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Additive Manufacturing of Copper — A Survey on Current Needs and Challenges
No full textAdditive manufacturing (AM) of copper is subject to dynamic development regarding available processes and the quality of produced parts. While challenging, AM processes for copper provide parts with a quality comparable to other metallic material groups like steels. The reasons for the lower prevalence of additive manufacturing of copper components in industrial applications are currently not sufficiently researched, especially in light of the significant progress made in the maturity of this technology. A survey is used to investigate the assessments of protagonists in the field of copper AM. The needs of current and potential users of copper AM are analyzed and outlined. This study reveals that the most relevant technical limitation for users is the reduced surface quality of parts, while overall processes need to become less costly and more reliable to find broader use. Answers given hint to a higher degree of automation, the possibility of multi-material processing, and the upscaling of machine and part sizes as relevant future trends in the copper AM sector
Energy deposition of ultrashort laser pulses in polyvinyl chloride measured by two-color pump-probe shadowgraphy
No full textWe report on the energy deposition of ultrashort laser pulses with two different intensities of 6 TW cm⁻² and 143 TW cm⁻² in polyvinyl chloride, using two-color pump-probe shadowgraphy. The interaction is imaged during the pulse propagation into the medium and up to 200 μs after. The shadowgraphs show that higher-intensity pulses induce significantly more ionization of the material. Furthermore, it is shown that lower-intensity pulses propagate over the entire visible range of the shadowgraph without major losses, while higher-intensity pulses fade significantly after about 200 μs. After the interaction, pulses of both intensities produce a similar temperature-induced shadowgraphy pattern. The observations of the ionization process, the propagation of the pulse in the medium, and the thermalization are explained based on theory regarding ultrashort pulse laser interaction with dielectrics. Furthermore, the ablation craters produced by multiple consecutive pulses of both intensities are compared. The crater produced with lower-intensity pulses shows trails of material change significantly below the ablation crater, while these trails do not exist when using pulses with higher intensity. This is attributed to the differences in pulse propagation observed in the shadowgraphs of single pulses. This work demonstrates, for the first time, the intensity dependence of energy deposition of ultrashort laser pulses in polyvinyl chloride and its consequences for laser micromachining
Analyzing spectral distributions of charge transfer character in ensembles: a case study on the reaction center of photosystem II
No full textUnderstanding the primary charge separation events in Nature's photosynthetic reaction centers is a key step toward harnessing the microscopic processes of light conversion into chemical energy. Despite intense research efforts employing state-of-the-art spectroscopic and theoretical techniques, the precise nature of energy transfer and charge separation events in these systems are still insufficiently understood. Herein, we present a computational approach that enables analysis of the charge transfer character in excited electronic states with inclusion of thermal effects in ensembles. We showcase an application of this approach to the reaction center of photosystem II, focusing on the Chl_D1Pheo_D1 and P_D1P_D2 pairs of pigments. We find that the Chl_D1Pheo_D1 pair is a more likely candidate for the primary charge separation than the P_D1P_D2 pair. Our computational approach is transferable to other biological and man-made charge separation and charge transfer systems
Elastic prolate spheroidal inclusion in an infinite elastic solid—an exact analysis of the inclusion stress by an engineering treatment of the problem based on the corresponding cavity solutions
No full textThe paper demonstrates the analysis of the stress and strain states of an inhomogeneous structure with an axial symmetrical spheroidal inclusion in an infinite solid under a remote uniform tension load derived from the conditions of the theory of elasticity. With respect to the inhomogeneous structure, the deformations produce constraints that require a complete 3-dimensional analysis in the z, r-coordinate system. The solution generates the stress state of the inclusion and at the interface of the matrix. Spheroidal inclusions in an uniform outer tension stress field deform self-similarly to a rather elongated spheroid. With respect to the compatibility condition and depending on the different elastic moduli and Poisson’s ratios in the inclusion and matrix, the solution procedure leads to a system of two linear equations with the magnitudes of the two tractions as unknowns. In this way, the solution is shortened to a twofold statically indeterminate system. The analysis performed leads to an exact solution of the general spheroidal problem in a formulation of stress concentration factors considering the different stiffness parameters of inclusion and matrix
A Concept for Shared Control of Unmanned Aircraft Systems
No full textWith the rise of agile air mobility, combined with low operating costs and advanced autonomous technologies, unmanned aircraft systems (UAS) are increasingly being integrated into various industries, including transportation, agriculture, and media. Typically, UAS guidance is managed either by autonomous systems or pilots. Autonomous systems offer advantages like stability and quick responsiveness but may lack effective emergency handling. Conversely, pilots excel in environmental perception and adaptive learning but are susceptible to fatigue.
Inspired by this contradiction, the concept of shared control is introduced to harmonize these two control modes, leveraging their strengths while mitigating weaknesses. Following an extensive review of relevant literature, a rigorous definition of shared control for UAS operation is established, distinguishing it from assistant and filtering control methods.
Two real-world scenarios are selected to assess the feasibility of shared control. In the first scenario, collision avoidance, a comprehensive shared control system is developed. The pilot's control authority is dynamically allocated based on collision risk, seamlessly integrating commands from both the pilot and autonomous systems. Field experiments validate the system's effectiveness, while Monte Carlo simulations further demonstrate its ability to increase the probability of avoidance, revealing potential additional collision risks. Additionally, user experiments are conducted to evaluate user satisfaction with the system.
In the second scenario, aerial cinematography, a novel shared control method is developed based on optimal control methodologies. This approach incorporates a human input model and utilizes model predictive control techniques to build the shared control system. Through simulated flights, all intended functionalities are effectively realized. After completing the simulated aerial cinematography tasks, participants provide objective evaluations that align with anticipated satisfaction levels.
The next step involves exploring the applicability of shared control across various scenarios. Future shared control systems should also be optimized for seamless integration with autonomous systems that possess learning capabilities. Additionally, mitigating the potential risks associated with implementing shared control remains critical
Adapting the control of the magnetic bearings of a highly flexible and gyroscopic rotor to the excitations by the motor
No full textA test rig was built to perform fatigue tests on thick-walled cylinders made of fibre reinforced plastic (FRP). During the fatigue test, the rotational speed of an FRP cylinder is periodically varied until it fails. The FRP cylinder is connected to a drive spindle that accelerates and decelerates it using a permanent magnet synchronous machine (PMSM). To avoid excessive wear, the rotor is supported by active magnetic bearings (AMB). After the fatigue test was finished with the first cylinder, a new cylinder was attached to the test stand. With this new specimen, previously uncritical radial vibrations became more severe. For high accelerations, these vibrations led to instability of the rotor. However, high accelerations are desirable to perform the fatigue tests in the shortest possible time. Hence, the AMB control should be made insensitive to these vibrations. Since the vibrations depend on the acceleration of the rotor, it is reasonable to assume that they are induced by the PMSM. To reduce the vibrations, these excitations from the PMSM are included in the model-based controller parametrization process for the radial AMB, in which the parameters are adjusted via optimization. With the adjusted control, the amplitude of the vibration was significantly reduced and higher accelerations were possible. The described parameter tuning process can easily be adapted to different AMB systems with disturbances and changes in the system
A stochastic model of myeloid cell lineages in hematopoiesis and pathway mutations in acute myeloid leukemia
No full textA model for hematopoiesis is presented that explicitly includes the erythrocyte, granulocyte, and thrombocyte lineages and their common precursors. A small number of stem cells proliferate and differentiate through different compartments to produce the vast number of blood cells needed every day. Growth factors regulate the proliferation of cells dependent on the current demand. We provide a steady state analysis of the model and rough parameter estimates. Furthermore, we extend the model to include mutations that alter the replicative capacity of cells and introduce differentiation blocks. With these mutations the model develops signs of acute myeloid leukemia
Experimental investigation of combustion characteristics during oxygen carrier aided combustion of solid recovered fuel and coal in a 1 MWth circulating fluidized bed reactor
No full textThis presentation investigates results on oxygen carrier aided combustion (OCAC) of solid recovered fuel (SRF) and hard coal in a circulating fluidized bed (CFB) boiler, using ilmenite as bed material. In the OCAC process, the oxygen carrier (OC) is used as a bed material with the ability to incorporate and release oxygen, resulting in a decrease of local excesses or demands of oxygen. This effect has been proven to buffer combustion, which results in lower CO concentrations in the flue gas while at the same time allowing an increase in boiler load. During the test campaign described in this paper, a reduction of CO concentration of more than 70% has been measured. The NO concentration in the flue gas has shown varying results in different experiments. While there was a reduction in one case, increased NO values were found elsewhere, which are in line with the slight increase of up to 7 % during this test campaign. The pilot plant used to conduct the experiments has an inner diameter of 0.59 m, a height of 8.6 m, a thermal load of 1 MWth and a high operational flexibility. The combustion tests were performed using 100% SRF and a mixture of SRF and coal in the ratio of nearly 80/20 by heating value to investigate the combustion characteristics. It was found that even though an increase in SRF share shifts the combustion towards higher reactor region and lowers the pressure inside the reactor, stable operation can be maintained. The combustion conditions inside the reactor were investigated using two in-bed gas measurements, where the components O2, CO and CO2 are measured as horizontal profiles through the entire reactor width of 590 mm
Direct and indirect effects of ivermectin on phytophagous, prugivorous and parasitoid insects
No full textIvermectin, an anthelmintic used in livestock, is excreted in faeces and can therefore affect non-target organisms. While its effects on coprophagous insects have been well studied, recent research suggests that it can be taken up by plants, raising the possibility that it may affect a much wider range of invertebrates than previously known. Our study investigated the effects of ivermectin on insects from different feeding guilds. First, we tested its effects on the larvae of the noctuid moths Spodoptera frugiperda and Helicoverpa armigera (chewing herbivores) using an artificial diet. Secondly, we investigated the effects of its presence in the soil of pea plants Pisum sativum on the pea-feeding aphid Acyrthosiphon pisum (phloem-feeding herbivore). Thirdly, we tested ivermectin in an artificial diet for Drosophila melanogaster used as a host for the parasitoid Pachycrepoideus vindemmiae. Our results showed that ivermectin reduced pupal weight and survival in moth larvae, inhibited aphid colony establishment and reduced parasitoid emergence rates from ivermectin-exposed Drosophila pupae. These results highlight the potential of ivermectin to affect multiple trophic levels and emphasise the need for sustainable veterinary practices in the use of anthelmintics in free-ranging livestock and companion animals
Perfect-Prismatic F-Crystals and p-adic Shtukas in Families
No full textWe construct an equivalence between the two categories in the title, thus establishing a link between Frobenius-linear objects of formal (schematic) and analytic
(adic) nature. We will do this for arbitrary p-complete rings, for objects equipped
with an action by an arbitrary affine flat group scheme over Zp and without making
use of the Frobenius-linear structur