928 research outputs found
Multiferroic BiFeO3-BiMnO3 Nanocheckerboard From First Principles
We present a first principles study of an unusual heterostructure, an
atomic-scale checkerboard of BiFeO3-BiMnO3, and compare its properties to the
two bulk constituent materials, BiFeO3 and BiMnO3. The "nanocheckerboard" is
found to have a multiferroic ground state with the desired properties of each
constituent: polar and ferrimagnetic due to BiFeO3 and BiMnO3, respectively.
The effect of B-site cation ordering on magnetic ordering in the BiFeO3-BiMnO3
system is studied. The checkerboard geometry is seen to give rise to a a novel
magnetostructural effect that is neither present in the bulk constituent
materials, nor in the layered BiFeO3-BiMnO3 superlattice.Comment: 15 pages, 14 figure
Chemical control of polar behavior in bicomponent short-period superlattices
Using first-principles density functional calculations, we study the
interplay of ferroelectricity and polar discontinuities in a range of 1-1 oxide
superlattices, built out of ferroelectric and paraelectric components. Studies
have been carried out for a varied choice of chemical composition of the
components. We find that, when polar interfaces are present, the polar
discontinuities induce off- centric movements in the ferroelectric layers, even
though the ferroelectric is only one unit cell thick. The distortions yield
non-switchable polarizations, with magnitudes comparable to those of the
corresponding bulk ferroelectrics. In contrast, in superlattices with no polar
discontinuity at the interfaces, the off-centric movements in the ferroelectric
layer are usually suppressed. The details of the behavior and functional
properties are, however, found to be sensitive to epitaxial strain, rotational
instabilities and second-order Jahn-Teller activity, and are therefore strongly
in uenced by the chemical composition of the paraelectric layer.Comment: 7 pages, 2 figure
Nanoparticle-doped electrospun fiber random lasers with spatially extended light modes
Complex assemblies of light-emitting polymer nanofibers with molecular
materials exhibiting optical gain can lead to important advance to amorphous
photonics and to random laser science and devices. In disordered mats of
nanofibers, multiple scattering and waveguiding might interplay to determine
localization or spreading of optical modes as well as correlation effects. Here
we study electrospun fibers embedding a lasing fluorene-carbazole-fluorene
molecule and doped with titania nanoparticles, which exhibit random lasing with
sub-nm spectral width and threshold of about 9 mJ cm^-2 for the absorbed
excitation fluence. We focus on the spatial and spectral behavior of optical
modes in the disordered and non-woven networks, finding evidence for the
presence of modes with very large spatial extent, up to the 100
micrometer-scale. These findings suggest emission coupling into integrated
nanofiber transmission channels as effective mechanism for enhancing spectral
selectivity in random lasers and correlations of light modes in the complex and
disordered material.Comment: 22 pages, 6 figure
A classification model for product-service offerings
Organisations have been approaching servitisation in an unstructured fashion. This is partially because there is insufficient understanding of the different types of Product-Service offerings. Therefore, a more detailed understanding of Product-Service types might advance the collective knowledge and assist organisations that are considering a servitisation strategy. Current models discuss specific aspects on the basis of few (or sometimes single) dimensions. In this paper, we develop a comprehensive model for classifying traditional and green Product-Service offerings, thus combining business and green offerings in a single model. We describe the model building process and its practical application in a case study. The model reveals the various traditional and green options available to companies and identifies how to compete between services; it allows servitisation positions to be identified such that a company may track its journey over time. Finally it fosters the introduction of innovative Product-Service Systems as promising business models to address environmental and social challenges.EPSRC, EPSRC supported the Cranfield IMRCThis is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.jclepro.2013.11.03
Grapevine cvs Primitivo, Zinfandel and Crljenak kastelanski: Molecular analysis by AFLP
Research Not
Diverse regimes of mode intensity correlation in nanofiber random lasers through nanoparticle doping
Random lasers are based on disordered materials with optical gain. These
devices can exhibit either intensity or resonant feedback, relying on diffusive
or interference behaviour of light, respectively, which leads to either
coupling or independent operation of lasing modes. We study for the first time
these regimes in complex, solid-state nanostructured materials. The number of
lasing modes and their intensity correlation features are found to be
tailorable in random lasers made of light-emitting, electrospun polymer fibers
upon nanoparticle doping. By material engineering, directional waveguiding
along the length of fibers is found to be relevant to enhance mode correlation
in both intensity feedback and resonant feedback random lasing. The here
reported findings can be used to establish new design rules for tuning the
emission of nano-lasers and correlation properties by means of the
compositional and morphological properties of complex nanostructured materials.Comment: 30 pages, 10 figure
Topological nature of polarization and charge pumping in ferroelectrics
Electric polarization or transferred charge due to an adiabatic change of
external parameters is expressed in terms of a vector field defined
in the space. This vector field is characterized by strings, i.e.,
trajectories of band-crossing points. In particular, the transverse component
is given by the Biot-Savart law in a nonlocal way. For a cyclic change of
along a loop C, the linking number between this string and C
represents the amount of the pumped charge, which is quantized to be an integer
as discussed by Thouless.Comment: 5 pages including 4 figure
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