2,018 research outputs found
Influence of O2 and N2 on the conductivity of carbon nanotube networks
We have performed experiments on single-wall carbon nanotube (SWNT) networks
and compared with density-functional theory (DFT) calculations to identify the
microscopic origin of the observed sensitivity of the network conductivity to
physisorbed O2 and N2. Previous DFT calculations of the transmission function
for isolated pristine SWNTs have found physisorbed molecules have little
influence on their conductivity. However, by calculating the four-terminal
transmission function of crossed SWNT junctions, we show that physisorbed O2
and N2 do affect the junction's conductance. This may be understood as an
increase in tunneling probability due to hopping via molecular orbitals. We
find the effect is substantially larger for O2 than for N2, and for
semiconducting rather than metallic SWNTs junctions, in agreement with
experiment.Comment: 6 pages, 5 figures, 1 tabl
Resolving and Tuning Mechanical Anisotropy in Black Phosphorus via Nanomechanical Multimode Resonance Spectromicroscopy
Black phosphorus (P) has emerged as a layered semiconductor with a unique
crystal structure featuring corrugated atomic layers and strong in-plane
anisotropy in its physical properties. Here, we demonstrate that the crystal
orientation and mechanical anisotropy in free-standing black P thin layers can
be precisely determined by spatially resolved multimode nanomechanical
resonances. This offers a new means for resolving important crystal orientation
and anisotropy in black P device platforms in situ beyond conventional optical
and electrical calibration techniques. Furthermore, we show that
electrostatic-gating-induced straining can continuously tune the mechanical
anisotropic effects on multimode resonances in black P electromechanical
devices. Combined with finite element modeling (FEM), we also determine the
Young's moduli of multilayer black P to be 116.1 and 46.5 GPa in the zigzag and
armchair directions, respectively.Comment: Main Text: 13 Pages, 4 Figures; Supplementary Information: 5 Pages, 2
Figures, 2 Table
The Renaissance of Black Phosphorus
One hundred years after its first successful synthesis in the bulk form in
1914, black phosphorus (black P) was recently rediscovered from the perspective
of a two-dimensional (2D) layered material, attracting tremendous interest from
condensed matter physicists, chemists, semiconductor device engineers and
material scientists. Similar to graphite and transition metal dichalcogenides
(TMDs), black P has a layered structure but with a unique puckered single layer
geometry. Because the direct electronic band gap of thin film black P can be
varied from 0.3 to around 2 eV, depending on its film thickness, and because of
its high carrier mobility and anisotropic in-plane properties, black P is
promising for novel applications in nanoelectronics and nanophotonics different
from graphene and TMDs. Black P as a nanomaterial has already attracted much
attention from researchers within the past year. Here, we offer our opinions on
this emerging material with the goal of motivating and inspiring fellow
researchers in the 2D materials community and the broad readership of PNAS to
discuss and contribute to this exciting new field. We also give our
perspectives on future 2D and thin film black P research directions, aiming to
assist researchers coming from a variety of disciplines who are desirous of
working in this exciting research field.Comment: 23 pages, 6 figures, perspective article, appeared online in PNA
Oxidative protein folding in the mitochondrial intermembrane space
Disulfide bond formation is a crucial step for oxidative folding and necessary for the acquisition of a protein's native conformation. Introduction of disulfide bonds is catalyzed in specialized subcellular compartments and requires the coordinated action of specific enzymes. The intermembrane space of mitochondria has recently been found to harbor a dedicated machinery that promotes the oxidative folding of substrate proteins by shuttling disulfide bonds. The newly identified oxidative pathway consists of the redox-regulated receptor Mia40 and the sulfhydryl oxidase Erv1. Proteins destined to the intermembrane space are trapped by a disulfide relay mechanism that involves an electron cascade from the incoming substrate to Mia40, then on to Erv1, and finally to molecular oxygen via cytochrome c. This thiol–disulfide exchange mechanism is essential for the import and for maintaining the structural stability of the incoming precursors. In this review we describe the mechanistic parameters that define the interaction and oxidation of the substrate proteins in light of the recent publications in the mitochondrial oxidative folding field
Ectodysplasin A (EDA) - EDA receptor signalling and its pharmacological modulation.
The TNF family ligand ectodysplasin A (EDA) regulates the induction, morphogenesis and/or maintenance of skin-derived structures such as teeth, hair, sweat glands and several other glands. Deficiencies in the EDA - EDA receptor (EDAR) signalling pathway cause hypohidrotic ectodermal dysplasia (HED). This syndrome is characterized by the absence or malformation of several skin-derived appendages resulting in hypotrychosis, hypodontia, heat-intolerance, dry skin and dry eyes, susceptibility to airways infections and crusting of various secretions. The EDA-EDAR system is an important effector of canonical Wnt signalling in developing skin appendages. It functions by stimulating NF-κB-mediated transcription of effectors or inhibitors of the Wnt, Sonic hedgehog (SHH), fibroblast growth factor (FGF) and transforming growth factor beta (TGFβ) pathways that regulate interactions within or between epithelial and mesenchymal cells and tissues. In animal models of Eda-deficiency, soluble EDAR agonists can precisely correct clinically relevant symptoms with low side effects even at high agonist doses, indicating that efficient negative feedback signals occur in treated tissues. Hijacking of the placental antibody transport system can help deliver active molecules to developing foetuses in a timely manner. EDAR agonists may serve to treat certain forms of ectodermal dysplasia
Comparative environmental analysis of soil sampling methods in precision agriculture for lime application in Paraná State, Brazil
Precision agriculture (PA) provides techniques that favour the localized application of
inputs allowing their rational use. This makes the PA a potential indicator of reduced operational
costs, input volume, and environmental impacts. The objective of this study was to evaluate and
compare the environmental effects of three different sampling methods used in PA for the lime
application. The first sampling method evaluated was the grid sampling (GS). It was performed
at a density of one sample per hectare in a 100×100 m georeferenced grid. The second method
was the directed sampling, that was performed after defining the management zones by soil
apparent electrical conductivity (ECa) using a soil electrical conductivity sensor. The lest
sampling method was the Altitude-based management zone (AMZ) sampling that was developed
based on altitude maps of the field. These sampling methods were tested in three different areas
in the south of Brazil. This study evaluated the spatial variability of the lime volume in the soil
and compared quantitatively and spatially the recommended application volumes achieved by
each sampling method. Results highlighted that the sensor-directed soil sampling method was the
alternative that would generate the lowest environmental impact
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