Austrian Academy of Sciences (OeAW)
Recent publications
In this work, we present and analyze a system of PDEs, which models tumor growth by taking into account chemotaxis, active transport, and random effects. Tumor growth may undergo erratic behaviors such as metastases that cannot be predicted simply using deterministic models. Moreover, random perturbations are evident in models accounting for therapeutic treatment in terms of therapy uncertainty or parameter identification problems. The stochasticity of the system is modeled by Wiener noises that appear in the tumor and nutrient equations. The volume fraction of the tumor is governed by a stochastic phase-field equation of Cahn–Hilliard type, and the mass density of the nutrients is modeled by a stochastic reaction-diffusion equation. We allow a variable mobility function and nonincreasing growth functions, such as logistic and Gompertzian growth. Via approximation and stochastic compactness arguments, we prove the existence of a probabilistic weak solution and, in the case of constant mobilities, the well-posedness of the model in the strong probabilistic sense. Lastly, we propose a numerical approximation based on the Galerkin finite element method in space and the semi-implicit Euler–Maruyama scheme in time. We illustrate the effects of stochastic forcings in tumor growth in several numerical simulations.
The Page-Wootters formalism is a proposal for reconciling the background-dependent, quantum-mechanical notion of time with the background independence of general relativity. However, the physical meaning of this framework remains debated. In this work, we compare two consistent approaches to the Page-Wootters formalism to clarify the operational meaning of evolution and measurements with respect to a temporal quantum reference frame. The so-called "twirled observable" approach implements measurements as operators that are invariant with respect to the Hamiltonian constraint. The "purified measurement" approach instead models measurements dynamically by modifying the constraint itself. While both approaches agree in the limit of ideal clocks, a natural generalization of the purified measurement approach to the case of non-ideal, finite-resource clocks yields a radically different picture. We discuss the physical origin of this discrepancy and argue that these approaches describe operationally distinct situations. Moreover, we show that, for non-ideal clocks, the purified measurement approach yields a time non-local evolution equation, which can lead to non-unitary evolution. Moreover, it implies a fundamental limitation to the operational definition of the temporal order of events. Nevertheless, unitarity and definite temporal order can be restored if we assume that time is discrete.
Bi-phase interfacial engineering is an effective method for improving irradiation resistance, as interfaces play a critical role in defect generation and annihilation. In this work, molecular dynamics simulations are performed to investigate the evolution of the high entropy crystalline/amorphous laminates under ion irradiation. The effects of the crystalline/amorphous interface (ACI) on the distribution of point defects in the high entropy alloy (HEA) as well as on the microstructure evolution in metallic glass (MG) plates are investigated. During irradiation, fewer activated point defects were found in the HEA plate of the MG/HEA laminates compared to a free-standing HEA. In addition, the interface acts as a defect sink, accelerating the annihilation of interstitials at the interface. As a result, residual vacancies accumulate in the crystalline region following the first cascade, leading to a segregated distribution and an imbalance between the vacancies and interstitials in the HEA plate. Vacancy accumulation and clustering are responsible for the formation of stacking faults and complex dislocation networks in the HEA plate in the subsequent overlapping cascades. The interface also acts as a crystallization seed, accelerating the crystallization of the MG plate during irradiation process. However, the structural damage in the MG plate is mitigated by the redistribution of the free volume generated in the collision cascade zone, resulting in structural stability of the MG plate in the overlapping cascades.
A facile synthesis platform for the formation of stable single crystalline Ag dendrites is demonstrated. Using a porous electrospun polyacrylonitrile nanofiber network on Al foil as a template facilitates more uniform dendritic growth in the presence of D‐glucose. In contrast, a denser polymer network restricts the nucleation site availability on the Al foil, highlighting the critical role of the substrate. The growth formation of silver dendrites is reduced in the solution when two simultaneous processes occur: The electroreduction of Ag⁺ in the D‐glucose solution and galvanic displacement driven by the interaction of Ag⁺ with the aluminum substrate. High‐resolution transmission electron microscopy analysis shows the single crystalline nature of Ag dendrites grown from the Al substrate, revealing atomic structures with closely packed layers forming highly faulted face‐centered cubic and hexagonal close‐packed structures. The remarkable long‐term stability of Ag dendrites is primarily attributed to their single crystalline structure, with additional contributions from capping by D‐gluconic acid, as confirmed by Raman analysis. This novel approach to the generation of highly stable Ag dendrites has significant potential for applications such as surface‐enhanced Raman scattering, which has to date been considered to be very sensitive to environmental effects.
In these proceedings, the measurements of the Ξ⁻, Ξ¯⁺, Ω¯, Ω¯⁺ masses and the mass differences between particle and anti-particle have been measured in pp collisions collected by the ALICE Collaboration during LHC Run 2. The results significantly improve the precision from previous experiments, thus allowing direct tests of CPT symmetry to an unprecedented level of precision in the multi-strange baryon sector.
This article explores the connections between David Hume's theory of prejudice, present‐day theories of structural ignorance, and Hume's own racist attitudes. Charles Mills has identified certain types of ignorance, including racial ignorance, that result from social structures. Here, I argue that Hume can do something similar. Hume uses the concept of prejudice to theorize the misjudgment of someone based on their perceived membership of a certain group. Despite its seemingly individualist presentation in the Treatise , Hume's theory can, as a result of his deeply social view of the mind, be expanded to account for social‐structural influences on the formation of prejudices. In fact, in several places he himself develops such structural explanations. On the resulting picture, both his racism and his theory of prejudice are seen to play important roles in his philosophy.
Zusammenfassung Sowohl in der historischen Linguistik als auch in der Mediävistik treten gelegentlich Fälle von sprachlicher Ambiguität auf, die aus unterschiedlichen Gründen innerhalb der jeweiligen Disziplin zu entsprechenden Diskussionen über die angemessene Interpretation des jeweiligen Beleges führen. Ausgehend vom Forschungsstand zu sprachlicher Ambiguität am Beispiel der Ambiguität relationaler Adjektive beschäftigt sich der folgende Beitrag mit der Frage der Mehrdeutigkeit von Adjektiven im Althochdeutschen anhand einer Auswahl von Beispielen aus dem Referenzkorpus Altdeutsch (ReA), die zunächst aus formalen Gründen im Hinblick auf eine relationale und qualitative Lesart mehrdeutig sind und im Rahmen des Forschungsprojektes Relational Adjectives in the History of German (RAHiG; gefördert vom FWF, P32415) auf Basis einer speziell dafür entwickelten Methode ermittelt wurden. Im Beitrag sollen, ausgehend von der linguistischen Identifikation ambiger Beispiele, mit Hilfe literaturwissenschaftlicher Methodologie verschiedene Typen von Mehrdeutigkeit bei relationalen Adjektiven herausgearbeitet werden und hierbei die Rolle von sprachlichem vs. außersprachlichem Wissen diskutiert werden.
After a long-distance migration, Avars with Eastern Asian ancestry arrived in Eastern Central Europe in 567 to 568 ce and encountered groups with very different European ancestry1,2. We used ancient genome-wide data of 722 individuals and fine-grained interdisciplinary analysis of large seventh- to eighth-century ce neighbouring cemeteries south of Vienna (Austria) to address the centuries-long impact of this encounter1,2. We found that even 200 years after immigration, the ancestry at one site (Leobersdorf) remained dominantly East Asian-like, whereas the other site (Mödling) shows local, European-like ancestry. These two nearby sites show little biological relatedness, despite sharing a distinctive late-Avar culture3,4. We reconstructed six-generation pedigrees at both sites including up to 450 closely related individuals, allowing per-generation demographic profiling of the communities. Despite different ancestry, these pedigrees together with large networks of distant relatedness show absence of consanguinity, patrilineal pattern with female exogamy, multiple reproductive partnerships (for example, levirate) and direct correlation of biological connectivity with archaeological markers of social status. The generation-long genetic barrier was maintained by systematically choosing partners with similar ancestry from other sites in the Avar realm. Leobersdorf had more biological connections with the Avar heartlands than with Mödling, which is instead linked to another site from the Vienna Basin with European-like ancestry. Mobility between sites was mostly due to female exogamy pointing to different marriage networks as the main driver of the maintenance of the genetic barrier.
Nearshore bathymetric data are essential for assessing coastal hazards, studying benthic habitats and for coastal engineering. Traditional bathymetry mapping techniques of ship-sounding and airborne LiDAR are laborious, expensive and not always efficient. Multispectral and hyperspectral remote sensing, in combination with machine learning techniques, are gaining interest. Here, the nearshore bathymetry of southwest Puerto Rico is estimated with multispectral Sentinel-2 and hyperspectral PRISMA imagery using conventional spectral band ratio models and more advanced XGBoost models and convolutional neural networks. The U-Net, trained on 49 Sentinel-2 images, and the 2D-3D CNN, trained on PRISMA imagery, had a Mean Absolute Error (MAE) of approximately 1 m for depths up to 20 m and were superior to band ratio models by ~40%. Problems with underprediction remain for turbid waters. Sentinel-2 showed higher performance than PRISMA up to 20 m (~18% lower MAE), attributed to training with a larger number of images and employing an ensemble prediction, while PRISMA outperformed Sentinel-2 for depths between 25 m and 30 m (~19% lower MAE). Sentinel-2 imagery is recommended over PRISMA imagery for estimating shallow bathymetry given its similar performance, much higher image availability and easier handling. Future studies are recommended to train neural networks with images from various regions to increase generalization and method portability. Models are preferably trained by area-segregated splits to ensure independence between the training and testing set. Using a random train test split for bathymetry is not recommended due to spatial autocorrelation of sea depth, resulting in data leakage. This study demonstrates the high potential of machine learning models for assessing the bathymetry of optically shallow waters using optical satellite imagery.
Adrian Kent has recently presented a critique \cite{Kent} of our paper \cite{MGM} in which he claims to refute our main result: the measurement postulates of quantum mechanics can be derived from the rest of postulates, once we assume that the set of mixed states of a finite-dimensional Hilbert space is finite-dimensional. To construct his argument, Kent considers theories resulting from supplementing quantum mechanics with hypothetical ``post-quantum'' measurement devices. We prove that each of these theories contains pure states (i.e. states of maximal knowledge) which are not rays of the Hilbert space, in contradiction with the ``pure state postulate'' of quantum mechanics. We also prove that these alternatives violate the finite-dimensionality of mixed states. Each of these two facts separately invalidates the refutation. In this note we also clarify the assumptions used in \cite{MGM} and discuss the notions of pure state, physical system, and the sensitivity of the structure of the state space under modifications of the measurements or the dynamics.
Satellite laser ranging and space debris laser ranging are two closely related range measurement techniques with slightly different setups relying on different lasers. Satellite laser ranging measures light reflections of corner cube retro reflectors at mm-level range precision. Space debris laser ranging gathers diffuse reflections from the whole space debris object and offers a precision down to the sub meter-level. Within this work we show the usage of Megahertz lasers to combine the strengths of both systems within one setup. During the regular tracking schedule to scientific satellite laser ranging targets, specific space debris objects of interest can then be tracked without the need of making adaptions to the system. Megahertz satellite laser ranging measurements to the defunct Jason-2 satellite lead to a measurement precision down to a few μm when ranging to retro reflectors. Space debris laser ranging data reveals reflections from individual surfaces of the target and allows to draw conclusions on the rotational behavior.
Self-motion is an essential but often overlooked component of sound localisation. As the directional information of a source is implicitly contained in head-centred acoustic cues, that acoustic input needs to be continuously combined with sensorimotor information about the head orientation in order to decode to a world-centred frame of reference. When utilised, head movements significantly reduce ambiguities in the directional information provided by the incoming sound. In this work, we model human active sound localisation (considering small head rotations) as an ideal observer. In the evaluation, we compared human performance obtained in a free-field active localisation experiment with the predictions of a Bayesian model. Model noise parameters were set a-priori based on behavioural results from other studies, i.e., without any post-hoc parameter fitting to behavioural results. The model predictions showed a general agreement with actual human performance. However, a spatial analysis revealed that the ideal observer was not able to predict localisation behaviour for each source direction. A more detailed investigation into the effects of various model parameters indicated that uncertainty on head orientation significantly contributed to the observed differences. Yet, the biases and spatial distribution of the human responses remained partially unexplained by the presented ideal observer model, suggesting that human sound localisation is sub-optimal.
Quantum computers are now on the brink of outperforming their classical counterparts. One way to demonstrate the advantage of quantum computation is through quantum random sampling performed on quantum computing devices. However, existing tools for verifying that a quantum device indeed performed the classically intractable sampling task are either impractical or not scalable to the quantum advantage regime. The verification problem thus remains an outstanding challenge. Here, we experimentally demonstrate efficiently verifiable quantum random sampling in the measurement-based model of quantum computation on a trapped-ion quantum processor. We create and sample from random cluster states, which are at the heart of measurement-based computing, up to a size of 4 × 4 qubits. By exploiting the structure of these states, we are able to recycle qubits during the computation to sample from entangled cluster states that are larger than the qubit register. We then efficiently estimate the fidelity to verify the prepared states—in single instances and on average—and compare our results to cross-entropy benchmarking. Finally, we study the effect of experimental noise on the certificates. Our results and techniques provide a feasible path toward a verified demonstration of a quantum advantage.
Ice accretion causes significant energy losses and safety risks across various sectors. Recent research shows that liquid‐like surfaces (LLS) with ice‐shedding properties can be created by covalently attaching linear polymer chains onto smooth substrates with sufficient hydroxyl group densities. To expand the substrate scope for LLS, a novel system using non‐halogenated organosilanes attached to a commercial epoxy‐silicon (EpSi) coating is proposed. The EpSi layer, easily applied using simple methods, serves as a smooth intermediate layer (Ra = 0.94 nm and Rq = 0.76 nm). Air plasma activation increases hydroxyl density on EpSi, enabling LLS formation via simple immersion in an organosilane solution. The resulting coating exhibits low contact angle hysteresis (<10°), sliding angle (SA < 14°), and ice adhesion strength (τice < 20 kPa). Effective LLS is generated regardless of substrate type, coating thickness, or application method. The coating retains its slippery properties after exposure to harsh conditions, including icing/deicing cycles, organic solvents, and acidic environment. It is also highly transparent (Tave = 84.5%, t = 500 µm) with self‐cleaning and anti‐staining capabilities. This methodology broadens the substrate scope of LLS, offering a sustainable solution to ice accretion challenges.
We consider the Cauchy problem for a damped Euler–Maxwell system with no ionic background. For smooth enough data satisfying suitable so-called dispersive conditions, we establish the global in time existence and uniqueness of a strong solution that decays uniformly in time. Our method is inspired by the works of D. Serre and M. Grassin dedicated to the compressible Euler system.
The concept of “irreversibility” and its counterpart “reversibility” have become prominent in environmental and ecological research on human-induced changes, thresholds, climate tipping points, ecosystem degradation, and losses in the cryosphere and biosphere. Through a systematic literature review, we show that in these research fields, these notions are not only descriptive terms, but can have different semantic functions and normative aspects. The results suggest that, in the context of environmental and ecological research the concepts of irreversibility and reversibility have taken on additional usages in comparison to their contexts in theoretical thermodynamics and mechanics. Irreversible as a classification of anthropogenic environmental change can be used categorically, in the sense of a finite end, or relatively, i.e. on time or spatial scales of interest. Surprisingly, most of the analyzed scientific articles that use the terminology of (ir)reversibility substantively do not provide an explicit conceptualization or definition (74.7%). The research on potential (ir)reversibility of environmental change may affect the social and political willingness to bear the costs of interventions to mitigate or prevent undesirable environmental change. In particular, classifying a change as reversible or irreversible and determining the timescale(s) and spatial scale(s) involved has implications for policy and ecosystem management decisions, as suggested by its use in several high-level scientific and policy reports on ecosystem and climate change. Therefore, it is important to explicitly present a clear definition of irreversibility or reversibility for the readers from other fields, even if it could be the case that within a specific community an implicit definition was considered to be sufficient. We propose further recommendations for inter- and transdisciplinary reflection and conceptual use in the context of environmental, ecological, and sustainability research.
The paper presents the results of the ParlaMint II project, which comprise comparable corpora of parliamentary debates of 29 European countries and autonomous regions, covering at least the period from 2015 to 2022, and containing over 1 billion words. The corpora are uniformly encoded, contain rich metadata about their 24 thousand speakers, and are linguistically annotated up to the level of Universal Dependencies syntax and named entities. The paper focuses on the enhancement made since the ParlaMint I project and presents the compilation of the corpora, including the encoding infrastructure, use of GitHub, the production of individual corpora, the common pipeline for producing their distribution, and use of CLARIN services for dissemination. It then gives a quantitative overview of the produced corpora, followed by the qualitative additions made within the ParlaMint II project, namely metadata localisation, the addition of new metadata, such as the political orientation of political parties, the machine translation of the corpora to English and its tagging with semantic classes, and the production of pilot speech corpora. Finally, outreach activities and further work are discussed.
Plasma flows with enhanced dynamic pressure, known as magnetosheath jets, are often found downstream of collisionless shocks. As they propagate through the magnetosheath, they interact with the surrounding plasma, shaping its properties, and potentially becoming geoeffective upon reaching the magnetopause. In recent years (since 2016), new research has produced vital results that have significantly enhanced our understanding on many aspects of jets. In this review, we summarise and discuss these findings. Spacecraft and ground-based observations, as well as global and local simulations, have contributed greatly to our understanding of the causes and effects of magnetosheath jets. First, we discuss recent findings on jet occurrence and formation, including in other planetary environments. New insights into jet properties and evolution are then examined using observations and simulations. Finally, we review the impact of jets upon interaction with the magnetopause and subsequent consequences for the magnetosphere-ionosphere system. We conclude with an outlook and assessment on future challenges. This includes an overview on future space missions that may prove crucial in tackling the outstanding open questions on jets in the terrestrial magnetosheath as well as other planetary and shock environments.
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763 members
Viktor Johannes Bruckman
  • Commission for Interdisciplinary Ecological Studies
Michael Nentwich
  • Institute of Technology Assessment
René Fries
  • Institute of Technology Assessment
Helge Torgersen
  • Institute of Technology Assessment
Michael Ornetzeder
  • Institute of Technology Assessment
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Address
Vienna, Austria
Head of institution
President Univ.-Prof. Dr. phil. Heinz Faßmann