Emergent charge ordering in near half doped Na0.46_{0.46}CoO2_{2}

We have utilized neutron powder diffraction to probe the crystal structure of layered Na$_{x}$CoO$_{2}$ near the half doping composition of $x=$0.46 over the temperature range of 2 to 600K. Our measurements show evidence of a dynamic transition in the motion of Na-ions at 300K which coincides with the onset of a near zero thermal expansion in the in-plane lattice constants. The effect of the Na-ordering on the CoO$_{2}$ layer is reflected in the octahedral distortion of the two crystallographically inequivalent Co-sites and is evident even at high temperatures. We find evidence of a weak charge separation into stripes of Co$^{+3.5+\epsilon}$ and Co$^{+3.5-\epsilon}$, $\epsilon\sim0.06e$ below \Tco=150K. We argue that changes in the Na(1)-O bond lengths observed at the magnetic transition at \tm=88K reflect changes in the electronic state of the CoO$_{2}$ layerComment: 7 pages, 6 figures, in press Phys. Rev.

The use of a cyber campus to support teaching and collaboration: An observation approach

The research reported in this paper is work in progress describing the experiences of the authors while using a cyber campus to support online learn- ing collaborative activities and investigate if a Transactive Memory System can be developed among group members, working together within a cyber campus in several pre-set tasks

Design methodology for 360° immersive video applications: the case study of a cultural heritage virtual tour

Three hundred sixty–degree (360°) immersive video applications for Head Mounted Display (HMD) devices offer great potential in providing engaging forms of experiential media solutions especially in Cultural Heritage education. Design challenges emerge though by this new kind of immersive media due to the 2D form of resources used for their construction, the lack of depth, the limited interaction and the need to address the sense of presence. In addition, the use of Virtual Reality (VR) headsets often causes nausea, or motion sickness effects imposing further implications in moderate motion design tasks. This paper introduces a methodological categorisation of tasks and techniques for the design of 360° immersive video applications. Following the design approach presented, a testbed application has been created as an immersive interactive virtual tour at the historical centre of the city of Rethymno in Crete, Greece, which has undergone user trials. Based on the analysis of the results of this study, a set of design guidelines for the implementation of 360° immersive video virtual tours is proposed

Rare earth magnetism and ferroelectricity in RMnO3

Magnetic rare earths R have been proven to have a significant effect on the multiferroic properties of the orthorhombic manganites RMnO3. A re-examination of previous results from synchrotron based x-ray scattering experiments suggests that symmetric exchange striction between neighboring R and Mn ions may account for the enhancement of the ferroelectric polarization in DyMnO3 as well as the magnetic-field induced ferroelectricity in GdMnO3. In general, adding a second magnetic species to a multiferroic material may be a route to enhance its ferroelectric properties.Comment: Contribution to ICM 2009; accepted for publication in Journal of Physics: Conference Serie

Engaging immersive video consumers: Challenges regarding 360-degree gamified video applications

360-degree videos is a new medium that has gained the attention of the research community imposing challenges for creating more interactive and engaging immersive experiences. The purpose of this study is to introduce a set of technical and design challenges for interactive, gamified 360-degree mixed reality applications that immerse and engage users. The development of gamified applications refers to the merely incorporation of game elements in the interaction design process to attract and engage the user through playful interaction with the virtual world. The study presents experiments with the incorporation of series of game elements such as time pressure challenges, badges and user levels, storytelling narrative and immediate visual feedback to the interaction design logic of a mixed reality mobile gaming application that runs in an environment composed of 360-degree video and 3D computer generated objects. In the present study, the architecture and overall process for creating such an application is being presented along with a list of design implications and constraints. The paper concludes with future directions and conclusions on improving the level of immersion and engagement of 360-degree video consumers

Commensurate Dy magnetic ordering associated with incommensurate lattice distortion in orthorhombic DyMnO3

Synchrotron x-ray diffraction and resonant magnetic scattering experiments on single crystal DyMnO3 have been carried out between 4 and 40 K. Below TN(Dy) = 5K, the Dy magnetic moments order in a commensurate structure with propagation vector 0.5 b*. Simultaneous with the Dy magnetic ordering, an incommensurate lattice modulation with propagation vector 0.905 b* evolves while the original Mn induced modulation is suppressed and shifts from 0.78 b* to 0.81 b*. This points to a strong interference of Mn and Dy induced structural distortions in DyMnO3 besides a magnetic coupling between the Mn and Dy magnetic moments.Comment: submitted to Phys. Rev. B Rapid Communication

139La NMR evidence for phase solitons in the ground state of overdoped manganites

Hole doped transition metal oxides are famous due to their extraordinary charge transport properties, such as high temperature superconductivity (cuprates) and colossal magnetoresistance (manganites). Astonishing, the mother system of these compounds is a Mott insulator, whereas important role in the establishment of the metallic or superconducting state is played by the way that holes are self-organized with doping. Experiments have shown that by adding holes the insulating phase breaks into antiferromagnetic (AFM) regions, which are separated by hole rich clumps (stripes) with a rapid change of the phase of the background spins and orbitals. However, recent experiments in overdoped manganites of the La(1-x)Ca(x)MnO(3) (LCMO) family have shown that instead of charge stripes, charge in these systems is organized in a uniform charge density wave (CDW). Besides, recent theoretical works predicted that the ground state is inhomogeneously modulated by orbital and charge solitons, i.e. narrow regions carrying charge (+/-)e/2, where the orbital arrangement varies very rapidly. So far, this has been only a theoretical prediction. Here, by using 139La Nuclear Magnetic Resonance (NMR) we provide direct evidence that the ground state of overdoped LCMO is indeed solitonic. By lowering temperature the narrow NMR spectra observed in the AFM phase are shown to wipe out, while for T<30K a very broad spectrum reappears, characteristic of an incommensurate (IC) charge and spin modulation. Remarkably, by further decreasing temperature, a relatively narrow feature emerges from the broad IC NMR signal, manifesting the formation of a solitonic modulation as T->0.Comment: 5 pages, 4 figure