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  • 1
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 18 October 2016, Vol.113(42), pp.11776-11781
    Description: Oceans dominate emissions of dimethyl sulfide (DMS), the major natural sulfur source. DMS is important for the formation of non-sea salt sulfate (nss-SO) aerosols and secondary particulate matter over oceans and thus, significantly influence global climate. The mechanism of DMS oxidation has accordingly been investigated in several different model studies in the past. However, these studies had restricted oxidation mechanisms that mostly underrepresented important aqueous-phase chemical processes. These neglected but highly effective processes strongly impact direct product yields of DMS oxidation, thereby affecting the climatic influence of aerosols. To address these shortfalls, an extensive multiphase DMS chemistry mechanism, the Chemical Aqueous Phase Radical Mechanism DMS Module 1.0, was developed and used in detailed model investigations of multiphase DMS chemistry in the marine boundary layer. The performed model studies confirmed the importance of aqueous-phase chemistry for the fate of DMS and its oxidation products. Aqueous-phase processes significantly reduce the yield of sulfur dioxide and increase that of methyl sulfonic acid (MSA), which is needed to close the gap between modeled and measured MSA concentrations. Finally, the simulations imply that multiphase DMS oxidation produces equal amounts of MSA and sulfate, a result that has significant implications for nss-SO aerosol formation, cloud condensation nuclei concentration, and cloud albedo over oceans. Our findings show the deficiencies of parameterizations currently used in higher-scale models, which only treat gas-phase chemistry. Overall, this study shows that treatment of DMS chemistry in both gas and aqueous phases is essential to improve the accuracy of model predictions.
    Keywords: Capram ; Dimethyl Sulfide ; Marine Aerosols ; Marine Multiphase Chemistry ; Multiphase Modeling
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 2
    Language: English
    In: Journal of Atmospheric Chemistry, 2013, Vol.70(1), pp.19-52
    Description: A new detailed multiphase halogen mechanism, the CAPRAM Halogen Module 2.0 (HM2), has been developed and coupled to the multiphase chemistry mechanism RACM-MIM2ext/CAPRAM 3.0n. The overall mechanism comprises 1,705 reactions including 595 reactions of the HM2. Halogen chemistry box model studies have been, for the first time, performed with a non-permanent cloud scenario for pristine open ocean regions in mid-latitudes. Moreover, detailed time-resolved reaction flux analysis has been used to investigate the multiphase halogen reaction cycles in more detail. Clouds significantly change the multiphase halogen chemical system and new reaction cycles are proposed for in-cloud conditions. While most gas phase concentrations are decreased for chlorine and iodine species, they are increased for bromine. Flux analyses determined the relative contributions of the methylene dihalides CH 2 IX (X = Cl, Br, I) as the main I atom source with a contribution of about 80 % to the total iodocarbon sources. Furthermore, HOI was confirmed to be important for chlorine activation. It is shown that 25 % of the ozone loss can be attributed to halogens. VOC oxidation by halogens is important as halogens account for about 20 % of the methane oxidation and up to 80 % of the oxidation of other VOCs. In other cases, enhanced VOC and VOC oxidation product concentration levels were found. For example, 15 % of the methyl peroxyl radicals are formed after the reaction of chlorine atoms with methane or methyl hydroperoxide. In the aqueous phase, changes in the oxidation of organics do only occur for highly oxidised organics without a C-H bond. For example, over 80 % of oxalic acid are oxidised by electron transfer with Cl 2 − in deliquescent particles during non-cloud periods.
    Keywords: Halogen chemistry ; Multiphase chemistry modelling ; CAPRAM Halogen Module
    ISSN: 0167-7764
    E-ISSN: 1573-0662
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  • 3
    Language: English
    In: Surface & Coatings Technology, August 15, 2013, Vol.228, p.S615-S618
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.surfcoat.2011.10.059 Byline: Katharina Koster, Peter Kaestner, Gunter Brauer, Holger Hoche, Torsten Tro[sz]mann, Matthias Oechsner Keywords: Plasma nitriding; Austenitic stainless steel; Corrosion resistance; Wear resistance Abstract: Austenitic stainless steel is equipped with an excellent corrosion resistance, whereby plasma nitriding of austenitic stainless steel principally results in a high hardness associated with an excellent wear resistance. Whenever a high wear resistance accompanied by the existing corrosion resistance of austenitic stainless steel is required, the application of plasma nitrided stainless steel is restricted. The research goal is maintenance of the wear resistance with the least possible loss of corrosion resistance. In the present study AISI 304 austenitic stainless steel was plasma nitrided in a range of temperature from 325[degrees]C to 550[degrees]C. Examinations revealed that in addition to treatment temperature, time, pulse ratio and the ratio of gas mixture affected the corrosion resistance of plasma nitrided austenitic steel. Results of microhardness tests and potentiodynamic polarization tests showed that an enhancement of corrosion resistance in addition to preservation of hardness is possible. A reduction of plasma power as well as the addition of argon to the process gas induced an increase of the corrosions resistance with just a slight drop in hardness. Characterization of the chemical composition was determined by glow discharge optical emission spectroscopy (GDOS). Phases of expanded austenite were detected by XRD analysis.
    Keywords: Steel Corrosion ; Stainless Steel ; Hardness (Materials)
    ISSN: 0257-8972
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Applied Surface Science, 2010, Vol.256(17), pp.5198-5203
    Description: Since the well-known dsorption ntegral quation (AIE) is an ill-posed problem, calculation of relevant energetic properties from gas and liquid adsorption isotherms on porous solids still remains a challenging field of research. There are two approaches for solving the AIE: (1) the numerical regularization method and (2) the fitting of the experimental adsorption data by functions possessing an analytical solution. Up to now the latter approach has been treated without consideration of the ill-posedness. The inclusion of ill-posedness in the approach leads to its specification which we call the ansatz method. By showing that a certain class of ansatz functions cannot be used for describing the total isotherms, we were urged to consider more general solutions being connected with the Stieltjes integrals. After applying a general inversion formula we can restrict the theoretically possible total isotherms and outline a feasible general ansatz.
    Keywords: Adsorption Integral Equation ; Gas and Liquid Adsorption ; Ill-Posedness ; Stieltjes Integral and Transform ; Ansatz Method ; Engineering
    ISSN: 0169-4332
    E-ISSN: 1873-5584
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  • 5
    Language: English
    In: World Pumps, December 2013, Vol.2013(12), pp.20,22-20,23
    Description: Diamond-face mechanical seals for boiler feed water pumps defy electrochemical corrosion and offer long service life. For decades, unexpectly early damage to components has caused problems to power station operators because of electrochemical corrosion. However, all that has changed since a German power station started using a high-tech sealing technology, and now the innovative ‘diamond-solution’ is in demand globally, writes Hans Peter Brauer.
    Keywords: Engineering
    ISSN: 0262-1762
    E-ISSN: 1873-2593
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  • 6
    Language: English
    In: Adsorption, 2011, Vol.17(5), pp.823-831
    Description: The well-known adsorption integral equation (AIE) for calculating pore size and adsorption energy distributions from adsorption isotherms on porous solids is, from the mathematical point of view, a linear Fredholm integral equation of the first kind and therefore an ill-posed problem. What can we realistically expect from the solution of such an ill-posed problem by regularization ? Does it make sense to restrict the number of possible solutions by the so-called ansatz method ? In this paper, the two methods for solving ill-posed problems are from scratch explained and illuminated by concrete examples. Their relevance and fundamental limitations are discussed.
    Keywords: Ill-posedness ; Unstable operators ; Regularization ; Ansatz method ; Adsorption integral equation ; Pore size and adsorption energy distributions
    ISSN: 0929-5607
    E-ISSN: 1572-8757
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  • 7
    In: Geophysical Research Letters, 16 January 2015, Vol.42(1), pp.1-8
    Description: We present a statistical study of the temporal‐ and spatial‐scale characteristics of different field‐aligned current (FAC) types derived with the Swarm satellite formation. We divide FACs into two classes: small‐scale, up to some 10 km, which are carried predominantly by kinetic Alfvén waves, and large‐scale FACs with sizes of more than 150 km. For determining temporal variability we consider measurements at the same point, the orbital crossovers near the poles, but at different times. From correlation analysis we obtain a persistent period of small‐scale FACs of order 10 s, while large‐scale FACs can be regarded stationary for more than 60 s. For the first time we investigate the longitudinal scales. Large‐scale FACs are different on dayside and nightside. On the nightside the longitudinal extension is on average 4 times the latitudinal width, while on the dayside, particularly in the cusp region, latitudinal and longitudinal scales are comparable. Temporal variability of field‐aligned currents Longitudinal correlation length of field‐aligned currents Small‐scale FACs show very different characteristics than large‐scale FACs
    Keywords: Field‐Aligned Currents ; Temporal Spatial Characteristics ; Auroral Ionosphere
    ISSN: 0094-8276
    E-ISSN: 1944-8007
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  • 8
    In: Geophysical Research Letters, 16 May 2015, Vol.42(9), pp.3069-3075
    Description: Based on magnetic field data sampled by the Swarm satellite constellation it is possible for the first time to determine uniquely region currents at low latitudes. Initial results are presented from the first 200 days of formation flight (17 April to 5 November 2014). Detailed results have been obtained for interhemispheric field‐aligned currents connecting the solar quiet day magnetic variation () current systems in the two hemispheres. We obtain prominent currents from the Southern (winter) Hemisphere to the Northern around noon. Weaker currents in opposite direction are observed during morning and evening hours. Furthermore, we could confirm the existence of vertical currents above the dip equator, downward around noon and upward around sunset. For both current systems we present and discuss longitudinal variations. Application of new approach for current determination is performed Characteristics of interhemispheric field‐aligned currents is presented Characteristics of F region dynamo currents is presented
    Keywords: Equatorial Ionosphere ; Midlatitude Ionosphere ; Ionospheric Currents ; Field‐Aligned Currents
    ISSN: 0094-8276
    E-ISSN: 1944-8007
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  • 9
    Language: English
    In: Journal of Physical Chemistry B, Feb 27, 2003, Vol.107(8), p.1821-1831
    Description: The possibility of reactivity enhancement by molecular traffic control (MTC) was rationalized by dynamic Monte Carlo simulations in a network of single-file systems. The obtained dependencies were explained by the peculiarities of molecular propagation in single-file systems and interpreted in a semiquantitative way by adopting a suitable modification of the Thiele concept for evaluating the effectiveness of catalytic reaction under transport limitation.
    Keywords: Physical Chemistry -- Research ; Adsorption -- Research ; Molecular Dynamics -- Usage ; Reactivity (Chemistry) -- Research
    ISSN: 1520-6106
    E-ISSN: 15205207
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  • 10
    Language: English
    In: Journal of Colloid And Interface Science, 2009, Vol.331(2), pp.329-334
    Description: Synthetic energy distributions and corresponding adsorption isotherms of binary liquid mixtures are presented. The relevance of information on a solid's energetic heterogeneity from liquid-phase adsorption isotherms is studied. Adsorption excess isotherms of binary liquid mixtures have been calculated from synthetic adsorption energy distribution functions characterizing energetic heterogeneity at the liquid/solid interface. In order to see consequences for the adsorption isotherms, the distribution functions were varied systematically. In this way, the sensitivity or the lack of sensitivity of liquid-phase adsorption isotherms over the whole concentration range for changes in energy distribution functions became evident. The question of to what extent it makes sense to use liquid adsorption measurements to obtain relevant information on a solid's energetic heterogeneity is answered.
    Keywords: Adsorption Excess Isotherm ; Binary Liquid Mixture ; Adsorption Energy Distribution Function ; Adsorption Integral Equation ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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