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Trushkevych O.,CMET - Photonics And Advanced Materials Laboratory | Xu H.,CMET - Photonics And Advanced Materials Laboratory | Lu T.,CMET - Photonics And Advanced Materials Laboratory | Zeitler J.A.,CB | And 4 more authors.
Applied Optics | Year: 2010

Tunable materials with high anisotropy of refractive index and low loss are of particular interest in the microwave and terahertz range. Nematic liquid crystals are highly sensitive to electric and magnetic fields and may be designed to have particularly high birefringence. In this paper we investigate birefringence and absorption losses in an isothiocyanate based liquid crystal (designed for high anisotropy) in a broad range of the electromagnetic spectrum, namely 0.1-4 GHz, 30 GHz, 0.5-1.8 THz, and in the visible and near-infrared region (400 nm-1600 nm). We report high birefringence (Δn = 0.19 - 0.395) and low loss in this material. This is attractive for tunable microwave and terahertz device applications. © 2010 Optical Society of America.

Norris M.A.,Max Planck Institute for Astronomy | Kannappan S.J.,CB | Forbes D.A.,Swinburne University of Technology | Romanowsky A.J.,San Jose State University | And 19 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We describe the structural and kinematic properties of the first compact stellar systems discovered by the Archive of Intermediate Mass Stellar Systems project. These spectroscopically confirmed objects have sizes (~6 < Re [pc] < 500) and masses (~2 × 106 < M*/M⊙< 6 × 109) spanning the range of massive globular clusters, ultracompact dwarfs (UCDs) and compact elliptical galaxies (cEs), completely filling the gap between star clusters and galaxies. Several objects are close analogues to the prototypical cE, M32. These objects, which are more massive than previously discovered UCDs of the same size, further call into question the existence of a tight mass-size trend for compact stellar systems, while simultaneously strengthening the case for a universal 'zone of avoidance' for dynamically hot stellar systems in the mass-size plane. Overall, we argue that there are two classes of compact stellar systems (1) massive star clusters and (2) a population closely related to galaxies. Our data provide indications for a further division of the galaxy-type UCD/cE population into two groups, one population that we associate with objects formed by the stripping of nucleated dwarf galaxies, and a second population that formed through the stripping of bulged galaxies or are lower mass analogues of classical ellipticals. We find compact stellar systems around galaxies in low- to high-density environments, demonstrating that the physical processes responsible for forming them do not only operate in the densest clusters. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Norris M.A.,CB | Norris M.A.,Durham University | Gebhardt K.,University of Texas at Austin | Sharples R.M.,Durham University | And 9 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

This paper presents further results from our spectroscopic study of the globular cluster (GC) system of the group elliptical NGC 3923. From observations made with the GMOS instrument on the Gemini South Telescope, an additional 50 GC and ultra-compact dwarf (UCD) candidates have been spectroscopically confirmed as members of the NGC 3923 system. When the recessional velocities of these GCs are combined with the 29 GC velocities reported previously, a total sample of 79 GC/UCD velocities is produced. This sample extends to over 6arcmin (> 6R e~ 30kpc) from the centre of NGC 3923 and is used to study the dynamics of the GC system and the dark matter content of NGC 3923. It is found that the GC system of NGC 3923 displays no appreciable rotation, and that the projected velocity dispersion is constant with radius within the uncertainties. The velocity dispersion profiles of the integrated light and GC system of NGC 3923 are indistinguishable over the region in which they overlap. We find some evidence that the diffuse light and GCs of NGC 3923 have radially biased orbits within ~130 arcsec. The application of axisymmetric orbit-based models to the GC and integrated light velocity dispersion profiles demonstrates that a significant increase in the mass-to-light ratio (from M/L V= 8 to 26) at large galactocentric radii is required to explain this observation. We therefore confirm the presence of a dark matter halo in NGC 3923. We find that dark matter comprises 17.5per cent of the mass within 1 R e, 41.2per cent within 2 R e and 75.6per cent within the radius of our last kinematic tracer at 6.9 R e. The total dynamical mass within this radius is found to be M ⊙. In common with other studies of large ellipticals, we find that our derived dynamical mass profile is consistently higher than that derived by X-ray observations, by a factor of around 2. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Ghidini M.,CB | Ghidini M.,University of Parma | Pellicelli R.,University of Parma | Prieto J.L.,Technical University of Madrid | And 5 more authors.
Nature Communications | Year: 2013

Repeatable magnetization reversal under purely electrical control remains the outstanding goal in magnetoelectrics. Here we use magnetic force microscopy to study a commercially manufactured multilayer capacitor that displays strain-mediated coupling between magnetostrictive Ni electrodes and piezoelectric BaTiO 3 -based dielectric layers. In an electrode exposed by polishing approximately normal to the layers, we find a perpendicularly magnetized feature that exhibits non-volatile electrically driven repeatable magnetization reversal with no applied magnetic field. Using micromagnetic modelling, we interpret this nominally full magnetization reversal in terms of a dynamic precession that is triggered by strain from voltage-driven ferroelectric switching that is fast and reversible. The anisotropy field responsible for the perpendicular magnetization is reversed by the electrically driven magnetic switching, which is, therefore, repeatable. Our demonstration of non-volatile magnetic switching via volatile ferroelectric switching may inspire the design of fatigue-free devices for electric-write magnetic-read data storage. © 2013 Macmillan Publishers Limited.

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