Publikationen an der Fakultät für Mathematik und Naturwissenschaften ab 2019

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Nozdrenko, Dmytro; Prylutska, Svitlana; Bogutska, Kateryna; Cherepanov, Vsevolod; Senenko, Anton; Vygovska, Oksana; Khrapatyi, Sergii; Ritter, Uwe; Prylutskyy, Yuriy; Piosik, Jacek;
Analysis of biomechanical and biochemical markers of rat muscle soleus fatigue processes development during long-term use of C60 fullerene and N-acetylcysteine. - In: Nanomaterials, ISSN 2079-4991, Bd. 12 (2022), 9, 1552, S. 1-15

The development of an effective therapy aimed at restoring muscle dysfunctions in clinical and sports medicine, as well as optimizing working activity in general remains an urgent task today. Modern nanobiotechnologies are able to solve many clinical and social health problems, in particular, they offer new therapeutic approaches using biocompatible and bioavailable nanostructures with specific bioactivity. Therefore, the nanosized carbon molecule, C60 fullerene, as a powerful antioxidant, is very attractive. In this study, a comparative analysis of the dynamic of muscle soleus fatigue processes in rats was conducted using 50 Hz stimulation for 5 s with three consistent pools after intraperitoneal administration of the following antioxidants: C60 fullerene (a daily dose of 1 mg/kg one hour prior to the start of the experiment) and N-acetylcysteine (NAC; a daily dose of 150 mg/kg one hour prior to the start of the experiment) during five days. Changes in the integrated power of muscle contraction, levels of the maximum and minimum contraction force generation, time of reduction of the contraction force by 50% of its maximum value, achievement of the maximum force response, and delay of the beginning of a single contraction force response were analyzed as biomechanical markers of fatigue processes. Levels of creatinine, creatine phosphokinase, lactate, and lactate dehydrogenase, as well as pro- and antioxidant balance (thiobarbituric acid reactive substances, hydrogen peroxide, reduced glutathione, and catalase activity) in the blood of rats were analyzed as biochemical markers of fatigue processes. The obtained data indicate that applied therapeutic drugs have the most significant effects on the 2nd and especially the 3rd stimulation pools. Thus, the application of C60 fullerene has a (50-80)% stronger effect on the resumption of muscle biomechanics after the beginning of fatigue than NAC on the first day of the experiment. There is a clear trend toward a positive change in all studied biochemical parameters by about (12-15)% after therapeutic administration of NAC and by (20-25)% after using C60 fullerene throughout the experiment. These findings demonstrate the promise of using C60 fullerenes as potential therapeutic nanoagents that can reduce or adjust the pathological conditions of the muscular system that occur during fatigue processes in skeletal muscles.
Dorner-Reisel, Annett; Ritter, Uwe; Moje, Jens; Freiberger, Emma; Scharff, Peter;
Effect of fullerene C60 thermal and tribomechanical loading on Raman signals. - In: Diamond and related materials, ISSN 0925-9635, Bd. 126 (2022), 109036, S. 1-14

Fullerene C60 powder was loaded by 1 N normal force and exposed to sliding under different frequencies for 15 min. It is shown that the velocity of the sliding movement determines the stability of the fullerene C60 powder. At slow velocity of movement with a frequency of 1 Hz under 1 N normal force, the fullerene C60 structure remains undamaged after 15 min sliding. On the contrary, high sliding velocities of 10 Hz and 50 Hz affected fragmentation of the fullerene C60, which resulted in a reduction of the coefficient of friction (COF). During sliding with 1 Hz, the friction reached the highest level with an average COF of 0.59 ± 0.03. The faster relative motion under 1 N normal force gave a lower average COF with 0.39 ± 0.03. The initial fullerene C60 powder formed a thick compressed layer in the tribomechanical loaded zone. As proven by Raman spectroscopy, operating the tribomechanical sliding test at 50 Hz stimulated the re-attraction of fresh C60 fullerene island onto the fragmented layer from outside of the loaded powder regions. The COF was increasing again up to 0.44 ± 0.04 for 1 N normal force and 50 Hz frequency. The fragmentation and decomposition of fullerene C60 with increasing sliding velocity is attributed to thermal heating up during fast relative movement. Raman spectra of the tribomechanical loaded fullerene C60 are compared with Raman spectra from slowly heated up C60 in air and with Raman spectra of laser irradiated fullerene C60.
Öztürk, Emrah; Rheinberger, Klaus; Faulwasser, Timm; Worthmann, Karl; Preißinger, Markus;
Aggregation of demand-side flexibilities: a comparative study of approximation algorithms. - In: Energies, ISSN 1996-1073, Bd. 15 (2022), 7, 2501, S. 1-14

Traditional power grids are mainly based on centralized power generation and subsequent distribution. The increasing penetration of distributed renewable energy sources and the growing number of electrical loads is creating difficulties in balancing supply and demand and threatens the secure and efficient operation of power grids. At the same time, households hold an increasing amount of flexibility, which can be exploited by demand-side management to decrease customer cost and support grid operation. Compared to the collection of individual flexibilities, aggregation reduces optimization complexity, protects households' privacy, and lowers the communication effort. In mathematical terms, each flexibility is modeled by a set of power profiles, and the aggregated flexibility is modeled by the Minkowski sum of individual flexibilities. As the exact Minkowski sum calculation is generally computationally prohibitive, various approximations can be found in the literature. The main contribution of this paper is a comparative evaluation of several approximation algorithms in terms of novel quality criteria, computational complexity, and communication effort using realistic data. Furthermore, we investigate the dependence of selected comparison criteria on the time horizon length and on the number of households. Our results indicate that none of the algorithms perform satisfactorily in all categories. Hence, we provide guidelines on the application-dependent algorithm choice. Moreover, we demonstrate a major drawback of some inner approximations, namely that they may lead to situations in which not using the flexibility is impossible, which may be suboptimal in certain situations.
Hörsch, Florian;
Checking the admissibility of odd-vertex pairings is hard. - In: Discrete applied mathematics, Bd. 317 (2022), S. 42-48

Nash-Williams proved that every graph has a well-balanced orientation. A key ingredient in his proof is admissible odd-vertex pairings. We show that for two slightly different definitions of admissible odd-vertex pairings, deciding whether a given odd-vertex pairing is admissible is co-NP-complete. This resolves a question of Frank. We also show that deciding whether a given graph has an orientation that satisfies arbitrary local arc-connectivity requirements is NP-complete.
Rothe, Karl; Néel, Nicolas; Bocquet, Marie-Laure; Kröger, Jörg;
Quantifying force and energy in single-molecule metalation. - In: Journal of the American Chemical Society, ISSN 1520-5126, Bd. 144 (2022), 16, S. 7054-7057

An atomic force microscope is used to determine the attractive interaction at the verge of adding a Ag atom from the probe to a single free-base phthalocyanine molecule adsorbed on Ag(111). The experimentally extracted energy for the spontaneous atom transfer can be compared to the energy profile determined by density functional theory using the nudged-elastic-band method at a defined probe-sample distance.
De Santis, Marianna; Eichfelder, Gabriele; Patria, Daniele;
On the exactness of the ε-constraint method for biobjective nonlinear integer programming. - In: Operations research letters, ISSN 0167-6377, Bd. 50 (2022), 3, S. 356-361

The ε-constraint method is a well-known scalarization technique used for multiobjective optimization. We explore how to properly define the step size parameter of the method in order to guarantee its exactness when dealing with biobjective nonlinear integer problems. Under specific assumptions, we prove that the number of subproblems that the method needs to address to detect the complete Pareto front is finite. We report numerical results on portfolio optimization instances built on real-world data and show a comparison with an existing criterion space algorithm.
Link, Steffen; Dimitrova, Anna; Krischok, Stefan; Ivanov, Svetlozar;
Reversible sodiation of electrochemically deposited binder- and conducting additive-free Si-O-C composite layers. - In: Energy technology, ISSN 2194-4296, Bd. 10 (2022), 5, 2101164, S. 1-9

Binder- and conducting additive-free Si-O-C composite layers are deposited electrochemically under potentiostatic conditions from sulfolane-based organic electrolyte. Quartz crystal microbalance with damping monitoring is used for evaluation of the layer growth and its physical properties. The sodiation-desodiation performance of the material is afterward explored in Na-ion electrolyte. In terms of specific capacity, rate capability, and long-term electrochemical stability, the experiments confirm the advantages of applying the electrochemically formed Si-O-C structure as anode for Na-ion batteries. The material displays high (722 mAh g^-1) initial reversible capacity at j = 70 mA g^-1 and preserves stable long-term capacity of 540 mAh g^-1 for at least 400 galvanostatic cycles, measured at j = 150 mA g^-1. The observed high performance can be attributed to its improved mechanical stability and accelerated Na-ion transport in the porous anode structure. The origin of the material electroactivity is revealed based on X-Ray photoelectron spectroscopic analysis of pristine (as deposited), sodiated, and desodiated Si-O-C layers. The evaluation of the spectroscopic data indicates reversible activity of the material due to the complex contribution of carbon and silicon redox centers.
Grundel, Sara; Heyder, Stefan; Hotz, Thomas; Ritschel, Tobias K. S.; Sauerteig, Philipp; Worthmann, Karl;
How much testing and social distancing is required to control COVID-19? : some insight based on an age-differentiated compartmental model. - In: SIAM journal on control and optimization, ISSN 1095-7138, Bd. 60 (2022), 2, S. S145-S169

In this paper, we provide insights on how much testing and social distancing is required to control COVID-19. To this end, we develop a compartmental model that accounts for key aspects of the disease: incubation time, age-dependent symptom severity, and testing and hospitalization delays; the model's parameters are chosen based on medical evidence, and, for concreteness, adapted to the German situation. Then, optimal mass-testing and age-dependent social distancing policies are determined by solving optimal control problems both in open loop and within a model predictive control framework. We aim to minimize testing and/or social distancing until herd immunity sets in under a constraint on the number of available intensive care units. We find that an early and short lockdown is inevitable but can be slowly relaxed over the following months.
Yang, Guowei; Wu, Yuhan; Fu, Qun; Zhao, Huaping; Lei, Yong;
Nanostructured metal selenides as anodes for potassium-ion batteries. - In: Sustainable energy & fuels, ISSN 2398-4902, Bd. 6 (2022), 9, S. 2087-2112

In next-generation rechargeable batteries, potassium-ion batteries (KIBs) have been deemed to be one of the most promising candidates as a complement for lithium-ion batteries. Anodes as a component of ion batteries have a great effect on the safety and electrochemical performance. Among various developed anode materials, metal selenides (MSs) have been a popular option by merits of their superior material properties and high specific capacities. However, they are restricted by some intrinsic problems, such as large volume expansion and severe side reactions during electrochemical reactions, which limit their application to a certain degree. The strategy of structural design can endow MSs with superior material and electrochemical properties, making MSs exhibit better electrochemical performance. In this review, we summarize the recent advances in nanostructured MCs as KIB anodes. Meanwhile, their electrochemical reaction mechanisms and material synthesis methods are introduced briefly. Finally, the present challenges and future research directions are discussed.
Zhang, Ying; Tao, Jie; Zhang, Chenglin; Zhao, Huaping; Lei, Yong;
KOH activated nitrogen and oxygen co-doped tubular carbon clusters as anode material for boosted potassium-ion storage capability. - In: Nanotechnology, ISSN 1361-6528, Bd. 33 (2022), 29, 295403, S. 1-9

Carbon nanomaterials have become a promising anode material for potassium-ion batteries (KIBs) due to their abundant resources, low cost, and excellent conductivity. However, among carbon materials, the sluggish reaction kinetics and inferior cycle life severely restrict their commercial development as KIBs anodes. It is still a huge challenge to develop carbon materials with various structural advantages and ideal electrochemical properties. Therefore, it is imperative to find a carbon material with heteroatom doping and suitable nanostructure to achieve excellent electrochemical performance. Benefiting from a Na2SO4 template-assisted method and KOH activation process, the KOH activated nitrogen and oxygen co-doped tubular carbon (KNOCTC) material with a porous structure exhibits an impressive reversible capacity of 343 mAh g^-1 at 50 mA g^-1 and an improved cyclability of 137 mAh g^-1 at 2 A g^-1 after 3000 cycles with almost no capacity decay. The kinetic analysis indicates that the storage mechanism in KNOCTC is attributed to the pseudocapacitive process during cycling. Furthermore, the new synthesis route of KNOCTC provides a new opportunity to explore carbon-based potassium storage anode materials with high capacity and cycling performance.