Estimating the effects on the dose distribution through the Bragg Peak degradation of lung tissue in proton therapy of thoracic tumors

Particle therapy offers to be a promising therapeutic option for tumors in the lung like Non-small cell lung cancer (NSCLC). However, the irradiation of NSCLCs with protons or carbon ions poses different challenges. The movement of the tumor, the heart and the entire thorax through breathing and the heartbeat requires a motion mitigated radiation application. In addition, the microscopic structure of the lung tissue holds further uncertainties of the calculation of the optimized dose distribution. In clinical CTs, on which treatment planning and dose calculation is based, the micrometer-sized air-filled alveoli of the lungs are not fully resolved, but are mapped through a medium density. As each particle of the beam passes a slightly different composition of air and tissue which leads to a slightly different range of the particles, the Bragg peak is degraded when irradiating such a heterogeneous tissue as lung. If this degradation of the Bragg peak is not taken into account into treatment planning, it can potentially lead to an underdose in the target volume and thus to a loss in tumor control. Additionally, the degradation can also lead to a higher dose in the organs at risk and normal tissue, endangering the success of the therapy by a higher toxicity of the treatment. In this dissertation, the effects of the Bragg Peak degradation on the dose distribution are calculated and analyzed so that an assessment of the effects for the clinical routine is available. For this purpose, CT images are manipulated with the help of a density modulation function, which modulates the density of the macroscopic lung voxel to reproduce the microscopic effect. Thus, a direct comparison between the dose distributions with and without the degrading effect is possible. Various dependencies like the tumor size, position and shape are systematically examined and the results of the degradation on clinical plans are presented for five patients. Hence, the clinical relevance can be estimated and assessed. In addition, measurements are presented which show the introduced material property of the "modulation power" of lung tissue. On the basis of this data, the uncertainties of the presented calculation and analysis can be reduced and estimated better. In addition, a mathematical model is presented which allows to estimate the modulation power on the basis of a clinical CT histogram analysis. Together, the works presented offer a basis for the patient-specific translation of the Bragg peak degradation of lung tissue into the clinical treatment planning procedure

TECHNOLOGY CLUSTERS AMONG FINTECHS: EXPLORING THE SIGNALING OF TECHNOLOGY SCOPE AND THE ROLE OF REGULATION

Financial technology ventures (FinTechs) use the latest technologies and act in a highly regulated industry. Yet, the technological scope of FinTechs and how this scope affects funding from investors remains unclear. Accordingly, research calls to examine the influence of technologies on the funding amount of FinTechs, especially in the context of different levels of regulatory freedom. We answer these questions by conducting an explorative cluster and regression analysis of 1,821 FinTechs and find three dominant clusters of FinTechs: technology newcomers, selective adopters, and full technology applicators. Technology newcomers have the lowest adoption rate of new technologies while full technology applicators combine several new technologies. Based on signaling theory and generalized linear models, we find that clusters significantly differ regarding their funding amount. However, we find that higher regulatory freedom decreases the differences between these clusters regarding the funding

Crossover of resources within formal ties: how job seekers acquire psychological capital from employment counselors

Unemployed job seekers experience stress which impedes their job search. Research suggests that psychological capital is a key resource which enables job seekers to cope with their stress. Yet it is still unclear how they acquire this key resource. During job search, job seekers engage in task-oriented, infrequent interactions with counselors in employment agencies and establish formal ties. We explore these largely neglected formal ties and draw on conservation of resources theory and the crossover model to show that psychological capital crosses over from counselors to job seekers. We examine 209 dyads collected from two sources—counselors and job seekers—in an employment agency in Germany. Our hierarchical linear modeling results support the crossover of psychological capital within formal ties: Our results indicate that counselors' psychological capital impacts job seekers' psychological capital, which in turn lowers their stress. This relationship is mediated by job seekers' perception of counselors' social support. This study advances research on job loss and the crossover model as it explains the transfer of key resources within an institutional context characterized by formal ties, and it reveals social support as underlying mechanism. The practical implication is that counselors serve as enablers transferring key resources to job seekers

Willy Brandt als Außenminister

Die erste historische Gesamtdarstellung über Willy Brandt als Außenminister der Großen Koalition 1966-196

Collaborating with Generative AI: Exploring Algorithm Appreciation in Creative Writing

Generative AI (GenAI) has recently attracted a tremendous amount of public attention showcasing the transformational capacity that AI-based systems have on society. By generating creative outputs in multimodal formats like texts and images, GenAI is entering domains formerly seen exclusive to human ingenuity. This raises concerns about how working with AI-based systems will affect employees. Existing research on human-AI collaboration is focusing on objective decision-making settings. We contribute to the growing IS research stream that considers AI collaboration on creative tasks. In particular, we conduct an online experiment to see whether employees appreciate GenAI-generated creative texts and how personality traits affect this interaction. We find that getting input from GenAI rather than a colleague relates to fewer modifications performed to the draft. This relationship is moderated by conscientiousness suggesting that conscientious employees are less inclined to accept suggestions and hence may not gain as much from GenAI tools

Lokale und nicht-lokale Modellierung und Simulation thermomechanischer Lokalisierung mit Schädigung für metallische Werkstoffe unter Hochgeschwindigkeitsbeanspruchungen

Hochgeschwindigkeitsbeanspruchungen metallischer Bauteile sind bei einer Vielzahl ingenieurtechnischer Anwendungsbereiche, beispielsweise bei Crash- oder Falltests, bei Umform- oder Spanprozessen mit hohen Belastungsgeschwindigkeiten oder bei Aufprallproblemen von Komponenten schnell rotierender Bauteile auf das umgebende Gehäuse, z. B. bei Flugzeugturbinen, relevant. Dabei treten in dem beanspruchten Bauteil typischerweise Zonen mit großen, lokalisierten Deformationen auf, die auf die Entfestigung des Werkstoffs durch die Entwicklung von Schädigung und durch die Temperaturerhöhung infolge plastischer Dissipation zurückzuführen sind. Die Ausbildung von Scherbändern stellt dabei eine typische Form der Deformationslokalisierung dar. Die kontinuumsmechanische Modellierung solcher Vorgänge erfordert im Allgemeinen die Berücksichtigung einer Vielzahl von Faktoren und Effekten, wie beispielsweise dehnratenabh ängiges Materialverhalten, mit adiabatischer Erhitzung einhergehende thermische Entfestigung, Reibung und Kontakt sowie Schädigung. Darüber hinaus sind die genannten Effekte in dem Rahmen der Theorie großer Deformationen zu betrachten. Dehnratenabhängige "lokale" Modelle resultieren dabei nicht zwangsläufig in einer physikalisch sinnvollen Scherbandabbildung, d. h. in einer endlichen Scherbandbreite. Die innere Länge, die eine Begrenzung des Lokalisierungsvolumens darstellt, strebt für verschiedene im Rahmen der Simulation von Hochgeschwindigkeitsbelastungen eingesetzte, nichtlinear dehnratenabhängige Modelle, wie z.B. Potenzgesetz-Modelle oder dem Modell nach JOHNSON & COOK, mit infolge von Entfestigung abnehmender Spannung sowie zunehmender plastischer Dehnrate sehr stark gegen null. Dadurch tritt ein Verlust der lokalisierungsbegrenzenden Wirkung dieser ratenabh ängigen Modelle ein, so dass insbesondere jedes, auf diesen Modellen aufbauende Finite-Element Verfahren eine pathologische Netzabhängigkeit der Ergebnisse aufweist. "Nicht-lokale" Gradientenmodelle der Plastizität sind dazu geeignet, die beschriebenen Nachteile zu vermeiden. Die innere Länge dieser Modelle weist eine im Vergleich zu lokalen Modellen deutlich reduzierte Abhängigkeit von dem vorherrschenden Spannungszustand sowie der plastischen Dehnrate auf und wird darüber hinaus wesentlich durch den Wert des nichtlokalen Modellparameters beeinflusst. Die Größenordnung der inneren Länge bleibt dabei selbst für kleine Werte dieses Parameters auch mit Einsetzen von Lokalisierungseffekten zunächst erhalten. Infolge der numerischen Umsetzung nicht-lokaler Modelle mittels der Methode der Finiten-Elemente zeigt sich, dass im Gegensatz zu den auf lokalen Modellen basierenden Verfahren das Volumen der Lokalisierungszone bei stetiger Netzverfeinerung gegen einen endlichen Wert konvergiert. Damit gelingt es durch die Verwendung nicht-lokaler Modelle, die Ausbildung endlicher Scherbanddicken diskretisierungsunabhängig zu simulieren und im Rahmen der Kontinuumsmechanik eine sinnvolle Lösung des zugrunde liegenden physikalischen Problems zu gewährleisten.High-speed loading of metals is encountered in several engineering applications, for example in crash and drop tests as well as in high-speed cutting or forming processes. Likewise, the impact of rapidly rotating structural components on their surrounding containment, encountered for instance in aircraft turbines, reveals significant, high loading velocities. Typically, this type of loading results in zones with highly localized deformation within the stressed component, as a consequence of softening according to damage evolution and heating due to plastic dissipation. In this context, the formation of shear-bands represents a typical form of thermomechanical localization. In general, the continuum mechanical description and modelling of such events involves a variety of processes and effects such as high strain-rates, hardening behaviour, thermal softening as a result of adiabatic heating, friction and contact as well as damage. Further, these effects need to be considered in the framework of large deformation theory. Rate-dependent "local" models do not generally result in a physical shear-band development, e.g., involving a finite, non-vanishing shear-band thickness. In general, the intrinsic length incorporated by the rate-dependency of the models acts as a localization limiter. However, for various nonlinearly rate-dependent models, such as power-law models or the model according to JOHNSON & COOK, which are frequently used for the simulation of high-speed loading applications, this intrinsic length tends to zero owing to both increasing strain-rates and stress-drop due to softening behaviour. Thus, a loss of the localization limiting property of these rate-dependent models is encountered, incorporating that each finite-element method based upon these models yields a pathological mesh-dependence of the results. "Non-local" gradient-plasticity models based on a corresponding extension of the rate-dependence of the material behaviour are appropriate to avoid these disadvantages. In contrast to local models, the intrinsic length of these non-local models reveals a significantly reduced dependence on both the prevailing stress state and the plastic strain-rate but is dominantly influenced by the non-local material parameter. According to the numerical simulation of localization phenomena using finite-element techniques, the domain of the localization zone does converge to a finite volume for subsequent mesh-refinement. Thus, using non-local models it is possible to simulate the development of finite shear-band widths and to ensure a physically reasonable solution of the governing problem within the framework of continuum mechanics

Pyrolysis/methylation of soil fulvic acids: benzenecarboxyllc acids revisited

4 páginas, 1 figura, 3 tablas, 20 referencias.Fulvic acid (FA) is, perhaps, the most complex fraction of soil humic substances due to its extremely variable composition depending on the nature of the environment (1) and the isolation method (2). Practically all available techniques and methods have been applied to FAs (3), in order to understand their chemical structure, but in spite of extensive studies, their nature is still a matter of debate. Chemical degradations have been widely used to characterize FAs in terms of structural units. However, they provide only partial information on the molecular constituents. For instance, acid hydrolysis reveals the presence of sugars and some phenols, while oxidations yield alkanes, fatty acids, phenolic acids, and benzenecarboxylic acids (4). Benzenecarboxylic acids were considered the building blocks of the humic molecule in the 19709, and on the basis of permanganate oxidations and other analyses, Schnitzer and Khan (4) proposed a model made up of phenolic and benzenecarboxylic acids held together by hydrogen bonds, which were suggested to account for a significant part of the FA structure.Peer reviewe

Room-temperature exciton-polaritons with two-dimensional WS2

Two-dimensional transition metal dichalcogenides exhibit strong optical transitions with significant potential for optoelectronic devices. In particular they are suited for cavity quantum electrodynamics in which strong coupling leads to polariton formation as a root to realisation of inversionless lasing, polariton condensationand superfluidity. Demonstrations of such strongly correlated phenomena to date have often relied on cryogenic temperatures, high excitation densities and were frequently impaired by strong material disorder. At room-temperature, experiments approaching the strong coupling regime with transition metal dichalcogenides have been reported, but well resolved exciton-polaritons have yet to be achieved. Here we report a study of monolayer WS$_2$ coupled to an open Fabry-Perot cavity at room-temperature, in which polariton eigenstates are unambiguously displayed. In-situ tunability of the cavity length results in a maximal Rabi splitting of $\hbar \Omega_{\rm{Rabi}} = 70$ meV, exceeding the exciton linewidth. Our data are well described by a transfer matrix model appropriate for the large linewidth regime. This work provides a platform towards observing strongly correlated polariton phenomena in compact photonic devices for ambient temperature applications.Comment: 12 pages, 6 figure

Understanding the effect of market orientation on circular economy practices: the mediating role of closed-loop orientation in German SMEs

The implementation of circular economy (CE) practices is considered a key driver towards sustainable development of firms. Earlier studies point to the general strategic approach of market orientation as an antecedent to CE practice implementation. Still, insights are limited as the mechanisms underlying this relationship remain unclear. Based on a sample of 121 German small and medium-sized enterprises (SME), we empirically examine how the strategic approach of closed-loop orientation mediates the relationship between market orientation and the implementation of three types of CE practices. Using structural equation modelling, we find that while market orientation is positively related to all three types of CE practices, closed-loop orientation mediates these relationships for only two. Our study extends CE literature by suggesting that market orientation is translated into closed-loop orientation to spur CE practice implementation. We also offer a differentiated understanding of CE practice implementation in the context of German SMEs