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Liquid metal droplet generation based on T-junction microchannels
No full textGalinstan liquid metal remains liquid at room temperature and exhibits unique physical properties including fluidity and high electrical conductivity, and its manipulation is a subject of extensive research interest. In contrast to existing control methods, such as electric and magnetic fields, we focus on a novel and efficient approach based on generating liquid metal droplets through microchannels. The present investigation mainly deals with generating liquid metal droplets through establishing a two-dimensional computational model based on the phase-field method for the droplet microfluidics in a T-junction structure. To enhance its performance, a constraint structure is added to expand the adjustment range of droplet formation. The constraint structure and increasing flow rate enhance the viscous shear effect, which reduces the droplet formation length and increases the generation frequency. Polymethyl methacrylate and pressure-sensitive adhesive are laser-cut to fabricate the microchannels. A peristaltic pump is utilized as the driving device, and a high-speed camera is employed to record the liquid metal droplet formation process. Both reducing the constraint ratio and increasing the flow ratio result in accelerated shear rate and increased droplet formation frequency, which is consistent with the simulation results. In experiments, the constraint structure enhanced the viscous shear effect, and relocation of the fracture location was observed. In addition, the high surface tension and inertia of the liquid metal released energy during droplet breakup, leading to noticeable oscillation and deformation of the droplet. Both the simulation and experimental results provide guidelines for the application of liquid metal generation in reconfigurable metasurfaces
Process Simulation of a Temperature Swing Absorption Process for Hydrogen Isotope Separation
Full text linkJoint Geometric and Probabilistic Constellation Shaping with MOKka
Full text linkMachine learning for optimization of the physical layer is currently a popular research topic. To aid research in this field, we introduce our Python library MOKka. We summarize the currently available signal processing modules in the library and explain our design rationale. In order to showcase the utility of this library, we have implemented a demo on joint geometric and probabilistic constellation shaping with a switchable channel model and interactive plotting and controls
Parameter Estimation in Adaptively Coupled Kuramoto Oscillators
Full text linkThe problem of joint state and parameter estimation for adaptively coupled Kuramoto oscillators consisting of the oscillator phases and coupling strengths is addressed, focusing on the analysis of underlying identifiability and observability properties required for convergence of the estimates. In particular, we focus on a solution provided by an Extended Kalman Filter, and characterize the state space in terms of regions for which local observability can be guaranteed - and thus the estimator should be able to reconstruct the actual state and parameter values - and those, in which local observability cannot be ensured. It turns out that trajectories typically cross through these regions several times. Furthermore, it is shown that for the case of oscillator phase locking local observability can not be guaranteed and an observer can at most estimate a ratio of parameters that characterizes the dynamics of the coupling strengths. The theoretical findings are illustrated for different scenarios using numerical simulation
Sub-GeV dark matter and nano-Hertz gravitational waves from a classically conformal dark sector
Full text linkStrong first-order phase transitions in a dark sector offer a compelling explanation for the stochastic gravitational wave background in the nano-Hertz range recently detected by pulsar timing arrays (PTAs). We explore the possibility that such a phase transition at the same time gives mass to a stable fermion that accounts for the observed dark matter abundance and leads to testable effects in laboratory experiments. Concretely, we consider a classically conformal dark sector with a hidden gauge symmetry that couples to the Standard Model via kinetic mixing. Since the PTA signal requires a phase transition in the MeV temperature range, spontaneous symmetry breaking gives rise to a sub-GeV dark matter candidate that couples to the Standard Model via a dark photon mediator and obtains its relic abundance via annihilations into electrons and dark Higgs bosons. Such a scenario is tightly constrained by laboratory searches for dark photons and cosmological constraints on the decays of dark Higgs bosons after the phase transition. We show that viable parameter regions can be found both for the case that the dark Higgs bosons remain in equilibrium with the Standard Model and that they decouple and only decay much later. In the latter case, the parameter regions preferred by the PTA signal and the dark matter relic abundance can be fully explored by future beam-dump experiments searching for missing energy
A self-sustainable service assembly for decentralized computing environments
Full text linkThe landscape of modern computing systems is shifting towards architectures built by combining available services under the “everything as a service” paradigm. These architectures are deployed on distributed cloud-edge infrastructures, aiming to provide innovative services to a wide range of users. However, it is crucial for these systems to address environmental sustainability concerns. This poses challenges in operating such systems in open, dynamic, and uncertain environments while minimizing their energy consumption. To tackle these challenges, we propose a decentralized service assembly approach that ensures the assembly is energetically self-sustainable by relying on locally harvested and stored energy. In our contribution, we introduce a general service selection template that enables the derivation of different selection policies. These policies guide the construction and maintenance of the service assembly. To evaluate their effectiveness in meeting the sustainability requirements, we conduct a comprehensive set of simulation experiments, providing valuable insights
LCA of the Pork Value Chain in Germany – Case Study of a German Slaughterhouse
Full text linkThe production of pork is a global environmental challenge, especially given its status as the most
widely consumed meat (Benton et al., 2023; Statista, 2023). The research project SPECK aims to
conduct a comprehensive life cycle assessment of pork production in Germany, the fourth-largest
pork producer in the world (FAO, 2023). This case study specifically focuses on the environmental
impacts of producing pork halves at a slaughterhouse. The results for the impact categories of
Global Warming Potential, Acidification, and Eutrophication are consistent with existing literature
(Dorca-Preda et al., 2021; González-Garcia et al., 2015; Reckmann et al., 2013). Notably,
slaughterhouse waste significantly impacts all categories. Furthermore, the production and use of
heat and power also contribute significantly to Global Warming Potential and Acidification
Ytterbium ions and color centers in silicon carbide as cavity-integrated quantum nodes with near-infrared optical transitions
Full text linkQuantentechnologien aller Art, wie Quantencomputer und Quantensensoren, entwickeln sich rasant fort. Daraus resultiert ein großes technologisches Bedürfnis, Quanteninformationen zwischen solchen lokalen Systemen über große Distanzen hinweg auszutauschen. Hierfür benötigt man effiziente Quanten-Netzwerkschnittstellen, die es erlauben Quanteninformationen auf Photonen zu übertragen. Optisch aktive Defektzentren und dotierte Ionen in Festkörpern sind ideale Kandidaten für solche Quanten-Netzwerkschnittstellen, da sie sowohl über einen langlebigen und kohärenten Spin-Freiheitsgrad, als auch kohärente optische Übergange verfügen. Um die optischen Übergänge effizient zu machen und auf diese Weise hohe Kommunikationsraten zu erzielen, müssen diese photonisch verstärkt werden. Dies kann durch die Kopplung an faserbasierte Fabry-Pérot Mikroresonatoren hoher Güte erzielt werden. Diese Arbeit untersucht die Eignung von Ytterbiumionen sowie Defektzentren in Siliziumkarbid als Quantennetzwerkschnittstellen in solch einer resonatorbasierten Geometrie. Zu Beginn werden Ytterbiumdotanden in nanoskaligen Kristallen spektroskopisch untersucht. Diese zeigen schmale Ensemble-Linienbreiten bei kryogenen Temperaturen. Mit Hilfe von Sättigungspektroskopie wurde zum ersten Mal für dieses Material eine Obergrenze für die optische Linienbreite eines einzelnen Ions von 5 MHz bestimmt. Zudem wurde gezeigt, dass sich diese Nanokristalle in einen faserbasierten Resonatoraufbau integrieren lassen, der optische Spektroskopie erlaubt.
Anschließend wurden die optischen Eigenschaften von Ytterbiumionen in verschiedenen organischen Molekülen charakterisiert. Diese unterscheiden sich teilweise deutlich voneinander. Durch einen systematischen Vergleich wurde versucht, diese Variationen durch die molekulare Struktur zu erklären. Insbesondere für die nichtradiative Zerfallsrate wurden dabei erste Korrelationen gefunden.
Schließlich wurden Experimente an Farbzentren in Siliziumkarbid in einem kryogenen Resonatorsystem durchgeführt. Dafür wurde eine wenige Mikrometer dicke Membran aus Siliziumkarbid in einen faserbasierten Hohlraumresonator integriert. Das Resonatorsystem wurde sorgfältig charakterisiert und für gut geeignet befunden, da nur minimale Verluste durch die Membran entstanden. Durch die hohe spektrale Selektivität des Resonator konnten die kohärenten Übergänge einzelner Farbzentren bei kryogenen Temperaturen aufgelöst werden, was durch Analyse der Photonenstatistik verifiziert wurde. Schließlich wurde die Purcell-Verstärkung anhand einer verstimmungsabhängigen Lebenszeitmessung bestimmt. Durch die Kopplung an den Resonator wird der kohärente Übergang eines einzelnen Farbzentrums bis zu 13-fach verstärkt, was zu einer hohen Rate an kohärenten Einzelphotonen führt
Role of Mg:Al ratio and Pt promotion on mitigating the deactivation of Ni-based methane steam reforming catalysts
No full textNi-based catalysts for CH steam reforming require fine tuning to withstand deactivation under dynamic operation conditions relevant to emerging H-driven technologies. This study investigates the impact of Mg:Al ratio and Pt presence in catalyst composition on the activity and stability of industrially relevant Ni-based mono- and bimetallic catalysts during simulated daily start-up and shut-down cycles in various gas atmospheres. The evolution of the catalyst structure during extensive testing procedures was investigated in detail by complementary electron microscopy, in situ/operando XAS and XRD. The results obtained revealed that the catalyst deactivation is promoted at high Mg:Al ratios and especially affects the monometallic catalysts. By converting CH at lower temperatures, Pt regulates Ni oxidation extent and its incorporation into MgO lattice. Further prevention of catalyst deactivation was achieved by optimizing the reactor shut-down procedure to minimize its simultaneous exposure to high temperatures and HO vapors. By flushing the reactor with N only around the reaction extinction temperature, a fraction of Ni species is maintained in metallic state, which is beneficial for the long-term activity and reaction operation economy