Publications at the Department of Mathematics and Natural Sciences

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Omidian, Maryam; Leitherer, Susanne; Néel, Nicolas; Brandbyge, Mads; Kröger, Jörg;
Electric-field control of a single-atom polar bond. - In: Physical review letters. - College Park, Md. : APS, ISSN 1079-7114, Bd. 126 (2021), 21, S. 216801-1-216801-6

We expose the polar covalent bond between a single Au atom terminating the apex of an atomic force microscope tip and a C atom of graphene on SiC(0001) to an external electric field. For one field orientation, the Au-C bond is strong enough to sustain the mechanical load of partially detached graphene, while for the opposite orientation, the bond breaks easily. Calculations based on density-functional theory and nonequilibrium Green's function methods support the experimental observations by unveiling bond forces that reflect the polar character of the bond. Field-induced charge transfer between the atomic orbitals modifies the polarity of the different electronegative reaction partners and the Au-C bond strength.
Li, Qianwen; Wang, Hang; Tang, Xinfeng; Zhou, Min; Zhao, Huaping; Xu, Yang; Xiao, Wei; Lei, Yong;
Electrical conductivity adjustment for interface capacitive-like storage in sodium-ion battery. - In: Advanced functional materials. - Weinheim : Wiley-VCH, ISSN 1616-3028, Bd. 31 (2021), 24, S. 1-11

Sodium-ion battery (SIB) is significant for grid-scale energy storage. However, a large radius of Na ions raises the difficulties of ion intercalation, hindering the electrochemical performance during fast charge/discharge. Conventional strategies to promote rate performance focus on the optimization of ion diffusion. Improving interface capacitive-like storage by tuning the electrical conductivity of electrodes is also expected to combine the features of the high energy density of batteries and the high power density of capacitors. Inspired by this concept, an oxide-metal sandwich 3D-ordered macroporous architecture (3DOM) stands out as a superior anode candidate for high-rate SIBs. Taking Ni-TiO2 sandwich 3DOM as a proof-of-concept, anatase TiO2 delivers a reversible capacity of 233.3 mAh g^-1 in half-cells and 210.1 mAh g^-1 in full-cells after 100 cycles at 50 mA g^-1. At the high charge/discharge rate of 5000 mA g^-1, 104.4 mAh g^-1 in half-cells and 68 mAh g^-1 in full-cells can also be obtained with satisfying stability. In-depth analysis of electrochemical kinetics evidence that the dominated interface capacitive-like storage enables ultrafast uptaking and releasing of Na-ions. This understanding between electrical conductivity and rate performance of SIBs is expected to guild future design to realize effective energy storage.
Gizatullin, Bulat; Gafurov, Marat; Murzakhanov, Fadis; Vakhin, Alexey; Mattea, Carlos; Stapf, Siegfried;
Molecular dynamics and proton hyperpolarization via synthetic and crude oil porphyrin complexes in solid and solution states. - In: Langmuir : the ACS journal of surfaces and colloids.. - Washington, DC : ACS Publ., ISSN 1520-5827, Bd. 37 (2021), 22, S. 6783-6791

The use of vanadyl porphyrins either in synthetic compounds or naturally occurring in asphaltenes is investigated as a source of proton hyperpolarization via dynamic nuclear polarization (DNP) in nuclear magnetic resonance (NMR) experiments. The features of dynamics and location of the vanadyl VO2+ complex in aggregates within the oil asphaltene molecules are studied by means of DNP, electron paramagnetic resonance (EPR), and NMR field cycling relaxometry. Both the solid effect and Overhauser DNP were observed for the asphaltene solution in benzene, as well as in the solution and solid states for synthetic compounds. By comparison with a solution of synthetic vanadyl porphyrins, it is shown that vanadyl porphyrins in asphaltene aggregates are localized outside of the interface of the asphaltene aggregates and more exposed to the maltene molecules than free carbon-centered radicals associated with the core of asphaltene molecules. The perceptible contribution of scalar interaction is observed in solutions for both synthetic and asphaltene vanadyl porphyrins.
Gernandt, Hannes; Trunk, Carsten;
Locally finite extensions and Gesztesy-Šeba realizations for the Dirac operator on a metric graph. - In: Operator theory. - Berlin : De Gruyter, (2021), S. 25-54

Behrndt, Jussi; Schmitz, Philipp; Teschl, Gerald; Trunk, Carsten;
Perturbations of periodic Sturm-Liouville operators. - Ilmenau : Technische Universität Ilmenau, Institut für Mathematik, 2021. - 1 Online-Ressource (17 Seiten). . - (Preprint. - M21,04)

We study perturbations of self-adjoint periodic Sturm-Liouville operators and conclude under L1-assumptions on the differences of the coeffcients that the essential spectrum and absolutely continuous spectrum remain the same. If a finite first moment condition holds for the differences of the coeffcients, then at most finitely many eigenvalues appear in the spectral gaps. This observation extends a seminal result by Rofe-Beketov from the 1960s. Finally, imposing a second moment condition we show that the band edges are no eigenvalues of the perturbed operator.
De Santis, Marianna; Eichfelder, Gabriele;
A decision space algorithm for multiobjective convex quadratic integer optimization. - In: Computers & operations research : an international journal.. - Amsterdam [u.a.] : Elsevier, ISSN 0305-0548, Bd. 134 (2021)

We present a branch-and-bound algorithm for minimizing multiple convex quadratic objective functions over integer variables. Our method looks for efficient points by fixing subsets of variables to integer values and by using lower bounds in the form of hyperplanes in the image space derived from the continuous relaxations of the restricted objective functions. We show that the algorithm stops after finitely many fixings of variables with detecting both the full efficient and the nondominated set of multiobjective strictly convex quadratic integer problems. A major advantage of the approach is that the expensive calculations are done in a preprocessing phase so that the nodes in the branch-and-bound tree can be enumerated fast. We show numerical experiments on biobjective instances and on instances with three and four objectives.
Nasori, Nasori; Cao, Dawei; Wang, Zhijie; Farahdina, Ulya; Rubiyanto, Agus; Lei, Yong;
Tunning of templated CuWO4 nanorods arrays thickness to improve photoanode water splitting. - In: Molecules : a journal of synthetic chemistry and natural product chemistry.. - Basel : MDPI, ISSN 1420-3049, Bd. 26 (2021), 10, S. 1-14
- Im Titel ist "4" tiefgestellt

The fabrication of the photoanode of the n-type CuWO4 nanorod arrays was successfully carried out through electrochemical deposition using anodic aluminum oxide (AAO) control templates and for the first time produced distinct gaps between the nanorod arrays. The effectiveness and efficiency of the resulting deposition was shown by the performance of the photoelectrochemical (PEC) procedure with a current density of 1.02 mA cm^-2 with irradiation using standard AM 1.5G solar simulator and electron changed radiation of 0.72% with a bias potential of 0.71 V (vs. Ag/AgCl). The gap between each nanorod indicated an optimization of the electrolyte penetration on the interface, which resulted in the expansion of the current density as much as 0.5 × 1024 cm^-3 with a flat band potential of 0.14 V vs. Ag/AgCl and also a peak quantum efficiency of wavelength 410 nm. Thus, also indicating the gaps between the nanorod arrays is a promising structure to optimize the performance of the PEC water splitting procedure as a sustainable energy source.
Chang, Shilei; Hou, Minjie; Xu, Bowen; Liang, Feng; Qiu, Xuechao; Yao, Yaochun; Qu, Tao; Ma, Wenhui; Yang, Bing; Dai, Yongnian; Chen, Kunfeng; Xue, Dongfeng; Zhao, Huaping; Lin, Xiaoting; Poon, Fanny; Lei, Yong; Sun, Xueliang;
High-performance quasi-solid-state Na-air battery via gel cathode by confining moisture. - In: Advanced functional materials. - Weinheim : Wiley-VCH, ISSN 1616-3028, Bd. 31 (2021), 22, S. 1-9
Chen, Liangzhi; Hotz, Thomas; Zhang, Haizhang;
Admissible kernels for RKHS embedding of probability distributions. - In: Statistical papers. - Berlin : Springer, ISSN 1613-9798, Bd. 62 (2021), 3, S. 1499-1518

Similarity measurement of two probability distributions is important in many applications of statistics. Embedding such distributions into a reproducing kernel Hilbert space (RKHS) has many favorable properties. The choice of the reproducing kernel is crucial in the approach. We study this question by considering the similarity of two distributions of the same class. In particular, we investigate when the RKHS embedding is "admissible" in the sense that the distance between the embeddings should become smaller when the expectations are getting closer or when the variance is increasing to infinity. We give conditions on the widely-used translation-invariant reproducing kernels to be admissible. We also extend the study to multivariate non-symmetric Gaussian distributions.
Nozdrenko, Dmytro; Abramchuk, Olga; Prylutska, Svitlana; Vygovska, Oksana; Soroca, Vasil; Bogutska, Kateryna; Khrapatyi, Sergii; Prylutskyy, Yuriy; Scharff, Peter; Ritter, Uwe;
Analysis of biomechanical parameters of muscle soleus contraction and blood biochemical parameters in rat with chronic glyphosate intoxication and therapeutic use of C60 fullerene. - In: International journal of molecular sciences. - Basel : Molecular Diversity Preservation International, ISSN 1422-0067, Bd. 22 (2021), 9, S. 1-11
- Im Titel ist "60" tiefgestellt