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HARNode: A Time-Synchronised, Open-Source, Multi-Device, Wearable System for Ad Hoc Field Studies
No full textHuman activity recognition (HAR) research often lacks accessi-
ble, comprehensive field data. Commercial systems are rarely open
source, hard to expand, and limited by issues like node synchro-
nisation, data throughput, unclear sensor placement, complexity,
and high cost. As a result, researchers typically use only a few
intuitively placed sensors and conduct limited field trials. HARN-
ode overcomes these challenges with a fully open-source hardware
and software platform. Each node includes an ESP32-S3 module
(AtomS3), a 9-axis IMU (Bosch BMX160), pressure and tempera-
ture sensors (Bosch BMP388), a display, and an I2C port. Data is
streamed via Wi-Fi, with NTP-based time synchronisation achiev-
ing 1 ms accuracy. The system runs for up to 8 hours and is built
using off-the-shelf parts, a simple online PCB service, and a com-
pact 3D-printed housing with Velcro straps, enabling flexible and
scalable body placement while requiring little hardware knowledge.
In a study with ten subjects wearing eleven HARNodes each, setup
took under five minutes per person. A random forest classifier dis-
tinguished walking from stair-climbing transitions, showing the
benefits of sensor-overprovisioning: Seven nodes achieved≈98%
accuracy, matching the performance of all eleven. These findings
confirm HARNode’s value as a fast-deploying, scalable tool for
field-based HAR research and optimised sensor placement
A Taxonomy of Collusion in Information Systems
No full textCollusion poses a pervasive threat to information systems (IS), undermining fairness, trust, and system integrity. Existing research, however, often focuses narrowly on specific cases or emphasizes either social or technical aspects, resulting in fragmented insights and limited generalizability. This narrow scope hampers the development of broadly effective protection strategies. Recognizing collusion as a sociotechnical phenomenon shaped by the interplay between social actors and technical artifacts, we developed a case-agnostic taxonomy that helps uncover and classify various forms of collusion in IS. Using an iterative approach, we synthesized insights from multidisciplinary academic literature and descriptive legal cases. Grounded in general systems theory, the taxonomy offers a robust structural foundation for analyzing collusion in IS. This taxonomy benefits practice by capturing the structural characteristics of collusion, enabling more systematic analysis, detection, and mitigation
Observable Semantics for Characterising Consistency Between Heterogeneous Models
No full textThe design of complex cyber-physical systems increasingly relies on heterogeneous, multi-domain models, each capturing different system aspects. As these models evolve independently, inconsistencies may arise. Such inconsistencies remain difficult to detect due to gaps between the modelling domains. We propose to bridge this gap by introducing a formal notion of observables, inspired by physics, as measurable system properties, such that every model can constrain the possible values of an observable. We define a semantic framework where observables induce consistency relations and show that any such relation can be expressed using suitable observable semantics. To capture realistic engineering scenarios, we extend the framework with meta-model spanning and compound observable semantics, enabling the modular construction of complex constraints. We also provide encodings of these observable semantics back into the original framework, preserving the original results and showing that extensions remain expressively equivalent to initial ones. Finally, we discuss some practical implications of our framework, namely how observables can support cross-domain communication, separation of concerns, and extensibility, allowing consistency requirements to evolve as part of the modelling process
Multi-component vaporisation: Tabulated distillation curve models for sustainable aviation fuels
No full textConventional kerosenes can currently be blended up to 50 % with certified sustainable aviation fuels from AtJ or HEFA processes in order to reduce the total carbon dioxide emissions from aviation. The blending changes the chemical and physical fuel properties, and it affects the vaporisation and combustion characteristics and hence the performance of jet engines. For an improved mathematical description of the vaporisation process, this study applied a new multi-component vaporisation approach to various blends of AtJ or HEFA fuels (10 %, 20 %, 30 %, 40 % and 50 %) with POSF-10325. The approach assumes uniform distributions of droplet temperature and droplet species concentrations and is based on tabulating a-priori computed numerical equilibrium distillation and physical property curves for isobaric conditions. Furthermore, single-droplet vaporisation simulations were employed to compare predictions based on tabulated distillation curves at both atmospheric and elevated pressures with predictions based on discrete components. The results show that tabulated distillation curves allow an accurate and efficient mathematical description of the vaporisation of sustainable aviation fuel blends. Therefore, models based on tabulated distillation curves are promising alternatives for surrogate, quasi-discrete component or continuous thermodynamics models and may be used for future CFD simulations of gas turbines
Research on the High-Energy Cosmic-Ray Anisotropies and Their Origins
No full textIn den letzten Jahrzehnten sind in der kosmischen Strahlungs-Physik mehrere offene Fragen deutlich geworden, insbesondere hinsichtlich des Ursprungs und der Beschleunigungsmechanismen hochenergetischer kosmischer Strahlung. Trotz verbesserter experimenteller Methoden bleiben die genauen Quellen von Teilchen mit Energien oberhalb des PeV-Bereichs unklar. Die Übergangsregion zwischen galaktischer und extragalaktischer kosmischer Strahlung – insbesondere um den Bereich des „Knies“ und des „Knöchels“ des Energiespektrums – wird weiterhin kontrovers diskutiert. Zudem ist der Einfluss galaktischer Magnetfelder auf die Ausbreitung und Anisotropien kosmischer Strahlung noch nicht vollständig verstanden. Die Lösung dieser Probleme ist entscheidend, um die grundlegenden Prozesse der Beschleunigung und Ausbreitung kosmischer Strahlung im Universum zu verstehen.
Kosmische-Strahlungs-Anisotropie ist ein weiterer wichtiger Aspekt zur Erklärung des Ursprungs kosmischer Strahlung und ihrer Bewegung im Raum. Anisotropien, die auf kleinen wie auch großen Skalen über verschiedene Energiebereiche hinweg beobachtet werden, liefern wertvolle Informationen über die Quellen kosmischer Strahlung und die Magnetfelder, die sie durchquert. Bei niedrigen Energien (unterhalb weniger TeV) werden großskalige Anisotropien wahrscheinlich durch die Verteilung naher Quellen und die Struktur des lokalen interstellaren Magnetfelds beeinflusst. Bei höheren Energien, insbesondere nahe dem „Knie“, werden die Anisotropien hingegen ausgeprägter und schwerer erklärbar, was auf komplexere Transportprozesse und mögliche nahe galaktische Quellen hinweist. Jenseits des „Knöchels“ nimmt die Anisotropie ab, was auf einen möglichen extragalaktischen Ursprung in diesem Bereich hindeutet, auch wenn dieser Übergang weiterhin untersucht wird. Zudem können kleinskalige Anisotropien, wie sie von Experimenten wie Tibet AS und IceCube beobachtet wurden, helfen, lokalisierte Quellen kosmischer Strahlung zu identifizieren und die Rolle der Turbulenz des Magnetfelds bei ihrer Ausbreitung zu beleuchten.
In dieser Dissertation wird zuerst die Empfindlichkeit des zukünftigen IceCube-Gen2-Oberflächenarrays für die Rekonstruktion der kosmischen Strahlungsanisotropie untersucht, und es wird gezeigt, dass IceCube-Gen2 wichtigen zusätzlichen Datenpunkten zum Gesamtbild beitragen wird. Anschließend optimiere ich analytische Methoden zur Rekonstruktion von Anisotropien der kosmischen Strahlung und zur Identifizierung signifikanter groß- und mittelskaliger Anisotropien oberhalb von in der Milchstraße. Die Empfindlichkeit der Daten für die Anisotropierekonstruktion wird zunächst mit traditionellen Methoden bewertet; anschließend werden mehrere optimierte Rekonstruktionsverfahren eingeführt, um statistische Einschränkungen zu überwinden und die Unsicherheiten in den rekonstruierten Dipolparametern zu verringern. Ein einheitliches Bild der kosmischen Strahlungsanisotropie wird durch die Kombination von Messungen großer Experimente gewonnen, die sich vom TeV-Bereich bis über EeV-Energien erstrecken. Dadurch ergibt sich eine kontinuierliche und globale Sicht auf die Entwicklung der Dipol-Anisotropien von galaktischen bis zu extragalaktischen Ursprüngen, wobei eine globale funktionale Anpassung der Dipolamplitude eine charakteristische „W-förmige“ Struktur zeigt. Aufgrund begrenzter Statistik bleibt jedoch die Dipolphase zwischen und unsicher. Insbesondere im Bereich von bis zeigen sich komplexe Phasenvariationen, insbesondere in den KASCADE-Grande-Daten. Die optimierten Methoden werden anschließend auf die KASCADE-Grande-Daten angewendet und zeigen Hinweise auf eine -Anisotropie bei , was auf Cygnus~OB2 als mögliche Quellregion hindeutet. Ausbreitungsstudien von Cygnus~OB2 zur Erde zeigen eine Übereinstimmung mit der beobachteten Anisotropie bei . Abschließend legt diese Dissertation nahe, dass Pulsarwindnebel (PWNe), die mit Supernovaüberresten (SNRs) assoziiert sind, als natürliche Beschleuniger galaktischer kosmischer Strahlen im PeV-Energiebereich wirken könnten und eine Erklärung für den Ursprung sowie die auf der Erde beobachteten Anisotropien liefern könnten
On the numerical discretization of a tumor progression model driven by competing migration mechanisms
No full textIn this work we explore a recently proposed biphasic cell-fluid chemotaxis-Stokes model which is able to represent two competing cancer cell migration mechanisms reported from experimental studies. Both mechanisms depend on the fluid flow but in a completely different way. One mechanism depends on chemical signaling and leads to migration in the downstream direction. The other depends on mechnical signaling and triggers cancer cells to go upstream. The primary objective of this paper is to explore an alternative numerical discretization of this model by borrowing ideas from [Qiao et al. (2020), M3AS 30]. Numerical investigations give insight into which parameters that are critical for the ability to generate aggressive cancer cell behavior in terms of detachment of cancer cells from the primary tumor and creation of isolated groups of cancer cells close to the lymphatic vessels. The secondary objective is to propose a reduced model by exploiting the fact that the fluid velocity field is largely dictated by the draining fluid from the leaky tumor vasculature and collecting peritumoral lymphatics and is more weakly coupled to the cell phase. This suggests that the fluid flow equations to a certain extent might be decoupled from the cell phase equations. The resulting model, which represents a counterpart of the much studied chemotaxis-Stokes model model proposed by [Tuval, et al. (2005), PNAS 102], is explored by numerical experiments in a one-dimensional tumor setting. We find that the model largely coincides with the original as assessed through numerical solutions computed by discrete schemes. This model might be more amenable for further explorations and analysis. We also investigate how to exploit the weaker coupling between cell phase dynamics and fluid dynamics to do more efficient calculations with fewer updates of the fluid pressure and velocity field
Improved Modeling of Gravity-Aided Spontaneous Imbibition Using Momentum-Equation-Based Relative Permeabilities
No full textIt is well known that relative permeabilities (RPs) can vary depending on the flow configuration and are lower during counter-current flow as compared to co-current flow.
In this paper we use a novel two-phase momentum-equation approach to generate effective RPs where this dependence (and others) is well captured whereby the fluids transfer momentum due to fluid-rock interaction and fluid-fluid interaction.
During co-current flow the faster moving fluid accelerates the slow fluid, but is itself decelerated, while for counter-current flow they are both decelerated.
We investigate recovery of oil from a matrix block surrounded by water due to a combination of gravity drainage (GD) and spontaneous imbibition (SI), relevant for fractured reservoirs.
In capillary-dominated systems the flow is counter-current and viscous coupling can result in increased time scale of the recovery process.
During gravity-dominated flow it is more co-current and applying co-currently measured relative permeabilities from the lab becomes a better assumption.
Using one set of parameters the momentum-equation approach is thus able to model the behavior of blocks of different operating at different Bond numbers in the reservoir
Numerical Investigation of Boundary Effects, Fluid Mobility, and Viscous Coupling in 2D Spontaneous Imbibition
No full textSpontaneous imbibition (SI) occurs in water-wet and mixed-wet porous media when capillary forces displace oil by water. In this work, we compare conventional modeling (using relative permeabilities) with application of a generalized model that includes viscous coupling (interphase drag) to investigate 2D matrix block imbibition. Boundary conditions were varied by opening surfaces to water or oil, and fluid viscosities were also adjusted. We report the oil recovery factor (RF) profiles and where the oil was produced, either from the water-exposed sides (countercurrent production) or oil-exposed sides (cocurrent production). Previous studies have not explored viscous coupling, mobilities, and their interplay with boundary conditions on production profiles, their distribution, and scaling. For water-wet cases, the imbibition rate increased as more matrix boundaries were opened to water or oil. Cocurrent imbibition was less efficient than countercurrent imbibition (0% oil area fraction) at early time (RF < 0.35), as higher water area fraction increased recovery (for same total open area). For intermediate mobility ratios, late time recovery (RF = 0.95) was achieved faster with cocurrent imbibition than countercurrent imbibition for an optimal oil area fraction of ~25%. However, at oil area fractions higher than 40% (45% for the generalized model), cocurrent imbibition took more time than countercurrent imbibition. At an unfavorable mobility ratio, the imbibition time was similar as for countercurrent imbibition up to 75% oil area. Favorable mobility ratio cases showed similar imbibition time up to 25% oil area, while higher oil area rapidly increased imbibition time. In the generalized model, viscous coupling increased the imbibition time when more of the production was countercurrent. For cases with the same open area and same areas exposed to water and oil, a more concentrated oil exposure gave slower recovery. Recovery scaled (increased) by water area for favorable mobility ratios and by total open area for unfavorable mobility ratios. Countercurrent production increased with higher mobility ratio and higher water area fraction; at high (unfavorable) mobility ratio, oil was produced equally from all open sides, and at low mobility ratio, oil was produced only from oil-exposed sides. More oil-wet cases had lower recovery, and the oil was produced more equally from all sides due to maintaining high oil mobility. Because water had low mobility for such states, the imbibition time increased when less open area was exposed to water (i.e., covering the full block with water was optimal)
Bipolar Hydrogen Production from a Hybrid Alkaline‐Acidic Formaldehyde‐Proton Fuel Cell
No full textDue to a positive standard reaction Gibbs free energy (ΔG) of 237.1 kJ mol, electric energy input is indispensable for hydrogen production by conventional electrochemical water splitting. This energy requirement can be reduced by replacing the anodic oxygen evolution reaction to thermodynamic favorable small-molecules oxidation reactions. In this work, anodic formaldehyde oxidation reaction (FOR) in alkaline media was paired with cathodic hydrogen evolution reaction (HER) in acidic media to establish a thermodynamically downhill system. The utilization of electrochemical neutralization energy in a hybrid alkaline-acidic electrolyte configuration enables a further decrease in ΔG. Therefore, the resulting hybrid alkaline-acidic formaldehyde-proton fuel cell (FPFC) exhibits a significantly reduced ΔG of −101.5 kJ mol. A bifunctional Ru-doped Cu catalyst (Ru─Cu NTs@CM) was designed and synthesized to simultaneously promote the kinetics of acidic HER and alkaline FOR, demonstrating superior catalytic activity and durability to pristine Cu and Ru catalysts. This catalyst enabled concurrent bipolar H production and electricity generation from the assembled FPFC, reaching a peak power density of 18.3 mW cm at 53.4 mA cm. A combination of (quasi) in situ characterizations and theoretical calculations unveiled the important mechanistic role of Ru-doping in enhancing the Cu catalyst\u27s activity and stability
