99 research outputs found
Biocrust amendments to topsoils facilitate biocrust restoration in a post-mining arid environment
Soil cryptogamic biocrusts provide many ecological functions in arid zone ecosystems, though their natural reestablishment in disturbed areas is slow. Accelerating reestablishment of biocrusts may facilitate the establishment of vascular plant communities within the timeframes of restoration targets (typically 5–15 years). One technique is to inoculate the soil surface using slurries of biocrust material harvested from another site. However, this is destructive to donor sites, and hence the potential to dilute slurries will govern the feasibility of this practice at large spatial scales. We conducted a replicated experiment on a disturbed mine site to test the individual and combined effects of two strategies for accelerating soil cryptogamic biocrust reestablishment: (1) slurry inoculation using biocrust material harvested from native vegetation; and (2) the use of psyllium husk powder as a source of mucilage to bind the soil surface, and to potentially provide a more cohesive substrate for biocrust development. The experiment comprised 90 experimental plots across six treatments, including different dilutions of the biocrust slurries and treatments with and without psyllium. Over 20 months, the reestablishing crust was dominated by cyanobacteria (including Tolypothrix distorta and Oculatella atacamensis), and these established more rapidly in the inoculated treatments than in the control treatments. The inoculated treatments also maintained this cover of cyanobacteria better through prolonged adverse conditions. The dilute biocrust slurry, at 1:100 of the biocrust in the remnant vegetation, performed as well as the 1:10 slurry, suggesting that strong dilution of biocrust slurry may improve the feasibility of using this technique at larger spatial scales. Psyllium husk powder did not improve biocrust development but helped to maintain a soil physical crust through hot, dry, and windy conditions, and so the potential longer-term advantages of psyllium need to be tested. Copyright © 2022 Schultz, Sluiter, Allen, Machado-de-Lima and Muñoz-Rojas
Proton transfer in surface-stabilized chiral motifs of croconic acid
The structure and cooperative proton ordering of two-dimensional sheets of croconic acid were studied with scanning tunneling microscopy and first-principles calculations. Unlike in the crystalline form, which exhibits a pleated, densely packed polar sheet structure, the confinement of the molecules to the surface results in hydrogenbonded chiral clusters and networks. First-principles calculations suggest that the surface stabilizes networks of configurational isomers, which arise from direct hydrogen transfer between their constituent croconic acid monomers. Some of these configurations have a net polarization. It is demonstrated through constrained molecular dynamics simulations that simultaneous proton transfer between any two molecules can occur spontaneously. This finding is a prerequisite for the occurrence of in-plane ferroelectricity based on proton transfer in 2D sheets
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Proton transfer in surface-stabilized chiral motifs of croconic acid
The structure and cooperative proton ordering of two-dimensional sheets of croconic acid were studied with scanning tunneling microscopy and first-principles calculations. Unlike in the crystalline form, which exhibits a pleated, densely packed polar sheet structure, the confinement of the molecules to the surface results in hydrogen-bonded chiral clusters and networks. First-principles calculations suggest that the surface stabilizes networks of configurational isomers, which arise from direct hydrogen transfer between their constituent croconic acid monomers. Some of these configurations have a net polarization. It is demonstrated through constrained molecular dynamics simulations that simultaneous proton transfer between any two molecules can occur spontaneously. This finding is a prerequisite for the occurrence of in-plane ferroelectricity based on proton transfer in 2D sheets
Characterization the Cool KOIs. II. The M Dwarf KOI-254 and its Hot Jupiter
We report the confirmation and characterization of a transiting gas giant planet orbiting the M dwarf KOI-254 every 2.455239 days, which was originally discovered by the Kepler mission. We use radial velocity measurements, adaptive optics imaging, and near-infrared spectroscopy to confirm the planetary nature of the transit events. KOI-254 b is the first hot Jupiter discovered around an M-type dwarf star. We also present a new model-independent method of using broadband photometry to estimate the mass and metallicity of an M dwarf without relying on a direct distance measurement. Included in this methodology is a new photometric metallicity calibration based on J – K colors. We use this technique to measure the physical properties of KOI-254 and its planet. We measure a planet mass of M_P = 0.505 M_(Jup), radius R_P = 0.96 R_(Jup), and semimajor axis a = 0.030 AU, based on our measured stellar mass M_* = 0.59 M_☉ and radius R_* = 0.55 R_☉. We also find that the host star is metal-rich, which is consistent with the sample of M-type stars known to harbor giant planets
Characterizing the Cool KOIs II. The M Dwarf KOI-254 and its Hot Jupiter
We report the confirmation and characterization of a transiting gas giant
planet orbiting the M dwarf KOI-254 every 2.455239 days, which was originally
discovered by the Kepler mission. We use radial velocity measurements, adaptive
optics imaging and near infrared spectroscopy to confirm the planetary nature
of the transit events. KOI-254b is the first hot Jupiter discovered around an
M-type dwarf star. We also present a new model-independent method of using
broadband photometry to estimate the mass and metallicity of an M dwarf without
relying on a direct distance measurement. Included in this methodology is a new
photometric metallicity calibration based on J-K colors. We use this technique
to measure the physical properties of KOI-254 and its planet. We measure a
planet mass of Mp = 0.505 Mjup, radius Rp = 0.96 Rjup and semimajor axis a =
0.03 AU, based on our measured stellar mass Mstar = 0.59 Msun and radius Rstar
= 0.55 Rsun. We also find that the host star is metal-rich, which is consistent
with the sample of M-type stars known to harbor giant planets.Comment: AJ accepted (in press
Strain Effects on the Work Function of an Organic Semiconductor
Establishing fundamental relationships between strain and work function (WF) in organic semiconductors is important not only for understanding electrical properties of organic thin films, which are subject to both intrinsic and extrinsic strains, but also for developing flexible electronic devices. Here we investigate tensile and compressive strain effects on the WF of rubrene single crystals. Mechanical strain induced by thermal expansion mismatch between the substrate and rubrene is quantified by X-ray diffraction. The corresponding WF change is measured by scanning Kelvin probe microscopy. The WF of rubrene increases (decreases) significantly with in-plane tensile (compressive) strain, which agrees qualitatively with density functional theory calculations. An elastic-to-plastic transition, characterized by a steep rise of the WF, occurs at ∼0.05% tensile strain along the rubrene π-stacking direction. The results provide the first concrete link between mechanical strain and WF of an organic semiconductor and have important implications for understanding the connection between structural and electronic disorder in soft organic electronic materials
Biocrust Amendments to Topsoils Facilitate Biocrust Restoration in a Post-mining Arid Environment
Soil cryptogamic biocrusts provide many ecological functions in arid zone ecosystems, though their natural reestablishment in disturbed areas is slow. Accelerating reestablishment of biocrusts may facilitate the establishment of vascular plant communities within the timeframes of restoration targets (typically 5–15 years). One technique is to inoculate the soil surface using slurries of biocrust material harvested from another site. However, this is destructive to donor sites, and hence the potential to dilute slurries will govern the feasibility of this practice at large spatial scales. We conducted a replicated experiment on a disturbed mine site to test the individual and combined effects of two strategies for accelerating soil cryptogamic biocrust reestablishment: (1) slurry inoculation using biocrust material harvested from native vegetation; and (2) the use of psyllium husk powder as a source of mucilage to bind the soil surface, and to potentially provide a more cohesive substrate for biocrust development. The experiment comprised 90 experimental plots across six treatments, including different dilutions of the biocrust slurries and treatments with and without psyllium. Over 20 months, the reestablishing crust was dominated by cyanobacteria (including Tolypothrix distorta and Oculatella atacamensis), and these established more rapidly in the inoculated treatments than in the control treatments. The inoculated treatments also maintained this cover of cyanobacteria better through prolonged adverse conditions. The dilute biocrust slurry, at 1:100 of the biocrust in the remnant vegetation, performed as well as the 1:10 slurry, suggesting that strong dilution of biocrust slurry may improve the feasibility of using this technique at larger spatial scales. Psyllium husk powder did not improve biocrust development but helped to maintain a soil physical crust through hot, dry, and windy conditions, and so the potential longer-term advantages of psyllium need to be tested
Ultrathin BaTiO3 templates for multiferroic nanostructures
Structural, electronic and dielectric properties of high-quality ultrathin
BaTiO3 films are investigated. The films, which are grown by ozone-assisted
molecular beam epitaxy on Nb-doped SrTiO3 (001) substrates and having
thicknesses as thin 8 unit cells (3.2 nm), are unreconstructed and atomically
smooth with large crystalline terraces. A strain-driven transition to 3D island
formation is observed for films of of 13 unit cells thickness (5.2 nm). The
high structural quality of the surfaces, together with the dielectric
properties similar to bulk BaTiO3 and dominantly TiO2 surface termination, make
these films suitable templates for the synthesis of high-quality metal-oxide
multiferroic heterostructures for the fundamental study and exploitation of
magneto-electric effects, such as a recently proposed interface effect in
Fe/BaTiO3 heterostructures based on Fe-Ti interface bonds
Surface state engineering of molecule-molecule interactions
Engineering the electronic structure of organics through interface
manipulation, particularly the interface dipole and the barriers to charge
carrier injection, is of essential importance to improved organic devices. This
requires the meticulous fabrication of desired organic structures by precisely
controlling the interactions between molecules. The well-known principles of
organic coordination chemistry cannot be applied without proper consideration
of extra molecular hybridization, charge transer and dipole formation at the
interfaces. Here we identify the interplay between energy level alignment,
charge transfer, surface dipole and charge pillow effect and show how these
effects collectively determine the net force between adsorbed porphyrin 2H-TPP
on Cu(111). We show that the forces between supported porphyrins can be altered
by controlling the amount of charge transferred across the interface accurately
through the relative alignment of molecular electronic levels with respect to
the Shockley surface state of the metal substrate, and hence govern the
self-assembly of the molecules
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