4,117 research outputs found
Hexagonal Rare-Earth Manganites as Promising Photovoltaics and Light Polarizers
Ferroelectric materials possess a spontaneous electric polarization and may
be utilized in various technological applications ranging from non-volatile
memories to solar cells and light polarizers. Recently, hexagonal rare-earth
manganites, h-RMnO (R is a rare-earth ion) have attracted considerable
interest due to their intricate multiferroic properties and improper
ferroelectricity characterized by a sizable remnant polarization and high Curie
temperature. Here, we demonstrate that these compounds can serve as very
efficient photovoltaic materials and, in addition, possess remarkable optical
anisotropy properties. Using first-principles methods based on
density-functional theory and considering h-TbMnO as a representative
manganite, we predict a strong light absorption of this material in the solar
spectrum range, resulting in the maximum light-to-electricity energy conversion
efficiency up to 33%. We also predict an extraordinary optical linear dichroism
and linear birefringence properties of h-TbMnO in a broad range of optical
frequencies. These results uncover the unexplored potential of hexagonal
rare-earth manganites to serve as photovoltaics in solar cells and as
absorptive and birefringent light polarizers.Comment: 26 pages, 8 figure
Rethinking Skip-thought: A Neighborhood based Approach
We study the skip-thought model with neighborhood information as weak
supervision. More specifically, we propose a skip-thought neighbor model to
consider the adjacent sentences as a neighborhood. We train our skip-thought
neighbor model on a large corpus with continuous sentences, and then evaluate
the trained model on 7 tasks, which include semantic relatedness, paraphrase
detection, and classification benchmarks. Both quantitative comparison and
qualitative investigation are conducted. We empirically show that, our
skip-thought neighbor model performs as well as the skip-thought model on
evaluation tasks. In addition, we found that, incorporating an autoencoder path
in our model didn't aid our model to perform better, while it hurts the
performance of the skip-thought model
Speeding up Context-based Sentence Representation Learning with Non-autoregressive Convolutional Decoding
Context plays an important role in human language understanding, thus it may
also be useful for machines learning vector representations of language. In
this paper, we explore an asymmetric encoder-decoder structure for unsupervised
context-based sentence representation learning. We carefully designed
experiments to show that neither an autoregressive decoder nor an RNN decoder
is required. After that, we designed a model which still keeps an RNN as the
encoder, while using a non-autoregressive convolutional decoder. We further
combine a suite of effective designs to significantly improve model efficiency
while also achieving better performance. Our model is trained on two different
large unlabelled corpora, and in both cases the transferability is evaluated on
a set of downstream NLP tasks. We empirically show that our model is simple and
fast while producing rich sentence representations that excel in downstream
tasks
Low-Lying Electronic Excitations and Nonlinear Optic Properties of Polymers via Symmetrized Density Matrix Renormalization Group Method
A symmetrized Density Matrix Renormalization Group procedure together with
the correction vector approach is shown to be highly accurate for obtaining
dynamic linear and third order polarizabilities of one-dimensional Hubbard and
models. The model is seen to show characteristically different
third harmonic generation response in the CDW and SDW phases. This can be
rationalized from the excitation spectrum of the systems.Comment: 4 pages Latex; 3 eps figures available upon request; Proceedings of
ICSM '96, to appear in Synth. Metals, 199
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