Quantitative contraction rates for Markov chains on general state spaces

We investigate the problem of quantifying contraction coefficients of Markov transition kernels in Kantorovich ($L^1$ Wasserstein) distances. For diffusion processes, relatively precise quantitative bounds on contraction rates have recently been derived by combining appropriate couplings with carefully designed Kantorovich distances. In this paper, we partially carry over this approach from diffusions to Markov chains. We derive quantitative lower bounds on contraction rates for Markov chains on general state spaces that are powerful if the dynamics is dominated by small local moves. For Markov chains on $\mathbb{R^d}$ with isotropic transition kernels, the general bounds can be used efficiently together with a coupling that combines maximal and reflection coupling. The results are applied to Euler discretizations of stochastic differential equations with non-globally contractive drifts, and to the Metropolis adjusted Langevin algorithm for sampling from a class of probability measures on high dimensional state spaces that are not globally log-concave.Comment: 39 page

Case Studies of Habitable Trojan Planets in the System of HD 23079

We investigate the possibility of habitable Trojan planets in the HD 23079 star-planet system. This system consists of a solar-type star and a Jupiter-type planet, which orbits the star near the outer edge of the stellar habitable zone in an orbit of low eccentricity. We find that in agreement with previous studies Earth-mass habitable Trojan planets are possible in this system, although the success of staying within the zone of habitability is significantly affected by the orbital parameters of the giant planet and by the initial condition of the theoretical Earth-mass planet. In one of our simulations, the Earth-mass planet is captured by the giant planet and thus becomes a habitable moon.Comment: 24 pages, 8 figures, 3 tables; International Journal of Astrobiology (in press

Pathophysiologie des Kapnoperitoneums: Implikationen für Beatmung und Hämodynamik

Zusammenfassung: Die laparoskopische Chirurgie wurde Anfang der 50er Jahre für gynäkologische Eingriffe eingeführt. Mit verbesserter Technik erweiterte sich das Spektrum in den letzten Jahrzehnten beträchtlich. Es wurden zunehmend komplexere und länger dauernde Operationen durchgeführt. Als Vorteile gegenüber offener Chirurgie wurden eine Reduktion der postoperativen Schmerzen, bessere kosmetische Ergebnisse, raschere Erholung und die Verkürzung der Krankenhausverweildauer angeführt. Infolgedessen wird die Laparoskopie mittlerweile auch bei immer älteren Patienten mit entsprechenden pulmonalen sowie kardiovaskulären Komorbiditäten und in der Chirurgie für adipöse Patienten eingesetzt. Eine sichere Anästhesieführung setzt detaillierte Kenntnisse der Pathophysiologie des Kapnoperitoneums voraus, insbesondere im Hinblick auf dessen respiratorische und hämodynamische Konsequenzen. Der Übersichtsartikel diskutiert die wichtigsten Effekte des Kapnoperitoneums und stellt aktuelle Forschungsergebnisse sowie deren Umsetzungsmöglichkeiten in der klinischen Praxis da

The Instability Transition for the Restricted 3-Body Problem. III. The Lyapunov Exponent Criterion

We establish a criterion for the stability of planetary orbits in stellar binary systems by using Lyapunov exponents and power spectra for the special case of the circular restricted 3-body problem (CR3BP). The centerpiece of our method is the concept of Lyapunov exponents, which are incorporated into the analysis of orbital stability by integrating the Jacobian of the CR3BP and orthogonalizing the tangent vectors via a well-established algorithm originally developed by Wolf et al. The criterion for orbital stability based on the Lyapunov exponents is independently verified by using power spectra. The obtained results are compared to results presented in the two previous papers of this series. It is shown that the maximum Lyapunov exponent can be used as an indicator for chaotic behaviour of planetary orbits, which is consistent with previous applications of this method, particularly studies for the Solar System. The chaotic behaviour corresponds to either orbital stability or instability, and it depends solely on the mass ratio of the binary components and the initial distance ratio of the planet relative to the stellar separation distance. Our theoretical results allow us to link the study of planetary orbital stability to chaos theory noting that there is a large array of literature on the properties and significance of Lyapunov exponents. Although our results are given for the special case of the CR3BP, we expect that it may be possible to augment the proposed Lyapunov exponent criterion to studies of planets in generalized stellar binary systems, which is strongly motivated by existing observational results as well as results expected from ongoing and future planet search missions.Comment: 10 pages, 8 figures, 3 tables; accepted by Astronomy and Astrophysic

Design requirements and challenges for intelligent power wheelchair use in crowds: learning from expert wheelchair users

An intelligent or smart power wheelchair is normally built on a standard power wheelchair with additional modules for perception, navigation or interaction purposes. It adds autonomy to the wheelchair and provides a technical solution to the safety concerns, thus opening the possibility for people who are considered not suitable to use a standard power wheelchair. Although the research in this field has been going on for decades, most of them focus on dealing with static or simple dynamic environments. In addition, the role of the user is sometimes overlooked during the design and development process. In our project, we aim to design a user-centred intelligent wheelchair and extend its application area to one of the most difficult scenarios faced by wheelchair users­, ­­navigating among crowds. As we start the process of designing a smart wheelchair, we present the results of an initial study with expert wheelchair users' to gain insights into their design requirements and challenges when navigating in crowds

The Stability of the Suggested Planet in the nu Octantis System: A Numerical and Statistical Study

We provide a detailed theoretical study aimed at the observational finding about the nu Octantis binary system that indicates the possible existence of a Jupiter-type planet in this system. If a prograde planetary orbit is assumed, it has earlier been argued that the planet, if existing, should be located outside the zone of orbital stability. However, a previous study by Eberle & Cuntz (2010) [ApJ 721, L168] concludes that the planet is most likely stable if assumed to be in a retrograde orbit with respect to the secondary system component. In the present work, we significantly augment this study by taking into account the observationally deduced uncertainty ranges of the orbital parameters for the stellar components and the suggested planet. Furthermore, our study employs additional mathematical methods, which include monitoring the Jacobi constant, the zero velocity function, and the maximum Lyapunov exponent. We again find that the suggested planet is indeed possible if assumed to be in a retrograde orbit, but it is virtually impossible if assumed in a prograde orbit. Its existence is found to be consistent with the deduced system parameters of the binary components and of the suggested planet, including the associated uncertainty bars given by observations.Comment: 11 pages, 10 figures, 3 tables; Monthly Notices of the Royal Astronomical Society (in press

Retrospective analysis of fish community change during a half-century of landuse and streamflow changes.

Ecological thresholds that lead to alternative community states can be exceeded through gradual perturbation or as a result of sudden disturbance. Many Great Plains streams have experienced dramatic changes in their hydrologic regime resulting from water and landuse changes that began as early as 1880. These changes, combined with the presence of many invasive species, have substantially altered the fish communities in this area. We quantified temporal changes in fish communities in 3 large river basins in relation to putative anthropogenic stressors, including increased sediment supply derived from row-crop agriculture (beginning in 1880), habitat fragmentation caused by reservoir construction (beginning in the 1950s), and reduced discharge caused by groundwater withdrawal (beginning in the 1960s). We hypothesized that these abiotic regime shifts, coupled with species invasions, would shift the system from a fish community dominated by lotic (flowing water) species to one dominated by lentic (still water) species. Further, we predicted that the timing and intensity of community change would vary across basins that experienced different types and levels of stressors. Restructuring of fish communities across the 3 river basins was driven primarily by similar increases in lentic species, with only a few declines in several large-river species. Current fish communities in these basins share ,50% of the species recorded in historic collections, and these differences were driven by species extirpations and invasions. The greatest levels of community divergence over time occurred in western Kansas basins that experienced the most intense groundwater withdrawals and fragmentation by reservoirs. An alarming result from this analysis was the recent (after 1991) expansion of several invasive species in the Arkansas and lower Kansas River basins and the decline or extirpation of several native species where flow regimes are less heavily altered. Accelerating changes in the biota and habitat identified by our retrospective analysis highlight potential complications for restoring the habitat and native fish communities to a previous state

A Creative Information System Based on the SCAMPER Technique

Lopes, R., Malta, P., Mamede, H., & Santos, V. (2020). A Creative Information System Based on the SCAMPER Technique. In M. Themistocleous, M. Papadaki, & M. M. Kamal (Eds.), Information Systems: 17th European, Mediterranean, and Middle Eastern Conference, EMCIS 2020, Proceedings (pp. 595-606). (Lecture Notes in Business Information Processing; Vol. 402). Springer Science and Business Media Deutschland GmbH. https://doi.org/10.1007/978-3-030-63396-7_40Nowadays, the use of creativity in business has been increasing drastically because it has been perceived to be important for the market to come up with new ways, focused on answers to the problems proposed by the users. Several different creativity techniques can be used in a myriad of contexts. One of the most important techniques is the SCAMPER technique, which is based on reorganizing, modifying, adding, and eliminating information. An automated system will provide answers and solutions to creativity problems and contribute to minimizing the cost of innovation in companies. The aim of this paper is, therefore, to design an architecture system for a creative information system based on the SCAMPER creativity technique, thus building an automated system of this technique.authorsversionpublishe