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Recent Publications

2016

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CO2 Methanation: Optimal Start-Up Control of a Fixed-Bed Reactor for Power-to-Gas Applications

Utilizing volatile renewable energy sources (e.g., solar, wind) for chemical production systems requires a deeper understanding of their dynamic operation modes. Taking the example of a methanation reactor in the context of power-to-gas applications, a dynamic optimization approach is used to identify control trajectories for a time optimal reactor start-up avoiding distinct hot spot formation. For the optimization, we develop a dynamic, two-dimensional model of a fixed-bed tube reactor for carbon dioxide methanation which is based on the reaction scheme of the underlying exothermic Sabatier reaction mechanism. While controlling dynamic hot spot formation inside the catalyst bed, we prove the applicability of our methodology and investigate the feasibility of dynamic carbon dioxide methanation. © 2016 American Institute of Chemical Engineers AIChE J, 2016

Original publication:

AIChE Journal /

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Extending the potential of moment analysis in chromatography

Essential goal of modeling chromatographic processes is to describe the dynamics of concentration fronts traveling through chromatographic columns. Most of the models developed originate from differential mass balances for the fluid and solid phases. Model reduction based on evaluating just a limited number of moments of the profiles is known to be a powerful tool to simplify the description of band profiles. This review article first describes the well-established method of moments for different standard models. Then the method is extended to evaluate more complex and realistic column models. The cases of applying columns packed with core-shell particles and the quantitative description of radial concentration profiles are analyzed.

Original publication:

Shamsul Quamar, Andreas Seidel-Morgenstern
Extending the potential of moment analysis in chromatography
Trends in Analytical Chemistry, Volume 81, Pages 87–101, July–August 2016.
DOI: 10.1016/j.trac.2016.01.007


2015

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Miniemulsion-Based Process for Controlling the Size and Shape of Zinc Oxide Nanoparticles

A miniemulsion-based approach to produce crystalline ZnO nanoparticles with narrowly distributed sizes and well-defined faces and shapes is presented. The synthesis reaction in the aqueous droplets of the water-in-oil miniemulsion is induced by mass transfer of the base triethylamine (TEA) across the liquid/liquid interface. In a preliminary study, the dosage of TEA was determined to ensure the required pH range in the aqueous phase. Miniemulsions with a mean droplet size of about 200 nm were produced with a rotor–stator device. The aqueous zinc salt concentration was varied as the parameter in the experimental study. At low zinc salt concentrations, platelike nanoparticles were obtained. An increase in the zinc ion concentration resulted in a decrease in the mean particle size. The shape of the ZnO crystals changed from platelike to rodlike. On the basis of the resulting particle size, it can be deduced that interdroplet exchange is an essential part of the presented miniemulsion-based process

Original publication:

Michael Fricke, Andreas Voigt, Peter Veit, and Kai Sundmacher
Miniemulsion-Based Process for Controlling the Size and Shape of Zinc Oxide Nanoparticles
Industrial and Engineering Chemistry Research, October 2015, 54 (42), pp 10293–10300
DOI: 10.1021/acs.iecr.5b01149



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Environment Effects on Spin States, Properties, and Dynamics from Multi-level QM/MM Studies

This chapter focuses on selected aspects of quantum mechanic/molecular mechanic (QM/MM) simulations, namely the effect of the QM region size on the spin states, the accuracy of obtained spectroscopic and energetic parameters of enzymatic and protein systems. The concept of a Spin-Hamiltonian (SH) based on QM, and its direct link to experimental observables from spectroscopy, is connected with the Neese group. Density functional theory (DFT) calculations are very often used as the sole alternative, and benchmarking to isolated bioinorganic complexes is done. The chapter discusses three examples where the use of QM/MM hybrid methods was critical to the elucidation of spin states of intermediates and their properties. QM/MM methods can be used to map electron transfer pathways in proteins, e.g., short-range electron transfer from a metallic cofactor to a nearby amino acid side chain and long-range electron transfer across protein-protein interactions.

Original publication:

Alexander Petrenko and Matthias Stein
Environment Effects on Spin States, Properties, and Dynamics from Multi-level QM/MM Studies
pp 327-368, In: Spin States in Biochemistry and Inorganic Chemistry: Influence on Structure and Reactivity
Marcel Swart, Miquel Costas (Eds.), November 2015, Wiley, Chichester, ISBN: 978-1-118-89831-4.


Enforced ATP futile cycling increases specific productivity and yield of anaerobic lactate production in Escherichia coli

The manipulation of cofactor pools such as ATP or NAD(P)H has for long been recognized as key targets for metabolic engineering of microorganisms to improve yields and productivities of biotechnological processes. Taking lactic acid as an economically relevant product, we demonstrate that induction of ATP futile cycling in Escherichia coli leads to increased yields and specific production rates under anaerobic conditions, even in the case where lactate is already produced with high yields.
However, trade-offs between specific and volumetric productivities must be considered when ATP wasting strategies are used to shift substrate conversion from biomass to product synthesis and we discuss potential solutions to design optimal processes. We think that enforced ATP futile cycling has great potential to optimize a variety of production processes and our study demonstrates that this holds true also for anaerobic processes.

Original publication:

Oliver Hädicke, Katja Bettenbrock und Steffen Klamt
Enforced ATP futile cycling increases specific productivity and yield of anaerobic lactate production in Escherichia coli.
Biotechnology and Bioengineering,  October 2015, Volume 112, Issue 10, 2195–2199

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Numerical Algebra, Matrix Theory, Differential-Algebraic Equations and Control Theory: Festschrift in Honor of Volker Mehrmann

This edited volume highlights the scientific contributions of Volker Mehrmann, a leading expert in the area of numerical (linear) algebra, matrix theory, differential-algebraic equations and control theory. These mathematical research areas are strongly related and often occur in the same real-world applications. The main areas where such applications emerge are computational engineering and sciences, but increasingly also social sciences and economics.

This book also reflects some of Volker Mehrmann's major career stages. Starting out working in the areas of numerical linear algebra (his first full professorship at TU Chemnitz was in "Numerical Algebra," hence the title of the book) and matrix theory, Volker Mehrmann has made significant contributions to these areas ever since. The highlights of these are discussed in Parts I and II of the present book. Often the development of new algorithms in numerical linear algebra is motivated by problems in system and control theory. These and his later major work on differential-algebraic equations, to which he together with Peter Kunkel made many groundbreaking contributions, are the topic of the chapters in Part III.

Besides providing a scientific discussion of Volker Mehrmann's work and its impact on the development of several areas of applied mathematics, the individual chapters stand on their own as reference works for selected topics in the fields of numerical (linear) algebra, matrix theory, differential-algebraic equations and control theory.

Original publication:

Peter Benner, Matthias Bollhöfer, Daniel Kressner, Christian Mehl, Tatjana Stykel (Editors)
Numerical Algebra, Matrix Theory, Differential-Algebraic Equations and Control Theory: Festschrift in Honor of Volker Mehrmann
Springer International Publishing; 21. Mai 2015

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Graphic taken from Fig. 6.: Comparison of uncontrolled solutions for the Burgers equation. Zoom Image
Graphic taken from Fig. 6.: Comparison of uncontrolled solutions for the Burgers equation.
Computational Methods in Science and Engineering

Two-Sided Projection Methods for Nonlinear Model Order Reduction

In this paper, we investigate a recently introduced approach for nonlinear model order reduction based on generalized moment matching. Using basic tensor calculus, we propose a computationally efficient way of computing reduced-order models. We further extend the idea of two-sided interpolation methods to this more general setting by employing the tensor structure of the Hessian. We investigate the use of oblique projections in order to preserve important system properties such as stability. We test one-sided and two-sided projection methods for different semi-discretized nonlinear partial differential equations and show their competitiveness when compared to proper orthogonal decomposition (POD).


Original publication:
Peter Benner and Tobias Breiten
Two-Sided Projection Methods for Nonlinear Model Order Reduction
SIAM J. Sci. Comput., 37(2), B239–B260. (22 pages) 2015
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