5,282 research outputs found
Improper Ferroelectric Polarisation in a Perovskite driven by Inter-site Charge Transfer and Ordering
It is of great interest to design and make materials in which ferroelectric
polarisation is coupled to other order parameters such as lattice, magnetic and
electronic instabilities. Such materials will be invaluable in next-generation
data storage devices. Recently, remarkable progress has been made in
understanding improper ferroelectric coupling mechanisms that arise from
lattice and magnetic instabilities. However, although theoretically predicted,
a compact lattice coupling between electronic and ferroelectric (polar)
instabilities has yet to be realised. Here we report detailed crystallographic
studies of a novel perovskite
HgMnMnO that is
found to exhibit a polar ground state on account of such couplings that arise
from charge and orbital ordering on both the A' and B-sites, which are
themselves driven by a highly unusual Mn-Mn inter-site charge
transfer. The inherent coupling of polar, charge, orbital and hence magnetic
degrees of freedom, make this a system of great fundamental interest, and
demonstrating ferroelectric switching in this and a host of recently reported
hybrid improper ferroelectrics remains a substantial challenge.Comment: 9 pages, 7 figure
Umbilic hypersurfaces of constant sigma-k curvature in the Heisenberg group
We study immersed, connected, umbilic hypersurfaces in the Heisenberg group
with We show that such a hypersurface, if closed, must
be rotationally invariant up to a Heisenberg translation. Moreover, we prove
that, among others, Pansu spheres are the only such spheres with positive
constant sigma-k curvature up to Heisenberg translations.Comment: 28 pages, 6 figure
Umbilicity and characterization of Pansu spheres in the Heisenberg group
For we define a notion of umbilicity for hypersurfaces in the
Heisenberg group . We classify umbilic hypersurfaces in some cases, and
prove that Pansu spheres are the only umbilic spheres with positive constant
(or horizontal)-mean curvature in up to Heisenberg translations.Comment: 32 pages, 2 figures; in Crelle's journal, 201
DARTS-ASR: Differentiable Architecture Search for Multilingual Speech Recognition and Adaptation
In previous works, only parameter weights of ASR models are optimized under
fixed-topology architecture. However, the design of successful model
architecture has always relied on human experience and intuition. Besides, many
hyperparameters related to model architecture need to be manually tuned.
Therefore in this paper, we propose an ASR approach with efficient
gradient-based architecture search, DARTS-ASR. In order to examine the
generalizability of DARTS-ASR, we apply our approach not only on many languages
to perform monolingual ASR, but also on a multilingual ASR setting. Following
previous works, we conducted experiments on a multilingual dataset, IARPA
BABEL. The experiment results show that our approach outperformed the baseline
fixed-topology architecture by 10.2% and 10.0% relative reduction on character
error rates under monolingual and multilingual ASR settings respectively.
Furthermore, we perform some analysis on the searched architectures by
DARTS-ASR.Comment: Accepted at INTERSPEECH 202
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The Association between Virus Prevalence and Intercolonial Aggression Levels in the Yellow Crazy Ant, Anoplolepis Gracilipes (Jerdon).
The recent discovery of multiple viruses in ants, along with the widespread infection of their hosts across geographic ranges, provides an excellent opportunity to test whether viral prevalence in the field is associated with the complexity of social interactions in the ant population. In this study, we examined whether the association exists between the field prevalence of a virus and the intercolonial aggression of its ant host, using the yellow crazy ant (Anoplolepis gracilipes) and its natural viral pathogen (TR44839 virus) as a model system. We delimitated the colony boundary and composition of A. gracilipes in a total of 12 study sites in Japan (Okinawa), Taiwan, and Malaysia (Penang), through intercolonial aggression assay. The spatial distribution and prevalence level of the virus was then mapped for each site. The virus occurred at a high prevalence in the surveyed colonies of Okinawa and Taiwan (100% infection rate across all sites), whereas virus prevalence was variable (30%-100%) or none (0%) at the sites in Penang. Coincidentally, colonies in Okinawa and Taiwan displayed a weak intercolonial boundary, as aggression between colonies is generally low or moderate. Contrastingly, sites in Penang were found to harbor a high proportion of mutually aggressive colonies, a pattern potentially indicative of complex colony composition. Our statistical analyses further confirmed the observed correlation, implying that intercolonial interactions likely contribute as one of the effective facilitators of/barriers to virus prevalence in the field population of this ant species
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