# Upcoming Events

- Tuesday, 30.09.2014, 10.00 Uhr (WIAS-ESH)
- Seminar Numerische Mathematik

Prof. W. Huang, University of Kansas, USA:

Computation of eigenvalue problems with anisotropic diffusion operators

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Abstract**

Anisotropic eigenvalue problems can come from application of the Laplace-Beltrami operator to geometric shape analysis and imaging segmentation. They also arise from stability and sensitivity analysis and construction of special solutions for anisotropic diffusion partial differential equations. The latter appears in many areas of science and engineering including plasma physics, petroleum engineering, and image processing. This talk is concerned with finite element computation of those eigenvalue problems, with emphasis on anisotropic mesh adaptation and preservation of basic structures. Both analytical analysis and numerical results are presented.**Host**

WIAS Berlin

- September 30 – October 2, 2014 (WIAS-ESH)
- Workshop/Konferenz: Electrochemical Interfaces - Recent Topics and Open Questions

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Host**

WIAS Berlin

- Thursday, 02.10.2014, 16.00 Uhr (WIAS-ESH)
- Seminar Numerische Mathematik

Prof. J. Lang, TU Darmstadt:

Adaptive moving meshes in large eddy simulation for turbulent flows

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Abstract**

In the last years considerable progress has been made in the development of Large Eddy Simulation (LES) for turbulent flows. The characteristic length scale of the turbulent fluctuation varies substantially over the computational domain and has to be resolved by an appropriate numerical grid. We propose to adjust the grid size in an LES by adaptive moving meshes. The monitor function, which is the main ingredient of a moving mesh method, is determined with respect to a quantity of interest (QoI). These QoIs can be physically motivated, like vorticity, turbulent kinetic energy or enstrophy, as well as mathematically motivated, like solution gradient or some adjoint-based error estimator. The main advantage of mesh moving methods is that during the integration process the mesh topology is preserved and no new degrees of freedom are added and therefore the data structures are preserved as well. I will present results for real-life engineering and meteorological applications.**Host**

WIAS Berlin

- Tuesday, 07.10.2014, 10.15 Uhr (WIAS-406)
- Seminar Nichtlineare Optimierung und Inverse Probleme

Prof. Dr. N. Meyendorf, Institut für Keramische Technologien und Systeme IKTS, Berlin:

Heinrich Barkhausen in Berlin and Dresden -- New applications of his ideas for electromagnetic non-destructive evaluation (NDE)

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)**Abstract**

After studying Physics Barkhausen graduated as Dr. phil. His Ph.D. thesis ``The problem of generation of vibrations under especial consideration of fast electric vibrations'' was published in 1907 and he immediately received an offer from Siemens Berlin where he worked as Engineer and habilitated in 1910 at the TH Berlin. In 1911 he accepted the world's first professorship in the communications branch of electrical engineering, at the Technical Academy in Dresden (1911) where he worked until his retirement in 1953 with short interruptions. His developments in modern amplifier techniques significantly impacted the electronics technology in Saxony (Germany) and Japan where some of his famous students came from and continued his work. The important effect that caries his name was discovered accidently by applying his new developed amplifiers (Physik. Zeitschrift., XX, 1919. Heinrich Barkhausen ``Zwei mit Hilfe der neuen Verstärker entdeckte Erscheinungen". - Two new phenomenos dicoverd by using the new amplifiers)Today Barkhausen noise measurement is an efficient nondestructive technique for materials characterization. Usually the noise is detected by a coil while the magnetic hysteresis of the test material is cycled by an electromagnet. Due to magnetostrictive effects Barkhausen noise is highly sensitive to materials stresses and can be used for quantitative determination of residual stresses and external mechanical loads. The interaction of the magnetic structure (magnetic Bloch walls) with the microstructure of the material results in Barkhausen noise signals that are very sensitive to microstructure variations. Quantification of plastic deformation, of hardness, tensile strength, yield strength, and hardness depth are typical applications.

Other innovative techniques of creating Barkhausen noise by electric current magnetization (Eddy field technique) or using other related effects like Villary Effect, Matteucci Effect or Procopiu Effect open new areas of applications for ENDE. When an alternating electric current is used to excite a ferromagnetic wire an electric potential noise can be detected within the electric circuit. This noise can be related to the Barkhausen effect and is sensitive to remagnetization processes. The sensitivity of the effect to residual and applied stresses can be used to develop this technique as a principle for stress sensor technology.

Rotation of the Magnetic fields and autocalibration algorithm overcome the present limitation of the technique. A new auto-calibration method was developed to analyze two-dimensional stresses. A fixed calibration function based on defined parameters (determined experimentally) was applied. To adjust the auto-calibration function to the experimental reference values by varying functional parameters, a large number of measurement points were used. A method that can calculate, based on the multi-dimensional stress state at the measuring point, the stress components σxx and σyy for two perpendicular magnetization directions using the Barkhausen Noise effect has been presented.

Barkhausen noise reflects the fractal behavior of the mesoscopic materials behavior during fatigue. It has been shown that determing the fractal dimension of the Barkhausen noise opens essential new applications. The first instrument that applies this principle (FracDim) has been successfully applied for several industrial tasks like for instance evaluation of the remaining service life of large industrial plants and facilities.

Barkhausens major achievement was the development of new amplifier techniques. An established application of high end amplifier technology in NDE is eddy current testing and for instance eddy current testing at very high frequencies up to 100 MHz.

Applications for ultra-high frequency EC technology for low conducting and non-conduction Materials are under development at the Institute for packaging (IAVT) of the University of Dresden that continues Barkhausens legacy.

It has been shown, that eddy current measurement devices cannot only be used for characterizing conductivity and permeability and related properties of electrical conductive materials but also for permittivity characterization of insulating or poor conductive materials. Maxwell?s equations, FEM simulation and experimental research are used to proof this hypothesis. When applying eddy current technology on isotropic materials dielectric properties of the sample influence the measurement results.

That is not only an important finding regarding measurement accuracy in traditional eddy current measurement tasks. It is rather opening a completely new field of application for eddy current technology. Especially the High-frequency technology has the potential to serve for dielectric measurements with its easy applicability and inherent non-destructiveness. A lot of applications are conceivable: Permittivity change can be controlled over time, e.g. for cure monitoring of CFRPs, GFRPs, lacquers or other polymer materials. Local dielectric properties can be mapped with high resolution allowing for example to identify curing defects. And quantitative permittivity measurements are also feasible with a corresponding calibration, e.g. to identify the dielectric volume content within a composite material. Although the eddy current technology can be applied also on insulators like polymers, GFRP or ceramics the most probable application might be testing of poor conductive materials, like CFRP. There it is more suitable than capacitive setups, which struggle with electrode polarization and it has a higher penetration depth than the approaches relying on high-frequency wave propagation. However, independent from the sample characteristic, the HFECD might convince with contact-free measurement, the possibility of single-sided inspection, no need for special sample preparation and a very robust setup.

**Host**

WIAS Berlin

- Wednesday, 08.10.2014, 15.15 Uhr (WIAS-ESH)
- BERLINER OBERSEMINAR Nichtlineare partielle Differentialgleichungen (Langenbach-Seminar)

Prof. Dr. U. Stefanelli, University of Vienna, Austria:

Carbon geometries as optimal configurations

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Abstract**

I would like to comment on the possibility of describing the geometry of some classes of three-dimensional carbon structures by minimizing suitable configurational potentials. The general aim is that of identifying regimes in which the specific 'objective structures' which can be experimentally observed are energetically favored. In particular, I will mention the case of fullerenes and concentrate on the discussion of nanotubes. This is joint work with E. Mainini, H. Murakawa, and P. Piovano.**Further Informations**

Berliner Oberseminar ``Nichtlineare Partielle Differentialgleichungen'' (Langenbach Seminar)**Host**

WIAS Berlin

Humboldt-Universität zu Berlin

- Friday, 10.10.2014, 10.15 Uhr (WIAS-ESH)
- Seminar Nichtlineare Optimierung und Inverse Probleme

Prof. Dr. M. Delfour, Université de Montréal, Canada:

Differentials and semidifferentials for metric spaces of shapes and geometries

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Host**

WIAS Berlin

- Wednesday, 15.10.2014, 10.00 Uhr (WIAS-405-406)
- Halbleiterseminar

Prof. V. Zagrebnov, Université d'Aix-Marseille, France:

How the spectral theory explains two critical points of Bose condensation

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406**Abstract**

I discuss how the spectral theory of Laplacian in different geometries is related to a generalised boson condensation à la van den Berg-Lewis-Pulé and to prediction of existence of two critical temperatures. It is curious that this mathematical prediction is tightly related to experimental ``Quasi-Condensate'' (2000-03) of cold gases in the cigar-type traps.**Further Informations**

WIAS-Halbleiterseminar**Host**

WIAS Berlin

- Thursday, 16.10.2014, 16.00 Uhr (WIAS-ESH)
- Forschungsseminar Mathematische Modelle der Photonik

Prof. U. Leonhardt, The Weizmann Institute of Science, Israel:

Transformation optics

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Abstract**

Science Magazine listed transformation optics among the top 10 science insights of the decade 2000-2010. The lecture gives an introduction into this subject that may, literally, transform optics. Transformation optics grew out of ideas for invisibility cloaking devices and exploits connections between electromagnetism in media and in geometries. Within a short time it grew into a lively research area with applications ranging from invisibility and perfect imaging to the quantum physics of black holes. Invisibility has been a subject of fiction for millennia, from myths of the ancient Greeks and Germans to modern novels and films. In 2006 invisibility turned from fiction into science, primarily initiated by the publication of first ideas for cloaking devices and the subsequent demonstration of cloaking for microwaves. Perfect imaging is the ability to optically transfer images with a resolution not limited by the wave nature of light. Advances in imaging are of significant importance to modern electronics, because the structures of microchips are made by photolithography; in order to make smaller structures, light with increasingly smaller wavelength is used, which is increasingly difficult. Black holes are surrounded by horizons that create quantum particles from the virtual particles of the quantum vacuum, Hawking radiation. Understanding and testing this mysterious phenomenon will shed light on connections between quantum physics and general relativity.**Host**

Humboldt-Universität zu Berlin

WIAS Berlin

- Tuesday, 21.10.2014, 15.15 Uhr (WIAS-ESH)
- Oberseminar Nonlinear Dynamics

Prof. E. Tobisch, Universität Linz, Institut für Analysis, Austria:

Nonlinear resonances in bounded domains

more ...**Location**

Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Abstract**

Evolutionary dispersive nonlinear PDEs with periodic boundary conditions are frequently met among the famous equations of mathematical physics, e.g. Boussinesq eq., Hasegawa-Mima eq., Kadomtsev-Petviashvili eq., Schroedinger eq. and others. We regard a PDE of this class in two space dimensions and with small nonlinearity. This allows reducing the study of entire Fourier space of solutions to the study of resonantly interacting Fourier modes. As resonance condition in this case is equivalent to a Diophantine equation of 6 to 8 variables in high powers, according to the 10th Hilbert problem there exists no general algorithm for solving it. However, the use of a special form of the Diophantine equations appearing in physics in this context allows solving them by the method of q-class decomposition, [1]. Once the solutions of resonance conditions are found, their structure can be studied; its most interesting property turned out to be the decomposition of the Fourier space into non-intersecting subspaces with independent time evolution. Application of these results to the problem of fluid mechanics is briefly described (water waves and atmospheric planetary waves).

References:

[1]. Kartashova E. Nonlinear resonance analysis: Theory, computation, applications (Cambridge University Press, 2010)**Further Informations**

Oberseminar Nonlinear Dynamics**Host**

WIAS Berlin

Freie Universität Berlin

- Thursday, 23.10.2014, 16.00 Uhr (WIAS-ESH)
- Forschungsseminar Mathematische Modelle der Photonik

Prof. E. Tobisch, Universität Linz, Institut für Analysis, Austria:

Energy cascades in physical systems with small and moderate nonlinearity

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Abstract**

We begin with a short overview of main historical concepts of energy cascading: Richardson (1922), Kolmogorov (1941) and Zakharov (1967). First two models are developed for a strongly nonlinear system (strong turbulence of vortexes) and the latter - for a very weakly nonlinear system (weak turbulence of waves). Both models predict a power law shape of the energy spectrum. A new model will be presented which is developed to fill the gap between strong and very weak nonlinearity: The dynamic cascade. Building on the sidebands from a modulational instability, the theory predicts a cascade of energy into additional sidebands, and the detailed cascade is described by the "chain equation". The shape of energy spectrum in common case is exponential but can be reduced to a power law, for some choice of initial excitation. The theory is applied to focusing NLS (water waves) and to mKdV; it is also supported by observations in the experiments with water waves.**Host**

Humboldt-Universität zu Berlin

WIAS Berlin

- Wednesday, 05.11.2014, 15.15 Uhr (WIAS-ESH)
- BERLINER OBERSEMINAR Nichtlineare partielle Differentialgleichungen (Langenbach-Seminar)

Dr. J. Fischer, MPI MIS, Leipzig:

Global existence of renormalized solutions to entropy-dissipating reaction-diffusion systems

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Abstract**

Consider a single reversible chemical reaction with mass-action kinetics. The corresponding reaction-diffusion equation then formally satisfies an entropy inequality. Nevertheless, in general global existence of solutions for the reaction-diffusion equation has remained an open problem due to the possibly steep growth of the reaction terms. We propose a notion of renormalized solutions for such equations and succeed in proving global existence of solutions for general initial data and coefficients. Our notion of renormalized solutions reduces to the usual notion of weak solutions if the reaction terms are integrable.**Further Informations**

Berliner Oberseminar ``Nichtlineare Partielle Differentialgleichungen'' (Langenbach Seminar)**Host**

WIAS Berlin

Humboldt-Universität zu Berlin

- Wednesday, 12.11.2014, 15.15 Uhr (WIAS-ESH)
- BERLINER OBERSEMINAR Nichtlineare partielle Differentialgleichungen (Langenbach-Seminar)

Prof. Dr. A. Mielke, WIAS Berlin:

On the microscopic origin of generalized gradient structures

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Further Informations**

Berliner Oberseminar ``Nichtlineare Partielle Differentialgleichungen'' (Langenbach Seminar)**Host**

WIAS Berlin

Humboldt-Universität zu Berlin

- November 20 – 21, 2014 (WIAS-ESH)
- Workshop/Konferenz: Workshop on Recent Advances in High-Frequency Statistics

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Host**

WIAS Berlin

SFB 649: Ökonomisches Risiko

Xiamen University

DFG Research Unit 1735

- November 24 – 26, 2014 (WIAS-ESH)
- Workshop/Konferenz: Collective dynamics in coupled oscillator systems

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Host**

WIAS Berlin

SFB 910 ``Control of self-organizing nonlinear systems: Theoretical methods and concepts of application''

- Thursday, 27.11.2014, 16.00 Uhr (WIAS-ESH)
- Forschungsseminar Mathematische Modelle der Photonik

Prof. Dr. R. Martin, Leibniz-Institut für Astrophysik Potsdam (AIP):

Highly stable mode-locked diode laser system for precision comparisons in microgravity

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Abstract**

The contemporary term ?Astrophotonics? has already been in use since about a decade, but it is still a relatively new discipline to most physicists and astronomers. Adopting the definition of ?manipulation of light by materials? for photonics, quite analogous to the term ?electronics?, we understand astrophotonics as a subdiscipline of physics research and engineering, that utilizes optical effects of advanced materials for novel applications in observational astronomy and instrumentation. Historically, the field of photonics has emerged from optoelectronics with revolutionary innovations for the telecommunication sector. In a broader sense, there exist today a growing number of applications in other fields, such as industrial process technologies, sensor and illumination technologies, life science (biophotonics), etc. Astrophotonics seems to be a logical evolution in the area of astronomy, with promising applications for a future generation of instrumentation. I shall present a review of the evolution of astrophotonics with some remarks about the impact on the advance of astrophysics to date, and then focus on selected examples of current research like OH suppression fibre bragg gratings, miniaturized spectrographs ?on-the-chip?, and laser frequency combs for wavelength calibration in spectroscopy. I shall conclude with a somewhat speculative vision of future directions.**Host**

Humboldt-Universität zu Berlin

WIAS Berlin

- March 11 – 13, 2015 (WIAS-ESH)
- Workshop/Konferenz: Applied Mathematics and Simulation for Semiconductors

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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal**Host**

WIAS Berlin