Christian Heinemann

Weierstrass Institute for Applied Analysis and Stochastics

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Christiane Kraus

Weierstrass Institute for Applied Analysis and Stochastics

Erwin Neher

Macau University of Science and Technology

Robert H. Chow

University of Southern California

Elisabetta Rocca

University of Pavia

Antonio Segatti

University of Pavia

Jürgen Klingauf

University of Münster

I. Gertner

Technion – Israel Institute of Technology

M. Hassan Farshbaf-Shaker

Weierstrass Institute for Applied Analysis and Stochastics

E. Bonetti

University of Pavia

B. Rosner

Technion – Israel Institute of Technology

Cooperative Institutions

Technische Universität Berlin

Max Planck Society

Max Planck Institute for Biophysical Chemistry

Saarland University

Technical University of Darmstadt

Regional Centre of Advanced Technologies and Materials

Palacký University Olomouc

Centre National de la Recherche Scientifique

Kansas State University

Harvard University

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Necessary conditions of first-order for an optimal boundary control problem for viscous damage processes in 2D

Mohammad Hassan Farshbaf Shaker Christian Heinemann

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Nanoscale Assembly of BiVO4/CdS/CoOx Core–Shell Heterojunction for Enhanced Photoelectrochemical Water Splitting

Catalysts (2021)

Hana Kmentová Olivier Henrotte Y. Rambabu Mareike Haensch Christian Heinemann

Porous BiVO4 electrodes were conformally decorated with CdS via a chemical bath deposition process. The highest photocurrent at 1.1 V vs. RHE was achieved for a BiVO4/CdS composite (4.54 mA cm−2), compared with CdS (1.19 mA cm−2) and bare BiVO4 (2.1 mA cm−2), under AM 1.5G illumination. This improvement in the photoefficiency can be ascribed to both the enhanced optical absorption properties and the charge separation due to the heterojunction formation between BiVO4 and CdS. Furthermore, the BiVO4/CdS photoanode was protected with a CoOx layer to substantially increase the photostability of the material. The new BiVO4/CdS/CoOx nanostructure exhibited a highly stable photocurrent density of ~5 mA cm−2. The capability to produce O2 was locally investigated by scanning photoelectrochemical microscope, which showed a good agreement between photocurrent and O2 reduction current maps. This work develops an efficient route to improve the photo-electrochemical performance of BiVO4 and its long-term stability.

Photocurrent

Chemical bath deposition

10.3390/catal11060682

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A degenerating Cahn--Hilliard system coupled with complete damage processes

Christian Heinemann Christiane Kraus

In this work, we analytically investigate a degenerating PDE system for phase separation and complete damage processes considered on a nonsmooth time-dependent domain with mixed boundary conditions. The evolution of the system is described by a degenerating Cahn–Hilliard equation for the concentration, a doubly nonlinear differential inclusion for the damage variable and a degenerating quasi-static balance equation for the displacement field. All these equations are highly nonlinearly coupled. Because of the doubly degenerating character of the system, the doubly nonlinear differential inclusion and the nonsmooth domain, the structure of the model is very complex from an analytical point of view. A novel approach is introduced for proving existence of weak solutions for such degenerating coupled system. To this end, we first establish a suitable notion of weak solutions, which consists of weak formulations of the diffusion and the momentum balance equation, a variational inequality for the damage process and a total energy inequality. To show existence of weak solutions, several new ideas come into play. Various results on shrinking sets and its corresponding local Sobolev spaces are used. It turns out that, for instance, on open sets which shrink in time a quite satisfying analysis in Sobolev spaces is possible. The presented analysis can handle highly nonsmooth regions where complete damage takes place. To mention only one difficulty, infinitely many completely damaged regions which are not connected with the Dirichlet boundary may occur in arbitrary small time intervals.

Differential inclusion

Weak solution

Cahn–Hilliard equation

Weak formulation

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Alteration of Ca²⁺Dependence of Neurotransmitter Release by Disruption of Ca²⁺Channel/Syntaxin Interaction

Journal of Neuroscience (1997)

Jens Rettig Christian Heinemann Uri Ashery Zu-Hang Sheng Charles T. Yokoyama

Presynaptic N-type calcium channels interact with syntaxin and synaptosome-associated protein of 25 kDa (SNAP-25) through a binding site in the intracellular loop connecting domains II and III of the alpha1 subunit. This binding region was loaded into embryonic spinal neurons of Xenopus by early blastomere injection. After culturing, synaptic transmission of peptide-loaded and control cells was compared by measuring postsynaptic responses under different external Ca2+ concentrations. The relative transmitter release of injected neurons was reduced by approximately 25% at physiological Ca2+ concentration, whereas injection of the corresponding region of the L-type Ca2+ channel had virtually no effect. When applied to a theoretical model, these results imply that 70% of the formerly linked vesicles have been uncoupled after action of the peptide. Our data suggest that severing the physical interaction between presynaptic calcium channels and synaptic proteins will not prevent synaptic transmission at this synapse but will make it less efficient by shifting its Ca2+ dependence to higher values.

Synaptosome

STX1A

P-type calcium channel

10.1523/jneurosci.17-17-06647.1997

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Citations (183)

A structural model of ultra-microelectrodes for shear-force based scanning electrochemical microscopy

Journal of Intelligent Material Systems and Structures (2018)

Vijay Venkatesh Robert Northcutt Christian Heinemann Vishnu-Baba Sundaresan

The incorporation of a shear-force (SF) feedback in scanning electrochemical microscopy (SECM) hardware has enabled topographically resolved electrochemical imaging of electroactive substrates. Despite the versatility of SECM-SF imaging, structural response of the ultra-microelectrode (UME) to various excitation inputs is poorly understood and predictive mathematical models for characterizing dynamic behavior, particularly at high operating frequencies (>100 kHz), are absent. In this article, we present a finite element model to characterize SF behavior by modeling the UME as a rigid cantilever with two distributed piezoelectric wafers (dither and receiver) and demonstrate the model’s ability to predict experimentally observed SF behavior. The obtained SF response under different dither-to-receiver distances for various UME geometries and loading conditions provides insight to the optimum placement of piezoelectric wafers on the UME for achieving a high SF amplitude at SF-sensitive frequencies. In addition, the variations in SF response under different dither-to-receiver orientations indicate the existence of a system transfer function that is dependent on the operating modes of the receiver. The agreement between simulated and experimental results suggests that the finite element model along with the experimental methodology can be extended to automated SF imaging using SECM hardware.

Dither

Scanning Electrochemical Microscopy

SIGNAL (programming language)

10.1177/1045389x18783899

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Modeling and analysis of a phase field system for damage and phase separation processes in solids

arXiv (Cornell University) (2013)

E. Bonetti Christian Heinemann Christiane Kraus Antonio Segatti

In this work, we analytically investigate a multi-component system for describing phase separation and damage processes in solids. The model consists of a parabolic diffusion equation of fourth order for the concentration coupled with an elliptic system with material dependent coefficients for the strain tensor and a doubly nonlinear differential inclusion for the damage function. The main aim of this paper is to show existence of weak solutions for the introduced model, where, in contrast to existing damage models in the literature, different elastic properties of damaged and undamaged material are regarded. To prove existence of weak solutions for the introduced model, we start with an approximation system. Then, by passing to the limit, existence results of weak solutions for the proposed model are obtained via suitable variational techniques.

Differential inclusion

Component (thermodynamics)

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ChemInform Abstract: Ground State of Co(N2)+.

ChemInform (1996)

Christian Heinemann Joseph Schwarz Helmut Schwarz

Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

10.1002/chin.199630001

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Existence of weak solutions for Cahn-Hilliard systems coupled with elasticity and damage

arXiv (Cornell University) (2015)

Christiane Kraus Christian Heinemann

A typical phase field approach for describing phase separation and coarsening phenomena in alloys is the Cahn-Hilliard model. This model has been generalized to the so-called Cahn-Larché system by combining it with elasticity to capture non-neglecting deformation phenomena, which occur during phase separation and coarsening processes in the material. In order to account for damage effects, we extend the existing framework of Cahn-Hilliard and Cahn-Larché systems by incorporating an internal damage variable of local character. This damage variable allows to model the effect that damage of a material point is influenced by its local surrounding. The damage process is described by a unidirectional rate-dependent evolution inclusion for the internal variable. For the introduced Cahn-Larché systems coupled with rate-dependent damage processes, we establish a suitable notion of weak solutions and prove existence of weak solutions.

Elasticity

10.48550/arxiv.1502.05826

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Citations (31)

Conclusion

Springer eBooks (2014)

Christian Heinemann Christiane Kraus

Differential inclusion

10.1007/978-3-658-05252-2_8

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Submembrane CA time course at secretory sites upon depolarization

Robert H. Chow Jürgen Klingauf Christian Heinemann Erwin Neher

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