TU Wien
  • Vienna, Vienna, Austria
Recent publications
This paper presents a method for determining the performance of shuttle-based storage and retrieval systems (SBS/RS) with tier-captive, single-aisle shuttles serving tiers of multiple-deep storage and using a class-based storage policy. This approach is used in the design process of SBS/RS and in the upgrading process of existing SBS/RS. With this approach, it is possible to evaluate the improvement in the performance of multiple-deep storage system by applying a class-based storage policy. The basis of this calculation method is a continuous-time, open-queueing system with limited capacity. The cycle times of lifts and shuttles, as determined by a spatial value approach, combined with a probability-based approach to mention the storage policy. To take the multiple-deep storage into account, another probability-based approach is applied. A European material handling provider had given the data used in this publication. Through an example, the influences of the storage policy and the storage depth are depicted.
Magnetoelectric phenomena are intimately linked to relativistic effects and also require the material to break spatial inversion symmetry and time-reversal invariance. Magnetoelectric coupling can substantially affect light–matter interaction and lead to non-reciprocal light propagation. Here, we confirm on a fully experimental basis, without invoking either symmetry-based or material-specific assumptions, that the optical magnetoelectric effect in materials with non-parallel magnetization ( M ) and electric polarization ( P ) generates a trilinear term in the refractive index, δ n ∝ k ⋅ ( P × M ), where k is the propagation vector of light. Its sharp magnetoelectric resonances in the terahertz regime, which are simultaneously electric and magnetic dipole active excitations, make Co 2 Mo 3 O 8 an ideal compound to demonstrate this fundamental relation via independent variation of M , P , and k . Remarkably, the material shows almost perfect one-way transparency in moderate magnetic fields for one of these magnetoelectric resonances.
Objective To assess the biomechanical effects of different prosthetic/implant configurations and load directions on 3-unit fixed prostheses supported by short dental implants in the posterior mandible using validated 3-D finite element (FE) models. Methods Models represented an atrophic mandible, missing the 2nd premolar, 1st and 2nd molars, and rehabilitated with either two short implants (implant length-IL = 8 mm and 4 mm) supporting a 3-unit dental bridge or three short implants (IL = 8 mm, 6 mm and 4 mm) supporting zirconia prosthesis in splinted or single crowns design. Load simulations were performed in ABAQUS (Dassault Systèmes, France) under axial and oblique (30°) force of 100 N to assess the global stiffness and forces within the implant prosthesis. Local stresses within implant/prosthesis system and strain energy density (SED) within surrounding bone were determined and compared between configurations. Results The global stiffness was around 1.5 times higher in splinted configurations vs. single crowns, whereby off-axis loading lead to a decrease of 39%. Splinted prostheses exhibited a better stress distribution than single crowns. Local stresses were larger and distributed over a larger area under oblique loads compared to axial load direction. The forces on each implant in the 2-implant-splinted configurations increased by 25% compared to splinted crowns on 3 implants. Loading of un-splinted configurations resulted in increased local SED magnitude. Conclusion Splinting of adjacent short implants in posterior mandible by the prosthetic restoration has a profound effect on the magnitude and distribution of the local stress peaks in peri-implant regions. Replacing each missing tooth with an implant is recommended, whenever bone supply and costs permit.
Aim There is a growing literature analyzing money laundering and the policies to fight it, but the overall effectiveness of anti-money laundering policies is still unclear. This paper investigates whether anti-money laundering policies affect the behavior of money launderers and their networks. Method With an algorithm to match clusters over time, we build a unique dataset of multi-mode, undirected, binary, dynamic networks of natural and legal persons. The data includes ownership and employment relations and associated financial ties and is enriched with criminal records and police-related activities. The networks of money launderers, other criminals, and non-criminal individuals are analyzed and compared with temporal social network analysis techniques and panel data regressions on centrality measures, transitivity and assortativity indicators, and levels of constraint. Findings We find that after the announcement of the fourth EU anti-money laundering directive in 2015, money laundering networks show a significant increase in the use of foreigners and corporate structures. At the individual level, money launderers become more dominant in criminal clusters (increased closeness centrality). This paper shows that (the announcement of) anti-money laundering policies can affect criminal networks and how such effects can be tested.
Polaron defects are ubiquitous in materials and play an important role in many processes involving carrier mobility, charge transfer and surface reactivity. Determining small polarons’ spatial distributions is essential to understand materials properties and functionalities. However, the required exploration of the configurational space is computationally demanding when using first principles methods. Here, we propose a machine-learning (ML) accelerated search that determines the ground state polaronic configuration. The ML model is trained on databases of polaron configurations generated by density functional theory (DFT) via molecular dynamics or random sampling. To establish a mapping between configurations and their stability, we designed descriptors modelling the interactions among polarons and charged point defects. We used the DFT+ML protocol to explore the polaron configurational space for two surface-systems, reduced rutile TiO 2 (110) and Nb-doped SrTiO 3 (001). The ML-aided search proposes additional polaronic configurations and can be utilized to determine optimal polaron distributions at any charge concentration.
The construction sector consumes high amounts of resources and energy while generating significant amounts of waste. This development is contrary to Circular Economy principles, which require buildings that are resource and energy efficient and enable material recycling to the greatest possible extent. To effectively tackle this problem, the EU places a strong focus on sustainable building design. However, to assess this development, indicators that measure the potential recyclability of buildings already at the design stage are necessary. In this study, the “Relative product-inherent recyclability” (RPR) assessment method is applied to evaluate the recyclability of buildings. The RPR method considers buildings’ material composition and structure (assembly) to measure recyclability, thereby describing recycling-relevant factors. The method is based on the statistical entropy approach, which aims to describe material distributions. The RPR increases the more building parts can be disassembled, allowing recovery of concentrated materials. A case study on a timber and concrete building is used to demonstrate the applicability of the RPR metric. The results show that the RPR metric is a suitable indicator for expressing buildings’ inherent recyclability, thus identifying significant differences between building variants. Relevant design optimizations can be deduced from the RPR results. In our case, the timber building achieves higher recyclability than the concrete building. Applying the RPR indicator on the EU level can be recommended and offers significant insights into the design and recyclability of buildings. Architects and constructors could use the metric as a planning and evaluation tool, thereby promoting circular building design concepts.
Modified atmosphere packaging (MAP) comprises a multilayer structure of polymers and adhesives offering excellent protection to food products. While this widely used structure improves shelf life, its recyclability is restricted by polymer incompatibilities and difficulty separating individual layers during sorting, which limits the viability of this prominent waste stream for 2030 European Union (EU) reuse and recycling targets. This study assessed the recycling potential of MAPs by system part and functional layer based on composition, component miscibility and temperature and incompatibility induced changes in physical and mechanical properties. Lids and trays alone exhibited similar compositions, but when combined their PET (polyethylene terephthalate)-PE (polyethylene) ratios varied considerably resulting in embrittlement and reduced toughness indicating limited compatibility and recyclability. Although PET-PE immiscibility resulted in phase separation causing inhomogeneity induced loss in ductility and toughness, barrier structures exhibited better phase adhesion and more homogeneous morphologies. Nonetheless, the PET dictated processing temperature, greatly exceeding that of PE, promoted cross-linking effects. The barrier and carrier layers of current MAPs must be delaminated within waste sorting processes to be recyclable. More economic and ecological recycling of MAPs to meet EU targets will require designs with more compatible polymer components.
We are interested in the quantitative analysis of the compaction ratio for two classical families of trees: recursive trees and plane binary increasing trees. These families are typical representatives of tree models with a small depth. Once a tree of size n is compacted by keeping only one occurrence of all fringe subtrees appearing in the tree the resulting graph contains only nodes. This result must be compared to classical results of compaction in the families of simply generated trees, where the analogous result states that the compacted structure is of size of order . The result about the plane binary increasing trees has already been proved, but we propose a new and generic approach to get the result. Finally, an experimental study is presented, based on a prototype implementation of compacted binary search trees that are modeled by plane binary increasing trees.
The influence of friction on machining processes as a function of pressure, velocity and temperature is neither deeply understood nor sufficiently definable for Finite-Element-Method (FEM) simulations. Current simulations therefore often use constant values for the friction coefficients. In this work, friction coefficients for SAE 1045 are determined from different tribometers. An empirical model is subsequently fit to the data and used in different FEM-tools to simulate orthogonal cutting. Results are compared to corresponding experiments. A final evaluation of the model reveals the challenges due to the elasto-plastic contact and thus the derivation and utilisation of such a model.
We study the combinatorial structure of the irreducible characters of the classical groups GLn(C), SO2n+1(C), Sp2n(C), SO2n(C) and the “non-classical” odd symplectic group Sp2n+1(C), finding new connections to the probabilistic model of Last Passage Percolation (LPP). Perturbing the expressions of these characters as generating functions of Gelfand-Tsetlin patterns, we produce two families of symmetric polynomials that interpolate between characters of Sp2n(C) and SO2n+1(C) and between characters of SO2n(C) and SO2n+1(C). We identify the first family as a one-parameter specialization of Koornwinder polynomials, for which we thus provide a novel combinatorial structure; on the other hand, the second family appears to be new. We next develop a method of Gelfand-Tsetlin pattern decomposition to establish identities between all these polynomials that, in the case of irreducible characters, can be viewed as branching rules. Through these formulas we connect orthogonal and symplectic characters, and more generally the interpolating polynomials, to LPP models with various symmetries, thus going beyond the link with classical Schur polynomials originally found by Baik and Rains (Duke Math. J., 2001). Taking the scaling limit of the LPP models, we finally provide an explanation of why the Tracy-Widom GOE and GSE distributions from random matrix theory admit formulations in terms of both Fredholm determinants and Fredholm Pfaffians.
Covid-19 is an infectious disease associated with cytokine storms and derailed sympathovagal balance leading to respiratory distress, hypoxemia and cardiovascular damage. We applied the auricular vagus nerve stimulation to modulate the parasympathetic nervous system, activate the associated anti-inflammatory pathways, and reestablish the abnormal sympatho-vagal balance. aVNS is performed percutaneously using miniature needle electrodes in ear regions innervated by the auricular vagus nerve. In terms of a randomized prospective study, chronic aVNS is started in critical, but not yet ventilated Covid-19 patients during their stay at the intensive care unit. The results show decreased proinflammatory parameters, e.g. a reduction of CRP levels by 32% after 1 day of aVNS and 80% over 7 days (from the mean 151.9mg/dl to 31.5mg/dl) or similarly a reduction of TNFalpha levels by 58.1% over 7 days (from a mean 19.3 pg/ml to 8.1 pg/ml) and coagulation parameters, e.g. reduction of DDIMER levels by 66% over 7 days (from a mean 4.5 μg/ml to 1.5 μg/ml) and increased anti-inflammatory parameters, e.g. an increase of IL-10 levels by 66% over 7 days (from the mean 2.7 pg/ml to 7 pg/ml) over the aVNS duration without collateral effects. aVNS proved to be a safe clinical procedure and could effectively supplement treatment of critical Covid-19 patients while preventing devastating over-inflammation.
Based on the principle of virtual power, equilibrium conditions are established for the forces within a cross section of a tunnel top heading driven according the New Austrian Tunneling Method (NATM). External forces, namely impost actions and ground pressure distributions following a third-order polynomial, are analytically linked with internal forces, such as axial forces and bending moments, arising as integrals over the shell thickness, of circumferential normal stresses. The latter are related, via an aging viscoelastic shotcrete material model, to circumferential normal strains, as well as to radial and circumferential displacement components. This allows for analytical transformation of displacement measurement data collected at the crown and the footings of the shell segment, into ground pressure and impost action evolutions, together with all the associated force and stress quantities. For the Sieberg tunnel, driven in Miocene clay marl, our data-driven analytical mechanics model evidences virtually uniform ground pressure distributions, leading to a first rapidly increasing, and then mildly decreasing utilization degree of the shotcrete shell.
Many difficulties are encountered during evacuation from construction sites in hazardous situations, which may lead to severe fatalities. These fatalities, especially caused by fire, may be significantly reduced by ensuring personal protective equipment (PPE) compliance of construction site workers and fire detection through proper surveillance. Thus, the detection of PPEs, fire and injured or trapped persons, can greatly assist in the reduction of fatalities and economic loss. This article presents a novel approach towards the detection of fire and PPEs to assist in the monitoring and evacuation tasks. This work utilizes the YOLOv4 and YOLOv4-tiny algorithms based on deep learning for carrying out the detection task. A self-made dataset has been utilized to train the model in the Darknet neural network framework. Moreover, a comparative analysis with previous works has been carried out in order to endorse the real-time efficacy of the proposed work. The results verify the strength of YOLOv4 algorithm in real-time detection and surveillance at construction sites with maximum mean average precision (mAP) of 76.86 %.
We present new probabilistic and combinatorial identities relating three random processes: the oriented swap process (OSP) on n particles, the corner growth process, and the last passage percolation (LPP) model. We prove one of the probabilistic identities, relating a random vector of LPP times to its dual, using the duality between the Robinson–Schensted–Knuth and Burge correspondences. A second probabilistic identity, relating those two vectors to a vector of “last swap times” in the OSP, is conjectural. We give a computer‐assisted proof of this identity for n≤6 after first reformulating it as a purely combinatorial identity, and discuss its relation to the Edelman–Greene correspondence. The conjectural identity provides precise finite‐n and asymptotic predictions on the distribution of the absorbing time of the OSP, thus conditionally solving an open problem posed by Angel, Holroyd, and Romik.
A review of the phenomenology and microscopy of cuprate superconductors is presented, with particular attention to universal conductance features, which reveal the existence of two electronic subsystems. The overall electronic system consists of 1+p\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1+p$$\end{document} charges, where p is the doping. At low dopings, exactly one hole is localized per planar copper–oxygen unit, while upon increasing doping and temperature, the hole is gradually delocalized and becomes itinerant. Remarkably, the itinerant holes exhibit identical Fermi liquid character across the cuprate phase diagram. This universality enables a simple count of carrier density and yields comprehensive understanding of the key features in the normal and superconducting state. A possible superconducting mechanism is presented, compatible with the key experimental facts. The base of this mechanism is the interaction of fast Fermi liquid carriers with localized holes. A change in the microscopic nature of chemical bonding in the copper oxide planes, from ionic to covalent, is invoked to explain the phase diagram of these fascinating compounds.
Backscatter measured by scatterometers and Synthetic Aperture Radars is sensitive to the dielectric properties of the soil and normally increases with increasing soil moisture content. However, when the soil is dry, the radar waves penetrate deeper into the soil, potentially sensing subsurface scatterers such as near-surface rocks and stones. In this paper we propose an exponential model to describe the impact of such subsurface scatterers on C-Band backscatter measurements acquired by the Advanced Scatterometer (ASCAT) on board of the METOP satellites. The model predicts an increase of the subsurface scattering contributions with decreasing soil wetness that may counteract the signal from the soil surface. This may cause anomalous backscatter signals that deteriorate soil moisture retrievals from ASCAT. We test whether this new model is able to explain ASCAT observations better than a bare soil backscatter model without a subsurface scattering term, using k-fold cross validation and the Bayesian Information Criterion for model selection. We find that arid landscapes with Leptosols and Arenosols represent ideal environmental conditions for the occurrence of subsurface scattering. Nonetheless, subsurface scattering may also become important in more humid environments during dry spells. We conclude that subsurface scattering is a widespread phenomenon that (i) needs to be accounted for in active microwave soil moisture retrievals and (ii) has a potential for soil mapping, particularly in arid and semi-arid environments.
Filled Sb-based skutterudites are considered one of the most appealing thermoelectric materials in the mid temperature range. Even though Sb is not one of the most abundant elements in nature, the large thermoelectric figure of merit of these materials makes them attractive for applications such as thermoelectric generators. In order to get deeper insight into the fundamental physical mechanisms of thermal and electronic transport properties, we studied the temperature dependent electrical resistivity, Seebeck coefficient, thermal conductivity and specific heat. Three groups of skutterudites with excellent thermoelectric performance were investigated: (a) DDyFe4-xCoxSb12 (0 ≤ x ≤ 4; 0.08≤ y ≤ 0.7), to study the influence of Fe/Co substitution and the resulting filling level y as well as the influence of grain size, (b) DD0.7Fe3CoSb12 samples prepared from the same powder to study the effect of different synthesis nanostructuring techniques (hot-pressed, hot pressed and processed via high pressure torsion and cold-pressed and processed via high pressure torsion) and (c), a DD-filled skutterudite with and without Sb/Sn substitution before and after annealing. An overview of experimental investigations of the low-temperature transport is given and appropriate phenomenological models are adopted to elucidate the temperature-dependent features and the origin of high thermoelectric performance in these systems.
SDTrimSP is a popular simulation program to compute several effects of the interaction between an impinging ion and a solid, such as ion implantation ranges, damage formation or sputtering of surface atoms. We now introduce a graphical user interface for SDTrimSP to make its operation more accessible for a broad group of users. It is written as a separate Python program and is not restricted to any specific operating system. The interface allows a quick and easy start as well as the direct evaluation of SDTrimSP simulations. Its capabilities are demonstrated here in the form of several example cases, including the dynamic simulations with SDTrimSP, where ion-induced target changes are taken into account. The presented graphical user interface is made freely available to support a large number of users in performing simulations of ion–solid interaction.
We design and analyze a coupling of a discontinuous Galerkin finite element method with a boundary element method to solve the Helmholtz equation with variable coefficients in three dimensions. The coupling is realized with a mortar variable that is related to an impedance trace on a smooth interface. The method obtained has a block structure with nonsingular subblocks. We prove quasi-optimality of the h\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$h$$\end{document}- and p\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$p$$\end{document}-versions of the scheme, under a threshold condition on the approximability properties of the discrete spaces. Amongst others, an essential tool in the analysis is a novel discontinuous-to-continuous reconstruction operator on tetrahedral meshes with curved faces.
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7,512 members
Paul Panek
  • Institute of Design and Assessment of Technology
Jörg Schmiedmayer
  • Institute of Atomic and Subatomic Physics
Peter Purgathofer
  • Institute of Visual Computing and Human Centered Technology
Jurgen Stampfl
  • Institute of Materials Science and Technology
Karlsplatz 13, A-1040, Vienna, Vienna, Austria
Head of institution
Sabine Seidler