On Tuesday, 28 August 2018 Julia Neuwirth presented the essence of here masterthesis on Adaptive Optics in two-photon microscopy and two-photon lithography:
Two-photon microscopy has become an indispensable tool in biological re- search allowing imaging of intracellular structures especially deep in tissue. Due to its capability of three-dimensional (3D) fabrication in lithography, two-photon excitation is also an essential tool for nanofabrication. However, both two-photon microscopy and two-photon lithography suffer from aberrations that are introduced by spatial variations in the refractive index of the specimen, leading to compromised image and structure quality. Specimen-induced aberrations can be compensated by adaptive optics. In this thesis, I propose a new correction scheme for two-photon microscopy and two-photon lithography adaptive optics, namely poke mode aberration correction. This new scheme simplifies the communication between the wavefront sensor and the deformable mirror, therefore eliminating the need for multiple conversions and in turn the potential to minimize the amount of error introduced during analysis. Using this new control system, we demonstrate that test aberrations can be reliably compensated using the developed feedback loop. In addition, aberrations induced by biological tissue, e.g. a 50 μm and 85 μm thick section of fixed mouse brain tissue, can be corrected leading to enhanced resolution and image quality. Furthermore, preliminary two-photon lithography fabricated structures illustrate the potential of smoother structure surfaces when aberration correction is conducted with the new control system.
Günter Auzinger is the Science Slam Winner 2018! It all began on March 20 when he did his first show at Posthof Linz and where he won against five other scientists from Upper Austria. With his winning sense of humor he managed to convince the audience to vote for him. The slamming show 2018 got to be continued on April 13 in Vienna, during a yearly public event called “Lange Nacht der Forschung”. The audience was much bigger than in Linz and competition was harder as Günter had to slam against all the other Austrian provinces winners.
Prouder than ever we had to keep our fingers crossed for nothing but the absolute European finals in Toulouse, France on July 7. He had 10 minutes for his show there instead of 6 minutes before at the Austrian finals, and also 6 minutes at the very first time in Linz. Therefore Günter had to adapt his show and he had to find jokes that work on an international basis. Somehow he managed it in a very successful way and the audience in Toulouse again voted for him. Well, pushing our thumbs and crossing our fingers seems to have paid off.
MathConsult had been the host institution of Laura Kaltenbrunner and Sophia Simmill. They worked on modelling interest rates (especially when they become negative) from a mathematical and an economic point of view. Their joint report “Mathematical and statistical analysis of negative interest rates” was among the best ones.
Young Talents is a programme organized by the Austrian research promotion agency (“Forschungsförderungsgesellschaft” FFG) and funded by the Austrian ministry for traffic, innovation and technology. Talents internships for pupils aim to encourage girls and boys to follow natural sciences, and engineering and technology. Pupils have the opportunity to have an internship in various companies and scientific research institutions for four weeks during the summer time. In 2015, more than 1400 internships were funded with 1000 YEUR each. Interns were invited to write reports on their achievements, and the best 20 reports were awarded on March 10, 2016.
Photos from the award ceremony can be found here.
Heinz W. Engl, founder of MathConsult, gives the opening lecture at the International Conference on Inverse Problems and Optimal Control in Hong Kong. He speaks on „Industrial Mathematics and Nonlinaer Inverse Problems“ and covers applications from steel industry, mathematical finance, medicine and biology.
For the conference web page, see https://www.math.cuhk.edu.hk/conference/ipoc2014/
On Nov. 20, we have released the UnRisk PRICING ENGINE 8.0.
The key features of UnRisk 8.0 include the valuation of moderately structured fixed income instruments under a multi curve model, and the Bachelier model.
The multicruve model allows to use (in the same currency) different interest rate curves for discounting, e.g., the EONIA curve, and for determining variable cashflows, e.g. Libor3m or Libor 6m.
The Bachelier model for caps, floors, swaptions can replace the Black76 model, when interest rates are low. In Black vs Bachelier revisited, I pointed out the difficulties with Black 76, when interest rates approach zero. In such cases, (Black) volatilties explode, and orders of magnitude of several 1000 percent for Black volatilities are quite common. With the Bachelier model and its data, which may be used as calibration input, negative interest rates may occur without nasty instabilities.
For more information: www.unrisk.com
At the CMMP Autumn School: Basics of Electronic Structure Calculations (Tampere University of Technology, November 12-14, 2014), Michael Aichinger speaks on „Numerical challenges in electronic structure calculations and beyond“. This is a joint work between Michael Aichinger, Eduardo Hernandez (ICMM-CSIC Madrid) Stefan Janecek, and Esa Räsänen (Tampere).
Version 5. 2. of the UnRisk FACTORY comes with further interaction
possibilities between the Excel frontend of the UnRisk ENGINE and the
FACTORY’s web services. For more information, see www.unrisk.com
Michael Liebrecht has successfully (and with honors) defended his Ph.D. thesis “Van der Waals potentials between metal clusters and helium atoms obtained with density functional theory and linear response methods”.
The importance of van der Waals interactions in many diverse research fields such as, e. g., polymer science, nano–materials, structural biology, surface science and condensed matter physics created a high demand for efficient and accurate methods that can describe van der Waals interactions from first principles. These methods should be able to deal with large and complex systems to predict functions and properties of materials that are technologically and biologically relevant.
Van der Waals interactions arise due to quantum mechanical correlation effects and finding appropriate models an numerical techniques to describe this type of interaction is still an ongoing challenge in electronic structure and condensed matter theory.
This thesis introduces a new variational approach to obtain intermolecular interaction potentials between clusters and helium atoms by means of density functional theory and linear response methods.
It scales almost linearly with the number of electrons and can therefore be applied to much larger systems than standard quantum chemistry techniques.
The main focus of this work is the development of an ab–inito method to account for London dispersion forces, which are purely attractive and dominate the interaction of non–polar atoms and molecules at large distances.
The first step in that method is to determine the ground states of the two interaction partners with mean-field approaches like density functional theory or Hartree-Fock. Then an iterative scheme that uses linear response functions is employed to calculate the dispersion energy of the two molecules. To obtain meaningful results in reasonable time, it has been necessary to implement the response algorithms so that they do not require any explicit knowledge of unoccupied states. The same response methods are used to construct a very efficient density update scheme that is able to significantly reduce the number of self-consistency iterations of density functional calculations.
It can be shown that our derived equations for the dispersion energy provide the same results as the adiabatic connection dissipation-fluctuation theorem, which can be applied to include correlation effects into density functional calculations. To test our method, the leading van der Waals interaction coefficients for several atom pairs were computed and compared to values from the literature. We found good agreement but also realized that pseudopotentials crucially influence our results.
The construction of intermolecular interaction potentials between clusters and helium atoms requires also the inclusion of the short-ranged Pauli-repulsion. To account for this effect, a semi-empirical helium pseudopotential with a tunable interaction strength is introduced. This pseudopotential is simply added to the effective Hamiltonian of the cluster. To determine the interaction strength of the helium pseudopotential, our results for the Mg-He interaction are fitted to reference potentials found in the literature. It turned out that additional reference potentials for the Na-He and Rb2-He interactions can be approximated remarkably well with the pseudopotential obtained for the Mg-He interaction. Finally, our new approach is applied to construct intermolecular potentials between larger clusters and helium atoms to demonstrate its effectiveness.
The challenges – both from the algorithmic and the data management point of view – in calculating CVA (“credit valuation adjustment”) and its modifications made us apply for a research grant with the Austrian Research Promotion Agency („Forschungsförderungsgesellschaft“ FFG) within their General Funding Programme. In their October meeting, this project was on the agenda. Our application was successful and will be cofunded by FFG.
Daniela Saxenhuber from the Industrial Mathematics Institute (JKU Linz) gets a Best Poster Award for her poster “A fast reconstruction method for complex adaptive optics systems“ presented at IPTA 2014, Bristol.
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