14,860 research outputs found
Ultracold mixtures of metastable He and Rb: scattering lengths from ab initio calculations and thermalization measurements
We have investigated the ultracold interspecies scattering properties of
metastable triplet He and Rb. We performed state-of-the-art ab initio
calculations of the relevant interaction potential, and measured the
interspecies elastic cross section for an ultracold mixture of metastable
triplet He and Rb in a quadrupole magnetic trap at a temperature of
0.5 mK. Our combined theoretical and experimental study gives an interspecies
scattering length , which prior to this work was
unknown. More general, our work shows the possibility of obtaining accurate
scattering lengths using ab initio calculations for a system containing a
heavy, many-electron atom, such as Rb.Comment: 11 pages, 11 figures, accepted for publication in Phys. Rev.
Modelling of epitaxial graphene functionalization
A new model for graphene, epitaxially grown on silicon carbide is proposed.
Density functional theory modelling of epitaxial graphene functionalization by
hydrogen, fluorine and phenyl groups has been performed with hydrogen and
fluorine showing a high probability of cluster formation in high adatom
concentration. It has also been shown that the clusterization of fluorine
adatoms provides midgap states in formation due to significant flat distortion
of graphene. The functionalization of epitaxial graphene using larger species
(methyl and phenyl groups) renders cluster formation impossible, due to the
steric effect and results in uniform coverage with the energy gap opening.Comment: 15 pages, 4 figures, to appear in Nanotechnolog
Mesoscopic circuits with charge discreteness:quantum transmission lines
We propose a quantum Hamiltonian for a transmission line with charge
discreteness. The periodic line is composed of an inductance and a capacitance
per cell. In every cell the charge operator satisfies a nonlinear equation of
motion because of the discreteness of the charge. In the basis of one-energy
per site, the spectrum can be calculated explicitly. We consider briefly the
incorporation of electrical resistance in the line.Comment: 11 pages. 0 figures. Will be published in Phys.Rev.
Composition and functionality of the wild and cultivated common bean rhizosphere microbiome.
Abstract: Plants rely on their rhizosphere microbiome for specific functions, such as, nutrient acquisition and protection against diseases. The domestication and subsequent plant breeding neglected the important role of the rhizosphere microbiome on plant performance. Here, we tested the hypothesis that ancestor materials have higher ability to host beneficial microorganisms in the rhizosphere when compared to modern cultivars. For this, we assessed the composition and functionality of the rhizosphere microbiome associated with a wild (Wild Mex) and with a cultivated (IAC Alvorada) common bean grown in highly biodiverse soil (Amazonian Dark Earth). Antagonistic bacteria were isolated from common bean rhizosphere and total rhizosphere DNA was extracted for shotgun sequencing using Illumina MiSeq. Eleven out of 104 isolated bacteria showed antagonistic in vitro activity against soil borne pathogens Rhizoctonia solani and Fusarium oxysporum f. sp. phaseoli. The bacterial isolates were identified belonging to Streptomyces, Kitasatospora, Alcaligenes, Achromobacter, Pseudomonas, Stenotrophomonas, Brevibacillus and Paenibacillus genus. The cultivation-independent approach revealed that microbial community composition in the Wild Mex bean rhizosphere was characterized by higher relative abundance of bacterial phyla Acidobacteria, Verrucomicrobia, Gemmatimonadetes and fungal phylum Glomeromycota when compared with IAC Alvorada cultivated bean, which showed a higher relative abundance of bacterial phyla Firmicutes, Planctomycetes, Deinococcus-Thermus and fungal phylum Ascomycota. Wild Mex rhizosphere microbiome showed higher relative frequency of nitrogen-fixing, nitrifying, antagonists and plant growth promoting microorganisms. The wild bean also showed higher relative abundance of functions related to nitrogen fixation, siderophore and indole acetic acid (IAA) production, when compared with IAC Alvorada bean. Ordination analysis revealed that the wild genotype is more selective in recruiting microorganisms and functions in the rhizosphere when compared with modern cultivar. In conclusion, the results revealed that domestication and plant breeding potentially undermined rhizosphere microbiome composition and functions debilitating the host?s ability to select and support beneficial microbes
The Development of Hydrophobic and Superhydrophobic Cementitious Composites
Freezing and thawing of water in saturated concrete induces stresses, cracks, spalling, and eventually allows chlorides, sulphates and other ions to penetrate through the porous space of concrete causing the corrosion and ultimately structural failure. These detrimental factors are limited if concrete has the ability to repel water. Water repellant concrete was achieved through internal and external surface applications. Hydrophobicity, over- and super-hydrophobicity are demonstrated by the ability of a surface to repel water and are characterized by contact angles. In cementitious composites internal hydrophobization can be achieved through the addition of superhydrophobic admixtures to fresh concrete resulting in an air void system with small, well-dispersed air bubbles to provide superior resistance to freezing and thawing. Hydrophobic, over- and super-hydrophobic surface coatings were achieved by the design of hierarchical surfaces tailoring the fiber content, mixture proportion, and superhydrophobic emulsions. Contact angle tests were used to characterize the developed coatings. The use of internal hydrophobization improves freezing and thawing resistance of fiber-reinforced composites as demonstrated by a durability factor of 100 through as many as 700 accelerated (-50°C to 20°C) cycles in 5% NaCl solution
Analysis of ASTEC-Na capabilities for simulating a loss of flow CABRI experiment
Abstract This paper presents simulation results of the CABRI BI1 test using the code ASTEC-Na, currently under development, as well as a comparison of the results with available experimental data. The EU-JASMIN project (7th FP of EURATOM) centres on the development and validation of the new severe accident analysis code ASTEC-Na (Accident Source Term Evaluation Code) for sodium-cooled fast reactors whose owner and developer is IRSN. A series of experiments performed in the past (CABRI/SCARABEE experiments) and new experiments to be conducted in the new experimental sodium facility KASOLA have been chosen to validate the developed ASTEC-Na code. One of the in-pile experiments considered for the validation of ASTEC-Na thermal–hydraulic models is the CABRI BI1 test, a pure loss-of-flow transient using a low burnup MOX fuel pin. The experiment resulted in a channel voiding as a result of the flow coast-down leading to clad melting. Only some fuel melting took place. Results from the analysis of this test using SIMMER and SAS-SFR codes are also presented in this work to check their suitability for further code benchmarking purposes
The distribution of oxygen at the Ni81Fe19/Ta interface
The knowledge of how oxygen atoms are distributed at a magnetic-metal /
oxide, or magnetic-metal / non-magnetic-metal interface, can be an useful tool
to optimize device production. Multilayered Ni81Fe19 / Ta samples consisting of
15 bilayers of 2.5 nm each, grown onto glass substrates by magnetron sputtering
from Ni81Fe19 and Ta targets, have been investigated. X-ray absorption near
edge structure, extended X-Ray absorption fine structure, small angle X-ray
diffraction, and simulations, were used to characterize the samples. Oxygen
atoms incorporated onto Ni81Fe19 films during O2 exposition are mainly bonded
to Fe atoms. This partial oxidation of the Ni81Fe19 surface works as a barrier
to arriving Ta atoms, preventing intermixing at the Ni81Fe19 / Ta interface.
The reduction of the Ni81Fe19 surface by the formation of TaO x is observed.Comment: 14 pages, 9 figures, accepted for publication in Advances in
Materials Science and Engineerin
The elephant in the room of density functional theory calculations
Using multiwavelets, we have obtained total energies and corresponding atomization energies for the GGA-PBE and hybrid-PBE0 density functionals for a test set of 211 molecules with an unprecedented and guaranteed μHartree accuracy. These quasi-exact references allow us to quantify the accuracy of standard all-electron basis sets that are believed to be highly accurate for molecules, such as Gaussian-type orbitals (GTOs), all-electron numeric atom-centered orbitals (NAOs), and full-potential augmented plane wave (APW) methods. We show that NAOs are able to achieve the so-called chemical accuracy (1 kcal/mol) for the typical basis set sizes used in applications, for both total and atomization energies. For GTOs, a triple-ζquality basis has mean errors of ∼10 kcal/mol in total energies, while chemical accuracy is almost reached for a quintuple-ζbasis. Due to systematic error cancellations, atomization energy errors are reduced by almost an order of magnitude, placing chemical accuracy within reach also for medium to large GTO bases, albeit with significant outliers. In order to check the accuracy of the computed densities, we have also investigated the dipole moments, where in general only the largest NAO and GTO bases are able to yield errors below 0.01 D. The observed errors are similar across the different functionals considered here
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