39 research outputs found
Autonomous Investigations over WS and Au{111} with Scanning Probe Microscopy
Individual atomic defects in 2D materials impact their macroscopic
functionality. Correlating the interplay is challenging, however, intelligent
hyperspectral scanning tunneling spectroscopy (STS) mapping provides a feasible
solution to this technically difficult and time consuming problem. Here, dense
spectroscopic volume is collected autonomously via Gaussian process regression,
where convolutional neural networks are used in tandem for spectral
identification. Acquired data enable defect segmentation, and a workflow is
provided for machine-driven decision making during experimentation with
capability for user customization. We provide a means towards autonomous
experimentation for the benefit of both enhanced reproducibility and
user-accessibility. Hyperspectral investigations on WS sulfur vacancy sites
are explored, which is combined with local density of states confirmation on
the Au{111} herringbone reconstruction. Chalcogen vacancies, pristine WS,
Au face-centered cubic, and Au hexagonal close packed regions are examined and
detected by machine learning methods to demonstrate the potential of artificial
intelligence for hyperspectral STS mapping.Comment: Updates from final journal publicatio
Emergent Spin Phenomena in Air-Stable, Atomically Thin Lead
A stable platform to synthesize ultrathin heavy metals, with a strong
interfacial Rashba effect, could lead to high efficiency charge-to-spin
conversion for next-generation spintronics. Here we report wafer-scale
synthesis of air-stable, epitaxially registered monolayer Pb on SiC (0001) via
confinement heteroepitaxy (CHet). The highly asymmetric interfacial bonding in
this heavy metal system lends to strong Rashba spin-orbit coupling near the
Fermi level. Additionally, the system's air stability enables ex-situ spin
torque ferromagnetic resonance (ST-FMR) measurements that demonstrate
charge-to-spin conversion in CHet-based 2D-Pb/ferromagnet heterostructures and
a 1.5x increase in the effective field ratio compared to control samples.Comment: 17 pages, 4 figures. Supporting Information included (20 pages, 9
figures, 1 table
Photo-physics and electronic structure of lateral graphene/MoS2 and metal/MoS2 junctions
Integration of semiconducting transition metal dichalcogenides (TMDs) into
functional optoelectronic circuitries requires an understanding of the charge
transfer across the interface between the TMD and the contacting material.
Here, we use spatially resolved photocurrent microscopy to demonstrate
electronic uniformity at the epitaxial graphene/molybdenum disulfide (EG/MoS2)
interface. A 10x larger photocurrent is extracted at the EG/MoS2 interface when
compared to metal (Ti/Au) /MoS2 interface. This is supported by semi-local
density-functional theory (DFT), which predicts the Schottky barrier at the
EG/MoS2 interface to be ~2x lower than Ti/MoS2. We provide a direct
visualization of a 2D material Schottky barrier through combination of angle
resolved photoemission spectroscopy with spatial resolution selected to be ~300
nm (nano-ARPES) and DFT calculations. A bending of ~500 meV over a length scale
of ~2-3 micrometer in the valence band maximum of MoS2 is observed via
nano-ARPES. We explicate a correlation between experimental demonstration and
theoretical predictions of barriers at graphene/TMD interfaces. Spatially
resolved photocurrent mapping allows for directly visualizing the uniformity of
built-in electric fields at heterostructure interfaces, providing a guide for
microscopic engineering of charge transport across heterointerfaces. This
simple probe-based technique also speaks directly to the 2D synthesis community
to elucidate electronic uniformity at domain boundaries alongside morphological
uniformity over large areas
Gene content evolution in the arthropods
Arthropods comprise the largest and most diverse phylum on Earth and play vital roles in nearly every ecosystem. Their diversity stems in part from variations on a conserved body plan, resulting from and recorded in adaptive changes in the genome. Dissection of the genomic record of sequence change enables broad questions regarding genome evolution to be addressed, even across hyper-diverse taxa within arthropods. Using 76 whole genome sequences representing 21 orders spanning more than 500 million years of arthropod evolution, we document changes in gene and protein domain content and provide temporal and phylogenetic context for interpreting these innovations. We identify many novel gene families that arose early in the evolution of arthropods and during the diversification of insects into modern orders. We reveal unexpected variation in patterns of DNA methylation across arthropods and examples of gene family and protein domain evolution coincident with the appearance of notable phenotypic and physiological adaptations such as flight, metamorphosis, sociality, and chemoperception. These analyses demonstrate how large-scale comparative genomics can provide broad new insights into the genotype to phenotype map and generate testable hypotheses about the evolution of animal diversity
Genome-enabled insights into the biology of thrips as crop pests
Background
The western flower thrips, Frankliniella occidentalis (Pergande), is a globally invasive pest and plant virus vector on a wide array of food, fiber, and ornamental crops. The underlying genetic mechanisms of the processes governing thrips pest and vector biology, feeding behaviors, ecology, and insecticide resistance are largely unknown. To address this gap, we present the F. occidentalis draft genome assembly and official gene set.
Results
We report on the first genome sequence for any member of the insect order Thysanoptera. Benchmarking Universal Single-Copy Ortholog (BUSCO) assessments of the genome assembly (size = 415.8 Mb, scaffold N50 = 948.9 kb) revealed a relatively complete and well-annotated assembly in comparison to other insect genomes. The genome is unusually GC-rich (50%) compared to other insect genomes to date. The official gene set (OGS v1.0) contains 16,859 genes, of which ~ 10% were manually verified and corrected by our consortium. We focused on manual annotation, phylogenetic, and expression evidence analyses for gene sets centered on primary themes in the life histories and activities of plant-colonizing insects. Highlights include the following: (1) divergent clades and large expansions in genes associated with environmental sensing (chemosensory receptors) and detoxification (CYP4, CYP6, and CCE enzymes) of substances encountered in agricultural environments; (2) a comprehensive set of salivary gland genes supported by enriched expression; (3) apparent absence of members of the IMD innate immune defense pathway; and (4) developmental- and sex-specific expression analyses of genes associated with progression from larvae to adulthood through neometaboly, a distinct form of maturation differing from either incomplete or complete metamorphosis in the Insecta.
Conclusions
Analysis of the F. occidentalis genome offers insights into the polyphagous behavior of this insect pest that finds, colonizes, and survives on a widely diverse array of plants. The genomic resources presented here enable a more complete analysis of insect evolution and biology, providing a missing taxon for contemporary insect genomics-based analyses. Our study also offers a genomic benchmark for molecular and evolutionary investigations of other Thysanoptera species
Cortical brain abnormalities in 4474 individuals with schizophrenia and 5098 control subjects via the enhancing neuro Imaging genetics through meta analysis (ENIGMA) Consortium
BACKGROUND: The profile of cortical neuroanatomical abnormalities in schizophrenia is not fully understood, despite hundreds of published structural brain imaging studies. This study presents the first meta-analysis of cortical thickness and surface area abnormalities in schizophrenia conducted by the ENIGMA (Enhancing Neuro Imaging Genetics through Meta Analysis) Schizophrenia Working Group.
METHODS: The study included data from 4474 individuals with schizophrenia (mean age, 32.3 years; range, 11-78 years; 66% male) and 5098 healthy volunteers (mean age, 32.8 years; range, 10-87 years; 53% male) assessed with standardized methods at 39 centers worldwide.
RESULTS: Compared with healthy volunteers, individuals with schizophrenia have widespread thinner cortex (left/right hemisphere: Cohen's d = -0.530/-0.516) and smaller surface area (left/right hemisphere: Cohen's d = -0.251/-0.254), with the largest effect sizes for both in frontal and temporal lobe regions. Regional group differences in cortical thickness remained significant when statistically controlling for global cortical thickness, suggesting regional specificity. In contrast, effects for cortical surface area appear global. Case-control, negative, cortical thickness effect sizes were two to three times larger in individuals receiving antipsychotic medication relative to unmedicated individuals. Negative correlations between age and bilateral temporal pole thickness were stronger in individuals with schizophrenia than in healthy volunteers. Regional cortical thickness showed significant negative correlations with normalized medication dose, symptom severity, and duration of illness and positive correlations with age at onset.
CONCLUSIONS: The findings indicate that the ENIGMA meta-analysis approach can achieve robust findings in clinical neuroscience studies; also, medication effects should be taken into account in future genetic association studies of cortical thickness in schizophrenia