Husimi functions for coupled optical resonators. - In: Journal of the Optical Society of America, ISSN 1520-8532, Bd. 38 (2021), 4, S. 573-578
Phase-space analysis has been widely used in the past for the study of optical resonant systems. While it is usually employed to analyze the far-field behavior of resonant systems, we focus here on its applicability to coupling problems. By looking at the phase-space description of both the resonant mode and the exciting source, it is possible to understand the coupling mechanisms as well as to gain insights and approximate the coupling behavior with reduced computational effort. In this work, we develop the framework for this idea and apply it to a system of an asymmetric dielectric resonator coupled to a waveguide.
https://doi.org/10.1364/JOSAA.422740
Finite rank perturbations of linear relations and matrix pencils. - In: Complex analysis and operator theory, ISSN 1661-8262, Bd. 15 (2021), 2, 37, insges. 37 S.
We elaborate on the deviation of the Jordan structures of two linear relations that are finite-dimensional perturbations of each other. We compare their number of Jordan chains of length at least n. In the operator case, it was recently proved that the difference of these numbers is independent of n and is at most the defect between the operators. One of the main results of this paper shows that in the case of linear relations this number has to be multiplied by n+1 and that this bound is sharp. The reason for this behavior is the existence of singular chains. We apply our results to one-dimensional perturbations of singular and regular matrix pencils. This is done by representing matrix pencils via linear relations. This technique allows for both proving known results for regular pencils as well as new results for singular ones.
https://doi.org/10.1007/s11785-021-01082-x
Funnel control of nonlinear systems. - In: Mathematics of control, signals, and systems, ISSN 1435-568X, Bd. 33 (2021), 1, S. 151-194
Tracking of reference signals is addressed in the context of a class of nonlinear controlled systems modelled by r-th-order functional differential equations, encompassing inter alia systems with unknown "control direction" and dead-zone input effects. A control structure is developed which ensures that, for every member of the underlying system class and every admissible reference signal, the tracking error evolves in a prescribed funnel chosen to reflect transient and asymptotic accuracy objectives. Two fundamental properties underpin the system class: bounded-input bounded-output stable internal dynamics, and a high-gain property (an antecedent of which is the concept of sign-definite high-frequency gain in the context of linear systems).
https://doi.org/10.1007/s00498-021-00277-z
Square roots of H-nonnegative matrices. - In: Linear algebra and its applications, ISSN 0024-3795, Bd. 621 (2021), S. 29-49
https://doi.org/10.1016/j.laa.2021.03.006
Dirac's theorem for random regular graphs. - In: Combinatorics, probability & computing, ISSN 1469-2163, Bd. 30 (2021), 1, S. 17-36
https://doi.org/10.1017/S0963548320000346
InP and AlInP(001)(2 × 4) surface oxidation from density functional theory. - In: ACS omega, ISSN 2470-1343, Bd. 6 (2021), 9, S. 6297-6304
The atomic structure and electronic properties of the InP and Al0.5In0.5P(001) surfaces at the initial stages of oxidation are investigated via density functional theory. Thereby, we focus on the mixed-dimer (2 × 4) surfaces stable for cation-rich preparation conditions. For InP, the top In-P dimer is the most favored adsorption site, while it is the second-layer Al-Al dimer for AlInP. The energetically favored adsorption sites yield group III-O bond-related states in the energy region of the bulk band gap, which may act as recombination centers. Consistently, the In p state density around the conduction edge is found to be reduced upon oxidation.
https://doi.org/10.1021/acsomega.0c06019
Atomic force extrema induced by the bending of a CO-functionalized probe. - In: Nano letters, ISSN 1530-6992, Bd. 21 (2021), 5, S. 2318-2323
The control and observation of reactants forming a chemical bond at the single-molecule level is a long-standing challenge in quantum physics and chemistry. Using a single CO molecule adsorbed at the apex of an atomic force microscope tip together with a Cu(111) surface, bending of the molecular probe is induced by torques due to van der Waals attraction and Pauli repulsion. As a result, the vertical force between CO and Cu(111) exhibits a characteristic dip-hump evolution with the molecule-surface separation, which depends sensitively on the initial tilt angle the CO axis encloses with the surface normal. The experimental force data are reproduced by model calculations that consider the CO deflection in a harmonic potential and the molecular orientation in the Pauli repulsion term of the Lennard-Jones potential. The presented findings shed new light on vertical-force extrema that can occur in scanning probe experiments with functionalized tips.
https://doi.org/10.1021/acs.nanolett.1c00268
Biomass-derived highly dispersed Co/Co9S8 nanoparticles encapsulated in S, N-co-doped hierarchically porous carbon as an efficient catalyst for hybrid Na-CO2 batteries. - In: Materials today, ISSN 2468-6069, Bd. 19 (2021), 100594, insges. 12 S.
Im Titel sind "9", "8" und "2" tiefgestellt
Na-CO2 batteries are prospective in energy storage and CO2 recycling applications; development of a high-efficiency, low-cost electrocatalyst to promote CO2 reduction and carbonate decomposition is extremely vital for practical Na-CO2 batteries. Herein, a highly efficient cathode catalyst for rechargeable hybrid Na-CO2 batteries is successfully synthesized by encapsulating highly dispersed Co/Co9S8 nanoparticles into carbon skeletons, consisting of biomass-derived S, N-co-doped hierarchically porous carbon (Co/Co9S8SNHC). The conductive and hierarchically porous framework structure of the Co/Co9S8@SNHC can not only accelerate electron transport, electrolyte infiltration, and CO2 diffusion but also can inhibit overgrowth and agglomeration of Co/Co9S8 nanoparticles and expose numerous high density of active sites, as well as offer sufficient space to store discharge products. Benefiting from the synergistic effect among S and N dopants, carbon defects, and Co/Co9S8 nanoparticles in robust porous carbon structure, the hybrid Na-CO2 batteries displayed a low charge overpotential (only ˜0.32 V) at 0.2 mA/cm2 and repeatedly charged and discharged over 200 cycles at 0.1 mA/cm2. Besides, an ultrahigh areal capacity of ˜18.9 mAh/cm2 was obtained at 0.5 mA/cm2, the highest value to date for Na-CO2 batteries. Meanwhile, the hybrid Na-CO2 battery charging from Na2CO3@C catalytic cathode demonstrated the high catalytic activity of biomass-derived S,N-co-doped hierarchically porous carbon (Co/Co9S8@SNHC) for CO2 reduction and carbonate decomposition. Given this finding, this work might open up a potential avenue for the reasonable design of low-cost and highly efficient catalysts for advanced metal-CO2 batteries systems.
https://doi.org/10.1016/j.mtener.2020.100594
Efficient and inexpensive MPCVD method to synthesize Co3O4/MoS2 heterogeneous composite materials with high stability for supercapacitors. - In: Journal of materials research and technology, ISSN 2214-0697, Bd. 10 (2021), S. 953-959
Large-sized metal oxide particles have the potential to constitute cheap, high-performance, and high-stability supercapacitor electrode materials. Herein, the marketable large-sized Co3O4 particles (˜6 [my]m) as the starting raw material, inexpensive Co3O4/MoS2 core-shell heterogeneous composites have been one-step fabricated via an improvised MPCVD system modified by a domestic microwave oven. After that, the surface morphology, composition structure, and valence state of elements were analyzed to the confirmed successful synthesis of MoS2 on the surface of Co3O4. Besides, the performance was tested by cyclic voltammetry and galvanostatic charge-discharge method. The results show that the synergistic effect of Co3O4 core and MoS2 shell can effectively improve the material's electrochemical performance. The specific capacitance of Co3O4/MoS2 composite can reach 337 F g^-1 with a current density of 0.5 A g^-1, which is six times more than the raw Co3O4 powder. Furthermore, it could maintain 93.6% of the initial specific capacitance after 2000 charges and discharges. Finally, the mechanism of material performance improvement is proposed.
https://doi.org/10.1016/j.jmrt.2020.12.101
Template-assisted fabrication of Ag-nanoparticlesZnO-nanorods array as recyclable 3D surface enhanced Raman scattering substrate for rapid detection of trace pesticides. - In: Nanotechnology, ISSN 1361-6528, Bd. 32 (2021), 14, 145302, S. 1-9
We present a template-assisted fabrication method for a large-scale ordered arrays of ZnO nanorods (ZnO-NRs) modified with Ag nanoparticles (Ag-NPs), which possess high-density three-dimensional (3D) hot spots uniformly dispersed all over the substrate, being beneficial to ultrahigh sensitivity of surface enhanced Raman scattering (SERS) detection. These achieved Ag-NPsZnO-NRs arrays show high sensitivity, good spectral uniformity and reproducibility as substrates for SERS detection. Using the arrays, both dye molecules (rhodamine 6G, R6G) and organic pollutants like toxic pesticides (thiram and methyl parathion) are detected, with the detection limits of thiram and methyl parathion being 0.79 x 10^-9 M and 1.51 x 10^-8 M, respectively. In addition, the Ag-NPs@ZnO-NRs arrays have a self-cleaning function because the analyte molecules can be photocatalytic degraded using ultraviolet irradiation, showing that the 3D recyclable arrays have promising opportunities to be applied in rapid SERS-based detection of toxic organic pesticides.
https://doi.org/10.1088/1361-6528/abc50e