A Moderated Mediation Model Explaining the Relationship Between Risk-Group Membership, Threat Perception, Knowledge, and Adherence to COVID-19 Behavioral Measures

Background: COVID-19 is a threat to individual and global health, thus, reducing the disease's spread is of significant importance. However, adherence to behavioral measures against the spread of COVID-19 is not universal, even within vulnerable populations who are at higher risk of exposure to the virus or severe COVID-19 infection. Therefore, this study investigates how risk-group membership relates to adherence to COVID-19 behavioral measures, whether perceived threat of COVID-19 is a mechanism explaining this relationship, and whether knowledge about COVID-19 moderates these effects. Methods: We conducted a web-based survey (N = 4,096) representative of the adult population in Germany with regard to gender, age (18 to 74), and province. Therein, we assessed risk group membership with two indicators (risk of exposure to COVID-19 and risk of severe COVID-19 infection), perceived COVID-19 threat with the Perceived Coronavirus Threat Questionnaire, knowledge about COVID-19 with a knowledge test; and adherence to six behavioral measures to protect against the spread of COVID-19 (e.g., keeping distance, using mouth-nose protection, and following contact restrictions). We used moderated mediation models to test whether perceived threat mediates the relationship between risk-group membership and adherence and whether knowledge about COVID-19 moderates this relationship. Results: We found that risk group members had more perceived COVID-19 threat and that knowledge about COVID-19 increased perceived threat. Moreover, risk group membership had a positive direct effect on adherence to most behavioral measures and risk group members with less knowledge about COVID-19 violated measures more frequently. Risk-group membership also had positive indirect effects on adherence via perceived COVID-19 threat. The moderated indirect effects of threat indicate that threat led to more adherence when knowledge was low, but lost relevance as knowledge increased. Conclusion: The results may help to evaluate disease-regulation measures and to combat the pandemic more effectively. For example, increasing COVID-19 knowledge in the general population could increase adherence to COVID-19 behavioral measures. However, policy makers should be mindful that this could also have negative mental health implications as knowledge increases perceived COVID-19 threat

Symmetric Functionals over Tensor Product Spaces in the Context of Quantum Information Theory

This thesis consists of three parts. We begin our investigation with a brief introduction into open quantum systems. Then we explain different measures of distinguishability of density operators, especially the Uhlmann Fidelity, which will be the basis for the model function we investigate in this work. We continue by explaining the time evolution of open quantum systems in more detail, and introducing the important notion of quantum channels as a concept in quantum information theory. This allows us to state a central problem of quantum information theory: the characterization of the quantum information capacity of a given quantum channel. The major challenge is the maximization of the coherent information, a function defined on a n-fold tensor product of a Hilbert space, which is non-additive and thus has to be considered in the limit as n→∞. To gain an insight into this unsolved problem, we study the channel fidelity of a quantum channel, which is a simpler function, also defined on n-fold tensor product spaces. It shares an essential feature with the coherent information in being non-additive. However, in contrast to the coherent information it is mathematically accessible. We establish the channel fidelity as a model for the coherent information and study its properties. In the second part, a short introduction to the representation theory of symmetric and unitary groups is followed by concrete instructions for Collins' and \'{S}niady's formula for the integration of functions of matrix elements of unitary groups with respect to the Haar measure. This exposition culminates in a simplification of the general formula that is optimal for investigating the channel fidelity. In the third part, we calculate channel fidelity moments for arbitrary n. In order to obtain more concrete results, we restrict ourselves to the study of Pauli channels. For these we discuss the transition of the average and variance from small n to the limit n→∞ and give an explicit formula for both in this limit. In particular, we find that for a large number n of Pauli channels, the channel fidelity distribution is peaked very strongly. Additionally, under certain restrictions, the simplified formula from part two also allows us to give concrete expressions for higher moments in the limit n→∞. We conclude by comparing our new results with results from a former work, where, in the search for maximizing states of the channel fidelity, we found states that maximize the channel fidelity of Pauli channels, at least locally. Because these local maxima have a much higher fidelity than the average of the very strongly peaked distribution, we infer that these states would not be found by a standard numerical maximization procedure. If the channel fidelity models the coherent information accurately in this regard, its maximization thus poses a very hard problem

Time domain boundary elements for dynamic contact problems

This article considers a unilateral contact problem for the wave equation. The problem is reduced to a variational inequality for the Dirichlet-to-Neumann operator for the wave equation on the boundary, which is solved in a saddle point formulation using boundary elements in the time domain. As a model problem, also a variational inequality for the single layer operator is considered. A priori estimates are obtained for Galerkin approximations both to the variational inequality and the mixed formulation in the case of a flat contact area, where the existence of solutions to the continuous problem is known. Numerical experiments demonstrate the performance of the proposed mixed method. They indicate the stability and convergence beyond flat geometries.Comment: 38 pages, to appear in Computer Methods in Applied Mechanics and Engineerin

Reconstructing depth from spatiotemporal curves

We present a novel approach for 3D reconstruction based on multiple video frames taken from a static scene. Our solution emerges from the spatiotemporal analysis of video frames. The method is based on a best fitting scheme for spatiotemporal depth curves, which allows us to compute 3D world coordinates of the objects within the scene. As opposed to a large number of current methods, our technique deals with random camera movements in a transparent way, and even performs better in these cases than with pure translation. Robustness against occlusion and aliasing is inherent to the method as well.Fundação para a Ciência e a Tecnologia – PRAXIS XXI/BD/20322/99

From spatiotemporal curves to reconstructed depth

We present a novel approach for 3D reconstruction based on a set of images taken from a static scene. Our solution is inspired by spatio temporal analysis of video sequences. The method is based on a best fitting scheme for spatio temporal curves, that allows us to compute 3D world coordinates of points within the scene. As opposed to a large number of current methods, our technique deals with random camera movements in a transparent way, and even performs better in these cases than with restrained motion such as pure translation. Robustness against occlusion and aliasing is inherent to the method as well

Reproducibility of a new signal processing technique to assess joint sway during standing

Postural control strategies can be investigated by kinematic analysis of joint movements. However, current research is focussing mainly on the analysis of centre of pressure excursion and lacks consensus on how to assess joint movement during postural control tasks. This study introduces a new signal processing technique to comprehensively quantify joint sway during standing and evaluates its reproducibility. Fifteen patients with non-specific low back pain and ten asymptomatic participants performed three repetitions of a 60-second standing task on foam surface. This procedure was repeated on a second day. Lumbar spine movement was recorded using an inertial measurement system. The signal was temporally divided into six sections. Two outcome variables (mean absolute sway and sways per second) were calculated for each section. The reproducibility of single and averaged measurements was quantified with linear mixed-effects models and the generalizability theory. A single measurement of ten seconds duration revealed reliability coefficients of 0.75 for mean absolute sway and 0.76 for sways per second. Averaging a measurement of 40 seconds duration on two different days revealed reliability coefficients higher than 0.90 for both outcome variables. The outcome variables’ reliability compares favourably to previously published results using different signal processing techniques or centre of pressure excursion. The introduced signal processing technique with two outcome variables to quantify joint sway during standing proved to be a highly reliable method. Since different populations, tasks or measurement tools could influence reproducibility, further investigation in other settings is still necessary. Nevertheless, the presented method has been shown to be highly promising

Surface-wave eikonal tomography for dense geophysical arrays

Surface-wave tomography often involves the construction of phase (or group) velocity maps through linearized inversion of measured phase (group) arrival times. Such inversions require a priori information about the medium (that is, a reference model) in order to calculate source-receiver paths, which is inaccurate for complex media, and requires regularization. The surface-wave eikonal tomography proposed here bypasses these limitations and has the advantage of being simple to implement and use, with virtually no input parameters. It relies on accurate phase arrival time measurement, which can be challenging for dispersive waves and complex waveforms. We present a measurement method based on the evaluation of phase arrival time diff erences at nearby receivers.We show, using an exploration data set, that the produced Rayleigh-wave velocity maps are in agreement with results from traditional tomography, but the latter have lower resolution due to the need of regularization to accommodate for the heterogeneity of the study area and noise in data. Eikonal tomography requires averaging over results from multiple sources to produce a proper image, and we evaluate this requirement to a 200 m source spacing in the considered scattering environment. In addition, we validate the approach of combining seismic interferometry and eikonal tomography, for the cases where the source coverage is inappropriate.Shell Researc

Boundary elements with mesh refinements for the wave equation

The solution of the wave equation in a polyhedral domain in $\mathbb{R}^3$ admits an asymptotic singular expansion in a neighborhood of the corners and edges. In this article we formulate boundary and screen problems for the wave equation as equivalent boundary integral equations in time domain, study the regularity properties of their solutions and the numerical approximation. Guided by the theory for elliptic equations, graded meshes are shown to recover the optimal approximation rates known for smooth solutions. Numerical experiments illustrate the theory for screen problems. In particular, we discuss the Dirichlet and Neumann problems, as well as the Dirichlet-to-Neumann operator and applications to the sound emission of tires.Comment: 45 pages, to appear in Numerische Mathemati

Low back pain and postural control, effects of task difficulty on centre of pressure and spinal kinematics

Association of low back pain and standing postural control (PC) deficits are reported inconsistently. Demands on PC adaptation strategies are increased by restraining the input of visual or somatosensory senses. The objectives of the current study are, to investigate whether PC adaptations of the spine, hip and the centre of pressure (COP) differ between patients reporting non-specific low back pain (NSLBP) and asymptomatic controls. The PC adaption strategies of the thoracic and lumbar spine, the hip and the COP were measured in fifty-seven NSLBP patients and 22 asymptomatic controls. We tested three "feet together" conditions with increasing demands on PC strategies, using inertial measurement units (IMUs) on the spine and a Wii balance board for centre of pressure (COP) parameters. The differences between NSLBP patients and controls were most apparent when the participants were blindfolded, but remaining on a firm surface. While NSLBP patients had larger thoracic and lumbar spine mean absolute deviations of position (MADpos) in the frontal plane, the same parameters decreased in control subjects (relative change (RC): 0.23, 95% confidence interval: 0.03 to 0.45 and 0.03 to 0.48). The Mean absolute deviation of velocity (MADvel) of the thoracic spine in the frontal plane showed a similar and significant effect (RC: 0.12 95% CI: 0.01 to 0.25). Gender, age and pain during the measurements affected some parameters significantly. PC adaptions differ between NSLBP patients and asymptomatic controls. The differences are most apparent for the thoracic and lumbar parameters of MADpos, in the frontal plane and while the visual condition was removed

Characterization of Hydrogen Plasma Defined Graphene Edges

We investigate the quality of hydrogen plasma defined graphene edges by Raman spectroscopy, atomic resolution AFM and low temperature electronic transport measurements. The exposure of graphite samples to a remote hydrogen plasma leads to the formation of hexagonal shaped etch pits, reflecting the anisotropy of the etch. Atomic resolution AFM reveals that the sides of these hexagons are oriented along the zigzag direction of the graphite crystal lattice and the absence of the D-peak in the Raman spectrum indicates that the edges are high quality zigzag edges. In a second step of the experiment, we investigate hexagon edges created in single layer graphene on hexagonal boron nitride and find a substantial D-peak intensity. Polarization dependent Raman measurements reveal that hydrogen plasma defined edges consist of a mixture of zigzag and armchair segments. Furthermore, electronic transport measurements were performed on hydrogen plasma defined graphene nanoribbons which indicate a high quality of the bulk but a relatively low edge quality, in agreement with the Raman data. These findings are supported by tight-binding transport simulations. Hence, further optimization of the hydrogen plasma etching technique is required to obtain pure crystalline graphene edges.Comment: 10 pages, 7 figure