Solving multiobjective mixed integer convex optimization problems. - In: SIAM journal on optimization, ISSN 1095-7189, Bd. 30 (2020), 4, S. 3122-3145
Multiobjective mixed integer convex optimization refers to mathematical programming problems where more than one convex objective function needs to be optimized simultaneously and some of the variables are constrained to take integer values. We present a branch-and-bound method based on the use of properly defined lower bounds. We do not simply rely on convex relaxations, but we build linear outer approximations of the image set in an adaptive way. We are able to guarantee correctness in terms of detecting both the efficient and the nondominated set of multiobjective mixed integer convex problems according to a prescribed precision. As far as we know, the procedure we present is the first non-scalarization-based deterministic algorithm devised to handle this class of problems. Our numerical experiments show results on biobjective and triobjective mixed integer convex instances.
https://doi.org/10.1137/19M1264709
Optische Systeme im Phasenraumbild. - In: DGaO-Proceedings, ISSN 1614-8436, Bd. 121 (2020), B29, insges. 2 S.
https://nbn-resolving.org/urn:nbn:de:0287-2020-B029-0
Preferentially engineering FeN4 edge sites onto graphitic nanosheets for highly active and durable oxygen electrocatalysis in rechargeable Zn-air batteries. - In: Advanced materials, ISSN 1521-4095, Bd. 32 (2020), 49, 2004900, insges. 9 S.
Im Titel ist "4" tiefgestellt
Single-atom FeN4 sites at the edges of carbon substrates are considered more active for oxygen electrocatalysis than those in plane; however, the conventional high-temperature pyrolysis process does not allow for precisely engineering the location of the active site down to atomic level. Enlightened by theoretical prediction, herein, a self-sacrificed templating approach is developed to obtain edge-enriched FeN4 sites integrated in the highly graphitic nanosheet architecture. The in situ formed Fe clusters are intentionally introduced to catalyze the growth of graphitic carbon, induce porous structure formation, and most importantly, facilitate the preferential anchoring of FeN4 to its close approximation. Due to these attributes, the as-resulted catalyst (denoted as Fe/N-G-SAC) demonstrates unprecedented catalytic activity and stability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) by showing an impressive half-wave potential of 0.89 V for the ORR and a small overpotential of 370 mV at 10 mA cm^-2 for the OER. Moreover, the Fe/N-G-SAC cathode displays encouraging performance in a rechargeable Zn-air battery prototype with a low charge-discharge voltage gap of 0.78 V and long-term cyclability for over 240 cycles, outperforming the noble metal benchmarks.
https://doi.org/10.1002/adma.202004900
Methods for multiobjective bilevel optimization. - In: Bilevel optimization, (2020), S. 423-449
This chapter is on multiobjective bilevel optimization, i.e. on bilevel optimization problems with multiple objectives on the lower or on the upper level, or even on both levels. We give an overview on the major optimality notions used in multiobjective optimization. We provide characterization results for the set of optimal solutions of multiobjective optimization problems by means of scalarization functionals and optimality conditions. These can be used in theoretical and numerical approaches to multiobjective bilevel optimization.As multiple objectives arise in multiobjective optimization as well as in bilevel optimization problems, we also point out the results on the connection between these two classes of optimization problems. Finally, we give reference to numerical approaches which have been followed in the literature to solve these kind of problems. We concentrate in this chapter on nonlinear problems, while the results and statements naturally also hold for the linear case.
A linear relation approach to port-Hamiltonian differential-algebraic equations. - [Hamburg[ : [Fachbereich Mathematik, Universität Hamburg], 2020. - 1 Online-Ressource (31 Seiten). - ([Hamburger Beiträge zur Angewandten Mathematik] ; [2020, 16])Titel der monographischen Reihe und Veröffentlichungsangabe von der Homepage entnommen
http://epub.sub.uni-hamburg.de/epub/volltexte/2020/112509/
Emerging structural and interfacial features of particulate polymers at the nanoscale. - In: Langmuir, ISSN 1520-5827, Bd. 36 (2020), 44, S. 13125-13143
Particulate polymers at the nanoscale are exceedingly promising for diversified functional applications ranging from biomedical and energy to sensing, labeling, and catalysis. Tailored structural features (i.e., size, shape, morphology, internal softness, interior cross-linking, etc.) determine polymer nanoparticles' impact on the cargo loading capacity and controlled/sustained release, possibility of endocytosis, degradability, and photostability. The designed interfacial features, however (i.e., stimuli-responsive surfaces, wrinkling, surface porosity, shell-layer swellability, layer-by-layer surface functionalization, surface charge, etc.), regulate nanoparticles interfacial interactions, controlled assembly, movement and collision, and compatibility with the surroundings (e.g., solvent and biological environments). These features define nanoparticles' overall properties/functions on the basis of homogeneity, stability, interfacial tension, and minimization of the surface energy barrier. Lowering of the resultant outcomes is directly influenced by inhomogeneity in the structural and interfacial design through the structure-function relationship. Therefore, a key requirement is to produce well-defined polymer nanoparticles with controlled characteristics. Polymers are amorphous, flexible, and soft, and hence controlling their structural/interfacial features through the single-step process is a challenge. The microfluidics reaction strategy is very promising because of its wide range of advantages such as efficient reactant mixing and fast phase transfer. Overall, this feature article highlights the state-of-the-art synthetic features of polymer nanoparticles with perspectives on their advanced applications.
https://doi.org/10.1021/acs.langmuir.0c02566
Ag-nanoparticlesbacterial nanocellulose as a 3D flexible and robust surface-enhanced raman scattering substrate. - In: ACS applied materials & interfaces, ISSN 1944-8252, Bd. 12 (2020), 45, S. 50713-50720
We present a well-designed, low-cost, and simple synthetic approach to realizing the hybrid composites of Ag nanoparticle-decorated bacterial nanocellulose (denoted as Ag-NPsBNC) as a three-dimensional (3D) flexible surface-enhanced Raman scattering (SERS) substrate with ultrahigh SERS sensitivity, excellent signal reproducibility, and stability. The homogeneous Ag-NPs with high density were in situ grown on the networked BNC fibers by the controlled silver mirror reaction and volume shrinkage treatment, which created uniformly distributed SERS "hot spots" in the 3D networked hybrid substrate. Attributed to these unique 3D hot spots, the as-presented Ag-NPs@BNC substrates exhibited ultrahigh sensitivity and good spectral reproducibility. Moreover, the hydrophilic BNC exhibits good permeability and adsorption performances, which could capture the target molecules in the highly active hot spot areas to further improve the SERS sensitivity. As a result, not only dye molecules (rhodamine 6G) but also toxic organic pollutants such as 2-naphthalenethiol and thiram have been detected using the hybrid substrates as SERS substrates, with sensitivities of 1.6 × 10-8 and 3.8 × 10-9 M, respectively. The good linear response of the intensity and the logarithmic concentration revealed promising applications in the rapid and quantitative detection of toxic organic pollutants. Besides, this self-supported Ag-NPs@BNC substrate demonstrated good stability and flexibility for varied detection conditions. Therefore, the 3D networked, flexible, ultrasensitive, and stable Ag-NPs@BNC substrate shows potential as a versatile SERS substrate in the rapid identification of various organic molecules.
https://doi.org/10.1021/acsami.0c13828
Hard X-ray photoelectron spectroscopy study of core level shifts at buried GaP/Si(001) interfaces. - In: Surface and interface analysis, ISSN 1096-9918, Bd. 52 (2020), 12, S. 933-938
We present a study of buried GaP/Si(001) heterointerfaces by hard X-ray photoelectron spectroscopy. Well-defined thin (4-50 nm) GaP films were grown on Si(001) substrates with 2˚ miscut orientations by metalorganic vapor phase epitaxy. Core level photoelectron intensities and valence band spectra were measured on heterostructures as well as on the corresponding reference (bulk) substrates. Detailed analysis of core level peaks revealed line broadening and energetic shifts. Valence band offsets were derived for the films with different thickness. Based on the observed variation of the valence band offsets with the GaP film thickness and on the experimental evidence of line broadening, the existence of charge displacement at the GaP/Si(001) interface is suggested.
https://doi.org/10.1002/sia.6829
Spin-orbit interaction of light in three-dimensional microcavities. - In: Physical review, ISSN 2469-9934, Bd. 102 (2020), 4, 043524
We investigate the spin-orbit coupling of light in three-dimensional cylindrical and tubelike whispering gallery mode resonators. We show that its origin is the transverse confinement of light in the resonator walls, even in the absence of inhomogeneities or anisotropies. The spin-orbit interaction results in elliptical far-field polarization (spin) states and causes spatial separation of polarization handedness in the far field. The ellipticity and spatial separation are enhanced for whispering gallery modes with higher excitation numbers along the resonator height. We analyze the asymmetry of the ellipticity and the tilt of the polarization orientation in the far field of conelike microcavities. Furthermore, we find a direct relationship between the tilt of the polarization orientation in the far field and the local inclination of the resonator wall. Our findings are based on finite-difference time-domain simulations and are supported by three-dimensional diffraction theory.
https://doi.org/10.1103/PhysRevA.102.043524
Recent research progress of anode materials for potassium-ion batteries. - In: Energy & Environmental Materials, ISSN 2575-0356, Bd. 3 (2020), 2, S. 105-120
The next-generation smart grid for the storage and delivery of renewable energy urgently needs to develop a low-cost and rechargeable energy storage technology beyond lithium-ion batteries (LIBs). Owing to the abundance of potassium (K) resources and the similar electrochemical performance to that of LIBs, potassium-ion batteries (PIBs) have been attracted considerable interest in recent years, and significant progress has been achieved concerning the discovery of high-performance electrode materials for PIBs. This review especially summarizes the latest research progress regarding anode materials for PIBs, including carbon materials, organic materials, alloys, metal-based compounds, and other new types of compounds. The reversible K-ion storage principle and the electrochemical performance (i.e., capacity, potential, rate capability, and cyclability) of these developed anode materials are summarized. Furthermore, the challenges and the corresponding effective strategies to enhance the battery performance of the anode materials are highlighted. Finally, prospects of the future development of high-performance anode materials for PIBs are discussed.
https://doi.org/10.1002/eem2.12059