26,367 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
Testing Gravity-Driven Collapse of the Wavefunction via Cosmogenic Neutrinos
It is pointed out that the Diosi-Penrose ansatz for gravity-induced quantum
state reduction can be tested by observing oscillations in the flavor ratios of
neutrinos originated at cosmological distances. Since such a test would be
almost free of environmental decoherence, testing the ansatz by means of a next
generation neutrino detector such as IceCube would be much cleaner than by
experiments proposed so far involving superpositions of macroscopic systems.
The proposed microscopic test would also examine the universality of
superposition principle at unprecedented cosmological scales.Comment: 4 pages; RevTeX4; Essentially the version published in PR
An assessment of Fe XX - Fe XXII emission lines in SDO/EVE data as diagnostics for high density solar flare plasmas using EUVE stellar observations
The Extreme Ultraviolet Variability Experiment (EVE) on the Solar Dynamics
Observatory obtains extreme-ultraviolet (EUV) spectra of the full-disk Sun at a
spectral resolution of ~1 A and cadence of 10 s. Such a spectral resolution
would normally be considered to be too low for the reliable determination of
electron density (N_e) sensitive emission line intensity ratios, due to
blending. However, previous work has shown that a limited number of Fe XXI
features in the 90-60 A wavelength region of EVE do provide useful
N_e-diagnostics at relatively low flare densities (N_e ~ 10^11-10^12 cm^-3).
Here we investigate if additional highly ionised Fe line ratios in the EVE
90-160 A range may be reliably employed as N_e-diagnostics. In particular, the
potential for such diagnostics to provide density estimates for high N_e
(~10^13 cm^-3) flare plasmas is assessed. Our study employs EVE spectra for
X-class flares, combined with observations of highly active late-type stars
from the Extreme Ultraviolet Explorer (EUVE) satellite plus experimental data
for well-diagnosed tokamak plasmas, both of which are similar in wavelength
coverage and spectral resolution to those from EVE. Several ratios are
identified in EVE data which yield consistent values of electron density,
including Fe XX 113.35/121.85 and Fe XXII 114.41/135.79, with confidence in
their reliability as N_e-diagnostics provided by the EUVE and tokamak results.
These ratios also allow the determination of density in solar flare plasmas up
to values of ~10^13 cm^-3.Comment: 7 pages, 3 figures, 2 tables, MNRAS in pres
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