IrGe4: A Predicted Weyl-Metal with a Chiral Crystal Structure.

Polycrystalline IrGe4 was synthesized by annealing elements at 800 °C for 240 h, and the composition was confirmed by energy-dispersive X-ray spectroscopy. IrGe4 adopts a chiral crystal structure (space group P3121) instead of a polar crystal structure (P31), which was corroborated by the convergent-beam electron diffraction and Rietveld refinements using synchrotron powder X-ray diffraction data. The crystal structure features layers of IrGe8 polyhedra along the b axis, and the layers are connected by edge- and corner-sharing. Each layer consists of corner-shared [Ir3Ge20] trimers, which are formed by three IrGe8 polyhedra connected by edge-sharing. Temperature-dependent resistivity indicates metallic behavior. The magnetoresistance increases with increasing applied magnetic field, and the nonsaturating magnetoresistance reaches 11.5% at 9 T and 10 K. The Hall resistivity suggests that holes are the majority carrier type, with a carrier concentration of 4.02 × 1021 cm-3 at 300 K. Electronic band structures calculated by density functional theory reveal a Weyl point with a chiral charge of +3 above the Fermi level.

Effect of seasonal succession of algal communities on fouling of MF membrane.

An emerging threat to membrane application is the seasonal proliferation of algae in water sources such as rivers, reservoirs and lakes. This study investigated the link between feed parameters and the membrane performance of a pilot-scale microfiltration (MF) plant for 7 months. The seasonal succession of algae in relation to temperature dynamics was monitored. Temperature-dependent seasonal patterns for algae species were observed. The water temperatures during the dominance of cyanobacteria, especially Microcystis, were relatively higher (over 25 °C) than those during the dominance of diatoms. Diatoms did not much affect membrane performance (less than 0.2 kgf/cm2), however, under the cyanobacterial dominance condition, especially Microcystis sp., transmembrane pressure (TMP) reached up to the limited level (0.4 kgf/cm2) within one month. Concurrently UV absorbance at 254 nm wavelength and dissolved organic carbon values increased significantly during the Microcystis bloom and the build-up rate of TMP increased up to 0.005 kgf/cm2/day. Membrane autopsy also showed that during the dominance of diatom, application of cleaning agents can fully remove foulants on the membrane surface. However, during the dominance of cyanobacteria, there is a lot of Al, Si and organic complex on the fouled membrane, indicating the formation of Al-organic complexes that contributed to the residual membrane fouling. It is suggested that the irrecoverable fouling layer still contained some Al, mostly in complex with organics. Thus, organic matter originated from cyanobacteria may cause a serious impact on membrane fouling by forming the complex with metal ions originated from coagulant.

Wallpaper Dirac Fermion in a Nonsymmorphic Topological Kondo Insulator: PuB4.

It has been recently predicted that nonsymmorphic crystalline insulators can host two exotic topological surface states (TSSs). One is the "hourglass fermion", and the other is the "wallpaper Dirac fermion". For the former, a few real materials were predicted and already confirmed experimentally. For the latter, however, no bulk-insulating and experimentally accessible candidate has been identified yet. Here we show that the localized 5f-electrons in PuB4, the single crystal of which was recently synthesized and was found to exhibit Kondo-insulating nature, form a closed manifold over the Brillouin zone via the Kondo coherence effect at low temperature, and host hitherto unobserved wallpaper Dirac fermions at the nonsymmorphic symmetry-preserving (001) surface. The topological nature of TSSs in PuB4 can be described by topological invariants of two Z4 indices [(χx, χy) = (1, 1)] of double-glide symmetries of p4g wallpaper group; thus, PuB4 is a 3D nonsymmorphic topological insulator that exhibits the TSSs of peculiar 4-fold surface Dirac fermions as well as 2-fold double-glide spin-Hall and nodal-line-type fermions. On top of its interesting 5f-electron Kondo-insulating nature, the unique 4-fold wallpaper Dirac fermions in PuB4, which are quite distinct from previously reported nonsymmorphic Dirac insulator or hourglass TCI fermions, broaden our recognition of the embedded fermions in strongly correlated Kondo systems with nonsymmorphic symmetries.