Breaking Dense Structures: Proving Stability of Densely Structured Hybrid Systems

Abstraction and refinement is widely used in software development. Such techniques are valuable since they allow to handle even more complex systems. One key point is the ability to decompose a large system into subsystems, analyze those subsystems and deduce properties of the larger system. As cyber-physical systems tend to become more and more complex, such techniques become more appealing. In 2009, Oehlerking and Theel presented a (de-)composition technique for hybrid systems. This technique is graph-based and constructs a Lyapunov function for hybrid systems having a complex discrete state space. The technique consists of (1) decomposing the underlying graph of the hybrid system into subgraphs, (2) computing multiple local Lyapunov functions for the subgraphs, and finally (3) composing the local Lyapunov functions into a piecewise Lyapunov function. A Lyapunov function can serve multiple purposes, e.g., it certifies stability or termination of a system or allows to construct invariant sets, which in turn may be used to certify safety and security. In this paper, we propose an improvement to the decomposing technique, which relaxes the graph structure before applying the decomposition technique. Our relaxation significantly reduces the connectivity of the graph by exploiting super-dense switching. The relaxation makes the decomposition technique more efficient on one hand and on the other allows to decompose a wider range of graph structures.Comment: In Proceedings ESSS 2015, arXiv:1506.0325

A 15-year evaluation of the Mississippi and Alabama coastline barrier islands, using Landsat satellite imagery

The Mississippi and Alabama barrier islands are sensitive landforms that are affected by hurricanes, longshore currents, and available sediment, yet these effects are difficult to quantify with traditional ground-based surveying. In this study, Landsat satellite imagery was used to evaluate changes in barrier island area and centroid position from 1990 and 2005. When hurricanes are infrequent (1999?2003), barrier islands generally increased in total area and showed only moderate repositioning of their centroid locations. However, when hurricanes were frequent (1994?1999 and 2004?2005), barrier islands showed substantial decreases in area and dramatic repositioning of their island centroid locations. This was especially true following Hurricane Katrina (2005). From 1990 to 2005, the general movement of barrier islands was westerly and most islands experienced an overall reduction in area (-18%). The results of this research are similar to findings reported in the literature and illustrate the suitability of using Landsat imagery to study geomorphic changes

A 15-year evaluation of the Mississippi and Alabama coastline barrier islands, using Landsat satellite imagery

The Mississippi and Alabama barrier islands are sensitive landforms that are affected by hurricanes, longshore currents, and available sediment, yet these effects are difficult to quantify with traditional ground-based surveying. In this study, Landsat satellite imagery was used to evaluate changes in barrier island area and centroid position from 1990 and 2005. When hurricanes are infrequent (1999?2003), barrier islands generally increased in total area and showed only moderate repositioning of their centroid locations. However, when hurricanes were frequent (1994?1999 and 2004?2005), barrier islands showed substantial decreases in area and dramatic repositioning of their island centroid locations. This was especially true following Hurricane Katrina (2005). From 1990 to 2005, the general movement of barrier islands was westerly and most islands experienced an overall reduction in area (-18%). The results of this research are similar to findings reported in the literature and illustrate the suitability of using Landsat imagery to study geomorphic changes

Factorial Ecology: Methodological Refinements Using 1960 Omaha Data

American sociologists have had an abiding interest in the causes and consequences of urban phenomena. Afterall, the emergent American metropolis has a certain lure to it, which is no doubt engendered by its marked cultural and social heterogeneity, and fluid spatial and social mobility. Then too, urban problems are highly visible problems; declining and dilapidated areas, poverty pockets , crime, etc., all command attention from diverse agencies and segments of the public

Sown Forb Performance in CP42 Fields

CP42 is a general conservation practice that attempts to establish pollinator-friendly habitat In total, \u3e500,000 acres have been converted to CP42 (\u3e40% of which is in Iowa) [1] To date, there has been no formal assessment of practice success (i.e., post-seeding forb establishment) In this study, we assess forb establishment in randomly selected CP42 fields near Cedar Falls, Iowa We identify forbs with high/low establishment and relate this to seed cost in an effort to improve seed mix desig

Regulating Nimbus and Focus: Organizing Copresence for Creative Collaboration

Creative collaboration often takes place in collaborative spaces that increasingly use virtual modes of interaction. To better understand the organizational conditions and organizing practices that facilitate collaboration in such spaces, we compare ethnographies of an online platform for collaborative songwriting and a physical songwriting camp, with each of these spatial settings coming with distinct advantages and disadvantages for creative collaboration. We identify the emergence of copresence – an active mutual orientation toward one another – as a common organizational condition for collaboration. Copresence was fostered by practices of regulating nimbus (i.e. making people more or less visible) and focus (i.e. directing attention to others) that not only stimulated moments of converging copresence marked by collaborative problem-solving, but also enabled diverging copresence marked by undirected attention and more serendipitous interactions. Our comparison reveals the challenges of negotiating between converging and diverging copresence to counteract tendencies towards excessive, or conversely, insufficient nimbus and focus of the participants, both of which are barriers to copresence. These insights contribute to ongoing debates about the organization of online and offline collaborative spaces by shifting the focus away from co-location towards copresence, highlighting the oscillation between converging and diverging copresence as important for a collaborative atmosphere and identifying practices by which copresence can be organized in different spatial settings

Crossover from attractive to repulsive induced interactions and bound states of two distinguishable Bose polarons

We study the impact of induced correlations and quasiparticle properties by immersing two distinguishable impurities in a harmonically trapped bosonic medium. It is found that when the impurities couple both either repulsively or attractively to their host, the latter mediates a two-body correlated behavior between them. In the reverse case, namely the impurities interact oppositely with the host, they feature anti-bunching. Monitoring the impurities relative distance and constructing an effective two-body model to be compared with the full many-body calculations, we are able to associate the induced (anti-) correlated behavior of the impurities with the presence of attractive (repulsive) induced interactions. Furthermore, we capture the formation of a bipolaron and trimer state in the strongly attractive regime. The trimer refers to the correlated behavior of two impurities and a representative atom of the bosonic medium and it is characterized by an ellipsoidal shape of the three-body correlation function. Our results open the way for controlling polaron induced correlations and creating relevant bound states.Comment: 34 pages, 11 figure

Correlation Between Wild Bee Populations and Vegetative Resources in the Conservation Reserve Program’s Pollinator Enhancement Plantings

Wild bee populations are in decline; and one of the main factors that caused this is habitat loss, which diminishes floral resources that bees utilize for nectar and pollen (Watanabe 2013) The Conservation Reserve Program (CRP) aims to combat habitat loss by implementing ecological restorations that provide resources for a variety of different wildlife In 2011, the CRP established a Pollinator Habitat Initiative called CP-42, which encompasses forbs and grasses to create adequate habitat for pollinators A primary goal of this program is to enhance pollinator abundance and diversit