Publications at the Department of Mathematics and Natural Sciences from 2019

Results: 873
Created on: Wed, 27 Mar 2024 23:21:20 +0100 in 0.0696 sec


Zhang, Keyu; Cui, Dingfang; Huang, Xiaopeng; Liang, Feng; Gao, Geng; Song, Tingyu; Zhang, Libo; Yao, Yaochun; Lei, Yong
Insights into the interfacial chemistry and conversion mechanism of iron oxalate toward the reduction by lithium. - In: The chemical engineering journal, ISSN 1873-3212, Bd. 426 (2021), 131446

The origin of excellent lithium storage ability and high irreversible capacity is probably the least understood component for transition-metal oxalates as anode materials in lithium-ion batteries. Considerable efforts have been put into understanding their electrochemical reaction mechanisms, but these insights have mostly been unilateral and unsystematic. Herein, the interface characteristic between iron oxalate anode and electrolyte and detailed conversion process were investigated to explore the source of irreversible Li+ storage. In particular, a gelatinous "organic" layer identified oxygen, fluorine and phosphorus as the main chemical elements can be re-oxidized and exhibits an obviously reversible conversion between sedimentation and decomposition during its initial lithiation process, despite the general belief that it shows similar electrochemically inert to solid-electrolyte interphase (SEI). Meanwhile, this special interface layer leads to higher ability of Li+ ions diffusion and smaller charge-transfer resistance, which is the vital role for excellent rate capability. Furthermore, ex situ FTIR analysis confirms the formation and residue of new intermediate compound of Li2Fe(C2O4)2, thus making a part of initial irreversible capacity. It is also found that the iron oxalate electrode with larger capacitive contribution still has more widely application in energy storage of supercapacitors in future.



https://doi.org/10.1016/j.cej.2021.131446
Zeußel, Lisa; Mai, Patrick; Sharma, Sanjay; Schober, Andreas; Ren, Shizhan; Singh, Sukhdeep
Colorimetric method for instant detection of lysine and arginine using novel Meldrum's acid-furfural conjugate. - In: ChemistrySelect, ISSN 2365-6549, Bd. 6 (2021), 27, S. 6834-6840

In the past few years Meldrum's acid furfural conjugate (MAFC) have been extensively explored as starting material for the synthesis of photo switchable donor acceptor stenhouse adducts (DASA). Hereby, we have explored the interaction of MAFC with various amino acids. To our surprise, nitrogen rich amino acids like lysine and arginine interact spontaneously with MAFC to give colored adduct immediately, whereas other amino acids, including nitrogen rich histidine, didn't show any coloration. Naked eye detection of lysine in benign solvent make this reagent an attractive new entry to the collection of chemosensors for the colorimetric detection of lysine and arginine. Intense coloration corresponds to the absorption at 514 nm under UV-Vis spectrometer. Lowest concentration of 100 m can be detected with UV-Vis spectrometer. NMR titrations reveals that the appearance of color is due to ring opening of a furfural that leads to the formation of conjugated triene species. Compared to previously reported chemosensors for lysine and arginine, MAFC offers advantages including simple synthesis, easy handling, high speed, low cost, good sensitivity/selectivity.



https://doi.org/10.1002/slct.202101140
Wu, Xiaocui; Wiame, Frédéric; Maurice, Vincent; Marcus, Philippe
Molecular scale insights into interaction mechanisms between organic inhibitor film and copper. - In: npj Materials degradation, ISSN 2397-2106, Bd. 5 (2021), 22, insges. 8 S.

A model experimental approach, providing molecular scale insight into the build up mechanisms of a corrosion inhibiting interface, is reported. 2-mercaptobenzimidazole (2-MBI), a widely used organic inhibitor, was deposited from the vapor phase at ultra-low pressure on copper surfaces in chemically-controlled state, and X-ray photoelectron spectroscopy was used in situ to characterize the adsorption mechanisms upon formation of the inhibiting film. On copper surfaces prepared clean in the metallic state, the intact molecules lie flat at low exposure, with sulfur and both nitrogen atoms bonded to copper. A fraction of the molecules decomposes upon adsorption, leaving atomic sulfur on copper. At higher exposure, the molecules adsorb in a tilted position with sulfur and only one nitrogen bonded to copper, leading to a densification of 2-MBI in the monolayer. A bilayer is formed at saturation with the outer layer not bonded directly to copper. In the presence of a pre-adsorbed 2D oxide, oxygen is substituted and the molecules adsorb intactly without decomposition. A 3D oxide prevents the bonding of sulfur to copper. The molecular film formed on metallic and 2D oxide pre-covered surfaces partially desorbs and decomposes at temperature above 400 ˚C, leading to the adsorption of atomic sulfur on copper.



https://doi.org/10.1038/s41529-021-00168-3
Jiang, Yuning; Sauerteig, Philipp; Houska, Boris; Worthmann, Karl
Distributed optimization using ALADIN for MPC in smart grids. - In: IEEE transactions on control systems technology, ISSN 1558-0865, Bd. 29 (2021), 5, S. 2142-2152

This article presents a distributed optimization algorithm tailored to solve optimization problems arising in smart grids. In detail, we propose a variant of the augmented Lagrangian-based alternating direction inexact Newton (ALADIN) method, which comes along with global convergence guarantees for the considered class of linear-quadratic optimization problems. We establish local quadratic convergence of the proposed scheme and elaborate its advantages compared with the alternating direction method of multipliers (ADMM). In particular, we show that, at the cost of more communication, ALADIN requires fewer iterations to achieve the desired accuracy. Furthermore, it is numerically demonstrated that the number of iterations is independent of the number of subsystems. The effectiveness of the proposed scheme is illustrated by running both an ALADIN and an ADMM-based model predictive controller on a benchmark case study.



https://doi.org/10.1109/TCST.2020.3033010
Bouza, Gemayqzel; Quintana, Ernest; Tammer, Christiane
A steepest descent method for set optimization problems with set-valued mappings of finite cardinality. - In: Journal of optimization theory and applications, ISSN 1573-2878, Bd. 190 (2021), 3, S. 711-743

In this paper, we study a first-order solution method for a particular class of set optimization problems where the solution concept is given by the set approach. We consider the case in which the set-valued objective mapping is identified by a finite number of continuously differentiable selections. The corresponding set optimization problem is then equivalent to find optimistic solutions to vector optimization problems under uncertainty with a finite uncertainty set. We develop optimality conditions for these types of problems and introduce two concepts of critical points. Furthermore, we propose a descent method and provide a convergence result to points satisfying the optimality conditions previously derived. Some numerical examples illustrating the performance of the method are also discussed. This paper is a modified and polished version of Chapter 5 in the dissertation by Quintana (On set optimization with set relations: a scalarization approach to optimality conditions and algorithms, Martin-Luther-Universität Halle-Wittenberg, 2020).



https://doi.org/10.1007/s10957-021-01887-y
Zhang, Huanming; Zhou, Min; Guo, Yaqiong; Yu, Zhenjiang; Xu, Rui; Wen, Liaoyong; Wang, Yi; Zhao, Huaping; Lei, Yong
Gas-flow-assisted wrinkle-free transfer of a centimeter-scale ultrathin alumina membrane onto arbitrary substrates. - In: ACS applied materials & interfaces, ISSN 1944-8252, Bd. 13 (2021), 29, S. 35124-35132

The transfer of an ultrathin membrane onto arbitrary substrates is important in different practical fields. Conventional wet-transfer methods inevitably induce wrinkle defects as a result of the large contact angle of the trapped droplet between the membrane and the substrate. Here, we demonstrate a gas flow-assisted method (GFAM) to transfer centimeter (cm)-scale ultrathin membranes onto arbitrary substrates (including a curved substrate) without wrinkles. GFAM makes use of contact angle hysteresis to bulge the trapped droplet between the substrate and the ultrathin membrane and simultaneously stretch the ultrathin membrane during rapid dewetting driven by gas flow. Moreover, GFAM can be easily fulfilled by using compressed air for seconds. Compared with conventional hydrophilic treatments or organic liquid wetting, this method has no durability concern and does not change the surface nature of substrates. Taking a widely used ultrathin anodic aluminum oxide (AAO) membrane as an example, we successfully demonstrate the application of a large-area wrinkle-free ultrathin AAO membrane to defect-free ordered nanostructure array fabrication and investigate the micro-scale details of macro-scale wrinkles generated by the conventional ways. In addition, its corresponding superiority over the defective counterpart is further studied in optical sensing. This method is highly valuable for promoting the simplicity of large-area ultrathin membrane transfer in practice.



https://doi.org/10.1021/acsami.1c07574
Halle, Johannes; Néel, Nicolas; Kröger, Jörg
Monolayer and bilayer graphene on Ru(0001): layer-specific and moiré-site-dependent phonon excitations. - In: The journal of physical chemistry letters, ISSN 1948-7185, Bd. 12 (2021), 29, S. 6889-6894

Graphene phonons are excited by the local injection of electrons and holes from the tip of a scanning tunneling microscope. Despite the strong graphene-Ru(0001) hybridization, monolayer graphene unexpectedly exhibits pronounced phonon signatures in inelastic electron tunneling spectroscopy. Spatially resolved spectroscopy reveals that the strength of the phonon signal depends on the site of the moiré lattice with a substantial red-shift of phonon energies compared to those of free graphene. Bilayer graphene gives rise to more pronounced spectral signatures of vibrational quanta with energies nearly matching the free graphene phonon energies. Spectroscopy data of bilayer graphene indicate moreover the presence of a Dirac cone plasmon excitation.



https://doi.org/10.1021/acs.jpclett.1c01802
Grundel, Sara; Heyder, Stefan; Hotz, Thomas; Ritschel, Tobias K. S.; Sauerteig, Philipp; Worthmann, Karl
How to coordinate vaccination and social distancing to mitigate SARS-CoV-2 outbreaks. - In: SIAM journal on applied dynamical systems, ISSN 1536-0040, Bd. 20 (2021), 2, S. 1135-1157

Most countries have started vaccinating people against COVID-19. However, due to limited production capacities and logistical challenges it will take months/years until herd immunity is achieved. Therefore, vaccination and social distancing have to be coordinated. In this paper, we provide some insight on this topic using optimization-based control on an age-differentiated compartmental model. For real-life decision-making, we investigate the impact of the planning horizon on the optimal vaccination/social distancing strategy. We find that in order to reduce social distancing in the long run, without overburdening the health care system, it is essential to vaccinate the people with the highest contact rates first. That is also the case if the objective is to minimize fatalities provided that the social distancing measures are sufficiently strict. However, for short-term planning it is optimal to focus on the high-risk group.



https://doi.org/10.1137/20M1387687
Cao-Riehmer, Jialan; Chande, Charmi; Kalensee, Franziska; Schüler, Tim; Köhler, Michael
Microfluidically supported characterization of responses of Rhodococcus erythropolis strains isolated from different soils on Cu-, Ni-, and Co-stress. - In: Brazilian journal of microbiology, ISSN 1678-4405, Bd. 52 (2021), 3, S. 1405-1415

We present a new methodological approach for the assessment of the susceptibility of Rhodococcus erythropolis strains from specific sampling sites in response to increasing heavy metal concentration (Cu2+, Ni2+, and Co2+) using the droplet-based microfluid technique. All isolates belong to the species R. erythropolis identified by Sanger sequencing of the 16S rRNA. The tiny step-wise variation of metal concentrations from zero to the lower mM range in 500 nL droplets not only provided accurate data for critical metal ion concentrations but also resulted in a detailed visualization of the concentration-dependent response of bacterial growth and autofluorescence activity. As a result, some of the isolates showed similar characteristics in heavy metal tolerance against Cu2+, Ni2+, and Co2+. However, significantly different heavy metal tolerances were found for other strains. Surprisingly, samples from the surface soil of ancient copper mining areas supplied mostly strains with a moderate sensitivity to Cu2+, Ni2+, and Co2+, but in contrast, a soil sample from an excavation site of a medieval city that had been covered for about eight centuries showed an extremely high tolerance against cobalt ion (up to 36 mM). The differences among the strains not only may be regarded as results of adaptation to the different environmental conditions faced by the strains in nature but also seem to be related to ancient human activities and temporal partial decoupling of soil elements from the surface. This investigation confirmed that microfluidic screening offers empirical characterization of properties from same species which has been isolated from sites known to have different human activities in the past.



https://doi.org/10.1007/s42770-021-00495-2
Lauer, Kevin; Brokmann, Geert; Bähr, Mario; Ortlepp, Thomas
Determination of piezo-resistive coefficient π44 in p-type silicon by comparing simulation and measurement of pressure sensors. - In: AIP Advances, ISSN 2158-3226, Bd. 11 (2021), 8, 085005, insges. 6 S.

https://doi.org/10.1063/5.0060034