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  • 1
    Publication Date: 2018
    Description: 〈p〉Argonaute/Piwi proteins can regulate gene expression via RNA degradation and translational regulation using small RNAs as guides. They also promote the establishment of suppressive epigenetic marks on repeat sequences in diverse organisms. In mice, the nuclear Piwi protein MIWI2 and Piwi-interacting RNAs (piRNAs) are required for DNA methylation of retrotransposon sequences and some other sequences. However, its underlying molecular mechanisms remain unclear. Here, we show that piRNA-dependent regions are transcribed at the stage when piRNA-mediated DNA methylation takes place. MIWI2 specifically interacts with RNAs from these regions. In addition, we generated mice with deletion of a retrotransposon sequence either in a representative piRNA-dependent region or in a piRNA cluster. Both deleted regions were required for the establishment of DNA methylation of the piRNA-dependent region, indicating that piRNAs determine the target specificity of MIWI2-mediated DNA methylation. Our results indicate that MIWI2 affects the chromatin state through base-pairing between piRNAs and nascent RNAs, as observed in other organisms possessing small RNA-mediated epigenetic regulation.〈/p〉
    Print ISSN: 0261-4189
    Electronic ISSN: 1460-2075
    Topics: Biology , Medicine
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  • 2
    Publication Date: 2018-02-03
    Description: Crystal defects of two synthesized diamonds doped with boron and phosphorus are compared by synchrotron radiation topography (SRT). The crystal defects in the specimen are mainly dislocations. The dislocations are assembled in bundles in the cone-shape and distributed in the directions approximately towards to and . The Burgers vectors of most of the dislocations are parallel to [202] and oblique to the dislocations, showing that the dislocations are of mixed type. The features of the crystal defects are quite different in several aspects compared with the diamonds without phosphorous doping. The ionic radius of phosphorous is 118.75 percent larger than that of carbon and intensive distortion may occur near the phosphorous ions. The dislocations thus originated in bundles to release the stress caused by the phosphorous doping.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 3
    Publication Date: 2019
    Description: 〈p〉Designing topological and geometrical structures with extended unnatural parameters (negative, near-zero, ultrahigh, or tunable) and counterintuitive properties is a big challenge in the field of metamaterials, especially for relatively unexplored materials with multiphysics coupling effects. For natural piezoelectric ceramics, only five nonzero elements in the piezoelectric matrix exist, which has impeded the design and application of piezoelectric devices for decades. Here, we introduce a methodology, inspired by quasi-symmetry breaking, realizing artificial anisotropy by metamaterial design to excite all the nonzero elements in contrast to zero values in natural materials. By elaborately programming topological structures and geometrical dimensions of the unit elements, we demonstrate, theoretically and experimentally, that tunable nonzero or ultrahigh values of overall effective piezoelectric coefficients can be obtained. While this work focuses on generating piezoelectric parameters of ceramics, the design principle should be inspirational to create unnatural apparent properties of other multiphysics coupling metamaterials.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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