences in impulsivity and sensation-seeking are related to vulnerability to drug use and abuse. Compulsive cocaine use has been thought to result from a failure in top-down executive control over maladaptive habit learning. However, whether the enhanced impulsivity observed in drug addicts predates the onset of compulsive drug use or is a consequence of protracted exposure to drugs is not clear. Belin et al. (p. 1352) now show in rats that an impulsive behavioral trait that is associated with reduced dopamine receptors in the nucleus accumbens predicts the switch to compulsive cocaine use and addiction.

  13. What's In a Face?

    Most macaque monkeys have six patches of face-selective cortex distributed throughout the brain's temporal lobe. These six face patches offer an ideal framework for dissecting the functional architecture of object recognition. What are the inputs and outputs of each of the six face patches? Do they form a functionally interconnected network? Or are they independent nodes, each processing a different aspect of faces? Moeller et al. (p. 1355) directly imaged connections of the macaque face patches by combining in vivo microstimulation and brain imaging. Stimulation of the lateral middle face patch resulted in strong, specific activation of all five other face patches. Stimulation in the other face patches also resulted in specific activation of a subset of face patches. The face patches are thus part of an interconnected network, which may generate a hierarchy of face processing stages.

  14. Protecting Telomeres

    Telomeres cap the ends of eukaryotic chromosomes, preventing them from being detected as damaged DNA, which might lead to the chromosome ends being degraded or erroneously repaired, which could in turn result in catastrophic genome rearrangements. The Pot1 protein binds to and protects telomeres, yet at the same time seems to regulate telomerase reactions. Miyoshi et al. (p. 1341; see the Perspective by Bianchi and Shore) have identified three fission yeast proteins, Ccq1, Poz1, and Tpz1, that form a complex with Pot1. The Pot1 complex is essential to prevent end-to-end fusions of chromosomes, which is similar to its role in mammals. Ccq1 plays a critical role in telomerase recruitment to the Pot1 complex, promoting telomere elongation, and Poz1 acts to negatively control telomerase.

  15. Transcriptome Mapping

    Whole genome sequencing is generally costly and has relatively low precision about the amount and location of the actual sequences detected. Nagalakshmi et al. (p. 1344, published online 1 May) performed an analysis of the entire poly−A+ transcriptome of yeast with a high-throughput sequencing method, called RNA-Seq, in which a very large number of short sequence reads of complementary DNA fragments were computationally mapped to the genome. This direct sequencing provided detailed information about the boundaries of transcription units and revealed boundaries that had been missed before, and increased information on introns and 3′ ends.