Local Structure of Ge／SI（100） Self—Assembled Quantum Dots

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Methane oxidation by an extremely acidophilic bacterium of the phylum Verrucomicrobia

Aerobic methanotrophic bacteria consume methane as it diffuses away from methanogenic zones of soil and sediment. They act as a biofilter to reduce methane emissions to the atmosphere, and they are therefore targets in strategies to combat global climate change. No cultured methanotroph grows optimally below pH 5, but some environments with active methane cycles are very acidic. Here we describe an extremely acidophilic methanotroph that grows optimally at pH 2.0-2.5. Unlike the known methanotrophs, it does not belong to the phylum Proteobacteria but rather to the Verrucomicrobia, a widespread and diverse bacterial phylum that primarily comprises uncultivated species with unknown genotypes. Analysis of its draft genome detected genes encoding particulate methane monooxygenase that were homologous to genes found in methanotrophic proteobacteria. However, known genetic modules for methanol and formaldehyde oxidation were incomplete or missing, suggesting that the bacterium uses some novel methylotrophic pathways. Phylogenetic analysis of its three pmoA genes (encoding a subunit of particulate methane monooxygenase) placed them into a distinct cluster from proteobacterial homologues. This indicates an ancient divergence of Verrucomicrobia and Proteobacteria methanotrophs rather than a recent horizontal gene transfer of methanotrophic ability. The findings show that methanotrophy in the Bacteria is more taxonomically, ecologically and genetically diverse than previously thought, and that previous studies have failed to assess the full diversity of methanotrophs in acidic environments.     

The mouse X chromosome is enriched for sex-biased genes not subject to selection by meiotic sex chromosome inactivation

Sex chromosomes are subject to sex-specific selective evolutionary forces. One model predicts that genes with sex-biased expression should be enriched on the X chromosome. In agreement with Rice's hypothesis, spermatogonial genes are over-represented on the X chromosome of mice and sex- and reproduction-related genes are over-represented on the human X chromosome. Male-biased genes are under-represented on the X chromosome in worms and flies, however. Here we show that mouse spermatogenesis genes are relatively under-represented on the X chromosome and female-biased genes are enriched on it. We used Spo11(-/-) mice blocked in spermatogenesis early in meiosis to evaluate the temporal pattern of gene expression in sperm development. Genes expressed before the Spo11 block are enriched on the X chromosome, whereas those expressed later in spermatogenesis are depleted. Inactivation of the X chromosome in male meiosis may be a universal driving force for X-chromosome demasculinization.     

Peculiarities of the rheological behavior and structure formation of aluminum under deformation at near-solidus temperatures

This paper deals with a peculiar rheological behavior of aluminum at near-solidus temperatures. It has been experimentally established that there is an inverse strain rate dependence of strain resistance at temperatures ranging between 560 and 640°С and strain rates ranging from 0.06 to 1.2 s-1. Electron backscatter diffraction analysis has shown that at temperatures ranging between 540 and 640°С and strain rates ranging from 0.06 to 0.1 s-1, the main process of softening is dynamic polygonization, resulting in in situ recrystallization. At higher strain rates, ranging between 0.8 and 1.2 s-1, and temperatures ranging between 560 and 640°С, the recovery is dynamic. This unusual behavior of the mechanism of softening and the presence of the inverse strain rate dependence of strain resistance can be explained by blocking the motion of free dislocations by foreign atoms, which occurs at strain rates ranging between 0.06 and 0.1 s-1. This process results in dislocation pile-up, thereby causing in situ recrystallization. At strain rates exceeding 0.16 s-1, there is no intensive blocking of dislocations, leading to a direct strain rate dependence of strain resistance.     

Resolving the time when an electron exits a tunnelling barrier

The tunnelling of a particle through a barrier is one of the most fundamental and ubiquitous quantum processes. When induced by an intense laser field, electron tunnelling from atoms and molecules initiates a broad range of phenomena such as the generation of attosecond pulses, laser-induced electron diffraction and holography. These processes evolve on the attosecond timescale (1?attosecond?≡?1?as = 10(-18)?seconds) and are well suited to the investigation of a general issue much debated since the early days of quantum mechanics--the link between the tunnelling of an electron through a barrier and its dynamics outside the barrier. Previous experiments have measured tunnelling rates with attosecond time resolution and tunnelling delay times. Here we study laser-induced tunnelling by using a weak probe field to steer the tunnelled electron in the lateral direction and then monitor the effect on the attosecond light bursts emitted when the liberated electron re-encounters the parent ion. We show that this approach allows us to measure the time at which the electron exits from the tunnelling barrier. We demonstrate the high sensitivity of the measurement by detecting subtle delays in ionization times from two orbitals of a carbon dioxide molecule. Measurement of the tunnelling process is essential for all attosecond experiments where strong-field ionization initiates ultrafast dynamics. Our approach provides a general tool for time-resolving multi-electron rearrangements in atoms and molecules--one of the key challenges in ultrafast science.