@misc{KuebartStabler, author = {Kuebart, Andreas and Stabler, Martin}, title = {Waves in time, but not in space - an analysis of pandemic severity of COVID-19 in Germany}, series = {Spatial and spatio-temporal epidemiology}, volume = {47}, journal = {Spatial and spatio-temporal epidemiology}, issn = {1877-5845}, doi = {10.1016/j.sste.2023.100605}, pages = {1 -- 9}, abstract = {While pandemic waves are often studied on the national scale, they typically are not distributed evenly within countries. This study presents a novel approach to analyzing the spatial-temporal dynamics of the COVID-19 pandemic in Germany. By using a composite indicator of pandemic severity and subdividing the pandemic into fifteen phases, we were able to identify similar trajectories of pandemic severity among all German counties through hierarchical clustering. Our results show that the hotspots and cold spots of the first four waves were relatively stationary in space. This highlights the importance of examining pandemic waves on a regional scale to gain a more comprehensive understanding of their dynamics. By combining spatial autocorrelation and spatial-temporal clustering of time series, we were able to identify important patterns of regional anomalies, which can help target more effective public health interventions on a regional scale.}, language = {en} } @misc{StrobelAlvaradoChavarinVoelkeletal., author = {Strobel, Carsten and Alvarado Chavarin, Carlos and V{\"o}lkel, Sandra and Jahn, Andreas and Hiess, Andre and Knaut, Martin and Albert, Matthias and Wenger, Christian and Steinke, Olaff and Stephan, Ulf and R{\"o}hlecke, S{\"o}ren and Mikolajick, Thomas}, title = {Enhanced Electrical Properties of Optimized Vertical Graphene-Base Hot Electron Transistors}, series = {ACS Applied Electronic Materials}, volume = {5}, journal = {ACS Applied Electronic Materials}, number = {3}, issn = {2637-6113}, doi = {10.1021/acsaelm.2c01725}, pages = {1670 -- 1675}, abstract = {The arrival of high-mobility two-dimensional materials like graphene leads to the renaissance of former vertical semiconductor-metal-semiconductor (SMS) hot electron transistors. Because of the monolayer thickness of graphene, improved SMS transistors with a semimetallic graphene-base electrode are now feasible for high-frequency applications. In this study we report about a device that consists of amorphous silicon, graphene, and crystalline silicon. For the first time, this device is fabricated by a four-mask lithography process which leads to significant improvements in the device performance. A strongly increased common-emitter current gain of 2\% could be achieved while the on-off ratio improved to 1.6 × 105, which is already higher than predicted theoretically. This could be mainly attributed to better interface characteristics and decreased lateral dimensions of the devices. A cutoff frequency of approximately 26 MHz could be forecasted based on the DC measurements of the device.}, language = {en} } @misc{StablerKuebart, author = {Stabler, Martin and Kuebart, Andreas}, title = {Tempo-spatial dynamics of COVID-19 in Germany: A phase model based on a pandemic severity indicator}, series = {medRxiv}, journal = {medRxiv}, doi = {10.1101/2023.02.17.23286084}, language = {en} } @misc{KahraBreussKleefeldetal., author = {Kahra, Marvin and Breuß, Michael and Kleefeld, Andreas and Welk, Martin}, title = {An Approach to Colour Morphological Supremum Formation using the LogSumExp Approximation}, series = {arXiv}, journal = {arXiv}, doi = {10.48550/arXiv.2312.13792}, pages = {1 -- 12}, abstract = {Mathematical morphology is a part of image processing that has proven to be fruitful for numerous applications. Two main operations in mathematical morphology are dilation and erosion. These are based on the construction of a supremum or infimum with respect to an order over the tonal range in a certain section of the image. The tonal ordering can easily be realised in grey-scale morphology, and some morphological methods have been proposed for colour morphology. However, all of these have certain limitations. In this paper we present a novel approach to colour morphology extending upon previous work in the field based on the Loewner order. We propose to consider an approximation of the supremum by means of a log-sum exponentiation introduced by Maslov. We apply this to the embedding of an RGB image in a field of symmetric 2×2 matrices. In this way we obtain nearly isotropic matrices representing colours and the structural advantage of transitivity. In numerical experiments we highlight some remarkable properties of the proposed approach.}, language = {en} } @misc{KahraBreussKleefeldetal., author = {Kahra, Marvin and Breuß, Michael and Kleefeld, Andreas and Welk, Martin}, title = {An Approach to Colour Morphological Supremum Formation Using the LogSumExp Approximation}, series = {Lecture Notes in Computer Science}, volume = {14605}, journal = {Lecture Notes in Computer Science}, publisher = {Springer Nature Switzerland}, address = {Cham}, isbn = {9783031577925}, issn = {0302-9743}, doi = {10.1007/978-3-031-57793-2_25}, pages = {325 -- 337}, abstract = {Mathematical morphology is a part of image processing that has proven to be fruitful for numerous applications. Two main operations in mathematical morphology are dilation and erosion. These are based on the construction of a supremum or infimum with respect to an order over the tonal range in a certain section of the image. The tonal ordering can easily be realised in grey-scale morphology, and some morphological methods have been proposed for colour morphology. However, all of these have certain limitations. In this paper we present a novel approach to colour morphology extending upon previous work in the field based on the Loewner order. We propose to consider an approximation of the supremum by means of a log-sum exponentiation introduced by Maslov. We apply this to the embedding of an RGB image in a field of symmetric matrices. In this way we obtain nearly isotropic matrices representing colours and the structural advantage of transitivity. In numerical experiments we highlight some remarkable properties of the proposed approach.}, language = {en} } @misc{FuenningPaulManganellietal., author = {F{\"u}nning, Tabea and Paul, Martin and Manganelli, Costanza Lucia and Wenger, Christian and Mai, Andreas and Steglich, Patrick}, title = {Comparative simulation analysis of photonic ultrasound sensors based on silicon waveguides}, series = {Scientific reports}, volume = {15}, journal = {Scientific reports}, number = {1}, publisher = {Springer Science and Business Media LLC}, address = {[London]}, issn = {2045-2322}, doi = {10.1038/s41598-025-01953-9}, pages = {1 -- 13}, abstract = {Pressure sensors based on photonic integrated circuits (PIC) offer the prospect of outstanding sensitivities, extreme miniaturization and have the potential for highly scalable production using CMOS compatible processing. PIC-based pressure sensors detect the change in optical properties, i.e. the intensity or phase of the optical carrier wave inside miniaturized waveguide structures. The detection of ultrasound is achieved by engineering the waveguide architecture such that a pressure causes a high change in the effective refractive index of the waveguide. A range of PIC-based pressure sensors have been reported, but a comparison of the sensitivity of the different approaches is not straightforward, since different pressure sensitive waveguide architectures as well as photonic layouts and measurement setups impact the performance. Additionally, the used sensitivity unit is not uniform throughout the different studies, further complicating a comparison. In this work, a detailed simulation study is carried out by finite element modeling of different pressure sensitive waveguide architectures for a consistent comparison. We analyze three different sensor architectures: (A) a free standing membrane located within a tiny air gap above the waveguide, (B) a waveguide located on top of a deflectable membrane as well as (C) a waveguide embedded inside a pressure-sensitive polymer cladding. The mechanical response of the structures and the resulting changes in mode propagation, i.e. the change of the effective refractive index, are analyzed. The waveguide sensitivities in RIU/MPa for different waveguide types (strip, slot) and polarization states (TE, TM) are compared. The results reveal inherent limitations of the different waveguide designs and create a basis for the selection of suitable designs for further ultrasound sensor development. Possibilities for enhancing waveguide sensitivity are identified and discussed. Additionally, we have shown that the studied approaches are extensible to SiN waveguides.}, language = {en} } @misc{KahraBreussKleefeldetal., author = {Kahra, Marvin and Breuß, Michael and Kleefeld, Andreas and Welk, Martin}, title = {Matrix-valued LogSumExp approximation for colour morphology}, series = {Journal of mathematical imaging and vision}, volume = {67}, journal = {Journal of mathematical imaging and vision}, number = {5}, publisher = {Springer US}, address = {New York}, issn = {0924-9907}, doi = {10.1007/s10851-025-01267-5}, abstract = {Mathematical morphology is a part of image processing that employs a moving window to modify pixel values through the application of specific operations. The supremum and infimum are pivotal concepts, yet defining them in a general sense for high-dimensional data such as colour is a challenging endeavour. As a result, a number of different approaches have been taken to try to find a solution, with certain compromises being made along the way. In this paper, we present an analysis of a novel approach that replaces the supremum within a morphological operation with the LogExp approximation of the maximum for matrix-valued colours. This approach has the advantage of extending the associativity of dilation from the one-dimensional to the higher-dimensional case. Furthermore, the minimality property is investigated and a relaxation specified to ensure that the approach is continuously dependent on the input data.}, language = {en} } @misc{VillasmuntaHeiseBreiteretal., author = {Villasmunta, Francesco and Heise, Patrick and Breiter, Manuela and Schrader, Sigurd and Schenk, Harald and Regehly, Martin and Mai, Andreas}, title = {Monolithically integrated optical through-silicon waveguides for 3D chip-to-chip photonic interconnects}, series = {IEEE journal of selected topics in quantum electronics}, volume = {32}, journal = {IEEE journal of selected topics in quantum electronics}, number = {2: 3-D Horizons in Photonics}, publisher = {Institute of Electrical and Electronics Engineers (IEEE)}, address = {New York, NY}, issn = {1077-260X}, doi = {10.1109/JSTQE.2025.3615001}, pages = {1 -- 15}, abstract = {The scaling limitations of electrical interconnects are driving the demand for efficient optical chip-to-chip links. We report the first monolithic integration of air-clad optical through-silicon waveguides in silicon, fabricated via Bosch and cryogenic deep reactive-ion etching. Rib, single-bridge, and double-bridge designs with 50 μm cores and up to 150 μm propagation lengths have been evaluated. Cryogenic-etched rib waveguides achieve the highest median transmission (66\%, -1.80 dB), compared to Bosch-etched ribs (62\%, -2.08 dB). Across all geometries, 3 dB alignment windows range from 9.3 μm to 49.2 μm, with Bosch-etched double-bridge waveguides providing the broadest tolerance. We show that geometric fidelity outweighs sidewall roughness for transmission and alignment in these large-core, multimode optical through-silicon waveguides. This technology provides a scalable, complementary metal-oxide semiconductor-compatible pathway toward 3D photonic interconnects.}, language = {en} } @misc{RachevaBasaloLouridoGurdaletal., author = {Racheva, Miroslava and Basalo Lourido, Javier and Gurdal, Enise Ece and Herbst, Martin and Bayar, Seyhmus and Radzik, Daniela and B{\"a}hr, Elen and Zwies, Constanze and Neffe, Axel T. and Pietzsch, Markus and Lendlein, Andreas and Wischke, Christian}, title = {Tyrosinase cross-linked PEG hydrogels with DAT and DATT as artificial substrates : design, structure, and functions}, series = {Biomacromolecules}, volume = {27}, journal = {Biomacromolecules}, number = {2}, publisher = {American Chemical Society (ACS)}, address = {Washington, DC}, issn = {1525-7797}, doi = {10.1021/acs.biomac.5c01929}, pages = {1317 -- 1336}, abstract = {Enzymes such as oxidases are sustainable tools for hydrogel synthesis, but complex competing reactions have limited the mechanistic understanding and biomedical applications of these materials. Guided by molecular docking and MM-GBSA calculations, we identified two artificial substrates, desaminotyrosine (DAT) and desaminotyrosyltyrosine (DATT), that were experimentally more efficiently converted by mushroom tyrosinase (mTyr) than the natural substrate tyrosine. These substrates were used to synthesize hydrogels from DAT/DATT-functionalized star-shaped oligoethylene glycol (sOEG). Model reactions elucidated the chemical nature and functionality of the hydrogel netpoints. Material properties were systematically investigated depending on sOEG molecular weight (5, 10, 20 kDa), substrate type, and mTyr concentration. Functional mesh sizes and controlled release functions were investigated with fluorescent dextrans (4-500 kDa) and heparin. Cell culture studies with L929 fibroblasts and THP-1 monocytes suggested inertness of the material. These findings provide fundamental insight into mTyr-catalyzed hydrogel formation and support further exploration for in situ hydrogel synthesis.}, language = {en} }