Canard-like phenomena in piecewise-smooth Van der Pol systems

We show that a nonlinear, piecewise-smooth, planar dynamical system can exhibit canard phenomena. Canard solutions and explosion in nonlinear, piecewise-smooth systems can be qualitatively more similar to the phenomena in smooth systems than piecewise-linear systems, since the nonlinearity allows for canards to transition from small cycles to canards ``with heads." The canards are born of a bifurcation that occurs as the slow-nullcline coincides with the splitting manifold. However, there are conditions under which this bifurcation leads to a phenomenon called super-explosion, the instantaneous transition from a globally attracting periodic orbit to relaxations oscillations. Also, we demonstrate that the bifurcation---whether leading to canards or super-explosion---can be subcritical.Comment: 17 pages, 11 figure

Measurement of atomic diffraction phases induced by material gratings

Atom-surface interactions can significantly modify the intensity and phase of atom de Broglie waves diffracted by a silicon nitride grating. This affects the operation of a material grating as a coherent beam splitter. The phase shift induced by diffraction is measured by comparing the relative phases of serveral interfering paths in a Mach-Zehnder Na atom interferometer formed by three material gratings. The values of the diffraction phases are consistent with a simple model which includes a van der Waals atom-surface interaction between the Na atoms and the silicon nitride grating bars.Comment: 4 pages, 5 figures, submitted to PR

Moulting phenology of the harbour seal in south-west Ireland

Studies on the phenology of harbour seal moult have been carried out in the Atlantic and Pacific, however there has been no research into this process in the Republic of Ireland, at the southern edge of the species range in the north-east Atlantic. Population estimates of harbour seals are derived by counts primarily during the moulting seasons. In the absence of information on the moult phenology planning the optimal timing of such surveys is impossible. Furthermore, changes in moult phenology may reflect changes in resource availability or competition, or demographic changes. The phenology of the harbour seal moult was investigated in south-west Ireland in this study. Timing of the moult differed among all cohorts, yearlings began moulting first followed by adult females and finally adult males. The number of seals hauled out was generally positively related to the proportion of seals in active moult. The timing of the moult period was different to other parts of the species' range and should be considered in determining optimal timing of future surveys for assessing populations abundance and trends in Ireland

Politics and power in national REDD+ policy processes

National Strategy and Policy Options Maria Brockhaus Arild Angelsen ... depend on existing institutions and legal structures, current political and economic processes, the distribution of power and wealth, and the REDD+ actions appropriate to ..

Automotive Stirling engine development program

The study of high power kinematic Stirling engines for transportation use, testing of Mod I and Mod II Stirling engines, and component development activities are summarized. Mod II development testing was performed to complete the development of the basic engine and begin characterization of performance. Mod I engines were used for Mod II component development and to obtain independent party (U.S. Air Force) evaluation of Stirling engine vehicle performance

Peter & friends talk about COVID-19 and having a learning disability and/or autism

We thought it important to write this book as many of us feel that people with learning disabilities have been largely forgotten during the Covid pandemic. This book gives this gorup a voice and helps those voices to be heard and not only the specific difficulties people have experienced but the remarkable resilience they and their carers have shown. In writing their story many people have been assisted by family, friends and carers in different ways. This is why the style changes, to try and catch the person and their preferred style of communication. In the book are stories from people in a variety of different situations, including workplaces, family homes, in supported living, people in hospital including patients or staff in general hospitals, Assessment and Treatment Units and Medium Secure Units. It is our strong belief that everyone has the right to speak up and be heard wherever they are, and this should be respected. Everybody has a voice, and everybody matters whoever they are, and it is our duty to assist them to be heard

Ice Caps and Ice Belts: The Effects of Obliquity on Ice−Albedo Feedback

Planetary obliquity determines the meridional distribution of the annual mean insolation. For obliquity exceeding 55°, the weakest insolation occurs at the equator. Stable partial snow and ice cover on such a planet would be in the form of a belt about the equator rather than polar caps. An analytical model of planetary climate is used to investigate the stability of ice caps and ice belts over the widest possible range of parameters. The model is a non-dimensional diffusive Energy Balance Model, representing insolation, heat transport, and ice-albedo feedback on a spherical planet. A complete analytical solution for any obliquity is given and validated against numerical solutions of a seasonal model in the "deep-water" regime of weak seasonal ice line migration. Multiple equilibria and unstable transitions between climate states (ice-free, Snowball, or ice cap/belt) are found over wide swaths of parameter space, including a "Large Ice-Belt Instability" and "Small Ice-Belt Instability" at high obliquity. The Snowball catastrophe is avoided at weak radiative forcing in two different scenarios: weak albedo feedback and inefficient heat transport (favoring stable partial ice cover), or efficient transport at high obliquity (favoring ice-free conditions). From speculative assumptions about distributions of planetary parameters, three-fourths to four-fifths of all planets with stable partial ice cover should be in the form of Earth-like polar caps

Response to freshwater inflow in the Rappahannock Estuary, Virginia : Operation HIFLO \u2778

More sediment, nutrients and pollutants are discharged into an estuary during a few days of flood inflow than during many months or years of average inflow (Meade, 1972; Schubel, 1977), but few observations document the sedimentary response of an estuary to high freshwater inflow. Such inflows are usually unexpected and estuarine water charact~ristics change too rapidly to permit systematic measurements. Moreover, the expenditure of effort and number of sampling vessels required on short notice is beyond the resources of a single research group or institute. Yet, freshwater inflow observations are a key to improving water quality; especially to ameliorate the effects of high turbidity, depleted oxygen and low salinity which can cause oyster motalities (Zaborski and Haven, 1980). Many si9nificant ecological effects are noted by Snedakar, et al., 1977. Exceptional sediment deposition shoals shipping channels, fills boat basins, and blanke~ts oyster grounds. Suspended sediments adsorb toxic contaminates, nutrients and organic matter, and thus can affect plant production and the distribution of shellfish, plants and other life. The HIFLO experiment was planned to observe and evaluate the response of an estuary to high freshwater inflow and high influx of suspended sediment. Of special interest are the questions: How far seaward does the sediment load from an event go before settling to the bed? How do the hydrodynamic conditions for sediment transport change? What is the sequence of estuarine processes triggered by a river flood