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Influence of disorder at insulator-metal interface on spin transport
No full textThe spin transport is carried by spin-polarized electrons in the metal and by magnons in the insulator. We compute the spin current in the presence of a spin accumulation in the metal, caused by the spin Hall effect, and a thermal gradient using Fermi's golden rule in the presence of interfacial disorder. For a perfectly clean interface, the in-plane momentum is conserved by the electron-magnon scattering events that govern the spin transport through the interface. We calculate how the disorder-induced broadening of scattering matrix elements with respect to the in-plane momentum influences the spin current. As a general result, we observe that, specifically for high temperatures, one should expect a rather small effect of interface disorder on the measured spin current, while for small temperatures there is a significant reduction of a spin current with increasing disorder
The role of pea protein content and carbohydrate molecular weight in the structure and stability of spray-dried emulsions
No full textWith increasing interest to replace dairy proteins in food products, questions of performance and stability of these alternatives rise. Plant-based proteins and carbohydrates that are used for dried emulsion systems, like plant-based milk or creamer powder, are expected to influence micro structure of final powders with further impact on storage stability. The aim of this work was to investigate the plant-based matrix, with focus on pea protein content and carbohydrate molecular weight, on spray-dried powder structure, fat distribution and oxidation stability of the bioactive component beta carotene. Spray-dried powders were produced from plant-based emulsions with varying protein content (2.4, 20% wt) and maltodextrin dextrose equivalent (DE 6, 21, 40). Both factors significantly impacted particle structure and free fat content of spray-dried powders. While the effect on structure and morphology did not follow clear trends, free fat differed greatly between powders (4.5–88.8%) and showed to increase with protein content and decreased maltodextrin DE. Beta carotene stability during storage followed similar trends, with highest retention after storage measured for coarse, low protein and maltodextrin DE 40 powder (37.9%), while poorest performance was found for powders with maltodextrin DE 6 (9.5–12.3%), independent of the protein content. The study showcases the high impact of carbohydrate molecular weight and plant proteins on structure and thus stability indicators of plant-based powders. For a sustainable substitution of dairy protein in food powders, these differences need to be considered during processing and production
Demonstration of a chemical recycling concept for polybutylene succinate containing waste substrates via coupled enzymatic/electrochemical processes
No full textChemical recycling of polymer waste is a promising strategy to reduce the dependency of chemical industry on fossil resources and reduce the increasing quantities of plastic waste. A common challenge in chemical recycling processes is the costly downstream separation of reaction products. For polybutylene succinate (PBS) no effective recycling concept has been implemented so far. In this work we demonstrate a promising recycling concept for PBS, avoiding costly purification steps. We developed a sequential process, coupling enzymatic hydrolysis of PBS with an electrochemical reaction step. The enzymatic step efficiently hydrolyses PBS in its monomers, succinic acid and 1,4-butanediol. The electrochemical step converts succinic acid into ethene as final product. Ethene is easily separated from the reaction solution as gaseous product, together with hydrogen as secondary product, while 1,4-butanediol remains in the aqueous solution. Both reaction steps operate in aqueous solvent and benign reaction conditions. Furthermore, the influence of electrolyte components on the electrochemical step was unraveled by applying molecular dynamic simulations. The final coupled process achieves a total ethene productivity of 91 μmol/cm2 over a duration of 8 hours, with 1110 μmol/cm2 hydrogen and 77 % regained 1,4-butanediol as valuable secondary products
Developing a climbing robot for stay cable maintenance with security and rescue mechanisms
No full textThe significance of climbing robotic systems for cable maintenance is escalating in both academic research and real-world applications. As these systems are poised for real-world deployment, it is imperative to develop security and rescue mechanisms that ensure robots' intrinsic safety and robustness in dealing with uncertainty factors. This study presents a novel cable climbing robot designed with a climbing platform, a robotic manipulator integrated with specialized maintenance tools, and a gripper to withstand dynamic loads and impacts from maintenance operations. In addition, we propose the variable-damping safe-landing mechanism, the rescue mechanism, and the fusible gripper mechanism to counteract substantial disturbances in worst-case scenarios. Extensive experiments have been conducted to evaluate the proposed robot and its security and rescue mechanisms. The cable climbing robot has a heavy-duty capacity of 45 kg and an obstacle-negotiation ability of 10 mm. It also demonstrated its capabilities in various maintenance tasks, such as cable inspection, grinding, or repair. The variable-damping safe-landing mechanism was tested, showing the maximum falling speed can decrease from 1 to 0.1 m/s to promise safety, and the falling time can increase from about 5 to 45 s. Meanwhile, the rescue mechanism successfully retrieved the trapped robot. The results demonstrate the capabilities of the cable climbing robot and the feasibility of using the security and rescue mechanisms for the climbing robotic system, which have implications that the cable climbing robot with security and rescue mechanisms is more reliable and can be deployed in the real world with greater confidence
New method for crack length determination in low-temperature DCB tests based on electrical capacitance
No full textThe double cantilever beam (DCB) test is a widely used method to evaluate interlaminar fractures in composite materials. However, conducting DCB tests at low temperatures reveals challenges, particularly in detecting and characterizing delaminations due to freezing of the specimen. This study proposes a novel approach to address this issue by employing capacitance measurements to identify and quantify delamination growth during DCB tests under low-temperature conditions. Different methods of evaluation are considered and compared in this paper. The results show that reliable results can be determined with the new measurement method and that the process is significantly less susceptible to human error than the usual evaluation methods. This work improves the accuracy and reliability of DCB tests under extreme environmental conditions and has the potential to support the development and application of composite materials in challenging environments like liquid hydrogen storage applications
Simple and general bounds on quantum random access codes
No full textRandom access codes are a type of communication task that is widely used in quantum information science. The optimal average success probability that can be achieved through classical strategies is known for any random access code. However, only a few cases are solved exactly for quantum random access codes. In this paper, we provide bounds for the fully general setting of n in-dependent variables, each selected from a d-imensional classical alphabet and encoded in a D-dimensional quantum system subject to an arbitrary quantum measurement. The bound recovers the exactly known special cases, and we demonstrate numerically that even though the bound is not tight overall, it can still yield a good approximation
Towards WebAssembly-based federated learning
No full textWebAssembly is a portable binary instruction format designed to serve as a compilation target for high-level languages. While originally developed to run performance-intensive applications directly in Web browsers, WebAssembly supports these days a number of different hardware platforms across the compute continuum. This makes it a promising option to run services for training and inference in Federated Learning. To the best of our knowledge, there have been only a few practical approaches to realize Federated Learning using WebAssembly. Therefore, in this paper, we present a framework to achieve this. Our prototypical implementation shows that WebAssembly-based Federated Learning applications are highly portable while providing acceptable runtime overhead during model training
N-Heterocyclic carbene vs. thiophene – chiral adsorption and unidirectional rotation on Au(111)
No full textN-Heterocyclic carbenes are highly effective ligands for anchoring functional organic molecules to metal surfaces and nanoparticles, facilitating the formation of self-assembled monolayers. However, their adsorption on surface is difficult to predict and control, and there is an ongoing debate on the geometry of NHC derivatives on gold surfaces and on the role of gold adatoms. We present two single molecules based on a benzimidazole NHC, one equipped with a thiophene substituent, and the other ending with a Br atom. By low temperature scanning tunneling microscopy we show that both molecules adsorb planar on Au(111) and are chiral on the surface. Our results indicate that in both cases a complex between NHC and a gold adatom is formed. Upon voltage pulses with the STM tip, both complexes move excited by inelastic tunneling electrons. For the derivative with thiophene, we observe a stepwise 60° unidirectional rotation around the S atom. The direction of rotation is determined by both the chirality and the position of the applied pulse. On the contrary, the NHC derivative without thiophene moves laterally on the surface. Adsorption, binding to gold atoms, and motion are discussed with the support of density functional theory calculations and image simulations
Approximate minimum tree cover in all symmetric monotone norms simultaneously
No full textWe study the problem of partitioning a set of n objects in a metric space into k clusters V1,...,Vk. The quality of the clustering is measured by considering the vector of cluster costs and then minimizing some monotone symmetric norm of that vector (in particular, this includes the ℓp-norms). For the costs of the clusters we take the weight of a minimum-weight spanning tree on the objects in Vi, which may serve as a proxy for the cost of traversing all objects in the cluster, for example in the context of Multirobot Coverage as studied by Zheng, Koenig, Kempe, Jain (IROS 2005), but also as a shape-invariant measure of cluster density similar to Single-Linkage Clustering.
This problem has been studied by Even, Garg, Könemann, Ravi, Sinha (Oper. Res. Lett., 2004) for the setting of minimizing the weight of the largest cluster (i.e., using ℓ∞) as Min-Max Tree Cover, for which they gave a constant-factor approximation algorithm. We provide a careful adaptation of their algorithm to compute solutions which are approximately optimal with respect to all monotone symmetric norms simultaneously, and show how to find them in polynomial time. In fact, our algorithm is purely combinatorial and can process metric spaces with 10,000 points in less than a second.
As an extension, we also consider the case where instead of a target number of clusters we are provided with a set of depots in the space such that every cluster should contain at least one such depot. One can consider these as the fixed starting points of some agents that will traverse all points of a cluster. For this setting also we are able to give a polynomial-time algorithm computing a constant-factor approximation with respect to all monotone symmetric norms simultaneously.
To show that the algorithmic results are tight up to the precise constant of approximation attainable, we also prove that such clustering problems are already APX-hard when considering only one single ℓp norm for the objective
Variants of Maker-Breaker games on complete and random graphs
No full textThis thesis studies two topics, both of which focus on different variants of positional games.
The first topic is the study of fast strategies in Waiter-Client games played on the edge set of the complete graph. We prove results for unbiased games, where the winning sets are perfect matchings, Hamilton cycles, pancyclic graphs, fixed spanning trees, or factors of a given graph. We also consider the biased versions of the perfect matching game and the Hamiltonicity game.
The second topic is the study of Connector-Breaker and Walker-Breaker games played on the edge set of a random graph. We prove bounds for the threshold probabilities for Walker's and Breaker's strategies.Diese Dissertation behandelt zwei verschiedene Varianten von Positional Games.
Die erste Variante sind schnelle Gewinnstrategien in Waiter-Client Games, die auf der Kantenmenge des vollständigen Graphen gespielt werden. Wir beweisen Resultate für unbiased sowie teilweise auch biased Games, bei denen die Gewinnmengen perfekte Matchings, Hamiltonkreise, pancyclische Graphen, festgelegte Spannbäume, oder Faktoren eines gegebenen Graphen sind.
Die zweite Variante sind Connector-Breaker und Walker-Breaker Games, die auf der Kantenmenge eines zufälligen Graphen gespielt werden. Wir beweisen Schranken für die Schwellenwertfunktionen der Strategien von Walker und Breaker