Design analysis of ductile failure in dovetail connections

The static plastic collapse of ductile dovetail structures is investigated by three analysis methods: slip-line field (SLF) theory based on a sheet drawing model, finite element limit analysis, and linear elastic finite element analysis with adapted pressure vessel design stress linearization and categorization methods. A range of angles and heights are considered in the investigation. Three experimental test cases are also presented. The limit analysis results are found to give the best comparison with the limited experimental results, indicating similar collapse loads and modes of ductile collapse. The SLF solution is found to give conservative but useful failure loads for small dovetail angles but, at angles greater than 30°, the solution is not generally conservative. The pressure vessel design by the analysis stress categorization procedure was adapted for dovetail analysis and was found to give reasonably conservative collapse loads in most cases. However, the procedure requires the designer to consider a number of different stress classification lines to ensure that a conservative collapse load is identified. It is concluded that the finite element limit analysis approach provides the best and most direct route to calculating the allowable load for the joint and is the preferred method when appropriate finite element analysis facilities are available

S wave superconductivity in newly discovered superconductor BaTi2_2Sb2_2O revealed by 121/123^{121/123}Sb-NMR/Nuclear Quadrupole Resonance measurements

We report the $^{121/123}$Sb-NMR/nuclear quadrupole resonance (NQR) measurements on the newly-discovered superconductor BaTi$_2$Sb$_2$O with a two-dimensional Ti$_2$O square-net layer formed with Ti$^{3+}$ (3$d^1$). NQR measurements revealed that the in-plane four-fold symmetry is broken at the Sb site below $T_{\rm A} \sim$ 40 K, without an internal field appearing at the Sb site. These exclude a spin-density wave (SDW)/ charge density wave (CDW) ordering with incommensurate correlations, but can be understood with the commensurate CDW ordering at $T_{\rm A}$. The spin-lattice relaxation rate $1/T_1$, measured at the four-fold symmetry breaking site, decreases below superconducting (SC) transition temperature $T_{\rm c}$, indicative of the microscopic coexistence of superconductivity and the CDW/SDW phase below $T_{\rm A}$. Furthermore, $1/T_1$ of $^{121}$Sb-NQR shows a coherence peak just below $T_{\rm c}$ and decreases exponentially at low temperatures. These results are in sharp contrast with those in cuprate and iron-based superconductors, and strongly suggest that its SC symmetry is classified to an ordinary s-wave state.Comment: 5 pages, 6 figure

Crossover from commensurate to incommensurate antiferromagnetism in stoichiometric NaFeAs revealed by single-crystal 23Na,75As-NMR experiments

We report results of 23Na and 75As nuclear magnetic resonance (NMR) experiments on a self-flux grown high-quality single crystal of stoichiometric NaFeAs. The NMR spectra revealed a tetragonal to twinned-orthorhombic structural phase transition at T_O = 57 K and an antiferromagnetic (AF) transition at T_AF = 45 K. The divergent behavior of nuclear relaxation rate near T_AF shows significant anisotropy, indicating that the critical slowing down of stripe-type AF fluctuations are strongly anisotropic in spin space. The NMR spectra at low enough temperatures consist of sharp peaks showing a commensurate stripe AF order with a small moment \sim 0.3 muB. However, the spectra just below T_AF exhibits highly asymmetric broadening pointing to an incommensurate modulation. The commensurate-incommensurate crossover in NaFeAs shows a certain similarity to the behavior of SrFe2As2 under high pressure.Comment: 5 pages, 5 figures, revised version to appear in J. Phys. Soc. Jp

Antiferromagnetic Order and Superconductivity in Sr4(Mg0.5-xTi0.5+x)2O6Fe2As2 with Electron Doping: 75As-NMR Study

We report an 75As-NMR study on iron (Fe)-based superconductors with thick perovskitetype blocking layers Sr4(Mg0.5-xTi0.5+x)2O6Fe2As2 with x=0 and 0.2. We have found that antiferromagnetic (AFM) order takes place when x=0, and superconductivity (SC) emerges below Tc=36 K when x=0.2. These results reveal that the Fe-pnictides with thick perovskitetype blocks also undergo an evolution from the AFM order to the SC by doping electron carriers into FeAs planes through the chemical substitution of Ti+4 ions for Mg+2 ions, analogous to the F-substitution in LaFeAsO compound. The reason why the Tc=36 K when x=0.2 being higher than the optimally electron-doped LaFeAsO with Tc=27 K relates to the fact that the local tetrahedron structure of FeAs4 is optimized for the onset of SC.Comment: 4 pages, 3 figures, 1 tabl

Observation of Jonscher Law in AC Hopping Conduction of Electron-Doped Nanoporous Crystal 12CaO7Al2O3 in THz Frequency Range

We have performed terahertz time-domain spectroscopy of carrier-doped nanoporous crystal 12CaO7Al2O3 showing the Mott variable range hopping at room temperature. The real part of the dielectric constant clearly demonstrates the nature of localized carriers. The frequency dependence of both the real and imaginary parts of the dielectric constant can be simply explained by assuming two contributions: a dielectric response by the parent compound with no carriers and an AC hopping conduction with the Jonscher law generally reported up to GHz range. The possible obedience to the Jonscher law in the THz range suggests a relaxation time of the hopping carriers much faster than 1ps in the carrier-doped 12CaO7Al2O3.Comment: 4pages 3figures. to be published in Phys. Rev.

Community engagement in preparing for natural water disasters of different time and magnitude scales – A comparative study between Japan and England

This exploratory research funded by the Daiwa Anglo-Japanese Foundation considers two chal-lenges recognised in the DRR community in recent years. One is the necessity of ‘all of society engagement’ emphasised in the Sendai Framework for DRR 2015-2030, which has led to the rein-forcement of community-based DRR. The other is, as the Red Cross World Disasters Report 2014 criticises, experts ‘persist’ in prioritising high-impact/low-frequency hazards. Inquiries into communi-ties’ DRR against hazards of different return periods and magnitudes have been scarce. The re-search focuses on natural water disasters, such as floods and typhoons generated due to atmos-pheric forcing factors, which have been intensified by climate change, as well as tsunamis. Both Japan and England have had a series of impacts of them in recent years. Applying a comparative approach, the research discusses four cases of under-researched water disaster-prone communities in Oita and Wakayama Prefectures, and the Essex and Devon Counties. The two research questions probed are: 1) to what extent the perceptions between DRR experts and community members differ in relation to disasters with different return periods and magnitudes; 2) what are the implications of the perception gap on the actualisation of ‘community-based’ and ‘participatory’ DRR. The interdis-ciplinary research team combines the observation of major structural mitigation solutions (e.g. barrier walls, embankments and evacuation shelters etc.) against water disasters of different scales in the four cases, and the analysis of non-structural measures through stakeholder interviews – policy-makers, academics, activists, community members – undertaken in the four communities. One of the key findings of the research is that both DRR experts and community members approach high-im-pact/low-frequency hazards with ‘prevention’ and ‘reduction’ measures, while for low-impact/high-frequency hazards, the countermeasures become ‘adaptation’. This has led us to consider develop-ing a new framework in categorising water disasters, applying a new index – the number of people ‘affected’ – in addition to scale and magnitudes. The novelty of the framework is to include community perspective so as to enable a community-based bottom-up approach in decision-making of DRR measures

Orbital Properties of Sr3Ru2O7 and Related Ruthenates Probed by 17O-NMR

We report a site-separated $^{17}$O-NMR study of the layered perovskite ruthenate Sr$_3$Ru$_2$O$_7$, which exhibits nearly two-dimensional transport properties and itinerant metamagnetism at low temperatures. The local hole occupancies and the spin densities in the oxygen $2p$ orbitals are obtained by means of tight-binding analyses of electric field gradients and anisotropic Knight shifts. These quantities are compared with two other layered perovskite ruthenates: the two-dimensional paramagnet Sr$_2$RuO$_4$ and the three-dimensional ferromagnet SrRuO$_3$. The hole occupancies at the oxygen sites are very large, about one hole per ruthenium atom. This is due to the strong covalent character of the Ru-O bonding in this compound. The magnitude of the hole occupancy might be related to the rotation or tilt of the RuO$_6$ octahedra. The spin densities at the oxygen sites are also large, 20-40% of the bulk susceptibilities, but in contrast to the hole occupancies, the spin densities strongly depend on the dimensionality. This result suggests that the density-of-states at the oxygen sites plays an essential role for the understanding of the complex magnetism found in the layered perovskite ruthenates.Comment: 9 pages, 5 figures, to be published in Phys. Rev.