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An Alternative Scheme for Pionless EFT: Neutron-Deuteron Scattering in the Doublet S-Wave
No full textUsing the effective-range expansion for the two-body amplitudes may generate spurious sub-threshold poles outside of the convergence range of the expansion. In the infinite volume, the emergence of such poles leads to the breakdown of unitarity in the three-body amplitude. We discuss the extension of our alternative subtraction scheme for including effective range corrections in pionless effective field theory for spinless bosons to nucleons. In particular, we consider the neutron-deuteron system in the doublet S-wave channel explicitly
The Clash of the Policies: The Joint Effect of EU Cohesion Policy and Common Agricultural Policy on the Public Support for European Integration
No full textA vital element of the European Union (EU) political system is the idea of further European integration. Whilst most existing works investigate the effects of the Cohesion Policy (CP), only a handful of studies consider the effects of the Common Agricultural Policy (CAP) on citizens' support for European integration. In this contribution, I argue that these two largest EU redistribution policies neutralise each other in their effects on the citizens' support for European integration: the CP improves public support due to its positively perceived redistributive nature and positive externalities, whilst the CAP decreases public support due to due to a limited target audience, somewhat elitarian distribution of resources and bureaucratic complexities. Using regional‐level CP and CAP data for 2017 and Eurobarometer surveys for 2018 and 2019, the empirical findings of multilevel regressions show that the CAP counteracts the positive effects of the CP on citizens' support for further European integration. The findings are robust to including a wide range of control variables, sample size change and alternative specifications of key independent variables. These findings also hint that policy evaluations should not disregard the differences between various policy instruments
City-wide multi-user quantum key distribution network without trusted nodes
No full textIn recent years, research on quantum computing has accelerated and attracted many
efforts from around the world. If larger, operable quantum computers are built, several
current cryptography solutions could be compromised.
Quantum key distribution (QKD) promises a path to restore means for the generation
of symmetric keys between distant users. Its security is independent of the computational resources of an attacker, as the key generation relies on fundamental properties of quantum mechanics such as the no-cloning theorem or entanglement. Despite many research projects, the development of real-world-ready QKD systems remains a challenge.
In this work, a prototype of a fiber-based multi-user QKD system, utilizing a time-bin
variant of the BBM92 protocol, is for the first time extended to a city-wide network - the
Darmstadt Quantum Local Area Network (DaQLAN). The time-bin variant makes the
system independent of polarization changes on the transmission links, simplifying the
hardware requirements and strengthening the setup’s robustness. The network consists
of a central photon pair source and four users (receivers), each connected to the source.
The source does not yield information on the generated keys and is therefore an
untrusted node in the network. The photon pairs are generated via spontaneous parametric down-conversion, which features a several tens of nanometers wide spectrum, allowing the connection of many users via wavelength demultiplexing. In this work, the emission properties of the photon source were investigated. The photon emission shows Poissonian statistics, excellent coincidental-to-accidental ratios, and a vastly noise-free output. This was accompanied by some adaptations of the photon source hardware.
To set up the network, the receivers are spread over the city of Darmstadt, Hesse. Each
pair of users can utilize the photons generated from the source to generate a shared secret key, independent of the other user pairs. The network features user-to-user total link losses of up to 27 dB and up to 62 km length. The flexibility of the network is demonstrated by testing all available combinations of the four users. Furthermore, several parameters are tuned to optimize the resulting secure key rates. Depending on the links, asymptotic optimized secure key rates between roughly 7.8 bit s⁻¹ and 65.6 bit s⁻¹ were observed. As a proof-of-concept experiment, the system’s laser wavelength was changed to enable a straightforward scalability of up to 110 users in future experiments.
Post-processing describes the evaluation of the measurement data such that the secure
key is obtained at the end of the key generation process and is required as the imperfections cause errors, i.e., mismatches, on the keys. In contrast to earlier local field-test experiments, a complete post-processing stack suitable for distributed receivers was implemented during this thesis, featuring two options for error correction: Cascade and low-density parity-check codes. Furthermore, an alternative mode to find approximations of the quantum bit error rate is introduced and tested for the DaQLAN.
Real-world QKD systems are prone to several setup imperfections, which have to be
taken into account for the post-processing to prevent unwanted key leakage. For the setup presented here, for instance, detector dead time effects, detection efficiency mismatches, and the state of security proofs are discussed. Additionally, every QKD system requires an authenticated classical channel. This authentication step is often marginalized in experiments. Here, three different algorithms, each providing different properties such as speed, key consumption, and security claims, are integrated into the DaQLAN and tested during live operation. To the best of the author’s knowledge, these tests manifest the first time the message authentication code (MAC) Chaskey has been considered and implemented in a QKD system
Floating wind turbine anchor piles under lateral multidirectional cyclic loading: experimental investigation
No full textThe use of open-ended steel piles with catenary mooring lines is a promising solution for anchoring Floating Offshore Wind Turbines (FOWTs) to the seabed. These piles face complex loading conditions, especially in shared anchor configurations, where multiple turbines are anchored to a single pile. This shared anchor approach offers valuable opportunities for optimizing foundations and reducing costs. However, it also increases the severity of cyclic multidirectional loading on the pile, making it essential to accurately predict its response for design optimisation. As part of the GEOLAB project SAM-WT, large-scale experiments were conducted in the geotechnical test pit at the Technical University of Darmstadt. An instrumented model pile with a diameter of 0.325 m and an embedment depth of 2 m was installed in dense compacted sand, representing a real anchor pile at 1/5 scale. A series of lateral cyclic loading packages was applied to the pile, considering first unidirectional cyclic loading to compare with a subsequent multidirectional cyclic loading test. The load was carefully controlled using a pair of actuators connected to the pile via a mechanically articulated system. A range of sensors was installed to measure pile displacement, rotation and applied load at the pile head, as well as strain along the shaft of the pile, while fibre optic sensing was implemented in the surrounding soil to assess the strains around the pile. The analysis presented in this paper focuses on the horizontal displacement of the pile head during cyclic loading, highlighting the differences between unidirectional and multidirectional loading. The findings contribute to a better understanding of pile behaviour under varying loading conditions, supporting the development of more efficient anchor systems for FOWTs
On Modified Halpern and Tikhonov–Mann Iterations
No full textWe show that the asymptotic regularity and the strong convergence of the modified Halpern iteration due to T.-H. Kim and H.-K. Xu and studied further by A. Cuntavenapit and B. Panyanak and the Tikhonov–Mann iteration introduced by H. Cheval and L. Leuştean as a generalization of an iteration due to Y. Yao et al. that has recently been studied by Boţ et al. can be reduced to each other in general geodesic settings. This, in particular, gives a new proof of the convergence result in Boţ et al. together with a generalization from Hilbert to CAT(0) spaces. Moreover, quantitative rates of asymptotic regularity and metastability due to K. Schade and U. Kohlenbach can be adapted and transformed into rates for the Tikhonov–Mann iteration corresponding to recent quantitative results on the latter of H. Cheval, L. Leuştean and B. Dinis, P. Pinto, respectively. A transformation in the converse direction is also possible. We also obtain rates of asymptotic regularity of order O(1/n) for both the modified Halpern (and so in particular for the Halpern iteration) and the Tikhonov–Mann iteration in a general geodesic setting for a special choice of scalars
Assigning orders and pods to picking stations in a multi-level robotic mobile fulfillment system
No full textThis paper addresses the operational planning problem of assigning orders and pods (i.e., mobile shelves) to picking stations in a multi-level robotic mobile fulfillment system (RMFS), which deals with two issues: deciding on which picking station handles which order, and from which pods to pick the ordered items, considering the limited storage capacity of the pods. Due to the relatively poor space utilization of single-level RMFS warehouses, such systems are often spread over multiple floors in practice. Therefore, we explicitly consider multi-level warehouse layouts with isolated levels (or zones) where a pod can only be brought to a station if both of them are on the same level. We optimize the problem with regard to a multi-criteria objective function that consists of three workload-oriented objectives: we aim to balance the total workload among all pickers, minimize the total order-consolidation effort for the packers, and the pod movement effort for the mobile robots. After formalizing the planning problem as a multi-objective optimization problem, we provide two mixed-integer linear programming models. Additionally, we propose a matheuristic that reduces the model size to the desired granularity so that realistically sized problem instances can be solved within less than four minutes of computation time. Moreover, we derive some managerial insights, such as the impact of the number of warehouse levels and picking waves on the objective values. We find evidence that running the RMFS warehouse in a multi-level facility can substantially compromise the consolidation effort at packing stations since it leads to a higher number of split orders. Furthermore, splitting the planning horizon into multiple short waves can lead to a higher number of pod-to-station assignments and, thus, to a raised pod-movement workload for mobile robots
Influence of the Shear Process on the Compaction Success and Friction Behavior During Asphalt Paving
No full textAs part of this research, the shear process during asphalt paving with the paver screed was investigated in the laboratory. An extensive international literature search revealed that the influence of the shear process on the compaction success during asphalt paving has not been investigated to date. In addition, only limited data on the coefficient of friction between the asphalt mix and the screed plate exist from in-situ measurements. The investigations in the laboratory were carried out with a customized frame shear device of the Institute of Geotechnics at the Technical University of Darmstadt. The asphalt mix types AC 11 DS, SMA 11 DS and AC 16 BS (according to the German guideline TL Asphalt-StB) were used for this purpose. In addition, the influence of temperature changes and grading curve changes was investigated using the AC 11 DS asphalt mix. On the basis of the results, it was possible to prove for the first time that a significant increase in density takes place as a result of the shear process under constant normal stress. Where the influence on the compaction success depends on the asphalt composition. In addition, in-situ measurements could be validated based on determined sliding friction coefficients. The friction coefficients showed a material and temperature-dependent behavior
Prognosewettbewerb zu Pfählen unter lateraler monotoner und zyklischer Belastung in Sand
No full textDislocation-based high-temperature plasticity of polycrystalline perovskite SrTiO₃
No full textDislocation networks have been demonstrated to substantially enhance functional properties. As-sintered samples are virtually devoid of dislocations, new innovative techniques for introducing sufficiently high dislocation densities into polycrystalline ceramics are needed. While dislocation-based plasticity at high temperatures has been demonstrated for a large range of ceramic single crystals, plasticity in polycrystals is much less understood. Here, we demonstrate plastic strains in excess of several % based on dislocation motion in polycrystalline SrTiO₃ at ≈ 1100 °C with 3.9 µm grain size. Ultra-high voltage electron microscopy reveals an associated increase in dislocation density by three orders of magnitude. Achievable strain rates are comparable to creep-based mechanisms and much less sensitive to applied stress than observed for metals. A specialized testing protocol allows quantification of the deformability via stress exponent, activation volume and activation enthalpy giving additional quantification. In conjunction with TEM images, the mechanical data gives insight into the underlying mechanisms
Turning a blind eye on the black sheep: when are voters loyal to corrupt politicians?
No full textWhen do voters turn a blind eye on corrupt politicians? Recent research suggests that voters might be willing to support corrupt politicians due to a lack of a ‘viable and clean alternative,’ i.e., voters prefer supporting a corrupt politician when the alternative is to support a politician who takes a fundamentally different policy stance. Following this argument, it has also been argued that especially corrupt politicians from radical parties are less likely to be punished by their voters as these voters are more hostile toward other parties. In other words, voters of radical parties are more likely to lack viable alternatives. Based on a survey experiment conducted in Germany, we put these hypotheses to an empirical test. We find evidence for the expected patterns. Supporters of radical parties are indeed less likely to switch their vote to a different party. However, our experiment also shows that this is because voters of radical parties are more likely to lack a viable alternative. When supporters of radical parties evaluate a clean alternative favorable, they are just as likely as voters of mainstream parties to switch away from the corrupt candidate. Finally, we show how strengths of partisan attachment affect voting for corrupt candidates