Radical detection in harsh environments by means of laser-induced fluorescence using a single bidirectional optical fiber

A new experimental method is describe enabling detection of hydroxyl radicals (OH) by Laser- Induced Fluorescence (LIF) in high-temperature gasphase reactions. This is accomplished by means of a bidirectional optical fiber probe, which is of interest for applications where optical access is limited. An optical setup has been developed that allows simultaneous excitation and detection of fluorescence using one and the same fiber. Complications resulting from coupling as well as laser-induced scattering are addressed, and different fibers are compared with regard to core material composition and geometric collection efficiency. On this basis a suitable fiber is identified and OH detection and profile measurements are demonstrated in a premixed laminar flame as reference experiment

BioSig: The Free and Open Source Software Library for Biomedical Signal Processing

BioSig is an open source software library for biomedical signal processing. The aim of the BioSig project is to foster research in biomedical signal processing by providing free and open source software tools for many different application areas. Some of the areas where BioSig can be employed are neuroinformatics, brain-computer interfaces, neurophysiology, psychology, cardiovascular systems, and sleep research. Moreover, the analysis of biosignals such as the electroencephalogram (EEG), electrocorticogram (ECoG), electrocardiogram (ECG), electrooculogram (EOG), electromyogram (EMG), or respiration signals is a very relevant element of the BioSig project. Specifically, BioSig provides solutions for data acquisition, artifact processing, quality control, feature extraction, classification, modeling, and data visualization, to name a few. In this paper, we highlight several methods to help students and researchers to work more efficiently with biomedical signals

Methane Pyrolysis for Zero-Emission Hydrogen Production: A Potential Bridge Technology from Fossil Fuels to a Renewable and Sustainable Hydrogen Economy

Hydrogen plays a key role in many industrial applications and is currently seen as one of the most promising energy vectors. Many efforts are being made to produce hydrogen with zero CO2 footprint via water electrolysis powered by renewable energies. Nevertheless, the use of fossil fuels is essential in the short term. The conventional coal gasification and steam methane reforming processes for hydrogen production are undesirable due to the huge CO2 emissions. A cleaner technology based on natural gas that has received special attention in recent years is methane pyrolysis. The thermal decomposition of methane gives rise to hydrogen and solid carbon, and thus, the release of greenhouse gases is prevented. Therefore, methane pyrolysis is a CO2-free technology that can serve as a bridge from fossil fuels to renewable energies

Oxygen Poisoning in Laboratory Testing of Iron‐Based Ammonia Synthesis Catalysts and its Potential Sources

The influence of oxygen poisoning on a state-of-the-art multipromoted iron-based industrial catalyst for ammonia synthesis as well as the effectivity of different gas purification methods to prevent oxygen poisoning for experiments on laboratory scale were studied in detail. Additionally, the observed results were compared to a common oxygen poisoning test from literature, which on the one hand confirmed its usability in a wide range of conditions, but on the other hand also demonstrated the limitations of this test

The potential of NO⁺ and O₂^+• in switchable reagent ion Proton Transfer Reaction time-of-flight Mass Spectrometry

Selected ion flow tube mass spectrometry (SIFT-MS) and Proton Transfer Reaction mass spectrometry with switchable reagent ion capability (PTR+SRI-MS) are analytical techniques for real-time qualification and quantification of compounds in gas samples with trace level concentrations. In the detection process, neutral compounds—mainly volatile organic compounds—are ionized via chemical ionization with ionic reagent or primary ions. The most common reagent ions are H3O+, NO+ and O2 +•. While ionization with H3O+ occurs by means of proton transfer, the ionization via NO+ and O2 +• offers a larger variety on ionization pathways, as charge transfer, hydride abstraction etc. are possible. The distribution of the reactant into various reaction channels depends not only on the usage of either NO+ or O2 +•, but also on the class of analyte compounds. Furthermore, the choice of the reaction conditions as well as the choice of either SIFT-MS or PTR+SRI-MS might have a large impact on the resulting products. Therefore, an overview of both NO+ and O2 +• as reagent ions is given, showing differences between SIFT-MS and PTR+SRI-MS as used analytical methods revealing the potential how the knowledge obtained with H3O+ for different classes of compounds can be extended with the usage of NO+ and O2 +•

Linear Stochastic Models of Nonlinear Dynamical Systems

We investigate in this work the validity of linear stochastic models for nonlinear dynamical systems. We exploit as our basic tool a previously proposed Rayleigh-Ritz approximation for the effective action of nonlinear dynamical systems started from random initial conditions. The present paper discusses only the case where the PDF-Ansatz employed in the variational calculation is ``Markovian'', i.e. is determined completely by the present values of the moment-averages. In this case we show that the Rayleigh-Ritz effective action of the complete set of moment-functions that are employed in the closure has a quadratic part which is always formally an Onsager-Machlup action. Thus, subject to satisfaction of the requisite realizability conditions on the noise covariance, a linear Langevin model will exist which reproduces exactly the joint 2-time correlations of the moment-functions. We compare our method with the closely related formalism of principal oscillation patterns (POP), which, in the approach of C. Penland, is a method to derive such a linear Langevin model empirically from time-series data for the moment-functions. The predictive capability of the POP analysis, compared with the Rayleigh-Ritz result, is limited to the regime of small fluctuations around the most probable future pattern. Finally, we shall discuss a thermodynamics of statistical moments which should hold for all dynamical systems with stable invariant probability measures and which follows within the Rayleigh-Ritz formalism.Comment: 36 pages, 5 figures, seceq.sty for sequential numbering of equations by sectio

Surface analysis of the ab-plane of MoVTeNbOx catalysts for propane (amm) oxidation by low energy ion scattering (LEIS)

There is great global interest in utilization of light alkane feedstocks in the prodn. of petrochems. by selective (amm)oxidn. due to current abundance and lower costs of alkanes compared to the corresponding olefins. However, direct oxidn. of alkanes requires multifunctional catalysts that cope with simultaneous activation of C-H bonds, mol. oxygen and ammonia and that concurrently provide selectively oxidizing oxygen atoms. For selective oxidn. of propane to acrylic acid and ammoxidn. to acrylonitrile, this multi-functionality is implemented in MoVTeNbOx catalysts, which show high activities and selectivities to acrylic acid and acrylonitrile. It has been suggested that the ab-planes of the M1 phase contain the active and selective surface sites. The catalytic role of these planes was investigated by combining the microreactor study of propane (amm)oxidn. over these model catalysts with Low Energy Ion Scattering (LEIS) to selectively det. the at. compn. of the outer surface of the ab-planes

Determination of trace compounds and artifacts in nitrogen background measurements by proton transfer reaction time-of-flight mass spectrometry under dry and humid conditions

A qualitative analysis was applied for the determination of trace compounds at the parts per trillion in volume (pptv) level in the mass spectra of nitrogen of different qualities (5.0 and 6.0) under dry and humid conditions. This qualitative analysis enabled the classification and discovery of hundreds of new ions (e.g., [Sx]H+ species) and artifacts such as parasitic ions and memory effects and their differentiation from real gas impurities. With this analysis, the humidity dependency of all kind of ions in the mass spectrum was determined. Apart from the inorganic artifacts previously discovered, many new organic ions were assigned as instrumental artifacts and new isobaric interferences could be elucidated. From 1140 peaks found in the mass range m/z 0–800, only 660 could be analyzed due to sufficient intensity, from which 463 corresponded to compounds. The number of peaks in nitrogen proton transfer reaction (PTR) spectra was similarly dominated by nonmetallic oxygenated organic compounds (23.5%) and hydrocarbons (24.1%) Regarding only gas impurities, hydrocarbons were the main compound class (50.2%). The highest contribution to the total ion signal for unfiltered nitrogen under dry and humid conditions was from nonmetallic oxygenated compounds. Under dry conditions, nitrogen-containing compounds exhibit the second highest contribution of 89% and 96% for nitrogen 5.0 and 6.0, respectively, whereas under humid conditions, hydrocarbons become the second dominant group with 69% and 86% for nitrogen 5.0 and 6.0, respectively. With the gathered information, a database can be built as a tool for the elucidation of instrumental and intrinsic gas matrix artifacts in PTR mass spectra and, especially in cases, where dilution with inert gases plays a significant role