Showing papers by "Vienna University of Technology published in 2022"

Bell nonlocality in networks

Abstract: Bell's theorem proves that quantum theory is inconsistent with local physical models. It has propelled research in the foundations of quantum theory and quantum information science. As a fundamental feature of quantum theory, it impacts predictions far beyond the traditional scenario of the Einstein-Podolsky-Rosen paradox. In the last decade, the investigation of nonlocality has moved beyond Bell's theorem to consider more sophisticated experiments that involve several independent sources which distribute shares of physical systems among many parties in a network. Network scenarios, and the nonlocal correlations that they give rise to, lead to phenomena that have no counterpart in traditional Bell experiments, thus presenting a formidable conceptual and practical challenge. This review discusses the main concepts, methods, results and future challenges in the emerging topic of Bell nonlocality in networks.

High-performance water gas shift induced by asymmetric oxygen vacancies: Gold clusters supported by ceria-praseodymia mixed oxides

Abstract: Modifying and controlling sites at the metal/oxide interface is an effective way of tuning catalytic activity, beneficial for bifunctional catalysis by reducible oxide supported metal nanoparticles. We employed mixed ceria-praseodymia supported Au clusters for the water gas shift reaction (WGSR). Varying the Ce: Pr ratio (4:1, 2:1, 1:4) not only allows to control the number of oxygen vacancies but, even more important, their local coordination, with asymmetrically coordinated O# being most active for water activation. These effects have been examined by X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, temperature programmed desorption/reduction (TPD/TPR), and density functional theory (DFT). Using the WGSR performance of Au/CeOx as reference, Au/Ce4Pr1Ox was identified to exhibit the highest activity, with a CO conversion of 75% at 300°, which is about 5-times that of Au/CeOx. Au/Ce4Pr1Ox also showed excellent stability, with the conversion still being 70% after 50 h time-on-stream at 300 °. Although a higher Pr content leads to more O vacancies, the catalytic activity showed a “volcano behavior”. Based on DFT, this was rationalized via the formation energy of oxygen vacancies, the binding energy of water, and the asymmetry of the O# site. The presented route of creating active vacancy sites should also be relevant for other heterogeneous catalytic systems.

High-performance water gas shift induced by asymmetric oxygen vacancies: Gold clusters supported by ceria-praseodymia mixed oxides

Abstract: Modifying and controlling sites at the metal/oxide interface is an effective way of tuning catalytic activity, beneficial for bifunctional catalysis by reducible oxide supported metal nanoparticles. We employed mixed ceria-praseodymia supported Au clusters for the water gas shift reaction (WGSR). Varying the Ce: Pr ratio (4:1, 2:1, 1:4) not only allows to control the number of oxygen vacancies but, even more important, their local coordination, with asymmetrically coordinated O# being most active for water activation. These effects have been examined by X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, temperature programmed desorption/reduction (TPD/TPR), and density functional theory (DFT). Using the WGSR performance of Au/CeOx as reference, Au/Ce4Pr1Ox was identified to exhibit the highest activity, with a CO conversion of 75% at 300°, which is about 5-times that of Au/CeOx. Au/Ce4Pr1Ox also showed excellent stability, with the conversion still being 70% after 50 h time-on-stream at 300 °. Although a higher Pr content leads to more O vacancies, the catalytic activity showed a “volcano behavior”. Based on DFT, this was rationalized via the formation energy of oxygen vacancies, the binding energy of water, and the asymmetry of the O# site. The presented route of creating active vacancy sites should also be relevant for other heterogeneous catalytic systems.

Broadband laser-based mid-infrared spectroscopy employing a quantum cascade detector for milk protein analysis

Abstract: Mid-infrared chemical sensors based on quantum cascade technology offer a number of properties surpassing conventional spectrometric techniques. In this work, we combine a tunable quantum cascade laser with a spectrally tailored in-house fabricated quantum cascade detector (QCD) to realize broadband detection of aqueous samples for selective sensing of bovine milk proteins. The developed setup enables broadband spectroscopy covering more than 260 cm−1 and was employed to record absorbance spectra of the amide I and amide II bands of β-lactoglobulin, α-lactalbumin and casein. A detailed comparison indicates similar performance of the laser-based setup with its uncooled QCD as a high-end FTIR spectrometer equipped with a liquid nitrogen cooled mercury-cadmium-telluride (MCT) detector. Furthermore, we discuss the characteristics and benefits of the quantum cascade detector for application in laser-based mid-infrared sensor systems and compare its performance to other common mid-infrared detector types. In conclusion, the combination of QCDs with EC-QCLs opens up new possibilities for next-generation MIR liquid-phase chemical sensors featuring low noise and high dynamic range.

Additive manufacturing of aluminum nitride ceramics with high thermal conductivity via digital light processing

Abstract: Aluminum nitride (AlN) powder systems for additive manufacturing (AM) via digital light processing (DLP) were successfully developed, shaped by a DLP-based manufacturing technique, and sintered at 1700 °C. Properties of the AM parts were compared to reference samples consolidated via cold-isostatic pressing. AlN powders from two different manufacturers were used in the powder mixtures, underlining the flexibility of the process. Thorough process control was crucial for obtaining materials with a high degree of densification, exhibiting microstructural, thermal, and mechanical properties comparable to conventionally processed reference materials. Thermal conductivity of AM samples exceeded 160 W m−1 K−1, while flexural strength of AM samples varied between 320 and 498 MPa, depending on the orientation of specimens with respect to the building direction. The feasibility of this approach to generate complex-shaped parts was successfully shown by fabrication of crack-free demonstrator parts, highlighting prospective novel use cases in advanced heat management applications.

Three-DoF Vibration Compensation Platform for Robot-Based Precision Inline Measurements on Free-Form Surfaces

Abstract: This article presents a three-degree-of-freedom (DoF) magnetically levitated vibration compensating measurement platform (MP) with arbitrary operation orientation for robot-based surface inspection of free-forms. The MP design comprises an internal position sensor system, which is used in feedback control to maintain a free-floating position in six DoFs with respect to its supporting frame when approaching a sample (stabilization mode). In addition, the integrated design includes three tracking sensors measuring the out-of-plane position of the MP to a sample surface. The entire system can be mounted as an end-effector of an industrial robot with the MP carrying a desired measurement tool. Disturbing environmental vibrations are actively compensated by maintaining a constant position of the MP with respect to a sample surface (tracking mode). The control design includes single-input single-output position controllers for all DoFs, achieving a bandwidth of about 130 Hz. By means of a cross-fading error gain, an efficient control transition between stabilization and tracking mode is enabled. A vibrating target is used to evaluate the vibration compensation performance of the tracking module for standardized floor vibration profiles. Attenuation between 35 and 20 dB for out-of-plane vibrations below 40 Hz is achieved. In the time domain, vibration profiles with 15.7 $\mu$ m rms and 95 $\mu$ rad rms are reduced to 1.6 $\mu$ m rms and 21 $\mu$ rad rms, respectively.

High-resolution satellite products improve hydrological modeling in northern Italy

Abstract: Abstract. Satellite-based Earth observations (EO) are an accurate and reliable data source for atmospheric and environmental science. Their increasing spatial and temporal resolutions, as well as the seamless availability over ungauged regions, make them appealing for hydrological modeling. This work shows recent advances in the use of high-resolution satellite-based EO data in hydrological modeling. In a set of six experiments, the distributed hydrological model Continuum is set up for the Po River basin (Italy) and forced, in turn, by satellite precipitation and evaporation, while satellite-derived soil moisture (SM) and snow depths are ingested into the model structure through a data-assimilation scheme. Further, satellite-based estimates of precipitation, evaporation, and river discharge are used for hydrological model calibration, and results are compared with those based on ground observations. Despite the high density of conventional ground measurements and the strong human influence in the focus region, all satellite products show strong potential for operational hydrological applications, with skillful estimates of river discharge throughout the model domain. Satellite-based evaporation and snow depths marginally improve (by 2 % and 4 %) the mean Kling–Gupta efficiency (KGE) at 27 river gauges, compared to a baseline simulation (KGEmean= 0.51) forced by high-quality conventional data. Precipitation has the largest impact on the model output, though the satellite data on average shows poorer skills compared to conventional data. Interestingly, a model calibration heavily relying on satellite data, as opposed to conventional data, provides a skillful reconstruction of river discharges, paving the way to fully satellite-driven hydrological applications.

A field investigation on debris flows in the incised Tongde sedimentary basin on the northeastern edge of the Tibetan Plateau

Abstract: An investigation on 152 gullies along the Daheba River in the Tongde sedimentary basin was performed. Debris flows develop in gullies with an excess topography ZE, which represents the sediment availability, above a critical threshold value. Debris flows in the Daheba watershed are supply-unlimited, i.e sediment is abundantly available from the steep erodible gully banks. Debris flows consist of a head and a body. The body propagates faster than the head and constantly supplies it with sediment. The body and head propagate in an intermittent way through the transient storage of sediment on the riverbed and its subsequent remobilization. Although the main sediment supply is provided by bank collapse, debris-flow events also incise the gully bed. The growth and incision of debris-flow gullies in supply-unlimited watersheds is mainly controlled by the frequency of occurrence of debris flows, which is closely related to ZE. With growth of the gully drainage area, ZE and the debris-flow frequency initially increase, until they reach maximum values in gullies with a drainage area of intermediate size, which are assumed to be the morphologically most active gullies. With further growth of the gully drainage area, ZE and the debris-flow frequency decrease, which opposes the development of debris flows and leads to a more stable gully morphology.

Model based estimation of the SARS-CoV-2 immunization level in austria and consequences for herd immunity effects

Abstract: Several systemic factors indicate that worldwide herd immunity against COVID-19 will probably not be achieved in 2021. On the one hand, vaccination programs are limited by availability of doses and on the other hand, the number of people already infected is still too low to have a disease preventing impact and new emerging variants of the virus seem to partially neglect developed antibodies from previous infections. Nevertheless, by February 2021 after one year of observing high numbers of reported COVID-19 cases in most European countries, we might expect that the immunization level should have an impact on the spread of SARS-CoV-2. Here we present an approach for estimating the immunization of the Austrian population and discuss potential consequences on herd immunity effects. To estimate immunization we use a calibrated agent-based simulation model that reproduces the actual COVID-19 pandemic in Austria. From the resulting synthetic individual-based data we can extract the number of immunized persons. We then extrapolate the progression of the epidemic by varying the obtained level of immunization in simulations of an hypothetical uncontrolled epidemic wave indicating potential effects on the effective reproduction number. We compared our theoretical findings with results derived from a classic differential equation SIR-model. As of February 2021, [Formula: see text] of the Austrian population has been affected by a SARS-CoV-2 infection which causes a [Formula: see text] reduction of the effective reproduction number and a [Formula: see text] reduction of the prevalence peak compared to a fully susceptible population. This estimation is now recomputed on a regular basis to publish model based analysis of immunization level in Austria also including the fast growing effects of vaccination programs. This provides substantial information for decision makers to evaluate the necessity of non pharmaceutical intervention measures based on the estimated impact of natural and vaccinated immunization.

Liquid‐ and Solid‐based Separations Employing Ionic Liquids for the Recovery of Platinum Group Metals Typically Encountered in Catalytic Converters: A Review

Abstract: The wide application range and ascending demand for platinum group metals combined with the progressive depletion of their natural resources renders their efficient recycling a very important and pressing matter. Primarily environmental considerations associated with state-of-the-art recovery processes has shifted the focus of the scientific community towards the investigation of alternative recycling approaches. Within this context, ionic liquids have gained considerable attention in the last two decades chiefly sparked by properties such as tunabilty, low-volatility and relatively easy recyclability. In this review we will provide an understanding of the state-of-the-art processes, including their drawbacks and limitations. The core of the discussion is focused on platinum group metal recovery with ionic liquid-based systems. A brief insight in some environmental considerations related to ionic liquids is also provided while some discussion on research gaps, common misconceptions related to ionic liquids and outlook on unresolved issues could not be absent from this review.

A reduced basis method for fractional diffusion operators I

Abstract: Abstract We propose and analyze new numerical methods to evaluate fractional norms and apply fractional powers of elliptic operators. By means of a reduced basis method, we project to a small dimensional subspace where explicit diagonalization via the eigensystem is feasible. The method relies on several independent evaluations of $$({{\,\mathrm{I}\,}}-t_i^2\Delta )^{-1}f$$ ( I - t i 2 Δ ) - 1 f , which can be computed in parallel. We prove exponential convergence rates for the optimal choice of sampling points $$t_i$$ t i , provided by the so-called Zolotarëv points . Numerical experiments confirm the analysis and demonstrate the efficiency of our algorithm.