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Steinau an der Strasse, Germany

Pfennig A.,University of Applied Sciences, Berlin | Kranzmann A.,BAM Federal Institute of Materials Research and Testing
International Journal of Greenhouse Gas Control

During the compression of emission gasses into deep geological layers (Carbon Dioxide Capture and Storage, CCS) CO2-corrosion will become a relevant safety issue. The reliability of the steels used at a geological onshore CCS-site in the Northern German Bassin 42CrMo4 (1.7225, AISI 4140) used for casing, and the injection pipe steels X46Cr13 (1.4034, AISI 420 C), X20Cr13 (1.4021, AISI 420 J) as well as X35CrMo17 (1.4122) is demonstrated in laboratory experiments. Samples were kept in a synthetic aquifer environment at T=60°C. This corrosive environment is then saturated with technical CO2 at a flow rate of 3l/h. Microstructures were characterized by X-ray diffraction, light microscopy, scanning electron microscopy, and energy dispersive X-ray analysis, after a series of heat treatments (700h to 2 years). The non-linear isothermal surface corrosion behaviour of the steels reveals surface corrosion rates around 0.1-0.8mm/year, when obtained by mass gain. Severe pit corrosion (pit heights ca. 4.5mm) are only located on the injection pipe steels. Main phases of the continuous scales are siderite FeCO3 and goethite α-FeOOH. The formation of the non-protective layer is likely to form via a transient Fe(OH)2-phase. © 2011 Elsevier Ltd. Source

Vogt H.,University of Applied Sciences, Berlin
Electrochimica Acta

Various types of uncontrolled potential increase must be distinguished at gas-evolving electrodes. A theoretical analysis on the basis of fundamental relationships shows that the increase in potential-commonly associated with the so-called anode effect at cells with constant or varied current-is caused in some cases by limitation of mass transfer. In other cases it is the result of reaching a summit current value created by the presence of gas bubbles in contact with the electrode surface. Which of the causes is the controlling one depends on the bulk concentration of the reacting substance and on the state of the electrode surface, particularly on material and roughness directly acting on the wettability. It is not sufficient to attribute any uncontrolled potential increase solely to mass transfer control as hitherto done. Several types must be taken into consideration. © 2012 Elsevier Ltd. Source

Gromping U.,University of Applied Sciences, Berlin
Quality and Reliability Engineering International

Fractional factorial 2-level experiments are often conducted without any error degrees of freedom. In such cases, a half-normal effects plot - also called Daniel plot according to its inventor Cuthbert Daniel - can be used for assessing effect significance. Half-normal effects plots are often accompanied by a numeric method for assessing effect significance, most prominently Lenth's method. There are, however, also situations for which a few error degrees of freedom are available, for example, from a replicated center point run. For such cases, besides the obvious possibilities of either ignoring the few replicates (i.e., using half-normal effects plot and Lenth's method, as if they were not there) or using analysis of variance with the replicates for estimating the error variance, several further proposals for assessing effect significance exist. This paper compares the published methods for significance testing, proposes an additional one (that might be very close to what JMP does) and advocates the use of an augmented half-normal effects plot that shows error points and a null reference line along with the effects. It is argued that such a plot can be useful in a fully replicated experiment for assessing whether the replication process was of adequate quality. The method is available in the author's R package DoE.base. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd. Source

Gromping U.,University of Applied Sciences, Berlin
Journal of Statistical Software

In linear models and multivariate normal situations, prior information in linear inequality form may be encountered, or linear inequality hypotheses may be subjected to statistical tests. R package ic.infer has been developed to support inequality-constrained estimation and testing for such situations. This article gives an overview of the principles underlying inequality-constrained inference that are far less well-known than methods for unconstrained or equality-constrained models, and describes their implementation in the package. Source

Luchko Y.,University of Applied Sciences, Berlin
Computers and Mathematics with Applications

In this paper, some uniqueness and existence results for the solutions of the initial-boundary-value problems for the generalized time-fractional diffusion equation over an open bounded domain G × (0, T), G ⊂ Rn are given. To establish the uniqueness of the solution, a maximum principle for the generalized time-fractional diffusion equation is used. In turn, the maximum principle is based on an extremum principle for the Caputo-Dzherbashyan fractional derivative that is considered in the paper, too. Another important consequence of the maximum principle is the continuous dependence of the solution on the problem data. To show the existence of the solution, the Fourier method of the variable separation is used to construct a formal solution. Under certain conditions, the formal solution is shown to be a generalized solution of the initial-boundary-value problem for the generalized time-fractional diffusion equation that turns out to be a classical solution under some additional conditions. © 2009 Elsevier Ltd. All rights reserved. Source

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