277 research outputs found
Perovskite-polymer composite cross-linker approach for highly-stable and efficient perovskite solar cells.
Manipulation of grain boundaries in polycrystalline perovskite is an essential consideration for both the optoelectronic properties and environmental stability of solar cells as the solution-processing of perovskite films inevitably introduces many defects at grain boundaries. Though small molecule-based additives have proven to be effective defect passivating agents, their high volatility and diffusivity cannot render perovskite films robust enough against harsh environments. Here we suggest design rules for effective molecules by considering their molecular structure. From these, we introduce a strategy to form macromolecular intermediate phases using long chain polymers, which leads to the formation of a polymer-perovskite composite cross-linker. The cross-linker functions to bridge the perovskite grains, minimizing grain-to-grain electrical decoupling and yielding excellent environmental stability against moisture, light, and heat, which has not been attainable with small molecule defect passivating agents. Consequently, all photovoltaic parameters are significantly enhanced in the solar cells and the devices also show excellent stability
Emergence of Quasiparticles in a Doped Mott Insulator
How a Mott insulator develops into a weakly coupled metal upon doping is a
central question to understanding various emergent correlated phenomena. To
analyze this evolution and its connection to the high- cuprates, we study
the single-particle spectrum for the doped Hubbard model using cluster
perturbation theory on superclusters. Starting from extremely low doping, we
identify a heavily renormalized quasiparticle dispersion that immediately
develops across the Fermi level, and a weakening polaronic side band at higher
binding energy. The quasiparticle spectral weight roughly grows at twice the
rate of doping in the low doping regime, but this rate is halved at optimal
doping. In the heavily doped regime, we find both strong electron-hole
asymmetry and a persistent presence of Mott spectral features. Finally, we
discuss the applicability of the single-band Hubbard model to describe the
evolution of nodal spectra measured by angle-resolved photoemission
spectroscopy (ARPES) on the single-layer cuprate LaSrCuO (). This work benchmarks the predictive power of the Hubbard
model for electronic properties of high- cuprates.Comment: 7 pages, 5 figure
Non-Thermal Emergence of an Orbital-Selective Mott Phase in FeTeSe
Electronic correlation is of fundamental importance to high temperature
superconductivity. Iron-based superconductors are believed to possess moderate
correlation strength, which combined with their multi-orbital nature makes them
a fascinating platform for the emergence of exotic phenomena. A particularly
striking form is the emergence of an orbital selective Mott phase, where the
localization of a subset of orbitals leads to a drastically reconstructed Fermi
surface. Here, we report spectroscopic evidence of the reorganization of the
Fermi surface from FeSe to FeTe as Se is substituted by Te. We uncover a
particularly transparent way to visualize the localization of the
electron orbital through the suppression of its hybridization with the more
coherent electron orbitals, which leads to a redistribution of the
orbital-dependent spectral weight near the Fermi level. These noteworthy
features of the Fermi surface are accompanied by a divergent behavior of a band
renormalization in the orbital. All of our observations are further
supported by our theoretical calculations to be salient spectroscopic
signatures of such a non-thermal evolution from a strongly correlated metallic
phase towards an orbital-selective Mott phase in FeTeSe as Se
concentration is reduced.Comment: 11 pages, 5 figure
Charge order induced Dirac pockets in the nonsymmorphic crystal TaTe
The interplay between charge order (CO) and nontrivial band topology has
spurred tremendous interest in understanding topological excitations beyond the
single-particle description. In a quasi-one-dimensional nonsymmorphic crystal
TaTe, the (2a2b3c) charge ordered ground state drives the
system into a space group where the symmetry indicator features the emergence
of Dirac fermions and unconventional double Dirac fermions. Using
angle-resolved photoemission spectroscopy and first-principles calculations, we
provide evidence of the CO induced Dirac fermion-related bands near the Fermi
level. Furthermore, the band folding at the Fermi level is compatible with the
new periodicity dictated by the CO, indicating that the electrons near the
Fermi level follow the crystalline symmetries needed to host double Dirac
fermions in this system.Comment: 9 pages, 4 figures. Second version of the manuscript following the
first submission in April 202
Expression Profiling of Calcium Induced Genes in Cultured Human Keratinocytes
Terminal differentiation of skin keratinocytes is a vertically directed multi-step process that is tightly controlled by the sequential expression of a variety of genes. To examine the gene expression profile in calcium-induced keratinocyte differentiation, we constructed a normalized cDNA library using mRNA isolated from these calcium-treated keratinocytes. After sequencing about 10,000 clones, we were able to obtain 4,104 independent genes. They consisted of 3,699 annotated genes and 405 expressed sequence tags (ESTs). Some were the genes involved in constituting epidermal structures and others were unknown genes that are probably associated with keratinocytes. In particular, we were able to identify genes located at the chromosome 1q21, the locus for the epidermal differentiation complex, and 19q13.1, another probable locus for epidermal differentiation-related gene clusters. One EST located at the chromosome 19q13.1 showed increased expression by calcium treatment, suggesting a novel candidate gene relevant to keratinocyte differentiation. These results demonstrate the complexity of the transcriptional profile of keratinocytes, providing important clues on which to base further investigations of the molecular events underlying keratinocyte differentiation
Phylogenetic classification of Cordyceps and the clavicipitaceous fungi
Cordyceps, comprising over 400 species, was historically
classified in the Clavicipitaceae, based on cylindrical asci,
thickened ascus apices and filiform ascospores, which often disarticulate into
part-spores. Cordyceps was characterized by the production of
well-developed often stipitate stromata and an ecology as a pathogen of
arthropods and Elaphomyces with infrageneric classifications
emphasizing arrangement of perithecia, ascospore morphology and host
affiliation. To refine the classification of Cordyceps and the
Clavicipitaceae, the phylogenetic relationships of 162 taxa were
estimated based on analyses consisting of five to seven loci, including the
nuclear ribosomal small and large subunits (nrSSU and
nrLSU), the elongation factor 1α (tef1), the largest
and the second largest subunits of RNA polymerase II (rpb1 and
rpb2), β-tubulin (tub), and mitochondrial ATP6
(atp6). Our results strongly support the existence of three
clavicipitaceous clades and reject the monophyly of both Cordyceps
and Clavicipitaceae. Most diagnostic characters used in current
classifications of Cordyceps (e.g., arrangement of perithecia,
ascospore fragmentation, etc.) were not supported as being phylogenetically
informative; the characters that were most consistent with the phylogeny were
texture, pigmentation and morphology of stromata. Therefore, we revise the
taxonomy of Cordyceps and the Clavicipitaceae to be
consistent with the multi-gene phylogeny. The family Cordycipitaceae
is validated based on the type of Cordyceps, C. militaris,
and includes most Cordyceps species that possess brightly coloured,
fleshy stromata. The new family Ophiocordycipitaceae is proposed
based on Ophiocordyceps Petch, which we emend. The majority of
species in this family produce darkly pigmented, tough to pliant stromata that
often possess aperithecial apices. The new genus Elaphocordyceps is
proposed for a subclade of the Ophiocordycipitaceae, which includes
all species of Cordyceps that parasitize the fungal genus
Elaphomyces and some closely related species that parasitize
arthropods. The family Clavicipitaceae s. s. is emended and
includes the core clade of grass symbionts (e.g., Balansia,
Claviceps, Epichloë, etc.), and the entomopathogenic
genus Hypocrella and relatives. In addition, the new genus
Metacordyceps is proposed for Cordyceps species that are
closely related to the grass symbionts in the Clavicipitaceae s.
s. Metacordyceps includes teleomorphs linked to
Metarhizium and other closely related anamorphs. Two new species are
described, and lists of accepted names for species in Cordyceps,
Elaphocordyceps, Metacordyceps and Ophiocordyceps
are provided
Functional characterization of cellulases identified from the cow rumen fungus Neocallimastix patriciarum W5 by transcriptomic and secretomic analyses
<p>Abstract</p> <p>Background</p> <p><it>Neocallimastix patriciarum</it> is one of the common anaerobic fungi in the digestive tracts of ruminants that can actively digest cellulosic materials, and its cellulases have great potential for hydrolyzing cellulosic feedstocks. Due to the difficulty in culture and lack of a genome database, it is not easy to gain a global understanding of the glycosyl hydrolases (<it>GHs</it>) produced by this anaerobic fungus.</p> <p>Results</p> <p>We have developed an efficient platform that uses a combination of transcriptomic and proteomic approaches to <it>N. patriciarum </it>to accelerate gene identification, enzyme classification and application in rice straw degradation. By conducting complementary studies of transcriptome (Roche 454 GS and Illumina GA IIx) and secretome (ESI-Trap LC-MS/MS), we identified 219 putative <it>GH </it>contigs and classified them into 25 <it>GH</it> families. The secretome analysis identified four major enzymes involved in rice straw degradation: β-glucosidase, endo-1,4-β-xylanase, xylanase B and Cel48A exoglucanase. From the sequences of assembled contigs, we cloned 19 putative cellulase genes, including the <it>GH1</it>, <it>GH3</it>, <it>GH5</it>, <it>GH6</it>, <it>GH9</it>, <it>GH18</it>, <it>GH43 </it>and <it>GH48 </it>gene families, which were highly expressed in <it>N. patriciarum </it>cultures grown on different feedstocks.</p> <p>Conclusions</p> <p>These <it>GH </it>genes were expressed in Pichia pastoris and/or Saccharomyces cerevisiae for functional characterization. At least five novel cellulases displayed cellulytic activity for glucose production. One β-glucosidase (W5-16143) and one exocellulase (W5-CAT26) showed strong activities and could potentially be developed into commercial enzymes.</p
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