6,795 research outputs found
Hydrogen adsorption in metal-organic frameworks: the role of nuclear quantum effects
The role of nuclear quantum effects on the adsorption of molecular hydrogen
in metal-organic frameworks (MOFs) has been investigated on grounds of
Grand-Canonical Quantized Liquid Density-Functional Theory (GC-QLDFT)
calculations. For this purpose, we have carefully validated classical H2 -host
interaction potentials that are obtained by fitting Born-Oppenheimer ab initio
reference data. The hydrogen adsorption has first been assessed classically
using Liquid Density-Functional Theory (LDFT) and the Grand-Canonical Monte
Carlo (GCMC) methods. The results have been compared against the semi-classical
treatment of quantum effects by applying the Feynman-Hibbs correction to the
Born-Oppenheimer-derived potentials, and by explicit treatment within the
Grand-Canonical Quantized Liquid Density-Functional Theory (GC-QLDFT). The
results are compared with experimental data and indicate pronounced quantum and
possibly many-particle effects. After validation calculations have been carried
out for IRMOF-1 (MOF-5), GC-QLDFT is applied to study the adsorption of H2 in a
series of MOFs, including IRMOF-4, -6, -8, -9, -10, -12, -14, -16, -18 and
MOF-177. Finally, we discuss the evolution of the H2 quantum fluid with
increasing pressure and lowering temperature
Grand-Canonical Quantized Liquid Density-Functional Theory in a Car-Parrinello Implementation
Quantized Liquid Density-Functional Theory [Phys. Rev. E 2009, 80, 031603], a
method developed to assess the adsorption of gas molecules in porous
nanomaterials, is reformulated within the grand canonical ensemble. With the
grand potential it is possible to compare directly external and internal
thermodynamic quantities. In our new implementation, the grand potential is
minimized utilizing the Car-Parrinello approach and gives, in particular for
low temperature simulations, a significant computational advantage over the
original canonical approaches. The method is validated against original QLDFT,
and applied to model potentials and graphite slit pores.Comment: 19 pages, 5 figure
Calibration of thickness-dependent k-factors for germanium X-ray lines to improve energy-dispersive X-ray spectroscopy of SiGe layers in analytical transmission electron microscopy
We show that the accuracy of energy-dispersive X-ray spectroscopy can be improved by analysing and comparing multiple lines from the same element. For each line, an effective k-factor can be defined that varies as a function of the intensity ratio of multiple lines (e.g. K/L) from the same element. This basically performs an internal self-consistency check in the quantification using differently absorbed X-ray lines, which is in principle equivalent to an absorption correction as a function of specimen thickness but has the practical advantage that the specimen thickness itself does not actually need to be measured
Synodical Address-1848
(The 1848 Synodical Address of C. F. Walther, which is presented here in translation, clearly sets forth his views on the relationship between the congregations and The Lutheran Church-Missouri Synod. Dr. Walther\u27s views were repeated almost verbatim in a Brother to Brother (Mein theurer Herr Amtsbruder} letter of Jan. 12, 1875, in which he assured the congregations of their freedom to accept or reject synodical resolutions, and then pleaded with them to freely accept a synodical resolution that called for a building fund collection for new construction at three synodical schools
3D simulations of self-propelled, reconstructed jellyfish using vortex methods
We present simulations of the vortex dynamics associated with the
self-propelled motion of jellyfish. The geometry is obtained from image
segmentation of video recordings from live jellyfish. The numerical simulations
are performed using three-dimensional viscous, vortex particle methods with
Brinkman penalization to impose the kinematics of the jellyfish motion. We
study two types of strokes recorded in the experiment1. The first type (stroke
A) produces two vortex rings during the stroke: one outside the bell during the
power stroke and one inside the bell during the recovery stroke. The second
type (stroke B) produces three vortex rings: one ring during the power stroke
and two vortex rings during the recovery stroke. Both strokes propel the
jellyfish, with stroke B producing the highest velocity. The speed of the
jellyfish scales with the square root of the Reynolds number. The simulations
are visualized in a fluid dynamics video.Comment: 1 page, 1 figur
Some assembly required: building the fly eye for motion detection and colour discrimination
Among the many eyes that have evolved on Earth, the insect compound eye is the most abundant. Its crystal-like lattice structure is a feat of engineering that has evolved over millions of years, and is exquisitely adapted to detect moving objects and discriminate colours. This enables many behaviours, including foraging for food, finding a mate and avoiding predators. Our understanding of how the compound eye is built and works has been greatly expanded by studying the humble fruit fly, Drosophila melanogaster. The simple outward appearance of the fly eye belies a host of sophisticated features. Through the precise arrangement of photosensitive cells in the retina and their connections to the brain, the fly eye packs an astonishing amount of hardware into a very tiny volume. In this primer, we introduce the molecular pathways that underpin the building and inner workings of the fly eye
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