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  • 1
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    Three-dimensional structure determination from a single view (2009)
    Nature Publishing Group (NPG)
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    Publication Date: 2009-12-18
    Description: The ability to determine the structure of matter in three dimensions has profoundly advanced our understanding of nature. Traditionally, the most widely used schemes for three-dimensional (3D) structure determination of an object are implemented by acquiring multiple measurements over various sample orientations, as in the case of crystallography and tomography, or by scanning a series of thin sections through the sample, as in confocal microscopy. Here we present a 3D imaging modality, termed ankylography (derived from the Greek words ankylos meaning 'curved' and graphein meaning 'writing'), which under certain circumstances enables complete 3D structure determination from a single exposure using a monochromatic incident beam. We demonstrate that when the diffraction pattern of a finite object is sampled at a sufficiently fine scale on the Ewald sphere, the 3D structure of the object is in principle determined by the 2D spherical pattern. We confirm the theoretical analysis by performing 3D numerical reconstructions of a sodium silicate glass structure at 2 A resolution, and a single poliovirus at 2-3 nm resolution, from 2D spherical diffraction patterns alone. Using diffraction data from a soft X-ray laser, we also provide a preliminary demonstration that ankylography is experimentally feasible by obtaining a 3D image of a test object from a single 2D diffraction pattern. With further development, this approach of obtaining complete 3D structure information from a single view could find broad applications in the physical and life sciences.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Raines, Kevin S -- Salha, Sara -- Sandberg, Richard L -- Jiang, Huaidong -- Rodriguez, Jose A -- Fahimian, Benjamin P -- Kapteyn, Henry C -- Du, Jincheng -- Miao, Jianwei -- England -- Nature. 2010 Jan 14;463(7278):214-7. doi: 10.1038/nature08705. Epub 2009 Dec 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉[1] Department of Physics and Astronomy, [2] California NanoSystems Institute.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20016484" target="_blank"〉PubMed〈/a〉
    Keywords: Algorithms ; Cryoelectron Microscopy ; Glass/*chemistry ; Imaging, Three-Dimensional/*methods ; Lasers ; Molecular Conformation ; Molecular Dynamics Simulation ; Molecular Imaging/*methods ; Poliovirus/*chemistry/ultrastructure ; *Scattering, Radiation ; Silicates/*chemistry ; X-Rays
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 2
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    Preserving electron spin coherence in solids by optimal dynamical decoupling (2009)
    Nature Publishing Group (NPG)
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    Publication Date: 2009-10-30
    Description: To exploit the quantum coherence of electron spins in solids in future technologies such as quantum computing, it is first vital to overcome the problem of spin decoherence due to their coupling to the noisy environment. Dynamical decoupling, which uses stroboscopic spin flips to give an average coupling to the environment that is effectively zero, is a particularly promising strategy for combating decoherence because it can be naturally integrated with other desired functionalities, such as quantum gates. Errors are inevitably introduced in each spin flip, so it is desirable to minimize the number of control pulses used to realize dynamical decoupling having a given level of precision. Such optimal dynamical decoupling sequences have recently been explored. The experimental realization of optimal dynamical decoupling in solid-state systems, however, remains elusive. Here we use pulsed electron paramagnetic resonance to demonstrate experimentally optimal dynamical decoupling for preserving electron spin coherence in irradiated malonic acid crystals at temperatures from 50 K to room temperature. Using a seven-pulse optimal dynamical decoupling sequence, we prolonged the spin coherence time to about 30 mus; it would otherwise be about 0.04 mus without control or 6.2 mus under one-pulse control. By comparing experiments with microscopic theories, we have identified the relevant electron spin decoherence mechanisms in the solid. Optimal dynamical decoupling may be applied to other solid-state systems, such as diamonds with nitrogen-vacancy centres, and so lay the foundation for quantum coherence control of spins in solids at room temperature.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Du, Jiangfeng -- Rong, Xing -- Zhao, Nan -- Wang, Ya -- Yang, Jiahui -- Liu, R B -- England -- Nature. 2009 Oct 29;461(7268):1265-8. doi: 10.1038/nature08470.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026, China. djf@ustc.edu.cn〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19865168" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    Ca(2+)/calmodulin regulates salicylic-acid-mediated plant immunity (2009)
    Nature Publishing Group (NPG)
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    Publication Date: 2009-01-06
    Description: Intracellular calcium transients during plant-pathogen interactions are necessary early events leading to local and systemic acquired resistance. Salicylic acid, a critical messenger, is also required for both of these responses, but whether and how salicylic acid level is regulated by Ca(2+) signalling during plant-pathogen interaction is unclear. Here we report a mechanism connecting Ca(2+) signal to salicylic-acid-mediated immune response through calmodulin, AtSR1 (also known as CAMTA3), a Ca(2+)/calmodulin-binding transcription factor, and EDS1, an established regulator of salicylic acid level. Constitutive disease resistance and elevated levels of salicylic acid in loss-of-function alleles of Arabidopsis AtSR1 suggest that AtSR1 is a negative regulator of plant immunity. This was confirmed by epistasis analysis with mutants of compromised salicylic acid accumulation and disease resistance. We show that AtSR1 interacts with the promoter of EDS1 and represses its expression. Furthermore, Ca(2+)/calmodulin-binding to AtSR1 is required for suppression of plant defence, indicating a direct role for Ca(2+)/calmodulin in regulating the function of AtSR1. These results reveal a previously unknown regulatory mechanism linking Ca(2+) signalling to salicylic acid level.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Du, Liqun -- Ali, Gul S -- Simons, Kayla A -- Hou, Jingguo -- Yang, Tianbao -- Reddy, A S N -- Poovaiah, B W -- England -- Nature. 2009 Feb 26;457(7233):1154-8. doi: 10.1038/nature07612. Epub 2009 Jan 4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Center for Integrated Biotechnology and Department of Horticulture, Washington State University, Pullman, Washington 99164-6414, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19122675" target="_blank"〉PubMed〈/a〉
    Keywords: Arabidopsis/genetics/*immunology/*metabolism ; Arabidopsis Proteins/antagonists & inhibitors/genetics/metabolism ; Calcium/*metabolism ; Calcium Signaling ; Calmodulin/*metabolism ; DNA-Binding Proteins/genetics/metabolism ; Gene Expression Regulation, Plant ; *Immunity, Innate ; Mutation/genetics ; Plant Diseases/genetics/*immunology ; Promoter Regions, Genetic ; Repressor Proteins/antagonists & inhibitors/genetics/metabolism ; Salicylic Acid/*metabolism ; Transcription, Genetic
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 4
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    Fractional quantum Hall effect and insulating phase of Dirac electrons in graphene (2009)
    Nature Publishing Group (NPG)
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    Publication Date: 2009-10-16
    Description: In graphene, which is an atomic layer of crystalline carbon, two of the distinguishing properties of the material are the charge carriers' two-dimensional and relativistic character. The first experimental evidence of the two-dimensional nature of graphene came from the observation of a sequence of plateaus in measurements of its transport properties in the presence of an applied magnetic field. These are signatures of the so-called integer quantum Hall effect. However, as a consequence of the relativistic character of the charge carriers, the integer quantum Hall effect observed in graphene is qualitatively different from its semiconductor analogue. As a third distinguishing feature of graphene, it has been conjectured that interactions and correlations should be important in this material, but surprisingly, evidence of collective behaviour in graphene is lacking. In particular, the quintessential collective quantum behaviour in two dimensions, the fractional quantum Hall effect (FQHE), has so far resisted observation in graphene despite intense efforts and theoretical predictions of its existence. Here we report the observation of the FQHE in graphene. Our observations are made possible by using suspended graphene devices probed by two-terminal charge transport measurements. This allows us to isolate the sample from substrate-induced perturbations that usually obscure the effects of interactions in this system and to avoid effects of finite geometry. At low carrier density, we find a field-induced transition to an insulator that competes with the FQHE, allowing its observation only in the highest quality samples. We believe that these results will open the door to the physics of FQHE and other collective behaviour in graphene.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Du, Xu -- Skachko, Ivan -- Duerr, Fabian -- Luican, Adina -- Andrei, Eva Y -- England -- Nature. 2009 Nov 12;462(7270):192-5. doi: 10.1038/nature08522. Epub 2009 Oct 14.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08855, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19829294" target="_blank"〉PubMed〈/a〉
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    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 5
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    Primate archaeology (2009)
    Nature Publishing Group (NPG)
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    Publication Date: 2009-07-17
    Description: All modern humans use tools to overcome limitations of our anatomy and to make difficult tasks easier. However, if tool use is such an advantage, we may ask why it is not evolved to the same degree in other species. To answer this question, we need to bring a long-term perspective to the material record of other members of our own order, the Primates.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Haslam, Michael -- Hernandez-Aguilar, Adriana -- Ling, Victoria -- Carvalho, Susana -- de la Torre, Ignacio -- DeStefano, April -- Du, Andrew -- Hardy, Bruce -- Harris, Jack -- Marchant, Linda -- Matsuzawa, Tetsuro -- McGrew, William -- Mercader, Julio -- Mora, Rafael -- Petraglia, Michael -- Roche, Helene -- Visalberghi, Elisabetta -- Warren, Rebecca -- England -- Nature. 2009 Jul 16;460(7253):339-44. doi: 10.1038/nature08188.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Leverhulme Centre for Human Evolutionary Studies, University of Cambridge, Cambridge CB2 1QH, UK. mah66@cam.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19606139" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Animals, Wild/physiology/psychology ; *Archaeology/trends ; *Behavior, Animal ; Hominidae ; Human Characteristics ; Humans ; *Primates/physiology/psychology ; *Technology/methods
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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