Electron spin finds a fresh excitation. - In: Nature physics, ISSN 1745-2481, Bd. 20 (2024), 1, S. 4-5
The Kondo effect - the screening of an impurity spin by conduction electrons - is a fundamental many-body effect. However, recent experiments combined with simulations have caused a long-standing model system for the single-atom Kondo effect to fail.
https://doi.org/10.1038/s41567-023-02265-3
Rooted minors and locally spanning subgraphs. - In: Journal of graph theory, ISSN 1097-0118, Bd. 105 (2024), 2, S. 209-229
Results on the existence of various types of spanning subgraphs of graphs are milestones in structural graph theory and have been diversified in several directions. In the present paper, we consider “local” versions of such statements. In 1966, for instance, D. W. Barnette proved that a 3-connected planar graph contains a spanning tree of maximum degree at most 3. A local translation of this statement is that if G is a planar graph, X is a subset of specified vertices of G such that X cannot be separated in G by removing two or fewer vertices of G, then G has a tree of maximum degree at most 3 containing all vertices of X. Our results constitute a general machinery for strengthening statements about k-connected graphs (for 1 ≤ k ≤ 4) to locally spanning versions, that is, subgraphs containing a set X ⊆ V (G) of a (not necessarily planar) graph G in which only X has high connectedness. Given a graph G and X ⊆ V (G), we say M is a minor of G rooted at X, if M is a minor of G such that each bag of M contains at most one vertex of X and X is a subset of the union of all bags. We show that G has a highly connected minor rooted at X if X ⊆ V (G) cannot be separated in G by removing a few vertices of G. Combining these investigations and the theory of Tutte paths in the planar case yields locally spanning versions of six well-known results about degree-bounded trees, Hamiltonian paths and cycles, and 2-connected subgraphs of graphs.
https://doi.org/10.1002/jgt.23012
Dual-functional electrode promoting dendrite-free and CO2 utilization enabled high-reversible symmetric Na-CO2 batteries. - In: Energy & Environmental Materials, ISSN 2575-0356, Bd. 7 (2024), 3, e12626, S. 1-10
Sodium-carbon dioxide (Na-CO2) batteries are regarded as promising energy storage technologies because of their impressive theoretical energy density and CO2 reutilization, but their practical applications are restricted by uncontrollable sodium dendrite growth and poor electrochemical kinetics of CO2 cathode. Constructing suitable multifunctional electrodes for dendrite-free anodes and kinetics-enhanced CO2 cathodes is considered one of the most important ways to advance the practical application of Na-CO2 batteries. Herein, RuO2 nanoparticles encapsulated in carbon paper (RuCP) are rationally designed and employed as both Na anode host and CO2 cathode in Na-CO2 batteries. The outstanding sodiophilicity and high catalytic activity of RuCP electrodes can simultaneously contribute to homogenous Na+ distribution and dendrite-free sodium structure at the anode, as well as strengthen discharge and charge kinetics at the cathode. The morphological evolution confirmed the uniform deposition of Na on RuCP anode with dense and flat interfaces, delivering enhanced Coulombic efficiency of 99.5% and cycling stability near 1500 cycles. Meanwhile, Na-CO2 batteries with RuCP cathode demonstrated excellent cycling stability (>350 cycles). Significantly, implementation of a dendrite-free RuCPNa anode and catalytic-site-rich RuCP cathode allowed for the construction of a symmetric Na-CO2 battery with long-duration cyclability, offering inspiration for extensive practical uses of Na-CO2 batteries.
https://doi.org/10.1002/eem2.12626
Structure-preserving model reduction for dissipative mechanical systems. - In: Calm, smooth and smart, (2024), S. 209-230
Suppressing vibrations in mechanical systems, usually described by second-order dynamical models, is a challenging task in mechanical engineering in terms of computational resources even nowadays. One remedy is structure-preserving model order reduction to construct easy-to-evaluate surrogates for the original dynamical system having the same structure. In our work, we present an overview of recently developed structure-preserving model reduction methods for second-order systems. These methods are based on modal and balanced truncation in different variants, as well as on rational interpolation. Numerical examples are used to illustrate the effectiveness of all described methods.
https://doi.org/10.1007/978-3-031-36143-2_11
Long running times for hypergraph bootstrap percolation. - In: European journal of combinatorics, Bd. 115 (2024), 103783, S. 1-18
Consider the hypergraph bootstrap percolation process in which, given a fixed r-uniform hypergraph H and starting with a given hypergraph G0, at each step we add to G0 all edges that create a new copy of H. We are interested in maximising the number of steps that this process takes before it stabilises. For the case where H = Kr+1(r) with r ≥ 3, we provide a new construction for G0 that shows that the number of steps of this process can be of order Θ (nr). This answers a recent question of Noel and Ranganathan. To demonstrate that different running times can occur, we also prove that, if H is K4(3) minus an edge, then the maximum possible running time is 2n − ⌊log2(n−2)⌋ − 6. However, if H is K5(3) minus an edge, then the process can run for Θ (n3) steps.
https://doi.org/10.1016/j.ejc.2023.103783
Master memory function for delay-based reservoir computers with single-variable dynamics. - In: IEEE transactions on neural networks and learning systems, ISSN 2162-2388, Bd. 35 (2024), 6, S. 7712-7725
We show that many delay-based reservoir computers considered in the literature can be characterized by a universal master memory function (MMF). Once computed for two independent parameters, this function provides linear memory capacity for any delay-based single-variable reservoir with small inputs. Moreover, we propose an analytical description of the MMF that enables its efficient and fast computation. Our approach can be applied not only to single-variable delay-based reservoirs governed by known dynamical rules, such as the Mackey-Glass or Stuart-Landau-like systems, but also to reservoirs whose dynamical model is not available.
https://doi.org/10.1109/TNNLS.2022.3220532
Limit sets in global multiobjective optimization. - In: Optimization, ISSN 1029-4945, Bd. 73 (2024), 1, S. 1-27
Inspired by the recently introduced branch-and-bound method for continuous multiobjective optimization problems from G. Eichfelder, P. Kirst, L. Meng, O. Stein [A general branch-and-bound framework for continuous global multiobjective optimization. J Glob Optim. 2021;80:195-227], we study for a general class of branch-and-bound methods in which sense the generated terminal enclosure and the terminal provisional nondominated set approximate the nondominated set when the termination accuracy is driven to zero. Our convergence analysis of the enclosures relies on constructions from the above paper, but is self-contained and also covers the mixed-integer case. The analysis for the provisional nondominated set is based on general convergence properties of the epsilon-nondominated set, and hence it is also applicable to other algorithms which generate such points. Furthermore, we discuss post-processing steps for the terminal enclosure and provide numerical illustrations for the cases of two and three objective functions.
https://doi.org/10.1080/02331934.2022.2092479
Modulating functions analysis for wireless data transmission because of advanced sensors in energy-saving process of washing. - In: Renewable energy & power quality journal, ISSN 2172-038X, Bd. 21 (2023), 6, S. 695-700
The vibration measurement of flows in transient or steady-state is a very complicated task. Moreover, to correlate it with a temperature process is quite important according to get information regarding molecular kinetic energy of thermal sources (such as flow measurement used in cleaning tasks) according to achieve heating transfer information of a thermal process. However, there is a trouble concerning the transduction stage in the measurement while it is not a transducer designed algorithm as a consequence of a mathematical model, which correlates the calibration data with the theoretical model of the heating/vibration transfer. For this reason, in this research is proposed intelligent sensors/transducers, which are based on Anodic Aluminium Oxide (AAO) and a mathematical procedure of the measurement instrumentation according to adaptive coefficients in the Modulating Functions strategies analysis and getting optimal measurements. In this research is explained and analysed the temperature measurement process and the transduction process as the strict correlation of the calibration of the temperature/vibration sensor. For this reason, there were evaluated different transducers and the temperature/vibration reference for the calibration. The based on nanostructures temperature sensors are designed by specific and complex procedures according to achieve quite operation range, robustness and precision. Moreover, the transduction can be obtained through different electrical answer variables such as voltage, electrical current or capacitance and possible to send by wireless mechanisms and protocols to the main control system. Therefore, the evaluation of the designed advanced sensor performance was achieved by the vibration and temperature measurement of the water surface of a ultrasound washing machine, for which the designed sensor enhances energy-saving of the washing process.
https://doi.org/10.24084/repqj21.453
Submicrometer optical frequency combs based on SPPs metallic multi-ring resonators. - In: Photonics research, ISSN 2327-9125, Bd. 11 (2023), 12, S. 2105-2112
Optical frequency combs (OFCs) have great potential in communications, especially in dense wavelength-division multiplexing. However, the size of traditional OFCs based on conventional optical microcavities or dispersion fibers is at least tens of micrometers, far larger than that of nanoscale electronic chips. Therefore, reducing the size of OFCs to match electronic chips is of necessity. Here, for the first time to our knowledge, we introduce surface plasmon polaritons (SPPs) to the construction of OFCs to realize a miniature device. The thickness of our device is reduced below 1 μm. Though the presence of SPPs may induce ohmic and scattering loss, the threshold of the device is obtained as 9 μW, comparable to the conventional device. Interestingly, the response time is 13.2 ps, much faster than the optical counterparts. This work provides a feasible strategy for the miniaturization of OFCs.
https://doi.org/10.1364/PRJ.488160
Structural fingerprints in the reflectance anisotropy of AlInP(001). - In: Physical review, ISSN 2469-9969, Bd. 108 (2023), 4, 045410, S. 045410-1-045410-6
The surface optical anisotropy of AlInP(001) surfaces is studied from both experiment and theory. The comparison of the data measured on epitaxially grown Al0.52In0.48P(001) epilayers lattice matched to GaAs with spectra calculated for energetically favored AlInP(001) surface structures suggests that the surface is covered with a monolayer of buckled phosphorus dimers, where half of the phosphorus atoms are hydrogen saturated. While the optical anisotropies for photon energies below about 3 eV provide clear fingerprints for the structure of the outermost surface atomic layer, the spectral features at higher energies provide insight into the near surface bulk ordering of AlInP. In particular optical anisotropies at the AlInP critical point energies are found to be related to the CuPt ordering in the material.
https://doi.org/10.1103/PhysRevB.108.045410