68 research outputs found
Steady-state initialization of object-oriented thermo-fluid models by homotopy methods
The steady-state initialization of large object-oriented
thermo-hydraulic networks is a difficult problem, because of the sensitivity of the convergence to the initial guesses of the iteration variables. This paper proposes an approach to this problem based on homotopy transformation, detailing specific criteria for model simplifications in this physical domain. The approach is successfully demonstrated on large power plant test cases, having several hundreds of iteration variables
Acceleration of Diffusional Jumps of Interstitial Fe with Increasing Ge Concentration in Si1 − x Ge x Alloys Observed by Mössbauer Spectroscopy
Radioactive 57Mn isotopes have been implanted into Si1 − x Ge x crystals (x ≤ 0.1) at elevated temperatures for Mössbauer studies of the diffusion of interstitial 57Fe daughter atoms. The atomic jump frequency is found to increase upon Ge alloying. This is attributed to a lowering of the activation energy, i.e. the saddle point energy at hexagonal interstitial sites with Ge neighbour atom
Induced magnetism in transition metal intercalated graphitic systems
We investigate the structure, chemical bonding, electronic properties, and
magnetic behavior of a three-dimensional graphitic network in aba and aaa
stacking with intercalated transition metal atoms (Mn, Fe, Co, Ni, and Cu).
Using density functional theory, we find induced spin-polarization of the C
atoms both when the graphene sheets are aba stacked (forming graphite) and aaa
stacked (resembling bi-layer graphene). The magnetic moment induced by Mn, Fe,
and Co turns out to vary from 1.38 {\mu}B to 4.10 {\mu}B, whereas intercalation
of Ni and Cu does not lead to a magnetic state. The selective induction of
spin-polarization can be utilized in spintronic and nanoelectronic
applications.Comment: 13 pages, 3 figures, 1 tabl
Fragmentation, auto-modification and post ionisation proton bound dimer ion formation: the differential mobility spectrometry of low molecular weight alcohols
Separation of different ion structures in atmospheric pressure photoionization-ion mobility spectrometry-mass spectrometry (APPI-IMS-MS)
Robustness of declarative modeling languages: Improvements via probability-one homotopy
Robustness issues with steady-state initialization remain a barrier in the practical use of declarative modeling languages for multi-domain modeling of large, complex, and heterogeneous technical systems. The objective of this paper is to illustrate how probability-one homotopy, an established method from topology, can solve this issue. This is achieved by establishing a framework for application-specific probability-one homotopy in declarative
modeling languages. The analysis is based on domain-specific probability-one homotopy maps, which were reformulated in a declarative fashion. Additionally, a novel probability-one homotopy map and associated coercivity proof is introduced for a class of thermo-fluid dynamics problems. It was found that the approach enables robust initialization for declarative modeling languages on several test cases and leads to a concise declarative problem formulation
Quantitation of Flavor Compounds in Refill Solutions for Electronic Cigarettes Using HS-GCxIMS and Internal Standards
New regulations on the use of flavor compounds in tobaccoless electronic cigarettes require comprehensive analyses. Gas chromatography coupled ion mobility spectrometry is on the rise as an analytical technique for analyzing volatile organic compounds as it combines sensitivity, selectivity, and easy usage with a full-range screening. A current challenge is the quantitative GCxIMS-analysis. Non-linear calibration methods are predominantly used. This work presents a new calibration method using linearization and its corresponding fit based on the relation between the reactant and analyte ions from the chemical ionization. The analysis of e-liquids is used to compare the presented calibration with an established method based on a non-linear Boltzmann fit. Since e-liquids contain matrix compounds that have been shown to influence the analyte signals, the use of internal standards is introduced to reduce these effects in GCxIMS-analysis directly. Different matrix mixtures were evaluated in the matrix-matched calibration to improve the quantitation further. The system’s detection and quantitation limits were determined using a separate linear calibration. A matrix-matched calibration series of 29 volatile compounds with 12 levels were used to determine the concentration of these substances in a spiked, flavorless e-liquid and a banana-flavored e-liquid, validating the quality of the different calibrations
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