@article{Morawetz2021, author = {Morawetz, Klaus}, title = {Exploring Anomalies by Many-Body Correlations}, series = {PSS B}, journal = {PSS B}, publisher = {Wiley}, doi = {10.25974/fhms-14283}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-142836}, year = {2021}, abstract = {The quantum anomaly is written alternatively into a form violating conservation laws or as non-gauge invariant currents seen explicitly on the example of chiral anomaly. By reinterpreting the many-body averaging, the connection to Pauli-Villars regularization is established which gives the anomalous term a new interpretation as arising from quantum fluctuations by many-body correlations at short distances. This is exemplified using an effective many-body quantum potential which realizes quantum Slater sums by classical calculations. It is shown that these quantum potentials avoid the quantum anomaly but approach the same anomalous result by many-body correlations. Consequently, quantum anomalies might be a shortcut way of single-particle field theory to account for many-body effects. This conjecture is also supported since the chiral anomaly can be derived by a completely conserving quantum kinetic theory. A measure for the quality of quantum potentials is suggested to describe these quantum fluctuations in the mean energy. The derived quantum potentials might be used to describe quantum simulations in classical terms.}, language = {en} } @inproceedings{WittrockWelp2006, author = {Wittrock, Ulrich and Welp, Petra}, title = {Adaptive laser resonator control with deformable MOEMS mirrors}, series = {MEMS/MOEMS Components and Their Applications III, Proc. SPIE}, volume = {6113}, booktitle = {MEMS/MOEMS Components and Their Applications III, Proc. SPIE}, publisher = {SPIE}, doi = {10.25974/fhms-653}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6537}, pages = {61130C}, year = {2006}, abstract = {Adaptive laser resonators with deformable MOEMS mirrors under closed-loop control are discussed and experimental results are presented. The requirements for deformable mirrors and for closed-loop control systems of these mirrors are analyzed. Several deformable mirrors have been characterized and the results are presented. Currently available membrane mirrors deform under laser load and need further development before they can be used for aberration correction of solid state lasers above some tens of Watts. Nevertheless, the results are encouraging and the requirements are within reach of currently available technology. Finally, we demonstrate an Nd.YVO4-laser with a closed-loop adaptive resonator and more than 6 W of output power. The closed-loop system was able to compensate artificially introduced aberrations from a phase plate.}, language = {de} } @article{HeuckNeumayerKuehletal.2006, author = {Heuck, Hans-Martin and Neumayer, Paul and K{\"u}hl, Thomas and Wittrock, Ulrich}, title = {Chromatic aberration in petawatt-class lasers}, series = {Appl. Phys. B}, volume = {84}, journal = {Appl. Phys. B}, publisher = {Springer}, doi = {10.25974/fhms-652}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-6523}, pages = {421 -- 428}, year = {2006}, abstract = {In order to avoid optical damage and non-linear effects, high-power, high-energy lasers of the petawatt class like PHELIX (petawatt high-energy laser for heavy-ion experiments) use large-aperture optics. Usually, chromatic aberration associated with these optical elements is neglected. By means of numerical simulations, we show how the chromatic aberration affects the focal intensity pattern. In particular, we make quantitative predictions of how chromatic aberration decreases the focused peak intensity. Furthermore, we prove the feasibility of a new interferometer that measures the temporal pulse front distortions which arise from expansion telescopes. We also propose a scheme that pre-compensates these distortions.}, language = {en} } @article{BuskeWittrock2006, author = {Buske, Ivo and Wittrock, Ulrich}, title = {Diffraction analysis of aberrated laser resonators}, series = {Appl. Phys. B}, volume = {83}, journal = {Appl. Phys. B}, doi = {10.25974/fhms-825}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-8252}, pages = {229 -- 233}, year = {2006}, abstract = {A numerical analysis of laser resonators with aberrations is presented. {T}he analysis shows that aberrations lead to large diffraction losses of laser resonators which are laid out to produce diffraction-limited beam quality. {S}tatic or dynamic compensation of the aberrations is possible and would yield much higher output power.}, language = {en} } @article{CarlHochmann2023, author = {Carl, Ann-Kathrin and Hochmann, David}, title = {Impact of the new European medical device regulation: a two-year comparison}, series = {Biomedical Engineering / Biomedizinische Technik}, journal = {Biomedical Engineering / Biomedizinische Technik}, issn = {1862-278X}, doi = {10.25974/fhms-17381}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-173816}, year = {2023}, abstract = {Objectives: In recent years, the European Union has revised its regulatory framework for medical devices, primarily to improve patient safety and public health. The Medical Device Regulation (MDR) is fully applicable since May 2021, strengthening the requirements for all stakeholders. As a result, many companies are facing enormous challenges. The aim of this study was to assess the impact of the MDR on the orthopaedic aids industry. Methods: Two surveys were conducted: one shortly before the MDR became applicable (146 respondents) and a second survey almost two years later (233 respondents). Results: Both surveys revealed that all businesses in the orthopaedic aids sector, regardless of size, have difficulty implementing the MDR. Key challenges include additional workload for technical documentation, increased resource expenditure and cost, and lack of clarity regarding the new requirements. Many companies are downsizing their product portfolio, resulting in potential supply shortages and a loss of competitive advantage and innovation for the medical device industry in Europe. Conclusions: The full extent of the MDR's impact on clinical practice is still unclear. However, many companies lack the necessary resources. The MDR can potentially be a bottleneck in the availability of medical devices.}, language = {en} } @inproceedings{CarlKirillovHochmannetal.2023, author = {Carl, Ann-Kathrin and Kirillov, Maxim and Hochmann, David and Quadrat, Eric}, title = {Towards credible computational models: Application of a risk-based framework for establishing credibility}, series = {Transactions on Additive Manufacturing Meets Medicine}, booktitle = {Transactions on Additive Manufacturing Meets Medicine}, issn = {2699-1977}, doi = {10.25974/fhms-17382}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-173821}, year = {2023}, abstract = {The use of computational modeling and simulation (CMS) as a tool for gaining insight into the technical performance and safety of medical devices has emerged continuously over the past years. However, to rely on information and decisions derived from model predictions, it is essential to establish model credibility for the specific context of use. Limited regulatory requirements and lack of consensus on the level of verification and validation activities required result in rare use of CMS as a source of evidence in the medical device approval process. The American Society of Mechanical Engineers (ASME) developed a risk-informed framework to establish appropriate credibility requirements of a computational model: the ASME V\&V 40?2018 standard. This paper aims to outline the concepts of this standard and to demonstrate its application using an example from the orthotics field. The necessary steps to establish model credibility for a custom?made 3D printed wrist hand orthosis (WHO) are presented. It is shown that the credibility requirements of each verification and validation activity depend on model risk by applying two different contexts of use to the same computational model.}, language = {en} } @article{Morawetz2023, author = {Morawetz, Klaus}, title = {Extended quasiparticle Pad{\´e} approximation for non-Fermi liquids}, doi = {10.25974/fhms-17712}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:836-opus-177120}, pages = {1 -- 16}, year = {2023}, abstract = {The extended quasiparticle picture is adapted to non-Fermi systems by suggesting a Pad´e approximation which interpolates between the known small scattering-rate expansion and the deviation from the Fermi energy. The first two energy-weighted sum rules are shown to be fulfilled independent of the interpolating function for any selfenergy. For various models of one-dimensional Fermions scattering with impurities the quality of the Pad´e approximation for the spectral function is demonstrated and the reduced density matrix or momentum distribution is reproduced not possessing a jump at the Fermi energy. Though the two-fold expansion is necessary to realize the spectral function and reduced density, the extended quasiparticle approximation itself is sufficient for the description of transport properties due to cancellation of divergent terms under integration. The T-matrix approximation leads to the delay time as the time two particles spend in a correlated state. This contributes to the reduced density matrix and to an additional part in the conductivity which is presented at zero and finite temperatures. Besides a localization at certain impurity concentrations, the conductivity shows a maximum at small temperatures interpreted as onset of superconducting behaviour triggered by impurities. The Tan contact reveals the same universal behaviour as known from electron-electron scattering.}, language = {en} }