Physical properties and lattice dynamics of bixbyite-type V2O3

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Some time ago, we reported the synthesis of bixbyite-type V2O3, a new metastable polymorph of vanadium sesquioxide. Since, a number of investigations followed, dealing with different aspects like electronic and magnetic properties of the material, the deviation from ideal stoichiometry or the preparation of nanocrystals as oxygen storage material. However, most of the physical properties were only evaluated on a theoretical basis. Here, we report the lattice dynamics and physical properties of bixbyite-type V2O3 bulk material, which we acquired from physical property measurements and neutron diffraction experiments over a wide temperature range. Besides attributing different possible orientations of the magnetic moments for V1 and V2 to the identified antiferromagnetic (AFM) ground state with a Néel temperature of 38.1(5) K, we use a first order Grüneisen approximation to determine lattice-dependent parameters for the relatively stiff cubic lattice, and, amongst others identify the Debye temperature to be as low as 350 ± 65 K.DFG, 73789094, SPP 1415: Kristalline Nichtgleichgewichtsphasen - Präparation, Charakterisierung und in situ-Untersuchung der Bildungsmechanisme

Technical Uncertainty and Value of Information with Application to Optimal Network Component Replacement

Optimal age replacement policies for network components such as cables, overhead lines or transformers are usually identified based on gathered knowledge about the state of a component and its stochastic deterioration process. In this context, uncertainty is an important challenge because current information about the aging process may be false. Especially in the context of innovative use of newly developed network equipment some experience knowledge from similar equipment might exist or pre-testing under laboratory conditions could allow setting up hypothesis about the characteristics of aging. Nonetheless, substantial uncertainty is still common in replacement. An example in this context is the lifetime of PE tubes in gas networks, which is not very well explored due to the fact that no tubes older than 40 years exist. The length of the aging process as well as the expected starting date can be inferred only to some confidence probability. Apart from newly developed equipment, production imperfections like the Water treeing Effect in cable insulations led to very early replacement of complete lots of cables because the insulation deteriorated much earlier than initially expected. Hence, the question arises how these different sources of uncertainty will impact the network operator's replacement decision. Further it is of interest how much value can be attributed to the reduction of the uncertainty. In this paper, an optimal replacement strategy in an analytical stationary state model is derived explicitly with local and global optima. Based on a discrete mixture model of failure rates under perfect replacement, we show how different assumptions about the underlying type of uncertainty will affect the replacement decision. In a further step, the value of information representing the cost difference between a state of parameter certainty and the state of parameter uncertainty is derived. Trough the course of some applications, it is shown that the value of information increases with the level of uncertainty. Some exemplary calculations are presented to show that the magnitude of the value of information is significant

Idiosyncratic risk and the cost of capital - The case of electricity networks

We analyze the treatment and impact of idiosyncratic or firm-specific risk in regulation. Regulatory authorities regularly ignore firm-specific characteristics, such as size or asset ages, implying different risk exposure in incentive regulation. In contrast, it is common to apply only a single benchmark, the weighted average cost of capital (WACC), uniformly to all firms. This will lead to implicit discrimination. We combine models of firm-specific risk, liquidity management and regulatory rate setting to investigate impacts on capital costs. We focus on the example of the impact of component failures for electricity network operators. In a simulation model for Germany, we find that capital costs increase by approximately 0.2 to 3.0 percentage points depending on the size of the firm (in the range of 3% to 40% of total cost of capital). Regulation of monopolistic bottlenecks should take these risks into account to avoid implicit discrimination

Lie Symmetry Analysis for Cosserat Rods

We consider a subsystem of the Special Cosserat Theory of Rods and construct an explicit form of its solution that depends on three arbitrary functions in (s,t) and three arbitrary functions in t. Assuming analyticity of the arbitrary functions in a domain under consideration, we prove that the obtained solution is analytic and general. The Special Cosserat Theory of Rods describes the dynamic equilibrium of 1-dimensional continua, i.e. slender structures like fibers, by means of a system of partial differential equations.Comment: 12 Pages, 1 Figur

Notifications in a multi-device environment

Notifications are an integral part of how smartphones are used today. Apps can use notifications to inform the user about new text messages, upcoming events or available updates. By using visual cues, auditory signals and tactile output the attention of the user can be gained, enabling him or her to react right away. Notifications on desktop computers existed years before the introduction of smartphones and tablets are already widespread and share most of their characteristics. Other types of connected devices will soon join or already have joined smartphones in daily life. Recent development in the field of wearable devices indicates an upcoming widespread adoption of smartwatches and smartglasses. These devices can be used in situations where the use of a smartphone would be impractical or inappropriate. Previous work showed that notifications can distract the user, inducing stress and anxiety. Such effects could worsen with a growing number of notifying devices. Therefore, it is necessary to explore how notifications should behave in this "multi-device" environment. For that reason, we developed a concept for a framework that allows synchronizing notifications across multiple devices, including smartphones, tablets and desktop computers. Based on the approach of research in the large, we implemented the framework with support for a large number of devices as an update to an existing application and deployed it to a user base of several thousand users. After two months in the wild, the updated application was actively used by more than 33,000 users. On a per app basis the application allows disabling the content or sending notifications altogether. We analyzed the user settings for over 36,000 apps and found, for example, that apps from the "tools" category were excluded from sending notifications most frequently. On the other hand, the users disabled sending the text for apps related to communication most often. In a final large-scale study, the users rated the usefulness of synchronized notifications on different devices. Overall, synchronized notifications from messenger apps received the highest usefulness rating across all devices. The gained insights can support the development of ubiquitous notification mechanisms that keep users informed without overloading them.Benachrichtigungen sind ein integraler Bestandteil bei der Nutzung von Smartphones. Apps können mithilfe von Benachrichtigungen den Benutzer über neue Nachrichten, anstehende Termine oder verfügbare Softwareaktualisierungen informieren. Die Aufmerksamkeit des Benutzers kann durch das Verwenden von visuellen Hinweisen, akustischen Signalen und taktilem Feedback gewonnen werden und ermöglicht dem Benutzer eine schnelle Reaktion auf die Benachrichtigung. Auf Desktop-Computern wurden Benachrichtigungen schon Jahre vor der Verbreitung von Smartphones eingesetzt. Auch Tablets sind bereits weit verbreitet und teilen sich viele Eigenschaften mit Smartphones. In absehbarer Zeit werden noch weitere Gerätetypen hinzukommen. Aktuelle Entwicklungen im Bereich des "Wearable Computing" deuten darauf hin, dass auch intelligente Uhren und Brillen bald verbreitet sein werden. Diese Geräte können in Situationen eingesetzt werden, in denen das Verwenden eines Smartphones unpraktisch oder unangemessen ist. Existierende Arbeiten zeigten, dass Benachrichtigungen den Benutzer von Aufgaben ablenken und Stress verursachen können. Mit einer wachsenden Anzahl von Geräten können diese negativen Effekte zunehmen. Daher sollte erforscht werden, wie sich Benachrichtigungen in einem Umfeld mit mehreren Geräten verhalten sollen. Aus diesem Grund wurde in dieser Arbeit ein Konzept für ein Framework entwickelt, das es ermöglicht, Benachrichtigungen über mehrere Geräte hinweg zu synchronisieren. Um das Framework im realen Umfeld mit einer großen Anzahl von Nutzern testen zu können, wurde eine bestehende Anwendung angepasst und die Änderungen wurden an eine bestehende Nutzerbasis mit mehreren tausend Benutzern verteilt. Nach zwei Monaten wurde die aktualisierte Anwendung von mehr als 33.000 Nutzern aktiv genutzt. Die Anwendung erlaubt es, für bestimmte Apps das Senden des Inhaltes oder die gesamte App auszunehmen. Die Analyse der Benutzereinstellungen für über 36.000 Apps ergab, dass Apps der Kategorie "Tools" am häufigsten vom Senden ausgenommen wurden. Andererseits wurde das Senden des Inhaltes meist für Apps deaktiviert, die im Zusammenhang mit Kommunikation stehen. In einer umfangreichen Studie haben die Benutzer die Nützlichkeit der synchronisierten Benachrichtigungen auf verschiedenen Geräten bewertet. Auf allen Geräten haben synchronisierte Benachrichtigungen von Messenger Apps die höchsten Bewertungen für die Nützlichkeit erhalten. Die gewonnen Erkenntnisse können die Entwicklung eines ubiquitären Benachrichtigungssystems unterstützen, das den Benutzer informiert, ohne ihn oder sie zu überlasten

Empirical assessment and improvement of ubiquitous notifications

Smart devices have become ubiquitous. Devices like smartphones, smartwatches, tablets, laptops, and smart TVs accompany us throughout the day. Advancements in computational efficiency and wireless technologies allow these devices to be always on and always connected. While some devices are used situationally, other devices like smartphones are always with the user. This inherently changed how we interact with these devices. Instead of manually looking for news and new messages, these devices can proactively inform us about new events through notifications around the clock. From new messages, reminders, to system updates, notifications are fundamentally personal and cover a wide range of topics. While notifications are valued by users and make them feel connected, they can also cause interruptions and distractions. With more and more services making use of notifications on more and more devices, potential adverse effects are amplified. For instance, a single email might alert a user on multiple devices using multiple modalities. To reduce adverse effects, an understanding of different categories of notifications, different devices, and user needs is required. Notification management is a balancing act between satisfying users' information needs and respecting their attention. This thesis investigates the empirical assessment and improvements of ubiquitous notifications. We present multiple user studies, from online surveys, lab studies, in-situ studies to large-scale in-the-wild studies. We first focus on the assessment and management of mobile notifications on smartphones, tackling the challenges of conducting in-situ controlled and in-the-wild user studies while preserving the users' privacy. We present a notification data set, propose user types, and introduce new approaches for users to reflect on and manage their notifications. We then expand the scope to include other device types such as smartwatches, tablets, and laptops to create a holistic understanding of how these devices differ regarding user expectations for receiving notifications by combining activity logging on multiple devices with experience sampling. Afterward, we expand the scope again to include large and pervasive displays. Finally, we present an open-source logging framework for mobile devices to enable other developers and researchers to build on top of this work. The contribution of this thesis is threefold. First, this thesis introduces multiple approaches to conducting research on ubiquitous notifications, from controlled lab studies to large-scale in-the-wild studies. Second, the thesis provides insights into users' notification preferences and interactions on different types of devices. Third, a technical contribution, including an open-source notification logging framework and notification data set. These contributions are a foundation for future research on ubiquitous notifications

Bereitstellung eines bestehenden Frameworks für die Analyse von Eye-Tracking-Daten als Web Service(s)

Im Zentrum aktueller Forschungsfragen auf dem Gebiet der Datenvisualisierung stehen mit zunehmendem Maße Eye-Tracking-Experimente, die verschiedene Visualisierungstechniken auf ihre Benutzerfreundlichkeit und Aufgabenangemessenheit hin untersuchen oder miteinander vergleichen. In Eye-Tracking-Benutzerstudien werden die Blickpunkte von Probanden beim Lösen einer Aufgabe aufgezeichnet und anschließend ausgewertet. Neben der eigentlichen Durchführung der Benutzerstudie ist vor allem die Analyse der gesammelten Eye-Tracking-Daten ein zeitintensiver Prozess. Das Ziel dieser Studienarbeit ist, ein Konzept zu entwickeln, das einen Benutzer mit Hilfe der Workflow-Technologie bei der Analyse einer Eye-Tracking-Benutzerstudie unterstützt. Dabei sollen die einzelnen Eye-Tracking-Analyseschritte aufWorkflow-Aktivitäten abgebildet werden. Hierzu wird zunächst ein bestehendes Eye-Tracking-Analyseframework in Bezug auf Funktionalität und Schnittstellen untersucht. Anschließend wird beschrieben, wie das Analyseframework erweitert oder angepasst werden muss, damit es mit Hilfe der Web Service-Technologie in BPEL-Workflows eingebunden werden kann. Das Konzept wird in Form eines prototypisch implementierten Web Service vorgestellt und anhand von zwei beispielhaften Szenarien demonstriert.In the field of data visualization eye tracking experiments are increasingly used to examine and compare different visualization techniques in regard to their usability and task appropriateness. In eye tracking user studies the gaze data of participants is recorded and evaluated subsequently. Apart from conducting the user study itself, the analysis of the collected eye tracking data is a time-intensive process. The aim of this work is to develop a concept to assist a user with the analysis of eye tracking user studies by using workflow technology. To do so the steps of an eye tracking analysis should be mapped to workflow activities. First, an existing framework for the analysis of eye tracking user studies is examined in terms of its functionality and interface. Afterwards, it is shown how the framework has to be extended or adapted, in order to integrate it into a BPEL-workflow by using web service technology. The concept is presented in form of a prototypically implemented web service and demonstrated in two exemplary scenarios

Compact object detection in self-lensing binary systems with a main-sequence star

Detecting compact objects by means of their gravitational lensing effect on an observed companion in a binary system has already been suggested almost four decades ago. However, these predictions were made even before the first observations of gravitational lensing, whereas nowadays gravitational microlensing surveys towards the Galactic bulge yield almost 1000 events per year where one star magnifies the light of a more distant one. With a specific view on those experiments, we therefore carry out simulations to assess the prospects for detection of the transient periodic magnification of the companion star, which lasts typically only a few hours binaries involving a main-sequence star. We find that detectability is given by the achievability of dense monitoring with the required photometric accuracy. In sharp contrast to earlier expectations by other authors, we find that main-sequence stars are not substantially less favourable targets to observe this effect than white dwarfs. The requirement of an almost edge-on orbit leads to a probability of the order of $3 \times 10^{-4}$ for spotting the signature of an existing compact object in a binary system with this technique. Assuming an abundance of such systems about 0.4 per cent, a high-cadence monitoring every 15~min with 5 per cent photometric accuracy would deliver a signal rate per target star of \gamma \sim 4 \times 10^{-7}~\mbox{yr}^{-1} at a recurrence period of about 6 months. With microlensing surveys having demonstrated the capability to monitor about $2 \times 10^{8}$ stars, one is therefore provided with the chance to detect roughly semi-annually recurring self-lensing signals from several compact compacts in a binary system. If the photometric accuracy was pushed down to 0.3 per cent, 10 times as many signals would become detectable.Comment: 7 pages, 5 figures, accepted in MNRA