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  • 1
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    High pressure behaviour of uranium dicarbide (UC2): Ab-initio study (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-08-25
    Description: The structural stability of uranium dicarbide has been examined under hydrostatic compression employing evolutionary structure search algorithm implemented in the universal structure predictor: evolutionary Xtallography (USPEX) code in conjunction with ab-initio electronic band structure calculation method. The ab-initio total energy calculations involved for this purpose have been carried out within both generalized gradient approximations (GGA) and GGA + U approximations. Our calculations under GGA approximation predict the high pressure structural sequence of tetragonal → monoclinic → orthorhombic for this material with transition pressures of ∼8 GPa and 42 GPa, respectively. The same transition sequence is predicted by calculations within GGA + U also with transition pressures placed at ∼24 GPa and ∼50 GPa, respectively. Further, on the basis of comparison of zero pressure equilibrium volume and equation of state with available experimental data, we find that GGA + U approximation with U = 2.5 eV describes this material better than the simple GGA approximation. The theoretically predicted high pressure structural phase transitions are in disagreement with the only high experimental study by Dancausse et al . [J. Alloys. Compd. 191 , 309 (1993)] on this compound which reports a tetragonal to hexagonal phase transition at a pressure of ∼17.6 GPa. Interestingly, during lowest enthalpy structure search using USPEX, we do not see any hexagonal phase to be closer to the predicted monoclinic phase even within 0.2 eV/f. unit. More experiments with varying carbon contents in UC 2 sample are required to resolve this discrepancy. The existence of these high pressure phases predicted by static lattice calculations has been further substantiated by analyzing the elastic and lattice dynamic stability of these structures in the pressure regimes of their structural stability. Additionally, various thermo-physical quantities such as equilibrium volume, bulk modulus, Debye temperature, thermal expansion coefficient, Gruneisen parameter, and heat capacity at ambient conditions have been determined from these calculations and compared with the available experimental data.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Prediction of new high pressure structural sequence in thorium carbide: A first principles study (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-05-12
    Description: In the present work, we report the detailed electronic band structure calculations on thorium monocarbide. The comparison of enthalpies, derived for various phases using evolutionary structure search method in conjunction with first principles total energy calculations at several hydrostatic compressions, yielded a high pressure structural sequence of NaCl type (B1) → Pnma → Cmcm → CsCl type (B2) at hydrostatic pressures of ∼19 GPa, 36 GPa, and 200 GPa, respectively. However, the two high pressure experimental studies by Gerward et al . [J. Appl. Crystallogr. 19 , 308 (1986); J. Less-Common Met. 161 , L11 (1990)] one up to 36 GPa and other up to 50 GPa, on substoichiometric thorium carbide samples with carbon deficiency of ∼20%, do not report any structural transition. The discrepancy between theory and experiment could be due to the non-stoichiometry of thorium carbide samples used in the experiment. Further, in order to substantiate the results of our static lattice calculations, we have determined the phonon dispersion relations for these structures from lattice dynamic calculations. The theoretically calculated phonon spectrum reveal that the B1 phase fails dynamically at ∼33.8 GPa whereas the Pnma phase appears as dynamically stable structure around the B1 to Pnma transition pressure. Similarly, the Cmcm structure also displays dynamic stability in the regime of its structural stability. The B2 phase becomes dynamically stable much below the Cmcm to B2 transition pressure. Additionally, we have derived various thermophysical properties such as zero pressure equilibrium volume, bulk modulus, its pressure derivative, Debye temperature, thermal expansion coefficient and Gruneisen parameter at 300 K and compared these with available experimental data. Further, the behavior of zero pressure bulk modulus, heat capacity and Helmholtz free energy has been examined as a function temperature and compared with the experimental data of Danan [J. Nucl. Mater. 57 , 280 (1975)].
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Structural, elastic, and lattice dynamic stability of yttrium selenide (YSe) under pressure: A first principle study (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-11-19
    Description: Structural, elastic, and lattice dynamical stability of YSe has been investigated as a function of pressure through first principles electronic band structure calculations. The comparison of enthalpies of rocksalt type (B1) and CsCl type cubic (B2) structures determined as a function of pressure suggests that the B1 phase will transform to B2 structure at ∼32 (30 GPa at 300 K obtained from comparison of Gibbs free energy at 300 K). The transition is identified to be of first order in nature with a volume discontinuity of ∼6.2% at the transition pressure. Furthermore, the theoretically determined equation of state has been utilized to derive various physical quantities, such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus. The single crystal elastic constants have been predicted at various pressures for both the B1 and B2 structures using the energy strain method. The activation barrier between B1 and B2 phases calculated at transition point is ∼19.7mRy/formula unit. Our lattice dynamic calculations show that both the B1 as well as B2 structures are lattice dynamically stable not only at ambient pressure but also at transition pressure. The B1 phase becomes lattice dynamically unstable at ∼112 GPa, i.e., much beyond the transition pressure. The effect of temperature on volume and bulk modulus of the YSe in B1 phase has also been examined.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Identification of a colonial chordate histocompatibility gene (2013)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2013-07-28
    Description: Histocompatibility is the basis by which multicellular organisms of the same species distinguish self from nonself. Relatively little is known about the mechanisms underlying histocompatibility reactions in lower organisms. Botryllus schlosseri is a colonial urochordate, a sister group of vertebrates, that exhibits a genetically determined natural transplantation reaction, whereby self-recognition between colonies leads to formation of parabionts with a common vasculature, whereas rejection occurs between incompatible colonies. Using genetically defined lines, whole-transcriptome sequencing, and genomics, we identified a single gene that encodes self-nonself and determines "graft" outcomes in this organism. This gene is significantly up-regulated in colonies poised to undergo fusion and/or rejection, is highly expressed in the vasculature, and is functionally linked to histocompatibility outcomes. These findings establish a platform for advancing the science of allorecognition.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3810301/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3810301/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Voskoboynik, Ayelet -- Newman, Aaron M -- Corey, Daniel M -- Sahoo, Debashis -- Pushkarev, Dmitry -- Neff, Norma F -- Passarelli, Benedetto -- Koh, Winston -- Ishizuka, Katherine J -- Palmeri, Karla J -- Dimov, Ivan K -- Keasar, Chen -- Fan, H Christina -- Mantalas, Gary L -- Sinha, Rahul -- Penland, Lolita -- Quake, Stephen R -- Weissman, Irving L -- 1R01AG037968/AG/NIA NIH HHS/ -- 1R56AI089968/AI/NIAID NIH HHS/ -- K12 HL087746/HL/NHLBI NIH HHS/ -- K99 CA151673/CA/NCI NIH HHS/ -- K99CA151673-01A1/CA/NCI NIH HHS/ -- R01 AG037968/AG/NIA NIH HHS/ -- R01 GM100315/GM/NIGMS NIH HHS/ -- R01GM100315/GM/NIGMS NIH HHS/ -- R56 AI089968/AI/NIAID NIH HHS/ -- T32 CA009302/CA/NCI NIH HHS/ -- Howard Hughes Medical Institute/ -- New York, N.Y. -- Science. 2013 Jul 26;341(6144):384-7. doi: 10.1126/science.1238036.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA. ayeletv@stanford.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23888037" target="_blank"〉PubMed〈/a〉
    Keywords: Alleles ; Animals ; *Genes ; Genome ; Genotype ; Histocompatibility/*genetics ; Immune Tolerance ; Molecular Sequence Data ; Sequence Analysis, DNA ; Transcriptome ; Up-Regulation ; Urochordata/*genetics/*immunology/physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , 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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    Imprints of modal metasomatism in the post-Deccan subcontinental lithospheric mantle: petrological evidence from an ultramafic xenolith in an Eocene lamprophyre, NW India (2017)
    Geological Society (of London)
    Details
    Publication Date: 2017-09-30
    Description: We report here on the occurrence of an interesting mantle-derived ultramafic xenolith entrained in an Eocene ( c. 55 Ma) lamprophyre dyke from the Dongargaon area of the Chhotaudepur alkaline subprovince located within the Narmada Rift Zone, NW India. The mineralogy of the xenolith comprises olivine, clinopyroxene and mica (phlogopite), with the latter occurring essentially as rims around the clinopyroxene. Inclusions of apatite, interstitial sulphide (pyrite) and micron-scale exsolved spinel are widespread. Olivine is forsteritic (Fo 85.34 ), displays little compositional variation and overlaps with that reported from worldwide mantle peridotite xenoliths. Clinopyroxene is a diopside with a compositional range of Wo 48.36 En 43.83 , Fs 6.53 and Ac 1.27 , and is conspicuous by its high CaO (up to 24.4 wt%) and TiO 2 (up to 1.6 wt%) content. Clinopyroxene is also compositionally similar to that reported from ‘enriched’ (metasomatized) peridotite xenoliths rather than those that occur in the ‘normal’ (depleted) peridotitic xenoliths. Phlogopites have a high concentration of fluorine (up to 1 wt%), whereas the apatites show an anomalous enrichment of F (up to 5 wt%), as well as enrichment in Sr (SrO up to 1.9 wt%). Our study provides the first direct petrographical evidence for the modal metasomatism in the post-Deccan subcontinental lithospheric mantle (SCLM) from this domain. From the textural and mineralogical assemblage of the xenolith, we infer that a possible olivine + garnet + orthopyroxene assemblage, in the presence of a metasomatic fluid, has given rise to clinopyroxene + phlogopite + spinel. The paragenesis of apatite essentially as inclusions suggests that it to be the earliest crystallized phase during the metasomatic event. Geothermobarometry of the clinopyroxene in the xenolith reveal temperatures of approximately 1200°C and pressures of approximately 12 kb, which are comparable with such data reported from other Deccan-related xenoliths. Preservation of phlogopite and apatite in the ultramafic xenolith imply that some of the readily fusible metasomatized portions in this domain escaped wholesale melting during the eruption of the Deccan Traps, possibly due to the variable thickness of the underlying SCLM. Supplementary material: A table detailing natural and synthetic standards used for calibration is available at https://doi.org/10.6084/m9.figshare.c.3815296
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 6
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    Hoxb5 marks long-term haematopoietic stem cells and reveals a homogenous perivascular niche (2016)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2016-02-13
    Description: Haematopoietic stem cells (HSCs) are arguably the most extensively characterized tissue stem cells. Since the identification of HSCs by prospective isolation, complex multi-parameter flow cytometric isolation of phenotypic subsets has facilitated studies on many aspects of HSC biology, including self-renewal, differentiation, ageing, niche, and diversity. Here we demonstrate by unbiased multi-step screening, identification of a single gene, homeobox B5 (Hoxb5, also known as Hox-2.1), with expression in the bone marrow that is limited to long-term (LT)-HSCs in mice. Using a mouse single-colour tri-mCherry reporter driven by endogenous Hoxb5 regulation, we show that only the Hoxb5(+) HSCs exhibit long-term reconstitution capacity after transplantation in primary transplant recipients and, notably, in secondary recipients. Only 7-35% of various previously defined immunophenotypic HSCs are LT-HSCs. Finally, by in situ imaging of mouse bone marrow, we show that 〉94% of LT-HSCs (Hoxb5(+)) are directly attached to VE-cadherin(+) cells, implicating the perivascular space as a near-homogenous location of LT-HSCs.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Chen, James Y -- Miyanishi, Masanori -- Wang, Sean K -- Yamazaki, Satoshi -- Sinha, Rahul -- Kao, Kevin S -- Seita, Jun -- Sahoo, Debashis -- Nakauchi, Hiromitsu -- Weissman, Irving L -- F30-HL122096/HL/NHLBI NIH HHS/ -- R01 CA086065/CA/NCI NIH HHS/ -- R01 HL058770/HL/NHLBI NIH HHS/ -- T32 GM007365/GM/NIGMS NIH HHS/ -- U01 HL099999/HL/NHLBI NIH HHS/ -- England -- Nature. 2016 Feb 11;530(7589):223-7. doi: 10.1038/nature16943.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, California 94305, USA. ; Ludwig Center for Cancer Stem Cell Research and Medicine, Stanford University School of Medicine, Stanford, California 94305, USA. ; Division of Stem Cell Therapy, Center for Stem Cell Biology and Regenerative Medicine, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26863982" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Antigens, CD/metabolism ; Biomarkers/analysis ; Bone Marrow/metabolism ; Cadherins/metabolism ; Cell Self Renewal ; Gene Expression Regulation ; Genes, Reporter/genetics ; Hematopoietic Stem Cell Transplantation ; Hematopoietic Stem Cells/*cytology/*metabolism ; Homeodomain Proteins/genetics/*metabolism ; Immunophenotyping ; Male ; Mice ; Mice, Inbred C57BL ; *Stem Cell Niche
    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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  • 7
    Electronic Resource
    Electronic Resource
    Study of precipitation in NaCl:Pb^2^+ by light scattering and ultramicroscopy
    Amsterdam : Elsevier
    Journal of Physics and Chemistry of Solids 45 (1984), S. 69-77 
    Details
    ISSN: 0022-3697
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0022-3697(84)90103-3
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  • 8
    Electronic Resource
    Electronic Resource
    Comments on ''light scattering from a fluid in a nonequilibrium steady state: Plane Couette flow''
    Amsterdam : Elsevier
    Physics Letters A 95 (1983), S. 491-492 
    Details
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0375-9601(83)90504-2
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  • 9
    Electronic Resource
    Electronic Resource
    Faxen's theorem for nonsteady motion of a sphere through a fluid with internal rotation
    Amsterdam : Elsevier
    Physica A: Statistical Mechanics and its Applications 196 (1993), S. 349-362 
    Details
    ISSN: 0378-4371
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0378-4371(93)90200-N
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  • 10
    Electronic Resource
    Electronic Resource
    Light scattering from a fluid in a nonequilibrium steady state: Plane Couette flow
    Amsterdam : Elsevier
    Physics Letters A 93 (1983), S. 476-478 
    Details
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0375-9601(83)90634-5
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