683 research outputs found
Helical Topological Edge States in a Quadrupole Phase
Topological electric quadrupole is a recently proposed concept that extends
the theory of electric polarization of crystals to higher orders. Such a
quadrupole phase supports topological states localized on both edges and
corners. In this work, we show that in a quadrupole phase of honeycomb lattice,
topological helical edge states and pseudo-spin-polarized corner states appear
by making use of a pseudo-spin degree of freedom related to point group
symmetry. Furthermore, we argue that a general condition for emergence of
helical edge states in a (pseudo-)spinful quadrupole phase is mirror or
time-reversal symmetry. Our results offers a way of generating topological
helical edge states without spin-orbital couplings
Probing the states through radiative decays
In this work, we have adopted the spin rearrangement scheme in the heavy
quark limit and extensively investigated three classes of the radiative decays:
, , , corresponding to the
electromagnetic transitions between one molecular state and bottomonium, one
bottomonium and molecular state, and two molecular states respectively. We also
extend the same formalism to study the radiative decays of the molecular states
with hidden charm. We have derived some model independent ratios when the
initial or final states belong to the same spin flavor multiplet. Future
experimental measurement of these ratios will test the molecular picture and
explore the underlying structures of the states.Comment: 21 pages, 10 tables Accepted by Phys.Rev.
3′-O-β-Glucosyl-4′,5′-didehydro-5′-deoxyadenosine Is a Natural Product of the Nucleocidin Producers Streptomyces virens and Streptomyces calvus
Leverhulme Trust - RPG-2021-0283′-O-β-Glucosyl-4′,5′-didehydro-5′-deoxyadenosine 13 is identified as a natural product of Streptomyces calvus and Streptomyces virens. It is also generated in vitro by direct β-glucosylation of 4′,5′-didehydro-5′-deoxyadenosine 12 with the enzyme NucGT. The intact incorporation of oxygen-18 and deuterium isotopes from (±)[1-18O,1-2H2]-glycerol 14 into C-5′ of nucleocidin 1 and its related metabolites precludes 3′-O-β-glucosyl-4′,5′-didehydro-5′-deoxyadenosine 13 as a biosynthetic precursor to nucleocidin 1.Publisher PDFPeer reviewe
Identification of genes essential for fluorination and sulfamylation within the nucleocidin gene clusters of Streptomyces calvus and Streptomyces virens
We thank the EPSRC, Leverhulme Trust (RPG-2021-028) and the EU Horizon 2020 Sinfonia consortia for financial support. The Chinese Scholarship Council is acknowledged for studentship support (YC).The gene cluster in Streptomyces calvus associated with the biosynthesis of the fluoro- and sulfamyl-metabolite nucleocidin was interrogated by systematic gene knockouts. Out of the 26 gene deletions most did not affect fluorometabolite production, nine abolished sulfamylation but not fluorination, and three precluded fluorination, having no effect on sulfamylation. In addition to nucI, nucG, nucJ, nucK, nucL, nucN, nucO, nucQ and nucP we identified two genes (nucW, nucA), belonging to a phosphoadenosine phosphosulfate (PAPS) gene cluster, as required for sulfamyl assembly. Three genes (orf(-3), orf2 and orf3) were found to be essential for fluorination, although the activities of their protein products are unknown. These genes as well as nucK, nucN, nucO and nucPNP, whose knockouts produced results differing from those described in a recent report, were also deleted in Streptomyces virens - with confirmatory outcomes. This genetic profile should inform biochemistry aimed at uncovering the enzymology behind nucleocidin biosynthesis.Publisher PDFPeer reviewe
Investigation of ultra-thin Al₂O₃ film as Cu diffusion barrier on low-k (k=2.5) dielectrics
Ultrathin Al(2)O(3) films were deposited by PEALD as Cu diffusion barrier on low-k (k=2.5) material. The thermal stability and electrical properties of the Cu/low k system with Al(2)O(3) layers with different thickness were studied after annealing. The AES, TEM and EDX results revealed that the ultrathin Al(2)O(3) films are thermally stable and have excellent Cu diffusion barrier performance. The electrical measurements of dielectric breakdown and TDDB tests further confirmed that the ultrathin Al(2)O(3) film is a potential Cu diffusion barrier in the Cu/low-k interconnects system
catena-Poly[[[tetraaquaerbium(III)]-μ-oxalato-κ4 O 1,O 2:O 1′,O 2′] [bromidobis(pyrazine-2-carboxylato-κ2 N 1,O)cuprate(II)] tetrahydrate]
In the title heterometallic complex, {[Er(C2O4)(H2O)4][CuBr(C5H3N2O2)2]·4H2O}n, the ErIII atom is eight-coordinated by four O atoms from two centrosymmetric oxalate ligands and four water molecules, displaying a bicapped trigonal-prismatic geometry. The oxalate ligands bridge the Er atoms into a polymeric cationic chain along [110]. The CuII atom is five-coordinated in a square-pyramidal geometry by two pyrazine-2-carboxylate ligands and a Br atom, forming a discrete anion. The polymeric cations, complex anions and uncoordinated water molecules are self-assembled into a three-dimensional supramolecular network through O—H⋯N, O—H⋯O and O—H⋯Br hydrogen bonds
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