6,766 research outputs found

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

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    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

    T/B scaling without quasiparticle mass divergence: YbCo2Ge4

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    YbCo2_2Ge4_4 is a clean paramagnetic Kondo lattice which displays non-Fermi liquid behavior. We report a detailed investigation of the specific heat, magnetic Gr\"uneisen parameter (Γmag\Gamma_{\rm mag}) and temperature derivative of the magnetization (MM) on a high-quality single crystal at temperatures down to 0.10.1~K and magnetic fields up to 7~T. Γmag\Gamma_{\rm mag} and dM/dTdM/dT display a divergence upon cooling and obey T/BT/B scaling. Similar behavior has previously been found in several other Yb-based Kondo lattices and related to a zero-field quantum critical point without fine tuning of pressure or composition. However, in the approach of B0B\rightarrow 0 the electronic heat capacity coefficient of YbCo2_2Ge4_4 saturates at low TT, excluding ferromagnetic quantum criticality. This indicates that T/BT/B scaling is insufficient to prove a zero-field quantum critical point.Comment: 6 pages, 6 figures (including supplemental material

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

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    We report the 121/123^{121/123}Sb-NMR/nuclear quadrupole resonance (NQR) measurements on the newly-discovered superconductor BaTi2_2Sb2_2O with a two-dimensional Ti2_2O square-net layer formed with Ti3+^{3+} (3d1d^1). NQR measurements revealed that the in-plane four-fold symmetry is broken at the Sb site below TAT_{\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 TAT_{\rm A}. The spin-lattice relaxation rate 1/T11/T_1, measured at the four-fold symmetry breaking site, decreases below superconducting (SC) transition temperature TcT_{\rm c}, indicative of the microscopic coexistence of superconductivity and the CDW/SDW phase below TAT_{\rm A}. Furthermore, 1/T11/T_1 of 121^{121}Sb-NQR shows a coherence peak just below TcT_{\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

    Continuity and change in disaster education in Japan

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    This article aims to describe post-war continuity and change in disaster education in Japan. Preparedness for natural disasters has been a continuous agenda in Japan for geographical and meteorological reasons, and disaster education has been practised in both formal and informal settings. Post-war disaster management and education have taken a follow-up approach, which means that clusters of measures have been developed after critical national-scale disasters have occurred. Following this clustering, with a minor amendment, the article discusses continuity and change in disaster education, looking at the different versions of the national curriculum (the Course of Study) at the compulsory school level. It is argued that disaster education has always been delivered at school in post-war Japan – this is the continuity – however, its treatment in the curriculum has changed over the years, from the scientific knowledge model, to the civic participation model, to the multi-hazard model, to the everyday life model within broader economic, political and social contexts – this is the change. Through this historical description, the article sheds light on the complexity of the field ‘disaster education’, particularly its two-dimensional aspect, namely, ‘the science of disasters’ on the one hand, and ‘life skills for disasters’ on the other. Currently, these two dimensions are addressed within the policy framework of School Safety. It is argued, however, that this complexity has been a challenge in the positioning of disaster education in the Japanese system. The article concludes by exploring the direction that disaster education has been taking since the Tohoku earthquake and tsunami of 2011

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

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    We report a site-separated 17^{17}O-NMR study of the layered perovskite ruthenate Sr3_3Ru2_2O7_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 2p2p 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 Sr2_2RuO4_4 and the three-dimensional ferromagnet SrRuO3_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 RuO6_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.

    Development of disaster risk reduction policy in Thailand

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    Purpose: This exploratory study discusses the policy learning process of the development of disaster risk reduction (DRR) policy. Design/methodology/approach: The paper discusses how DRR has and has not developed in Thailand through the two major disasters: the 2004 Indian Ocean Tsunami and the 2011 Great Flood. The information was collected by documentary analysis to gain a historical and critical understanding of the development of the system and policy of DRR in Thailand. Additionally, key stakeholders' interviews were undertaken to supplement the analysis. Findings: The paper demonstrates that Thailand's DRR development has been “reactive” rather than “proactive”, being largely directed by global DRR actors. Research limitations/implications: Being a small-scale study, the sample size was small. The analysis and argument would be consolidated with an increase in the number of interviews. Practical implications: The model can help deconstruct which dimension of the learning process a government has/has not achieved well. Originality/value: The application of the “restrictive-expansive policy learning” model, which identifies different dimensions of policy learning, reveals that the Thai government's policy learning was of a mixed nature

    Conceptualising ‘disaster education’

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    ‘Disaster education’ has been studied in various disciplines such as disaster risk management and environmental studies. However, disaster education is a relatively ‘new enquiry’ in the field of education. Particularly, the literature that conceptualises ‘disaster education’ in education is minimal. This paper aims to fill this gap by synthesising existing disaster education literature linking them with educational concepts. The paper suggests three possible conceptualisations for disaster education. The first is based on a temporal distinction between education undertaken in usual times or unusual times. The second conceptualisation applies modes of learning and teaching: formal, non-formal and informal. Thirdly, establishing disaster education as a sub-discipline in the field of education is proposed: one sub-discipline is lifelong learning and the other is public pedagogy. Critiquing each method of conceptualisation, the paper argues for the suitability and usefulness of locating ‘disaster education’ within public pedagogy

    Questioning 'integrated' disaster risk reduction and 'all of society' engagement: can 'preparedness pedagogy' help?

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    This paper contributes to the conceptual and empirical development of ‘preparedness pedagogy’. Preparedness involves learning, thus disaster risk reduction (DRR) should be discussed more in the field of education, particularly its sub-discipline of public pedagogy. Disaster risk reduction education should have an element of a pedagogy in the interest of publicness, which is an experimental pedagogy in which citizens act in togetherness to develop their own preparedness. The paper pays attention to the two phrases utilised in the recent DRR discourse – ‘integrated’ DRR and ‘participation by all’ – and examines the case of Japan, applying whole-system thinking. It is suggested that ‘the mesosystem’ of the DRR system yields relationships and learning, and thus enables collaboration, change and ‘participation by all’. Preparedness pedagogy has a role to play in this. The mesosystem functions as the confluence between state-led and community-based DRR to truly integrate the system

    Disaster risk reduction activities as learning

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    The purpose of this paper is to relate disaster risk reduction activities to learning perspectives and theories. The paper refers to ‘disaster risk reduction activities’ encompassing various terms used in the existing disaster risk management literature, such as ‘disaster education’ and ‘capacity building’. One thing they have in common is the involvement of the general public in preparing for natural hazards. Disaster risk reduction activities involve learning, because they aim to change people’s behaviour, perception and emotion. An overview of the relationships between disaster risk reduction activities and learning theories has not been offered, and that is what this paper aims to achieve. ‘How people learn’ has been studied in the fields of psychology and education over the years. Evolving from the primary focus of acquisition of knowledge and skills, the understanding of ‘what learning is’ has broadened to envisage emotional and social dimensions. Referring to the historical development of five major learning perspectives, the paper links each perspective with specific disaster risk reduction activities. The foci of the studies of disaster risk reduction activities have been what people should learn, rather than how people learn. Engagement with learning perspectives and theories will allow conceptualising how people learn to be prepared and resilient, which will benefit disaster risk management

    Exploring 'everyday-life preparedness': Three case studies from Japan

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    This paper aims to contribute to the conceptualisation and practice of ‘everyday-life preparedness [seikatsu bosai]’ (EP) initially proposed by Yamori. It reinforces existing community-based disaster risk reduction (CBDRR) systems through embedding preparedness thinking and practice in communities’ daily lives. International agencies, governments and experts promote CBDRR to engage ‘all of society’ and to achieve ‘a culture of DRR’. At the same time, the challenges of how to engage communities in DRR actions and how to sustain them in the communities are also recognised. Drawing on three case studies from Japan, the paper suggests that EP could be one approach to respond to these challenges. A need for integrating DRR and community development has already been identified by some authors. Taking this position further, the paper proposes EP as one of the methodologies of integrated CBDRR approaches
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