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  • 1
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    P-V-T equation of state and high-pressure behavior of CaCO3 aragonite (2015)
    Mineralogical Society of America
    Details
    Publication Date: 2015-10-02
    Description: The equation of state of aragonite was determined by in situ synchrotron X-ray diffraction experiments on a hot-pressed polycrystalline specimen of aragonite within its stability field up to 5.8 GPa and 1173 K. As a complement to this experimental study, first-principle density functional theory calculations were performed up to 20 GPa at 0 K. Thermoelastic parameters for aragonite (CaCO 3 ) were derived by a least-squares fit of the experimental P-V-T data to the third-order Birch-Murnaghan equation of state (EOS), yielding the bulk modulus and its pressure and temperature derivatives K 0 = 65.24 ± 0.24 GPa, K ' 0 = 4.95 ± 0.12, ( K T / T ) P = –0.024 ± 0.002 GPa/K and volume thermal expansion α 300 = (6.1 ± 0.7) x 10 –5 K –1 . The analyses of the axial compressibility at ambient temperature show that the c -axis is much more compressible than the a - and b- axes. Based on first-principle calculations, the anisotropic compression behavior of aragonite structure is explained by the heterogeneous shortening of 〈Ca-O〉 and 〈C-O〉 bond lengths and the rotation of 〈O-C-O〉 angles along the a -, b -, and c -axes, whereas the unit-cell volume change of aragonite under compression is accommodated by comparable compression rate of the CaO 9 polyhedra and the voids in the crystal lattice. The results attained from this study provide important thermoelastic parameters for understanding the thermodynamic behavior and chemical reactions involving aragonite at subduction zone conditions.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 2
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    A statistical study of the relative locations of electron and proton auroral boundaries inferred from meridian scanning photometer observations (2012)
    Wiley
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    Publication Date: 2012-06-07
    Description: We present the results of a statistical study of the absolute and relative locations of the equatorward boundaries of the proton and diffuse electron auroras. The boundaries were analyzed using latitude scans of 630.0 and 486.0 nm (“Hβ”) emissions obtained with the meridian scanning photometers at Gillam and Pinawa, Canada with DMSP overflights. The aurora data were classified into three different steady geomagnetic activity states, one being long-duration quiet intervals and the other two being moderate and active steady magnetospheric convection (SMC) events. Both case and statistical studies show that the quiet times dusk-premidnight proton aurora extends slightly equatorward of the electron aurora. This is reversed on the dawnside. In contrast, the electron aurora during moderate and active SMC intervals lies equatorward of the proton aurora throughout the entire nightside covered in this work (20–03 MLT). There is a dawn-dusk offset in the auroral oval location, with the proton aurora shifting toward premidnight and the electron aurora toward postmidnight. Moreover, with increasing geomagnetic activity, both of the auroras intrude to lower latitude. The penetration of the electron boundary equatorward of the proton precipitation across this MLT range has not been previously identified. We attribute this to the fact that the equatorward part of the diffuse electron aurora is produced by lower energy electrons to which the 630.0 nm emission is more responsive and so marks a more realistic location of the electron equatorward boundary than do the 557.7 nm and UV emissions used in previous intercomparisons of these boundaries.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Statistical relationships between enhanced polar cap flows and PBIs (2013)
    Wiley
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    Publication Date: 2013-12-13
    Description: [1]  Poleward boundary intensifications (PBIs) are auroral intensifications along the poleward boundary of the auroral oval and occur during all levels of geomagnetic activity. However, little is known about the triggering of PBIs. Recent case studies have indicated the existence of longitudinally localized flow channels in the polar cap near, and directed towards, the nightside open-closed field line boundary just before PBIs. Motivated by these studies, we analyze 115 events of coordinated observations by the THEMIS all-sky imager and SuperDARN HF radar at Rankin Inlet to determine if this polar cap flow-PBI relationship is commonly observed. We start with isolated and intense PBIs and examine the probability of them being associated with equatorward-directed polar cap flows. Our results show the association to be frequent (90%), with one-to-one correlations occurring in ~50% of events. Considering the limitations of the radar observations, this result indicates that PBIs are commonly correlated with polar cap flow channels directed towards, and then traversing, the open-closed field line boundary. The flows statistically occur ~1-2 min before the PBI initiations, and the duration and width of the flows are comparable to those of the PBIs. We also perform a reverse study by starting with isolated polar cap flows and obtain similar results. The remarkably high occurrence of association between enhanced polar cap flows and PBIs indicates that enhanced meso-scale flows within the open field line region that traverse the open-closed field line boundary are an important driver of PBI formation.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Arabidopsis pollen tube integrity and sperm release are regulated by RALF-mediated signaling (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-12-22
    Description: In flowering plants, fertilization requires complex cell-to-cell communication events between the pollen tube and the female reproductive tissues, which are controlled by extracellular signaling molecules interacting with receptors at the pollen tube surface. We found that two such receptors in Arabidopsis , BUPS1 and BUPS2, and their peptide ligands, RALF4 and RALF19, are pollen tube–expressed and are required to maintain pollen tube integrity. BUPS1 and BUPS2 interact with receptors ANXUR1 and ANXUR2 via their ectodomains, and both sets of receptors bind RALF4 and RALF19. These receptor-ligand interactions are in competition with the female-derived ligand RALF34, which induces pollen tube bursting at nanomolar concentrations. We propose that RALF34 replaces RALF4 and RALF19 at the interface of pollen tube–female gametophyte contact, thereby deregulating BUPS-ANXUR signaling and in turn leading to pollen tube rupture and sperm release.
    Keywords: Botany, Cell Biology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Lack of CUL4B leads to increased abundance of GFAP-positive cells that is mediated by PTGDS in mouse brain (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-24
    Description: Astrocytes are the most abundant cell type in the mammalian brain and are important for the functions of the central nervous system. Glial fibrillary acidic protein (GFAP) is regarded as a hallmark of mature astrocytes, though some GFPA-positive cells may act as neural stem cells. Missense heterozygous mutations in GFAP cause Alexander disease that manifests leukodystrophy and intellectual disability. Here, we show that CUL4B, a scaffold protein that assembles E3 ubiquitin ligase, represses the expression of GFAP in neural progenitor cells (NPCs) during brain development. Lack of Cul4b in NPCs in cultures led to increased generation of astrocytes, marked by GFAP and S100β. The GFAP+ cells were also found to be more abundant in the brains of nervous system-specific Cul4b knockout mice in vivo . Moreover, we demonstrated that the increased generation of GFAP+ cells from Cul4b -null NPCs was mediated by an upregulation of prostaglandin D2 synthase PTGDS. We showed that the increased GFAP expression can be attenuated by pharmacological inhibition of the PTGDS enzymatic activity or by shRNA-mediated knockdown of Ptgds . Importantly, exogenously added PTGDS could promote the generation of GFAP+ cells from wild-type NPCs. We further observed that Ptgds is targeted and repressed by the CUL4B/PRC2 complex. Together, our results demonstrate CUL4B as a negative regulator of GFAP expression during neural development.
    Print ISSN: 0964-6906
    Electronic ISSN: 1460-2083
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 6
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    KLL dielectronic recombination resonant strengths of He-like up to O-like tungsten ions (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-05-05
    Description: Dielectronic recombination (DR) is an important process in hot plasma physics as well as in atomic structure and collision theory. This work reports the studies of the KLL DR resonance strengths of He-, Li-, Be-, B-, C-, N-, and O-like tungsten ions, through both experiment and calculation. The experimental resonance strengths were determined within uncertainty below 11% at the Shanghai electron beam ion trap by employing a fast electron beam-energy scanning technique. A fully relativistic configuration interaction method implemented in the flexible atomic code was employed to calculate DR process and also radiative recombination (RR). The consideration of the interference effect between DR and RR was revealed to be necessary to determine the resonance strength.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
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    A New Structural Insight into XPA-DNA Interaction (2014)
    Portland Press
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    Publication Date: 2014-11-11
    Description: Xeroderma pigmentosum group A (XPA) protein is an essential factor for nucleotide excision repair (NER) which is believed to be involved in DNA damage recognition/verification, NER factor recruiting, and stabilization of repair intermediates. Past studies on the structure of XPA have focused primarily on XPA interaction with damaged DNA. However, how XPA interacts with other DNA structures remains unknown though recent evidence suggest that these structures could be important for its roles in both NER and non-NER activities. Previously, we reported that XPA recognizes undamaged DNA double-strand/single-strand (ds/ssDNA) junctions with a binding affinity much higher than its ability to bind bulky DNA damage. To understand how this interaction occurs biochemically we implemented a structural determination of the interaction using a mass spectrometry-based protein footprinting method and limited proteolysis. By monitoring surface accessibility of XPA lysines to NHS-biotin modification in the free protein and the DNA junction-bound complex we show that XPA physically interacts with the DNA junctions via two lysines, K168 and K179, located in the previously known XPA(98-219) DNA-binding domain (DBD). Importantly, we also uncovered new lysine residues, outside of the known DBD, involved in the binding. We found that residues K221, K222, K224, K236 in the C-terminal domain are involved in DNA binding. Limited proteolysis analysis of XPA-DNA interaction further confirmed the observation. Structural modeling with these data suggests a clamp-like DNA binding domain for the XPA binding to ds/ssDNA junction. Our results provide a novel structure-function view of XPA-DNA junction interaction.
    Print ISSN: 0144-8463
    Electronic ISSN: 1573-4935
    Topics: Biology , Chemistry and Pharmacology
    Published by Portland Press
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  • 8
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    Structural basis of the mercury(II)-mediated conformational switching of the dual-function transcriptional regulator MerR (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-29
    Description: The mer operon confers bacterial resistance to inorganic mercury (Hg 2+ ) and organomercurials by encoding proteins involved in sensing, transport and detoxification of these cytotoxic agents. Expression of the mer operon is under tight control by the dual-function transcriptional regulator MerR. The metal-free, apo MerR binds to the mer operator/promoter region as a repressor to block transcription initiation, but is converted into an activator upon Hg 2+ -binding. To understand how MerR interacts with Hg 2+ and how Hg 2+ -binding modulates MerR function, we report here the crystal structures of apo and Hg 2+ -bound MerR from Bacillus megaterium , corresponding respectively to the repressor and activator conformation of MerR. To our knowledge, the apo-MerR structure represents the first visualization of a MerR family member in its intact and inducer-free form. And the Hg 2+ -MerR structure offers the first view of a triligated Hg 2+ -thiolate center in a metalloprotein, confirming that MerR binds Hg 2+ via trigonal planar coordination geometry. Structural comparison revealed the conformational transition of MerR is coupled to the assembly/disassembly of a buried Hg 2+ binding site, thereby providing a structural basis for the Hg 2+ -mediated functional switching of MerR. The pronounced Hg 2+ -induced repositioning of the MerR DNA-binding domains suggests a plausible mechanism for the transcriptional regulation of the mer operon.
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 9
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    Optical configuration optimization and calibration for the POINT system on EAST (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-08-23
    Description: Calibration of the polarimeter system is one of the key elements to determine the overall measurement accuracy. The anisotropic reflection and transmission properties of the mesh beam splitters can easily distort the polarization state of the circularly polarized beams. Using a rotating crystal quartz λ/2-waveplate to replace the plasma can effectively allow us to obtain the ratio of the measured Faraday rotation angle to the known rotation angle of the waveplate. This ratio is used to estimate the calibration factor for each chord to be accurately determined and help to minimize distortions introduced by the wire-mesh beam splitters. With the novel configuration optimization, the distortion of polarization state is effectively eliminated.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 10
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    Dual Fano and Lorentzian line profile properties of autoionizing states (2015)
    American Physical Society (APS)
    Details
    Publication Date: 2015-06-25
    Description: Author(s): B. Tu, J. Xiao, K. Yao, Y. Shen, Y. Yang, D. Lu, W. X. Li, M. L. Qiu, X. Wang, C. Y. Chen, Y. Fu, B. Wei, C. Zheng, L. Y. Huang, B. H. Zhang, Y. J. Tang, R. Hutton, and Y. Zou Photon absorption spectroscopy is a powerful tool for uncovering the structure of atoms, molecules, and solids. Symmetric Lorentzian and asymmetric Fano line shapes are fundamental spectroscopic signatures related to the structural and dynamical properties. Recently, Ott et al. [ Science 340 , 716 (20... [Phys. Rev. A 91, 060502(R)] Published Mon Jun 22, 2015
    Keywords: Atomic and molecular structure and dynamics
    Print ISSN: 1050-2947
    Electronic ISSN: 1094-1622
    Topics: Physics
    Published by American Physical Society (APS)
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