1,195 research outputs found
Electronic bulk and domain wall properties in B-site doped hexagonal ErMnO
Acceptor and donor doping is a standard for tailoring semiconductors. More
recently, doping was adapted to optimize the behavior at ferroelectric domain
walls. In contrast to more than a century of research on semiconductors, the
impact of chemical substitutions on the local electronic response at domain
walls is largely unexplored. Here, the hexagonal manganite ErMnO is donor
doped with Ti. Density functional theory calculations show that
Ti goes to the B-site, replacing Mn. Scanning probe microscopy
measurements confirm the robustness of the ferroelectric domain template. The
electronic transport at both macro- and nanoscopic length scales is
characterized. The measurements demonstrate the intrinsic nature of emergent
domain wall currents and point towards Poole-Frenkel conductance as the
dominant transport mechanism. Aside from the new insight into the electronic
properties of hexagonal manganites, B-site doping adds an additional degree of
freedom for tuning the domain wall functionality
Unconventional order-disorder phase transition in improper ferroelectric hexagonal manganites
The improper ferroelectricity in YMnO and other related multiferroic
hexagonal manganites are known to cause topologically protected ferroelectric
domains that give rise to rich and diverse physical phenomena. The local
structure and structural coherence across the ferroelectric transition,
however, were previously not well understood. Here we reveal the evolution of
the local structure with temperature in YMnO using neutron total scattering
techniques, and interpret them with the help of first-principles calculations.
The results show that, at room temperature, the local and average structures
are consistent with the established ferroelectric symmetry. On
heating, both local and average structural analyses show striking anomalies
from K up to the Curie temperature consistent with increasing
fluctuations of the order parameter angle. These fluctuations result in an
unusual local symmetry lowering into a \textit{continuum of structures} on
heating. This local symmetry breaking persists into the high-symmetry non-polar
phase, constituting an unconventional type of order-disorder transition.Comment: 10 pages, 5 figure
Transcriptome-wide analysis of regulatory interactions of the RNA-binding protein HuR
Posttranscriptional gene regulation relies on hundreds of RNA binding proteins (RBPs) but the function of most RBPs is unknown. The human RBP HuR/ELAVL1 is a conserved mRNA stability regulator. We used PAR-CLIP, a recently developed method based on RNA-protein crosslinking, to identify transcriptome-wide ~26,000 HuR binding sites. These sites were on average highly conserved, enriched for HuR binding motifs and mainly located in 3' untranslated regions. Surprisingly, many sites were intronic, implicating HuR in mRNA processing. Upon HuR knockdown, mRNA levels and protein synthesis of thousands of target genes were downregulated, validating functionality. HuR and miRNA binding sites tended to reside nearby but generally did not overlap. Additionally, HuR knockdown triggered strong and specific upregulation of miR-7. In summary, we identified thousands of direct and functional HuR targets, found a human miRNA controlled by HuR, and propose a role for HuR in splicing
The mRNA-bound proteome of the early fly embryo
Early embryogenesis is characterized by the maternal to zygotic transition (MZT), in which maternally deposited messenger RNAs are degraded while zygotic transcription begins. Before the MZT, post-transcriptional gene regulation by RNA-binding proteins (RBPs) is the dominant force in embryo patterning. We used two mRNA interactome capture methods to identify RBPs bound to polyadenylated transcripts within the first two hours of D. melanogaster embryogenesis. We identified a high-confidence set of 476 putative RBPs and confirmed RNA-binding activities for most of 24 tested candidates. Most proteins in the interactome are known RBPs or harbor canonical RBP features, but 99 exhibited previously uncharacterized RNA-binding activity. mRNA-bound RBPs and TFs exhibit distinct expression dynamics, in which the newly identified RBPs dominate the first two hours of embryonic development. Integrating our resource with in situ hybridization data from existing databases showed that mRNAs encoding RBPs are enriched in posterior regions of the early embryo, suggesting their general importance in posterior patterning and germ cell maturation
Intrinsic and extrinsic conduction contributions at nominally neutral domain walls in hexagonal manganites
Conductive and electrostatic atomic force microscopy (cAFM and EFM) are used
to investigate the electric conduction at nominally neutral domain walls in
hexagonal manganites. The EFM measurements reveal a propensity of mobile charge
carriers to accumulate at the nominally neutral domain walls in ErMnO3, which
is corroborated by cAFM scans showing locally enhanced d.c. conductance. Our
findings are explained based on established segregation enthalpy profiles for
oxygen vacancies and interstitials, providing a microscopic model for previous,
seemingly disconnected observations ranging from insulating to conducting
domain wall behavior. In addition, we observe variations in conductance between
different nominally neutral walls that we attribute to deviations from the
ideal charge-neutral structure within the bulk, leading to a superposition of
extrinsic and intrinsic contributions. Our study clarifies the complex
transport properties at nominally neutral domain walls in hexagonal manganites
and establishes new possibilities for tuning their electronic response based on
oxidation conditions, opening the door for domain-wall based sensor technology.Comment: 5 pages, 3 figure
Maf links Neuregulin1 signaling to cholesterol synthesis in myelinating Schwann cells
Cholesterol is a major constituent of myelin membranes, which insulate axons and allow saltatory conduction. Therefore, Schwann cells, the myelinating glia of the peripheral nervous system, need to produce large amounts of cholesterol. Here, we define a crucial role of the transcription factor Maf in myelination and cholesterol biosynthesis and show that Maf acts downstream from Neuregulin1 (Nrg1). Maf expression is induced when Schwann cells begin myelination. Genetic ablation of Maf resulted in hypomyelination that resembled mice with defective Nrg1 signaling. Importantly, loss of Maf or Nrg1 signaling resulted in a down-regulation of the cholesterol synthesis program, and Maf directly binds to enhancers of cholesterol synthesis genes. Furthermore, we identified the molecular mechanisms by which Nrg1 signaling regulates Maf levels. Transcription of Maf depends on calmodulin-dependent kinases downstream from Nrg1, whereas Nrg1-MAPK signaling stabilizes Maf protein. Our results delineate a novel signaling cascade regulating cholesterol synthesis in myelinating Schwann cells
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