Volume 457 Issue 7226, 8 January 2009

Space is not completely empty; the vacuum teems with quantum mechanical energy fluctuations able to generate an attractive force between objects that are very close to each other. This Casimir Lifshitz force can cause static friction or stiction in nanomachines, which must be strongly reduced. Until now only attractive interactions have been reported but in theory, if vacuum is replaced by certain media, Casimir-Lifshitz forces should become repulsive. This has now been confirmed experimentally. Repulsion, weaker than the attractive force, was measured in a carefully chosen system of interacting materials immersed in fluid. The magnitude of both forces increases as separation decreases. The repulsive forces could conceivably allow quantum levitation of objects in a fluid and lead to new types of switchable nanoscale devices with ultra-low static friction. Levitation depends only on the dielectric properties of the various materials. The cover illustrates repulsion between a tiny gold sphere and a silica substrate (left). Replace the silica with gold (right), and the force becomes attractive.

Authors

Editorial

  • Editorial |

    Initiatives for digital research infrastructure should focus more on making standardized data openly available, and less on developing new portals.

  • Editorial |

    Samuel Huntington will be remembered for his ideas, controversial as they might have been.

  • Editorial |

    The United States would do well to end restrictions on collaborations with the island nation's scientists.

Research Highlights

Journal Club

News

  • News |

    The biotechnology industry is weathering the financial crisis better than some. That doesn't mean it's in great shape, reports Heidi Ledford.

    • Heidi Ledford

News in Brief

Correction

News Feature

  • News Feature |

    The best way to study life beneath the waves is to live there. Mark Schrope describes his experiences in the world's longest-running undersea laboratory.

    • Mark Schrope
  • News Feature |

    If growing forests in India can generate lucrative carbon credits, then why isn't everyone planting trees? Paroma Basu reports.

    • Paroma Basu

Correspondence

Essay

  • Essay |

    Poetry it is not. Nor is it particularly romantic. But reducing love to its component parts helps us to understand human sexuality, and may lead to drugs that enhance or diminish our love for another, says Larry J. Young.

    • Larry J Young

Books & Arts

News & Views

  • News & Views |

    Many organic syntheses are target-oriented — each multi-step route is designed to make just one compound. But now a diversity-oriented synthesis can make 80 different molecular skeletons in just a few steps.

    • Stuart L. Schreiber
  • News & Views |

    Epilepsy is characterized by repetitive seizures due to abnormal electrical activity in the brain. Immune cells promote development of this disorder by mediating the breakdown of the blood–brain barrier.

    • Richard M. Ransohoff
  • News & Views |

    The experimental verification that a bizarre quantum effect — the Casimir force — can manifest itself in its repulsive form is pivotal not only for fundamental physics but also for nanotechnology.

    • Steve K. Lamoreaux
  • News & Views |

    During protein synthesis, mistakes in adding amino acids to the growing polypeptide chain are usually prevented. If they are not, a quality-control mechanism ensures premature termination of erroneous sequences.

    • Kurt Fredrick
    •  & Michael Ibba
  • News & Views |

    How low-mass stars produce their ubiquitous magnetic fields has long puzzled astronomers. Models of how Earth accomplishes this task could hold the key to understanding the phenomenon on such stars.

    • Christopher M. Johns-Krull
  • News & Views |

    Not only is the aromatase enzyme implicated in a common form of breast cancer, but it also catalyses an unusual biochemical reaction. Its crystal structure therefore offers both practical and fundamental insights.

    • Michael R. Waterman

Article

  • Article |

    The DNA and RNA polymerases encode proofreading activities that help to ensure the fidelity of the readout. The ribosome, which synthesizes protein, was believed to lack a similar activity that would recognize errors after a peptide bond had been formed. This study provides evidence that the ribosome does have such a quality control mechanism. It is shown that after an incorrect amino acid has been incorporated into the growing polypeptide chain, there is a general loss of specificity in the ribosome's active site, leading to an accumulation of errors that triggers premature termination of peptide synthesis.

    • Hani S. Zaher
    •  & Rachel Green

Letter

  • Letter |

    The magnetic fields of Earth and Jupiter, along with those of rapidly rotating, low-mass stars, are generated by convection-driven dynamos that may operate similarly, although the field strengths vary. The critical factor unifying field generation in such different objects, while still causing a large variation, has been unclear. This paper reports an extension of a scaling law derived from geodynamo models to rapidly rotating stars. The unifying principle is that the energy flux available for generating the magnetic field sets the field strength.

    • Ulrich R. Christensen
    • , Volkmar Holzwarth
    •  & Ansgar Reiners
  • Letter |

    In a vacuum, the Casimir–Lifshitz force causes friction effects that either hinder or may be exploited in nanomechanical device applications. So far, only attractive interactions have been measured, but theory predicts that when vacuum is replaced with certain media, the Casimir–Lifshitz force can also be repulsive. This effect is now experimentally confirmed in this study, which carefully chooses a system of interacting materials immersed in a fluid. The measured repulsive interaction is found to be weaker than the attractive force whereas in both cases the magnitude of the force increases with decreasing surface separation.

    • J. N. Munday
    • , Federico Capasso
    •  & V. Adrian Parsegian
  • Letter |

    The spectral location of terahertz radiation, between optical and microwave frequencies, has hindered the development of compact semiconductor terahertz sources. One approach is to make use of photonic-crystal structures, which allows surface emission of radiation so that the spectral and spatial modes can be simultaneously engineered. To fabricate electrically-driven devices, it is necessary to define boundary structures around the active, pumped area and this paper now demonstrates a general technique to implement such boundaries.

    • Y. Chassagneux
    • , R. Colombelli
    • , W. Maineult
    • , S. Barbieri
    • , H. E. Beere
    • , D. A. Ritchie
    • , S. P. Khanna
    • , E. H. Linfield
    •  & A. G. Davies
  • Letter |

    Age and compositional data for the newly discovered, paired and differentiated meteorites Graves Nunatak (GRA) 06128 and GRA 06129 are reported. These meteorites are feldspar-rich, with andesite bulk compositions. Their age of 4.52 Gyr demonstrates formation early in Solar System history, and their composition is most consistent with an origin as partial melts from a volatile-rich, oxidized asteroid.

    • James M. D. Day
    • , Richard D. Ash
    • , Yang Liu
    • , Jeremy J. Bellucci
    • , Douglas Rumble III
    • , William F. McDonough
    • , Richard J. Walker
    •  & Lawrence A. Taylor
  • Letter |

    Diatoms constitute a vital part of the oceanic ecosystem. As they are dependent on silica, they are thought to have risen to prominence alongside grasslands in the Miocene epoch, when the first large-scale weathering of grassland-derived silica took place. A new analysis of an ocean-bed database contradicts that scenario; it is shown that diatom diversity peaked at the Eocene–Oligocene boundary, long before grasslands became prominent.

    • Daniel L. Rabosky
    •  & Ulf Sorhannus
  • Letter |

    Living in noisy colonies, songbird vocal learning requires individuals to differentiate self-generated vocalizations from other sound sources to accurately match the learned song template. However, neurons responding to vocal output have not been identified. This study identifies neurons in the auditory forebrain of zebra finch that specifically responded to either song or playback perturbations, suggesting the existence of a computational error-checking function in the forebrain auditory areas.

    • Georg B. Keller
    •  & Richard H. R. Hahnloser
  • Letter |

    Repeated exposure to pathogens and generation of T-cell memory is thought to result in attrition of the pre-existing memory T cell pool to maintain the overall size of the memory compartment constant. This work shows that new effector memory cells can be generated in large numbers without greatly impacting pre-existing memory.

    • Vaiva Vezys
    • , Andrew Yates
    • , Kerry A. Casey
    • , Gibson Lanier
    • , Rafi Ahmed
    • , Rustom Antia
    •  & David Masopust
  • Letter |

    Inflammatory heptocellular adenomas (IHCAs) show activation of an acute-phase inflammatory response signalling pathways, and it is found that this is due to gain-of function mutations in the IL6ST gene encoding gp130, a coreceptor for IL-6 and other cytokines that activate inflammatory signalling pathways. These mutations lead to constitutive activation of STAT3 signalling, contributing to the inflammatory phenotype of IHACs.

    • Sandra Rebouissou
    • , Mohamed Amessou
    • , Gabrielle Couchy
    • , Karine Poussin
    • , Sandrine Imbeaud
    • , Camilla Pilati
    • , Tina Izard
    • , Charles Balabaud
    • , Paulette Bioulac-Sage
    •  & Jessica Zucman-Rossi
  • Letter |

    In teleosts, proper balance and hearing depend on mechanical sensors in the inner ear. These sensors include actin-based microvilli and microtubule-based cilia that extend from the surface of sensory hair cells and attach to biomineralized 'ear stones', orotoliths. This paper show that in zebra fish, fluid flow generated by cilia influences the number, growth and localization of otoliths, as well as their mineralization during development.

    • Jessica R. Colantonio
    • , Julien Vermot
    • , David Wu
    • , Adam D. Langenbacher
    • , Scott Fraser
    • , Jau-Nian Chen
    •  & Kent L. Hill
  • Letter |

    To survive in an harsh environment, Caenorhabditis elegans larvae enter a state called dauer, during which the worms do not eat, remain active, but become stress-resistant and extremely long-lived. A typical dauer has reduced insulin-like signalling, full nutrient stores and changes in its metabolism. It is shown that without AMPK (LKB1) signalling dauers rapidly consume their stored energy and expire prematurely, due to vital organ failure.

    • Patrick Narbonne
    •  & Richard Roy
  • Letter |

    This paper presents a general thermodynamic model that accurately captures the relationship between a gene promoter sequence, including weak, stastically undetectable regulatory sites, and its expression output. The work implies a relatively minor role of chromatin and will facilitate rational genetic design in biotechnology and synthetic biology.

    • Jason Gertz
    • , Eric D. Siggia
    •  & Barak A. Cohen
  • Letter |

    Aromatase cytochrome P450 is the only enzyme in vertebrates known to catalyse the biosynthesis of all oestrogens from androgens. This paper solves the X-ray crystal structure of the first natural mammalian, full-length P450, human placental aromatase.

    • Debashis Ghosh
    • , Jennifer Griswold
    • , Mary Erman
    •  & Walter Pangborn

Prospects

Futures

  • Futures |

    A life-changing experience.

    • Graeme Wistow
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