The 2022 solar fuels roadmap. - In: Journal of physics, ISSN 1361-6463, Bd. 55 (2022), 32, 323003, S. 1-52
Renewable fuel generation is essential for a low carbon footprint economy. Thus, over the last five decades, a significant effort has been dedicated towards increasing the performance of solar fuels generating devices. Specifically, the solar to hydrogen efficiency of photoelectrochemical cells has progressed steadily towards its fundamental limit, and the faradaic efficiency towards valuable products in CO2 reduction systems has increased dramatically. However, there are still numerous scientific and engineering challenges that must be overcame in order to turn solar fuels into a viable technology. At the electrode and device level, the conversion efficiency, stability and products selectivity must be increased significantly. Meanwhile, these performance metrics must be maintained when scaling up devices and systems while maintaining an acceptable cost and carbon footprint. This roadmap surveys different aspects of this endeavor: system benchmarking, device scaling, various approaches for photoelectrodes design, materials discovery, and catalysis. Each of the sections in the roadmap focuses on a single topic, discussing the state of the art, the key challenges and advancements required to meet them. The roadmap can be used as a guide for researchers and funding agencies highlighting the most pressing needs of the field.
https://doi.org/10.1088/1361-6463/ac6f97
Anisotropy of the ΔE effect in Ni-based magnetoelectric cantilevers: a finite element method analysis. - In: Sensors, ISSN 1424-8220, Bd. 22 (2022), 13, 4958, S. 1-16
In recent investigations of magnetoelectric sensors based on microelectromechanical cantilevers made of TiN/AlN/Ni, a complex eigenfrequency behavior arising from the anisotropic ΔE effect was demonstrated. Within this work, a FEM simulation model based on this material system is presented to allow an investigation of the vibrational properties of cantilever-based sensors derived from magnetocrystalline anisotropy while avoiding other anisotropic contributions. Using the magnetocrystalline ΔE effect, a magnetic hardening of Nickel is demonstrated for the (110) as well as the (111) orientation. The sensitivity is extracted from the field-dependent eigenfrequency curves. It is found, that the transitions of the individual magnetic domain states in the magnetization process are the dominant influencing factor on the sensitivity for all crystal orientations. It is shown, that Nickel layers in the sensor aligned along the medium or hard axis yield a higher sensitivity than layers along the easy axis. The peak sensitivity was determined to 41.3 T−1 for (110) in-plane-oriented Nickel at a magnetic bias flux of 1.78 mT. The results achieved by FEM simulations are compared to the results calculated by the Euler-Bernoulli theory.
https://doi.org/10.3390/s22134958
The deuteron NMR Hahn echo decay in polyethylene oxide melts. - In: AIP Advances, ISSN 2158-3226, Bd. 12 (2022), 7, S. 075219-1-075219-12
The deuteron transverse relaxation properties of polyethylene oxide melts of four different molecular weights, covering the range from the onset of entanglements to the regime of fully entangled chains, are investigated using Hahn echo decays over an extensive time interval up to ten times the effective transverse spin relaxation time. The results are compared to predictions based on the Rouse and reptation formalisms, taking into account the dynamical heterogeneity of linear polymer chains produced by the end segments. The experimental results can be described qualitatively by a combination of both models, with the contribution of reptation dynamics increasing with growing chain length. The transition is continuous, rather than being characterized by sharp regime boundaries. Up to a molecular weight of 300.000 g/mol, the predicted limit of pure reptation dynamics is not yet reached. Quantitative deviations from the predicted decays as computed by numerical procedures become observable toward the long-time limit of the Hahn echo decays and are being discussed in terms of shortcomings of the available reptation theories.
https://doi.org/10.1063/5.0099293
Coherent acoustic phonon oscillations and transient critical point parameters of Ge from femtosecond pump-probe ellipsometry. - In: Physica status solidi, ISSN 1862-6270, Bd. 16 (2022), 7, 2200058, S. 1-7
Herein, the complex pseudodielectric function of Ge and Si from femtosecond pump-probe spectroscopic ellipsometry with 267, 400, and 800 nm pump-pulse wavelengths is analyzed by fitting analytical lineshapes to the second derivatives of the pseudodielectric function with respect to energy. This yields the critical point parameters (threshold energy, lifetime broadening, amplitude, and excitonic phase angle) of E 1 and E 1 + Δ 1 in Ge and E 1 in Si as functions of delay time. Coherent longitudinal acoustic phonon oscillations with a period of about 11 ps are observed in the transient critical point parameters of Ge. From the amplitude of these oscillations, the laser-induced strain is found to be on the order of 0.03% for Ge measured with the 800 nm pump pulse, which is in reasonable agreement with the strain calculated from theory.
https://doi.org/10.1002/pssr.202200058
On sparse random combinatorial matrices. - In: Discrete mathematics, Bd. 345 (2022), 11, 113017
Let Qn,d denote the random combinatorial matrix whose rows are independent of one another and such that each row is sampled uniformly at random from the subset of vectors in {0,1}n having precisely d entries equal to 1. We present a short proof of the fact that P[det(Qn,d)=0]=O(n1/2log3/2nd)=o(1), whenever ω(n1/2log3/2n)=d≤n/2. In particular, our proof accommodates sparse random combinatorial matrices in the sense that d=o(n) is allowed. We also consider the singularity of deterministic integer matrices A randomly perturbed by a sparse combinatorial matrix. In particular, we prove that P[det(A+Qn,d)=0]=O(n1/2log3/2nd), again, whenever ω(n1/2log3/2n)=d≤n/2 and A has the property that (1,-d) is not an eigenpair of A.
https://doi.org/10.1016/j.disc.2022.113017
Reachability in arborescence packings. - In: Discrete applied mathematics, ISSN 1872-6771, Bd. 320 (2022), S. 170-183
Fortier et al. proposed several research problems on packing arborescences and settled some of them. Others were later solved by Matsuoka and Tanigawa and by Gao and Yang. The last open problem is settled in this article. We show how to turn an inductive idea used in the latter two articles into a simple proof technique that allows to relate previous results on arborescence packings. We prove that a strong version of Edmonds’ theorem on packing spanning arborescences implies Kamiyama, Katoh and Takizawa’s result on packing reachability arborescences and that Durand de Gevigney, Nguyen and Szigeti’s theorem on matroid-based packing of arborescences implies Király’s result on matroid-reachability-based packing of arborescences. Further, we deduce a new result on matroid-reachability-based packing of mixed hyperarborescences from a theorem on matroid-based packing of mixed hyperarborescences due to Fortier et al.. Finally, we deal with the algorithmic aspects of the problems considered. We first obtain algorithms to find the desired packings of arborescences in all settings and then apply Edmonds’ weighted matroid intersection algorithm to also find solutions minimizing a given weight function.
https://doi.org/10.1016/j.dam.2022.05.018
From microtiter plates to droplets - there and back again. - In: Micromachines, ISSN 2072-666X, Bd. 13 (2022), 7, 1022, S. 1-13
Droplet-based microfluidic screening techniques can benefit from interfacing established microtiter plate-based screening and sample management workflows. Interfacing tools are required both for loading preconfigured microtiter-plate (MTP)-based sample collections into droplets and for dispensing the used droplets samples back into MTPs for subsequent storage or further processing. Here, we present a collection of Digital Microfluidic Pipetting Tips (DMPTs) with integrated facilities for droplet generation and manipulation together with a robotic system for its operation. This combination serves as a bidirectional sampling interface for sample transfer from wells into droplets (w2d) and vice versa droplets into wells (d2w). The DMPT were designed to fit into 96-deep-well MTPs and prepared from glass by means of microsystems technology. The aspirated samples are converted into the channel-confined droplets’ sequences separated by an immiscible carrier medium. To comply with the demands of dose-response assays, up to three additional assay compound solutions can be added to the sample droplets. To enable different procedural assay protocols, four different DMPT variants were made. In this way, droplet series with gradually changing composition can be generated for, e.g., 2D screening purposes. The developed DMPT and their common fluidic connector are described here. To handle the opposite transfer d2w, a robotic transfer system was set up and is described briefly.
https://doi.org/10.3390/mi13071022
Good acyclic orientations of 4-regular 4-connected graphs. - In: Journal of graph theory, ISSN 1097-0118, Bd. 100 (2022), 4, S. 698-720
An st-ordering of a graph G=(V,E) is an ordering v1,v2,…,vn of its vertex set such that s=v1,t=vn and every vertex vi with i=2,3,…,n-1 has both a lower numbered and a higher numbered neighbor. Such orderings have played an important role in algorithms for planarity testing. It is well-known that every 2-connected graph has an st-ordering for every choice of distinct vertices s,t. An st-ordering of a graph G corresponds directly to a so-called bipolar orientation of G, that is, an acyclic orientation D of G in which s is the unique source and t is the unique sink. Clearly every bipolar orientation of a graph has an out-branching rooted at the source vertex and an in-branching rooted at the sink vertex. In this paper, we study graphs which admit a bipolar orientation that contains an out-branching and in-branching which are arc-disjoint (such an orientation is called good). A 2T-graph is a graph whose edge set can be decomposed into two edge-disjoint spanning trees. Clearly a graph has a good orientation if and only if it contains a spanning 2T-graph with a good orientation, implying that 2T-graphs play a central role. It is a well-known result due to Tutte and Nash-Williams, respectively, that every 4-edge-connected graph contains a spanning 2T-graph. Vertex-minimal 2T-graphs with at least two vertices, also known as generic circuits, play an important role in rigidity theory for graphs. Recently with Bessy and Huang we proved that every generic circuit has a good orientation. In fact, we may specify the roots of the two branchings arbitrarily as long as they are distinct. Using this, several results on good orientations of 2T-graphs were obtained. It is an open problem whether there exists a polynomial algorithm for deciding whether a given 2T-graph has a good orientation. Complex constructions of 2T-graphs with no good orientation were given in work by Bang-Jensen, Bessy, Huang and Kriesell (2021) indicating that the problem might be very difficult. In this paper, we focus on so-called quartics which are 2T-graphs where every vertex has degree 3 or 4. We identify a sufficient condition for a quartic to have a good orientation, give a polynomial algorithm to recognize quartics satisfying the condition and a polynomial algorithm to produce a good orientation when this condition is met. As a consequence of these results we prove that every 4-regular and 4-connected graph has a good orientation, where, as for generic circuits, we may specify the roots of the two branchings arbitrarily as long as they are distinct. We also provide evidence that even for quartics it may be difficult to find a characterization of those instances which have a good orientation. We also show that every graph on n≥8 vertices and of minimum degree at least has a good orientation. Finally we pose a number of open problems.
https://doi.org/10.1002/jgt.22803
Microtoxicology by microfluidic instrumentation: a review. - In: Lab on a chip, ISSN 1473-0189, Bd. 22 (2022), 14, S. 2600-2623
Microtoxicology is concerned with the toxic effects of small amounts of substances. This review paper discusses the application of small amounts of noxious substances for toxicological investigation in small volumes. The vigorous development of miniaturized methods in microfluidics over the last two decades involves chip-based devices, micro droplet-based procedures, and the use of micro-segmented flow for microtoxicological studies. The studies have shown that the microfluidic approach is particularly valuable for highly parallelized and combinatorial dose-response screenings. Accurate dosing and mixing of effector substances in large numbers of microcompartments supplies detailed data of dose-response functions by highly concentration-resolved assays and allows evaluation of stochastic responses in case of small separated cell ensembles and single cell experiments. The investigations demonstrate that very different biological targets can be studied using miniaturized approaches, among them bacteria, eukaryotic microorganisms, cell cultures from tissues of multicellular organisms, stem cells, and early embryonic states. Cultivation and effector exposure tests can be performed in small volumes over weeks and months, confirming that the microfluicial strategy is also applicable for slow-growing organisms. Here, the state of the art of miniaturized toxicology, particularly for studying antibiotic susceptibility, drug toxicity testing in the miniaturized system like organ-on-chip, environmental toxicology, and the characterization of combinatorial effects by two and multi-dimensional screenings, is discussed. Additionally, this review points out the practical limitations of the microtoxicology platform and discusses perspectives on future opportunities and challenges.
https://doi.org/10.1039/D2LC00268J
State of charge and state of health assessment of viologens in aqueous-organic redox-flow electrolytes using in situ IR spectroscopy and multivariate curve resolution. - In: Advanced science, ISSN 2198-3844, Bd. 9 (2022), 17, 2200535, S. 1-10
Aqueous-organic redox flow batteries (RFBs) have gained considerable interest in recent years, given their potential for an economically viable energy storage at large scale. This, however, strongly depends on both the robustness of the underlying electrolyte chemistry against molecular decomposition reactions as well as the device's operation. With regard to this, the presented study focuses on the use of in situ IR spectroscopy in combination with a multivariate curve resolution approach to gain insight into both the molecular structures of the active materials present within the electrolyte as well as crucial electrolyte state parameters, represented by the electrolyte's state of charge (SOC) and state of health (SOH). To demonstrate the general applicability of the approach, methyl viologen (MV) and bis(3-trimethylammonium)propyl viologen (BTMAPV) are chosen, as viologens are frequently used as negolytes in aqueous-organic RFBs. The study's findings highlight the impact of in situ spectroscopy and spectral deconvolution tools on the precision of the obtainable SOC and SOH values. Furthermore, the study indicates the occurrence of multiple viologen dimers, which possibly influence the electrolyte lifetime and charging characteristics.
https://doi.org/10.1002/advs.202200535