5,492 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
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
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
Fatal lymphoproliferation and acute monocytic leukemia-like disease following infectious mononucleosis in the elderly
Three elderly patients are reported, in whom serologically confirmed recent infectious mononucleosis is followed by fatal lymphoproliferation (case 1), by acute monocytic leukemia (case 2), and by acute probably monocytic leukemia (case 3)
Study to establish cost projections for production of Redox chemicals
A cost study of four proposed manufacturing processes for redox chemicals for the NASA REDOX Energy Storage System yielded favorable selling prices in the range 1.91/kg of chromic chloride, anhydrous basis, including ferrous chloride. The prices corresponded to specific energy storage costs from under 17/kWh. A refined and expanded cost analysis of the most favored process yielded a price estimate corresponding to a storage cost of $11/kWh. The findings supported the potential economic viability of the NASA REDOX system
Nonclassical Imaging for a quantum search of trapped ions
We discuss a simple search problem which can be pursued with different
methods, either on a classical or on a quantum basis. The system is represented
by a chain of trapped ions. The ion to be searched is a member of that chain,
consists, however, of an isotopic species different to the others. It is shown
that the classical imaging may lead as fast to the final result as the quantum
imaging. However, for the discussed case the quantum method gives more
flexibility and higher precision when the number of ions considered in the
chain is increasing. In addition, interferences are observable even when the
distances between the ions is smaller than half a wavelength of the incident
light.Comment: 5 pages, 5 figure
Monitoring of the fatigue state of single-lip deep-drilled specimens made of the quenched and tempered steel AISI 4140 using micromagnetic methods
Fatigue is one of the main causes for the failure of technical components. Therefore, the monitoring of fatigue-related material degradation is a target-oriented way to extend the lifetime of safety-relevant components. In terms of sustainability and resource conservation, the implementation of reliable fatigue monitoring is of crucial importance. Fatigue damage is manifested by a variety of microstructural and micromechanical property changes such as grain refinement, relaxation of residual stresses, increase of dislocation density and hardness change. An application of micromagnetic techniques is very promising, since it is known that Barkhausen noise analysis and eddy current testing are sensitive to these parameters.
This work deals with the separation of the micromagnetic parameters with respect to fatigue-induced changes. This separation is necessary to identify, quantify and evaluate the relevant fatigue damage mechanisms and thereby assess the remaining lifetime of the monitored components. In this work, multiple amplitude fatigue tests were performed on specimens drilled under different conditions and as a consequence partly feature a white etching layer. Under these aspects the capability of Barkhausen noise analysis and eddy current testing was compared and assessed
FOSE: a framework for open science evaluation
Pre-publication peer review of scientific literature in its present state suffers from a lack of evaluation validity and transparency to the community. Inspired by social networks, we propose a framework for the open exchange of post-publication evaluation to complement the current system. We first formulate a number of necessary conditions that should be met by any design dedicated to perform open scientific evaluation. To introduce our framework, we provide a basic data standard and communication protocol. We argue for the superiority of a provider-independent framework, over a few isolated implementations, which allows the collection and analysis of open evaluation content across a wide range of diverse providers like scientific journals, research institutions, social networks, publishers websites, and more. Furthermore, we describe how its technical implementation can be achieved by using existing web standards and technology. Finally, we illustrate this with a set of examples and discuss further potential
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