Highly accurate calculation of rotating neutron stars: Detailed description of the numerical methods

We give a detailed description of the recently developed multi-domain spectral method for constructing highly accurate general-relativistic models of rapidly rotating stars. For both "ordinary" and "critical" configurations, it is exhibited by means of representative examples, how the accuracy improves as the order of the approximation increases. Apart from homogeneous fluid bodies, we also discuss models of polytropic and strange stars.Comment: 22 pages, 4 figures, 9 tables, version accepted by A&

Uniformly rotating axisymmetric fluid configurations bifurcating from highly flattened Maclaurin spheroids

We give a thorough investigation of sequences of uniformly rotating, homogeneous axisymmetric Newtonian equilibrium configurations that bifurcate from highly flattened Maclaurin spheroids. Each one of these sequences possesses a mass-shedding limit. Starting at this point, the sequences proceed towards the Maclaurin sequence and beyond. The first sequence leads to the well known Dyson rings, whereas the end points of the higher sequences are characterized by the formation of a two-body system, either a core-ring system (for the second, the fourth etc. sequence) or a two-ring system (for the third, the fifth etc. sequence). Although the general qualitative picture drawn by Eriguchi and Hachisu in the eighties has been confirmed, slight differences turned out in the interpretation of the origin of the first two-ring sequence and in the general appearance of fluid bodies belonging to higher sequences.Comment: 10 pages, 11 figures, 5 tables, submitted to MNRA

Highly Constrained Dithienylethenes

Diarylethene sind molekulare Schalter, welche sich unter Einwirkung von Licht zwischen einem offenen und einem geschlossenen Isomer umwandeln. Die Effizienz dieser beiden Photoreaktionen ist von verschiedenen Parametern abhängig, welche bisher nur unzureichend verstanden sind. Ein entscheidender Faktor für die Hinreaktion ist das Verhältnis zweier Konformere, von denen jedoch nur eines photochemisch aktiv ist. In der vorliegenden Arbeit wird eine neue Klasse von Diarylethenen beschrieben, in welcher die aktive Konformation durch kovalente Verbrückungen unterschiedlicher Länge stabilisiert wird. Gleichzeitigeröffnet sich ein zusätzlicher Reaktionspfad in Form einer Doppelbindungsisomerisierung. Es stellte sich heraus, dass bei geeigneter Verbrückungslänge das zyklisierte Isomer mit ungewöhnlich hoher Effizienz gebildet wird, während die Effizienz der Ringöffnung nicht beeinflusst wird. Der Mechanismus und die Dynamik der Photoreaktion wurden anhand ausgewählter Vertreter durch Ultrakurzzeitspektroskopie untersucht. Weiterhin konnte gezeigt werden, dass der Ringschluss auch durch elektrochemische Oxidation oder Reduktion erfolgen kann. Die vorgestellten Systeme agieren bei direkter photochemischer Anregung wie herkömmliche Diarylethene nur im Ringschluss/Ringöffnungsregime. Durch Tripletsensibilisierung kann jedoch eine selektive Z→E Isomerisierung erzielt werden, was diese Diarylethenklasse zu reversiblen 3-Zustandssystemen erweitert. In Erweiterung des Projektes wurde die Struktur des Diarylethens noch stärker fixiert. Nach vielseitigen Syntheseversuchen konnten zwei Vertreter dieser Klasse erhalten und photochemisch untersucht werden, wobei ein Umsatz zu etwa 60% zyklisiertem Isomer bei der Bestrahlung mit UV-Licht gefunden wurde. Zusammengefasst stellt die kovalente Verbrückung der Diarylethenstruktur eine erfolgreiche Strategie dar, um sowohl die Effizienz der Ringschlussreaktion zu steigern als auch photochrome Verbindungen mit drei Schaltzuständen zu kreieren.Diarylethenes are molecular switches that interconvert reversibly between an open and a closed isomer by irradiation with light. The efficiency of both photochemical reactions depends on several parameters, which, so far, are only insufficiently understood. One important factor in the cyclization reaction is the presence of two conformations of the open isomer of which only one is photochemically active. In the current work, a new class of diarylethenes is presented, in which the active conformation is covalently stabilized by alkyl chains of different lengths. As the central double bond is not fixated, double bond isomerization emerges as an additional pathway in these annulated diarylethenes. In dependence of the chosen ring size both open isomers convert with increased efficiency to the closed isomer upon irradiation. The efficiency of the cycloreversion process remains unaffected. The mechanism and dynamic of the photoreaction were investigated for selected compounds using transient absorption spectroscopy. Furthermore, electrochemical studies revealed that both the E- and the Z-isomer cyclize rapidly upon anodic oxidation or cathodic reduction. In general, the photochemical reactivity of annulated diarylethenes parallels that of normal diarylethenes and takes place exclusively in the cyclization/cycloreversion regime if irradiated directly. However, it was demonstrated that a selective Z→E double bond isomerization is possible, thus implementing a 3-state photoswitchable system. In extension of the project, the structure of diarylethenes was further stiffened. Using diverse synthetic approaches, two members of this class could be obtained. Photochemical investigation showed a conversion to the closed isomer of 60% upon irradiation with UV-light. In brief, the covalent fixation of diarylethenes represents an attractive strategy to increase the efficiency of the photochemical cyclization and extent the scope of diarylethenes to 3-state photochromic systems

Four examples demonstrating the impact of Applied Botany on plant-based industrial processes

Currently, many producers of plant-derived commodities indicate a scarcity of associates whose skills cover the entire field of plant biology and who bolster industrial research by linking it to basic plant biology. This scarcity is of particular concern to small and medium sized companies.To illustrate the benefit of appropriate mediation between basic science and product-oriented research, four innovative examples of collaborative research are presented here. The examples cover a broad range of economically relevant issues, including green coffee processing, malting, production of spice and medicinal plants, and prevention of contamination with toxic natural products, such as nicotine or pyrrolizidine alkaloids. These examples illustrate that Applied Botany has the potential to improve even well-established production processes.This article argues that innovative product-oriented research must focus on the relevant physiological processes occurring in the plants. In particular, the impact of cultivation and post-harvest processes on related metabolic processes should be considered, rather than placing continued focus on physical parameters or on economic aspects. In order to achieve practical and feasible solutions that also meet economic demands, interdisciplinary and cross-functional approaches between partners are essential

Modern Applied Botany: Changes in the perception of applied botanists to themselves and others during the last century.

Subsequent to a short chronicle of the history of applied research in plant biology in Germany, the relevance of modern Applied Botany is illustrated by three relevant post-harvest processes. The metabolic reactions that play a key role in the determination of quality of the related plant-derived commodities from each are presented. Increased understanding of the processes involved in these processes has facilitated improvement of product quality in the resulting products. In each instance, it has been necessary to regard plant metabolism comprehensively and not to focus on a single physiological process. Moreover, the various interactions with the environment have to be considered. These illustrations demonstrate that transfer and application of basic plant knowledge into product-related research can provide significant information that is valuable for improvement of plant-derived products. In some instances, these correlations can even account for traditional and well-established processes, as illustrated for the malting process.  However, interdisciplinary work and intensive cooperation with growers and producers must be an integral part of developing feasible and economically acceptable solutions that can be transferred into practice. Ultimately, the major challenge in Applied Botany today is the implementation of new concepts and ideas into product-related research.  In consequence, modern Applied Botany acts as a mediator between basic plant science and industrial, product-related research

Equilibrium Configurations of Homogeneous Fluids in General Relativity

By means of a highly accurate, multi-domain, pseudo-spectral method, we investigate the solution space of uniformly rotating, homogeneous and axisymmetric relativistic fluid bodies. It turns out that this space can be divided up into classes of solutions. In this paper, we present two new classes including relativistic core-ring and two-ring solutions. Combining our knowledge of the first four classes with post-Newtonian results and the Newtonian portion of the first ten classes, we present the qualitative behaviour of the entire relativistic solution space. The Newtonian disc limit can only be reached by going through infinitely many of the aforementioned classes. Only once this limiting process has been consummated, can one proceed again into the relativistic regime and arrive at the analytically known relativistic disc of dust.Comment: 8 pages, colour figures, v3: minor additions including one reference, accepted by MNRA

On the multipole moments of a rigidly rotating fluid body

Based on numerical simulations and analytical calculations we formulate a new conjecture concerning the multipole moments of a rigidly rotating fluid body in equilibrium. The conjecture implies that the exterior region of such a fluid is not described by the Kerr metric.Comment: 5 pages, 4 figures, to appear in Annalen der Physi

Collisions of rigidly rotating disks of dust in General Relativity

We discuss inelastic collisions of two rotating disks by using the conservation laws for baryonic mass and angular momentum. In particular, we formulate conditions for the formation of a new disk after the collision and calculate the total energy loss to obtain upper limits for the emitted gravitational energy.Comment: 30 pages, 9 figure