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Berlin Brandenburg

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  • Nature
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  • 1
    Language: English
    In: Nature, December 2018, Vol.564(7734), pp.E2-E4
    Description: While it is still not known whether a material geometry exists that can achieve the Hashin-Shtrikman shear upper bound away from the low-density limit, the cubic + octet foam achieves 94.7% of the HashinShtrikman upper bound on shear modulus, and 95.2% of the bound on Young's modulus, at a moderate relative...
    Keywords: New York ; Fillets ; Anisotropy ; Webs ; Structural Analysis ; Materials Science ; Thickness Ratio ; Wall Thickness ; Mechanical Engineering ; Elasticity ; Homogenization ; Structural Analysis ; Microstructure ; Density ; Foam ; Mechanical Engineering ; Density ; Shear Modulus ; Upper Bounds ; Modulus of Elasticity;
    ISSN: 00280836
    E-ISSN: 1476-4687
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  • 2
    In: Nature, 2015, Vol.523(7562), p.531
    Keywords: Fossils ; Hominidae ; Museums ; Paleontology -- Education;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 3
    In: Nature, 2011, Vol.476(7359), p.163
    Description: This year, 2011, marks the forty-year anniversary of the statistical analysis of retinoblastoma that provided the first evidence that tumorigenesis can be initiated by as few as two mutations. This work provided the foundation for the two-hit hypothesis that explained the role of recessive tumour suppressor genes (TSGs) in dominantly inherited cancer susceptibility syndromes. However, four decades later, it is now known that even partial inactivation of tumour suppressors can critically contribute to tumorigenesis. Here we analyse this evidence and propose a continuum model of TSG function to explain the full range of TSG mutations found in cancer.
    Keywords: Sciences (General) ; Physics;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 4
    Language: English
    In: Nature, July 30, 2015, Vol.523(7562), p.531(1)
    Keywords: Fossil Hominids -- Study And Teaching
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 5
    In: Nature, 2011, Vol.478(7368), p.209
    Description: Many replication initiators form higher-order oligomers that process host replication origins to promote replisome formation. In addition to dedicated duplex-DNA-binding domains, cellular initiators possess AAA+ (ATPases associated with various cellular activities) elements that drive functions ranging from protein assembly to origin recognition. In bacteria, the AAA+ domain of the initiator DnaA has been proposed to assist in single-stranded DNA formation during origin melting. Here we show crystallographically and in solution that the ATP-dependent assembly of Aquifex aeolicus DnaA into a spiral oligomer creates a continuous surface that allows successive AAA+ domains to bind and extend single-stranded DNA segments. The mechanism of binding is unexpectedly similar to that of RecA, a homologous recombination factor, but it differs in that DnaA promotes a nucleic acid conformation that prevents pairing of a complementary strand. These findings, combined with strand-displacement assays, indicate that DnaA opens replication origins by a direct ATP-dependent stretching mechanism. Comparative studies reveal notable commonalities between the approach used by DnaA to engage DNA substrates and other, nucleic-acid-dependent, AAA+ systems.
    Keywords: Nucleic Acid Conformation ; Replication Origin ; Bacterial Proteins -- Metabolism ; DNA, Bacterial -- Chemistry ; DNA-Binding Proteins -- Metabolism;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 6
    In: Nature, 2011, Vol.472(7342), p.197
    Description: Coronal cavities are large low-density regions formed by hemispheric-scale magnetic flux ropes suspended in the Sun's outer atmosphere. They evolve over time, eventually erupting as the dark cores of coronal mass ejections. Although coronal mass ejections are common and can significantly affect planetary magnetospheres, the mechanisms by which cavities evolve to an eruptive state remain poorly understood. Recent optical observations of high-latitude 'polar crown' prominences within coronal cavities reveal dark, low-density 'bubbles' that undergo Rayleigh-Taylor instabilities to form dark plumes rising into overlying coronal cavities. These observations offered a possible mechanism for coronal cavity evolution, although the nature of the bubbles, particularly their buoyancy, was hitherto unclear. Here we report simultaneous optical and extreme-ultraviolet observations of polar crown prominences that show that these bubbles contain plasma at temperatures in the range (2.5-12)10 super(5) kelvin, which is 25-120 times hotter than the overlying prominence. This identifies a source of the buoyancy, and suggests that the coronal cavity-prominence system supports a novel form of magneto-thermal convection in the solar atmosphere, challenging current hydromagnetic concepts of prominences and their relation to coronal cavities.
    Keywords: Solar Convection ; Corona ; Coronal Observations ; Coronal Studies ; Solar Prominences ; Coronal Mass Ejections ; Convection Development ; Rayleigh-Taylor Instabilities ; Buoyancy ; Temperature ; Convection ; Plumes ; Atmosphere ; Sun ; Solar Prominences (523.987);
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 7
    In: Nature, 2015, Vol.519(7543), p.321
    Description: Initiation of cellular DNA replication is tightly controlled to sustain genomic integrity. In eukaryotes, the heterohexameric origin recognition complex (ORC) is essential for coordinating replication onset. Here we describe the crystal structure of Drosophila ORC at 3.5 [Angstrom] resolution, showing that the 270 kilodalton initiator core complex comprises a two-layered notched ring in which a collar of winged-helix domains from the Orc1-5 subunits sits atop a layer of AAA+ (ATPases associated with a variety of cellular activities) folds. Although canonical inter-AAA+ domain interactions exist between four of the six ORC subunits, unanticipated features are also evident. These include highly interdigitated domain-swapping interactions between the winged-helix folds and AAA+ modules of neighbouring protomers, and a quasi-spiral arrangement of DNA binding elements that circumnavigate an approximately 20 [Angstrom] wide channel in the centre of the complex. Comparative analyses indicate that ORC encircles DNA, using its winged-helix domain face to engage the mini-chromosome maintenance 2-7 (MCM2-7) complex during replicative helicase loading; however, an observed out-of-plane rotation of more than 90[degrees] for the Orcl AAA+ domain disrupts interactions with catalytic amino acids in Orc4, narrowing and sealing off entry into the central channel. Prima facie, our data indicate that Drosophila ORC can switch between active and autoinhibited conformations, suggesting a novel means for cell cycle and/or developmental control of ORC functions.
    Keywords: Crystal Structure -- Research ; Eukaryotes -- Origin ; Dna Replication -- Research ; Genetic Research;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 8
    In: Nature, 2007, Vol.449(7165), p.972
    Keywords: Legislation, Drug -- Trends ; Patents As Topic -- Legislation & Jurisprudence;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 9
    In: Nature, 2017
    Description: A wide variety of high-performance applications require materials for which shape control is maintained under substantial stress, and that have minimal density. Bio-inspired hexagonal and square honeycomb structures and lattice materials based on repeating unit cells composed of webs or trusses, when made from materials of high elastic stiffness and low density, represent some of the lightest, stiffest and strongest materials available today. Recent advances in 3D printing and automated assembly have enabled such complicated material geometries to be fabricated at low (and declining) cost. These mechanical metamaterials have properties that are a function of their mesoscale geometry as well as their constituents, leading to combinations of properties that are unobtainable in solid materials; however, a material geometry that achieves the theoretical upper bounds for isotropic elasticity and strain energy storage (the Hashin-Shtrikman upper bounds) has yet to be identified. Here we evaluate the manner in which strain energy distributes under load in a representative selection of material geometries, to identify the morphological features associated with high elastic performance. Using finite-element models, supported by analytical methods, and a heuristic optimization scheme, we identify a material geometry that achieves the Hashin-Shtrikman upper bounds on isotropic elastic stiffness. Previous work has focused on truss networks and anisotropic honeycombs, neither of which can achieve this theoretical limit. We find that stiff but well distributed networks of plates are required to transfer loads efficiently between neighbouring members. The resulting low-density mechanical metamaterials have many advantageous properties: their mesoscale geometry can facilitate large crushing strains with high energy absorption, optical bandgaps and mechanically tunable acoustic bandgaps, high thermal insulation, buoyancy, and fluid storage and transport. Our relatively simple design can be manufactured using origami-like sheet folding and bonding methods.
    Keywords: Stiffness ; Strain-Energy ; Upper-Bounds ; 3d-Printing ; Elasticity ; Honeycomb ; Unit-Cells ; Solid-Materials ; Materials-Stress ; Optical-Band-GAP ; Acoustics ; Heat-Insulation ; Fluid-Transport ; Steifigkeit ; Verformungsenergie ; Oberer Grenzwert ; 3d-Druck ; Elastizität ; Wabenstruktur ; Zelleinheit ; Feststoff ; Materialbeanspruchung ; Optische Bandlücke ; Akustik ; Wärmeisolation ; Flüssigkeitstransport ; Sciences (General) ; Physics;
    ISSN: 0028-0836
    E-ISSN: 1476-4687
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  • 10
    In: Nature, 2007, Vol.447(7143), p.407
    Description: An important development in understanding the influence of chromatin on gene regulation has been the finding that DNA methylation and histone post-translational modifications lead to the recruitment of protein complexes that regulate transcription. Early interpretations of this phenomenon involved gene regulation reflecting predictive activating or repressing types of modification. However, further exploration reveals that transcription occurs against a backdrop of mixtures of complex modifications, which probably have several roles. Although such modifications were initially thought to be a simple code, a more likely model is of a sophisticated, nuanced chromatin "language" in which different combinations of basic building blocks yield dynamic functional outcomes. [PUBLICATION ]
    Keywords: Control ; Histones ; Genes ; Compact Disks ; Crystal Growth ; Repressing ; Carbon Monoxide ; Recruitment ; General and Nonclassified (MD) ; General and Nonclassified (EC) ; General and Nonclassified (Ed) ; General and Nonclassified (Ep) ; Surveying, Theory, and Analysis (CE) ; Design Principles, Theory, and Analysis (Mt) ; Computing Milieux (General) (Ci) ; Electronics and Communications Milieux (General) (Ea) ; Solid State Milieux (General) (So) ; Article;
    ISSN: 0028-0836
    E-ISSN: 14764687
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