20,540 research outputs found
Supergravity duals of gauge theories from F(4) gauged supergravity in six dimensions
We construct supergravity solutions dual to twisted field theories that are
the worldvolume theories of D4-branes wrapped on 2, 3-cycles, and NS-fivebranes
on 3-cycles. We first obtain the solutions for the Romans' six-dimensional
gauged supergravity theories and then up-lift them to ten dimensions. In
particular, we find solutions for field configurations with either non-Abelian
fields or B-fields being excited. One of these solutions, in the massless case,
is up-lifted to the massless type IIA string theory. This is the first example
of such a kind. The cases studied provide new examples of the AdS/CFT duality
involving twisted field theories.Comment: 26 pages, 3 figures, minor changes and references added to match the
published versio
Metal-insulator transition in the quarter- filled frustrated checkerboard lattice
We study the electronic structure and correlations in the geometrically
frustrated two dimensional checkerboard lattice. In the large U limit
considered here we start from an extended Hubbard model of spinless fermions at
half-filling. We investigate the model within two distinct Green's function
approaches: In the first approach a single-site representation decoupling
scheme is used that includes the effect of nearest neighbor charge
fluctuations. In the second approach a cluster representation leading to a
'multiorbital' model is investigated which includes intra-cluster correlations
exactly and those between clusters on a mean field basis. It is demonstrated
that with increasing nearest-neighbor Coulomb interaction V both approaches
lead to a metal-insulator transition with an associated 'Mott-Hubbard' like gap
caused by V. Within the single site approach we also explore the possibility of
charge order. Furthermore we investigate the evolution of the quasiparticle
bands as funtion of V
Submicrometric Films of Surface-Attached Polymer Network with Temperature-Responsive Properties
Temperature-responsive properties of surface-attached
poly(N-isopropylacrylamide) (PNIPAM) network films with well-controlled
chemistry are investigated. The synthesis consists of cross-linking and
grafting preformed ene-reactive polymer chains through thiol--ene click
chemistry. The formation of surface-attached and cross-linked polymer films has
the advantage of being wellcontrolled without any caution of no-oxygen
atmosphere or addition of initiators. PNIPAM hydrogel films with same
cross-link density are synthesized on a wide range of thickness, from
nanometers to micrometers. The swelling-collapse transition with temperature is
studied by using ellipsometry, neutron reflectivity, and atomic force
microscopy as complementary surface-probing techniques. Sharp and high
amplitude temperature-induced phase transition is observed for all
submicrometric PNIPAM hydrogel films. For temperature above LCST,
surface-attached PNIPAM hydrogels collapse similarly but without complete
expulsion of water. For temperature below LCST, the swelling of PNIPAM
hydrogels depends on the film thickness. It is shown that the swelling is
strongly affected by the surface attachment for ultrathin films below 150
nm. For thicker films above 150 nm (to micrometers), surface-attached polymer
networks with the same cross-link density swell equally. The density profile of
the hydrogel films in the direction normal to the substrate is confronted with
in-plane topography of the free surface. It results that the free interface
width is much larger than the roughness of the hydrogel film, suggesting
pendant chains at the free surface.Comment: in Langmuir, American Chemical Society, 2015, LANGMUIR, 31 (42),
pp.11516-1152
Suppressed silicide formation in FePt thin films by nitrogen addition
Copyright © 2013 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Magnetism and Magnetic Materials. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Magnetism and Magnetic Materials Vol. 331 (2013), DOI: 10.1016/j.jmmm.2012.11.045FePt and FePtN thin films have been prepared on silicon substrates by the relatively new deposition technique known as High Target Utilization Sputtering. Films were annealed post-deposition at temperatures up to 800 °C in order to induce the high-anisotropy L10 phase. The FePt films initially showed an improvement in magnetic properties with annealing temperature, but for annealing above around 400 °C the magnetic properties deteriorated markedly. The magnetic properties of the FePtN films, however, continued to improve with increasing annealing temperature, right up to the maximum temperature applied of 800 °C. Analysis by X-ray diffraction revealed the formation of iron and platinum silicides in FePt films above 400 °C, but that such silicides are absent from the FePtN at all annealing temperatures except 800 °C. This behavior is attributed to the nitrogen in FePtN films reacting preferentially with the silicon in the substrate to form silicon nitride, thus suppressing the formation of platinum and iron silicides. Thus, by introducing nitrogen during the deposition of FePt films on Si substrates the formation of deleterious silicides appears to be suppressed during thermal treatment, thereby offering protection against silicon pollution.Plasma Quest Lt
Strategies for Teaching Information Literacy to English Language Learners
Academic librarians are encountering a growing number of English Language Learners (ELLs) every day, as our classrooms have become more linguistically diverse every year. In this dramatically changing environment, academic librarians are expected to meet the needs of increasingly diverse students speaking multiple languages. The purpose of this paper is to present widely used teaching strategies to support ELLs based on an exhaustive literature review. Study also suggests collaboration among ESL or classroom instructors and librarians to enhance semester-long learning experience
Interplay of plasma-induced and fast thermal nonlinearities in a GaAs-based photonic crystal nanocavity
We investigate the nonlinear response of GaAs-based photonic crystal cavities
at time scales which are much faster than the typical thermal relaxation rate
in photonic devices. We demonstrate a strong interplay between thermal and
carrier induced nonlinear effects. We have introduced a dynamical model
entailing two thermal relaxation constants which is in very good agreement with
experiments. These results will be very important for Photonic Crystal-based
nonlinear devices intended to deal with practical high repetition rate optical
signals.Comment: 10 pages, 8 figures, Phys Rev A (accepted
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